# EDGAR Filing Document

**Accession Number:** 0001708035
**File Stem:** 0001193125-23-058328
**Filing Date:** 2023-3
**Character Count:** 128595
**Document Hash:** a361633457ca63eeb7415ad81e5cdddb
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-23-058328.hdr.sgml**: 20230302

**ACCESSION NUMBER**: 0001193125-23-058328

**CONFORMED SUBMISSION TYPE**: 424B7

**PUBLIC DOCUMENT COUNT**: 4

**FILED AS OF DATE**: 20230302

**DATE AS OF CHANGE**: 20230302

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Ecovyst Inc.
- **CENTRAL INDEX KEY:** 0001708035
- **STANDARD INDUSTRIAL CLASSIFICATION:** CHEMICALS & ALLIED PRODUCTS [2800]
- **IRS NUMBER:** 813406833
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 424B7
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-255514
- **FILM NUMBER:** 23700231

**BUSINESS ADDRESS:**
- **STREET 1:** 300 LINDENWOOD DRIVE
- **CITY:** MALVERN
- **STATE:** PA
- **ZIP:** 19355
- **BUSINESS PHONE:** 484-617-1200

**MAIL ADDRESS:**
- **STREET 1:** 300 LINDENWOOD DRIVE
- **CITY:** MALVERN
- **STATE:** PA
- **ZIP:** 19355

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** PQ Group Holdings Inc.
- **DATE OF NAME CHANGE:** 20170531

##### [**Table of Contents**](#toc)
**The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to the securities has become effective under the Securities Act of 1933, as amended. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities, and we are not soliciting an offer to buy these securities, in any jurisdiction where the offer or sale is not permitted.** 

**Filed Pursuant to Rule 424(b)(7)<br>Registration File No. 333-255514** 

**Subject to completion, dated March 2, 2023** 

**Prospectus Supplement to Prospectus dated April 26, 2021** 

**11,490,444 Shares**![LOGO](g474686g56a33.jpg)

**Ecovyst Inc.** 

**Common Stock** 

------

The selling stockholders named in this prospectus supplement are offering 11,490,444 shares of our common stock. We will not receive any proceeds from the sale of our common stock by the selling stockholders.

Subject to the completion of this offering, we have agreed to purchase from the underwriter 3,000,000 shares of our common stock that are subject to this offering at a price per share equal to the price per share paid by the underwriter to the selling stockholders in this offering.

Our common stock is listed on the New York Stock Exchange under the symbol "ECVT." On March 1, 2023, the last sale price of our common stock as reported on the New York Stock Exchange was $10.20 per share.

***Investing in our common stock involves substantial risk. Please read "[Risk Factors](#supp474686_5)" beginning on page S-4.***

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

The underwriter has agreed to purchase shares of our common stock from the selling stockholders at a price of $ per share, which will result in approximately $ of proceeds to the selling stockholders before expenses. The underwriter may offer the shares of common stock from time to time for sale in one or more transactions on the New York Stock Exchange, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related prevailing market prices or at negotiated prices, subject to receipt and acceptance by it and subject to its right to reject any order in whole or in part. We have agreed to reimburse the underwriter for certain expenses in connection with this offering. See "Underwriting" beginning on page S-17.

The underwriter expects to deliver the shares against payment in New York, New York on or about , 2023.

------

**Jefferies** 

Prospectus supplement dated , 2023

------

##### [**Table of Contents**](#toc)
**TABLE OF CONTENTS** 

**Prospectus Supplement** 

---

| | |
|:---|:---|
|  [ABOUT THIS PROSPECTUS SUPPLEMENT](#supp474686_1) | S-ii |
|  [TRADEMARKS AND TRADENAMES](#supp474686_2) | S-ii |
|  [SUPPLY SHARE AND INDUSTRY INFORMATION](#supp474686_3) | S-ii |
|  [PROSPECTUS SUPPLEMENT SUMMARY](#supp474686_4) | S-1 |
|  [RISK FACTORS](#supp474686_5) | S-4 |
|  [CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS](#supp474686_6) | S-8 |
|  [USE OF PROCEEDS](#supp474686_7) | S-10 |
|  [DIVIDEND POLICY](#supp474686_8) | S-10 |
|  [SELLING STOCKHOLDERS](#supp474686_9) | S-11 |
|  [MATERIAL U.S. FEDERAL INCOME AND ESTATE TAX CONSIDERATIONS FOR NON-U.S. HOLDERS OF COMMON STOCK](#supp474686_10) | S-12 |
|  [UNDERWRITING](#supp474686_11) | S-17 |
|  [LEGAL MATTERS](#supp474686_12) | S-23 |
|  [EXPERTS](#supp474686_13) | S-23 |
|  [WHERE YOU CAN FIND MORE INFORMATION](#supp474686_14) | S-23 |
|  [INCORPORATION OF CERTAIN INFORMATION BY REFERENCE](#supp474686_15) | S-23 |

---

**Prospectus** 

---

| | |
|:---|:---|
|  [ABOUT THIS PROSPECTUS](#rom474686_1) | 1 |
|  [RISK FACTORS](#rom474686_2) | 2 |
|  [CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS](#rom474686_3) | 2 |
|  [USE OF PROCEEDS](#rom474686_4) | 3 |
|  [DESCRIPTION OF CAPITAL STOCK](#rom474686_5) | 4 |
|  [PLAN OF DISTRIBUTION](#rom474686_6) | 8 |
|  [LEGAL MATTERS](#rom474686_7) | 10 |
|  [EXPERTS](#rom474686_8) | 10 |
|  [WHERE YOU CAN FIND MORE INFORMATION](#rom474686_9) | 10 |
|  [INCORPORATION OF CERTAIN INFORMATION BY REFERENCE](#rom474686_10) | 10 |

---

**None of the Company, the selling stockholders or the underwriter have authorized anyone to provide any information or to make any representations other than those contained in or incorporated by reference into this prospectus supplement, the accompanying prospectus or in any free writing prospectuses we have prepared. None of the Company, the selling stockholders or the underwriter take any responsibility for, or can provide any assurance as to the reliability of, any other information that others may give you. This prospectus supplement and the accompanying prospectus are an offer to sell only the shares offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. The information contained in this prospectus supplement and the accompanying prospectus is current only as of the date of the applicable document.** 

S-i

------

##### [**Table of Contents**](#toc)
**ABOUT THIS PROSPECTUS SUPPLEMENT** 

*Unless otherwise indicated or the context otherwise requires, references in this prospectus supplement to the "Company," "ECVT," "we," "us" and "our" refer to Ecovyst Inc. and its consolidated subsidiaries.* 

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this common stock offering and certain other matters relating to us, our business and prospects. The second part, the accompanying prospectus, contains a description of our common stock and certain other information.

The information contained in this prospectus supplement may add, update or change information contained in the accompanying prospectus or in documents that we file or have filed with the Securities and Exchange Commission (the "SEC"). To the extent the information contained in this prospectus supplement differs or varies from the information contained in the accompanying prospectus or documents incorporated by reference filed before the date of this prospectus supplement, the information in this prospectus supplement will supersede such information.

**TRADEMARKS AND TRADENAMES** 

We own or have rights to trademarks or trade names that we use in conjunction with the operation of our business. In addition, our name, logo and website name and address are our service marks or trademarks. Each trademark, trade name or service mark by any other company appearing in this prospectus supplement, the accompanying prospectus or in the documents incorporated by reference herein and therein belongs to its holder. Some of the more important trade names and trademarks that we use include Ecovyst, Ecoservices, Catalyst Technologies, Zeolyst, and Zeolyst International. We also own or have the rights to copyrights that protect the content of our products. Solely for convenience, the trademarks, service marks, trade names and copyrights referred to in this prospectus supplement, the accompanying prospectus and in the documents incorporated by reference herein and therein are listed without the TM, SM, <sup>®</sup> and <sup>©</sup> symbols, but we will assert, to the fullest extent under applicable law, our rights to these trademarks, service marks, trade names and copyrights.

**SUPPLY SHARE AND INDUSTRY INFORMATION** 

Certain statistical information used throughout this prospectus supplement and in the documents incorporated by reference herein is based on independent industry publications, reports by research firms or other published independent sources. Some statistical information is also based on our good faith estimates, which are derived from management's knowledge of our industry and such independent sources referred to above. Certain supply share statistics, ranking and industry information included in this prospectus supplement and in the documents incorporated by reference herein, including the size of certain markets and our estimated supply share position and the supply share positions of our competitors, are based on management estimates. These estimates have been derived from our management's knowledge and experience in the industry and end uses into which we sell our products, as well as information obtained from surveys, reports by research firms, our customers, distributors, suppliers, trade and business organizations and other contacts in the industries into which we sell our products. We believe these data to be accurate as of the date of this prospectus supplement. However, this information may prove to be inaccurate because this information cannot always be verified with complete certainty due to the limitations on the availability and reliability of raw data, the voluntary nature of the data gathering process and other limitations and uncertainties. Unless otherwise noted, all of our supply share position information presented in this prospectus supplement and in the documents incorporated by reference herein is an approximation based on management's knowledge and is based on our, or, in the case of our zeolite catalysts product group, our Zeolyst Joint Venture's, sales volumes relative to the estimated sales volumes for the year ended December 31, 2022 in relevant products or end uses into which we sell our products. In the case of our Ecoservices segment, including the products and services thereof, such supply share position information excludes volume attributable to manufacturers who produce primarily for their own consumption. References to our being a leader in a supply share position or product group refer to our belief that we have one of the leading supply share positions, unless otherwise indicated or the context otherwise requires. In addition, references to various end uses into which we sell our products are based on how we define the end uses for our products.

S-ii

------

##### [**Table of Contents**](#toc)
**PROSPECTUS SUPPLEMENT SUMMARY** 

*This summary highlights information appearing elsewhere or incorporated by reference in this prospectus supplement and the accompanying prospectus. This summary is not complete and does not contain all of the information that you should consider before investing in our common stock. You should carefully read the entire prospectus supplement, the accompanying prospectus and the financial data and related notes and other information incorporated by reference in this prospectus supplement and the accompanying prospectus before deciding whether to invest in our common stock.* 

**Our Company** 

We are a leading integrated and innovative global provider of specialty catalysts and services. We believe that our products, which are predominantly inorganic, and services contribute to helping improve the sustainability of the environment.

We conduct operations through two reporting segments: (1) Ecoservices and (2) Catalyst Technologies (including our 50% interest in the Zeolyst Joint Venture).

Ecoservices: We are a leading provider of sulfuric acid recycling services to North American refineries for the production of alkylate, an essential gasoline component for lowering vapor pressure and increasing octane to meet stringent gasoline specifications and fuel efficiency standards. We are also a leading North American producer of on-purpose virgin sulfuric acid for water treatment, mining and industrial applications.

Catalyst Technologies: We are a global supplier of finished silica catalysts and catalyst supports necessary to produce high strength and high stiffness plastics used in packaging films, bottles, containers and other molded applications. This segment includes our 50% interest in the Zeolyst Joint Venture, where we are a leading global supplier of zeolites used for catalysts that help produce renewable fuels and remove nitrogen oxides from diesel engine emissions as well as sulfur from fuels during the refining process.

We believe we are a leader in each of our business segments, holding what we estimate to be a number one or number two supply share position for products that generated more than 90% of our 2022 sales and our proportionate 50% share of sales attributable to the Zeolyst Joint Venture, respectively. We believe that our global footprint and efficient network of strategically located manufacturing facilities provide us with a strong competitive advantage in serving our customers both regionally as well as globally.

We believe our long history of established customer relationships and our reputation for providing reliable and high quality products and services enables us to deliver significant value to our customers, as demonstrated by our profit margins. Although our products and services typically constitute a small portion of our customers' overall end-product costs, we believe they are critical to product performance.

We have a long track record of innovation that is reflected in our technical and production expertise in silica, zeolites and catalyst technologies. We are highly diversified by business, geography and end use. In 2022, the majority of our sales were for applications that have historically had relatively predictable, consistent demand patterns driven by consumption or frequent replacement cycles. We believe our strong commercial contract structure and the secular trends supporting our business segments have generally allowed us to maintain stable margins through changing macro economic cycles.

We are focused on implementing and accelerating sustainability initiatives and supporting the production of low carbon technologies. We believe our commitment to innovation is how we differentiate ourselves in the marketplace. We have the ability to tailor our products and services for the changing needs of our customers and support them in addressing their technical and operational challenges. Through close collaboration with our

------

##### [**Table of Contents**](#toc)
global customers, we have been long standing suppliers of products and services that we believe support sustainability, addressing tightening global regulatory standards and changing consumer preferences. For example, we continue to develop products that improve air quality through lower sulfur content in fuels and capturing nitrogen oxide emissions from heavy duty vehicles. We are focused on catalyst innovation that enables stronger and lighter plastics and zeolites that can facilitate more efficient recycling of mixed plastics. Our sulfuric acid recycling is critical to the production of alkylate for improved fuel economy and our catalyst products support the novel technologies that transform biomass into biofuels and synthetic rubber for green tires. We segment our projects into distinct development themes that we believe are core to our sustainability efforts. With greater focus and resources, Ecovyst has historically expanded and accelerated the commercialization of its portfolio of sustainable products and solutions.

In 2022, we served global customers across many end uses and, as of December 31, 2022, operated out of ten strategically located manufacturing facilities.

**Share Repurchase** 

We intend to purchase from the underwriter 3,000,000 shares of our common stock that are subject to this offering at a price per share equal to the price per share paid by the underwriter to the selling stockholders in this offering. We refer to this repurchase as the "Share Repurchase." The Share Repurchase is part of our existing $450 million common stock repurchase program approved by our board of directors on April 27, 2022, which became effective immediately. After giving effect to the Share Repurchase, we will have remaining authorization to repurchase up to approximately $ million of our common stock under the repurchase program. We intend to fund the Share Repurchase with cash on hand and cash generated from operations. The closing of the Share Repurchase is contingent on the closing of this offering. The Share Repurchase was approved by a special committee of our board of directors, which is comprised entirely of disinterested directors.

The description and the other information in this prospectus supplement regarding the Share Repurchase is included in this prospectus supplement solely for informational purposes. Nothing in this prospectus supplement should be construed as an offer to sell, or the solicitation of an offer to buy, any of our common stock subject to the Share Repurchase.

**Corporate Information** 

Our principal executive offices are located at 300 Lindenwood Drive, Malvern, Pennsylvania 19355, and our telephone number is (484) 617-1200. Our Internet website address is www.ecovyst.com. The information on, or that can be accessed through, our website is not part of this prospectus supplement or the accompanying prospectus, and you should not rely on any such information in making the decision whether to purchase our common stock.

------

##### [**Table of Contents**](#toc)
**The Offering** 

Common stock offered by the selling stockholders 11,490,444 shares

Use of proceeds We will not receive any of the proceeds from the sale of shares of common stock by the selling stockholders.

---

| | |
|:---|:---|
| Share Repurchase  | Subject to completion of this offering, we have agreed to repurchase 3,000,000 shares of our common stock that are subject to this offering from the underwriter at a price per share equal to the price paid by the underwriter to the selling stockholders in this offering. The closing of the Share Repurchase is contingent on the closing of this offering. The Share Repurchase was approved by a special committee of our board of directors, which is comprised entirely of disinterested directors. |

---

Risk factors You should read carefully the information set forth under "Risk Factors" herein and in the accompanying prospectus for a discussion of factors that you should consider before deciding to invest in our common stock.

New York Stock Exchange trading symbol "ECVT"

------

##### [**Table of Contents**](#toc)
**RISK FACTORS** 

*An investment in our common stock involves various risks. You should carefully consider the following risks and all of the other information contained in this prospectus supplement and the accompanying prospectus before investing in our common stock. In addition, you should read and consider the risk factors associated with our business included in the documents incorporated by reference in this prospectus supplement, including our Annual Report on Form 10-K for the year ended December 31, 2022. See "Where You Can Find More Information." The risks described below and incorporated herein by reference are those which we believe are the material risks that we face. The trading price of our common stock could decline due to any of these risks, and you may lose all or part of your investment in our common stock.* 

**Risks Related to Our Common Stock and this Offering** 

***CCMP and INEOS have had, and INEOS may continue to have, significant influence over us, which could limit your ability to influence the outcome of key transactions, including a change of control.***

Upon the completion of this offering and the Share Repurchase, based on the 123,194,080 shares of common stock outstanding as of February 23, 2023, which, after giving effect to the Share Repurchase, will result in 120,194,080 shares of common stock outstanding, investment funds affiliated with CCMP Capital Advisors, LP ("CCMP") will not beneficially own any shares of our outstanding common stock and INEOS Limited ("INEOS") will beneficially own approximately 20.6% of our outstanding common stock. Assuming completion of the offering and the Share Repurchase, CCMP will no longer beneficially own any shares of our outstanding common stock. However, for as long as INEOS continues to beneficially own a substantial percentage of the voting power of our outstanding common stock, they will continue to have significant influence over us. For example, INEOS will be able to strongly influence the election of all of the members of our board of directors and our business and affairs, including any determinations with respect to mergers or other business combinations, the acquisition or disposition of assets, the incurrence of additional indebtedness, the issuance of any additional shares of common stock or other equity securities, the repurchase or redemption of shares of our common stock and the payment of dividends.

Additionally, CCMP and INEOS are in the business of making investments in companies and may acquire and hold interests in businesses that compete directly or indirectly with us. CCMP and INEOS may also pursue acquisition opportunities that may be complementary to our business, and, as a result, those acquisition opportunities may not be available to us.

***Our stock price could be extremely volatile and, as a result, you may not be able to resell your shares at or above the price you paid for them.***

Since January 1, 2022, the price of our common stock, as reported on the New York Stock Exchange, has ranged from an intraday low of $8.20 on November 15, 2022 to an intraday high of $12.05 on March 29, 2022. In addition, the stock market in general has been highly volatile. As a result, the market price of our common stock is likely to be similarly volatile, and investors in our common stock may experience a decrease, which could be substantial, in the value of their stock, including decreases unrelated to our operating performance or prospects, and could lose part or all of their investment. The price of our common stock could be subject to wide fluctuations in response to a number of factors, including those described elsewhere herein and others such as:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• variations in our operating performance and the performance of our competitors;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• actual or anticipated fluctuations in our quarterly or annual operating results;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• publication of research reports by securities analysts about us, our competitors or our industry;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our failure or the failure of our competitors to meet analysts' projections or guidance that we or our
competitors may give to the market;

------

##### [**Table of Contents**](#toc)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• additions or departures of key personnel;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• strategic decisions by us or our competitors, such as acquisitions, divestitures, spin-offs, joint ventures,
strategic investments or changes in business strategy;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the passage of legislation or other regulatory developments affecting us or our industry;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• changes in legislation, regulation and government policy as a result of the U.S. presidential and congressional
elections;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• speculation in the press or investment community;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• changes in accounting principles;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• terrorist acts, acts of war or periods of widespread civil unrest;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• natural disasters and other calamities; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• changes in general market and economic conditions.

In addition, broad market and industry factors may negatively affect the market price of our common stock, regardless of our actual operating performance, and factors beyond our control may cause our stock price to decline rapidly and unexpectedly. We are exposed to the impacts of any global or domestic economic disruption that may occur, including any impacts resulting from the war in Ukraine and the economic effects of COVID-19.

In the past, securities class action litigation has often been initiated against companies following periods of volatility in their stock price. This type of litigation could result in substantial costs and divert our management's attention and resources, and could also require us to make substantial payments to satisfy judgments or to settle litigation.

***Your percentage ownership in us may be diluted by future issuances of capital stock, which could reduce your influence over matters on which stockholders vote.***

Our board of directors has the authority, without action or vote of our stockholders, to issue all or any part of our authorized but unissued shares of common stock, including shares issuable upon exercise of options, or shares of our authorized but unissued preferred stock, subject to the applicable rules of the New York Stock Exchange. Issuances of common stock or voting preferred stock would reduce your influence over matters on which our stockholders vote and, in the case of issuances of preferred stock, would likely result in your interest in us being subject to the prior rights of holders of that preferred stock.

***There may be sales of a substantial amount of our common stock after this offering by our current stockholders, and these sales could cause the price of our common stock to fall.***

As of February 23, 2023, there were 123,194,080 shares of our common stock outstanding. Of our issued and outstanding shares, all of the common stock sold in our initial public offering or in this offering will be freely transferable, except for any shares held by our "affiliates," as that term is defined in Rule 144 under the Securities Act of 1933, as amended (the "Securities Act"). Following completion of this offering and the Share Repurchase, which will result in 120,194,080 shares of common stock outstanding, approximately 20.6% of our outstanding common stock will be held by INEOS. Sales of substantial amounts of our common stock in the public market after this offering, or the perception that such sales will occur, could adversely affect the market price of our common stock and make it difficult for us to raise funds through securities offerings in the future.

In connection with this offering, each of our officers and directors, INEOS and each of the selling stockholders have entered into a lock-up agreement with the underwriter, which regulates their sales of our common stock for a period of 30 days after the date of this prospectus supplement, subject to certain exceptions.

------

##### [**Table of Contents**](#toc)
In addition, we have registered shares of our common stock that are reserved for issuance under our 2016 Stock Incentive Plan and 2017 Omnibus Incentive Plan, as amended and restated.

***Provisions in our charter documents and Delaware law may deter takeover efforts that may be beneficial to stockholder value.***

In addition to the beneficial ownership by INEOS of a substantial percentage of our common stock, provisions in our certificate of incorporation and bylaws and Delaware law could make it harder for a third party to acquire us, even if doing so might be beneficial to our stockholders. These provisions include a classified board of directors and the ability of our board of directors to issue preferred stock without stockholder approval that could be used to dilute a potential hostile acquiror. Our certificate of incorporation imposes some restrictions on mergers and other business combinations between us and any holder of 15% or more of our outstanding common stock other than INEOS and investment funds affiliated with CCMP. As a result, you may lose your ability to sell your stock for a price in excess of the prevailing market price due to these protective measures, and efforts by stockholders to change the direction or management of the company may be unsuccessful.

***Our certificate of incorporation designates courts in the State of Delaware as the sole and exclusive forum for certain types of actions and proceedings that may be initiated by our stockholders, which could limit our stockholders' ability to obtain a favorable judicial forum for disputes with us or our directors, officers or employees.***

Our certificate of incorporation provides that, subject to limited exceptions, the Court of Chancery of the State of Delaware is the sole and exclusive forum for:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any derivative action or proceeding brought on our behalf;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers or other
employees to us or our stockholders;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any action asserting a claim against us arising pursuant to any provision of the General Corporation Law of the
State of Delaware, our certificate of incorporation or our bylaws;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any action to interpret, apply, enforce or determine the validity of our certificate of incorporation or bylaws;
or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any other action asserting a claim against us that is governed by the internal affairs doctrine (each, a
"Covered Proceeding").

In addition, our certificate of incorporation provides that if any action the subject matter of which is a Covered Proceeding is filed in a court other than the specified Delaware courts without the approval of our board of directors (each, a "Foreign Action"), the claiming party will be deemed to have consented to (i) the personal jurisdiction of the specified Delaware courts in connection with any action brought in any such courts to enforce the exclusive forum provision described above and (ii) having service of process made upon such claiming party in any such enforcement action by service upon such claiming party's counsel in the Foreign Action as agent for such claiming party.

Any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock shall be deemed to have notice of and to have consented to these provisions. These provisions may limit a stockholder's ability to bring a claim in a judicial forum that it finds favorable for disputes with us or our directors, officers or other employees, which may discourage such lawsuits against us and our directors, officers and employees. Alternatively, if a court were to find these provisions of our certificate of incorporation inapplicable to, or unenforceable in respect of, one or more of the specified types of actions or proceedings, we may incur additional costs associated with resolving such matters in other jurisdictions, which could adversely affect our business and financial condition.

------

##### [**Table of Contents**](#toc)
***Our certificate of incorporation contains a provision renouncing our interest and expectancy in certain corporate opportunities, which could adversely impact our business.***

Each of CCMP and INEOS, and the members of our board of directors who are affiliated with CCMP and INEOS, by the terms of our certificate of incorporation, are not required to offer us any corporate opportunity of which they become aware and can take any such corporate opportunity for themselves or offer it to other companies in which they have an investment. We, by the terms of our certificate of incorporation, expressly renounce any interest or expectancy in any such corporate opportunity to the extent permitted under applicable law, even if the opportunity is one that we or our subsidiaries might reasonably have pursued or had the ability or desire to pursue if granted the opportunity to do so. Our certificate of incorporation may not be amended to eliminate our renunciation of any such corporate opportunity arising prior to the date of any such amendment.

CCMP and INEOS are in the business of making investments in companies and may from time to time acquire and hold interests in businesses that compete directly or indirectly with us. These potential conflicts of interest could have a material adverse effect on our business, financial condition, results of operations or prospects if CCMP or INEOS allocate attractive corporate opportunities to themselves or their affiliates instead of to us.

***We may not pay additional dividends on our common stock and, consequentially, you may not receive any return on investment unless you sell your common stock for a price greater than that which you paid for it.***

Although we paid special cash dividends in December 2020 and August 2021, our board of directors may decide to retain future earnings, if any, for future operations, expansion and debt repayment and may not pay any special or regular dividends for the foreseeable future. Any decision to declare and pay special or regular dividends in the future will be made at the discretion of our board of directors and will depend on, among other things, our results of operations, financial condition, cash requirements, contractual restrictions and other factors that our board of directors may deem relevant. In addition, our ability to pay dividends may be limited by covenants of any existing and future outstanding indebtedness we or our subsidiaries incur, including our credit facilities and outstanding notes. As a result, you may not receive any return on an investment in our common stock unless you sell your common stock for a price greater than that which you paid for it.

------

##### [**Table of Contents**](#toc)
**CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS** 

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein include statements that express our opinions, expectations, beliefs, plans, objectives, assumptions or projections regarding future events or future results and therefore are, or may be deemed to be, "forward-looking statements." These forward-looking statements can generally be identified by the use of forward-looking terminology, including the terms "believes," "expects," "may," "will," "should," "seeks," "projects," "approximately," "intends," "plans," "estimates" or "anticipates," or, in each case, their negatives or other variations or comparable terminology. These forward-looking statements include all matters that are not historical facts. They appear in a number of places throughout this prospectus supplement, the accompanying prospectus and the documents incorporated herein and therein by reference and include, but are not limited to, statements regarding our future results of operations, financial condition, liquidity, prospects, growth, strategies, capital allocation program, product and service offerings, including the impact of Russia's invasion of Ukraine on such items, expected demand trends and our 2023 financial outlook.

By their nature, forward-looking statements involve risks and uncertainties because they relate to events and depend on circumstances that may or may not occur in the future. Some of the key factors that could cause actual results to differ from our expectations include the following risks related to our business:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• as a global business, we are exposed to local business risks in different countries;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we are affected by general economic conditions and economic downturns;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• exchange rate fluctuations could adversely affect our financial condition, results of operations and cash flows;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our international operations require us to comply with anti-corruption laws, trade and export controls and
regulations of the U.S. government and various international jurisdictions in which we do business;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• alternative technology or other changes in our customers' products may reduce or eliminate the need for
certain of our products;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our new product development and research and development efforts may not succeed and our competitors may develop
more effective or successful products;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our substantial level of indebtedness could adversely affect our financial condition;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• if we are unable to manage the current and future inflationary environment and to pass on increases in raw
material prices, including natural gas, or labor costs to our customers or to retain or replace our key suppliers, our results of operations and cash flows may be negatively affected;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we face substantial competition in the industries in which we operate;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we are subject to the risk of loss resulting from non-payment or non-performance by our customers;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we rely on a limited number of customers for a meaningful portion of our business;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• multi-year customer contracts in our Ecoservices segment are subject to potential early termination and such
contracts may not be renewed at the end of their respective terms;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our quarterly results of operations are subject to fluctuations because the demand for some of our products is
seasonal;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our growth projects may result in significant expenditures before generating revenues, if any, which may
materially and adversely affect our ability to implement our business strategy;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we may be liable to damages based on product liability claims brought against us or our customers for costs
associated with recalls of our or our customers' products;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we are subject to extensive environmental, health and safety regulations and face various risks associated with
potential non-compliance or releases of hazardous materials;

------

##### [**Table of Contents**](#toc)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• existing and proposed regulations to address climate change by limiting greenhouse gas emissions may cause us to
incur significant additional operating and capital expenses and may impact our business and results of operations;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• production and distribution of our products could be disrupted for a variety of reasons, including as a result of
supply chain constraints, and such disruptions could expose us to significant losses or liabilities;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the insurance that we maintain may not fully cover all potential exposures;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we could be subject to damages based on claims brought against us by our customers or lose customers as a result
of the failure of our products to meet certain quality specifications;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our failure to protect our intellectual property and infringement on the intellectual property rights of third
parties;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• disruption, failure or cyber security breaches affecting or targeting computers and infrastructure used by us or
our business partners may adversely impact our business and operations; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the impact of the COVID-19 pandemic on the global economy and financial
markets, as well as on our business and our suppliers, and the response of governments and of our company to the outbreak including variants of the virus and associated containment, remediation and vaccination efforts.

The above is not a complete list of factors that could cause actual results to differ from our expectations, and it is not possible for us to predict all of them. Important factors that could cause actual results to differ materially from our expectations are more fully described in our other filings with the SEC, including in the "Risk Factors" section in our Annual Report on Form 10-K for the year ended December 31, 2022, incorporated by reference in this prospectus supplement. See "Where You Can Find More Information."

Although we base these forward-looking statements on assumptions that we believe are reasonable when made, we caution you that forward-looking statements are not guarantees of future performance and that our actual results of operations, financial condition and liquidity, and the development of the industry in which we operate may differ materially from those made in or suggested by the forward-looking statements contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein. In addition, even if our results of operations, financial condition and liquidity, and the development of the industry in which we operate, are consistent with the forward-looking statements, those results or developments may not be indicative of results or developments in subsequent periods.

Given these risks and uncertainties, you are cautioned not to place undue reliance on these forward-looking statements. Any forward-looking statement that we make in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein speaks only as of the date of such statement, and we undertake no obligation to update any forward-looking statements or to publicly announce the results of any revisions to any of those statements to reflect future events or developments, except as required by law.

------

##### [**Table of Contents**](#toc)
**USE OF PROCEEDS** 

We will not receive any proceeds from the sale of shares of our common stock by the selling stockholders.

**DIVIDEND POLICY** 

Although we paid a special cash dividend of $1.80 per share on December 29, 2020 and a special cash dividend of $3.20 per share on August 23, 2021, each of which were financed with the net proceeds from the sale of our Performance Materials business and our Performance Chemicals business, respectively, we may retain future earnings, if any, for future operations, expansion and debt repayment and may not pay any special or regular dividends for the foreseeable future. Any decision to declare and pay special or regular dividends in the future will be made at the discretion of our board of directors and will depend on, among other things, our results of operations, financial condition, cash requirements, contractual restrictions and other factors that our board of directors may deem relevant. In addition, our ability to pay dividends may be limited by covenants of any existing and future outstanding indebtedness we or our subsidiaries incur, including our credit facilities and outstanding notes.

------

##### [**Table of Contents**](#toc)
**SELLING STOCKHOLDERS** 

The following table and footnotes set forth information with respect to the beneficial ownership of our common stock as of February 23, 2023 by each of the selling stockholders.

The percentage ownership information shown in the table below with respect to the shares of common stock owned before this offering is based upon 123,194,080 shares of common stock outstanding as of February 23, 2023. The percentage ownership information shown in the table below with respect to the shares owned after this offering is based upon 120,194,080 shares of common stock outstanding, which gives effect to the Share Repurchase.

Beneficial ownership is determined in accordance with the rules of the SEC and generally includes voting or investment power with respect to the shares. Except as indicated in the footnote to this table, we believe that each of the selling stockholders identified in the table below possesses sole voting and investment power over all shares shown as beneficially owned by such selling stockholder.

---

| | | | | | |
|:---|:---|:---|:---|:---|:---|
|  | **Shares Owned Before the<br>Offering** | **Shares Owned Before the<br>Offering** | **Shares<br>Offered<br>Hereby** | **Shares Owned After<br>the Offering <sup>(1)</sup>** | **Shares Owned After<br>the Offering <sup>(1)</sup>** |
| **Name** | **Number** | **Percentage** |  | **Number** | **Percentage** |
|  CCMP Capital Investors III, L.P. and related investment funds<sup>(2)</sup> | 11490444 | 9.3% | 11490444 |  | —% |

---

(1) Assumes the consummation of the Share Repurchase of 3,000,000 shares of our common stock from the underwriter
concurrently with the closing of this offering.

(2) Includes 5,446,572 shares of our common stock held by CCMP Capital Investors III, L.P. ("CCMP Capital
Investors"), 552,064 shares of our common stock held by CCMP Capital Investors III (Employee), L.P. ("CCMP Employee"), 1,660,544 shares of our common stock held by CCMP Capital Investors III (AV-7), L.P. ("CCMP AV-7"), 93,947 shares of our common stock held by CCMP Capital Investors III (AV-8), L.P.
("CCMP AV-8"), 1,878,125 shares of our common stock held by CCMP Capital Investors III (AV-9), L.P. ("CCMP AV-9"), 123,059 shares of our common stock held by CCMP Capital Investors III (AV-10), L.P. ("CCMP AV-10" and,
together with CCMP Capital Investors, CCMP Employee, CCMP AV-7, CCMP AV-8 and CCMP AV-9, the "CCMP Capital Funds") and
1,736,133 shares of our common stock held by Quartz Co-Invest, L.P. ("Quartz" and, together with the CCMP Capital Funds, the "CCMP Investors"). The general partner of the CCMP Capital Funds
is CCMP Capital Associates III, L.P. ("CCMP Capital Associates"). The general partner of CCMP Capital Associates is CCMP Capital Associates III GP, LLC ("CCMP Capital Associates GP"). The general partner of Quartz is CCMP Co-Invest III A GP, LLC ("CCMP Co-Invest GP"). CCMP Capital Associates GP and CCMP Co-Invest GP are each wholly owned by CCMP
Capital, LP. The general partner of CCMP Capital, LP is CCMP Capital GP, LLC ("CCMP Capital GP"). CCMP Capital GP ultimately exercises voting and investment power over the shares of our common stock held by the CCMP Investors. As a result,
CCMP Capital GP may be deemed to share beneficial ownership with respect to the shares of our common stock held by the CCMP Investors. The investment committee of CCMP Capital GP with respect to the shares of our common stock includes Timothy Walsh
who serves as a director of the Company. Each of the CCMP entities has an address of c/o CCMP Capital Advisors, LP, 1 Rockefeller Plaza, 16th Floor, New York, New York 10020.

Following the consummation of this offering, none of the foregoing entities will beneficially own any shares of our common stock.

------

##### [**Table of Contents**](#toc)
**MATERIAL U.S. FEDERAL INCOME AND ESTATE TAX CONSIDERATIONS FOR NON-U.S. HOLDERS OF COMMON STOCK** 

The following is a summary of the material U.S. federal income and estate tax considerations relating to the purchase, ownership and disposition of our common stock by Non-U.S. Holders (defined below). This summary does not purport to be a complete analysis of all the potential tax considerations relevant to Non-U.S. Holders. This summary is based upon the Internal Revenue Code of 1986, as amended (the "Internal Revenue Code"), the Treasury regulations promulgated or proposed thereunder and administrative and judicial interpretations thereof, all as of the date hereof and all of which are subject to change at any time, possibly on a retroactive basis.

This summary assumes that shares of our common stock are held as "capital assets" within the meaning of Section 1221 of the Internal Revenue Code. This summary does not purport to deal with all aspects of U.S. federal income and estate taxation that might be relevant to particular Non-U.S. Holders in light of their particular investment circumstances or status, nor does it address specific tax considerations that may be relevant to particular persons (including, for example, financial institutions, broker-dealers, taxpayers subject to special tax accounting rules under Section 451(b) of the Internal Revenue Code, insurance companies, partnerships or other pass-through entities, certain U.S. expatriates, tax-exempt organizations, pension plans, "controlled foreign corporations", "passive foreign investment companies", corporations that accumulate earnings to avoid U.S. federal income tax, persons in special situations, such as those who have elected to mark securities to market or those who hold common stock as part of a straddle, hedge, conversion transaction, synthetic security or other integrated investment, or holders subject to the alternative minimum tax). In addition, except as explicitly addressed herein with respect to estate tax, this summary does not address estate and gift tax considerations, the Medicare contribution tax on net investment income, or considerations under the tax laws of any state, local or non-U.S. jurisdiction.

For purposes of this summary, a "Non-U.S. Holder" means a beneficial owner of common stock that for U.S. federal income tax purposes is not classified as a partnership and that, for U.S. federal income tax purposes, is not:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an individual who is a citizen or resident of the United States;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• a corporation or any other organization taxable as a corporation for U.S. federal income tax purposes, created or
organized in or under the laws of the United States, any state thereof or the District of Columbia;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an estate, the income of which is included in gross income for U.S. federal income tax purposes regardless of its
source; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• a trust if (1) a U.S. court is able to exercise primary supervision over the trust's administration and
one or more U.S. persons have the authority to control all of the trust's substantial decisions or (2) the trust has a valid election in effect under applicable U.S. Treasury regulations to be treated as a U.S. person.

If an entity that is classified as a partnership for U.S. federal income tax purposes holds our common stock, the tax treatment of persons treated as its partners for U.S. federal income tax purposes will generally depend upon the status of the partner and the activities of the partnership. Partnerships and other entities that are classified as partnerships for U.S. federal income tax purposes and persons holding our common stock through a partnership or other entity classified as a partnership for U.S. federal income tax purposes are urged to consult their own tax advisors.

There can be no assurance that the Internal Revenue Service ("IRS") will not challenge one or more of the tax consequences described herein, and we have not obtained, nor do we intend to obtain a ruling from the IRS with respect to the U.S. federal income or estate tax consequences to a Non-U.S. Holder of the purchase, ownership or disposition of our common stock.

------

##### [**Table of Contents**](#toc)
THIS SUMMARY IS FOR GENERAL INFORMATION ONLY AND IS NOT INTENDED TO BE TAX ADVICE. NON-U.S. HOLDERS ARE URGED TO CONSULT THEIR TAX ADVISORS CONCERNING THE U.S. FEDERAL INCOME AND ESTATE TAXATION, STATE, LOCAL AND NON-U.S. TAXATION AND OTHER TAX CONSEQUENCES TO THEM OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF OUR COMMON STOCK.

**Distributions on Our Common Stock** 

As discussed under "Dividend Policy" above, we may retain future earnings, if any, for future operations, expansion and debt repayment and may not pay any special or regular dividends for the foreseeable future. However, we expect to reevaluate our dividend policy on a regular basis following this offering and may, subject to compliance with the covenants contained in our senior secured credit facilities and other considerations, determine to pay dividends in the future. In the event that we make a distribution of cash or property with respect to our common stock, any such distributions generally will constitute dividends for U.S. federal income tax purposes to the extent of our current and accumulated earnings and profits, as determined under U.S. federal income tax principles. If a distribution exceeds our current and accumulated earnings and profits, the excess will constitute a return of capital and will first reduce the holder's adjusted tax basis in our common stock, but not below zero. Any remaining excess will be treated as capital gain, subject to the tax treatment described below in "—Gain on Sale, Exchange or Other Taxable Disposition of Our Common Stock." Any such distribution would also be subject to the discussions below under the sections titled "—Additional Withholding and Reporting Requirements" and "—Backup Withholding and Information Reporting."

Dividends paid to a Non-U.S. Holder generally will be subject to a 30% U.S. federal withholding tax unless such Non-U.S. Holder provides us or the applicable withholding agent, as the case may be, with the appropriate IRS Form W-8, such as:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• IRS Form W-8BEN or IRS Form W-8BEN-E (or successor forms) certifying, under penalties of perjury, a reduction in, or exemption from, withholding under an applicable income tax treaty, or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• IRS Form W-8ECI (or successor form) certifying, under penalties of
perjury, that a dividend paid on common stock is not subject to withholding tax because it is effectively connected with a trade or business in the United States of the Non-U.S. Holder (in which case such
dividend generally will be subject to regular graduated U.S. tax rates as described below).

The certification requirement described above must be provided to us or the applicable withholding agent prior to the payment of dividends and may be required to be updated periodically. The certification also may require a Non-U.S. Holder that provides an IRS form or that claims treaty benefits to provide its U.S. taxpayer identification number. Special certification and other requirements apply in the case of certain Non-U.S. Holders that hold shares of our common stock through intermediaries or are pass-through entities for U.S. federal income tax purposes.

Each Non-U.S. Holder is urged to consult its own tax advisor about the specific methods for satisfying these requirements. A claim for exemption will not be valid if the person receiving the applicable form has actual knowledge or reason to know that the statements on the form are false.

If dividends are effectively connected with a trade or business in the United States of a Non-U.S. Holder (and, if required by an applicable income tax treaty, are attributable to a U.S. permanent establishment), the Non-U.S. Holder, although exempt from the withholding tax described above (provided that the certification requirements described above are satisfied), generally will be subject to U.S. federal income tax on such dividends on a net income basis in the same manner as if it were a United States person, as defined under the Internal Revenue Code. In addition, if a Non-U.S. Holder is treated as a corporation for U.S. federal income tax purposes, the Non-U.S. Holder may be subject to an additional "branch profits tax" equal to 30% (unless reduced by an applicable income treaty) of its earnings and profits in respect of such effectively connected dividend income.

------

##### [**Table of Contents**](#toc)
Non-U.S. Holders that do not timely provide us or the applicable withholding agent with the required certification, but which are eligible for a reduced rate of U.S. federal withholding tax pursuant to an income tax treaty, may obtain a refund or credit of any excess amount withheld by timely filing an appropriate claim for refund with the IRS.

**Gain on Sale, Exchange or Other Taxable Disposition of Our Common Stock** 

Subject to the discussions below under the sections titled "—Additional Withholding and Reporting Requirements" and "—Backup Withholding and Information Reporting", in general, a Non-U.S. Holder will not be subject to U.S. federal income tax or withholding tax on gain realized upon such holder's sale, exchange or other taxable disposition of shares of our common stock unless (i) such Non-U.S. Holder is an individual who is present in the United States for 183 days or more in the taxable year of disposition, and certain other conditions are met, (ii) we are or have been a "United States real property holding corporation", as defined in the Internal Revenue Code (a "USRPHC"), at any time within the shorter of the five-year period preceding the disposition and the Non-U.S. Holder's holding period in the shares of our common stock, and certain other requirements are met, or (iii) such gain is effectively connected with the conduct by such Non-U.S. Holder of a trade or business in the United States (and, if required by an applicable income tax treaty, is attributable to a permanent establishment maintained by such Non-U.S. Holder in the United States).

If the first exception applies, the Non-U.S. Holder generally will be subject to U.S. federal income tax at a rate of 30% (or at a reduced rate under an applicable income tax treaty) on the amount by which such Non-U.S. Holder's capital gains allocable to U.S. sources exceed capital losses allocable to U.S. sources during the taxable year of the disposition. If the third exception applies, the Non-U.S. Holder generally will be subject to U.S. federal income tax with respect to such gain on a net income basis in the same manner as if it were a resident of the United States and a Non-U.S. Holder that is a corporation for U.S. federal income tax purposes may also be subject to a branch profits tax with respect to any earnings and profits attributable to such gain at a rate of 30% (or at a reduced rate under an applicable income tax treaty).

Generally, a corporation is a USRPHC only if the fair market value of its United States real property interests (as defined in the Internal Revenue Code) equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests plus its other assets used or held for use in a trade or business. Although there can be no assurance in this regard, we believe that we are not, and do not anticipate becoming, a USRPHC. However, because the determination of whether we are a USRPHC depends on the fair market value of our United States real property interests relative to the fair market value of other business assets, there can be no assurance that we will not become a USRPHC in the future. Even if we are or were to become a USRPHC, a Non-U.S. Holder would not be subject to U.S. federal income tax on a sale, exchange or other taxable disposition of our common stock by reason of our status as USRPHC so long as our common stock is "regularly traded" (as defined by applicable Treasury regulations) on an established securities market at any time during the calendar year in which the disposition occurs and such Non-U.S. Holder does not own and is not deemed to own (directly, indirectly or constructively) more than 5% of our common stock at any time during the shorter of the five-year period ending on the date of disposition and the holder's holding period. However, no assurance can be provided that our common stock will be regularly traded on an established securities market for purposes of the rules described above. Prospective investors are encouraged to consult their own tax advisors regarding the possible consequences to them if we are, or were to become, a USRPHC.

**Additional Withholding and Reporting Requirements** 

Sections 1471 through 1474 of the Internal Revenue Code and the related Treasury regulations, together with other U.S. Treasury and IRS guidance issued thereunder and intergovernmental agreements, legislation, rules and other official guidance adopted pursuant to such intergovernmental agreements (collectively, "FATCA")

------

##### [**Table of Contents**](#toc)
generally impose U.S. federal withholding at a rate of 30% on payments of dividends on our common stock on certain non-U.S. entities (including certain intermediaries) unless such persons establish that they are compliant with or exempt from FATCA. This regime requires, among other things, a broad class of persons to enter into agreements with the IRS to obtain, disclose and report information about their investors and account holders. An intergovernmental agreement between the U.S. and an applicable foreign country may, however, modify these requirements.

Under the applicable Treasury regulations and administrative guidance, withholding under FATCA generally applies to payments of dividends on shares of our common stock to such applicable non-U.S. entities that fail to establish they are compliant with or exempt from FATCA. While withholding under FATCA would have also applied to payments of gross proceeds from the sale or other disposition of stock on or after January 1, 2019 by such applicable non-U.S. entities, proposed Treasury regulations (on which taxpayers may currently rely) eliminate FATCA withholding on payments of gross proceeds from the sale or other disposition of stock entirely. Taxpayers generally may rely on these proposed Treasury regulations until final Treasury regulations are issued.

Prospective investors should consult their own tax advisors regarding the possible impact of these rules on their investment in our common stock, and the entities through which they hold our common stock, including, without limitation, the process and deadlines for meeting the applicable requirements to prevent the imposition of this 30% withholding tax under FATCA.

**Backup Withholding and Information Reporting** 

In general, information reporting will apply to distributions on our common stock paid to a Non-U.S. Holder and the tax withheld, if any, with respect to the distributions. Non-U.S. Holders may have to comply with specific certification procedures to establish that the holder is not a United States person (as defined in the Internal Revenue Code) in order to avoid backup withholding at the applicable rate, currently 24%, with respect to dividends on our common stock. Dividends paid to Non-U.S. Holders subject to the U.S. withholding tax, as described above under the section titled "—Distributions on Our Common Stock," generally will be exempt from U.S. backup withholding.

Information reporting and, depending on the circumstances, backup withholding will generally apply to the proceeds of a disposition of our common stock by a Non-U.S. Holder effected by or through the U.S. office of any broker, U.S. or foreign, unless the holder certifies its status as a Non-U.S. Holder and satisfies certain other requirements, or otherwise establishes an exemption. Generally, information reporting and backup withholding will not apply to a payment of disposition proceeds to a Non-U.S. Holder where the transaction is effected outside the United States through a non-U.S. office of a broker. However, for information reporting purposes, dispositions effected through a non-U.S. office of a U.S. broker or a foreign broker with substantial U.S. ownership or operations generally will be treated in a manner similar to dispositions effected through a U.S. office of a broker. Prospective investors should consult their own tax advisors regarding the application of the information reporting and backup withholding rules to them.

Copies of information returns may be made available to the tax authorities of the country in which the Non-U.S. Holder resides or in which the Non-U.S. Holder is incorporated, under the provisions of a specific treaty or agreement.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules from a payment to a Non-U.S. Holder may be refunded or credited against the Non-U.S. Holder's U.S. federal income tax liability, if any, provided that an appropriate claim is timely filed with the IRS.

------

##### [**Table of Contents**](#toc)
**Federal Estate Tax** 

Shares of our common stock that are owned (or treated as owned) by an individual who is not a citizen or resident of the United States (as specially defined for U.S. federal estate tax purposes) at the time of death will be included in such individual's gross estate for U.S. federal estate tax purposes, unless an applicable estate or other tax treaty provides otherwise, and therefore may be subject to U.S. federal estate tax.

------

##### [**Table of Contents**](#toc)
**UNDERWRITING** 

Jefferies LLC is acting as the underwriter in connection with this offering. Subject to the terms and conditions set forth in an underwriting agreement among the Company, the selling stockholders and the underwriter, the underwriter has agreed to purchase 11,490,444 shares of common stock from the selling stockholders at a price of $ per share, which will result in $ of proceeds to the selling stockholders before expenses.

The underwriting agreement provides that the obligations of the underwriter to purchase the shares included in this offering are subject to approval of legal matters by counsel and to other conditions. The underwriter is obligated to purchase all the shares if the underwriter purchases any of the shares.

Subject to the completion of this offering, we have agreed to purchase 3,000,000 shares of our common stock that are subject to this offering from the underwriter at a price per share equal to the price per share paid by the underwriter to the selling stockholders in this offering. The closing of the Share Repurchase is contingent on the closing of this offering.

We, our officers and directors, INEOS and the selling stockholders have agreed that, for a period of 30 days from the date of this prospectus supplement, we and they will not, without the prior written consent of the underwriter, dispose of or hedge any shares or any securities convertible into or exchangeable for our common stock, subject to certain exceptions. The underwriter, in its sole discretion, may release any of the securities subject to these lock-up agreements at any time without notice.

The shares are listed on the New York Stock Exchange under the symbol "ECVT."

The underwriter may receive from purchasers of the shares normal brokerage commissions in amounts agreed with such purchasers. The underwriter may offer the shares of common stock for sale from time to time in one or more transactions on the New York Stock Exchange, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices, subject to receipt and acceptance by the underwriter and subject to its right to reject any order in whole or in part. The underwriter may effect such transactions by selling shares of common stock to or through dealers, and such dealers may receive compensation in the form of discounts, concessions or commissions from the underwriter and/or purchasers of shares of common stock for whom they may act as agents or to whom they may sell as principals. The difference between the price at which the underwriter purchases shares of common stock and the price at which the underwriter resells such shares of common stock may be deemed underwriting compensation.

The expenses of the offering, including expenses incurred by the selling stockholders, are estimated at $616,000 and are payable by us. We have agreed to reimburse the underwriter for expenses relating to clearance of this offering with the Financial Industry Regulatory Authority up to $25,000.

In connection with the offering, the underwriter may purchase and sell shares in the open market. Purchases and sales in the open market may include short sales, purchases to cover short positions and stabilizing purchases.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Short sales involve secondary market sales by the underwriter of a greater number of shares than they are
required to purchase in the offering, and a short position represents the amount of such sales that have not been covered by subsequent purchases.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Covering transactions involve purchases of shares in the open market in order to cover short positions.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Stabilizing transactions involve bids to purchase shares so long as the stabilizing bids do not exceed a
specified maximum.

------

##### [**Table of Contents**](#toc)
Purchases to cover short positions and stabilizing purchases, as well as other purchases by the underwriter for its own account, may have the effect of preventing or retarding a decline in the market price of the shares. They may also cause the price of the shares to be higher than the price that would otherwise exist in the open market in the absence of these transactions. The underwriter may conduct these transactions on the New York Stock Exchange, in the over-the-counter market or otherwise. If the underwriter commences any of these transactions, it may discontinue them at any time.

**Relationships** 

The underwriter is a full service financial institution engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, principal investment, hedging, financing and brokerage activities. The underwriter and its respective affiliates have in the past performed commercial banking, investment banking and advisory services for us from time to time for which they have received customary fees and reimbursement of expenses and may, from time to time, engage in transactions with and perform services for us in the ordinary course of their business for which the underwriter may receive customary fees and reimbursement of expenses. In the ordinary course of their various business activities, the underwriter and its respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (which may include bank loans and/or credit default swaps) for the underwriter's own account and for the accounts of its customers and may at any time hold long and short positions in such securities and instruments. Such investments and securities activities may involve securities and/or instruments of ours or our affiliates. The underwriter and its affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or financial instruments and may hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

We have agreed to indemnify the underwriter against certain liabilities, including liabilities under the Securities Act, or to contribute to payments the underwriter may be required to make because of any of those liabilities.

**Notice to Prospective Investors in the European Economic Area** 

In relation to each EEA Member State (each a "Relevant Member State"), no shares have been offered or will be offered pursuant to this offering to the public in that Relevant Member State prior to the publication of a prospectus in relation to such shares which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Regulation, except that such shares may be offered to the public in that Relevant Member State at any time:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) to any legal entity which is a qualified investor as defined under Article 2 of the Prospectus Regulation;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of the
Prospectus Regulation) subject to obtaining the prior consent of the underwriter for any such offer; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iii) in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

provided that no such offer of shares shall require the issuer and/or selling stockholders or the underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation.

For the purposes of this provision, the expression an "offer to the public" in relation to the shares described in this prospectus in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the shares to be offered so as to enable an investor to decide to purchase any shares, and the expression "Prospectus Regulation" means Regulation (EU) 2017/1129.

------

##### [**Table of Contents**](#toc)
Each person in a Relevant Member State who receives any communication in respect of, or who acquires any shares under, the offering contemplated hereby will be deemed to have represented, warranted and agreed to and with the underwriter and its affiliates and the issuer that:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) it is a qualified investor within the meaning of the Prospectus Regulation; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) in the case of any shares described in this prospectus acquired by it as a financial intermediary, as that term
is used in Article 5 of the Prospectus Regulation, (i) such shares acquired by it in this offering have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view
to their offer or resale to, persons in any Relevant Member State other than qualified investors, as that term is defined in the Prospectus Regulation, or have been acquired in other circumstances falling within the points (a) to (d) of Article
1(4) of the Prospectus Regulation and the prior consent of the underwriter has been given to the offer or resale; or (ii) where such shares have been acquired by it on behalf of persons in any Relevant Member State other than qualified
investors, the offer of those shares to it is not treated under the Prospectus Regulation as having been made to such persons.

The issuer, the underwriter and its affiliates, and others will rely upon the truth and accuracy of the foregoing representation, acknowledgement and agreement. Notwithstanding the above, a person who is not a qualified investor and who has notified the underwriter of such fact in writing may, with the prior consent of the underwriter, be permitted to acquire shares in this offering.

**Notice to Prospective Investors in the United Kingdom** 

This prospectus and any other material in relation to the shares described herein is only being distributed to, and is only directed at, and any investment or investment activity to which this Prospectus relates is available only to, and will be engaged in only with, persons who are (i) persons having professional experience in matters relating to investments who fall within the definition of investment professionals in Article 19(5) of the Financial Promotion Order (the "FPO"); (ii) high net worth entities falling within Article 49(2)(a) to (d) of the FPO; (iii) outside the United Kingdom; or (iv) persons to whom an invitation or inducement to engage in investment activity (within the meaning of Section 21 of the Financial Services and Markets Act 2000 (the "FSMA")) in connection with the issue or sale of any shares may otherwise lawfully be communicated or caused to be communicated, (all such persons together being referred to as "Relevant Persons"). The shares described in this prospectus are only available in the United Kingdom to, and any invitation, offer or agreement to purchase or otherwise acquire the shares will be engaged in only with, the Relevant Persons. This prospectus and its contents are confidential and should not be distributed, published or reproduced (in whole or in part) or disclosed by recipients to any other person in the United Kingdom. Any person in the United Kingdom that is not a Relevant Person should not act or rely on this prospectus or any of its contents.

No shares have been offered or will be offered pursuant to the offering to the public in the United Kingdom prior to the publication of a prospectus in relation to the shares which has been approved by the Financial Conduct Authority, except that the shares may be offered to the public in the United Kingdom at any time:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) to any legal entity which is a qualified investor as defined under Article 2 of the UK Prospectus Regulation;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of the UK
Prospectus Regulation), subject to obtaining the prior consent of the underwriter for any such offer; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iii) in any other circumstances falling within Section 86 of the FSMA;

provided that no such offer of the shares shall require the issuer and/or the underwriter or any of its affiliates to publish a prospectus pursuant to Section 85 of the FSMA or supplement a prospectus pursuant to Article 23 of the UK Prospectus Regulation. For the purposes of this provision, the expression an "offer to the public" in relation to the shares in the United Kingdom means the communication in any form and by any means of

------

##### [**Table of Contents**](#toc)
sufficient information on the terms of the offer and any shares to be offered so as to enable an investor to decide to purchase or subscribe for any shares and the expression "UK Prospectus Regulation" means Regulation (EU) 2017/1129 as it forms part of domestic law by virtue of the European Union (Withdrawal) Act 2018.

Each person in the United Kingdom who acquires any shares in this offering or to whom any offer is made will be deemed to have represented, acknowledged and agreed to and with the issuer, the underwriter and its affiliates that it meets the criteria outlined in this section.

**Notice to Prospective Investors in Canada** 

The shares may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser's province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser's province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 *Underwriting Conflicts* (NI 33-105), the underwriter is not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

**Notice to Prospective Investors in France** 

Neither this prospectus nor any other offering material relating to the shares described in this prospectus has been submitted to the clearance procedures of the *Autorité des Marchés Financiers* or of the competent authority of another member state of the European Economic Area and notified to the *Autorité des Marchés Financiers*. The shares have not been offered or sold and will not be offered or sold, directly or indirectly, to the public in France. Neither this prospectus nor any other offering material relating to the shares has been or will be:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• released, issued, distributed or caused to be released, issued or distributed to the public in France; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• used in connection with any offer for subscription or sale of the shares to the public in France.

Such offers, sales and distributions will be made in France only:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• to qualified investors (*investisseurs qualifi é s*) and/or to a restricted circle of
investors (*cercle restreint d ' investisseurs*), in each case investing for their own account, all as defined in, and in accordance with articles L.411-2, D.411-1, D.411-2, D.734-1, D.744-1, D.754-1 and D.764-1 of the French Code monétaire et financier;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• to investment services providers authorized to engage in portfolio management on behalf of third parties; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• in a transaction that, in accordance with article L.411-2-II-1° -or-2° -or 3° of the French *Code mon é taire et financier* and article 211-2 of the General Regulations (*R è glement G é n é ral)* of the Autorité des Marchés Financiers, does not constitute a public offer (*appel public à I ' é pargne*).

------

##### [**Table of Contents**](#toc)
The shares may be resold directly or indirectly, only in compliance with articles L.411-1, L.411-2, L.412-1 and L.621-8 through L.621-8-3 of the French *Code monétaire et financier*.

**Notice to Prospective Investors in Hong Kong** 

The shares may not be offered or sold in Hong Kong by means of any document other than (i) in circumstances which do not constitute an offer to the public within the meaning of the Companies Ordinance (Cap. 32, Laws of Hong Kong), or (ii) to "professional investors" within the meaning of the Securities and Futures Ordinance (Cap. 571, Laws of Hong Kong) and any rules made thereunder, or (iii) in other circumstances which do not result in the document being a "prospectus" within the meaning of the Companies Ordinance (Cap. 32, Laws of Hong Kong) and no advertisement, invitation or document relating to the shares may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the laws of Hong Kong) other than with respect to shares which are or are intended to be disposed of only to persons outside Hong Kong or only to "professional investors" within the meaning of the Securities and Futures Ordinance (Cap. 571, Laws of Hong Kong) and any rules made thereunder.

**Notice to Prospective Investors in Japan** 

The shares offered in this prospectus have not been and will not be registered under the Financial Instruments and Exchange Law of Japan. The shares have not been offered or sold and will not be offered or sold, directly or indirectly, in Japan or to or for the account of any resident of Japan (including any corporation or other entity organized under the laws of Japan), except (i) pursuant to an exemption from the registration requirements of the Financial Instruments and Exchange Law and (ii) in compliance with any other applicable requirements of Japanese law.

**Notice to Prospective Investors in Singapore** 

This prospectus has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares may not be circulated or distributed, nor may the shares be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the "SFA"), (ii) to a relevant person pursuant to Section 275(1), or any person pursuant to Section 275(1A), and in accordance with the conditions specified in Section 275 of the SFA or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA, in each case subject to compliance with conditions set forth in the SFA.

Where the shares are subscribed or purchased under Section 275 of the SFA by a relevant person which is:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business
of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each
beneficiary of the trust is an individual who is an accredited investor, shares, debentures and units of shares and debentures of that corporation or the beneficiaries' rights and interest (howsoever described) in that trust shall not be
transferred within six months after that corporation or that trust has acquired the shares pursuant to an offer made under Section 275 of the SFA except:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• to an institutional investor (for corporations, under Section 274 of the SFA) or to a relevant person
defined in Section 275(2) of the SFA, or to any person pursuant to an offer that is made on terms that such shares, debentures and units of shares and debentures of that corporation or such rights and interest in that trust are acquired at a
consideration of not less than S$200,000 (or its equivalent in a

------

##### [**Table of Contents**](#toc)
foreign currency) for each transaction, whether such amount is to be paid for in cash or by exchange of securities or other assets, and further for corporations, in accordance with the conditions specified in Section 275 of the SFA; <br>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• where no consideration is or will be given for the transfer; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• where the transfer is by operation of law.

Solely for the purposes of its obligations pursuant to section 30913(1)(a) and 30913(1)(c) of the SFA and the Securities and Futures (Capital Markets Products) Regulations 2018 of Singapore (the "CMP Regulations 2018"), the issuer has determined, and hereby notifies all relevant persons (as defined in Section 309A(1) of the SFA), that the shares are "prescribed capital markets products" (as defined in the CMP Regulations 2018) and Excluded Investment Products (as defined in MAS Notice SFA 04-N12: Notice on the Sale of Investment Products; and MAS notice FAA-N16: Notice on Recommendations on Investment Products).

------

##### [**Table of Contents**](#toc)
**LEGAL MATTERS** 

The validity of the issuance of the shares of common stock to be sold in this offering will be passed upon for us by Ropes & Gray LLP. Certain legal matters in connection with this offering will be passed upon for the underwriter by Latham & Watkins LLP.

**EXPERTS** 

The financial statements and management's assessment of the effectiveness of internal control over financial reporting (which is included in Management's Annual Report on Internal Control over Financial Reporting) of Ecovyst Inc. incorporated in this Prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2022 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

The financial statements of Zeolyst International incorporated in this Prospectus by reference to the Annual Report on Form 10-K of Ecovyst Inc. for the year ended December 31, 2022 have been so incorporated in reliance on the report (which includes an emphasis of matter paragraph relating to the Zeolyst International's significant related party transactions as described in Footnote 15 to the financial statements) of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

**WHERE YOU CAN FIND MORE INFORMATION** 

We have filed with the SEC a registration statement on Form S-3 under the Securities Act with respect to the shares of our common stock being offered by this prospectus supplement and the accompanying prospectus. This prospectus supplement and the accompanying prospectus do not contain all of the information set forth in the registration statement. For further information with respect to us and the shares of our common stock, reference is made to the registration statement and its exhibits. Statements contained in this prospectus supplement or the accompanying prospectus as to the contents of any contract or other document are not necessarily complete. We are required to file annual, quarterly and current reports, proxy statements, and other information with the SEC. Such materials may be accessed electronically by means of the SEC's website at www.sec.gov.

**INCORPORATION OF CERTAIN INFORMATION BY REFERENCE** 

The SEC allows us to "incorporate by reference" into this prospectus supplement information we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement and information in documents that we file later with the SEC will automatically update and supersede information in this prospectus supplement. We incorporate by reference into this prospectus supplement the documents listed below and any future filings made by us with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, except for information "furnished" under Items 2.02, 7.01 or 9.01 on Form 8-K or other information "furnished" to the SEC which is not deemed filed and not incorporated in this prospectus supplement, until the termination of this offering. We hereby incorporate by reference the following documents:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1708035/000170803523000007/ecvt-20221231.htm) for the year ended December 31, 2022, filed with the SEC on February 28, 2023;

------

##### [**Table of Contents**](#toc)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• portions of our [Definitive Proxy Statement](http://www.sec.gov/Archives/edgar/data/1708035/000114036122016997/ny20001161x1_def14a.htm) on Schedule 14A, filed with the SEC on April 
29, 2022, that are incorporated by reference into Part III of our Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1708035/000170803522000006/ecvt-20211231.htm) for the year ended December 31, 2021, filed with the SEC on March 1, 2022; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the description of our common stock contained in the Registration Statement on [Form 8-A](http://www.sec.gov/Archives/edgar/data/1708035/000119312517298321/d451059d8a12b.htm) , as filed with the SEC on September 29, 2017, and any amendment or report filed with the SEC for the purpose of updating such description.

You may request a copy of these filings, at no cost, by writing or telephoning us at the following address:

Ecovyst Inc.

300 Lindenwood Drive

Malvern, PA 19355

(484) 617-1200

Copies of these filings are also available, without charge, on the SEC's website at www.sec.gov and on our website at www.ecovyst.com as soon as reasonably practicable after they are filed electronically with the SEC. The information contained on our website is not a part of this prospectus supplement or the accompanying prospectus.

------

##### [**Table of Contents**](#toc)
![LOGO](g474686g01v00.jpg)

## PQ Group Holdings Inc.
Common Stock

The selling stockholders to be named in a prospectus supplement may offer and sell shares of our common stock from time to time in amounts, at prices and on terms that will be determined at the time of the offering. We will not receive any proceeds from the sale of shares by the selling stockholders.

This prospectus describes the general manner in which the shares of our common stock may be offered and sold by the selling stockholders. The identity of, and specific information required with respect to, the selling stockholders, and the specific manner in which shares of our common stock may be offered and sold will be described in a supplement to this prospectus.

You should carefully read this prospectus and any accompanying prospectus supplement, together with the documents we incorporate by reference, before you invest in our common stock.

Our common stock is listed on the New York Stock Exchange (the "NYSE") under the symbol "PQG." The last reported sale of our common stock on the NYSE on April 23, 2021 was $16.66 per share.

***Investing in our common stock involves substantial risk. Please read "[Risk Factors](#cov474686_1)" beginning on page 2 of this prospectus and any risk factors described in any applicable prospectus supplement and in the documents we incorporate by reference.***

**Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.** 

Prospectus dated April 26, 2021

------

##### [**Table of Contents**](#toc)
**TABLE OF CONTENTS** 

---

| | |
|:---|:---|
|  | **Page** |
|  [ABOUT THIS PROSPECTUS](#rom474686_1) | 1 |
|  [RISK FACTORS](#rom474686_2) | 2 |
|  [CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS](#rom474686_3) | 2 |
|  [USE OF PROCEEDS](#rom474686_4) | 3 |
|  [DESCRIPTION OF CAPITAL STOCK](#rom474686_5) | 4 |
|  [PLAN OF DISTRIBUTION](#rom474686_6) | 8 |
|  [LEGAL MATTERS](#rom474686_7) | 10 |
|  [EXPERTS](#rom474686_8) | 10 |
|  [WHERE YOU CAN FIND MORE INFORMATION](#rom474686_9) | 10 |
|  [INCORPORATION OF CERTAIN INFORMATION BY REFERENCE](#rom474686_10) | 10 |

---

**We have not authorized anyone to provide any information or to make any representations other than those contained or incorporated by reference in this prospectus, any accompanying prospectus supplement or in any free writing prospectuses we have prepared. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus and any accompanying prospectus supplement are an offer to sell only the shares offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. The information contained or incorporated by reference in this prospectus and any accompanying prospectus supplement is current only as of the date of the applicable document.** 

i

------

##### [**Table of Contents**](#toc)
**ABOUT THIS PROSPECTUS** 

*Unless otherwise stated in this prospectus or the context requires otherwise, references to "we," "our," "us," "PQ Group Holdings Inc." and the "Company" and similar terms refer to PQ Group Holdings Inc. and its consolidated subsidiaries.* 

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission ("SEC") as a "well-known seasoned issuer" as defined under Rule 405 under the Securities Act of 1933, as amended (the "Securities Act"), using a "shelf" registration process. Under this shelf registration process, the selling stockholders may from time to time sell shares of our common stock in one or more offerings. This prospectus provides you with a general description of our common stock. Each time the selling stockholders sell shares of our common stock under this shelf registration, we will provide a prospectus supplement that will contain specific information about the terms of that offering, including the specific amounts and prices of the shares of our common stock offered and information about the selling stockholders. The prospectus supplement may also add, update or change information contained in this prospectus. Any statement that we make in this prospectus will be modified or superseded by any inconsistent statement made by us in a prospectus supplement. Before making your investment decision, you should read both this prospectus and any prospectus supplement, including all documents incorporated herein or therein by reference, together with additional information described under "Where You Can Find More Information."

------

##### [**Table of Contents**](#toc)
**RISK FACTORS** 

*Investing in shares of our common stock involves a high degree of risk. See "Item IA. Risk Factors" in our most recent Annual Report on Form I0-K and in subsequent Quarterly Reports on Form 10-Q, which are incorporated by reference in this prospectus, and the "Risk Factors" section in the applicable prospectus supplement for a discussion of the factors you should carefully consider before deciding to purchase shares of our common stock.* 

**CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS** 

This prospectus, any prospectus supplement and any information incorporated by reference into this prospectus or such prospectus supplement may contain certain "forward-looking statements." You can generally identify these forward-looking statements by forward-looking words such as "believe," "anticipate," "expect," "intend," "plan," "will," "may," "estimate," "could," "continue," "ongoing," "predict," "potential," "likely," "seek," and other similar expressions, as well as variations or negatives of these words. You can also identify forward-looking statements by the fact that they do not relate strictly to historical or current facts. Such forward-looking statements are based on current expectations and involve inherent risks and uncertainties, including factors that could delay, divert or change any of them, and could cause actual outcomes to differ materially from current expectations.

Forward-looking statements are not guarantees of future performance and our actual results could differ materially from the results discussed in the forward-looking statements we make. In particular, you should consider the numerous risks described in the "Risk Factors" section of our most recent Annual Report on Form 10-K and in subsequent Quarterly Reports on Form 10-Q, which are incorporated by reference in this prospectus, and the risk factors contained in any applicable prospectus supplement or free writing prospectus. See "Where You Can Find More Information."

As a result of these and other factors, we may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. The forward-looking statements contained in this prospectus reflect our views as of the date hereof. We do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

------

##### [**Table of Contents**](#toc)
**USE OF PROCEEDS** 

We will not receive any proceeds from the sale of shares of our common stock by the selling stockholders.

------

##### [**Table of Contents**](#toc)
**DESCRIPTION OF CAPITAL STOCK** 

**General** 

Our authorized capital stock consists of 450,000,000 shares of common stock, par value $0.01 per share, and 50,000,000 shares of undesignated preferred stock. The following summary describes all material provisions of our capital stock. We urge you to read our certificate of incorporation and our bylaws, which are included as exhibits to the registration statement of which this prospectus forms a part.

Our certificate of incorporation and bylaws contain provisions that are intended to enhance the likelihood of continuity and stability in the composition of our board of directors and which may have the effect of delaying, deferring or preventing a future takeover or change in control of our company unless such takeover or change in control is approved by our board of directors. These provisions include a classified board of directors, elimination of the ability of stockholders to call special meetings, advance notice procedures for stockholder proposals and the ability of our board of directors to issue preferred stock without stockholder approval that could be used to dilute a potential hostile acquiror.

**Common Stock** 

As of December 31, 2020, there were 136,318,557 shares of our common stock outstanding held of record by approximately 84 stockholders. Holders of our common stock are entitled to the following rights:

*Dividend Rights*. Subject to preferences that may apply to shares of preferred stock outstanding at the time, holders of outstanding shares of our common stock will be entitled to receive dividends out of assets legally available at the times and in the amounts as our board of directors may from time to time determine.

*Voting Rights*. Each outstanding share of our common stock is entitled to one vote on all matters submitted to a vote of stockholders. Holders of shares of our common stock shall have no cumulative voting rights.

Except as otherwise required under the Delaware General Corporation Law or provided for in our certificate of incorporation, all matters other than the election of directors are determined by a majority of the votes cast on the matter and all elections of directors are determined by a plurality of the votes cast. However, we have implemented a Majority Voting Policy for uncontested director elections (elections in which the number of nominees for election does not exceed the number of directors to be elected). In the event that the votes "withheld" from a nominee's election exceed the votes cast "for" that nominee's election, such nominee shall be required to submit his or her resignation to our board of directors for consideration. Our board of directors will then have the opportunity to determine whether to accept or reject such tendered resignation. Our board of directors, in making its decision, may consider any factors or other information that it considers appropriate or relevant.

Our board of directors will act within 120 days following certification of the shareholder vote. Thereafter, our board of directors will promptly publicly disclose, in a report furnished to the SEC, its decision regarding the tendered resignation, including its rationale for accepting or rejecting the tendered resignation. Our board of directors may accept a director's resignation or reject the resignation. If our board of directors accepts a director's resignation, or if a nominee for director is not elected and the nominee is not an incumbent director, then our board of directors, in its sole discretion, may fill any resulting vacancy or may decrease the size of our board of directors, in each case pursuant to our bylaws. If a director's resignation is not accepted by our board of directors, such director will continue to serve until the next annual meeting of shareholders when such director's class is up for re-election and until his or her successor is duly elected, or his or her earlier resignation or removal.

*Preemptive Rights*. Our common stock is not entitled to preemptive or other similar subscription rights to purchase any of our securities.

------

##### [**Table of Contents**](#toc)
*Conversion or Redemption Rights*. Our common stock does not have any conversion rights and there are no redemption or sinking fund provisions applicable to our common stock.

*Liquidation Rights*. Upon our liquidation, the holders of our common stock will be entitled to receive pro rata our assets that are legally available for distribution, after payment of all debts and other liabilities and subject to the prior rights of any holders of preferred stock then outstanding.

*Stock Exchange Listing*. Our common stock is listed on the New York Stock Exchange under the symbol "PQG."

**Preferred Stock** 

Our board of directors may, without further action by our stockholders, from time to time, direct the issuance of shares of preferred stock in series and may, at the time of issuance, determine the designations, powers, preferences, privileges, and relative participating, optional or special rights as well as the qualifications, limitations or restrictions thereof, including dividend rights, conversion rights, voting rights, terms of redemption and liquidation preferences, any or all of which may be greater than the rights of our common stock. Satisfaction of any dividend preferences of outstanding shares of preferred stock would reduce the amount of funds available for the payment of dividends on shares of our common stock. Holders of shares of preferred stock may be entitled to receive a preference payment in the event of our liquidation before any payment is made to the holders of shares of our common stock. Under certain circumstances, the issuance of shares of preferred stock may render more difficult or tend to discourage a merger, tender offer or proxy contest, the assumption of control by a holder of a large block of our securities or the removal of incumbent management. Upon the affirmative vote of a majority of the total number of directors then in office, our board of directors, without stockholder approval, may issue shares of preferred stock with voting and conversion rights which could adversely affect the holders of shares of our common stock and the market value of our common stock. As of December 31, 2020, there were no shares of preferred stock outstanding.

**Anti-Takeover Effects of our Certificate of Incorporation and Bylaws** 

Our certificate of incorporation and bylaws contain certain provisions that are intended to enhance the likelihood of continuity and stability in the composition of our board of directors and which may have the effect of delaying, deferring or preventing a future takeover or change in control of the company unless such takeover or change in control is approved by our board of directors. These provisions include:

*Classified Board*. Our certificate of incorporation provides that our board of directors be divided into three classes of directors, with the classes as nearly equal in number as possible. As a result, approximately one-third of our board of directors is elected each year. The classification of directors has the effect of making it more difficult for stockholders to change the composition of our board. Our certificate of incorporation also provides that, subject to any rights of holders of preferred stock to elect additional directors under specified circumstances, the number of directors is fixed exclusively pursuant to a resolution adopted by our board of directors. Our board of directors currently has eleven members.

*Special Meetings of Stockholders*. Our certificate of incorporation and bylaws provide that, except as otherwise required by law, special meetings of the stockholders can only be called by the chairman of our board or pursuant to a resolution adopted by a majority of our board of directors. Except as otherwise required by law, stockholders are not permitted to call a special meeting or to require our board of directors to call a special meeting.

*Removal of Directors*. Our certificate of incorporation provides that our directors may be removed only for cause by the affirmative vote of at least a majority of the voting power of our outstanding shares of capital stock entitled to vote generally in the election of directors, voting together as a single class.

------

##### [**Table of Contents**](#toc)
*Advance Notice Procedures*. Our bylaws establish an advance notice procedure for stockholder proposals to be brought before an annual meeting of our stockholders, including proposed nominations of persons for election to our board of directors. Stockholders at an annual meeting are only able to consider proposals or nominations specified in the notice of meeting or brought before the meeting by or at the direction of our board of directors or by a stockholder who was a stockholder of record on the record date for the meeting, who is entitled to vote at the meeting and who has given our Secretary timely written notice, in proper form, of the stockholder's intention to bring that business before the meeting. Although the bylaws do not give our board of directors the power to approve or disapprove stockholder nominations of candidates or proposals regarding other business to be conducted at a special or annual meeting, the bylaws may have the effect of precluding the conduct of certain business at a meeting if the proper procedures are not followed or may discourage or deter a potential acquiror from conducting a solicitation of proxies to elect its own slate of directors or otherwise attempting to obtain control of the company.

*Authorized but Unissued Shares*. Our authorized but unissued shares of common stock and preferred stock are available for future issuance without stockholder approval. These additional shares may be utilized for a variety of corporate purposes, including future public offerings to raise additional capital, corporate acquisitions and employee benefit plans. The existence of authorized but unissued shares of common stock and preferred stock could render more difficult or discourage an attempt to obtain control of a majority of our common stock by means of a proxy contest, tender offer, merger or otherwise.

*Business Combinations with Interested Stockholders*. We have elected in our certificate of incorporation not to be subject to Section 203 of the Delaware General Corporation Law, an antitakeover law. In general, Section 203 prohibits a publicly held Delaware corporation from engaging in a business combination, such as a merger, with a person or group owning 15% or more of the corporation's voting stock for a period of three years following the date the person became an interested stockholder, unless (with certain exceptions) the business combination or the transaction in which the person became an interested stockholder is approved in a prescribed manner. Accordingly, we are not subject to any anti-takeover effects of Section 203. However, our certificate of incorporation contains provisions that have the same effect as Section 203, except that they provide that INEOS Limited (as a permitted transferee of INEOS Investments Partnership) ("INEOS") and investment funds affiliated with CCMP Capital Advisors, LP ("CCMP"), and certain of their respective transferees and affiliates will not be deemed to be "interested stockholders," regardless of the percentage of our voting stock owned by them, and accordingly will not be subject to such restrictions.

*Exclusive Forum*. Our certificate of incorporation provides that, subject to limited exceptions, the Court of Chancery of the State of Delaware is the sole and exclusive forum for (i) any derivative action or proceeding brought on our behalf, (ii) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers or other employees to us or our stockholders, (iii) any action asserting a claim against us arising pursuant to any provision of the Delaware General Corporation Law, our certificate of incorporation or our bylaws, or (iv) any other action asserting a claim against us that is governed by the internal affairs doctrine. Any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock shall be deemed to have notice of and to have consented to the provisions of our certificate of incorporation described above. Although we believe these provisions benefit us by providing increased consistency in the application of Delaware law for the specified types of actions and proceedings, the provisions may have the effect of discouraging lawsuits against our directors and officers. The enforceability of similar choice of forum provisions in other companies' certificates of incorporation has been challenged in legal proceedings, and it is possible that, in connection with one or more actions or proceedings described above, a court could find the choice of forum provisions contained in our certificate of incorporation to be inapplicable or unenforceable.

------

##### [**Table of Contents**](#toc)
**Corporate Opportunities** 

Our certificate of incorporation provides that we renounce any interest or expectancy of the company in the business opportunities of CCMP and INEOS and of their respective officers, directors, agents, stockholders, members, partners, affiliates and subsidiaries and each such party shall not have any obligation to offer us those opportunities.

**Limitations on Liability and Indemnification of Officers and Directors** 

Our certificate of incorporation limits the liability of our directors to the fullest extent permitted by the Delaware General Corporation Law or any other law of the state of Delaware and our bylaws provide that we may indemnify our directors and our officers that are appointed by our board of directors to the fullest extent permitted by applicable law. We have entered into indemnification agreements with our current directors and executive officers and expect to enter into similar agreements with any new directors or executive officers.

**Transfer Agent and Registrar** 

The transfer agent and registrar for our common stock is American Stock Transfer and Trust Company, LLC.

------

##### [**Table of Contents**](#toc)
**PLAN OF DISTRIBUTION** 

The selling stockholders may sell shares of our common stock in any of the ways described below or in any combination thereof:

• to or through underwriters or dealers;

• through one or more agents; or

• directly to purchasers or to a single purchaser.

The distribution of shares of our common stock by the selling stockholders may be effected from time to time in one or more transactions:

• at a fixed price, or prices, which may be changed from time to time;

• at market prices prevailing at the time of sale;

• at prices related to such prevailing market prices; or

• at negotiated prices.

Each time we offer and sell securities covered by this prospectus, we will make available a prospectus supplement or supplements. Each prospectus supplement will describe the method of distribution of the shares of our common stock and any applicable restrictions.

Each prospectus supplement will describe the terms of the offering of shares of our common stock, including the following:

• the name or names of any underwriters, dealers or agents and the number of shares of our common stock
underwritten or purchased by each of them;

• if a fixed price offering, the public offering price of the shares of common stock and the proceeds to the
selling stockholders;

• any discounts, commissions or concessions allowed or reallowed or paid to underwriters, dealers or agents, and
other items constituting underwriters', dealers' or agents' compensation;

• any options under which underwriters may purchase additional securities;

• any delayed delivery arrangements; and

• information about the selling stockholders, including the relationship between the selling stockholders and us.

Any offering price and any discounts or concessions allowed or reallowed or paid to dealers will be specified in the applicable prospectus supplement and may be changed from time to time.

Only the agents or underwriters named in each prospectus supplement will be agents or underwriters in connection with the shares of our common stock being offered thereby.

The selling stockholders may authorize underwriters, dealers or other persons acting as our agents to solicit offers by certain institutions to purchase securities from the selling stockholders pursuant to delayed delivery contracts providing for payment and delivery on the date stated in each applicable prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in each applicable prospectus supplement. Institutions with whom the contracts, when authorized, may be made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions and other

------

##### [**Table of Contents**](#toc)
institutions, but shall in all cases be subject to our approval. Delayed delivery contracts will be subject only to those conditions set forth in the applicable prospectus supplement, and the applicable prospectus supplement will set forth any commissions we pay for solicitation of these contracts.

Agents, underwriters and other third parties described above may be entitled to indemnification by us and the selling stockholders against certain civil liabilities, including liabilities under the Securities Act, or to contribution from us and the selling stockholders with respect to payments which the agents, underwriters or third parties may be required to make in respect thereof. Agents, underwriters and such other third parties may be customers of, engage in transactions with, or perform services for us or the selling stockholders in the ordinary course of business. We and the selling stockholders may also use underwriters or such other third parties with whom we or such selling stockholders have a material relationship. We and the selling stockholders will describe the nature of any such relationship in the applicable prospectus supplement.

Certain underwriters may use this prospectus and any accompanying prospectus supplement for offers and sales related to market-making transactions in shares of our common stock. These underwriters may act as principal or agent in these transactions, and the sales will be made at prices related to prevailing market prices at the time of sale. Any underwriters involved in the sale of shares of our common stock may qualify as "underwriters" within the meaning of Section 2(a)(11) of the Securities Act. In addition, the underwriters' commissions, discounts or concessions may qualify as underwriters' compensation under the Securities Act and the rules of the Financial Industry Regulatory Authority.

Our common stock is listed on the New York Stock Exchange. Underwriters may make a market in shares of our common stock, but will not be obligated to do so and may discontinue any market making at any time without notice. We can make no assurance as to the development, maintenance or liquidity of any trading market in shares of our common stock.

Certain persons participating in an offering may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids in accordance with rules and regulations under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Overallotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of shares of our common stock in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the shares of our common stock originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of shares of our common stock to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time.

There can be no assurance that the selling stockholders will sell any of the shares of our common stock registered pursuant to the registration statement of which this prospectus or any applicable prospectus supplement forms a part.

------

##### [**Table of Contents**](#toc)
**LEGAL MATTERS** 

The validity of the shares of common stock offered hereby will be passed upon for us by Ropes & Gray, LLP, Boston, Massachusetts. Certain legal matters relating to the shares of our common stock offered hereby will be passed upon on behalf of the underwriter(s) by counsel that we will name in the applicable prospectus supplement.

**EXPERTS** 

The financial statements and management's assessment of the effectiveness of internal control over financial reporting (which is included in Management's Report on Internal Control over Financial Reporting) of PQ Group Holdings Inc. incorporated in this Prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2020 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

The financial statements of Zeolyst International incorporated in this Prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2020 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

**WHERE YOU CAN FIND MORE INFORMATION** 

We have filed with the SEC a registration statement on Form S-3 under the Securities Act with respect to the shares of our common stock being offered by this prospectus. This prospectus, which forms a part of the registration statement, does not contain all of the information set forth in the registration statement. For further information with respect to us and the shares of our common stock, reference is made to the registration statement and its exhibits. Statements contained in this prospectus as to the contents of any contract or other document are not necessarily complete. We are required to file annual, quarterly and current reports, proxy statements and other information with the SEC. Such materials may be accessed electronically by means of the SEC's website at *www.sec.gov*.

**INCORPORATION OF CERTAIN INFORMATION BY REFERENCE** 

The SEC allows us to "incorporate by reference" into this prospectus information we file with it, which means that we can disclose important information to you by referring to these documents. The information incorporated by reference is considered to be part of this prospectus and information in documents that we file later with the SEC will automatically update and supersede information in this prospectus. We incorporate by reference into this prospectus the documents listed below and any future filings made by us with the SEC under Section 13(a), 13(c), 14, or 15(d) of the Exchange Act, except for information "furnished" under Items 2.02, 7.01, or 9.01 on Form 8-K or other information "furnished" to the SEC which is not deemed filed and not incorporated in this prospectus, until the termination of the offering of securities described in the applicable prospectus supplement. We hereby incorporate by reference the following documents:

• our Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/1708035/000170803521000005/pqg-20201231.htm) for the year ended December 31, 2020, filed with the SEC on March 17, 2021;

• the portions of our Definitive Proxy Statement on [Schedule 14A](http://www.sec.gov/Archives/edgar/data/1708035/000114036121011255/nc10018983x1_def14a.htm) , filed with the SEC on April 
1, 2021, that are incorporated by reference in our Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/1708035/000170803521000005/pqg-20201231.htm) for the year ended
December 31, 2020;

------

##### [**Table of Contents**](#toc)
• our Current Reports on Form 8-K filed with the SEC on [March 4, 2021](http://www.sec.gov/Archives/edgar/data/1708035/000119312521069600/d335516d8k.htm) , [March 16, 2021](http://www.sec.gov/Archives/edgar/data/1708035/000119312521082857/d69322d8k.htm) , [March 23, 2021](http://www.sec.gov/Archives/edgar/data/1708035/000119312521091244/d141313d8k.htm) and [April 26, 2021](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001708035/000119312521131499/d272209d8k.htm) , excluding, in each case, information "furnished" pursuant to Items
2.02, 7.01 or 9.01; and

• the description of our common stock contained in the Registration Statement on [Form 8-A](http://www.sec.gov/Archives/edgar/data/1708035/000119312517298321/d451059d8a12b.htm) , as filed with the SEC on September 29, 2017, and any amendment or report filed with the SEC for the purpose of updating such description.

You may request a copy of these filings, at no cost, by writing or telephoning us at:

**PQ Group Holdings Inc.** 

**300 Lindenwood Drive** 

**Malvern, PA 19355** 

**Phone: (610) 651-4400** 

Copies of the filings are also available, without charge on the SEC's website, www.sec.gov, and on our website, https://www.pqcorp.com, as soon as reasonably practicable after they are filed electronically with the SEC. The information contained on our website is not a part of this prospectus.

------

##### [**Table of Contents**](#toc)

------

**11,490,444 Shares** 

**Ecovyst Inc.** 

**Common Stock**![LOGO](g474686g43c41.jpg)

------

**Prospectus Supplement** 

------

**Jefferies** 

------