1 

MEMORANDUM 

DATE: March 24, 2011 

SUBJECT: Revised Regulatory Alternative Impacts for ExxonMobil Group 1 Polymers and 

Resins Facilities 

FROM: Bradley Nelson, EC/R Incorporated 

TO: Nick Parsons, EPA/OAQPS/SPPD/RCG 

Paula Hirtz, EPA/OAQPS/SPPD/RCG 

 

 The purpose of this memorandum is to present revised estimated impacts of regulatory 

alternatives identified to reduce hazardous air pollutant (HAP) emissions from The ExxonMobil 

facilities that are subject to the Group 1 Polymers and Resins National Emission Standards for 

HAP (NESHAP) – 40 CFR 63, subpart U. The revisions are a result of comments received from 

ExxonMobil on the proposed changes to the NESHAP after the Risk and Technology Review 

(RTR) evaluation under section 112(d)(2), 112(d)(6) and 112(f)(3) of the Clean Air Act. The 

facilities include a Butyl Rubber Production facility in Baytown, TX and a Halobutyl Rubber 

Production/ Ethylene Propylene Rubber Production facility in Baton Rouge, LA. Section 1 

provides background information, followed by an identification of the regulatory alternatives in 

Section 2. Section 3 summarizes the estimated costs and HAP emission reductions of the 

alternatives, and Section 4 summarizes the secondary impacts. 

1.0 BACKGROUND 

 Regulatory alternatives were developed and evaluated for the process “front-end” for 

Butyl Rubber Production, Halobutyl Rubber Production, and Ethylene Propylene Rubber 

Production at Baytown and Baton Rouge to reduce hydrochloric acid (HCl) emissions. The 

front-end butyl rubber and halobutyl rubber processes are included in the same subcategory and 

regulatory alternatives were developed for this subgroup. Regulatory alternatives were also 

developed and evaluated for the process “back-end” for Butyl Rubber Production and Halobutyl 

Rubber Production at the Baytown and Baton Rouge facilities to reduce hazardous air pollutant 

(HAP) emissions. Again, these back end processes are included in the same subcategory and 

regulatory alternatives were developed for this subgroup. During the comment period, 
2 

ExxonMobil provided design flow rates, HCl and HAP emissions, and control equipment costs 

for the controlling the emission sources at these facilities. EPA used these design flow rates and 

HCl and HAP emissions to re-evaluate the regulatory alternatives for these sources and develop 

revised control equipment costs and cost per ton values for these sources. 

2.0 REGULATORY ALTERNATIVES

 Regulatory alternatives were evaluated for the process “front-end” for butyl rubber 

process at the Baytown facility, and halobutyl rubber and ethylene propylene rubber processes at 

the Baton Rouge facility. Each of the “front-end” processes was evaluated for the reduction of 

HCl emissions. Two “front-end” process regulatory alternatives were identified. The first 

alternative was to establish an emissions limit based on the current level of HCl emissions. This 

option did not require the installation of any additional controls, only that HCl emissions be 

maintained at the current level. The second alternative was to require a 99 percent reduction of 

the HCl created from the combustion of chlorinated organic compounds. In each case, the HCl is 

generated by the combustion of chlorinated organic compounds in a flare. Since it is not 

possible to install an add-on device to reduce these HCl emissions following the flare, the 

impacts are based on the replacement of the flares currently in use with incinerators followed by 

scrubbers that will achieve 99 percent reduction in the HCl emissions. 

 Regulatory alternatives were also identified for the process “back-end” for the Butyl 

Rubber Production at the Baytown facility, and the Halobutyl Rubber Production at the Baton 

Rouge facility. Each of the “back-end” processes were evaluated for the reduction of HAP 

emissions. Two alternatives were considered for each source category/subcategory. The 

alternative was to establish an emission limit based on the current HAP emissions levels 

considering existing levels of HAP stripping and recovery plus any existing controls. This 

option did not require the installation of any additional controls, only that HAP emissions be 

maintained at the current level. The second regulatory alternative identified was to reduce the 

organic HAP emissions by requiring a 98 percent reduction in organic HAP emissions by using 

an incinerator. 
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3.0 RELEVANT EMISSION POINTS AND BASELINE EMISSIONS 

 Information about emission points and emissions were provided by the industry in 

response to a questionnaire distributed by the EPA using their authority under section 114 of the 

CAA for the proposed rule. During the comment period, ExxonMobil provided additional 

information for the emission points for their Baytown and Baton Rouge facilities. The sections 

below summarize the new information and compares it to the emission point information used 

for the proposed rule. 

3.1 Front-End Emissions 

ExxonMobil had two facilities that reported emissions of HCl from the flaring of 

chlorinated organic compounds present in front-end process vent emissions, one producing Butyl 

Rubber and one producing Halobutyl Rubber and Ethylene Propylene Rubber. In the proposal, 

HCl controls were estimated using the emissions and flow rates obtained from the section 114 

letter. During the comment period, ExxonMobil provided design flow rates and revised 

emissions for the front-end processes. A summary of the changes in flow rate and reported HAP 

emissions are presented in Table 1. The two facilities are in compliance with the current MACT 

standard, which requires that organic HAP emissions from continuous group 1 front-end process 

vents be reduced by 98 percent, or by using a flare. 
4 

Table 1. Comparison of the Proposal and Revised Inputs for the “Front-End” Process 

Vent Cost Estimate and Baseline Emissions 

Source Category Pollutant 

Proposal 

Estimate 

Emissions 

(Tons/yr) 

Revised 

Estimate 

Emissions 

(Tons/yr) 

Proposal 

Flow Rate 

(ft3

/sec) 

Revised 

Flow Rate 

(ft3/sec) 

Butyl Rubber 

Hydrochloric Acid 30.1 24.7

205.98 5,700

Methyl Chloride 0.779 0.779

Hexane 6.53 6.53

1,3 Butadiene 0.001 0.001

Xylenes 0.0002 0.0002

Ethylene 

Propylene 

Rubber 

Hydrochloric Acid 19.8 24.1

459.4 1,325

Hexane 0.188 0.188

Halobutyl 

Rubber 

Hydrochloric Acid 76.8 76.9

Methyl Chloride 0.53 0.53 459.43 1,325

Hexane 0.06 0.06

3.2 Back-End Process Emissions 

Following are HAP emission summaries of the back-end process emissions for the butyl 

and halobutyl source subcategory. The HAP emissions from the back-end process operations at 

the butyl rubber facility are approximately 54 TPY. There are two separate dryer vent streams at 

the butyl rubber facility, with one stream controlled. The controlled stream emits around 28 

TPY of hexane, while the uncontrolled stream emits around 26 TPY of hexane. The regenerative 

thermal oxidizer used to control emissions achieves approximately 98 percent control. The 

comments from ExxonMobil listed the design flow rate for the thermal oxidizer to be 15,000 

cubic feet per minute, which is much greater than the 213 cubic feet per minute flow rate used in 

the proposal cost estimates. A summary of the proposal and revised estimate emissions and flow 

rate used to cost the thermal oxidizer are presented in Table 2. 

The emissions from the back-end process operations at the halobutyl rubber facility are 

approximately 53 TPY. There are four separate dryer vents at the halobutyl facility and only one 
5 

vent is controlled. The controlled vent emits around 18 TPY of hexane and 0.04 TPY of 

hydrochloric acid. The regenerative thermal oxidizer used to control emissions achieves 

approximately 97 percent control of the hexane emissions. The three uncontrolled vents 

collectively emit around 42 TPY of hexane. A summary of the HAP emissions used for the 

proposal and the revised emission are shown in Table 2. Both the HAP emission rate and flow 

rate provided in the comments from ExxonMobil were greater than the values that were used for 

the proposal costs and were used to develop the control costs for the re-evaluation of the 

regulatory alternatives. 

Table 2. Comparison of the Proposal and Revised Inputs for the “Back-End” Process Vent 

Cost Estimate and Baseline Emissions 

Source Category Pollutant 

Proposal 

Estimate 

Emissions 

(Tons/yr) 

Revised 

Estimate 

Emissions 

(Tons/yr) 

Proposal 

Flow Rate 

(ft3

/sec) 

Revised 

Flow Rate 

(ft3/sec) 

Butyl Rubber Hexane 26.19 25.8 213 15,000

Halobutyl Rubber Hexane 34.7 41.7 454 80,000

4.0 COSTS AND EMISSION REDUCTIONS OF REGULATORY ALTERNATIVES 

4.1 Front-End Process Vents 

As noted in Section 2, there were two regulatory alternatives identified to address HCl 

emissions from front-end process vents from the Butyl Rubber/Halobutyl Rubber and Ethylene 

Propylene Rubber source categories. The first alternative would ensure that the current levels of 

HCl emissions are maintained. The only impact of this alternative would be costs due to the 

labor costs associated with the calculations, records, and reports to demonstrate compliance. 

These costs are summarized in Table 3. 

 
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Table 3. Estimated Impacts for Front-End Regulatory Alternative 1 

Source Category 

Baseline Organic 

HAP Emissions 

(tpy) 

Emission 

Reduction 

(tpy) 

Capital Costs 

($) 

Annual 

Costs ($/yr) 

Cost 

Effectivenes

s ($/ton) 

Butyl Rubber 7.31 0 $0 $1,000 N/A 

Ethylene Propylene 

Rubber 0.188 0 $0 $1,000 N/A 

Halobutyl Rubber 0.59 0 $0 $1,000 N/A 

As noted in section 2, the organic HAP emissions from these front-end vents are already 

controlled by a flare. The costs estimated are to replace the flare with an incinerator followed by 

a scrubber. The costs were estimated using cost spreadsheets developed to estimate control costs 

using the EPA control cost algorithms1

 for thermal incinerators, ducting, and acid-gas absorbers 

(scrubbers). The uncontrolled HAP emissions from the streams that are currently controlled 

were calculated by assuming the flare achieves 98 percent reduction in organic HAP emissions. 

Flow rates from ExxonMobil’s comments were used to estimate the size and cost of the thermal 

oxidizers. In addition to the costs included in the EPA Air Pollution Costs Manual, auxiliary 

costs submitted in the comments from ExxonMobil were also included. This auxiliary 

equipment include: piperacks and piperack modifications, utility piping, and a new motor control 

center. 

Table 4 presents the costs based on the second regulatory alternative requiring 99 percent 

reduction in HCl emissions. The Ethylene Propylene Rubber and Halobutyl Rubber processes 

are located at the same facility. The control costs were estimated by splitting the total flow rate 

from the combined stream using the HCl and organic HAP emissions rates. The control costs for 

the Baytown and Baton Rouge Butyl Rubber sources were totaled to develop an average cost of 

controlling HCl emissions from the butyl rubber process. This is shown in the Baytown/Baton 

Rouge Butyl Total column of Table 4. Details of these costs estimates are provided in 

Attachment 1. 

 

1

 EPA Air Pollution Control Cost Manual, Sixth Edition, January 2002, EPA/452/B-02-001 
7 

Table 4. Estimated Impacts for Front-End Regulatory Alternative 2 

Parameter Baytown Butyl 

Rubber 

Baton Rouge 

Butyl Rubber 

Baytown/Baton 

Rouge Butyl 

Total 

Baton Rouge 

Ethylene 

Propylene 

Rubber 

HCl Emissions at Baseline (tpy) 24.7 76.9 101.6 24.1 

Incinerator 

 Capital $399,696 $308,373 $708,069 $231,440 

 Annual $246,036 $174,376 $420,412 $116,645 

Scrubber 

 Capital $529,852 $110,558 $640,410 $55,327 

 Annual $188,508 $106,431 $294,939 $82,726 

Auxiliary Equipment 

 Capital $1,541,367 $1,657,628 $3,198,995 $1,657,628 

 Annual $266,629 $257,498 $524,127 $257,498 

Total 

 Capital $2,470,915 $2,076,560 $4,547,475 $1,944,396 

 Annual $701,174 $538,306 $1,239,480 $456,868 

HCl Emission Reduction (tpy) 24.5 76.1 100.5 23.8 

HCl Cost Effectiveness $28,674 $6,694 $12,329 $19,188 

HCl after control (tpy) 0.2 0.8 1.0 0.2 

4.2 Back-End Process Operations 

 As noted in Section 2, there were two regulatory alternatives identified to address backend emissions from the Butyl Rubber/ Halobutyl Rubber category. The first alternative would 

ensure that the current levels of emissions are maintained. The only impact of this alternative 

would be costs due to the labor costs associated with the calculations, records, and reports to 

demonstrate compliance. These costs are summarized in Table 5. 
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Table 5. Estimated Impacts for Back-End Regulatory Alternative 1 

Source Category 

Baseline 

Emissions 

(tpy) 

Emission 

Reduction 

(tpy) 

Capital Costs 

($) 

Annual 

Costs ($/yr) 

Cost 

Effectivenes

s ($/ton) 

Butyl Rubber 54 0 $0 $981.84 N/A 

Halobutyl Rubber 53 0 $0 $981.84 N/A 

The Table 6 costs were estimated using the EPA control cost algorithms for thermal 

incinerators. Flow rates from ExxonMobil’s comments were used to estimate the size and cost 

of the thermal oxidizers. Some of the back-end streams are already controlled. Further emission 

reductions for the controlled streams were not considered. Instead, the cost impacts were 

calculated based on the control of the uncontrolled streams. Details of these costs estimates are 

provided in Attachment 2. 

Table 6. Estimated Cost and Emission Reductions for Back-End Regulatory Alternative 2 

Parameter Butyl Rubber Halobutyl 

Rubber 

Butyl/Halobutyl 

Total 

HAP Emissions at Baseline (tpy) 25.8 41.7 67.5 

Incinerator 

 Capital $848,334 $2,470,051 $3,318,385 

 Annual $325,558 $1,151,729 $1,477,287 

Auxiliary Equipment 

 Capital $62,691 $71,123 $133,814 

 Annual $14,793 $16,977 $31,770 

Total 

 Capital $911,025 $2,541,175 $3,452,200 

 Annual $340,351 $1,168,706 $1,509,057 

HAP Emission Reduction (tpy) 25.3 40.9 66.2 

HAP Cost Effectiveness $13,461 $28,598 $22,795 

HAP after control (tpy) 0.5 0.8 1.3 
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5.0 SECONDARY ENVIRONMENTAL IMPACTS 

 While the primary impact of the regulatory alternatives is to address HCl emissions on 

the front-end and organic HAP emissions on the back-end, the application of the control 

technologies that would be required under the second regulatory alternatives can also have other 

environmental effects. These impacts can be positive, such as a reduction in non-HAP volatile 

organic compound air emissions; or negative, such as the generation of additional wastewater or 

energy consumption. In this section the secondary impacts on air pollution, water pollution, and 

energy are discussed. The methodologies used to calculate secondary impacts can be found in 

documentation for the MACT standard.2

 

Air Pollution

 For the sources included in this project, the secondary air pollution impacts are the 

increased criteria pollutant emissions caused by the on-site combustion of organic HAPs and 

fuels. This combustion results in the emission of nitrogenous oxides (NOx), carbon monoxide 

(CO), particulate matter (PM), and sulfur dioxide (SO2). In addition to these five criteria 

pollutants, emissions of carbon dioxide (CO2) are also expected. Table 7 presents the estimated 

secondary air impacts for regulatory alternative 2 for the front-end process vents, and Table 8 

presents those for back-end process vents. The total criteria pollutant emissions for the front-end 

are estimated to be around 7 tpy, with NOx emissions from incinerators accounting for 6 tpy. 

The total criteria pollutant emissions for the back-end are estimated to be around 267 tpy, with 

NOx emissions from incinerators accounting for 225 tpy. The CO2 emissions are estimated to be 

around 2,607 tpy and 131,086 tpy for front-end and back-end, respectively. 

 

2 Memorandum. Estimated Regulatory Alternative Impacts for Elastomer Production Facilities (Polymers and 

Resins I). Norwood, P., EC/R, to Evans, L., EPA/OAQPS/ESD/OCG. May 10, 1995. Contained in Hazardous Air 

Pollutant Emissions from Process Units in the Elastomer Manufacturing Industry--Supplementary Information 

Document for Proposed Standards. EPA-453/R-95-005a. May 1995. 
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Table 7. Secondary Air Impacts for Front-End Regulatory Alternative 2 

Source Category Emissions (tpy) 

PM SO2 NOX CO CO2

Butyl Rubber 0.004 0.001 2 0.05 162

Halobutyl Rubber 0.03 0.006 2 0.40 1,233

Ethylene Propylene Rubber 0.03 0.006 2 0.40 1,219

Combined HBR AND EPR 0.06 0.012 4 0.70 2,445

Table 8. Secondary Air Impacts for Back-End Regulatory Alternative 2 

Source Category Emissions (tpy) 

PM SO2 NOX CO CO2

Butyl 0.01 0.003 8 0.2 593

Halobutyl 0.25 0.05 17 3 10,160

Water Pollution 

 The only impact on water pollution for the second regulatory alternatives identified in 

Section 2.0 is associated with the incinerator/scrubber system for control of HCl from the frontend process vents. Control of organic HAP emissions using combustion only does not result in 

any significant increase in wastewater discharge, since no water effluents are generated by the 

thermal incinerator. 

 In the scrubber control system, water is used to remove the acid gas contained in the 

thermal oxidizer outlet stream. The amount of wastewater generated is equal to the amount of 

water needed by the scrubber to absorb the acid gas leaving the incinerator. It is estimated that 

about 90 million gallons of wastewater will be generated annually from acid scrubbers at Butyl 

Rubber, Halobutyl Rubber, and Ethylene Propylene Rubber facilities. Almost 60 million of this 

total is from the Halobutyl and Ethylene Propylene Rubber facility. The same assumptions were 
11 

used for this analysis as those used in the MACT.3

 Table 9 presents the water pollution impacts 

from front-end regulatory alternative 2. 

Table 9. Water Pollution Impacts from Front-End Regulatory Alternative 2 

Source Category 

Flow Rate to 

Scrubber 

(scfm) 

Operating 

Hours (hr/yr) 

Wastewater 

Treatment Flow 

Rate (1000 gal/yr) 

Butyl Rubber 7,000 8,760 75.8

Halobutyl Rubber 3,045 8,760 236

Ethylene Propylene Rubber 955 8,760 73.9

Energy Impacts 

 The energy demands associated with the control technologies for the second regulatory 

alternatives include the need for additional electricity and natural gas. The total nationwide 

energy demands that would result from implementing regulatory alternative 2 for front-end and 

back-end process vents are presented in Tables 10 and 11, respectively. Overall, the controls 

would require approximately 1.0 x 109 Btu electricity and 4.4 x 1010 Btu natural gas annually for 

front-end process vent control. Back-end process vents would require approximately 3.7 x 1010

Btu electricity and 2.2 x 1012 Btu natural gas annually. More details about the methodologies 

used can be found in the MACT documentation.4

 

 

3 See footnote 1 

4 See footnote 1 
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Table 10. Energy Requirements for Front-End Regulatory Alternative 2 

Source 

Category

Incinerator Scrubber 

Annual 

Electricity 

Cost 

($/yr) 

Electricity 

(Kw-hr) 

Natural 

Gas Cost 

($/yr) 

Natural 

Gas 

(Mscf/yr) 

Annual 

Electricity 

Cost 

($/yr) 

Electricity 

(Kw-hr) 

Natural 

Gas Cost 

($/yr) 

Natural 

Gas 

(Mscf/yr) 

Butyl 

Rubber $13,444 196,257 $104,110 19,906 $33,608 490,628 0 0 

Halobutyl 

Rubber $4,763 69,536 $54,810 10,480 $4,150 60,584 0 0 

Ethylene 

Propylene 

Rubber 

$1,511 22,063 $11,854 2,266 $1,302 19,007 0 0 

Table 11. Energy Requirements for Back-End Regulatory Alternative 2 

Source Category 

Annual 

Electricity Cost 

($/yr) 

Electricity (Kwhr) Natural Gas 

Cost ($/yr) 

Natural Gas 

(Mscf/yr) 

Butyl $35,185 513,650 $94,686 18,104 

Halobutyl $187,668 2,739,675 $525,450 100,468 
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Attachment 1 

Capital and Annual Cost Summary Sheets