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                                                                 Exhibit 10.19


                         PLEDGE AND SECURITY AGREEMENT

     PLEDGE AND SECURITY AGREEMENT, dated as of December 14, 1998 made by and
between Frank R. DiPietro, an individual with an address at 2 Cummings Road,
Merrimack, NH 03054 (the "PLEDGOR"), in favor of SIPEX CORPORATION, a
Massachusetts Corporation, having its principal place of business at 22 Linnell
Street, Billerica, Massachusetts 01821 ("SIPEX") (the "Agreement").

     WHEREAS, that certain Pledge and Security Agreement dated December 21, 1998
is hereby canceled and superseded in its entirety by the Agreement.

     WHEREAS, the Pledgor is the beneficial owner of shares of the Common Stock,
$.01 par value per share, of SIPEX (the "SHARES");

     WHEREAS, SIPEX has agreed to loan to the Pledgor $250,000 pursuant to this
Agreement, and such loan is to be evidenced by a Promissory Note in the
principal amount of $250,000, issued by the Pledgor in favor of SIPEX as of the
date hereof and attached hereto as EXHIBIT A (the "NOTE");

     WHEREAS, the Pledgor's obligations arising under the Note and this
Agreement are to be secured by certain Collateral (as defined herein); and

     WHEREAS, the obligation of SIPEX to advance said loan to the Pledgor under
the Note is subject to the condition that the Pledgor execute and deliver this
Agreement and grant the security interest hereinafter described.

     NOW, THEREFORE, in consideration of the covenants and conditions set forth
herein and to induce SIPEX to advance the loan to the Pledgor, the Pledgor
hereby agrees with SIPEX as follows:

     SECTION 1. DEFINED TERMS. The following terms have the following meanings:

     "CODE" means the Uniform Commercial Code from time to time in effect in the
Commonwealth of Massachusetts.

     "COLLATERAL" means the Pledged Stock and all Proceeds.

     "FORECLOSURE DATE" means any date on which SIPEX sends to the Pledgor a
Foreclosure Notice.

     "FORECLOSURE NOTICE" means written notice that SIPEX may give to the
Pledgor when an Event of Default occurs and is continuing, which notice shall
state (i) that SIPEX is exercising its rights under this Agreement and (ii) the
nature of the Event of Default.


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     "OBLIGATIONS" means the unpaid principal of and interest on the Note and
all other obligations and liabilities of the Pledgor to SIPEX, whether direct or
indirect, absolute or contingent, due or to become due, or now existing or
hereafter incurred, which may arise under or in connection with the Note or this
Agreement, whether on account of principal, interest, reimbursement obligations,
fees, indemnities, costs, expenses or otherwise.

     "PLEDGED STOCK" means the number of Shares that Pledgor may acquire,
whether by stock option exercise or otherwise.

     "PROCEEDS" means all "proceeds" as such term is defined in Section 9-306(1)
of the Uniform Commercial Code in effect in the Commonwealth of Massachusetts on
the date hereof and, in any event, includes, without limitation, all dividends
or other income from the Pledged Stock, collections thereon or distributions
with respect thereto.

     SECTION 2. PLEDGE; GRANT OF SECURITY INTEREST. The Pledgor hereby pledges
to SIPEX the Pledged Securities and hereby grants to SIPEX a first priority
security interest in the Collateral, as collateral security for the prompt and
complete payment and performance when due of the Obligations.

     SECTION 3. REPRESENTATIONS AND WARRANTIES. The Pledgor represents and
warrants that:

          (a) this Agreement has been duly executed by the Pledgor, and
constitutes a valid and binding obligation of the Pledgor enforceable in
accordance with its terms;

          (b) no consent or authorization of, filing with, or other act by or
with respect to, any arbitrator or governmental authority and no consent of any
other person (including, without limitation, any creditor of the Pledgor), is
required in connection with the execution, delivery, performance, validity or
enforceability of this Agreement; and

          (c) the Pledgor will be the record and beneficial owner of any shares
that become pledged securities after the date hereof, and the Shares will be (in
the case of Shares acquired after the date hereof), free of any and all liens,
pledges, security interests, encumbrances or options in favor of, or claims of,
any other person, except the lien created by this Agreement.

     SECTION 4. COVENANTS. The Pledgor covenants and agrees with SIPEX that,
from and after the date of this Agreement until the Obligations are paid in
full:

          (a) The Pledgor shall deliver within five (5) business days of
acquisition of any Shares the stock certificate or certificates representing the
Pledged Stock, together with an undated stock power or powers coveting such
certificate or certificates, duly executed in blank, and with, if SIPEX so
requests, signature guaranteed.

          (b) At any time and from time to time, upon the written request of
SIPEX, and at the sole expense of the Pledgor, the Pledgor shall promptly and
duly execute and deliver such further instruments and documents and take such
further actions as SIPEX may reasonably


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request for the purposes of obtaining or preserving the full benefits of this
Agreement and of the rights and powers herein granted. If any amount payable
under or in connection with any of the Collateral is or becomes evidenced by any
promissory note, other instrument or chattel paper, such note, instrument or
chattel paper shall be promptly delivered to SIPEX, duly endorsed in a manner
satisfactory to SIPEX, to be held as Collateral pursuant to this Agreement.

          (c) The Pledgor agrees to pay, and to save SIPEX harmless from, any
and all liabilities with respect to, or resulting from any delay in paying, any
and all stamp, excise, sales or other taxes which may be payable or determined
to be payable with respect to any of the Collateral or in connection with any of
the transactions contemplated by this Agreement.

          (d) The Pledgor shall not transfer, dispose of or otherwise alienate
his rights in the Collateral, except that the Pledgor may at any time and from
time to time sell a portion of the Shares, PROVIDED that upon completion of each
sale of Shares, the Pledgor shall remit the proceeds of such sale to SIPEX in
payment of the principal of the Note.

          (e) Without the prior written consent of SIPEX, the Pledgor shall not
create, incur or permit to exist any lien or option in favor of, or any claim of
any person or entity with respect to, any of the Collateral or any interest
therein.

     SECTION 5. CASH DIVIDENDS; VOTING RIGHTS. Until an Event of Default has
occurred and SIPEX has given a Foreclosure Notice in accordance with Section 11
hereof to the Pledgor, the Pledgor shall be permitted to receive all cash
dividends paid by SIPEX with respect to the Pledged Stock and to exercise all
voting and corporate rights with respect to the Pledged Stock.

     SECTION 6. DEFAULT. The occurrence of any Event of Default (as defined in
the Note) shall constitute a default hereunder (an "EVENT OF DEFAULT").

     SECTION 7. RIGHTS OF SIPEX. (a) If an Event of Default occurs and SIPEX
gives a Foreclosure Notice to the Pledgor (i) SIPEX shall have the right to
receive any and all cash dividends paid with respect to the Pledged Stock and
make application thereof to the Note in such order as it may determine, and (ii)
all shares of the Pledged Stock shall be registered in the name of SIPEX or its
nominee, and SIPEX or its nominee may thereafter exercise (A) all voting,
corporate and other rights pertaining to such shares of the Pledged Stock at any
meeting of shareholders of SIPEX or otherwise and B) any and all rights of
conversion, exchange, subscription and any other rights, privileges or options
pertaining to the option or any shares of the Pledged Stock as if it were the
absolute owner thereof (including, without limitation, the right to exchange at
its discretion any and all of the Pledged Stock upon the merger, consolidation,
reorganization, recapitalization or other fundamental change in the corporate
structure of SIPEX, or upon the exercise by the Pledgor or SIPEX of any right,
privilege or option pertaining to such shares of the Pledged Stock, and in
connection therewith, the right to deposit and deliver any and all of the
Pledged Stock with any committee, depository, transfer agent, registrar or other
designated agency upon such terms and conditions as it may determine), all
without liability except to account for property actually received by it, but
SIPEX shall have no duty to exercise any such right, privilege or option and
shall not be responsible for any failure to do so or delay in so doing.



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          (b) SIPEX shall not be under any obligation to sell or otherwise
dispose of any Collateral upon the request of the Pledgor or any other person or
to take any other action whatsoever with regard to the Collateral or any part
thereof.

          (c) When the Obligations have been paid in full, the pledge of the
Collateral shall cease, and the Collateral shall revert to the Pledgor free and
clear of all liens securing any obligation or liability of the Pledgor to SIPEX,
and SIPEX's rights, title, and interest therein shall cease and become void.

     SECTION 8. SEVERABILITY. Any provision of this Agreement that is prohibited
or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

     SECTION 9. NO WAIVER; CUMULATIVE REMEDIES. No failure to exercise, nor any
delay in exercising, on the part of SIPEX, any right, power or privilege
hereunder shall operate as a waiver thereof. No single or partial exercise of
any right, power or privilege hereunder shall preclude any other or further
exercise thereof or the exercise of any other right, power or privilege.

     SECTION 10. WAIVERS AND AMENDMENTS; SUCCESSORS AND ASSIGNS; GOVERNING LAW.
None of the terms or provisions of this Agreement, may be waived, amended,
supplemented or otherwise modified except by a written instrument executed by
the Pledgor and SIPEX, provided that any provision of this Agreement may be
waived by SIPEX in a letter or agreement executed by SIPEX in favor of the
Pledgor and delivered to the Pledgor in accordance with Section 11. This
Agreement shall be binding upon the successors and assigns of the Pledgor and
shall inure to the benefit of SIPEX and its successors and assigns. This
Agreement shall be governed by, and construed and interpreted in accordance
with, the laws of the Commonwealth of Massachusetts. Each party hereto consents
to the jurisdiction of the state courts of the Commonwealth of Massachusetts and
the United States courts for the District of Massachusetts with respect to the
transactions contemplated hereby.

     SECTION 11. NOTICES. Notices under this Agreement may be given by express
overnight courier service or by facsimile transmission, addressed to the parties
hereto at their respective addresses set forth in the first paragraph to this
Agreement and shall be effective when sent. Either party may change their
respective addresses by written notice to the other party.

     SECTION 12. COUNTERPARTS. This Agreement may be executed in counterparts,
each of which shall constitute an original, but all of which, when taken
together, shall constitute but one agreement.



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     IN WITNESS WHEREOF, the undersigned has caused this Pledge and Security
Agreement to be duly executed and delivered as of the date first above.


                                             PLEDGOR:

                                              /s/ Frank R. DiPietro
                                             ----------------------------
                                             Frank R. DiPietro




                                             SIPEX CORPORATION



                                             By: /s/ James E. Donegan
                                             ----------------------------
                                                  James E. Donegan

                                             Title: Chairman, CEO