Composition and method for inhibiting polymerization and polymer growth

Abstract

A method for inhibiting the premature polymerization and the polymer growth of ethylenically unsaturated monomers is disclosed wherein the method comprises adding to said monomers an effective amount of at least one hydrogen donor or electron acceptor. In a preferred embodiment, the hydrogen donor or electron acceptor is used in combination with a stable nitroxyl free radical.

Description

[0001] This is a division of U.S. application Ser. No. 09 / 580,343, filed May 25, 2000, for which the benefit under Title 35, United States Code, § 120 to U.S. Provisional Application No. 60 / 168,623, filed Dec. 3, 1999, entitled COMPOSITION AND METHOD FOR INHIBITING POLYMERIZATION AND POLYMER GROWTH has been claimed.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention is directed to the inhibition of polymerization and polymer growth of ethylenically unsaturated monomers by means of the addition thereto of hydrogen donors and / or electron acceptors, either alone or in combination with at least one stable nitroxide free radical compound. [0004] 2. Description of Related Art [0005] Many ethylenically unsaturated monomers undesirably polymerize at various stages of their manufacture, processing, handling, storage, and use. Polymerization, such as thermal polymerization, during their purification results in the loss of the monomer, i.e., a lower yield,...

AI Technical Summary

Benefits of technology

[0060] In accordance with the present invention, inhibiting systems have been developed in which a component that is a hydrogen donor or electron acceptor or a combination of two or more of such components is used in the purification train, either alone or, preferably, in combination with a nitroxyl radical to prevent polymer growth via a “living” polymerization mechanism. When the component is used in combination with the nitroxyl radical, the effectiveness of the nitroxyl radical inhibitor can be preserved and utilized without risking high molecular weight polymer formation and / or coating of the internal parts of the purification train owing to excessive polymer growth over time.

Problems solved by technology

Many ethylenically unsaturated monomers undesirably polymerize at various stages of their manufacture, processing, handling, storage, and use.

Polymerization, such as thermal polymerization, during their purification results in the loss of the monomer, i.e., a lower yield, and an increase in the viscosity of any tars that may be produced.

The processing and handling of the higher viscosity tars then requires higher temperature and work (energy cost) to remove residual monomer.

Polymerization can also result in equipment fouling, especially in the case of production of acrylic monomers.

Such polymerization causes loss in production efficiency owing to the deposition of polymer in or on the equipment being used.

These deposits must be removed from time to time, leading to additional loss in production of the monomer.

However, many of these compounds have not been fully satisfactory.

Under the conditions in which inhibitors are normally used, the concentration of the inhibiting species should be sufficiently high to cause reaction (2) to be much faster than reaction (3), otherwise it would not be an effective inhibiting system for commercial use.

However, we have realized that even at an effective inhibiting amount of the inhibitor, growth can still occur, given sufficient time and temperature.

First, the use of recycle can significantly increase the amount of time that the “living” polymer can remain in the purification train.

If this polymer grows via the “living” polymerization mechanism, excessive polymerization would cause loss in product yield, increased waste residues from the process, and potential plugging of equipment due to excessively high molecular weight polymer in the purification stream.

Second, occasionally, conditions in the plant / purification process can result in the formation of polymer within the purification train that is not dissolved by the monomer stream.

If this polymer grows via the “living” polymerization mechanism, it could coat the inside of the equipment, causing inefficient separation of the monomer stream components and / or insufficient heating of the stream to enable purification.

Such a situation would cause loss in product yield and could potentially cause an unscheduled shut-down of the plant in order to clean out the undissolved polymer in the equipment.

Such a shut-down results in loss of monomer production and additional expense to clean out and dispose of the undissolved polymer.

These nitroxyl radicals are highly efficient polymerization inhibitors under normal use, providing better performance than most other inhibitors on the market, but their incapacity to prevent “living” polymerization has hindered their full utilization.

Even small quantities of air used in combination with the nitroxyl inhibitors are said to result in vastly prolonged inhibition times for the monomers.

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