Processes for the recovery of poly(arylene sulfide)

Details Processes for the recovery of poly(arylene sulfide) Processes for the recovery of poly(arylene sulfide)

1998-12-02

2001-06-05

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Process of treating scrap or waste product containing solid...

C521S149000, C528S388000, C528S373000, C528S379000, C528S488000, C528S489000, C528S501000, C528S50200C, C528S503000

Reexamination Certificate

active

06242501

ABSTRACT:

FIELD OF INVENTION
This invention relates to processes for the recovery of poly(arylene sulfide), hereinafter referred to as PAS. Particularly, this invention relates to the recovery of PAS utilizing at least one extraction agent followed by vacuum drying.
BACKGROUND OF THE INVENTION
The production of PAS for a variety of industrial and commercial uses is known. PAS is moldable into various articles including, but not limited to, parts, films, and fibers by means of, for example, injection molding and extrusion molding techniques. These articles have been employed in a variety of fields where heat and chemical resistance properties are desired. For example, PAS is utilized as a material for preparing electrical and electronic parts and automotive parts.
Lower molecular weight PAS compounds comprising PAS oligomers contained in PAS polymer product can cause the product to have relatively poor mechanical properties. Therefore, a relatively high oligomer content in the PAS product is disadvantageous in molding and other process applications. In addition, when the PAS product is melted, these lower molecular weight compounds can volatilize and can produce undesired off-gassing.
It has been found that certain extraction agents, such as, for example, N-methyl-2-pyrrolidone, hereinafter referred to as NMP, can successfully remove oligomers from PAS. However, the PAS can become imbibed with an extraction agent. For example, upon addition of NMP to poly(phenylene sulfide), hereinafter referred to as PPS, PPS can absorb NMP up to about 1.5 times its weight.
Various techniques have been utilized to remove extraction agents, but these techniques have disadvantages. For example, water washing to remove extraction agents from PAS can produce large quantities of extraction agent laden wastewater that must be reclaimed due to environmental and economic considerations, thereby increasing equipment and energy costs for production of PAS.
There is a need in the PAS industry for a process to produce PAS having a higher molecular weight, i.e., a lower oligomer content. In addition, there is a need for processes effectively to remove extraction agents from PAS to produce the most economical and highest quality PAS.
SUMMARY OF THE INVENTION
It is an object of this invention to provide processes for recovery of PAS from a polymerization reaction mixture.
It is another object of this invention to provide processes for the recovery of PAS utilizing at least one extraction agent followed by vacuum drying, thereby producing PAS with a lower melt flow index and less volatile organic compounds than PAS not vacuum dried.
In accordance with the present invention, a process is provided for recovery of PAS from a PAS polymerization reaction mixture, wherein said mixture comprises PAS, at least one polar organic compound, an alkali metal halide byproduct, PAS oligomers, unreacted reactants, and water, said process comprising:
a) cooling said reaction mixture to form particulate PAS;
b) contacting said cooled reaction mixture with an effective amount of at least one polar organic extraction agent under suitable conditions to form a slurry comprising particulate PAS and liquid wherein said liquid comprises at least one polar organic compound, PAS oligomers, unreacted reactants, and water;
c) removing said particulate PAS from said slurry; and
d) vacuum drying said particulate PAS to remove a majority of contaminants comprising at least one extraction agent, wherein vacuum dried, particulate PAS has a lower melt flow index and less volatile organic compounds than PAS not vacuum dried.
A second embodiment of this invention provides a process for producing PAS comprising:
a) contacting a least one sulfur source, at least one polar organic compound, and at least one base under dehydration conditions to form a dehydrated mixture;
b) contacting said dehydrated mixture with at least one dihalogenated aromatic compound under suitable conditions to form a PAS polymerization reaction mixture comprising PAS, at least one polar organic compound, an alkali metal halide byproduct, PAS oligomers, unreacted reactants, and water;
c) optionally, adding at least one separating agent to facilitate separating PAS from said reaction mixture;
d) cooling said reaction mixture to form particulate PAS;
e) contacting said cooled reaction mixture with an effective amount of at least one polar organic extraction agent under suitable conditions to form a slurry comprising particulate PAS and liquid wherein said liquid comprises at least one polar organic compound, PAS oligomers, unreacted reactants, and water;
f) removing said particulate PAS from said slurry; and
g) vacuum drying said particulate PAS to remove a majority of contaminants comprising at least one extraction agent, wherein vacuum dried, particulate PAS has a lower melt flow index and less volatile organic compounds than PAS not vacuum dried.
A third embodiment of this invention provides a process for producing PAS comprising:
a) contacting at least one sulfur source, at least one polar organic compound, and at least one base under dehydration conditions to form a dehydrated mixture;
b) contacting said dehydrated mixture with at least one dihalogenated aromatic compound under suitable conditions to form a PAS polymerization reaction mixture comprising PAS, at least one polar organic compound, an alkali metal halide byproduct, PAS oligomers, unreacted reactants, and water;
c) subjecting said reaction mixture to low pressure evaporation removing a majority of at least one polar organic compound from said reaction mixture to produce a flash recovered reaction mixture;
d) contacting said flash recovered reaction mixture with an effective amount of at least one polar organic extraction agent under suitable conditions to form a slurry comprising particulate PAS and liquid wherein said liquid comprises at least one polar organic compound, PAS oligomers, unreacted reactants, and water;
e) removing said particulate PAS from said slurry; and
f) vacuum drying said particulate PAS to remove a majority of contaminants comprising at least one extraction agent, wherein vacuum dried, particulate PAS has a lower melt flow index and less volatile organic compounds than PAS not vacuum dried.
A fourth embodiment of this invention provides articles of manufacture prepared from the PAS resulting from the first, second, and third embodiments previously disclosed.
DETAILED DESCRIPTION OF THE INVENTION
A process for recovery of PAS from a PAS polymerization reaction mixture comprising PAS, at least one polar organic compound, an alkali metal halide byproduct, PAS oligomers, unreacted reactants, and water is provided comprising:
a) cooling said reaction mixture to form particulate PAS;
b) contacting said cooled reaction mixture with an effective amount of at least one polar organic extraction agent under suitable conditions to form a slurry comprising particulate PAS and liquid wherein said liquid comprises at least one polar organic compound, PAS oligomers, unreacted reactants, and water;
c) removing said particulate PAS from said slurry; and
d) vacuum drying said particulate PAS to remove a majority of contaminants comprising at least one extraction agent, wherein vacuum dried, particulate PAS has a lower melt flow index and less volatile organic compounds than PAS not vacuum dried.
Processes of the present invention are suitable for recovery of PAS produced by any method that results in a PAS polymerization reaction mixture comprising PAS, at least one polar organic compound, an alkali metal halide byproduct, PAS oligomers, unreacted reactants, and water as the major identifiable components of the mixture. The most common impurities of PAS can be byproduct alkali metal halides principally sodium chloride (NaCl), and PAS oligomers which are gelatinous materials commonly described as “slime” because of their physical properties. The process of the present invention is particularly suitable for use in recovering PPS.
PAS can be produced by contacting, under suitable reaction conditions, components compri

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