Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From sulfur-containing reactant
Reexamination Certificate
2002-03-26
2003-11-11
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From sulfur-containing reactant
C528S488000, C528S491000, C528S492000, C528S50200C, C528S50200C, C528S503000
Reexamination Certificate
active
06646105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for treating a by-product salt that is formed as a by-product in the production of a polyarylene sulfide (hereinafter sometimes referred to as “PAS”). More particularly, it pertains to a process for treating a by-product salt which comprises treating the by-product salt that is formed as a by-product in the production of the polyarylene sulfide, and efficiently recovering an aprotic organic solvent as a reaction solvent.
2. Description of the Related Arts
A polyarylene sulfide, especially polyphenylene sulfide is known as an engineering plastic which is excellent in mechanical strength, heat resistance and the like and which has good electrical characteristics and high rigidity. Thus it is widely employed as a variety of materials such as electronic machinery parts and electrical machinery parts.
As a process for producing polyarylene sulfide, there has heretofore been employed in general, a process in which a dihalogenated aromatic compound such as p-dichlorobenzene and a sodium salt such as sodium sulfide are reacted with each other in the presence of an aprotic organic solvent such as N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated to “NMP”) to effect a polymerization condensation reaction.
In the above-mentioned process however, a sodium halogenide as a by-product, which is insoluble in a solvent such as NMP, is incorporated in a resin, as a result, the removal of the solvent by cleaning has been far from easy. Moreover, it has been extremely difficult to continuously treat at a high temperature, a polymer and sodium halogenide as a by-product that are formed in the aforesaid process.
Under such circumstances, it has been found that continuous treatment of the polymer at a high temperature is made possible by a method in which the polymerization condensation reaction is conducted by using a lithium salt in place of the sodium salt in the presence of NMP as a solvent so as to form a lithium halogenide, since the lithium halogenide is soluble in a number of aprotic organic solvents such as NMP as a polymerization solvent, thereby enabling it comparatively easy to lower the concentration of lithium in the resin (refer to Japanese Patent Application Laid-Open No. 207027/1995 (Heisei 7).
In the above-mentioned process however, lithium sulfide as a starting raw material for polymerization reaction is obtained, for instance, by reacting lithium chloride with sodium hydroxide to obtain lithium hydroxide, reacting the resultant lithium hydroxide with hydrogen sulfide to obtain lithium hydrosulfide, and subjecting the resultant lithium hydrosulfide to hydrogen sulfide removing reaction. In such reaction system, when lithium chloride is reacted with sodium hydroxide, sodium chloride is formed as a reaction by-product. The resultant sodium chloride, when being subjected to polymerization reaction as such, gives rise to the problem same as the foregoing. Accordingly, it is customary that slurry solution containing lithium hydrosulfide thus formed is subjected to solid-liquid separation to separate it into a solvent portion containing lithium hydrosulfide and a solid matter containing a by-product salt such as sodium chloride, and the solvent portion is subjected to next lithium sulfide synthesis step.
However, when an attempt is made to recover the solvent by drying the solid mixture containing sodium chloride as mentioned above, there is caused a problem in that the solvent is unlikely to be separated because of markedly small particle diameter of the sodium chloride contained in the foregoing solid matter. In addition, in the case of recycling the solvent phase or the like formed by solid-liquid separation of PAS polymerization reaction mixture to use as a starting material, there is also caused a problem in that a small amount of an oligomer present in the solid mixture unfavorably increases the viscosity of the solvent phase. Moreover, another problem is raised thereby in that the use of a conventional dryer such as a disc dryer increases the viscosity of an object to be dried during the course of drying, the object adheres to machinery and equipment, and thereby makes it impossible to continue drying treatment, whereby the objective solvent recovery is made insufficient.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a process for producing a polyarylene sulfide at a low cost by efficiently recovering an aprotic organic solvent as a reaction solvent in the case of producing the polyarylene sulfide under such circumstances.
Other objects of the present invention will become obvious from the text of the specification hereinafter disclosed.
In such circumstances, intensive extensive research and investigation were accumulated by the present inventors in order to achieve the above-mentioned objects. As a result, it has been found that the objects of the present invention can be achieved by dry treating a solid mixture containing an aprotic organic solvent and a by-product salt by using a dryer having a specific drying system, said salt being formed in the case of producing a polyarylene sulfide from an alkali metal sulfide and a dihalogenated aromatic compound in the aprotic organic solvent. The present invention has been accomplished on the basis of the foregoing findings and information.
Specifically, the present invention provides a process for treating a by-product salt from a polyarylene sulfide which comprises treating a solid mixture containing an aprotic organic solvent and the by-product salt that is formed as a by-product in the case of producing the polyarylene sulfide by subjecting an alkali metal sulfide and a dihalogenated aromatic compound to polymerization condensation reaction in the aprotic organic solvent, characterized in that the foregoing aprotic organic solvent is recovered by dry treating the aforesaid solid mixture by the use of a dryer having a self-cleaning property.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, more detailed description will be given of the present invention.
The polymerization condensation reaction between an alkali metal sulfide and a dihalogenated aromatic compound is put into practice in an aprotic organic solvent.
Examples of the aprotic organic solvent include in general, aprotic organic polar solvents such as amide compounds, lactam compounds, urea compounds, organosulfur compounds and cyclic organophosphorus compounds.
The above-mentioned amide compounds among aprotic organic polar solvents are exemplified by N,N-dimethylformamide; N,N-diethylformamide; N,N-dimethylacetoamide; N,N-diethylacetoamide; N,N-dipropylacetoamide; N,N-dimethylbenzoic acid amide, etc.
The aforesaid lactam compounds are exemplified by N-alkyl-caprolactam such as caprolactam; N-methylcaprolactam; N-ethylcaprolactam; N-isopropylcaprolactam; N-isobutylcaprolactam; N-n-propylcaprolactam; N-n-butylcaprolactam; and N-cyclohexylcaprolactam; N-methyl-2-pyrrolidone(NMP); N-ethyl-2-pyrrolidone; N-isopropyl-2-pyrrolidone; N-isobutyl-2-pyrrolidone; N-n-propyl-2-pyrrolidone; N-n-butyl-2-pyrrolidone; N-cyclohexyl-2-pyrrolidone; N-methyl-3-methyl-2-pyrrolidone; N-ethyl-3-methyl-2-pyrrolidone; N-methyl-3,4,5-trimethyl-2-pyrrolidone; N-methyl-2-piperidone; N-ethyl-2-piperidone; N-isopropyl-2-piperidone; N-methyl-6-methyl-2-piperidone; N-methyl-3-ethyl-2-piperidone, etc.
The aforesaid urea compounds are exemplified by tetramethylurea; N,N′-dimethylethyleneurea; N,N′-dimethylpropyleneurea, etc.
The aforesaid organosulfur compounds are exemplified by dimethylsulfoxide; diethylsulfoxide; diphenylsulfone; 1-methyl-1-oxosulfolane; 1-ethyl-1-oxosulfolane; 1-phenyl-1-oxosulfolane etc.
The aforesaid cyclic organophosphorus compounds are exemplified by 1-methyl-1-oxophosfolane; 1-n-propyl-1-oxophosfolane; 1-phenyl-1-oxophosfolane, etc.
Any of the above-exemplified aprotic organic polar solvent can be used alone or by mixing with at least one other or by mixing with a solvent which is not cited above and does not impair
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Petroleum Energy Center
Truong Duc
LandOfFree
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