Method for forming polyarylene sulfide

Abstract

To provide a method for forming a polyarylene sulfide with a relatively low content of volatile malodorous compounds.SOLUTION: Such low compound levels may be achieved by a step of subjecting a washed polyarylene sulfide to heat treatment in the presence of an atmosphere that includes an inert gas, wherein the heat treatment occurs at a temperature of from about 150°C to about 275°C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Related Applications

[0001] This application claims priority to U.S. Provisional Application No. 62 / 951,096, filed December 20, 2019, the entire contents of which are incorporated herein by reference. [Background technology]

[0002]

[0002] Polyarylene sulfides are high-performance polymers that can withstand high thermal, chemical, and mechanical stresses and are beneficially utilized in a wide range of applications. Polyarylene sulfides are typically formed by the polymerization of dihaloaromatic monomers and alkali metal sulfides or alkali metal hydrosulfides in organic amide solvents. After formation, polyarylene sulfides are washed to separate the polymer from the solvent, unreacted monomers, and other impurities. Many conventional washing solutions rely on the use of acetone to quickly remove a substantial portion of the reaction solvent and partially polymerized oligomers from the polyarylene sulfide. Unfortunately, polyarylene sulfides washed with such solutions tend to contain residual, malodorous compounds, such as mesityl oxide ("MO"), mercapto-4-methylpentan-2-one ("MMP"), and / or butyrolactone ("BL"), which are formed when acetone and NMP come into contact. Therefore, there currently exists a need for polyarylene sulfides and improved processes for forming polyarylene sulfides that have reduced levels of malodorous compounds. Summary of the Invention [Means for solving the problem]

[0003] According to one embodiment of the present invention, a method for forming polyarylene sulfide is disclosed. The method includes subjecting polyarylene sulfide to a washing cycle to form washed polyarylene sulfide, and then subjecting the washed polyarylene sulfide to a heat treatment in the presence of an atmosphere comprising an inert gas. The heat treatment is conducted at a temperature of about 150° C. to about 275° C.

[0004]

[0004] Other features and aspects of the present invention are described in more detail below.

[0005] The present disclosure may be better understood with reference to the following figures. [Brief explanation of the drawings]

[0005] [Figure 1]

[0006] FIG. 1 shows one embodiment of a sedimentation column that may be used in the present invention. [Figure 2]

[0007] 2 is a cross-sectional top view showing an intermediate portion of the settling column of FIG. 1 at the slurry inlet. [Figure 3]

[0008] 1A-1D show several different embodiments of longitudinal cross-sectional shapes of sedimentation columns that can be used in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0006]

[0009] Those skilled in the art will appreciate that this discussion is merely a description of exemplary embodiments and is not intended as a limitation on the broader aspects of the present invention.

[0010] Generally, the present invention relates to methods for forming polyarylene sulfides having a relatively low content of volatile compounds, specifically compounds including mesityl oxide ("MO"), mercapto-4-methylpentan-2-one ("MMP"), butyrolactone ("BL"), diacetone alcohol ("DAA"), thiophenol ("PhSH"), p-dichlorobenzene ("pDCB"), methylthiophenol ("MeSPh"), and / or N-methylpyrrolidone ("NMP"). More particularly, the polyarylene sulfides of the present invention are useful in the manufacture of polyarylene sulfides. The polyarylene sulfides may have a total volatile content of about 175 parts per million ("ppm") or less, in some embodiments about 100 ppm or less, and in some embodiments, 0 to about 70 ppm. Such compounds may have an unpleasant odor or be precursors to other compounds that have unpleasant odors. For example, the polyarylene sulfides may have an MMP content of about 75 ppm or less, in some embodiments about 60 ppm or less, in some embodiments about 50 ppm or less, and in some embodiments, 0 to about 25 ppm. The polyarylene sulfides may also have a BL content of about 65 ppm or less, in some embodiments about 55 ppm or less, in some embodiments about 40 ppm or less, and in some embodiments, 0 to about 35 ppm. Similarly, the polyarylene sulfide may have an NMP content of about 20 ppm or less, in some embodiments about 15 ppm or less, and in some embodiments, 0 to about 10 ppm, and in some embodiments, a pDCB content of about 4 ppm or less, in some embodiments about 3.5 ppm or less, and in some embodiments, 0 to about 3 ppm. The inventors have discovered that such low volatilization levels can be achieved by selectively controlling the manner in which the polyarylene sulfide is treated after it has been washed.

[0007]

[0011] More specifically, the process includes subjecting the polyarylene sulfide to a heat treatment at a relatively high temperature of about 150°C to about 275°C, in some embodiments about 180°C to about 270°C, and in some embodiments about 225°C to about 265°C. The heat treatment may be carried out in one or more steps, and the temperature may be increased to the above temperature or simply maintained constant at the desired temperature throughout the treatment. However, the duration of the heat treatment is typically about 0.1 to about 15 hours, in some embodiments about 0.5 to about 10 hours, and in some embodiments about 1 to about 5 hours. The heat treatment is also typically carried out at or near an atmospheric pressure of about 0.6 to about 1.2 atm, and in some embodiments about 0.8 to about 1.2 atm.

[0008]

[0012] To prevent the heat treatment from adversely affecting the color of the polyarylene sulfide, the heat treatment is generally carried out in the presence of an inert gas. Inert gases may include, for example, nitrogen, helium, argon, xenon, neon, krypton, radon, and the like, and mixtures thereof. Typically, the inert gas constitutes a substantial majority of the atmosphere within the housing, e.g., about 50% to 100% by weight, in some embodiments about 75% to 100% by weight, and in some embodiments about 90% to 100% by weight of the atmosphere (e.g., 100% by weight). If desired, relatively small amounts of non-inert gases, such as carbon dioxide, oxygen, water vapor, and the like, may be used. However, in such cases, the non-inert gas typically constitutes no more than 10% by weight, in some embodiments no more than 5% by weight, in some embodiments no more than about 2% by weight, in some embodiments no more than about 1% by weight, and in some embodiments, about 0.01% to about 1% by weight of the atmosphere. The yellowness index of the polyarylene sulfide obtained after heat treatment can be maintained at a relatively low value, such as about 25 or less, in some embodiments about 15 or less, in some embodiments about 10 or less, and in some embodiments about 0.1 to about 9.5, as determined in accordance with ASTM E313-15 (illuminant D65, observer 10 degrees). The purity of the obtained polyarylene sulfide can likewise be relatively high, such as about 90% or more, in some embodiments about 95% or more, and in some embodiments, or about 98% or more.

[0009]

[0013] Throughout the above process, the inventors have also discovered that the polyarylene sulfide maintains a relatively high oligomer content, thereby helping to minimize melt viscosity. The oligomer content may range, for example, from about 0.5 wt % to about 2 wt %, in some embodiments from about 0.8 wt % to about 1.8 wt %, and in some embodiments, from about 1.2 wt % to about 1.6 wt %. The polyarylene sulfide also exhibits a high melt viscosity of 1,200 s. -1The polyarylene sulfide may have a melt viscosity of about 4,000 poise or less, in some embodiments about 2,500 poise or less, and in some embodiments about 100 to about 2,000 poise, as determined in accordance with ISO Test No. 11443:2005 at a shear rate of 1000 sq. ft. and a temperature of 310°C. In addition, the crystallization temperature of the polyarylene sulfide may also be maintained at a relatively low value, such as about 240°C or less, in some embodiments about 230°C or less, and in some embodiments, about 180°C to about 225°C. The weight average molecular weight of the polyarylene sulfide may also be about 10,000 to about 120,000 daltons, in some embodiments about 15,000 to about 110,000 daltons, and in some embodiments about 20,000 to about 100,000 daltons. The polydispersity index (weight average molecular weight divided by number average molecular weight) may be relatively low, thus resulting in a polymer that is more easily formed into particles having a narrow particle size distribution. For example, the polyarylene sulfide may have a polydispersity index of about 4.3 or less, in some embodiments about 4.1 or less, and in some embodiments, about 2.0 to about 4.0. The polyarylene sulfide may have a number average molecular weight of, for example, about 5,000 to about 80,000 daltons, in some embodiments about 10,000 to about 70,000 daltons, and in some embodiments, about 20,000 to about 60,000 daltons.

[0010]

[0014] Various embodiments of the present invention are described in detail below. I. Polyarylene sulfide

[0015] Polyarylene sulfides generally have the formula: -[(Ar 1 ) n -X] m -[(Ar 2 ) i -Y] j -[(Ar 3 ) k -Z] l -[(Ar 4 ) o -W] p - [In the formula, Ar 1 , Ar 2, Ar 3 and Ar 4 are independently arylene units of 6 to 18 carbon atoms; W, X, Y and Z are independently a divalent linking group selected from -SO2-, -S-, -SO-, -CO-, -O-, -C(O)O-, or an alkylene or alkylidene group of 1 to 6 carbon atoms; wherein at least one of the linking groups is -S-; n, m, i, j, k, l, o, and p are independently 0, 1, 2, 3, or 4, provided that the sum thereof is 2 or greater. It has the repeating unit:

[0011]

[0016] Arylene unit Ar 1 , Ar 2 , Ar 3 and Ar 4 may be optionally substituted or unsubstituted. Advantageous arylene units are phenylene, biphenylene, naphthylene, anthracene, and phenanthrene. Polyarylene sulfides typically contain more than about 30 mol%, more than about 50 mol%, or more than about 70 mol% of arylene sulfide (-S-) units. For example, polyarylene sulfides may contain at least 85 mol% of sulfide bonds directly bonded to two aromatic rings. In a specific embodiment, polyarylene sulfides contain a phenylene sulfide structure -(C6H4-S) as a component thereof. n -, where n is an integer greater than or equal to 1.

[0012]

[0017] Polyarylene sulfides can be homopolymers or copolymers. For example, selective combinations of dihaloaromatic compounds can result in polyarylene sulfide copolymers containing two or more different units. For example, when p-dichlorobenzene is used in combination with m-dichlorobenzene or 4,4'-dichlorodiphenyl sulfone, polyarylene sulfide copolymers can be produced having the formula:

[0013] [ka]

[0014] A portion having the structure and the formula:

[0015] [ka]

[0016] A portion having the structure or the expression:

[0017] [ka]

[0018] A portion having the structure It can be formed to contain:

[0018] Polyarylene sulfides can be linear, semi-linear, branched, or crosslinked. Linear polyarylene sulfides typically contain 80 mol% or more of the repeating unit -(Ar-S)-. Such linear polymers may also contain a small amount of branched or crosslinked units, but the amount of branched or crosslinked units is typically less than about 1 mol% of the total monomer units of the polyarylene sulfide. Linear polyarylene sulfide polymers can be random copolymers or block copolymers containing the above repeating units. Semi-linear polyarylene sulfides similarly have a crosslinked or branched structure introduced into the polymer, in which a small amount of one or more monomers have three or more reactive functional groups.

[0019]

[0019] Various techniques can generally be used to synthesize polyarylene sulfides. For example, a process for producing polyarylene sulfides may include reacting a material that provides hydrosulfide ions (e.g., an alkali metal sulfide) with a dihaloaromatic compound in an organic amide solvent. The alkali metal sulfide may be, for example, lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulfide, or a mixture thereof. When the alkali metal sulfide is a hydrate or an aqueous mixture, the alkali metal sulfide may be treated according to a dehydration operation prior to the polymerization reaction. The alkali metal sulfide may also be in In addition, a small amount of alkali metal hydroxide may be included in the reaction to remove or react (e.g., convert such impurities to harmless substances), such as, for example, alkali metal polysulfides or alkali metal thiosulfates that may be present in trace amounts with the alkali metal sulfide.

[0020]

[0020] The dihaloaromatic compound may be, without limitation, o-dihalobenzene, m-dihalobenzene, p-dihalobenzene, dihalobenzene, dihalotoluene, dihalonaphthalene, methoxydihalobenzene, dihalobiphenyl, dihalobenzoic acid, dihalodiphenyl ether, dihalodiphenyl sulfone, dihalodiphenyl sulfoxide or dihalodiphenyl ketone. The dihaloaromatic compound may be used alone or in any combination thereof. Specific exemplary dihaloaromatic compounds may include, but are not limited to, p-dichlorobenzene, m-dichlorobenzene, o-dichlorobenzene, 2,5-dichlorotoluene, 1,4-dibromobenzene, 1,4-dichloronaphthalene, 1-methoxy-2,5-dichlorobenzene, 4,4'-dichlorobiphenyl, 3,5-dichlorobenzoic acid, 4,4'-dichlorodiphenyl ether, 4,4'-dichlorodiphenyl sulfone, 4,4'-dichlorodiphenyl sulfoxide, and 4,4'-dichlorophenyl ketone. The halogen atom may be fluorine, chlorine, bromine, or iodine, and the two halogen atoms in the same dihaloaromatic compound may be the same or different. In one embodiment, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, or a mixture of two or more of these compounds is used as the dihaloaromatic compound. As is known in the art, it is also possible to use monohalo compounds (not necessarily aromatic compounds) in combination with dihaloaromatic compounds to form end groups of polyarylene sulfides or to control the polymerization reaction and / or molecular weight of polyarylene sulfides.

[0021]

[0021] Although by no means required, polyarylene sulfides can be formed in certain embodiments in a multi-stage process including at least two separate formation stages. One stage of the formation process can include the reaction of a complex including an organic amide solvent and the hydrolysis product of an alkali metal hydrogen sulfide with a dihaloaromatic monomer to form a prepolymer. Another stage of the process can include further polymerization of the prepolymer to form a final product. Optionally, the process can include yet another stage in which an organic amide solvent and an alkali metal sulfide react to form a complex. The different stages can be carried out in a single reaction vessel or in separate reactors.

[0022] In one embodiment, for example, a multi-step process may be used, in which the first step of the process involves reacting an organic amide solvent and an alkali metal sulfide in a reactor to form a complex containing the hydrolysis product of the organic solvent (e.g., an alkali metal organic amine carboxylate) and the alkali metal hydrosulfide. Exemplary organic amide solvents that can be used to form polyarylene sulfides include, but are not limited to, N-methyl-2-pyrrolidone; N-ethyl-2-pyrrolidone; N,N-dimethylformamide; N,N-dimethylacetamide; N-methylcaprolactam; tetramethylurea; dimethylimidazolidinone; hexamethylphosphoric triamide, and mixtures thereof. The alkali metal sulfide may be, for example, lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulfide, or mixtures thereof. The alkali metal sulfide may also be generated in situ. For example, sodium sulfide hydrate can be prepared in the first reactor from sodium hydrogen sulfide and sodium hydroxide, which can be fed to the reactor. When alkali metal hydrogen sulfide and alkali metal hydroxide are fed to the reactor to form the alkali metal sulfide, the molar ratio of alkali metal hydroxide to alkali metal hydrogen sulfide can be from about 0.80 to about 1.50. Additionally, a small amount of alkali metal hydroxide can be included in the first reactor to remove or react (e.g., convert such impurities to harmless substances), for example, with impurities such as alkali metal polysulfides or alkali metal thiosulfates that may be present in trace amounts with the alkali metal sulfide.

[0023] The feed to the reactor may include sodium sulfide (Na2S) (which may be in hydrate form), N-methyl-2-pyrrolidone (NMP), and water. The reaction with NMP follows the reaction scheme below:

[0024] [ka]

[0025] According to the method of the present invention, a complex (SMAB-NaSH) containing sodium methylaminobutyrate (SMAB, a hydrolysis product of NMP) and sodium hydrogen sulfide (NaSH) can be formed. According to one embodiment, although not a requirement of the formation step, a stoichiometric excess of alkali metal sulfide may be utilized. For example, the molar ratio of organic amide solvent to sulfur in the feed may be from 2 to about 10, or from about 3 to about 5, and the molar ratio of water to sulfur source in the feed may be from about 0.5 to about 4, or from about 1.5 to about 3.

[0026] During complex formation, the pressure in the reactor may be maintained at or near atmospheric pressure. To maintain the low pressure, vapor may be removed from the reactor. The major components of the vapor may include water and hydrogen sulfide by-product. The hydrogen sulfide in the vapor may be separated, for example, in a condenser. A portion of the water separated in such a condenser may be returned to the reactor to maintain reaction conditions. Another portion of the water may be removed from the process to dehydrate the SMAB-NaSH solution formed in the first stage. For example, the molar ratio of water to NaSH (or the ratio of oxygen to sulfur) in the product solution in the first reactor may be about 1.5 or less, or from about 0.1 to about 1, so that the SMAB-NaSH complex solution fed to the second-stage reactor is substantially anhydrous.

[0027] Once formed, the SMAB-NaSH complex is then reacted with a dihaloaromatic monomer (e.g., p-dichlorobenzene) and a suitable solvent to form a polyarylene sulfide prepolymer in the second stage of the process. This reaction can be carried out in the same or a different reactor as the first stage of the process. The amount of dihaloaromatic monomer per mole of effective alkali metal sulfide charge can generally be from about 1.0 to about 2.0 moles, in some embodiments from about 1.05 to about 2.0 moles, and in some embodiments from about 1.1 to about 1.7 moles. If desired, a complex having a relatively low molar ratio of dihaloaromatic monomer to alkali metal hydrogen sulfide can be used. For example, the molar ratio of dihaloaromatic monomer to sulfur can be from about 0.8 to about 1.5, in some embodiments from about 1.0 to about 1.2. The relatively low molar ratio of dihaloaromatic monomer to alkali metal hydrogen sulfide in the complex can be favorable for the formation of a final high molecular weight polymer via a condensation polymerization reaction. The solvent to sulfur ratio in the second stage can also be relatively low. For example, the alkali metal hydrogen sulfide to organic amide solvent (including any solvent added and remaining in the complex solution) of the second stage complex can be from about 2 to about 2.5. This relatively low ratio can increase the reactant concentration, which can increase the relative polymerization rate and the rate of polymer production per volume.

[0028] The second stage polymerization reaction may generally be carried out at a temperature of about 200°C to about 280°C, or about 235°C to about 260°C. The duration of the second stage may be, for example, about 0.5 to about 15 hours, or about 1 to about 5 hours. Following the second stage polymerization reaction, the average molar mass M of the prepolymer, expressed as a weight average molecular weight, is w is about 500 g / mol to about 3 It may be 0,000 g / mol, about 1000 g / mol to about 20,000 g / mol, or about 2000 g / mol to about 15,000 g / mol.

[0029] The product of the second stage may include prepolymer, solvent, and one or more salts formed as a by-product of the polymerization reaction. For example, the volume ratio of salts formed as by-products of the reaction to the prepolymer solution may be about 0.05 to about 0.25, or about 0.1 to about 0.2. The salts contained in the reaction mixture may include salts formed as by-products during the reaction and salts added to the reaction mixture, for example, as reaction promoters. These salts may be organic or inorganic, i.e., any combination of organic or inorganic cations and organic or inorganic anions. They may be at least partially insoluble in the reaction medium and may have a concentration different from that of the liquid reaction mixture. According to one embodiment, at least a portion of the salts in the prepolymer mixture formed during the second stage may be removed from the mixture. For example, salts may be removed by the use of screens or sieves, as utilized in conventional separation processes. A salt / liquid extraction process may alternatively or additionally be utilized to separate the salts from the prepolymer solution. In one embodiment, a hot filtration process may be utilized, in which the solution is filtered at a temperature at which the prepolymer is in solution and the salt is in a solid phase. According to one embodiment, the salt separation process may remove at least about 95% of the salt, including the prepolymer, formed during the second stage. For example, greater than about 99% of the salt may be removed from the prepolymer solution.

[0030] Following the prepolymer polymerization reaction and filtration process in the second stage of the process, an optional third stage of forming an increasing molecular weight prepolymer may be carried out. This stage may also be carried out in the same or a different reactor as the first and second stages. The reactants used during this stage may include the prepolymer solution obtained from the second stage, a solvent, one or more dihaloaromatic monomers, and a sulfur-containing monomer. For example, the amount of sulfur-containing monomer added in the third stage may be about 10% or less of the total amount required to form the product polyarylene sulfide. In the illustrated embodiment, the sulfur-containing monomer is sodium sulfide, but this is not a requirement for the third stage; other sulfur-containing monomers, such as alkali metal hydrogen sulfide monomers, may alternatively be utilized.

[0031] The third reaction conditions may be substantially anhydrous, with a water to sulfur-containing monomer ratio of about 0.2, e.g., 0 to about 0.2. A low water content during the third stage of the process increases the weight rate and polymer yield and reduces the formation of undesirable side reaction by-products. These conditions are due to the nucleophilic aromatic substitution, as discussed above. Furthermore, because the pressure increase during the third stage is generally due to water evaporation, a low water content during this stage allows the third reaction to be carried out at a relatively low, constant pressure, e.g., about 1500 kPa.

[0032] The reaction conditions during the third stage may include a relatively low molar ratio of solvent to sulfur-containing monomer. For example, the ratio of sulfur-containing monomer may be from about 2 to about 4, or from about 2.5 to about 3. The third-stage reaction mixture may be heated to a temperature of from about 120°C to about 280°C, or from about 200°C to about 260°C, and polymerization may be continued until the melt viscosity of the polymer thus formed is raised to the desired final level. The duration of the second polymerization step may be, for example, from about 0.5 to about 20 hours, or from about 1 to about 10 hours. The weight-average molecular weight of the polyarylene sulfide formed may vary as known, but in one embodiment may be from about 1,000 g / mol to about 500,000 g / mol, from about 2,000 g / mol to about 300,000 g / mol, or from about 3,000 g / mol to about 100,000 g / mol. Following the third stage and any desired post-forming processing steps, the polyarylene sulfide is typically discharged from the reactor through an extrusion orifice attached to a die of desired configuration, cooled, and can be recovered. Generally, the polyarylene sulfide is extruded through a perforated die. The polyarylene sulfide may also be in the form of a strand, granules, or powder.

[0033] II. Wash Cycle Once formed, the polyarylene sulfide may be subjected to a washing cycle in which the polyarylene sulfide is contacted with a washing solution that typically contains water and / or an organic solvent. If used, the organic solvent is typically an aprotic solvent. Particularly suitable aprotic organic solvents include, for example, halogen-containing solvents (e.g., methylene chloride, 1-chlorobutane, chlorobenzene, 1,1-dichloroethane, 1,2-dichloroethane, chloroform, and 1,1,2,2-tetrachloroethane); ether solvents (e.g., diethyl ether, tetrahydrofuran, and 1,4-dioxane); ketone solvents (e.g., acetone and cyclohexanone); ester solvents (e.g., ethyl acetate); lactone solvents (e.g., butyrolactone); carbonate solvents (e.g., ethylene carbonate and propylene carbonate); amine solvents (e.g., triethylamine and pyridine); nitrile solvents (e.g., acetonitrile and succinonitrile); amide solvents (e.g., N,N'-dimethylformamide, N,N'-dimethylacetamide, tetramethylurea, and N-methylpyrrolidone); nitro-containing solvents (e.g., nitromethane and nitrobenzene); sulfide solvents (e.g., dimethyl sulfoxide and sulfolane), and the like. Of course, other types of organic solvents may be used. In certain embodiments, for example, protic solvents may be used, such as glycols (e.g., propylene glycol, butylene glycol, triethylene glycol, hexylene glycol, polyethylene glycol, ethoxydiglycol, and dipropylene glycol); carboxylic acids (e.g., formic acid); alcohols (e.g., methanol, ethanol, n-propanol, isopropanol, and butanol); etc. Particularly suitable protic solvents are aliphatic alcohols such as ethanol, propanol, methanol, isopropanol, and butanol.

[0034] The wash cycle may include one or more wash stages in which the polyarylene sulfide is contacted with a wash solution. In one particular embodiment, for example, the wash cycle may include a first wash stage in which the polyarylene sulfide is contacted with a first wash solution containing an organic solvent as a major component. The first wash stage may include one or more separate wash steps. For example, the first wash stage may include 1 to 10, in some embodiments 1 to 6, and in some embodiments 2 to 4 separate steps in which the first wash solution is contacted with the polyarylene sulfide. In this step, the solids (e.g., polymer) to liquid ratio is typically in the range of about 1 to about 10, in some embodiments about 2 to about 8. The first wash stage may also generally be carried out over a time interval of about 1 minute to about 500 minutes, in some embodiments about 5 minutes to about 360 minutes. However, the first wash solution generally contains organic solvent in an amount of about 50% by weight or more, in some embodiments about 60% by weight or more, in some embodiments about 75% by weight or more, and in some embodiments about 85% to 100% by weight of the first wash solution. The use of such a "solvent-rich" wash solution can easily remove organic impurities that would otherwise cause odor and minimize the extent to which oligomers are removed. In certain cases, it may be desirable to use a first wash solution containing organic solvent in an amount of about 95% by weight or more (e.g., 100% by weight). However, in other embodiments, the first wash solution may also contain water, which helps minimize the extent to which the organic solvent inadvertently removes shorter polymer chains. When such mixtures are used, the organic solvent typically comprises from about 50% to about 99% by weight, in some embodiments from about 60% to about 98% by weight, in some embodiments from about 75% to about 96% by weight, and in some embodiments from about 85% to about 95% by weight of the first cleaning solution, while water typically comprises from about 1% to about 50% by weight, in some embodiments from about 2% to about 30% by weight of the first cleaning solution. In some embodiments, the composition comprises from about 4% to about 25% by weight, and in some embodiments, from about 5% to about 15% by weight.

[0035] After the first washing step, the polyarylene sulfide may also be subjected to a second washing step in which the polyarylene sulfide is contacted with a second washing solution containing water (e.g., deionized water, recycled water, etc.) as a major component. The second washing step may include one or more different washing steps. For example, the second washing step may include 1 to 20, in some embodiments 2 to 15, and in some embodiments 4 to 10, separate steps in which the second washing solution is contacted with the polyarylene sulfide. In this step, the solids (e.g., polymer) to liquid ratio is typically in the range of about 1 to about 10, in some embodiments about 2 to about 8. The first washing step may also be carried out for a time period generally ranging from about 1 minute to about 500 minutes, in some embodiments about 5 minutes to about 360 minutes. However, the second cleaning solution typically contains water in an amount of about 50% by weight or more, in some embodiments about 70% by weight or more, in some embodiments about 80% by weight or more, and in some embodiments about 85% to about 100% by weight of the second cleaning solution. In certain cases, it may be desirable to use the second cleaning solution in an amount of about 95% by weight or more (e.g., about 100% by weight). However, in other embodiments, the second cleaning solution may also contain an organic solvent, if desired. When such a mixture is used, the organic solvent typically constitutes 0.1% by weight to about 30% by weight, in some embodiments about 0.2% by weight to about 20% by weight, and in some embodiments about 0.5% by weight to about 10% by weight of the second cleaning solution, while water typically constitutes about 70% by weight to about 99.9% by weight, in some embodiments about 80% by weight to 99.8% by weight, and in some embodiments about 90% by weight to about 99.5% by weight of the first cleaning solution. The use of such a "water-rich" washing step helps extract residual organic solvents, unreacted compounds and / or impurities from the polymer without causing excessive removal of short-chain polymer molecules.

[0036] If desired, both the first and second cleaning solutions may be generally free of acetyl compounds (e.g., acetone and / or acetic acid), with such compounds being present in amounts of about 0.1% by weight or less, in some embodiments about 0.05% by weight or less, and in some embodiments about 0.01% by weight or less of the cleaning solution. Without wishing to be bound by theory, the use of such cleaning solutions can minimize the extent of odor-generating side reactions that would otherwise occur in acetyl-based cleaning processes. Naturally, various other suitable materials, such as stabilizers, surfactants, pH adjusters, etc., may also be used in the cleaning solutions. For example, a basic pH adjuster may be used to raise the pH of the cleaning solution to a desired level. This pH is typically greater than 7, and in some embodiments, from about 8.0 to about 13.5, in some embodiments, from about 9.0 to about 13.5, and in some embodiments, from about 11.0 to about 13.0. Suitable basic pH adjusters may include, for example, ammonia, alkali metal hydroxides (sodium hydroxide, lithium hydroxide, potassium hydroxide, etc.), alkaline earth metal hydroxides, etc., and combinations thereof. Additionally, the solution may also contain low levels of impurities (e.g., chloride, sodium, products of monomer decomposition and solvents, etc.), especially when recycled solution is used.

[0037] The use of certain washing temperatures can help to increase the purity of the resulting polymer and improve the effectiveness of the washing process. For example, the second "water-rich" washing solution may be at a temperature of about 90°C or higher, in some embodiments from about 90°C to about 200°C, in some embodiments from about 95°C to about 180°C, and in some embodiments from about 100°C to about 160°C. The use of such higher temperatures for the "water-rich" solution allows any remaining oligomers to dissolve and be more easily extracted. The temperature of the first "solvent-rich" washing solution can vary, but is typically lower than the temperature used for the "water-rich" solution. For example, the temperature of the "solvent-rich" solution may be from about 10°C to about 90°C, in some embodiments from about 15°C to about 8°C. The heating temperature may be 0°C, in some embodiments from about 20°C to about 60°C, and in some embodiments from about 25°C to about 50°C. The use of lower temperatures, particularly for "solvent-rich" solutions, can minimize the extent to which oligomers are removed, resulting in less heat being required and therefore economically advantageous. In certain cases, heating is performed at a temperature above the atmospheric boiling point of the solvent in the mixture. In such embodiments, heating is typically performed under relatively high pressures, such as above 1 atm, in some embodiments above about 2 atm, and in some embodiments, from about 3 to about 10 atm.

[0038] The method for contacting the polyarylene sulfide with the first and second wash solutions can vary as desired. In one embodiment, for example, a system can be used in which the polyarylene sulfide is contacted with the wash solution in a vessel such as a thermostatic bath or a settling column. Referring to Figures 1-3, for example, one embodiment of a settling column 10 configured to receive the polyarylene sulfide and wash solution is shown. The settling column 10 can include an upper compartment 12 including a liquid outlet 20, a middle compartment 14 including an inlet 24, and a lower compartment 16 including a solids outlet 22 and a liquid inlet 26. While illustrated in a vertical configuration, it is understood that the settling column can be utilized in an orientation other than vertical, and the settling column can be angled relative to the vertical, so long as solids flow by gravity through the settling column from the inlet 24 to the outlet 22.

[0039] The upper and lower compartments 12 and 16 may have a cross-sectional area larger than that of the middle compartment 14. In one embodiment, the compartments of the settling column 10 may be circular in cross-section, in which case the upper and lower compartments 12 and 16 may have a cross-sectional diameter larger than that of the middle compartment 14. For example, the upper and lower compartments 12 and 16 may have a diameter about 1.4 to about 3 times larger than that of the middle compartment. For example, the upper and lower compartments may independently have a diameter about 1.4, about 2, or about 2.5 times larger than that of the middle compartment 14. The larger cross-sectional area of ​​the upper compartment 12 may prevent solids overflow at the outlet 20, and the larger cross-sectional area of ​​the lower compartment 16 may prevent solids flow restriction at the outlet 20. It should be understood that the settling column 10 is not limited to a particular geometric shape, and the cross-sectional area of ​​the settling column is not limited to a circular shape. Furthermore, the cross-sectional shapes of the compartments of the settling column may vary relative to one another. For example, one or two of the upper section 12, middle section 14 and lower section 16 may have an oval cross section, while the other sections may have a circular cross section.

[0040] The intermediate section 14 of the settling column 10 may include an inlet 24 through which a polymer slurry may be fed into the settling column 10. The slurry may contain polyarylene sulfide along with other by-products from the formation process, such as reaction solvents (e.g., N-methylpyrrolidone), salt by-products, and unreacted monomers or oligomers. As shown in FIG. 2, the inlet 24 intersects with the wall 25 of the intermediate section 14 substantially tangentially to the wall 25. The term "substantially tangential" as used herein may be determined by the distance between the true tangent to the wall 25 of the intermediate section 14 and the outer wall 27 of the inlet 24. When the inlet 24 intersects with the wall 25 of the intermediate section 14 in a perfect tangential direction, this distance is zero. Typically, this distance is less than about 5 centimeters, e.g., less than about 3 centimeters. Positioning the inlet 24 so that the inlet 24 is substantially tangential to the outer wall 25 of the intermediate section 14 may avoid disrupting the fluid flow pattern within the settling column 10. This arrangement can improve contact and mass transfer between the downwardly flowing solids and the upwardly flowing liquid, and can also avoid the loss of solids through the outlet 20 of the upper compartment 12. To further ensure that solids are not lost through the outlet 20, the inlet 24 can be located in the middle compartment 14 at a distance from the junction 23 where the middle compartment 14 meets the upper compartment 12. For example, the vertical distance between the midpoint of the inlet 24 and the junction 23 can be equal to or about 5% greater than the total height of the middle compartment 14. For example, the vertical distance between the midpoint of the inlet 24 and the junction 23 can be about 5% to about 50% of the total height of the middle compartment 14. The total height of the middle compartment 14 can be about 100% to about 150% of the total height of the middle compartment 14. This is the distance between junction point 23 and junction point 21 where middle section 14 meets lower section 16.

[0041] A conduit at the inlet 24 can carry the slurry from the polymerization reactor to the intermediate section 14 of the settling column 10. The intermediate section 14 of the settling column can include an agitator 30 incorporating an axial shaft 31 and a series of agitator blades 32 along the axial length of the intermediate section 14. The agitator 30 can minimize liquid drift within the settler (fluidized bed), maintain contact between the slurry contents and the upwardly flowing solvent, and also maintain solids flow through the settling column 10. The agitator blades 32 can extend from the axial shaft 31 toward the outer wall 25 of the intermediate section 14. Generally, the agitator blades can extend at least half the distance from the axial shaft to the wall 25, and in one embodiment, can extend substantially the entire distance to the wall 25. In one embodiment, the settling column can be free of settling plates or trays utilized in known settling columns.

[0042] As shown, the axle shaft 31 can support a series of agitator blades 32 along the length of the intermediate section 14. Generally, at least two agitator blades 32 may extend from the axle shaft 31 in a balanced arrangement at each point of blade extension. However, this is not a requirement, and three, four, or more agitator blades may extend from the axle shaft 31 at a single location. Alternatively, a single blade may extend from a single location on the shaft 31, and the agitator blades may be offset from one another along the length of the shaft 31 to maintain balance of the agitator 30 during use. The axle shaft 31 may have agitator blades 32 extending from it at multiple locations along the shaft 31. For example, the axle shaft may have agitator blades extending from it at about 3 to about 50 locations along the shaft, with two or more agitator blades 32 extending from it at each location. In one embodiment, the distribution of blades along axial shaft 31 may be such that there are more blades in the bottom fluidized bed compartment compared to the number of blades in the upper part of compartment 14. During operation, axial shaft 31 may rotate at a speed that is typically from about 0.1 rpm to about 1000 rpm, such as from about 0.5 rpm to about 200 rpm or from about 1 rpm to about 50 rpm.

[0043] In the illustrated embodiment, countercurrent flow is employed, in which the polymer slurry flows in a direction opposite to that of the wash solution. Referring again to FIG. 1, the polymer slurry is fed to the middle section 14 of the settling column 10 via input 24. In contrast, the wash solution is fed to the lower section 16 of the column 10 via inlet 26. In this embodiment, the wash solution flows upward through the column and can contact the polymer slurry flowing downward through the column toward the solids outlet 22. If desired, the inlet 26 may include a distributor 35, which can enhance fluid flow through the solids and prevent solids from entering the inlet 26. The lower section 16 may also have a conical shape to concentrate the solids at the outlet 22. The solids content of the slurry at the outlet 22 is generally about 20% by weight or greater, or in some embodiments, about 22% by weight or greater. If desired, the wash solution may be heated before being fed to the inlet 26, as described above. In such embodiments, the settling column may include a heating element to maintain an elevated temperature during the washing process.

[0044] If desired, a fluidized bed may be formed within the settling column, increasing the concentration of solids from the top to the bed toward the solids outlet 22. The fluidized bed height may be monitored and controlled so that the residence time of the solids within the settling column is better controlled. Through improved control of the residence time of the settling column, the effectiveness of the separation process carried out within the settling column may be improved, which may translate into lower operating costs and improved separation. Additionally, control of the fluidized bed height and residence time may help avoid solids loss via the liquid outlet 20 in the upper section 12. A sensor may be used to monitor the fluidized bed height within the settling column. The type of sensor is not limited and may include internal and external sensors capable of monitoring the fluidized bed height. The sensor may be any suitable sensor capable of detecting the fluidized bed height. For example, without limitation, the sensor may utilize optical, infrared, radio frequency, displacement, radar, vibration, acoustic, thermal, pressure, nuclear, and / or magnetic sensing mechanisms to determine the fluidized bed height of the sedimentation column 10. For example, in one embodiment, an optical sensor 40 (e.g., a laser-based sensor including a laser source and detector) may be located within the intermediate section 14 of the sedimentation column 10, e.g., near the level of the inlet 24, and the sensor may detect the reflection of the laser and determine the relative density difference within the sedimentation column 10, thereby communicating information regarding the location of the top of the fluidized bed to a control system. The control system may relay that information to a valve that can control the flow of solids from the sedimentation column at outlet 22 and / or to the sedimentation column at inlet 24 to control the fluidized bed height. A surge tank may also be included in the conduit leading to or leaving the sedimentation column, known to maintain control of the fluidized bed height. Other systems known in the art for controlling the fluidized bed height may also be utilized, and the method and system utilized to control the fluidized bed height are not particularly limited. The top of the fluidized bed may be at or near the inlet 24. To improve control of the residence time of solids in the settling column 10, the variation in the settled bed height during the process may be less than about 10% of the total height of the intermediate section 14. For example, the variation in the fluidized bed height during the process may be less than about 5% of the total height of the intermediate section 14.

[0045] Although shown as a cylindrical column in FIG. 1, the longitudinal cross-sectional shape of the intermediate section 14 is not limited to this embodiment. For example, as shown in FIG. 3, the intermediate sections 14a, 14b, and 14c of the sedimentation column can be straight or tapered, with an increasing angle from the cylindrical intermediate section as shown in 14a, and an increasing angle as shown in 14b and 14c. When tapered, the intermediate sections are wider at the top than at the bottom, increasing the solids concentration at the bottom of the sedimentation column without impeding solids transport. That is, if the taper angle is too large, solids flow may be impeded by the walls of the middle section. The preferred taper angle will vary for each system depending on the flow rate, the physical properties of the compounds being transported in the system, such as particle size and shape, and the column material and surface roughness.

[0046] The first and second washing steps may be carried out in a single apparatus (e.g., a settling column), as shown in Figures 1-3. In such an embodiment, the polyarylene sulfide may first be contacted with a first washing solution at inlet 26. The first washing solution may flow through the column in the opposite direction to the polymer slurry, leading to outlet 20, where the solution is removed. The polyarylene sulfide may then be contacted with a second washing solution via inlet 26. The second washing solution also flows through the column in the opposite direction to the polymer slurry, leading to outlet 20. Of course, in alternative embodiments, multiple settling columns may be used in series, one or more of which may have a counterflow as described above. In one embodiment, for example, the first washing solution is fed to the first settling column, where it flows in the opposite direction to the polymer slurry, leading to the outlet. The solids outlet may then feed the solids from the first settling column to the slurry inlet of the second settling column. The second wash solution then flows through the column in the opposite direction to the solids to the outlet.

[0047] During the washing process, the polyarylene sulfide is typically separated from the washing solution (e.g., in a backwashing device), although additional separation techniques such as vibration screening may be used if desired.

[0048] III. Heat Treatment Regardless of the particular washing technique used, the washed and optionally separated polyarylene sulfide may be subjected to a heat treatment to reduce the volatile content. As noted above, the heat treatment is generally performed at a relatively high temperature, such as from about 150°C to about 275°C, in some embodiments from about 180°C to about 270°C, and in some embodiments from about 225°C to about 265°C. The heat treatment is carried out in the presence of an inert gas. If desired, the inert gas may be recycled. As a result of this treatment, the polyarylene sulfide can have a relatively low volatile content and a yellowness index as indicated above. Although not required, it may be desirable to subject the polyarylene sulfide to a drying step before the heat treatment. When carried out, the drying step is typically carried out at a relatively low temperature, such as from about 80°C to about 150°C, in some embodiments from about 90°C to about 145°C, and in some embodiments from about 100°C to about 140°C. If desired, drying can be carried out in an atmosphere (e.g., air) or in the presence of an inert gas as described above.

[0049]

[0048] The present invention may be better understood with reference to the following examples. Test Method Molecular weight: A sample of PPS can be first converted to PPSO by oxidation with a mixture of cold HNO3 (50%) in trifluoroacetic acid mixture. The resulting PPSO is dissolved in warm hexafluoroisopropanol (HFIP) for 1 hour and then analyzed by GPC equipped with a PSS-hexafluoroisopropanol (HFIP) gel column. The gel column is fitted with an HFIP gel guard column using HFIP as the mobile phase and refractive index (RI) as the detector.

[0050] Melt Viscosity: Melt viscosity was determined as the shear rate viscosity at 1,200 s using a Dynisco 7001 capillary rheometer. -1The shear rate may be determined according to ISO test number 11443:2005 (technically equivalent to ASTM D3835-08) at a shear rate of 100 rpm and a temperature of 310°C. The rheometer orifice (die) may have a diameter of 1 mm, a length of 20 mm, an L / D ratio of 20.1, and an entrance angle of 180°. The diameter of the body may be 9.55 mm + 0.005 mm, and the length of the rod was 233.4 mm. Prior to measurement, the sample is dried in a vacuum oven at 150°C for 1.5 hours.

[0051] Crystallization temperature: The crystallization temperature can be determined by differential scanning calorimetry ("DSC"), which is known in the art. Under the DSC procedure, a sample is heated to a temperature of 340°C at a rate of 50°C per minute during a first heat cycle, cooled to a temperature of 50°C at a rate of 10°C per minute, and then heated to a temperature of 340°C at a rate of 50°C per minute during a second heat cycle, and cooled again to a temperature of 50°C at a rate of 10°C per minute, and the DSC measurement is performed on a TA Q2000 Instrument. The temperature at the highest point of the exotherm curve obtained during the second heat cycle is generally referred to herein as the "crystallization temperature."

[0052] Oligomer Content: The oligomer content of a sample can be determined by contacting the sample with an extraction solution containing 100% by weight chloroform at a temperature of 60°C and a pressure of 1,500 psi. The sample is rinsed twice with the extraction solution, after which the extracted solvent is dried and the weight of the extract is measured. The oligomer content is determined by dividing the weight of the extract by the weight of the original sample and then multiplying by 100.

[0053] Volatile Content: The volatile content is determined by subjecting a sample to high temperature and then measuring the resulting "outgassing." " is trapped and then analyzed by gas chromatography using known techniques. More specifically, 3.0 grams of the dried sample is placed in a glass tube and then heated to 320°C for 20 minutes. The off-gas or volatiles produced are trapped in a cold trap. Once trapped, the off-gas is analyzed in a solution of acetonitrile by gas chromatography to determine the presence of volatile compounds (e.g., MO, MMP, BL, DAA, PhSH, MeSPh, pDCB, NMP, etc.). Biphenyl is used as an internal standard for the analysis.

[0054] Residual Ash: An ash test can be performed to determine the amount of inorganic residue (e.g., sodium chloride) remaining. More specifically, approximately 4 grams of dried sample is placed on a quartz cover. The mixture can be placed in a clean porcelain crucible equipped with a muffle furnace. The crucible is placed in a muffle furnace and heated to 750°C for 12 hours. After cooling, the crucible is allowed to cool to room temperature in a desiccator. The weight of the residual ash is determined.

[0055] Yellowness Index: The yellowness index of the samples can be determined according to ASTM E313-15 (illuminant D65, observer 10 degrees). [Example]

[0056]

[0056] Polyphenylene reaction slurry is produced from a process involving the reaction of NaSH, pDCB, NMP, NaOH, and water. After the polymerization process, a significant amount of NaCl by-product and NMP is removed from the slurry by shaking it over a sieving screen (106 microns). The polymer is then reslurried in acetone containing 200 ppm MMP and 1500 ppm MO (PPS:acetone (by weight) = 1:5). After mixing for 10 minutes, the slurry is filtered through a 106 micron screen. The acetone reslurry step is repeated three more times. The polymer granules are washed six times with water and dried in an oven at 105°C under a constant nitrogen purge for 1.5 hours. During this time, light exposure is minimized to preserve the flake's initial yellowness index. The PPS sample is divided into three portions. Two portions are then subjected to heat treatment under air or nitrogen. To carry out the heat treatment, approximately 4.5 grams of dried PPS flakes are placed in a 0.5 inch OD glass tube, which is then placed in an aluminum heating block and maintained at 250°C. The heat treatment is carried out under air for 3 hours, and under nitrogen for 3 hours by connecting a slow flow nitrogen supply. After cooling, the samples are then analyzed for volatile content. The results are shown in Table 1 below.

[0057] [Table 1]

[0058] The yellowness index was also determined and was 6.25 without heat treatment, 53.31 with heat treatment under air, and 9.49 with heat treatment under nitrogen. While particular embodiments of the present disclosure have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this disclosure.

Claims

1. 1. A method for forming polyarylene sulfide, comprising the steps of subjecting polyarylene sulfide to a washing cycle to form washed polyarylene sulfide, and thereafter subjecting the washed polyarylene sulfide to a heat treatment in the presence of an atmosphere comprising an inert gas, wherein the heat treatment is conducted at a temperature of from about 150°C to about 275°C.

2. The method of claim 1, wherein the heat treatment is carried out for a period of about 0.1 to about 15 hours.

3. The method of claim 1 , wherein the inert gas comprises nitrogen, helium, argon, xenon, neon, krypton, radon, or a mixture thereof.

4. The method of claim 1 , wherein the inert gas comprises about 90% to 100% by weight of the atmosphere.

5. The method of claim 1 , wherein the inert gas is recycled.

6. 10. The method of claim 1, wherein after being subjected to said heat treatment, said polyarylene sulfide has a volatile content of about 175 ppm or less.

7. 2. The method of claim 1, wherein after being subjected to the heat treatment, the polyarylene sulfide has a mesityl oxide content of about 75 ppm or less, a butyrolactone content of about 65 ppm or less, an N-methylpyrrolidone content of about 20 ppm or less, and / or a pDCB content of about 4 ppm or less.

8. 10. The method of claim 1, wherein after being subjected to said heat treatment, said polyarylene sulfide has a yellowness index of about 15 or less.

9. 10. The method of claim 1, wherein after being subjected to said heat treatment, said polyarylene sulfide has an oligomer content of about 0.5% to about 2% by weight.

10. The method of claim 1 , wherein the polyarylene sulfide is a linear polyphenylene sulfide.

11. The method of claim 1 , wherein the cleaning cycle comprises contacting the polyarylene sulfide with a cleaning solution.

12. 12. The method of claim 11, wherein the cleaning cycle comprises a first cleaning stage followed by a second cleaning stage, the first cleaning stage comprising contacting the polyarylene sulfide with a first cleaning solution, and the second cleaning stage comprising contacting the polyarylene sulfide with a second cleaning solution.

13. 12. The method of claim 11, wherein the first cleaning solution contains an organic solvent in an amount of about 50% by weight or greater and the second cleaning solution contains water in an amount of about 50% by weight or greater.

14. 14. The method of claim 13, wherein the second cleaning solution is at a temperature of about 90°C or greater.

15. The method of claim 13, wherein the organic solvent comprises N-methylpyrrolidone.

16. The method of claim 13, wherein the first cleaning solution also contains water.

17. The method of claim 11 , wherein the cleaning solution is generally acetone-free.

18. The method of claim 11 , wherein the polyarylene sulfide is contacted with the wash solution in a sedimentation column.

19. The method of claim 11 further comprising separating the washed polyarylene sulfide from the washing solution prior to the heat treatment.

20. The method of claim 1 further comprising the step of drying the washed polyarylene sulfide before the heat treatment.

21. 21. The method of claim 20, wherein the drying is carried out at a temperature of from about 80°C to about 150°C.

22. After the heat treatment, the polyarylene sulfide is heated for 1,200 seconds. －１ 10. The method of claim 1, wherein the composition has a melt viscosity of about 100 to about 2,000 poise as determined according to ISO Test No. 11443:2005 at a shear rate of 100 psi and a temperature of 310°C.

23. 10. The method of claim 1, wherein after being subjected to said heat treatment, said polyarylene sulfide has a number average molecular weight of about 20,000 to about 60,000 daltons.

24. 2. The method of claim 1, wherein after being subjected to said heat treatment, said polyarylene sulfide has a yellowness index of about 10 or less, determined according to ASTM E313-15 (Illuminant D65, Observer 10 degrees).

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