CA2039916A1 - Corrosion-resistant material for sulfur-containing alkali metal salts and equipment for producing polyarylene sulfide using the same, and polyarylene sulfide and process for producing the same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A corrosion-resistant material against sulfur-containing alkali metal salt which comprises high purity metallic chromium having a relative density of 95% or higher and a purity of 99.7% or higher and equipment for production of polyarylene sulfides which is composed of such a corrosion-resistant material, and a polyarylene sulfide containing substantially no heavy metal and a process for producing such a polyarylene sulfide comprising reacting an alkali metal sulfide and a dihalogenated aromatic compound in a polar aprotic solvent by using equipment made of high purity chromium having a purity of 99.7% or higher and having a relative density of 95% or higher at least at parts in contact with a liquid are disclosed.

Description

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CORROSION-RESISTANT MATERIAL FOR SULFUR-CONTAINING ALRALI METAL SALTS AND EQUIPMENT FOR
PRODUCING POLYARYL~NE SULFIDE USING TH~ SAME, AND
POLYARYLENE S~LFIDE AND PROCESS FOR PRODUCING THE SAM~

FILED OF THE_INVENTION

This invention relates to a corrosion-resistant material suitable as a material of equipment in contact with a solution of various alkali metal salts containing sulfur and equipment for producing a polyarylene sulfide (hereinafter abbreviated as PAS) which is made of such a corrosion-resistant material, and PAS substantially containing no heavy metal and a process for producing PAS by reacting an alkali metal sulfide and a di-halogenated aromatic compound in a polar aprotic solvent.

BACKGROUND OF THE INVENTION

The corrosion-resistant material of this invention can be used as a corrosion-resistant material for various kinds of equipment. The equipment to which the corrosion-resistant material of this invention is applicable embraces distillation to~-ers, evaporators, heat exchangers, pipes, tanks, etc. in the chemical plant. The corrosion-resistant material of the invention is particularly effective as a basic material or a cladding or lining material of such equipment as well as a vessel for sodium-sulfur electric cell and lithium-iron sulfide electric cell.
PAS has recently attracted attention as electric and electronic materials and automobile materials because of its - 1 - !

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excellent heat resistance and chemical resistance. Besides, PAS can be molded into various shapes, films, sheets, fibers, etc. by injection molding or extrusion moldin~ for use in a wide range of applications. In these applications, PAS of extremely high purity has been demanded. Accordingly, PAS
containing substantially no heavy metal according to this invention is expected to be highly valuable for use in these fields.
Typical processes for producing PAS include a process comprising reacting an alkali metal sulfide and an aromatic halogen compound, for example, a process in which an alkali metal sulfide hydrate and a dihalogenated aromatic compound are reacted in an aprotic polar organic solvent by use of equipment made of general-purpose austenite stainless steel (e.g., SUS
304, SUS 316). In this process, an alkali metal halide which is by-produced together with PAS is soluble in solvents, e.g., water, so that it can be removed in the course of working-up procedures, such as phase separation, extraction or washing of PAS with water or a like solvent. However, during the reaction, a sulfide used as a part of the reactant is reacted with a reactor material to form a metal sulfide, e.g., iron sulfide and nickel sulfide. Since the by-produced metal sulfide is insoluble in solvents, it is hardly removed by the subsequent working-up procedures and unavoidably remains in the produced PAS. PAS containing such a metal sulfide is excluded :

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rom use where high functional performance is required, such as ~upports of magnetic recording materials.
In addition, incorporation of a heavy metal sulfide into ?AS causes a change in color tone of the product, and also PAS
?roduced under such an environment is inferior in heat ~tability.
In an attempt to solve the problem of contamination with ~etal sulfides, it has been proposed to produce PAS by using ~quipment made of titanium as disclosed in JP-A-61-23627 (the -erm "JP-A" as used herein means an "unexamined published Japanese patent application''). With Ti-made equipment, incorporation of a sulfide of iron, chromium, nickel, etc. into 'AS as having been observed with conventional stainless steel~
~ade equipment can be prevented. It turned out, nevertheless, -hat a Ti component is incorporated into PAS, which adversely affects electrical characteristics. Thus, it has been ~mpossible to obtain substantially heavy metal-free PAS by ;-onventional techniques.
The amount of oligomers present in PAS produced with Ti-~ade equipment is reduced to some extent as compared with that ?roduced with general-purpose austenite stainless steel-made ~quipment but not to a satisfactory extent.
Moreover, conventional equipment for PAS production ~ndergoes corrosion at parts to which PAS is liable to adhere, e.g., a dehydrator, a purification tank, and carrying pipes, . . .
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making it impossible to continue operation in a stable manner for a long time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a corrosion-resistant material suitable as a material of equipment in contact with a solution of vari3us alkali metal salts containing sulfur, which exhibits excellent corrosion resistance and durability and undergoes no c~rrosion cracking even at parts under influences of heat.
Another object of the present inventio~ is to provide e~uipment for production of PAS which is ma~e of the above-described corrosion-resistant material.
A further object of the present inventior. is to provide a process for producing PAS containing substantially no heavy metal by using the above-described equipment and reacting an alkali metal sulfide and a dihalogenated aroEatic compound in a pclar aprotic solvent.
A still fu~ther object of the present invention is to provide PAS produced by the above-described process, which is not contaminate~d with heavy metals.
That is, the present invention relates to a corrosion-resistant material against a sulfur-containing alkali metal salt which comprises high purity metallic c~romium having a relative density of 95% or higher and a purity of 99.7% or higher.

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The present invention also relates to equipment for production of PAS whlch comprises reacting an alkali metal sulfide and a dihalogenated aromatic compound in a polar aprotic solvent, said equipment being composed of high purity metallic chromium having a relative density of 95% or higher and a purity of 99.7% or higher.
The present invention further relates to a process for producing PAS comprising reacting an alkali metal sulfide and a dihalogenated aromatic compound in a polar aprotic solvent, in which equipment used is comprised of high purity chromium having a relative density of 95% or higher and a purity of 99.7% or higher at least at parts in contact with a liquid.
The present invention furthermore relates to PAS containing substantially no heavy metal, which is produced by the above-described process.

DETAILED DESCRIPTION OF THE INVENTION
The sulfur-containing alkali metal salt as referred to herein in this invention includes, for example, sulfides such as Na2S, KSH, and K2S, and materials which incorporate thereinto include alkalis such as NaOH and KOH.
The high purity chromium material must have a relative density of 95% or higher. If the relative density is less than 95%, sufficient strength, workability and corrosion resistance cannot be obtained. At the same time, the metallic chromium must have a purity of 99.7% or higher. Metallic chromium of lower purity, i.e., containing more than 0.3% of impurities not .~
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only has reduced workability and easily develops cracks during rolling but also undergoes considerable deterioration on welding. The terminology '~elative density" as used herein means a value obtained from a measured density obtained in a usual manner and a theoretical density of chromium according to equation:

MeasurRelative Density (%) = x 100 Theoretical Density In addition to the above-specified conditions, it is desirable that a chromium rolled sheet has a tensile strength of 20 kg/mm2 or more.
The corrosion-resistant material according to the present invention can be used in place of materials conventionally employed as tanks, reactors, heat exchangers, pipes, and so on.
What is more characteristic of the corrosion-resistant material of the invention is that it is also fit for use as a cladding material or a lining material to which conventional high chromium-based alloys could not be applied in view of workability. As a matter of course, the corrosion-resistant material of the invention should not be lmited to the use for only chemical plant.
In the production of the corrosion-resistant material of the invention, it is preferable to use high purity metallic ' ' ' ' ' ~ ~ . '. . :

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chromium powder (purity: 99.7~ or higher) as a raw material.
Such high purity metallic chromium powder can be obtained by grinding metallic chromium obtained by electrolysis of a chromium salt solution or metallic chromium obtained by purifying a chromium salt solution by solvent extraction, oxidizing the resulting chromium salt solution or a chromium salt isolated therefrom, and reducing the chromium oxide by hydrogen reduction, etc.
The thus prepared metallic chromium powder is sealed into, for example, a vacuum- and heat-resistant vessel. Although the vessel to be used is not strictly limited in material and shape, economical consideration recommends a stainless steel-made or copper-made vessel.
The shape of the vessel is appropriately decided according to a desired shape of a rolled shape. The vessel into which the metallic powder is sealed is evacuated to 10-5 mmHg, and the powder is then hot rolled at a temperature of from 600 to 1000C by means of a grooved roll. General-purpose grooved rolls may be employed, and two-staye rolling mill is usually used. Within the above-recited rolling temperature range, solid solubility of nitrogen into metallic chromium is suppressed to 3 to 17 ppm. A rolling degree is preferably set in the range of from 50 to 80% in favor of a dense structure.
Cooling after hot rolling is preferably effected yradually.
Should the cooliny be rapid, there is a fear that thermal , -:

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stress is non-uniformly imposed to the internal chromium structure to cause cracks.
The resulting rolled shape is then subjected to annealing at a temperature of from 800 to 1000C to homogenize and soften the structure. While not limiting, the annealing time is usually 1 hour or longer.
A process for producing the corrosion-resistant material of the present invention is not limited to the above-described process. For example, the corrosion-resistant material may be obtained by once preparing an ingot by various melting methods using a high-frequency atmosphere furnace or a high~frequency arc furnace and subjecting the ingot to plastic working such as hot rolling.
PAS production by the use of the equipment made of the above-described material will be explained below. Processes for produclng PAS and steps involved therein with which the present invention is concerned are in accordance with known techniques as disclosed, e.g., in JP-B-45-3368, in which an alkali met~l sulfide and a dihalogenated a~omatic compound are reacted in a polar aprotic solvent.
Exampl2s of suitable alkali metal sulfides are lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulide, and mixtures thereof, either in an anhydrous form or in a hydrated form. These alkali metal sulfides are obtained by the reaction between an alkali metal hydrosulfide and an al~ali metal base or between hydrogen sulfide and an . - . ._ .

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alkali metal base. An alkali metal sulfide may be prepared in situ prior to addition of a dihalogenated aromatic compound to a polymerization system, or a previously prepared alkali metal sulfide may be used. Of the above-mentioned alkali metal sulfides, preferred is sodium sulfide. Commercially available 60~ pure sodium sulfide hydrate, Na2S 5H2O, anhydrous Na2S
prepared by heating a hydrate, e.~., Na2S 9H2O, under reduced pressure (see U.S. Patent 2,533,163), and anhydrous sodium sulfide single crystal disclosed in JP-A-64-28207 are also useful.
In carrying out polymerization reaction between the above-described alkali metal sulfide and a dihalogenated aromatic compound, it is preferable that a water content in the polymerization system be controlled not to exceed about 4 mole per mol of the alkali metal sulfide. The water content may be adjusted during polymerization by distillation and the like.
Examples of suitable dihalogenated aromatic compounds include p-dichlorobenzene, m-dichlorobenzene 7 o-dichloro-benzene, p--dibromobenzene, p-diiodobenzene, dichloro-naphthalene, dibromonaphthalene, dichlorodiphenyl sulfone, dichlorobenzophenone, dichlorodiphenyl ether, dichlorodiphenyl sulfide, dichlorodiphenyl, dibromodiphenyl, dichlorodiphenyl sulfoxide, 2,6-dichlorobenzonitrile, 1,4-N,N'-(bis-4-chloro-phenylcarbamoyl)benzene, and mixtures thereof. Of these compounds, p-dihalobenzene compounds are preferred, with p-dichlorobenzene being particularly suitable. If desired, these .

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dihalogenated aromatic compounds may be used in combination with polyhalogenated aromatic compounds containing three or more halogen atoms per molecule, e.g., trichlorobenzene, tribromobenzene, triiodobenzene, tetrachlorobenzene, tri-chloronaphthalene, and tetrachloronaphthalene.
As pol~merization solvents, polar solvents are preferred.
In particular, solvents which are aprotic and stable to alkalis in high temperatures are more preferred. Such preferred solvents include N,N-dimethylacetamide, N,N-dimethylformamide, hexamethylphosphoramide, N-methyl--caprolactam, N-ethyl-2-pyrrolidone, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), 1,3-dimethylimidazolidinone, dimethyl sulfoxide, sulfolane, tetramethylurea, and mixtures thereof.
Polymerization is carried out usually at a temperature of from 200 to 300C, and preferably from 220 to 280C, for a period of from 0.5 to 30 hours, and preferably from 1 to 15 hours, under stirring.
The alkali metal sulfide and the dihalogenated aromatic compound are preferably used at a molar ratio of from 1.00:0.90 to 1.00:1.10. The polar aprotic solvent is used in such an amount that PAS produced may form a proportion of from 3 to 60%
by weight, and preferably from 7 to 40% by weight, in the resultin~ reaction mixture.
With respect to the reaction between an alkali metal sulfide hydrate and a dihalogenated aromatic compound in a polar aprotic solvent, many modes have been proposed, and any . . . . ........ .

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of known modes of reaction can be utilized in the present invention without any restriction as long as equipment composed of high purity chromium satisEying the above-described conditions of purity and density is employed.
If desired, the thus obtained PAS may be compounded with reinforcing fillers, such as glass fibers, carbon fibers, ceramic fibers (e.g., alumina fibers), aramid fibers, wholly aromatic polyester fibers, metallic fibers, and potassium titanate whiskers; and inorganic fillers or organic or inorganic pigments, such as calcium carbonate, mica, talc, silica, barium sulfate, calcium sulfate, kaolin, clay, pyroferrite, bentonite, sericite, zeolite, nepheline syenite, attapulgite, wollastonite, PMF, ferrite, calcium silicate, magnesium carbonate, dolomite, antimony irioxide, zinc oxide, titanium oxide, magnesium oxide, iron oxide, molybdenum disulfide, graphite, gypsum, glass beads, glass powder, glass balloon, quartz, and quartz glass.
Glass fibers which can be used include chopped strands having a fiber length of 1.5 to 12 mm and a fiber diameter of

3 to 24 ~m, milled fibers having a fiber diameter of 3 to 8 ~m, and glass flakes or powders of 32~ mesh or smaller.
If desired, PAS may also be compounded with other additives, such as plasticizers or releasing agents, e.g., aromatic hydroxy derivatives; coupling agents, e.g., silane coupling agents and titanate coupling agents; lubricants, thermal stabilizers, weather stabilizers, nucleating agents, 2~3~

expanding agents, rust inhibitors, ion trapping agents, flame retardants, flame retardant assistants, and the like.
If desired, PAS may further be compounded with thermo-plastic elastomers (e.g., those of olefin type, styrene type, urethane type, ester type, fluorine type, amide type, and acryl type), polyethylene, polypropylene, rubber components (e.g., polybutadiene, polyisoprene, polychloroprene, polybutene, a styrene-butadiene rubber and hydrogenated products thereof, an acrylonitrile-butadiene rubber, an ethylene-propylene copolymer, an ethylene-propylene-ethylidene-norbornene copolymer), polyamide resins (e.g., nylon 6, nylon 66, nylon 610, nylon 12, nylon 11, nylon 46), polyester resins (e.g., polyethylene terephthalate, polybutylene terephthalate), polystyrene, poly(~-methylstyrene), polyvinyl acetate, polyvinyl chloride, polyacrylates, polymethacrylates, polyacrylonitrile, otherpolyolefins, polyurethane,polyacetal, polycarbonate, polyphenylene oxide, polysulfone, polyether sulfone, polyallyl sulfone, polyphenylene sulfide sulfone, polyether ketone, polyether ether ketone, polyphenylene sulfide ketone, polyamide-imide, silicone resins, phenoxy resins, fluorine resins, and resins capable of melt processing to form an anisotropic molten phase; and mixtures of these polymers or modified polymers thereof.
The equipment for PAS production as referred to in the present invention embraces reactors, evaporators, dehydrators, purification towers, carrying pipes, reservoirs, etc.

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According to the present invention, sinc~ the PAS
production system can be prevented from contamination with heavy metals resulting from corrosion of equipment materials, PAS of extremely high purity with a reduced amount ~I oligomers can be obtained. Therefore, the PAS of the present invention provides injection molded or extrusion molded articles excellent in color tone, heat stability, and electrical characteristics; films excellent in color tone, hea stability, surface smoothness, and electrical characteristics; or fibers excellent in color tone, heat stability, and strength.
The heavy metal-free PAS of the present invention can be prepared by a process comprising reacting an alkali metal sulfide and a dihalogenated aromatic compound in a polar aprotic solvent, in which equipment used is comprised of high purity chromium having a relative density of 95~ or higher and a purity of 99.7% or higher at least at parts in contact with a liquid.
PAS according to the present invention is char2cterized by containing substantially no heavy metal. The term "heavy metal" as used herein means metals having a specific gravity of

4.0 or more and includes, for example, iron, manganese, chromium, copper, lead, molybdenum, cobalt, nickel, and titanium. The terminology "substantially no heavy metal" as used herein means that a total heavy metal content in PAS is not more than lO ppm, preferably not more than 5 ppm, and more preferably less than 0.5 ppm.

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PAS of the present invention is a polymer predominantly com.prising a repeating unit represented by any of formulae (1) to (6) shown below, in which the aromatic residues are linked Vi2 a thioether linkage:

' ~}5~ (1) ~ S -t- ~2) Yd S -t- (3) .. . . .

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+ ~1 S-~- (4) ~,Y8 Yh Yi ~5~ (5) Y; Yk ~ X ~ S ) (6) wherein Y represents -R, -OR, -OM, -COOR, -COOM, -NR2, -CONR2, or -CN, wherein R represents a hydrogen atom, an alkyl group having from 1 to 24 carbon atoms, or a cycloalkyl, aryl or aralkyl group having from 6 to 24 carbon atoms, and M
represents an alkali metal; X represents -CO-, -CONRl-, -O-, -S-, -SO-, -SO2-, -CR2R3-, wherein Rl, R2, and R3 each represent a hydrogen atom, an alkyl group having from 1 to 24 carbon atoms, or a cycloalkyl, aryl or aralkyl group having from 6 to 2~3~9~

~4 carbon atoms; a represents 2n integer of from 0 to 4; b _epresents an integer of from 0 to 2; c represents an integer of from 0 to 4; d represents an inteyer of ~rom 0 to 3; e -epresents an integer of from C to 3; f represents an integer of from 0 to 3; q represents an integer of from 0 to 5; h -epresents an integer of from C to 4; i r~presents an integer of from 0 to 4; i represents an integer of from 0 to 4; k -epresents an integer of fro~! 0 to 4; and n represents an integer of from 1 to 3.
PAS of the invention may be either a homopolymer comprising one of the repeating units rep-esented by formulae (1) to (6) or a copolymer comprising two or more of them. The copolymer ~AS may be a random copolymer or a block copolymer. Further, PAS may be a linear polymer or may have a branched or cross-linked structure resulting from copolymeri~ation of a poly-nalogenated aromatic compound c~r.taining three or more halogen atoms per molecule or heat-curing in air.
Some examples of the above-described PAS include poly(p-?henylene sulfide) as disclose-` in JP-B-45-3368 and JP-B-52-12240 (the term ~JP-B~' as used herein means an "examined published Japanese patent applic~tion"); polyphenylene sulfide '~etone as disclosed in Indian Journal of Chemistry, Vol. 21, p.
501 (1982); polyphenylene sulfide sulfone as disclosed in JP-B-53-25880; polybiphenylene sulfide as disclosed in JP-B-45-3368;
and polyphenylene sulfide amide as disclosed in JP-A-63-83135.

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PAS of the present invention suitably has ~ ~-eight average molecular weight of from 10,000 to 500,000 as ~sured by means of a gel permeation chromatograph (hereinafte- abbreviated as &PC). For example, weight average molecular w~ight of poly(p-~henylene sulfide) can be determined by means o_ GPC at 210C
using l-chloronaphthalene as a solvent.
~ ccordingly, the PAS of the pr~esent inven-ion is of great pr~ctical utility owing to its freedom from h_a~.-y metals.
The equipment for PAS production of the p-esent invention is expected to have an extended working life ~ecause of its remarkable corrosion resistance even under conditions which easily induce corrosion of the conventional ma~erials, such as stainless steel, Ti, or chromium plated mater_a~s.
The present invention is now illustrated i~ greater detail with reference to Examples, but it should be understood that ~he present invention is not deemed to be lim ted thereto.
Molecular weight of poly(p-phenylene sulfile) thereinafter abbreviated as PPS) was measured with an ultra~ h temperature GPC equipped with a W detector at 210C i~ a l-chloro-naphthalene solvent and calculated from the c~libration curve of polystyrene as a standard.
Molecular weight of polyphenylene sulfide ketone (hereinafter abbreviated as PPSK) was meas~resd with a GPC
equipped with an RI detector at room temperat~re in a mixed solvent of p-chlorophenol and chloroform (15:~ ~y weight) and , .
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calculated from the calibration curve of polystyrene as a standard.
Molecular weight of polyphenylene sulfide sulfone (hereinafter abbreviated as PPSS) was measured with a GPC
equipped with an RI detector at room temperature in a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (3:2 by weightl and calculated from the calibration curve of polystyrene as a standard.
EXAMPLE 1 AND CO~ARATIVE EXAMPLE 1 Corrosion-resistant materials (Sample Nos. 1 to 3) a~d comparative materials ~Sample Nos. 4 to 8) having the composition, relative density and tensile strength as shown in Table 1 below were produced as follows.
Metallic chromium powder having a purity of 99.7% or more having the composition shown in Table 1 was sealed into a stainless steel-made vessel. The vessel was evacuated ~o 10-5 mmHg. The powder was subjected to hot rolling using a grooved roll at 800C to a final rolling degree of 70%, and the resulting rolled sheet was subjected to annealing at 1000C for 1 hour. A test piece (2 cm x 3 cm) was cut out of the roll~
sheet. A test piece of the same size was cut out of SUS 3~4 (Sample No. 8), Ti (Sample No. 7) or Ni (Sample No. 6) w~ose composition is shown in Table 2. In Tables 1 and 2, t~e rem~inder of the composition shown therein comprised other impurities.

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Each test piece was dipped in a solution shown in Table 3 below to determine an average rate of corrosion. The results obtained are shown in Table 3.
As can be seen from Table 3, materials of low purity had poor corrosion resistance, and cracks developed after the testing in test pieces having a low relative density.

Sample Composition Relative Tensile No. _Cr O N Density Strenqth (%) ~%) (%) (%) (kg/mm2) 1 99.910.04 0.03 96 30.5 2 99.940.03 0.02 98 31 3 99.930.03 0.03 99 32 4 99.910.04 0.03 91 10.5 98.100.08 0.05 96 31 Sample ComPosition _ No. Cr Ni_ Ti Fe (%) (%) (%) ~%) 6 99.9 8 17.9 7.6 74.2 - .

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TAsLE 3 Rate of Corrosion at 130C (mm/y~ar Sample 60% 40~ Na2S10% KSH
No. Na2S 20% NaOH40% KOH
<O.001 <O.001 <O.001 2 <0.001 <0.001 <0.001 3 <0.001 <0.001 <0.001 4 0.05 0.09 0.07 0.16 0.17 0.11 6 >10 >10 >10 7 0.1 0.4 0.5 8 >10 >10 >10 A crucible was prepared from a chromium plate having a relative density of 99% and a ~urity of 99.8~ in the same manner as in Example 1. A 60~ Na2S aqueous solution was concentrated in the crucible at a temperature between 130 and 150C for 10 hours, and the amount of chromium dissolved into the Na2S solution was measured by ICP (induced coupling plasma). For comparison, the same test was carried out using a crucible made of Ti.
The amount of chromium dissolved from the Cr crucible ~as found to be not more than 1 ppm, while the amount of titanium dissolved from the Ti crucible was 500 ppm.

Metallic chromium pow~er having a purity of 99.7% or higher and containing impurities shown in Table 4 below was sealed -`; ' . . .. . - .
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into a stainless steel vessel, and the vessel was evacuated to 1 o-5 mmHg. The powder was then subjected to hot rolling by means of a grooved roll at 800C to a finzl rolling degree of 70~, followed by annealing at 1000C for 1 ~our. A test piece of 2 cm x 3 cm was cut out of the resulting rolled sheet (Sample Nos. 9 to 13). A test piece of the same size was prepared from comparative materials, S~S 304 or Ti whose composition is shown in Table 5 below (Sam-le Nos. 14 and 15).
In Tables 4 and 5, the remainder of the composition shown comprised other impurities.
Each test piece was fixed to a 2 Q-volu~e autoclave made of SUS 316. In the autoclave were charged 2.45 mole of Na~S 2.9X20 and 600 m~ of NMP, and the mixture was heated to 200~C while stirring in a nitrogen stream to thereby ~move 90.8 mQ of a distillate mainly comprising water. Afte~ cooling to 170C, 2.4 mole of p-dichlorobenzene and 200 ml of NMP were added thereto, and the system was sealed in a nitrogen stream, followed by heating to 250C to conduct polymerization for 3 hours. After completion of the polymerization, the system was cooled, and the reaction product was ta~en out. The above procedure was repeated 10 times.
The test piece was taken out of the sys~em, and the rate of corrosion ~as determined. The result o~ained is shown in Table 6 below.

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Sample Composition _ __ Relative Tensil~
No. Cr . O NDensity_ Stren~
(%) (%) (%) (%) (kg/~') 9 99.91 0.04 0.03 96 30.~
99.94 0.03 0.02 98 31.Q
11 99.93 0.03 0.03 99 32.
12 99.91 0.04 0.03 91 10.
13 98.10 0.0~ 0.05 96 31.

Sample ComPosition ' No. Cr Ni Ti Fe (%) (%) (%) (%) 14 99.9 17.9 7.6 74.2 Sample No.Rate of Corrosion (mm/year) :`
9 <O.001 <O. 001 11 <O.001 12 0.05 13 0.06 ~
14 0.08 --:
0.51 .
16 <0.001 (Exa~ple 4) :
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-2~3 As can be seen from the results in Table 6, corrosion of the equipment materials according to the present invention (Sample Nos. 9 to 11) is below a detection limit, proving marked corrosion resistance and durability of these materials.
To the contrary, the chromium material of low purity (Sample No. 13) has poor corrosion resistance, and the chromium material, though highly pure, having a low relative density (Sample No. 12) underwent cracking after testing. Known materials (Sample Nos. 14 and 15) suffered local corrosion, turning out to be unsuitable as equipment material for PAS
production.

Corr~sion test was carried out in the same manner as in Example 3 by using a single crystal of anhydrous sodium sulfide prepared according to the process disclosed in JP-A-64-28207.
A test piece (2 cm x 3 cm) having the same composition as Sample No. 9 of Example 3 was fixed to a 2 ~-volume autoclave made of SUS 316, and polymerization was conducted under the following conditions.
In the autoclave were charged 2.45 mole of anhydrous Na2S
single crystal (purity: 99.42%), 2.45 mole of p-dichloro-~enzene, 1.23 mole of water, and 800 mQ of NMP. After sealing the autoclave in a nitrogen stream, the mixture was heated to 225C to polymerize for 2 hours. The temperature was elevated up to 250C, and polymerization was continued at that temperature for an additional 3 hours. After completion of the 2~3~

polymerization, the system was cooled, and the reaction product was taken out. The above procedure was repeated lO times.
The test piece was taken out of the system, and the rate of corrosion was determined. The result obtained are shown in Table 6 as Sample No. 1~.
As is apparent from Table 6, the equipment material of the present invention undergoes no corrosion even under very severe conditions using anhydrous Na2S, proving markedly resistant to corrosion and markedly durable.

A cylinder made of high purity chromium having the same composition as Sample No. 9 was fixed to a 500 ~-volume autoclave as an inner cylinder, and PPS was produced using the autoclave under the following conditions.
In the autoclave were charged 0.6 mole of Na2S-2.9H2O and 150 mQ of NMP. The mixture was heated up to 21iC with stirring in a nitrogen stream to remove 23.0 mQ of a distillate mainly comprising water. After cooling the system to 150C, 0.6 mole of p-dichlorobenzene and 50 mR of NMP we_e added thereto, and the system was sealed in a nitrogen stream. The temperature was raised to 250C to conduct polymerization for 3 hours. After completion of the polymerization, the system was cooled, and the resulting product was poured into water.
The precipitated polymer was collected by filtration and washed with about 5 Q of warm water. Filtration and washing with water were repeated to remove by-produced NaCQ. The resulting I

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wet cake was dried by heating at 100C ~or one day under reduced pressure to isolate 61.6 g (yield: 95%) of PPS.
The resulting PPS had a weight average molecular weight (hereinafter abbreviated as Mw) of 33,000 as measured with GPC.
Heavy metal contents were measured on Cr, Ni, Fe, and Ti by atomic-absorption spectroscopy and found to be below a detection limit tthe terminology "below detection limitll as used here means that each heavy me_~l content is less than 0.5 ppm)-In order to determine an oligomer content, the product wasextracted with methylene chloride fo- ~ hours by means of a Soxhlet apparatus, and a weight loss was measured. The results obtained are shown in Table 7 below.
It can be seen from Table 7 that P~S obtained by the use of the equipment material according to the present invention is free from contamination with heavy me~als originated from the autoclave used and, at the same time, has a reduced oligomer content.
In order to evaluate heat stability, flow characteristics of the resulting PPS were examined ~y means of a ~OHKA type flow tester (manufactured by Shimadzu Corporation) equipped with a die having a diameter of 0.5 mm and a length of 2 mm heated at 330C. A ratio (~30/~5) of a melt viscosity after 30~
minute preheating (~30) to a melt ~iscosity after 5-minute preheating (~5 ) was obtained as an indication of heat `

2 ~

stability. The above prepared PPS had an ~30/~r of 1.05, indicating excellent heat stability.
Further, the resulting PPS was melt-pressed at 320~C for 30 seconds to prepare a 0.3 mm thick sheet. The PPS sheet had a degree of whiteness as high as 83 as determined with a color meter (manufactured by Suga Shikenki) (see Table 7).

PPS was produced in the same manner as in Example 5, except for using a 500 mQ-volume autoclave equipped with an inner cylinder made of high purity chromium having the same composition as Sample No. 10 or 11.
The yield, Mw, heavy metal content, heat stability, oligomer content, and degree of whiteness of the resulting PPS
are shown in Table 7.

PPS was produced under the following conditiors by using the same apparatus as used in Example 5.
In the autoclave were charged 0.6 mole of anhyd~ous Na2S
single crysta:1 (purity: 99.42~), 0.6 mole of p-dichlcrobenzene, 0.3 mole of water, and 200 mQ of NMP, and the system was sealed in a nitrogen stream. The system was allowed to poly~erize at 225C for 2 hours and then at 250C for 3 houIs. After completion of the polymerization, the system was cooled, and the reaction mixture was poured into water. The plecipitated ~olymer was collected by filtration and washed with about 5 Q
~f warm water. The filtration and washing were repeated to i .. . . . .. .... . .... . ... ~ .. .
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remove by-produced NaC~, and the finally obtained wet cake was dried by heating at 100C under reduced pressure for one day to obtain PPS.
The yield, Mw, heavy metal content, heat stability, oligomer content, and ~egree of whiteness of the resulting PPS
are shown in Table 7.

PPSK was prepared under the following conditions by using the same apparatus as used in Example 5.
In the autoclave were charged 0.166 mole of Na2S 2.8H2O, 0.168 mole of 4,4'-dichlorobenzophenone, and 200 mQ of NMP, and the system was sealed in a nitrogen stream. The temperature was elevated to 260C to conduct polymeriza~ion for 1.5 hours.
After completion of the polymerization, Lhe system was cooled, and the reaction product was poured into water. The precipitated polymer was collected by filtration and washed with about 5 Q of warm water. The filtration and washing were repeated to remove by-produced NacQl and the finally obtained wet cake was dried by heating at 100C under reduced pressure for one day to isolate PPSK.
The yield, Mw, heavy metal content and heat stability o~
the resulting PPSK are shown in Table 7 below.

PPSS was prepared under the following conditions by using the same apparatus as used in Example 5.

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In the autoclave were charged 0.200 mole ~f Na2S.2.8H20 0.202 mole of 4,4'-dichlorodiphenyl sulfone, 2.0 mole of water, O.100 mole of lithium acetate, and 200 mQ of N~P, and the system was sealed in a nitrogen str~am. The temperature was elevated to 200C to conduct polymerization for 5 hours. After completion of the polymerization, the system was cooled, and the reaction product was poured into water. The precipitated polymer was collected by filtration and washed with about 5 Q
of warm water. The filtration and washing were repeated to remove by-produced NacQr and the finally obtained wet cake was dried by heating at 100C under reduced pressure for one day to isolate PPSS.
The yield, ~w, heavy metal content, heat stability, and degree of whiteness of the resulting PPSS are shown in Table 7.
C~MPARATIVE EXAMPLES 4 TO 7 PPS was prepared in the same manner as in Example 5, except for using a 500 mQ-volume autoclave equipped ~ith an inner cylinder made o the same material of Sample Nos. 12 to 15 shown in Tables 4 and 5.
The yield, Mw, heavy metal content, heat stability, oligomer content, and degree of whiteness of the resulting PPS
are shown in Table 7.
It can be seen from Table 7 that PPS obtained by using equipment made of materials other than the corrosion-resistant material according to the present invention are contaminated - : .

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with heavy metals originated from the autoclave used and i~ferior in heat stability and degree of whiteness.

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While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

:- .. . :

Claims (6)

WHAT IS CLAIMED IS:

1. A corrosion-resistant material against sulfur-containing alkali metal salt which comprises high purity metallic chromium having a relative density of 95% or higher and a purity of 99.7% or higher.

2. Equipment for production of a polyarylene sulfide by the reaction between an alkali metal sulfide and a dihalogenated aromatic compound in a polar aprotic solvent, said equipment being composed of high purity metallic chromium having a relative density of 95% or higher and a purity of 99.7% or higher.

3. Equipment as in claim 2, wherein said equipment is a tank, a reactor, a heat exchnager, or a pipe.

4. A process for producing a polyarylene sulfide comprising reacting an alkali metal sulfide and a dihalogenated aromatic compound in a polar aprotic solvent, in which equipment used is comprised of high purity chromium having a purity of 99.7% or higher and having a relative density of 95%
or higher at least at parts in contact with a liquid.

5. A process as in claim 4, wherein the reaction is carried out at a temperature of from 200 to 300°C for a period of from 0.5 to 30 hours.
6. A polyarylene sulfide containing substantially no heavy metal, produced by a process as in claim 4.

7. A polyarylene sulfide as in claim 6, wherein the total heavy metal content in said polyarylene sulfide is not more than 10 ppm.
8. A polyarylene sulfide as in claim 6, wherein the total heavy metal content in said polyarylene sulfide is not more than 0.5 ppm.
9. A molded article comprising a polyarylene sulfide as in

claim 6.