JP5387573B2 - Method for producing polycarbonate resin granular material - Google Patents

Description

  The present invention relates to a method for producing a polycarbonate resin granular material. Specifically, the present invention relates to a method for producing a high-quality polycarbonate resin granular material excellent in hue while recycling a poor solvent having high purity.

  As a method for producing a polycarbonate resin, in general, many production methods by a phosgene method are adopted. In this method, a dihydric phenol compound (bisphenol) is reacted with phosgene by an interfacial polymerization method using an organic solvent such as methylene chloride in the presence of a small amount of a molecular weight regulator and optionally a branching agent. This is a polymerization method.

  The polymerization resin solution of the polycarbonate resin produced in the polymerization reaction step is purified by operations such as catalyst removal, neutralization, and water washing to become a purified polycarbonate resin solution, and then a solidification step for separating the organic solvent from the polycarbonate resin solution, And it is commercialized as a polycarbonate powder granular body through a drying process. The used organic solvent is recycled after being purified by distillation in the solvent recovery step.

  Here, as a method of separating the organic solvent from the purified polycarbonate resin solution and solidifying the polycarbonate resin, a method of adding a poor solvent to the purified polycarbonate resin solution to precipitate the polycarbonate, or an organic solvent from the purified polycarbonate resin solution The method of distilling off and concentrating to form a powdery body can be mentioned.

  Furthermore, as a method for producing a polycarbonate powder having better properties, a poor solvent is mixed with a purified polycarbonate resin solution, and then the mixture is continuously added to warm water under heating and suspended in warm water. After that, a method of distilling off a mixed solvent of an organic solvent and a poor solvent (for example, see Patent Document 1) is known. In addition, the poor solvent used in these methods is also recovered as a mixed solvent and then recycled through distillation purification.

  However, in the polycarbonate production method using phosgene as a raw material as described above, it is known that carbon tetrachloride of several hundred ppm by weight (hereinafter simply referred to as ppm) is contained in ordinary phosgene. (For example, refer patent document 2) When polycarbonate resin is manufactured using the phosgene containing such carbon tetrachloride, most of the carbon tetrachloride in this phosgene melt | dissolves in an organic solvent. When such an organic solvent in which carbon tetrachloride is dissolved is collected and recycled, the residual carbon tetrachloride causes a hue failure of the polycarbonate resin and corrosion of the molding die.

As a means for solving this, there is known a method in which the recovered organic solvent is purified to remove carbon tetrachloride and then recycled (for example, see Patent Document 3).
However, when a method of adding a poor solvent to a purified polycarbonate resin solution and solidifying the polycarbonate resin is adopted, even if carbon tetrachloride, an organic solvent, is removed and used, the hue of the polycarbonate resin is poor or the mold is molded. Corrosion occurs.

  This is considered to be because carbon tetrachloride in phosgene is dissolved in the poor solvent, and as a result, a considerable amount of carbon tetrachloride remains in the poor solvent. However, when the poor solvent is recovered and recycled, it has not yet been made to recycle after the poor solvent is purified and carbon tetrachloride is removed.

  Also, a poor solvent is mixed with the purified polycarbonate resin solution, and then the mixture is continuously added to warm water under heating and suspended in warm water, and then the mixed solvent of the organic solvent and the poor solvent is distilled off. In the method, it is preferable to distill and purify the binary mixed solvent of the recovered organic solvent and poor solvent and recycle each, but in that case, carbon tetrachloride in the poor solvent is selectively and efficiently removed. It is necessary to do.

  As a method for selectively removing carbon tetrachloride in the poor solvent, a method of selectively distilling the target product from the mixture by batch distillation purification may be employed (for example, see Patent Document 4). In this method, when the target object to be removed is a very small amount, components other than the target object are often excessively extracted at the time of extraction, and efficient and selective extraction is difficult. Therefore, carbon tetrachloride in the poor solvent is selectively removed from the binary mixed solvent of the organic solvent and the poor solvent, and each of the organic solvent and the poor solvent is recycled without causing a deterioration in the quality of the polycarbonate resin product. No effective method has been found yet.

JP-A-4-202427 Japanese Patent Publication No. 55-14044 JP-A 63-268736 JP-A-7-207060

  The problem to be solved by the present invention is that even when adopting a process of solidifying a purified polycarbonate resin solution using a poor solvent, the polycarbonate resin obtained has a high quality without causing hue failure or corrosion of the molding die. It is an object to provide a method of obtaining a polycarbonate resin granular product of the present invention, and to provide a method of efficiently removing carbon tetrachloride from the poor solvent and recycling it with good economic efficiency.

  As a result of intensive studies to solve the above problems, the present inventors recovered a mixed solvent of an organic solvent and a poor solvent used for solidifying a polycarbonate resin, and then removed carbon tetrachloride in the poor solvent. The present invention has been reached by finding a method for recycle after purification and a method for selectively removing carbon tetrachloride from the mixed solvent.

That is, this invention relates to the manufacturing method of the polycarbonate resin granular material shown below.
(1) A polycarbonate resin powder comprising a solidification step in which a poor solvent is added to a purified polycarbonate resin solution to solidify, and a recovery step in which the poor solvent used in the solidification step is collected by distillation purification and recycled. In the method for producing a granular material, the recovery step comprises subjecting carbon tetrachloride contained in a poor solvent by batch distillation in the presence of a third component having a boiling point 1 to 20 ° C. lower than the boiling point of carbon tetrachloride. A method for producing a polycarbonate resin granular material comprising a carbon tetrachloride removing step of distilling together with the third component to reduce the carbon tetrachloride concentration in the poor solvent to 0 to 5000 ppm by weight.

(2) In the solidification step, a poor solvent is added to and mixed with the purified polycarbonate resin solution, and the mixture is continuously added to the heated warm water and suspended in the warm water while the purified polycarbonate resin solution is used. The method for producing a polycarbonate resin granular material according to (1), comprising a step of distilling off the organic solvent and the poor solvent.

(3) The production method according to (1) or (2), wherein the poor solvent is heptane.
(4) The distillate containing carbon tetrachloride and the third component is determined based on the distillation timing of the third component specified by observing the top temperature of the batch distillation column in the batch distillation step. The manufacturing method according to any one of (1) to (3), including a step of extracting.

(5) The method according to any one of (1) to (4), wherein the third component is chloroform.
(6) The production according to any one of (1) to (5), wherein in the recovery step, the concentration of carbon tetrachloride in the poor solvent before the distillation purification operation is 1.2% by weight or less. Method.

  According to the production method of the present invention, since carbon tetrachloride in the recovered poor solvent is also removed and recycled, the content of carbon tetrachloride in the entire reaction system of polycarbonate resin production can be reduced, and the hue Can be obtained. In removing carbon tetrachloride, the poor solvent is distilled and purified in the presence of a third component having a boiling point lower than that of carbon tetrachloride, and the carbon tetrachloride is selectively distilled off. It is possible to selectively and efficiently remove even a small amount of carbon, which is excellent in terms of economy. In addition, the said 3rd component is removed to the level (1 ppm or less) which does not affect quality in the process of drying and removing the solvent in the polycarbonate resin granular material after a solidification process.

It is the schematic of the distillation purification equipment which shows one embodiment of this invention. It is the schematic of the distillation purification equipment which shows a prior art example. The composition of the distillate containing concentrated carbon tetrachloride distilled from the top of the batch distillation column 7 of Example 2 and the relationship between the tower top temperature of the batch distillation column 7 and the elapsed time are shown. It is a graph.

  Polycarbonate resins are generally produced from bisphenol compounds and carbonate ester-forming compounds. Specifically, direct reaction between bisphenol compounds and phosgene (phosgene method), transesterification reaction between bisphenol compounds and bisaryl carbonate (transesterification method). However, the method for producing the polycarbonate resin of the present invention is the same as the method for producing a polycarbonate resin by a so-called phosgene method using a conventional organic solvent, that is, a method for producing by an interfacial polymerization method. In this method, a bisphenol compound is first polymerized after reacting with phosgene using an organic solvent in the presence of a small amount of molecular weight regulator and optionally a branching agent (polymerization reaction step).

Next, the solution (polycarbonate resin solution) containing the polycarbonate resin obtained in the polymerization reaction step is subjected to catalyst removal, neutralization, water washing, concentration, etc. by a conventional method, and further purified by precision filtration to obtain a purified polycarbonate resin solution. (Purification process).
In the method for producing a polycarbonate powder granule of the present invention, a poor solvent is further added to the purified polycarbonate resin solution to solidify it (solidification step) to obtain a polycarbonate resin granule. The obtained granular material is usually dried by a method such as hot air drying (drying step) to become a product. The poor solvent used in the solidification step is recovered and recycled (recovery step).

  The production method of the present invention comprises an aromatic homopolycarbonate resin (polycarbonate homopolymer) or a copolycarbonate resin (polycarbonate copolymer) using a normal bisphenol compound, a further branched one, and a long end. The present invention can be applied to various polycarbonate resins such as those having a chain alkyl group introduced therein.

  Further, a polycarbonate resin is produced using a carbon-carbon double bond or other end-capping agent or comonomer having a graftable point, and grafted with styrene or the like, or a polystyrene-based phenolic hydroxyl group or other polycarbonate. The present invention can be used for a solvent-soluble polycarbonate resin such as a copolymer obtained by copolymerizing a compound having a resin graft polymerization starting point and a graft polymer obtained by graft polymerization of a polycarbonate resin.

  As the aromatic polycarbonate resin that is usually used, a polycarbonate mainly composed of 2,2-bis (4-hydroxyphenyl) propane [bisphenol A] is exemplified, and examples thereof include 1,1- (4-hydroxy Phenyl) cyclohexane [bisphenol Z], 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane [tetrabromobisphenol A], etc., and polycarbonate copolymers obtained by branching these and terminal Applicable to long-chain alkyl-modified products.

  The molecular weight of the polycarbonate resin to which the production method of the present invention is applied is not particularly limited, but is preferably used for a polycarbonate resin having a viscosity average molecular weight of 1,000 to 100,000.

(1) Polymerization reaction step In the polymerization reaction step in the polycarbonate resin production method of the present invention, the bisphenol compound is converted to phosgene using an organic solvent in the presence of a small amount of a terminal terminator or molecular weight regulator and optionally a branching agent. And then polymerized.

<Bisphenol compound>
Specific examples of the bisphenol compound used in the present invention include bis (4-hydroxyphenyl) methane, bis (3-methyl-4-hydroxyphenyl) methane, bis (3-chloro-4-hydroxyphenyl) methane, Bis (3,5-dibromo-4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, 1,1-bis (2-tert-butyl-4-hydroxy-3-methylphenyl) ethane 1,1-bis (2-tert-butyl-4-hydroxy-5-methylphenyl) ethane, 1-phenyl-1,1-bis (3-fluoro-4-hydroxy-3-methylphenyl) ethane, 2 , 2-bis (4-hydroxyphenyl) propane (bisphenol A; BPA), 2,2-bis (4-hydroxy-3,5-dibromophenyl) propyl Pan (TBA), 2,2-bis (4-hydroxyphenyl) butane, 2,2-bis (2-methyl-4-hydroxyphenyl) propane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) ) Propane, 2,2-bis (4-hydroxy-3,5-difluorophenyl) propane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 2,2-bis (4-hydroxy) -3-bromophenyl) propane, 2,2-bis (4-hydroxy-3-chlorophenyl) propane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxy) -3-fluorophenyl) propane, 2,2-bis (4-hydroxy-1-methylphenyl) propane, 2,2-bis (3-bromo-4-hydroxy) 5-chlorophenyl) propane, 2,2-bis (3-phenyl-4-hydroxyphenyl) propane, 1,1-bis (2-tert-butyl-4-hydroxy-5-methylphenyl) butane, 1,1- Bis (2-t-butyl-4-hydroxy-5-methylphenyl) isobutane, 1,1-bis (2-t-amyl-4-hydroxy-5-methylphenyl) butane, 1,1-bis (3 5-dichloro-4-hydroxyphenyl) butane, 1,1-bis (3,5-dibromo-4-hydroxyphenyl) butane, 4,4-bis (4-hydroxyphenyl) heptane, 1,1-bis (2 Bis (hydroxyaryl) alkanes such as -t-butyl-4-hydroxy-5-methylphenyl) heptane, 2,2-bis (4-hydroxyphenyl) octane; 1,1 -Bis (4-hydroxyphenyl) cyclopentane, 1,1-bis (4-hydroxyphenyl) cyclohexane (bisphenol Z; BPZ), 1,1-bis (3-methyl-4-hydroxyphenyl) cyclohexane, 1,1 -Bis (3-cyclohexyl-4-hydroxyphenyl) cyclohexane, 1,1-bis (3-phenyl-4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,5,5-trimethyl Bis (4-hydroxyphenyl) cycloalkanes such as cyclohexane; 4,4′-dihydroxybiphenyl, 4,4′-dihydroxy-2,2′-dimethylbiphenyl, 4,4′-dihydroxy-3,3′-dimethyl Biphenyl, 4,4′-dihydroxy-3,3′-dicyclohexylbiphenyl, etc. Dihydroxybiphenyls; bis (hydroxyaryl) ethers such as bis (4-hydroxyphenyl) ether and bis (4-hydroxy-3-methylphenyl) ether; bis (4-hydroxyphenyl) sulfone, bis (3-methyl- Bis (hydroxyaryl) sulfones such as 4-hydroxyphenyl) sulfone; bis (4-hydroxyphenyl) sulfoxide, bis (3-methyl-4-hydroxyphenyl) sulfoxide, bis (3-phenyl-4-hydroxyphenyl) sulfoxide Bis (hydroxyaryl) sulfoxides such as bis (4-hydroxyphenyl) sulfide, bis (3-methyl-4-hydroxyphenyl) sulfide and other bis (hydroxyaryl) sulfides; Le) ketone, other, etc. at both ends phenol-modified siloxanes and both ends phenol-modified silanes are exemplified. Two or more of these may be used in combination. Among these, those selected from bisphenol A, 1,1-bis (4-hydroxyphenyl) cyclohexane and 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane are desirable.

<End terminator or molecular weight regulator>
Examples of the terminal terminator or molecular weight regulator used in the present invention include monohydric phenolic hydroxyl groups such as ordinary phenol, Pt-butylphenol, tribromophenol, long-chain alkylphenol, hydroxybenzoic acid alkyl ester, and alkyl etherphenol. In addition to the compounds having carboxylic acids, carboxylic acids and carboxylic acid halides such as aliphatic carboxylic acid chlorides, aliphatic carboxylic acids, aromatic carboxylic acids, and aromatic acid chlorides may be mentioned.

  In addition, phenols having a reactive double bond may be used as a terminal terminator, and examples thereof include acrylic acid, vinyl acetic acid, 2-pentenoic acid, 3-pentenoic acid, 5-hexenoic acid, 9- Unsaturated carboxylic acids such as undecenoic acid; acid chlorides or chloroformates such as acrylic acid chloride, sorbic acid chloride, allyl alcohol chloroformate, isopropenyl phenol chloroformate or hydroxystyrene chloroformate; isopropenyl phenol, hydroxy Examples include phenols having an unsaturated group such as styrene, hydroxyphenylmaleimide, hydroxybenzoic acid allyl ester or hydroxybenzoic acid methyl allyl ester, one-end phenol-modified siloxanes, and one-end phenol-modified silanes. . Two or more of these end terminators can be used in combination.

  The terminal terminator or molecular weight regulator described above is usually used in the range of 1 to 25 mol%, preferably 1.5 to 10 mol%, relative to 1 mol of the bisphenol compound.

<Organic solvent>
As the organic solvent used in the reaction, an organic solvent which is inert to the reaction and dissolves the polycarbonate and does not substantially dissolve in water is used. Examples of such organic solvents include chlorinated aliphatic or aromatic hydrocarbons, and more specifically, methylene chloride (methylene chloride), 1,1-dichlorotoluene, chlorobenzene, chlorotoluene and the like. It is done. Of these, methylene chloride is particularly preferred.

<Branching agent>
In the production method of the present invention, a branching agent is further used in combination in the range of 0.01 to 5 mol%, particularly 0.1 to 3.0 mol% with respect to the bisphenol compound. You can also. As the branching agent, phloroglucin, 2,6-dimethyl-2,4,6-tri (4-hydroxyphenyl) heptene-3, 4,6-dimethyl-2,4,6-tri (4-hydroxyphenyl) Heptene-2,1,3,5-tri (2-hydroxyphenyl) benzol, 1,1,1-tri (4-hydroxyphenyl) ethane, 2,6-bis (2-hydroxy-5-methylbenzyl)- 4-methylphenol, α, α ′, α ″ -tri (4-hydroxyphenyl) -1,3,5-triisopropylbenzene, 3,3-bis (4-hydroxyphenyl) oxindole (= isatin bisphenol) ), 5-chlorouisatin bisphenol, 5,7-dichloroisatin bisphenol, 5-bromoisatin bisphenol and the like.

<Catalyst>
Examples of the polymerization reaction catalyst include tertiary amines such as triethylamine or quaternary ammonium salts.

<Molecular weight>
The molecular weight of the polycarbonate resin to be produced is selected from the range of 1,000 to 100,000 as the viscosity average molecular weight, but required physical properties such as impact resistance and wear resistance of the molded product, moldability, etc. Therefore, the range of 5,000 to 50,000 is preferable.

<Reaction conditions>
Usually, in the interfacial polymerization step, a bisphenol compound is dissolved in a caustic aqueous solution, reacted with phosgene in the presence of an organic solvent, and then a polymerization catalyst is added and stirred as necessary to carry out the polymerization reaction. It is preferable that the density | concentration of the polycarbonate resin at the time of a polymerization reaction is 5 to 30 weight% normally as a polycarbonate organic solvent solution. If the concentration of the polycarbonate resin is too high, the viscosity increases, which is not preferable.
The reaction temperature is usually 0 to 40 ° C., preferably 5 to 30 ° C. While the reaction time depends on the reaction temperature, it is generally 0.5 min-10 hr, preferably 1 min-2 hr. Further, during the reaction, it is desirable to maintain the pH of the reaction system at 10 or more.

  When the polymerization reaction is completed, it consists of an organic solvent solution (oil phase) of polycarbonate and an aqueous solution (aqueous phase) containing impurities such as unreacted organic compounds, by-product chlorides, carbonates, and caustic alkalis during the polymerization reaction. A mixture is obtained. Although this mixture may separate into an oil phase and an aqueous phase, the oil phase still contains some moisture, and the mixture after polymerization is in the form of an emulsion. The required oil phase is often W / O (water-in-oil dispersion type).

(2) Purification step The polycarbonate resin solution produced by the above method is then subjected to catalyst removal, neutralization, water washing, concentration, etc. by a conventional method, and further purified by precision filtration to obtain the purified polycarbonate resin solution of the present invention. (Purification process).

(3) Solidification process In this solidification process, a poor solvent is added to the polycarbonate resin solution refine | purified at the said process, and a polycarbonate resin is solidified. More preferably, a poor solvent is added to and mixed with the purified polycarbonate resin solution at room temperature, and then the mixed solution is continuously added to warm water under heating (preferably 40 to 60 ° C.) to remove the organic solvent and the poor solvent. While distilling off, the mixed solution is circulated and pulverized in a wet pulverizer.

  As the poor solvent (solidification solvent), those having a boiling point higher than that of the organic solvent used in the polymerization reaction step are preferred, and those having a boiling point of 20 to 80 ° C. are more preferred than those of the organic solvent used in the polymerization reaction. Specifically, those having a boiling point of 60 to 120 ° C. are preferable, and examples of such a poor solvent include hexane, heptane, toluene and the like. Of these, heptane is particularly preferable.

  The poor solvent is usually used in an amount of 0.2 to 0.6 times, preferably 0.3 to 0.5 times the volume of the purified polycarbonate resin solution. The amount of addition of the poor solvent and the addition temperature are the amount and temperature that will form a gel when the solution after the addition of the same amount of the poor solvent is allowed to stand at the same temperature, or when the temperature is lowered below the same temperature. The amount and temperature at which precipitation occurs.

  In the solidification step, usually, a mixed solution of a purified polycarbonate resin solution and a poor solvent is dropped into warm water under heating, and then the mixed solvent (an organic solvent and a poor solvent) is distilled from the mixed solution at the same time. There are no particular restrictions on the method of distilling the mixed solvent, but considering the quality of the resulting polycarbonate resin granules, the organic solvent and the poor solvent may be distilled off sequentially sequentially by changing the distillation temperature stepwise. preferable. For example, a good solvent having a low boiling point (an organic solvent used in the polymerization reaction step, for example, methylene chloride: boiling point 40 ° C.) is mainly distilled off in a low temperature range (40 to 60 ° C.), and then the temperature is raised to a high temperature range ( It is preferable to mainly distill off the poor solvent at 80-100 ° C. Both the good solvent and the poor solvent distilled off are collected in the collection tank.

  In the present invention, since the good solvent (organic solvent) in the purified polycarbonate resin solution is compatible with both the polycarbonate resin and the poor solvent, the phenomenon is that the organic solvent is mixed with the polycarbonate resin and the poor solvent. Therefore, a poor solvent prevails and a precipitate is formed.

  Thus, in this invention, solidification is performed by distilling this mixed solvent (an organic solvent and a poor solvent) simultaneously from the liquid mixture of the organic solvent solution of polycarbonate resin, and a poor solvent. In the case of the mixed solvent of the present invention, the polycarbonate resin and the mixed solvent are not completely compatible. Therefore, when the mixed solvent decreases with respect to the polycarbonate resin, a precipitate is formed at a concentration that is not normally considered. As a result, it is estimated that the mixed solvent is distilled off while forming a precipitate.

The distillation (distillation) of the organic solvent and the poor solvent is usually performed for 0.1 to 1.0 hour, preferably 0.5 to 1.0 hour. Along with this, the liquid in the solidification process (= solidification liquid; gelled polycarbonate resin solution containing some solvent obtained after distilling off the organic solvent and the poor solvent) is circulated to the wet pulverizer. Alternatively, wet pulverization may be performed. The amount of circulation is 1 to 30 times / hour, preferably 5 to 20 times / hour of the total solidified liquid (total amount of the solidified liquid).
By the above method, a polycarbonate resin powder is obtained.

(4) Recovery step The poor solvent discharged from the solidification step is reused (recycled) through the recovery step. In the method of the present invention, the recovery step includes a carbon tetrachloride removal step of removing carbon tetrachloride contained in the poor solvent by a distillation operation.

In addition, it is desirable that the carbon tetrachloride concentration in the poor solvent discharged from the solidification process (that is, the poor solvent before the distillation purification operation in the recovery process) is 1.2% by weight or less.
If the carbon tetrachloride concentration in the poor solvent discharged from the solidification process is too high, the carbon tetrachloride concentration in the poor solvent during reuse (recycling) will be sufficiently reduced even if it is distilled and purified by the method of the present invention. In some cases, the hue of the obtained polycarbonate resin powder may deteriorate.

In addition, the concentration of carbon tetrachloride in the poor solvent is 0.5% by weight or less, more preferably 0.01% by weight or less when recovered and reused as a solidification solvent after distillation purification operation in the recovery process. It is desirable to be.
In the method of the present invention, since the carbon tetrachloride concentration in the poor solvent can be efficiently reduced, the carbon tetrachloride concentration in the poor solvent during recycling can be lowered to 0.5% by weight or less. When the carbon tetrachloride concentration in the poor solvent at the time of recycling exceeds 0.5% by weight, the hue of the obtained polycarbonate resin powder may be deteriorated.

  In the carbon tetrachloride removal step, the carbon tetrachloride contained in the poor solvent is subjected to a batch distillation operation in the presence of a third component having a boiling point 1-20 ° C. lower than that of carbon tetrachloride, together with the third component. The carbon tetrachloride concentration in the poor solvent is reduced to 0 to 5000 ppm by weight, preferably 0 to 100 ppm. Thereby, carbon tetrachloride in the poor solvent can be selectively removed efficiently, and the recovery rate of the poor solvent is improved.

  The third component is not particularly limited as long as it is an organic compound that is easily soluble in a poor solvent and has a boiling point that is 1 to 20 ° C. lower than the carbon tetrachloride to be removed (boiling point 76.8 ° C.). A chlorinated hydrocarbon compound having a boiling point 1 to 20 ° C. lower than that of carbon tetrachloride is used. Particularly preferably, a chlorinated hydrocarbon compound having a boiling point of 10 to 15 ° C. lower than that of carbon tetrachloride is used. Specific examples of the third component include chloroform, 1,1-dichloroethane and the like. Preferably, chloroform is used.

  For example, when heptane is used as the poor solvent, chloroform (boiling point 62 ° C.) is preferably present as the third component in the poor solvent solution when removing carbon tetrachloride in the heptane. The content ratio of the third component with respect to the poor solvent solution (column top liquid) is usually preferably 10 to 40% by weight, more preferably 15 to 35% by weight, and still more preferably 15 to 25% by weight. .

  Such a third component is preferably added to the purified polycarbonate solution before the poor solvent is added in the solidification step, or added directly to the poor solvent in the poor solvent recovery step. Moreover, the case where it originally contains as raw material phosgene with carbon tetrachloride as an impurity may be sufficient.

  According to the preferred method of the present invention, the poor solvent discharged from the solidification step is first concentrated and distilled in a continuous distillation column. Thereby, carbon tetrachloride in the poor solvent is concentrated, and a poor solvent solution in which carbon tetrachloride is reduced (preferred carbon tetrachloride concentration; 0.5 wt% or less, more preferably 0.01 wt% or less) and Separated into a poor solvent mixture containing concentrated carbon tetrachloride. The poor solvent solution with reduced carbon tetrachloride is recovered from the bottom part of the continuous distillation column (column bottom liquid), and the poor solvent mixture containing concentrated carbon tetrachloride is recovered from the top part of the continuous distillation column ( Tower top liquid).

The poor solvent solution (column bottom liquid) with reduced carbon tetrachloride recovered from the bottom of the continuous distillation column is returned to the solidification step and reused as a solidification solvent.
On the other hand, carbon tetrachloride is removed from the poor solvent mixture (concentrated liquid) containing concentrated carbon tetrachloride collected from the top of the continuous distillation column. Carbon tetrachloride is removed by distillation using a batch distillation column.

At this time, it is preferable that the top liquid of the continuous distillation column contains a third component having a boiling point 1 to 20 ° C. lower than the above-described carbon tetrachloride.
In addition, the 3rd component which has a boiling point 1-20 degreeC lower than carbon tetrachloride has an influence on the quality of a product in the drying process (process which dry-removes the solvent in a polycarbonate resin granular material) after a solidification process. It can be easily removed to a level that does not appear (1 ppm or less).
In addition, the poor solvent mixture (column top liquid) may contain a small amount of water and / or polycarbonate resin.

  In the recovery step of the present invention, even the trace amount of carbon tetrachloride is selectively removed by subjecting the tower top liquid (poor solvent mixture) to distillation using a batch distillation tower in the presence of the third component. can do. That is, by removing the distillate from the top of the batch distillation column at the time when most of the third component is removed during the distillation process and carbon tetrachloride begins to be distilled, components other than the target product are also accompanied during the extraction. Thus, it is possible to prevent excessive extraction.

  When most of the third component is removed and carbon tetrachloride begins to distill, the temperature at the top of the batch distillation column (top temperature) is observed and the top temperature is in the boiling range of the third component. The time when it starts to rise after being stabilized can be used as a guide. At this time, it is possible to efficiently remove a small amount of carbon tetrachloride while preventing the excessive extraction of the poor solvent which is the main component by extracting the distillate by determining when the third component has been removed. be able to. Furthermore, it is also possible to suppress a decrease in production efficiency with respect to the poor solvent polycarbonate resin.

  Thus, the poor solvent from which carbon tetrachloride has been efficiently removed is recovered and recycled again as a solidifying solvent. The carbon tetrachloride concentration in the poor solvent recovered from the batch distillation column is 0 to 5000 ppm, preferably 0 to 100 ppm. If the carbon tetrachloride concentration in the recovered poor solvent is too high, the hue of the obtained polycarbonate resin powder may be deteriorated.

Hereinafter, the present invention will be described in detail with reference to FIG.
FIG. 1 is a schematic view of a solvent distillation purification facility showing one embodiment of the present invention. FIG. 2 is a schematic view of a general solvent continuous distillation purification facility. 1 is a continuous distillation column, 2 is a continuous distillation column reboiler, 3 is a continuous distillation column bottom pump, 4 is a continuous distillation column condenser, 5 is a reflux tank, 6 is a buffer tank, 7 is a batch distillation column, and 8 is a batch distillation. A tower reboiler, 9 is a batch distillation bottom pump, 10 is a batch distillation condenser, 11 is an aftercooler, 12 is an extraction tank, 13 is a poor solvent tank, and 14 is a recovery tank.

  First, the poor solvent solution is continuously fed to the continuous distillation column 1 and carbon tetrachloride in the poor solvent is concentrated by reflux. The poor solvent in which carbon tetrachloride is reduced (the bottoms = the same as the bottom liquid above) is recovered by the continuous distillation tower bottom pump 3 through the after cooler 11 and then in the poor solvent tank 13.

  On the other hand, the poor solvent mixture containing carbon tetrachloride concentrated by the continuous distillation column 1 is temporarily stored in the buffer tank 6 from the reflux tank 5. Thereafter, the poor solvent mixed liquid is dropped into the batch distillation tower 7 and heated by the batch distillation tower reboiler 8 to concentrate a distillate (condensate at the top of the batch distillation tower) composed of carbon tetrachloride. The carbon tetrachloride is fractionated into a poor solvent solution in which carbon tetrachloride is reduced (the bottom liquid of a batch distillation tower).

  The concentrated distillate composed of carbon tetrachloride is condensed by the batch distillation column condenser 10 and is refluxed again to the batch distillation column 7 by switching the line, or is drawn to the extraction tank 12 or the recovery tank 14. It is. The frequency of line switching depends on the set reflux ratio. In order to reduce the heat load on the batch distillation column condenser 10 due to the evaporation of a large amount of low-boiling components, the reflux ratio in the batch distillation column 7 can be changed stepwise as appropriate.

  In order to selectively remove the target carbon tetrachloride out of the system from the poor solvent mixture containing carbon tetrachloride concentrated in the former stage (continuous distillation column 1) in the latter stage (batch distillation column 7), the present invention In the preferred method, the top temperature of the batch distillation column 7 is monitored. When the tower top temperature starts to rise from the boiling point region of the third component, the destination of the distillate (the tower top liquid of the batch distillation tower 7) is switched from the recovery tank 14 to the extraction tank 12, and carbon tetrachloride is removed. It is extracted as a waste liquid. The distillate that distills when the top temperature starts to rise from the boiling point region of the third component is the distillate with the highest carbon tetrachloride concentration. By selectively leading to the outlet tank, carbon tetrachloride can be efficiently removed out of the system while preventing excessive extraction of the poor solvent as the main component.

The poor solvent which is the bottoms (column bottom liquid) of the batch distillation column 7 from which carbon tetrachloride has been removed is sent to the aftercooler 11 by the batch distillation tower bottom pump 9 and is cooled to the poor solvent tank 13 after cooling. Collected. The poor solvent recovered in the poor solvent tank 13 is returned to the solidification step and recycled again as a solidification solvent. The carbon tetrachloride concentration in the poor solvent recovered in the poor solvent tank 13 is 0 to 5000 ppm, preferably 0 to 100 ppm. The poor solvent recovered in the recovery tank 14 is lower in purity than the poor solvent recovered in the poor solvent tank 13, but can be recycled and reused as a solidification solvent after being purified by distillation in a separate step.
When the general solvent continuous distillation purification equipment shown in FIG. 2 is used, the poor solvent mixed liquid containing carbon tetrachloride concentrated in the continuous distillation tower 1 is extracted from the reflux tank 5 to the extraction tank 12. Or it is directly supplied to the continuous distillation column 1 again and recycled.

(5) Drying process The polycarbonate resin granular material obtained by the above method normally performs hot-air drying. The drying temperature is usually 100 to 170 ° C., preferably 120 to 150 ° C., and the time is usually 3 to 7 hours. By passing through this drying step, the polycarbonate resin powder is commercialized.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. In addition, the test method of the polycarbonate manufactured by the Example, the comparative example, etc. was based on the following method.
(1) Concentration of chlorine compound in heptane solution:
It measured by sampling 3 microliters from the obtained heptane solution, and inject | pouring into the gas chromatograph apparatus with a thermal conductivity detector (GC-14A by Shimadzu Corporation).
(2) YI value:
Using a polycarbonate resin powder granule, a test piece of a 3 mm thick press sheet was obtained using an extruder (Tanabe Plastics Co., Ltd .; V-40-NSIII) and a molding machine (Nihon Steel Works Co., Ltd .; J50E-D). It created and measured with the color difference meter (Nippon Denshoku Industries Co., Ltd. SE2000).
(3) Concentration of chlorine compound in the polycarbonate resin granular material:
After the polycarbonate resin granular material obtained through the drying step is dissolved in 1,4-dioxane, 1 μl of the solution is sampled, and a gas chromatograph device with an electrocapture (ECD) detector (GC-17A, manufactured by Shimadzu Corporation) Was measured by injection.

<Example 1>
The distillation purification equipment shown in FIG. 1 was used for distillation purification for the purpose of removing carbon tetrachloride contained when heptane was used as a poor solvent in the production of polycarbonate resin powder granules.
The purified polycarbonate resin solution used in this example was collected from the existing plant purification process before the addition of the poor solvent (bisphenol A type polycarbonate resin having a viscosity average molecular weight of 27,400, resin liquid concentration = 10. weight%).

To 20 liters of the purified polycarbonate resin solution, 5 liters of heptane as a poor solvent was added and mixed at room temperature to obtain a mixed solution.
Next, the organic solvent (methylene chloride) was distilled off while adding the mixed solution into warm water at 48 ° C. with heating and stirring, and then the poor solvent (heptane) was distilled off and recovered. This operation was repeated.

  When heptane (raw heptane solution = poor solvent solution) recovered from the polycarbonate solidification step was analyzed by a gas chromatograph, carbon tetrachloride was 210 ppm, methylene chloride was 510 ppm, and chloroform was 0.46 wt%.

  This raw heptane solution was continuously fed to the continuous distillation column 1 at a rate of 5.2 kg / H for 72 hours. The mixture was concentrated at a reflux ratio of 100, and the bottom of the column was 102 ° C. A heptane solution in which carbon tetrachloride was reduced to about 78 ppm was extracted from the bottom of the continuous distillation column 1 to the poor solvent tank 13.

  72 hours later, the distillate withdrawn from the reflux tank 5 to the buffer tank 6 (concentrated poor solvent mixture containing carbon tetrachloride; carbon tetrachloride concentration = 0.8 wt%, chloroform = 22 wt%) 3.0 kg was dropped into the batch distillation tower 7 and distilled and purified by the batch distillation tower reboiler 8.

  While measuring the composition of the distillate containing concentrated carbon tetrachloride distilled from the top of the batch distillation column 7, the top temperature of the batch distillation column 7 was continuously observed. As a result, it was stable at about 64 ° C., which was close to the boiling point of chloroform (62 ° C.) for a while, but after about 40 hours from the start of observation, the tower top temperature began to rise above this temperature. At that time, the destination of the distillate was switched from the recovery tank 14 to the extraction tank 12 and extracted until the tower top temperature rose to around the boiling point (98.4 ° C.) of heptane, which is the main component. The composition of the chlorine compound in the heptane solution in the extraction tank 12 was 10.21% by weight of carbon tetrachloride and 13.4% by weight of chloroform, and the amount extracted was 533g.

  The solvent remaining in the batch distillation column 7 was sent to the poor solvent tank 13, and the carbon tetrachloride concentration in the final recovered heptane solution in the poor solvent tank 13 was 83 ppm.

Of this recovered heptane solution, 5 L was added to 20 L of a polycarbonate resin methylene chloride solution having a viscosity average molecular weight of 27,400 (concentration: 10.0 wt%) collected from the solidification step with stirring at room temperature. . Next, while adding this mixed solution to 48 ° C. warm water with heating and stirring, the methylene chloride as an organic solvent and heptane for solidification were distilled off, and this liquid was added to a wet pulverizer in an amount of 6 m ³ / H. And then wet pulverized to obtain an aqueous slurry of beaded polycarbonate resin solids. The solidification time was about 1 hour. The solid content was separated from this water slurry and dried at 120 ° C. for 5 hours with a dryer in which hot air was circulated. The solid had a YI value of 1.8, a carbon tetrachloride concentration of less than 1 ppm, and a chloroform concentration of less than 1 ppm. The results are shown in Table 1.

<Example 2>
In the initial stage of operation, in order to reduce the heat load on the batch distillation column condenser 10 due to evaporation of a large amount of low-boiling components, in the batch distillation column 7, the reflux ratio is up to 10 to 20 hours from the start of operation to 10 hours. Except that the operation conditions are changed stepwise so that the reflux ratio becomes 20 after 20 hours and the reflux ratio becomes 80, and the heat load by the batch distillation reboiler 8 is increased stepwise according to the change of the reflux ratio. Same as Example 1. The results are shown in Table 1.

  In addition, a graph showing the relationship between the composition of the distillate containing concentrated carbon tetrachloride distilled from the top of the batch distillation column 7 and the top temperature of the batch distillation column 7 and the elapsed time. As shown in FIG. In FIG. 3, the graph curve a is the tower top temperature (° C.), b is the carbon tetrachloride concentration (wt%) in the distillate, c is the methylene chloride concentration (wt%), d is the chloroform concentration (wt%), e represents the heptane concentration (% by weight).

<Example 3>
A raw heptane solution of carbon tetrachloride 0.15% by weight, methylene chloride 510ppm, chloroform 0.46% by weight is distilled in the continuous distillation column 1 in the same manner as in Example 2 and then batch-distilled in the batch distillation column 7. And purified by distillation. The results are shown in Table 1.

<Example 4>
A heptane solution of 1.2% by weight of carbon tetrachloride, 510 ppm of methylene chloride and 0.46% by weight of chloroform was distilled in the continuous distillation column 1 in the same manner as in Example 2 and then in the batch distillation column 7 for distillation. Purified. The results are shown in Table 1.

<Example 5>
A raw heptane solution containing 0.46% by weight of 1,1-dichloroethane (boiling point 57 ° C.) instead of chloroform as a third component was purified by distillation in the same manner as in Example 5. The results are shown in Table 1.

<Comparative Example 1>
A raw heptane solution of carbon tetrachloride 2.0% by weight, methylene chloride 510ppm, chloroform 0.46% by weight was directly sent to the extraction tank 12 without being purified by distillation, and the heptane solution stored in the extraction tank ( The poor solvent) was recycled for solidification in the same manner as in Example 1. The polycarbonate resin obtained had a YI value of 2.9, a carbon tetrachloride concentration of 40 ppm, and a chloroform concentration of less than 1 ppm. The results are shown in Table 1.

<Comparative example 2>
The raw heptane solution of Comparative Example 1 was distilled in the continuous distillation column 1 in the same manner as in Example 2 and then purified by distillation in the batch distillation column 7. The results are shown in Table 1.

<Comparative Example 3>
Distillation purification of the same heptane solution as Example 1 was performed using the distillation purification equipment shown in FIG.
The heptane solution was continuously supplied to the continuous distillation column 1 and purified by distillation at a reflux ratio of 100. The carbon tetrachloride in the heptane solution in the poor solvent tank 13 was 78 ppm. The polycarbonate resin obtained by solidification with this heptane solution had a YI value of 1.8, a carbon tetrachloride concentration of less than 1 ppm, and a chloroform concentration of less than 1 ppm. However, the amount of the heptane solution extracted from the reflux tank 5 to the extraction tank 12 is 6.633 kg, and the composition of the chlorine compound in the heptane solution is 0.83% by weight of carbon tetrachloride, 22% by weight of chloroform, The methylene chloride was 2.5% by weight. Each impurity could not be concentrated any more, and the extraction amount (6633 g) was larger than in each Example, and carbon tetrachloride could not be selectively and efficiently removed by this apparatus. The results are shown in Table 1.

<Comparative Example 4>
The distillation purification equipment shown in FIG. 1 was used, and the purification of the heptane solution of carbon tetrachloride 210 ppm and methylene chloride 510 ppm was performed in the same manner as in Example 2 without adding the third component chloroform. The heptane solution was distilled by the batch distillation column reboiler 8 until the top temperature of the batch distillation column 7 rose to the boiling point of heptane (98.4 ° C.), but it did not contain the third component chloroform. Therefore, the tower top temperature was not stabilized before the distillation of carbon tetrachloride as in Examples 1-5. After the column top temperature exceeded the boiling point of carbon tetrachloride (76.8 ° C.), the extraction destination of the distillate from the column top was switched to the extraction tank 12. However, the solution in the extraction tank 12 has a high residual heptane concentration of 80.87% by weight as compared with Examples 1 to 4, and the extraction amount is 1227 g, and the loss of heptane accompanying extraction is large. It was. The results are shown in Table 1.

<Comparative Example 5>
A raw heptane solution containing 1.3% by weight of carbon tetrachloride, 510 ppm of methylene chloride and 0.46% by weight of chloroform was purified by distillation in the same manner as in Example 2. The carbon tetrachloride in the heptane solution in the poor solvent tank 13 was 5232 ppm. The YI value of the polycarbonate resin obtained by solidification with this heptane solution was 1.9, which was larger than any of the YI values of Examples 1 to 5. The carbon tetrachloride concentration was 11 ppm and the chloroform concentration was less than 1 ppm. The results are shown in Table 1.

<Comparative Example 6>
A heptane solution containing 0.46% by weight of benzene (boiling point: 80.1 ° C.) instead of chloroform as a third component was purified by distillation in the same manner as in Example 2. The top temperature of the batch distillation column 7 was stable at around 81 ° C., which is close to the boiling point of benzene, but from the beginning of the operation until the temperature at the top of the column rises to around the boiling point of heptane (98.4 ° C.), which is the main component, The distillate from the top of the column contained 3 to 5% by weight of carbon tetrachloride, and carbon tetrachloride could not be selectively removed efficiently. Along with this, the extraction amount to the extraction tank 12 was 1576 g, which was larger than any extraction amount in each example. The results are shown in Table 1.

<Comparative Example 7>
A raw heptane solution of carbon tetrachloride 1.2% by weight, methylene chloride 510ppm, chloroform 0.46% by weight was directly sent to the extraction tank 12 without being purified by distillation, and the heptane solution ( The poor solvent) was recycled for solidification in the same manner as in Example 1. The polycarbonate resin obtained had a YI value of 2.4, a carbon tetrachloride concentration of 24 ppm, and a chloroform concentration of less than 1 ppm. The results are shown in Table 1.

  According to the production method of the present invention, since carbon tetrachloride in the recovered poor solvent is removed and recycled to the solidification step, the content of carbon tetrachloride in the entire reaction system of polycarbonate resin production is reduced. It is possible to obtain a high-quality polycarbonate resin granular material that is less corrosive, excellent in hygiene, hue, and the like. In addition, by distilling and purifying the poor solvent together with the third component having a boiling point lower than that of carbon tetrachloride, carbon tetrachloride in the poor solvent is selectively distilled off. It is possible to remove efficiently while preventing excessive extraction, which is excellent in terms of economy.

Claims (6)

  A polycarbonate resin granule comprising a solidification step of adding a poor solvent to a purified polycarbonate resin solution to solidify, and a recovery step of collecting and recycling the poor solvent used in the solidification step by distillation purification operation In the production method, the recovering step comprises subjecting the carbon tetrachloride contained in the poor solvent to a third component by batch distillation in the presence of a third component having a boiling point of 1 to 20 ° C. lower than the boiling point of carbon tetrachloride. And a carbon tetrachloride removal step of distilling together and reducing the carbon tetrachloride concentration in the poor solvent to 0 to 5000 ppm by weight.   In the solidification step, a poor solvent is added to and mixed with the purified polycarbonate resin solution, and the mixture is continuously added to warm water under heating and suspended in warm water, while the organic solvent for the purified polycarbonate resin solution and The method for producing a polycarbonate resin granular material according to claim 1, comprising a step of distilling off the poor solvent.   The production method according to claim 1 or 2, wherein the poor solvent is heptane.   The batch distillation step is a step of extracting a distillate containing carbon tetrachloride and the third component based on the distillation timing of the third component specified by observing the top temperature of the batch distillation column. The manufacturing method in any one of Claims 1-3 characterized by the above-mentioned.   The method according to claim 1, wherein the third component is chloroform.   In the said collection | recovery process, the carbon tetrachloride density | concentration in the poor solvent before distillation refinement | purification operation is 1.2 weight% or less, The manufacturing method in any one of Claims 1-5 characterized by the above-mentioned.

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