JP2010144079A - Method for producing acrylonitrile copolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for allowing the viscosity of a polymerization suspension to be kept at a low level while coagulating polymer fine particles in a polymerization system, in aqueous suspension polymerization of an acrylonitrile copolymer. <P>SOLUTION: In the method for producing the acrylonitrile copolymer, a monomer composition containing acrylonitrile, a sulfite as a reducing agent, a persulfate as an oxidizing agent, and ammonium sulfate are continuously supplied into the system and subjected to aqueous suspension polymerization, and the acrylonitrile copolymer is continuously discharged to the outside of the system, wherein formula (1) and (2) are satisfied, wherein formula (1) is 5.7≤Y/X≤9.2 and formula (2) is 0.7≤Y/(X+Z)≤3.7, and X, Y, and Z are respectively molarity of the persulfate ion originating from the oxidizing agent, molarity of the sulfite ion originating from the reducing agent, and molarity of the sulfate ion originating from ammonium sulfate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an acrylonitrile-based copolymer.

  The acrylonitrile copolymer used as the carbon fiber precursor is produced by aqueous suspension polymerization of a monomer composition containing acrylonitrile. In the aqueous suspension polymerization, it is important to uniformly disperse the monomer, the polymerization initiator, the auxiliary agent and the polymer by keeping the viscosity of the polymerization suspension in the polymerization system low. However, it is generally known that when a large amount of polymer fine particles are present in the polymerization system, the viscosity of the polymerization suspension in the polymerization system increases.

In Patent Document 1, aluminum sulfate and ethylenediaminetetraacetic acid are added after aqueous suspension polymerization to aggregate and associate polymer fine particles in the polymerization suspension, thereby forming polymer particles suitable for filtration and washing.
JP-A 63-43907

  However, in order to filter and wash this polymerization suspension, it is necessary to keep the pH at 3.7 or lower. Moreover, when manufacturing carbon fiber from the obtained acrylonitrile-type copolymer, the aluminum hydroxide which remained in the polymer particle after washing | cleaning becomes a cause of various trouble after a spinning process. In addition, since further operation must be added to the polymerization suspension after polymerization, there is a problem that the operation tends to be complicated.

  An object of the present invention is to provide a method capable of agglomerating polymer fine particles in a polymerization system and maintaining the viscosity of the polymerization suspension in an aqueous suspension polymerization of an acrylonitrile copolymer.

  In the present invention, a monomer composition containing acrylonitrile, a sulfite as a reducing agent, a persulfate as an oxidizing agent, and ammonium sulfate are continuously supplied into the system to carry out aqueous suspension polymerization, A method for producing an acrylonitrile-based copolymer that discharges acrylonitrile-based copolymer to the outside, wherein the following formulas (1) and (2) are satisfied.

5.7 ≦ Y / X ≦ 9.2 (1)
0.7 ≦ Y / (X + Z) ≦ 3.7 (2)
However, X, Y and Z are respectively the molar concentration of persulfate ions derived from the oxidizing agent, the molar concentration of sulfite ions derived from the reducing agent, and the molar concentration of sulfate ions derived from ammonium sulfate, which are supplied into the polymerization system. is there.

  According to the present invention, in the aqueous suspension polymerization of an acrylonitrile copolymer, polymer fine particles can be aggregated, and the viscosity of the polymerization suspension can be kept low.

(About monomer composition)
The monomer used in the present invention is acrylonitrile and a vinyl monomer copolymerizable with acrylonitrile. Examples of the copolymerizable vinyl monomer include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. Vinyl halides such as vinyl chloride, vinyl bromide and vinylidene chloride; acids such as (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid and crotonic acid and salts thereof; maleic acid imide, phenylmaleimide, (Meth) acrylamide, styrene, α-methylstyrene, vinyl acetate and the like can be mentioned. These can be used alone or in combination of two or more.

  For example, in order to produce an acrylonitrile copolymer having a carboxylic acid group, as a copolymerizable vinyl monomer, carboxyl such as (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, etc. A vinyl monomer having a group may be used. Of these, (meth) acrylic acid and itaconic acid are preferred. In order to produce an acrylonitrile copolymer having an acrylamide unit, acrylamide may be used as a copolymerizable vinyl monomer.

  The composition ratio of the monomer composition can be appropriately set according to the composition of the target acrylonitrile-based copolymer.

(Acrylonitrile copolymer)
The acrylonitrile-based copolymer produced in the present invention contains 90% by mass or more of acrylonitrile units for the purpose of reducing defects caused by copolymerization components when converted into carbon fibers and improving the quality and performance of carbon fibers. The content is preferably 96% by mass or more, more preferably 98.5% by mass or more.

  The acrylonitrile-based copolymer preferably has a carboxylic acid group from the viewpoint of enhancing the flame resistance reactivity in the firing step.

While the carboxylic acid group contained in the acrylonitrile-based copolymer serves to improve the flame resistance reactivity in the firing step, it becomes a defect point of the carbon fiber, so it is necessary to adjust the content of the carboxylic acid group. is there. The content of the carboxylic acid group in the acrylonitrile-based copolymer is preferably 5.0 × 10 ⁻⁵ equivalent / g or more and 2.0 × 10 ⁻⁴ equivalent / g or less, and 6.0 × 10 ⁻⁵ equivalent / g. More preferably, it is 1.5 × 10 ⁻⁴ equivalent / g or less. When the content of the carboxylic acid group is 5.0 × 10 ⁻⁵ equivalent / g or more, the flameproofing reactivity in the firing step is not lowered, and further, the treatment at a high temperature is not required. When the treatment is performed at a high temperature, a runaway reaction is likely to occur, and it is difficult to obtain a stable firing process passability. On the other hand, firing at a low speed in order to suppress the runaway reaction is not economical. If the content of the carboxylic acid group is 2.0 × 10 ⁻⁴ equivalent / g or less, the cyclization reaction of the nitrile group in the polymer does not become rapid, so that the oxidation reaction proceeds to the inside of the fiber. If the flame-resistant structure advances only in the vicinity of the fiber surface layer, since the decomposition of the undeveloped portion of the fiber core at the next higher temperature carbonization process cannot be suppressed, the performance of the carbon fiber, particularly the tensile modulus, It may be significantly reduced.

  The acrylonitrile copolymer preferably has an acrylamide unit. The flameproofing reactivity and thermal cyclization reaction rate in the firing step are dominated by the content of carboxylic acid groups, but increase rapidly due to the coexistence of a small amount of acrylamide units. Further, by including an acrylamide unit, the solubility in a solvent is improved, and the denseness of a coagulated yarn obtained by wet spinning or dry-wet spinning is improved. The content of acrylamide units in the acrylonitrile copolymer is preferably 0.5% by mass or more and 5% by mass or less, and more preferably 1% by mass or more and 4% by mass or less.

  The average particle diameter of the polymer particles is preferably 7 μm or more and 9 or less, and more preferably 7.5 μm or more and 8.5 or less. If the average particle diameter of the polymer particles is 7 μm or more, the polymer particles are moderately aggregated, the viscosity in the kettle during polymerization is kept low, and the monomer, polymerization initiator, auxiliary agent and polymer are uniformly distributed. Can be dispersed. If the average particle diameter of the polymer particles is 9 μm or less, the solvent can quickly permeate and dissolve uniformly when dissolved in the solvent.

(Reducing agent)
In the present invention, sulfite is used as a reducing agent constituting the redox polymerization initiator. As the sulfite, ammonium bisulfite, sodium bisulfite, sodium sulfite and the like can be used.

(Oxidant)
In the present invention, persulfate is used as a reducing agent constituting the redox polymerization initiator. As the persulfate, ammonium persulfate, sodium persulfate, potassium persulfate and the like can be used.

(About the ratio of reducing agent to oxidizing agent)
When the molar concentration of the persulfate ions derived from the oxidizing agent supplied into the polymerization system is X and the molar concentration of the sulfite ions derived from the reducing agent is Y, the following formula (1) is satisfied.

5.7 ≦ Y / X ≦ 9.2 (1)
If the molar concentration ratio (Y / X) is 5.7 or more, radical generation by the oxidation-reduction reaction of the catalyst occurs efficiently and the polymerization reaction efficiency increases, which is industrially very advantageous. Moreover, if the molar concentration ratio (Y / X) is 9.2 or less, the increase in the concentration of hydrogen sulfite radicals generated by the oxidation-reduction reaction is suppressed, and conversely, the polymerization rate of the radicals reacts and deactivates The decrease can be suppressed. The molar concentration ratio (Y / X) is more preferably 6.5 or more and 8.3 or less.

(Ammonium sulfate)
In the present invention, ammonium sulfate is further used as an auxiliary agent. The amount of ammonium sulfate used satisfies the following formula (2), where Z is the molar concentration of ammonium sulfate-derived sulfate ions supplied into the polymerization system.

0.7 ≦ Y / (X + Z) ≦ 3.7 (2)
If the molar concentration ratio (Y / (X + Z)) is 0.7 or more, the molar concentration of sulfate ions in the polymerization system is maintained appropriately, the aggregation of the polymer particles is gradually promoted, and the viscosity in the polymerization system is increased. Can be kept low. Furthermore, it is easy to wash off ammonium sulfate in filtration and washing after polymerization. Further, if the molar concentration ratio (Y / (X + Z)) is 3.7 or less, since sulfate ions necessary to agglomerate the polymer particles existing in the polymerization system are present, the viscosity in the polymerization system is reduced. Can be kept low. Further, when the molar concentration ratio (Y / (X + Z)) exceeds 3.7, the polymer particles are remarkably aggregated at the initial stage of polymerization, and the viscosity within the polymerization system is increased despite the increase in the average particle diameter of the polymer. Becomes higher. The molar concentration ratio (Y / (X + Z)) is more preferably 1.2 or more and 3.2 or less.

(Aqueous suspension polymerization)
In the present invention, a monomer composition containing acrylonitrile, a sulfite as a reducing agent, a persulfate as an oxidizing agent, and ammonium sulfate are continuously supplied into the system to carry out aqueous suspension polymerization.

  It is preferable to use ion-exchanged water as the polymerization medium. The ratio of water to the monomer composition (hereinafter referred to as water / monomer composition mass ratio) may be any ratio, but is preferably in the range of 1.0 to 5.0. The hydrogen ion concentration in the polymerization reaction vessel may be within a range in which the catalyst used promptly undergoes an oxidation / reduction reaction, and an acidic region having a pH of 2.0 to 3.5 is preferable. The average residence time of the monomer composition in the polymerization reaction vessel may be a normal time employed when an acrylonitrile polymer is produced by an aqueous suspension polymerization method. The reaction temperature of the aqueous suspension polymerization is preferably 30 to 80 ° C. By setting the reaction temperature to 80 ° C. or less, the polymerization conversion rate is improved without the acrylonitrile evaporating and being dispersed outside the reaction system. Further, by setting the reaction temperature to 30 ° C. or higher, not only the polymerization rate is increased and the productivity is improved, but also the polymerization stability is increased.

  Then, the acrylonitrile copolymer is continuously discharged out of the system. At this time, removal of unreacted monomer, polymerization catalyst residue, and other impurities as much as possible from the acrylonitrile copolymer obtained by aqueous suspension polymerization inhibits hydrolysis of sulfate groups at the polymer terminals. Therefore, it is preferable.

  Specifically, first, a polymerization terminator is added to the polymer aqueous solution taken out from the polymerization reaction kettle to stop the reaction. The polymerization terminator is not a problem as long as it is usually used when an acrylonitrile-based polymer is produced by aqueous suspension polymerization. After adding the polymerization terminator, the unreacted monomer is recovered from the polymer aqueous solution. There are two methods for recovering the unreacted monomer: a method in which the aqueous polymer solution is directly distilled, and a method in which the unreacted monomer is once dehydrated and separated from the polymer, followed by distillation. is there. As the dehydrating and washing machine in the latter, a rotary vacuum filter, a centrifugal dehydrator or the like that is a generally known filter dehydrator is used. Water remaining in the polymer is removed by a normal drying method.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following, “%” represents mass%.

(Composition ratio of acrylonitrile copolymer)
The composition ratio of acrylonitrile-based copolymer (ratio of each monomer unit (mass ratio)) was determined by ¹ H-NMR method (manufactured by JEOL Ltd., product name: GSZ-400 type superconducting FT-NMR). Dimethyl sulfoxide-d ₆ solvent was used, and the number of times of integration was 40, and the measurement temperature was 120 ° C.

(Viscosity of polymerization suspension)
The viscosity of an aqueous dispersion obtained by adding 400 ml of a polymerization suspension to 100 ml of a 0.1% polymerization stopper aqueous solution was measured at 43 ° C. using a B-type viscometer.

(Average particle diameter of polymer particles)
The particle size distribution of the polymer particles is adjusted to a refractive index of 1.330-0.01i and a shape factor of 1.000 using an SK laser micronizer system (product name: LMS-350, manufactured by Seishin Enterprise) based on the laser diffraction scattering method. The value of 50% normal distribution calculated from the volume average was taken as the average particle size.

Example 1
First, put 76.5 liters of deionized water in a polymerization vessel with a turbine stirring blade of 240φ, 55mm x 57mm, 2 stages and 4 blades, made of stainless steel with a capacity of 80 liters, so that the deionized water reaches the overflow port of the polymerization vessel. Add 0.01 g of ferrous sulfate (Fe ₂ SO ₄ · 7H ₂ O) and adjust with sulfuric acid so that the pH of the reaction solution becomes 3.0, and keep the temperature in the polymerization vessel at 57 ° C. did. Next, from 30 minutes before the start of the polymerization, 0.39% of ammonium persulfate as the oxidizing agent constituting the redox polymerization initiator and 1% of ammonium bisulfite as the reducing agent are used for the monomer composition used for the polymerization. .18%, deionized water with 0.59% ammonium sulfate as auxiliary, 0.3 ppm ferrous sulfate (Fe ₂ SO ₄ .7H ₂ O), and 0.1% sulfuric acid, respectively. The mixture was continuously dissolved and supplied, and stirred at a stirring speed of 200 rpm and a stirring power of 2.4 KW / m ^{3 so} that the average residence time of the monomer composition in the polymerization kettle was 70 minutes. . Further, at the start of polymerization, in addition to these, a monomer composition having a composition ratio shown in Table 1 was continuously supplied so that water / monomer composition = 4 (w / w). Thereafter, 1 hour after the start of the polymerization, the polymerization reaction temperature was lowered to 50 ° C., and the polymerization suspension was continuously taken out from the polymerization kettle overflow port.

  With respect to this polymerization suspension, the viscosity at 7 hours after the start of polymerization was measured using a B-type viscometer, and it was 300 cp (0.3 Pa · s) at 43 ° C.

  In the polymerization suspension, an aqueous solution of a polymerization stopper prepared by dissolving 0.5% sodium oxalate and 1.5% sodium bicarbonate in deionized water, the pH of the polymerization suspension is 5.5 to 6.0. It was added to become. The polymer suspension was dehydrated by an Oliver type continuous filter, and then 10 times the amount of 70 liters of deionized water was added to the polymer and dispersed again. The polymer suspension after re-dispersion was again dehydrated with an Oliver type continuous filter, formed into pellets, dried in a hot air circulation type dryer at 80 ° C. for 8 hours, and then pulverized with a hammer mill. The average particle diameter of the obtained polymer particles was 7.90 μm.

(Example 2)
Polymerization was carried out in the same manner as in Example 1 except that the polymerization conditions were changed as shown in Table 1. The results are shown in Table 2.

(Comparative Example 1)
Polymerization was carried out in the same manner as in Example 1 except that the polymerization conditions were changed as shown in Table 1. The results are shown in Table 2.

(Comparative Example 2)
Polymerization was carried out in the same manner as in Example 1 except that the polymerization conditions were changed as shown in Table 1. The results are shown in Table 2.

  In Examples 1 and 2, compared to Comparative Examples 1 and 2, by adding ammonium sulfate appropriately, the viscosity in the polymerization system is kept low, and the polymer has an average particle size suitable for dissolution in a solvent. Particles could be obtained.

Claims (1)

A monomer composition containing acrylonitrile, a sulfite as a reducing agent, a persulfate as an oxidizing agent, and ammonium sulfate are continuously supplied into the system for aqueous suspension polymerization. A method for producing an acrylonitrile copolymer, which discharges the copolymer, and satisfies the following formulas (1) and (2).
5.7 ≦ Y / X ≦ 9.2 (1)
0.7 ≦ Y / (X + Z) ≦ 3.7 (2)
However, X, Y and Z are respectively the molar concentration of persulfate ions derived from the oxidizing agent, the molar concentration of sulfite ions derived from the reducing agent, and the molar concentration of sulfate ions derived from ammonium sulfate, which are supplied into the polymerization system. is there.