RU2193571C2 - Butadiene-nitrile rubbers production process - Google Patents

Abstract

FIELD: rubber industry. SUBSTANCE: in a process of production of butadiene-nitrile rubbers via wateremulsion copolymerization of butadiene with acrylonitrile in presence of initiator system and molecular weight regulator and using, as emulsifying agent, carboxylic acid soaps followed by coagulation of latex with calcium chloride, sodium C12-C14-alkylsulfoethoxylate with degree of ethoxylation 1-5 is used as additional emulsifier in amounts 0.05 to 0.50 wt parts per 100 wt parts of monomers, summary amount of emulsifier being 0.55 to 2.50 wt parts. Invention allows achieving high steadiness of polymerization system at low amounts of emulsifier and preserving a good ability of resulting latex to coagulate, and also allows production of "pure" butadiene-nitrile rubbers with reduced content of residual emulsifier therein. EFFECT: improved physicochemical characteristics of vulcanizates and increased frost resistance. 6 tbl

Description

 The invention relates to the field of synthetic rubbers, namely nitrile butadiene rubbers (BNC) emulsion polymerization, and can be used in the petrochemical industry.

A known method of producing butadiene nitrile rubbers, characterized by storage stability, Mooney viscosity, water-emulsion radical copolymerization at a temperature of 35-55 ^o With 65-85 parts of butadiene with 15-35 parts of acrylic acid nitrile in 200 parts of water in the presence of 0.5-5 , 0% anionic surfactants - alkylarylsulfonates, 0.05-0.40% initiators - persulfates, 0.2-0.8% molecular weight regulators, 0.4-1.0% buffers - monobasic alkali metal phosphates MN ₂ PO ₄ , where M = Li, K, Na (USA, patent 4435555, IPC C 08 F 236/12, 4/08, publ. 6.04.84).

 The disadvantage of this method is the discharge of the emulsifier into wastewater during the isolation of rubber from latex.

A known method for producing butadiene nitrile rubbers containing ≥10% nitrile of acrylic acid, using as an emulsifier and dispersing agent 0.1-10.0 wt. hours per 100 wt. including monomers of Na-, K- or NH ₄ -salts of sulfuric acid esters and adduct 0.1-5.0 mol of ethylene oxide with 1 mol of primary alcohols С ₇ -С ₁₁ - alkyl sulfoethoxylate (ASET) followed by rubber isolation with calcium chloride (Japan , application 56-10510, IPC C 08 F 236/12, 2/30, publ. 3.02.81).

The disadvantage of this method is the use of sodium alkyl sulfoethoxylate based on alcohols of the C ₇ -C ₁₁ fraction, which, due to the presence of residual primary C ₇ -C ₁₁ alcohols in the emulsifier, especially octyl, has an unpleasant odor, as well as the insufficiently high efficiency of C ₇ -C ₁₁ sodium alkyl sulfoethoxylate , not allowing to maintain the stability of the polymerization system when using low dosages of the specified emulsifier.

A known method of producing butadiene nitrile rubbers by water-emulsion copolymerization at a temperature of 28-30 ^o Butadiene with nitrile of acrylic acid using 4 parts by weight of emulsifier per 100 parts by weight monomers of potassium soaps of synthetic fatty acids of fraction C ₁₀ -C ₁₆ with subsequent isolation of rubber from latex by the action of a saturated solution of sodium chloride and a weak solution of sulfuric, hydrochloric or acetic acid at a pH of 5-7 flocculate and washing coagulated rubber from fatty acids and their salts, first alkaline water at pH = 11-12, and then water to a content of free and bound fatty acids in rubber of not more than 0.7% (V.S. Chunin, Yu.N. Zafransky et al. Copolymerization of butadiene with acrylic acid nitrile in an emulsion at 28-30 ^o With the use of in as an emulsifier of potassium soaps of synthetic fatty acids. M: TSNIITneftekhim, Synthetic rubber industry, 1971, 10, p. 4-9).

 The disadvantage of this method is the use of a significant amount of emulsifier in the polymerization recipe (4 parts by weight per 100 parts by weight of monomers), which results in the loss of valuable surfactants with wastewater during the isolation of rubber from latex, which significantly worsens economic and environmental characteristics of the process for producing nitrile butadiene rubbers.

 When 1 ton of rubber is isolated, the amount of emulsifier to be washed out is directly dependent on its amount in the polymerization recipe (Table 1).

 Thus, reducing the dosage of the emulsifier by 1 mAh calculated on the monomers will lead to savings of 15 kg of emulsifier per ton of polymer.

The solution to such a problem is to increase the manufacturability of the process for producing nitrile butadiene rubbers by reducing the amount of emulsifier is devoted to the method by which butadiene nitrile rubbers are obtained using 0.3-1.5 wt.c. as an emulsifier. at 100 max. sodium alkyl sulfoethoxylate monomers (C ₁₂ -C ₁₄ ) or 0.55-2.3 wt. at 100 max. monomers of the mixture of the latter with additional emulsifiers — sodium alkyl sulfate, sodium alkyl sulfonate, sodium dodecylbenzenesulfonate, sodium olefin sulfonate, nonionic emulsifier [polyethylene glycol PEG-9, ethoxylated alcohols of the formula RO (CH ₂ CH ₂ O) _n OH with a chain length of C ₁₂ -C ₁₄ , where C ₁₂ -C ₁₄ , n = 6, (neonol AP C ₁₂ -C ₁₄ ), ethoxylated alkyl phenols with a degree of hydroxyethylation 9-10 (neonol AF 9-10)] at a mass ratio of C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate: additional emulsifier 1: 1-40 followed by the release of rubber from latex x calcium Oridi washing with water and rubber crumb (USSR auth. svid. 1685951, IPC C 08 F 236/12, priority 07/05/89, publ. 23.10.91, BI 39).

 The disadvantage of this method is the discharge of the emulsifier into wastewater, because all emulsifiers used, when isolating rubber from latex, calcium chloride form water-soluble salts.

The closest in technical essence and the achieved result to the proposed is a method for producing butadiene nitrile rubbers by water-emulsion copolymerization of 50-90% butadiene and 10-50% acrylic acid nitrile in the presence of 0.5-3.0 wt. % to the sum of monomers of C ₁₂ -C ₂₀ fatty acid soaps as emulsifier, followed by rubber isolation from latex with metal salts of group II-III - halides or sulfates of Ca, Mg, Al, in particular calcium chloride. (Japan, Application 47-30300, CL 26 (3) C 112, publ. 7.08.72).

 The method has environmental advantages, since due to the insolubility of the calcium salts of carboxylic acids formed during the coagulation process, the emulsifier remains in the rubber and is not discharged into wastewater.

 The disadvantage of this method is the inability to achieve the necessary stability of the polymerization system at low dosages of the emulsifier, which complicates the process of polymerization and degassing of latex.

 The technical task of the invention is to achieve high stability of the polymerization system at low dosages of the emulsifier while maintaining good coagulation ability of the obtained latex.

The problem is solved in that in the method for producing butadiene nitrile rubbers by water-emulsion copolymerization of butadiene with acrylic acid nitrile in the presence of an initiating system, a molecular weight regulator using carboxylic acids as an emulsifier, followed by coagulation of latex with calcium chloride, an additional emulsifier - C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate with a degree of hydroxyethylation equal to 1-5, in an amount of 0.05-0.50 parts by weight per 100 parts by weight monomers at a total dosage of a mixture of emulsifiers of 0.55-2.50 wt.h. per 100 parts by weight monomers.

 The inventive method is of great practical importance, since the process of producing rubbers using carboxylic acid soaps as emulsifier with the release of rubber from latexes by calcium chloride was introduced at OJSC Krasnoyarsk Plant SK, and rubber is produced annually by tens of thousands of tons. Reducing the amount of emulsifier in the polymerization recipe compared with the existing one will reduce the mass fraction of residual emulsifier in rubber and, thus, solve the problem of obtaining pure rubber. The method for producing butadiene-nitrile rubbers used at Krasnoyarsk Zavod SK OJSC has environmental advantages, since, due to the insolubility of the calcium salts of carboxylic acids formed during coagulation, the emulsifier remains in the rubber and is not discharged into wastewater. However, a significant amount of emulsifier in the polymerization recipe (2.5-3.5 parts by weight per 100 parts by weight of monomers) and, accordingly, in rubber (up to 5% by weight per rubber) due to its non-washability, can lead to a decrease in frost resistance of rubber and rubbers based on it and changes in the amount of swelling of rubbers in oils and fuels during the operation of products.

 Thus, the tasks of saving material resources and obtaining clean rubbers by technology without emulsifier discharge into wastewater, used at JSC Krasnoyarsk Plant SK, urgently require the development of a method for producing rubber using a reduced amount of emulsifier, while maintaining high stability of the polymerization system and good ability the resulting latex to coagulation.

Thus, from the analysis of the current level of technology, we can conclude that the set of essential features of the claimed invention is the use of a mixture of emulsifiers - C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate with a degree of hydroxyethylation of 1-5 in the amount of 0.05-0.50 wt.h. and soaps of carboxylic acids with a total dosage of a mixture of emulsifiers of 0.55-2.50 wt.h. per 100 parts by weight monomers, followed by the isolation of rubber from latex with calcium chloride, makes it possible to solve a whole range of problems in the industrial production of nitrile butadiene rubbers: to reduce the amount of emulsifier in the polymerization recipe while maintaining high stability of the polymerization system and good coagulation ability, to obtain “pure” rubbers with a reduced emulsifier content, characterized by a high range of performance properties when using rubbers based on them.

 The proposed solution is applicable both to the production of nitrile butadiene rubbers and their modified analogues, for example carboxylate nitrile butadiene rubbers.

Butadiene rubber obtained aqueous emulsion copolymerization of butadiene and acrylonitrile in the presence of a radical initiator, a molecular weight regulator according to the recipes given in Table 2. As the emulsifier, use C ₁₂ -C ₁₄ sodium alkilsulfoetoksilat mixed with soaps of carboxylic acids. Soaps of acids with a number of carbon atoms of 6 or more are used: hexane-, octane-, decane-, dodecanecarboxylic acids, lauryl, stearic, palmitic, resin acids, abietic and other aliphatic and aromatic acids in the form of alkali metal salts and ammonium salts as in the individual composition, and in mixed compositions.

The polymerization of monomers is carried out at 2-15 ^o With, preferably at 5-6 ^o With up to the conversion of monomers 60-85%.

0.3 L of latex is selected to determine the thermal and mechanical stability of the latex. After degassing, the latex is coagulated with a solution of calcium chloride. The coagulation temperature is selected so that the time until the formation of transparent serum (coagulation τ) is no more than 7-10 s (the time spent by the crumbs in the coagulation zone of industrial production). The crumb of rubber is separated, washed with softened water with a temperature of 50-60 ^o C, dried. Rubber is analyzed for the content of emulsifier.

To obtain butadiene nitrile rubbers using an emulsifier of sodium alkyl sulfoethoxylate use:
- fraction of the emulsifier of sodium alkyl sulfoethoxylate R (OCH ₂ CH ₂ ) _n OSO ₃ Na, obtained on the basis of straight-chain olefins with a chain length of R = C ₁₂ -C ₁₄ , the degree of hydroxyethylation n = 1-5;
- fraction of potassium soap FFA with a chain length of C ₁₀ -C ₁₆ ;
- potassium soap disproportionate rosin.

The choice of an emulsifier of potassium soap of synthetic fatty acids with a chain length of C ₁₀ -C ₁₆ is due to the fact that this fraction is used in domestic factories - manufacturers of emulsion rubbers. Used in the prototype fraction of soaps of fatty acids C ₁₂ -C ₂₀ in the territory of the Russian Federation is not performed, and its purchase by import is difficult. The fraction of synthetic fatty acids C ₁₇ -C ₂₀ available on the territory of the Russian Federation cannot be used due to the high viscosity created by this emulsifier.

 The stability of the polymerization system is evaluated by the amount of coagulum formed in latex after thermal or mechanical action. The method of determining thermal stability is based on bubbling a portion of latex with hot steam for 30 minutes, drying and weighing the resulting coagulum. Resistance to mechanical stress is determined by the method of Maron-Ulevich Maron S.H. Ulevitch J. Determination of mechanical stability of latexes. Analit. Chem., 1953, v. 25, N7, p. 1037-1044).

 The emulsifier content in the rubber is determined based on calcium stearate according to TU 38.30313-94. The method consists in fusing the rubber ash with sodium carbonate and potassium carbonate, dissolving the obtained alloy in hydrochloric acid, separating calcium from other metals in excess of ammonia and determining calcium calcium in the filtrate calculated on the basis of calcium stearate titration with trilon B.

 The essence of the proposed method is confirmed by the following examples.

Example 1. Receive BNX-28AMN butadiene rubber by water-emulsion copolymerization of butadiene and acrylic acid nitrile using recipe 1 of table 2 and using emulsifier potassium soap of synthetic fatty acids (CMSJ) C ₁₀ -C ₁₆ in the amount of 1.5 wt.h . per 100 parts by weight monomers mixed with an additional emulsifier of C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate with a degree of hydroxyethylation equal to 5, in an amount of 0.5 wt.h. calculated on the monomers. The total dosage of the mixture of emulsifiers in this case is 2.0 wt.h. per 100 parts by weight monomers. The polymerization is carried out in an apparatus of 20 l. The sum of the monomers when loading is 6.12 liters. After the polymerization was terminated during the conversion of 67% monomers, 0.3 L of latex was taken to determine its stability during thermal and mechanical processing. The duration of the polymerization reaction is 12 hours. In the experiment according to the known method, rubber is obtained in a similar manner, but only potassium soap of synthetic fatty acids of the same fraction in an amount of 1.5 parts by weight is used as an emulsifier. calculated on the monomers. The duration of polymerization to monomer conversion of 67% is 12.5 hours. The latexes are discharged from the apparatus, distilled off with steam to remove unpolymerized monomers and coagulated with a 1% solution of calcium chloride. During coagulation, the time to the formation of a transparent serum is noted (τ coagulation, s)
The properties of the samples of latexes BNX-28AMN obtained by the known and proposed methods are shown in table 3.

 The results of the experiments show that the proposed method has achieved the necessary and higher stability of the polymerization system using a low dosage of emulsifier (1.5 parts by weight) while maintaining good latex coagulation ability.

Example 2. In a reactor with a volume of 60 l to obtain rubber BNKS-28AN load all the components in accordance with recipe 2 of table 2. As an emulsifier use potassium soap of synthetic fatty acids and potassium soap of rosin in an amount of 1 wt.h. in a mixture with an additional emulsifier C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate with a degree of hydroxyethylation equal to 3, in an amount of 0.05 wt.h. per 100 parts by weight monomers. The total dosage of the mixture of emulsifiers in this case is 2.05 parts by weight. calculated on the monomers. The copolymerization is carried out at a temperature of 5-6 ^o With stirring until the conversion of monomers 70%. Then 0.2 wt.h. sodium dimethyldithiocarbamate to terminate the polymerization and, after distillation of the residual monomers, the latex is coagulated with calcium chloride. The rubber is dried in an air dryer at a temperature of 70 ^o C. Similarly, rubber is obtained by a known method, but potassium soap FFA in the amount of 2.8 wt.h. is used as an emulsifier. The emulsifier content is determined in the rubber samples obtained. On the rollers, rubber mixtures of the composition are prepared: 100 parts by weight rubber, 3 parts by weight zinc oxide, 1.5 wt. parts of sulfur, 1 part by weight stearic acid, 40 parts by weight carbon black brand P 324 and 0.7 wt.h. N-cyclohexyl-2-benzthiazolylsulfenamide. Then rubber compounds are vulcanized at (142 ± 1) ^o C for 40 minutes and the properties of the vulcanizates are determined (table 4).

 The test results of rubbers based on rubber BNKS-28AN show that with a lower content of residual emulsifier in rubber (according to the proposed method), the polymer is characterized by the best complex of physico-mechanical properties and better frost resistance.

Example 3. Receive BNX-18AMN butadiene rubber by copolymerization of butadiene with acrylate nitriles according to the known method using 1.2 wt. Of synthetic fatty acids as potassium soap emulsifier. Polymerization is carried out in an apparatus of 20 l volumes. All components are loaded according to the recipe 3 of table 2. The sum of the monomers when loading is 6.2 liters. The polymerization is carried out to a conversion of 67%. Unpolymerized monomers are distilled off. Thermal and mechanical stability of latex is determined. The distilled latex is coagulated with a 3% solution of calcium chloride. With a similar loading of monomers according to recipe 3, latex is prepared according to the proposed method, using as an emulsifier a mixture of potassium soap of synthetic fatty acids with an additional emulsifier - C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate with a degree of hydroxyethylation of 1 in quantities of 0.5 and 0.05 wt.h. . respectively. The resulting latex is also analyzed for resistance to thermal and mechanical stress and coagulated with calcium chloride. The separated rubbers are washed, dried in an air dryer and analyzed for residual emulsifier content.

Table 5 shows the data obtained. The use of highly effective C ₁₂ -C ₁₄ alkyl sulfoethoxylate sodium in the proposed method in a mixture with potassium soap of synthetic fatty acids allows you to maintain latex stability at a lower dosage of emulsifiers.

 Due to the decrease in the amount of anionic surfactant in the proposed method, a decrease in the mass fraction of the residual emulsifier in rubber is achieved.

Example 4. Get BNX-40AMN butadiene rubber by copolymerization of butadiene with acrylic acid nitrile according to the known method using 3.0 wt.h. synthetic fatty acids as potassium soap emulsifier The polymerization is carried out in an autoclave with a volume of 20 l according to the recipe 4 of table 2. The sum of the monomers at loading is 5.84 l. The polymerization of monomers is carried out to a dry matter content of 18.7 wt.%, Which corresponds to a polymerization depth of 67%. Selected 0.3 l of latex to determine resistance to thermal and mechanical stress. Unpolymerized monomers are distilled off from latex and coagulated with a 1% solution of calcium chloride. With a similar loading of monomers according to the recipe 4, BNX-40AMN butadiene rubber is obtained according to the proposed method using a mixture of synthetic fatty acids and C ₁₂ -C ₁₄ sodium alkyl sulfoethoxylate with an oxyethylation degree of 3 in amounts of 2.2 and 0.3 wt.% As an emulsifier. hours respectively. The total dosage of the mixture of emulsifiers is 2.5 wt. h. During coagulation of latexes, the time to the formation of a transparent serum is noted (coagulation τ, s). The rubber crumb isolated after coagulation is washed with softened water, dried in an air dryer and analyzed for the content of emulsifier. The properties of the samples of latexes and rubbers BNKS-40AMN obtained by the known and proposed methods are shown in table 6.

 The results of the experiments show that the proposed method in comparison with the known achieved the necessary stability of the polymerization system using a lower dosage of emulsifier while maintaining good latex coagulation ability.

 As can be seen from the data given in examples 1-4 and tables 2-6, the inventive method allows to achieve high stability of the polymerization system at low dosages of the emulsifier while maintaining good coagulation ability of the obtained latex, to obtain “pure” butadiene nitrile rubbers with a low content of residual emulsifier in them, characterized by a higher complex of physical and mechanical properties and better frost resistance.

Claims (1)

A method of producing butadiene nitrile rubbers by water-emulsion copolymerization of butadiene with acrylic acid nitrile in the presence of an initiating system, molecular weight regulator using carboxylic acid soaps as an emulsifier, followed by coagulation of latex with calcium chloride, characterized in that they use an additional emulsifier - C ₁₂ -C ₁₄ alkyl sulfoethoxylate sodium with a degree of hydroxyethylation 1-5 in the amount of 0.05-0.50 wt. hours per 100 wt. including monomers with a total dosage of a mixture of emulsifiers of 0.55-2.50 wt. hours per 100 wt. including monomers.

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