RU2109018C1 - Method of isolating synthetic rubbers from latexes - Google Patents

Abstract

FIELD: RUBBER INDUSTRY. SUBSTANCE: objective of invention is to reduce power consumption on liquefying cooling agent used when coagulating latex through freezing (by 10-14%); eliminate consumption of fresh softened water and heating agent for thawing coagulum with serum; diminish loss of fine rubber crumb; utilize main and side products of serum- containing water purification; and prevent environmental damage. Objective is accomplished by introducing additional freezing stage at superatmospheric pressure and specified rate of separating coagulum in hydrocyclone. Thawing coagulum with serum is effected using heat of vapors originated from decontamination of rubber crumb to remove residual monomers. Fine rubber crumb is concentrated in serum- containing water by means of self-purifying filter and returned into process. Filtrate is additionally purified on membrane by reverse osmosis technique and softened water is reused in the process of polymerization of monomers and concentrate of surfactants in building industry. Heat from latex under freezing is drawn off with low- boiling monomer first at superatmospheric pressure and rate of latex temperature drop 10-30 deg/h. Vapors of boiling monomer are separated from latex emulsion using centrifugal force in hydrocyclone. Frozen coagulum particles are separated from cooling agent in worm conveyor positioned at angle 30 deg. to horizon, whereas lower end of worm is located above the level of cooling agent in coagulator and on the outlet of worm there is hydraulic gate-separator. To thaw frozen coagulum with serum, heat of excess hot serum-containing water and of a part of decontamination vapors is utilized. Productivity of installation is increased by 28-40%. EFFECT: enhanced efficiency of process and improved environmental condition. 4 cl, 1 dwg, 4 tbl

Description

 The invention relates to methods for isolating synthetic rubbers from latexes, including wastewater treatment, and can be used in the chemical and petrochemical industries.

 Known methods for the allocation of synthetic rubbers from latexes using electrolytes and freezing [1].

In practice, the most widely used method of coagulation using electrolytes. But this method has significant drawbacks: high consumption of electrolyte (up to 1 ton of salt / ton of rubber) and fresh softened water (up to 8 m ³ / ton of rubber): salinization of wastewater discharged to treatment plants.

 Another way of isolating synthetic rubbers from latex by freezing a metal roll cooled from the inside by a refrigerant on the wall is characterized by low productivity, pollution of the working area and the environment with volatile monomers due to the impossibility of sealing the freezing unit and high energy consumption when receiving refrigerant, water vapor when thawing coagulum with serum.

 Closest to the proposed method is a method for producing emulsion rubbers, which consists in coagulating latex in a low-boiling refrigerant by freezing under vacuum, followed by thawing of the coagulum, and distillation of non-polymerized monomers [2].

 The method reduces emissions of volatile monomers into the environment and reduces the loss of monomers with rubber, increases the productivity of the process.

However, it is characteristic of him:
- the consumption of a relatively large amount of electricity due to the use of a larger number of units of compression equipment. This is due to the need to increase the stages of compression to reduce the total volume of butadiene vapor under vacuum (4.5 tons of reduced butadiene are spent on coagulating 1 ton of rubber);
- high heat consumption of water vapor to repel coagulum with serum (0.7 gcal of heat is consumed per 1 ton of rubber).

 In addition, in the considered method, the problems of purification and disposal of wastewater, the loss of fine rubber crumbs were not solved.

The aim of the invention is
- reducing the cost of electricity to reduce the refrigerant used in coagulation of latex by freezing:
- the exclusion of fresh softened water and heat agent for thawing coagulum with serum;
- reduction of losses of fine crumb rubber;
- disposal of the main and by-products of the purification of serum-containing water;
- prevention of environmental damage.

This goal is achieved by the fact that in the known method for the isolation of synthetic rubbers from latexes, including coagulating the latex by freezing in a refrigerant medium under vacuum, thawing the coagulum, followed by water degassing of the non-polymerized monomers from the rubber crumb and its dehydration:
- heat removal of the frozen latex is carried out with a low-boiling monomer, first at a pressure higher than atmospheric and a latex temperature drop rate of 10-30 deg / h;
- separation of the boiling monomer vapors from the latex emulsion at a pressure higher than atmospheric is carried out due to centrifugal forces in the hydrocyclone;
- the separation of frozen coagulum particles from the refrigerant is carried out in a screw conveyor installed at an angle of 30 ^o to the horizon and the lower end of the screw is higher than the level of the refrigerant in the coagulator, and a water trap separator is installed at the outlet of the screw;
- thawing of frozen coagulum is carried out due to the heat of excess serum-containing water and part of the degassing vapors of the stage of distillation of unpolymerized monomers;
- spend the concentration of small crumbs in serum-containing water using a self-cleaning filter design according to ed. St. 1669491 (USSR) from 06.19.89 with the withdrawal of the filtrate for additional purification;
- conduct additional purification of serum-containing water from surface-active substances using reverse osmosis.

 The proposed method can be implemented according to the technological scheme shown in the drawing.

 The latex obtained by copolymerization of monomers - butadiene with acrylonitrile or styrene (alpha-methylstyrene) in an aqueous emulsion is stopped and sent to rubber by freezing.

In contrast to the known method, an additional stage of latex freezing is introduced, where 30-40% of the total heat of the latex is removed by low-boiling butadiene at a pressure higher than atmospheric and a latex temperature drop rate of 10-30 deg / h. To do this, the gas-suspension mixture with a temperature of plus 5 - 10 ^o C is first dispersed in reduced butadiene in a ratio of 1: 3, supplied respectively through lines 1 and 2 to the mixer 3. From line 2, part of the butadiene is fed to the freezing apparatus through line 4. The resulting latex emulsion in reduced butadiene, line 4 is introduced into the lower part of the hollow sealed bubbler type mixer 5, where the initial stage of latex freezing is carried out. In the bubbler mixer 5 along the movement of the latex emulsion from the lower to the upper part due to the pressure drop, intensive boiling of butadiene occurs while cooling the latex emulsion. The temperature drop in the mixer 5 is 10-30 deg / h.

 In contrast to the known method, the separation of boiling monomer vapors from latex is carried out by centrifugal forces in a hydrocyclone. For this, the vapor-liquid mixture from the upper part of the mixer 5 is tangentially introduced into the hydrocyclone 7 through line 6. In the hydrocyclone, due to centrifugal force, vapors of butadiene vapor are actively squeezed out of the latex. After that, butadiene vapors with a pressure of 0.13 - 0.15 MPa are transferred to line 8 via line 8 for compression.

The latex emulsion in residual butadiene cooled to a temperature of 0 to minus 2 ^o C is throttled via line 9 to a coagulator 10 operating under vacuum, where the rubber is finally frozen from the latescope due to the low boiling point of butadiene (minus 15 ^o C at a residual pressure of 0, 08 MPa). An additional amount of butadiene is supplied to coagulator 10 through line 4 and a residual pressure of 0.08 MPa (608 mm Hg) is maintained in the coagulator due to the operation of vacuum equipment (steam injection unit, vacuum pump and compressors). This pressure ensures the boiling of vapors of butadiene at a temperature of -15 ^o C. By mixing the stirrer in the coagulator creates a homogeneous suspension of particles consisting of coagulum frozen in serum in liquid butadiene. The ratio of the solid dispersed phase to butadiene at the output of the coagulator is maintained 1: 8 to allow the suspension to be transported through line 11 by pump 12. The butadiene vapor via line 13 enters the droplet eliminator 14, from which the liquid phase flows via line 15 back to the coagulator, and the vapor passes through line 16 enter the vacuum line.

In contrast to the known method, the flow of the suspension by the pump 12 is sent along line 17 to the screw conveyor 18, installed at an angle of 30 ^o to the horizontal. Butadiene, due to the gap between the screw and the casing, flows down the inclined casing of the screw conveyor via line 19 back to the coagulator, and the frozen particles are thawed through the hydraulic lock - separator 20. Vapors of butadiene from the top of the auger conveyor through line 21 enter the drop eliminator 14. From the water trap - separator 20, particles of frozen coagulum with serum enter the melter 22 with a stirrer and a jacket.

The separation of the solid dispersed phase from the dispersion medium - the refrigerant is carried out in the proposed method due to the following technical solutions:
installation of the inclined screw at an angle of 30 ^o to the horizontal, which ensures the transportation of the solid dispersed phase and at the same time, the flow of refrigerant through the inclined cylindrical body of the screw back into the freezing apparatus;
the lower end of the screw conveyor must be higher than the level of liquid refrigerant in the freezing apparatus;
as a separator and thermal shutter, which allows to supply only pieces of frozen coagulum and prevents the penetration of vapors from the defrosting apparatus into the auger and freezing apparatus, a water trap is installed.

 In contrast to the known method, thawing frozen coagulum with serum is thawed due to the heat of the excess of hot sulfur-containing water and part of the degassing vapors of the distillation stage of unpolymerized monomers. For this, part of the degassing vapors and a hot excess of untreated sulfur-containing water are introduced into the melter 22, and an excess of filtered sulfur-containing water is introduced into the melter jacket. In melter 22, particles of frozen coagulum with serum are thawed due to the heat of serum-containing water and degassing vapors, with the formation of rubber crumbs in serum diluted with a condensate of degassing vapors.

 Vapors of butadiene from the melter 22 enter line 23 into a vacuum manifold.

 Next, the aqueous pulp of rubber crumbs from the melter 22 is fed to the pump 25 through line 24, and from it through the line 26 to the first stage degasser 27. Part of the degassing vapors through line 28 enters the vacuum manifold, and part of them through line 29 is fed to the melter 22 The rubber pulp from the degasser 27 through line 30 enters the pump 31, and from it to the second stage of degassing to the degasser 32. Vapors from the degasser 32 pass through line 33 to the degasser of the first stage 27, and fresh water vapor is supplied to the degasser 32 through line 34. The process of water degassing rubber is similar to the process of water degassing mortar rubber SKI-3, SKD. The degassed pulp of rubber crumb from the degasser 32 is fed first through line 35 with a pump 36, and then through line 37 for washing from the emulsifier to a collector with mixer 38. The washing is carried out with softened water, which is fed from above the apparatus. The washed pulp through line 39 enters the pump 40 and then through line 41 it is fed to a vibrating screen 42 to separate it from the main amount of sulfur-containing water. It is allowed to supply degassed pulp immediately along line 37 to a vibrating screen without washing. The dehydrated crumb of rubber after the vibrating screen is sent for drying in a known manner. In turn, the sulfur-containing water after the vibrating screen is collected in a collector 43, from which, via line 44, a pump 45 is fed through line 46 to a filter 47 for subsequent purification and heat recovery.

 In contrast to the known method, small crumbs are concentrated in sulfur-containing water using a self-cleaning filter design according to ed. St. 1669491 (USSR) from 06/19/89 with the conclusion of the filter for additional cleaning. The ratio of the flows of pulp of crumb rubber to filtered sulfur-containing water is 1: (1-2). The fine rubber crumb concentrate in serum-containing water after filter 47 passes through line 48 for defrosting to melter 22, and pure water is collected in collector 50.

 From the collector 50, through line 51, with a pump 52, hot sulfur-containing water is fed through line 53 to the melter jacket 22 for heating. Then, this water is taken from above along line 54 and sent for additional cleaning of surfactants.

 In contrast to the known method, an additional purification of serum-containing water from surfactants is carried out using reverse osmosis. To do this, water through line 54 is sent to a reverse osmosis unit 55, from which two streams are removed. The deeply purified water of the first stream 56 through line 57 enters the washing of the rubber crumbs in the apparatus 38, and the excess water through line 58 is fed to prepare the aqueous phase in the polymerization unit. Concentrated surfactants through line 59 go to the warehouse for sale as a commercial product. The ratio of the flows exiting the reverse osmosis unit, aqueous surfactant solution: deeply purified water is 1:10. The concentration of surfactants in the solution increases by about 10 times, compared with the content of surfactants in the initial serum-containing water.

Example 1 (control). The selection of rubbers SKN-26, SKS-30ARK from latex with a temperature at the exit of polymerization of 5 and 7 ^o C is carried out in a known manner described in the prototype. Latex is dispersed with a medium of reduced butadiene and coagulated in one step by freezing under vacuum (residual pressure 0.08 MPa) and a temperature of -15 ^o C in the presence of syntanol DS-10. Thawing of coagulum with serum is carried out by direct mixing with hot water and sharp steam. Sulfur-containing wastewater is not cleaned and disposed of.

 The known method is characterized by the indicators presented in table. one.

 The known method is characterized by a low productivity of the latex vacuum coagulation stage due to the difficulty of removing a large number of discharged butadiene vapors from the freezing zone, as well as a large energy consumption for reducing discharged butadiene (4.5 t / t rubber), as well as a large consumption of fresh softened water and the heat of water vapor and, accordingly, the discharge of contaminated waste water, the loss of fine rubber crumbs.

 Example 2

The selection of rubbers SKN-26, SKS-30ARK from latex with a temperature at the exit of polymerization of 5 and 10 ^o C is carried out by the proposed method. Latex is coagulated by freezing in two stages. The initial stage of latex cooling is carried out at a more atmospheric pressure in a bubbler type hydrodynamic mixer. The separation of butadiene vapor from the gas-liquid stream is realized in a hydrocyclone at a pressure of 0.135 MPa. The final stage of cooling is carried out under vacuum (residual pressure of 0.08 MPa and a temperature of 15 ^o C. Thawing of the coagulum with serum is carried out by degassing pairs.

 The proposed method is characterized by the indicators presented in table. 2, 3.

 The proposed method is characterized by an increase in the efficiency of the final stage of latex vacuum coagulation, which manifests itself in an increase in productivity and a decrease in energy consumption during liquefaction of the refrigerant. This is achieved by pre-cooling latex at a pressure higher than atmospheric and reducing the proportion of discharged refrigerant vapors.

 Further redistribution of the heat load from the final stage of coagulation to the initial one with an increase in the rate of drop in latex temperature of more than 30 deg / h is impractical due to a decrease in the productivity of the initial stage against the background of stabilization of energy consumption. In turn, a decrease in the rate of drop in latex temperature below 10 deg / h leads to an excessive consumption of electricity due to an increase in the proportion of discharged refrigerant vapors.

 Example 3

 The selection of rubbers SNK-26, SKS-30ARK from latex is carried out according to the proposed method, similar to the conditions described in example 2. The rate of fall of the temperature of the latex in the initial stage of freezing can withstand 20 deg / h. Fine rubber crumb is concentrated in the sulfur-containing wastewater and the concentrate is returned to the process. Additionally, the excess filtered sulfur-containing water on the membrane is purified and 80% is returned to the polymerization process (Table 4).

Thus, the implementation of the proposed method will reduce electricity consumption by reducing the refrigerant by 10 - 14% by reducing the stage of compression of butadiene, increase the productivity of the process by 28 - 40%, eliminate both the consumption of fresh softened water and the consumption of heat agent for thawing coagulum with serum , significantly reduce the discharge of wastewater (up to 1.0 m ³ / t of rubber) and the loss of fine crumbs of rubber, prevent the discharge of wastewater containing mineral salts and surfactants from the environment.

Sources of information:
1. O. B. Litvin. Fundamentals of rubber synthesis technology. - M.: 1972, p. 292 - 311, 334 - 335, 347 - 351.

 2. Copyright Certificate, 454807, C 08 C 1/14, 1991.

Claims (4)

 1. A method of isolating synthetic rubbers from latexes, including coagulating the latex by freezing in a medium of a boiling refrigerant under vacuum, thawing the coagulum, followed by water degassing of the non-polymerized monomers from the rubber crumb and its dehydration, characterized in that heat is removed from the freezing freeze-dried latex the pressure is greater than atmospheric, the rate of drop in temperature of the latex is 10 - 20 deg./h and the separation of the vapor of the boiling monomer from the latex emulsion due to of centrifugal forces in the hydrocyclone, and thawing of the frozen coagulum is carried out due to the heat of the excess of hot sulfur-containing water and part of the degassing vapors of the stage of distillation of unpolymerized monomers. 2. The method according to claim 1, characterized in that the separation of the frozen particles of coagulum from the refrigerant is carried out in a screw conveyor installed at an angle of 30 ^o to the horizon and the lower end of the screw is higher than the level of the refrigerant in the coagulator, and a water trap separator is installed at the outlet of the screw .  3. The method according to claim 1, characterized in that the concentration of fine rubber crumbs in serum-containing water is carried out using a self-cleaning filter with the filtrate withdrawal for further purification.  4. The method according to claim 1, characterized in that they carry out additional purification of serum-containing water from surfactants using reverse osmosis.

Images