RU2593205C1 - Method for extracting concentrated epichlorohydrin from products of allyl chloride epoxidation with hydrogen peroxide on titanium-containing zeolite catalyst - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to industrial technology for production of epichlorohydrin (ECH) by means of liquid-phase allyl chloride epoxidation with hydrogen peroxide in methanol on titanium-containing catalyst, more specifically to step for extracting concentrated ECH from reaction mixture. Proposed method for extracting concentrated ECH from products of allyl chloride epoxidation with hydrogen peroxide on titanium-containing zeolite catalyst in presence of methanol involves separation of allyl chloride and methanol from reaction mixture in primary distillation column, separation of remained bottom residue to aqueous and organic solutions, azeotropic rectification of aqueous and organic solutions, return of azeotropic rectification stripping, containing mixture of water, ECH, and methanol residue, into lower part of primary fractionation column. Return of azeotropic rectification stripping therein is carried out in vapour state into lower part of primary fractionation column.

EFFECT: technical result is simplification of process flow of extraction, and reducing specific consumption of heat energy per 1 kg of ECH.

3 cl, 1 dwg, 5 ex

Description

The invention relates to industrial technology for the production of epichlorohydrin (1,2-epoxy-3-chloropropane, hereinafter ECP) by the method of liquid-phase epoxidation of allyl chloride in methanol on a titanium-containing catalyst with hydrogen peroxide, and specifically to the stage of separation of concentrated epichlorohydrin from the reaction mixture.

Known methods for producing ECP and the industrial technology for its production from allyl chloride at ZAO Kaustik (Sterlitamak) are considered in the monograph [Epichlorohydrin. Production methods, physical and chemical properties, production technology. / D.L. Rakhmankulov, B.Kh. Kimsanov, N.A. Loktionov et al. - Chemistry. 2003. - 244 p.]. Industrial technology includes the chemical stages of liquid-phase hypochlorination of allyl chloride and dehydrochlorination of the obtained glycerol dichlorohydrins; subsequent mass transfer stages of heteroazeotropic rectification and isolation of concentrated ECP from an organic solution. According to this technology, more than 30 m ^{3 of} chemically contaminated wastewater is formed per 1 ton of SEC, which is its main drawback.

A known method of producing epichlorohydrin from allyl chloride and hydrogen peroxide in the presence of a titanium-containing zeolite catalyst with a molar ratio of allyl chloride to hydrogen peroxide of at least 1.5: 1 using methanol as a solvent [RU 2456279. IPC C07D 303/08, C07D 301/12. Publ. 07/20/2012]. The reaction mixture is fed into the middle section of a distillation column with 10-50 theoretical plates. The distillation is carried out at a pressure in the upper part of the column in the range from 20 to 300 kPa (0.2-3 bar) and a reflux ratio from 0.5 to 5. Allyl chloride and methanol are removed by distillation, a mixture of water and ECP are removed by bottoms. In this patent, the process of isolating concentrated ECP from the reaction mixture is not considered.

A known method of producing epichlorohydrin by liquid-phase epoxidation of allyl chloride with an aqueous solution of hydrogen peroxide in methanol in the presence of a titanium-containing zeolite (analogue) [Ovcharova A.V. Development of technology for producing epichlorohydrin. 05.17.04. Abstract of diss. Cand. Chem. sciences. M .: 2012. S. 12]. According to this method, epoxidation is carried out at an initial molar ratio of allyl chloride: hydrogen peroxide equal to 3: 1, a temperature of 40 ° C and a methanol content of 55% by weight. Under these conditions, complete conversion of hydrogen peroxide is achieved, the yield of ECP is 90%. To isolate concentrated ECP from the reaction mixture, a technological scheme with six distillation columns is used. At the first stage, allyl chloride and methanol are successively separated from the reaction mixture by distillates. Azeotropic composition distillate is separated from the remaining bottoms of the second column and the return aqueous solution from the phase separator in the third column, which is separated into aqueous and organic solutions in the phase separator. Concentrated SEC is obtained from the organic solution in the fourth column by the bottom residue of azeotropic distillation, concentrated distillation is returned in liquid form to the phase separator. In order to isolate 1000 kg of SEC from the remaining bottoms and return water in the form of an azeotropic distillate (ECP content of 75 wt%), 1000 kg of SEC (heat consumption 435 MJ) and 306 kg water (heat consumption 691 MJ) must be evaporated, which is the main disadvantage of this method.

The closest in technical essence is the method of separation of concentrated ECP from a mixture of an azeotropic composition in the presence of impurities (prototype) [Savelyev NI, Lukin PM Drying of epichlorohydrin by azeotropic rectification // Actual problems of chemical technology and environmental protection: Sat. Materials IV All-Russian. conf. - Cheboksary: LLC Publishing House "Pegasus", 2014. - S. 166-167]. The method includes separation of allyl chloride and methanol from the reaction mixture, separation of the remaining bottoms in the phase separator into aqueous and organic solutions, azeotropic distillation of aqueous and organic solutions, return of azeotropic distillation distillations containing water, epichlorohydrin and methanol residues in liquid form to the phase separator. To extract methanol from the reaction mixture to a content in the bottom residue of less than 0.5% of the mass. a distillation column with a separating capacity of 20 theoretical plates and a reflux number of more than 2 is required. Moreover, the specific heat consumption per 1 kg of SEC in the column evaporator exceeds 15 MJ / kg, which is the main disadvantage of the known method.

Another disadvantage of the known method is the presence in the dried ECP of high-boiling by-products, for example glycerol.

The objective of the invention is to reduce the energy intensity of the process of separation of concentrated epichlorohydrin from the products of epoxidation of allyl chloride with hydrogen peroxide on a titanium-containing zeolite catalyst in the presence of methanol.

The technical result of the claimed invention is to reduce the specific energy consumption of the process by 10-17% and to reduce the content of high boiling point by-products, for example glycerin, in dried ECP by 10 times or more.

The technical result is achieved by the fact that in the method for the separation of concentrated epichlorohydrin from the products of epoxidation of allyl chloride with hydrogen peroxide on a titanium-containing zeolite catalyst in the presence of methanol, which includes separation from the reaction mixture of allyl chloride and methanol, separation of the remaining bottoms residue in aqueous and organic solutions, azeotropic distillation organic solutions, return of azeotropic distillation distillates containing a mixture of water, epichlorohydrin and meth anola, according to the invention, the return of azeotropic distillation distillates is carried out in the vapor mixture in the reaction mixture.

In this case, the organic solution obtained by separating the remaining bottoms, before azeotropic distillation is washed with water, taken in an amount of 2-10% by weight of the organic solution.

In this case, washing is carried out in a countercurrent liquid extractor with a separating capacity of 2-5 theoretical contact levels.

The figure shows the basic flowchart of the separation of concentrated epichlorohydrin from the products of epoxidation of allyl chloride with hydrogen peroxide in the presence of methanol.

The scheme for isolating concentrated epichlorohydrin from the allyl chloride hydrogen peroxide products of the invention according to the invention includes a primary distillation column 1 with a separation capacity of 15-30 theoretical contact stages, a phase separator 2, columns 3 and 4 of azeotropic distillation without condensers with a separation capacity of 5-10 theoretical contact levels .

The reaction mixture is fed to the middle feed section of the primary column 1 from the epoxidation unit (stream 5). Rectification is carried out at atmospheric pressure and the number of phlegmy 0.5-3.0. The distillate containing allyl chloride and methanol is returned to the epoxidation reaction unit (stream 6). The bottom residue from the primary column (stream 7) in the phase separator 2 is separated into an aqueous solution (stream 8) and an organic solution (stream 9).

An aqueous solution containing ECP (stream 8) is fed into the upper part of the azeotropic rectification column 3, an aqueous solution without ECP (stream 10) is removed from it by bottoms, and the distilled vapors of methanol, water and ECP of an azeotropic composition (stream 11) are returned to the lower part of the primary column 1. An organic SEC solution containing dissolved water (stream 9) is fed to the top of the azeotropic distillation column 4, concentrated ECP (stream 12) is removed from it by bottoms, and the distilled vapors of methanol, water and SEC of an azeotropic composition (stream 13) return the lower portion of the primary column 1.

The bottom residue of column 3 (stream 10) is sent to neutralization, neutralization and purification of organic substances. Concentrated ECP (stream 12) is sent to a warehouse or additional purification from non-volatile and high boiling impurities by known methods.

Below are the main parameters of the processes of separation of concentrated ECP according to the invention (examples 1-3) and the prototype (examples 4 and 5) under identical initial conditions, obtained using the ChemCAD simulation program.

The initial model mixture (stream 5) 7085 kg / h, taking into account the processes of hydrolysis of EPH and by-products, contains,% wt .: allyl chloride - 21.7; methanol - 54.3; water - 9.7; ECP - 12.9, glycerol - 1.4.

Example 1 (according to the invention). Column 1 has, including a condenser and an evaporator, 16 theoretical stages. In its middle part, at the 7th step, a reaction mixture stream of the above composition is fed from above. At the 12th stage (counting from above) they are fed into steam streams from azeotropic distillation columns 3 and 4 with a total flow rate of 279 kg / h, which contain,% wt .: methanol - 10.8; water - 27.3; ECP - 61.9. Column 1 operating conditions: pressure - atmospheric; the number of reflux flow - 0.5; the predetermined mass fraction of methanol in the bottom residue (stream 7) is 3.0%. Get 5546 kg / h of distillate and 1818 kg / h of bottoms, containing,%: methanol - 3.0; water - 35.8; ECP - 55.7, glycerol - 5.5. The thermal load on the evaporator of column 1 is 8210 MJ / h.

VAT residue is divided into aqueous and organic solutions, glycerin is distributed between them in a ratio of 60: 1. The solutions are fed to the first stages of azeotropic distillation columns 3 and 4 without condensers, which have 6 theoretical stages of contact, including evaporators. Separation is carried out to values of mass fractions in the still bottoms of column 3 (stream 10) ECP 0.05% and column 4 (stream 12) water - 0.05%. Get 693 kg / h of an aqueous solution with traces of ECP and 847 kg / h of concentrated ECP. Thermal loads on the evaporators of columns 3 and 4, respectively, are 218 and 113 MJ / h. The total specific heat energy consumption per 1 kg of SEC in the concentrated product (stream 12) is 10.2 MJ / kg.

Example 2 (according to the invention). The process is carried out in accordance with example 1, but the specified mass fraction of methanol in the bottom residue (stream 7) is increased to 6.0%. The thermal load on the evaporator of the primary column 1 is 8012 MJ / h. In the phase separator, glycerin is distributed between aqueous and organic solutions in a ratio of 47: 1. Steam flows from columns 3 and 4 are 318 and 159 kg / h. The thermal loads on the evaporators of the columns of azeotropic distillation 3 and 4 are respectively 396 and 179 MJ / h. The total specific consumption of thermal energy per 1 kg of ECP is 10.2 MJ / kg. The concentrated product (stream 12) contains 99.5% SEC.

Example 3 (according to the invention). The process is carried out under identical conditions as in Example 2, but an additional aqueous washing of the organic solution in a liquid extractor with a separation capacity of 2 theoretical contact stages is carried out. 1010 kg / h of organic solution and 40 kg / h of water are fed countercurrently to the extractor. 55 kg / h of wash water and 995 kg / h of purified organic solution are obtained. The glycerol content in the organic solution is reduced 11 times from 2.05 to 0.18 kg / h. Wash water and purified organic solution are sent to the appropriate azeotropic distillation columns. The concentrated product (stream 12) contains 99.8% ECP.

Example 4 (prototype). The process is carried out under identical conditions as in Example 1, but columns 3 and 4 are equipped with condensers and distillates from them in a liquid state (streams 11 and 13) are fed to phase separator 2. From 7085 kg / h of the initial reaction mixture in column 1 with reflux number 1 0 get 5396 kg / h of distillate and 1689 kg / h of bottoms containing,% wt .: methanol - 1.5; water - 38.7; ECP - 53.9, glycerol 5.9. The thermal load on the evaporator of column 1 is 10324 MJ / h.

The bottoms of column 1 and the distillates of azeotropic distillation columns 3 and 4 in phase separator 2 are separated into aqueous and organic solutions, which are fed to the second (top) stages of stripping columns 3 and 4. Columns 3 and 4 have 6 theoretical contact stages, including condensers (1st stage) and evaporators (6th stage). Columns 3 and 4 operate at atmospheric pressure; the number of phlegm - 0.1; the mass fraction of ECP in the cubic residue of column 3 (stream 10) is set equal to 0.05%, the mass fraction of water in the cubic residue of column 4 (stream 12) is set to 0.05%. 222 kg / h of distillate (stream 11) and 771 kg / h of bottoms are withdrawn from column 3 (column 10). 106 kg / h of distillate (stream 13) and 914 kg / h of bottom residue (stream 12) are removed from column 4.

Thermal loads on evaporators of azeotropic rectification columns 3 and 4 are equal to 301 and 142 MJ / h, respectively. The total specific heat energy consumption per 1 kg of SEC in the concentrated product (stream 12) is 11.9 MJ / kg.

Example 5 (prototype). The process is carried out under identical conditions with Example 4, but the predetermined mass fraction of methanol in the bottom residue of the primary distillation column 1 (stream 7) is increased to 3%. In the phase separator 2, the methanol content increases in an avalanche, and the azeotropic distillation columns 3 and 4 do not provide the release of concentrated ECP.

The examples considered show that the allocation of the concentrated SEC according to the invention in comparison with the known method allows to reduce the specific heat consumption per 1 kg of SEC in the concentrated product (stream 12) by 16% (from 11.9 to 10.2 MJ / kg) . At the same time, the stable operation of the concentrated ECP separation unit is ensured while the separation ability of the primary distillation column of separation of the allyl chloride and methanol chloride from the reaction mixture is reduced, and the process flow chart is simplified, since there is no need for heat exchangers for condensing steam flows from two azeotropic distillation columns.

Claims (3)

1. The method of separation of concentrated epichlorohydrin from the products of epoxidation of allyl chloride with hydrogen peroxide on a titanium-containing zeolite catalyst in the presence of methanol, including separation from the reaction mixture of allyl chloride and methanol in a primary distillation column, separation of the remaining bottoms residue in aqueous and organic solutions, azeotropic distillation and azeotropic distillation with water solutions, return of distillates of azeotropic distillation, containing a mixture of water, epichlorohydrin and methanol residue, characterized in that the return of distillates of azeotropic distillation is carried out in a vapor state in the lower part of the primary distillation column. 2. The method according to claim 1, characterized in that the organic solution obtained by separating the remaining bottoms, before azeotropic distillation is washed with water, taken in an amount of 2-10% by weight of the organic solution. 3. The method according to claim 2, characterized in that the washing is carried out in a countercurrent liquid extractor with a separating capacity of 2-5 theoretical contact stages.

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