RU2436759C1 - Method of extracting organic products from aqueous layer formed during synthesis of dimethyl dioxane in production of isoprene from isobutylene and formaldehyde - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to a method of extracting organic compounds (DMD, TMK, unsaturated alcohols, methylal) from an aqueous layer during synthesis of dimethyl dioxane in production of isoprene from isobutylene and formaldehyde via partial extraction of said compounds from the end of the column for stripping the aqueous layer of the isobutane-isobutylene fraction, coming in for synthesis of dimethyl dioxane in weight ratio 1:0.8 - 1.0, followed by fortification and removal of methanol from formaldehyde, characterised by that the raffinate from partial extraction of organic compounds is subjected to additional extraction of isobutane-isobutylene fraction in ratio of 1:0.5 - 0.8 and the obtained raffinate is mixed with formaldehyde water obtained from decomposition of DMD, and also with the distillate of the formalin fortification column and taken for fortification and removal of methanol from formaldehyde, followed by feeding the distillate from the column for removing methanol from formaldehyde for extraction of organic compounds concentrated therein through the return isobutane fraction, extracted after synthesis of dimethyl dioxane in ratio 1:1.0 - 1.2, followed by feeding the extraction for extraction of the return isobutane fraction once more. ^ EFFECT: method enables to stabilise the rectification process and increase output of formaldehyde during extraction, and also increase service life of formaldehyde water fortification columns, and reduce loss of hydrocarbons. ^ 1 cl, 1 dwg, 3 ex, 3 tbl

Description

The invention relates to a method for producing dimethyldioxane in the production of isoprene and, in particular, to the allocation of organic compounds from the aqueous layer during the strengthening and demethanolation of formaldehyde.

A known method of producing dimethyldioxane (DMD) from isobutylene and formaldehyde in reactors in the presence of an acid catalyst with the production and subsequent separation of the organic and aqueous layers.

The aqueous layer containing 7-8 wt.% Unreacted formaldehyde, as well as a certain amount of formed and unseparated organic compounds (DMD, trimethylcarbinol (TMK), unsaturated alcohols, methanol, methylal) is fed to the stripping unit, which is run after partial extraction of organic compounds with isobutane -isobutylene fraction together with formaldehyde water from the DMD decomposition shop to isoprene and the distillate of the formaldehyde strengthening column is sent to the formaldehyde strengthening and demethanolization unit. The distillate of the de-methanolation column is fed to the oxidation of methanol to formaldehyde (S.K. Ogorodnikov, G.S. Idlis. Isoprene production. Chemistry, Lenizdat, 1973, p. 55).

The content of the above organic compounds in all these streams at first glance is insignificant, however, given the large total volume of these streams, the amount of these organic compounds reaches several hundred kilograms per hour, which creates known difficulties in the process of strengthening and demethanolation of formaldehyde, as well as in the preparation of formalin . In practice, only one stream is partially purified from the indicated organic compounds — by extraction of an aqueous layer of residue from the overhead column. The remaining streams, and especially formaldehyde water, after decomposition of DMD into isoprene are fed to the rectification without purification.

The disadvantage of this method is the ingress of a significant amount of organic compounds (DMD, TMK, unsaturated alcohols, methylal, methanol) into the streams of the aqueous layer processing, which destabilizes the operation of distillation columns, and along with high-boiling products and formaldehyde contributes to the clogging of the internal structures of formaldehyde water processing columns with polymers and resins. These organic compounds, falling on the formaldehyde production unit, are partially lost with exhaust gases, and are partially decomposed into by-products and resins, worsen the performance of the catalyst for the oxidation of methanol to formaldehyde, and partially recycle to formalin demethanolation columns.

The proposed method is devoid of these drawbacks, as it allows you to completely remove DMD, TMK, unsaturated alcohols and methylal from streams of the aqueous layer into finished products, stabilize the work of formaldehyde strengthening and demethanolation columns and increase the performance of methanol to formaldehyde oxidation reactors.

This goal is achieved by the method according to which the raffinate of the partial extraction of organic compounds is subjected to additional extraction with the isobutane-isobutylene fraction in a weight ratio of 1: 0.5-0.8 and the resulting raffinate is combined with formaldehyde water obtained from the decomposition of DMD, as well as with a distillate of a formalin strengthening column and fed to the strengthening and demethanolation of formaldehyde, followed by the supply of distillate of the column of demethanolation of formaldehyde for the extraction of the indicated organics chemical products with a return isobutane fraction isolated after synthesis of dimethyldioxane in a weight ratio of 1: 1.0-1.2, followed by feeding the extract again to isolate a return isobutane fraction.

In the absence of additional extraction of the overhead of the evaporation column of the aqueous layer, the extraction of organic compounds from the distillate of the demethanolation column is also carried out with the isobutane-isobutylene fraction fed to the synthesis of dimethyldioxane.

The implementation of this method in the production of isoprene will allow:

- almost completely eliminate the ingress of DMD, TMK and unsaturated alcohols into methanol oxidation reactors in formaldehyde, which will naturally improve their performance;

- to stabilize the work of the columns for strengthening and demeaning formaldehyde, which will also reduce the loss of hydrocarbons, including formaldehyde and reduce energy consumption;

- slightly increase the mileage of the columns for strengthening formaldehyde water from cleaning to cleaning from polymers, by reducing the amount of organic compounds that enter them, some of which (DMD, TMK, NS 130 °, methylal) are decomposed into by-products, including and with the formation of isoprene, which separately and together with high-boiling products forms a polymer;

- reduce the loss of such valuable products as DMD, TMK, n.s. 130 °, which, in turn, will lower the specific consumption of isobutylene and methanol, as well as water vapor.

The separation of organic compounds from the streams of the aqueous layer and from the raw materials supplied to the oxidation of methanol to formaldehyde is possible without additional extraction of the raffinate after partial extraction, however, the run of the formaldehyde strengthening columns from cleaning to cleaning does not increase.

In this method, the raffinate of the column for partial extraction with the isobutane-isobutylene fraction from the overhead of the column of vacuum evaporation of the aqueous layer through line 1 is sent to additional extraction with the isobutane-isobutylene fraction (along line 2) in a weight ratio of 1: 0.5-0.8 to column 3 ( see drawing).

The extract of this column through line 4 is fed to the DMD synthesis reactor block, and the output raffinate from line 5 is combined with the aqueous layer coming through line 6 from the DMD decomposition unit and the distillate of the formaldehyde strengthening column (line 7), after which the resulting mixture is sent through line 8 to the formaldehyde water strengthening column 9, the bottled liquid of this column is sent to line 10 in a chemically contaminated sewer, and the distillate is sent along line 11 together with methanol formalin from line 12 to the formaldehyde column dehydrate 13.

The bottoms product of this column is sent via line 14 to the formalin strengthening column, and the distillate via line 15 - to extract the remaining amount of organic compounds into column 16. Organic compounds are extracted using the isobutane recovery fraction taken along line 21 from the distillate of column 20 after it is separated from oil "layer of the reactor block for the synthesis of DMD entering the column 20 along line 22 in a weight ratio of 1: 1.0-1.2. The rest of the isobutane fraction is sent via line 25 to the isobutane dehydrogenation workshop.

The extract of column 16, taken along line 18, is combined with the “oil” layer coming from the reactor block through line 22, and fed through line 19 to column 20. The separated organic compounds remain in the “oil” layer and are released to the isolation of DMD and other organic products in line 23.

In the absence of additional extraction of the overhead of the evaporation column of the aqueous layer (column 3), the extraction is carried out instead of the isobutane fraction by an excess of the direct isobutane-isobutylene fraction through line 24 and the extract is returned to the dimethyldioxane synthesis reactor through line 26. The methanol fraction purified from the indicated organic compounds from column 16 line 17 is sent to the formalin production unit.

The invention is illustrated by the following examples.

Example 1 (according to the existing method)

The epaulette column of the evaporation column of the aqueous layer is fed to a partial extraction of organic compounds (DMD, TMK, NS 130 °, methylal). An isobutane-isobutylene fraction is used as an extractant before it enters the dimethyldioxane synthesis reactor block. The ratio by weight of the shoulder strap of the stripping column of the aqueous layer and the extractant is 1: 0.8-1.0.

At the same time, about 69% of the organic compounds from the incoming are recovered. The resulting raffinate in an amount of 32300 kg / h is combined with formaldehyde water obtained by the decomposition of dimethyldioxane (75200 kg / h) and the distillate of the formalin strengthening column (6100 kg / h) are sent to the formaldehyde strengthening columns, where some of the organic compounds are decomposed into secondary products, apparently joins with high-boiling products and contributes to the clogging of internal structures with resins. The overhead of this column, together with methanol formalin, is sent to a formaldehyde demethanolation column, where organic compounds are concentrated in the distillate along with methanol, which are transferred to the oxidation of methanol to formaldehyde. At the same time, part of these valuable organic compounds is lost, and part is recycled again for distillation. The number and composition of incoming and receiving products is given in table No. 1.

Example 2 (by the proposed method)

The raffinate after partial extraction of organic compounds together with formaldehyde water after DMD decomposition into isoprene and distillate of the formalin strengthening column is fed to the formaldehyde water strengthening column, and then to the formaldehyde 13 decontamination column in the quantity and composition indicated in Example 1.

The distillate of the demethanolation column, in which the above organic compounds are concentrated, is subjected to extraction on column 16 in a weight ratio of 1: 1.0-1.2 of the return isobutane fraction, after it is separated from the organic layer from the reaction mass of DMD synthesis reactors on column 20.

The extract after extraction is returned again to the feed of the recovery isobutane recovery column 20.

The number and composition of the products for this example are shown in table No. 2.

Thus, the main part of DMD, TMK, unsaturated alcohols and methylal is returned to the dimethyldioxane isolation and purification unit. However, as a result of the ingress of part of the organic compounds with the extraction column raffinate, the mileage of the formaldehyde strengthening column from cleaning to cleaning does not increase.

The withdrawal of the above organic compounds from the de-methanolation columns will also help to reduce the formaldehyde content in the distillate, i.e. will reduce its loss during the oxidation of methanol.

In the absence of additional extraction of the overhead of the evaporation column of the aqueous layer, the organic compounds are also extracted from the distillate of the demethanolation columns by the isobutane-isobutylene fraction fed to the synthesis of dimethyldioxane.

Example 3 (by the proposed method)

Purification of the aqueous layer from organic compounds is carried out according to the scheme specified in example 2, with the difference that after partial extraction of DMD, TMK, unsaturated alcohols and methylal from the stream of the column of the residue from the aqueous layer, additional organic extraction of these organic compounds by isobutane-isobutylene fraction in a weight ratio is carried out 1: 0.5-0.8 on column 3 followed by the supply of raffinate also together with formaldehyde water of the DMD decomposition shop and the distillate of the formaldehyde strengthening column to the formaldehyde demeanation column final extraction with the above organic compounds from the column distillate fraction obezmetanolivaniya direct isobutane in a weight ratio of 1: 1.0-1.2.

After additional extraction, the extract is returned to the reactor block, and after the column of demethanolation, to the reaction mixture to isolate the isobutane return fraction.

The number and composition of organic compounds in this method are given in table No. 3.

According to this method, along with a decrease in the specific consumption of raw materials and energy resources, the mileage of the formaldehyde-water strengthening columns from cleaning to cleaning is somewhat increased due to a decrease in the amount of decomposed organic compounds (DMD, TMK, unsaturated alcohols and methylal) and the formation of them along with high boiling products polymers and resins.

A comparison of indicators of existing and proposed schemes is given below: Name Existing method The proposed method Example 1 Example 2 Example 3 1. Supply to the column strengthening formaldehyde water, kg / h: - raffinate columns partial extraction column evaporation of the aqueous layer 32300 32300 32300 - formaldehyde water from the DMD decomposition unit 75200 75200 75200 - distillate formalin strengthening columns 6100 6100 6100 2. Total filed, 113600 113600 113600 including organic compounds (DMD, TMK, NS, methylal), kg / h: - in the raffinate of the partial extraction column 418 418 418 - in formaldehyde water after decomposition of DMD 75 75 75 3. Total received, kg / h: - raffinate fed to the oxidation of methanol to formaldehyde, 4300 3880 3840 including organic compounds 493 73 33 - extracted organic compounds - 420 460 4. The recovery rate of organic compounds,% - 85 93 5. The savings in terms of raw materials is, kg / t DMD, taking into account losses from rectification: methanol 5 7 isobutylene 8 9

Thus, the proposed scheme for the extraction of organic products from the water layer will reduce the specific consumption of isobutylene and methanol, stabilize and optimize the process of strengthening and demethanolation of formaldehyde, which, in turn, will reduce the loss of hydrocarbons and energy resources, as well as increase the yield of formaldehyde during the oxidation of methanol and several will increase the mileage of the formaldehyde water strengthening column from cleaning to cleaning.

Claims (1)

The method of separation of organic compounds (DMD, TMK, unsaturated alcohols, methylal) from the aqueous layer in the synthesis of dimethyldioxane in the production of isoprene from isobutylene and formaldehyde by partial extraction of these compounds from the overhead of the column of the aqueous layer isobutane-isobutylene fraction, supplied to the synthesis of dimethyldioxane in a weight ratio 1: 0.8-1.0, followed by strengthening and demeaning formaldehyde, characterized in that the raffinate of the partial extraction of organic compounds is subjected to additional extraction and the isobutane-isobutylene fraction in a ratio of 1: 0.5-0.8 and the resulting raffinate is combined with formaldehyde water obtained by decomposition of DMD, as well as with a distillate of a formalin strengthening column and fed to the strengthening and demethanolation of formaldehyde, followed by feeding the distillate of the formaldehyde demeanation column to extraction of the organic compounds concentrated in it with a return isobutane fraction isolated after synthesis of dimethyldioxane in a ratio of 1: 1.0-1.2, followed by feeding the extract again for isolation in zvratnoy isobutane fraction.