A method of producing isoprene

 

(57) Abstract:

The invention relates to an improved method of producing isoprene liquid-phase dehydration of 3-methyl-1,3-butanediol MBD at 105-135oIn the presence as catalyst of 2-40 wt.% phosphoric acid at a pressure of 1.1 to 3.0 ATA. Target product are distilled in the form of a distillate at 40-80oC. MBD served on dehydration in pure form or in the form of technical mixtures or in the form of an aqueous solution containing phosphoric acid. The method allows to increase the yield of isoprene to 92 mol.% on turned MBD. 2 C.p. f-crystals.

The invention relates to petrochemical technology, in particular the production of isoprene - industrial monomer for the manufacture of rubber.

A known method of producing isoprene liquid-phase catalytic dehydration of 3-methyl-1,3-butanediol (MBD) in aqueous solution at 80 - 150oC in the presence of a hydrocarbon solvent and trimethylarsine. As catalyst, use oxalic acid in the amount of 18 wt.% in aqueous solution or sulfuric acid - 2 wt.%. The yield of isoprene reaches of 93.5 mol.% on turned MBD /EN, 681735C, 1996/. However, this method requires the additional use of trimethylarsine, the WMD of the invention is a method of producing isoprene liquid-phase dehydration MBD in aqueous solution at elevated temperature using as catalyst oxalic acid in the presence of potassium oxalate at a weight ratio of acid oxalate, equal to 1:1.5 to 2.5. Isoprene highlights by distillation at atmospheric pressure in the form of a distillate at a temperature of 34oC. the Yield of isoprene is 82 mol. % converted MBD /SU, 1034365 A1, 1987/. However, the yield of isoprene is not high enough.

The present invention is to increase the yield of isoprene by increasing the selectivity of the dehydration MBD, as well as selection of distillate under conditions that reduce contact with the distillate impurities.

The technical result is achieved in that the dehydration MBD is carried out in aqueous medium in the presence as catalyst of phosphoric acid at a concentration of 2 to 40 wt.% in the reaction mixture, the target product are distilled at a pressure of 1.1 to 3.0 ATA in the form of distillate, which is taken at a temperature of 40 - 80oC.

Distinctive features of the process is to conduct dehydration MBD in the presence as catalyst of phosphoric acid at a concentration of 2 to 40 wt. % in the reaction mixture. Another difference is that the distillation is carried out at an elevated pressure of 1.1 to 3.0 ATA (atmosphere absolute). Another difference is that the distillate containing isoprene, taken at a temperature of 40 - 80oC.

The former is the wt.% the selectivity of the formation of isoprene. Selectivity decreases with further increase in the concentration of phosphoric acid due to the increased formation of high-boiling by-products. Compared with phosphoric acid when using other acid catalysts such as sulfuric, oxalic acid, benzosulfimide, achieved the worst results in terms of selectivity.

The increase in the yield of isoprene also contribute to carrying out the distillation at a pressure of 1.1 to 3.0 ATA that allows you to increase the relative volatility of isoprene, and the selection of the distillate at a temperature of 40 - 80oC, which reduces contact with the distillate viscida isoamylenes spirits.

The dehydration is carried out at a temperature of 105 - 135oC. MBD served on dehydration in pure form or in the form of technical mixtures obtained directly after synthesis MBD by known methods, for example, /SU, 422719 A1, 1974 or SU, 574431 A1, 1977). The impurities in the technical product can be, for example, methanol, trimethylarsine, 4,4-dimethyl-1,3-dioxane, formaldehyde, isoamylene alcohols, dioxane alcohols, triola, peranovic alcohol. MBD is fed to the dehydration in the form of an aqueous solution containing phosphoric acid.

In this way as R pairs, for example, one or more devices of the tubular type, the devices column type - hollow, plate or filled with nozzle /Reaction-distant column/. In this apparatus, there is a simultaneous reaction of dehydration MBD with the formation of isoprene, which flows in an acidic aqueous medium, and the release of isoprene from the reaction zone by evaporation and transition in the vapor phase. Pair of products removed from the reaction-distant column at a temperature of 40 - 80oC, condense and thereby receive the distillate containing the target product.

From the obtained distillate allocate the rectification of pure isoprene, and the residue after the separation of isoprene return in the reaction-distant column.

In this way the yield of isoprene increases to 92 mol.% on turned MBD.

The possibility of carrying out the invention the following examples.

Example 1.

Synthesis of isoprene is carried out in the reaction-distant column (ROCK), equipped with bubble cap plates in quantities of 50 pieces and heated. In the cubic part of the ROCK, where 5 l water reaction mixtures containing 2 wt.% phosphoric acid, serves MBD at the rate of 900 g/H. IN ROCK support UP>C select the vaporized products, condense them in the refrigerator, and the distillate is collected in the tank. In the tank distillate splits into the water layer, which return in the ROCK, and oil layer from which further rectification emit pure isoprene in the amount of 530 g/h CC residue after the separation of isoprene return to the ROCK.

To save the material balance of the process water and high-boiling by-products (WFP) of the ROCK deduce a part of the reaction water mixture in the amount of 377,6 g/h, and at the same time in ROCK type phosphoric acid in the amount of 7.6 g/h

Conversion MBD is 98,9%. The yield of isoprene is 91,0 mol.% on turned MBD.

Example 2.

The process is carried out analogously to example 1 with the difference that the concentration of phosphoric acid in the reaction water mixture is 40 wt.%, MBD is served with a speed of 2500 g/h, pressure is 1.1 ATA, the boiling point of the reaction water mixture 105oC temperature selection distillate 40oC.

Conversion MBD 99.5%. The yield of isoprene is 90,6 mol.% on turned MBD.

Example 3.

The process is carried out analogously to example 1 with the difference that the concentration of phosphate to the Noi water mixture 119oC temperature selection distillate 56oC, ROCK with a speed of 3000 g/h serves a technical mixture after synthesis MBD following composition, wt.%:

MBD - OF 92.7

dioxane alcohols - 3,9

trioli - 2,6

peranovic alcohol - 0,8

Conversion MBD is 99.1%. The yield of isoprene 91.7 mol.% on turned MBD.

Example 4.

The process is carried out analogously to example 1 with the difference that the concentration of phosphoric acid in the reaction water mixture is 30 wt.%, the pressure is 1.2 ATA, the boiling point of the reaction water mixture 110oC temperature selection distillate 50oC, ROCK with a speed of 3200 g/h serves a technical mixture after synthesis MBD following composition, wt.%:

MBD - 94,2

dimethyldioxanes - 1,5

methanol - 0,5

formaldehyde - 0,3

dioxane alcohols - 1,0

water - 2,5

Conversion of MBD was 99.4%. The yield of isoprene is 92,0 mol.% on turned MBD.

Example 5.

The process is carried out analogously to example 1 with the difference that in the ROCK with a speed of 4000 g/h serves aqueous solution after synthesis MBD following composition, wt.%:

water - 73,7

phosphoric acid - 15,0

MBD - 9,0

dimethyldioxanes - 0,2

trimethylaminuria water reaction mixture 128oC temperature selection distillate 67oC.

Conversion MBD is 88.6%. The yield of isoprene is of 92.1 mol.% on turned MBD.

Example 6.

The process is carried out analogously to example 1 with the difference that in the ROCK with a speed of 5000 g/h serves aqueous solution after synthesis MBD following composition, wt.%:

water - 59,5

phosphoric acid - 25,4

MBD - 5,5

dimethyldioxanes - 3,0

trimethylamino - 5,5

by-products - 0,8

formaldehyde - 0,3

In the ROCK pressure is 2.0 ATA, the boiling point of the reaction water mixture 123oC temperature selection distillate 63oC.

Conversion of MBD is to 90.4%. The yield of isoprene is 92,3 mol.% on turned MBD.

1. A method of producing isoprene liquid-phase dehydration of 3-methyl-1, 3-butanediol in an aqueous medium at an elevated temperature in the presence of an acid catalyst with the separation of the target product by distillation in the form of distillate, characterized in that the catalyst used phosphoric acid at a concentration of 2 to 40 wt.% in the reaction mixture, the distillation is carried out at a pressure of 1.1 to 3.0 ATA and the distillate is taken at 40 - 80oC.

2. The method according to p. 1, characterized in that the Chol served on dehydration in its pure form, or in the form of technical mixtures or in the form of an aqueous solution containing phosphoric acid.

 

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SUBSTANCE: invention relates to production of isoprene for use in synthesis of isoprene rubber and butyl rubber used in tire industry and manufacture of general mechanical rubber goods. In the method of invention, isoprene is obtained by decomposition of 4,4-dimethyl-1,3-dioxan in reactors caused by interaction of isobutylene-containing C4 fraction with aqueous formaldehyde solution (prepared by oxidation of methanol) at elevated temperature and pressure in presence of acid catalyst to form reaction medium composed of oil and water layers followed by separation of oil layer into unreacted C4-hydrocarbons and 4,4-dimethyl-1,3-dioxan by rectification leaving bottom residue containing dioxan alcohols (high-boiling by-products to be processed into additional product), separation of water layer, condensation of 4,4-dimethyl-1,3-dioxan decomposition contact gas, and recovery of desired isoprene by rectification. Bottom residue is processed at residual pressure 0.002-0.010 MPa, elevated reflux ratio equal to 2.0-5.0, and continuous circulation of bottom fluid under lower plate of rectification column at weight ratio of circulating bottom fluid as additional product to bottom residue of 4,4-dimethyl-1,3-dioxan rectification equal to 20-35. Column distillate - low-boiling by-products are sent to 4,4-dimethyl-1,3-dioxan synthesis reactors or subjected to catalytic decomposition, separately or jointly with 4,4-dimethyl-1,3-dioxan.

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SUBSTANCE: invention relates to production of isoprene for use in synthesis of isoprene rubber, butyl rubber, and isoprene-containing polymers used in tire industry and manufacture of general mechanical rubber goods. In the method of invention, isoprene is obtained by decomposition of 4,4-dimethyl-1,3-dioxan on calcium phosphate catalyst comprising synthesis of 4,4-dimethyl-1,3-dioxan by interaction of isobutylene-containing C4 fraction with formaldehyde-containing blend based on methanol-free formalin obtained by oxidation of methanol followed by rectification of formalin, accomplished at elevated temperature and pressure in presence of acid catalyst followed by separation of reaction medium into oil and water layers including extraction of organic products from water layer, isolation of 4,4-dimethyl-1,3-dioxan, unreacted C4-hydrocarbons, and high-boiling by-products from oil layer, condensation of 4,4-dimethyl-1,3-dioxan decomposition contact gas and isolating from condensate isoprene, unreacted 4,4-dimethyl-1,3-dioxan, recycling isobutylene and formaldehyde-containing water, performing also withdrawal of extracted water layer to be vacuum evaporated followed by sending evaporated water layer to preparation of formaldehyde-containing blend. Evaporation of extracted water layer containing acid catalyst is carried out at temperature of boiler wall in rectification column 80-105°C and residual pressure 0.015-0.025 MPa. Distillate is mixed with above-indicated formaldehyde-containing water and resulting mixture is subjected to two-step concentration of formaldehyde. Second-step distillate, namely recycle methanol, is sent to oxidation zone. Bottom residues of the second step of formaldehyde concentration and those of the extracted water layer evaporation are combined with methanol-free formaldehyde and acid catalyst continuously supplied as replenishment, after which used as formaldehyde-containing blend in the 4,4-dimethyl-1,3-dioxan synthesis. Concentration of acid catalyst is maintained between 1.60 and 1.75 wt %.

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2 cl, 1 dwg, 5 ex

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SUBSTANCE: tert-butyl alcohol, 4,4-dimethyl-1,3-dioxan and/or formaldehyde are fed into reaction zone in the form of homogenous mixture with recycled aqueous solution of acid catalyst, which mixture is preliminarily prepared in a separate apparatus at heated to 80-90°C and said aqueous acid solution freed of organics is preliminarily passed through cationite at volume flow rate 15-20 h-1. Process is conducted at elevated temperature and pressure exceeding pressure of water steam at this temperature, and at molar excess of tert-butyl alcohol relative to summary amount of formaldehyde in hollow apparatus mounted coaxially over shell-and-tube heat exchanger and provided with circulation pipe connecting top part of hollow apparatus to bottom part of shell-and-tube heat exchanger, diameter of this pipe being at least three times lass than that of hollow reactor. Circulating factor at least 100 h-1 is achieved with the aid of pump installed in feed supply line into bottom part of hollow apparatus. Reaction products and part of aqueous acid solution are removed from the top of hollow apparatus in one stream passed into separator.

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SUBSTANCE: isoprene is produced via reaction of tert-butyl alcohol with 4,4-dimethyl-1,3-dioxane and/or formaldehyde in one reaction zone, namely upright hollow apparatus with, disposed inside it, shell-and-tube heat exchanger dividing apparatus space into top and bottom parts. Reaction mixture circulates through tubes of this apparatus in liquid-phase mode in presence of aqueous acid catalyst solution, at elevated temperature and pressure exceeding water vapor pressure at the same temperature, using molar excess of tert-butyl alcohol relative to summary formaldehyde equivalent. Reaction products are continuously withdrawn from reaction zone and subjected to condensation. Water phase is extracted with condensed distillate to remove organics, wherefrom isobutylene is recovered and sent to production of tert-butyl alcohol. Hollow apparatus is provided with one or two external circulation tubes connecting top and bottom spaces of apparatus, volume ratio of which is (2-2.5):1, respectively. Diameter of external tubes is at least fivefold greater that that of heat exchanger tubes. Feed is supplied to reaction zone in the form of homogenous mixture, preliminarily prepared in a separate apparatus and preheated to 80-90°C, together with recycle aqueous catalyst solution, the latter having been preliminarily freed of organics and passed at flow rate 15-20 h-1 through cationite. Process is carried out at circulation rate at least 100 h-1.

EFFECT: simplified technology and increased yield of isoprene.

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SUBSTANCE: isoamylenes are subjected to dehydrogenation in presence of overheated water steam and catalyst containing, wt %: potassium oxide and/or lithium oxide, and/or rubidium oxide, and/or cesium oxide, 10-40; cerium(IV) oxide 2-20; magnesium oxide 2-10; calcium carbonate 2-10; sulfur 0.2-5; and ferric oxide - the rest.

EFFECT: increased isoamylene dehydrogenation degree due to increased catalyst selectivity with regard to isoprene and prolonged service time of catalyst.

2 tbl, 22 ex

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