RU2167138C2 - Method of synthesis of isoprene from isobutene-containing hydrocarbon mixtures and formaldehyde - Google Patents

Abstract

FIELD: organic chemistry, chemical technology. SUBSTANCE: invention relates to method of synthesis of isoprene from isobutene-containing C₄-hydrocarbon mixtures and formaldehyde by chemical conversion in the presence of acid water-soluble and/or solid catalyst in at least three reaction zones. In the first zone isobutene is extracted from hydrocarbon mixture by hydration process; in the second zone formation of semiproducts is carried out that are able to decompose further to isoprene and in the third zone the decomposition of semiproducts is carried out followed by separation of reaction mixtures obtained in this zone and their recirculation of at least part of isobutene to be isolated into the zone of synthesis of semiproducts. Part of the parent formaldehyde is fed to the zone of isobutene extraction, reaction mass of indicated zone is stratified for an aqueous and organic flows. An aqueous flow containing at least tert.-butanol, 3-methylbutanediol-1,3 and 4,4-dimethyldioxane-1,3 and other part of the parent formaldehyde is fed to the zone of semiproducts synthesis. An aqueous and organic flows are removed from the zone of semiproducts synthesis that are fed to the decomposition zone, possibly passing their through the hydrolysis zone. Organic flow in isobutene extraction zone is fed to the distillation off unit of C₄-hydrocarbons and residue after distillation off of C₄-hydrocarbons containing at least tert.-butanol and 4,4-dimethyldioxane-1,3 is fed to the zone of synthesis of semiproducts and/or the zone of decomposition, and/or the zone of hydrolysis. Possible variant involves addition of nontertiary alcohol with carbon number atoms from 2 to 6 to the zone of isobutene extraction. EFFECT: optimal technological relationship between processes of isobutene extraction and isoprene synthesis, simplified method, improved efficiency. 8 cl, 2 tbl, 2 dwg, 2 ex

Description

 The invention relates to the field of production of isoprene - a monomer for synthetic rubbers.

 More specifically, the invention relates to the field of production of isoprene from isobutene-containing hydrocarbon mixtures and formaldehyde.

The known method [in the book. Synthetic rubber, L., Chemistry, 1976, p. 696-709] obtaining isoprene from isobutene-containing mixtures of C ₄ hydrocarbons and formaldehyde by contacting them in the presence of aqueous solutions of strong acids with the predominant formation of 4,4-dimethyldioxane-1,3, followed by separation of the reaction mixtures, distillation of unreacted hydrocarbons, isolation of concentrated 4.4 -dimethyldioxane-1,3, its thermocatalytic decomposition and the allocation of isoprene from the resulting mixture.

The method has significant disadvantages:
- the synthesis process of 4,4-dimethyldioxane-1,3 is carried out with a large molar excess of formaldehyde relative to isobutene (≈2: 1) and a high concentration of formaldehyde. As a result, it is necessary to include an expensive unit for the isolation and concentration of formaldehyde in the process scheme;
- the method requires costs for the allocation of concentrated 4,4-dimethyldioxane-1,3;
- gas-phase decomposition of 4,4-dimethyldioxane-1,3 is carried out at high temperature (370-390 ^o C) and is very energy-intensive.

The known method [US Pat. RU N 1216940, March 20, 1996]] producing isoprene from concentrated isobutene and / or tertiary butanol and formaldehyde in the presence of an acid catalyst in two reactors connected in series, operating at different temperatures: the first, preferably at 100-130 ^o C and the second, preferably at 165 -180 ^o C; in the first reactor, the formation of intermediates predominantly capable of further decomposing with the formation of isoprene occurs, and in the second, their decomposition with the formation and subsequent release of isoprene occurs.

The disadvantage of this method is the need to use concentrated isobutene and / or tert-butanol. Obtaining them from available raw material sources (and they are usually isobutene-containing mixtures of C ₄ hydrocarbons) requires a complex and very energy-intensive procedure.

Known and closest to our proposed invention method [US Pat. RU N 2099319, 12/20/1997] the production of isoprene by reacting isobutene contained in the C ₄ hydrocarbon fraction with water in the presence of an acid catalyst, followed by isolation of the resulting tert-butanol by distillation and reacting it with formaldehyde in the presence of an acid catalyst at an elevated temperature and pressure, followed by separation of the reaction mass and the allocation of isobutene, recycled to the isoprene synthesis zone, and the resulting isoprene. Moreover, as can be seen from all the examples cited in RU 2099319, the synthesis of isoprene from the isolated tert-butanol and the introduced formaldehyde is carried out in two consecutive reaction zones, in the first of which (intermediates operating at a lower temperature than the subsequent zone) are formed, including 4,4-dimethyldioxan-1,3, and in the second they decompose with the formation of isoprene and isobutene, accompanied by the formation of also by-products.

 In general, taking into account the interaction zone of isobutene with water, isoprene is produced using at least three reaction zones. As for acid catalysts, in US Pat. RU 2099319 (in the examples), both water-soluble and solid acid catalysts are used.

A significant disadvantage of the method according to US Pat. RU 2099319 are high costs in the area of extraction of isobutene from the hydrocarbon (s) mixture (s) by hydration, carried out with the supply of a large amount of water. In all examples of this patent, when extracting isobutene from a C ₄ mixture with its 42.6% content, 14,500 g of pure water per 2,400 g of C ₄ mixture are fed into the hydration zone (i.e. 142 g of water per 1 g of isobutene, contained in the original C ₄ mixture). The tert-butanol is extracted from the hydration mixture by a very complicated procedure, including extraction of a part of tert-butanol from the aqueous solution with an isobutene stream and then two rectifications: one to distill the hydrocarbons (isobutene) from the extracted tert-butanol and the other to distill the remaining tert-butanol from an aqueous solution (in the form of an azeotrope with water).

 We unexpectedly found a very economical and simple method based on the use of the optimal technological relationship between the processes of isobutene extraction and isoprene synthesis.

We propose a method for producing isoprene from isobutene-containing C ₄ hydrocarbon mixtures and formaldehyde by chemical conversion in the presence of an acidic water-soluble and / or solid catalyst in at least three reaction zones, in the first of which isobutene is extracted from the hydrocarbon mixture by hydration, in the second - predominant the formation of intermediates capable of further decomposing into isoprene, and the third - the predominant decomposition of intermediates with subsequent separation obtained in this non-reaction mixtures and recirculation of at least a portion of the isobutene emitted to the intermediate synthesis zone, namely that part of the starting formaldehyde is fed to the isobutene extraction zone, the reaction mass of this zone is separated into aqueous and organic streams, an aqueous stream containing at least tert-butanol, 3-methylbutanediol-1,3 and 4,4-dimethyldioxane-1,3, and the rest of the starting formaldehyde are sent to the synthesis zone of intermediates, aqueous and organic streams that direct into the decomposition zone, possibly preliminarily passing through the hydrolysis zone, and the organic stream of the isobutene extraction zone is fed to the C ₄ hydrocarbon stripping unit and the residue after the C ₄ hydrocarbon stripping, containing at least tert-butanol and 4,4-dimethyldioxane-1,3, is directed into the synthesis zone of intermediates and / or the decomposition zone, and / or the hydrolysis zone.

As a variant, a method is proposed, namely, that a non-tertiary alcohol with a number of carbon atoms from 2 to 6 is introduced into the isobutene extraction zone, and after the C ₄ hydrocarbons are removed from the organic stream of the specified zone, the residue containing at least tert-butanol, 4,4- dimethyldioxane-1,3, a non-tertiary alcohol and a non-tertiary alcohol tert-butyl ether are sent to the synthesis zone of the intermediates and / or to the zone of their decomposition, and / or to the hydrolysis zone.

Alternatively, a method is proposed that consists in the partial evaporation of the reaction mass in the isobutene recovery zone and the vaporized stream is returned after condensation to the inlet of the isobutene extraction zone and / or sent to the C ₄ hydrocarbon stripping unit.

 Alternatively, a method is proposed that consists in the fact that at least part of the isobutene is distilled off from the organic stream into the decomposition zone from the organic stream, which is returned to the intermediate synthesis zone, and methylal and methanol are possibly distilled from the aqueous stream from the intermediate synthesis zone.

 Alternatively, a method is proposed that consists in the fact that after separation of the reaction mixtures removed from the decomposition zone of the intermediates, non-tertiary alcohol and possibly part of tert-butanol are returned to the isobutene recovery zone.

 Alternatively, a method is proposed that consists in the fact that in the decomposition zone, incomplete decomposition of 4,4-dimethyldioxane-1,3 is carried out, and after separation of the organic mixture (s) removed from the decomposition zone, the undecomposed part 4,4 β-dimethyldioxane-1,3 and, possibly, by-products are returned to the intermediate synthesis zone and / or the isobutene recovery zone and / or the decomposition zone.

 Alternatively, a method is proposed, which consists in the fact that in the decomposition zone, the resulting isoprene is continuously distilled off with at least part of the water.

 Alternatively, a method is proposed in which immobilized forms of strong acids, for example sulfocationites, and / or water-soluble strong acids with the addition of corrosion inhibitors, the aqueous solution of which from the decomposition zone are returned to the isobutene recovery zone and / or are used as catalysts in the reaction zones zone for the synthesis of intermediates.

 You can use the proposed options in various mutual combinations, subject to the main essence of the invention according to claim 1 of the formula.

 The names of the reaction zones used in the claims and the description of the invention are given conditionally based on the main objective function of each zone. In fact, in the reaction zones, two or more functions are combined. In the first reaction zone, the functions of extracting isobutene and obtaining at least a portion of the intermediates capable of further decomposing with the formation of isoprene, as well as the conversion of intermediates and by-products (if they are recycled from the separation unit), for example, hydrolysis of 4,4-dimethyldioxane-1,3 in 3-methylbutanediol-1,3. In other reaction zones, functions can also combine and various reactions proceed: hydration and dehydration, synthesis and decomposition of intermediates, hydrolysis, isobutenolysis, etc.

 The hydrolysis zone (where the isobutenolysis of 4,4-dimethyldioxane-1,3 can also occur) is also essentially a synthesis zone for intermediates capable of decomposing into isoprene, mainly 3-methylbutanediol-1,3, decomposing into isoprene more easily and with less side formation products than 4,4-dimethyldioxane-1,3. However, given the specifics of this zone, we usually indicate it separately.

 As the catalysts, highly acidic solid catalysts can be used, for example cation exchangers (in particular, sulfation cation exchangers) and / or strong water-soluble acids, for example phosphoric, boric, oxalic, sulfuric, or mixtures thereof. The simultaneous use of water-soluble (s) and solid (s) catalyst (s). It is also possible to use the same catalyst or different acidic (water-soluble and / or solid) catalysts in different reaction zones.

 The starting formaldehyde is preferably supplied as an aqueous solution (formalin).

 Various substances or mixtures of substances can be used as corrosion inhibitors in the aqueous solution of an acid catalyst: amines, amino alcohols, pyridines, hexamethylenetetramine, imidozolines, chemical bases, condensation products of nitrogen-containing compounds with aldehydes and ketones, alkylidene diphosphonic acids, etc.

 Reactors of various types with different methods for supplying and removing heat can be used: once-through, counter-current, recirculation, reaction-distillation, reaction-extraction, etc.

 Various distribution (including nozzles) and mixing devices can be used both in reactors and in joint feed streams.

 It is possible to use several zones of predominant formation of intermediates that can further decompose into isoprene, for example, the inclusion of zones (s), where hydrolysis or hydroisobutenolysis of intermediates, in particular 4,4-dimethyldioxane-1,3, is carried out in the presence of water and, possibly, isobutene obtaining more 3-methylbutanediol-1,3, the subsequent decomposition of which into isoprene proceeds more easily than 4,4-dimethyldioxane-1,3, and with less formation of by-products.

 The use of the invention is illustrated in FIG. 1-2 and examples 1-2. The figures and examples given do not exhaust all possible techniques and schemes for implementing the invention, subject to the essence of the invention set forth in its claims.

Designations of flows in the drawings and examples:
F is the initial hydrocarbon mixture, RF is an aqueous solution of formaldehyde, RK is a catalyst solution, B is water, IB is isobutene, TB is tert-butanol, NTS is a non-tretic alcohol, DMD is 4,4-dimethyldioxane-1,3, MBD is 3-methylbutanediol-1,3, MDHP - fraction containing methyldihydropyran, WFP - a mixture of high-boiling by-products, MM - methanol-methyl mixture, P - hydrocarbon solvent.

Designations of devices by target (primary) functions:
RI is the isobutene extraction reactor from the hydrocarbon mixture, RS is the intermediate product synthesis reactor, PP is the isoprene decomposition reactor, RG is the hydrolysis reactor, K is distillation columns, and O is a settling tank.

 According to FIG. 1 hydrocarbon mixture F (stream 1) is fed to an isobutene recovery reactor. It also contains a return water stream 2, possibly containing an acid catalyst and corrosion inhibitors, and an aqueous solution of formaldehyde (stream 3), as well as, possibly, a stream of non-tertiary alcohol (s) NTS (stream 4) and additional (compensating losses) water flows (stream 2A) and an acid solution of PK (stream 2B).

 After leaving the reaction zone, the mixture is delaminated and stream 5, containing water and the components dissolved in it, enters the RS synthesis reactor, and organic stream 6 enters the distillation column K.

 A stream of unreacted hydrocarbons is withdrawn from the top of the column (stream 7), and a stream containing predominantly tert-butanol, DMD and, possibly, non-tertiary alcohol (stream 8), which is preferably fed to the RS synthesis reactor and / or PP decomposition reactor, is withdrawn from the cube.

 An isobutene stream recycled from the separation unit (stream 15A), preferably part of an aqueous formaldehyde solution (stream 3 '), and possibly streams recycled from the separation unit containing tert-butanol, DMD, MDHP and other by-products, are also introduced into the RS reactor. An “aqueous” stream 9 and an organic stream 10 are removed from the RS reactor, which are sent to the PP decomposition reactor, possibly having previously passed through the RG hydrolysis reactor (shown by a dotted line). Together with the indicated streams, a portion of the isobutene stream recycled from the separation unit (stream 15B) can be directed to the PP (possibly previously to the WP).

 Preferably, a stream 11 containing a hydrocarbon solvent is also introduced into the PP.

 From the reactor PP, a liquid-phase “water” (“water-acid”) stream 12 is discharged, which is preferably directed, after distillation of part of the water and purification (indicated as a purification unit), to the RI and / or RS, and the gas-phase stream 13 (containing isoprene, isobutene and a number of oxygen-containing substances) and a liquid-phase organic stream 14. Streams 13 and 14 are sent to a separation unit, including several distillation zones and possibly extraction zones.

 Several streams with a predominant content of certain substances are removed from the separation unit: isobutene IS (stream 15), isoprene (stream 16), tert-butanol TB (stream 17), MDHP (stream 18), water B (stream 19), non-tretic alcohol NTS (stream 20), the runway (stream 21), and possibly DMD (stream 22) and a hydrocarbon solvent (stream 23).

 According to FIG. 2, in contrast to FIG. 1, the process in the isobutene extraction reactor (RI) is carried out with partial evaporation of the reaction mass. Feed streams are denoted similarly to FIG. 1. A vaporous stream 6 'is withdrawn from the top of the RI reactor, which, after condensation, is returned to the RI inlet (stream 6A) or / and sent to the K-1 distillation column (stream 6B). In K-1 serves the organic layer (stream 6), obtained by separation in the sump-separator "O" of the liquid mass entering it from the reactor RI.

 The aqueous layer (stream 5) from the sump "O" is fed to the synthesis reactor RS.

 Also, unlike FIG. 1, the organic stream 10 and possibly the aqueous stream 9 removed from the RS synthesis reactor are rectified in columns K-2 and K-3, respectively. The methanol-methyl mixture MM (stream 9A) is distilled off from stream 9, and isobutene-containing stream 10A is returned from stream 10, which is returned to the PC inlet. The bottoms flows (9B and 10B, respectively) from K-2 and K-3 are sent to the PP reactor.

 The use of the PP reactor with the distillation of the main products from above and the withdrawal of the "water" stream from the cube is shown.

 Example 1

 Processing is carried out in accordance with FIG. 1.

 An isobutane-isobutene mixture obtained by isobutane dehydrogenation and containing 45% isobutene is used as the source of isobutene.

 Formaldehyde is supplied as a 40% solution in water.

 As a catalyst in the reactors RI, RS and PP placed sulfonation Amberlist-35.

 Technological data are given in table. 1.

 Example 2

 Processing is carried out in accordance with FIG. 2.

As a source of isobutene, a C ₄ pyrolysis fraction (after recovery of 1,3-butadiene) containing 45% isobutene is used.

 Formaldehyde is supplied as a 40% solution in water.

 As a catalyst, phosphoric acid (FC) with the addition of corrosion inhibitors is used.

 As a substance that increases the mutual solubility of hydrocarbons and water, n-butanol is introduced into the RI reactor.

As a hydrocarbon solvent in the reactor PP use a mixture of alkenes with a boiling point of 150-200 ^o C.

 Technological data are given in table. 2.

Claims (8)

1. A method of producing isoprene from isobutene-containing C ₄ hydrocarbon mixtures and formaldehyde by chemical conversion in the presence of an acidic water-soluble and / or solid catalyst in at least three reaction zones, in the first of which isobutene is extracted from the hydrocarbon mixture by hydration, in the second - predominant the formation of intermediates capable of further decomposing into isoprene, and the third is the predominant decomposition of intermediates with subsequent separation of the reaction obtained in this zone mixtures and recirculation of at least part of the isobutene emitted to the intermediate synthesis zone, characterized in that part of the initial formaldehyde is fed to the isobutene extraction zone, the reaction mass of this zone is separated into aqueous and organic streams, an aqueous stream containing at least tert-butanol, 3- methylbutanediol-1,3 and 4,4-dimethyldioxane-1,3, and the rest of the starting formaldehyde are sent to the synthesis zone of intermediates, aqueous and organic streams are removed from the synthesis zone of intermediate products, which are sent to the decomposition zone tions may previously by passing through the hydrolysis zone, the organic stream isobutene extraction zone is fed to the stripping unit C ₄ hydrocarbons and the residue after distillation of the C ₄ hydrocarbons containing at least tert-butanol and 4,4-dimethyl dioxane-1,3, directed to a zone for the synthesis of intermediates, and / or a decomposition zone, and / or a hydrolysis zone. 2. The method according to p. 1, characterized in that a non-tertiary alcohol is introduced into the isobutene extraction zone with the number of carbon atoms from 2 to 6 and, after distillation of C ₄ hydrocarbons from the organic stream of the specified zone, a residue containing at least tert-butanol, 4.4 -dimethyldioxane-1,3, non-tertiary alcohol and tert-butyl ether of non-tertiary alcohol are sent to the synthesis zone of the intermediates, and / or to the zone of their decomposition, and / or to the hydrolysis zone. 3. The method according to claim 1, characterized in that in the extraction zone of isobutene, partial evaporation of the reaction mass is carried out and the vaporized stream is returned after condensation to the entrance to the extraction zone of isobutene and / or sent to the C ₄ hydrocarbon stripping unit.  4. The method according to claim 1, characterized in that at least part of isobutene is distilled off from the organic stream of the intermediate synthesis zone before being fed to the decomposition zone, which is returned to the intermediate synthesis zone, and methylal and methanol are possibly distilled from the aqueous stream of the intermediate synthesis zone.  5. The method according to claims 1 and 2, characterized in that after separation of the reaction mixtures withdrawn from the decomposition zone of the intermediates, non-tertiary alcohol and, possibly, part of tert-butanol are returned to the isobutene extraction zone.  6. The method according to claim 1, characterized in that in the decomposition zone carry out the incomplete decomposition of 4,4-dimethyldioxane-1,3 and after separation of the organic substances removed from the decomposition zone, the undecomposed part of 4,4-dimethyldioxane-1,3 and perhaps the by-products are returned to the intermediate synthesis zone, and / or to the isobutene recovery zone, and / or to the decomposition zone.  7. The method according to claim 1, characterized in that in the decomposition zone carry out continuous distillation of the forming isoprene with at least part of the water.  8. The method according to claim 1, characterized in that the catalysts in the reaction zones use immobilized forms of strong acids, for example sulfocationites, and / or water-soluble strong acids with the addition of corrosion inhibitors, the aqueous solution of which from the decomposition zone is returned to the isobutene recovery zone and / or into the synthesis zone of intermediates.

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