RU2230054C2 - Method for preparing isoprene - Google Patents

Abstract

FIELD: organic chemistry, chemical technology. SUBSTANCE: invention proposes a method for preparing isoprene based on liquid-phase interaction of isobutylene or isobutylene-containing fractions of C₄-hydrocarbons with formaldehyde or 4,4-dimethyldioxane-1,3 an aqueous solution. Process is carried out in two reaction zones. In the first zone isobutylene hydration is carried out at 70-90^oC under pressure 15-20 atm in the presence of a solid cationite catalyst and in feeding part of the parent solution of formaldehyde or 4,4-dimethyldioxane-1,3 to this zone. The parent raw is fed to this zone as preliminary prepared liquid homogenous mixtures "trimethylcarbinol-C₄-water-hydrocarbons-formaldehyde" or "trimethylcarbinol-C₄-hydrocarbons-water-4,4-dimethyldioxane-1,3" taken in the definite ratio and taking into account the molar ratio water : isobutylene = 0.9, not less. After distilling off non-converted C₄-hydrocarbons the prepared reaction mixture is fed to the second reaction zone together with the remained part of the parent formaldehyde or 4,4-dimethyldioxane-1,3. In the second zone the process is carried out at temperature 150-170^oC under pressure 5-7 atm in the presence of water-soluble acidic catalyst and in continuous distilling off highly volatile reaction products and part of water. Isobutylene isolated from reaction mass of the second reaction zone is recirculated to the first reaction zone. Homogenous raw is prepared by mixing the parent components under pressure followed by stirring and separation of isolated aqueous phase. Utilization of this raw results to minimizing water consumption in isobutylene hydration and to enhance activity of cationite catalyst sharply that provides preparing part of isoprene and its precursors even in the first reaction zone. Except for, invention provides simplifying the process technology and enhancing its selectivity. EFFECT: improved preparing method. 2 cl, 2 tbl, 6 ex

Description

The present invention relates to the field of basic organic and petrochemical synthesis, more specifically to methods for producing isoprene from isobutylene and formaldehyde.

Numerous methods are known for producing isoprene from isobutylene and formaldehyde in the presence of acid catalysts, carried out through various intermediates. The essence of these methods is that the starting materials react in the presence of acid at an elevated temperature and pressure, ensuring that the reactants remain in the liquid phase, with the formation of intermediate products containing 5 or 6 C-atoms, which then decompose under the influence of temperature and catalysts to form isoprene. The most widely used method in the industry is the synthesis of isoprene through an intermediate stage of the formation of 4,4-dimethyl-1,3-dioxane (DMD), which includes the stage of liquid-phase condensation of isobutylene contained in the C ₄ hydrocarbon fraction with formaldehyde in the form of 20-40% aqueous solution, followed by isolation of the resulting DMD and its decomposition over a solid acid catalyst in the presence of water vapor [Ogorodnikov SK, Idlis GS Isoprene production. L .: Chemistry, 1973, p.12-91]. The application of this method provides the production of isoprene of monomeric purity, allows you to combine the production of DMD with the extraction of isobutylene from C ₄ fractions, provides high performance contact equipment.

However, the principal disadvantage of this method is the increased energy consumption associated with the consumption of superheated water vapor at the stage of DMD decomposition (wt. Ratio of H ₂ O / DMD of at least 2.0), catalyst regeneration and strengthening of diluted formalin solutions formed at both stages of the process, and also a high yield of high boiling point by-products (WFP), reaching 0.40-0.42 t / t of isoprene.

There is also known a method for producing isoprene from isobutylene and formaldehyde, which consists in the fact that isobutylene pre-isolated from the C ₄ fraction in a mixture with compounds easily forming isobutylene, for example trimethylcarbinol (TMK) or methyl tert-butyl ether (MTBE), is reacted with dilute formaldehyde solution at a molar ratio of iso-C ₄ H ₈ / CH ₂ O, greater than 2.5-3.0, and a temperature of 80-100 ° C, and then the entire reaction mass is transferred to a second reactor, where the intermediate products formed are precursors isoprene such ka to DMD, 3-methylbutanediol-1,3 (MBD), isobutenylcarbinol (IBC, 3-methyl-3-buten-1-ol), dioxane alcohols (DS), etc., decompose at a temperature of ≥130-140 ° С and 5-10 atm pressure with the formation of isoprene, which is distilled off from the reaction zone together with unconverted isobutylene, part of the water and volatile organic substances. This stream is freed from isobutylene and isoprene and recycled to the isoprene precursor synthesis reactor. Since the technology does not provide for the isolation of intermediate products, this process is conventionally called the one-stage synthesis of isoprene from isobutylene and formaldehyde (OIF) [Pavlov S.Yu., Surovtsev A.A. Chem. industry, 1997, No. 7, p. 466]. The method involves the preliminary separation of isobutylene from the C ₄ hydrocarbon fraction by hydrating it in a reactor filled with molded cation exchanger, with the resulting TMC and isobutylene being fed into stage I and II reactors, i.e. in fact, the technology of the UIF includes 3 steps.

The presence of excess isobutylene in the reaction mass in both reactors provides an almost complete conversion of formaldehyde, which eliminates the need for its recovery. The application of this method also provides monomeric purity isoprene, significantly reduces energy consumption, compared with the two-stage process, however, the principal disadvantage of the UIF is the low productivity of the contact equipment associated with the use of a large excess of isobutylene (molar ratio of iso-C ₄ H ₈ / CH ₂ O not less than 2.5-3.0). The low conversion of isobutylene, not exceeding 33-40%, leads to significant costs for condensation and the return of the unconverted olefin to the reaction zone. In addition, the need for the use of large amounts of isobutylene causes an increased load on the hydrocarbon phase in the hydration reactor of this olefin at the stage of its separation from the C ₄ fraction.

The disadvantage of this method is the need to supply large quantities of water to the hydration zone. It is sufficient to indicate that in order to extract the olefin from the C ₄ fraction containing 42% isobutylene, it is necessary to supply 142 g of water per 1 g of isobutylene [US Pat. RF №2099319, publ. 12/20/1997].

Improved OIF technology options are also known, which provide for maintaining process parameters (temperature, amount of catalyst and contact time) in the decomposition zone of intermediate products at a level that ensures MBD conversion of at least 90-95%, and DMD conversion of no more than 80%, and return of non-converted DMD mixed with TMK or individually in the synthesis zone [US Pat. RF №2131863, publ. 06/27/1999]. The use of this technique allows to reduce the runway yield to 0.17-0.31 t / t isoprene.

The closest in technical essence to the present invention is a method for producing isoprene, which consists in the fact that the synthesis of isoprene is carried out in at least three reaction zones, namely, the isobutylene extraction zone by hydrating it at 85-90 ° C, the synthesis zone of intermediate products at 75 -90 ° C and the decomposition zone of the latter at 110-135 ° C. According to the prototype, the process in the first zone is carried out on a cation exchange catalyst, in the second and third zones in the presence of a water-soluble acid catalyst. A distinctive feature of the method is that C ₄ hydrocarbons, together with part of the starting formaldehyde in the form of a 40% aqueous solution, are introduced into the isobutylene recovery zone, in which, along with hydration, the reaction of formation of intermediate products proceeds, and then the reaction mass of the first zone is separated into the aqueous and organic phases, the unconverted C ₄ hydrocarbons are distilled off from the latter, and the bottom residue is sent to the second or third zone. The aqueous phase together with the second part of the starting formaldehyde is fed into the second zone, from where the reaction mass enters the third zone, from which the reaction products are removed for separation. Isobutylene isolated in the separation unit is returned to the intermediate synthesis zone, and isoprene is removed from the system.

The method provides several options for carrying out the process, in particular the inclusion in the technological scheme between the first and second zones of hydrolysis or isobutenolysis zones, in which the DMD formed in the first or second zones is converted into MBD, from which it is easier to obtain isoprene. As a possible option, it is also envisioned that a hydration zone is added to the hydration zone to increase the mutual solubility of isobutylene and an organic solvent in the form of a non-tertiary alcohol, for example n-butanol [US Pat. RF №2167138, publ. 03/20/2000 - prototype].

The use of this technology allows to reduce the amount of water supplied to the system to about 10-11 g / 1 g of isobutylene (calculated according to the data given in the examples of the prototype patent), which is 1-1.5 orders of magnitude less than in the analogue. However, the formation of isoprene does not proceed selectively enough and 0.20-0.23 tons of runways are formed per ton of isoprene. Together with 1 t of isoprene, 0.77-1.00 t of undecomposed DMD is removed from the system, the processing of which into isoprene also requires additional costs.

The introduction of n-butanol into the extraction zone of isobutylene practically does not affect the performance of the process and only complicates the process technology.

The objective of the proposed method is to improve the process by simplifying its technology, increasing productivity and increasing the yield of isoprene.

The problem is solved and the goals are achieved using the proposed method, the essence of which is as follows.

The isoprene synthesis process is carried out in two reaction zones, the main purpose of which is isobutylene hydration in TMC on an ion-exchange catalyst at 70-90 ° C and a pressure of 15-20 atm (zone I) and contacting the resulting TMC with formaldehyde and / or with DMD to form isoprene in the presence of a water-soluble acid catalyst at 150-170 ° C and a pressure of 5-7 atm (zone II). At the same time, along with isobutylene hydration, isoprene and its precursors are simultaneously synthesized in zone I, for which raw materials in the form of non-stratified, homogeneous mixtures of “TMK-hydrocarbons C _4- water-formaldehyde” or “TMK-hydrocarbons C” are fed to the ionite catalyst ₄ -water-DMD ”, in which the molar ratio of water: isobutylene is not less than 0.9. Then, at the exit from Zone I, unreacted C4 hydrocarbons are distilled off from the reaction mass, and the bottom residue containing at least isoprene, TMK, DMD, MBD, TMK ether and MBD (ETM), 4-methyl-5,6-dihydropyran (MDGP), together with the remainder of the starting formaldehyde or DMD, they are sent to zone II, in which there is an aqueous solution of an acid catalyst, for example phosphoric acid, and in which, under the above conditions, the formation and decomposition reactions of isoprene precursors occur simultaneously.

Isoprene is obtained in the reaction zone II by heating the reaction mass at a temperature of 10-15 ° C below the temperature of saturated water vapor at a given pressure and continuously removing isobutylene, isoprene, part of water and volatile organic compounds from the reaction zone. The distillate is cooled, separated into the organic and aqueous phases, and the organic compounds dissolved in it are extracted from the aqueous distillation phase using fresh C ₄ -fraction, and then it is discharged into ChZK. The organic portion of the overhead is mixed with the acid-containing bottoms of the second zone and organic products are extracted from the latter, after which they are returned to the second zone. Isobutylene, isoprene, volatile organic compounds are distilled off from the extract sequentially (returned to zone II), and the bottom residue is removed from the system. In contrast to the prototype, distilled isobutylene is returned only to reaction zone I and, thus, the only source of olefin, TMK, enters the isoprene production zone.

The raw material is prepared by mixing an aqueous solution of formaldehyde or a mixture of DMD-water with C ₄ hydrocarbons under pressure, ensuring the latter to remain in the liquid phase in the presence of TMC, selecting, if necessary, the exfoliated aqueous phase and analyzing the composition of the mixture. To achieve a technically acceptable conversion of isobutylene (at least 65-70%), it is necessary to maintain a molar ratio of water / isobutylene in a homogeneous feedstock close to 1.

The salient features of the invention are that the process is carried out in two reaction zones, the first of which feeds in the form of an unstratified homogeneous mixture of “TMK-hydrocarbons C _4- water-formaldehyde” or “TMK-hydrocarbons C ₄ -water- DMD ”, taken in a certain ratio established experimentally with the conservation of the molar ratio of water: isobutylene not less than 0.9.

Due to the homogeneity of the feed, the contact of the reactants is improved, and all reactions on the surface and in the pores of the ion-exchange catalyst proceed at a faster rate than reactions in a heterophase system. The catalytic activity of the cation exchanger itself also increases, since the proton of the sulfo group is not solvated by water molecules, but by less polar molecules of organic substances. The activity of cation exchanger increases so much that when formaldehyde or DMD is introduced into the I zone, significant amounts of isoprene and ETM are found in the reaction products, which are formed in negligible amounts in the traditional synthesis of DMD in the presence of water-soluble acid and at a higher temperature. All this allows us to achieve a sufficiently deep olefin conversion in the reaction zone I with the minimum amount of water required by stoichiometry, avoiding the formation of isobutylene dimers and significant amounts of by-products of the interaction of isobutylene with formaldehyde. As a result, a reaction mass arriving in zone II (after liberation from unreacted C ₄ hydrocarbons) contains, in addition to TMC, also isoprene and intermediates — sources of isoprene production, which significantly increases plant productivity.

The advantages of the proposed method, compared with the prototype, are:

- the effective use of a cation exchange catalyst, providing, firstly, a deep conversion of isobutylene to TMC (not less than 68-70%) with the minimum required amount of water entering the reactor, and, secondly, the formation of a part of isoprene and its precursors is already at the stage olefin hydration, due to which the productivity of the isoprene production unit increases;

- simplification of the synthesis technology of isoprene, carried out in two reaction zones, and not requiring the installation of additional zones (hydrolysis or isobutenolysis) and the introduction of an additional inert solvent into the system;

- higher process selectivity, due to which the runway yield per 1 ton of isoprene is reduced to 80-100 kg.

The advantages and industrial applicability of the invention are illustrated by the following examples.

EXAMPLE 1

A pre-prepared homogeneous mixture of the following composition is passed through a tube reactor filled with 250 cm of Lewatit K 2629 brand cation exchange resin for 2 hours at 70 ° C and a pressure of 15-17 atm at a speed of 300 cm ³ / h (215 g / h) (wt.%): isobutane - 22.26, isobutylene - 19.74, TMK - 47.0, water - 6.60, formaldehyde - 4.40. The molar ratio of H ₂ O: i-C ₄ H ₈ in the feed is 1.05. The volumetric feed rate per C ₄ fraction (W) is 1 h ⁻¹ . The raw material is prepared by mixing TMK, a 40% aqueous solution of formaldehyde and a technical isobutane-isobutylene fraction containing 47% isobutylene, under pressure in an autoclave, followed by stirring for 1-2 minutes, holding with the mixer turned off for 5-10 seconds and turnover through the lower leave of the separated aqueous phase. The composition of the raw materials is analyzed by GLC.

At the outlet of the reactor, the reaction mixture is throttled, cooled, and collected in a receiver from which unconverted C ₄ hydrocarbons are vaporized. Waste gas is passed through a gas clock and discharged into the atmosphere.

During the experiment received 46 l (112.0 g) of gas and 323 g of homogeneous non-stratified liquid. Losses in the experiment amounted to 7 g (1.63% of the missed raw materials). In accordance with the results of GLC analysis, the gas phase contains (wt.%): Isobutane - 81.18, isobutylene - 19.69, isoprene - 0.03. The composition of the liquid phase is as follows (wt.%): Isobutane - 0.02, isobutylene - 0.01, isoprene - 4.47, TMK - 82.83, MDHP - 1.37, isoamylene alcohols - 0.1, DMD - 1 60, ETM - 3.20, pyran alcohol (PS) - 0.13, MBD - 1.28, ΣDS - 0.11, ΣX - 0.64, heavy residue - 0.20, CH ₂ O - 0, 02, H ₂ O - 4.02.

In accordance with the results of the analysis, the conversion of isobutylene is 73%, the conversion of formaldehyde is 99.5% (the formaldehyde content in the product was determined by potentiometric titration with hydrochloric acid hydrochloramine). The water consumption for the extraction of 1 g of isobutylene is 0.47 g.

To 330 g of the reaction mass discharged from the reactor, add 70 g of DMD of 99.7% purity and the resulting mixture is pumped for 2 hours at a speed of 190 g / h into a cube of a laboratory packed reaction-distillation column operating at high blood pressure. 250 cm ^{3 of a} 5.5% aqueous solution of orthophosphoric acid (OFC) were preliminarily filled into a 0.5 L cube and the contents of the cube were heated to a temperature of 150-152 ° С at a pressure of 5 atm. During the entire experiment, low-boiling reaction products are taken from the top of the column, adjusting the selection so that a approximately constant level is maintained in the cube. The cooled distillate is collected in a receiver. After 2 hours, the supply of raw materials and the heating of the column are stopped and the bottoms product is unloaded. In total, 370 g of shoulder straps and 263 g of bottled product were unloaded. Losses in the experiment amounted to 17 g (2.7% of the mass of loaded and skipped raw materials).

The composition of the bottoms product (wt.%): H ₃ SO ₄ - 4.96, TMK - 1.4, DMD - 0.36, MDGP - 0.28, PS - 0.08, ΣX - 1.1, ΣDS - 0.11, a heavy residue - 1.61, CH ₂ O - 0.04, water - the rest.

When standing, the epaulettes are stratified into organic (272 g) and aqueous phases (78 g). According to the analysis, the organic phase of the overhead has the following composition (wt.%): Isobutylene - 50.21, isoprene - 33.08, TMK - 9.90, MDHP - 2.24, DMD - 1.05, ΣX - 0.34 formaldehyde 0.04; water 3.14. The aqueous phase of the overhead contains 6.4% TMK, 1.3% DMD, 0.08% formaldehyde, 0.40% ΣX, the rest is water.

The organic portion of the overhead is mixed at room temperature with a still product and kept in an autoclave at room temperature and stirring for 1 hour. Then, the oil and aqueous phases are subsequently unloaded from the autoclave. As a result of extraction, 10.9 g of organic substances dissolved in it are extracted from the bottom liquid.

The extract was separated on a laboratory distillation column (10 T.T.) and three fractions were sequentially isolated: isobutylene, isoprene and low boiling organic compounds. As a result of distillation, 166 g of isobutylene, 90 g of isoprene and 38 g of a fraction of the following composition (wt.%) Are collected: MDHP - 13.1, DMD - 1.5, TMK - 35.3, PS - 2.0, ΣDS - 0 , 7, ΣX - 4.3, a heavy residue - 1.4, formaldehyde - 0.1, water - the rest.

Without taking into account the recycle of the organic phase isolated by separation of the overhead of the reaction-distillation column, the yield of isoprene to converted isobutylene is 94.0% with an isobutylene conversion of 25.25%. The yield of the target product, calculated on converted formaldehyde, taking into account the formaldehyde released during the decomposition of DMD. accounts for 89.5%. The conversion of formaldehyde is 99.1%, the conversion of DMD is 95.0%. The main results of the experiment are presented in tables 1.1 and 1.2.

Example 2

The experiment is carried out analogously to example 1, however, in the first reaction zone (extraction of isobutylene) maintain a temperature of 80 ° C and a pressure of 18 atm. The results of the experiment are presented in table. 1.1 and 1.2.

Example 3

The experiment is carried out analogously to example 1, however, in the first reaction zone maintain a temperature of 90 ° C and a pressure of 20 ATM. The results of the experiment are presented in table. 1.1 and 1.2.

Example 4

The experiment is carried out analogously to example 1, however, the catalyst used is Lewatit K 1461 granular sulfocationionite in an amount of 100 cm ³ , and a homogeneous mixture of the following composition (wt.%): Isobutylene - 18.60, isobutane - 14, 00, TMK - 48.44, DMD - 10.65, water - 8.31. The mixture is prepared by mixing technical C ₄ fraction containing 47% of isobutylene with isobutylene obtained by dehydration of TMC in the cube of the reaction-distillation column during the experiment of Example 3. The feed rate of the mixture is 185 g / h. The duration of the experiment is 2 hours

After distillation from the reaction mass of C ₄ hydrocarbons, 55.7 g of a 37% aqueous formaldehyde solution are added to the bottom product and the resulting mixture is processed as described in Example 1. The results of the experiment are shown in Table. 1.1 and 1.2.

Example 5

This example illustrates the possibility of carrying out the claimed method using concentrated isobutylene as raw material.

A homogeneous mixture of TMK-water-isobutylene-DMD is fed at a speed of 140 g / h to the upper part of a steel tubular reactor filled with 50 cm ^{3 of} granular Amberlist WET 36 cation exchanger. The composition of the raw material has the following form (wt.%): Isobutane - 0.15, isobutylene - 30.85. TMK - 54.00, water - 7.00, DMD - 8.00. The volumetric feed rate per isobutylene is 1.5 h ^-1 . The experiment is carried out at a temperature of 70 ° C for 1 hour

After distillation from the reaction mass of C ₄ hydrocarbons, 45 g of a 36.5% solution of CH ₂ O are added to the bottoms product and the resulting mixture is processed as described in Example 1. The results of the experiment are shown in Table. 1.1 and 1.2.

Example 6

This example illustrates the possibility of carrying out the inventive method in a shelf reactor, on the first shelf of which only hydration of isobutylene is carried out, and on the second, it is preferable to obtain isoprene precursors.

A raw material in the form of a homogeneous mixture of the following composition (wt.%) Is passed through a steel tube reactor with a volume of 50 cm ³ filled with a Lewatit K 2629 granular sulfation-cation catalyst Lewatit K 2629 from top to bottom: TMK - 54.5, water - 9 , 8, iC ₄ H ₈ - 24.8, iC ₄ H ₁₀ - 10.6. Based on the C ₄ hydrocarbon fraction, the volumetric feed rate (W) is 1.3 h ⁻¹ . At the outlet of the reactor, the reaction mass enters the lower part of the tubular heated mixer filled with pieces of quartz (fraction 2-4 mm), where it simultaneously enters at a speed of 20 g / h of DMD containing 3.2% water. It was preliminary established that when mixing the reaction mass at the outlet of the reactor containing (wt.%): TMK - 77.06, water - 4.43, iC ₄ H ₈ -7.93, iC ₄ H ₁₀ - 10.6, with the indicated amount of DMD, a stable mixture of the following composition (wt.%) that is not stratified in the temperature range from 20 to 80 ° C is formed: TMK - 64.96, water - 4.20, DMD - 15.21, iC ₄ H ₈ - 6 69, iC ₄ H ₁₀ - 8.94.

The resulting mixture from the top of the mixer is fed into the upper part of a reactor similar in design, also filled with 50 cm ^{3 of} Lewatit K 2629 sulfocationite, in which the temperature is maintained at 80 ° C, and at the outlet from which the reaction mass is throttled, cooled and separated in a separator into gas and liquid phase. The gas phase is passed through the gas clock, and the liquid phase freed from C ₄ hydrocarbons is collected in the receiver.

The duration of the balance sheet experiment is 5 hours. 371.5 g of raw materials were skipped, 364.9 g were collected, including liquids - 323.8 g, gas - 41.6 g, loss 1.8%.

45 g of DMD are added to the unloaded liquid phase and the resulting mixture is processed as described in example 1. The results of the experiment are shown in table. 1.1 and 1.2.

Claims (2)

1. A method of producing isoprene based on the liquid-phase interaction of isobutylene or isobutylene-containing fractions of C ₄ hydrocarbons with an aqueous solution of formaldehyde or 4,4-dimethyldioxane-1,3 in the presence of an acid catalyst at an elevated temperature, comprising carrying out isobutylene hydration in the first reaction zone in the presence of solid cationic catalyst when feeding into this zone part of the initial aqueous solution of formaldehyde or 4,4-dimethyldioxane-1,3, characterized in that the process is carried out in two reaction zones, p When in use, feedstock is fed into the first reaction zone in a liquid homogeneous mixture "trimethyl - C ₄ hydrocarbons - water - formaldehyde" or "trimethyl - C ₄ hydrocarbons - water - 4,4-dimethyl dioxane-1,3 ', taken in a certain ratio with taking into account the conservation of the molar ratio water: isobutylene of at least 0.9, and the process in the first zone is carried out at 70-90 ° C and a pressure of 15-20 atm., the resulting reaction mixture after distillation of non-converted C ₄ hydrocarbons from it is sent to the second reaction zone together with the rest of the original forms ldegida or 4,4-dimethyldioxane-1,3, wherein the process is conducted at a temperature of 150-170 ° C and a pressure of 5-7 atm in the presence of a water-soluble acid catalyst with continuous distilling off volatile reaction products and the water. 2. The method according to claim 1, characterized in that isobutylene isolated from the reaction mass of the second reaction zone is recycled to the first reaction zone.

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