RU2099318C1 - Method for production of isoprene - Google Patents

Abstract

FIELD: production of high molecular weight compounds. SUBSTANCE: isoprene is prepared by interaction of formaldehyde with isobutylene and/or with trimethyl carbinol, the process is carried out in liquid phase at elevated temperature and at increased pressure in the presence of aqueous solution of acid catalyst. Process takes place in two consequent steps of contact. The second step has zone of heat supply, separation zone and contour of circulation of liquid phase in between them. Reaction products are separated from separation zone of the second step of contact and then isoprene is isolated of reaction products. After the first step of contact reaction mass is separated into aqueous and hydrocarbon streams. Hydrocarbon stream is divided in two portions, their ratio being from 3:1 to 1:3, the first portion is fed into contour of circulation of liquid phase of the second step of contact which takes place before and (or) after zone of heat supply. The second portion is separated while fractions having boiling points not more than 140 C and higher than 140 C or fractions having boiling points not higher 120 C, 120-140 C and higher than 140 C are isolated; the process takes place by rectification. At the first case the first fraction is returned into hydrocarbon stream being fed on the second step of contact. At the second case the first fraction is returned into the same stream. The second fraction is separated while preferable dimethyl dioxane fraction is isolated and is returned into hydrocarbon stream being fed on the second step of contact (quantity of said fraction being up to 100 %) and preferable fraction of unsaturated alcohol is also isolated. The third fraction is isolated or is returned into the same stream, its quantity being up to 100 %, aqueous stream being fed into contour of circulation of liquid phase before feeding of hydrocarbon stream, or into separation zone of the second step of contact. Hydrocarbon stream is fed into contour of circulation of liquid phase of the second step of contact before and (or) after zone of heat supply at ratio from 3:1 to 1:3, respectively. EFFECT: improved efficiency of the method. 2 cl, 3 dwg

Description

 The invention relates to the field of production of isoprene, which finds application as a monomer for the production of synthetic rubber with properties close to natural, as well as in organic synthesis.

 A two-stage method for producing isoprene from isobutylene and formaldehyde is known, in the first stage of which liquid-phase condensation of isobutene with formaldehyde occurs in the presence of a sulfuric acid catalyst to form mainly 4,4-dimethyldioxane-1,3 (DMD), in the second stage, previously isolated DMD undergoes heterogeneous catalytic decomposition into isoprene (S.K. Ogorodnikov, G.S. Idlis. Isoprene production. L. Chemistry, 1973, p. 47).

 This process is characterized by a large consumption of raw materials, significant energy consumption and a large amount of chemically contaminated wastewater.

 Closest to the proposed one is a one-step method for producing isoprene by liquid-phase interaction of formaldehyde with isobutene in the presence of an acid catalyst in two reactors connected in series, in the first of which isoprene precursors are obtained at low temperatures, and in the second, these precursors decompose into isoprene (Pat. Japanese application N 59-25337).

 The disadvantage of this method is the instability of the thermal regime in a reactor of a high temperature zone, which worsens the performance of the process, as well as the relatively high cost of isoprene, although lower than in the two-stage method for producing isoprene from formaldehyde and isobutylene.

 The problem solved by the invention is to improve the process technology and, as a consequence of this, reduce the cost of isoprene.

A method for producing isoprene by liquid-phase interaction of formaldehyde with isobutylene and / or trimethylcarbinol, provided in the presence of an aqueous solution of an acid catalyst, at elevated temperature and pressure in two successive contacting stages, the second of which includes a heat supply zone, a separation zone and a liquid phase circulation circuit between them. From the separation zone of the second stage of contacting, reaction products are taken and isoprene is isolated from them. In this case, the reaction mass after the first stage of contacting is divided into hydrocarbon and water streams. The hydrocarbon stream is divided into two parts in a ratio of 3: 1 to 1: 3, the first part is fed into the circulation circuit of the liquid phase of the second contact stage before and / or after the heat supply zone. The second part is separated by rectification with the separation of fractions of components with boiling points not exceeding 140 ^o C and above 140 ^o C or fractions of components with boiling points not higher than 120 ^o C, 120 140 ^o C and above 140 ^o C. In the first case, the first fraction is returned in the hydrocarbon stream supplied to the second contacting stage, in the second case, the first fraction is returned to the same stream, the second fraction is separated by rectification with the separation of the predominantly dimethyldioxane fraction, which is isolated or returned to the hydrocarbon stream, the second stage of contacting, in an amount of up to 100% and a fraction of predominantly unsaturated alcohol - isopropenylethyl alcohol (IPES), up to 100% is isolated or returned to the third fraction in the same stream, while the aqueous stream is fed into the liquid phase circulation circuit before introducing the hydrocarbon flow or into the zone of circulation of the liquid phase before entering the hydrocarbon stream or into the separation zone of the second stage of contacting.

 The hydrocarbon stream is fed into the circulation circuit of the liquid phase of the second contact stage before and / or after the heat supply zone in a ratio of 3: 1 1: 3, respectively (preferably 1: 1).

 As a reactor of the first contacting stage, a hollow apparatus, a shell-and-tube apparatus, or apparatus with integrated structures (plates, grids, tubes, nozzle, etc.) can be used.

 The reactor of the first stage of contacting may consist of one or more devices connected in series or in parallel.

 Before the first contacting stage is fed into the reactor, the starting products are mixed.

 The separation into hydrocarbon and water streams after the first stage of contacting can be carried out both in the separation zone of the reactor of the first stage, and in a separate apparatus.

 After separation, the hydrocarbon layer may be washed away from the acids in the wash column and the wash water may be used in the process, for example, to prepare a catalyst.

 In the second contact zone, apparatuses with a highly developed heat exchange surface can be used, for example, any tubular apparatus having both an internal and external circulation circuit or a reaction-separation apparatus.

 The reaction-separation apparatus may be a dish column (separation zone) with a remote boiler (heat supply zone). The bottom of the column and the remote boiler are connected by a circulation circuit.

 The shell-and-tube apparatus may have external circulation pipes, which, together with internal ones, make up the general circulation circuit. The separation zone is the space above the tube sheet.

 When fed to the second stage of contacting, the hydrocarbon stream is subjected to distribution (for example, using a bubbler).

 The circulation of the aqueous phase in the circulation circuit of the second stage of contacting can be carried out both naturally (by convection), and forced using a circulation pump.

 As the acid catalyst in the proposed method uses a catalytic system, for example, based on sulfuric or phosphoric acids with various additives or without them.

 The molar ratio of formaldehyde: isobutylene and / or trimethylcarbinol is 1: 5 15.

In the proposed method, the fraction of components with a boiling point of not higher than 120 ^o C mainly contains isobutylene, trimethylcarbinol, methyldihydropyran, as well as impurities of higher boiling components. This fraction is returned to the hydrocarbon stream supplied to the second stage of contacting.

The fraction of components with a boiling point of 120 140 ^o C contains mainly unsaturated isopropenylethyl alcohol (IRES), 4,4-dimethyldioxane-1,3 (DMD), as well as impurities of lower and high boiling components. This fraction in this method is divided into a fraction of DMD, which is isolated or returned to the hydrocarbon stream to the second stage of contacting, and the fraction of IPES, which is the raw material for obtaining the valuable chemical product of dimethylvinylcarbinol (DMVK), which, in turn, is the starting material for obtaining synthetic vitamin preparations.

The fraction of components with a boiling point above 140 ^o C is a high-boiling intermediate products (runways) of this process. It contains predominantly higher boiling components than DMD.

 In the proposed method, it is isolated as the final product or partially, or completely returned to the hydrocarbon stream entering the second stage of contacting. The isolated runway fraction can be used as a flotation reagent, a corrosion inhibitor, and also for the synthesis of polymer resins such as novolac phenol formaldehyde.

A fraction with a boiling point up to 140 ^o C contains mainly the components listed in the above-mentioned fractions with a boiling point not higher than 120 ^o C and 120 140 ^o C. This fraction in the proposed method is returned to the hydrocarbon stream, which is fed to the second stage of contacting.

 The differences of the proposed method from the prototype are as follows.

The reaction mass after the first stage of contacting is divided into hydrocarbon and water streams. The hydrocarbon stream is divided into two parts in a ratio of 3: 1 to 1: 3. The first part of the hydrocarbon stream is fed into the circulation circuit of the liquid phase of the second contacting stage before and / or after the heat supply zone. The second part of the hydrocarbon stream is separated by rectification with the separation of fractions of components with boiling points not exceeding 140 ^o C and above 140 ^o C or fractions of components with boiling points not higher than 120 ^o C, 120 140 ^o C and above 140 ^o C. In the first case, the first the fraction is returned to the hydrocarbon stream supplied to the second stage of contacting. In the second case, the first fraction is returned to the same stream, the second fraction is separated by rectification into a predominantly DMD fraction, which is isolated or returned to the hydrocarbon stream supplied to the second contact stage in an amount of up to 100% and a predominantly unsaturated alcohol fraction, and the third fraction is isolated or return to the same stream in an amount of up to 100%. In this case, the water stream is fed into the circulation circuit of the liquid phase before the hydrocarbon stream is introduced or into the separation zone of the second contacting stage.

 The hydrocarbon stream is fed into the circulation circuit of the liquid phase of the second contact stage before and / or after the heat supply zone in a ratio of 3: 1 1: 3, respectively.

 When using the proposed separation method, the supply of water and hydrocarbon streams to the second contacting stage allows intensifying heat and mass transfer processes, as well as stabilizing the thermal regime of the heat supply zone of the second contacting stage.

The separation of the above fractions from the hydrocarbon stream allows, along with isoprene, to obtain additionally valuable chemical products. At the same time, the yield of the target product (isoprene) decreases very slightly, while the total yield of all target products increases significantly (taking into account the IPES fraction and the runway fraction, which are valuable and expensive products). In addition, in order to maintain a high yield of isoprene, the stream after separation of IPES from the fraction of 120 140 ^o C is mainly returned to the second stage of contacting the isoprene production process.

The selection of the fraction of components with a boiling point above 140 ^o C allows you to get an additional valuable product and to a lesser extent to obtain various oligomeric reaction products of isoprene production in the second stage of contacting. Although recycling this fraction gives an additional amount of isoprene.

 Using a combination of the proposed techniques allows to improve the process technology, reduce energy and material costs, and, if necessary, allows you to get valuable chemical products. All this taken together reduces the cost of isoprene.

 The invention is illustrated by the following examples.

 Example 1. The process is carried out on a continuous installation, consisting of two successive stages of contacting.

 Starting materials: formaldehyde, isobutylene, trimethylcarbinol, water, a catalyst solution, both fresh and recycle, are introduced into the lower part of the reactor of the first contact stage. A shell-and-tube apparatus is used as a first-stage reactor.

 The reaction mass is removed from the first stage reactor and is divided into hydrocarbon and water streams.

 As a second-stage reactor, a shell-and-tube apparatus with an external circulation loop is used.

 The water stream is fed into the circulation circuit of the liquid phase of the second stage of contacting before entering the hydrocarbon stream.

 The hydrocarbon stream after the first stage is divided into two parts in a ratio of 1: 1. The first part of the hydrocarbon stream is fed into the circulation circuit of the liquid phase of the second contact stage to the heat supply zone and after the heat supply zone in a ratio of 1: 3.

The second part of the hydrocarbon stream is fed for separation in order to obtain two fractions with a boiling point of not higher than 140 ^o C and above 140 ^o C.

A fraction with a boiling point not higher than 140 ^o C is returned to the hydrocarbon stream going to the second stage of contacting.

A fraction with a boiling point above 140 ^° C. is isolated as a product (runway fraction).

 The reaction mass for the synthesis of isoprene from the reactor of the second stage of contacting is withdrawn in two streams: from the top of the reactor, unreacted isobutylene, isoprene, other low boiling organic products and partially water are taken from the top of the reactor, and an aqueous catalyst solution is removed from the top of the reactor, which after extraction of high boiling by-products are recycled to the first contact stage.

 The steam stream taken from the top of the second stage reactor is condensed and divided into an oil and water layer.

 Analysis of the reaction mass is carried out with stable operation of the installation for a certain period of time. The composition of the reaction products is determined by gas chromatography, formaldehyde and the catalyst are determined by potentiometric titration.

 The process diagram is shown in FIG. one.

 293.52 kg / h of an initial charge (stream 1) containing, kg / h: 16.02 formaldehyde (in the form of formalin with a formaldehyde content of 34% and 5%) is fed into the reaction block to the first contacting step (reactor R-1) 7% by weight of methanol); 67.22 trimethylcarbinol (as an azeotrope with water); 169.64 isobutylene; 37.89 water (total); 0.17 sulfuric acid and 0.02 hexamethylenetetramine, as well as a circulating catalyst solution of 36.33. The supply of fresh catalyst is stopped when the concentration of sulfuric acid in the circulating catalyst solution is 0.30 0.50% wt.

The temperature in the first stage of contacting 110 ^o C, a pressure of 20 ATM. Contact time 40 min.

The reaction mass after 1 step of contacting in the amount of 329.85 kg / h is divided into hydrocarbon and water streams (streams 5 and 4). Half of the hydrocarbon stream (stream 6) is sent to the second stage of contacting, the second half (stream 7) to isolate the runway fraction with a boiling point above 140 ^o C, as a commodity product, which is output in the amount of 4.77 kg / h (stream 11). A fraction with a boiling point below 140 ^o C (stream 10) is sent to stage II.

At the second stage of contacting (reactor R-2), a hydrocarbon layer in the amount of 257.08 kg / h (stream 6 ^a ) and an aqueous layer in the amount of 68.00 kg / h (stream 4) are fed.

The temperature in the second stage of contacting 170 ^o C, a pressure of 15 ATM. Contact time 20 min.

 After the decomposition of the precursors into isoprene from stage II, the following results are discharged: steam stream 9 in an amount of 287.44 kg / h to isolate isoprene and recycle catalyst solution (streams 8 and 16) by side extraction. Stream 8 in the amount of 36.33 kg / h after preliminary extraction of high-boiling by-products from it is fed to the first stage of contacting as a recycled catalyst solution.

 The conversion of formaldehyde is 99.8%. The yield of isoprene on the reacted formaldehyde is 77.9 mol%. In addition, a runway fraction of 168.8 kg per 1 ton of isoprene is withdrawn as a marketable product.

 Example 2. The methodology of the experiment as in example 1. The difference is that in the second stage of contacting, a reaction-separation apparatus, which is a plate column with a remote boiler, is used as a reactor.

 The process diagram is presented in figure 2.

 392.37 kg / h of the initial charge (stream 1) containing, kg / h: 18.60 formaldehyde (in the form of an aqueous solution of formalin) is fed into the reactor block to the first stage of contacting (reactor R-1); 337.70 isobutylene; 32.20 water (total); 9.24 phosphoric acid; 0.18 hydroxyethylidene diphosphophonic acid; 0.36 hexamethylenetetramine, as well as a circulating catalyst solution of 164.09. The supply of fresh catalyst is stopped when the concentration of phosphoric acid in the circulating catalyst solution is 6 8% wt.

The temperature in the first stage of contacting 90 ^o C, a pressure of 16 atm. Contact time 60 min.

 The reaction mass after the first stage of contacting in the amount of 559.24 kg / h (stream 3) is divided into hydrocarbon and water streams (5 and 4).

 The water stream is fed into a dish column (separation zone) of the second contacting stage.

 The hydrocarbon stream after the first stage is divided into two parts in a ratio of 1: 2.

 The first part of the hydrocarbon stream in an amount of 129.91 kg / h (stream 6) is fed into the circulation circuit of the liquid phase of the second contact stage to the heat supply zone and after the heat supply zone in a 3: 1 ratio.

The second part of the hydrocarbon stream in an amount of 259.82 kg / h (stream 7) is fed for separation by rectification to obtain three fractions of components with boiling points: not higher than 120 ^o C, 120 140 ^o C and above 140 ^o C.

The fraction of components with a boiling point not higher than 120 ^o C in the amount of 239.59 kg / h (stream 10) is returned to the hydrocarbon stream supplied to the second stage of contacting.

The fraction of components with a boiling point of 120-140 ^o C is isolated and sent to the separation unit of the IPES fraction, in which the IPES fraction in the amount of 1.11 kg / h (stream 15) and the DMD fraction in the amount of 15.09 are isolated from this fraction as a commercial product kg / h, which is returned to the hydrocarbon stream to the second stage of contacting. Part of the fraction of components with a boiling point above 140 ^o C (stream 13) in an amount of 2.89 kg / h (stream 17), which is 50% of the whole fraction, is isolated as a commercial product (runway fraction), the rest of this fraction return to the hydrocarbon stream supplied to the second stage of contacting.

The temperature in the second stage of contacting 160 ^o C, a pressure of 13 atm. Contact time 30 minutes

 After the decomposition of the isoprene precursors (reactor R-2) from the II stage, the steam stream 9 is removed in an amount of 381.83 kg / h for the release of isoprene. The recycle catalyst solution (stream 8) in an amount of 164.09 kg / h is returned to the first stage of contacting.

 The conversion of formaldehyde is 99.9%. The yield of isoprene on the reacted formaldehyde is 78.7 mol%.

 As commodity products, an additional 33.4 kg of IPES fraction and 87.3 kg of runway fraction per 1 ton of isoprene were obtained.

 Example 3. The methodology of the experiment as in the previous examples. The difference is that in the first stage of contacting, two serially connected hollow apparatuses are used, and in the second stage, a reaction-separation apparatus is used.

 The process diagram is shown in FIG. 3.

 In the reactor block (reactor R-1) serves 482.99 kg / h of the original mixture (stream 1), containing, kg / h: 12.20 formaldehyde (in the form of an aqueous solution of formalin); 391.11 trimethylcarbinol (as an azeotrope); 72.91 water (total); 10.54 phosphoric acid, 0.11 hydroxyethylidenephosphonic acid and 0.22 hexamethylenetetramine, as well as a circulating catalyst solution.

 The supply of fresh catalyst is stopped when the concentration of phosphoric acid in the circulating catalyst solution is 6 8% wt.

The temperature in the first stage of contacting 80 ^o C, a pressure of 15 amt. Contact time 80 min.

 The reaction mass after the first stage of contacting in the amount of 1518.73 kg / h (stream 3) separation into hydrocarbon and water streams (5 and 4).

 The water stream is fed into the circulation circuit of the liquid phase of the second stage of contacting before entering the hydrocarbon stream.

 The hydrocarbon stream after the first stage of contacting (272.14 kg / h) is divided into two parts in a ratio of 1: 3.

 The first part of the hydrocarbon stream is fed into the circulation circuit of the liquid phase of the second contact stage to the heat supply zone and after the heat supply zone in a 1: 1 ratio.

The second part of the hydrocarbon stream is fed for separation and three fractions of components with boiling points are isolated: not higher than 120 ^o C, 120 - 140 ^o C and above 140 ^o C.

The fraction of components with a boiling point of not higher than 120 ^o C in the amount of 196.06 kg / h (stream 9) is returned to the hydrocarbon stream supplied to the second stage of contacting.

The fraction of components with a boiling point of 120-140 ^o C (stream 12) is sent to the IPES separation unit, where the IPES fraction in the amount of 0.30 kg / h (stream 15) and the DMD fraction in the amount of 4.88 kg are isolated as a commercial product / h (stream 14), which is returned to the second stage of contacting.

The fraction of components with a boiling point above 140 ^o C completely return to the hydrocarbon stream supplied to the second stage.

The temperature in the second stage of contacting 125 ^o C, a pressure of 5 ATM. Contact time 40 min.

 From the second stage (reactor R-2), steam stream 9 in the amount of 429.16 kg / h is withdrawn to isolate isoprene and a recycle catalyst solution (stream 8) in the amount of 1035.74 kg / h is returned to the first stage.

 The conversion of formaldehyde is 99.8%. The yield of isoprene on the reacted formaldehyde is 81.3 mol%.

 At the same time, an IPES fraction in the amount of 13.5 per 1 ton of isoprene is obtained as an additional commercial product.

 Example 4. The methodology of the experiment and the process diagram as in example 1. The difference is that the hydrocarbon stream after the first stage of contacting is fed to the second stage and to the separation unit in a ratio of 3: 1.

 306.43 kg / h of the initial charge (stream 1), containing, kg / h: 16.40 formaldehyde (in the form of formalin with formaldehyde content of 34% wt. And 5.8% wt.) Is fed into the reaction block (reactor R-1) methanol); 68.02 trimethylcarbinol (as an azeotrope); 180.54 isobutylene; 38.65 water (total); 0.17 sulfuric acid; 0.02 hexamethylenetetramine, as well as a circulating catalyst solution.

 The supply of fresh catalyst is stopped when the concentration of sulfuric acid in the circulating catalyst solution of 0.3 to 0.5% wt.

 The operating mode of the reactor block as in example 1. The reaction mass after the first stage of contacting in the amount of 340.26 kg / h (stream 3) is divided into hydrocarbon and water streams (5 and 4).

 The water stream is fed into the circulation circuit of the liquid phase of the second stage of contacting before entering the hydrocarbon stream.

 After the first stage of contacting (276.65 kg / h), the hydrocarbon flow is divided into two parts in a ratio of 3: 1.

 The first part of the hydrocarbon stream (stream 6) in an amount of 207.49 kg / h is fed into the circulation circuit of the liquid phase of the second stage of contacting to the heat zone and after the heat supply zone in a 1: 1 ratio.

The second part of the hydrocarbon stream in an amount of 69.16 kg / h (stream 7) is sent for separation to obtain a fraction of components with a boiling point of not higher than 140 ^o C, to which 65.56 kg / h (stream 10) is returned to the hydrocarbon stream fed to the second stage of contacting, and a fraction with a boiling point above 140 ^o C in the amount of 3.60 kg / h (stream 11), which is allocated as a commercial product fraction of the runway.

 From the second stage (reactor R-2) the steam stream 9 is removed in an amount of 301.61 kg / h to isolate isoprene and a recycle catalyst solution (stream 8) in an amount of 33.84 kg / h is returned to the first stage.

 The conversion of formaldehyde is 99.8%. The yield of isoprene on the reacted formaldehyde is 80.6 mol%.

 In this case, a runway fraction in the amount of 120.2 kg per 1 ton of isoprene is obtained as an additional commercial product.

Claims (2)

1. A method of producing isoprene by liquid-phase interaction of formaldehyde with isobutylene and / or trimethylcarbinol in the presence of an aqueous solution of an acid catalyst, carried out at elevated temperature and pressure in two successive contacting stages, the second of which includes a heat supply zone, a separation zone and a liquid phase circulation circuit between them, with the selection from the separation zone of the second stage of contacting the reaction products and the release of isoprene from them, characterized in that the reaction mass after the contacting stage is divided into water and hydrocarbon streams, the hydrocarbon stream is divided into two parts in a ratio of 3 1 1 3, the first part is fed into the liquid phase circuit of the second contact stage before and / or after the heat supply zone, the second part is separated by rectification with evolution components of fractions with a boiling point not higher than 140 ^o C and above 140 ^o C or fractions of components having boiling points not higher than 120 ^o C 120 140 ^o C and above 140 ^o C, in the first case a first fraction is recycled to the hydrocarbon feed stream to a contact stage, in the second case, the first fraction is returned to the same stream, the second fraction is separated by distillation to isolate a fraction of predominantly dimethyldioxane, the second fraction is isolated or returned to the hydrocarbon stream supplied to the second contact stage in an amount of up to 100% and the fraction is mainly unsaturated alcohol and the third fraction is isolated or returned to the same stream in an amount of up to 100%, while the water stream is fed into the circulation circuit of the liquid phase before the hydrocarbon stream is introduced or into the separation zone tion of the second stage of contacting.  2. The method according to claim 1, characterized in that the hydrocarbon stream is fed into the circulation circuit of the liquid phase of the second contact stage before and / or after the heat supply zone in a ratio of 3 1 1 3, respectively.

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