RU2341508C1 - Method of obtaining isoprene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: isoprene is obtained by liquid-phase interaction of formaldehyde and, possibly, substances, which are source of formaldehyde, with tret-butanol, possibly, isobutylene or substances, which are source of isobutylene, and, possibly, semi-products - isoprene precursors in presence of strong acid catalyst and water using mole excess of tret-butanol (isobutylene) at higher temperature and pressure, ensuring transition of isoprene in vapour phase with its further isolation, realised with supply of heat into reaction zone, including circulation and heating of formed in process acid water layer, which is characterised by the following: heat supply is carried out only due to circulation of heated acid water layer, layer being heated to temperature lower than its boiling temperature, and amount of circulating acid water layer must ensure drop of temperature on reaction zone height not more than 5°C.

EFFECT: increase of efficiency of process realisation and simplification of its technology.

6 cl, 4 ex, 1 tbl, 5 dwg

Description

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

A known method of producing isoprene by the interaction of trimethylcarbinol (TMK) with 4,4-dimethyldioxane-1,3 (DMD) and / or formaldehyde in the presence of an aqueous solution of an acid catalyst at elevated temperature and pressure and a molar excess of trimethylcarbinol relative to the total amount of formaldehyde (RF Patent No. 2266888, published on December 27, 2005). The process is carried out in a reactor inside which a shell-and-tube heat exchanger is installed, dividing the apparatus into the upper and lower parts connected by external circulation pipes. Heat is supplied to the reaction zone due to the circulation of the reaction mass through the pipes of the heat exchanger, into the annular space of which the coolant is supplied.

The disadvantages of this method are associated with the presence of the reaction mass in the tubes of the heat exchanger. Undesirable processes occur on hot pipes both from the point of view of selectivity of raw material transformations and corrosion, aggravated by exposure of pipe surfaces as a result of intense evolution of gaseous decomposition products and concentration of acid catalyst.

As follows from the operating experience of such installations, severe corrosion of the equipment metal and its resinification, especially on the hot surfaces of the heat exchanger tubes, proceeds at the liquid-gas phase boundary. In this case, corrosion salts can accumulate, which adversely affect the selectivity of the process. This necessitates the withdrawal of the catalyst solution for purification from metal salts (corrosion products) using sulfocationionites, which complicates the technology.

Closest to the proposed invention is a method for producing isoprene in accordance with the patent of the Russian Federation No. 2203878, publ. October 5, 2003. According to this patent, a liquid-phase interaction of formaldehyde and, possibly, a source of formaldehyde is carried out with tert-butanol and possibly isobutene in the presence of a strong acid catalyst and water at elevated temperature and a molar excess of the supplied tert-butanol. The process is carried out in a vertical reaction zone connected from below to a boiler. The pressure in the reactor is maintained such that there is no condensation of isoprene. It is selected as part of the steam stream, from which it is then released. Moreover, most of the water, formaldehyde and a significant part of tert-butanol are in the liquid phase, forming an aqueous layer containing also a strong acidic catalyst. The heat supply in the known method is carried out through a boiler by evaporating the reaction mass coming from the bottom of the apparatus, and possibly circulating through the boiler part of the acidic water layer formed in the process, which is removed from the top of the apparatus when steam and liquid move in the reaction zone from the bottom up.

The disadvantages of the prototype are due to the same phenomena that were described in the analogue and which are associated with the presence of the reaction mass in the tubes of the boiler.

The problem solved by the present invention is to increase the efficiency of the isoprene production process and simplify its technology.

A method for producing isoprene by liquid-phase interaction of formaldehyde and, possibly, substances that are the source of formaldehyde, with tert-butanol, possibly isobutylene or substances that are the source of isobutylene, and, possibly, intermediates - isoprene precursors in the presence of a strong acid catalyst and water during molar excess tert-butanol (isobutylene). In the process, temperature and pressure are maintained, which ensure the formation of isoprene in the vapor phase with its subsequent release. In this case, most of the water, formaldehyde, tert-butanol remains in the liquid phase, forming an aqueous layer containing a significant amount of acid catalyst. The supply of heat to the reaction zone is provided only by circulation and heating of the resulting acidic aqueous layer. In this case, the heating temperature should be lower than the boiling temperature of the acidic water layer, and its amount should ensure that the temperature difference along the height of the reaction zone is not more than 5 ° C. The reaction mass containing the feedstock is not supplied to the heater.

The circulation of the acidic water layer in the reactor - heat exchanger - reactor circuit is realized due to the difference in the densities of this layer and the reaction mass. In this case, a direct-flow movement of the circulating layer and raw materials is carried out.

Alternatively, a method is proposed according to which the circulation of the acidic aqueous layer is carried out by force using a pump. In this case, it is possible to direct the circulating flow countercurrent to the feed.

It is possible to install the heater for the circulating acidic aqueous layer below the reaction zone coaxially with it in the same apparatus.

On the circulation line of the acidic aqueous layer, a separator can be installed. It is preferable to use a cyclone type separator as such a separator.

It is possible to fill the reaction zone of the reactor with a mass transfer nozzle.

In the proposed method for the synthesis of isoprene can be used:

- as isobutylene-containing raw materials - concentrated isobutylene, trimethylcarbinol, C ₄ hydrocarbon fractions of various origin (isobutane dehydrogenation, pyrolysis, cracking). When using isobutylene or the above C ₄ fractions, the step of recovering isobutylene through the formation of TMC and / or isoprene precursors is necessary;

- formaldehyde feedstocks can be used - formaldehyde in the form of an aqueous solution and / or products which under the conditions of synthesis can form formaldehyde and / or isoprene (the so-called isoprene precursors). These include DMD, methylbutanediol (MBD), unsaturated C ₅ alcohols and other products that are formed by the interaction of isobutylene with formaldehyde under the conditions of synthesis of isoprene precursors.

As a catalyst, for example, organic (oxalic, etc.) and / or mineral (sulfuric, phosphoric, boric, etc.) and / or phosphonic (hydroxyethylidene diphosphonic (HEDPA), nitrile trimethylene phosphonic, and other) acids with various additives can be used. (amines, piperidine compounds and their derivatives).

Distinctive features of the proposed method in relation to the prototype are:

- lack of circulation of the reaction mass containing the feedstock through a heater;

- heating the acidic aqueous layer to a temperature lower than its boiling point;

- the amount of circulating acidic aqueous layer, providing a temperature difference along the height of the reaction zone of not more than 5 ° C.

In the inventive method for producing isoprene, the reaction zone is separated from the heat supply zone. In this case, isoprene synthesis reactions do not proceed in the heater tubes. There is no formation of a vapor phase and local concentration of acid on the surface of the tubes. Thus, the conditions for the occurrence of corrosion processes at the interface between the vapor - liquid phases on the hot wall of the heat exchanger are excluded. There is no accumulation of corrosion salts in the circulating acidic aqueous layer, and due to this, there is no decrease in performance during operation of the installation.

The claimed limitation of the temperature difference along the height of the reaction zone allows to soften the process conditions, and the high intensity of the circulation of the acidic water layer with a temperature below the boiling point provides a lower wall temperature of the heat exchanger tubes, which reduces the formation of by-products.

Thus, the proposed method for producing isoprene provides an increase in the efficiency of the process and simplification of its technology.

The present invention is illustrated in figures 1-5.

The drawings do not exhaust all the possibilities of implementing this invention. Other technical solutions are possible, subject to its essence, as set forth in the claims.

According to figure 1, the feedstock and the acid catalyst solution enter the reactor R-1 through line 1. In the reactor in the mixing zone (ZS) on line 1, a switchgear is installed.

In the reaction zone (ZR), the components of the feedstock react with the formation of mainly isoprene. Isoprene under the reaction conditions passes into a vapor state, is separated from the resulting acidic aqueous layer in the separation zone (C3) and is discharged from the reactor along with part of the water through line 3 into the separation system.

The acidic water layer, after being released from the reaction products in the separation zone (C3) and additionally in the C-3 separator, passes through line 2 to the T-2 heater, in which it is heated to a temperature below its boiling point through the wall using water vapor.

In this embodiment, a direct-flow scheme of the movement of the reaction mass and the circulating acidic aqueous layer is implemented. The acidic aqueous layer enters from the heater into the mixing zone (ZS) with the feedstock, where due to the distribution device their good mass transfer is ensured, and then to the reaction zone (ZR).

Part of the circulating acidic aqueous layer is removed from the reactor through the C-3 separator via line 4 for processing in order to withdraw the balance excess of water and high boiling point by-products (WFP), and then returns to the reactor via line 5.

In figure 2, in contrast to figure 1, the circulation of the acidic water layer is carried out using a circulation pump H-3.

In Fig. 3, in contrast to Fig. 1, the T-2 heater is located directly below the reaction zone coaxially with it in a single apparatus.

In Fig. 4, in contrast to Fig. 2, a countercurrent flow pattern of the reaction mass and the circulating acidic aqueous layer is realized. A circulating acidic water layer is pumped to the upper part of the reaction zone towards the rising reaction products by means of a pump N-3. This technique can improve process performance.

Figure 5 presents a schematic diagram of a process for the synthesis of isoprene from formaldehyde and isobutylene in an embodiment using C ₄ fractions of various origins. In this scheme, isoprene precursors are obtained in reactors R-1 and R-2, which are sent to the decomposition reactor P-3. As the reactor P-3, the reactors shown in FIGS. 1-4 can be used.

According to Fig. 5, a formaldehyde solution is fed to line P 1 in the first step in the synthesis of isoprene precursors, and formaldehyde solution is fed through line 1, and C ₄ isobutylene-containing hydrocarbon fraction through line 2. Fresh catalyst is fed via line 3 to reactor P-1 and, possibly, to reactor P-3.

The R-1 reactor, depending on the performance of the installation, may consist of one or more devices operating in series or in parallel, in the forward or counterflow mode. When working in the direct flow from the reactor R-1, the reaction mass stream is withdrawn (line 4), which is layered in the O-1 separator settler. The hydrocarbon layer from the sump O-1 directly (line 5) and / or after intermediate washing with water in a K-0 column is fed to a K-1 distillation column (line 6), from which unreacted C ₄ hydrocarbons are removed as a distillate (line 7) . The bottoms product of the K-1 column is sent to the K-2 column (line 8) to separate from products with a boiling point above 135 ° C (line 9). The distillate of the K-2 column is sent to the decomposition reactor P-3 (line 10).

The aqueous layer from the separator-settler O-1 and / or from the reactor R-1 (when working in countercurrent) together with the wash water from the column K-0 (line 11) is fed into the second stage of synthesis - reactor R-2. Recycled isobutylene is also fed from the isoprene recovery unit and from the K-3 column (line 12) or concentrated isobutylene from the side. When working in the direct flow from the top of the reactor R-2 output stream 13, which is stratified in the sump O-2. The hydrocarbon layer is sent to the K-3 column (line 14) to distill off all or part of the isobutylene sent for recycling to the P-2 reactor and, possibly, in a small amount periodically to the P-1 reactor. Bottom of the sump O-2 and, possibly, from the reactor P-2 (when working in countercurrent), water stream 16 is discharged, which is sent to the decomposition reactor P-3.

The bottoms product of the K-3 column (stream 17) is also sent to the decomposition reactor P-3.

The R-2 reactor is similar in design to the R-1 reactor, but operates on a fundamentally different raw material (the aqueous layer of the R-1 reactor and pure recycled isobutylene).

To the decomposition reactor P-3, a mixture of products is fed via line 18 to the lower part of the reaction zone.

At the top of the P-3 reactor, a stream is output via line 20, which is condensed in a T-3 capacitor and the condensate is sent to an O-4 phase separator, where it is separated into aqueous and hydrocarbon layers. The aqueous layer from the O-4 phase separator (stream 21), possibly after extraction with pure isobutylene, is removed for purification.

The acidic water layer formed in the upper part of the R-3 reactor, freed from the reaction products in the separation zone and, optionally, in the C-4 cyclone separator, is circulated through the R-3 reactor-T-2 heater system using the N-3 pump in such an amount so that the temperature difference along the height of the reaction zone does not exceed 5 ° C. In this case, the acidic aqueous layer in the heater is heated to a temperature below its boiling point. A part of the circulating acidic aqueous layer (stream 19) is removed from the C-4 cyclone separator, cooled in a heat exchanger (not shown in the diagram) and mixed with the organic layer from the O-4 phase separator (stream 22). The mixture is sent to a container E-1, in which the layers are delaminated.

Organic stream 24 from tank E-1 is led to a separation system where recycle isobutylene (stream 25), commercial isoprene (stream 26), as well as fractions of methyldihydropyran (MDHP) (stream 27), TMC with DMD (stream 30) and runway are isolated (stream 28).

Recycled isobutylene stream 25 is sent to the P-2 reactor and, possibly, to the extraction of water streams discharged from the bottom of the P-1, P-2 reactors and O-4 sump.

The aqueous layer from the tank E-1 is partially removed for processing (stream 31), and partially fed into the reactor P-1 (stream 32) and / or into the reactor P-3 (stream 29) in a line in front of the T-2 heater.

Stream 30 fractions TMK and DMD are returned to the reactor R-3 as part of stream 18.

Example 1

The synthesis of isoprene is carried out as described in the drawing of figure 2. The reactor is a cylindrical hollow apparatus with an inner diameter of 0.25 m, a height of 5.5 m, equipped with a distribution device for supplying raw materials. The switchgear is located 0.1 m above the bottom cover of the R-1 reactor, forming a mixing zone of the ZS. The rest of the apparatus is divided into a reaction zone (4.4 m high) and a separation zone (1 m high). The T-2 heating zone is a shell-and-tube heat exchanger (inner diameter of tubes 20 mm, height of pipes 2 m, number of pipes 28 pieces). The heating zone is connected with the reaction zone by a pipe with a diameter of 50 mm. The circulation pump N-3 provides the supply of an acidic water layer in an amount of up to 4.2 m ² / h. In this case, the temperature difference along the height of the reaction zone does not exceed 3 ° C.

The feedstock containing TMK, formaldehyde (F), DMD and the catalyst are fed to the reactor through line 1.

The catalyst is a 5% aqueous solution of phosphoric acid with the addition of HEDPA and hexamethylenetetramine in a mass ratio of 1: 0.1: 0.1.

In the reaction zone (ZR), the components of the feedstock interact with the formation of mainly isoprene and isobutylene with a small amount of by-products: MDHP, WFP, etc. Isobutylene and isoprene under the reaction conditions pass into a vapor state and are removed from the reactor together with some water and unreacted products (TMK, DMD, etc.) through line 3 to the separation system. The circulating acidic water layer after being released from vapor in the separation zone (C3) and additionally in the cyclone separator C-4 through line 2 enters the heating zone (T-2), in which it is heated through the wall using water vapor supplied to the annulus of the heater .

The heated circulating acidic aqueous layer enters the mixing zone (ZS) with the feedstock and then into the reaction zone (ZR). Part of the circulating acidic aqueous layer is removed from the reactor via line 4 for processing in order to withdraw the balance excess of water and runway, and then returns to the reactor through line 5.

The parameters of the reactor and the results are shown in table 1.

Example 2

The synthesis of isoprene is carried out as described in the drawing of figure 1. The difference from example 1 is that in the reaction unit, the circulation of the acidic water layer is provided due to the difference in densities without using a circulation pump.

TMK and DMD are used as raw materials.

The temperature difference along the height of the reaction zone does not exceed 5 ° C.

The parameters of the reactor and the results are shown in table 1.

Example 3

The synthesis of isoprene is carried out as described in the drawing of figure 4. The difference from example 1 is that TMK and formaldehyde are used as raw materials. The direction of circulation of the acidic water layer also reverses (counterflow option). In this case, the input point of the feedstock is transferred higher by a distance of 1 m from the bottom cover of the reactor R-1. Due to this, the height of the reaction zone decreases by 0.9 m, and the part of the reactor R-1 below the switchgear (ZS) increases accordingly and changes its purpose, turning into an exhaustion zone. The circulating acidic water layer from the bottom of the R-1 reactor is pumped through the T-2 heater in an amount of 6.2 m ³ / h using the N-3 pump and is fed through line 2 to the upper part of the R-1 reaction zone towards the rising reaction products. The temperature difference along the height of the reaction zone does not exceed 2 ° C.

The parameters of the reactor and the results are shown in table 1.

Table 1 1. The feed was fed to the reactor, kg / h - CH ₂ O 2.0 - 4.0 - DMD 4.0 10.6 - - TMK 30,2 21,4 29.6 - water 13.0 7.3 16.6 the concentration of phosphoric acid in the aqueous layer, wt.% 4,5 4.7 4.2 - temperature at the entrance to the reaction zone, ° C 153 155 145 - pressure in the reactor, kg / cm ² 9 10 8 2. Withdraw products from the reactor, kg / h - isobutylene 15.6 10.9 14.1 - isoprene 8.5 10.3 8.5 - TMK 2,3 1.7 1.8 - DMD 0.04 0.2 0.04 - MDGP 0.2 0.32 0.23 - runway 0.67 1.7 0.5 3. The conversion of CH ₂ About,% 99.7 - 99.7 4. The conversion of DMD,% 98.7 98.3 - 5. Conversion of TMK,% 92.5 92.0 94.0 6. The selectivity of the conversion of CH ₂ O and DMD into products: - isoprene 85.6 81.6 86.9 - MDGP 5.8 6.2 3.8 - runway 8.6 12,2 9.3

Example 4

The synthesis of isoprene is carried out according to figure 5. 14.5 kg / h of a solution of formaldehyde in water containing 40 wt.% Formaldehyde and 0.5 wt.% Methanol are fed to the first stage synthesis reactor through line 1.

As isobutylene-containing raw materials fed through line 2 in the amount of 27.1 kg / hour isobutane-isobutylene fraction (IIF) containing 40 wt.% Isobutylene.

2.5 kg / hr of an aqueous catalyst solution containing phosphoric acid, HEDPA and hexamethylenetetramine in a mass ratio of 1: 0.1: 0.1, and a recycle aqueous layer along line 32 in an amount of 9.8 are also fed to the reaction unit R-1; kg / hour.

In the reaction unit P-1 maintain a temperature of 85-90 ° C, a pressure of 16 atm. The conversion of isobutylene is 94.9%, the conversion of formaldehyde is 52%. In reactor R-1, DMD, methylbutanediol (MBD), C ₅ unsaturated alcohols, and TMK are formed. An organic stream containing hydrocarbons C ₄ , DMD (15.2%), tert-butanol (23.6%), unsaturated C ₅ alcohols is negligible from the reaction unit P-1 through line 5 in an amount of 29.2 kg / h the amount of methyl tert-butyl ether, runway (0.6%) and other impurities. Line 11 displays an amount of 23.0 kg / h of an aqueous stream containing water (62.2%), a catalyst with additives, TMC and formaldehyde (11.3%) with a small amount of runway.

Organic stream 5 after washing with water (stream 6) is fed to a distillation column K-1. Distillate (stream 7) containing C ₄ hydrocarbons (including 3.4% isobutylene) is removed from K-1 column in an amount of 16.8 kg / h. From the bottom, from K-1, a stream containing 38.9% DMD, 55.9% TMK, unsaturated C ₅ alcohols, a small amount of runway (1.5%), and others; to the K-2 column.

In the K-2 column, hydrocarbons are separated completely or partially from high-boiling hydrocarbons with a boiling point above DMD. High boiling products are removed in the form of a cubic product in an amount of 0.45 kg / h and are used as raw materials for flotation reagents and plasticizers.

Streams 11 and 12 are fed to the reaction unit P-2, in which the further conversion of formaldehyde occurs when it interacts with concentrated isobutylene. In the reactor R-2 maintain a temperature of 80-85 ° C, a pressure of 16 atm.

The conversion of formaldehyde is 80%, of isobutylene - 75.4%. In reactor R-2, DMD, MBD, unsaturated C ₅ alcohols and TMK are also formed.

From reactor R-2, products are withdrawn through line 13 to a phase separator O-2, where separation occurs into organic and aqueous layers. Organic stream 14, containing isobutylene, DMD (23.2%), TMK (34.8%), unsaturated alcohols, a small amount of runway (1.0%), etc., is sent to the K-3 column to distill off the recycled isobutylene. Recycled isobutylene from the K-3 column through line 15 to feed into reactor P-2 and a small amount to reactor P-1 (stream 15a).

The water layer from the R-2 reactor and the O-2 phase separator, containing water (71.4%), a catalyst with additives, TMK and formaldehyde (2.5%) with a small amount of runway, is withdrawn through line 16 to the R-3 reactor at the amount of 20.7 kg / hour. The bottoms product of the K-3 column is also sent to reactor R-3 along line 17 in an amount of 10.4 kg / h. All products fed into reactor R-3 from reactors R-1 and P-2, columns K-2 and K-3 are mixed before being introduced into the reactor and fed in a single stream 18 to the lower part of the reaction zone.

The molar ratio of the sum of TMC and isobutylene to the sum of formaldehyde and DMD in the stream entering the decomposition stage in the P-3 reactor is 2.2: 1.

The design of the reactor R-3 is similar to the design shown in figure 2.

In P-3, the temperature in the lower part of the reaction zone is maintained at ~ 153 ° C, in the upper ~ 150 ° C due to the circulation of the acidic aqueous layer freed from the reaction products through the T-2 heater. The pressure in the reactor R-3 support 9 ATM. A steam stream in the amount of 29.5 kg / h, containing 36.1% of isoprene, 20.6% of isobutylene, 34.4% of water, and also impurities is discharged from line 20 above the P-3 reactor. The vapor stream is condensed in a T-3 condenser, the condensate is stratified in an O-4 phase separator, and the organic layer is discharged through line 22 and the water layer along line 21. The organic layer consists of isobutylene, isoprene, water, TMK. The water layer consists mainly of water (91.9%).

The acidic aqueous layer freed from the reaction products in the separation zone of the R-3 reactor and, in addition, in the S-4 cyclone separator, is circulated through the R-3 reactor system - the T-2 heater using an N-3 pump in an amount of 3.5 m ³ / h This ensures that the temperature difference along the height of the reaction zone is not more than 3 ° C. A part of the acidic water layer in an amount of 1.3 kg / h (stream 19) is removed from the cyclone separator C-4 of the R-3 reactor, cooled in a heat exchanger (not shown in the diagram) and mixed with the organic layer from the O-4 phase separator (stream 22) ) The mixture is sent to a container E-1, in which the layers are delaminated.

The upper organic layer (stream 24) in the amount of 19.3 kg / h from the tank E-1 is sent to the separation. The lower aqueous layer in the amount of 9.8 kg / h (stream 32) is fed into the reactor R-1 and in the amount of 1.7 kg / hour (stream 29) into the reactor R-3 in the circulation line in front of the T-2 heater. A small portion (stream 31) is recycled.

Polymerization isoprene (stream 26) is isolated by simple distillation in an amount of 10.6 kg / h.

According to the proposed method, in addition to isoprene, valuable commodity products are additionally obtained - raw materials for flotation reagents and plasticizers (stream 9) in an amount of 0.45 kg / hour.

The yield of isoprene per 1 ton of the starting formaldehyde fed to the P-1 reactor is 1.83 tons.

Claims (6)

1. A method of producing isoprene by liquid-phase interaction of formaldehyde and, possibly, substances that are the source of formaldehyde, with tert-butanol, possibly isobutylene or substances that are the source of isobutylene, and, possibly, intermediates - isoprene precursors in the presence of a strong acid catalyst and water with using a molar excess of tert-butanol (isobutylene) at elevated temperature and pressure, ensuring the transition of isoprene to the vapor phase with its subsequent isolation, carried out with heat to the reaction zone, including circulation and heating of the acidic water layer formed in the process, characterized in that heat is supplied only by circulating the heated acidic water layer, while the layer is heated to a temperature below its boiling point, and the amount of circulating acidic water layer should provide a temperature difference along the height of the reaction zone of not more than 5 ° C. 2. The method according to claim 1, characterized in that the circulation of the acidic aqueous layer is carried out using a pump. 3. The method according to claim 1, characterized in that the heater for the acidic aqueous layer is installed below the reaction zone coaxially with it in a single apparatus. 4. The method according to claim 1, characterized in that a separator is installed on the supply line of the acidic aqueous layer to the heater. 5. The method according to claim 4, characterized in that a cyclone type apparatus is used as a separator on the supply line of the acidic aqueous layer to the heater. 6. The method according to claim 1, characterized in that the reaction zone is filled with a mass transfer nozzle.

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