RU2765441C2 - Method for producing isoprene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for producing isoprene from isobutylene and formaldehyde in an aqueous medium in the presence of a water-soluble acid in a reactor with three conversion areas, followed by separation of the products of synthesis into recyclable products returned to the beginning of the process, waste, and commercial isoprene, wherein isoprene is synthesised by dehydration of methyl butanediol at a temperature of 120 to 150°C in the aqueous phase in the presence of acid, and prior to dehydration, the aqueous phase is subjected to deep purification from formaldehyde in a counter-current reaction-extraction apparatus at a temperature of 60 to 110°C using a solvent inert to acid, formaldehyde, isobutylene, and alcohols.

EFFECT: proposed method is more efficient with simultaneous simplification of the process as a whole, leading simultaneously to a significant increase in the efficiency of the isoprene production process, reduction in the consumption of raw materials and vapour, as well as elimination of gas emissions, exponential reduction in the amount of effluents and pollution.

5 cl, 1 dwg

Description

The invention relates to the petrochemical industry and can be used in the production of isoprene from isobutylene and formaldehyde, for example, for the manufacture of synthetic rubber.

Solutions close to the claimed invention are known from the prior art. So, for example, a method for producing isoprene is known (RF patent No. 2266888, publ. 12/27/2005), in which isoprene is obtained by reacting trimethylcarbinol with 4,4-dimethyldioxane-1,3 and / or formaldehyde in one reaction zone - a vertical floor apparatus with a shell-and-tube heat exchanger located inside it, dividing the volume of the apparatus into upper and lower parts, with circulation of the reaction mass through the pipes of this heat exchanger, in the liquid phase, in the presence of an aqueous solution of an acid catalyst, at elevated temperature and pressure exceeding the vapor pressure of water at this temperature , with a molar excess of trimethylcarbinol relative to the total amount of formaldehyde, with the continuous withdrawal of the resulting reaction products from the reaction zone, followed by their condensation and extraction of organic substances from the aqueous phase using a condensed distillate, followed by the isolation of isobutylene sent to obtain TMK, and isoprene.

In addition, the so-called. one-stage method for obtaining isoprene (RF patent No. 2184107, publ. 06/27/2002) from formaldehyde and trimethylcarbinol or a compound that forms formaldehyde during hydrolysis, for example, 4,4-dimethyldioxane-1,3 and trimethylcarbinol (with a stoichiometric excess of the latter) in the presence of acid-catalyst, carried out when the initial reagents are fed into the bottom of the reactive distillation column, over the top of which, at a set reflux ratio, isoprene and isobutylene are distilled off. The process is carried out at a temperature in the cube of the column, equal to 130-170°C under pressure, 20-30% higher than the vapor pressure of water at a given temperature and at a TMC conversion of 20-60%.

Also known is a method for producing isoprene (see RF patent 2255928, publ. 07/10/2005), in which - at the first stage, 4,4-dimethyl-1,3-dioxane (DMD) is synthesized by condensation of isobutylene with formaldehyde in the presence of an acid catalyst at 80-100°C, pressure 1.6-2.0 MPa. DMD and a mixture of high-boiling by-products (WFP) are isolated from the oil layer of the reaction mass. At the second stage, DMD is decomposed on a calcium phosphate catalyst at 290-380°C, a pressure of 0.12-0.16 MPa in the presence of steam. After further processing of the contact gas, isoprene is obtained. The WFP mixture is distilled in two series-connected vacuum distillation columns. On the first column receive a distillate in the amount of 60-70 wt. % of food. Then this distillate is distilled on the second column, from where the distillate is removed in the amount of 75-90 wt. % of nutrition and VAT residue, which is sent to the DMD synthesis zone. The distillate of the second column is decomposed into isoprene on a ceramic nozzle at 400-450°C, a pressure of 0.12-0.16 MPa in the presence of water vapor supplied in a mass ratio to the runway (2-5):1. The contact gas after the decomposition of the WFP is processed together with the contact gas after the decomposition of DMD.

Also (description to the patent RU No. 2255928, published on 10.07.2005), two methods are known for producing isoprene from isobutylene and formaldehyde. According to the older, carried out in Togliatti rubber, an aqueous solution of non-methanolic formalin is mixed with a circulating, stripped off aqueous layer containing, in addition to organic components, phosphoric acid, and in a three-vessel reactor interacts with an isobutane-isobutylene fraction containing about 45% isobutylene at a temperature of about 100 C The reaction products are cooled, separated, after which the aqueous layer is evaporated in a vacuum apparatus, and the distillate is subjected to extraction with the isobutane-isobutylene fraction, which then enters the reactor. Formaldehyde water purified by extraction from DMD is subjected to rectification in order to separate methanol and TMK, which contain formaldehyde and water, the entire mixture is burned without heat recovery. Formaldehyde water contaminated with DS and MBD impurities enters the formalin recovery unit. The oil layer, after separation from the water layer, is washed from formaldehyde and acid, then isobutane is distilled off at the top of the distillation column (isobutylene content is about 14%), the bottom liquid is fed to the separation of a wide fraction containing methylal, TMK, DMD, water and formaldehyde, the entire mixture is returned to the reactor. The remainder enters the system of vacuum columns, where DMD is first distilled off for further conversion to isoprene. The heavy residue is separated by vacuum distillation into two approximately equal parts, the heavy-boiling part, mainly DS formals, is sold as a commodity. The lighter distillate is again separated, the smaller part, mainly MBD and MBD ether with isobutylene, is processed into isoprene together with DMD, the rest - DS is displayed as a commodity.

A mixture of DMD and the light part of the heavy residue is fed to thermal catalytic decomposition on a calcium phosphate catalyst at a temperature of 350-300 C, with a weight ratio of DMD to water vapor of 1:2. Heat is supplied by superheated steam up to 650 C. The contact gas is cooled with partial heat recovery, condensed and fed to the stratification. The decomposition reactors operate periodically: three hours of contact and three hours of regeneration with a steam-air mixture. After stratification, the aqueous layer containing formaldehyde, DMD, unsaturated alcohol and some DS is fed to the distillation of volatiles, the aqueous azeotropes of DMD, unsaturated alcohol and partially formaldehyde are distilled off. The entire mixture is returned to the sump, and the formaldehyde water enters the formaldehyde recovery unit. The oil layer from the sump is fed to formaldehyde removal, the wash water enters the processing stream of all formaldehyde decomposition water. The isoprene-isobutylene fraction is distilled off from the oil layer, which is then divided into pure isobutylene and raw isoprene, which is subjected to fine distillation in a three-column unit, then mixed with cyclohexanone and a solution of potassium alkali in n-butyl alcohol. The result is purification from cyclopentadiene due to its binding with cyclohexanone. The mixture is subjected to distillation, the cube is returned for dry cleaning, and the isoprene is washed and transferred to polymerization. The heavy products of the DMD decomposition oil layer are subjected to separation in a vacuum column into a pyran fraction with a DMD return and liquid heavy-boiling waste. In general, the process is characterized by a high steam consumption for the production of isoprene - 16 Gcal/t, high costs for formaldehyde 825 kg/t and isobutylene 1100 kg/t, a large amount of waste about 415 kg/t sold at low prices, a large amount of heavily polluted effluents , large emissions into the atmosphere.

The second, newer method of obtaining isoprene, implemented in NKNKH, is also based on the synthesis and isolation of DMD, which then undergoes a liquid-phase transformation into isoprene. All heavy by-products of DMD synthesis are subjected to thermal catalytic decomposition in two-shelf, periodically operating reactors: 3 hours of contact, 3 hours of regeneration. Steam with a temperature of 650 C maintains a temperature of 450-400 C and dilution of the runway: steam = 1:3.5-4. To process DMD, it is required to produce a large amount of TMK, for 1 mol of DMD, 5 moles of TMK. TMK is produced in six cation-exchange tray reactors. From above, the isobutane-isobutylene fraction, TMK-recycle and a small amount of water are fed into the reactor, as it moves to the underlying shelves, the reaction mixture is cooled and water is added to it, after leaving the reactor, the mixture enters the distillation column, where the spent fraction with an isobutylene content of 18 is distilled off %, TMK is removed by cube, which is partially returned to the hydration reactor, and the excess is removed to the liquid-phase isoprene synthesis reactor. Most TMK is obtained from high concentration recycle isobutylene in similar reactors, followed by isobutylene distillation. A mixture of DMD and TMK in the indicated ratio is fed into the lower part of the reactor, which is a vertical heat exchanger, the upper and lower covers of which are connected by a circulation pipe. Further, the process is carried out in accordance with the patent of the Russian Federation No. 2266888, published on December 27, 2005.

This option is characterized by a lower steam consumption of about 9-10 Gcal/t, The production of heavy waste is 500 kg/t, which is significantly higher than in the first option. The volume of effluents and gas emissions is lower than in the first option, but pollution is relatively higher.

Other similar technical solutions are also known: RU 2230054, publ. 06/10/2004, RU 2261855, publ., 10/10/2005, RU 2554354, publ., 06/27/2015, RU 2554009, publ. 06/20/2015

All of the analogues listed above have a well-known drawback - the excessive technological complexity of the process and its insufficiently high efficiency (the so-called "efficiency"). In addition, the listed analogues are characterized by high consumption of raw materials and steam, large volume and pollution of effluents, large volume and pollution of gas emissions, the need for chemical purification of isoprene from CPD with the cost of destroying waste containing butyl alcohol, isoprene oligomers, fulvenes and potassium alkali.

The problem to be solved by the claimed invention: the elimination of the above disadvantages by creating a more efficient method for producing isoprene, the implementation of which simplifies the technological complexity of the process as a whole.

The technical result of the invention: increasing the efficiency of the isoprene production process, as well as reducing the cost of raw materials and steam, eliminating gas emissions, reducing effluents and pollution by several times.

This task is solved as follows:

In the claimed method for the production of isoprene from isobutylene and formaldehyde in an aqueous medium in the presence of a water-soluble acid in a reactor with three transformation zones, followed by separation of the synthesis products into recycle products returned to the beginning of the process, waste and commercial isoprene, in which isoprene synthesis is carried out by dehydration of methylbutanediol at temperature 120-150°C in the aqueous phase in the presence of acid;

In addition, before dehydration, the aqueous phase is subjected to deep purification from formaldehyde in a countercurrent reaction-extraction apparatus at a temperature of 60-110°C, using a solvent inert to acid, formaldehyde, isobutylene and alcohols, for example hexane.

In addition, the interaction of isobutylene with formaldehyde is carried out at a temperature of 60-110°C and with complete recycling of the oil layer.

In addition, the synthesis is carried out using a mixture containing 8%-16% formaldehyde, which, before being fed into the reactor, is obtained by mixing formalin with a circulating acid solution and kept at a temperature of 70-110°C for 10-30 minutes.

In addition, the circulating acid is subjected to reaction-extraction purification with an inert solvent at a temperature of 120-150°C before being fed to the batch preparation.

When implementing the method, the following equipment is used: a unit for the hydrolysis of polyoxymethylenes, the essential components of non-methanol concentrated formalin; node interaction of a dilute acidic solution of formaldehyde with concentrated isobutylene in a reactor with at least three reaction zones; node for stratification of the reaction mass with recirculation of the oil layer into the reactor; unit for cleaning the aqueous layer from formaldehyde by extracting dimethyldioxane (DMD) with an inert solvent, such as hexane; extractant distillation unit with extract recycle to the reactor; unit for distillation of water and volatile products from the aqueous layer and dehydration of methylbutanediol (MBD), trimethylcarbinol (TMC), triols with the formation of isoprene, isobutylene, pyrans, heavy by-products; unit for condensing vapors of the reaction-stripping column, stratification for further processing; unit for high-temperature extraction of the acidic aqueous layer from the bottom of the reaction-stripping column with an inert solvent, followed by regeneration of the extractant and removal of heavy by-products; unit for separating volatile products of the reactive stripping column with the release of isobutylene recycle, TMK recycle, liquid waste and commercial isoprene.

To implement the method, in the conditions of Togliatti Kauchuk, it will be necessary to build a plant for the extraction of isobutylene from a 45% fraction consisting of two reactors: esterification and ether decomposition; additional reaction-extraction apparatus; equipping two hollow apparatus with trays for use as a reaction-stripping column and changing the piping.

The invention is illustrated in the flow diagram (see Fig. 1).

In Fig 1:

1 - container for batch preparation and complete hydrolysis of polyoxymethylenes that came with formalin.

2.1, 2.2 and 2.3 - three-zone reactor block for the synthesis of diol, intermediates and by-products.

3 - capacity for stratification of oil and water phases.

4 - extraction tray column for deep purification of the aqueous phase from formaldehyde.

5 - distillation column, with all the necessary equipment, for distillation of hexane from the extracted substances.

6 - reaction-stripping column for dehydration of MBD, triols and TMK, with a large volume of liquid on the trays.

7 - sump for separating isoprene-containing oils from methanol water.

8 - extractor to complete the dehydration of heavy and their separation from acidic water.

9 - distillation vacuum column for the regeneration of hexane and the separation of heavy liquid waste.

10 - distillation column for distillation of the isoprene-isobutylene fraction.

11 - distillation column for separating n-butylene from isoprene.

12 - isoprene distillation column.

13 - column for distillation of TMK from pyrans and hexadiene alcohol.

14 - chemical waste treatment column with distillation of a mixture of TMK and methanol.

The claimed method is carried out as follows.

Methanol-free formalin containing at least 40% formaldehyde is mixed with a hot circulating acidic water layer and enters the supply tank 1, where at a temperature of 100-110 ° C, a concentration of phosphoric acid of 3% and formaldehyde of 12%, polyoxymethylenes are completely converted into monomeric forms. Next, the formaldehyde mixture is mixed with 100% isobutylene, with a molar ratio of formaldehyde : isobutylene=1:1.3, and through the distribution device enters the synthesis reactor 2, which includes at least three stages. At a temperature of 60-110°C, isobutylene interacts with formaldehyde, the concentration of the latter decreases below 2%, with the formation of various synthesis products. A slight excess of isobutylene significantly reduces the extraction of products from the aqueous layer, which shifts the process towards the predominant formation of MBD. The reaction products are stratified in the separator 3 and the oil layer is returned to the beginning of the process. The aqueous layer, containing all possible reaction products, is supplied to formaldehyde removal, which is carried out in a vertical countercurrent extractor 4. The continuous phase is an acidic aqueous layer, the dispersed phase is an inert solvent. First of all, DMD begins to be extracted, which shifts the equilibrium and exhaustion of formaldehyde occurs due to its interaction with MBD with the formation of o DMD, while the hydrolysis of dioxane alcohols (DS) begins with the release of formaldehyde and the formation of triols. All formaldehyde released during the hydrolysis of DS is also bound in DMD and removed from the acidic aqueous phase. Thus, due to some reduction in the content of MBD in the aqueous phase, it is possible to purify it to a residual formaldehyde content of not more than 0.1%. The extract enters the tray column 5 for distillation, where the solvent is taken off at the top, and the heavier products from the bottom of the column are returned to the synthesis reactor.

The purified aqueous layer containing MBD, triols, TMA, pyran alcohol, acid and water enters the sixth plate from the top into the reaction-stripping column 6, where at a temperature of 120-150 ° C and a pressure of 1 atm, dehydration of MBD, triols and TMA occurs. The required volume for the reaction is achieved due to the fact that the diameter of the column is much larger than required based on the optimal vapor velocity, while there are few valves on the plate, and the level is high, which will increase the distance between the plates to 800 mm. To prevent the entrainment of acidic foam from the column, a part of the stripped water is supplied to the upper plate in the amount of 0.2-0.3 of the total water distillation, the rest of the water, the amount of which is equal to the water that came with formalin and water chemically bound into the formaldehyde molecule, enters the column 14 units for distillation of methanol and TMK. The bottom product of almost pure water is sent to the sewer. The stripped off aqueous layer containing low volatile resins enters extractor 8, where, at the same temperature, the final conversion of heavy-boiling unsaturated alcohols into water-insoluble polyolefins takes place, which are removed from acidic water with the extractant. The acid is directed to the preparation of formaldehyde charge. The oil layer from the sump 7 is sent to the block of distillation columns, where the isoprene-isobutylene fraction is separated in column 10, which is separated in column 11 into isobutylene - recycle, returned to the synthesis reactor and raw isoprene, by simple rectification in column 12 turns into a commercial product, the bottom liquid of column 12, rectification of raw isoprene, returns to column 10, distillation of the isoprene-isobutylene fraction, heavy products from the bottom of this column enter column 13 where TMK is distilled off, which is returned to the synthesis reactor. The remains of heavy liquid waste are removed from the cube. Т.о. the proposed method for the production of isoprene is characterized by significantly better performance.

So the steam consumption is 5.5-6 Gcal / t, the yield of liquid waste is 195-200 kg / t, the consumption of isobutylene is 940 kg / t, the consumption of formaldehyde is 565-570 kg / t. The amount of drains is minimized, their pollution is very low. Improvement of indicators was achieved due to the rejection of DMD as a source of isoprene production. In the process of interaction of isobutylene and formaldehyde, MBD and unsaturated alcohol are simultaneously formed, which, under the conditions of existing production, are converted into DMD and DS, the latter interacts with polyoxymethylenes, from formalin, with the formation of heavy, thermally stable formals, in the DS reactor it is esterified with isobutylene, all these reactions lead to the cost of raw materials for the formation of heavy waste.

During the thermal catalytic decomposition of DMD according to the first variant, formaldehyde, unsaturated alcohol and other unsaturated products are simultaneously present on the active sites of the catalyst, which ensures the loss of raw materials for the formation of coke and green oil. At a temperature of 359-300°C, formaldehyde is not stable and decomposes to form H2, CO. CO2 and methanol. The processing of formaldehyde water in the formalin fortification column also leads to significant losses in the formation of tar, formic acid, H2, CO, CO2 and methanol and in physical losses with effluent. According to the second variant, during the hydrolysis of DMD in a hot circulating acid stream, MBD, unsaturated alcohol, and formaldehyde are simultaneously formed, the interaction between the latter leads to the formation of resins.

According to the proposed method, formalin is mixed with a hot stream of acid in alcohol-free water, therefore, polyoxymethylenes are rapidly hydrolyzed into monomeric forms and the formation of polyformals is completely prevented. The concept adopted in the proposed method for the production of isoprene from MBD, with complete suppression of the formation of DMD, made it possible to reduce by a third the loss of formaldehyde for waste generation. An increase in the yield of MBD was achieved through the use of 100% isobutylene with a minimum excess and formaldehyde mixture diluted to 8-16%. These measures allowed all the resulting DMD to be returned to the synthesis reactor and converted into MBD. Purification of the MBD solution from formaldehyde made it possible to selectively extract one mole of formaldehyde from dioxane alcohol, successively converting it into DMD, MBD, and isoprene.

Purification of the MBD solution from formaldehyde provided a highly selective course of dehydration reactions without additional formation of resins. High-temperature extraction of the stripped off acidic water layer prevented the ingress of unsaturated alcohols into the synthesis reactor and the loss of raw materials to increase waste.

As can be seen from the above, in the implementation of the claimed invention, the problem is solved - the creation of a more efficient method for producing isoprene while simplifying the process as a whole, which at the same time leads to a significant increase in the efficiency of the process of obtaining isoprene, reducing the cost of raw materials and steam, as well as eliminating gas emissions, reducing times of sewage and pollution.

Claims (5)

1. A method for the production of isoprene from isobutylene and formaldehyde in an aqueous medium in the presence of a water-soluble acid in a reactor with three transformation zones, followed by separation of the synthesis products into recycle products returned to the beginning of the process, waste and commercial isoprene, in which isoprene synthesis is carried out by dehydration of methyl butanediol at a temperature 120-150°C in the aqueous phase in the presence of acid, and before dehydration, the aqueous phase is subjected to deep purification from formaldehyde in a countercurrent reaction-extraction apparatus at a temperature of 60-110°C using a solvent inert to acid, formaldehyde, isobutylene and alcohols. 2. A method for the production of isoprene according to claim 1, characterized in that hexane is used as a solvent. 3. Method for the production of isoprene according to any one of paragraphs. 1-2, characterized in that the interaction of isobutylene with formaldehyde is carried out at a temperature of 60-110°C and with a complete recycle of the oil layer. 4. Method for the production of isoprene according to any one of paragraphs. 1-3, characterized in that the synthesis is carried out using a mixture containing 8-16% formaldehyde, which, before being fed into the reactor, is obtained by mixing formalin with a circulating acid solution and kept at a temperature of 70-110°C for 10-30 minutes. 5. Method for the production of isoprene according to any one of paragraphs. 1-4, characterized in that the circulating acid is subjected to reaction-extraction purification with an inert solvent at a temperature of 120-150°C before being fed to the batch preparation.

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