RU2330009C1 - Method of obtaining isoprene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the method of obtaining isoprene by liquid-phase interaction of formaldehyde and isobutylene or the substances, which are their sources, for example 4, 4-dimethyl-1, 3-dioxane and trimethyl-carbinol, in the presence of the aqueous solution of an acidic catalyst, achieved at elevated temperatures and pressure with the obtaining of the products of the reaction and the remaining quantity of water in the form of steam flow, with subsequent cooling, by condensation and by separation into an aqueous and an organic layer, with the processing of the organic layer, which includes the isolation of hot isobutylene, isoprene, hot trimethyl-carbinol and antecedents of isoprene, including the isolation of hot isobutylene, isoprene, hot methyl-hydropropane, fractions of the hydrocarbons C₈-C₁₀ and carbonyl connections C₅H₁₀O and the high temperature boiling remainder, with the processed aqueous layer, with the discharge of organic products, and with the withdrawal of the liquid flow of the aqueous solution of the catalyst for extraction, with the subsequent return into the zone of synthesis, in this case the removal of trimethyl-carbinol, methyl-dihydropropane and the antecedents of isoprene, fractions of hydrocarbons C₈-C₁₀ and carbonyl connections C₅H₁₀O are accomplished by azeotropic rectification with the addition of water in the necessary quantity for the forming of the azeotrope with the distilled products in the column.

EFFECT: it makes it possible to carry out a continuous process with the recycling of the antecedents of isoprene isolated from the products of the synthesis, to avoid the worsening of the indices of the synthesis, exclude the losses of trimethyl-carbinol and the antecedents of isoprene, to improve the indices of expenditure of raw materials and power consumption.

6 cl, 6 ex, 1 dwg

Description

The invention relates to methods for producing isoprene from isobutylene and formaldehyde.

Isoprene is widely used as a monomer for the production of rubbers with properties close to natural, as well as in organic synthesis.

A number of methods are known for producing isoprene by liquid-phase interaction of formaldehyde and isobutylene or the substances that are their sources, for example, 4,4-dimethyl-1,3-dioxane and trimethylcarbinol, in the presence of an aqueous solution of an acid catalyst, carried out at elevated temperature and pressure of one or more contacting stages, with selection at the last contacting stage of reaction products and the balance amount of water in the form of a steam stream, followed by cooling, condensation and separation into water and rganichesky layers, with recycling of the organic layer comprising selection isobutylene isoprene fraction of trimethyl carbinol, metildigidropirana fractions, fractions of isoprene and high boiling residue precursor with the withdrawal of an aqueous solution of the catalyst in the liquid stream extraction, followed by return to the synthesis zone [USP 4511751, US Pat. RF 2280022, EP 0106323].

In all known methods, the processing of distilled synthesis products includes their cooling and condensation, separation of the condensate into the aqueous and organic layers, isolation from the organic layer by subsequent distillation of recycled isobutylene, target isoprene, trimethylcarbinol recycled fraction, 4-methyl-5,6-dihydro-2Н fraction -pyran (hereinafter methyldihydropyran), the recycle fraction of unconverted dimethyldioxane and isoamylene alcohols and a high-boiling residue, the isolation of low-boiling organic products from the aqueous layer (in particular ram trimethyl carbinol) and output the remaining water for cleaning.

To ensure high selectivity, the synthesis of isoprene, as a rule, is carried out with a stoichiometric excess of isobutylene and / or trimethylcarbinol. Regardless of whether isobutylene or trimethylcarbinol is used in the process, the effluent from the process contains a mixture of these substances in a ratio close to equilibrium [EP 0106323]. Thus, all known methods for producing isoprene involve the isolation and recycling of trimethylcarbinol.

In all known methods for producing isoprene by liquid-phase interaction of formaldehyde and isobutylene or the substances that are their sources, for example, 4,4-dimethyl-1,3-dioxane and trimethylcarbinol, in the presence of an aqueous solution of an acid catalyst, the conversion of the starting reagents is not complete. In addition, the synthesis products contain a significant amount of substances that differ from the raw materials used, but are precursors of isoprene (4,4-dimethyl-1,3-dioxane, 3-methyl-1-buten-3-ol, 3-methyl-3 butene-1-ol, 3-methyl-2-buten-1-ol, etc.). Isolation and recycling of unreacted raw materials and products that are precursors of isoprene is an integral part of the technology for the synthesis of isoprene.

One of the main by-products of the synthesis of isoprene is methyldihydropyran, which can be isolated from the synthesis products and subjected to vapor-phase decomposition (thermal or catalytic) in isoprene [US Pat. RF 2167710, 2134679]. The decomposition of methyldihydropyran can significantly (by 5-7%) increase the production of isoprene and, as a whole, increase the selectivity of its formation by 5-7% for formaldehyde and 3-5% for isobutylene.

Our studies of known isoprene production methods showed that the trimethylcarbinol fraction and the isoprene precursor fraction isolated from distillation synthesis products contain a significant amount (up to 20%) of hydrocarbon impurities, alcohols and carbonyl compounds, which have close boiling points, are azeotropic with the target products fractions and cannot be separated by simple distillation.

The recycling of fractions of trimethylcarbinol and fractions of isoprene precursors isolated by simple distillation into the reaction zone for the synthesis of isoprene leads to the accumulation of the above impurities in the synthesis products, which are practically inert under the process conditions, which in turn leads to the need to divert part of the fractions for utilization and, accordingly, to the deterioration of the process raw material consumption and energy costs.

The aim of the present invention is to remedy these disadvantages.

The goal was achieved by developing technical methods that allow separating the impurities of non-separate boiling and near boiling substances from the target fractions and eliminating their accumulation in the reaction mixture and in the synthesis products during recycling of the trimethylcarbinol fraction and the isoprene precursor fraction.

We propose a method for producing isoprene by liquid-phase interaction of formaldehyde and isobutylene or substances that are their sources, for example, 4,4-dimethyl-1,3-dioxane and trimethylcarbinol, in the presence of an aqueous solution of an acid catalyst, carried out at elevated temperature and pressure of one or more contacting stages, with selection at the last contacting stage of reaction products and the balance amount of water in the form of a steam stream, followed by cooling, condensation and separation into water and the organic layer, with the processing of the organic layer, including the isolation of recycle isobutylene, target isoprene, recycle trimethylcarbinol and precursors of isoprene, methyldihydropyran directed to decomposition, and a high boiling residue, with the withdrawal of the liquid stream of the aqueous catalyst solution for extraction, followed by return to the synthesis zone wherein the isolation of trimethylcarbinol, methyldihydropyran and isoprene precursors is carried out by azeotropic distillation with water.

We found that when the synthesis products are separated by azeotropic distillation with water, it is possible to separate impurities of by-products (hydrocarbons, alcohols and carbonyl compounds), which are inert under the process conditions and, when recycled to the reaction zone, trimethylcarbinol fractions and isoprene precursors accumulate in the flows and interfere with normal the course of the process and its performance worsen.

More detailed studies have shown that impurities of by-products (hydrocarbons, alcohols and carbonyl compounds) either do not form azeotropes with water, or form azeotropes with boiling points outside the boiling point range of the desired product azeotropes (79-97 ° C), which makes it possible to separate them with azeotropic distillation with water.

When water is added to the total fraction of by-products obtained after the isolation of isobutylene and isoprene, and the distillation of the fractions in the form of aqueous azeotropes with boiling points N.K. 78 ° C (heterogeneous), 78-87 ° C (homogeneous), 87-90 ° C (heterogeneous), 90-97 ° C (heterogeneous), followed by recycling of the fraction 78-87 ° C (trimethylcarbinol fraction) into the process and fractions of 90-97 ° С (isoprene precursors fraction), there is no accumulation of any by-products in the synthesis products, and it becomes possible to carry out a continuous process with recycling of trimethylcarbinol and isoprene precursors isolated from the synthesis products, to avoid deterioration of the synthesis due to recycling and accumulation impurities, eliminate loss of trimeth ilcarbinol and isoprene precursors.

The addition of water for the implementation of azeotropic distillation of isoprene synthesis products can be carried out by fractional supply of the required amount to each distillation column.

From the total fraction of by-products by azeotropic distillation with water, a wide fraction of products having a boiling point of water azeotropes up to 97 ° C can be distilled off first, followed by the isolation of the desired fractions from it.

The total fraction of by-products can be previously separated by simple distillation into a trimethylcarbinol fraction, a methyldihydropyran fraction, an isoprene precursor fraction and a high boiling residue, followed by purification of the trimethylcarbinol fraction and an isoprene precursor fraction by azeotropic distillation with water.

The amount of added water during the implementation of azeotropic distillation should be sufficient for the formation of azeotropic mixtures. The best results are achieved by adding 5-15% water in relation to the weight of the total fraction of by-products. With a smaller amount of added water, an accumulation of impurities in the recycled fractions of trimethylcarbinol and isoprene precursors is observed, and with a larger amount of excess water remains in the bottom residue as a separate poorly separated phase, which complicates its disposal.

Part of the fractions distilled off during azeotropic distillation with water forms heteroazeotropes, which, after condensation, are stratified into organic and aqueous layers. The resulting water layers can be used as water added to the initial total fraction of by-products or added fractionally to separate distillation columns.

If there is a vapor-phase thermocatalytic decomposition unit of methyldihydropyran in the isoprene production unit, the isoprene precursor fraction can be isolated as a total fraction with methyldihydropyran and thermocatalytically decomposed into isoprene, isobutylene and formaldehyde.

The essential characterizing features of the proposed method is the isolation of trimethyl carbinol synthesis products, and precursors of isoprene metildigidropirana azeotropic distillation with water and recycled to the process and trimethyl carbinol precursor of isoprene purified from impurities nerazdelnokipyaschih blizkokipyaschih hydrocarbons and C ₈ -C ₁₀ and oxygenates.

The proposed method allows to isolate a more concentrated fraction of methyldihydropyran, which, when decomposed, reduces energy consumption, increases productivity and improves the quality of isoprene.

In addition, the possibility of separating impurities allows you to process the decomposition products of the pyran fraction together with the products of isoprene synthesis.

The method allows to carry out a continuous process with the recycle of trimethylcarbinol and isoprene precursors isolated from the synthesis products, to avoid deterioration of the synthesis due to recycle and accumulation of impurities, to eliminate the loss of trimethyl carbinol and isoprene precursors and, as a result, to improve the process indicators in terms of raw material consumption and energy consumption.

The industrial feasibility of the method is illustrated by examples 1-5, example 6 is given for comparison.

Example 1

Schematic diagram of the installation for implementing the method according to the invention is shown in the drawing.

The installation includes a R-1 reactor, an E-2 separator, an X-3 refrigerator, an X-4 refrigerator-condenser, an E-5 settling tank, an S-6 mixer, an E-7 settling tank, an isobutylene K-8 stripping column, K-9 isoprene distillation column, K-10 hydrocarbon and carbonyl compounds distillation column, K-11 trimethyl carbinol distillation column, K-12 methyldihydropyran fraction distillation column, K-13 isoprene precursor fraction distillation column, organic products distillation column from the aqueous layer synthesis of K-14, a technological unit for the decomposition of a pyran tail coat ii URPF.

In the R-1 reactor, which is a 5 liter autoclave with a stirrer with a sealed electromagnetic drive and a thermostatic jacket, 4.5 liters of a 7% aqueous phosphoric acid solution are charged, with the stirring turned on, a hot coolant is fed into the thermostatic jacket and the reactor is heated to a temperature 160 ° C.

40% formalin with a flow rate of 256.5 g / h and concentrated isobutylene with a flow rate of 1747.2 g / h are fed to the reactor. The vapor-liquid stream exiting the reactor enters the separator E-2, where it is separated into liquid and vapor phases.

Vapors of reaction products and unconverted feedstock leaving the E-2 separator pass through the X-4 refrigerator-condenser, where they are cooled and condensed, and enter the E-5 settling tank, where they are stratified into aqueous and organic layers.

The pressure in the reaction unit (reactor, separator, refrigerator, sump) is maintained at 12-14 atm.

The liquid product stream, which is a mixture of an orthophosphoric acid aqueous solution and high boiling point by-products, is discharged from the E-2 separator in an amount of 1.6 l / hr, cooled in the X-3 refrigerator and fed to the C-6 mixer for extraction of organic products. As an extractant in the mixer C-6 serves an organic layer of synthesis products from the tank E-5. The mixture leaving the S-6 mixer enters the E-7 sump, where it is stratified into an organic layer containing high-boiled by-products extracted and an aqueous solution of phosphoric acid.

An aqueous solution of orthophosphoric acid purified from high-boiling organic products is returned from the E-7 tank by a pump to the R-1 reactor.

The organic layer from the tank E-7 is fed to the separation. First, in the distillation column K-8, isobutylene in the amount of 1561.6 g / h is recovered, which is recycled to the reactor R-1, and then in the distillation column K-9 isoprene in the amount of 177.4 g / h is recovered, which is fed for purification.

The bottoms product of the K-9 column in an amount of 297.9 g / h, which is a mixture of synthesis by-products and containing 74.8% trimethylcarbinol, 1.7% C ₈ -C ₁₀ hydrocarbons, 2.1% carbonyl compounds of the general formula C ₅ H ₁₀ O, 4.0% methyldihydropyran, 0.3% dimethyldioxane, 1.0% isoamylene alcohols and 16.1% other products, are mixed with 44.5 g / h of water and fed to the block of distillation columns K-10, K -11, K-12 and K-13 for separation into fractions by azeotropic distillation with water. During the sequential distillation of the fractions in the K-10 column, the fraction of C ₈ -C ₁₀ hydrocarbons and carbonyl compounds of the general formula C ₅ H ₁₀ O are distilled off in the form of a heterogeneous azeotrope with water having a boiling point of N.K. 78 ° C, in the amount of 11.8 g / h, in the K-11 column, the trimethylcarbinol fraction is distilled off in the form of a homogeneous azeotrope with water having a boiling point of 79-81 ° C, in the amount of 258.1 g / h, in the K- column 12, the methyldihydropyran fraction is distilled off in the form of a heterogeneous azeotrope with water having a boiling point of 83-89 ° C in an amount of 13.4 g / h; in the K-13 column, the isoprene precursors fraction (a mixture of dimethyldioxane and isoamylene alcohols) is distilled off as a heterogeneous azeotrope with water having a boiling point of 92-97 ° C, in the amount of 4.9 g / hour. The aqueous layers formed in the reflux tanks of the K-10, K-12 and K-13 columns during the condensation of heterogeneous azeotropes are combined into a common stream and sent to mix with the feed stream of the K-10 column.

The water layer of the condensate of the synthesis products from the E-5 tank is recycled in the required amount to the R-1 reactor to maintain the volume and acidity of the reaction water layer, and the balance amount is removed to the K-14 column for distillation of low-boiling organic products. As a distillate in a K-14 column, 22.5 g / hr of a fraction containing 85.9% trimethylcarbinol, 13.8% water and 0.3% other organic products were selected, and water was removed for purification.

The by-product fraction distilled off in the K-10 column and the bottoms from the K-13 column are taken out for disposal.

The trimethylcarbinol fraction distilled in the K-11 and K-14 columns and the isoprene precursor fraction distilled in the K-13 column are recycled to the P-1 reactor.

The fraction of methyldihydropyran, distilled off in a K-12 column, is sent for decomposition into the process unit of the URPF.

The decomposition of methyldihydropyran is carried out by contacting its vapors at a temperature of 400-450 ° C in the presence of water vapor with an aluminosilicate-containing catalyst, followed by cooling and condensation of the decomposition products and separation of the condensate into aqueous and organic layers.

13.4 g / h of the pyran fraction separated in the K-12 column and 40.0 g / h of water vapor are fed into the decomposition reactor and are contacted with the K-97 aluminosilicate-containing catalyst at a temperature of 400-450 ° C. Vapors of decomposition products and water leaving the reactor are cooled, condensed, and layered in the settling tank into the aqueous and organic layers. The aqueous layer containing 8.1% formaldehyde in an amount of 43.2 g / h is fed to the isoprene synthesis reactor P-1. The organic layer containing 82.9% of isoprene, 4.6% of isobutylene and 12.5% of other products, in the amount of 9.4 g / h, is fed into the tank E-5 for subsequent processing together with the organic layer of isoprene synthesis.

In accordance with the process balance, the yield of isoprene is 76.3 mol.% For formaldehyde and 78.7 mol.% For isobutylene.

The process is carried out continuously for 180 hours. An analysis of the composition of the flows in the samples taken after 48, 120, and 180 hours of operation shows identical results, which indicates the absence of any by-products in the synthesis products.

Example 2

The process is carried out as described in example 1, except that in the K-10 column a wide fraction of products with a boiling point of aqueous azeotropes is distilled off to 97 ° C, in the K-11 column, a fraction of hydrocarbons and carbonyl compounds with a boiling point of aqueous azeotropes N is distilled off .TO. 78 ° C, a trimethylcarbinol fraction is distilled off in a K-12 column. The bottoms product of the K-10 column and the distillate of the K-11 column are sent for disposal. The distillate of the K-12 column is recycled to the P-1 reactor. The bottoms product of the K-12 column, which is the total fraction of methyldihydropyran and isoprene precursors, is sent to the URPF technological unit for decomposition into isoprene and feedstock. Column K-13 is excluded from the scheme.

In accordance with the balance of the process, the yield of isoprene is 76.2 mol.% For formaldehyde and 78.9 mol.% For isobutylene.

The process is carried out continuously for 180 hours. An analysis of the composition of the flows in the samples taken after 48, 120, and 180 hours of operation shows identical results, which indicates the absence of any by-products in the synthesis products.

Example 3

The process is carried out as described in example 1, except that the water supply is fractional in each column, with a breakdown of the total number of columns in the following ratio: in K-10 - 15%, in K-11 - 55%, in K -12 - 20% and in K-13 - 10%.

In accordance with the balance of the process, the yield of isoprene is 76.4 mol.% For formaldehyde and 78.8 mol.% For isobutylene.

The process is carried out continuously for 180 hours. An analysis of the composition of the flows in the samples taken after 48, 120, and 180 hours of operation shows identical results, which indicates the absence of any by-products in the synthesis products.

Example 4

The process is carried out as described in example 1, except that as a source of formaldehyde in the reactor serves 4,4-dimethyl-1,3-dioxane in an amount of 396.7 g / h, and instead of fresh isobutylene (185.6 g / hour) as a raw material in the process serves trimethylcarbinol in an amount of 245.2 g / hour.

In accordance with the process balance, the yield of isoprene is 151.8 mol.% For dimethyldioxane (75.9% of the theoretical) and 158.2 mol.% For trimethylcarbinol (79.1% of the theoretical).

The process is carried out continuously for 180 hours. An analysis of the composition of the flows in the samples taken after 48, 120, and 180 hours of operation shows identical results, which indicated the absence of any by-products in the synthesis products.

Example 5

The process is carried out as described in example 1, except that the N.K. fraction is distilled off in column K-10. 83.0 ° C without the addition of water, from which the N.K. fraction is distilled off in the K-11 column with the addition of water. 77 ° C; water is added to the cubic product of the K-10 column, and a fraction of methyldihydropyran and a fraction of isoprene precursors are isolated in successive azeotropic distillation in K-12 and K-13 columns. The bottoms product of the K-11 column (trimethylcarbinol fraction) and the isoprene precursor fraction are recycled to the P-1 reactor.

In accordance with the balance of the process, the yield of isoprene is 76.1 mol.% For formaldehyde and 79.0 mol.% For isobutylene.

The process is carried out continuously for 180 hours. An analysis of the composition of the flows in the samples taken after 48, 120, and 180 hours of operation shows identical results, which indicates the absence of any by-products in the synthesis products.

Example 6 (for comparison).

The process is carried out as described in example 1, except that the rectification of the products is carried out without adding water. Moreover, in accordance with the boiling points of the components of the mixture in the column K-10, the N.K. 78 ° C, in the column K-11 - fraction 79-83 ° С, in the column K-12 - fraction 84-119 ° С and in the column K-13 - fraction 120-140 ° С. Fractions 79-83 ° C (trimethylcarbinol fraction) and 120-140 ° C (isoprene precursors fraction) are recycled to the P-1 synthesis reactor. The fraction 84-119 ° C (methyldihydropyran fraction) is fed for decomposition to the URPF unit. Fractions N.K. 78 ° C and bottoms product K-13 (fractions of by-products) are removed for disposal.

As the process is carried out, an increase in the number of distilled fractions and a decrease in the concentration of the target products occur.

After 30 hours of operation:

- the amount of the trimethylcarbinol fraction increases 1.7 times, and the trimethylcarbinol content in it decreases from 81.4% to 52.6%;

- the amount of the fraction of methyldihydropyran increases by 3.0 times, and the content of methyldihydropyran in it decreases from 66.3% to 23.3%;

- the amount of the fraction of isoprene precursors increases by 2.3 times, and the content of isoprene precursors in it decreases from 82.1% to 43.5%.

With further operation of the installation, the number of distilled fractions continues to increase, and due to the limited capacity of the columns in the number of distilled fractions, in order to stabilize the operating mode and prevent further accumulation of impurities in the recycled fractions, part of the distilled fractions is allocated for disposal.

After 90 hours of operation, in accordance with the process balance, the yield of isoprene is 71.2 mol.% For formaldehyde and 72.3 mol.% For isobutylene.

Claims (6)

1. The method of producing isoprene by liquid-phase interaction of formaldehyde and isobutylene or substances that are their sources, for example, 4,4-dimethyl-1,3-dioxane and trimethylcarbinol, in the presence of an aqueous solution of an acid catalyst, carried out at elevated temperature and pressure to obtain reaction products and the balance amount of water in the form of a steam stream, followed by cooling, condensation and separation into aqueous and organic layers, with the processing of the organic layer, including the allocation of recycled isobut len, target isoprene, recycle trimethylcarbinol and isoprene precursors, methyldihydropyran fraction, C ₈ -C ₁₀ hydrocarbon fraction and C ₅ H ₁₀ O carbonyl compounds and high boiling residue, with the processing of the aqueous layer, including the separation of organic products, with the conclusion of a liquid stream of an aqueous catalyst solution for extraction, followed by return to the synthesis zone, wherein the selection trimethyl carbinol, metildigidropirana and isoprene precursor, -C ₁₀ hydrocarbon fraction of C ₈ and carbonyl compounds C ₅ H ₁₀ O impl tvlyayut by azeotropic distillation with the addition of water in an amount necessary for the formation of the azeotrope distilled off in the product column. 2. The method according to claim 1, characterized in that the addition of water is carried out fractionally in each individual distillation column. 3. The method according to claim 1 or 2, characterized in that the amount of added water is 5-15% with respect to the organic layer obtained after the isolation of isobutylene and isoprene. 4. The method according to claim 1, characterized in that the fraction of C ₈ -C ₁₀ hydrocarbons and C ₅ H ₁₀ O carbonyl compounds, the trimethylcarbinol fraction, the methyldihydropyran fraction and the fraction are distilled from the organic layer obtained after isolation of isobutylene and isoprene by sequential azeotropic distillation precursors of isoprene. 5. The method according to claim 1, characterized in that a wide fraction containing trimethylcarbinol, methyldihydropyran and isoprene precursors is distilled off from the organic layer obtained after isolation of isobutylene and isoprene by azeotropic distillation, from which the C ₈ -C ₁₀ hydrocarbon fraction is distilled off by sequential azeotropic distillation and carbonyl compounds C ₅ H ₁₀ O, the trimethylcarbinol fraction and the methyldihydropyran fraction, and the isoprene precursors fraction is obtained as the bottom product. 6. The method according to claim 1, characterized in that the organic layer is previously separated by simple distillation into two fractions: a fraction of trimethylcarbinol and lower boiling products and a fraction of methyldihydropyran and higher boiling products, followed by separation from the first fraction by azeotropic distillation with water of the hydrocarbon fraction C ₈ - C ₁₀ and carbonyl compounds C ₅ H ₁₀ O, and from the second fraction, by azeotropic distillation with water, the fractions of methyldihydropyran and isoprene precursors.