RU2076093C1 - Method for production of alkyl-tert-alkyl ethers - Google Patents

Abstract

FIELD: organic chemistry, production of synthetic rubber. SUBSTANCE: method involves dehydrogenation of isoalkanes at 500-580 C. Thus prepared hydrocarbon mixture which comprises isoalkenes is brought into contact with alcohol in the presence of acid heterogeneous catalyst. Hydrocarbons are isolated of thus prepared alkyl-tert-butyl ether and are returned at dehydrogenation stage. Mentioned above contact is carried out at conversion 75-95 %. EFFECT: improves efficiency of the method.

Description

 The invention relates to the field of production of alkyl tert-alkyl esters used as high-octane components of motor fuels or which are intermediates in the processes of the isolation of isoolefins used as monomers for synthetic rubber.

 The raw materials for the production of alkyl tert-alkyl esters are isoolefin-containing hydrocarbon fractions of various origins, in particular gasoline pyrolysis, catalytic cracking, etc. Due to the sharp increase in the production of methyl tert-butyl ether (MTBE), which reached 92 in 1991. more than 10 million tons / year, processes for the production of isoolefin-containing fractions based on the isomerization of n-paraffins into isoparaffins followed by dehydrogenation of isoparaffins to isoolefins are becoming more widespread.

A known method of producing esters, including the following processes (US patent N 4118425, 3.10.1978):
isomerization of n-paraffin hydrocarbons into isoparaffinic;
separation of isoparaffin hydrocarbons;
dehydrogenation of isoparaffin hydrocarbons to isoolefin hydrocarbons;
esterification of isoolefins with alcohols;
washing alcohols from unreacted hydrocarbons;
separation of ethers by distillation.

 The synthesis of ether is carried out in a once-through reactor in the presence of a hydrocarbon recycled to the column for washing the reaction mixture from methanol. This scheme is complex and energy-intensive, since the synthesis of ether is carried out in excess of alcohol from 1.2 to 4.0 and in excess of hydrocarbon.

A known method of producing alkyl tert-alkyl esters (US patent N 4465870, 08/14/84) from n-butane and methanol comprising the following processes:
isomerization of n-butane to isobutane;
separating isobutane from n-butane;
dehydrogenation of isobutane to isobutylene;
obtaining MTBE from methanol and isobutylene;
purification of isobutane-recycle from oxygen-containing compounds, in particular from methanol, MTBE, etc. by adsorption on solid sorbents.

 The presence in the technological scheme of an additional process for the purification of isobutane-recycle from impurities of oxygen-containing compounds complicates it and increases its energy intensity.

A known method of producing MTBE (US patent N 4329516, 05/11/1982) from methanol and isobutylene, including the following processes:
isomerization of butane to isobutane;
separating isobutane from n-butane;
dehydrogenation of isobutane to isobutylene;
isolation of the isoolefin-containing fraction;
synthesis of MTBE in a once-through reactor;
separation of unreacted hydrocarbons from MTBE.

 The isobutane content in the product obtained at the stage of isomerization of n-butane to isobutane is 70–90% (the rest is n-utane and n-butylenes), and the product fed to the dehydrogenation step is at least 95 wt. the rest is mainly n-butane and butylenes.

Isobutane dehydrogenation is carried out at a temperature in the range of 538-849 ^° C and at a pressure of 0.2 0.9 ata, i.e. under vacuum. The C ₄ fraction isolated from the dehydrogenation products contains predominantly isobutane and isobutylene and is sent for esterification with methanol. The molar ratio of methanol to isobutene is from 1: 1 to 2: 1, preferably from 1.1: 1 to 1.4: 1. At a preferred temperature of 60 to 90 ^o C and a pressure of 10 22 atm. isobutylene is almost quantitatively converted to methyl tert-butyl ether. The reaction mixture, containing mainly isobutane, methyl tert-butyl ether and methanol, is sent for separation in a two-column scheme. In the first column, a mixture of isobutane and methanol is separated and returned to dehydrogenation as recycling. The second column separates the remaining part of methanol in the distillate, consisting of an azeotropic mixture of methanol and ether, and returns to the esterification reactor. Methyl tert-butyl ether is taken from the bottom of the column. Isobutane, obtained as a recycle, is mixed with isobutane obtained in the isomerization stage with a concentration of 70 to 90% and served for dehydrogenation. The content of isobutane supplied to the dehydrogenation reactor is 90 99%. The main part of the impurities is n-butane and n-butylenes.

The disadvantages of this method are:
1. High energy intensity of the process of obtaining methyl tert-butyl ether.

 2. The complex scheme of the esterification site.

High energy intensity of the process is caused by the following factors:
1. The esterification process is carried out at a high conversion of isoolefin.

 2. The separation of methyl tert-butyl ether is carried out according to a complex two-column scheme, where a large proportion of the energy is spent on separating an azeotropic mixture of methanol and ether from methyl tert-butyl ether.

 The task of the proposed method is to reduce the energy intensity of the process and its simplification.

The indicated result is achieved by the method of producing alkyl tert-alkyl esters, including catalytic dehydrogenation of isoalkanes at 500 -580 ^° C, subsequent contacting of the hydrocarbon mixture extracted from the dehydrogenation products with alcohol in the presence of an acidic heterogeneous catalyst, separation of hydrocarbons from the resulting ether and alcohol and their return to a dehydrogenation step in which dehydrogenation is carried out in the presence of a catalyst suspended in a hydrocarbon stream and contacting is carried out with alcohol t with isoalkenes conversion 75 95 rel. with the return to the stage of dehydrogenation of a hydrocarbon mixture containing from 5 to 20% isoalkenes.

 Reducing the energy intensity of the process and its simplification in the proposed method is achieved due to the lower conversion of the isoolefin and a single-column scheme for the isolation of the resulting ether due to the exclusion of the column separating methyl tert-butyl ether from the azeotropic mixture of ether and methanol.

 The invention allows the synthesis of ether with a sufficiently high selectivity with a low residual alcohol content in the reaction mixture after synthesis. Low alcohol concentration in the reaction mixture, for example methanol at the level of 1 to 5 wt. allows you to separate unreacted hydrocarbons from ether in one distillation column.

The process of dehydrogenation in the presence of a catalyst suspended in a hydrocarbon stream at a lower temperature at the level of 500 580 ^o C allows to reduce the consumption of isoalkanes even with a high content of azoalkenes in a cyclic azoalkane in particular from 5 to 20 wt.

 Example 1

Isobutane dehydrogenation is carried out in several fixed bed reactors. The dehydrogenation temperature of 540 ^o C, the absolute pressure of 300 mm RT.article the volumetric feed rate of raw materials in liquid form is 2.5 h ^-1 . As a catalyst, an aluminum chromium catalyst in the form of tablets is used containing 18 to 20% chromium oxide. Heat for the reaction is supplied by the combustion of coke, which is formed during the dehydrogenation process. With a lack of coke, fuel gas is additionally introduced. Thus, the process is cyclic, the reaction cycle is replaced by a regeneration cycle, the duration of the cycles is 20 minutes. As the feedstock, the starting isobutane obtained by any method having a concentration of up to 99 in the amount of 1875 parts and recycled isobutane containing 3 isobutylene in the amount of 1881 parts are used.

The product of dehydrogenation after cooling and processing with circulating oil is compressed to 12 at. The total amount of the dehydrogenation product is 3851 parts. After processing the dehydrogenation product by condensation, absorption, desorption, stabilization and rectification from heavy, the isolated isobutane-isobutylene fraction in an amount of 3398 parts contained at least 98% isobutane and isobutylene in a molar ratio of 1.07: 1, as well as small amounts of butane, n-butylenes and C ₄ and C ₅ hydrocarbons. Additionally, 422 parts of propane and light gases, including hydrogen, were obtained. In addition, the obtained fraction of hydrocarbons With ₅ and above in an amount of 5 parts.

882 parts of methanol are mixed with 3398 parts of the isobutane-isobutylene fraction, as well as 1737 parts of unreacted methanol in the form of an azeotrope with MTBE taken from the top of the MTBE rectification column from unreacted methanol and sent to the esterification reactor. The esterification is carried out at a temperature of about 60 ^o C in the liquid phase on a sulfion-ionic macroporous catalyst with a molar ratio of methanol to isobutylene equal to 1.3: 1.

The catalyst from the esterification reactor is separated on a distillation column under atmospheric pressure. 1881 parts of isobutane containing 3 isobutylene and 0.7 methanol, forming an azeotrope with isobutane, as well as small amounts of other unreacted hydrocarbons that are returned to dehydration, are taken from the top of the column. 4100 parts of MTBE and unreacted methanol are taken from the column cube. This mixture is separated by distillation under atmospheric pressure. An azeotropic mixture of unreacted methanol with MTBE is taken from the top of the column in an amount of 1737 parts, which is returned as a recycle to the esterification reactor, and 2363 parts of MTBE are taken from the cube of the column, with a concentration of about 98
Energy consumption amounted to 0.3 tons of standard fuel (here). The amount of coke formed was 30 parts. The conversion of isobutylene was 96
The increased energy consumption is primarily due to the use of a large molar ratio of methanol to isobutylene in the synthesis of MTBE, which led to the need for a significant recycling of unreacted methanol to the esterification reactor in the form of an azeotropic mixture with MTBE. A decrease in the molar ratio leads to a decrease in the conversion of isobutylene and to an increase in the content of isobutylene in recycled isobutane. The recycling of isobutylene in the composition of recycled isobutane gives additional coke formation, which under the conditions of a cyclic isobutane dehydrogenation process leads to a reduction in cycle time, the possibility of overheating of the catalyst during the regeneration process, to reduce its service life and increase the energy consumption of the process.

 Example 2

Isobutane dehydrogenation is carried out in reactors with a dusty fluidized bed of catalyst. The dehydrogenation temperature is 500 580 ^o C, gauge pressure 300 mm Hg the volumetric feed rate of the feedstock in the form of gas is 120,200 hours. A dust-like alumina-chromium catalyst is used as a catalyst. Heat for the reaction is supplied by the combustion of coke, which is formed in the process of dehydrogenation. Coke combustion takes place in a regenerator. A pulverized catalyst circulates between the reactor and the regenerator. If there is a lack of coke, fuel gas is additionally introduced into the regenerator. Thus, the process is continuous. As the feedstock, the starting isobutane obtained by any method having a concentration of up to 99 in the amount of 1875 parts and recycled isobutane containing 20 isobutylene in the amount of 2264 parts is used.

The product of dehydrogenation after cooling and processing with circulating water is compressed to 12 at. The total amount of the dehydrogenation product is 4248 parts. After processing the dehydrogenation product by condensation, absorption, desorption, stabilization and rectification from heavy, the isolated isobutane-isobutylene fraction in the amount of 3688 parts contained at least 98 isobutane and isobutylene in a molar ratio of 1: 1.1, as well as small amounts of butane, n -butylene and C ₄ and C ₅ hydrocarbons. Additionally, 520 parts of propane and light gases, including hydrogen, were obtained. In addition, a hydrocarbon fraction of C ₅ and higher in an amount of 15 parts was obtained.

872 parts of methanol are mixed with 3688 parts of the isobutane-isobutylene fraction and sent to the esterification reactor. The esterification is carried out at 50–80 ^{° C.} in the liquid phase on a sulfoionite macroporous catalyst with a molar ratio of methanol to isobutylene equal to 0.81: 1.

The catalyst from the esterification reactor is separated on a distillation column under a pressure of 6 atm. 2323 parts of isobutane containing 19.5 isobutylene and 2.5 methanol, forming an azeotrope with isobutane, as well as small amounts of other unreacted hydrocarbons, are taken from the top of the column. This mixture is washed from methanol and returned to dehydrogenation, methanol is isolated from wash water and returned to esterification. 2237 parts of MTBE having a concentration of more than 98% are taken from the cube of the first column. The energy consumption was 0.24 tons of standard fuel (here) per 1 t MTBE. The amount of coke formed was 320 parts. Isobutylene conversion was 79%
Example 3

Isobutane dehydrogenation is carried out in reactors with a dusty fluidized bed of catalyst. The dehydrogenation temperature is 500 580 ^o C, gauge pressure 300 mm Hg the volumetric feed rate of the feedstock in the form of gas is 120,200 hours. A dust-like alumina-chromium catalyst is used as a catalyst. Heat for the reaction is supplied by the combustion of coke, which is formed in the process of dehydrogenation. Coke combustion occurs in the regenerator. A pulverized catalyst circulates between the reactor and the regenerator. If there is a lack of coke, fuel gas is additionally introduced into the regenerator. Thus, the process is continuous. As the feedstock, the starting isobutane obtained by any method, having a concentration of up to 99% in the amount of 1875 parts, and recycled isobutane containing 5% of isobutylene in the amount of 1911 parts are used.

The product of dehydrogenation after cooling and processing with circulating water is compressed to 12 at. The total amount of the dehydrogenation product is 3894 parts. After processing the dehydrogenation product by condensation, absorption, desorption, stabilization and rectification from heavy, the isolated isobutane-isobutylene fraction in an amount of 3437 parts contained at least 98 isobutane in a molar ratio of 1.06: 1, as well as small amounts of butane, n-butylene and C ₄ and C ₅ hydrocarbons. Additionally, 426 parts of propane and light gases, including hydrogen, were obtained. In addition, a hydrocarbon fraction of C ₅ and higher in an amount of 5 parts was obtained.

922 parts of methanol are mixed with 3437 parts of the isobutane-isobutylene fraction and sent to the esterification reactor. The esterification is carried out at 50–80 ^{° C.} in a liquid fraction on a sulfoionite macroporous catalyst with a molar ratio of methanol to isobutylene equal to 1: 1.

 The catalyst from the esterification reactor is separated on a distillation column under a pressure of 6 atm. 1960 parts of isobutane containing 4.9 isobutylene and 2.5 methanol, forming an azeotrope with isobutane, as well as small amounts of other unreacted hydrocarbons, are taken from the top of the column. This mixture is washed from methanol and returned to dehydrogenation, methanol is isolated from the washings and returned to esterification.

 2399 parts of MTBE having a concentration of more than 98 are selected from the cube of the first column. The energy consumption amounted to 0.20 tons of standard fuel (here) per 1 ton of MTBE. The amount of coke formed was 300 parts. The conversion of isobutylene was 95

Claims (1)

A method of producing alkyl tert-alkyl esters, including catalytic dihydrogenation of isoalkanes at a temperature of 500 580 ^° C, subsequent contacting of a hydrocarbon mixture containing isoalkenes extracted from dehydrogenation products with alcohol in the presence of an acidic heterogeneous catalyst, separation of hydrocarbons from the resulting ether and alcohol and their return at the stage of dehydrogenation, characterized in that the dehydrogenation is carried out in the presence of a catalyst suspended in a hydrocarbon stream and contacting with alcohol bred with isoalkenes conversion 75 95 rel. returning to the stage of dehydrogenation of the hydrocarbon mixture containing 5 to 20% isoalkenes.