RU2259992C1 - Method for preparing methyl-tertiary-butyl ester - Google Patents

Abstract

FIELD: organic chemistry, chemical technology, petroleum chemistry.

SUBSTANCE: method involves interaction of methanol and isobutylene as components of hydrocarbons of (C₄)-fraction in the presence of the macroporous sulfocation-exchange resin in H⁺-form under enhanced temperature and pressure providing liquid-phase carrying out the process followed by separation of reaction products in fractionating column for the commercial methyl-tert.-butyl ester removing from vat and (C₄)-fraction of hydrocarbons and methanol as distillate by extraction of methanol from distillate with water and isolation of methanol from an aqueous extract by rectification with feeding for spraying the column with methanol-free (C₄)-fraction of hydrocarbons and removing the balance amount of this fraction from the process. Methanol from the distillate is extracted by feeding steam or water to the distillate vapors flow removing from the fractionating column. After condensation and separating into layers an aqueous layer is fed to isolation of methanol by fractionation and organic layer is fed to spraying of the fractionating column. Method provides simplifying the technology process.

EFFECT: improved preparing method.

2 cl

Description

The invention relates to the field of organic synthesis, and more specifically to methods for producing methyl tert-butyl ether, a high-octane component of gasolines for internal combustion engines.

Methyl tert-butyl ether (MTBE) is prepared by reacting in the presence of acidic catalysts methanol and isobutylene, which is usually part of the C ₄ fractions of hydrocarbons of various origins.

The reaction of methanol with isobutylene with the formation of MTBE is in equilibrium, due to which the depth of conversion of the reactants depends on the process conditions (temperature and ratio of reactants).

When using isobutylene-containing C ₄ fractions of hydrocarbons as raw materials, the isobutylene conversion depth is the most important indicator, since it determines not only the consumption of raw materials for MTBE production, but also the suitability of the remaining hydrocarbons for further use.

The technology for the production of MTBE from isobutylene-containing C ₄ fractions of hydrocarbons and methanol (“Production of methyl tert-alkyl ethers - high-octane gasoline components”, TsNIITEneftekhim, Moscow, 1988. “Oil processing” series, issue No. 9), as a rule, includes the following stages:

- synthesis of MTBE by the interaction of isobutylene with methanol in the presence of an acid catalyst in one or more reactors of various designs at a temperature of 40-100 ° C and pressure, providing a liquid-phase process;

- the allocation of the reaction products of the fraction of hydrocarbons With ₄ , return methanol and commodity MTBE using distillation and extraction.

A deep conversion of isobutylene is achieved by maintaining a low temperature (40-50 ° C) at the outlet of the last reactor (or reaction zone) along the reactor and using a stoichiometric excess of methanol.

The methanol content in commercial MTBE is regulated by TU 38.103704-90 (not more than 0.5%), therefore, excess (unreacted) methanol must be isolated and returned to the reactor.

Depending on the amount of excess methanol used, not only the conversion depth of isobutylene, but also the recovery scheme of the return methanol changes.

A known method of producing MTBE proposed by the company "Huls" (Hydrocarbon Process, 1977, 56, No. 11, 185) with a methanol / isobutylene ratio close to stoichiometric or with a small excess of methanol supplied to the synthesis of MTBE. The separation of unreacted methanol is carried out by distillation in the form of an azeotrope with C ₄ hydrocarbons, followed by washing (extraction of methanol with water) and distillation of recycle methanol from the wash water. However, the conversion of isobutylene with this process variant is ~ 95%.

A further increase in the conversion of isobutylene (up to 98%) can be achieved by increasing the ratio of methanol / isobutylene in the feedstock, however, there is a need for an additional stage of separation of excess methanol, namely the use of a second distillation column for distillation and recirculation into the azeotrope reactor methanol-MTBE ”(10-30% methanol), which complicates the process technology.

Closest to the essential distinguishing features of the proposed method is a method for producing MTBE from isobutylene-containing C ₄ fractions and methanol (US Pat. No. 5414147, publ. 05/09/1995 - prototype). In accordance with the prototype, the process is carried out at an elevated temperature (100-40 ° C) in the presence of an acid catalyst with an increased ratio of methanol / isobutylene and a pressure that ensures the liquid-phase process. Commodity MTBE is isolated from the reaction products by rectification, and the vapors of the C ₄ hydrocarbons and methanol azeotrope leaving as a distillate are condensed and sent to a container, from where liquid products are fed to an extractor in which C ₄ hydrocarbons are washed from methanol with water. C ₄ hydrocarbons washed from methanol are fed to the column for irrigation, and their balance amount is removed from the process. Methanol from the aqueous extract is isolated by distillation (see figure 1).

The prototype MTBE synthesis method is carried out at a higher methanol / isobutylene ratio (to increase the conversion of isobutylene without installing an additional column), and an increase in the output of unreacted methanol is achieved by supplying a distillation column designed to isolate MTBE with C ₄ hydrocarbons after methanol extraction from them . The methanol conversion is increased to 98%.

The disadvantage of the prototype method is a significant increase in the flow of hydrocarbons supplied to the washing. So, during the operation of the column with reflux number 2, the amount of hydrocarbons supplied to the washing from methanol increases three times. An increase in the flow of hydrocarbons, in turn, requires an increase in the overall dimensions of the extractor and the diameter of the pipelines, i.e. increases the intensity of the process.

The entire stream of C ₄ hydrocarbons exiting from the top of the column is subjected to deep cleaning from methanol, including both the balance amount withdrawn from the system and the stream returned to the column irrigation, which requires an increase in the water flow coming from methanol for washing. In addition, deep purification from methanol of that part of the stream that returns to the column irrigation is impractical.

The challenge facing the authors of the proposed method was to develop the synthesis of MTBE from methanol and isobutylene in the composition of C ₄ fractions of hydrocarbons, which allows for a high conversion of reagents to reduce the metal consumption and energy consumption of the process and simplify the process technology. According to this goal, we propose a method for producing MTBE by reacting methanol and isobutylene in the composition of C ₄ -fractions of hydrocarbons in the presence of macroporous sulfocationite in the N-form at elevated temperature and pressure, providing a liquid-phase process, followed by separation of the reaction mass by distillation into commercial MTBE and fraction hydrocarbons and methanol (azeotrope), with the extraction of methanol from the distillate with water, with the separation of methanol from the aqueous extract by distillation and feeding the columns for irrigation non-methanolic C ₄ fractions of hydrocarbons. The separation of methanol from the distillate before feeding it to the column irrigation is carried out by supplying water vapor or water to the distillate vapor stream leaving the column, followed by condensation of the vapors, separation of the condensate by the organic and aqueous layers, feeding of the organic layer to the column irrigation and withdrawal of the aqueous layer by distillation of methanol (see figure 2).

The C ₄ hydrocarbons removed from the process can be re-extracted in order to extract methanol by mixing with water, which, after separation in an additional tank, is fed into the distillate vapor stream leaving the column. With this scheme of the process, the decrease in the amount of water supplied to the washing will slightly reduce the degree of de-methanolization of the flow coming to the column irrigation (for example, from 99.9 to 99.0%, which is technically and economically justified), at the same time this amount of water is more than enough for exhaustive demethanolation of that part of the stream of hydrocarbons With ₄ , which is derived from the process (see figure 3).

An essential distinguishing feature of the proposed method from the prototype is the separation of methanol from the distillate before the latter is fed to the column for irrigation, not in a separate extractor, but by supplying water vapor or water to the distillate vapor stream leaving the column, which allows to simplify the technological scheme and reduce the metal consumption of the process (the unit is eliminated technological scheme - a separate extractor).

The proposed method allows to reduce the amount of water supplied to the washing, and to regulate different requirements for the degree of purification from methanol for flows supplied to the column irrigation and removed from the process.

In general, the proposed method for producing MTBE allows, in comparison with the known prototype method, to reduce the metal consumption of the process equipment and energy costs due to the pumping and washing of the increased flow of C ₄ -fraction of hydrocarbons.

Industrial applicability of the proposed method is illustrated by examples 1-3.

EXAMPLE 1 (in accordance with figure 2)

5294 kg / h of isobutane-isobutylene fraction containing 18.2% isobutylene and 601 kg / h of methanol are passed through a reactor filled with macroporous sulfocathionite and equipped with a device for removing heat generated by the reaction. The molar ratio of methanol / isobutylene is 1.091. The volumetric feed rate to the reactor is 2.0 h ⁻¹ , the temperature at the outlet of the reactor is maintained at a level of not more than 40 ° C. The effluent from the reactor is directed to a distillation column with an efficiency of 28 theoretical plates, operating with a reflux ratio of 2.5.

Isobutane and methanol vapors leaving the top of the column are mixed with water vapor supplied in an amount of 1500 kg / h to the head of the column, after which the vapors are condensed in a condenser refrigerator and the condensed products flow together with water into a reflux tank, where they are separated into water a layer containing methanol and an organic layer. The organic layer, which is an isobutane fraction containing 0.4% isobutylene and less than 0.01% methanol, is pumped to the column irrigation (10875 kg / h), and the balance amount (4350 kg / h) is taken out to the warehouse.

The water layer from the reflux tank in the amount of 1601 kg / h is discharged into the methanol stripping column. Distilled methanol (101 kg / h) is recycled to the MTBE synthesis reactor, and water is discharged into the sewer.

From the cube of the distillation column, 1444 commercial MTBEs are withdrawn that meet the requirements of TU 38.103704-90 (methanol content not more than 0.5%). Under the conditions of Example 1, the conversion of isobutylene is 98.2% and the spent isobutane fraction contains 0.4% isobutylene and less than 0.01% methanol.

EXAMPLE 2 (in accordance with figure 2)

5294 kg / h of isobutane-isobutylene fraction containing 18.2% isobutylene and 601 kg / h of methanol are passed through a reactor filled with macroporous sulfocathionite and equipped with a device for removing heat generated by the reaction. The molar ratio of methanol / isobutylene is 1.091. The volumetric feed rate to the reactor is 2.0 h ⁻¹ , the temperature at the outlet of the reactor is maintained at a level of not more than 40 ° C. The effluent from the reactor is directed to a distillation column with an efficiency of 28 theoretical plates, operating with a reflux ratio of 2.5.

1000 kg / h of water is introduced into the helium pipe of the column into the isobutane and methanol vapor stream exiting from the top of the column. The vapor-liquid mixture after passing through the refrigerator-condenser and condensation of the vapor flows into the tank, where it is stratified into aqueous and organic layers. The aqueous layer containing methanol is discharged to a methanol distillation column. The distilled methanol (101 kg / h) is recycled to the MTBE synthesis reactor, and the water is discharged into the sewer. The organic layer, which is an isobutane fraction containing 0.4% isobutylene and less than 0.1% methanol, is pumped to the column irrigation (10885 kg / h), and the balance amount (4354 kg / h) is re-mixed in a mixer with water in the amount of 1000 kg / h and again stratified in a second container into the aqueous and organic layers. The organic layer from the second tank, which is an isobutane fraction containing less than 0.01% methanol, is removed from the process (to the warehouse). The aqueous layer from the second tank, containing a small amount of methanol (less than 0.5%), is mixed with vapors of isobutane and methanol leaving the top of the distillation column, i.e. spray (sprayed) into the helmet pipe of the column.

From the cube of the distillation column, 1444 commercial MTBEs are withdrawn that meet the requirements of TU 38.103704-90 (methanol content not more than 0.5%).

Under the conditions of example 2, the conversion of isobutylene is 98.2% and the spent isobutane fraction contains 0.4% isobutylene and less than 0.01% methanol.

EXAMPLE 3

The process is carried out analogously to example 2, however, as the isobutylene-containing fraction using C ₄ fraction of catalytic cracking of the following composition (% wt.):

propylene 0.99 isobutane 26.70 n-butane 8.52 isobutylene 25.36 n-butylene 38.43

Under the conditions of example 3, the conversion of isobutylene is 97.9% and the spent isobutane fraction contains 0.7% isobutylene and less than 0.01% methanol.

The quality of MTBE meets the requirements of TU 38.103704-90 (methanol content not more than 0.5%).

Claims (2)

1. The method of producing methyl tert-butyl ether by reacting methanol and isobutylene in the composition of C ₄ -fractions of hydrocarbons in the presence of macroporous sulfocationite in the N-form at elevated temperature and pressure, providing a liquid-phase process, followed by separation of the reaction products in a distillation column into commercial methyl tert-butyl ether, removed from the bottom, and C ₄ -fraction of hydrocarbons and methanol in the form of a distillate, extraction of methanol from the distillate with water and separation of methanol from the aqueous extract and by distillation, followed by supplying a column of C ₄ -fractionless hydrocarbons to the column for irrigation and withdrawing the balance amount of this fraction from the process, characterized in that the extraction of methanol from the distillate is carried out by supplying water vapor or water to the distillate vapor stream leaving the distillation column and after condensation and stratification of the condensate, the aqueous layer is directed to the separation of methanol by distillation, and the organic layer to irrigation of the distillation column. 2. The method according to claim 1, characterized in that the balance amount of C ₄ -fraction of hydrocarbons before being withdrawn from the process is subjected to repeated extraction by mixing with water, followed by separation of the mixture and supplying an aqueous layer to the distillate vapor stream leaving the distillation column.

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