CN1044804C

CN1044804C - Method for production of methyl tertbutyl ether for production of high-purity isobutylene

Info

Publication number: CN1044804C
Application number: CN94110765A
Authority: CN
Inventors: 郝兴仁; 刘明久; 杨宗仁; 王伟; 王进善
Original assignee: Qilu Petrochemical Co of Sinopec
Current assignee: Qilu Petrochemical Co of Sinopec
Priority date: 1994-08-30
Filing date: 1994-08-30
Publication date: 1999-08-25
Anticipated expiration: 2014-08-30
Also published as: CN1117958A

Abstract

The present invention relates to a method for preparing methyl tert-butyl ether. Under the action of an acidic catalyst, isobutylene and methanol in four distillation fractions of carbon carry out etherifying reaction under the conditions that the airspeed is from 0.5 h<-1> to 30 h<-1>, the pressure is from 2MPa to 15MPa, the temperature is from 20 DEG C to 140 DEG C, and the molar ratio of the isobutylene to the methanol is from 0.5 to 3.0; the conversion rate is controlled to be less than 95%, and the content of methyl sec-butyl ether in the produced methyl tert-butyl ether is less than 0.1%(M/M). The method can be directly used for the cracking production of polymerizated-grade isobutene with high purity.

Description

Process for producing methyl tert-butyl ether for producing high-purity isobutylene

The present invention relates to a process for producing methyl t-butyl ether, and more particularly to a process for producing methyl t-butyl ether as a raw material for producing high-purity isobutylene.

It is known that, under the action of a catalyst of montmorillonite clay, silicotungstic acid, strong acid type cation exchange resin or molecular sieve, isobutene in mixed carbon four reacts with water to produce tert-butyl alcohol, and then the tert-butyl alcohol is decomposed to produce polymerization grade high-purity isobutene, and the method has low tert-butyl alcohol yield, so that the device investment is large and the energy consumption is high; the other method is to produce the methyl tert-butyl ether by the reaction of isobutene in mixed C4 and methanol under the action of a catalyst, and then produce the high-purity isobutene by the reaction, wherein the production process mainly comprises four modes: tubular fixed bed reaction processes, simple external circulation reaction processes, expanded bed reaction processes such as Fr 24245019 and catalytic distillation processes such as USP4471154, all of which have the following reactions:

main reaction: isobutylene + methanol- → methyl tert-butyl ether

Side reaction: isobutylene + Water- → Tert-Butanol

N-butene + water- → methyl sec-butyl ether

Isobutene + water- → isobutanol

The presence of these side reactions results in the formation of different impurities, among which tert-butanol, which, after the decomposition of isobutanol, forms isobutene without affecting the purity of the isobutene product, and which can also beremoved from the C-octaolefin in the refining of the methyl tert-butyl ether, whereas methyl sec-butyl ether has a boiling point very close to that of the methyl tert-butyl ether and, once formed, cannot be separated by conventional rectification methods, so that the formation of methyl sec-butyl ether is strictly controlled and the formation of n-butenes after the decomposition of methyl sec-butyl ether makes the n-butene content in isobutene higher than desired for the production of butyl rubber and the like.

The invention aims to reduce the amount of side reaction and improve the purity of the methyl tert-butyl ether when the carbon four mixed fraction reacts with methanol to produce the methyl tert-butyl ether.

To achieve the above object. The idea of the invention is to reduce the conditions causing the side reactions as much as possible according to the reaction mechanism.

The etherification reaction of the isobutene-containing mixed C4 and methanol is a reversible equilibrium exothermic reaction, the reaction speed can be accelerated by increasing the reaction temperature, but the conversion rate is not good, in order to obtain higher product yield, the etherification reaction is carried out under a proper temperature condition, when the isobutene concentration is reduced to a certain concentration, the n-butene adsorbed on the surface of the catalyst reacts with the methanol to generate methyl sec-butyl ether, the reaction temperature is reduced, the generation amount of the methyl sec-butyl ether is favorably reduced, but in order not to reduce the etherification reaction speed of the isobutene, a catalyst with high low temperature activity can be selected, the water content in the raw materials is controlled, the generation amounts of tert-butyl alcohol and isobutanol are controlled, the E8 and the generation amount of unsaturated hydrocarbons can be greatly reduced by increasing the methanol and reducing the reaction temperature, in addition, the etherification and polymerization of diolefin in the raw materials influence the purity of the methyl tert-butyl ether product, thereby affecting the purity of the isobutene after the methyl tert-butyl ether is decomposed,

the present invention is described in detail below:

a. under the action of catalyst in reaction equipment, the material containing no diolefin, alkyne or carbon four whose content is not more than 40PPM required by index and methanol are reacted to synthesize methyl tert-butyl ether, the reaction condition and conversion rate are controlled to be not more than 95%, so that the content of methyl sec-butyl ether in the produced methyl tert-butyl ether is not more than 0.1% (M/M), when the reacted mixture is separated, the product methyl tert-butyl ether flows out from the tower bottom, the azeotrope of unreacted carbon four fraction and methanol also flows out from the tower top, and can be continuously reacted in the second-stage reaction, so that the total conversion rate can be up to above 95% (M/M).

b. And extracting the azeotrope of the unreacted carbon four and the methanol by using water to recover the methanol for recycling.

c. In the case of a product methyl tert-butyl ether with particularly high purity requirements, traces of carbon four and methanol are further removed in a dehydrogenation column. The methyl tert-butyl ether thus obtained can be decomposed to produce high-purity polymer-grade isobutene.

D. If the hydrocarbon contains diene and alkyne which exceed the index requirements, the hydrocarbon can be selectively hydrogenated and removed under the action of the catalyst.

When the content of diolefin in the raw materialis less than 40 PPM. The etherification reaction can be carried out in a shell and tube fixed bed reactor, a simple external circulation, an expanded bed reactor, a mixed phase reactor or a catalytic distillation tower in an intermittent or continuous mode under the conditions of liquid phase and vapor-liquid mixed phase without selective hydrogenation, and under specific conditions, an acid catalyst can be used as a catalyst for the etherification reaction, preferably a strong acid type anion exchange resin catalyst.

The etherification reaction can be carried out under substantially any conditions, but in order to control the occurrence of side reactions such as methyl sec-butyl ether, preferable results can be obtained under the conditions of the following temperature, pressure and space velocity; the temperature range is 20-140 ℃, the pressure is 0.2-2.0 Mpa, and the airspeed is 0.5-30h^-1However, the molar ratio of methanol to isobutylene in the carbon four fraction should be greater than 0.8.

The raw material mixed with the carbon four and the methanol enter a reactor according to a certain alcohol-olefin ratio, etherification reaction is carried out under specific conditions, azeotrope of the unreacted carbon four and the methanol is extracted by water washing equipment to obtain the methanol, methanol aqueous solution is rectified in methanol rectifying equipment to recover the methanol for recycling, methyl sec-butyl ether in the separated methyl tert-butyl ether is less than 500PPM, the carbon four is less than 100PPM, the methanol is less than 100PPM, the produced high-purity methyl tert-butyl ether is cracked in decomposing equipment, the cracked methanol is recycled, the obtained high-purity polymer-grade isobutene is used as a raw material for producing butadiene styrene rubber or other chemical products,

the effects of the invention will befurther illustrated below by means of examples which are intended to be purely illustrative and not limitative of the invention, and any modification within the technical scope should be evident,

typical test feedstock composition: (% M/M)

Carbon three 0.46

Isobutane 0.94

N-butenes 41.40

Isobutene 20.20

N-butane + maleic acid 12.28

Fumaric acid 16.72

Diolefin 20PPM

Total of 100.0

Example 1 Synthesis of methyl tert-butyl/methyl Ether from the above starting materials in a cylindrical external circulation reactor at a pressure of 1.2MPa and a temperature of 30-60 deg.C, a ratio of external circulation to feed of 2.0, a molar ratio of the alcohol to the olefin of 1.0, and a space velocity of 2h^-1The conversion of isobutylene was 93.5%, and the purity of the methyl t-butyl ether produced was 98.5%, wherein t-butyl alcohol was 0.9%, isobutyl alcohol was 0.5%, methyl sec-butyl ether was 700PPM, and C8 olefin was 300 PPM.

Example 2.

The raw materials are synthesized into the methyl tert-butyl ether in a mixed phase reactor, the temperature is 30-60 ℃, the alcohol-olefin molar ratio is 1.05, and the space velocity is 4h^-1The conversion of isobutylene was 92.8%, and the purity of the methyl t-butyl ether produced was 98.5%, wherein t-butyl alcohol was 0.8%, isobutyl alcohol was 0.3%, methyl sec-butyl ether was 600PPM, and C8 olefin was 100 PPM.

Example 3.

The raw materials are synthesized into the methyl tert-butyl ether in a catalytic distillation tower, the pressure is 0.6MPa, the temperature is50 ℃ (tower top) to 130 ℃ (tower bottom), the alcohol-olefin molar ratio is 1.05, the reflux ratio is 1.0, and the space velocity is 5h^-1The conversion of isobutylene was 92.1%, and the purity of the produced methyl t-butyl ether was 98.8%, wherein t-butyl alcohol was 0.85%, isobutyl alcohol was 0.3% methyl sec-butyl ether was 600PPM, and C8 olefin was 150 PPM.

Example 4.

The raw materials are subjected to etherification reaction in a pre-reactor, the reaction temperature is 30-60 ℃, the molar ratio of alcohol to olefin is 1.05, and the space velocity is 4h^-1The reaction was carried out under a pressure of 0.6 MPa. The conversion of isobutylene was 94.2%, the purity of refined methyl t-butyl ether was 98.75%, and the tertiary alcohol was 0.8 percent of isobutanol, 0.3 percent of isobutanol, 500PPM of methyl sec-butyl ether, 100PPM of C8 olefin and unreacted C4 material enter a distillation tower for further reaction, the total conversion rate is 99.5 percent, and the residual carbon four can be used for producing the high-purity butene-1.

From the above examples, t-butyl alcohol and isobutanol greatly affect the purity of methyl t-butyl ether, and these impurities do not affect the purity of isobutylene produced by cracking methyl t-butyl ether, and saturated water in the raw material may be removed to reduce the amount of isobutylene produced, and the produced methyl t-butyl ether may be further refined to remove alcohols and C8 olefins.

Claims

1. A process for preparing methyl tert-butyl ether used for producing high-purity isobutene includes reaction of four carbon fractions containing isobutene, no diolefin, alkyne or not more than 40PPM with methanol under the action of catalyst and separation in subsequent equipment, and features that: the reaction conditions are controlled at the reaction temperature of 20-140 ℃, the pressure of 0.2-2 Mpa and the airspeed of 2-5 h^-1And the conversion rate of isobutene is not more than 95%.

2. The process as claimed in claim 1, wherein the reaction is carried out in a shell-and-tube fixed-bed reactor, a drum external circulation, an expanded-bed reactor, a mixed-phase reactor or a catalytic distillation column.

3. The process as claimed in claim 1, wherein the conversion of isobutene is controlled to below 95%, the methyl-sec-butyl ether content of the resulting methyl tert-butyl ether product is less than 0.1%, and the carbon four remaining after the first stage reaction can be reacted further in the second stage reaction to a total conversion of more than 99.5%.

4. The process as claimed in claim 1, wherein the C.sub.four-fraction used as starting material is selected from the group consisting of catalytically cracked C.sub.four, steam cracked C.sub.four, and carbon four-fractions containing isobutene of other origin.

5. The process of claim 4, wherein the isobutylene content of the carbon four-fraction is 5 to 50% by weight.

6. The process as claimed in claim 1, wherein the catalyst used is a strongly acidic macroporous sulfonic acid resin catalyst or other solid acidic catalyst.

7. The method as claimed in claim 4, wherein if the content of diolefin and alkyne in the C-C feedstock exceeds the required index, the diolefin and alkyne can be removed by selective hydrogenation before the etherification reaction with methanol,or the diolefin and alkyne can be removed and the etherification reaction can be carried out simultaneously on one catalyst by using a bifunctional catalyst with hydrogenation and etherification reactions.