CN112759499B

CN112759499B - Process for preparing isobutene by decomposing high-efficiency methyl tertiary butyl ether

Info

Publication number: CN112759499B
Application number: CN201911000785.1A
Authority: CN
Inventors: 吕爱梅; 侯磊; 孟宪谭; 杨忠梅; 李玉田; 张敏; 郭岩锋
Original assignee: China Petroleum and Chemical Corp; Qilu Petrochemical Co of Sinopec
Current assignee: China Petroleum and Chemical Corp; Qilu Petrochemical Co of Sinopec
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2023-10-20
Anticipated expiration: 2039-10-21
Also published as: CN112759499A

Abstract

The invention belongs to the technical field of isobutene preparation, and in particular relates to a process for preparing isobutene by decomposing high-efficiency methyl tertiary butyl ether, which comprises the following steps: A. refining MTBE raw material; B. MTBE decomposition; C. isobutene is de-weighted; D. and (5) recovering methanol. MSBE in the mixture is separated to a required degree before MTBE decomposition reaction, high-purity isobutene with purity more than 99.9% can be prepared, all indexes of polymerization-grade isobutene are met, the MTBE reaction conversion rate is high, the MSBE reaction conversion rate is low, the investment and energy consumption for removing MSBE from MTBE raw materials are low, the raw material application range is wide, all methanol is separated from light components such as isobutene through rectification, the content of isobutene in the recovered methanol is low, the residual MTBE is recycled, the flow is short, and the product yield is high.

Description

Process for preparing isobutene by decomposing high-efficiency methyl tertiary butyl ether

Technical Field

The invention belongs to the technical field of preparation of isobutene, and particularly relates to a process for preparing isobutene by decomposing methyl tertiary butyl ether with high efficiency.

Background

Isobutene is an important organic chemical raw material, can be used for synthesizing various products, such as medicine, pesticide intermediates and auxiliary agents, and can also be used for producing methyl methacrylate, butyl rubber, polyisobutene and other fields. In the production of downstream products from isobutylene as the main raw material, it is most often required that the purity of isobutylene reach the polymerization level (i.e., the superior product in SH/T1482-2004).

MTBE decomposition is one of the main technologies for preparing high-purity isobutene, and is the most widely used technical route at present. The main MTBE decomposition reaction is that MTBE is decomposed into isobutene and methanol, and the side reaction comprises that (1) methyl sec-butyl ether (MSBE) is decomposed into linear butene (1-butene and 2-butene) and methanol; (2) polymerization of isobutene to Diisobutene (DIB); (3) dehydrating methanol to generate dimethyl ether. Wherein the linear butene produced in side reaction (1) severely affects the purity of the isobutylene product.

Patent CN 101134705, win-wound octocrylno, germany, discloses a process for the preparation of isobutene by gas phase decomposition of MTBE, step a: the MTBE-containing material is separated by distillation, which material consists of the MTBE material and the return material, and a top material containing MTBE and a bottom material having a higher boiling point than MTBE are obtained. Catalytically decomposing the overhead obtained in step a to obtain a decomposition product, distillatively separating the decomposition product obtained into an overhead containing more than 90% by weight of isobutene and a bottom containing diisobutene, MTBE and more than 50% of methanol, distillatively separating the bottom obtained and returning the overhead to step a. The patent mainly carries out reprocessing on the bottom product obtained when the reaction product is separated by distillation, and MTBE, DIB and MSBE in methanol are separated by adding a distillation column, so that the obtained methanol is pure and can be used as a commercial product for conventional industrial synthesis, such as esterification. At the same time, unreacted MTBE is recovered to be decomposed continuously, so that the yield of isobutene is improved. The field of application of this technology is when the isobutylene unit is not a combined unit with MTBE synthesis but a stand-alone MTBE decomposition unit. Since the above-described functions of the combined device with MTBE synthesis can be implemented in existing equipment of the MTBE synthesis device. In the process step f of the method, methanol recovered by water washing and rectification is not subjected to any treatment, and isobutene in the methanol is not recycled. In the method, if MSBE is to be separated in the tower in the process step a, 50-40 theoretical plates are needed in the distillation tower, a catalyst consisting of magnesium oxide, aluminum oxide and silicon oxide is used, the MSBE concentration in the tower top material of the MTBE refining tower is allowed to be controlled to be not more than 2500 mass ppm, the number of the theoretical plates needed in the MTBE refining tower is 95, the reflux ratio is 3.7, the number of the theoretical plates in the refining tower is too large, the investment is too large, and the energy consumption is also high.

Patent CN 103992202 discloses a system and a method for preparing high-purity isobutene by decomposing methyl tert-butyl ether, wherein a mixture of gas-phase isobutene and liquid-phase methanol is sent into a gas-liquid separation tank to separate the gas-phase isobutene and the liquid-phase methanol; after being discharged from a gas-liquid separation tank, the gas-phase isobutene is compressed and cooled into liquid by a compressor, and then is sent into a methanol water scrubber to remove methanol in isobutene, and the isobutene after the methanol removal is sequentially sent into an isobutene light component removal tower and an isobutene heavy component removal tower to remove light components and heavy components in isobutene, so that high-purity isobutene is finally obtained; and sending the liquid-phase methanol into a methanol recovery tower from a gas-liquid separation tank to recover the methanol, sending a methanol aqueous solution in a methanol water washing tower into the gas-liquid separation tank, and sending the methanol aqueous solution into the methanol recovery tower to recover the methanol after one-time vapor-liquid flash evaporation to finally obtain a methanol product. In the method, most of methanol products are sent into a methanol recovery tower from a gas-liquid separation tank to recover methanol, in the methanol recovery tower, methanol and light components such as carbon four and MTBE which are lighter than methanol are tower top products, and water is tower bottom products, namely, the separation of most of methanol products and light components such as carbon four and MTBE is carried out by only one gas-liquid separation tank, and only one gas-liquid flash separation is carried out; in addition, a small part of methanol enters a methanol water scrubber along with isobutene, and part of carbon four is dissolved in a methanol water solution at the bottom of the methanol water scrubber, and the methanol water scrubber is subjected to vapor-liquid flash evaporation separation once and is not subjected to rectification separation, so that isobutene, other carbon four, MTBE and the like with a small quantity are always carried in a methanol product, and meanwhile, the isobutene in the methanol reduces the yield of the isobutene product. Another disadvantage of this method is that all the methanol in the methanol recovery column is separated from water by rectification, which is energy intensive. The process did not isolate MSBE in the MTBE feed prior to the reaction.

Patent CN 2015105061383 discloses a method for preparing isobutene from methyl tert-butyl ether, which comprises the following steps: synthesizing methyl tertiary butyl ether raw material at 55-65 ℃; separating methyl tertiary butyl ether raw materials in a catalytic rectifying tower to obtain refined methyl tertiary butyl ether; after heat exchange of the heat exchanger, the refined methyl tertiary butyl ether is sent into a tubular fixed bed reactor for decomposition reaction under the action of an aluminum silicate catalyst to obtain mixed liquid of gas-phase isobutene and liquid-phase methanol; gas-liquid separation; sequentially feeding the isobutene after methanol removal through a methanol water washing tower into two isobutene light-removing towers connected in series to remove light components in isobutene, and feeding the isobutene light-removing towers into two isobutene heavy-removing towers connected in series to remove heavy components in isobutene to obtain high-purity isobutene; and (3) feeding the methanol generated by the reaction and the aqueous solution of the methanol generated by the extraction of the isobutene into a methanol recovery tower of an etherification unit to recover the methanol, thereby obtaining a methanol product. The recovery method of the patent methanol is similar to that of the patent CN 103992202, and has the same problems. In addition, the MTBE directly enters an MTBE decomposition reactor from a catalytic rectifying tower, no refining treatment of heavy components is carried out, the service life of a catalyst is influenced by heavy components DIB, and the purity of an isobutene product is influenced by linear butene generated by MSBE decomposition; the method removes light components in isobutene through two isobutene light component removal towers connected in series, and removes heavy components in isobutene through two isobutene heavy component removal towers connected in series, so that the flow is long and the investment is large.

From the above technology, it can be seen that the existing MTBE decomposition process for preparing high-purity isobutene has unseparated components such as DIB (for example, patent CN 2015105061383), which results in short service life of the catalyst; most of the MSBE is not separated before the reaction (for example, the patents CN 2015105061383 and CN 103992202), if the isobutene with high purity is to be produced, the method is only applicable to the raw materials with extremely low MSBE content; if the recovered methanol product is used for MTBE synthesis, which contains MSBE remaining from the reaction, the concentration of MSBE entering the MTBE decomposition reactor is increased, the linear butene content is increased, and the purity of the isobutene product is reduced; although some cases consider the separation of MSBE impurities, the separation process is costly and energy-consuming (e.g., patent CN 101134705), and some cases have the above-mentioned problems. In the above technology, the separation and recovery processes of the methanol of the patents CN 2015105061383 and CN 103992202 are unreasonable, the recovered methanol contains a large amount of isobutene, and the methanol recovered by the patent CN 101134705 azeotropy with isobutene also contains a certain amount of isobutene.

Disclosure of Invention

The invention aims to solve the technical problems that: the process has the advantages that the defects of the prior art are overcome, the process for preparing the isobutene through decomposing methyl tert-butyl ether is provided, MSBE in the process is separated to a required degree before MTBE decomposition reaction, high-purity isobutene with purity higher than 99.9% can be prepared, all indexes of polymerization-grade isobutene are met, the MTBE reaction conversion rate is high, the MSBE reaction conversion rate is low, the investment and energy consumption for removing the MSBE from MTBE raw materials are low, the application range of raw materials is wide, all methanol is separated from light components such as isobutene through rectification, the isobutene content in the recovered methanol is low, the residual MTBE in the reaction can be recycled, the flow is short, and the product yield is high.

In order to achieve the above purpose, the invention adopts the following technical scheme:

the process for preparing isobutene by decomposing the high-efficiency methyl tertiary butyl ether comprises the following steps:

A. refining MTBE raw material

Feeding MTBE raw material into a refining tower for refining to obtain a tower top material containing MTBE and a tower bottom heavy component with a boiling point higher than that of MTBE, wherein the MTBE refining tower is used for removing DIB and part of MSBE at the same time;

B. MTBE decomposition

Sending the refined tower top material containing MTBE into a reactor, and carrying out decomposition reaction under the action of a catalyst to generate isobutene and methanol;

C. isobutene weight removal

The isobutene and methanol which are the decomposition reaction products are sent to an isobutene heavy removal tower for rectification separation, isobutene containing azeotropic methanol is obtained at the top of the tower, methanol is obtained at the bottom of the tower, and the methanol is returned to an MTBE synthesis device to be used as raw material;

D. methanol recovery

The isobutene containing azeotropic methanol is sent to a methanol washing tower for washing, the material at the bottom of the tower after washing is sent to a methanol recovery tower, process water is obtained at the bottom of the methanol recovery tower, the process water is sent to the methanol washing tower for recycling, and the material extracted from the top of the methanol recovery tower is sent to an isobutene heavy removal tower for recovering isobutene therein; the isobutene is obtained from the top of the methanol water washing tower, and the isobutene material is sent to an isobutene light component removing tower to remove light components, and then the isobutene product is obtained from the bottom of the tower.

The method comprises the following process steps:

in process step a, the MTBE feedstock may be any commercially available MTBE-containing material, such as MTBE obtained from a chemical reaction, e.g., an MTBE-containing material synthesized from the reaction of isobutylene and methanol in mixed carbon four, an outsourced MTBE-containing material, a single source of MTBE-containing material, or two or more different sources of MTBE-containing material, preferably an MTBE-containing material synthesized from the reaction of isobutylene and methanol in mixed carbon four. The MTBE mass percentage in the MTBE raw material is preferably 90% or more, more preferably 95% or more. The mixed carbon four usually contains 1-butene, and the 1-butene and methanol generate MSBE in the MTBE production process. If the raw material for producing MTBE contains MSBE, for example, the methanol raw material is methanol obtained by separating and recovering MTBE after the MTBE is decomposed into isobutene and methanol, the MSBE content in the MTBE product is the sum of MSBE generated in the production process and MSBE contained in the raw material. If the MTBE decomposition unit is a combination unit with an MTBE production unit, it is preferred that the mass fraction of MSBE produced during the MTBE production be 3000ppm or less (based on the MTBE product).

The MTBE raw material can directly enter an MTBE refining tower, or can enter the MTBE refining tower after light components in the MTBE raw material are separated through rectification.

The purpose of the process step A is mainly to remove high-boiling substances such as DIB, MSBE and the like from raw materials. DIB causes reduced catalyst activity and reduced service life, MSBE can be decomposed in the reactor into 1-butene and methanol, and part of 1-butene is isomerized into 2-butene; 1-butene and 2-butene can affect isobutylene specifications.

The specification of the polymer grade isobutene (superior product in SH/T1482-2004) has not only requirements for the isobutene content but also strict requirements for the 1-butene and 2-butene content, the 1-butene content being not more than 200ppm and the 2-butene content being not more than 300ppm. Because the boiling points of the 1-butene and the 2-butene are very close to that of the isobutene and are not easy to separate, the content of MSBE impurities in the tower top material of the MTBE refining tower must be strictly controlled below a certain amount to ensure that the content of the 1-butene and the 2-butene meets the requirements. The amount of MSBE allowed in the overhead of the MTBE purification column varies depending on the conversion of MSBE in the reactor. And if the conversion rate of MSBE is high, the allowable content of MSBE in the tower top material is low, otherwise, the allowable content is higher. The conversion of MSBE is strongly dependent on the catalyst used, in addition to the reaction conditions. The inventor finds that under certain catalyst and reaction conditions, the conversion rate of MSBE is much lower than MTBE, only a small amount of MSBE in raw materials is subjected to decomposition reaction in the reaction process, and the residual MSBE in the reaction is discharged out of the reactor along with reaction products and enters a subsequent separation link, wherein most of MSBE exists in the recovered methanol product. If the methanol product is returned to the MTBE synthesis unit as feed, as previously described, this will result in an increase in MSBE content in the MTBE product. If MSBE is not removed in the MTBE refining tower, MSBE is accumulated in the system, so that the linear butene content in the isobutene product exceeds the standard and the isobutene specification is influenced.

However, the atmospheric boiling point of MTBE is 55.05 ℃, the atmospheric boiling point of MSBE is 59.00 ℃, the difference between the atmospheric boiling point and the atmospheric boiling point is only 3.95 ℃, the theoretical plates of the tower needed by rectification separation are numerous, the reflux ratio is great, the investment of the tower is great, and the energy consumption is great, so that most of MTBE refining towers used in the existing MTBE decomposing and isobutene preparing technology are used for separating DIB with higher boiling point and easier separation, the separation of MSBE is not considered, and the number of the tower plates of the MTBE refining tower is not great; only a few MTBE refining towers are arranged for separating DIB and MSBE, for example, patent CN 101134705 adopts a catalyst composed of magnesium oxide, aluminum oxide and silicon oxide, when the conversion rate of MTBE is 85-95%, the concentration of MSBE in the material at the top of the refining tower needs to be controlled to be not more than 2500 mass ppm because of higher conversion rate of MSBE, 50-140 theoretical plates are needed for the MTBE refining tower, reflux ratio is 1-20, and separation cost is higher. The linear butene content of the product isobutene can only reach less than 1000 mass ppm. The inventor finds that by adopting a specific catalyst, the separation requirement of the MTBE refining tower can be greatly reduced, so that the theoretical plate number and reflux ratio of the MTBE refining tower are greatly reduced, and the separation cost is reduced. And meanwhile, isobutene products with lower linear butene content can be produced.

The higher the mass percentage of MSBE in the feed to the MTBE refining column, the less readily the product isobutylene will be to meet the requirements of not greater than 200ppm 1-butene content and not greater than 300ppm 2-butene content, and vice versa. When the catalyst which takes silicon dioxide as a carrier and takes heteropolyacid or a mixture of heteropolyacid and metal salt as an active component is used, when the MTBE conversion rate is 98-99.5%, the MSBE conversion rate is very low, the MSBE concentration in the tower top material of the MTBE refining tower is allowed to be controlled to be not more than 6000 mass ppm and even 9000 mass ppm, the MSBE concentration in the feeding material of the MTBE refining tower is allowed to be controlled to be not more than 0.9 mass percent and even 1.2 mass percent, and linear butene generated by decomposing the MSBE can meet the requirements that the 1-butene content in the product isobutene is not more than 200ppm and the 2-butene content in the product isobutene is not more than 300ppm after the subsequent separation and purification. The MSBE mass percentage in the feed of the MTBE refining tower is 0.6-1.2%, more preferably 0.6-0.9% and 0.9-1.2%, and the requirements can be met, so that the advantages of the invention can be further embodied. The number of theoretical plates of the MTBE refining tower is preferably 30-49, the reflux ratio is 0.5-20, more preferably 35-49, the reflux ratio is 0.5-2.5, and particularly preferably the reflux ratio is 0.5-2.0.

The pressure in the MTBE purifying column is preferably 0.1 to 1.0MPa, more preferably 0.1 to 0.5MPa.

And (B) a process step:

the MTBE decomposition reaction may be carried out in a liquid phase or a gas phase/liquid phase or in a gas phase, preferably in a gas phase, and the reaction pressure is low, preferably 0.1 to 0.4MPa, more preferably 0.2 to 0.3MPa. The low reaction pressure may allow the MTBE refining column of process step a to operate at a lower pressure. The MTBE decomposition reaction temperature is preferably 180 to 350℃and more preferably 190 to 260 ℃.

The catalyst may be any known acidic catalyst suitable for MTBE decomposition, such as metal oxide, metal mixed oxide catalysts, the catalysts described in patent CN 101134705 consisting of magnesium oxide, aluminum oxide and silicon oxide.

Preferably, silica is used as a carrier, and the active component is a catalyst of heteropolyacid or a mixture of heteropolyacid and metal salt. Such catalysts are described in detail in patent CN 00129388.5. Particularly preferably, the metal salt is Cr, mn, fe, mg, co, ni, bi, cu or Zn inorganic salt or Zn organic salt, the mass of the heteropolyacid accounts for 2-12% of the mass of the silica carrier, and the pore diameter of the carrier silica is as followsThe pore volume of the above pores occupies the pore diameter of +.>The pore volume of the above pores is more than 2%, and the pore diameter is +.>The specific pore volume of the above pores is 0.3-1.5ml/g. The heteropolyacid is preferably phosphomolybdic acid, phosphotungstic acid or silicotungstic acid. The silica used as support is generally spherical and has a particle size of 1 to 10mm, preferably 3 to 6mm.

The preparation method of the catalyst using silica as a carrier and the active component as a mixture of heteropolyacid and metal salt may employ any method of introducing the active component, such as ion exchange method, impregnation method, mechanical mixing method, etc. The impregnation method is preferred. When the catalyst is prepared by adopting the impregnation method, a saturated impregnation method or a solution impregnation method can be adopted, and the impregnated catalyst can be dried for a certain time at a temperature of more than 100 ℃ and then baked for 1-10 hours at a temperature of 200-500 ℃.

When the catalyst using the silicon dioxide as a carrier is used, and the MSBE concentration in the tower top material of the MTBE refining tower is controlled below 6000ppm by mass and the MTBE conversion rate is 98-99.5%, the linear butene content in the outlet material of the reactor can meet the conditions that the 1-butene content in the isobutene product is not more than 200ppm and the 2-butene content is not more than 300ppm. Preferably, the MSBE concentration in the overhead material of the MTBE refining column is allowed to be controlled below 1.2% by mass.

The process according to the invention is preferably carried out in a tubular reactor, in a shell-and-tube reactor, more preferably in a shell-and-tube reactor. The liquid hourly space velocity of MTBE in the reactor is preferably 0.1 to 10h ^-1 More preferably 0.3 to 5 hours ^-1 。

And (C) a process step:

the products of the decomposition, i.e., isobutene and methanol, are preferably cooled prior to entering the isobutylene heavy ends removal column and then enter a vapor-liquid separation tank for vapor-liquid flash separation, more preferably after heat exchange with the MTBE feedstock, and then cooled. The MTBE raw material is heated by utilizing the heat of the material at the outlet of the reactor, so that the energy consumption can be reduced. The gas phase at the top of the gas-liquid separation tank is compressed by a compressor and then is sent to the isobutene heavy-removing tower, and the liquid phase at the bottom is sent to the isobutene heavy-removing tower by a pump.

The decomposed product is rectified and separated by an isobutene heavy removal tower, most of methanol is firstly separated from the bottom of the tower, only a small amount of methanol and isobutene form an azeotrope, and the azeotrope is discharged from the top of the tower and enters a subsequent methanol water washing and recycling unit. The top pressure of the isobutylene heavy-removal tower is preferably 0.4-1.0MPa, and the reflux ratio is preferably 0.3-3. The top product is preferably isobutene with a purity of more than 95% by weight. The bottoms product is primarily methanol, contains small amounts of unreacted MTBE, MSBE, and small amounts of byproduct DIB, and is typically recycled as feed to the MTBE synthesis unit. The rest MTBE is returned to the MTBE synthesis part along with the methanol and finally becomes a part of MTBE raw materials of the MTBE refining tower, and the MTBE is recycled. The MSBE remaining from the decomposition reaction is also returned to the MTBE synthesis unit with methanol. MSBE generated by the MTBE synthesis device is usually controlled to be below 0.3% of MTBE products, the concentration of the residual MSBE in the decomposition reaction is increased, and if no MSBE removal measures are taken, the MSBE in the MTBE decomposition raw material is accumulated continuously, so that linear butene in isobutene in the decomposed product is increased, and the specification of isobutene in the product is influenced. The method removes the isobutene to the required degree through the refining tower in the step A, and ensures the specification of isobutene as a product. The returned DIB can be removed from the refining column.

And (D) a process step:

the azeotrope formed by the methanol and the isobutene obtained from the top of the isobutene heavy removal tower enters the methanol water washing tower in a liquid phase state, and has better water washing effect than a gas phase state. The top of the methanol water washing tower is provided with isobutene without methanol, the bottom of the methanol water washing tower is provided with methanol water solution, and the methanol water solution is sent to the methanol recovery tower. The preferred operating temperature of the methanol water scrubber is 25-40 ℃ and the oil-water ratio is 1-10. As most of methanol generated by the decomposition reaction is rectified and removed, the amount of methanol forming an azeotrope with the carbon four is small, so that the water consumption of the methanol water scrubber is small, and compared with the process that all materials from the decomposition reactor enter the methanol water scrubber to wash the methanol, the methanol water scrubber and the methanol recovery tower have the advantages of small treatment amount, and greatly reduced equipment investment and device energy consumption.

The pressure at the top of the methanol recovery tower is preferably 0.1-0.4MPa, and the reflux ratio is 1-20. In the methanol water scrubber, since isobutene has a certain solubility in water, a small amount of isobutene is inevitably dissolved in the aqueous methanol solution at the bottom of the column and enters the methanol recovery column. This results in a small amount of isobutene contained in the methanol feed withdrawn from the top of the methanol recovery column. This is unavoidable with any methanol water wash, rectification technique. In the prior art, the methanol after washing is directly returned to a methanol raw material tank or an outsourcing methanol storage tank of an MTBE synthesis device, and the tanks are all at normal pressure, so that the isobutene is completely lost, and even if the isobutene is not lost, the single pass yield of the isobutene is reduced, and the energy consumption is increased. The method sends the isobutene to the step C, enters an isobutene heavy removal tower, is rectified by the isobutene heavy removal tower, and separates the isobutene from the tower top, so that the isobutene is recovered, the yield of isobutene products is improved, the purity of methanol is improved, and the methanol can be taken as a product for take-off or an MTBE (methyl tert-butyl ether) synthesis device raw material. Preferably, the methanol material extracted from the top of the methanol recovery tower is firstly sent to the vapor-liquid separation tank in the step C, a vapor-liquid flash evaporation process is added, and then the methanol material enters the isobutene heavy removal tower for rectification, so that isobutene in methanol is separated more cleanly.

The isobutene obtained at the top of the methanol water washing tower possibly contains light components such as dimethyl ether and the like which are byproducts generated by the methanol dehydration reaction, an isobutene light component removal tower can be optionally added to remove the light components according to the content of the isobutene light component, the pressure at the top of the isobutene light component removal tower is preferably 0.1-2.0MPa, and the reflux ratio is preferably less than 300.

Compared with the prior art, the invention has the following beneficial effects:

(1) Most of the methanol is separated from the decomposition products, only a small amount of methanol is recovered by water washing and rectification, the treatment capacity of a methanol water washing tower and a methanol recovery tower is small, and the equipment investment and the device energy consumption are greatly reduced; the methanol recovered by water washing is subjected to rectification separation, does not contain light components such as isobutene, has low isobutene content in a methanol product and high isobutene yield, and all the methanol is subjected to rectification and light components such as isobutene separation, so that the methanol purity is high.

(2) The MTBE decomposition reaction conversion rate is high, the one-time yield of isobutene and methanol products is high, and the energy consumption is low.

(3) MSBE in the MTBE raw material is separated to a required degree through an MTBE refining tower, the methanol product contains a small amount of MSBE, the MSBE can be completely returned to the MTBE synthesis part, accumulation of the MSBE is avoided, the methanol product contains MTBE remained after the reaction, and the MTBE remained after the reaction is returned to the MTBE synthesis part is recycled.

(4) The MTBE conversion rate is high, the MSBE conversion rate is low, the MSBE concentration in the reactor feed, namely the material at the top of the MTBE refining tower, is allowed to be controlled to be not more than 6000 mass ppm and even 9000 mass ppm, and the maximum allowable mass percentage of the MSBE fed into the MTBE refining tower is 0.9% or even 1.2%. The process has loose requirement on the MSBE content in the raw material MTBE, and the raw material application range is wide.

(5) The MTBE refining tower has the advantages of less theoretical plates, small reflux ratio, low investment and energy consumption.

(6) The method has the advantages that the method is short in flow and low in energy consumption through a reverse five-tower flow, the purity of the produced isobutene is more than 99.9%, the 1-butene content is not more than 200ppm, the 2-butene content is not more than 300ppm, and all indexes of the high-quality isobutene are met.

Drawings

FIG. 1 is a schematic illustration of a process flow of the present invention;

in the figure: 1. a refining tower; 2. a reactor; 3. a gas-liquid separation tank; 4. an isobutene heavy removal tower; 5. a methanol water scrubber; 6. a methanol recovery column; 7. an isobutene light component removing tower.

Detailed Description

The invention is further described below with reference to the drawings and examples.

Example 1

Preparation of catalyst R.

Surface area after drying was 325m ² Per gram, specific pore volume of 0.78ml/g, pore diameter ofThe pore volume of the above pores occupies the pore diameter of +.>Silica with 13.7% of the pore volume of the above pores is used as a carrier. The phosphotungstic acid and Mg (NO) are loaded as required ₃ ) ₂ Dissolving in distilled water, wherein the amount of distilled water is 1.05 g of water per g of silicon dioxide; adding silicon dioxide into the solution, stirring and uniformly soaking; then baking for 2 hours at the temperature of 100 ℃ in the oven; bi (NO) to be supported ₃ ) ₃ Dissolving in distilled water, wherein the distilled water is loaded with phosphotungstic acid and Mg (NO ₃ ) ₂ To 1.05 g of water, the loaded phosphotungstic acid and Mg (NO ₃ ) ₂ Adding silica into the solution, stirring to make impregnation uniform; then, the mixture was baked in an oven at 100℃for 2 hours, and finally, baked in a muffle furnace at 350℃for 4 hours to obtain catalyst R. The mass of phosphotungstic acid in the catalyst R is 6.5 percent of the mass of silicon dioxide, and Bi is as follows ³⁺ /Mg ²⁺ The molar ratio of the catalyst to the phosphotungstic acid is 0.2/1:1.

example 2

The MTBE decomposition catalyst used was catalyst C described in the example of patent CN 001293885. The process flow shown in fig. 1 is adopted. The raw material MTBE enters an MTBE refining tower to remove heavy components, and the refined MTBE is discharged from the tower top and is sent to a reaction part. The catalyst C is filled in the reactor, and the gas phase MTBE reacts in the reactor to generate products such as isobutene, methanol and the like.

The raw material MTBE is synthesized by etherification reaction of isobutene and methanol in mixed carbon four, the methanol raw material of a synthesis device is the MTBE which is outsourced and accords with the industrial methanol specification of GB338-2004, wherein the MSBE is not contained in the methanol raw material, the MTBE specification generated by the reaction is shown in the MTBE raw material in a table a, and the MSBE generated in the etherification reaction process is 0.3%; when methanol is derived from MTBE generated by an MTBE synthesis device and is decomposed out by an MTBE decomposition device and returned to be recycled, 0.6% MSBE is carried in the methanol (a feeding flow meter of an MTBE refining tower), and the raw material MTBE composition is fed into the MTBE refining tower in the table a, wherein the flow rate is 12500kg/h.

Table a MTBE composition (mass fraction, kg/kg)

Sequence number	Component (A)	MTBE raw material	MTBE refining tower feed
				1	MTBE	0.97965	0.9738
2	Carbon four	0.001	0.001
				3	C5	0.0015	0.0015
4	Methanol	0.0085	0.00835
				5	Tert-butanol	0.003	0.003
6	MSBE	0.003	0.009
				7	DIB	0.0033	0.0033
8	Water and its preparation method	0.00005	0.00005

The MTBE refining column had 49 theoretical plates with a reflux ratio of 1.4 and a head pressure of 0.5MPa. The reaction temperature of the ether decomposition reactor is 210 ℃, the reaction pressure is 0.2MPa, and the liquid hourly space velocity of MTBE is 1h ^-1 . The MTBE conversion was 98.6% and the MSBE conversion was 4.3%. The top pressure of the isobutylene heavy-removing tower is 0.65MPa, the reflux ratio is 0.3, the top temperature is 50.6 ℃, and the bottom temperature is 116.4 ℃. The oil-water ratio of the methanol water washing tower is 2.0, and the operation temperature is 40 ℃. The top pressure of the methanol recovery tower is 0.3MPa, the reflux ratio is 8.0, the top temperature is 51.9 ℃, and the bottom temperature is 154.0 ℃. The top pressure of the isobutene light component removing tower is 0.95MPa, and the reflux ratio is 25.

Example 2 the relevant material compositions are listed in table 1.

Table 1 example 2 related Material composition (mass fraction, kg/kg)

The isobutylene product obtained in example 2 had an isobutylene content of 99.91%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 3

The MTBE decomposition catalyst used was catalyst E described in the examples of patent CN 001293885. The MTBE refining column had 39 theoretical plates with a reflux ratio of 2.3 and a head pressure of 0.4MPa. The reaction temperature of the ether decomposition reactor is 240 ℃, the reaction pressure is 0.2MPa, and the liquid hourly space velocity of MTBE is 1.5h ^-1 . The MTBE conversion was 99.5% and the MSBE conversion was 7.5%. The other conditions were the same as in example 2.

Example 3 the relevant material compositions are listed in table 2.

Table 2 example 3 related materials composition (mass fraction, kg/kg)

The isobutylene product obtained in example 3 had an isobutylene content of 99.95%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 4

The MTBE decomposition catalyst used was catalyst G described in the example of patent CN 001293885. The MTBE refining column had 34 theoretical plates with a reflux ratio of 5.0 and a head pressure of 0.5MPa. The reaction temperature of the ether decomposition reactor is 190 ℃, the reaction pressure is 0.3MPa, and the liquid hourly space velocity of MTBE is 0.5h ^-1 . The MTBE conversion was 99.0% and the MSBE conversion was 5.0%. The other conditions were the same as in example 2.

Example 4 the relevant material compositions are listed in table 3.

TABLE 3 example 4 related Material composition (mass fraction, kg/kg)

The isobutylene product obtained in example 4 had an isobutylene content of 99.99%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 5

The MTBE decomposition catalyst used was catalyst I described in the example of patent CN 001293885. The MTBE refining column had 42 theoretical plates with a reflux ratio of 1.9 and a column top pressure of 0.2MPa. The reaction temperature of the ether decomposition reactor is 200 ℃, the reaction pressure is 0.1MPa, and the liquid hourly space velocity of MTBE is 0.8h ^-1 . The MTBE conversion was 98.1% and the MSBE conversion was 2.9%. The other conditions were the same as in example 2.

Example 5 the relevant material compositions are listed in table 4.

TABLE 4 example 5 related Material composition (mass fraction, kg/kg)

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The isobutylene product obtained in example 5 had an isobutylene content of 99.93%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 6

The mass fraction of MSBE generated in the MTBE production process is 0.3%, when the methanol raw material is derived from MTBE generated by an MTBE synthesizing device, methanol is decomposed by an MTBE decomposing device and returned to be recycled, 0.9% MSBE is carried in the methanol (with an MTBE feeding flow meter of an MTBE refining tower), and the raw material MTBE composition entering the refining tower is fed into the MTBE refining tower in the table b.

Table b example 6MTBE refining column feed composition (mass fraction, kg/kg)

Sequence number	Component (A)	MTBE refining tower feed
			1	MTBE	0.9709
2	Carbon four	0.001
			3	C5	0.0015
4	Methanol	0.00825
			5	Tert-butanol	0.003
6	MSBE	0.012
			7	DIB	0.0033
8	Water and its preparation method	0.00005

The MTBE decomposition catalyst used was catalyst R described in example 1 above. The MTBE refining column had 49 theoretical plates with a reflux ratio of 0.8 and a column top pressure of 0.5MPa. The reaction temperature of the ether decomposition reactor is 200 ℃, the reaction pressure is 0.2MPa, and the liquid hourly space velocity of MTBE is 1h ^-1 . The MTBE conversion was 98.6% and the MSBE conversion was 1.4%. The other conditions were the same as in example 2.

Example 6 the composition of the materials is shown in Table 5.

TABLE 5 example 6 related Material composition (mass fraction, kg/kg)

The isobutylene product obtained in example 6 had an isobutylene content of 99.97%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 7

The MTBE refining column had 39 theoretical plates with a reflux ratio of 1.8 and a head pressure of 0.4MPa. The reaction temperature of the ether decomposition reactor is 230 ℃, the reaction pressure is 0.2MPa, and the liquid hourly space velocity of MTBE is 1.5h ^-1 . The MTBE conversion was 99.5% and the MSBE conversion was 4.5%. The other conditions were the same as in example 6.

Example 7 the composition of the materials is shown in Table 6.

TABLE 6 example 7 related Material composition (mass fraction, kg/kg)

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The isobutylene product obtained in example 7 had an isobutylene content of 99.99%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 8

The MTBE refining column had 34 theoretical plates with a reflux ratio of 4.0 and a head pressure of 0.5MPa. The reaction temperature of the ether decomposition reactor is 190 ℃, the reaction pressure is 0.3MPa, and the liquid hourly space velocity of MTBE is 0.6h ^-1 . The MTBE conversion was 99.0% and the MSBE conversion was 2.3%. The other conditions were the same as in example 6.

Example 8 the relative compositions of the materials are shown in Table 7.

TABLE 7 example 8 related Material composition (mass fraction, kg/kg)

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The isobutylene product obtained in example 8 had an isobutylene content of 99.96%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Example 9

The MTBE refining column had 42 theoretical plates with a reflux ratio of 1.3 and a column top pressure of 0.2MPa. The reaction temperature of the ether decomposition reactor is 210 ℃, the reaction pressure is 0.1MPa, and the liquid hourly space velocity of MTBE is 0.9h ^-1 . The MTBE conversion was 98.1% and the MSBE conversion was 0.4%. The other conditions were the same as in example 6.

Example 9 the relevant material compositions are listed in table 8.

Table 8 example 9 related Material composition (mass fraction, kg/kg)

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The isobutylene product obtained in example 9 had an isobutylene content of 99.97%, a 1-butene content of less than 200ppm, a 2-butene content of less than 300ppm, and the remaining indexes meeting the requirements of the superior products in the standard SH/T1482-2004.

Description of tables 1-8:

after the subsequent separation process, MSBE in the reactor outlet material is returned to the MTBE synthesis part along with the recovered methanol, namely MSBE carried in the methanol described in example 1.

Comparative example 1

The difference between the process flow and the process flow shown in the figure 1 is that the methanol at the top of the methanol recovery tower is not sent to the isobutene heavy removal tower for recovering isobutene, but is directly mixed with the methanol at the bottom of the isobutene heavy removal tower to be used as a methanol product, and the rest process flows are the same as the figure 1. The other conditions were the same as in example 2.

Example 2 the isobutene content of the methanol product of example 2 was reduced from 1.7% to 0.01% compared to comparative example 1, and the isobutene yield of the product was increased by 74kg.

Of course, the foregoing is merely preferred embodiments of the present invention and is not to be construed as limiting the scope of the embodiments of the present invention. The present invention is not limited to the above examples, and those skilled in the art will appreciate that the present invention is capable of equally varying and improving within the spirit and scope of the present invention.

Claims

1. A process for preparing isobutene by decomposing methyl tertiary butyl ether is characterized by comprising the following steps: the method comprises the following steps:

A. refining MTBE raw material

Feeding MTBE raw material into a refining tower for refining to obtain tower top material containing MTBE and tower bottom heavy component;

B. MTBE decomposition

Sending the refined tower top material containing MTBE into a reactor, and carrying out decomposition reaction under the action of a catalyst to generate isobutene and methanol; the conversion rate of MTBE is 98-99.5%;

C. isobutene weight removal

The decomposition products isobutene and methanol exchange heat with MTBE raw materials through a heat exchanger before entering an isobutene heavy-removal tower, are cooled through a cooler and enter a vapor-liquid separation tank for vapor-liquid flash separation, the gas phase at the top of the vapor-liquid separation tank is compressed through a compressor and then is sent to the isobutene heavy-removal tower, and the liquid phase at the bottom is sent to the isobutene heavy-removal tower through a pump; the top of the isobutene heavy removal tower is provided with isobutene containing azeotropic methanol, and the bottom of the isobutene heavy removal tower is provided with methanol;

D. methanol recovery

The isobutene containing azeotropic methanol is sent to a methanol water washing tower in a liquid phase state for water washing, the material at the bottom of the water washing tower is sent to a methanol recovery tower, process water is obtained at the bottom of the methanol recovery tower, part of the process water is sent to the methanol water washing tower for recycling, and the material extracted from the top of the methanol recovery tower is sent to an isobutene heavy removal tower for recovering isobutene therein; isobutene is obtained from the top of the methanol water washing tower, isobutene materials are sent to an isobutene light component removal tower to remove light components, and isobutene products are obtained from the bottom of the tower;

the maximum mass percentage of MSBE in the MTBE raw material in the step A is 1.2%; in the step A, controlling the concentration of MSBE in the tower top material of the MTBE refining tower to be no more than 9000 mass ppm; the theoretical plate number of the refining tower in the step A is 35-49, the tower top pressure is 0.1-1.0MPa, and the reflux ratio is 0.5-2.5;

the catalyst in the step B is a catalyst taking silicon dioxide as a carrier, and the active component is heteropolyacid or a mixture of heteropolyacid and metal salt; the mass of the heteropolyacid accounts for 2-12% of the mass of the silica carrier, and in the carrier silica, the pore volume of pores with the pore diameter of more than 200A accounts for more than 2% of the pore volume of pores with the pore diameter of more than 22A, and the specific pore volume of pores with the pore diameter of more than 22A is 0.3-1.5ml/g;

and D, feeding the materials extracted from the top of the methanol recovery tower into the vapor-liquid separation tank in the step C, and then feeding the materials into the isobutene heavy removal tower.

2. The process for preparing isobutene by decomposing methyl tert-butyl ether according to claim 1, wherein: the mass percentage of MSBE in the MTBE raw material in the step A is 0.6-0.9% or 0.9-1.2%.

3. The process for preparing isobutene by decomposing methyl tert-butyl ether according to claim 1, wherein: the metal salt is inorganic salt or organic salt of Cr, mn, fe, mg, co, ni, bi, cu or Zn.