CN112759499A

CN112759499A - Process for preparing isobutene by high-efficiency decomposition of methyl tert-butyl ether

Info

Publication number: CN112759499A
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: 2021-05-07
Anticipated expiration: 2039-10-21
Also published as: CN112759499B

Abstract

The invention belongs to the technical field of preparation of isobutene, and particularly relates to a process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether, which comprises the following steps: A. refining MTBE raw material; B. decomposing MTBE; C. removing the weight of isobutene; D. and (4) recovering the methanol. The MSBE in the MTBE is separated to the required degree before the MTBE decomposition reaction, high-purity isobutene with the purity of more than 99.9 percent 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, investment and energy consumption for removing the MSBE from the MTBE raw material are low, the raw material application range is wide, all methanol is separated from light components such as isobutene through rectification, the content of the isobutene in the recovered methanol is low, the MTBE left in the reaction is recycled, the process is short, and the product yield is high.

Description

Process for preparing isobutene by high-efficiency decomposition of methyl tert-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 high-efficiency methyl tert-butyl ether.

Background

Isobutene is an important organic chemical raw material, can be used for synthesizing various products, such as intermediates and auxiliaries of medicines and pesticides, and can also be used for the fields of production of methyl methacrylate, butyl rubber, polyisobutylene and the like. When isobutene is used as a main raw material to prepare downstream products, the purity of the isobutene is required to reach a polymerization grade (namely, 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 the decomposition of MTBE into isobutene and methanol, and the side reaction comprises the decomposition of (1) methyl sec-butyl ether (MSBE) into linear butene (1-butene and 2-butene) and methanol; (2) the polymerization of isobutene to Diisobutylene (DIB); (3) the methanol is dehydrated to produce dimethyl ether. Wherein the linear butylene generated in the side reaction (1) seriously influences the purity of the isobutene product.

Patent CN 101134705 of oxkenson noco, won in germany, discloses a method for preparing isobutene by gas phase decomposition of MTBE, comprising the following steps: the MTBE-containing material consisting of the starting MTBE and the return material is separated by distillation to obtain an MTBE-containing top material and a bottom material boiling higher than MTBE. Catalytically decomposing the top material obtained in step a to obtain a decomposition product, separating the obtained decomposition product by distillation into a top material containing more than 90 wt.% isobutene and a bottom material containing diisobutylene, MTBE and more than 50% methanol, separating the obtained bottom material by distillation and returning the top product to step a. This patent essentially reprocesses the bottoms obtained in the distillative separation of the reaction products, and by adding an additional distillation column, the methanol obtained is very pure and can be used as a commercial product for conventional industrial syntheses, such as esterification, for example, to separate off MTBE, DIB and MSBE from the methanol. Meanwhile, the unreacted MTBE is recovered and continuously decomposed, so that the yield of isobutene is improved. The field of application of this technology is when the isobutene plant is not a combined plant with MTBE synthesis but a separate MTBE decomposition plant. Since the above functions can be implemented in the existing equipment of the MTBE synthesizer. In the process step f of the method, methanol recovered by water washing and rectification is not treated at all, and isobutene in the methanol is not recycled. In the case of this process, in which MSBE is separated in the column of process step a, 50 to 40 theoretical plates are required for the distillation column, a catalyst composed of magnesium oxide, aluminum oxide and silicon oxide is used, the concentration of MSBE in the top material of the MTBE refining column is allowed to be controlled to not more than 2500 mass ppm, the number of theoretical plates required for the MTBE refining column is 95, the reflux ratio is 3.7, the number of theoretical plates of the refining column is too large, the investment is too large, and the energy consumption is 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 for separation of the gas-phase isobutene and the liquid-phase methanol; after gas phase isobutene is discharged from the gas-liquid separation tank, the gas phase isobutene is compressed and cooled by a compressor to form liquid, the liquid is sent into a methanol washing tower to remove methanol in the isobutene, the isobutene after the methanol removal is sent into an isobutene light component removal tower and an isobutene heavy component removal tower in sequence to remove light components and heavy components in the isobutene, and finally high-purity isobutene is obtained; and (3) sending the liquid-phase methanol from the gas-liquid separation tank to a methanol recovery tower to recover the methanol, sending the methanol water solution in the methanol washing tower to the gas-liquid separation tank, carrying out primary vapor-liquid flash evaporation, and then sending the methanol water solution to the methanol recovery tower to recover the methanol, thereby finally obtaining a methanol product. 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, the methanol and light components such as carbon four, MTBE and the like which are lighter than the methanol are tower top products, and water is a tower bottom product, namely, most of the methanol products are separated from the light components such as the carbon four, the MTBE and the like only through one gas-liquid separation tank and only through once gas-liquid flash separation; in addition, a small part of methanol enters a methanol washing tower along with isobutene, part of carbon four is dissolved in methanol water solution at the bottom of the methanol washing tower, and the methanol water solution is subjected to once vapor-liquid flash evaporation separation and is not subjected to rectification separation, so that a large amount of isobutene, other carbon four, MTBE and the like are carried in a methanol product, and the yield of the isobutene product is reduced by the isobutene in the methanol. Another disadvantage of this process is that all the methanol in the methanol recovery column is rectified and separated from the water, which results in high energy consumption. The process does not isolate the MSBE in the MTBE feedstock prior to the reaction.

Patent CN 2015105061383 discloses a method for preparing isobutylene from methyl tert-butyl ether, which comprises the following steps: synthesizing a methyl tert-butyl ether raw material at the temperature of 55-65 ℃; separating the raw material of the methyl tert-butyl ether in a catalytic rectifying tower to obtain refined methyl tert-butyl ether; after heat exchange is carried out on refined methyl tert-butyl ether by a heat exchanger, the refined methyl tert-butyl ether is sent into a tubular fixed bed reactor, and decomposition reaction is carried out under the action of an aluminum silicate catalyst to obtain a mixed solution of gas-phase isobutene and liquid-phase methanol; gas-liquid separation; sequentially feeding the isobutene subjected to methanol removal by the methanol washing tower into two isobutene light component removal towers connected in series to remove light components in the isobutene, and feeding the isobutene light component removal towers into two isobutene heavy component removal towers connected in series to remove heavy components in the isobutene to obtain high-purity isobutene; and (3) feeding the methanol generated by the reaction and the methanol aqueous solution generated by extracting the isobutene into a methanol recovery tower of the etherification unit to recover the methanol, thereby obtaining a methanol product. The recovery method of methanol in the patent is similar to that in the patent CN 103992202, and has the same problems. In addition, the MTBE directly enters the MTBE decomposition reactor from the catalytic distillation tower without any refining treatment for removing heavy components, wherein the heavy components DIB can influence the service life of the catalyst, and the linear butylene generated by the decomposition of the MSBE can influence the purity of the isobutylene product; the method removes light components in the isobutene through two isobutene light component removing towers connected in series, removes heavy components in the isobutene through two isobutene heavy component removing towers connected in series, and has the advantages of long flow and large investment.

As can be seen from the technology, the existing MTBE decomposition process for preparing high-purity isobutene has unseparated DIB and other heavy components (for example, patent CN 2015105061383), which results in short service life of the catalyst; most do not isolate MSBE before reaction (for example, patent CN 2015105061383 and CN 103992202), if high purity isobutene is produced, only suitable for raw materials with extremely low MSBE content; if the recovered methanol product is used for MTBE synthesis and contains residual MSBE in the reaction, the concentration of the MSBE entering an MTBE decomposition reactor is increased, the content of linear butylene is increased, and the purity of the isobutene product is reduced; some methods consider the separation of MSBE impurities, but the separation process has large investment and high energy consumption (for example, patent CN 101134705), and some methods have the problems. In the above technology, the separation and recovery processes of the methanol in patents CN 2015105061383 and CN 103992202 are not reasonable, the recovered methanol contains a large amount of isobutylene, and the methanol azeotropic with isobutylene recovered in patent CN 101134705 also contains a certain amount of isobutylene.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the process for preparing the isobutene by decomposing the methyl tert-butyl ether efficiently overcomes the defects of the prior art, the MSBE in the MTBE is separated to the required degree before the MTBE decomposition reaction, the high-purity isobutene with the purity of more than 99.9 percent 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 the MTBE raw material are low, the raw material application range is wide, all methanol is separated from light components such as isobutene by rectification, the content of the isobutene in the recovered methanol is low, the residual MTBE in the reaction can be recycled, the process is short, and the product yield is high.

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

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

A. MTBE raw material refining

The MTBE raw material is fed into a refining tower for refining to obtain a tower top material containing MTBE and tower bottom heavy components with boiling points higher than that of the MTBE, and the MTBE refining tower has the task of removing DIB and removing part of MSBE;

B. MTBE decomposition

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

C. removal of isobutene by weight

Feeding the decomposition reaction product isobutene and methanol into an isobutene de-heavy tower for rectification separation, obtaining isobutene containing azeotropic methanol at the tower top, obtaining methanol at the tower bottom, and returning the methanol to the MTBE synthesis device as a raw material;

D. methanol recovery

Delivering isobutene containing azeotropic methanol to a methanol water washing tower for water washing, delivering materials at the bottom of the tower after water washing to a methanol recovery tower, obtaining process water at the bottom of the methanol recovery tower, delivering part of the process water to the methanol water washing tower for recycling, and delivering materials extracted from the top of the methanol recovery tower to an isobutene de-weighting tower for recovering isobutene therein; and (3) washing the tower top with methanol to obtain isobutene, sending the isobutene material to an isobutene lightness removing tower to remove light components, and obtaining an isobutene product at the tower bottom.

The process step A:

in process step A, the MTBE feed can be any industrial MTBE-containing material, such as a chemically synthesized MTBE feed obtained by reacting isobutylene and methanol in C4, an off-stream MTBE-containing material, a single MTBE-containing feed, two or more different MTBE-containing feeds, preferably an MTBE-containing feed synthesized by reacting isobutylene and methanol in C4. The mass percentage content of MTBE in the MTBE raw material is preferably 90% or more, and more preferably 95% or more. Mixed C4 usually contains 1-butene, which reacts with methanol during the MTBE production process to produce MSBE. If the raw material for producing MTBE contains MSBE, for example, methanol raw material is methanol which is separated and recovered after MTBE is decomposed into isobutene and methanol, the content of MSBE 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 and the MTBE production unit are integrated, it is preferable that the mass fraction of MSBE produced during the MTBE production is 3000ppm or less (based on the MTBE product).

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

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

The specification of polymerization grade isobutene (superior product in SH/T1482-2004) has requirements on isobutene content and strict requirements on 1-butene and 2-butene content, the 1-butene content is required to be not more than 200ppm, and the 2-butene content is required to be not more than 300 ppm. Because the boiling points of the 1-butene and the 2-butene are very close to that of isobutene and are not easy to separate, the content of the impurity MSBE in the tower top material of the MTBE refining tower must be strictly controlled below a certain amount so as to ensure that the content of the 1-butene and the 2-butene meets the requirements. The allowable content of MSBE in the top material of the MTBE refining tower varies according to the conversion rate of MSBE in the reactor. And when the conversion rate of the MSBE is high, the allowable content of the MSBE in the tower top material is low, and conversely, the allowable content is higher. The conversion of MSBE depends, in addition to the reaction conditions, also on the catalyst used. The inventor finds that under certain catalyst and reaction conditions, the conversion rate of the MSBE is much lower than that of MTBE, only a small amount of MSBE in raw materials is subjected to decomposition reaction in the reaction process, and residual MSBE in the reaction is discharged out of a reactor along with reaction products and enters a subsequent separation link, wherein most of MSBE exists in a recovered methanol product. If the methanol product is returned to the MTBE synthesis unit as feed, this will result in an increase in the MSBE content of the MTBE product, as described above. If the removal of the MSBE in the MTBE refining tower is not considered, the MSBE is accumulated in the system more and more, and finally the content of linear butylene in an isobutene product exceeds the standard, so that the specification of isobutene 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 of MSBE is only 3.95 ℃, the number of theoretical plates of the tower required by rectification separation is large, the reflux ratio is large, the investment of the tower is large, and the energy consumption is too high, so that most of MTBE refining towers arranged in the existing MTBE decomposition isobutene preparation technology are used for separating DIB with higher boiling point and easier separation, and the number of plates of the used MTBE refining towers is not large regardless of the separation of MSBE; only a few MTBE refining towers are arranged for separating DIB and MSBE simultaneously, for example, a catalyst consisting of magnesium oxide, aluminum oxide and silicon oxide is adopted in patent CN 101134705, when the MTBE conversion rate is 85-95%, the MSBE conversion rate is higher, so the concentration of the MSBE in the material at the top of the refining tower needs to be controlled to be not more than 2500 mass ppm, the MTBE refining tower needs 50-140 theoretical plates, the reflux ratio is 1-20, and the separation cost is higher. The linear butene content of the isobutene product can only reach less than 1000 mass ppm. The inventor finds that the separation requirement of the MTBE refining tower can be greatly reduced by adopting a specific catalyst, so that the theoretical plate number and the reflux ratio of the MTBE refining tower are greatly reduced, and the separation cost is reduced. And can also produce isobutene products with lower linear butene content.

The higher the mass percent of MSBE in the feed of the MTBE refining tower, the less easily the product isobutene can reach the requirements that the content of 1-butene is not more than 200ppm and the content of 2-butene is not more than 300ppm, and vice versa. When the catalyst which takes silicon dioxide as a carrier and takes heteropoly acid or a mixture of heteropoly acid and metal salt as active components is used in the following step B, when the MTBE conversion rate is 98-99.5%, the MSBE conversion rate is very low, the concentration of MSBE in the top material of the MTBE refining tower is allowed to be controlled to be not more than 6000 mass ppm, even 9000 mass ppm, the concentration of MSBE in the feed of the MTBE refining tower is allowed to be controlled to be not more than 0.9 mass percent, even 1.2 mass percent, and linear butene generated by the decomposition of MSBE can meet the requirements that the content of 1-butene in isobutene product after subsequent separation and purification is not more than 200ppm and the content of 2-butene in isobutene product is not more than 300 ppm. The mass percent of MSBE 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, and the superiority of the invention can be embodied. The number of the theoretical plates of the MTBE refining column is preferably 30 to 49, and the reflux ratio is 0.5 to 20, more preferably 35 to 49, and the reflux ratio is 0.5 to 2.5, particularly preferably 0.5 to 2.0.

The pressure of the MTBE refining column is preferably 0.1 to 1.0MPa, more preferably 0.1 to 0.5 MPa.

And a process step B:

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 0.3 MPa. The low reaction pressure may allow the MTBE finishing column of process step a to operate at lower pressures. The MTBE decomposition reaction temperature is preferably 180 ℃ and 350 ℃, and more preferably 190 ℃ and 260 ℃.

Catalysts all known acidic catalysts suitable for the decomposition of MTBE can be used, such as metal oxide, metal mixed oxide catalysts, catalysts consisting of magnesium oxide, aluminum oxide and silicon oxide as described in patent CN 101134705.

The catalyst which takes silicon dioxide as a carrier and takes heteropoly acid or a mixture of heteropoly acid and metal salt as an active component is preferred. Such catalysts are described in detail in patent CN 00129388.5. Particularly preferably, the metal salt is inorganic salt or organic salt of Cr, Mn, Fe, Mg, Co, Ni, Bi, Cu or Zn, the mass of the heteropoly acid accounts for 2-12% of the mass of the silica carrier, and the pore diameter in the silica carrier is within the range of

The pore volume of the above pores is within the pore diameter

More than 2% of the pore volume of the pores, the pore diameter is within

The specific pore volume of the pores is 0.3-1.5 ml/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 from 1 to 10mm, preferably from 3 to 6 mm.

The preparation method of the catalyst using the silicon dioxide as the carrier and the active component as the mixture of the heteropoly acid and the metal salt can adopt any method for introducing the active component, such as an ion exchange method, an impregnation method, a mechanical mixing method and the like. The impregnation method is preferred. When the catalyst is prepared by adopting an 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 the temperature of more than 100 ℃ and then calcined for 1 to 10 hours at the temperature of 200-500 ℃.

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

The process of the invention is preferably carried out in a tubular reactor, 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 from 0.1 to 10h^-1More preferably 0.3 to 5 hours^-1。

And C, process step:

before entering the isobutene de-heavy tower, the decomposition products isobutene and methanol are preferably cooled and then enter a vapor-liquid separation tank for vapor-liquid flash separation, and more preferably are subjected to heat exchange with the MTBE raw material and then cooled. The energy consumption can be reduced by heating the MTBE raw material by using the heat of the material at the outlet of the reactor. The gas phase at the top of the gas-liquid separation tank is compressed by a compressor and then sent into an isobutene de-weighting tower, and the liquid phase at the bottom is sent into the isobutene de-weighting tower through a pump.

The decomposed product is rectified and separated by an isobutene heavy-removing tower, most of methanol is 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 washing and recovering unit. The top pressure of the isobutene de-heavy 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 bottom product is mainly methanol, contains a small amount of unreacted MTBE, MSBE and a small amount of byproduct DIB, and is generally recycled as a raw material of an MTBE synthesis unit. The residual MTBE is returned to the MTBE synthesis part along with methanol and finally becomes a part of MTBE raw materials of the MTBE refining tower, and the MTBE is recycled. The residual MSBE from the decomposition reaction is also returned to the MTBE synthesis unit with methanol. The MSBE generated by the MTBE synthesis device is generally controlled to be less than 0.3 percent of the MTBE product, the concentration of the MSBE is increased by the residual MSBE in the decomposition reaction, and if no MSBE removing measure is adopted, the MSBE in the MTBE decomposition raw material is continuously accumulated, so that the linear butylene in the isobutene of the decomposition product is increased, and the isobutene specification of the product is influenced. The invention removes the isobutene to the required degree through the refining tower in the step A, thereby ensuring the specification of the isobutene product. The returned DIB can be removed from the finishing column.

And a process step D:

the azeotrope formed by the methanol obtained from the top of the isobutene de-heavy tower and the isobutene enters the methanol water washing tower in a liquid phase state, and the water washing effect is better than that in a gas phase state. Washing the top of the tower with methanol to obtain isobutene containing no methanol, and washing the bottom of the tower with methanol water solution to be fed into a methanol recovery tower. The methanol water washing tower is preferably operated at 25-40 deg.C with oil-water ratio of 1-10. Most of the methanol generated by the decomposition reaction is removed by rectification, and the amount of the methanol forming azeotropy with carbon four is small, so that the water consumption of the methanol washing tower is small, and compared with the process that the materials discharged from the decomposition reactor are all fed into the methanol washing tower to wash the methanol, the process brings the advantages that the treatment amounts of the methanol washing tower and the methanol recovery tower are small, and the equipment investment and the device energy consumption are greatly reduced.

The preferable tower top pressure of the methanol recovery tower is 0.1-0.4MPa, and the reflux ratio is 1-20. In the methanol water washing tower, a small amount of isobutene inevitably dissolves in the methanol aqueous solution at the bottom of the tower and enters a methanol recovery tower because the isobutene has certain solubility in water. This results in a methanol feed withdrawn from the top of the methanol recovery column containing a small amount of isobutene. This is unavoidable with any methanol washing and rectification technique. In the prior art, the washed methanol is directly returned to a methanol raw material tank or an external methanol storage tank of an MTBE synthesis device, and because the tanks are all normal pressure, all isobutene in the methanol raw material tank or the external methanol storage tank is lost, even if the isobutene is not lost, the once-through yield of the isobutene is reduced, and the energy consumption is increased. The isobutene is sent to the step C, enters an isobutene de-heavy tower and is rectified by the isobutene de-heavy tower, the isobutene in the isobutene de-heavy tower is separated from the top of the tower, the isobutene is recovered, the yield of isobutene products is improved, the purity of methanol is improved, and the methanol can be sold as a product and can also be used as a raw material of an MTBE (methyl tert-butyl ether) synthesis device. 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 process of primary vapor-liquid flash evaporation is added, and then the methanol material enters the isobutene de-heavy tower for rectification, so that the isobutene in the methanol is separated more cleanly.

The isobutene obtained from the top of the methanol washing tower may contain light components such as dimethyl ether and the like which are byproducts generated by the methanol dehydration reaction, and an isobutene lightness-removing tower can be selectively added to remove the light components according to the content of the light components, the tower top pressure of the isobutene lightness-removing 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 recycled by water washing and rectification, the treatment capacity of a methanol water washing tower and a methanol recycling tower is small, and the equipment investment and the energy consumption of a device are greatly reduced; methanol recovered by washing is rectified and separated, light components such as isobutene are not contained, the content of isobutene in a methanol product is low, the yield of isobutene is high, all methanol is rectified and separated from the light components such as isobutene, and the purity of the methanol is high.

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

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

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

(5) The MTBE refining tower needs few theoretical plates, small reflux ratio and low investment and energy consumption.

(6) The process is short, the energy consumption is low, the purity of the produced isobutene is more than 99.9 percent, the content of 1-butene is not more than 200ppm, the content of 2-butene is not more than 300ppm, and all indexes of high-quality isobutene are met.

Drawings

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

in the figure: 1. a refining tower; 2. a reactor; 3. a gas-liquid separation tank; 4. an isobutylene de-heaving column; 5. a methanol water washing tower; 6. a methanol recovery tower; 7. and (4) an isobutene lightness-removing tower.

Detailed Description

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

Example 1

And (3) preparing a catalyst R.

Using a surface area of 325m after drying²A specific pore volume of 0.78ml/g and a pore diameter of

The pore volume of the above pores occupies the pore diameter

Silica having 13.7% of the pore volume of the above pores was used as a carrier. Loading phosphotungstic acid and Mg (NO) required to be loaded₃)₂Dissolving in distilled water, wherein the amount of the distilled water is calculated by 1.05 g of water per gram of silicon dioxide; adding silicon dioxide into the solution, and stirring to ensure that the solution is uniformly impregnated; then baking for 2 hours in an oven at the temperature of 100 ℃; bi (NO) to be loaded as required₃)₃Dissolving in distilled water in an amount per gram of phosphotungstic acid and Mg (NO)₃)₂The silica is mixed with 1.05 g of water, and loaded with phosphotungstic acid and Mg (NO)₃)₂Adding the silicon dioxide into the solution, and stirring to ensure that the impregnation is uniform; then baking for 2 hours in an oven at the temperature of 100 ℃, and finally roasting for 4 hours in a muffle furnace at the temperature of 350 ℃ to prepare the catalystAn oxidizing agent R. The mass of phosphotungstic acid in the catalyst R accounts for 6.5 percent of the mass of silicon dioxide, and Bi³⁺/Mg²⁺The molar ratio of the catalyst to the phosphotungstic acid is 0.2/1: 1.

example 2

MTBE decomposition catalyst C described in the examples of patent CN 001293885 was used. The process flow shown in fig. 1 is adopted. Raw material MTBE enters an MTBE refining tower, heavy components in the raw material MTBE are removed, and refined MTBE is discharged from the top of the tower and is sent to a reaction part. The reactor was packed with the above catalyst C, and the gaseous MTBE was reacted in the reactor to produce isobutylene, methanol and the like.

The raw material MTBE is synthesized by the etherification reaction of isobutene in mixed C4 and methanol, the methanol raw material of a synthesizer is the MTBE raw material which does not contain MSBE when the methanol raw material is purchased and meets the GB338-2004 industrial methanol specification, the specification of the MTBE generated by the reaction is shown in the table a, and the MSBE generated in the etherification reaction process is 0.3 percent; when the methanol is derived from MTBE generated by the MTBE synthesis device, and then the methanol is decomposed by the MTBE decomposition device and returned to be recycled, 0.6 percent of MSBE is carried in the methanol (by an MTBE refining tower feeding flow meter), the composition of the raw material MTBE is shown as the feeding of the MTBE refining tower in the table a, and the flow rate is 12500 kg/h.

TABLE a MTBE raw Material composition (mass fraction, kg/kg)

Serial number	Components	MTBE starting material	MTBE finishing column 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-butyl alcohol	0.003	0.003
6	MSBE	0.003	0.009
				7	DIB	0.0033	0.0033
8	Water (W)	0.00005	0.00005

The MTBE refining column had 49 theoretical plates, a reflux ratio of 1.4 and a column top pressure of 0.5 MPa. 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. MTBE conversion was 98.6% and MSBE conversion was 4.3%. The top pressure of the isobutene de-weighting tower is 0.65MPa, the reflux ratio is 0.3, the temperature at the top of the tower is 50.6 ℃, and the temperature at the bottom of the tower 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 temperature at the top of the tower is 51.9 ℃, and the temperature at the bottom of the tower is 154.0 ℃. The top pressure of the isobutene lightness-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 materials composition (mass fraction, kg/kg)

The isobutene content of the isobutene product obtained in example 2 is 99.91%, the 1-butene content is less than 200ppm, the 2-butene content is less than 300ppm, and the other indexes meet the requirements of the superior product in the standard SH/T1482-2004.

Example 3

MTBE decomposition catalyst the catalyst E described in the examples of patent CN 001293885 was used. The MTBE refining column had 39 theoretical plates, a reflux ratio of 2.3 and a column top pressure of 0.4 MPa. The reaction temperature of the etherification 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 remaining conditions were the same as in example 2.

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

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

The isobutene content of the isobutene product obtained in example 3 is 99.95%, the 1-butene content is less than 200ppm, the 2-butene content is less than 300ppm, and the other indexes meet the requirements of the superior product in the standard SH/T1482-2004.

Example 4

MTBE decomposition catalyst the catalyst G described in the examples of patent CN 001293885 was used. The MTBE refining column had 34 theoretical plates, a reflux ratio of 5.0 and a column top pressure of 0.5 MPa. The reaction temperature of the etherification 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 remaining conditions were the same as in example 2.

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

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

The isobutene content of the isobutene product obtained in example 4 is 99.99%, the 1-butene content is less than 200ppm, the 2-butene content is less than 300ppm, and the other indexes meet the requirements of the superior product in the standard SH/T1482-2004.

Example 5

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

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

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

The isobutene content of the isobutene product obtained in example 5 was 99.93%, the 1-butene content was less than 200ppm, the 2-butene content was less than 300ppm, and the remaining criteria met the requirements of the premium product in the standard SH/T1482-2004.

Example 6

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

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

Serial number	Components	MTBE finishing column feed
			1	MTBE	0.9709
2	Carbon four	0.001
			3	C5	0.0015
4	Methanol	0.00825
			5	Tert-butyl alcohol	0.003
6	MSBE	0.012
			7	DIB	0.0033
8	Water (W)	0.00005

The MTBE decomposition catalyst employed was catalyst R described above in example 1. The MTBE refining column had 49 theoretical plates, a reflux ratio of 0.8 and a column top pressure of 0.5 MPa. 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. MTBE conversion was 98.6% and MSBE conversion was 1.4%. The remaining conditions were the same as in example 2.

Example 6 the relevant material compositions are listed in table 5.

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

The isobutene content of the isobutene product obtained in example 6 is 99.97%, the 1-butene content is less than 200ppm, the 2-butene content is less than 300ppm, and the other indexes meet the requirements of the superior product in the standard SH/T1482-2004.

Example 7

The MTBE refining column had 39 theoretical plates, a reflux ratio of 1.8 and a column top pressure of 0.4 MPa. The reaction temperature of the etherification 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 remaining conditions were the same as in example 6.

Example 7 the relevant material compositions are listed in table 6.

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

The isobutene content of the isobutene product obtained in example 7 was 99.99%, the 1-butene content was less than 200ppm, the 2-butene content was less than 300ppm, and the remaining indices met the requirements of the premium product in the standard SH/T1482-2004.

Example 8

The MTBE refining column had 34 theoretical plates, a reflux ratio of 4.0 and a column top pressure of 0.5 MPa. The reaction temperature of the etherification 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 remaining conditions were the same as in example 6.

Example 8 the relevant material compositions are listed in Table 7.

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

The isobutene content of the isobutene product obtained in example 8 is 99.96%, the 1-butene content is less than 200ppm, the 2-butene content is less than 300ppm, and the other indexes meet the requirements of the superior product in the standard SH/T1482-2004.

Example 9

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

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

TABLE 8 example 9 pertinent composition of materials (mass fraction, kg/kg)

The isobutene content of the isobutene product obtained in example 9 was 99.97%, the 1-butene content was less than 200ppm, the 2-butene content was less than 300ppm, and the remaining indices met the requirements of the premium product in the standard SH/T1482-2004.

Description of tables 1-8:

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

Comparative example 1

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

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

Of course, the foregoing is only a preferred embodiment of the invention and should not be taken as limiting the scope of the embodiments of the invention. The present invention is not limited to the above examples, and equivalent changes and modifications made by those skilled in the art within the spirit and scope of the present invention should be construed as being included in the scope of the present invention.

Claims

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

A. MTBE raw material refining

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

B. MTBE decomposition

C. removal of isobutene by weight

Feeding the decomposition reaction product isobutene and methanol into an isobutene de-heavy tower for rectification separation, obtaining isobutene containing azeotropic methanol at the tower top, and obtaining methanol at the tower bottom;

D. methanol recovery

2. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: and C, before entering the isobutene de-weighting tower, the decomposition products isobutene and methanol exchange heat with the MTBE raw material through a heat exchanger, then enter a vapor-liquid separation tank for vapor-liquid flash separation after being cooled through a cooler, and the top gas phase and the bottom liquid phase of the vapor-liquid separation tank are both sent to the isobutene de-weighting tower.

3. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: and D, feeding the material extracted from the top of the methanol recovery tower into the vapor-liquid separation tank in the step C, and feeding the material into the isobutene de-heavy tower.

4. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: the maximum mass percentage of the MSBE in the MTBE raw material in the step A is 1.2%, and the conversion rate of the MTBE is 98-99.5%.

5. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: in the MTBE raw material in the step A, the mass percent of MSBE is 0.6-0.9% or 0.9-1.2%, and the conversion rate of MTBE is 98-99.5%.

6. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: the number of theoretical plates of the refining tower in the step A is 30-49, the pressure at the top of the tower is 0.1-1.0MPa, and the reflux ratio is 0.5-10.

7. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: the number of theoretical plates of the refining tower in the step A is 35-49, the pressure at the top of the tower is 0.1-1.0MPa, and the reflux ratio is 0.5-2.5.

8. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: the catalyst in the step B is a catalyst which takes silicon dioxide as a carrier and takes heteropoly acid or a mixture of the heteropoly acid and metal salt as an active component.

9. The process for preparing isobutylene according to claim 8, wherein the reaction is carried out by the following steps: the metal salt is inorganic salt or organic salt of Cr, Mn, Fe, Mg, Co, Ni, Bi, Cu or Zn; the mass of the heteropoly acid accounts for 2-12% of that of the silica carrier, and the pore diameter of the silica carrier is within the range

The pore volume of the above pores is within the pore diameter

More than 2% of the pore volume of the pores, the pore diameter is within

The specific pore volume of the pores is 0.3-1.5 ml/g.

10. The process for preparing isobutene by decomposing high-efficiency methyl tert-butyl ether according to claim 1, wherein: the reaction pressure in the step B is 0.1-0.4MPa, the reaction temperature is 180-350 ℃, and the liquid hourly space velocity is 0.1-10h^-1。