JPS6123769B2 - - Google Patents

Abstract

PURPOSE:To obtain isobutene under mild conditions without external heating, in high yield, by the dehydration decomposition of a tertiary buranol (TBA) continuously supplying a gaseous TBA into the reaction vessel containing liquid TBA, water and a catalyst. CONSTITUTION:The starting material TBA is supplied from the tube 5, vaporized with the heater 4, and led into the reaction vessel 1 containing a cationic exchange resin catalyst and a 2-70 wt% aqueous solution of TBA. The temp. in the reaction vessel shold be maintained at 90-180 deg.C, and the pressure under 1.5-15 atm. The temp. and the pressure of the gaseous TBA supplied should be maintained higher than those inside the reaction vessel. The formed gaseous isobutene is led to the distillation tower 3 via the tube 6, and high purity isobutene is taken out from the tube 11. The mixture of the unreacted TBA, water and impurities in the gaseous TBA is led to the distillation tower 2 via the tube 8. TBA and the vapor are taken out from the tower top via the tube 9 and recycled.

Description

[Detailed description of the invention]

The present invention relates to a method for producing isobutene by carrying out a dehydrolysis reaction of tertiary-butanol. Tertiary butanol (TBA)
As for the method of obtaining isobutene by dehydration decomposition of (abbreviated as ), a method using a solid acid such as alumina as a catalyst is known. However, when implementing this method, US Pat.
12403), usually as seen in Tokuko Sho 48-10121
Requires a high reaction temperature of 250°C or higher. Under these conditions, the reaction proceeds as a gas phase reaction, but this dehydration decomposition reaction of TBA is an endothermic reaction, and many industrial devices are used to supply this reaction heat and allow the reaction to proceed at high temperatures. In addition to requiring investment, it is also difficult to maintain the quality of the isobutene produced due to the isomerization reaction to isobutene that progresses at high temperatures, which is contaminated with butene-2 and the like. On the other hand, a method using sulfuric acid as a catalyst has been implemented industrially as a method of carrying out decomposition reactions at relatively low temperatures; It has the disadvantage of needing something. Several methods using cation exchange resins have been suggested to avoid these drawbacks.
Journal of Catalysis Volume 3,
Page 25 (1964) (Journal of Catalysis Vol3,
P25 (1964)), also Volume 31, Page 27
(1973) (Vol. 31, P. 27 (1973)) and others disclose that a strong acid type cation exchange resin can be an effective catalyst for the dehydration and decomposition reaction of TBA in the liquid phase. However, the method described therein supplies reaction heat to a stirred reactor using external heat, and when scaling up to industrial equipment above a certain scale, the reactor's heat resistance must be within the range of the catalyst's heat resistance. It is necessary to keep the wall temperature below 150℃, but under these conditions, the temperature difference between the inside and outside of the wall is small, and even with the maximum allowable temperature difference, it is impossible due to insufficient heat transfer area. It is. U.S. Patent No. 3,510,538 (Japanese Patent Publication No. 46-3042) states that the use of an inert organic liquid such as benzene is effective in maintaining the rate of the liquid phase dehydration reaction of TBA. TBA is dropped into benzene, and the produced isobutylene gas and azeotropic gas of water and benzene are extracted from the top of the reactor. There is no suggestion as to how to supply the endothermic reaction heat, which is the same and is the most important issue when implementing it industrially, and the reaction temperature is limited to 100℃ or less, so the resulting reaction rate is has its limits. US Pat. No. 4,012,456 (Japanese Unexamined Patent Publication No. 51-59802) describes a dehydration and decomposition reaction using a tower reactor filled with a cation exchange resin. In this method, the reaction proceeds in the gas phase, so the isobutene production rate per unit catalyst is lower than in the liquid phase reaction, and the reaction heat is supplied using an external heating method, so the reactor becomes extremely large. There are many difficulties in implementing it on an industrial scale. The present inventors researched a continuous dehydration method for TBA that solved the drawbacks of these conventional methods.
We have found an excellent method that does not have these drawbacks. In the present invention, in the presence of a cation exchange resin catalyst,
In a method for continuously producing isobutene by a dehydrolysis reaction of TBA, the catalyst is contained, a liquid mixture of TBA and water is present, and the temperature is 90 to 180.
Heated gaseous TBA at a pressure higher than the pressure inside the reactor is continuously supplied into the liquid mixture in the reactor, which is maintained at a pressure of 1.5 to 15 atm at a temperature of 1.5 to 15 atm. A mixed gas of gaseous TBA is continuously extracted from the top of the reactor, isobutene is recovered from this mixed gas, and the
The present invention relates to a method for producing isobutene, characterized in that a portion of a liquid mixture of TBA and water is continuously extracted from a liquid phase portion of the liquid mixture in a reactor. The present invention will be explained in more detail below. The TBA raw material referred to in the present invention is not only pure TBA, but also organic substances that do not undergo chemical reactions under the reaction conditions, such as saturated hydrocarbons, unsaturated hydrocarbons, alcohols, ethers, carboxylic acids, etc., as impurities in small amounts, for example, 10%. It is also possible to use a substance mixed with the following amount. In addition, the water content should be 90wt% or less, preferably 10~
TBA containing 40 wt% can be used. Water-containing TBA has a low freezing point, making it convenient to handle, and moreover, it can be effectively used as a reaction raw material in the present invention. In the present invention, TBA or TBA mixed with other substances is heated and vaporized as will be described in detail later, and then supplied under pressure to a reactor. On the other hand, the cation exchange resin used as the catalyst in the present invention has acid groups and has cation exchange performance, and strong acid type resins such as styrene sulfonic acid type resins and phenolsulfonic acid type resins are representative examples thereof. be. Styrene-based sulfonic acid type ion exchange resin is a sulfonated resin obtained by copolymerizing styrene and polyunsaturated compounds such as divinylbenzene, and -SO ₃ H groups are introduced into the crosslinked polymer. It is. Furthermore, the phenolsulfonic acid type resin is usually a condensation product of phenolsulfonic acid and formaldehyde. In the present invention, these cation exchange resins usually have an average particle size of about 0.1 mm to about 10 mm, preferably 0.3 to 2 mm.
used as particles. In addition, the reactor used in the present invention has at least a raw material TBA supply port and an upper part for producing product and unreacted TBA.
It is a pressure-resistant sealed container that has an outlet for mixed gas and an outlet for the liquid mixture of TBA and water. One of the features of the present invention is that the reactor can be equipped with no equipment for supplying or removing heat by selecting the reaction conditions as described later, but it is possible to have a reactor without any equipment for supplying or removing heat, but it is possible to use a reactor with these equipment or heat-retaining equipment. It does not prevent this in any way. The method of the present invention will be explained in more detail below with reference to FIG. The raw material TBA, TBA aqueous solution, or a mixture containing TBA is continuously supplied from the tube 5, and the raw material is heated and vaporized in the heater 4 (hereinafter, cases containing TBA and other substances are also described as gaseous TBA) do). This gaseous TBA is preferably fed into the reactor 1 via a disperser. The reactor is filled with a cation exchange resin catalyst, and a liquid mixture containing TBA and water is housed in contact with the catalyst. This liquid mixture is preferably present as a liquid phase in most of the reactor, particularly in the area where the catalyst is present. This liquid mixture is usually an aqueous solution containing about 2 to 70 wt% TBA, preferably 10 to 60 wt%. The catalyst may be present as a fixed bed or in a suspended or fluidized state in a liquid mixture of TBA and water. The catalyst in the reactor is suspended by providing a stirring blade in the reactor or by circulating the liquid mixture with a pump.
Maintaining a fluidized state and allowing intimate contact give favorable results to the dehydration and decomposition reaction of TBA. This is particularly convenient for continuously replacing deteriorated catalysts with new catalysts. The interior of the reactor containing the catalyst and the liquid mixture is maintained at a temperature of 90 to 180°C, preferably 105 to 140°C, and a pressure of 1.5 to 15 atmospheres, preferably 3 to 10 atmospheres. The raw material gaseous TBA is supplied into the reactor as described above, but at a pressure higher than the internal pressure of the reactor, for example,
It is preferably supplied at a high pressure of about 0.1 to 5 atm, and at a temperature higher than the internal temperature of the reactor, for example, about 1 to 50°C. However, in order to control the reaction, feeding at a temperature about 1 to 30° C. lower than the internal temperature of the reactor is sometimes adopted. This gaseous TBA is introduced into the liquid mixture in the reactor, and is usually at a location below 1/3 from the top of the liquid phase of the liquid mixture, preferably from 1/2 to 9/1 from the top.
Introduced at location 0. If gaseous TBA is introduced into the upper part of the reactor, the supplied gaseous TBA will not react sufficiently and the amount of unreacted TBA drawn out from the upper part of the reactor will increase. The introduced gaseous TBA comes into contact with the liquid mixture of TBA and water that already exists at the predetermined temperature and pressure, is absorbed and condensed therein, and at the same time, a dehydration decomposition reaction takes place on the surface of the existing catalyst. It can be done. If the temperature in the reactor is too low, the amount of isobutene produced per unit catalyst will decrease, and if it is too high, catalyst deterioration will be accelerated, and there will be disadvantages in using a high-temperature heat source. Furthermore, if the pressure is too low, the raw material TBA supplied in the form of a gas will not be sufficiently absorbed and condensed into the mixed liquid in the reactor after being supplied, and an effective reaction will not take place. Furthermore, if the pressure is too high, the partial pressure of isobutene produced in the reaction system becomes high, making it difficult to carry out the dehydration decomposition reaction in an equilibrium manner. As described above, by supplying gaseous TBA into the reactor, the reaction proceeds, producing isobutene and water. This generated isobutene is advantageous when the catalyst is used in a fluidized state because it helps fluidize the catalyst. The isobutene produced by the reaction is continuously withdrawn in gaseous form from the top of the reactor via tube 6. This gaseous isobutene contains unreacted gaseous TBA and also contains a small amount of water produced by the decomposition reaction in the form of water vapor. Furthermore, a trace amount of a low-amount polymer (mainly a dimer) of isobutene produced as a by-product from the reaction may be contained. In the present invention, the conversion rate of TBA is 20-95%,
Preferably 30-90%, more preferably 40-80%
When the conversion rate of one reactor is not high, it is not only effective to use two or three reactors in series to increase the conversion rate, but also to increase the conversion rate of the catalyst. This helps prevent a drop in production during replacement. The mixed gas extracted from the top of the reactor usually contains 1/10 to 2 times the weight of isobutene, preferably 1/1
Although 5 to 1 times the weight of TBA is contained, if the amount of TBA is excessive, it can be controlled by raising the reaction temperature, moving the feed port of the raw material gaseous TBA to a lower position, etc. Product isobutylene is recovered from a stream containing gaseous isobutylene withdrawn from the top of the reactor.
This recovery method is not particularly limited, but may be achieved, for example, by conventional distillation. That is, this stream is introduced into the distillation column 3, and highly pure isobutene can be obtained from the top of the column via pipe 11, and a stream containing a small amount of liquid TBA and other impurities can be obtained from the bottom of the column via pipe 1.
Obtained through step 2. A portion of this stream can be discarded and the majority can be recycled and used as a raw material. On the other hand, a portion of the liquid mixture containing TBA and water present in the reactor is continuously withdrawn from the liquid phase portion in the reactor through pipe 8. When extracting the liquid mixture from inside the reactor, it is preferable to extract it from the liquid phase in the lower part of the reactor, which is about 1/2 or less of the height of the liquid phase of the liquid mixture in the reactor. More preferably, the raw material gaseous TBA is extracted from a location at approximately the same height as or lower than the supply location. Furthermore, in the case where the liquid mixture is circulated within the reactor using a circulation pump as described above, a part of the circulating flow can also be extracted. This liquid mixture can be extracted through a screen or the like so that catalyst particles are not entrained. This withdrawal allows the level of the liquid phase in the reactor to be kept constant while the reaction can be effectively carried out continuously. The flow extracted from this is the unreacted
TBA is water and most of the impurities contained in the raw material gaseous TBA. When the reaction is operated continuously and at a steady state, the composition of the mixture of TBA and water in the reactor is similar, and most of the water produced by the reaction and unreacted liquid TBA are in this mixture. It is extracted by the flow. This stream 8 can normally be recycled to the reaction. That is, by supplying this stream 8 to the distillation column 2 and performing a distillation operation, the stream 8 is passed from the top of the column through the pipe 9.
A stream containing TBA and water vapor is obtained which can be recycled to the reactor. A stream containing mainly water is discharged from the bottom of the distillation column 2 via a line 10. In the present invention, by the above method,
Isobutene is produced from TBA,
In the case of the present invention, isobutene can be obtained in high yield without requiring particularly high temperature or high pressure, with few by-products such as isobutene dimer, and furthermore, it is necessary to supply the heat necessary for the reaction with external heat. Since there is no or a small amount of waste, it is possible to carry out the process using a large reactor, which is industrially advantageous. Further, in the present invention, unreacted TBA is discharged from two places, but since both can be recovered and recycled with a simple operation, no inconvenience occurs. Furthermore, in the method for producing isobutylene of the present invention, even if the raw material TBA contains impurities such as secondary butanol, the decomposition of this alcohol to produce n-butenes is extremely rare, and High purity isobutene can be produced. The present invention will be explained in more detail with reference to Examples below. Example 1 A well-insulated cylindrical reactor with a diameter of 15 cm and a volume 5 equipped with a stirrer was filled with 630 ml of PK228 manufactured by Mitsubishi Kasei Corporation as a strong acid type cation exchange resin in a wet state. Prior to the start of the reaction, approximately 30 wt% TBA aqueous solution is charged so that the reactor level is around 4. At a feeding rate of 2Kg/HR while stirring.
An aqueous solution with a TBA concentration of 88.4wt% is heated to 125℃ and is blown into the reactor as a mixed vapor from the bottom of the reactor (approximately 4/5 of the way from above the liquid phase in the reactor) through a disperser. . A gaseous portion containing produced isobutene and unreacted TBA is taken out from the top of the reactor. This outlet pipe is equipped with an automatic pressure regulating valve, and the pressure within the system is automatically maintained at 5 atmospheres. Also, take out the mixed liquid portion of TBA and water from the bottom of the reactor. This pipe is equipped with an automatic adjustment valve to keep the liquid level in the system constant, and is set so that the volume of liquid containing the catalyst is automatically maintained at 4. The reaction proceeded continuously in the absence of any heat source other than steam, and the steady state finally obtained was as follows.

[Table] From the above results, the conversion rate of TBA was 63.5% and the selectivity to isobutene was 99.7%. The reaction continued stably for a long time, with little deterioration of the catalyst. The mixed gas extracted from the gas extraction tube was distilled to obtain isobutene with a purity of 99.98%. Example 2 Amberlite (Rohm & Haas, Inc., USA) was used as a strong acid type cation exchange resin in a well-insulated cylindrical stainless steel reactor with a diameter of 35 cm and a volume of 100 cm.
Pack 45Kg of 120B (effective diameter 0.45-0.6mm) as a fixed bed. Prior to the start of the reaction, approximately 30 wt% TBA aqueous solution is charged so that the level inside the reactor is around 80. Thereafter, an aqueous solution with a TBA concentration of 80 wt% is heated to 150°C and evaporated to form a mixed vapor, which is blown into the reactor from the bottom at a rate of 200 kg/hr through a disperser. A mixed gas portion containing produced isobutene and unreacted TBA is taken out from the top of the reactor.
This outlet pipe is equipped with an automatic pressure regulating valve, and the pressure within the system is automatically maintained at 7 atmospheres. Also, a mixed liquid portion of TBA and water is taken out from the bottom of the reactor. This pipe has an automatic adjustment valve to keep the liquid level in the system constant, and the volume of the liquid containing the catalyst is automatically maintained at 80. The reaction proceeded continuously without any heat source other than the evaporator for vaporizing the raw materials, and the steady state finally obtained was as follows.

[Table] From the above results, the conversion rate of TBA was 67.2% and the selectivity to isobutene was 99.6%. The reaction continued for a long time, with little deterioration of the catalyst. The mixed gas extracted from the gas extraction tube was distilled to obtain isobutene with a purity of 99.99%.

[Brief explanation of the drawing]

FIG. 1 is a flowchart illustrating the method for producing isobutene of the present invention. 1: Reactor, 2: TBA distillation column, 3: Isobutene distillation column, 4: Heater, 5: Raw material supply pipe, 6: Produced isobutene extraction pipe, 8: Liquid mixture extraction pipe.

Claims (1)

[Claims] 1. A method for continuously producing isobutene by dehydration decomposition reaction of tertiary-butanol in the presence of a cation exchange resin catalyst, in which the catalyst is accommodated, a liquid mixture of tertiary-butanol and water is present, and the temperature is 90-90°C. Heated gaseous tertiary butanol at a pressure higher than the pressure inside the reactor is continuously supplied into the liquid mixture in the reactor maintained at 180°C and a pressure of 1.5 to 15 atm. A mixed gas of isobutene and unreacted gaseous tertiary-butanol is continuously extracted from the top of the reactor, isobutene is recovered from this mixed gas, and a part of the liquid mixture of tertiary-butanol and water in the reactor is extracted. A method for producing isobutene, characterized in that isobutene is continuously extracted from a liquid phase portion of the liquid mixture in a reactor.