JPH0618794B2 - Method for producing isobutene - Google Patents

Description

The present invention relates to a process for selectively producing isobutene by catalytic cracking of a hydrocarbon stream.

Environmental and other political bills adopted by some countries for the use of tetraethyl lead in motor fuels include other additives, including oxygen-containing additives to improve the octane number of motor fuels. Guided the petroleum industry to explore. Among these additives, asymmetric ethers, especially methyl tert-butyl ether (MTBE), have proven to be very effective gasoline additives. The most common method of making MTBE consists of reacting isobutene with methanol.

Isobutene can be used in t-butyl alcohol (used as a solvent), t-butylphenol (used as a stabilizer), low molecular weight polymer (used to improve the viscosity index of lubricating oils), etc. It is also used as a starting material for the production of other valuable compounds. As a result of this increased interest in isobutenes, the current availability of isobutene does not allow the production of sufficient amounts of these derivatives to satisfy their potential market.

Butenes, including 1-butene, cis- and trans-2-butene and isobutenes, are now cracked.
gas), in particular naphtha and the like, can be obtained by various methods including extraction from the cracked gas obtained in the production of ethylene by thermal decomposition. Ethylene and propylene make up the majority of these gases and the butene content generally does not exceed about 8% by volume. Subjecting naphtha to catalytic cracking instead of pyrolysis has been shown to include C ₃ and C ₄ hydrocarbons, middl distillates (middl).
Preference is given to the formation of products with a high content of e distillates) and gasoline. For example, catalytic cracking of naphtha with a moving bed catalyst gives a product containing up to 12% total butenes, with isobutene representing less than 25% of that amount. As can be seen from the above, the catalytic cracking process produces only small amounts of isobutene.

Therefore, it can be seen that there is currently a need for a method for the simple and economical removal of isobutene, in particular a method which makes use of readily available starting materials.

Several methods for enhancing these olefinic gases have been described in the literature. S, Jei, Mirror
U.S. Pat. No. 4,404,423 to (S. J. Miller)
Disclosed is a process for enhancing a feed, which normally contains gaseous olefins, by an oligomerization reaction in at least two stages leading to the formation of high boiling hydrocarbons. This method can be applied to propylene or a mixture of propane and propylene as a starting material. Normally, liquid olefins are formed by oligomerization in the first stage and then converted to higher oligomers in the second stage. The purpose of the process described in this patent is to give good yields of high boiling hydrocarbons. Low amount of C ₄ olefin during Phase 1
(The isobutene is only one of the three isomers) is formed starting from a mixture of propane and propylene.
Therefore, such a process cannot be used for the selective production of isobutene from propylene or from a gaseous feed containing propylene. U.S. Pat. No. 4,407,086 to Miller and U.S. Pat. No. 4,417,088 to Miller disclose a process for the oligomerization of liquid olefins using medium pore size molecular sieves. . However, none of these presently known processes are available for the production of meaningful quantities of isobutene.

It is an object of the present invention to provide a new method for producing isobutene.

Another object of the present invention is to selectively produce isobutene from a hydrocarbon stream having 5 or more carbon atoms.

The process of the present invention essentially comprises feeding a C ₅ + hydrocarbon feed to a crystalline silica polymorph of the silica mineral type (cryicalite type).
catalytic cracking in the presence of steam in the presence of a catalyst consisting of stalline silica polymorph) at a water / feed molar ratio of about 0.5 to about 5.

The hydrocarbon feed of the present invention is typically a light distillate.
istillates). Light distillates are obtained at refineries from distillation of crude oils and have a boiling range (b) of about 36 ° C to about 196 ° C.
These fractions have an iling range).
This includes eliminates C ₄ and from lower hydrocarbons and gasoline, light naphtha and heavy naphtha. The process of the invention is also applicable to light distillates obtained from certain operations in the chemical industry, for example light distillates produced in olefin oligomerization.

In a preferred embodiment of the present invention, the light distillate according to the present invention is a light distillate obtained from propylene or as a by-product in the process of producing isobutene by isomerization of n-butenes. These processes are 198
US Patent Application No. 719,19, filed April 3, 5
No. 2 and U.S. Patent Application No. 719,198, filed April 3, 1985, which are hereby incorporated by reference in their entirety.

The catalyst used in the present invention is a silica mineral type unmodified crystalline polymorph of silica.
line silica polymorph). The catalyst is therefore essentially pure silica, which means that it contains no impurities or modifying elements or that it contains only traces of them. Methods for making such silica mineral type catalysts and structures are described in US Pat. No. 4,061,724 by Grose, which is incorporated herein by reference in its entirety.

The C ₅ + hydrocarbon feed is contacted with the silica mineral in the presence of steam. Unexpectedly, the presence of water not only improves catalyst life by reducing the formation of heavier products, but more importantly, butene,
In particular, it has been found to result in promoting the production of isobutene. The presence of steam increases isobutene selectivity when all other factors are equal. The term "isobutene selectivity" means the weight of isobutene formed, calculated on 100 parts by weight of the converted feed. This improvement in selectivity is achieved even when the feed is treated in the presence of as little as 0.5 moles of water per mole of feed.
Comparative experiments have also shown that it is preferable to keep a water / feed molar ratio of no more than about 5. The reason is that higher proportions do not significantly improve the results. The water / feed molar ratio is preferably about 0.5 to 3.0, and most preferably about 0.75 to about 2.0.

The method of the invention is very versatile and can be used in the gas phase and / or
Or it can be applied in the liquid phase. The reaction temperature is generally about 450 ° C to about 600 ° C. Temperatures below 450 ° C give very low yields, and temperatures above 600 ° C cause some degradation of the reaction products.

Generally, temperatures of about 475 ° C to about 550 ° C are preferred.
Temperature fluctuations within these ranges do not significantly alter the distribution of the formed product.

The hourly space velocity (WHSV) of the reaction mixture, expressed by weight of the mixture per weight of catalyst per hour, can vary from about 5 to about 100. WHSV depends, among other factors, on the nature of the feed and the decomposition temperature. High space velocities allow better isobutene selectivity but also allow for loss of feed conversion. Reduced space velocities, especially below 2, may result in product degradation. A space velocity of about 2 to about 20 is preferred, but about 5
Most preferred is a WHSV of from about 15 to about 15.

The pressure at which the reaction takes place can vary within rather wide ranges, for example below atmospheric pressure (sub-atm
The osphenic pressure) to the absolute pressure for carrying out the reaction can vary from about 0.5 to about 20 bar. It is advantageous to operate at low pressure to favor the production of isobutene.

One skilled in the art can determine the operating conditions that give the best yield within the ranges given above, taking into account not only the composition of the feed but also the desired result. Thus, certain conditions, such as high WHSV, favor isobutene formation with low conversion of the feed under such conditions.

In a preferred embodiment of the process of the invention, the light distillate subjected to catalytic cracking is obtained as a by-product in the production of isobutene from a feed stock containing propylene or from a feed stack containing n-butenes. . These light distillates have boiling ranges on the order of 36 ° C to 196 ° C and represent a very valuable feed stock. In fact, treating them by the method of the present invention produces additional amounts of isobutene. Thus, by combining the above processes, a particularly high yield of isobutene from propylene or n-butenes is obtained. The above process can be combined in this way using two reactors in series, the first reactor treating a feedstock containing propylene or n-butenes with formation of isobutene. And the second reactor is used to carry out the catalytic cracking of the distillate formed as a by-product in the first reactor. Another embodiment consists of carrying out the two stages of these combined processes in a single reactor operating under adiabatic conditions and having a suitable temperature profile.

The following examples are meant to be illustrative and are not intended to be limiting of the invention.

A feedstock consisting of propane 28.93 (wt%) and propylene 71.07% in the presence of silica minerals and steam,
It was treated with a WHSV of 79.8 at a water: feed stock molar ratio of 0.78 at a temperature of 303 ° C. and an absolute pressure of 14 bar.

This gave isobutene and light distillates with selectivity of 11.3% and 64.6%, respectively. This distillate is 36 ° C to 19
As a fraction with a boiling range of 6 ° C., ie C ₅
Obtained as a light distillate consisting of + hydrocarbons.

The process according to the invention is then carried out by treating this distillate in the presence of silica minerals and steam at a water: distillate molar ratio of 1.26 at a temperature of 550 ° C. and an absolute pressure of 2 bar at a WHSV of 9.91. Applied

This gave isobutene with a selectivity of 18.1%.

A feedstock consisting of 5.84% propane (by weight) and 94.16% propylene in the presence of silica minerals and steam,
Treated using a WHSV of 35.6 at a water: feed molar ratio of 0.92 at a temperature of 316 ° C. and an absolute pressure of 4 bar.

This gave isobutene and light distillates with a selectivity of 12.4% and 62.8%, respectively. This distillate is 36 ° C to 19
As a fraction having a boiling range of 6 ° C., ie C
Obtained as a light distillate consisting of ₅ + hydrocarbons.

The process of the invention is then treated with this distillate in the presence of silica minerals and steam using a water: distillate molar ratio of 2.71, a temperature of 500 ° C. and an absolute pressure of 5.4 bar using a WHSV of 8.57. Applied by

This gave isobutene with a selectivity of 12.8%.

Although the present invention has been described in terms of preferred embodiments, it should be understood that modifications and changes can be made without departing from the spirit and scope of the invention, as will be readily appreciated by those skilled in the art. Such modifications and variations are considered to be within the scope of the claims.

Continuation of the front page (72) Inventor Francisco Martin Mendes Seresijyo B-7190 Ecogene Lyupuriyumukoku 32 Belgium

Claims (9)

[Claims] 1. A) In the presence of a catalyst comprising crystalline silica polymorphs of the silica mineral type in the presence of a sufficient amount of water such that the water / feed molar ratio is 0.5 to 5. A method for producing isobutene, which comprises subjecting the mixture to catalytic cracking with a feed comprising a hydrocarbon having 5 or more carbon atoms; and b) recovering a stream containing isobutene. 2. A process according to claim 1, wherein the water / feed molar ratio is 0.5 to 3. 3. The method according to claim 1, wherein the step (a) is carried out at a temperature of 450 ° C. to 600 ° C. 4. The method according to claim 1, wherein step (a) is carried out at a temperature of 475 ° C. to 550 ° C. 5. A process according to claim 1 wherein step (a) is carried out at a reaction mixture weight per catalyst weight per hour (WHSV) of from 2 to 20. 6. A process according to claim 1, wherein step (a) is carried out at a reaction mixture weight per catalyst weight per hour (WHSV) of 5 to 15. 7. The method according to claim 1, wherein step (a) is carried out at an absolute pressure of below atmospheric pressure to 50 bar. 8. A process according to claim 1, wherein step (a) is carried out at an absolute pressure of 0.5 bar to 20 bar. 9. (a) Light distillate hydrocarbon feed, wherein the hydrocarbon has a boiling range of 36 ° C. to 196 ° C., at a temperature of 475 ° C. to 550 ° C. under an absolute pressure of 0.5 bar to 20 bar. In the presence of a catalyst consisting essentially of crystalline silica polymorphs of the silica mineral type, in the presence of a sufficient amount of water such that the water / feed molar ratio is 0.5 to 1.5. A method of producing isobutene comprising subjecting to decomposition and (b) recovering a stream containing isobutene.