JP2005200364A - Process for producing n-butenes by isomerization of isobutene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing n-butenes with high selectivity by suppressing the formation of heavy substances and coke in the isomerization reaction of isobutene.
An n-butene is produced by bringing a feedstock containing isobutene and a saturated hydrocarbon having 1 to 10 carbon atoms into contact with a solid acid catalyst to skeleton isomerize isobutene. The concentration of isobutene in the feedstock is preferably 10 to 90% by volume, and the concentration of the saturated hydrocarbon in the feedstock is preferably 10 to 90% by volume. The solid acid catalyst is preferably silica alumina or activated alumina.
[Selection figure] None

Description

  The present invention relates to a method for producing n-butenes by skeletal isomerization of isobutene.

Conventionally, there has been much demand for methyl-tert-butyl ether (MTBE) obtained by reacting isobutene and methanol as an octane number improver for gasoline. For the purpose of increasing production of isobutene, isomerization of n-butenes to isobutene Many methods have been proposed.
On the other hand, n-butene is useful as a copolymerization component of polyolefin. In addition, for the purpose of increasing the production of propylene for which demand is increasing, research on propylene production by a metathesis reaction between ethylene and n-butene is actively conducted, and the demand for n-butene is increasing. Therefore, isomerization from isobutene to n-butenes for the purpose of increasing production of n-butene is also an important reaction.

As a method for skeletal isomerization of isobutene into n-butenes, a method using a catalyst in which the surface of alumina is pretreated with an organosilicon compound using pure isobutene has been proposed (see, for example, Patent Document 1). There are industrial problems such as requiring special treatment in the process.
In addition, isobutylene is isomerized into n-butenes using a catalyst containing aluminum and an oxide composed of any one or two elements of titanium, tungsten, zirconium, silicon, bismuth and barium and chlorine and / or fluorine. However, since chlorine and fluorine are contained, there are problems such as corrosion of the apparatus and environmental pollution.
In addition, a method is disclosed in which ferrilite is used as a catalyst and an isomerization reaction of pure isobutene is performed at a low pressure of 7 to 20 kPa and a low temperature of about 260 ° C. (see, for example, Non-Patent Document 1), n -The yield of butenes is as low as about 6% and is not practical.
Furthermore, we are investigating the isomerization reaction from pure isobutene to n-butenes at a pressure as low as 30 kPa and 450 ° C. using catalysts such as MFI-type zeolite, ferrierite, alumina, and fluorinated alumina. Although there is an example (for example, refer nonpatent literature 2), since either one of a conversion rate and a selectivity is low, a yield is as low as about 1-20%, and the production | generation of the heavy material and coke which are industrially problematic is produced. Inevitably, no specific method for suppressing these is disclosed.
Japanese Patent Laid-Open No. 51-39605 (Example 9) JP 59-123538 A (Reference Examples 1 to 8) “Journal of Catalysis” (USA), 2000, vol.191, p.1-11 “Catalysis Today” (Netherlands), 1998, vol.44, pp.215-222

  The object of the present invention is to suppress the formation of heavy substances and coke without using a specially treated catalyst in the isomerization reaction of isobutene, and to produce n-butenes with high conversion and high selectivity and high yield. It is to provide a method of manufacturing.

  The first of the present invention is a method for producing n-butenes by bringing a feedstock containing isobutene and a saturated hydrocarbon having 1 to 10 carbon atoms into contact with a solid acid catalyst, and subjecting isobutene to skeletal isomerization.

  A second aspect of the present invention is the method for producing n-butenes according to the first aspect of the present invention, wherein the concentration of isobutene in the feedstock is 10 to 90% by volume.

  A third aspect of the present invention is the method for producing n-butenes according to the first or second aspect of the present invention, wherein the concentration of the saturated hydrocarbon in the feedstock is 10 to 90% by volume.

  A fourth aspect of the present invention is the method for producing n-butenes according to any one of the first to third aspects of the present invention, wherein the saturated hydrocarbon is butanes.

  A fifth aspect of the present invention is the method for producing n-butenes according to any one of the first to fourth aspects of the present invention, wherein the solid acid catalyst is silica alumina or activated alumina.

  According to the present invention, in the isomerization reaction from isobutene to n-butenes, the formation of heavy materials and coke can be suppressed without using a specially treated catalyst, and the conversion can be achieved with high conversion and high selectivity. It is possible to efficiently produce n-butenes and improve the catalyst life.

Hereinafter, the present invention will be described in detail.
In the present invention, when the skeletal isomerization reaction is performed using isobutene as a feedstock, saturated hydrocarbons are allowed to coexist in the feedstock. Compared with the case where only isobutene is used as a feedstock, the formation of heavy substances and coke is suppressed, and the selectivity of n-butenes and the catalyst life are improved.

  There are many saturated hydrocarbons that can be used in the present invention, such as methane, ethane, propane, butane, pentane, hexane, etc., but as the number of carbons increases, by-products due to thermal decomposition increase, Furthermore, 5 or less is preferable. In particular, butanes (n-butane, isobutane) coexisting with isobutene in the C4 fraction produced from the thermal cracking or catalytic cracking of petroleum such as naphtha do not require any special operation or equipment. This is preferable because it can be used as it is without separation. Furthermore, isobutane is particularly preferable because it hardly causes cracking and the like even at a high temperature, so that by-products such as light are hardly generated and the isolation / purification process does not become complicated.

The amount of saturated hydrocarbons to coexist is preferably 10 to 90% by volume in the feedstock. If it is less than 10 volume%, the effect which suppresses the byproduct and coking of a heavy material will fall. On the other hand, when it exceeds 90 volume%, reaction efficiency will fall. More preferably, it is 40-80 volume%. The concentration of isobutene in the feed is preferably 10 to 90% by volume. If the concentration of isobutene is too high, heavy products and coke are severely generated, and the selectivity of n-butenes is lowered. If the concentration is too low, the yield is lowered and the productivity is lowered. More preferably, it is 20-60 volume%.
If there are many unsaturated components other than isobutene such as n-butene, propylene, and pentenes in the feedstock, side reactions such as isomerization, disproportionation, and polymerization are caused by the components, which is not preferable because efficiency is lowered. Therefore, it is preferable to suppress the concentration of other unsaturated components in the feedstock to 20% by volume or less, and further to 10% by volume or less. In the present invention, water vapor may coexist with the saturated hydrocarbon.

  As the solid acid catalyst used in the present invention, those commercially available can be used, but silica alumina and activated alumina are preferable, and silica alumina is particularly preferable. They are preferably subjected to a treatment such as firing when used. Examples of the silica alumina catalyst include zeolite catalysts such as ferrierite, MFI-type zeolite, AEL-type zeolite, TON-type zeolite, Y-type zeolite, mordenite, hurlandite, chabasite, and erionite. These catalysts are optionally pretreated. Particularly preferred are zeolites having an eight-membered ring or a ten-membered ring, and ferrierite having a two-dimensional structure of an eight-membered ring and a ten-membered ring is preferred. When the pore diameter of zeolite is large, an isobutene polymer, a compound having a ring structure and the like easily enter, so that by-products increase and the selectivity of n-butenes decreases. On the other hand, if the pore diameter is too small, isobutene cannot enter, so that the skeletal isomerization reaction does not proceed easily. As the active alumina catalyst, γ-alumina is particularly preferable.

The isomerization reaction from isobutene to n-butenes is in equilibrium with the reverse reaction, and reaches the maximum yield when equilibrium is reached. The equilibrium composition changes with temperature, and as the temperature increases, the proportion of isobutene decreases and the proportion of n-butenes increases. For example, at 100 ° C., isobutene: n-butenes = 74: 26, and at 600 ° C., isobutene: n-butenes = 37: 63.
The n-butenes produced are 1-butene, cis-2-butene, and trans-2-butene. Their production rate depends on the equilibrium composition at the reaction temperature. The n-butenes contained in the reaction mixture can be separated by a known method such as distillation. Since 1-butene and isobutene have close boiling points, they can be separated by isomerization of 1-butene to 2-butene or polymerization of isobutene.

  The reaction temperature in the skeletal isomerization reaction of the present invention is 300 ° C to 600 ° C, preferably 400 to 550 ° C. When the temperature is higher than 600 ° C., the equilibrium is easily reached and the ratio of n-butenes in the equilibrium composition becomes high. However, coke formation is remarkable and the life of the catalyst is extremely reduced, which is not preferable. Further, if it is less than 300 ° C., it is difficult to reach equilibrium, and since the ratio of isobutene in the equilibrium composition is high and isobutene dimer is likely to be formed, the yield of n-butenes is undesirably lowered.

  The reaction pressure is 3 MPa or less, preferably 0.5 MPa or less, more preferably 0.1 MPa or less. In particular, atmospheric pressure (0.1 MPa) is preferable. High pressure is not preferable because the collision frequency between molecules increases, which causes generation of heavy substances and coke.

A weight hourly space velocity (WHSV) is based on the feed, 0.1～100H ^-1, preferably 0.2～30H ^-1, more preferably 0.5 to 20 h ^-1. In the region where WHSV is high, the conversion rate of isobutene decreases, which is not preferable. In a region where WHSV is low, isobutene dimer is likely to be produced, and by-products such as heavy substances are increased, the selectivity of n-butenes is lowered and coke is liable to be produced, which is not preferable.

  The reaction mode is not particularly limited and may be any of a fixed bed, a moving bed, a fluidized bed, etc., but a fixed bed flow reaction formula is particularly preferable.

[Example]
As in Examples 1 to 6 and Comparative Examples 1 and 2 below, isobutene was isomerized to produce n-butene. The results are summarized in Table 1. Note that. The composition of n-butene was 1-butene / cis-2-butene / trans-2-butene = about 25% / about 30% / about 45% in all cases.

  Fixed bed flow reactor with 60g length and 10mm ID tube packed with Zeolist ferrilite (crushed to 0.425-1.0mm, calcined at 500 ° C for 3 hours), silica alumina based solid acid catalyst. In addition, a raw material of isobutene / isobutane = 5/95 (volume ratio) was supplied at 12 g / h in a down flow and operated for 3 hours. N-butenes were produced at a reaction temperature of 400 ° C. and a pressure of atmospheric pressure.

  The same reaction as in Example 1 was carried out except that the raw material was isobutene / isobutane = 20/80 (volume ratio).

  The same reaction as in Example 1 was performed, except that the raw material was isobutene / isobutane = 50/50 (volume ratio).

  The same reaction as in Example 1 was performed, except that the raw material was isobutene / isobutane = 80/20 (volume ratio).

  The same reaction as in Example 1 was performed, except that the raw material was isobutene / n-butane = 50/50 (volume ratio).

[Comparative Example 1]
The same reaction as in Example 1 was performed except that the raw material was 100% isobutene.

  As a solid acid catalyst, γ-alumina (pulverized to 0.425 to 1.0 mm, calcined at 500 ° C. for 3 hours) was charged into a fixed bed flow reactor filled with 6.0 g in a reaction tube with a length of 60 cm and an inner diameter of 10 mm, and isobutene / isobutane = 50 / A 50 (volume ratio) raw material was supplied at a down flow of 6 g / h and operated for 3 hours. N-butenes were produced at a reaction temperature of 400 ° C. and a pressure of atmospheric pressure.

[Comparative Example 2]
The same reaction as in Example 6 was carried out except that the raw material was 100% isobutene.

  As shown in Table 1, Examples 1 to 4 using ferrierite (Examples 1 to 4 and Comparative Example 1) or γ-alumina (Example 6 and Comparative Example 2) as a catalyst and coexisting saturated hydrocarbons were used. In Comparative Examples 1 and 2 not coexisting with No. 6, not only the yield of n-butene is equal or improved, but also the production amount of C5 or more heavy component, the production amount of C5 or more heavy component / isobutene It is apparent that the feed amount, the amount of coke produced, and the amount of coke produced / the amount of isobutene supplied and the amount of catalyst are remarkably improved.

Claims (5)

  A method for producing n-butenes by bringing a feedstock containing isobutene and a saturated hydrocarbon having 1 to 10 carbon atoms into contact with a solid acid catalyst and subjecting isobutene to skeletal isomerization.   The method for producing n-butenes according to claim 1, wherein the concentration of isobutene in the feedstock is 10 to 90% by volume.   The method for producing n-butenes according to claim 1 or 2, wherein a concentration of the saturated hydrocarbon in the feedstock is 10 to 90% by volume.   The method for producing n-butenes according to any one of claims 1 to 3, wherein the saturated hydrocarbon is butanes.   The method for producing n-butenes according to any one of claims 1 to 4, wherein the solid acid catalyst is silica alumina or activated alumina.