KR900008104B1 - Improved catalyst for hydrocarbon dehydrogenation - Google Patents

Abstract

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Description

Process for dehydrogenation of hydrocarbons using an improved catalyst

1 is a plot showing selectivity versus conversion for isobutane dehydrogenation.

The present invention relates to catalytic dehydrogenation of C ₃ -C ₅ hydrocarbons, and in particular to improved catalyst preparation for use in such a process.

The production of olefins by catalytic dehydrogenation of the corresponding paraffins, more particularly by catalytic dehydrogenation of C ₃ to C ₅ paraffins, is known and any of these processes is carried out commercially. A catalyst commonly used in typical commercial examples is chromium oxide (Cr ₂ O ₃ ) precipitated on an alumina carrier, which must constitute alumina in gamma, eta or chi phase form.

공정으로서, 이것은 원래 합성고무의 수요를 충족시키기 위해 부탄에서 부타디엔을 제조하기 위해 설계된 것이다. 상기 공정은 Chemical Engineering Progress, February 1979 at pages 62-65에서 Craig, R.G., et al 이 쓴 최근 논설을 포함한 수많은 관련 기술 간행물에 기술되어 있다. 본 공정은 단열, 고정-베드, 다수-반응기 형태이며, 여기서 C₁충진원료는 18-20% 산화크롬으로 함침된 활성알루미나로 구성된 촉매상에서 탈수소화된다.The most widely used commercial dehydrogenation process is Houdry Catadiene

As a process, it was originally designed to produce butadiene from butane to meet the demand of synthetic rubber. The process is described in numerous related technical publications, including a recent article by Craig, RG, et al in Chemical Engineering Progress, February 1979 at pages 62-65. The process is in the form of adiabatic, fixed-bed, multi-reactor, wherein the C ₁ fillstock is dehydrogenated on a catalyst consisting of activated alumina impregnated with 18-20% chromium oxide.

Related CATOFIN ^™ processes have been developed for the preparation of C ₃ to C ₅ mono-olefins and work under conditions comparable to conventional CATADINE processes. In the CATOFIN process, C ₃ -C ₅ paraffins or mixed hydrocarbon feedstocks are charged.

An important aspect of the process is the conversion of isobutane to isobutylene, which isoolefins react with methanol to produce MTBE (methyl-tert-butyl-ether) for use as a high octagasoline mixed component. Typical conditions advocated for the production of C ₃ -C ₅ monoolefins from the corresponding saturated hydrocarbons include temperatures of 1,000 to 1400 ° F. (538-760 ° C.) and atmospheric pressures of 250-500 mmHg. An absolute space velocity of less than 1 (v / hr / v) is introduced into the catalyst consisting of 15-25 percent Cr ₂ O ₃ (catalyst weight) on the alumina carrier. The preparation of C ₃ -C ₅ monoolefins is described in Hydrocarbon Processing of November 1983 at page 117. An extensive discussion of the history and development of catalytic dehydrogenation processes for the preparation of mono and diolefins is described in Advances in Petroleum Chemistry and Refining, (Interscience Publishers, NY1961), vol. 4, Chapter 10 (starting on page 451). Of these, pages 479-485 are more relevant. The editorial by Gussow, S., et al in the Oil and Gas Journal, December 8.1980, pages 96-101 describes the Houdry CATOFIN process for the preparation of C ₃ and C ₄ mono-olefins, and the process design for converting the obtained isobutylene to MTBE. It is describing.

Chromia on the alumina catalyst used for the dehydrogenation of hydrocarbons is generally prepared by immersing the granules or pellets of the substrate in the chromium compound solution with the excess volume required to cover the pellets, the solution being a soluble chromium compound. It contains a good concentration of. After impregnation of the chromium solution, the excess solution in the pellet is removed, dried and calcined.

Satisfactory performance on the other hand was obtained in a dehydrogenation process using a commercially available chromia-alumina catalyst with 15-25% by weight Cr ₂ O ₃ , typically 18-20% Cr ₂ O ₃ , increasing the catalyst life. Attempts have been made over the years to improve the properties of the catalyst or to improve the catalytic properties such as activity, selectivity and wear resistance. The patented process for the preparation of an improved chromia-alumina dehydrogenation catalyst is as follows:

US Pat. No. 2,945,823 describes a process in which 0.5 to 2.0% sodium bentonite is added to improve the stability of the chromia-alumina catalyst.

The pelletized alumina substrate containing the added bentonite stabilizer was impregnated with the chromic acid solution by absorbing the pellets in a conventional, "excess" technique, i.e., in the amount of chromic acid solution much larger than the pellet can absorb. The pellet is then dried to remove excess solution.

US Pat. No. 2,956,030, which corresponds to the 823 patent, also describes the addition of sodium bentonite in an alumina carrier, but introduces a slightly different technique for forming a substrate into a chromic acid solution added by sorption. In addition, the patent describes that the presence of alkali metal ions in a catalyst within narrow limits has an effective effect. The optimal Na ₂ O content advocated is 0.25 to 0.45%.

The use of the "excess solution" technique is the most common and is mainly introduced in the commercial preparation of chromia-alumina dehydrogenation catalysts, while in some cases other metals or metal oxides are used instead of or in addition to chromium oxide. Also referred to as "volume absorption" techniques, so-called "small volume" techniques are used. This method is described in the United States patent on the preparation of a dehydrogenation catalyst comprising an alumina carrier with addition of 0.1 to 2% chromium and 0.2 to 5% precious metals of white metal.

It has been found that chromia-alumina catalysts with particularly improved activity and selectivity to dehydrogenation of isobutane can be prepared by spray impregnation of the alumina carrier to an initial infiltration with chromium compounds and then through conventional drying and calcination.

플롯트이며, 곡선 B는 본 발명에 따라 제조된 촉매로 얻어진 결과를 나타낸 플롯트이다.The attached figures show the mole% iC ₄ conversion (abscissa) and the mole% selectivity (ordinate) for iC ₄ , where curve A shows the results obtained with a conventional chromia-alumina catalyst.

Plot, curve B is a plot showing the results obtained with a catalyst prepared according to the present invention.

The following examples describe the preparation of chromia-alumina (Cr ₂ O ₃ / Al ₂ O ₃ ) dehydrogenation catalysts according to the present invention.

Example 1

The CrO ₃ (80g CrO ₃ / 100ml solution) is an aqueous solution of NaOH solution and 170ml 1ml (0.3g NaOH / 1ml solution) and diluted with distilled water to 205ml. (This diluted chromium solution is calculated to fill 90% of the pore volume of the alumina carrier.) The diluted solution is sprayed onto 500 g of etaalumina 1/8 inch pellets over 5 minutes using a rotary spray impregnator. The alumina pellet is contained in an angled grooved glass beaker, which is rotated while the solution is pumped through a glass rod with small pinholes, through which the solution rotates. It is directed to the pellets. After all the solutions have been sprayed, the further rotation is continued for 5 minutes.

The impregnated pellets were dried for 2 hours at 250 ° F. (about 120 ° C.) through air circulation, then heat treated for 2 hours in a furnace at 1200 ° F. (about 650 ° C.) and 4 at 760 ° C. in 20% steam-80% flow air. Time to deal. The carrier used for the obtained catalyst has the following physical properties:

Surface Area: 150㎡ / g

Bulk Density: 0.836㎏ / Liter

Porosity: 61cc / 100cc Carrier

H ₂ O absorption rate (%): 45 gH ₂ O / 100 g carrier

Pellet Density: 1.36g / cc

Density: 3.53g / cc

Total Pore Volume: 0.435cc / g

Average pore diameter: 0.011 micron

The resulting catalyst has a calculated chromium content of about 17 Cr ₂ O ₃ weight percent.

Catalyst preparation of the present invention is not limited to using only etaalumina substrates. Other forms of alumina may be used, such as gamma or chi. It is also possible to use other soluble Cr salts or Cr compounds such as chromium nitrate, acetate and the like instead of CrO ₃ .

Spray impregnation of the carrier is preferably carried out at room temperature but is generally satisfactory at a temperature of 10-90 ° C. The spraying time is not particularly important and is generally carried out for 2-15 minutes, preferably about 5 minutes.

The content and concentration of the chromium-containing solution used to impregnate the alumina carrier depends of course on the good content of Cr ₂ O ₃ that will precipitate on the substrate. The preferred range for dehydrogenation of C ₄ hydrocarbons is in the range of about 15 to 25 Cr ₂ O ₃ weight percent of Al ₂ O ₃ , with 17 to 19% being most preferred. The impregnation solution contains 0.5% by weight of alkali. The total volume of the solution should be able to fill 75-105%, preferably 90%, of the pore volume of the carrier. Drying of the impregnated pellets is carried out at temperatures ranging from 212-350 ° F. (100-180 ° C.), preferably at 250 ° F. (120 ° C.) for 2 hours. Continuous heat treatment of the dried catalyst is carried out for 2-6 hours at a temperature range of 1200-1470 ° C (650-800 ° C), preferably 4 hours at 760 ° F (1400 ° C).

The conditions conventionally adopted for use as conventional chromia-alumina catalysts for dehydrogenation of isobutane to isobutylene can be introduced in the same operating conditions using the catalyst of the invention. Typically these dehydrogenation conditions include a temperature range of 540-650 ° C. at a partial pressure of isobutane above 0.5 atm and gas hourly space velocity (GHSV) of 1440-2880 with or without inert carrier gas charging iC ₄ . do. Typically a preferred operation is a temperature range of 580-620 ° C. and a GHSV of 2160 filling about 17% iC ₄ or other inert carrier gas in helium.

Example 2

a) A series of runs is carried out under the preferred conditions using the catalyst of Example 1 for the dehydrogenation of 17% isobutane in helium at the selected temperature, atmospheric pressure and GHSV of 2160. Analyze the product obtained for 10 minutes. The results are shown in Table 1 below.

b) Another set of runs for comparison with the run in Example 2 (a) was conducted under the same conditions except using the standard Cr ₂ O ₃ -Al ₂ O ₃ prepared by the excess solution technique.

These results are shown in Table 1.

Prior to testing at each temperature, the catalyst is treated with 120 cc / min of flow air at 650 ° C. for 30 minutes and then at 240 cc / min H ₂ flow from GHSV of 1440 to 650 ° C.

TABLE 1

The comparison of selectivity versus conversion is shown in the plot, where curve A is a plot showing the results with standard Cr ₂ O ₃ -Al ₂ O ₃ catalyst and curve B is a catalyst prepared according to the invention (Example 1). It is a plot which shows the result obtained using.

Selectivity is calculated based on the mole percent of isobutylene in the formed product.

As can be seen from the results reported above, the catalyst prepared by initial impregnation by spray impregnation showed superior efficacy in terms of activity and selectivity under conventional working conditions than that prepared by conventional excess solution technology.

While the advantages exhibited by the catalysts prepared according to the invention are shown in the conversion of isobutane to isobutylene, the catalysts are characterized by different C ₃ −-in previously advocated operating conditions using typical commercial chromia-alumina dehydrogenation catalysts. It will be appreciated that it can be beneficially used to dehydrogenate C ₅ hydrocarbons.

Claims (7)

Initially infiltrating by spraying an alumina carrier with a solution of soluble chromium compound followed by drying and heat treatment to use a dehydrogenation catalyst prepared on a C ₃ -C under chromia-alumina catalyst under conditions for monoolefin production. ₅ Dehydrogenation of hydrocarbons. The method of claim 1, wherein the solution of the soluble chromium compound is sprayed at a content necessary to fill 75% to 105% of the pore volume of the alumina carrier and the chromium content required to precipitate 15 to 25% Cr ₂ O ₃ in the carrier mentioned. Improved process, characterized in that. _{3. The} improved process according to claim 2, wherein the soluble chromium compound is sprayed on the carrier mentioned in the amount required to precipitate 17-19% Cr ₂ O ₃ . 3. The improved process of claim 2 wherein the solution mentioned is sprayed in an amount necessary to fill about 90% of the alumina carrier pore volume. 2. The improved process according to claim 1, wherein the carrier mentioned consists essentially of etaalumina. 2. The improved process according to claim 1, wherein the dehydrogenation is carried out at atmospheric pressure and at a temperature of 580-620 [deg.] C. and at a space velocity of 2160 GHSV while filling isobutane in an inert carrier gas. 7. The improved process of claim 6 wherein said inert gas is helium.

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