US3303237A - Unsaturated hydrocarbons by oxidative dehydrogenation over ironalumina catalyst - Google Patents

Description

United States Patent 3,303,237 UNSATURATED HYDROCARBONS BY OXIDA- TIVE DEHYDROGENATIUN OVER IRON- ALUMHNA CATALYST Louis J. Croce, East Brunswick, Laimonis Bajars, Princeton, and Maigonis Gabliks, Highland Park, N.J., assignors to Petro-Tex Chemical Corporation, Houston, Tex.. a corporation of Delaware N0 Drawing. Filed Apr. 2, 1964, Ser. No. 356,941 Claims. (Cl. 260--680) This invention relates to a process for the preparation of unsaturated hydrocarbons by the dehydrogenation of hydrocarbons at elevated temperatures in the presence of oxygen and a particular catalyst.

It is known that some dehydrogenation takes place when hydrocarbons are heated at elevated temperature in the presence of oxygen. However, even under controlled conditions the yield of dehydrogenated product of the same number of carbon atoms as the starting material is low and generally the predominant products are combustion products. In order to increase the yield of desired product, catalysts have been employed in this reaction. Although initially fairly high yields have sometimes been obtained, it has been found difficult to maintain high yields of product for any appreciable period of time. It is one of the objects of this invention to provide a process whereby hydrocarbons are dehydrogenated at elevated temperatures in the presence of oxygen and a catalyst. It is also an object of this invention whereby a process is provided wherein high yields of product are obtained for prolonged periods of time without frequent regeneration of the catalyst.

According to this invention it has been found that hydrocarbons having at least four carbon atoms may be dehydrogenated to a product having the same number of carbon atoms by passing a gaseous mixture of from 2 to mol percent of the hydrocarbon, together with from 40 to 95 mol percent of stream and from 0.3 to 2.0 mol of oxygen per mol of the said hydrocarbon through a fixed bed catalyst at a temperature of at least 325 C. at a contact time with the fixed bed catalyst of an average particle size of at least /s inch of from 0.01 to 0.6 second. The catalytic surface of the fixed bed catalyst is an intimate combination of iron and alumina wherein the iron constitutes from to 98 weight percent of the total weight of the atoms of iron and aluminum.

The process of this invention is especially well adapted for the production of olefins and diolefins from aliphatic and cycloaliphatic compounds. The compounds to be dehydrogenated will have from 4 to 7 carbon atoms, and the aliphatic hydrocarbons will have a straight chain of at least four carbon atoms. The hydrocarbon to be dehydrogenated may be either saturated or unsaturated. Examples of preferred feed materials are butene-l, cisbutene-2, trans-butene-Z, Z-methyIbutene-l, 2 methylbutene-2, 2-methylbutene-3, n-butane, butadiene-l,3, methylbutane, 2-methylpentene-1, cyclohexene, Z-methylpentene-2 and mixtures thereof. The major proportion of the hydrocarbon converted will be to less saturated hydrocarbons of the same number of carbon atoms. Particularly preferred products are butadiene-l,3 and isoprene. Although various mixtures of hydrocarbons are used, the preferred hydrocarbon feed contains at least 50 mol percent of a hydrocarbon selected from the group consisting of butene-l, butene-2, n-butene, butadiene-l,3, Z-methylbutene-l 2-methylbutene-2, 2-methylbutene-3, and mixtures thereof, and more preferably contains at least 70 mol percent of one or more of these hydrocarbons. Especially preferred feeds are the monoolefins.

. Patented Feb. 7, 1967 Steam will be present in the reaction mixture in an amount from about 40 to mol percent and preferably will be present in an amount of at least 60 mol percent of the total gaseous stream entering the reactor. The gaseous stream will contain the hydrocarbon to be dehydrogenated in an amount from about 2 to 10 mol percent of the total and this amount will suitably be within the range of 3 to 8 mol percent of the gaseous stream. Oxygen is utilized in an amount of from 0.3 to 2.0 mol of oxygen per mol of hydrocarbon to be dehydrogenated, and the ratio will preferably be from 0.4 to 1.5. The oxygen may be fed as pure oxygen or may be fed as oxygen combined with diluents such as nitrogen or helium. Air is the preferred source of oxygen.

The gaseous mixture is conducted through the fixed bed catalyst at a critical contact time. The contact time is from 0.01 to 0.6 second, with the best results being obtained between 0.05 and 0.45 second. The contact time is the calculated dwell time of the reaction mixture in the reaction zone, assuming the mols of product mixture are equivalent to the mols of feed mixture. Calculated in another way, the flow rates will be within the range of about .8 to 10 liquid volumes of the hydrocarbon to be dehydrogenated per volume of reactor containing catalyst per hour (referred to as LHSV), wherein the volumes of hydrocarbon are calculated at standard conditions of 25 C. and 760 mm. of mercury. For calculation, the volume of reactor containing catalyst is that volume of reactor space excluding the volume displaced by the catalyst. For example, if a reactor has a particular volume of cubic feet of void space, when that void space is filled with catalyst particles, the original void space is the volume of reactor containing catalyst for the purpose of calculating the fiow rate.

The gaseous composition is passed through a fixed catalyst bed under the described conditions. The catalyst bed contains catalyst particles having a catalytic surface of iron and aluminum wherein the atoms of iron are present in an amount of from 25 to 98 weight percent of the total Weight of the atoms of iron and aluminum. The preferred percent is from 60 to 97 weight percent iron. Gamma alumina is the preferred form of the aluminum. The iron and aluminum are in intimate combination. It is difiicult to determine in what state the iron and aluminum are present such as a chemical compound or as a mixture. The catalytic surface will contain some oxygen. It is one of the features of this invention that improved results are obtained if the catalytic surface contains less than 0.5, such as less than 0.4, weight percent sodium or potassium or combinations thereof based on the catalytic surface.

The catalytic surface described is the surface which is exposed in the dehydrogenation zone to the reactor, that is, if a catalyst carrier is used, the composition described as a catalyst refers to the composition of the surface and not to the total composition of the surface coating plus carrier. Catalyst binding agents or fillers may be used, but these will not ordinarily exceed about 50 percent or 60 percent by weight of the catalytic surface. These binding agents and fillers will preferably be essentially inert. The quantity of catalyst utilized will be dependent upon such variables as the temperature of reaction, the concentration of oxygen, the age of the catalyst, and the flow rates of the reactants. The catalyst will by definition be present in a catalytic amount and the iron and aluminum will be the main active constituents. The amount of catalyst will ordinarily be present in an amount greater than 10 square feet of catalyst surface per cubic foot of reaction zone containing catalyst. Of course, the amount of catalyst may be much greater, particularly when irregular surface catalysts are used. When the catalyst is in the form of particles,

either supported or unsupported, the amount of catalyst surface may be expressed in terms of the surface area per unit weight of any particular volume of catalyst particles. The ratio of catalytic surface to Weight will be dependent upon various factors, including the particle size, particle size distribution, apparent bulk density of the particles, amount of active catalyst coated on the carrier, density of the carrier, and so forth. Typical values for the surface to weight ratio are such as about one-half to 200 square meters per gram, although higher and lower values may be used. The catalyst is autoregenerative and the process is continuous.

Improved catalysts may be obtained by reducing the catalyst of the invention. The reduction of the catalyst may be accomplished prior to the initial dehydrogenation, or the catalyst may be reduced after the catalyst has been used. It has been found that a used catalyst may be regenerated by reduction and, thus, even longer catalyst life obtained. The reduction may be accomplished with any gas which is capable of reducing iron oxide to a lower valence such as hydrogen, carbon monoxide or hydrocarbons. Generally the flow of oxygen will be stopped during the reduction step. The temperature of reduction may be varied but the process is most economical at temperatures of at least about 200 C., with the upper limit being about 750 C. or 900 C. or even higher under certain conditions.

The dehydrogenation reaction may be carried out at atmospheric pressure, superatmospheric pressure or at subatmospheric pressure. The total pressure of the system will normally be about or in excess of atmospheric pressure, although sub-atmospheric pressure may also desirably be used. Generally, the total pressure will be between about 4 p.s.i.a. and about 100 or 125 p.s.i.a. Preferably the total pressure will be less than about 75 p.s.i.a. and excellent results are obtained at about atmospheric pressure.

The temperature for the dehydrogenation reaction will be greater than 325 C., such as greater than about 375 C. Excellent results are obtained within the range of or about 300 C. to 575 C. such as from or about 325 C. to or about 525 C. The temperatures are measured at the maximum temperature in the reactor. An advantage of this invention is that lower temperatures of dehydrogenation may be utilized than are possible in conventional dehydrogenation processes. Another advantage is that large quantities of heat do not have to be added to the reaction as was previously required.

Several methods of catalyst preparation may be employed, but the preferred methods are those wherein the iron is combined as an iron salt which decomposes upon heating to moderate temperatures, e.g. less than 500 C.

In the following examples will be found specific embodiments of the invention and details employed in the practice of the invention. Percent conversion refers to the mols of hydrocarbon consumed per 100 mols of hydrocarbon fed to the reactor, percent selectivity refers to the mols of product formed per 100 mols of hydrocarbon consumed, and percent yield refers to the mols of product formed per mol of hydrocarbon fed.

Example 1 A catalyst was prepared by impregnating an alumina support with a solution of iron nitrate and calcining to decompose the nitrate as follows: 210 g. Fe (NO -9H O were dissolved in 200 mls. distilled H 0. 168 g. /s diameter alumina pellets were. added to this solution. The mixture was heated to dryness and the coated tablets calcined for 1 hour at 500 C. A mixture of 80 cc. catalyst and 80 cc. 6 mm. Vycor raschig rings was charged to a 1" IPS stainless steel reactor fitted with flanges and a centrally positioned thermocouple. The reactor was heated in a conventional electric tube furnace. Butene-2, having a purity of at least 98 mol percent, was dehydrogenated to butadiene-1,3. The feed consisted of 3.2 mol percent butenes, 93.6 mol percent steam, 3.2 mol percent 0 (fed as air). The catalyst was reduced with H for 1 hour at 500 C. before starting the butenes, steam and 0 (air). Contact time was about 0.075 second at a reaction temperature of 570 C. Butene conversion under these conditions was 68 mol percent with 76 percent selectivity to butadiene for 52 percent yield per pass.

Example 2 Butene containing 99 minimum mol percent butene-2 was dehydrogenated to butadiene-1,3. The catalyst was prepared from Fe O -H O and Al(NO -9H O. The catalyst was prepared by mixing an aqueous slurry of 135.8 g. of Fe O -H O and 53 g. of Al(NO -9H O in 500 cc. distilled H O. The slurry was precipitated by the addition of NH OH to pH 7.0. The slurry was then filtered, washed three times with distilled water, and dried at about 135 C. The dry filter cake was broken and screened into four to eight mesh granules for testing. The reactor used was a standard 1" IPS stainless steel pipe, 22 inches long, flanged at both ends and fitted with a centrally positioned thermocouple along the longitudinal axis. The reactor was heated by a conventional 3 zone electric furnace. 80 cc. of catalyst 4-8 mesh granules were diluted with 89 cc. of 43" x Ms diameter tabular refractory alumina and charged to the reactor. The catalyst was reduced by feeding hydrogen for one hour over the catalyst with the catalyst at a temperature of 500 C. A gaseous mixture containing 3.2 mol percent of the butene, 94.3 mol percent steam and 2.5 mol percent oxygen (fed as air) was fed to the reactor. Steam was generated by feeding distilled water to the preheat zone whereby it was vaporized. The maximum temperature in the reactor was 950 F. The contact time in the reactor was 0.075 second. Under these conditions the conversion of butene was 72 mol percent and the selectivity to butadiene was 88 mol percent for an overall yield of 63 mol percent.

Example 3 84 grams of Houdry 1008 hard alumina catalyst support having approximately 98.5 percent A1 0 and from about 0.1 to 0.2 weight percent of Na o and a surface area of 75 to 85 square meters per gram were placed in a suction flask and vacuum was applied. While under vacuum a solution of g. of Fe(NO -9H O, 10 g. of AI(NO -9H O and 125 ml. of distilled water were added during about a 15 minute period. The vacuum was then released and the composition was transferred to a porcelain dish wherein the catalytic composition was heated and coated on the carrier. 50 g. of the coated pellets were used to make a 4 inch catalyst bed in a 36" x 1'' LD. Vycor glass tube, with the remainder of the tube being filled with inert Vycor raschig rings. Butene-2 was dehydrogenated to butadiene by feeding butene-2 at an LHSV of 0.85, based on the volume of catalyst, and a ratio of 0.75 mol of oxygen per mol of butene-2. Steam was also incorporated in an amount of 20 mols of steam per mol of butene-2. At a reactor temperature of 450 C., 61 mol percent of the butene-2 was converted at a. selectivity of 86 mol percent to give a yield of butadiene- 1,3 of 53 mol percent.

We claim:

1. A process for the dehydrogenation of hydrocarbons having at least four carbon atoms which comprises passing a gaseous mixture of from 2 to 10 mol percent of said hydrocarbon, from 40 to mol percent steam, and from 0.3 to 2.0 mol of oxygen per mol of said hydrocarbon through a fixed bed catalyst having an average particle size of at least /8 inch at a temperature of at least 325 C. and at a contact time of the gaseous mixture with the said fixed bed catalyst of from 0.01 to 0.6 second, said catalyst comprising as a catalytic surface an intimate combination of iron and aluminum wherein the iron constitutes from 25 to 98 weight percent of the total weight of the atoms of iron and aluminum, said catalytic surface containing less than 0.5 weight percent of an element selected from the group consisting of sodi urn, potassium and mixtures thereof.

2. A process for the dehydrogenation of hydrocarbons having from 4 to 7 carbon atoms which comprises passing a gaseous mixture of from 2 to mol percent of said hydrocarbon, from 40 to 95 mol percent steam, and from 0.3 to 2.0 mol of oxygen per mol of said hydrocarbon through a fixed bed catalyst having an average particle size of at least inch at a temperature of at least 375 C. and at a contact time of the gaseous mixture with the said fixed bed catalyst having an average particle size of at least /8 inch of from 0.01 to 0.5 second, said catalyst comprising as a catalytic surface an intimate combination of iron and aluminum wherein the iron constitutes from 25 to 98 weight percent of the total weight of the atoms of iron and aluminum, said catalytic surface containing less than 0.5 weight percent of an element selected from the group consisting of sodium, potassium and mixtures thereof.

3. A process for the dehydrogenation of butene to butadiene which comprises passing a gaseous mixture of from 2 to 10 mol percent of said butene, from 40 to 95 mol percent steam, and from 0.3 to 2.0 mol of oxygen per mol of said hydrocarbon through a fixed bed catalyst having an average particle size of at least A; inch at a temperature of 325 C. to 575 C. and at a contact time of the gaseous mixture With the said fixed bed catalyst of from 0.01 to 0.4 second, said catalyst comprising as a catalytic surface an intimate combination of iron and aluminum, wherein the iron constitutes from 25 to 98 weight percent of the total weight of the atoms of iron and aluminum, said catalytic surface containing less than 0.5 weight percent of an element selected from the group consisting of sodium, potassium and mixtures thereof.

4. A process for the dehydrogenation of butene to hutadiene which comprises passing a gaseous mixture of from 2 to 10 mol percent of said butene, from at least mol percent steam, and from 0.4 to 1.5 mol of oxygen per mol of said hydrocarbon through a fixed bed catalyst having an average particle size of at least /3 inch at a temperature of 375 C. to 575 C. and at a contact time of the gaseous mixture with the said fixed bed catalyst having an average particle size of at least A3 inch of from 0.01 to 0.45 second, said catalyst comprising as a catalytic surface an intimate combination of iron and aluminum wherein the iron constitutes from 60 to 97 weight percent of the total weight of the atoms of iron and aluminum.

5. A process for the dehydrogenation of butene to butadiene which comprises passing a gaseous mixture of from 2 to 10 mol percent of said butene, from at least 60 mol percent steam, and from 0.4 to 1.5 mol of oxygen per mol of said hydrocarbon through a fixed bed catalyst having an average particle size of at least A2 inch at a temperature of 375 C. to 575 C. and at a contact time of the gaseous mixture with the said fixed bed catalyst having an average particle size of at least A; inch of from 0.01 to 0.45 second, said catalyst comprising as a catalytic surface an intimate combination of iron and-aluminum wherein the iron constitutes from 60 to 97 weight percent of the total weight of the atoms of iron and aluminum, said catalytic surface containing less than 0.4 weight percent of an element selected from the group consisting of sodium, potassium or mixtures thereof.

References Cited by the Examiner UNITED STATES PATENTS 3,168,587 2/1965 Michaels et al 260-6833 3,179,707 4/1965 Lee 260669 3,207,811 9/1965 Bajars 260-680 DELBERT E. GANTZ, Primary Examiner. G. E. SCHMITKONS, Assistant Examiner.

Claims (1)

1. A PROCESS FOR THE DEHYDROGENATION OF HYDROCARBONS HAVING AT LEAST FOUR CARBON ATOMS WHICH COMPRISES PASSING A GASEIOUS MIXTURE OF FROM 2 TO 10 MOL PERCENT OF SAID HYDROCARBON, FROM 40 TO 95 MOL PERCENT STEAM, AND FROM 0.3 TO 2.0 MOL OF OXYGEN PER MOL OF SAID HYDROCARBON THROUGH A FIXED BED CATALYST HAVING AN AVERAGE PARTICLE SIZE OF AT LEAST 1/2 INCH AT A TEMPERATURE OF AT LEAST 325*C. AND AT A CONTACT TIME OF THE GASEOUS MIXTURE WITH THE SAID FIXED BED CATALYST OF FROM 0.01 TO 0.6 SECOND, SAID CATALYST COMPRISING AS A CTALYTIC SURFACE AN INTIMATE COMBINATION OF IRON AND ALUMINUM WHEREIN THE IRON CONSTITUTES FROM 25 TO 98 WEIGHT PERCENT OF THE TOTAL WEIGHT OF THE ATOMS OF IONS AND ALUMINUM, SAID CATALYSTIC SURFACE CONTAINING LESS THAN 0.5 WEIGHT PERCENT OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM AND MIXTURES THEREOF.