GB1570646A - Dehydrogenation process - Google Patents

Description

(54) DEHYDROGENATION PROCESS (71) We, PHILLIPS PETROLEUM COM PANY, a corporation organised and existing under the laws of the State of Delaware, United States of America, of Bartlesville, Oklahoma, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to the dehydrogenation of hydrocarbons.

Known catalytic dehydrogenation processes are generally characterised by the particular catalyst material employed and the conditions under which the processes are operated, e.g. in the absence or presence of oxygen. While a number of such catalytic processes have achieved some measure of success, there is a continuing search to develop catalytic materials and processes which exhibit high activity, high yield of desired product, high selectivity to desired product, and longevity, and which keep undesirable side reactions to a minimum.

In accordance with the present invention there is provided a process for catalytically dehydrogenating a dehydrogenatable organic compound which comprises containing an organic compound with a regenerable dehydrogenation catalyst, as described below, in the substantial absence of free oxygen under dehydrogenation conditions for a reaction period. Thereafter an oxygen-containing gas can be passed in contact with the catalyst under regeneration conditions for a regeneration period.

The process of this invention provides, with respect to known processes for oxidative dehydrogenation of organic compounds, several advantages: The cost of separating and purifying the products of the process is reduced. Selectivity to the desired product is increased. Less steam is required.

The dehydrogenation catalyst employed in the process of the present invention is a calcined composition consisting essentially of zinc, titanium and sufficient oxygen to satisfy the valence requirements of zinc and titanium, wherein the atomic ratio of zinc to titanium is in the approximate range 1-74:1 to 2-15:1, preferably about 2:1, which corresponds to zinc orthotitanate.

The catalyst can be prepared by intimately mixing suitable proportions of zinc oxide and titanium dioxide, and calcining the mixture in air at a temperature in the range of 650" to 10500 C, preferably from 675" to 975"C. It is presently preferred that the titanium dioxide used in preparing the catalyst have an average particle size of less than about 100 millimicrons.

The catalyst can also be prepared by coprecipitation from aqueous solutions of a zinc compound and a titanium compound.

The aqueous solutions are mixed together and the hydroxides are precipitated by the addition of ammonium hydroxide. The precipitate is then washed, dried and calcined, as above.

The process of the present invention is particularly suited to the dehydrogenation of organic compounds having from 2 to 12 carbon atoms per molecule and characterised by having at least one

grouping, i.e. adjacent carbon atoms, each having at least one hydrogen atom. Suitable compounds include paraffins, olefines, cycloaliphatics and alkyl aromatic compounds having from 2 to 12 carbon atoms -per molecule. Particularly suitable are paraffins and monoolefins, branched or unbranched. Some examples of such appli- cable hydrocarbon feedstocks are ethane, propane, butane, isobutane, pentane, iso pentane, hexane, l-methylhexane, n-octane, n-dodecane, 1-butene, 2-methyl-butene-l, 2-methyl-butene-2, 2-hexene, l-octene, 3methyl-nonene-4, l-dodecene and cyclohexane and mixtures thereof. Particularly appropriate is the conversion of ethane to ethylene, propane to propylene, butanes to butenes and butadiene, and isopentane to isoamylenes and isoprene.

The preferred cyclical process of this in- - vention can be carried out by means of any apparatus whereby there is achieved an alternate contact of the catalyst with the gaseous phase containing the dehydrogenatable organic compound and thereafter of the catalyst with the oxygen-containing gaseous phase, the process being in no way limited to the use of a particular apparatus.

The process of this invention can be carried out using a fixed catalyst bed, fluidized catalyst bed or moving catalyst bed. Presently preferred is a fixed catalyst bed.

In order to avoid any casual mixing of the organic compound and oxygen, provision can be made for intermediate supple- mental injection of an inert purging gas, such as, for example, nitrogen, carbon dioxide or steam.

The time of reaction, i.e. dehydrogenation, for the dehydrogenatable organic compound may range from 0-05, preferably 0 5 seconds, to 10 minutes, more preferably from 1 second to 5 minutes.

The time of regeneration of the catalyst may range from 1 to 10 times the reaction period. The temperature of the reaction will generally range from 42S705 C, preferably from 482450 C, depending upon the nature of the organic feedstock.

The pressure of the reaction may range from 0 05 to 250 psia (5 to 1724 kPa).

The organic compound feed rate will preferably be in the range 50 to 5000 volumes of feedstock per volume of catalyst per hour (GHSV), depending upon the feedstock, and the temperature and pressure employed, more preferably from 100 to 2500. The presence of steam is fre quently beneficial and steam : hydrocarbon mol ratios of up to 50: 1 can be used, preferably from 0-1:1 to 20:1. An inert gaseous diluent, such as nitrogen or carbon dioxide, can also be used, and if used, will generally be in the same amounts as specified for the steam.

Steam can also be employed in admixture with the oxygen-containing gas during regeneration period. Generally, the amount of oxygen, from any source, sup plied during the regeneration step is from 1 5 to 5 times the volume of hydrocarbon feed processed during the dehydrogenation step. The regeneration step is conducted at the same temperature and pressure recited for the dehydrogenation step, although somewhat higher temperatures can be used in some instances.

Thus, the preferred operating cycle will include the successive steps of: (1) Contacting the organic compound with the catalyst, resulting in the production or more unsaturated compounds. This step is optionally conducted in the additional presence of steam.

(2) Optionally, purging the catalyst with an inert gas.

(3) Contacting the catalyst with free oxygen.

(4) Optionally, purging the catalyst with an inert gas.

(5) Repeating step 1.

EXAMPLE I A zinc titanate catalyst was prepared by slurrying 162 grams of powdered zinc oxide, having an average particle size of about 130 microns, and 80 grams of finely divided titanium doixide, having an average primary particle size of 30 millimicrons, in 1200 cc of water. The mixture was mixed in a high speed blender for 10 minutes. The resulting mixture was dried overnight in a forced draft oven at 2200F (104"C). The filter cake was divided into 4 equal portions and each portion was calcined in air for 2 hours at the temperature indicated in Table I. Each portion, after cooling, was ground and screened to obtain 2040 mesh particles (U.S. Sieve Series). A 2 cc sample of each composition was used in dehydrogenating isopentane in a fixed bed, low-pressure, automated testing unit.

Each run was conducted at 11000F (593"C) at atmospheric pressure at an isopentane feed rate of about 250 GHSV.

After charging the reactor with catalyst, the reactor and contents were brought up to reaction temperature in the presence of about 1250 GHSV steam and about 1250 GHSV nitrogen. Each cycle from this point on consisted of contacting the catalyst with a mixture of steam, nitrogen and air for a 6-minute regeneration period.

Nominal GHSV of each component amounted to 1250, 1250 and 1800, respectively.

Following regeneration, the air was cut off while steam and nitrogen at the same rates as before continued to flow for 6 minutes to purge out the air. The isopentane feed (250 GHSV) was then cut in and it was allowed to flow for 3 minutes to complete a 15-minute cycle. The hydrocarbon was carried into the reactor by a helium stream flowing at 930 GHSV.

The steam was condensed from the re actor effluent and the gas phase was analyzed by means of gas/liquid chromatography for isoprene, isoamylenes, carbon oxides and cracked products only. The analyzed values shown in Table I were obtained after 85 cycles.

Table I Effect of Zinc Titanate Calcining Temperature on Isopentane Dehydrogenation Catalyst Yields, Products, Mole % Apparent Conver Run Calcining Surface Bulk sion Selectivity to No. Temp. C Area Density Mole Isoamy- Carbon Isoprene + m/g g/cc % Isoprene lenes Cracked Oxides Isoamylenes, % 1 594 16.2 0.84 6.2 1.1 3.1 1.6 0.4 68 2 655 9.0 0.88 11.3 2.2 8.2 0.4 0.0 92 3 816 6.7 0.87 38.5 10.7 20.7 5.1 2.0 82 4 927 4.5 1.06 34.4 9.7 18.9 4.2 1.6 83 5 1010 1.2 1.38 7.6 1.6 4.0 1.6 0.4 74 The above results show that the calcining temperature used in preparing a zinc orthotitanate are important in obtaining active catalysts for isopentane dehydrogenation. Runs 3 and 4 show that the calcining temperatures ranging from about 800 to about 950"C provide optimum catalysts for use in this process.

EXAMPLE II A series of zinc titanate catalysts was prepared by blending powdered zinc oxide with commercially available titanium dioxide as described in Example I. Each titanium dioxide was characterized by a different average particle size. Each resulting blend, after drying overnight, was calcined in air for 3 hours at 816"C, cooled, ground and sieved to obtain 20-40 mesh particles for testing. Additionally, a coprecipitated catalyst was prepared by mixing an aqueous solution containing 118 grams of zinc nitrate hexahydrate and 71 grams of potassium titanium oxalate dihydrate and precipitating the hydroxides by increasing the pH of the solution to 8-3 by the addition of ammonium hydroxide.

The precipitate was washed with hot, distilled water to essentially remove soluble salts, dried in the forced draft oven at 220"F, calcined in air for 3 hours at 8160C, cooled, ground and sieved to obtain 2040 mesh particles for testing.

A 2 cc sample of each catalyst was individually charged to a reactor contained in the test unit used in the Example L Dehydrogenation of isopentane was conducted at atmospheric pressure at 1050"F (566"C) in a cyclic fashion as described in Example I. The flow rates of reactants and diluents were the same as used in Example I except that steam was absent in all the runs. Each effluent was analyzed by gas-liquid chromatography as before. The average particle size of the titanium dioxide used in preparing the catalyst and the results obtained are presented in Table II.

Table II Effect of Zinc Titanate Preparation on Isopentane Dehydrogenation Selectivity to Iso Catalyst Titania Yields, Products, Mole % prene Catalyst Surface Apparent Particle Con- + Run Pre- Area Bulk Size version Iso- Isoamy No. para- m/g Density Microns Cycles Mole prene Isoamy- Carbon lenes tion g/cc % lenes Cracked Oxides % 1 C 10.6 0.65 141 34.8 11.3 20.6 2.2 0.7 92 2 M 6.6 0.88 0.030 141 42.7 11.4 28.1 2.3 0.8 93 3 M 2.3 1.00 1404 57 5.3 0.8 1.3 3.1 0.2 40 4 M 2.1 1.06 2304 85 11.5 2.5 6.7 2.0 0.3 80 C means coprecipitation; M means mixed.

Not applicable.

Flame hydrolyzed titanium dioxide.

4 Commercially available powdered titanium dioxide.

The above results show that the most active zinc orthotitanate catalyst is obtained when such catalyst is prepared using a small particle size titania or by coprecipitation.

When a comparatively large particle size titania is used, as shown in Runs 3 and 4, the results show that a much less active catalyst is produced, based on yield of products and conversion of feed.

EXAMPLE Ill A zinc orthotitanate catalyst was prepared in the manner of Example I by slurrying a 40-gram portion of the same zinc oxide with a 20-gram portion of the titania used in Run 2 of Example II in 300 cc of distilled water for about 5 minutes in a high-speed blender. The slurry was dried overnight at 1200C in a forced draft oven and the cake was calcined for 3 hours at 816"C. The product, after cooling, was ground and screened to obtain 2040 mesh particles. 2-cc portions of this catalyst were used in dehydrogenating propane in a fixed bed, low pressure automated testing unit. The catalyst had a surface area of 6-5 m2/g and an apparent bulk density of 0.96 g/cc.

The dehydrogenation was conducted in a cyclic fashion at atmospheric pressure as described in Example I, except that no steam was employed. In these tests, the flow rate of propane was 500 GHSV, the flow rate of nitrogen was 1000 GHSV and the flow rate of regeneration air was 1800 GHSV.

The reactor temperatures used, the number of cycles and the results obtained are presented in Table III. Each effluent was analyzed by gas-liquid chromatography as before.

Table III Dehydrogenation of Propane Over Zinc Titanate Catalyst Run No. 1 2 Reactor Temp. F( C) 1150 (621) 1200 (649) Products Mole %: Methane 2-0 3-6 CO 0.6 1-5 CO2 1 0 1-1 Ethylene 2-3 3.9 Propylene 62-4 64-1 Propane 31-7 25-8 Conversion Mol of: 683 742 Selectivity To Propylene, %: 91 86 Cycles: 364 392 The above results show that zinc orthotitanate converts propane primarily to propylene under the reaction conditions employed.

The activity of the dehydrogenation catalyst used in the process of the present invention can be increased by the presence of lithium or magnesium, and sufficient oxygen to satisfy the valence requirements of the zinc, titanium and the lithium or magnesium. The amount of lithium or magnesium ranges from 0001 to 05, preferably 0005 to 0.2, grams-equivalents of lithium or magnesium per 100 grams of the combined weight of zinc, titanium and oxygen combined therewith.

This modified catalyst can be prepared by intimately mixing suitable proportions of zinc oxide, titanium dioxide and a suitable compound of lithium or magnesium, and calcining the mixture in air at a temperature in the range 650" to 1050"C, preferably from 675" to 975"C. Suitable compounds of lithium or magnesium are those compounds which can be calcined to lithium oxide or magnesium oxide, without having undesirable residues in the catalyst, such as, for example, lithium hydroxide, lithium nitrate, lithium acetate, magnesium hydroxide, magnesium nitrate and magne- sium acetate.

The catalyst can also be prepared by coprecipitation from aqueous solutions of a zinc compound, a titanium compound and a lithium or magnesium compound. The aqueous solutions are mixed together and the hydroxides are precipitated by the addition of ammonium hydroxide. The precipitate is then washed, dried and calcined, as above. Alternatively, the zinc and titanium can be coprecipitated and the coprecipitate impregnated with a suitable lithium or magnesium compound, then dried and calcined.

EXAMPLE IV Catalyst Preparation A series of catalysts was prepared from zinc oxide, titanium dioxide and the metal promoter. Each catalyst was prepared by slurrying 40 g of powdered zinc oxide having an axerage primary particle size of about 130 microns with 20 grams of titanium dioxide prepared by flame hydrolysis having an average primary particle size of about 30 millimicrons in 300 cc of distilled water in a high speed blender. An aqueous solution of the promotor metal compound, when used, was added t othe slurry and blended about 6 minutes. Each mixture was dried overnight in a forced draft oven at 1200C, calcined in air for 3 hours at 1500"F (816"C), cooled, ground and sieved to obtain particles of 2040 mesh in size (U.S. Sieve Series). The promoter metal compounds used, the analyzed concentration of promoter metal found in each catalyst and surface area and apparent bulk density of each catalyst are presented in Table IV.

Table IV Catalyst Preparation Promoter Apparent Surface Bulk Catalyst Metal Area, Density Designation Compound Wt. % gm-eq. m/g g/cc A None 0 0 6.5 0.96 B LiOH 0.07 0.01 8.0 1.02 C LiOH 0.16 0.02 7.9 1.17 D LiOH 0.36 0.05 8.2 1.18 E LiOH 0.68 0.10 7.4 1.23 F LiOH 1.08 0.16 6.8 1.35 G KNO3 0.72 0.02 nd 1.00 H Cs2CO3 2.4 0.02 nd 1.04 I Mg(NO3)2.6H2O 1.5 0.03 nd 1.09 J Mg(NO3)2.6H2O 2.5 0.05 6.1 1.05 K Ba(NO3)2 6.2 0.025 nd 0.98 Analyzed value.

Gram-equivalents per 100 grams of Zn2TiO4.

Not determined.

EXAMPLE V Ethane was dehydrogenated at atmospheric pressure in a cyclic manner with each cycle consisting of a 3-minute reaction period, 6-minute regeneration period and 6-minute nitrogen purge flow period.

The same temperature was employed for the reaction and regeneration periods.

Feed, air and nitrogen were passed to a preheat zone and then to the reactor. A 4-cc sample of each catalyst was charged to a fixed bed automated testing unit and the reactor and catalyst brought up to temperature in the presence of about 250 GHSV nitrogen. Each cycle from this point on consisted of contacting the catalyst with a mixture of nominal 250 GHSV nitrogen and 900 GHSV for 6 minutes. Air was cut off and nitrogen continued to flow for 6 more minutes to purge air from the system. Ethane, nominal 250 GHSV, was then cut in and allowed to flow for 3 minutes to complete the cycle.

The effluent gas phase, collected from 12 consecutive cycles, was analyzed by means of gas-liquid chromatography for oxygen, nitrogen, ethylene, methane, and carbon oxides. The analyzed values (average of duplicate runs) are shown in Table V along with the reactor temperatures employed.

In this and the following examples, the selectivity is based on the gas-phase products only and is expressed as the nearest whole number.

Table V Cyclic Ethane Dehydrogenation Product Yields, Mole % Selec Catalyst Conver- tivity Run Designa- Reactor Temp. sion, Ethy- Carbonlene, % Remarks No. tion Metal/wt.% F C Mole % lene Cracked Oxides to Ethyl1 A 0 1050 566 13.1 8.8 0 4.3 67 Control 2 B Li/0.07 1050 566 12.9 9.8 0 3.0 76 3 C Li/0.16 1050 566 12.5 10.2 0.1 2.2 82 4 D Li/0.36 1050 566 11.0 10.5 0 0.4 96 5 A 0 1150 621 30.5 20.0 1.9 8.6 66 Control 6 B Li/0.07 1150 566 35.1 7.1 12.9 15.0 20 7 C Li/0.16 1150 621 24.1 15.8 2.9 5.3 66 8 D Li/0.36 1150 621 23.0 18.2 1.6 3.0 79 These data shown in Runs 2, 3 and 4 and in Runs 6, 7 and 8, at reactor temperatures of 1050 and 1150"F, respectively, that the ethylene yield increases as the lithium promoter level increases from 007 wt. % to 0.36 wt. %. At a given promoter level, highest ethylene yields and selectivities to ethylene were obtained at a 10500F reactor temperature. The results show that the lithium promoted zinc titanate catalyst is more active for ethane dehydrogenation in a cyclic process at 1050"F than the unpromoted control as shown in Run 1. At 1150"F, it is necessary to have at least about 0.16 wt. % lithium present to equal or surpass the control catalyst on a selectivity to ethylene basis. The added lithium appears to primarily suppress formation of carbon oxides.

EXAMPLE VI Propane was dehydrogenated at atmospheric pressure with the catalysts of this invention and effluents analyzed in the manner described in Example V except that gas phase effluents from 28 consecutive samples were accumulated. Duplicate runs were made. The propane feed rate was 250 GHSV, the nitrogen rate was 250 GHSV and the air rate was 900 GHSV.

The effluents were analyzed for oxygen, nitrogen, methane, propane, carbon oxides and propylene. The results are presented in Table VI.

Table VI Cyclic Propane Dehydrogenation Catalyst Product Yields, Mole Selecti De- Con- % vity to Run signa- Li, Reacto Temp. version Pro- Carbon Me- Pro- Ethyl- Propy- Re No. tion Wt. % F C Mole % pylene Oxides thane pane lene lene, % marks 1 A 0 1050 566 42.3 40.8 0.85 0 57.65 0.65 96 Control 2 B 0.07 1050 566 40.1 38.15 0.85 0.15 60.0 1.0 95 3 C 0.16 1050 566 37.0 35.65 0.60 0 63.0 0.7 96 4 D 0.36 1050 566 30.05 28.8 0.75 0 69.9 0.55 96 5 E 0.68 1050 566 22.0 21.1 0.40 0 78.0 0.45 96 6 F 1.08 1050 566 8.9 8.35 0.15 0 91.05 0.40 94 7 A 0 1150 621 75.05 61.6 4.45 4.4 25.0 4.1 82 Control 8 B 0.07 1150 621 77.9 65.1 4.65 3.85 22.1 4.35 84 9 C 0.16 1150 621 78.15 67.75 3.7 2.85 21.85 3.8 87 10 D 0.36 1150 621 77.15 67.6 3.4 2.45 22.8 3.8 88 11 E 0.68 1150 621 72.7 66.0 2.25 1.5 27.35 3.0 91 12 F 1.08 1150 621 49.25 46.1 0.65 0.55 50.75 1.95 94 At a reactor temperature of 1050"F, the results show the lithium-promoted catalysts to be active for dehydrogenation of propane in a cyclic process but that the unpromoted catalyst is more active. When a reactor temperature of 1150"F is used, however, the data in runs 8-11 show the beneficial results in increased propylene formation as well as increased selectivity to propylene compared with control Run 7.

Run 12 indicates that the highest selectivity to propylene is obtained when the lithium concentration on the catalyst is about 1 weight percent. With this catalyst, the lowest production of carbon oxides, methane and propylene was obtained.

EXAMPLE VII In another series of tests, n-butane was dehydrogenated with the lithium promoted catalysts. In a closely related series, butene-2 was also dehydrogenated with the lithium promoted catalysts. The cyclic conditions employed were similar to those used in Example VI, except that the feed rate was 1000 GHSV and the oxygen rate was 440 GHSV (air 2300 GHSV). The effluent collected from 28 consecutive cycles was analyzed for oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, ethane plus ethylene, propylene, n-butane, butene- 1, cis-butene-2, trans-butene-2 and butadiene. The results are presented in Tables VII A and VII B.

Table VII A Cyclic Butane Dehydrogenation Catalyst Product Yields, Mole % De- Con- Selectivity, % Run signa- Li, Reactor Temp. version Buta- Carbon Buta- Re No. tion Wt. % F C Mole % Butenes diene Cracked OxidesButenes diene marks 1 A 0 1050 566 23.6 19.0 2.9 1.4 0.3 81 12 Control 2 B 0.07 1050 566 25.35 19.75 3.4 1.8 0.5 78 13 3 D 0.36 1050 566 23.5 18.0 3.5 1.5 0.4 77 15 4 E 0.68 1050 566 18.35 13.75 2.8 1.4 0.3 75 15 5 F 1.08 1050 566 10.2 7.5 1.45 1.05 0.2 74 14 6 A 0 1150 621 34.2 21.55 6.55 5.65 0.5 63 19 Control 7 B 0.07 1150 621 39.6 24.05 7.9 6.85 0.75 61 20 8 D 0.36 1150 621 40.2 24.55 8.35 6.5 0.7 61 21 9 E 0.68 1150 621 35.5 21.45 7.2 6.3 0.6 60 20 10 F 1.08 1150 621 23.25 12.65 4.6 5.65 0.4 54 20 Table VII B Cyclic Butene-2 Dehydrogenation Con- Product Yields, Mole % Run Catalyst Reactor Temp. version Buta- Carbon Selectivity to No. Designation Li, Wt. % F C Mole %diene Cracked Oxides Butadiene, % 1 A 0 1050 566 10.8 9.9 0.2 0.2 92 2 B 0.07 1050 566 13.1 11.7 0.35 0.45 89 3 D 0.36 1050 566 13.85 12.3 0.5 0.4 89 4 E 0.68 1050 566 11.95 10.7 0.35 0.4 90 5 F 1.08 1050 566 5.55 5.0 0.05 0.2 90 Catalysts previously used for 56 cycles in butane dehydrogenation, 112 cycles in isobutane dehydrogenation and 56 cycles in butene-2 dehydrogenation.

The cyclic butane dehydrogenation results shown in Table VII A indicate that the lithium-promoted catalysts improve selectivity to butadiene with concomittant decrease in selectivity to butenes compared to the control Runs 1 and 6 at both 1050"F and 1150"F reactor temperatures. In general, the catalysts containing from about 0.05 to about 0.7 weight percent lithium, in Runs 2, 3, 4 and 8, 9, 10, also yield more butadiene than the control catalysts under the conditions employed.

The cyclic butene-2 dehydrogenation results, in general, parallel those obtained with n-butane with respect to increased production of butadiene. The selectivities to butadiene, however, are slightly lower than that shown by the control catalyst.

It is noteworthy that the catalysts used in the butene-2 dehydrogenation had been previously employed for 224 cycles in nbutane, isobutane and butene-2 dehydrogenation studies before the results shown in Table VII B were obtained.

EXAMPLE Vlll In a series of runs, isopentane was dehydrogenated with each catalyst shown in Table IV. The cyclic conditions employed were similar to those used in Example VI.

The effluent collected from 29 consecutive cycles was analyzed for oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, ethane plus ethylene, propylene, butene-1, cis-butene-2, trans-butene-2, isopentane, npentane, 3-methylbutene-1, 2-methylbutene-l, pentene-l, 3-methylbutene-2, isoprene and trans-piperylene. The conditions employed and results obtained are summarized in Table VIII.

The reactor temperature employed in each run was 1Q50"F (566 C).

Table VIII Cyclic Isopentane Dehydrogenation Catalyst Conver- Product Yields, Mole % Selectivity, % Run Designa- Metal/ sion Isoamy- Iso- Carbon Isoamy Iso- Re No. tion Wt. % Mole % lene prene Cracked Oxides lene prene marks 1 A 0 43.35 28.25 11.45 2.55 1.1 65 26 Control 2 B Li/0.07 46.7 31.3 11.3 2.75 1.0 67 24 3 C Li/0.16 52.55 35.55 11.5 2.8 1.0 68 22 4 D Li/0.36 49.65 33.7 11.5 2.7 1.05 68 23 5 E Li/0.68 48.35 32.1 13.2 2.35 0.7 66 27 6 F Li/1.08 33.75 22.4 9.45 1.35 0.5 66 28 7 G K/0.72 1.65 0 0 1.5 0.2 0 0 8 G K/0.72 1.75 0 0 1.6 0.2 0 0 9 H Cs/2.4 1.95 0 0 1.5 0.3 0 0 10 H Cs/2.4 2.15 0 0 1.8 0.3 0 0 11 K Ba/6.2 4.55 1.9 1.4 1.25 0 42 31 12 K Ba/6.2 4.0 2.15 0.7 1.15 0 54 18 13 I Mg/1.5 41.1 26.95 11.2 2.1 0.8 66 27 14 J Mg/2.5 40.95 28.05 10.0 2.15 0.8 68 24 15 I Mg/1.5 44.65 29.45 12.15 2.15 0.85 66 27 16 J Mg/2.5 45.5 31.15 11.15 2.35 0.9 68 25 The results presented in Table VIII demonstrate that the lithium-promoted catalysts are active in isopentane dehydrogenation under the cyclic conditions employed.

The data show the catalysts containing from about 0 07-0 68 weight percent lithium generally produce more isoamylenes and about the same amount of isoprene as does the control catalyst. The catalyst of Run 5 (0.68 weight percent lithium), however, produces more isoamylenes and isoprene than all the other catalysts tested The invention catalyst containing about 1-08 weight percent lithium, Run 6, is less active in producing the desired products (as shown in other Examples) but generally has a somewhat higher selectivity to these products than does the control catalyst.

The results presented in Runs 7-12 show that promotion of zinc titanate with potassium or cesium is not equivalent to lithium promotion since the catalysts are inactive under the conditions employed.

The results shown in Runs 13-16 with the magnesium-promoted catalysts show that selectivity to isoamylenes and/or isoprene is slightly higher than that obtained with the unpromoted catalyst. The yields of those products obtained are slightly lower with the magnesium-promoted catalysts than with the control catalyst. Runs 11 and 12 show that barium promotion is not equivalent to magnesium promotion since the barium-containing catalyst is inactive under the process conditions employed.

Claims (18)

WHAT WE CLAIM IS:-

1. A process for catalytically dehydrogenating a dehydrogenatable organic compound, which comprises contacting the organic compound, at a temperature in the range 426 to 705"C with a dehydrogenation catalyst, wherein the catalyst comprises a calcined mixture of zinc and titanium oxides containing an atomic ratio of zinc: titanium in the range 1-74: 1 to 2:15:1 and sufficient oxygen to satisfy the valences of the zinc and titanium, said catalyst having been prepared by calcination in air, at a temperature in the range 650 to 1050 C, of a mixture of zinc and titanium oxides or of a mixture of zinc and titanium compounds convertable to their respective oxides upon calcination.

2. A process according to claim 1, wherein the organic compound is contacted with the catalyst at a temperature in the range 482-650"C.

3. A process according to claim 1 or 2, wherein the organic compound is contacted with the catalyst at a pressure of from 0.05 to 250 p.s.i.a.

4. A process according to claim 1, 2 or 3, wherein'the organic compound- is contacted with- said catalyst in the presence of steam at a steam:organic compound-mol ratio of up to 50:1.

5. A process according to - claim 4, wherein said mol ratio is from 0I:1 1, to 20: 1.

6. A process according to any one of the preceding claims, wherein the organic compound contains from 2-12 carbon atoms per molecule and contains one or more dehydrogenatable groups of the formula

7. A process according to claim 6, wherein the organic compound comprises one or more of the following: ethane, propane, butane, isobutane, pentane, isopentane, hexane, 2-methylhexane, n-octane, n-dodecane, l-butene, 2-methyl-butene-1, 2-methyl-butene-2, 2-hexane, l-octene, 3methyl-nonene-4, l-dodecane and cyclohexane.

8. A process according to any one of the preceding claims, wherein the atomic ratio of zinc to titanium in the catalyst is about 2: 1.

9. A process according to any one of the preceding claims, wherein said calcination temperature is from 675 to 975"C.

10. A process according to any one of the preceding claims, wherein the catalyst is prepared by admixing oxides of zinc and titanium, the latter oxide having an average particle size of less than 100 microns, and calcining the mixture so formed.

11. A process according to any one of claims 1-9, wherein the catalyst is formed by coprecipitating from aqueous solution a mixture of zinc and titanium hydroxides, drying said mixture and calcining the mixture in air to convert the hydroxides into the oxides.

12. A process according to any one of claims 1-11, wherein the catalyst is periodically regenerated by contacting the catalyst with a free oxygen-containing gas at a temperature of from 426-705 C.

13. A process according to claim 12, wherein the amount of oxygen in said freeoxygen-containing gas is from 1-5 to 5 times the volume of the organic compound processed during the immediately preceding dehydrogenation step.

14. A process according to claim 12 or 13, wherein the free oxygen-containing gas used in the regeneration step also contains steam.

15. A process according to claim 1, substantially as hereinbefore described in Example I, II or III.

16. A process according to any one of claims 1-14, wherein the catalyst additionally contains from 0.001 to 0.5 gm. equivalents of lithium or magnesium (present in oxide form) per 100 gms. of the combined weight of zinc, titanium and the oxygen associated therewith.

17. A process according to claim 16, wherein said amount of lithium or magnesium is from 0.005 to 0-2 gram equivalents.

18. A process according to claim 16, substantially as hereinbefore described in Example IV-VIII.