[CONTRIBUTION FROM
THE
SCHOOL OF CHEMICAL TECHNOLOGY OF NORTHDAKOTA AGRICULTURAL COLLEGE]
PREPARATION AND USE OF COPPER-CHROMIUM-OXIDE CATALYSTS I N DEHYDROGENATIONS RALPH E. DUNBAR Received June 16, 1938
Investigations involving the dehydrogenation of various alcohols to the corresponding aldehydes have been reported from time to time. Bouveaultl in 1908 reported the use of a copper catalyst but Conant, Webb, and Mendium2later found that while this catalyst was suitable for trimethylacetaldehyde and dimethylacetaldehyde, it was easily susceptible to poisoning. Oxide catalysts are less easily poisoned but require a higher temperature, induce a greater amount of dehydration, and do not retain their activity over as long a period. Among such catalysts are zinc oxide, zinc-chromium-oxide3 and copper-chromium-oxide.4 Adkins, Kommes, Struss, and Dazler6 report a special type of equipment for these dehydrogenations using the copper-chromium-oxide catalyst. In this equipment the alcohol was fed by gravity through a horizontal tube at the rate of one to two ml. per minute. The unchanged alcohol was recovered by fractionation and again passed through the equipment. The yields of aldehyde, based upon the amount of alcohol passed once over the catalyst, ranged from 28 to 35 per cent. In using this equipment the catalyst was pressed into pellets of approximately 0.15 gram each. In the dehydrogenation of alcohols there are at least four rather important types of reactions which occur when alcohols are passed over catalysts of this type, i.e., (I) dehydrogenation; (11) dehydration; (111) aldol condensation, possibly followed by dehydration; and (IV) ester formation by the Tischtchenko reaction, i.e., (1) (11) (111) (IV)
+
nZ-C4H90H-+ n-C3H7CHO HZ n-C4HgOH --+ C4Hs H2O 2 TL-C~H~CHO + CH~CHZCH~CH (0H)CH (CZHs)CHO -+ CH,CH2CH2CH=C(CpH5)CHO H20 2 w C ~ H ~ C H+ O n-C3H?COOC4Hg-n
+
+
BOUVEAULT, BUZZ.SOC.chim., [4], 3, 119 (1908). CONANT, WEBB,AND MENDIUM, J . Am. Chem. SOC.,61, 1250 (1929). 3 ADKINS,FOLKERS, AND KINSEY,i b i d . , 63, 2714 (1931). WESTON,AND ADKINS,ibid., 60, 1930 (1928). 6 A ~ ~KOMMES, ~ ~ s STRUSS, , AND DAZLER,i b i d . , 66, 2292 (1933). 2 12 1 2
USE OF CATALYSTS IN DEHYDROGENATIONS
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The various types of equipment previously described for these dehydrogenations are either unnecessarily complicated or possess limited possibilities. The formation of the catalyst into pellets is also extremely laborious and time-consuming. For these reasons it seemed advisable to modify and improve, if possible, the type of equipment, and to find a suitable support for the catalyst that would eliminate the operation of forming pellets from the catalyst. I t was also hoped that the yields might be increased. EXPERIMENTAL
The best results in the preparation of this catalyst have been achieved by precipitating and decomposing with heat the catalyst in the presence of finely divided porous material that might serve as a carrier for the catalyst. The following method has been found to be most satisfactory, after experimenting with numerous possibilities. Two solutions were prepared as follows. ( A ) Three hundred milliliters of a solution containing 87 g. of cupric nitrate trihydrate and 10.4 g. of barium nitrate. The barium nitrate was first dissolved in the least amount of water possible a t a temperature near the boiling point of the water. The cupric nitrate trihydrate was then added, and the solution was diluted to 300 ml. Solution ( B ) was prepared from 300 ml. of a solution containing 50.4 g. of ammonium dichromate and 75 ml. of a twenty-eight per cent. solution of ammonium hydroxide. Solution ( A ) was heated to 80°, and 177 g. of the carrier was added. Thus far three of these inert carriers have been used, namely acid-washed Italian pumice of mesh 20; Activated Alumina, Grade A, 8 to 14 mesh size, supplied by the Aluminum Ore Company, of East St. Louis, Ill.; and Johns-Manville Celite, Grade C-12, 212 supplied by the Johns-Manville Co., of Manville, IY. J. This solution ( A ) was then digested for several hours on a steam bath in the presence of the carrier and with frequent stirring. Water was added to compensate for evaporation. While solution ( A ) was still a t a temperature of approximately 80’ solution ( B ) was slowly added with thorough stirring. Solution ( B ) a t no time was heated above room temperature. The precipitate formed and the carrier were then separated by suction filtration, and dried with frequent stirring over a period of 24 hours in an oven a t a temperature of 70-80”. The treatment from this point on was similar to that of Connor, Folkers, and Adkinss except that the product was thoroughly stirred in the moist condition each time to obtain a uniform distribution of the catalyst over the carrier, and also in that the final decomposition was carried out in five portions with very slow, cautious heating and continual stirring. Lazier and Vaughen? have found that the final heat treatment materially affects the activity of the catalyst. The material was then leached with 600 ml. of ten per cent. acetic acid and washed with six 600-ml. portions of water. The catalyst, after drying a t 125”, was sifted on a twenty-mesh sieve before use to remove the fine material. The material that did not pass through the sieve was used for the dehydrogenation of the normal butanol. The yields of catalyst using this method averaged 220 g. The equipment used in these dehydrogenations was similar to that described by Conant*. The tube of the dehydrogenator was a 15-mm. Pyrex tube with four ~
~~
CONNOR,FOLKERS, AND ADKINS, i b i d . , 64, 1138 (1932). 7 LAZIERAND VAUGHEN, ibid., 64, 3080 (1932). 8 CONANT, “The Chemistry of Organic Compounds,’’ The Macmillan Co., New York City, 1933, p. 106.
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RALPH E. DUNBAR
indentations near the bottom to support the catalyst. A side-arm was sealed to the upper end. The capacity of the tube for catalyst was approximately 50 ml. The dehydrogenator was wrapped with one layer of asbestos paper, then with 30 feet of B. and S. gauge No. 22 chromel wire (22 ohms), and finally with six layers of asbestos paper. The ends of the chromel wire were attached to binding posts, firmly imbedded in the asbestos paper. The whole was held in place by wrapping with electrician's tape. For the final separation of the products from each determination an eight-inch Widmer column was used. Representative determinations for the three carriers previously suggested are tabulated in Table I. All values included are the average of several determinations. One hundred grams of n-butanol was used in each determination. The temperature of the catalyst a t all times was maintained a t 330" to 350". The values for butylene
PRODUCTS
TABLE I RECOVERED BY THE DEHYDROGENATION O F 100 G. n-BUTANOL PRODUCTS
PUMICE
ALUMINA
CELITPl
n-Butraldehyde (b.p. 72.577").. . . . . . . . . . . . . n-Butanol (b.p. 113-117"). . . . . . . . . . . . . . . . . . . n-Butyl butrate (b.p. 160-163'). . . . . . . . . . . . . Condensation products (above 180") . . . . . . . . Gases collected.. . . . . . . . . . . . . . . . . . . . . . . . . . . . Water, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Butylene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54.6 g. 14.3 g. 10.5 g. 1.8 g. 26.1 1. 2 . 7 g. 3 . 2 1. 8.0 g.
31.5 g. 19.9 g. 17.1 g. 6 . 4 g. 18.0 1. 4 . 8 g. 5 . 8 1. 14.6 g.
56.7 g. 30.0 g. 1.0 g. 1 . 5 g. 17.9 1. 0 . 7 g. 0 . 9 1. 2 . 2 g.
Hydrogen, by difference.. . . . . . . . . . . . . . . . . . . Theoretical hydrogen, ......................
22.9 1. 17.0 1. 1.6 g.
12.2 1. 9 . 8 1. 0 . 9 g.
17.0 1. 17.6 1. 1.6 g.
Total products recovered. . . . . . . . . . . . . . . . . . . 93.5 g. Mechanical loss, . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . 5 g.
95.2 g. 4 . 8 g.
93.7 g. 6 . 3 g.
are derived theoretically from the amount of water recovered, although they agree closely with values obtained by the analysis of the escaping gas, from representative runs. All values tabulated in Table I represent actual amounts of material obtained directly or by fractionation from the reaction mixture. n-Butanol was selected for a study of the effectiveness of this equipment and catalyst, largely because of its tendency to give consistent yields of aldehyde and a minimum yield of unsaturated hydrocarbon and ester. The yields of butyraldehyde reported do not necessarily represent maximum yields possible but merely averages under normal operating conditions. High percentages of n-butyl butrate and other condensation products are of course undesirable, and the Celite is definitely superior in this respect. The rates and amounts of gases collected, which is normally and predominately hydrogen, may be used as a measure of the effectiveness of the catalyst while the equipment is in actual operation. The greater the amount of water, naturally, the greater the amount of butylene, since both result from the dehydration of the butanol. The
USE OF CATALYSTS IN DEHYDROGENATIONS
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dehydration of any aldol formed would also produce a proportionate amount of water. When all facts and products are considered i t is quite obvious t h a t the Celite catalyst is definitely the superior catalyst. The 56.7 g. of aldehyde collected does not necessarily represent the maximum yield possible, because of the large amount of unreacted butanol yet available, and the small amounts of the condensation products produced. It has also been found that the ester produced can be easily saponified by the use of solid potassium hydroxide at the conclusion of each run, and thus noticeably increase the amount of the aldehyde produced. S o final information is yet available as to the possible life of these catalysts. Runs with each varying from 3 to 15 hours continuous use show little if any deterioration either in terms of noticeable reduction or decreased activity. SUMMARY
Copper-chromium-oxidecatalysts can be conveniently precipitated upon inactive material as an adequate support where this catalyst is used in the dehydrogenation of n-butanol, and other similar alcohols. The supporting materials studied can be arranged in the increasing order of effectiveness as alumina, pumice, and celite. The catalyst retains its activity well over prolonged periods. A satisfactory arrangement of equipment for such dehydrogenations has been described. Temperatures of 330" to 350" appear to be superior to lower teniperatures, previously used by other investigators, with this catalyst and equipment for the dehydrogenation of n-butanol. An efficient fractionating column for the separation of the aldehyde and alcohol during the'dehydrogenation is extremely desirable for the maximum yields of aldehyde.
