GB485178A - Improvements relating to the production of catalysts, more particularly for the dehydrogenation of hydrocarbons - Google Patents

Abstract

Active catalysts of high mechanical strength, are obtained by mixing with an effective catalytic substance, which is preferably in a minor proportion, at least two other substances, one as a major and the other as a minor ingredient, capable of reacting with each other to the exclusion of the effective catalyst to form a compound or a solid solution having a melting point substantially higher than the reaction temperature, and then heating the mixture at a temperature above 1600 DEG F. and for a time sufficient to effect an increase in mechanical strength but insufficient to cause substantial melting, the amount of compound or solid solution formed being less than 10 per cent of the total catalyst. The catalysts are suitable for reactions occurring above 900 DEG F., e.g. production of hydrogen from steam and hydrocarbons; cracking of hydrocarbons to produce olefines, diolefines and acetylenes; destructive hydrogenation reactions; polymerization of unsaturated gaseous hydrocarbons to aromatic hydrocarbons; dehydrogenation of hydrocarbons and the synthesis of methanol. The reacting substances may be acidic and basic in nature, e.g. alumina, oxides and acids of Group VI, silica, oxides of bismuth, tin, lead, antimony, cobalt, arsenic and vanadium, oxides and acids of phosphorus and boron as acidic substances, and oxides and other compounds of the alkalis and alkaline-earth as basic substances, or substances which react to form double salts, e.g. metal oxides with fluorides or silicates, preferably alkali. The effective catalyst may be nickel, iron or chromium oxide and one of the reacting substances is preferably a difficulty reducible oxide. The mixture may be moulded into shapes before the heating step, and may be subjected to reducing conditions afterwards if desired. The catalysts are preferable packed in upright reaction chambers, particularly for the dehydrogenation of hydrocarbons. The final heating step is carried out at a temperature of about 2000 DEG F. for a period of 10-20 hours. Where the catalyst itself is capable of reacting with the major added ingredient, the other added ingredient must possess a greater affinity for the major ingredient than the catalyst. According to examples, (1) a mixture of 4 per cent chromic oxide and 96 per cent alumina obtained by saturating alumina with chromium nitrate and heating at 350 DEG F., is mixed with 1 per cent of graphite and 2 per cent of boric acid and compressed into pills. On heating to 1700 DEG F., the crushing strength increases from 240 lb. sq. in. to 1300 lb. sq. in. The catalyst is used for the dehydrogenation of butane, mainly into butylenes. The boric acid may be replaced by 3 per cent of phosphoric acid or 1 per cent of sodium fluoride; (2) a mixture of 52 gms. chromic oxide and 150 gms. of magnesia, with 1 per cent of graphite and 2 per cent of boric acid was compressed into tablets and heated at 1700 DEG F., giving a strength of 2670 lb. sq. in. Heating to 2000 DEG F. gave a strength of 5400 lb. sq. in. The catalyst was used for the dehydrogenation of hydrocarbons. Loss of activity by oxidation may be avoided by heating in an inert or reducing atmosphere, or a subsequent reduction step; (3) 1455 pts. of nickel nitrate hydrate were dissolved in 500 pts. water, 22 pts. boric acid and 750 pts. magnesia were added, and the paste dried and heated to 850-900 DEG F. The powder was screened and compressed into tablets. These may be strengthened by crushing to about 10 mesh and reforming into tablets. They are then heated to 1700-2000 DEG F. for about 36 hours, and the nickel oxide then reduced by hydrogen. The catalyst may be used to obtain hydrogen from methane and steam at 1525 DEG F.; (4) the comparative strengths of catalysts containing nickel and magnesia, without addition and with added boric acid, phosphoric acid and sodium fluoride is shown before heating, after heating and after use in the methane-steam reaction; (5) the strengths of a catalyst of nickel and magnesia containing varying amounts of boric acid, cobalt oxide, sodium fluoride and phosphoric acid are shown; (6) this example illustrates the effect of increasing the temperature and the duration of heating. Specifications 272,555, [Class 1 (i)], and 359,620 are referred to.ALSO:Active catalysts of high mechanical strength, suitable for reactions carried out above 900 DEG F., e.g. cracking of hydrocarbons to produce olefines, diolefines and acetylenes, polymerization of unsaturated hydrocarbons to aromatic hydrocarbons and the synthesis of methanol, are obtained by mixing with an effective catalytic substance, which is preferably in minor proportion, at least two other substances, one as a major and the other as a minor ingredient, capable of reacting with eath other to the exclusion of the effective catalyst to form a compound or a solid solution having a melting point substantially higher than the reaction temperature, and then heating the mixture at a temperature above 1600 DEG F., and for a time sufficient to effect an increase in mechanical strength but insufficient to cause substantial melting, the amount of compound or solid solution formed being less than 10 per cent of the total catalyst. The reacting substances may be acidic and basic in nature, e.g. alumina, oxides and acids of Group VI, silica, oxides of bismuth, tin, lead, antimony, cobalt, arsenic and vanadium; oxides and acids of phosphorus and boron as acidic substances, or substances which react to form double salts, e.g. metal oxides with fluorides or silicates, preferably alkaline. The effective catalyst may be nickel, iron or chromium oxide and one of the reacting substances is preferably a difficulty reducible oxide. The mixture may be moulded into shapes before the heating step, and may be subjected to reducing conditions afterwards if desired. Specifications 272,555, [Class 2 (iii)], and 359,620, [Group III], are referred to.