| 摘要 |
Spheroidal alumina particles are prepared by mixing an alumina sol with a weak base having a strong buffering action at pH 4-10 and an increased rate of hydrolysis at an elevated temperature without evolution of gas, thereafter passing the mixture into a water-immiscible suspending medium, e.g. Nujol (Registered Trade Mark), or a mixture thereof with o-dichlorbenzene, maintained at 50-105 DEG C, and retaining the sol in the suspending medium until gelation occurs. The sol may be produced (i) by reacting a solution of aluminium chloride or nitrate with metallic aluminium in the mol ratio 1 : 3-7 at 80 DEG C to the boiling point, if desired in the presence of a metal lower than aluminium in the Electromotive Series or with the passage of oxygen, (ii) by electrolyzing an aluminium salt in a cell having a porous partition, the sol being obtained from the cathode compartment, or (iii) by treating an aluminium salt solution with an anion exchange material to remove acid. The sol suitably contains 15-35 per cent Al2O3. Suitable bases are hexamethylene tetramine in 15-40 per cent solution, the reaction products of ammonia and other aldehydes, e.g. acetaldehyde, propionaldehyde, and a mixture of ammonium acetate and ammonia of pH below 8.5. The concentrations, proportions &c. of the solutions used are interdependent. After gelation, the spheres are aged at elevated temperatures in hexamethylene tetramine solution, or firstly in an oil, which is preferably the same as the suspending medium, and then in ammonia solution, or merely in the suspending medium itself. By varying the conditions, the spheres obtained may have a density ranging from below 0.5 to above 0.7. The aged spheres are then washed with water or a dilute solution of ammonia and/or ammonium nitrate, dried at 93-315 DEG C in a humid atmosphere, and calcined at 425-760 DEG C. The material is suitable for use as an absorbing or refining agent, or a contact agent in dehydration, dehydrohalogenation, desulphurization &c. reactions. It may be composited with 5-40 per cent by weight of chromium, molybdenum, vanadium and other oxides of elements of the left-hand column of Groups 4-6 of the Periodic Table for use as a catalyst in reforming, hydrogenation, dehydrogenation and dehydrocyclization of hydrocarbons &c. Catalysts containing .01 per cent platinum and .1-8 per cent halogen, especially fluorine, may be prepared by incorporating these ingredients in the spheres prior to or after drying and calcining. Alternatively, a hydrogen or ammonium halide, or a free halogen may be added to the alumina sol. The platinum may be added as a solution of chloroplatinic acid, ammonium platinochloride, trimethyl benzyl ammonium platinochloride, tetramino platinochloride, ammonium platinonitrate, dinitrodiamino platinum, or as a colloidal suspension of platinum sulphide. After the addition, the catalyst is calcined at 315-540 DEG C in the presence of air or hydrogen. The platinum-containing catalyst is suitable for reforming and controlled cracking of saturated gasoline, the treatment of kerosene, gas oil &c. to produce a highly aromatic product, the destructive hydrogenation or hydrocracking of oils heavier than gasoline, the non-destructive hydrogenation of mono-and diolefines and of unsaturated cyclic hydrocarbons, ketones, acids &c., the oxidation of olefines to form the corresponding oxides and of alcohols, ketones &c. Temperature and pressure conditions suitable for these operations are indicated. The catalysts may be regenerated by treatment with air or other oxygen - containing gas at a temperature not exceeding 540 DEG C. |
