Patent GB-345649-A (GB)
Title: Improvements in or relating to catalytic processes
IPC: B01J37/34
Filed: 1929-09-18
Abstract: In the manufacture of chemical compounds by methods involving the use of metal oxides or hydroxides, e.g. those of zinc, chromium and cobalt, as catalysts, the oxides or hydroxides employed are prepared by the electrolysis of solutions of the corresponding metal salts. The metallic oxides or hydroxides may thus be prepared free from alkali metal compounds or other impurities; by effecting the electrolysis at low temperatures, e.g. below 30 DEG  C. the products may be obtained in a highly colloidal state.  Accurately known proportions of alkali metal compounds may be added to the pure oxides when necessary.  The invention is applicable to catalytic reactions involving oxidation, reduction, hydrogenation and dehydration and is particularly applicable to the synthesis of methyl alcohol from carbon monoxide and hydrogen using as catalyst zinc oxide or a mixture of zinc and chromium oxides.  The voltage employed in the electrolytic preparation of the oxides should be greater than is necessary for the deposition of metal, 20 volts being the practicable minimum.  Nitrates or formates may be employed as the metal salts to be electrolyzed.  Any nitrate or other salt remaining as impurity in the precipitate may be removed, e.g. by electrolysis.  In an example a solution of zinc and chromium nitrates containing 3 to 4 atoms of zinc to one atom of chromium is passed into the cathode compartment of a cell at the bottom and the overflowing liquid containing colloidal zinc and chromium oxides in suspension is led to a settling tank, the supernatant liquid being passed through a cooling coil, regenerated and returned to the cell at 15-20 DEG  C.  A zinc cathode and a magnetite anode enclosed in a diaphragm in the form of a flat bag of filter cloth are employed.  Dilute nitric acid is continuously withdrawn from the anode compartment.  Using a voltage of 30 with electrodes 2 cms. apart the current density is about 2 amps per sq. dcm.  A number of cells for working in parallel may be built up of plates of insulating material separated by U-shaped members of similar material each provided at the top with an overflow spout or pipe and at the bottom with a tube for connection to the anode space. The salt solution is admitted to the bottom of the anode chamber by a long tube.  The electrodes are formed with lugs which rest on the upper ends of the U-shaped members.  In a modification the cathode is enclosed by a diaphragm impermeable to metallic ions the cathode space being filled with a solution supplying hydroxyl ions to which the diaphragm is permeable.  The diaphragm may be of fabric on which finely divided material, conveniently the oxide to be precipitated, is deposited, e.g. by electrophoresis.  In an example, a 3-compartment cell comprising two diaphragms of closely woven linen fabric is filled with water.  In the middle compartment a screen of wide-mesh material is adjusted at a short distance from the cathodic diaphragm.  Some sodium carbonate, e.g. 0,1 per cent is added to the cathodic liquid, and a suspension of colloidal zinc hydroxide and chromic hydroxide to the middle compartment where it is kept in suspension by bubbling air through or by an agitator.  Direct current of 120 volts is applied.  When a coat of sufficient density has been applied a mixture of zinc and chromium nitrates is admitted to the middle compartment at such a rate that a current density at the cathode of 2 amps per sq. dcm. is maintained.  A precipitate of the hydroxides is formed on the cathode diaphragm and eventually grows through the screen from which it may be removed by scrapers.  The mixture of hydroxides prepared in accordance with either example is washed, thickened by filtering or pressing, shaped into pellets or beads, dried, heated in a reducing atmosphere and used as a catalyst in the synthesis of methanol.ALSO:In the synthesis of methyl alcohol from carbon monoxide and hydrogen, the metal oxides or hydroxides employed as catalysts, are prepared by the electrolysis of solutions of the corresponding metal salts.  The metallic oxides or hydroxides may thus be prepared free from alkali metal compounds or other impurities; by effecting the electrolysis at low temperatures e.g. below 30 DEG  C. the products may be obtained in a highly colloidal state. Accurately known proportions of alkali metal compounds may be added to the pure oxides when necessary.  The voltage employed in the electrolytic preparation of the oxides should be greater than is necessary for the deposition of metal, 20 volts being the practicable minimum.  Nitrates or formates may be employed as the metal salts to be electrolyzed.  Any nitrate or other salt remaining as impurity in the precipitate may be removed e.g. by electrolysis.  In an example a solution of zinc and chromium nitrates containing 3 to 4 atoms of zinc to one atom of chromium is passed into the cathode compartment of a cell at the bottom and the overflowing liquid containing colloidal zinc and chromium oxides in suspension is led to a settling tank the supernatant liquid being passed through a cooling coil, regenerated and returned to the cell at 15-20 DEG  C.  A zinc cathode and a magnetite anode enclosed in a diaphragm in the form of a flat bag of filter cloth are employed.  Dilute nitric acid is continuously withdrawn from the anode compartment.  Using a voltage of 30 with electrodes 2 cms. apart the current density is about 2 amps. per sq. dcm.  A number of cells for working in parallel may be built up of plates of insulating material separated by U-shaped members of similar material each provided at the top with an overflow spout or pipe and at the bottom with a tube for connection to the anode space. The salt solution is admitted to the bottom of the anode chamber by a long tube.  The electrodes are formed with lugs which rest on the upper ends of the U-shaped members.  In a modification the cathode is enclosed by a diaphragm impermeable to metallic ions the cathode space being filled with a solution supplying hydroxyl ions to which the diaphragm is permeable.  The diaphragm may be of fabric on which finely divided material, conveniently the oxide to be precipitated, is deposited e.g. by electrophoresis.  In an example, a 3-compartment cell comprising two diaphragms of closely woven linen fabric is filled with water. In the middle compartment a screen of wide-mesh material is adjusted at a short distance from the cathodic diaphragm. Some sodium carbonate, e.g. 0,1 per cent is added to the cathodic liquid, and a suspension of colloidal zinc hydroxide and chromic hydroxide to the middle compartment where it is kept in suspension by bubbling air through or by an agitator.  Direct current of 120 volts is applied.  When a coat of sufficient density has been applied a mixture of zinc and chromium nitrates is admitted to the middle compartment at such a rate that a current density at the cathode of 2 amps. per sq. dem. is maintained.  A precipitate of the hydroxides is formed on the cathode diaphragm and eventually grows through the screen from which it may be removed by scrapers. The mixture of hydroxides prepared in accordance with either example is washed, thickened by filtering or pressing, shaped into pellets or beads, dried, and heated in a reducing atmosphere.