GB814073A - Catalytic oxidation of methanol and catalyst and catalyst precursor therefor - Google Patents

Abstract

An inactive catalyst precursor suitable for conversion to an active catalyst for the oxidation of methanol to formaldehyde (see Group IV (b)) is prepared by mixing an aqueous solution of an iron salt with an aqueous solution of a molybdate and partially drying the precipitate; the mixture of solutions should have a pH of 0.5-3.5 and the precipitate a molar ratio of MoO3 to Fe2O3 of 3.3:1 to 11.2:1. The catalyst precursor has good mechanical strength and is stable during storage and transport. Suitable iron salts are ferric chloride, bromide, acetate, and sulphate and ferrous chloride and acetate; suitable molybdates are ammonium, potassium, and sodium molybdates, and molybdates of organic amines. Trace amounts of Al, Ca, Cr, Co, Mg, Ni and Si in the catalyst precursor are not harmful. The molybdate solution should preferably be adjusted to a pH of 2.25 to 5.0 by addition of hydrochloric or hydrobromic acid. After washing and filtering the precipitate is dried, preferably in stages at increasing temperatures up to 300 DEG F. to a water content of 2-30 per cent. In examples: (1) a solution of sodium molybdate, made by dissolving molybdenum trioxide in sodium hydroxide solution, is treated with concentrated hydrochloric acid to a pH of 5 and then added to ferric chloride solution of pH 1.7; the precipitate is washed, filtered and dried; (2) a solution of ammonium molybdate is adjusted to pH 2.25 with hydrochloric acid and is added to ferric chloride solution, the precipitate being treated as in (1). In each example the product is loaded into the tubes of a converter and an active catalyst formed by heating to a temperature of 500 DEG F. in a stream of air, which may be dehydrated, until all water and volatile substances are removed. U.S.A. Specification 1,913,405 is referred to.ALSO:Formaldehyde is prepared by passing methanol and an oxidizing gas through a catalyst formed by heating at 300-495 DEG F. in the presence of air a catalyst precursor which has been produced by mixing an aqueous solution of an iron salt with an aqueous solution of a molybdate and partially drying the precipitate; the mixture of solutions should have a pH of 0.5-3.5 and the precipitate a molar ratio of MoO3 to Fe2O3 of 3.3 : 1 to 11.2 : 1 (see Group III). A mixture of 9 per cent methanol and 91 per cent air may be passed at 480 DEG F. through parallel tubes containing the catalyst. A suitable arrangement of apparatus is shown diagrammatically. U.S.A. Specification 1,913,405 is referred to.