GB565371A - Improvements in or relating to photocatalytic processes and apparatus therefor - Google Patents

Abstract

<PICT:0565371/IV/1> <PICT:0565371/IV/2> Photocatalytic reactions are effected by submitting the reactants to the action of electric discharges passing through a multiplicity of transparent discharge vessels, packed closely in the space occupied by the said reactants in the reaction chamber, under conditions such as to produce luminescence. In continuous operation, the reactants are passed through the chamber between the discharge vessels which fill substantially the entire cross-section of the reactant stream. The apparatus may comprise a receptacle made of a dielectric having electrodes at the ends and containing a plurality of small discharge tubes containing one or more gases or vapours at reduced pressure, generally below 20 mm. mercury. The application of a high frequency and/or high voltage fluctuating or alternating current induces a discharge glow. Voltages from about 50,000 down to 100 or less may be used, the product of frequency and voltage preferably being about 20,000-100,000,000 or more. Radiations of the desired wavelength are produced by choice of the gas or vapour in the tubes. This may be the same as one of the reactants, for example, chlorine in chlorination reactions. Different gases may be used to catalyse different reactions in different parts of the reaction vessel. The small discharge tubes are conveniently of 1/2 -1\ba1/2 " diameter, of spherical or elongated shape, and may have focal discharge areas comprising metal nodes or spots on the inner walls, preferably at opposite points, metal wires or rods passing through the walls, or external metal caps or coatings. They may be connected by wires, metal foils or the like. The reaction vessel has metal ends 3, 4 fitted with gas and liquid inlets and outlets and connected to a source of high tension alternating current, and is filled with glass vessels 10 containing the desired gas which gives the discharge glow. Reactants are admitted and products removed in batch or continuous operation. In a modification, Fig. 2 (not shown) adapted for continuous operation the vessel may be of plastic material with metal foil on the ends to form electrodes. A liquid reactant flows downwardly around the discharge tubes and a gaseous reactant, admitted part-way up the vessel, passes upwardly in counter-current. A selective solvent for the product may also be admitted at the top. The discharge tubes are of material selected according to the wavelength of the light transmitted. Glass, quartz, fluorte, silica and "Lucite" are materials specified. The tubes may be of coloured glass or lacquered to filter out undesired radiations, and may be lined with fluorescent materials which emit visible light on activation by ultra-violet light or X-rays. Reactions to which the invention is applicable include halogenations, cracking, hydrogenation and dehydrogenation of hydrocarbons, oil hardening and reactions with sulphur dioxide and chlorine or with sulphuryl chloride of organic compounds, especially aliphatic compounds, e.g. hydrocarbons, alcohols, acids and their chlorinated or other derivatives, of from 8-26, preferably 12-20, carbon atoms. In examples: (1) the apparatus of Fig. 1 contains discharge tubes filled with chlorine at 5-10 mm. It is filled with toluene, and current at 20,000 volts and 1,000 cycles applied. Air is removed and chlorine passed in to form benzyl, benzal and benzenyl chlorides; (2) pentane and chlorine are continuously passed into the apparatus at about 40 DEG C. to form monochlorpentanes; (3) the apparatus of Fig. 2 is used to react a paraffinic mineral oil with a mixture by volume of 3 parts of sulphur dioxide being added as a solvent for the sulphonyl chlorides produced. The product can be hydrolysed with caustic soda at about 90 DEG C., extracted to remove unsulphonated material and the solid sulphonate recovered. The sulphonation may also be effected in liquid phase, and the discharge tubes may be filled with gases other than chlorine, or part may contain chlorine and others sulphur dioxide or argon. The Specification as open to inspection under Sect. 91 comprises also the use of the reaction vessel itself as a discharge tube, the small tubes being dispensed with. The glass vessel 21, Fig. 3 (cancelled), has point electrodes 29, cooling jacket 22 and connection 25 to a vacuum pump. In a further example (4), quinoline and part of the required bromine are drawn into this apparatus which is cooled to - 25 DEG C., giving a pressure below 10 mm. More bromine is admitted as necessary to produce bromquinoline hydrobromide. In place of the multiplicity of discharge tubes, a single vessel of an undulate shape may be used over which the reactants flow in a film. This subject-matter does not appear in the Specification as accepted.