GB1122121A - Determining the oxygen demand of combustible materials in aqueous dispersions - Google Patents

Abstract

1,122,121. Electro-chemical analysis. DOW CHEMICAL CO. May 3, 1966 [May 3, 1965], No. 19533/66. Heading G1N. The total oxygen demand of an aqueous dispersion of combustible material is measured by passing a continuous steady stream of an inlet gas containing a known small amount of oxygen through a combustion tube 66, scrubber 74 and oxygen detector 78 and then injecting a known amount of the aqueous dispersion from a syringe 57 into the gas stream upstream of the combustion tube and the drop in detected oxygen due to combustion of the aqueous dispersion is measured. The combustion tube is of fused silica and quartz and contains a porous bed of combustion supporting catalyst 61 (e.g. platinum gauze balls; palladium, rhodium, osmium or ruthenium gauze or particles; or particulate oxides of nickel or cobalt) and a quartz wool plug 60. An electrical resistance heating element (14), Fig. 1 (not shown), heats the tube to between 600‹C. and 1200‹C. The scrubber 74 contains 25 weight per cent aqueous KOH 75 to remove CO 2 from the combustion gases before they pass to the oxygen detecting electrolytic cell 78. The cell comprises a lead (Pb) foil electrode 81 wrapped round an inert plastics core 80 and covered by a water swellable ethyl cellulose film. membrane 82 round which is a silver wire spiral electrode 84. The cell is a quarter full of 25%, KOH. Intermittent known small amounts of the aqueous dispersion are taken from a continuous stream 58-59 and are injected through a stainless steel needle 57 under pressure from a branch 44 of the gas supply. Although it is unnecessary for the gas flow rate to be known, a flowmeter 47 is provided. Suitable inert gases are nitrogen, helium and argon. Instead of a graphic recorder, an electronic integrator may be used. The apparatus may be calibrated against samples of known oxygen demand.