The removal of organic sulphur from town's gas

Abstract

This work consists of a study of the removal of organic sulphur compounds to synthesis purity limits, from vertical retort coal gases and similar gases. A survey of the existing processes was made and catalytic hydrogenation of the organic sulphur was chosen as a feasible process. Catalysts available commercially for this purpose were reviewed and Peter Spence 3.5/10 Nimox was chosen for further investigations. Peter Spence Luxmasse was used as the absorbent. A suitable six-stage apparatus was constructed to study the conversion of organic sulphur. Synthetic mixtures containing carbon monoxide, hydrogen and individual organic sulphur compounds were purified by giving single and multiple stage treatment. Conversion of carbonyl sulphide, by using single-stage, was 94 - 95% at 350 °C and atmospheric pressure. Thiophene conversion was 50% at 350 °c and atmospheric pressure, while at 350 psia and 400 °C, conversion rose to 97% Conversion of carbon disulphide was complete at less than 350 °C and conversion of Butyl mercaptan was 99% at this temperature. Purification of coal gas containing 15 - 20% carbon monoxide was carried out at atmospheric and higher pressure, by providing single and multiple stage treatment. While removal of total organic sulphur depended upon the extent of thiophene present, it was found that conversion of organic sulphur was about 97% on a single conversion stage, at 350 °C. Conversion rate fell gradually with the passage of time. With six-stage treatment, an outlet gas containing 0.2 p.p.m. of organic sulphur was obtained. Higher pressure and 5% of water vapour were found beneficial. High space velocity could be used when the catalyst was comparatively fresh, but with the passage of time lower space velocity was needed for maintaining the same rate of conversion. The Luxmasse at a higher temperature also helped the conversion of organic sulphur. Blockage of the Luxmasse bed above 350 °C was noted with gas free from sulphur, but at a lower temperature of 300 °C this difficulty was obviated. Results of conversion by using another type of Nimox (4.5/12); and I.C.I. Comox and zinc oxide were obtained. It was found that zinc oxide alone would remove 90% of total organic sulphur both by conversion and simultaneous absorption at 400 °C. A preliminary design for a small scale package unit has been worked out.