Catalytic ‘reduction’ of organic wastes

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smell of hydrogen sulphide left behind by automobiles on roads and parking places can be a significant problem. Union Carbide has developed (see a report by Ward Wo~hy in Chemical and Engineering News, May 1988, p.30) a new family of synthetic molecular sieves that have strong affinity for “odor molecules” and which are not deactivated by moisture. The company is marketing these molecular sieves under the names of Abscents and Smellrite for deodorising applications. These compounds offer a fresh approach to odour control by actually eliminating odours at their source instead of merely masking them with another scent. The main problem with earlier molecular sieves have been that they were very effective in adsorbing water, Thus they were not effective deodorisers in humid air because the adsorptive sites were quickly saturated with water molecules. According to Union Carbide, the new molecular sieves seem to have unique selectivity for odour compounds in competition to water. Details of the composition are proprietary. However, what is known is that they are ~~stalline inorganic powders, non oxidisable, chemically inert and thermally stable up to 800°C. These molecular sieves are effective with many different types of compounds, including organic acids, aldehydes, ketones, mercaptans, ammonia, amines, etc. The company says that these molecular sieves do not seem to have any catalytic activity in these applications. There is catch: these molecular sieves wilt adsorb the good odours as well as the bad. K. SESHAN Catalytic ‘Reduction’ of Organic Wastes

rently a great deal of interest in the treat= ment and recycling of waste organic streams. The waste disposal industry is constantly at ioggerheads with the environmentalists on this issue, pa~i~ularly with regard to waste incineration of organic residues containing chlorinated aromatic compounds. In this context, there is welcome news (see The Chemical Engineer, Nov, 1989, p. 30) from Universal Oil Products, U.S.A., who have announced the introduction of a new technology which reduces the waste catalytically rather than oxidising it thermally, The process is promoted as an alternative to incineration and similar thermal oxidative process. Based on hydroprocessing, the technique separates and/or converts the heter~~om~~ontaminants such as halogens, sulphur, nitrogen, or oxygen from the waste organic matrix. As the technology uses a hydrogen reducing environment, it does not generate oxygenated by-products such as dioxins etc. The heart of the technology is catalytic reduction. Firstly the reaction inhibitors such as metals and solids are removed. The liquid waste is then mixed with hydrogen at raised temperatures and pressures and passed over a selective reduction catalyst, when the heteroatom-contaminants are reduced and separaied. UOP says that, depending on the quality, the hydrocarbon produced by this process can be recycled, used as a feedstock elsewhere, or, in the worst case, used as a fuel, The process offers considerable energy saving as compared even to incineration with heat recovery. No details of the catalyst systems used are given (The Chem. Engineer, Nov 1989). K. SESHAN

As someone has aptly said, “the future of chemist is in garbage”. There is cur-

applied catalysis -

Volume 58 No. 2 -4 5 December 1989