The combustion of hydrocarbons for the production of thermal energy usually involves the production of undesired "chimney gases." In theory these gases should only contain CO2 + H2O, but in reality they contain important amounts of polluting gases (mainly NO*, SO*, CO). A common strategy for the removal and recovery of the SO2 consists in reacting it with a base [typically Ca(OH)2] to produce a non-toxic substance (CaSO^). However, this salt is not of industrial interest. A more important substance from the industrial standpoint is gypsum, CaS04, that is a useful material for construction purposes.

In Chapter 12 we defined Green Chemistry as the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Because the present experiment involves an environmentally benign chemical synthesis using a waste substance, it falls within the scope of Green Chemistry.

The present desulfurization modeling experiment (called Obendrauf's method) is based on the reaction between SO2 and CaCOs to produce

Ca(HSOa)2, which is then oxidized by dioxygen to the sparingly soluble CaS04. In fact, CaS03 is such a good dioxygen scavenger that it has been under study as a means of preventing acid formation during pyrite oxidation (discussed and exemplified in Experiment 11 on acid mine drainage). (See Hao, 2000). No hazardous wastes are produced.

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