Chapter 30
Other Opportunities for Catalysts in Environmental Problems: An Overview John N . Armor Air Products & Chemicals, Inc., 7201 Hamiliton Boulevard, Allentown, PA 18195
The actual number of applications of catalysis to solve environmental problems is quite large (1). A number of topics were only touched upon in this symposium, and those manuscripts are grouped together within this section of the book. Topics which were not discussed at all within this Symposium included: catalysts for the preparation of HFCs as replacements for CFCs, removal of ozone emissions; removal of nitrous oxide; destruction of toxic gases such as nerve gas; alternative catalytic technology to displace the use of chlorine-based intermediates in chemical synthesis and processing; and waste minimization. With the implementation of the Clean Air Act Amendments of 1990, there are intense efforts by companies that produce or consume chemicals to reduce the amount of chemical waste they generate. Where even small amounts of multiple by-products are produced, at a multi-million pound per year scale, these by-products can become sizable in volume (see Table I). Disposal costs or imposed reduction of waste by local regulations will force suppliers and users to minimize the generation of waste. Alternatively, one can try to avoid undesirable by-products by developing new process routes or finding ways to convert these "wastes" into marketable products. For example a process which uses formaldehyde, a known carcinogen, is now much less desirable than one which uses alternative Ci feedstocks (e.g., methanol, CO/H2, etc.). There are a number of processes for removing SOx from exhaust streams. The problem is there is still no universally acceptable solution. Figure 1 shows the atmospheric sulfur cycle showing the number of ways sulfur enters the atmosphere (3). In the atmosphere SOx contributes to atmospheric pollution and smog. It is a major contributor to acid rainfall. Current commercial approaches to remove SOx from stack gas exhausts produce large quantities of sulfur by-products which need to be sold or buried. Large amounts of elemental sulfur are produced by petroleum refineries in the process of desulfurization of petroleum feedstocks. In the United States, the preference for burial of waste has come under increasing economic pressure as the availability of
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Other Opportunities: An Overview
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ENVIRONMENTAL CATALYSIS
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Table I. Production o f by-products Product
K g of By-product per K g of products
Product (tons)
O i l Refinery Bulk Chemicals Pharmaceuticals Fine Chemicals
-0.1
