Chapter 24
Volatile Organic Compounds: An Overview
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John N. Armor Air Products & Chemicals, Inc., 7201 Hamilton Boulevard, Allentown, P A 18195
Like automotive catalysts, the area of heterogeneous catalysts for the control of volatile organic compounds [VOC] is an established technology and business. There are several detailed reviews on this topic (1,2) which include opportunities for using catalysts to resolve tougher emission control problems (3,4). The Clean Air Act of 1990 calls for a 90% reduction in the emissions of 189 toxic chemicals (70% of these are VOCs) over the next 8 years. Catalytic VOC destruction at certain concentrations permits oxidation at lower temperatures which saves fuel costs and avoids other emissions problems. Typical catalysts include metal oxides and Pt or Pd supported alumina on a metal mesh, a ceramic honeycomb, or on beads. Key operational parameters are temperature, space velocity, contaminant level and composition, and poisons or inhibitors. In the field, impurities and poisons, especially sulfur and chlorohydrocarbon compounds, can limit optimal performance. Recently developed catalysts are designed to extend the useful life of oxidation catalysts by improving their tolerances to these poisons. Because o f the low contaminant levels (~1000 ppm) and the large volumes o f gas to be heated, it is necessary to use very active catalysts operating at low temperatures . There are a number o f new catalysts being developed as well as several others already commercially available. Catalytic combustion is a way to control V O C s and includes methane combustion and C O oxidation (5). [Thermal combustion is also another popular alternative.] Beyond traditional combustion, areas where catalysts are used to eliminate V O C emissions include: can, paper and fabric coating chemicals; manufacture of organic chemicals (e.g., acrylonitrile, formaldehyde, cumene, caprolactam, maleic anhydride, etc.); plywood manufacture; tire production; asphalt blowing; odor control from fish meal processing; odor control from offset printing; évaporants from waste water plants; volatiles from urine ; oxidation o f formaldehyde emissions; removal of gasoline vapors; and contaminated air within a submarine. One common technique for catalytic incineration employs an afterburner with a catalyst to promote the oxidation o f V O C s to CO2 and H2O. Generally the waste gas is pre-heated to ~ 3 0 0 ° C using natural gas or o i l fuel burners. A mixing chamber
0097-6156/94/0552-0298$08.00/0 © 1994 American Chemical Society In Environmental Catalysis; Armor, John N.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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Volatile Organic Compounds: An Overview
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downstream from the preheater distributes the combustion products from the burner into the waste gas. Following the mixing chamber is a catalyst bed usually consisting of finely divided P t / A h C h on a ceramic or metal structure. A heat exchanger follows to transfer heat from the hot exhaust gas to the cooler, inlet waste gas (4). Jerry Spivey and Sanjay Agarwal of the Research Triangle Institute led the sessions on V O C s . They summarized the papers within there sessions as follows: A total o f 16 papers were presented in this full day session on V O C Control. Increased environmental awareness, coupled with governmental regulations, has resulted in control requirements for V O C emissions from various sources. In addition to conventional catalytic oxidation, other technologies, including photocatalytic oxidation, are being developed as an alternative. The advantage o f photocatalytic oxidation is the very low temperature required for this process. Dave Ollis (North Carolina State University) discussed the prospects and promises of this technology for V O C control. A l i T. Raissi (Florida Solar Energy Center) showed a specific application of photocatalysis: destruction of nitroglycerin vapors. A Gervasini (Universita di Milano) discussed the use of only ozone to lower the reaction temperature for V O C oxidation. The catalytic oxidation of a wide variety o f V O C s , including hydrocarbons, chlorocarbons, chlorofluorocarbons, and nitrogen-containing compounds was presented. These types o f compounds present a challenge since they poison many traditional deep oxidation catalysts. Steve Homeyer (Allied Signal) discussed a new family of commercial catalysts for the destruction of nitrogen-containing compounds. A . R. Amundsen (Engelhard) also discussed the development of a commercial catalyst for chlorocarbon destruction. Martin Abraham (University of Tulsa) also discussed the oxidation of amines using P d and other catalysts. Gary Masonick (Prototech) showed how to regenerate oxidation catalysts. Several interesting applications of V O C control were discussed in this session. Linda Parker (New Zealand Institute for Industrial Research) presented an interesting application o f removing ethylene and C O from fruit cold storage containers. O f the various catalysts investigated for this application, a Ptzeolite was found to be the most active with complete conversion of ethylene below 100°C. C 0 lasers represent another application of oxidation catalysis where there is a need to continuously convert C O to C 0 . Kenneth B r o w n (Old Dominion University) discussed the noble-metal/reducible-oxide catalysts developed by N A S A for this application. Joe Rossin (Geo Centers) discussed the transient response of oxidation catalysts for military applications, where very high conversion and minimal deactivation are essential. Variations of catalytic oxidation system are being developed to improve the overall system performance. Y u r i Matros (Washington University) described the reverse flow process for V O C oxidation. This process offers low energy requirements, making it cost effective for gases with fairly low V O C concentrations. In addition to metal oxides, other materials such as zeolites are also being examined for V O C oxidation. S. Karmakar and S. Chatterjee (University of Akron) described the metal exchanged/impregnated zeolite catalysts for the oxidation o f chlorocarbons and C F C s . Russell Drago (University of Florida) and M a r k Vandersall (Rohm and Haas) showed the applicability of Ambersorb® carbon-based catalysts for chlorocarbon and hydrocarbon oxidation. Eric Lundquest (Rohm and Haas) presented work on related catalysts for the esterification o f industrial chemicals, reducing waste and V O C emissions. 2
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In Environmental Catalysis; Armor, John N.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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Many o f the presentations within this day long session are described further within this section o f the book. Topical areas reflecting future research needs in V O C s include: increased catalyst life; reduced operating costs v i a catalyst improvements [temperature, activity, resistance to poisons, etc.]; and extended catalyst performance. The latter refers to making these catalysts operate under more extreme conditions, such as the catalytic oxidation of trace impurities in aqueous media or the ability o f a catalyst to remove a wider spectrum of volatile organic components.
References 1. 2. 3. 4. 5.
Spivey, J.J. Ind. Eng. Chem. Res. 1987, 26, 2165-2180. Drohan, D. Pollution Engn. September 15, 1992, pp. 30-33. Chiang, P-C; Chang, P; You, J-H. J. Hazardous Matls. 1992, 31, 19-28. Armor, J. N. Appl. Catal. B, 1992, 1, 221-256. Pferfferle,L.D.;Pferfferle, W.C.Catal.Rev. Sci. Eng., 1987, 29, 219-267.
RECEIVED November 8, 1993
In Environmental Catalysis; Armor, John N.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
