Regenerative Catalytic Oxidation Catalysts

Case 3 Regenerative Catalytic Oxidation Catalysts 7.4.1. Introduction 

Pascaline Tran, James M. Chen and Robert J. Farrauto 

The other approach to reduce the energy cost is to lower the oxidation temperature. This is normally achieved by employing a catalyst to accelerate the oxidation reaction. Instead of 800°C for thermal oxidation, commercial catalytic systems typically operate at temperatures of 300 to 550°C to achieve the required VOC destruction efficiency. To further reduce energy requirements most catalytic abatement systems include a recuperative heat exchanger that enables recovery of up to 65% of the thermal energy from the exhaust gases. 

RCO combines both energy saving approaches to achieve the best overall energy efficiency for an oxidation abatement system. RCO systems can provide the high heat recovery efficiency of an RTO system and with special catalyst-coated media installed on top of the heat sink material RCO systems can also provide VOC destruction at lower temperatures than those associated with catalytic oxidation to further reduce energy requirements. 

The RCO operating temperature relies on the stability and activity of the RCO catalyst to oxidize VOC s in the process streams. With the Clean Air Act Amendments of 1990, many industries are required to reduce VOC emissions. Since the exhaust 

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The reverse flow reactor (RFR) concept was originally patented by Cottrell in 1938 [64] in the United States and further developed and appHed to different purposes by several researchers, for example, Matros and coworkers [65]. This technology has found its application also in the field of catalytic oxidation [66]. The incinerator containing two sets of regenerative-type heat exchangers and at least two catalyst honeycombs uses flow reversal to recover the heat produced in exothermal oxidation reactions [67]. A regenerative heat exchanger can typically achieve a heat... 

Typical operating conditions and performance for the REGENOX regenerative heat exchange catalytic oxidation process as provided by Haldor Topspe (1990) are conversion efEciency >99%, heat exchange efficiency 95%, operating temperature in hottest zone 300°C (572°F). The system uses a metal oxide-based catalyst that is capable of operating at temperatures up to 600 C (1,112°F). 

The oxygen cathode—for which platinum catalyst due to its outstanding structural and catalytic capability is the rule—is not used as an oxygen evolution anode in the electrolyzer operation mode because oxidation of Pt and fast catalyst deterioration would be the consequence. Therefore an oxygen cathode based on a platinum catalyst must operate as a -evolving cathode in the regenerative mode. 

The mechanism and kinetics of the WGS reaction over Fe-Cr catalysts have been the subject of numerous publications. Despite intense investigations, still there is no full agreement as to the reaction mechanism. The two competing approaches are a redox (regenerative) mechanism first proposed by Kulkova and Temkin as early as 1949 which presumes reduction of an oxide center (O) by a CO molecule yielding CO2 and a vacant surface center ( ), followed by reoxidation of the vacant center by water that produces hydrogen and regenerates the oxide center for the catalytic cycle. 

Regenerative heat exchange can be used with catalytic as well as thermal oxidation. Such a system is offered by Haldor Topspe A/S as the REGENOX process (Haldor Topspe, 1990). In this process the catalyst also acts as the heat transfer medium for regenerative heat... 

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