CO2 Conversion and Utilization - American Chemical Society

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Chapter 3

CO Emission Reductions: An Opportunity for New Catalytic Technology 2

Leo E. Manzer DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880-0262

Summary The theme of this symposium is related to reducing carbon dioxide emissions by conversion of the CO to other products. While this is a worthwhile object, the real goal where possible, should be to avoid the production of CO in the first place. It is the purpose of this paper to review processes that generate CO and provide some opportunities for research, which ultimately will reduce CO at the source to avoid end of pipe treatment. 2

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Introduction Catalytic oxidations are among the least selective of all catalytic reactions and the source of much of the carbon dioxide from chemical processes. These processes are often operated at very high temperatures, with selectivity to desired oxygenated products of less than 90%. The major byproduct is usually carbon dioxide. Table 1 shows typical selectivity to the major product in these large-scale commercial operations. Most of these processes have production capacities of several hundred million lb./year, so the amount of C 0 generated is quite significant. For example, for a maleic anhydride plant operating at a capacity of 200-MM lb./year, with 60% selectivity, over 500-MM lb./year of 2

© 2002 American Chemical Society

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carbon dioxide is produced. Therefore, there is a large incentive to improve yield to the hydrocarbon product in these processes. This can be done by improving the catalyst in these existing processes or by completely changing chemistry and engineering of existing processes. This paper will provide a brief overview of current trends and opportunities to reduce CO2. Table 1. Selectivity to Major Product for a few Commercial Catalytic Oxidation Reactions Oxidation Process Butane Oxidation Propylene Oxidation Propylene Ammoxidation Ethylene Oxidation

Major Product Maleic Anhydride Acrolein/Aery lie Acid Acrylonitrile Ethylene Oxide

Selectivity 60% 75% 80% 88%

Discussion

2.1 Anaerobic vs. Aerobic Oxidations It has been known for many years that in certain oxidation reactions the most selective catalysis occurs when the oxygen in the final product is derived directly from the lattice of the oxide catalyst. However, most large-scale commercial processes are carried out in the non-flammable region, which often requires a feed of less