http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
study of the methanol conversion to ethylene and propylene using small pore size zeolites
Olefins represent the starting point in the formation of the majority of the petrochemical products. The components can be polymerized, copolymerized, and selectively oxidized to a large number of useful products. As crude oil and natural gas which are the conventional sources of olefins increase in price, unconventional sources such as coal and biomass become more attractive. Methanol can be readily produced from coal via synthesis gas, whereas coal represents a highly abundant and scarcely utilized raw material in the United States. In the short term a 60% carbon yield of methanol to olefins would allow methanol to displace naphtha feedstocks in Western Europe and Japan. This project consisted of the study of the kinetics of the reaction of methanol to olefins. A combined selectivity to ethylene and propylene of 90% is readily achieved by selecting a proper set of operating conditions. The investigation encompassed the study of external and internal diffusion, adsorption and reaction. Instantaneous and overall material balances were developed, and a minimization technique was used to calculate the rate of formation of coke, the amount of coke deposited on the catalyst, and the hydrogen to carbon ratio. This procedure allowed the adjustment of several parameters in order to satisfy the material balances. The results were used to calculate the rate constants of the proposed model. The results indicated that the dehydration of methanol was inhibited by the adsorption of methanol. In general low methanol partial pressures, achieved by decreasing the total pressure in the case of pure methanol feeds, or by diluting methanol with water or nitrogen, increased the selectivity toward olefins. All the catalysts studied showed deactivation due to the accumulation of aromatic compounds ("coke"), which had a hydrogen to carbon ratio close to 1.1. The maximum amount of coke that can be deposited on the catalyst was about 0.16 grams coke/gram catalyst. The catalyst was regenerated by burning the coke with air. Residence time distribution experiments using a step input change showed that perfect mixing could be obtained with 200 grams of powder catalyst of 30-100 microns particle size by using flow rates smaller than 5 cc/sec measured at reactor conditions, and impeller speeds higher than 12 rev/sec.
Includes bibliographical references (leaves 134-139).