oxygenates used as octane enhancers are methyl tertiary-butyl ether (MTBE) and ethanol (EtOH). However, other oxygenates (e.g., alcohols, ethers, acetates, and carbonates) are known octane boosters. Some of these compounds have been evaluated only partially for their performance characteristics and may represent major growth opportunities in oxygenated fuels. Currently, approximately 150,000 barrels per day of oxygenated compounds (MTBE, EtOH) is added to gasoline in the United States. By the year 2000 it is projected that 750,000 barrels per day (the equivalent of roughly 10% of current U.S. production of petroleum) of oxygenates will be required for the gasoline pool. In the United States, the 1990 MTBE production capacity was 117,200 barrels per day. By 1993 it is targeted at 256,400 barrels per day. Iso-olefins (e.g., isobutylene) are now produced as a by-product of fluidized catalytic crackers in petroleum refineries. These quantities will support production of ether at a rate of only 200,000-300,000 barrels per day.
The process technology leading to the majority of oxygenates now in use has been made very efficient through catalyst modifications and engineering design. However, new processes leading to the same oxygenates may have cost advantages if different building blocks and feedstock sources (crude oil versus coal versus natural gas) are utilized.
The precursors of established octane enhancers—alcohols and ethers—rely heavily on natural gas and crude oil as their feedstock supply. With the United States importing approximately 55% of its crude oil, the price of oxygenates will track that of crude oil, which is currently approximately $20 per barrel. Industry estimates suggest that when crude oil prices pass approximately $30 per barrel, coal gasification to syngas and the conversion of syngas to hydrocarbons and oxygenates become cost competitive. Therefore, indirect liquefaction of coal offers promise for oxygenated fuels for the transportation industry.
Methanol dissociation to carbon monoxide (CO) and hydrogen (H2) on-board a vehicle would provide a fuel that is even cleaner and more fuel efficient than undissociated methanol. The heat required for endothermic dissociation of methanol can be supplied readily by engine exhaust gas. This recovers waste heat and increases the heating value of the fuel. Fuel efficiency is further enhanced because an internal combustion engine running on dissociated methanol can be operated with excess air (i.e., lean combustion). Lean and complete combustion would ensure low CO and hydrocarbon emissions. The problems associated with formaldehyde emission would be significantly reduced. Reduction of nitrogen oxide (NOx) emissions by an order of magnitude has been demonstrated because of lower combustion temperatures.