Since the early 1970's extensive research has been performed to increase the efficiency of use of crude oil through quantitative and qualitative improvements of fossil fuels and related feedstocks, petrochemical products and alternative fuels. A primary motivation for this research has been to ensure that the phasing-out of lead alkyl in gasoline would not adversely affect the gasoline pool and the octane pool. While the increase in gasoline prices during the 1970's motivated investors and researchers to develop alternative energy sources, the drop in oil prices in recent years has caused a virtual cessation of investment in alternative fuels.
Today, the passage of the Clean Air Act (CAA) amendments of 1990 is leading to landmark changes in all major transportation fuels in the United States, and a substantial promotion of alternative motor fuels, mainly so-called "oxygenates." In order to comply with the CAA, gasoline marketers are not only admixing oxygenates into gasoline, but also changing the hydrocarbon composition, for example, benzene content, total aromatics, butane content, total olefins, etc. It is these considerations and others that will determine the reactivity of new gasolines and which will translate into the performance characteristics of admixed oxygenates, i.e., distillation, volatility, azeotropic behavior, oxidation stability, solubility, octane values, vapor pressure, etc.
Over the last fifteen years research regarding oxygenated fuel substitutes and components have focused on certain alcohols and ethers, mainly methanol, ethanol, isopropanol, t-butanol, methyl t-butyl ether (MTBE), ethyl t-butyl ether (ETBE), and t-amyl methyl ether (TAME). Many processes and compositions of such materials have been described in the art.
For example, U.S. Pat. No. 5,001,292 to Harandi et al, describes a process for reducing the cost of producing MTBE and other alkyl t-butyl ethers by converting unreacted hydrocarbons and alkanols from the etherification process to gasoline boiling range hydrocarbons.
Generally, oxygenate gasoline components have been blended into gasoline separately. However, there have been mixtures of such components disclosed, such as blends of gasoline containing components other than ethers, such as alcohols, and even esters. For example, U.S. Pat. No. 4,468,233 to Bruderreck et al. describes a t-butyl ether containing motor fuel composition including MTBE and isopropyl t-butyl ether (i-PTBE) and sec-butyl t-butyl ether (s-BTBE) which is said to provide a high octane number, reduced emissions and improved solubility. However, some experiments contradict the finding that ether blends improve alcohol solubility in gasoline.
Gasoline has historically pressures of 10-15 psi. Ether components have provided advantageous vapor pressure blending characteristics for such gasolines. The CAA has now caused refiners to reformulate gasoline to achieve vapor pressures of 7.5 to 8.5 psi with such lower vapor pressures the motivation to use MTBE, the strongest oxygenate gasoline component in the marketplace, becomes weakened because MTBE has a vapor pressure of approximately 8.4 psi.
The future use of more highly oxygenated fuels will inevitably be tied to environmental improvement efforts, but the blending of MTBE and ethanol with gasoline for octane improvement or supply extension with improved profitability will also continue. Even areas presently unaffected by carbon monoxide or ozone loss will probably be required to use oxygenates by 1995 or earlier because of anti-dumping provisions in the CAA. The need for more oxygenates is clear. Hence, more feedstocks and technologies must be developed to supply the market demand.
The CAA deals not only with mobile emissions, but also static emissions, which are of concern to the oil industry. RCRA hazardous waste management rules affecting refiners will provide new incentives for research related to more efficient conversion of heavy crudes, still bottoms and residues, all generally referred to as the "bottom of the barrel". Other energy related and overall environmental concerns will be addressed in this research as well, such as use and conversion of oil shale, use of coal and lignite, the recovery of industrial and urban waste, etc.
Several technologies and processes exist that, operating in liquid phase for methanol and gaseous phase for mixed alcohols production can, either connected, or operated independently, provide new opportunities for fuel alcohol synthesis. Their flexibility enables them to be used either with the products of gasification derived from, for example, coal, lignite, heavy residues, biomass, urban and industrial wastes, or with synthesis gas (Syn-Gas) produced by partial oxidation and/or steam reforming of natural gas or light napthas, or even heavy oils and crudes, crude oil bottoms and residues.
Such processes can be used to produce a linear combination of alcohols composed of at least 30 to 40% longer alcohol chains.