In recent years, a major technical challenge presented to the petroleum refining industry has been the requirement to establish alternative processes for manufacturing high octane lead-free gasoline which produces lower levels of airborne pollutants. The economic impact of these requirements on the cost of gasoline is significant and workers in the field have intensified their effort to develop new processes to manufacture environmentally acceptable gasoline products. One approach which has been taken in view of the regulatory requirement for oxygenates in the gasoline is the use of gasolines blended with lower aliphatic alkyl ethers such as methyl-tertiary butyl ether (MTBE) or methyl tertiary amyl ether (TAME) as octane boosters and supplementary fuel components. Ethers of this type, especially the C.sub.5 -C.sub.7 methyl alkyl ethers, especially tertiary alkyl ethers such as methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME), or the corresponding tertiary alcohol, have been found particularly useful for enhancing gasoline octane.
MTBE and TAME are known to be high octane ethers. The article by J. D. Chase, et al., Oil and Gas Journal, Apr. 9, 1979, discusses the advantages one can achieve by using these materials to enhance gasoline octane. The octane blending number of MTBE when 10% is added to a base fuel (R+O=91) is about 120. For a fuel with a low motor rating (M+O=83) octane, the blending value of MTBE at the 10% level is about 103. On the other hand, for an (R+O) of 95 octane fuel, the blending value of 10% MTBE is about 114.
Isobutylene may be reacted with methanol over an acidic catalyst to provide methyl tertiary butyl ether (MTBE) and isoamylenes may be reacted with methanol over an acidic catalyst to produce tertiary-amyl methyl ether (TAME). Similarly, these iso-olefins can be hydrated in the presence of an acid catalyst to give alcohols. In these processes, a problem of major importance is the separation of the reaction products and separation of unreacted hydrocarbons. For instance, the feedstream to an etherification process can be the C.sub.4 and/or C.sub.5 fraction from a fluid catalytic cracking (FCC) unit containing a range of isomeric alkanes and alkenes; of these, only the iso-olefins react with the alcohol (methanol or ethanol) to form the tertiary butyl or tertiary amyl ether.
Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,262,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,848; 3,989,762, to which reference is made for a description of such processes. Olefin hydration processes employing zeolite catalysts are disclosed, for example, in U.S. Pat. No. 4,214,107, to which reference is also made. In this process, lower olefins, particularly propylene, are catalytically hydrated over a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of from 1 to 12, e.g., HZSM-5 zeolite, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product.
Recently, synthetic lubricant compositions (referred to here as HVI-PAO lubricants) comprising high viscosity index polyalpha-olefins and methods for their preparation using a reduced chromium oxide catalyst have been disclosed in U.S. Pat. Nos. 4,827,064 and 4,827,073, to which reference is made for a description of thse olefin oligomers, their preparation and properties. The process described in these patents comprises contacting a C.sub.6 -C.sub.20 1-olefin feedstock with a reduced chromium oxide catalyst on a porous silica support under oligomerizing conditions to produce a high viscosity, high VI liquid hydrocarbon lubricant. The product is characterized by a branch ratio less than 0.19 and low pour point, typically below -15.degree. C. The process is notable in that internal or iso-olefins are unreactive in the oligomerization; only terminal olefinic groups participate in the coordination catalyzed oligomerization using the reduced chromium oxide catalyst. The same process may also be applied to the production of high VI lubricants from lower olefins, such as propylene and butene, as described in U.S. Pat. No. 4,990,709, to which reference is made for a description of the process using these olefins and of the oligomer products.
USPTO Backgrounds
USPTO Backgrounds