Production of alcohol blend usable in flexible fuel vehicles via fischer-tropsch synthesis field of the invention

Abstract

Alternative fuel compositions, blends of the alternative fuel compositions and gasoline, and methods for their preparation and use are disclosed. The alternative fuel compositions ideally include ethanol, isopropyl alcohol, and one or more of sec-butanol and t-butanol, and ideally include no more than 3% methanol, and no more than 15% C5 or higher alcohols. The fuel compositions can be prepared using Fischer-Tropsch synthesis to convert syngas to a product stream comprising C2-4 olefins, and hydrolyzing these olefins. The process facilitates isolation of C2-4 alkanes, because the boiling point difference of these alkanes is significantly lower than that of the C2-4 alcohols. Ideally, the compositions provide more energy per unit volume than E85, even without the addition of gasoline, although the compositions can be blended with gasoline in any desired ratio. The resulting alternative fuel can be derived, at least in part, from renewable resources, in that the syngas can be derived from renewable resources, and a significant portion of the molecule is derived from the water used to hydrolyze the olefins. The alternative fuel compositions, and blends thereof with gasoline, can help reduce U.S. dependence on foreign crude oil.

Description

[0001]This application is a continuation-in-part of PCT application No. PCT / US07 / 069,635, filed May 24, 2007, which claims priority to U.S. Provisional Application No. 60 / 896,099, filed Mar. 21, 2007.[0002]The present invention relates to alternative fuel compositions which comprise ethanol, isopropyl alcohol, and secondary-butanol and / or t-butanol, as well as blends of these compositions with gasoline.BACKGROUND OF THE INVENTION[0003]Gasoline is derived from crude oil, which is a non-renewable resource of finite supply. Extensive research effort is now being directed toward replacing some or all petroleum-based transportation fuels with gasoline / ethanol blends such as E85 (85% ethanol and 15% gasoline by volume). E85 suffers from a significant loss (roughly 20%) in energy per unit volume relative to gasoline. However, flexible fuel vehicles can run efficiently on these fuels, and the high oxygenate content makes them very clean burning fuels.[0004]Because ethanol suffers from relat...

AI Technical Summary

Benefits of technology

[0013]There are several ways to produce the alcohols that make up the alcohol blends described herein. The alcohols can be produced by olefin hydration, by fermentation, by hydroformylation of the C2-4 olefin products of Fischer-Tropsch synthesis, and by conducting Fischer-Tropsch synthesis in a way that maximizes alcohol formation. That is, normal straight chain alcohols can be formed during Fischer-Tropsch synthesis under certain conditions, and if they do not dehydrate under the Fischer-Tropsch conditions, they can be isolated (often in yields approximating 60%).

[0016]The alcohol blends can further be combined with conventional gasoline, thereby increasing the energy per unit volume.

[0020]Thus, fuel products that burn in flexible fuel vehicles can be obtained in significant yields from Fischer-Tropsch reactors, using relatively inexpensive iron-containing catalysts, without the need for a hydrocracker (such as is used to crack Fischer-Tropsch wax). Product yields are improved, relative to the volume of the olefins produced, by the addition of water across the double bond. Further, the resulting product is more stable than the olefins, which are otherwise prone to polymerization or other further reactions. The separation of C2-4 alkanes from C2-4 alcohols is significantly easier than the separation of C2-4 alkanes from C2-4 olefins. Further, the cost of setting up the plant is significantly reduced by using a combination of relatively inexpensive Fischer-Tropsch catalysts and conditions, and relatively inexpensive (compared with a hydrocracker) olefin hydration reactor. The amount of water present in the hydration reaction is significantly less than that present in a fermentation plant, so distillation costs are relatively lower.

[0021]The fuel compositions described herein can be blended with biofuels such as ethanol and “biobutanol” (n-butanol derived by fermentation) to maximize the yield of alternative fuels that run on flexible fuel vehicles. Unlike biobutanol, olefin hydration tends to form secondary and / or tertiary alcohols, which do not oxidize to corrosive and odiferous carboxylic acids such as butyric acid. Unlike E85, which requires gasoline to work in a flexible fuel vehicle, the presence of higher molecular weight alcohols means that the fuel can work in flexible fuel vehicles without adding any gasoline. Also, the presence of higher molecular weight alcohols means that the fuel can be used in conventional gasoline engines at higher concentrations than ethanol (i.e., at concentrations greater than 5% by volume, ideally up to or greater than 10% by volume).

[0022]The resulting alternative fuel can be derived, at least in part, from renewable resources, in that the syngas can be derived from renewable resources, and a significant portion of the molecule comes from the water used to hydrolyze the olefins. The alternative fuel compositions, and blends thereof with gasoline, can help reduce U.S. dependence on foreign crude oil.

Problems solved by technology

E85 suffers from a significant loss (roughly 20%) in energy per unit volume relative to gasoline.

However, the use of n-butanol as a viable energy source is not without its problems.

That is, sugar can be fermented, but it is difficult and expensive to convert lignocellulosic materials to the component parts, such as lignin, cellulose, and hemicellulose, and to then depolymerize the cellulose and / or hemicellulose to the component sugars.

Further, fermentation produces a significant amount of carbon dioxide.