Process for converting gaseous alkanes to olefins and liquid hydrocarbons

Abstract

A process for converting gaseous alkanes to olefins and liquid hydrocarbons wherein a gaseous feed containing alkanes is reacted with a dry bromine vapor to form alkyl bromides and hydrobromic acid vapor. The mixture of alkyl bromides and hydrobromic acid are then reacted over a synthetic crystalline alumino-silicate catalyst, such as an X or Y type zeolite, at a temperature of from about 250° C. to about 500° C. so as to form olefins, higher molecular weight hydrocarbons and hydrobromic acid vapor. Various methods are disclosed to remove the hydrobromic acid vapor from the higher molecular weight hydrocarbons and to generate bromine from the hydrobromic acid for use in the process.

Description

REFERENCE TO RELATED PATENT APPLICATION: [0001] This application is a continuation-in-part of copending U.S. patent application Ser. No. 11 / 101,886 filed on Apr. 8, 2005 and entitled “Process for Converting Gaseous Alkanes to Liquid Hydrocarbons” which is a continuation-in-part of copending U.S. patent application Ser. No. 10 / 826,885 filed on Apr. 16, 2004 and entitled “Process for Converting Gaseous Alkanes to Liquid Hydrocarbons”.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a process for converting lower molecular weight, gaseous alkanes to olefins that are useful as monomers and intermediaries in the production of chemicals, such as lubricant and fuel additives, and higher molecular weight hydrocarbons, and more particularly, to a process wherein a gas containing lower molecular weight alkanes is reacted with a dry bromine vapor to form alkyl bromides and hydrobromic acid which in turn are reacted over a crystalline alumino-...

AI Technical Summary

Benefits of technology

[0008] Other prior art processes propose the catalytic chlorination or bromination of methane as an alternative to generation of synthesis gas (CO and H2). To improve the selectivity of a methane halogenation step in an overall process for the production of methanol, U.S. Pat. No. 5,998,679 to Miller teaches the use of bromine, generated by thermal decomposition of a metal bromide, to brominate alkanes in the presence of excess alkanes, which results in improved selectivity to mono-halogenated intermediates such as methyl bromide. To avoid the drawbacks of utilizing fluidized beds of moving solids, the process utilizes a circulating liquid mixture of metal chloride hydrates and metal bromides. Processes described in U.S. Pat. No. 6,462,243 B1, U.S. Pat. No. 6,472,572 B1, and U.S. Pat. No. 6,525,230 to Grosso are also capable of attaining higher selectivity to mono-halogenated intermediates by the use of bromination. The resulting alkyl bromides intermediates such as methyl bromide, are further converted to the corresponding alcohols and ethers, by reaction with metal oxides in circulating beds of moving solids. Another embodiment of U.S. Pat. No. 6,525,230 avoids the drawbacks of moving beds by utilizing a zoned reactor vessel containing a fixed bed of metal oxide / metal bromide that is operated cyclically in four steps. These processes also tend to produce substantial quantities of dimethylether (DME) along with any alcohol. While DME is a promising potential diesel engine fuel substitute, as of yet, there currently exists no substantial market for DME, and hence an expensive additional catalytic process conversion step would be required to convert DME into a currently marketable product. Other processes have been proposed which circumvent the need for production of synthesis gas, such as U.S. Pat. Nos. 4,655,893 and 4,467,130 to Olah in which methane is catalytically condensed into gasoline-range hydrocarbons via catalytic condensation using superacid catalysts. However, none of these earlier alternative approaches have resulted in commercial processes.

Problems solved by technology

Due to the low density of natural gas, transportation thereof in gaseous form by pipeline or as compressed gas in vessels is expensive.

Accordingly, practical and economic limits exist to the distance over which natural gas may be transported in gaseous form exist.

However, this LNG process is expensive and there are limited regasification facilities in only a few countries that are equipped to import LNG.

SMR and GHR operate at high pressures and temperatures, generally in excess of 600° C., and require expensive furnaces or reactors containing special heat and corrosion-resistant alloy tubes filled with expensive reforming catalyst.

POX and ATR processes operate at high pressures and even higher temperatures, generally in excess of 1000° C. As there are no known practical metals or alloys that can operate at these temperatures, complex and costly refractory-lined reactors and high-pressure waste-heat boilers to quench & cool the synthesis gas effluent are required.

Also, significant capital cost and large amounts of power are required for compression of oxygen or air to these high-pressure processes.

Thus, due to the high temperatures and pressures involved, synthesis gas technology is expensive, resulting in a high cost methanol product which limits higher-value uses thereof, such as for chemical feedstocks and solvents.

Furthermore production of synthesis gas is thermodynamically and chemically inefficient, producing large excesses of waste heat and unwanted carbon dioxide, which tends to lower the conversion efficiency of the overall process.

Fischer-Tropsch Gas-to-Liquids (GTL) technology can also be used to convert synthesis gas to heavier liquid hydrocarbons, however investment cost for this process is even higher.

In each case, the production of synthesis gas represents a large fraction of the capital costs for these methane conversion processes.

However, to date, none of these alternatives has attained commercial status for various reasons.

However, halogenation of methane using chlorine as the preferred halogen results in poor selectivity to the monomethyl halide (CH3Cl), resulting in unwanted by-products such as CH2Cl2 and CHCl3 which are difficult to convert or require severe limitation of conversion per pass and hence very high recycle rates.

While DME is a promising potential diesel engine fuel substitute, as of yet, there currently exists no substantial market for DME, and hence an expensive additional catalytic process conversion step would be required to convert DME into a currently marketable product.

However, none of these earlier alternative approaches have resulted in commercial processes.

However due to the high cost of methanol production, and at current or projected prices for gasoline, the MTG process is not considered economically viable.

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