Method for bio-oxidative desulfurization of liquid hydrocarbon fuels and product thereof

Abstract

Disclosed herein is a method for producing ultra-low-sulfur content hydrocarbon fuel and product thereof. The method comprises selective biocatalytic oxidation of sulfur containing compounds present in the fuels employing enzyme lipase as biocatalyst in presence of controlled and incremental amount of hydrogen peroxide and carboxylic acid without using water or any co-factor for the reactivity of said enzymes.

Description

FIELD OF THE INVENTION[0001]This invention, in general, relates to the field of hydrocarbon fuel, in particular to the method for desulfurization of the liquid hydrocarbon fuel and product thereof. More specifically but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice, this invention provides a method for selective biocatalytic oxidation of sulfur containing compounds present in fossil fuels employing enzyme lipase as a biocatalyst.BACKGROUND OF THE INVENTION[0002]Sulfur compounds are widely distributed in petroleum distillates of all boiling ranges. In gasoline, the principal sulfur compounds are mercaptans, aliphatic sulfides, disulfides, five and six membered ring cyclic sulfides, while diesel fuel is rich in benzothiophenes and alkyl substituted benzothiophenes. The removal of sulfur from fuels is necessary for both industrial and environmental reasons. Sulfur in fuels poisons catalytic converters, corrodes the ...

AI Technical Summary

Benefits of technology

[0021]Further object of the present invention is to provide a method for bio-oxidative desulfurization of fossil fuel to remove sulfur content from said fuel by selective activity on carbon-sulfur-carbon bonds in said sulfur-containing compounds without apparently changing non-sulfur-bearing components of the fuel.

[0024]In accordance with another mode of the invention, there is provided a method to produce ultra-low-sulfur fuel oils, wherein hydrogen peroxide is added in controlled and incremental amounts in the reaction mixture under proper mixing conditions to avoid excess concentration of hydrogen peroxide in the fuel.

[0026]The high effectiveness of the present process is the observation that dibenzothiophene and related sulfur-bearing organic sulfides, which are the most refractory organic sulfur compounds in fossil fuels, are readily converted by this process to the corresponding sulfoxides and sulfones under ambient conditions, however, this catalyst is active up to 70° C., preferably 35 to 60° C.

[0027]In accordance with another preferred mode of the present invention, there is provided an industrial and environmental friendly hydrocarbon fuel having ultra-low-sulfur content which is effectively produced by the method described above.

Problems solved by technology

Sulfur in fuels poisons catalytic converters, corrodes the parts of internal combustion engines and refinery equipment because of the formation of oxy-acids of sulfur.

However, more active catalysts and recent developments in fixed bed hydro treating technology have reduced the time spent in the reactor, thus lowering the required reactor volume and operating costs but it is limited in treating benzothiophene and dibenzothiophene especially DBTs having alkyl substitutions on their 4 and / or 6 positions.

The 4,6 disubstituted compounds do not adsorb on the active sites of the catalyst due to steric limitations.

But the usage of such oxidants is known to be very non-selective and slow.

The use of large amount of hydrogen peroxide make it environment reactive and moreover, safety-related issues are also an area of concern.

Chemical oxidation route as described above are known to be very non-selective and slow.

The use of large amount of hydrogen peroxide makes it environment reactive and moreover, safety-related issues are also an area of concern.

Although this process is effective, it is energy-intensive and requires aqueous medium for reaction.

Microbial desulfurization, however, requires a vast amount of water during the desulfurization process to sustain microbial activity (intrinsic mass transfer issue).

Beside this, microorganisms for desulfurization also degrade some aliphatic or aromatic fractions of fuels causing the decrease of fuel yield.

The method reported in prior art for biocatalytic oxidation of organosulfur compounds require considerable amount of water in diesel mixture for reaction leading to stable emulsion formation and poor recovery of water soluble products.

Moreover, some of the enzyme requires costly co-factors (co-enzymes) and are pH sensitive.

The major drawback of these co-factor dependent enzymatic desulfurization reactions is that co-factors are gradually destroyed due to undesired side reactions.

These co-factors (co-enzymes) are very expensive.