Renewable energy sources, such as biofuels, provide a substitute for fossil fuels and a means of reducing dependence on petroleum oil. In light of its low cost and wide availability, biomass is often used as a feedstock to produce pyrolysis oil (which is relatively soluble in water) or bio-oil which, in turn, is used to produce biofuel.
Many different conversion processes have been developed for converting biomass to bio-oil or pyrolysis oil. Existing biomass conversion processes include, for example, combustion, gasification, slow pyrolysis, fast pyrolysis, liquefaction and enzymatic conversion. Pyrolysis oil is the resultant of thermal non-catalytic treatment of biomass. The thermocatalytic treatment of biomass renders liquid products that spontaneously separate into an aqueous phase and an organic phase. Bio-oil consists of the organic phase. Pyrolysis oil and bio-oil may be processed into transportation fuels as well as into hydrocarbon chemicals and/or specialty chemicals.
While thermolysis processes and other conversion processes produce high yields of such oils, much of the pyrolysis oil and bio-oil produced is of low quality due to the presence of high levels of low molecular weight oxygenates having 5 or less carbon atoms (C5−). Such low MW oxygenates can be in alcohols, aldehydes, ketones, carboxylic acids, glycols, esters, and the like. Those having an isolated carbonyl group include aldehydes and ketones like methyl vinyl ketone and ethyl vinyl ketone.
Such oils thus require secondary upgrading in order to be utilized as drop-in oxygen free transportation fuels due to the high amounts of such oxygenates. A known method for converting oxygenates into hydrocarbons is hydrotreating wherein the stream is contacted with hydrogen under pressure and at moderate temperatures, generally less than 750° F., over a fixed bed reactor.
Transportations fuels predominately contain hydrocarbons having six or more carbon atoms (C6+) (though small amounts of C5 hydrocarbons are present in some gasolines). Thus, hydrocarbons derived by hydrotreating C5− oxygenates are of little value in transportation fuels. Additionally, hydrotreating C5− oxygenates consumes valuable hydrogen in the reactor. Thus, the efficiency of secondary upgrading of pyrolysis oil and bio-oil is compromised by the presence of the C5− oxygenates.
Alternative processes have therefore been sought for enhancing the efficiency in hydrotreating of oils derived from biomass. Processes for enhancing the yield of hydrotreated pyrolysis oil and bio-oil from streams containing C5− oxygenates, especially C3 to C5 oxygenates, have been sought.