Advanced Biomass Feedstocks for High Value Chemicals & Fuels

Energy analysts cannot allow themselves to get stuck on one form of energy or fuel. In fact, the best energy analysts familiarise themselves with parallel industries and processes which overlap with or complement the energy and fuel processes on which they most closely focus.

So while cheap natural gas has temporarily postponed the economical development of many types of advanced biofuels and renewable chemical feedstocks, in the long run natural gas will be used to facilitate the production of chemicals and fuels from renewable biomass feedstocks.

Researchers at the University of Wisconsin led by Dr. Jim Dumesic report the conversion of the hemicellulose fraction of lignocellulosic biomass to furfural and levulinic acid using biphasic reactors with alkylphenol solvents in a new paper in the journal ChemSusChem. The furfural and levulinic acid products are valuable compounds for a variety of chemical applications, and they serve as precursors for the synthesis of liquid transportation fuels.

The conversion of lignocellulosic biomass into fuels and chemicals requires effective utilization of the C5 and C6 sugars present in hemicellulose and cellulose, respectively, by either processing these fractions together or separating and processing them separately. While simultaneous processing, such as in gasification or pyrolysis, offers the potential for simplicity of operation, the fractionation of hemicellulose and cellulose allows the processing of each fraction to be tailored to take advantage of the different chemical and physical properties of these fractions, and provides increased flexibility of operation.

For example, chemical processing methods can be employed to convert C5 sugars into fuels/chemicals in hemicellulose, while employing recent advances in biological conversions allows to convert the C6 sugars in cellulose into fuels and/or chemicals. One can also take advantage of the physical properties of cellulose for pulp and paper applications.

Herein, we show that the hemicellulose fraction of lignocellulosic biomass can be converted into furfural [FuAL] and levulinic acid [LA] by using biphasic reactors with alkylphenol solvents that selectively partition furanic compounds from acidic aqueous solutions. These furfural and levulinic acid products are valuable compounds for a variety of chemical applications, and they serve as precursors for the synthesis of liquid transportation fuels.

—Gürbüz et al.

...The basic steps of the process include:

Solid biomass is subjected to mild pretreatment in a dilute-acid, aqueous solution to solubilize the hemicellulose as xylose.

After filtering the solution from the solid cellulose and lignin, an organic solvent is added to the aqueous solution, and these liquids are heated in a biphasic reactor to achieve dehydration of xylose to FuAL.

FuAL can be distilled from the solvent and sold as a chemical or converted to LA by first hydrogenating FuAL to furfuryl alcohol (FuOH) over a metal-based catalyst (e.g. , copper) and then reacting the FuOH with water in a biphasic reactor to form LA.

Similar to FuAL, the LA product can be distilled from the organic solvent and sold as a chemical.

In the paper, they demonstrated three organic solvents—2-sec-butylphenol (SBP), 4-n-hexylphenol (NHP) and 4-propyl guaiacol (PG)—to be effective extracting agents for the production of FuAL and LA in these biphasic systems. These solvents (i) have high partition coefficients for extraction of FuAL, FuOH, and LA; (ii) do not extract significant amounts of mineral acids from aqueous solutions; (iii) have higher boiling points than the final product; and (iv) could potentially be synthesized directly from biomass (i.e., lignin), such that these solvents would not have to be transported to the site of the biomass conversion steps. _GCC

It will take time for biomass feedstocks to find their niches in the larger scheme of things. In the near future, cheap natural gas will overwhelm many markets and postpone many alternative fuels projects.

But as more and more uses are found for natural gas -- including lucrative gas to liquids (GTL) processes which are beginning to catch on -- methane is likely to become ubiquitous as a feedstock, reactant, and heat source in a wide range of new industrial processes, including the conversion of biomass to fuels and chemicals.