Shell, the Netherlands based international oil company has no less than three research teams collaborating and coordinating in an effort to get biomass made into transport fuels.  From Shell Global Solutions International B.V. Shell Technology Centre in Amsterdam to the Shell Global Solutions (UK), Shell Technology Centre in Thornton UK and on to Shell Global Solutions in Hamburg Germany with twelve people involved one has to think this ‘Big Oil’ firm is serious.

Using acid hydrolysis of lignocellulose to levulinic acid, followed by hydrogenation to valeric acid and its subsequent esterification the Shell team can produce valeric esters or ethyl valerate (EV).  The ethyl valerate can be used as biofuels that are fully compatible for blending with gasoline or diesel, and have passed a road trial of 250,000 kilometers at fuel proportions of up to 20%.  This is serious and one can be certain that an eye was kept on commercial scale during the research period.

Shell's Ethyl Valerate Process Diagram. Click image for more info.

The team has published a paper on the work in the journal Angewandte Chemie International Edition, May 5, 2010.

The key point in the process is the production of γ-valerolactone (GVL) as an intermediate chemical produced from biomass-derived carbohydrates.  Using nothing more complex that acid hydrolysis the biomass is made into a product that can be made into a transport fuel supplement.  As a supplement the EV also raises the octane a small amount. It looks like EV is good stuff for a petroleum fuel extender with at least 20% market potential.

Gasoline blended with 10 and 20% of ethyl valerate (EV) largely complies with the European gasoline specification (EN 228). When compared to the base gasoline, the EV blends without fuel deterioration properties such as corrosion and gum formation. EV blending also increases the gasoline density and oxygen-content, reduced its volatility (lower RVP and lower E70-E120 numbers) and lowered its content of aromatics, olefins and sulfur.  EV seems to clean up the gasoline, at least to the extent that EV makes up the whole.

The authors note that non-compliant variability in volatility or density can be corrected for by minor reformulation of the base gasoline as currently done for ethanol blending.  Modern cars can use the EV biofuels without any modification to their engines; similarly, the existing network of fueling stations could be used for their distribution without the stop for “splash blending” as is required for ethanol.

Testing is pretty far along.  In one road test, ten current types of vehicle, new and used, were fueled exclusively with a mixture of normal gasoline mixed with 15% by volume of EV, and were sent out on the road to cover 500 km a day. After a total distance of 250,000 km, no negative impacts were found in the motor, tank, or fuel lines.

The authors point out the multistep process described in the paper provides maximum flexibility and robustness, integrating several of these steps can deliver significant process simplifications and intensification.

The authors note that a production process could be reduced to just two steps.

The levulinic acid can be converted to valeric acid in a single reactor loaded with a catalyst and operated with a large temperature gradient from 150°C at the inlet to 250°C from the middle of the reactor onwards. Or the levulinic acid can be converted to valeric acid under reactive distillation conditions, in which the bottom of the reactor is loaded with a simple Pt-based catalyst and operated under a hydrogen flow at a temperature that allows selective stripping of the GVL and water from levulinic acid. The middle part of the reactor is loaded with a catalyst to convert the GVL vapor.

Or, again, the levulinic acid can be converted to EV in a single step by co-feeding ethanol with levulinic acid as a physical or chemical mixture, in the form of ethyl levulinate, over a zeolite-based catalyst leading to the co-production of valeric acid and EV in a single step. The valeric acid intermediate over run can be recycled back to the reactor for further upgrading to EV.  It seems there is no lost hydrogen or carbon in the process.  Adding hydrogen rich ethanol is one kind of process choice.  The economics of the biomass and the location of a facility might decide which of the three paths might be most productive and economical.

The second and last reaction handles the undesired co-production of diethyl ether.  Diethyl ether can be minimized by co-feeding ethanol and levulinic acid to a reactive distillation reactor that contains a bifunctional catalyst in the bottom segment and a simple hydrogenation catalyst in the rectification segment.  Levulinic acid is hydrogenated to GVL over the hydrogenation catalyst, which is subsequently converted to ethyl pentenoate upon reaction with EtOH in the presence of the acid catalyst.

The last step is to handle the volatile ethyl pentenoate, which is stripped off the solution by hydrogen and is hydrogenated to EV upon passing over a hydrogenation catalyst.  Or skip the step and sell the ethyl pentenoate because it is a promising gasoline component and chemical intermediate.

The glitches are going to be all that acid to start the whole thing off and recycling it or working out a way to reuse it economically.  Whether that is or will be addressed isn’t answered.  Acid wastes can be awfully messy and one hopes the team has a clean and elegant solutions or the process might never get any further.  All the mineral components and insoluble organics of the biomass will be in the acid waste stream and should go back to the soil.

The other glitch might be in the catalysts.  From what was disclosed, no exotic or ‘expensive’ catalysts are involved, but that doesn’t preclude issues aren’t there.

On the plus side – little process heat is involved.  The note of 250°C at one point is quite low by pyrolysis standards or Fischer-Tropsch.   That suggests the energy input isn’t high.

This looks good with only an acid issue to deal with.

On the other hand, Dr. James Dumesic at the University of Wisconsin is exploring a different biofuel pathway involving the use of GVL.  The UW process converts already aqueous solutions of GVL to liquid alkenes in the molecular weight range appropriate for drop-in replacement transportation fuels by using an integrated catalytic system that does not require an external source of hydrogen or precious metal catalysts.

The process upgrades GVL to C9 alkenes, which are then oligomerized over an acid catalyst to produce longer chain alkenes that, after hydrogenation, can be used as drop-in fuels.

If one were to guess on what path might be used at scale for biomass to fuel, at least in the higher carbon atom count molecules, Shell is likely the leader now.  Dumesic is surely elegant and innovative, but the Shell researchers have commercial scale as one aspect that stood tall when the budget was set.  Ability to scale will be the first criteria of any successful biomass to fuel process.  Shell can see a world market for 22 million barrels per day of EV.  That’s the scale.


10 Comments so far

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