The manufacture of valeric biofuels consists of the acid hydrolysis of lignocellulosic materials to LA, the hydrogenation of the acid to gVL and valeric acid (VA), and finally esterification to alkyl (mono/di)valerate esters. One of these steps, the hydrogenation of gVL to VA, has not been reported in the literature and was developed in our laboratory. All the other steps are known but were nevertheless revisited and, wherever possible, improved.

—Lange et al.

Gasoline blended with 10 and 20% of ethyl valerate (EV) largely comply with the European gasoline specification (EN 228). When compared to the base gasoline, the EV blends shows a favorable increase in octane number (RON and MON) without deterioration of properties such as corrosion and gum formation. EV blending increased 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.

Non-compliant deviations in volatility or density can be corrected for by minor reformulation of the base gasoline, the authors note, as currently practices for ethanol blending.

Modern cars can use the valerate biofuels without any modification to their motors; similarly, the existing network of fueling stations could be used for their distribution.

The new fuels have passed a number of tests. In one road test, ten current types of vehicle, new and used, were fuelled exclusively with a mixture of normal gasoline mixed with 15% by volume of ethyl valerate (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.

While the multistep process (hydrogenation of levulinic acid to GVL; hydrogenation of GVL to valeric acid; esterification) described in the paper provides maximum flexibility and robustness, the authors note, integrating several of these steps can deliver significant process simplifications and intensification.

Levulinic acid (LA) can be converted to valeric acid (VA) in a single reactor loaded with a catalyst and operated with a large temperature gradient along the reactor length, e.g. from 150°C at the inlet to 250°C from the middle of the reactor onwards. Alternatively, LA can be converted to VA 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 GVL and water from LA. The middle part of the reactor is loaded with a catalyst to convert the GVL vapor.

LA can be converted to EV in a single step as well. Co-feeding ethanol with LA as a physical or chemical mixture (in the form of ethyl levulinate) over a zeolite-based catalyst leads to the co-production of VA and EV in a single step. The VA intermediate can be recycled to the reactor for further upgrading to EV.

In the last reaction, the undesired co-production of diethyl ether can be minimized by co-feeding ethanol and LA to a reactive distillation reactor that contains a bifunctional catalyst in the bottom segment and a simple hydrogenation catalyst in the rectification segment. LA 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 volatile ethyl pentenoate is stripped off the solution by hydrogen and is hydrogenated to EV upon passing over a hydrogenation catalyst. Omission of the last hydrogenation catalyst delivers ethyl pentenoate, which is a promising gasoline component and chemical intermediate.

Resources

• Jean-Paul Lange, Richard Price, Paul M. Ayoub, Jurgen Louis, Leo Petrus, Lionel Clarke, Hans Gosselink (2010) Valeric Biofuels: A Platform of Cellulosic Transportation Fuels. Angewandte Chemie International Edition, doi: 10.1002/anie.201000655