At the beginning of the 21st century mankind is facing an energy challenge as a consequence of the world s increasing energy demand, the depletion of "easy" oil and gas fields, and the impact of CO 2 emissions on the Earth s climate ("three hard truths"). [1] Much research is therefore being devoted to the exploration and development of new, carbon-lean energy sources. These include biofuels, which are the most promising option for the transportation sector in the coming decades. [2] The first generation of biofuels is presently produced from sugars, starches, and vegetable oil. Although instrumental in developing the market, these biofuels are not likely to deliver the large volumes needed for the transport sector because they directly compete with food for their feedstock. A more promising feedstock is lignocellulosic material, which is more abundant, has a lower cost, and is potentially more sustainable. [3] Lignocellulose is recalcitrant and, therefore, requires complex and expensive processes for upgrading to biofuels. [4] Interestingly, it has been claimed that levulinic acid (LA) can be easily and cheaply produced from lignocellulosic materials by using a simple and robust hydrolysis process. [5] Several LA derivatives have been proposed for fuel applications, for instance ethyl levulinate (EL), g-valerolactone (gVL), and methyl tetrahydrofuran (MTHF). [5,6] However, these components do not exhibit satisfactory properties when blended in current fuels. Herein, we present a new platform of LA derivatives, the "valeric biofuels", which we have been developing since 2004 and which can deliver both gasoline and diesel components that are fully compatible with transportation fuels.The manufacture of valeric biofuels (Scheme 1) 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 (Scheme 1, step 3), 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. This holds for the acid-catalyzed hydrolysis of lignocellulose to LA, [5,7] the hydrogenation of LA to gVL with the use of supported metal catalysts, [8] as well as the familiar esterification of carboxylic acids. Herein, we present the main results of the hydrogenation of gVL to VA (Scheme 1, step 3), key improvements in the hydrogenation of LA to gVL (step 2), options for integrating steps 2-4, and finally a thorough evaluation of the fuel performance of the resulting

At the beginning of the 21st century mankind is facing an energy challenge as a consequence of the worlds increasing energy demand, the depletion of "easy" oil and gas fields, and the impact of CO 2 emissions on the Earths climate ("three hard truths").[1] Much research is therefore being devoted to the exploration and development of new, carbon-lean energy sources. These include biofuels, which are the most promising option for the transportation sector in the coming decades.[2]The first generation of biofuels is presently produced from sugars, starches, and vegetable oil. Although instrumental in developing the market, these biofuels are not likely to deliver the large volumes needed for the transport sector because they directly compete with food for their feedstock. A more promising feedstock is lignocellulosic material, which is more abundant, has a lower cost, and is potentially more sustainable. [3] Lignocellulose is recalcitrant and, therefore, requires complex and expensive processes for upgrading to biofuels. [4] Interestingly, it has been claimed that levulinic acid (LA) can be easily and cheaply produced from lignocellulosic materials by using a simple and robust hydrolysis process.[5] Several LA derivatives have been proposed for fuel applications, for instance ethyl levulinate (EL), g-valerolactone (gVL), and methyl tetrahydrofuran (MTHF). [5,6] However, these components do not exhibit satisfactory properties when blended in current fuels. Herein, we present a new platform of LA derivatives, the "valeric biofuels", which we have been developing since 2004 and which can deliver both gasoline and diesel components that are fully compatible with transportation fuels.The manufacture of valeric biofuels (Scheme 1) 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 (Scheme 1, step 3), 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. This holds for the acid-catalyzed hydrolysis of lignocellulose to LA, [5,7] the hydrogenation of LA to gVL with the use of supported metal catalysts, [8] as well as the familiar esterification of carboxylic acids. Herein, we present the main results of the hydrogenation of gVL to VA (Scheme 1, step 3), key improvements in the hydrogenation of LA to gVL (step 2), options for integrating steps 2-4, and finally a thorough evaluation of the fuel performance of the resulting

Biomass is an interesting starting material for transportation fuels because of its renewable nature. The main constituents of biomass are the carbohydrate polymers cellulose and hemi-cellulose, and lignin. Current transportation fuels are mixtures of mainly hydrocarbons derived from crude oil. Biomass derived biofuels are preferably used as blends with fossil fuels to avoid the need for adaptations in the existing car fleet. The total blend then needs to meet the set fuel specifications for fossil fuels. The conversion of biomass to biofuels therefore centres on the removal of oxygen from carbohydrates to obtain hydrocarbons. Oxygen is preferably eliminated in the form of CO 2 or H 2 O, because the heat of combustion of these molecules is zero and all energy is concentrated in the remaining products. Based on gross chemical formulae, the conversion options from biomass to biofuels have been investigated, and interesting intermediates have been identified. Conversion routes from carbohydrates to hydrocarbons tend to proceed via C 1 -intermediates (CO, CH 4 and carbon). Gasification and subsequent Fischer Tropsch synthesis seems the logical processing route to obtain hydrocarbons from biomass via these intermediates. If oxygen containing products are allowed, conversion can proceed via larger intermediates. For blending with gasoline, ethanol emerges as an interesting component. Longer carbon chain molecules are required for diesel. These can only be obtained by at least two process steps, involving the combination of carbon chains (e.g. by etherification or esterification), and reduction of polarity (by hydrogenation or oligomerisation). The lignin present in biomass has a complex, highly cross-linked structure, and can probably best be converted to syngas via gasification or applied directly as solid fuel.

No abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.