Production of liquid hydrocarbons from biomass.

Research is being conducted worldwide to develop new technologies for the generation of liquid fuels from renewable resources. In this context, it was stated recently that “biomass is the only practical source of renewable liquid fuel”. This is of utmost importance for sustainable development. Currently, biodiesel is produced by transesterification of vegetable oils and ethanol by fermentation of glucose. Processes for the efficient gasification of biomass to produce CO and H2 (synthesis gas) are being developed. The synthesis gas can be further processed to produce methanol or liquid alkanes by Fischer– Tropsch synthesis using well-established industrial processes. In Agenda 21, Chapter 4.20, the United Nations call for “criteria and methodologies for the assessment of environmental impacts and resource requirements throughout the full lifecycle of products and processes”. A simple metric for biofuel production is the overall energy efficiency, that is, the heating value of the biofuel divided by the energy required to produce the biofuel from the respective biomass. Biodiesel production from rapeseed oil in Germany has an overall energy efficiency (not taking into account potential glycerol use) of about 1.9 and from soybean oil in the USA of about 3. The overall energy efficiency for the production of ethanol from corn in the USA equals about 1.1 without energy credits for coproducts. However, Pimentel pointed out quite recently: “In the U.S. ethanol system, considerably more energy, including high-grade fossil fuel, is required to produce ethanol than is available in the energy ethanol output. Specifically about 29% more energy is used to produce a gallon of ethanol than the energy in a gallon of ethanol.” Approximately 67% of the energy required for ethanol production is consumed in the fermentation/distillation process, of which over half is used to distill ethanol from water. A process without the energy-consuming distillation step would be most important. Huber et al. have recently demonstrated that it is possible to produce light alkanes by aqueous-phase reforming (APR) of biomass-derived oxygenates such as sorbitol, which can be obtained from glucose by hydrogenation. 11] The production of alkanes from aqueous carbohydrate solutions would be advantageous because of the easy separation of the alkanes from water. Accordingly, it was estimated that the overall energy efficiency for alkane production from corn would be increased to approximately 2.2, assuming that this process eliminates the energy-intensive distillation step but still requires all of the remaining energy input needed for the production of ethanol from corn. Much hydrogen is needed to reduce biomass-derived oxygenates to alkanes as shown in Equation (1). The main