Process ups biodiesel efficiency
By
Kimberly Patch,
Technology Research NewsThe fuel produced when cornstarch is converted to sugar, then the sugar converted to ethanol, takes a fair bit of energy to make. About one third of the energy required to produce ethanol is used in the conversion step of separating ethanol from water.
Researchers from the University of Wisconsin at Madison have shown that it is possible to convert biomass materials like corn into fuel that could be used in diesel engines in a way that automatically separates the fuel from water. "This is a new process to produce liquid fuels from biomass," said James Dumesic, a professor of chemical and biological engineering at the University of Wisconsin.
Because no energy is required to separate the fuel from water, the process has a relatively high overall energy efficiency.
The fuel could eventually be blended with diesel fuel produced from petroleum sources to reduce oil needs, according to Dumesic. The process could also eventually produce diesel fuel that does not have to be blended with petroleum-based fuel, he said.
The researchers' method converts biomass into liquid alkanes within a self-sustained refinery.
Alkanes are hydrocarbons. The simplest is methane. More complex alkanes are the main components of gasoline. The new method uses existing processes to convert biomass to sugar, to convert part of the sugar to hydrogen, and to convert part of the sugar to carbonyl-containing compounds. Carbonyl compounds contain oxygen atoms double-bonded to carbon atoms.
The researchers devised a process to convert carbonyl compounds to a useful fuel. The first step condenses the carbonyl-containing compounds with acetone to convert them to large, water-soluble organic compounds. The second step involves a four-phase dehydration-hydrogenation reactor that converts these compounds into liquid alkanes.
Key to the process is the order in which the conversion takes place. The bonds between carbon atoms, which are broken to gain energy when fuel is burned, are formed before the hydrogenation phase.
The alkane fuel contains 90 percent of the energy of the glucose and hydrogen that the reaction begins with, said Dumesic. "Thus burning the alkane fuel would give you 90 percent of the energy compared to burning the glucose and the hydrogen."
The advantage of the researchers' process is that when alkanes are produced they spontaneously separate from water, said Dumesic. "In contrast to our process... ethanol must be separated from water by an energy-intensive distillation step," he said. "For our process, no energy is required to separate the alkane products from water."
This boosts the overall energy efficiency of the fuel. The ratio of energy derived from ethanol to the energy required to produce it is 1.1 to 1. The researchers' process has an estimated ratio of 2.2 to 1, according to Dumesic.
The current disadvantage of the process is that it takes a lot of steps. This can be improved, however, said Dumesic. "Now that we have elucidated the chemical pathways, we believe that we can intensify our process by combining various steps... by using multi-component catalysts," he said.
The conversion process has the potential to allow domestically-available biomass to become part of the solution to the United States' current dependence on fossil fuels, according to Dumesic. "The main obstacle to the more widespread utilization of our low-cost biomass resources is the absence of low-cost processing technologies," he said.
The key is building biorefineries that balance the energy. A refinery balances energy requirements of each process with those of other processes and the chemical intermediaries of each process are either separated as final products or used elsewhere in the refinery, said Dumesic.
Dumesic's research colleagues were George Huber, Juben N. Chheda and Christopher J. Barrett. The work appeared in the June 2, 2005 issue of Science. The research was funded by the Department of Energy (DOE), the National Science Foundation (NSF) and Conoco-Phillips.
Timeline: Unknown
Funding: Corporate; Government
TRN Categories: Energy; Chemistry
Story Type: News
Related Elements: Technical paper, "Production of Liquid Alkalines by Aqueous-Phase Processing of Biomass-Derived Carbohydrates," Science, June 2, 2005
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June 15/22, 2005
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