What is Green Gasoline?
September 29, 2008
- Green gasoline is a mixture of chemical compounds that is nearly identical to standard gasoline, yet it comes from plants, not petroleum.
- Researchers around the world are working on different approaches to creating green gasoline. The tools range from microbes to catalysts (materials that speed up reactions without sacrificing themselves in the process), with each approach having its own advantages and disadvantages.
- Scientists and engineers using catalysts have made a number of recent breakthroughs, including conversion of wood chips into high-octane fuel components and the conversion of sugar (potentially derived from plants) into gasoline, diesel and jet fuel materials and precursors for pharmaceuticals and plastics.
- There are three main catalytic mechanisms to convert plants into gasoline:
- Gasification is one of the oldest mechanisms to make gasoline from non-petroleum sources, but since it had primarily been used to convert coal or natural gas into gasoline, it is only now finding applications as a green gasoline process. In gasification, extreme heat breaks the plants down to the fundamental components of carbon monoxide (CO) and hydrogen (H2). The gasses are passed over catalysts which grab the CO and H2, and depending on which catalysts are used, recombines them into gasoline. The process is well-established but is currently only feasible at large scales. It is expensive and not efficient when plants are the feedstock.
- Pyrolysis is also a mechanism that uses heat, but it uses less than gasification, and like all of the catalytic approaches (including the method used in George Huber's laboratory at the University of Massachusetts Amherst) it is so efficient that it does not require any external energy source. Researchers even hope to eventually use the heat produced by the pyrolysis process to generate electricity. While new for green gasoline applications, the process has a number of advantages in that it can use any plant starting material, including waste paper and grass clippings, and is efficient. So far, the process can produce components of gasoline, but not yet the full suite of components found in transportation fuels.
- Aqueous Phase Processing starts with sugar, but sugar is somewhat easily derived from plants. At room temperature, the sugar is mixed with water and passed over specialized catalysts. If the catalysts are properly selected, the end result can be a wide range of substances, from gasoline (all 300-plus chemical components) to diesel to jet fuel to the precursors for pharmaceuticals and plastics. The process, under development at Virent Energy Systems, Inc. in Madison, Wisc. and initially at the University of Wisconsin, Madison, in James Dumesic's laboratory, is currently being scaled up for commercial applications. With buy-in from a number of major industry partners, Virent is hoping to bring this green gasoline process to market within the next five to 10 years.
- The sugar source for aqueous phase processing can come from such plants as sugar beets and sugar cane, and many researchers are devising ingenious ways to create sugars from all the parts of a plant. Some researchers are also working on growing new plants that are easier to convert into sugars.
- Source plants, such as switchgrass, can be grown on marginal lands, so neither food sources nor pristine forests need to be impacted.
- Green gasoline technologies recycle carbon instead of adding net carbon to the atmosphere. The same carbon that comes out of a tailpipe when green gasoline is burned is taken out of the atmosphere by the next crop of green gasoline plants. With non-renewable sources of fuel, the source carbon had been isolated within the Earth, but adds to total atmospheric carbon when it burns.
Joshua A. Chamot, NSF, (703) 292-7730, email: email@example.com
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