“Cellulose ethanol” production involves the conversion of plant cellulosic biomass into ethanol. The cellulose (chains of glucose molecules) in plant cell walls are broken down (by a process known as “saccharification”) into individual glucose units. The individual glucose molecules are then converted into ethanol by microbial fermentation. Lignin is a chemical substance that tightly wraps the cellulose fibers in the plant cell walls, and acts as a barrier for effective cellulose utilization. The destruction of the “lignin barrier” is one of the challenges in cellulose ethanol production technology. Physico-chemical methods like steam explosion or use of chemicals are commonly used.

Scientists from the U.S. Dairy Forage Research Center (DRFC) are taking an alternative approach to finding solutions for the “lignin barrier”. By understanding lignin formation and structure in plant cell walls, they hope to “provide opportunities to modify lignin composition and content”, probably in “designer” crops specifically planted for biofuels. John Ralph, a chemist at DFRC, has been studying changes in altered lignin structures in transgenic plants, and these studies have provided basic knowledge on how lignin formation occurs in plant cell walls. One of his interesting findings: lignin formation has “metabolic plasticity”; that is, plants have many possible combinations for assembling lignin in plant cell walls from a variety of building blocks. Ralph sees lignin formation as an “evolved solution that allows plants considerable flexibility in dealing with various environmental stresses”. Another researcher from Ralph’s laboratory, Fachuang Lu, has developed a tool for studying ultrafine chemical structure of the entire plant cell wall. Their work is featured in the April 2007 issue of Agricultural Research.

Related Information: Plant cell wall basics: http://genomicsgtl.energy.gov/biofuels/placemat2.shtml.

Engineers from North Carolina State University (NCSU) and Diversified Energy Corporation (DEC) in the United States are testing a patent-pending process which can convert any lipid-based raw material (oils or fats derived from plant or animal sources) into high value aviation biofuel (for jet engines) or additives for cold-weather biofuels. New advantages of the process is that even low quality lipid products like cooking grease can be used, and that there are no more disposal problems associated with the waste by-product, glycerol. Aviation biofuels have more stringent requirements for energy density, combustion, and cold flow properties than traditional biofuels. The process (called “CentiaTM), involves a three-step thermo-catalytic reforming process. In the first stage (called hydrolysis), the feedstock is subjected to high temperature and pressure to strip off the free fatty acids (FFA) from the glycerol backbone of the lipid. The glycerol waste by-product is burned off for energy, while the FFA enters the second step. In the second stage (the decarboxylation step), the FFA’s and a solvent are heated under pressure with a catalyst to remove carbon dioxide, resulting in the formation of straight chain hydrocarbons (called “alkanes”) that are 15 or 17 carbon atoms (C15 or C17) long. The aviation biofuel is then produced in the third step (the reforming step), where the straight chained C15 or C17 alkanes are reformed into branched “iso-alkanes” containing 10 to 14 carbon atoms. So far, this is said to be the first process ever to produce a biofuel that is jet-compliant. The team is currently furthering the maturity of the technology and is “seeking investors and strategic partners for full-scale bench testing, pilot plant development, feedstock supply, and fuels purchase agreements.”.