|Elements of the ZeaChem process. Click to enlarge.|
ZeaChem Inc., the developer of an indirect process for the production of cellulosic ethanol, raised $34 million in initial Series B financing. The funding round was co-led by venture capital investors Globespan Capital Partners and PrairieGold Venture Partners with follow-on investment by MDV-Mohr Davidow Ventures, Firelake Capital and Valero Energy Corporation, the largest petroleum refiner in the United States.
ZeaChem’s process combines the outputs of two traditional ethanol production pathways (fermentation of sugars and gasification of biomass) into a third catalytically-driven step—hydrogenation—to produce ethanol. (Earlier post.) Zeachem now says that it can produce 40% more ethanol per ton of biomass over any known competitor. The company will use the new funds to build its first cellulosic biorefinery this year.
In the ZeaChem process, the biomass is chemically fractionated to produce a sugar stream containing both xylose (C5) and glucose (C6) sugars, and a lignin residue stream.
The sugars are fermented by a carbon-efficient acetogen—Clostridium thermoaceticum, found in termites—to acetic acid without CO2 as a by-product. (Conventional yeast fermentation creates one molecule of CO2 for every molecule of ethanol.) The acetic acid is converted to an ester which is then be reacted with hydrogen to produce ethanol.
The hydrogen is produced by the gasification of the lignin residue to produce syngas. The hydrogen is separated from the syngas and used for ester hydrogenation and the remainder of the syngas is burned to create steam and power for the process. The net effect of combining the two processes is that about 2/3 of the energy in the ethanol comes from the sugar stream and 1/3 comes from the lignin steam in the form of hydrogen, according to ZeaChem.
An analysis of the ZeaChem process included in a report on ethanol by the University of Illinois, published in November 2007, notes that:
In this process, 3 moles of ethanol are produced from 1 mole of glucose resulting in a 50% improvement over the conventional route where 2 moles of ethanol are produced from 1 mole of glucose. The energy for the third mole of ethanol is supplied by hydrogen, which can be generated by the gasification of the lignocellulosic biomass.
ZeaChem says that it expects to be able to deliver an Nth plant yield of 135 gallons of ethanol per bone dry ton (BDT) of biomass.
In February 2008, ZeaChem and GreenWood Resources, Inc. (GWR) signed a non-binding Letter of Intent for the supply of poplar tree (Pacific Albus) feedstock under a long-term agreement to support the operation of an initial 1.5 million gallon per year (MGPY) ZeaChem cellulosic biorefinery near one of Greenwood’s Pacific Albus tree farms in the Columbia River Basin. (Earlier post.)