|ZeaChem’s process. Click to enlarge.|
ZeaChem Inc. announced the successful production of ethanol at a capacity that can be scaled to commercial production. ZeaChem currently uses harvested hybrid poplar trees as the feedstock of choice in its combined biochemical and thermochemical process for the production of ethanol. (Earlier post.)
A recent lifecycle analysis by CH2M HILL calculates that ZeaChem ethanol produced from the farmed hybrid poplar trees offers a 94-98% reduction in greenhouse gas emissions compared to petroleum-derived gasoline. Results are based on a farm yield of 10 bone dry tons (BDT) per acre and 135 gallons of ethanol per BDT.
ZeaChem’s production results have been confirmed by third party vendors who will enable production of ZeaChem biofuels and bio-based chemicals. The company will now demonstrate the integration of its biorefining processes at its 250,000 gallon per year Boardman, Oregon biorefinery. The integrated facility is being partially funded by a $25-million grant from the US Department of Energy (DOE) through the American Recovery and Reinvestment Act of 2009. (Earlier post.)
The company will use the grant to build the chemical fractionation on the front end and the hydrogenation process on the back end for making cellulosic ethanol. The facility will begin to produce cellulosic ethanol in 2011. ZeaChem intends to build commercial biorefineries upon successful operations at the Boardman facility.
The process. After fractionating the biomass, the sugar stream—both xylose (C5) and glucose (C6)—are sent to fermentation where a naturally occuring acetogen ferments the sugars to acetic acid. Acetogens have several advantages to yeast: they convert all xylose (C5) and glucose (C6) sugars and tolerate all breakdown products of biomass; they operate in harsh environments; and they produce no CO2 as a by-product.
In comparison, traditional yeast fermentation creates one molecule of CO2 for every molecule of ethanol. Thus the carbon efficiency of the ZeaChem fermentation process is nearly 100% vs. 67% for yeast.
The acetic acid is converted to an ester which is then hydrogenated to make ethanol. To get the hydrogen necessary to convert the ester to ethanol, ZeaChem takes the lignin residue from the fractionation process and gasifies it to create a hydrogen-rich syngas stream. 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. At an expected Nth plant yield of 135 gallons per bone dry ton (gal/BDT), the process is nearly balanced with the necessary steam and power generated from the non-hydrogen portion of the syngas stream.
Accounting for yield per acre, ZeaChem calculates, this is five times more than corn-based ethanol and about three times more than other cellulosic processes, either biological or thermochemical. At the Nth plant, says CEO Jim Imbler, the process cost will be less than $1.00 per gallon.
Other products. ZeaChem’s approach can deliver a range of chemicals and fuels within the carbon chain product groups. Imbler says that the company has started work on its C3 organism (which would produce lactic acid, rather than the acetic acid produced by its current C2 organism). The C3 product platform would include propionic acid, propanol and propylene. Moving on to C4 could produce butanol.
Through the successful production of ethanol, we’ve completed ZeaChem’s C2 carbon chain suite of products, which includes acetic acid, ethyl acetate, and ethanol. The next step is to integrate these known processes to achieve the ultimate target of commercial production of economical and sustainable biofuels and bio-based chemicals.
|ZeaChem Carbon Chain Product Groups|
|C2 Chain||C3 Chain||C4 Chain||C6 Chain|
Acrylic Acid & Esters
Methacrylic Acid & Esters
Feedstock. Although the ZeaChem process is feedstock agnostic, it is initially concentrating on its farmed hybrid poplar trees. ZeaChem’s analysis has shown the use of short rotation hybrid poplars offers the lowest cost per BDT/acre/year. These short-rotation hybrids can be harvested as often as three years, and require replanting only once every five harvests.
A successful, low-cost feedstock strategy requires three things, Imbler says. The feedstock needs to be
- Dedicated; and
- Have “term”
The latter refers to long-term supply agreements. ZeaChem has a contract with GreenWood Resources (GWR) for its feedstock.