Third-Generation Cellulosic Biofuels: Sustainable, Efficient, Cost-Effective | AIChE

Third-Generation Cellulosic Biofuels: Sustainable, Efficient, Cost-Effective

Increased emphasis is being placed on renewable, sustainable, domestic forms of energy, including transportation fuels, at national, state and local levels. Successful deployment of alternative solutions to petroleum-based liquid fuels for the transportation industry is dependent upon technical, economic and environmental factors.

ZeaChem Inc. has developed a hybrid cellulose-based biorefinery platform capable of producing third-generation biofuels and biochemicals. This new approach to cellulosic biofuels provides significant technological, economic and environmental advantages compared to other, current biofuels production processes.

ZeaChem's third-generation cellulosic fuel and chemical technology is differentiated from first and second generation technology by a number of key elements:

1.      The hybrid process ? incorporating biochemical and thermochemical processes ? delivers the highest theoretical yield of any biorefinery technology, a 40% advantage.

2.      Use of proven technology and process components and a naturally occurring organism.

3.      Feedstock flexibility allows for geographic diversity of biorefinery locations.

4.      Product flexibility of cellulosic biofuels and biochemicals production to meet market demand for renewable products.


ZeaChem's unique hybrid process combines the best of biochemical and thermochemical platforms. Utilizing a naturally occurring acetogen, found for example in termites, ZeaChem's process fully utilizes all of the available carbon from the cellulose and hemi-cellulose fractions of the feedstock, while adding hydrogen from the lignin fraction to create the highest net conversion efficiency of any known process.  By efficiently extracting the most energy possible from sustainable energy crops, ZeaChem significantly increases output while reducing both production costs and environmental impacts.

As the diagram above shows, after fractionating the biomass, the sugar stream (both xylose [C5] and glucose [C6]) are sent to fermentation where an acetogenic process is utilized to ferment the sugars to acetic acid without 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 can then be reacted with hydrogen 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. The process is nearly balanced with the necessary steam and power generated from the non-hydrogen portion of the syngas stream.

For every bone dry ton (BDT) of feedstock, ZeaChem's technology will produce a theoretical maximum of 160 gallons of ethanol, with an expected yield of approximately 135 gallons per BDT (gal/BDT). Accounting for yield per acre, this is five times more than corn based ethanol processes and about 1.5 times more than other cellulosic processes, either biological (enzymatic) processes or thermochemical (gasification) processes. ZeaChem's high-yield process gives it sustainable competitive advantage in both economics and environmental impact.


Given its 40% yield advantage, ZeaChem's process has the lowest operating (<$1.00) and capital cost (<$3.00) per gallon. ZeaChem's advantage in operating costs puts its process at a competitive advantage to both corn based ethanol producers and cellulosic ethanol competitors. Assuming a yield of 15 BDT/acre, a biomass farm with an approximate 5 mile radius could support a ZeaChem biorefinery with capacity of 100 million gallons per year (MM GPY). This translates into net land productivity rates nearly five times higher than existing approaches, a substantial environment improvement and benefit that also translates into significant cost advantages.

Farm Yield

Factory Yield

Auto Efficiency

Land Productivity

1st Generation - Corn Ethanol

150 Bu/ac/yr

2.7 Gal/bu

14 mi/Gal EtOH

5,670 mi/ac/yr

2nd Generation ? Cellulosic Ethanol

7.5 BDT/ac/yr

90 Gal/BDT

14 mi/Gal EtOH

9,450 mi/ac/yr

3rd Generation ? Advanced Cellulosic Ethanol (ZeaChem Inc.)

15 BDT/ac/yr

135 Gal/BDT

14 mi/Gal EtOH

28,350 mi/ac/yr

3rd Generation + Auto Efficiency

15 BDT/ac/yr

135 Gal/BDT

25 mi/Gal EtOH

50,625 mi/ac/yr

ZeaChem's technology has the ability to produce a wide range of biofuels and biochemicals. This flexibility allows for ZeaChem to provide the most economic, renewable products to the marketplace. Currently, ZeaChem is focusing its deployment efforts on two carbon (C2) products, including ethanol. Future technology deployment will expand into other carbon chain product groups and include biofuels such as butanol, hexanol and hexene production. 

ZeaChem Carbon Chain Product Groups

C2 Chain

C3 Chain

C4 Chain

C6 Chain

Acetic Acid 

Ethyl Acetate



Ethylene Glycol

Lactic Acid

?       Propylene Glycol

?       Acrylic Acid & Esters

Propionic Acid

?       Propylene

?       Methacrylic Acid & Esters





The ZeaChem process results in a 40% yield advantage of ethanol per ton of feedstock compared to other conversion technologies because the process efficiently utilizes all fractions of the feedstock.

A third-party lifecycle analysis found that ZeaChem cellulosic ethanol has an advantage over traditional ethanol with its high biorefinery yields and low fossil fuel usage. The ZeaChem process was found to be a highly efficient, low net GHG emissions method of producing ethanol and was found to have an advantage in both net energy value (
NEV), and net energy ratio (NER). (
NEV is the energy content of the ethanol minus the fossil fuel energy input into the process of making the ethanol. NER is the ratio of output energy of ethanol to input energy of fossil fuels.)

The analysis was based on a conservative dedicated farm producing 10 BDT/acre/year with Nth plant ethanol yield of 135 gal/BDT in comparison with published corn ethanol data from the USDA. As shown, the ZeaChem process has a very high
NEV when compared to corn. The analysis also determined that ZeaChem ethanol has about eight times lower fossil fuel CO2 emissions than traditional corn ethanol and about eleven times fewer emissions than conventional gasoline. Likewise, ZeaChem's high yield will provide a competitive advantage with respect to both
NEV and CO2 over any cellulosic competitor.

ZeaChem Ethanol

Traditional Corn Ethanol

Conventional Gasoline

Crop Yield (tons/acre)




Biorefinery Yield (gallon/ton)




Net Energy Value (BTU/gal)




Net Energy Ratio




Pounds of CO2e per BTU (lbs/MMBTU)




Utilizing dedicated energy crops for biofuels production is a key component of ZeaChem's biofuels strategy from both an economic and environmental standpoint. Sustainable dedicated energy crops are cost effective due to the ability to lock in long-term contracts, have a low-carbon footprint based on maximizing yield per acre and harvesting techniques, and when planned in coordination with a biorefinery, offer significant transportation and storage logistics simplification.

 ZeaChem has partnered with GreenWood Resources (GWR), a leading hybrid poplar tree farm operator. Engineering is currently underway for ZeaChem's first biorefinery, which is proposed to be built near GWR's existing tree farm in
Boardman, Oregon.

ZeaChem believes that third-generation biofuels that balance technological, economic and environmental impacts, offer a sustainable solution to the transportation industry.