ZeaChem uses termite gut microbe for ethanol: up to 50% yield increase
A type of bacteria that helps termites digest wood could be key to making ethanol cheaply from non-food crops such as wood and grass. ZeaChem, a startup based in Menlo Park, California, has developed a hybrid biochemical and thermochemical process that utilizes all fractions of the biomass feed and converts it with Moorella thermoacetica. The process can yield 50 percent more ethanol from a given amount of biomass than conventional processes. The net energy ratio of biofuel produced this way is between 10 and 12, compared with first generation biofuels like corn ethanol, which come in at around 1.5. The new net energy ratio benchmark radically changes any biofuel policy debate.
The company has demonstrated the new method in a laboratory setting and is now drawing up plans for an ethanol plant that will produce about two million gallons of ethanol a year. Construction could begin as early as this year, says Dan Verser, a founder and vice president of research and development at ZeaChem. It is one of a growing number of biofuel companies seeking to make ethanol from biomass instead of corn, since corn requires large amounts of land, water, and energy to grow.
Acetic acid
ZeaChem's approach to biorefining uses a combination of biochemical and thermochemical processing steps (schematic, click to enlarge). The hybrid process improves yield by making more efficient use of biomass than conventional techniques do. It begins, as do other techniques for making ethanol, with breaking down biomass into sugars. At this point, conventional processes use yeast to ferment the sugars into ethanol. But this process is wasteful: about a third of the carbon in the sugars never makes it into the fuel. Instead, it's released into the atmosphere as carbon dioxide.
ZeaChem replaces yeast with a type of bacteria called Moorella thermoacetica, which can be found in a number of places in nature, including termite guts and the ruminant of cows, where it helps break down grass. Instead of making ethanol and carbon dioxide, the bacteria convert sugars into a component of vinegar called acetic acid, a process that releases no carbon dioxide.
To convert acetic acid into ethanol, ZeaChem turns to chemistry. First, the company's researchers convert the acid into a common solvent called ethyl acetate - something that chemists have long known how to do. The final step - making ethanol - requires adding energy to the system in the form of hydrogen.
To get the hydrogen, ZeaChem uses material left over from the process that converts biomass into sugars. This material, called lignin, can be converted into a hydrogen-rich mixture of gases by gasification. The hydrogen is then combined with ethyl acetate to make ethanol:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: ethanol :: gasification :: fermentation :: lignocellulose :: efficiency ::
The remaining gases in the mixture are fed back into the process to provide the energy needed for gasification, making use of material that otherwise would have gone to waste and eliminating the need to use fossil fuels. So far, the company has shown more than 40 percent better yield compared with conventional approaches, and it sees a theoretically possible improvement of 50 percent.
The new approach allows both fermentable and non-fermentable fractions of the feedstock to contribute chemical energy to the ethanol product. Other techniques have theoretical restrictions that limit ethanol production to 60-100 gallons per dry ton of biomass. The ZeaChem technology gets up to half more than that out of a ton.
Because the yield is so much higher and because energy integration is tighter, the ZeaChem process is friendlier to the environment. According to the company, ethanol produced by corn dry milling in the US has a net energy ratio of under 1.6, meaning that fewer than 1.6 units of renewable energy are produced for each unit of fossil energy used in the production the crops and conversion of the crops into fuel ethanol. In contrast, the ZeaChem technology enables a net energy ratio of 10-12. Such high values fundamentally change the nature of any policy debate on the environmental aspects of ethanol as a liquid transportation fuel.
The biochemical processing step can ferment any fermentable sugar, including simple sugars like those found in sugar cane juice, more complex sugars found in corn starch, and the mixed sugars commonly found in cellulosic hydrolyzates. Any material that isn't readily fermented, such as lignin, can be processed via thermochemical means to produce hydrogen. The result is that the ZeaChem technology is highly flexibile and can be implemented anywhere in the world.
According to James McMillan, a research scientist and group manager at the National Renewable Energy Laboratory (NREL), says this is a very innovative process. He says that it's important to get as much ethanol from the feedstock as possible, since the final cost of ethanol depends heavily on the cost of feedstock. Although ZeaChem's process is more complicated than methods used now, and building ethanol plants that use it will cost more, McMillan says that the improved yield could make up for these increased costs.
Picture: a rare sample of ethanol created from wood chips using a new process. So far the alcohol is made a few bottles at a time, but in a couple of years millions of gallons could be available. Credit: Karen T. Borchers/Mercury News
References:
ZeaChem: Technology Overview.
MIT Technology Review: Creating Ethanol from Wood More Efficiently - February 5, 2008.
The company has demonstrated the new method in a laboratory setting and is now drawing up plans for an ethanol plant that will produce about two million gallons of ethanol a year. Construction could begin as early as this year, says Dan Verser, a founder and vice president of research and development at ZeaChem. It is one of a growing number of biofuel companies seeking to make ethanol from biomass instead of corn, since corn requires large amounts of land, water, and energy to grow.
Acetic acid
ZeaChem's approach to biorefining uses a combination of biochemical and thermochemical processing steps (schematic, click to enlarge). The hybrid process improves yield by making more efficient use of biomass than conventional techniques do. It begins, as do other techniques for making ethanol, with breaking down biomass into sugars. At this point, conventional processes use yeast to ferment the sugars into ethanol. But this process is wasteful: about a third of the carbon in the sugars never makes it into the fuel. Instead, it's released into the atmosphere as carbon dioxide.
ZeaChem replaces yeast with a type of bacteria called Moorella thermoacetica, which can be found in a number of places in nature, including termite guts and the ruminant of cows, where it helps break down grass. Instead of making ethanol and carbon dioxide, the bacteria convert sugars into a component of vinegar called acetic acid, a process that releases no carbon dioxide.
To convert acetic acid into ethanol, ZeaChem turns to chemistry. First, the company's researchers convert the acid into a common solvent called ethyl acetate - something that chemists have long known how to do. The final step - making ethanol - requires adding energy to the system in the form of hydrogen.
To get the hydrogen, ZeaChem uses material left over from the process that converts biomass into sugars. This material, called lignin, can be converted into a hydrogen-rich mixture of gases by gasification. The hydrogen is then combined with ethyl acetate to make ethanol:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: ethanol :: gasification :: fermentation :: lignocellulose :: efficiency ::
The remaining gases in the mixture are fed back into the process to provide the energy needed for gasification, making use of material that otherwise would have gone to waste and eliminating the need to use fossil fuels. So far, the company has shown more than 40 percent better yield compared with conventional approaches, and it sees a theoretically possible improvement of 50 percent.
The new approach allows both fermentable and non-fermentable fractions of the feedstock to contribute chemical energy to the ethanol product. Other techniques have theoretical restrictions that limit ethanol production to 60-100 gallons per dry ton of biomass. The ZeaChem technology gets up to half more than that out of a ton.
Because the yield is so much higher and because energy integration is tighter, the ZeaChem process is friendlier to the environment. According to the company, ethanol produced by corn dry milling in the US has a net energy ratio of under 1.6, meaning that fewer than 1.6 units of renewable energy are produced for each unit of fossil energy used in the production the crops and conversion of the crops into fuel ethanol. In contrast, the ZeaChem technology enables a net energy ratio of 10-12. Such high values fundamentally change the nature of any policy debate on the environmental aspects of ethanol as a liquid transportation fuel.
The biochemical processing step can ferment any fermentable sugar, including simple sugars like those found in sugar cane juice, more complex sugars found in corn starch, and the mixed sugars commonly found in cellulosic hydrolyzates. Any material that isn't readily fermented, such as lignin, can be processed via thermochemical means to produce hydrogen. The result is that the ZeaChem technology is highly flexibile and can be implemented anywhere in the world.
According to James McMillan, a research scientist and group manager at the National Renewable Energy Laboratory (NREL), says this is a very innovative process. He says that it's important to get as much ethanol from the feedstock as possible, since the final cost of ethanol depends heavily on the cost of feedstock. Although ZeaChem's process is more complicated than methods used now, and building ethanol plants that use it will cost more, McMillan says that the improved yield could make up for these increased costs.
Picture: a rare sample of ethanol created from wood chips using a new process. So far the alcohol is made a few bottles at a time, but in a couple of years millions of gallons could be available. Credit: Karen T. Borchers/Mercury News
References:
ZeaChem: Technology Overview.
MIT Technology Review: Creating Ethanol from Wood More Efficiently - February 5, 2008.
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