Ethanol made from corn starch sources requires a sizable amount of farmland resources as close to two-thirds of the total corn cultivated is dedicated to produce ethanol for biofuel and animal distillers grains [refer to National Corn Growers Association].
In other words it requires close to 60 million acres of farmland dedicated mainly for ethanol production in order to manufacture around 15 billion gallons of ethanol per year, which is about the amount needed to fulfill ethanol as a 10 % by volume fuel additive to gasoline. It is claimed that ethanol is needed as an oxygenated fuel additive in order to raise the octane number of the fuel and reduce carbon monoxide emissions.
In addition, world wide organizations have asserted that corn production in the United Stated for the main purpose of providing it as a fuel additive to gasoline has caused world food prices to rise dramatically and has also contributed to world food shortages. It is asserted then that the US should come up with alternative renewable fuel production methods that would not compete with the food supply but also be energy efficient in method too.
This essay is dedicated to show that there are alternative alcohol production methods available not only for ethanol but also for higher molecular weight alcohols.
Ethanol manufacture can be done at high volume cost effectively and energy efficiently using lignocellulosic-based wastes utilizing hybrid ethanol manufacture, thermochemical and even algae based production methods.
Mixed alcohols of higher molecular weight that are either branched or linear in structure can be made through carboxylate counter-current fermentation. Mixed alcohols that are linear in structure can also be manufactured through a modification of the thermochemical gasification technology that has mainly been utilized in the past to manufacture diesel fuel.
The butanol family of alcohols are an interesting topic as they are being manufactured from a wide variety of sources such as algae.
n-butanol manufacture, in fact in concept, should be easier to produce than ethanol through fermentation due to the increased ability of bacteria to breakdown cellulose and hemicellulose using their own internal enzymes.
Isobutanol manufacture, another very interesting recent development within the last decade, is starting to compete with other types of alcohol manufacture even though this method depends on genetically modified microbes or algae to accomplish this.
Some of these technologies described below are proprietary or are being developed by research institutions.
lignocellulosic Methods
Alternative ethanol production done with large capacity refineries is not only possible but with the proper support should be cost effective and energy efficient utilizing lignocellulosic based feedstocks.
For example, a synthesis gas fermentation process developed by the company Coskata was supported by the automaker GM as it was claimed that the ethanol at that time could be manufactured under 1 dollar per gallon.
At least four varieties of alternative ethanol manufacture exist, those being:
- thermochemical gasification
- synthesis gas fermentation
- algae based ethanol and
- fermentative acetic acid conversion (The Zeachem production model).
These technologies are all supported by the Integrated Biorefinery Demonstration Program.
Both synthesis gas fermentation and fermentative acetic acid conversion could be considered hybrid ethanol processing methods, since a combination of fermentation and thermochemical processing are both implemented in order to manufacture the ethanol.
A rough diagram of the synthesis gas production model is shown in the image above.
It is similar to thermochemical gasification, since it also produces synthesis gas from biomass but adds the capability of fermenting the carbon from the synthesis gas towards the eventual manufacture of ethanol.
The fermentative acetic acid conversion process is similar to the counter-current fermentation technology but yet is very different in the idea that it uses a specialized bacteria that are able to convert cellulosic sources specifically into acetic acid instead of a combination of organic acids as is done by the carboxylate counter-current fermentation.
n-butanol manufacture can be done through a variety of fermentation methods, most notably the ABE (Acetone-Butanol-Ethanol) fermentation method developed on an industrial scale during the early part of the 1900′s.
It is a very effective fermentation method since it can implement a variety of common bacteria called Clostridia spp.
The USDA has been doing a good amount of research on converting lignocellulosic crop wastes such as corn stover, wheat straw and even switchgrass into butanol. Less chemical intensive and more energy efficient pretreatment methods allow lignocellulosic material to be converted into butanol through fermentation as is done by the company Cobalt Technologies located in California.
Butanol production also has another interesting caveat not yet fully developed as of yet. It is theoretically possible, in fact perhaps even easier to ferment lignocellulosic waste material into n-butyrate.
However, the n-butryate must then be further converted into n-butanol either through hydrogen or electrochemical based reduction methods, which still requires some research. Related to butyrate fermentation is caproate fermentation, which by the same reduction methods could be turned into n-hexanol.
The process of separating caproate from the fermentation solution is also reported to be easier than working with n-butyrate due to its high insolubility in water. Researchers both from the Netherlands and Cornell University are working on such projects.
Genetically modified microbes or algae developed during the last decade or so are also allowing the manufacture of either ethanol or isobutanol to be made.
The company Algenol has already patented a process called Direct to Ethanol(R) in order to produce ethanol from seawater and carbon dioxide utilizing outdoor photobioreactors. They have done this in part, by genetically modifiying algae with the ability to directly convert pyruvate into ethanol. However, the important breakthrough is the ability of the genetically modified algae assimilating carbon dioxide for the eventual production of ethanol.
Algenol is also one of the three algae based companies that have qualified for DOE grant funding based on the Integrated Biorefineries Demonstration Program. This manufacturing method also has other potential attractive environmental and energy related developments for refineries that are built in desert regions near the ocean such as providence of fresh water and cooperatives with other manufacturing or electrical generation plants.
Two other companies (BAL and Dupont), are also working cooperatively to ferment the sugars contained in macroalgae (ie kelp) with genetically modified microbes in order to produce isobutanol (ethanol production has also been accomplished too).
Macroalgae itself in the future could be implemented as another major biofuel feedstock as it contains a large amount of various sugar sources. In the mid-part of the 1900′s, macroalgae had been cultivated on a large scale in order to manufacture a variety of chemicals, mainly in areas off the coast of California.
In addition, researchers from the University of California have successfully cultivated another type of genetically modified cyanobacteria that can assimilate either carbon dioxide or bicarbonate in order to make isobutyraldehyde (which can further be converted into isobutanol). The yields from such a process appear to be quite promising.
Of very important mention is the ability to manufacture mixed alcohols either from counter-current fermentation or through thermochemical gasification, which is a variation of the Fischer-Tropsch production model developed by the Germans around the mid 1900′s.
Counter-current fermentation is a potentially useful alcohol or hydrocarbon based mid to high volume refinery manufacturing method developed by researchers at Texas A & M (Dr. Mark Holtzapple) during the 1990′s. It can manufacture either straight chained alcohols such as ethanol, propanol, butanol, pentanol from an esterification based method or branched alcohols like the three shown at the header image of the website (isopropanol, 2-butanol, 2-pentanol, etc.) from a ketonization method.
Branched alcohols such as these would also make an excellent oxygenated fuel additive, even better than ethanol since they have a higher energy content, are less chemically corrosive and due to their branched chemical structure, they should be potentially much better in increasing the octane number of gasoline fuel when mixed into it.
The image above shows a rough outline of the manufacturing process in general.
Carboxylate counter-current fermentation manufacture similar to fermentative acetic acid conversion provides for its own electrical power requirements and hydrogen providence for the alcohol conversion process utilizing the left over waste resources during pre-treatment or fermentation. This method also has the added ability to recycle water as well as carbon dioxide from technologies such as Pressure Swing Adsorption and vapor compression steam stripping (VCSS).
The counter-current fermentation method also has major implications towards environmental remediation as it has the potential to recycle various types of municipal waste towards the manufacture of vehicle fuels.
The company Terrabon in Texas liscenses the MixAlco(R) patented process for the counter-current fermentation process developed by Dr. Holtzapple. Also important to mention is that thermochemical gasification (F-T manufacture) is another potentially high volume production method capable of manufacturing ethanol or mixed alcohols from municipal waste sources as well. Several companies are already developing integrated biorefineries that make ethanol from landfill wastes.
Some of these include Enerkem, based out of Canada and Fulcrum Sierra Biofuels constructing a facility in Reno Nevada. Also of environmental importance is the possible conversion of lumber mill waste into ethanol through fermentation of the hydrosylate waste from the manufacturing process. American Process Inc. in Michigan is in the process of manufacturing ethanol, potassium acetate and possibly butanol from panelling board lumber mill type of wastes.
The key to getting these alternative fuels ‘off the ground’ so to speak is to further develop the Departments of Energy and Agricultures concept of the Integrated Biorefinery, which has the potential advantage of bringing forth biofuel refineries that would manufacture alcohols comparable to the production capacity of ethanol based dry grind corn mills (ie millions of gallons of biofuel per year per refinery).
The inclusion of an Integrated Biorefinery Program is and should be necessary in order to achieve initial alternative biofuel based pilot plant production goals of under 1 million gallons of fuel per year per refinery. Since many of these technologies are fairly recent in development, they would require demonstration plant capacity type of planning before many other larger volume capacity refineries can be built and utilized.
Also, the key to effectively converting possible switchgrass into biofuel is developing numerously scattered integrated biorefineries in certain regions of the United States. This is necessary in order to induce switchgrass cultivators to deliver their energy crop since the transportation and storage costs for farmers are a large part of the overall cost of cultivation. The option of retrofitting existing corn starch ethanol refineries are also not amenable to alternative ethanol manufacture since the equipment contained at a dry grind mill is meant specifically for both corn starch ethanol and animal feed production, corn kernel material is drastically different in structure and thus requires very different separation technologies than what is needed for lignocellulosic based alcohol manufacture.
In the future, a greater explanation of the material presented in this short synopsis should be useful not only for energy policy related matters but also for interested students and other professionals as well.