Ethanol as the Alternative Fuel for Vehicle By Yong Sam Ng, Chemical Engineering student Introduction Ethanol is a primary liquid fuel synthesized from renewable sources. World ethanol production for transport fuel in 2000 increased from 17 billion Liters to 52 billion Liters in 2008. [1] This proves ethanols potential as a gasoline subsidiary/substitute in powering our vehicles. This paper discusses why ethanol is the right candidate for replacing gasoline as the transport fuel and how advances in technology will make ethanol production from biomass feedstock more efficient and profitable than traditional production method. Why not longer chain alcohols? Longer chain alcohols such as propanol and butanol are more reduced than ethanol and have higher energy density. They can be used as drop-in fuels while ethanol cannot. So, why are they not synthesized from biomass resources? The product from photosynthesis, also known as photosynthate, is primarily comprised of 1 part of carbon, 2 parts of hydrogen and 1 part of oxygen. This photosynthate serves as the building block for many types of biomass compound. To synthesize highly reduced biomass compound from photosynthate, more photosynthate will be used and multi-step biochemical conversion is required. Thermodynamically, this is not favored and the product yield for highly reduced compound will be very low. Thus, many biomass feedstocks, such as corn stover, eucalyptus, sugarcane bagasse, switchgrass, hybrid poplar and Monterey pine, have a general CHO composition of CH1.45O0.65, which is close to CH2O composition. [2]

Synthesizing longer chain alcohols from this CH2O feedstock requires a compensation for a lower product yield. The theoretical product yield of CH2O conversion to ethanol is 51%. The theoretical yield for CH2O conversion to butanol is 41%. [2] Therefore, the winning strategy for biomass fuel production is to synthesize a product which has found successful application as fuel blend/substitute and has higher product yield in the synthesis process. And that product is ethanol. Compatibility of car engine with ethanol-blended fuels In the 1860s, Nicholas Otto from Germany invented the spark fired internal combustion engine, which is the most commonly used type of engine in cars, aircraft and boats nowadays. In 1896, Henry Ford designed his first car which ran purely on ethanol. He later produced cars capable of

running on gasoline, ethanol or a combination of both. Cheaper gasoline price in the 1900s had made gasoline the primary choice of many car users. The internal combustion engine functions by the basic principle of high pressure fuel combustion to produce mechanical energy. The fuel will first be compressed, resulting in an increase of pressure, temperature and density, before it is sent into a chamber. Combustion of high pressure and temperature fuel in the chamber produces energy to move the crank shaft of the engine. This type of engine requires liquid fuels of good volatility and high octane rating. Ethanol is particularly suitable for the engine, especially in a blend with gasoline at an ethanol composition between 3% and 85%. [2]

Comparative properties with gasoline The comparative properties between ethanol and gasoline have made ethanol suitable for blending with gasoline or as gasoline substitute. While gasoline has a density between 0.72 to 0.78 g/mL, ethanol has a density of 0.7893 g/mL. While gasoline has a boiling point between 25 to 225 C, ethanol has a boiling point of 78.5 C. [2] Ethanol is also shown to have higher octane rating than gasoline, with the MON (Motor Octane Number) for ethanol being 92 while the MON for gasoline being 82 to 90. [2] The octane rating shows that ethanol can withstand higher compression before it detonates, which is required by the internal combustion engine. However, being a more oxygenated fuel than gasoline, ethanol is approximately 33% lower in heat of combustion than gasoline. [2] Due to the presence of oxygen atom in ethanol, hydrogen bonding increases the attraction between ethanol molecules. As a result, ethanol has a higher heat of vaporization and a lower vapor pressure than gasoline. Emissions Gasoline was ranked as the number one source of toxic emissions in 1995 due to its carcinogenic components. [3] On the other hand, ethanol is cleaner than gasoline; it emits less hydrocarbons, nitrogen oxides and carbon monoxide. Blending ethanol in gasoline is able to reduce emissions of carbon monoxide, volatile organic compounds (VOC), toxics content and fine particulate matter at combustion. Public concerns over the air quality prompted the government to enact the Clean Air Act Amendments in 1990. Standards for reformulated gasoline (RFG) have been specified. Being a cleaner fuel and having comparative properties with gasoline, ethanol thus becomes a key component in RFG to meet the clean fuel specifications set by the law. RFG formulated with ethanol has been found to reduce the cancer risk caused by toxic emissions from gasoline by 20 to 30%. [3]

Engine efficiency Higher fuel compression ratio can be achieved with the use of ethanol as the combustion fuel because of its higher octane rating than gasoline. This in turn allows increased volume of ethanol to be sent into the chamber, as a compensation for its lower energy content than gasoline. Besides having a higher octane rating, ethanol also has faster flame propagation speeds than gasoline. This results in increased engine efficiency for high ethanol composition blend with gasoline. The increased efficiency (measured in miles per BTU of energy present in the fuel used) was observed in 2006-2007 vehicles in a study of EPA certification data by Chevron. The EPA certification data for vehicle models in year 2010 have also shown that the use of E85 in 2010 model vehicles improves engine efficiency by 2%, when compared to pure gasoline use. [2]

What limits the use of higher ethanol content RPG (more than 15% ethanol) is the difficulty to transition from a predominantly gasoline fuel to a predominantly ethanol fuel at commercial scale in a short period of time. The transition also requires modification of the engine to accommodate higher compression ratio which becomes necessary with the use of predominantly ethanol fuel. Two pathways of ethanol production from biomass Two primary methods of producing ethanol from biomass feedstock are the biochemical approach and the thermochemical approach. The biochemical approach emulates the metabolic process wherein sugar is broken down to produce energy and ethanol as the side product in an anaerobic condition. The biochemical process is named fermentation. The thermochemical approach processes biomass feedstocks at high pressure and converts them into syngas (carbon monoxide, hydrogen and carbon dioxide). The syngas can then be converted into ethanol through a catalyzed reaction. Several challenges associated with both approaches have limited the commercialization of either process to produce bulk quantity of ethanol. Before the biomass feedstock is sent to the batch reactor for fermentation, it needs to be pretreated at high pressure and high temperature to separate cellulose and hemicellulose from the lignin. This pretreatment process is expensive and increases waste productions, production cost, and capital cost. The discarded lignin wastes are rich in energy content. Lignin consists of 25 to 35% of the total energy content in the feedstock. [2] Fermentation is unable to convert lignin into ethanol. The reactor condition (temperature, pressure, and pH) also has to be carefully monitored to ensure maximum conversion since the biological enzyme only functions efficiently at its optimum condition. One of the major drawbacks for the thermochemical process is the lack of selectivity. A typical catalysis reaction fed with syngas produces a mixture of alcohols ranging from C1 to C6. The selectivity for ethanol production is only 45%. [2] Therefore, separation of ethanol from other types of alcohol at downstream processing will be challenging and increase the manufacturing

cost. Gasification also has to be carried out under high pressure (more than 1000 psig), [2] which increases the mechanical complexity and the capital cost. Before syngas is sent to the catalysis reactor, it has to be purified to avoid other components from poisoning the catalyst. The purification process is very rigorous and thus, adds to the capital and operating costs. Hybrid process Indeed, both processes offer a few advantages which the other one does not. Therefore, the combination of thermochemical and biochemical elements has been proposed. In this hybrid process, biomass feedstock will be first converted into syngas by using gasification. Microorganisms are used to ferment the syngas into ethanol. The ethanol product is then separated from water to produce fuel grade ethanol. The biomass feedstock conversion to syngas is more than 75%. The syngas conversion to ethanol has a theoretical yield of more than 95%. [2]

The heat generated in the gasification process can be exploited for downstream processing step, especially for drying and distillation to recover fuel grade ethanol. This hybrid process is superior to either process alone. Commercialization of the process has been proven possible by companies such as INEOS Bio, Lanzatech and Coskata. Details are illustrated in the following sections. First advanced waste-to-fuel commercial biorefinery in US INEOS Bio The first commercial biorefinery in US, which is located in Vero Beach, Florida, is expected to start its production in mid-2012. This biorefinery was developed under the INEOS New Planet BioEnergy (INPB), a joint venture between INEOS Bio and New Planet Energy. The plant will produce 8 million gallons of bioethanol per annum and 6 Megawatts of renewable power from local yard, vegetative and household wastes. 2 Megawatts of the renewable power will be exported to local community to power approximately 1,400 homes. [4]

The plant runs on INEOS Bio gasification and fermentation technology. The hybrid technology has been patented by INEOS in 2009 (WO 2009/112334 A1). The process for ethanol production illustrated in the patent comprises of three stages. At the first stage, fermentable biomass feedstock is first subjected to anaerobic fermentation to produce a solution consisting of acetic acid as the predominant product. The gasifiable biomass feedstock is subjected to gasification to produce gaseous mixture of carbon monoxide and hydrogen. At the second stage, both acetic acid solution and gaseous mixture produced in the first stage are subjected to further fermentation to produce ethanol. At the last stage, the ethanol product stream is sent to a distillation column and then to drying molecular sieves to produce ethanol product of more than 99 wt%. [5]

This process is claimed to offer a few advantages over the conventional gasification process. Even though carbon dioxide is also produced during gasification at the first stage, the amount is less than the carbon monoxide produced. The bacteria used for fermentation at the second stage

can produce ethanol from both carbon dioxide and carbon monoxide with different reaction pathways. However, CO conversion to ethanol is higher than CO2 conversion. [5] The fermentation process at the first stage also increases conversion at the second stage. Converting acetic acid to ethanol is a more efficient use of carbon content than gasification. This process also efficiently utilizes the mixed waste feedstock which often comprises of both fermentable and gasifiable components. Coskata technology progress Coskata is a biology-based renewable energy company that produces feedstock flexible ethanol through its proprietary microorganisms from a variety of material such as biomass, agricultural and municipal wastes. [6] Coskatas ethanol production process also consists of three stages. At the first stage, lignocellulosic feedstock is gasified to produce syngas that contains carbon monoxide and hydrogen. At the second stage, the syngas is sent to a bioreactor for fermentation by using Coskatas proprietary microorganisms. The types of microorganisms selectively produce ethanol from the syngas. At the last stage, ethanol product is purified via distillation and molecular sieve dehydration. [2]

A few key advantages of the Coskata process include feedstock flexibility because the process can utilize any biomass feedstock such as switchgrass, forestry products, corn stover, bagasse, and agricultural wastes, municipal and industrial organic wastes. Gasification at the first stage allows all biomass material to be utilized in the process. [2] Coskatas proprietary microorganisms selectively produce ethanol, with higher selectivity than chemical catalysis. The lower operating cost and capital cost allows the process to be commercialized. The LanzaTech Process LanzaTech was founded in early 2005. Its primary goal is to develop and commercialize proprietary technologies for the production of low carbon fuels that do not compromise food or land resources. [7] The Lanzatech process inputs carbon monoxide containing gases produced by industries (such as steel manufacturing, oil refining and chemical production), gasification of forestry and agricultural residues, municipal waste and coal to produce valuable fuel and chemical products. [8] The carbon monoxide containing gas is converted to fuels/chemical products in a bioreactor which contains LanzaTechs proprietary microbes. This process provides a route to reuse carbon while minimizing environmental impact caused by waste gases. Conclusion: In this paper, it has been established that most biomass feedstock is highly oxygenated. The viable product to be synthesized from this biomass feedstock is ethanol because it is thermodynamically favored over longer chain alcohols and has comparative properties with gasoline to be used as transport fuel. The internal combustion engine performs more efficiently and emits less pollutant when gasoline/ethanol blend is used as the fuel, especially at an ethanol

composition between 3% and 85%. Hybrid process that combines fermentation and gasification to produce ethanol has made ethanol production from biomass more efficient and profitable. The process has been commercialized by Coskata, INEOS-Bio and Lanzatech companies in the US. References: 1. Wikipedia, updated April 23, 2012, Ethanol fuel, retrieved May 3, 2012, from: http://en.wikipedia.org/wiki/Ethanol_fuel . 2. Datta, R., Maher, M. A., Jones, C. and Brinker, R. W., Ethanolthe primary renewable liquid fuel, pp. 473480, J. Chem. Technol. Biotechnol., 86, 2011. 3. Ethanol Fact Book, Clean Fuels Development Coalition, www.cleanfuelsdc.org, 2010. 4. Cummings, D., McClenahan, H., Akbarzad, S., INEOS Bio JV breaks ground on 1st advanced waste-to-fuel commercial biorefinery in US, INEOS press releases, Feb 9, 2011. 5. International patent WO 2009/112334 A1, Sept 17, 2009. 6. Coskata Inc., updated 2012, Introduction to company, retrieved April 30, 2012, from: http://www.coskata.com/ . 7. Lanzatech, updated 2010, Who we are, retrieved April 30, 2012, from: http://www.lanzatech.co.nz/content/who-we-are. 8. Lanzatech, updated Dec 16, 2011, The Lanzatech Process, retrieved April 30, 2012, from: http://www.lanzatech.co.nz/content/lanzatech-process.