3.1 Fuel Ethanol from Corn

Ethanol is one of the simplest alcohols that have long been consumed in human history. Ethanol can be readily produced by fermentation of simple sugars that are obtained from sugar crops or converted from starch crops. This has long been practiced throughout the world. Feedstock for such fer­mentation ethanol includes corn, barley, rice, and wheat. This type of etha­nol may be called grain ethanol, whereas ethanol produced from cellulosic biomass such as trees and grasses is called cellulosic ethanol or biomass ethanol. Both grain ethanol and cellulosic ethanol are produced via biochemical pro­cesses, whereas chemical ethanol is synthesized by chemical synthesis routes that do not involve any fermentation step.

Ethanol, ethyl alcohol [C2H5OH], is a clear and colorless liquid. Ethanol has a substituted structure of ethane, with one hydrogen atom replaced by a hydroxyl group, — OH. Ethanol is a clean-burning fuel thanks to its oxygen content and has a high octane rating by itself (Research Octane Number (RON) of 108.6). Therefore, ethanol is most commonly used as an oxygen­ated blend fuel to increase the octane rating of blend gasoline as well as to improve the emission quality of gasoline engines. Due to the presence of the oxygen atom in its molecular structure, ethanol is classified as an oxygenated fuel. In many regions of the United States, ethanol is blended up to 10% with conventional gasoline. The blend between 10% ethanol and 90% conventional gasoline is called "E10 blend" or simply "E10". Ethanol is quite effective as an oxygenated blending fuel, because its Reid vapor pressure is marginally low; that is, it does not increase the volatility of the blend gasoline significantly, unlike methanol. Reid vapor pressure (RVP) is defined as the absolute vapor pressure exerted by a liquid at 100°F (37.8°C) as determined by the standard testing method following ASTM-D-323. The test method also applies to volatile crude oil and volatile nonviscous petro­leum liquids, except liquefied petroleum gases (LPG). Even though the Reid vapor pressure of ethanol is lower than that of methanol, fuel experts still consider it higher than they desire.

Ethanol can be produced from any biological materials that contain appre­ciable amounts of sugars or feedstock that can be converted into sugars. The former include sugarbeets and sugarcane, whereas the latter include starch and cellulose. For example, corn contains starch that can be easily converted into sugar and is, therefore, an excellent feedstock for ethanol fermentation. Because corn can be grown and harvested repeatedly, this feedstock emi­nently qualifies as a renewable feedstock, that is, this feedstock is not going to be simply depleted by exhaustive consumption.

Fermentation of sugars produces ethanol and this process technology has been practiced for well over 2,000 years in practically all regions of the world. Sugars can also be derived from a variety of sources. In Brazil, as an example, sugar from sugarcane is the primary feedstock for the country’s ethanol industry which has been very successful and active. In North America, the sugar for ethanol production is usually obtained via enzymatic hydrolysis of starch-containing crops such as corn or wheat. The enzymatic hydrolysis of starch is a simple, relatively inexpensive, and effective process, and is also a mature commercial technology. Therefore, this process is used as a baseline or a benchmark against which other hydrolysis processes can be compared. The principal merit of ethanol pro­duction by fermentation of sugar/starch is in its technological simplicity and efficiency, however, its demerit is that the feedstock tends to be expen­sive and also competitively used for other principal applications such as food. Therefore, "food versus fuel" or "food versus oil" is an unavoidable critical issue addressing the risk of diverting farmland or crops for produc­tion of biofuels including corn ethanol to the detriment of the food supply on a global or regional scale. It has also contributed to the increase in food price, which in turn raises the cost of feedstock and hurts the profitability of the ethanol industry.

Technoeconomically speaking, this high cost of feedstock can be favorably offset to a certain extent by the sale of by-products or coproducts such as dried distillers grains (DDGs), provided that the high oil price is sustained in the market. Many corn refineries produce both ethanol and other corn by­products such as cornstarches, sweeteners, and DDGs so that the capital and manufacturing costs can be kept as low as possible by maximizing the over­all process revenue. While they are manufacturing ethanol, corn refiners also produce valuable co-products such as corn oil and corn gluten feed. The North American ethanol industry is, therefore, investing significant efforts in developing new value-added by-products (and coproducts) that are higher in value and minimizing the process wastes, thus constantly making the grain ethanol industry more cost-competitive.

Corn refining in the United States has a relatively long history going back to the time of the Civil War with the development of the cornstarch hydro­lysis process. Before this event, the main sources for starch had been com­ing from wheat and potatoes. In 1844, the Wm. Colgate & Company’s wheat starch plant in Jersey City, New Jersey, unofficially became the first dedicated cornstarch plant in the world. By 1857, the cornstarch industry accounted for a significant portion of the U. S. starch industry. However, for this early era of corn processing, cornstarch was the only principal product of the corn refin­ing industry and its largest customer was the laundry business. Cornstarch has also been used as a thickening agent in liquid-based foods such as soups, sauces, and gravies.

The industrial production of dextrose from cornstarch started in 1866. This industrial application and subsequent scientific developments in the chemistry of sugars served as a major breakthrough in starch technology and its processing. Other product developments in corn sweeteners fol­lowed and took place with the first manufacture of refined corn sugar, or anhydrous sugar, in 1882. In the 1920s, corn syrup technology advanced significantly with the introduction of enzyme-hydrolyzed products. Corn syrups contain varying amounts of maltose (a disaccharide formed by a condensation reaction of two glucose molecules joined with an a (1^4) bond) and higher oligosaccharides. Even though the production of etha­nol by corn refiners had begun as early as after World War II, major quan­tities of ethanol via this process route were not produced until the 1970s, when several corn refiners began fermenting dextrose to make beverage and industrial alcohol. As such, the corn refiners’ entry into the fermen­tation business has become a significant milestone for major changes and transformation of the industry, especially in the fuel ethanol indus­try. The corn refining industry seriously began to develop an expertise in industrial microbiology, fermentation technology, separation process technology, energy integration and process design, and by-product and waste utilization.

As of today, starch and glucose (or dextrose) are still important products of the corn wet milling industry. However, the products of microbiology and biochemical engineering including ethanol, fructose, food additives, and target chemicals have gradually outpaced them. New research and devel­opments have significantly expanded the industry’s product/by-product/ coproduct portfolio, thus making the industry more profitable, flexible to market demands, competitive, and technologically advanced.

Lignocellulosic materials such as agricultural, hardwood, and softwood residues are also potential sources of sugars for ethanol production. The cel­lulose and hemicellulose components of these materials are essentially long and high molecular weight chains of sugars. They are protected by lignin, which functions more like "glue" that holds all of these materials together in the structure. Therefore, the liberation of simple sugars from lignocellulosic materials is not as simple and straightforward as that from sugar crops or starch crops. However, the biggest undeniable advantage of cellulosic etha­nol is its use of nonfood feedstock and no detrimental use of arable land for fuel production. Details of cellulosic ethanol technology are covered in Chapter 4 and, therefore, not repeated here.

Ethanol plays three principal roles in today’s economy and environment and they are

1. Ethanol in the United States replaces a significant amount of imported oil with a renewable domestic fuel.

2. Ethanol is an important oxygenated component of gasoline reformu­lation to reduce air pollution in many U. S. metropolitan areas, which are not achieving air quality standards mandated by the Clean Air Act Amendments (CAAA) of 1990. Ethanol is a cleaner-burning fuel due to its oxygen-containing molecular structure and also a superior gasoline blend fuel due to its renewability as a fuel and relatively low Reid vapor pressure of the blended fuel.

3. Ethanol provides a major income boost to farmers and agricultural communities where most ethanol feedstock is produced. Global corn prices have escalated more sharply than other crops due to the increased demand and higher corn prices have in turn motivated farmers to increase corn acreage at the expense of other crops, such as soybeans and cotton, raising their prices as well.

Ethanol, blended with gasoline at a 10% level (E10) or in the form of ethyl tertiary-butyl ether (ETBE) synthesized from ethanol, is effective in reducing carbon monoxide (CO) emission levels, ozone pollution, and NOx emissions from automobile exhaust. Two of the major barriers to the wide acceptance of ethanol as a gasoline blend fuel are: (1) its Reid vapor pressure being not low enough, and (2) its high moisture-absorbing (hygroscopic) characteristics. As mentioned earlier, the Reid vapor pressure of ethanol is lower than that for methanol; however, it is still marginally high.

In its early years the U. S. fuel ethanol industry was expanding to meet the increased demand for oxygenated fuel that resulted from a withdrawal of methyl-tertiary-butyl ether (MTBE) from the domestic gasoline marketplace. In response to sharply rising national concern about the presence of MTBE in groundwater as well as potential risk to public health and the environment, the U. S. Environmental Protection Agency (EPA) convened a Blue Ribbon Panel to assess policy options regarding MTBE. The Blue Ribbon Panel rec­ommended that the use of MTBE be dramatically reduced or eliminated. The EPA has subsequently stated that MTBE should be removed from all gasoline. Many U. S. states including California and New York mandated their own schedules of MTBE phase-outs and bans. As of September 2005, 25 states had signed legislation banning MTBE. According to a survey conducted in 2003, 42 states reported that they had action levels, cleanup levels, or drinking water standards for MTBE [1]. It is a remarkable turnaround in the chemical and petrochemical marketplace considering that MTBE used to be the fastest growing chemical in the United States in the 1990s. Recovering or retrofit­ting the MTBE plant investments would become an issue for this industry for years to come. Even with a rapid decline and disappearance of MTBE in the U. S. market, global production of MTBE has remained relatively constant at about 18 million tons/year, as of 2005, mainly due to the growth in Asian markets, where the use of ethanol or other oxygenated replacements is not established and ethanol subsidies are not provided.

United States fuel ethanol production has been increasing very rapidly for the first decade of the twenty-first century. According to the Renewable Fuels Association (RFA) [2], the U. S. ethanol production in 2002, 2003, and 2004 was 2.13, 2.80, and 3.40 billion U. S. gallons, respectively. Considering the pro­duction level of 2000 being 1.63 billion gallons, this is more than a twofold increase over five years. The U. S. production of ethanol in 2006, 2007, 2008, 2009, and 2010 was 4.9, 6.5, 8.9, 10.75, and 13.2 billion U. S. gallons, respectively. Comparing between the 2007 and 2010 statistics, it took only four years to double U. S. production. The trend in ethanol production in the United States is presented in Figure 3.1, which shows an exponential growth in ethanol production in the United States for the first decade of the twenty-first cen­tury. Due to the high cost of petroleum crude in recent years, the role of etha­nol has realistically expanded far beyond the oxygenated fuel additive into that of a true alternative renewable transportation fuel. The increased use of ethanol in the United States has significantly contributed to the alleviation of dependence on imported petroleum.

Corn refining has also become America’s premier by-products industry, and its success has set a desirable business model for future biofuel indus­tries. Increased production of amino acids, proteins, antibiotics, and biode­gradable plastics has added further value to the U. S. corn crop. In addition to cornstarches, sweeteners, and grain ethanol, corn refiners also produce corn

oils as well as a variety of important feed products. Corn products in the modern world are found in a large variety of areas and applications: (a) live­stock feed grains; (b) food ingredients including sweeteners, starches, and polyols; (c) oil products including corn oil, acid oil, middlings, and corn wax oil; (d) cornstarches for papermaking and corrugated products; (e) personal care products utilizing natural polymers; (f) health and nutrition including sugar-free and low-sugar foods; (g) animal feeds including corn gluten meal, corn germ meal, and steepwater grain solubles; (h) pharmaceutical products including anhydrous dextrose; (i) manufacture of biodegradable polymer, poly(lactic acid; PLA), using cornstarch; and more.

Corn is the most traded crop product in the world with the United States being the leading exporter and Japan being the largest importer. The U. S. annual export of corn was about 50 million metric tons in the fiscal year 2010. Since 1980, the annual amount of U. S. export of corn has been fluctuating between 35 and 60 million metric tons. Even though the United States dominates the global trading market of corn, it accounts for about 15.2% of the total U. S. corn production. As such, corn prices are largely determined by supply-and-demand relationships in the U. S. mar­ket. The U. S. corn crop was valued at $66.7 billion in the fiscal year 2010 and production for the year was 331 million metric tons, which is equiva­lent to 12.1 billion bushels. The U. S. corn growth/production accounted for about 39% of the world production [3]. About 80 million acres were planted to grow corn and most corn production was in the heartland of the United States. Of the total corn produced in the United States in 2010, about 34.9% or 116 million metric tons were used for corn ethanol produc­tion. Figure 3.2 shows the breakdown of 2010 end-uses of corn by end-use categories and sectors in the United States.

The production of ethanol from starch and sugar-based resources in the United States reached 13.2 billion U. S. gallons in 2010. The amount of gaso­line used by the United States for transportation was approximately 140 bil­lion U. S. gallons per year in 2011, with ethanol used as a blend stock of up to 10% in marketed gasoline (E10) and also with a smaller E85 (85% ethanol) market. As ethanol production increases, the demand for ethanol in the fuel supply chain has nearly reached the 10% "blend wall" of 14 billion gallons. The Energy Independence and Security Act (EISA) of 2007 requires a manda­tory Renewable Fuel Standard (RFS) requiring transportation fuels sold in the United States to contain a minimum of 36 billion gallons of renewable biofuels by 2022, including advanced and cellulosic biofuels and biomass — based diesel. The EISA further specifies that 21 billion U. S. gallons of the 2022 total biofuel blends in gasoline must be derived from noncornstarch products. Certainly, biomass-derived methanol, biomass-derived diesel, cel — lulosic ethanol, algae biodiesel, vegetable oil biodiesel, and others qualify as noncornstarch based biofuels.