Although propanols are three carbon alcohols with the general formula C3H8O, they are rarely used as fuels. Isopropanol (also called rubbing alcohol) is fre­quently used as a disinfectant and considered to be a better disinfectant than ethanol, but it is rarely used as a fuel. It is a colorless liquid like the other alcohols and is flammable. It has a pungent odor that is noticeable at concentrations as low as 3 ppm. Isopropanol is also used as an industrial solvent and as a gasoline additive for dealing with problems of water or ice in fuel lines. It has a freezing point of -89°C and a boiling point of 83°C. Isopropanol is typically produced from propene from decomposed petroleum, but can also be produced from fer­mentation of sugars. Isopropanol is commonly used for chemical synthesis or as a solvent, so almost 2M tons are produced worldwide.

CONCLUSIONS

In today’s fuel market, methanol and ethanol are the only commercially viable fuels. Both methanol and ethanol have been blended with gasoline, but ethanol is the current choice for gasoline blends. Methanol has found its place in the market as an additive for biodiesel and as a fuel for direct methanol fuel cells, which are being studied as an alternative for rechargeable batteries in small electronic devices. Currently, butanol is too expensive to compete with ethanol in the blended fuel market, but researchers are working on methods to decrease cost and efficiency of production to allow for butanol blends, because the vapor pressure difference has environmental advantages. Governmental initiatives should ensure an increased use of alcohol-based fuels in automobiles and other energy conversion devices.

REFERENCES

1. Ford Predicts Fuel From Vegetation, The New York Times, Sept. 20, 1925, p. 24.

2. National Geographic, 31, 131, 1917.

3. Borth, C., Chemists and Their Work, Bobbs-Merrill, New York, 1928.

4. Kovarik, B., Henry Ford, Charles F. Kettering and the Fuel of the Future, Automot. Hist. Rev., 32, 7-27, 1998.

5. Toxicology and Applied Pharmacology, Academic Press, Inc., 16, 718, 1970.

6. Raw Material Data Handbook, Vol. 1: Organic Solvents, Nat. Assoc. Print. Ink Res. Inst., 1, 44, 1974.

7. National Institute for Occupational Safety and Health, U. S. Dept. of Health, Education, and Welfare, Reports and Memoranda, DHHS, 92-100, 1992.

Ethanol was promoted at the end of the twentieth century for its environmental benefits as an oxygenate in reducing organic carbon emissions. Now, however, the advantages associated with reduced CO2 emissions and oil imports are increas­ingly cited. A prime concern in justifying the use of bioethanol is calculating the benefit of using it for fuel, from an energy savings basis. Most energy analyses have shown that ethanol contains more energy than the fossil fuels used to produce it [3-5]. The average energy output/input ratio is 1.57 and 1.77 for the wet-milling and dry-grind ethanol processes, respectively [6]. These values are life-cycle estimates, meaning that they include all energy inputs and outputs from growing the corn to transporting the ethanol to market. In other words, on average approx­imately 67% more energy captured from the sun (by photosynthesis) is retained in ethanol than the fossil fuel energy used to grow and harvest the corn and convert it to ethanol. By comparison, the energy obtained from gasoline is 20% lower than the fossil inputs for production [5].

Advances in agronomics, fertilizer production and application, and the etha­nol production process have significantly decreased energy requirements, reduc­ing by half the energy currently required for ethanol production compared to that required in the late 1970s. As the ethanol industry matures, the net energy gains are likely to increase further. A recent example is the cold-starch hydrolysis process, discussed later in this chapter, which uses less energy for ethanol pro­duction. Another key consideration regarding the use of fuel ethanol is how well it acts as a replacement for imported liquid transportation fuel. Much of the energy that goes into making ethanol is in the form of coal and natural gas used to operate fertilizer and ethanol plants. Therefore, it has been estimated that more than six gallons of ethanol are produced for each gallon of petroleum used [7].

Thaddeus C. Ezeji,1 Nasib Qureshi,2 Patrick Karcher,1 and Hans P. Blaschek1

1University of Illinois, Biotechnology & Bioengineering Group, Department of Food Science & Human Nutrition, Urbana

2United States Department of Agriculture, National Center for Agricultural Utilization Research, Fermentation/Biotechnology, Peoria, Illinois

CONTENTS

Introduction…………………………………………………………………………………………………… 100

Butanol Production from Corn……………………………………………………………………… 101

Amylolytic Enzymes and Solventogenic Clostridia………………………….. 101

Biochemistry of Butanol Production from Corn……………………………….. 103

Butanol Production from Corn Coproducts……………………………………… 106

Corn Fiber……………………………………………………………………………….. 106

Corn Steep Water……………………………………………………………………. 107

Butanol Production Processes…………………………………………………………… 108

Batch Process………………………………………………………………………….. 108

Batch Process with Concentrated Sugar Solutions………………….. 110

Fed-Batch Fermentation…………………………………………………………. 111

Continuous Fermentation……………………………………………………….. 111

Enhancement of Substrate Utilization and Butanol Productivity…………………. 113

Novel Downstream Processing………………………………………………………….. 113

Gas Stripping…………………………………………………………………………… 113

Pervaporation………………………………………………………………………….. 114

Liquid-Liquid Extraction…………………………………………………………. 116

Perstraction……………………………………………………………………………… 116

Economic Scenarios………………………………………………………………………………………. 117

Economics of Butanol Production……………………………………………………. 117

Conclusion…………………………………………………………………………………………………….. 117

References…………………………………………………………………………………………………….. 118

Abstract The last few decades have witnessed dramatic improvements made in the production of fuels and chemicals from biomass and fermentation derived butanol production from corn is no exception. The art of producing butanol from corn that existed during World Wars I and II is no longer seen as an art but rather as science. Recent developments have brought, once again, the forgotten acetone butanol ethanol (ABE) fermentation from corn closer to commercialization. Supe­rior strains have been developed, along with state-of-the-art upstream, down­stream, and fermentation technologies. Butanol can be produced not only from corn starch as was done decades ago, but also from corn coproducts such as corn fiber and corn steep liquor (CSL) as a nutrient supplement. These additional substrates add to the improved yield and superior economics of the butanol process. Downstream processing technologies have enabled the use of concen­trated sugar solutions to be fermented, thereby resulting in improved process efficiencies. Application of fed-batch fermentation in combination with in situ/inline product recovery by gas stripping and pervaporation is seen as a superior technology for scale-up of butanol production. Similarly, continuous fermentations (immobilized cell and cell recycle) have resulted in dramatic improvement in reactor productivities. This chapter details all the above devel­opments that have been made for production of butanol from corn. As of today, butanol production from corn is competitive with petrochemically produced butanol.

INTRODUCTION

Butanol is a four-carbon alcohol, a clear neutral liquid with a strong characteristic odor. It is miscible with most solvents (alcohols, ether, aldehydes, ketones, and aliphatic and aromatic hydrocarbons), is sparingly soluble in water (water solu­bility 6.3%) and is a highly refractive compound. Currently, butanol is produced chemically by either the oxo process starting from propylene (with H2 and CO over rhodium catalyst) or the aldol process starting from acetaldehyde (Sherman, 1979). Butanol is also produced by fermentation of corn and corn-milling by­products. Butanol is a chemical that has excellent fuel characteristics. It contains approximately 22% oxygen, which when used as a fuel extender will result in more complete fuel combustion. Use of butanol as fuel will contribute to clean air by reducing smog-creating compounds, harmful emissions (carbon monoxide) and unburned hydrocarbons in the tail pipe exhaust. Butanol has research and motor octane numbers of 113 and 94, compared to 111 and 92 for ethanol (Ladisch, 1991). Some of the advantages of butanol as a fuel have been reported previously (Ladisch, 1991).

Butanol production by fermentation dates back to Louis Pasteur (1861) who discovered that bacteria can produce butanol. In 1912, Chaim Weizmann (who later became the first president of Israel) isolated a microorganism that he called BY, which was later named Clostridium acetobutylicum. This microorganism is able to ferment starch to acetone, butanol, and ethanol. The first commercial butanol fermentation plant in the United States was built in Terre Haute, Indiana in 1918 by commercial Solvents Corporation using com as the substrate and C. acetobutylicum as the fermenting microorganism. By 1945, the acetone — butanol fermentation was second in importance only to ethanol production by yeast (Durre, 1998). The ultimate demise of the commercial butanol fermentation process in the United States occurred in the early 1960s due to unfavorable economic conditions brought about by competition with the petrochemical indus­try. Additionally, butanol fermentation suffered from severe limitations including low product yield, low productivity, and low final product concentrations due to butanol toxicity (Qureshi et al., 1992). However, recent advances in strain devel­opment combined with advanced fermentation and product recovery technologies have, at least partially, overcome the above problems (Annous and Blaschek, 1991; Durre, 1998; Qureshi and Blaschek, 2001a; Ezeji et al., 2003 and 2004). The strain that was used for the commercial production of acetone (butanol was C. acetobutylicum P262) (Jones and Woods, 1986). The other species that have been widely studied for the bioconversion of corn to butanol include C. beijerinckii, C. thermosulfurogenes EM1, C. saccharolyticum, and C. thermo- saccharolyticum.

Recent developments in liquid biofuel technology, uncertainty of petroleum supplies, the finite nature of fossil fuels and environmental concerns have revived research efforts aimed at obtaining liquid fuels from renewable resources. The U. S. Department of Energy has declared that “decreasing U. S dependence on imported oil through the use of biomass-based fuels, power and products is an issue of national security (U. S. Department of Energy 2003).” Butanol is one of the biofuels that has the potential to substitute for gasoline and can be produced from domestically abundant biomass sources including corn. This chapter describes the production of butanol from corn and corn coproducts and the latest developments in butanol production technology including culture development, upstream and downstream processing, and fermentation technology. The formu­lation of such a chapter is a clear indication that technology to produce butanol from corn is maturing and getting ready for commercialization.

The future for E85 use in vehicles remains uncertain. The use of ethanol has grown dramatically in the United States, rising from about 175,000 gallons in 1980 to a projected 4.4 billion gallons in 2005.22 Yet the use of E85 is still relatively small. The United States has over 4.1 million E85 capable vehicles on the road. While this sounds impressive, consider that in 1999 the United States had almost 0.8 vehicles per capita, or over 200 million vehicles in use.27 Thus E85 vehicles represent only about 2-3% of all vehicles. This means that the consumer demand is not yet high enough to provide economic incentive for the fuel-producing companies to produce large quantities of E85 at the pump. Further, most, if not all, of the E85 capable vehicles are FFVs, which means that they operate well on gasoline, reducing the consumer demand for E85.

Still, as more experience is gained using lower blends of ethanol fuels, governments and fleet operators have shown a greater willingness to use E85. For example in 2005, the state of Minnesota legislature voted to require E20 use, up from the current requirement of E10. Furthermore, the U. S. Postal Service Northern District has a large fleet of E85 FFVs, comprising about 13% of the total fleet.

The turning point for E85 use in vehicles appears to hinge on the total market penetration of FFVs and on the total fuel cost. As the market develops in size, owners of FFVs will demand E85 when it is economically advantageous to use. If this happens then, perhaps, Henry Ford was correct when he proclaimed ethanol the fuel of the future and designed the Model T to operate on ethanol or gasoline.

Steam reforming reactions are catalyzed by metals of Groups 8-10 of the Periodic Table, nickel being preferred for industrial applications [5]. However, early stud­ies on ethanol steam reforming were carried out over copper-based catalysts [18].

They were previously used extensively for methanol steam reforming because they were well-known catalysts for methanol synthesis and were available and highly cost effective. Moreover, copper is a very appropriate catalyst for dehy­drogenation and WGS reactions, and both reactions may be involved in the total process of ethanol steam reforming. However, over copper-based catalysts under steam reforming conditions, ethanol can be transformed to ethyl acetate or acetic acid. The former transformation takes place via a nucleophilic addition of ethox — ide or ethanol species to acetaldehyde, while the formation of acetic acid takes place via the nucleophilic addition of OH — or H2O to acetaldehyde [18]. Both transformations are favored only at temperatures below 600 K, and their rate is lower than the dehydrogenation reaction [18,19]. Iwasa and Takezawa have already pointed out differences between the behavior of copper-based catalysts in methanol and ethanol steam reforming [18]. In the former, the dehydrogenation of methanol to formaldehyde was found to be the rate-determining step, and then carbon dioxide and hydrogen were selectively produced. For ethanol steam reforming, acetaldehyde was formed by ethanol dehydrogenation, but then ethyl acetate and acetic acid were produced. Consequently, copper shows a lower selectivity in ethanol steam reforming because of its effectiveness in the cleavage of C-C bonds. Other metals such as cobalt, nickel, or noble metals, which show greater ability to break C-C bonds [20], were preferred for steam reforming of higher alcohols than methanol. Thus, ethanol steam reforming has been mainly studied over supported metal catalysts of Groups 9 and 10. Several studies indicate the influence of the nature of the support on the behavior of the catalysts. The support itself can promote the formation of different products under steam reform­ing conditions, depending on its acidic/basic properties and redox characteristics [21]. Over acidic supports dehydration of ethanol to ethylene may occur. Once it is formed, ethylene would adsorb very strongly on the metal component of the catalyst and become a precursor of coke formation. In this case the neutralization of the acid centers of the support by introduction of alkaline additives prevents the formation of ethylene and consequently diminishes the catalyst deactivation. On the other hand, basic centers may be involved in the ketonization reaction:

2CH3CH2OH ^ CH3COCH3 + CO + 3H2

which occurs through several successive reactions such as dehydrogenation and aldol condensation. Consequently, a decrease of hydrogen yield and the formation of undesired by-product could occur.

In what follows, relevant aspects of nickel, cobalt, and noble metal catalytic systems, including catalysts for autothermal operation, will be discussed. How­ever, before entering into a discussion of the behavior of specific catalysts in the process, general trends of mechanistic aspects will be introduced. Then, the behavior of different catalysts in the steam reforming of ethanol will be analyzed in the light of their behavior in the consecutive steps that must be completed in order to ensure the total process.

Mechanistic Aspects

As stated above, the overall reaction network of ethanol steam reforming is highly complex because numerous reactions may coexist in equilibrium in the experi­mental conditions in which the process is carried out. Moreover, both the active metallic phase and the support can interact with ethanol, and consequently the proposed pathway depends not only on the reaction conditions but also on the nature of the catalyst.

For Ni — [7,22], Pd — [23], Co — [24-26], and Rh-based [8,27,28] catalysts, it has been proposed that the first step is the dehydrogenation of ethanol:

CH3CH2OH о CH3CHO + H2

and in several cases the reaction has been determined to occur via a surface ethoxide species (CH3CH2O-). Over Ni-, Pd-, and Rh-based catalysts the subse­quent decomposition of acetaldehyde into CH4 and CO is proposed:

CH3CHO ^ CH4 + CO

and then, depending on the temperature, reforming of CH4 and/or WGSR occurs, and, consequently, the extension of both reactions controls the final distribution of products:

CH4 + H2O о CO + 3H2 AH0 = 205.8 kJ mol-1

CO + H2O о CO2 + H2 AH° = -41.1 kJ mol-1

Concerning rhodium-based catalysts, for Rh/CeO2-ZrO2 the direct decompo­sition of ethanol to CH4, CO and H2 have been proposed [29]. This seems to occur via an oxametallacycle intermediate, -CH2CH2O-, formed from a surface ethoxide species by abstraction of an H from the methyl group by Rh. Then, the reforming of methane and WGS reaction takes place. Other studies, which com­pare Rh-based catalysts on supports with different ceria content, point to the production of CO2 as the primary product in the ethanol steam reforming and then its transformation to CO via the WGSR to reach thermodynamic equilibrium [30].

For the steam reforming of ethanol over Rh/Al2O3, the mechanism proposed by Cavallaro contemplates the dehydration of ethanol over the support and the dehydrogenation of ethanol over Rh. Then, ethylene is reformed and acetaldehyde is decomposed to CO and CH4. At 923 K, both reactions are faster than the formation of intermediates [27].

Concerning cobalt-based catalysts, studies of ethanol and acetaldehyde steam reforming employing microcalorimetry and infrared spectroscopy to investigate the adsorption of ethanol and acetaldehyde onto Co/ZnO catalysts, have shown that acetaldehyde transforms to surface acetate species over the fresh catalyst, and these species have been related to the production of H2 and CO2 from the steam reforming of acetaldehyde [24,26]. On the other hand, the deactivated catalyst Co/ZnO, which does not show surface acetate species after the acetalde­hyde adsorption, promoted the decomposition of acetaldehyde to CO and CH4 under reforming conditions [26].

Two reactor types predominate in plants built after 1970 (Cybulski 1994; Kirk — Othmer 1995). The ICI low-pressure process is an adiabatic reactor with cold unreacted gas injected between the catalyst beds (Figure 2.5, left). The subsequent heating and cooling leads to an inherent inefficiency, but the reactor is very reliable and therefore still predominant. The Lurgi system (Figure 2.5, right), with the catalyst loaded into tubes and a cooling medium circulating on the outside of the tubes, allows near-isothermal operation. Conversion to methanol is limited by equilibrium considerations and the high temperature sensitivity of the catalyst. Temperature moderation is achieved by recycling large amounts of hydrogen-rich gas, utilizing the higher heat capacity of H2 gas and the higher gas velocities to enhance the heat transfer. Typically a gas phase reactor is limited to about 16% CO gas in the inlet to the reactor, in order to limit the conversion per pass to avoid excess heating.

The methanol synthesis temperature is typically between 230 and 270°C. The pressure is between 50 and 150 bar. Higher pressures give an economic benefit,

FIGURE 2.5 Methanol reactor types: adiabatic quench (left) and isothermal steam raising (right).

since the equilibrium then favors methanol. Only a part of the CO in the feed gas is converted to methanol in one pass through the reactor, due to the low temperature at which the catalyst operates. The unreacted gas is recycled at a ratio typically between 2.3 and 6.

The copper catalyst is poisoned by both sulfur and chlorine, but the presence of free zinc oxides does help prevent poisoning.

As mentioned earlier in the discussion of dry-grind technology, the dry-grind process is being adapted to capture some of the advantages of the wet-milling system. The Quick Germ [34] and Quick Fiber [35] fractionation methods increase processing efficiency as well as the value of feed coproducts. These methods add technology to the beginning of the dry-grind process, removing the germ and fiber fractions of the corn kernel prior to starch processing. First, the corn is soaked in water for 3-12 hours to hydrate the germ, which is recovered by density separation. Next, the specific gravity of the mash is adjusted and pericarp fiber is recovered using hydrocyclones. The starch is then fermented in the traditional dry-grind process, and the germ and fiber can be processed sepa­rately into other value-added products: corn oil (from germ) and corn fiber oil and corn fiber gum (from corn fiber). Corn fiber oil, which is distinct from traditional corn germ oil, is potentially a valuable coproduct because it contains phytosterols known to have cholesterol-lowering properties. Another process, known as enzymatic milling or the E-mill process, refers to the addition of proteases and amylases prior to germ separation [36]. E-milling allows recovery of the gluten, while avoiding a full steeping process and the health and environ­mental concerns associated with sulfite.

Because the germ and fiber do not enter the fermenter, the fermentation residuals have lower fiber content and correspondingly higher protein content, resulting in a higher-value feed product. On the process side, these modified milling technologies increase the effective capacity of fermentation tanks, because removal of the germ and fiber frees reactor volume for additional starch. Bringing these modified processes to the dry-grind plant would therefore increase the facility’s ethanol production by 8 to 27% [37].

Over the last 30 years, ethanol has been used widely to blend with gasoline in the United States, Brazil, and other countries. In the United States, ethanol is usually blended in a mix of 10% ethanol and 90% gasoline. Early in the use of ethanol blends, this blend was referred to as gasohol, but it is now commonly referred to as E10. The purpose of blending a small percentage of ethanol into gasoline is to oxygenate the fuel for cleaner combustion and fewer carbon mon­oxide and hydrocarbon exhaust emissions. The most common additive to gasoline to improve oxygen is methyl tertiary butyl ether (MTBE), but it is an extremely toxic chemical that has been found to contaminate groundwater. A comparison of the emission of sulphur, olefins, carbon dioxide, aromatics, and NOx from MTBE oxygenated gasoline and ethanol oxygenated gasoline is shown in Table 7.1. The U. S. Environmental Protection Agency is beginning the process of eliminating MTBE from gasoline (6). Iowa and South Dakota have already phased out MTBE (2). If MTBE were completely replaced with ethanol, it would produce a 12-billion-gallon market for ethanol each year (2), which is considerably more

ethanol than is currently produced in the United States. To be considered an oxygenated gasoline, the fuel must contain at least 2.7% oxygen by weight. This can be obtained by blending 15% by volume MTBE or 7.5% by volume ethanol, but there is a difference in emissions between the two as shown below (2). Ethanol produces dramatically fewer sulfur and olefin emissions, but comparable emis­sions of other environmental hazards.

It is important to note most countries do not blend the minimum amount (7.5%) of ethanol for use as an oxygenate. Each country has its own concentration of ethanol to blend with gasoline. E10 has been the choice in the United States. It has also been the choice in areas of Canada. From 1929 to 1957, E10 was the only type of gasoline sold in Queensland. In 2001, E10 was reintroduced to Queensland by the government (7). On the other hand, all gasoline in Brazil is 22% ethanol (E22) (7). Finland has shown that E15 (15% ethanol/85% gasoline) vehicles can operate with stock engines (8). Other countries have considered or employed variations in ethanol concentration from E10 to E25. Table 7.2 below shows how relative emissions change as a function of ethanol concentration. It is important to note that carbon monoxide, hydrocarbon, and NOx emissions

decrease with increasing ethanol concentration, but aldehyde emissions increase with ethanol concentrations. Also, Thailand has shown that the emission rates of benzene, toluene, and xylene are decreased in cars using E10 and E15 fuels (9). This decrease in emissions is important due to the major health effects (including leukemia) of long-term inhalation of benzene and toluene (10). However, E10 and E15 fuels show an increase in formaldehyde and acetaldehyde emissions and exposure to formaldehyde and acetaldehyde has been shown to cause eye irrita­tion, respiratory problems, and nervous disorders (9).

It is also important to consider that E10 is considered an oxygenated fuel, but not an alternative fuel. E85, E95, and biodiesel have large enough biofuel concentrations to be considered alternative fuels, but E10 is simply considered an oxygenated fuel. From 1992 to 1998, the U. S. consumption of vehicle fuel increased by 14.5% (11). However, the U. S. consumption of alternative fuels increased 49.1% and the U. S. consumption of oxygenated fuels has increased 96.9% (11). This shows that more consumers are using alternative and oxygenated fuels today than in 1992. However, there has only been a 21.6% increase in the use of ethanol as an oxygenate (12). This will likely increase as MTBE is phased out due to environmental issues.

Ethanol is an easy fuel to work with because it is liquid at room temperature, can be stored in conventional fuel tanks, is less toxic than many fuels, and is easy to splash blend with gasoline at any stage of the production/distribution process.

Until the hydrogen economy is well established, it is more sensible to generate electricity directly from alcohols or hydrocarbons. SOFCs may become very attractive for portable, transportation, and stationary applications if alcohols and hydrocarbons can be utilized directly without applying any fuel pretreatments. The main advantage of liquid hydrocarbons is their relatively higher energy density compared to alcohols. However, most hydrocarbon fuels such as natural gas, bioderived gases, diesel, and gasoline contain impurities such as hydrogen sulfide and halogens, which may lead to poisoning of the SOFC electrode mate­rials. Particularly, sulfur content in such fuels should be reduced through pre­treatments to prevent the fuel cell electrodes from poisoning. Alternatively, progress is being made toward development of sulfur-resistant electrode materials for long-lasting operation of SOFCs using hydrocarbon fuels, which generally contain sulfide compounds in relatively high concentrations. For instance, a highly sulfur-tolerant anode composed of Cu, CeO2, and YSZ was developed to operate a SOFC using hydrogen with H2S levels up to 450 ppm at 1073 K [6]. Another study based on LaxSr1-xVO3- as anode material for SOFC showed a maximum power density of 135 mW/cm2 at 280 mA/cm2 when the fuel was a 5% H2S-95% H2 mixture at 1273K [7].

The advantage of liquid oxygenated hydrocarbons, such as alcohols, in com­parison to gasoline is that they are cleaner (low sulfur content) and can be derived from agricultural by-products and biomass as a renewable energy source. Alcohol is an ideal fuel for the fuel cells because of ease of transportation, storage, and handling, as well as their high energy density. Partially oxidized (hydrated) fuels may be easily reformed, such as alcohols, as they contain oxygen, in a liquid form. Since water is often used for internal reforming of the fuel, water solubility of alcohols (especially methanol, ethanol, and propanol) offers the advantage that additional fuel processing may not be necessary for operation of the fuel cell.

An anode-supported SOFC utilizing direct alcohol was reported by Jiang and Virkar [8]. A thin-film YSZ electrolyte was deposited on a Ni-YSZ anode with a composite of Sr-doped LaMnO3 and YSZ as a cathode. Pure methanol and an equivolume mixture of ethanol and water were used as fuels to operate the cells over a range of temperatures. Power densities achieved with ethanol and water mixtures were between 0.3 W/cm2 at 650°C and 0.8 W/cm2 at 800°C, and with methanol between 0.6 W/cm2 at 650°C and 1.3 W/cm2 at 800°C as shown in Figures 11.2 and 11.3. Carbon deposition on the electrodes was not observed when methanol was used as fuel. On the other hand, maximum power density using humidified H2 was 1.7 W/cm2 at 800°C. This indicates that a lack of H2 in the fuel may substantially increase concentration polarization thus limiting the performance of the cell.

Another study on direct-alcohol SOFCs reported a comparison of methanol, ethanol, propanol, and butanol as fuel sources [9]. With an increasing carbon number of the alcohol, a decrease in cell voltage was observed, which was attributed to slower decomposition and/or reforming kinetics of alcohols. Decreasing operational temperatures led to an increase of unreacted alcohols, aldehydes, and aromatic compounds. Thermochemical calculations were used to reveal the equilibrium amounts of reaction products of fuels during fuel cell operation [10,11]. Figure 11.4 shows the limit lines of carbon deposition as a function of temperature in the C-H-O diagram. No carbon deposition is expected if the carbon-to-oxygen ratio is less than unity. It is shown that the addition of

C

Further development of electrode materials that do not require introduction of water, will lead to better performance of the SOFCs, provided carbon deposi­tion can be suppressed. Recent studies showed that coking issues can be resolved through selection of appropriate catalysts and anode materials in fuel cell devel­opment [4,5]. Because nickel is an excellent catalyst for hydrocarbon cracking, Ni/ZrO2 cermets are used as anode materials for YSZ-based SOFCs. As mentioned earlier, these cermets can only be used in hydrocarbon or alcohol fuels if excess water is present to ensure complete fuel reforming. Mixing /Vo-octane with water, alcohol, and surfactant to produce an oil in water microemulsion was successful in reducing the carbon formation significantly, while retaining a high octane number [12]. It has been shown that the problem of carbon deposition may be avoided by using a copper-ceria anode [13] or applying an yttria-ceria interface between YSZ and Ni-YSZ cermet anode [3]. A nickel-free SOFC anode, La0.75Sr0 25Cr0.5Mn0 5O3 with comparable electrochemical performance to Ni/YSZ cermets was developed for methane oxidation without using excess steam [5]. A recent study showed that a Ru-CeO2 catalyst layer with a conventional anode allows internal reforming of /Vo-octane without cocking and yields stable power densities of 0.3 to 0.6 W/cm2 in a SOFC design operating at intermediate tem­peratures [14].

The seedling greenhouse is a smaller structure designed to provide replacement plants for those harvested in the aquaponics greenhouse. Very shortly after sprout­ing, the young plants are switched to being irrigated with fish tank effluent. This provides the maximum growth potential in the shortest amount of time. This part of the project will be an extremely rich learning environment.

Energy Plantation

The majority of the energy crops grown will be hybrid poplar and the project will utilize whole tree technology in the harvest and use of the trees. This means the entire tree is cut during the winter and processed into chips. The stump does not die — the root system is well established by this time — but rather the stump sprouts new shoots, which are then trimmed to one central leader. Because of the extensive root system, the tree reaches its original size again in 3 years rather than 5 and is ready for harvest once more. At least one year will be needed to assess the potential of the property, but in particular to plant cover crops and build soil fertility before planting energy crops. Given these restrictions, it will take 5 years from planting before the project is able to harvest a first crop of trees. Also, the project will be experimenting with salix (willow), alfalfa, and rapeseed (canola) crops during this 5-6 year lag in time. The project will also establish fish grow-out tanks on this land. However, the effluent will be used to irrigate outdoor energy crops during the summer and only produce vegetables during the fall, winter, and spring. The heart of this phase of the project is the gasification unit, which converts crop residues, stems from hay, and wood chips into synthesis gas. Feedstock is placed in the unit, which heats it to about 1500 degrees. The heat chamber is without oxygen so the feedstock will not burn, but rather give off a gas that is then filtered, cooled, and stored. This fuel cannot only provide heat and electricity, but also used directly in an internal combustion engine. The unit can also produce alcohol fuel and diesel fuel, #2 home heating fuel, and accommodate rubber tires as a feedstock. Excess heat from the operation of the gasifier will be used to dehydrate certain components for fish feed including the protein remains (DDGS — distillers dried grains and solubles) from the alcohol fuel project, vegetable waste and fish meal from the aquaponics project and other experimental feeds such as duckweed.