Overview

Methanol is produced by a catalytic reaction of carbon monoxide (CO), carbon dioxide (CO2), and hydrogen (H2). These gases, together called synthesis gas, are generally produced from natural gas. One can also produce synthesis gas from other organic substances, such as biomass. A train of processes to convert biomass to required gas specifications precedes the methanol reactor. These processes include pretreatment, gasification, gas cleaning, gas conditioning, and methanol synthesis, as are depicted in Figure 2.1 and discussed in Sections 2.2-2.6.

Pretreatment

Chipping or comminution is generally the first step in biomass preparation. The fuel size necessary for fluidized bed gasification is between 0 and 50 mm (Pierik et al. 1995). Total energy requirements for chipping woody biomass are approx­imately 100 kJe/kg of wet biomass (Katofsky 1993) down to 240 kWe for 25-50 tonne/h to 3 x 3 cm in a hammermill, which gives 17-35 kJe/kg wet biomass (Pierik et al. 1995).

The fuel should be dried to 10-15% depending on the type of gasifier. This consumes roughly 10% of the energy content of the feedstock. Drying can be

FIGURE 2.1 Key components in the conversion of biomass to methanol.

done by means of hot flue gas (in a rotary drum dryer) or steam (direct/indirect), a choice that among others depends on other steam demands within the process and the extent of electricity coproduction. Flue gas drying gives a higher flexibility toward gasification of a large variety of fuels. In the case of electricity generation from biomass, the integration in the total system is simpler than that of steam drying, resulting in lower total investment costs. The net electrical system effi­ciency can be somewhat higher (van Ree et al. 1995). On the other hand, flue gas drying holds the risk of spontaneous combustion and corrosion (Consonni et al. 1994). For methanol production, steam is required throughout the entire process, thus requiring an elaborate steam cycle anyway. It is not a priori clear whether flue gas or steam drying is a better option in methanol production. A flue gas dryer for drying from 50% moisture content to 15% or 10% would have a specific energy use of 2.4-3.0 MJ/ton water evaporated (twe) and a specific electricity consumption of 40-100 kWh^twe (Pierik et al. 1995). A steam dryer consumes 12 bar, 200°C (process) steam; the specific heat consumption is 2.8 MJ/twe. Electricity use is 40 kWh/twe (Pierik et al. 1995).

The wet milling and dry grind fermentation processes share the same biological basis for conversion of corn starch to ethanol: starch is converted by the combined actions of heat and enzymes to glucose and maltose, which are fermented by yeast to ethanol. Starch is a mixture of two glucose polymers: amylose, a linear molecule with a-1-4 linkages, and amylopectin, a branched molecule which has the same a-1-4 linkages and also contains a-1-6 branch points. Starch forms crystalline granules in the seed [15]. The granules (Figure 4.2) are insoluble in water and, in fact, have hydrophobic interiors. Pores extend from the surface into the hollow core of the granule. Heating an aqueous starch suspension weakens the hydrogen bonds within and between starch molecules, causing swelling of the starch granules due to absorption of water. The swelling process is called gelatinization [16]. Gelatinized starch is converted to glucose in the industrial process primarily by two enzymes, alpha-amylase and glucoamylase. First, the starch polymer is hydrolyzed by alpha-amylase to shorter chains called dextrins in a process known as liquefaction because the breakdown of polymers yields a thinner solution. Finally, the dextrins are degraded to glucose and maltose (a glucose dimer) by glucoamylase. The release of simple sugars from a polymer is called saccharification [17].

Corn fiber is a coproduct of the corn wet-milling industry. It is a mixture of corn kernel hulls and residual starch not extracted during the wet-milling process. Corn fiber is composed of approximately 40% hemicellulose, 12% cellulose, 25% starch, 10% protein, 3% oil, and 10% other substances such as ash and lignin (Singh et al., 2003). Corn fiber represents a renewable resource that is available in significant quantities from the corn dry — and wet-milling industries. Approxi­mately 6.3 x 106 dry tons of corn fiber is produced annually in the United States. Typically 4.5 lb of corn fiber is obtained from a bushel (56 lb) of corn, which can be converted to about 3.0 lb of fermentable sugars. The major fermentable sugars from hydrolysis of lignocellulosic biomass, such as softwood, hardwood and grasses, rice and wheat straw, sugarcane bagasse, corn stover and corn fiber, are D-glucose and D-xylose (except that softwood also contains substantial amounts of mannose) (Sedlak and Ho, 2004). Industrial Saccharomyces yeast strains used for fermenting sugars to ethanol lack the ability to utilize xylose, one of the major end products of hemicellulose hydrolysis. This is a major obstacle for the utilization of corn fiber or other forms of lignocellulosic-based biomass.

Economically, it is important that both xylose and glucose present in corn fiber be fermented to butanol in order for this renewable biomass to be used as feedstock for butanol production. Solventogenic clostridia have an added advan­tage over many other cultures as they can utilize both hexose and pentose sugars (Singh and Mishra, 1995) released from lignocellulosic biomass upon hydrolysis to produce butanol. Fond and Engasser (1986), during their evaluation of the fermentation of lignocellulosic hydrolysates to butanol by C. acetobutylicum ATCC 824, demonstrated that the culture utilized both xylose and glucose, although xylose was utilized more slowly than glucose and also supported lower butanol production. However, C. beijerinckii BA101 has been shown to utilize xylose and can effectively coferment xylose and glucose to produce butanol (Ebener et al., 2003). Parekh et al. (1988) produced acetone-butanol from hydroly­sates of pine, aspen, and corn stover using C. acetobutylicum P262. Similarly Marchal et al. (1984) used wheat straw hydrolysate and C. acetobutylicum, while Soni et al. (1982) used bagasse and rice straw hydrolysates and C. saccharoper — butylacetonicum to convert these agricultural wastes into butanol.

An important limitation of corn fiber utilization comes from the pretreatment and hydrolysis of corn fiber to glucose and xylose. Saccharification of corn fiber can readily be achieved by treatment with dilute H2SO4. However, this acid — catalyzed reaction leads to the degradation of glucose to hydroxy methyl furfural (HMF) and xylose to furfural at the temperatures of hydrolysis, resulting in inhibition of fermentation by these degradation products. Other degradation prod­ucts include syringaldehyde, acetic, ferulic, and glucuronic acids. The formation of these degradation products lowers the yield of fermentable sugars obtained from the corn fiber and the degradation products are inhibitory to yeast and bacterial fermentations. C. beijerinckii BA101 is able to completely utilize enzyme-hydrolyzed corn fiber to produce acetone-butanol, but performed poorly in the bioconversion of acid-hydrolyzed corn fiber to acetone-butanol due to the presence of inhibitory compounds generated during hydrolysis (Ebener et al., 2003). Therefore, the development of strains that can tolerate the inhibitory compounds generated during acid pretreatment and hydrolysis of corn fiber remains a priority.

Pioneering work in DMFC technology was undertaken by Shell, Exxon-Alsthom, Allis Chalmers, and Hitachi during the 1960s and 1970s [1,6]. Research focused on developing noble metal catalysts in liquid acid and alkaline electrolytes [1]. During this period, the mechanistics of methanol oxidation at Pt-based catalysts were studied [1,7,8]. While fundamental understanding of methanol oxidation became more clear, maximum current densities remained low. It was thought the limitation on current density was largely due to inadequate ionic conduction and stability of the PEMs employed in the fuel cells.

Membrane Development

In the mid 1960s, DuPont introduced the perfluorinated superacid membrane Nafion®. It was considered a major advancement in PEM materials [3]. Earlier, less effective PEM materials included polystyrene-based ionomers and heteroge­neous sulfonated divinylbenzene cross-linked polystyrene [2,3]. These early PEMs had poor long-term chemical stability and low proton conductivity. Nafion performance was considerably better than these other materials, however, it was quickly recognized that methanol crossover through Nafion would limit its use­fulness as a separator in DMFCs [9]. Crossover diminishes cell efficiency and occurs when fuel that is fed to the anode crosses through the membrane to the cathode and reacts directly with the oxidant. The process also poisons the cathode electrocatalyst with methanol oxidation products.

In the mid-1980s, Nafion membranes became more widely available and solubilized Nafion was introduced to the market. As Nafion became more widely available, PEFC research began in earnest and has since continued. The most notable improvement is a dramatic reduction in catalyst loading at ever-increasing power outputs [6]. Another important discovery was that the stability of the Pt electrocatalyst is greatly enhanced when Nafion is added to the electrocatalyst later. These developments set the stage for a revival of interest in low-temperature DMFCs during the late 1990s [6,10,11,12]. Figure 9.3 demonstrates the increase in DMFC research activity over this period.

As will be seen in later sections of this chapter, current efforts in DMFC research include minimizing methanol crossover through the separator of DMFCs while maintaining high proton conductivity, developing methanol tolerant oxygen reduc­tion catalysts, and identifying more cost-effective methanol oxidation catalysts [13].

As mentioned above, one possibility of operation with a more favorable energetic balance is under autothermal steam reforming conditions, which are produced by introducing oxygen in the reaction mixture. As has occurred for hydrocarbons and methanol feedstock [5,51], research is now under way to develop catalysts that control the oxidation process through the combining of catalytic partial oxidation and steam reforming of ethanol. The oxidizing environment reduces the carbon poisoning of the catalyst and could promote the decomposition of intermediate molecules such as ethylene and acetaldehyde. On the other hand, an excess of oxygen leads to a strong reduction of hydrogen as reaction product. In this respect, studies under partial oxidation conditions could contribute to a better knowledge of autothermal ethanol steam reforming. Some studies on cat­alytic behavior of Ni- [52], Pt — [53] and Ru-based [54] catalysts have recently been reported.

In autothermal conditions, reports concerned the use of Ni and Cu catalysts [38-40,55] and promoted noble metals supported on highly stable carriers, i. e., Pt-CeO2-La2O3/Al2O3 [13], Rh/CeO2 [14], Rh/Al2O3 [56]. The main role of pro­moters is related in this case to metal-promoter interactions [13], which affect the adsorption-decomposition of ethanol to CH4 and CO and their subsequent reforming with steam to produce H2. Most of the results reported point to the need to operate in a narrow range of water/oxygen/ethanol ratios to achieve 100% ethanol conversion, maximum hydrogen yield and minimum methane and carbon monoxide production.

The synthesis gas from the gasifier contains a considerable amount of CO2. After reforming or shifting, this amount increases. To get the ratio (H2-CO2)/(CO + CO2) to the value desired for methanol synthesis, part of the carbon dioxide could be removed. For this purpose, different physical and chemical processes are available. Chemical absorption using amines is the most conventional and com­mercially best-proven option. Physical absorption, using Selexol, has been devel­oped since the seventies and is an economically more attractive technology for gas streams containing higher concentrations of CO2. As a result of technological development, the choice for one technology or another could change in time, e. g., membrane technology, or still better amine combinations, could play an important role in future.

Chemical absorption using amines is especially suitable when CO2 partial pressures are low, around 0.1 bar. It is a technology that makes use of chemical equilibria, shifting with temperature rise or decline. Basically, CO2 binds chem­ically to the absorbent at lower temperatures and is later stripped off by hot steam. Commonly used absorbents are alkanolamines applied as solutions in water. Alkanolamines can be divided into three classes: primary, secondary, and tertiary amines. Most literature is focused on primary amines, especially monoethanola — mine (MEA), which is considered the most effective in recovering CO2 (Farla et al. 1995; Wilson et al. 1992), although it might well be that other agents are also suitable as absorbents (Hendriks 1994). The Union Carbide “Flue Guard” process and the Fluor Daniel Econamine FG process (formerly known as the

Dow Chemical Gas/Spec FT-1 process) use MEA, combined with inhibitors to reduce amine degradation and corrosion. The cost of amine-based capture are determined by the cost of the installation, the annual use of amines, the steam required for scrubbing and the electric power. There is influence of scale and a strong dependence on the CO2 concentration (Hendriks 1994). The investment costs are inversely proportional to the CO2 concentration in the feed gas when these range from 4% to 8%. MEA is partly entrained in the gas phase; this results in chemical consumption of 0.5-2 kg per tonne CO2 recovered (Farla et al. 1995; Suda et al. 1992). The presence of SO2 leads to an increased solvent consumption (Hendriks 1994).

When the CO2 content makes up an appreciable fraction of the total gas stream, the cost of removing it by heat regenerable reactive solvents may be out of proportion compared to the value of the CO2. To overcome the economic disadvantages of heat-regenerable processes, physical absorption processes have been developed that are based on the use of essentially anhydrous organic sol­vents, which dissolve the acid gases and can be stripped by reducing the acid-gas partial pressure without the application of heat. Physical absorption requires a high partial pressure of CO2 in the feed gas to be purified, 9.5 bar is given as an example by Hendriks (1994). Most physical absorption processes found in the literature are Selexol, which is licensed by Union Carbide, and Lurgi’s Rectisol (Hendriks 1994; Hydrocarbon Processing 1998; Riesenfeld et al. 1974). These processes are commercially available and frequently used in the chemical indus­try. In a countercurrent flow absorption column, the gas comes into contact with the solvent, a 95% solution of the dimethyl ether of polyethylene glycol in water. The CO2 rich solvent passes a recycle flash drum to recover co-absorbed CO and H2. The CO2 is recovered by reducing the pressure through expanders. This recovery is accomplished in serially connected drums. The CO2 is released partly at atmospheric pressure. After the desorption stages, the Selexol still contains 25-35% of the originally dissolved CO2. This CO2 is routed back to the absorber and is recovered in a later cycle. The CO2 recovery rate from the gas stream will be approximately 98% to 99% when all losses are taken into account. Half of the CO2 is released at 1 bar and half at elevated pressure: 4 bar. Minor gas impurities such as carbonyl sulfide, carbon disulfide and mercaptans are removed to a large extent, together with the acid gases. Also hydrocarbons above butane are largely removed. Complete acid-gas removal, i. e., to ppm level, is possible with physical absorption only, but is often achieved in combination with a chem­ical absorption process. Selexol can also remove H2S, if this were not done in the gas-cleaning step.

It has been suggested by De Lathouder (1982) to scrub CO2 using crude methanol from the synthesis reactor that has not yet been expanded. The pressure needed for the CO2 absorption into the methanol is similar to the methanol pressure directly after synthesis. This way only a limited amount of CO2 is removed, and the required CO2 partial pressure is high, but the desired R can be reached if conditions are well chosen. The advantage of this method is that no separate regeneration step is required and that it is not necessary to apply extra
cooling of the gas stream before the scrubbing operation. The CO2 loaded crude methanol can be expanded to about atmospheric pressure, so that the carbon dioxide is again released, after which the methanol is purified as would normally be the case.

Physical adsorption systems are based on the ability of porous materials (e. g., zeolites) to selectively adsorb specific molecules at high pressure and low tem­perature and desorb them at low pressure and high temperature. These processes are already commercially applied in hydrogen production, besides a highly pure hydrogen stream a pure carbon dioxide stream is coproduced. Physical adsorption technologies are not yet suitable for the separation of CO2 only, due to the high energy consumption (Ishibashi et al. 1998; Katofsky 1993).

Displacement of petroleum by fuel ethanol is approaching 3% of the liquid transportation fuel used in the United States. Expanding ethanol to replace more than 10% of fuel needs will require development of additional and lower-cost feedstocks. Only lignocellulosic biomass is available in sufficient quantities to augment starch as an ethanol feedstock source. As discussed previously, corn fiber and corn stover are potential sources of lignocellulosic biomass for fermen­tation. Other possible feedstocks are agricultural residues such as wheat and rice straws and sugar cane bagasse, energy crops including switch grass and softwood trees, and waste materials such as pulp and paper sludge and recycled office paper. The capacity to process and ferment even one of these categories of biomass would significantly increase production of ethanol; however, practical aspects of collection and storage must be addressed for many of these resources.

Several technological constraints limit fermentation of biomass feedstocks. Lignocellulosic biomass can be pretreated and enzymatically hydrolyzed to yield a mixture of sugars including glucose, galactose, arabinose, and xylose [32]. However, hydrolytic enzymes are inefficient and expensive. More-effective pre­treatment methods, as well as active and cost-effective enzymes, are needed for an economical process. As mentioned previously, microbes that efficiently fer­ment multiple sugars to ethanol must be developed in order to convert biomass to ethanol. Fermenting microbes also must tolerate the inhibitory compounds generated during biomass hydrolysis, or alternatively, cost-effective methods for inhibitor abatement must be in place. A study comparing dry-grind production of ethanol from corn and ethanol produced from corn stalks concluded that producing ethanol from corn stover would cost $1.45 per gallon compared to $0.96 from corn starch [33]. Despite these obstacles, one company, Iogen Corp. (Ottawa) has begun to produce ethanol from biomass.

Shelley D. Minteer

Department of Chemistry, Saint Louis University, Missouri

CONTENTS

History of Ethanol-Based Fuels……………………………………………………………………. 125

Oxygenated Fuels…………………………………………………………………………………………. 126

Ethanol Production……………………………………………………………………………………….. 128

Engine Issues………………………………………………………………………………………………… 129

E-Diesel…………………………………………………………………………………………………………. 131

Conclusions…………………………………………………………………………………………………… 133

References…………………………………………………………………………………………………….. 133

Abstract Ethanol was first used as a fuel for a combustion engine in 1897, but it has not emerged into the fuel market as a fuel, but rather as an oxygenate. The United States, Canada, Brazil, and many other countries have adopted the use of ethanol blended with gasoline at low concentration to improve emissions. Ethanol can also be blended with diesel at low concentrations (10% to 15%). Most commonly, ethanol is blended with gasoline at concentration of 10% and this oxygenated fuel is referred to as E10 or gasohol.

Alloys of platinum and ruthenium have become common electrocatalysts for fuel cells, because it is believed that alloying ruthenium with platinum will help increase the carbon monoxide tolerance of the platinum catalysts. Alloys of platinum and ruthenium have also been used extensively for DMFC fuel cells, along with hydro — gen/oxygen fuel cells that employ hydrogen gas formed from a reformation process that may have carbon monoxide or carbon monoxide-like by-products. Although

extensive research was done on Pt/Ru alloys on carbon supports and platinum on carbon supports, there was no statistical difference between the selectivity of the two catalysts for ethanol electrooxidation [13]. Figure 10.2 shows a comparison of fuel cell performance for different alcohol fuels employing Pt/Ru alloys as catalysts. It is apparent that methanol performance is better at high current densities (at a current density of 250mA/cm2, the cell voltages are 0.354V for methanol, 0.305V for ethanol, 0.174V for 1-propanol, and 0.054V for 2-propanol [13]), but ethanol performance is better at low current densities (>0.05V at low current densities). The excellent performance of ethanol at low current density is likely due to a decrease in crossover of ethanol versus methanol to the cathode. It is also interesting to note that propanol performance is significantly worse than methanol and ethanol. 1-propanol oxidation forms carbon dioxide and propionaldehyde, but 2-propanol oxidation forms carbon dioxide and acetone [14]. The direct alcohol fuel cells studied in Figure 10.2 are being operated at a temperature of 170°C [13]. This temperature is extremely high (harsh enough that Nafion is not particularly stable and another polymer electrolyte (polybenzimidazole) was used) and is above the temperatures that are realistic for portable power applications, but they provide a benchmark for comparing the 4 alcohols.

PtSn Catalysts

Zhou and coworkers have studied the effect of other alloys on ethanol electro­oxidation. Figure 10.3 shows representative cyclic voltammograms of alloys of

platinum with ruthenium, tungsten, palladium, and tin. These voltammograms were taken at room temperature in solutions that contain 1.0 M ethanol and 0.5 M sulfuric acid. The voltammograms show the largest catalytic activity (current density at the oxidation peak) for PtSn on carbon, but the PtRu on carbon has the lowest over­potential for the ethanol oxidation peaks (0.23 V lower than pure platinum on carbon) [15]. Figure 10.4 shows voltage-current curves and power curves for the same catalysts in a direct ethanol fuel cell at 90°C. The results indicate that Sn, Ru, and W increase the catalytic activity for ethanol oxidation on platinum (max­imum power density of 52.0 mW/cm2, 28.6 mW/cm2, and 16.0mW/cm2, respec­tively, compared to 10.8 mW/cm2 for pure platinum on carbon [15]). Tin and ruthenium are believed to have a bifunctional mechanism to supply surface oxygen containing species for the oxidative removal of carbon monoxide like species that typically passivate the surface of pure platinum [16]. The proposed mechanism for ethanol oxidation at Pt/Sn alloys is shown below [17]:

C2H5OH + Pt(H2O) ^ Pt(C2H5OH) + H2O Pt(C2H5OH) + Pt ^ Pt(CO) + Pt(res) + xH++ xe — Pt(C2H5OH) ^ Pt(CH3CHO) + 2H + + 2e-

Pt(CH3CHO) + SnCl4(OH)2- ^ CH3COOH + SnCl2- + 2H2O + e — + H+ Pt(CO), Pt(res) + SnCl4(OH)2- ^ CO2 + SnCl2- + H2O + Pt H2O + Pt = Pt(OHU + e — + H+

2Pt(OH)a* + SnCl4- = SnCl4(OH)2- + 2Pt

where Pt(res) is an oxidized residue adsorbed to the surface of platinum, Pt(H2O) is water adsorbed to the surface of platinum, Pt(CO) is carbon mon­oxide adsorbed to the surface of platinum, Pt(C2H5OH) is ethanol adsorbed to the surface of platinum, and Pt(CH3CHO) is acetaldehyde adsorbed to the surface of platinum.

After Pt/Sn alloys were determined to be the optimal elemental alloy, Zhou and coworkers examined the importance of tin content and temperature on the fuel cell power curves. Figure 10.5 shows the effect of altering the tin content on the direct ethanol fuel cell performance at a temperature of 60°C. The figure shows both current voltage curves and power curves. The results clearly show that Pt3Sn2 on carbon is the best catalyst choice for 60°C [18]. Figure 10.6 shows the effect of altering tin catalyst content on the fuel cell performance at a tem­perature of 90°C. The results clearly show that Pt2Sn1 on carbon is best for temperatures that are greater than 75°C [18]. Figure 10.5 and Figure 10.6 show that tin content does affect fuel cell performance and temperature affects the catalytic activity of each fuel cell differently. The operating temperature for DEFC

is a function of application. Most portable power applications need to operate between room temperature and 50°C, but performance tends to increase with temperature until crossover and/or polymer electrolyte membrane degradation take over. At 30°C, DEFC have maximum power densities that range from 2 to 10 mW/cm2 [19]. Figure 10.7 shows the effect of a wider range of temperatures (50°C-110°C) for a DEFC with a Pt-Sn (9:1)/C anode. It is important to note that fuel cell performance is a function of temperature and a degradation is not seen at high temperatures [5]. Open circuit potentials do not vary significantly with temperature, but maximum power ranges from 6 to 26 mW/cm2 [5].

Catalyst loading and catalyst supports have also been investigated as para­meters that may affect DEFC performance. Studies in hydrogen/oxygen and DMFC have shown that loading of the catalyst can affect fuel cell performance. If the catalyst loading of the DEFC in Figure 10.5 is changed from 30% metal on vulcanized carbon XC-72 to 60% metal on vulcanized carbon XC-72, the maximum power can increase to 28 mW/cm2 and the open circuit potential can increase from 0.72V to 0.75 V [5]. Research has also shown that transitioning from vulcanized carbon supports (XC-72) to multiwall carbon nanotubes (MWNTs) increases both the open circuit potential and the maximum power density of a DEFC with a platinum/tin alloy catalyst [9]. This is shown in Figure 10.8 where the open power curve shows an increase from 30 mW/cm2 to 38 mW/cm2 with an increase of 80 mV in open circuit potential.

DEFCs can be fabricated by methods similar to DMFCs. The most common format is the membrane electrode assembly (MEA). A MEA is a single assembly that contains the anode, the cathode, and the polymer electrolyte membrane

in ionic contact with each other. MEAs are formed most commonly using a conventional heat pressing method, but they can also be fabricated using a decal transfer method. The conventional method involves sandwiching the PEM between an anode and cathode and heat pressing the sandwich at a temperature above the glass transition temperature of the PEM to melt the electrodes into ionic contact with the PEM. The conventional method shows a 34% decrease in power density over a 10-hour period and delamination of the electrodes from the Nafion [20]. This is likely due to the increased swelling of Nafion in the presence of ethanol, but the decal transfer method only shows a 15% decrease and no delamination, along with no change in resistance [20]. Therefore, the decal transfer method is a better method for forming DEFC MEAs. The decal transfer method involves spray painting the catalyst layer directly onto the polymer electrolyte membrane, instead of onto an electrode support (such as carbon paper) and then heat pressing into the polymer electrolyte membrane.

Researchers have also studied tertiary catalyst systems, but the fuel cell performance has not been greatly affected by adding a third component to the system for alloys containing platinum and ruthenium with a third component of tungsten, tin, or molybdenum [15]. Tertiary catalysts with tungsten and tin did show a measurable increase in power compared to pure Pt/Ru alloys, but both power densities are less than pure Pt/Sn alloys under the same operating condi­tions [15].

CONCLUSIONS

Direct ethanol fuel cells are a relatively new technology for portable power generation. Results have concluded that electrochemical oxidation of ethanol on platinum-based catalysts is not significantly lower than for methanol [21] and the intermediate products of ethanol oxidation are less toxic than methanol oxidation. Although catalytic performance with pure platinum catalysts is low, the perfor­mance of Pt/Sn and Pt/Ru alloys is good. Future research will focus on the development of electrocatalysts that show improved catalytic activity and lower electrode fouling at low and moderate temperatures (room temperature to 50°C). Research on fuel cell lifetimes will also be conducted to study the long-term effects of continuous operation on the catalysts, electrode support, and polymer electrolyte membranes. Improved lifetimes are an issue for both methanol and ethanol, because both oxidation processes produce carbon monoxide and carbon monoxide-like products that adsorb/passivate the catalyst and both alcohols swell the polymer electrolyte membrane, which typically decreases the lifetime and stability of the membrane. Overall, DEFCs are a relatively new technology compared to DMFCs, but ethanol has advantages over methanol in decreased toxicity and environmental issues. From a catalytic perspective, the catalytic rates are similar between ethanol and methanol oxidation, but methanol oxidation is more efficient (produces a larges percentage of carbon dioxide (the complete oxidation product)).

Tilapia are a tropical fish and require warm water. As a result, shipping fingerlings during the winter is extremely risky. Therefore, the project will produce all needed fingerlings on-site. The project will require from 1100 to 3300 fingerlings per week. It can also act as a regional resource for others that require fingerlings as well. The bulk of the equipment needed to breed these fingerlings is already in place. Whereas the hatchery is somewhat labor intensive, it does guarantee a continuous supply of fingerlings. The males are kept in tanks by themselves and the females are brought to them to mate. Once mating has stopped and the female has a mouth full of eggs, the males are removed and the female is left alone and undisturbed to hatch her young (about 72 hours). After this time, the hatchlings will remain in the mother’s mouth for another 3-7 days, taking short excursions outside to feed on minute particulates and then dart back inside. At a time determined by the mother, she spits them all out and she will accept feed again. When this occurs, she is removed to an isolation tank and full fed until she regains weight. She is then ready to breed again. The particular variety of tilapia to be used is patented and produces all males (males grow 40% faster than females), which are a bright red in color. They are a very forgiving fish, adaptable to many different cultural conditions and, from past experience with them, quite easy to breed and raise. Presently, there is enough room for future expansion to other species, i. e., giant Australian Red Claw crawfish (Cherax quadricarinatus — a lobster-sized crawfish that lives in fresh water), giant freshwater prawns (macro — braccium Rosenbergii) which grow to one pound, and a variety of giant sunfish (bream), which grows to a weight of 5 pounds. All these species, except for sunfish, are tropical or subtropical and must be bred on-site to have a year-long supply. The sunfish will remain isolated from the environment, since interbreeding with native varieties will dilute their genetic uniqueness, resulting in much smaller, stunted fish. The hatchery will be connected to its own smaller aquaponics greenhouse, which will provide biofiltration and a use for the waste generated from the hatchery. It will also add to the weekly harvest of vegetables. Breeding fish on-site will also enable the project to add genetics to its teaching curriculum.