An additional characteristic of alfalfa that makes it attractive for biorefinement is that it is amenable to genetic transformation. Rapid and efficient methods for transformation using Agrobacterium tumefaciens have been developed and gene

promoters identified for high constitutive expression and for tissue-specific expression (reviewed by Samac and Temple, 2004; Somers et al., 2003). Trans­formation has been used to alter alfalfa for production of valuable coproducts (Table 5.2) and for improving digestion of alfalfa fiber. Transgenic alfalfa has been shown to be capable of producing high levels of phytase (Austin-Phillips and Ziegelhoffer, 2001; Ullah et al., 2002), a feed enzyme that degrades phytic acid and makes phosphorus in vegetable feeds available to monogastric animals such as swine. Adding phytase to feeds reduces the need to add supplemental phosphorus to feed and reduces the amount of phosphorus excreted by animals. In field studies, juice from wet-fractionated alfalfa plants contained 1-1.5% phytase. Phytase activity in juice was stable over two weeks at a temperature of 37°C. Activity is also stable in dried leaf meal. Both juice and dried leaf meal added to feed were as effective in feeding trials as phytase from microbial sources. The value of the enzyme and xanthophyll in the juice was estimated at $1900/acre (Austin-Phillips and Ziegelhoffer, 2001). A wide range of feed enzymes is used to enhance digestion of feed and improve animal performance. Use of feed enzymes in monogastric and ruminant animals in expected to increase worldwide (Sheppy, 2001). Production of feed enzymes in transgenic plants, particularly in plants used as animal feed, would be an opportunity to increase feed utilization as well as value of the feed.

Transgenic alfalfa has also been used to produce several industrial enzymes. A manganese-dependent lignin peroxidase, which can be used for lignin degra­dation and biopulping in the manufacture of paper, was expressed in alfalfa. However, high levels of production of this enzyme appeared to be detrimental to plants (Austin et al., 1995). In the same study, a-amylase was produced at a level of approximately 0.01% of soluble protein without having a negative effect on plant development. Two cellulases, an endogluconase and a cellobiohydrolase, have been expressed at low levels in alfalfa (Ziegelhoffer et al., 1999). These enzymes were stable in dried leaf meal. Expression of cellulose degrading enzymes in biomass plants is one strategy to decrease the costs of saccharification that precedes ethanol fermentation. Alfalfa plants have also been shown to be an excellent “factory” for the production of chitinase (Samac et al., 2004). Chitin, found in shells of crustaceans, is the second most abundant carbohydrate after cellulose, and a potential feedstock in a biorefinery.

In addition to production of proteins, the use of transgenic alfalfa to produce other industrial feed stocks has been explored. Polyhydroxyalkanoates (PHAs) are produced by many species of bacteria and some PHA polymers are commer­cially valuable as biodegradable plastics. PHA synthesis in plants is seen as a more economically viable means of producing large quantities of these polymers (Poirier, 1999; Slater et al., 1999). Alfalfa was engineered to constitutively express three bacterial genes for the production of poly-p-hydroxybutyrate (PHB) (Saruul et al., 2002). Granules of PHB were shown to accumulate in chloroplasts without any negative impact on plant growth. Yield of PHB by chemical extrac­tion was relatively low (1.8 g kg-1 DM), but may be improved by optimizing extraction methods or by utilizing stronger gene promoters.

A major limitation to use of biomass in the production of ethanol is the recalcitrance of the material to saccharification. Cross-linking of lignin with cell — wall polysaccharides interferes with enzymatic degradation of cellulose and can severely limit the conversion of herbaceous plant material into ethanol. Lignin in alfalfa stems also limits digestion of feed by ruminant animals. In experiments aimed at increasing feed digestion by ruminants, transgenic alfalfa was produced that had decreased expression of caffeoyl coenzyme A 3-O-methyltransferase, an enzyme involved in synthesis of lignin precursors. These plants were shown to have approximately 20% less lignin and 10% additional cellulose than the controls (Marita et al., 2003). The rate of digestion of the transgenic material was deter­mined by in vitro rumen digestibility assays. In the transgenic material, a 2.8-6.0% increase in the rate of digestion was observed (Guo et al., 2001). This material could have a very significant impact on both animal nutrition and alfalfa biorefining. Casler and Vogel (1999) determined that a 1% increase in forage digestibility would lead to a 3.2% increase in average daily live-weight gain by beef steers. Although this material has not yet been tested with different pretreat­ment methods or used in saccharification or fermentation studies, based on chem­ical analyses, it may also have improved qualities as a feedstock for bioethanol production.

During the past several years, barrel medic (Medicago truncatula) has been the object of a broad range of research efforts worldwide. This annual plant, which is closely related to alfalfa, is a model plant for study of plant-microbe interactions and plant development (Cook, 1999). Chromosome mapping has shown that there is a high degree of gene synteny between the two species as well as a high degree of DNA sequence homology (Choi et al., 2004). Numerous genomic tools have been developed for M. truncatula including isolation of over 189,000 expressed sequence tags (ESTs), identification and sequencing of more than 36,000 unique genes (http://www. tigr. org/tigr-scripts/tgi/T_index. cgi? spe- cies=medicago), extensive genetic and physical mapping (Choi et al. 2004), development of microarrays for transcript profiling, and a genome sequencing project is currently underway (http://www. medicago. org). In particular, micro­arrays are valuable tools for identifying genes involved in important agricultural processes as they enable researchers to measure expression of thousands of genes simultaneously. More than 100 genes are involved in cell-wall biosynthesis in plants and little is known about regulation of their expression. EST resources may be useful both as markers for selecting plants with favorable characteristics in bioconversion and in modifying gene expression in transgenic plants for enhancing the efficiency of ethanol production or enhancing yields of valuable coproducts.

One of the main motivations for using E85 is its ability to help reduce the impact of vehicle emissions on the environment. E85 provides major reductions in some tailpipe emissions compared to gasoline. E85 is also less toxic than gasoline. Furthermore, the ethanol used in E85 can be derived from renewable resources, thus reducing net greenhouse gas emissions.

Vehicle Tailpipe Emissions

Determining the effect of E85 on vehicle emissions is complex, since many factors influence the emissions of vehicles. Further, E85 use is a politically charged issue, effecting the environment, domestic employment, and petroleum imports. Finding reliable emissions data is, therefore, challenging. Actual emissions will vary with engine design and calibration. One of the more recent sources, the U. S. Environ­mental Protection Agency (EPA), reports potential substantial tailpipe emissions benefits when using E85 relative to conventional gasoline.18 These benefits are shown in Figure 8.1. This source suggests these benefits for an engine optimized to operate on E85. The EPA also reports that fewer total toxics are produced, and that the hydrocarbon emissions have a lower reactivity. The use of E85 does produce higher ethanol and acetaldehyde emissions than gasoline.

Other sources provide different values, but most sources tend to show sub­stantial reductions in carbon monoxide. For example, the Renewable Fuels Asso­ciation reports a reduction of 25%.19 E85 typically results in slightly reduced levels of unburned hydrocarbons. Emissions of nitrous oxides (NOx) are slightly

Emissions Species

FIGURE 8.1 Estimated emissions reductions for an engine optimized to use E85 com­pared to those when operating on gasoline. Source: Data compiled from U. S. Environ­mental Agency, EPA420-F-00-035, Mar. 2002.

reduced with some sources showing slight increases and others showing decreases. Again, much of the data is subject to the test schedule used, and the vehicle and its optimization for E85.

Data from a snowmobile powered by a four-stroke, spark-ignited engine modified to operate using blends up to E85 is shown in Figure 8.2.20

If the ethanol used in E85 comes from renewable resources such as corn, E85 can show substantial reductions in greenhouse gas emissions. In 1998, the U. S. DoE Argonne National Laboratory estimated that 1 gallon of E85 reduces greenhouse gas emissions by 16-28% compared to gasoline.21 Other references suggest higher reductions exceeding 50%.22

Pilar Ramirez de la Piscina and Narcfs Homs

Inorganic Chemistry Department,

Universitat de Barcelona, Spain

CONTENTS

Background…………………………………………………………………………………………………… 233

Energetically Integrated Ethanol Reforming Processes………………………………… 236

Catalytic Systems…………………………………………………………………………………………. 238

Mechanistic Aspects…………………………………………………………………………. 240

Nickel — and Cobalt-Based Catalysts………………………………………………… 241

Noble Metal-Based Catalysts…………………………………………………………… 243

Catalysts for Autothermal Steam Reforming………………………………….. 244

Perspectives…………………………………………………………………………………………………… 244

References…………………………………………………………………………………………………….. 245

BACKGROUND

Energy is one of the main factors that must be taken into account when sustainable development of our society is envisioned because there is an intimate connection between energy, the environment and development. In response to the need for cleaner and more efficient energy technology, a number of alternatives to the current energy network have emerged. In this context, the general use of fuel cells for automotive purposes or stationary power generation is envisioned in the medium term. This is a promising advance in the production of electrical energy from chemical energy, since the efficiency of a fuel cell is much higher than that of a combustion engine.

The fuel most widely studied for use in a fuel cell is hydrogen. Although the ideal situation would be the production of hydrogen from water, using renewable energy sources (e. g., solar energy), this is unlikely to become extensively oper­ative in the short to medium term. At present, hydrogen is mainly produced by steam reforming of fossil fuel-derived feedstock, mostly natural gas and naphtha.

The main objective of the steam reforming process is to extract the hydrogen from the substrate. From hydrocarbons, hydrogen is obtained via the general equation:

CnH2n+2 + nH2O о nCO + (2n + 1)H2 AH0 > 0

Then, the production of hydrogen is completed by the successive water gas shift reaction (WGSR):

CO + H2O о CO2 + H2 AH° = -41.1 kJ mol1

Both reactions can only be carried out in a practical way by catalytic means. The steam reforming reaction is endothermic and the real amount of energy required depends on both the stability of the substrate to be reformed and the ability of the catalyst to activate and transform the substrate into the products. The WGSR is slightly exothermic, and the forward reaction is not favored at the temperature used for steam reforming, which is higher than 1000 K for CH4. Therefore, the overall process requires the use of different catalysts, which operate under different reaction conditions in separate reactors. In the case of natural gas and naphtha, many years of industrial practice have led the total process to become technologically mature. However, if a strong increase in the demand for hydrogen is contemplated, some advanced research and development in catalysis and tech­nology would still be needed in the next few years [1,2].

On the other hand, society has become environmentally conscious and sen­sitive to its oil dependency because petroleum is likely to become scarce and expensive and the reserves are concentrated in a few countries. If a long-term global solution is envisioned, other, nonfossil-derived fuels, which are renewable and environmentally friendly must be contemplated for the supply of hydrogen. In this context, ethanol is a very promising alternative. As has been stated in previous chapters, ethanol, which can be considered a renewable and ecofriendly hydrogen carrier, can be produced from a large variety of biomass-based sources.

The catalytic steam reforming of ethanol may provide up to 6 moles of hydrogen per mol of ethanol reacted:

CH3CH2OH + 3H2O о 2CO2 + 6H2 AH° = 173.4 kJ mol-1

If the primary production of CO is considered in the steam reforming of ethanol, the WGS reaction must be taken into account. The overall process, then, will be the combination of both reactions:

CH3CH2OH + H2O о 2CO + 4H2
CO + H2O о CO2 + H2

Although globally the reaction releases 2 moles of carbon dioxide, the total process is almost neutral from the point of view of CO2 generation, since it may be assumed that the CO2 produced is consumed in biomass growth. Consequently, the use of the steam reforming of ethanol as a source of hydrogen can contribute to the global reduction of CO2 emissions. Moreover, other emissions of green­house or polluting gases such as hydrocarbons and NOx could also be mitigated.

As we have just said, the reaction of ethanol steam reforming is highly endothermic. However, theoretical and experimental studies have shown that ethanol steam reforming can take place at temperatures above 500 K [3]. Table 13.1 shows that relatively high values of equilibrium constant (Kp) can be achieved for temperatures of over 600 K. On the other hand, it is worth mentioning that, in this case, the energy required per mol of hydrogen generated (Table 13.1) is lower than half of that required to obtain hydrogen from the steam reforming of hydrocarbons. As an example, values of H (kJ per mol of hydrogen generated) at 600 K can be considered; 32.33 kJ must be supplied when H2 is obtained from ethanol, and 72.82 kJ if methane is used [4].

An issue of major importance in ethanol steam reforming is the development of catalysts that operate with high levels of activity, selectivity, and stability. Several products that can be formed under reaction conditions could need other experimental conditions to be reformed. Consequently, the total process leading to an effluent that mainly contains H2 and CO2 and is free of undesirable products may be complex. Depending on the reaction conditions and catalyst used, the following reactions could contribute to a low selectivity of the process, among others:

CH3CH2OH ^ CH3CHO + H2
CH3CH2OH ^ CH2CH2 + H2O
CH3CH2OH ^ CH4 + CO + H2
CH3CHO ^ CH4 + CO

COx + (2 + x)H2 ^ CH4 + xH2O

Thus, after the steam reforming, an additional purification of the effluent could be necessary, but this will depend on the fuel cell to be fed. For hydrogen operating in a polymer membrane fuel cell (PEMFC) or phosphoric acid fuel cell (PAFC) the limit of CO concentration in the fuel is 50 ppm and 0.05%, respec­tively [5]. These low CO concentrations may be achieved by subsequent catalytic selective oxidation or methanation processes or by the use of H2 selective mem­branes. An additional purification of the reformed effluent might be unnecessary when a molten carbonate fuel cell (MCFC) or a solid-oxide fuel cell (SOFC) is used. Both fuel cells, which operate at high temperatures, may convert impurities of CH4 and CO in the anode chamber [5,6].

Moreover, to make the steam reforming of ethanol operative in practice it must be energetically integrated with other exothermic processes, e. g., combus­tion or partial oxidation, which may supply the energy required for the steam reforming.

In the following sections, some propositions for globally energetically inte­grated processes and the main catalytic systems used to date for the different reactions will be analyzed. Finally, relevant perspectives of the development of the ethanol reformation to hydrogen in the near future will be presented.

Today’s military has become increasingly reliant on portable power to main­tain a devastating advantage over less sophisticated enemies. Vital communica­tions equipment, night-vision goggles, and weapon systems are being developed and deployed that require immense amounts of portable power available to the individual soldier. Lieutenant Marc Lewis was quoted in Iraq in June 2003 stating, “If we run out of batteries, this war is screwed.” Soldiers are typically employing disposable batteries and some rechargeables for their equipment. Batteries can account for up to 50 pounds of a soldier’s rucksack due to inability to recharge batteries in the field. To reinforce the reliance on batteries, a 12-person Special Forces team on a 30-day deployment can go through 3000 batteries at a cost of $350,000 [3]. Many of these batteries are only used for 10-20% of their capacity before being discarded. This may immediately seem wasteful but imagine staking your combative edge on being able to see at night or communicate with other troops; one would much rather pop open a new battery than use one that was not fully charged.

Portable fuel cells could provide incredible advantages to the military. Rather than carrying a number of disposable or rechargeable batteries, a solider could carry a couple fuel cells and the fuel needed to refuel them as needed in the field. Additionally, because fuel cells can provide more energy for longer periods of time than batteries, they could enable the next generation of electronic devices for the military to further enhance its combative advantage.

Especially in atmospheric gasification, larger hydrocarbons are formed, generally categorized as “tars.” When condensing, they foul downstream equipment, coat surfaces, and enter pores in filters and sorbents. To avoid this, their concentration throughout the process must be below the condensation point. On the other hand, they contain a lot of potential CO and H2. They should thus preferably be cracked into smaller hydrocarbons. Fluidized beds produce tar at about 10 g/mNTP3 or 1-5 wt% of the biomass feed (Boerrigter et al. 2003; Milne et al. 1998; Tijmensen 2000). BTX, accounting for 0.5 volume % of the synthesis gas, have to be removed prior to the active carbon filters, which otherwise sorb the BTX com­pletely and quickly get filled up (Boerrigter et al. 2003).

Three methods may be considered for tar removal/cracking: thermal cracking, catalytic cracking, and scrubbing. At temperatures above 1000-1200°C, tars are destroyed without a catalyst, usually by the addition of steam and oxygen, which acts as a selective oxidant (Milne et al. 1998). Drawbacks are the need for expensive materials, the soot production, and the low thermal efficiency. Catalytic cracking (dolomite or Ni based) is best applied in a secondary bed and avoids the mentioned problems of thermal cracking. However, the technology is not yet fully proven (Milne et al. 1998). It is not clear to what extent tars are removed (Tijmensen 2000) and the catalyst consumption and costs are matters of concern.

TABLE 2.2 Estimated Contaminant Specifications for Methanol Synthesis1 and Cleaning Effectiveness of Wet and Dry Gas Cleaning Treatment Method and Remarks
	Dry Gas Cleaning3
Sorbents under development. All tar and BTX: Catalytic tar cracker, other catalytic operations. Under development. In-bed sorbents or in-stream sorbents. <1 ppm. Guardbeds necessary.
All nitrogen: catalytic decomposition, combined removal of NH3/H2S. Selective oxidation under development. All sulfur: In-bed calcium sorbents. Metal oxide sorbents <20 ppm.

TABLE 2.2 (CONTINUED)

Estimated Contaminant Specifications for Methanol Synthesis1 and Cleaning Effectiveness of Wet and Dry Gas Cleaning

1 Most numbers are quoted from Fischer-Tropsch synthesis over a cobalt catalyst (Bechtel 1996; Boerrigter et al. 2003; Tijmensen 2000). Gas turbine specifications are met when FT specifications are.

2 Cleaning requirements for MeOH synthesis are 0.1 (van Dijk et al. 1995) to 0.25 ppm H2S (Katofsky 1993). Total sulfur <1 ppmV (Boerrigter et al. 2003). For Fischer-Tropsch synthesis requirements are even more severe: 10 ppb (Tijmensen 2000).

3 Hot gas cleaning was practiced in the Varnamo Demonstration plant, Sweden (Kwant 2001). All data on dry gas cleaning here is based on the extensive research into high-temperature gas cleaning by Mitchell (Mitchell 1997; Mitchell 1998).

4 Bergman et al. (Bergman et al. 2003).

Per kg dry wood (15% moisture), 0.0268 kg dolomite. Part of the H2S and HCl present adsorb on dolomite (van Ree et al. 1995). The tar crackers can be integrated with the gasifier.

Tars can also be removed at low temperature by advanced scrubbing with an oil-based medium (Bergman et al. 2003; Boerrigter et al. 2003). The tar is subsequently stripped from the oil and reburned in the gasifier. At atmospheric pressures BTX are only partially removed, about 6 bar BTX are fully removed. The gas enters the scrubber at about 400°C, which allows high-temperature heat exchange before the scrubber.

After steeping, the germ (which contains most of the corn oil) is dislodged from the kernel by gentle disruption using a germ mill. The germ fraction is separated in hydroclones based upon its low density (high oil content) and then washed to remove loose starch and gluten. The germ is pressed and dried, and the oil is either extracted on-site or sold to a corn oil refiner. If the oil is extracted on-site, the residual material is blended into corn gluten feed. The slurry exiting the hydroclones is screened to separate fiber from protein (gluten) and starch. Fiber is repeatedly washed and the destarched fiber is incorporated with steepwater solids and the bottoms of the distillation column into corn gluten feed. Gluten is separated from starch by centrifugation and dried to produce corn gluten meal. Corn steep liquor, the liquid remaining after removal of kernel components, can also be sold separately as either a feed or fermentation ingredient.

Novel Downstream Processing

Gas Stripping

Gas stripping is a simple technique that can be applied for recovering butanol (ABE) from the fermentation broth (Maddox, 1989; Qureshi and Blaschek, 2001b). Oxygen-free nitrogen or fermentation gases (CO2 and H2) are bubbled through the fermentation broth followed by cooling the gas (or gases) in a condenser. As the gas is bubbled through the fermentor, it captures ABE, which is condensed in the condenser followed by collection in a receiver. Once the solvents are condensed, the gas is recycled back to the fermentor to capture more ABE. This process continues until all the sugar in the fermentor is utilized by the culture. In some cases, a separate stripper can be used to strip off solvents followed by recycling the stripper effluent that is low in ABE. Figure 6.3 shows a typical schematic diagram of solvent removal by gas stripping. Gas stripping has been successfully applied to remove solvents from batch (Ennis et al., 1986b; Maddox et al., 1995; Ezeji et al., 2003), fed-batch (Qureshi et al., 1992, Ezeji et al., 2004), fluidized bed (Qureshi and Maddox, 1991a) and continuous reactors (Groot et al., 1989; Ezeji et al., 2002). In addition to removal of solvents, a concentrated sugar solution was fed to the reactors to reduce the volume of process streams and economize the butanol production process. The reader is referred to the Batch process with concentrated sugar solutions and fed-batch fermentation sections of this chapter where concentrated sugar solutions were successfully fermented in combination with product recovery by gas stripping. In these pro­cesses, the reactor productivities and product yield were also improved (Maddox

et al., 1995; Qureshi and Maddox, 1991a; Ezeji et al., 2002). Additional advan­tages of gas stripping included achieving a high product concentration in the condensed stream and the requirement for no membrane or chemicals for the recovery process.

Strategies for tailoring the properties of Nafion membranes include surface mod­ification of the membrane with a barrier less permeable to methanol that still allows facile proton conduction, addition of intercalants into the membrane to react with methanol to reduce crossover, and blending Nafion with other polymers to form hybrid membranes.

Palladium metal is of particular interest for researchers as it is impermeable to methanol but not proton [33,56]. A variety of methods to apply the Pd layer to Nafion have been assessed and the effectiveness of the modification in reducing methanol crossover evaluated.

Ma et al. looked at the effectiveness of reducing methanol crossover by sputtering a Pt/Pd-Ag/Pt layer onto Nafion [32]. It was found that while the layers were not crack-free, the Pd alloy-coated Nafion had increased performance over uncoated Nafion. A DMFC made with a Nafion membrane coated with a 1-pm thick Pd alloy layer generated a maximum current density roughly 35% (2.3 vs. 1.7 mW cm-2) higher than a control DMFC made with twice the electrocatalyst loading, though, the power densities are lower than one might expect.

Hejze et al. evaluated the performance of electrolessly deposited Pd-coated Nafion 117 to that of unmodified Nafion 117 membrane [56]. Here, Pd layers were coated onto fully hydrated Nafion substrates and the performance as a separator evaluated in a specialized cell for methanol concentrations <10%. Over the course of 10 hours, methanol crossover through the Pd-coated membrane was found to be much lower than for the unmodified Nafion control. The design of the fuel cell and large iR drop disallowed using realistic current densities. The authors think the technology can be applied to MEA type cells and acknowledge the increased cost of using another noble metal in a DMFC.

Methods to deposit Pd onto the surface of Nafion membranes by means of ion exchange and chemical reduction were studied by Hong et al. [33]. Palladi — nized Nafion PEMs were found to be less permeable to methanol and uptake more water then unmodified Nafion. A DMFC made with the palladinized Nafion PEM generated roughly 40% higher maximum current density than the Nafion control cell. Of the palladinized membranes tested, the best performers were found to have nanoparticles deposited near the surface of the membrane.

Choi et al. modified Nafion membranes in one of three ways: plasma etching the Nafion surface, sputtering Pd onto the Nafion surface, and combining both plasma etching and Pd sputtering [34]. Plasma etching changes the membrane morphology. Sputtering Pd “plugs” the pores of the water-rich domain of the membrane that allow proton conduction, but acts as a barrier to methanol cross­over. When tested against an untreated Nafion membrane, it was found that all three treated membranes had lower permeability to methanol with the plasma/Pd sputtered membrane having the lowest permeability. When the membranes were tested in single DMFCs, it was found all of the test cells had higher open circuit potentials than the control cell. The current-voltage performance of the Pd sput­tered and plasma-etched cells were superior to the control cell. The test cell with both treatments performed poorly relative to the control cell. The Pd sputtered cell had a power maximum of ~80 mW cm-2, which is slightly more than twice the control cell power maximum.

Kim et al. used supercritical carbon dioxide (sCO2) to graft polystyrene onto Nafion 115 as sCO2 produces low thermal stress and has a plasticizing effect when used as a swelling agent in polymers [35]. Following impregnation, the membrane was sulfonated and its properties compared to unmodified Nafion. Impregnated membranes have higher ion exchange capacity and lower perme­ability to methanol. DMFCs made with impregnated membranes generate more current at 350 mV (~140 mA cm-2) than a Nafion 115 control cell (—113 mA cm-2).

Kang et al. deposited thin (0.1 pm), clay-nanocomposite films onto Nafion 117 using layer-by-layer assembly [57]. The purpose was to reduce methanol crossover using exfoliated (leaf-like) clay nanosheets that are efficient compo­nents in barrier membranes for gas and water vapor. Permeability of methanol and ionic conductivity of the treated Nafion are measured and compared to a Nafion control. The control membrane has a methanol permeability of 1.91 x 10-6 cm2 s-1 and in-plane conductivity of 0.122 S cm-1. The Nafion modified with a 20-bilayer nanocomposite, has roughly half the methanol permeability as the control Nafion, 7.58 x 10-7 cm2 s-1 and nearly the same in-plane ionic conductivity, 0.124 S cm-1.

Chan et al. modified Nafion 115 membranes using in situ acid-catalyzed polymerization of furfuryl alcohol (PFA) to introduce highly cross-linked and methanol impermeable domains into the Nafion matrix. Modified and untreated Nafion PEMs were prepared and characterized [58]. It was found that methanol flux through the membranes, measured potentiostatically, changed as a function of the wt% of PFA in the membranes. A “sweet spot” of 8 wt% showed the lowest methanol flux, nearly 3x smaller than unmodified Nafion, while membranes with lower and higher PFA content had methanol flux intermediate to the 8 wt% and control. The PFA membranes were integrated into DMFCs and the output at room temperature and 60°C compared to that of a native Nafion control DMFC. Under all conditions, the DMFCs made with PFA PEMs generated significantly more power than the control DMFC. Peak power densities for DMFCs made with the PFA membranes were 2 to 3x larger than the unmodified Nafion DMFC.

One strategy to enhance water retention in PEFCs is to incorporate inorganic particulates into the PEMs of fuel cells [59,60,61]. Nafion membranes impreg­nated in this fashion act as a barrier to methanol crossover and can be used in high temperature (—150°C) direct alcohol fuel cells and H2/air fuel cells [44]. Arico et al. evaluated the surface properties of basic and neutral alumina, ZrO2, SiO2, and SiO2-phosphotungstic acid (SiO2-PWA) using X-ray photoelectron spectroscopy (XPS), Brunauer Emmett and Teller (BET) surface area, and acid — base characterizations. Composite membranes were prepared by recasting Nafion with the inorganic fillers. The resulting membranes were incorporated into DMFCs [44]. All of the membranes showed similar methanol crossover behavior of 4 ± 1 x 10-6 mol min-1 cm-2 at 145°C and 0.5 A cm-2. The electrochemical performance and conductivity of the composite membranes tracks the acidity of the intercalants and follow the series: SiO2-PWA > SiO2 > ZrO2 > n-Al2O3 > b — Al2O3. That is, the membranes with the best performance were the most acidic. Here “n” stands for neutral and “b” for basic. The DMFC made with the hybrid SiO2-PWA/Nafion membrane produced 400 mW cm-2 at 900 mV using pressur­ized O2 and a cell temperature of 145°C.

In another study Baglio et al. studied Nafion-TiO2 membranes for use in high temperature DMFCs [45]. The electrochemical performance of the membrane is significantly influenced by the properties of the intercalants such as surface area and pH. Here, the TiO2 intercalated into the membranes had been calcined at temperatures ranging between 500 and 800°C. The pH of the resulting particles trends with the temperature; a lower calcination temperature gives a particle with lower pH. As seen in [44], the membrane with the highest acidity generated the most power. Under similar operating conditions of 145°C cell temperature, 2.0 M methanol solution, and pressurized O2, a DMFC using TiO2 calcined at 500°C generated 350 mW cm-2. This DMFC, subjected to longevity tests, operated for a month with daily cycles of start-up and shut-down under the conditions men­tioned above. The cell potential was potentiostatically held at 400 mV. At start­up, the cell generated ~800 mA cm-2 (320 mW cm-2) and decreased to roughly 760 mA cm-2 (304 mW cm-2) after 4 hours of operation. This occurred daily. Upon feeding water to the anode, start-up performance was restored the following day.

Bauer and Willert-Porada characterized Zr-phosphate-Nafion membranes as candidate materials for use in DMFCs [62]. The inorganic filler reduced methanol permeability and the phosphate layer had preferred permeability to water over methanol. The preliminary results suggest Zr-phosphate can be used to tailor such Nafion properties.

The type of fish the project will use are tilapia. They are a very forgiving fish, adaptable to a wide range of environments. They are fecund (have lots of babies) and grow from birth to marketable size in 6 months. They are efficient users of feed (5 pounds of feed = 1 pound of fish). By contrast, beef requires 19 pounds of feed to produce 1 pound of gain. Tilapia are the answer to a hungry world. The flesh is mild and flavorful. They are mouth breeders (the mother carries the eggs in her mouth until they hatch) and a tropical fish that require warm water, so there is no danger of their “escape” from cultivation and contamination of local waterways.

Auto-Feeders

The fish finish tank will be equipped with auto-feeders, which hold a reserve of feed and are activated by hungry fish bumping a rod that projects down into the water. When activated, it releases a small amount of pellets to the fish below. The fish always have a supply of feed before them that is released on their demand. As a result, the feed is always fresh and overfeeding is reduced thereby enhancing
the quality of tank water. Water quality drops when uneaten feed is present on the bottom of the tank. This eliminates the need for 5-6 hand feedings throughout the day. Labor then is only required to assure that the auto-feeders are kept full. The fish are trained in the hatchery to receive food in this manner.

A broad range of hydrocarbons, ranging from methane to waxes of high molecular weight can be produced from synthesis gas using an iron or cobalt catalyst. These are called Fischer-Tropsch (FT) liquids or Gas-to-Liquids (GTL). By cracking the longer hydrocarbons and refining, a diesel is produced that can be blended into standard diesel. FT diesel has very low levels of sulfur and aromatic com­pounds compared to ordinary diesel and, when processed in an internal combus­tion engine, emit less NOx and particulates than diesel fuels.

The FT process was first developed at commercial scale for the production of synthetic oil in Germany during the Second World War and was further developed by Sasol in South Africa. Sasol remains today the only producer of FT products from low grade coals. The rising oil price, availability of large amounts of “stranded gas,” and decreasing investment costs have increased the interest in FT liquids. Qatar seems to be the driver of FT development, with planned projects totaling to 800,000 bbl/day or about 114 ktonne/day (Bensaid 2004).

In 1999 when the world had a considerable surplus of methanol production capacity, several companies proposed to retrofit methanol plants to produce alter­native products, e. g., Fischer-Tropsch liquids or hydrogen (Brown 1999; Yakob — son 1999). The demonstration unit of Choren in Freiberg Germany, has produced both FT liquids and methanol.