Solid oxide fuel cells are very promising energy conversion systems that can generate electricity at high efficiencies using not only hydrogen but also alcohol and hydrocarbon fuels. Further progress on the development of fuel cell materials, particularly the electrodes, which prevents carbon deposition and sulfur-resis­tance, will play a key role to achieve a stable operation of direct-alcohol SOFCs with high power densities. In contrast to double-chamber SOFCs, the single­chamber solid-oxide fuel cells offer a simple design that are not affected by the challenges of high temperature sealing and may be a cost-effective alternative

with a mechanically more robust structure. Recent developments in single-cham­ber SOFCs show promising results toward achieving significantly high power densities using hydrocarbon fuel gases mixed with air.

The fish sold will be processed into fillets to increase consumer sales appeal, although the project has potential customers presently who wish to purchase live fish. The project will process the fish in a specially designed portable unit. Processing will be done by special equipment that strips off all the scales from the fish and automatically fillets them. The equipment is very fast, using no more than a few seconds to process each fish. All waste from this processing is saved and made into fish meal, another very important feed ingredient making the project just that much more efficient. The need for marine, or salt water, fish meal is thereby eliminated and the protein signature of the meal is identical to the requirements of the fish being raised.

Methanol (also called methyl alcohol) is the simplest of alcohols. Its chemical structure is CH3OH. It is produced most frequently from wood and wood by­products, which is why it is frequently called wood alcohol. It is a colorless liquid that is quite toxic. The LD50 for oral consumption by a rate is 5628 mg/kg. The LD50 for absorption by the skin of a rabbit is 20 g/kg. The Occupational Safety and Health Administration (OSHA) approved exposure limit is 200 ppm for 10 hours. Methanol has a melting point of -98°C and a boiling point of 65°C. It has a density of 0.791 g/ml and is completely soluble in water, which is one of the hazards of methanol. It easily combines with water to form a solution with minimal smell that still has all of the toxicity issues of methanol. Acute methanol intoxication in humans leads to severe muscle pain and visual degeneration that can lead to blindness. This has been a major issue when considering methanol as a fuel. Dry methanol is also very corrosive to some metal alloys, so care is required to ensure that engines and fuel cells have components that are not corroded by methanol. Today, most research on methanol as a fuel is centered on direct methanol fuel cells (DMFCs) for portable power applications (replace­ments for rechargeable batteries), but extensive early research has been done on methanol-gasoline blends for combustion engines.

Utilizing landfill gas to manufacture methanol has many significant advantages over the current suppliers of methanol. •

• “Green methanol” will allow the manufacturer to take advantage of various tax credits and incentives passed by the United States Congress to promote renewable products and fuels. One example is the 60-cents — per-gallon “alcohol fuel credit” that applies to methanol used in trans­portation fuels.

• The utilization of landfill gas in the manufacture of methanol results in the sequestering of methane and carbon dioxide, this process is credited with reducing greenhouse gas emissions.

The emerging markets for renewable methanol are becoming more defined and mature as demand is being driven by environmental statutory requirements and U. S. government mandates regarding the reduction of global warming gases and ending U. S. reliance upon foreign oil and energy. To that end, landfill gas to methanol offers a compelling opportunity to develop a significantly large domestic industry to support the growing demand for domestic renewable fuels and energy.

For the purposes of this chapter, the high temperature, dilute acid pretreatment and subsequent enzymatic saccharification method will be examined in more detail as a conversion technology for ethanol production from alfalfa stem fractions. The high temperature, dilute acid pretreatment is designed to remove noncellulosic cell wall polysaccharides and lignin, because these constituents will interfere with the cellulase enzyme cocktails used for hydrolysis of the cellulose. One design goal of this pretreatment is to reduce the pH of the feedstock reaction mixture to 1.3-1.5 prior to heating (National Renewal Energy Laboratory, Golden, CO; Laboratory Analytical Procedure-007, May 17, 1995). The amount of sulfuric acid required to reach this pH target for alfalfa stems was 8.1 mmol g-1 biomass DM in a 1% solids slurry, compared to 6.4 mmol for switchgrass and corn stover (Jung, unpublished). Maturity of alfalfa stems and switchgrass did not influence the acid requirement. Dien et al. (2005) observed that the sulfuric acid loading required to maximize release of nonglucose sugars from alfalfa stems when heated at 121°C for 1 h was 2.5% (wt/vol), whereas 1.5% was sufficient for switchgrass. The higher acid require­ment for alfalfa stems is most likely due to the greater pectin content of alfalfa cell

Immature Mature

walls compared to grasses; however, the hemicellulose content is lower and lignin content is similar in alfalfa stems compared to the grasses (Dien et al., 2005). Torget et al. (1990, 1992) also observed that legume feedstocks are more recalcitrant to acid pretreatment than grasses.

The efficiency of glucose release by acid pretreatment, followed by enzymatic saccharification from cell wall polysaccharides (cellulose and xyloglucans), declined as alfalfa stems became more mature (Figure 5.2). While efficiency of glucose conversion declined with maturity, the total yield of glucose was not altered (Figure 5.2), because cellulose content increased in more mature alfalfa stems. Similar declines in efficiency with maturity were observed for switchgrass and reed canary grass (Dien et al., 2005), but the efficiency of glucose release from the grasses was greater than from alfalfa stems. This may reflect the higher concentration of lignin in the alfalfa stems because across all three species, efficiency of glucose release was negatively correlated with lignin content of the feedstock. Increasing the temperature of the acid pretreatment resulted in improved efficiency of glucose release from alfalfa stems (Dien, personal com­munication). While efficiency of glucose release was lower for alfalfa than for grasses, total yield of glucose was very similar between the feedstocks. This again reflects the interaction of efficiency with glucose content of the feedstocks.

Pure ethanol becomes difficult to vaporize when cold, leading to poor cold startability. In fact ethanol will not form an air/fuel vapor mixture high enough to support combustion below 11 °C.12 Therefore, gasoline is added to the ethanol in order to support cold startability and increased cold start enrichment is used to achieve combustible vapor air mixtures in the engine.

Additional difficulties when cold starting with E85 can be attributed to its high conductivity. During cold starts, the spark plug electrodes can become wetted with fuel. Since E85 is much more conductive, this can leading to plug shorting and misfire.8

These problems have been addressed by the major automakers through better cold-start fuel calibrations. Most manufacturers now report good cold starts at temperatures below 0°F (-18°C) when using E85 in a winter blend (E70).

Safety

E85 has wider flammability limits on the rich side, and it has a higher flame speed compared to gasoline. This increases the probability of encountering flash­back or fuel vapor ignition during fuel filling.17 Because of this, vehicles using

E85 require a flame arrestor, which is installed into the fuel filling tube. This device will extinguish any flame that might occur.

Since enzymes are highly selective, there are limited problems associated with fuel crossover from the anode to the cathode in a biofuel cell. If an anode and cathode are both selective, then a polymer electrolyte membrane is no longer required to separate the anode and cathode solutions. Topcagic et al. have devel­oped the first ethanol membraneless biofuel cell. At the cathode, bilirubin oxidase has been chosen to replace platinum as the reducing catalyst to increase specificity of the cathode. A schematic showing the simplicity of a membraneless biofuel cell can be seen in Figure 12.7.

Alternatives for platinum found in the literature typically use laccase enzyme as studied by Heller’s Group [27]. Laccase lowers the power of a biofuel cell due to the maximum turnover rate of laccase occuring at pH 5.0 and deactivation in the presence of chlorine ions. Bilirubin oxidase has been chosen as a catalyst for future studies, because it has optimum performance in a physiological envi­ronment (near-neutral pH and presence of various ions). The second problem associated with many biocathodes in the literature is that electrodes are osmium — based creating a toxicity hazard to the surrounding environment. Topcagic et al. have replaced the osmium-based mediator with a ruthenium-based complex of

similar structure that is less toxic and has a higher self-exchange rate. A third problem associated with anodes and cathodes in the literature is a technique of immobilizing the enzyme at the electrode surface. Literature enzyme immobili­zation employs covalent bonding of the enzyme to the surface of the electrode or to the mediator. This method does not protect the enzyme from its surroundings and its optimal activity is lowered due to the conformational change that resulted from physically attaching the enzyme to the surface to the electrode [23]. How­ever, instead of physically attaching the enzyme, Topcagic et al. have immobilized it in modified Nafion®; therefore optimum enzyme activity is retained and the enzyme is protected from the surrounding environment.

The membraneless biofuel cell operates at room temperature, which varies from 20-25°C in a phosphate buffer pH 7.15 containing 1.0 mM ethanol. Since the polymer electrolyte membrane has been eliminated, the electrodes have to be specific enough to work in same compartment. Both electrodes, bioanode and biocathode, consisted of immobilized enzyme casting solution at the surface of the 1-cm2 carbon fiber paper. The performance of NAD+-dependent ADH and PQQ-dependent ADH bioanodes coupled to biocathodes was also studied and is

Electrical Load

summarized in Table 12.3. The bioanode used for most studies had PQQ-depen — dent alcohol dehydrogenase enzymes, while the biocathode had bilirubin oxidase, bilirubin with Ru(bpy)3+2 immobilized at the surface of the electrode. Maximum open circuit potential is 1.04 V with maximum current density of 8.47 mA/cm2 [28]. For the membraneless system comprised of a PQQ-dependent ADH anode and bilirubin oxidase biocathode, the fuel cell has an increased lifetime of greater than 353%, increased open circuit potential of 15%, and increased power density of 97% compared to the NAD+-dependent ADH bioanode [28].

CONCLUSIONS

Research has succeeded in increasing the stability of enzymes at the electrode surface, which in turn increases the open circuit potential, current and power of a biofuel cell. Also, by eliminating the need for an electrocatalyst layer and a polyelectrolyte membrane, it reduces the cost of production of the current biofuel cell and simplifies fabrication. Replacing NAD+-dependent ADH with PQQ — dependent ADH is a step toward reaching the goal of increasing the overall lifetime of the biofuel cell for future use in multiple power applications. The most important phenomenon to examine is the increase in lifetime of the mem­braneless system with PQQ-dependent bioanodes. The PQQ-dependent bioanodes are more stable than NAD+-dependent bioanodes. In addition to better data results, PQQ-dependent ADH serves as an invaluable replacement for NAD+-dependent ADH due to the simplicity it offers in bioanode fabrication.

There are a number of opportunities for new power sources aside from replacing petroleum for transportation. Beginning at the small end of the scale, alternatives to today’s battery chemistry are in critical demand. Proliferation of portable electronics and increasing functionality has exceeded the capabilities of the lith­ium-ion battery. Indeed, the features able to be offered to consumers by the major electronics development companies are limited by the battery, an example being the delay of mass introduction of the 4G cell phone. Many outside of Japan may not be familiar with these phones, known as “power eaters,” which last for all of 15 minutes when being used to watch television or movies. The Japanese suffer through this shortfall because their long daily work commutes are brightened by the entertainment. Batteries’ limitations have at least created a new market oppor­tunity, known as “juice bars,” where the Japanese cannot only receive liquid refreshment, but for a fee can recharge their cell phones as well.

This, of course, is a temporary solution to an obvious problem: the need for new portable power sources. Fuel cells have been studied for over 40 years as a potential battery replacement technology. With a potential $4-billion-plus lithium battery market takeover opportunity, there are a plethora of entities working to deliver portable fuel cells [2]. The Direct Methanol Fuel Cell (DMFC) has probably received the majority of attention in this area. Despite hundreds of millions in research and development dollars, in early 2005 there is no consumer product on the market. DMFC has applications and viability in other markets, but the size, cost, and performance requirements for rechargeable battery replace­ment have thus far proved insurmountable. New catalyst developments as well as new membrane technology may push DMFCs over the hump to widespread commercialization; however, toxicity will remain a serious obstacle.

Enter the opportunity for fuels other than methanol in the portable battery market. Ethanol is the obvious choice because it is already widely available in day-to-day life and on airlines as well, a necessity. Additionally, ethanol has certain chemical properties making it desirable as a fuel, such as higher energy density than methanol while remaining a small enough molecule for good diffu­sion properties. As discussed in this book, innovations in catalysts are required to employ ethanol. Efficacy has been demonstrated; however, catalyst stability and operating temperature must still be addressed for metal-based systems.

Perhaps a previously considered fringe effort, now gaining momentum, is the use of nontraditional catalysts, i. e., biological catalysts. The advantages are cost savings from elimination of precious metals, simplification of system design due to high selectivity for analyte, dramatically increased fuel options, and efficient operation at room temperature, among others discussed. Enzymes in particular, have the potential to compete (and in some cases already are competing) with DMFC and DEFCs and surpass their performance. It may be breakthroughs in this area of research that ultimately enable commercial applications. Elimination of PEMs, bipolar plates, and precious metal catalysts are significant advantages.

SOFC fuel cells have also had a resurgence of effort, most likely driven by military interest. Advances in catalysts and insulating materials are showing promise for portable applications, portable meaning 20-W systems.

Overall, it is the opinion of this author that the portable fuel cell effort emerged too early for its time. Hundreds of millions of dollars, if not billions, have been taken in by start-up companies through institutional, noninstitutional, and government sources over the past 10+ years with no product to show for it. The technology continues to suffer from essentially the same key hurdles that it did since the start of effort. Many investors are losing interest and have become calloused to the excitement surrounding portable fuel cells. That is unfortunate because we are nearing the opportune time for this market. Key breakthroughs are on the verge of occurring, which will hopefully burst the bubble and pave the way for commercial applications. Some venture firms recognize this oppor­tunity and are sticking with fuel cells in the belief that we are near the gold rush.

The raw synthesis gas produced by gasification contains impurities. The most typical impurities are organic impurities like condensable tars, BTX (benzene, toluene, and xylenes), inorganic impurities (NH3, HCN, H2S, COS, and HCl), volatile metals, dust, and soot (Tijmensen 2000; van Ree et al. 1995). These contaminants can lower catalyst activity in reformer, shift, and methanol reactor, and cause corrosion in compressors, heat exchangers and the (optional) gas turbine.

The estimated maximal acceptable contaminant concentrations are summa­rized in Table 2.2 together with the effectiveness of wet and dry gas cleaning, as described below.

The gas can be cleaned using available conventional technology, by applying gas cooling, low-temperature filtration, and water scrubbing at 100-250°C. Alter­natively, hot gas cleaning can be considered, using ceramic filters and reagents at 350-800°C. These technologies have been described thoroughly by several authors (Consonni et al. 1994; Kurkela 1996; Tijmensen 2000; van Dijk et al. 1995; van Ree et al. 1995). The considered pressure range is no problem for

TABLE 2.1 (CONTINUED) Characteristics of Gasifiers

1 640 ktonne dry wood annual, load is 8000 h.

2 Calculated from LHVwet = HHV^ X (1 — W) — Ew X (W + Hwet x mH2O); with Ew the energy needed for water evaporation (2.26 MJ/kg), Hwet the hydrogen content on wet basis (for wood Hdry = 0.062) and mH2O the amount of water created from hydrogen (8.94 kg/kg).

3 Wet biomass: 80/0.7 = 114 tonne/hr to dry biomass 80/0.85 = 94.1 tonne/hr for IGT П evaporate water 20.2 tonne/hr at 1.3 ts/twe in Niro (indirect) steam dryer. Calculation for BCL is alike. The steam has a pressure of 12 bar and a temperature of minimally 200°C (Pierik et al. 1995).

4 Pressure is 34.5, 25, or 1.2 bar, temperature is minimally 250, 240, or 120°C.

5 Calculated from the total mass stream, 188.5 tonne/hr.

6 Quoted from OPPA (1990) by Williams et al. (1995).

7 Knight (1998).

8 Compiled by Williams et al. (1995).

either of the technologies. Hot gas cleaning is advantageous for the overall energy balance when a reformer or a ceramic membrane is applied directly after the cleaning section, because these processes require a high inlet temperature. However, not all elements of hot gas cleaning are yet proven technology, while there is little uncertainty about the cleaning effectiveness of low temperature gas cleaning. Both cleaning concepts are depicted in Figure 2.4.

In contrast to the dry-grind process (where the whole corn kernel is ground and enters the fermenter) in wet milling, the kernel is first fractionated into separate components and only the starch enters the fermenter. Corn wet milling plants are often referred to as biorefineries, comparable to petroleum refineries, because wet milling fractionates corn into its components and then processes the components into more valuable products [20]. Wet milling separates the kernel into germ (oil), gluten (protein), fiber, and starch fractions, yielding corn oil, animal feed, and a variety of products derived from starch.

Steeping

The wet-milling process starts with steeping, which enables isolation of the different kernel fractions [20]. Corn is screened to remove foreign material, and soaked in dilute (0.12-0.20%) sulfurous acid at 52°C for (typically) 30-36 h. Lactobacillus and related bacteria growing in the steep water produce lactic acid and other metabolites that further acidify the medium. Steeping occurs in a series of large stainless steel tanks, with steep water recirculated countercurrently from tanks holding “older” corn that is nearing the end of the steeping process to “newer” corn that is beginning the steep. The effect of recycling the steep liquid is the progression of the corn up a SO2 concentration gradient. The combined action of sulfurous acid and lactic acid, and probably also direct effects of microbes growing in the steep, prepare the kernels for processing into fractions. Steeping softens and swells the kernels, disrupts disulfide bonds between the protein and starch in the endosperm, and releases the starch granules into solution.