Both the prawns and crawfish go through a critical juvenile phase in their devel­opment. At this time, they become cannibalistic and will feed on each other. Molting is frequent, on the order of every 3-5 days, since the growth rate is so very rapid during this stage of development. When they molt, they remain motion­less until the outer skin hardens into a new shell. But this immobility is a signal to other juveniles nearby that they are vulnerable. Before the shell hardens, they can literally be torn to pieces. In a clearwater system, even with adequate hiding places, there is considerable loss. This is because they can see each other, and their appetites are so great at this time, they are almost continually hungry. To address both of these causes for loss, the project will utilize a greenwater system for this stage of development. Greenwater is simply clearwater that has so much algae growing in it, that it becomes opaque and vision is limited to less than one inch, which provides considerable concealment to molting individuals. It looks much like pea soup. The project will deliberately seed the greenwater system with spirulina, a very nutritious form of algae, high in protein and essential amino acids in addition to vitamins, minerals, and microelements. Between feedings, it makes an excellent snack for juveniles. Even though both of these species are cannibalistic in the juvenile phase, between feedings they will forage vigorously on algae, which are all around them. The algae then becomes a continuous supply of high-quality feed — much the same as pasture for ruminants. There is no biofiltration used in this rearing system, rather simple oxygenation. Spirulina act as biofilters by digesting spent feed and wastes from the juveniles for their growth and reproduction. Algae also add oxygen to the water, and remove carbon dioxide. Once past the juvenile stage, these species lose their cannibalistic tendencies and will not return to them unless they are overcrowded and underfed.

William H. Wisbrock

President, Biofuels of Missouri, Inc., St. Louis

CONTENTS

Landfills and Landfill Gas………………………………………………………………………………. 51

Methanol, Present, and Future………………………………………………………………………… 53

Landfill Gas to Methanol……………………………………………………………………………….. 54

Renewable Methanol……………………………………………………………………………………… 56

New Uses for Domestic Methanol…………………………………………………………………… 57

Abstract An explanation of how market forces, governmental mandates, and tax incentives have placed the use of landfill gas as an alternative energy source into a growing industry in the United States. Also included is a description of the opportunities and challenges that face this emerging domestic energy industry, along with a description of the Acrion Technology CO2 Wash process that cleans landfill gas, so that it can be utilized for the manufacture of methanol.

Because alfalfa leaves contain approximately 300 g CP kg-1 DM, this portion of the crop has greater value as an animal feedstuff than for conversion to ethanol. Based simply on its protein concentration, alfalfa leaf meal was estimated to have a value of $138 Mg-1 (Linn and Jung, unpublished). This price far exceeds the target feedstock value of $33 Mg-1 assumed in a functioning corn stover-to — ethanol production system (Aden et al., 2002). In an extensive series of studies involving lactating dairy cows and fattening beef cattle, alfalfa leaf meal was shown to be an acceptable protein feed supplement in place of soybean meal (DiCostanzo et al., 1999). Besides providing protein for beef steer growth, alfalfa leaf meal also reduced the incidence of liver abscesses at slaughter, thereby increasing the market value of the cattle. Furthermore, alfalfa leaf meal could replace alfalfa hay in the diet of lactating dairy cows as a source of both protein and fiber to support normal milk production (Akayezu et al., 1997). Suckling beef calves actually gained weight more rapidly when fed alfalfa leaf meal in a supplemental creep feed than observed with a soybean meal-based supplement (DiCostanzo et al., 1999). From these results, it is clear that alfalfa leaf meal could provide a valuable coproduct for an alfalfa-to-ethanol production system.

Like gasoline, ethanol is liquid at room temperature and pressure. It can be handled and dispensed using equipment designed for gasoline-with some modi­fications to accommodate material incompatibilities as discussed above. Most consumers would not notice any difference when fueling their vehicles using E85.

One of the major differences between using E85 and gasoline affecting engine operation is due to the differences in vapor pressure and latent heat of vaporiza­tion. In order for combustion to begin in an engine, a portion of the fuel must be vaporized. Gasoline is a mixture of many hydrocarbon compounds with varied vapor pressures and latent heats of vaporization. This means that even under cold conditions a portion of gasoline will still evaporate. Because ethanol is a pure substance, it becomes difficult to vaporize when cold. In fact ethanol will not form an air/fuel vapor mixture high enough to support combustion below 11°C.12 This led to the use of E85. Gasoline is added to the ethanol in order to support cold startability. Most E85 is blended with regular grade unleaded gasoline.

A comparison of E85 and gasoline is presented in Table 8.1. One complication in using values from this table is the fact that E85 is made from ethanol that has been denatured with up to 5% gasoline; thus E85 is usually composed of less than 85% pure ethanol. This means that the data in Table 8.1 is an approximation of E85 as it is based upon a true blend of 85% ethanol.

Further, E85 is determined on a volume basis, but many users mistakenly use a mass basis in order to determine its composition.3 Fortunately, the densities of gasoline and E85 are similar as shown in Table 8.1. Assuming constant component volumes during mixing, 85% ethanol on a volume basis produces about 85.7% ethanol on a mass basis.

Finally, the actual blends of E85 are seasonally adjusted depending on the geographical region and the season. During warm weather the blends have higher levels of ethanol to lower vapor pressure; thus minimizing evaporative emissions and vapor lock. These blends of E85 typically contain 85% denatured ethanol. While in cold weather, more gasoline is added to the blend to avoid starting problems. Most winter blends of E85 are actually 70% ethanol by volume. Of course, the gasoline, too, is seasonally adjusted to minimize vapor pressure during the warmer months and to aid in cold startability during the colder months. As one can see, the values in Table 8.1 are simply nominal values. Samples of E85 used in emissions testing should first be analyzed by a qualified laboratory to obtain precise property values.

American Society for Testing and Materials (ASTM) standards for E85 are presented in the following table. These standards, although generally voluntary, are usually followed by major fuel producers. Table 8.2 lists physical properties

for the different seasonal blends. Note that this table lists the true levels of pure ethanol; thus the levels appear lower than expected due to the gasoline used as the denaturant in the ethanol.

Class 1 (minimum 79% ethanol) is generally considered summer blend; it is used by most states during the warm months. This is the fuel that is closest to “true” E85. Classes 2 and 3 are considered winter, or spring/fall blends. Class 2 (minimum 74% ethanol) is generally used during spring and fall in cooler cli­mates, and in the winter in mild climates. Class 3 (minimum 70% ethanol) is used during the winter, early spring and late fall, in cooler climates.

One additional property of ethanol that is not shown in either table is its high miscibility with water. Water entrainment in the ethanol can cause the ethanol and gasoline to separate, leading to vehicle stalls and poor drivability.15 Fuel handling and storage systems must be designed to keep moisture levels out of the fuel. On the positive side, regular use of E85 helps to eliminate moisture in vehicle fuel storage systems as the moisture is entrained in the ethanol and then removed from the system.

The technique developed by Minteer et al. [20-22] involves modifying Nafion® with quaternary ammonium bromide salts. This technique provides an ideal environment for enzyme immobilization due to the biocompatibility and structure of the micellar pores. This method helps to keep the enzyme at the electrode surface as well as maintain high enzymatic activity and protect the enzyme from the surrounding environment. Previous studies by Schrenk et al. have shown that mixture-cast films of quaternary ammonium bromide salts and Nafion® have increased the mass transport of small analytes through the films and decreased the selectivity of the membrane against anions [21].

Enzyme entrapped within a micellar polymer

Metal based electrode

FIGURE 12.5 Enzymes immobilized by entrapment.

Quaternary ammonium bromide salts have a higher affinity to the sulfonic acid side chain than the proton; therefore, they can be utilized to modify the polymer and extend the enzymes lifetime because protons are less likely to exchange back into the membrane and reacidify it. A much higher preference to the quaternary ammonium bromide salts than to the proton has been shown by titrating the number of available exchange sites to protons in the membranes [21]. Due to the fact that quaternary ammounium bromide salts are larger in size than protons, the micellar structure will also be enlarged to facilitate enzyme entrapment.

Immobilizing enzymes in micellar pores will eliminate the issue of covalent bonding, which “wired” techniques are plagued with, because the process can buffer the pH of the membrane for optimal enzyme catalytic activity. In addition, the pore structure also provides a protective and restrictive 3D pore, unlike “wired” techniques where an enzyme is freely subjected to the surroundings and can be easily denatured if introduced to a harsh environment. Also, quaternary ammonium bromide salts have similar hydrophobicity as the enzymes. Nafion® modified with quaternary ammonium bromide salts will not only provide a buff­ered micellar structure for easier enzyme immobilization, but will also retain the electrical properties of unmodified Nafion® as well as increase the mass transport

2NAD

FIGURE 12.6 Oxidation schemes for methanol (top) and ethanol (bottom).

flux of ions and neutral species through the membrane minimizing problems associated with slow diffusion [20].

In Towers

Potatoes and strawberries lend themselves nicely to the use of vertical space. Potatoes especially can be grown in this manner using individual stacks of waste tires to contain the growing medium (compost) and provide room for the tubers to develop. The black of the tire absorbs heat and there is usually a heavy yield. Strawberries are a more economically advantageous crop as Louisiana State University has demonstrated. Grown in vertical stacks of pots, the university was able to fit the equivalent of 10 acres of strawberries into a 6000-square-foot greenhouse. Total space for each tower is 1 square foot and the reported yield is 32 pints from each tower. The growing medium is perlite and pine bark and nutrients can be supplied through either hydroponic or fish effluent fluids.

The IGT gasifier (Figure 2.2) is directly heated, which implies that some char and/or biomass are burned to provide the necessary heat for gasification. Direct heating is also the basic principle applied in pressurised reactors for gasifying coal. The higher reactivity of biomass compared to coal permits the use of air instead of pure oxygen.

Steam + oxygen

This could be fortuitous at modest scales because oxygen is relatively costly (Con — sonni and Larson 1994a). However, for the production of methanol from biomass, the use of air increases the volume of inert (N2) gas that would have to be carried through all the downstream reactors. Therefore, the use of oxygen thus improves the economics of synthesis gas processing. Air-fired, directly heated gasifiers are considered not to be suitable before methanol production.

This gasifier produces a CO2 rich gas. The CH4 fraction could be reformed to hydrogen, or be used in a gas turbine. The H2:CO ratio (1.4:1) is attractive to produce methanol, although the large CO2 content lowers the overall yield of methanol. The pressurized gasification allows a large throughput per reactor volume and diminishes the need for pressurization downstream, so less overall power is needed.

The bed is in a fluidized state by injection of steam and oxygen from below, allowing a high degree of mixing. Near the oxidant entrance is a combustion zone with a higher operation temperature, but gasification reactions take place over the whole bed, and the temperature in the bed is relatively uniform (800-1000 °C). The gas exits essentially at bed temperature. Ash, unreacted char, and particulates are entrained within the product gas and are largely removed using a cyclone.

An important characteristic of the IGT synthesis gas is the relatively large CO2 and CH4 fractions. The high methane content is a result of the nonequilibrium nature of biomass gasification and of pressurized operation. Relatively large amounts of CO2 are produced by the direct heating, high pressure, and the high overall O:C ratio (2:1). With conventional gas processing technology, a large CO2 content would mean that overall yields of fluid fuels would be relatively low. The synthesis gas has an attractive H2:CO ratio for methanol production, which

reduces the need for a shift reactor. Since gasification takes place under pressure, less downstream compression is needed.

When operated with higher steam input the IGT gasifier produces a product gas with a higher hydrogen content. This maximum hydrogen mode is especially useful if hydrogen would be the desired product, but the H2:CO ratio is also better for methanol production. However, the gasifier efficiency is lower and much more steam is needed.

Wet-Milling and Dry-Grind Corn Processes for Ethanol Fermentation

Corn is prepared for ethanol fermentation by either wet milling [20] or dry grinding [16] (Figure 4.4). One quarter of the ethanol produced in the United States comes from large-capacity wet-milling plants, which produce ethanol along with a variety of valuable coproducts such as pharmaceuticals, nutriceuticals, organic acids, and solvents. Dry-grind facilities, which account for the remainder of domestic ethanol production, are designed specifically for production of eth­anol and animal feed coproducts. Due to the relatively lower capital cost of dry — grind plants and the spread of ethanol plants out of the heart of the U. S. cornbelt, new plants under development and construction are dry-grind facilities.

Although both the dry-grind and wet-mill processes produce ethanol, they are very different processes. In dry grinding, dry corn is ground whole and fermented straight through to ethanol. The only coproduct, distillers dry grains with solubles (DDGS), is sold as animal feed. DDGS, which consists of the dried residual materials from the fermentation, contains the nonfermentable parts of the corn and the yeast produced during the fermentation. CO2 can also be collected and sold to soft-drink producers, but represents a low-profit and limited market.

In wet milling, by contrast, corn kernels are fractionated into each of their major individual components: starch, gluten, germ, and fiber. This imparts two very important advantages compared to dry grinding. First, the parts of the corn can each be marketed separately. So, the germ is used to produce corn oil, the gluten is sold as a high-protein feed to the poultry industry, and the fiber is combined with liquid streams, dried, and sold as a low-protein animal feed. Second, the wet mill produces a pure starch steam, which allows for the starch to be made into numerous different products. In addition to being fermented to ethanol, the starch can be modified for use in textiles, paper, adhesives, or food. Maltodextrins and high-fructose corn syrup, the major sweetener used by the U. S. food industry, are made enzymatically from starch. The starch can also be con­verted enzymatically to a fairly pure glucose stream and then fermented to any number of products. A partial list includes amino acids, vitamins, artificial sweet­eners, citric acid, and lactic acid, in addition to ethanol. If ethanol is produced, the yeast can be spray-dried and marketed as distillers yeast, a high-protein, low — fiber product suitable for feeding animals and fishes. Although no wet mill makes all of these products, it is not unusual for large facilities to have multiple starch product streams.

Dry-grind plants do not have the capability to ferment corn starch to these products in part because the additional products are nonvolatile and, therefore, cannot be simply separated by distillation from all of the other material in the fermentation. In summary, a wet mill that converts all its starch to ethanol produces at least two or three additional high-value products compared to a dry-grind facility. Of course, these additional products are realized only with much higher capital expenses. As discussed later in this chapter, there are several efforts under­way to develop less capital-intensive processes for either totally or partial frac­tionating corn that would be suitable for implementation at dry-grind facilities.

Batch fermentation is the most commonly studied process for butanol production. In the batch process the substrate (feed) and nutrients are charged into the reactor that can be used by the culture. In a batch process, a usual substrate concentration of 60-80 gL-1 is used as higher concentration results in residual substrate being in the reactor. The reaction mixture is then autoclaved at 121°C for 15 minutes followed by cooling to 35-37°C and inoculation with the seed culture. During cooling, nitrogen, or carbon dioxide is swept across the surface to keep the medium anaerobic. After inoculation, the medium is sparged with these gases to mix the inoculum. Details of seed development and inoculation have been pub­lished elsewhere (Formanek et al., 1997; Qureshi and Blaschek, 1999a). Depend­ing on the size of the final fermentor, the seed may have to be transferred several times before it is ready for the production fermentor.

Various substrates can be used to produce butanol including corn, molasses, whey permeate, or glucose derived from corn (Qureshi and Blaschek, 2005). However, some substrates may require processing prior to fermentation, known as “upstream processing,” such as dilution, concentration, centrifugation, filtra­tion, hydrolysis, etc. The usual batch fermentation time lasts from 48 to 72 h after which butanol is recovered, usually by distillation. During this fermentation period, ABE up to 33 gL-1 is produced using hyperbutanol producing C. beijer­inckii BA101 (Chen and Blaschek, 1999; Formanek et al., 1997). This culture results in a solvent yield of 0.40-0.42 (Formanek et al., 1997). The ABE con­centration in the fermentation broth is limited due to butanol inhibition to the cell. At a butanol concentration of approximately 20 gL-1, strong cell growth inhibition occurs that kills the cells and stops the fermentation. Butanol produc­tion is a biphasic fermentation where acetic and butyric acids are produced during acidogenic phase followed by their conversion into acetone and butanol (solven — togenic phase). During the acidogenic phase, the pH drops due to acid production and subsequently rises during solvent production. At the end of fermentation, cell mass and other suspended solids (if any) are removed by centrifugation and sold as cattle feed. Figure 6.2 shows fermentation profile of butanol production in a typical batch fermentation process from cornstarch using C. beijerinckii BA101.

Butanol can be produced both by using corn coproduct from i) corn dry-grind and ii) wet-milling processes. During the dry-grind process corn fiber and germ are not removed prior to fermentation. At the end of fermentation (after starch utilization during fermentation), corn fiber and other insoluble solids are removed by centrifugation, dried, and sold as cattle feed. The dried solids are known as “Distillers Dry Grain Solids” or DDGS. On the contrary, during the wet-milling

process, corn fiber and germ are removed prior to fermentation. In this process, cornstarch can be converted to any of the three products (liquefied cornstarch, glucose syrup, or glucose) each of which is fermentable by C. beijerinckii to produce butanol. It should be noted that often corn refineries add sodium met­abisulfite during the wet-milling operation as a corn kernel softening agent and preservative to the liquefied cornstarch. The presence of sodium metabisulfite may interfere with the direct fermentation of the liquefied cornstarch. However, glucose syrup or glucose does not contain any such fermentation inhibitors. The unit operations that are applicable to the corn dry-grind and wet-milling fermen­tation of butanol are given in Table 6.2.

During the 1940s and 1950s, production of butanol on an industrial scale (Terre Haute, IN, and Peoria, IL) was carried out using large fermenters ranging in capacity from 200,000 to 800,000 L. The industrial process used 8-10% corn mash, which was cooked for 90 min at 130-133°C. Corn contains approximately 70% (dry weight basis) starch. The use of molasses offers many advantages over using corn, including the presence of essential vitamins and micronutrients (Paturau, 1989). In industrial processes, beet and invert and blackstrap molasses were diluted to give a fermentation sugar concentration of 50 to 75 gL-1, most commonly 60 gL-1. The molasses solution was sterilized at 107 to 120°C for 15 to 60 min followed by adding organic and inorganic nitrogen, phosphorus, and buffering chemicals. The yield of solvent using C. acetobutylicum was usually low at 0.29-0.33. Distillation has been the method of choice to recover butanol; however, during the last two decades a number of alternative techniques have been investigated for the economical recovery of butanol, which will be discussed in the recovery section.

Discussions of performance targets and efficiencies for DMFCs are complicated due to the wide-ranging conditions, fuel and oxidant sources, and intended appli­cations for DMFCs. In this section, a survey of performance data and examples of target system requirements listed by government agencies are used to give a sense of the state of the art. Also, targets set by researchers in the literature are discussed.

In 2002, Jorissen et al. suggested DMFC performance targets to compete in terms of efficiency with reformate fed PEFCs [24]. The target they set for a DMFC is a power density of 250 mW cm-2 at a cell voltage of 500 mV and that furthermore, parasitic power loss due to methanol crossover should be no more than 50 mA cm-2 at a power density of 250 mW cm-2.

In a 1999 review of advanced electrode materials for use in DMFCs, Lamy and Leger discussed the suitability of a number of energy systems in relation to DMFCs for use in automobiles [17]. Secondary batteries (e. g., Li-ion) are limited by recharge time and power density (100-150 Wh kg-1 at maximum). PEFCs are attractive with specific power densities on the order of 1000 W kg-1 and specific energy density >500 Wh. Energy density of pure H2 is 33 kWh kg-1 but storage concerns make it less attractive and less efficient. Performance characteristics of DMFCs circa 1999 is 200 mA cm-2 at 0.5 V, or 100 mW cm-2 with electrocatalyst loadings under 1 mg cm-2.

Performance targets for a complete DMFC power system were posted in the Spring of 2005 by the U. S. Army Operational Test Command (OTC). The spec­ifications are target requirements for a ruggedized DMFC power plant for use in the field on armored and other military vehicles [25]. The specifications outline threshold requirements and objective targets for the power system. A summary of the requirements are listed in Table 9.1. In an effort to meet the objectives listed in Table 9.1, a 300-W prototype DMFC power plant was developed by T. Valdez and his team at the Jet Propulsion Laboratory [26]. The demonstration

power plant was designed for 100 hours of continuous operation and used 80 cells with active areas of 80 cm2. The electrocatalyst was PtRu at the anode and cathode. The plant generated 370 W during bench testing and had a start-up time of 18 minutes. The plant was operated continuously for 8 hours, generating a lower than expected power of 50 W. The continuous operation test was ended due to water accumulation in the stack exhaust manifold.

Subsequent to testing of the prototype power plant, the stack was torn down and components evaluated. The wettability of the cathodes of the MEAs had increased and evidence of the ruthenium migration was observed. These obser­vations were the impetus to study of the long-term stability of DMFC MEAs. The team at JPL individually ran four MEAs on a single-cell test stand for 250 hours. All of the MEAs showed irreversible voltage decay ranging from 0.2 to 0.6 mV hr-1 at a current density of 100 mA cm-2 that resulted in an average decline in power of 20%. However, unlike when the MEAs were run as compo­nents of the stack in the prototype power plant, the individually run MEAs showed no evidence of electrocatalyst migration. The important issue of electrocatalyst migration will be addressed again in the final section of this chapter.

According to Knights et al. at Ballard Power Systems, fuel cell power plants used in automobile, bus, and stationary applications require operational lifetimes on the order of 4000, 20,000, and 40,000 hours, respectively [27]. The degradation rate of the power supply is set by the beginning-of-life (BOL) and end-of-life (EOL) performances; a degradation rate on the order of 10 to 25 p V hr-1 is common for DMFCs. The group studied the strategy of load cycling in DMFCs to reduce performance degradation caused by water build-up at the cathode with time.

Ball Aerospace is developing a personal DMFC power system to meet the needs of the U. S. foot soldier [28]. It was developed under the Defense Advanced Research Projects Agency (DARPA) Palm Power program and produces average power of 20 W at 12 V and has a 30-W peak power. The unit operates for 50 hours on the fuel provided by one fuel cartridge, and is ten times lighter than the equivalent battery power plant; weighing in at three pounds with full fuel complement.

Yi et al. characterize the changes in MEA morphology of a single-cell DMFC run for a little longer than three days [29]. Long-term stability of the cell and electrocatalyst are important questions. The cell was run at 100 mA cm-2 and suffered from irrecoverable performance degradation, degrading at the rate of 1.0 to 1.5 mV hr-1. Following the run, Yi and his group found signs of delamination between the layers of the MEA and that both of the carbon-supported electrocat­alysts, PtRu/C on the anode and Pt/C on the cathode, had undergone a particle size redistribution resulting in larger particle sizes on average. The redistribution for the PtRu electrocatalyst was more pronounced than for Pt and more severe in the anode.

An assessment of the state of the art in DMFC performance can be made from relevant data from references in this chapter; data are listed in Tables 9.2 and 9.3. Where possible, the data listed from a particular reference includes data for the “best” test cell and the associated control cell. The best test cell is considered the one with highest maximum power density. The control cell is usually of a typical Nafion MEA construction consisting of carbon-supported PtRu on the anode, car­bon-supported Pt on the cathode and a Nafion 115 membrane as the separator. Efforts have been made to include operating conditions and loadings. Where an entry is listed as “n/a” the value for that parameter is not available. That is, the reference does not explicitly state the value of that parameter.