Methanol is produced by the hydrogenation of carbon oxides over a suitable (copper oxide, zinc oxide, or chromium oxide-based) catalyst:

CO + 2H2 о CH3OH (2.5)

CO2 + 3H2 о CH3OH + H2O (2.6)

The first reaction is the primary methanol synthesis reaction, a small amount of CO2 in the feed (2-10%) acts as a promoter of this primary reaction and helps maintain catalyst activity. The stoichiometry of both reactions is satisfied when R in the following relation is 2.03 minimally (Katofsky 1993). H2 builds up in the recycle loop; this leads to an actual R value of the combined synthesis feed (makeup plus recycle feed) of 3 to 4 typically.

H2 — CO2 CO + CO2

The reactions are exothermic and give a net decrease in molar volume. Therefore, the equilibrium is favored by high pressure and low temperature. During production, heat is released and has to be removed to keep optimum catalyst life and reaction rate. 0.3% of the produced methanol reacts further to form side products such as dimethyl ether, formaldehyde, or higher alcohols (van Dijk et al. 1995).

The catalyst deactivates primarily because of loss of active copper due to physical blockage of the active sites by large by-product molecules; poisoning by halogens or sulfur in the synthesis gas, which irreversibly form inactive copper salts; and sintering of the copper crystallites into larger crystals, which then have a lower surface area-to-volume ratio.

Conventionally, methanol is produced in two-phase systems, the reactants and products forming the gas phase and the catalyst forming the solid phase. The
production of methanol from synthesis gas was first developed at BASF in Germany in 1922. This process used a zinc oxide/chromium oxide catalyst with poor selectivity, and required extremely vigorous conditions—pressures ranging from 300-1000 bar and temperatures of about 400°C. In the 1960s and 1970s the more active Cu/Zn/Al catalyst was developed allowing more energy-efficient and cost-effective plants, and larger scales. Processes under development at present focus on shifting the equilibrium to the product side to achieve higher conversion per pass. Examples are the gas/solid/solid trickle flow reactor, with a fine adsorbent powder flowing down a catalyst bed and picking up the produced methanol, and liquid phase methanol processes where reactants, product, and catalyst are suspended in a liquid. Fundamentally different could be the direct conversion of methane to methanol, but despite a century of research this method has not yet proved advantageous.

Corn wet mills have a long history of converting starch to a wide variety of products in addition to or instead of ethanol. As described above in the discussion of wet milling, starch products from wet milling also have many applications beyond the food and beverage industries in pharmaceutical, cosmetic, paper, and packaging industries. Recently, corn wet millers have begun to adopt processes for converting starch into biodegradable polymers. Such products represent a fundamental shift from other nonethanol products, because they directly compete with petroleum-based products and have the potential for virtually unlimited growth. A number of corn processors in the United States have a biopolymer either on the market or under development. Cargill Dow produces PLA (polylac — tide) polymer fiber under the trade name Nature Works, for use in packaging, films, and resins. ADM and Metabolix have formed an alliance to scale-up and commercialize PHA (polyhydroxyalkanoate) polymers, for marketing as renew­able alternatives to traditional petrochemical plastics used in making molded goods, films, and coated papers. A joint venture between DuPont and Tate and Lyle was formed to produce 1,3-propanediol (Bio-PDO™) from corn starch as an alternative to petrochemically-derived PDO. Sorona®, a family of polymers made from PDO, is used in fibers and fabrics, films, and resins.

The use of ethanol in an internal combustion engine was first investigated in 1897 (1). Henry Ford originally designed the Model T in 1908 to run on ethanol, but increasing taxes limited its use (2). The concept of employing ethanol as a fuel was reintroduced during the fuel shortages during both World Wars, but the U. S. federal ethanol program was not started until the oil crisis of the 1970s (2). In 1973, OPEC quadrupled the cost of purchasing crude oil (3), which started the resurgence of promoting ethanol as an alternative fuel for combustion engines. However, ethanol as an alternative fuel has not infiltrated the fuel market in the way blended ethanol/gasoline fuels have for automobiles.

Although research in the United States from the Society of Automotive Engineers showed extensive engine testing of E10 (10% ethanol/90% gasoline) in 1933, it was not until 1978 that the U. S. government established a National Alcohol Fuel Commission (4). In 1980, President Carter signed into the law the Energy Security Act containing Title 11, which is commonly called the Biomass Energy and Alcohol Fuels Act of 1980 (4). The Clean Air Act of 1970 allowed the Environmental Protection Agency (EPA) to set standards for vehicle emissions of carbon monoxide, nitrogen oxides, and ozone (4). In 1992, the EPA started requiring cities that were considered to have serious or moderate carbon monoxide pollution problems to establish oxygenated fuel programs. The oxygen content of 2.7% by wt is a required minimum for gasoline sold in these cities. This corresponds to approximately 7.5% by volume ethanol and approximately 15.0% by volume methyl tertiary butyl ether (MTBE) in gasoline.

In 1994, the EPA proposed a policy that at least 30% of the oxygenate be derived from renewable resources (4). However, this proposed policy was not passed by Congress. Ninety-five percent of the oxygenate used in Chicago is ethanol (4). Ethanol has been marketed in every state except California (MTBE has been the mandated oxygenate) (4), but currently MTBE is being phased out of California and ethanol is being phased in due to environmental issues.

In view of the recent Kyoto Conference at which the United States committed to decreasing greenhouse gas emissions by 2012 to below the 1990 level (5), ethanol/gasoline blends from E10 to E85 are an excellent way to achieve these greenhouse gas reductions. Argonne National Laboratory has shown that green­house gas emissions is 2.4 to 2.9% less for E10 than 100% gasoline overall (5). Most of this decrease is due to a decrease in greenhouse gas emissions from vehicle combustion because there is actually a small increase in greenhouse gas emission from the fuel due to volatility.

Fatih Dogan

Department of Materials Science and Engineering University of Missouri-Rolla

CONTENTS

Introduction………………………………………………………………………………………………….. 204

Fuels for Solid-Oxide Fuel Cells…………………………………………………………………. 205

Single-Chamber Solid-Oxide Fuel Cells and Hydrocarbon Fuels…………………… 209

Summary………………………………………………………………………………………………………. 211

References…………………………………………………………………………………………………….. 212

Abstract This chapter addresses utilization of alcohol and other hydrocarbon — based fuels to generate electricity in solid-oxide fuel cells (SOFCs). One of the key advantages of SOFC is that both external as well internal fuel reforming is possible to operate the fuel cell under stable conditions. While alcohol fuels can be obtained sulfur-free and in high purity, hydrocarbon fuels have higher energy density and existing infrastructure of production and distribution. Development of more energy-efficient and chemically stable electrode materials is necessary for SOFC operating at high (800-1000°C) and intermediate (500-800°C) tem­peratures. Significant progress has been made in recent years in the development of carbon monoxide-tolerant fuel electrodes (anodes) to prevent carbon deposition on the catalyst that results in a reduced performance of the fuel cell. Development of fuel electrodes compatible with alcohol and hydrocarbon fuels will lead to more efficient and widespread applications of SOFCs in double-chamber and single-chamber modes.

INTRODUCTION

Fuel cells are viewed as environmentally compatible and efficient energy conver­sion systems. A fuel cell works much like a battery with external fuel supplies. Chemical fuels are electrochemically converted into electricity at high efficiencies without producing significant amount of pollutants such as nitrogen oxides as compared to combustion engines. Hydrogen is the ideal fuel since it reacts with oxygen in the air to produce water and an electric current, but hydrogen is expensive and difficult to store. Until the hydrogen economy is well established, other fuels can be used indirectly with an external reformer or directly to operate fuel cells. Hydrogen is stored naturally in alcohols (e. g., ethanol and methanol) or hydrocarbons such as propane and methane, which are available to produce cleaner power if the electrochemical processes of hydrocarbon oxidation reactions are well understood.

Among various fuel cells, solid oxide fuel cells (SOFCs) and molten car­bonate fuel cells can be operated using hydrogen as well as carbon monoxide. Particularly, SOFC is viewed as the most flexible fuel cell system that can operate using various fuel gases directly supplied to the fuel electrodes [1-3]. Removal of CO from H2 fuel is essential for polymer electrolyte membrane fuel cells, which are generally considered to be the most viable approach for mobile applications.

The application of high and intermediate temperature SOFCs range from small-scale domestic heat and power to large-scale distributed power generation. SOFCs offer high efficiencies up to 60-70% in individual systems and up to 80% in hybrid systems by extracting the energy present in the high-temperature exhaust gases, e. g., by using gas or steam turbines [4]. High-temperature SOFC applica­tions include multimegawatt-scale centralized power generation, distributed power generation up to 1 MW and combined heat/power (CHP) plants in the 100-kW to 1-MW range. Potential areas of application for intermediate SOFCs are in the transport sector (up to 50 kW), military and aerospace (5 to 50 kW), domestic CHP (up to 10 kW) and miniaturized fuel cells “palm-power” in the 10-W range.

In SOFC, the electrolyte is typically a dense yttria-stabilized zirconia (YSZ), which is an ionic conductor blocking electron transport as shown in Figure 11.1. The electrolyte allows the transport of oxygen ions via the oxygen vacancies from the interface at the air electrode (cathode) to the interface with the fuel electrode (anode). The cathode is typically composed of a porous lanthanum strontium manganese oxide with YSZ and facilitates the reaction for the reduction of oxygen gas to oxygen ions at the electrode/electrolyte interface. The anode material is typically a porous Ni-YSZ composite allowing the oxi­dation of the fuel and transport of the electrons from the electrolyte/electrode interface to the interconnect of the fuel cell stack. The interconnect material is typically lanthanum strontium chromite for high-temperature operation while corrosion-resistant metallic alloys are employed in the development of SOFCs operating at intermediate temperatures. The role of the interconnect is to transfer

the electrons between the individual cells in the stack and to prevent mixing of fuel and oxidant gases [5].

A diverse range of fuels can be used in SOFCs since the internal temperature is high enough to initiate fuel conversion reactions. Hence, SOFCs have an efficiency advantage over polymer electrolyte membrane fuel cells when alcohol or hydrocarbon fuels are to be used, even though direct-methanol fuel cells with polymer electrolyte membranes are widely studied. The use of these fuels in SOFCs without preprocessing, however, requires further advances in development of appropriate electrode materials toward preventing unwanted reactions such as carbon formation on the anode, which significantly affects the performance of the fuel cell.

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.