Bioethanol can also be obtained by means of chemical processes (Sanchez & Cardona, 2008; Demirbas, 2005), which may or may not demand the presence of microorganisms in the fermentation stage. Gasification of a biomass to obtain syngas (CO + H2), followed by the catalytic conversion of the syngas, has the potential for producing ethanol in large quantities. The catalysts most often used and studies are those based on rhodium (Rh) (Holy & Carey, 1985; Yu-Hua et al., 1987; Gronchi et al.; 1994).

The geometrical structure of the active site seems to be:

(Rh° Rhy +)- O — Mn+ (9)

where part of the Rh occurs as Rh+ and the promoter ion (Mn+) is in close contact with these Rh species. The carbon monoxide is then hydrogenated to form an absorbed species — CHx- that is then inserted in the absorbed CO. Hydrogenation of these absorbed species leads to the formation of ethanol (Subramani & Gangwal, 2008).

Another mechanism considered valid for ethanol formation involves the use of acetate (acetaldehyde formation followed by reduction) and is known, in the cases of Rh-based catalysts, to be promoted by manganese (Luo et al., 2001).

In this case, ethanol is formed by direct hydrogenation of tilt-absorbed CO molecules, followed by CH2 insertion on the surface of the CH2-O species to form an absorbed intermediate species. Ethanol is produced by hydrogenation of the intermediate species of CH2-O. Acetaldehyde is formed by the insertion of CO on the surface of the CH3-Rh species, followed by hydrogenation. The catalyst’s performance can be improved by modifying its composition and preparing the ideal conditions for the reaction (Subramani & Gangwal, 2008). Manganese (Lin et al., 1995), Samarium and Vanadium (Luo et al., 2001) can also be used as promoter ions in processes involving Rh.

The "Norin Biomass No. 3" Test Plant (Fig. 9, 10), which represents a "Suspension/ external heating type" with a boiler (1-2 Dry t/day) was newly developed for improving the disadvantages associated with the "Norin Green No. 1" test plant through the introduction of a new type of gasification called "high-calorie gasification reaction".

Gasifier: entrained — type; processing 240 dry kg/day of biomass

Method: gasification through partial oxidation

Gasifying Agent: O2,

H2O

Pressure/temp.:

Standard

pressure/750-

1100°C

Methanol Synthesis: processing equivalent to 50 dry kg/day of biomass

Method: Cu/Zn-
based catalyst

Pressure/temp.:

3-12 MPa/180- 250°C

Fig. 8. "Norin Green No. 1", a test plant of gasification and biomethanol production, located in Nagasaki Research & Development Center, Mitsubishi Heavy Industries ltd, Nagasaki, Japan.

All biodiesel production facilities should be equipped with a laboratory so that the quality of the final biodiesel product can be monitored. It is also important to monitor the quality of the feedstocks. One strategy used by many producers is to draw a sample of the oil (or alcohol) from each delivery and use that sample to produce biodiesel in the laboratory. This test can be fairly rapid (1 or 2 hours) and can indicate whether serious problems are likely in the plant. Measuring feedstock quality can usually be limited to acid value and water content. These are not too expensive and can be operated by less experienced technicians.

To monitor the completeness of the reaction according to the total glycerol level specified in ASTM D 6751 requires the use of a gas chromatograph and a skilled operator. Large producers will find that having this equipment on-site is necessary. Commercial laboratories are available that can analyze the samples but there are costs and the time required may be several days. Smaller producers will need to use a more robust production process involving extra methanol or ethanol and probably multiple reaction steps. Then the product quality can be monitored through periodic testing by an outside laboratory.

Other possibilities for monitoring the transesterification reaction and assessing fuel quality are methods based on spectroscopy (such as near- infrared spectroscopy) or physical properties (such as viscometry). These methods are usually faster and easier to use than gas chromatography. However, some of them require extensive calibration. They also cannot accurately quantify glycerol at the low levels called for in the ASTM standard. To circumvent this, comparison to a reaction and product known to meet ASTM standards is needed.

In the most general of terms, biofuels are biologically derived forms of chemical energy, such as hydrocarbons, that are compatible with the existing infrastructure. In a sense, petroleum is a biofuel because it is the oil-enriched remains of ancient biomass that has been unearthed. In a modern context, however, by actively converting photosynthetic biomass

into liquid biofuel, solar energy can be readily stored and utilized to replace the use of petroleum as a transportation fuel. This is not a new concept; in fact, Rudolph Diesel envisioned his piston-driven engine to run on peanut oil so that farmers could grow their own fuel (Nitschke and Wilson, 1965). Currently, biofuels are gaining attention as a valuable piece of the renewable energy puzzle because they fit so seamlessly into the carbon cycle. According to recent data, liquid transportation fuel use in the United States is between 130 and 140 billion gallons each year. This usage is anticipated to continue increasing to approximately 150 to 160 billion gallons per year, peaking around 2015 (U. S. Energy Information Administration, 2009). Fuel consumption appears likely to remain stable or decrease slowly as we approach the mid-century. Even in the United States, where a more rapid transition to hybrid or fuel-efficient vehicles is predicted, there will be a continued high demand for liquid transportation fuels.

In contrast to the high energy density of liquid fuels, hydrogen-based transportation seems to be a far-reaching goal and may never fully make sense for transportation. With current practices, hydrogen production is an energy intensive process and still requires a large investment in distribution infrastructure. Alternatively, plug-in electric vehicles have cost and environmental limitations related to batteries and would require a significant amount of time to replace the currently fleet of cars. For these reasons, an intensified focus on liquid biofuels is warranted. Moreover, liquid transportation fuels are currently the major use of petroleum throughout the world. In certain cases, the reliance on liquid fuels we have developed cannot easily be substituted (e. g. aviation, trucking, and construction industries). Furthermore, emerging economies will likely opt for the lowest cost vehicle solutions (i. e. internal combustion engines) and will still have a petroleum requirement.

Biomass resources usually contain a large amount of moisture, leading to higher transportation costs, debasement during storage, and reduction of thermal efficiency during conversion. Drying is a key technology for utilizing the biomass (McCormick & Mujumdar 2008). In addition to the use of biomass for fuel, the energy required for drying occupies a large amount of energy in the production due to the large latent heat of water during evaporation. Moreover, this characteristic of the drying process is the same as for the thermal and distillation processes. Therefore, a drying process based on self-heat recuperation technology was recently proposed (Fushimi et al., 2011).

Figure 6 a) shows a schematic image of a self-heat recuperative drying process. The wet sample is heated in a heat exchanger (1^2). The heated wet sample and vapor are then fed into an evaporator (dryer) with dry gas to assist evaporation (16). The heat for evaporation is supplied by superheated steam and gas (7). The hot dry sample (3) is separated and cooled by the dry gas (15) (3^5). After eliminating the unseparated sample to prevent it from entering the compressor, the evaporated steam and gas (4) are compressed (7) by a

compressor. The sensible and latent heats of the compressed steam and gas are exchanged in the heat exchanger (7^8) and fed into a condenser to separate the water and gas; the water is then drained (10). The pressure and temperature of drain water are adjusted by a valve and cooler (10^12^14). Simultaneously, the pressure energy of the gas (9) is partially recovered in an expander. The temperature of the gas is then cooled by a cooler (13). This exhausted gas can be recycled as the gas feed (15). To use this gas as the dry gas feed, makeup gas is necessary to compensate for the loss, because a small amount of gas dissolves in water in the condenser. Considering a real application for a drying process, the dried sample is separated immediately after the evaporation and reversed back to the heat exchanger for heat utilization. However, with the aim of reducing drying time (higher drying rate) and providing the driving force required in the drying process, gas that has been preheated by the sample enters the evaporator. It should be noted that an increase in gas flow rate causes an increase in the energy required for compression for the following reasons: (1) an excess amount of gas must be compressed and (2) a smaller partial pressure of steam requires larger compression pressure for condensation. Consequently, the gas flow rate should be optimized.

Figure 6 b) shows a temperature-heat diagram of the self-heat recuperative drying process. Note that the numbers beside the composite curve in this temperature-heat diagram correspond to the stream numbers in Figure 6 a). It can be seen that the condensation heat of the steam in the effluent stream (7^8) is exchanged with the evaporation heat of the feed stream (1^2), as well as the sensible heats in a heat exchanger. At the same time, the heat of solid sample after evaporation is exchanged with the heat of the gas stream in the other heat exchanger and this heat is supplied to the feed solid sample. These lead to minimization of the exergy loss in the heat exchangers. From this figure, it can be understood that all process heat is recirculated without heat addition, and that the total heating duty is covered by internal heat recovery. All of the compression work in each module was discarded into coolers, because the base conditions of the stream are fixed at standard conditions. As a consequence, to circulate the process stream heat in the process using heat exchangers and a compressor, the energy required for the self-heat recuperative drying process is 1/7 of that of the conventional heat recovered drying process.

1.2 Structure of lignocellulosic material

Lignocellulosic material refers to plant biomass that is composed of cellulose, hemicellulose, and lignin (Fig. 2) (Lin and Tanaka, 2006). The major combustible component of non-food energy crops is cellulose, followed by lignin.

Cellulose: Cellulose is an organic polysaccharide consisting of a linear chain of several hundreds to over nine thousand P(1^4) linked D-glucose (C6Hi0O5)n units (Crawford, 1981; Updegraff, 1969). Cellulose, a fibrous, tough, water-insoluble substance, is found in the cell walls of plants, particularly in the stalks, stems, trunks and all the woody portions of the plant body (Nelson and Cox, 2005). Cellulose comprises 40-60% of the dry weight of plant material (the cellulose content of cotton is 90% and that of wood is 50%) (Encyclopedia Britannica, 2008; USDE, 2006).

Zandersons et al. (2004) and Shaw (2008) reported that binding of wood material during hot pressing / densification is mainly dependent on the transition of cellulose into the amorphous state. According to Hon (1989), due to the semi-crystalline structure, hydrogen bonded cellulose cannot be dissolved easily in conventional solvents, and it cannot be melted before it burns; hence, cellulose itself is not a suitable adhesive. This can be overcome by breaking the hydrogen bonds, thus making the cellulose molecule more flexible (Hon 1989). Cellulose requires a temperature of 320°C and pressure of 25 MPa to become amorphous in water (Deguchi et al., 2006).

Hemicellulose: Hemicellulose is made of several heteropolymers (matrix polysaccharides) present in almost all plant cell walls along with cellulose (Fig. 2). While cellulose is crystalline, strong, and resistant to hydrolysis; hemicellulose has a random, amorphous structure with less strength. Hemicellulose is a polysaccharide related to cellulose and comprises 20-40% of the biomass of most plants. In contrast to cellulose, hemicellulose is derived from several sugars in addition to glucose, including especially xylose but also mannose, galactose, rhamnose and arabinose (Shambe and Kennedy, 1985). Branching in hemicellulose produces an amorphous structure that is more easily hydrolyzed than cellulose (Shaw, 2008). Also, hemicellulose can be dissolved in strong alkali solutions. Hemicellulose provides structural integrity to the cell. Some researchers believe that natural bonding may occur due to the adhesive properties of degraded hemicellulose (Bhattacharya et al., 1989).

Lignin: Lignin is a complex chemical compound most commonly derived from wood and is an integral part of the cell walls of plants (Lebo et al., 2001; Zandersons et al., 2004). The compound has several unusual properties as a biopolymer, not the least its heterogeneity in lacking a defined primary structure. Lignin fills the spaces in the cell wall between cellulose and hemicellulose (Fig. 2). It is covalently linked to hemicellulose and thereby crosslinks different plant polysaccharides, conferring mechanical strength to the cell wall and consequently to the whole plant structure (Chabannes et al., 2001).

Lignin acts as a binder for the cellulose fibres (Fig. 2). van Dam et al. (2004) have reported that lignin can be used as an intrinsic resin in binderless board production due to the fact that when lignin melts (temperatures above 140°C), it exhibits thermosetting properties. Lignin is the component that permits adhesion in the wood structure, and is a rigidifying and bulking agent (Angles et al., 2001). Lehtikangas (2001) reported that water (8-15%) in pellets will reduce the softening temperature of lignin to 100-135°C by plasticizing the molecular chains. The adhesive properties of thermally softened lignin are thought to contribute considerably to the strength characteristics of briquettes made of lignocellulosic materials (Granada et al., 2002; Shaw, 2008).

The densification of biomass into durable compacts is an effective solution to meet the requirement of raw material for biofuel production. The compression characteristics of ground agricultural biomass vary under various applied pressures. It is important to understand the fundamental mechanism of the biomass compression process, which is required to design an energy efficient compaction equipment to mitigate the cost of production and enhance the quality of the product. To a great extent, the strength of manufactured compacts depends on the physical forces that bond the particles together. These physical forces are generated in three different forms during compaction operations: a) thermal; b) mechanical; and c) atomic forces. To customize and manufacture high quality products that can withstand various forces during transportation and handling, it is essential to predict desirable and dependent quality parameters (density and durability) with respect to various independent variables (pre-treatment, grind size, applied pressure, hold time, die temperature, and moisture content). In addition, specific energy requirements of manufacturing biomass pellets should be established, which can assist in determining the economic viability of densification process.

The density of biomass pellet has been observed to significantly increase with an increase in applied pressure and a decrease in hammer mill screen size. In addition, application of pre­treatment has observed to significantly increase the pellet density since pre-treated straw has lower geometric particle diameters and significantly higher particle densities. Statistically, agricultural biomass did not have any significant effect on pellet density, while steam explosion pre-treatment, applied pressure, moisture content, pre-heat temperature and screen size had significant effect. A negative correlation has been observed between the pellet bulk density and moisture content, while a positive correlation exists between bulk density and pellet mill die temperature. In general, average pellet bulk densities obtained for customized straw samples is higher as a direct result of increase in particle densities. Agricultural biomass, steam explosion pre-treatment, applied pressure, moisture content, pre-heat temperature and screen size all had significant effect on pellet durability. In general, durability of pellets increases with an increase in applied pressure and grind size, and application of pre-treatment. An increase in pellet mill die temperature, steam conditioning temperature and die thickness resulted in an increase in pellet durability. No specific trend in durability was observed with customization of straw by mixing non-treated and steam exploded straw grinds.

The specific energy required to form a pellet has been significantly affected by the type of agricultural biomass, steam explosion pre-treatment, applied pressure and screen size. The total and compression specific energy for compaction of non-treated and steam exploded barley, canola, oat and wheat straw at any particular hammer mill screen size significantly increased with an increase in applied pressure and significantly decreased with a decrease in hammer mill screen size. Durability of pellets was negatively correlated to pellet mill throughput and was positively correlated to specific energy consumption. An overall energy balance was performed, which showed that a significant portion of original agricultural biomass energy (92-94%) is available for the production of biofuels.

Biodiesel use in diesel engines is more limited. As well as ethanol, biodiesel is produced by fast pyrolysis of lignocellulosic biomass and mainly fermentation, because fast pyrolysis is a more expensive way (Bridgwater et al., 2002), it is a renewable oxygenated fuel with low cetane components (Ikura et al., 2003). Its heating value is about 60% of ethanol, but its high density makes up for its percentage. When using biodiesel in machines and engines there are some problems (Lopez & Salva, 2000) because of its higher viscosity and acidity, tar and fine particles resulting during working hours and solid residues during the combustion. Following the direction of ethanol research, attempts have been made to overcome these problems by blending bio-oil with diesel to form an emulsion (Chiaramonti et al., 2003). In some success these efforts solve the operation with these fuels, however it is necessary to prove the feasibility and the additional cost of surfactant required to stabilize the blending which is a barrier for using it.

It must be considered that the blending of biodiesel and ethanol makes a stable blend and a fast pyrolysis, without using additives and surfactants. Current research on these blends is limited to gas turbines (Lopez & Salva, 2000) and their use in these engines has shown positive results. Biodiesel blended with ethanol shall not exceed the problems of direct ethanol use in diesel engines without modification. However, using modified engines to use ethanol blends of ethanol/biodiesel could overcome the problems related to pure biodiesel combustion. As all new fuels, it is necessary to solve technical problems such as fuel storage, material compatibility, and procedures for turning engines on and off and long operation periods (Nguyen & Honnery, 2008).

In this study, we investigated the greenhouse facility at Miyagi of Japan where paprika is brought into cultivation. In this facility, the annual product yields are around 200 t/yr. The energy of electricity, kerosene and bunker A for lighting and a heater, and the input of CO2 gas as a growth agent are consumed. Here, since the energy data of time series was necessary, the boiler fuels of kerosene and/or bunker A were assumed to be in proportion to a difference between the minimum temperature for growing and the atmospheric one. Also, electricity was assumed to be consumed for 12 hours per a day.

Next, the consumption of CO2 gas as a growth agent would be analysed statistically. In a plant such as paprika, CO2 is consumed through photosynthesis. That is, this volume would be proportional to the duration of bright sunshine and an intensity of radiation. Fig.11 shows the statistically estimated CO2 consumption.

10,000

7.500 О О ся

5,000

з ’ о. с

Cd

О

2.500 0

0 1,000 2,000 3,000 4,000 5,000 6,000

Radiation*Duration of sunshine [Wh/m2 ]

Fig. 11. CO2 supply volume as a growth agent.

On the other hand, fertilizers of N, P2O5 and K2O only were considered, however another chemical inputs were ignored (Dowaki et al., 2010b).

A microbial fuel cell (MFC) converts chemical energy to electrical energy by the catalytic processes of microorganisms. Microorganisms in the MFC oxidize organic substrates and generate both electrons and protons on the anode. Electrons transfer from the anode to the cathode through an external circuit and simultaneously the protons migrate to the cathode and reduce the oxygen with the electrons available at the cathode surface. Various kinds of microorganisms are reported in association with electrodes in MFC systems. For example, brevibacillus sp. PTH1 is one of the most abundant microorganisms in a MFC system. Pure cultures used for generating current in a MFC include firmicutes, acidobacteria, proteobacteria and yeast strains Saccharomyces cerevisiae and hansenula anomala (Allen & Bennetto, 1993). These microorganisms interact with fuels through a variety of direct and indirect processes to generate energy. Microbial biofuel cells have major advantage of

thorough oxidation of the fuels due to the use of microorganism as catalyst system and they can be typically operated for long lifetimes. Besides, a MFC has no intermediated processes thus it is a very efficient energy producing process. In addition, as a fuel cell, a MFC does not need charging during operation (Willner et al., 1996; Katz et al., 2003 and Calabrese et al., 2004). However, the bottlenecks of MFC still remain. Power generation of a MFC is affected by many factors including microbe type, fuel biomass type and concentration, ionic strength, pH, temperature, and reactor configuration.

The principle cell performance of MFCs lies in the electron transfer from microbial cells to the anode electrode. The direct electron transfer from the microorganism to electrodes is hindered by overpotential due to transfer resistance. The overpotential lowers the potential of a MFC and significantly affects the cell efficiency. In this case, the practical output potential is less than ideal because the electron transfer efficiency from the substrate to the anode varies from microbe to microbe. Microorganism species do not readily release electrons and hence the redox mediators are needed. A desirable mediator should have a whole range of properties: Firstly, its potential should be different from the microorganism potential to facilitate electron transfer. Secondly, it should have a high diffusion coefficient in the solution. Lastly, it is suitable for repeatable redox cycles in order to remain active in the electrolyte. Widely used Dye mediators such as neutral red (NR), methylene blue (MB), thionine (Th), meldola’s blue (MelB) and 2-hydroxy-1,4-naphthoquinone (HNQ) can facilitate electron transfer for microorganism such as Proteus, Enterobacter, Bacillus, Pseudomonas and Escherichia coli. In the electron transfer process, these mediators are reduced by interacting with electron generated within the cell then these mediators in reduced form diffuse out of the cell to the anode surface where they are electrocatalytically oxidised. The oxidised mediator is then capable to repeat this redox cycle.

Better performing electrodes can improve the cell performance of a MFC because different anode materials can result in different activation of a polarization loss, which is attributed to an activation energy that must be overcome by the reactants. Carbon or graphite based materials are widely used as electrodes due to their large surface area, high conductivity, biocompatibility and chemical stability according to Table 1. Also, platinum and gold are popular as electrode system although they are expensive. Compared with carbon based electrode materials, platinum and gold electrodes are superior in the performance of the cells based on the Table 1. Besides, they have a higher catalytic kinetics towards oxygen compared to carbon based materials and hence the MFCs with Pt based cathodes yielded higher power densities than those with carbon based cathodes (Moon et al., 2009).

Electrode modification is another way to improve MFC performance of cells. (Park & Zerkeis, 2003) reported an increase of 100-folds in current compared to the previous results by using (neutral red) NR-woven graphite and Mn4+-graphite anode instead of the woven graphite anode alone. Four times higher current was reported in 2004 using the combination of Mn4+-graphite anode and Fe3+-graphite cathode (Niessen et al., 2004). NR and Mn4+ doping ions serve as mediators in their MFC systems and also catalyze the cathodic reactions to facilitate electricity generations. Electrodes modifications including adsorption of AQDS or 1,4-naphthoquinone (NQ) and incorporation with Mn2+, Ni2+, Fe3O4 increased the cell performance of MFCs in their long-term operations (Lowy et al., 2006). In addition, the fluorinated polyanilines, poly (2-fluoroaniline) and poly (2, 3, 5, 6-tetrafluoroaniline) outperformed polyaniline were applied for electrode modification (Niessen et al., 2006). These conductive polymers also serve as mediators due to their structural similarities to conventional redox mediators.

Proton exchange membrane (PEM) can also significantly affect a MFC system’s internal resistance and concentration polarization loss because the internal resistance of MFC decreases with the increase in the PEM surface area (Oh & Logan, 2006). Nafion (DuPont, Wilmington, Delaware) is the most popular proton exchange membrane material due to its highly selective permeability of protons (Min et al., 2005). Compared with the performance of MFC using a PEM or a salt bridge, the power density using the salt bridge MFC was

2.2 mW/m2 that was an order of magnitude lower than that attained using Nafion. However, side effect is unavoidable with the use of PEM. For example, the concentration of cation species such as Na+, K+, NH4+, Ca2+, Mg2+ is much higher than that of proton so that transportation of cation species dominates. In this case, Nafion used in the MFCs is not an efficient proton specific membrane but actually a cation specific membrane (Rozendal et al., 2006). Subsequent studies have implied that anion-exchange or bipolar membranes has better properties than cation exchange membranes regarding to cell performance (Zhang et al., 2009).

Two promising applications of MFCs in the future are wastewater treatment and electricity generation (Feng et al., 2008 and Katuri & Scott, 2010). Although some noticeable development has been made in the MFC research, there are still a lot of challenges to be overcome for large-scale applications. The primary challenge is how to improve the cell performance in terms of power density and energy efficiency. In addition, catalytic effect of bioelectrodes needs to be further enhanced to solve the problems caused by enzyme activity loss and other degradation processes. Moreover, the lifetime of the MFC must be significantly improved.