According to Forest Products Laboratory (U. S. Department ofAgriculture) data [38], the efficiency of wood-fired power plants is 18-24 %. And wood is used as a fuel by millennia and is one of easiest to use energy resources. The efficiency of electricity generation can be increased up to ~29 % using gasification and combined cycle technologies, and using plasma gasification up to ~35 % [39, 40]. That is why the development of energy industry technologies based on plasma gasification is one of the most promising ways of evolution of energy use. During plasma generation, the molecules disintegrate to electrons, ions, atoms, and radicals [41], which makes it highly reactive. Plasma application leads to an increase in rates of chemical reactions, which in particular enhances the conversion in endothermal gas-phase processes [42]. Plasma is a universal oxidizer using for gasification of virtually any kind of feedstock including wood waste [43,44], coal [45], RDF [46], etc. Though plasma has not yet widely used, such advantages as reduction of trace contaminants [47], tar conversion

[48] , high rates of heat exchange [49], and also high throughput at low plasma flow rate [50] attract attention to its use in pyrolysis and gasification. The main deficiency of plasma technologies is low level of their industrialization [51].

Tian et al. [42] designed a simple OES system composed of [AMIM]Cl and DMSO, to treat microcrystalline cellulose for enzymatic saccharification. [AMIM]Cl is one of the most effective ILs for dissolving and pretreating wood chips [86]. Compared to [BMIM]Cl, it has a lower melting point. The dissolution mechanism of cellulose in [AMIM]Cl was proposed as: The free Cl — anions associated with cellulose hydroxyl protons and the free cations combined with the cellulose hydroxyl oxygen to form electrovalent bonds, leading to disruption of hydrogen bonding in the cellulose and its consequent dissolution [98]. When an anti solvent, such as water, containing large

quantities of hydrogen bonds was homogeneously mixed with [AMIM]Cl-cellulose solution to remove the ILs, the electrovalent bonds were replaced oppositely by the reforming of hydrogen bonds among cellulose chains. However, the structures consisting of cellulose chains and regenerated hydrogen bonds were never arranged as regularly as the crystalline cellulose prior to the pretreatment (see Fig. 14.3). DMSO is an important polar aprotic solvent that dissolves both polar and non-polar compounds and is miscible in a wide range of organic solvents [99]. Therefore, despite of the relatively lower price, it is an important and efficient co-solvent for cellulose dissolution and pretreatment.

In the OES-dissolving pretreatment study, 5 % microcrystalline cellulose was de­posited in each of these OES which had different molar fractions of [AMIM]Cl (i. e., X [AMIM]Cl = 0.1-0.9). Followed by being kept at 110 °C for 1 h under a continu­ous stirring, the regenerated cellulose was precipitated by water and enzymatically hydrolyzed for 72 h.

Results revealed that the microcrystalline cellulose was rapidly dissolved in the OES (when x [AMIM]Cl > 0.2) within 10 min. During the hydrolysis, with the increase of OES from 0.1 to 0.9, both hydrolysis yield and initial hydrolysis rate of the regenerated cellulose increased gradually. After 72 h, the glucose yield of cellulose treated by OES (at x [AMIM]Cl = 0.7) was 54.1 %, which was 7.2 times that of the untreated cellulose, and was only slightly lower than the value (59.6 %) obtained by using pure [AMIM]Cl. Characterization of the regenerated cellulose samples was conducted subsequently. With increasing molar fractions of [AMIM]Cl, the crystallinity index (CI) of cellulose I decreased from 0.834 to 0.319, whereas the CI of cellulose II stayed at around 0.284. Meanwhile, the average specific surface area

Fig. 14.4 Variable viscosities of OES against the increasing molar fractions of [AMIM]Cl at 110 °C (Calculated according to the Grunberg-Nissan mixing law. Viscosities of DMSO and [AMIM]Cl at 110 °C were caculated according to Arrhenius model and VFT equation, respectively.) [42]

and degree of polymerization remained without significant change, being 4.174 m2/g and 137.2, respectively.

Although DMSO has no positive effect on promoting cellulose dissolution for being unable to donate cations and anions [42, 90], the OES mixed with DMSO and [AMIM]Cl has positive effect on decrystallinity of cellulose I, which may account for the higher hydrolysis yield and rate [18].

The unique advantages of employing OES as a cellulose solvent in the pretreat­ment can be summarized below [42, 85]:

1. Replacing a portion of ILs by less expensive OES, which can lower the processing cost.

2. Shortening the dissolution time to form cellulose homogenerous solutions due to its rapid diffusion efficiency.

3. Being more practical and easier for large-scale operations (stirring and pipeline transportation) due to the reduced viscosity of the OES system. For example, the viscosity of OES with molar fraction of [AMIM]Cl = 0.7, is only 37.28 % of the pure IL at 110 °C (see Fig. 14.4).

4. Enabling a higher cellulose recovery rate (95.37 ± 1.41 %) opposite to significant decomposition of polysaccharides in other chemical pretreatment methods [100].

5. Proving to be a simple but effective process to prepare cellulose with controlled CI than some other methods [101, 102]. The CI of cellulose I in the regenerated samples has a strong negative linear correlation against the molar fraction of IL in OES (i. e., with a correlation coefficient of 0.98).

Referring to the advantages, employing OES as a cellulose solvent has a bright per­spective for efficient pretreatment of lignocellulosic biomass. However, recycling of OES should be taken into account to remove the barriers to large-scale application. It can be achieved by using commercial distillation technology to separate water
from ILs due to their lower vapor pressures. Alternately, using aqueous ethanol or aqueous acetone instead of pure water as an antisolvent would reduce the tempera­ture and vacuum requirement in the distillation. Otherwise, some new technologies, such as nanoflltration, reverse osmosis, and pervaporation [103], three-phase system precipitation [104], and supercritical CO2 extraction [103, 105] may have potential applications in recycling of OES.

Moreover, investigation of OES on the pretreatment of various lignocellulosic biomass, such as corn stover, switchgrass, poplar, and pine, should be performed to determine the chemical components isolation, cellulose decrystallization, and improvement of enzymatic saccharification against the solvent constituents as well as their molar ratio in OES. Physical features of samples, such as moisture, particle size, and homogeneity, which have been proposed to affect the cellulose-dissolving ability in ILs [106], should also be considered and optimized in the OES system.

Addition of sulfur dioxide (SO2) at elevated temperatures has been described as an alternative approach to enhance the recovery of both cellulose and hemicellulose fractions from SB [14, 29]. Carrasco et al. [39] studied SO2 explosion mediated pretreatment of SB at temperatures 180-205 °C, with residence times of 5-10 min using SO2 as a catalyst. Pretreatment at 190 °C for 5 min generated pentose yield 57 %. The pretreated SB showed 87 % hydrolysis at 2 % substrate concentration after enzymatic hydrolysis.

16.3.2.4 Ammonia Fiber Expansion (AFEX)

Ammonia fiber expansion (AFEX) is an attractive method of pretreatment for SB/SL because of several advantages such as economic, fast, and highly efficient. However, handling of ammonia solution for the pretreatment at large scale is a problem due to the environmental concerns [14, 15]. Ammonia acts strongly toward lignin removal with the minimum degradation of hemicelluloses and ameliorating the accessibility of cellulase enzyme action on cellulose and remaining hemicellulose [8, 20]. Am­monia acts on C-O-C linkage in lignin including ether and ester bonds in cellulignin complex [20]. Ammonia after pretreatment can be recycled for further applications. It is important to emphasize that the formation of sugar degradation products are minimized during ammonia pretreatment of SB/SL [8, 40]. This process can im­prove the enzymatic hydrolysis of lignocellulosic material depending on use and the optimal conditions used in the process [41].

In this method, SB/SL is exposed to liquid aqueous ammonia (1-2 kg of am — monia/kg of dry biomass) under moderate or high temperature (40-140 °C) and pressure (250-300 psi) for a period of time (<30 min). During AFEX, no significant inhibitory by-products are produced and ammonia can be recycled after pretreatment

[15] . Maximum polysaccharide conversion of AFEX pretreated SB and SL by enzy­matic hydrolysis using cellulases was almost 85 % while the use of hemicellulases promoted the xylan conversion to 95-98 % levels [8]. Xylanase supplementation also promoted the cellulose conversion into glucose [8, 42].

Ammonia recycle percolation (ARP), modified method of ammonia-mediated pre­treatment uses aqueous ammonia (10-15 %) at elevated temperatures (150-170 °C) followed by its recovery and separation of biomass. Similar to steam explosion, this method also promotes the high degree of depolymerization of lignin and cleavage of lignin-carbohydrate linkages, increasing the accessibility of cellulolytic enzymes to carbohydrate skeleton of SB/SL [15,43]. Ammonia pretreatment in any form (aque­ous ammonia pretreatment, soaking in aqueous ammonia, ammonia freeze explosion, ammonia recycling percolation) is generally preferred to low lignin containing lig — nocellulosic substrates like corn stover than SB/SL [20, 29]. In fact, more research needs to be done for ammonia pretreatment optimization of SB/SL.

Physical-chemical pretreatment methods include steam explosion, ammonia fiber explosion (AFEX), microwave pretreatment, and ultrasonic pretreatment, etc. Steam explosion is the most commonly used physical-chemical method for the pretreatment of lignocellulosic materials in particular for hardwood and agricultural biomass [12]. In this method, biomass is treated with high-pressure saturated steam and then the pressure is suddenly reduced such that the biomass undergoes an explosive decom­pression. Steam explosion is typically carried out at 160-260 °C and 0.69-4.83 MPa for several seconds to a few minutes before the materials are exposed to atmospheric pressure [13]. Like a hydrothermal pretreatment, steam explosion removes hemicel — lulose mainly by autohydrolysis and partially by chemical effects and mechanical forces. The high temperature and pressure promote the acetyl groups present in hemicellulose to be automatically hydrolyzed to acetic acid; on the other hand, the water may act as an acid under such high-temperature condition. All of these acids formed in the steam explosion process could thus hydrolyze hemicellulose. Removal of hemicellulose exposes the cellulose surface and increases enzyme accessibility to the cellulose microfibrils [14]. In the stream explosion process, lignin can also be removed to a certain extent, but is redistributed on the fiber surfaces as a re­sult of melting and depolymeriation/repolymerization reactions [15]. The removal and redistribution of hemicellulose and lignin could swell the pretreated sample and increase its accessible surface area [7]. The main drawback of this method is that many enzyme-inhibitors are produced in the pretreatment. For example, the pen­toses and hexoses formed from the hydrolyzed hemicellulose and cellulose can be further degraded to furfural, 5-hydroxymethylfurfural (HMF), levullinic acid, and formic acid, which would deactivate the enzymes used in the consecutive enzymatic hydrolysis process. In the AFEX pretreatment process, lignocellulosic materials are treated with liquid ammonia at the temperature between 60 °C and 100 °C under high pressure for a certain period of time, normally 10 min, before the pressure is released swiftly, which would cause mechanical explosion of the materials from the inside. Recycling of ammonia in the system after the pretreatment is economically feasi­ble due to the high volatility of ammonia at atmospheric pressure [16]. The AFEX process was employed for the pretreatment of a variety of lignocellulosic materials such as alfalfa, wheat straw, wheat chaff, barley straw, corn stover, rice straw, mu­nicipal solid waste, softwood newspaper, kenaf newspaper, coastal Bermuda grass, switchgrass, aspen chips, and bagasse [17, 18]. AFEX pretreatment does not remove much hemicellulose and lignin, but it can decrease the cellulose crystallinity, disrupt the lignin-carbohydrate linkages and remove the acetyl groups from hemicellulose [19]. After pretreatment, the enzymatic digestibility of lignocellulosic materials can be increased. Moniruzzaman et al. [20] achieved more than 80 % of the theoretical sugar yield from corn fiber pretreated usingAFEX at 90 °C, an ammonia-to-corn fiber mass ratio of 1:1 and 200 psi for 30 min. Superior to the steam-explosion pretreat­ment where many inhibitors are formed from the degradation of hemicellulose and cellulose, the AFEX pretreatment is likely more advantageous as no toxic byprod­ucts are formed except for some phenolic fragments from lignin [3]. However, the AFEX process was not very effective for biomass with higher lignin content such as newspaper and woody biomass [12, 13].

Microwave pretreatment may be considered a physico-chemical process since it involves both non-thermal and thermal effects. The microwave method has proved to be effective for improving enzymatic hydrolysis of many agricultural residues/biomass such as rice straw and wheat straw [21, 22]. Ma et al. [22] sys­tematically optimized the pretreatment conditions for rice straw hydrolysis, and studied the effects of microwave intensity, irradiation time, and substrate concen­tration on the hydrolytic conversion of cellulose and hemicellulose. It was believed that microwave and microwave-based pretreatment could hydrolyze hemicellulose and solubilize lignin. Moreover, the thermal and non-thermal effects arising from heating could enlarge the pore size of the lignocellulosic materials, and enhance the accessibility of cellulose to enzymes [23]. Ultrasonic pretreatment could be an­other promising method for the removal of hemicellulose and lignin, and it has been widely used in the extraction of hemicellulose and enzyme proteins from biomass and organic waste materials such as biosludge [24, 25], although there is very limited published literature with respect to the effects of ultrasonic pretreat­ment on the glucose yield and carbohydrate conversion during enzymatic hydrolysis of lignocellulosic materials. Yachmenev et al. [26] reported that saccharification of cellulose was enhanced considerably by ultrasonic pretreatment. The increased en­zymatic hydrolysis yields after ultrasonic pretreatment could be explained by the effects of ultrasonic pretreatment: cracking of the cell wall, dislocation of the sec­ondary wall of the middle layer of the cell wall, and exposure of the middle layer to enzymes [27]. Yu et al. [28] investigated the effects of ultrasonic pretreatment on enzymatic hydrolysis of rice hull using 250 W, 40 kHz at 25 °C for different period of time ranging from 10 min to 60 min. Their results showed that the yields of total sugar and glucose increased from 11.7 % to 10.9-16.3 % and 15.8 %, respectively, via ultrasonic pretreatment for 30 min. In summary, ultrasonic treatment can cause cavitation, crash the cell wall structure, and provide more accessible surfaces in the substrate. Ultrasonic pretreatment can thus be a potential method for pretreatment of lignocellulosic materials due to its lower energy consumption. Due to the limited research in this respect, it is of interest to examine the effects of ultrasonic pre­treatment on enzymatic hydrolysis of lignocellulosic materials, in particular, when combining it with other chemical pretreatment approaches such as organosolv and alkaline methods.

Enzymatic saccharification was done on the pretreated solid wood following the LAP method 009 [16]. The hydrolysis was conducted in 250 mL Erlenmeyer flasks in an oil bath for 3 days in citrate-Na2PO4 buffer (pH 4.8, 100 mL), at 50 °C, and with magnetic stirring (200 rpm). The pH was adjusted using 4M NaOH. The enzyme loading for experimental design samples was 1 mL cellulase (612 u/(g mL), Fisher Scientific, IL, USA). Samples were taken every 24 h to determine sugar content by high performance liquid chromatography (HPLC).

Two commercial enzyme solutions (Cellic CTec2 (1.238 g/mL) and HTec2 (1.209 g/mL), Novozymes North America Inc., NC, USA) were also evaluated as received. Enzyme loading was based on solution weight % (100 x g enzyme solu — tion/g wood)). The enzyme loadings used here were 1.5 % (CTec2 0.06 mL, HTec2

0. 06 mL), 3 % (CTec2 0.12 mL, HTec2 0.12 mL), 6 % (CTec2 0.24 mL, HTec2

0. 25 mL), and 30 % (CTec2 1.21 mL, HTec2 1.24 mL).

Updraft gasifiers are the oldest and simplest type of gasifier. In these reactors, the gasifying gas travels upward while the solid fuels move downward as shown in Fig. 10.1a. The major advantage of this type of gasifier is its simple structure and design, low capital cost, and high char burn-out, which leads to low gas exit temper­atures and high equipment efficiency, as well as the possibility to process feedstock of various shapes [66].

On the other hand, poor heat and mass transfer can increase the risk of “chan­nelling” in the equipment, which may lead to an oxygen breakthrough and rapid gas-phase combustion reactions (and, possibly, an explosion). Fuels that are prone to agglomeration during gasification are not suitable for these types of reactors due to poor heat and mass transfer. However, high-ash, high-moisture or low-volatile feedstocks are suitable fuels for updraft gasifiers. Also, there are problems asso­ciated with high tar production that require gas cleaning operations. This is of minor importance, though, if the gas is used for direct heat applications, where the tar simply can be burnt. Nonetheless, this is not recommended for engine applications.

Pyrolysis of biomass with catalysts has been widely studied and they are sometimes used to tailor the yields of the pyrolysis products. However, catalysis chemistry is extremely complex and only a very few research groups in the world can explain catalysis mechanism for specific reactions and in highly controlled conditions. Thus, understanding (in a fundamental mechanistic way) the effects of adding catalysts on the evolution of pyrolysis products distribution and their composition is not currently feasible. The effects of catalysis on pyrolysis reactions are therefore determined empirically and undesired behaviours were often observed: significant drops in liquid yield have been the most common [47].

Yoshiaki Kimura, Seiichi Yasui, Takahisa Hinata, Toshiyuki Imai and Hideyuki Takenaka

Abstract Currently, the biogas produced by biogas plants at dairy farms in Japan is a carbon-neutral energy. However, utilization of biogas has thus far been restricted solely to the farms where it is produced because there is no effective method of transporting unused biogas. Thus, there is a need to establish practical methods for biogas refinement and transport from operating systems. In this study, a biogas refining-compressing-filling facility using a gas membrane that would allow the use of surplus biogas produced by privately owned biogas plants was manufactured. Furthermore, field tests of biogas utilization systems (BGUS) made up of equipment that could use purified gas obtained from such a facility were performed. Finally, the possibility of a regional purified biogas system of Japan was validated in rural areas. The refining-compressing-filling facility was able to achieve a biogas Wobbe index of 49.2-53.8 and a combustion rate equivalent to 34-47 m/s. The total carbon load of the common portions of the BGUS was 102 t-CO2 eq. Compared with the carbon load of the common portion of the biogas plant before introduction of the BGUS and of the gas utilizing equipment inside and outside the farm production system (209 t-CO2 eq), a reduction of 107 t-CO2 eq was achieved. The area’s carbon dioxide emissions could be reduced through the standardization of biogas products through refinement; this would allow for the export of biogas outside of the system for use in common gas appliances. Currently, purified gas is locally produced and consumed as a source of carbon-neutral energy on dairy farms and adjacent residences. Packing the purified gas into tanks and supplying it to the town create the possibility of further reducing the carbon emissions of rural areas.

Keywords Biogas plant ■ Biogas purifier ■ Biogas utilization system (BGUS) ■

Gas membrane — Wobbe index

Y. Kimura (H) ■ T. Hinata ■ H. Takenaka

Hokkaido Central Agricultural Experiment Station, Hokkaido Naganuma, Japan e-mail: kimura-yoshiaki@hro. or. jp

S. Yasui

Zukosha. Co. Ltd, Hokkaido Obihiro, Japan

T. Imai

Green Plan. Co. Ltd, Hokkaido Sappro, Japan

Z. Fang (ed.), Pretreatment Techniques for Biofuels and Biorefineries,

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_13, © Springer-Verlag Berlin Heidelberg 2013

13.1 Introduction

Anaerobic fermentative treatment of livestock waste by biogas plants is more effec­tive in lowering the environmental load than other methods. The biogas produced can be used as an energy source. Biogas from anaerobic digestion using livestock waste consists primarily of methane (typically 60 %) and carbon dioxide [1]. Other com­ponents can include oxygen and nitrogen, originating from air, sulfur compounds, particularly hydrogen sulfide, and water.

Approximately 80 biogas plants have been built in Japan as a means of effectively utilizing livestock waste. However, because many of the power generators installed in the plants to produce electricity—a representative method of utilizing biogas that has not been completely consumed by the facilities where it is produced—are foreign — made, repairing the generators when problems occur is difficult. Furthermore, the price of surplus electricity being sold is too low to recover the running cost. Use of biogas in Japan is premised on “consumption within the farm production system only used by farm management.” Because of this, a method of transporting biogas outside the farm production system is needed to capture the full potential of this agricultural biogas.

It was assumed that effective utilization of biogas outside the farm production sys­tem could be accomplished by simple application to general gas equipment. However, the amount of biogas produced and the concentration of methane fluctuates daily, its caloric value is not stable, and there is residual hydrogen sulfide; thus, domes­tic gas equipment manufacturers have shown reluctance to directly use general gas equipment for biogas. Also, as part of the IGF21 Plan, the Ministry of Economy, Trade and Industry, Japan has been advancing the integration of the highly caloric natural gases, for use as town gas [2, 3]. Thus, there is need for standardization of high-caloric biogas and stabilization of its caloric value.

A method of resolving this problem would necessarily involve the construction of a system that purifies biogas, fills storage cylinders at high pressure with the gas, and distributes it within the region. Purified biogas is used as transportation fuel in a number of countries but in Europe, it has reached a major breakthrough in Sweden [4-6] and German [7]. Thus, it is necessary to introduce a system of equipment that carries out in a single effort the basic technological sequence of biogas refining for Japanese rural areas, standardized high calorification of the gas, compression (high pressurization of the gas), and flow to storage cylinders [8]. There is also a need to extensively troubleshoot the problems that could occur in the actual use of this biogas purifier and clarify measures on how to solve these problems for rural areas in Japan.

In this chapter, a biogas refining-compressing-filling (RCF) facility that uses surplus biogas produced by privately owned biogas plants was devised and evaluated in terms of greenhouse gas (GHG) reduction, and field tests of biogas utilization systems made up of equipment that using purified gas obtained from the facilities were performed. Thus, the possibility of a regional purified biogas system of Japan was validated in rural areas.

Fig. 13.1 Gas membrane biogas refinement using membranes. (Hollow fiber separation)

Most solid acid catalysts presented excellent catalytic active in the first run. However, a considerable loss in catalytic activity occurred when the catalyst was recycled for several times [51-53]. Hegner et al. [51] reported that glucose yield from the hydrolysis of cellulose with FeCl3/silica was 11 %, while for the second and third cycles, it reduced to 8 % and 7 %, respectively. Dhepe et al. [52] studied the hydrolysis of sucrose using water-tolerant sulfonated mesoporous silicas. The reactions were tested at 80 °C for 24 h up to three recycles, and no decrease in activity was found. However, the catalysts were not tested for cellulose hydrolysis which needs a higher reaction temperature (~150 °C). Up to now, an amorphous carbon bearing — SO3H, — COOH and — OH groups showed the best recyclability among the reported results [42]. No decrease in activity was observed even after 25 cycles of the catalyst (total reaction time, 150 h). Although such sulfonated carbons are highly efficient for cellulose hydrolysis, there are needs for their improvement in the areas of separation and recovery from un-hydrolyzed cellulose residues.

A modification technology to increase the surface area, mechanical strength, and stability of catalyst supports and improve the acid density, strength, and recyclability of acid sites is required. The modification usually starts with discovering the cause of catalyst deactivation and seeking cheap raw materials to reduce the cost of catalyst preparation. Reusability is a unique character of solid catalysts as distinguished from liquid catalysts, also is the key to reduce the cost of catalytic process. Metal oxides, zeolites, cation-exchange resins, and carbonaceous solid are common supports of solid acids. Herein, modification of catalyst supports is discussed in detail.

Pre-treatment methods for biomass prior to conversion into fuels and chemicals can be classified into physical, thermal, biological, and chemical, or any combination of these methods. The selection of appropriate pre-treatment should be based on the aspects to enhance the biomass properties that increase the efficiency of the conversion process.

Biomass contains varying amounts of cellulose (40-60%), hemicellulose (20-40 %), lignin (10-25 %), and small amount of extractives. These wide range of these fractions lead to different thermal behavior and digestability. Hemicellu — lose, which is the most reactive compound in biomass, decomposes at relatively low temperature, that is, within the range of 225-325 °C. Meanwhile, cellulose degrades between 305 and 375 °C and lignin decomposes gradually over the temperature range of 250-500 °C [5].

The four methods reviewed in this chapter are physical, thermal, biological, and chemical pre-treatments. Physical and thermal treatments are mainly to remove mois­ture; hence increase the energy density of that particular biomass. The chemical and biological treatments are performed to de-polymerize lignin.