Ammonia Fiber Explosion/Ammonia Recycle Percolation)

The ammonia fiber/freeze explosion (AFEX) process is a physicochemical process in which the biomass is subjected to liquid anhydrous ammonia under high pressures and moderate temperatures and then is rapidly depressurized. The AFEX resembles very much the steam-explosion pretreatment technology. However, compared to the steam-explosion process the temperatures (60—100°C) are much more moderate, meaning less energy input and overall energy costs associated with the AFEX process. Major variables in the process are the operation temperature, ammonia concentration and reaction time. The temperature will influence the degree of disruption to the biomass struc­ture, as it will affect the rapidness of the ammonia vaporization within the reactor during depressuriza­tion. Typical ammonia loading for many feedstocks are around 1 kg ammonia per kilogram dry biomass. The residence time can be altered from minutes to half an hour duration depending on the degree of satu­ration needed for the selected biomass (Chundawat et al., 2007). The biomass is saturated for a period of time with the ammonia in a pressurized reactor before being released to atmospheric temperature resulting in a rapid expansion of the ammonia gas causing swelling of the biomass feedstock. This creates hydrolysis of the hemicellulose fraction, a disruption in the lignin- carbohydrate linkages, ammonolysis of glucuronic cross-linked bonds, and partial decrystallization of the cellulose structure, all leading to a higher accessible surface area for enzymatic attack (Chundawat et al., 2007). An important prerequisite to make the process economic is a very efficient recovery of the ammonia gas. Under typical AFEX conditions this pretreatment does not remove lignin or any other substances from the biomass; however, the lignin-carbohydrate com­plexes are cleaved, and the lignin is deposited on the surfaces of the material possibly causing blockage of cellulases to cellulose (Kumar et al., 2009; da Costa Sousa et al., 2009). An overview of the advantages and disadvantages is listed in Table 17.5. Ammonia recycle percolation (ARP) has often been paired with the AFEX pretreatment process, but it can have some different characteristics. In the ARP process, aqueous ammonia of concentration between 5 and 15% (wt%) is sent through a packed bed reactor containing the biomass feedstock at moderately high temperatures (140—210 °C) and longer reaction times compared to the AFEX process, increasing the energy costs (Bro — deur). The advantage of the ARP process over AFEX is its ability to remove the majority of the lignin (75—85%) as well as solubilize more than half of the hemicellulose (50—60%) while keeping the cellulose in its polymeric form. This results in short-chained cellu — losic material containing a high amount of glucan with a high degree (>86%) of enzymatic digestibility and a limited amount of inhibitors. Up to now mostly herbaceous biomass has been treated with this process. Many of the primary concerns with the AFEX process (high energy costs and liquid loadings, along with many disadvantages associated with the AFEX process)

need to be addressed before an economical process can be envisioned (Brodeur et al., 2011).

Aromatic amino acids include tryptophan, phenylala­nine, tyrosine and histidine and all of them were isolated in the 1880s. Tyrosine was isolated by Liebig in 1846 and phenylalanine from lupins by Schulze in 1881. While histidine was reported by Kossel and Hedin in 1896, tryptophan was first isolated from casein by Frederick Hopkins in 1901. Even though the aromatic amino acids are produced by microbial fermentation, high produc­tion levels are not reached. Commercial production of these amino acids also includes extraction and enzymatic conversion. In 2006, Kyowa Hakko Kogyo claimed devel­opment of the world’s first fermentation-based method for the commercial production of L-tyrosine. Biodiesel industry-generated crude glycerol can be biorefined by phenylalanine-producing E. coli cells (Khamduang et al., 2009). The use of glycerol resulted in phenylalanine yields up to 0.58 g/g, which is twice as compared to pro­duction with sucrose. Tryptophan and histidine were produced from mixed sugars pentoses and hexoses by genetically modified E. coli (Savrasova et al., 2004).

Microbial amino acid production process for bio­refining application will be technically feasible, only if the nutrient requirements are met in invariably same quantity and quality. These raw material production costs must be lower than starch hydrolysates or refined sugars and the coproducts have to use the existing fermentation machinery and infrastructure for economic feasibility. Most of the microbial amino acid fermenta­tions occurs at a temperature range of 30—40 °C and at near neutral pH. The fermentation medium has to be neutralized and proper cooling systems for temperature maintenance, agitation and aeration has to be in place for the amino acid production to match with the expected values. Alternatives are development or utilization of strains that are pH and temperature tolerant and over­produce amino acids or choosing coproducts and organ­isms having the same substrate utilization spectrum and physical requirements. The use of microbial amino acid fermentation for biorefining resulted in improved ground water quality, lower ammonia and nitrate excre­tion from poultry and livestock. This is due to the substi­tution of optimal quantities of the limiting amino acids in place of soybean meal. The sugar solutions from the lignocellulose feedstock biorefinery will have a fair con­centration of inhibitors like furfural and hydroxymethyl furfurals and syringaldehyde, which is toxic to the micro­organisms. The inhibitor tolerance of amino acid pro­ducers will also be a deciding factor in the biorefining concept. Fortunately, the amino acid producer C. glutami — cum has shown tolerance toward inhibitors at growth — arrested conditions and high cell densities.

As mentioned above, all metabolic pathways leading to H2 production in green algae are extremely sensitive to O2 due to fast and irreversible inhibition of [Fe—Fe]- hydrogenase enzyme(s) and competition from different respiratory processes for the reductants. Significant efforts to surmount the O2 sensitivity issue have been made, but still the algal strain with the O2-tolerant H2 photoproduction has not been generated (Ghirardi, 2006; Ghirardi and Mohanty, 2010). Therefore, in photosynthetically active algal cells under saturating light conditions the most efficient H2 photoproduction process (via direct biophotolysis) lasts for a few seconds. For the industrial system, however, H2 photoproduction should be extended from the scale of seconds to at least days. When optimized, such process may yield H2 at a cost of around $3/kg H2 for the upper bound performance (~9% STHE) and slightly above $8/kg H2 for the near term performance (~ 1.5—2% STHE) (Blake et al., 2008; James et al., 2009). Unfortunately, at the current state sustained H2 photoproduction in photosynthetically active green algae is only possible at the expense of efficiency. For example, long-term H2 production is usually observed in cultures under very low light intensities or even in the dark when O2 evolu­tion proceeds very slowly or does not proceed at all (Kondratieva and Gogotov, 1983; Aparicio et al., 1985). Interestingly, Batyrova et al. (2012) recently observed a stable but negligible rate of H2 production in very dense cultures placed under normal light conditions. The algal cells demonstrated a high hydrogenase activity, but efficient H2 photoproduction was not observed. Most probably, under these conditions H2 evolution was driven by the cells in the inner part of the photobioreac­tor, while H2 photoproduction in the illuminated algae was limited by the coevolved O2.

One of the possibilities of driving the process under normal photosynthetic conditions is to sparge cultures continuously with inert gas, such as argon or nitrogen, that removes rapidly the PSII-evolved O2 gas (Greenbaum, 1982; Greenbaum et al., 2001). Before the sulfur-deprivation protocol was developed, this was the only way for the long-term H2 generation in algal cultures. Using a confined bioreactor, Greenbaum et al. (2001) showed several cycles of simultaneous H2 and O2 photoproduction during 1 h intervals after extensive purging the cultures in the dark for 2 h by N2. The exper­iment lasted for over 1400 h (58 days) and required peri­odic additions of CO2 gas into the photobioreactor for restoration of photosynthetic activity and replenishment of carbohydrates in algal cells. The average stoichio­metric ratio of H2 to O2 was 2.8, indicating that reducing equivalents for H2 were derived from endogenous reductants, most likely starch, as well as water. There­fore, H2 photoproduction in this case was partly driven by the cells via indirect biophotolysis pathway. Never­theless, even under extensive purging of the cultures with N2 and good mixing conditions in the photobior­eactor, the H2 evolution rate was limited due to O2 buildup in the liquid phase (Greenbaum et al., 2001). These experiments were later repeated under sulfur — deprived conditions (but with some modifications) and demonstrated a simultaneous improvement in the rate of H2 photoproduction upon declining the O2-evolving activity in algal cultures (Ghirardi et al., 2000).

The prolonged H2 evolution by green algae can also be induced by a full or partial inhibition of the water­splitting activity of PSII in cells. The full inhibition can be achieved by applying DCMU (Gfeller and Gibbs, 1984; Fouchard et al., 2005). In contrast to the N2-sparging approach, H2 photoproduction in

DCMU-treated cultures depends totally on the amount of carbohydrates or other substrates stored by the cells during the growth period and, thus, the process is limited to only one cycle. The partial inhibition of the PSII activity occurs in sulfur-deprived algae (Melis et al., 2000) and in certain mutants with manipulated expression levels of the D1 reaction center protein (Surzycki et al., 2007) or in the mutant cells affected in the PSII water-splitting complex (Makarova et al., 2005,

2007) . For the establishment of an anaerobic environ­ment and H2 production in algal cultures, the partial inhibition of the PSII activity in cells should achieve the point when the O2 produced by the PSII centers is consumed sufficiently by respiration. However, H2 photoproduction under these conditions usually proceeds at lower rates as compared to the initial rates in dark-adapted algae exposed to the light. In contrast to the full inhibition approach, several cycles of H2 pro­duction are possible (Ghirardi et al., 2000), and thus the process can be driven continuously (Laurinavichene et al., 2006, 2008; Kim et al., 2010).

Jatropha (Jatropha curcas) is an oilseed species that has generated the most excitement in recent years in terms of its potential as a feedstock for biodiesel production. It is a multipurpose bush or low-growing tree, native to tropical America that can be used as a hedge, to reclaim land and as a commercial crop (Carriquiry et al., 2010; Azam et al., 2005; Openshaw, 2000). Jatropha is now grown in many tropical and subtropical regions within Asia and Africa. The oil derived from Jatropha has been shown to yield a biodiesel that meets European and US quality standards (Pandey et al., 2012; Akbar et al., 2009; Azam et al., 2005). Jatropha is known as a diesel fuel plant; the seed can yield a substantial quan­tity of oil that can be converted to biodiesel without prior refining (Carriquiry et al., 2010; Becker and Makkar, 2009). This plant is currently underutilized but could help in meeting the challenges of global bio­fuel demand (37 billion gallon) by 2016. Jatropha can be grown in semiarid conditions and/or marginal soils without large investment inputs (Jongschaap et al.,

2007) . While nonedible and toxic to humans and some animals (toxic substances include toxalbumin curcin, phorbol, saponins, trypsin inhibitor and a toxic lectin; Rakshit et al., 2013; Pimentel et al., 2012; Carels, 2009), its oil can be burnt directly or processed into biodiesel, which makes it an especially attractive biofuel crop in remote rural areas (Akbar et al., 2009; Jongschaap et al., 2007). The interest in Jatropha has been fueled by very optimistic claims of a concurrent capability to producing high oil yields and recovering wasteland (Achten et al., 2008). However, to date, critical questions remain regarding its ability to be economically viable

when grown in poor environmental conditions. Attain­ment of consistently high yields has only been achieved with relatively high levels of nutrient inputs and on good soils (International Energy Agency (IEA) Bio­energy, 2008). Nonetheless, the possibility of cultivating energy crops such as J. curcas L. has the potential to enable some smallholder farmers, producers and pro­cessors to improve their economic and social conditions, and support rural development. In addition to growing on degraded and marginal lands, this crop has special appeal, in that it grows under drought conditions and animals do not graze on it (Pandey et al., 2012; Carri — quiry et al., 2010).

Another important biodiesel feedstock are microalgae, which comprise a diverse group of aquatic photosyn­thetic microorganisms that grow rapidly and have the capability to yield large quantities of lipids adequate for biodiesel production (Ahmad et al., 2011; Amaro et al., 2011; Singh et al., 2011; Carriquiry et al., 2010; Mata et al., 2010; Li et al., 2008; Chisti, 2007; World Watch Insti­tute (WWI), 2007). Algae were initially investigated as a potential source of fuel during the gas scare of the 1970s (Li et al., 2008). The National Renewable Energy Labora­tory (NREL) started its algae feedstock studies in the late 1970s, but its research program was discontinued in 1996. Recent renewed interest has led the NREL to restart its research into the bioenergy/biodiesel potential of algae (Donovan and Stowe, 2009). The potential for algae to provide biomass for biodiesel production is now widely accepted. Furthermore, algae are recognized among the most efficient raw material for this purpose, and some studies (Carriquiry et al., 2010; Chisti, 2007) assert microalgae represent the "only source of biodiesel that has the potential to completely displace fossil diesel". One of the main advantages is the ability of microalgae to produce large amounts of biomass per unit of land. In addition, microalgae can be grown in saline water, coastal seawater, freshwater and on nonarable land, hence reducing the competition for land with conventional agri­culture (Khan et al., 2009), and creating economic oppor­tunities in arid or salinity affected regions (Carriquiry et al., 2010; Schenk et al., 2008)

Cultivation of microalgae, which is considered one of the major bottlenecks to commercial development, is being done mainly on open ponds, on closed bioreac­tors, and in hybrid systems (Brennan and Owende, 2010; Mata et al., 2010; Ugwu et al., 2008). While conven­tional open ponds are old systems for biomass produc­tion and account for the majority of microalgae cultivated today, closed bioreactors that achieve higher biomass productivity are being developed (Khan et al., 2009; Schenk et al., 2008). Open ponds are often perceived to be less expensive than bioreactors, as they require less capital and are cheaper to operate (Carriquiry et al., 2010; Khan et al., 2009). However, open ponds are more susceptible to contamination from unwanted species (Schenk et al., 2008), suffer from high water losses due to evaporation and reduced process control and reproducibility. Algal biomass production systems can be adapted to various levels of operational and technological skills; some microalgae yield chemically useful fatty acid profiles and an unsa­ponifiable fraction, which supports biodiesel production with high oxidation stability (Natrah et al., 2007; Minowa et al., 1995; Dote et al., 1994; Milne et al., 1990). In a biorefinery context, the lipid profiles of micro­algae can also provide a valuable source of omega-3 fatty acids, such as docosahexaenoic acid and eicosapen — taenoic acid (Yen et al., 2013; Doughman et al., 2007). Some important microalgal species are listed in Table

2.7 with their corresponding oil content. The physical and fuel properties of biodiesel from algal oil are compa­rable, in general, to those of fuel diesel (Amin, 2009; Rana and Spada, 2007; Miao and Wu, 2006).

The use of microalgae could be a suitable alternative in the future, if improved high-rate production systems are available at scale, because these algae are one of the most efficient biological producers of oils on the planet and are a versatile biomass source (Demirbas, 2011; Mata et al., 2010; Macedo, 2007; Campbell, 1997). In fact, microalgae with a lower oil content (~ 30% of the dry biomass) could yield 58,700 L oil/hectare per year or 51,927 kg biodiesel/hectare per year. In comparison, Jatropha (J. curcas L.), with an oil content of 28% (dry weight), can yield 741 L oil/hectare or a biodiesel pro­ductivity of 656 kg biodiesel/hectare per year (Mata et al., 2010). On average, the biodiesel production yield from microalgae can be 10—20 times higher than the yield obtained from oleaginous seeds and/or vegetable oils (Mata et al., 2010; Gouveia and Oliveira, 2009; Chisti, 2007; Tickell, 2000). Therefore, in the future microalgae may become one of the Earth’s most important renew­able fuel feedstocks for an number of reasons: their higher photosynthetic efficiency, biomass productivities, faster growth rates (in comparison with terrestrial plants), higher CO2 fixation and O2 production rates, and ability to grow in liquid medium, in variable climates and in ponds on nonarable land including marginal areas unsuitable for agricultural purposes (e. g. desert and seashore lands). Microalgae can also grow in nonpotable water or even in systems to combine waste treatment and biomass production (Zeng et al., 2012). They also use far less water than traditional crops and do not displace food crops; their production is not seasonal and biomass can be harvested daily (Chisti, 2007, 2008; Spolaore et al., 2006; Campbell, 1997).

CONCLUSIONS

In summary, achieving the feedstock yields to meet bioenergy requirements will generally require lignocel — lulosic crops rather than food crops. Pretreatment is likely to be required, and could be conducted close to the site of harvesting, as the pretreated biomass would be reduced in bulk, and thus cheaper to transport. The ideal pretreatment should be low cost, yield mini­mum levels of inhibitory compounds, result in a minimum loss of the main polysaccharides and enable maximum recovery of different fractions from the biomass. Pretreated biomass is also more amenable to downstream enzymatic bioconversion. There are major challenges ahead to reduce bioenergy production costs, many of which can provide significant opportu­nities for fundamental research and innovation in science and engineering. Bioenergy production, espe­cially from second — and third — generation feedstocks, can yield many socioeconomic benefits. Selection of the appropriate feedstocks in combination with positive sustainable agronomic and resource management ap­proaches will reduce global dependency on fossil fuels. However, well-integrated and well-conceived strategies are required so that bioenergy can maintain the environ­ment, support biodiversity, conserve water resources, lead to a reduction in emissions and enable rural development. Lignocellulosic biomass has several advantages over conventional sugar — and starch-based raw materials and has been projected to be one of the main sources of bioenergy and biofuels in the near future. With the application of existing technologies and future advances, biomass to bioenergy can provide a significant positive alternative in the energy and biofuel sector.

Acknowledgments

The authors are grateful for research funding from Enterprise Ireland and the Industrial Development Authority, through the Technology Centre for Biorefining and Bioenergy (TCBB), as part of the Compe­tence Centre program under the National Development Plan 2007—2013. The support of Mr B. Bonsall, Technology Leader (TCBB), and Prof. V. O’Flaherty, Chair of Microbiology, School of Natural Sci­ences, & Deputy Director of the Ryan Institute for Environmental, Marine and Energy Research at NUI Galway, Ireland, is gratefully acknowledged.

The use of microorganisms in conversion processes to produce usable material from biomass sources has been ongoing for several decades. Most of the reports in the literature discuss the development of bioprocesses that are involved in the production of simple sugars, which are then used to produce bioethanol or related com­pounds for use as biofuels. However, there are new trends emerging for the use of biomass conversion by microbes, as shown in Table 5.2. Biomass conversion processes may eventually be implemented to produce a much greater array of useful bioproducts, in addition to biofuels.

STRATEGIES OF USING MICROBIAL PRETREATMENT TO ENHANCE SUGAR RELEASE FOR BIOFUEL AND BIOPRODUCT PRODUCTION 85 TABLE 5.2 List of Bioproducts Produced by Different Microorganisms

Acetate and glucose are two common substrates in laboratory studies. Compared to the recalcitrant substrates, they are far more readily utilized by microbes for energy generation. Thus, they are usually used as the carbon source for microbes used in MFCs. Acetate has an advantage that at normal temper­atures, it is not a good nutrient for fermentation and methanogenesis. In contrast, glucose is a fermentable sugar that can be consumed by the processes of fermen­tation and methanogenesis (Pant et al., 2010). Thus, the Coulombic efficiency of acetate is usually higher than glucose. However, glucose can be used to promote the microbial diversity of a biofilm consortium. When glucose was used as the substrate, a maximum power density of 216 mW m~2 was achieved (Rabaey et al.,

2003) , while it reached 506 mW m~2 for acetate (Liu et al., 2005b). Some other simple substrates such as buty­rate have also been used as the substrate in MFCs.

146

Wastewater Types

Various wastewaters have been tested as substrates for MFCs because they contain many different kinds of organic carbon molecules. They are attractive for use in MFCs because the organic carbons are otherwise wasted. As shown in Table 9.3, the output power density is dependent on the wastewater quality (high COD values) and the MFC reactor structure. For example, a maximum power density of 528 mW m~2 for brewery wastewater was obtained (Feng et al., 2008), while an average power density of 72 mW m~2 was achieved for domestic waste­water (Sharma and Kundu, 2010). Some biorefractory wastewaters such as dye, leachates and pharmaceutical wastewater have also been tested for MFC power gener­ation. A landfill leachate containing heavy metals, dis­solved organic matters and other matters achieved a maximum power density of 1.38 mW m-2 (Greenman et al., 2009). A maximum power density of 9.1 W m~3 was achieved when using phenol as the sole carbon source. While glucose was added as a supplement, the maximum power density increased to 28.3 W m~3 (Luo et al., 2009a). In addition, some refractory compounds such as pyridine, quinoline and indole were also used as substrates for MFCs (Hu et al., 2011).

In this method, finely ground biomass is placed in a porous bag or "thimble" made of strong cellulose, which is placed in the extraction chamber of a Soxhlet appa­ratus. The menstruum is heated, and the condensed extractant drips into the thimble containing the biomass, ensuring intimate continuous contact with the biomass. When the level of liquid in the extraction chamber reaches overflow, the liquid contents siphon into the heating chamber. This process is continuous and is carried out until complete extraction is achieved (Morrison and Coventry, 2006). The advantage of this method is that large amounts of lipid can be extracted with a much smaller quantity of solvent.

Countercurrent Extraction

Counter-current extraction is a process whereby wet raw material is pulverized using toothed disc disinte­grators to produce slurry in a semicontinuous stream. As the pulverization of the biomass is in aqueous media, the heat generated during comminution is counterbal­anced by the slurry water, preserving thermolabile compounds. The slurry stream is moved in one direction within the cylindrical extractor where it comes into discreet contact with a suitable menstruum (Vishwakarma, 2010). Complete extraction is possible when the quantities of solvent and material and their respective flow rates are optimized. The quantity of solvent required is generally minimal and as the process is most often conducted at room temperature, the threat to thermodegradation of volatile compounds is negated (Handa, 2008).

Ultrasound Extraction (Sonication)

The use of sonication is an emerging technology that is gaining widespread industrial acceptance due to recent advances in the scalability of the technology (Awad et al., 2012b; Dolatowski et al., 2007). In the context of lipid extraction from biomass, ultrasound technology is used to increase the permeability of biomass cell walls by generating cavitation events. These events are created by the use of high frequencies (20—2000 kHz) to generate a microbubble in solution; the intensity of the waves leads to the eventual collapse of the bubble generating extreme localized pressure and temperature events in close proximity to the biomass. These cavitation events assist in the rupturing of the cell walls to release the intercellular constituents into the surrounding environment. Once the biomolecules of interest are released from the biomass they can be recovered using conventional techniques. One disadvantage of using ultrasonics in the occurrence of sonolysis, i. e. the occasional but deleterious effect that when high power (typically greater than 20 kHz) is applied in aqueous media it can lead to the formation of free radicals and hydrogen peroxide. These are generated at the interfacial double layer established during cavitations, which subse­quently diffuse into solution (O’Donnell et al., 2010).

Clay minerals are composed of hydrous layered sili­cates that are part of the phyllosilicates family. The phyl — losilicates family is broad and is roughly separated by layer types, groups, subgroups and species (Brindley and Brown, 1980). Two basic units are important to build the clay minerals, the first is silicon atoms coordinated tetrahedrically to oxygen atoms (SiO4) and divalent or trivalent metals coordinated octahedrically to hydroxyls (M+2/M+3(OH)g). The silicon tetrahedral face can share the three corners with other silicon tetrahedral to build a hexagonal two-dimensional pattern, the tetrahedral sheet. A similar procedure can be adopted by the octahe­dral, where basically two differences can be obtained when M+2 or M+3 atoms occupy the center of the octahedral.

When M+2 is used and the octahedral share the edges, all octahedral sites are occupied and a two-dimensional unit is formed, the so-called octahedral sheet. This unit resembles the structure of brucite (Mg(OHD and the sheet is called trioctahedral. When M+3 is used and the octahedral share the edges, only 2/3 of the octahedral sites are occupied and the resulting two-dimensional unit resembles the structure of gibbsite Al(OHL; in this case, the sheet is named dioctahedral. In the ideal condition, the apical oxygen of the tetrahedral sheets can be linked to one octahedral, building the clay min­erals of the 1:1 layer type. The unshared hydroxyls of the octahedra lie at the center of the tetrahedra at the same "z" level of the shared apical oxygen.

Under ideal conditions, two clay minerals of the 1:1 layer type can be obtained. When M+2 occupies the center of the octahedral, the structure of chrysotile (Mg3(OH)4 Si2O5) is obtained and the replacement of M+2 by M+3 yields the structure of kaolinite (Al2(OH)4Si2O5).

As both sides of the octahedral have hydroxyls to share, one octahedral sheet can also be combined with two tetrahedral sheets, originating the 2:1 layer-type clay minerals. Again, when M+2 occupies the center of the octahedral, the structure of talc is obtained (Mg3(OH)2Si4O^) while its replacement by M+3 results in the structure of pyrophyllite (AL(OH)4Si4O10). Figure 16.1 shows the lateral (A) and top (B) views of the above-cited compounds.

In nature, the phyllosilicates are obtained through weathering, which is the phenomenon related to the

disintegration and chemical alteration of rocks and min­erals at the Earth’s surface in direct contact with the at­mosphere, water and organism. Through this process, many different isomorphic substitutions occur either in the tetrahedral (Si by Al or Fe+3) or in the octahedral sheets (Al or Mg by Fe+2/+3, Li, Ti, V, Cr, Mn, Co, Ni, Cu and Zn), mainly in clay minerals of the 2:1 type. The isomorphic substitution generates an excess of negative charge into the layers, which needs to be compensated with the intercalation of hydrated cations between the layers. Hence, this substitution generates

the cationic exchange capacity and the plastic properties of these clay minerals, particularly when they are dispersed in water.

Using the example of talc and pyrophyllite, these minerals can give origin to trioctahedral saponite ((Mty -nH2O)(M g3_y(A l, F e)y)(Si4_*A l*O 0(O H)2)), where Mg+2 is substituted by Al and Fe and Si, by Al. After this substitution, the excess of negative charges in the clay layers are compensated by the intercalation of hydrated cations (M+_y • nH2O). Another example of
trioctahedral mineral derived from pyrophyllite is the clay mineral hectorite ((M+•MH2O)(Mg3_yLiy)(Si4Oio (OH)2)). In the case of dioctahedral talc, the derived clay minerals are montmorillonite ((M+-n^O^A^_yMgy) (Si4Oio(OH)2)), beidellite ((M+-nH2O)Al2(Si4_* Al*) O1o(OH)2) and nontronite ((M+-:nH2O)Fe+3(Si4_xAlx) Oio(OH)2).

HDO is a promising upgrading technology to remove the oxygen from biomass-derived streams, for example obtained after pyrolysis. Strong emphasis is put on finding selective catalysts to minimize the use of hydrogen while maintaining the aromatic function­ality of lignin. HDO of lignin model compounds can be efficiently performed over a copper chromite catalyst (Deutsch and Shanks, 2012). The hydroxymethyl group of benzyl alcohol is highly reactive to HDO. Demethox — ylation of anisole is the primary reaction pathway in contrast to demethylation and transalkylation. The latter are more prevalent for conventional hydrotreating catalysts. The hydroxyl group of phenol strongly acti­vated the aromatic ring toward cyclohexanol and cyclohexane.

When applied directly to isolated technical lignin a wide range of chemical reactions occur at 380—430 °C including cleavage of interunit linkages, deoxygenation, ring hydrogenation, and removal of alkyl and methoxyl moieties. A complex bio-oil is the result, but the oxygen content of this hydropyrolysis oil is lower compared to pyrolysis oil and therefore this HDO bio-oil is chemi­cally more stable. The hydrogen pressure, typically 50—150 bar, strongly influences the oil yield. Ideal cata­lysts should have high activity for hydrogenolysis and/or cracking of C—O—C and C—C linkages; low ac­tivity for ring hydrogenation; meaningful selectivity to­ward a certain aromatic compound or class of compounds to allow effective product isolation; high resistance against coke formation and easy regeneration; high sulfur resistance for processing sulfur-containing lignins. Bifunctional catalysts comprise an active hydro­genation metal (e. g. NiMo-Cr2O3, Pd, Co-Mo) and an acidic support such as zeolites to selectively open some C—C bonds. By using catalysts the yield of HDO bio-oil has been improved from 15% up to 81% (Azadi et al., 2013). For development of viable catalytic HDO bio-oil upgrading technologies to produce trans­portation fuel include (1) improved catalysts, (2) alterna­tive hydrogen source, (3) detailed kinetics study and

(4) optimizing the HDO reactions conditions suitable for existing refinery infrastructure (Bu et al., 2012).

Phytochemicals with a wide diversity in structure and bioactivity have long been sources for pharmaceu­tical agents ("phytomedicines", Pandey et al., 2011). One important bioactive group is carotenoids. Astaxan — thinhas uses as anticarcinogens, antioxidant, antiinflam­mation (da Fonseca et al., 2011), cholesterol effector, pain reliever (Skjanes et al., 2012) or immune system booster (Abad and Turon, 2012). Canthaxanthin also suits for antioxidant or antiinflammation uses (Skjanes et al., 2012). b-Carotene may serve to prevent erythema or arthritis (Skjanes et al., 2012).

Another major bioactive phytochemical group is iso — flavones, especially those from soybean. For instance, daidzein, genistein and glycitein are antioxidative or estrogenic, potentially beneficial in cancer, heart disease or obesity prevention.

Phytosterols or triterpenes are phytochemicals benefi­cial for cholesterol, cancer or immune system-related con­siderations. Saponins (saponenols glycosides) are also thought to be beneficial for certain cancer, heart, liver illness treatments (Wu and Kang, 2011; Guclu-Ustundag and Mazza, 2007; Zhao and Moghadasian, 2010). Organic sulfur compounds, such as allylsulfides, also have

anticancer potential (Cerella et al., 2011). Polyamine — hydroxycinnamic amide conjugates are antioxidative and antimelanogenic (Choi et al., 2007). Lignans are also antioxidants; so are phytic and cinnamic acid ester glycosides (Wu and Kang, 2011; Guclu-Ustundag and Mazza, 2007). Menthol and essential oils are used as topical analgesic or antiitching agents, decongestants or oral hygiene ingredients. Capsaicin also has topical uses for relieving pain, itch or inflammation.

Highly effective, pharmacologically well-studied med­icines originated from plants include quinine, ephedrine, artemisinin, paclitaxel (Taxol) and vinblastine, galanth — amine and digoxin, as well as opiates like morphine and cocaine. Plant-derived precursors for medicines include 10-deacetylbaccatin (for paclitaxel), (—)-shikimic
acid (for oseltamivir phosphate or Tamiflu), diosgenin (for various steroid hormones), salicylic acid or salicin (for acetylsalicylic acid or aspirin) (Pandey et al., 2011).

There are also phytochemicals that can be used for agriculture or forestry protection (‘agrochemicals’, Huter, 2011; Dayan et al., 2009). For example, leptosper — monefromCalHstemoncitrinusplant is used as herbicide (Salim et al., 2008); lemongrass oil as pesticide or herbi­cide; essential oils (e. g.D-limonene), pyrethrum, nicotine and rotenone as insecticide; thymol and pyrolyzed to­bacco bio-oil as biocide (O’Brien et al., 2009; Dayan et al., 2009); and corn gluten meal and essential oils for weed control.

The structures of many bioactive phytochemicals are shown in Figure 20.4.

Phytochemicals for Personal Care or Other Uses

Various phytochemicals are used for personal care because of their performance and renewability. Betaine (trimethylglycine ammonium salt) has significant poten­tial for hair care (Kripp, 2006), lutein and b-carotene as colorant, and menthol and citronella oil for insect repelling.

There are other industrial uses of phytochemicals. Lecithin is useful for antifoaming, dispersion, stabiliza­tion, or wetting. Tannin is used for leather processing (tannery), wood products (e. g. particle board) adhesion (Frihart, 2010), or anticorrosion. Lignin may be used for making resins.