Biomass properties and composition vary widely. As a result, products from thermochemical conversion processes can be quite variable. The most routinely used biomass properties relevant for thermochemical conversions are heating value, proximate analysis, ultimate analysis and biochemical composition. Proximate analysis includes contents of moisture, volatiles, ash and fixed carbon. Ultimate analysis includes contents of carbon, hydrogen, oxygen, nitrogen, and sulfur. These contents can be reported on a dry basis (d. b.), wet basis (w. b.) or dry and ash-free basis (d. a.f.). The difference among these bases is the mass that the content (such as carbon content) is compared with. Content given in dry basis implies that the content is compared with moisture-free biomass. Content given in wet basis implies that the content is compared with biomass containing moisture. Content given in dry and ash-free basis implies that the content is compared with moisture and ash-free biomass material. Properties of several biomass are presented in Tables 1 (proximate analysis), 2 (ultimate analysis) and 3 (biochemical compositions). However, the above properties do not

completely characterize any biomass feedstock because biomass feedstocks with similar properties and composition stated above may differ in their polymer structure resulting in different products through thermochemical conversion processes.

To understand and reliably predict the effects of the biomass composition and properties on thermochemical conversion processes and products, several equipment have been used by researchers. The most common equipment includes thermogravimetric analyzer (TGA), dynamic thermogravimetric analyzer (DTA), pyrolyzer (Py), Fourier-transformed infrared spectrophotometer (FTIR), gas chromatography (GC) and mass spectrometer (MS) (Lapuerta et al. 2004; Dejong et al. 2007; Fahmi et al. 2007; Boateng et al. 2010; Pasangulapati et al. 2012; Ribechini et al. 2012). TGA provides weight loss of biomass as temperature is varied. Different weight loss stages in gasification and pyrolysis modes can be observed in the TGA data. The stages are separated more clearly using the derivative of the weight loss with time or temperature. Heating rates available in pyrolyzer is much higher than those in TGA, hence pyrolyzer is widely used to obtain volatiles simulating pyrolysis condition. The volatiles evolved from the biomass thermal degradation is detected by FTIR and MS.

Alkaline pretreatment mainly includes ammonium hydroxide, sodium hydroxide, potassium hydroxide and lime pretreatment. Among these, ammonium hydroxide is widely popular due to its ease in recovering ammonium hydroxide after the pretreatment process by evaporation method. Ammonium hydroxide can be used in its native form or diluted with solvents such as water. Ammonia fiber explosion (AFEX) is performed using ammonia in a pressurized vessel (Dale et al. US Patent 2009/0053771 A1). Aqueous ammonia can be used in different ways to achieve delignification of lignocellulosic biomass. Recycle percolation and soaking in aqueous ammonia (SAA) pretreatments are widely in use. SAA pretreatment operates at moderate temperatures ranging from 30-80°C with less formation of inhibitory compounds compared to other pretreatments (Kim and Lee 2007). In addition, SAA pretreatment preserves cellulose and hemicellulose in a solid state; the use of ammonium hydroxide potentially makes the SAA process more economical than other pretreatment methods because of its relative ease of recovery, ability to reduce enzyme loading in subsequent steps and its abundance as a commodity chemical (Mosier et al. 2005; Kim and Holtzapple 2006; Kim et al. 2006, 2008; Kim and Lee 2007). SAA pretreatment has been effective for herbaceous crops such as switchgrass. However, the recalcitrance of softwood (primarily due to the higher lignin content and crystallinity) would be ineffective using aqueous ammonium hydroxide pretreatment. Gupta (2008) mentioned in his dissertation, "In alkaline pretreatment using sodium hydroxide/potassium hydroxide, lignin degradation occurs mainly due to the breakage of aryl ether linkages which constitute approximately 50-70% of total lignin linkages. However, diaryl ethers and carbon-carbon bonds of the lignin are relatively stable, and thus present barriers to complete degradation. In addition, hydroxyl ions catalyze the cleavage of ether linkages in the lignin and can result in the formation of byproducts that can inhibit microbial fermentation such as soluble sodium phenolates."

Several practical issues are evident related to land. The vast majority of land in the U. S. that is capable of producing switchgrass is privately owned. Every unit of land is used for some purpose by its current owners. The primary uses range from intensive crop production to recreation and aesthetics. A number of practical issues are likely to be encountered by a business that depends on the establishment of a dedicated energy crop on thousands of hectares owned by hundreds of individuals.

The incentive structure required to entice land owners to enable conversion of millions of hectares from current use to establish switchgrass or some other dedicated energy crop remains to be determined. A high risk would be involved for a biorefinery to depend on spot markets for feedstock. In the absence of spot markets, obtaining a reliable flow of feedstock from a dedicated energy crop such as switchgrass could involve: (1) contracts with individual growers; (2) contracts with a group of growers through a cooperative arrangement; (3) long-term land leases similar to Conservation Reserve Program (CRP) leases; and/or (4) land acquisition. The most cost efficient of these systems remains to be determined. However, land owners have experience engaging in long term (10-15 year) CRP contracts (Osborn et al. 1995). In May of 2012 there were 11,977,326 contracted ha under 737,064 contracts on 408,932 farms (U. S. Department of Agriculture

2012) . The typical contract was for 10 years. These contracts may provide a blueprint for biorefineries that need to ensure a reliable flow of feedstock and for landowners that desire a reliable rent and little risk. Since the U. S. government has several decades of experience of leasing CRP land, writing CRP contracts, and managing CRP acres, one potential contribution of the government might be to use their existing contracting infrastructure to assist private companies with contracting land for switchgrass biomass production (Epplin and Haque 2011).

The CRP provides a U. S. example of how the services of a substantial quantity of land could be acquired and used to produce switchgrass biomass. While thousands of U. S. land owners have experience with long­term land leases as a result of the CRP, some important differences between these leases and a lease to a biorefinery are likely. For instance, the risk of default would be higher with a privately funded biorefinery than with the government, and land owners may require a premium to compensate for this risk (Fewell et al. 2011; Song et al. 2011). Also, a prudent biorefinery management team could be expected to screen potential acres and adjust lease bids based on expected productivity, distance from the proposed biorefinery, and proximity to all-weather roads (Epplin and Haque 2011).

Syngas is converted into alcohols using microbial or chemical catalysts. Syngas fermentation research using micro-organisms such as strains of Clostridium ljungdahli, Clostridium autoethanogenum, Clostridium carboxidivorans, Clostridium ragsdalei and Alkalibaculum bachi yielded ethanol, butanolisopropanol and acetic acid. Recent advances in the syngas fermentation include developing new strains of microorganisms, improved reactor design and optimized conditions such as temperature, pH, buffer presence and media to increase yield and reduce the cost for production of alcohols (Kundiyana et al. 2010, 2011a, b; Maddipati et al. 2011; Liu et al. 2012).

Chemical catalysts have also been used to convert syngas into mixed alcohols. The process takes places at high pressure and low temperature in presence of catalysts with the function of hydrogenation, C-O bond breaking and CO insertion. Catalysts based on both noble and non-noble metals have been used for synthesis of mixed alcohols. Noble metal based catalysts containing Rh, Ru or Re and supported on oxides such as SiO2 and Al2O3 have high alcohol selectivity but are not economical for commercial applications. Major non-noble metal based catalysts for mixed-alcohol synthesis contain MoS2, Cu-Co, Cu-Zn-Al and Zn-Cr-K (Fang et al. 2009). Recent advances in mixed alcohols production using chemical catalysts include synthesis and development of new catalysts, optimization of reaction conditions to increase yield and reduce cost of alcohols production. However, the alcohol synthesis process still suffers from low yield and poor selectivity of the desired alcohol product (Subramani and Gangwal 2008). Syngas is also considered building block for many chemicals, such as aldehydes and acetic acid, produced through catalytic and microbial conversions. Hydrogen can also be separated from syngas for producing ammonia or refining hydrocarbon fuels.

Crystallinity is due to H-bonding between cellulose polymers of lignocellulosic biomass which differs from feedstock to feedstock. The purpose of the pretreatments prior to enzymatic hydrolysis is not only to remove lignin, but also to decrease crystallinity. Reducing the crystallinity of lignocellulosic biomass, sometimes requires the reduction in particle size with associated cost. Since the smaller particle size has more surface area, more effective removal of lignin may occur creating greater H-bond interactions within the pretreatment solvent (Puri 1984). The enzymatic hydrolysis rate is affected by the available surface area. In addition, the complete hydrolysis is a function of surface area per unit of initial pore size volume. The large surface area of a small particle results in better enzymatic sugar yields compared to small surface areas of a large particle. Most of the cellulase enzymes including endoglucanase, exoglucanase and P-glucosidase have molecular weights in the range of 30-170 KDa. Increased pore size of lignocellulosic biomass becomes crucial during the enzymatic hydrolysis (Mooney et al. 1998).

Second-generation bioenergy crops (also known as ‘next generation’ energy crops), often perennial plants as lignocellulosic sources from which biofuel is derived, have been championed as an avenue to avoid the food vs. fuel dilemma (Valentine et al. 2012). The use of lignocellulosic sources from second-generation bioenergy crops for ethanonl production has gained popularity, particularly since recent price increases in grains from first-generation bioenergy crops (e. g., maize) have been attributed, in the popular press and elsewhere (BRDI 2008), to diversions towards biofuels. Indeed, as recently as August 2012, the United Nations has urged the U. S. to reconsider its ethanol mandates. The latest U. S. government figures indicate that approximately 40% of the maize production in the U. S. is dedicated to ethanol production (Wise 2012). The use of lignocellulosic ethanol sources is therefore welcome in this regard, especially if second-generation bioenergy crops can be grown in areas that would not compete with current food and feed crop (e. g., maize, soybean) production (e. g., on "marginal" lands; see Cai et al. 2011), such that the latter could be utilized exclusively for direct and indirect (i. e., as animal forage) human consumption.

Switchgrass, Panicum virgatum L. (Poaceae), is one of a number of second-generation biomass energy crops that can be converted to lignocellulosic ethanol to the transportation sector. Other herbaceous candidates being considered worldwide for agronomic production include, but are not limited to, Miscanthus x giganteus, Miscanthus spp., sorghum, flaccidgrass, Napiergrass, sugarcane bagasse (residue), and maize stover (more commonly referred to as corn stover). Switchgrass is native to North America (Fig. 1), and is a perennial, obligate-outcrossing C4 grass capable

of producing reliable biomass yields in agronomic production fields (Fig. 2) for approximately 10 yr after planting (U. S. Department of Energy 2011). Two ecotypes (also called cytotypes) have been noted in this species: with a few exceptions, ‘lowland’ ecotypes are predominantly tetraploid (2n = 4x = 36) and tend to comprise southeastern and coastal U. S. populations, while the ‘upland’ ecotypes are mostly octaploid (2n = 8x = 72) and tend to be more interior in their U. S. distribution (Zalapa et al. 2011; Zhang et al.

2011) . Switchgrass occasionally reaches "common" status in certain prairies (Howe et al. 2002; Baer et al. 2005; Haught and Myster 2008), marshes (Ford and Grace 1998), conservation reserve program (CRP) settings (Mulkey et al. 2006; Adler et al. 2009), and along roadsides and waste places (Radford et al. 1968). Elsewhere, it is typically not a large component of natural areas (Grelen and Duvall 1966) and hence is often found in much lower densities than those grown in agronomic settings.

Switchgrass is a leading cellulosic biofuel feedstock candidate owing to its high productivity (Sanderson et al. 1996). Even before President George W. Bush’s specific mention of switchgrass in his 2006 State of the Union address, switchgrass had been the target of extensive development as a bioenergy crop by the U. S. Department of Energy (DOE) and other entities (Sanderson et al. 1996), due in part to its high forage yields (Parrish and Fike 2005), which was one of its original utilizations. Switchgrass’ current favored status as a biomass-based renewable energy crop stems from its high yield and seed production under low-input conditions in monoculture at different regional cultivar testing fields in several states in the U. S. (Sanderson et al. 1996). This is complemented by substantial predicted biomass yields, particularly in the Midsouth (approaching 23 Mg/ha; Wulschleger et al. 2010). In terms of biomass and ethanol production, with

Color image of this figure appears in the color plate section at the end of the book.

some exceptions, switchgrass is comparable to other second-generation herbaceous lignocellulosic bioenergy crops and first-generation crops (Table 1). If such yields are feasible in areas where maize and other row crops for human consumption are not being grown, switchgrass cultivation may indeed successfully avoid "food vs. fuel" controversies. However, aspects of associated landscape and land-use change, coupled with concurrent improvements, including multi-use strategies that could lead switchgrass indirectly into the food supply chain (e. g., first-cut for forage), will ultimately dictate the long-term sustainability of switchgrass as a bioenergy crop.

Esterification. The carboxylic acids and aldehydes of the bio-oil can be converted into esters by removing oxygen in the form of H2O. The reaction takes place at temperatures of 50-80°C in presence of acid catalysts. Alcohols such as methanol and ethanol, obtained from fermentation of cellulosic materials, are used for the esterification process. The esterification process drastically reduces the aging rate of bio-oil. Methanol was found to reduce the aging rate by a factor of 20 (Diebold and Czernik 1997). The esterification reactions can be represented by the following equations (Bulushev and Ross 2011).

RjCOOH + R-OH^R1COOR + H2O (3)

R1CHO + 2R-OH^R1CH(OR)2 + H2O (4)

Where R and R1 are alkyl groups.

Aqueous Reforming. Recently Dumesic and others have proposed aqueous reforming techniques to selectively produce alkane products, with reduced or no need of external hydrogen. The process takes place through aldol condensation and hydrogenation of carbohydrate-derived compounds, to make large water soluble intermediates which are then converted into alkanes (Barrett et al. 2006; Chheda and Dumesic 2007; West et al. 2008).

Steam Reforming. Reforming of the bio-oil using steam produces H2-rich syngas which can be used as a source of hydrogen for hydrogenation reactions in bio-oil upgrading and conversions.

Modeling Biomass Production

Simulating Plant Growth

Agro-BGC, ALMANAC, BIOCRO, DAYCENT, EPIC, and SWAT are six mechanistic models that have been used to simulate switchgrass productivity (Williams et al. 1989; Kiniry et al. 1992; Kiniry et al. 1996; Arnold et al. 1998; Del Grosso et al. 2005; Di Vittorio et al. 2010; Miguez et al. 2011). Each model keeps track of the number of growing degree-days to specify the developmental rate or phenological stage of switchgrass. The number of growing degree-days is determined by the average of the daily maximum and minimum temperature above the specified baseline temperature (Williams et al. 1984). ALMANAC, EPIC, and SWAT use a function relating radiation use efficiency to biomass based on the leaf area and the amount of light intercepted (Williams et al. 1989). For switchgrass, plant development is initiated when temperatures exceed 12°C (ALMANAC, EPIC, and SWAT). Senescence begins when plants exceed the maximum number of growing degree days (Williams et al. 1989; Kiniry et al. 1992).

Biomass is partitioned into roots and shoots. The DAYCENT model uses a constant energy biomass conversion factor (Parton et al. 1998). BIOCRO was developed from WIMOAC and uses an empirical derivation of the relationship between photosynthesis, stomatal conductance, and biomass production (Humphries and Long 1995; Miguez et al. 2011). Agro-BGC relies on a mechanistic formulation of carbon uptake and assimilation (Di Vittorio et al. 2010).

Chapter 2

Chapter 4

Figure 4. Schematic model of the regulatory network of secondary cell wall biosynthesis based primarily on studies in Arabidopsis. Peach circles represent transcription factors known to function in Arabidopsis. The red circles demarcate the transcription factors whose function has been studied in grasses. The yellow octagons represent enzymes. The grey squares represent secondary cell wall polymers. The green triangle represents a property of the cell wall, saccharification. Arrows signify positive regulation; whereas, dashed edges with T ends indicate negative regulation. Cis-elements are labeled on the edges as follows: Secondary wall NAC Binding Element (SNBE), Tracheary Element Responsive Element (TERE), Secondary wall MYB Responsive Element (SMRE), and the AC-rich elements found in lignin biosynthesis gene promoters (AC). See text for references and further discussion. For simplicity, not all known or suspected interactions are shown. Abbreviations are as follows: Lig Bios Enz, lignin biosynthesis enzymes; SCW Enz, secondary cell wall biosynthesis enzymes the specific identity of which has not been specified; PAL1, Phenylalanine Ammonium Lyase 1; 4CL1, 4-Coumaroyl Ligase 1; COMT, Caffeic acid O-MethylTransferase; C4H, Cinnamate 4-Hydroxylase; CESA, Cellulose Synthase A; SHN, shine/wax inducer 1; VND, Vasculature-related NAC-Domain; SND, Secondary wall-associated NAC-Domain protein; NST, NAC Secondary wall Thickening factor; VNI2, VND-interacting 2 NAC protein 2.

4RN, UK

[1]Research Agronomist, USDA-ARS, Grain, Forage, and Bioenergy Research Unit, 137 Keim Hall, University of Nebraska East Campus, Lincoln, NE 68583-0937.

[2]Research Agronomist, USDA-ARS, Agroecosystem Management Research Unit, 131 Keim Hall, University of Nebraska East Campus, Lincoln, NE 68583-0937.

Email: marty. schmer@ars. usda. gov *Corresponding author: rob. mitchell@ars. usda. gov

Virginia Tech, 365 Smyth Hall, Blacksburg, VA 24061.

[4]Noble Foundation, Ardmore OK 73402.

Email: tjbutler@noble. org

[5]USDA-ARS, 137 Keim Hall, Lincoln, NE 68583. Email: rob. mitcheU@ars. usda. gov ^Corresponding author: jfike@vt. edu

[6]The Institute for Sustainable and Renewable Resources, The Institute for Advanced Learning and Research, Danville, VA, USA; Departments of Horticulture and Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.

Email: barry. ftinn@ialr. org

[7]The Institute for Sustainable and Renewable Resources, The Institute for Advanced Learning and Research, Danville, VA, USA.

Email: alejandra. lara@ialr. org

[8]The Institute for Sustainable and Renewable Resources, The Institute for Advanced Learning and Research, Danville, VA, USA; Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.

Email: scott. lowman@ialr. org

Corresponding author: chuansheng. mei@ialr. org

department of Plant and Soil Science, Oklahoma State University, 368 AG Hall, Stillwater, OK74078-6028, USA.

Email: yanqi. wu@okstate. edu

2National Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing 210095, China.

[10]Corresponding author: liulinglong@njau. edu. cn

[11]Clemson University Genomics Institute, Clemson University, Biosystems Research Complex, Clemson, SC 29634.

Email: Saski@clemson. edu

[12]Department of Genetics and Biochemistry, Clemson University, 110 Biosystems Research Complex, Clemson, SC 29634.

Corresponding author: hluo@clemson. edu

[13]State Key Laboratory of Plant Genomics and National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.

Email: dyli@genetics. ac. cn

[14]Department of Genetics and Biochemistry, Clemson University, 110 Biosystems Research Complex, Clemson, SC 29634.

^Corresponding author: hluo@clemson. edu

[15]228 Agricultural Hall, Biosystems and Agricultural Engineering Department, Oklahoma State University, Stillwater, OK 74078.

[16]223 Agricultural Hall, Biosystems and Agricultural Engineering Department, Oklahoma State University, Stillwater, OK 74078.

Email: raymond. huhnke@okstate. edu *Corresponding author: ajay. kumar@okstate. edu

department of Environmental Engineering and Earth Sciences, Clemson University, Clemson, SC 29634.

aEmail: arpanj@clemson. edu; arpanjain0211@gmail. com bEmail: walker4@clemson. edu

2Clemson Department of Economic Development, Clemson University, Clemson, SC 29634. Email: karl@clemson. edu

[18]Corresponding authors

[19]USDA-ARS, Grassland, Soil and Water Research Laboratory, 808 East Blackland Road, Temple, TX 76502.

“Email: Jim. Kiniry@ars. usda. gov

[20]Texas AgriLife Blackland Research and Extension Center, 720 East Blackland Road, Temple, TX 76502.

Email: nmeki@brc. tamus. edu

[21]Oklahoma State University, Department of Plant and Soil Sciences, 368 Agricultural Hall, Stillwater, OK 74078.

Email: yanqi. wu@okstate. edu

^Corresponding author: Kate. Behrman@ars. usda. gov

department of Agricultural Economics, Oklahoma State University, Stillwater, Oklahoma, USA 74078.

Email: f. epplin@okstate. edu

department of Agricultural and Resource Economics, University of Tennessee, 314B Morgan Hall, 2621 Morgan Circle, Knoxville, Tennessee, USA 37996.

Email: agriff14@utk. edu

[24]The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, Oklahoma, USA 73401.

Email: mhaque@noble. org *Corresponding author

One of the biggest advantages of thermochemical conversion technologies is that these can produce many fuels and chemicals—many of which can supplement the demand currently met by petroleum industry. Fuels include hydrocarbons such as gasoline, diesel, jet, charcoal, alcohols and fuel additives. Recently, hydrocarbon fuels and higher alcohols have become preferred forms of biofuels because these are more compatible with petroleum infrastructure and have higher energy density than ethanol. Several demonstrations for hydrocarbon production through thermochemical conversion processes are currently underway (Regalbuto 2009). Chemicals include hydrogen, ammonia-based fertilizer, alcohols such as methanol, ethanol and butanol, acetone, activated carbon, fine chemicals, lubricants, food additives and resins (Balat et al. 2009a, b; Brown et al. 2012). Electrical power can be produced using intermediates, i. e., syngas and bio-oil using internal combustion engines such as reciprocating engines and gas turbines, steam-based external combustion engine, or fuels cells such as solid oxide fuel cells (SOFC). Heat production can be done in conjunction with electrical power production or separately through direct combustion.