Complete degradation of 1 mol of glucose can yield a 12 mol of hydrogen by combining fermentation and photofermentation in a two stage system. According to the Gibbs free energy of this reaction, complete oxidation of glucose into hydrogen and carbon dioxide is not feasible thermodynamically (Eq. 10.15).

C6H12O6 + 6H2O! 12H2 + 6CO2 AG0 = +3.2 kJ/mol (10.15)

Photon energy in photofermentation can be a useful external energy supply to reach the theoretical values of conversion. To achieve this, external light source is needed. In the case that an external light source cannot be applied and with only dark fermentation process by glucose consumption maximum 4 mol of hydrogen with acetate as a by-product will be produced (Eq. 10.1)

The by-product of dark fermentation stage acetate can be oxidized by photo­synthetic bacteria to produce hydrogen energy and to complete the oxidation of glucose totally into H2 and CO2 (Eq. 10.16).

CH3COOH + 2H2O + ‘elight energy’ ! 4H2 + 2CO2 AG0 = +104 kJ/mol

(10.16)

Integrating the photofermentation with dark fermentation process (Fig. 10.4) can result as the maximum yield of hydrogen production [67].

There are some studies reported about two-stage systems that are a combination of dark fermentation step with pure cultures and photofermentation step. The combination of dark fermentation and photofermentation steps with pure cultures like Caldicellulusiruptor saccharolyticus and Rhodobacter capsulatus, Rhodob — acter capsulatus hup-mutant and Rhodopseudomonas palustris [132] to produce hydrogen from beet molasses; Caldicellulusiruptor saccharolyticus and Rhodob — acter capsulatus to produce hydrogen from glucose, potato steam peels and molasses [119]; Clostridium butyricum and Rhodopseudomonas palustris to pro­duce hydrogen from glucose [133], Clostiridium pasterianum and Rhodopseudo­monas palustris from sucrose [134], Clostridium saccharoperbutylacetonicum and Rhodobacter sphaeroides from glucose [135] resulted in higher hydrogen pro­duction values in comparison with single systems.

Glucose and the sucrose are the most studied organic substrates for hydrogen production by two-stage systems. Using the glucose in a dark fermentation process with mixed anaerobic bacteria 1.36 mol H2/mol hexose yield achieved. By using the effluents of this system which includes mainly acetate, propionate and butyrate in a photobioreactor inoculated by Rhodopseudomonas capsulatus the overall yield increased to 4.46 mol H2/mol hexose [81]. Cattle dung batch at 38°C was

used as inoculum in the dark fermentation stage to produce hydrogen from sucrose and 1.29 mol H2/mol hexose, hydrogen yields are achieved. Using the effluents of first stage in photofermentation stage by Rhodobacter sphaeroides increased the overall yield to 3.32 mol H2/mol hexose [136].

One of the main advantages of two-stage systems is the usability of organic wastes and wastewaters. Carbohydrate-rich raw materials, especially starch and cellulose containing renewable biomass resources, are used in many studies of two-stage systems. After hydrolyzing by acidic or enzymatic pre-treatment methods wheat starch becomes a suitable substrate for two-stage systems [137]. After dark fermentation with anaerobic sludge a concentration of 1950 mg/l vol­atile fatty acids was produced. By using the produced volatile fatty acids 27 ml H2/ l/day hydrogen production rate was achieved at 72 h HRT with a PC controlled fermenter by R. sphaeroides (NRRL — B1727) [138]. For using wheat powder as a carbon source it is important to keep the concentrations at low levels to prevent the system from substrate inhibition [137]. A two-stage system is used with mixed bacterial cultures in dark fermentation and Rhodopseudomonas palustris in photofermentation to produce hydrogen from cassava. Cassava has a high content of 15-20% starch and 4-6% free sugar and it is a low cost biomass. It is a good source for biohydrogen production of 6.07 mol H2/mol hexose totally which was 2.53 mol H2/mol hexose after dark fermentation step [1]. Pre-treating the cassava starch by hydrolyzing with amylase and glucoamylase could increase the hydrogen production rates from 84.4 to 172 and 262 mlH2/h, respectively. The overall hydrogen yields were improved from 240 ml H2/g starch by dark fermentation to 402 ml H2/g starch by adding the photofermentation to the system [8] which shows that hydrogen production from cassava starch using a combination of dark fermentation and photofermentation is feasible. While using agricultural wastes as a carbon source it is important to choose the best pre-treatment option from the view of both system efficiencies and overall costs of the system. Acid pretreatment is decided to be the best option for corncob which is a cellulose-rich waste used to obtain biohydrogen. It is found that by dark fermentation of corncob with anaer­obic mixed culture 120 mL H2/g corncob and using the effluents of dark

fermentation in photofermentation resulted in 713 ml H2/g COD [139]. With a high content of carbohydrates sugar beet molasses is another good candidate for biohydrogen production by two-stage systems. With a low nitrogen content olive mill effluent (OME) is a good source for photofermentation but the dark color of color affects the light penetration negatively. Because of the high organic content and dark color of OME combining the system with dark fermentation could improve the overall yields. Treating the OME with active sludge cultures in dark fermentation step and using the effluents of this process in photofermentation step by R. sphaeroides O. U.001 resulted in 29 l H2/l OME hydrogen production [140]. The main wastewater of the cheese processing industry, cheese whey wastewater is used as carbon source in a two-stage system which is a combination of dark fermentation with anaerobic mixed sludge and photofermentation with Rhodo — pseudomonas palustris. Diluting the wastewater by 1/5 ratio with malic acid gave the highest yield of 349 ml H2/g COD [85]. Potato homogenate (PH) is utilized in an integrated study by combining dark and photofermentation sequentially. Dark fermentation was conducted by anaerobic mixed bacteria obtained from silo pit liquid and resulted as 0.7 mol H2/mol glucose and 350 mM VFA production with a concentration of 400 g/l medium. High fermentation effluents concentration negatively affected the performance of photofermentation therefore diluted efflu­ents were used with supplementation of Fe/Mg/phosphate. By using Rhodobacter capsulatus 4.9 mol H2/mol glucose hydrogen yields were achieved by using 5% fermentation effluent [141].

10.5 Conclusion

Producing hydrogen by biological methods have some advantages compared to chemical and physical methods such as; possibility to use sunlight and organic wastes as substrates which help environmental conversions and use of moderate conditions like room temperature which is very economical compared with sys­tems that need high energy. By combining the systems the individual problems of the systems can be solved and the overall performance can be improved. Com­bining dark and photofermentation is one of the most promising technologies for biological hydrogen production. This type of combinations can be operated in continuous mode for several days. It can be easily seen that the performance of the integrated systems is more than the individual systems. Moreover integration of dark and photofermentation could be an economical solution in terms of waste reduction. Taking into account all the system requirements and deciding the best reactor configurations hydrogen production yields can be improved effectively. While using the dark fermenter effluents for photofermentative hydrogen com­position it is important to adjust the composition for best biomass growth therefore biohydrogen production. Treating the highly concentrated wastes within the dark fermentation step by mixed anaerobic cultures which are already modified from wastewater treatment systems without sterilization then using the organic acids produced in photofermentation process is a very effective way of biohydrogen production

Acknowledgments Biofuels research in the laboratory of PCH is supported by FQRNT (Le Fonds quebecois de la recherche sur la nature et les technologies), Tugba Keskin thanks the TUBITAK DB-2214 (Turkey) for support.

The typical profiles of phenolic products and temperature as function of time is shown in Fig. 12.8 for the oxidation of a softwood kraft lignin (a) and hardwood organosolv lignin (b) [20]. The yields of vanillin and syringaldehyde clearly predominate over the vanillic acid and syringic acid. The concentration of the phenolic aldehydes and their respective acids increases continuously until a maximum value which is coincident with the maximum temperature (Tmax). In fact the reaction is exothermic, increasing the initial temperature (Ti) of reaction (393 K): the values of AT (Tmax-Ti) reported in these reactions were 13 and 9 K for softwood and hardwood lignins, respectively, (Fig. 12.8). For a commercial kraft lignin, Indulin AT, increases at the same order (10-15 K) were found [121], although the rate of oxidation as well as the heat of reaction differs between lignins. After that maximum, the concentration of products decreases continuously due to the dominance of degradation over the production reactions.

The phenolic acids are formed by the cleavage of Ca-Cb in the propane chain of ppu (as shown in Fig. 12.7), as for aldehydes, but they undergo further oxidation. The profiles of vanillic acid and syringic acid are very close to the corresponding alde­hydes, with a maximum at the same reaction time, followed by an analogous decline. The ratio between these two products is a measure of process selectivity for the aldehydes. For the lignins and conditions corresponding to data presented in Fig. 12.8, it is noteworthy that, at the maximum yield for softwood (40 min) and hardwood (25 min), the calculated vanillin/vanillic acid ratio is 1.7 and 1.6, respectively. This is a rather similar value, considering that the individual yields are quite different. One other side, the ratio syringaldehyde/syringic acid for the hard­wood lignin (values taken at the maximum—12 min) is much higher: 13.1. This is an
indication of higher selectivity of the process for the syringyl units of lignin. The oxidation of vanillin is pointed out as the main route for vanillic acid production (as well as for other secondary products) [155]. However, it is interesting to notice the similar and parallel behavior of formation and degradation of the aldehydes and respective acids, and also the strong decrease of vanillic acid for long reaction time in comparison to vanillin. Gierer et al. [146] reported different routes for vanillin and vanillic acid production from lignin oxidation, and not as subsequent reactions, which, at least partially, would be the reason for the behavior observed.

The increase on the production of syringaldehyde in the first 10 min of reaction, and the pronounced decrease after the maximum (Fig. 12.8b) were remarkably high compared to the behavior of vanillin. These facts are related with the different oxidation rates of guaiacyl and syringyl units of lignin. The syringyl units have higher reactivity than guaiacyl counterparts in alkaline systems [156] and under conditions of O2 oxidation in alkaline medium [110, 157]. Thus, the oxidation of syringyl units is faster than guaiacyl units for both production and degradation of aldehydes.

Besides vanillin and syringaldehyde, and their respective acids, acetovanillone was also found as secondary product. Acetosyringone was also found in the case of hardwood LOrgsB, as well as p-hydroxybenzaldehyde in both lignins, but in rather low concentration (<0.05 wt% lignin, not shown in Fig. 12.8). Vanillin, vanillic acid, and acetovanillone have been reported as the three principal compounds found in the reaction mixture. For example, yields of 2-8% of these three major compounds were obtained from alkaline oxidation of lignosulfonates from Nor­wegian spruce [155].

The mechanism for the lignin oxidation that expresses the formation of aceto derivatives as acetovanillone and acetosyringone [140] is based on the competing addition of OH — to a-position and to у-position of quinonemethide: the first leads to the acetoderivatives and the second leads to vanillin and syringaldehyde. Acetovanillone (also known as acetoguaiacone, or apocynin, with an odor similar to vanillin) is an interesting precursor of veratric acid (3,4-dimethoxybenzoic acid), a building block for synthesis of pharmaceuticals. Acetovanillone is already isolated after the lignosulfonate oxidation at Borregaard [158].

Other compounds have been also referred as secondary products from lignin oxidation with O2 in alkaline medium as for example, guaiacol, dehydrovanillin, 5-carboxyvanillin, 5-carboxyvanillic acid, homovanillin, and the syringaldehyde counterpart [113, 155].

• Calcination for carbonate ore: In this process carbonate ores when heated in absence of air get converted into into oxides.

• Roasting for sulfide ore: In this process sulfide ores converted into oxides on heating in the presence of air.

Pretreatment by using dilute-acid processes for the hydrolysis of hemicellulose renders the cellulose fraction more amenable for a further enzymatic treatment, but in this case a two-step-hydrolysis is required. The dilute acid process is conducted under high temperature and pressure, and has a reaction time in the range of seconds or minutes, which facilitates continuous processing. The difference between these two steps is mainly the operational temperature, which is high in the second step (generally around 230-240°C) [108, 196, 197]. Example cited by using a dilute acid process with 1% sulfuric acid in a continuous flow reactor at a residence time of 0.22 min and a temperature of 510 K with pure cellulose pro­vided a yield of over 50% sugars. In this case, 1,000 kg of dry wood would yield about 164 kg of pure ethanol. The biggest advantage of dilute acid processes is their fast rate of reaction, which facilitates continuous processing.

Compared to the concentrate acid hydrolysis, one of the advantages of dilute — acid hydrolysis is the relatively low acid consumption, limited problem associated with equipment corrosion, and less energy demanding for acid recovery. Under controlled conditions, the levels of the degradation compounds generated can also be low. As an alternative to the conventional dilute-acid processes, the addition of CO2 to aqueous solutions, taking advantage of the carbonic acid formation has been described [190], but the results obtained were not interesting enough to consider application.

In organic acid fractionation process, the obtained pulp after cooking is generally washed with fresh organic solvent to avoid the lignin precipitation on the pulp, and then washed with water. After the solid is filtrated, the black liquors rich in lignins can be diluted with water to obtain crude lignin. It was observed that a water to liquor ratio of 6 in the lignin-precipitation step resulted in lignin recovery of 88.0 and 77.2% (based on the Klason lignin content in the original material) for formic acid and acetic acid fractionation processes, respectively [99]. In another study, most of the lignin was centrifuged with a water to liquor ratio of 7, and the solid phase (lignin) was washed repeatedly with water to remove the maximum possible amount of carbohydrates to recover a purified lignin [90].

The main operate cost in organic acid pulping, especially for formic acid pulping, is the solvent-recovery section. The black liquor, together with washing liquor, is evaporated to recover the solvent. The organic acid staying in the evaporation residue is recovered by spray drying. Then the organic acid is con­centrated for further use in cycle. Distillation, azeotropic distillation, extractive

distillation, extraction, membrane and adsorption are potential methods for con­densation of organic acid [111]. By using pinch technology for heat integration of the Milox process, the needs for external heating and cooling were reduced by about 40 and 50%, respectively.

A simplified process for simulation of material balance of acetosolv fraction­ation has been proposed [112, 113] (Fig. 11.3). In this process, wood is mixed with the cooking reagents and recycle streams and reacts in the reactor. After cooking, the resulting suspension is subjected to separation by filtration, and the resulting pulp is washed with water in a percolation unit. In the solvent — and HCl-recovery section, liquors and a recycle stream from the secondary recovery section are processed by flash evaporation, stripping and distillation to recover HCl, formic acid and water. In the by-products recovery section, the concentrated liquors are mixed with water to precipitate hydrophobic materials, and the precipitations are recovered by centrifugal filtration. The liquors from the lignin-precipitation unit are sent to heteroazeotropic distillation unit to give a head stream that is rectified to obtain furfural and a bottom stream. In the secondary solvent-recovery section, the above liquors are evaporated to separate the non-volatile solutes as a con­centrated solution, whereas the vapor is recycled. According to the computer simulation [112], the proposed process allowed recovery of 97.6% of acetic acid and 91.7% of HCl, whereas furfural with a high purity of 99.5% was obtained as a valuable by-product.

Simulation of solvent recovery in peroxyacid pulping has been carried out by shortcut simulations and pinch technology [2]. It was found that simple distillation seems to be the preferable solution for recovering the solvents. The presence of a low percentage of acetic acid in formic acid/water system was not favorable to the distillation. However, this can be avoided by using a high percentage of acetic acid in the pulping process since pulping with formic acid/acetic acid/water was also feasible. By using pinch technology, up to 40% energy savings were achieved during the separation of formic acid/acetic acid/water mixture.

Another direct method to recover vanillin from the oxidized liquor is based on adsorption and ion exchange principles. Using a strong sulfonic acid resin in its Na+ form, sodium vanillate can be separated from lignosulfonates, sodium hydroxide and sodium carbonate, which are eluted first [166, 167]. This treatment should be performed between oxidation and extraction steps in vanillin production showing as main advantages the separation of around 80% of dry matter, lignin, and sodium from vanillin reactor effluent and the smaller quantity of acid needed to neutralize the vanillin fraction when compared to other processes. Moreover, the ion exchange resin does not require regeneration step and the lignin and the sodium can be returned to the chemical recovery of the pulp mill without any neutralization [166].

The process patented by Logan [168] reported weak ion exchange resins in acid form for vanillin isolation. In this case, the sodium vanillate and other phenolates contained in the alkaline oxidized solution were converted into a phenolic form. This is one of the steps in designed cyclic recovery of vanillin. This invention describes the suitable treatment for vanillin reactor effluent where any type of weak cationic resin may be used since it accepts sodium ion from the sodium hydroxide solution and also can be regenerated back to the hydrogen form. This particular method applying a strong cationic resin in H+ form was also studied in detail by Zabkova et al. [134] including the influence of the alkalinity and con­centration of the vanillin solution on the ion exchange process. The presence of a buffer system comprising of vanillin/vanillate in the ion exchange process affects the expected rectangular behavior of isotherm in ion exchange coupled with neutralization reaction. Recently, non-polar macroporous resins have been applied for separating vanillin and syringaldehyde from oxygen delignification spent liquor [137]. It was verified that adsorption equilibrium constant decreased remarkably with the increasing pH due to the acid dissociation of the aromatic aldehydes, since ionic species are not adsorbed by these resins. The recoveries of vanillin and syringaldehyde were 96.2 and 94.7%, respectively [137].

A wide range of different organic substrates can be used for biohydrogen pro­duction by dark fermentation. As noted above, carbohydrates are the most suitable, and thus the most studied carbon sources, since they have a hydrogen production potential 20 times higher than with fat and proteins [62]. Biodegradability, availability, cost and carbohydrate content are the most important factors for selection of substrates for hydrogen production. Glucose, sucrose and lactose are the most widely studied simple sugars. Carbohydrate-rich substrates undergoing dark fermentation by mixed anaerobic bacteria produce H2, CO2 and organic acids (Fig. 10.2).

Pure mono and disaccharides are mostly used for dark fermentation with pure cultures. Dark fermentative hydrogen production from glucose with different pure cultures has given different hydrogen yields; Enterobacter cloacae 2.2 mol H2/mol [63]; Clostridium beijerinckii 2.4 mol H2/mol [64]; Thermoanaerobacterium
thermosaccharolyticum 2.42 mol H2/mol [65]; Pantoea agglomerans, 1.6 mol H2/ mol [66]; Escherichia coli 0.23 mol H2/mol [67]; Caldicellulosiruptor saccharo — lyticus 3.6 mol H2/mol [68]. Dark fermentative hydrogen production from glucose with mixed cultures resulted in yields between 1.70 and 2.75 mol H2/mol glucose [69-72]. Sucrose is another widely used pure substrate. Hydrogen yields from sucrose have been examined with pure cultures: Clostridium butyricum 0.5 mol H2/mol [73]; Thermoanaerobacterium thermosaccharolyticum 1.89 mol H2/mol [74]. Using mixed cultures to produce hydrogen from sucrose resulted in yields between 0.87 and 1.72 mol H2/mol [69, 75].

Pure substrates are not an effective approach for large-scale applications. Instead, using a waste or wastewater which has a high organic content will create a win-win solution, reducing wastewater disposal costs at the same time as creating an energy source, hydrogen, in a cost effective manner. In addition to various residues and wastes, energy crops can be a very good substrate option for dark fermentative hydrogen production. Among the different types of crops; sugar, starch, lignocellulosic based, the first two groups have been more widely used. The use of different kinds of energy crops resulted in different hydrogen yields; wheat starch 1.9 mol H2/mol glucose [76]; sweet sorghum plant 0.86 mol H2/mol glu­cose [77]; starch from paper mill 1.5 mol H2/mol glucose [46]; molasses 3.47 mol H2/mol glucose [78]. Some types of energy crops, especially lignocellulosic based, need pre-treatment before use for hydrogen production, increasing the process costs.

As well, various types of wastes and wastewaters have been used as substrates for dark fermentative hydrogen production with different hydrogen yields such as: sugar factory wastewater; 2.6 mol H2/mol hexose [79]; olive mill wastewater, 0.15 ml H2/ml OMW [4]; rice winery wastewater, 2.14 mol H2/mol hexose [80]; food waste, 1.8 mol H2/mol hexose [81]; cheese whey, 5.9 mol H2/mol lactose, 0.9 mol H2/mol hexose, 22 mmol H2/g COD, 10 mM/gCOD [82-86]. In these cases, high yields of hydrogen production by microbial processes can be achieved without any pretreatment. However, in most cases dilution is necessary to lower organic loading, and to prevent possible toxic effects of the substrate on the bacteria. In general, wastes can include a variety of organic and inorganic chemicals, some of which can be inhibitory for hydrogen production. Therefore, it is important to know the composition of the wastewater before using it as a substrate.

Kraft lignin is presently available from MeadWestvaco Corp. (USA) and Borreg — aard Lignotech (about 10 thousand t/year at Backhammar plant), accounting for a total annual production around 1 million t [5]. This is a rather low production value considering that a mill with capacity for 500 thousand t of kraft pulp can produce about 200 thousand t of lignin in black liquor. The potential for lignin production in the existing pulp and paper industry is more than 50 million t/year [35].

Currently, few kraft pulp mills recover the lignin. The main utilization of black liquor is energy production in the recovery boiler, allowing the simultaneous recovery of cooking chemicals to reintroduce in the digesters. This is economically advantageous, unless the recovery boiler becomes the bottleneck of the process.

In this case, separation of lignin could be one solution to increase the pulp production capacity. Alternatively, the deviation of a fraction of lignin could become sustainable by the upgrading lignin for materials and specialty chemicals with high added-value [36].

Commercial kraft lignins are usually modified to their increase it solubility in aqueous solutions by means of oxidative sulfonation, carboxylation, and sulf- omethylation. The major final application of these lignins is as dispersant: the use of sulfomethylated kraft lignin was patented in 1954 [37]. MeadWestvaco Corp. and LignoTech Sweden produce lignosulfonates by sulfonation of kraft lignin, but the product has a much lower molecular weight than the lignosulfonates produced from sulfite pulping [38]. Other end uses are asphalt emulsions, lead-acid storage battery industry and products for cement and concrete industries [39]. This lignin, after chemical modification, competes with the lignosulfonates coming from the sulfite pulping industry.

12.2.1.2 Characteristics

In general, hardwood kraft lignin presents lower weight-average molecular weight (around 1 kDa) than the respective wood lignin (2-3 kDa) [10, 20, 40]. Com­paratively to hardwood, softwood kraft lignin Mw, in general, is higher (2-3 kDa) [23]. Other characteristics of kraft lignin are the higher contents of phenolic hydroxyl groups and condensed structures than the respective wood lignin [20, 41]. The predominant inter-unit linkage is still the fi-O-4, although in lower absolute amount than in wood lignin. The extension of lignin reactions depends fundamentally on kraft pulping conditions and wood species [10]. Some infor­mation about the composition and chemical structure of lignin recovered from kraft pulping streams can be found in literature [10, 20, 42] and is presented in Table 12.2.

Bioextraction incorporates a range of technologies that not only use plants to remove, reduce, degrade, or immobilize environmental pollutants from soil and water, for restoration of contaminated sites to a relatively clean, non-toxic envi­ronment but also use microbes to extract metals from the low grade ores. This relatively new and growing technology uses natural processes to break down, stabilize, or accumulate pollutants and for extraction of metals [3]. It basically incorporates two phenomena:

• Phytoextraction

• Biomining

Phytoextraction is the removal of pollutants by the roots of plants, followed by translocation to aboveground plant tissues, which are subsequently harvested. Biomining is the extraction of metals by the help of naturally growing thermal sensitive microbes.

Ming-Fei Li, Shao-Ni Sun, Feng Xu and Run-Cang Sun

11.1 Introduction

Fractionation of lignocellulosic materials into their major macromolecular fractions—cellulose, hemicelluloses and lignin, is a challenging work that attracted increased attention in recent years. As a matter of fact, in addition to chemical pulping, an existing fractionation process used worldwide, numerous approaches for the separation of lignocelluloses have been studied lastingly for more than a century. These approaches are generally categorized into physical, physico-chemical, chemical and biological processes. Among these approaches, one of the most promising processes is organosolv fractionation, which degrades the lignocellulosic feedstocks by using organic solvents under mild conditions in an environmentally friendly manner to mainly produce cellulose for energy or materials usage. In addition, the dissolved sugars and lignin are easy to be recovered and are valuable feedstocks for chemicals and materials applications.

This chapter updates and extends the previous reviews on organic solvents fractionation of lignocelluloses for pulping [1-6], lignin extraction [7] and bio­ethanol production [8], focusing particularly on new research on the fractionation process and product utilization for fuels, chemicals and materials via organic solvents in a biorefinery manner. After a brief introduction of the development of

M.-F. Li • S.-N. Sun • F. Xu (&) • R.-C. Sun (&)

Institute of Biomass Chemistry and Technology, Beijing Forestry University, Qinghua Road No. 35, Haidian District, 100083 Beijing, China e-mail: xfx315@bjfu. edu. cn

R.-C. Sun

State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Wushan Road No. 381, Tianhe District, 510640 Guangzhou, China e-mail: rcsun3@bjfu. edu. cn

C. Baskar et al. (eds.), Biomass Conversion,

DOI: 10.1007/978-3-642-28418-2_11, © Springer-Verlag Berlin Heidelberg 2012 organosolv fractionation, this chapter will focus on the recent achievements in organosolv fractionation of cellulose, hemicelluloses and lignin from traditional and novel feedstocks including wood, grasses, forestry residues and so on. Etha­nol-based fractionation process, the main organosolv fractionation process used for ethanol production especially in the past decade, is discussed extensively. Formic acid and acetic acid fractionations, two useful processes used for fractionation of lignin under mild conditions, are also discussed in detail. The fractionation mechanism and technical flow involved in the fractionation process are elaborated, and the potential applications of the fraction products (mainly cellulose-rich fraction, degraded sugars and soluble lignin) are discussed. Other types of organic solvents for fractionations attracted current attention are also covered in this chapter.