The natural cellulosic fibers using agricultural by-products have become more urgent and currently used due to higher price and availability of natural and synthetic fibers (Reddy and Yang 2009). These agricultural by-products can be used for the develop­ment of novel cellulose, protein, and synthetic fibers for textile, composite, and biomedical applications (Huda et al. 2007). Research groups have been encouraged to develop suitable technologies such as the use of raw material for textile fiber pro­duction due to the availability and composition of sugarcane straw which would give innovative and nonpolluting destination. Lu et al. (2009) reported that sugarcane straw has three main macromolecular components: cellulose, polyoses, and lignin. The physical, biological, and chemical processes can be used for separation of the macromolecular fractions of lignocellulosic materials. The sugarcane straw cellulose fiber could be produced by a wet-spinning method that can show tensile strength compatible with lyocell fibers in the textile market.

There are very limited literature on kinetics modeling for biomass gasification sup­ported by kinetics parameters determined using experimental data. Sheth and Babu (2009) estimated kinetics parameters for biomass pyrolysis process using kinetics modeling approach. The kinetics constant of two reactions involved in the pyrolysis was calculated by minimization of least square error between the model results and the experimental data. The experimental data were chosen from the literature. The values of activation energy and pre-exponential factor of Arrhenius constants for both reac­tions were calculated by the minimization of the objective function as follows:

F (ЛЛЛЛ ) = £(,j — Wt, j )2

І=1

Wang and Kinoshita (1993) developed a reaction kinetics model for biomass O2- steam gasification. The wood was taken as biomass and the generalized equation was presented as follows:

CH14O0.59 + yO2 + zN2 + wH2O = XjC + x2H2
+x^CO + X4H2O + X5CO2 + x6CH4 + x7N

Furthermore, four main reactions were considered including char gasification, boudouard, methanation, and methane reforming reaction as follows:

Char Gasification

C + H2O ® CO + H2

Boudouard

C + CO2 ® 2CO

Methanation

C + 2H2 ® CH4

Steam Reforming

CH4 + H2O ® CO + 3H2

The rate constant of all these reactions was calculated by the minimization of the difference between the experimental data and calculated data. The equation used was as follows:

m 0 2

Minf (*ap К2 . К3 . К4 ) = МІП ZZ (j — Xexp, j)

The experimental data were taken from their previous work on O2-steam gasification using sawdust as biomass (Wang and Kinoshita 1992). Moreover, the modeling results were validated with the experimental work. In addition, residence time, temperature, pressure, equivalence ratio, and moisture have been investigated on the product gas composition.

Resende and Savage (2010) described the kinetics model for the supercritical steam gasification for hydrogen production. The model consists of 11 reactions. The rate equations of each reaction were taken as first order for each species. The final concentration was calculated using mole balance equations; for example, the con­centration of CO2 was calculated using the equitation as follows:

where k10 is for forward water gas shift reaction and k10r is for reversible water gas shift reaction. The equilibrium constant for the water gas shift reaction was calculated as follows:

C C

H2 CO2

C C

CO H2O

The kinetics parameters were calculated by the minimization of the objective function which is the sum squared difference between the model results and experi­mental values. The experimental data were taken from their previous work based on the supercritical steam gasification of lignin and cellulose (Resende and Savage

2009) . Furthermore, the model was validated with the experimental data and the results showed good agreement.

Salaices (2010) developed a reaction kinetics model for catalytic steam gasifica­tion of biomass surrogates using as model compounds. The kinetics model was based on the coherent reaction engineering approach. The reaction rates were based on the dominant reactions. The reactions like methanation and boudouard reactions were neglected. So the rate of each species was calculated as follows;

ri = Ifij = rWRG + rSR + rDRM

There are only dominant reactions, i. e., water gas shift, steam reforming, and dry methane reforming considered. For example, the rate of formation of hydrogen was calculated as follows:

Furthermore, the kinetics constants have been calculated using experimental data with best parameter estimations and minimizing the least squares objective function via optimization toolbox of MATLAB.

19.2 Conclusion

The literature review on the experimental work of biomass steam gasification showed that the pure steam is best gasification agent for hydrogen production. Steam gasification with CaO as sorbent improved the concentration of hydrogen in

the system and also acts as catalyst. Catalytic steam gasification showed higher yield of hydrogen. So, there is need to integrate steam, CaO, and catalyst together for high purity and higher yield. Furthermore, EFB has potential for hydrogen pro­duction, so there is also need to study the biomass steam gasification using EFB as biomass for hydrogen production. The literature review on the modeling and simu­lation of biomass gasification showed that there are several works published on kinetics modeling for conventional gasification but limited work on biomass steam gasification specifically for hydrogen production. So there is a need to develop reac­tion kinetics model including the carbonation reaction along with the main steam gasification reactions. As kinetics model provides important data regarding the con­version of biomass to hydrogen which is essential to improve the process. The pre­dictions from the kinetics model are more accurate compared to the thermodynamic equilibrium models, so the process can be simulated better with the experimental data. In addition, there is also need to work on the determination of the Arrhenius kinetic constant for all reactions involved in steam gasification with CaO for hydrogen production from biomass.

It was proved that the properties of the natural fiber composites depend on con­stituents (fiber/matrix) and their interfacial bonding (Agoudjil et al. 2011; Al-Khanbashi et al. 2005; Huda et al. 2008; Kalia et al. 2011b). The interfacial

bonding between the reinforcing natural fibers and the polymer matrix in the composite has a vital role in determining its final mechanical properties. That is, the reinforcement efficiency depends upon the stress transfer between the matrix and fibers. Most of the thermoplastic polymers are nonpolar, hydrophobic com­pounds whereas natural fibers are polar, hydrophilic ones. Because of this inher­ent dissimilarity, the NFRPC are usually not compatible and interfacial adhesion in these composites tends to be poor. Therefore, the surfaces of the natural fibers are usually treated via different means in order to improve the interfacial bonds between the fibers and the matrix. Several methods of surface modification by physical, chemical, or mechanical means have been investigated to improve the fiber properties and to increase the bond ability as well as the wettability between the cellulosic fibers and the polymer matrix. Such used methods of treatment are tabulated in Table 1.5.

Several studies had proved the efficiency of such surface treatments on the date palm fibers for different polymer matrices when treated with suitable means of treatments particularly the chemical one (Abdal-hay et al. 2012; Al-Khanbashi et al. 2005; Alsaeed et al. 2012; Sbiai et al. 2010; Shalwan and Yousif 2014). The effect of different treatment process on the data palm fiber was investigated by sev­eral studies (Alawar et al. 2009) where different concentrations of alkali treatment were used to modified the fiber surface (Alawar et al. 2009), a range from 0.5 to 5 %, and acid treatment with 0.3, 0.9, and 1.6 N were used and performed at 100 °C for 1 h. Results demonstrated that the surface morphology was improved. NaOH treated fibers showed an increase in tensile and considerable advancement in sur­face morphology. On the other hand, fibers treated with hydrochloric acid were found to be unfavorable due to its negative impact on tensile strength and surface morphology. Microscopic examinations were demonstrated the effectiveness of the chemical treatment on the date palm fiber as can be shown in Fig. 1.9 where untreated fibers are demonstrated having a weak outer layer that can prevent strong bonding with the polymer matrix in one hand, and another treated one where the weak outer layer was removed through the treatment process which can lead to stronger bonding with the matrix.

It is worthy to note that the proper treatment conditions like the suitable solution type, concentration, and time can dramatically enhance the mechanical properties of the fiber. The effect of the chemical treatment of the date palm fiber on its mechanical

Table 1.5 Physical and chemical treatments methods for cellulosic natural fibers

Physical treatments processes change the fiber’s structural and surface properties; thereby influence the mechanical bonding with the matrix. Such treatments involve surface fibrillation, electric discharge (corona, cold plasma), etc. The Cold plasma method is a very effective one that can clean the bio-fibers and modify its surface imparting different functional groups and changes in surface energies. Steam treatment of the natural fiber can be performed by applying of high pressure steaming, where heating at high temperatures and pressures are preformed, then mechanical disruption by violent discharge or explosion is usually used (Kalia et al. 2011b; Arbelaiz et al. 2005)

Natural fibers are highly polar-owing to the hydroxyl groups. Such groups are readily available for chemical bonding (hydrogen bonding) with compatible polymer matrices and physical interlocking (wetting) with the nonpolar matrices. Several chemical treatments were investigated having potential to remove both waxes and oils from the fiber’s surface in one hand, and to make it rough, and stop the water uptake

Alkaline treatment: Alkaline treatment (mercerization) is one of the most popular chemical treatments of natural fibers. The major modification done by this treatment is the disruption of hydrogen bonding in the network structure, herewith increasing surface roughness. Alkaline treatment by adding of aqueous sodium hydroxide (NaOH) to natural fiber can remove a certain amount of lignin, wax, and oils covering the external surface of the fiber cell wall, depolymerizes cellulose, and exposes the short length crystallites (Mohanty et al. 2001; Nouira and Frein 2014). Thus, alkaline processing can directly affect the cellulosic fibril, the degree of polymerization, and the extraction of lignin and hemi cellulosic compounds (Li et al. 2007; Osman 1983)

Liquid ammonia treatment: Liquid ammonia has the ability to penetrate quickly to the interior of cellulose fibers, forming a complex compound after the rupture of hydrogen bonds. This ability of ammonia is due to its low viscosity and surface tension. In addition, the relatively small molecule of ammonia is able to increase the distances between cellulose chains and penetrate crystalline regions. Therefore, the liquid ammonia treatment can change the original crystal structure of cellulose I into cellulose III. Then, after hot water treatment, cellulose III changes into cellulose I again (Pickering 2008; Rachini et al. 2012). This type of treatment results in deconvolution and smoothing of the natural fibers’ surface. At the same time, the fiber cross-section becomes round and lumens decrease (Kozlowski and Wladyka-Przybylak 2004; Rowell et al. 1997)

Silanization: Silane is a chemical compound with chemical formula of SiH4. Silanization of cellulosic fibers can minimize the disadvantageous effect of moisture on the properties of fiber composites in one hand and can increase the adhesion between the fiber and its polymer matrix. Thus, upgrading the composite strength, proper conditions like the type of silane used, its concentration in solution, time and temperature of fiber silanization, in addition to the moisture content, can determine the effectiveness of the silanization (Li et al. 2007; Osman 1983)

Table 1.5 (continued)

Graft copolymerization: Grafting copolymerization can be used to modify the surface of the natural fibers. The cellulose is treated in this process with an aqueous solution containing selected ions and is exposed to a high-energy radiation. After that, cellulose molecules crack and radicals are formed (Bledzki and Gassan 1997; Salem et al. 2008). Afterwards, the radical sites of the cellulose are treated with a suitable solution usually compatible with the polymer matrix type like, vinyl monomer, acrylonitrile, and methyl (Kalia et al. 2011b; Arbelaiz et al. 2005)

Esterification: Esterification is a popular chemical treatment method usually involves the reactions with organic acids or anhydrides. Many esters are possible to be used depending on the nature of the organic acid involved in the reaction. Esters containing 1-4 carbon atoms are formate, acetate, propionate, and butyrate; laurate has 12 carbon atoms and stearate has 18 carbon atoms. Maleate and fumarate are esters of dicarboxylic acids containing double bonds in the carbon chain. Such treatment modification can alter polarization of the fibers to make them more compatible to nonpolar matrix (Kalia et al. 2011b; Arbelaiz et al. 2005) Acrylation and maleic anhydride treatment and treatment with

isocyanates: Other types of chemical natural fiber’s treatment can be performed by Acrylation and Maleic Anhydride Treatment and Treatment with Isocyanates to enhance the mechanical properties of cellulose fiber silanization (Arbelaiz et al. 2005; Kalia et al. 2011b; Li et al. 2007; Osman 1983)

properties is demonstrated in Fig. 1.10 where proper treatments demonstrate a dra­matically enhancement of the tensile strength as well as the Young’s modulus of the fiber. Stress/strain diagrams of date palm fibers treated with different NaOH concen­tration can be shown in Fig. 1.11.

1.4

Matrices for Date Palm Fibers

The composites’ shape, appearance, as well as the environmental and overall dura­bility are dominated by the matrix type whereas fillers carry most of the structural loads hereby they provide macroscopic stiffness and strength. Polymers domi­nated the market of the commodity plastics with about 80 % consuming materials
based on nonrenewable resources (Faruk et al. 2012). Due to the public awareness of the environment as well as the limited fossil fuel resources, alternative matrices of the conventional petroleum-based ones are emphasized by different governing and industrial sectors. Therefore bio-based plastics that consist of renewable resources have experienced a revival in the past few decades. Polymers and their composites have recently emerged in wide different applications of modern indus­tries due to their desirable properties like: low weight, low cost, recyclability, biodegradability, availability, and high specific properties (Alves et al. 2010; Faruk et al. 2012).

The petrochemical-based matrices such as thermoplastics and thermoset were extensively investigated for natural fiber composites. Thermoplastics such as Polyethylene (PE) (Alawar et al. 2009), polypropylene (PP) (Rachini et al. 2012), polystyrene (PS) (Singha and Rana 2012), and PVC (polyvinylchloride) (Huang et al. 2012) were used as polymeric base of the natural fiber composites, whereas Phenol formaldehyde (Zhang et al. 2012), Polyester (Al-Khanbashi et al. 2005), Epoxy resin (Shalwan and Yousif 2014), and Vinyl esters (Huo et al. 2012) were widely used as thermosets matrix.

Due to the undesirable properties as well as the technical drawback of natural fibers such as high moisture absorption and anisotropic characteristics (Arbelaiz et al. 2005), and the low permissible processing temperature, proper polymer matri­ces have to be selected for a particular fiber type to avoid the possibility of any lig- nocellulosic degradation and to prevent volatile emissions that could hurt composite characteristics (Rowell et al. 1997). Different mechanical properties, deformations, thermal analysis, degradability, weather resistance, and thermo-mechanical proper­ties of different composites were studied (Abdal-hay et al. 2012; Abu-Sharkh and Hamid 2004; Agoudjil et al. 2011; Al-Khanbashi et al. 2005; Alawar et al. 2009; Dehghani et al. 2013; Ibrahim et al. 2014). In these studies, researchers used date palm fibers with different matrix such as Polypropylene, Polyester, Epoxy, High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE), Polyester, and ethylene terephthalate. Moreover, date palm fibers were used with other types of fibers to make completely biodegradable hydride natural fiber composites like flax fibers and starch-based composites (Ibrahim et al. 2014). A typical SEM micro­graph of fracture surface of date palm fiber/polyester composite is shown in Fig. 1.12 using raw date palm fiber.

Generally, it was reported that using date palm fibers with different polymer types can enhance the beneficial desired characteristic of the composites like the tensile strength, Young’s modulus, flexural strength and modulus, thermal and acoustical properties (Abdal-hay et al. 2012; Al-Kaabi et al. 2005; Al-Khanbashi et al. 2005; Shalwan and Yousif 2014) which can with no doubt demonstrate the effectiveness and competitiveness of the date palm fibers to be used in different natural fiber composites for wide industrial applications (Al-Oqla and Sapuan 2014). Data of a single fiber pull out treated date palm fiber/Epoxy composite with different NaOH concentrations to determine the maximum stress is shown in Fig. 1.13.

Fig. 1.12 Atypical SEM micrograph of fracture surface of date palm fiber/ polyester composite. From Al-Kaabi et al. (2005)

Botanically Musa texitilis and commonly known as abaca or Manila hemp or Cebu hemp or Davao hemp belongs to family Musaceae (Moreno 2001). The plant is native to Asia (Philippines) and is widely distributed in the humid tropics and grows abundantly in Philippines, Ecuador, and Costa Rica (Ocfemia 1930). Philippines is the leading producer of abaca in the world followed by Ecuador (Umali and Brewbaker 1956; Hadi et al. 2011). Morphologically the plant resembles the banana plant (Musa sapientum) which grows from the rootstock producing about 25 fleshy stalks (fiberless) and forms a circular mat called as “mat” or “hill.” About 12-25 leaves are produced from each stock and these leaves have overlapping petioles that cover the stalk to give a shrubby appearance and form a “false trunk” or “pseud­ostem.” The diameter of the pseudostem is about 30-40 cm and the leaves grow in acropetal succession. The leaves are bright green on the adaxial surface and yellow­ish green on the abaxial surface whose length ranges from 1 to 2.5 m (3-8 ft) and width ranges from 20 to 30 cm. The plant grows to a height of about 12 ft (4-8 m) as the oldest petioles develop from the base of the stalk while the younger ones develop successively from the higher points on the stalk. The sheaths or petioles yield the valuable abaca fibers whose length range from 1.5 to 3.5 m and are vari­ously colored including white, brown, red, black, or purple which is reported to depend on the plant variety and the position of petiole. It has been found that the fibers obtained from outer sheaths are darkest in color than those obtained from the inner sheaths. A mature abaca plant produces an inflorescence of small dark red flowers arranged in spikes which ultimately develop into banana-like fruits. These fruits (8 cm long and 2.5 cm in diameter) are inedible having green skins with white pulp inside consisting of large and black seeds (Fig. 3.1).

Yian Zheng and Aiqin Wang

Contents

6.1 Introduction…………………………………………………………………………………………………….. 102

6.2 Structure of Kapok Fiber…………………………………………………………………………………….. 102

6.3 Properties of Kapok Fiber……………………………………………………………………………………. 105

6.3.1 Spinning Property………………………………………………………………………………….. 105

6.3.2 Dyeing Property…………………………………………………………………………………….. 105

6.3.3 Mechanical Properties……………………………………………………………………………… 106

6.3.4 Hydrophobic-Oleophilic Property………………………………………………………………… 106

6.3.5 Adsorption Property……………………………………………………………………………….. 107

6.3.6 Microbiological Properties………………………………………………………………………… 108

6.4 Conclusions and Future Perspective………………………………………………………………………… 108

References………………………………………………………………………………………………………….. 109

Abstract Due to the development of sustainable technology, green renewable resources have attracted increasing interests in recent years. Kapok fiber belongs to a typical cellulosic fiber, which is obtained from the seed hairs of kapok trees (Ceiba pentandra). Kapok fiber possesses the features of thin cell wall, large lumen, low density, and hydrophobic-oleophilic properties. This chapter focuses on the struc­ture and properties of kapok fiber.

Keywords Kapok fiber • Structure • Properties

Y. Zheng • A. Wang (*)

Lanzhou Institute of Chemical Physics, Chinese Academy of Science, 18# Tianshui Middle Road, Lanzhou, China e-mail: aqwang@licp. cas. cn

K. R. Hakeem et al. (eds.), Biomass and Bioenergy: Processing and Properties,

DOI 10.1007/978-3-319-07641-6_6, © Springer International Publishing Switzerland 2014

6.1 Introduction

Kapok fibers are obtained from the fruits of kapok trees (Ceibapentandra) which belong to the family of Bombacaceae and are growing in Asia, Africa, and South America. Their color is yellowish or light brown with a silk like luster. Kapok fiber is odorless, fluffy, nontoxic, nonallergic, and resistant to rot. Traditionally, kapok fiber is used as the stuffing for pillows, bedding, and some soft toys. Owing to excel­lent buoyancy and air-filled lumen, kapok fiber is also utilized as the buoyant mate­rial (such as life preservers) and insulation materials against sound and heat. As a kind of natural biodegradable fibers, kapok fiber is now receiving more attention in scientific researches.

9.4.1 Erosion of Soil

Effective soil erosion control is dependent upon decreasing the impact of drops of rain and the velocity of water running over the surface of soil (Andraski et al. 1985; Timm et al. 2002). This involves soil surface protection by utilizing mulch or cover crop to prevent soil striking, directly by the rain. This is done by avoiding the practices that compact the soil, thus causing reduction in the infiltration (Hillel 2007).

Many studies have been done in order to understand the protection of soil provided by the straw blanket spread on the ground especially for corn stover. According to one study, it was assessed that even after the removal of corn stover from the soil, it still provides adequate protection against the erosion of soil, considering implicitly the impact on recycling of nutrients and taking into consideration the local yield and tillage practices (Graham et al. 2007). A study revealed that 20-30 % of the corn stover could be removed to still provide the adequate cover for protection (Wilhelm et al. 2004). In another study which preceded the previous one, an estimation was done which stated that the amount of stover that is required for keeping the soil ero­sion to a level that is acceptable was dependent highly on the crop management and practices of tilling that ranged from 1 to 8 mg ha-1 (Wilhelm et al. 2007). Environmental protection agency (EPA) considers that 100 % of corn stover could be removed when no tillage is used and there is a decrease in the amount to 35 % when conservationist agricultural practices are used. In practices of conventional tillage, no residue is removed from the soil (EPA 2010). Sheehan et al. (2004) built a life cycle model stimulating corn stover collection in the state of Iowa for the production and use of a fuel mixture consisting of 85 % ethanol and 15 % gasoline, by volume. The individual impact on dynamics of soil carbon, erosion of soil, agro­nomic aspects of collection of stover and transport, and conversion of bioethanol was separately modeled. For the conditions in Iowa corn field, the average mini­mum amount of the residues that could be left on the field was 4.9 and 2.5 mg ha-1 for the typical operation of tilling and no-till operation, assuming that the corn is continuously grown.

Erosion of soil in case of sugarcane is generally limited as compared to conven­tional agricultural crops such as soybeans and corn, since the canopy closes rap­idly, thus providing cover to the soil, and disturbance of soil is limited to the replanting period (once every 5 or 6 years). However, losses in the soil for sugar­cane may dramatically vary depending on many factors like the annual rainfall, the management and system of harvesting, etc (Sheehan et al. 2004).

A recent study considered effects of no tillage techniques and also conservation of soil practices like contoured seeding, ripping and furrowing, use of absorption terraces, unburned harvesting, and others (De Maria and Dechen 1998). Other stud­ies revealed that during an experiment of over eleven years, there was no significant effect of production of sugarcane on the soil horizon thickness or physiochemical composition of the soil (Macedo 2005) . The increase in mechanical harvesting (without straw burning) reduces erosion of soil due to mulching effect of straw (Macedo 2005).

In a study conducted by Andrade et al., quantification of economic and technical impacts on nutrient and soil losses through erosion in the sugarcane cultivation in Brazil was carried out. The greatest losses of nutrients of soil as well as the erosion occurred in areas of burned sugarcane. Taking into consideration the average of five cuts, burned sugarcane lost 56.45 % of K, 48.82 % of soil, and 60.78 % of P more than the unburned sugarcane (mechanical harvesting). On the average, the nutrient replacement cost for burned cane is 16.96 $/ha which was higher than the unburned cane. The unburned sugarcane had lower cost of production as compared to the burned sugarcane and higher average economic return with respect to the burned sugarcane (Leal et al. 2013).

Erosion rates are also influenced by management of straw on the ground. Burned or buried straw as well as the straw on the surface results in soil erosion rates of 20.2, 13.8, and 6.5 mg ha-1a-1 and runoff of 8, 5.8, and 2.5 % of rainfall, respectively (Macedo 2005).

Normalized Difference Vegetation Index (NDVI) is a simple graphical indicator used for the analysis of remote sensing measurements most probably recorded from a satellite. By making use of this, one can estimate the biomass by generating target images in colourful format and then comparing it against the greenery vegetation. The multispectral systems which function on Landsat and SPOT (Satellite Probatoired’ Observation de la Terre) programs are used by NDVI for accessing the greenery biomass. The NDVI serves as a valuable quantitative vegetation monitor — ing tool on a worldwide basis, in addition to several other applications including the continuous monitoring and estimation of agricultural production, extrapolation of hazardous fire zones related to forest fires and infringements of desert maps (Lillesand et al. 2004).

According to Rouse et al. (1974), the following Eq. 12.15 can be used to calcu­late the NDVI

Tr — R

NDVI = (12.15)

TR + R

Where IR and R corresponds to the spectral reflectance measurements in the near-infrared band and visible red band, respectively.

Cost, purity, availability, the processing steps, and intended application of the product are the valuable factors for considering the precursor of ACs (Al Bahri et al. 2012). A variety of carbonaceous materials including agricultural wastes or indus­trial wastes can be used to prepare ACs with high surface area and pore volumes. Although the materials used as a precursor and the preparation method determines the textural properties of ACs, however a variety of natural and synthetic materials have been used as precursors (Yagmur et al. 2008). Almost half of the raw materials used are lignocellulosic ones (Duran-Valle et al. 2005; Sudaryanto et al. 2006). Agricultural wastes due to their abundance are a rich source for activated catalyst production; it also supports to elucidate environmental problems and also reduces the expenses of activated carbon preparation.

Lignocellulosic agricultural wastes considered as a perfect precursor for the pro­duction of activated carbon (Kirubakaran et al. 1991; Al-Khalid 1995; Toles et al. 1998; Shawabkeh et al. 2002; Dastgheib and Rockstraw 2001). The most widely used carbonaceous materials for the industrial production of activated carbons are coal, wood, and coconut shell (Vernersson et al. 2002; Yang and Lua 2006) although these precursors are costly and are often imported in the country from developed ones thus there is need to utilize low-cost carbonaceous materials as feedstocks. As the demand for vegetable oils for food and oleo chemicals increased recently, the contribution of discarded by product of oils and wastes will have to play a crucial rule. Nowadays both conventional (from agriculture and wood industry) and non­conventional (from municipal and industrial activities) wastes employed to prepare activated catalyst (Diasa et al. 2007). The use of OCW as starting material for catalyst production can partly address issues concerning waste disposal and it can simultane­ously help to generate revenue from a potential waste (Konwar et al. 2013).

Press-cake is residue matter which remains as a by-product after oil extraction from the Jatropha seeds. The cake is made up of the seed husks and kernel and contains mainly proteins and carbohydrates. About 50-75 % of seed weight remains as press — cake (Staubmann et al. 1997; Singh et al. 2008). Press-cake contains oil which is about 9-12 % of its weight (Achten et al. 2008). Press-cake has about 18.2 MJ kg-1 gross energy value (Achten et al. 2008). Press-cake contains 6 % nitrogen 2.8 % phos­phorus, and 0.9 % potassium respectively (Del Greco and Rademaker 1998). Out of total 94 % solids present in press-cake, 93 % are volatile solids. One hectare

Jatropha plantation can produce about one ton of press-cake which can supply about

18.2 GJ of energy.

The press-cake has high organic content making it a good potential entity for production of biogas that can be used to supply electricity, process steam, heat, and methanol. Biogas is produced by digestion of adequate amounts of carbohydrates and proteins present in press-cake by anaerobic bacteria (Staubmann et al. 1997; Singh et al. 2008). Staubmann et al. (1997) using pig manure as inoculums, obtained 0.446 m3 of biogas containing 70 % methane per kg of dry seed press-cake. Singh et al. (2008) observed J. curcas press-cake produced 60 % higher biogas than cattle dung and contains 66 % methane. Jatropha press-cake via pyrolytic processes can be materialized for biofuel production (Demirba§ 2002). Cellulose, hemicellulose, and lignin, which are major components of press-cake during pyrolysis are broken down to produce char, bio-oils, and gas which are important energy carriers. Press-cake if present in large quantities can be as a fuel for steam turbines to generate electricity.

Ethanol fermentation is a biological process in which organic material is converted by microorganisms to simpler compounds, such as sugars. These fermentable com­pounds are then fermented by microorganisms to produce ethanol and CO2.

Several reports and reviews have been published on production of ethanol fer­mentation by microorganisms, and several bacteria, yeasts, and fungi. Among those microbes that are capable of yielding ethanol as the major product, Saccharomyces cerevisiae and Zymomonas mobilis can accumulate high concentration of ethanol in fermentation media. Historically, the most commonly used microbe has been yeast. Among the yeasts, Saccharomyces cerevisiae, which can produce ethanol to give concentration as high as 18 % of the fermentation broth, is the preferred one for most ethanol fermentation (Lin and Tanaka 2006). This yeast can grow both on simple sugars, such as glucose, and on the disaccharide sucrose. Some other yeast species which produce ethanol are summarized in Table 20.2.

As mentioned before, that the accumulation of hydrolysis products in the medium will inhibit hydrolysis process, hydrolysis and fermentation process combination in one-step reaction could be one way to overcome the problem. Known as simultane­ous saccharification and fermentation (SSF), the process allows the glucose pro­duced from hydrolysis to be fermented immediately. This allows the concentration of the glucose in the SSF medium to remain low, so that the hydrolysis process continues without significant inhibition (Takagi 1976).

SSF possess some other advantages, such as shorter the length of time required for the lignocellulosic biomass to ethanol conversion process, fewer enzymes needed compared to that for regular enzymatic hydrolysis. Furthermore, the chances of contamination are reduced because the process occurs within the same reaction vessel. However, there are fundamental problems with SSF: hydrolysis and fermen­tation both require specific temperature ranges for optimal operation. S. cerevisiae shows the best activity at temperatures around 32 °C with a pH of between 4 and 5 (Wasungu 1982). Any extreme of temperature during fermentation, either high or low, produces lower ethanol concentrations. Yeast does not grow well in temperatures lower than 20 °C or higher than 40 °C. The hydrolysis process, however, performs best at temperatures of about 50-55 °C (Palmqvist 2000). If the temperature is lower than the optimum one, the enzymes will not digest material optimally.

The presence of the ethanol in the fermentation medium during SSF has the pos­sibility of inhibiting the fermentation reaction. As the concentration in ethanol increases, the ethanol attacks the various microorganisms in the system. Both the enzymes and the yeast undergo plasma membrane degradation as the ethanol con­centration increases. Eventually, the ethanol concentration will become high enough to cause cell death in both the enzymes and the yeast (D’amore 1991). Therefore, thermostable strains capable of producing substantial amounts of ethyl alcohol at optimum temperature saccharification and suitably resistant to ethanol are needed to

Scheme 20.1 Conversion of glucose to ethanol and co-products explore (Szczodrak and Targonski 1988) . Such thermostable yeast strains make possible to conduct the fermentation at 42 °C with increased ethanol production (Sree et al 1999). One example of thermostable yeast strain is Kluyvero mycesmarx — ianus CHY1612 which is possible to shift temperature for SSF (Kang et al. 2012). Furthermore, the negative effects which excessive concentrations of ethanol have on yeast activity and cellulase within the SSF system are eliminated with a vacuum cycling reactor where the concentration of ethanol was kept at a relatively low level by its removal from the flash chamber (Roychoudhury et al. 1992).

However, more efforts have to be made in the development of microorganisms for industrial ethanol production. In addition, it is important to know the rate- limiting step. In SSF, the ethanol production rate is controlled by the cellulase hydrolysis rate and not the glucose fermentation, and hence, steps to increase the rate of hydrolysis will lower the cost of ethanol production via SSF.