The pyrolysis conditions affect the global kinetics by promoting specific elemental reactions. The main operational parameters for pyrolysis are temperature (and heating rate), pressure, co-feeding of different feedstocks and presence of catalysts.

11.3.3.1 Temperature and Heating Rate

Pyrolysis is governed by many parallel and series reactions characterized by their specific kinetics and the relative importance of each of these reactions will depend on the temperature of the system [41, 42]. Also, a slow heating process implies that the biomass remains at every temperature for a longer time period. As pyrolysis kinetics and heat transfer compete, pyrolysis occurs during the heating of the particles and might even be completed (at thermodynamic equilibrium) before reaching the temperature set-point. At low heating rate, more decomposition happens at low temperature such that more bio-char and less volatiles (condensable (bio-oil) and non-condensable gases) are produced.

One of the main mechanisms controlling the interaction between the temperature and the heating rate is the stabilization and reorganization of the macromolecular solids. Thermal decomposition brings lighter molecules to unbind from the solids (biomass or waste in the present case) to form a volatile phase. In parallel, this creates physicochemical instabilities that lead to a molecular rearrangement. The kinetics associated to these intra-molecular modifications then inhibits the volatile formation kinetics. If the heating rate is slow, stabilization occurs and higher char yield is obtained. On the other hand, heating faster will impede stabilization and volatile production will be promoted. Temperature has a different effect on the pyrolysis products. Char production decreases with increasing temperature and the yield of gas increases (both condensable and non-condensable). The extent of the gas thermal cracking determines the yield of non-condensable gas and average molecular weight of the volatile fraction. Thermal cracking kinetics becomes important with increasing temperature and gas residence time.

The important stage of experiment is determination of moisture and composition of investigated fuel. The fuel moisture is determined by the method of long-time drying at air ambient of 105 °C. The total carbon and hydrogen content in a fuel is determined by ISO 625-96 technique.

Before the experiment, the gasifier shaft is completely filled with char coal. This kind of solid fuel is the most suitable for a stage of preliminary heating up as it possesses the low content of volatile matter.

Ignition of one of the gasifier’s plasma torches is considered as the beginning of the experiment (timing is counted from this point). Supply of air plasma improves heating and firing of fuel. Heating up the reactor shaft takes at least 8 h and comprises several stages differing by oxidant flow rate. Gasifier lining has very high thermal inertia that is why practically all experiments are carried out at quasi-stationary mode.

The analysis of syngas composition begins at the final stage of preheating and the charcoal feeding is replaced by the investigated material feeding. The transient process from the charcoal gasification to the investigated fuel gasification starts when the investigated material reaches drying and pyrolysis zone. The transient process could be considered completely finished when the whole gasifier shaft is filled by this fuel and the products of its gasification. When the experimental program is completed the fuel feeding into the reactor stops and starts after-burning of fed materials and their remnants, and when they are burned out the installation cools.

Experiments on plasma gasification have been carried out for such fuels as char­coal, wood (of various types: woodchips, pressed sawdust, and chocks), coal, lignite, Refuse Derived Fuel (RDF), and others.

Co-precipitation or filling supports with an aqueous solution of active precursor is a conventional method for preparing solid acid catalysts. Metal oxides are widely used as catalyst supports because of their thermal and mechanical stability, high specific surface area, and large pore size (15 nm) and pore volume (>0.2mL/g) [25, 26]. Because solid acids function the same as [H+] for cellulose hydrolysis, sulfonated metal oxides, such as SO42-/Al2O3, SO42-/TiO2, SO42-/ZrO2, SO42-/SnO2, and SO42-/V2O5, can supply many acidic species. Such solid acids are usually prepared by impregnating the hydroxides from ammonia precipitation of corresponding metal salt solutions with aqueous sulfuric acids followed by calcination. One limitation of these types of solid catalysts is that the acidic sites are leached under hydrolytic con­ditions. It is difficult to control the catalyst particle size and shape, therefore, novel synthesis technology should integrate with conventional methods to resolve these is­sues. Fang et al. [27] have successfully prepared activated hydrotalcite nanoparticles by co-precipitation of Mg(NO3)2 ■ 6H2O and Al(NO3)3 ■ 9H2O in urea solution and subsequent with microwave-hydrothermal treatment. The particles were activated with Ca(OH)2 and used to hydrolyze cellulose. X-ray diffraction (XRD) pattern in­dicated that it had layered and well-crystallized structures with characteristic and symmetric reflections.

Carbonaceous solid acid catalysts are known to have one of the highest catalytic activities for cellulose hydrolysis. These catalysts were typically prepared from car­bohydrates by carbonizing at 400 °C under N2 and then sulfonating at 150 °C [28]. Glucose, sucrose, cellulose, lignin, and activated-carbon can be used as raw materi­als for their preparation [28-31]. The carbon in the catalysts is in amorphous forms consisting of polycyclic aromatic carbon sheets. All S-atoms in the catalysts are in — SO3H groups, which are the active sites. Carboxylic acid species, -COOH, gener­ally provide more active sites than Nafion NR50 and Amberlyset-15 which could not help to hydrolyze cellulose into glucose. Pang et al. [29] reported that high glucose yield of up to 74.5 % with 94.4 % selectivity was obtained at 150 °C and 24 h. Lignin is the second-most abundant natural organic material after cellulose, and the richest aromatic organic biopolymer. It has high carbon content and should be usable as a precursor for activated carbon. Pua et al. [30] prepared a solid acid catalyst from Kraft lignin by treatment with phosphoric acid, pyrolysis, and sulfuric acid, and subsequently it was successfully used as catalyst to synthesize biodiesel from high acid value Jatropha oil. It is speculated that lignin derived carbonaceous catalyst is more advantageous for cellulose hydrolysis.

Homogeneous catalysis by heteropoly acids (HPAs) is in principle similar to sulfuric acid in that [H+] leaches into solution and interacts with the oxygen atoms in the glycosidic bonds of cellulose. However, recovery of the homogeneous catalysts is problematic. Cellulose hydrolysis using solid HPAs was reported by Tian et al. [32]. Several types of acidic cesium salts, CsxH3-xPW12O40 (X = [1-3]), were prepared. The salt Cs1H2PW12O40 was found to give the highest glucose yield (30 %) at 160 °C for 6h reaction time. CsxH3-xPW12O40 catalysts were prepared by adding dropwise the required amount of aqueous solution of cesium carbonate to aqueous solution of H3PW12O40 with cesium content ranging from 1 to 3 at room temperature with stirring. After the resultant milky suspension was aged at room temperature overnight, the solution was slowly heated at 50 °C to obtain white solid powers. It was found that Cs1H2PW12O40, with strong protonic acid sites, showed the best catalytic performance in terms of the conversion of cellulose and the yield for glucose. Cs2,2H0 8PW12O40 showed the highest selectivity in terms of glucose, which is due to its micro-porous structure.

For industrial applications, low cost catalysts with good performance are required. The catalyst cost can be reduced by selecting cheap materials and simple preparation process. Relatively speaking, carbonaceous solid acid catalysts are considered as the cheapest catalyst, since they were obtained from biomass (such as glucose, cellulose, lignin, wood et al.) by a simple process of carbonization and sulfonation.

Pretreatment is an important process to overcome the recalcitrance of SB/SL. The primary goal of pretreatment is either to remove lignin or hemicellulose making the remaining carbohydrate accessible for enzymatic hydrolysis into simple sugars. Each pretreatment method has its pros and cons. The enzymatic hydrolysis effi­ciency directly depends upon the effectiveness of pretreatment strategy. In the last five years, several reports have been published describing the pretreatment method applied to sugarcane residues. The choice of pretreatment option depends upon max­imum removal of lignin, less generation of inhibitors and high recovery of sugars with minimum enzyme dosage. Dilute acid hydrolysis, steam explosion and NAOH pretreatment are largely studied for SB hydrolysis. AFEX has been studied rationally less to pretreat SB or SL. Pretreatment of lignocellulose in tandem with enzyme cost play a very crucial role in overall economics of biorefinery or other lignocellulose based bioconversion industries. An effective pretreated lignocellulosic material re­quires less enzyme amount for complete holocellulose degradation. Since enzymes are expensive hence the fewer amounts of enzymes for the maximum degradation of cellulosics will impact the cost economics of lignocellulose based industries. Ta­ble 16.4 presents the effect of different pretreatment methods on sugarcane residues for the sugars recovery after enzymatic hydrolysis. It is clearly evident with the ta­ble that effective pretreatment of SB/SL require less enzyme loading in order to get maximum depolymerization of cellulose/hemicelluloses into their constituent sugar monomers.

The biomass properties have significant effects on the product compositions (through conservation of mass) and the gasification conditions (corrosion, slagging, etc.). Biomass includes any form of non-fossilized and biodegradable material derived from living species, such as plants and animals. The term “biomass” designates a very wide spectrum of substances, which includes products, byproducts, residues, and wastes from industries (forestry, agricultural, food, etc.) and municipalities [1, 2]. Each type of biomass is characterized by its specific physical and chemical properties: moisture, heating value, bulk density, chemical composition as well as ash and volatile contents. The biomass properties determine its performance as a fuel in gasification or any other process. Furthermore, the availability of the types of biomass as well as their properties is a function of a geographical location.

One of the most available biomass is wood, but it is a valuable material due to its current applications as a construction material. Wood residues (sawdust, bark, and misshapen pieces), however, have very little market value and are therefore prime candidates to be used as gasification feedstock. Other types of industrial residues (agricultural, forestry, etc.) could also be used as feedstock: husks from rice, coffee or coconut, bagasse from sugar cane, and verge grass. Energy cropping, such as poplar, sugar cane, and sweet sorghum, which consists of growing biomass specifically for fuels, is also another interesting possibility in renewable energy and the agricultural sector.

Gas composition exiting a gasifier often varies from the composition predicted by equilibrium models [76]. This is caused by the fact that products exit from the reactor before reaching an equilibrium state and thus demonstrates the need for kinetic models to simulate gasifier behavior. Gasification reactions are divided into three categories: drying, devolatilization, and gasification. The time taken for drying and devolatilization is much faster than gasification of char. Some models assume the first two steps to be instantaneous and that the rate of char gasification controls the overall process [89, 90].

Kinetic models provide information on the progress of the reaction by taking into account the reactor type, size, and its hydrodynamics. In the kinetic model, the reaction kinetic is solved simultaneously with bed hydrodynamics, mass and energy balance to achieve the gas, and tar and char yield at specific operating conditions. Unlike other models, the kinetic model is sensitive to the gas-solid mixing and the flow pattern in the gasifier. Based on the process, this type of model can be divided into three groups: (1) fluidized bed; (2) fixed bed; and (3) entrained flow.

Dewatering and drying should be considered, since heating the biomass may only vaporize the water while delaying the biomass pyrolysis reactions and increasing the operation costs. Also, studies suggest that steam explosion of biomass could influence the quality of pyrolysis products [55].

Particle size reduction is also important to minimize heat transfer limitations and internal temperature gradients in biomass particles. The Biot number criterion of

0. 1 suggests that the maximum wood chips size that should be fed to a BFB to avoid heat transfer limitations (and product yields issues) is ~2 cm (by estimation with typical wood properties). This calculation assumes that the wood chips have a thickness five times lower than their diameter (parallelepiped shape). Particle size reduction is therefore recommended for biomass particles that are larger than that value. Heterogeneous feedstocks such as MSW would not be recommended with this technology since pyrolysis operation temperatures do not promote slagging, in opposition to gasification. Undesired particulate would then need to be removed from the bed, which is a difficult operation in BFBs, considering the wide particle size and densities distribution of the inorganics.

Figure 13.8 shows the amount of refined biogas produced and consumed at the farm. Figure 13.9 shows the composition of gases produced at the farm and the percentage of consumption of refined biogas. The biogas plant produced an average of

185,0 Nm3 biogas per year. Of the amount of biogas produced, about 35.3 % of the gas was consumed by gas boilers within the plant.

Raw biogas to be refined made up 42.5 % of the gas produced, and unused biogas (biogas that was not used in any stage of the process) made up 22.2 %. The amount of refined biogas completely treated by the RCF facility was about 35,000 Nm3/yr (19.1 % of the total biogas produced). The amount of refined biogas used within the farm production system as energy substitute for LPG by kitchen gas appliances and CNG trucks was about 600 Nm3/yr (CNG trucks, 462 Nm3/yr; kitchen appliances, 150 Nm3/yr).

Fig. 13.8 Composition of refined gas produced and consumed at the farm

Fig. 13.9 Percentage and breakdown of refined gas produced and consumed in Town A

This amount made up 0.3 % of the refined gas produced in a year. The amount of refined gas transported outside the farm production system was 35,000 Nm3/yr. This made it possible to supply 219 out of 3661 residences (as of November 2008) in Town A (roughly 6 % of all households).

Water is the mostly used medium for cellulose hydrolysis. It was also shown that catalyst activity and selectivity are closely determined by the amount of water. When the amount of water is close to the weight of solid catalyst, a maximum yield of glucose is obtained. However, a lower amount of water and longer reaction time (e. g., 24 h) mainly drive the reaction towards the formation of water-soluble |5-1,4-glucans. ILs are efficient for the pretreatment and hydrolysis of lignocellulosic materials, and can dissolve biomass and overcome many of the physical and biochemical barriers for hydrolysis at ambient conditions. [BMIM][Cl] and 3-allyl-1-methylimidazolium chloride {[AMIM][Cl]} can dissolve 10 wt% cellulose at 50-100 °C [85]. Wang et al. [86] conducted a study on the extraction of cellulose from wood chips with [AMIM][Cl] and found that 62 wt% cellulose dissolved in [AMIM][Cl] under mild conditions. So far, water, organic solvents, ILs, and their mixtures are widely used as reaction media.

Zhang et al. [87] demonstrated that high yield of total-reducing-sugars (TRS) (60 %) was achieved when depolymerization of chitosan was performed in ILs in the presence of mineral acids. This might be due to the fact that the reaction medium 1-butyl-3-methylimidazolium bromine {[BMIM][Br]} reinforced the acidity of the mineral acids. A physical barrier for hydrolysis disappeared through the formation of a solution with [BMIM][Br]. With good solubility to dissolve cellulose, IL is a good medium for directly catalytic hydrolysis of cellulose with high efficiency. ILs can promote the dissolution and dispersion of cellulose molecules, leading to the complete mixture between cellulose and acidic sites in a homogeneous phase. Relatively, small cations are often efficient in dissolving cellulose. In another work [88], when hydrolysis reaction was carried out in [BMIM][Cl] in the presence of 7 wt% HCl at 100 °C under atmospheric pressure for 60 min, TRS yield was 66 %, 74 %, 81 %, and 68 % for the hydrolysis of corn stalk, rice straw, pine wood, and bagasse, respectively. The high TRS yield is due to the dissociated Cl-1/Br-1 and the electron-rich aromatic system of [BMIM+] weakening the glycosidic linkage to facilitate hydrolysis.

Water addition was found to have a significant impact on the degree of cellulose hydrolysis, because water acts both as a reactant (for producing monosaccharides) and an inhibitor [for producing 5-hydroxymethylfurfural (5-HMF)] in the overall cellulosic conversion. As mentioned above, Qi et al. [75] developed an effective con­version technique for transforming cellulose into 5-HMF via a two-step process. In the first step, high glucose yield (83 %) was obtained from the cellulose hydrolysis by a strong acidic cation-exchange resin in [EMIM][Cl] with gradual addition of water. In their study, cellulose firstly dissolved in [EMIM][Cl]. Then a certain amount of water and the cation-exchange resin was added. Hydrolysis reaction started when the system was heated to 110 °C. Compared with one-time addition of water, glu­cose yield was improved by adding water to [EMIM][Cl] system during reaction. In the hydrolysis step, increasing the amount of water could increase the yield of monosaccharides, and the maximum yield of 25 % (monosaccharides + 5-HMF) was obtained when H2O/cellulose molar ratio was 10 [89]. However, excessive water addition caused cellulose to precipitate from IL.

Ahmed Tafesh and Sobhi Basheer

Abstract Biodiesel has emerged as one of the most growing biofuels to replace diesel fuel. Its preference as one of the most popular alternative fuels was based on its characteristics as it is environment friendly, sustainable, biodegradable, and non-toxic. Biodiesel is mandated by many governments worldwide for incorporation into their diesel supply base. Biodiesel is easily produced through transesteriflcation reactions of vegetable oils (triglycerides). However, current commercial usage of refined vegetable oils for biodiesel production is impractical and uneconomical due to high feedstock cost and priority as food resources.

Low-grade oils, typically waste cooking oils, brown greases, crude corn oils, etc., can be better alternatives; however, the high free fatty acids (FFAs) content in such oils has become the main constrain for those potential feedstocks, and therefore pre­treatment methods become necessary to prepare such feedstocks to make biodiesel. The chapter highlights the pretreatment methods to utilize and convert the FFAs from various feedstocks to biodiesel and presents the advantages and limitations of using enzymes and conventional catalysts, distillation, blending, and glycerolysis meth­ods to lower FFAs in the feedstocks. An overview on the current status of biodiesel production, the feedstocks and the FFAs factors are also discussed. With the proper pretreatment methods, the high-FFAs feedstocks can indeed become the next ideal feedstocks for the production of biodiesel.

Keywords Enzymes ■ Vegetable oil ■ Biodiesel ■ Pretreatment ■ FFA ■ Triglyceride

18.1 Introduction

Biodiesel production is a globally advancing field, with biodiesel fuel increasingly being used in compression diesel engines to replace diesel fuel which stands at a market value of $200 billion US dollars per year worldwide. The biodiesel, which

A. Tafesh (H) ■ S. Basheer

TransBiodiesel Ltd, Nazareth Street 79, P. O. Box 437, Shefar-Am 20200, Israel e-mail: atafesh@transbiodiesel. com

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

Green Energy and Technology,

DOI 10.1007/978-3-642-32735-3_18, © Springer-Verlag Berlin Heidelberg 2013 is becoming one of the most popular alternative and environment-friendly fuels, is mandated by many governments for incorporation into their diesel-supply base. Society’s concerns with the environment have made governments, industries, and businesses start to assess how their activities affect the environment. Such biodiesel is a more natural, more sustainable biofuel known to reduce carbon dioxide emission by 78 % when compared to regular diesel and its energy content is 88-95 % that of diesel [1].

Production scale of biodiesel in the European Union in 2006 was estimated to be approximately 4.8 million tons, which constitutes about 77 % of the produced biodiesel in the world followed by the US with 13 %, and the rest of the world to be 10 %. Market growth rate data in Europe was over 50 % in 2006 after growth of 37 % in 2005. It is estimated that biodiesel will reach 3.3 billion gallons by 2022, an increase of 2.5 billion gallons from 2011, where nearly 80% of the increase comes from three feedstocks: soybean oil (31 %), corn oil (22 %), and palm fatty acid distillate (26 %) [2]. The volume of all biodiesel is growing at a 10 % rate per year and stood at $22 billion market value in 2007, and is estimated to reach $88 billion by 2020 [3, 4].