As noted in Fig. 3, bio-oil from canola had lower viscosity than that of aspen. Among the bio-oils produced from corn cob, the viscosity of bio-oil with catalyst (corn cob 4) was lower than other bio-oils due to more water content. The viscosity of bio-oil produced from corn cob without catalyst was similar to that of liquid phase of canola and it was lower than that of liquid phase of aspen.

All the bio-oils from different feedstocks were behaved as a non-Newtonian fluid. Similar behaviors have been reported for bio-oils (upper layer) obtained from forest residues (Garcia-Perez et al., 2006a) and pine and oak bark (Ingram et al., 2008). However, Ingram et al (2008) reported Newtonian behavior at 25°C for the bio-oils produced from pine and oak wood through auger reactor but at higher temperatures (50 and 80°C) they showed mild shear thinning behaviors. Rheological data of shear rate and shear stress of the bio-oils were fitted according to the Power-Law model

A = ky-1 (1)

where, g is the viscosity (Pa-s), k is the consistency coefficient (Pa. sn), у is the shear rate, 1/s and n is the flow behavior index of the fluid (dimensionless). The power law conststants for different bio-oils are presented in Table 1. The flow behavior indexes n less than 1 suggests that presence of the pseudoplastic behavior (shear thinning). A possible reason might be breakdown of (waxy) structure would result in low viscosity at high shear rate. In general, the values of flow behavior index are more reliable than that of consistency coefficient (Johnson, 1999).The deviation of flow behavior index from ‘unity’ indicates the degree of deviation from Newtonian behavior. For shear thinning, the index value can be anywhere between 0 and 1. The smaller the value of n, the greater is the degree of shear thinning (Chhabra & Richardson, 1999). Considering the above points, canola aqueous phase

exhibited strong shear thinning behavior than that of the rest. In general, the bio-oils from corn cob approaches Newtonian behavior as the n values were close to unity.

2.2 Comparison of viscosity viscosity measurements and bio-oil viscosities

Accurate measurement of the viscosity of bio-oil/fuel is essential for the proper operation of fuel supply systems and atomisers. The viscosity of bio-oil can be measured according to the ASTM D 445 using the following equation

q = жРг1 t / 8lv = Tthpgr4t / 8lv (2)

where n is the viscosity (dynes/cm2 or poise), v is the volume of liquid (c. c.), t is the liquid flowing time (s), r is the radius of narrow tube (cm), l is the length of narrow tube (cm). This is most widely followed method, as evident from table 2. The viscosity of bio-oil can be measured using capillary or rotational viscometers and they are reported as kinematic (cSt) or dynamic viscosity (mPa. s). The kinematic viscosity of the bio-oil can be converted into dynamic viscosity if the density (kg/ dm3) of bio-oil is known at a given temperature using the following formula

According to ASTM D445, the viscosity of standard fuels, which are Newtonian fluids, is typically measured as kinematic viscosity. Leroy et al (1988) conducted extensive studies on rheological characterization of several bio-oils from wood and concluded that those bio-oils exhibited an essentially Newtonian behavior at the shear rate range of 1 to 1000/s. In contrary, bio-oils used in this study showed shear thinning behavior. For Newtonian fluid, the viscosity remains constant with increasing shear rate. Radovanovic et al (2000) reported a procedure to measure bio-oil viscosity using falling ball viscometer. Recently, Osamaa et al (2009) recommended using Cannon-Fenske viscometer tubes because the flow direction in these tubes compared to Ubbelohde tubes ensured more accurate results with dark coloured liquids. No prefiltration of the sample is required if the bio-oil is visually homogenous. Elimination of air bubbles before sampling and an equilibration time of 15 min are essential for viscosity measurement at a given temperature. Comparison of viscosity measurement and viscosity of bio-oils from produced different feedstocks through different pyrolysis reactors are presented in Table 2. Bio-oil density measurement and density values are also included for converting the viscosity from kinematic to dynamic units. According to ASTM D445-88, viscosity should be measured at 20 and 40°C, as seen from the table the viscosity was reported at different temperatures ranging from 20 to 100°C. The viscosity of bio-oils used in this study had lower viscosity than the viscosities listed in the table irrespective of temperatures.

The various organic products were subjected to a standardized liquid-liquid fractionation protocol (Oasmaa, 2003, Figure 1) to gain insights on the severity of the hydrotreatment process on product composition. The results are compiled in Figure 8 and show major changes in composition upon reaction. The pyrolysis oil feed mainly consist of ether solubles, ether insolubles and water. The components in these fractions originate from the cellulose and hemi-cellulose fraction in the biomass feed and particularly the ether insoluble fraction is rich in carbohydrates. The amounts of DCM solubles and insolubles, from the lignin fraction of the biomass feed, are by far lower and are about 20% in total.

100

Fig. 8. Comparison of the fractionation results for various process severities

1.1.1.3 Thermal reactions

When comparing the composition of the pyrolysis oil feed with the product from the thermal route, it is clear that the ether insolubles are converted to DCM-solubles and — insolubles, and additional water. A similar change occurs in wood oils, stored for several months or years, where water insoluble products are produced at the expense of the sugar fraction (Oasmaa&Kuoppala, 2003). At higher temperatures and residence times, especially this sugar fraction is responsible for charring, likely through the formation of first DCM solubles and subsequently DCM insolubles (‘char’). Solids production upon heating aqueous solution of C-6 sugars (e. g. D-glucose, D-mannose) to temperatures up to 400 oC is well known. Thermal decomposition, either catalytic (mostly by acids) or non-catalytic, leads to solid products referred to as humins (Girisuta et al., 2006; Watanabe et al., 2005a; Watanabe et al., 2005b). The proposed reaction pathway consists of C-6 sugar conversion to
5-hydroxymethyl furfural (HMF) and subsequently levulinic acid (LA) and formic acid (FA). Both reactions also accompanied by solids (human) formation (Scheme 1).

Solids formation is highly undesirable and limits the yields of the two promising biobased chemicals LA and HMF. Despite large research efforts, it has so far not been possible to avoid solids/humin formation when performing the reactions in aqueous media.

Scheme 1. Decomposition reactions of D-glucose at elevated temperatures.

Higher temperatures and the presence of acid catalysts (homogeneous and heterogeneous) increase the rate of D-glucose decomposition (Girisuta et al., 2006). Such reactions may also occur in the fast pyrolysis oil matrix. The oil is acidic in nature due to the presence of organic acids and these will catalyse the depolymerisation of oligmeric sugars to D-glucose and other C-6 sugars followed by the reaction to solids and hydroxymethylfurfural and levulinic acid/formic acid.

Knezevic et al. (2009) studied the thermal decomposition of D-glucose in hot compressed water under conditions of relevance for the catalytic hydrotreatment of pyrolysis oil (240­374 °C). It was shown that D-glucose decomposes mainly to char and some gaseous components (primarily CO2), while only a limited number of components remained in the water phase (for example formaldehyde). At these conditions, the reactions are very fast and decomposition to char takes place on the time scale of seconds to minutes.

Cooper and Eaton (1962) studied the compaction behavior of four ceramic powders. In each case it, was assumed that compression is attained by two nearly independent probabilistic processes, namely, the filling of voids having equal size as particles and filling of voids smaller than particles. Based on these assumptions, the following equation (2) was given:

V0-V

—— тг=а1е p +a2e p

v0 VS

where, VO = volume of compact at zero pressure, m3; V = volume of compact at pressure P, m3; Vs = void free solid material volume, m3; ait a2, ki, and k2 = Cooper-Eaton model

constants.

The difficulty in practical use of equation (2) is the assignment of some physical significance to the constant parameters. In addition, another drawback of this model is its applicability to only one-component system (Comoglu, 2007).

Elkin Alonso Cortes-Marln and Hector Jose Ciro-Velazquez

Universidad Nacional de Colombia — Sede Medellin

Colombia

1. Introduction

The non-renewable nature of fossil fuels combined with the high level of participation within transportation sector in the total consumption of primary energy and atmospheric pollution, have become the primary forces propelling research of alternative sources for vehicles, mainly those sources derived from biomass. This has resulted in an increased environmental consciousness that seeks to replace fossil fuels or to provide blends that reduce their overall consumption. Mainly searching for these sources in agribusiness, and taking into account that tropical countries play lead roles here in Colombia is where the greatest variety of plant species can be found and where the environmental conditions make production of these more advantageous.

The global energy problem leads to express the scope, opportunities and threats that the use and partial replacement of conventional fossil fuels by biofuels or agrofuels represent for the development of a country, focusing in Colombia as a case study. The growing importance of new energy sources, (which can be derived from a variety of crops) and raw materials, which demands high biomass amounts, must generate some level of concern about the possible harmful effects of deforestation, jungle loss and replacement of crop fields essential for human diet (food safety). Not to mention the challenges in the climatic, geographical and physical fields, i. e. on whole nations’ economies (Cortes et al., 2009) .

Today, these new energy sources are the new financial, political and even environmental strategies. Their importance is such that currently there are more than 30 raw materials being tested worldwide. Despite this big boost they still do not provide a solution to the global energy crisis (Cortes & Alvarez, 1998).

The possibility of using biofuels in the development of cars and engines, has been considered from the very beginning, but only as a result of the current energy and environmental situation, do conditions exist for the shaping of a global biofuels industry. The development of alternate energy has allowed the concepts of biofuel and energy crops gain importance every day, with greater strength in agricultural and energy policies of both industrialized and developing countries. The motivating factors have been, among others, the evident depletion of fossil fuels, the periodic oil crisis and the so-called greenhouse effect caused by the accumulation of CO2 in the atmosphere. Despite of this, it is important to recognize that biofuels will not end industrialized countries oil dependency, because there will not be enough land and water to meet the energy requirements of the automotive industry.

As a result, in order to prevent irreversible changes and reduce the impact of greenhouse gases on Earth’s climate, many countries, including Colombia, have developed strategies to diversify energy production by using renewable sources. The first strategy has been replacing Oil-Derived Fuels with biofuels thus defining a reduction of CO2 emissions generated by mobile sources. It is therefore imperative to begin using alternative energies, that is to say those considered clean and renewable. For this reason biofuels could be a valid choice. Therefore, the use of renewable energy sources as an alternative to fossil fuels is a key strategy to reducing greenhouse gas emissions (Consejo Nacional de Politica Economica y Social (CONPES, 2008)

It is at this stage that recently a dialogue, debate and confrontation regarding biofuels have been facilitated which allows for the development of new technologies and refineries to produce them. Such importance is not only the result of a sudden leap in scientific knowledge, although that has taken place, but rather it is a leap in governments funding, which seem concerned about oil prices rising and geostrategic dependence on them. Whatever the reason, if funding continues, in the short term a new generation of biofuels could be available.

Despite the enthusiasm, promotion and advocacy, there is a question: are biofuels a technical and economically viable energy and environmental option for replacing future fuel imports? But at the same time with the promotion and incentives (legal, regulatory, fiscal and financial framework), of alcohol fuels and bio-oils, employment rates will see a positive impact in farming regions. It is necessary not only to encourage biofuels production but also define programs that support the new refineries’ biomass needs, so that the price of raw materials with dual purpose (food and biofuel) is not affected.

Certainly for Colombia it is necessary to diversify its raw materials portfolio for anhydrous alcohol and biodiesel production, incentivize the research and development of proprietary technology programs that produce biofuels at competitive levels for the domestic demand in the short and medium term and, in the long term to start exports.

In order to delay the depletion of reserves, to avoid the rising cost of imports, reduce gas emissions and the impact of particulate matter into the atmosphere, the policies of replacing energy sources, for the Colombian biofuel industry, provide an excellent opportunity due to the oil rising price, i. e. energy vulnerability risk decreasing.

In general, the text aims to illustrate the production and replacement of fossil fuels with bioenergy (ethanol, biodiesel), the progress, uncertainties and problems resulting from these processes for new energies generation and use, mainly with regards to the food safety and environmental consequences of poor countries. In particular, it presents the political, regulatory and legal framework, by which the Colombian government promotes the production and use of biofuels.

Based on the above data, CO2 emissions of CGS (electricity and/or thermal energy) and Bio — H2 fuels are shown in Fig. 5.

According to Fig. 5, the entire CO2 emissions are 16.3-65.7 g-CO2/MJ of CGS and 39.6-95.3 g — CO2/MJ of Bio-H2, respectively. Especially, in the CGS case, the specific CO2 emissions of electricity are 5.9-23.9 g-CO2/MJ, and the reduction percentages in comparison to the conventional electricity in Japan are 80.6-95.2%. In the case of Bio-H2 case, the reduction percentages against the conventional H2 production (121.3 g-CO2/MJ, Natural gas origin) are 21.4-67.3%.

CO2 emissions at the material drying and at the auxiliary power of a purification process of PSA occupy a large portion of the entire CO2 emission. Especially, the influence due to the compression power of H2 purification would be significant. In the case of Bio-H2, the amount of 35.1% to 84.4 % of the total CO2 emissions would be emitted from the auxiliary power including the power for BT operation. Also, in the case of CGS, that of 16.5% to 66.6 % would be emitted from the auxiliary power origin, even if the PSA operation is not equipped.

The deviations of CO2 emissions (the maximum value — the minimum one) due to the uncertainties on the moisture content and the transportation distance would be within 49.5 g-CO2/MJ of CGS and 55.7 g-CO2/MJ of Bio-H2, respectively.

That is, the range of collection of biomass feedstock would be extremely significant from the viewpoint of CO2 emission reduction on basis of LCA methodology.

Mixing bioethanol with petrol, even in modest proportions, increases the octane number of the fuel and reduces the percentage of aromatic and carcinogenic compounds, and emissions of NOx, smoke, CO, SOx and volatile organic compounds (VOC). But there is also an increase in the emissions of formaldehyde and acetaldehyde. On the other hand, modern bioethanol production systems have an energy ratio (or net usable energy) of around 2 to 7, depending on the crops and processes used. The composition of petrols can influence the emissions of organic compounds: those containing aromatic hydrocarbons such as benzene, toluene, xylene and olefins produce relatively high concentrations of reactive hydrocarbons, while petrols formulated using oxygenated compounds (such as those mixed with bioethanol) may contain lower quantities of aromatic compounds.

The problem of petrols with high concentrations of aromatic compounds lies in their marked tendency to emit uncombusted hydrocarbons, which are difficult for catalytic converters to oxidize as well as being precursors of photochemical contamination. All oxygenated fuels have the potential for reducing the emissions of carbon monoxide (CO) and uncombusted hydrocarbons, which are also "photochemically" less reactive than the hydrocarbons of normal petrols. Because ethanol acts as an oxygenating agent on the exhaust gases of an internal combustion engine fitted with a three-way catalytic converter, adding ethanol to petrol (Poulopoulos et al., 2001) leads to an effective 10% reduction in the emission of CO, as well as a general reduction in aromatic hydrocarbon emissions. Using four-stroke engines, with four cylinders and electronic injection, fueled with various ethanol and petrol mixtures (Al-Hasan, 2003) reduced the CO emissions by about 46.5%. The anti­detonating features of petrols are very important and depending essentially on their chemical composition.

Life cycle analysis taking the "well to wheel" approach showed that the GHG emissions from bioethanol obtained from sugar beet are around 40-60% lower than the emissions from petrols obtained from fossil fuels (Reijinders & Huijbregts, 2007). Mixing bioethanol with diesel oil improves the fuel’s combustion (Lapuerta et al., 2008) and reduces the size of the particles in the exhaust without increasing their quantity. Using an E10 mixture reduces the total hydrocarbon emissions because of ethanol’s greater heat of vaporization.

CO emissions increase if moderate amounts of ethanol are added to diesel oil, while they diminish as the proportion of ethanol increases (Li et al., 2005). Conversely, NOx emissions decrease with a low or moderate quantity of ethanol, but increase if more ethanol is added. The total hydrocarbons (THC) also increase with different proportions of ethanol and different speeds.

4. Conclusions

Although bioethanol is a valid alternative to fossil fuels and has a low environmental impact, its use is nonetheless posing problems relating to the use of raw materials such as cereals, which are fundamental to the food industry.

Increasing the farmland used to grow energy crops for the production of biofuels means competing with food crops. Many studies have attempted to assess the need for farmland for crops for producing ethanol. The yield in bioethanol per hectare naturally depends on the crops used, but reference can be made to the mean productivity in Europe (weighted according to the type of crop), which is currently estimated at around 2790 liters/hectare (based on a mean yield in seeds of 7 tons/hectare and 400 liters/ton).

Although bioethanol can be produced successfully in temperate climates too, the tropical climates are better able to ensure a high productivity. In Brazil, sugar cane is used to produce approximately 6200 liters/hectare (an estimate based on a crop yield of 69 tons/hectare and 90 liters/ton). The productivity of bioethanol from sugar cane is high in India too, with a yield of approximately 5300 liters/hectare. If bioethanol from sugar cane becomes a commodity used worldwide, then South America, India, Southeast Asia and Africa could become major exporters.

Research is focusing on alternatives, concentrating on innovative raw materials such as Miscanthus Giganteus, an inedible plant with a very high calorific value (approximately 4200 Kcal/kg of dry matter), or filamentous fungi such as Trichoderma reesei, which can break down the bonds of complex lignocellulose molecules.

This article summarizes the main raw materials that can be used to produce bioethanol, from the traditional to the more innovative, and the principal production processes involved. It also analyses the issues relating to emissions and carbon sequestering.

Flash point is a measure of flammability of fuels and thus an important safety criterion in transport and storage. The flash point of petrol diesel fuel is only about half the value of those for biodiesels, which therefore represents an important safety asset for biodiesel.

The flash point of pure biodiesels is considerably higher than the prescribed limits, but can decrease rapidly with increasing amount of residual alcohol. As these two aspects are strictly correlated, the flash point can be used as an indicator of the presence of methanol in the biodiesel. Flash point is used as a regulation for categorizing the transport and storage of fuels, with different thresholds from region to region, so aligning the standards would possibly require a corresponding alignment of regulations.

1.5 Sulfur

Fuels with high sulfur contents have been associated with negative impacts on human health and on the environment, which is the reason for current tightening of national limits. Low sulfur fuels are an important enabler for the introduction of advanced emissions control systems. Engines operated on high sulfur fuels produce more sulfur dioxide and particulate matter, and their emissions are ascribed a higher mutagenic potential. Moreover, fuels rich in sulfur cause engine wear and reduce the efficiency and life-span of catalytic systems. Biodiesel fuels have traditionally been praised as virtually sulfur-free. The national standards for biodiesel reflect the regulatory requirements for maximum sulfur content in fossil diesel for the region in question.

Algae are a diverse group of aquatic, photosynthetic organisms generally categorized as either macroalgae (i. e. seaweed) or microalgae, which are typically unicellular. Although the emerging field of algal biofuels remains in its infancy, microalgae have great potential to bring the promise of clean, sustainable fuel production before we must face the reality of fossil fuel depletion and exacerbated climate change. Algae are perhaps the most effective photosynthetic organisms for generating chemical energy from sunlight — the most abundant and renewable global energy source. It is believed that a large percentage of today’s fossil fuels, particularly petroleum, originated as prehistoric algal blooms. As single — celled organisms, microalgae are capable of producing a large portion of their biomass as small molecule biofuel precursors since they lack macromolecular structural and vascular components needed to support and nourish terrestrial plants. As such, algae provide one of the most direct routes for the photosynthetic conversion of carbon dioxide and other organic substrates to biofuel. Moreover, the large surface area to volume ratio of these aquatic microorganisms is advantageous for absorption of nutrients and sunlight, which is reflected in the rapid growth rates observed in many species.

As aquatic organisms, microalgae offer many advantages over the terrestrial bioenergy crops with which they contend. Some of the most serious drawbacks of allocating portions of existing food crops to produce biofuels, particularly ethanol from corn and biodiesel from soy or rapeseed, are the obvious competition with food production and encouragement of subsidized operations. Both outcomes are coupled with severe economic ramifications. While cellulosic ethanol may avoid the food versus fuel controversy, this technology has yet to fully mature and will likely remain at the developmental stage for a number of years. In general, terrestrial crops have relatively long growing seasons and require arable land, oftentimes supplemented with costly fertilizers that can have harmful effects on the surrounding ecosystems. Additionally, there are greenhouse gases released in the process of generating fertilizer and harvesting terrestrial biomass. Furthermore, constant irrigation of these crops is yet another impediment, as this can be taxing on natural freshwater resources. While great strides are being made toward the optimization of cellulases for enzymatic degradation of lignocellulose, a significant amount of energy is still required to harvest and pre-treat (thermochemically breakdown) the cellulosic biomass, which constitutes an additional input of fossil fuel-derived energy.

Unlike terrestrial bioenergy crops, microalgae do not require fertile land or extensive irrigation and can be harvested continuously. Several species of algae provide an alternative to freshwater use by growing in brackish, sea, and even hypersaline water. Additionally, since algae consume carbon dioxide through the process of photosynthesis, large-scale cultivation can be used to remediate the CO2 emissions from fossil fuel combustion (Benemann and Oswald, 1996) (Figure 1). Algal biomass also possesses secondary co­products such as antioxidant pigments, edible proteins, and nutraceutical oils that other alternative fuel crops lack (Spolaore et al., 2006). Lastly, since nearly all microalgae have a simple unicellular structure, algal biomass is devoid of lignocellulose. This strong structural polymer has proven to be a significant obstacle to releasing the energy trapped in terrestrial biomass. Not only do microalgae fully address each of the disadvantages of land-based biofuel crops, but they also are amenable to genetic engineering for the enhanced biosynthesis of a wide range of advanced biofuels and high-value added products. Currently, three fundamental objectives remain critical to the implementation of economically — and technologically-feasible algal biofuel production: [1] increase of biological productivity through species selection and genetic engineering as well as optimization of culture conditions; [2] development of low-cost vessels for cultivation, whether they be closed photobioreactors or open pond systems; and [3] improvement of inexpensive downstream processing techniques for algal biomass, including harvesting, dewatering, and extraction of biofuel metabolites (Hejazi et al., 2004a; Shelef et al., 1984; Danquah et al., 2009). As with many novel sources of bioenergy, the complexity of the microalgal biofuel production process calls for a multidisciplinary approach in which biotechnological progress will be accompanied by advances in process engineering.

Stephane C. Marie-Rose, Alexis Lemieux Perinet and Jean-Michel Lavoie

Industrial Research Chair on Cellulosic Ethanol Department of Chemical and Biotechnological Engineering Universite de Sherbrooke, Sherbrooke, Quebec

Canada

1. Introduction

Reducing greenhouse gas emissions, rising energy prices and security of supply are reasons that justify the development of biofuels. However, food prices recorded in 2007 and 2008 affected more than 100 million of people that became undernourished worldwide (Rastoin, 2008) The food crisis has been caused by several factors: underinvestment in agriculture, heavy speculation on agricultural commodities and competition of biofuels vs. food. It is estimated that by 2050, it will be essential to increase by 50% the food production to support the 9 billion people living on the planet (Rastoin, 2008).

Recycling the carbon from residual waste to produce biofuels is one of the challenges of this new century. Several companies have been developing technologies that are able to transform residual streams into syngas, which is subsequently converted into alcohols. "Green" ethanol plays an important role in reducing dependency toward petroleum and providing environmental benefit, through its role in the fuel additive market. Ethanol is an oxygenate and also serves as an octane enhancer. The waste-to-syngas approach is an alternative to avoid the controversy food vs. fuel whilst reducing landfills and increasing carbon recuperation. Using this approach, yields of ethanol produced are above 350 liters/dry tonne of feedstock entering the gasifier (Enerkem’s technology is taken as example). Residual heat, also a product of the process, is used in the process itself and, as well, it can be used for outside heating or cooling. Enerkem Inc. is moving the technology from bench scale, to pilot, to demo to commercial implementation (a 12,500 kg/h of sorted and biotreated urban waste, is being constructed in Edmonton, Alberta). Economics of the process are favorable at the above commercial capacity, given the modular construction of the plant, reasonable operational costs and a tipping fee for the residue going into the gasifier.

The first part of this chapter will present feedstock preparation, gasification and gas conditioning. The characteristics of the heterogeneous feedstock will determine its performance during gasification for syngas production whose composition has the appropriate H2/CO ratio for downstream synthesis. The second part of the chapter will be directed at the methanol synthesis in a three-phase reactor using syngas. The third and last part of the chapter will focus on the catalytic steps to convert methanol into bio-ethanol.

1.3 Need for pre-treatment

Upon densification, many agricultural biomass materials, especially those from straw and stover, result in a poorly formed pellets or compacts that are more often dusty, difficult to handle and costly to manufacture. This is caused by lack of complete understanding on the natural binding characteristics of the components that make up biomass (Sokhansanj et al., 2005). The natural binding characteristics of lignocellulosic biomass can be enhanced by modifying the structure of cellulose-hemicellulose-lignin matrix by application of pre­processing and pre-treatment methods (Sokhansanj et al. 2005). It is postulated that by disrupting the lignocellulosic matrix of biomass materials via application of various chemical, physico-chemical (steam explosion, microwave, and radio frequency heating), and biological pre-treatment, the compression and compaction characteristics can be improved (Shaw 2008; Kashaninejad and Tabil, 2011). When high molecular amorphous polysaccharides are reduced to low molecular components, the polymer becomes more cohesive in the presence of moisture (Chen et al., 2004). The cellulose-hemicellulose-lignin matrix can be broken down to smaller amorphous molecules through acid or alkaline hydrolysis as well as through steam explosion (Ladisch, 1989; Vlasenko, 1997). Alkaline or acid solutions are often used for pre-treatment of biomass and the effect of pre-treatment depends on the lignin content of biomass. When biomass is treated with dilute alkaline solution, the internal surface area of the material is increased by swelling. Swelling causes a decrease in the degree of polymerization, separation of structural linkages between lignin and carbohydrates and disruption of the lignin structure (Fan et al., 1987). Increased moisture content resulting from chemical and enzymatic treatments is a problem, as the treated biomass has to be dried prior to densification. Steam explosion results in the hemicelluloses being hydrolyzed and water soluble, the cellulose is slightly depolymerized, the lignin melts and is depolymerized, which aid in binding particles together during densification. Zandersons et al. (2004) stated that activation of lignin and changes in the cellulosic structure during the steam explosion process facilitate the formation of new

chemical bonds. Lam et al. (2008) reported that the quality (durability) of compacts produced from steam exploded sawdust was 20% higher than non-treated sawdust.