Biodiesel usually costs over 0.5 US$/l, compared to 0.35 US$/l for petroleum-based diesel (Demirba§ et al., 2009). It is reported that the high cost of biodiesel is mainly due to the cost of virgin vegetable oil (Krawczyk, 1996; Connemann & Fischer, 1998). For example, the soybean oil price is currently 1.27 $/l while the palm oil price is 1.18 $/l (World-Bank, 2011). Biodiesel from animal fat is currently the cheapest option (0.4-0.5 US$/l), while the traditional transesterification of vegetable oil is, at present, around 0.6-0.8 US$/l (Bender, 1999). Zhang et al. (2007) stated that there is no global market for ethanol. Within the reasons for this, crop types, agricultural practices, land labour costs, production plant sizes, processing technologies and government policies can be cited. The cost of ethanol production in a dry mill plant currently totals 0.44 US$/l. Corn represents 66% of operating costs while energy (electricity and natural gas) to fuel the production plant represents nearly 20% of operating costs. Nevertheless, ethanol from sugar cane, produced mainly in developing countries with warm climates, is generally much cheaper to produce than ethanol from grain or sugar beet (Bender, 1999). For this reason, in countries like Brazil and India, sugar cane-based ethanol is becoming an increasingly cost-effective alternative to petroleum fuels. On the other hand, ethanol derived from cellulosic feedstock using enzymatic hydrolysis requires much greater processing than from starch or sugar-based feedstock, but feedstock costs for grasses and trees are generally lower than for grain and sugar crops. If targeted reductions in conversion costs are achieved, the total cost of producing cellulosic ethanol in EOCD countries could fall below that of grain ethanol. Estimates show that ethanol in the EU becomes competitive when the oil price reaches 70 US$/barrel, while in the USA it becomes competitive at 50-60 US$/barrel. For Brazil and other efficient sugar producing countries such as Pakistan, Swaziland and Zimbabwe, the competitive ethanol price is much cheaper, between 25-30 US$/barrel. However, anhidrous ethanol, blendable with gasoline, is still more expensive, although prices in India have declined and are approaching the price of gasoline. Although the feedstock costs represent the majority of biofuels’ cost, the production plant size can reduce the final cost of the fuel. Thus, the generally larger USA conversion plants produce biofuels, particularly ethanol, at lower cost than plants in Europe. Production costs are much lower in countries with a warm climate such as Brazil, with less than half the costs of Europe. But, in spite of the reduced costs of production, ethanol from Brazil is competitive with gasoline owing to the huge sugar cane production and the cogeneration of electricity (Demirba§ et al., 2009).

Two main types of processes for production of bio-oils from biomass are flash pyrolysis and hydrothermal conversion, as shown in Fig.1. Both of the processes belong to the thermochemical platform in which feedstock organic compounds are converted into liquid products. An advantage of the thermochemical process is that it is relatively simple, usually requiring only one reactor, thus having a low capital cost. However, this process is non­selective, producing a wide range of products including a large amount of char (Huber & Dumesic, 2006).

The characteristic and technique feasibility of the two thermochemical processes for bio-oil production are compared in table 1. Flash pyrolysis is characterized by a short gas residence time (~1s), atmospheric pressure, a relatively high temperature (450-500 °C). Furthermore, feedstock drying is necessary. Hydrothermal processing (also referred to in the literature as liquefaction, hydrothermal pyrolysis, depolymerisation, solvolysis and direct liquefaction), is usually performed at lower temperatures (300-400 °C), longer residence times (0.2-1.0 hr.), and relatively high operating pressure (5-20 Mpa). Contrary to flash pyrolysis and gasification processes, drying the feedstock is not needed in the hydrothermal process, which makes it especially suitable for naturally wet biomass. However, a reducing gas and/or a catalyst is often included in the process in order to increase the oil yield and quality.

The reaction mechanisms of the two processes are different, which have been studied by many investigators (Demirba§, 2000a; Minowa et al., 1998). The hydrothermal process occurred in aqueous medium which involves complex sequences of reactions including solvolysis, dehydration, decarboxylation, and hydrogenation of functional groups, etc. (Chornet and Overend, 1985). The decomposition of cellulose was studied by Minowa et al. (1998). The effects of adding a sodium carbonate catalyst, a reduced nickel catalyst, and no

catalyst addition in the decomposition of cellulose in hot-compressed water were investigated. They found that hydrolysis can play an important role in forming glucose/oligomer, which can quickly decompose into non-glucose aqueous products, oil, char and gases (Fig. 2). Without a catalyst, char and gases were produced through oil as intermediates. However, in the presence of an alkali catalyst, char production was inhibited because the oil intermediates were stabilized, resulting in oil production. Reduced nickel was found to catalyze the steam reforming reaction of aqueous products as intermediates and the machination reaction. Typical yields of liquid products for hydrothermal conversion processes were in the range of 20-60%, depending on many factors including sustrate type, temperature, pressure, residence time, type of solvents, and catalysts employed (Xu and Etcheverry, 2008).

Fig. 2. Reaction pathway for the hydrothermal processing of cellulose

With flash pyrolysis, the light small molecules are converted to oily products through homogeneous reactions in the gas phase. The principle of the biomass flash pyrolysis process is shown in Fig.3. Biomass is rapidly heated in the absence of air, vaporizes, and quickly condenses to bio-oil. The main product, bio-oil, is obtained in yields of up to 80% wt on dry feed, together with the by-product char and gas (Bridgewater and Peacocke, 2000).

Fig. 3. Reaction pathway for the biomass flash pyrolysis process

4.1 Related research development of flash pyrolysis and hydrothermal process

Flash pyrolysis for the production of liquids has developed considerably since the first experiments in the late 1970s. Several pyrolysis reactors and processes have been investigated and developed to the point where fast pyrolysis is now an accepted, feasible and viable route to renewable liquid fuels, chemicals and derived products. Since the 1990s, several research organizations have successfully established large-scale fast pyrolysis plants. Bridgwater and Peacocke (2000) have intensively reviewed the key features of fast pyrolysis and the resultant liquid product, and described the major reaction systems and processes that have been developed over the last 20 years.

Unlike flash pyrolysis, technological developments in the area of hydrothermal conversion present new ways to turn wastes to fuel. Hydrothermal processing was initially developed for turning coal into liquid fuels, but recently, the technique has been applied to a number of feedstocks, including woody biomass, agricultural residues, and organic wastes (e. g., animal wastes, municipal solid wastes (MSW), and sewage sludge). Table 2 summarizes representative literature data of hydrothermal processing of common types of biomass and the most influential operating parameters. As can be seen from Table 2, organic waste materials are more favourable than woody biomass and agricultural residues for hydrothermal processing, owing to their higher oil yield and the higher heating value of their bio-oil products.

This earlier work was very promising, showing that hydrothermal technology can be used as an efficient method to treat different types of biomass and produce a liquid biofuel. In particular, hydrothermal conversion processes present a unique approach to mitigate the environmental and economic problems related to disposing of large volumes of organic wastes. It not only reduces the pollutants, but also produces useful energy in the form of liquid fuel. Compared with flash pyrolysis, hydrothermal conversion is at an early developmental stage, and the reaction mechanisms and kinetics are not yet fully understood.

There has been interest in the use of virgin plant oils to fuel diesel engines. At least 2,000 oleaginous species, growing in almost all climates and latitudes, have been identified. There are more than 350 plant species that produce oil that could be used to power diesel engines (Goering et al., 1982). The plant oils are made up of 98% triglycerides and small amounts of mono — and diglycerides. There are basically two types of vegetable oils: those in which the majority of fatty acids are in C12 (e. g., palms) and those in which the majority of fatty acids are in C18.

The direct use of plant oils (and/or blends of these oils with fossil fuels) has generally been considered to be unsatisfactory or impracticable for both direct and indirect diesel engines. Obvious problems include their high viscosity (Ramadhas et al., 2005), acidic composition, free fatty acid content, tendency to deposit carbon, tendency for lubricating-oil thickening, and gum formation because of oxidation polymerization during storage and combustion. When blending vegetable oils with fossil diesel fuel, the viscosity can be extensively adjusted. Based on EN 14214 recommendations, the maximum blending rate of most vegetable oils is B30 (30% plant oil/fossil diesel, v/ v) (Abolle et al., 2008). The oil viscosity (because of the presence large triglycerides) can also be reduced by pyrolysis, which produces an alternative fuel for diesel engines (Lima et al., 2004). Using plant oils in blends also significantly increases their cloud points and thus limits their use to climatically compatible countries.

The authors experience in the use of a car with a modified diesel engine is described in this section. The car which engine was adapted to run with SVO is a VW Caddy 2.0 SDI using the parts described in section 4.1.

Table 3 presents the results of a test performed by the authors of this paper with the modified VW Caddy 2.0 SDI after 45000 km of trial. The consumption of this vehicle using diesel is nearly the same as with SVO, as the calorific value of both fuels are almost the same.

Table 3. SVO consumption as fuel.

From the technical data available from Volkswagen, the urban consumption for this vehicle is 7.5 l/100km, the extra-urban is 5.3 l/100km and the combined consumption is 6.1 l/100km. The test carried out with the above-mentioned 70 HP vehicle shows that maintaining an average speed of 70-80 km/h leads to an average consumption of about 6 l/100km. Driving faster, maintaining 120 km/h during long periods of the ride, leads to a consumption of about 9 l/100km.

Microalgae are not the only option to produce biofuels from oily biomass. Multiple prokaryotes and eukaryotes can accumulate high amounts of lipids. But, as occurred with microalgae, not all species are suitable for biodiesel production owing to differences in the kind of storage lipids. Thus, as stated by Waltermann & Steinbuchel (2010), many prokaryotes synthesize polymeric compounds such as poly(3-hydroxybutyrate) (PHB) or other polyhydroxyalkanoates (PHAs), whereas only a few genera show accumulation of triacylglycerols (TAGs) and wax esters (WEs) in the form of intracellular lipid bodies. On the other hand, storage TAGs are often found in eukaryotes, while PHAs are absent, and WE accumulation has only been reported in jojoba (Simmondsia chinensis). All these lipids are energy and carbon storage compounds that ensure the metabolism viability during starvation periods. Similar to the formation of PHAs, TAGs and WE, synthesis is promoted by cellular stress and during imbalanced growth; for instance, by nitrogen scarcity alongside the abundance of a carbon source (Kalscheuer et al., 2004).

The most interesting prokaryote genera in terms of accumulation of TAGs are nocardioforms such as Mycobacterium sp., Nocardia sp., Rhodococcus sp., Micromonospora sp., Dietzia sp., and Gordonia sp, alongside streptomycetes, which accumulate TAGs in the cells and the mycelia. TAGs storage is also frequently shown by members of the gram-negative genus Acinetobacter (although, in this case, WE are the dominant inclusion bodies components) (Waltermann & Steinbuchel, 2010). Within eukaryotes, with the exception of algae, yeasts of the genera Candida (non albicans) (Amaretti et al., 2010), Saccharomyces (Kalscheuer et al., 2004; Waltermann & Steinbuchel, 2010) and Rhodotorula (Cheirsilp et al., 2011) are the most interesting ones to produce biodiesel feedstocks.

Steinbuchel and collaborators have worked on the heterologous expression of the non specific acyl transferase WS/DGAT from Acinetobacter calcoaceticus ADP1 in Saccharomyces cerevisiae H1246 (a mutant strain unable of accumulating TAGs) (Kalscheuer et al., 2004). These authors found that the yeast recovered the ability to accumulate TAGs, as well as fatty acid ethyl esters and fatty isoamyl esters. This finding showed that the Acinetobacter calcoaceticus transferase had a high potential for biotechnological production of a large variety of lipids, either in prokaryotic and eukaryotic hosts. From this basis, as will be discussed in detail in Section 4.3, they worked on Escherichia coli TOP 10 (Invitrogen) and obtained an engineered strain able to produce fatty acid ethyl esters (biodiesel) directly from oleic acid and glucose (Kalscheuer et al., 2006).

Another possibility is combining the biomass obtained from microalgae and yeast, as recently proposed by Cheirsilp et al. (2011). These authors studied a mixed culture of oleaginous yeast Rhodotorula glutinis and microalga Chlorella vulgaris in industrial wastes. The used effluents, including both a seafood processing wastewater and molasses from a sugar cane plant. They found a synergistic effect in the mixed culture. R. glutinis grew faster and accumulated more lipids in the presence of C. vulgaris, that acted as an oxygen generator for yeast, while the microalgae obtained surplus CO2 from yeast. The optimal conditions for lipid production were 1:1 microalga to yeast ratio initial pH of 5.0, molasses concentration at 1%, 200 rpm shaking, and light intensity at 5.0 klux under 16:8 hours light and dark cycles (Cheirsilp et al., 2011).

This microbial transformation of organic matter in soil is mineralisation when organic carbon of organic substances is transformed to CO2 and from mineralised organic matter those mineral nutrients are released that were already contained in organic matter in mineral (ionic) form and those that were in it in organic form. CO2 is an important fertiliser in agriculture; it is the basic component for photosynthetic assimilation, for the formation of new organic matter produced by plants. As plants can take up only nutrients in mineral form (K+, NH+, NO3-, Ca2+, Mg2+, H2PO4-, HPO42-, SO42- etc.) and nutrients in organic form (e. g. protein nitrogen, phosphorus of various organophosphates), it is not accessible to plants, and besides its main function — energy production for the soil microedaphon — the mineralization of organic matter in soil is an important source of mineral nutrients for

plants. It is applicable solely on condition that organic matter in soil is easily mineralisable,

i. e. degradable by soil microorganisms.

5.1 Fuel cells

The fuel cell is the central component of hydrogen cars; it performs the conversion of fuel energy into electricity through proton mobilization. Fuel cells do not have moving parts, they produce only clean water and low-voltage electricity using hydrogen and oxygen, they are not noisy and they are 60% efficient, which is more than internal combustion engines (ICE, 45% efficiency). Laboratory tests indicate that fuel cells have a potential efficiency of 85% or more, which when combined with an 80%-efficient electric motor could make them 2 times more efficient than the direct use of hydrogen in an ICE (Ross, 2006).

Because of the security and cost problems related to infrastructure for hydrogen distribution and storage, ethanol is currently the most convenient alternative for fuel cells. Ethanol can be converted in hydrogen by onboard steam reforming or can be more conveniently used as a proton donor in specific fuel-cell technologies (Lamy et al., 2004). Ethanol-based steam reforming is performed following equation (13) (Velu et al., 2005).

C2H5OH + 3H2O ^ 2CO2 + 6H2 (13)

Deluga et al. (2004) described an onboard system for hydrogen production by auto-thermal reforming from ethanol. Following this system, ethanol and ethanol-water mixtures were converted directly into H2 by catalytic oxidation with ~100% selectivity and >95% conversion and with a residence time on rhodium catalysts of <10 milliseconds. This process has great potential for low-cost H2 generation in fuel cells for small portable applications in which liquid-fuel storage is essential and in which systems must be small, simple, and robust.

Another strategy of energy extraction from simple organic molecules is the glycerol biofuel cell (Arechederra et al., 2007). A biofuel cell is similar to a traditional proton exchange membrane (PEM) fuel cell. Rather than using precious metals as catalysts, biofuel cells rely on biological molecules (such as enzymes) to carry out the reactions. Arechederra et al. (2007) were able to immobilize two oxidoreductase enzymes (pyrroloquinoline quinine — dependent alcohol dehydrogenase and pyrroloquinoline quinine-dependent aldehyde dehydrogenase) at the surface of a carbon anode and to undertake a multi-step oxidation of glycerol into mesoxalic acid with 86% use of the glycerol energy. The bioanodes resulted in power densities of up to 1.21 mW/cm2 using glycerol at concentrations up to 99 %. Because Nafion (the membrane) does not swell under glycerol, the biofuel cell longevity is expected to be higher than the technology used at moment.

Formula 1 has entered the race for optimizing green technologies. From 2009 on, new regulations for Formula 1 have forced the racing teams to recover the energy lost in braking and to use it to propel the car (Trabesinger, 2007). The technology that accomplishes this is called a "kinetic-energy recovery system" (KERS, better known as "regenerative braking"). In a hybrid car with both combustion and electric motors, batteries can be charged either by the ICE or by regenerative braking. The stored electric energy is then used to power the car at low speeds (i. e., in the city traffic) where the ICE efficiency is low because of continuous "stop-and-go" motion.

Fuel cells are still very expensive and currently cost approximately US$ 4,000/kW, which is 100 times more expensive than the cost of ICEs. Fuel-cell stacks must be replaced 4-5 times during the lifetime of current generations of vehicle. It is thus the cost of 4-5 fuel-cell units that must be compared with alternative ICEs (Marcinkoski et al., 2008; Sorensen, 2007).

Therefore, to be competitive with ICEs, the technology must reach the threshold of US$ 30/kW. To address this situation, Honda is selling its first prototype fuel-cell car under a leasing contract in California. BMW has been a pioneer of fuel-cell technology and produced its first hydrogen-car prototype in the 1960s (Hissel et al., 2004). Its current vehicle uses liquid hydrogen with autonomy of up to 386 km. The Ford Motor Company has set a new land-speed record for a fuel-cell powered car (334 km/h).

Despite these pilot experiments, it is likely that urban buses will be among the first large scale commercial applications for fuel cells. This is due to the fact that urban buses are highly visible to the public, contribute significantly to air and noise pollution in urban areas, have few size limitations and are fueled via a centralized infrastructure. Folkesson et al. (2003) reported the following: (i) the net efficiency of a Scania bus powered by a hybrid PEM fuel-cell system was approximately 40%; (ii) the fuel consumption of the hybrid bus was between 42 and 48% lower than that of a standard ICE Scania bus; and (iii) regenerative braking saved up to 28% energy. The bus prototype was equipped with a fuel cell of 50 kW and was fueled with compressed ambient air and compressed hydrogen stored on the roof. All of the fossil fuel options result in large amounts of GHG emissions. Ethanol and hydrogen have the potential to significantly reduce greenhouse gas emissions. However, their use will be highly dependent on pathways of ethanol and hydrogen production. Some of the hydrogen options result in higher GHG emissions than do ICEs running on gasoline. The vehicle options that will be competitive during the next two decades are those that use improved ICEs (including hybrids burning ‘clean’ gasoline or diesel). In the present state of the technology, cars running on hydrogen using onboard reforming of carbon fuel are still ecologically less efficient than are gasoline ICEs. The relatively high energy consumption required to produce hydrogen is expected to affect the geographic distribution of hydrogen — powered cars. One can speculate that such cars would be more appropriate in areas where solar (Eugenia Corria et al., 2006), wind or hydro-electricity power sources are abundant.

All previous presentation and discussion referred to solid nano-particles playing a catalytic role in the obtaining biofuels from algae, landfill methane and biomass. The following segments will examine the practical opportunities that exist for liquid nano-particles or droplets [21]. Consider multifunctional surface active liquid additives, whose lubricity enhancement is achieved via the formation of a monolayer over the surfaces in contact with additized fuel. [22] The treat rate for lubricity is determined by the adsorption saturation concentration. Speculate that the improved detergency and water co-solvency is obtained by the formation of nano emulsions. Also, postulate that the more complete combustion and consequent fuel efficiency increase is the result of the behaviour of nano droplets. These nano droplets result from the surfactant action of the additive in the fuel formulation and the presence of some water in all commercial fuel systems, usually due to evening condensation. Research by Wulff and colleagues [23] has shown that nano emulsions, which the authors call micro emulsions, with fuel (biofuel included most likely), water and surfactant are:

• Thermodynamically stable and

• Microscopically isotropic, and

• Nano-structured (thus, nano emulsions).

Their research concluded that:

• The use of these nano structures with fuel, water and surfactant is able to break the usual trade off between reduction of soot and NOx emissions, by achieving them simultaneously, and

• For the same fuel consumption, higher efficiency is obtained.

Strey and collaborators filed patent applications for what they call micro-emulsions used as fuel [24]. The interpretation offered for the behaviour of stable diesel (and most likely biodiesel)-water-surfactant nano emulsions is as follows:

• The surfactant components — oleic acid and nitrogen containing compounds (amines) — dissolve readily in diesel (and possibly in biodiesel) fuel and bind water to it without stirring;

• The water droplets are as small as a nanometer across, helping stabilize the emulsion

• The result is a "liquid sponge", can be stored indefinitely, like ordinary diesel fuel, without risk of phase separation

• This fuel formulation, when burned, results in the near-complete elimination of soot, and a reduction of up to 80% in nitrogen-oxide emissions

• The surfactant in the formulation also burns without creating emissions beyond water, carbon dioxide and nitrogen

Biomass can be converted to a wide range of useful forms of energy through several processes. As shown in Figure 1, there are two primary biorefinery platforms: sugar and thermochemical. Both platforms can produce chemicals and fuels including methanol, ethanol and polymers. The "sugar platform" is based on the breakdown of biomass into aqueous sugars using chemical and biological means. The fermentable sugars can be further processed to ethanol, aromatic hydrocarbons or liquid alkanes by fermentation, dehydration and aqueous-phase processing, respectively. The residues — mainly lignin — can be used for power generation (co­firing) or may be upgraded to produce other products (e. g., etherified gasoline). In the thermochemical platform, biomass is converted into synthesis gas through gasification, or into bio-oils through pyrolysis and hydrothermal conversion (HTC). Bio-oils can be further upgraded to liquid fuels such as methanol, gasoline and diesel fuel, and other chemicals.

1.1 Fuel structural transformation by pyrolysis

Pyrolysis causes significant changes of physical and chemical properties of fuel particles. Measurements showed a two-fold reduce of bio-fuel particle density in a narrow temperature range. Particle shrinks insignificantly, not more than 30% of its initial size. Since the change of volume does not exceed 20% of initial value, whereas the density decreases greatly, the porosity of particles increases. Due to pore opening the oxygen can reach new surface which was inaccessible earlier (fig. 2).

In the range from 200 to 700оС the specific surface area of wood chip greatly depends on rate of heating, i. e. in case of fast heating it will be one or two orders higher than area during slow heating. Fuel porosity curves (fig. 3) for test samples revealed three steady peaks at 5­50, 100-3000 и 10000-50000 nm in mezzo — and macro porosity domain (5-50000 nm).

The porosity of the first nanolevel is typical of dense fuel particles. For most coals the pores’ average diameter is within 4-10 nm, and more rarely in the range of 30-40 nm. Artificial materials with such pores are highly-scorched activated coals intended for absorption of large molecules such as organic dyes. When a particle enters the furnace the volume of pores of this class will greatly increase due to thermal decomposition of organic compound which is initiated by temperature rise and depressed with pressure increase being a natural regulator of gas formation process in material pores.

Nuclei of pore formation at nanolevel are thinner pores and cracks and it is within their volume that the detachment of gaseous "fragments" of splitting macro molecule of coal material occurs. Initial size of these pores is close to that of gas molecule diameter (0.4-1.0 nm). Cavity degasification process is retarded by molecular repulsion forces hindering the pass through "contracted" points in ultra microcracks and requiring great energy (activation) to overcome them which results in change of the state of dispersion phase. Materials with flexible structure (wood) form swollen-state colloidal systems resistive to both contraction and further expansion. In solid materials (cokes) structures similar to those observed in metals of interstitial compounds can be formed. The speed of gas diffusion from these pores depends on activation energy and temperature level. Gas molecule travel during typical in-furnace process time is compatible with the size of coal macro molecule.

Gas emission from numerous ultra micropores into larger ones acting as collectors continues during the entire particle burning period.

Significant flow resistance due to system porosity results in intra-pore pressure rise (up to saturation pressure) at initial destruction stage and in development of positive flow in the largest pores that hinders external gas inlet into particle pores. Simultaneously mechanical (rupture) stress may develop in the particle. With destruction process transit in its damping stage and intra-pore pressure reduction, pyrolysis gaseous products will be able to react with external oxidizing agent not only on the surface of the particle but inside the latter creating quite favorable conditions for homogeneous intra-pore burning.

As soon as degasification process is completed, free molecule diffusion (Knudsen diffusion) mode is established in nanolevel pores, coupled with convective Stefan’s flow. Based on numerous estimates, for particles from 10 to 1000 pm the degree of such porous space (with specific surface area Sp) participation in reaction insignificantly depends on particle size and at 600 °С it is for oxygen within the range of Sp / Scar < 0.1 (for fast heating cokes) and Sp / Scar < 0.03 (for slow heating cokes).

Pores of the second (medium) peak (dp = 0.1-3 pm) occur in the domain of transition from Knudsen mode to normal diffusion. They provide a better access for oxidant and can participate in reaction in larger volume. In pores of the third peak (dp > 10 pm) diffusion runs similar to that in unrestricted space. These pores constitute insignificant part of internal surface and their contribution to burnout rate is known to be negligible. However, their role is quite significant as they can deliver reagent to joined pores of first and second peaks.

The obtained data show that wood particles and pellets have low-porous structure (S0 < 2 m2/g), charcoal has mesoporous (S0 < 8.6 m2/ g) and seed has dense microporous structure (S0 < 0.01 m2/g). Specific surfaces vary quite significantly in original state but this difference tends to flatten out for products of their thermal treatment. It increases to the third order for

In seed which relates to bio fuels with the highest natural density and occupies intermediate place between wood and fossil coal the first peak pores dominate (more than 65% by volume). They are followed by the third peak pores (25%). Total volume of seed pores (0.045 cm3/ g) is 2,7 times less than that of pellet (0.12 cm3/g) and 27 times less than that of the wood (1.22 cm3/ g). Specific surface area of seeds is two orders lower than that of the wood. After thermal treatment the pore volume of the seed increased 10 folds and there appeared a second peak on the background of the first and the third peaks which is compatible with these two peaks, although their heights increased by one order.

In bio fuels with natural density (wood) the pores of second type dominate, whereas the pores of the first type have not been revealed and volume of the third type is insignificant. Thermal treatment of wood results in slight increase of total pore volume (twice), whereas its structure changes to form larger pores. The height of second peak reduced three times and the height of the third peak increased three times.

In pellet the structure of the wood subjected to sever mechanical processing (crushing, pressing) differs greatly from the original one, forming larger pores with drastic reduction of their original total volume (10 fold reduction). Pore distribution in pellet after thermal treatment is qualitatively identical to original one but the total volume increased 4 times and peaks became twice as high.

Comparison of porosity curves for various fuels shows that thermal treatment of bio fuels with different original structure will flatten out the difference with the formation of common transport pore structure for all fuels which may result in similar burn out rates by volume for their coke residues.