Several research centres, universities and companies have been working for years in the co-processing of renewable raw materials in FCC refining units. In the studies performed by these authors, it has been shown the technical viability of the co-processing of vegetable oils (palm, rapeseed, soybean or sunflower oils), waste cooking oil and animal fats and vacuum gasoil under FCC conditions (Bormann and Tilgner, 1994; Bormann et al., 1993; Buchsbaum et al., 2004; Carlos de Medeiros et al., 1985; Pinho et al., 2007). Not only the operation conditions registered but also the final products obtained after the catalytic cracking reactions are perfectly compatible with the conditions and products usually related to the FCC unit. However, there is a strong effect of the feedstock composition on the cracking products distribution.

Figure 15.6 illustrates the results of the co-processing of pure PO blended with vacuum gasoil in FCC conditions (Melero et al., 2010b). Data clearly show that the production of all gases (dry gas and LPG) is enhanced by the increase of the non-petrol feedstock in the feed. This fact comes from the presence of triglyceride molecules in the initial feedstock, which reduce the concentration of aromatic rings, which tend to be refractory and more difficult to be cracked. However, comparing the results obtained in the experiments performed by different authors, there is an important difference in the olefin gases production. In some studies (Bormann et al., 1993; Couch, 2007; Ramakrishan, 2004), it is claimed that the

15.6 Products yields for catalytic cracking of feedstocks with different content in palm oil. Reaction temperature of 565°C and a catalyst-to-oil ratio of 4 g catalyst/g oil. (a) Palm oil/VGO (wt.%) 0/100, (b) Palm oil/ VGO (wt.%) 30/70, (c) Palm oil/VGO (wt.%) 100/0 (Melero etal., 2010b).

presence of vegetable oils in the feedstock may enhance the olefins production in comparison with a petrol feedstock, and even UOP has patented a process for the production of olefins C2-C5 from renewable raw materials in FCC conditions (Marker, 2007). In contrast, in the work reported by Melero et al. (2010b), the olefinity of LPG is not enhanced by the presence of renewable raw materials in the feedstock, and in the case of the VGO, cracking is even slightly higher (see Table 15.3). Nevertheless, these data are in fair agreement with the increase of aromatic compounds in the liquid effluent as the vegetable oil content increases in the feed stream (see data in Table 15.3). The removal of hydrogen from the hydrocarbon molecules to form water under reaction conditions (high temperature, low pressure and high residence time) yielding olefinic hydrocarbons will suffer subsequent cyclization and hydrogen transfer reactions to form aromatic compounds (Dupain et al., 2007; Melero et al., 2010b).

As observed in Fig. 15.6, the increasing content of triglyceride-based biomass in the feed gradually diminishes the yields towards liquids, this effect being more relevant for LCO and DO fractions as compared with GLN (Melero et al., 2010b). Similar conclusions have been achieved by Bormann et al. (1993). These results are associated with the higher crackability of vegetable oils and animal fats in comparison with the petrol feedstocks. Hence, the gasoline content in the OLP is always enhanced as the percentage of vegetable oil is increased in the initial feedstock (Bormann et al., 1993; Carlos de Medeiros et al., 1985). For example,

Bormann et al. (1993) indicate that the percentage of gasoline in the liquid products rises from 60.3% to 61.1%, when they use rapeseed oil instead of vacuum gasoil in their cracking experiments. Similar results have been obtained by Carlos de Medeiros et al. (1985), whose yield to gasoline in OLP is increased by 8.6 points when they crack soybean oil instead of the typical vacuum gasoil. This better crackability of triglyceride-based biomass is also clearly confirmed by the research group of Melero et al. (2010b) in their gasoline distribution, where the medium (MN; 90-140°C) and heavy (HN; 140-221°C) naphthas yields are gradually reduced with the presence of vegetable oil in the feedstock (see data in Table 15.3).

Several authors have pointed to the reduction of the heavier fractions with the co-processing of renewable raw materials in the FCC unit (Bromann et al., 1993; Couch, 2007; Carlos de Medeiros et al., 1985; Melero et al., 2010b). Carlos de Medeiros et al. (1985) obtained LCO and DO yields ranging from 16.98% to 11.85% and from 9.98% to 3.33%, respectively, when cracking vacuum gasoil and soybean oil in FCC conditions. Similar results have been described by Holmgren et al. (2007), and LCO and DO yields changed from 9.5% to 5.0% and from 5% to 3%, respectively, if they crack a triglyceride-based feedstock instead of vacuum gasoil in the FCC unit. LCO is obtained either by means of the heavier fractions cracking or polymerization reactions. In case of the renewable raw materials based on triglycerides, most of the fatty acids of the initial molecules have a length similar to the hydrocarbons in the LCO range as well as an easier trend to be cracked. Something similar takes place with the DO fraction, whereas in the case of petrol feedstocks, it is mainly referred to the percentage of unconverted feed, and in the case of renewable raw materials, DO is always produced via polymerization reactions of olefins and aromatic rings. Triglycerides will be decomposed in reaction conditions, leading to free fatty acids that are never longer than a C22 (DO fraction is in a range of C18-C30 approximately). Since DO is heavier than LCO, its formation by means of polymerization reactions will be more hindered, and hence this fraction being dramatically reduced with the presence of renewable feedstocks in the feed. Thus, DO yield can be remarkably reduced (even more than a 75%) by the presence of a renewable raw material in comparison with the petrol feedstocks (Fig. 15.6).

Considering that polymerization reactions play a significant role when renewable raw materials are processed in FCC conditions, it is interesting the study of the aromaticity of the final liquid product. The aromaticity of the FCC liquid product is enhanced by the presence of vegetable oils and animal fats in the initial feedstock (Bormann et al., 1993; Carlos de Medeiros et al., 1985; Melero et al., 2010b). Data in Table 15.3 also evidence that the presence of renewable raw materials in the feedstock induces changes in the distribution of aromatic rings. The presence of polyaromatic species in the untreated petrol feedstocks leads to higher yields of these refractory compounds since they remain in the final products. Vegetable oils do not have these heavy compounds in their initial composition. Therefore, the cracking product from a triglyceride-based biomass always has lower polyaromatic content than the cracking product of vacuum gasoil. A different trend is observed for the case of monoaromatic (in the range of gasoline) and diaromatic (in the range of diesel) compounds because, although they are absent in the initial vegetable oils, they are easier to form than polyaromatic compounds, especially in the presence of renewable raw materials in the feedstock (Melero et al., 2010b).

Obviously, in the same way that excessive hydrogen elimination from hydrocarbons would produce a higher yield of aromatic compounds, if the removal of hydrogen continues, an increase in the coke production will be observed (highly favoured in case of the renewable raw materials because of the water formation) (Dupain et al., 2007; Melero et al, 2010b). Therefore, coke production is enhanced with the increase of triglyceride-based biomass in the feedstock (Buchsbaum et al., 2004; Carlos de Medeiros et al., 1985; Melero et al., 2010b; Ramakrishan, 2004), as clearly stated in Fig. 15.6.

Finally, some studies of the co-processing of triglyceride-based feedstocks with different features have been performed under FCC conditions. These preliminary studies indicate that the most saturated vegetable oils and animal fats lead to higher LPG yields and lower yields to liquid products as compared with more unsaturated feedstocks (Melero et al., 2010b). On the other hand, the co-processing of crude and refined vegetable oils might induce some deactivation of the FCC catalyst. Wlaschitz et al. (2004) have reported that the conversion can be reduced to 5.4% when crude feedstock is processed. These data are in agreement with the trend depicted by Chew and Bhatia (2009), who observed a slight decrease in the final conversion from 72.9% to 70.9% when they cracked unblended crude PO and used PO, respectively, under FCC conditions.

Water under the HTL conditions has different roles. It is a reaction medium and can serve as a distribution medium for homogeneous and heterogeneous catalysts. Moreover, water itself has a catalytic role in various acid — or base-catalyzed processes due to its higher degree of ionization at the increased temperature. The presence of water in some organic reactions (including hydrolysis and decarboxylation reactions) can cause a decrease of the activation energy, thus affecting their kinetics.15 Water is also directly involved in chemical reactions under the HTC conditions. Next to hydrolysis, water can oxidize some organic species in both the liquid (e. g. alcohols to ketones) and the gaseous phase (e. g. CO to CO2 in the water-gas shift reaction).

Under HTL conditions, water is a powerful polar organic solvent due to the strong decrease of its dielectric constant with temperature. Water molecules isolate the reaction intermediates and serve as a physical barrier between them (dilution effect, reducing the higher order repolymerization reactions). In this way, the reaction intermediates are stabilized.

Biomass reforming in hot compressed water (T = 230-700°C, pressure high enough to keep water in the liquid/supercritical phase) can convert very wet streams to a gas5,36 without paying a huge energetic penalty for water evaporation. To achieve this, heat exchange between the reactor effluent and the feed stream is essential which requires operation at high pressures.54 Figure 20.7 shows a

conceptual flow sheet of such a process. The efficiency of the heat exchanger is high leading to a feed stream outlet temperature of only 100-150°C below the reactor outlet stream.55 Make-up heat for the reactor can be delivered by e. g. burning of a part of the product gas or exothermic reaction heat in case of methanation. Further promises of the technology are: (i) the product gas is available at high pressure (>200 bar) and thus, for its application, expensive gas compression can be avoided, (ii) the product gas is clean; minerals, metals, and the undesired gases like CO2, H2S, and NH3 (which have a high solubility in compressed water) remain in the water phase and can thus be separated and recovered, (iii) the product gas is not diluted with inert gas, (iv) sequestration of (pure) CO2 seems readily possible.

These promises however go together with a series of problems that need to be solved in the process development. Pumping of biomass slurries to pressures of up to 300 bar is a challenge. The high temperatures and pressures involved put serious demands on the construction materials to be used, especially because corrosion problems are expected. Here separation of functionalities might be a solution: one material to withstand the pressure and another one for the temperature. Heat exchange between the reactor feed and effluent is required to make the process efficient, but heating of biomass slurry is likely to cause fouling and plugging as the biomass starts to decompose already around 200°C. Catalysts, if employed, need to operate under severe and fouling conditions. However, hot compressed water is a good solvent for most organic chemicals and thus especially useful to keep coke precursors dissolved. Ash deposits will cause problems, and an effective ash removal system must therefore be part of the process. At the time of writing several pilot plants are in operation to facilitate the process development. These pilot plants are still moderate in size: maximally 100 kg/hr wet feedstock.

Without catalysis the process suffers from incomplete conversion and an uncontrollable gas distribution.5 Catalysis research for reforming in hot compressed water is discussed below for low (230-400°C) and high (400-700°C) temperature separately. Reviews on reforming of biomass in hot compressed water are those by Matsumura.5 Van Rossum,36 Elliott,55 Peterson,56 Kruze and co-workers.57

Chu et al. (2004) separated tocopherols from PFAD using silica in a stirred batch adsorption reactor. The equilibrium of the adsorption process as a function of the reaction temperature, the agitation rate and the silica mass on tocopherols adsorption onto silica was investigated over a concentration range of tocopherols. A lower reaction temperature led to a higher tocopherols uptake at equilibrium, indicating that the adsorption process in this study was exothermic. The adsorption capacity increased with the rise in agitation rate. However, in this study the maximum adsorption capacity remained unchanged when the silica mass was increased. The thermodynamic parameters of the adsorption process helped in predicting how the retention of vitamin E might vary with a temperature change. However, information on the separation performance, such as tocopherols recoveries, is not available.

Fabian et al. (2009) described a new approach for the separation of a NPLF from SODD using a stirred batch-wise hexane desorption to achieve the same degree of separation as that obtained by a modified Soxhlet extraction that was reported in a previous study by Gunawan et al. (2008). The effects of the operation parameters, such as the silica gel to SODD mass ratio, the solvent volume to SODD mass ratio and the adsorption-desorption temperature on separation, were systematically investigated. Starting with SODD that contains 4% FASEs, 2% squalene, 13% tocopherols and 9% free phytosterols, it was possible to obtain an NPLF enriched with FASEs (19%, recovery 97%) and squalene (9%, recovery 100%). The contents of FFAs, TAGs, tocopherols and free phytosterols remained in the NPLF were 12%, 1%, 5% and 1%, respectively. In addition, the NPLF contained squalene and FAS Es that could be processed further to obtain pure squalene and FASEs as described in the previous work (Gunawan et al., 2008). The batch extraction employed in this study yielded about the same degree of separation as compared to that of modified Soxhlet extraction. However, the advantage of the method of this study is that it can be scaled-up easily.

22.5 Future trends

Economic consideration is a key driving force behind the development of the technologies to process inexpensive biodiesel feedstocks and to recover the minor components.

The purification of minor components from DDs is a complex process that implies multiple steps and techniques. When a desired material is produced industrially, the way of processing affects the cost of production. Therefore, in order to make a process industrially viable, the number of steps has to be reduced. However, their valorization should be considered when the DD from chemical refining is used for the production of biodiesel.

There are different routes (direct conversion or acylglycerol route) to convert the DDs to biodiesel/biofuel, some of which have found industrial application. A pretreatment of the feedstock or post-treatment of the final biodiesel are necessary in order to meet the quality specifications.

A combination of technologies opens broad opportunities to convert low-price lipid resources into biodiesel/biofuel that complies with the EU and ASTM specifications and to valorize minor components for different applications.

In terms of pyrolysis being used to generate a suitable alternative to petroleum products, pyrolysis is seen as one of a family of more environmentally sound products compared to fossil fuel use. The main alternatives to fossil fuels are bioethanol, bio-diesel and bio-(pyrolysis oil). As briefly outlined in the introduction there are advantages and disadvantages of all of these. In economic terms, it is clear that bioethanol currently has a clear advantage over any second generation biofuels with bioethanol from Brazilian sugar cane being within a price range of 0.20-0.30 €/l76 compared to ethanol from lignocellulose or other biofuels which are around 0.80-1.00 €/l.76 Because of the cost of first generation bio-diesels (i. e. from vegetable or other plant oils) where production costs are 0.35-0.65 €/l, bioethanol production has greatly outstripped biodiesel production.77 The rate of growth of both of these is expected to increase as petroleum prices continue to increase but biodiesel has and will continue to rely on legislation and governmental

support.78

One advantage that second generation fuels that are recovered from low cost sources such as wood or waste materials have is that raw material costs are significantly lower than vegetable oils or animal fats.78 The cost of, e. g., rice husks is around 15-20 €/ton.79 The drawback in the use of pyrolysis to obtain usable oil products from cheap feedstocks is the high capital, maintenance and labour costs associated with the technology.79 However, as shown by Islam and Ani, provided large scale plants can be built, pyrolysis can be economic for as-produced pyrolysis oil and catalytically upgraded pyrolysis oil.79 Another advantage of pyrolysis lies in the use of materials that can be grown on relatively poor land. The IEA report data that suggest that by 2030, biofuels will contribute around 7% of transport fuel usage.80 This target can be achieved through conventional ethanol production but will significantly affect land usage with loss of pasture land to, e. g., sugar cane crops.81 This fuel driven use of land must be balanced by growing fears of food security82 and the availability of low value materials grown in non-arable areas can alleviate some of the fears associated with growth of fermentable crops. Pyrolysis also offers a considerable technical advantage as large-scale production of ethanol from lignocellulose is not generally thought possible within the next few years.83 There are now a number of demonstration plants built in the EU and USA, one of the largest being at Bastardo (Umbria) Italy which has a maximum throughput of 650 kg/h and is funded by the EU for research purposes.

There are other technologies for producing energy and bio-oils from waste materials and biomass. These can be grouped into prospective and established technology areas. Amongst the prospective methodologies are microalgal, supercritical fluid techniques and liquefaction. Microalgal production of bio-oils has been known since the early 1950s84 and is still an active area of research.85 Here, algae (microrganisms that convert sunlight, water and carbon dioxide to lipids or triaceylglycerol) can be used to effectively trap CO2 from emissions or organic degradation and can be harvested to yield up to 80% of their weight as oil. However, scale-up remains a problem and prices are not currently competitive with ethanol or plant oils. Supercritical fluids are being explored as potential technologies. They can be used to affect hydrolysis of biomass to a mixture of methane, carbon dioxide, carbon monoxide and hydrogen.86 Supercritical-CO2 is becoming an important industrial solvent (e. g. dry-cleaning, coffee extraction) because its ‘solvency’ can be controlled precisely through pressure. It has been used to extract useful products from biomass directly.87 Liquefaction of biomass is another area of research that has shown some promise but the products are normally quite high in viscosity and usually needs reducing gases such as CO and H2 to be present and this can further increase costs.88

Conventional technologies include (as mentioned above) various established catalyst methods. Combustion remains a proven technique and the combination of catalytic combustion with biomass gasification may afford opportunities to develop both sustainable and environmental friendly energy production.89 The use of fluidised bed gassifiers has been shown to be commercially viable for biomass use as demonstrated by Hamelinck and Faaij.90 The product of the gasification is syn gas (together with char and some methane) which is then used to generate methanol which is a useful fuel with a higher octane rating than petrol. For economy, char and hydrocarbons must also be used and a boiler to capture heat in the combined process alleviates some of the cost burden.90 Leduc et al. have shown that choice of site is all important in operating such plants economically.91 Syn gas can also be used to create petroleum-like fuels via the Fischer-Tropsch process.92,93 The product of the reaction is a distribution of largely aliphatic hydrocarbons. The Fischer-Tropsch process is an engineering challenge taking place at temperatures up to 300°C in pressures of up to 40 atmospheres. The catalysts, either cobalt or iron based, can have limited life and strongly effect the product distribution. Many of the challenges associated with catalysts for use in the high temperature, high hydrocarbon and high pressure environments needed for synthesis of oils via the Fischer-Tropsch process are the same when developing catalysts for catalytic pyrolysis.

Some of the novel designs of gasifiers are shown in Fig. 16.11.

The chemical looping gasifier is a novel concept to produce a product gas rich in hydrogen and free from nitrogen and at the same time facilitate carbon dioxide capture using sorbent and its regeneration to produce a pure stream of carbon dioxide. It consists of two reactors; one is a bubbling fluidized bed gasifier where the biomass is gasified with steam in the presence of sorbent calcium oxide. The carbon dioxide produced during gasification is captured by calcium oxide. The calcium carbonate thus formed moves into another reactor: a regenerator working as a fast bed. The regenerator is heated to a temperature of 950°C. At this temperature, the calcium carbonate calcines to calcium oxide and carbon dioxide. The solid calcium oxide is separated in a cyclone and sent to the gasifier, while

16.11 Novel designs of gasifiers (a), Acharya et al. (2009); (b), Jinhu et al. (2004)).

(Continued)

carbon dioxide is separated for sequestration. A laboratory scale 5 kW unit is being investigated by the authors.

A novel approach of integrating a fluidized bed with an entrained bed has been proposed by Wu et al. (2004). The lower portion of the reactor is the fluidized bed where, under a moderate temperature of 1000°C, coal with higher reactivity will be converted. The unconverted char in fly ash is trapped in the cyclone separator and is then fed into two chambers of entrained flow gasifiers, further converting it into useful gases. The entrained flow chamber is maintained at 1200-1400°C. The fly ash may contain 30-70% of the char. This system can be flexible in adjusting the composition of CO and H2 in the product gas by controlling gasification in the fluidized bed and the entrained bed. An experiment done in a bench scale shows an overall carbon conversion of 95% with a CO and H concentration in the product gas within the range of 78-82%. By adjusting the gasification taking place in fluidized bed and the entrained bed, the H2/CO ratio can be varied from 0.70 to 1.25.

The rotating fluidized bed process is based on a new concept of injecting fluidization gas tangentially in the fluidization chamber. The basic principal is that the drag force is overcome by the centrifugal force. With this method, a more uniform fluidization is obtained at high centrifugal forces. Finally, inter-particle van derWaals forces can be overcome, allowing fluidization of very fine particles, such as cohesive (Geldart group C) micro — and nano-particles. The fluidization gas enters tangentially and leaves from the central chimney.

In a multitubular fixed bed reactor, the catalyst particles are packed into narrow tubes, grouped in bundles and enclosed in an outer shell (see Fig. 19.4). The tube bundles are immersed in water, which abstracts the heat and converts to high

pressure steam. The use of narrow tubes, high syngas velocities and large catalyst particles ensure rapid heat exchange and minimize exothermic temperature rise (Dry, 1996). The increased particle size of the catalyst is also necessary in order to avoid large pressure drops (Sie and Krishna, 1999), a problem encountered with this reactor type. Still, catalytic particles with a large diameter reduce the effectiveness of the material and the overall reaction rate due to intra-particle diffusion limitation.

Overall, the fixed bed reactor choice is easy to operate and scale-up. It can be used over a wide temperature range and the liquid/catalyst separation can be performed easily and at low costs, rendering this reactor type suitable for LTFT. Moreover, in case of syngas contamination with H2S, the H2S is absorbed by the top catalyst layer and does not affect the rest of the bed; thus, no serious loss of activity occurs (Dry, 1996). On the down side, fixed bed reactors are expensive to construct and the high gas velocities required translate to high gas compression costs for the recycled gas feed. Moreover, it is maintenance and labour intensive and has a long down time due to the costly and time-consuming process of periodical catalyst replacement (Tijmensen et al., 2002).

Recent advances in this type of reactor are the multitubular fixed bed reactors applied in the SMDS process for the conversion of syngas from methane in a heavy, waxy FT product (Eilers et al., 1990; Sie et al, 1991). Shell operates such reactors in its GTL plant in Bintulu, with a capacity of approximately 3000 bbl/ day per reactor. This capacity has an order of magnitude higher than previous fixed bed reactors, developed by Lurgi and Ruhrchemie, and is attained due to the specially developed Shell catalyst formulation and reactor design (Geerlings et al, 1999; Sie and Krishna, 1999).

Butanol is of interest as a fuel for internal combustion engines. Butanol has a higher energy density and lower vapour pressure than ethanol, which makes it more attractive as fuel or blending agent. Butanol is produced during fermentation by solvent producing bacteria (e. g. Clostridia acetobutylicum) in a process that is generally referred to as ABE (i. e. acetone, butanol, ethanol fermentation). Production of butanol and acetone from biomass via fermentation started during World War I, but declined in the course of the twentieth century primarily due the lower production cost of non-renewable butanol produced by the petrochemical industry (Lopez-Contreras, 2003). However, with the increasing demand for renewable biofuels there is great renewed interest in fermentative production of butanol. Currently, a number of industrial facilities are producing butanol (Johnson, 2008), although uniquely from starch and sugar feedstocks such as corn and molasses. Production of ABE from lignocellulosic feedstocks (i. e. cellulosic butanol) is currently at the R&D stages. One of the main advantages of cellulosic butanol fermentation is that most solvent-producing bacteria can convert both pentose sugars (a main component of lignocellulose) as well as hexose sugars to butanol. Major challenges in further development of ABE processes at industrial scale are overcoming the low volumetric productivity of the fermentation, which requires development of new microorganisms for ABE fermentation that have a higher tolerance for the end products. In addition, a particular challenge in butanol fermentation is the efficient separation of the three end products acetone, butanol and ethanol (Ezeji et al, 2007). It is expected that with advances in cellulosic ethanol and, in particular, pre-treatment of lignocellulosic biomass, butanol production from lignocellulosic biomass will get further implemented.

Cellulosic hydrogen

Hydrogen is predicted to be an important energy carrier in the future. It can be produced from renewable biomass feedstocks either by thermo-chemical conversion or by biological conversion. The use of microorganisms for biological hydrogen production via fermentation is increasingly attracting attention recently (Hagen, 2006). Carbohydrates, such as sugars, starch or (hemi) cellulose, are the prime substrates for fermentative processes, including biohydrogen. For future sustainability of the energy supply, the utilisation of (hemi)cellulose is of prime interest, as this component is most abundant in crops that can be grown for the purpose of energy supply (de Vrije et al., 2009). In the proposed bioprocess, thermophilic and phototrophic bacteria are employed consecutively, producing clean hydrogen at small scale (Claassen and de Vrije, 2006). The utilisation of a great variety of biomass feedstocks has been studied within the last decade for biohydrogen production, in particular for thermophilic bacteria. Lignocellulosic biomass types that were evaluated for application to bio-hydrogen production include Miscanthus, delignified wood fibres (de Vrije et al., 2009), Sweet Sorghum Bagasse (Panagiotopoulos and Bakker, 2008) and barley straw and corn stalks (Panagiotopoulos et al., 2009). In general, thermophilic bacteria, including Caldicellulosiruptor saccharolyticus and Thermotoga Neapolitana, appeared to be able to simultaneously and completely utilise all soluble monomeric C5 and C6 sugars derived from pre-treated lignocellulosic biomass. In addition, these bacteria may also convert di — and oligosaccharides. Simultaneous and complete substrate utilisation from pre-treated lignocellulosic biomass will add to an energy-efficient process and would be a major advantage in industrial scale production facilities. As with cellulosic ethanol and butanol, advances in pre-treatment of lignocellulosic biomass achieved in the near future will greatly accelerate prospects for producing biohydrogen at the demo — or industrial scale.

Biofuel-driven biorefinery

The costs of lignocellulosic biomass derived advanced biofuels (i. e. ethanol, ABE and hydrogen) produced by biochemical conversion in general are too high to be market competitive without any governmental support. The production of added- value Bio-based Products from process residues like hemicellulose and lignin/ stillage has the potential to significantly increase the market competitiveness of the total biomass-to-products value chain. Currently, a lot of effort is put in the development processes potentially being part of biofuel-driven biorefineries. Examples are technology developments for the conversion of hemicellulose to furfural-derived chemicals and pentoside surfactants; lignin/stillage to phenolics — derived wood adhesives, resins and thermosets; and cellulose to HMF and xylonic acids (Reith et al., 2009).

From many years experience researching the applications of alternative fuels, it is clear that the alternative fuels depend on the design requirements of the prime mover matching the characteristic properties of the fuel used and the characteristic properties of possible alternative fuels. When the designed fuel requirement of the prime mover is matched with the characteristic properties of an alternative fuel, the prime mover will operate as designed. But when the properties of an alternative fuel do not match, the prime mover will operate outside (off design) its designed operating conditions and naturally the output (performance: power, fuel consumption, efficiency, etc., emission: exhaust gas emission, noise, etc., life time) will also be affected.

There are two ways to solve this problem. Firstly the prime mover design requirement for fuel characteristics may be converted (adapted) to match the characteristic properties of the alternative fuel. Alternatively the characteristic properties of the alternative fuel may be converted (adapted) to match the designed fuel requirements of the prime mover. This concept is illustrated in Fig. 23.25. The most important requirement for the interface is that the standard must be met to satisfy requirements of both sides. Which choice to use and how far to convert each will depend on many factors, including location, technical, and economic, social and political aspects. For example in the case of biofuel for a high technology engine which has a design requirement for a high quality fuel, fuel conversion (adaptation) to a vegetable based oil may require transesterification to produce FAME to fulfil the high quality standard of fuel needed. But, for a stationary diesel engine where the operating condition is relatively constant, the required level of fuel quality may be relatively low, so a PPO with a lower production cost may be suitable. However, adapting the engine to use the PPO fuel may require the addition of a fuel heating system, a second fuel tank and a switching system to enable starting of the engine on diesel to warm up the engine and heat the PPO

23.25

The concept of using alternative fuel (AE) on prime mover (PM).

fuel and switch back to diesel before stopping the engine to flush the fuel system with diesel.

Clearly, when an engine designed for a certain fuel is converted to run on an alternative fuel, it is very important to see that the design need of the engine for the characteristic properties of the fuel is matched by the characteristic properties of the alternative fuel. Consequently it is very important to establish effective standards for alternative fuels.

23.3 Conclusions

As the majority of ASEAN countries are located in humid tropical regions, many different plant oils and animal fats are available as sources of biofuel feedstock. Consequently the properties and quality of differing biofuels vary considerably. The use of alternative fuels depends on matching the characteristic properties of the fuel for which the engine was originally designed with the characteristic properties of possible alternative fuels. When the design fuel requirement of the engine closely matches the characteristic properties of the alternative fuel, the engine will operate as designed, whereas if the properties of the alternative fuel do not match, the engine will operate outside (off design) the design operating conditions and performance will be affected.

To solve this problem the engine design requirement for fuel characteristics may be altered or adapted to match the characteristic properties of the alternative fuel or the characteristic properties of the alternative fuel may be adjusted or adapted to match the design fuel requirements of the engine. The requirements of both sides must be satisfied. What choices are made and how far adjustments are made in either respect, depends on many factors, including location, technical, and economic, social and political aspects.

Transition metals and their oxides have well-known ability to crack hydrocarbons96,97 due largely to the dissociative chemisorption of organic materials on their surface.218 They are widely used in the oil industry as hydroprocessing catalysts particularly in the treatment of heavy oil fractions derived from crude oil.206 Hydroprocessing usually consists of three separate processes; hydrotreating (removal of poisons, etc. from the feedstock notably sulphur), hydrogenation (addition of hydrogen across C-C single, double and triple bonds that can lead to molecular dissociation) and hydrocracking. The ability of metal based catalysts to crack large molecules into smaller ones has led to their use in pyrolysis as gasification catalysts for hydrogen production using water (steam reforming).219 Iron and nickel based catalysts have been shown to significantly increase the proportion of gas (notably hydrogen).39 Chromium oxide has also been shown to be highly effective in gasification of sawdust.29 However, against this background of gasification reactions, some transition metal oxide based catalysts have been used for the production of liquid fuels from biomass. Zinc oxide has been used for the pyrolysis of wood sawdust.220 Zinc oxide was found to be a rather gentle catalyst that did not completely dehydrolyse the biomass affecting largely sugars and polysaccharides.220 It did, however, produce stabilised oil.220 Chang et al. have found that alumina supported CoMo and NiMo catalysts were effective materials for production of petroleum products from wood sources.136 The CoMo catalyst produced the greatest yield of light aromatics whilst NiMo produced the highest amount of methane.136

This is as expected since nickel is a more effective cracking catalyst than cobalt. Transition metal catalysts have also been used for the generation of fuel oils from triglycerides (see chapters later in this book). da Rocha Filho et al. found that an alumina supported NiMo catalyst could be used to produce alkanes and alkyl benzenes from a number of vegetable oils.221 Craig and co-workers have similarly shown the effectiveness of transition metals in this area.222

14.7.1 Carbonate derived catalysts

The final group of catalysts used in pyrolysis are the carbonates. Their use is based on the availability and low cost of these minerals (e. g. dolomite — CaMg(CO3)2). This ensures that these catalysts are essentially disposable and expensive regeneration processing is not required. Their primary use has been as gasification catalysts rather than as liquid fuel oil generators.223 For use (the catalysts are pre-calcined to remove carbonate as CO2) and in use, the materials are in oxide form and their activity decreases if carbonate is present.224 Reviews of work can be found under the authorship of Delgado et al.225 and Sutton et al. 226 Because of the relative inactivity of these catalysts, the process temperatures used are significantly greater than for the catalysts described above. Encinar and co-workers have described the catalytic pyrolysis of olive oil waste over dolomite135 and their work is fairly representative of many of these studies. The dolomite derived catalysts show great thermal and mechanical robustness and can be used several times with little sign of performance decrease.135 The yield of hydrogen was seen to increase markedly with temperature (at the cost of a decrease in liquid yield) and amount of catalyst.135 Sodium carbonate has been successfully used in the catalytic pyrolysis of vegetable oils. There is some debate on the production of aromatics using this catalyst. Konwer et al.227 and Zaher and Taman228 suggest that sodium carbonate can yield significant amounts of aromatics from seed oil pyrolysis. These results are somewhat contrary to those of Dandik and Aksoy who found that very little aromatic content was produced.229