The hydrogen feed-rate is another important parameter as it also defines hydrogen partial pressure depending on the hydrogen consumption of each application. It actually favours both heteroatom removal and saturation re­action rates. However, as hydrogen cost defines the overall unit operating cost, hydrogen feed-rate is normally optimized depending on the system requirements. Furthermore the use of renewable energy sources for hydro­gen production is also envisioned as a potential cost improvement option.

5.2.1 CATALYST CHARACTERIZATION

The silica sulfuric acid (SSA), prepared by reacting silica gel with chlo — rosufonic acid in dichloromethane was obtained as a white solid in 98% yield. Table 1 summarizes the physical properties (surface area, pore size, pore volume and acidity amount) as well as chemical compositions of SSA and other four catalysts. The specific surface area was calculated using the BET equation. The total pore volume was determined at 77K for 300 min and also the average pore diameter were was calculated using the Barrett-Joyner-Halenda (BJH) method. The amount of H+ was calculated by titration of catalyst samples in water with standard sodium hydroxide (0.495M). These results show that SSA have a good specific surface area than the three ion exchange resins and high pore volume than Cs25/K10. This might be a reason for high catalytic performance of the SSA catalyst in the experimental conditions. Negligible decreases in pore volume, sur­face area and pore diameter of once used SSA catalyst (Table 1) displayed its good reusability.

Table 2 summarizes its typical IR absorptions and their assignments. The strong broad absorption bands from 1000 to 1100 cm-1 correspond to Si-O-Si bridge stretching vibrations (1097 and 1065 cm-1) in silica [23]. The peak at ca. 971 cm-1 is associated with Si-OH stretching vibrations in silica. Bands appearing at ca. 852 and 886 cm-1 were assigned to the sym­metrical and asymmetrical S-O stretching, respectively [24]. The peak at ca. 1178 cm-1 is the asymmetric S=O stretching vibration, while S=O sym­metrical stretching vibrations lies at 1010-1080 cm-1, overlapped by Si-O stretching bands [24]. The strong broad absorption at about 3200-3500 cm-1 is due to hydrogen bonded — OH in SSA. Characteristic IR absorp­tions of Cs25/K10 are also summarized in Table 2. The IR bands at ca. 1075 cm-1, 1032 cm-1 and 982 cm-1 were due to P-O in the central tetrahe­dron, K10 clay and terminal W=O, respectively. The peaks at ca.886 and 790 cm-1 (asymmetric W-O-W vibrations) are associated with the Keggin polyanion [18].

a All the characteristics of the three resin catalysts were provided by the manufacturer; NA: not available; The corresponding characteristics of once used SSA (washed 3 times with acetone, dried in an oven at 105 °C for 30 min prior to test) are shown in parentheses as bold italic type.

As mentioned, CO2 can be used as raw material for the synthesis of sev­eral chemicals [99]. Moreover, if CO2 is concentrated or separated by a membrane system exhibiting high CO2 permeation and permselectivity, this open up the possibility to develop a continuous process of membrane reaction to simultaneously capture and chemically convert CO2. For exam­ple, if the membrane is able to separate CO2 at intermediate and even high temperatures, it can be used for the design of a membrane reactor for the production and purification of hydrogen and syngas. Syngas is a gaseous fuel with a main chemical composition of CO, H2, CO2, and CH4. Syngas can be used as feedstock for the synthesis of several other clean fuels such as H2, methanol, ethanol, diesel and other hydrocarbons synthesized via the Fischer-Tropsch process [100-104].

Among the different processes for the synthesis of syngas and hydro­gen, CO2 methane reforming Eq. (11) and the water-gas shift reaction (WGS) Eq. (12) are the most promising options.

CH4 + CO2 ~ 2CO + 2H2 (11)

CO + H2O ~ CO2 + H2 (12)

Figure 6 schematizes the membrane reactor concept considering the two reactions described above. Figure 6A shows a membrane reactor for dry reforming of methane to produce syngas at temperatures between 700 and 800 °C. Figure 6B illustrates the use of ceramic oxide membranes for hydrogen purification by separating the CO2 from water-gas shift products at about 550 °C. Additionally, Figure 6B shows the possibility of using a ceramic sorbent to chemically trap the permeate CO2 and therefore en­hance the CO2 permeation process by reducing the concentration of CO2 in the permeate side.

The editor and publisher thank each of the authors who contributed to this book. The chapters in this book were previously published in various places in various formats. To cite the work contained in this book and to view the individual permissions, please refer to the citation at the begin­ning of each chapter. Each chapter was read individually and carefully selected by the editor; the result is a book that provides a nuanced look at the possibilities of a new generation of biofuels. The chapters included are broken into three sections, which describe the following topics:

• Chapter 1 describes some breakthroughs in analytical tools and synthetic approaches toward improved energy efficiency and catalyst stability.

• As a part of a basic overview of this topic, Chapter 2 looks at a range of processes and applications.

• Again as a part of a basic overview on the book’s topic, Chapter 3 offers insights into the various analytical methods that are useful for evaluating the efficiency of catalytic reactions in the transformation of biomass into usable fuel.

• The authors of Chapter 4 investigate the aqueous-phase routes used for the reactions that convert sugars into liquid hydrocarbons, focusing on the sus­tainability of using a small number of reactors with minimum use of hydro­gen sources from fossil fuels.

• The authors of Chapter 5 select phenol, water, acetic acid, acetaldehyde hydroxyacetone, D-glucose, and 2-hydroxymethylfuran as typical bio-oil components and mixed them as a synthetic bio-oil, in order to demonstrate some of the competing reaction pathways that occur in bio-oil upgrading by acid-catalyzed alcohol/olefin treatment.

• The authors of Chapter 6 take a novel approach to the problem of high emissions during small-scale biomass production by investigating the prac­tical use of catalytic components in a downdraft wood stove.

• The research in Chapter 7 considers some cross-coupling reactions that use relatively economic nucleophilic partners. The authors propose that this type of catalysis might be useful for extracting some high-value products from bio-oil mixtures, and they indentify several new protocols for cross­coupling.

• The authors of Chapter 8 describe an optimized biphasic system that could aid the development of a simple and cost-effective protocol for the conver­sion of various carbohydrates. Their results offer several advantages over some of the other methodologies, including mild reaction conditions, satis­factory product yields, and a simple isolation process.

• The recyclability experiments in Chapter 9 indicate that sulfonated Periodic Mesoporous Organosilica (PMO) is a reusable and stable option as a cata­lyst in biofuel productions.

• Chapter 10 enhances our understanding of the use of ultrasonic sound waves to accelerate the transesterification process, which could potentially lead to substantial improvement in both batch and continuous production systems, thus making biomass conversion a more sustainable process.

Any planning of analytical procedures should be based on the goals and scope of the study. The following critical steps in an analytical process can be listed: problem definition and formulation of analytical objectives; set­up of an analytical plan; sampling; sample transport and storage; sample pretreatment; analytical determination; data calculation; evaluation of re­sults to see if the objectives are achieved.

It is apparently clear from this list that the actual analytical determina­tion is just one step among the others and sometimes could not even be the crucial one. Moreover, preparation of the samples, pretreatment and evaluation of data could be more demanding or at least time-consuming. Since in catalytic transformation of lignocellulosic biomass often wood or various streams from pulping are used as raw materials, a special atten­tion should be devoted to sampling. Inappropriate sampling could under­mine the value of the whole study, therefore it should be carefully planned. Sampling and sample storage is important since samples may be altered or destroyed due to temperature, light, presence of oxygen, humidity, en­zymes or microbes (bacteria, fungi, etc.). For instance, enzymatic and mi­crobiological attack can happen for samples of fresh wood, wet pulp and paper, sludge, process waters and effluents, while polyunsaturated extrac­tives like abietic acid could be subjected to oxidation.

Wall catalyst based on MMO/Al2O3-foam: As evident from the Table 2, after the catalyst incorporation, the emissions of CO and VOC (Org.-C)

were reduced by 21% and 42% respectively (in comparison to the refer­ence test). Moreover, the dust emissions were also abated by 55%.

Reduction ofpollutants with the integration of wall catalysts and heat reflecting plate: In order to lower the emissions, the temperature of wall catalysts in the lower combustion chamber was increased by placing a heat reflecting plate (made of vermiculite) in front of the door in the lower combustion chamber (Table 3).

Integration of the MMO/a-Al2O3 catalyst synthesized through Tech­nique 1: After recording positive results concerning emission control by using a suitable catalyst, the active phase of mixed metal oxide (as used in previous experiments) was brought onto the aluminium oxide foam through a novel technique, which is termed here as “Technique 1” (de­scribed in the section 2.2).

As can be seen from the Table 4, the emissions of CO and Org.-C were reduced by 58%, clearly indicating the suitability of both the active phase and the corresponding synthesis route.

Integration of the mixed metal oxide/a-Al2O3 catalyst synthesized through Technique 2: On experimental basis, another technique, “Technique 2” (de­scribed in the section 2.2), has been adopted to observe the suitability of the procedure regarding better oxidation activity of the catalyst.

As evident from the Table 5, the selected synthesis route was not proved to be fruitful, as emission values were higher than using “Tech­nique 1” (Table 6).

Aging behavior of the wall catalyst MMO/a-AfO3: For the determina­tion of the thermal and chemical deactivation of the catalyst, it was aged by fitting into a downdraft stove and subjected to real operating conditions for 630 h (equal to one heating period). The longterm/ aging experiments were planned in such a way that the catalyst was exposed to real operating conditions for three weeks (except the first aging cycle was 6 weeks) and after that immediately tested for its activity. Shortly after, the catalyst was again subjected to a long-term experiment for three weeks before being analyzed again for its stability. The results have indicated that, as shown in Table 7, the catalyst showed initially quite a promising oxidation of pollutants namely, carbon monoxide, volatile organic compounds and dust (particulate matter). This behavior can be attributed to the thermal activa­tion of the catalyst caused by the diffusion of active phase species into the support material, resulting into the synthesis of more active catalytic phase [5]. However, as clear from Table 7, the activity of the catalyst dwindled with the passage of time. This can be possibly due to the poisoning of the active phase on the support material. However, there is so far no evi­dence for the provided assumptions as catalyst characterization (e. g. XRD, XPS) is planned to be done at the end of the aging experiments (after the fifth cycle).

Aging behavior of the wall catalyst synthesized through Technique 2: In order to get verification about thermal activation in case of mixed metal oxide catalyst, another long-term/aging experiment was performed with a selected wall catalyst, as tested earlier (see section 3.3.4), where the catalyst was exposed to real conditions in the stove for about 4.5 h. As can be seen from the Table 8, there is quite a substantial amount of reduction in the emissions. The emissions of CO and VOC (Org.-C) were reduced by 62% and 77% respectively. Clearly, there is a thermal activation ef­fect which can be observed in regard to the selected MMO/Al2O3 cata­lyst. However, like pointed out earlier, a catalyst characterization has to be done in order to support this assumption but it is very obvious that there exists quite a high probability of thermal activation, as can be observed from multiple experimental results.

The catalytic hydrotreatment of liquid biomass converts the contained triglycerides/lipids into hydrocarbons at high temperatures and pressures over catalytic material under excess hydrogen atmosphere. The catalytic hydrotreatment of liquid biomass process is quite similar to the typical process applied to petroleum streams, as shown in Figure 3. A typical cata­lytic hydrotreatment unit consists of four basic sections: a) feed prepara­tion, b) reaction, c) product separation and d) fractionation.

In the feed preparation section the liquid biomass feedstock is mixed with the high pressure hydrogen (mainly from gas recycle with some additional fresh make-up hydrogen) and is preheated before it enters the reactor section. The reactor section consists normally of two hydrotreat­ing reactors, a first guard mild hydrotreating reactor and a second one where the main hydrotreating reactions take place. Each reactor contains two or more catalytic beds in order to maintain constant temperature profile throughout the reactor length. Within the reactor section all as­sociated reactions take place, which will be presented in more detail at a later paragraph.

Light hydrocarbons C1-C4
Isomerization product	Fuel gas
Isomerization
Rotor mate
Naphtha
Hydrotreating
Liquid gas
wyM
Alkylation
Alkylation gasodine
Av at on
I ucls
Straight-run kerozene
Hydrotreating
Straight run diesel
■ ■
Hydrotreatin
Jn ended
Gasoline
Hydrocracking gasoline	Heating
Light Vacuum Gasoil
Hydrocracking
Hydrocracking mid-distillate
Heavy Vacuum Gasoil
	Lubricants
МВМЙ
FIGURE 1: Catalytic hydroprocessing units within a refinery, including distillate hydrotreating and hydrocracking

The reactor product then enters the separator section where, after it is cooled down, it enters the high pressure separator (HPS) flash drum in which the largest portion of the gas and liquid product molecules are separated. The gas product of the HPS includes the excess hydrogen that has not reacted within the reactor section as well as the side products of the reactions including CO, CO2, H2S, NH3 and H2O. The liquid product of the HPS is lead to a second flash drum, the low pressure separator (LPS), for removing any residual gas contained in the liquid product, and subse­quently is fed to a fractionator section. The fractionator section provides the final product separation into the different boiling point fractions that yield the desired products including off-gas, naphtha, kerosene and diesel. The heaviest molecules return from the bottom of the fractionator into the reactor section as a liquid recycle stream.

In order to improve the overall efficiency, a liquid recycle stream is also incorporated, which in essence consists of the heavy molecules that were not converted. The gas product from the HPS and LPS, after being treated to remove the excess NH3, H2S, CO and CO2, is compressed and fed back to the reactor section as a gas recycle stream in order to maintain a high pressure hydrogen atmosphere within the reactor section.

The main pathways for the production of liquid transportation fuels from biomass are shown in Fig. 4. As indicated in previous sections, food crops such as corn grain or sugar cane can be converted into ethanol by fer­mentation processes. Alternatively, second generation ethanol can be pro­duced from lignocellulosic sources by means of pretreatment-hydrolysis and subsequent fermentation of soluble sugars. Butanol, with energy den­sity and polarity similar to gasoline, can be also produced by this route, representing an interesting alternative to overcome many of the technical shortcomings of ethanol as a fuel. [43,44] Interestingly, the microorgan­isms utilized for fermentation can be engineered to convert sugars to liq­uid alkanes instead of alcohols. [45] This new technology could achieve improvements over classical fermentation approaches, because hydrocar­bons separate spontaneously from the aqueous phase, thereby avoiding poisoning of microbes by the accumulated products and facilitating sepa­ration/ collection of alkanes from the reaction medium.

Vegetable oils, obtained from food sources such as soybeans, palm or sunflower, can serve as feedstocks for the production of first-generation biodiesel through transesterification processes. Since vegetable oils are expensive and compete with food sources, the challenge of the biodiesel industry is to find non-edible sources of lipids. Algae crops are receiv­ing interest in this respect, [46] although the high cost associated with feedstock production is an important barrier, and related technologies are presently at an early stage of development. Green diesel can be produced from plant oils and animal fats by means of deoxygenation reactions under hydrogen pressure in hydrotreating processes. [47,48] This recent technol­ogy has potential in that it can be carried out in existing petroleum refinery infrastructure. [49]

Representative examples of non-food lignocellulosic feedstocks such as forest wastes, agricultural residues like corn stover, or municipal paper wastes are shown in Fig. 4. Apart from their intrinsic recalcitrance, these feedstocks are characterized by a high degree of chemical and structural complexity, and, consequently, technologies for the conversion of these resources into liquid hydrocarbon fuels typically involve a combination of different processes. The methodology most commonly used to overcome lignocellulose complexity involves the transformation of non-edible feed­stocks into simpler fractions that are subsequently more easily converted into a variety of useful products. This approach, similar to that used in conventional petroleum refineries, would allow the simultaneous produc­tion of fuels, power, and chemicals from lignocellulose in an integrated facility denoted as a biorefinery. [50,51] Current technologies for convert­ing lignocellulose to liquid hydrocarbon transportation fuels involve three major routes: gasification, pyrolysis and pretreatment-hydrolysis (Fig. 4). By means of these primary routes, lignocellulose is converted into gaseous and liquid fractions that are subsequently upgraded to liquid hydrocarbon fuels. Thus, gasification converts solid biomass to synthesis gas (syngas), a valuable mixture of CO and H2 which serves as a precursor of liquid hydrocarbon fuels by Fischer — Tropsch (F-T) reactions. This pathway is commonly known as biomass to liquids (BTL). Pyrolysis allows trans­formation of lignocellulosic biomass into a liquid fraction known as bio­oil that can be subsequently upgraded to hydrocarbon fuels by a variety of catalytic processes. The third route involves pretreatment-hydrolysis steps to yield aqueous solutions of C5 and C6 sugars derived from lig — nocellulose. While gasification and pyrolysis are pure thermal routes in which lignocellulose is decomposed with temperature under controlled atmosphere, aqueous-phase processing, in contrast, involves a series of catalytic reactions to selectively convert sugars and important platform chemicals derived from them into targeted liquid hydrocarbon fuels with

molecular weights and structures appropriate for gasoline, diesel and jet fuel applications.

The synthesis of this material was extensively described by our research group [38,46]. A certain amount of EP was first brominated with bromine gas under vacuum for 3 h. The resulting material was then dried at 90 °C for 16 h. Magnesium (0.74 g), iron(III) chloride (0.54 g) and dry tetrahydrofu — ran (THF) (30 mL) were mixed under inert atmosphere and stirred for 30 min at 50 °C. Next, 3-chloro-1-propanethiol (0.22 mL) was added and left to stir for 4 h at room temperature. Subsequently, the solution was added to 0.70 g of dry brominated EP. The resulting mixture was stirred for an ad­ditional 24 h at 40 °C. Then, the solid was filtered and washed several times with THF, 2 mol L-1 HCl, H2O and acetone. Finally, the material was dried at 90 °C for 16 h under vacuum (~0.1 Pa) and denoted as EP^CH^-SH.

Even though liquid biomass is currently being exploited as a renewable feedstock for fuels production, its characteristics are far beyond suitable for its use as fuel. More specifically liquid biomass, just as other types of biomass, has a small H/C ratio and high oxygen content, lowering its heat­ing value and increasing CO and CO2 emissions during its combustion. Moreover liquid biomass contains water, which can cause corrosion in the downstream processing units if it’s not completely removed, or even in the engine parts where its final products are utilized. In addition to the above, liquid biomass has an increased concentration in oxygenated compounds, mainly acids, aldehydes, ketones etc, which not only reduce the heating value, but also decrease the oxidation stability and increase the acidity of the produced biofuels. For all the aforementioned reasons it is impera­tive that liquid biomass should be upgraded and specifically that its H/C should be increased while the water and oxygen removed.

The effectiveness of catalytic hydroprocessing towards improving these problematic characteristics of liquid biomass is presented in Table 1, where the H/C ratio, the oxygen content and density before and after cata­lytic hydrotreatment of basic liquid biomass types are given. The H/C ratio exhibits a significant increase that exceeds 50% in all cases. This is due to the substitution of the heteroatoms by hydrogen atoms as well as in the saturation of double bonds that enriches the H/C analogy. The oxygen con­tent (including the oxygen contained in the water) from over 15%wt can be decreased down to 5wppm. Actually the deep deoxygenation achieved via catalytic hydrotreatment is the most significant contribution of this biomass conversion technology, as it improves significantly the oxidation stability of the final biofuels. Furthermore significant improvement is also observed in the biomass density, which is never below 0.9 kg/l while after hydrotreatment it reduces to values less than 0.8 kg/l

Catalytic hydroprocessing has been proven as the most efficient tech­nology for the upgrading of liquid biomass as it achieves to increase the H/C ratio and to remove oxygen and water. However the effectiveness of this technology is also shown in other parameters. For example the distil­lation curve of raw liquid biomass shows that over 90% of its molecules have boiling points exceeding 600°C and only 5% are within diesel range (220-360°C), while after catalytic hydrotreatment upgrading most of 90% of the product molecules are within diesel range [13].

TABLE 2: Fatty acid composition of most common vegetable oils [14][15] C8:0 C10:0 C12:0 C14:0 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:0/C22:0 C20:1/ C22:1 EU Rapeseed oil 0.0 0.0 0.0 0.0 3.5 1.0 1.5 12.5 15.0 7.5 9.0 50.0 Soybean oil 0.0 0.0 0.0 0.3 8.2 0.5 4.5 25.0 49.0 5.0 7.5 0.0 Sunflower oil 0.0 0.0 0.0 0.0 6.0 0.0 4.2 18.8 69.3 0.3 1.4 0.0 Corn oil 0.0 0.0 0.0 1.0 9.0 1.5 2.5 40.0 45.0 0.0 0.0 1.0 non-EU Palm oil 0.0 0.0 0.0 3.5 39.5 0.0 3.5 47.0 6.5 0.0 0.0 0.0 Peanut oil 0.0 0.0 0.0 0.5 8.0 1.5 3.5 51.5 27.5 0.0 7.5 0.0 Canola oil 0.0 0.0 0.1 0.1 4.7 0.1 1.6 65.9 21.2 5.2 1.2 0.0 Castor oil 0.0 0.1 0.2 10.6 1.4 9.5 29.7 29.7 41.3 3.3 3.8 0.0

In the following sections the basic types of liquid biomass and their corresponding products via catalytic hydrotreatment are presented.