1.1 Introduction

Billions of years ago the Earth’s atmosphere was filled with CO2. Thus there was no life on the planet. Life on Earth started with Cyanobacterium and algae. These humble photosynthetic organisms sucked out the atmospheric CO2 and started re­leasing oxygen. As a result, the levels of CO2 started decreasing to such an extent that life evolved on Earth. Once again these smallest organisms are poised to save us from the threat of global warming.

Algae, like corn, soybeans, sugar cane, wood, and other plants, use photosyn­thesis to convert solar energy into chemical energy. They store this energy in the form of oils, carbohydrates, and proteins. The more efficient a particular plant is at converting that solar energy into chemical energy, the better it is from a biodiesel perspective, and algae are among the most photosynthetically efficient plants on earth. A 1-ha algae farm on wasteland can produce over 10 to 100 times of oil as compared to any other known source of oil crop. Algae-based technologies could provide a key tool for reducing greenhouse gas emissions from coal-fired power plants and other carbon-intensive industrial processes.

Algae range from small, single-celled organisms to multicellular organisms, some with fairly complex and differentiated forms. Algae are usually found in damp places or bodies of water and thus are common in terrestrial as well as aquatic envi­ronments. Like plants, algae require primarily three components to grow: sunlight, carbon dioxide, and water. Photosynthesis is an important biochemical process in which plants, algae, and some bacteria convert the energy of sunlight into chemical energy.

Microalgae are fast-growing beasts with a voracious appetite for carbon dioxide. They have the potential to produce more oil per acre than any other feedstock being used to make biodiesel, and they can be grown on land that’s unsuitable for food crops (Demirbas 2009a).

A. Demirbas, M. Fatih Demirbas, Algae Energy DOI 10.1007/978-1-84996-050-2, © Springer 2010

Algae are simple organisms that are mainly aquatic and microscopic. Microalgae are unicellular photosynthetic microorganisms living in saline or freshwater envi­ronments that convert sunlight, water, and carbon dioxide into algal biomass (Ozkurt 2009). They are categorized into four main classes: diatoms, green algae, blue-green algae, and golden algae. There are two main populations of algae: filamentous and phytoplankton. These two species, in particular phytoplankton, increase in numbers rapidly to form algae blooms (Demirbas 2009b). Like higher plants, they produce storage lipids in the form of TAGs. Many species exhibit rapid growth and high productivity, and many microalgal species can be induced to accumulate substan­tial quantities of lipids, often greater than 60% of their dry biomass (Sheehan et al. 1998). Microalgae are very efficient solar energy converters and can produce a great variety of metabolites. Humans have always tried to take advantage of these proper­ties through algal mass culture.

To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable but also capable of sequestering atmo­spheric CO2. Currently, nearly all renewable energy sources target the electricity market, while fuels make up a much larger share of the global energy demand. Biofuels are therefore rapidly being developed. Second-generation microalgal sys­tems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane, and biohydrogen. Biodiesel is cur­rently produced from oil synthesized by conventional fuel crops that harvest the Sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approx. 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for the global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to repre­sent the only current renewable source of oil that could meet the global demand for transport fuels (Schenk et al. 2008).

Producing biodiesel from algae has been touted as the most efficient way to make biodiesel fuel. Algal oil processes into biodiesel as easily as oil derived from land — based crops. The difficulties in efficient biodiesel production from algae lie not in the extraction of the oil but in finding an algal strain with a high lipid content and fast growth rate that is not too difficult to harvest and a cost-effective cultivation system (i. e., type of photobioreactor) that is best suited to that strain.

Algae are the fastest growing plants in the world. Microalgae have much faster growth rates than terrestrial crops. The per-unit area yield of oil from algae is es­timated to be between 18,927 and 75,708 L/acre/year; this is 7 to 31 times greater than the next best crop, palm oil, at 2,404 L/acre/year.

Algae are very important as a biomass source. Different species of algae may be better suited for different types of fuel. Algae can be grown almost anywhere,

Table 6.7 Advantages of biodiesel from algae oil

Rapid growth rates Grows practically anywhere

A high per-acre yield (7 to 31 times greater than the next best crop, palm oil)

No need to use crops such as palms to produce oil A certain species of algae can be harvested daily Algae biofuel contains no sulfur Algae biofuel is nontoxic Algae biofuel is highly biodegradable

Algal oil extracts can be used as livestock feed and even processed into ethanol High levels of polyunsaturates in algal biodiesel are suitable for cold weather climates Can reduce carbon emissions based on where it’s grown

Table 6.8 Disadvantages of biodiesel from algal oil

Produces unstable biodiesel with many polyunsturates Biodiesel performs poorly compared to its mainstream alternative Relatively new technology

even on sewage or salt water, and does not require fertile land or food crops, and processing requires less energy than the algae provides. Algae can be a replacement for oil-based fuels, one that is more effective. Algae consume CO2 as they grow, so they could be used to capture CO2 from power stations and other industrial plant that would otherwise go into the atmosphere. Tables 6.7 and 6.8 show the advantages and disadvantages of biodiesel from algal oil.

Vegetable oil (m)ethyl esters, commonly referred to as biodiesel, are prominent can­didates as alternative diesel fuels. The name biodiesel has been given to transesteri — fied vegetable oil to describe its use as a diesel fuel (Demirbas 2002). There has been renewed interest in the use of vegetable oils for making biodiesel due to its less pol­luting and renewable nature as against the conventional diesel, which is a fossil fuel that will eventually be exhausted. Biodiesel is technically competitive with or offers technical advantages over conventional petroleum diesel fuel. The vegetable oils can be converted into their (m)ethyl esters via a transesterification process in the presence of a catalyst. Methyl, ethyl, 2-propyl, and butyl esters were prepared from vegetable oils through transesterification using potassium or sodium alkoxides as catalysts. The purpose of the transesterification process is to lower the viscosity of the oil. Ideally, transesterification is potentially a less expensive way of transform­ing the large, branched molecular structure of bio-oils into smaller, straight-chain molecules of the type required in regular diesel combustion engines.

Biodiesel is a domestic fuel for diesel engines derived from natural oils like soy­bean oil. It is the name given to a variety of ester-based oxygenated fuel from renew­able biological sources that can be made from processed organic oils and fats. The inedible oils such as jatropha curcas, madhuca indica, ficus elastica, azardirachta indica, calophyllum inophyllum jatropha, neem, pongamia pinnata, rubber seed, mahua, silk cotton tree, tall oil, microalgae etc. are easily available in developing countries and are very economical comparable to edible oils. Biodiesel obtained from waste cooking vegetable oils, tallow fat, and poultry fat have been consid­ered promising options. Waste cooking oil is available at relatively cheap prices for biodiesel production in comparison with fresh vegetable oils.

The biodiesel esters were characterized for their physical and fuel properties in­cluding density, viscosity, iodine value, acid value, cloud point, pure point, gross heat of combustion, and volatility. The biodiesel fuels produced slightly lower power and torque and higher fuel consumption than No. 2 diesel fuel. Biodiesel is bet­ter than diesel fuel in terms of sulfur content, flash point, aromatic content, and biodegradability (Bala 2005).

Most of the biodiesel that is currently made uses soybean oil, methanol, and an alkaline catalyst. The high value of soybean oil as a food product makes production of a cost-effective fuel very challenging. However, there are large amounts of low- cost oils and fats such as restaurant waste and animal fats that could be converted into biodiesel. The problem with processing these low-cost oils and fats is that they often contain large amounts of free fatty acids (FFA) that cannot be converted into biodiesel using an alkaline catalyst (Demirbas 2003).

Biodiesel is an environmentally friendly alternative liquid fuel that can be used in any diesel engine without modification. There has been renewed interest in the use of vegetable oils for making biodiesel due to its less polluting and renewable nature as against the conventional petroleum diesel fuel. If biodiesel is used for engine fuel, this would in turn benefit the environment and local populations.

Microalgae contain oils, or lipids, that can be converted into biodiesel. The idea of using microalgae to produce fuel is not new, but has received renewed attention recently in the search for sustainable energy. Biodiesel is typically produced from plant oils, but there are widely voiced concerns about the sustainability of this prac­tice. Biodiesel produced from microalgae is being investigated as an alternative to conventional crops, such as rapeseed: microalgae typically produce more oil, con­sume less space, and can be grown on land unsuitable for agriculture. However, many technical and environmental issues, such as land use and fertilizer input, still need to be researched and large-scale commercial production has still not been at­tained.

Using microalgae as a source of biofuels could mean that enormous cultures of algae will be grown for commercial production, which would require large quan­tities of fertilizers. While microalgae are estimated to be capable of producing 10 to 20 times more biodiesel than rapeseed, they need 55 to 111 times more nitrogen fertilizer: 8 to 16 tons/ha/year. Such quantities of nitrogen and phosphorus could damage the environment. Additionally, it could limit the economic viability of mi­croalgae. Nitrogen and phosphorus found in algal waste, after the oils have been extracted, must therefore be recycled.

Microalgae contain lipids and fatty acids as membrane components, storage products, metabolites, and sources of energy. Algae present an exciting possibil­ity as a feedstock for biodiesel, especially when you realize that oil was originally formed from algae.

Algal oil is converted into biodiesel through a transesterification process. Oil extracted from algae is mixed with alcohol and an acid or a base to produce the fatty acid methylesters that makes up biodiesel (Chisti 2007).

Many algae are exceedingly rich in oil, which can be converted to biodiesel. The oil content of some microalgae exceeds 80% of dry weight of algae biomass. The use of algae as energy crops has the potential, due to their easy adaptability to growth conditions, of growing either in fresh or marine waters and avoiding the use of land. Furthermore, two thirds of earth’s surface is covered with water, thus algae would truly be renewable option of great potential for global energy needs. Figure 5.1 shows world production of biodiesel from 1980 to 2008.

Possessing approximately identical energy potential with mineral diesel fuel, the bio-diesel engine has a number of essential advantages:

— It is not toxic, contains practically no sulfur or carcinogenic benzene;

— Decays in natural conditions;

— Provides significant reduction in harmful emissions in the atmosphere upon burn­ing, both in internal combustion engines and in technological units;

— Increases cetane number of fuel and its greasing ability, which essentially in­creases the engine performance;

— Has high ignition temperature (more than 373 K), which makes its use rather safe;

— It is derived from renewable resources.

Exergy is defined as the maximum amount of work that can be obtained from a mate­rial stream, heat stream, or work interaction by bringing this stream to environmen­tal conditions. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its environment. Exergy is then the energy that is available to be used. After the system and surroundings reach equilibrium, the exergy is zero. Energy is never destroyed during a process; it changes from one form to another.

Exergy analysis is a relatively new method of thermodynamic analysis that has recently been applied in power and heat technology, chemical technology, and other fields of engineering and science. The exergy method takes into account not only the quantity of materials and energy flows but also the quality of materials and energy flows. The exergy concept is based on both the first and second laws of thermody­namics. The main reason for exergy analysis is to detect and evaluate quantitatively the losses that occur in thermal and chemical processes (Ptasinski 2008).

The development of efficient technologies for biomass gasification and synthesis of biofuels requires the correct use of thermodynamics. Among the different forms of exergy, three forms are the major contributors to total exergy: thermal exergy, work exergy, and exergy of material, which contains chemical and physical exergy components.

Exergy analysis is a convenient tool for the development and optimization of future biomass processes. Biomass gasification followed by synthesis of biofuels seems to be more promising for the medium and longer terms. The conversion effi­ciency of all investigated biomass-to-biofuel routes can be increased by improving the operation of biomass gasifiers, which show the highest exergy losses in all con­sidered processes. The exergetic efficiency of biomass-to-biofuel processes depends not only on the feedstock quality but also on the degree of energy integration in these processes (Ptasinski 2008).

5.4.1 Small Molecules

The microalga Dunaliella salina can contain up to 40% of its dry weight as glycerol. However, the low price of glycerol (as a coproduct of biodiesel production) means that the algal product would not be competitive. Other algal species accumulate high concentrations of proline under conditions of high salinity (Benemann and Oswald 1996).

Although a number of algal strains were investigated for growth and lipid pro­duction properties, the best candidates were found in two classes, Chlorophyceae (green algae) and Bacilliarophyceae (diatoms). Organisms were identified in both classes that showed high productivity, an ability to grow in large-scale culture, and lipid accumulation upon nutrient stress. However, in some ways the diatoms may turn out to be better candidate organisms for biofuel production.

A dozen potential by — and coproducts can be obtained from algae. These are io­dine, algin, mannitol, and lignin-related fraction, the first three being commercial products. The lignin-related fraction was suggested as a feedstock or as a compo­nent for making specialty plastics, adhesives, and timed-release substances such as pharmaceuticals or pesticides (Chynoweth et al. 1993).

Algal organisms are photosynthetic macroalgae or microalgae growing in aquatic environments. Macroalgae, or “seaweeds,” are multicellular plants growing in salt or fresh water. They are often fast growing and can reach sizes of up to 60 m in length (McHugh 2003). They are classified into three broad groups based on their pigmen­tation: (1) brown seaweed (Phaeophyceae), (2) red seaweed (Rhodophyceae), and (3) green seaweed (Chlorophyceae).

Microalgae are microscopic photosynthetic organisms that are found in both ma­rine and freshwater environments. Biologists have categorized microalgae into a va­riety of classes, mainly distinguished by their pigmentation, life cycle, and basic cellular structure. The three most important classes of microalgae in terms of abun­dance are the diatoms (Bacillariophyceae), the green algae (Chlorophyceae), and the golden algae (Chrysophyceae). The cyanobacteria (blue-green algae) (Cyano — phyceae) are also referred to as microalgae. This applies, for example, to Spirulina (Arthrospira platensis and A. maxima). Diatoms are the dominant life form in phy­toplankton and probably represent the largest group of biomass producers on Earth. It is estimated that more than 100,000 species exist.

Microalgae are primitive organisms with a simple cellular structure and a large surface-to-volume-body ratio, which gives them the ability to uptake large amounts of nutrients (Sheehan et al. 1998). The photosynthetic mechanism of microalgae is similar to land-based plants, but, due to their simple cellular structure and to the fact they are submerged in an aqueous environment where they have efficient access to water, CO2, and other nutrients, they are generally more efficient in converting solar energy into biomass (Carlsson et al. 2007). The growth medium must contribute the inorganic elements that help make up the algal cell such as nitrogen, phosphorus, iron, and sometimes silicon (Grobbelaar 2004).

Microalgae can be used for bioenergy generation (biodiesel, biomethane, bio­hydrogen), or combined applications for biofuel production and CO2 mitigation. Microalgae are veritable miniature biochemical factories and appear more photo­synthetically efficient than terrestrial plants (Pirt 1986) and are efficient CO2 fixers (Brown and Zeiler 1993).

The existing large-scale natural sources of algae are bogs, marshes, and swamps — salt marshes and salt lakes. Microalgae contain lipids and fatty acids as membrane components, storage products, metabolites, and sources of energy. Algae contain anywhere from 2 to 40% of lipids/oils by weight. Essential elements include nitro­gen (N), phosphorus (P), iron, and, in some cases, silicon (Chisti 2007). Minimal nutritional requirements can be estimated using the approximate molecular formula of the microalgal biomass: CO0.48Hi.83N0.hP0.0i. This formula is based on data pre­sented by Grobbelaar (2004).

The production of microalgal biodiesel requires large quantities of algal biomass. Macro — and microalgae are currently mainly used for food, in animal feed, in feed for aquaculture, and as biofertilizer. Biomass from microalgae is dried and marketed in the human health food market in the form of powders or pressed in the form of tablets. Aquatic biomass could also be used as raw material for cofiring to produce electricity, for liquid fuel (bio-oil) production via pyrolysis, or for biomethane gen­eration through fermentation. Biomethane can be produced from marine biomass (Demirbas 2006).

7.1 Introduction

Energy needs are increasing continuously because of increases in industrialization and population. The growth of the world’s energy demand raises urgent problems. The larger part of petroleum and natural gas reserves is located within a small group of countries. Today’s energy system is unsustainable because of equity issues as well as environmental, economic, and geopolitical concerns that have implications far into the future. Bioenergy is one of the most important components of greenhouse — gas-emissions mitigation and fossil-fuel replacement (Goldemberg 2000; Dincer 2008). Renewable energy is one of the most efficient ways to achieve sustainable development.

Plants use photosynthesis to convert solar energy into chemical energy, which is stored in the form of oils, carbohydrates, proteins, etc. This plant energy is converted into biofuels. Hence biofuels are primarily a form of solar energy. For biofuels to succeed at replacing large quantities of petroleum fuel, the feedstock availability needs to be as high as possible. There is an urgent need to design integrated biore­fineries that are capable of producing transportation fuels and chemicals.

In recent years, the recovery of liquid transportation biofuels from biorenewable feedstocks has became a promising method. The biggest difference between biore­newable and petroleum feedstocks is oxygen content. Biorenewables have oxygen levels from 10 to 44%, while petroleum has essentially none, making the chemical properties of biorenewables very different from those of petroleum (Demirbas 2008; Balat 2009). For example, biorenewable products are often more polar; some easily entrain water and can therefore be acidic.

There are two global transportation fuels — gasoline and diesel fuel. The main transportation fuels that can be obtained from biomass using different processes are sugar ethanol, cellulosic ethanol, grain ethanol, biodiesel, pyrolysis liquids, green diesel, green gasoline, butanol, methanol, syngas liquids, biohydrogen, algae diesel, algae jet fuel, and hydrocarbons. Renewable liquid biofuels for transportation have recently attracted considerable attention in various countries around the world be-

A. Demirbas, M. Fatih Demirbas, Algae Energy DOI 10.1007/978-1-84996-050-2, © Springer 2010

cause of their renewability, sustainability, widespread availability, and biodegrad­ability, as well as for their potential role in regional development, rural manufactur­ing jobs, and the reduction of greenhouse gas emissions (Demirbas 2008). Trans­portation fuels, both petroleum-based and biorenewable, are given in Figure 7.1.

The term biofuel or biorenewable fuel (refuel) is referred to as solid, liquid, or gaseous fuels that are predominantly produced from biomass. Liquid biofuels being considered the world over fall into the following categories: (a) bioalcohols, (b) veg­etable oils and biodiesels, and (c) biocrude and synthetic oils. Biofuels are important because they replace petroleum fuels. It is expected that the demand for biofuels will rise in the future. Biofuels are substitute fuel sources for petroleum; however, some still include a small amount of petroleum in the mixture. It is generally considered that biofuels address many concerns, including sustainability, reduction of green­house gas emissions, regional development, social structure and agriculture, and supply security. Biofuels, among other sources of renewable energy, are attracting interest as alternative to fossil diesel. With an increasing number of governments now supporting this cause in the form of mandates and other policy initiatives, the biofuel industry is poised to grow at a phenomenal rate (Balat 2007; Demirbas 2002, 2003,2007; Demirbas and Karslioglu 2007; Khoiyangbam 2008; Chhetri and Islam 2008).

Policy drivers for biorenewable liquid biofuels have attracted support for rural development and economic opportunities for developing countries (Keskin 2009). The EU ranks third in biofuel production worldwide, behind Brazil and the USA. In Europe, Germany is the largest and France the second largest producer of biofuels.

The term modern biomass is generally used to describe traditional biomass use through efficient and clean combustion technologies and sustained supply of

biomass resources, environmentally sound and competitive fuels, heat, and elec­tricity using modern conversion technologies. Biomass, as an energy source, has two striking characteristics. First, biomass is the only renewable organic resource to exist in abundance. Second, biomass fixes carbon dioxide in the atmosphere by photosynthesis. Direct combustion and cofiring with coal for electricity pro­duction from biomass holds great promise. Biomass thermochemical conversion technologies such as pyrolysis and gasification are certainly not the most impor­tant options at present; combustion is responsible for over 97% of the world’s bioenergy production. Ethanol and fatty acid (m)ethylester (biodiesel), as well as diesel produced from biomass by Fischer-Tropsch synthesis (FTS), are modern biomass-based transportation fuels. Liquid transportation fuels can be economically produced by biomass-integrated gasification Fischer-Tropsch (BIG-FT) processes. Modern biomass produced in a sustainable way excludes traditional uses of biomass as fuel wood and includes electricity generation and heat production, as well as transportation fuels, from agricultural and forest residues and solid waste. On the other hand, traditional biomass is produced in an unsustainable way and is used as a noncommercial source — usually with very low efficiencies for cooking in many countries. Biomass energy potentials and current use in different regions are given in Table 7.1 (Parikka 2004).

Like a petroleum refinery, a biorefinery uses every component of the biomass raw material to produce usable products. Bio-based products are prepared for economic use by an optimal combination of different methods and processes (physical, chem­ical, biological, and thermal). Therefore, basic biorefinery concepts must be devel­oped. A biorefinery, as a new approach, is a processing plant where biomass feed­stocks are converted and extracted into a spectrum of valuable products. Biorefining refers to fractionating biomass into various separated products that possibly undergo further chemical, biochemical, biological, and thermochemical processing and sepa­ration. The molecules produced by biorefining can be obtained using thermal, chem­ical, mechanical, enzymatic, or microbial processes, and they can be used in trans­port fuels, therapeutics, food additives, or as secondary chemicals with a range of applications. By coproducing chemicals, the production costs of secondary energy carriers (fuels, heat, power) could potentially become more profitable, especially

when bioreflning is integrated into the existing chemical, material, and power in­dustries. Coproduction of bioproducts, materials, chemicals, transportation fuels, power, or heat in technically, economically, and ecologically fully optimized inte­grated bioreflnery systems will be required.

Ethanol is the most widely used liquid biofuel. It is an alcohol and is fermented from sugars, starches, or cellulosic biomass. Most commercial production of ethanol is from sugar cane or sugar beet, as starches and cellulosic biomass usually require expensive pretreatment.

Carbohydrates (hemicelluloses and cellulose) in plant materials can be converted into sugars by hydrolysis. Fermentation is an anaerobic biological process in which sugars are converted into alcohol by the action of microorganisms, usually yeast. The resulting alcohol is ethanol. The value of any particular type of biomass as feedstock for fermentation depends on the ease with which it can be converted into sugars.

Bioethanol is a fuel derived from renewable sources of feedstock, typically plants such as wheat, sugar beet, corn, straw, and wood. Bioethanol is a petrol addi- tive/substitute. It is possible that wood, straw, and even household wastes may be economically converted into bioethanol.

Bioethanol can be used as a 5% blend with petrol under EU quality standard EN 228. This blend requires no engine modification and is covered by vehicle war­ranties. With engine modification, bioethanol can be used at higher levels, for exam­ple, E85 (85% bioethanol). Figure 5.2 shows world ethanol production from 1980 to 2008 (RFA 2009).

Bioethanol can be produced from a large variety of carbohydrates with a general formula of (CH2O)n. Fermentation of sucrose is performed using commercial yeast such as Saccharomyces ceveresiae. The chemical reaction is composed of enzymatic hydrolysis of sucrose followed by fermentation of simple sugars. First, invertase enzyme in the yeast catalyzes the hydrolysis of sucrose to convert it into glucose and fructose. Second, zymase, another enzyme also present in yeast, converts the glucose and the fructose into ethanol.

Glucoamylase enzyme converts the starch into D-glucose. The enzymatic hy­drolysis is then followed by fermentation, distillation, and dehydration to yield an­hydrous bioethanol. Corn (60 to 70% starch) is the dominant feedstock in the starch- to-bioethanol industry worldwide.

Carbohydrates (hemicelluloses and cellulose) in lignocellulosic materials can be converted into bioethanol. The lignocellulose is subjected to delignification, steam explosion, and dilute acid prehydrolysis, which is followed by enzymatic hydrolysis and fermentation into bioethanol. A maj or processing step in an ethanol plant is enzy­matic saccharification of cellulose to sugars through treatment by enzymes; this step requires lengthy processing and normally follows a short-term pretreatment step.

Hydrolysis breaks down the hydrogen bonds in the hemicellulose and cellulose fractions into their sugar components: pentoses and hexoses. These sugars can then

be fermented into bioethanol. The most commonly applied methods can be classified into two groups: chemical hydrolysis (dilute and concentrated acid hydrolysis) and enzymatic hydrolysis. In chemical hydrolysis, pretreatment and hydrolysis may be carried out in a single step. There are two basic types of acid hydrolysis processes commonly used: dilute acid and concentrated acid.

The biggest advantage of dilute acid processes is their fast rate of reaction, which facilitates continuous processing. Since 5-carbon sugars degrade more rapidly than 6-carbon sugars, one way to decrease sugar degradation is to have a two-stage pro­cess. The first stage is conducted under mild process conditions to recover the 5-carbon sugars, while the second stage is conducted under harsher conditions to recover the 6-carbon sugars.

Methanol, also known as “wood alcohol,” is generally easier to find than ethanol. Sustainable methods of methanol production are currently not economically viable. Methanol is produced from synthetic gas or biogas and evaluated as a fuel for in­ternal combustion engines. The production of methanol is a cost-intensive chemical process. Therefore, in current conditions, only waste biomass such as old wood or biowaste is used to produce methanol.

Before modern production technologies were developed in the 1920s, methanol was obtained from wood as a coproduct of charcoal production and, for this reason, was commonly known as wood alcohol. Methanol is currently manufactured world­wide by conversion or derived from syngas, natural gas, refinery off-gas, coal, or petroleum:

2H2 C CO! CH3OH (5.1)

The chemical composition of syngas from coal and then from natural gas can be identical with the same H2/CO ratio. A variety of catalysts are capable of causing the conversion, including reduced NiO-based preparations, reduced Cu/ZnO shift preparations, Cu/SiO2 and Pd/SiO2, and Pd/ZnO (Takezawa et al. 1987; Iwasa et al.

1993).

The conversion of wood into chemicals for the production of most of our synthetic plastics, fibers, and rubbers is technically feasible. Synthetic oils from liquefaction of wood might serve as feedstocks for cracking into chemicals in the same way that crude oil is presently used.

Upgrading of condensed liquid from biomass involves three stages. There are physical upgrading (differential condensation, liquid filtration, and solvent addi­tion), catalytic upgrading (deoxygenating and reforming), and chemical upgrading (new fuel and chemical synthesis).

The bio-oil obtained from the fast pyrolysis of biomass has high oxygen content. Because of the reactivity of oxygenated groups, the main problem of the bio-oil is its instability. Therefore, study of the deoxygenation of bio-oil is needed. In previous

work the mechanism of hydrodeoxygenation (HDO) of bio-oil in the presence of a cobalt molybdate catalyst was studied (Zhang et al. 2003).

The main HDO reaction is represented in Equation 8.1:

-(CH2O)- C H2 ! -(CH2)- C H2O (8.1)

This is the most important route of chemical upgrading. Reaction 8.1 has strong analogies with typical refinery hydrogenations like hydrodesulfurization and hy­drodenitrification. In general, most of the HDO studies have been performed using existing hydrodesulfurization catalysts (NiMo and CoMo on suitable carriers). Such catalysts need activation using a suitable sulfur source, and this is a major drawback when using nearly sulfur-free resources like bio-oil.

Bioflocculation occurs in high-rate ponds. This process involves removing algae from the paddlewheel-mixed ponds and placing them in a quiescent container, where they would spontaneously flocculate and rapidly settle. There are several apparently distinct mechanisms by which algae flocculate and then settle, including “autofloc­culation,” which is induced by high pH in the presence of phosphate and divalent cations (Mg+2 and Ca+2), and flocculation induced by N limitation. Bioflocculation refers to the tendency of normally repulsive microalgae to aggregate in large flocs, which then exhibit a rather high sedimentation velocity. The mechanisms of biofloc­culation involve extracellular polymers excreted by algae, but the details remain to be investigated (Sheehan et al. 1998).

Organic flocculants at about 2 to 6 g/kg and FeCl3 at about 15 to 200 g/kg of algal biomass are required to remove 90% or more of the algal cells. Because of the high cost of the organic flocculants, costs are comparable for both flocculants tested. The polymers can be used in very small amounts without contributing a major cost to the overall process (Sheehan et al. 1998).

Macroalgae have long been used for the production of phycocolloids such as al­ginates, carrageenans, or agars. They make up the major industrial products derived from algae (Radmer 1996; Pulz and Gross 2004). These polymers are located ei­ther in cell walls or within the cells serving as storage materials. A characteristic of marine algae is the abundance of sulfated polysaccharides in their cell walls.