Dimethyl ether (DME or CH3-O-CH3), is a new fuel that has attracted much atten­tion recently. Today DME is made from natural gas, but DME can also be produced by gasifying biomass. DME can be stored in liquid form at 5 to 10 bars pressure at normal temperature. A major advantage of DME is its naturally high cetane number, which means that self-ignition is easier. The high cetane rating makes DME most suitable for use in diesel engines, which implies that the high level of efficiency of the diesel engine is retained when using DME. The energy content of DME is lower than in diesel.

DME can be produced effectively from biosyngas in a single-stage, liquid-phase (LPDME) process. The origin of syngas includes a wide spectrum of feedstocks such as coal, natural gas, biomass, and others. Nontoxic, high-density, liquid DME fuel can be easily stored at modest pressures. The production of DME is very similar to that of methanol. DME conversion to hydrocarbons, lower olefins in particular, has been studied using ZSM-5 catalysts with varying SiO2/Al2O3 ratios, whereas the DME carbonization reaction to produce methyl acetate has been studied over a variety of group VIII metal-substituted heteropolyacid catalysts.

There are small numbers of economic feasibility studies on microalgae oil (Richard­son et al. 2009). Currently, microalgae biofuel has not been deemed economically feasible compared to the conventional agricultural biomass (Carlsson et al. 2007).

Critical and controversial issues are the potential biomass yield that can be ob­tained by cultivating macro — or microalgae and the costs of producing biomass and derived products. The basis of the estimates is usually a discussion of three param­eters: photosynthetic efficiency, assumptions on scaleup, and long-term cultivation issues. For microalgae the productivity of raceway ponds and photobioreactors is limited by a range of interacting issues.

Typical productivity for microalgae in open ponds is 30 to 50 t/ha/y (Benemann and Oswald 1996; Sheehan et al. 1998). Several possible target areas to improve productivity in large-scale installations have been proposed (Benemann and Oswald 1996; Grobbelaar 2000; Suh and Lee 2003; Torzillo et al. 2003; Carvalho et al. 2006).

Harvesting costs contribute 20 to 30% to the total cost of algal cultivation, with the majority of the cost attributable to cultivation expenses. Genetic engineering, development of low-cost harvesting processes, improvements in photobioreactor,
and integration of coproduction of higher-value products/processes are other alter­natives in reducing algal oil production costs (Chisti 2007). The harvested algae then undergo anaerobic digestion, producing methane that could be used to produce electricity.

In commercial photobioreactors, higher productivities may be possible. Typical productivity for a microalga (Chlorella vulgaris) in photobioreactors is 13 to 150 (Pulz 2001). Photobioreactors require ten times more capital investment than open — pond systems. The estimated algal production cost for open-pond systems ($ 10/kg) and photobioreactors ($ 30 to $ 70/kg) is, respectively, two orders of magnitude higher and almost three orders of magnitude higher than conventional agricultural biomass (Carlsson et al. 2007). Assuming that biomass contains 30% oil by weight and carbon dioxide is available at no cost (flue gas), Chisti (2007) estimated the production cost for photobioreactors and raceway ponds at $ 1.40 and $ 1.81 per liter of oil, respectively. However, for microalgal biodiesel to be competitive with petrodiesel, algal oil should be less than $0.48/L (Chisti 2007).

It is useful to compare the potential of microalgal biodiesel with bioethanol from sugar cane, because on an equal energy basis, sugar cane bioethanol can be pro­duced at a price comparable to that of gasoline (Bourne 2007). Bioethanol is well established for use as a transport fuel (Gray et al. 2006), and sugar cane is the most productive source of bioethanol (Bourne Jr. 2007). For example, in Brazil, the best bioethanol yield from sugar cane is 7.5 m3/ha (Bourne Jr. 2007). However, bioethanol has only approx. 64% of the energy content of biodiesel. Therefore, if all the energy associated with 0.53 billion m3 of biodiesel that the USA needs an­nually (Chisti 2007) were to be provided by bioethanol, nearly 828 million m3 of bioethanol would be needed. This would require planting sugar cane over an area of 111 million ha, or 61% of total available US cropland.

Recovery of oil from microalgal biomass and conversion of oil into biodiesel are not affected by whether the biomass is produced in raceways or photobiore­actors. Hence, the cost of producing the biomass is the only relevant factor for a comparative assessment of photobioreactors and raceways for producing microal­gal biodiesel. If the annual biomass production capacity is increased to 10,0001, the cost of production per kilogram reduces to roughly $ 0.47 and $ 0.60 for pho­tobioreactors and raceways, respectively, because of economies of scale. Assuming that the biomass contains 30% oil by weight, the cost of biomass for providing a liter of oil would be something like $ 1.40 and $ 1.81 for photobioreactors and raceways, respectively (Chisti 2007).

Biodiesel from palm oil costs roughly $ 0.66/L, or 35% more than petrodiesel. This suggests that the process of converting palm oil into biodiesel adds about $0.14/L to the price of oil. For palm-oil-sourced biodiesel to be competitive with petrodiesel, the price of palm oil should not exceed $0.48/L, assuming no tax on biodiesel. Using the same analogy, a reasonable target price for microalgal oil is $ 0.48/L for algal diesel to be cost competitive with petrodiesel.

Historically, algae have been seen as a promising source of protein and have been ac­tively cultured by humans for centuries, mainly for food. Growing algae as a source of protein on a large scale in open ponds was first conceived by German scientists during World War II (Soeder 1986). The first attempt in the USA to translate the biological requirements for algal growth into engineering specifications for a large — scale plant was made at the Stanford Research Institute (1948-1950). During 1951, Arthur D. Little made a further advance through the construction and operation of a Chlorella pilot plant for the Carnegie Institute (Burlew 1953). These studies even­tually provided some of the most comprehensive early information on the growth, physiology, and biochemistry of algae.

Under certain growth conditions, many microalgae can produce lipids that are suitable for conversion into liquid transportation fuels. In the late 1940s, nitrogen limitation was reported to significantly influence microalgal lipid storage. Spoehr and Milner (1949) published detailed information on the effects of environmental conditions on algal composition and described the effect of varying nitrogen supply on the lipid and chlorophyll content of Chlorella and some diatoms. Investigations by Collyer and Fogg (1955) demonstrated that the fatty acid content of most green algae was between 10 and 30% DCW. Werner (1966) reported an increase in the cellular lipids of a diatom during silicon starvation. Coombs et al. (1967) reported that the lipid content of the diatom Navicula pelliculosa increased by about 60% during a 14-h silicon starvation period. In addition to nutrition, fatty acid and lipid composition and content were also found to be influenced by a number of other factors such as light (Constantopolous and Bloch 1967; Nichols 1965; Pohl and Wagner 1972; Rosenberg and Gouaux 1967) and low temperatures (Ackman et al. 1968). With the advent of the oil embargo in the early 1970s, a search for alternative energy sources set the stage for an almost 20-year research effort devoted to biofuel production from algal lipids.

The main energy crops are short-rotation woody crops, herbaceous woody crops, grasses, starch crops, sugar crops, forage crops, and oilseed crops. Energy crops are fast-growing, genetically improved trees and grasses grown under sustainable conditions for harvest at 1 to 10 years of age.

Agricultural residues, grasses, algae, kelps, lichens, and mosses are also impor­tant biomass feedstocks in the world. Algae can grow practically wherever there is sufficient sunshine. Some algae can grow in saline water. The most significant feature of algal oil is its yield and, hence, its biodiesel yield. According to some estimates, the yield (per acre) of oil from algae is over 200 times the yield from the best-performing plant/vegetable oils (Sheehan et al. 1998). Microalgae are the fastest growing photosynthesizing organisms. They can complete an entire growing cycle every few days. Approximately 46 tons of oil/ha/year can be produced from diatom algae. Different algae species produce different amounts of oil. Some algae produce up to 50% oil by weight.

Commercial energy crops are typically densely planted, high-yielding crop spe­cies where the energy crops are burnt to generate power. Woody crops such as wil­low and poplar are widely utilized, and tropical grasses such as miscanthus and pennisetum purperium (both known as elephant grass) are receiving more attention from emerging energy crop companies.

Genetic research into dedicated energy crops is still at a very early stage. Cur­rent research is focused on mapping gene sequences and identifying key locations where modifying genetic code could provide significant benefits. Modern biotech­nology can also be used for increasing yields and modifying plant characteris­tics to enhance their conversion into fuels. Genetic engineering may result in en­ergy crops that have a higher percentage of cellulose or hemicellulose and lower lignin content for increasing alcohol production yield, as well as a greater ability to take up carbon in their root systems. Crops could also be modified to produce large quantities of the enzymes that are necessary for feedstock conversion into ethanol. Oilseed crops could be bioengineered to become the source of bio-based lubricants and esterified fatty acids, which are the main ingredient in biodiesel (UN 2006).

Genetic modification of fuel-dedicated crops may raise fears linked to perceived threats of agrobiotechnology to plant life and health, to the conservation of bio­diversity, and to the environment at large. The environmental, sustainability, and public-perception aspects of genetically modified energy crop plantations should be carefully evaluated before widespread production starts (UN 2006).

Hydrocarbons of algal cells have been separated by extraction with organic solvent after freeze-drying and sonicating the algal cells. However, these procedures are not suitable for separation on a large scale because they are costly. Therefore, an effec­tive method is liquefaction for separating hydrocarbons as liquid fuel from harvested algal cells with high moisture content. The direct thermochemical liquefaction can convert wet biomass such as wood and sewage sludge into liquid fuel at around 575 K and 10 MPa using a catalyst such as sodium carbonate (Demirbas 2007). At the same time, the liquid oil can be easily separated (Ogi et al. 1990).

Processes relating to liquefaction of biomass are based on the early research of Appell et al. (1971). These workers reported that a variety of biomass such as agri­cultural and municipal wastes could be converted, partially, into a heavy oil-like product by reaction with water and carbon monoxide/hydrogen in the presence of sodium carbonate. The heavy oil obtained from the liquefaction process is a viscous tarry lump, which sometimes causes troubles in handling. For this purpose, some organic solvents can be added to the reaction system. These processes require high temperature and pressure.

In the liquefaction process, biomass is converted into liquefied products through a complex sequence of physical structure and chemical changes. The feedstock of liquefaction is usually a wet matter. In liquefaction, biomass is decomposed into small molecules. These small molecules are unstable and reactive and can repoly­merize into oily compounds with a wide range of molecular weight distributions (Demirbas 2000).

Liquefaction can be accomplished directly or indirectly. Direct liquefaction in­volves rapid pyrolysis to produce liquid tars and oils or condensable organic va­pors. Indirect liquefaction involves the use of catalysts to convert noncondensable, gaseous products of pyrolysis or gasification into liquid products. Alkali salts, such as sodium carbonate and potassium carbonate, can induce the hydrolysis of cellulose and hemicellulose into smaller fragments. The degradation of biomass into smaller products mainly proceeds by depolymerization and deoxygenation. In the liquefac­tion process, the amount of solid residue increases in proportion to the lignin con­tent. Lignin is a macromolecule, which consists of alkylphenols and has a complex three-dimensional structure. It is generally accepted that free phenoxyl radicals are formed by thermal decomposition of lignin above 500 K and that the radicals have a random tendency to form a solid residue through condensation or repolymerization (Demirbas 2000).

The changes during liquefaction process involve all kinds of processes such as solvolysis, depolymerization, decarboxylation, hydrogenolysis, and hydrogenation. Solvolysis results in micellarlike substructures of the biomass. The depolymeriza­tion of biomass leads to smaller molecules. It also leads to new molecular rear­rangements through dehydration and decarboxylation. When hydrogen is present, hydrogenolysis and hydrogenation of functional groups, such as hydroxyl groups, carboxyl groups, and keto groups, also occur.

Direct hydrothermal liquefaction in subcritical water conditions is a technology that can be employed to convert wet biomass material into liquid fuel. A number of technical terminologies have been used in the literature to refer to this technology, but it essentially utilizes the high activity of water in subcritical conditions in order to decompose biomass materials down into shorter and smaller molecular materials with a higher energy density or more valuable chemicals.

Past research in the use of hydrothermal technology for direct liquefaction of al­gal biomass was very active. Minowa et al. (1995) reported an oil yield of about 37% (organic basis) by direct hydrothermal liquefaction at around 300 °C and 10 MPa fromDunaliella tertiolecta with a moisture content of 78.4%wt. The oil obtained at a reaction temperature of 340 °C and holding time of 60 min had a viscosity of 150 to 330 mPas and a calorific value of 36 kJ/g, comparable to those of fuel oil. It was concluded that the liquefaction technique was a net energy producer from the energy balance. In a similar study on oil recovery from Botryococcus braunii, a maximum yield 64% dry wt. basis of oil was obtained by liquefaction at 300 °C catalyzed by sodium carbonate (Sawayama et al. 1995). Also, Aresta et al. (2005) have compared different conversion techniques, viz., supercritical CO2, organic solvent extraction, pyrolysis, and hydrothermal technology, for the production of microalgal biodiesel. The hydrothermal liquefaction technique was more effective for extracting microal­gal biodiesel than supercritical CO2. From these two studies, it is reasonable to believe that, among the selected techniques, hydrothermal liquefaction is the most effective technological option for the production of biodiesel from algae. Never­theless, due to the level of limited information in the hydrothermal liquefaction of algae, more research in this area is needed.

Liquefaction of B. braunii, a colony-forming microalga, with high moisture con­tent was performed with or without sodium carbonate as a catalyst for conversion into liquid fuel and recovery of hydrocarbons. A greater amount of oil than the con­tent of hydrocarbons in B. braunii (50 wt% db) was obtained, in a yield of 57 to 64wt% at 575 K. The oil was equivalent in quality to petroleum oil. The recovery of hydrocarbons was maximized (>95%) at 575 K (Banerjee et al. 2002).

Methanol and ethanol are not the only transportation fuels that might be made from wood. A number of possibilities exist for producing alternatives. The most promis­ing bio-oxygenated fuels, and closest to being competitive in current markets with­out subsidy, are ethanol, methanol, ethyl-tert-butyl ether, and anti-methyl-tert-butyl ether. Other candidates include isopropyl alcohol, sec-butyl alcohol, tert-butyl alco­hol, mixed alcohols, and tert-amylmethyl ether.

Another possibility for bio-oxygenated fuels is methanol. Methanol could con­ceivably be made from grain, but its most common source is natural gas. The use of natural gas is better for reducing carbon dioxide production in comparison to other fossil fuels, but the use of renewable fuels instead of natural gas would be better still. It can be made from coal or wood with more difficulty and lower efficiency than from natural gas. The cost of making methanol from natural gas is around US$ 0.40 per gallon. It could probably be sold as a motor fuel for about US$ 0.60 to $ 0.70 per gallon. This would be equivalent to gasoline selling at about US$ 0.92 to $ 1.03 per gallon. Methanol was once produced from wood as a byproduct of charcoal manufacture, but overall yields were low. To produce methanol from wood with a significantly higher yield would require production of synthesis gas in a pro­cess similar to that used for production of methanol from coal. Such processes for gasifying wood are less fully developed than the two-stage hydrolysis process for the production of ethanol.

A high octane rating is characteristic of all oxygenated fuels, including ethanol, methanol, ethyl-tert-butyl ether (ETBE), and MTBE. MTBE is made by reacting isobutylene with methanol. ETBE is made by using ethanol instead of methanol. Thus either ethanol or methanol from either grain or wood could be a factor in making tert-butyl ether octane enhancers. The characteristics of ethers are generally closer to those of gasolines than those of alcohols. Ethers are benign in their effect on fuel system materials and are miscible in gasoline; therefore, they are not subject to phase separation in the presence of water, as are methanol and ethanol.

Algae are among the fastest growing plants in the world, and about 50% of their weight is oil. That lipid oil can be used to make biodiesel for cars, trucks, and airplanes. Algae will some day be competitive as a source of biofuel.

Only renewable biodiesel can potentially completely displace liquid fuels derived from petroleum. The economics of producing microalgal biodiesel need to improve substantially to make it competitive with petrodiesel, but the level of improvement necessary appears to be attainable (Demirbas 2009b).

Biodiesel has great potential; however, the high cost and limited supply of re­newable oils prevent it from becoming a serious competitor with petroleum fuels. As petroleum fuel costs rise and supplies dwindle, biodiesel will become more at­tractive to both investors and consumers. For biodiesel to become the alternative fuel of choice, it requires an enormous quantity of cheap biomass. Using new and inno­vative techniques for cultivation, algae may allow biodiesel production to achieve the price and scale of production needed to compete with, or even replace, petroleum (Campbell 2008).

It has been estimated that 0.53 billion m3 of biodiesel would be needed to replace current US transportation consumption of all petroleum fuels (Chisti 2007). Neither waste oil nor seed oil can come close to meeting the requirement for that much fuel; therefore, if biodiesel is to become a true replacement for petroleum, a more productive source of oil such as algal oil is needed (Scott and Bryner 2006; Chisti 2007).

The cost of producing microalgal biodiesel can be reduced substantially by us­ing a bioreflnery-based production strategy, improving capabilities of microalgae through genetic engineering and advances in photobioreactor engineering. Like a petroleum refinery, a biorefinery uses every component of the biomass raw ma­terial to produce usable products (Chisti 2007).

The term biofuel refers to solid, liquid, or gaseous fuels that are predominantly pro­duced from biorenewable or combustible renewable feedstocks. Liquid biofuels will be important in the future because they will replace petroleum fuels. The biggest dif­ference between biofuels and petroleum feedstocks is oxygen content. Biofuels are nonpolluting, locally available, accessible, sustainable, and reliable fuels obtained from renewable sources.

There are two global biorenewable liquid transportation fuels that might replace gasoline and diesel fuel. These are bioethanol and biodiesel. Bioethanol is a good alternative fuel that is produced almost entirely from food crops. Biodiesel has be­come more attractive recently because of its environmental benefits.

Transport is one of the main energy consuming sectors. It is assumed that biodiesel is used as a fossil diesel replacement and that bioethanol is used as a gaso­line replacement. Biomass-based energy sources for heat, electricity, and transporta­tion fuels are potentially carbon dioxide neutral and recycle the same carbon atoms. Due to the widespread availability of biofuels, opportunities in biorenewable fuel technology can potentially employ more people than fossil-fuel-based technology.

Renewable liquid biofuels for transportation have recently attracted considerable attention in different countries around the world because of their renewability, sus­tainability, widespread availability, and biodegradability and the benefits they bring with respect to regional development, rural manufacturing jobs, and reduction in greenhouse gas emissions. Table 5.2 shows the major benefits of biofuels.

Biofuels can be classified based on their production technologies: first-generation biofuels (FGBs), second-generation biofuels (SGBs), third-generation biofuels (TGBs), and fourth-generation biofuels.

The FGBs refer to biofuels made from sugar, starch, vegetable oils, or animal fats using conventional technology. The basic feedstocks for the production of FGBs are often seeds or grains such as wheat, which yields starch that is fermented into

Table 5.2 Major benefits of biofuels

Economic impacts Sustainability

Fuel diversity

Increased number of rural manufacturing jobs

Increased income taxes

Increased investments in plant and equipment

Agricultural development

International competitiveness

Reduced dependency on imported petroleum

Environmental impacts Greenhouse gas reductions

Reduced air pollution Biodegradability Higher combustion efficiency Improved land and water use Carbon sequestration

Energy security Domestic targets

Supply reliability Reduced use of fossil fuels Ready availability Domestic distribution Renewability

bioethanol, or sunflower seeds, which are pressed to yield vegetable oil that can be used in biodiesel. Table 5.3 shows the classification of renewable biofuels based on their production technologies.

SGBs and TGBs are also called advanced biofuels. SGBs are made from nonfood crops, wheat straw, corn, wood, and energy crops using advanced technology. Algae fuel, also called algal oil or TGB, is a biofuel from algae (Demirbas 2007). Algae are low-input/high-yield (30 times more energy per acre than land) feedstocks to produce biofuels using more advanced technology. On the other hand, an emerg­ing fourth-generation is based on the conversion of vegetable oil and biodiesel into biogasoline using the most advanced technology.

There are some barriers to the development of biofuel production. They are tech­nological, economical, supply, storage, safety, and policy barriers. Reducing these barriers is one of the driving factors in the government’s involvement in biofuel and biofuel research and development. Production costs are uncertain and vary with the feedstock available. The production of biofuels from lignocellulosic feedstocks can be achieved through two very different processing routes: biochemical and ther­mochemical. There is no clear candidate for “best technology pathway” between the competing biochemical and thermochemical routes. Technical barriers for enzy­matic hydrolysis include: low specific activity of current commercial enzymes, high cost of enzyme production, and lack of understanding of enzyme biochemistry and mechanistic fundamentals.

The major nontechnical barriers are restrictions or prior claims on use of land (food, energy, amenity use, housing, commerce, industry, leisure or designations as areas of natural beauty, special scientific interest, etc.), as well as the environmental and ecological effects of large areas of monoculture. For example, vegetable oils are a renewable and potentially inexhaustible source of energy with energy content close to that of diesel fuel. On the other hand, extensive use of vegetable oils may lead to other significant problems such as starvation in developing countries. The vegetable oil fuels were not acceptable because they were more expensive than petroleum fuels.

There are few technical barriers to building biomass-fired facilities at any scale, from domestic to around 50 MW, above which considerations of the availability and cost of providing fuel become significant. In general, however, the capacity and generating efficiency of biomass plants are considerably less than those of modern natural-gas-fired turbine systems. The main nontechnical limitations to investment in larger systems are economic, or in some countries reflect planning conditions and public opinion, where a clear distinction may not be made between modern effective biomass energy plants and older polluting incinerator designs.

Serious problems face the world food supply today. The rapidly growing world pop­ulation and rising consumption of fossil fuels is increasing demand for both food and biofuels. This will exacerbate both food and fuel shortages. The human population faces serious food shortages and malnutrition (WHO 2005).

Producing biofuels requires huge amounts of both fossil energy and food re­sources, which will intensify conflicts among these resources. Using food crops such as corn grain to produce ethanol raises major nutritional and ethical concerns. Nearly 60% of humans in the world are currently malnourished, so the need for grains and other basic foods is critical (WHO 2005). Growing crops for fuel squan­ders land, water, and energy resources vital for the production of food for people.

Food versus fuel is the dilemma regarding the risk of diverting farmland or crops for liquid biofuel production to the detriment of the food supply on a global scale. There is disagreement about how significant this is, what is causing it, what the impact is, and what can or should be done about it. Biofuel production has increased in recent years. Some commodities such as corn, sugar cane, and vegetable oil can be used as food or feed or to make biofuels. For example, vegetable oils have become more attractive recently because of their environmental benefits and the fact that they are made from renewable resources. Vegetable oils are a renewable and potentially inexhaustible source of energy, with energy content close to that of diesel fuel. On the other hand, extensive use of vegetable oils may cause other significant problems such as starvation in developing countries.

Several studies have shown that biofuel production can be significantly increased without increased acreage.

Hexane solubles of raw algal cells are shown in Table 5.14. Hexane soluble was obtained at a high yield of 58% of its dry weight and had good fluidity with a vis­cosity of 56 cP and a high heating value (49 MJ/kg). The properties of primary oil are shown in Table 5.15. The yield of the primary oil obtained at 575 K was 52.9% and that at 475 K was 56.5%; these values were slightly lower than the yield of the hexane soluble of the raw algal cells. This suggests that hydrocarbons of raw algal cells were partly converted into dichloromethane insoluble materials such as char (Dote et al. 1994).

The heating value of the primary oil obtained at 575 K was 47.5 MJ/kg and that at 475 K was 42.0 MJ/kg; these values were equivalent to petroleum oil. In particular, the heating value of the primary oil obtained at 575 K was much higher than that of the oil obtained by liquefaction of other biomasses. The viscosity of the primary oil obtained at 575 K was as low (94 cP) as that of the hexane soluble of the raw algal cells. However, the viscosity of the primary oil obtained at 475 K was too high to measure: the primary oil was like rubber. Therefore, the primary oil obtained at 575 K could be used as fuel oil. The oxygen content of the primary oil obtained

at 575 K was slightly higher than that of the hexane soluble of the raw algal cells. However, it was much lower than that of the oil obtained by liquefaction of other biomasses (Dote et al. 1994).

The properties of the hexane soluble of primary oil are shown in Table 5.16. The yield of the hexane soluble of the primary oil obtained at 575 K was 44% and that at 475 K was 39% on a dry-algal-cell basis. This means that the primary oil obtained at 575 K contained 83% of hexane soluble and that at 475 K contained 69% of hexane soluble. The elemental composition of the three hexane solubles was almost equal. The hexane solubles of the primary oil obtained at 575 and 475 K had good fluidity, as did the hexane soluble of the raw algal cells. Despite thermal treatment at high temperature, the hexane soluble of primary oil has properties that are similar to those of the hexane soluble of raw algal cells (Dote et al. 1994). Figure 5.10 shows the liquefaction of algal cells by hexane extraction obtained for primary oil.