PHYSICALCHEMICAL CHARACTERIZATION AND OF DEGRADATION OF OIL FROM CHLORELLA SPECIES
This research project reviews the microalgal Chlorella species as a potential feedstock for biodiesel production, including its cultivation, harvesting, oil extraction, physicochemicalproperties and application of Arrhenius kinetics to evaluate the oxidative stability of the algal oil. In addition, based on the Arrhenius plot, reaction rate constants (K), activation energies (Ea), enthalpies (H), entropies (S) and free energies (G) for oxidative stability of algal oil were
calculated. The results obtained showed that the algal specific growth rate, biomass productivity, lipid productivity and lipid content were 0.006h-1, 0.22g/L/day, 15.16mg/L/day and 5.99 % respectively. The main components of fatty acids are; palmitic acid (C10:0), oleic acid (C18:1), myristic acid (C14:0), palmitoleic acid (C16:1), capric acid (C10:0), myristol(C14:1), and caprylic acid (C8:0). The microalgal lipid was composed of 32.8% unsaturated fatty acid.
Properties such as the iodine value, peroxide value, acid value, free fatty acid value, saponification value, ash content, viscosity, refractive index, relative density, moisture content, flash point and cloud point were 31.24g12/100g, 8.73mEq/kg, 5.54mg/KOH, 2.27%, 167.83mgKOH/g, 1.97%, 12.96mm2/s, 1.245, 0.877g/ml, 0.36%, 2580C and 6.90C respectively.
The algal oil exhibited good physicochemical properties and met most of the specifications given by American Society for Testing and Materials (ASTM) D6751, and European Nations ISO 15607 and EN 14214. Algal oil degraded via at least two different pathways while being heated, i.e., autocatalysis and first order reactions. The activation energies were found to be 17.33KJ/mol and 24.43KJ/mol for the first and second phase of degradation respectively, which is an indication that a higher temperature change was needed to induce a change in the rate of degradation.
BACKGROUND OF THE STUDY
Biodiesel is a mixture of fatty acid methyl esters (FAMEs), which is produced from vegetable oils (edible or non edible) or animal fats (Srivastava and Prasad, 2000). Since vegetable oils may also be used for human consumption, it can lead to an increase in price of food-grade oils, causing the cost of biodiesel to increase and limiting its usage. The potential market for biodiesel far surpasses the availability of plant oils not designated for other markets. For example, to fulfill a 10% target in Europian union (EU) from domestic production, the actual feedstocks supply is not enough to meet the current demand and the land requirements for biofuels production, would be more than the potential available arable land for bio-energy crops (Scarlat et al.,2008). The extensive plantation and pressure for land use change and increase of cultivated fields may lead to land competition and biodiversity loss, due to the cutting of existing forests and the utilization of ecological importance areas (Renewable Fuel Agency, 2008).
To become a more viable alternative fuel and to survive in the market, biodiesel must compete economically with diesel. The end cost of biodiesel mainly depends on the price of the feedstocks that accounts for 60–75% of the total cost of biodiesel fuel (Canakci and Sanli, 2008). Biodiesel from algae may be the only way to produce enough automobile fuels to replace current gasoline usage (Campbell, 1997). Microalgae have much more oil than macroalgae and it is much faster and easier to grow and harvest (Shay, 1993). The use of microalgae can be a suitable alternative because algae are the most efficient biological producer of oil on the planet and a versatile biomass source and may soon be one of the Earth’s most important renewable fuel crops (Campbell, 1997). Their production is not seasonal and can be harvested throughout the year (Chisti, 2007).
Different types of biofuels can be derived from microalgae. These include methane produced by anaerobic digestion of algal biomass (Spolaore et al. 2006), biodiesel derived from microalgal oil (Thomas, 2006) and photo-biologically produced bio-hydrogen (Gavrilescu and Chisti, 2005) . More also, heating is an important part of many industrial applications. However, during heating, lipids (oils) are very sensitive and susceptible to quality changes, caused by chemical instability, that are dependent on both chemical composition and environmental factors (Paul and Mittal, 1997, Tan and Che Man, 1999). Lipid oxidation is one of the major deleterious reactions during heating that markedly affects the quality of vegetable oils (Smouse, 1995). Temperature is one of the main environmental factors that influence the rate of loss of quality. The dependence on temperature of most reactions in industrial production can be
expressed more precisely by the Arrhenius model (Van Boekel, 1996).
A good understanding of lipid oxidation kinetics in oils can improve abilities to formulate products that maintain the existing quality and minimize the appearance of undesirable breakdown products. Kinetic datas are essential for predicting oxidative stability of oils under various heat processing, storage and distribution conditions (Van Boekel, 1996).
PHYSICAL CHEMICAL CHARACTERIZATION AND OF DEGRADATION OF OIL FROM CHLORELLA SPECIES
Algae that contain chlorophyll are photosynthetic microorganisms and convert inorganic carbon, such as carbon dioxide, in the presence of light, water and nutrients to algal biomass (Pokoo-Aikins et al., 2010, Vyas et al.,2010, Demirbas and Faith, 2011). Majority of algae are living in aquatic (saline or freshwater) environments, whereas some of them can be found in other environments such as snow, desert soils, and hot springs (Lee, 2008). They can be either autotrophic or heterotrophic. Autotrophic algae require only carbon dioxide, light, and salts to grow, whereas heterotrophic require an organic source of carbon, like glucose, as well as nutrients (Brennan and Owende, 2010, Pokoo-Aikins et al.,2010,). However, heterotrophic algae are not as efficient as autotrophic algae for oil production (Chisti 2007, Patil et al.,2008). Autotrophic is more favourable as it does not require glucose which is a food source and at the same time fixes CO2, which has positive effect on the environment. Microalgae also can be either phototrophic or chemotrophic. Phototrophic algae use light as an energy source, whereas chemotrophic type use oxidizing compounds (Lee, 2008). Additionally, some algae are capable of behaving in both autotrophic and heterotrophic modes.
These are called mixotrophic algae (Crane and Grover, 2010). Algae range from unicellular to multicellular forms (Pokoo-Aikins et al., 2010). Some
algae are motile while others are non motile. They may exist as colonies, filaments, or amoeboids (Crane and Grover, 2010). Based on their internal structure, algae cells are generally categorized into eukaryotes and prokaryotes. Prokaryotic cells do not have nuclear membrane3 bound DNA, organelles and other membranous structures as eukaryotic cells. As shown in Table 1, almost all the algae are eukaryotes. In eukaryotes, microalgae cells consist of cell wall, plasma membrane, cytoplasm, nucleus, and organelles such as mitochondria, lysosomes, and golgi apparatus ( Barsanti and Gualtieri, 2006 ). As shown in Table 5, microalgae oil contents are usually between 20–50% of dry algae biomass weight. However, many microalgae oil content may exceed 80% of dry algae biomass weight (Spolaore et al., 2006, Meng et al., 2009). Besides, microalgae can grow very fast by doubling biomass in 24 hours, and during exponential growth phase they can double their biomass in about 3.5 hours (Chisti, 2007, Patil et al., 2008, Meng et al., 2009).
Algal species may change their composition, shape, and colour based on growing culture and growth condition such as light, nutrients, temperature, and pH. It is well known that using stressful environment may cause algae to store more oil (Chisti 2007). Unlike glycerolipids that are found in membranes under optimal conditions, many microalgae alter towards accumulations of neutral lipids in form TAG (Triacylglycerol) ( Hu, 2008 ). Microalgae composition is species specific and varies between different microalgae depending on nutrient, salinity, medium pH, temperature, light intensity, and growth phase. In all
cells, lipid and fatty acids are constituents that act as membrane compounds, storage product, metabolites, and energy source. It is known that under stress condition, photosynthesis decreases, therefore, lipid synthesis occurs (Chisti 2007). Most of microalgae-produced oils have fatty acid constitutions similar to most common vegetable oils (Huang et al., 2010).
In general, lipids may include neutral lipids (non polar), polar lipids, wax esters, sterols, and hydrocarbons as well phenyl derivatives ( Naik et al., 2010 ). Major part of non polar lipids of microalgae is triacylglycerides (TAGs) and Free Fatty Acid (FFA). Typically, algae lipids have a carbon number range C12–C22. Most of fatty acids found in algae lipids are straight chain with even number of carbon atoms. They may be either saturated or unsaturated ( Becker, 2004). Table 3 gives a summary of the range of lipid reported in different algae species. Microalgae are classified into four main classes according to their pigment components: diatoms (Bacillariophyceae), green algae (Chlorophyceae), blue-green algae (Cyanophyceae), and golden algae Chrysophyceae) (Khan et al.,2009, Brennan and Owende, 2010, Demirbas and Faith, 2011) Microalgae biomass contains three main components: protein, carbohydrates, and lipids and, therefore, can be used in different applications ranging from food products to biofuels. They are usually used as animal feed (Knauer and Southgate, 1999), human health food (Becker, 2004 ), and as biofertilizer (Chisti, 2007).
Additionally, microalgae can be used for atmospheric CO2 mitigation (Chisti, 2007). It was reported that there are over 40,000 species of algae (Hu, 2008), but only limited number of these have been studied and have commercial significance (Harwood and Guschina, 2009).
Table 3: Biomass productivity, lipid content and lipid productivity of some microalgal strains
cultivated in 250-ml flasks ( Rodolfi et al., 2009 ).
Algal Group Microalgae Habitat Biomass
y (g1—1- d-
Chaetoceros muelleri F&M-M43
C. calcitrans CS 178
P. tricornutum F&M-M40
Skeletnoma costatum CS 181
Skeletonoma sp. CS 252
Thalassionsira pseudonana CS 172
Chlorella sp. E&M-M48
Chlorella sorakiniana IAM-212
C. vulgaris CCAP 211/11b
C. vulgaris F&M-M49
Chlorococcum sp. UMACC112
secnedesmus sp. Dm
Tetraselmis. Suecica F&M-M33
Tetraseslmis sp. F&M-M33
T. suecica F&M-M35
Ellipsoidion sp F&M-M31
Monodus subterraneus UTEX 151
Nannochloropsis sp. CS246
Nannochloropsis Sp. F&M-M26
Nannochloropsis Sp. F&M-M27
Nannochloropsis Sp. F&M-M24
Nannochloropsis Sp. F&M-M29
Nannochloropsis Sp. F&M-M28
Isochrysis sp (T-ISO) CS 177
Isochrysis sp F&M-M37
Prymesiophytes Pavlova salina CS
Pavlova lutheri CS
Red algae Porphyridium cruentum Marine 0.37 9.5 34.8
Photoautotrophic microalgae need light and carbon dioxide as energy and carbon sources, respectively. Thus, photoautotrophic algae cultivation is carried out in the presence of light in open ponds and photobioreactors. Open ponds are the most commonly used systems, and their structure has been well
documented. Open ponds are made of a closed loop with recirculation channels. A paddlewheel that continuously operates is usually used to prevent sedimentation and provide mixing. During daylight, the culture is fed continuously in front of the paddlewheel where the flow begins and
circulates through the loop to the harvesting point. On completion of the circulation loop, broth is harvested behind the paddlewheel (Richmond, 1992, Chisti, 2007, Demirbas, 2010,). Inclined, circular, and raceway ponds are operated at large scale. On the other hand, photobioreactors are
closed bioreactors, which are designed as tubular, plate, or bubble column reactors. Among these, the most common type is tubular photobioreactors. These consist of less than 0.1m diameter transparent tubes made from plastic or glass. Tube diameter is a critical design criteria as light does not penetrate too deeply in dense culture broths (Chisti, 2007).
This leads to O2 accumulation and thus inhibits the photosynthesis process. Typically, open ponds are the preferred large scale cultivation system (Chisti, 2007). This is due to their simplicity and low construction and capital costs (Tredici and Materassi, 1992). However, these systems are open to the atmosphere, which lead to water evaporation and unwanted species contaminations. Besides, cell’s poor utilization of light and low mass productivity, due to the low CO2 deficiencies and inefficient mixing, are other limitations (Chaumont, 1993, Mata et al., 2010). Therefore, for water, energy, and chemicals saving purposes, photobioreactors have been proposed, but they are not yet commercialized. Main advantages of using photobioreactors are better algal culture and environment controlling (Tredici and Materassi, 1992), large surface to volume ratio, reduced evaporation of water, better isolation from outside contaminations, and higher mass productivity (Scragg, 2009). However, photobioreactors are usually made of plastic, and UV deterioration of plastic surface is the main disadvantage.
PHYSICAL CHEMICAL CHARACTERIZATION AND OF DEGRADATION OF OIL FROM CHLORELLA SPECIES