The World is in a Energy Crisis associated with irreversible depletion of traditional sources of fossil fuels. Sustainable liquid fuels are essential for infrastructure and transportation. Compared with other forms of Renewable Energy, Biofuels allow energy to be chemically stored, and can also be used in existing engines and transportation infrastructures. The benefits of biofuels over traditional fuels include greater energy security, reduced environmental impact, foreign exchange savings, etc. Biofuels from Algae: ◦ Potential to produce more biomass per unit area in a year than any other form of biomass
Algae (Latin: seaweed) are a large and diverse group of simple, typically autotrophic eukaryotic organisms, ranging from unicellular to multicellular forms. ◦ Simple: Their tissues are not organized into the many distinct organs found in land plants. ◦ Autotrophic: Organisms that produce complex organic compounds from simple inorganic molecules using energy from light. ◦ Eukaryotic: Organisms that contain cell nucleus. Examples of eukaryotic algae are green algae (Chlorophyta) and diatoms (Bacillariophyta). Organism that do not contain cell nucleus are prokaryotic such as cyanobacteria (commonly referred to as blue-green algae). In the past, Cyanobacteria was referred to as algae. Now they are classified as bacteria because they have no cell nucleus. Life on earth started with Cyanobacteria and algae. These organisms converted a Carbon Dioxide rich atmosphere to an oxygen rich atmosphere by sucking out Carbon dioxide and converting it into Oxygen. Will these organisms save the Earth once again? Algae are dated back to approximately 3 billion years in the Precambrian age (4600 Ma to 542 Ma; 88% of geological time). They show a wide range of reproductive strategies, from asexual cell division to complex forms of sexual reproduction. The first plants on earth evolved from shallow freshwater algae.
Microalgae (microphytes) are microscopic algae that live in saline (oceans) or freshwater environments. They can also be found on terrestrial ecosystems. ◦ Estimated 50,000 species exist. They are unicellular species which exist individually, or in chains or groups. Depending on the species, their sizes range from a few micrometers to a few hundred micrometers. ◦ Microalgae do not have roots, stems and leaves. ◦ These microalgae produce half the atmospheric oxygen, and consume a lot of the Green House Gasses. Thus these micro-organisms convert sunlight, water and carbon dioxide to algal biomass. ◦ These organisms also can produce carotenoids, antioxidants, fatty acids, enzymes, polymers, peptides, toxins and sterols. The chemical composition of microalgae depends on species and cultivation conditions. ◦ Can achieve desired products in microalgae to a large extent by changing environmental factors such as temperature, illumination, pH, CO2 supply, salt and nutrients. Microalgae constitute the basic food for numerous aquaculture species.
•Different Species contain different Chemical Compositions.•Higher Lipid yields are desired. •Many microalgae can be induced to accumulate substantial quantities of lipids.•Conditions of growth are also important in determining what type of species to use.•Generally Chlorella is a species preferred for lipid production .
Each different strain of algae has different fatty acids, therefore deciding on strain is very complex. Although the microalgae oil yield is strain-dependent, it is generally much greater than other vegetable oil crops. Figure shows that although oil content is similar for plants and algae, there are significant variations in the overall biomass productivity and resulting oil yield with an advantage for algae.
Easy to cultivate and harvested within 10 days. Grow with little attention and diverse locations. High growth rate. Use water unsuitable for human consumption. ◦ Treats waste water by removing harmful contaminates. Easy to obtain nutrients. Carbon neutral and carbon fixing. ◦ Removal of Carbon dioxide from industrial flue gasses while producing biodiesel. Can grow almost anywhere as long as there is carbon dioxide, water and sunlight. Algae oil extraction creates useful byproducts. Microalgae can provide a feedstock for several different types of renewable fuels such as biodiesel, ethanol, methane, hydrogen and others. ◦ After extraction of oil, other by-products can be produced.
Microalgae differ from other biodiesel feedstock in that they are microorganisms living in liquid environments. ◦ Thus with particular cultivation, harvesting, and processing techniques. Processes for biodiesel production from microalgae include: 1. Production unit where Cells are grown. 2. Followed by separation the cells from the growing media 3. Lipid extraction. 4. Production of biodiesel or other biofuels. Traditionally biodiesel produced through transesterification reaction Other possibilities for biofuels production are being pursued. ◦ Pyrolysis (thermal cracking ◦ And others
Is the key step that determines the economic viability of the process. Several criteria must be considered for cultivation site: ◦ Water Supply/demand and chemistry; land topography, geology; climate/weather conditions; access to nutrients. ◦ Also determine if will use Open/closed systems. Use most efficient species for Cultivation conditions.
Microalgae are adapted to scavenge their environments for resources. ◦ They can grow under different conditions. ◦ Different strains grow more efficiently under different conditions. Microalgae double their biomass within 24 h. Microalgae have a trade-off between growth and oil content. ◦ Higher growth results lower oil content. Several Factors controlling growth and composition: ◦ Abiotic factors: light, temperature, nutrient concentration, O2, CO2, pH, salinity and toxic chemicals. ◦ Biotic factors: pathogens, competition from other algae ◦ Operational factors: shear produced by mixing, dilution rate, depth, harvest frequency, etc.
Microalgae cultivation using sunlight energy can be carried out in open or covered ponds/lakes or closed photobioreactors (PBRs), based on tubular, flat plate or other designs. ◦ Closed Systems are much more expensive and also hard to Scale Up. Nutrients can be provided through runoff water from nearby land areas or by channeling the water from sewage/water treatment plants. ◦ Water, nutrients and CO2 are controlled, while Oxygen is removed. Algal cultures consist of a single or several specific strains optimized for producing the desired product.
Open ponds are the oldest and simplest systems for mass cultivation of microalgae. ◦ Are shallow ponds. Pond is designed in a raceway configuration. ◦ Paddlewheel circulates and mixes the algal cells and nutrients. System is operated in a continuous mode. ◦ The fresh feed is added in front of the paddlewheel, and algal broth is harvested behind the paddlewheel through the loop. Productivity is affected by contamination with unwanted algae and micro-organisms that feed on algae. Are economically more favorable than others, but raise the issues of land use cost, water availability, and appropriate climatic conditions.
Closed Pond systems are the same as Open Pond systems except that they can control the environment better ◦ Creates a GHG. Photobioreactors have the ability to produce algae while performing beneficial tasks, such as scrubbing power plant flue gasses or removing nutrients from wastewater. ◦ Also offer a closed culture environment which is protected from direct fallout, relatively safe from invading micro-organisms compared to an open system. ◦ Photobioreactors have higher efficiency and biomass concentration (2-5 g/L), shorter harvest time (2-4 weeks) than open pounds. Closed Systems consist of numerous designs: tubular, flat-plated, rectangular, continued stirred reactors, etc. Tubular Photobioreactor: Growth medium circulates from a reservoir to the reactor and back to the reservoir.
Harvesting the algae from the tank and separating the oil from the algae is hard and energy intensive. ◦ Constitutes 20-30% cost of algal biomass. Conventional processes: ◦ Sedimentation (low quality) ◦ Concentration through centrifugation (high quality) ◦ Foam fractionation ◦ (Ultra)Filtration ◦ Flocculation* Used to aggregate cells. ◦ Ultrasonic separation
Processing is highly specific and depends on the desired products. Drying is important to increase shelf-life of final product Extraction after drying. ◦ Mechanical: homogenizers, bead mills, ultrasounds etc. ◦ Non-Mechanical: freezing, organic solvents, acid, etc. For biodiesel Production: lipids and fatty acids have to be extracted ◦ For lipids a solvent extraction is normally done directly from the lyophilized biomass. Solvents used: hexane, ethanol (can extract contaminants). ◦ Using Ultrasound can greatly increase extraction time and yield.
Microalgae biomass is generally more expensive than growing crops. ◦ PBRs have the potential to yield 19,000 to oil per acre per year. (200x more than plant/vegetable oils. 57,000 Liters of oil) The theoretical calculated cost of algae oil per barrel is only $20. While that of oil in the U.S. is $100. ◦ Assumptions: ◦ Oil supply is based on the theoretical claims that 47,000 -308,000 liter/hectare/year of oil could be produced using algae. (Culture of algae can yield 30-50% oil). NOTE: None of the projected algae and oil yields have been achieved. ◦ Reason: Require large quantities of fertilizer, water and fossil energy inputs in addition to consistent light and temperatures.
Compared to with second generation biofuels, algal fuels (third generation fuels) have a higher yield. ◦ They can produce 30-100x more energy per hectare compared to terrestrial crops. Algae can produce different biofuels: bioethanol, vegetable oils, biodesiel, bio-oil, bio-syngas, and bio- hydrogen. Production of these biofuels can be coupled with flue gas CO2 improvement, wastewater treatment, and the production of high-value chemicals.
Chemical processes include transesterification. ◦ Products: Biodiesel Thermochemical processes include liquefaction, hydrogenation, pyrolysis and gasification. ◦ Products: Bio-Oil and Gas Biochemical processes ◦ Products: Bioethanol, Biomethane, Bio-Hydrogen
Produces Biodiesel. ◦ Biodiesel is a mixture of fatty acid alkyl esters obtained by transesterification. Composed of methyl esters of long-chain fatty acids. ◦ Biodiesel refers to any diesel equivalent biofuel made from Renewable Source. Transesterification is multiple step reaction, including three steps in series. ◦ Triglycerides are converted to diglycerides, then diglycerides are converted to monoglycerides. ◦ Monoglycerides are then converted to esters (biodiesel) and glycerol (by- product).
Oil or fat and a short chain alcohol (usually methanol) are used as reagents in the presence of a catalyst (usually NaOH). ◦ A molar ratio of 6:1 (alcohol:oil) is used to complete reaction accurately. Theoretical is 3:1. ◦ Feedstock mass input to biodiesel mass output is 1:1. 1 kg of oil results in about 1 kg of biodiesel. ◦ Scenedesmus obliquus is considered a good species for biodiesel production. Contains mainly saturated and mono-unsaturated fatty acids, which give it high oxidative stability. ◦ Also, Neochlris oleoabunadans and Nannochloropis sp. are good species for biofuel production because of high oil content.
Thermochemical liquefaction can convert wet biomass to liquid fuel at 575 K and 10 MPa (CO/H2) using a catalyst such as sodium carbonate. (Appell et al.) ◦ Biomass is converted to liquefied products through a complex sequence of physical structure and chemical changes. ◦ Biomass is decomposed into small molecules. These molecules are unstable and reactive, and can repolymerize into oily compounds with varying MW distribution. Direct liquefaction of microalgae by dichloromethane extraction. ◦ Performed in an aqueous solution of alkali salt at 575 K and 10 MPa. ◦ Use Autoclave with mechanical mixing. ◦ 37 % oil yield (Organic basis) from Dunaliella tertiolecta The Oil had a viscosity of 150 to 330 MPa s and a Heating Value of 36 MJ/kg. Net Energy Producer ◦ Another study obtained a max yield of 64 % dry wt. basis of oil. (Botryococcus braunii).
Liquefaction of algal cells by hexane extraction can also be done.
Conversion of microalgae (Chlorella pyrenoidosa) to liquid products was also developed. ◦ Algal hydrogenation was performed batch wise, using an autoclave under high temperature and pressure conditions in the presence of a catalyst and a solvent. Results indicated that Algae was converted to Hydrocarbons. ◦ Conditions: Temp: 400-430 Celsius Retention Time: 200 min Pressure: 1000-2250 Psig Catalyst: Cobalt Molybdate Oil Yields of 46.7 wt% achieved. ◦ 10 wt% liquid and 34 wt% HC rich gas obtained. Higher temperature and time resulted in higher yield. Max yield at pressure of 1200 Psig
Pyrolysis at different temperatures was done on Microalgae to produce bio-oils ◦ The higher the temperature the higher the oil yield. From Previous work.
Similar Experiments done on Increasing temperature ◦ Used Mosses as comparison Bio-oil yields from algae were higher. HHVs were higher quality for algae 21.5-24.8 MJ/kg-Moss (PC/TT) 32.5 MJ/kg for Algae (CF) 39.7 MJ/kg for Microalgae (CP) Fossil Oil – 42 MJ/kg
Bioethanol can be made from Algae through a Biochemical Process similar to corn ethanol. Algal biomass is ground, and the starch is converted by enzymes to sugar. Sugars are converted to ethanol by yeast.
Process for Converting Algae into Ethanol: ◦ 1. Growing starch-accumulating, filament-forming, or colony- forming algae in an aqua culture environment 2. Harvesting the grown algae to form a biomass 3. Initiating decay of the biomass Initiating decay means that the biomass is treated in such a way that the cellular structure of the biomass begins to decay and release carbohydrates. 4. Contacting the decaying biomass with a yeast capable of fermenting it to form a fermentation solution 5. Separating the resulting ethanol from the fermentation solution. Some prominent strains of algae that have a high carbohydrate content: ◦ Sargassum ◦ Glacilaria ◦ Prymnesium parvum ◦ Euglena gracilis
Meier proposed the production of methane gas from the carbohydrate fraction of algae cells. Methane gas as well as carbon dioxide can be produced by anaerobic digestion of bio-wastes in the absence of air. ◦ This type of gas is referred to as biogas. ◦ Biogas is a valuable fuel which is produced in digesters filled with feedstock. ◦ Digestion takes a period from10 days to a few weeks. Algal biomass can be used for biogas production. ◦ Digestion of algal biomass produces carbon dioxide, methane and ammonia. ◦ Some microalgae have been explored as potential methane sources. ◦ Anaerobic digestion for biogas appear to be uneconomic.
Hydrogen from algae can be produced under specific conditions. ◦ Direct Photolysis: Photosynthesis and water-splitting are coupled, resulting in the simultaneous production of hydrogen and oxygen. Is possible when the resulting hydrogen and oxygen are continuously flushed away. Safety risk, high costs to separate hydrogen and oxygen. ◦ Hydrogen can also be made from anaerobic fermentation of Algae via hydrogenase. The reactions are similar to electrolysis involving splitting of water into oxygen and hydrogen.
Carbon Dioxide Capture ◦ Flue gases from power plants are responsible for more than 7% of total world emissions. Microalgae can use Carbon Dioxide for growth. Thus reducing emissions. 10-50x better fixation of gas compared to terrestrial plants. Wastewater management. ◦ Microalgae will use the contaminants in waste water to clean the water. Microalgae will consume Sulfur and Nitrogen for growth. Average removal efficiency or 72% nitrogen and 28% sulfur. Fine chemicals and bioactive compound ◦ Depending on microalgae, various high-value chemical compounds may be extracted. Pigments, antioxidants, Beta-carotenes, polysaccharides, triglycerides, fatty acids, and vitamins. Human health. ◦ Have protein quality higher than other vegetable sources. ◦ Contain several different sterols (for cardiovascular disease). ◦ Antioxidants. ◦ Omega fatty acids. ◦ Extraction of lutein which helps for degenerative diseases. ◦ S.platensis and Spirulina maxima re the most popular edible algae Use as healthy food since it boosts immune system, increase LA bacteria in GI tract. Many civilizations used such food as a diet. Animal feed ◦ Normally used for aquatic animals.
Current companies marketing that they are close to making biodiesel from algae economical within the next few years ◦ Have limited technical expertise Limitations concern the optimization of: ◦ Harvesting ◦ Oil extraction processes ◦ Supply of Carbon Dioxide ◦ Also, light, nutrients, temperature, turbulence, Oxygen and Carbon dioxide levels need to be optimal. Need to reduce costs. ◦ Using cheap Carbon Dioxide sources. Use of flue gas. ◦ Use wastewater. ◦ Optimal conditions. ◦ GMO’s to increase oil yields. Considerable investments needed.