Biofuel Production & Types

Cheatsheet Content

Biofuel Overview Definition: Any fuel derived from biomass (plant, algae, or animal waste). Renewable: Feedstock can be replenished, making it a source of renewable energy. Advantages: Cost-effective, eco-friendly, alternative to petroleum/fossil fuels, especially with rising prices and global warming concerns. Ecofriendly Aspects of Biofuels "Greener": Feedstocks are renewable and have less impact on food supply (compared to first-generation). Sustainability: Considers feedstock availability, effect on greenhouse gas emissions, and impact on biodiversity. Second-generation biofuels: Still largely experimental/developmental. Types of Biofuels Solid Biofuels: Wood, grass, and other biomass can be burned directly for heat or electricity. Liquid Biofuels: Of particular interest for transportation. Ethanol (ethyl alcohol): Made by fermenting starch or sugar. Leading producers include Brazil and the United States. Biofuel Classification by Biomass Feedstock Dedicated Crops: Sugar crops, starch crops, oil crops, lignocellulosic crops, algae, aquatic biomass. Novel Feedstocks: Aquatic plants, macroalgae (seaweed), microalgae, microbial biomass. Wastes and Residues: Oil-based residues, lignocellulosic residues, organic residues, waste gases. Sustainable Feedstocks: Used for producing advanced biofuels and intermediate bioenergy carriers. Biofuel Generations Conventional (First-generation) Biofuels: Produced from food crops (sugar, starch, oil). Examples: Palm, rapeseed, soy, beets, cereals (corn, wheat). Advanced (Second-generation and Third-generation) Biofuels: Produced from feedstocks that do not compete with food/feed crops (e.g., wastes, agricultural residues). Cellulosic Ethanol: Derived from low-value biomass (wood chips, crop residues, municipal waste) with high cellulose content. Often from sugarcane bagasse or grasses cultivated on low-quality land. Cellulosic Materials: Contain cellulose and hemicellulose with varying amounts of lignin. Some are easy to break down into fermentable substrates (e.g., citrus peel to plant sugars). Currently, advanced biofuels cover only about 2% of total biofuel production. Biodiesel: Second most common liquid biofuel. Made primarily from oily plants (soybean, oil palm) and other oily sources (e.g., waste cooking fat). Predominantly used in Europe, blended with petroleum diesel. Algae and Cyanobacteria: Promising "third-generation" biodiesel sources, though economically challenging. Some algal species contain up to 40% lipids, convertible to biodiesel or synthetic petroleum. Algae/cyanobacteria can yield 10-100 times more fuel per unit area than second-generation biofuels. Vegetable Oil (Edible and Non-edible) Advantages as Biodiesel Feedstock: Transportability, availability, sustainability, high combustion ability, minor sulfur content, lesser aromatic content, eco-friendly. Drawbacks: Highly viscous nature, unsaturated hydrocarbon chain reactivity. Non-edible Oil-producing Plants: Jatropha curcas, Pongamia pinnata, Hevea brasiliensis, Madhuca indica, Ricinus communis, Azadirachta indica, Nicotiana tabacum, Gossypium hirsutum, Simmondsia chinensis, Moringa oleifera, Mesua ferrea, Simarouba glauca. Bioethanol Production from Different Feedstocks Bioethanol Sources Potential biofuel for energy security and environmental challenges. Biomass resources classified into: sugar products , starch , and lignocellulosic biomass . Cellulosic Biomass Sources: Agricultural wastes, forest residues, municipal solid waste, dedicated energy crops. Common Agricultural Residues: Wheat/rice straw, corn leaves/stalks, sugarcane bagasse, sugar production residues. Forestry Waste: Logs and tree roots. Municipal Solid Waste: High percentage of cellulosic materials (paper, cardboard). Bioethanol Production Process (General) Cellulose Starch Sugar Hydrolysis Saccharification Fermentation Distillation Bioethanol Feedstock milled/ground to reduce particle size. Cellulose and starch converted to fermentable sugars (glucose) via saccharification (enzymes). Fermentable sugars diluted with water. Bacteria, yeasts, or other microorganisms added. Sugars converted to bioethanol and $CO_2$ through fermentation. Basics of Bioethanol Production Carbohydrate polymers broken down into simple pentose and hexose sugars . Hexose sugars easily fermented; pentose sugars require specific microorganisms. Simultaneous Saccharification and Fermentation (SSF): Hemicelluloses and cellulose breakdown and sugar fermentation occur concurrently. Production of BIOETHANOL (Five-step process) Pre-treatment: Bioconversion of lignocellulosic biomass into reducing sugars, then fermented. Plant cell wall (lignin, hemicelluloses, crystalline microfibrils) forms lignin carbohydrate complexes (LCCs) . LCCs make substrates unavailable for cellulases. Pre-treatment (e.g., mechanical chopping) opens LCCs for enzymatic breakdown. Hydrolysis: Breaks down feedstock into fermentable sugars. Common methods: acidic and enzymatic . Lignocellulosic compounds broken down chemically (dilute sulfuric acid) or enzymatically (lignocellulose degrading enzymes). Enzymes for Cellulose Breakdown: Cellobiohydrolases, $\beta$-glucosidases, endo-$\beta$-1,4-glucanases. Enzyme activity influenced by concentration and source. Optimal conditions: $45-50^\circ C$, pH $4.8-5.0$. Enhancing Enzymatic Saccharification: Surfactants (block lignin), Tween 20, PEG (reduce cellulase adsorption on lignin). Complete hydrolysis via synergistic action of exo-glucanases, $\beta$-glucosidase, and endo-glucanases (collectively cellulase ). Enzymatic hydrolysis preferred over chemical due to higher yields, milder conditions, higher selectivity, lower energy cost. Enzymes work in synergism to combat crystalline cellulose, remove cellobiose, and produce glucose. Cellulose degrading enzymes released by fungi (e.g., Trychoderma reesei, Aspergillus, Schisophyllum, Penicillium). Fermentation of Sugars: Conversion of fermented sugars into bioethanol. Feedstocks: Molasses (45-50% Total Reducing Sugars), a major feedstock in India. Solid State Fermentation (SSF): Microbes grow in solid media; moisture required. Submerged Fermentation (SmF): Liquid media (sugar source, nutrients, water); optimum pH adjusted. Attractive due to uniform distribution, favorable conditions, easy modification of growth conditions. Separate Hydrolysis and Fermentation (SHF): Saccharification and fermentation carried out sequentially in separate units. Advantages: Each process can operate at its optimal pH and temperature (e.g., 45-50°C for enzymatic hydrolysis, 30-37°C for fermentation). Simultaneous Saccharification and Fermentation (SSF): Hydrolysis and fermentation occur simultaneously in the same reactor. Sugars (pentose/hexose) directly used by microbes. Advantages: Lower capital cost, less contamination risk, simpler reactor design. Example: Candida acidothermophilum for bioethanol production. Simultaneous Saccharification and Co-Fermentation (SSCF): Saccharification, pentose, and hexose sugar co-fermentation occur simultaneously in the same reactor. Pretreated substrate hydrolyzed by enzymes/microbes into oligomers. Requires microbial strains that convert both pentose and hexose sugars (e.g., Saccharomyces cerevisiae for hexose, Pichia stipitis for both). Economically feasible and high production rate. Distillation: Recovers bioethanol. Separates water and alcohol to produce 95% pure ethanol. Involves distillation column to reach azeotropic composition, followed by vapor permeation membranes or extractive distillation. Azeotrope: Mixture of two or more liquids boiling at a constant temperature with the same vapor phase composition. Vapor Permeation (VP) Membrane: Dense, non-porous material for separating vapor mixtures. Sorption: Permeable components dissolve into the membrane. Diffusion: Dissolved components diffuse through the membrane matrix. Desorption: Components evaporate and are removed on the low-pressure side. Properties of Bioethanol Chemical Identity: Flammable, colorless chemical, $C_2H_6O$ (ethyl alcohol). Octane Number: Higher than conventional petrol, allowing greater compression and more efficient engine operation. Oxygenate Additive: Replaces MTBE to improve octane ratings. Energy Yield: Lower than petrol; recommended for use in blends. Biodiesel Definition: Diesel fuel substitute derived from renewable resources. Composition: Alkyl esters of fatty acids from vegetable oils or animal fats combined with alcohol (methanol or ethanol). Production Method: Transesterification. Feedstocks: Natural oils (rapeseed, soybean), recycled cooking oils, microalgae, animal fats, oilseed crops. Potential: Microalgae, animal fats, and waste oils are promising for fuel production. Biodiesel Process Steps Extraction: Jatropha oil extracted from seeds. Pre-esterification (if needed): For high Free Fatty Acid (FFA) levels, oil reacts with alcohol and acid catalyst to convert FFAs to methyl esters. Transesterification: Treated oil reacts with alcohol in presence of catalyst. Separation: Mixture centrifuged to separate methyl esters (biodiesel) from glycerol. Purification: Biodiesel washed with distilled water to remove catalyst/glycerol, then dried. Oil Extraction Methods: Mechanical, chemical/solvent, enzymatic/biological, accelerated solvent, supercritical fluid, microwave-assisted. Most Used: Mechanical and solvent extraction. Mechanical Extraction: High pressure devices (Ram Press, Hydraulic Press, Screw Presses). Chemical (Solvent) Extraction: Solvent isolates oil from solids/liquids, recovers residual oil after mechanical extraction. Pressed cake can be repurposed (fertilizer, animal feed). Extracted oil is filtered and dehydrated to produce pure plant oil (PPO) . Oil Refining Components to Remove from PPO: Phosphatides, Free Fatty Acids (FFAs), colorants. Degumming: Removes phosphatides. Water degumming: Mix water with oil at $60-90^\circ C$. Acid degumming: Uses citric or phosphoric acid. Deacidification: Removes FFAs via neutralization with alkali, distillation, or esterification. Bleaching: Removes colorants, enhances storage life. Adsorbents (bleaching earth, silica gel, activated carbon) or heating to $200^\circ C$. Deodorization: Steam distillation to eliminate odorous substances (ketones, aldehydes). Dehydration: Distillation under reduced pressure to remove water. Transesterification Purpose: Converts plant oils into biodiesel, addressing high viscosity issues in raw oils. Process: Lipid molecules in refined oil converted into methyl or ethyl esters (biodiesel) and glycerin (byproduct). Begins with hydrolysis of lipid molecules to produce FFAs, then mixed with methanol/ethanol to create fatty acid esters. Mixture settles into two layers: glycerin (bottom) and biodiesel (top). Glycerin removed, biodiesel purified. Catalysts: Alkaline materials, acids, silicates, lipases. Preferred Alcohol: Methanol (low cost, high reactivity). Eco-friendly Alternative: Bioethanol (renewability, lower toxicity, improved fuel quality). Transesterification Reaction (General) $$ \text{1 Triglyceride (refined PPO)} + \text{3 Methanol} \xrightarrow{\text{Catalyst}} \text{3 Methylester (biodiesel)} + \text{1 Glycerin} $$ Transesterification of Jatropha oil involves reacting it with an alcohol (typically methanol) in presence of a catalyst (acid, base, or enzyme) to produce biodiesel (fatty acid methyl esters) and glycerol as a byproduct. Enzyme Catalysts: Lipases can catalyze the reaction, sometimes with solvents like t-butanol to mitigate methanol/glycerol adverse effects. Catalysts Used in Biodiesel Production Catalyst Type Examples Homogeneous Catalyst Alkaline earth and alkali metal-based, mixed metal-based, transition metal-based Heterogeneous Catalyst Boron group based, hydrotalcite based, waste based, cation exchange resins, heteropoly acid derivatives, sulphonic acid-based, sulphated oxide-based Biocatalyst Nanocatalyst PPO vs. Fossil-Derived Diesel Viscosity: PPO is 10x higher than fossil diesel, making blending difficult. Biodiesel's viscosity is similar to fossil diesel. Flashpoint: PPO's higher flashpoint makes it safer for storage/handling. Energy Content: Biodiesel has lower energy content but offers more complete combustion due to oxygen. Sulfur: Biodiesel produces no sulfur oxides. Oxidation: Biodiesel is prone to oxidation during long-term storage; additives can help. Biogas Definition: Gaseous mixture produced from anaerobic decomposition of organic matter. Composition: Methane (50-75%), carbon dioxide (25-50%), nitrogen (2-8%). Biomethane: High efficiency, clean-burning properties. Raw Materials: Dairy/swine farm manures, food processing residues, organic household waste, vegetable oil residues, energy crops. Biomethane Production Steps: Biogas production from raw materials. Biogas processed/cleaned to obtain biomethane for transport. Anaerobic Digestion Stages: Hydrolysis: Complex organic materials broken down by bacteria (Bacteriocides, Clostridia, Bifidobacteria) into acetate, hydrogen, volatile fatty acids. Acidogenesis: Anaerobic bacteria convert compounds into short-chain organic acids, alcohols, hydrogen, $CO_2$. Acetogenesis: Acidogenic bacteria convert products into hydrogen, $CO_2$, and acetate. Methanation: Methanogenic bacteria (e.g., Methanosarcina barkeri , Methanosaeta concilii ) convert materials into biogas. Temperature: Affects bacterial activity. $20^\circ C$ minimum; higher temperatures speed up process. Bacteria Classification: Psychrophiles ($25^\circ C$), mesophiles ($32-38^\circ C$), thermophiles ($42-55^\circ C$). Digestion Times: Vary (weeks to months) based on feedstock, digester type, temperature. Kinetics depend on substrate, temperature, pH, enzyme activity. Types of Biomethane First-Generation Biomethane: Anaerobic decomposition of organic wastes. Produces biogas ($CH_4$, $CO_2$). Second-Generation Biomethane: Thermochemical conversion of lignocellulosic biomass (wood, straw). Stages: Synthetic gas production from biomass, then conversion to biomethane using a catalyst. Third-Generation Biomethane: From microalgae in high-yield photosynthetic reactors (natural light, water, minerals, $CO_2$ recycling). Emerging technology (2020-2030). Syngas: Gaseous mixture of carbon monoxide (CO), hydrogen ($H_2$), carbon dioxide, other trace gases. Properties of Biomethane Methane ($CH_4$): Simplest hydrocarbon, combustible, odorless. Biomethane: 95-100% methane content, chemically similar to natural gas. Suitable for all natural gas applications. Biohydrogen Hydrogen ($H_2$): Most abundant element, rarely free in nature (combined in water, biomass, fossil fuels). Production: Microorganisms convert wastes, sugars, water into clean energy. Potential to exploit renewable energy and reduce GHG emissions. Challenges remain in achieving high production yields. Production of Biohydrogen Biomass Gasification: Heating biomass without oxygen. Produces mixture of CO, $CO_2$, $H_2$. Higher $H_2$/CO production at higher temperatures. Biomass Digestion: Converts wet feedstocks (manure) to $CH_4$ and $CO_2$. $CH_4$ converted to $H_2$ via steam reforming (endothermic process: $CH_4 + H_2O \rightarrow H_2 + CO$). Both methods require purification to increase $H_2$ concentration. Biohydrogen Production Methods Biological: Enzymatic (Direct photolysis - Oxygenic) Photo-fermentation (Indirect Photolysis - Oxygenic, Light-fermentation - Anoxygenic) Anaerobic fermentation (Dark fermentation) Thermochemical: Microbial electrolysis Hydrogen Producing Microorganisms Prokaryotes: Cyanobacteria (Dark fermentation) Bacteria (Dark fermentation) Eukaryotes: Algae (Photofermentation) Fermentative End Products: Lactic acid, butyric acid, butanol acetate, mixed acids. Temperature Tolerance: Thermophiles, mesophiles, psychrophiles. $O_2$ Tolerance: Obligate anaerobes, facultative anaerobes, aerobes. Photofermentation Types: Purple (Sulfur, Nonsulfur), Green (Sulfur, Gliding). Properties of Biohydrogen Chemical Identity: Chemically identical to conventional hydrogen gas. Source: Produced from gasification or digestion of biomass. Characteristics: Colorless, highly flammable, lightest of all gases. Transportation and Storage: Challenging due to large volume. Requires safe handling. Stored in liquid form at cryogenic temperatures ($-253^\circ C$). Other options: Solutions containing $NaBH_4$, rechargeable organic liquids, anhydrous $NH_3$ with catalysts. Algal Biofuel Productivity: Can produce oil year-round, higher productivity than most efficient crops. Land Use: Grows in brackish water and non-arable land, no impact on food supply. Environmental Benefits: Nontoxic, highly biodegradable. Fixes $CO_2$ (1 kg algal biomass fixes ~1.83 kg $CO_2$). Growth Rate: Fast-growing, completes cycle in days. Lipid Content: Several species have 20-50% oil content by dry biomass. Nutrients: Can use wastewater for cultivation (nitrogen, phosphorus). No herbicides or pesticides needed. Co-products: Algae can produce proteins and biomass for animal feed, medicines, fertilizers, or fermentation to ethanol/methane. Oil Yield: Biochemical composition can be modulated by growth conditions to improve oil yield. Capable of photobiological production of biohydrogen. Algal Biofuel Pathways Overview Microalgae/Macroalgae: Biohydrogen (Biophotolysis product e.g., C. reinhardtii ) $\rightarrow$ Hydrogen gas Hydrocarbons (e.g., B. braunii ) $\rightarrow$ Hydrocracking & distillation $\rightarrow$ Oil refinery products Lipids (e.g., N. salina ) $\rightarrow$ Transesterification $\rightarrow$ Biodiesel Carbohydrates (e.g., Golenkinia sp. , Laminaria sp. ) $\rightarrow$ Fermentation $\rightarrow$ Biohydrogen, Bioethanol, Biobutanol Whole Biomass $\rightarrow$ Anaerobic digestion $\rightarrow$ Biogas Whole Biomass $\rightarrow$ Hydrothermal liquefaction $\rightarrow$ Biocrude Whole Biomass $\rightarrow$ Pyrolysis, Gasification, Direct combustion $\rightarrow$ Energy rich gas mixture, Syngas Potential Algae for High Lipid Production Microorganism Biomass productivity (g/L d) Lipid content (%, w/w) Lipid productivity (mg/L d) Botryococcus braunii 0.02 25.0-75.0 5-15 Chlorella emersonii 0.036-0.041 25.0-63.0 10.3-50.0 Chlorella protothecoides 2.00-7.70 14.6-57.8 1214 Chlorella pyrenoidosa 2.90-3.64 2.0 58-72.8 Chlorella sorokiniana 0.23-1.47 19.0-22.0 43.7-323.4 Chlorella sp. 0.02-2.5 10.0-48.0 2-1200 Chlorococcum sp. 0.28 19.3 54 Dunaliella salina 0.22-0.34 6.0-25.0 13.2-85 Euglena gracilis 7.70 14.0-20.0 1078-1540 Nannochloropsis sp. 0.17-1.43 12.0-53.0 20.4-757.9 Phaeodactylum tricornutum 0.003-1.9 18.0-57.0 0.54-1083 Scenedesmus obliquus 0.004-0.74 11.0-55.0 0.44-407 Scenedesmus sp. 0.03-0.26 19.6-21.1 5.88-54.6 Spirulina platensis 0.06-4.3 4.0-16.6 2.4-713.8 Spirulina maxima 0.21-0.25 4.0-9.0 0.84-2.25 Tetraselmis sp. 0.30 12.6-14.7 43.4 Algae Cultivation Methods Natural cultivation method Artificial cultivation methods: flat plate photobioreactor, tubular photobioreactor, column photobioreactor. Lipid Extraction from Algae Standard Protocol (Energy Intensive): Harvesting (centrifugation) $\rightarrow$ Washing with solvent $\rightarrow$ Freeze drying $\rightarrow$ Reduce energy of drying. Acid Catalyzed Transesterification: Eliminates energy of drying. Hexane Extraction: Of transesterified lipids. Algal Biofuel - Metabolic Pathways Cell division stops under stress, leading to TAG accumulation (carbon storage). Nitrogen ($N$) depletion $\rightarrow$ decreased Glucose Assimilation $\rightarrow$ increased AMP Deaminase $\rightarrow$ increased IMP+NH4. $NH_4$ alleviates N deficiency. AMP $\rightarrow$ Isocitrate Dehydrogenase $\rightarrow$ Citrate. Citrate transported from mitochondria to cytoplasm. ATP-Citrate Lyase: Citrate + CoASH + ATP $\rightarrow$ Acetyl CoA + ADP + Pi $\rightarrow$ Fatty Acid Synthesis. Algae Biomass Products Fuel & Energy: Transesterification (biodiesel), anaerobic digestion (biogas), hydrogenation/gasification (bio-jet), fermentation (bioethanol), pyrolysis (bio-oil, bio-char, biogas), direct combustion ($CO_2$, energy). Food & Non-food Products: Pharmaceuticals, cosmetics, chemicals, animal feeds/fertilizers, synthetic substitutes, bioremediation.