--- title: "Synthetic fuel from biomass, bio fuel cells" subject: "Energy Environment and Society" chapter: 3 key: "semester_7/energy_environment_and_society:synthetic-fuel-biofuel-cell" source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/synthetic-fuel-biofuel-cell site: BCT Engineering --- # Synthetic fuel from biomass, bio fuel cells Energy Environment and Society · Chapter 3: Renewable Energy Sources - Asked in: 2074 Chaitra, 2+4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/synthetic-fuel-biofuel-cell - Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3 ## Question How does the synthetic fuel from the biomass work? Explain about bio fuel cells. ## Short answer Biomass-to-liquid fuel involves gasifying biomassto syngas, cleaning and conditioning, then Fischer-Tropsch synthesis to get synthetic diesel. A microbial fuel cell uses bacteria to oxidise organic matter directly into electricity, while enzymatc cells use enzymes for small-scale power. ## Answer #### Synthetic fuel from biomass (biomass-to-liquid, BTL) Synthetic fuels are liquid or gas fuels (diesel, petrol, methanol, methane) made from biomass instead of crude oil. Steps: 1. **Preparation:** biomass (wood, straw, waste) is dried and crushed. 2. **Gasification:** with oxygen and steam at 800–1200 °C, biomass becomes **syngas**, a mix of CO and H₂. 3. **Gas cleaning and conditioning:** tar, dust and sulphur are removed, and the CO:H₂ ratio is adjusted by the water-gas shift reaction (CO + H₂O → CO₂ + H₂). 4. **Synthesis:** - *Fischer–Tropsch:* n CO + (2n+1) H₂ → CₙH₂ₙ₊₂ + n H₂O, over an iron or cobalt catalyst, gives synthetic diesel and kerosene. - *Methanol synthesis:* CO + 2H₂ → CH₃OH. - *Methanation:* CO + 3H₂ → CH₄ + H₂O gives synthetic natural gas. 5. **Upgrading:** distillation into fuels. ```text Biomass -> Gasifier -> Syngas -> Cleaning -> F-T reactor -> Synthetic fuel ``` The fuel is sulphur free and can be used in existing engines, but the process is capital-intensive. #### Bio fuel cells A **biofuel cell** is a fuel cell that uses biological catalysts (microbes or enzymes) to convert chemical energy of organic matter (sugar, wastewater, glucose) directly into electricity. - **Microbial fuel cell (MFC):** bacteria at the anode oxidise organic matter and release electrons and protons; electrons flow through an external circuit to the cathode where they combine with oxygen and protons to form water. Can produce power while treating wastewater. - **Enzymatic fuel cell:** isolated enzymes (for example glucose oxidase) catalyse the reactions; can be used for small implants and sensors. ```text Organic matter -> [Anode: bacteria] -e-> load -> [Cathode] H+ ---- membrane ----> O2 -> H2O ``` Advantages: works at room temperature and neutral pH, uses waste, no precious metal. Limits: very low power density, low efficiency, and early stage of development. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the correct sequence for biomass-to-liquid synthetic fuel? A. Fermentation - distillation - blending B. Preparation - gasification to syngas - cleaning/conditioning - synthesis - upgrading C. Pyrolysis - combustion - synthesis D. Digestion - compression - storage Answer: B. Biomass is gasified to syngas (CO + H2), cleaned, synthesised (e.g. Fischer-Tropsch) and upgraded. (Key point: BTL route) 2. What does Fischer-Tropsch synthesis do? A. Converts syngas to hydrocarbons such as synthetic diesel over iron or cobalt catalyst B. Converts sugar to ethanol C. Splits water D. Makes biogas Answer: A. n CO + (2n+1) H2 → CnH2n+2 + n H2O over Fe or Co catalyst. (Key point: Fischer-Tropsch) 3. How does a microbial fuel cell work? A. Bacteria at the anode oxidise organic matter, electrons flow through external circuit to cathode and combine with oxygen and protons to form water B. Bacteria at the cathode make hydrogen C. Electrons pass through the membrane D. Bacteria burn fuel to drive a turbine Answer: A. Anode oxidation releases electrons and protons; electrons go through the load and reduce oxygen to water at the cathode. (Key point: Microbial fuel cell) 4. What is a main limitation of biofuel cells? A. They require platinum B. Very low power density and early stage of development C. They need high temperature D. They cannot use wastewater Answer: B. They work at room temperature with waste but produce little power. (Key point: Biofuel cell limits) ## Related in Energy Environment and Society - [Bio-chemical conversion of biomass](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abiochemical-conversion-biomass) — Energy Environment and Society, chapter 3 - [Proton exchange membrane fuel cell](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apemfc-working) — Energy Environment and Society, chapter 3 ## Related in other subjects - [Working principle and types of fuel cells](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Apem-fuel-cell-working-types) — Energy Resources, chapter 6 - [Biomass compared with geothermal energy](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abioenergy-vs-geothermal) — Power Plant Design, chapter 1 - [Fuel cell voltage, efficiency and hydrogen use](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Afuel-cell-stack-numerical) — Energy Resources, chapter 6 - [Biomass and the carbon neutral cycle](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abiomass-carbon-neutral-cycle) — Power Plant Design, chapter 1