Synthetic fuel from biomass, bio fuel cells

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.

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.

 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.