biofuels

Biofuels are any fuel whose energy is obtained by biological carbon fixation.

Recently living things are the biomass used to get this energy. This could be wood or oils or algae all different types of biomass. When these are used for energy they are considered biofuels.

• Lignin seems a general term for a polymer found in biomass. Lignin binds cellulose bundles together. Needs to be broken down. Depending on type of lignin, can be broken down in different ways.
• Cellulose is a specific type of polymer. C6H10O5

Biofuels

• Ethanol (replace gasoline).
• Biodiesel
• Methanol (replace methane).
• Biobutanol (replace gasoline/butane).

1st generation

• Vegetable oils.
• Sugars. Sugar cane, soy beans. Corn.
• Processed in different ways. One by transesterifaction for bio oils, the other by hydrolysis or fermentation.
• Hydrolysis is the breakdown of polysaccharides into simpler sugar units by water. Typically catalysed by an acid but also by enzymes in the case of the body.
• Fermentation also breaks down sugars by the metabolic processes of yeast.
• Transesterificatoin is replacement of the glycerol with a methanol group.

Hydrothermal processing

• Hydrothermal processing involves heating aqueous slurries of biomass or organic wastes at elevated pressures to produce an energy carrier with increased energy density.
• https://www.youtube.com/watch?v=3K1zWAYDvMA

Conversion

• The processes involved in conversion are commonly classified as:
  • Thermo-chemical (e.g. Pyrolysis, gasification).
  • Biochemical (e.g. Fermentation).
  • Physio-chemical (e.g. transesterifaction).

What are the nutrients that life (the biosphere) needs?

• The mnemonic: CHNOPS (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur).
• So you’ve a water cycle (H2O), carbon cycle (C), nitrogen cycle, phosphorus cycle, sulfur cycle.
• N and S are big components in protein. Phosphorus needed for atp.
• Abiotic are the non biotic parts of the planet. The atmosphere, lithosphere

Why Carbon

• First things is structure, so immediately, you rule out all atoms that are not good at forming covalent bonds.
• If you get rid of big atoms, that don’t hold their valence electrons too tightly, you’re left with CHNOPS and silicon.
• Silicon is the only other element that can support scaffolds (2d and 3d structures). Carbon only makes up 0.02% of the earth’s crust and silicon makes up 28%. Most silicon scaffolds are unstable with water.

Life cycle Assessment Biomass

Relate science to policy and politics.

• Land usage change: Growing biomass for biofuels can displace food production. It can cause existing non-agricultural land to be converted to agricultural land to keep up with demand. This is indirect land use change.
• Because trees absorb CO2 from the atmosphere, removing them for biofuel production may result in an increase in net greenhouse gases instead of a decrease.
• The RED and FQD both restrict production of biofuels on land with high biodiversity status and/or high carbon content.
• RED II pushes towards the use of non-feedstock biomass to account for land use change problems.

LCA

• Evaluating the energy and resource consumption and all pollutant emissions over the entire life cycle needed to satisfy a defined function (e.g. filling up a tank with 1MJ of energy at a filling station).
• Inputs and outputs are analysed to determine overall benefits.
• Main emission sources in biofuel:
  • Production of raw materials.
  • Processing/conversion.
  • Transport (and storage).
  • Distribution of fuel to consumer.
  • Consumer fuel use.
• The reference flow is the physical flow of energy or materials needed to achieve a functional unit.
• A functional unit is used to compare processes under study with the same function.
• A reference flow provides a use case example (I think).
• The product system should include all processes required to perform functional unit. System boundaries put a limit on whats included here.
• Why focus on advanced biofuels:
  • Stop competition with food.
  • Waste based biofuels would otherwise be landfilled, burned or left to decay, resulting in GHG emissions.
  • Algae have potential for higher yield.
  • Residual biomass (from logging etc.) can be used for conversion.
  • Use of marginal land (not usable for food) for developing fuels.

Hydrogen

• In general, the notes talk about the bond dissociation energy of H2, but I don’t see where this is explicitly done for hydrogen power. It make sense that this makes it very energy dense but where is the process for this dissociation taking place?
• Electricity is proving relatively easy to decarbonise. Transportation and heating, not so much.
• Hydrogen combustion is less efficient than a fuel cell and releases NOx so it’s not expected to be a replacement in this sense for ICE’s.
• Fuel cells is the creation of current through ‘reverse’ electrolyses.
  • A current is generated by dissociating the electrons from input hydrogen. The ions of hydrogen pass through an electrolyte and the electrons through the external circuit to do work.
• Most hydrogen today is produced through steam reformation from methane. Syngas, a mix of CO, CO2 and H2. Have to figure out a way to do the endothermic process of getting hydrogen with clean fuels.
  • Hydrogen more naturally occurs bonded in things like water and methane.

Production

• Centrally, or distributed. Large scale benefits from economies of scale but comes with high capital costs. Central production is needed to really get it started in widespread use.
• Thermal production: Steam reforming, reacting hydrocarbons with water. This is endothermic and requires a catalyst (like Nickel also). Temperatures of 800C or so are needed.
• Electrolytic: Electricity used to split water into hydrogen and oxygen. Split water at the anode, the electrons flow through the external circuit and recombine of the other side to form H2. Operate at about 100C. There are also high temp. cells. PEM and alkali set ups more suitable for renewables and distributed production.
• Photolytic: Use energy from the sun directly to power splitting. Algae and solar cells.
• Catalysts play a key role as they are often critical elements like platinum. There is research into catalyst design.

Storage

• Liquefaction requires temperatures of -273C.

• Compressed hydrogen maintained at around 700bar which is not too high for transmission but very high for transport use.

• Transport by tanker is currently most economically viable. Once hydrogen energy market exceeds 10% gas pipe infrastructure is expected to become viable.

• In general, the supply of catalyst is a problem.

• Environmental factors like cold temperatures freezing the water generated is a problem.

• The general source of H2 is mainly using fossil fuels.

Anki cards

• What is a biofuel?
  • any fuel whose energy is obtained by biological carbon fixation; i.e. fuels derived from biomass
• What are the 4 components of LCA?
  • Goal/scope definition.
  • Inventory analysis.
  • Impact assessment.
  • Interpretations at each of these steps.
• What is a functional unit in LCA analysis?
  • The ability of a system to carry out some defined function.
  • What is the magnitude of service.
  • e.g. transport fuel must move a vehicle a certain distance per unit mass/volume, should not damage engine etc.
• What is arguable the most important component of LCA analysis?
  • A functional unit.
• What is the average thermal energy from biomass combustion according to suppl. notes paper?
  • 20MJ/kg.
• What is pyrolysis in a biomass processing context?
  • The conversion process of specific biomass into liquid (bio-oil), solid (charcoal), and gaseous (combustible gas) products through partial combustion at temperatures around 500 °C and in the absence of oxygen.