51 Biofuel Production

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    Biofuel Production

    Prof. Tony Bridgwater

    Bioenergy Research Group

    Aston University, Birmingham B4 7ET

    AV Bridgwater 2008

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    Biomass

    Carbohydrates e.g. corn, wheat

    Sugarfrom cane or beet

    Vegetable oil e.g. rape, palm, soy, jatropha

    Lignocellulosics (lignin, cellulose and hemicellulose)e.g. wood, grass, straw, residues

    Fertiliser and other inputs have a major impact on thesustainability of crops. Lignocellulosics generally have alower requirement.

    There are many agronomical criteria for crop selection ofwhich yield (dry t / ha.y) is important for maximising use

    of land

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    Biofuels

    Oxygenates

    Methanol Ethanol

    Butanol Mixed alcohols Dimethyl ether

    Hydrocarbons Biodiesel Synthetic diesel

    Synthetic gasoline Methane (CSNG)Other

    Hydrogen

    Generation

    2G1G & 2G

    1G & 2G2G2G

    1G2G

    2G1G & 2G

    1G & 2G

    First generation (1G)biofuels are from food suchas:

    Ethanol from sugar, corn Biodiesel from rape oil

    Second generation (2G)biofuels are from wholecrops such as wood andgrasses:

    Synthetic diesel Methanol Ethanol

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    Feeds, processes, products

    Thermalconversion

    Esterification

    Ethanol,Butanol,

    Chemicals

    Biodiesel(FAME,RME)

    Chemicals

    Synthetic H/C,Ethanol, Butanol

    Methanol,Chemicals

    Power, Heat

    Starch & sugars Oil plants

    Biologicalconversion

    Residues ResiduesLignocellulose

    1G1G2G 2G

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    1st and 2nd generation biofuels

    First generation biofuels are from foodstuffs such as:

    Ethanol from sugar, wheat or corn about 2 t/ha/y inEurope and USA, up to 6 t/ha/y from sugar cane in Brazil

    Biodiesel from vegetable oils about 1 t/ha/yThese are important in introducing biofuels and increasingawareness.

    Second generation biofuels are from whole crops such aswood, energy crops, residues, such as:

    Synthetic diesel about 4 t/ha/y

    Methanol about 8 t/ha/y Ethanol about 5 t/ha/yHigher yields and absence of competition with food give

    these a longer term future

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    Feeds, processes, products

    Thermalconversion

    Esterification

    Ethanol,Butanol,

    Chemicals

    Biodiesel(FAME,RME)

    Chemicals

    Synthetic H/C,Ethanol, Butanol

    Methanol,Chemicals

    Power, Heat

    Starch & sugars Oil plants

    Biologicalconversion

    ResiduesLignocellulose

    Residues

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    Bioethanol 5% limit in gasoline in Europe for cars (E5).

    E85 (85% ethanol) is used in USA and E100 in Brazil

    Concerns:

    Logistical and market compatibility Vapour pressure

    Hygroscopicity andlow temperature properties Materials compatibility

    Low energy density ~1/3 Fuel compatibility

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    Bioethanol technologyBiological processes

    Mature technology for 1G from sugar, grain and corn.

    Developing technology for 2G from lignocellulosics.

    Hydrolysis releases C6 & C5 sugars, separates lignin. C6 sugars fermentation is commercial. C5 sugars fermentation needs to be demonstrated

    Lignin needs to be utilised for energy efficiency In 1G technology, more energy is often input than is

    derived in the ethanol, and significant improvements are

    needed.Thermal processes

    Commercial but mixed product with other alcohols.

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    2 Generation bio-ethanol

    Sugars

    Byproducts

    ResiduesWastesDistillation

    Bioethanol

    Hydrolysis

    Syngas

    Ethanol synthesis

    Thermal Gasification

    Syngas

    Fermentation

    Other alcohols

    Biomass

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    Feeds, processes, products

    Thermalconversion

    Esterification

    Ethanol,Butanol,

    Chemicals

    Biodiesel(FAME,RME)

    Chemicals

    Synthetic H/C,Ethanol, Butanol

    Methanol,Chemicals

    Power, Heat

    Starch & sugars Oil plants

    Biologicalconversion

    Residues ResiduesLignocellulose

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    Biodiesel

    Methyl esters of vegetable oil e.g. rape, soy, palm,sunflower to reduce viscosity and improve otherproperties.

    The process is lowtemperature and catalytic:batch, semi-batch, semi-continuous, or continuous

    Byproduct glycerine needsto be used

    Concerns

    Different oil sources result in different quality productsthat is difficult to control

    Low temperature performance is variable and poor

    Limited to 5% in diesel for vehicles in Europe due tomaterials and compatibility concerns

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    Current status 1st generation Bioethanol is attractive as the technology is available

    commercially Concerns over properties and energy density

    Biological 1G technology from corn has low efficiency Biological 2G has some development challenges Thermal 2G gives mixed alcohol product

    Biodiesel is attractive as a motor fuel as it can be readilyblended with diesel The quality is variable Low temperature characteristics are variable and poor Low yields and crops have high energy inputs

    Competition of food vs fuel has led to high food price rises; There is also competition for land and sustainability issues

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    Feeds, processes, products

    Thermalconversion

    Esterification

    Ethanol,Butanol,

    Chemicals

    Biodiesel(FAME,RME)

    Chemicals

    Synthetic H/C,Ethanol, Butanol

    Methanol,Chemicals

    Power, Heat

    Starch & sugars Oil plants

    Biologicalconversion

    ResiduesResiduesLignocellulose

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    Synthetic hydrocarbons

    Synthetic hydrocarbons include diesel, gasoline, kerosene

    They are entirely compatible with conventional fuels in all

    proportions, but are much cleaner. At least in the medium term, these are likely to be the

    biofuels of choice due to their ease of assimilation into

    markets, familiarity by the vehicle industry and consumers,energy density,

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    Routes to 2nd G hydrocarbons

    1. Thermal gasification

    a) + Fischer Tropsch

    b) + Methanol synthesis + upgrading by MTG or MOGD2. Pyrolysis + upgrading

    a) by hydro-processing

    b) by zeolites3. Hydro-processing vegetable oil

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    Syngas

    1: Biofuels via thermal gasification

    Biomass

    Solid Biomass Gasification

    Fischer Tropsch

    MTG

    Conventional synthetic gasoline and diesel

    Mt synfuelMOGD

    Refining

    Methanol

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    Challenges

    The process most commonly considered is thermalgasification to clean syngas and synthesis of hydrocarbonsby Fischer-Tropsch (FT)

    Biomass is a widely dispersed resource that must betransported over large distances at significant cost.

    Biomass preparation for entrained flow gasification can be:

    Torrefaction to render biomass more friable for grinding Liquefaction by fast pyrolysis

    Gasification technology is unproven at large scale.

    Gas cleaning is a major challenge and unproven The minimum economic size of Fischer Tropsch is widely

    considered to be 20,000 bbl/day or nearly 1 million t/y

    biofuels requiring nearly 5 million t/y biomass.

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    Fischer Tropsch

    Syngas

    Pretreatment by pyrolysis

    MTG

    Conventional synthetic gasoline and diesel

    Fast pyrolysis

    75% wt. liquid

    Gasification

    Torrefaction

    85% wt. solid

    Biomass

    Mt synfuelMOGD

    Refining

    Methanol

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    Pretreatment Torrefaction is low temperature pyrolysis to dry and

    partially devolatilise biomass. The product yield isaround 85% and can be more readily ground like coalfor gasification.

    Fast pyrolysis produces a mobile liquid (bio-oil) with upto 10 times the energy density of biomass. The productyield is up to 75%

    Liquids are easier to handle, store and transport. Fast pyrolysis can be decentralised and located nearthe biomass resources

    Conversion of biomass to a liquid near sourcereduces transport costs, and reduces gasificationcosts.

    Pressurised oxygen gasification of liquids is easier

    and lower cost than solid biomass

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    Pyrolysis + Fischer Tropsch

    Gasn.

    F-T

    Biomass

    Biomass

    Biomass

    Biomass

    Biomass

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    Capital costs

    0

    2000

    4000

    6000

    8000

    10000

    12000

    14000

    16000

    0 2 4 6 8 10 12

    Pyrolysis + large FT

    Small gasification +small FT

    Biomass input million dry t/y

    Capital cost, million

    Large gasification + FT

    Small FTunproven

    Large

    gasificationunproven

    Small pyrolysis& large FT

    proven

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    Solid vs liquid gasi