Biofuels

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Biofuels
Bioethanol, Biodiesel, Biohydrogen, Biogas and
Biomethanol.

• wstafford_at_uwc.ac.za

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The problem of finite, polluting fossil-fuels

• The stocks of oil and coal are uneven in
  distribution and are being rapidly depleted- it
  has been estimated that oil supplies will only
  last until 2080.
• Oil/coal are Non-renewable fossil fuels causing
  carbon depletion, global warming
• Oil/coal are also polluting during combustion
  SOx, NOx

Alternative sources of fuel are urgently required!
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Global warming is our warning!
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Biofuels combustion, pyrolysis
The direct combustion of biomass in the form of
wood has been with us for thousands of years as a
source of heat. Some 90 of the biomass energy is
held in trees timber is used not only for energy
but also for a number of other industries- The
trees are not being replaced at the same rate as
they are being harvested so that the resource is
being depleted and carbon dioxide added to the
atmosphere. Pyrolysis is the heating of the
biomass in the absence of air at temperatures of
300-500C. The solids which remain are charcoal,
and the volatiles if they are collected can be
used as fuel oil (bio-oil).
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Biofuels Gasification,

• Gasification is a process where the biomass
  ferments anaerobically (methanogens predominate)
  to produce a biogas of 50-75 methane, carbon
  dioxide, hydrogen suphide, and hydrogen. It
  contains sufficient energy (20-25 MJ/kg) to be
  used as a fuel in boilers and dual-fuel engines
  and can be used to generate electricity.
• Landfill sites when capped can produce methane,
  which can be collected if pipes or channels are
  incorporated into the construction. Small
  anaerobic digesters have been installed on farms.
  A number of industrial wastes are treated
  anaerobically and the biogas used to run the
  pumps and heaters. Also on-site treatment of
  waste and the production of low-pressure gas for
  domestic use (China and India).

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Syngas, methane, methanol and hydrogen

• Under some conditions gasification can produce
  synthesis gas (syngas), which is a mixture of
  methane and hydrogen. The methane can be
  converted (catalyst at 900C) to carbon monoxide
  and hydrogen.
• A further reaction with water converts any excess
  carbon monoxide to carbon dioxide, which can be
  removed by a solvent process or pressure-swing
  adsorption. The remaining mixture of carbon
  monoxide and hydrogen can be either converted to
  methanol by reaction over a catalyst at 450C or
  if hydrogen is required the two gases can be
  separated (Larson et al., 1996).

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Bio-hydrogen

• Hydrogen production is triggered in
  cyanobacterium Anabena cylindrica by anaerobic
  conditions, which induces the reversible
  hydrogenase. The hydrogenase is inhibited by
  oxygen so physical separation occurs with the
  photosynthetic vegetative cells generating oxygen
  and heterocysts producing hydrogen.
• Bacterial production of hydrogen can occur with
  photosynthetic bacteria such as Rhodospirillum
  rubrum and Rhodobacter sphaeroides and
  Clostridium bifermentans, under anaerobic
  conditions. (Wang et al., 2003).

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Biodiesel

• Transport and industry is widely used to power
  tractors, pumps, and generators. The engine
  designed by Diesel (1893) and the patent proposed
  that the fuel could be powdered coal, groundnut
  oil, castor oil, or a petroleum-based fuel (Shay,
  1993 Machacon et al., 2001). At the time the
  growing petrochemical industry provided the best
  fuel, a crude oil fraction now called diesel..
• Conventional diesel produced by the distillation
  of crude oil collecting middle distillate
  fractions in the range of 175-370C. The fuel
  contains hydrocarbons, naphthenes, olefins, and
  aromatics.

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Bio-oil

• Plant-derived oils have been used to replace
  diesel in emergency situations but a renewal of
  interest on using oils as a renewable and
  carbon-neutral replacement for diesel.
• Plant oils are normally extracted from
  oil-containing seeds-soybean, sunflower, rapeseed
  and oil palm and these can be grown in most
  climates and locations.
• A number of algae are capable of producing
  terpenoid oils, one of which is Botrycoccus
  braunii which can accumulate up to 86 dry weight
  as oil (Calvin, 1985).

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Transesterification to Biodiesel

• These oils need to be treated further to be used
  in combustion (reduce viscosty, increase octane
  rating and reduce waxes) by
• Blending or pyrolysis or cracking OR
• Transesterification-treat the oil with methanol
  or ethanol in acid or alkaline conditions. The
  methyl or ethyl ester mixture is known as
  biodiesel.

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Conversion of the triglycerides making up the
oils to fatty acid esters and glycerol
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Advantages of Biodiesel

• Compared to diesel
• Biodiesel is non-toxic and more biodegradable (Ma
  and Hanna, 1999), with a very low sulphur
  content, which on combustion produces less carbon
  and nitrogen monoxides, soot, hydrocarbons
  (Peterson et al.., 1996)
• Biodiesel be used in diesel engines without
  modification.

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Bioethanol production
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Integrated Biomass Utilization system.
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Bioethanol

• Ethanol can be used as a fuel to replace petrol
  and ethanol-fuelled cars started in the 1930s in
  the USA where ethanol produced from maize was
  used at a concentration of 20 to produce gasohol
  called Agrol. Still competes with the
  availability of cheaper petrol.
• The large-scale production of ethanol as a fuel
  started in Brazil in 1975 followed by the USA in
  1978, probably initiated by the increases in
  crude oil

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Raw materials to Bioethanol
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Production of BioethanolPDC and ADH

• The ability of micro-organisms to produce alcohol
  from sugars has been known since Egyptian
  times-the yeast Saccharomyces cerevisiae that
  ferments sugars to ethanol and carbon dioxide.
• The pathway involved in the production of ethanol
  in S. cerevisiae is initially glycolysis and then
  pyruvate is converted to acetaldehyde by the
  enzyme pyruvate decarboxylase with the release of
  carbon dioxide. The Acetaldehyde is converted by
  the enzyme alcohol dehydrogenase to ethanol with
  the regeneration of NADH.

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PDC mediated Bioethanol production
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PDC

• Pyruvate decarboxylase (PDC, EC 4.1.1.1) is one
  of several enzymes that require thiamine
  diphosphate (TPP) and a magnesium as essential
  cofactors. PDC has a sequence motif that is
  common to all TPP- binding enzymes (Hawkins et
  al., 1989.) The protein is a tetramer with 60 kDa
  subunits.

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Yields of 91, ethanol production to 10-18 max.
Ethanol removal from a bioreactor-?-high
temperature for evaporation-hydrophobic membrane
for selective filtration
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Bioethanol production

• Brazil started in 1975 with a National Alcohol
  Programme to produce 95.5 hydrous ethanol
  (Alcool) and by 1980s the majority of cars used
  this fuel. Initially ethanol was produced by the
  fermentation of sugar from sugar cane (Saccharum
  officinarum) in simple batch fermenters with
  capacities of up to 1.5 million L.
• The main renewable substrate for fermentation in
  the USA is starch extracted from maize. Initiated
  1988 with over 51 plants were operating. Amylase
  and an Aspergillus niger amyloglucosidase used to
  convert the starch to glucose prior to the
  S.cerevisiae fermentation

Challenges Using cellulosic substartes
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A future with Biofuels..

• A global world contribution to CO2 saving of
  about 4.5 billion tons of CO2 a year (from
  bioethanol use alone),
• A further significant reduction of noxious
  pollutants (Sox, NOx, CO, and other very toxic
  polycyclic aromatic hydrocarbons) in urban areas.
  
• The creation, worldwide (mostly in rural regions)
  of an estimated 85 million new jobs. This
  calculation does not take into account jobs
  created in the secondary services sector. (The
  total number of jobs lost in the petroleum
  industry, as a result of fuel substitution, has
  been estimated at around 2 million.)