Production of Biobutanol from biomass which is most renewable energy resource

1. PRODUCTION OF BUTANOL FROM BIOMASS
K.R.Padma
Assistant Professor
SPMVV
Tirupati
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 Butanol may be used as a fuel in an internal combustion engine.
 It is more similar to gasoline than it is to ethanol.
 A C4-hydrocarbon, butanol is a drop-in fuel and thus works in vehicles
designed for use with gasoline without modification.
 It can be produced from biomass (as "biobutanol")
 Butanol from biomass is called biobutanol
 as well as fossil fuels (as "petrobutanol").
 Both biobutanol and petrobutanol have the same chemical properties.
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3.  Fossil fuels are the primary source of energy production.
 However, owing to their negative effects and ever increasing demand of
energy, biofuels, especially, biobutanol is gaining increased interest.
 At present, the biofuel market is dominated by biodiesel, bioethanol,
biobutanol, and biogas, much relying on the substrates such as- sugars, starch,
oil crops, agricultural and animal residue, and lignocellulosic biomass.
 Butanol (C4H9OH) has superior fuel properties over traditional fuel ethanol in
terms of energy density and hygroscopicity.
 There are some bottlenecks that need to be overcome in the production of
butanol in order to get a sustainable alternative for fossil fuels.
 Lignocellulosic biomass due to its low cost and yearlong availability, is a
suitable raw material for butanol production.
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4.  Fossil fuels, such as petroleum, are the most utilized energy resources which are not
renewable and fast depleting.
 The continuous and abundant use of petroleum fuels has increased the greenhouse gases
(GHG) emissions including CO, CO2, NOx, and other gases.
 By reducing the use of petroleum fuels, these emissions could be reduced which can lead to
a cleaner environment.
 Considerable interest has been evoked in alternative energy resources due to several
environmental concerns.
 All over the world, the focus of research is to develop novel processes for producing fuel and
related products from renewable resources like biomass, to find efficient and sustainable
energy sources that are economically competitive, technically feasible, easily available and
eco-friendly.
 In Indian context, there is an immense need to develop a sustainable technology for
alternative fuel production.
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15.  As in the conversion of starch to ethanol, the plants must be processed in a similar way but we
just use different enzymes, and end processing may be different because of the different
chemicals produced.
 Starch must be hydrolyzed in acid before using the enzyme.
 And, as with using cellulose and hemicellulose as the starting material, it must first be pretreated
to separate out the cellulose, then treated again to eventually produce glucose in order to make
butanol from fermentation.
 Remember the glucose to ethanol reaction? Starch will produce the following products:
 3 parts acetone (3 CH3-CO-CH3), 6 parts butanol (6 CH3-CH2-CH2-CH2OH), and 1 part ethanol (1
CH3-CH2-OH).
 So, what feed materials are used for butanol production?
 Similar to what is used for ethanol production,
 which includes: 1) grains, including wheat straw, barley straw, and corn stover,
 2) by-products from paper and sugar production, including waste paper, cotton woods, wood
chips, corn fiber, and sugarcane bagasse,
 and 3) energy crops including switchgrass, reed canarygrass, and alfalfa.
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19.  Solvent producing clostridia during its initial growth phase (acidogenisis) produces carbon
dioxide, hydrogen, acetate and butyrate which results to decrease in pH of the culture medium.
 While the culture attains the stationary growth phase, cells undergo shift from acid to solvent
production (solventogenic phase).
 At this phase, there is an increase in pH of the culture medium due to continued consumption
sugar and resulting in reformation of acid.
 In fermentation, conversion of carbohydrate to acids, solvents and other gases occurs using
carbohydrate hexose and pentose.
 Hexose sugars are metabolized to pyruvate through
 whereas pentose sugars initially undergo yielding pentose-5-
phosphate and through transketolase-transaldolase sequence which results in fructose-6-
phosphate which enters glycolysis.
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22.  This pentose sugar conversion was metabolized by solvent producing clostridia.
 The pyruvate obtained through glycolysis was cleaved to acetyl CoA and carbon dioxide in
presence of coenzyme A (CoA).
 This acetyl CoA considered as precursor for both acid and solvent production in the fermentation
pathway.
 It seems that acetyl-CoA is mostly used to form butyryl-CoA, based on the fact that the
conversion of acetyl-CoA to butyryl -CoA exhibits enhanced thermodynamic stability.
 A high concentration of acetyl-CoA is needed to make this reaction go smoothly, and the
quantity of acetyl-CoA plays an important role in determining the ratio of C3 and C4 products to
C2 products.
 This shift induction is controlled either by the decrease in pH (2 g L-1)
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 In addition to acetyl-CoA, CO2 and reduced-ferredoxin products are also formed during
the reaction.
 In many Clostridium species the primary role of NADH ferredoxin-oxidoreductase, which
requires acetyl CoA as an activator, is NAD+ regeneration by reduced ferredoxin-
oxidoreductase production to produce NADPH by biosynthesis.
 Under appropriate NADPH conditions, the reduced ferredoxin is able to transfer electrons
to iron and permitting the use of protons as a final electron acceptor, resulting in the
production of molecular hydrogen.
 Ferrodoxin is oxidised during this step and hydrogen gas is released from the cell
 Acetyl-CoA is a branch point between acid- versus solvent-production in C. acetobutylicum
and it can be different, depending on the clostridial species.
 It can be converted into a mixture of ethanol, acetate and or butyrate. The ratio in which
these products are formed depends on the amount of H2 involved.

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27.  Lignocellulosic materials contain lignin, hemicellulosic, and cellulose with their varying proportions.
Climate and associated environmental factors govern the availability of lignocellulosic materials in
different parts of the world.
 As they are abundant and renewable resources, lignocellulosic materials have the potential to be the
largest source of biomass for the production of biofuels.
 Agricultural residues like wheat straw, rice straw, barley straw, wheat bran, switch grass, corn stover
, bagasse, etc. have been extensively studied.
 Apart from agricultural residues, other feedstocks, such as municipal waste, used paper, soil organic
carbon, wheat flour, and other type of lignocellulosic materials have also been studied extensively.
 Lignocellulosic biomass with higher content of cellulose and hemicellulose can be hydrolysed readily
into pentoses and hexoses, which are potential feedstock for biobutanol production
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28.  The major factor in determining the economy of ABE fermentation is the cost of substrate.
 Initially starch or carbohydrate sources such as potatoes, rice, sorghum, pearl millet, apple
pomace, cheese whey, and Jerusalem artichokes were used as substrate.
 But these substrates are used as food source.
 In this context, lignocellulosic biomass can be used as a cheaper substrate for biobutanol
production due to its several advantages such as availability in abundance and no competetion
with the food chain.
 Lignocellulosic biobutranol production consists of major three steps: pretreatment, enzymatic
hydrolysis and fermentation.
 After pretreatment, there is a need of hydrolysis step for fermentabe sugar production. The use of
enzymes for hydrolysis could be expensive and also causes end point inhibition due to the
incomplete hydrolysis
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30.  In a recent study, batch fermentation of acidic pre-treated rice straw under anaerobic
condition was carried out. Clostridium acetobutylicum NCIM 2337, an obligate anaerobic
and mesophilic strain used for this process, capable of utilizing a range of carbohydrates
 During the process of conventional hydrolysis of lignocellulosic biomass at higher
temperature, an additional high pressure and shear stress can also be applied.
 There was a rapid release of fermentable sugar mainly glucose and other sugars such
as xylose, arabinose, etc. in minor concentrations as a result of such pre-treatment.
 This stress assisted with acid hydrolysis of rice straw resulted in maximum sugar yield
with the concentration of ~3.9% (w/v) from aqueous solution of the 5% (w/v) rice straw.
 Total fermentable sugar utilized during fermentation found to be 61.4%, with reducing
sugars 57.8% and glucose with 55.1%.
 This study manifests that rice straw as an economical and easily available substrate for
butanol production.
 Further improvement of this process can be done by nutrient supplementation of rice
straw hydrolyzates, using genetically modified strains and optimization of physical
parameters
 Lignocellulosic biomass hydrolysis by enzymes is carried out at 45ºC or 50ºC .
 Another advantage of pretreatment at high temperature is the inhibition of the growth of
other mesophilic anaerobic microbes thereby minimizing of contamination in ABE
fermentation process by these organisms
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Isobutanol
 is a second-generation biofuel with several qualities that resolve issues presented by ethanol.
 Isobutanol's properties make it an attractive biofuel:
 relatively high energy density, 98% of that of gasoline.
 does not readily absorb water from air, preventing the corrosion of engines and pipelines.
 can be mixed at any proportion with gasoline, meaning the fuel can "drop into" the existing
petroleum infrastructure as a replacement fuel or major additive.
 can be produced from plant matter not connected to food supplies,
 preventing a fuel-price/food-price relationship

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n-Butanol
 better tolerates water contamination and is less corrosive than ethanol and more suitable for
distribution through existing pipelines for gasoline.
 In blends with diesel or gasoline,
 butanol is less likely to separate from this fuel than ethanol if the fuel is contaminated with
water.
 There is also a vapor pressure co-blend synergy with butanol and gasoline containing
ethanol, which facilitates ethanol blending.
 This facilitates storage and distribution of blended fuels

34. Biobutanol (C4H9OH) is one such superior biofuel and could be seen as a potential alternative to
conventional fuels. The comparative analysis of different fuels with respect to their fuel properties
is summarized in (Table 1)
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 The octane rating of n-butanol is similar to that of gasoline but lower than that of ethanol and
methanol.
 n-Butanol has a RON (Research Octane number) of 96 and a MON (Motor octane number) of
78 (with a resulting "(R+M)/2 pump octane number" of 87, as used in North America)
 while t-butanol has octane ratings of 105 RON and 89 MON.
 t-Butanol is used as an additive in gasoline but cannot be used as a fuel in its pure form because
its relatively high melting point of 25.5 °C (79 °F) causes it to gel and solidify near room
temperature.
 On the other hand, isobutanol has a lower melting point than n-butanol and favorable RON of
113 and MON of 94, and is thus much better suited to high fraction gasoline blends, blends with
n-butanol, or as a standalone fuel.
 A fuel with a higher octane rating is less prone to knocking (extremely rapid and spontaneous
combustion by compression)
 and the control system of any modern car engine can take advantage of this by adjusting the
ignition timing.
 This will improve energy efficiency, leading to a better fuel economy than the comparisons of
energy content different fuels indicate.
 By increasing the compression ratio, further gains in fuel economy, power and torque can be
achieved.
 Conversely, a fuel with lower octane rating is more prone to knocking and will lower efficiency.
Knocking can also cause engine damage. Engines designed to run on 87 octane will not have
any additional power/fuel economy from being operated with higher octane fuel.

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Butanol characteristics: air-fuel ratio, specific energy, viscosity, specific heat
Air-Fuel Ratio
 Alcohol fuels, including butanol and ethanol, are partially oxidized and therefore need to
run at richer mixtures than gasoline.
 Standard gasoline engines in cars can adjust the air-fuel ratio to accommodate
variations in the fuel,
 but only within certain limits depending on model.
 If the limit is exceeded by running the engine on pure ethanol or a gasoline blend with a
high percentage of ethanol, the engine will run lean, something which can critically
damage components.
 Compared to ethanol, butanol can be mixed in higher ratios with gasoline for use in
existing cars without the need for retrofit as the air-fuel ratio and energy content are
closer to that of gasoline.
Specific Energy
 Alcohol fuels have less energy per unit weight and unit volume than gasoline.
 To make it possible to compare the net energy released per cycle a measure called the
fuels specific energy is sometimes used.
 It is defined as the energy released per air fuel ratio.
 The net energy released per cycle is higher for butanol than ethanol or methanol and
about 10% higher than for gasoline.

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Viscosity
 The viscosity of alcohols increase with longer carbon chains.
 For this reason, butanol is used as an alternative to shorter alcohols when a more viscous
solvent is desired.
 The kinematic viscosity of butanol is several times higher than that of gasoline and about as
viscous as high quality diesel fuel.
Specific Heat
 The fuel in an engine has to be vaporized before it will burn.
 Insufficient vaporization is a known problem with alcohol fuels during cold starts in cold weather.
 As the heat of vaporization of butanol is less than half of that of ethanol, an engine running on
butanol should be easier to start in cold weather than one running on ethanol or methanol.

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Butanol Fuel Mixtures
 Standards for the blending of ethanol and methanol in gasoline exist in many countries, including the
EU, the US, and Brazil.
 Approximate equivalent butanol blends can be calculated from the relations between
the stoichiometric fuel-air ratio of butanol, ethanol and gasoline.
 Common ethanol fuel mixtures for fuel sold as gasoline currently range from 5% to 10%. It is estimated
that around 9.5 gigaliter (Gl) of gasoline can be saved and about 64.6 Gl of butanol-gasoline blend
16% (Bu16) can potentially be produced from corn residues in the US, which is equivalent to 11.8% of
total domestic gasoline consumption.
 Consumer acceptance may be limited due to the potentially offensive banana-like smell of n-butanol.
 Plans are underway to market a fuel that is 85% Ethanol and 15% Butanol (E85B), so existing E85
internal combustion engines can run on a 100% renewable fuel that could be made without using any
fossil fuels. Because its longer hydrocarbon chain causes it to be fairly non-polar, it is more similar to
gasoline than it is to ethanol.
 Butanol has been demonstrated to work in vehicles designed for use with gasoline without
modification.

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 The toxicity of accumulated butanol and the intermediates is a very important feature of the ABE
fermentation.
 The growth rates of Clostridium acetobutylicum in presence of BuOH, EtOH, Me2CO, acetate and butyrate.
 Acetate and butyrate were the most toxic compounds, with concentrations of 5 and 8.5 g/L, respectively,
stopped the cell growth.
 An EtOH concentration of 51 g/L or 11 g BuOH/L reduced cell growth by 50%.
 Acetone did not inhibit cell growth at 29 g/L, thus ethanol and acetone were nontoxic at a normal
fermentation.
 Some mutant strains, however, more tolerant towards butanol, for example Lin and Bladchek [17]
obtained a derivative of C. acetobutylicum ATCC 824 which grew at concentrations of BuOH that
prevented growth of the wild-type strain at a rate which was 66% of the uninhibited control.
 This strain produced consistently higher concentrations of BuOH (5-14%) and lower concentrations of
acetone (12.5-40%) than the wild-type strain in 4-20% extruded corn broth.
 Characterization of the wild-type and the mutant strain demonstrated the superiority of the latter in terms of
growth rate, time of onset of BuOH production, carbohydrate utilization, pH resistance, and final BuOH
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 Moreira et al. initiated a fundamental study attempting to elucidate the mechanism for BuOH
toxicity in the acetone-BuOH fermentation by Clostridium acetobutylicum.
 Butanol as a hydrophobic compound inserted into the membrane increases the passive proton
flux, forms a “hole” for proton on the membrane.
 This eliminates hydrogen ions form the cell and the intracellular pH increases.
 The strains which are able to decrease the membrane fluidity are more resistant towards butanol.
 The cells have deacidifying mechanism to keep the intracellular pH value at 6 when the pH value
of the ferment liquor is located between 4 and 5 can reduce acids into alcohols, whichincreases
their butanol producing ability.
 Lepage et al [19] studied the changes in membrane lipid composition of C. acetobutylicum during
ABE fermentation.
 Large changes were found in phospholipid composition and in fatty acid composition, the latter
characterized mainly by a decrease in the unsaturated/saturated fatty acid (U/S) ratio.

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 Effects of the addition of alcohols (EtOH, BuOH, hexanol, and octanol) and of acetone
were also studied.
 In all cases, large changes were observed in the U/S ratio,
 but with differences which were related to the chain length of the alcohols.
 The effect of solvents appears to account for a large part of changes in lipid composition
observed during the fermentation.
 The pH was also important, a decrease in pH resulting in a decrease in the U/S ratio and
in an increase in cyclopropane fatty acids.
 The effect of increasing temperature was mainly to increase fatty acid chain lengths

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