Abstraction ABE fermentation along with n-butanol acetone and

Abstraction
of hydrogen atom is easy from inner carbon to hydrogen bonds (C-H bond) than
terminal. This is because energy requires for
breaking inner C-H bond is
less than terminal
C-H bonds Gu et al., 2010.  As compared to other butanol isomers n-butanol has more number
of inner C-H bonds that can be easily breakable because of this n-butanol
has higher laminar burning velocity and lower
self-ignition temperature. The absence of inner C-H
bond in Tert-Butanol results in highest self-ignition temperature and lowest laminar
burning velocity among all other butanol isomers.  For iso-butanol and sec-butanol laminar burning
speed and adiabatic flame temperature are lies in between n-butanol and
tert-butanol. However, based on type of butanol isomer adiabatic flame
temperature varies a little. For fuel air equivalence ratio of 1.1, the laminar burning
velocity and adiabatic flame temperature peaks for all butanol
isomers Gu et al., 2010. Based on availability and
physical properties of different butanol isomers, 1-butanol (n-butanol) is chosen
as an alternative renewable fuel for this research work. However, some
experiments were also being done with ethanol fuel as well will be explained
later.       

2.2.3.
Production of butanol

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Butyl
alcohol was first produce
from anaerobic conversion of calcium
lactate lactic acid. N-butanol was produce through fermentation process which is
called ABE fermentation along with n-butanol acetone and ethanol were also by
product of fermentation process. N-butanol is the immediate
product of the fermentation process. Other butanol isomers are
derived as by-products during the production of chemicals like acetone,
isobutylene and propylene. Fermentation
is basically a metabolic reaction of bacteria or yeast in the absence of
oxygen. From fermentation three products namely
organic acids (acetic acid, lactic acid and butyric acid),
solvents (acetone, ethanol and butanol) and gases (carbon dioxide, and hydrogen)
were produced. (Durre, 2011, Green, 2011). The ABE
process uses bacteria to produce a 6:3:1 ratio of
butanol, acetone and ethanol. The substrates considered for
acetone–butanol production includes fruit processing industry waste Jesse TW,
2002, starch-based packaging materials Jesse TW,
2002, soy molasses Qureshi N,
2001, corn fiber hydrolysate Ebener J, 2003, and whey
permeate Maddox IS, 1993. By using bio-synthetic
genes of yeast, low cost agricultural residues like corn cobs, sugarcane
bagasse, wheat straw and municipal solid waste fermentation reaction can be accelerated
for production of n-butanol. (Jin et al., 2011; Kumar and Gayen, 2012; Chen et
al., 2012;). Gas stripping or distillation or reverse osmosis
techniques were used to recover n-butanol after the fermentation
reaction. For instance, developing countries like India
generates over 370 million tonnes of biomass every year directly from rice husk
from rice mills, bagasse from sugar mills, saw dust from
saw mills, plants, etc. which can be for
enhancing production of n-butanol in near future Chauhan,
Suresh, 2010

 

 

2.2.4.
Production of ethanol.

Ethanol can
be produced from variety of feed stocks. The feed stocks can be bagasse,
switch grass, sugar beet, sugar cane, molasses, straw, cotton, grain, and other
biomass. The ethanol production process
contains eight basics steps – Milling, Liquefaction, saccharification,
fermentation, distillation, dehydration, denaturing and
co-products. The greenhouse gases i.e. CO2
can be reduced if ethanol is produced from
waste wood (beer, 2007).  The most effective microorganism
for fermentation of ethanol is Saccharomyces cerevisiae (Balat et al., 2008; Srirangan
et al 2012). Synthetic gas can be used to produce ethanol. In
this process synthetic gas (mixture of hydrogen and carbon
monoxide) is passed through a reactor containing a catalyst, which causes the
gas mixture to be converted into ethanol. Synthetic gas is by product
of industrial process, oil wells and biomass gasifiers. USA,
Brazil, China, India, France are the top five countries producing bio-ethanol effectively
from its bio-resources

2.3. USE OF
ALCOHOLS IN COMPRESSION IGNITED ENGINES

Alcohol can
be used in compression ignited engine in following three ways –

A.    Direct of blending of alcohol and diesel in a stable binary blend.

B.     Use of neat alcohols by Port fuel injection or direct high-pressure injection.

C.     Dual fuel mode, i.e. port fuel injection of
alcohols into intake air and direct injection of diesel into combustion
chamber.

2.3.1. Direct of blending of alcohol in diesel

Alcohols
can be used in CI engine along with diesel in the form of blend. In this mode
alcohol and diesel fuels are mixed first, after this
it is injected into the cylinder
through the fuel injector. However, in blending amount alcohol which can be
mixed with diesel depends on type alcohol, temperature and water content.
Alcohols like ethanol and methanol are hydrophilic in nature and due to this
they can be blended in small quantities. In addition to this methanol and
ethanol are short-chain alcohols due to this they have solubility issue with
diesel. It is possible that they can separate inside fuel tank if this happen
it is not good for engine system because of this they need a co-solvent for
making stable blend. At a temperature of 25ºC the miscibility of methanol is
less than 5 vol% and that of ethanol is less than 20 vol% in the absence of
water. However, butanol can be mixed in any proportion with diesel at this
temperature when there is no water Lapuerta, 2010. Presence of water decrease
solubility of ethanol and methanol with diesel. It is observed that 1% of water
in ethanol can decrease solubility by 2% with as compared to without water case
Lapuerta, 2007. In case of ethanol tetrahydrofuran and ethyl acetate are used
to improve solubility of ethanol in diesel. In presence of water butanol diesel
blends are less prone to separate because of this it did not require co-solvent.
This is because butanol has lower solubility with water Hajba, 2011. Even
butanol is use as a co-solvent in case of preparing
blends of methanol-diesel Huang, 2005 and ethanol-diesel Asfar, 1998. At down
to 0 ºC for ensuring complete miscibility of ethanol in diesel the ratio of ethyl
acetate (co solvent) to ethanol needed was found as 1:2 Hansen, 2004. As
methanol and ethanol are more corrosive and their viscosity is also poor which
leads to lower lubricity of blended fuel. Lower viscosity can lead to damage
injection system because of additives are required for increasing viscosity,
resistance corrosion and other properties in order to protect injection system.
It is observed that in some cases, quantity of additive may be considerable Adelman,
1979. Heating value of blends significantly affected by additives Waterland,
2003. In summary, addition of alcohols into diesel changes physical
and chemical properties of diesel fuel. In addition to this blend of alcohol
with diesel fuel results in decrease in following properties viscosity, heating
value and cetane number.

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