Ijah* Department of Chemical Engineering, Federal University of Technology Minna, Nigeria Abstract The possibility of producing ethanol from biomass such as maize cobs and groundnut
Trang 1The Production of Ethanol from Maize Cobs and Groundnut Shells
U.G Akpan, A.S Kovo, M Abdullahi, and J J Ijah*
Department of Chemical Engineering, Federal University of Technology
Minna, Nigeria
Abstract
The possibility of producing ethanol from biomass such as maize cobs and
groundnut shells was investigated Different concentrations of sulphuric acid (H 2 SO 4 )
were used to determine the acid concentration that could produce an optimal yield of
glucose The results revealed that 4.5M H 2 SO 4 produced the optimal yield of glucose
and ethanol This acid concentration was then used for the study of temperature effects
on yield of glucose The results indicated that glucose yield increased with temperature
within the experimental set-up The maize cobs and groundnut shells were mixed at
various ratios and pretreated to remove all extractives The ratio of 3:1 of maize cobs
to groundnut shells and at 4.5M acid gave a better glucose yield than those obtained
from individual biomass The ultimate product (glucose) was hydrolyzed and 8%
ethanol was obtained within three hours
Keywords: Alcohol, glucose, biomass, hydrolysis, fermentation
Introduction
The rapid growth of industries and
technological advancement in the world call for
development in the chemical sector The
production of industrial chemicals will enhance
the economic progress of any nation Ethanol,
one of the important industrial chemicals, can
be produced extensively from biomass such as
maize cob and groundnut shell The main
constituents of this class of crop by-product are
cellulose (Chang, et al 1981) and
hemicelluloses, making them lignocelluloses
(Cowling 1976) that can be excellent energy
sources
The practice of mechanized farming has
led to extensive discharge of agricultural
wastes that have had negative effects on the
environment The utilization of such wastes has
been a source of concern to many researchers
(Oyenuga 1959; Akpan 1999; Amosun 2000)
Therefore, this work was designed to look into
the possibility of converting some of such
by-products into industrial chemicals of economic
importance Ethanol is one such chemical It is
* Department of Biological Sciences, Federal
University of Technology, Minna, Nigeria
used as a solvent for chemicals Ethanol is used
as an intermediate in the production of liquid detergents It is also used in the manufacture of drugs, plastics, polishes, plasticizers, perfumes, cosmetics, rubbers, accelerators, and cellulose nitrate It is further used as an anti-freeze Ethanol produced from regenerable sources is
an attractive petrochemical feedstock in
petroleum for poor countries (Gordon, et al
1979) The various uses of ethanol and the importance of ridding the environment of the harmful effects of these agricultural by-products (biomass) underscore the significance
of this work
Ethanol is produced from palm wine by fermentation process (Harris 1963) Fermentation is one of the oldest processes known to man, and it is used in making a variety of products including foods, flavorings, beverages, pharmaceuticals, and chemicals Ethanol is made from a variety of products such as grain, molasses, fruit, cobs, and shell; its production, excluding that of beverages, has been declining since the 1930s because of the low cost (Othman 1981) In 1975, only 76×106
L of proof industrial ethanol were produced by fermentation compared to 7.95×106
L by synthesis
Trang 2During 1974, Nigeria was spending N 2
million annually on spirits and alcohol
(Madrella, et al 1981) This expenditure
represents a big market for a country like
Nigeria, with a population of over 120 million
people A crude estimate of the total market for
alcoholic beverages in Nigeria is about
2,500,500 L/year Therefore, provision must
be made to balance the shortfall to complement
the imported, hence the need for this work
Neverthless, the production of chemical
feedstock from biomass making use of locally
sourced material that is very cheap and within
reach can be accomplished (Eweke, et al
1979) In this work, agricultural wastes, which
are readily available, were used for ethanol
production
Methodology
Collection and Processing of Substrate Used
Maize cobs and groundnut shells were
collected in polythene bags from the farm of
Government Technical School, Kontagora,
Niger State, Nigeria and transported to the
laboratory A serrated disc grinder was used to
reduce the maize cobs and groundnut shells
into very small sizes of particle These particles
were then sieved to obtain average particle
sizes of 300μm in diameter The cellulose was
isolated by the procedure described by
Layokun (1981) To 10g of each sample of the
agricultural waste was added 20ml of diethyl
ether in a 250ml Erlenmeyer flask in order to
remove extractives and the residue left was
washed with distilled water 20ml of 14M
H2SO4 was added to the residue to isolate
lignin The hemicelluloses and cellulose were
dissolved leaving lignin as a hard precipitate
This modified procedure described by Layokun
(1981) was used to isolate the sample of maize
cobs and groundnut shells individually This
procedure was repeated for mixture of both
samples in the ratio 1:1, 1:2, 1:3 and 3:1 in
order to obtain best mixture that could produce
high quality of ethanol
To determine the effect of different acid
concentrations on the hydrolysis 2M solution
of concentrated H2SO4 was prepared and 10g of
the leached maize cobs and groundnut shells
were added to 50ml of the 2 M solution of
H2SO4, respectively under room temperature in
a stirred 250ml conical flask which serve as a reactor This reaction was allowed to proceed for 2.5 hrs Some quantities of the hydrolyzed sample at an interval of 30 min was collected and filtered, the resulting filtrates analyzed for the glucose using a refractometer (Abbe 60) The entire procedure was repeated for 3M, 4M, 4.5M and 5M of H2SO4 and the various acid concentrations recorded Using the best concentration of H2SO4 (4.5M), a mixture
of maize cobs and groundnut shells in the ratio
of 1:1, 1:2, 2:1, 1:3 and 3:1 were leached and the hydrolyzed samples were filtered The resulting filtrate was analyzed for glucose and the best ratio determined
Using the best maize cobs to groundnut shells of 3:1, the effect of temperature on its hydrolysis was investigated using a thermostated water bath (Gallenkamp, England) at 40o, 50o, 60o, 70o and 80oC 4.5M H2SO4 was used for the hydrolysis, and 10g of the mixture were pretreated by a modified procedure described by Layokun (1981) The reaction was allowed to proceed for 2.5 at constant temperature
The resulting hydrolyzed sample was filtered leaving a filtrate with high percentage
of glucose and this acted as the substrate The substrate in the fermentation medium was
inoculated with S cerevisiae as the started
culture and the time noted The conical flask, which has been sterilized, was tightly sealed with glass stopper to avoid air entering the reactor medium The entire process was allowed to remain for three hours Every 30 minutes, a sample was withdrawn and both glucose and the ethanol concentration were determined using a refractometer
In order to obtain a large quantity of pure ethanol, the quantity of maize cobs and groundnut shells were increased using the same ratio (3:1) The entire hydrolysis process was carried out to produce large quantity of glucose, which was fermented simultaneously After the fermentation process, alcohol was recovered using a simple batch distillation method Confirmatory tests were carried out to ascertain that the distillate was actually ethanol
Trang 3Results and Discussion
Acid hydrolysis of maize cobs and
groundnut shells at different acid
concentrations and at ambient temperatures
showed an increase in glucose concentration
with time (Tables 1 and 2) The concentration
of glucose was higher for both biomass when
the concentration of 4.5M H2SO4 was used
The glucose yield of maize cobs was higher
than that of groundnut shells, and ranged from
0 to 0.89g/cm3 for maize cobs (Table1) and 0
to 0.53g/cm3 for groundnut shells (Table2)
Table 1 Glucose yields for acid hydrolysis of
maize cobs at ambient temperature using
different acid concentrations
Glucose yield (g/cm3 Time
[min] 2Ma
3Ma 4Ma 4.5Ma 5Ma
0
6
12
18
30
60
90
120
150
0 0.02 0.07 0.15 0.21 0.33 0.39 0.42 0.43
0 0.03 0.11 0.19 0.24 0.34 0.41 0.46 0.48
0 0.04 0.14 0.20 0.26 0.42 0.53 0.60 0.64
0 0.05 0.17 0.28 0.46 0.67 0.79 0.86 0.89
0 0.02 0.13 0.26 0.35 0.49 0.57 0.60 0.02
a = acid concentration
Table2 Glucose yields for acid hydrolysis of
groundnut shells at ambient temperature
using different acid concentrations
Time Glucose yield (g/cm3)
(min) 2Ma 3Ma 4Ma 4.5Ma 5Ma
0
6
12
18
30
60
90
120
150
0
0.01
0.04
0.06
0.10
0.17
0.23
0.28
0.34
0 0.02 0.05 0.08 0.13 0.21 0.28 0.36 0.37
0 0.03 0.06 0.10 0.17 0.29 0.36 0.40 0.43
0 0.04 0.07 0.14 0.28 0.37 0.43 0.49 0.53
0 0.05 0.09 0.15 0.23 0.37 0.45 0.45 0.46
a = acid concentration
There was a drop in glucose concentration for both biomasses when hydrolyzed at 5M H2SO4 This could be attributed to the fact that at a higher concentration of acid, glucose can be converted
to levulinic and formic acid (Ghose 1956), which leads to decrease in glucose yield These then suggest that highest glucose yield can be obtained at moderate acid concentration of 4.5M H2SO4, which also serves as the optimal
pH condition for yeasts to metabolize its
substrate (Fan, et al 1980; Adams and Moses
1995)
Acid hydrolysis of maize cobs and groundnut shell at varying temperature using the optimal acid concentration of 4.5M H2SO4
brought about increase in glucose yield with time as shown in Tables 3 and 4
Tables 3 Glucose yields for acid hydrolysis of maize cobs at varying temperatures using 4.5M H2SO4
Glucose yield (g/cm3) Time
(min) 40oC 50oC 60oC 70oC 80oC
0
6
12
18
30
60
90
120
150
0 0.11 0.30 0.50 0.71 0.73 0.75 0.78 0.80
0 0.15 0.35 0.61 0.73 0.74 0.76 0.78 0.83
0 0.21 0.50 0.65 0.74 0.78 0.79 0.82 0.85
0 0.35 0.62 0.81 0.76 0.80 0.83 0.84 0.87
0 0.43 0.67 0.85 0.87 0.93 0.95 0.97 0.98
Table 4 Glucose yield for acid hydrolysis of groundnut shells at varying temperatures using 4.5M H2SO4
Glucose yield (g/cm3) Time
(min)
40oC 50oC 60oC 70oC 80oC
0
6
12
18
30
60
90
120
150
0 0.09 0.20 0.31 0.42 0.42 0.43 0.44 0.45
0 0.11 0.23 0.34 0.44 0.45 0.47 0.48 0.49
0 0.14 0.30 0.40 0.45 0.47 0.49 0.50 0.51
0 0.19 0.35 0.43 0.49 0.50 0.51 0.52 0.53
0 0.21 0.38 0.47 0.52 0.54 0.55 0.56 0.63
Trang 4At 80OC, glucose yield for both biomass
was at the peak and ranged 0 - 0.98g/cm3 for
maize cobs and 0 - 0.63g/cm3 for groundnut
shells This indicates that, at higher
temperatures and at moderate acid
concentrations, the yield of glucose increases
Consequently, acid hydrolysis of a mixture of
maize cobs and groundnut shells at different
ratios using 4.5 M H2SO4 at ambient
temperature shows an increase in glucose yield
as shown in Table 5
Table 5 Glucose yield for acid hydrolysis for
mixture of maize cobs and groundnut shells
using 4.5M H2SO4 at ambient temperature
Glucose yield (g/cm3) Time (min)
1:1 1:2 2:1 1:3 3:1
0
6
12
18
30
60
90
120
150
0 0.05 0.13 0.23 0.36 0.54 0.65 0.71 0.75
0 0.04 0.10 0.19 0.25 0.39 0.49 0.55 0.58
0 0.09 0.17 0.33 0.43 0.63 0.75 0.83 0.86
0 0.01 0.04 0.06 0.14 0.23 0.31 0.35 0.36
0 0.12 0.22 0.36 0.51 0.73 0.86 0.89 0.94
The ratio 1: 3 (maize cobs, groundnut
shells) shows a drastic decrease in glucose
yield from 0to0.36g/cm3 when compared to
other ratios This is probably due to high
amount of groundnut shells with structures,
which contain high degree of crystallinity and
polymerization thereby, limit accessibility to
acid attack Ratio 3:1 of maize cobs and
groundnut shells and 4.5M H2SO4 at varying
temperature shows an increase in glucose yield,
as shown in Table 6 Though glucose yield
increases with temperature, it is important to
note that it may denature at temperature above
its boiling point Therefore, the experiment
above 80oC will not be advantageous
During fermentation, the amount of
ethanol produced and glucose used were
determined and the results are shown in Table
7 The ethanol in the product increased from 0
to 8.2, while that of glucose decreased from
1.53g/cm3 to 0.07g/cm3 after 2.5 hours of the
fermentation The increase in ethanol
production and decrease in the amount of
glucose is due to the fact that, during
fermentation the yeast (S ceresiae) utilized the
glucose as a source of carbon and energy, whereas ethanol is produced as a result (Nester,
et al 1995) A test was carried out using
iodoform and dichromate solution confirmed that the distillate was ethanol
Table 6 Glucose yield for hydrolysis for mixture of maize cobs and groundnut shells in ratio 3:1 using 4.5M H2SO4 at different temperatures
Glucose yield (g/cm3) Time
(min)
40oC 50oC 60oC 70oC 80oC
0
6
12
18
30
60
90
120
150
0 0.03 0.28 0.56 0.83 0.85 0.86 0.88 0.90
0 0.10 0.40 0.62 0.86 0.89 0.90 0.92 0.93
0 0.25 0.58 0.68 0.90 0.92 0.95 0.96 0.97
0 0.28 0.62 0.76 0.93 0.95 0.98 1.00 1.01
0 0.31 0.65 0.94 1.07 1.25 1.29 1.43 1.53
Table 7 Percentage of ethanol produced and glucose concentration
Time (h)
Specific gravity
Ethanol (%)
Glucose concentration (g/cm3)
0 0.5 1.0 1.5 2.0 2.5 3.0
1.00 1.008 1.014 1.021 1.028 1.038 1.043
0 0.6 2.6 3.8 4.7 8.2 8.0
1.53 1.32 1.16 1.10 0.93 0.68 0.06
Conclusion
The results obtained from the experiment reveal that glucose is present in a reasonable amount in maize cobs and groundnut shells mixed together in the ratio 3:1 If the product (glucose) is fermented under the stipulated
experiment conditions with Saccaharomyces
cerevisiae (baker’s yeast), a substantial amount
of ethanol, which is used as a chemical feedstock, will be produced Thus, the
Trang 5importation of ethanol can be reduced if
substantial energy is devoted to the production
of ethanol from biomass This will also have a
multiplier effect such as jobs for the
unemployed
References
Adams, M.R.; and Moss, M.O 1995 Food
Microbiology Royal Society of Chemistry,
Cambridge, UK, pp 252-5
Akpan, U.G 1999 Acid demethylation of
agricultural waste (citrus peel) Paper
presented at the 8th Annual Sci Conf
Nigeria Society for Biol Conserv.,
University of Uyo, Uyo Nigeria
Amosun, A.O 2000 Gasification of biomass
for methanol production An unpublished
B.Eng Chemical Engineering Dept., Federal
Univ of Technology, Minna, Nigeria
Chang, M.M.; Chou, J.Y.; and Tsao, G.T
1981 Structure, pretreatment and hydrolysis
of cellulose Adv Biochem Engin 16: 40-5
Cowling, E.B 1976 Physical and chemical
constraints in the hydrolysis of cellulose and
lignocellulose’s material Biotech Bioengin
Symp Series 5:163-81
Ghose, T.K 1956 Cellulose biosynthesis and
hydrolysis of cellulosic substances
Adv Biotech J 2: 105-11
Gordon, G.B.; and Michael, S 1979 Food Science pp 21, 37-97 Pergamon Int Popular Sci Series, Oxford, UK
Harris, J.F 1963 Wood as a Chemical Raw Material The Chemistry of Wood Interscience Publ., New York, NY, USA Layokun, S.K 1981 Kinetics of acid hydrolysis of cellulose from sawdust Proc
11th Annual Conf Nigeria Soc Chem Engin., pp 63-8
Madrella, R.B.; and Lauch, H.W 1981 Alcohol production and recovery Adv Biochem Engin., pp 43: 92
Nester, E.W.; Roberts, C.E.; and Nester, M.T
1995 Microbiology - A Human Perspective W.C Brown Pub., Dubuque, Iowa, USA, pp.116-8
Othman, Kirk 1981 Encyclopedia of Chemical Technology, Vol 2, pp 393-6 John Wiley, New York, NY, USA
Oyenuga, V.A 1959 Nigeria Foods and Feeding Stuffs, 2nd ed Revised Univ Press, Ibandan, Nigeria, pp 56-7, 71
Robinson, C.W.; Moo-Young, M.; and Lampten, T 1980 Ethanol production by immobilized yeast cells in a packed tower Proc 6th Int Fermentation Symp., London, England