Potential of using maize stalks for fuel ethanol production.
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Date
2012-02
Authors
Mwangi, Lucy K.
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Abstract
In Kenya, a country that has not been successful in getting its own fossil fuel
deposits, the main material used for ethanol production has been molasses but its
supply compared to demand is becoming limited. There is need for alternative
materials to produce ethanol without affecting food supply. This study
investigated the potential of juice from maize stalks grown locally and normally a
byproduct of maize farming, for production of fuel ethanol. Selected Kenyan
maize varieties were grown in two seasons, March and September of year 2008.
This was done under typical field conditions and sampled at three growth stages,
the silking, the milk stage and dry maize stage. Maize varieties for three agroecological
zones in Kenya were used, the low dry lands, the medium altitude and
the highlands varieties. The juice was extracted by crushing the stalks with a 3-
roller mill sugarcane crusher and analyzed for total sugars using a digital
refractometer (NR-151, China) and specific sugars using a high performance
liquid chromatography (HPLC) with a reverse phase column and refractive index
detector (RID). The juice was then fermented using baker's yeast (Saccharomyces
cerevisiae) at constant temperature of 27DC and a pH range of 4-5, distilled at 78
DC and the yield of alcohol determined. The ethanol obtained was tested in a
Chinese wick stove (wheel brand model 62) for fuel properties (specific fuel
consumption, fire power, burning rate and thermal efficiency) for domestic
cooking application. Its performance was compared to that of kerosene fuel. The
highest juice yield obtained was 176.67mllstalk (18840litres/hectare) for maize
variety HB625 at the green maize stage, while the lowest was 8.33ml/stalk
(616Iitres/hectare) for variety Katumani in the dry maize stage. The two varieties
also had the highest and lowest ethanol yields at 1445.5litres/hectare and
42litres/hectare respectively. Hybrids had the highest juice and ethanol yields per
hectare. The three main sugars identified in the maize stalk juice were sucrose,
glucose and fructose. The trend for the sugars was a decrease for fructose and
glucose and an increase in sucrose as the maize plant matured. Ethanol obtained
burnt with a blue flame compared to the yellow flame of kerosene, with a power
output of 1.08kW and a thermal efficiency of 38.2%. However, about 2 times the
quantity of fuel and heating time was required for ethanol compared to kerosene
to bring to boiling point the same amount of water at the same conditions. The
average cost of producing llitre of ethanol (93%v/v) from the maize stalks was
found to be KSh.63.56 (about 1USD). The study has contributed positively to the
search for a clean sustainable energy resource and consequently reduction of
dependence on the fossil petroleum fuels in Kenya and other countries. Use of
maize stalks as feedstock for ethanol production gives a renewable source of
energy for the motor industry and for domestic cooking. Maize grows in plenty in
Kenya and this can boost energy security for the country and also contribute to
economic growth for the country, specifically the rural economy through
diversification of the agro-industry.
Description
Department of Energy Engineering, 158p. 2012, TP 339 .M9