Potential of using maize stalks for fuel ethanol production.
Mwangi, Lucy K.
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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.