Assessmant of the potential for lignocellulosic bioethanol production in Nigeria

• Main Author: Iye, Edward Lucky
• Published: University of Newcastle Upon Tyne 2011
• Subjects: 662.88
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578550

Lignocellulosic materials are promising alternative feedstocks for bioethanol production. This dissertation focuses on 2nd generation bioethanol production from lignocellulosic biomass. The first part of this thesis examined the enzymatic production of fennentable sugars from a range of lignocellulosic biomass and agricultural residues e.g. miscanthus, switchgrass, reedcanary grass, wheat straw, cassava peel and millet straw. The 2n part analysed supply of feedstocks in Nigeria with respect to bioethanol yield and models the potential supply in specific geographical locations with a view to establishing commercial cellulosic ethanol facilities. The overall goal of the dissertation is to evaluate cellulosic feedstock availability in Nigeria and their potential for bioethanol production. In this study the Van Soest detergent fibre analysis method was used to determine the chemical composition of a range of feedstocks. Barley and wheat straw showed the highest cellulose content while switchgrass had the highest hemicellulose. The theoretical ethanol yield based on cellulose content for the herbaceous energy crops and agricultural residue showed that barley straw had the highest potential yield of 145.35 IIton and cassava peels had the lowest yield of 94.28 IItone because starch was not taken into account. The study also analysed varietal variation in chemical composition of wheat straw from a HGCA Recommended list Trial. Cordiale had the highest cellulose content. Cordiale and Alchemy had significantly higher ethanol yield than all the other varieties studied. Oakley, Deben and Consort had significantly lower ethanol yield than the other varieties. Using wheat straw as a model feedstock, biomass pre-treatment conditions eg acid vs alkali concentration, solid loading, temperature and residence time were optimized. The optimization showed that reducing sugar yield from NaOH pre-treated wheat straw was 2x higher than that from acid pre-treated wheat straw. The optimal pre-treatment conditions for wheat straw were 3% NaOH and132°C for 40 minutes A range of agricultural residues were examined regional wise based on the six zones in Nigeria for their potential for lignocellulosic ethanol production while forestry and grassland resources were evaluated on national basis. Agricultural residues were split into two including field residues and processing residues. In evaluating field residue, provisions were made to account for current uses in terms of soil cover and animal feed, which are the two existing uses for field residues. From the findings, maize stalk and cassava peel are two of the major processing residues available for use. Maize stalk when used as a single feedstock can only power 18 commercial bioethanol processing facilities in the North and only 7 facilities in the South. Cassava peel as a single feedstock, can power 13 bioethanol facility in the North where 9 of them would be based in the North central but power 20 facilities in the South, where they are evenly spread across the 3 Southern zones. When the total agricultural residues produced in each zone are put together in the scenario where the bioethanol processing facilities are based on multi-feedstocks, 44 - 54 ethanol processing facilities could be sited in each northern zone and only 16 - 19 facilities southern. Based on 2008 petrol consumption of 9.5 billion litres in Nigeria, a 10% blend would require 950 million litres of bioethanol per annum. Using the entire field and processing residues examined in this study produces 6.7 billion litres of bioethanol per annum which exceeds the 10% mandate. Therefore Nigeria has enough agricultural residues to exceed its bioethanol blending requirement but the big issue is collection and financial return to the fanner. Fuel wood and sawdust were evaluated at national level for lack of regional data. Potentially, fuelwood can power 153 ethanol processing facilities, sawdust can power 7 and the grassland resource can power 542 bioethanol processing facilities. There is considerable potential to cultivate purposely grown energy crops eg switchgrass and miscanthus for lignocellulosic ethanol production exists. This is dependent on identifying species suited to the climate, geographical zones and potential for genetic improvement in these species and potential for improving production via management practices.