The Production of Ethanol from Maize Cobs and Groundnut Shells

AU J.T. 9(2): 106-110 (Oct. 2005) The 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 (H2SO4) were used to determine the acid concentration that could produce an optimal yield of glucose. The results revealed that 4.5M H2SO4 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 76×106L of proof industrial ethanol were produced by fermentation compared to 7.95×106L by synthesis. 106 AU J.T. 9(2): 106-110 (Oct. 2005) During 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. 107 AU J.T. 9(2): 106-110 (Oct. 2005) Results 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 Time Glucose yield (g/cm3 [min] 2Ma 3Ma 4Ma 4.5Ma 5Ma 0 0 0 0 0 0 6 0.02 0.03 0.04 0.05 0.02 12 0.07 0.11 0.14 0.17 0.13 18 0.15 0.19 0.20 0.28 0.26 30 0.21 0.24 0.26 0.46 0.35 60 0.33 0.34 0.42 0.67 0.49 90 0.39 0.41 0.53 0.79 0.57 120 0.42 0.46 0.60 0.86 0.60 150 0.43 0.48 0.64 0.89 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 0 0 0 0 0 6 0.01 0.02 0.03 0.04 0.05 12 0.04 0.05 0.06 0.07 0.09 18 0.06 0.08 0.10 0.14 0.15 30 0.10 0.13 0.17 0.28 0.23 60 0.17 0.21 0.29 0.37 0.37 90 0.23 0.28 0.36 0.43 0.45 120 0.28 0.36 0.40 0.49 0.45 150 0.34 0.37 0.43 0.53 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 Time Glucose yield (g/cm3) (min) 40oC 50oC 60oC 70oC 80oC 0 0 0 0 0 0 6 0.11 0.15 0.21 0.35 0.43 12 0.30 0.35 0.50 0.62 0.67 18 0.50 0.61 0.65 0.81 0.85 30 0.71 0.73 0.74 0.76 0.87 60 0.73 0.74 0.78 0.80 0.93 90 0.75 0.76 0.79 0.83 0.95 120 0.78 0.78 0.82 0.84 0.97 150 0.80 0.83 0.85 0.87 0.98 Table 4. Glucose yield for acid hydrolysis of groundnut shells at varying temperatures using 4.5M H2SO4 Time Glucose yield (g/cm3) (min) 40oC 50oC 60oC 70oC 80oC 0 0 0 0 0 0 6 0.09 0.11 0.14 0.19 0.21 12 0.20 0.23 0.30 0.35 0.38 18 0.31 0.34 0.40 0.43 0.47 30 0.42 0.44 0.45 0.49 0.52 60 0.42 0.45 0.47 0.50 0.54 90 0.43 0.47 0.49 0.51 0.55 120 0.44 0.48 0.50 0.52 0.56 150 0.45 0.49 0.51 0.53 0.63 108 AU J.T. 9(2): 106-110 (Oct. 2005) At 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 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 Time Glucose yield (g/cm3) (min) 40oC 50oC 60oC 70oC 80oC Time (min) 0 6 12 18 30 60 90 120 150 Glucose yield (g/cm3) 1:1 1:2 2:1 1:3 3:1 0 0 0 0 0 0.05 0.04 0.09 0.01 0.12 0.13 0.10 0.17 0.04 0.22 0.23 0.19 0.33 0.06 0.36 0.36 0.25 0.43 0.14 0.51 0.54 0.39 0.63 0.23 0.73 0.65 0.49 0.75 0.31 0.86 0.71 0.55 0.83 0.35 0.89 0.75 0.58 0.86 0.36 0.94 0 0 0 0 0 0 6 0.03 0.10 0.25 0.28 0.31 12 0.28 0.40 0.58 0.62 0.65 18 0.56 0.62 0.68 0.76 0.94 30 0.83 0.86 0.90 0.93 1.07 60 0.85 0.89 0.92 0.95 1.25 90 0.86 0.90 0.95 0.98 1.29 120 0.88 0.92 0.96 1.00 1.43 150 0.90 0.93 0.97 1.01 1.53 Table 7. Percentage of ethanol produced and glucose concentration 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 Time Specific Ethanol Glucose (h) gravity (%) concentration (g/cm3) 0 1.00 0 1.53 0.5 1.008 0.6 1.32 1.0 1.014 2.6 1.16 1.5 1.021 3.8 1.10 2.0 1.028 4.7 0.93 2.5 1.038 8.2 0.68 3.0 1.043 8.0 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 109 AU J.T. 9(2): 106-110 (Oct. 2005) importation 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. 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