Bioethanol Production from Corn Residue

Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 Bioethanol Production from Corn Residue M. M. Manyuchi1,2* 1 BioEnergy and Environmental Technology Centre, Department of Operations and Quality Management, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa 2 Department of Chemical and Processing Engineering, Faculty of Engineering, Manicaland State University of Applied Sciences, Zimbabwe [email protected] C. Muganu3 3 Department of Chemical and Process Systems Engineering, Harare Institute of Technology, Zimbabwe [email protected] C. Mbohwa1 BioEnergy and Environmental Technology Centre, Department of Operations and Quality Management, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa [email protected] 1 E. Muzenda1,4 1 BioEnergy and Environmental Technology Centre, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa 4 Department of Chemical, Materials and Metallurgical Engineering, Faculty of Engineering and Technology, Botswana International University of Science and Technology, P Bag 16, Palapye, Botswana [email protected]; [email protected] Abstract Currently, many developing countries are facing fuel challenges while corn stover waste remains unutilized. This study utilized excess corn Stover to make bioethanol a value added product by designing a plant that manufactures 150 tons per day of 99.5% pure cellulosic bioethanol operating over a 10-year period. The process that converted crude corn Stover to cellulosic bioethanol was evaluated for conversion via hydrolysis of lignocelluloses in the corn Stover then the cofermentation of the Carbon 5 and Carbon 6 monosaccharides obtained from the hydrolysis process. The hydrolysis process is a route to the bioethanol through 86% co-fermentation of Carbon 5 and Carbon 6 sugars obtained from the 75% saccharification of corn Stover to fermentable sugars to produce 99.5% pure cellulosic bioethanol that can be used to blend petrol. The economic analyses indicated a payback period of 1.5 years, a rate of return on investment of 86%, and a selling price of $1.10/liter for the bioethanol that indicated the feasibility of the project. Waste corn Stover to bioethanol technology can be applied as a waste management tool to meet energy demands in agro-based industries. Keywords-Bioethanol; Biofuels; Corn Stover; Economic assessment 2530 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 1. Introduction The intensive use of fuels for vehicles obtained from non-renewable natural oil is exposing a threat of oil depletion and climate change (Luo et al., 2009; Kazi et al., 2010). In contrast, the destruction of maize plant wastes, known as corn Stover, by burning causes undesirable effects such as air pollution, depletion of the ozone layer, global warming, the greenhouse effect, and the formation of acidic rain (Sheehan et al., 2004; Klein-Marcuschamer et al., 2011). Increasing the use of biofuels for energy generation purposes is of particular interest nowadays because it can decrease the dependence on foreign oil, reduce trade deficits, provide means of energy independence, and potentially offer new employment possibilities (Sheehan et al., 2004). Biofuels are being investigated as possible substitutes for current high pollutant fuels obtained from conventional sources making waste corn Stover attractive (Varga et al., 2004; Ranum et al., 2014). Using lignocellulose materials, such as waste maize corn Stover, in bioethanol production has an advantage over using sugar and starch because it minimizes the conflict between using land for food production or for energy feedstock production. Zimbabwe is an agro-based economy with an annual maize production rate of roughly 1,000 metric tons per annum (Table 1), which would benefit immensely from the beneficiation of waste maize corn Stover to bioethanol. This availability of corn Stover showed the need for the technoeconomic feasibility of a plant that produces 150 tons per day of cellulosic-based bioethanol from corn Stover, assuming that approximately a third of the annual production is maize corn Stover. Table 1. The annual maize production in Zimbabwe for the past five years in metric tons (KleinMarcuschamer et al., 2011) Production Year Production (Metric tons) 2009 650 2010 1000 2011 1450 2012 965 2013 900 2. Experimental 2.1 Materials The corn Stover used in this work was obtained from a plot in Chegutu, Zimbabwe. The following reagents and chemicals were used in the study: Distilled water (pH 7), 0.4 M of sulphuric acid (H2SO4), 8.0 M of sodium hydroxide (NaOH), Escherichia coli (E. Coli), weighing balance, incubator, stirring rod, incubator, pH meter, thermometer, conical flasks, beaker hydrometer inoculating loop, and burner were used. All chemicals and reagents were obtained from Sunfirm Distributors in Harare, Zimbabwe. A 64825 Sigma Aldrich IL Soxhlet Apparatus (Johannesburg, South Africa) was used for fermentable sugars extraction. 2.2 Methods 2.2.1 Determination of fermentable sugars yield The corn Stover was first washed and dried. Afterwards, 150 g of shredded corn Stover was divided into three parts and 250 mL of dilute H2SO4 solution was poured in the conical flask of the Soxhlet unit. Sample A was placed in thimbles and put in the top limb of the Soxhlet unit. The Soxhlet unit was switched on at level 3 and ran for 8 h. The fermentable sugar sample was collected and weighed. The procedure was repeated for all samples. The pH of the obtained samples was measured and a drop of concentrated NaOH solution was added until a pH of approximately 4.5 was reached. The solution obtained was sieved to remove the sodium sulphate produced. 2.2.2 Determination of the amount of bioethanol yield The culturing of the bacteria was performed 48 h before commencing the experiment. Then, 10 g of potato dextrose agar was completely dissolved in 250 mL of water in a conical flask. The mixture was covered with cotton wool and foil paper and then sterilized in an autoclave at 121 °C for 5 min. Upon removal, it was cooled, poured into petri dishes, and set aside to solidify. The E. Coli was then introduced into the petri 2531 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 dishes with the aid of a sterilized inoculating loop. The petri dishes were then sealed and kept in an incubator for 48 h at a temperature of 25 °C. 2.2.3 The co-fermentation of C5 and C6 sugars The three process solutions obtained from the experiment that hydrolyzed corn Stover were heated to 30 °C and 3 drops from the sterilized inoculating loop of cultured E. coli were added to the three flasks. All of the flasks that contained the samples were clogged with cotton wool to hinder aerobic conditions. The three samples were put in the incubator and were maintained at 30 °C for 36 h to allow complete fermentation. Every 4 h the mixtures were tested for their sugar contents using a hydrometer. A sample with 100 mL of the co-fermented sugars was distilled in a distillation bath. The solution obtained after 36 h was filtered to remove the froth and scum. The froth that formed at the upper layer and the remaining broth was placed in a water bath to inhibit the enzyme activity. After every 4 h of fermentation duration the hydrometer was dipped in the fermentation liquor to determine the rate of degradation of the fermentable sugars. This determined the rate of accumulation of bioethanol and the reaction time for co-fermentation. A few drops of cooking oil were added to a dry test tube with 2 cm3 of bioethanol and the test tube was shaken thoroughly. Then, 2 cm3 of deionized water was added to the solution and observations were noted by the experimenter. 3. Results and Discussion 3.1 Characterization of the Corn Stover The characterization of the waste corn Stover used in this study is shown in Table 2. A lignin value of 20.1 was achieved and was ideal for bioethanol production. Table 2. Characterization of the corn residue Component Composition (%) Glucan 38.6 Xylan 23.5 Arabinan 2.4 Mannan 3.1 Galactan 2.7 Lignin 20.1 Ash 4.2 Acetate 2.8 Protein 3.1 3.2 Analysis of the hydrolysis and fermentation of corn Stover to bioethanol A yield of 76.8% conversion was attained after hydrolyzing the corn Stover. The amount of bioethanol yielded in fermentation also involve a test of the sugar concentration every 4 h. The sugar concentration decreased as the bioethanol formed increased in quantity. However, an optimum yield of 86% for the bioethanol production was achieved. The bioethanol-oil mixture emulsified when droplets of distilled water were added, which showed that bioethanol was present in the fermented samples. The characteristics of the bioethanol produced in this work are shown in Table 3. Table 3. Properties of cellulosic bioethanol Physicochemical Parameter Boiling Point Melting Point Refractive Index Surface Tension Vapor Pressure Specific Heat Capacity Value 78.3 °C 117.3 °C 1.37 22.3 dyne /cm 43 mm Hg at 20 °C 0.618 cal/g K 2532 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 Flash Point 12.7 °C The fermentation produced bioethanol with an alcohol content of 12% that was slightly lower and this was attributed to the low mixing during fermentation. The experimental results showed that it was feasible to extract cellulosic bioethanol from the local corn Stover. Therefore, it is possible to setup a manufacturing plant that extracts cellulosic bioethanol from corn Stover. The 76.8% conversion of the corn Stover to fermentable sugars and 86% conversion of the fermentable sugars to cellulosic bioethanol determined from the experiments conducted in the laboratory were used for the mass balances. 4. Bioethanol Production Process Design 4.1 Process Description of Making Cellulosic Bioethanol from Corn Stover by the Cellulolysis Method The corn Stover from the fields in Chegutu, Zimbabwe was cleaned with water to remove any loose dirt. Afterwards, the corn Stover was dried and shredded for particle reduction. The washed and shredded corn Stover was fed by a conveyor belt to the pre-steamer where low pressure steam at 163 °C and 4.46 bar was added to maintain a temperature of approximately 100 °C. The pre-steamed corn Stover was conveyed into the hydrolyzing reactor. The reactor temperature, pressure, and residence time was maintained at 190 °C, 11.6 bar, and 2 min, respectively. The corn Stover slurry was then flashed to 1.0 bar in the blow down tank. The solid fraction was separated from the slurry in a pneumapress pressure filter. To reduce the toxicity to the fermentation organisms and downstream processing costs, a limiting step of lime was added to neutralize the excess H2SO4 in the hydrolyzate. The reaction between lime and H 2SO4 that forms gypsum was separated from the hydrolyzate as a solid cake. The corn Stover remains were dried and used as a fuel to heat the boiler. The enzyme Zymononas mobilis, which was used in the anaerobic fermentation to produce cellulosic bioethanol, was genetically modified bacteria. Therefore, they were provided with the necessary conditions in the bioreactor so that they could multiply and produce a large strain of bacteria. The pentose (xylose and arabinose) and hexose (glucose, mannose, and galactose) sugars obtained from the hydrolysis were mixed with the bacteria Zymomonas mobilis at 30 °C for 36 h in a semi-batch reactor. The fermentation process alone did not produce a bioethanol solution with an alcohol content greater than 15%. Distillation is the separation technique that was used to concentrate the bioethanol solution from 12% to 95% bioethanol content based on the different boiling points of bioethanol and water. The 95% hydrous bioethanol obtained was an azeotrope. To obtain a 99.5% pure bioethanol solution, molecular sieves were used to dehydrate the azeotropic solution. The bioethanol’s molecules were small enough to pass into the pores of the molecular sieves allowing for dehydration of the bioethanol. In the first stage, the hydrous alcohol was pre-heated, vaporized, and superheated before being admitted to the vessels that contained the molecular sieve material. In this superheated, vapor phase at a controlled temperature and pressure, the adsorption of the water molecules by the sieve was optimized, while the alcohol molecules passed through. For this to be achieved, the molecular sieves with pores of approximately a diameter of 3 mm were used. Water molecules of diameter 2.8 mm entered the pores while the bioethanol molecules could not and the separation of the molecules occurred. The wastewater generated was sent to the wastewater treatment plant while the bioethanol was stored in a storage tank before it was sold to the customer. 4.2 Material Balances The mass balances were used as the basis for calculating the plant equipment design parameters as well as the economic evaluation. The objective was to produce 150 tons of bioethanol per day. Assuming a 24 hour working day, 6.25 tons/h of bioethanol was produced. The mass balance determined the feed and the components for each stream. Table 4 shows the summary of the mass balance calculations performed on all of the equipment involved in the manufacture of cellulosic bioethanol from corn stover. Table 4. Summary of the process mass balances in tons/h Equipment Shredder Pre-steamer Chemical Species Corn Stover Corn Stover Steam Mass In 78.45 78.45 5.00 Mass Out 78.45 78.45 4.50 2533 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 Hydrolyzer Co-fermenter Distillation Column Corn Stover Water H2SO4 Fermentable Sugars Lime Gypsum Fermentable Sugars Bacteria Bioethanol From Fermentation Carbon Dioxide Bioethanol From Fermentation Water Hydrous Bioethanol 78.45 10.00 0.20 0.12 60.26 0.10 51.82 - 18.19 10.00 60.26 0.28 8.44 0.10 51.82 30.00 45.51 6.31 Anhydrous Bioethanol Water Hydrous Bioethanol 6.31 6.25 0.06 - Dehydrating Vessel 4.3 Energy Balances Bioethanol production is an energy intensive process which involves multiple steps. Table 5 is a summary of the 4 energy changing steps that occurred on the specified plant equipment. The energy balances are over the preheater, hydrolyser, co-fermenter, and the distillation column. Table 5. Summary of the energy changes for the bioethanol producing plant Equipment Energy Changes (Kj/h) Pre-heater 1.57 x 102 Hydrolyzer 5.06 x 102 Co-fermenter -1.42 x 104 Distillation Column 2.87 x 104 5. Economic Analyses The experimental financial appraisal, done at the preliminary stage of this study, showed that it is beneficial to invest in the project of making 150 tons per day of cellulosic bioethanol from corn stover. However, because this is a promising big project, it required a formal financial appraisal. The formal financial appraisal covered the calculations of the following financial parameters: Return on investment, payback period, internal rate of return (IRR), net present value (NPV), and breakeven point. This assessment demonstrated the economic and financial viability of the conversion of bioethanol from corn stover with regard to fixed capital investment. To achieve this, the ratio and factors for estimating capital investment items based on delivered equipment from Peters and Timmerhaus (1980) were used. The values presented are applicable for major process plant additions to an existing site where the necessary land is available through present ownership. 5.1 Fixed capital investment This is the total cost required for starting a plant and is referred to as FCI. The FCI is a once off cost and is not recovered at the end of the project. 5.2 Equipment costing The sixth tenths rule was used to estimate equipment cost, and cost indices were also used to approximate the cost of the equipment needed to install the plant today. Table 6 indicates the bill of quantities for installation of the corn stover to bioethanol plant. Table 6. Bill of quantities for the bioethanol from corn residue plant Component Quantity Distillation Column 2 Semi-batch Co-fermenter 1 Boiler 1 Unit Price ($) 25,000 20,000 40,000 Total Cost ($) 50,000 20,000 40,000 2534 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 Cooling Tower Positive Displacement Pumps Centrifugal Pump Bioethanol Storage Tank Conveyer Belts Seed Fermenter Pre-steamer Hydrolyzer Condenser Dehydrating Vessel Re-boiler Diaphragm Valves Gate Valves Safety Relief Valves Stainless Steel Pipe 15 mm Diameter Cast Iron Pipe 15 mm Diameter Carbon Steel Pipe 10 mm Diameter M12 × 30 mm Bolts M16 × 50 mm Bolts Pipe Flanges I-Beam Support Mild Steel Angle Iron Support Flat Bar Support Total Cost 1 6 7 1 3 3 1 1 1 1 1 11 4 3 19m 10m 50.5m 800 640 160 20 15 10 20,000 350 500 2,000 300 5,000 3,000 8,000 1,500 5,265 1,500 30 35 45 210/m 60/m 40/m 0.81 0.44 5.60 240 180 19.20 20,000 2,100 3,500 2,000 900 5,000 3,000 8,000 1,500 5,265 1,500 330 140 135 3,990 600 2,020 648 284 896 4,800 2,700 192 184,500 5.3 Cost estimation of direct costs The cost estimation for the project was done using the Factorial Method (Sinnot, 2009). The project fixed cost is often defined as a function of the total equipment purchase price as indicated by Equation 1. =� (1) Where Cf is the cost for fixed capital, Ft is the Lang Factor Ce is the total cost of all delivered equipment. For this project, 4.7 was the Lang factor used. Therefore, the total fixed cost was $867,150.00. 5.4 Indirect costs The indirect costs are expenses that are not directly involved with the material and labor of the actual complete facility installation and they range from 15% to 30% of the fixed capital investment. However, the calculations are based on the direct costs as indicated in Table 7. The fixed capital investment, which is the sum of the direct costs ($867,150) and indirect costs ($260,145) totaled $1,127,295.00 for this study. Table 7. Indirect costs Economic Parameter Engineering and Supervision Construction and Contractor’s Fees Contingency Typical DC Range (%) 5 to 30 DC Chosen DC (%) Cost ($) 15 130,072.50 6 to 30 DC 10 86,715 5 to 15 DC 5 43,357.50 Total Indirect Costs 260,145 5.4 Working capital The working capital for this project was 20% of the total capital investment (TCI), which totaled $1,409,118.75. 5.5 Estimation of total production costs Total production costs (TPC) are the sum of direct and indirect production costs, fixed charges, and plant overhead costs. Depreciation depends on the lifetime of the plant. The salvage value and the method of calculation is approximately 10% of the fixed capital investment for machinery and equipment. The estimation of the total production cost as evaluated from the TCI and FCI amounted to $298,733.19, as indicated in Table 8. 2535 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 Economic Parameter Fixed Charges Depreciation for Machinery Depreciation for Machinery Local Taxes Insurance Table 8. Estimation of total production costs Typical TCI / FCI Chosen TCI / Range (%) FCI (%) 10 to 20 TCI 10 10 FCI 10 2 to 3 TCI 2 1 to 4 FCI 1 0.4 to 1 FCI 0.5 Total TPC Cost ($) 140,911.88 112,729.50 28,182.38 11,272.95 5,636.48 298,733.19 5.6 Plant overhead cost Plant overhead costs are costs within a plant that are not directly attributed to any one production or processing unit and are allocated on some arbitrary basis believed to be equitable. Plant overhead costs include plant management salaries, the payroll department, local purchasing, and the accounting department. The plant overhead cost of this project was 10% of the total production cost and amounted to $29,873.32. 5.7 Plant utilities The plant utilities include electricity, steam, oxygen, and process water. The total plant utilities costs were $29,873.32, as indicated in Table 9. Table 9. Annual plant utilities cost Utility Quantity Required/Year Electricity 1.5163 x 104 kWh Steam 60,000 m3 Oxygen (Compressed Air) 400 m3 Process Water 108,000 m3 Total Annual Plant Utilities Cost Unit Price ($) 0.01/Kw 0.10/m3 10/m3 0.09 m3 Total Cost ($) 14,000.00 6,000.00 4,000.00 9,873.32 29,873.32 In addition, the raw materials required for bioethanol production from corn stover required a total cost of $2,914,600.00 per annum, as indicated in Table 10. Table 10. Raw materials estimation cost for a year Material Unit Cost ($) Quantity /Annum Zymnonas moblilis $100/ton 720 tons H2SO4 $10/ton 1,440 tons Corn Stover $5/ton 564,840 tons Lime 80/ton 50 tons Total Raw Materials Estimation Cost The total plant operating costs amounted to $3,858,735.97, as indicated in Cost ($) 72,000.00 14,400.00 2,824,200.00 4,000.00 2,914,600.00 Table 11. Table 11. Plant operating costs Typical TPC / POC Range (%) Raw Materials 1 to 10 TPC Direct Supervisory And Clerical 10 to 25 TPC Operation Labor Cost 10 to 20 TPC Utilities 10 to 20 TPC Maintenance And Repairs 2 to 10 FCI Operating Supplies 1 to 2 POC Laboratory Charges 15 to 25 POC Patent And Royalties 0 to 6 TPC Total Operating Costs Economic Parameter TPC / POC Chosen (%) 10 10 10 3 3 25 2 Cost ($) 2,914,600 29,873.32 29,873.32 29,873.32 33,818.85 879.18 7,143.32 5,974.66 3,858,735.97 5.8 Total manufacturing costs The total cost of manufacturing a product includes the direct labor costs, direct material costs, overhead costs, and any other expenses associated with production. The total manufacturing cost of this project included the operational cost, total capital investment, and plant overhead cost previously mentioned, which amounted to $5,297,728.04. 2536 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 5.9 General expenses General expenses are the sum of administrative costs, distribution costs, selling costs, and research and development costs. The distribution and selling costs include the cost for sales offices, salesmen, shipping, and advertising. The total general expenses for the bioethanol to corn stover amounted to $62,733.98, as indicated in Table 12. Table 12. General expenses Economic Parameter Range (%) Administrative Costs 2 to 6 PC Distribution and Selling Costs 12 to 20 PC Research and Development 5 PC Financing (Interest) 0 to 10 TCI* Total General Expenses *Total capital investment Chosen 2 12 5 2 Cost ($) 5,974.66 35,848.00 14,936.66 56,974.66 62,733.98 5.10 Total product cost The total product cost is the sum of all manufacturing costs, the total general expenses, and the cost of utilities. For this project, the total amounted to $40,360,462.02. 5.11 Gross earnings The market selling price of bioethanol was $1.10 per liter. The market selling price of carbon dioxide (CO2) was $20 per ton. The total income of this project was calculated through a summation of the selling price and a summary of the gross earnings is shown in Table 13. Table 13. Summary of gross earnings Variable Market selling cellulosic bioethanol/L Market selling price of CO2/ton Market selling price of corn stover residue/ton Total income Gross income Taxes Net profit Rate of return on investment (%) Value (USD) 1.10 20.00 5.00 56,644,200.00 16,283,737.98 4,070,934.50 12,212,803.48 86.7% 5.12 Payback period The payback period is the time required for the cumulative net cash flow taken from the startup of the plant to equal the fixed capital investment. Assumptions The calculations for this project used the assumption that there was a constant cash flow, as well as a constant inflation rate. A payback period of 1.15 years was determined using Eq. 1, = � � �� � � � � � � � � …… Where the total capital investment for this project was $14,091,187.50 and the net profit per year was $12,212,803.48. 5.13 Net present value A plant lifetime of 10 years was considered due to the change in technology in the processing plants. Table 14. Net Present Value Calculation Year 1 2 3 4 5 6 7 Calculation -3234580 × (1 + 0.1)-1 -0 × (1 + 0.1)-2 540000 × (1 + 0.1)-3 1620000 × (1 + 0.1)-4 2700000 × (1 + 0.1)-5 3780000 × (1 + 0.1)-6 4860000 × (1 + 0.1)-7 Net Present Value (USD) 2940527.27 0 405710.00 1106482.00 1676487.57 2133711.46 2493948.46 2537 Proceedings of the International Conference on Industrial Engineering and Operations Management Paris, France, July 26-27, 2018 5940000 × (1 + 0.1)-8 7020000 × (1 + 0.1)-9 8100000 × (1 + 0.1)-10 8 9 10 2771053.84 2977165.28 3122900.64 The NPV for this project was $13,746,931.76, since the net present value is positive it means that the present value of cash inflows is greater than the present value of cash outflows, thus the investment proposal is acceptable. 5.14 Rate of return The rate of return refers to the annual income from an investment expressed as a proportion (usually a percentage) of the original investment, shown in Eq. 2, � = � ℎ × and the internal rate of return (IRR) was calculated by Eq. 3, � ��� = ℎ � ℎ …….. − � ……………… Where the cash flow was $1,346,931 and the initial cost was $10,975,717.72. The IRR of this project was 25.2%, which is a value greater than the cost of capital (discount rate of 10%). Therefore, the decision is to go ahead with the project. 5.15 Breakeven analysis The breakeven point is the point at which the income from sale of a product or service equals the invested costs, resulting in neither profit nor loss. It is the stage at which income equals expenditure, shown in Eq. 4, = � ……………. Where the contribution margin is the selling price minus the variable costs. Based on this, the contribution margin for this project was 15,000 tons. 6. Conclusion The production of 150 tons per day of cellulosic bioethanol from corn stover is technically and economically feasible as a waste management technology while meeting energy needs. The designed plant will be innovative because it optimizes the process by allowing the co-fermentation of C5 and C6 sugars to obtain a substantial yield of cellulosic bioethanol from corn stover selling at $1.1/L. 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