Life Cycle Analysis of Ethyl Lactate Production and Controlled Flow
Transcription
Life Cycle Analysis of Ethyl Lactate Production and Controlled Flow
Life Cycle Analysis of Ethyl Lactate Production and Controlled Flow Cavitation at Corn Ethanol Plants Prepared by: Steffen Mueller, PhD University of Illinois at Chicago Energy Resources Center [email protected] Modeling Support Provided By: Brent Riffel, Life Cycle Associates June 16, 2010 Table of Contents Introduction......................................................................................................................... 1 1) Ethyl Lactate Co-Production .......................................................................................... 1 Process Parameters...................................................................................................... 1 Greenhouse Gas Life Cycle Modeling........................................................................ 3 2) Controlled Flow Cavitation ............................................................................................ 6 Process Parameters...................................................................................................... 6 Greenhouse Gas Life Cycle Modeling........................................................................ 7 Appendix A: GREET Modeling Inputs for Ethyl Lactate Production................................ 9 Appendix B: GREET Modeling Inputs for Controlled Flow Cavitation.......................... 10 List of Tables Table 1: Ethyl Lactate Production at Corn Ethanol Plant................................................... 2 Table 2: Ethanol Plant Co-Producing Ethyl Lactate; Yields and Energy Consumption .... 3 Table 3: Lactic Acid Fuel Cycle Emissions........................................................................ 4 Table 4: Ethyl Lactate Fuel Cycle Emissions ..................................................................... 5 Table 5: Ethyl Lactate Life Cycle Greenhouse Gas Comparison ....................................... 5 Table 6: Ethanol Plant with CFC; Yields and Energy Consumption.................................. 7 Table 7: CFC Life Cycle Greenhouse Gas Comparison..................................................... 7 List of Figures Figure 1: Ethyl Lactate Production at Corn Ethanol Plant ................................................. 2 Figure 2: Ethyl Lactate Life Cycle Greenhouse Gas Comparison...................................... 5 Figure 3: Controlled Cavitation Life Cycle Greenhouse Gas Comparison ........................ 8 ii Introduction The present study examines the life cycle greenhouse gas implications from a) ethyl lactate co-production and b) the adoption of controlled flow cavitation at dry grind corn ethanol plants. Co-producing ethyl lactate at dry grind ethanol plants has been pilot tested at Michigan State University and controlled flow cavitation is commercially deployed at two plants. 1) Ethyl Lactate Co-Production Process Parameters Researchers at Michigan State University are currently commercializing technologies that co-produce ethyl lactate at dry mill corn ethanol plants by esterification of lactic acid with ethanol. Biobased ethyl lactate holds particular promise as an organic solvent. A biobased chemical can be identical to the petrochemical product (such as biobased PTT and petrochemical PTT) in which case the technical substitution potential is 100%. Alternatively, a biobased chemical can be similar as is the he case, for example, for ethyl lactate replacement of ethyl acetate, often resulting in substitution rates close to 100%. The BREW report presents fuel cycle results for several petrochemicals that are molecularly different from ethyl lactate, but chemically similar, suggesting close to 100% displacement ratios.1 The data in Figure 1 and Table 1 below were provided by Dennis Miller from Michigan State University for this analysis. The data details the ethyl lactate mass and energy balance.2 As can be seen, co-producing 25 million pounds of ethyl lactate at a 30 million gallon per year corn ethanol plant would decrease corn ethanol yield by 1.5 million gallon per year and consume 20 million pounds of lactic acid. This process would consume 166.3 MWh and 53,728 MMBtu. Table 2 provides a comparison of an average corn ethanol plant (the base case) and a corn ethanol plant co-producing ethyl lactate using the energy and mass balances detailed above. Data for the standard corn ethanol plant are taken from Mueller (2010).3 An average natural gas fired corn ethanol plant (normally consuming 26,206 Btu/gal, 0.73 kWh/gal, and yielding 2.78 gal/bu) equipped to produce ethyl lactate would consume 29,599 Btu/gal, 0.78 kWh/gal and yield 2.64 gal/bu of corn ethanol. This plant would also consume 0.702 lbs/gal lactic acid but produce 0.877 lbs/gal ethyl lactate (or 0.8 pounds of lactic acid per pound of ethyl lactate). Due to the lower ethanol yield of the ethyl lactate co-producing plant, the DDGS production on a per gallon basis increases to 5.98 lbs/gal. 1 Medium and Long-term Opportunities and Risks of the Biotechnological Production of Bulk Chemicals from Renewable Resources – The Potential of White Biotechnology. The BREW Project; Final Report; Prepared under the European Commission’s GROWTH Programme; Utrecht University, September 2006. 2 “Reactive Distillation: Utilizing Ethanol for the Production of Organic Acid Esters”; Presentation by Dennis Miller (Michigan State University) and Richard Glass (National Corn Growers Association). 3 Mueller, S. “2008 National dry mill corn ethanol survey”; Biotechnol Lett DOI 10.1007/s10529-0100296-7, May 15, 2010. Integrated Ethyl Lactate / Ethanol Production Fermentation Raw ethanol 30 Mgal/yr Corn (11.2 M bu/yr) $23 Million/yr Azeotrope (EtOH/H2O) Distillation 30/1.0 Mgal/yr EtOH/H2O recycle 2.3/0.1 Mgal/year Lactic acid (88%) (20 M lb/yr) $10 MM/yr Esterification process Azeotropic EtOH/H2O 32.3/1.1 Mgal/yr H2O Ethanol purification Absolute EtOH 3.8 Mgal/yr Ethyl lactate 25 M lb/yr ($28 Million/yr) Absolute EtOH 32.3 Mgal/yr Absolute EtOH 28.5 Mgal/yr ($60 Million/yr) Figure 1: Ethyl Lactate Production at Corn Ethanol Plant Table 1: Ethyl Lactate Production at Corn Ethanol Plant Ethanol In (mgpy) 30 Ethanol Out (mgpy) 28.5 Yield Decrease 0.95 Ethyl lactate out (million lbs/yr)) 25 Lactic acid in (million lbs/yr) 20 Ethyl Lactate Product (lbs/hr) 3,157 Ethyl Lactate Product (lbs/yr) 25,000,000 Hours of Model Plant Operation 7,919 Electricity (kWh/h) 21 Electricity Use (kWh) 166,297 Natural Gas (cfm) 110 Btu/cubic foot 1,028 Nautral Gas Use (Btu) 53,728,222,997 2 Table 2: Ethanol Plant Co-Producing Ethyl Lactate; Yields and Energy Consumption Base Plant Ethyl Lactate Plant ETOH Yield (gal/bu) 2.78 2.64 Btu/gal LHV 26,206 27,585 Btu/gal LHV Incremental 1,885 Btu/gal LHV for purification 129 Total (Btu/gal): 26,206 29,599 Electricity use (kWh/gal, base) 0.73 0.77 Electricity use (kWh/gal Incremental) 0.01 Total (kWh/gal) 0.73 0.78 Lactic Acid In (lbs/gal) 0.70 Ethyl Lactate Out (lbs/gal) 0.88 Lactic Acid per Ethyl Lactate (lbs/lbs) 0.80 DDGS Bone Dry (lbs/gal) 5.68 5.98 Greenhouse Gas Life Cycle Modeling Life cycle greenhouse gas modeling was performed using Argonne National Laboratory’s GREET model, Version 1.8c.0. GREET was first parameterized with the energy and yield values from the base case followed by the energy and yield values from the ethyl lactate producing ethanol plant. This analysis returned the greenhouse gas emissions for each stage along the ethanol production pathway including emissions from farm equipment, farm chemicals, downstream N2O, feedstock transport, ethanol production (plant energy consumption), DDGS credit, ethanol transmission and distribution, and combustion emissions (net of biogenic carbon). The results are listed in Table 5. All GREET input parameters are listed in Appendix A. Separately, the greenhouse gas lifecycle emissions of ethyl lactate production (from lactic acid at the yields listed in Table 2) and the greenhouse gas credit from substituting ethyl lactate for different petrochemicals needed to be evaluated. The BREW Report lists the greenhouse gas emissions on a cradle to full-oxidation (use) basis for lactic acid and the petroleum solvents substituted by ethyl lactate. The greenhouse gas emissions for the various lactic acid processes in tonnes of carbon dioxide equivalent per tonne of lactic acid produced are listed in the BREW Report and reproduced in Table 3. The lactic acid process requirements of 0.702 lbs/gal of produced ethanol are first converted to tonnes of lactic acid required per MMBtu of ethanol produced.4 This value is multiplied by the life cycle factors stated in tonnes CO2e emitted per tonne of lactic acid produced from the BREW Report to derive tonnes of CO2 emitted per mmBtu of corn ethanol and then converted to grams per MJ. For example, as noted in Table 3 lactic acid produced according to the BioLA-Anaer-GA-Fed process results in life cycle greenhouse gas emissions of 1.2 tonnes CO2e per tonne of lactic acid. Using 4 0.702 (lbs/gal) /2000 (lbs/ton)/76,330 Btu/gal ethanol*1,000,000 Btu/MMBtu*0.907 metric tones/ton=0.0042 tonnes/MMBtu 3 0.702 lbs of this type of lactic acid per gallon ethanol results in overall lifecycle greenhouse gas emissions of 4.7 g CO2e/MJ. Next, the greenhouse gas credit from substituting ethyl lactate for different petrochemicals is being assessed (see Table 4). The selected chemically similar petrochemicals to ethyl lactated are Ethyl Acetate, Benzene, EGBE, MEK, and Acetone. Following the same equations as described above with process yields of 0.877 lbs/gal of ethyl lactate substituting for MEK, for example, would generate life cycle greenhouse gas savings of 28.2 gCO2e/MJ. Finally, we compare the life cycle greenhouse gas emissions for base case corn ethanol to the emissions for co-producing ethyl lactate at an ethanol plant. As shown in Table 5 the emissions for base case corn ethanol total 51.5 g CO2e/MJ.5 The CO2e for each pathway component are also shown in Figure 2. Assuming lactic acid production using the BioLAAnaer-GA-Fed described above (emitting 4.7 g CO2e/MJ) and producing ethyl lactate substituting for MEK (a 28.2 g CO2e/MJ credit) and adding the other life cycle components of the corn ethanol production process we derive total emissions of 32.3 gCO2e/MJ. The pathway details are listed as Case 1 in Table 5. The pathway details for the least favorable production conditions (producing lactic acid via BioLA-SRITpH6cont and substituting ethyl acetate) are listed as Case 2 in Table 5.6 In summary, depending on the lactic acid production process and the petrochemical substituted by ethyl lactate, co-producing ethyl lactate at corn ethanol plants can reduce ethanol’s life cycle greenhouse gas emissions by 8% to 37%. Table 3: Lactic Acid Fuel Cycle Emissions BioLA-SRI-TpH6cont (Lactic acid via anaerobic, continuous ph6 fermentation by Lactobacillus delbruecki on dextrose, workup via extraction), BioLA-SRI-FlowpH (Lactic acid via anaerobic, continuous low ph fermentation by homolactic bacteria on dextrose, work up via extraction), BioLA-NW-Tu (Lactic acid via anaerobic fermentation on dextrose, workup involving neutralization and acidification), BioLA-Sh-Fex (Lactic acid anaerobic, continuous low ph fermentation, workup via solvent extraction), BioLA-Sh-Fed (Lactic acid via anaerobic, low ph fermentation, workup via electrodialysis, BioLA-Anaer-GA-Fed (Lactic acid via anaerobic continuous fermentation on dextrose, workup via electrodialysis), BioLA-NW-FU (lactic acid via anaerobic fermentation on dextrose) CO2e tonne/tonne 2.7 CO2e g/MJ ethanol 10.7 BioLA-SRI-FlowpH 2.4 9.5 BioLA-NW-Tu 2.0 7.9 BioLA-Sh-Fex 1.9 7.5 BioLA-Sh-Fed 1.8 7.1 BioLA-Anaer-GA-Fed 1.2 4.7 BioLA-NW-FU 1.2 4.7 BioLA-SRI-TpH6cont 5 This does not include emissions from land use change Note that the farm related emissions also increase for Case 1 and Case 2 over the Base Case due to lower ethanol output from the same amount of bushels, which results in a smaller denominator for fixed inputs. 6 4 Table 4: Ethyl Lactate Fuel Cycle Emissions CO2e tonne/tonne 3.9 CO2e g/MJ ethanol -19.3 Benzene 4.9 -24.2 EGBE 4.0 -19.8 MEK 5.7 -28.2 Acetone 4.2 -20.8 Average 4.5 -22.4 Petroleum Solvents Ethyl Acetate Table 5: Ethyl Lactate Life Cycle Greenhouse Gas Comparison Pathway Component Base Ethanol gCO2e/MJ Farm Equipment Farm Chemicals Downstream N2O Feedstock Transport Plant Energy DDGS Credit Lactic Acid Ethyl Lactate Credit Petr. Substitute Ethanol T&D Combustion (net) Total Fuel Cycle Reduction from Base Ethanol Ethyl Lactate Case 1 Ethyl Lactate Case 2 gCO2e/MJ gCO2e/MJ 5.0 7.9 15.6 2.2 29.4 -13.0 0.0 5.3 8.3 16.4 2.3 32.8 -13.6 4.7 5.3 8.3 16.4 2.3 32.8 -13.6 10.7 0.0 1.4 2.9 51.5 -28.2 1.4 2.9 32.3 -37.2% -19.3 1.4 2.9 47.2 -8.3% gCO2e/MJ Life Cycle Analysis: Ethyl Lactate Co-Produced with Corn Ethanol 100.0 100.0 90.0 90.0 80.0 80.0 70.0 70.0 60.0 60.0 50.0 50.0 40.0 40.0 Lactic Acid 30.0 30.0 DDGS Credit 20.0 20.0 Plant Energy 10.0 10.0 Feedstock Transport 0.0 0.0 Downstream N2O -10.0 -10.0 -20.0 -20.0 -30.0 -30.0 -40.0 -40.0 -50.0 -50.0 -60.0 Combustion (net) Ethanol T&D Ethyl Lactate Credit Petr. Substitute Farm Chemicals Farm Equipment Total Fuel Cycle -60.0 Base Ethanol Ethyl Lactate Case 1 Ethyl Lactate Case 2 Figure 2: Ethyl Lactate Life Cycle Greenhouse Gas Comparison 5 2) Controlled Flow Cavitation Process Parameters Controlled flow cavitation (CFC), a process enhancement developed by Arisdyne Systems, Inc., is currently utilized by 2 operating ethanol plants. The process improvement routes the corn and enzyme slurry through a narrow nozzle, which reduces the particle size distribution and enhances starch accessibility to enzymes. The resulting yield increases range between 3% to 5%. Besides increased starch conversion, laboratory testing has shown that CFC also holds particular promise for corn kernel fiber to ethanol conversion, which would increase yield by an additional 3% to 5%. We model both the additional starch conversion from CFC and a combined starch and fiber to ethanol case. Employing CFC alters the feed production and energy requirements of an ethanol plant. While feed production on a mass basis is reduced, the protein and fat content remain unchanged from the base process. Since less DDGS are being dried, the thermal requirements are reduced, but electricity needs increase to operate an additional 500 hp motor needed for the process (see Table 6).7 For our analysis we model the following cases: 1) A base case corn ethanol plant yielding 2.72 gal/bu and producing 312,500 tons of DDGS per year. Lower yielding base plants would likely stand to gain higher yield increases from CFC. 2) An ethanol plant with CFC yielding 2.83 gal/bu and producing 286,100 tons of DDGS per year. However, due to the DDGS’ protein and fact content the feed value is equivalent to the base plant’s production of 312,500 tons. 3) An ethanol plant with CFC and corn kernel fiber conversion yielding 2.94 gal/bu and producing 259,700 tons of DDGS per year. However, due to the DDGS’ higher protein and fact content (on a mass basis) the feed value is equivalent to the base plant’s production of 312,500 tons. 4) An ethanol plant with CFC and corn kernel fiber conversion yielding 2.94 gal/bu and producing 259,700 tons of DDGS per year. This case, however, assumes that the feed value is evaluated on a mass basis and therefore equivalent to 259,700 tons. 7 Note that in the CFC&fiber case, the electricity consumption is slightly less than in the CFC only case because the CFC&fiber increases yield without incremental electricity thus slightly reducing electricity use on a per gallon basis. 6 Table 6: Ethanol Plant with CFC; Yields and Energy Consumption Million Gallon Per Year Yield (gal/bu) DDG Displacement lbs/gal (bone dry) Modeled DDGS Displacement (tons/yr) Actual DDGS Production (tons/yr) Energy Consumption (Btu LHV/gal anhydrous) Base Case Energy Consumption (kWh /gal anhydrous) 100,000,000 2.72 5.63 312,500 312,500 30,000 0.710 Starch 104,000,000 2.83 5.41 312,500 286,100 29,023 0.742 CFC&fiber 1 108,000,000 2.94 5.21 312,500 259,700 28,118 0.741 CFC&fiber 2 108,000,000 2.94 4.33 259,700 259,700 28,118 0.741 Greenhouse Gas Life Cycle Modeling Life cycle greenhouse gas modeling was performed using Argonne National Laboratory’s GREET model, Version 1.8c.0. GREET was first parameterized with the energy and yield values from the base case followed by the energy and yield values for the various process improvement cases. The GREET input parameters are summarized in Appendix B. The resulting greenhouse gas emissions by individual pathway component are listed in Table 7 and Figure 3. The results indicate that CFC reduces greenhouse gas emissions on a life cycle basis by 2.3% and CFC combined with corn kernel fiber conversion reduces greenhouse gas emissions by 4.9%.8 In the less likely case that DDGS is not valued for its protein and fat content, greenhouse gas emissions in the CFC combined with corn kernel fiber conversion are reduced by 1.3% over the base case. Table 7: CFC Life Cycle Greenhouse Gas Comparison Pathway Component Farm Equipment Farm Chemicals Downstream N2O Feedstock Transport Base Case (g CO2e/MJ) 5.1 CFC Only (g CO2e/MJ)) 4.9 CFC&Fiber 1 (g CO2e/MJ) 4.7 CFC&Fiber 2 (g CO2e/MJ) 4.7 8.1 7.8 7.5 7.5 15.9 15.3 14.7 14.7 2.2 2.1 2.1 2.1 Plant Energy 32.5 32.0 31.2 31.2 DDGS Credit -12.8 -12.3 -11.9 -9.9 Ethanol T&D 1.4 1.4 1.4 1.4 Combustion (net) 2.9 2.9 2.9 2.9 Total Fuel Cycle 55.4 % Reduction from Base Case 54.1 52.7 54.7 2.3% 4.9% 1.3% 8 Note that the farm related emissions decrease for the CFC and CFC&fiber cases over the Base Case due to higher ethanol output from the same amount of bushels, which results in a larger denominator for fixed inputs. 7 gCO2e/MJ Life Cycle Analysis: Contolled Flow Cavitation 70.0 70.0 65.0 65.0 60.0 60.0 55.0 55.0 50.0 50.0 45.0 45.0 40.0 40.0 35.0 35.0 30.0 30.0 25.0 25.0 20.0 20.0 15.0 15.0 10.0 10.0 5.0 5.0 0.0 0.0 -5.0 -5.0 -10.0 -10.0 -15.0 Combustion (net) Ethanol T&D DDGS Credit Plant Energy Feedstock Transport Downstream N2O Farm Chemicals Farm Equipment Total Fuel Cycle -15.0 Base Case CFC CFC & Fiber 1 CFC & Fiber 2 Figure 3: Controlled Cavitation Life Cycle Greenhouse Gas Comparison 8 Appendix A: GREET Modeling Inputs for Ethyl Lactate Production Corn Farming Fuel Inputs (Corn Basis) Diesel Gasoline Natural gas LPG Parameter 5,715 2,298 1,835 2,119 Electricity Input Electricity kW h/bu Chemical Inputs N P2O5 Parameter Units Btu/bu Btu/bu Btu/bu Btu/bu Btu/bu 0.2 667.3 Units Ammonia 70.7% Urea 21.1% Amm. Nitrate 8.2% 1,202 g/bu Atrazine Metolachlor Acetochlor Cyanazine 8.10 g/bu 0.68 g/bu 31.2% 28.1% 23.6% 17.1% 420 g/bu 149 g/bu K 2O 174 g/bu CaCO3 Herbicide Insecticide Soil N Emissions (g/bu corn) N content of ag system N in N 2O as % of N in fertilizer and 141.6 1.3% Corn Transport to Ethanol Plant Transport Segment Corn to stack Stack to Ethanol plant Mode Medium Duty Truck Heavy Duty Truck Capacity (tons) Distance (mi) 8 15 10 40 Share 100.0% 100.0% Ethanol Plant Select scenario Yields Ethanol DGS DGS moisture content Thermal Energy Inputs Natural gas Coal Electricity Input Electricity Products Displaced by DDGS Feed corn Soybean meal N-urea Ethyl Lactate Scenario Parameter Units 2.64 gal/bu 6.64 wet lbs/gal 10.0% dry lbs/gal Baseline 2.78 6.31 Btu/gal Btu/gal 26,206 0 29,599 0 kWh/gal Btu/bu 0.78 kWh/gal 2,656 Displacement Ratio 0.99 0.31 0.02 Ethyl Lactate Scenario 2.64 6.64 Btu/gal 29,599 0 kWh/gal 0.73 0.78 Displacement Ratio Displacement Ratio 0.99 0.99 0.31 0.31 0.02 0.02 Ethyl Lactate Production Ethanol Allocation Ethanol fuel Ethanol feedstock Total M gal/yr Inputs Ethanol Lactic acid lbs/lb EL Output Ethyl Lactate Thermal Energy Inputs Natural gas M lbs/yr 95.0 5.0 100.0 625.8 32.9 658.7 0.40 0.80 lbs/lb Ethanol Input 2.53 lbs/lb Ethanol Fuel lbs/gal Ethanol Fuel 0.13 0.88 Btu/lb EL 2,055 9 Appendix B: GREET Modeling Inputs for Controlled Flow Cavitation Corn Farming Fuel Inputs (Corn Basis) Diesel Gasoline Natural gas LPG Parameter Units 5,715 2,298 1,835 2,119 Electricity Input Electricity kW h/bu Chemical Inputs N P2O5 K2O CaCO3 Herbicide Insecticide Parameter Btu/bu Btu/bu Btu/bu Btu/bu Btu/bu 0.2 Units 420 149 174 1,202 8.10 0.68 Soil N Emissions (g/bu corn) N content of ag system N in N2O as % of N in fertilizer and biomass 667.3 g/bu g/bu g/bu g/bu g/bu g/bu Ammonia 70.7% Urea 21.1% Amm. Nitrate 8.2% Atrazine 31.2% Metolachlor 28.1% Acetochlor 23.6% Cyanazine 17.1% 141.6 1.3% Corn Transport to Ethanol Plant Transport Segment Corn to stack Stack to Ethanol plant Mode Medium Duty Truck Heavy Duty Truck Capacity (tons) Distance (mi) 8 15 10 40 Share 100.0% 100.0% Ethanol Plant Select scenario Yields Ethanol DDGG DGS moisture content Thermal Energy Inputs Natural gas Coal Electricity Input Electricity Products Displaced by DDGS DGS:Corn DGS:Soy Bean Meal DGS:N in Urea Baseline Parameter Units 2.94 gal/bu 4.81 wet lbs/gal 10.0% Baseline Btu/gal 28,118 0 kWh/gal Btu/bu 0.741 2,527 Displacement Ratio (lb/wet lb DGS) 0.992 0.306 0.022 Starch Starch & Fiber 1 Starch & Fiber 2 2.94 2.94 6.25 4.81 2.72 6.25 2.83 6.25 Btu/gal 30,000 0 Btu/gal 29,023 0 Btu/gal 28,118 0 Btu/gal 28,118 0 kWh/gal 0.710 kW h/gal 0.742 kWh/gal 0.741 kW h/gal 0.741 Ratio Ratio 0.992 0.306 0.022 Ratio 0.992 0.306 0.022 Ratio 0.992 0.306 0.022 0.992 0.306 0.022 Ethanol Transport and Distribution Transport Segment Fuel transport Fuel distribution Mode Rail Barge Heavy Duty Truck Heavy Duty Truck Capacity (tons) 25 25 Distance (mi) 800 520 80 30 Share 40.0% 40.0% 20.0% 100.0% 10