United States Department of Agriculture

Office of
the Chief Economist

Office of Energy Policy

and New Uses

Agricultural

Economic Report

Number 845

September 2009



# Energy Life-Cycle Assessment of Soybean Biodiesel

A. Pradhan

D.S. Shrestha

A. McAloon

W. Yee

M. Haas

J.A. Duffield

H. Shapouri

### Table of Contents

Summary

............................................................................................................................... ...... iii

Energy Life-Cycle Assessment of Soybean Biodiesel ................................................................1

Methodology

............................................................................................................................... ..2

Data Description and Trends ......................................................................................................3

Energy Life-Cycle Inventory ......................................................................................................7

Feedstock Production ..................................................................................................................7

Estimating Energy for Transporting Soybeans to Biodiesel Plant ..........................................8

Estimating Energy for Oil Crushing and Biodiesel Conversion ..............................................9

Oil Extraction From Soybeans ..............................................................................................9

Conversion of Soybean Oil Into Biodiesel ..........................................................................10

Biodiesel Transport ....................................................................................................................12

Calculating Energy Coproduct Values ....................................................................................12

Results

............................................................................................................................... ..........14

The Effects of Adding Inputs to the LCI .................................................................................15

The Effect of Adding Lime to the LCI .................................................................................16

Effect of Oil Transport ........................................................................................................16

Effect of Soybean Yield ..............................................................................................................17

Summary and Conclusion .........................................................................................................17

References

............................................................................................................................... ....18

Appendix

............................................................................................................................... .....21

Glossary

............................................................................................................................... ......22

iAbout the Authors

A. Pradhan is a graduate student and D. Shrestha is an assistant professor in the Departm ent of Biological and Agricultural Engi neering, University of Idaho.

A. McAloon is a cost engineer, W. Yee is a chemical engineer, and M. Haas is a lead scientist at the Eastern Regional Research Center in USDA’s Agricultural Research Service.

J.A. Duffield and H. Shapouri are agricultural economists in the Office of Energy Policy and

New Uses in USDA’s Office of the Chief Economist.

Acknowledgements

The authors would like to thank all the review ers and others who provi ded useful comments on this report. In particular, we would like to thank Mark Ash, Bill McBride, Gary Knothe, Jim Pollack, and Michael Wang for their suggestions , which significantly improved the study.

This report is available on the Web at: http://www.usda.gov/oce/global_change/index.htm Printed copies may be purchased from the National Technical Information Service. Call 1-800-553-NTIS (6847) or 703-605-6000, or visit: http://www.ntis.gov

.

iiSummary

The first comprehensive life-cycle inventory (LCI) for biodiesel produced in the United S tates from soybean oil was completed by Sheehan et al. in 1998. The purpose of the study was to conduct a life-cycle assessment (LCA) to quantif y and compare the environmental and energy

flows associated both with biodies el and petroleum-based diesel. One of the most often cited

results from Sheehan et al. is that the fossil ener gy ratio of biodiesel is equal to 3.2. In other words, biodiesel yields 3.2 units of energy for ev ery unit of fossil energy consumed over its lifecycle. By contrast, it was found that petroleu m diesel’s life cycle yi elded only about 0.84 units of energy per unit of fossil energy consumed. The purpose of the following analysis is to update the energy life cycle of the model to determin e if any significant changes in the original inventory have occurred since the mode l was first developed 10 years ago.

The LCI of biodiesel in this an alysis includes four subsystems : feedstock production, feedstock transportation, soybean processing with biodies el conversion, and produc t distribution. All significant sources of energy are in cluded in the inventory, such as the liquid fuel and electricity used to directly power equipment in the syst em. The energy requirements to produce materials that are made from energy resources, such as fert ilizers, pesticides, and other petrochemicals, are also included in the inventory. The soybean crushing model in th is analysis uses the hexane extraction method to extract oil from soybean see d, and transesterificati on is used to convert soybean oil into biodiesel. Oil extraction and transester ification result in the production of two important coproducts, soybean meal and crude gl ycerin, respectively. A mass-based allocation method is used to account for the energy associated with the soybean meal and crude glycerin.

The fossil energy ratio (FER), which is used in this study to measure the energy balance of biodiesel, is defined as the rati o of the energy output of the fi nal biofuel product to the fossil energy required to produce the biofuel. The en ergy requirements of biodi esel include all the fossil energy in the LCI and do not include any re newable energy, such as solar or hydroelectric energy. The analysis first constructed a base ca se, in which the inventory was kept basically the same as the inventory used in the Sheehan et al. report. Then addi tional inputs that were excluded by Sheehan et al., such as agricultu ral machinery and energy embodied in building materials, were added to study their impact on the FER.

The Sheehan et al. study used data from a U.S. Department of Agriculture (USDA) conducted survey on soybean production in 1990, and this study used data from a 2002 USDA survey. Given the long time period between surveys, the newer data would be expected to reflect some changes in soybean production practices over time. One major change that has occurred is the increased adoption of no-till practices by soybean farmers, which reduces fuel requirements. Another change is the widespread adoption of genetica lly engineered (GE) soybeans, which have had a major effect on pesticide use. Soybean yields have been improving over time because of new seed varieties, improved fertilizer and pesticide applications , and new management practices. Energy savings have also occurred in the s oybean crushing industry because facilities

that have been built in recent times are far mo re energy efficient than the older plants.

iiiThe first subsystem constructed for the LCI wa s soybean production, which is the feedstock

source for the biodiesel examined in this st udy. Energy requirements for producing soybeans were estimated for both direct energy, such as di esel fuel, and gasoline, and indirect energy, such as fertilizers and pesticides. Diesel fuel us e required the most energy on the farm, followed by fertilizers, and herbicides. Next, the energy re quired to transport soyb eans from the farm to processing plants was estimated based on inform ation from the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (G REET) Model. It requires about 6,393 British Thermal Units (Btu) to transport 1 bushel of soybeans to a processing facility.

The model used in this study was designed to re present a processing facility that combines a soybean processing plant with a biodiesel c onversion unit producing 9.8 million gallons of biodiesel, 151,515 tons of soybean meal, 9,000 tons of soybean hulls, and 4,380 tons of crude glycerin. The soybean crusher uses energy in the form of electricity to power motors and provide lighting. Natural gas and process steam are used to provide heat for drying. Hexane is

used for oil extraction. The to tal amount of energy required for removing the soybean oil is about 23,000 Btu per gallon of biodi esel. The soybean oil is conve rted into biodiesel using a process called transesterification, which is done by reacting the oil with an alcohol and a catalyst in large reactors. This reaction also results in the produc tion of crude glycerin, which is a valuable coproduct. The conversion of the soybean oil into biodiesel and the treatment of the glycerin requires almost 19,000 Btu per gallon of bi odiesel. Energy is also required to ship the biodiesel from the processing plant to marketing outlets. Using the GREET model, it was determined that on average it requires about 1,000 Bt u to ship a gallon of biodiesel to its final

destination.

Combining the energy input estimates from the f our subsystems complete d the base case lifecycle assessment for biodiesel. After adjus ting the energy inputs by en ergy efficiency factors and allocating energy by coproducts, the total en ergy required to produce a gallon of biodiesel was 25,696 Btu. Biodiesel conversion used the mo st energy, accounting for about 60 percent of the total energy required in th e life-cycle inventory. Soybean agriculture accounted for 18 percent of the total energy requirements, fo llowed by soybean crushing, which required almost 15 percent of the total energy. The net energy va lue (i.e., biodiesel energy output, minus fossil energy input) was about 91,000 Btu per gallon. The estimated FER of biodiesel was 4.56, which is about 42 percent higher than th e FER reported by Sheehan et al.

The next step in this analysis was to add s econdary energy inputs to the LCI that were not included in Sheehan et al. to determine how they af fect the overall results. The secondary inputs added were farm machinery, build ing materials for a crushing plan t, and building materials for a biodiesel conversion plant. When the input en ergy for both agricultural machinery and building material are added to the inventory, FER dec lines to 4.40, still consider ably higher than the 3.2 FER reported by Sheehan et al. In addition, Shee han et al. omitted lime from their LCI, whereas this study included lime in the base case LCI. However, lime use only accounted for about 500 Btu per bushel of soybeans, and adding it to the LCI only lowered the FER by 0.22 percent.

The final step in this analysis was to examine the effect of rising soybean yields on the FER of biodiesel. The analysis found that the FER of soybean biodiesel is expected to reach 4.69 when projected soybean yield reaches 45 bushels per acre in 2015. This is about a 3-percent increase

ivv compared to the 2002 FER estimate. This result suggests that the FER of biodiesel will continue to improve over time. In addition to higher yiel ds, improvements can be expected to occur in other areas of the life cycle as the agricultural sector, along with the biodiesel industry, continues to make energy efficiency gains in order to lower production costs.

### Energy Life-Cycle Assessme nt of Soybean Biodiesel

A. Pradhan, D. S. Shrestha, A. McAloon, W. Yee , M. Haas, J. A. Duffield, and H. Shapouri

Much of the attention directed toward renewabl e fuels, such as biodiesel, is focused on the perception that they have superior environmenta l properties compared to their petroleum fuel counterparts (U.S. Environmental Protection Ag ency, 2002; Knothe et al.). In addition, developing renewable fuels is desirable because they are derived from sustainable sources of energy, whereas petroleum fuels come from a fin ite resource that is ra pidly being depleted. However, the production of renewable fuels ge nerally involves a significant amount of fossil energy (e.g., petroleum-derived diesel fuel is used to cultivate and harvest the soybeans used to make biodiesel). The amount of fossil energy used for biodiesel must be measured over the entire life cycle of biodiesel production to dete rmine the extent to which it depends on petroleum fuels. The degree to which biodi esel is renewable is largely a factor of the amount of fossil energy used for its production.

It is beneficial to know the renewability of a biof uel for two reasons. First, it is useful to know how much a biofuel relies on petroleum-derive d energy for its producti on; the less a biofuel depends on petroleum energy, the more potential it has for diversifying our total fuel supply. Secondly, the renewability factor is one of many criteria that may be used by policymakers and others to evaluate and compare va rious biofuels. Renewability is a useful measurement that can be used along with other measurements, including environmental, economic, and social criteria,

to assess the benefits of biofuels.

In 1998, the first comprehensive life-cycle invent ory (LCI) for biodiesel produced in the United States from soybean oil was completed by Sheehan et al. The inventory and model assumptions were developed by a large stakeholders group and se veral peer reviewers, including experts from numerous disciplines and institutions. The purpose of the study was to conduct a life-cycle assessment (LCA) to quantify and compare the environmental and energy flows associated both with biodiesel and petroleum-based diesel. Th e LCI flows examined included greenhouse gases, energy use, and other air emissions . Other biodiesel LCAs have been done since Sheehan et al.,

but none have matched the detailed information or collaborative effort used to produce the original report (Hill et al. and Huo et al.).

One of the most often cited results from Sheehan et al. is that the fossil energy ratio of biodiesel is equal to 3.2. In other words, biodiesel yields 3.2 units of energy for every unit of fossil energy consumed over its life cycle. By contrast, it was found that petroleum di esel’s life cycle yielded only about 0.84 units of energy per unit of fossil energy consumed. The purpose of the following analysis is to update the energy life cycle of the model to determ ine if any significant changes in the original inventory have occurred since th e model was first developed 10 years ago. For example, the adoption of new technologies in the farm sector, the soybean processing sector, and in the biodiesel industry are expected to affect life-cycle energy use.

1Methodology

Following Sheehan et al., the form ula used in th is study to estimate the fossil energy ratio (FER) is defined in equation 1:

FER Input Energy Fossil Output Energy Fuel Renewable

 . (1)

A biofuel’s FER is defined as the ratio of the energy output of the final biofuel product to the fossil energy required to produce the biofuel. The FER as defined above only includes fossil energy in the denominator. For example, it doe s not include the energy value of the soybeans used to make biodiesel, and it does not include any solar or hydroelectric energy because these sources of energy are renewable.

Estimating FER begins with defining the entire production system of biodiesel, which includes four subsystems in this analysis: feedstoc k production, feedstock transportation, soybean processing with biodiesel convers ion, and product distribution. An inventory is then developed that identifies and quantifies all the fossil energy inputs used in each subsystem. All significant sources of energy are included in the inventory, such as the liquid fuel and electricity used to directly power equipment in the system. The en ergy content of materials that are made from energy resources, such as fertilizers, pesticides, and other petrochemicals, is also included in the inventory. The energy values of all fossil ener gy used in the system are adjusted by energy efficiency factors to take into account the ener gy used to convert fossil resources into usable energy (table A2). The energy efficiency factor s also adjust for any energy required to mine, extract, and manufacture the ra w energy sources. Estimates of electricity generation used throughout the life cycle are based on the U.S. weighted average of all sources of power, including coal, natural gas, nuc lear, and hydroelectric. About 70 percent of the electricity generated in the United States comes from fo ssil fuel (Energy Information Administration); hydroelectric and other nonfo ssil sources provide about 30 percent. The efficiency of electricity generation in the U.S. increased from 32 percent as reported in Sheehan et al. to 33.71 percent in 2007 based on data from the Energy Information Ad ministration. In addition to generation loss, there is also a loss of electricity over the dist ribution lines, which reduces the overall efficiency of electricity to 31.29 percent. Therefore, all electricity used over the life cycle is increased by a factor of 3.2 to account for generation and distribution losses.

Similarly to Sheehan et al., the soybean crushi ng model in this analysis uses the hexane extraction method to extract oil from soybean see d, and transesterificati on is used to convert soybean oil into biodiesel. Oil extraction and transester ification result in the production of two important coproducts, soybean meal and crude glycer in respectively. Since this energy life cycle focuses exclusively on biodiesel, the energy asso ciated with the production of the other two coproducts must be estimated a nd excluded from the inventory. Since detailed information is often not available to measure the exact energy requirements of the individual coproducts, an allocation method can be used to assign coproduct values. There are several allocation methods that can be used to estimate the energy valu e of coproducts. For example, the energy method uses the energy content of each coproduct to a llocate energy. Another example is the economic method, which uses the relative market value of each coproduct to allocate energy. Sheehan

2et al. used a m ass-based allocation method, and to be consistent with th eir analysis, this study

also uses the mass-based allo cation method. In general, no allocation method is always applicable, and the appropriate method should be chosen on a case-by-case basis. For more

discussion on allocation met hods, see Shapouri et al.

The mass-based allocation method is commonly us ed because it is easy to apply and provides very reasonable results (Vigon et al., 1993). This method simply allocates energy to the various coproducts by their relative weight s. This allocation rule sepa rates the energy used to produce the soybean oil from the energy used to produce the soybean meal and glycerin in the following

manner:

Energy input allocation for biodiesel = E 1 f 1 + E 2 f 2 + E 3 (2)

where E 1 is energy input for agriculture, s oybean transport and soybean crushing, f 1 is the mass fraction of soybean oil used to produce biodiesel; E 2 is the energy used du ring transesterification and the transport of the soybean oil, and f 2 is mass fraction of the transesterified oil used to produce biodiesel. E 3 is energy input for biodiesel transport.

Over the past several years, the FER, also calle d energy balance, of soybean biodiesel has been reported by different researchers with considerable va riation in results (Hill et al.; Huo et al., and Pimentel and Patzek.). A major cause for the cont radicting results is the difference in the amount of energy allocated between the soybean oil used to make biodiesel and the soybean meal. Historically, soybean demand is driven by the de mand for soybean meal, which is used as a highprotein animal feed. Crushing soybeans yields cons iderably more meal than oil, as well as more revenue. Clearly, soybean meal is not a byproduct of biodiesel produc tion. Rather, soybean meal and oil are jointly produced and sold in sepa rate markets. Therefor e, an allocation method must be used to determine how the energy used for crushing soybeans should be divided between the two products. Unfortunately, different allo cation methods can produce significantly different coproduct energy values. For a detailed compar ison and discussion of the different coproducts used in the literature, see Pradhan et al.

Data Description and Trends

At the time of the Sheehan et al. study, the most recent detailed data available on soybean production was from the U.S. Department of Ag riculture’s (USDA) 1990 Farm Costs and Return Survey (FCRS). The FCRS, which was replaced by the Agricultural Resource Management Survey (ARMS) in 1996, is conducted annually, but to reduce survey costs, USDA does not undertake detailed surveys of every commodity each year. Thus, the ARMS covers a major commodity in detail about every 4 years, with the most recent survey conducted on soybeans in 2006. This study, however, uses the 2002 data, becau se the 2006 data became available just prior to the release of this study. The ARMS s oybean survey only covers major soybean producing States, and detailed data are onl y reported for a selected number of these States. In 1990, Statelevel estimates were available for 14 States a nd the 2002 soybean survey provided detailed Statelevel data on 20 States. These 20 States are re sponsible for 98 percent of the soybean production (table 1). The USDA uses other versions of the ARMS to gather annual data for national soybean production estimates, but they are lim ited compared to the ARMS soybean survey,

34 which is the only USDA source th at provides detailed data on machinery and fuel use. Data from the 2002 ARMS soybean survey on chemicals a nd fertilizers were not made available at the time of this study, so other USDA data sources were obtained (table 1).

To stay competitive, U.S. farmers are conti nually minimizing their i nput costs and increasing productivity. Therefore, soybean data would be expected to reflect some changes in soybean production practices over time. One major change that has occurred is the increased adoption of no-till practices by soybean farmers. No-till us e increased in soybean production from about 10 percent of acreage in 1990 to a bout a third in 2000. Thus, signi ficantly fewer soybean acres required fuel for tilling over this time peri od (USDA Economic Research Service [ERS], 2003). The most significant change in U.S. soybean production since 1990 is the use of genetically engineered (GE) soybeans, which have had a ma jor effect on pesticide (includes herbicides, insecticides, and fungicides) use. The 1990 ARMS soybean production data used in the Sheehan et al. report did not include any GE soybeans be cause they had not been introduced into U.S. agriculture yet. However, by 2002 the rapid rise in GE soybeans had reached 75 percent of the soybeans planted, and today almost all soybeans in the United States are GE varieties (USDA ERS, 2007). Genetically engineered soybeans wi th herbicide-tolerant and pest-management traits increase yields through improved weed and pest control. Using GE soybeans also reduces pesticide use and costs (Heimlich et al., 2000) . Based on data published in the National Agricultural Statistics Service’s (NASS) Agricultural Chemical Usage survey, over the 5-year period from 1990 to 1994; 1995 to1999; and 2000 to 2004, the average he rbicide use was 1.18, 1.11 and 1.09 lb/acre/year respectively (US DA, NASS, 1990-2005). However this average decrease in herbicide use may not be realized from year to ye ar because annual pesticide use depends on the level of infestation. For instance , the insecticide applicat ion rate was higher for the years 2005 and 2006, mostly because of higher a phid infestation (Thorson). Some herbicides are also less toxic today. For exam ple, most of the herbicide used on soybeans is now in the form of glyphosate, which is about 10 times less toxic in terms of the oral Reference Dose (RfD) established by the Environmental Pr otection Agency (EPA) than herbicides used in the past, such as Alachlor (EPA, 2008). Kovach et al. found th at the environmental impact quotient (EIQ), which encompasses 11 different types of toxic ity measurements and environmental impacts, was found more favorable for glyphosate (EIQ =15.3) than for alachlor (EIQ = 18.3).Table 1 – Soybean agriculture system inputs, major States, 2002StateARILINIAKSKYLAMDMIMNMSMONENCNDOHSDTNVAWIWeightedAverage*InputSeedlbs/ac59.469.971.763.659.566.154.467.477.467.351.468.667.954.172.384.265.156.984.979.767.9FertilizerNitrogenlbs/ac1.763.553.000.894.447.440.135.5111.92.242.572.344.9110.616.52.977.6512.57.55.974.26Phosphoruslbs/ac19.613.611.74.6410.423.56.965.9215.64.7511.012.517.018.418.913.224.026.915.212.312.65Potashlbs/ac22.440.147.615.72.1536.19.4914.358.15.4317.931.33.1137.81.2458.25.7442.038.335.525.52Direct EnergyGasolinegal/ac1.30.901.601.101.101.401.102.101.501.101.201.401.301.501.401.301.401.301.202.401.26Dieselgal/ac9.902.502.303.402.902.106.502.904.004.004.304.3012.92.403.202.002.802.201.905.204.06Propanegal/acNR0.00NR0.001.80NRNRNRNRNRNRNR4.40NRNRNR0.00NRNR0.000.73ElectricitykWh/ac11.2NR1.300.009.104.50NR0.80NRNR3.80NR39.40.600.800.00NR1.00NRNR6.62Natural GasCf/acNR0.00NR0.003490.00NR0.000.000.000.000.005860.000.000.000.000.000.000.0058.41ChemicalsHerbicideslbs/ac1.001.231.351.261.071.151.601.541.220.981.661.171.281.001.261.341.201.291.230.811.21Insecticideslbs/ac0.040.000.000.010.000.000.600.340.000.000.020.000.010.070.000.000.020.000.050.000.02Limelbs/ac53.7595668.8286.4146.7865.670.7NA323.3181.8120818.5123.9652.9NR394.6NR828.3769.7379.3357.96YieldBu/ac33.543.041.548.023.033.032.023.038.543.532.034.038.524.033.032.031.031.023.044.038.0Source: USDA, National Agricultural Statistics Service (NASS), 2005; USDA, EconomicResearch Service (ERS) (a); USDA, ERS(b); and USDA, NASS, 2003.*Weighted by area harvested in each State.NR: Not reported in that State due to small sample size.5Lim e use was not reported by Sheehan et al.; however, farmers apply lime periodically to increase soybean yield. In 2002, the average lime application for soybean production was 2 tons per treated acre (USDA, ERS b). About 52 percen t of the total planted acres were treated with lime, and the lime was applied on average every 5.9 years. Adjusting for the soybean planted acres and the annual rate, the lime application rate was estimated to be 358 pounds per acre.

Soybean yields also have been improving over time because of new seed varieties, improved fertilizer and pesticide applica tions, and new management practices (Ash et al., 2006). The data show a significant increase in soybean yield since 1990 (figure 1). Soybean yields have increased steadily since 1990 when the U.S. av erage yield was 34.1 bushels per acre, and by 2002, U.S. soybean yield increased to 38 bushels pe r acre (Ash and Dohlman). The latest USDA estimate for soybean yield is 41.7 bushels per acr e for the 2007 crop year (USDA, Office of the Chief Economist-b). The data trend shows a continuous increase in yield but there was no significant increase in other agricult ural inputs. Conseque ntly, as shown later in this report, the FER increases with crop productivity.

There have also been major changes in the soyb ean crushing industry that are expected to reduce the energy requirements of biodiesel. Unfortunately , the best data available to Sheehan et al. on oil crushing were based on a single facility that was 17 years old at the time of the study. Although adjustments were made to the model to m odernize the plant, it is unlikely that it was a good representative of a typical crusher of the time. Thus, the typical plant in operation today is much newer than the plant modeled by Sheehan et al. For example, the oil extraction rate has increased since the Sheehan et al. study, whic h used 10.16 pounds per bushel (Table 79, pp 134).

Figure 1

 U.S. national average soybean yield 1980-2007 and expected trend to 2010

25 30 35 40 45

1980 1985 1990 1995 2000 2005 2010Yield (bu/acre)

Year

Source: Ash and Dohlman; and USDA, Office of the Chief Economist (b).

6The oil extraction rate for cr op year 2002/2003 was 1 1.39 pounds per bushel and increased to 11.55 pounds per bushel in crop year 2007/2008 (USDA ERS, 2009). Even though the oil extraction rate for year 2007/2008 was higher, th e oil extraction rate of 2002/2003 was used in this report to be consistent w ith the 2002 ARMS agri cultural input data. Furthermore, newer plants are more energy efficient due to the a doption of energy saving t echnologies that reduce production costs. Process improvement in extr action plants has con tinued with increasing emphasis on energy efficiency, reducing hexane loss, and increasing capacity. For instance, the current acceptable level of solvent loss is one-thi rd the level used by U.S. extraction plants in 1970 (Woerfel).

Likewise, the amount of energy required to convert soybean oil into biodiesel using transesterification may have d ecreased over the past decade ifproducers have adopted energysaving processing equipment to minimize production cost s. The rise in larg er biodiesel facilities with corresponding larger ener gy requirements has prompted greater emphasis on minimizing energy costs. The capital cost of adding energy saving technologies would be justified if the investment cost is less than the savings from lo wer energy costs. For example, heat integration technologies have resulted in the capture and reus e of heat that was previously discharged. Improvements in the catalytic t echnology used to produce biodie sel have resulted in higher conversion efficiencies of soybean oil into bi odiesel. Reclaiming and reusing the wash-water stream used to purify biodiesel eliminates the need for wastewater treatment.

Energy Life-Cycle Inventory

This section describes the invent ory and data used to construct the four subsystems of the biodiesel life cycle: feedstoc k production, feedstock transportation, soybean processing with biodiesel conversion, and product dist ribution. The analysis first cons tructs a base case, in which the inventory was kept basically the same as the inventory in the Sheehan et al. report. Then additional inputs that were not in cluded in Sheehan et al., such as agricultural machinery and energy embodied in building materials, were added to study their impact on the FER.

Feedstock Production

The farm input data for soybean production were obtained from ARMS and the National Agricultural Statistics Service (NASS). Th e direct energy data came from the 2002 ARMS, which were the most recent soybean survey data available at the tim e of this study (table 1). The State soybean yield data are USDA estimates reported by NASS (USDA, NASS, 2005). The fertilizer and chemical data for year 2002 s oybeans are from the USDA’s NASS Agricultural Chemical Survey. The lime-application rates and the seed-application rate s shown in table 1 are State averages from the 2002 ARMS (USDA, ERS-a; and USDA ERS-b).

The farm input data in table 1 we re weighted by State acreage to derive average energy used for U.S. soybean production. The weighted averag e soybean yield for the State data equaled 38 bushels per acre in year 2002. Th e weighted average energy input use and the weighted average yield were used to estimate the energy required to produce a bushel of soybeans in the United States (table 2). The direct energy inputs we re converted to British th ermal units (Btu) using low-energy heating values, assuming that electr icity generation came from a combination of

7coal, natural gas, nuclear, and hydropower at the sam e proporti on as the national average. Electricity use only includes electricity gene rated from fossil sources, which on a national average equals 70 percent. The energy used for planting the seed and other farm activities, such as land preparation, plowing, weed ing, fertilizer and pesticide a pplication, irrigating, harvesting, and drying, is included in total fa rm fuels and electricity estimates . The fuel required for hauling the soybeans from the field to the first destinatio n point, either farm storage or local market, is

also included in the fuel estimates. The convers ion factors used to convert farm energy inputs into Btus are listed in Appendix table 1.

Estimating Energy for Transporting Soybeans to Biodiesel Plant

The amount of energy required to transport s oybeans to processing pl ants came from the Greenhouse Gases, Regulated Emissions, and En ergy Use in Transportation (GREET) Model (Argonne National Laboratory). The energy requ ired for transporting soybeans to processing

Table 2 – Energy equivalents for base case soybean agriculture system inputs before allocating coproduct values, 2002

20 States Weighted Average Inputs* (Btu/bu) Btu/gal

Seed 3,617 2,428

Fertilizer:

Nitrogen 2,482 1,666
Phosphorus 1,313 881

Potash 1,721 1,155

Direct Energy:

Diesel 16,280 10,928

Gasoline 4,782 3,210
Propane 1,817 1,220
Electricity** 1,330 893

Natural Gas 1,607 1,079

Ag. Chemical Application:

Herbicides 4,368 2,932

Insecticides 55 37

Lime 506 340
Total Fossil Energy for Agriculture 39,878 26,769

* Inputs are adjusted by energy efficiency factors. **Assumes 70 percent of electri city generated from fossil sources.

8plants was estimated to be 6,393 Btu/bushel, whic h is equivalent to a bout 4,291 Btu per gallon of

biodiesel. The estimation was based on a distan ce of 50 miles for trucking soybeans from a distribution center to the soybean crusher/biodiesel plant.

Estimating Energy for Oil Crushing and Biodiesel Conversion

The production of biodiesel from soybeans occurs in two stages: the soybean s are first treated to remove the oil, and then the soyb ean oil is converted into biodiese l. The first stage, the removal of the oil from the soybean, is often called crushing, and the most common method used to

convert the oil into biod iesel is a process known as transest erification. Since actual industry data for soybean crushing and biodiesel produc tion were not available, this study had to develop a generic model to estimate the energy require d to crush soybeans and produce biodiesel using transesterification. The energy requirements for soybean crushing and transesterification were estimated using a computer model utilizing chem ical process engineeri ng and cost engineering technology that were developed by USDA’s Agricultural Research Service (Haas et al.). The

model measures the electrical and thermal ener gy inputs required for a joint facility that combines a soybean processing plant with a biodiesel conversion plant producing 9.8 million gallons of biodiesel, 151,515 tons of soybean me al, 9,000 tons of soybean hulls, and 4,380 tons of crude glycerin. The model provides a blue print of a biodiesel plant based on the best information available, but it does not represent an actua l plant, since actual industry data were

not used.

Oil Extraction From Soybeans

The separation of the soybean into oil and soyb ean meal, which is generally referred to as crushing, can be done by crushing using mechanical extruders, but more commonly the oil is extracted from the soybeans using chemical hexa ne extraction (figure 2). A soybean processing facility uses energy in the form of electricity to power motors and provide lighting. Natural gas and process steam are used to pr ovide heat for drying. The model used in this analysis allows the plant to generate its ow n steam from natural gas with a boiler efficiency of 80 percent. Thus, the energy value for steam is incorporated in the energy value of natural gas used to generate the required steam. Soybeans entering the process ar e first cleaned and then heated and dried to obtain a 10-percent moisture cont ent (Erickson, 1995). Then the b eans are cracked into several pieces by passing them through mechanical rolls. The soybean hulls, which account for about 8 percent of the soybean, are removed by aspiration. The hulls may be blended with the soybean meal that is later extracted in the process or th ey may be further treated by toasting and grinding

and sold as animal feed. The dehulled beans or meats are conditioned by heating, cut into flakes,

and fed to the oil extraction unit where the oil from the beans is dissolved with hexane. The oil and hexane mixture is treated with steam to separate the hexane from the oil. Once the hexane is removed, it is recycled for additional processing. Hot air and cooling water are used in the final heating and drying of the oil. The crude soybean oil is de gummed and may be deodorized, bleached, and neutralized. The oil-depleted, dried soybeans are ground to a uniform size to make soybean meal, and in some cases, the hu lls are blended with the soybean meal. The combined total thermal and electric energy requir ed for preparing the soybeans, extracting the oil from the beans, and drying the soybean meal is 23,151 Btu per gallon of biodiesel (table 3).

9Conversion of Soybean Oil Into Bio diesel

The conversion of soybean oil into biodiesel is do ne by reacting the oil with an alcohol, usually methanol, and a catalyst, such as sodium hydroxide, in large reactors. After the soybean oil, methanol, and catalyst have reacted, the result ing mixture is centrifuged to remove excess methanol, glycerin, and other impurities. After th e centrifuge step, the mixture is then washed

with a water acid solution and dr ied to become a methyl ester, which is commercially known as biodiesel (figure 2). The stream of methanol, gl ycerin, and other impurities is then treated with a small amount of acids and bases to remove any remaining fatty acids. The remaining material

is then distilled to recover the methanol and mo st of the water. The excess methanol and water

are recovered and reused to avoid waste and reduce input costs. Th e crude glycerin is often sold to companies that refine the glycerin to be used in the production of various other products, including fiberglass resin, cosmetics, pharmaceutic als, liquid laundry detergents, soaps, deicers,

and antifreeze. Electrical en ergy is used to drive the pumps , centrifuges, and mixers, while thermal energy is needed in the distillation colu mn to recover the excess methanol and remove

the final rinse water from the biodiesel. Thermal energy is also used to heat the soybean oil to accelerate the conversion process. The conversion of the soybean oil into biodiesel, the recovery of the excess methanol, and the treatment of the glycerin requires 18,772 Btu per gallon of biodiesel (table 3).

10Figure 2

 Soybean crushing and biodiesel conversion

11T able 3 – Fossil energy requirements for soybea n crushing and conversion before allocating coproduct values, per gallon of biodiesel

Inputs Equivalent Energy (Btu/gal) Adjusted Equivalent

Energy* (Btu/gal) Source

Soybean crushing:

Electricity** 2,738 6,124 ARS

Natural Gas/Steam 14,532 15,460 ARS

Hexane

-- 1,567 Huo et al.

Total fossil energy for crushing 23,151

Biodiesel conversion:

Electricity 439 981 ARS

NG/Steam 3,551 5,840 ARS

Methanol 7,193 10,633 Huo et al.

Sodium Methoxide

-- 1,256 Huo et al.

Sodium Hydroxide

-- 24 Huo et al.

Hydrochloric Acid

-- 38 Huo et al.

Total fossil energy for conversion 18,772

* Inputs are adjusted by en ergy efficiency factors.

** Assumes 70 percent of electricity generated from fossil sources, which is adjusted for

generation and line losses.

Biodiesel Transport

The GREET model was used to estimate the energy required for transporting biodiesel. Transporting biodiesel to marketing outlets requ ires 8,767 Btu per million Btu of biodiesel. This is equivalent to 1,027 Btu per gallon of biodiesel transported. The estimation was based on the total distance of 335 miles using a combination of tr uck, barge, and rail. It required a distance of about 32 miles for truck, 42 miles for barge, and 232 miles for rail to transp ort biodiesel from the plant to a distribution ce nter, and another 30 miles by truck to get it to its final destination.

Calculating Energy Coproduct Values

The energy used to produce the meal portion of the soybean and the crude glycerin that is produced during the transesterification stage must be excluded from the LCI. Several allocation methods can be used to estimate the energy value of coproducts. The Sheehan et al. study used a

12m ass-based allocation method, which simply allocat es energy to the vari ous coproducts by their relative weights. In order to pr ovide a consistent comparison to the original Sheehan et al. study,

we also use the mass-based allo cation method (figure 3) . Soybean crushing produces oil, meal,

Figure 3

─ Mass-based energy allocation for biodiesel coproducts

Agriculture, Bean transport, Crushing

Oil transport,

Biodiesel Conversion E 1

E 2 Oil Meal

Biodiesel Glycerol

Biodiesel transport 20.6%

82.4% 17.6%

E 3

Biodiesel 100% 79.4 %

Waste

Waste

gum, and waste material. USDA ERS (2009) repo rted a U.S. average o il yield of 11.39 pounds per bushel of soybeans, a soybean meal yiel d of 43.9 pounds per bushel, and a hull yield of 3.27 pounds per bushel in 2002/2003. Excluding th e hulls and waste mate rial, 20.6 percent of the total energy used for soybean agriculture, soyb ean transport, and crushing is allocated to the oil used to make biodiesel, and 79.4 percen t is allocated to the meal (figure 3).

Crude degummed soybean oil contains a small amount of unsaponifiable matter and free fatty acids that must be removed because they are detrimental to the transesterification process (Sheehan et al., pp 145). The free fatty acids can turn into soap when transesterified, resulting in more difficult phase separation of the methyl ester and glyceri n. The crude degummed oil is treated with sodium hydroxide to obtain dry re fined oil, with a yield of about 96 percent (Sheehan et al., pp 146). The othe r 4 percent is consid ered waste. Following transesterification, the proportion of refined biodiesel to crude glyc erin (with a purity of about 80 percent) is 82.4 percent biodiesel and 17.6 percen t crude glycerin. Therefore, 82.4 percent of the total energy used to convert degummed soybean oil into biodiesel is allocated to biodiesel and 17.6 percent is allocated to crude glycerin (figur e 3). In addition, the coproduct energy value of crude glycerin must be deducted from soybean agriculture, crushing, and soybean tr ansport, so that f 1 in equation (2) = 0.170 = (0.206  0.824), and f 2 = 0.824. All the energy used to transport biodiesel is allocated to biodiesel (figure 3).

13Results

Com bining the energy input estimates from the four subsystems completes the base case lifecycle assessment for biodiesel (table 4). As discussed a bove, the energy requirements for producing the biodiesel coproducts (i.e., soybean meal and crude gl ycerin) have been removed from the biodiesel inventory. The energy use estimates in table 4 are adjusted by energy efficiency factors (appendix table 2). All es timates of electricity generation were based on weighted average of all sources of power used in the United States, including coal, natural gas, nuclear, and hydroelectric. Electricity use onl y includes electricity generated from fossil sources, which on a natural aver age equals 70 percent.

After adjusting the inputs by energy efficiencies and allocating energy by coproducts, the total energy required to produce a gallon of biodiesel is 25,696 Btu (table 4). Biodiesel conversion uses the most energy, accounting for about 60 per cent of the total energy required in the lifeTable 4 – Base case energy use for biodiesel a nd FER with coproduct allocation and adjusted by energy efficiency factors

Fossil Energy Use (Btu/gal of Biodiesel) Life-Cycle Inventory

Total Biodiesel

fraction 1

Agriculture 26,769 4,544

Soybean transport 4,291 728

Soybean crushing 23,151 3,930

Biodiesel conversion 18,772 15,467

Biodiesel transport 1,027 1,027

Total Energy Input for Biodiesel Adjusted for Coproducts 25,696

Biodiesel Total Energy Output 117,093

Net Energy Value 91,397

Fossil Energy Ratio (FER) 4.56

1 Coproducts are allocated as shown in figure 3.

cycle inventory. Soybean agriculture accounts fo r 18 percent of the tota l energy requirements, followed by soybean crushing, which requires almo st 15 percent of the total energy. The net energy value (i.e., biodiesel energy output, minus fossil en ergy input) is about 91,000 Btu per gallon. The estimated FER of biodiesel is 4.56, which is about 42 percent higher than the FER reported by Sheehan et al.

14A major reason for this improvement is that th e soybean crusher modele d for this study more accurately measured the energy used by a modern f acility. Soybean crushing facilities that have been built in recent times are far more energy efficient than the older plant used by Sheehan et al. In addition, since 2002, EPA has required soybean plants to limit their hexane use, thus the amount of hexane reported by Sheehan et al. ha d to be adjusted to reflect the new industry standard (EPA, 2001). The new hexane energy value that was used in this study is one-half of that reported by Sheehan et al. Overall, the energy required for crushi ng fell from 9,321 Btu to 3,930 Btu per gallon of biodiesel, about a 58-percen t reduction (figure 4). The reduction in the crushing energy is primarily due to a reduction in th e electricity and natural gas/steam inputs. The fossil energy inputs for soybean agriculture fell from 7,681 Btu to 4,544 Btu (41 percent reduction) per gallon of biodiesel (figure 4). This reduction is primarily due to less diesel, gasoline, fertilizer, and chemical usage. A lik ely reason for the decrease in fuel use is the increased adoption of less intens ive tilling practices by soybean farmers. The lower chemical use in 2002 is partially related to the adoption of GE soybeans; however, differences in weather and other factors unrelated to energy efficiency can cause annual variation in chemical use.

Figure 4 – Comparing energy requirements for se lected biodiesel subsystems and total lifecycle energy requirements between this study and Sheehan et al.

The energy required for transesterification estim ated in this study was about 12 percent lower than the estimate reported by Sheehan et al. (f igure 4). The fossil energy for electricity decreased and methanol usage decreased; how ever, natural gas and steam usage slightly increased. Overall, the tota l life-cycle energy required for biodiesel fell from 36,416 Btu to 25,696 Btu per gallon.

The Effects of Adding Inputs to the LCI

Figure 5 shows the effects of adding secondary en ergy inputs to the LCI that were not included in Sheehan et al. to determine how they affect th e overall results. Hill et al. estimated the energy associated with manufacturing farm machiner y to be 7,547 Btu per bushel (5,066 Btu/gal of 7

. 7 9.3 17

. 7 36 .4

4 .5 3

. 9 15 .5 25.7

0 10 20 30 40

Agriculture Crushing Conversion TotalThousandsBtu/galofBD

Sheehan et al.

Updated 36 38

35 36 37 38 39

YieldBu/acre

15biodiesel). Adding the biodiesel share of this energy to soybean production reduces the base case

FER of 4.56 to 4.41. Hill et al. also estimated th e energies associated with building materials193 Btu per bushel (129 Btu/gal of biodiesel) for a crushing plant and 100 Btu per bushel (67 Btu/gal of biodiesel) for a biodi esel conversion plant. Adding the biodiesel share of energy related to building materials lo wered the FER to 4.54. If the i nput energy for both agricultural machinery and building material were added to the inventory, FER would decline to 4.40, still considerably higher than the 3.2 FER reported by Sheehan et al.

The Effect of Adding Lime to the LCI

Our base case LCI included lime unlike the Sheehan et al. inventory that omitted lime. Lime is added to soil periodically, and the annual lime application rates reported in table 1 are adjusted by average years between applications.

Figure 5 – Effect on fossil energy ratio from adding the energy from secondary energy inputs to the life-cycle inventory

4.56

4.41

4.54

4.40

012345 Base

Base + Ag. Mach.

Base + Build. Mat.

Base + Ag. Mach. + Build. Mat.

FER

Since farmers do not apply lime every year and so me acreage never receives lime, the adjusted annual average lime application ra te is relatively small. Lime use only accounts for 506 Btu per bushel of soybeans and lowers the FER by only about 0.22 percent. Therefore, including lime in the Sheehan et al. inventory would not have changed the results significantly.

Effect of Oil Transport

The generic biodiesel plant modeled in this study combined an oil crushing facility with a biodiesel conversion plant at the same location. Soybeans are shipped to the plant and crushed

into oil that is converted to bi odiesel onsite; hence oil transport was not included in the baseline inventory. There are many biodies el plants in the industry that do not have crushing capability, so they must purchase oil and have it transporte d to their plant. The model used by Sheehan et

16al. separated the crusher from the biodiesel conve rsion facility, so their inventory included the energy required to transport th e oil to the biodiese l plant, which was 843 Btu per gallon of biodiesel for 571 miles. When adding this ener gy to our inventory, the FER declines to 4.41 compared to the baseline result of 4.56.

Effect of Soybean Yield

Even though yields have been hi gher in recent years, yield data for year 2002 were used to calculate FER in this study to correspond to the 2002 ARMS agricu ltural input data. Yield plays

a critical role in the FER calculation because as soybean yields increase over time, the FER of biodiesel is also expected to increase. The US DA projects soybean yield to increase annually by 0.4 to 0.5 bushel/acre through the year 2017 (USDA, Office of the Chief Economist-a). For every 1 bushel increase in soybean yield, FER incr eases by about 0.45 percent. Holding all other variables constant, the FER of soybean biodiesel is estimated to reach 4.69 in the year 2015, when soybean yield is projected to increase to 4 5.3 bushels per acre. This is about a 3- percent increase compared to the 2002 FER estimate.

Summary and Conclusion
The fossil energy ratio (FER) of biodiesel is 4.56 based on data from 2002 soybean production. This is a significant improvement over the 1998 Sh eehan et al. study that reported a FER of 3.2. A major reason for this improvement is that th e soybean crusher modele d for this study more accurately measured the energy used by a modern f acility. Soybean crushing facilities that have been built in recent times are far more energy efficient than the older plant used by Sheehan et al. In addition, improved soybean yields and overall less energy used on the farm helped increase the energy balance of biodiesel. When comp aring the 2 study years (1990 and 2002), less fertilizers and pesticides were applied in the la tter year. The lower chemical use in 2002 can partially be explained by the a doption of GE soybeans that resulted in reduced pesticide use. However, differences in weather and other factors unrelated to en ergy efficiency may have also partially been responsible for the lower farm energy estimates in 2002.

The life-cycle inventory used for this study was c onstructed to resemble the Sheehan et al. study in order to make comparisons between the two tim e periods. To be consistent with Sheehan et al., secondary inputs such as bu ilding materials and farm machin ery were not included in the base case inventory. However, the results show that the FER of biodiesel changes very little when adding secondary inputs to th e life-cycle inventory. The model used to estimate the energy required to convert soybean oil into biodiesel represents a so ybean processing plant combined

with a transesterificat ion unit with an annual capacity of 9.8 million gallons per year. Although plants under 10 million gallons are quite common, there has been a recent trend in the industry towards larger plants. Larger plants with more capital investment would be expected to be more energy efficient.

Finally, the results from this rese arch suggest that the FER of biodiesel will continue to improve over time. This improvement will occur because increases in soybean yields are expected to continue and for every one bushel per acre incr ease in soybean yield, the FER increases by 0.45 percent. In addition, the agricultural sector , along with the biodie sel industry, will likely

17continue to make energy efficiency gains in order to lower production costs. In the future, as the United States develops its rene wable energy resources, more non-fo ssil energy will be included in the biodiesel life-cycle i nventory; for example, more el ectricity may be generated from biomass, wind, and solar power, and more farm equipment may use biofuels. Replacing fossil energy with renewable energy over the life cycle could also significantly increase the energy

balance of biodiesel over time.

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20Appendix

Appendix Table 1 – Energy coefficients used to convert inputs into British thermal units (Btu)

Inputs Energy Value Sources

Fuel Inputs Low Heating Value

Diesel (Btu/gal) 128,450 Huo et al.
Gasoline (Btu/gal) 116,090 Huo et al.
Propane(Btu/gal) 84,950 Huo et al.
Natural Gas (Btu/cft) 983 Huo et al.
Electricity (Btu/kWh) 3,412 Huo et al. Material Inputs

Nitrogen (Btu/lb) 22,136 Hill et al
Phosphorus (Btu/lb) 3,944 Hill et al.
Potassium (Btu/lb) 2,563 Hill et al.
Lime (Btu/lb) 53.72 Graboski
Seeds (Btu/lb) 2,024 Sheehan et al.
Herbicide (Btu/lb) 137,191 Hill et al.
Insecticide (Btu/lb) 139,772 Hill et al.

Methanol (Btu/lb) 9,750 American Methanol

Institute

Appendix Table 2 -- Life-cycle energy efficien cy factors for fossil fuels and electricity

Inputs Life-Cycle Efficiency
percent

Diesel 84.3

Gasoline 80.5

Propane 89.8

Natural Gas 94.0

Steam 60.8

Electricity 31.3

Methanol 67.7

Source: Shapouri et al.; Ener gy Information Administration; United State Department of Agriculture, Agricultural Resear ch Service; and Wang and Huang.

21Glossary

Allocation Method

─ R ules to determine the fraction of to tal input energy that is assigned to each coproduct. For example, both biodi esel and glycerin are produced during the transesterification process, but the energy us ed to produce the two products cannot be easily

delineated. Therefore an allocation method has to be used, such as a mass-based rule that allocates energy to the various copro ducts by their relative weights.

ARMS

 USDA's Agricultural Resource Management Survey (ARMS) is sponsored jointly by the Economic Research Service (ERS) and the Nati onal Agricultural Statisti cs Service (NASS). ARMS began in 1996 as a synthesis of the form er USDA cropping practice, chemical use, and farm costs and returns surveys, which dated b ack to 1975. It is USDA's primary source of

information on the financial c ondition, production practices, re source use, and economic wellbeing of America's farm households. http://www.ers.usda.gov/data/arms/GlobalAbout.htm#Use

British Thermal Units (Btu)

─ British thermal units are widely used in the United States to describe the heat value or energy content of fuels and other types of energy. One Btu is equivalent to 1,055 joules, which is an energy un it in the international system of weights and

measures.

Catalyst

─ A substance that enables a chemical reacti on to proceed usually at a faster rate or under different conditions (as at a lower temperature) than otherwise possible.

Centrifuge

─ A process of separating liquids with di fferent specific gravities by rotating the fluid at high speed.

Coproduct

─ When a production process results in two or more products, the products are called coproducts. For example, a soybean processing pl ant crushes soybeans to obtain two marketable coproducts (i.e., soybean oil and soybean meal).

Degummed Soybean Oil

─ Soybean oil after re moving phosphotides and some unsaponifiable matter commonly known as gums.

Dehulled Beans or Meats

─ That part of the soybean rema ining after removi ng the hull. The hull is the skin of the soybean, which is removed to facilitate solvent extraction of the oil and improve protein content of the meal.

Direct Energy Inputs

─ Inputs in the form of energy, such as gasoline, diesel, natural gas, and electricity. Inputs that depend on energy for thei r production, such as fert ilizers and pesticides, are indirect energy inputs.

Energy Balance of a Biofuel

─ An energy life-cycle assessment that measures the fossil energy required to produce a biofuel relative to its energy output value.

Energy Efficiency Factor

─ A coefficient used to account for the energy required to bring a raw energy resource from the environment to its final useable form. For example, for every unit of

22electrical energy produced, it takes on average 3.2 units of ener gy to get that energy into its final

for m and transport it to its fina l destination. Therefore, 3.2 is the energy efficiency factor for electricity, and the electrical en ergy used to produce a product mu st be multiplied by this factor to account for the total energy asso ciated with electricity use.

Energy Life-Cycle Assessment

─ A life-cycle assessment that focuses just on the energy inputs and outputs of a product.

Environmental Impact Quotient (EIQ)

─ A measurement that estimates the environmental impacts of a pesticide taking in to account several environmenta l variables, in cluding fish toxicity, bird toxicity, bee toxi city, and leaching potential.

Fatty Acids

 Fats or triglycerides, which are the primary constituents of vegetable oils and

animal fats. When using transesterification, the triglyce rides are transformed to esters and crude glycerin. The esters become biodiesel and the gl ycerin can be further processed to make other products.

Free Fatty Acids

─ Fatty acid groups that have broken off from the vegetable oil triglyceride molecule. Unless properly accounted for, free fatty acids consume catalyst needed for transesterification, lowering yi eld, increasing the reaction ti me, or potentially stopping the reaction altogether. Feedstocks with high free fatty acid levels will often be pretreated to remove free fatty acids before transesterification.

Feedstock

─ Raw material used in making an energy product. For example, biodiesel can be made from various feedstocks, including soybean oil, animal fat, and recycled cooking oil.

Fossil Energy

─ Energy derived from fossil fuel, which includes petroleum oil, coal, and natural

gas.

Fossil Energy Ratio (FER)

─ The energy output of a biofuel divided by the life-cycle energy required to produce the product. The FER only in cludes fossil energy in the denominator, and it is often the measurement used to quan tify the energy balance of a biofuel.

Genetically Engineered (GE) Soybeans

─ A soybean variety that has been genetically modified

to make it more resistant to herbicide applications, primarily glyphosate, commercially known as Roundup. GE soybeans were developed to survive the application of gly phosate that previously would have destroyed the crop along with the targeted weeds.

Glycerin or Glycerol

─ An organic compound present in all an imal and vegetable fats that is produced along with biodiesel when using the transesterification production process. Historically, refined glycerin has been a product of the commercial soap industry; however, a synthetic glycerin is also produced on a commercial scale by the petroleum industry. Commercial glycerin is found in many products , including solvents, sweeteners, cosmetics, liquid soaps, candy, liqueurs, and dynamite

.

23GREET Model

─ The Greenhouse Gases, Regulated Em issions, and Energy Use in Transportation (GREET) Model was devel oped by Argonne National Laboratory, U.S. Department of Energy. It fully evaluates life- cycle energy and emission impacts of advanced vehicle technologies and ne w transportation fuels. http://www.transportation.anl.gov/m odeling_simulation/GREET/index.html

Life Cycle

─ Consecutive and interlinked stages of a product system, from raw material acquisition or generation from natural resources to final disposal (ISO 14040). The life cycle of soybean biodiesel is assumed to start from th e beginning of the soybean production and end with the delivery of the biodiesel to a gas station or the point of the final use.

Life-Cycle Assessment (LCA)

─ Also known as life-cycle analysis , it is a technique to assess or measure certain aspects of a product over its entire life cycle. Life-cycle assessments are most often used to assess the environmental aspects of a product, but LCAs can also be used to measure the social impacts of a product.

Life-Cycle Inventory (LCI)

─ The database that contains th e amounts of all inputs and outputs of processes that occur during the life cycle of a product. The LCI is typically organized by a set of subsystems (e.g., biodiesel includes a feedstock subsystem and a conversion subsystem). The LCI sets boundaries for each subsystem to avoid unnecessary data collection.

Methyl Ester

─ Biodiesel is called a methyl ester if the alcohol used for transesterification is

methanol.

Net Energy Value (NEV)

─ The energy content of 1 gallon of biodiesel minus the life-cycle fossil energy required to produce 1 gallon of biodiesel. A biofuel has a positive energy balance if its NEV is greater than one, and a negative energy balance if the NEV is less than one.

No-Till

─ A crop residue management (CRM) system that maintains additional crop residue on the soil surface through fewer and/or less intensiv e tillage operations. CRM is generally cost effective in protecting soil and water resources and can lead to higher farm economic returns by reducing fuel, machinery, and labor costs while maintaining or increa sing crop yields.

Pest Management

─ A set of techniques used to redu ce pest populations or prevent their detrimental effect on crops and livestock. A pest is any noxious and damaging organism, including mites, insects, plan t pathogens, and weeds. Pest management techniques can be broadly classified into chemical , cultural, and biological.

Renewability

─ The degree in which a biofuel is rene wable. The fossil energy ratio (FER), which is the ratio of renewable energy output to fossil energy input, is a me asure of renewability. Biofuels that use less fossil energy per unit of renewable energy output have a higher degree of renewability.

Secondary Inputs

─ Secondary inputs have no energy value per se, but it requires energy to produce them (e.g., building materials used to constr uct processing plants and farm vehicles used for cultivation). These inputs are often exclude d from the LCI because they do not provide

2425 direct energy to the system and they’re difficu lt to quantify. Energy estimates for secondary inputs are generally very small, so their exclus ion from the inventory has little effect on the

LCA.

Soybean Crusher

─ A generic term used for a plant that primarily processes soybeans into two products: soybean meal and soybean oil.

System Boundaries

─ Limits set in the life-cycle inventory (LCI) to prevent boundless production systems and unnecessary data collection. Whether to include or exclude energy used beyond direct inputs, such as energy embodied in labor, building materials, and manufacturing equipment, depends on several factors, including goal and scope of the LCA, availability of data, reliability of data, time and cost of collecting th e data, and the extent to which the inclusion will

make difference in the final result.

Thermal Energy

─ The energy required for heating, for example, the heat generated from natural gas to dry soybeans.

Transesterification

─ A process for producing alkyl esters (biodiesel) by re acting a vegetable

oil or animal fat with an alcohol , usually ethanol or methanol. Th is reaction also results in the production of crude glycerin.

Unsaponifiable Matter

─ Non-triglyceride part of oil and fat that does not convert into soap. It is removed from the oil because it is detrimental to the transesterification

process.

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