Biodistillate Fuels and Emissions in the U.S. Presented to the Institute of Medicine Roundtable on Environmental Health Sciences, Research, and Medicine The Nexus of Biofuels, Energy, Climate Change, and Health Washington, D.C. January 24-25, 2013 S. Kent Hoekman Desert Research Institute 1
Outline Drivers for Biodiesel/Biodistillates Biodistillate Terminology and Production Fuel Composition and Properties Emissions Standards and Controls Effects of Fuel Composition on Emissions Mobile Source Air Toxics (MSAT) Conclusions/Recommendations 2
Drivers for Biodiesel/Biodistillates Interest in biodiesel is motivated by: Concerns about greenhouse gas emissions Desire to develop renewable/sustainable energy sources U.S. Renewable Fuel Requirements Advanced Biofuel: Unspecified Advanced Biofuel: Biomass-Based Diesel Advanced Biofuel: Cellulosic Biofuel Conventional Biofuel Desire to develop secure, domestic fuel supplies Interest in rural development Air quality and health concerns are minor drivers for biodiesel 3
Biodistillate Terminology Biodiesel Fuel (BD) ASTM D 6751: Mono-alkyl esters of long chain fatty acids derived from vegetable oils and animal fats. Transesterified triglycerides Fatty acid methyl esters (FAME) B100 (but not B20) Renewable Diesel (RD) Hydroprocessed triglycerides Hydrocarbons, not FAME Green Diesel NExBTL (specific commercial product) 4
Biodistillate Terminology (cont.) Co-Processed Renewable Diesel Renewable diesel produced by adding vegetable oils or animal fats to petroleum streams that are being hydrotreated to produce diesel fuel Contains mixture of bio and fossil hydrocarbons Cellulosic Biodiesel Fuel (or synthetic biodiesel) - Produced by pyrolysis and/or gasification of lignocellulosic feedstocks - Generally requires considerable additional processing/upgrading before blending into petroleum fuel stocks 5
Bio-Distillate Production Technologies Feedstocks Fats and Oils soy rapeseed palm waste cooking oil sunflower corn jatropha camelina algae mix with petroleum methanol H 2 catalyst H 2 catalyst Processing Transesterification Hydrotreatment Hydrotreatment Fuels Biodiesel + Glycerine Renewable Diesel Co-Processed Renewable Diesel Chemical Type FAME HC HC Lignocellulosic Feedstocks woods grasses ag. wastes food wastes MSW algae Gasification Syngas Pyrolysis Pyrolysis Oil catalyst upgrading F-T Distillate Distillate Blendstock HC HC 6
Biodiesel Feedstocks and Production Volumes At present, biodistillates are dominated by biodiesel (FAME) Soy oil is the main feedstock in the U.S. (lesser amounts of waste cooking oil, sunflower, corn, and other oils) Rapeseed is the main feedstock in Europe Palm oil is the main feedstock elsewhere Total U.S. biodiesel production exceeded 1 bgy in 2011 (and 2012) Total U.S. petro-diesel fuel production is about 60 bgy 7
Typical Distillate Fuel Properties Property No. 2 Petroleum ULSD Biodiesel (FAME) Renewable Diesel Carbon, wt.% 86.8 76.2 84.9 Hydrogen, wt.% 13.2 12.6 15.1 Oxygen, wt.% 0.0 11.2 0.0 Specific Gravity 0.85 0.88 0.78 Cetane No. 40-45 45-50 70-90 T 90, C 300-330 330-360 290-300 Viscosity, mm 2 /sec. @ 40 C 2-3 4-5 3-4 Energy Content (LHV) Mass basis, MJ/kg 43 39 44 Mass basis, BTU/lb. 18,500 16,600 18,900 Vol. basis, 1000 BTU/gal 130 121 122 8
Biodiesel Chemical Composition Two critical factors influence physical properties and performance attributes of biodiesel (including emissions): 1. Carbon chain length of fatty acids (C 16 and C 18 predominate) 2. Degree of unsaturation in fatty acid High unsaturation poor oxidative stability Low unsaturation poor low temperature operability Compared to biodiesel, conventional diesel has: 1. Broader molecular distribution: approximately C 12 C 24 2. Lower unsaturation 3. More branching of hydrocarbon chain 9
Biodiesel Chemical Composition Compositional profiles of biodiesel from two main feedstocks 60 50 Soybean Oil Soybean Oil 60 50 Rapeseed Oil Rapeseed Oil 61% Weight % 40 30 20 Weight % 40 30 20 10 10 0 10 12 14 14:1 16 16:1 18 18:1 18:2 18:3 20 20:1 0 10 12 14 14:1 16 16:1 18 18:1 18:2 18:3 20 20:1 Carbon Number and Unsaturation Linoleic Acid (C18:2) Oleic Acid (C18:1) O O OH OH 10
Diesel Emissions Standards and Controls Diesel engine/vehicle emissions are regulated by EPA (and some States) Different sets of standards are defined for: light-duty, medium-duty, and heavy-duty applications on-road and off-road applications Four criteria emissions are regulated: hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx) and particulate matter (PM) For air quality reasons, NOx and PM have been of greatest concern 11
Diesel Emissions Standards and Controls Emissions standards have become much more stringent over the past 25-years Roughly 2-orders of magnitude reduction in emissions levels for NOx and PM Emissions standards apply to new engines/vehicles only Fleet turnover is very slow for some diesel applications 12
Diesel Emissions Standards and Controls Large emissions reductions are achieved by a combination of modern engines and emissions control systems Engine improvements: High pressure, common rail fuel injection Variable injection timing Electronic monitoring and control systems Emissions control systems: Particulate traps require regeneration by combustion of collected PM Selective catalytic reduction (SCR) for NOx Urea injection used to convert NOx to N 2 Ultra-low sulfur diesel (ULSD) fuel is required to enable satisfactory long-term operation of emissions control systems 13
Effect of Biodiesel on HD Engine Emissions Traditional understanding based upon EPA report from 2002 EPA considered many emissions studies conducted prior to 2002 Increasing B-level is predicted to: Substantially reduce HC, CO, and PM Slightly increase NOx So-called NOx Effect has been the source of much controversy and concern. Change from base fuel, % 10 0-10 -20-30 -40-50 -60-70 NOx PM CO HC 0 20 40 60 80 100 Biodiesel blend level, % In most real-world applications, biodiesel is used at concentrations of B5-B20 14
Effect of Biodiesel Fuel on Engine Emissions More recent study was undertaken by DRI on behalf of the Coordinating Research Council (CRC) Project AVFL-17a: Investigation of Biodiesel Chemistry, Carbon Footprint and Regional Fuel Quality o o o o Over 1000 literature sources were reviewed Emissions data selection criteria: Full vehicle or multi-cylinder engine 1987 and newer engines/vehicles Standardized test cycle Biodiesel (FAME) from commercially available vegetable oils or animal fats Petroleum-based reference diesel fuel tested Various data analysis methods were used Final report issued in 2011; available from CRC website 15
Effects of Biodiesel Blend Level on NO x Emissions (HD/MD Engines) Change from base fuel, % 40 30 20 10 0-10 -20 NOx HD/MD Engine Dyno. Emissions 0 20 40 60 80 100 Biodiesel blend level, % Black points: 2-stroke engines Redpoints : 4-stroke engines Best-fit logarithmictrend line shown for all data points Change from base fuel, % Includes all feedstocks, base fuels, test cycles, and model years Most data at B20 and B100 levels Data scatter is just as large for HC, CO, and PM emissions 30 20 10 0-10 -20-30 NOx HD/MD Chassis Dyno. Emissions 0 20 40 60 80 100 Biodiesel blend level, % 16
Emissions Effects of Biodiesel from HD Engines Solid lines = EPA (2002) Dashed lines = This study Results from recent CRC study are largely consistent with earlier EPA results 10 0 Change from base fuel, % -10-20 -30-40 -50-60 -70 Red = NOx Green = PM Black = CO Blue = HC 0 20 40 60 80 100 Biodiesel blend level, % 17
Overall Emissions Results for B20 B20 Effects in 4-Cycle Engines Error bars represent 1 standard deviation Comparison of B20 results with previous studies (HD dynamometer tests) 18
Further Investigation of B20 Fuel Effects Literature data were sorted to investigate effects of: Biodiesel type: soy, rapeseed, yellow grease, palm Base fuel: No. 2 Diesel, ULSD, CARB Diesel Engine year: binned by NOx standard levels Test cycle load: light, medium, heavy Large data scatter makes it very difficult to detect any significant effects 19
Effects of Feedstock on Emissions from B20 Soy-based biodiesel was used most often No consistent differences seen in results among different feedstocks 30 HD/MD Engine + Chassis Change from base fuel, % 20 10 0-10 -20-30 -40-50 Soy Rapeseed Tallow Yellow Grease HC AVG. CO AVG PM AVG NOx AVG 20
Effects of Base Fuel on Emissions from B20 Conventional No. 2 diesel was used most often as base fuel No consistent differences seen in results among different base fuels 30 HD/MD Engine + Chassis Change from base fuel, % 20 10 0-10 -20-30 -40-50 No. 2DF ULSD CARB HC CO PM NOx 21
Effects of Engine Year on Emissions from B20 Engine model year classifications chosen to match major changes in NOx certification standards Most commonly used HD/MD engines were 1991-1997 No consistent differences seen in results among different model years 20 HD/MD Engine + Chassis % Change from from base base fuel, fuel % 10 0-10 -20-30 -40-50 1987-1990: 6g 1991-1997: 5g 1998-2003: 4g 2004-Present: 2g HC CO PM NOx 22
Effects of Test Cycle on Emissions from B20 Test cycles were categorized as light, medium, or heavy-load, based upon classification scheme in EPA s Regulatory Impact Analysis for RFS2 No consistent differences seen in results among different test cycle loads 20 Impact of Test Cycle Load 10 Change from base fuel, % 0-10 -20-30 -40-50 5a -Light-load 5b -medium-load 5c -heavy-load HC CO PM NOx 23
MSAT Emissions from Biodiesel Mobile Source Air Toxics (MSAT) list includes numerous chemical compounds MSATs of greatest interest with respect to biodiesel include: Total PM (already discussed) PAH (polycyclic aromatic hydrocarbons) Aldehydes: formaldehyde, acetaldehyde, propionaldehyde, and acrolein Oxygenated organics might be expected to produce higher levels of oxygenated MSATs Very little relevant experimental data is available to address this Existing data suggest that use of biodiesel does not consistently increase emissions of these MSATs 24
Formaldehyde Emissions from Diesel Engines and Vehicles Biodiesel blends vs. base fuel (data from CRC AVFL-17a study) 250 Biodiesel Emissions (all B-Levels) 200 150 100 50 Study 2 Study 1 HD Engine (mg/bhp-hr) LD Engine (mg/bhp-hr) LD Chassis (mg/mi) 0 0 20 40 60 80 100 120 140 160 180 Base Fuel Emissions 25
Summary and Conclusions Biodiesel (FAME) currently dominates total biodistillate volumes, but use of non-oxygenated biodistillates is likely to grow. Recent reviews of the biodiesel literature confirm earlier conclusions that increasing B-level in diesel fuel can provide significant reductions of HC, CO, and PM; while NOx emissions increase slightly. Emissions data from non-oxygenated biodistillate fuels are sparse, but available information suggests that these fuels provide emissions reductions as large (or larger) than biodiesel fuel. Diesel engine/vehicle exhaust standards have become much more stringent in the past 25-years, resulting in development of advanced emissions control systems. Advanced emissions control systems provide much larger emissions reductions than does the use of biodistillate fuels. 26
Summary and Conclusions (cont.) Determining fuel effects upon fleet-wide emissions is difficult due to variability of engine/vehicle types, test cycles, emissions control systems, and other factors. High data variability prevents firm conclusions regarding effects of biodiesel feedstock, base fuel type, engine model year or test cycle upon diesel emissions when using B20. While reliable data are sparse, use of biodiesel does not appear to affect aldehyde emissions in a consistent or significant way. Effects of biodiesel upon PAH emissions are unclear, but probably small. Advanced diesel emissions control systems have only been in use for a short time. Additional research is needed to assess the effects of biodiesel (and its impurities) on long-term operation of these systems. 27
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