Energy Fuels 2010, 24, 6624–6632 Published on Web 11/15/2010
: DOI:10.1021/ef101223a
Producing Stable Pyrolysis Liquids from the Oil-Seed Presscakes of Mustard Family Plants: Pennycress (Thlaspi arvense L.) and Camelina (Camelina sativa)† A. A. Boateng,* C. A. Mullen, and N. M. Goldberg United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, United States Received September 9, 2010. Revised Manuscript Received October 25, 2010
Natural oil from non-food oil seeds, such as camelina, jatropha, and pennycress, is increasingly becoming the feedstock of choice for biodiesel production through transesterification to fatty acid methyl esters (FAMEs) and green diesel via catalytic hydrotreating. Unlike the presscakes from food-based feedstocks, such as soy and palm fruits, the residual oil-extracted presscakes are often not suitable for consumption as animal feed. However, their abundance and the fact that these feedstocks are already collected give them a logistic advantage as a bioenergy resource over conventional lignocellulosic biomass, which is yet to be harvested. Vegetable oil-seed presscakes make an ideal thermochemical conversion feedstock because of their inherently high initial calorific value. We carried out fast pyrolysis of the entire value chain of two of the mustard family oil seeds, pennycress and camelina, and found that, at the optimum fast pyrolysis conditions, not only can high-carbon, high-energy liquid fuel intermediates be produced but also these liquids are low-oxygen, stable intermediates that do not oligomerize over time to higher molecular weight or increase in viscosity over time according to the accelerated aging test. Liquid fuel quality was high, with gross calorific value ranging between 29.0 MJ/kg for defatted oil to 34.7 MJ/kg for the whole seed on a dry basis. The corresponding carbon conversion efficiency, defined as feed carbon converted to the liquid pyrolysate, ranged between 60 and 80%. It is envisioned that co-location of a fast pyrolysis process with a green-diesel plant that uses these feedstocks could provide additional gallons of renewable biofuels and a reliable source of aromatic hydrocarbon compounds needed for the formulation of renewable jet fuels.
that can be sustainably cultivated on marginal lands and efficiently processed and delivered have been mapped out on a region by region basis. However, efforts to increase the production of oil seeds that are non-food have not been emphasized. Also, not accounted for is the potential use of the biomass residue of the oil seed extraction value chain. While some biomass presscakes of certain origins, such as soybean and palm fruit, can be a valuable source of protein for animal feed, non-food sources, such as jatropha (Jatropha curcas) and some from the mustard family, such as pennycress (Thlaspi arvense L.), may not be used as animal feed because of their potential toxicity due to the presence of glucosinolates.3 Pyrolysis of these presscakes can potentially provide added quantities of advanced biofuels to the RFS. Given the high yield and high concentration of oxygenated hydrocarbons, including aromatic compounds, pyrolysis oil shows promise for producing large amounts of fungible biomass-based hydrocarbon fuels, such as gasoline and diesel, by employing conventional petroleum-refining techniques, such as hydrotreating and hydrocracking. However, its use has been limited because of stability problems caused by high oxygen (typically 40 wt %) and high water contents. Therefore, a typical “as produced” pyrolysis liquid from cellulosic feedstocks is acidic and, over time, olgiomerizes, increasing viscosity and presenting storage and use problems for an existing refinery.4 However, because oil-seed presscakes contain residual vegetable oils, they possess a higher calorific value than typical cellulosic materials, which
Introduction There is no doubt that the major barrier to the successful production of biofuels is feedstock production and logistics. For example, 30-50% of ethanol production cost can be attributed to delivering the feedstock to the refinery.1 To meet requirements for the renewable fuel standards (RFS) of 2007 by the United States Environmental Protection Agency (U.S. EPA), which call for 36 billion gallons of biofuels by 2022, the feedstock challenge must be sustainably met. Of the 36 billion gallons, corn ethanol is to be capped at 15 billion gallons, with the remaining 21 billion gallons coming from advanced biofuels from various sources. Of this amount, oil seeds are already contributing about 0.5 billion gallons of biodiesel to the RFS, with a projected rise to 1 billion gallons by 2022. That means 20 billion gallons of advanced biofuels must come from cellulosic resources.2 For this, the United States Department of Agriculture (USDA) is embarking on a massive effort that invests in cross-cutting and trans/multidisciplinary research efforts in the sustainable feedstock development, preprocessing, and feedstock logistics value chain. An array of cellulosic feedstocks † Disclaimer: The mention of trade names or commercial products in this paper is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the United States Department of Agriculture. *To whom correspondence should be addressed. E-mail: akwasi.
[email protected]. (1) Hess, J. R.; Wright, C. T.; Kenney, K. L. Biofuels, Bioprod. Biorefin. 2007, 1181–1190. (2) United States Department of Agriculture (USDA). USDA Biofuels Strategic Production Report; USDA: Washington, D.C., June 23, 2010 (http://www.usda.gov/documents/USDA_Biofuels_Report_6232010.pdf).
This article not subject to U.S. Copyright. Published 2010 by the American Chemical Society
(3) Tripathi, M. K.; Mishra, A. S. Anim. Feed Sci. Technol. 2007, 132, 1–27. (4) Huber, G. W.; Corma, A. Angew. Chem. 2007, 46, 7184–7201.
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pubs.acs.org/EF
Energy Fuels 2010, 24, 6624–6632
: DOI:10.1021/ef101223a
Boateng et al.
Table 1. Feedstock Elemental Composition and Higher Heating Value (HHV)a
water (wt %) carbon (wt %) hydrogen (wt %, organic) nitrogen (wt %) sulfur (wt %) oxygen (wt %, organic) ash (wt %) lipid (wt %, dry basis) HHV (MJ/kg) HHV (BTU/lb) a
PCb presscake
defatted PCb pressckae
PCb seed
camelina presscake
3.06 44.79 (53.15) 5.32 (6.31) 5.66 (6.72) 1.29 (1.48) 27.26 (32.34) 12.08 7.90 (8.99) 18.7 (22.2) 8040 (9544)
2.59 42.08 (49.43) 5.41 (6.35) 5.90 (6.93) 0.84 (0.98) 30.93 (36.32) 12.27 1.56 (1.78) 17.8 (21.1) 7652 (9071)
2.84 53.89 (59.13) 7.37 (8.08) 3.92 (4.30) 0.66 (0.72) 25.30 (27.76) 6.02 29.60 (31.5) 25.1 (27.6) 10791 (11866)
2.64 49.55 (53.73) 6.81 (7.38) 5.81 (6.30) 0.86 (0.93) 29.19 (31.67) 4.96 12.53 (13.30) 21.8 (23.5) 9372 (10103)
Dry and ash-free values are in parentheses. b PC = pennycress.
enables them to be successfully burned for energy “as is”, or they can be converted to refinery feedstocks if stable pyrolysis oils are produced from them. Importantly, these feedstocks are often already collected; therefore, co-location of such thermochemical conversion unit operations with the primary biodiesel/green-diesel plants should provide not only a feedstock preprocessing, logistics, and transportation advantage, but also the economics of the primary biodiesel plant operation will improve. Ultimately, the net energy production of the collective renewable operation will be expected to result in a reduction of the carbon footprint. We report, herein, the unusual stability characteristics of pyrolysis oils produced from field pennycress (T. arvense L.) and camelina (Camelina sativa) presscakes in a fluidized bed of sand. Both seeds are members of the mustard family. Pyrolysis liquids have been produced from rapeseed (Brassica napus L.),5,6 also of the mustard family, jatropha (J. curcas),7 and palm fruit 8 presscakes. However, no information on the pyrolysis of pennycress or camelina biomass has been reported in the literature. Pennycress is found throughout the northern corn-belt and grows as a winter annual, with a short life-cycle capable of producing viable seeds in a few days following anthesis. Therefore, pennycress can be grown within a conventional soybean/corn rotation and not displace a food crop nor require additional land. Pennycress is a prolific seed producer; studies indicate that both wild and cultivated stands can produce yields in the range of 1000 kg of seed per acre. The seeds contain up to 36 wt % oil, which is nearly twice that of soybeans.9 For these reasons, pennycress is an ideal candidate for use as a dedicated energy crop for the production of liquid biofuels in a conventional corn/soybean rotation cycles.
Table 2. Operational Conditions for Fluidized-Bed Pyrolysis Pennycress and Camelina condition fluidized-bed material particle size (bed material) (U.S. mesh) fluidizing gas gas flow rate (L/min) minimum fluidization velocity (m/s) superficial velocity (m/s) biomass feed rate (g/h) biomass/N2 ratio feed mean particle size (mm) bed temperature (°C) condenser 1 temperature (°C) condenser 4 temperature (°C) ESPa temperature (°C) estimated heat rate (°C/s) total quench rate (°C/s) a
value silica sand -20 þ 25 N2 100 0.23 0.65 1300-2700 0.46
