Energy Fuels 2010, 24, 1305–1315 Published on Web 01/13/2010
: DOI:10.1021/ef901163a
Catalytic Hydrothermal Conversion of Triglycerides to Non-ester Biofuels Lixiong Li,* Edward Coppola, Jeffrey Rine, Jonathan L. Miller, and Devin Walker Applied Research Associates, Inc., 430 West Fifth Street, Suite 700, Panama City, Florida 32401 Received September 9, 2009. Revised Manuscript Received December 10, 2009
This paper describes a catalytic hydrothermolysis (CH) process aimed at converting triglycerides to nonester biofuels. The CH conversion was carried out at temperatures ranging from 450 to 475 °C and a pressure of 210 bar in the presence of water with and without a catalyst. The organic phase (biocrude) from the CH process underwent post-treatment involving decarboxylation and hydrotreating. Results derived from soybean oil, jatropha oil, and tung oil show that certain biofuel fractions met JP-8 specifications and Navy distillate specifications. One of the CH biofuel characteristics is their high levels of cyclics and aromatics. Tung-oil-based biofuels derived from the CH process contain up to 60% aromatics, which can be a desirable ingredient for fuel blends involving biofuels derived from other processes or feedstocks. Results from these crop oils also suggest that the CH process can be adapted to a variety of other triglyceride feedstocks. direct pyrolysis or catalytic cracking is the most common approach.3-8 Pilot plant demonstrations of fast pyrolysis of soybean oil9 and waste fish oil10 have been reported. Converting soybean oil into fatty acid salt (soap) followed by catalytic cracking has also been reported.11 Recently, biodiesel production from transesterification of triglycerides has become popular.12-14 The role and importance of catalysis in these processes have been reviewed.15,16 As shown in Figure 1B, high-pressure processes for both hydrolysis17-19 and transesterification of soybean oil20,21 and fats22 have been recently demonstrated. Both of these processes proceed more rapidly than the low-pressure processes and do not require catalysts. Pressure also appears to enhance direct pyrolysis and/or catalytic cracking of vegetable oils. Cheng reported a yield of 75% “crude” by cracking tung oil at pressures ranging from 4 to 12 bar and at temperatures from
Introduction Non-ester renewable fuels are pure hydrocarbons that are indistinguishable from their petroleum counterparts. Benefits of non-ester fuels may include (1) higher energy content than alcohols or ester-based fuels [such as fatty acid methyl esters (FAMEs)], (2) excellent combustion quality, similar to FischerTropsch fuels (low soot and high cetane), (3) good low-temperature properties (viscosity, freeze point, pour point, and cloud point), and (4) superior thermal stability, storage stability, and materials compatibility. As such, non-ester renewable fuels have great potential to meet current specifications for petroleum-derived fuels. There is a growing interest in developing technologies for non-ester biofuels, such as Hydrotreated Renewable Jet (HRJ) and non-esterified renewable diesel (NERD). This study focuses on using triglycerides derived from plants as the feedstock for the production of non-ester biofuels. The concept of converting vegetable oils into engine fuels was first attempted more than 100 years ago. From the late 1930s to the 1940s, because of the shortage of petroleum, industrial-scale plants became operational to produce gasoline, kerosene, and other grades of fuel from vegetable oils. According to recent reviews,1,2 various processes for converting triglycerides into biofuels can be summarized into three categories (Figure 1A). Among conventional processes that are typically carried out at near atmospheric pressures,
(9) Wiggers, V. R.; Meier, H. F.; Wisniewski, A., Jr.; Chivanga Barros, A. A.; Wolf Maciel, M. R. Bioresour. Technol. 2009, 100, 6570–6577. (10) Wiggers, V. R.; Wisniewski, A., Jr.; Madureira, L. A. S.; Chivanga Barros, A. A.; Meier, H. F. Fuel 2009, 88, 2135–2141. (11) Demirbas, A. Energy Sources, Part A 2003, 25, 457–466. (12) Bournay, L.; Casanave, D.; Delfort, B.; Hillion, G.; Chodorge, J. A. Catal. Today 2005, 106, 190–192. (13) Sulistyo, H.; Rahayu, S. S.; Winoto, G.; Suardjaja, I. M. World Acad. Sci. Eng. Technol. 2008, 48, 485–488. (14) Dupont, J.; Suarez, P. A. Z.; Meneghetti, M. R.; Menghetti, S. M. P. Energy Environ. Sci. 2010, in press. (15) van Santen, R. A. Renewable catalytic technologies;A perspective. In Catalysis for Renewables; Centi, G., van Santen, R. A., Eds.; WileyVCH, KGaA: Weinheim, Germany, 2008; pp 1-20. (16) Kersten, S. R. A.; van Swaaij, W. P. M.; Lefferts, L.; Seshan, K. Options for catalysis in the thermochemical conversion of biomass into fuels. In Catalysis for Renewables; Centi, G., van Santen, R. A., Eds.; Wiley-VCH, KGaA: Weinheim, Germany, 2008; pp 119-145. (17) Holliday, R. L.; King, J. W.; List, G. R. Ind. Eng. Chem. Res. 1997, 36, 932–935. (18) King, J. W.; Holliday, R. L.; List, G. R. Green Chem. 1999, 261– 264. (19) Chen, L.; Lu, X. Nongye Gongcheng Xuebao 2006, 22 (4), 230– 232. (20) Saka, S.; Kusdiana, D. Fuel 2001, 80, 225–231. (21) Kunchana, B.; Makmee, S.; Sawangkeaw, R.; Ngamprasertisith, S. Energy Fuels 2006, 20 (2), 812–817. (22) Marulanda, V. F.; Anitescu, G.; Tavlarides, L. L. Energy Fuels 2010, in press.
*To whom correspondence should be addressed. Telephone: 850-9143188. E-mail:
[email protected]. (1) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70, 1–15. (2) Lestari, S.; Maki-Arvela, P.; Beltramini, J.; Lu, G. Q. M.; Murzin, D. Y. Chem. Sustainability 2010, in press. (3) Demirbas, A.; Kara, H. Energy Sources, Part A 2006, 28, 619–626. (4) Lima, D. G.; Soares, V. C. D.; Ribeiro, E. B.; Carvalho, D. A.; Cardoso, E. C. V.; Rassi, F. C.; Mundim, K. C.; Rubim, J. C.; Suarez, A. Z. J. Anal. Appl. Pyrolysis 2004, 71, 987–997. (5) Idem, R. O.; Katikaneni, S. P. R.; Bakhshi, N. N. Energy Fuels 1996, 10, 1150–1162. (6) Schwab, A. W.; Dykstra, G. J.; Selke, E. J. Am. Oil Chem. Soc. 1988, 65 (11), 1781–1786. (7) Alencar, J. W.; Alves, P. B.; Craveiro, A. A. J. Agric. Food Chem. 1983, 31 (6), 1268–1270. (8) Kubickova, I.; Snare, M.; Eranen, K.; Vaki-Arvela, P.; Murzin, D. Y. Catal. Today 2005, 106, 197–200. r 2010 American Chemical Society
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Energy Fuels 2010, 24, 1305–1315
: DOI:10.1021/ef901163a
Li et al. TM
the UOP/Eni Ecofining processing technology is currently being adopted by Sustainable Oils, Solazyme, and UOP to supply 2.23 million liters (590 000 gallons) of renewable jet fuel to the U.S. military. However, the UOP/Eni EcofiningTM process is intrinsically associated with a monotonic spectrum of paraffinic products and high consumption of hydrogen. The former results in jet fuels of inferior quality, and the latter increases product costs. In addition, hydrogen used in the conventional petroleum hydrotreating process is derived from non-renewable sources, such as natural gas steam reforming. To overcome these shortcomings, a novel technical approach based on high-temperature water chemistry, known as catalytic hydrothermolysis (CH), has been proposed. The presence of water serves as a reactant, catalyst, and solvent for typically acid- or base-catalyzed reactions.25 Hydrogen is supplied in part by water for hydrocarbon cracking,26 as well as hydrolysis of triglycerides followed by decarboxylation. High-temperature and high-pressure water reduces the formation of gaseous products and minimizes the formation of chars. Water also functions as an effective heat-transfer and catalytic reaction medium. The triglycerides used in this study are derived from crop oils that can vary significantly in their fatty acid compositions. Because polyunsaturated fatty acids provide opportunities for structural modifications prior to or during the thermal conversion processes, crop oils that contain more than 30% polyunsaturated fatty acids have been selected for this study. As shown in Table 1, these include corn oil, cottonseed oil, linseed oil, peanut oil, safflower oil, soybean oil, sunflower oil, camelina oil, hemp oil, tung oil, and jatropha oil. Soybean oil was used as the baseline feedstock for this study. Tung oil is a non-edible oil feedstock that has been used for centuries as a water protection coating for wooden ships. Tung oil has a unique composition of extremely high polyunsaturated fatty acids (83 wt %; C18:2 and C18:3), which are predominately in the conjugated form (69 wt %; C18:3 eleostearic acid) fractions. This property makes tung oil a unique feedstock for conversion to motor fuels.27 Tung oil is one of a few naturally occurring triglycerides that contain conjugated polyunsaturated fatty acids. The tung tree (Aleurites fordii Hemsl.) is native to southern China, Burma, and northern Vietnam. Tung trees were successfully introduced to other parts of the world. Tung tree plantations flourished in northern Florida beginning in 1906.28 By 1928, 40 000 acres were planted for oil production northwest of Gainesville, FL. Oil production from these tung tree plantations exceeded 12 million pounds. Historical records show that some of these plantations yielded over 1000 pounds of tung oil per acre, mostly because of the unique climate and soil conditions in north Florida.29 The Jatropha curcas plant, originating in Central America, has the potential to produce crop oils for biofuel production. The current worldwide plantation for jatropha is about 1 million hectares.30 The plantation is expected to reach about 13
Figure 1. Processing options for converting triglyerides to biofuels.
400 to 500 °C.23 On the basis of the boiling point, the resulting “crude oil” consisted of 50% gasoline, 30% kerosene, and 20% fuel oils. Therefore, high-pressure processes hold the potential for converting vegetable oils and other triglycerides into biofuels with high mass and energy conversion efficiencies and desirable non-ester hydrocarbon product distributions. However, information about high-pressure processes for cracking and pyrolysis of triglycerides in the presence of water is lacking from the literature. In 2006, Defense Advanced Research Projects Agency (DARPA) initiated a biofuel program aimed at converting triglycerides to bio JP-8. The contract amounts and feedstocks being explored by the three selected contractors are as follows: General Electric Global Research ($3.1 million; camelina and canola oils), Universal Oil Products (UOP), A Honeywell Company ($6.2 million; soy and coconut oils and algae), and The University of North Dakota Energy and the Environment Research Center ($4.7 million; cuphea, coconut, and soy). All three teams attempted similar processes involving primarily hydrotreating triglycerides to achieve deoxygenation and decarboxylation.24 According to an announcement by the U.S. Navy and Air Force in September 2009,
(25) Kuhlmann, B.; Arnett, E. M.; Siskin, M. J. Org. Chem. 1994, 59, 3098–3101. (26) Nakahara, M.; Tennoh, T.; Wakai, C.; Fujita, E.; Enomoto, H. Chem. Lett. 1997, 26 (2), 163. (27) Chang, C.-C.; Wan, S.-W. Ind. Eng. Chem. 1947, 39 (12), 1543– 1548. (28) Langdon, K. R. The Tung Oil Tree, Aleurites fordii, Nematology (Botany) Circular No. 45; Florida Department of Agriculture and Consumer Services, Division of Plant Industry: Tallahassee, FL, Nov 1978. (29) Phillips, M. O. Econ. Geogr. 1929, 5 (4), 348–357. (30) Gexsi. Global market study on jatropha;Final report. London, U.K., May 8, 2008.
(23) Cheng, F.-W. China produces fuels from vegetable oils. Chem. Metall. Eng. 1945, January, 99. (24) Kalnes, T.; Marker, T.; Shonnard, D. R. Green diesel: A second generation biofuel. Int. J. Chem. React. Eng. 2007, 5 (A48), 1–9.
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: DOI:10.1021/ef901163a
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Table 1. Composition of Selected Triglycerides42 fatty acid (wt %) crop oil
14:0
16:0
16:1
18:0
18:1
18:2
18:3
20:0
22:0
fatty acid name corn oil linseed oil peanut oil soybean oil sunflower oil camelina oila hemp oil tung oil tung oil (this work) jatrophac jatropha (this work)
myristic
palmitic 12.2 7.0 11.6 11.0 6.8 7.8
palmitoleic 0.1
stearic 2.2 4.0 3.1 4.0 4.7 3.0
oleic 27.5 39.0 46.5 23.4 18.6 16.8 9 11.2 4.0 12.8 42.1
linoleic 57.0 15.0 31.4 53.2 68.2 23.1 54 14.6 8.5 47.3 37
linolenic 0.9 35.0
arachidic 0.1
behenic
1.5 0.3 0.4
3.0 0.1
4.7
0.6
a
0.1 0.1 0.2
3.1 5.5 11.3 12.5
0.2 0.1
0.9
2.1 0 17.0 7.5
7.8 0.5 31.2 26 69.0b 82.0b
Also contains 12% C20:1 and 2.8% C22:1.43 b Eleosteric acid. c Also contains 4.4% C24:0.44
million hectares by 2015 worldwide. Jatropha oil production reportedly ranges from 300 to 1200 gallons per acre. Jatropha oil contains less polyunsaturated fatty acids and more stearic acid than soybean oil. The fatty acid distribution of jatropha oil is closer to that of peanut oil. The objective of this study is to explore and demonstrate novel applications of hydrothermal processes for conversion of triglycerides to non-ester biofuels. The technology targets sustainable crop oils including non-edible feedstock, such as oils derived from tung, jatropha, camelina, hemp, and algae, and non-food-grade feedstock, such as residue corn oil from corn ethanol plants. The feasibility of CH conversion of several triglycerides, including soybean, tung, jatropha, corn, and algal oils, was assessed in this study. This paper focuses on the introduction of the integrated CH processing concept followed by a discussion of the results derived from CH conversion of soybean, tung, and jatropha oils to non-ester biofuels.
Experiments were conducted using either two feed pumps (configuration “A”) or a single-feed pump (configuration “B”). In configuration “A”, water is pumped independently through a fluidized sand bath and preheated to 540 °C, while the oil is pumped independently through an electric circulation heater and preheated to 350 °C. These two streams are mixed at a point near the inlet of the reactor. In configuration “B”, oil and water are premixed to form an emulsion and pumped to the preheater and reactor as a single stream. The emulsion is formed by adding a few drops of 1 N NaOH solution and blending the mixture in a laboratory blender for approximately 45-60 s. In each of the configuration “B” experiments, 900 mL of oil and 100 mL of distilled deionized (DDI) water were typically used. For experiments involving the catalyst, 5 g of zinc acetate was first dissolved in 100 mL of DDI water, which was then mixed with the 900 mL of oil feedstock without adding the NaOH solution. The total feed flow rate typically ranged from 10 to 20 mL/min with a water/oil ratio of approximately 1:9. The reactor residence time was estimated as a reference rather than an independent variable for this work. It was assumed that the fluid was a single component and pressure-volume-temperature (PVT) properties of water were used. The reactor residence time averaged about 2 min and was calculated from the reactor volume divided by the volumetric flow rate of water-oil mixture at the reaction temperature and pressure. The reactor pressure was maintained by the pressure regulator downstream of the cooling coil, as shown in Figure 3. The liquid reactor effluent was accumulated in an effluent tank. At the end of the experiment, all liquid samples were separated into organic and aqueous phases. The organic phase was analyzed by gas chromatography coupled to a flame ionization detector (GC/FID) and GC-mass spectrometry (MS). The aqueous phase was analyzed by both HPLC and GC-MS. Volumetric production of the gaseous reactor effluent was measured using a wet test meter with samples collected periodically and analyzed by GC/ FID and GC-MS. Decarboxylation/Hydrotreating Experiment. Because of the presence of carboxylic acids, other oxygenated species, and unsaturated molecules, the CH crude required decarboxylation (removal of oxygen as CO2) and hydrogenation. Both processes were carried out using commercially available reduced and stabilized nickel catalyst (BASF Nysofact 120) in a 1 L benchtop autoclave reactor (Parr model 4520). The crude and 5-10 wt % catalyst were added to the reactor, mixed in a slurry form, and heated to 300-350 °C. A hydrogen sweep of 500 mL/min at about 30 bar was used to remove carbon dioxide and water vapor from the reactor, maintain the catalyst in a reduced form, prevent treated material from boiling, and saturate olefins. Liquid samples were taken intermittently for GC analysis to determine when the material was fully decarboxylated and adequately hydrotreated. The experiment typically lasts for 4 h, up to a maximum of 6 h, depending upon the
Experimental Section Apparatus and Procedure. The laboratory-scale production of biofuel from triglycerides reported in this project involves three processing steps. The first step is the CH process that converts triglyceride to biocrude. The biocrude is then decarboxylated and hydrotreated. The resulting non-ester biofuel is fractionated into JP-8, naval distillate, and gasoline cuts. Equipment and procedures for these experiments are described below. CH Experiment. The CH reaction is the key conversion step in the triglyceride to biofuel process. Temperature, pressure, reactor residence time, water/oil ratio, and catalyst have been identified as five key process parameters. Figure 3 shows the schematic of the continuous-flow reactor system used for this study. Major components of the system are listed as follows: (i) air-driven pump for oil (Williams Instruments, V-Series, model P250 V225), (ii) high-performance liquid chromatography (HPLC) pump for water (Scientific Systems, Inc. Prep 100 or Waters, model 510), (iii) electronic scales (Denver Instrument, MX-2001), (iv) electric circulation heater (Watlow, CastX 500), (v) fluidized sand bath (Techne, model SBL-2D, 600 °C max), (vi) coiled preheater (6.1 m length 6.35 mm outer diameter 0.89 mm wall thickness, 316 SS tubing), (vii) coiled reactor (3.1 m length 6.35 mm outer diameter 0.89 mm wall thickness, 316 SS tubing), (viii) pressure regulator (HyLok, RV1 6.35 mm relief valve, model RV1MH-4N4T-316SS), (ix) wet test meter (Precision Scientific, model 63125), (x) pressure indicators (i.e., 3-D Instruments, 414 bar full scale, 1.38 bar divisions and Stewarts-USA, 414 bar full scale, 6.9 bar divisions), and (xi) thermocouples (Omega Engineering, KQIN-116G, 1.59 mm outer diameter, Inconel, type K). 1307
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: DOI:10.1021/ef901163a
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Figure 2. Processing train of integrated triglyceride-biofuel concept.
Figure 3. Hydrothermal reactor system.
catalyst was supplied by BASF (Nysofact 120). The hydrogen gas used for hydrotreating was supplied in a size K cylinder (AirGas, ultra-high purity).
extent of hydrotreating based on GC analysis of the treated samples. Fractionation Experiment. The treated product contained n-paraffins, isoparaffins, cycloparaffins, and aromatic hydrocarbons ranging from 6 to 28 carbons in size based on GC-MS analysis. The product was fractionated in a 1 L Ace Glass distillation apparatus. On the basis of the boiling points, naphtha (
