Applied Mechanics and Materials Online: 2014-03-12 ISSN: 1662-7482, Vols. 541-542, pp 904-910 doi:10.4028/www.scientific.net/amm.541-542.904 2014 Trans Tech Publications, Switzerland Component Characteristics of Coal-based Jet Fuel and Petroleum-based Jet Fuel Yang Lin 1,, Tingya Zhou 1, Xin Wang 1, Xiaoyi Yang 1,a, * 1 School of Energy and Power Engineering, Energy and Environment International Center, Beihang University, 37 Xueyuan Rd., Haidian District, Beijing, P. R. China a yangxiaoyi@buaa.edu.cn Keywords: jet fuel, coal-based, petroleum-based, component characteristics Abstract. There are mainly four pathways to get liquid fuels from the coal including the direct liquefaction process, the Fischer-Tropsch process, coal-tar refining, and pyrolysis process. The characteristics of these four processed have been described. As the first two pathways are considered to be promising, the characteristics of these two types of coal-based jet fuels are discussed and the component characteristics of coal-based synthesis fuels are investigated, respectively. The component characteristics of coal-based jet fuels are compared with the traditional petroleum-based jet fuels. There are large differences between the properties of the coal-based jet fuel via direct and indirect liquefaction pathways. Comparing with the conventional petroleum-based jet fuel, the coal-based jet fuel via direct liquefaction pathway has the higher aromatics content, while the fuel via indirect pathway (F-T process) has more paraffin and nearly no naphthenes or aromatics. In additional, the carbon numbers of the coal-based synthesis jet fuels are compared with the conventional petroleum-based jet fuel. Introduction Coal-based alternative jet fuels refer to the liquid fuels obtained from solid coal, using coal as raw material. As early as 1978, the National Aeronautics and Space Administration (NASA) made an evaluation of the possibility of the application of the coal-based synthetic fuels in aviation [1]. Large-scale applications of coal-based jet fuels have many advantages. The coal-based jet fuel could compensate the shortage of kerosene before biomass-based alternative jet fuels come into the market. As a substitute for aviation fuel, the coal-based synthetic fuel could guarantee the energy supply within a short time. The development of coal preparation technology and the use of local coal-based production of fuels or chemicals, can not only decrease the petroleum supply pressure, but also help promote the in-place conversion of coal, and improve the economic efficiency and undoubtedly play an important role in the economic developments [2]. Fuel from liquefaction process is one of the main directions of clean utilization of coal resources [3], because the liquid fuel emissions are far below the direct combustion of coal, and its applications are more extensive. Although the standard specification of jet fuel do not limit the components, the properties of jet fuel are required in the range which indicated that the carbon numbers of components in jet fuel are from carbon number 8 to carbon number16. In this paper, the carbon numbers of the coal-based synthesis jet fuels are compared with the conventional petroleum-based jet fuel. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-08/04/16,23:08:35)
Applied Mechanics and Materials Vols. 541-542 905 Pathways to jet fuel There are mainly four pathways to obtain jet fuels from coal, as shown in Fig. 1. Direct liquefaction Indirect liquefaction (F-T) Coal-based jet fuels Coal-tar blending Coal-oil co-refining Co-coking Pyrolysis Fig. 1 Pathways to coal-based jet fuels Direct liquefaction process. The direct liquefaction process refers to the process that the coal is degraded and hydrogenated at constant conditions (temperature and pressure). Usually, the coal pyrolysis begins at 400 C. However, when the temperature exceeds 450 C, the conversion of coal and the oil yield do not increase substantially. The higher the pressure makes it more theoretically tend to the liquefaction reaction, but high pressure could increase the difficulties and risks of the operation, which also reduce the production economy. It is generally considered that high volatile coal could be liquefied easily, and researches show that when H/C is smaller, the conversion rate would be larger. The direct liquefaction process is picky about the qualities of the coal, while the indirect process is not so stricter. Currently, several typically foreign technologies of direct liquefaction are: the Integrated Gross Oil Refine (IGOR) process in Germany, the H-Coal, Catalytic Two-Stage Liquefaction (TSL), HTI and Exxon Donor Solvent (EDS) process in the United States, and NEDOL process in Japan, while the domestic technology is that Shenhua of China Coal Liquefaction Project process, which has its own features and is developed on the basis of other liquefaction processes [4]. Indirect liquefaction process (Fischer-Tropsch process). The indirect coal liquefaction technology requires the production of syngas (a gaseous mixture of hydrogen and carbon monoxide) from coal, which is then fed into the liquid fuel conversion process. The Sasol Company in South Africa leads the world in the technology of converting the natural gas and coal to the liquid fuel and its application, and has developed a semisynthetic technology and synthetic technology respectively for the alternative jet fuels [5]. Sasol has fifty years of experience in the conversion technology, plant design and operation. Now 25% liquid fuel in South Africa is obtained from coal, and this enables South Africa to be the country that drives and flies on coal. The research and development of coal liquefaction technology of China are developing in the recent year. The Inner Mongolia Yitai Group Co., Ltd. has built a plant that convert the coal to the fuel by indirect liquefaction process. Coal-tar co-refining. The coal-tar co-refining is the combination of the coal direct liquefaction process and the tar hydrocracking process. Using the petroleum residue as a solvent in the direct process, it is essentially that the coal is converting into liquid oil via a hydrogenation and liquefaction process, while the petroleum is cracked into the lower boiling point liquid oil. Research showed that the oil yield via this process was higher than that the coal and petroleum was hydrogenated separately [4]. Coal-tar blending and the co-coking are two common pathways. The coal-tar blending pathway is blending the bituminous coal and the by-product oil in the petroleum refining process after sedimentation. When
906 Engineering and Manufacturing Technologies heated, the mixture becomes liquefaction and the jet fuel components can be obtained after distillation. The co-coking process is that the mixes of the light cycle oil (another by-product of refining), the refining chemical oil (a by-product of coke industry) are hydrogenated and then distilled to get the fuels [6]. The United States Pennsylvania Institute of Energy obtained a coal-based synthetic jet fuel JP900 via the synthesis method of coal and tar oil and the co-coking pathway [7]. The jet fuels from these two processes contained more aromatic and hydrogenated aromatic hydrocarbons, and the high thermal stability could adapt to the requirements of the future fighter aircrafts. Pyrolysis process. The pyrolysis of coal is a complex process that when the coal is heated to a high temperature range, series of physical changes and chemical reactions would take place in ambient no oxygen. The chemical cross bonds could break while the generated products could recombine and react again. As a result, the final products included the gas (coal gas), liquid (coal tar), and solid (coke), etc [8]. The pyrolysis of coal for jet fuels is theoretically feasible that the coal tar via pyrolysis process and then be hydrogenated and refined, which should be proved by the further research. Characteristics of different processes. The direct liquefaction process and the indirect liquefaction process are general pathways and Table 1 summarizes the differences between the direct and indirect liquefaction processes of coal-to-oil. Table 1 Characteristics of coal-based jet fuels via direct and indirect processes [6] Production rate Coal consumption Obtaining efficiency Operation costs Gasification Reaction conditions Products Else Direct liquefaction (hydrogenation) High yield Small coal consumption. Output/Input: 1 ton (liquefaction oil)/2.4 tons (refined coal). High obtaining efficiency of target products. The majority are gasoline and diesel oil. Small devices, low investment, and low operation costs. Not completely depending on the coal gasification. More demanding. Pressure: 17-30[Mpa]. Temperature: 430-470 [ C]. Complex components. Highly viscous and difficult in solid-liquid separation. Large hydrogen consumption. Requires cycle oil to be solvent and decrease the yield. Indirect liquefaction (F-T process) High yield Large coal consumption. Output/Input:1 ton (F-T oil)/3.3 tons (refined coal). Low obtaining products. efficiency of target Large devices, high investment, and high operation costs. Depending on the coal gasification. Pressure 2.0-3.0 [Mpa]. Temperature: below 350 [ C]. The temperature decreasing, the heavy hydrocarbons yield growing while the light hydrocarbons yield decreasing. Theoretic production rate (Effective product CH 2 ) is as low as 43.75%, while the production of wastewater is 56.25%. Since China already has a mature industrial device for application of coal-to-fuel, the sources of feedstock via the direct or the indirect process seems no problem. Now the further studies should focus on the refined oil for aviation from the base oil. The establishment and operation of the coal-based liquid fuel projects in China have provided one platform for the researches and developments of the coal-based jet fuel. Overall, the developments of coal-to-fuel in China should be divided into three steps: a. the construction of coal-based oil platform; b. the technology development from the base oil to jet fuels; c. the certification and application of the jet fuel products.
Applied Mechanics and Materials Vols. 541-542 907 Components of coal-based jet fuels Characteristics of coal-based jet fuel via direct liquefaction. The coal-based oils via direct liquefaction are the mixture of different kinds of hydrocarbons. The aromatics generally consist of 1-5 rings, and the aromatic content in the oils can be as high as 60-70 percent. The saturated hydrocarbons content is about 25 percent and the carbon number is generally not more than 24. The olefins is about 10 percent. In addition, the nitrogen content of coal-based oils is several times to that of petroleum-based oils, for it varies from 0.9 percent to 1.1 percent [9]. Table 2 Components of coal-based jet fuels via direct liquefaction [10] Components Mass fraction [%] Paraffin 5.1 Monocycloparaffin 19.0 Dicycloparaffin 5.0 Tricycloparaffin 1.4 Total naphthenes 25.4 Total saturated hydrocarbons 30.5 Alkylbenzene 11.1 Indane/ tetralin 22.3 Indene 2.9 Total monocyclic aromatics 36.3 Naphthalene 1.3 Naphthalene series 2.6 Acenaphthene 0.4 Acenaphthylene 0.2 Total dicyclic aromatics 4.5 tricycloaromatics 0.0 Total aromatics 40.8 Resins 28.7 Total mass 100.0 The coal-based jet fuels via direct liquefaction consist of complex hydrocarbons, too. The components are mainly the monocycloparaffin, the alkyl-substituted monocyclic aromatics and alkyl phenolic compounds. The coal-based jet fuels can be the raw material of jet fuel of high stability because of its large quantities of aromatics and naphthenes, as shown in Table 2. Table 2 shows that the mass fraction of the alkyl benzene and indane/tetralin reaches 11 percent and 22 percent respectively. In addition, the resins, taking up a mass fraction of 28.7 percent, mainly consists of phenolic compounds [11]. As the main components, the phenolic compounds exceeds 80 percent of the relative content of the mixed phenolic components, and then the following are indan phenol (about 15%), tetralin phenol (approximately 3%), and naphthol in descending order. Among the phenolic compounds, the alkylphenol content that has a smaller carbon number of the alkyl side chain is highest, and the methyl-substituted compounds are the most [11]. Characteristics of coal-based jet fuel via indirect process (F-T). The commercial application of alternative jet fuels via indirect liquefaction from coal has already matured internationally. Using the coal as raw material, SASOL from South Africa obtained the semi-synthetic jet fuel (SSJF) and fully synthetic jet fuel (FSJF) via the F-T process. Suggesting the potential to replace conventional aviation fuels, the two fuels have passed the qualification and approval process of the commercial aircrafts in 2002. Furthermore, the semi-synthetic jet fuel (SSJF) has been applied to the aviation transportation for ten years without any problems. In China, the yielding of gasoline and diesel oil obtained from coal have been commercial, while the studies that focuses on the jet fuels are few.
908 Engineering and Manufacturing Technologies Table 3 shows the components of hydrocarbon group of kerosene cuts via indirect liquefaction from coal. It can be seen that the FSJF from SASOL contains 20.24% aromatics and 79.71% saturated hydrocarbons. In China, the oil via the F-T process refers to the kerosene cuts that obtained by the hydrocracking of synthetic heavy hydrocarbon. It is made up of 90.4% paraffin and 9.2% naphthenes, but only 0.4% monocyclic aromatics and no dicyclic aromatics or tricycloaromatics. Having a lower content of the sulfur, nitrogen, and aromatics, etc., the F-T oil would be significantly lower in emissions when burned and this makes it ideal for the clean fuel. Meanwhile, fine thermal stability enables the F-T oil to be the best feedstock for jet fuels. Table 3 Components of coal-based jet fuels via indirect liquefaction [12, 13] Components FSJF (Mass fraction [%]) Merox (Mass fraction [%]) Chinese F-T oil (Mass fraction [%]) Total saturated hydrocarbons 79.71 77.23 99.6 Paraffin 45.48 49.63 90.4 Naphthenes 34.23 27.6 9.2 Monocycloparaffin 13.84 20.34 8.1 Dicycloparaffin 20.39 6.73 0.8 Tricycloparaffin 0 0.53 0.3 Aromatics 20.24 22.77 0.4 Alkylbenzene 11.21 14.05 0.4 Dicyclic aromatics 0.35 0 Tricycloaromatics 8.68 0 Total mass 99.95 99.95 100 Component characteristics in comparison with kerosene The feedstock from coal via the direct liquefaction has many advantages such as the high C/H ratio, the high density, the high flash point, the low freezing point, the high naphthenes content, the high hydrogenated aromatics content and so on. However, compared with the petroleum-based jet fuel, the coal-based fuel could not satisfy completely for the standard properties, so that it could not be used as the alternative jet fuel directly. It needs to be hydrotreated to reduce the adverse impact on the stability property, and then to meet the jet fuel specification [14, 15, 16]. The jet fuel via F-T process is mainly made up of saturated hydrocarbons, and it has the similar components with the conventional jet fuel. Among the saturated hydrocarbons is 90% paraffin, but mere naphthenes or aromatics in comparing with the conventional jet fuels. Rina analyzed the components of the FSJF from Sasol and the jet fuel Merox, and then concluded that the two fuels had highly similar chemical components (Fig. 2), but differed in the carbon number (Table 4) [13]. The synthetic fuels had more branched paraffin and dicycloparaffin, but lacked the aromatic species, especially naphthalene and its derivatives. The FSJF from Sasol had a lower aromatics content which was closely to the specification.
Applied Mechanics and Materials Vols. 541-542 909 Fig. 2 Components of jet fuels [13] Table 4 Analysis of components of jet fuels [12, 13] 13.24
910 Engineering and Manufacturing Technologies Conclusion There are large differences between the properties of the coal-based jet fuel via direct and indirect liquefaction pathways. Comparing with the conventional petroleum-based jet fuel, the coal-based jet fuel via direct liquefaction pathway has the higher aromatics content while the fuel via indirect pathway (F-T process) has more paraffin and nearly no naphthenes or aromatics. The coal-based jet fuels via direct liquefaction has the military value for higer thermal stability. The feedstock via indirect pathway has the similar carbon component distribution with the petroleum-based jet fuel, and it can be applied to the commercial aviation engines after further improvements. Acknowledgements This project was supported by Key program of Beijing Municipal Science & Technology Commission (D131100003113003) and the Hi-Tech Research and Development Program (863) of China (2012AA052102). References [1] R.D. Witcofski. Progress on coal-derived fuels for aviation systems. NASA Technical Memorandum 78696(1978) [2] J.L. Zhou, Z.X. Zhang, B.J. Zhang. Modified FT(MFT) process of synfuel from coal-based syngas. Fuel Chemistry and Technology, Vol.27(1999), p.58-64 [3] G.F. Chen. New Developments and Aims of Clean Coal Technologies. Proceedings of fiftieth anniversary of the high-level academic forum of China Coal Society (2012) [4] Y.L. Li, R.S. Hu, Y.Q. Bai. Coal chemical base. Beijing: Chemical Industry Press (2006) [5] C.A. Moses, P.N. Roets. Properties, Characteristics, and Combustion Performance of Sasol Fully Synthetic Jet Fuel l. Journal of Engineering for Gas Turbines and Power, Vol.131(2009), p.131 [6] C.L. Zheng. Development and application of coal-to-oil technology. Proceedings of Shanghai Petroleum Institute (2007) [7] D.Y. Wang. Preparation and performance of the jet fuel JP900 of high thermal stability. Energy research and Information, Vol.22(2006), p.232-236 [8] D.H. Hang, Y.Q. Hu, J.S. Wang, et al. Study and Analysis of Influence Factors of Coal Pyrolysis. Coal technology, Vol.67(2011), p.164-166 [9] P. Zhao, W.B. Li, S.D. Shi. Development of Study on Structure,Property and Upgrading Process of Direct Coal Liquefaction oil. Proceedings of Chinese new coal chemical development and demonstration project progress forum (2010) [10] Y. Xue, S.L. Wang, J. Liu. Analysis of chemical constituents of coal liquefied jet fuel distillate. Acta petrolei sinica (Petroleum processing section, 2010) [11] Z.N. Gao, W.H. Li. Distribution and characterization of phenolics in direct coal liquefaction oil. Coal conversion, Vol.33 (2010), p.27-42 [12] Y. Xue, S.L. Wang, W.J. Cao. A laboratory study of using Fischer-Tropsch synthetic fuel as jet fuel. Petroleum processing and petrochemicals,vol.40(2009), p.44-47 [13] V.D. Rina W, A. Mariam, D.C. Piet. Comprehensive two-dimensional gas chromatography for the analysis of synthetic and crude-derived jet fuels. Journal of Chromatography A, 1218 (2011), p.4478-4486 [14] ASTM D7566, Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons. U.S.: ASTM International (2013) [15] ASTM D1655, Standard Specification for Aviation Turbine Fuels. U.S.: ASTM International (2012) [16] GB/T 6537, No.3 Jet Fuel. Beijing: China Standard Press (2006)
Engineering and Manufacturing Technologies 10.4028/www.scientific.net/AMM.541-542 Component Characteristics of Coal-Based Jet Fuel and Petroleum-Based Jet Fuel 10.4028/www.scientific.net/AMM.541-542.904