Energy Fuels 2009, 23, 6156–6162 Published on Web 08/25/2009
: DOI:10.1021/ef9006214
Practical Method of Gravimetric Tar Analysis That Takes into Account a Thermal Cracking Reaction Scheme Tomoaki Namioka,*,† Young-il Son,‡ Masayuki Sato,† and Kunio Yoshikawa† †
Department of Environmental Science and Technology, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, S2-18, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan, and ‡ Korea Institute of Energy Research, Korea Received June 19, 2009. Revised Manuscript Received August 6, 2009
For biomass gasification to be effective, some difficult problems associated with tars must be overcome. One of these is the lack of a way to quantitatively analyze all of the gravimetric tar components with a single analytical device. Therefore, gravimetric tar components have been identified and their yields have been measured with a combination of two or more devices. However, a simple and practical analytical method is required for process development and pilot-scale testing. Here, we propose a practical method of gravimetric tar analysis that reflects the gravimetric tar reaction scheme and is suitable for industrial use. We applied this method to gravimetric tars produced by secondary biomass tar thermal cracking experiments. This method uses both ultimate analysis and 1H NMR analysis. Ultimate analyses showed that the h/c molar ratio of the gravimetric tars decreased with increasing secondary thermal cracking temperature. 1H NMR analyses showed that the hydrogen distribution depended on the thermal cracking temperature: as the temperature was increased, the number of aliphatic hydrogens decreased and the number of aromatic hydrogens increased. Analysis of the chemical shifts of 1H NMR peaks of the main biomass tar components in a reference material showed that the components could be separated into monocyclic aromatics and polycyclic aromatics at a threshold chemical shift of 7.4 ( 0.1 ppm. From these results, we proposed a modified reaction scheme and converted the hydrogen distributions obtained by 1 H NMR analysis to carbon distributions. Even though gravimetric tar yields decreased with increasing thermal cracking temperature, the yields of polycyclic aromatics were almost constant and were independent of thermal cracking temperature. The yields of monocyclic aromatics decreased with increasing thermal cracking temperature, whereas the yields of monocyclic aromatics in the volatile organic compound fraction increased. The yields of monocyclic aromatics were almost constant at temperatures below 1073 K. Thus, the occurrence of ring-opening reactions was negligible below 1073 K. Decomposition of monocyclic aromatics started at temperatures above 1173 K. Dealkylation reactions were accelerated at temperatures above 1073 K.
the effects of different types of reactors8-11 and the optimization of gasification agents.12 Simulation techniques have been used to improve reactor design.13 Before commercialization of biomass gasification systems, tar yields must be measured at pilot-scale plants or by using process development units (PDUs). One of the reasons why tar problems associated with biomass gasification are complicated is that there is no way of quantitatively analyzing all of the components of gravimetric tar with a single analytical device. To date, gravimetric tar components have been identified and their yields have been measured with a combination of two or more devices. For example, molecular weight distribution has been measured by gas permeation chromatography (GPC),14,15 functional
1. Introduction One of the biggest challenges for the realization of biomass gasification as an effective energy source is dealing with tar problems. Consequently, a lot of research has been directed toward various aspects of tar reduction.1-3 Some theoretical studies have used model substances,4,5 and others have used various types of real biomass.6,7 Some studies have considered *Corresponding author. Telephone: þ81-45-924-5585. Fax: þ81-45924-5585. E-mail:
[email protected]. (1) Sutton, D.; Kelleher, B.; Ross, J. R. H. Fuel Process. Technol. 2001, 73, 155–173. (2) Devi, L.; Ptasinski, K. J.; Janssen, F. J. J. G. Biomass Bioenergy 2003, 24, 125–140. (3) Li, C.; Suzuki, K. Renewable Sustainable Energy Rev. 2009, 13, 594–604. (4) Fushimi, C.; Katayama, S.; Tasaka, K.; Suzuki, M.; Tsutsumi, A. AIChE J. 2009, 55, 529–537. (5) Coll, R.; Salvad o, J.; Farriol, X.; Montane, D. Fuel Process. Technol. 2001, 74, 19–31. (6) Hanaoka, T.; Inoue, S.; Uno, S.; Ogi, T.; Minowa, T. Biomass Bioenergy 2005, 28, 69–76. (7) Tomishige, K.; Miyazawa, T.; Kimura, T.; Kunimori, K. Catal. Commun. 2005, 6, 37–40. (8) Wang, Y.; Yoshikawa, K.; Namioka, T.; Hashimoto, Y. Fuel Process. Technol. 2007, 88, 243–250. (9) Gil, J.; Caballero, M. A.; Martin, J. A.; Aznar, M. P.; Corella, J. Ind. Eng. Chem. Res. 1999, 38, 4226–4235. r 2009 American Chemical Society
(10) Matsuoka, K.; Kuramoto, K.; Murakami, T.; Suzuki, Y. Energy Fuels 2008, 22, 1980–1985. (11) Yamazaki, T.; Kozu, H.; Yamagata, S.; Murao, N.; Ohta, S.; Shiya, S.; Ohba, T. Energy Fuels 2005, 19, 1186–1191. (12) Gil, J.; Corella, J.; Aznar, M. P.; Caballero, M. A. Biomass Bioenergy 1999, 17, 389–403. (13) Sanz, A.; Corella, J. Fuel Process. Technol. 2006, 87, 247–258. (14) Qin, Y. H.; Huang, H. F.; Wu, Z. B.; Feng, J.; Li, W.; Xie, K. C. Biomass Bioenergy 2007, 31, 243–249. (15) Prauchner, M. J.; Pasa, V. M. D.; Otani, C.; Otani, S. Energy Fuels 2001, 15, 449–454.
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Energy Fuels 2009, 23, 6156–6162
: DOI:10.1021/ef9006214
Namioka et al. Table 1. Proximate and Ultimate Analyses of Wood Chip Samples and Char Produced at 923 K value unit
Figure 1. Jess’s reaction scheme. Reprinted with permission from ref 21. Copyright Elsevier 1996.
groups have been analyzed by Fourier transform infrared (FT-IR) techniques,16 and representative components and yields of gravimetric tar have been measured by GC mass spectroscopy (GC-MS),16,17 molecular beam mass spectrometry (MB-MS)11,18 and GC flame ionization detection (GC-FID).19,20 13C NMR15 has been used to determine aromaticity. The analytical results from the systems described above provide detailed information, so combinations of these methods are useful for considering the reaction mechanisms that produce gravimetric tars. However, from an engineering viewpoint, it is not absolutely necessary to identify all of the tar constituents and yields. In fact, there are both time and cost disadvantages inherent in acquiring such detailed analyses. For example, the time required to acquire sufficient sample material and the cost of using multiple analytical methods can be prohibitive. What is needed are necessary and sufficient data on gravimetric tars to allow macroscopic pilot-scale testing. For industrial use of biomass gasification, necessary and sufficient data on gravimetric tars are data that represent the gravimetric tar reaction scheme. Jess21 proposed a thermal reaction scheme for aromatic hydrocarbons (Figure 1) from detailed experimental data acquired under thermal cracking conditions. According to this scheme, there are two main paths to intermediate products: one pathway leads to light gases by way of benzene, the other to soot by way of soot precursors. Data that represent the reaction scheme, benzene and soot-precursors yields in this case, would provide an exact guideline for optimization of operational conditions and designing a reactor. Both 13C NMR and 1H NMR can be used to evaluate the aromaticity of hydrocarbons. However, 1H NMR has three advantages over 13C NMR: the amount of a sample required for 1H NMR analysis is about 1/10 that required for 13C NMR, the number of hydrogen atoms can be estimated in 1H NMR by integrating signal peak area, and 1H NMR analysis is much faster than 13C NMR analysis. Because gravimetric tars from biomass gasification have rarely been measured by 1H NMR,16 we first investigated the influence of secondary thermal cracking temperature on 1H NMR. We then used the results to modify Jess’s scheme and
wood chips
volatile matter fixed carbon ash HHV
proximate analysis wt %a 80.8 18.9 0.3 19.3 MJ/kga
C H N O S Cl
ultimate analysis 49.7 wt %b 6.4 0.1 43.8
