Energy & Fuels 2006, 20, 383-387
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Molecular Mass Distribution and Structural Characterization of Liquefaction Products of a Biomass Waste Material Fatma Karaca* Yildiz Technical UniVersity, Department of Chemical Engineering, DaVutpasa Cad. No: 127, 34210, Esenler-Istanbul, Turkey ReceiVed NoVember 9, 2005. ReVised Manuscript ReceiVed NoVember 22, 2005
A sample of pine barks has been liquefied in a tetralin-creosote oil mixture, under 30 bar hydrogen at 350 °C. The overall conversion was 96.3% (by wt). The product slurry was fractionated to hexane, toluene, and tetrahydrofuran solubles. Gas plus hexane solubles accounted for 32.4% of the product, while toluene solubles and tetrahydrofuran solubles were 6.7 and 57.2%, respectively. The fractions were examined by size exclusion chromatography, UV-fluorescence, and FT-infrared spectroscopy. In size exclusion chromatography, the tolueneand tetrahydrofuran-soluble fractions gave large peaks for material excluded from column porosity, suggesting the presence of high molecular mass material. The concentration of large molecular mass material increased from hexane solubles to toluene solubles and tetrahydrofuran solubles. UV-fluorescence spectra of the fractions showed shifts to shorter wavelengths and gains in intensity with increasing elution times in SEC. The structures and molecular masses of the product mixture do not appear amenable to upgrading by conventional catalytic methods.
1. Introduction Present oil prices are at a level that would encourage the manufacture of synthetic fuels. To date, however, biomass liquefaction has remained marginal to such considerations, since upgrading the complex primary product mixtures does not appear straightforward. Only small proportions of the products are amenable to analysis by gas chromatography coupled to mass spectrometry (GC-MS). The present study forms part of an attempt to characterize these materials in greater detail, with the objective of designing upgrading methods more appropriate to the feedstock. The present work will focus on pulp and paper mill wastes. The utilization of biomass materials as a source of renewable energy provides the additional benefit of avoiding landfill use or dumping.1-4 In attempting to uncover the structures and molecular mass distributions of complex mixtures, GC and GC-MS are powerful tools that immediately come to mind.5 However, GC and GC-MS are unable to analyze polynuclear aromatic materials with molecular masses much greater than about 300350 u. Similarly, biomass-derived liquefaction products are complex mixtures containing material with a multiplicity of structural features. In particular, a large proportion of these are highly oxygenated and highly polar compounds of molecular mass above 300 u and are not normally amenable to analysis
by GC or GC-MS. This is because a large proportion of components in biomass-derived liquids simply do not go through chromatographic columns, due to their high molecular masses and/or high polarities.6-9 With these complex mixtures, no single analytical technique is able to provide an overall picture, and as many analytical techniques as one can muster are required to improve the level of characterization of high molecular mass materials found in biomass-derived material. Recent advances in work on molecular mass distributions of hydrocarbon materials have taken place through the parallel use of separation techniques and selected analytical methods capable of characterizing high-mass materials. Several mass spectroscopic techniques as well as allied techniques have been extensively used in the works aiming to determine molecular mass distributions of these materials.10 Biomass-derived materials can also be investigated by similar techniques used for characterization of coal or petroleum-type fuel-derived materials in terms of products similarity. During the characterization, previous work has shown that more abundant fractions tend to mask the features of the less abundant fractions.11-13 Separation into molecular size fractions containing narrower bands of molecular masses and structural features also enhances the resolution of most analytical tools and serves to identify structural differences between fractions with increasing ranges of molecular masses.12-14 Thus complex,
* Tel: +90 212 4491738. Fax: +90 212 4491895. E-mail: karaca@ yildiz.edu.tr;
[email protected]. (1) Lappas, A. A.; Samolada, M. C.; Iatridis, R. K.; Voutetakis, S. S.; Vasalos, I. A. Fuel 2002, 81, 2087. (2) Oasmaa, A.; Kuoppala, E.; Gust, S.; Solanusta, Y. Energy Fuels 2003, 17-1, 1-12. (3) Aguado, R.; Olazar, M.; Jose, M. J. S.; Aguirre, G.; Bilbao, J. Ind. Eng. Chem. Res. 2000, 39, 1925. (4) Karago¨z, S.; Bhaskar, T.; Muto, A.; Sakata, Y.; Uddin, Md. A. Energy Fuels 2004, 18, 234. (5) Pindora, R. V.; Lim, J. Y.; Hawkes, J. E.; Lazaro, M.-J.; Herod, A. A.; Kandiyoti, R. Fuel 1997, 76, 1013.
(6) Evans, R. J.; Milne, T. A. Energy Fuels 1987, 1, 123. (7) Evans, R. J.; Milne, T. A. Energy Fuels 1987, 1, 311. (8) Milne, T. A. J. App. Anal. Pyrol. 1983, 5, 93. (9) Evans, R. J.; Milne, T. A. IGT’s 11th Symposium on Energy from Biomass and Wastes; 1987; p 807. (10) Domin, M.; Li, S.; Lazaro, M.-J.; Herod, A. A.; Larsen, J. W.; Kandiyoti, R. Energy Fuels 1998, 12, 485. (11) Lazaro, M.-J.; Herod, A. A.; Kandiyoti, R. Fuel 1999, 78, 795. (12) Islas, C. A.; Suelves, I.; Li, W.; Morgan, T. J.; Herod, A. A.; Kandiyoti, R. Fuel 2003, 82, 1813. (13) Lazaro, M.-J.; Domin, M.; Herod, A. A.; Kandiyoti, R. J. Chromatogr. A 1999, 840, 107.
10.1021/ef050369f CCC: $33.50 © 2006 American Chemical Society Published on Web 12/22/2005
384 Energy & Fuels, Vol. 20, No. 1, 2006
Karaca
Table 1. Proximate Analysis Data for Pine Bark moisture (original sample, %) ash (%, dba) volatile matter (%, db) fixed carbon (%, db) calorific value (kcal/kg) a
10.2 1.8 80.1 18.1 5100
Dry basis.
fuel-derived samples are usually fractionated, using one of several available methods such as planar chromatography,11 column chromatography,12 or solvent extraction.11 Fractionation is particularly useful for identifying the presence of materials found in relatively low concentrations in complex mixtures. The characterization of separated fractions may thus lead to the acquisition of information not easily available from the direct characterization of the original sample itself. We recently reported that size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) could be used in parallel for the structural characterization of large molecular mass materials derived from various fuels.15 Progress in the use of these two independent techniques has often leapfrogged each other as well as providing supporting evidence for each other.16-22 Superposing results from these techniques have made it possible to reliably identify molecular masses up to about 3000 u and to characterize mass distributions of complex mixtures.15 The present study outlines an attempt to examine molecular mass distribution and structural features of liquefaction products of pine barks. Sample particles were liquefied and the products fractionated by Soxhlet extraction into hexane-, toluene-, and tetrahydrofuran-soluble fractions. The whole (original) sample and its fractions were examined by size exclusion chromatography using 1-methyl-2-pyrrolydinone (NMP) as eluent and by UV-fluorescence spectroscopy. The molecular mass distributions of the sample and fractions were assessed using calibrations described previously.15 The whole (original) sample, the hexane solubles, and the residues were further examined by FTIR spectrometry. 2. Experimental Section 2.1. Sample Preparation. The pine bark sample was obtained from SEKA (in Balikesir, Turkey) as a paper industry waste. It was ground to particle size
