Energy Fuels 2010, 24, 4470–4475 Published on Web 07/21/2010
: DOI:10.1021/ef100363c
Effect of the Temperature on the Composition of Lignin Pyrolysis Products Guozhan Jiang,* Daniel J. Nowakowski, and Anthony V. Bridgwater Bioenergy Research Group, Aston University, Birmingham B4 7ET, United Kingdom Received March 24, 2010. Revised Manuscript Received June 28, 2010
The temperature dependence of the pyrolysis products of two types of lignin (Alcell lignin and Asian lignin) was investigated using pyrolysis-gas chromatography-mass spectrometry (PyGC-MS). About 50 compounds were identified and quantified for each type of lignin over a temperature range of 400800 °C. The maximum yield of phenolic compounds was obtained at 600 °C for both lignins, which was 17.2% for Alcell lignin and 15.5% for Asian lignin. Most of the phenolic compounds had an individual yield of less than 1%; however, for Alcell lignin, 5-hydroxyvanillin was the highest yield at 4.29 wt % on dry ash-free lignin, and for Asian lignin, 2-methoxy-4-vinylphenol was the highest yield at 4.15 wt % on dry ash-free lignin.
products in the reactor was longer. Saiz-Jimenez et al.4 performed a qualification of the pyrolysis products of lignins at 510 °C using pyrolysis-gas chromatography-mass spectrometry (PyGC-MS). They identified 47 phenolic compounds from the pyrolysis of five milled wood lignins from different origins. In the 1990s, Caballero et al. investigated the pyrolysis of Klason lignin5 and Kraft lignin6 using a Pyroprobe 1000 at a temperature range of 500-900 °C. They quantified gaseous products and light liquids but not phenolic products. Very recently, de Wild et al.7 performed the fast pyrolysis of Alcell lignin in a fluid bed reactor at 400 °C and obtained 13% of condensable organics from Alcell lignin and 21% condensable organics from Asian lignin but with no information provided on the phenolics content. The above work either quantified gaseous and light liquids or qualitatively investigated the phenolic compounds in the pyrolysis products at one or two fixed temperatures. There is a lack of quantitative information on the temperature dependence of the interesting phenolic compounds in the literature, which is important for converting lignin into value-added aromatic compounds through the pyrolysis route. There are two main reasons for the lack of information. One is due to the thermoplastic characteristics of lignin, resulting in difficulty in feeding for bench-scale pyrolysis. The second is the difficulty in calibrating the PyGC-MS. Lignin is a co-polymer of three phenylpropanoid monomers via various C-O and C-C linkages,8,9 which is different from the C-O linkages in cellulose. The C-C linkages need a higher temperature to cleave. Therefore, a different temperature is expected to achieve the maximum liquid yield from
1. Introduction With the development of ethanol biorefineries, lignin has become a significant potential feedstock for biofuels and aromatic chemicals. In the past half century, a continuous effort has been made into lignin conversion. The basic objective is to break down the various linkages between lignin monomers into low-molecular-weight value-added compounds via thermal and/or chemical pathways. However, lignin conversion is still a challenge because of technological barriers and adverse economic considerations. Fast pyrolysis is a relatively simple process. It was first attempted to produce phenolic compounds from lignin in the late 1970s. Iatridis et al.1 conducted fast pyrolysis of a Kraft lignin at a temperature of 400-650 °C in a “captive sample” electric screen reactor. Because of the limitations of analytical chemistry at that time, only five phenolic compounds (phenol, guaiacol, cresol, 4-methylguaiacol, and 4-ethylguaiacol) were quantified. The sum of the phenols was found to increase steadily with the temperature over the range studied. In the 1980s, Nunn et al.2 studied the fast pyrolysis of a milled wood lignin at a higher temperature range of 327-1127 °C in the same type of reactor. They investigated the evolution of gaseous products (CO, CO2, and C1-C4 hydrocarbons) and light liquids (water, methanol, acetone, and aldehyde). A maximum tar yield of 53% was obtained at 627 °C. However, the components in the tar were not analyzed. Jegers et al.3 performed the pyrolysis of a Kraft lignin in a microreactor at 400 °C and quantified 19 phenolic compounds and their evolution with time. They found that the demethylation reaction of guaiacol took place when the residence time of the
(5) Caballero, J. A.; Font, R.; Marcilla, A.; Garcia, A. N. Flash pyrolysis of klason lignin in a pyroprobe 1000. J. Anal. Appl. Pyrolysis 1993, 27, 221–244. (6) Caballero, J. A.; Font, R.; Marcilla, A. Pyrolysis of Kraft lignin: Yields and correlations. J. Anal. Appl. Pyrolysis 1997, 39, 161–183. (7) de Wilde, P.; van der Laan, R.; Kloekhorst, A.; Heeres, E. Lignin valorisation for chemicals and (transportation) fuels via (catalytic) pyrolysis and hydrodeoxygenation. Environ. Prog. Sustainable Energy 2009, 28, 461–469. (8) Freudenberg, K. Lignin: Its constitution and formation from p-hydroxycinnamyl alcohols. Science 1965, 148, 595–600. (9) Nimz, H. Beech lignin;Proposal of a constitutional scheme. Angew. Chem., Int. Ed. 1974, 13, 313–321.
*To whom correspondence should be addressed. Telephone: þ44121-2043393. E-mail:
[email protected]. (1) Iatridis, B.; Gavalas, G. R. Pyrolysis of a precipitated Kraft lignin. Ind. Eng. Chem. Process Des. Dev. 1979, 18, 127–130. (2) Nunn, T. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Product compositions and kinetics in the rapid pyrolysis of milled wood lignin. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 844–852. (3) Jegers, H. E.; Klein, M. T. Primary and secondary lignin pyrolysis reaction pathways. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 173–183. (4) Saiz-Jimenez, C.; Deleeuw, J. W. Lignin pyrolysis products; Their structures and their significance as biomarkers. Org. Geochem. 1986, 10, 869–876. r 2010 American Chemical Society
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pubs.acs.org/EF
Energy Fuels 2010, 24, 4470–4475
: DOI:10.1021/ef100363c
Jiang et al.
pyrolysis of lignin than from pyrolysis of whole biomass or cellulose. In this paper, we report quantification of the temperature dependence of production of different phenolic compounds from lignin pyrolysis using GC-MS with a new model of Pyroprobe 5200 series. This work is a guide toward choosing the pyrolysis temperature for bench- or larger scale fast pyrolysis units to maximize the yield of specific or general phenolic compounds by lignin pyrolysis.
Table 1. Proximate and Elemental Analysis of Alcell and Asian Lignins Alcell lignin (wt %)
moisture ash fixed carbon volatiles
2. Experimental Section
carbon hydrogen nitrogen oxygen
2.1. Materials. Two types of lignins were used in this study: Alcell lignin and Asian lignin. Alcell lignin was provided by the Energy Research Centre of The Netherlands (ECN), which was produced via the organosolv pulping process from a mixture of hardwoods. Asian lignin Protoband 1000 was provided by Asian Lignin Manufacturing of India, which was a co-product of pulp and paper via the soda pulping process from a mixture of wheat straw and Sarkanda grass. Alcell lignin is in the form of fine dark brown powder, and Asian lignin is a fine gray powder, both with a particle size less than 200 μm. Before use, both lignins were dried at high vacuum at 60 °C for 24 h. 2.2. Proximate and CHNO Analysis. The ash content of the lignins was derived by ashing at 575 °C for 3 h (ASTM E153493). The moisture content of the lignin was analyzed using a moisture analyzer (Sartorius MA35), in which a sample of about 1 g was placed in an aluminum pan and then dried at 105 °C to a constant weight. The reported data for ash and moisture content were the average of three measurements. The volatiles and fixed carbon were determined using a PerkinElmer Pyris 1 thermogravimetric analyzer. The sample was heated from 105 to 950 °C at a heating rate of 10 °C/min under a nitrogen atmosphere. The final weight after correction for ash and moisture content was the fixed carbon. The volatiles were calculated on a dry ash-free basis as the difference between fixed carbon and original weight. The carbon, hydrogen, and nitrogen content in the sample were analyzed by Medac Ltd. (Surrey, U.K.) by duplicate analysis. The oxygen content was determined by difference. 2.3. PyGC-MS. PyGC-MS tests were performed on each sample using a CDS 5200 pyrolyser coupled to a Varian 450-GC gas chromatograph with a Varian 220-MS mass spectrometer. The column was a Varian FactorFour (14% cyanopropylphenyl, 86% dimethylpolysiloxane; 30 m, 0.25 mm inner diameter, 0.25 μm film thickness). The gas chromatograph oven was held at 45 °C for 5 min and then programmed at 5 °C/min to 250 °C, with a dwell time of 5 min. The mass spectrometer was configured for electron impact ionization at 70 eV, with an interface temperature of 250 °C. Electron impact mass spectra were obtained by a Varian 220MS mass spectrometer at the mass range from m/z 45 to 300. Proposed assignments of the main peaks were made from mass spectral detection (NIST05 MS library) and the retention time of the standard compounds. Prior to analysis, the spectrometer was mass-calibrated and abundance-tuned using heptacosafluorotributylamine. Full scan data were acquired and processed using Varian software. 2.4. Calibration of the GC Column. A list of target compounds for quantitative determination was compiled from information in previously published literature and from initial PyGC-MS analysis of the lignin, followed by the qualitative identification based on mass spectral library matches. The list of the standard compounds was as follows: phenol, guaiacol, syringol, catechol, eugenol, vanillin, 2-methoxy-4-methylphenol, 3-methylcatechol, 1,2,3-trimethoxybenzene, 2-methoxy-4-vinylphenol, and syringaldehyde. A concentrated stock solution was prepared by weighing 0.5 g of each individual calibration compound to the nearest 0.1 mg and dissolving them in a 50 mL volumetric flask using GC-grade ethanol. Aliquots of the 10 000 μg/mL stock solution were then
Asian lignin (wt %)
Proximate Analysis
