Evaluation of Guaiacol and Syringol Emission upon Wood Pyrolysis for some Fast Growing Species

Wood pyrolysis for Casuarina glauca, Casuarina cunninghamiana, Eucalyptus camaldulensis, Eucalyptus microtheca was made at 450°C with 2.5°C/min. in a flowing N2-atmosphere. The Eucalyptus genus wood gave higher values of specific gravity, ash , total extractives, lignin, N2-liquid trap distillate (NLTD) and water trap distillate (WSP) than those for Casuarina genus. The GHC of NLTD was higher for Casuarina genus than that for Eucalyptus genus with the highest value for Casuarina cunninghamiana. Guiacol, 4-ethyl-2-methoxyphenol and syringol were observed in the NLTD of all the four wood species reflecting their parent hardwood lignin origin. Eucalyptus camaldulensis wood had the highest lignin content (28.89%) and was pyrolyzed to the highest values of phenolics (73.01%), guaiacol (11.2%) and syringol (32.28%) contents in methylene chloride fraction (MCF) of NLTD. Accordingly, recoveries of syringol and guaiacol may become economically attractive from Eucalyptus camaldulensis. Keywords—Wood; Pyrolysis; Guaiacol; Syringol S an option for mitigating the threat of global warming, the utilization of biomass for energy and/or chemical recoveries is under consideration for today’s society [1]. Renewable energy is of growing importance in satisfying environmental concerns over fossil fuel usage. Wood and other forms of biomass are one of the main renewable energy resources available that give heat and power, biomass represents the only source of liquid, solid and gaseous fuels. Wood and other biomass can be treated in a number of different ways to provide such fuels. In general such methods are divided into biological (anaerobic digestion and fermentation) and thermal [2]. Thermochemical processes, especially pyrolysis, are the most common route for converting the biomass to energy and chemicals feedstock. Along with guaiacol, syringol and its derivates are characteristic products of pyrolysis of lignin [1]. As such, syringol is an important component of wood smoke. In preparation of food by smoking, syringol is the main chemical responsible for the smoky aroma, while guaiacol contributes mainly to taste. Further, Assessment of the chemical components in smoke from biomass burning is important for both accidental and planned fires and with respect to both environmental impact Dr. Sherif S. Z. Hindi is with Faculty of Meteorology, Environment and Arid Land Agriculture with the Department of Arid Land Agriculture and the Manager of Agricultural Research Center, King Abdul-Aziz University, Jeddah, Saudi Arabia ([email protected]). and health hazards [3].The pyrolysis behavior of biomass has been widely investigated, which depends on the three main components, i.e. cellulose, hemicellulose and lignin [4]. Lignin units are divided into three types, guaiacyl(4-hydroxy-3methoxyphenyl), syringyl (3, 5-dimethoxy-4-hydroxyphenyl) and p-hydroxy-phenyl [5]-[6]. Lignin thermally decomposes over a broad temperature range, because various oxygen functional groups from its structure have different thermal stabilities, their scission occurring at different temperatures [7].Wood lignin undergoes in three consecutive stages, corresponding to the evaporation of water, the formation of primary volatiles and the subsequent release of small molecular gases. The main pyrolysis sections and the maximum weight loss rates are quite different for different wood species. Phenols are the main volatile products, in addition to alcohols, aldehydes, acids, and so on. As the main gaseous products, CO, CO2 and CH4 are released out greatly [8].The semivolatile mono cyclic methoxyphenols are emitted as gases, and quantitative proportions have been reported from controlled analytical pyrolysis of wood and pulp [9]. At ambient temperatures, the methoxyphenols tend to condense, and they are present in extracts of smoke aerosols together with non-volatile compounds [10]. Small amounts of the most volatile methoxyphenols remain gaseous in smoke from different forest biomass materials [11].It was found that the guaiacol-type and syringol-type compounds as the primary products of lignin pyrolysis are predominant in bio-oil, acting as the significant precursors for the formation of the derivatives such as the phenol-, cresoland catechol-types. Further, The methoxy group (-OCH(3)) is suggested to work as an important source for the formation of the small volatile species (CO, CO2 and CH4) through the relevant free radical coupling reactions [12].Only minute amounts of material, mostly guaiacol or syringol, were released at either 200 or 300 C. Upon increase of the temperature to 400 C, the hardwood lignin was found to release substantial amounts of phenols, and at 500 C, a maximum in the release of material was found. No loss of material could be detected at 700 C or higher, however. For the hardwood lignins, the dominant products were of similar types with syringol, 4-methylsyringol and 4vinylsyringol constituting about 60 % of the mixture at either 500 or 600 C. In addition, substantial amounts of guaiacol and 4-methylguaiacol were present at 600 C [13].The pyrolysis of milled wood lignin generated a higher yield of bio-oil, mainly composed of phenols, guaiacols, syringols and catechols, and a less yield of char. In addition, guaiacol and Sherif S. Z. Hindi Evaluation of Guaiacol and Syringol Emission upon Wood Pyrolysis for some Fast Growing Species A World Academy of Science, Engineering and Technology International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering Vol:5, No:8, 2011 659 International Scholarly and Scientific Research & Innovation 5(8) 2011 scholar.waset.org/1999.2/7020 In te rn at io na l S ci en ce I nd ex , M at er ia ls a nd M et al lu rg ic al E ng in ee ri ng V ol :5 , N o: 8, 2 01 1 w as et .o rg /P ub lic at io n/ 70 20 syringol were the typical products from G-lignin and S-lignin, probably attributed to the easier cleavage of the aryl-alkyl linkage in the side chain compared with the C-OCH3 bond in the benzene ring [1]. Pyrolysis of raw maple wood produced 67 wt% of condensable liquid products (or bio-oils) that were a mixture of compounds including sugars, water, phenolics, aldehydes, and acids. pyrolysis of the lignin residue produced only 44.8 wt% of bio-oil that mostly composed of phenolics such as guaiacol and syringol compounds [14]. The pyrolytic condensates of about 53.9%, including 8% reaction water, was obtained upon pyrolysis of birch wood. The steam-distilled fractions of pyrolytic oil were found to be chemically and thermally stable when subjected to further purification processes. The syringol-rich fraction was separated and purified with a purity of about 92.3% [15].Wood, twigs, bark and needles from the conifers Norway spruce and Scots pine emitted twelve reported 2-methoxyphenols in similar proportions. Grass, heather and birchwood released the same 2-methoxyphenols as well as 2,6-dimethoxyphenols which are characteristic of angiosperms [3]. The lignin of vascular plants decomposes to fuel-specific methoxyphenols from biomass burning. Qualitative gas chromatographic and mass spectrometric data for 36 methoxyphenols from wood burning were recently presented [16].The purpose of this study was to determine and characterize the amounts of methoxyphenols released, especially guaiacol and syringol, as well as the NLTD yielded from the four wood species upon the pyrolysis process. MATERIALS AND METHODS Branches of four Egyptian hardwood species, namely Casuarina glauca Sieb., Casuarina cunninghamiana Miq., Eucatyptus camaldulensis Dehn., and Eucalyptus microtheca F.V.M were used in the present study. Three trees were selected from each species from the same location. The ages of the selected trees and the specified branches were about 15 and 8 years old, respectively. The diameter outside bark of the selected trees ranged from 30-45 cm. From each of the selected trees, one of the primary branches was selected. Accordingly, three branches were selected from each species. The diameter outside bark of the selected branches ranged from 15-20 cm. Each of the selected branches was cut at height of 10 cm above its base at about 140-170 cm above ground level. From each isolated branch, one disc of about 30 cm along the grain was cut, converted into meal after discarding both the pith and outerzone wood and sieved for wood determinations and pyrolysis process. The pyrolysis runs were carried out with a bench scale reactor (Fig. 1) which consists of an electric tube furnace (carbolite furnace modle MTF 12/338) controlled by a microprocessor temperature programmer with an error of ±5°C with an accuracy of 1°C and heating rate of 0.01°C/min., digital thermometer with a chromel alumel thermocouple (type K with an error of ±1°C), nitrogen regulator system consisted of a regulator and a flowmeter with an accuracy of ±2% of the full scale and the reactor body made up of Pyrex glass that consists of the samples tube (with outer diameter of 2.8 cm) and the train of traps. This train is consisted of two connected traps: The first one is immersed in covered Dewar flask filled with liquid nitrogen and the second one is simply a water scrubber, held at room temperature. Electric tube furnace (carbolite furnace modle MTF 12/338) Nitrogen regulator system NLTD trap