ARTICLE pubs.acs.org/EF
Bio-oil from Sawdust: Effect of Operating Parameters on the Yield and Quality of Pyrolysis Products Ebrahim Salehi, Jalal Abedi,* and Thomas Harding Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada ABSTRACT: This study investigated the effects of the pyrolysis temperature, feedstock particle size, and vapor residence time on the distribution and quality of liquid and char products from pyrolysis of sawdust in a fluidized-bed reactor. Sawdust and char samples were characterized with elemental and thermogravimetric analyses. Liquid bio-oil sample characterization was performed by Karl Fischer titration, elemental analysis, and gas chromatographymass spectrometry (GCMS). The bio-oil yield appeared to be maximized (≈62 wt %) at 500 °C, and the highest concentration of phenols was also produced at this temperature. Both the pyrolysis temperature and sawdust particle size had significant effects on the water content of the bio-oil with the water content being minimized at 500 °C. The yield of bio-oil showed a decreasing trend as the sawdust particle size was increased mainly because of the lower heating rate of larger sawdust particles. The effect of the residence time on the pyrolysis product distributions and their elemental compositions was negligible.
1. INTRODUCTION Environmental pollution, global climate change, and depletion of fossil fuel resources have raised interest in the development of energy supplies from renewable sources. Biomass is an important source of renewable energy, currently estimated to contribute 1014% to the world’s total energy supply.1 Among the renewable sources of energy that provide heat and power, biomass is the only source of liquid, solid, and gaseous fuels.2 Pyrolysis, among the thermochemical methods, is a promising means of converting biomass to bio-oil that can be used as a fuel for transportation3 and stationary engines.4 Hydrogen production is another use for bio-oil.510 It can also be a source of more than 300 chemical feedstocks.1113 Bio-oil is formed by rapid heating and simultaneous fragmentation of the cellulose, hemicellulose, and lignin present in biomass.14 Lignin, as one of the three main building blocks of biomass, has been a concern because of its phenolic nature. However, a wide variety of phenolic compounds can be derived from lignin that can be used in the phenolic resin industry.15 Many research studies have examined fast pyrolysis of biomass over the past 3 decades. Different reactor configurations have been employed, such as fixed-bed, fluidized-bed, rotating-cone, and ablative pyrolysis reactors.12 Fluidized-bed reactors are, however, the most popular configurations, because of their ease of operation and ready scale-up.16,17 The fast pyrolysis of biomass is influenced by a large number of factors, including the pyrolysis temperature, feedstock particle size, and residence time. Given the complexity of the process, reactor configurations, and feedstock variations, the influence of the operating parameters on the yield and quality of pyrolysis products is very process-specific.13 It is well-known that the maximum yields of bio-oil are achieved at temperatures between 450 and 550 °C, at which up to 70 wt % of the biomass can be converted to bio-oil.18 There have been intensive research studies that have investigated the effects of the pyrolysis operating parameters on the product distribution; however, less work has been reported that r 2011 American Chemical Society
examines the influence of operating conditions on the quality of pyrolysis products.1825 Garcia-Perez et al.23 pyrolyzed mallee woody biomass in a fluidized-bed reactor and investigated the effect of the pyrolysis temperature on the yields and quality of the pyrolysis products. They specifically studied the influence of the temperature on the formation of lignin-derived oligomers in the bio-oil.18 In another work, the effect of the mallee woody biomass particle size on the yield and composition of bio-oil was studied by Shen et al.24 Wang et al.25 pyrolyzed various types of wood in a fluidized-bed pyrolysis system. They examined the influence of the operating conditions on the yield and elemental composition of the liquid and solid phases. The operating conditions for the maximum bio-oil yield may not be the same as those for producing the best quality bio-oil.3 There is, therefore, a need to adjust the operating conditions for producing biooil considering its final application. In this paper, fast pyrolysis of sawdust in a 100 g/h laboratoryscale fluidized-bed reactor is presented. The objective of this research was to investigate the influence of different operating parameters, such as the reaction temperature, sawdust particle size, and vapor residence time on the yields and quality of the pyrolysis products. The produced bio-oils and chars were subjected to physical and chemical analyses, and the effects of the operating parameters on the characteristics and quality of the produced bio-oils and chars were studied. Well-accepted analytical techniques, such as gas chromatographymass spectroscopy (GCMS) and Karl Fischer titration for the liquid-phase characterization and carbon, hydrogen, and nitrogen (CHN) elemental analysis for the characterization of both liquid and solid phases, were employed to follow the evolution of the bio-oil and char characteristics, as a function of the pyrolysis operating conditions. Received: May 6, 2011 Revised: August 12, 2011 Published: August 12, 2011 4145
dx.doi.org/10.1021/ef200688y | Energy Fuels 2011, 25, 4145–4154
Energy & Fuels
ARTICLE
2. EXPERIMENTAL SECTION 2.1. Biomass Sample. A mixture of sawdust obtained from a waste wood recycling company, which represented a mixture of different wood types, was the feedstock for producing the bio-oil samples studied herein. The feedstock was sieved into three different fractions of particle size:
