Effects of Pyrolysis Conditions on Yield of Bio-Chars from Pine Chips

The influences of temperature, heating rate, purge gas type, and flow rate on the yield of chars produced from pyrolyzing southern pine chips were investigated. Pyrolysis temperatures were between 450°C and 1,000°C, with heating rates of 0.5°C/min, 1.0°C/min, 10°C/min, 30°C/min, 50°C/min, and 100°C/min. Purge gases, nitrogen (N2), hydrogen (H2), and N2-H2 mixture (10% H2), were used at flow rates from 100 to 1,000 mL/min. Pine char yield decreased as temperature, heating rate, or purge gas flow rate increased. Two regions with significantly different decrease rates of pine char yield can be identified for temperature or heating rate as they increase. The yield decrease rate turning points were 550°C and 10°C/min for yieldtemperature and yield-heating rate charts, respectively. The pine char yield was lowest when hydrogen was the purge gas and highest with nitrogen. The synthesis of novel carbon-based materials from biomass is motivated by possible applications in many fields, such as water purification, energy storage, fuel cell catalysis, bio-imaging, and drug delivery (Hu et al. 2008). The abundant, renewable, and low-costcarbon sources from biomass such as wood are an easily obtained raw carbon precursor material for value-added carbonaceous materials production. Carbon content ofwood varies from about 47 to 53 percent due to varying lignin and extractives content (Ragland and Aerts 1991); almost 30 to 50 percent of the carbon in the wood is converted to solid char during the pyrolysis process. Chemical components of loblolly pine (Pinus taeda) wood are 42 to 46 percent glucose in cellulose; 1 to 5 percent glucose, 10 to 11 percent mannose, 7 percent xylose, 1 to 2 percent arabinose, and 1.5 to 2.5 percent galactose in the hemicelluoses; and 27 to 30 percent lignin, to give a total carbohydrate content of 66 to 69 percent by weight (Koch 1972). Pyrolysis converts organics such as biomass into three phases: solid (char), liquid (tars, condensable vapors, etc.), and gas by heating in the absence of oxygen (Wampler 2006). Pyrolysis processes may be conventional or fast pyrolysis, depending on the operating conditions. Conventional slow pyrolysis has been applied for thousands ofyears in processes such as charcoal production (Demirbas 2009). In slow pyrolysis, biomass is heated to 500°C with a vapor residence time from 5 to 30 minutes. For fast pyrolysis, biomass is rapidly heated for less than 1 minute in the absence of oxygen. Fast pyrolysis processes produce 60 to 75 percent by weight liquid bio-oil, 15 to 25 percent by weight solid char, and 10 to 20 percent by weight noncondensable gases (Mohan et al. 2006). FOREST PRODUCTS JOURNAL VOL. 61, NO. 5 The operating conditions, such as pyrolysis temperatures or heating rates, are key factors affecting the three fractions (Baumlin et al. 2006). For example, higher char yields are obtained at low temperatures or low heating rates than at higher temperatures or fast heating rates. Yields ofthe liquid phase and/or gas phase are enhanced (Bridgwater 1994). To use biomass such as wood as an alternative carbon source for producing novel carbon-based materials, studies on the effects of pyrolysis process conditions will be necessary to maximize the yields of the most economically valuable products. In the conversion of coal to char, it has been discovered that both raw material and operating conditions such as the heating rate, the pyrolysis temperature, and the pyrolysis time influence char yield (Guerrero et al. 2005). Studies on the influence of the coal feedstock and the experimental conditions on the characteristics of the char from copyrolysis of coal and petroleum residue indicated that char yields increased as temperature and pressure increased The authors are, respectively, Postdoctoral Research Associate, Dept. of Agric. and Biological Engineering ([email protected] [corresponding author]), Associate Professor, Dave C. Swalm School of Chemical Engineering ([email protected]), and Assistant Professor, Dept. of Agric. and Biological Engineering (fyu@abe. msstate.edu), Mississippi State Univ., Mississippi State; Project Leader, USDA Forest Serv., Forest Products Lab., Madison, Wisconsin ([email protected]); and Professor, Dept. of Forest Products, Mississippi State Univ., Mississippi State ([email protected]). This paper was received for publication in March 2011. Article no. 11-00030. ©Forest Products Society 2011. Forest Prod. J. 61(5):367-371.