Evaluation of the porous structure development of chars from pyrolysis of rice straw: Effects of pyrolysis temperature and heating rate

The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000 degrees C under low heating rate (LHR) and high heating rates (HEIR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N-2 physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000 degrees C. The carbon structure shrinkage and pore narrowing occurred above 600 degrees C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000 degrees C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900 degrees C. The total surface area (S-total) and micropore surface area (S-micro) reached maximum values of 30.94 and 21.81 m(2)/g at 900 degrees C and decreased slightly at higher temperatures. The influence of heating rate on S-total and S-micro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship. (C) 2012 Elsevier B.V. All rights reserved.