Organic oxygen transformation during pyrolysis of Baiyinhua lignite

Fast pyrolysis of a lignite containing a high content of oxygen was investigated to understand the effects of pyrolysis temperature and gas resident time on the yields of pyrolysis products and the distributions of organic oxygen species (OOSs). OOSs in the lignite contain carboxyl, carbonyl, hydroxyl and ether by the results of XPS and FTIR analyses. The tar yield reached the maximum of 15.3% at 500 degrees C and a gas resident time of 2.5 s. CO2 was found to be the predominant oxygenous gas at 600 degrees C, and the significant release of CO2 at temperatures lower than 400 degrees C should be related to the high carboxyl content in the lignite. The CO yield increased significantly with the raising temperature and reached 46.4 mL/g (daf) at 700 degrees C. The O yield in water was lower than 20% during pyrolysis at 200 degrees C, and sharply increased to 30.6% at 700 degrees C because of thermal cracking of volatiles. Above 400 degrees C, the OOSs are mainly released as pyrolysis water and gas. The OOSs detected in the tar include phenols, ketones, ethers, alcohols, and dibenzofuran and its substitute, among which phenols (phenol, cresol, and xylenol) are the main components with yield up to 27.1% (based on tar) at 500 degrees C and gas residence time of 10s. The possible oxygen transformation routes for BYHL pyrolysis are also discussed in this work. Such an approach may lead to the development of efficient lignite upgrading technology. (C) 2015 Elsevier B.V. All rights reserved.