Insights into effect of Ca(OH)2 on pyrolysis behaviors and products distribution of Hongshaquan coal

Abstract

Pyrolysis is an important approach for the thermochemical transformation of low rank coal. In this work, catalytic effects of Ca(OH)2 on the pyrolysis of coal were investigated by fixed-bed and in-situ pyrolysis time-of-flight mass spectrometry. The catalytic pyrolysis reactivity and chemical structure of coal/chars were analyzed by means of TG, XPS, XRD, FTIR, N2 adsorption/desorption and Ex-situ electron paramagnetic resonance. The results showed that the calcium primarily exists in the form of “Ca-organic” structure in coal, and the loading of calcium could promote the release of gas and water and reduce the yield of char and tar during coal pyrolysis. Moreover, the yields of alkyl benzene, phenols, naphthol, and dihydroxybenzene are significantly different under the condition with or without the calcium addition, and the generation of tar and products distribution have an obvious dependency on calcium compounds in coal. It was demonstrated that the Ca(OH)2 could change the thermal reaction process of oxygen-containing functional groups in coal during pyrolysis process, thereby regulating the distribution of pyrolysis products (tar, gas and char). Calcium species has a significant effect on the thermal conversion of phenols and carboxylic acids structure into tar. Finally, the catalytic process of Ca(OH)2 on the pyrolysis of the coal was discussed.