Co-pyrolysis of lignin and low rank coal for the production of aromatic oils

Abstract

The co-pyrolysis of hydrolysis lignin and low rank coal was studied in a drop-tube fixed bed reactor. Baganuur (BN) coal blending into hydrolysis lignin with mass ratio of 50:50 decreased the yields of oil and gas significantly, and then increased the yield of char compared to their predicted values after the co-pyrolysis at 450 °C. This toxic effect was explained by the easier coupling reaction of BN coal derived poly-aromatic radicals with hydrolysis lignin (HL)-derived aromatic compounds to form solid product - char. However, when the amount of BN coal in the blend decreased from 50% to 30%, the toxic effect decreased, and experimental yields of char, oil and gas approached to their predicted values. In case of HL-AC (50:50) blend, a synergistic effect was observed during the co-pyrolysis of hydrolysis lignin and Aduunchuluun (AC) coal. The oil yield slightly increased, and the yields of gas and char decreased compared to their predicted values after the co-pyrolysis at 450 °C. Amount of aromatic hydrocarbons in acetone soluble of the oil was close to its predicted value, and several kinds of aliphatic alcohols, aldehydes and ketones were detected in toluene soluble of the oil product, even though there were no such compounds existed in the toluene soluble from the pyrolysis of single feed-AC coal. It was supposed that additional hydrogen was produced by the secondary water-gas shift reaction of CO gas evolved from AC coal with large amount of inherent alkali and alkali earth metals during the HL-AC co-pyrolysis. It was also supported by the larger H/C ratios of oil and char compared to their predicted values after the co-pyrolysis of HL-AC blend.