The effect of alkali metal chlorides and temperature on acid-hydrolysis residual pyrolysis products

Abstract

Acid-hydrolysis residual (AHR) offers significant potential for harvesting chemical energy with simultaneous reduction of environmental pollution, providing carbon neutral (or even carbon negative) sustained energy production, energy security and alleviating social concerns associated with the wastes. In this study, the different effects of intrinsic and extrinsic K and Na were compared firstly. In addition, the effect of different content of alkali metal chlorides doped into AHR and temperature on pyrolysis products were investigated, especially for the phenolic products in bio-oil, along with the grey relational analysis. The results showed that KCl and NaCl promoted the generation of char and gas at the expense of the bio-oil yield. While, addition of KCl and NaCl could increase the yields of total phenolic species. Specifically, the yields of phenols and hydroxy phenols increased, while the guaiacols and syringols content decreased. The effect of KCl on the distribution of pyrolysis products and phenolic species was somewhat greater than NaCl, especially for bio-oil yield. The increasing of pyrolysis temperature would increase gas yield and reduce the char yield. While the bio-oil yield was peaked at 650 ℃. Besides, higher temperature restrained the generation of syringols and promoted the generation of phenols and hydroxy phenols. The grey relational analysis of KCl and temperature showed that KCl content was the major factor in the generation of bio-oil in pyrolysis process, while temperature played more notable role on the yields of total phenolic species, phenols, hydroxy phenols, guaiacols and syringols. The addition of alkali metal chlorides could promote the pyrolysis process and enhance the maximum lower heating value (LHV) of pyrolysis gas, especially the addition of NaCl. The optimal value of addition amount of KCl and NaCl was found to be 2 wt.% and 0.5 wt.%, respectively. Besides, the addition of KCl and NaCl could improve pore quality and activation of AHR pyrolysis char. Based on the pyrolysis products from cellulose, it can be proposed that cellulose has two main pathway depending on the alkali metal chlorides content.