Inhibition on Chloroaromatics during thermal conversion processes of Municipal Solid Waste by oxygen-induced low-temperature pre-dechlorination and hydrogen-assisted in-situ Cl capture

Abstract

In thermal treatment of Municipal Solid Waste (MSW), oxygen-induced low-temperature pre-dechlorination coupled with hydrogen-assisted Cl capture in subsequent pyrolysis was proposed as an economical and competitive way for the inhibition of chloroaromatics. Dechlorination and pyrolysis processes were experimentally investigated, and formation of chloroaromatics in both processes was quantitatively compared, using PVC as the model. Due to the low bond energy of CCl, most of Cl released at low temperature, ahead of common volatiles, providing a feasible temperature window for the pre-dechlorination of feedstock. Chlorobenzene and benzyl chloride were the major chloroaromatics in pyrolysis product, formed at 300 °C and higher temperature. Therefore, dechlorination should be proceeded below 300 °C to prevent the generation of chloroaromatics from itself. However, under inert atmosphere, dechlorination efficiency was heavily dependent on temperature, being poor at 250 °C and 275 °C. O2 had a clear inductive effect on low-temperature dechlorination, lowering the peak temperature of HCl release to 234 °C. After a 30 min oxygen-induced dechlorination at 250 °C, 97.525% of Cl in feedstock was removed, and chloroaromatics in the subsequent pyrolysis was reduced by 90.2%. For a further inhibition of chloroaromatics, 2% H2 was introduced for in-situ Cl capture in the pyrolysis of pre-dechlorinated feedstock, as a result, no chloroaromatic was detected.