Decarbonylation Reaction of Saturated and Oxidized Tar from Pyrolysis of Low Aromaticity Biomass Boost Reduction of Hexavalent Chromium

Hua Shanga, Xiangdong Zhua,b,^⁎, Minghao Shena, Jiewen Luoa, Shaojie Zhoua, Lijie Lic, Quan Shic, Dongmei Zhoud, Shicheng Zhanga,e,^⁎, Jianmin Chena, Zhiyong Jason Renb

a Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China

b Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder, CO 80309, United States 

c State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China 

dKey Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China 

e Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China

Corresponding authors: E-mail addresses: zxdjewett@fudan.edu.cn (X. Zhu), zhangsc@fudan.edu.cn (S. Zhang)

DOI: 10.1016/j.cej.2018.10.168

Keywords: Cr(VI) reduction; Pollution remediation; Pyrolysis reduction; Decarbonylation

Abstract: Biomass pyrolysis is a promising method and often used to reduce hexavalent chromium Cr(VI) residue. However, the pyrolysis reduction mechanisms of Cr(VI) remain unclear, particularly regarding which tar compositions help the Cr(VI) reduction. In the present study, on-line MS analysis suggests that yields of CO and CH₄ from biomass pyrolysis can principally represent the rate of Cr(VI) reduction. FT-ICR MS results indicate that high-molecular-weight compounds in tar (m/z > 350) located in the lignin/CRAM-like structure region or saturated (H/C = 0.7–1.5) and oxidized (oxygen number > 6) compounds preferentially crack by catalysis of Cr (VI) to produce CO via decarbonylation reaction, further promoting the reduction of Cr(VI). Pyrolysis material with low stability (low aromaticity) can release more reducing gases and more easily cracks tar to promote Cr (VI) reduction. Lastly, chromite slag from a polluted site was successfully remediated by pyrolysis of a hydrochar sample. An extremely low leaching Cr concentration from remediated chromium slag can be obtained due to the carbon layer coating on Cr element. This study provides a novel perspective on the pyrolysis remediation mechanism of Cr(VI) and is highly significant for developing thermal remediation techniques for polluted sites.