Influences of Temperature and Metal on Subcritical Hydrothermal Liquefaction of Hyperaccumulator: Implications for the Recycling of Hazardous Hyperaccumulators

Feng Qian, Xiangdong Zhu^*, Yuchen Liu, Quan Shi, Longhua Wu, Shicheng Zhang^*, Jianmin Chen and Zhiyong Jason Ren

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

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

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

Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing210008, China

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

Corresponding Author: ^*(X.Z.) Phone/fax: + 86-21-65642297; e-mail: zxdjewett@ fudan.edu.cn. ^*(S.Z.) E-mail: zhangsc@fudan.edu.cn.

DOI: 10.1021/acs.est.7b03756

Keywords: Biofuels; Biomass; Liquids; Metals; Organic Acids

Abstract: Waste Sedum plumbizincicola, a zinc (Zn) hyperaccumulator during phytoremediation, was recycled via a subcritical hydrothermal liquefaction (HTL) reaction into multiple streams of products, including hydrochar, bio-oil, and carboxylic acids. Results show approximately 90% of Zn was released from the S. plumbizincicola biomass during HTL at an optimized temperature of 220 ℃, and the release risk was mitigated via HTL reaction for hydrochar production. The low-Zn hydrochar (~200 mg/kg compared to original plant of 1558 mg/kg) was further upgraded into porous carbon (PC) with high porosity (930 m²/g) and excellent capability of carbon dioxide (CO₂) capture (3 mmol/g). The porosity, micropore structure, and graphitization degree of PCs were manipulated by the thermal recalcitrance of hydrochar. More importantly, results showed that the released Zn²⁺ could effectively promote the production of acetic acid via the oxidation of furfural (FF) and 5-(hydroxymethyl)-furfural (HMF). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with negative electrospray ionization analysis confirmed the deoxygenation and depolymerization reactions and the production of long chain fatty acids during HTL reaction of S. plumbizincicola. This work provides a new path for the recycling of waste hyperaccumulator biomass into value-added products.