Enhanced oxygen activity of LaFeO3 oxygen carriers in biomass chemical looping gasification coupled with CO2/H2O splitting by fragmented flaky structure

Abstract

Considering that the conventional modification of metal doping may bring excessive cost escalation and more pollution, for the sol–gel method, a more cost-effective and eco-friendly modification method was proposed to enhance the oxygen activity of LaFeO3 and its doped oxygen carriers (OCs). In this work, LaFeO3 OCs with fragmented flaky structure was prepared by modification of adjusting the sol to weak alkalinity with ammonia and adding the complexing agent ethylene glycol. Then, it was applied in Biomass chemical looping gasification (BCLG) coupled with CO2/H2O splitting to produce high-quality syngas and achieve cascade conversion of carbon in biomass, and its performance and reaction mechanism were investigated by fixed bed test. The results showed that the fragmented flaky structure endowed the LaFeO3 OCs with more robust oxygen activity, thus realizing efficient lattice oxygen migration which increased the gas yield of BCLG stage from 695.6 mL/g to 851.2 mL/g at 900 °C, and the carbon conversion and gasification efficiency reached 65.6% and 64.4%, respectively. Despite the predominant role of residual char in the gas generation of splitting stage, the reduced OCs still possesses exceptional CO2 and H2O splitting ability. Among them, CO2 splitting was mainly carried out by the activation of Fe0 and alkaline active sites from the reduced OCs, while H2O splitting depended more on the decomposition of H2O molecules by oxygen vacancies. Moreover, this OCs exhibited outstanding stability in 10 cycles, and the total gas yield in two stages was consistently maintained around 1030.1 mL/g and 1069.6 mL/g, respectively. This work found that the LaFeO3 OCs with fragmented flaky structure is a prospective material for chemical looping technology.