Synthesis of Mesoporous Biochar-Supported MgO Nanoparticles and Their Performance in Catalytic Dechlorination of PVC Pyrolysis

Pyrolysis is an important method for treating PVC waste and recovering resources. However, the formation and emission of chlorine (Cl)-based compounds (e.g., HCl and small molecule chlorinated hydrocarbons) during PVC pyrolysis significantly limit the potential applications of the pyrolysis products. This poses a major challenge for PVC waste treatment via pyrolysis. To address this challenge, we propose a catalytic pyrolysis method for the dechlorination of PVC without affecting the quality of the pyrolysis products. Mesoporous biochar-supported magnesium oxide nanoparticles were investigated as a catalyst for catalytic dechlorination during PVC pyrolysis. The catalyst can be produced on a large scale through pyrolysis of lignocellulosic biomass supported with hydrated magnesium chloride. During material preparation, mesoporous biochar-supported magnesium oxide nanoparticles can be obtained in a yield of nearly 40%. Simultaneously, bio-oil, in which phenolic compounds are the main components, can be obtained with a yield of 55%, achieving environmentally friendly disposal and resource recovery of biomass waste. The synthesized mesoporous biochar-supported magnesium oxide nanoparides were then used as a catalyst for dechlorination of PVC via pyrolysis, efficiently immobilizing the chlorine from PVC in the pyrolytic char. During the catalytic pyrolysis process, hydrogen chloride emissions are reduced to 20%, compared to 90% in conventional pyrolysis without catalysis. During typical PVC pyrolysis, the hydrogen chloride formed in situ reacts with O2− active sites on the MgO surface in the catalyst to form MgCl2, thereby fixing the Cl from the PVC in the pyrolytic char. The active sites, specific surface area and pore structure of the catalyst play a crucial role in this process, significantly enhancing the adsorption and conversion efficiency of chlorine. The abundance of C—Cl bonds in the PVC pyrolysis products at different temperatures was further compared using a Thermogravimetric Infrared Spectroscopy (TG-FTIR) to evaluate the dechlorination efficiency of the catalytic pyrolysis process, demonstrating that the abundance of C—Cl bonds in the products from non-catalytic pyrolysis is significantly higher than that from catalytic pyrolysis. This process effectively minimizes secondary pollution caused by the volatilization of Cl-based compounds into pyrolysis oil or gas, thereby simultaneously achieving pollution control and resource recovery during the pyrolysis of waste PVC plastics. This work presents a novel waste-to-resource approach, offering significant application potential and value.