Production of bio-oil from waste cooking oil via microwave-assisted pyrolysis in the presence of waste eggshell CaO and HZSM-5: Process optimization and catalyst lifetime exploration

Preparing bio-oil from pyrolysis of waste cooking oil (WCO) has the potential to alleviate the energy crisis and turn waste into a useful resource. In this study, CaO made from waste eggshells (EGC), along with zeolite HZSM-5, were used as catalysts, and the process optimization and catalyst lifetime were investigated. Monocyclic aromatic hydrocarbons made up the majority of the bio-oil produced. EGC largely facilitated decarboxylation when the EGC/WCO ratio was less than 0.4. However, when the ratio increased above 0.4, EGC was able to promote deoxygenation of alcohols, ketones, and esters in addition to decarboxylation. The appropriate pyrolysis temperature of WCO was 450 °C, and the EGC/HZSM-5 (EGC/HZ) ratio was 1: 1. After four further trials using the ideal EGC/HZ catalytic pyrolysis conditions, the catalyst lost its catalytic activity. Coke deposition and the CaCO3 formation changed the porosity and alkalinity of EGC, resulting in a decrease in its activity. The capacity of HZSM-5 was also reduced by coke deposition. This study reveals the causes of the progressive decrease in catalyst activity during catalytic pyrolysis and allow the development of practical solutions to improve catalyst performance.