Seashell-derived catalysts for biodiesel production : reaction kinetics, energy balance, and process optimization

Abstract

Recently, the usage of waste materials as a catalyst source for biodiesel production has been of great interest in search for a sustainable and eco-friendly process. The seafood industry produces over 100 million pounds of seashell waste every year. With landfill space diminishing quickly, ways to recycle and valorize waste materials are becoming increasingly attractive. The purpose of this work is to study the transesterification reaction of refined sunflower oil into biodiesel using basic calcium oxide (CaO) from waste seashells as a renewable source. CaO catalyst was prepared from the calcination of Noble Pectin, a type of scallop seashells, at 700°C for 3 hours (10 °C/min). Fresh CaO catalyst was then characterized using Fourier Transform Infrared Spectroscopy (FTIR), and Thermal Gravimetric Analysis (TGA). The transesterification reactions were all performed in a round bottom flask batch reactor coupled with a condenser at 65 °C and under atmospheric pressure. In order to optimize the reaction conditions, methanol to oil molar ratio was varied, along with the stirring rate and calcination temperature to determine the highest biodiesel yield. A FAME content of 97% was achieved after 4 hours of reaction using a methanol to oil ratio of 12/1, a catalyst to oil ratio of 10 wt.%, and a stirring rate of 700 rpm. The reusability study showed that the prepared CaO catalyst was stable over 4 consecutives runs, with a slight decrease in the catalytic activity. Moreover, biodiesel properties were tested and found to be in good accordance with the American Society for Testing and Materials (ASTM) requirements. The kinetic study was also performed at 55, 60, and 65C. The activation energy (Ea) and the pre-exponential factor (A) were found to be 133.57 kJ/mol and 4.025 x 1018 min-1, respectively. On the other hand, using and valorizing a second-generation feedstock such as waste cooking oil (WCO) to produce biodiesel is gaining much interest, as wastes could be potentially reduced while generating a renewable biofuel. Thus, this is a forward step to a safer, sustainable and eco-friendly environment. The catalytic activity using waste cooking oil (WCO) was also examined. Similar results (97%) were achieved under the optimum conditions. An energy balance and an economic analysis for biodiesel production from both edible sunflower oil and waste cooking oil were performed. It was found that the use of WCO for biodiesel production was an energy gain process, with a positive energy balance and a conversion efficiency higher that 1. The total energy input and energy output were calculated as 36.18 and 44.82 MJ/L, respectively. The energy balance revealed a net energy gain of 8.64MJ per 1 liter of produced biodiesel. Moreover, the economic analysis showed that the benefit to cost ratio was found to be 2.60. Therefore, this is an innovative and cost-effective methodology for producing second-generation biofuels by using WCO as a feedstock. Based on the obtained results in this work, CaO-derived from waste seashells could be a promising heterogeneous catalyst for biodiesel commercialization, especially when waste cooking oil is adopted as a feedstock.