Sustainable production of raw materials from waste cooking oils†

Abstract

The current industrial process for recycling Waste Cooking Oils (WCOs) into vegetable lubricants relies on basic decantation and filtration methods, lacking the scientific foundation needed for technical optimization and sustainability. This research addresses these limitations by thoroughly evaluating the technical and environmental impacts of bentonite treatment and water washing techniques. Using a Design of Experiments (DoE) approach coupled with multivariate statistical analysis, key process parameters—temperature, bentonite content, pH, and oil-to-water ratio—were optimized to improve performance and sustainability. Results showed that bentonite had a negligible effect when water treatment was conducted at 75 °C and pH 6 or at 25 °C and pH 2. The efficiency of both recycling methods, as measured by nuclear magnetic resonance spectroscopy and rheological tests, was comparable. However, the green metrics (mass yield, mass productivity, E-factor, and process mass intensity), along with the EcoScale penalty ranking, indicated that water treatment at 75 °C and pH 6 offers the most viable solution. Linear regression of the data acquired through the multivariate analysis driven by the DoE approach provided a mathematical equation which relates the temperature, time, and the oil/water ratio to the equivalent of CO₂ eventually produced. This tool provides recycling industries with a practical framework for optimizing process conditions, balancing technical efficiency with minimized environmental impact, a crucial factor for compliance with green certification programs. The results present a scalable, scientifically validated pathway for the WCO recycling industry to enhance both operational performance and sustainability.