Review of current practices and catalysts for biodiesel production from on‐grade and off‐grade crude palm oil

Abstract

Biodiesel is a renewable fuel made from vegetable oils, such as on‐grade and off‐grade crude palm oil (CPO). The quality of the starting oil, especially its free fatty acid (FFA) content, affects how catalysts are chosen and how well biodiesel is produced. This review looks at how different catalysts perform in making biodiesel from both on‐grade and off‐grade CPO. It covers catalyst types, reaction setups, how much biodiesel is produced, how stable the catalysts are, and the overall quality of the fuel. For this review, research articles published between 2010 and 2026 were gathered from Scopus, ScienceDirect, SpringerLink, and Google. A total of 96 studies were included. The findings show that acid catalysts are generally better for converting oils with high FFA through esterification, while alkaline and heterogeneous catalysts work well for transesterification after the oil has been properly treated. Heterogeneous catalysts are easier to separate and reuse, but issues like leaching, becoming less effective over time, and slow reactions can be problematic. Comparing catalyst performance directly is tricky, since studies use different oils and conditions. This review offers a side‐by‐side look at catalyst choices and highlights the main challenges and future opportunities for making CPO‐based biodiesel more sustainable and suitable for industry.