Immobilized lipases for biodiesel production: Current and future greening opportunities

As green catalysts, lipases' productivity, and wide substrate selectivity are preferable over chemical catalysts in biodiesel production. Lipases require milder reaction conditions and produce cleaner downstream products. To ensure practical recovery of lipases for repeated uses in biodiesel production, immobilizing lipases into solid forms has been suggested to complement its efficiency, utility, and sustainability. Immobilization, however, adds to the cost of the already economically inviable lipases. Most immobilization protocols also largely depend on fossil derivatives and produce an ever-increasing amount of waste. Therefore, it has been deemed necessary to delineate a scope for the fundamental success of using immobilized lipases for large-scale biodiesel production. Hence, this review presents a way forward to address immobilized lipase cost by using green chemistry strategies that have shown success in recent studies. A comparison of lipases with other biodiesel catalysts is presented in the early part of this review. Conventional and emerging immobilization protocols are also evaluated. The choice between synthetic and natural polymers for immobilization emphasizes the importance of using green chemistry metrics in addressing reusability, toxicity, resource efficiency, water, and carbon footprint of lipase immobilization. Therefore, this review advances immobilized lipase technology by identifying gaps that can be used by research and industry for its deployment to supplant chemical catalysts currently used in biodiesel production.