Biodiesel Production Using Homogeneous, Heterogeneous, and Enzyme Catalysts via Transesterification and Esterification Reactions: a Critical Review

Abstract

The excessive utilization of petroleum resources leads to global warming, crude oil price fluctuations, and the fast depletion of petroleum reserves. Biodiesel has gained importance over the last few years as a clean, sustainable, and renewable energy source. This review provides knowledge of biodiesel production via transesterification/esterification using different catalysts, their prospects, and their challenges. The intensive research on homogeneous chemical catalysts points to the challenges in using high free fatty acids containing oils, such as waste cooking oils and animal fats. The problems faced are soap formation and the difficulty in product separation. On the other hand, heterogeneous catalysts are more preferable in biodiesel synthesis due to their ease of separation and reusability. However, in-depth studies show the limited activity and selectivity issues. Using biomass waste-based catalysts can reduce the biodiesel production cost as the materials are readily available and cheap. The use of an enzymatic approach has gained precedence in recent times. Additionally, immobilization of these enzymes has also improved the statistics because of their excellent functional properties like easy separation and reusability. However, free/liquid lipases are also growing faster due to better mass transfer with reactants. Biocatalysts are exceptional in good selectivity and mild operational conditions, but attractive features are veiled with the operational costs. Nanocatalysts play a vital role in heterogeneous catalysis and lipase immobilization due to their excellent selectivity, reactivity, faster reaction rates owing to their higher surface area, and easy recovery from the products and reuse for several cycles.

Sustainability of biodiesel production using immobilized enzymes: A strategy to meet future bio‐economy challenges

“…In the esterification process, the FFA reacts with alcohol to produce fatty acid alkyl esters (FAAE) and water. In transesterification, triglycerides react with alcohol and produce FAAE and glycerol 49 …”

“…In transesterification, triglycerides react with alcohol and produce FAAE and glycerol. 49 Other than chemical and enzymatic biodiesel conversion processes, there are also some other processes like pyrolysis, micro emulsification, and blending that are also used to produce biodiesel. 51 Pyrolysis, the thermochemical route of biomass conversion, is employed at a temperature above 350 C to 800 C to get a product distribution in biofuel, biochar, and synthesis gas.…”

Functionalized organic–inorganic hybrid porous coordination polymer-based catalysts for biodiesel production via trans/esterification

“…78 In the presence of an enzyme catalyst, high alcohol concentration may even inactivate the enzyme. 189 For instance, in a solvent-free medium catalyzed by immobilized Thermomyces lanuginosus lipase, the maximum initial reaction rate was 9.0 g l −1 min −1 for a 1 : 1 molar ratio of methanol to oil. When the molar equivalent of methanol exceeds 1.5, the inactivation of the enzyme was observed.…”

Conversion of Plastic Waste into Supports for Nanostructured Heterogeneous Catalysts: Application in Environmental Remediation

“…While homogeneous catalysts offer many advantages like high reaction rates, easy accessibility of active sites, and minimal diffusion barriers, separation from the reaction mixture is a tedious task, and, in some cases, it is a challenging process [300]. Heterogeneous catalysis is preferably used in industrial applications because of its easy separation, which usually results in lower operating costs [301]. Heterogeneous catalysis and solid catalysts play an essential role in the field of chemical engineering, renewable energy and batteries [302], but one of the challenges is to obtain catalytic systems that can be recovered and reused in subsequent reaction cycles, thus minimizing costs, and also obtaining materials with a high surface area.…”