Dependence on fossil fuels for meeting the growing energy demand is damaging the world’s environment. There is a dire need to look for alternative fuels that are less potent to greenhouse gas emissions. Biofuels offer several advantages with less harmful effects on the environment. Biodiesel is synthesized from the organic wastes produced extensively like edible, non-edible, microbial, and waste oils. This study reviews the feasibility of the state-of-the-art feedstocks for sustainable biodiesel synthesis such as availability, and capacity to cover a significant proportion of fossil fuels. Biodiesel synthesized from oil crops, vegetable oils, and animal fats are the potential renewable carbon-neutral substitute to petroleum fuels. This study concludes that waste oils with higher oil content including waste cooking oil, waste palm oil, and algal oil are the most favorable feedstocks. The comparison of biodiesel production and parametric analysis is done critically, which is necessary to come up with the most appropriate feedstock for biodiesel synthesis. Since the critical comparison of feedstocks along with oil extraction and biodiesel production technologies has never been done before, this will help to direct future researchers to use more sustainable feedstocks for biodiesel synthesis. This study concluded that the use of third-generation feedstocks (wastes) is the most appropriate way for sustainable biodiesel production. The use of innovative costless oil extraction technologies including supercritical and microwave-assisted transesterification method is recommended for oil extraction.

The energy demand of the world is skyrocketing due to the exponential economic growth and population expansion. To meet the energy requirement, the use of fossil fuels is not a good decision, causing environmental pollution such as CO₂ emissions. Therefore, the use of renewable energy sources like biofuels can meet the energy crisis especially for countries facing oil shortages such as Pakistan. This review describes the comparative study of biodiesel synthesis for various edible oils, non-edible oils, and wastes such as waste plastic oil, biomass pyrolysis oil, and tyre pyrolysis oil in terms of their oil content and extraction, cetane number, and energy content. The present study also described the importance of biodiesel synthesis via catalytic transesterification and its implementation in Pakistan. Pakistan is importing an extensive quantity of cooking oil that is used in the food processing industries, and as a result, a huge quantity of waste cooking oil (WCO) is generated. The potential waste oils for biodiesel synthesis are chicken fat, dairy scum, WCO, and tallow oil that can be used as potential substrates of biodiesel. The implementation of a biodiesel program as a replacement of conventional diesel will help to minimize the oil imports and uplift the country’s economy. Biodiesel production via homogeneous and heterogeneous catalyzed transesterification is more feasible among all transesterification processes due to a lesser energy requirement and low cost. Therefore, biodiesel synthesis and implementation could minimize the imports of diesel by significantly contributing to the overall Gross Domestic Product (GDP). Although, waste oil can meet the energy needs, more available cultivation land should be used for substrate cultivation. In addition, research is still needed to explore innovative solvents and catalysts so that overall biodiesel production cost can be minimized. This would result in successful biodiesel implementation in Pakistan.

High production of biodiesel results in a surplus of glycerol as a byproduct that leads to a drastic decline in the glycerol price as well as overall biodiesel production. Alternative methods must be introduced for the economical process for biodiesel production via utilization of crude glycerol into valuable chemicals or fuel additives. This study introduces an ecofriendly process of solketal synthesis from glycerol and acetone in the presence of a novel metakaolin clay catalyst, which is a useful additive in biodiesel or gasoline, in order to enhance the octane number and to control the emissions. Moreover, kaolin clay catalysts are low cost, abundantly available, eco-friendly and one of the more promising applications for solketal synthesis. In this study, raw kaolin clay was activated with an easy acid activation technique, modification in physicochemical and textural properties were determined by using X-ray diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) and Field Emission Scanning Electron Microscope. Among all acid-treated catalysts, metakaolin K3 have shown best catalytic properties, high surface area and pore size after acid activation with 3.0 mol/dm³ at 98 °C for 3 h. Acetalization of glycerol with acetone carried out in the presence of an environmentally friendly and inexpensive novel metakaolin K3 catalyst. The maximum yield of solketal obtained was 84% at a temperature of 50 °C, acetone/glycerol molar ratio 6/1 and for 90 min with novel metakaolin clay catalyst. Effect of various parameters (time, temperature, acetone/glycerol molar ratio, catalyst loading) on the solketal yield and glycerol conversion was discussed in detail. This approach offers an effective way to transform glycerol into solketal—a desirable green chemical with future industrial applications.