Biodiesel production through microbubble mediated mass transfer using zwitterion catalysts

Abstract

The total energy consumption is increased due to the rapid expansion of industries and metropolitan development. Biodiesel is a substitute fuel to conventional diesel, which is non-carcinogenic, sustainable, and has a high cetane number. The conventional methods used for biodiesel synthesis are energy-intensive, and operational cost is high. Catalytic esterification and transesterification methods are employ for the cleaner production of biodiesel. Due to the presence of high content of free fatty acid (FFA), transesterification carries the drawback of sponification. In the esterification reaction, FFA was reduced using an acidic catalyst. However, thermodynamic equilibrium restricts the overall conversion and slows the pace of the reaction—the current study used microbubble-mediated mass transfer technology to overcome this problem. Acid catalysts are used for esterification, show good activity, and produce high-quality biodiesel. Although the rate of the reaction is slower, it takes longer and at a higher temperature to achieve the maximal conversion. Various basic catalysts have been used for biodiesel synthesis to overcome the acid catalysts' drawbacks. Under mild conditions, show high catalytic activity in the transesterification process. However, base catalysts are limited due to high water affinity and moisture during storage. Saponification is another disadvantageous feature of these catalysts. Esterification and transesterification could both be performed by a catalyst that has both acidic and basic sites. This study aims to propose a sustainable strategy to energy generation using microbubble technology and bi-functional catalyst. As a heterogeneous catalyst for the generation of biodiesel, strontium zirconium oxide (7% Sr/ZrO2) was produced, and compared with naturally occurring bi-functional catalysts such as zwitterions is also used to investigate biodiesel production. To optimize the synthetic bifunctional catalyst response surface methodology (RSM) was used.