Green biodiesel production from Nannochloropsis microalgae-derived oil using ZnAl-LDH catalyst: Process optimization and kinetic study

Abstract

The green production of biodiesel using Nannochloropsis microalgae, a renewable and environmentally friendly source, was successfully conducted by application of a calcined ZnAl layered double hydroxides structure (LDH) catalyst. The ZnAl-LDO catalyst was prepared through the urea synthesis method, followed by calcination at 400 °C. XRD was used to investigate the crystallite characteristics, N2-BET to analyze surface properties and pore size, and CO2-TPD to identify the active basic sites strength. Bligh and Dyer’s method was utilized for oil extraction with a yield of 38 %. Upon analyzing the fatty acid profile of derived oil, a synthetic oil containing oleic and palmitic acids was utilized in this process. The experiments were designed using the response surface methodology (RSM) method and the optimized parameters were obtained at 149.59 °C, 118.92 min, 3.91 wt% catalyst loading, and 11.68:1 methanol to oil molar ratio for the biodiesel yield of > 98 %. The pseudo-first-order esterification reaction kinetic was investigated and the activation energy was determined to be 28.53 kJ.mol−1. Furthermore, the process can be applied to microalgae solid biomass as well. In-situ transesterification of microalgae with a yield of FAME over 90 % also has been carried out.