Simultaneous esterification and transesterification of microbial oil from Chlorella minutissima by acid catalysis route: A comparison between homogeneous and heterogeneous catalysts

•The built photo-bioreactor was found to be suitable for Chlorella minutissima cultivation.•The function desirability was used to simultaneously analyze the process variables.•Microalgal oil revealed as main fatty acids: C16:0 (57.1%) and C18:1 (26.3%).•Microbial oil can be considered a good candidate for biofuel synthesis using (H2SO4) and (Nb2O5/SO4).•Higher biodiesel yield was attained by heterogeneous catalyst.