Integration of reactive extraction with supercritical fluids for process intensification of biodiesel production: Prospects and recent advances

Current world energy usage is trying to gradually shift away from fossil fuels due to the concerns for the climate change and environmental pollutions. Liquid energy from renewable biomass is widely regarded as one of the greener alternatives to partially fulfil the ever-growing energy demand. Contemporary research and technology has been focussing on transforming these bio-resources into efficient liquid and gaseous fuels which are compatible with existing petrochemical energy infrastructure. Due to the wide range of properties and compositions from different types of biomass, there are ample of processing routes available to cater for different demands and requirements. In addition, they can produce multi-component products which can be further upgraded into higher value products. This conceives the idea of bio-refinery where different biomass conversion processes are incorporated and proceed simultaneously at one location. However, the underlying complexity in integrating different processes with varying process conditions will undoubtly incurs prohibitive cost. Consequently, process intensification plays an important role in minimizing both the capital and operating costs associated with process integration in bio-refineries. Recently, process intensification for biodiesel production has been developing rigorously due to increasing demand for cost-cutting measures. Supercritical fluid process allows biodiesel production to be performed without any addition of catalyst. Meanwhile, catalytic in situ or reactive extraction process for biodiesel production successfully combines the extraction and reaction phase together in a single processing unit. In this review, the important characteristics and recent progress on both of the intensification processes for biodiesel production will be critically analyzed. The prospects and recent advances of supercritical reactive extraction (SRE) process which integrates both of the processes will also be discussed. This review will also scrutinize on the methods for these processes to compliment future bio-refinery setup and more efficient utilizing of all of the products generated.