ABSTRACT
The revolutionized era of biodiesel production from unconventional feedstock has paved a possible way to futuristic biodiesel production. Microalgae had received wide attention as the chief raw material for biodiesel production due to its many applications over conventional fuel. Biodiesel is a monoalkyl ester synthesized from the stepwise sequential process and is a low-emission liquid fuel. Conventionally, microalgae biodiesel is produced via catalytic transesterification using acid, alkali or enzyme. Acid-catalyzed transesterification is good for high-free fatty acid (FFA)-containing microalgae, whereas it is a slow and corrosive reaction process. Alkali-catalyzed reaction is non-corrosive and fast but can form soap. Enzyme-catalyzed reaction is, however, superior to both the processes but is expensive. However, these demerits can be eliminated with technological advancements. Moreover, the environmental factors, algal strain, extraction, downstream processing and reaction parameters significantly affect biodiesel yield and quality, which need a careful selection. Various strategies have been adopted for process intensification to attain high-quality microalgae biodiesel. Hence, the incorporation of advanced techniques such as the supercritical method, BIOX method and nanocatalyst is a valuable approach to work with low-grade oil feedstocks having high FFA and moisture content.
