Biomass is an environmentally favorable renewable resource that may be used to make a variety of valuable chemicals and fuels. A biorefinery, which is similar to a petroleum refinery, is necessary to manufacture fuels and valuable chemicals from biomass. The flexibility of input, processing capacities, and product generation have all been used to classify biorefineries into three phases. In any of the three categories stated, phase I has less or no flexibility. While Phase II has fixed input and processing capabilities, it allows for product generation flexibility. Phase III, which is based on the notion of high-value low-volume (HVLV) and low-value high-volume (LVHV) outputs, offers flexibility in all three processes. Biorefineries are becoming increasingly significant in providing chemical industry operations whilst achieving sustainable goals.