Selected Thermo-Chemical Biorefining: Evaluation of the Current Trends and Progressions

Abstract

The review paper embodies the current trends and advancements involved in the transformation of biomass to enhanced products, bioenergy, and chemicals. Some selected chemical process like the slow-fast pyrolysis, catalytic fast pyrolysis, hydrothermal liquefaction, transesterification and lignin valorization by depolymerization are aptly suited for biorefinery processing, and were discussed in this review. The (catalytic) fast pyrolysis and hydrothermal liquefaction are quite similar, but differ in their feedstock preparations, reactor configuration and thermal or energy optimization. The review covers the biomass selection, chemical conversion techniques and most importantly the required heterogeneous catalysts (where applicable). The work further suggests the superiority of dedicated chemicals over drop-in and smart drop-in chemicals, due the complete usage of biomass. Relative to the oil refinery process, biorefining is quite novel and accompanied by its drawbacks. These challenges range from catalyst poisoning and deactivation to energy intensiveness and eventually as being cost-ineffective. The challenge encountered in biorefinery is in the economic feasibility, as it is inferred from this review that the pre-treatment process takes up to about 20% of the conversion cost. Although the biorefinery plant employ lignocellulosic biomass, but study shows that the use of biomass is largely under-utilized. The solid products/ wastes from pyrolysis for example, can be utilized as source of energy for the process. In the pursuit for sustainability, it is essential to ensure a balance-energy-mix, where every other type of energy will have a role to play to avoid dependence on only one solution for the future. Therefore, in contrast to the dwindling fossil fuels, it can be generally speculated that the future for biorefining is bright. It was concluded that with vast knowledge on the suitable heterogeneous catalysts and proper optimization of process parameters (temperatures, pressure, and reactant species); some of the biorefining processes will result into a significant increase in industrial fuels and bio-based drop-in chemicals leading towards commercialization.