A comprehensive review of the adsorption mechanisms and factors influencing the adsorption process from the perspective of bioethanol dehydration

The production of bioethanol is growing, as it is been used as biofuel which is termed as a clean energy fuel. When ethanol is blended with gasoline, the octane number of the mixture increases and acts as an antiknock agent, besides releasing fewer pollutant emissions. To use as an automobile fuel when blended with gasoline, this ethanol should have less than 0.5 wt% of water. Therefore, ethanol has to be dehydrated; but it forms an azeotrope with water. In these scenarios, the implementation of conventional distillation technique is difficult and therefore unconventional techniques like extractive distillation have to be implemented. But this process leads to high operating costs, and hence researchers have investigated adsorption-based techniques. This methodology is not only very effective but also less expensive. The performance of the adsorption process depends on the type of adsorbent, its physical characteristics like particle and pore size, the phase in which it is carried and process parameters like temperature, initial concentration, and dosage. Thus, this paper presents a comprehensive review of the intrinsic characteristics of adsorbents, the effect of process parameters on adsorption efficiency and the influence of the phase of operation. Various types of isotherm and kinetic models utilized in the adsorption process are also presented in detail. Mathematical models describe the inherent mechanisms of the adsorption process; hence the governing equations like mass, energy and momentum balances for both liquid and gas phase are also reviewed.