Simultaneous refining of biodiesel-derived crude glycerol and synthesis of value-added powdered catalysts for biodiesel production: A green chemistry approach for sustainable biodiesel industries

Abstract

Glycerol is one of the industrially important chemicals having a wide range of applications in many fields. One of the important processes to obtain glycerol is during the biodiesel production, where it is formed as a by-product. However, it is crude and needs to be purified. Interestingly, the purification process of glycerol can be versatile, where it is possible to purify the crude glycerol and synthesize value-added chemical simultaneously. In this context, herein, we have developed an acidification-based process and demonstrated the concurrent purification of biodiesel-derived glycerol and the synthesis of sodium sulphate (Na2SO4) and potassium sulphate (K2SO4) as value-added chemicals. . The obtained results reveal that the established process is promising and yields commercial-grade glycerol (with ∼95% purity) along with the value-added chemicals Na2SO4 and K2SO4 with a purity of ∼95 and 98%, respectively. In addition, these synthesized powders have also been utilized as catalyst in biodiesel production with a yield of 96.1 and 94.8%, respectively with 3.5 wt% catalyst concentration. From the kinetic study, which is the pseudo-first order reaction, the activation-energy and frequency-factor for Na2SO4 and K2SO4 are estimated to be 38.27 kJ/mol and 2.2 × 104 min−1 and 44.69 kJ/mol and 2.4 × 105 min−1, respectively. The thermodynamic parameters of enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) of Na2SO4 and K2SO4 catalysed process suggested the endothermic, endergonic, and non-spontaneous nature of the reaction. Further, the recovered Na2SO4 and K2SO4 were reused for four times in biodiesel production, which showed a consistent yield of biodiesel in all the four cycles.