Continuous separation and purification of glycerol distillation residues in the sense of circular economy: Experimental proof-of-concept and techno-economic assessment

The residue obtained in the course of the distillative purification of crude glycerol from biodiesel production contains mainly inorganic salts like sodium chloride and potassium sulphate, glycerol and matter-organic-non-glycerol. This residue is often discarded, since organic matter is present in the salts which prohibits further use where higher salt purities are needed. However, separation and purification of the residue is of interest, from an environmental but also economic point of view. Here, we demonstrate an experimental proof-of-concept for the separation and purification of glycerol-salt mixtures with ethanol as solvent in continuous counter-current solid-liquid operation in a stirred extraction column, the Taylor-Couette disc contactor. The Taylor-Couette disc contactor proves to be a viable apparatus for this application, especially in view of its simple and robust design with absence of static internals, which limits fouling and prevents accumulation of solids. Furthermore, a techno-economic assessment of the process based on a simulation in AspenPlus was conducted. Economics were evaluated on the basis of capital and operating expenditures, also taking into account waste disposal costs and profits from the sale of value-added products such as purified salt.