Supercritical fluid extraction of spent coffee grounds: Measurement of extraction curves, oil characterization and economic analysis

Abstract

This work addresses scientific and techno-economic aspects of supercritical fluid extraction (SFE) of spent coffee grounds which are of interest under the biorefinery context. Soxhlet experiments were carried out and SFE curves were measured at 190 bar and 40 degrees C/55 degrees C. The extracts were characterized by GC-FID, and the triacylglycerides profiles were almost constant along an extraction curve, and similar to the n-hexane Soxhlet results: linoleic and palmitic acids content in both extracts are 44.5 and 37.5% (wt.), respectively. The oil solubility, intraparticle diffusion, convective mass transfer coefficient, and oil removal flux (this one estimated for infinite dilution) were calculated and discussed in detail in the ranges of operating conditions under analysis. It was concluded that solubility is the chief parameter behind the distinct cumulative extraction curves, and that all experiments are subjected to equivalent mass transfer resistances. An economic analysis involving cost of manufacturing (COM) and net income calculations were performed for distinct operating conditions and unit arrangements. The optima results were obtained for an arrangement of 3 beds of 1 m(3), extraction time of 2.0 h, 300 bar, 50 degrees C and 30 kg(CO2) kg(SCG)(-1)h(-1). Under these conditions production can reach 454 ton year(-1), a cost of manufacturing (COM) around 2.4M(sic), and process net income of 56.6 M(sic). A sensitivity analysis varying the unit capacity, extraction time and precipitation pressure (extract vessel), showed the process economics to remain viable. (C) 2013 Elsevier B.V. All rights reserved.