Process scale-up, economic, environmental assessment of vibratory nanofiltration of coffee extracts for soluble coffee production process intensification

Abstract

This study investigated the viability of a vibratory nanofiltration system as a low-energy alternative to evaporation in concentrating coffee extracts before final dehydration. Film model correlations for permeate fluxes and characteristics (turbidity, conductivity, and chemical oxygen demand) were determined from vibratory nanofiltration experiments on different coffee extract concentrations at 50 °C and 400 psi. Vibratory amplitude of 2.54 cm at 54.7 Hz frequency enhanced permeate fluxes by up to 3 times that of crossflow filtration by reducing the gel layer concentration on the membrane surface. Experimental results were used to propose a scaled-up vibratory nanofiltration operation recovering 378,500 L/day of reusable water from concentrating coffee extracts up to 35% wt/wt. The design flux exponentially decreased with increasing feed coffee extract concentrations requiring larger systems with majority of the operating cost associated with membrane replacement. The energy usage and cost of the vibratory nanofiltration system were substantially lower than those of evaporation in terms of steam consumption. However, the low design flux limited the proposed membrane system to feed concentrations less than 3% wt/wt but may be improved using optimization studies. Economic assessment for this feed concentration corresponded to a 7-module i84 VSEP filtration system with a capital cost of $2,100,000 with estimated annual savings of $481,900/year and corresponding payback period of 10 years. Lastly, the proposed alternative opens opportunities in the intensification of soluble coffee production in terms of energy efficiency, water recovery, and wastewater reduction that overall reduce the environmental emissions of the process by approximately 40%.