Mass transfer and transient response time of a split-feed nanofiltration pilot unit

Abstract

The transient response of a center-port nanofiltration membrane process was evaluated using a step-input dose of a sodium chloride solution. The pilot was configured as a two-stage, split-feed, center-port, 7:2 pressure vessel array process, where the feed water is fed to both ends of six-element pressure vessels, and permeate and concentrate streams are collected after only three membrane elements. The transient response was described as a log-logistic system with a maximum delay time of 285 s for an 85% water recovery and 267 gallon per minute feed flowrate. The log-logistic model was shown to be >98% accurate in predicting the transient response of the permeate streams. When compared with a first-order nonlinear regression model, there was no difference in the predictability of transient response when using the log-logistic model in first-stage and second-stage membrane processes. However, the log-logistic model was found to be more predictive in describing third-stage transient response by a factor of 236 over a first-order method. Furthermore, the homogeneous solution diffusion model was shown to effectively predict the permeate concentration for any transient permeate perturbation.