Effect of transmembrane pressure, linear velocity, and temperature on permeate water flux of high-density vertically aligned carbon nanotube membranes

Vertically aligned carbon nanotubes (VA CNTs) were fabricated as an ultrafiltration membrane by a simple polyurethane reinforcing procedure. Pure water permeation properties were investigated using the membrane. During the membrane operation, pure water permeate fluxes were achieved at various transmembrane pressures (TMPs), linear velocities, and feed water temperatures. In comparison to the dependence of the permeate water flux on the three membrane operating parameters, the VA CNT membrane showed less sensitivity with increasing linear velocity and feed water temperature, likely due to the superfast water transport property of carbon nanotubes. This property of the VA CNT membrane can provide an advantage in terms of energy consumption when operated under mild operating conditions such as low linear velocities and low water temperatures. The optimal operating condition of the VA CNT membrane was calculated by dividing the permeate water flux by the energy consumption. An operating condition of 1 bar of TMP, 5 cm/s of linear velocity, and 30°C of water temperature was optimal in terms of energy consumption, if no heating control of water was used. This study quantitatively provides the detailed membrane operation results under diverse operating conditions. It also provides useful engineering data of the VA CNT membrane operation for the first time.