Separation performance of polyimide nanofiltration membranes for solvent recovery from dewaxed lube oil filtrates

In order to save energy, a kind of novel nanofiltration membrane was prepared from polyimide based on 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) for recovering chilled solvents from lube oil filtrates. The separation performance of this membrane was investigated under different operating conditions. The influence of operating pressure, temperature, flowrate of feedstock and concentration of lube oil on the permeation flux, rejection to lube oil and the ratio of methyl ethyl ketone to toluene in permeate was studied. The membrane shows a steady permeate rate and high rejection to lube oil. The permeation flux can reach 12 L/(m2·h) and above, and the rejection to oil is generally over 96% under the condition of −18°C, 3 MPa and 20% lube oil concentration. The results show that there is an optimal operating condition for better solvent recovery capacity.