Date juice concentration by vacuum membrane distillation

In this work, date juices were concentrated at low temperature by Vacuum Membrane Distillation (VMD). Tests were conducted at fixed operating conditions (feed flowrate, 28 L/h; feed temperature, 28 °C; vacuum pressure, 4 mbar) on two commercial flat polypropylene membranes, different in pore size and thickness. Date concentrates (70 °Bx) were obtained starting from juices at 18 °Bx, and pure permeates (0 °Bx) were collected. The water vapour trans-membrane flux depended on membrane properties until a concentration of ~50 °Bx was reached; then, the resistance at the feed side controlled the process.