The aim of this study is to develop the ultrafiltration process for the separation of phytosterols and proteins from orange juice using synthetic membranes made from regenerated cellulose acetate, polyethersulfone and fluoropolymer. This project was derived from the issues found in utilisation of by-products of rubber processing waste called natural rubber serum (NRS) that contains phytosterols compounds. Owing to the difficulty of securing supplies of NRS, a cheap and readily available alternative was sought. Orange juice was found to have similar total phytosterols content (0.2 – 0.3 mg ml-1) to those present in NRS. A cross-flow filtration rig with a total filtration area of 336 cm2 was operated at transmembrane pressure (TMP) of 1 bar and the process was optimised at 10 to 40 oC. The ultrafiltration performance has been determined in terms of flux, resistances and rejection ratio towards phytosterols and proteins. The membrane surface modification due to fouling and cleaning has been investigated in terms of membrane hydrophobicity, surface roughness, charge and porosity. A desirable membrane separation rejects proteins whilst transmitting phytosterols. The best separation of phytosterols from orange juice (43 ± 2 mg L-1) with the lowest rejection of phytosterols (32 ± 4%) and the highest rejection of proteins (96 ± 1%) with a selectivity factor of 17, was achieved using RCA 10 kDa membrane at 20 °C using 3 L orange juice. Ultrafiltration at low temperature was found to be more effective in separating phytosterols in orange juice to reduce membrane fouling. Membrane surface roughness and surface charge varied as a function of molecular weight cut-off (MWCO) such that RCA30 kDa > RCA100 kDa > RCA10 kDa. Membranes with rougher surfaces exhibited a higher fouling than those with smoother surfaces. Fouling increased the membrane porosity and decreased the membrane hydrophobicity. It can be concluded that membranes properties were more important than MWCO in determining the performance of ultrafiltration membranes in this system. The fluid dynamic gauging (FDG) obtained 80 - 95% surface removal at shear stress values of 3.9 Pa, corresponding to a water velocity of 1.3 m s-1. By applying the FDG, the fouling layer on RCA membranes can be removed without affecting the membrane surface modification caused by chemical cleaning.
|Date of Award||16 Jun 2021|
|Sponsors||Malaysian Rubber Board|
|Supervisor||Michael Bird (Supervisor), John Chew (Supervisor) & Tony James (Supervisor)|
- Orange juice