Evaluating the use of in-situ ultrasonication to reduce fouling during natural rubber skim latex (waste latex) recovery by ultrafiltration

Membrane fouling is universally accepted as one of the critical problems limiting the wider application of membranes in liquid–solid separation. The in-situ ultrasonic application is one of the promising methods for reducing the extent of concentration polarization and increasing permeate flux during the membrane separation. A study was conducted to investigate flux behavior during a cross-flow ultrafiltration (UF) process to concentrate natural rubber skim latex, with in-situ sonication. Tubular polyvinylidine fluoride (PVDF) membranes with 200 kD molecular weight cut-off (MWCO) were selected for this study. Experiments were conducted to study the effect of skim latex preservation level with and without sonication at a transmembrane pressure (TMP) of 2 bar. Results showed the permeate flux remained constant with sonication, and a decline in flux was observed without sonication. This study was also able to determine the ideal preservation level where the in-situ sonication improved the permeate flux without affecting the stability of the feed. This ideal preservation becomes the optimum preservation level required for skim latex recovery by ultrafiltration with in-situ sonication. The study also showed that an intermittent ultrasonic application with sonication ratio of 1 was comparable to that of continuous sonication.

Composite preservation solution of 0.3% ammonia and 0.2% ammonium laurate is the optimum level for a continuous in-situ sonication gave an improved permeates flux without affecting the stability of skim latex. This becomes the optimum preservation system for skim latex recovery by ultrafiltration with an in-situ sonication. This study assures that an optimum composite preservation solution is the key factor which prevented the coagulation of the rubber particles and maintained the feed stability thus enabling ultrasonication to be performed intermittently as an in-situ membrane cleaning operation to maintain permeate flux. This study also showed that the flux with an intermittent ultrasonication ratio of 1 was comparable to that for continuous sonication. This would bring about energy savings and a shorter processing time. In addition the economic life of a membrane could be prolonged with a lower usage of chemicals for cleaning membranes.