Journal Article

Mikrofiltracija sa periodicnim povratnim ispiranjem kao alternativna tehnika za povecanje fluksa permeata/MICROFILTRATION WITH PERIODIC GAS BACKWASHING AS AN ALTERNATIVE TECHNIQUE FOR INCREASING PERMEATE FLUX

Urosevic, Tijana, Povrenovic, Dragan, Vukosavljevic, Predrag, Urosevic, Ivan

2018

Overview

U ovom radu je ispitan uticaj radnih parametara (transmembranski prtisak, temperatura, brzina strujanja retentata) na unakrsnu (cross--flow) mikrofiltraciju model rastvora vocnog soka i periodicno povratno ispiranje vazduhom. U eksperimentima je korišcena keramicka Kerasep W5 membrana sa granicom separacije od 0,2 [micro]m. Odreden je optimalni transmembranski pritisak, koji iznosi 2 bara. Optimalna temperatura procesa bistrenja vocnih sokova mikrofiltracijom je 55[degrees]C. Više temperature se ne koriste zbog degradativnog efekta na hemijski sastav soka i dugog procesa mikrofiltracije. Sa porastom temperature retentata od 22[degrees]C do 55[degrees]C ostvaruje se porast fluksa permeata do 60 %. Povecanjem brzine strujanja retentata smanjuje se debljina formiranog sloja na površini membrane. Zbog ogranicenja korišcene aparature i velike površine membrane, postignute specificne brzine strujanja retentata su male, pa efekat unakrsne filtracije izostaje. Periodicnim povratnim ispiranjem se nataloženi sloj na membrani podiže, fluks permeata je u visokoj zoni i sprecava se uspostavljanje stacionarnog stanja u zoni niskih flukseva. Vreme utrošeno na povratno ispiranje je malo u odnosu na povecanje sakupljene mase permeata. U svim eksperimentima sa povratnim ispiranjem sakupljena masa permeata je veca do 72,5 % u odnosu na eksperimente bez povratnog ispiranja. Povecanjem vremena trajanja povratnog ispiranja povecanje fluksa je do 5 %, što može biti znacajno za mikrofiltraciju u industrijskim uslovima. Kljucne reci: mikrofiltracija, periodicno povratno ispiranje, model rastvor vocnih sokova. In this paper, the influence of operating parameters (transmembrane pressure, temperature, the flow rate of retentate) on the cross - flow microfiltration of synthetic fruit juice and periodic backwashing with air was examined. In the experiments, the Kerasep W5 ceramic membrane with a separation limit of 0.2 [micro]m was used. The results of experiments in which different transmembrane pressures were used showed that stationary fluxes, at stationary conditions, after 60 minutes, have similar values. So, it can be concluded that the value of the driving force is irrelevant at steady state conditions. However, until the steady state conditions are established, a positive effect of the increase in the driving force is opposed to the negative effect of the increased polarization resistance, as a result of the driving force increase. Thus, the optimal transmembrane pressure was determined amounting to 2 bars. The optimum temperature of the process of clearing the fruit juices by microfiltration is reported as 55 [degrees]C. Higher temperatures are not used due to a degrading effect on the chemical composition of the juice and a long microfiltration process. With an increase in the temperature of retentate from 22 [degrees]C to 55 [degrees]C, the permeate flux increased up to 60 %. Increasing the flow rate of retentate reduces the thickness of the formed layer on the surface of the membrane. Due to limitations of the experimental setup and the large surface area of the membrane, the specific velocity of the retentate was low, so that the effects of cross-flow filtration were absent. The use of cross-flow filtration is one of the main requirements for increasing permeate flux, but in the present case it was in overall insufficient, so we have applied periodic air backwashing for improving fruit juice flux during membrane clarification. With this technique, the deposited layer on the membrane is lifted and the permeate flux is maintained at high levels preventing establishment of the steady state in the low flux zone. The time spent for the periodic backwashing was low as compared to the benefits of the increase in the collected permeate quantity. In all experiments with periodic backwashing with air, the collected permeate quantity is higher for up to 72.5 % as compared to experiments without backwashing. By increasing the backwashing duration, the flux increase is up to 5 %, which can be significant for microfiltration at industrial scale. Therefore, this technique is certainly recommended for microfiltration in the production of fruit juices. Keywords: microfiltration * backwashing with air * synthetic fruit juice

• Publisher: Association of Chemical Engineers of Serbia
• Subject: Engineering models / Filtration / Juices (Beverages) / Production processes