Influence of gas sparging on membrane performance

Abstract: A new oxygen barrier film that is made of arabinoxylan has been developed by the company Xylophane. Arabinoxylan is available among other things in wheat bran. But a problem with the method of extracting the arabinoxylan is that after an alkali extraction is ultrafiltration used to remove impurities and the flux during this is quite low. In this project is it investigated if gas sparging with air can improve the flux for the ultrafiltration step. But first is a study of how gas sparging a silica sol solution affects the flux made. Because silica sol has a similar density and viscosity as the alkali extraction solution from wheat bran. Two different mem-brane modules were used: a polymeric tubular membrane in the experiments with silica, and a ceramic tubular membrane when treating the hemicellulose solution. The influence of air/liquid ratio, pressure and temperature was investigated. For the silica sol study the result was that the flux improved when the liquid flow was sparged with air. The studied air flow interval did not reach the point where the flux increase levelled off or decreased. Therefore, a higher flux can be expected when using a higher air flow than the ones studied. The optimal transmembrane pressure (TMP) for the two examined concentra-tions of silica were 1 bar for the low concentration and 0.6 bar for the higher. When the hemicellulose solution was studied air was added into the feed tank by letting the retentate flow whip the liquid surface in the feed tank, instead of directly adding it to the liquid flow as in the silica experiments. Hence the amount of air added could not be meas-ured, but the effect it had when the temperature of the solution was 80 °C was substantial. A flux increase over 200 % was reached and if the air addition was terminated, the flux still re-mained the same. When the temperature instead was 30 °C there was no increase in flux ac-companied with the air addition. After performing several analyses on the samples taken from the start of and during, the air addition it was it clear that a degradation of molecules had oc-curred at 80 °C, but not at 30 °C. This degradation can contribute to the increase in flux, but if it is the only factor can not be determined. No examination was made regarding the effect the heat and addition of air on the arabinoxy-lan. Such effects need to be examined before the method can by recommended for the indus-try this must be examined.