Polarized light based scheme to monitor column performance in a continuous foam fractionation column

BACKGROUND: A polarized light scattering technique was used to monitor the performance of a continuously operated foam fractionation process. The S(11 )and S(12 )parameters, elements of the light scattering matrix, combined together (S(11)+S(12)) have been correlated with the bubble size and liquid content for the case of a freely draining foam. The performance of a foam fractionation column is known to have a strong dependence on the bubble size distribution and liquid hold up in foam. In this study the enrichment is used as a metric, representative of foam properties and column performance, and correlated to the S(11)+S(12 )parameter. RESULTS: Three different superficial gas velocities (6.9, 7.5, and 10.6 cm/min) and four different pH values (4.8, 5.5, 6.5, and 7.5) are tested for the foam fractionation of a dilute solution of bovine serum albumin (0.1 mg/ml). As a result, at scattering angle of 125° the magnitude of S(11)+S(12 )is higher as the pH increases. When the bubble sizes are small with a larger liquid content, the foam is strongly back scattering resulting in lower values of S(11)+S(12 )(at 125°) at pH = 4.8. The light scattering data and the enrichment values are measured over a period of 90 minutes and correlated using a linear model. The predictive power of the model was found to be statistically significant. CONCLUSION: The time average S(11)+S(12 )shows a direct proportionality with the enrichment value, indicating that polarized light should be a valuable technique for monitoring foam fractionation columns. Additional knowledge of the nature of dependence between foam properties and S(11)+S(12 )combined with models relating the enrichment to the bubble size and liquid hold up is needed to develop an accurate diagnostics tool for monitoring enrichment utilizing S(11)+S(12 )measurements.