Examination of the bubble gas transport method to estimate the membrane pore size distribution

The pore size distribution (PSD) of the membrane is often measured by the bubble gas transport method. However, the method is not free from some concerns over its accuracy. In the present work, two questions are raised; 1) the validity of the computational procedure commonly used to calculate PSD 2) the validity of the assumption that all pores are open to gas transport in the linear part of the flow rate versus pressure curve. To answer these questions, the flow rate versus pressure lines were generated rigorously based on a given PSD by the model that we have recently developed [1], and using the lines so produced, the PSD was back-calculated. It was found that the agreement of original PSD and the back-calculated PSD is reasonable when the PSD is narrow, but when the PSD is broad, the back-calculated PSD shifts toward the larger pore sizes. It was also found that the calculated PSD is slightly affected when some small pores are not included in the linear part of flow rate versus pressure wet-line.