Chemometrical approach in studies of membrane capacity in pulp and paper mill application

In the pulp and paper mill membrane filtration applications the volumes of processed water are huge. Due to this high and stable capacity of the membrane is required. Since the membrane capacity is a result of many different factors, finding the most suitable membrane for a certain application usually needs a considerable number of experiments, which produces huge amounts of experimental results. Traditionally experimental filtration results are examined with univariable methods. The univariable examination is time-consuming and, due to the multivariate nature of the filtration phenomena, univariable examination cannot show effectively the correlation structure between the variables in the filtration system. Thus, multivariate examination methods are needed for obtaining well-defined information about membrane performance in a certain application. In this study the experimental results from a pilot-scale paper mill filtration application were examined with multivariate methods principal component analysis (PCA) and parallel factor analysis (PARAFAC). Both methods revealed crucial information about the membrane, which was not obtained when univariable examination was used. The methods tested were evaluated to be very effective tools in the examination of membrane filtration results.

In this case study the experimental data from a membrane filtration pilot plant at a paper mill site was examined with univariable and multivariate methods. The aim of the study was to test the usefulness of the multivariate methods PCA and PARAFAC in the examination of membrane filtration results, when the aim of the experiments was to find the most optimal membrane for a certain application. In this case study both of the tested multivariate methods were found to be effective tools. With multivariate examination crucial information about the differences between the membranes was obtained. This information was not found in the univariable examination. Based on the available data the cellulose membranes seemed to be the most optimal membranes for the studied application. However, the PCA and PARAFAC showed interesting differences in the stability of the performance of these membranes in different conditions, and for clarification of these differences follow-up studies have to be done. The greatest advantages of the multivariate examination are, according to this study, that all the measured variables can be examined at the same time and that only the crucial part of the original data is used in interpreting the results. Due to these advantages multivariate examination shows the real correlation structure interacting between the measured process variables. The use of PCA and PARAFAC also simplifies the visualisation of the results and makes them thus very easy to compare. Based on the results of this case study it can be concluded, that multivariate examination is needed for obtaining well-defined information about the phenomena occurring in membrane filtration.