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Abstract Organic solvent nanofiltration (OSN) offers great potential as a versatile tool for process intensification in the chemical industry. Nevertheless, the mass transfer mechanism through OSN membranes is not fully understood. The complex interactions between membrane, solvent and solute make it difficult to predict the separation performance of the membrane. In order to increase the fundamental understanding of the underlying transport phenomena systematic experimental investigations were carried out. A matrix of solvents, solutes and membranes was defined, covering a wide range of properties. The selection of the solutes was based on their industrial relevance to cover representative solute properties. Another criterion was their molecular weights, which should be rather low in order to obtain rejection less than 100%, to evaluate potential solute specific impact factors. The separation characteristics of 17 polar to apolar solutes with molecular weights from 114 g/mol to 339 g/mol were investigated. Moreover, five solvents and two membranes were included in the systematic investigation. On the basis of the results different solvent dependent solute sensitivity regions were identified for each membrane which differ by the impact of solute properties on the rejection. Different transport mechanisms seem to dominate within the different solute sensitivity regions. A correlation of the hydrogen bonding capacity of the solvents with the impact of solute properties on the rejection was found. This new insight offers new perspectives for the prediction of membrane rejection behavior in OSN. Highlights • Organic solvent nanofiltration membranes show solvent dependent solute sensitivities. • Depending on the solvent different phenomena seem to dominate the mass transfer. • Hydrogen bonding of solvent correlates with solute impact on the rejection. [ABSTRACT FROM AUTHOR]

Organic solvent nanofiltration has emerged as a versatile tool for process intensification in chemical production. Due to the complex interactions between membrane, solvent and solute, the transport mechanism has not yet been clarified and it is rather difficult to identify the best membrane for a given separation problem. Currently, this is solved by time-consuming and costly membrane screening experiments. To accelerate process development an heuristic for membrane selection is required. Therefore, the rejections of different substances with varying functional groups out of a material class of specialty chemicals were measured. The most typical membrane materials (Polydimethylsiloxane and Polyimide) and a wide range of solvents were used. From these experiments, parameters were identified which influence the membrane performance. A combination of these parameters in an heuristic allows for the identification of the most suitable membrane for a given separation problem. [ABSTRACT FROM AUTHOR]

In this work, a transport model based on equations for aqueous nanofiltration has been adapted to describe the rejection of ceramic membranes for nanofiltration in organic solvents. Required membrane parameter were taken from permporometry measurements of the respective membrane. The calculated results were validated by rejection measurements with different membranes of MWCOs between 350 and 1200 g/mol. By selecting an appropriate standard deviation of the pore size, rejection curves measured with polystyrenes in THF were successfully described using the model without any fitting parameters. Differences between the calculated and the experimental rejections were smaller than 0.7% for the membrane with the smallest pore size. The use of the model for a real life solute system has been checked with different specialty chemicals and indicates a good transferability. Variations of process parameters as temperature, pressure and feed velocity were in excellent accordance with the experimental observations. However, to reflect the incomplete rejection of membranes with a high amount of defect pores (detectable by the permporometry measurement), the model has to be extended as well as for the applicability to different solvents. [ABSTRACT FROM AUTHOR]

Organic solvent nanofiltration (OSN) is still a niche technology in the chemical industry due to time and money consuming process development, as organic solvents cause complex interactions between membrane, solvent, and solute. These interactions are not fully identified, and a fundamental understanding of mass transfer through OSN membranes is not established so far. Accordingly, mathematical models in OSN lack a general predictive capability. To overcome this problem, we aim to extend the current knowledge by a comprehensive experimental investigation of two polyimide membranes in combination with 17 solutes with molecular weights of 114–339 g/mol covering the range from nonpolar to polar, and five solvents with various properties. The results indicate solvent-dependent rejection phenomena that may be explained by a difference in the impact of solute properties on the rejection in dependency of the solvent. Based on these findings, three solvent-dependent solute sensitivity regions are derived similarly to previous results for PDMS membranes. The investigation of membrane–solvent interactions revealed an impact of the spatial distance in the 3D space of the total Hansen solubility parameter between solvent and membrane with a specific impact on membrane–solute sensitivity. These new findings contribute to a better understanding of transport phenomena and can serve as a new basis for predicting the separation performance in OSN. • Solvent-dependent solute sensitivity regions were identified. • Depending on the specific sensitivity region, different transport phenomena occur. • Solute properties determine solute transport when membrane-solvent affinity is low. [ABSTRACT FROM AUTHOR]