The projections recently published by the United Nations (UN) suggest that the global population may reach 8.9 billion people by the year 2050. Life expectancy is assumed to rise constantly with no upper limit and by the year 2100 is expected to vary from 66 to 97 years. As the population ages the demand for effective medicines is rising. At the same time the pharmaceutical industry keeps applying pressure to shorten development timelines for new chemical entities, so that new medicines can reach patients much faster. In the development and manufacturing of drugs the purification steps often consume the highest proportion of the processing time and costs. In parallel, there has been a surge in the expectations of patients regarding the purity of the desired pharmaceuticals. There are several processes available for yielding purified product: liquid chromatography, crystallization or distillation among others most of them, however have limitations. Therefore, progress is required in innovative technologies and processes characterized by higher stability, better selectivity and lower energy requirements. Applying membrane technology in the separation and purification of compounds can result in lower operating temperatures being needed, and less harsh conditions required, when compared to other processes. Thus it is of interest for Active Pharmaceutical Ingredient (API) manufacturing. Polymeric membranes are the most widely used for industrial membrane applications. However, an important challenge is to apply the existing polymeric membranes (suitable for aqueous operations) to non-aqueous solutions. Recent progress has led to the development of Organic Solvent Nanofiltration (OSN). OSN utilises solvent-resistant polymeric membranes to selectively retain solutes, and simultaneously allows smaller molecules to pass through the membrane. Nevertheless, ways in which membrane performance impacts the overall purification process have not yet been fully studied. Developing mathematical models of purification processes might help to better understand, and therefore better predict and control, the membrane process. Knowing the importance of a membrane in a filtration process, one should try to identify the areas where new membranes are desired. At the same time, one should try to understand how factors influencing membrane formation will affect membrane's final performance. As a benefit of the research conducted, by the end of this study the knowledge gained should result in the fabrication of membranes with enhanced capabilities.