Many industrial processes use organic solvents, which have to be recovered at a later point in time. This recovery is accomplished primarily through thermal separation methods, which require a lot of energy, usually in the form of heat.
An energy-efficient, resource-efficient alternative is provided by organophilic nanofiltration. The challenge of this separation method: It requires membranes that have good separation characteristics for the specific mixture of materials and are stable in a variety of organic solvents. Since December 2015, the High Performance Polymers Business Line at Evonik has had three new membranes in its product range under the brand name PuraMem®. At the suggestion of High Performance Polymers, the technological basis for these membranes was created and embedded in the overall strategy of the Membranes Growth Field at Creavis in the OPHINA project (organophilic nanofiltration for energy-efficient processes), which was subsidized by the German Federal Ministry of Education and Research.
From the very beginning, it was clear to the researchers that only a polymer-based composite membrane could meet the requirements. To accomplish their goal, they utilized materials and skills available in the Evonik group. As polymer, they selected polyimide and, with the aid of Process Technology, developed a durable membrane as supporting structure. They gave it a silicone coating based on silicones from the Nutrition & Care Business Line, which is decisive for the separation characteristics. The resulting composite membrane was then transferred to spiral wound membrane modules, in order to create a maximum surface for the separation processes in a handy form.
After the end of the project in April 2013, the High Performance Polymers Business Line took over the task of developing these composite membranes into marketable products for specific applications. As target industries, the polymer experts set their sights on specialty chemicals, petrochemicals, and the pharmaceutical industry, among others. In all these industries, material separation is part of the day-to-day business. The membrane technology from Evonik can be used, for example, for efficient recovery of valuable homogeneous catalysts, recycling of solvents, or careful processing of natural oils. The advantages of organophilic nanofiltration compared to thermal separation methods include lower energy consumption, low impact on the product, and simple process integration.
The product family of composite membranes was also expanded technologically by thin-film composite membranes, in which a thin layer of silicone is applied to a supporting structure made of polyacrylonitrile. In the latest membrane generation, it is less than one micrometer thick. As a result, separation performance has been increased distinctly. Creavis has provided support for this process and is once again playing a central role: The system for producing the gossamer membrane coatings, which are custom-tailored on the molecular level, is located at Creavis in Marl. The further processing of the membrane into solvent-resistant and/or gas-tight spiral wound membrane modules is handled by Evonik Membrane Extraction Technology in London.
The first industrial scale systems at customer locations are already under construction. And the development of new membranes is continuing.