Polymer Materials for Membrane based Processes
The balance between the permeability and selectivity of a membrane material with respect to specific compositions of the gases, vapors, or liquids to be separated in specific applications with substantial market potential, such as natural gas purification or CO2 management, require an extremely high degree of optimization, which is frequently not attainable with traditional homopolymers. For this reason, multicomponent polymers are also being developed. There is little known to date concerning the relationships between the topologies and properties of these polymers.
The stabilization of the structure of polymers with intrinsic microporosity which could be used for applications in the field of gas and vapor separation (e.g. separating nitrogen and oxygen), and also demonstrate particularly interesting properties in the separation of liquid material mixtures, offers another challenge.
Development of new materials is accompanied by developments in process engineering aimed at optimizing the design of separation processes.
The activities in this area are divided into three groups: Polymer Multicomponent Systems, Organic-inorganic Hybrid Materials and Process Design. These individual working areas are discussed below.
Polymer Multicomponent Systems:
Integral-asymmetrical block copolymer membrane
The molecular self-organization of block copolymers with different topologies presents a remarkably fascinating strategy for the formation of nanostructured membrane materials. Molecular self-organization is the spontaneous arrangement of molecules in highly-ordered structures held together by intermolecular bonds. Although synthetic membranes are much more simply structured and demonstrate much lower degrees of functionality than biological membranes, their mechanisms of structural formation are nonetheless very similar.
To this end, tailor-made block copolymers of differing chemical composition are synthesized, using controlled polymerization processes, and morphologically characterized. During this process, additional functionality can be provided by integrating stimuli-sensitive blocks, which results in switchable membranes. The process of structural formation during membrane production also plays a substantial role here.
Also studied, in addition to pure block copolymers, are mixtures of various polymers, which are normally available commercially. All these systems should incorporate at least one semipermeable component, while other insoluble and non-swellable components serve to stabilize the membrane. Part of this work is carried out in the EU project SELFMEM (Self-Assembled Polymer Membranes).
Organic-inorganic Hybrid Materials:
Polymer membrane with silver nanoparticles
One of our objectives is the manufacturing of membranes with very high gas selectivity that can be used for the separation of condensable hydrocarbons from, for example, natural gas, biogas or air.
For applications in the field of gas separation, glass polymers with large free volumes are particularly promising. Here, polymers with intrinsic microporosity are investigated, such as functionalised polyacetylene or Teflon® AF 2400 and/or 1600.
The greatest challenges, in addition to mechanical stability, include the optimisation of the long-term maintenance of the selectivity and permeability of membranes, which is vital for making industrial use possible. For stabilising the membrane performance, inorganic nanoparticles are added to the polymers, e.g. in the form of charcoal, carbon nanotubes, and metallic or ceramic nanoparticles.
The hybrid membranes produced from this are tested for their separation characteristics in long-term tests in our own pilot installations and under real industrial conditions.
Part of the work is carried out together with project partners in the framework of the CNT Initiative, supported by the BMBF, and in the framework of the EU project HARCANA.
This development is expected to lead to new industrial applications in the field of gas separation and in the separation of liquids. One example is the enrichment of oxygen from the air for the optimisation of combustion processes, and use in chemical process technology in the manufacturing of fine chemicals (organophilic nanofiltration) is another possible application.
Membran module (section)
The new types of membrane materials improve existing membrane processes and open up new applications. The R&D work on these concentrates upon flat membranes. The permeation behaviour of these membranes is investigated on the laboratory scale for pure materials and mixtures of materials as a function of pressure and temperature. For these investigations we use equipment that has been developed at the Helmholtz-Zentrum Geesthacht.
Another focus of the work is the manufacturing of composite membranes on a semi-industrial scale for pilot applications. The membrane manufactured in this way must be integrated into a membrane module, which is then a central element of the whole separating plant.
We use Computer Aided Engineering tools for the module development with the aim of transferring the intrinsic membrane characteristics over to an industrial scale with as little loss as possible. The efficiency of the membrane materials and the modules is investigated under realistic conditions in pilot installations. The results of the piloting phase are also used for testing the accuracy of our process simulations. The models for membrane modules used for this are also developed at the Helmholtz-Zentrum Geesthacht.
An important aspect is the description of the permeation behaviour on multi-material systems in polymer-based membranes as a function of the characteristics of the polymer and permeating components and of temperature and pressure.
These simulation tools also allow the prediction of operating performance of processes, which are composed of membrane stages and conventional ground operations.
Our aim consists of establishing these processes in industrial applications in close cooperation with the licensees of the Helmholtz-Zentrum Geesthacht and other partners. The investigated membrane processes are gas and vapour permeation and non-watery nanofiltration based upon membranes developed at the Helmholtz-Zentrum Geesthacht.