(494f) Hyperbranched Polymers as Absorbents for CO2 Capture: Experimental Solubilities and Process Simulation

Direct conversion of methane into other useful products is one of the most challenging subjects to be studied in heterogeneous catalysis. The Oxidative Coupling of Methane (OCM) process, in which methane is catalytically converted to C2 products (ethane and ethylene), is considered as a suitable technology with high potential to exploit the huge amounts of natural gas resources. Since the undesired CO2 production reduces the process efficiency drastically, obtaining simultaneously a high C2 yield and selectivity remains still as a challenge. This process is currently being investigated at the Berlin Institute of Technology within the excellence cluster named UniCat (Unifying Concepts of Catalysis). In the downstreaming process subsequent to the OCM reaction, a purification step takes place, where carbon dioxide has to be removed from the raw gas. This is done by chemical absorption using an aqueous amine solution, which can have several disadvantages such as a high energy demand for regeneration or solvent losses. However, it has been shown that hyperbranched polymers are promising candidates for gas absorbents with a high capacity for CO2 and with large selectivities.

Hyperbranched polymers are macro-molecules, which possess a globular structure and a large number of functional groups that can differ in their type. Unlike dendrimers, they can be easily synthesized via one-step reactions and exhibit polydispersity and irregularity in terms of branching and structure. However, many applications do not require structural perfection. Therefore, hyperbranched polymers represent economically promising products also for large-scale industrial applications. Potential applications range from the use as selective solvents in distillation of azeotropic mixtures or extraction to the control of flow characteristics, the use as drug delivery system and many more.

In this work, commercially available hyperbranched polymers (Boltorn Perstorp) are investigated. The potential for their use as absorbent in the separation of CO2 is evaluated by measuring solubilities. The results obtained are reported in terms of Henry constants within the temperature range of 283.15 to 313.15 K. In addition, the densities of the pure polymer or its solution with ethanol are measured in the same temperature range. Moreover, simulation studies using Aspen® will be presented to validate the potential of hyperbranched polymers in removing CO2. Furthermore, a miniplant has been built for the complete OCM downstreaming process within the UniCat project. Thus, suitable hyperbranched polymers can be investigated further on a larger scale in the downstreaming miniplant.

Acknowledgment: The authors acknowledge support from the Cluster of Excellency ?Unifying Concepts in Catalysis? coordinated by the Berlin Institute of Technology and funded by the German Research Foundation ? Deutsche Forschungsgemeinschaft.