The Optimization of Dispersion and Application Techniques for Nanocarbon-Doped Mixed Matrix Gas Separation Membranes

Ruben Hammerstein,Tobias Wolf,Antje Quade,Tim Schubert,Gerd Braun,Dionysios S Karousos,Stéphan Barbe,Evangelos P Favvas,Rüdiger Foest

doi:10.3390/membranes12010087

Abstract

In this work, supported cellulose acetate (CA) mixed matrix membranes (MMMs) were prepared and studied concerning their gas separation behaviors. The dispersion of carbon nanotube fillers were studied as a factor of polymer and filler concentrations using the mixing methods of the rotor–stator system (RS) and the three-roll-mill system (TRM). Compared to the dispersion quality achieved by RS, samples prepared using the TRM seem to have slightly bigger, but fewer and more homogenously distributed, agglomerates. The green γ-butyrolactone (GBL) was chosen as a polyimide (PI) polymer-solvent, whereas diacetone alcohol (DAA) was used for preparing the CA solutions. The coating of the thin CA separation layer was applied using a spin coater. For coating on the PP carriers, a short parameter study was conducted regarding the plasma treatment to affect the wettability, the coating speed, and the volume of dispersion that was applied to the carrier. As predicted by the parameter study, the amount of dispersion that remained on the carriers decreased with an increasing rotational speed during the spin coating process. The dry separation layer thickness was varied between about 1.4 and 4.7 μm. Electrically conductive additives in a non-conductive matrix showed a steeply increasing electrical conductivity after passing the so-called percolation threshold. This was used to evaluate the agglomeration behavior in suspension and in the applied layer. Gas permeation tests were performed using a constant volume apparatus at feed pressures of 5, 10, and 15 bar. The highest calculated CO2/N2 selectivity (ideal), 21, was achieved for the CA membrane and corresponded to a CO2 permeability of 49.6 Barrer.

Highlights

Membrane-based gas separation is an interesting technology for a multitude of tasks regarding CO2 separation for natural gas sweetening [1], biogas treatment, and carbon capturing [2]
The electrically conductive additives in a non-conductive matrix showed a steeply increasing electrical conductivity after passing the so-called percolation threshold, where the more electrically conductive paths of the additive can be found in the multi-phase system and the shorter the continuous 3D pathways are to bridging the distance between the electrodes, the lower the electrical resistivity is
The electrically conductive additives in a non‐conductive matrix showed a steeply increasing electrical conductivity after passing the so‐called percolation threshold, where the more electrically conductive paths of the additive can be found in the multi‐phase system and the shorter the continuous 3D pathways are to bridging the distance b8etowf 2e3en the electrodes, the lower the electrical resistivity is

Summary

Introduction

Membrane-based gas separation is an interesting technology for a multitude of tasks regarding CO2 separation for natural gas sweetening [1], biogas treatment, and carbon capturing [2]. Polymeric membranes are widely applied in industrial gas separation due to their beneficial properties, such as good mechanical resistance and high availability [5]. Undesirable effects such as the trade-off limit between permeability and selectivity [6] and plasticization effects caused by acid gases hinder the widespread utilization of polymeric membranes in CO2 separation [1,4]. On the other hand, exhibit excellent gas separation properties well above the trade-off limit of polymeric membranes and are stable at high temperatures, but they are not manufacturable in sufficient quantities/sizes for an actual reasonable industrial application [7]. CA has the benefit of being considered a green polymer with high availability [13]

Methods

Results

Conclusion