CO2/CH4 and He/N2 Separation Properties and Water Permeability Valuation of Mixed Matrix MWCNTs-Based Cellulose Acetate Flat Sheet Membranes: A Study of the Optimization of the Filler Material Dispersion Method.

Tobias Esser,George Maistros,George V Theodorakopoulos,Tobias Wolf,Tim Schubert,Dionysios S Karousos,Evangelos P Favvas,Andreas A Sapalidis,Stefan Forero,Stéphan Barbe,Jan Benra

doi:10.3390/nano11020280

Abstract

The main scope of this work is to develop nano-carbon-based mixed matrix cellulose acetate membranes (MMMs) for the potential use in both gas and liquid separation processes. For this purpose, a variety of mixed matrix membranes, consisting of cellulose acetate (CA) polymer and carbon nanotubes as additive material were prepared, characterized, and tested. Multi-walled carbon nanotubes (MWCNTs) were used as filler material and diacetone alcohol (DAA) as solvent. The first main objective towards highly efficient composite membranes was the proper preparation of agglomerate-free MWCNTs dispersions. Rotor-stator system (RS) and ultrasonic sonotrode (USS) were used to achieve the nanofillers’ dispersion. In addition, the first results of the application of the three-roll mill (TRM) technology in the filler dispersion achieved were promising. The filler material, MWCNTs, was characterized by scanning electron microscopy (SEM) and liquid nitrogen (LN2) adsorption-desorption isotherms at 77 K. The derivatives CA-based mixed matrix membranes were characterized by tensile strength and water contact angle measurements, impedance spectroscopy, gas permeability/selectivity measurements, and water permeability tests. The studied membranes provide remarkable water permeation properties, 12–109 L/m2/h/bar, and also good separation factors of carbon dioxide and helium separations. Specifically, a separation factor of 87 for 10% He/N2 feed concentration and a selectivity value of 55.4 for 10% CO2/CH4 feed concentration were achieved.

Highlights

Membrane systems possess many advantages such as small footprint, low capital and operating costs, being environmentally friendly, and no moving parts for separation and as such exhibit process flexibility [1]
High purity carbon nanotubes were produced by catalyst-assisted chemical vapor deposition [26,27]
scanning electron microscopy (SEM) micrographs illustrate the multi-walled carbon nanotubes (MWCNTs) morphology and their interwoven and entangled arrangement. They appeared in the form of ribbon complexes with no sign of any impurities

Summary

Introduction

Membrane systems possess many advantages such as small footprint, low capital and operating costs, being environmentally friendly, and no moving parts for separation and as such exhibit process flexibility [1]. Nanomaterials 2021, 11, 280 available polymeric membranes (cellulose acetate (CA), cellulose triacetate (CTA), and polyimide (PI), etc.), especially when they are used for high pressure natural gas sweetening. In this regard, the relatively low separation performance (i.e., low CO2 /CH4 selectivity) and low CO2 permeances, due to membrane compaction and plasticization, are the two major disadvantages. The improved properties of CA, such as high biocompatibility, good desalting, high potential flux, good toughness, and relatively low cost classified the CA membranes in a high position [4,5] Due to these characteristics, CA membranes have found wide uses in numerous applications, such as gas separations, microfiltration, and reverse osmosis-desalination [6]. Special attention is given to reverse osmosis applications thanks to the excellent hydrophilicity of the cellulose acetate, an important factor in the minimization of fouling phenomena [7,8]

Methods

Results

Conclusion