High performance of Ternary Mixed Matrix Membrane Containing Calix[4]arene and TiO2 Nanoparticles

Remarking the importance of the greenhouse gases removal in current century, multi-component membranes have been prepared on the basis of Matrimid for CO₂/CH₄ separation. Moreover, calix[4]arene and TiO₂ nanoparticles have been introduced into the polymer matrix as organic and inorganic fillers to improve its properties. According to the results, fabrication of the two component membranes using calix[4]arene was led to higher selectivity due to its effect on the chain packing via non-covalent bonds. On the other hand, addition of the TiO₂ particle increased both gases permeation and reduced selectivity due to incompatibility of the organic phase of the polymer and inorganic phase of the nanoparticle. Moreover, addition of the excess contents than 0.5 %wt of calix[4]arene was led to agglomeration of this particle that reduced selectivity. Therefore, two component membrane containing 0.5 %wt of calix[4]arene was determined as the optimized content for CO₂/CH₄ separation. Growing consumption of the fossil fuels during the past century causes many environmental problems.^1-3 Global warming and climate changes resulted from the increment of the greenhouse gases, especially CO₂, are highlighted as the most concerns and the main treat for ecosystem all around the world.⁴ Many efforts have been performed to decrease the destructive effects of the greenhouses gases in last 20 years including distillation and cryogenic technologies that remove the produced CO₂ in industries.⁵ However, presence of the some disadvantages like environmental problems, high energy consumption, numerous complicated operation units as well as high investment cost make these methods undesirable for many countries.^6-8 on the other hand, the membrane separation technologies which are identified as green environmental friendly technology are assumed as one of the best solution for this challenge.^9-10 Among various materials for fabrication of the membranes, polymer membranes has been considered in many studies due to their suitable properties.¹¹ In particular, matrimid 5218 has been interested in many studies for gas separation because of its unique properties.¹² Matrimid is a common commercial polyimide polymer with relatively high gas permeability and selectivity, along with excellent mechanical properties, solubility in non-hazard organic solvents as well as commercial availability. However, good solubility of Matrimid in organic solvents makes it easy to swell in the environment of organic chemicals, thus deteriorating the separation performance of membranes.¹³ The presence of solvent plasticization causes the transport rates of all penetrants in a mixture to increase, which may result in significant selectivity losses because the increase for the slower permeating component is larger than for the faster permeating component.¹⁴ However, this category of materials faces many difficulties for using in membranes including plasticization, structure instability, and low selectivity as well as their limitation in comparison to the Robeson’s upper bound trade-off.^15-16 Hence, the recent studies are focused on the properties enhancement of the polymeric membranes. Introducing fillers in the polymer matrix to mixed matrix membranes is considered as one of the best methods in modification of the membranes properties.^17-19 TiO₂ nanoparticles consider as on the most frequented applied particles in fabrication of the mixed matrix membranes. Low cost and minimum incompatibility with organic phase in comparison to other inorganic particles make this particle interested in many studies.^20-24 on the other hand, introducing of the organic fillers in the mixed matrix membranes have been recently investigated and exhibited promising results. Nadeali et al. established the constructive effects of calix[4]arene particles on improving selectivity of Pebax-1657 based mixed matrix membranes.⁴ according to this report, calix[4]arene could be highlighted as new generation of the organic fillers with extraordinary properties. Vase body shape, presence of the versatile functional groups, presence of the plenty binding sites, and many other advantages make this susceptible host desirable for fabrication of the gas separation membranes.²⁵ Preparation of the two- and three-component membranes on the basis of the matrimid has been pursued in the current study. Noteworthy, calix[4]arene and TiO₂ nanoparticles were used as organic and inorganic fillers, respectively, in the matrix of the polymeric membrane. The permeation of the fabricated membranes for CO₂ and CH₄ gases was evaluated at 35 °C and pressure range 2-10 bar. Moreover, the structure of the membranes was investigated by FTIR spectroscopy, SEM and AFM imaging, and XRD crystallography.

Author(s): Mona Zamani Pedram

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