Development of mixed matrix zeolite membranes functionalized with ionic liquids for CO2 separation

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The functionalization of PES/SAPO-34 mixed matrix membrane with [emim][Tf2N] ionic liquid to improve CO2/N2 separation properties

Publication . Cardoso, Jonathan; Lin, Zhi; Brito, Paulo; Gando-Ferreira, Licínio M.

The use of ionic liquid [emim][Tf2N] as an additive in polyethersulphone (PES) and nanosized silico-aluminophosphate-34 (SAPO-34) mixed matrix membrane was studied through the incorporation of different amounts of [emim][Tf2N] in the membrane composition, as presented in this work, varying from 10 to 40 wt%. Through gas permeation tests using CO2 andN2, the membrane composition containing 20 wt% [emim][Tf2N] led to the highest increase in CO2 permeability and CO2/N2 selectivity. The use of low concentrations of additive (10–20 wt%) promoted a state called antiplasticization; in this state, the permeability was even more regulated by the kinetic diameter of the species which, in this work, permitted achieving a higher CO2/N2 selectivity while increasing the CO2 permeability until an optimal condition. [emim][Tf2N] also promoted a better dispersion of SAPO-34 particles and an increase in the flexibility of the polymeric matrix when compared to a film with the same composition without [emim][Tf2N]. Moreover, the characterizations corroborated that the inclusion of [emim][Tf2N] increased the zeolite dispersion and improved the polymer/zeolite compatibility and membrane flexibility, characterized by a decrease in glass transition temperature, which helped in the fabrication process while presenting a similar thermal resistance and hydrophilicity as neat PES membrane, without affecting the membrane structure, as indicated by FTIR and a contact angle analysis.

2023Journal article

Open access

Optimization and performance studies of PES/SAPO-34 membranes for CO2/N2 gas separation

Publication . Cardoso, Jonathan; Fonseca, Joel P.; Lin, Zhi; Brito, Paulo; Gando-Ferreira, Licínio M.

SAPO-34 nanocrystals were prepared and used as inorganic filler in polyethersulfone (PES) membranes. The influence of preparation conditions on permeation properties of CO2 and N2 gases and CO2/N2 selectivity were studied to achieve the highest separation performance possible for this mixed-matrix membrane. Gas permeation properties of PES/SAPO-34 MMMs with different contents of SAPO-34, PES and initial film thickness were investigated according to a full factorial design of experiments (DOE). The permeation tests and DOE results revealed that the optimized conditions to maximize the selectivity for PES/SAPO-34 are: composition of 18.5 wt % of SAPO-34, 15 wt% of PES, and a casted film thickness of 400 μm resulting in a CO2/N2 selectivity of 30.85. The findings showed that a multivariable model was validated and able to predict the selectivity with determination coefficient R2 of 0.969 and the results are in accordance with values presented in literature for PES/ SAPO-34 membranes. An economic analysis shows that the commercial grade price for the optimized membrane is EUR 9.43/m2 which represents around 2.2 times cheaper than polymeric commercial membranes.

2024Journal article

Restricted access

Enhancing CO2/N2 and CO2/CH4 Separation Properties of PES/SAPO-34 Membranes Using Choline Chloride-Based Deep Eutectic Solvents as Additives

Publication . Cardoso, Jonathan S.; Lin, Zhi; Brito, Paulo; Gando-Ferreira, Licínio M.

CO2 separation is an important environmental method mainly used in reducing CO2 emissions to mitigate anthropogenic climate change. The use of mixed-matrix membranes (MMMs) arrives as a possible answer, combining the high selectivity of inorganic membranes with high permeability of organic membranes. However, the combination of these materials is challenging due to their opposing nature, leading to poor interactions between polymeric matrix and inorganic fillers. Many additives have been tested to reduce interfacial voids, some of which showed potential in dealing with compatibility problems, but most of them lack further studies and optimization. Deep eutectic solvents (DESs) have emerged as IL substitutes since they are cheaper and environmentally friendly. Choline chloride-based deep eutectic solvents were studied as additives in polyethersulfone (PES)/SAPO-34 membranes to improve CO2 permeability and CO2/N2 and CO2/CH4 selectivity. SAPO-34 crystals of 150 nm with a high surface area and microporosity were synthesized using dry-gel methodology. The PES/SAPO-34 membranes were optimized following previous work and used in a defined composition, using 5 or 10 w/w% of DES during membrane preparation. All MMMs were characterized by their ideal gas permeability using N2 and CO2 pure gasses. Selected membranes were also tested using CH4 pure gas. The results presented that 5 w/w%, in polymer mass, of ChCl–glycerol presented the best result over the synthesized membranes. An increase of 200% in CO2 permeability maintains the CO2/N2 selectivity for the non-modified PES/SAPO-34 membrane. A CO2/CH4 selectivity of 89.7 was obtained in PES/SAPO-34/ChClglycerol membranes containing 5 w/w% of this DES, which is an outstanding ideal separation performance for MMMs when compared to other results in the literature. FTIR analysis reiterates the presence of glycerol in the membranes prepared. Dynamic Mechanical Thermal Analysis (DMTA) shows that the addition of 5 w/w% of DES does not impact the membrane flexibility or polymer structure. However, in concentrations higher than 10 w/w%, the inclusion of DES could lead to high membrane rigidification without impacting the overall thermal resistance. SEM analysis of DESenhanced membranes presented asymmetric final membranes and reaffirmed the results obtained in DMTA about rigidified structures and lower zeolite–polymer interaction with higher concentrations of DES.

2024Journal article

Open access