High performance and commercially attractive mixed-matrix membranes were developed for H2/CO2 separation via a scalable hollow fiber spinning process. Thin (~300 nm) and defect-free selective layers were successfully created with a uniform distribution of the nanosized (~60 nm) zeolitic-imidazole framework (ZIF-8) filler within the polymer (polybenzimidazole, PBI) matrix. These membranes were able to operate at high temperature (150 °C) and pressure (up to 30 bar) process conditions required in treatment of pre-combustion and syngas process gas streams. Compared with neat PBI hollow fibers, filler incorporation into the polymer matrix leads to a strong increase in H2 permeance from 65 GPU to 107 GPU at 150 °C and 7 bar, while the ideal H2/CO2 selectivity remained constant at 18. For mixed gas permeation, there is competition between H2 and CO2 transport inside ZIF-8 structure. Adsorption of CO2 in the nanocavities of the filler suppresses the transport of the faster permeating H2 and consequently decreases the H2 permeance with total feed pressure down to values equal to the pure PBI hollow fibers for the end pressure of 30 bar. Therefore, the improvement of fiber performance for gas separation with filler addition is compromised at high operating feed pressures, which emphasizes the importance of membrane evaluation under relevant process conditions.@en

Clathrates are well-known compounds whose low thermal stability makes them extremely rare and appreciated. Although their formation mechanism is still surrounded by many uncertainties, these ice-like structures have the potential to be an alternative for transport and storage of different gases, especially methane. For the formation of methane clathrates extreme pressure conditions and a narrow temperature window are needed. Microporous materials have been proposed to provide nucleation sites that, theoretically, promote clathrate formation at milder conditions. While activated carbons and Metal-Organic Frameworks (MOFs) have already been studied, very little is known about the role of zeolites in this field. In this work, we study the formation of methane clathrates in the presence of RHO zeolite. Experimental results based on adsorption and operando synchrotron X-Ray diffraction demonstrate the formation of clathrates at the surface of the zeolite crystals and reveal mechanistic aspects of this formation at mild conditions.@en

Xe is only produced by cryogenic distillation of air, and its availability is limited by the extremely low abundance. Therefore, Xe recovery after usage is the only way to guarantee sufficient supply and broad application. Herein we demonstrate DD3R zeolite as a benchmark membrane material for CO2/Xe separation. The CO2 permeance after an optimized membrane synthesis is one order magnitude higher than for conventional membranes and is less susceptible to water vapour. The overall membrane performance is dominated by diffusivity selectivity of CO2 over Xe in DD3R zeolite membranes, whereby rigidity of the zeolite structure plays a key role. For relevant anaesthetic composition (<5 % CO2) and condition (humid), CO2 permeance and CO2/Xe selectivity stabilized at 2.0×10−8 mol m−2 s−1 Pa−1 and 67, respectively, during long-term operation (>320 h). This endows DD3R zeolite membranes great potential for on-stream CO2 removal from the Xe-based closed-circuit anesthesia system. The large cost reduction of up to 4 orders of magnitude by membrane Xe-recycling (>99+%) allows the use of the precious Xe as anaesthetics gas a viable general option in surgery.@en

Xe is only produced by cryogenic distillation of air, and its availability is limited by the extremely low abundance. Therefore, Xe recovery after usage is the only way to guarantee sufficient supply and broad application. Herein we demonstrate DD3R zeolite as a benchmark membrane material for CO2/Xe separation. The CO2 permeance after an optimized membrane synthesis is one order magnitude higher than for conventional membranes and is less susceptible to water vapour. The overall membrane performance is dominated by diffusivity selectivity of CO2 over Xe in DD3R zeolite membranes, whereby rigidity of the zeolite structure plays a key role. For relevant anaesthetic composition (<5 % CO2) and condition (humid), CO2 permeance and CO2/Xe selectivity stabilized at 2.0×10−8 mol m−2 s−1 Pa−1 and 67, respectively, during long-term operation (>320 h). This endows DD3R zeolite membranes great potential for on-stream CO2 removal from the Xe-based closed-circuit anesthesia system. The large cost reduction of up to 4 orders of magnitude by membrane Xe-recycling (>99+%) allows the use of the precious Xe as anaesthetics gas a viable general option in surgery.@en

The use of an azine-linked covalent organic framework (ACOF-1) as filler in mixed-matrix membranes (MMMs) has been studied for the separation of CO2 from N2. To better understand the mechanisms that govern separation in complex composites, MMMs were prepared with different loadings of ACOF-1 and three different polymers as continuous phase: low flux-mid selectivity Matrimid®, mid flux-high selectivity Polyactive™ and high flux-low selectivity 6FDA:DAM. The homogeneous distribution of ACOF-1 together with the good adhesion between the ACOF-1 particles and the polymer matrices were confirmed by scanning electron microscopy. In mixed-gas CO2/N2 separation a clear influence of the polymer used was observed on the performance of the composite membranes. While for Matrimid® and 6FDA:DAM an overall enhancement of the polymer's separation properties could be achieved, in case of Polyactive™ penetration of the more flexible polymer into the COF porosity resulted in a decreased membrane permeability. The best improvement was obtained for Matrimid®-based MMMs, for which a selectivity increase from 29 to 35, together with an enhancement in permeability from 9.5 to 17.7 Barrer for 16 wt% COF loading, was observed. Our results demonstrate that the combination of the filler-polymeric matrix pair chosen is crucial. For a given filler the polymer performance improvement strongly depends on the polymeric matrix selected, where a good match between the discontinuous and continuous phase, both in the terms of compatibility and gas separation properties, is necessary to optimize membrane performance.@en

In a world where capture and separation processes represent above 10% of global energy consumption, novel porous materials, such as Metal-Organic Frameworks (MOFs) used in adsorption-based processes are a promising alternative to dethrone the high-energy-demanding distillation. Shape and size tailor-made pores in combination with Lewis acidic sites can enhance the adsorbate-adsorbent interactions. Understanding the underlying mechanisms of adsorption is essential to designing and optimizing capture and separation processes. Herein, we analyze the adsorption behaviour of light hydrocarbons (methane, ethane, ethylene, propane, and propylene) in two synthesized copper-based MOFs, Cu-MOF-74 and URJC-1. The experimental and computational adsorption curves reveal a limited effect of the exposed metal centers on the olefins. The lower interaction Cu-olefin is also reflected in the calculated enthalpy of adsorption and binding geometries. Moreover, the diamond-shaped pores' deformation upon external stimuli is first reported in URJC-1. This phenomenon is highlighted as the key to understanding the adsorbent's responsive mechanisms and potential in future industrial applications.@en

A mathematical model is used to predict adsorption isotherms from experimentally measured breakthrough curves. Using this approach, by performing only breakthrough experiments for a mixture of two (or more) components, one can obtain pure component adsorption isotherms up to the pressure of the experiment. As a case study, the adsorption of an equimolar mixture of CO2 and CH4 in zeolite ITQ-29 is investigated. Pure component linear adsorption isotherms for CO2 and CH4 are predicted by fitting the theoretical breakthrough curves to the experimental ones. Henry coefficients obtained from our approach are in excellent agreement with those measured experimentally. A similar procedure is applied to predict the complete Langmuir adsorption isotherm from breakthrough curves at high pressures. The resulting adsorption isotherms are in very good agreement with those measured experimentally. In our model for transient adsorption, mass transfer from the gas phase to the adsorbed phase is considered using the Linear Driving Force model and dispersion of the gas phase in the packed bed is taken into account. IAST is used to compute the equilibrium loadings for a mixture of gases. The influence of the dispersion coefficient and the effective mass transfer coefficient on the shape of breakthrough curves is investigated and discussed. Rough estimations of these values are sufficient to predict adsorption isotherms from breakthrough curves.@en

Separation of propylene/propane is one of the most challenging and energy consuming processes in the chemical industry. Propylene demand is increasing and a 99.5% purity is required for industrial purposes. Adsorption based solutions are the most promising alternatives to improve the economical/energetic efficiency of the process. Zeolitic Imidazolate Frameworks (ZIFs) combine the desired characteristics from both MOFs and zeolites: tunability and flexibility from metal organic frameworks, and exceptional thermal and chemical stability from zeolites. In order to enlighten the role of the cation in the sodalite ZIF-8 framework for propane/propylene separation, dynamic breakthrough measurements have been performed over ZIF-8(Zn), ZIF-67 (i.e. ZIF-8(Co)) and MUV-3 (i.e. ZIF-8(Fe)), all isostructural materials based on the same linker (2-methylimidazole). Cation substitution has a remarkable influence in the framework flexibility, and, consequently, in SOD-ZIF selectivity for light hydrocarbons. The differences between the crystallographic pore sizes of the material and the molecular dimensions of propane and propylene are so small, that the slightest change in the framework causes notable advantages/disadvantages in the final application. While cobalt is known to promote a more rigid framework resulting in an adsorption selectivity towards propane, iron presents the inverse effect yielding selectivity to propylene. Zinc has an intermediate effect. A threshold pressure in the isotherm is observed for propylene uptake by ZIF-67 at 273 and 298 K, and only at the lower temperature for ZIF-8. Inlet mixture composition does not highly influence the adsorptive selectivity, although it clearly affects the pure hydrocarbon recovery. Over ZIF-67 breakthrough experiments at 298 K yield a temporary pure propylene flow representing 10–15% of the amount fed. ZIF-67 is a promising candidate for propylene/propane adsorptive separation.@en

The cobalt-based ZIF-67 has been evaluated for the adsorptive propylene/propane separation in a fixed bed. Characterization techniques and dynamic measurements have been performed over ZIF-67 to evaluate its potential in this defiant process. Cobalt promotes a more rigid framework than zinc in the isostructural ZIF-8. Although the adsorption affinity of ZIF-67 for both hydrocarbons is similar, the lower flexibility of the framework makes ZIF-67 behave with a clear preference towards propane. This inverse selectivity promotes the enrichment in propylene content upon breakthrough, and may simplify the separation scheme. Therefore, ZIF-67 adsorptive separation is presented as an alternative to energy-demanding distillation.@en

Biobased 2-butanol offers high potential as biofuel, but its toxicity toward microbial hosts calls for efficient techniques to alleviate product inhibition in fermentation processes. Aiming at the selective recovery of 2-butanol, the feasibility of a process combining in situ vacuum stripping followed by vapor adsorption has been assessed using mimicked fermentation media. The experimental vacuum stripping of model solutions and corn stover hydrolysate closely aligned with mass transfer model predictions. However, the presence of lignocellulosic impurities affected 2-butanol recovery yields resulting from vapor condensation, which decreased from 96 wt % in model solutions to 40 wt % using hydrolysate. For the selective recovery of 2-butanol from a vapor mixture enriched in water and carbon dioxide, silicalite materials were the most efficient, particularly at low alcohol partial pressures. Integrating in situ vacuum stripping with vapor adsorption using HiSiv3000 proved useful to effectively concentrate 2-butanol above its azeotropic composition (>68 wt %), facilitating further product purification.@en

This thesis, Gas Adsorptive Separation through Microporous Materials, presents the research done on gas separation processes in the Catalysis Engineering team. This thesis intends to collect the knowledge and results of five years’ experimental research dealing with gas mixtures and microporous materials, but also with tubing, and setup maintenance and designing. This thesis contains a first introduction chapter, four research chapters (based on journal publications) and this last summarizing chapter with an outlook about the field of adsorption regarding the thesis' results.@en