Polyurethane-based poly (ionic liquid)s for CO2 removal from natural gas

Carbon dioxide separation from CH₄ is important to the environment and natural gas processing. Poly (ionic liquid)s (PILs) based on polyurethane structures are considered as potential materials for CO₂ capture. Thus, a series of anionic PILs based on polyurethane were synthesized. The effects of polyol chemical structure and counter-cations (imidazolium, phosphonium, ammonium, and pyridinium) in CO₂ sorption capacity and CO₂/CH₄ separation performance were evaluated. The synthesized PILs were characterized by NMR, DSC, TGA, dinamical mechanical thermo analysis (DMTA), SEM, and AFM. CO₂ sorption, reusability, and CO₂/CH₄ selectivity were assessed by the pressure-decay technique. The counter-cation and polyol chemical structure play an important role in CO₂ sorption and CO₂/CH₄ selectivity. PILs exhibited competitive thermal mechanical properties. Results showed that PILPC-TBP was the best poly (ionic liquid) for CO₂/CH₄ separation. Moreover, poly (liquid ionic) base polyol (polycarbonate) with phosphonium (PILPC-TBP) demonstrated higher CO₂ sorption capacity (21.4 mgCO₂/g at 303.15 K and 0.08 MPa) as compared to other reported poly (ionic liquids). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47536.     

Functional mesoporous poly(ionic liquid)-based copolymer monoliths: From synthesis to catalysis and microporous carbon production

Ionic liquid-functionalized mesoporous polymeric networks with specific surface area up to 935 m²/g have been successfully synthesized one pot by solvothermal copolymerization of divinylbenzene and monomeric ionic liquids. The as-obtained polymers exhibit a monolithic structure featuring large pore volumes, an abundant mesoporosity and an adjustable content of ionic liquids. The effect of the reaction conditions on the pore structure has been studied in detail. These poly(ionic liquid)-based porous networks (PILPNs) have then been employed as precursors in two distinct applications, namely organocatalysis and production of microporous carbon monoliths. Selected organocatalyzed reactions, including carbonatation of propylene oxide by cycloaddition with carbon dioxide, benzoin condensation, and cyanosilylation of benzaldehyde have been readily triggered by PILPNs acting as crosslinked polymer-supported (pre)catalysts. The two latter reactions required the prior deprotonation of the imidazolium salt units with a strong base to successfully generate polymer-supported N-heterocyclic carbenes, referred to as poly(NHC)s. Facile recycling and reuse of polymer-supported (pre)catalysts was achieved by simple filtration owing to the heterogeneous reaction conditions. Furthermore, PILPNs could be easily converted into microporous carbon monoliths via CO₂ activation.     

Tailoring the pore structure of PCL scaffolds for tissue engineering prepared via gas foaming of multi-phase blends

The aim of this study was the design of poly(ε-caprolactone) (PCL) scaffolds characterized by well controlled pore structures obtained by gas foaming of multi-phase blends of PCL and thermoplastic gelatin (TG). Co-continuous blends made of PCL and TG were prepared by melt mixing and, subsequently gas foamed in an autoclave to induce the formation of the porous network. A mixture of N₂ and CO₂ was used as blowing agent and the foaming process performed at temperature higher than PCL melting, in the range 70–110 °C. The foams were finally soaked in water at 37 °C to selectively extract the TG and achieve the final pore structure. The results of this study demonstrated that the proposed approach allowed to tailor the micro-structural properties of PCL scaffolds for tissue engineering.     

Controllable preparation of porous ZrB2–SiC ceramics via using KCl space holders

In this work, a novel and facile technique based on using KCl as space holders, along with partial sintering (at 1900 °C for 30 min), was explored to prepare porous ZrB₂–SiC ceramics with controllable pore structure, tunable compressive strength and thermal conductivity. The as-prepared porous ZrB₂–SiC samples possess high porosity of 45–67%, low average pore size of 3–7 μm, high compressive strength of 32–106 MPa, and low room temperature thermal conductivity of 13–34 W m⁻¹ K⁻¹. The porosity, pore structure, compressive strength and thermal conductivity of porous ZrB₂–SiC ceramics can be tuned simply by changing KCl content and its particle size. The effect of porosity and pore structure on the thermal conductivity of as-prepared porous ZrB₂–SiC ceramics was examined and found to be consistent with the classical model for porous materials. The poring mechanism of porous ZrB₂–SiC samples via adding pore-forming agent combined with partial sintering was also preliminary illustrated.     

Environment-oriented low-cost Al2O3 ceramics with hierarchical pore structure fabricated from SiC solid waste

Environment-oriented low-cost Al₂O₃ reticulated porous ceramics with hierarchical pore structure were fabricated by the polymer sponge replica method combined with vacuum infiltration methods, using Al₂O₃ powders and SiC solid waste (SCSW) as raw material and a pore-forming agent. The effects of SCSW addition amount on mechanical properties, microstructure and pore size of Ceramics were investigated. The results showed that the thermal shock resistance of specimens increased gradually with addition of SCSW, however, the median pore diameter increased firstly and then decreased, due to the generation of mullite and liquid phase. After calcination, the residual stress was generated within the coating layer because of the difference in the thermal expansion coefficients of ceramic matrix and coating layer, which could improve the properties of Ceramics by deflecting and bifurcating crack growth path. The results showed that the best dosage of SCSW was 30 wt%.     

A new approach of ionic liquid containing polymer sorbents for post-combustion CO2 scrubbing

Room temperature task-specific ionic liquids (TSIL) of 1-(2-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Im₂₁OH][Tf₂N]) or 2-hydroxyethyl(dimethyl)-isopropylammonium bis(trifluoromethylsulfonyl)imide ([N_ip,211OH][Tf₂N]) with superbase, 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU), has been combined with Torlon^® powders (<106 um) to simulate the potential benefits of integrating equimolar amounts of ionic liquids and superbase into hollow fibers in terms of both sorption uptake and kinetics. Approximately 44 wt% of an equimolar [Im₂₁OH][Tf₂N]-DBU in Torlon^® powders achieved CO₂ sorption uptake of 0.57 mmol CO₂/g at a CO₂ feed pressure of 0.1 atm and at 35 °C. Similar amounts of an equimolar [N_ip,211OH][Tf₂N]-DBU in Torlon^® powders showed CO₂ sorption uptake of 0.45 mmol CO₂/g at the same condition. The half time (time to reach M_t/M_∞ of 0.5) for Torlon^®, Torlon^®(62 mg)/[Im₂₁OH][Tf₂N]-DBU(48 mg) and [Im₂₁OH][Tf₂N]-DBU at low feed pressure (～1.5 psia CO₂) was approximately 4, 55, and 298 s, respectively demonstrating that imbibing an equimolar [Im₂₁OH][Tf₂N]-DBU into polymer powders substantially improved sorption kinetics compared to the neat counterpart. The sorption half time is expected to be even shorter for fibers with smaller characteristic polymer morphology domains. The current study also demonstrates a new experimental approach to characterize CO₂ sorption in an equimolar mixture of ionic liquids and superbase.     

New crosslinked-porous poly-ammonium microparticles as CO2 adsorbents

A new porous polymeric microparticle, poly[4-vinylbenzyltriethylammonium chloride] (P[VBTEA][Cl]), is prepared from the crosslinking polymerization of 4-vinylbenzyltriethylammonium chloride with N,N-methylenebisacrylamide via inverse suspension polymerization using cyclohexane as continuous phase, Span 80-Tween 80 as dispersant, and PEG600 as porogen. Two other microparticles, P[VBTEA][BF₄] and P[VBTEA][PF₆] are further obtained through ion-exchange. FT-IR, TGA, SEM, and EDS analyzes indicate that these microparticles have good porosity (apparent porosities are 55.0%, 69.7% and 64.3%, respectively), high thermal stability, and large specific surface area, which make them potentially applicable as adsorbent agents. Their CO₂ adsorption–desorption performance is investigated. It is observed that such porous polymeric microparticles present high CO₂ sorption capability; typically, the CO₂ sorption of P[VBTEA][PF₆] is 1.38 wt% at 25 °C and 1 bar. Such porous polymeric microparticles are good candidates for CO₂ adsorption.     

Preparation of calcium hexaluminate porous ceramics by gel-casting method with polymethyl methacrylate as pore-forming agent

Calcium hexaluminate (CA₆) porous ceramics were prepared by gel-casting method, with α-Al₂O₃ and CaCO₃ as raw materials and polymethyl methacrylate (PMMA) microspheres as pore-forming agent. The effects of the amount of pore-forming agent PMMA microspheres on the phase composition, bulk density, apparent porosity, flexural strength, microstructure, thermal shock stability and thermal conductivity of CA₆ porous ceramics were systematically studied. The pores of CA₆ porous ceramics are mainly formed by the burning loss of PMMA microspheres and the decomposition of organic matter. Adding an appropriate amount of PMMA microspheres as pore-forming agent has a positive effect on the thermal shock stability of CA₆ porous ceramics. When the amount of pore-forming agent is 15 wt%, the volume density of CA₆ porous ceramics is 1.33 g/cm³, the porosity is 63%, the flexural strength is 13.9 MPa, the thermal shock times can reach 9 times, and the thermal conductivity is 0.293 W/(m·K), which can meet the application in refractory, ceramics or high temperature cement industries.     

Petroleum products and water sorption by expanded graphite enhanced with magnetic iron phases

The liquid hydrocarbon sorption behavior of expanded graphite (EG) enhanced with iron phases (α-Fe, α-Fe₂O₃, Fe₃O₄, and FeOOH) was studied. Iron phases were shown not to affect the porous structure of EG or its sorption capacity. The utilization of the three EG samples with the high magnetic saturation (10.5, 30, and 35 emu/g) as magnetic sorbents for the petroleum products spill response was considered. The requirements in values of the magnetic saturation of EG to be attracted by a magnet were estimated. Also, the water sorption of EG was studied, which competes with liquid hydrocarbons for pore spaces. The method of the dynamic contact angle measurement in water is suggested as a useful characterization of EG surface chemistry for this application.     

A novel strategy for synthesizing porous ZrB2-SiC ceramics via boro/carbothermal reaction process templated pore-forming approach

In this work, pure ZrB₂-SiC composite powders were obtained using ZrO₂, SiO₂, B₄C and carbon black as raw materials via a boro/carbothermal reduction (BCTR) reaction process at 1500 °C for 2 h in vacuum condition. Based on this finding, porous ZrB₂-SiC ceramics were in-situ synthesized via a novel and facile boro/carbothermal reaction process templated pore-forming (BCTR-TPF) method. The phase composition, linear shrinkage, and pore size distribution were also methodically studied. Results show that the porous ZrB₂-SiC ceramics with controllable porosity of 67–78%, compressive strength of 0.2–9.8 MPa and thermal conductivity of 1.9–7.0 W·m⁻¹K⁻¹ can be fabricated by varying of ZrO₂ and B₄C particle sizes. The formation of ZrB₂ grains was controlled via solid-solid and solid-liquid-solid growth mechanisms, the growth process of SiC grains was mainly regulated by solid-solid, vapor-vapor and vapor-solid growth mechanisms during the overall synthesis process. Finally, the pore-forming mechanism of porous samples prepared via the BCTR-TPF method was gases combined with template pore-forming mechanism, i.e., B₄C and carbon black acted as pore-forming templates, and gaseous products generated in the BCTR reaction were also applied as gas pore-forming agent.     

Pore development during gasification of South African inertinite-rich chars evaluated using small angle X-ray scattering

Pore development arising from steam and CO₂ gasification of a char, prepared from an inertinite-rich Witbank Seam 4 coal, was investigated using small angle X-ray scattering. The char, ∼75 μm, was gasified to specific conversions (10, 25, 35 and 50%) using two gasification reagents, CO₂ and steam. A novel ratio analysis technique was developed to study the pore development from experimental data. Differently sized pores grow at different rates with the difference not being simply due to gas accessibility. In particular, the pores between 1 and 40 nm in size showed more pore growth than larger or smaller sizes. Steam gasification created a more porous char with increased pore growth of pore sizes between 1 and 40 nm than CO₂ gasification. The pore growth rate of steam was up to a factor 7 times faster than CO₂, compared at the highest gasification temperatures. For the smaller pores, <1 nm, it was found that the rate of pore generation was slower compared to larger pores, though pore growth was still evident with the critical cross over pore size for CO₂ to be 1 nm compared to 0.6 nm for steam. This may be a direct consequence of CO₂'s greater kinetic diameter.     

Tailored pore structures and mechanical properties of porous alumina ceramics prepared with corn cob pore-forming agent

In this work, the effects of porosity and different particle sizes of pore-forming agent on the mechanical properties of porous alumina ceramics have been reported. Different grades of porous alumina ceramics were developed using corn cob (CC) of different weight contents (5, 10, 15, and 20 wt%) and particle sizes (<63 µm, 63-125 µm and 125-250 µm) as the pore-forming agent. Experimental results showed that total porosity and pore cavity size of the porous alumina ceramics increased with rising addition of CC pore former. Total porosity increased with increasing particle size of CC with the Al₂O₃-^<63CC₅ sample exhibiting the lowest total porosity of 41.3 vol% while the highest total porosity of 68.1 vol% was exhibited by the Al₂O₃-^125-250CC₂₀. The particle size effect of CC on the mechanical properties revealed that diametral tensile strength and hardness of the porous alumina ceramics deteriorated with increasing particle size of CC pore former. The Al₂O₃-^<63CC₅ sample exhibited the highest diametral tensile strength and hardness of 25.1 MPa and 768.2 HV, respectively, while Al₂O₃-^125-250CC₂₀ exhibited the lowest values of 1.1 MPa and 35.9 HV. Overall, porous alumina ceramics with the smallest pore sizes under each particle size category exhibited superior mechanical properties in their respective categories.     

Characterization of the porous structure of biodegradable scaffolds obtained with supercritical CO<Subscript>2</Subscript> as foaming agent

Poly(ε-caprolactone) foams were prepared, via a batch process, by using supercritical CO₂ as foaming agent. Their porous structure was characterized through mercury porosimetry, helium and mercury pycnometry, scanning electron microscopy (SEM) and X-ray microtomography observations coupled with image analysis. The pore size distributions obtained by these two latter techniques show that the pore structure is more homogeneous when the foaming process is performed under a high CO₂ saturation pressure (higher than 250 bars).     

Silicate and zirconium phosphate modified Nafion/PTFE composite membranes for high temperature PEMFC

The PEMFC performance of MEAs prepared from Nafion-212 (thickness 50 μm, Du Pont Co), porous poly(tetrafluoro ethylene) (PTFE, thickness 15 ~ 18 μm) film reinforced Nafion (NF, thickness 20 ± 2 μm), silicate hybridized NF (NF-Si, thickness 21 ± 2 μm), and zirconium phosphate hybridized NF (NF-Zr, thickness 21 ± 2 μm) membranes were investigated at 110 °C/ 51.7% RH, 120 °C/ 38.2% RH, and 130 °C/ 28.6% RH. We show PEMFC performances of these MEAs decrease in the sequence of: NF-Zr> NF-Si> NF> Nafion-212. The NF, NF-Si, and NF-Zr membranes have lower membrane thickness and lower Nafion content and require less water for proton transport than Nafion-212 at temperatures above 110 °C, and thus have higher conductivity and better PEMFC performance than Nafion-212. Incorporating silicate and zirconium phosphate into NF membranes enhances water retention of membranes at temperatures above 110 °C and improves PEMFC performances. Besides enhancing water retention, incorporating zirconium phosphate into membranes also provides more routes for proton transport via H⁺ exchange between H₃ ⁺O and HPO₄-Zr- and between H₂ ⁺PO₄-Zr- and HPO₄-Zr-. Thus NF-Zr has a higher conductivity and better PEMFC performance than NF and NF-Si.     

Synthesis,structure and gas adsorption properties of a microporous metal–organic framework assembled from a semi-rigid tripodal carboxylic acid ligand

The design, synthesis, and structural characterization of a new cubic three-dimensional microporous metal–organic framework featuring a semi-rigid tripodal carboxylic acid ligand, 4,4′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H₃cpbda), is reported. Single-crystal X-ray diffraction analysis indicates that compound 1 possesses a novel (3,4,4)-connected network with the point symbol of {8³}₄{8⁴·10²}₂{8⁶}. In the framework of 1, there co-exist two types of 1D channels with different pore size (15 Å and 4.5 Å). The pore characteristics and gas sorption properties of this compound were investigated both at cryogenic temperatures and room temperature by experimentally measuring N₂ and CO₂ sorption isotherms. These studies show that compound 1 is highly porous with a pore volume of 0.98 cm³/g and BET surface of 1926 cm³/g. In addition, the activated 1 also shows excellent CO₂ storage capacity around room temperature.     

Polyamide-silica gel hybrids containing metal salts: Preparation via the sol-gel reaction

The hydrolysis and condensation of tetramethoxysilane in a DMF solution of polyamides containing LiCl, CaCl₂ or ZnCl₂, both in presence and absence of polyoxazoline, resulted in the facile formation of polyamide-silica gel hybrids. Films were cast from the resulting mixtures and evaporation of the solvent resulted in the formation of clear, transparent hybrids with the salts dispersed at the molecular level. Pyrolysis of hybrids at 600 °C gave porous silica. Pore size and surface characteristics of these silica gel samples indicated a porous nature with a pore radius of 1.1 nm for silica gels obtained from hybrids HPA-6 (containing no salt) and HPA-9 (containing ZnCl₂) and a surface area of 213 m² g⁻¹ and 310 m² g⁻¹, respectively. Silica gel from hybrid HPA-7 (containing LiCl) had a pore radius of 1.9 nm and a surface area of 15 m² g⁻¹. The silica gel samples obtained from hybrids HPA-6, HPA-7 and HPA-9 exhibited narrow slit-like pores with a pore volume of 0.68 cm³ g⁻¹. Received: 7 January 1997/Accepted: 6 March 1997     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.     

Ionic liquid modified poly(2,6-dimethyl-1,4-phenylene oxide) for CO2 separation

Ionic liquid modified poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was synthesized by introducing imidazolium-based, pyridinium-based, and ammonium-basd ionic liquid groups to the methyl position of PPO. Membranes were prepared from the different types of ionic liquid modified PPO (IPPO), and the permeability of CO₂ and N₂ in these membranes was characterized. For having the CO₂-philic ionic liquid groups in the structure, the CO₂ solubility of the IPPO is better than that of PPO, while the CO₂ diffusivity in the IPPO is proportional to glass transition temperatures. The adsorption and desorption of CO₂ in the IPPO were also investigated, and the results manifest that the adsorption and desorption of CO₂ in IPPO are completely reversible, which makes the polymer promising as solid adsorbent materials for CO₂ separation.     

Formation of porous glass via core/shell-structured poly(methyl methacrylate)/powder glass prepared by ultrasonic irradiation in liquid CO2

The formation of porous glass ceramic via core/shell-structured poly(methyl methacrylate)(PMMA)/powder glass was investigated. Core/shell structures were prepared via ultrasonic irradiation in high-pressure liquid carbon dioxide (CO₂) using PMMA microspheres as the core material and glass powder as the shell material. The mean particles sizes of PMMA template microspheres and glass powder were 9.8 μm and 0.9 μm, respectively. After removal of the PMMA template by calcination in air, porous glass was obtained. The products were characterized by scanning electronic microscopy (SEM) and thermogravimetric-differential thermal analysis (TG-DTA). The average pore diameter of porous glass was 4.3 μm. Compared with porous glass prepared by the other method, the porous glass prepared by ultrasonic irradiation of liquid CO₂ was achieved the narrow pore size distribution (CV = 35%) and the higher porosity (89%). The pores are not isolated and connected each other. Furthermore, the effects of experimental conditions, such as coating method, crosslink density of the template PMMA microspheres, ultrasonic intensity and calcination temperature, on the product morphology were investigated. The higher ultrasound intensity achieved the uniform coating of PMMA templates with powder glass. The calcination temperature and crosslinked density of PMMA template microspheres affect the pore structure.     

Effect of crosslinking structure on sorption of CO2 in photocrosslinked PVCA film

The sorption behavior of CO₂ gas in photocrosslinked poly(vinyl cinnamate) film was examined under atmospheric pressure. The sorption isotherm was well described by the Langmuir equation, suggesting that sorption of CO₂ is mainly governed by adsorption in the microvoids. The amount of sorbed CO₂ was significantly affected by the degree of crosslinking. The CO₂ sorption was enhanced at a lower degree of crosslinking but was decreased at a higher degree of crosslinking. The unexpected increase in the amount of adsorbed CO₂ correlated with the increase in the number of microvoids that occurred as a result of the crosslinking reaction. However, further crosslinking led to a decrease in the mean size of the microvoids. The smaller microvoids, in comparison to CO₂ molecules, did not act as adsorption sites, so that the amount of sorbed CO₂ decreased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1744–1750, 2000