Highly efficient and reversible CO2 capture by tunable anion‐functionalized macro‐porous resins

Anion functionalized strategy has been proposed for the synthesis of macro‐porous resins [IRA‐900][An] through the neutral reaction of the basic resin [IRA‐900][OH] with the corresponding donors. Combining CO₂ adsorption results and FT‐IR, solid‐state ¹³C NMR characterization as well as quantum chemical calculations, chemical adsorption mechanism was verified and tunable capture of CO₂ was realized. Among them, the anion functionalized resin [IRA‐900][Triz] exhibits an extremely high adsorption capacity (4.02 mmol g^?1 at 25°C, 0.15 bar), outperforming many other good adsorbents. Finally, we discuss the thermostability and recycling stability of [IRA‐900][Triz], which shows a great potential in the industrial capture of CO₂. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3008–3015, 2017     

Low‐Temperature Synthesis of Mesoporous SiC Hollow Spheres by Magnesiothermic Reduction

Mesoporous silicon carbide hollow spheres (SiC‐HS) with a large specific surface area (690.2 m² g^?1) are synthesized at a relatively low temperature of 650°C by magnesiothermic reduction using the template of carbon‐coated mesoporous silica hollow spheres and molten salt as the heat absorbent and solvent. The mesoporous SiC‐HS comprising many small primary crystals (2–4 nm) with a well‐maintained microstructure have good thermal stability and adsorption ability, and are promising as adsorbents to remove organic pollution from water. The synthesis technique can be extended to other nanostructured carbide ceramic materials.     

CO2 capture efficiency in post‐combustion using MWNT‐PAA in a packed bed column

The adsorption capacity of polyaspartamide (PAA) and multi‐wall carbon nanotubes with polyaspartamide (MWNT‐PAA) was investigated through a packed bed column with the flowing of flue gas composed of 15 % CO₂, 5 % O₂ and the balance N₂. The adsorption performed at 25 °C, 110 kPa and inlet gas flow rate of 60 mL/min resulted in high CO₂ adsorption capacity of 5.70 and 10.20 mmol‐CO₂/g for PAA and MWNT‐PAA, respectively. The adsorption kinetics was very high, so 7 min were enough for the effluent gas to reach the breakthrough after saturation. The consistency of adsorbents in recurring regeneration was successful through a continuous TSA system of 10 cycle adsorption‐desorption with temperatures of 25–100 °C. The evaluation of heat through differential scanning calorimetry (DSC) resulted in exothermic adsorption with heat release of 45.14 kJ/mol and 124.38 kJ/mol for PAA and MWNT‐PAA, respectively. The heat release was found favourable to promote the desorption as the temperature could rise after adsorption. This is an advantage for energy efficiency, as it depicts the potential of energy recovery. Thus, both adsorbent PAA and MWNT‐PAA were demonstrated to be promising for CO₂ adsorption capture in post‐combustion.     

Adsorption and heat‐energy‐aid desorption of cationic dye on a new thermo‐sensitive adsorbent: Methyl cellulose/calcium alginate beads

The adsorption and heat‐energy‐aid desorption of methylene blue (MB) on a thermo‐sensitive adsorbent of methyl cellulose/calcium alginate beads (MC/CABs) has been studied. The addition of methyl cellulose intensified the desorption ability of adsorbent, and boosted the difference of adsorption capacity of adsorbent between low temperature and high temperature. At the mass ratio of methyl cellulose to sodium alginate of 2:1, the difference of adsorption capacity of MC/CABs between 20 and 60°C reached 20.48 mg g^?1. The effects of temperature, time and initial MB concentration on adsorption performance were investigated in detail. The MB adsorption on MC/CABs followed the pseudo‐second‐order kinetic model. The equilibrium data was fitted well with Langmuir isotherm. The maximum adsorption capacity of 336.70 mg g^?1 exhibited MC/CABs had a good adsorption capability. Thermodynamic analyses showed high temperature was not favorable to MB adsorption, and MC/CABs had a distinct superiority in desorption of adsorbate with heat‐energy‐aid. Lastly, the possible mechanisms involving in adsorption and heat‐energy‐aid desorption were presented. POLYM. ENG. SCI., 56:1382–1389, 2016. © 2016 Society of Plastics Engineers     

A novel carbonized polydopamine (C‐PDA) adsorbent with high CO2 adsorption capacity and water vapor resistance

Novel carbonized polydopamine adsorbents (C‐PDAs) with high surface area, high CO₂ adsorption capacity and superior moisture resistance performance were prepared by one‐step synthesis method using polydopamine as carbon precursor at different KOH/C ratios, and then characterized. CO₂ and water vapor adsorption performances of C‐PDAs were examined separately by static adsorption and fixed‐bed experiments. Results showed that BET area and pore volume of C‐PDA‐4 were up to 3342 m²/g and 2.01 cm³/g, respectively. Its CO₂ adsorption capacity reached up to 30.5 mmol/g at 25 bar, much higher than many other adsorbents including metal‐organic frameworks (MOFs). C‐PDAs prepared with high KOH/C ratios had low surface element concentrations of O and N resulting in low surface hydrophilic property. H₂O(g) isotherm of C‐PDA was much lower than those on Mg‐MOF‐74, Cu‐BTC, and MIL‐101(Cr). Fixed‐bed experiments showed that co‐presence of water vapor in feed stream with 30% RH had negligible impact on CO₂ working capacity of C‐PDA. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3730–3738, 2016     

Synthesis of Nanofiber‐like Mesoporous γ‐Al2O3 toward Its Adsorption Efficiency for Congo Red

Nanofiber‐like mesoporous γ‐Al₂O₃ was synthesized using freshly prepared boehmite sol in the presence of triblock copolymer, P123 following evaporation‐induced self‐assembly (EISA) process followed by calcinations at 400°C–1000°C. The samples were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X‐ray diffraction (XRD), N₂ adsorption–desorption, and transmission electron microscopy (TEM). The adsorption efficiency of the samples with Congo red (CR) was studied by UV – vis spectroscopy. XRD results showed boehmite phase in the as‐prepared sample while γ‐Al₂O₃ phase obtained at 400°C was stable up to 900°C, a little transformation of θ‐Al₂O₃ resulted at 1000°C. The Brunauer‐Emmett‐Teller surface area of the 400°C‐treated sample was found to be 175.5 m²g ^{? 1}. The TEM micrograph showed nanofiber‐like morphology of γ‐Al₂O_3. The 400°C‐treated sample showed about 100% CR adsorption within 60 min.     

CO<Subscript>2</Subscript> adsorption at high pressures in MCM-41 and derived alkali-containing samples: the role of the textural properties and chemical affinity

The adsorption properties of N₂ and CO₂ of MCM-41 and derived alkali-containing samples were analyzed over a wide range of pressures (up to ~4500 kPa) and temperatures (between 30 and 300 °C). The high-pressure and high-temperature experiments were carried out on pure MCM-41 and K- and Na-impregnated derived samples. It was analyzed the influence of pressure and temperature on the CO₂ capture capacity on pure and impregnated samples. The adsorption performance was correlated to the structure and textural properties of the materials using X-ray diffraction and N₂ adsorption–desorption measurements. The addition of an alkaline element changes the textural properties of the material increasing the pore size, which positively affected the CO₂ adsorption capacity of these materials at high pressure. In addition, the isosteric heats of adsorption gave information about the chemical affinity between the impregnated materials and CO₂. The CO₂ adsorption at ~ 4500 kPa for the samples with 5 wt% Na at 100 and 200 °C were 77.98 and 9.79 mmol g^?1, respectively, while the pure MCM-41 adsorbs only 8.92 mmol g^?1.     

Potassium salt-assisted synthesis of highly microporous carbon spheres for CO2 adsorption

Highly microporous carbon spheres for CO₂ adsorption were prepared by using a slightly modified one-pot Stöber synthesis in the presence of potassium oxalate. Formaldehyde and resorcinol were used as carbon precursors, ammonia as a catalyst, and potassium oxalate as an activating agent. The resulting potassium salt-containing phenolic resin spheres were simultaneously carbonized and activated at 800 °C in flowing nitrogen. Carbonization of the aforementioned polymeric spheres was accompanied by their activation, which resulted in almost five-time higher specific surface area and total pore volume, and almost four-time higher micropore volume as compared to analogous properties of the carbon sample prepared without the salt. The proposed synthesis resulted in microporous carbon spheres having the surface area of 2130 m² g⁻¹, total pore volume of 1.10 cm³ g⁻¹, and the micropore volume of 0.78 cm³ g⁻¹, and led to the substantial enlargement of microporosity in these spheres, especially in relation to fine micropores (pores below 1 nm), which enhance CO₂ adsorption. These carbon spheres showed three-time higher volume of fine micropores, which resulted in the CO₂ adsorption of 6.6 mmol g⁻¹ at 0 °C and 1 atm.     

Influence of regeneration conditions on the cyclic performance of amine-grafted mesoporous silica for CO2 capture: An experimental and statistical study

This work deals with the behavior of amine-grafted mesoporous silica (referred to as TRI-PE-MCM-41) throughout adsorption–desorption cycles in the presence of 5% CO₂/N₂ using various regeneration conditions in batch experiments. The criteria proposed to determine the optimum regeneration conditions are the working adsorption capacity, the rate of desorption and the change of adsorption capacity between consecutive cycles. Using a 2³ factorial design of experiments, the impact on the performance of the adsorbent of different levels of temperature, pressure, and flow rate of purge gas during desorption was determined. It was found that all the parameters under study have a statistically significant influence on the working adsorption capacity, but only temperature is influential with respect to desorption rate. Regeneration using temperature swing was found to be attractive, as the highest CO₂ adsorption capacity (1.95 mmol g^?1) and the fastest desorption rate (9.82×10^?4 mmol g^?1 s^?1) occurred when desorption was carried out at 150 °C. However, if vacuum is applied, regeneration can be achieved at a temperature as low as 70 °C with only a 13% penalty in terms of working adsorption capacity. It was also demonstrated that under the proper regeneration conditions, TRI-PE-MCM-41 is stable over 100 adsorption–desorption cycles.     

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

CeO₂‐CrO_y loaded on γ‐Al₂O₃ was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N₂ adsorption‐desorption measurements, H₂‐temperature‐programmed reduction, O₂‐temperature‐programmed desorption, NH₃‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H₂‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO₂ can enhance the oxygen capacity of CrO_y. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO₂ can inhibit the evolution of lattice oxygen (O^2?) to electrophilic oxygen species (O₂^?), causing the average CO_x (CO and CO₂) selectivity to decrease from 9.64% to 6.31%.     

Carbon dioxide capture under postcombustion conditions using amine-functionalized SBA-15: Kinetics and multicyclic performance

ABSTRACT

In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N₂ adsorption/desorption, field–emission scanning electron microscopy (FE-SEM), high–resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO₂) uptake on the sorbents, kinetics of CO₂ adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO₂ adsorption capacity ~3.09 mmol g^?1 using 10% pre-humidified CO₂ at 75°C. The presence of moisture in flue gas showed a promoting effect in CO₂ sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO₂.     

Synthesis of new crosslinked porous ammonium‐based poly(ionic liquid) and application in CO2 adsorption

A new poly(ionic liquid) of N,N‐methylenebisacrylamide (MBA)‐crosslinked‐poly(4‐vinylbenzyltriethylammonium hexafluorophosphate)(MBA‐crosslinked‐P[VBTEA][PF₆]) is prepared through the ion exchange of KPF₆ with the precursor of MBA‐crosslinked‐P[VBTEA][Cl]; the precursor is synthesized by 4‐vinylbenzyltriethylammonium chloride and MBA via inverse suspension polymerization. MBA‐crosslinked‐P[VBTEA][PF₆] is a thermally stable (decomposes at nearly 300°C) and porous (apparent porosity of 64.3% and specific surface of 39.12 m²/g) polymer particle with high purity, as indicated by Fourier transformed infrared, energy dispersive spectroscopy, thermogravimetric, scanning electron microscopy, and porous analyses. It is observed that MBA‐crosslinked‐P[VBTEA][PF₆] has good CO₂ adsorption capability of 14.04 mg/g at 0.2 MPa and 25°C, and can be recovered by desorption at vacuum and 80°C, and reused with 99% CO₂ adsorption after four cycles. POLYM. ENG. SCI., 54:59–63, 2014. © 2013 Society of Plastics Engineers     

Synthesis,characterization, and evaluation of unsupported porous NiS submicrometer spheres as a cathode material for lithium batteries

Synthesis of a nanostructured pure phase nickel sulfide in a single step is a challenge. In this work, a new method for direct synthesis of uniform NiS–SiO₂ submicrospheres was developed by ultrasonic spray pyrolysis. Colloidal silica was used as a sacrificial template to create the porous structure. After silica removal, hollow, porous pure phase NiS nanospheres were obtained. The product was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, and N₂ adsorption/desorption isotherm. The results confirmed the formation of single phase millerite NiS porous nanospheres with a high surface area of 312 m² g^?1. The NiS spheres were tested as cathode for lithium batteries. A discharge capacity of 340 mAh g^?1 with good capacity retention during multiple cycles was obtained.     

Synthesis and CO2 adsorption behavior of amine‐functionalized porous polystyrene adsorbent

A solid amine adsorbent was prepared by modifying a porous polystyrene resin (XAD‐4) with chloroacetyl chloride through a Friedel–Crafts acylation reaction, followed by aminating with tetraethylenepentamine (TEPA). The adsorption behavior of CO₂ from a simulated flue gas on the solid amine adsorbent was evaluated. Factors that could determine the CO₂ adsorption performance of the adsorbents such as amine species, adsorption temperature, and moisture were investigated. The experimental results showed that the solid amine adsorbent modified with TEPA (XAD‐4‐TEPA), which had a longer chain, showed an amine efficiency superior to the other two amine species with shorter chains. The CO₂ adsorption capacity decreased obviously as the temperature increased because the reaction between CO₂ and amine groups was an exothermic reaction, and its adsorption amount reached 1.7 mmol/g at 10 °C in dry conditions. The existence of water could significantly increase the CO₂ adsorption amount of the adsorbent by promoting the chemical adsorption of CO₂ on XAD‐4‐TEPA. The adsorbent kept almost the same adsorption amount after 10 cycles of adsorption–desorption. All of these results indicated that amine‐functionalized XAD‐4 resin was a promising CO₂ adsorbent. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45046.     

Preparation of amine-modified SiO<Subscript>2</Subscript> aerogel from rice husk ash for CO<Subscript>2</Subscript> adsorption

Amine-modified SiO₂ aerogel was prepared using 3-(aminopropyl)triethoxysilane (APTES) as the modification agent and rice husk ash as silicon source, its CO₂ adsorption performance was investigated. The amine-modified SiO₂ aerogel remains porous, the specific surface area is 654.24 m²/g, the pore volume is 2.72 cm³/g and the pore diameter is 12.38 nm. The amine-modified aerogel, whose N content is up to 3.02 mmol/g, can stay stable below the temperature of 300 °C. In the static adsorption experiment, amine-modified SiO₂ aerogel (AMSA) showed the highest CO₂ adsorption capacity of 52.40 cm³/g. A simulation was promoted to distinguish the adsorption between the physical process and chemical process. It is observed that the chemical adsorption mainly occurs at the beginning, while the physical adsorption affects the entire adsorption process. Meanwhile, AMSA also exhibits excellent CO₂ adsorption–desorption performance. The CO₂ adsorption capacity dropped less than 10 % after ten times of adsorption–desorption cycles. As a result, AMSA with rice husk ash as raw material is a promising CO₂ sorbent with high adsorption capacity and stable recycle performance and will have a broad application prospect for exhaust emission in higher temperature.     

Hypercrosslinked silole‐containing microporous organic polymers with N‐functionalized pore surfaces for gas storage and separation

Novel hypercrosslinked microporous organic polymers (MOPs) derived from N‐functionalized siloles as basic building units have been designed and synthesized via Friedel–Crafts alkylation reaction. The resulting N‐functional silole‐containing polymer networks exhibit high thermal stabilities and moderate Brunauer–Emmett–Teller surface area ranging from 666 to 1137 m² g^?1. The incorporation of carbazole or triphenylamine moieties into the polymer skeleton increases the number of electron donating basic nitrogen sites in the porous frameworks. Thus, the corresponding polymer PDMCzS shows enhanced CO₂ adsorption capacities of 3.23 mmol g^?1 at 273 K and 1.13 bar, and higher CO₂/N₂ selectivity (43.99) at 273 K than the analogous silole‐containing polymers P1–P3. These results demonstrated that the N‐functionalized silole‐containing polymer network is a very promising candidate for potential applications in post‐combustion CO₂ capture and sequestration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45907.     

CO2 adsorption performance of polyethyleneimine-modified ion-exchange resin

A series of solid amine adsorbents were prepared by the template method with ion-exchange resin (D001) as the carrier and polyethyleneimine (PEI) as the modifier. The absorbents were characterized by energy disperse spectroscopy (EDS), scanning electron microscope (SEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) techniques. The effects of PEI loading, adsorption temperature and influent velocities on CO₂ adsorption capacity in a fixed-bed reactor were investigated. The results show that the solid amine adsorbent prepared by the template method had a better PEI dispersion, stability and CO₂ adsorption capacity. The maximum CO₂ adsorption capacity was 3.98 mmol·g^?1 when PEI loading was 30%, the adsorption temperature was 65°C and the influent velocity was 40 mL·min^?1. The CO₂ adsorption capacity decreased only by 9.50% after 10 cycles of adsorption–desorption tests. The study of kinetics indicates that both chemical adsorption and physical adsorption occurred in the CO₂ adsorption process. The CO₂ adsorption process included fast breakthrough adsorption and gradually approaching equilibrium stage. The particle internal diffusion process was the control step for CO₂ adsorption.     

SO42−/ZrO2 supported on γ‐Al2O3 as a catalyst for CO2 desorption from CO2‐loaded monoethanolamine solutions

In this work, the composite catalysts, SO₄²/ZrO₂/γ‐Al₂O₃ (SZA), with different ZrO₂ and γ‐Al₂O₃ mass ratios were prepared and used for the first time for the carbon dioxide (CO₂)‐loaded monoethanolamine (MEA) solvent regeneration process to reduce the heat duty. The regeneration characteristics with five catalysts (three SZA catalysts and two parent catalysts) of a 5 M MEA solution with an initial CO₂ loading of 0.5 mol CO₂/mol amine at 98°C were investigated in terms of CO₂ desorption performance and compared with those of a blank test. All the catalysts were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption–desorption experiment, ammonia temperature programmed desorption, and pyridine‐adsorption infrared spectroscopy. The results indicate that the SZA catalysts exhibited superior catalytic activity to the parent catalysts. A possible catalytic mechanism for the CO₂ desorption process over SZA catalyst was proposed. The results reveal that SZA1/1, which possesses the highest joint value of Brφnsted acid sites (BASs) and mesopore surface area (MSA), presented the highest catalytic performance, decreasing the heat duty by 36.9% as compared to the catalyst‐free run. The SZA1/1 catalyst shows the best catalytic performance as compared with the reported catalyst for this purpose. Moreover, the SZA catalyst has advantages of low cost, good cyclic stability, easy regeneration and has no effect on the CO₂ absorption performance of MEA. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3988–4001, 2018     

Novel Thermomorphic Biphasic Amine Solvents for CO2 Absorption and Low‐Temperature Extractive Regeneration

The key challenge in amine‐based CO₂ capture from flue gases is to reduce the energy consumption required for solvent regeneration. Lipophilic amines exhibit a thermomorphic phase transition upon heating, giving rise to autoextractive behavior, which intensifies desorption at temperatures well below the boiling point of aqueous solutions. The low regeneration temperature of less than 80 °C together with the high cyclic CO₂ loading capacity of ～0.9 mol mol_absorbent^–1 of such thermomorphic biphasic solvent (TBS) systems permit the use of low‐value and even waste heat at temperatures below 100 °C for desorption. In order to reduce the exergy demands still further, techniques for enhancing CO₂ release using extractive regeneration with inert solvent addition were investigated at temperatures of 40–50 °C to permit the use of waste heat at temperatures of ～70 °C or less. The regeneration of 3 M absorbed lipophilic amine solutions with 0.93 mol mol^–1 CO₂ loading by using various additional solvents and the evaluation of the extractive performance in multiple‐stage crosscurrent and countercurrent configurations indicated the promise of adding certain hydrophobic solvents to enhance the low‐temperature regeneration of TBS absorbents.     

Synthesis and characterization of novel saponified guar‐graft‐poly(acrylonitrile)/silica nanocomposite materials

The combination of carbohydrates with silicon‐based ceramic materials offers attractive means of production for high performance materials. Present article describes the synthesis of novel nanocomposites out of SiO₂ and saponified guar‐graft‐poly(acrylonitrile) (SG). Tetraethoxysilane was used as the precursor for silica and growth of SiO₂ phase was allowed concurrently in the presence of SG. The material so obtained was thermally treated at 80°C, 160°C, 500°C, and 900°C to study the effect of thermal curing on its properties. During the curing process, silanol surface groups of silica globules reacted to create the reinforced SiO₂‐SG substance. It was observed that at 900°C, the SiO₂ phase crystallized out in tetragonal shape (similar to Cristobalite form of silica) in presence of SG. The chemical, structural and textural characteristics of the composites were determined by FTIR, XRD, TGA‐DTA, SEM and BET studies. The materials were also evaluated as efficient Zn²⁺ metal binder. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 536–544, 2007