Modification of ABS Membrane by PEG for Capturing Carbon Dioxide from CO2/N2 Streams

Carbon dioxide capture and storage (CCS) has been propounded as an important issue in greenhouse gas emissions control. In this connection, in the present article, the advantages of using polymeric membrane for separation of carbon dioxide from CO₂/N₂ streams have been discussed. A novel composition for fabrication of a blend membrane prepared from acrylonitrile-butadiene-styrene (ABS) terpolymer and polyethylene glycol (PEG) has been suggested. The influence of PEG molecular weight (in the range of 400 to 20000) on membrane characteristics and gas separation performance, the effect of PEG content (0–30 wt%) on gas transport properties, and the effect of feed side pressure (ranging from 1 to 8 bar) on CO₂ permeability have been studied. The results show that CO₂ permeability increases from 5.22 Barrer for neat ABS to 9.76 Barrer for ABS/PEG20000 (10 wt%) while the corresponding CO₂/N₂ selectivity increases from 25.97 to 44.36. Furthermore, it is concluded that this novel membrane composition has the potential to be considered as a commercial membrane.     

Synthesis of soluble oligsiloxane-end-capped hyperbranched polyazomethine and their application to CO2/N2 separation membranes

Three soluble hyperbranched polyazomethines containing oligosiloxane end group HBP-PAZ-SiO_n were successfully synthesized. HBP-PAZ-SiO_ns were used as modifiers of ethyl cellulose (EC) and polysulfone (PS) membranes. Blend membranes, HBP-PAZ-SiO_n/EC and HBP-PAZ-SiO_n/PS were prepared by blending the THF solution of HBP-PAZ-SiO_n with ethanol solution of EC and dichloromethane solution of PS, respectively. Surprisingly, the permeabilities for CO₂ of the blend membranes were more than 15–16 times higher than those of pure EC and PS membranes without any drop of pemselectivity to N₂. This unusual improvement has been achieved by both enhancement of diffusivity for carbon dioxide and nitrogen by the oligosiloxane groups and enhancement of affinity of the amino groups with carbon dioxide at the end groups of HBP-PAZ-SiO_n.     

用于分离DMF/H2O体系的Me-silicalite-1渗透汽化分子筛膜的制备

采用二次生长法制备了用于渗透汽化分离DMF/H2O体系的杂原子取代Me-silicalite-1/α-Al2O3(Me=Co、Fe)分子筛复合膜,通过X射线衍射(XRD)、扫描电镜(SEM)、傅里叶红外光谱(FT-IR)和紫外漫反射(UV-Vis)等方法对分子筛膜进行表征,结果表明金属离子进入分子筛骨架。渗透汽化实验显示,金属离子掺杂的silicalite-1/α-Al2O3分子筛复合膜,具有较好的分离性能且优先透过有机胺,有利于工业中DMF溶剂的回收和利用。随着操作温度升高,分离因子减小,渗透通量增加。40℃分离质量分数为5%的DMF/H2O混合液时,Co-silicalite-1/α-Al2O3分子筛膜和Fe-silicalite-1/α-Al2O3分子筛膜的分离因子分别为4.4和2.9,渗透通量分别为0.66和0.84 kg·m-2·h-1。     

CO2, N2 gas sorption and permeation behavior of chitosan membrane

The sorption equilibria for CO₂ and N₂ in dry chitosan membrane at 20 and 30 ‡C were measured by a pressure decay method. The steady-state permeation rates for CO₂ and N₂ in dry and wet (swollen with water vapor) chitosan membranes at 20 and 30 ‡C were measured by a variable volume method. The sorption equilibrium for N₂ obeyed Henry’s law, whereas that for CO₂ was described apparently by a dual-mode sorption model. This non-linear sorption equilibrium for CO₂ could be interpreted by the interaction of sorbed CO₂ with the chitosan matrix expressed as a reversible reaction. The logarithm of the mean permeability coefficient for CO₂ in dry chitosan membrane increased linearly with upstream gas pressure. A linear increase of the logarithmic mean permeability coefficient for CO₂ with the pressure could be interpreted in terms of a modified free-volume model. The mean per-meability coefficient for N₂ in dry chitosan membrane only slightly increased with upstream gas pressure. The per-meabilities for CO₂ and N₂ in wet chitosan membrane increased by 15 to 17 times and 11 to 15 times, respectively, as compared to those in the dry membrane.     

CO2 Capture/Separation Control by SiO2 Nanoparticles and Surfactants

In this study, the performance enhancement of CO₂ capture and separation by the SiO₂ nanoparticles and surfactants is evaluated. The main objectives are to test the dispersion stability of nanofluids (DI water with nanoparticles and surfactants), to quantify the effect of the nanoparticles and surfactants on the CO₂ capture and separation performance, and to find the optimum conditions of the nanoparticles and surfactants. It is found that the CO₂ capture and separation performances are enhanced up to 13.1% and 7.8% at the nanoparticle concentration of 0.01 vol%, respectively. It is concluded that nanoparticles enhance both CO₂ capture and separation rates, while the surfactants enhance the CO₂ capture rate but they interrupt the CO₂ separation rate.     

纳米晶种涂层法合成Silicalite-1沸石膜

用纳米晶种涂层二次生长成膜法在大孔a-Al2O3(孔径4~6 mm)陶瓷管上合成Silicalite-1沸石膜. 用X射线衍射(XRD)和扫描电镜(SEM)表征分析了沸石膜的形态,并通过单组分气体渗透实验对合成膜管的渗透性能进行了测试. 结果表明,合成的Silicalite-1沸石膜连续、互生,看不出晶间孔;沸石膜层厚8~10 mm;常温常压下H2/N2的理想分离系数为3.9,超过其努森扩散值3.74,H2/C3H8的理想分离系数为19.1,远大于其Knudsen扩散比值4.69,且H2的渗透率达到1.43′10-6 mol/(m2×s×Pa). 气体分离数据表明,该膜没有明显的缺陷存在.     

Membranes for CO2 /CH4 and CO2/N2 Gas Separation

Membrane technology has emerged as a leading tool worldwide for effective CO₂ separation because of its well-known advantages, including high surface area, compact design, ease of maintenance, environmentally friendly nature, and cost-effectiveness. Polymeric and inorganic membranes are generally utilized for the separation of gas mixtures. The mixed-matrix membrane (MMM) utilizes the advantages of both polymeric and inorganic membranes to surpass the trade-off limits. The high permeability and selectivity of MMMs by incorporating different types of fillers exhibit the best performance for CO₂ separation from natural gas and other flue gases. The recent progress made in the field of MMMs having different types of fillers is emphasized. Specifically, CO₂/CH₄ and CO₂/N₂ separation from various types of MMMs are comprehensively reviewed that are closely relevant to natural gas purification and compositional flue gas treatment     

CO2 and CO adsorption equilibrium on ZSM-5 for different SiO2/Al2O3 ratios

CO₂ and CO adsorption on MFI type zeolites with different SiO₂/Al₂O₃ ratios (ZSM-5(30), ZSM-5(50), ZSM-5(280), and silicalite) were investigated in this study by a static gravimetric analyzer for pure isotherms at 30°C, 65°C, 100°C, and 135°C over the pressure range of 0–10 atm. Adsorption capacity of CO increases with decreasing SiO₂/Al₂O₃ ratios within ZSM-5. The adsorption of CO₂ for decreasing SiO₂/Al₂O₃ ratios, showed stronger adsorption at lower pressures and at higher pressures, the highest capacity varied from ZSM-5(50) to ZSM-5(30). ZSM-5(280) was found to have the highest selectivity for CO₂ within the widest range of pressures and temperatures tested.     

Nanocrystalline Zeolite Tetraethylammonium‐Beta Membrane for Preferential Sorption and Transport of CO2 over N2

CO₂/N₂ gas separation was performed over a nanocrystalline zeolite tetraethylammonium (TEA)‐beta membrane prepared on a stainless‐steel porous disc by repeated hydrothermal crystallization. Two to three consecutive hydrothermal syntheses were required to form a membrane comprised of a continuous and compact layer of zeolite beta nanocrystals on the support. The membrane TEA‐BEA3 obtained by three consecutive syntheses, in which the membrane from two consecutive syntheses was used as support, exhibited the highest structural order. When the separation experiment was performed over this membrane without applying any external applied pressure, 100 % selectivity of CO₂ over N₂ was observed. The separation was driven by differences in chemical potentials of the molecules generated only by the adsorption‐desorption behavior of the gases into the membrane. The novel zeolite TEA‐beta membrane provided promising results for the separation of small gas molecules due to the combined influence of diffusion and sorption selectivity.     

Membrane separation process modeling for CO2 partial removal in prepurification of air separation units

A novel membrane/adsorption hybrid system was proposed for air prepurification in large scale air separation units. Mathematical models were established for cocurrent and countercurrent flow patterns with crude nitrogen as purge stream to describe the membrane separation performance. The experimental and predicted results are in good agreement confirming the validity of the mathematical models. Effects of membrane properties and operation parameters on O₂ recovery, N₂ recovery, and membrane area requirement were investigated. For countercurrent flow pattern, O₂ recovery and N₂ recovery were larger than 98 and 99%, respectively, and membrane area requirement was less than 0.25?m²/m³?h^?1 with feed side pressure of 0.6?MPa and the purge gas/feed gas ratio of 0.2.     

Efficient CO2 Separation Using a PIM-PI-Functionalized UiO-66 MOF Incorporated Mixed Matrix Membrane in a PIM-PI-1 Polymer

Metal–organic framework (MOF) incorporated mixed–matrix membranes (MMMs) attract great interest for gas separation applications because they overcome limitations faced by typical polymer membranes, including permeability–selectivity trade-off, aging effect, and plasticization phenomenon. However, optimal MOF–polymer interface compatibility is the key challenge in fabricating defect-free high-performance gas-separation MMMs. Here, a surface modification strategy of the UiO-66-NH₂ MOF using a covalently bound PIM-PI-oligomer is developed to engineer interface compatibility with the polymer that has an identical chemical structure (PIM-PI-1) in the MMMs. A series of MMMs are prepared with different loadings of homogeneously distributed PIM-PI-functionalized MOFs (PPM). Significant improvements in CO₂/N₂ and CO₂/CH₄ selectivity and permeability are achieved with these MMMs, ranging from 5 to 10 wt% of the PPM loadings. The MMM with 10 wt% loading (PPM-10@MMM) shows a CO₂ permeability of 3827.3 Barrer and a CO₂/N₂ and CO₂/CH₄ selectivity of 24 and 13.4, respectively. This surpasses the 2008 Robeson upper bound for CO₂/N₂ and is very close to the 2008 upper bound for CO₂/CH₄. The experimental results are further compared using Maxwell's equation for MMMs. The resulting MMMs show a plasticization resistance against CO₂ up to 25 atm pressure and anti-aging performance for 180 h.     

真空晶种引入法制备Silicalite-1沸石膜及其性能表征

采用抽真空法在多孔a-Al2O3载体管表面预先引入Silicalite-1沸石晶种,再通过水热合成二次晶化法在涂有Silicalite-1沸石晶种的a-Al2O3载体管上合成沸石膜. 用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对合成的沸石分子筛及膜进行了表征,考察了晶种大小、真空度对合成沸石膜渗透性能的影响,用单组分气体渗透实验检测合成沸石膜的渗透性能. XRD检测结果表明,制备的沸石膜是典型的Silicalite-1沸石膜,合成的分子筛粒径分别约为0.2, 0.5, 1和2 mm,且分布均匀;SEM检测结果表明引入的晶种涂层连续、均匀,制备的Silicalite-1沸石膜致密、互生,不存在裂缺;常温常压下,H2/N2和H2/SF6的理想分离系数分别达到4.1和133.2,大于其Knudsen扩散比值3.7和8.7.     

Effects of Synthesis Temperature and Support Material on CO2 and CH4 Permeation through SAPO-34 Membranes

In this research, continuous SAPO-34 membranes were synthesized via secondary growth method onto both α-Al₂O₃ and mullite supports at three levels of synthesis temperature: 185, 195, and 220°C for 24 h. The synthesized membranes were characterized using XRD and SEM analysis and single gas permeation experiments. It was found out that support material and synthesis temperature both have significant effects on the membrane performance. At higher synthesis temperature, SAPO-34 crystals grown over the mullite support become more uniform and smaller in size but those grown on the α-Al₂O₃ support become larger. Effect of synthesis temperature on single gas permeation properties of the synthesized SAPO-34 membranes was also studied. For the mullite supported membranes, the CH₄ and CO₂ permeances decrease as synthesis temperature increases; but in the case of the alumina supported membranes, by increasing synthesis temperature, CH₄ and CO₂ permeances first decrease up to 195°C and then increase up to 220°C. Even in equal membrane thicknesses, the mullite supported membrane shows lower gas permenaces. Increasing synthesis temperature decreases CO₂/CH₄ ideal selectivity for the α-Al₂O₃ supported membranes, while increases for the mullite supported membranes. Under optimum synthesis conditions, at room temperature and 2 bar feed pressure, the CO₂ permeance through the α-Al₂O₃ and the mullite supported SAPO-34 membranes are 8.2 × 10^?7 and 8.5 × 10^?8 (mol/m² · s · Pa), respectively, and CO₂/CH₄ ideal selectivities are 51 and 61, respectively.     

Enhancement of C2H6 Oxidation by O2 in the Presence of N2O over Fe Ion-Exchanged BEA Zeolite Catalyst

Selective catalytic reduction (SCR) of N₂O with C₂H₆ took place effectively over Fe ion-exchanged BEA zeolite catalyst (Fe-BEA) even in the presence of excess oxygen. The mechanism in the SCR of N₂O with C₂H₆ over Fe-BEA catalyst was studied by a transient response experiment and an in situ DRIFT spectroscopy. No oxidation of C₂H₆ by O₂ took place below 350 °C (in C₂H₆/O₂). In the N₂O/C₂H₆/O₂ system, however, it was found that the reaction of C₂H₆ with O₂ was drastically enhanced by the presence of N₂O even at low temperatures (200-300 °C). Therefore, it was concluded that N₂O played an important role in the oxidation of C₂H₆ (i.e., activation of C₂H₆ at an initial step). On the basis of these findings, the mechanism in the SCR of N₂O with C₂H₆ is discussed.     

Comparative CO2 Adsorption Analysis in Pure and Amine-Modified Composite Membranes

In this study, the CO₂ adsorption analysis in cellulose acetate–TiO₂- and cellulose acetate–3-aminopropyl-trimethoxysilane TiO₂-blended membranes was performed. The membranes were also characterized using scanning electron microscopy and Fourier transform infrared analysis techniques. The adsorption results indicated that 120 and 90°C were considered as optimized temperatures for regeneration of cellulose acetate–TiO₂ and cellulose acetate–3-aminopropyl-trimethoxysilane-modified TiO₂ membranes. The testing results revealed that adsorption capacity reached maximum at 3.0 bars. Validation of experimental results was performed by pseudo-first-order, second-order and intraparticle diffusion models. The correlation factor R² represented that the second-order model was fitted well with the experimental data. The intraparticle diffusion model represented that adsorption is not a single-step process.     

Separation of CO2 by 2-amino-2-methyl-1-propanol aqueous solution in microporous hydrophobie hollow fiber contained liquid membrane

The absorption of CO₂ from a mixture of CO₂/N₂ gas was carried out using a flat-stirred vessel and the polytetrafluoroethylene hollow fiber contained aqueous 2-amino-2-methyl-1-propanol (AMP) solution. The reaction of CO₂ with AMP was confirmed to be a second order reversible reaction with fast-reaction region. The mass transfer resistance in the membrane side obtained from the comparison of the measured absorption rates of CO₂ in a hollow fiber contained liquid membrane with a flat-stirred vessel corresponded to about 90% of overall-mass-transfer resistance. The mass transfer coefficient of hollow fiber phase could be evaluated, which was independent of CO₂ loading.     

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Abstract

Single and multicomponent fixed-bed adsorption of CO₂, N₂, and CH₄ on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO₂ and the loadings of CH₄ and N₂ are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO₂ is one order of magnitude faster than for CH₄ and N₂.     

The Characterization of the Micropore Structures of Some Activated Carbons of Plant Origin by N2 and CO2 Adsorptions

Abstract

In this study, active carbons prepared from almond and hazelnut shells under various experimental conditions were investigated. Merck-2514 and Merck-2184 active carbons were used for comparison. N₂ (77 K) gas and CO₂ (273 and 195 K) gas adsorptions were determined as comparison criteria. Regarding the specific surface area and micropore volume results obtained from these adsorption data, it is concluded that N₂ (77 K) adsorption by itself is inadequate in the characterization of active carbons which are low-sized microporous dominated. In addition, it is concluded that it would be useful to investigate CO₂ (195 and 273 K) adsorption. The iodine and methylene blue tests at 298 K were also applied for the characterization of the carbon adsorbents mentioned. From these data it was seen that the iodine test can be applied as a total porosity indicator and that the methylene blue test can be used as a developed microporosity indicator. These results indicate that the best adsorbents were those prepared from hazelnut shells. Depending on the preparation conditions, the physically activated carbon has an activation time up to 4 hours and has adsorption properties on the level of Merck commercial carbons.     

CuO Modified by 7,7,8,8-Tetracyanoquinodimethane and Its Application to CO2 Separation

7,7,8,8-Tetracyanoquinomethane (TCNQ) was added to polyvinylpyrrolidone (PVP)/CuO composites to modify and prevent agglomeration of the particles, and thus the CuO particles were well dispersed to a small size, thereby increasing CO₂ solubility and separation performance. When the separation performance of the PVP/CuO/TCNQ composite membrane was measured for CO₂/N₂ gases, a CO₂ separation of about 174 was measured. This improvement in performance was attributed to the fact that TCNQ was applied to PVP and CuO to prevent agglomeration between particles with surface modification. Due to TCNQ, CuO could be dispersed to a small size in PVP; the bonds between chains in PVP weakened; the interaction between molecules weakened; and the free volume increased, as confirmed by FT-IR, TGA, and UV–Vis spectroscopy.