Dehydrogenation of ethylbenzene with CO2 over Cr-MCM-41 catalyst

M-MCM-41 catalysts (M: V, Cr, Fe, and Ga) prepared by direct hydrothermal synthesis (DHT) have been tested for dehydrogenation of ethylbenzene with CO₂. The synthesized materials were characterized by X-ray diffraction (XRD), N₂ adsorption (77 K), and diffuse reflectance UV–vis spectroscopic measurements. Cr-MCM-41 showed the highest activity among M-MCM-41 catalysts tested, resulting in the production of styrene with the conversion of 65% and the selectivity above 90%. The rate of styrene formation increased with increasing Cr loading up to 1.7 wt.%. It is suggested that Cr(VI)O₄ in tetrahedral coordination is formed as an active monochromate species and reduced to Cr(III)O₆ in octahedral coordination as a less active polychromate species during the reaction. Deactivated catalyst was regenerated by a treatment with gaseous oxygen or CO₂, during which redistribution as well as reoxidation of polymeric Cr(III)O₆ octahedra to monomeric Cr(VI)O₄ tetrahedra was observed. The rate of CO formation increased together with that of styrene formation, while the rate of H₂ formation decreased, with increasing partial pressure of CO₂. It was confirmed that reverse water-gas shift reaction took place over Cr-MCM-41 by a separate experiment. The rate of CO formation during the dehydrogenation of ethylbenzene with CO₂ over Cr-MCM-41 was well accounted for by assuming parallel occurrence of two reactions, i.e., direct oxidative dehydrogenation of ethylbenzene with CO₂ and simple dehydrogenation of ethylbenzene thermodynamically assisted by reverse water-gas shift reaction.     

In situ FT-IR study on CO2 hydrogenation over SiO2-supported PtM (M = Cr, Mo, W) complex catalysts

The in situ FT-IR spectra were used to study the CO₂ hydrogenation reaction over the SiO₂-supported heterobinuclear metal complex catalysts, PtM (M=Cr, Mo, W). The bands, which correspond to the formate species absorbed on the catalysts, were observed. During the hydrogenation reactions, the adsorbed linear and bridging CO was not observed. The experimental results suggest that for the CO₂ and CO hydrogenation reaction over the same catalysts, their catalytic active intermediate species and the reaction mechanisms should be different.     

Mg-Ni/BaTiO_3催化剂上CH_4/CO_2重整反应研究

采用等体积浸渍法制备了MgO改性的一系列Mg-Ni/BaTiO3催化剂,并在固定床反应装置上考察了这些催化剂对CO2重整CH4反应的催化活性。结果表明,MgO质量负载为5%的Mg-Ni/BaTiO3催化剂活性最好。考察了不同浸渍顺序对催化剂性能的影响,结果表明,先浸镁盐后浸镍盐制得的催化剂催化性能更为理想。XRD、TPR和TPD表征发现,与催化剂Ni/BaTiO3相比,MgO的添加有利于提高催化剂的催化活性和抗积炭性能,对催化剂起到了良好的改性作用。     

Promotion of hydrocarbon selectivity in CO2 hydrogenation by Ru component

We investigated catalytic behavior of iron in CO₂ hydrogenation with and without a ruthenium component. Calcined iron-based catalysts were reduced by H₂ and characterized by XRD, BET surface area and CO₂, CO and C₂H₄ temperature-programmed desorption (TPD), and tested for CO₂ hydrogenation. When Fe-K/γ-Al₂O₃ was used as a catalyst, CO₂ conversion was 36%, but when Fe-Ru-K/γ-Al₂O₃ was used, CO₂ conversion was 41%. The product selectivities for catalysts with and without the ruthenium component were also compared. Fe-K/γ-Al₂O₃ exhibited higher methane (16 mol%) and C₂–C₄ selectivity (39.6 mol%) than Fe-Ru-K/γ-Al₂O₃. The main products obtained with Fe-Ru-K/γ-Al₂O₃ were higher hydrocarbons such as C₅⁺ hydrocarbons. For Fe-Ru-K/γ-Al₂O_3, the product distribution followed the Anderson–Schultz–Flory (ASF) distribution. However, in the case of Fe-Ru-K/γ-Al₂O₃, the hydrocarbon distribution deviates from the ideal ASF distribution. It is concluded that the readsorption rates of the primary hydrocarbon product increase exponentially with chain length in the ruthenium promoted catalytic system. The behavior of catalysts with and without the ruthenium will be explained by the CO₂-, CO- and C₂H₄– profiles. In this study, it was confirmed that ruthenium component promoted the readsorption ability of -olefin, and then the chain length of hydrocarbon is higher. In addition, the microcrystalline wax produced in CO₂ hydrogenation was a high-crystalline and olefin-rich hydrocarbon.     

二氧化碳在Pd/SiO2和La-Pd/SiO2上的催化氢化反应

对CO₂在附载型Pd催化剂上的氢化反应的研究迄今报道不多^[1,2],且都在加压条件下进行,对常压下助催剂如何改善Pd的催化行为未见报道。本文探讨了Pd/SiO₂催化剂,未加与掺加助催剂La(NO₃)₃后,其Pd粒大小、CO₂的吸附性能及CO₂/H₂催化活性等方面都有显著差异。     

Oxidative Dehydrogenation of 1-Butene to 1,3-Butadiene Using CO2 over Cr-SiO2 Catalysts Prepared by Sol-gel Method

A series of Cr-SiO₂ catalysts with a Cr content(mass fraction) ranging from 0.5% to 9% was prepared by a sol-gel method. The catalysts were characterized by XRD, N₂ adsorption, EDX elemental mapping, Raman spectroscopy, UV-Vis spectroscopy, XPS and H₂-TPR, and their catalytic behavior in the dehydrogenation of 1-butene to 1,3-butadiene(BD) using CO₂ as a soft oxidant was studied. The initial BD yield is well correlated with the amount of Cr⁶⁺ in the fresh catalysts. The highest BD yield of ca. 34% is achieved on the catalysts with 5%-9% Cr at 600℃ and weight hourly space velocity(WHSV) of 4.5 g·g_cat^-1·h^-1. The promoting effect of CO₂ on the BD yield was observed, which can be attributed to the reaction coupling between a simple dehydrogenation of 1-butene and the reverse water-gas shift reaction as well as regaining the oxidation state(lattice oxygen) of reduced Cr³⁺ species due to the mild oxidation ability of CO₂. The Cr-SiO₂ catalyst exhibits higher BD yield than the Cr catalyst supported on SBA-15, which is attributed to the higher amount of Cr⁶⁺ present on the former catalyst.     

Novel CO2 selectively permeating membranes containing PETEDA dendrimer

Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy. The composite membranes for selectively permeating CO₂ were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO₂ and CH₄ gases and the gas mixture containing 10 vol.% CO₂ and 90 vol.% CH₄, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO₂ permeance of 8.14 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO₂ permeance reaches 3.56 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity is 19. For the gas mixture, the membrane has a CO₂ permeance of 6.94 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO₂ permeance of 3.29 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO₂/CH₄ gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO₂ permeance and CO₂/CH₄ selectivity increase and CH₄ permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS).     

一锅法合成Ce_xZr_(1-x)O_2固溶体催化剂用于热化学循环分解CO_2制CO

采用一锅蒸发诱导自组装法(EISA)制备了一系列不同铈锆物质的量比的铈锆固溶体催化剂,用TGA研究了其热化学循环分解CO_2制CO的催化性能,并采用XRD、Raman光谱、H2-TPR、XPS、SEM和N_2吸附-脱附等手段对催化剂的物相结构、还原性能和表面化学性质进行了表征分析,用热重分析(TGA)研究了铈锆固溶体对热化学循环分解CO_2制CO的催化性能。结果表明,随着Ce/Zr物质的量比增加,铈锆固溶体催化剂的CO_2高温分解活性先增大后减小。Ce/Zr物质的量比为1的Ce_(0.5)Zr_(0.5)O_2催化剂由于具有较多的晶格缺陷和氧空穴,氧迁移能力强,催化活性高,而Ce/Zr物质的量比为3的Ce_(0.75)Zr_(0.25)O_2催化剂具有相对稳定的氧空穴数,循环稳定性好。循环反应后,所有的催化剂均出现了一定程度的烧结,且富锆固溶体发生了相分离,这可能会影响催化剂的性能。     

Liquid-phase alkylation of phenol with long-chain olefins over WOx/ZrO2 solid acid catalysts

The liquid-phase alkylation of phenol with 1-dodecene was carried out over WO_x/ZrO₂ solid acid catalysts. The catalysts were prepared by wet impregnation method using zirconium oxyhydroxide and ammonium metatungstate. Catalysts with different WO₃ loading (5–30 wt.%) were prepared and calcined at 800 °C and catalyst with 15% WO₃ was calcined from 700–850 °C. All the catalysts were characterized by surface area, XRD, and FTIR. The catalyst with 15% WO₃ calcined at 800 °C (15 WZ-800) was found to be the most active in the reaction. The effect of temperature, molar ratio and catalyst weight on dodecene conversion and products selectivity was studied in detail. Under the optimized reaction conditions of 120 °C, phenol/1-dodecene molar ratio 2 and time 2 h, the catalyst 15 WZ-800 gave >99% dodecene conversion with 90% dodecylphenol selectivity. Comparison of the catalytic activity of 15 WZ-800 with sulfated zirconia calcined at 500 °C (SZ-500) and Hβ zeolite showed that activity of SZ-500 was lower than that of 15 WZ-800, while Hβ zeolite showed negligible activity. It is observed that the presence of water in the reaction mixture was detrimental to the catalytic activity of WO_x/ZrO₂. The catalyst 15 WZ-800 also found to be an efficient catalyst for alkylation of phenol with long-chain olefins like 1-octene and 1-decene.     

CaO对Cu-ZnO-ZrO_2催化CO_2加H_2合成甲醇性能影响

用CaO作为改性助剂,采用并流共沉淀法制备了CuO∶ZnO∶ZrO_2为5∶4∶1(物质的量比),CaO添加量为0、1%、2%、4%、8%、16%(摩尔分数)的六组催化剂。用X射线衍射(XRD)、微商热重(TG-DTG)、傅里叶红外(FT-IR)、N2吸附脱附(BET)、X射线光电子能谱(XPS)、氢气程序升温还原(H_2-TPR)、CO_2程序升温脱附(CO_2-TPD)、NH_3程序升温脱附(NH_3-TPD)对催化剂进行了表征。用自制固定床评价了催化剂活性。结果表明,添加CaO后,催化剂路易斯酸性和表面碱性增强;催化剂母体中高温碳酸盐含量增加,热稳定性增强,CuO颗粒粒径变小,Cu-Zn协同作用增强,Cu比表面积增大,分散性变好。催化剂活性受到表面酸碱性、铜比表面积、Cu-Zn协同作用和铜分散性共同影响。当CaO为2%时,铜比表面积为79.3 m2/g、铜分散度为34.8%、CO_2转化率为24.55%、甲醇选择性为19.01%、甲醇收率为0.044 g/(gcat·h),催化剂活性最好。过量CaO占据催化剂孔道和覆盖表面活性位,使催化剂路易斯酸性和表面碱性过强,CuO与H_2有效接触减少,CO_2难以脱附,催化活性下降。因此,适量CaO(2%)添加可促进CO_2加氢反应合成甲醇。     

柠檬酸盐凝胶法制备纳米CuO-ZnO-ZrO_2的工艺分析及CO_2加氢制甲醇的性能

采用柠檬酸盐凝胶法制备出纳米CuO-ZnO-ZrO_2(CZZ)催化剂,应用XPS、BET、XRD、H_2-TPR、H_2-TPD、CO_2-TPD和TG-DTA等检测手段对催化剂及前驱体的结构进行表征。研究了湿凝胶干燥时间和柠檬酸用量对催化剂结构的影响,并与燃烧法制得的催化剂进行对比,考察了不同催化剂CO_2加氢制甲醇的性能。研究表明,延长湿凝胶干燥时间可有效防止催化剂焙烧时发生喷溅,有利于催化剂中各组分的分散,提高催化剂对H_2和CO_2的吸附能力;112℃干燥48h制得的催化剂(CZZ-48h)BET比表面积为43.5m~2/g,高于燃烧法;柠檬酸用量等于化学计量比时催化剂的性能最佳,在240℃、2.6MPa、空速为3600h-1、H_2/CO_2(体积比)为3的条件下甲醇时空收率达109.4g/(kg·h);柠檬酸过量会影响催化剂组分的分散度,并造成分解残留覆盖催化剂表面活性位而不利于CO_2加氢反应。     

Palladium-catalyzed Heck coupling reactions using different fluorinated phosphine ligands in compressed carbon dioxide and conventional organic solvents

Palladium-catalyzed Heck reaction of iodobenzene and styrene was investigated in compressed CO₂ using different fluorinated phosphine compounds as ligands at a temperature of 70 °C. The reaction mixture is a single phase at 12 MPa but biphasic at 8 MPa, a little higher than the critical pressure of pure CO₂ under the reaction conditions used. Although the solubility of fluorinated ligands is very high in dense CO₂, they have marginal improvements in Heck conversion in this medium compared with a non-fluorinated ligand of triphenylphosphine. The activity of palladium complexes strongly depends on the kind of phosphine compound used, in the order of bis(pentafluorophenyl)phenylphosphine (III)>triphenylphosphine (I), tris(pentafluorophenyl)phosphine (IV)>diphenyl(pentafluorophenyl)phosphine (II), tris(p-fluorophenyl)phosphine (V)>tris(p-trifluoromethyl phenyl)phosphine (VI), 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (VII), for the homogeneous reaction at 12 MPa. This order of effectiveness of these ligands is different from those obtained in conventional organic solvents. Hexane, toluene, ethanol, and N-methylpyrrolidone (NMP) showed maximum conversions with the ligands VI, IV, V and VII, respectively. The conversion in CO₂ with the ligand III is comparable with those in polar solvents of ethanol and NMP, and larger than those in hexane and toluene in the presence of the best ligands. The dense CO₂ may affect the specific activity of palladium complex catalysts and/or the reactivity of reacting species. Small quantities of fluorinated products were observed to form at high pressure of CO₂ and this is direct evidence of P–C bond cleavage during Heck reaction in dense CO₂. The activity of palladium complexes with those ligands is higher in more polar solvent.     

Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

Effect of electron beam irradiation on CO2 reforming of methane over Ni/Al2O3 catalysts

The effect of electron beam irradiation on the CO₂ reforming of methane over Ni/Al₂O₃ was investigated. The conversion rate of CO₂ and CH₄ forming H₂ and CO using various catalysts irradiated with an absorbed dose greater than 2 MGy was 5–10% higher than when using an untreated catalyst. The Ni/O ratio on the catalyst surface increased after treatment with an electron beam, and was more prominent for catalysts with a higher Ni content. As such, based on XRD and XPS measurements, electron beam treatment was found to result in either the desorption of oxygen from NiO or the removal of OH groups from the outermost surface layer of the catalyst. In addition, the concentration of active sites, such as Ni²⁺ and NiO, or surface defects was also found to increase with the absorbed radiation dose, thereby increasing the conversion rate.     

氧化还原刻蚀铜表面对二氧化碳电催化还原性能的研究

大规模化石燃料的使用排放了大量的二氧化碳（CO₂）,导致环境中二氧化碳的含量急剧增加. 为了降低大气中二氧化碳的含量,以电催化的方法将二氧化碳转化为有用的化工原料和燃料是解决能源和环境问题的重要途径. 本文主要利用氧化还原刻蚀法,在铜表面形成复合纳米结构,用于二氧化碳的电催化还原反应研究. 首先,作者通过一定浓度的三氯化铁（FeCl₃）溶液与铜片的氧化还原反应,在刻蚀铜表面时形成具有立方体结构的氯化亚铜纳米材料,用于二氧化碳的电催化还原反应. 为了研究反应时间对催化性能的影响,作者通过改变反应时间（1、2、3和4 h）合成了不同结构的铜基催化剂. 研究发现,在反应3 h后,Cu-3h催化剂对二氧化碳的电催化还原具有较小的起始电压（-0.3 V vs. RHE）和较大的电流密度值,表现出了较强的还原能力. 经检测,所得到主要还原产物为一氧化碳（CO）和甲烷（CH₄）. 在-0.6 V时,二氧化碳催化还原的法拉第效率可达到60%,表明以氧化还原法刻蚀铜表面具有较好的改善二氧化碳电催化还原的能力.     

焙烧温度对Pt-FeOx/γ-Al2O3催化剂催化甲醛氧化性能的影响

采用胶体沉积法制备了Pt-FeO_x/γ-Al₂O₃催化剂,通过XRD、TEM、BET、XPS、H₂-TPR和FT-IR等技术对催化剂进行了表征,考察了焙烧温度对Pt-FeO_x/γ-Al₂O₃催化剂表面结构及其催化甲醛氧化性能的影响。结果表明,焙烧温度对Pt-FeO_x/γ-Al₂O₃催化剂的氧化还原性能、Pt物种的化学状态以及表面羟基的数量有较大的影响。在室温下,所有Pt-FeO_x/γ-Al₂O₃催化剂均表现出催化氧化活性,其中,200℃焙烧的Pt-FeO_x/γ-Al₂O₃催化剂表现出最好的催化性能,可以将甲醛100%转化为CO₂和H₂O。较低温度焙烧的Pt-FeO_x/γ-Al₂O₃催化剂表面Pt物种具有较好的价态分布以及更多的界面活性位,如Pt-O-Fe物种,因而在温和条件下对甲醛的催化氧化活性较高。     

The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al₂O₃ samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al₂O₃ methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO₄²⁻/γ-Al₂O₃ was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO₂. On the other hand, when the calcination temperature of SO₄²⁻/γ-Al₂O₃ increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO₂. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO₄²⁻/γ-Al₂O₃ with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.     

N,P掺杂型C@Mo_2C催化剂的制备及其催化CO_2加氢反应研究

以三聚氰胺苯甲酸盐为碳源和氮源、以三聚氰胺磷钼酸盐为钼源、磷源和氮源,采用程序升温的方法制备了系列N,P掺杂型C@Mo_2C催化剂。采用XRD、SEM、TEM和XPS等对催化剂的结构、形貌和表面特性进行了表征,研究了三聚氰胺苯甲酸盐中n(三聚氰胺)/n(苯甲酸)、前驱体中n(C)/n(Mo)等因素对所制备催化剂的结构及其在二氧化碳加氢反应中催化性能的影响。在反应温度为220℃、反应压力为3.0 MPa、空速为3 600 m L/(g·h)的条件下,在N,P掺杂型C@Mo_2C的催化作用下,CO_2转化率可以达到12.2%,此时产物中CH_3OH的选择性达到52.2%。     

Gas transport property of polyallylamine–poly(vinyl alcohol)/polysulfone composite membranes

Polyallylamine (PAAm) was synthesized by free radical polymerization and characterized by Fourier transform infrared resonance (FT-IR) spectroscopy, hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy and differential scanning calorimetry (DSC). The composite membranes were prepared by using PAAm–poly(vinyl alcohol) (PVA) blend polymer as the separation layer and polysulfone (PSF) ultrafiltration membranes as the support layer. The surface and cross-section morphology of the membrane was inspected by environmental scanning electron microscopy (ESEM). The gas transport property of the membranes, including gas permeance, flux and selectivity, were investigated by using pure CO₂, N₂, CH₄ gases and CO₂/N₂ gas mixture (20 vol% CO₂ and 80 vol% N₂) and CO₂/CH₄ gas mixture (10 vol% CO₂ and 90 vol% CH₄). The plots of gas permeance or flux versus feed gas pressure imply that CO₂ permeation through the membranes follows facilitated transport mechanism whereas N₂ and CH₄ permeation follows solution–diffusion mechanism. Effect of PAAm content in the separation layer on gas transport property was investigated by measuring the membranes with 0–50 wt% PAAm content. With increasing PAAm content, gas permeance increases initially, reaches a maximum, and then decreases gradually. For CO₂/N₂ gas mixture, the membranes with 10 wt% PAAm content show the highest CO₂ permeance of about 1.80 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ KPa⁻¹ and CO₂/N₂ selectivity of 80 at 0.1 MPa feed gas pressure. For CO₂/CH₄ gas mixture, the membranes with 20 wt% PAAm content display the highest CO₂ permeance of about 1.95 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ KPa⁻¹ and CO₂/CH₄ selectivity of 58 at 0.1 MPa feed gas pressure. In order to explore the possible reason of gas permeance varying with PAAm content, the crystallinity of PVA and PAAm–PVA blend polymers was measured by X-ray diffraction (XRD) spectra. The experimental results show an inverse relationship between crystallinity and gas permeance, e.g., a minimum crystallinity and a maximum CO₂ permeance are obtained at 20 wt% PAAm content, indicating that the possibility of increasing CO₂ permeance with PAAm content due to the increase of carrier concentration could be weakened by the increase of crystallinity.     

Modified poly(phenylene oxide) membranes for the separation of carbon dioxide from methane

Two types of poly(phenylene oxide) (PPO) membranes were prepared: one by chemical modification through sulfonation using chlorosulfonic acid and another by physical incorporation with a heteropolyacid (HPA), viz., phosphotungstic acid. These membranes were tested for the separation of CO₂/CH₄ mixtures. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction techniques were used to confirm the modified structure of PPO as well as to understand its interactions with gaseous molecules. Scanning electron microscopy (SEM) was used to investigate the membrane morphology. Thermal stability of the modified polymers was assessed by differential scanning calorimetry (DSC), while the tensile strength was measured to evaluate their mechanical stability. Both chemical and physical modifications did not adversely affect the thermally and mechanical stabilities. Experiments with pure CO₂ and CH₄ gases showed that CO₂ selectivity (27.2) for SPPO increased by a factor of 2.2, while the PPO–HPA membrane exhibited 1.7 times increase in selectivity with a reasonable permeability of 28.2 Barrer. An increase in flux was observed for the binary CO₂/CH₄ mixture permeation with an increasing feed concentration (5–40 mol%) of CO₂. An enhancement in feed pressure from 5 to 40 kg/cm² resulted in reduced CO₂ permeability and selectivity due to the competitive sorption of methane. Both the modified PPO membranes were found to be promising for enrichment of methane despite exhibiting lower permeability values than the pristine PPO membrane.