Composite hollow fiber membranes for CO2 capture

Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material.The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO₂. The composite PVAm/PSf HF membranes having a 0.7–1.5 μm PVAm selective layer, showed CO₂/N₂ selectivity between 100 and 230. The selectivity was attributed to the CO₂ facilitated transport imposed by PVAm selective layer. The CO₂ permeance changed from 0.006 to 0.022 m³(STP)/(m² bar h) in direct correlation with CO₂ permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO₂ partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO₂/N₂ selectivity ranged between 20 and 500 and the CO₂ permeance from 0.11 to 2.3 m³(STP)/(m² bar h) depending on the operating conditions.For both PVAm/PSf and PVAm/PPO membranes, the CO₂ permeance was similar with the CO₂ permeance of uncoated hollow fiber supports, confirming that the CO₂ diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO₂ diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO₂ diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 μm PVAm top layer becomes the CO₂ diffusion rate limiting step.     

Facilitated transport of CO2 across a liquid membrane: Comparing enzyme, amine, and alkaline

In this work we compare the efficiency of facilitated transport of CO₂ across a liquid membrane by different facilitators as tested in either a supported liquid membrane (SLM) or a hollow fiber contained liquid membrane (HFCLM) configuration. Permeance and selectivity were evaluated by both experimental test and numerical simulation. These comparisons were used to define the best liquid membrane composition to maximize separation performance. We also consider other factors that affect the choice of the facilitator, e.g. operation temperature and cost. Under ambient operating conditions, carbonic anhydrase (CA) combined with an alkaline carbonate gives better performance than does diethanolamine (DEA).     

Ni-Sm_x/SiC催化剂甲烷二氧化碳重整性能研究

用浸渍法制备了不同钐含量的Ni-Sm_x/SiC催化剂,其中,镍的质量分数为9%,氧化钐的质量分数分别为0、2%、3%、4%、5%、7%。采用常压微型固定床反应器考察了不同催化剂在甲烷二氧化碳重整反应中的催化性能,并用BET、ICP、XRD、H2-TPR、TG-DTA、XPS和TEM等技术对反应前后催化剂进行表征。结果表明,加入钐后,重整反应中甲烷和二氧化碳转化率明显提高。当钐含量为5%时,Ni-Sm5/SiC表现出最好的活性和稳定性,而且反应后催化剂表面积炭量最少。其原因是钐的加入提高了活性组分与载体的相互作用,有效减少了表面积炭、提高了催化剂的稳定性。     

Yb_2O_3助剂对Ni/SiC催化剂甲烷二氧化碳重整性能的影响

采用浸渍法制备了Ni/SiC和Ni-Ybx/SiC(x=2%、4%、6%、10%,质量分数)催化剂,在固定床反应装置中考察了催化剂在甲烷二氧化碳重整反应中的性能。利用BET、ICP-AES、XRD、H2-TPR、TG-DTA、XPS和TEM等技术对催化剂进行了表征。实验结果表明,Yb的适宜添加量为4%~6%。在800℃条件下Ni-Yb4/SiC和Ni-Yb6/SiC催化剂具有优异的催化活性和稳定性,在100 h的重整反应中,甲烷和二氧化碳的转化率始终保持在90%以上。Yb2O3助剂能够抑制镍颗粒的生长和减少碳沉积量,因此,Ni-Yb/SiC催化剂在连续反应中表现出稳定的活性。     

Facilitated transport of CO2 in novel PVAm/PVA blend membrane

A defect-free ultra thin PVAm/PVA blend facilitated transport membrane cast on a porous polysulfone (PSf) support was developed and evaluated in this study. The target membrane was prepared from commercial polyvinyl amine (PVAm) and polyvinyl alcohol (PVA). Effects of experimental conditions were investigated for a CO₂–N₂ mixed gas. A CO₂/N₂ separation factor of up to 174 and a CO₂ permeance up to 0.58 m³(STP)/(m² h bar) were documented. Experimental results suggest that CO₂ is being transported according to the facilitated transport mechanism through this membrane. The fixed amino groups in the PVAm matrix function as CO₂ carriers to facilitate the transport whereas the PVA adds mechanical strength to the blend by entanglement of the polymeric chains hence creating a supporting network. The good mechanical properties obtained from the blend of PVA with PVAm, enabled an ultra thin selective layer (down to 0.3 μm) to be formed on PSf support (with MWCO of 50,000), resulted in both high selectivity and permeance. The PVAm/PVA blend membrane also exhibited a good stability during a 400 h test.     

Ionic liquid mediated CO2 activation for DMC synthesis

Promoted catalytic reaction between methanol and CO2 for dimethyl carbonate(DMC) synthesis is conducted over K2CO3/CH3 I catalyst in the presence of ionic liquid under microwave irradiation.The effect of ionic liquids incorporated with microwave irradiation on the yield of DMC is investigated.DMC was found to form at lower temperature in a relative short time,which indicated an enhanced catalytic process by ionic liquid.Among the ionic liquids used,1-butyl-3-methylimidazolium chloride is the most effective promoter.Density functional theory calculations indicate that CO2 bond lengths and angles changed due to the molecular interaction of ionic liquid and CO2,resulting in the activation of CO2 molecules and consequently the acceleration of reaction rate.     

Li4SiO4对CO2捕集性能的实验研究

以Li₂CO₃和SiO₂为原料,通过高温固相合成法合成了CO₂捕集剂Li₄SiO₄,并用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)对所合成的材料在CO₂捕集前后的晶相变化以及微观结构进行了表征。通过热重分析仪(TGA)研究了Li₄SiO₄材料吸附CO₂的性能,并在小型热态实验台架上进行了CO₂热态捕集实验。实验结果表明,Li₄SiO₄对CO₂的捕集性能受Li₄SiO₄合成温度、CO₂的吸附温度以及气体中CO₂含量的影响,在700 ℃下制得的Li₄SiO₄具有最佳的CO₂吸附特性,最大吸附增量可达34%。Li₄SiO₄的吸附能力随着CO₂含量和吸附时间的增加而增加,当CO₂浓度分别为75%、67%、60%时,700 ℃ Li₄SiO₄对CO₂最大吸附量分别可达6.68 mmol/g、3.37 mmol/g、2.02 mmol/g (理论量8.33 mmol/g)。     

Effect of temperature on intrinsic permeation properties of 6FDA-Durene/1,3-phenylenediamine (mPDA) copolyimide and fabrication of its hollow fiber membranes for CO2/CH4 separation

We have determined the effect of temperature on intrinsic permeation properties of 6FDA-Durene/1,3-phenylenediamine (mPDA) 50/50 copolyimide dense film and fabricated high performance hollow fiber membranes of the copolyimide for CO₂/CH₄ separation. The hollow fiber membranes were wet-spun from a tertiary solution containing 6FDA-Durene/mPDA (PI), N-methyl-pyrrolidone (NMP) and tetrahydrofuran (THF) with a weight ratio of 20:50:30 at different shear rates within the spinneret. We observed the following facts: (1) the CO₂/CH₄ selectivity of the copolyimide dense film decreased significantly with an increase in temperature; (2) the performance of as-spun fibers was obviously influenced by the shear rate during spinning. For uncoated fibers, permeances of CH₄ and CO₂ decreased with increasing shear rate, while selectivity of CO₂/CH₄ sharply increased with shear rate until the shear rate reached 2169 s⁻¹ and then the selectivity leveled off; (3) After silicone rubber coating, permeances of CH₄ and CO₂ decreased, the selectivity of CO₂/CH₄ was recovered to the inherent selectivity of its dense film. Both the permeances and selectivity with increasing shear rate followed their same trends as that before the coating; (4) there was an optimal shear rate at which a defect-free fiber with a selectivity of CO₂/CH₄ at 42.9 and permeance of CO₂ at 53.3 GPU could be obtained after the coating; and (5) the pressure durability of the resultant hollow fiber membranes could reach 1000 psia at room temperature.     

Combination of CO2 reforming and partial oxidation of CH4 over Ni/Al2O3 catalysts using fluidized bed reactor

The effects of the Ni loading, total feed flow rate, prereduction temperature, reaction temperature and feed gas ratio for combination of CO₂ reforming and partial oxidation of CH₄ over Ni/Al₂O₃ were investigated using a fluidized bed reactor. Methane conversion to syngas was drastically enhanced using a fluidized bed reactor over Ni/Al₂O₃ catalyst calcined at high temperature. The fluidized bed and the fixed bed reactor were compared and a promoting mechanism of the fluidized bed reactor was proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fabrication of polymer/fluoride-containing salts blend composite membranes for CO2 separation

Poly (N, N-dimethylaminoethyl methacrylate)-poly (ethylene glycol methyl ether methacrylate) (PDMAEMA-PEGMEMA) and cesium fluoride (CsF) were blended and used as the separation material of composite membranes. Hollow fiber composite membranes were fabricated by coating the blend on polysulfone (PSf) hollow fiber substrate. Introduction of fluorine ion improved the separation performance of the membrane. The concentration of coating solution was adjusted to obtain a membrane with high permeance. The composite membrane showed good performance with the CO2 permeance of 30.4 GPU (1 GPU = 10^-6 cm³(STP)/(cm²·s·cmHg)), and selectivities to CO2/N2, CO2/CH4, CO2/H2 and O2/N2 of 47.2, 37.6, 1.75 and 4.70, respectively. Potassium fluoride (KF), due to its low cost, was also used as a substitute of CsF to prepare composite membrane and the permeation data showed that CsF can be replaced by KF. The effect of operating temperature on the permeation properties of the composite membrane was also investigated.     

Surface modification of γ-alumina membranes by silane coupling for CO2 separation

Top layers of γ-Al₂O₃ composite membranes have been modified by the silane coupling technique using phenyltriethoxysilane for improving the separation factor of CO₂ to N₂. The separation efficiency of the modified membranes was strongly dependent upon the hydroxylation tendency of the support materials and the amount of the special functional group (i.e. phenyl radical) which was coupled onto a top layer. The separation factor through the TiO₂ supported γ-Al₂O₃ membrane was found to be fairly enhanced by silane coupling, but in case of the -Al₂O₃ supported membrane was not. The CO₂/N₂ separation factor through the modified γ-Al₂O₃/TiO₂ composite membrane is 1.7 at 90°C and ΔP = 2 × 10⁵ Pa for the binary mixture containing 50 vol% CO₂. The separation factor is proportional to the CO₂ concentration in the gas mixture, and the modified membrane is stable up to 100°C. The main mechanism of the CO₂ transport through the modified γ-Al₂O₃ layer is known to be a surface diffusion.     

CH_4和CO_2在油页岩中矿物质结构内部吸附的分子模拟

利用Materials Studio2017模拟软件构建了蒙脱石、高岭石、方解石和生石膏四种矿物质分子模型。采用巨正则蒙特卡洛(GCMC)方法和分子动力学(MD)方法对四种模型的吸附量和吸附热进行了模拟计算。研究表明,相同温度和压力条件下四种矿物质对CH_4和CO_2分子吸附量大小为:蒙脱石高岭石生石膏方解石;CH_4和CO_2分子的单组分吸附量随压力的增大而增大,两种气体吸附均符合Langmuir吸附规律;四种矿物质对CH_4和CO_2分子的等量吸附热均小于42 k J/mol,即为物理吸附;随着温度的升高,CH_4和CO_2分子的吸附量和吸附热均减小,且CH_4和CO_2分子的等量吸附热和等温吸附量之间呈良好的正相关。     

CO2/H2 separation by facilitated transport membranes immobilized with aqueous single and mixed amine solutions: Experimental and modeling study

An experimental and theoretical analysis to separate CO₂ using facilitated transport membranes immobilized with different aqueous single and mixed amine solutions have been performed. The membranes containing monoethanolamine (MEA), diethanolamine (DEA), monoprotonated ethylenediamine (EDAH⁺) and piperazine (PZ), as well as aqueous blends of PZ with MEA, DEA or EDAH⁺ were considered. The aqueous solution of PZ showed the highest CO₂ permeation rate with respect to other single amine solutions. Therefore blends of PZ with MEA, DEA and EDAH⁺ increased the permeance of carbon dioxide through mixed amine membranes.     

PAMAM dendrimer composite membrane for CO2 separation: Formation of a chitosan gutter layer

A poly(amidoamine) (PAMAM) dendrimer composite membrane with an excellent CO₂/N₂ separation factor was developed in-situ. The In-situ Modification (IM) method was used to modify the surface of commercial porous membranes, such as ultrafiltration membranes, to produce a gas selective layer by controlling the interface precipitation of the membrane materials in the state of a received membrane module. Using the IM method, a chitosan layer was prepared on the inner surface of a commercially available ultrafiltration membrane as a gutter layer, in order to affix PAMAM dendrimer molecules on the porous substrate. After chitosan treatment, the PAMAM dendrimer was impregnated into the gutter layer to form a PAMAM/chitosan hybrid layer. The CO₂ separation performance of the resulting composite membrane was tested at a pressure difference of 100 kPa and a temperature of 40 °C, using a mixed CO₂ (5 vol%)/N₂ (95 vol%) feed gas. The PAMAM dendrimer composite membrane, with a gutter layer prepared from ethylene glycol diglycidyl ether and a 0.5 wt% chitosan solution of two different molecular weight chitosans, revealed an excellent CO₂/N₂ separation factor and a CO₂ permeance of 400 and 1.6 × 10⁻⁷ m³ (STP) m⁻² s⁻¹ kPa⁻¹, respectively. SEM observations revealed a defect-free chitosan layer (thickness 200 nm) positioned directly beneath the top surface of the UF membrane substrate. After PAMAM dendrimer treatment, the hybrid chitosan/PAMAM dendrimer layer was observed with a thickness of 300 nm. XPS analysis indicated that the hybrid layer contained about 20–40% PAMAM dendrimer.     

离子液体支撑液膜分离CO2

支撑液膜是一种在湿法冶金、生物技术以及气体分离等多个领域都有应用的重要膜分离技术。本文回顾了支撑液膜技术分离CO2的研究进展,按照液膜相的不同,分类介绍了常规载体支撑液膜和离子液体支撑液膜,指出了常规载体支撑液膜分离CO2的局限性,重点介绍了离子液体支撑液膜分离CO2的发展,分析了气体在离子液体支撑液膜中的传质机理以及常规离子液体结构、含量和支撑膜材料等对分离效果的影响;讨论了离子液体的功能化方法以及功能化离子液体支撑液膜分离CO2的渗透率、选择性和液膜稳定性;介绍了两种新的离子液体支撑液膜改进方法:聚离子液体膜与凝胶化离子液体支撑液膜。最后指出了今后用于CO2分离的离子液体支撑液膜的发展方向。     

热等离子体与催化剂协同重整CH4-CO2

考察了热等离子体与催化剂协同作用于重整反应过程。实验采用三种不同的模式进行:等离子体单独作用、等离子体与催化剂协同作用、等离子体与催化剂协同作用且部分原料气引入等离子体放电区。结果表明,在模式三下,当原料气的总流量为5 m³/h、CH₄/CO₂物质的量比为4/6、等离子体的输入功率为14.4 kW时,CH₄-CO₂重整过程可获得最佳结果,CH₄转化率为77.00%、CO₂转化率为62.40%、H₂选择性为96.70%、CO选择性为88.60%、反应比能为193 kJ/mol、过程的能量转化率为66.4%,该结果已十分接近CH₄-H₂O(g)重整的技术指标。最佳结果主要得益于模式三下的三种不同的反应路径,放电反应、热化学反应与催化反应。     

MFI型分子膜的制备与H2S/CH4分离性能

采用二次生长法在多孔α-Al₂O₃载体上制备MFI型（ZSM-5和silicate-1）分子筛膜;通过XRD和SEM检测,证明所合成的分子筛膜为致密、交联和无取向的MFI型分子筛膜,厚度为5 μm;单组分气体渗透实验检测中,所制备样品膜的N₂渗透量均小于10^-11 mol/（m²·s·Pa）,可认为其无缺陷;同时,考察了样品分子筛膜对H₂S/CH₄混合气的分离效果,在渗透压分别为0.3和0.5 MPa时,silicate-1分子筛膜的H₂S/CH₄的分离因子分别为1.99和4.44,而ZSM-5分子筛膜的CH₄/H₂S的分离因子分别为6.71和12.85。     

低阶煤半焦利用热重在O2/CO2、O2/N2和O2/Ar气氛下燃烧特性研究

利用热重研究了两种中国西北典型低阶煤半焦的燃烧特性。探究了不同气氛（O₂/CO₂、O₂/N₂和O₂/Ar）和不同氧气浓度对其燃烧特性的影响。实验结果表明,无论是反应气氛还是氧气浓度都会对低阶煤半焦的燃烧产生影响。相比于N₂和Ar,CO₂明显有利于燃烧反应进行：当反应气氛由O₂/CO₂变为O₂/Ar时,两种不同低阶煤半焦的燃尽温度分别升高了63.7和68.8℃;而当反应气氛由O₂/CO₂变为O₂/N₂时,两种不同低阶煤半焦的燃尽温度分别升高了135.9和129.6℃。在研究范围内,氧气浓度的提高也能明显提高半焦的燃烧性能。与此同时,半焦燃烧特性的动力学分析表明,随着氧气浓度提高,两种半焦燃烧反应的表观活化能E和指前因子A均呈增大趋势。通过对E和A两者关系的分析结果表明,半焦富氧燃烧的活化能和指前因子存在动力学补偿效应。     

增压O_2/CO_2气氛下煤燃烧特性实验研究

增压O2/CO2燃烧是一种可高效分离回收CO2的新兴燃烧技术,其燃烧机理与常压空气、常压O2/CO2燃烧存在较大差异。在加压热重分析仪上研究了增压条件下总压、氧浓度、气氛及粒径等反应参数对美国烟煤和淮北无烟煤燃烧特性的影响,确定了煤的着火温度,并对其进行燃烧动力学分析。结果表明,增压O2/CO2气氛下,随着压力或氧浓度的增加,DTG曲线向低温区移动,煤样整体燃烧速率加快。压力提升、氧浓度增加及煤粉细化均可改善O2/CO2气氛下煤样的着火特性。常压O2/CO2气氛下煤粉燃烧基本属于一级反应;增压O2/CO2气氛下,低温区属于0.5级反应,而高温区属于1.5级反应。     

Sn/Cu电极电化学还原CO2的研究

采用电沉积法制备Sn/Cu电极,由SEM观察并研究了电沉积电流密度对电极形貌的影响.在碱性三电极体系中考察了Sn/Cu电极对析氢、CO2还原的影响.发现10 mA.cm-2和15 mA.cm-2电沉积电流密度下制得的电极活性较高,尤以15 mA.cm-2时电极性能更佳,并指出了电还原CO2关键材料的结构特性.