K_2CO_3活化制备淀粉基碳分子筛

以可溶性淀粉为碳源、三嵌段共聚物F127为模板剂和K_2CO_3为活化剂,采用一步合成法制备系列淀粉基碳分子筛。通过扫描电子显微镜和N_2吸附-脱附分析淀粉基碳分子筛孔隙形貌和孔结构,采用热重-TG和傅里叶红外光谱表征原料和样品的物质结构官能团。结果表明,K_2CO_3浓度、F127添加比例、反应时间和反应温度影响淀粉基碳分子筛的孔隙结构。在炭化温度800℃、K_2CO_3浓度为0.50 mol·L~(-1)、F127与淀粉质量比=1∶3、反应温度50℃和反应时间12 h条件下制备的淀粉基碳分子筛,孔径集中于0.63 nm,比表面积为1 069.290 4 m~2·g~(-1),单点孔容0.667 901 cm~3·g~(-1)。     

金属离子改性分子筛吸附水的Monte Carlo模拟

金属离子改性分子筛吸附脱水具有节能环保、吸附容量高、净化精度高等特点,受到广泛关注,但还缺乏平衡吸附量等基础数据。本文利用Materials Studio软件中Sorption模块进行落位计算得到合理的金属离子落位和分子筛构型,同时利用Reflex模块计算分子筛的XRD谱图,计算结果与国际分子筛协会（IZA-SC）的XRD标准谱图一致。采用蒙特卡罗法（Monte Carlo）的"COMPASS"力场对NaX、NaY和NaA 3种分子筛以及Ca²⁺、Fe³⁺、Mg²⁺和K⁺改性分子筛吸附水进行分子模拟。结果表明,水的吸附属于第Ⅰ型Langmuir吸附等温线。NaX、NaY和NaA分子筛对水的平衡吸附量分别为360.3mg/g、393.8mg/g和295.5mg/g,Mg²⁺取代的X型、Y型和A型分子筛对水的吸附能力增加幅度最大。MgX的平衡吸附量达472.6mg/g,较未改性时增加了112.3mg/g。本研究可为高效分子筛脱水吸附剂的筛选及其应用提供一定的理论依据和指导。     

碱处理Beta分子筛吸附脱硫动力学

当吸附质尺寸与分子筛的孔结构尺寸相当时才能进入分子筛的内部,分子筛的孔道尺寸是影响吸附性能的重要因素之一,NaOH溶液处理可实现分子筛孔径的调变,以改善分子筛对吸附质的选择性和扩散传质能力。通过对碱处理后的Beta分子筛进行BET、TEM、FT-IR、XRD和NH₃-TPD表征,以考察碱处理对Beta分子筛晶体结构、表面酸性和孔结构参数的影响。碱处理Beta分子筛吸附脱硫的结果显示,碱处理后Beta分子筛吸附量和吸附速率明显增加,尤其动力学尺寸较大的二苯并噻吩吸附量达到了5.06 mg·g^-1。吸附动力学研究显示,该吸附过程符合准二级动力学方程,碱处理后分子筛吸附速率常数和粒子内扩散速率常数明显增大,有效地改善了硫化合物在孔道内扩散传质性能,脱硫效率增加。     

PHYSICAL ABSORPTION OF CARBON DIOXIDE IN WATER FLOWING IN AN INCLINED CELL

Studies of the mass transfer mechanisms which occur when CO₂ is absorbed into flowing water films in an inclined cell are described. The amount of gas absorbed is small and therefore a highly sensitive optical apparatus was used to obtain direct concentration readings. Gas bulk concentrations in the liquid were obtained by titration. The experimental work was mainly confined to angles of inclination less than 5^°.

Hydrodynamic studies showing increased flow rates at the sides of the inclined cell, due to meniscus effects, are presented. Hydrodynamic “end effects” at the liquid exit from the cell, which cause increases in the absorption, have been successfully minimised by the design of the apparatus and the experimental technique employed.

It is demonstrated, for angles of inclination less than 3^°, that convective disturbances (in the form of micioflows, eddies or perturbations) are present in the liquid. These perturbations are not visible or directly determinable. They produce an increased solute transport from the liquid surface over that which can occur by molecular diffusion alone. Beyond 3^° inclination the disturbances or perturbations persist and are reinforced by hydrodynamic instabilities eventually leading to observable wave formation.     

碳分子筛变压吸附提纯沼气的性能

选择碳分子筛,以CH₄和CO₂为原料气,对变压吸附法提纯沼气中生物甲烷的分离性能进行了研究。采用高精度智能重量分析仪IGA-100测定了25℃下CH₄、CO₂和N₂纯组分气体在碳分子筛上的吸附平衡等温线,计算了3种气体在碳分子筛内的扩散速率CO₂>N₂>CH₄。使用单塔变压吸附装置测量了动态吸附穿透曲线,考察了吸附压力、气体流量和少量氮气等因素对吸附分离的影响,并对吸附机理做了初步探讨。实验结果表明,在吸附压力为0.4MPa、气体流量为200mL/min时,在碳分子筛上CO₂穿透吸附量为35.9mL/g,CH₄穿透吸附量为5.4mL/g,CO₂/CH₄分离系数高达12.6,可直接从吸附塔顶富集纯净的CH₄,而且碳分子筛可以通过抽真空完全再生,是一种理想的吸附材料;在有少量氮气存在的实验条件下,由于碳分子筛对CH₄和N₂具有动力学分离效应,仍能在塔顶富集高浓度的CH₄。     

铁离子改性碳分子筛对氮气/甲烷分离性能的研究

针对碳分子筛对氮气/甲烷分离体系分离比低的问题,采用浸渍法以市售空分碳分子筛（CMS）为基体,制备了分离氮气/甲烷的铁离子改性碳分子筛。通过静态吸附量、分离比、吸附动力学及热力学性质考察了铁离子负载量对碳分子筛吸附分离氮气/甲烷性能的影响。结果表明：铁（Ⅲ）的负载减小了CMS的比表面积、微孔体积和孔径,使CMS超微孔的孔径分布呈现更集中的趋势。这种集中性以动力学性能下降为代价,明显提高了碳分子筛对氮气/甲烷的吸附分离比。在303 K、0.7 MPa条件下,综合性能优异的0.3%铁改性CMS具有6.03的氮气/甲烷吸附分离比。     

Phase transition phenomena of the adsorbed 1-dodecanol monolayer at the air–water interface

Phase transition phenomenon of the 1-dodecanol monolayer at the air/water interface was studied by the dynamic γ(t) curves and the adsorption isotherm obtained by ellipsometry at 20 °C. The surface-concentration adsorption isotherm clearly showed three abrupt increases at bulk concentration C of 1.3 × 10⁻⁹, 2 × 10⁻⁹ and 3.7 × 10⁻⁹ mol/mL, respectively. The 1st and the 3rd transitions observed herein, that were typical 2D first-order transitions, were consistent with the gas to liquid expanded (G–LE) and the liquid expanded to liquid condensed (LE–LC) phase transitions observed in a previous tensiometry study. The 2nd transition that occurred at C = 2 × 10⁻⁹ mol/mL was not identified from any previous dynamic surface-tension profiles. Judging from the substantial increase in the film thickness of the transition, it was believed that the orientation change of the adsorbed molecule was involved in the LE phase. A LE_h and a LE_v phase, that denoted the “lie-down” and “stand-up” types of adsorption, respectively, was used to describe this transition and a cusp, instead of a constant surface-tension region, was observed in the dynamic γ(t) curves for this transition. This suggested that, since the surface tension varied during the transition process, the newly identified LE_h and LE_v transition might not be the typical first-order type of phase transition.     

The Anisotropy of the Surface Tension of Polar Liquids: The Case of Liquid Crystals

The contact angle of the liquid crystal (LC) 4-phentyl, 4'-cyano biphenyl (5CB) on glass or polyethylene does not correspond to the value expected from its surface tension measured by the “du Nouy” method (29 × 10^-3 JM^-2). The value deduced from the Young-Dupre law is 40 × 10^-3 JM^-2.

Both these values have already been reported in the literature. Their apparent discrepancy is explained by the LC surface tension anisotropy. We show that 5CB as many other LCs orient perpendicular to the free surface but parallel to glass or polyethylene Thus both values of the surface tension correspond to two different molecular orientations.

The LC oriented perpendicularly has a surface tension of 29 × 10^-3 JM^-2 and 40 × 10^-3 JM when it lies parallel to the surface. We suggest that the anisotropy between the perpendicular and parallel state of LCs also exists between two perpendicular orientations. Furthermore, such anisotropy associated with any polar molecules explains the difference of the interfacial energy of similar polar or non polar (i.e., octanol-octane) compounds and water.     

ROTATING DRUM HEAT EXCHANGER

A Sparcely Filled Liquid/Liquid Rotating Drum Heat Exchanger (RDHE) was investigated for its heat transfer characteristics. Drums upto 10cm in diameter and 1.0m long were rotated upto 350 rpm. Liquids investigated varied in kinematic viscosity from water at 2.2 × 10^-3m²/hr to 32wt% LiCl solution at 6.3× 10^-3m²/hr. In this range data showed that the film heat transfer coefficient did not depend on kinematic viscosity. This resulted in a “best fit” correlation of Nusselt Number (100 to 800) with Peclet Number (200,000 to 2,000,000) as oppossed to Nusselt Number with Reynolds Number (2000 to 20,000). Analysis suggested that the heat transfer between two liquid films adhering to opposite surfaces of a rotating drum was controlled by conduction not a convection mechanism. The RDHE has found application in the heat transfer between two liquids of similar pressure where little to no pressure drops are allowed.     

Dechlorination of chlorinated hydrocarbons by catalytic steam reforming

Past research in this laboratory on catalytic steam reforming of chlorinated hydrocarbons demonstrated extremely high levels of destruction (0.99999+) at 600–750 °C, with GHSVs as high as 2.5 × 10⁵ h⁻¹. Feasible operation was demonstrated with chlorinated alkanes, alkenes, aromatics and PCBs using Pt/γ-Al₂O₃ catalysts. The major mechanism for deactivation with trichloroethylene was sintering of the γ-Al₂O₃ support and encapsulation of Pt crystallites.

Evidence is presented here that ZrO₂ is a superior support for steam reforming of trichloroethylene (TCE), due to its low acidity and ability to store oxygen. Formulations of 0.8 wt.% Pt/ZrO₂ tested at a GHSV of 20,000 h⁻¹ and a H₂O/C ratio of 20 operated for 42 days at 750 °C, with only slight carbon deposits in the first 15% of the catalyst bed. No pyrolysis was found, and the product CO/CO₂ ratio was at equilibrium, indicating high water gas shift activity with very low CO concentrations. Kinetic measurements revealed a pseudo-first order rate equation, sintering of the support and Pt was much less than with γ-Al₂O₃ supports, and no encapsulation was detected. Slow deactivation occurred due to deposition of catalytic carbon. This carbon was removed by combustion with air, and the rate of deactivation indicated the 42-day run would have lasted seven months.     

一步法制备多级孔全硅分子筛silicalite-1及其在丙烷脱氢中的应用

调节硅源、原料比例、加料顺序等结晶条件,采用一步水热法直接制备具有多级孔结构和高比表面积的全硅分子筛silicalite-1。SEM,BET及XRD表征表明其平均粒径250 nm,比表面积500 m~2·g~(-1),具有多级孔径结构,NH_3-TPD及红外测试表明其表面具有大量的弱酸位。将其作为催化剂载体,应用到丙烷脱氢制丙烯反应中,表现出优异的催化活性和稳定性。丙烷转化率超过40%,接近平衡转化率,丙烯选择性约95%,连续运行120 h催化性能基本保持稳定,相比传统丙烷脱氢Al2O3载体催化剂体系具有广阔的开发潜力和市场前景。     

Continuous amino-functionalized University of Oslo 66 membranes as efficacious polysulfide barriers for lithium−sulfur batteries

The shuttle effect of soluble polysulfides is a serious problem impeding the development of lithium−sulfur batteries. Herein, continuous amino-functionalized University of Oslo 66 membranes supported on carbon nanotube films are proposed as ion-permselective interlayers that overcome these issues and show outstanding suppression of the polysulfide shuttle effect. The proposed membrane material has appropriately sized pores, and can act as ionic sieves and serve as barriers to polysulfides transport while allowing the passage of lithium ions during electrochemical cycles, thereby validly preventing the shuttling of polysulfides. Moreover, a fast catalytic conversion of polysulfides is also achieved with the as-developed interlayer. Therefore, lithium−sulfur batteries with this interlayer show a desirable initial capacity of 999.21 mAh·g^–1 at 1 C and a durable cyclic stability with a decay rate of only 0.04% per cycle over 300 cycles. Moreover, a high area capacity of 4.82 mAh·cm^–2 is also obtained even under increased sulfur loading (5.12 mg·cm^–2) and a lean-electrolyte condition (E/S = 4.8 μL·mg^–1).     

The entrapment of UO2 in mesoporous MCM-41 and MCM-48 molecular sieves

A method based on direct template-ion-exchange was employed for the entrapment of UO₂²⁺ ions in MCM-41 and MCM-48 molecular sieves via swapping of cetyltrimethylammonium cations present in the mesoporous channels by the UO₂²⁺ ions in an aqueous solution. The samples were characterized by XRD, FT-IR, and ICP-AES techniques. The entrapment of UO₂²⁺ ions is facilitated by the large pore size vis-a-vis the high surfactant content in the as-synthesized host materials. A higher loading of UO₂²⁺ ions was achieved in MCM-48 as compared to MCM-41, which could be attributed to its three-dimensional pore system and higher surfactant-to-silica ratio. FT-IR results provide an evidence of a strong binding of UO₂²⁺ groups with the defect silica sites of mesoporous molecular sieves.     

Synthesis and characterization of tantalum silicalite molecular sieves with MFI structure

Tantalum silicalite-1 (TaS-1) with MFI structure was prepared using the hydrothermal synthesis method. X-ray diffraction, scanning and transmission electron microscopies, Fourier transform infrared spectroscopy, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, ²⁹Si magic-angle spinning nuclear magnetic resonance spectroscopy, temperature-programmed desorption of ammonia (NH₃-TPD), physical adsorption of nitrogen and elemental analysis were then performed to evaluate its physico-chemical properties and provided evidence for the incorporation of Ta⁵⁺ into the zeolite framework. The unit cell volume of tantalum silicalite-1 increased linearly with increasing tantalum content, suggesting isomorphous substitution of Si⁴⁺ by Ta⁵⁺ in the lattice framework. The characteristic framework infrared spectra shifted to lower frequencies as Ta⁵⁺ was incorporated into the silicalite lattice and showed a characteristic absorption band at 965 cm⁻¹, probably due to Si---O---Ta linkages. In the UV–vis spectrum, the absorption assigned to the presence of Ta⁵⁺ in the zeolite framework was observed at around 200 nm. In addition, NH₃-TPD studies revealed weak acidity in tantalum silicalite-1 due possibly to [Ta(OH)---Si] sites in the framework.     

Kinetische Untersuchungen der adsorptiven Luftzerlegung an Kohlenstoffmolekularsieben

In recent years, the adsorptive air separation was established as one of the most important thermal separation processes for the generation of nitrogen and oxygen from air. Both the effects of equilibrium and kinetics can be applied for the separation of nitrogen and oxygen. Nitrogen can be enriched by an equilibrium effect in the adsorbed phase of zeolites, whereas oxygen remains in the gas phase. In contrast to zeolites, oxygen can diffuse much faster into the pores of carbon molecular sieves resulting in a gas phase enriched with nitrogen. In order to exploit this kinetic separation effect in industrial applications, the properties of carbon molecular sieves, e.g., pore aperture, overall pore volume, or release of heat of adsorption are important. Furthermore, research activities are focused on theoretical approaches to describe the kinetic behavior.     

Synthesis and characterization of a new microporous cesium silicotitanate (SNL-B) molecular sieve

Ongoing hydrothermal Cs–Ti–Si–O–H₂O phase investigations has produced several new ternary phases including a novel microporous Cs–silicotitanate molecular sieve, SNL-B with the approximate formula of Cs₃TiSi₃O_9.5 · 3H₂O. SNL-B is only the second molecular sieve, Cs–silicotitanate phase reported to have been synthesized by hydrothermal methods. Crystallites are very small (0.1×2 μm²) with a blade-like morphology. SNL-B is confirmed to be a three-dimensional molecular sieve by a variety of characterization techniques (N₂ adsorption, ion exchange, water adsorption/desorption, solid state cross polarization-magic angle spinning nuclear magnetic resonance). SNL-B is able to desorb and adsorb water from its pores while retaining its crystal structure and exchanges Cs cations readily. Additional techniques were used to describe fundamental properties (powder X-ray diffraction, FTIR, ²⁹Si and ¹³³Cs MAS NMR, DTA, SEM/EDS, ion selectivity, and radiation stability). The phase relationships of metastable SNL-B to other hydrothermally synthesized Cs–Ti–Si–O–H₂O phases are discussed, particularly its relationship to a Cs–silicotitanate analogue of pharmacosiderite, and a novel condensed phase, a polymorph of Cs₂TiSi₆O₁₅ (SNL-A).     

Plating on anodized aluminum—I. The mechanism of charge transfer across the barrier-layer oxide film on 1100 aluminum

The mechanism of plating on anodized aluminum was investigated. Porous anodic films were formed on 1100 aluminum and the electrochemical behaviour of a number of test reactions (Ag⁺/Ag, Cu²⁺/Cu, [Fe(CN)₆]⁴⁻ /[Fe(CN)₆]³⁻ and QH₂/Q) was determined. Hydrogen evolution can damage the oxide film and enhance the rate of electrochemical reactions on the surface. It is not a prerequisite, however, for metal deposition and other electrode reactions. Under the experimental conditions studied, the activity of the pores was not uniform and metal was plated in only a fraction of the pores, even when the total charge passed exceeded that required to fill all the pores tenfold or more. Metal ions can penetrate the barrier layer at the bottom of the pores by migration or diffusion, to be discharged at the aluminum surface. The barrier layer may also act as a heavily doped semiconductor which allows passage of charges with no specificity for the reversible potential of the redox couple tested. Observation of the uniformity of deposition of metals into the pores at an early stage by SEM with electron microanalysis can serve as a powerful tool in determining the best conditions for uniformly filling the pores. This should lead to improvements in the quality of plating on anodized aluminum.     

Water Flow in,Through, and Around the Gas Diffusion Layer

Liquid water produced in polymer electrolyte membrane fuel cells is transported from the cathode catalyst/membrane interface through the gas diffusion layer (GDL) to the gas flow channel. Liquid water travels both laterally (in the plane of GDL) and transversely through the largest pores of the porous GDL structure. Narrow apertures in the largest pores are the primary resistance to liquid water penetration. Carbon paper has limiting apertures ∼20 μm in diameter and ∼1 μm in length whereas carbon cloth has apertures ∼100 μm in diameter and ∼200 μm in length. After sufficient hydrostatic pressure is applied, water penetrates the limiting aperture and flows through the pore. The pressure required for water to flow through the pores is less than the pressure to penetrate the limiting aperture of the pores. Water moved laterally and directed through a small number of transverse pores. There is less resistance to lateral liquid water flow at the interface between the GDL and a solid surface than through the GDL. The results from these experiments suggest that water flow through the GDL is dominated by a small number of pores and most pores remain free of liquid water.     

Catalytic hydroxylation of benzene over vanadium-containing molecular sieves

Vanadium-containing molecular sieves with mesopore structures such as MCM-41 and MCM-48, and micropore structures such as BEA and MFI were synthesized by hydrothermal method. XRD, FT-IR, UV–Vis DRS, EPR and XANES were used to characterize their structure, electronic states, and active sites of vanadium species. All the vanadium containing molecular sieves exhibit a pre-edge peak in the V K-edge XANES. The charge transfer transition bands appear at 250 and 340 nm are attributed to the [V^V=O]³⁺ species in the tetrahedral framework position and in the surface wall, respectively. Upon calcining the as-synthesized vanadium-containing samples in the air, V^IV species are oxidized to V^V which is EPR silent. V^V is reduced reversibly by dehydration at 723 K. As for catalytic hydroxylation of benzene, V-MCM-41 shows the highest activity where the turnover number is 64 h⁻¹ at 343 K. Under the higher temperature and the higher acidic conditions, respectively, the catalytic activity is enhanced.     

PREPARATION AND TESTING OF CARBON/SILICALITE-1 COMPOSITE MEMBRANES

Methods for preparation of carbon/silicalite-1 composite membranes have been developed. First, silicalite-1 membranes were prepared by in-situ hydrothermal synthesis on both porous alumina and metal disks. Preparation of the carbon/silicalite-1 composite membranes was accomplished by polymerizing furfuryl alcohol on the surface of the silicalite-1 membrane, followed by carbonizing the polymer layer in an inert atmosphere at 773 K. The pure silicalite-1 membrane showed no selectivity for single gases, indicating the presence of intercrystalline diffusion and viscous flow as the dominant transport mechanism. The carbon/zeolite composite membrane exhibited ideal selectivities for He/N₂, CO₂/N₂, and N₂/CH₄ of 11.99, 17.12, and 3.58 at room temperature. No permeation of n-butane and i-butane for the composite membrane was detected up to temperatures of 453 K, indicating that the pore size for the composite membrane was approximately 0.4 nm. By carefully oxidizing the carbon layer in air at 623 K, the pore size of the composite membrane was adjusted such that n-butane permeation could be detected. No permeation of i-butane was apparent, suggesting that the pore size of the composite membrane had been enlarged to approximately 0.5 nm. Further oxidation of the carbon layer produced a finite n-/i-C₄H₄ ideal selectivity, indicating that the pore size of the membrane was now larger than 0.55 nm. Therefore, selective oxidation of the carbon layer can be used to control the pore size of the composite membrane.