An FT-IR study of the adsorption of aromatic hydrocarbons and of 2,6-lutidine on H-FER and H-ZSM-5 zeolites

The interaction of aromatic hydrocarbons benzene, toluene, o-, m- and p-xylene and of methyl pyridines (in particular 2,6-lutidine) with H-ZSM-5 and H-FER zeolites has been studied. Two different H-ZSM-5 samples with strongly different intensity ratios between the two main OH stretching bands have been used. Benzene, toluene and p-xylene enter easily the cavities and give rise to three different H-bonded complexes. Two of them are strongly bonded while the third is likely a very hindered and distorted one. o-Xylene enters slowly the cavities and m-xylene even more slowly. Faster diffusion occurs at higher temperatures. On the contrary, xylenes do not enter the FER cavities. In spite of its steric hindrance, supposed to be the same of m-xylene, 2,6-lutidine enters fast the ZSM channels and is protonated by the internal sites. On the contrary, it does not enter the FER cavities, but it is protonated too on the external silanols sites. Evidence is provided for some kind of heterogeneity of the internal sites of ZSM-5 zeolite. Additionally, it is concluded that other effects besides the molecular sieving effect may play a role in the access and diffusion of molecules into the zeolite channels.     

Poly(1-trimethylsilyl-1-propyne)/MFI composite membranes for butane separations

The separation of equimolar mixtures of i-butane and n-butane through poly(1-trimethylsilyl-1-propyne)/MFI composite membranes was studied. Membranes were characterized by XRD and SEM. Addition of 50 wt% MFI particles into a PTMSP matrix showed increased permeability and simultaneous improved selectivity in the temperature range 25–200 °C. The best improvement was seen at 150 °C for the composites, giving almost threefold increase in permeability and 56% higher n-butane/i-butane selectivity over the pure polymer. To our knowledge, this is the first successful demonstration of the incorporation of a molecular sieve into a polymer matrix for butane isomer separations. The composite membranes were also tested for separations of n-hexane/2,2-dimethylbutane and p-xylene/o-xylene.     

Hydrocarbon sorption properties of pure silica MCM-22 type zeolite

The adsorption properties of the MWW compositional end member, ITQ-1, have been explored empirically and via computer simulation using n-hexane, 3-methylpentane, 2,3-dimethylbutane, p-xylene and ethylbenzene as adsorbate probes. n-Hexane and 3-methlypentane diffuse rapidly and both have a sorption limit of four molecules per unit cell, three of which are in the large channel cavities. 2,3-dimethylbutane sorbs more slowly through the 10-ring windows; the limiting three molecules per unit cell are all in the large cavities. The two aromatics adsorb in both channel systems, with p-xylene diffusing rapidly and ethylbenzene more slowly but much faster than 2,3-dimethylbutane. No clear distinction between intra- and extra-crystalline adsorption was observed. Computer modeling indicated distinctions between the two channel systems.     

COMPOSITION AND QUALITY OF THE GASOLINE OBTAINED FROM SYNGAS ON Cr2O3-ZnO/ZSM5 CATALYSTS

The kinetic equations for the formation of the lumps of the gasoline produced (C₅⁺ fraction), paraffins (C₅-C₈), xylenes (o-xylene, m-xylene and p-xylene) and aromatics (benzene, toluene, C₉-C₁₁) in the transformation of syngas on Cr₂O₃-ZnO/ZSM5 bifunctional catalyst have been established as a function of the concentration of both reactants (CO and H₂) and CO₂ byproduct. The effect of the operating conditions on the RON and on the molecular weight of the gasoline has been studied by experimentation in an integral fixed bed reactor in the range between 10 and 50atm and between 300 and 425°C. The octane index increases with Cr/Zn atomic ratio of the Cr₂O₃-ZnO metallic function, with Si/Al ratio of the HZSM5 zeolite, with space time and with the CO/H₂ molar ratio in the feed, in that order, whereas it passes through a maximum with pressure (at 20 atm) and with temperature (at 375°C). On the other hand, the molecular weight of the gasoline increases with the Cr/Zn atomic ratio, pressure, CO/H₂ molar ratio and space time, and decreases with the Si/Al ratio and temperature.     

Diffusion of linear paraffins in NaCaA studied by the ZLC method

The zero length column (ZLC) technique has been applied to investigate the kinetics of linear alkanes (n-hexane to n-tetradecane) in a sample of zeolite NaCaA. The diffusivity values are found to be monotonically decreasing with chain length from n-hexane to n-undecane, slightly increasing between n-undecane and n-tridecane, and eventually levelling-off at n-tetradecane. The initial monotonic decreasing trend is similar to previous ZLC studies, although the values are somewhat higher for the heavier alkanes. The values found are reasonably close to PFG-NMR results and have similar qualitative trends, but do not show a marked maximum in comparison to recent neutron spin echo (NSE) results. The difference between the infinite dilution ZLC data and the microscopic techniques can not be ascribed to the intrusion of surface resistances since partial loading experiments provide clear evidence that the measurements are controlled by internal diffusion. The activation energy of linear alkanes in NaCaA lies between 20 and 26 kJ/mol.     

Influence of exchanged cations (Na, Cs, Sr and Ba) on xylene permeation through ZSM-5/SS tubular membranes

Na-ZSM-5 membranes were synthesized by secondary growth on the outer surface of stainless steel porous tubes. The membranes were ion-exchanged with Cs⁺, Ba²⁺ and Sr²⁺ to investigate their effect upon the separation of p-xylene from m-xylene and o-xylene. The permeation through the membranes was measured between 150 and 400 °C using each xylene isomer separately and a ternary mixture. All the membranes were selective to p-xylene in the temperature range studied. N₂ and xylene permeation measurements together with SEM observations were used to determine whether or not cracks and/or pinholes developed after exposure to the xylene isomers at high temperature (400 °C). Neither pore blockage nor extra-zeolitic pores developed after the ion exchange procedure and subsequent calcination. Furthermore, duplicate synthesized membranes of each cation form had similar separation factors and permeances. The duplicate values differ much less than the measurement error. The p-xylene permeation flux decreased in the order: Na-ZSM-5 > Ba-ZSM-5 > Sr-ZSM-5  Cs-ZSM-5 while the permeation flux of the m- and o-xylene decreased in the order Na-ZSM-5 > Sr-ZSM-5 > Ba-ZSM-5 > Cs-ZSM-5. The membrane that exhibited the best performance was Ba-ZSM-5, with a maximum p/o separation factor of 8.4 and a p-xylene permeance of 0.54 × 10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹ at 400 °C.     

Tracer diffusion of aromatic hydrocarbons in n-hexane up to the supercritical region

Tracer diffusion coefficients are determined with the Taylor-Aris dispersion method for benzene, toluene, p-xylene, mesitylene, naphthalene and phenanthrene in liquid n-hexane along the vapour-liquid coexistence curve from 333.2 to 485.4 K and in supercritical n-hexane at 507.4, 522.0, 533.3, 543.2K and several pressures. A rough-hard-sphere model is found to represent quite well (to within ± 6%) the observed tracer diffusivities in the density region where computer simulation results for D₁₂^SHS/D₁₂^E are available, i.e. 1.5 V/V₀ 3. Furthermore, Hildebrand's free volume model together with the excluded-volume effect provides the basis for a general linear relationship between D₁₂V_C12 and V for tracer diffusion in liquid n-hexane up to its critical temperature. For diffusion in the supercritical region two definitions of reduced tracer diffusivity, one based on the rough-hard-sphere theory of tracer diffusion and the other on the extension of Helfand-Rice corresponding state principle for self-diffusion, permit generalized correlations that are capable of representing the experimental results in both supercritical n-hexane and carbon dioxide to within ±4% on average.     

无黏结剂ZSM-35沸石的制备与催化反应性能

考察了不同硅铝比无黏结剂ZSM-35沸石分子筛的合成条件及催化反应性能。以多种有机胺（乙二胺、环己胺、正丁胺）为模板剂,在SiO₂/Al₂O₃为30～40的情况下均可以水热合成无黏结剂ZSM-35沸石。在乙二胺模板剂体系中,ZSM-35合适的晶化温度为130～160℃。提高SiO₂/Al₂O₃至58时,在乙二胺和正丁胺模板剂体系下,合成产物易出现ZSM-5和石英相,而环己胺作为模板剂可以成功制备纯相的无黏结剂ZSM-35沸石。在SiO₂/Al₂O₃为72时,以乙二胺、环己胺、正丁胺为模板剂均难合成纯相ZSM-35沸石,易产生杂晶。在二甲苯异构化反应中,制备的ZSM-35沸石表现出比ZSM-5沸石更好的对二甲苯选择性和更低的二甲苯损失。     

邻二甲苯高效降解菌的分离及其降解特性

以邻二甲苯作为唯一碳源,从长期受焦化废水污染的土壤中分离得到一株能降解邻二甲苯的高效菌株LJ5,经生理生化和16S rDNA鉴定,该菌株属于假单胞菌属(Pseudomonas sp.)。菌株LJ5适宜的降解条件为:培养温度35℃,pH=7.0～8.0,摇床转速150r/min。菌株LJ5在邻二甲苯浓度高达2500mg/L时,对其的去除率在30h内可达到73%,它对邻二甲苯的降解过程符合Monod动力学方程,当邻二甲苯浓度远远大于64.32mg/L时,LJ5降解底物速率最高,达到43.29mg/(L·h)。菌株LJ5能在实际焦化废水中很好的生长,菌液投加48h后可使COD降解率达到34.74%。     

Kinetics of sorption of aromatics in zeolite ZSM-5

The kinetics of sorption of benzene, p-xylene and o-xylene into crystals of zeolite ZSM-5 in the hydrogen form were investigated gravimetrically for well-defined constant boundary conditions and constant temperature (298 K) of the sorbent. Zeolite crystals were mounted on aluminium foil separated in space, the metal foil acting as sample holder and heat sink in the exothermic sorption process. The influence of crystal size on the rate of sorption was studied by comparing two samples of the zeolite differing only in crystal size.

Sorption of benzene into ZSM-5 follows a pattern expected on the basis of the diffusion equation with constant diffusivity. p-Xylene is sorbed initially faster than benzene; its rate of sorption decreases at higher degrees of loading where a hysteresis loop in the isotherm is observed. Sorption of o-xylene proceeds much more slowly than that of p-xylene and does not seem to be controlled by diffusion.     

燃煤烟气条件下锰铈基催化剂对邻二甲苯催化氧化

燃煤烟气中有机污染物的排放逐渐引起重视。锰铈（MnCe）基催化剂被认为是一种低温高效、低成本的可应用于燃煤烟气污染物脱除的催化剂。本文通过浸渍法制备了MnCe基催化剂,通过物理化学表征和烟气模拟台架实验,研究了MnCe基催化剂配比、反应工况、烟气复杂组分（H₂O、SO₂、NH₃、NO）以及典型污染物脱除过程（Hg⁰和NO催化转化）对催化脱除烟气中邻二甲苯行为的影响和规律。实验结果表明,Mn和Ce摩尔比为6∶4时催化剂脱除邻二甲苯效率良好。反应空速和MnCe负载量在低温下对催化脱除效率影响显著。烟气中H₂O、SO₂、NH₃、NO等组分对催化产生抑制作用,但抑制程度与作用机理具有显著差异。MnCe基催化剂对烟气SCR脱硝与Hg⁰催化氧化皆具有较高效率,且受烟气中邻二甲苯影响较小;但受SCR气氛与Hg⁰抑制,邻二甲苯催化脱除反应效率明显降低。     

甲苯与甲醇择形催化制对二甲苯技术进展

对二甲苯是一种重要的芳烃原料,在石油化工行业中有着举足轻重的地位。近十年来,我国对二甲苯的需求保持持续增长的态势,为了保障我国对二甲苯产业健康、稳步的发展,迫切需要开发更为低成本、高效的对二甲苯生产工艺。甲苯与甲醇择形催化制对二甲苯是目前最具前景和竞争力的新技术之一,然而如何在保持高选择性的前提下提高催化剂的稳定性是该技术面临的严峻挑战。低碳烯烃的生成是导致催化剂积炭失活的主要原因之一。本文通过对催化反应机理和催化剂研究进展的介绍,认为开发高选择性、高稳定性的催化剂可以从合成既有择形效应又有优良扩散特性的分子筛母体、协同调控分子筛的孔结构和酸性质以及抑制低碳烯烃的形成三个方向发力。     

ZSM-5沸石分子筛膜的制备及脱盐性能研究

淡水资源日益短缺,发展膜法海水淡化技术是满足世界淡水供应需求的重要途径,但是寻找合适的膜材料依然是人类面临的挑战。ZSM-5沸石分子筛膜（简称沸石膜）具有规则的孔道结构、合适的孔径尺寸（0.51~0.56 nm）以及可调变的硅铝比,在有机物脱水分离应用中展示了优异的选择性及良好的渗透性和稳定性。基于其孔径尺寸介于水分子和盐离子之间,其在海水淡化脱盐领域也具有应用潜力。在大孔α-Al₂O₃载体上采用二次生长法制备了ZSM-5沸石膜,考察了晶化时间与合成液的硅铝比对ZSM-5沸石膜成膜和渗透蒸发脱盐性能的影响,并采用XRD、SEM、EDS与水接触角表征了合成膜的相结构与结晶度、骨架组成表面特性等膜的结构性质。结果表明：通过二次水热法采用合成液摩尔配比为n（Al₂O₃）∶n（SiO₂）∶n（Na₂O）∶n（NaF）∶n（H₂O）=0.05∶1∶0.21∶1.01∶55的合成液在175℃下晶化48 h为最佳的合成条件,制备了Si/Al比为10、接触角为17.5°的亲水纯相致密ZSM-5沸石膜,并在75℃下对3.5%（质量）的NaCl水溶液进行了渗透蒸发测试,水的通量和盐离子截留率达到8.35 kg·m^-2·h^-1和99.99%,且性能在60 h的时间依存性测试后依然稳定,表现出了很高的海水淡化工业应用潜力。     

Synthesis and evaluation of ZSM-5 films on cordierite monoliths

Well-defined ZSM-5 films were prepared on cordierite monoliths using the seed film method. The monoliths were seeded with silicalite-1 seeds and hydrothermally treated either at 75 or at 150 °C in a single or several steps. By adding sodium hydroxide to the solution, the aluminum concentration in the zeolite increased. Consequently, films with different Si/Al ratios were prepared. The film thickness could be controlled from 110 nm to 9 μm. Multi-step synthesis was used to prevent bulk crystallization and ultrasound treatment was found to be beneficial (in order) to remove sedimented crystals on the top of the coatings. The zeolite-coated monoliths were active for p-xylene isomerization, and the test results indicated that the films became less deactivated than the films prepared on alumina beads.     

Study of intermolecular interactions in binary mixtures of methyl acrylate with benzene and methyl substituted benzenes at different temperatures: An experimental and theoretical approach

The ultrasonic speeds, u and viscosities, η of the binary mixtures of methyl acrylate with benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene over the whole mole fraction range were measured at six different temperatures and at atmospheric pressure. From the experimental data, the excess isentropic compressibility, K_S^E, excess ultrasonic speed, u^E, excess molar isentropic compressibility, K_s,m^E, excess specific impedance, Z^Eand deviations in viscosity, Δηhave been calculated. The partial molar isentropic compressions, K_s,m,1 and K_s,m,2, and excess partial molar isentropic compressions, ${\mathop K\limits^{ - E}}$_s,m,1 and ${\mathop K\limits^{ - E}}$_s,m,2 over the whole composition range, partial molar isentropic compressions, and , and excess partial molar isentropic compressions, $\mathop K\limits^{ - \hat E} $_s,m,1 and $\mathop K\limits^{ - \hat E} $_s,m,2 of the components at infinite dilution have also been calculated. The results specified the existence of weak interactions between unlike molecules, and these interactions follow the order: benzene > toluene > p-xylene > m-xylene > o-xylene > mesitylene. The magnitude of interactions was found to be dependent on the number and position of the methyl groups in these aromatic hydrocarbons.     

纳米Ga-ZSM-5分子筛的合成及其在苯和稀乙烯烷基化反应中的应用

采用晶种导向法合成了一系列不同硅镓比的纳米级Ga-ZSM-5分子筛,经过挤条成型、酸洗以及高温焙烧等处理后得到了纳米Ga-ZSM-5分子筛催化剂。利用多种表征技术对Ga-ZSM-5分子筛的结构和酸性质进行了表征,研究了其催化苯与稀乙烯烷基化反应性能。结果表明,水热合成的Ga-ZSM-5分子筛具有十字孪晶状形貌,晶粒尺寸均匀。与相同n（Si）/n（T）（T为金属原子）的Al-ZSM-5分子筛相比,Ga-ZSM-5分子筛的酸量和酸强度明显降低。在反应温度为360 ℃、压力为1.4 MPa、乙烯质量空速（WHSV）为1.5 h^-1、n（苯）∶n（乙烯）=1∶1,n（乙烯）∶n（氮气）=1∶5.67的反应条件下,Ga-ZSM-5分子筛催化剂表现出了较高的乙基选择性,副产物二甲苯比Al-ZSM-5减少了30%~50%,且在100 h内稳定运转,具有更好的抗积炭能力。     

An integrated system of biological and catalytic oxidation for the removal of o-xylene from exhaust

Biofiltration is an efficient technology for treatment of gaseous waste. Its disadvantages, however, include large volume of bioreactor and slow adaptation to fluctuating concentrations in waste gas. Catalytic oxidation offers a high destructive efficiency at relatively low operating temperature and small unit. A bench scale system integrated with a biofilter and a catalytic oxidation unit for the treatment of gases containing o-xylene was investigated in this study. The catalytic oxidation unit was packed with Cu/Al₂O₃ catalyst. The results showed that 90% of o-xylene could be removed in the biofilter at the load below 38.2 g m⁻³ h⁻¹. High o-xylene concentration in inlet gas resulted in an overload of the biofilter. Using the Cu/Al₂O₃ catalytic oxidation unit, the concentration of o-xylene could be reduced evidently. The combination of the chemical and microbial processes not only led to a high and stable efficiency of o-xylene conversion, but also improved capacity resisting the shock loads. The Cu/Al₂O₃ was studied for o-xylene oxidation in temperature range of 90–320 °C. The o-xylene conversion was improved correspondingly with the increasing of oxidation temperature. The reaction mechanism of o-xylene oxidation on Cu/Al₂O₃ was also investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).     

Dehydrogenative cracking of n-butane using double-stage reaction

Dehydrogenation-cracking double-stage (tandem) reaction of n-butane was studied using a Pt-Sn type dehydrogenation catalyst and a cracking catalyst (rare earth-loaded HZSM-5). n-Butane was firstly dehydrogenated to n-butene (1- and 2-butene) over the Pt-Sn catalyst loaded at the upper part of the reactor. Then n-butene was successively converted to ethylene and propylene over the cracking catalyst loaded at the lower part of the reactor. The yield of light olefins (ethylene+propylene) was 58% at 650 °C. The key to obtaining ethylene and propylene in high yield was to determine how the bimolecular reactions of olefins to aromatic and heavier products can be inhibited. It was proved that the loaded rare earths played an important role in inhibiting the bimolecular reactions.     

Studies on adsorption equilibrium of xylenes in AEL framework using biased GCMC and energy minimization

The adsorption of xylene isomers in AlPO₄-11 (AEL network) was investigated using biased grand canonical Monte Carlo (GCMC) simulations. Preferential o-xylene adsorption was predicted by the simulations, in agreement with previously reported experimental data. In AlPO₄-11 the selective adsorption behavior comes from the smaller length of the o-xylene molecule along the crystallographic c-axis compared to p-xylene. This is in contrast to AlPO₄-5 and AlPO₄-8, where the ortho-selectivity is caused by the characteristic face-to-face positioning of o-xylene. Energy minimization studies were also performed in a flexible AlPO₄-11 lattice to study the structural changes upon xylene adsorption. The energy minimization study showed that the AlPO₄-11 crystal distorts upon p- and o-xylene adsorption. The distortion mechanism is related to the strong interaction between xylene methyl groups and the sieve oxygen atoms in the O3 position in the wide region of the pore.     

Antifouling agent release from marine coatings-ion pair formation/dissolution for controlled release

In marine coatings, the ability to sustain constant release of antifouling agents (AFA(s)) over a long period of time has become increasingly important. One efficient approach to prevent that diffusion depletes the paint film's antifouling activity is to adsorb the AFA strongly to a specie with low translational mobility, such as a high molecular weight polymer. Therefore, the AFA, Medetomidine, was adsorbed onto a sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SDPS) generating a Medetomidine–SDPS ion pair in an organic solvent. The interaction was investigated by ¹H NMR in butanol (BuOH-d₁₀) and on solid surfaces by the quartz crystal microbalance with dissipation monitoring technique (QCM-D) in two different solvents, seawater and o-xylene. From the NMR studies in butanol (BuOH-d₁₀), a strong interaction between Medetomidine and SDPS was observed. From the QCM-D measurements, differences in affinity between Medetomidine and the SDPS was observed when changing from seawater to o-xylene. In seawater, the interaction was weak and displayed a large degree of reversibility compared to in o-xylene, where the interaction was strong and almost irreversible. Different swelling behaviour was also observed at the solid surfaces depending on the solvent used with o-xylene exhibiting the largest swelling of the polymer layer.