频率响应法研究噻吩和苯在NiY分子筛上的吸附行为

The adsorption behavior of thiophene and benzene on NiY zeolite has been investigated by the frequency response(FR) method.The FR spectra of thiophene and benzene on NiY zeolite were recorded at 302—335 K in a pressure range of 26.6—266 Pa.The results showed that adsorption was found to be the rate-controlling process for the thiophene/NiY zeolite system,and there were two different adsorption processes.Two kinds of adsorption models have been proposed,namely:the S-M interaction(low frequency adsorption) an...     

The Density Functional Study of Thiophene Adsorption on Zeolite Clusters

The density functional theory and the cluster model methods have been employed to investigate the interactions between thiophene and the HZSM-5 zeolites. The molecular complexes formed by the adsorption of thiophene on silanol H3SiOH with two coordination forms, and the model Brrnsted acid sites of zeolite cluster H3Si（OH）AI（OH）2SiH3 upon the interaction with thiophene have been comparatively studied. Full optimization and frequency analysis of all cluster models have been carried out using the B3LYP hybrid method at 6-31G basis level for hydrogen atoms and 6-31＋G（d） basis set level for silicon, aluminum, oxygen, carbon, and sulfur atoms. The calculated results showed that the nature of interactions leading to the formation of the zeolite cluster-thiophene and silanol-thiophene complexes was associated with the van der Waals force confirmed by a slight change of geometric structures and properties. Thiophene is adsorbed on bridging hydroxyl group prior to silanol OH group judging from the magnitude of adsorption heat. The cluster model calculation reproducing the experimental prediction to form the experimental adsorption spectra of thiophene in HZSM-5 zeolite has illustrated the validity of the proposed adsorption models.     

Study of Isothermal Equilibrium,Kinetics and Thermodynamics of Adsorptive Desulfurization on Synthesized Cu~ⅠY~ⅢY Zeolite

Deep adsorptive desulfurization of low sulfur content gasoline via zeolite is a promising process.Herein,the Cu~ⅠY~ⅢY zeolite was prepared and the effect of adsorption conditions and aromatics on the performance of adsorptive desulfurization was studied.And the isothermal equilibrium and kinetics were also investigated.The results showed that upon using 10 m L of model oil and 0.2 g of the Cu~ⅠY~ⅢY adsorbent during the adsorption reaction,which was carried out at 323 K for 60 min,the benzothiophene(BT) desulfurization rate reached 98.4%.The impact of aromatics on the adsorptive desulfurization over the Cu~ⅠY~ⅢY zeolite decreased in the following order:ortho-xylene meta-xylene para-xylene.The equilibrium isotherm shows that the adsorption of benzothiophene over the as-prepared CuIYIIIY zeolite can be represented by the Langmuir model.And the kinetics can be more perfectly represented by the pseudo-second-order model than that of the pseudo-first-order one.The thermodynamic parameters(ΔG,ΔH) were both negative,which suggested that the adsorption process is monostratal,mass transfer controlled,spontaneous,and exothermic.     

La和Ce调变Y分子筛性能的差异及其密度泛函理论研究

In this paper,the different influences of lanthanum (La) and cerium (Ce) species on the stability of Y zeolite were studied by X-ray diffractometry (XRD),X-ray photoelectron spectroscopy (XPS),and multinuclear (27Al,29Si) solidstate nuclear magnetic resonance spectroscopy (NMR).It was found that the stability of Y zeolite could be enhanced by the introduction of La or Ce species;however,the former effect was more remarkable than the latter.These results were also confirmed theoretically by density functional calculations.There was a strong interaction between the rare earth (La or Ce) species and Y zeolite clusters,which restrained the formation of extra-framework aluminum and enhanced evidently the stability of Y zeolite.Furthermore,the interaction between La species and Y zeolite was stronger than that of Ce species with Y zeolite.     

浸渍法制备Al-SBA-15分子筛的稳定性和催化性能研究

The mesoporous Al-SBA-15 zeolite was obtained via impregnation of pure silica-based SBA-15 zeolite with aluminum nitrate.The Al-SBA-15 sample was calcined in air at 800 ℃ for 6 h and hydrothermally treated at near 100 ℃ for 120 h,respectively,and then the thermal and hydrothermal stability of Al-SBA-15 sample was investigated by X-ray diffractometry (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM) and nitrogen adsorption and desorption techniques.The Al-SBA-15 sample was also studied by 27 Al nuclear magnetic resonance (27 Al NMR) and ammonia temperature programmed desorption (NH 3-TPD) techniques.In addition,the catalytic activity of Al-SBA-15 zeolite was investigated by the Friedel-Crafts reactions of 2,4-di-tert-butylphenol with cinnamyl alcohol.The test results showed that the thermal and hydrothermal stability of Al-SBA-15 zeolite was better than that of SBA-15 zeo-lite.The Al-SBA-15 zeolite sample prepared by impregnation method exhibits more framework aluminum species and Al-O-Si units.Therefore,the number of the surface hydroxyl groups was reduced,resulting in the stabilization of framework structure ofAl-SBA-15 zeolite.The aluminum species can form weak and medium-strong acid sites with catalytic activity.     

催化裂化干气组分在沸石Y上吸附的分子模拟

Adsorption of catalytic cracking dry gas components, hydrogen (H2), nitrogen (N2), methane (CH4), ethane (C2H6) and ethylene (C2H4) in zeolite Y was studied by performing the Grant Canonical Monte Carlo (GCMC) simulations at 298 and 823K and a pressure range up to 10MPa. Simulation results were analyzed using Langmuir model and it presented fitting of dry gas components adsorption suggesting monolayer adsorption. C2H4 presented most single adsorption amount, which reached 7.63mol/kg at 298K under 200kPa. Thermodynamic parameters of Gibbs free energy change, enthalpy change and entropy change were analyzed based on adsorption equilibrium constant obtained from the GCMC simulations. The results suggested that it was more favorable for C2H4 to adsorb in zeolite Y. Adsorption molecules were in ordered arrangement in zeolite, and C2H4 exhibited more orderly arrangement than other components. Additionally, it was found that there was a competition between dry gas components for mixture adsorption, supercages were prior adsorption space. The competition was favorable to CH4 and C2H6, and competitive power was affected by temperature.     

改性Y型分子筛对石脑油脱硫效果的研究

NH4Y zeolite was prepared through ion-exchange of NaY zeolite with an ammonium salt. Then LaY zeolite was obtained through a secondary ion-exchange of NH4Y zeolite with a rare earth salt solution followed by calcination of the zeolite product. Dynamic adsorptive desulfurization of naphtha was conducted in the presence of the modified LaY zeolite, and the sulfur content of the treated naphtha samples was analyzed by microcoulometry. The test results showed that under dynamic conditions the LaY zeolite prepared through secondary ion-exchange of NH4Y zeolite, which was prepared using 1.0 mol/L ammonium salt, with the rare earth salt exhibited a better desulfurization efficiency. Furthermore, the LaY zeolite achieved a best desulfurization effect at an adsorption temperature of 45 ℃ and an adsorbent/oil ratio of 1:2.     

离子交换树脂应用于Y型分子筛离子交换过程的研究

Ion-exchange process of zeolite Y using ammonium-type resin as an exchange reagent was successfully carried out. The effect of temperature, space velocity and ion concentration on the breakthrough curves was carefully investigated. At the first exchange section, the maximum proportion of qualified zeolites(QR) was obtained at a temperature of 70 ℃, a weight hourly space velocity of 0.61 h-1, and an ion concentration of 197 mg/L. The minimum length of mass-transfer zone(MTZ) of the resin bed was achieved at a temperature of 70 ℃, a space velocity of 0.61 h-1, and an ion concentration of 423 mg/L. At the second exchange section, the length of MTZ of the resin bed was significantly increased, and the exchange of Na+ ions contained in zeolite Y was more difficult than that achieved at the first exchange section. In both the first and the second exchange sections, the zeolite Y subjected to ion exchange with the resin maintained the similar physical and chemical properties as compared to those exchanged by the conventional approaches, but the zeolite Y, which was obtained after ion exchange, contained a significantly lower content of Na2 O.     

对二甲苯在高岭土原位晶化NaY沸石上的吸附热力学和扩散动力学研究

Para-xylene was chosen as the probe molecule to study adsorption thermodynamics and diffusion kinetics onNaY zeolite and composite structured NaY zeolite synthesized by in-situ crystallization from kaolin microsphere （designatedas NaY/kaolin composites ） separately, using a high precision intelligent gravimetric analyzer （IGA）. The adsorption isothermsshowed normal Langmuir type-. behaviors. The increased adsorption heat with an increasing p-xylene coverage supporteda mechanism of phase transition, diffusion and re-arrangement of p-xylene molecules during the adsorption process.The rearrangement seemed to be most pronounced at an adsorption loading of 2.13 and 2.29 mmol/g for NaY zeolite andNaY/kaolin composites respectively. Compared with NaY zeolite, a 2.3 times higher in the diffusion coefficient ofp-xylene was observed on NaY/kaolin composites when the pressure was more than 50 Pa. Temperature-programmed desorption（TPD） of p-xylene on two samples from room temperature to 450 亷 at a special loading has also been investigatedby IGA. Results showed only single desorption peak appeared for NaY zeolite, indicating that adsorption can only occur inthe super-cage structure. Comparably, there were two different peaks for in-situ synthesized NaY zeolite, corresponding tothe two thermo desorption processes in both super-cage structure and the channels provided by kaolin, respectively.     

Synthesis of La-Modified Ultra Stable Zeolite L and Its Application to Catalytic Cracking Catalyst

A new type of zeolite La-USL (ultra stable zeolite L (zeolite USL) modified by La), which has superior activity, stability and selectivity in catalytic cracking of hydrocarbons and thus can be used as an active catalyst component, is reported in this paper. The zeolite L with relative crystallinity of above 90% was synthesized by the hydrothermal crystallization method under optimum conditions and characterized by means of XRD, NH3-TPD and isotherm adsorption techniques. The in-situ synthesized zeolite L with a SiO2/Al2O3 mole ratio of 5-6 was modified by cation ion exchange, hydrothermal dealumination and chemical modifications with La in order to prepare La-containing USL with a higher framework SiO2/Al2O3 mole ratio of 15-30. The modified zeolite La-USL was used as an active additive component of fluid catalytic cracking (FCC) catalyst and the resulting catalysts were evaluated by microactivity test (MAT) and fixed-fluidized bed (FFB) experiments using heavy oil as feedstock. The influence of La content in La-USL on cracking product distribution, gasoline group composition and research octane number (RON) was investigated. The results showed that when La content in La-USL was 0.8 wt%, the addition of the corresponding La-USL could result in a FCC catalyst that produced significant improvement in product distribution and gasoline quality.     

Effect of Carrier Processing Temperature on Its Properties for Adsorption of Active Metals

The influence of the carrier pseudo-boehmite (PB), which was impregnated with a Ni-Mo-P solution under over-saturation conditions and treated at different temperatures, on its property for adsorption of active metals (Ni, Mo) was studied. The results showed that the amount for adsorption of active metal was decreased with an increasing treatment temperature of the carrier. After phase transition of the carrier PB to γ-Al2O3, its capacity for adsorption of active metals was significantly reduced. The difference in properties for adsorption of active metals (Ni, Mo) by PB dried at 120 ℃ and γ-Al2O3 calcined at 600 ℃ was studied in detail. The results suggested that the ability of the PB carrier to adsorb metals was higher than that of the γ-Al2O3 carrier. Especially, the ratio of chemically adsorbed metals on the PB support was much higher than γ-alumina. The chemical adsorption sites on the PB carrier were proved to be much more than those on the γ-Al2O3 carrier. Ni and Mo chemical adsorption sites differed a lot on the carrier possibly because of the difference in chemical adsorption sites.     

Synthesis, characterization and catalytic properties of Y-β zeolite composites

Y-β zeolite composites were hydrothermally synthesized by using high silica Y zeolite as the precursor and characterized by XRD,N2 adsorption,SEM and IR spectra of pyridine.The result showed that the N2 adsorption-desorption isotherm of the zeolite composites had a distinct hysteresis loop,and the SEM result showed that the zeolite composites had a different morphology from Y,β and the corresponding physical zeolite mixture.The acid catalytic performance of the zeolite composite catalysts was investigated in the hydrocracking and hydroisomerization of n-octane,and the results showed that the composite materials exhibited an excellent hydrocracking activity and good hydroisomerization performance.The yield of i-C4 over the zeolite composite catalyst was 4.45% higher than that on the corresponding zeolite mixture in the n-octane hydrocracking process at 553 K.The isomerization ability of n-octane over the composite catalyst was 3.6 fold that of the corresponding mixture at 503 K.     

Comparison on Adsorptive Separation of n-Paraffins Based on Binderless and Binder-containing Zeolite 5A Pellets

Binderless zeolite is considered to be a potential alternative for binder-containing zeolite in the industrial applications of adsorptive separation process. Synthesized binderless zeolite and commercial binder-containing product were used in adsorptive separation of n-paraffins from a model oil, with their performance compared. It is indicated that the binderless zeolite exhibits by 25%—35% higher in saturated adsorption capacity and by 115%—130% more adsorption amount at the breakthrough point with much shorter length of mass-transfer zone. Adsorptive separation of n-paraffins from naphtha was carried out in a fixed-bed adsorber containing the synthesized binderless zeolite 5 A under the operating conditions covering a feed space velocity of 90 h~(-1) and an adsorption temperature of 573 K. As compared to original naphtha, the raffinate shows by 34 units more in research octane number and by around 10% more of potential aromatic content, while the desorption oil exhibits by 13.3% more ethylene yield and by 11.7% higher in total olefins yield.     

Dearomatization of normal paraffin by adsorption process using synthesized NaX zeolite

Linear alkyl benzenes (LABs) are the main materials for detergent production. The presence of aromatic compounds in this material can decrease the quality of the final product and enhance the deactivation rate of catalysts. In this research we used zeolite NaX for de-aromatization of the recycled paraffin from the alkylation unit of an LAB production complex. The effect of different parameters on the removal efficiency of adsorbent was studied and optimized. To study the re-usability of the adsorbent, the breakthrough curves were obtained by using a fixed bed column filled with the adsorbent. The results indicated that the adsorbent capacity remained unchanged after three regeneration cycles. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. It was concluded that the Langmuir model agreed well with the experimental data. The calculated thermodynamic parameters of the adsorption showed that the adsorption process was spontaneous and exothermic. The reaction rate was estimated by the pseudo-second order kinetic model.     

Kinetic and Thermodynamic Studies on Raney Ni/Al_2O_3 Adsorption for Deep Desulfurization of Benzene Stream

How to remove trace amount of sulfur in benzene is of significance,and deep desulfurization by Ni-containing absorbents is an efficient and promising method.In this paper,The Raney Ni/Al_2 O_3 adsorbent was prepared and its kinetic and thermodynamic characteristics on adsorptive desulfurization of benzene were studied.The results showed that Raney Ni/Al_2 O_3 adsorbent exhibited good adsorption performance.The equilibrium isotherms indicated that the adsorption of thiophene over the Raney Ni/Al_2 O_3 adsorbent complied with the Freundlich model.The results of adsorption kinetics studies showed that the pseudo-second-order kinetics equation was more advantageous than the pseudo-first-order kinetics equation in describing the adsorption kinetics of thiophene on Raney Ni/Al_2 O_3.The rate constant value(k_p) was positively correlated with the temperature whereas the adsorption mass transfer process was mainly determined by the intraparticle and film diffusion.The adsorption thermodynamic analysis proved that △G~0 0,△H~0 0,and △S~0 0,implying that the adsorption was a spontaneous,entropy-increasing and endothermic process.     

The Effect of Non-Framework Aluminum on the Stability and Activity of REY Zeolite

The present study is focused on the influence of a routine step, washing, following the preparation of calcined rare earth exchanged Y zeolite, on its hydrothermal stability. The hydrothermal stability of REY products, which were washed by different reagents, was observed and characterized by XRD, ICP, NMR, etc. The results reveal that the amount and the chemical type of the acidic media used for washing can significantly influence the content of remaining non-framework aluminum （NFA） and consequently further affect the hydrothermal stability of the washed REY products. The content of remaining non-framework aluminum can be well correlated with the crystallinity of REY products.     

Theoretical Study on Adsorption of Methanol on Zeolite and Phosphorus Modified Zeolite

Methanol adsorption in zeolite and phosphorus modified zeolite has been investigated within the cluster model framework of quantum chemical calculation. Full optimization and frequency analysis of all cluster model have been carried out using Gaussian 94 soft package with Hartree-Fock method and B3LYP, B3P86 hybrid methods of density functional theory at 3-21G, 6-31G basis set level for hydrogen atoms and 6-31G (d) basis set level for the other atoms performed on small cluster model for CH3OH, H3Al(OH)SiH2(H2PO4), H3Al(OH)SiH2(H3SiO4), H3Al(OH-CH3OH)SiH2(H2PO4) and H3Al(OHCH3OH)SiH2(H3SiO4). The results show that phosphorus grafting in the zeolite framework has modified the chemical environment in the vicinity of the zeolite bridging hydroxyl. Phosphorus modification can enhance the acid strength of zeolite bridging hydroxyl, which was suggested by the lengthening of zeolite bridging hydroxyl O-H bond and the increasing methanol adsorption energy. This may be favorable to the initial CH3OCH3 formation in the methanol to gasoline (MTG) process.     

Comparative Study of the Adsorption Thermodynamic Parameters Estimated through Different Approaches

The equilibrium constant （K0）, change in free energy （△G）, enthalpy （△H） and entropy （△S） of ammonium adsorption by a Cuban natural zeolite were estimated at the temperatures of 25, 35, 45 and 55℃ using extensively used approaches. Equilibrium data were obtained in the concentration range 50-1,200 mg·L-1 of ammonium and used in the estimation of thermodynamic parameters. Freundlich＇s isotherm model was found as with the best adjustment to equilibrium data at 25, 45 and 55℃, whereas, Redlich-Peterson＇s model had a better performance at 35 ℃. A discontinuous and unusual behavior was observed on adsorption capacity of the zeolite, with an increase from 25 ℃ to 35 ℃ followed by a decrease from 35℃ to 55 ℃. K0 values presented differences that reached up to 105 from one methodology to other. Depending on the method considered, AS results indicated both increase or decrease in system degree of disorder and △G indicated both physisorption or chemisorption process, proving the poor correlation between the estimation proceedings of such important data. The results from Gaines and Thomas method were recognized as the most correlated to calorimetric studies, as well as to equilibrium data and observations related to system entropy.     

The Function of β Zeolite for Enhancing the Propylene Yield in FCC Process

The ultra-stable Y zeolite, modified β zeolite, and modified ZSM-5 zeolite were characterized by NH3-TPD analysis. The results showed that the acidic substance of modified β zeolite is between that of the Y zeolite and the ZSM-5 zeolite. These three kinds of zeolites were evaluated by using hexane, decane and light diesel serving as feedstocks with different molecular size. The results showed that these three kinds of zeolites had different cracking capability and product distribution obtained for cracking hydrocarbons with different molecular sizes as a result of the difference in pore structure and acidic substances. The modified β zeolite can produce much more C_5~= —C_8~= olefins, which are excellent precursors of propylene. Then the mixed samples of these three kinds of zeolites were tested in the VGO microreactor unit, and the test results showed that the modified β zeolite played a ‘relay role' between the ultra-stable Y zeolite and the modified ZSM-5 zeolite, so that the composite made of the ultra-stable Y zeolite, the modified β zeolite, and the modified ZSM-5 zeolite showed a highest propylene yield and selectivity.     

Studies of Cyclohexane Catalytic Oxidation Processes over Titanium Silicate-1 Zeolite

The catalytic oxidation processes for cyclohexane/H202/acetone system over the TS-1 zeolite was studied. Study results have revealed that the cyclohexane conversion was 27% after the reaction proceeded at 100℃ for 2 hours at a cyclohexane/H2O2 molar ratio of 0.8. The cyclohexanol/cyclohexanone molar ratio was 1.3 along with a certain amount of organic acids and esters, the formation of which was closely associated with the oxidation of reaction solvent and deep oxidation of cyclohexanone and cyclohexanol contained in the reaction products. With respect to the catalytic oxidation ofsolvent was critically important.cyclohexane/H202 system the selection of appropriate solvent was critically important.