Dealuminated ZSM—5 Zeolite Catalyst for Ethylene Oligomerization to Liquid Fuels

Ethylene oligomerization using ZSM-5 zeolite was investigated to study the role of Broensted acid sites in the formation of higher hydrocarbons,The oligomeriztion of olefins,dependent on the acidity of ZSM-5 zeolite ,is an important step in the conversion of natural gas to liquied fuels,The framework Si/Al ratio reflects the number of potential acid sites and the acid strength of the ZSM-5 catalyst,ZSM-5 with the mole ratio SiO2/Al2O3 equal to 30 was dealuminated for different periods of time according to the acidic ion-exchange method to produce ZSM-5 with various Si/Al ratios,The FT-IR analysis revealed that the integrated framework aluminum band,non-framework aluminum band,and silanol groups areas of the ZSM-5 zeolites decreased after being dealuminated,The performanc of the dealuminated zeolite was tested for ethylene oligomerization.The results demonstrated that the dealumination of ZSM-5 led to higher ethylene conversion,but the gasoline selectivity was reduced compared to the performance of a ZSM-5 zeolite ,The characterization results revealed the amount of aluminum in the zeolitic framework,the crystallinity of the ZSM-5 zeolite,and the Si/Al ration affected the formation of Broensted acid sites,The number of the Broensted acid sites on the catalyst active sites is important in the olefin conversion to liquied hydrocarbons.     

NON-EXISTENCE OF CONJUGATE-SYMPLECTIC MULTI-STEP METHODS OF ODD ORDER

We prove that any linear multi-step method G1^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（Zk） with odd order u （u≥ 3） cannot be conjugate to a symplectic method G2^T of order w （w 〉 u） via any generalized linear multi-step method G3^T of the form ∑k=0^mαkZk = T∑k=0^mβkJ^-1↓ΔH（∑l=0^mγklZl）. We also give a necessary condition for this kind of generalized linear multi-step methods to be conjugate-symplectic. We also demonstrate that these results can be easily extended to the case when G3^T is a more general operator.     

Evaluation of the Secondary Pore Structure of Hydrothermally- and Acid-treated Faujasite Type Zeolites

With regard to H-Y type zeolites dealuminated by hydrothermal and acid treatments, their physical properties were characterized by measurements of 29Si- and 27Al-MAS-NMR, IR, and X-ray diffraction. The secondary pores were quantitatively analyzed by the t-plot method for nitrogen adsorption isotherm at liquid nitrogen temperature and were then compared with the results of samples dealuminated by SiCl4 treatment.The plateau region of the nitrogen adsorption isotherm diminished as hydrothermal and acid treatments proceeded, with the result that the shape of the t-plot changed to that of three straight sections. This t-plot shape suggested that the secondary pores with relatively consistent sizes could develop with the progress of the treatment. On the other hand, SiCl4 treatment was found to produce less secondary pores than hydrothermal and acid treatments. The surface area of micropores calculated from the t-plots gave a considerably higher value than values obtained from the BET equation and from that calculated geometrically. This is attributable to the micropore filling effect.     

丝光沸石水蒸气/酸浸渍脱铝的多核固体核磁共振研究

采用¹H,²⁹Si,²⁷Al魔角旋转固体核磁共振(MASNMR)及¹H-²⁹Si交叉极化(CP)技术研究丝光沸石水蒸气/酸浸渍脱铝过程中各种铝物质的结构与性质.结果表明,丝光沸石上骨架铝原子在水分子作用下,生成非骨架四配位铝物质[Al(OH)₃(H₂O)],分别在²⁷Al谱δ45和¹H谱δ3.0处出现共振信号,这种铝物质不同于扭曲四配位铝,在高温下进一步水合生成Al(OH)₃(H₂O)₂和Al(OH)₃(H₂O)₃,即非骨架五配位和六配位铝物质.¹H-²⁹SiCP和¹H谱证实,水蒸气脱铝使丝光沸石产生了大量的硅羟基和铝羟基.     

Kinetic modeling of the ethylbenzene/xylene isomerization reaction over HZSM-5 zeolites revisited

In this article, a binderless dealuminated HZSM-5 zeolite (Si/Al = 41.4) was used as a catalyst for the isomerization of a mixture of ethylbenzene and xylene. The experimental results indicated that at low residence times the catalyst is effective to isomerize the ethylbenzene into xylenes. A comprehensive kinetic model considering chemisorption, surface chemical reactions, and diffusional processes was developed for this reaction. The intrinsic activation energy (71.99 kJ mol⁻¹) for the surface reaction of ethylbenzene into m-xylene was calculated for the first time, and the corresponding intrinsic activation energies for o-xylene to m-xylene and m-xylene to p-xylene surface reactions were calculated to be 59.45 and 50.68 kJ mol⁻¹, respectively. Lower apparent values have been reported in the literature, and we rationalize that they correspond to multistep processes and intrinsically include a negative activation energy pertaining to chemisorption. The results also revealed that the ethylbenzene diffusion within the zeolite channels was four orders of magnitude smaller than p-xylene.     

NANOPARTICLE DESIGN AND HANDLING--CHALLENGES FOR ENGINEERS AND PARTICLE TECHNOLOGISTS

In this paper, the opportunities and challenges which future applications based on nanoparticles offer to engineers are described. New high-added value products induce us to rethink ways to control nanoparticle design and handling. Several challenges are described and typical solutions are given: (1) finding relevant engineering tasks outside traditional process industry; (2) the importance of mixing reactants; (3) obtaining monodisperse particles; (4) gaining efficient control via electric forces and (5) developing multi-step processes which allow more control over particle properties.     

Phosphatation of Zeolite H‐ZSM‐5: A Combined Microscopy and Spectroscopy Study

A variety of phosphated zeolite H‐ZSM‐5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse ²⁷Al, ²⁹Si, ³¹P, ¹H‐³¹P cross polarization (CP), ²⁷Al‐³¹P CP, and ²⁷Al 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X‐ray microscopy (STXM) and N₂ physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H‐ZSM‐5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue. Phosphatation of pre‐steamed H‐ZSM‐5 gives rise to the formation of a crystalline tridymite AlPO₄ phase, which is found in the mesopores of dealuminated H‐ZSM‐5. Framework aluminum species interacting with phosphorus are not affected by hydrothermal treatment. Dealuminated H‐ZSM‐5, containing AlPO₄, retains relatively more framework Al atoms and acid sites during hydrothermal treatment than directly phosphated H‐ZSM‐5.     

Adiabatic multi-step separation method and its application to coupled oscillators

Extension of the adiabatic approach to a multi-step separation method is presented. This method step by step reduces the multi-dimensional Schrödinger equation to the effective equations of lower dimensions. The reduction procedure allows to take advantage of multi-level hierarchy of various physical systems. The multi-step separation method is applied in the calculation of vibrational energies of coupled oscillators. The new method is found to be very effective and accurate.     

Application of Multi-step Excitation Schemes for Detection of Actinides and Lanthanides in Solutions by Luminescence/Chemiluminescence Laser Spectroscopy

The use of laser radiation with tunable wavelength allows the selective excitation of actinide/lanthanide species with subsequent registration of luminescence/chemiluminescence for their detection. This work is devoted to applications of the time-resolved laser-induced luminescence spectroscopy and time-resolved laser-induced chemiluminescence spectroscopy for the detection of lanthanides and actinides. Results of the experiments on U, Eu, and Sm detection by TRLIF method in blood plasma and urine are presented. Data on luminol chemiluminescence in solutions containing Sm(III), U(IV), and Pu(IV) are analyzed. It is shown that appropriate selectivity of lanthanide/actinide detection can be reached when chemiluminescence is initiated by transitions within 4f- or 5f-electron shell of lanthanide/actinide ions corresponding to the visible spectral range. In this case chemiluminescence of chemiluminogen (luminol) arises when the ion of f element is excited by multi-quantum absorption of visible light. The multi-photon scheme of chemiluminescence excitation makes chemiluminescence not only a highly sensitive but also a highly selective tool for the detection of lanthanide/actinide species in solutions.     

并行多步法及其在两铰圆拱动力响应中的应用

本文在基于个人计算机的transputer并行处理子母板系统上提出了一种结构动力分析中适合于并行处理的对时间域积分的多步法——并行多步法。并用此方法对两铰弹性圆拱在矩形荷载作用下的动力响应进行分析。算例表明,对于四处理器系统算法加速比可达3.05,效率为76.25％。对圆拱的分析表明,当中心角之半θ_0较小时,矩形荷载作用完后圆拱在偏离原静止状态的位置附近自由振动。这主要是由于几何非线性所致。