Multi-zone TAP-reactors theory and application. III Multi-response theory and criteria of instantaneousness

A general theory of multi-response state-defining experiments for a multi-zone temporal analysis of products reactor, is developed using the Laplace transform and a generalization of the transfer matrix formalism previously introduced for single-response experiments. The theory provides a unified approach to multi-response modelling and an efficient means to compute the actual profiles of gases and surface species concentration in the reactor, as well as the values of the outlet fluxes numerically, using e.g. fast fourier transform. We investigate the kinetic/mathematical conditions under which explicit expressions for the moments of the outlet fluxes and series expansions for their transient values can be obtained. Several important examples are analyzed in detail, leading to simple criteria of instantaneousness for different reactants within a catalytic mechanism. In the case of thin-zone reactors, the criteria are significantly simplified, with equality (within experimental error) of “shifted residence times” of reactants being proposed as the criterion of instantaneousness. This is illustrated for the oxidation of propene on a vanadium oxide catalyst.     

Studies on fluorinated polyurethanes by X-ray diffraction and density functional theory calculations with periodic boundary conditions

Thin-film wide-angle X-ray diffraction, small-angle X-ray scattering, and density functional theory calculations using B3LYP hybrid functional with the two-dimensional periodic boundary conditions (2D-PBC) have been applied to study the crystal structures of parent and fluorinated polyurethanes. The crystal structures from 2D-PBC-B3LYP calculation and experiments showed the hard-segment chains within crystallites adopted an extended-chain conformation for polyurethanes. Energetically, the parent polyurethane preferred an alternating hydrogen-bonded sheet structure while the fluorinated one adopted a progressive hydrogen-bonded sheet structure.     

Comparison between regression analysis and moment analysis for transport and kinetic parameter estimation in TAP experiments under a non-ideal inlet condition

Regression analysis and moment analysis for estimation of transport and kinetic parameters in TAP experiments were compared using different types of responses, including exit flow rate curves and normalized responses. The experimental responses were obtained from simulation under a non-ideal inlet flow condition. The parameter estimation was performed using the ideal model. The quantities used in the comparison are the percentage differences between the estimated and the real parameters including the gas diffusivity and the first order irreversible reaction rate constant. These quantities also indicate the validity/invalidity of the ideal inlet condition. For typical domains in TAP experiments, the diffusivity percentage difference obtained from the regression and the moment analyses was found to be small. However, the percentage difference of the reaction rate constant can be large and depends on the estimation methods, the types of the response, and the gas conversion. Small percentage differences of the reaction rate constant are obtained from the estimation method that uses the conversion as a measured quantity. Besides, the percentage difference from this method does not depend on the conversion due to the same conversion expression in the ideal and the non-ideal cases.     

UNIFORMITY OF CHANGE IN POROUS CATALYST ACTIVITY DURING A MULTI-PULSE TAP EXPERIMENT

Uniformity of change in catalyst activity during a multi-pulse TAP experiment with porous catalyst was theoretically analyzed for a TAP reactor with the ratio of the catalyst bed thickness to the reactor length of 1/30. The analysis was performed by simulation of an irreversible adsorption process. The catalyst change is described by the change in the occupied/unoccupied fractional surface coverages. The intraparticle uniformity is indicated by a small magnitude of Δθ _p,max , the maximum difference between the occupied fractional surface coverages at the outermost and the innermost of the catalyst pellet during the multi-pulse experiment. In the interparticle region, the indicating quantity is Δθ _b,max , the maximum difference between the pellet-outermost fractional surface coverages at the inlet and the outlet of the catalyst bed. It was found that Δθ _p,max generally depends only on the effectiveness factor in the first pulse experiment, η. For η ≥ 0.94, Δθ _p,max  ≤ 0.05. In addition, Δθ _b,max depends only on the gas conversion in the first pulse experiment, X. For X ≤ 0.7, Δθ _b,max  ≤ 0.05.     

Characteristics of the boundary layer with hydrogen combustion with variations of thermal conditions on a permeable wall

The paper describes a numerical study of the influence of thermal and boundary conditions on the structure of laminar and turbulent diffusion flames in the cases with hydrogen injection through a porous surface and with hydrogen combustion in an air flow. Two types of boundary conditions are compared: with a given constant temperature T _w = const over the length of the porous surface for arbitrary intensities of fuel injection and with a constant temperature T′ = const of the fuel injected through the porous wall. The first case occurs during combustion of a liquid fuel whose burning surface temperature remains unchanged. Injection of gaseous fuel usually leads to the second case with T′ = const. Despite significant differences in velocity and temperature profiles, the skin friction coefficients in the laminar flow are close to each other in these two regimes. In the turbulent regime, the effect of the thermal boundary conditions on friction and heat transfer is more pronounced. Moreover, the heat flux to the wall as a function of fuel-injection intensity is characterized by a clearly expressed maximum. A principal difference of the effect of combustion on friction and heat transfer in the laminar and turbulent flow regimes is demonstrated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 3–11, May–June, 2009.     

靖边气田水平井适应性评价及其应用

本文根据靖边气田下古生界马五1+2储层地质特点,通过数值模拟及技术经济评价等方法,确定了马五1+2储层水平井经济界限产量、最低有效长度以及经济界限渗透率等参数,在此基础上确立了水平井适应性评价标准。通过应用适应性评价标准部署水平井,靖边气田水平井开发效果显著,尤其在低渗区水平井增产效果明显,水平井开发潜力大。     

The activity and mechanism of uranium oxide catalysts for the oxidative destruction of volatile organic compounds

Uranium oxide based catalysts have been investigated for the oxidative destruction of volatile organic compounds (VOCs) to carbon oxides and water. The catalysts have been tested for the destruction of a range of organic compounds at space velocities up to 70 000 h⁻¹. Destruction efficiencies greater than 99% can be achieved over the appropriate uranium based catalyst in the temperature range 300–450°C. Volatile organic compounds investigated include benzene, butylacetate, cyclohexanone, toluene, methanol, acetylene, butane, chlorobutane and chlorobenzene. The catalysts are thermally stable, destroy low concentrations and mixtures of VOCs and lifetime studies indicate that deactivation during oxidation of chlorinated VOCs did not occur. A temporal analysis of products (TAPs) reactor is used to investigate the mechanism of oxidation of VOCs by uranium oxide catalysts. Studies indicated that VOCs were oxidised directly to carbon oxides on the catalyst surface. A combination of TAP pulse experiments with oxygen present and absent in the gas phase has indicated that the lattice oxygen from the catalyst is responsible for the total oxidation activity. This has been confirmed by studies using isotopically labelled oxygen which indicates that the catalyst operates by a redox mechanism.     

基于复变量求导法的共轭梯度法及其在热传导反问题边界条件辨识中的应用

为了利用共轭梯度法的计算精度高和收敛速度快的优点, 避免传统共轭梯度法在求解非线性热传导反问题中的微分处理、复杂的推导过程等问题, 给出一种改进的共轭梯度法, 即将复变量求导法引入传统的共轭梯度法, 准确计算了各灵敏度系数, 进而对瞬态非线性热传导反问题进行求解, 并对边界条件进行辨识。算例验证了本文方法的有效性与精度。与传统共轭梯度法相比, 在处理非线性问题方面, 本文方法具有操作简单和精度高的优点。     

Transient studies of carbon dioxide reforming of methane over Pt/ZrO2 and Pt/Al2O3

The mechanism of the CO₂ reforming of methane reaction over the Pt/ZrO₂ catalyst was investigated using a temporal analysis of products (TAP) reactor system. For comparative purposes, the reaction pathway using a Pt/Al₂O₃ catalyst was also examined. A reaction sequence is suggested for both catalysts. Over both catalysts, methane decomposition takes place over platinum. The main difference between the two catalysts concerns the carbon dioxide dissociation. Over Pt/Al₂O₃ this step is assisted by hydrogen. Over Pt/ZrO₂ this step takes place over the zirconia support and involves surface vacancies. Moreover, large pools of formate and carbonate species are present on the zirconia. Transient studies conducted to determine the origin of carbon species accumulated during CO₂ reforming revealed that more than 99% of the carbon was derived from the methane molecule over both catalysts. Over the Pt/ZrO₂ catalyst, only a single very reactive carbon species was detected, while over the Pt/Al₂O₃ a second less active species was also formed.     

HCN synthesis from methane and ammonia over platinum

The mechanism of the HCN formation from ammonia and methane over Pt black was investigated using a temporal analysis of products (TAPs) reactor system. At 1173 K the hydrogen cyanide production rate depends on the order of introducing the reactants. HCN is formed rapidly on the methane pulse just after introducing ammonia. However, a slow formation of HCN is observed on the ammonia pulse that follows a methane pulse. Moreover the form of the HCN response resembles closely that of the nitrogen and hydrogen also released during the ammonia pulse. Thus, the rate-determining step for the formation of HCN is the decomposition rate of ammonia. A reaction sequence based on elementary steps is proposed for the HCN synthesis. The formation of HCN after pulsing H₂ points to a pool of surface intermediate species that are hydrogenated to HCN.     

The Friction and Wear Behaviors of Vegetable Oil-Based Waxes,Natural Beeswax,and Petroleum Paraffin Wax

Quantitative analyses on the coefficient of friction of common coating waxes are necessary and essential for designing systems for coating, conveying, packaging operations, transporting, and storing of papers and paperboards, while analyses on wear behavior can be helpful for predicting performance durability of the coating surface. In this study, we investigated the friction and wear behaviors of six waxes including four commercial waxes and two soybean oil-based wax developed in our lab for bulk corrugated coating. The effect of normal load, sliding velocity, and environmental temperature was evaluated. The friction coefficient of different waxes varies with sliding conditions. Higher normal load, sliding velocity, and environmental temperature resulted in significantly greater wear loss. Crystalline morphology and crystallinity of waxes were affected by the environmental temperature, and they correlate to the variations in friction coefficient and wear loss of these materials.     

Starch derivatives with high degree of functionalization. III. Influence of reaction conditions and starting materials on molecular structure of carboxymethyl starch

Carboxymethyl starch (CMS) was prepared in a completely heterogeneous procedure in a methanol/water slurry activated with aqueous sodium hydroxide (45%, w/v) using monochloroacetic acid as the etherifying agent. The influence of the reaction conditions and the type of starting starch (amylose content and preactivation) was evaluated in regard to the formation of the main repeating units (i.e., unfunctionalized and mono‐, di‐, tri‐, and tetra‐O‐carboxymethylated) and the pattern of functionalization within the anhydroglucose units (AGU). The reproducible synthesis gave products with a maximal degree of substitution of CM groups (DS_CM) of 0.66, which was reached in a one‐step synthesis. Repeated carboxymethylation led to products with a DS_CM of 0.88. As revealed by means of HPLC analysis after complete acidic depolymerization, in any sample the mono‐O‐carboxymethylated glucose (mono‐O‐CMglc) was preferably present while the di‐O‐CMglc was formed to a very low extent only. The tri‐O‐CMglc was found in some samples while tetra‐O‐CMglc was not detected. The mole fractions determined did not follow the simple Spurlin statistic as shown for CM cellulose synthesized under comparable conditions. Within the carboxymethylated AGUs a preferred functionalization at position 2 was analyzed by means of ¹H‐NMR spectroscopy after hydrolytic chain degradation. Consequently, the CMS samples synthesized contained mainly 2‐mono‐O‐CM‐AGU. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2036–2044, 2001     

Functionalized cellulose‐supported triphenylphosphine and its application in Suzuki cross‐coupling reactions

A new heterogeneous cellulose tagged triphenylphosphine (Cell‐OPPh₃) was synthesized and subsequently coordinated with Pd(OAc)₂ to form a cellulose‐supported triphenylphosphine palladium complex (Cell‐OPPh₃‐Pd). Cell‐OPPh₃ and the corresponding palladium complex were fully characterized by TGA, SEM, TEM, and NMR analysis. Results of catalytic activity experiments indicate that the Cell‐OPPh₃‐Pd complex can efficiently catalyze Suzuki–Miyaura cross‐coupling reactions of aryl halides with arylboronic acids at mild reaction conditions. The coupling products can be obtained in good to excellent yields (up to 98%). The work‐up procedure is simple and the catalyst could be easily recovered by filtration, and then reused in next run. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41427.     

Condensed combustion products of aluminized propellants. IV. Effect of the nature of nitramines on aluminum agglomeration and combustion efficiency

The condensed combustion products of two model propellants consisting of ammonium perchlorate, aluminum, nitramine, and an energetic binder were studied by a sampling method. One of the propellants contained HMX with a particle size D ₁₀ ≈ 490 μm, and the other RDX with a particle size _{D 10} ≈ 380 μm. The particle-size distribution and the content of metallic aluminum in particles of condensed combustion products with a particle size of 1.2 μm to the maximum particle size in the pressure range of 0.1–6.5 MPa were determined with variation in the particle quenching distance from the burning surface to 100 mm. For agglomerates, dependences of the incompleteness of aluminum combustion on the residence time in the propellant flame were obtained. The RDX-based propellant is characterized by more severe agglomeration than the HMX-based propellant — the agglomerate size and mass are larger and the aluminum burnout proceeds more slowly. The ratio of the mass of the oxide accumulated on the agglomerates to the total mass of the oxide formed is determined. The agglomerate size is shown to be the main physical factor that governs the accumulation of the oxide on the burning agglomerate. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 78–92, July–August, 2006.     

有限元分析在塑料加工与制品性能分析中的应用

主要介绍了在加工方面利用有限元分析法对模具的结构、浇注系统和冷却系统进行合理的设计以及对挤出成型过程中挤出胀大现象的预测;在制件性能分析方面对制件的结构进行模拟,并结合制件结构特点对其力学性能、电学性能、热学性能等进行预测和分析.     

Surface modification of microcrystalline cellulose (MCC) and its application in LDPE‐based composites

Microcrystalline cellulose (MCC) was modified by grafting onto its surface ferulic acid, methacryloyl chloride and oleoyl chloride. The efficacy of the chemical modification was confirmed by X‐ray photoelectron spectroscopy. In addition, the size distribution of the cellulosic particles was investigated by optical microscopy and laser granulometry and its hydrophobicity was evaluated using a contact angle method. Finally, to investigate the affinity of modified MCC with a nonpolar polymer and to assess its potential as a biobased reinforcing filler, the modified MCC was compounded into low‐density polyethylene. An organic peroxide, dicumyl peroxide, was added at selected formulations to see if it could further enhance mechanical bonding between the polymer and the particulates. The dispersion was assessed by scanning electron microscopy. Mechanical properties were investigated through tensile testing while the melt rheology of the composites was monitored by small angle oscillatory shear rheology. The acylation modification of the MCC improved the dispersion within LDPE and enhanced the mechanical properties of the composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44348.     

Theoretical Study for High-Energy-Density Compounds Derived from Cyclophosphazene. IV. DFT Studies on 1,1-Diamino-3,3,5,5,7,7-hexaazidocyclotetraphosphazene and Its Isomers

In the present study, a theoretical study of 1,1-diaminohexaazidocyclotetraphophazene (DAHA) and its isomers has been performed, using quantum computational density functional theory (B3LYP and B3PW91 methods) with 6-31G* and 6-31G** basis sets implemented in Gaussian 03 program suite. Molecular structure and bonding, vibrational frequencies, Milliken population analysis, and natural bond orbit (NBO) have been studied. The heats of formation from atomization energies have also been calculated based on the optimized geometry. The obtained heats of formation data are compared with their homologous cyclophosphazene in order to demonstrate the accuracy of the methods, which indicate that the studied compounds might be potentially used as high energetic materials. In addition, the relative stability of five isomers have been deduced based on the total energy and the gap of frontier orbital energies.     

压力管道设计中的低温低应力工况及其应用

简要分析了目前国内低温管道设计的技术状况 ,提出在低温管道设计中也存在低温低应力工况 ,和低温压力容器设计中的有关内容相似 ,并通过实例分析验证了其工程实用性。     

Evaluation of a structural epoxy adhesive for timber-glass bonds under shear loading and different environmental conditions

This article presents a study of timber-glass adhesive joints. It examines the shear specimen and shear tools preparation process and the evaluation of the results backed up with an overview of existing similar studies. The chosen adhesive was a cold-curing two-component structural bonding epoxy resin (Mapei Adesilex PG1). The shear tests were performed under different temperatures and the timber samples had different moisture contents. A simple shear test tool was designed and was clamped into a universal testing machine for the shear test. The force and crosshead displacement values from the universal testing machine were used for evaluating the results. The environmental conditions of 20 °C and 5% timber moisture content resulted in the highest average shear strength obtained from the shear tests of the analysed joints (9.89 MPa), whereas the environmental conditions of 50 °C and 20% timber moisture content resulted in the lowest average shear strength (3.42 MPa). It was found that the joint strength is dependent on the environmental temperature and timber moisture content. Moreover, the shear specimen load-displacement behaviour at the environmental temperature of 50 °C was linear and nonlinear – depending on the timber moisture content. The most frequent failure type was timber failure. Additionally, a nonlinear contact finite element analysis was performed to demonstrate the additional shear specimen rotation due to the clearance between the shear specimen and shear tools. This impact was evaluated regarding the stress distribution in the bond line. The evaluated epoxy resin adhesive was proved to be suitable for timber-glass bonds.     

Synthesis and characterization of microcrystalline cellulose‐graft‐poly(methyl methacrylate) copolymers and their application as rubber reinforcements

In this study, redox‐initiated free radical graft copolymerization of microcrystalline cellulose (MCC) and methyl methacrylate (MMA) has been carried out in aqueous media to develop a novel cellulose‐based copolymer. Cerium ammonium nitrate was used as the initiator in the presence of nitric acid. Effects of monomer concentration, initiator concentration, polymerization time, and polymerization temperature on the graft parameters of copolymers were studied. The successful grafting copolymerization between MCC and MMA was validated through attenuated total reflection, wide‐angle X‐ray diffraction, field‐emission scanning electron microscopy, and thermal gravimetric analysis. In comparison to native MCC, the resultant copolymers exhibited enhanced thermal stability and better compatibility with natural rubber, suggesting its potential application as reinforcement material in rubber industry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42666.