Strong Reactivity Enhancement through Molecular Traffic Control in Zeolites

In the past, the investigation of catalytic reactivity enhancement through molecular traffic control (MTC) by means of dynamical Monte Carlo simulations of catalysis was initiated in simple, idealized zeolite channel networks. These results are reviewed here and, emphasizing more recent work, the conditions of reactivity enhancement through MTC are examined for a realistic channel topology based on the pore structure of the zeolite TNU‐9. For a wide range of reaction rates a very strong MTC effect can be found that increases with grain size. This effect is argued to be a generic feature of a certain class of zeolite pore topologies.     

Methane Transport Capacity of Rice Plants. II. Variations Among Different Rice Cultivars and Relationship with Morphological Characteristics

Of the total methane (CH4) emitted from a rice field during the growing season 60–90% is emitted through the rice plants. We determined the methane transport capacity (MTC) of rice plants at different physiological growth stages using an automatic measuring system under greenhouse conditions. A total of 12 cultivars (10 inbred varieties and 2 hybrids) were studied in sets of two experiments and was distinguished into three groups according to the patterns of MTC development. MTC is generally increasing from seedling stage to panicle initiation (PI), but differs in the development from PI to maturity. While the hybrid showed a gradual increase in MTC, the inbred cultivars showed either minor changes in MTC or a drastic decrease from flowering to maturity. Among tall cultivars, Dular showed the highest MTC, followed by B40; the lowest MTC was found in Intan. High-yielding dwarf cultivars showed MTC in the descending order of IR72 > IR52 > IR64 > PSBRc 20. New plant type cultivars showed very low MTC with IR65600 exhibiting the smallest MTC at PI, flowering, and maturity. Hybrids (Magat and APHR 2) showed the largest MTC that continued to increased with plant growth. The MTC patterns were attributed to growth parameters and the development of morphological characteristics of the aerenchyma. These results suggest that in tall, dwarf, and NPT cultivars, increase in root or aboveground biomass during initial growth determines a corresponding increase in MTC. Once aerenchyma has fully developed, further increase in plant biomass would not influence MTC. However, in the case of hybrids, a positive relationship of MTC with root + shoot biomass (r = 0.672, p 0.05) and a total plant biomass including grain (r = 0.849, p 0.01) indicate continuous development of aerenchyma with plant growth, resulting in enhanced MTC. In all cultivars, tiller number, but not height, was linearly related to MTC, indicating that the number of outlets/channels rather than plant size/biomass determines the transport of CH₄. These results clearly demonstrate that rice cultivars differ significantly in MTC. Therefore, the use of high-yielding cultivars with low MTC (for example, PSBRc 20, IR65598, and IR65600) could be an economically feasible, environmentally sound, and promising approach to mitigate CH₄ emissions from rice fields.     

矿渣MTC技术的应用

本文简要概括了矿渣MTC技术在我国的应用情况,对于当前存在的不足之处以及发展前景也作了简单的介绍。文章主要论述了该项技术中相关的一些材料(包括矿渣、分散剂和激活剂体系等)的性能和他们在转化液中的作用。文章对该技术的主要成分——高炉水淬矿渣(BFS)做了详细的介绍,包括结构、组成、水化产物等。矿渣MTC水泥浆由钻井液转变而来,它与钻井液有很好的兼容性,在提高界面的胶结质量上发挥了很好的作用。矿渣MTC技术具有广阔的发展前景,有深入研究的必要。     

Strategies for size reduction of microreactors by heat transfer enhancement effects

One of the likely aims of reactor miniaturization in the field of chemical production and energy generation is to increase the conversion to the desired product and the selectivity of the process through better control of heat and mass transfer. In addition to the effects related to miniaturization, a further increase of the transfer coefficients is achieved by applying microstructuring techniques. In this context, three different approaches for heat transfer enhancement in miniaturized reaction systems are presented. The ideas put forward rely on entrance flow effects, inertial flows in meandering channels, and suppression of axial heat conduction. Among these ideas the entrance flow effect, realized by an arrangement of microfins with a typical dimension of a few hundred micrometers, provides the most efficient heat transfer. It is found that a heat transfer enhancement of at least one order of magnitude can be achieved compared to unstructured channels. On this basis, a miniaturized heat-exchanger reaction system is investigated, where a kinetic model of an endothermic, heterogeneously catalyzed gas-phase reaction is used. The miniaturized heat-exchanger reactor, both with and without heat transfer enhancement, is subsequently benchmarked against conventional fixed-bed technology. It is shown that, for the reaction system under study, a substantial reduction of the required amount of catalyst can be achieved in microsystems.     

STRATEGIES FOR SIZE REDUCTION OF MICROREACTORS BY HEAT TRANSFER ENHANCEMENT EFFECTS

One of the likely aims of reactor miniaturization in the field of chemical production and energy generation is to increase the conversion to the desired product and the selectivity of the process through better control of heat and mass transfer. In addition to the effects related to miniaturization, a further increase of the transfer coefficients is achieved by applying microstructuring techniques. In this context, three different approaches for heat transfer enhancement in miniaturized reaction systems are presented. The ideas put forward rely on entrance flow effects, inertial flows in meandering channels, and suppression of axial heat conduction. Among these ideas the entrance flow effect, realized by an arrangement of microfins with a typical dimension of a few hundred micrometers, provides the most efficient heat transfer. It is found that a heat transfer enhancement of at least one order of magnitude can be achieved compared to unstructured channels. On this basis, a miniaturized heat-exchanger reaction system is investigated, where a kinetic model of an endothermic, heterogeneously catalyzed gas-phase reaction is used. The miniaturized heat-exchanger reactor, both with and without heat transfer enhancement, is subsequently benchmarked against conventional fixed-bed technology. It is shown that, for the reaction system under study, a substantial reduction of the required amount of catalyst can be achieved in microsystems.     

Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis

The reactions of phenol with dichloromethane using quaternary ammonium salts as a liquid–liquid phase-transfer catalyst in an organic solvent/alkaline solution were investigated. The technique of phase-transfer catalysis had a dramatic accelerating effect on the reaction and increased the yield of diphenoxymethane by more than 95%. The effects of catalysts, temperature, and basic concentration on reaction rate were studied in order to find the optimum operating conditions for this reaction. Experimental results indicated that a potassium hydroxide was preferred over sodium hydroxide in order to enhance the reactivity of the reaction. The reaction rate constant and the distribution coefficient of the intermediate product were obtained. During the reaction, the concentration of the intermediate product was also measured in order to study its behavior in the liquid–liquid system.     

Some aspects of reaction between epoxy and bisphenol

Summary This study deals with a new system based on the reaction between a, dihydroxy polyaryleneoxy-2,6 pyridylene (PAOP) and a Novolac epoxy prepolymer. The functionality of the later is higher than two which allows to reach a cross-linked network without curing agent. The reactivity of this mixture is compared to the reactivity of a system in which PAOP is replaced by a bisphenol without pyridine ring. It appears that the phenol functions — pyridine ring association catalyses the epoxide — phenol reaction.Not only are the kinetics of reaction of some systems with different stoichiometric ratio studied, but the effect on these ones of an external catalyst like imidazole as well.     

Strain enhanced defect reactivity at grain boundaries in polycrystalline graphene

Grain boundaries dominate the property of polycrystalline graphene. We report first-principles calculations and classical molecular dynamics simulations that reveal enhanced defect reactivity induced by an inhomogeneous strain field at grain boundaries. Strained carbon bonds located at heptagons and pentagons can accumulate interstitials and single vacancies, respectively. We find that recombination of vacancies and interstitials can occur locally at grain boundaries, which serve as effective sinks, resulting in efficient annealing of defects. The enhanced defect reactivity indicates that grain boundaries may be manipulated by point defects.     

1,2-Dichloroethane production by two-step oxychlorination reactions in a fluidized bed reactor

The reaction characteristics of two-step oxychlorination to produce 1,2-dichloroethane as a feedstock of PVC production were determined in a fluidized bed reactor. The effects of superficial gas velocity and gas composition on the reactivity and fluidization stability have been determined to find the optimum operating conditions in the continuous fluidized bed reactor system. It has been found that the average ethylene conversion is 94% with ethylene dichloride (EDC) selectivity of 97-98%, the average HCl conversion is 97.4%, the solid reactant conversion is 54% and a solid inventory ratio for the optimum reaction conversion is 3.3 in the process.     

Kinetic study on the reaction of 2,4‐ and 2,6‐tolylene diisocyanate with 1‐butanol in the presence of styrene,as a model reaction for the process that yields interpenetrating polyurethane–polyester networks

A classical method was utilized for determination of free isocyanates to study the kinetics of a model reaction of 2,4‐ and 2,6‐tolylene diisocyanate (TDI) with 1‐butanol, which was run in the reaction medium of liquid aliphatic hydrocarbons. Such conditions made it possible to find rate constants and activation energy values for the second‐order reactions under isothermal conditions. Those reactions can be employed to produce isocyanate prepolymers, which make intermediates for downstream polyurethanes. The findings are commented upon against the background of earlier kinetic data that can widely be found in the research reports published. Further, part of our work utilized the findings to provide interpretation of kinetic parameters for analogous reactions, the kinetic data being found in the presence of styrene—the monomer employed when producing polyurethane–polyester interpenetrating polymer network (IPN) systems. The hypothesis was put forward that styrene and isocyanate component(s) could react at the final stages of the process when the system becomes short in the hydroxyl substrate. That hypothesis was based on disturbances observed in the reactivity of ? NCO groups (in 2,4‐TDI) in the reaction system studied. The rate constants and activation energy values were determined and presented for the urethanization reaction of 1‐butanol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 327–336, 2003     

Urea and Thiourea-Functionalized Mesoporous Silica Nanoparticle Catalysts with Enhanced Catalytic Activity for Diels–Alder Reaction

A series of urea- and thiourea-functionalized mesoporous silica nanoparticles (MSN) was synthesized. These materials exhibited a superior catalytic reactivity for Diels–Alder reaction than their homogeneous analogues. The reactivity enhancement was attributed to the site isolation effect induced by the heterogenization of individual catalytic group. The surface hydrogen bonding between the organic catalysts and silanols also improved the catalytic reactivity.     

Formation of nanostructured epoxy networks containing polyhedral oligomeric silsesquioxane (POSS) blocks

Nanostructured epoxy networks, based on DGEBA and poly(oxypropylene)diamine (Jeffamine D), containing nano-sized inorganic blocks, polyhedral oligomeric silsesquioxanes (POSS), were investigated. The POSS were incorporated in the network as crosslinks or as pendant units by using octa- or monoepoxy-POSS monomers, respectively, as well as diepoxides with pendant POSS. The authors focused on investigating the relationship between the network formation process and the final product properties. The reactivity of the epoxy-functional POSS monomers, the hybrid systems' time of gelation, the gel fractions and the phase structure of the networks were determined using ¹H or ¹³C NMR spectroscopy, chemorheology experiments, sol-gel analysis and transmission electron microscopy (TEM).All the POSS epoxides tested show a reduced reactivity if compared to their respective model compounds due to sterical crowding in the neighborhood of their functional groups and due to reduced epoxy group mobility. The incorporation of pendant POSS into networks of the type DGEBA-Jeffamine D-monoepoxy-POSS hence took place only in the late reaction stage. Together with the high tendency of these POSS to aggregation, the kinetics favors the formation of small nano-phase-separated POSS domains, which act as physical crosslinks due to their covalent bonds to the organic matrix. At POSS loadings higher than 70%, topological constraint by POSS leads to a strongly reduced elastic chain mobility, thus additionally strongly reinforcing the networks. The network build-up and gelation of the octaepoxy-POSS-Jeffamine D system were slow compared to the reference DGEBA-Jeffamine D network due to a low octaepoxy-POSS reactivity and due to its strong tendency to cyclization reactions with primary amines. The topology of the amino groups is shown to be very important. In contrast to monoepoxy-POSS, the octaepoxy-POSS becomes dispersed as oligomeric junctions (purely chemical crosslinks) of the network in the cured product. The octaepoxide's reinforcing effect is small and is given only by its high functionality and not by its inorganic nature. The functionality effect is reduced by the mentioned cyclizations.     

Gasification kinetics of five coal chars with CO<Subscript>2</Subscript> at elevated pressure

For five coals, the reactivity of char-CO₂ gasification was investigated with a pressurized thermogravimetric analyzer (PTGA) in the temperature range 850-1,000 C and the total pressure range 0.5-2.0 MPa. The effect of coal rank, initial char characteristics and pressure on the reaction rate were evaluated for five coal chars. The reactivity of low lank coal char was better than that of high rank coal char. It was found that Meso/macro-pores of char markedly affect char reactivity by way of providing channels for diffusion of reactant gas into the reactive surface area. Over the range of tested pressure, the reaction rate is proportional to CO₂ partial pressure and the reaction order ranges from about 0.4 to 0.7 for five chars. Kinetic parameters, based on the shrinking particle model, were obtained for five chars.     

Modification of the adsorptive properties of charcoal by treatments with pyridines

Studies on the use of various pyridines (e.g., pyridine, 4-vinylpyridine, 4-aminopyridine, 4-cyanopyridine, and 4-n-propylpyridine) to modify the adsorptive properties of charcoal are described. The impregnated charcoals are compared with respect to adsorption capacity for carbon tetrachloride and cyanogen chloride under dynamic conditions and relative affinity for methyl iodide under equilibrium conditions. In several cases, the effect of impregnant concentration and method of impregnation were examined in detail. As part of the overall study, it was interesting to find that adsorption of 4-vinylpyridine resulted in the formation of ethanol intractable material (presumably polymer) on the surface of the charcoal which still exhibited chemical reaction activity. It would appear that adsorption of 4-vinylpyridine results in polymerization with a molecular orientation which allows pyridine nitrogens to be available for chemical reactivity. A charcoal prepared by adsorption of poly-4-vinylpyridine showed little chemical reactivity.     

螺旋通道内流动沸腾传热研究进展

螺旋通道因其优越的传热性能在强化传热领域有着重要的应用。近年来,高热流密度下设备的散热问题严重制约着先进技术的高速发展,传统螺旋通道单相强化传热技术已难以满足如此高的散热要求。由此,学者们开始探索以螺旋通道和流动沸腾传热相结合的复合强化传热技术。但由于螺旋通道特有的结构导致管内工质会受离心力的影响产生二次流,使得流动沸腾的情况较直通道更复杂,因此许多学者研究螺旋通道流动沸腾传热得出的结论并不一致。本文主要综述了近年来常规和微细尺度螺旋通道内流动沸腾的研究进展,阐述和分析了质量流率、干度、压力等参数对螺旋通道传热系数及临界工况的影响。指出了实验工况及螺旋通道结构的不同可能是导致结果存在分歧的主要原因,重点归纳了研究者根据实验结果拟合得到的流动沸腾传热实验关联式,并对经典直通道及螺旋通道沸腾传热关联式用于预测螺旋通道沸腾传热系数时的优缺点给予评价,指出今后螺旋通道内流动沸腾流传热的研究方向。     

Experimental and Theoretical Study of CO Oxidation on PdAu Catalysts with NO Pulse Effects

The effect of NO on CO oxidation was studied for Pt, Pd and PdAu catalysts. It was found that NO inhibits significantly the CO oxidation reactivity on both Pt and Pd catalysts. On PdAu catalyst, however, the presence of NO resulted in an enhancement of CO oxidation activity. In order to gain an atomistic understanding of this effect, density-function theory (DFT) calculations were performed on the adsorption and reaction properties of NO and CO on these metal surfaces. We have identified that the inhibition effects on Pt and Pd catalysts are due to stronger NO binding, and that the enhanced reactivity on PdAu is due to the reduced NO oxidation barrier on PdAu leading to NO₂ formation.     

磷矿的反应活性及其评价方法研究

介绍评价磷矿反应活性的实验装置;用磷矿在一定浓度酸液中,在一定温度、一定反应时间下的分解率表示磷矿的反应活性。实验研究了不同因素对磷矿反应活性的影响,并测试了11种磷矿的反应活性指数及抗硫酸的阻缓性能。评价方法与实验结果均具有参考价值。     

Structural modification and characterization of lignosulfonate by a reaction in an alkaline medium for its incorporation into phenolic resins

We studied the enhancement of lignin reactivity in an alkaline medium, using sodium hydroxide in a microreactor set. The chemical composition and structural characterization of the reacted lignosulfonate in terms of the phenolic hydroxyl groups, aromatic protons, weight‐average molecular weight, number‐average molecular weight, and lignosulfonate content of all reacted lignins were determined. The techniques that we used were ultraviolet spectroscopy, proton nuclear magnetic resonance spectroscopy, and aqueous gel permeation chromatography. Using response surface methodology, we studied how the temperature and reaction time affected the lignin properties. The reaction conditions were temperatures between 116 and 180°C and reaction times between 18 and 103 min. Modeled response surfaces showed that the two factors affected the lignin properties within the studied ranges. The phenolic hydroxyl groups, aro matic protons, and lignosulfonate content increased when the severity of the treatment increased. The weight‐average molecular weight, number‐average molecular weight, and solid yield (%) decreased when the severity of the treatment increased. The reactivity of the modified lignins was studied with a formaldehyde reactivity test: more severe conditions produced greater improvements in the formaldehyde reactivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3286–3292, 2006     

Feasibility of producing geopolymer binder based on a brick clay mixture

A brick clay mixture from a company localized in the north west of France is used for this study. The feasibility of producing geopolymer materials from a clay mixture was investigated. The final aim is to find a new application for this aluminosilicate material. One metakaolin (for a reference), the brick clay mixture, and the clay mixture calcined at two temperatures were compared after reaction with each of three alkaline solutions with different reactivity (the reactivity of each is defined). Physical, chemical, structural (FTIR and XRD) and thermal characterization (DTA) were first performed on the raw materials. Then, the structural evolution of the formed geopolymers was investigated using FTIR spectroscopy and XRD. Thus, this study demonstrates the feasibility of producing consolidated materials from a calcined brick clay (containing calcium oxides), which exhibits higher reactivity than brick clay. Plus, from a mixture of 25 wt% of less reactive materials such as ground brick clay and 75 wt% of reactive materials, it is possible to obtain geopolymer materials. FTIR study reveals the presence of a Ca²⁺ release phenomena, with a simultaneous polycondensation reaction for products based on calcined brick clay, which is different according to the silicate solution. Moreover, a link between [M⁺+M²⁺] and the different networks formed in the samples based on calcined clay was found. Indeed, it appears that the concentration within the range 10.5–14 mol/l favors the geopolymer network formation.