Search

Alkane dehydrogenation to alkene represents a promising alternative route for conventional petroleum cracking processes heavily reliant on fossil resources. This Concept outlines the latest advancements of novel alkane dehydrogenation routes that offer potential solutions to intrinsic problems existing in routine direct dehydrogenation or oxidative dehydrogenation reactions, including CO2 assisted alkane dehydrogenation, chemical looping alkane oxidative dehydrogenation, dual‐path dehydrogenation and auto‐accelerated multiple alkane dehydrogenation route. These novel reaction routes exhibit unique advantages in enhancing the activity, selectivity and stability of the alkane dehydrogenation reaction system. The rational design of novel catalysts and proper choice of the reaction condition that well‐fitted these reaction routes is the key for achieving highly efficient and stable alkane dehydrogenation process. These present examples in this manuscript also highlight the importance of fundamental in‐depth understandings on the mechanism and structure‐function relations, which is the foundation for developing novel alkane dehydrogenation routes for practical applications. [ABSTRACT FROM AUTHOR]

The fabrication of composites of two or more materials with different polarities requires the use of compatibilisers to improve interface properties. However, most compatibilisers used for industrial production are derived from the cracking products of petroleum, which is a limited resource susceptible to price fluctuations and pollutes the environment. In this study, a new compatibiliser derived from renewable plant‐oil‐based products, ESO–G–OA, was designed and synthesized using epoxy soybean oil, oleic acid, and glycerol. Scanning electron microscopy results showed that ESO–G–OA can effectively improve the dispersion of CaCO3 in a recycled high‐density polyethylene (reHDPE) matrix and reduce the interfacial gap between the two phases. The analysis of the mechanical properties showed that the ESO–G–OA‐modified composite has higher tensile and impact strength than unmodified samples. The ESO–G–OA modification improved the thermal stability and melt flow of the composite and reduced the energy consumption during processing. Moreover, the excellent compatibility of ESO–G–OA can improve the comprehensive properties of CaCO3/reHDPE composites, compensating for the performance reduction caused by the multiple processing steps necessary to obtain reHDPE. This confirmed that ESO–G–OA has promising application prospects in the production of composites requiring compatibilisers. [ABSTRACT FROM AUTHOR]

Zr based metallosilicalites, especially Zr‐ß, is promising catalyst for the conversion of ethanol to 1,3‐butadiene, which is considered to be a sustainable alternative to petroleum steam cracking. However it is suffering from deactivation derived from coking and unsatisfied catalytic activity derived from deficient Lewis acidity. For these issues, a dissolution‐recrystallization process through tetraethyl ammonium hydroxide treatment (TEAOH) for enhancing porosity and Lewis acidity of Zr‐ß zeolite was developed in this study. A balance of dissolution and recrystallization existed in this process, which was produced by OH− etching and templating of TEA+ ions, creating additional mesoporosity. Zirconium active sites maintained tetrahedral coordination, while the Lewis acidity was enhanced by creating higher proportion open sites in framework. The recrystallized Zr‐ß exhibited higher catalytic activity and stability in the conversion of ethanol‐acetaldehyde to butadiene due to the compromise of microporosity and mesoporosity, as well as the appropriate enhancement of Lewis acidity. [ABSTRACT FROM AUTHOR]

Bulk chemical 2‐methyl‐2‐butene, one of the main C5 distillates of the petrochemical industry, has scarcely been utilized directly in synthesizing high‐value‐added fine chemicals. Herein, we use 2‐methyl‐2‐butene as the starting material to develop a palladium‐catalyzed highly site‐ and regio‐selective C‐3 dehydrogenation reverse prenylation of indoles. This synthetic method features mild reaction conditions, a broad substrate scope, atom‐ and step‐economies. [ABSTRACT FROM AUTHOR]

The article talks about novel sensor and material technologies designed to help identify bridges most at risk of failure or collapse so they can be repaired and strengthened. Topics covered include the aging bridge infrastructure in both the U.S. and Europe, automated versions in monitoring bridges for crack formation that are being developed by researchers, and a flexible strain-sensing sheet for monitoring bridges developed by a team led by Branko Glisic at Princeton University.

The article discusses issues associated with science industry. Topics discussed include antivirals as another promising route to decrease risk of Covid-19 pandemic risks alongside vaccination; joint venture technology firm created by Reaction Engines in Oxfordshire; new approach to treat Alzheimer's disease by using an engineered form of a protein associated with the disease.

The adsorption and reaction properties of heterogeneous zeolite catalysts (e.g. for catalytic cracking of petroleum, partial oxidation of natural gas) depend strongly on the types and distributions of Al heteroatoms in the aluminosilicate frameworks. The origins of these properties have been challenging to discern, owing in part to the structural complexity of aluminosilicate zeolites. Herein, combined solid‐state NMR and synchrotron X‐ray powder diffraction analyses show the Al atoms locate preferentially in certain framework sites in the zeolite catalyst Al‐SSZ‐70. Through‐covalent‐bond 2D 27Al{29Si} J‐correlation NMR spectra allow distinct framework Al sites to be identified and their relative occupancies quantified. The analyses show that 94 % of the Al atoms are located at the surfaces of the large‐pore interlayer channels of Al‐SSZ‐70, while only 6 % are in the sub‐nm intralayer channels. The selective siting of Al atoms accounts for the reaction properties of catalysts derived from SSZ‐70. [ABSTRACT FROM AUTHOR]

A new theoretical and practical framework has been developed through operando study of the zeolite catalytic cracking of low‐density polyethylene (as a model reaction) under reaction conditions. Results show that microporous ZSM‐5 gives rise to less cracking products. Hierarchical ZSM‐5 zeolites are more active cracking catalysts, rendering more C2‐C5 hydrocarbons, with a delayed deactivation due to the secondary porosity. This tool in combination with thermogravimetric analysis provides complementary and valuable information for the study, and design of advanced catalysts. A cracking catalyst: Operando study provides valuable information about how the ZSM‐5 catalyst works under reaction conditions for the low‐density polyethylene cracking. This study illustrates that microporous ZSM‐5 gives rise to less cracking and deactivates faster, whereas hierarchical ZSM‐5 cracking catalysts are more active with delayed deactivation due to the secondary porosity. [ABSTRACT FROM AUTHOR]

Abstract: The monomolecular cracking rates of propane and n‐butane over MFI, CHA, FER and TON zeolites were determined simultaneously with the coverage of active sites at reaction condition using IR operando spectroscopy. This allowed direct determination of adsorption thermodynamics and intrinsic rate parameters. The results show that the zeolite confinement mediates enthalpy–entropy trade‐offs only at the adsorbed state, leaving the true activation energy insensitive to the zeolite or alkane structure while the activation entropy was found to increase with the confinement. Hence, relative cracking rates of alkanes within zeolite pores are mostly governed by activation entropy. [ABSTRACT FROM AUTHOR]

Abstract: Among the options for clean energy production, the gasification process is receiving increasing attention as it offers the best combination of investment and value of produced electricity compared to other methods. An Aspen Plus model of co‐gasification of biomass and coal with in situ CO2 capture was developed to evaluate its potential for hydrogen production and cracking of organic impurities, i.e., tars. The effects of some critical operational variables on gas composition and yields of hydrogen gas and tar were investigated. The obtained results indicate that the fuel particle size plays a minor role in the process; smaller particles favor the conversion of tar and production of more hydrogen gas. [ABSTRACT FROM AUTHOR]

In this paper, a finite element model to analyze the cracking process of a steel fiber-reinforced concrete ( SFRC) beam on grade, loaded in two points, is presented. Already validated in the past, the numerical model used is a probabilistic explicit cracking model. The motivation of the present work is to evaluate the influence of the degree of redundancy of the mechanical system on the mechanical behavior of the beam (bearing capacity and cracking process). The main conclusion of this work is that for analyzing and properly designing SFRC structural members on grade, the only relevant tool is the finite element method using a cracking model. [ABSTRACT FROM AUTHOR]

Heterogeneous Brønsted acid catalysts are tremendously important in industry, particularly in catalytic cracking processes. Here we show that these Brønsted acid sites can be directly observed at natural abundance by 17O DNP surface-enhanced NMR spectroscopy (SENS). We additionally show that the O−H bond length in these catalysts can be measured with sub-picometer precision, to enable a direct structural gauge of the lability of protons in a given material, which is correlated with the pH of the zero point of charge of the material. Experiments performed on materials impregnated with pyridine also allow for the direct detection of intermolecular hydrogen bonding interactions through the lengthening of O−H bonds. [ABSTRACT FROM AUTHOR]

Three-dimensional computational fluid dynamics simulations were performed to study gas flow, heat transfer, and catalytic reactions of vacuum gas oil inside spherical and ellipsoidal clusters consisting of fluid catalytic cracking catalyst particles. Simulation results with respect to gas flow inside the cluster and convective heat transfer between the gas and catalyst particle agreed well with results from the literature. Simulation results indicated that the gas stayed longer and had a higher temperature inside the cluster than that in the main stream, which intensified secondary reactions of gasoline species in the gas. At a higher cluster porosity, it was predicted that the gas could flow through the cluster with lower resistance and that secondary reactions lessened. [ABSTRACT FROM AUTHOR]

Despite rigorous models of the steam cracking processes being available for simulation of naphtha cracking, the simulation is often carried out using limited characterization of such a feedstock due to unavailability of detailed composition at the time when the simulation is required. A method was developed for generation of substitute naphtha composition meeting specified properties. Sets of alternative compositions were generated, matching the density, distillation curve, and optionally PIONA of real naphtha feedstocks. Its cracking product yields were calculated using a validated cracking model. Simulated product yields were evaluated in terms of result variability and deviation from the experimental data, depending on the level of available feedstock characterization. [ABSTRACT FROM AUTHOR]

An internal cracking indicator is designed to quantify the risk of hot tearing in the continuous casting of round billets. For this purpose, the tensional state of the bar is acquired by implementing a thermo-mechanical model that uses a steel material law calibrated with hot tension tests. The cracking indicator is then applied to the phenomenon of diametral pinch-roll compression. Critical combinations of casting speed and steel carbon content are defined to estimate the cracking risk. At last, macro-etching is applied on industrial bars in order to reveal internal cracking, which is then compared to model results to assess its predictability. Influence of pinch-roll pressure and roll shape on the cracking risk is also analyzed. [ABSTRACT FROM AUTHOR]

High energy consumption during distillation is a problem in petrochemical and refining industry. Therefore, the distillation of hydrocarbons was investigated with the aim to reduce the energy consumption by applying columns with fully or partially thermally coupled heat and material flows. The elements of downstream processes were considered, such as the separation of catalytic cracking gas and the recovery of benzene from petroleum and coking coal products by extractive distillation with N-methylpyrrolidone. It was found that the thermally coupled columns applied for the separation reduced the energy consumption for catalytic cracking gas separation by up to 13.1 % and for benzene recovery by up to 28.7 %. [ABSTRACT FROM AUTHOR]

Sulfur-containing compounds play a key role in many industrial processes. Particularly for the steam cracking process, they have been linked with increased olefin selectivity, CO formation, and coke inhibition. The influence of four different sulfur-containing additives, methanedithione, (methyldisulfanyl)methane, (methylsulfanyl)methane, and dimethyl sulfoxide, on product selectivity, coke deposition, and CO production during steam cracking of a surrogate light naphtha feed is investigated. The use of online comprehensive 2D gas chromatography with sulfur chemiluminescence detection (GC×GC-SCD) is the key enabling technology to characterize the sulfur compounds. Steam cracking in a pilot-plant unit revealed that all studied sulfur compounds are efficient in reducing the CO yield. Simultaneously, they strongly promote coke. [ABSTRACT FROM AUTHOR]

Fluid catalytic cracking (FCC) catalysts play a central role in the chemical conversion of crude oil fractions. Using scanning transmission X-ray microscopy (STXM) we investigate the chemistry of one fresh and two industrially deactivated (ECAT) FCC catalysts at the single zeolite domain level. Spectro-microscopic data at the Fe L3, La M5, and Al K X-ray absorption edges reveal differing levels of deposited Fe on the ECAT catalysts corresponding with an overall loss in tetrahedral Al within the zeolite domains. Using La as a localization marker, we have developed a novel methodology to map the changing Al distribution of single zeolite domains within real-life FCC catalysts. It was found that significant changes in the zeolite domain size distributions as well as the loss of Al from the zeolite framework occur. Furthermore, inter- and intraparticle heterogeneities in the dealumination process were observed, revealing the complex interplay between metal-mediated pore accessibility loss and zeolite dealumination. [ABSTRACT FROM AUTHOR]

ABSTRACT Nonreactive and reactive computational fluid dynamic simulations were applied to optimize the design of a laboratory scale jet stirred reactor for measuring intrinsic kinetics of gas-phase and gas-solid reactions, i.e. kinetics determined by chemical steps only and not by heat or mass transfer. In the past these reactors were designed and tested based on empirical design criteria and residence time distribution experiments. This work shows that these do not always capture important local effects that are vital for kinetic studies. First the degree of macro-mixing was evaluated for three different geometries (down case, 45° case and 90° case) by performing in silico residence time distribution experiments at 900 K, showing that with these type of experiments only minor differences are observed. However, the ethane steam cracking simulations revealed major differences, with the 45° case being the most uniform in terms of temperature and the 90° case being by far the worst. The species nonuniformity in all geometries was acceptable and was in some cases even partly masked by important shortcut streams such as those observed in the 90° case. The existing gradients on the substrate surface are sufficiently small to be neglected in modeling efforts. As temperature is the major parameter determining the rate of the surface reactions, the 45° case is suggested as the best geometry for measuring intrinsic kinetics. [ABSTRACT FROM AUTHOR]

Through analyzing the integrated oil and gas production process, a multi-objective optimization model for the integrated oil and gas production process is established through considering nonlinear reservoir behaviour, multiphase flow in wells, and constraints from the surface facilities. In order to reduce the influence of model parameter uncertainty in the oil and gas production process, an error compensation method based on the Gaussian mixture model (GMM) is proposed to compensate the model. Non- dominated sorting genetic algorithm-II (NSGA-II) is used as the optimization algorithm. Moreover, an operational strategy using post- optimization is applied to solve the optimization model, so as to ensure the feasibility of the obtained optimal set-point. Finally, a novel optimization approach for the oil and gas production process considering model parameter uncertainty is proposed. Simulation results indicate that the proposed optimization method is feasible and effective. [ABSTRACT FROM AUTHOR]

A cracking furnace, which is the major unit involved in ethylene production, produces various petrochemical products ranging from ethylene to pitch and determines the production yield of an ethylene plant. It is essential to consider the operational performances of the cracking furnaces and to incorporate them into the whole plant's planning problem. Facing this challenge, this paper developed an optimization model, which integrates the scheduling problem of upstream cracking furnaces and the operational planning of the downstream units under a synchronized global time scale. Moreover, a modified Lagrangian decomposition algorithm is proposed for solving the large-scale mixed integer nonlinear optimization problem. An industrial case study demonstrates the feasibility of the integrated model and the effectiveness of the solution algorithm. [ABSTRACT FROM AUTHOR]

In surrogate modelling, a simple functional approximation of a complex system model is always constructed to reduce the computational expense, and the selection of a suitable surrogate model and a sampling method are key to obtaining a surrogate model for a complex system. To construct an appropriate surrogate model, three methods of adaptive surrogate modelling that use artificial neural networks (ANN) are developed by incorporating a new mechanism for automatically determining the number of hidden nodes and/or a new prediction error-based mixed adaptive sampling method. In the automatic determination, the number of hidden nodes can adaptively change according to the effective rate of parameters in the ANN during the adaptive surrogate modelling process. As a result, an improper number of hidden nodes determined by the empirical method can be avoided. The prediction error-based mixed adaptive sampling method is capable of finding the strong nonlinear behaviour of the underlying system, which is easily missed by the traditional prediction variance-based sampling method. The three methods and the previous method for adaptive surrogate modelling that use ANN are tested and compared in terms of replicating the behaviours of three types of challenge functions to determine the efficacy of the developed methods. Furthermore, these methods are used in an engineering problem of surrogate modelling for a cracking reaction simulator to validate the efficacy of the developed methods. [ABSTRACT FROM AUTHOR]

A discrete six-lump kinetic model for the thermal cracking of vacuum residue in the visbreaking process has been developed, and the time-dependent behavior of each individual lump has been determined. A combination of the heuristic method and gradient-based method (hybrid method) has been taken into account to optimize the parameters of the model. A new concept of objective functions has been presented and applied for optimization, so more acceptable results have been obtained. Such an approach has not been presented before. A number of 60 parameters was considered primarily, which has been reduced to 36 with the aim of flash calculation information, and optimized. The obtained results are in good agreement with experimental data. The analysis of the estimated rate constants showed that the cracking of vacuum residue to lighter products was the more dominant reaction pathway during the visbreaking process over the temperature range of 400-430 °C. [ABSTRACT FROM AUTHOR]

A kinetic model of steam-cracking in industrial-scale steam crackers was developed by a combination of mechanistic and empirical approach. Kinetic parameters of the model were optimized using the data of process experiments, carried out in full-scale industrial crackers, the product yields being determined by hot-gas sampling for the usual types of feedstock, including ethane, liquefied petroleum gas, gasoline, atmospheric gas oil, and hydrocracked vacuum distillate. Experimental and simulated results were compared for a wide range of feedstock and reaction conditions. Data on cracker control parameters and feedstock composition were collected by monitoring the whole production unit consisting of ten crackers and simulation results of total production compared to those of process balance. [ABSTRACT FROM AUTHOR]

A novel process design for a more cost-effective, greener process for making chemicals from shale gas and bioethanol is presented. The oxidative coupling of methane and cocracking technologies are considered for converting methane and light natural gas liquids, into value-added chemicals. Overall, the process includes four process areas: gas treatment, gas to chemicals, methane-to-ethylene, and bioethanol-to-ethylene. A simulation-optimization method based on the NSGA-II algorithm for the life cycle optimization of the process modeled in the Aspen HYSYS is developed. An energy integration model is also fluidly nested using the mixed-integer linear programming. The results show that for a 'good choice' optimal design, the minimum ethylene selling price is $655.1/ton and the unit global-warming potential of ethylene is 0.030 kg CO2-eq/kg in the low carbon shale gas scenario, and $877.2/ton and 0.360 kg CO2-eq/kg in the high carbon shale gas scenario. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1209-1232, 2015 [ABSTRACT FROM AUTHOR]

This study aimed to prepare KF/CaO catalyst with high catalytic activity that can be applied to produce bio-fuel from Cornus wisoniana oil. The KF/CaO catalyst was characterized by Brunauer-Emmett-Teller surface area (BET), XRD, scanning electron microscopy (SEM), and temperature programmed desorption (TPD). The chemical compositions of C. wisoniana oil and bio-fuel oil were analyzed by GC-MS. The effect of the catalyst preparation conditions on catalytic activity was investigated. The optimal process conditions for the KF/CaO preparation were KF loading rate of 40%, calcination temperature of 600°C, and 4 h calcination time. Under the optimum process conditions, the bio-fuel yield reached 82.7 and 65% bio-fuel yield was obtained after being reused nine times. The bio-fuel oil obtained by catalytic cracking has similar chemical compositions to petroleum-based diesel, which exhibited good fuel properties. KF/CaO was used as a catalyst for the production of bio-fuel from cracking of Cornus wisoniana oil. [ABSTRACT FROM AUTHOR]

Developments in modeling of the fluid catalytic cracking (FCC) process have progressed along two lines. One emphasizes composition-based kinetic models based on molecular characterization of feedstocks and reaction products. The other relies on computational fluid dynamics. The aim is to develop an FCC model that strikes a balance between the two approaches. Specifically, we present an FCC riser model consisting of an entrance-zone and a fully developed zone. The former has four overlapping, fan-shaped oil sprays. The model predicts the plant data of Derouin et al. and reveals an inherent two-zone character of the FCC riser. Inside the entrance zone, cracking intensity is highest and changes rapidly, resulting in a steep rise in oil conversion. Outside the entrance zone, cracking intensity is low and varies slowly, leading to a sluggish increase in conversion. The two-zone model provides a computationally efficient modeling approach for FCC online control, optimization, and molecular management. © 2014 American Institute of Chemical Engineers AIChE J, 61: 610-619, 2015 [ABSTRACT FROM AUTHOR]

A table of contents for the January 2014 issue of the journal is presented along with the authors' name index.

The effects of high pressures on the yield and kinetics of gas generated by the cracking of crude oil were investigated in laboratory simulation experiments. Samples of a low-maturity non-marine oil were recovered from the Paleogene Shahejie Formation in the Dongying depression, Bohai Bay Basin, eastern China. The oils were cracked to gas under different pressure and temperature conditions in an autoclave. Initial temperatures of 300 °C were increased to 650 °C at rates of either 30 or 100 °C/h. Reaction products were analysed at the end of each 50 °C temperature increase. Pressure conditions were either 0.1 MPa (i.e. atmospheric) or 20 MPa. Results show that high pressures inhibit or delay oil-to-gas cracking and retard the initiation of the cracking process. The temperature at which oil was cracked and the activation energy of the formation of C1-5 hydrocarbons increased under high pressure conditions, demonstrating the effects of pressure on the kinetics of the oil-to-gas cracking process. High pressures and high temperatures inhibited the conversion of C2-5 hydrocarbons to methane during secondary cracking. In addition, high pressures retarded the generation of N2, H2 and CO during cracking of oil. The presence of water increased the yields of total cracked gas, C2-5 hydrocarbons and CO2 in high-pressure conditions. The simulation results show that CO2 and C2-5 hydrocarbons have similar yields during oil-to-gas cracking. Using the kinetic parameters determined from the laboratory experiments, the yield and production rate of gas generated during the cracking of oil from Member 4 of the Paleogene Shahejie Formation in the Minfeng-Lijin sag (Dongying depression) were calculated. The results indicate that only limited volumes of natural gas in this area were derived from the cracking of oil, and that most of the gas was derived from the thermal decomposition of kerogen. [ABSTRACT FROM AUTHOR]

Learning from experience is one of the four pillars of Risk-Based Process Safety [CCPS, Guidelines for Risk Based Process Safety, New York, 2007]. Incidents that occur at one facility often provide opportunities to strengthen management systems at other facilities. Sharing the technical lessons learned from incidents is morally right and vital to improving process safety performance across the process and related industries. Most incidents also involve human factors, often as a key causal factor. Understanding these performance shaping factors can also be essential to minimizing future failures. Most articles regarding case studies on process safety incidents are written and presented by a third party who was not directly involved in the incident. As such, the articles may lack the human element and other insights that can only be properly appreciated and articulated by someone directly involved in the incident. In his early career the author was involved in two major incidents while managing the day-to-day operation of refinery process units. This article describes the first incident involving two major fires. In both incidents, the author found himself decidedly too close for comfort and could easily have become a casualty himself. This article will raise awareness of lessons learned relating to a number of elements of Risk-Based Process Safety [CCPS, Guidelines for Risk Based Process Safety, New York, 2007] and human factors. © 2013 American Institute of Chemical Engineers Process Saf Prog 32: 255-259, 2013 [ABSTRACT FROM AUTHOR]

Heat integration is commonly skipped when evaluating a process' relief systems design. Failing to evaluate the heat integration (or energy balance) for a process can result in overly conservative results and possibly lead to costly expenditures. Evaluating the effects of heat integration in relief systems design is a process that evaluates the physical limitations of the system and does not require taking credit for control system response. It is important to understand the effects that heat integration has on both individual relief devices, and in some cases, the significant affect it can have on flare system design. This becomes even more imperative in cases where relief devices that once discharged to the atmosphere are modified to discharge into a closed flare system. This article covers two examples where evaluating the effects of heat integration on the relief systems prevented costly modifications to those systems. © 2013 American Institute of Chemical Engineers Process Saf Prog, 32: 244-247, 2013 [ABSTRACT FROM AUTHOR]

To maximize oil yields in the fast pyrolysis of biomass it is generally accepted that vapors need to be rapidly quenched. The influence of the heterogeneous and homogeneous vapor-phase reactions on yields and oil composition were studied using a fluidized-bed reactor. Even high concentrations of mineral low char (till 55 vol %) appeared not to be catalytically active. However, the presence of minerals, either in biomass or added, does influence the yields, especially by the occurrence of vapor-phase charring/polymerization reactions. Contradictory, in the absence of minerals, homogeneous vapor-phase cracking reactions were dominant over polymerization/charring reactions (400-550°C, 1-15 s). With increasing vapor residence time, the oil yield reached an asymptotic value, which decreased with temperature. At a vapor temperature of 400°C no decrease in oil yield was observed, but dedicated analysis showed that homogeneous vapor to vapor reactions had occurred. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

We have performed a direct comparison of n-hexane cracking catalysed by a zeolite (H-ZSM-5) and a heteropoly acid (phosphotungstic acid, HPW). This comparison was examined by employing density functional theory, including dispersion energy, M06-L, for the purpose of understanding these two catalysts for this industrially important reaction. The predicted adsorption energies of hexane are −21.4 and −6.8 kcal/mol for H-ZSM-5 and HPW, respectively. The protolytic cracking mechanism is proposed to proceed via the first step of the C-C activation and is found to be the rate-determining step with activation energies of 42.8 and 41.4 kcal/mol for H-ZSM-5 and HPW, respectively. We also discuss the advantages and disadvantages of both catalysts for hydrocarbon cracking and give a perspective of utilising cutting-edge molecular design for a tailor-made hybrid catalyst. © 2011 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]

Modeling of complex reaction systems is necessary in the design, analysis, and optimization of many technologically important processes such as pyrolysis, steam cracking, coking, partial oxidation, and combustion. The complexity in kinetic modeling of all these processes is introduced both by the feed, which is a hydrocarbon mixture, and the high reactivity of radical intermediates. Recent advances in automated mechanism generation tools, although capable of establishing the complex reaction network, pose a big challenge of assigning rate parameters for all the reactions or devising appropriate estimation rules for all reaction classes in the network. The kinetics of free radical reactions dictates the chemistry of technologically important thermal processes. Intermolecular hydrogen abstraction by radicals is one of the dominant reaction types and constitutes a major part (often >50%) in any thermal reaction network owing to their profound effect on product distribution. While abstraction reactions by H atoms (and to some extent by methyl radicals) have been studied extensively in the past, the abstraction kinetics by vinyl radical is less explored even though vinyl radicals play an important role in molecular weight growth chemistry and in predicting acetylene concentrations in pyrolysis and fuel-rich hydrocarbon flames. This study presents the hierarchical tree structure for intermolecular hydrogen abstraction by vinyl radicals from {C/H} molecules and provides generic rate rules that account for most of the variation in CH bond energy in the family of aliphatic, aromatic, naphthenic, olefinic, and aromatic naphtheno hydrocarbons. Reaction classes developed in this work are still dictated by immediate neighbors within the spirit of group additivity, although some efforts were made to access the effect of non-next neighbors on generic rate parameters. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 327-349, 2012 [ABSTRACT FROM AUTHOR]

The article discusses a study which imaged the external coke deposited on catalytic particles containing MFI zeolite during the cracking of high-density polyethylene (HDPE) in a spouted bed reactor. The steps involved in the mechanism of cracking of HDPE are cited. The imaging methodologies applied in the study include polarized-visible light microscopy, reflective-fourier transform infrared (FTIR) microscopy, and confocal Raman microscopy.

This article deals with the effect of temperature variations on crack tip kinematics in rubbers, especially in crystallising rubbers. In such materials, the high deformation level encountered at the crack tip engenders the formation of crystallites. As a consequence, the crack tip is reinforced and resists crack growth. However, this phenomenon is significantly affected by variations in material temperature. This is classically observed at the macroscopic scale in terms of crack propagation rate and path. In this study, the effect of temperature is studied at the local scale, by measuring the change in the kinematic field at the crack tip during thermal cycles. Results show that, in crystallisable natural rubber, the effect of temperature depends on the stretch ratio attained in the zone under consideration. In slightly stretched zones, the stretch ratio increases with the increase in temperature, whereas it decreases in highly stretched zones. This highlights the competition between the effects of the variations in internal energy and in entropy on the thermomechanical response. Moreover, if crystallites form in highly stretched zones, the increase in temperature leads to crystallite melting, which increases the stretch ratio. This is explained by the fact that crystallites act as fillers by concentrating the stress and therefore by increasing the apparent stiffness of the material. [ABSTRACT FROM AUTHOR]

A newly developed hybrid solution algorithm applicable on turbulent multiphase, gas-solid, reactive flows is presented. A finite volume (FV) and a probability density function (PDF) method are combined. The FV technique is used to solve the total mass and momentum conservation equations together with the k-ε turbulence equation for the gas phase and the granular temperature equation for the solid phase. The PDF method is applied to solve the species continuity equations and avoids the need to model the chemical source terms in the latter. Stochastic differential equations (SDEs) are introduced as replicas of the transported composition PDF equations. The notional-particle-based Monte-Carlo technique is used to solve the PDF model equations. The hybrid FV/PDF solution algorithm is applied to simulate a fluid catalytic cracking (FCC) riser using a 12-lump kinetic model. A good agreement between simulated results and available plant data is obtained. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this in vitro study was to evaluate porcelain cracking induced by abrasive grinding with a conventional dental air turbine and abrasive diamond burs. Materials and Methods: Four commercially available porcelains were examined-Wieland ALLUX, Wieland ZIROX, IPS e.max Ceram, and IPS Empress Esthetic Veneering porcelain. Sixty discs of each porcelain type were fabricated according to manufacturer instructions, followed by an auto-glaze cycle. Abrasive grinding using fine, extra-fine, and ultra-fine diamond burs was carried out, using a conventional dental air turbine. The grinding parameters were standardized with regard to the magnitude of the force applied, rotational speed of the diamond bur, and flow rate of the water coolant. A testing apparatus was used to control the magnitude of force applied during the grinding procedure. The ground surfaces were then examined under scanning electron microscope. Results: Cracking was seen for all porcelain types when ground with the fine bur. Cracking was not seen for specimens ground with the extra-fine or the ultra-fine bur. Conclusion: Wet abrasive grinding with a conventional dental air turbine and fine grit diamond burs has the potential to cause cracking in the four porcelain types tested. Similar abrasive grinding with smaller grit size particles does not cause similar observable cracking. [ABSTRACT FROM AUTHOR]

ABSTRACT Research on fatigue crack formation from a corroded 7075-T651 surface provides insight into the governing mechanical driving forces at microstructure-scale lengths that are intermediate between safe life and damage tolerant feature sizes. Crack surface marker-bands accurately quantify cycles ( Ni) to form a 10-20 μm fatigue crack emanating from both an isolated pit perimeter and EXCO corroded surface. The Ni decreases with increasing-applied stress. Fatigue crack formation involves a complex interaction of elastic stress concentration due to three-dimensional pit macro-topography coupled with local micro-topographic plastic strain concentration, further enhanced by microstructure (particularly sub-surface constituents). These driving force interactions lead to high variability in cycles to form a fatigue crack, but from an engineering perspective, a broadly corroded surface should contain an extreme group of features that are likely to drive the portion of life to form a crack to near 0. At low-applied stresses, crack formation can constitute a significant portion of life, which is predicted by coupling macro-pit and micro-feature elastic-plastic stress/strain concentrations from finite element analysis with empirical low-cycle fatigue life models. The presented experimental results provide a foundation to validate next-generation crack formation models and prognosis methods. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, the interaction between multiple cracks in crack growth direction is studied in an aluminium alloy under static and fatigue loading. Self similar as well as non-self-similar crack growth has been observed which depends on the relative crack positions defined by crack offset distance and crack tip distance. On the basis of experimental observations, the criterion for crack coalescence and crack growth direction are expressed in terms of the crack positions defined by crack offset and crack tip distances. The criterion presented in this study can be used to determine the limiting value of crack tip and crack offset distance and to determine the mode in which cracks coalesce during their growth process. Experimental results and crack interaction criterion presented under various crack positions and size conditions could be used to derive a new evaluation method of crack growth in multiple crack geometry. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, a model using the energy approach was established to investigate the formation of fish-eye shape in the gigacycle fatigue failure. The model was used to predict the size of the fish-eye formed by a given subsurface inclusion. The predicted results were comparable with the fractography of SNCM439 steel and other experimental results of gigacycle fatigue available in the literature. The current model can capture the fish-eye shape and can be used to predict the life of crack initiation during fatigue failure. [ABSTRACT FROM AUTHOR]

ABSTRACT Sliding contact of a rigid rough surface with a semi-infinite medium including a horizontal subsurface crack was investigated by using linear elastic fracture mechanics and finite element method (FEM). The fractal geometry was used to characterize the rigid rough surface. The propagation of crack was studied with the shear and tensile stress intensity factors. The effect of surface roughness, crack length to depth ratio and friction at the contact and crack interfaces was investigated by using the FEM. It was shown that increasing friction coefficient at the contact interface increases both KII and KI. [ABSTRACT FROM AUTHOR]

Good predictions of the extent of crack growth during thermal shock can normally be obtained by calculating the crack driving force for a single crack while assuming that the cracking has no effect on the temperature distribution in the body. However, experiments have shown that sometimes cracks grow much deeper than predicted. To ascertain whether this might be due to cooling by water penetration into the cracks, the effect of cooling along the crack faces on the crack driving force is calculated and predictions for the extent of cracking are compared with experiments on soda-lime glass. It is confirmed that cooling along the crack faces causes self-driven crack propagation. The effect of cooling in the cracks is only important when the fracture energy is low compared with the severity of the thermal shock, consistent with the observation that excessive cracking tends to be observed only in materials with low fracture energies. [ABSTRACT FROM AUTHOR]

The article presents a study that aims to examine the possibility of rectorite replacing kaolin for preparing fluid catalytic cracking (FCC) catalysts using in-situ synthesis technique. Rectorite is a natural aluminosilicate mineral that has physicochemical properties comparable to kaolin like its chemical composition, thermal behavior, and chemical reactivity. It was concluded that a suitably treated rectorite mineral can substitute kaolin for synthesizing FCC catalysts.

High-toughness, high-strength ceramics, such as self-reinforced Si3N4, derive their superior mechanical properties from microstructures that promote very steeply rising R curves. Furthermore, accurately evaluating the R curve at the earliest stages of crack growth is necessary for correctly understanding, and predicting, the mechanical behavior. Compliance- and optical-based methods for evaluating the crack length, and R curve, at the early stages of crack extension from machined notches are discussed. The earliest stages of crack growth are missed during measurements of the crack length by optical observations due to the nonuniform extension of the crack front during initial crack extension. The most accurate method of evaluating the crack length over all amounts of crack extension is from compliance measurements analyzed by solving a system of equations that incorporates both the effects of the notch and the changes in compliance with the development of bridging tractions. Such a method is computationally expensive, but for materials with steeply rising R curves, simply applying the linear-elastic compliance evaluation, which only accounts for the notch, but not the bridging tractions, gives a result within about 1%. At longer crack extensions, such an approximation method will incur significant errors; however, at this stage, optical measurements can provide accurate assessments of crack length and enable an accurate assessment of the R curve. [ABSTRACT FROM AUTHOR]

Bipolar fatigue of ferroelectric lead zirconate titanate ceramics can be partly recovered by thermal annealing. For samples of initially, intermediately, or highly fatigued state, subsequent refatiguing yields a much more rapid decay in polarization and piezoelectric constant than the initially nonfatigued samples despite very similar recovery from annealing. The “material memory” of the prior fatigue treatment is discussed in the framework of microcracking and fixed polarization by crack face charges. [ABSTRACT FROM AUTHOR]

The camber of asymmetric laminates has been experimentally measured and predicted. Two cases are distinguished: (i) sintering of a viscous layer on a viscous substrate and (ii) sintering of a viscous layer on an elastic substrate. In the first case, particular attention is paid to the microstructure of the shrinking layer: a gradient in porosity as well as in pore size has been found along the thickness. Microstructural observations have been rationalized through an asymmetric stress state in the shrinking layer. In the second case, substrate cracking is predicted as function of Young's modulus and thickness ratio of the elastic substrate. [ABSTRACT FROM AUTHOR]

The article focuses on a study which proposed a multi-scale model to simulate the heat transfer, mass transfer, momentum transfer, fluid flow with reactions together at different spatiotemporal scales of riser reactor for secondary reactions of fluid catalytic cracking gasoline (SRFCCG) process. Particular focus is given to SRFCCG subsystems. According to the study, results obtained from simulation were similar with the experimental ones. Included are charts showing radial voidage distribution in riser reactor and the distribution of slip velocity.

The article presents a study of the impacts of melt cooling rate on the environmental stress cracking resistance (ESCR) of high-density polyethylene (HPDE) using differential scanning calorimetry (DSC), Raman spectroscopy, and microhardness. It demonstrates the association of ESCR and crystal thickening. It says that the proposed model by Sharif and colleagues based on the analogy of crack growth across the amorphous phase of semicrystalline polymers predicts the time to failure.

To extend the predictive capability of existing crack growth models for fibre metal laminates under constant amplitude fatigue loading to variable-amplitude loading, further research on variable-amplitude fatigue mechanisms in fibre metal laminates is necessary. In response to this need, an experimental study into the effects of multiple overloads, underloads and various block-loading sequences on crack growth in the fibre metal laminate Glare was investigated. Crack growth retardation effects were observed in the tests; however, the magnitude of these effects was lower than seen in monolithic aluminium because of fibre bridging. As a result, predictions of the observed behaviour were attempted using an existing constant-amplitude fatigue crack growth model for Glare in combination with a linear damage accumulation law. [ABSTRACT FROM AUTHOR]