Liquid‐phase axial dispersion of turbulent gas–liquid co‐current flow through screen‐type static mixers

This article discusses the characteristics of turbulent gas–liquid flow through tubular reactors/contactors equipped with screen‐type static mixers from a macromixing perspective. The effect of changing the reactor configuration, and the operating conditions, were investigated by using four different screen geometries of varying mesh numbers. Residence time distribution experiments were conducted in the turbulent regime (4500 < Re < 29,000). Using a deconvolution technique, the RTD function was extracted to quantify the axial/longitudinal liquid‐phase dispersion coefficient. The findings highlight that axial dispersion increases with an increasing flow rate and/or gas‐phase volume fraction. However, regardless of the number and geometry of the mixing elements, reactor configuration, and/or operating conditions, the recorded liquid‐phase axial dispersion coefficients in the presence of screens was lower than that for an empty pipe. Furthermore, the geometry of the screen was found to directly affect the axial dispersion coefficient in the reactor. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1390–1403, 2017     

A Laboratory Reactor for Gas‐Phase Olefin Polymerization

A new reactor system for gas‐phase ethylene/α‐olefin polymerization is described. Good gas‐phase temperature control at high polymerization rates was achieved with the 2‐L semi‐batch reactor. Ethylene/1‐hexene and ethylene polymerization results showing the effects of operating conditions on temperature profiles are presented. Good gas‐phase temperature control is required to obtain reliable activity profiles. A gas‐sampling and analysis system, which allows relatively rapid (< 3 min) and accurate determination of ethylene/1‐hexene contents in the gas‐phase of the reactor, is also described. Rapid and reliable hydrogen contents were also measured with this relatively inexpensive system.     

New two‐phase and three‐phase Rachford‐Rice algorithms based on free‐water assumption

Based on the free‐water assumption that the water‐rich liquid phase contains only pure water, we develop two simple free‐water Rachford‐Rice methods: 1) a two‐phase free‐water Rachford‐Rice method where the phase fractions can be analytically solved; and 2) a three‐phase free‐water Rachford‐Rice method where there is only one unknown in the objective function (i.e. the vapour‐phase fraction) that is used for solving the phase fractions. Combining these two Rachford‐Rice methods, a new free‐water flash algorithm is developed to perform multiphase flash calculations where single‐phase equilibria, two‐phase equilibria, and three‐phase vapour‐liquid‐aqueous equilibria can be considered. In this free‐water flash algorithm, we first test if the mixture is stable; if the mixture is found to be unstable, we directly initiate the three‐phase free‐water flash. A set of criteria is developed for one to properly switch from a three‐phase free‐water flash to either a two‐phase free‐water flash or a conventional two‐phase flash, depending on whether a water‐rich phase is present in the two‐phase equilibrium. We also develop efficient and robust methods for initializing the equilibrium ratios for the two‐phase flashes. The negative flash is allowed in the flash calculation algorithms. A number of example calculations are carried out to demonstrate the robustness of the newly developed algorithm. A good agreement can be achieved between the flash results obtained by the new flash algorithm and those obtained by the conventional full three‐phase flash algorithm.     

Accurate determination of hexanal in beef bouillons by headspace solid‐phase microextraction gas‐chromatography mass‐spectrometry

Lipid oxidation has great impact on the quality of food products through flavor and taste deterioration, reduction in nutritive value, and potential toxicity of the oxidized food components. Flavor and taste deterioration can be easily perceived and it represents one of the major causes of consumer complaints in the food industry. The deterioration of sensory properties is due to the decomposition products of hydroperoxides that easily isomerize and degrade into volatile compounds. Volatile products are responsible for flavor and taste deterioration. In this study, we present the development of the solid‐phase microextraction gas chromatography‐mass spectrometry (SPME‐GC‐MS) technique to quantify low amounts (μg/g range) of secondary oxidation products, i.e. hexanal. The optimization of SPME parameters is a difficult task because of the possibility of further formation of volatile products during analysis. Different parameters such as type of fiber, exposure time of the fiber to the sample headspace and the optimal temperature of absorption have also been investigated. The complete validation of the method was achieved by the determination of linearity, limits of detection and quantification and repeatability. We demonstrated that the SPME method is a valuable tool for the quantification of low amounts of secondary oxidation products such as hexanal. Therefore, this technique can be used to detect early formation of volatiles.     

Polymerization‐induced bimodal phase separation in a rubber‐modified epoxy system

The bimodal phase separation process of a rubber‐modified epoxy system, consisting of diglycidyl ether of bisphenol A (DGEBA), and a hydroxyl‐terminated butadiene–acrylonitrile random copolymer (HTBN), during curing with tetrahydro‐phthalic anhydride was studied by time‐resolved small‐angle light scattering (TRSALS), differential scanning calorimetry (DSC), and digital image analysis (DIA). The HTBN/DGEBA mixture reveals an upper critical solution temperature (UCST). At higher curing temperatures, double‐peak structure from the matrix was investigated by TRSALS and confirmed by DIA. The special two characteristic size distribution behavior was explained qualitatively by nucleation growth coupled with spinodal decomposition (NGCSD) and the competition between phase separation and polymerization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 59–67, 1999     

Liquid/solid two‐phase carbonization of low‐molecular‐weight chloro‐/bromo‐hydrocarbons

A novel liquid/solid two‐phase reaction has been discovered that enables destruction of a series of low‐molecular‐weight chloro‐/bromo‐hydrocarbons to carbon‐based materials. The solid phase is anhydrous potassium hydroxide and the liquid phase is a benzene or tetrahydrofuran solution of halide and contains a certain amount of tetrabutyl ammonium bromide (TBAB) as phase transfer catalyst. The structure of the carbon‐based materials have been characterized by elemental analysis, Fourier transform infrared (FT‐IR), FT‐Raman, and X‐ray photoelectron spectroscopies, and their morphologies have been examined by wide‐angle X‐ray diffraction and transmission electron microscopy. The results indicate that the products are amorphous nanoparticles and contain mainly elemental carbon. They consist of sp, sp², and sp³ carbon atoms simultaneously and can be regarded as carbyne analogues. This work provides a convenient method for synthesizing new carbon‐based materials in relatively high yields. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1510–1515, 2000     

Photografting of unable‐to‐be‐irradiated surfaces. I. Batch vapor‐phase process by one‐step method

Surfaces unable‐to‐be‐irradiated are those that could not be directly exposed to UV irradiation because of their irregular structure or instability under UV irradiation. It is difficult to conduct surface photografting on these kinds of surfaces with conventional photografting methods. Here, a novel one‐step surface photografting method is introduced, by which some monomers were smoothly grafted on the surface of polymer substrates located in a region out of the reach of UV radiation. The mechanism is that the photochemical reaction is separated into three events, absorbing UV light in one place, then transporting light energy to another place, and reacting there; in other words, the conventional photochemical reaction is separated by space and time, and the key point is that the substrate does not need to be exposed to UV irradiation. The occurrence of grafting polymerization was proved by UV–vis, ATR‐IR, SEM, XPS, and water contact angle measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2269–2276, 2006     

Between‐phase‐based statistical analysis and modeling for transition monitoring in multiphase batch processes

Between‐phase transition analysis and monitoring are a critical problem in multiphase (MP) batch processes. An improved statistical analysis, modeling, and monitoring strategy are proposed for MP processes with between‐phase transition. It is realized that between‐phase transition may show complex “irregular dynamics” over different batches. That is, transition patterns may follow different trajectories with different durations and reveal different characteristics in different batch cycles. Phase centers are defined to capture the transition irregularity, and the relationship between two neighboring phase centers is analyzed by performing between‐phase analysis. Two different subspaces are thus separated in each phase, driven by the phase‐common and dependent correlations, respectively. The basic assumption is that despite their different operation patterns, the two neighboring phases share a certain common correlations immune to phase shift. Then, reconstruction‐based transition identification algorithm is designed, by which, between‐phase transition can be supervised automatically and dynamically without the need of transition model development. The proposed method captures the between‐phase transition from a new viewpoint. Its feasibility and performance are illustrated with a practical case. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Influence of ethyl methacrylate content on the volume‐phase transition of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] microgels

A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry     

Phase behavior of side‐chain liquid‐crystalline elastomers and their precursors containing para‐nitro azobenzene

Side‐chain liquid‐crystalline copolymethacrylates (PMm's), containing para‐nitro azobenzene as the mesogenic group and 2‐hydroxylethyl methacrylate (HEMA) as a comonomer, were synthesized by radical polymerization, and their corresponding liquid‐crystalline elastomers (LCEm's) were prepared through chemical crosslinking. All of the polymers (PMm's) and the elastomers studied showed enantiotropic smectic A phases; the clearing temperature (T_i) of the PMm polymers decreased with increasing amount of HEMA, and the T_i of the corresponding LCEm's decreased compared to that of their precursors. Small‐angle X‐ray scattering studies on the copolymers quenched from their liquid‐crystalline phases indicated that the characteristic distance increased with increasing amorphous component content and thus, the amorphous components were in between the smectic layers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2275–2279, 2003     

Temperature‐insensitive piezoelectricity in lead‐free NaNbO3‐based ceramics

In this work, we report a lead‐free piezoelectric ceramic of (0.9‐x)NaNbO₃‐0.1BaTiO₃‐xBaZrO₃, and the effects of BaZrO₃ on the phase structure, microstructure, electrical properties and temperature stability are investigated. A morphotropic phase boundary‐like region consisting of rhombohedral (R) and tetragonal (T) phases is constructed in the compositions with x = 0.035‐0.04. More importantly, in situ temperature independence of the piezoelectric effect {piezoelectric constant (d₃₃) and strain} can be achieved below the Curie temperature (T_c). Intriguingly, the electric field‐induced strain is still observed at T ≥ T_c due to the combined actions of the electrostrictive effect and the electric field‐induced phase transition. We believe that NaNbO₃‐based ceramics of this type have potential for applications in actuators and sensors.     

Multi‐rate observer design for process monitoring using asynchronous inter‐sample output predictions

In this article, the problem of observer design in linear multi‐output systems with asynchronous sampling is addressed. The proposed multi‐rate observer is based on a continuous‐time Luenberger observer design coupled with an inter‐sample predictor for each sampled measurement, which generates an estimate of the output in between consecutive measurements. The sampling times are not necessarily uniformly spaced, but there exists a maximum sampling period among all the sensors. Sufficient and explicit conditions are derived to guarantee exponential stability of the multi‐rate observer. The proposed framework of multi‐rate observer design is examined through a mathematical example and a gas‐phase polyethylene reactor. In the latter case, the amount of active catalyst sites is estimated, with a convergence rate that is comparable to the case of continuous measurements. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3384–3394, 2017     

Spray Characteristics of Two‐phase Feed Nozzles

The present study focuses on understanding the spray characteristics of a turbulent gas‐liquid jet (Re_liq = 24,000). Air and water are used as the test fluids. The angles of injection of the two phases upstream of the nozzle are varied (θ = 20°, 45° and 90°) and the effect of carrier gas on the droplet characteristics is are also investigated. The droplet size and velocity are non‐intrusively measured using a Phase‐Doppler Particle Analyzer (PDPA). In some respects, the characteristics of the present two‐phase jet are similar to those noticed in previous studies, while revealing some important differences. The centreline mean droplet velocities (15 ～ 20 m/s) increase in the initial region of the jet, attain a maximum and then decrease at larger distances from the nozzle exit. Most of the entrainment occurs at the tip of the nozzle and the jet expansion rate decreases significantly at distances where the spray velocity profiles become self‐similar. A Lorentz‐type fit has been used to model the normalized radial velocity profiles. The results indicate that the test configuration with θ = 45° may be beneficial for the scenario discussed.     

Effects of B‐site doped elements in the electronic‐conducting perovskite phase on the property of dual‐phase membranes

A series of dense oxygen permeable dual‐phase membranes with a composition of 60 wt% Ce_0.8Gd_0.2O_2?δ‐40 wt% Ba_0.95La_0.05Fe_0.9M_0.10O_3?δ (CGO‐ BLFM_0.10, M=Fe, Nb, Zr, Zn, Sc, Y) were successfully synthesized and evaluated as potential ceramic membranes for oxy‐fuel combustion. The effects of B‐site doped elements in electronic‐conducting phase (BLFM_0.10) on the crystal structure, microstructure, chemical compatibility, oxygen permeability, as well as chemical stability of CGO‐BLFM_0.10 were systematically investigated. All electronic‐conducting phase BLFM_0.10 oxides exhibited a pure cubic perovskite structure and showed good chemical compatibility with ionic‐conducting phase CGO. CGO‐BLFSc_0.10 showed the best oxygen permeation stability under a pure CO₂ atmosphere. CO₂‐corrosion on the perovskite phase is the main reason for the property deterioration of fluorite‐perovskite‐typed dual‐phase membrane materials. The stability of dual‐phase membrane materials can be effectively enhanced by reducing the basicity of electronic‐conducting phase of perovskite materials.     

Profiles of volatile compounds in milk containing fish oil analyzed by HS‐SPME‐GC/MS

Long‐chain polyunsaturated fatty acids (LC‐PUFA) have various positive biological effects. Fish oil represents a major source of LC‐PUFA; therefore it is extensively used to enrich food products as, for example, infant formulae, dairy products and fruit juices. However, in the presence of oxygen and metals, LC‐PUFA readily degrade, producing off‐flavors and decreasing the nutritional value of the product. The deterioration of sensory properties (taste and odor) can be easily perceived by the consumer, due to the formation of volatile compounds that are formed by decomposition of lipid hydroperoxides, also known as primary oxidation products. In this study, we used the headspace solid‐phase microextraction‐gas chromatography/mass spectrometry technique (HS‐SPME‐GC/MS) to characterize and quantify volatile compounds in a food matrix supplemented with fish oil. We demonstrated that the HS‐SPME‐GC/MS method is a valuable tool to monitor lipid oxidation at early stages. We identified t‐2‐hexenal and c‐4‐heptenal as possible oxidation markers during the storage of milk enriched with 5% of cod oil.     

Multistage rotor‐stator spinning disc reactor

The scale up of a rotor‐stator spinning disc reactor by stacking single stage rotor‐stator units in series is demonstrated. The gas‐liquid mass transfer per stage is equal to the mass transfer in a single stage spinning disc reactor. The pressure drop per stage increases with increasing rotational disc speed and liquid flow rate. The pressure drop is more than a factor 2 higher for gas‐liquid flow than for liquid flow only, and is up to 0.64 bar at 459 rad s^?1. The high mass and heat transfer coefficients in the (multistage) rotor‐stator spinning disc reactor make it especially suitable for reactions with dangerous reactants, highly exothermic reactions and reactions where selectivity issues can be solved by high mass transfer rates. Additionally, the multistage rotor‐stator spinning disc reactor mimics plug flow behavior, which is beneficial for most processes. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Extended glass‐forming region in the AgCl‐Ag2S‐As2S3 ternary system

In the present work, glass formation property of the AgCl‐Ag₂S‐As₂S₃ ternary system is investigated. An extended glass‐forming region rich in the AgCl content (up to 80 mol.%) is observed. It is also found that there exists a small devitrification domain dividing the whole glass‐forming region into two parts. XRD analyses confirm that the precipitated crystals in the crystallized samples are pure AgCl, or Xanthoconite and Proustite Ag₃AsS₃, depending on the Ag₂S/As₂S₃ ratio and the AgCl content. Structural evolutions of the selected samples 15AgCl‐yAg₂S‐zAs₂S₃ are examined by high‐resolution XPS, and Raman spectroscopy. The crystallization mechanisms are studied comprehensively by SEM, DSC, and XRD measurements, and tentatively assigned to the presence of phase separation. The results reported in this article are expected to serve as a guide for the selection of suitable electrode materials for electrochemical applications.     

An improved algorithm for the three‐fluid‐phase VLLE flash calculation

The VLLE flash is important in water and hydrocarbons mixtures, hydrocarbon and CO₂ rich mixtures, and hydrocarbon methane rich mixtures that are encountered in reservoir performance and recovery studies. A robust VLLE flash algorithm is proposed. The equilibrium and mass balance equations are solved as a constrained minimization problem. An inverse barrier function is used to handle the inequality constrains to solve for the phase fractions. It warrants always arriving to the solution. The challenging cases analyzed showed that the initialization procedure proposed, together with successive substitution iteration in the outer loop, is a good method for a stable VLLE flash algorithm, even near critical points. Whenever the result is in the region outside the three‐phase physical domain, the solution suggests that the system has fewer phases. In one of the cases analyzed, a region with three liquid phases was encountered and the algorithm found two different solutions with positive phase fractions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3081–3093, 2015