Growth kinetics of hydrate formation from water–hydrocarbon system

Gas hydrates have drawn global attentions in the past decades as potential energy resources. It should be noted that there are a variety of possible applications of hydrate-based technologies, including natural gas storage, gas transportation, separation of gas mixture, and seawater desalination. These applications have been critically challenged by insufficient understanding of hydrate formation kinetics. In this work, the literatures on growth kinetic behaviors of hydrate formation from water-hydrocarbon were systematically reviewed. The hydrate crystal growth, hydrate film growth and macroscopic hydrate formation in water system were reviewed, respectively. Firstly, the hydrate crystal growth was analyzed with respect to different positions, such as gas/liquid interface, liquid–liquid interface and gas–liquid–liquid system. Secondly, experimental and modeling studies on the growth of hydrate film at the interfaces between guest phase and water phase were categorized into two groups of lateral growth and thickening growth considering the differences in growth rates. Thirdly, we summarized the promoters and inhibitors reported (biological or chemical, liquid or solid and hydrophobic or hydrophilic) and analyzed the mechanisms affecting hydrate formation in bulk water system. Knowledge gaps and suggestions for further studies on hydrate formation kinetic behaviors are presented.     

Dissolution kinetics of aluminum and iron from coal mining waste by hydrochloric acid☆

The extraction of aluminum from coal mining waste (CMW) is an important industrial process. The two major problems in applications are low aluminum dissolution efficiency and high iron content in the r...     

Computation of maximum rate of water–sulphuric acid nucleation in diesel exhaust

The origin of nucleation mode observed in the diesel engine exhaust is unclear. In this work, the mechanism of simple classical homogeneous water–sulphuric acid nucleation was studied using the parameterization of Vehkamäki, Kulmala, Lehtinen, and Noppel [2003. Modelling binary homogeneous nucleation of water–sulfuric acid vapours: Parameterisation for high temperature emissions. Environmental Science and Technology, 37, 3392–3398]. In the simple model used, condensation and coagulation were taken into account as sink terms in respective equations. The focus of the study was on the total amount of stable clusters formed, which provides an upper limit for nucleation mode number concentration. It was seen that the nucleation can be achieved even with relatively low sulphuric acid concentrations (of the order of $5\times {10}^{17}{\mathrm{m}}^{-3}$). However, the efficiency depends strongly on the cooling and dilution experienced by the exhaust. According to the results obtained, the assumption of homogeneous sulphuric acid–water nucleation depicted by Vehkamäki parameterization gives physically meaningful results with low-sulphur content fuels if the sulphur-to-sulphuric acid conversion factor is close to 100%. Nonetheless, there are published results of nucleation mode in diesel exhaust which cannot be explained by the sulphuric acid–water mechanism.     

Performance improving with temperature in liquid–liquid extraction using cumene–isobutyric acid–water chemical system

The performance of single drops was investigated in liquid–liquid extraction while temperature was changed within the range of 15–40 °C. The recommended system of cumene–isobutyric acid–water with mass transfer resistance mainly in aqueous phase was used. An average enhancement of 75.6% in the rate of transfer was revealed. The extraction efficiency is the most influencing term due to molecular diffusivity enhancement. For modeling, a simple correlation was proposed for the effective diffusivity in Newman's equation, while continuous phase mass transfer coefficient was directly included. Using this model, relative deviation of the overall mass transfer coefficient was within only ±5.6%.     

Anodization of n and p-GaAs in ethylene glycol–water–tartaric acid mixture

This paper describes the pulsed constant current anodization of n+ and p+-GaAs in ethylene glycol–water–tartaric acid (AGW) mixture, up to 17mAcm–2. A 0.26m thick film is obtained for a final voltage of 135V at 4.3mAcm–2 pulsed current density. Cyclic voltammetry showed that the initial growth of a monolayer anodic oxide can be described by a charge transfer with uncompensated cell resistance model. The relationship between peak current, peak voltage and scan rate has been verified for this process, based on the above model.     

Analysis of Fe(Ⅵ) characteristics and its application to water treatment

Ferrate（Fe(Ⅵ)）is a new type of water treatment chemicals. From the point of view of structural chemistry,electrochemistry,thermal decomposition characteristics and stability,the physical and chemical characteristics of Fe(Ⅵ) were analyzed,and the preparation of ferrate was described. Its application to water treatment was summarized,such as pre-oxidation by ferrate,and the specific applications were outlined. The results showed that 1.0 mg / L ferrate pre-oxidation could significantly improve the effect on coagulation,Water after sedimentation and filtration turbidity removal rate reached 98.58% and 99.9% respectively. Water colority,UV₂₅₄ and other organic composite indicator were significantly decreased. At the same time,manganese and iron were also significantly reduced. In addition,ferrate pre-oxidation could effectively remove bacteria and E.coli. Finally,according to the practical situation,the paper offers advice on engineering application of ferrate.     

Synthesis and characterization of new Mg–O–F system and its application as catalytic support

The Mg–O–F system (MgF₂–MgO) with different contents of MgF₂ (100–0%) and MgO is tested as support of iridium catalysts in the hydrogenation of toluene as a function of the MgF₂/MgO ratio. Mg–O–F samples have been prepared by the reaction of magnesium carbonate with hydrofluoric acid. The MgF₂–MgO supports, after calcination at 500 °C, are classified as mesoporous of surface area (34–135 m²·g^− 1) depending on the amount of MgO introduced. The Ir/Mg–O–F catalysts have been tested in the hydrogenation of toluene. The highest activity, expressed as TOF, min^− 1, was obtained for the catalyst supported on Mg–O–F containing 75 mol%MgF₂.     

Fabrication,swelling behavior,and water absorption kinetics of genipin-crosslinked gelatin–chitosan hydrogels

Gelatin/chitosan hydrogels have attracted considerable attention over the last 2 decades in various fields of applications. In this paper, chemically crosslinked composite hydrogels with different gelatin-to-chitosan weight ratios were fabricated and crosslinked with different amounts of genipin via the solvent casting technique combined with freeze-drying. Fourier-transform infrared, scanning electron microscopy (SEM), liquid displacement method, and gravimetric analysis were used to examine the chemical, microstructural, and physical properties of the hydrogels. IR spectra confirmed the formation of covalent bonds between the amino groups of the parent's macromolecules and genipin. SEM micrographs indicated that the hydrogels possessed a highly porous structure with well-defined pore geometries. The swelling capacity and degradation rate of the specimens reduced with increasing the amounts of chitosan and/or genipin. In-depth swelling measurements revealed that the first-order kinetic model was only applicable in the early stage of the swelling study; however, the water absorption behavior of the hydrogels was best described by the pseudo-second-order kinetic model (Schott's model) throughout the swelling experiment. The genipin-crosslinked hydrogels were found to support MC3T3-E1 cell proliferation. The results of this paper thus suggest the 1.5% genipin-crosslinked gelatin/chitosan hydrogels as promising candidates for on-demand drug delivery applications or more precisely osteoarthritis drug delivery systems.     

Thermodynamics and crystallization kinetics of REEs in CaO–SiO2–Ce2O3 system

Rare earth elements (REEs) have become increasingly important as ceramic materials. The RE-bearing slags contain massive REEs resources, whereas the lack of thermodynamic and kinetic data of REEs has brought great difficulties to efficient recovery of REEs from RE-bearing slags and the application in ceramics. According to the compositions of the RE-bearing slags in industrial production, the isothermal phase equilibria of CaO–SiO₂–Ce₂O₃ system at 1500°C and 1300°C were constructed by means of liquid-quenching method combined with a series of analyses, which provides the thermodynamic data for the equilibria of REEs. On this basis, the crystallization behaviors of the RE phase (Ce_9.33−xCa_x(SiO₄)₆O_2−0.5x) was investigated, and the temperature range in which the RE phase crystallized singly in RE-bearing slags with a selected compositions was acquired. CCT and TTT diagrams for CaO–SiO₂–Ce₂O₃ system were established to characterize the crystallization kinetics of the RE phase, and the favorable conditions for its crystallization and growth in RE-bearing slags were determined. In this study, the complete thermodynamic and kinetic basic data of REEs in CaO–SiO₂–Ce₂O₃ system are provided for RE-bearing slags.     

Encapsulation of BSA in polylactic acid–hyperbranched polyglycerol conjugate nanoparticles: preparation, characterization, and release kinetics

Nanoparticles based on an amphiphilic copolymer with polylactic acid (PLA) grafted onto hyperbranched polyglycerol (HPG) were prepared by the use of BSA as a model protein. The characteristics of the nanoparticles were evaluated using particle size analyzer, transmission electron microscopy, and X-ray photoelectron spectroscopy. The secondary structure of BSA released from nanoparticles were analysed by circular dichroism experiments. Cell viability of nanoparticles was also evaluated by using NIH 3T3 cells. The mechanism of BSA release was studied by fitting experimental data to three model equations. Results indicated that BSA diffusion and the polymeric relaxation jointly governed the overall release process. The detailed analysis of BSA release was performed using the first-order kinetic model equation, which gave a good fit to the experimental release data. The influence of different copolymer structures and BSA loading capacities on release profiles were also evaluated for the potential of using nanoparticles as controlled release protein delivery systems.     

Study air–water system in horizontal loop geometry

To enhance the understanding of hydrodynamic of air–water multi-phase flow inside a toroidal geometry, experiments were carried out in horizontal torus reactor. Compared with vertical flow, the flow in horizontal milli torus reactor was characterized by one additional flow pattern. In vertical position two flow regimes are considered: not-dispersed and dispersed flow while in horizontal position three flow regimes have been distinguished: stratified flow, dispersed flow and mixed flow regimes. The mixing time is measured by a conductimetric method as described by (Benkhelifa et al., 2000). The effect of both superficial gas velocities and impeller rotation speeds has been studied. The mixing time has been decreased by increasing both the superficial gas velocity and the impeller rotation speed and has been shorter than the one given for the horizontal configuration. The axial dispersion inside the reactor was modelled by the Zhang's model. The obtained results are in a good agreement with Zhang's model.     

Investigation of the curing kinetics of alkyd–melamine–epoxy resin system

Properties of coatings based on alkyd resin can be improved via blending with other suitable resins. Recent studies assessed that many properties could be improved by blending with epoxy resins as well as with melamine resins. The aim of this work was to investigate the effect of epoxy resin content on the curing process in alkyd–melamine–epoxy three component blends. The coatings with two mixing ratios of alkyd/melamine (70:30 and 80:20) were formulated. They were made into baking enamels by blending with 3 and 5 wt% of epoxy resin on total resin solid. Curring kinetics was investigated by differential scanning calorimetry (DSC) and application of Ozawa isoconversional method. Fourier transform infrared spectroscopy (FTIR) was used to follow major curing reactions. The absorbance of –OH and –N–CH₂R, showed significant reduction and confirmed that the epoxy resin reacts and inserts in enamel structure. It was found that resin system with alkyd/melamine ratio of 70:30 and 3 wt% of epoxy resin has the lowest apparent activation energy of 141.5 kJ mol⁻¹ and needs the shortest time of 34.2 min to reach final apparent degree of cure. Isothermal DSC experiments have confirmed these findings. The samples with 30 wt% of melamine resin had higher hardness of baked enamels then samples with 20 wt%. They also showed an increase of hardness with the increase of epoxy resin content.     

Acriflavine–cobaloxime–triethanolamine homogeneous photocatalytic system for water splitting and the multiple effects of cobaloxime and triethanolamine

Acriflavine dye, with a long-lived triplet excited state, has a strong sensitizing ability for photodriven water splitting when [Co^III(dmgH)₂(py)Cl] complex is used as a catalyst and triethanolamine as electron donor. This catalytic system is an example of a noble-metal-free homogeneous system for hydrogen generation from water. Moreover, the mechanistic details of the overall reaction pathway, as well as Acriflavine fading, is presented to offer significant guidance to developing more robust photocatalytic systems.     

Study on optimal conditions and adsorption kinetics of copper from water by collodion membrane cross-linked poly-γ-glutamic acid

Poly-γ-glutamic acid (γ-PGA) is a novel polyamino acid formed through microorganism fermentation and biosynthesis. In the present test, membrane (PGA-C) formation by γ-PGA and collodion was performed by using 0.1% glutaraldehyde as a cross-linking agent. A study was conducted on the PGA-C adsorption of Cu²⁺, specifically the related adsorption equilibrium and kinetics, desorption and regeneration. The results show that with an initial solution pH=5.5 and at 318 K, the static adsorption isotherm behavior of PGA-C is in compliance with the Langmuir model and is beneficial to the adsorption of the metal. Meanwhile, with the reaction lasting for 30min, adsorption equilibrium was reached with a maximum adsorption capacity up to 7.431 mg/g. The entire reaction process follows the pseudo-second-order kinetics. By using PGA-C, good regeneration results were obtained after adsorption-generation-adsorption cycling with an HCl solution (0.1 mol/L) as regeneration liquid.     

Graphene oxide–TiO2 composite filtration membranes and their potential application for water purification

Graphene oxide-particle composite films with filtration function have been successfully synthesized by a two-step method. First, graphene oxide–TiO₂ composite sheets are prepared, which can form stable dispersion in water. Then, by assembling these composite sheets, graphene oxide–TiO₂ films are obtained. In these as-prepared films, dilated space and channels are desirably formed by introducing nanoparticles between these carbon sheets, making them promising separation membranes. We used these films as filtration membranes to remove dye molecules (methyl orange and rhodamine B) from water. The results show that apart from the adsorption capacities of these dyes, these graphene oxide–TiO₂ films can also capture additional amount of dye molecules, indicating their potential applications in water purification areas.     

Phase equilibria in the calcium nitrate–water–isopropyl alcohol system

Results of an investigation of the solubility of the components of the water–isopropyl alcohol system in the temperature range of 253–268 K are given. Using fractional fusion, the concentrations of twocomponent water–isopropyl alcohol system have been determined, where fusion occurs more homogeneously. Phase diagrams of the calcium nitrate–water–isopropyl alcohol systems have been plotted at temperatures of 253, 263, and 268 K. The working area where compositions can be chosen for preparing the process liquid with a low freezing point has been determined.     

Mechanistic modelling of kinetics and mass transfer for a solid–liquid system: Leaching of zinc with ferric iron

A systematic approach was developed to consider liquid–solid reactions with rough solid particles and shrinking particle model. The model is able to predict the reactivities of both non-porous and porous solid particles; the reaction order with respect to the solid material varies from zero (non-porous slab) to one (porous particle).As a model system, leaching of zinc sulphide (sphalerite) with ferric iron in an acidic environment was considered. The modelling was based on experimental data obtained in a batch reactor system, for which both conventional mixing and ultrasound was applied. Rival models based on plausible reaction mechanisms were derived and discriminated qualitatively and with regression analysis. The best model described the leaching reaction as a stepwise process, where ferric ions react with solid zinc sulphide in consecutive surface reaction steps. Shrinking particle model along with the surface roughness approach was used. The model predicts first order behaviour with respect to zinc sulphide, while the reaction order with respect to ferric iron varies from one to two as the reaction progresses. This is in accordance with experimental observations. The intrinsic kinetics, liquid–solid mass transfer and the effect of ultrasound were well described by the best kinetic model.     

New modelling approach to liquid–solid reaction kinetics: From ideal particles to real particles

Typical features of liquid–solid reactions were reviewed: reaction kinetics, mass transfer effects and particle morphology. It was concluded that classical liquid–solid models based on ideal, non-porous geometries (sphere, infinite cylinder, slab) cannot satisfactorily describe real reactive solid particles with various surface defects, such as cracks, craters and limited porosity. Typically a too low reaction order for the reactive solid is predicted by the classical models. The surface morphology can be revealed by electron microscopy, which gives inspiration to develop new mathematical models for reactive solids.