Effect of electrolyte solubility and column inclination on the performance of monoethylene glycol regeneration process

In this study, the solubilities of potassium-chloride (KCl) in aqueous monoethylene glycol (MEG) solution and the vapour pressure of aqueous MEG solution containing KCl were investigated. A thermodynamic model was modified based on the data obtained to predict the solubilities of KCl, which was then applied to optimize the MEG regeneration process that is widely used in offshore gas fields. The solubility of KCl in the aqueous MEG solution decreased with an increase in MEG concentration and a decrease in temperature. The presence of KCl in aqueous MEG solution decreased the vapour pressure, thus increasing the boiling temperature at the corresponding pressure. A thermodynamic model based on the electrolyte non-random two-liquid (NRTL) coupled with the Redlich–Kwong (RK) equation of state was employed by modifying the binary interaction parameters using the experimental data. The modified model predicted the solubilities of KCl and the vapour pressure of aqueous MEG solutions, which were in good agreement with the experimental data. Moreover, the distillation column in pilot-scale MEG regeneration was inclined to simulate the movement of the offshore platform, showing decreasing MEG concentration, possibly due to the distribution issues inside the column.     

An investigation on dissolution kinetics of single sodium carbonate particle with image analysis method

Dissolution kinetics of sodium carbonate is investigated with the image analysis method at the approach of single particle. The dissolution experiments are carried out in an aqueous solution under a series of controlled temper-ature and pH. The selected sodium carbonate particles are al spherical with the same mass and diameter. The dissolution process is quantified with the measurement of particle diameter from dissolution images. The concentration of dissolved sodium carbonate in solvent is calculated with the measured diameter of particle. Both surface reaction model and mass transport model are implemented to determine the dissolution mecha-nism and quantify the dissolution rate constant at each experimental condition. According to the fitting results with both two models, it is clarified that the dissolution process at the increasing temperature is controlled by the mass transport of dissolved sodium carbonate travelling from particle surface into solvent. The dissolution process at the increasing pH is control ed by the chemical reaction on particle surface. Furthermore, the dissolution rate constant for each single spherical sodium carbonate particle is quantified and the results show that the disso-lution rate constant of single spherical sodium carbonate increases significantly with the rising of temperature, but decreases with the increasing of pH conversely.     

Effect of carboxymethyl cellulose on dissolution kinetics of carboxymethyl cellulose-sodium carbonate two-component tablet

Sodium carbonate and carboxymethyl cellulose powders are compressed into two-component tablets with three mass ratios, 97%:3%, 95%:5% and 93%:7%. The dissolution tests for two-component tablets and reference pure sodium carbonate tablets are carried out at various temperatures. The dissolution process of each tablet is measured by electrical conductivity tracking method and the concentration of dissolved sodium carbonate is quantified with calibrated conductivity-concentration converting equation of sodium carbonate. The quantified dissolution data is fitted with both surface reaction model and diffusion layer model and the results clearly show that surface reaction model is suggested as the appropriate dissolution model for all measured tablets. Therefore, it is determined that carboxymethyl cellulose is a stable element to remain the dissolution mechanism of tablet unchanged. The dissolution rate constant quantified with surface reaction model presents that carboxymethyl cellulose-sodium carbonate two-component tablets obtain significant higher dissolution rate constant than pure sodium carbonate tablet and higher proportion of carboxymethyl cellulose leads to apparent higher dissolution rate constant. The results prove for the usage of carboxymethyl cellulose in most practical applications at a relative low-level, the effect of carboxymethyl cellulose is effective and positive for two-component tablet to enhance the dissolution process and improve dissolution rate constant and this effect is speculated coming from its dynamic physical transforming process in water including dilation and conglutination.     

Dissolution of a South African calcium based material using urea: An optimized process

The rate at which limestone dissolves is very important in wet flue gas desulfurization process (FGD). High dissolution rates provide better alkalinity, which is important for sulfur dioxide (SO₂) absorption. This study investigates the use of urea to improve the dissolution rate of limestone. The dissolution characteristics have been studied by using a pH-Stat method. The dissolution rate constant was measured according to the shrinking core model with surface control, i.e. (1−(1−X)^1/3)=k _r t. The effect of experimental variables such as temperature, amount of urea, solid to liquid ratio and stirring speed on the dissolution rate of limestone were investigated. Using a central composite design (CCD) of experiments variables, a mathematical model was developed to correlate the experimental variables to the dissolution rate constant. The experimental value was found to agree satisfactorily with predicted dissolution rate constant. The model shows that high temperature and low solid to liquid ratio improves the dissolution rate. The dissolution rate increased slightly with increase in the stirring speed. In the presence of urea the dissolution rate constant increased by 122%. The dissolution reaction follows a shrinking-core model with the chemical reaction control as the rate-controlling step.     

2种C1化工路线制乙二醇技术经济分析

介绍了以煤炭或天然气衍生的合成气为原料,一步法直接合成和经甲醛(或草酸酯)间接法合成乙二醇工艺的历史和进展,并对这2条被认为是有希望在不远的将来实现产业化的技术路线进行了工艺比较和经济性比较。认为CO经草酸酯合成乙二醇技术路线具有反应条件温和、设备投资小、环境友好等优点,并且其产品工厂成本低18.7%,是首选的C1化工合成乙二醇技术路线。     

Adsorption of methylene blue from aqueous solutions by modified expanded graphite powder

The modified expanded graphite (MEG) powder was used as a porous adsorbent for the removal of the cationic dye, methylene blue (MB), from aqueous solutions. The dye adsorption experiments were carried out with the bath procedure. Experimental results showed that the basic pH, increasing initial dye concentration and high temperature favored the adsorption. The dye adsorption equilibrium was attained rapidly after 5 min of contact time. Experimental data related to the adsorption of MB on the MEG under different conditions were applied to the pseudo-first-order equation, the pseudo-second-order equation and the intraparticle diffusion equation, and the rate constants of first-order adsorption (k₁), the rate constants of second-order adsorption (k₂) and intraparticle diffusion rate constants (k_int) were calculated, respectively. The experimental data fitted very well in the pseudo-second-order kinetic model. The thermodynamic parameters of activation such as Gibbs free energy, enthalpy, and entropy were also evaluated. The results indicated that the MEG powder could be employed as an efficient adsorbent for the removal of textile dyes from effluents.     

Modeling calcium dissolution from oil shale ash: Part 2.: Continuous washing of the ash layer

In the present work a possible approach to the utilization of oil shale ash containing free lime in precipitated calcium carbonate (PCC) production is elucidated. This paper investigates the Ca (calcium) dissolution process during continuous washing of pulverized firing (PF) and fluidized bed combustion (FBC) oil shale ash layers in a packed-bed leaching column. The main characteristics of the Ca dissolution process from ash are established. The effect of water flow rate is investigated by conducting leaching experiments of oil shale ashes formed in boilers operating with different combustion technologies. The values of the overall and liquid phase mass transfer coefficients are evaluated based on experiments using the developed ash layer washing model. The model is a set of partial differential equations that describe the changes in Ca content in the stagnant layer of ash and in the water flowing through the ash layer. An example in which the model is applied to environmental assessment and estimation of Ca leaching from industrial oil shale ash fields is provided.     

Stepwise dissolution of silica surface in alkaline solution revealed by molecular modeling

The atomic scale solid–liquid interfacial process dominates the macro-dissolution of silica, yet its direct experimental observation is challenging. Here we employed the reactive molecular dynamics to model this process in alkaline condition. An elevated temperature strategy under canonical ensemble (NVT) was applied to accelerate the process for sufficient sampling at temporal domain. A stepwise transformation from fully linked SiO₄ network (Q³ and Q⁴) to reduced linkage and eventually aqueous species (Q⁰) was revealed. The simulated dissolution rate agrees well with the value predicted by empirical model. By tracing hydrogen atoms, we found that the dehydroxylated silica surfaces in alkaline electrolyte solutions underwent a transition from Si–O–Si bond cleavage-dominated (mainly reacted with OH⁻) to hydroxylation-dominated surface reactions. The free-energy reconstruction of well-tempered metadynamics reveals that 1500 K accelerates dissolution without altering the reaction pathways. These findings offer novel insights into the evolution of atomic-scale surface configurations during the dissolution kinetics of silica.     

A Dissolution‐Diffusion Model and Quantitative Analysis of Drug Controlled Release from Biodegradable Polymer Microspheres

Controlled release behaviours of nifedipine loaded poly (D,L‐lactide) (PLA) and poly(D,L‐lactide‐co‐glycolide) (PLGA) microspheres are investigated and modelled in this paper. Based on the integrated consideration of diffusion, finite dissolution rate, moving front of dissolution and size distribution of microspheres, a mathematic model is presented to quantitatively describe the drug release kinetics. The coupled partial differential equations are numerically solved. Dynamic concentration profiles of both dissolved and undissolved drug in the microspheres are analyzed. In comparison with the diffusion model and Higuchi model, the proposed dissolution‐diffusion model is characteristic of describing the whole release process without limitation of different dissolution rate or dissolubility. The diffusion coefficient and the dissolution rate constants are evaluated from measured release profiles. The effects of microstructures of polymer microspheres on release behaviours are related to parameters of the model. Based on the mathematical model and in vitro release data, intrinsic mass transfer mechanism is further investigated.     

部分冷凝工艺制取CO模拟分析

随着化工产品深加工的需要,对一氧化碳纯度要求进一步提高（纯度达到98．5％）。所以提高一氧化碳产品纯度对企业节能降耗及增加经济效益等方面均有着至关重要的作用。本文利用Unisim化工流程模拟软件用部分冷凝方法模拟乙二醇工艺中的一氧化碳深冷分离单元。结果表明,用该方法制取的C可满足下游化工生产对CO产品纯度的要求,且装置提取率可达95％。另外,第一换热器表现比较稳定,第二换热器与CO液体节流压力及流量有较大关系。     

A phase-field model for the study of isothermal dissolution behavior of alumina particles into molten silicates

Particle dissolution process refers to the dissolving of one liquid or solid phase into another solvent phase. This process is of vital importance in the engineering material science, and chemical engineering, etc. Here, we develop a phase-field model with diffusion-controlled processes at interfaces for isothermal dissolution of alumina inclusion particles in molten silicates, referred as “slag,” with comprehensive compositions applied in process metallurgy. The interfacial energy between solid inclusion particle and molten silicate can vary with different temperatures and chemical compositions. This model is validated using experimental data of high-temperature confocal laser scanning microscopy (HT-CLSM) technique. Moreover, the developed model is applicable to predict the dissolution behavior of solid particle in a realistic size scale. The possibility of the model application is illustrated with studies of different physical parameters that affect particle dissolution behavior. The phase-field simulations show that inclusion morphology influences both the dissolution profile and time, and the influence decreases with the increased temperature. Increasing same amount of Al₂O₃ component in slag, the increased degrees of the alumina dissolution time in silicates with different V-ratio values, a ratio between the mass percent of CaO and that of SiO₂, are almost the same. If the V-ratio of slag is relatively small, an increased MgO component in the silicate will significantly decrease the particle dissolution time. On the contrary, the change in MgO component in the silicate will have a minor effect if the value of V-ratio is quite large. In order to rapidly dissolve the inclusion, basicity index (BI) of molten silicate should be larger than 1.4. A balance between BI and MgO component in slag is suggested to be considered to design or optimize molten silicate (slag) for its application in the refining process of steel manufacturing.     

An overview of mono-ethylene glycol synthesis via CO coupling reaction: Catalysts,kinetics, and reaction pathways

Monoethylene glycol (MEG) is a promising chemical and a useful feedstock for the synthesis of several industrial products. The current commercial process of MEG production utilizes petroleum feedstock (ethylene) and an expensive catalyst, and the yield is low. Syngas is an attractive alternate feedstock for MEG. Syngas to MEG proceeds in two steps: the self-closing, green step of carbonylation of alkyl nitrile to produce dialkyl oxalate, and further hydrogenation of oxalate to MEG. Many reviews which focused on catalyst development, reaction mechanisms, and process variables were published earlier. The present work covers the developments in the syngas-to-MEG synthesis process after 2014. It overviews the performance of novel catalyst systems reported in literature. A discussion on reaction pathways and kinetic models is also presented. This work will provide useful insight into syngas-to-MEG conversion.     

Solid dissolution in a batch process with intraparticle diffusion and lumped kinetics

In this paper, a general unsteady-state model of particle dissolution is applied to a case of ore leaching in a batch process. The model equations are solved numerically with an implicit finite-difference method which is second-order approximate in space and time. It is shown how a non-constant concentration of liquid leachants outside the pore may highly condition the yield of the global process. The results are discussed and compared with experimental data concerning a dissolution process of manganese dioxide dispersed in a porous matrix.     

Dissolution Kinetics of Nickel(II) and Nickel(III) Oxides in Acid Media

The rate of nickel(II) and nickel(III) oxide dissolution in sulfuric, hydrochloric, and nitric acids was measured as a function of the acid concentration and temperature, and a kinetic model of this process is suggested. The limiting step of the dissolution process is the passage of the complexes forming on the oxide surface into the solution.     

Dissolution of silicon and junction delineation in silicon by the CrO3-HF-H2O system

The dissolution of single crystal silicon by aqueous solutions of hydrofluoric acid and chromium (VI) oxide was studied as a function of the resistivity of silicon and the composition of the etchant. In the concentration range under study, the dissolution rate is dependent on the resistivity of the silicon. The dissolution process is controlled by the chemical reaction rather than by the diffusion of chemical species; the rate of the chemical reaction is limited by the supply of carriers at the silicon surface. When the etchant was 2 M in chromium (VI) oxide, the dissolution rate of silicon of a given resistivity is second order with respect to hydrogen fluoride, suggesting that the formation of bivalent silicon is probably the rate-determining step of the chemical reaction.

An aqueous solution of hydrofluoric acid and chromium (VI) oxide can be used for delineating electrical junctions and revealing certain resistivity variations in silicon. A technique for this purpose is described and applied to multilayer silicon specimens. The relative etch rates of the various layers depend on resistivity somewhat differently from isolated specimens of similar resistivities, presumably     

THE USE OF THE PENETRATION MODEL FOR THE DISSOLUTION OF LIMESTONE IN THE CO2-WATER SYSTEM

The penetration model was implemented for the dissolution of limestone in the CO₂-water system. The model includes the acid-base reactions of the carbonate species as well as the autoprotolysis of water. It was also assumed that there is no surface resistance to the dissolution of the solid. This assumption restricts the use of the model to those conditions where the dissolution rate is limited by the rate of mass transfer. When using the model, only the hydrodynamics of the water solution need to be experimentally determined and put in terms of the model's hydrodynamic parameter. All other model inputs are either physical constants or known bulk concentrations. Dissolution experiments, performed on a rotating cylinder system, were used to test the ability of the model to predict the dissolution rate of limestone in an aqueous solution. Of special significance was the ability of the model to predict the dissolution rate at different pH-values, CO₂ partial pressures, temperatures and hydrodynamic conditions. An explicit finite differences method was used to deal with the system of non-linear partial differential and algebraic equations, which arose from the implementation of the penetration model. This investigation has shown that the limestone dissolution process in the mass transfer controlled region, can be modelled and described by the penetration model. The penetration model accurately describes the effects of all parameters investigated, including the enhancement effect from CO₂ (up to a factor of 10 compared with dissolution in a CO₂-free atmosphere) and temperature. The penetration model has also been compared with the film theory model. The comparison of the two models shows that the penetration model yields a better correlation to the experimental data in a CO, atmosphere. In a CO₂-free atmosphere the models are almost identical. However, the penetration model is computationally more difficult. A numerical procedure for solving the penetration model has been designed. This procedure includes a method of dealing with the unusual boundary conditions at the surface.     

Measurement of hysteresis in crystallization with a quartz crystal sensor

Monitoring of the cycle of crystal formation and dissolution gives important information for manipulating solute concentration and solution temperature for the preparation of mother solution in crystallization processes. In this study a direct monitoring technique using a quartz crystal sensor is applied to the crystallization of potassium bromide solution, and the monitoring performance is investigated. The experimental results indicate that the monitoring shows the detailed process of crystal formation and dissolution, and there is a hysteresis of 0.98 °C between the initiation temperature of crystal formation and the completion temperature of dissolution in the first measurement. In addition, it is demonstrated that the application of the technique is simple and efficient for the control of crystallization processes.     

Synergy between surface mechanochemistry and subsurface dissolution on wear of soda lime silica glass in basic solution

The polishing of oxide glass in aqueous solution is sensitive to not only the mechanical conditions applied by abrasives but also the chemistry of solution. This study elucidates the synergistic interactions of mechanical and chemical effects—especially, the synergetic effects of surface mechanochemical wear and subsurface dissolution are studied by measuring the material removal rate of soda lime silica (SLS) glass upon rubbing with a Pyrex glass ball in noncorrosive (neutral pH) in corrosive solutions (pH 10 and 13 NaOH) as a function of sliding speed. Based on the synergetic model of surface wear and subsurface dissolution, it is found that the mechanochemical surface reaction dominates the wear behavior of SLS glass in neutral and pH 10 solution conditions; the wear of SLS glass in pH 10 is enhanced, compared to the neutral pH case, due to the presence of OH^- ions at the sliding interface. In the case of pH 13, the dissolution of the densified subsurface region, which is formed due to interfacial friction during the surface wear, becomes significant, further enhancing the material removal yield. The finding provides an insight for designing an efficient polishing process in manufacturing of oxide glass materials with a good surface finish.     

Apparent Dissolution Kinetics of Diatomite in Alkaline Solution

The dissolution kinetics of diatomite in alkaline solution is the theoretical basis for the process optimization of alkali-diatomite reaction and its applications. In this study, the dissolution kinetics of diatomite in NaOH solution is investigated. The results indicate that the dissolution reaction fits well the unreacted shrinking core model for solid-liquid heterogeneous reactions. The apparent reaction order for NaOH is 2 and the apparent activation energy for the reaction (E_a) is 28.06 kJ·mol^-1. The intra-particle diffusion through the sodium silicate layer is the rate-controlling step. When the dissolution reaction occurs at the interface of unreacted diatomite solid core, the diffusion in the trans-layer (the liquid film around the wetted particle) reduces the rate of whole dissolution process.     

乙二醇生产和精制技术研究进展

乙二醇是一种重要的大宗化工原料,广泛应用于聚酯等行业,具有消耗量大、产品纯度要求高的特点。本文综述了石油基、煤基和生物质基乙二醇生产和精制技术的最新研究进展,介绍了不同路线乙二醇的生产工艺、催化剂体系和精制技术,分析了不同工艺路线的优缺点,总结了乙二醇精制到聚酯级乙二醇生产中存在的问题。提出未来乙二醇生产的研究重点应该放在高稳定催化剂的设计、大规模工艺的集成和原料的绿色化上。