Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column–Part III: Mass Transfer Characteristics

Abstract

The mass transfer characteristics of a pulsed disc and doughnut column with a 0.04 m internal diameter and 4.24 m active column length are investigated in order to evaluate its contacting efficiency for caprolactam extraction with toluene. Pilot plant experiments for both the forward and back‐extraction process were performed in order to determine the concentration profile along the column length in both the extract and raffinate phase as a function of the operating conditions. The experimental conditions covered the industrial operating range. Furthermore the dispersed phase hold‐up, average droplet diameter and operating regime were determined and compared with the results obtained for the equilibrium situation, as discussed in Part II.

In the forward extraction process a significant influence of operating conditions was observed, where an increase in the flux decreased the separation efficiency, but an increase in pulsation intensity, temperature, or the addition of ammonium sulphate increased the separation efficiency. In the back‐extraction all concentration profiles were comparable and all caprolactam was extracted after a column length of L/m=2. Compared to the equilibrium situation the drop diameter and pulsation intensity required for the transition of the mixer‐settler to the dispersion operating regime were found to increase under mass transfer conditions, while the hold‐up decreased. HETS values were determined for both the forward and back‐extraction. For the latter HETS=0.28 to 0.41, whereas in the forward extraction HETS=0.32 to 0.67.

The concentration profiles were described with the backflow model, using a constant backflow parameter for the continuous phase and a constant overall mass transfer coefficient. The interfacial area was correlated using drop diameter and hold‐up expressions derived for the equilibrium situation, taking into account the relative effect of mass transfer. Using these expressions the measured data could be correlated and described well.     

Comparison of the Axial Dispersion Performance of Pulsed Solvent Extraction Columns with Tenova Pulsed Column–Kinetics Internals and Standard Disc and Doughnut Internals

Axial dispersion performance of a 2-m high 76-mm diameter pilot-scale pulsed solvent extraction column has been studied using two liquid–liquid systems, Alamine 336/isodecanol/Shellsol 2046 (continuous)–tap water (dispersed) and LIX 84/Shellsol 2046 (continuous)–tap water (dispersed). The pulsed column was operated with standard disc and doughnut internals and Tenova pulsed column–kinetics internals using pulsation intensities from 0.005 m/s to 0.025 m/s with polyvinylidene fluoride internal plates of 22.4% open area. The effect of pulsation intensity, dispersed phase velocity, and continuous phase velocity on axial dispersion coefficient have been investigated and compared with the two different column internals, and the experimental data has been correlated with empirical relationships.     

Extraction of Caprolactam from Aqueous Ammonium Sulfate Solution in Pulsed Packed Column Using 250Y Mellapak Packings

1 INTRODUCTION Caprolactam is a major ingredient in the manufacture of nylon 6 fibers. In the process of caprolactam production, there is about 1% caprolactam in the aqueous ammonium sulfate solution after Beckmann rearrangement and neu-tralization. So far, the 1% caprolactam has been extracted by benzene in an ordinary sieve-plate column with 60% recovery in Zhejiang Juhua Group Company in China, while being extracted in a pulsed packed column with 95% recovery abroad[1—3]. Because …     

CFD Simulation of Liquid–Liquid Two-Phase Hydrodynamics and Axial Dispersion Analysis for a Non-Pulsed Disc and Doughnut Solvent Extraction Column

A two-phase computational fluid dynamics (CFD) simulation for a non-pulsed disc and doughnut solvent extraction column has been developed with commercial CFD software FLUENT. Simulated hydrodynamic results including phase distribution, velocity fields, and holdup are given, which enables predicted holdup to be compared with experimental data. Average absolute relative deviation (AARD) of experimental data and CFD prediction in this study is found to be 10.8%, which is comparable to the estimated error in the experimental data and the predictions from traditional correlations in the literature. To estimate the extent of axial dispersion, a species transport model is used for the continuous phase with a small amount of tracer introduced in the continuous phase, when Sauter mean diameter of the dispersed phase is set to be 3.5 mm. A two-point monitoring method is used to estimate a Peclet number. The tracer concentration distribution in the two-dimensional distance–time space is interpreted with MATLAB along with the experimental measurement. The simulated Peclet numbers are compared with column experiments, and in general the simulation underestimates the experimental data by 60%. Introducing a modified drag law improves the predictions. This work shows that CFD can successfully model the performance of a non-pulsed disc and doughnut solvent extraction column.     

Extraction of Uranium Nitrate with 30% (v/v) Tributyl Phosphate in Kerosene in an Pilot Annular Pulsed Disc-and-Doughnut Column—Part I: Hydraulic Performance

The annular pulsed disc-and-doughnut column (APDDC) is an important extraction contactor used in the PUREX process. In this work, hydraulic investigation was carried out in a stainless-steel APDDC, with 30% (v/v) tributyl phosphate (TBP)-kerosene + uranium nitrate + nitric acid + water as the test system. Two operation modes with aqueous phase and organic phase as the continuous fluid were performed separately. The equations, which were previously developed for 30% TBP-kerosene + nitric acid + water system in aqueous phase continuous operation mode, were presently used to predict the holdup, the Sauter drop diameter, the flooding holdup, the flooding throughput, and the operating regimes in both operation modes. Good agreement with the experimental data was observed because the wettability of the dispersed phase on the internals in both the operation modes was similar with that in the aqueous phase continuous operation mode in the previous work. An exception is the flooding properties of the organic continuous operation mode because of a different flooding mechanism. And so new equations were proposed to calculate the flooding properties for the organic continuous operation mode.     

Extraction of Uranium Nitrate with 30% (v/v) Tributyl Phosphate in Kerosene in a Pilot Annular Pulsed Disc-and-Doughnut Column—Part II: Axial Mixing and Mass Transfer Performance

Mass transfer experiments were carried out in an annular pulsed disc-and-doughnut column (APDDC) using 30% (v/v) TBP-kerosene + uranium nitrate + nitric acid + water system (uranium nitrate system) for both extraction and stripping processes. Parameters in the axial dispersion model (ADM) and plug-flow model (PFM), namely, the axial dispersion coefficient of the continuous phase and the number of mass transfer units, were regressed by correlating the respective model with the experimental concentration profile. The mass transfer coef?cient is calculated, and new correlations are developed to predict the axial mixing coefficient of the continuous phase and the volumetric mass transfer coefficient. The height of a transfer unit is also calculated. The influence of axial mixing on mass transfer performance for the uranium nitrate system is discussed.     

Mass Transfer and Axial Mixing Characteristics in a Coalescence-Dispersion Pulsed-Sieve-Plate Extraction Column

A new configuration of coalescence-dispersed pulsed-sieve-plate extraction column (CDPSEC) was developed, and the mass transfer and axial mixing characteristics were evaluated with the two-point dynamic method. The influence of operation conditions was discussed with experimental results, showing that the mass transfer performance of CDPSEC mainly depends on the energy input and the holdup of dispersed phase. Higher energy input results in higher holdup of the dispersed phase, the axial mixing of the continuous phase is suppressed, and the true height of mass transfer unit decreases markedly. On the other hand, higher energy input leads to more serious forward mixing of the dispersed phase, so the energy input should be limited. Accordingly the operation conditions were divided into two regions, and empirical correlations for predicting the mass transfer and axial mixing characteristics in different regions with a satisfactory accuracy were suggested.     

Kinetic and Thermodynamic Separation of Cu(II) and Fe(III) by Liquid-Liquid Extraction with a β-Hydroxy-oxime in Toluene

Abstract

A quantitative study of the thermodynamic and kinetic separation of Cu(II) and Fe(III) by liquid-liquid extraction with toluene solutions of the oxime 2-hydroxy-5-t-octyl (acetophenone oxime) has been conducted. On the basis of the stoichiometry, equilibrium constants, rate laws and rate constants of the extraction reactions of Cu(II) and Fe(III) an equation has been derived which describes how the separation of Cu from Fe varies with the chemical composition of the system, the hydrodynamics of the extracting apparatus and the contact time between the aqueous and the organic phases. Our results show that separations which are not feasible thermodynamically are possible when the contact time between the two phases is kept much shorter than that required to reach equilibrium.     

Stability of rare earth oxides in a moist environment at elevated temperatures—Experimental and thermodynamic studies: Part II: Comparison of the rare earth oxides

Volatilisation tests enabled to quantify the stability of different rare earth sesquioxides, RE₂O₃ (where RE = Sc, Dy, Er, Yb) and to understand the corrosion process. These tests were carried out at temperatures ranging from 1000 to 1400 °C in moist air with 50 kPa of water at atmospheric pressure, under a flowing gas velocity of 5 cm s^?1. Besides the volatilisation rate, the nature of the volatile gaseous species was determined. The proposed experimental method allowed too to assess the Gibbs free energy of formation of these gaseous volatile species. Finally, the stability of each rare earth oxide under a moist environment at high temperature was compared.     

Adsorption Characteristics of Toluene and p‐Xylene in a Reversed‐Phase C18 Column for Simulated Moving Bed Chromatography

Abstract

The adsorption equilibria and transport properties of toluene and p‐xylene on a Eurosil 100‐30‐C₁₈ column were measured from a chromatographic response in a reversed‐phase HPLC. Moment method was applied to the effluent peaks obtained from various temperatures and eluent compositions. The adsorption equilibrium constants were obtained from the first moment analysis. On the other hand, the transport properties such as the axial dispersion coefficient and effective diffusivity were obtained from the second moment analysis. The simulated results of the simulated moving bed process using the parameters obtained from the moment analysis agreed well with the experimental results. And the separation of toluene/p‐xylene mixture could be successfully separated by the simulated moving bed process.     

Studying the Sorption Processes of Rare-Earth Elements with the Use of Sulfocationites from Nitric Acid–Phosphoric Acid Solutions in a Pulsed Column

Theoretical Foundations of Chemical Engineering - The kinetics of sorption and regeneration from industrial nitric acid–phosphoric acid solutions with the use of ion-exchange resins like KU-2...     

Unipolar Field and Diffusion Charging in the Transition Regime—Part II: Charging Experiments

Unipolar charging of narrowly distributed 30–100 nm DEHS aerosols in air is investigated, in order to determine the influence of the external electric field (E ₀ ≤ 5 kV/cm) and high charging intensities (n·t ≤ 5 · 10 ¹⁴ s/m ³ ) on the charging efficiency. The results are compared with a combined diffusion and field charging model based on the limiting-sphere concept described in Part I.

The experiments were carried out in a wire corona charger under conditions of complete radial turbulent mixing, which makes the determination of charging history straightforward and very accurate. The state of mixing was verified on the basis of the Deutsch model, by separate measurements of particle losses.

For positive charging, the agreement between measured and predicted mean charge was generally better than 5% for particles larger than 45 nm, which typically carried more than 4 unit charges; for 30 nm particles and relatively low charge levels the uncertainties in the model lead to deviations up to 30%.

In case of negative charging, the observed charge levels progressively exceeded those predicted on the basis of mean ion mobilities by factors up to 2 as the charging intensity increased, and there was evidence of additional charging by free electrons.     

Stress Distribution in Single Lap Joints with a Cracked Composite Adherend—Part II: Laminated Adherends

The effect of a crack in the overlap region of an adhesive single lap joint is studied on the shear stress distribution in adhesive layer. Each adherend is considered to be a laminated composite material with unidirectional fibers aligned in the direction of the applied load. Crack location is selected to be in the top adherend laminate, in the form of cut fibers and matrix bays. The crack can occur in any layer. The shear-lag model is used to derive the equilibrium equations which are then solved by means of eigenvector expansion. The effects of adhesive thickness, crack size, and location in the adherend, total number of layers in each adherends, volume fraction of fibers, and type of fibers are investigated on the shear distribution in the adhesive as well as load distribution in the intact fiber at the crack tip located in the top adherend. The effect of dissimilar laminated adherends is also investigated on the adhesive shear stress distribution. According to the results, in the presence of a crack, the peak shear stress in the adhesive layer and load concentration in the fibers are very susceptible to the adhesive thickness and number of layers in laminated adherends.     

Clarification of suspensions: a study of particle deposition in granular media: Part II—A theory of clarification

The observations in Part I [1] on particle deposition have been incorporated into theoretical equations to describe pressure drop and concentration over the complete clarification run—i.e. from the initial transient to the final steady state. The equations differ from those of previous workers in having no arbitrary constants or empirical correlations—all parameters have a precise physical significance and the pressure drop is derived directly from the Kozeny equation. Experiments were performed on a model bed, a packed bed and a sintered disc filter. In all three cases, deviation from the theoretical curves was about 5 per cent maximum in those runs in which parameter values were measured directly, and about 15 per cent maximum when these parameters were estimated completely independently of the run.     

Interphase Distribution of Thiophene,Toluene, and o-Xylene in the Hexane–Polymer–Water Extraction System

Theoretical Foundations of Chemical Engineering - The extraction of sulfur-containing and aromatic compounds from light hydrocarbons using water-soluble polymers has been studied experimentally and...     

Column adsorption of Cu(Ⅱ) by polymer-supported nano-iron oxides in the presence of sulfate: Experimental and mathematical modeling

Polymer-supported hydrous iron oxides (HFOs) are promising for heavy metals removal from aqueous systems.The ubiquitous inorganic ligands,e.g.,sulfate,are expected to exert considerable impacts on pollutants removal by these hybrid sorbents.Herein,we obtained a hybrid sorbent HFO-PS by encapsulating nanosized HFO into macroporous polystyrene (PS) resin.Both batch and column sorption experiments of Cu(Ⅱ) by HFO-PS were carried out in the presence of sulfate.Obviously,the presence of sulfate is favorable for Cu(Ⅱ) sorption onto HFO-PS.The performances of column Cu(Ⅱ) removal were fitted and predicted with Adams-Bohart,Clark,Thomas and BDST models.Thomas model is suggested best-fit to predict the breakthrough curves.Besides,a linear correlation is observed between breakthrough time and column length based on BDST model,which might be useful for predicting the breakthrough time for Cu(Ⅱ) removal by HFO-PS.     

Experimental and Numerical Investigations of Single Drop Mass Transfer in Solvent Extraction Systems with Resistance in Both Phases

Numerical simulation of transient mass transfer to a single drop controlled by the internal resistance or by the resistance in both phases was mathematically formulated and simulated in a boundary-fitted orthogonal coordinate system. The simulated results on the transient mass transfer dominated by the internal resistance are in good agreement with the Newman and Kronig-Brink models for drops with low Reynolds number. When the drop Reynolds number is up to 200, the mass transfer coefficient from numerical simulation is very low as compared with the Handlos-Baron model. The cases with mass transfer resistance residing in both the continuous and drop phases were simulated successfully and compared with the experimental data in three extraction systems recommended by European Confederation of Chemical Engineering (EFCE). For single drops with Re < 200, the numerically predicted values of the extraction fraction and overall mass transfer coefficient are in reasonable coincidence with the experimental data. I     

Structural Basis for Intumescence—Part II: Synthesis and Characterization of Intumescent Polymers Containing Spirophosphorus Moiety in the Backbone

Taking the spirophosphorus compound 3,9-dichloro-2,4,8,10-tetraoxo-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxide as one of the reactive monomers, a family of aromatic spirophosphates was synthesized using dihydric phenols, viz., resorcinol, hydroquinone, 4,4′–dihydroxydiphenyl, bisphenol-A and fluorene dicarbinol as the other monomers. The polymers were synthesized employing melt condensation technique under vacuum and characterized using FT-IR, ¹H-, ¹³C- and ³¹P-NMR spectroscopic methods. The number average molecular weight of the polymers was determined using vapour phase osmometry. Thermal properties of the polymers were studied using differential scanning calorimetry and thermogravimetry techniques. These studies indicated that the polymers containing spirophosphato moiety undergo eruptive degradations in the temperature region 310°–380°C leading to the formation of dense carbonaceous foam. The present study confirmed the spirophosphate structure as an essential requirement to show intumescence.