The Q-Cascade Explanation

The physical meaning of a continuous profile cascade, which is frequently used in the study of multicomponent isotope separation and named as the Q-cascade is explained. It is found that the parameter Q for a component at a stage is nothing but the relative increase of the concentration of the component, and is constant at all cascade stages. The Q-cascade is classified as the quasi-ideal cascade playing an importantrole for fast evaluation of the separation cascade parameters for multi-isotope mixture separation.     

Influence of Holdups and Feed on the Transient Process of Pulse Cascades

In isotope separation pulse cascades are non-conventional and transient processes take place at each stage and in the whole cascade. A numerical method is developed to study the transient process of reaching steady state and applied to square pulse cascades to identify the majors of influence. Without feed and withdrawals, the main factors influencing the transient process are the cascade length and the ratio of the centrifuge holdup to the pipe holdup. With feed and withdrawals, the factors influencing the transient process include the feed, the centrifuge holdup, the pipe holdup, and the cascade length.     

钯钇合金膜分离器级联分离氢同位素理论计算

钯合金膜分离氢同位素具有分离能力强、氚滞留量小以及装置设计简单等优点,是一种很有发展潜力的氢同位素分离方法,但受膜及泵输系统等因素的制约,目前仍处于概念设计阶段。文中针对级联分离建立了考虑返混的近似模型。模型表明:各级的分流比和分离系数相同时,对含氚体积分数0.065%的氢同位素混合气体,在0.2分流比(体积比),分离系数为2.5时,经过3级富集和4级贫化就可以得到含氚体积分数1.5%的产品和含氚体积分数0.000 5%的贫料;相同分离系数下,分流比较大时分离系统的规模较小。     

Comparison study of schemes for separation of intermediate isotope components

ABSTRACT

This paper uses the Q-cascade model to investigate the separation performance of eight schemes, comprising variations of two single-cascades and two double-cascades, to separate an intermediate isotope component. Optimization determines the relationship between the minimum relative total flow and concentration for different concentration requirements of the intermediate component. The results show that single-cascade schemes are not efficient. Rather, the optimal scheme is a double-cascade scheme that uses a three-stream cascade and a cascade with two feeds and an intermediate withdrawal. The successful optimization of all schemes indicates that this approach can be generalized to optimize various multistep separation processes.     

Maximizing separation performance of q-cascades for multicomponent isotope separation

The Q-cascade is a type of model cascade that is particularly useful for studying multicomponent isotope separation. The cascade segmentation technique is further developed to optimize Q-cascades, which minimizes the relative total flow by splitting a cascade into smaller segments that each use the mass number of the virtual component as a decision variable. Application of this technique to Cadmium isotope separation shows that it is always effective. If the number of segments into which a cascade is split increases, then the minimum relative total flow decreases. A progressive segmentation strategy is developed to maximize the number of segments.     

Analysis of Gas Centrifuge Cascade for Separation of Multicomponent Isotopes and Optimal Feed Position

Abstract

Analysis of the concentration distribution in a gas centrifuge cascade for separation of multicomponent isotope mixtures is different from that in a cascade for separation of two-component mixtures. This paper presents the governing equations for a multicomponent isotope separation cascade. Numerically predicted separation factors for the gas centrifuge cascade agree well with the experimental data. A theoretical optimal feed position is derived for a short square cascade for a two-component mixture in a close-separation case. The optimal feed position for a gas centrifuge cascade for separation of multicomponent mixture is discussed.     

渗透汽化技术在液体分离中的研究新进展

渗透汽化是近年膜科学研究中最活跃的领域之一,在分离液体混合物,尤其是痕量、微量物质的移除,近、共沸物质的分离等方面有独特优势。简要介绍了渗透汽化技术的历史及发展过程,着重介绍了近几年渗透汽化技术在液体分离方面的研究进展。从研究结果来看,从水溶液中分离有机物研究主要集中在醇、酯的分离。在有机物脱水方面,开发出了选择性更好、渗透量更高的膜,乙醇脱水也有不少新的研究成果。特别是在有机混合物分离方面,取得了长足的进展,可以分离更多的有机物。     

Isotopically Selective Mass Transfer in the Q-Cascade with Losses of Working Substance

The theory of the model Q-cascade is generalized for the case of presence of losses of working substance. Analytical solutions are obtained to determine the cascade parameters for specified rates of losses. Calculations to reveal the effect of the losses on the total and feed flows for given concentrations of a target component in the product and waste flows are carried out. The dependence of the total and feed flows on the losses for multi- and binary isotope mixtures is defined.     

硼同位素分离过程中络合剂的气提干燥模型

硼同位素分离富集的过程中,为了减少操作系统的副反应,需要原料液苯甲醚的含水质量分数在30×10-6以下.采用干燥剂氮气脱除苯甲醚的微量水分.应用解吸因子法设计了气提塔的理论模型,计算了最小和操作气液比、组分的气提率、塔釜液的组成及气提气用量,用Aspen Plus软件对气提塔进行了模拟,最后对整个过程进行了实验验证.实...     

Modeling fluid behavior and droplet interactions during liquid-liquid separation in hydrocyclones

A mechanical separation process in a hydrocyclone is described in which disperse water droplets are separated from a continuous diesel fuel phase. This separation process is influenced by droplet-droplet interaction effects like droplet breakup and coalescence resulting in a change of droplet size distribution. A simulation model is developed coupling the numerical solution of the flow field in the hydrocyclone based on computational fluid dynamics with population balances. The droplet size distribution is discretized and each discrete droplet size fraction is assumed to be an individual phase within a multiphase-mixture model. The droplet breakup and coalescence rates are defined as mass transfer rates between the discrete phases by the aid of user-defined functions. All model equations are solved with the CFD software package FLUENT™. The investigations show the impact of the cyclone geometry on the coupled population and separation dynamics. Cyclone separators with an optimized geometry show less steep velocity gradients increasing the coalescence rates and improving the separation efficiency. The calculated droplet size distributions at the cyclone overflow and at the underflow show good accordance with experimental data. The basic modeling approach can be extended and adapted to other disperse multiphase flow systems.     

Continuous fractionation of multicomponent mixtures with sequential centrifugal partition chromatography

The applicability of sequential centrifugal partition chromatography for continuous fractionation of multicomponent mixtures, represented here by a mixture of four parabens with very similar molecular structure, was studied. The fractionation of the quaternary feed mixture was regarded as a separation of a pseudo‐binary mixture. The model‐based approach was used to select the biphasic liquid system and the unit operating parameters. All desired fractions were recovered with purities >99%. The influence of the solute concentration on the density, viscosity and volume ratio of the phases as well as on the partitioning of the solutes between the two phases was investigated. According to these results, possibilities for increasing the throughput were proposed and validated experimentally. For example, butyl paraben with a purity ≥99% was continuously separated from the rest of the parabens in a 250 mL unit with a throughput of 3.24 g h^?1 and a solvent consumption of 0.33 L g^?1. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1659–1673, 2017     

Modeling and parametric analysis of hollow fiber membrane system for carbon capture from multicomponent flue gas

The modeling and optimal design/operation of gas membranes for postcombustion carbon capture (PCC) is presented. A systematic methodology is presented for analysis of membrane systems considering multicomponent flue gas with CO₂ as target component. Simplifying assumptions is avoided by namely multicomponent flue gas represented by CO₂/N₂ binary mixture or considering the co/countercurrent flow pattern of hollow‐fiber membrane system as mixed flow. Optimal regions of flue gas pressures and membrane area were found within which a technoeconomical process system design could be carried out. High selectivity was found to not necessarily have notable impact on PCC membrane performance, rather, a medium selectivity combined with medium or high permeance could be more advantageous. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Modeling multicomponent adsorption of monoclonal antibody charge variants in cation exchange columns

Transport models are developed for the adsorption of monoclonal antibody charge variants in cation exchange columns for two different matrices: UNOsphere S, which has a macroporous architecture, and Capto S, which contains charged dextran polymers grafted to an agarose matrix. The UNOsphere S protein adsorption kinetics is described by a macropore diffusion model with effective pore diffusivity D_e = 8.3 × 10^?8 cm²/s, which successfully predicts resolution of charge variants by frontal analysis at residence times, L/u, between 0.9 and 5.4 min. The Capto S adsorption kinetics is very fast for individual charge variants and for coadsorption of their mixtures, but is dramatically slower for sequential adsorption, when a more strongly bound variant displaces a more weakly bound one. A Maxwell‐Stefan model assuming single‐file diffusion predicts, in agreement with experiments, poor resolution of charge variants by frontal analysis even at long residence times as a result of highly hindered counterdiffusion. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2503–2511, 2012     

Characterization of permeation behaviors of ethanol–water mixtures through sodium alginate membrane with crosslinking gradient during pervaporation separation

Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique, which had different extents of crosslinking gradient structures. The SA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while blocking the other side by a polyester film to prevent the reaction solution from contacting it. The extent of the crosslinking gradient was controlled by the exposing time. When the swelling measurements were performed with uniformly crosslinked membranes in aqueous solutions of 70–90 wt % ethanol contents, it was observed that the crosslinking could reduce both the solubility of water in the membrane and the permselectivity of the membrane toward water. The pervaporation separation of the ethanol–water mixture of 90 wt % ethanol content was carried out with membranes with different extents of crosslinking gradients. As the crosslinking gradient was developed more across the membrane, the resulting flux as well as the separation factor to water was found to decrease while the membrane became stable against water. The pervaporation performances of the membranes with different membrane loadings in a membrane cell were also discussed using the schematic concentration and activity profiles of the permeant developed in them. The pervaporation separations of the ethanol/water mixtures through the membrane with an optimal crosslinking gradient were performed at different feed compositions and temperatures ranging from 40 to 80°C. The change in the membrane performance due to the relaxation process during pervaporation was observed with the operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis of the experimental data of the membrane performance measured by repeating the operation in a given temperature range. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1607–1619, 1998     

Experimental investigation and modeling of the separation of ternary mixtures by hydrophilic pervaporation

ABSTRACT

In the course of the present study, the pervaporative dehydration of two ternary mixtures: ethanol/n-butanol/water and ethanol/ethyl acetate/water were investigated through hydrophilic polymer composite PERVAP 1210 membrane. The effects of temperature and the concentrations of water and organic components on permeation were studied through pervaporation experiments. The influence of Hansen solubility parameters of the components and mixtures on their permeation was also examined. It has been found that changes of organic ratios in the feed solution affect organic permeation due to mutual interactions and flux coupling. This interaction was built in a suggested semi-empirical mass-transport model for ternary mixtures with optional simplifications. The modeled partial fluxes are in good accordance with the measured values.     

二甲苯模拟移动床分离过程建模与仿真

模拟移动床（SMB）是混合二甲苯分离的重要技术。模拟移动床区域回流比是决定产品质量的关键参数。在真实移动床（TMB）建模方法基础上,结合实际工况数据,建立了模拟移动床吸附分离过程机理模型,并通过分析区域回流比对产品质量的影响,得到不同产品质量要求以及进料品质的情况下区域回流比的操作区间。仿真结果表明,TMB建模方法能较好地描述模拟移动床实际工况。基于机理模型对操作区间的分析结果可以为模拟移动床分离过程的工艺设计和操作提供指导意见。     

Modeling and monitoring of multimode process based on subspace separation

In the paper, a new process monitoring approach is proposed for handling the multimode monitoring problem in the industrial batch processes. Compared to conventional method, the contributions are as follows: a new method of extracting the common subspace of different modes is proposed based on the subspace separation; after that the two different subspaces are separated, the kernel principal component models is built for the common and specific subspace respectively and the monitoring is carried out in subspace. The monitoring is carried out in the subspaces. The corresponding confidence regions are constructed according to their models respectively.     

Pervaporation separation of water/alcohol mixtures through hydroxypropylated chitosan membranes

The present study investigated the pervaporation performance of novel hydroxypropylated chitosan (HPCS) membranes to separate water from an aqueous alcohol solution. Hydroxypropylated chitosan was prepared from the reaction of chitosan and propylene oxide. The results show that the separation factor decreases and the flux increases with increasing of the substitution degree of the hydroxypropylated chitosan membrane. Crosslinking with glutaraldehyde or treatment with Cu²⁺ can improve the pervaporation performance of modified chitosan membrane grately. The performance data indicate that the crosslinking hydroxypropylated chitosan membrane treated with Cu²⁺ is an excellent pervaporation membrane for the separation of alcohol–water mixtures, and one-stage separation is attainable for some alcohol–water mixtures such as an n-propanol–water and an isopropanol–water system, which has a good separation factor of 220 for the n-PrOH/water system and 240 for the i-PrOH/water system using 85 wt % alcohol concentration at 60°C. The flux for both cases is around 0.5 kg m⁻² h⁻¹. At the same time, the structure of the chemically modified chitosan membranes and their separation characteristics for aqueous alcohol solutions are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2035–2041, 1998     

Phase separation in segmented polyurethanes derived from mixtures of polyether polyols with different functionality

A series of segmented polyurethanes containing 60 wt° of hard segments (HS) was prepared from MDI (4,4-diphenylmethane diisocyanate) ethylene glycol and mixtures of a polyoxyethylene end-capped polyoxypropylene triol and a polyoxyethylene end-capped polyoxypropylene diol. The effects of the content of polyether diol in polyether polyols on phase separation and properties was investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and investigation of tensile properties. The DSC and DMA results indicate that the polyurethane derived from only polyether triol exhibits obvious phase separation and that the HS is immiscible with the SS, but that the HS is compatible with the HS for the polyurethane derived from polyether diol. As the content of polyether diol increases, the compatibility between HS and SS increases. As the content of polyether diol increases, the tensile strength. elongation. toughness and tear resistance of the polyurethanes increases. but their moduli decrease. The modulus-temperature dependence in the temperature region of –30 to 65 °C increases as the polyether diol content increases.     

Separation of multicomponent aromatic/aliphatic mixtures by simulated moving bed adsorption: Modeling and experiments

Simulated moving bed (SMB) adsorption has potential for efficient separation of many valuable chemical mixtures, but considerably less attention has been devoted to multicomponent feeds relative to binary mixtures. We take a rigorous experimental and modeling approach to study multicomponent separation of aromatics and aliphatics with a mesoporous silica adsorbent, which is relevant in many petrochemical applications such as separation of reformate and distillate streams. Our approach involves refining multicomponent adsorption, mass transfer, and SMB process parameters based upon detailed experimental inputs, with progressive addition of components. We develop a robust model that quantitatively predicts the influence of key operating parameters such as stream flow rates, desorbent/feed ratio, and switch time on the separation results and concentration profiles. The model is validated as a function of feed complexity by SMB experiments and column concentration profile measurements in a 16-column mini-plant. Furthermore, conditions for clear separation of each mixture are developed.