Foam fractionation of solutions containing two surfactants in stripping and reflux columns

An experimental and theoretical investigation was undertaken in order to examine the effect of concentration, foam flow rate and feed flow rate on the separation of sodium dodecylbenzene sulfonate and sodium lauryl sulphate from solutions containing the two surfactants, in stripping and reflux columns. The experimental results indicated the conditions under which a stripping foam fractionation column behaves according to the model of an infinite column. Within the present experimental range reflux columns behaved always according to the model of an infinite column. Using this model it is possible to predict relative separation of surfactants in stripping and reflux columns from experimental data obtained in simple columns. Experiments with modified total reflux columns indicate great potential for batch foam fractionation.     

Élements de calcul des colonnes de fractionnement par moussage continu

Foam fractionation is considered as a unit operation. A theory based upon dimensional analysis is used for calculating continuous fractionation columns. Internal reflux ratio resulting from foam instability was taken into consideration and a numerical value is given. The concepts of specific productivity of the column P* and specific energy consumption E* are introduced. A formula is given for the correlation between P* and the parameters characterizing the column geometry (column diameter, foam height) and operating conditions (gas rate, external reflux ratio, feed concentration, feed rate, feed level).     

Foam fractionation with reflux

This paper shows that the foam drainage characterisation of Stevenson (2006a) provides a useful basis for the modelling of foam fractionation systems with and without reflux following the conceptual approach first proposed by Lemlich (1968a). Furthermore, the paper shows that surfactant transport between the rising and falling streams during foam fractionation with reflux can be characterised by a simple mass transfer coefficient. A set of non-dimensionalized process parameters is proposed and, using these, it is shown that this approach enables the whole operating regime of a foam fractionation device to be mapped out from a small number of relatively simple experiments to measure the surfactant adsorption isotherm, foam drainage characteristics, bubble size and mass transfer coefficient.The validity of this approach was demonstrated experimentally for a foam fractionation system continuously separating cetylpyridinium chloride (CPC) from a solution of constant concentration under total reflux. The dimensionless mass transfer group appeared to be invariant for this system, with a mean value of 3.7, over the studied range of rising gas to liquid flux ratio. It was shown for this case that the operation could be summarised in a small number of simple heuristic rules which gave valuable insight into the design and operation of this foam fractionation system.     

Kolonnenschäumen I: The Technique of Laminae Column Foaming

Abstract

Laminae column foaming is a special type of column foaming (foam separation). The foam is degraded to fast-moving, nearly planar laminae, which are rinsed by reflux. The method is distinguished by a simple technique, quick establishment of the steady state, and the possibility of working even with low-foaming solutions and handling small quantities of substances. The uncomplicated surface formation and laminae/wall system enable the principles of foam separation to be studied. The phenomena of laminae column foaming are described, as are types of laminae producers, countercurrent columns, and laminae destroyers, and a complete apparatus with circulating gas. Column foaming is compared with column distillation and column crystallization, and its place in the system of column separation methods is discussed.     

Temperature–enthalpy curve for energy targeting of distillation columns

The temperature–enthalpy (T–H) diagram of a distillation column at practical near-minimum thermodynamic condition (PNMTC) or the column grand composite curve (CGCC) is a useful representation for energy targeting studies and may be generated from a converged simulation of a base-case column design. The calculation procedure for the CGCC involves determination of the net enthalpy deficit at each stage by generating envelopes from either the condenser end (top-down approach) or the reboiler end (bottom-up approach). However, the values calculated by the two approaches differ for stages with feeds because existing procedures for CGCC generation do not consider the enthalpy balances at the feed stages. In fact, the net enthalpy deficits at feed stages calculated by both approaches are erroneous even for the simplest case of binary distillation. A feed stage correction (FSC) that rigorously considers the mass and enthalpy balance equations at feed stages is proposed in this work to resolve the discrepancy. Instead of assuming that the compositions obtained from the converged simulation for a feed stage will remain unchanged at PNMTC, the pinched compositions for the feed are determined by the intersection of the equilibrium curve and the feed q-line. Rather than perform an additional flash calculation to establish the pinched feed compositions, a quadratic approximation is developed here for column targeting purposes by assuming the relative volatility obtained from the simulation to remain constant in the neighborhood of the feed stage. The proposed FSC ensures that the CGCC is identical whether the calculations are performed by the top-down approach or the bottom-up approach. The effect of the FSC on the targets for energy conservation by reflux modification, feed conditioning, and introduction of side reboilers/condensers is discussed. As the energy target for reflux modification is determined by the CGCC pinch which typically occurs at or close to the feed location, the significance of the FSC on the reflux modification target is highlighted through several case studies including a complex column featuring multiple feeds and consequently multiple pinch points. The CGCCs for these case studies are generated by a computer program based on the FSC and a single analytical equation for the calculation of the net enthalpy deficits that allows every stage to have a feed, liquid product, vapor product, and side exchanger. The studies show that the reflux modification targets may be erroneous in many cases, if the FSC is ignored.     

基于优化的反应精馏塔简捷设计

基于G ibbs自由能最小原理达到反应和相平衡的假设,提出了一种适用于初步设计的新的设计方法。以甲基叔丁基醚和碳酸二乙酯的反应精馏过程为例,应用Aspen软件模拟,经分析发现,通过改变理论级数和回流比,可得到合理的塔内温度分布,从而使塔底产品组成得到最大程度的提高,为此提出基于优化的设计法:以产品组成最大为目标函数,以回流比、精馏段和提馏段理论板数为决策变量,采用遗传算法进行优化计算。结果表明,2个设计实例均能在保证低能耗的同时得到较高的产品纯度,说明该设计方法可以设计出较好的反应精馏塔。     

分批蒸馏优化策略与微机控制的研究(Ⅰ)——分批蒸馏的优化策略

本文提出了塔顶累积全回流及变压强综合回流两个分批蒸馏的新操作策略及相应的优化操作法,通过数学模拟和θ收敛计算法求出了二元(乙醇—异丙醇)和多元(正庚烷—正辛烷—正壬烷—正癸烷)物系的数值解.计算结果表明,两种新操作法分别较传统的操作法缩短生产周期30%和50%以上.     

Foam Fractionation of Mercury(ll) Nitro Complexes

Abstract

Using a recycle foam separation apparatus, the foam fractionation distribution factor, γ/C, of the anionic metal nitro complexes of mercury(II) with the cationic surfactant, hexadecyltrimethylammonium bromide, was determined. The distribution factor was measured as a function of nitric acid concentration. The maximum occurred at 0.1 N nitric acid, which is in agreement with the anionic ion-exchange column distribution coefficient. Total reflux foam fractionation experiments yielded a 150-fold increase in the enrichment factor with a 20% recovery of the mercury(II) ion.     

立板式隔板塔分离直馏汽油工艺

对利用一种新型立板式隔板精馏塔切割直馏汽油工艺进行了研究。首先,利用模拟软件HYSYS对该分离过程进行模拟,得到较优的工艺条件。在此基础上,利用立板式隔板塔实验装置,考察了塔顶总回流量、液体分配比等操作参数对产品的影响及装置的操作稳定性。结果表明,塔顶总回流量的增大有助于产品的分离,且液体分配比的选择范围更广。液体分配比的改变对中间侧线产品质量的影响较大,是操作的关键变量。     

恒全回流塔顶累积间歇精馏过程的研究

提出了一种过程始终为全回流操作的间歇精馏新型操作方式,其特征在于沿塔身不同高度设置有多个中间累积罐,操作中整塔始终处于全回流状态,每隔一段时间将下一级储罐内的液体转移至上一级储罐,塔顶储罐内液体作为产品转移到产品储槽。建立了该流程的数学模型并采用Matlab软件进行模拟,当目标产品浓度相同时,新操作方式的可以节省操作时间,在最优化的中间累计罐密集程度下,可节省50%左右,与具体操作参数相关;最后采用乙酸-水二元物系对该操作方式进行了试验验证,且整塔运行稳定易于操作控制。     

Decentralized control of a kinetically controlled ideal reactive distillation column

Two-point and three-point temperature control structures are proposed for a kinetically controlled ideal reactive distillation (RD) column. The control structures maintain stable column operation for large throughput changes. However, large deviations in the final product purities are seen with three-point control giving comparatively lower deviations. The large product purity deviations are due to the kinetic regime so that two temperature set-points are adjusted in a cascade arrangement to maintain the distillate and bottoms purity. The proposed two-point and three-point structures with cascade compensation of the temperature set-points effectively maintain the distillate and bottoms purity for a large throughput decrease. However, the two-point structures fail for a large throughput increase. This is because in the kinetically controlled regime, maintaining the distillate purity requires an increase in the effective reflux ratio to internally recycle the escaping reactants back into the reactive zone. The two-point structures that use the fixed reflux ratio policy thus fail as an infeasible steady state is sought. The three-point structures effectively maintain the product purities as the reflux ratio is indirectly adjusted through the manipulation of the reflux rate. The work highlights the need for understanding the interaction between the reaction and separation sections for effective RD control system design.     

Flowsheet synthesis and complex distillation column design for separating ternary heterogeneous azeotropic mixtures

The boundary value method for design of distillation columns separating ternary heterogeneous azeotropic mixtures is extended to include complex configurations, i.e. columns with integrated decanters and with multiple heterogeneous stages; double-feed columns; columns with intermediate decanters. The methods can be used for establishing product feasibility in a column and evaluating a column design in terms of cost. Multiple feasible designs can be generated for a given set of product specifications, according to the reflux ratio, number of heterogeneous stages and liquid phase ratio; these designs may be evaluated with respect to operating and equipment costs. Case studies illustrate the design method.An algorithmic approach is presented for synthesising novel sequences for separating, by distillation and decanting, ternary heterogeneous azeotropic mixtures. Existing synthesis procedures that consider only simple single-feed columns with decanters and integrated decanters are extended to include more industrially relevant options such as columns with several heterogeneous stages, double-feed columns, columns with intermediate decanters, and those accepting a heterogeneous liquid feed. With these advanced column configurations included in the synthesis method, a wider range of sequences may be considered systematically, allowing sequences that are more economically attractive than conventional designs to be identified. A case study illustrates the approach.     

Simulation and analysis of extractive distillation process in a valve tray column using the rate based model

Valve trays are becoming popular in the chemical process industries owing to their flexibility to handle a wide range of vapor throughputs. Using the rigorous rate based model, the importance of the non-equilibrium approach is demonstrated for a typical extractive distillation process in a Glitsch V-1 valve tray column. Simulation results based on an in-house developed code indicated that the rate based model predictions for a valve tray column operation showed significant differences relative to the equilibrium model. Even small errors in product purities translated into nonoptimal feed stage locations and inaccurate number of stages required. The counter-intuitive effect of high reflux ratio on separation is explained.     

Control of reflux and reboil flow rates for milli and micro distillation

An accurate control of reflux and reboil flow rates for small scale distillation unit has been evaluated. Its feasibility was studied with a distillation column with good results. The distillation column was planar in shape, and it was operated in a horizontal orientation. Porous, open-cell metal foam was used as the column packing. The distillation unit could be operated at extremely low mass fluxes. The operation of the distillation unit was extremely stable, which was achieved thanks to the rigorous control of the fluid flow rates, and heat losses. The heat loss model was regressed based on distillation experiments with total reflux, and the model was used to optimize the temperature of the column shell in order to minimize the heat losses from the column. The volume of the reboiler, the preheaters, and the heat exchangers was minimized with the use of flat channels for intensified heat exchange. The total liquid holdup of the system was less than 40 cm³. The efficiency of the distillation unit was characterized for two binary and one ternary system.     

采用反应-精馏法对焦化纯苯进行脱硫精制的研究

采用反应-精馏法对焦化纯苯中噻吩进行脱除,探讨了硫酸用量、填料层高度、填料种类及回流情况等主要影响因素对噻吩脱除率的影响。结果表明,对400mL噻吩质量浓度为0.030g/100mL的噻吩-苯溶液,采用玻璃多圈柱状填料,填料层高度为40cm,硫酸用量为80mL,人工控制回流情况,噻吩脱除率可达94%以上,苯中噻吩的质量分数小于2×10-5。     

氨蒸馏工艺中蒸氨塔的模拟计算

以AspenPlus软件为平台,对氨蒸馏工艺的蒸氨塔进行了模拟计算。通过对塔板数、进料位置、回流比与进料热状态的模拟,研究了各参数的影响特点。认为塔板数宜取大一些,进料位置靠近塔下端有利,回流比的选择应首先考虑满足产品质量,进料温度接近泡点为佳。确定塔板数8,在第6块塔板处进料,进料温度100℃,回流比1,灵敏板为第7块塔板,得到塔顶液氨产品氨摩尔浓度〉99．5％,塔底残留液氨摩尔浓度〈5％,满足设计规定。     

Reactive separation of isobutene from C4 crack fractions by catalytic distillation processes

Reactive distillation is a hybrid process where chemical reaction and distillative separation are performed in a single equipment. Even though reactive distillation could increase the selectivity of the desired product by the selective reaction this is not always true as shown in this work. A study on the MTBE reaction system using two coupled reactive distillation columns to separate a C4 crack mixture is carried out, where methanol acts as reactive entrainer and MTBE is the intermediate product. In the first column, isobutene and methanol react to form MTBE hence separating the inert C4 component, while in the second column MTBE splits back to methanol and isobutene. Methanol is recycled back to the MTBE formation column and isobutene is obtained as a product. This coupled process with direct recycle of methanol is possible only if no side reactions occur. When the side reactions are taken into account, byproducts such as diisobutene, dimethyl ether and water will be produced so that higher purity methanol can not be obtained at the bottom of the splitting column. The outlet of the splitting column must be firstly separated rather than being recycled directly to the formation column. Moreover, an attempt has been made to show how the selectivity of the desired product isobutene can be critically influenced by the operating parameters such as the reflux ratio. If the reflux ratio increases, a high quantity of diisobutene and dimethyl ether will be obtained which seriously affects the selectivity of isobutene. The influence of operating parameters is investigated by using a continuation method, which shows that bifurcation behavior can appear in both MTBE formation and decomposition process.     

Minimum reflux calculation for multicomponent distillation in multi-feed,multi-product columns: Mathematical model

Multi-feed, multi-product distillation columns are ubiquitous in multicomponent distillation systems. The minimum reflux ratio of a distillation column is directly related to its energy consumption and capital cost. Thus, it is a key parameter for distillation systems design, operation, and comparison. In this series, we present the first accurate shortcut based algorithmic method to determine the minimum reflux condition for any general multi-feed, multi-product (MFMP) distillation column separating any ideal multicomponent mixture. The classic McCabe-Thiele or Underwood method is a special case of this general approach. Compared with existing techniques, this method does not involve any rigorous tray-by-tray calculation, nor does it require guessing of key components. In this first part of the series, we present the mathematical model for a general MFMP column, derive constraints for feasible separation and minimum reflux condition, discuss their geometric interpretations, and present an illustrative example to demonstrate the effectiveness of our approach.     

Séparation isotopique d'azote 15—II Modèle mathematique pour le fonctionnement avec soutirage d'une colonne de séparation pour le système NOHNO3

The authors develop a mathematical model of the operation with draw-off of a nitrogen 15 separating column. The model allows to predict the transitory and steady states of a column operating with draw-off by simply knowing the total reflux level and the nitrogen hold-up of the column.Good agreement was found between the results of the model and experiments with draw-off.The model shows, that for a given column a feed flow exists for each concentration of the desired product which leads to a maximum production.     

高效导向筛板及填料在醋酸乙烯精馏塔中的应用

对醋酸乙烯 -醋酸甲酯精馏塔进行了技术改造。采用计算机模拟精馏塔的回流比、塔板数、能耗、冷却负荷等 ,优选出最佳方案 ,即采用回流比 15、塔板数 70 ,并应用高效导向筛板塔及填料代替原浮阀塔 ,改造后生产能力、产品质量均得到提高