Using membrane-supported liquid-liquid extraction for the measurement of extraction kinetics

Membrane-supported liquid-liquid extraction uses artificial membranes for the generation of a phase interface between the two liquid phases involved in extraction. Additional equipment for the generation of droplets as well as phase separation afterwards is no longer necessary. Since the membranes used for this special type of extraction are quite well described concerning thickness, porosity, tortuosity and material it is possible to generate information about the diffusion coefficient of the component to be extracted within the preferred solvent from extraction trails easily. This article describes an experimental set-up for both the proof of principle of membrane-supported liquid-liquid extraction and, using a dedicated computer-aided data treatment, how to calculate the overall mass transfer coefficient as well as the diffusion coefficient for a given system within moderate testing duration.     

A fully automated liquid-liquid extraction system utilizing interface detection

The development of the Abbott Liquid-Liquid Extraction Station was a result of the need for an automated system to perform aqueous extraction on large sets of newly synthesized organic compounds used for drug discovery. The system utilizes a cylindrical laboratory robot to shuttle sample vials between two loading racks, two identical extraction stations, and a centrifuge. Extraction is performed by detecting the phase interface (by difference in refractive index) of the moving column of fluid drawn from the bottom of each vial containing a biphasic mixture. The integration of interface detection with fluid extraction maximizes sample throughput. Abbott-developed electronics process the detector signals. Sample mixing is performed by high-speed solvent injection. Centrifuging of the samples reduces interface emulsions. Operating software permits the user to program wash protocols with any one of six solvents per wash cycle with as many cycle repeats as necessary. Station capacity is eighty, 15 ml vials. This system has proven successful with a broad spectrum of both ethyl acetate and methylene chloride based chemistries. The development and characterization of this automated extraction system will be presented.     

A minimum time operating policy for a liquid-liquid extraction column

Two methods, both based on linear programming techniques, have been applied to determining the minimum time control policy for effecting a grade change in the product from a liquid-liquid extraction column. The method was made possible by the existence of a linear dynamic model for the column derived from a previous frequency response study of the laboratory unit. Both methods predicted policies of a partial bang-bang nature. As expected the control paths were not the same; additional control criteria such as minimum control effort or minimum number of switchings are suggested as a means of further defining a best control policy. Suitable bounds on the controlled variables were found in the study so that physically realizable control policies were formulated.     

The application of liquid-liquid extraction to the fractionation of coconut oil

Summary In order to investigate the value of liquid-liquid extraction as a means of studying the glyceride structure of fats and oils, coconut oil was subjected to liquid-liquid extraction with ethanol, using both the batch method and a continuous counter-current extractor. Both methods yielded essentially similar results. Extraction effected the separation of coconut oil into fractions different in composition from the original oil, but they were not simple enough in composition to aseertain the glyceride structure of the oil. On the contrary, all the glyceride fractions contained at least six and in most cases all of the eight fatty acids present in coconut oil. In general, proportions of the lower fatty acids (caproic to lauric) in the glyceride fractions decreased as extraction progressed, whereas the proportions of the higher fatty acids increased. These facts were in agreement with changes in solubility, neutral equivalents, refractive indices, and iodine numbers. Condensed from theses presented by M. H. Menaker and by William R. Fish to the faculty of the Graduate School of Pennsylvania State College in partial fulfillment of the requirements for the degree of Doctor of Philosophy. This work was supported in part by a grant established by General Mills, Inc.     

Measurement of concentration profiles in a liquid-liquid extraction column

A novel experimental technique for withdrawing uncontaminated samples of each phase from a highly agitated two liquid phase system (primary dispersion) is presented. The technique has been applied in the study of the continuous and dispersed phase axial mixing characteristic of a mechanically agitated liquid Scheibel extraction column operating under different conditions treating the chemical system acetone-toluene-water. The column mixing compartments were separated by a mixed stainless steel-polypropylene knitted mesh packed bed which was completely ‘wetted’ by the organic dispersed phase. Several concentration profiles are presented and the non-ideal flow parameters as well as the mass transfer coefficients for the column and system under study are reported.     

Fractionation of castor oil methyl esters by liquid-liquid extraction

Summary and Conclusions A solubility diagram has been constructed for methanol-castor oil methyl esters-heptane at 8.4°C. and 24°C. A selectivity diagram has been prepared for methanol-castor oil methyl esters-heptane at 8.4°C. and 24°C. Castor oil methyl esters have been fractionated by continuous countercurrent liquid-liquid extraction at 3°C. and at 6°C. with methanol-heptane and heptane-methanol as solvents, using an extraction column containing four equilibrium stages. The methyl ricinoleate fraction produced compared favorably with pure methyl ricinoleate with respect to hydroxyl value and optical activity. It should be noted that there were undoubtedly some mono- and diglycerides in the castor oil methyl esters used in this study. These go along with the methyl ricinoleate and cause discrepancies between hydroxyl value and optical activity (2). The column feeds ranged from 2.9 to 10.3% methyl esters by weight in methanol-heptane. Solvent-feed ratios were from 0.49 to 1.21 lb. per pound. The flow rates were from 706 to 1,020 lb. per hour per square foot of column cross section (based on the cross section of the empty column).     

Fractionation of castor oil methyl esters by liquid-liquid extraction

Conclusion The phase equilibrium data are presented for methyl esters-furfural-hexane and methyl esters-nitromethane-hexane at 30°C. The hydroxyl values of ester samples obtained from the furfural and nitromethane phases indicate that furfural and nitromethane can be used as solvents for fractionating hydroxy esters from the mixed esters obtained by the methanolysis of castor oil.     

多级逆流液液萃取法浓缩糠醛的研究

分别选择1,1,1-三氯乙烷和四氯化碳为萃取溶剂,研究液液萃取法浓缩糠醛过程,以UNIQUAC方程为平衡模型,建立逆流模拟计算框图,计算结果表明1,1,1-三氯乙烷和四氯化碳是糠醛浓缩的有效溶剂,在N=4时,分离后糠醛质量分数达99.3%以上,萃余液中糠醛质量分数可降至0.07%以下,以1,1,1-三氯乙烷为萃取剂,分离后糠醛质量分数达99.9%以上,收率达到98.5%以上;在模拟计算的基础上,建立液液萃取装置并进行试验,试验和模拟结果基本一致,研究结果为进一步放大试验研究提供了有效的依据。     

Dynamic behaviour and simulation of a liquid-liquid extraction column

Dynamic behaviour of a stirred liquid-liquid extraction column was studied experimentally. Various input variables of the column were varied stepwise and the resulting variations in the system and output variables were measured. In addition to experimental work, a computer model was developed on the basis of the dispersion model to simulate the dynamic behaviour of the extractor. This model forms a component program of the dynamic process simulator DIVA, developed at the TU Stuttgart. The experiments showed that the hydrodynamic parameters exhibit no significant dynamic behaviour of their own. Therefore, changes occurring in these parameters closely follow variations in input and system variables. As a result, steady-state relationships for the calculation of flow parameters could be used in the simulation program. The simulator satisfactorily reproduced the experimental results for a number of disturbances. However, this was not always the case. As shown in the following, the model did not take into account the column level controller which, under certain conditions, exerts a very strong influence on the column's dynamic behaviour. As a result, larger differences occurred between experimental and simulated data. This influence on the extractor's dynamic behaviour can, however, be eliminated by a simple modification of the level controller arrangement.     

Neural network model-based predictive control of liquid-liquid extraction contactors

The inherent complex nonlinear dynamic characteristics and time varying transients of the liquid-liquid extraction process draw the attention to the application of nonlinear control techniques. In this work, neural network-based control algorithms were applied to control the product compositions of a Scheibel agitated extractor of type I. Model predictive control algorithm was implemented to control the extractor. The extractor hydrodynamics and mass transfer behavior were modeled using the non-equilibrium backflow mixing cell model. It was found that model predictive control is capable of solving the servo control problem efficiently with minimum controller moves. This study will be followed by more work concentrated on using different neural network-based control algorithms for the control of extraction contactors.     

Modelling of liquid-liquid extraction columns: Use of published model correlations in design

Design of several liquid-liquid extraction columns — packed, pulsed-packed, pulsed-plate, Oldshue-Rushton columns and the rotating disc contactor — was attempted utilizing available correlations for drop size, holdup of dispersed phase, flooding velocities, mass transfer coefficients and axial mixing coefficients. Correlations in many cases were vaguely defined and often based on very limited data. Results indicated that for given flow rates and extraction efficiency, the height of a packed or Oldshue-Rushton column must be considerably greater than the predicted minimum heights of the other three columns, which were comparable considering the limited data utilized in the developed correlations. A critical evaluation of the correlations should be carried out to guide the further experimental effort required to confirm the utility of the axial dispersion model in liquid-liquid extraction column design. Extension of the theory to include drop size variation is highly desirable.     

Investigating the process of liquid-liquid extraction by means of computational fluid dynamics

Liquid-liquid two-phase flow in extraction columns of the rotating disc contactor type is analysed using the multi-dimensional computational fluid dynamics (CFD) technique. Euler-Euler and Euler-Lagrange models are employed to give insight into the global flow structure and to analyse the turbulence related dispersion processes. Laser-Doppler velocity measurements are used to check the Euler-Euler results while a measured residence time distribution allows the assessment of the Euler-Lagrange approach. The results give rise to the expectation that CFD will become an accepted design tool in chemical engineering.     

润滑油糠醛萃取相平衡模型建立和过程优化

在工艺设计中,建立合理的、对原料有广泛适应性的润滑油-糠醛萃取模型具有重要工业意义。文中采用族组分划分法-Kuop法对润滑油温度馏分进行族组分划分,结果表明:各虚拟族组分K值基本保持不变,与实沸点温度无关,可以合理地描述不同馏程的原料油族组成;采用Aspen plus倾析器模块与UNIFAC热力学方程进行萃取模拟计算,原料油和产品物性及族组成计算值与实际值一致,误差小于5%;最佳操作温度为90—100℃,剂油比为2—4,与工业值一致;在平衡操作条件下,当理论级数为5,塔顶100℃,塔底65℃,剂油比为2时,塔顶抽余油收率(质量分数)为73.10%,芳香分质量分数为13.97%,润滑油基础油产品质量较好,符合工业实际值。     

A model for liquid-liquid extraction column performance — The influence of drop size distribution on extraction efficiency

A precise model for predicting liquid-liquid extraction column efficiency based upon assumed hydrodynamic, axial mixing and mass transfer behaviour has been formulated and solved numerically. The complex nature of the dispersed phase can be better described by drop-size-dependent residence time distribution (RTD). Both the variation of axial velocities due to drops of different sizes, i.e. forward mixing, and the axial dispersion for the drops of the same size have been considered in this model. The computed results reveal that the effects of both varying velocities and dispersion of drops on extraction efficiency are appreciable and cannot be neglected, and the efficiency may be overestimated if only a forward mixing model is adopted. The comparison of the experimental values of N_ODP with those predicted shows that the mass transfer data obtained in RDC agree well with the values predicted by the present model for the case of solute transfer in c→d direction, and are slightly higher than the predicted ones for the transfer in d→c direction.     

Optimisation of drop size in countercurrent flow liquid-liquid extraction columns

Experimental data obtained in a pilot plant rotating disc contactor were used to obtain values of parameters for the hydrodynamic and mass transfer models representing column operation. The unique feature of the data was that drop size within the column did not vary appreciably with vertical position. Column performance measurements were therefore truly representative of the particular drop size generated. The models, with the resulting parameter values, were then used in design mode to determine column dimensions as a function of drop size. An optimum drop diameter of 0.20–0.25 cm is indicated for the toluene-acetone-water system.     

Effect of system properties on the performance of liquid-liquid extraction columns—1: Packed column

Mean drop size, fractional hold-up of dispersed phase, and axial mixing have been determined in a 72 mm dia. packed column, packed with 8 mm glass Raschig rings, using the systems toluene-acetone-water and MIBK-acetic acid-water, in an attempt to assess the effects of the solute transfer processes on column operation.For the MIBK-system, where the packing size corresponded to the normal recommended conditions d_p > d_FC (packing size greater than the critical size of packing), solute presence and the direction of solute transfer was found to affect drop size, fractional hold-up and the axial mixing in the dispersed phase appreciably, in a manner which was consistent with either suppressed or enhanced coalescence characteristics according to the appropriate changes in solute system.For the toluene system, however, with the packing size corresponding to the condition d_p < d_FC, the drop behaviour was dominated by the action of the packing void spaces and mean drop size was independent of solute presence and direction of transfer.In both cases, axial mixing in the continuous phase was independent of solute effects, except in so far as these changes modified hold-up of the dispersed phase.     

反应精馏和液液萃取结合合成二甲氧基甲烷

以对甲苯磺酸为催化剂,以甲醇、甲醛为原料,采用反应精馏合成二甲氧基甲烷,二甲氧基甲烷的质量分数达到92%以上;采用液液萃取法对产物进一步提纯,研究液液萃取过程中,转速、搅拌时间、静置时间、溶剂比等因素对分离过程的影响,二甲氧基甲烷的收率可以达到90%以上;经一级萃取,二甲氧基甲烷的纯度可达到97%以上,二级萃取纯度可达到99.3%以上,萃取剂经处理,可循环使用;并对结果进行关联,关联和实验结果平均相对误差均小于1%,其结果为进一步放大实验研究提供依据。     

On the action of surface active agents on mass transfer in liquid-liquid extraction

The effect of the surface active agents sodium hexadecanyl sulphate and sodium undecanyl sulphate on the rate of mass transfer, droplet oscillation and terminal velocity has been studied during extraction of o-nitrophenol and iodine from aqueous solutions by single drops of carbon tetrachloride. The effect is caused by the pure surface active agents and does not depend on the presence of impurities. The hydrodynamic character of the effect has been confirmed. A comparison with solid spheres shows that the surface active agents can make the rates of mass transfer and the terminal velocities equal to those for solid bodies, internal circulation, oscillation and the zig-zag path being completely eliminated. Evidence is presented indicating that the high rates of mass transfer obtained in the absence of surface active agents, about three times that for solid spheres, are not caused by the droplet oscillation, and that, at the most, they can be accounted for only partly by internal circulation. It is suggested that the explanation must be sought in the micro structure of the flow pattern.     

Mathematical modeling of a modified scheibel liquid-liquid extraction column in the frequency domain

The frequency response of a modified Scheibel liquid-liquid extraction column was experimentally determined from pulse testing data obtained by Pollock. Mathematical modeling was carried out in the frequency domain. Several non-identical, non equilibrium, perfect mixing stage models were used to describe the dynamic behavior of the column. A signal flowgraph technique was found to be suitable for determining the theoretical frequency response of the non-identical stage models. All models proposed in this study appeared to simulate satisfactorily the behavior of both the extract and raffinate phases. The theoretical frequency and transient responses agreed very well with experimental data     

Extraction and separation of carboxylic acids by liquid-liquid extraction and chromatography

The possibilities of using the extraction and extraction-chromatographic methods to solve the problem of the recovery and separation of carboxylic acids are investigated.