Hollow fiber ultrafiltration: The concept of partial backwashing

In dead-end hollow fiber filtration with humic acid solutions, we observed that the humic material accumulates in the final part of the fiber. We proved the hypothesis that backwashing of the last part of the fiber is sufficient to operate the filtration process in a sustainable manner. This strategy works very well for feed solutions that result in either local accumulation of the material at the end of the fiber, or that form a well-defined concentration polarization layer that does not lead to deposition. When deposition throughout the whole module occurs, the proposed cleaning strategy is unsuccessful. This overall deposition occurs when a force balance over the particle, results in net transport to the membrane surface over the entire length of the module. We simulated such conditions by the addition of calcium to the feed solutions. The latter results in large aggregates carried towards the whole membrane area by convective water flow, and an increased interaction between the aggregates and the membrane.     

Effect of operating variables on the flux and selectivity in sweep gas membrane distillation for dilute aqueous isopropanol

Sweep gas membrane distillation was examined as a possible technique for isopropanol (IPA)–water separation using PTFE hollow fiber membrane module. The composition and flux of the permeate were monitored when feed concentration, operating temperature and flow rate were varied. The upper feed concentration tested was 10 wt.% IPA. Within the feed temperature range of about 20–50°C, IPA selectivity of 10–25 was achieved. Since the concentration near the surface on the membrane increased by the selective adsorption of IPA on the hydrophobic membrane, the selectivity increases. The permeate flux and IPA selectivity increase as feed temperature increase. The flux and selectivity increase at higher flow rates is mainly due to the reduced effects of concentration and temperature polarization. The effect of salt addition to the feed mixture was also examined.     

中空纤维分散液膜富集稀土元素

采用2-乙基己基膦酸单-2-乙基己基酯(HEHEHP)-正庚烷为萃取剂,盐酸为反萃取剂,中空纤维膜作支撑膜,研究中空纤维分散液膜技术富集稀土镱(Yb~(3+))离子。考察了体系物性:反萃分散相中反萃剂浓度、萃取剂浓度、萃取剂与反萃剂体积比、料液相p H值、稀土离子浓度;流体流动状态:反萃分散相与料液相流速变化等因素对富集稀土离子的影响。中空纤维分散液膜富集Yb~(3+)的最佳条件为:萃取剂浓度为0.25 mol/L,反萃取剂HCl浓度为4.00 mol/L,萃取剂与反萃剂体积比为10∶40,料液相p H=2.80,稀土离子浓度为0.025 mol/L。反萃分散相体积流量和料液相体积流量较小时,萃取率随流量的增加呈现逐渐增大的趋势。若两相体积流量过大,反萃过程进行不完全,萃取率反而下降。研究结果表明,中空纤维分散液膜技术可实现稀土离子的有效富集。     

Coiled fiber membrane chromatography

A new type of particle-loaded membrane adsorber module was prepared by coiling adsorptive fibers. In order to characterize the material and predict the module performance, the protein accessibility and mass flux of single fibers were tested in incubation experiments. The coil's layout spacing and winding tension are useful parameters for tailoring the module for stabilization, polishing, or pharmaceutical applications. Decreasing the distance between two adjacent fibers during the coiling process affects the flow resistance and the dynamic adsorption capacity of the module. Higher flow resistance creates a higher convective flow through the fibers resulting in faster adsorption processes. Exerting a high winding tension causes fiber deformation, resulting in modules with high packing density. The feed flow is then forced through the fibers to a greater extent, thereby reducing the diffusive distance to the active sites located in the interior of the fiber, which results in steeper breakthrough curves and better ligand utilization.     

Temperature drop of feed liquid during pervaporation

Heat transfer during pervaporation through a membrane module of silicone-rubber microtubes was studied for ammonia/water and ethanol/water feeds. The temperature drops of the feed mixture were measured as a function of flow rate, concentration and permeate side pressure. A model calculation with a vapor-phase driving force was compared with the data. The vapor permeability of the permeate components needed in the model were independently measured using an original measurement method with a differential transformer. The present simple model for heat and mass transfer during pervaporation proved to be applicable to the theoretical calculation for a membrane module of pervaporation to be used as a heat-transfer unit.     

Optimization of tocopherol concentration process from soybean oil deodorized distillate using response surface methodology

Soybean oil deodorized distillate is a product derived from the refining process and it is rich in high value-added products. The recovery of these unsaponifiable fractions is of great commercial interest, because of the fact that in many cases, the "valuable products" have vitamin activities such as tocopherols (vitamin E), as well as anticarcinogenic properties such as sterols. Molecular distillation has large potential to be used in order to concentrate tocopherols, as it uses very low temperatures owing to the high vacuum and short operating time for separation, and also, it does not use solvents. Then, it can be used to separate and to purify thermosensitive material such as vitamins.In this work, the molecular distillation process was applied for tocopherol concentration, and the response surface methodology was used to optimize free fatty acids (FFA) elimination and tocopherol concentration in the residue and in the distillate streams, both of which are the products of the molecular distiller. The independent variables studied were feed flow rate (F) and evaporator temperature (T) because they are the very important process variables according to previous experience. The experimental range was 4-12 mL/min for F and 130-200 degrees C for T. It can be noted that feed flow rate and evaporator temperature are important operating variables in the FFA elimination. For decreasing the loss of FFA, in the residue stream, the operating range should be changed, increasing the evaporator temperature and decreasing the feed flow rate; D/F ratio increases, increasing evaporator temperature and decreasing feed flow rate. High concentration of tocopherols was obtained in the residue stream at low values of feed flow rate and high evaporator temperature. These results were obtained through experimental results based on experimental design.     

Polyethylene fiber formation in tubular flow. I. Observations of growth pattern and fiber properties

The process of seeded growth of fibrillar polyethylene crystals has been studied in a tubular flow geometry for 0.01-wt % solutions of a high-molecular-weight polyethylene in xylene. The transformation sequence has been followed visually by using polarized-light illumination in conjunction with a video camera. Data are presented to show that transformation is initiated by the formation of a concentrated, unoriented, amorphous precursor fiber within which oriented birefringent crystals subsequently grow in consequence of the stresses transmitted by the flowing solution. Time constants for the precursor formation, birefringence initiation, and completion of birefringence were measured as functions of temperature and flow rate over a range of growth conditions. Wide-angle x-ray diffraction, overall birefringence, and optical hot-stage melting data were also obtained on the grown fibers. The net result of these observations is to conclude that fibrillar crystal growth during flow is always preceded by the formation of a liquidlike phase transformation which produces the concentrated, unoriented precursor. Subsequent orientation is in consequence of stress-induced crystallization with overall fiber orientation showing an increase with solution flow rate at a fixed temperature and a decrease with temperature at a fixed flow rate. At higher temperatures and lower flow rates, birefringence develops in an oscillatory fashion, indicating a remelting process possibly due to slippage of trapped chain entanglements formed by flow. A discussion is given of the implications of these observations for the understanding of flow-induced structure development, phase transformation, and oriented crystallization; this is expanded upon in a companion paper, Part II.     

Studies on the applicability of artificial neural network (ANN) in emulsion liquid membranes

An artificial neural network (ANN) model of emulsion liquid membrane (ELM) process is proposed in the present study which is able to predict solute concentration in feed during extraction operation and ultimate % extraction at different initial solute concentration in feed phase, internal reagent concentration, treat ratio, volume fraction of internal aqueous phase in emulsion and time. Because of the complexity in generalization of the phenomenon of ELM process by any mathematical model, the neural network proves to be a very promising method for the purpose of process simulation. The network uses the back-propagation algorithm (BPA) for evaluating the connection strengths representing the correlations between inputs (initial solute concentration in feed phase, internal reagent concentration, treat ratio, volume fraction of internal aqueous phase in emulsion and time) and outputs (solute concentration in feed during extraction operation and % extraction). The network employed in the present study uses five input nodes corresponding to the operating variables and two output nodes corresponding to the measurement of the performance of the network (solute concentration in feed during extraction and % extraction). Batch experiments are performed for separation of nickel(II) from aqueous sulphate solution of initial concentration in the 200–100 mg/l ranges. The network employed in the present study uses two hidden layers of optimum number of nodes being thirty and twenty. A leaning rate of 0.3 and momentum factor of 0.4 is used. The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be well within ±10%.     

Influence of channel-width ratio on solvent extraction through a double-pass parallel-plate membrane module

The effect of the location of an impermeable barrier, which is placed for double pass in the raffinate phase, on solvent extraction through a parallel-plate membrane module, has been investigated. Theoretical predictions are in fairly good agreement with the experimental results. Considerable improvement in performance is obtainable if the subchannel width, as well as the mass-transfer area, of concurrent flow is as large as possible than that of concurrent flow, especially for low flow rate operation. It has been also checked that the hydraulic dissipated power due to the friction loss of fluid flow is very small and generally, the operating cost in all devices may be ignored.     

Application experiment and numerical simulation analysis of oil–water separator with two-oriented corrugated coalescence plate

The new structure of two-oriented corrugated plate is developed in an oil–water separator. The surface of the corrugated plate is modified so that one side is provided with a hydrophobic property and the other side is provided with a hydrophilic property. The effect of feed flow rate and composition on the separation efficiency of the separator is analyzed by experiments. A three-dimensional model of the separator is established for simulation by using the fluent software. The separation effect is characterized by the maximum concentration and thickness of the two constituents. The simulation results are in good agreement with the experimental results. The feed composition and feed flow rate can be worked together in the coalescence process. Both in the experiment and in the simulation, the concentration of the outlet of this polynode separator can reach more than 99% in the treatment of oil-bearing rate from 30% to 60% and inlet flow rate at 800?L/h～2000?L/h, which confirms the high separation efficiency of the device structure. At the same time, it also can be concluded that the lower oil phase concentration is suitable for larger inlet flow, while higher oil phase concentration is more applicable for lower flow rate in the appropriate range.     

Development of novel backwash cleaning technique for reverse osmosis in reclamation of secondary effluent

The objective of the study was to further develop a novel cleaning technique for reverse osmosis in reclamation of municipal secondary effluent. This technique is a new backwash method via direct osmosis (DO) by intermittent injection of the high salinity (HS) solution without stopping of high pressure pump and it is environment and membrane friendly technique. In the study, DO-HS trials were carried out with a UF-RO pilot system which was operated on site with the secondary treated effluent as the raw feed. Different operating conditions for DO-HS treatment in the actual process were investigated. It was found that the operation for implementation of the DO-HS cleaning technique developed was easy. For the first time, the actual profiles of HS concentration, DO backwash flow rate, brine flow rate and permeate pressure during DO-HS treatment have been demonstrated. It was observed that turbidity of the brine stream during DO-HS treatment at 3 NTU was 5 times higher than that before DO-HS treatment. The results from this study have confirmed the previous hypothesis with DO-HS treatment that there would be a strong driving force for DO backwash to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal plant operating conditions in terms of RO feed flow rate, HS concentration and HS injection time are ready for the DO-HS method to be adopted and validated in a long-term continuous plant operation.     

热致相分离聚偏氟乙烯膜接触器法高压吸收CO2过程及数学模拟

研究了膜接触器法高压吸收混合气中CO2的过程,考察水作为吸收剂时,操作压力、气体和吸收剂流量对聚偏氟乙烯(PVDF)中空纤维膜脱除CO2效果的影响.通过物理传质模型得出气相、膜相和液相的传质方程式,构建了二维数学模型,并结合边界层条件和多物理场耦合分析软件(COMSOL MULTIPHYSICS)对膜接触器法高压物理吸收CO2的过程进行了模拟预测.结果表明,吸收过程中膜的润湿情况显著影响CO2传质效果;在数学模型中引入润湿率,可以较准确预测CO2的物理吸收效果.     

Simulation study of particle–fluid two-phase coupling flow field and its influencing factors of crystallization process

Obtaining the morphology of two-phase flow field accurately through experiments is very challenging, due to the complexity and the drainage area diversity of particle–fluid two-phase flow. Depending on the particle concentration, size, flow velocity, and so on, the two-phase flow tends to be in a more complex form, known as coupled flow status. Crystallisation process within a crystalliser is a typical engineering application of particle–fluid two-phase flow, and hence, the flow field within a potassium salt crystallizer is implemented to simulate the crystal suspension and to mix flow state during a continuous crystallisation process. Because the two-fluid model treats the particle phase and fluid phase as two distinct continuous media, this simulation model takes the effect of virtual mass force into considerations. The enhanced two-fluid model is then applied to investigate the influencing factors of the coupled flow field between the potassium salt particles and the fluid in the crystalliser under various operating conditions. The results indicated that the stirring speed, the concentration of the feed particles, and the particle size affected the distribution of coupled flow field at different levels and, thus, affected the crystallisation phenomena of a potassium salt. Among those factors, the stirring speed appears to have the most obvious effect on the flow field, as it affects the velocity of the two-phase flow. In the conditions listed in this paper, the minimum stirring speed is roughly 50 rpm to form a stable and circular flow field in the crystallizer, and the maximum particle size is controlled at around 12 mm and the feed particle concentration of roughly 32% to ensure cyclic crystallization. The research method used in this article provides a baseline for the study of the coupled flow field of particle–fluid two-phase flow and its influencing factors. This research also states theoretical guidance for the optimisation of operating conditions in the production and application of potassium salt crystallizer.     

Ultrafiltration of BSA in pulsating conditions: an artificial neural networks approach

The aim of the present paper is to analyze membrane systems behavior, operating in pulsating conditions, by means of artificial neural networks (ANNs). Different ANNs have been developed, by means of Matlab^® Neural Network Toolbox, to model the ultrafiltration process of aqueous BSA solutions through poly-ethersulfone membranes. A specific neural network architecture, constituted by one input layer, two hidden layers and one output layer, has been finally identified by a trial-and-error procedure. The network has been trained through a selected set of experimental data obtained for a lab-scale flat sheet membrane module, equipped with a device capable of producing periodic pulses of the applied trans-membrane pressure (TMP) and feed flow rate. It has been found that the developed neural network is capable of offering very accurate predictions of actual system behavior either when it is tested within the range used for training or when the inputs combination has been never exploited during learning phase. The observed reliability of neural networks predictions of membrane performances has suggested to use them for searching an optimal pulsation frequency profile able to maximize permeate flux. The utilization of such a pulse frequency profile allows obtaining, on the basis of theoretical evaluations only, significant improvements of membrane performances with respect to UF experiments performed at fixed and constant pulsation frequencies.     

Effect of fiber variation on the performance of cross-flow hollow fiber gas separation modules

A quantitative analysis of the effects of variable fiber properties on the performance of a cross-flow hollow fiber gas separation module is presented. The effects of variations in size, permeance, and selectivity are considered. Fiber variability is detrimental to performance. The recovery and flow rate of an enriched retentate stream decrease as variability increases. Some fibers may actually stop producing product as purity increases. Additionally, performance is poorer if the permeate from all fibers is not well mixed. The results of this work can be used to determine quality control guidelines for fiber manufacture and evaluate process enhancements.     

Modelling the effect of operating conditions on hydrodynamics and mass transfer in a Pd–Ag membrane module for H2 purification

In this work a novel modelling approach based on Computational Fluid Dynamics (CFD) for the prediction of the gas separation process in a Pd–Ag membrane module for H₂ purification is presented. With this approach, the pressure and velocity flow fields of the gas mixture and the species concentration distribution in the selected three-dimensional domain are simultaneously and numerically computed by solving the continuity, momentum and species transport equations, including a gas-through-gas diffusion term derived from the Stefan–Maxwell formulation. As a result, the H₂ permeation calculations depend on the local determination of the mass transfer resistances offered by the gas phase and by the membrane, which is modelled as a permeable surface of known characteristics. The applicability of the model to properly predict the separation process under a wide range of pressure, feed flow rate, temperature and gas mixtures composition is assessed through a strict comparison with experimental data. The influence of inhibitor species on the module performance, that is obtained by implementing in the CFD model a suitable literature correlation, is also discussed.     

高效液相色谱法测定涤纶中的间苯二甲酸含量

 涤纶中加入少量的间苯二甲酸对改进涤纶性能有一定的影响。用高效液相色谱法对涤纶样品中的间苯二甲酸的含量进行测定 ,用甲醇和氢氧化钠溶液充分水解样品 ,利用NovaparkC18柱 ,以甲醇 水 (体积比为 15∶85 ,pH 3 )溶液为流动相 ,分析了不同国家和地区的涤纶样品 ,并对最佳水解条件及色谱条件的选择等方面进行了讨论。     

Sensitivity of Americium and Curium Splitting Flowsheet and Running Procedure

As part of the 2006 French Act on sustainable radioactive waste and waste management, CEA has been developing a process, (EXAm), in order to separate americium from curium and fission product downstream of COEXTM or PUREX processes. The goal is to recover Am up to 99%. The first step mainly consists of splitting americium from curium thanks to the diamide in organic phase combined with a complexing agent in high nitric acid. The low separation factor between Am and Cm leads to a very sensitive process flowsheet towards operating conditions. It is then difficult to manage high recovery yields with good purity. A model has been built taking into account complexation equilibria by TEDGA in aqueous phase and extraction equilibria in organic phase for each element. This model was put into the PAREX code to find the correct flowsheet, and then to conduct sensitivity studies regarding several parameters such as feed flow, acidity, temperature, solvent flow and reagent concentration. These studies have pointed out a high correlation between americium yield and decontamination factor and, also, an equivalence between any change of the most sensitive parameters and a change in TEDGA concentration. A running procedure was followed during two hot tests: the main concept was to start with a less efficient process and then to improve it during the test in order to reach required performances by adjusting the TEDGA flow rate.     

Measurement of adsorption of a single component from the liquid phase: modelling investigation and sensitivity analysis

In this work, we consider an alternative approach for the measurement of adsorption from the liquid phase. Consider a mixture consisting of a non-adsorbed component (B) and an adsorbed component (A) present at some low concentration. Initially, a feed of component B only flows through a column packed with an adsorbent. Then, the feed is switched to the mixture of A and B. As soon as the mixture enters the column, there will be a reduction in the outlet flow rate as component A leaves the liquid phase and passes into the adsorbed phase. There are three stages to this work. The first is to develop overall and component balances to show how the amount adsorbed of component A can be determined from the variation in the column outlet flow rate. The second is to determine the actual variation in the column outlet flow rate for both plug flow and axial-dispersed plug flow. The final stage is to consider the suitability of a gravity-fed system to deliver the feed to the column. An analysis of the results shows that the experimental arrangement should be able to accurately monitor adsorption from the liquid phase where the mass fraction of the solute is of the order of 1%: the limiting experimental factor is how constant the volumetric flow rate of the liquid feed can be maintained.     

Influence of the reactive distillation column configuration on its performance: A computational study

Comparison of the performance of a reactive distillation column with three different hardware configurations is presented. As a reaction system the methyl tertiary-butyl ether (MTBE) synthesis has been chosen. The sieve tray columns with catalyst (encased inside wire gauze envelopes) placed along the liquid flow path differ in the number of reactive trays. The column simulations have been performed using the nonequilibrium model. The steady state behaviour of the three different hardware configurations was studied regarding the three input parameters; feed flow rate of methanol, feed flow rate of butenes, and reflux ratio. It has been shown that by varying the location of the methanol feed stage, the columns exhibit significantly different solution diagrams using the butenes feed flow rate as a continuation parameter. Using dynamic simulations, different perturbations of the manipulated variables were found to cause transitions between multiple steady states and these were also investigated. The major objective of this paper is to demonstrate the importance of the hardware choice in the performance of a reactive distillation column e.g. during the start-up or if occasional variations of the operating parameters occur. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.