Mass transfer of long chain fatty acids through liquid–liquid interface stabilized by porous membrane

Long chain fatty acids are usually undesirable contaminants in food oils and removal of these acids is an important task for the oil industry. In this paper the mechanism of transfer of fatty acids from liquid organic phase through flat porous membrane into water was investigated. The membrane pores initially were filled with the same organic solvent without fatty acid. It was demonstrated that the rates of transfer from octane into aqueous solution at pH 4 are inversely proportional to the distribution coefficients (K_d) and are mostly determined by diffusion in aqueous unstirred layers. Increase of pH of aqueous solutions from four to 12 results in a 20-fold increase of transfer rate for octanoic acid, and more than 1000-fold increase for oleic acid. Time lag values necessary for the kinetics of fatty acid transfer to reach the steady state were very small for the transfer from octane, but they were much higher in the case of viscous mineral oil. These last values were in good agreement with Barrer’s equation for diffusion through two unstirred layers. In both cases, there is no significant interface resistance for the transfer of relatively long chain fatty acids from organic solvent into water. Ion exchange processes take place in the aqueous phase and the thickness of the corresponding reaction layer decreases to zero at high pH. This final state is equivalent to the reaction, taking place at the interface. This method could be used for kinetic separation of short and long chain fatty acids at acidic pH and non-selective removal of different fatty acids into alkaline aqueous solutions. The membrane-based process does not need elevated temperature and probably is less energy consuming than distillation.     

离子膜烧碱蒸发工艺综述

介绍了离子膜烧碱蒸发的特点,主要因素,及引进SET蒸发工艺技术。     

水膜闪蒸真空制冰的换热特性

引言当一定温度的液体突然暴露在低于其饱和压力的环境下时,液体由最初的平衡状态变成过热状态,液体中的过热量已经不能以显热的方式来包含能量,不能继续存在于液体中,会迅速转换为蒸发潜热,形成汽泡,同时液体温度迅速下降,这个过程被称为液体的闪蒸。由于闪蒸现象伴随着大量的水蒸气生成和剧烈的温度下降,在现代工业中,闪蒸被广泛应用在海     

质子交换膜燃料电池强化传质

传质问题制约着燃料电池性能的提高。通过理论分析、Fluent模拟,针对质子交换膜燃料电池流道中加凸台和电极扩散层开孔两种方法,分别研究其对强化电池内部传质的效果。结果表明,上述两种方式均能有效强化电池内部传质,提高电池性能。但是加凸台增加了风机的寄生功率,综合性能提升不显著。     

Fabrication of PVDF-HF membrane for bubble-free gas transfer via wet phase inversion

In this study, the characterization of gas permeable hollow fiber membranes fabricated from PVDF polymer by using wet phase inversion method was investigated. During preparation of dope solution for fabrication process, after PVDF polymer was resolved in N-methyl-2-pyrrolidone of 70%–80%, two additives of 5 wt% poly(vinylpyrolidone) K10 and propionic acid (PA) were tried by adding into dope solutions to determine the effect of additives on membrane characterization. SEM images showed that when the PVP K10 additive was used at high PVDF ratio of 25 wt%, a dense structure formed in the inner section and the large finger-like macro-voids reduced through the cross-section of each fiber. FTIR results indicated that both additives were not maintained in the fabricated membranes due to the passage into the water during phase inversion. However, it was realized that using of PVP K10 and PA in the membrane fabrication adversely affected contact angle and gas transfer performance.     

An efficient preparation of porous polymeric microspheres by solvent evaporation in foam phase

This paper reports an efficient method of preparing porous polymeric microspheres by solvent evaporation in foam phase, in which phase separation between polymer and porogen occurs in foam phase instead of that in water phase by using the traditional solvent evaporation method. The method provides outstanding features, including being time-saving, of high-yield and able for continuous production, in which formation of porous polymeric microspheres finished within 3 min with a high production yield up to approximate 95 wt% and the process was able to be developed into a continuous process for production of porous polymeric microspheres. It was also universal to non-crosslinked polymers since the method is a development on the traditional emulsion solvent evaporation method. The new method is efficient and can be used potentially on the industrial scale for continuous production of porous polymeric microspheres.     

微反应器与溶剂挥发法制备相变蓄热材料微胶囊

采用正十六烷为芯材,聚砜为壳材,二氯甲烷为有机溶剂,十二烷基磺酸钠与明胶的溶液为水相,在液相中利用溶剂挥发法制备了相变蓄热材料微胶囊。根据微胶囊形成机理将制备过程解耦成两个步骤,先利用微尺度反应器可控产生粒径均一的O/W型液滴,再将液滴在固化浴中脱除溶剂固化得到微胶囊。考察了连续相流速、分散相流速、微通道尺寸等因素对微反应器错流剪切模式产生液滴的粒径及单分散性的影响;并对微胶囊的结构和蓄热特性进行了扫描电镜和差示扫描量热仪的表征。结果表明这种解耦方法能够实现可控制备粒径均匀的相变蓄热材料微胶囊,相变热大于75 J·g^-1。     

Characterization of membrane distillation membranes prepared by phase inversion

In this paper, flat membrane distillation membranes have been successfully manufactured from PVDF/DMAc and PVDF/DMF blends by using phase inversion induced by an immersion precipitation technique. The structure of the membranes is asymmetric with a porous top layer and macrovoids, as assessed by SEM. The existence of MD fluxes in these membranes is established by performing various pure water flux experiments. A maximum in the MD fluxes for a particular value of the polymer content in the casting solution from which the membrane is manufactured has been observed. The dependence of the magnitude of the fluxes on the membrane thickness is also discussed and the influence of temperature polarization evaluated.     

传质对热天平坩埚内煤焦气化反应的影响

热天平标准配置的坩埚为四周及底部密封的敞口容器,气流不能穿过物料层从坩埚底部流出,从而影响煤焦气化反应的动力学行为.研究了坩埚尺寸、物料床层厚度对杯状坩埚内煤焦-CO₂气化（气固相反应）影响.采用PHOENICS软件模拟分析了杯状坩埚附近及内部流体运动、浓度分布,同时建立了杯状坩埚内煤焦-CO₂反应-扩散模型,两者能很好地吻合.杯状坩埚中进行的煤焦-CO₂反应模型参数φ和D_a反映了气体质量传递对反应的影响.     

化学法传热强化技术在烧碱蒸发过程的应用前景

讨论了烧碱溶液蒸发结垢、传热效率低、蒸发冷凝液带碱的原因。介绍了化学法传热 强化技术的理论基础。详细介绍了YH-1蒸发促进剂的特点、工业应用情况和前景。     

Mass transfer coefficients in a pulsed packed extraction column

The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for the toluene/acetone/water system. The experiments were carried out for both mass transfer directions. The effects of operational variables such as pulsation intensity and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The experimental findings indicate that pulsation intensity and mass transfer direction have great influence on volumetric overall mass transfer coefficient. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. The experimental results obtained in the present work are compared with some other types of extraction columns. Finally, two empirical correlations for prediction of the continuous phase overall mass transfer coefficient is derived in terms of Sherwood and Reynolds numbers. Good agreement between prediction and experiments was found for all operating conditions that were investigated.     

Color removal from dye wastewaters by adsorption using powdered activated carbon: Mass transfer studies

Color removal from synthetic dye wastewater which typically emanates from the Taiwan textile industry has been studied using powdered activated carbon (PAC) as an adsorbent. The CIE colorimetric system has been used in the measurement of color for the treatment of disperse-red-60 dye wastewater. The effect of contact time, dye concentrations and PAC dosage on color and color removal has been investigated. A film-pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, D_eff, for the adsorption of disperse-red-60 dye wastewater to PAC.     

Oxygen mass transfer in a gas/membrane/liquid system surrogate of membrane blood oxygenators

Oxygen mass transfer in a membrane blood oxygenator (MBO) surrogate system has been addressed in this work. It consists of a slit for water circulation as a surrogate blood flow channel and a constant pressure oxygen chamber separated by an integral asymmetric hemocompatible polyurethane‐based membrane. The oxygenated stream enters a well‐mixed reservoir of constant volume, V, for the oxygen average concentration, , measurement as a function of time, t. In a range of short times, the linearity of vs. t allows the direct determination of the permeation fluxes , with no recourse to dimensionless correlations for the determination of mass‐transfer coefficients. The experimental fluxes are in very good agreement with the predictions based in unidimensional axial convection and unidimensional transversal diffusion. This custom‐made benchmark system allows the optimization of the flow and oxygen mass transfer for the design of a novel flat‐sheet MBO. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3756–3763, 2018     

竖直多孔管降膜蒸发传热实验

研究了内表面烧结型多孔管对降膜蒸发换热效果的影响。采用单管降膜蒸发器,由壳程的蒸汽加热管程的水降膜传热。在热通量q=13~90 kW·m^-2,传热温差ΔT=2.87~9.5℃,液体Reynolds数Re_L=4500~15000 范围内,求不同工况下管内降膜传热系数,并将其与相对应的光管换热性能进行比较。比较数据可知:多孔管的管内降膜传热系数是光管的2.03 倍,总传热系数是光管的1.78 倍,多孔管强化传热效果明显。     

Determination of the peripheral contact angle of sessile drops on solids from the rate of evaporation

A method was developed to determine the initial peripheral contact angle of sessile drops on solid surfaces from the rate of drop evaporation for the case where ₁ < 90°. The constant drop contact radius, the initial weight, and the weight decrease with time should be measured at the ambient temperature for this purpose. When water drops are considered, the relative humidity should also be known. The peripheral contact angle so obtained is regarded as the average of all the various contact angles existing along the circumference of the drop. Thus, each determination yields an average result not unduly influenced by irregularities at a given point on the surface. In addition, the error in personal judgment involved in drawing the tangent to the curved drop profile at the point of contact can be eliminated. The application of this method requires the use of the product of the vapor diffusion coefficient with the vapor pressure at the drop surface temperature. This product can be found experimentally by following the evaporation of fully spherical liquid drops.     

Mass transfer modeling during cross-flow filtration of non-newtonian fluids

The film theory was used to determine the mass transfer coefficient for the cross-flow filtration of guar gum solutions. We investigated their variation with cross-flow velocity and concentration. Comparing the experimental results with the Sherwood correlation generalized for power law fluids and with two models found in the literature led to the evaluation of an effective diffusion coefficient for each model. This parameter was shown to depend on cross-flow velocity and concentration.     

Characteristics of phenylalanine imprinted membrane prepared by the wet phase inversion method

A phenylalanine imprinted membrane without a sponge layer containing macrovoids was prepared by the wet phase inversion method. The structure of the phenylalanine imprinted membrane prepared by an in-situ implanting procedure was denser than that of the membrane prepared by post implanting. Consecutive washings with distilled water and acetic acid solution removed nearly all of the template molecules from the membrane prepared by the post implanting procedure, although much of the template molecules remained in the membrane prepared by in-situ implanting. The removal of the template molecules from the membrane increased the population of the free COOH groups but reduced that of the dimerized COOH groups in the membrane. A D-Phenylalanine imprinted membrane prepared by post implanting selectively adsorbed D-phenylalanine from a racemate solution, where the adsorption selectivity reached 4.79. A D-phenylalanine imprinted membrane prepared by in-situ implanting exhibited an inverse adsorption affinity.     

烧碱蒸发工艺的自动化控制技术应用总结

总结了大沽化工厂十几年来研究,推广烧碱蒸发控制技术的情况,介绍了针对烧碱蒸发过程的各种实用模型和控制方案。     

单个液滴蒸发模型中不同质量传递公式的有效性分析

液滴蒸发是液体喷雾的重要物理过程,文献中使用了不同的模型计算液滴蒸发中的质量流率。依据质量传递驱动力HM的处理,可将这些模型归类于三种不同形式,即经典模型、质量类比模型和漂移流动模型。本文对这些模型的来源和假设作了分析和总结,发现漂移流动模型考虑了Stefan效应和质量迁移,应为正确的表述,而经典模型忽略了瞬态效应,质量类比模型忽略了Stefan流效应。最后以两种不同蒸发率条件下的液滴蒸发为例进行计算,研究了不同质量传递驱动力对液滴蒸发的影响, 发现经典模型和质量类比模型都对液滴的蒸发估计过低,且高蒸发率下三种模型对液滴蒸发特性的影响更显著。     

磁电复合场下正极钒离子的跨膜传质

探究了全钒液流电池在外加磁场、电场、磁电复合场下正极电解液中的钒离子在Nafion117膜上的跨膜传质过程,以及在磁电复合场下硫酸浓度和电解液添加剂对传质过程的影响。根据达西定律拟合得出相应的扩散传质系数。实验结果表明正向电场会加剧钒离子渗透,且当电场强度达到30 V·m^-1时渗透情况严重可达到无电场时的2.53倍。非匀强磁场的加入可明显降低钒离子的跨膜渗透性。且当外加磁场和电场复合场时,磁场对降低钒离子跨膜渗透的作用更加显著。实验还得出在不同的外加复合场中较高浓度硫酸有利于降低钒离子的跨膜渗透。此外丙三醇、木质素磺酸钠正极电解液添加剂的加入也降低了VO₂⁺的跨膜渗透性。