Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300^°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90^°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013     

The possibility of the desalination of actual 1,3-propanediol fermentation broth by electrodialysis

Electrodialysis (ED) was employed to remove the organic and inorganic salts from actual 1,3-propanediol (PDO) fermentation broth. These salts cause many problems during the purification of PDO if not removed. Suitable operation parameters such as applied potential and the flow rate of streams were selected to ensure a stable and durative desalination process for PDO fermentation broth. Under these conditions, the membrane fouling can be alleviated effectively by changing pole and cleaning membranes so that further industrial production is possible. The experiment results show that about 90% of organic acid salts in PDO broth are removed by the ED process. In addition, a simulated diffusion PDO experiment proved that the diffusion of PDO results in its loss from fermentation broth and the loss ratio is less than 6% under the chosen operating conditions.     

Use of simulated evaporation to assess the potential for scale formation during reverse osmosis desalination

The tendency of solutes in input water to precipitate efficiency lowering scale deposits on the membranes of reverse osmosis (RO) desalination systems is an important factor in determining the suitability of input water for desalination. Simulated input water evaporation can be used as a technique to quantitatively assess the potential for scale formation in RO desalination systems. The technique was demonstrated by simulating the increase in solute concentrations required to form calcite, gypsum, and amorphous silica scales at 25°C and 40°C from 23 desalination input waters taken from the literature. Simulation results could be used to quantitatively assess the potential of a given input water to form scale or to compare the potential of a number of input waters to form scale during RO desalination. Simulated evaporation of input waters cannot accurately predict the conditions under which scale will form owing to the effects of potentially stable supersaturated solutions, solution velocity, and residence time inside RO systems. However, the simulated scale-forming potential of proposed input waters could be compared with the simulated scale-forming potentials and actual scale-forming properties of input waters having documented operational histories in RO systems. This may provide a technique to estimate the actual performance and suitability of proposed input waters during RO.     

Improvements of a hollow fiber reverse osmosis desalination model: Analysis of numerical results

In this work, a rigorous model describing the processes taking place in hollow fiber modules for reverse osmosis desalination is analyzed. The Kimura–Sourirajan model is used for describing transport phenomena through the membrane. The concentration polarization phenomenon is mathematically described using the film theory, while the Hagen–Poiseuille and Ergun equations describe the pressure drop in the fiber bore and on the shell side of the fiber bundle, respectively. Improving the previous model, in this work the salt concentration of the permeate accumulated along the fiber is calculated from appropriate mass balances. Hence, the osmotic pressure and the water and salt fluxes through the membrane that depend on this concentration change through the module; and it also influences indirectly the calculation of other process parameters. The solutions of all the differential equations involved in the model are accurately approximated by the finite differences method applied over an appropriate discretization. The value of the output variables changes less than 1% when the finite difference mesh is increased from 6 to 7 grid points in the range of each domain, axial and radial. The flow rates and salt concentrations profiles obtained by the proposed model are analyzed. The influences of the transmembrane and osmotic pressures over the permeate flow rates and salt concentrations are studied. The effect of incorporating the accumulated permeate salinity is showed. It is proved that errors committed by ignoring the permeate accumulated salinity can be significant. Sensitivity analysis for the permeate flow rate and permeate salt concentration is performed by studying the influence of different kind of data: input variables, physical coefficients and design variables.     

CDI二维浓度传质模型的建立以及实验验证

电容去离子技术(CDI)作为一种新兴的水处理脱盐技术,因其具有诸多优异性能而受到广泛关注。厘清CDI的传质机制是理论研究的焦点。通过对已有经验模型的分析,从沿流向方向和垂直流向方向两个方面,考虑了电场迁移以及传质扩散等因素,提出了一种新的CDI二维浓度传质模型,对CDI在除盐过程中的离子扩散及浓度分布规律进行模拟探究,根据实际实验结果对该模型进行实验验证及参数修正。结果表明,该二维模型可以较好地模拟CDI除盐过程。将该二维模型利用COMSOL软件进行模拟,观测CDI在除盐过程中的内部浓度变化。并针对存在问题提出合理化建议,为CDI技术的未来发展提供理论支撑。     

CDI二维浓度传质模型的建立以及实验验证

电容去离子技术(CDI)作为一种新兴的水处理脱盐技术,因其具有诸多优异性能而受到广泛关注。厘清CDI的传质机制是理论研究的焦点。通过对已有经验模型的分析,从沿流向方向和垂直流向方向两个方面,考虑了电场迁移以及传质扩散等因素,提出了一种新的CDI二维浓度传质模型,对CDI在除盐过程中的离子扩散及浓度分布规律进行模拟探究,根据实际实验结果对该模型进行实验验证及参数修正。结果表明,该二维模型可以较好地模拟CDI除盐过程。将该二维模型利用COMSOL软件进行模拟,观测CDI在除盐过程中的内部浓度变化。并针对存在问题提出合理化建议,为CDI技术的未来发展提供理论支撑。     

Influence of Drying Method on Enzymatic Stain and Contact Angle of Maple

Lumber enzymatically stained has a significantly reduced value. The process involved in producing this degradation has not been well characterized. The influence of temperature and fluid flow transport of sap solutes were probed using contact angle analysis. Temperature effects on surface chemistry, as detected by polar components, was identified but was found not to attribute to staining. Dispersal components, used to indicate fluid flow transport of solutes, pointed to a positive influence on the production of stain. A more detailed layer-by-layer analysis was discussed to provide a more definitive conclusion of attributing the degree of staining to fluid flow transport of sap solute.     

Influence of Drying Method on Enzymatic Stain and Contact Angle of Maple

Lumber enzymatically stained has a significantly reduced value. The process involved in producing this degradation has not been well characterized. The influence of temperature and fluid flow transport of sap solutes were probed using contact angle analysis. Temperature effects on surface chemistry, as detected by polar components, was identified but was found not to attribute to staining. Dispersal components, used to indicate fluid flow transport of solutes, pointed to a positive influence on the production of stain. A more detailed layer-by-layer analysis was discussed to provide a more definitive conclusion of attributing the degree of staining to fluid flow transport of sap solute.     

矿井水脱盐过程中卷式反渗透膜性能的数值模拟研究

为了更好地研究矿井水中无机盐组分对于反渗透过程产水、结垢及脱盐效果的影响,以内蒙古某煤矿矿井水水质组分作为进水水质条件,采用计算流体力学（CFD）模拟单支商用标准8寸卷式反渗透膜元件（陶氏BW30-400）内部的传质以及局部浓差极化的分布,预测实际运行情况下微溶盐结垢的风险。进水通道采用以阿基米德螺旋曲线为卷制轨迹的几何模型。无机盐的混盐作用通过混盐渗透压模型模拟。从全尺度卷式反渗透膜元件的模拟结果可以看出,卷式反渗透膜内的水流主要以轴向流速为主,沿切向阿基米德螺旋线的流速较低,对整体盐度分布的影响较小（<1%）,可以忽略不计,在后续模拟中采用简化模拟单元或几何模型或网格。在模拟操作条件下,卷式膜元件的浓水网产生的水头损失占整体水头损失约86%,为卷式膜元件中的主要水头损失来源。在没有安装浓水网的进水流道中最高Na₂SO₄浓度位于元件浓水出口处,高达3594 mg/L,约为有浓水网情况下的1.8倍。而且有浓水网的进水流道内,浓差极化现象主要发生在浓水网背水侧局部区域,影响范围较小。该模型模拟得到的产水量与实测产水量做对比,误差小于5%,同时模拟结果也接近ROSA9.1模拟数据（误差<4.4%）,因此可以对卷式反渗透膜的无机盐脱盐过程进行较精确的模拟仿真。与商业设计软件如ROSA（反渗透系统分析）相比,其只提供产水和浓水中的盐浓度信息,本文开发的模型可以提供浓度极化的特征信息,加深了对卷式反渗透膜在不同位置的潜在结垢风险的理解。     

稀土浸出过程溶质传递的格子Boltzmann模拟

采用耦合传质的格子Boltzmann方法模拟风化壳淋积型稀土矿中稀土浸出的溶质传递过程,在验证模型有效性的前提下,获得了稀土矿填充孔隙中流体流动的速度分布和伴随流动过程的溶质浓度分布. 通过考察浸取流速对溶质传递过程的影响,得到最佳浸取流速,约为0.25~0.35 mm/s,使溶质传递效率最高. 浸取流速小于0.2 mm/s导致浸取周期过长、浸取剂消耗量大;浸取流速大于0.4 mm/s引起沟流,导致稀土不能有效地浸出. 此外,模拟所得传质舍伍德数Sh随雷诺数Re的变化关系与经验关系式吻合,表明提出的模型可用于预测稀土浸出过程的溶质传递规律.     

正渗透过程中水与溶质的传递现象

正渗透是一种利用渗透原理的新兴膜技术,近年来在国内外受到了广泛的关注。解析该过程中溶剂水的传递和驱动溶质的反向传递对其发展和应用至为关键。首先开展了两种膜的取向下,正渗透过程中的水通量和溶质反向摩尔通量的实验研究。当驱动溶液在膜分离层侧时,水通量更高,而溶质反向摩尔通量更低,表明水的传递对溶质的反向传递有限制作用。而后分别考察了不同的单一溶质和二元混合溶质作为驱动溶质时,水和溶质的传递现象。当单一中性溶质或电解质作为驱动溶质时,水通量和溶质反向摩尔通量均随驱动溶液浓度的升高而增大;在相同操作条件下,驱动溶质的扩散系数越小,溶质反向摩尔通量越小;中性溶质与电解质混合溶液为驱动溶液时,溶质分子之间存在耦合传递效应。     

Transport properties of graphene oxide nanofiltration membranes: Electrokinetic modeling and experimental validation

There is a need for developing reliable models for water and solute transport in graphene oxide (GO) membranes for advancing their emerging industrial water processing applications. In this direction, we develop predictive transport models for GO and reduced-GO (rGO) membranes over a wide solute concentration range (0.01–0.5 M) and compositions, based on the extended Nernst–Planck transport equations, Donnan equilibrium condition, and solute adsorption models. Some model parameters are obtained by fitting experimental permeation data for water and unary (single-component) aqueous solutions. The model is validated by predicting experimental permeation behavior in binary solutions, which display very different characteristics. Sensitivity analysis of salt rejections as a function of membrane design parameters (pore size and membrane charge density) allows us to infer design targets to achieve high salt rejections. Such models will be useful in accelerating structure-separation property relationships of GO membranes and for separation process design and optimization.     

降雨蒸发条件下渗流区污染物迁移的数值模拟

采用溶质传递方程和水流动方程联立耦合进行数值求解,模拟土壤渗流区中有机污染物的垂直一维迁移过程。传递方程综合考虑气相扩散和液相的对流扩散过程,并且在水流动方程的边界条件中包含有降雨、蒸发的气候条件。数值模拟过程中将有机污染物苯作为研究对象,采用美国加州地区实际的土壤物性数据和气候条件,得到的模拟结果和Grifoll的研究结果基本一致。实验结果显示500 h污染物到达的深度近似为125 cm,2 000 h已经达到180 cm。另外,在模拟区域的不同深度设置数值模拟数据采集点,结果发现越接近不饱和区上表面的地方,受气候边界条件影响越大。     

A MODEL OF CAPILLARY SOLUTES AND FLUID EXCHANGE

A model is developed to describe the exchange of solute and fluid across the capillary wall. The local driving forces for transport are attributed to an imbalance between hydrostatic and oncotic pressures as well as concentration gradients existing across the capillary wall. The present approach takes into account hydrostatic pressure gradients along the capillary as well as changing values of concentrations and hematocrit in the blood as fluid exchange occurs. The intrinsic permeability of the capillary wall is examined initially from a phenomenological approach and then in terms of a pore model. Simulations are then made on the interactions of the various driving forces for capillary transport, the intrinsic capillary permeability characteristics, and the size of solutes in the process of fluid and solute exchange.     

A MODEL OF CAPILLARY SOLUTES AND FLUID EXCHANGE

A model is developed to describe the exchange of solute and fluid across the capillary wall. The local driving forces for transport are attributed to an imbalance between hydrostatic and oncotic pressures as well as concentration gradients existing across the capillary wall. The present approach takes into account hydrostatic pressure gradients along the capillary as well as changing values of concentrations and hematocrit in the blood as fluid exchange occurs. The intrinsic permeability of the capillary wall is examined initially from a phenomenological approach and then in terms of a pore model. Simulations are then made on the interactions of the various driving forces for capillary transport, the intrinsic capillary permeability characteristics, and the size of solutes in the process of fluid and solute exchange.     

Characterization of transport across cellulose acetate membranes in the presence of strong solute–membrane interactions

Certain organic solutes, including phenol, undergo anomalous enrichment when hyperfiltered through cellulose acetate membranes: the solute concentration is higher in the permeate than in the feed solution. A number of existing theoretical approaches describing hyperfiltration phenomena are presented and their merits and limitations upon application to the transport of phenol discussed. A new two-parameter transport relationship is derived based on an extension of the solution–diffusion model. The enrichment, or negative solute rejection by the membrane, is predicted to occur whenever the pressure-induced solute permeation velocity exceeds that of water. By acknowledging and incorporating the effect of pressure on the chemical potential of the solute, the present extended solution–diffusion model relationship successfully describes hyperfiltration data of phenol in homogeneous and asymmetric cellulose acetate membranes provided the contribution of convective flow to the overall solute transport is insignificant. In addition to the transport parameters of the extended solution–diffusion model, the transport parameters of the phenomenological, Kedem–Spiegler, and combined viscous flow–frictional relationship are evaluated from hyperfiltration data obtained with 0.05 and 0.1 wt % phenol feed solutions and homogeneous cellulose acetate membranes of different acetyl content.     

高浓度分散染料废水电渗析脱盐可行性试验

采用"MgO中和、Fe/C微电解、混凝沉淀"组合工艺对高盐度分散染料废水进行生化前预处理工艺研究,小试和中试试验结果表明,对COD为8 000～12 000 mg/L、色度为2 000倍、含盐量由17.75%、酸度为5.2%当量硫酸的废水,经组合工艺前处理及ED膜脱盐后,COD去除率为78%;色度小于150倍,去除率为92.5%;含盐量小于1%,脱盐率高达94.8%;BOD5/COD从0.02～0.05上升至0.42。结果表明,应用该组合工艺对分散染料废水进行预处理和ED膜脱盐具有技术可行性。     

Resistance and Mass Transfer Control through Passive Porous Films. I. A Transport Model for Diffusive Permeability

Abstract

The first part of this work describes a model for the passive transport of solutes through membrane systems formed by a low porosity film and the adjacent boundary layers. Model equations allow correlation of the overall phenomenological coefficient of diffusive resistance with the morphological and structural characteristics of the membrane system. Based on the general solution, the total resistance appears to be the result of three contributions related to the membrane itself, the associated boundary layers, and the pore end effects. Under specific conditions it is possible to obtain an explicit and simple functional dependence for each of these contributions as well as to express the solute concentrations in the membrane-boundary layer interfaces.     

Transport phenomena with reactions in drug delivery: Towards a quantitative description

A distributed system called a Krogh cylinder is used here to quantify the transport of a solute from the capillary into the extravascular tissue. The capillary network is broken down into cylindrical cells, each containing a capillary and an appropriate amount of extravascular tissue. The flow in the cylinder model has two-dimensional velocities, which are in the axial and radial directions. All parameters of the system, together with the geometric ones, have been included in the model. For a given bioavailability, the uptakes of reactive and nonreactive solutes have been obtained. Very large or massive molecules have been considered. The diffusion in the tissue is found to be very low. Most of the drug uptake happens through convection, which is slowed down in the presence of a reaction. Further, this convection is entirely due to the flow out into the lymphatic system. For the case where a reaction takes place, local equilibrium is assumed, which both cuts down the computation times and provides good results in the case of reactive solutes. The full results of a distributed system have been obtained for the first time, and the mechanics of how the area-under-the-curve can be used to calculate the actual solute uptake have been determined.