陶瓷膜净化溶剂油的实验研究

研究了平均孔径0.2 mm的陶瓷膜对含杂质溶剂油的微滤过程,选用不加水和加0.5%(w)水2种料液,考察了操作时间、跨膜压差、错流速度、温度和铝粉含量对膜通量及铝粉截留率的影响,研究了反冲操作、浓缩和污染膜清洗过程. 结果表明,不加水较加水料液的膜通量明显增大;随操作时间延长,膜通量下降至稳定,铝粉截留率迅速增大至100%;跨膜压差增大或温度升高使稳定通量增大;错流速度增大,稳定通量先升高之后不变;铝粉含量越高,膜通量越低. 适宜的操作参数为跨膜压差0.16 MPa、错流流速3.9 m/s和温度40℃. 反冲操作能有效提高膜通量;浓缩过程中膜通量快速下降至平缓阶段再较快降低,净化溶剂油澄清透明;采用0.15%(w)洗洁精和0.25%(w)硝酸清洗可使通量恢复到新膜通量的94.9%.     

Treatment of Oily Wastewaters Using the Microfiltration Process: Effect of Operating Parameters and Membrane Fouling Study

This work focuses on the treatment of oily wastewater using the cross-flow microfiltration (MF) process to determine the effect of different operating parameters such as transmembrane pressure (TMP) and cross-flow velocity on the separation performance and to study the mechanism of membrane fouling during microfiltration of oil in water emulsions. In this regard, the permeation flux and oil rejection of a polyvinylidene fluoride (PVDF) membrane in a flat-frame MF module for separation of 3000 ppm oil/water emulsions were measured. The results indicated that the permeate flux increased by an enhancement in both TMP and cross-flow velocity, while the oil rejection decreased. The analysis of variance (ANOVA) showed that the individual effect of TMP and cross-flow velocity is more important than the interactional effect of these operating parameters on the permeate flux and oil rejection. The results of fouling modeling revealed that the membrane fouling mechanism was affected by the applied TMP. The cake filtration model dominates the fouling mechanism at lower operating pressures. The fouling mechanism was changed from the cake formation to intermediate pore blocking and then to standard pore blocking as the TMP varied from 1 to 3 bar. Finally, a five-step procedure was used for cleaning the oil/water fouled membranes.     

Sugar Purification from Enzymatic Rice Straw Hydrolysis Products using Cross-Flow Diafiltration

The sugars produced by enzymatic hydrolysis of rice straw are separated using cross-flow diafiltration in this study. The effects of membrane type, membrane pore size, cross-flow velocity and transmembrane pressure on the filtration flux, sugar rejection, and sugar mass flux transported to the filtrate are discussed. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. When the membrane made of mixed cellulose ester (MCE) is used, over 70% filtration resistances are caused by the membrane fouling; while the resistance due to virgin membrane is dominant when regenerated cellulose (RC) membranes are used. A force balance model is applied to relate the filtration flux and filtration resistance to operating conditions. The calculated data of filtration flux based on this model agree fairly well with experimental data. In addition, a theoretical model is used to explain the sugar transmission through the cake and membrane pores. The sugar rejection coefficient decreases with increasing cross-flow velocity because of the effect of cake reduction. This effect is more significant when the MCE membrane is used. Comparing the sugar mass flux transported into the filtrate, it is more effective for sugar purification by using 10 kD RC membrane and under higher transmembrane pressures.     

Separation of oil from oily wastewater using low cost ceramic membrane

Safe disposal of oily wastewater is a global issue across the industrial world. Stable oil-in-water emulsion has been separated by dead end filtration using low cost ceramic membrane. The efficiency of separation at different oil-water emulsion concentrations was evaluated at different trans-membrane pressures. Maximum rejection of oil 95.4% was observed for membrane sintered at 850 °C for oil concentration of 250 mg/L at 137.89 kPa. The permeate oil concentration was within the permissible range of environmental tolerance (<12 mg/L). The flux decline data was compared with various pore blocking models and it was appraised that cake filtration model best represents the fouling mechanism within the experimental range of pressure and oil-in-water concentration. Solvent permeation studies revealed that nonpolar solvents were more permeable than the polar solvents. The selection parameter of 14.78×10^?6m³/m²·s indicates a good combination of flux permeation, declination and rejection for the membrane sintered at 900 °C.     

Treatment of Oily Waste Water Using Low-Cost Ceramic Membrane: Flux Decline Mechanism and Economic Feasibility

Abstract

This work addresses the applicability of different membrane pore blocking models for the prediction of flux decline mechanisms during dead end microfiltration (MF) of stable oil-in-water (o/w) emulsions using relatively low-cost ceramic membranes. Circular disk type membranes (52.5 mm diameter and 4.5 mm thickness) were prepared by the paste method using locally available low-cost inorganic precursors such as kaolin, quartz, calcium carbonate, sodium carbonate, boric acid, and sodium metasilicate. Characterization of the prepared membrane was done by SEM analysis, porosity determination, and pure water permeation through the membrane. Hydraulic pore diameter, hydraulic permeability, and hydraulic resistance of the membrane was evaluated as 0.7 µm, 1.94 × 10^?6 m³/m²·s·kPa and 5.78 × 10¹¹ m²/m³, respectively. The prepared membrane was used for the treatment of synthetic stable o/w emulsions of 40 and 50 mg/L crude oil concentration in batch mode with varying trans-membrane pressure differentials ranging from 41.37 to 165.47 kPa. The membrane exhibited 96.97% oil rejection efficiency and 21.07 × 10^?6 m³/m²·s permeate flux after 30 min of experimental run at 165.47 kPa trans-membrane pressure for 50 mg/L oil concentration. Different pore blocking, models such as complete pore blocking, standard pore blocking, intermediate pore blocking and cake filtration were used to gain insights into the nature of membrane fouling during permeation. The observed trends for flux decline data convey that the decrease in permeate flux was initially due to intermediate pore blocking (during 1 to 10 minutes of experimental run) followed with cake filtration (during 10 to 30 minutes of experimental run). Based on retail prices of the inorganic precursors, the membrane cost was estimated to be 130 $/m². Finally, preliminary process economic studies for a single stage membrane plant were performed for the application of the prepared membrane in industrial scale treatment of o/w emulsions. A process economics study inferred that the annualized cost of the membrane plant would be 0.098 $/m³ feed for treating 100 m³/day feed with oil concentration of 50 mg/L.     

Effect of cake layer structure on colloidal fouling in reverse osmosis membranes

A series of reverse osmosis (RO) membrane filtration experiments was performed systematically in order to investigate the effects of various hydrodynamic and physicochemical operational parameters on a cake layer formation in colloidal and particulate suspensions. Bench-scale fouling experiments with a thin-film composite RO membrane were performed at various combinations of trans-membrane pressure (TMP), cross-flow velocity (CFV), particle size, pH, and ionic strength. In this study, silica particles with two different mean diameters of 0.1 and 3.0 μm were used as model colloids. Membrane filtration experiments with colloidal suspensions under various hydrodynamic operating conditions resulted that more significant permeate flux decline was observed as TMP increased and CFV decreased, which was attributed to the higher accumulative mass of particles on the membrane surface. Results of fouling experiments under various physicochemical operating conditions demonstrated that the rate of flux decline decreased significantly with an increase of the ionic strength as well as particle size, while the flux decline rate did not vary when solution pH changed. The experimentally measured cake layer thickness increased with a decrease in particle size and solution ionic strength. Furthermore, the model estimation of cake layer thickness by using a cake filtration theory based on the hydraulic resistance of membrane and cake layer was performed under various ionic strength conditions. The primary model parameters including accumulated mass and specific cake resistance were calculated from the cake layer resistance. This result indicated that the formation of cake layer could be closely related with solution water chemistry. The model estimated cake layer thickness values were in good agreement with the experimentally measured values.     

Separation of Dissolved Phenolics from Aqueous Waste Stream using Micellar Enhanced Ultrafiltration

The micellar enhanced ultrafiltration (MEUF) process has been used for the separation of phenol and o-cresol from aqueous solutions at room temperature (30 + 2°C) using a cationic surfactant, cetyltrimethylammonium bromide (CTAB), and polyethersulfone membrane of molecular weight cut-off 10 kDa. The effect of the cross-flow rate, the surfactant to pollutants (S/P) concentration ratio in feed, the variation of pollutants concentration in the feed keeping S/P constant, the presence of Na₂SO₄ and NaCl salts and mixed surfactants on the rejection of each solute and permeate flux have been studied in detail. The % rejection of phenol and o-cresol without using the surfactant observed was 24% and 41% respectively, which was increased to 60% for phenol and 80% for o-cresol at S/P ratio of 8. The effect of salts was also investigated. There was no significant effect of the cross-flow rate on the % rejection of the solutes. The effect of the membrane pore size was also investigated using 1 KDa and 30 KDa PES membranes. Characteristic parameters of MEUF such as the distribution coefficient, micelle loading, and the micelle binding were also estimated.     

Evaluation of the fouling potential of ceramic membrane configurations designed for the treatment of oilfield produced water

During the treatment of oilfield produced water (PW) with ceramic membranes, process efficiency is primarily characterized by the specific permeate flux and the oil separation performance. In addition to membrane properties, the increase in total filtration resistance (fouling) and the decline in permeate flux are strongly dependent on the constituents of the PW as well as process conditions such as trans-membrane pressure and cross-flow velocity. The extensive study presented herein describes the characterization, application and performance of various ceramic membrane filtration technologies designed and developed for the efficient treatment of PW generated from tank dewatering and several oily model systems.     

Treatment of oily wastewater using low cost ceramic membrane: Comparative assessment of pore blocking and artificial neural network models

This work addresses the performance and modeling of the separation of oil-in-water (o/w) emulsions using low cost ceramic membrane that was prepared from inorganic precursors such as kaolin, quartz, feldspar, sodium carbonate, boric acid and sodium metasilicate. Synthetic o/w emulsions constituting 125 and 250 mg/L oil concentrations were subjected to microfiltration (MF) using this membrane in batch mode of operation with varying trans-membrane pressure differentials (ΔP) ranging from 68.95 to 275.8 kPa. The membrane exhibited 98.8% oil rejection efficiency and 5.36 × 10⁻⁶ m³/m² s permeate flux after 60 min of experimental run at 68.95 kPa trans-membrane pressure and 250 mg/L initial oil concentration. These experimental investigations confirmed the applicability of the prepared membrane in the treatment of o/w emulsions to yield permeate streams that can meet stricter environmental legislations (<10 mg/L). Subsequently, the experimental flux data has been subjected to modeling study using both conventional pore blocking models as well as back propagation-based multi-layer feed forward artificial neural network (ANN) model. Amongst several pore blocking models, the cake filtration model has been evaluated to be the best to represent the fouling phenomena. ANN has been found to perform better than the cake filtration model for the permeate flux prediction with marginally lower error values.     

Membrane-assisted production of S1P loaded SLNs for the treatment of acne vulgaris

The incorporation of the sparingly soluble drug sphingosine-1-phosphate (S1P) into solid lipid nanoparticle (SLN) formulations using a ceramic membrane-assisted emulsification technique was investigated. SLNs have been used as an alternative to emulsions and liposomes in cosmetic and pharmaceutical preparations for the last two decades. They were prepared by replacing the liquid lipid part of the emulsions with a lipid part, which is solid at room temperature and/or at body temperature. The influence of a number of parameters on the particle size and size distribution of formulation and on the lipid flux were issued here. The chosen experiment parameters were: Lipid concentration varied from 5 to 20% w/w at various trans-membrane pressures (4-6 bar) and at aqueous phase cross-flow velocities varied from 2 to 12.5 m/s. A mono-channel ceramic membrane with a pore size of 0.2 µm and a 0.4 µm 19-channel membrane were used. It was shown that the investigated membrane system allows the preparation of SLNs with a mean particle size between 0.2 and 1 µm. The advantages of using a membrane-supported process are excellent scaling-up abilities and the control of the particle size through an appropriate selection of process parameters such as aqueous phase cross-flow velocity, lipid phase pressure and membrane properties.     

Permeate flux decline in cross-flow microfiltration at constant pressure

Microfiltration processes are frequently used to separate solids from aqueous suspensions. The rejection of suspended matter is facilitated by means of a size exclusion mechanism and is affected by membrane properties, characteristics of the suspension and operating conditions. Therefore, the filtration performance of a single polymeric hollow-fibre membrane was investigated by monitoring the permeate flux decline for a filtration at constant transmembrane pressure (TMP). For these bench-scale experiments, a model suspension consisting of silica particles in xanthan gum solutions was used in order to represent the characteristics of biological suspensions such as activated sludge properly. In the framework of this study, it was confirmed that the permeate flux declines rapidly during the first stage of filtration until an equilibrium of particle deposition and entrainment is reached. The steady-state permeate flux was found to increase with an increase in cross-flow velocity, a decrease in solid concentration, a decrease in particle size (for this ratio of particle to pore diameter) and a decrease in apparent viscosity of the suspension. However, the equilibrium permeate flux was not affected by variations in TMP, which is in agreement with the limiting flux theory.     

Microfiltration of apple juice using inorganic membranes: Process optimization and juice stability

Crossflow membrane microfiltration of low-pectine raw apple juice was studied using inorganic membranes (TECH SEP Carbosep®, Lyon, France) having a nominal pore size of 0.2 μm. Permeate flux was measured at different operation conditions (trans-membrane pressure between 100 and 500 kPa, feed velocities between 1 and 6 m/s, and temperatures of 293, 298 and 323 K). Some concentration experiments were made in order to study the rejection of pectins and polyphenols at different VCR (volume concentration ratio) values. Final stabilization tests were carried out to analyze the long-term clarified juice behaviour.     

操作条件对γ-Al2O3膜分离性能的影响

通过正交实验探讨了酸性条件下,温度、压力、PH值、流速、浓度对γ-Al2O3管式多孔膜渗透通量和Mg2+的截留率的影响。实验采用溶胶–凝胶法自制管式纳米孔膜和错流循环过滤方式。结果表明,操作压力和温度对膜通量的影响显著,同时压力及pH对截留率影响显著,而酸性环境下有利于γ-Al2O3多孔膜对阳离子的脱除。     

Modeling of fouling layer deposition in cross-flow microfiltration during tomato juice clarification

The effect of parameters, such as transmembrane pressure and axial flow rate, on membrane fouling during tomato juice clarification were studied by cross-flow microfiltration using flat sheet polyvinylidenefluoride membranes. The effect of fouling on permeate flux was modeled using a classical constant pressure dead-end filtration equation and its modified form for cross-flow filtration. The main physico-chemical properties of tomato juice were evaluated. The clarified juice was very similar to the feed except for insoluble solids and lycopene, which were concentrated in the retentate. Cake formation was identified as the main reason for flux decline. At different axial flow rates, the fouling mechanism evolves from cake filtration to an intermediate pore blocking mechanism with increasing pressure.     

Boron removal from seawater using high rejection SWRO membranes — impact of pH, feed concentration, pressure, and cross-flow velocity

The main objective of this work was to investigate boron removal from seawater using two commercial high rejection SWRO membranes. The impact of solution pH, feed concentration, pressure, and cross-flow velocity on boron rejection and permeate flux was determined. The membranes used were the Toray™ UTC-80-AB and Filmtec™ SW30HR. A lab-scale cross-flow flat-sheet configuration test unit was used for all RO experiments. Seawater sample was collected from the Mediterranean Sea, Alanya-Kızılot shores, south Turkey. For all experiments, mass balances were between 91% and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Operation modes did not have any impact on boron rejection, indicating that boron rejection were independent of feedwater boron concentrations up to 6.6 mg/L. For both membranes, much higher boron rejection were obtained at pH of 10.5 (>98%) than those at original seawater pH of 8.2 (about 85–90%). Permeate boron concentrations less than 0.1 mg/L were easily achieved at pH 10.5 by both membranes. The dissociated boron species are dominant at this pH, thus both electrostatic repulsion and size exclusion mechanisms are responsible for the higher boron rejection. The rejection of salts in seawater did not correlate with boron rejection at constant conditions. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5, which may be partially explained by membrane fouling and enhanced scale formation by Mg and Ca compounds from concentration polarization effect at higher pH values. While somewhat higher boron rejection was found for one membrane type as the pressure was increased from 600 to 800 psi, increasing pressure did not affect boron rejection for the other membrane. Feed flowrate thus the cross-flow velocity (0.5–1.0 m/s) did not exert any significant impact on boron rejection at constant conditions.     

纳滤分离中性溶质的截留分子量参数细孔模型

基于纳滤膜截留分子量（MWC）所对应的分子Stokes半径(rs)与膜的等效细孔半径(rp)相等的假设,通过建立rs与分子量(MW)之间、rp与MWC之间的定量关系方程,并以立体阻碍－细孔模型（SHP）和Spiegler-Kedem模型为基础,组建了一个以截留分子量为特征参数的纳滤分离中性溶质的细孔模型（MWC-SHP）。通过NF270纳滤膜对葡萄糖和蔗糖的透过实验,采用MWC-SHP模型对NF270纳滤膜的开孔率与膜厚之比（Ak/Δx）和rp进行了估算,估算结果同SHP模型一致。应用MWC-SHP模型预测中性溶质分子的截留率随透过通量的变化关系,与实验结果吻合.因此,MWC-SHP模型同SHP模型一样,可用于纳滤膜结构评价和分离性能预测。与SHP模型相比,MWC-SHP模型的求解更方便,具有较好的实用性。     

超细TiO_2粉体洗涤过程中膜污染和再生方法研究

针对陶瓷膜洗涤超细TiO2粉体中Cl-的过程,确定了适合的跨膜压差和膜表面流速,并采用阻力系列模型分析膜污染机理,确定有效的膜再生方法。此过程渗透通量随跨膜压差和膜表面流速的增长而增长,但是增长幅度减缓。合适的跨膜压差和膜表面流速分别为0.10—0.15 MPa和2.0 m/s;主要的膜污染来自粉体在膜表面的沉积;单一的化学和物理清洗方法无法达到理想的清洗效果,采用纯水浸泡、超声波清洗和质量分数0.5%的HCl清洗可使纯水通量恢复至新膜的72%以上,且多次的清洗效果稳定。     

基于CFD的恒通量陶瓷膜厚度设计

膜厚度对膜渗透性能有着显著影响。本文结合Navier-Stokes公式和Darcy定律对恒通量膜的膜厚度沿程分布进行了模拟计算。膜通道内的主体流动采用Navier-Stokes公式来描述,多孔介质内的流动采用Darcy定律来描述,多孔介质比阻采用Konzey-Carmen方程来计算。结果表明,膜厚度的沿程分布趋近于线性分布,并随操作压力、错流速率、操作温度的变化而变化。错流速率对膜厚度分布的影响尤为显著,而压力和温度的影响较小。在不同的错流速率下,要实现恒通量操作,必须有合适的膜厚沿程分布的膜。本计算结果为恒通量膜的制备、应用提供了依据。     

Effect of operating parameters on permeate flux decline caused by cake formation — a model study

A phenomenological model employing cake formation theory has been developed for describing permeate fluxdecline in cross-flow membrane filtration. In the model the physicochemical parameters, which are often difficult to estimate, were excluded. Instead, the flux decline due to cake formation caused by inorganic scaling/precipitation was related to the operating parameters for fouling prediction. The processes of solute deposition on membrane surface and its re-dissolution back to the bulk phase were modeled to estimate dynamic cake formation and permeate flux profiles. The modeled results show that the permeate flux declined rapidly at the early stage of cake formation, then gradually leveled off as time progressed, and eventually reached a steady-state “ultimate” flux when the rate of solid deposition was balanced by back dissolution. Sensitivity analyses show that an increase of cross-flow velocity from 0.06 to 0.14 m/s increased the ultimate flux from 0.016 m/h to 0.035 m/h. Membrane permeability and transmembrane pressure (400-750 kPa) affected the initial flux but not the ultimate flux. The flux decline pattern strongly depended on the specific cake resistance, which affects the time to reach steady state but not the ultimate flux. Verification of the model with data in the literature showed excellent agreement.