Mass transfer enhancement in the Membrane Aromatic Recovery System (MARS): theoretical analysis

This work investigates three different models describing mass transfer enhancement by a reversible and instantaneous second-order chemical reaction. The three models are applied to the study of mass transfer phenomena occurring in a membrane process for recovery of organic chemicals, the Membrane Aromatic Recovery System (MARS). Typical MARS operating conditions are used as model inputs, and the results obtained are used to assess the degree of complexity that should be taken into account in describing the mass transfer phenomena. The most complex model derived (N-P model) accounts for chemical reaction reversibility and the Nernst-Planck effect created by ionic species and is solved numerically. Following Olander model for a second order reversible instantaneous reaction model is proposed, for which we derive an analytical solution in terms of bulk solution properties. Finally, the simplest model follows the analysis of Hatta, assuming irreversible chemical reaction and neglecting the Nernst-Planck effect. The reversibility of the reaction is shown to be important, while N-P effects are negligible. The Olander model is recommended for use in describing the mass transfer phenomena. The models developed can be applied further to other processes of similar type.     

甲苯-TNT-水体系膜萃取传质特性的研究

以甲苯-TNT-水体系为对象,对膜萃取过程进行了研究,求取了该体系膜萃取过程的分传质系数关联式,并通过实验进行了验证.结果表明,在实验的操作范国内,所得的分传质系数关联式相对偏差在10%以内,关联精度是令人满意的.     

Modeling extraction separation of Cu(II) in hollow-fiber modules

The mass transfer problems in the hollow-fiber membrane extractor module with concurrent- and countercurrent-flow were investigated theoretically and experimentally in this study. A two-dimensional mathematical model of the hollow-fiber membrane extractor module was developed theoretically and the shell side flow described by Happel's free surface model was taken into account. The analytical solution is obtained using an eigenfunction expansion in terms of the power series and an orthogonal expansion technique. The theoretical predictions were represented graphically with the mass-transfer Graetz number (Gz), flow pattern and packing density (φ) as parameters and the theoretical results were also compared with those obtained by experimental runs. The highest extraction rate, extraction efficiency and mass transfer efficiency can be achieved by arranging the packing density φ=0.3. The results show that the device performance of the countercurrent-flow device is better than that of the concurrent-flow device. The experiments of the extraction of Cu²⁺ by using D2EHPA with PVDF hollow fibers is also set up to confirm the accuracy of the theoretical predictions. The accuracy of the theoretical predictions for concurrent- and countercurrent-flow are 5.87×10^-2≤E₁≤6.69×10^-2 and 2.46×10^-2≤E₁≤3.48×10^-2, respectively, for Gz_a=40.8.     

Performance of hollow fiber supported liquid membrane on the extraction of mercury(II) ions

The extraction and recovery or stripping of mercury ions from chloride media using microporous hydrophobic hollow fiber supported liquid membranes (HFSLM) has been studied. Tri-n-octylamine (TOA) dissolved in kerosene was used as an extractant. Sodium hydroxide was used as a stripping solution. The transport system was studied as a function of several variables: the concentration of hydrochloric acid in the feed solution, the concentration of TOA in the liquid membrane, the concentration of sodium hydroxide in the stripping solution, the concentration of mercury ions in the feed solution and the flow rates of both feed and stripping solutions. The results indicated that the maximum percentages of the extraction and recovery of mercury ions of 100% and 97% were achieved at the concentration of hydrochloric acid in the feed solution of 0.1 mol/l, the concentration of TOA at 3% v/v, the concentration of sodium hydroxide at 0.5 mol/l and the flow rates of the feed and stripping solutions of 100 ml/min. However, the concentration of mercury ions from 1–100 ppm in the feed solution had no effect on the percentages of extraction and recovery of mercury ions. Thus, these results have identified that the hollow fiber supported liquid membrane process has high efficiency on both the extraction and recovery of mercury (II) ions. Moreover, the mass transfer coefficients of the aqueous phase (k _i ) and membrane or organic phase (k _m ) were calculated. The mass transfer coefficients of the aqueous phase and organic phase are 0.42 and 1.67 cm/s, respectively. The mass transfer coefficient of the organic phase is higher than that of the aqueous phase. Therefore, the mass transfer controlling step is the diffusion of the mercury ions through the film layer between the feed solution and the liquid membrane.     

Recovery of 2,4‐dichlorophenol from acidic aqueous streams by Membrane Aromatic Recovery System (MARS)

This study describes the successful recovery of 2,4‐dichlorophenol (DCP) from wastewater using the Membrane Aromatic Recovery System (MARS). In the MARS process a non‐porous membrane separates a wastewater stream and a stripping solution. DCP is extracted from the wastewater and concentrated in its ionic form in the stripping solution, with pH ? pK_a DCP. The MARS extraction stage was operated in batch mode with the stripping solution placed inside, and the wastewater stream outside, the membrane tubes. Advantages of this configuration are avoidance of membrane blockage, reduction of stripping solution volume and operational flexibility. The stability and mass‐transfer characteristics of two different membrane materials, poly(dimethylsiloxane) (PDMS) and ethylene–propylene diene terpolymer (EPDM), were tested in DCP solutions with different acidities in order to simulate real industrial waste streams. EPDM exhibits one order of magnitude lower mass‐transfer rates than PDMS (1.4 × 10^?7 m s^?1 vs 20 × 10^?7 m s^?1 at 30 °C and 2.4 × 10^?7 m s^?1 vs 39 × 10^?7 m s^?1 at 60 °C), however its higher resistance to acid attack provides higher membrane lifetimes. This can be crucial for MARS processes treating real acidic industrial wastewater. A 97% recovery of DCP with a water content of 15 wt% was obtained upon neutralisation of the stripping solution. Copyright © 2004 Society of Chemical Industry     

Mass Transfer Investigation of Liquid Membrane Transport of Gold (III) by Methyl Isobutyl Ketone Mobile Carrier

Extraction of Au^III ions by an emulsion liquid membrane (ELM) system with methyl isobutyl ketone (MIBK) as the mobile carrier and also liquid‐liquid extraction of Au^III from aqueous solutions have been studied. Experiments on the transport of the gold ions in a liquid‐liquid extraction system and stripping of the extracted ions from the organic phase as well as the extraction by a three‐phase W/O/W emulsion liquid membrane system have been performed. The results showed that even when the distribution coefficient of the diffusing species in the phases is small, the extraction by emulsion liquid membranes would be an effective process. A first‐order extraction rate was proposed and examined for the extraction system.     

Separation of As(III) and As(V) by hollow fiber supported liquid membrane based on the mass transfer theory

Separation of As(III) and As(V) ions from sulphate media by hollow fiber supported liquid membrane has been examined. Cyanex 923 was diluted in toluene and used as an extractant. Water was used as a stripping solution. The extractability of As(V) was higher than As(III). When the concentration of sulphuric acid in feed solution and Cyanex 923 in liquid membrane increased, more arsenic ions were extracted into liquid membrane and recovered into the stripping solution. The mathematical model was focused on the extraction side of the liquid membrane system. The mass transfer coefficients of the aqueous phase (k _i ) and organic phase (k _m ) are 7.15×10⁻³ and 3.45×10⁻² cm/s for As(III), and 1.07×10⁻² and 1.79×10⁻² cm/s for As(V). Therefore, the rate-controlling step for As(III) and As(V) in liquid membrane process is the mass transfer in the aqueous film between the feed solution and liquid membrane. The calculated mass transfer coefficients agree with the experimental results.     

渗透模式影响纳米涂层修饰陶瓷微滤膜分离性能的研究

研究了膜分离技术处理含油废水存在因油滴变形引起的膜堵塞问题。为减少膜污染,使用在市场上销售氧化铝微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,具有良好的效果。考虑其工业应用条件,重点研究了循环模式（模拟大量废水处理）和浓缩模式（模拟少量废水处理）对膜渗透通量的影响。结果表明：循环模式下料液的油浓度为恒定的,纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m／s时,修饰陶瓷膜的最大渗透通量为280L／（m^2·h）,油截留率为96．4％。在浓缩模式下,料液的油浓度随渗透液的排出呈指数性增加,随着油浓度的增加,渗透通量持续衰减,油截留率持续上升。当油浓度达到一定程度后,修饰陶瓷微滤膜不能有效地实现稳定含油废水的油水分离。     

Mass transfer modeling of membrane carrier system for extraction of Ce(IV) from sulfate media using hollow fiber supported liquid membrane

A theoretical and experimental study on the extraction and stripping of Ce(IV) ions from sulfate media using microporous hydrophobic hollow fiber supported liquid membrane has been performed. The experiments were made in the recycling mode. Tri-n-octylamine (TOA) was used as extractant diluted in kerosene and sodium hydroxide was use as strip solution. The mathematical model focused on the extraction side of a liquid membrane system. The aqueous feed mass transfer coefficient (k_i) and the organic mass transfer coefficient (k_m) which were calculated from the model were 9.47 X 10^-2 and 6.303 cm/s, respectively. Therefore, the rate controlling step is the diffusion of the cerium complex across a liquid membrane. In addition, the mass transfer modeling was performed and the validity of the developed model was evaluated with experimental data and found to tie in well with the theoretical value when the concentration of TOA was higher than 5% (v/v).     

Viability study of different reverse osmosis membranes for application in the tertiary treatment of wastes from the tanning industry

The tanning industry uses large quantities of water and produces a correspondingly large amount of wastewater with high levels of salts and organic materials. Before these wastewaters can be eliminated, they must be submitted to a suitable depuration treatment. However, conventional treatments such as those used for urban wastewater are not able to reduce the salt content sufficiently and new methods need to be studied in the light of new technologies. In this aspect, membrane technology is increasingly used as a separation technique in chemical and environmental engineering, including desalination, selective separation and wastewater treatment. In this paper, we describe a comparative study of six different reverse osmosis membranes, which were tested for their ability to reduce the salt content in the tertiary treatment after the elimination of chromium salts and organic matter of an effluent from a pilot plant for treating industrial wastewater from the tanning industry to reach the legal levels established for their safe disposal. The membranes were checked using a 3×10⁻³ m² flat cell, where the concentrated streams were recirculated to the feed reservoir.     

Selective Separation of Arsenic(III) and (V) Ions with Ferric Complex of Chelating Ion-Exchange Resin

Abstract

Trace levels of aqueous arsenic(III) and (V) ions were adsorbed selectively onto the ferric complex of a chelating resin, Uniselec UR-10. The adsorption was markedly dependent upon the pH of the aqueous phase. The distribution ratio and the specific adsorption capacity of arsenic(III) were 23,000 and 0.47 mmole/g, respectively, at the optimum pH for the adsorption, 9.2. The corresponding values of arsenic(V) were 22,000 and 0.53 mmole/g at the optimum pH 5.5. In the column operation the adsorption of the arsenic ions was also dependent upon the flow velocity and the size of the resin particle. A velocity of 60 cm/hr and 100 to 200 mesh size afforded satisfactory results. Adsorbed arsenic was recovered quantitatively by eluting the resin with 2 N hydrochloric acid, where the complexed iron was also eluted. A trace level of arsenic in wastewater from a geothermal power plant was successfully separated in the presence of a large excess of diverse cations and anions. Trace arsenic in natural seawater was also successfully preconcentrated 100 to 200 times over the original level by adsorption onto the ferric resin followed by elution with hydrochloric acid.     

Recovery of carbon monoxide from flue gases by reactive absorption in ionic liquid imidazolium chlorocuprate(I):Mass transfer coefficients

Recovery of carbon monoxide from flue gases by selective absorption of carbon monoxide in an imidazolium chlorocuprate(I) ionic liquid is considered in this work as an alternative to the use of molecular volatile solvents such as aromatic hydrocarbons. The present work evaluates the CO mass transfer rates from the gas phase to the ionic liquid solutions in the absence of chemical reaction. To that end, carbon dioxide was employed as an inert model gas and absorption experiments were performed to assess the influence of different process variables in a batch reactor with flat gas–liquid interface. The experimental mass transfer coefficients showed significant var-iation with temperature, (3.4–10.9) × 10-7 m·s-1 between 293 and 313 K; stirring speed, (10.2–33.1) × 10-7 m·s-1 between 100 and 300 r·min-1;and concentration of copper(I), (6.6–10.2) × 10-7 m·s-1 between 0.25 and 2 mol·L-1. In addition, the mass transfer coefficients were eventually found to follow a poten-tial proportionality of the type kL∝μ-0.5 and the dimensionless correlation that makes the estimation of the mass transfer coefficients possible in the studied range of process variables was obtained:Sh=10-2.64·Re1.07·Sc0.75. These results constitute the first step in the kinetic analysis of the reaction between CO and imidazolium chlorocuprate(I) ionic liquid that determines the design of the separation units.     

Effects of the boundary layer and interfacial reaction on the time lag in supported liquid membranes

A mathematical model is proposed to describe the effects of boundary layer resistance and interfacial reaction on the time lag in supported liquid membranes for metal ion separation. The model shows that the presence of boundary layer resistance and interfacial reaction delays the time-lag, compared with the limiting case that rapid equilibrium at the interfaces and negligible boundary layer resistance are assumed. Calculated result describes the expected trend and the model equation allows one to predict the lumped parameters which represent the ratios of the diffusion time in the membrane to the characteristic time for boundary layer transfer and interfacial reactions.     

膜分离技术在石化工业中的应用与研究

概述了膜分离技术在石油化学工业中的应用及其所进行的研究。     

The capture and release of biomass using a high voidage fibrous filter (marked revision)

This paper is concerned with the capture and subsequent release of wastewater biomass using a high voidage filter. A semi-automated experimental rig was developed where both the hydraulic response of the filter and the capture of biomass were investigated as a function of throughput and filter voidage. The hydraulic response of the clean filter was found to correlate well with the Jackson-James permeability model for gas filtration, and the hydraulic measurements give information about the average shear stresses present during the initial stages of biomass deposition. Biomass capture in the filter was achieved for low Reynolds number throughput followed by a characteristic breakthrough of particles to the effluent stream. Subsequent release of biomass and regeneration of the filter was accomplished by high intensity oscillation of the fluid in the filter, causing the re-suspension of the biomass, which could then be drained from the column. The performance of the filter is evaluated in terms of its cycle and energy efficiency, and its potential for scale-up.     

The Study on the Ceramic Membrane Wastewater Reuse System with Pre-Ozonation and Coagulation

A new wastewater reuse system using ozonation, coagulation and MF ceramic membrane (0.1 μm) filtration was developed. The testing was performed using secondary effluent treated at the wastewater treatment plant (WWTP) in Tokyo, Japan. The volume of treated water by the pilot study equipment is about 90 m³/day. The combination of pre-ozonation and coagulation processes achieves continuous stable membrane filtration with flux of 4m³/m²/day (167 LMH). A stable membrane filtration could be maintained by controlling ozone dosing rate depending on secondary effluent (raw water) quality fluctuation. The COD (Mn) removal ratio in raw water was 50 to 60%, and the color removal ratio satisfied 80% or higher. The quality of the treated water that was obtained from our pilot study was better than the California's standards.     

Immersed Membrane BioReactor (IMBR) for treatment of combined domestic and dairy wastewater in an isolated farm: An exploratory case study implementing the Facet Analysis (FA)

In many regions dairy farms and milk processing industries, discharge large quantities of their wastes to the surroundings which pose serious environmental risks. With the purpose of treating the combined dairy and domestic wastewater from a small dairy farm in the Negev Desert of Israel, the use of a recent emerging technology of Immersed Membrane BioReactor (IMBR) was evaluated over the course of 500 test hours, under a variety of wastewater feed quality conditions.Field experiments were performed at the Kornmehl farm, an isolated dairy farm located 30 km south of Beer-Sheva, in the Negev Desert of Israel. The operating conditions for this experiment included constant product flow of 7 (L/h)], and the transmembrane pressure was increased smoothly during the experiment from 0.05 to 0.13 bar. Temperatures ranged between 30 °C and 37 °C, pH ranged between 4 and 9, TSS varied between 353 mg/L to 1000 mg/L and COD changed from 900 mg/L to 12,800 mg/L.The overall performance of a pilot-scale Ultrafiltration (UF) IMBR process for a combined domestic and dairy wastewater was analyzed based on the Facet Analysis (FA) method. Preliminary results of the FA model indicate: (i) the Trans-Membrane Pressure (TMP); the pH and the temperature do not have an effect on the performance of the permeate normalized flux and on the specific normalized flux, and; (ii) the bioreactor is characterized by high concentration of organic matters and it can be estimated that the IMBR normalized flux decline is dependent on other variables (air blower performance, backwash procedure and chemical cleaning).