Showing papers in "Separation and Purification Reviews in 2015"

Inorganic Nanomaterials in Polymeric Ultrafiltration Membranes for Water Treatment

Abstract: Due to the rapid expansion of nanotechnology and the increasing range of nanomaterials under production and development, a significant amount of research interest has been dedicated to the innovative exploitations of various inorganic nanomaterials in environmental applications. The incorporation of inorganic nanomaterials as fillers within a polymeric matrix has expanded opportunities to produce a multifunctional nanocomposite membrane that is capable of performing tasks beyond separation alone. The architectures and performances of these nanocomposite membranes have triumphed over polymeric membranes to overcome the underlying conspicuous drawbacks. This review aims to shed more light on the roles of inorganic nanomaterials in advancing the characteristics and separation performance of polymeric ultrafiltration membranes. Inorganic nanofillers such as metal oxides, metals and carbon-based materials are incorporated into polymeric membranes to render the desired properties for ultrafiltration separations...

Organic Solvent Nanofiltration in Pharmaceutical Industry

Abstract: Organic solvent nanofiltration (OSN) is a promising energy and waste efficient unit process to separate mixtures down to a molecular level, which gained attention in the pharmaceutical industry, in particular in the process development of Active Pharmaceutical Ingredients (APIs). This article focuses on all aspects related to OSN (i.e., membrane materials, commercial membranes, transport theories, applications) to understand the role of this technology in pharmaceutical industry. The most important results in the last five years on OSN applications in the process development of APIs are reviewed extensively.

Membranes with Great Hydrophobicity: A Review on Preparation and Characterization

Abstract: Membranes are commonly designed with great hydrophilicity or hydrophobicity to promote or prohibit the transportation of water, respectively. There are vast applications of hydrophobic membranes such as filtration, gas separation, membrane gas absorption, pervaporation, membrane distillation and more that cannot be attained with hydrophilic membranes. However, the development of hydrophobic membranes was relatively slow in the past, as membrane technologists and researchers were more interested in reducing membrane hydrophobicity for permeability enhancement or fouling control in the aqueous separation. Thus, literature related to hydrophobic membranes has not been reviewed elsewhere. This review reported on the characterization and preparation methods for hydrophobic membranes. Hydrophobic ceramic membranes are commonly prepared by chemical modification. Besides using different types of chemicals, the membrane surface is roughened to enhance its hydrophobicity. For polymeric membranes, great hydrophobici...

Characterization Methods of Thin Film Composite Nanofiltration Membranes

Abstract: This review provides a comprehensive survey on the characterization methods used to study the properties and performances of thin film composite nanofiltration (NF) membranes in water separation processes. In general, the intrinsic properties of NF membranes are characterized with respect to chemical properties and physical properties using various analytical instruments. For instance, FTIR spectroscope, zeta potential analyzer, XPS, XRD, and NMR spectroscope are some of the widely used instruments to evaluate the membrane chemical properties while SEM, FESEM, TEM, AFM, contact angle goniometer, and positron annihilation spectroscopy are those that have been commonly employed to study the membrane structural properties. With respect to permeability and selectivity, NF membranes are generally characterized through filtration experiments using appropriate feed properties under specific testing conditions. Furthermore, this review also covers the characterization techniques used to study the resistance of NF...

State-of-the-Art Technologies for Separation of Azeotropic Mixtures

Abstract: Azeotropic separation technologies have been classified broadly into two major categories, i.e., distillation and membrane processes. Because normal distillation has limitations for azeotropic mixtures, enhancements have been proposed that either introduce a third component serving as an entrainer in extractive and azeotropic distillation processes or apply a pressure swing distillation system. Among the membrane processes, pervaporation was reported to be most promising for azeotropic separations. More recently, an approach known as process intensification has been proposed for combining multiple processes into single units such as a dividing wall distillation column or exploiting sonication phenomena to break an azeotrope in an ultrasonic distillation system. This article reviews the state-of-the-art technologies covering all the separation techniques mentioned here. Existing techniques are appraised, and technology gaps are identified. Based on these insights, areas for further development are suggested, aiming at satisfying the process objectives by inherently safer, environmentally benign and economically more attractive techniques.

Recovery and Purification of Crude Glycerol from Vegetable Oil Transesterification

Abstract: This article reviews the purification techniques involved in producing high-purity glycerol in the biodiesel industry. Utilization of glycerol by-products (contains less than 50 wt.% of glycerol and the remaining contents are water, salts, unreacted alcohol and catalyst) in biodiesel production affords greener and less costly processes. Research has focused on several purification steps that are capable of producing high-purity glycerol. Various new techniques for purifying glycerol promise better quality and lower cost and technologies are required to fulfil increasing worldwide demand. Neutralization, ultrafiltration, the use of ion exchange resins, vacuum distillation and other methods have been utilized in single or multiple stages. Recent studies have demonstrated that the combination of more than one technique produces high-purity glycerol (>99.2%). Purifications cost can be as low as 0.149 USD$/kg. For many applications, high-purity glycerol is more useful. In some cases, it is even necessary, part...

Applications of Graphene-Based Materials in Solid-Phase Extraction and Solid-Phase Microextraction

Abstract: Graphene, a carbon nanomaterial made of a two-dimensional layer of a single atome thick with 100% sp2 hybridization C, has exhibited excellent adsorption capacity for sample preparation in analytical science. This review will provide an overview of the applications of graphene-based materials in sample preparation based on π-π interaction between the graphene layers and aromatic containing analytes. In the field of sample preparation, solid-phase extraction (SPE) is performed passing the sample solution onto a graphene containing cartridge for selective retention of analytes. Solid-phase microextraction (SPME) is performed using small graphene-coated fibers plunged into the liquid sample to extract analytes later desorbed by heat in a gas chromatography injector. In this review, recent applications of graphene and its composites for SPE and SPME are summarized, and future applications of graphene and graphene-based materials are discussed.

Simulated Moving Bed Strategies and Designs: From Established Systems to the Latest Developments

Abstract: The simulated moving bed (SMB) technology has evolved significantly since its inception. The appearance of several variants to conventional SMB has led to better performance in productivity and product purity, and lower operating costs, thus creating new opportunities for different applications. This trend is clearly visible in the increasing number of papers and patents published in this field in recent years. This review aims to gather and discuss several modifications and operation modes that have been proposed, from the most well-known Varicol and PowerFeed to the latest Intermittent-SMB and variable external stream systems, giving particular emphasis to innovations and applications of each SMB strategy. SMB valve designs are also covered in this article for their importance in the application of the operation modes discussed, which require ever more flexible units capable of variable switch times, column expandability, zone bypasses, and reduced solvent consumption while still avoiding contamination ...

Water Stability and Competition Effects Toward CO2 Adsorption on Metal Organic Frameworks

Abstract: Metal-organic frameworks (MOFs) are compounds consisting of metal cations and organic anions organized in porous three-dimensional structures. MOFs exhibit higher selective adsorption performance for CO2-containing gas mixtures than traditional porous materials, making them promising candidates in CO2 capture. However, it is important to understand H2O effects on CO2 adsorption in MOFs before making them more applicable in the process designed to separate CO2 from wet gas mixtures. In this review, we summarize the current state of MOF development for CO2 adsorption. The stability of MOFs toward water and the strategies of enhancing the water stability for MOFs were discussed. The different effects of water on the CO2 adsorption and separation performance and the mechanism of the effects were analyzed.

Adsorption of Cationic Dyes onto Bentonite

Abstract: The removal of dyes from wastewater effluents is a challenging issue in environmental engineering. Among the techniques employed, adsorption technology is generally considered highly efficient and industrial bentonite clay has been extensively used for this purpose. The aim of this study is the systematic and comparative presentation of the available information on the adsorption of cationic dyes from aqueous solution onto raw or modified bentonites. The review outlines the bentonite modification methods and presents a list of isotherm and kinetic models used for the interpretation of adsorption. A brief description of each article and information on the type and the characteristics of the adsorbent are given in tables. In addition, data is included concerning single and competitive adsorption of basic dyes on bentonite. Experimental conditions are outlined and the kinetic and isotherm parameter values of proposed models are listed in tables. The effect of various factors on the adsorption efficiency is d...

Solvent Extraction for the Separation of Zr and Hf from Aqueous Solutions

Abstract: The present review mainly focused on the recent extraction and separation studies of Zr and Hf from various acidic aqueous solutions using liquid-liquid extraction. The general purpose associated with the use of liquid-liquid extraction, research on the recent developments from the view point of technological applications and chemistry involved in liquid-liquid extractions of Zr and Hf from acidic aqueous solutions is particularly described. In addition, the well-known conventional methodologies devoted to the selective extraction and separation of Zr and Hf metal ions is presented. The involved extraction reaction in the given system is also discussed and the data provided is systematically classified according to their structural and nature of the extractants participated. The extracted speciation or complexation of metal ion in the organic phases have also been mentioned, types of species responsible for metal extraction, whenever possible, is referred.

Liquid Phase Microextraction Techniques as a Sample Preparation Step for Analysis of Pesticide Residues in Food

Abstract: Many conventional sample preparation methods are tedious, time-consuming, and use high volume of organic solvent. Minimized sample preparation methods, which use significantly smaller volume of organic solvent, represent an alternative to these methods. Three liquid phase microextraction (LPME) techniques: single drop microextraction, dispersive liquid-liquid microextraction, and hollow fiber liquid phase microextraction and a variety of its modifications are reviewed. Advantages and limitations are discussed. Extraction parameters influencing the extraction efficiency are evaluated. Applicability of LPME methods for pesticide residues analysis in various food matrices is overviewed. Determination of low-level pesticide residues was realized predominantly by chromatographic methods utilizing selective detectors. Powerful features of mass spectrometric detection for identification and determination of pesticide residues are pointed out.

Issues and Challenges in the Development of Deca-Dodecasil 3 Rhombohedral Membrane in CO2 Capture from Natural Gas

Abstract: Removal of CO2 from natural gas using a membrane-based process has been adopted on an industrial scale, and about 200 membrane separation plants have been installed all over the world. In industry, inorganic membranes are preferred over the polymeric and mixed matrix membranes in CO2 separation from natural gas because of their good chemical stability and high separation performance. Among all inorganic membranes, deca-dodecasil 3 rhombohedral zeolite (DDR) membrane exhibits the highest selectivity in CO2 separation from natural gas. However, synthesis of DDR membranes requires a long duration, with a minimum of 25 days. Therefore, reduction of duration in the synthesis of the DDR membrane remains a challenging issue. In this review, separation performance of polymeric, mixed matrix and inorganic membranes are compared. Synthesis methods of DDR membranes and their performance in CO2 separation reported by various researchers are discussed. The challenges and issues related to the formation of DDR membrane...

Electrodialysis in Aqueous-Organic Mixtures

Abstract: This review investigates the effects of hydro-organic solvents on ion exchange membranes used in conventional electrodialysis. The thermodynamics of electrodialysis is first presented in relation to operation in purely aqueous solutions, where the Donnan potential describes the equilibrium partitioning at the membrane/solvent interface. The mass transfer kinetics through the membrane are described using the Nernst–Planck equation, and concentration polarization describes the mass transfer resistance in the solution boundary layer. Each of these relationships is found to change significantly as the organic concentration in the solvent is increased and the system consequently deviates from ideality. The extent of membrane swelling in these mixed solvents is also critical, as it determines the diffusion coefficient of both ionic and non-ionic species within the membrane structure.

Kinetic Modeling of Pure and Multicomponent Gas Permeation Through Microporous Membranes: Diffusion Mechanisms and Influence of Isotherm Type

Abstract: The main transport mechanisms involved in pure and multicomponent gas permeation through real microporous membranes are reviewed in this article. They include viscous flow, Knudsen diffusion, bulk diffusion (in mixtures), surface diffusion, and activated gaseous diffusion. The individual contribution of each mechanism may be discriminated from permeation experiments, and can be used to detect the occurrence of defects in the membrane structure. In the case of multicomponent mixtures, the milestone theory of Maxwell–Stefan can be advantageously applied to model the transfer mechanisms embodied. The separation of mixtures can be predicted from data measured for pure gases; here, computer simulations may provide relevant information concerning the loading influence upon diffusivities. With respect to surface diffusion, equilibrium plays a major role in the process, which requires accurate isotherms to compute the corresponding Maxwell–Stefan thermodynamic factors. New single/multicomponent factors are derive...

Current Trends in Separation and Purification of Fatty Acid Methyl Ester

Abstract: In a recent scenario, fatty acide methyl esters (FAMEs) as sustainable, biodegradable, and clean energy has attracted, worldwide, renewed, and growing interest nowadays, chiefly due to development in FAME fuel and ecological pressures that include climatic changes. In the manufacturing of FAME from biomass, separation, and purification of FAME is a most important aspect. As per Traditional technologies used for FAME separation such as gravitational settling, decantation, filtration, and FAME purification such as water washing, acid washing, washing with ether and absorbents have proven to be not efficient, time and energy consumptive, and less cost effective. The involvement of membrane reactor and preparative membrane proves more advantageous for the separation and purification of FAME. In this article, both traditional and most recent membrane technologies used in refining FAME have been critically reviewed. Activated carbons prepared from, e.g., spent tea waste were used for the purification of crude F...