Membrane-based Separation Processes Research Articles

A comprehensive review on biodiesel purification and upgrading

Serious environmental concerns regarding the use of fossil-based fuels have raised awareness regarding the necessity of alternative clean fuels and energy carriers. Biodiesel is considered a clean, biodegradable, and non-toxic diesel substitute produced via the transesterification of triglycerides with an alcohol in the presence of a proper catalyst. After initial separation of the by-product (glycerol), the crude biodiesel needs to be purified to meet the standard specifications prior to marketing. The presence of impurities in the biodiesel not only significantly affects its engine performance but also complicates its handling and storage. Therefore, biodiesel purification is an essential step prior to marketing. Biodiesel purification methods can be classified based on the nature of the process into equilibrium-based, affinity-based, membrane-based, reaction-based, and solid-liquid separation processes. The main adverse properties of biodiesel – namely moisture absorption, corrosiveness, and high viscosity – primarily arise from the presence of oxygen. To address these issues, several upgrading techniques have been proposed, among which catalytic (hydro)deoxygenation using conventional hydrotreating catalysts, supported metallic materials, and most recently transition metals in various forms appear promising. Nevertheless, catalyst deactivation (via coking) and/or inadequacy of product yields necessitate further research. This paper provides a comprehensive overview on the techniques and methods used for biodiesel purification and upgrading.

A Review of Post-combustion CO2 Capture Technologies from Coal-fired Power Plants

Reducing CO2 emissions has become a worldwide research topic. Of all the sources of CO2 emissions, power plants burning fossil fuels, especially coals, account for a very large portion. For CO2 capture from existing coal-fired power plants, post-combustion technology is thus far considered the most viable method due to its “end-of-pipe” characteristic. Chemical absorption or scrubbing process is currently the technology most likely to be implemented in the near future but rather energy-intensive. Membrane-based CO2 separation process in recent years appears to be a competitive substitution for conventional chemical absorption technology. This paper reviews the basic process designs of chemical absorption and membrane-based separation processes for CO2 capture, as well as corresponding optimization methods including optimizing operational parameters, process modifications, membrane module types and so forth. In addition, some energetic and economic estimates from other researchers for these two CO2 capture technologies are summarized. It is found that membrane-based separation process does not possess obvious advantage over MEA-based chemical absorption process at the typical 90% CO2 capture degree in terms of both energy consumption and cost. Therefore, various optimization methods have not changed the fact that CCS technology will lay more burdens on power plants unless they can get enough allowances from government. In recent years, hybrid system with the target of utilizing more than one single capture technology seems to be new direction from the perspective of capture process design. However, it still needs to be further investigated.

Enhancement of synthesis gas and methanol production by flare gas recovery utilizing a membrane based separation process

Proposing novel strategies for minimization of gas flaring is currently of a great importance. Such strategies could eliminate the drawbacks of burning purge gas and even lead to higher process efficiency. Accordingly, a recovery unit based on membrane separation is proposed in the present contribution. This separation unit is aimed to remove hydrogen, carbon oxides, and methane from the purge gas. Furthermore, the recovered streams are sent to the upstream units as supplementary feeds. In this regard, the stream containing methane is sent to the steam reformer, while the hydrogen and carbon dioxide rich stream is injected into the methanol synthesis reactor. Different strategies are suggested and the best one is selected in terms of enhanced production capacities of synthesis gas and methanol. In order to implement the evaluations, a mathematical model composed of mass and heat balances is applied. Furthermore, the response surface methodology is employed to determine the optimum operating conditions. Consequently, more than 300tons/year emission of carbon dioxide is inhibited by applying the proposed configuration. Besides, more than 4.6% increase in the methanol production capacity and about 1% decrease in the stoichiometry number of product are the advancements of system working under optimum conditions.

(Invited) Plasmon-Enhanced Hybrid Materials for Global Health Solutions

New methods for scalable water desalination has been identified as the most impactful and necessary scientific technology for human prosperity in a 2015 report by the Institute for Globally Transformative Technologies, surpassing malaria vaccines, synthetic fertilizers, and improved TB drugs. Due to the climate change, rapidly expanding global population, and worldwide water scarcity, the demand for purification of non-traditional sources such as brackish and seawater with low environmental impacts is extensively growing. There is an increasingly urgent need for low-cost methods for water desalination that can effectively couple to, or piggyback on, renewable energy sources. In this talk I will describe our efforts in developing new materials to enhance the efficacy and utility of forward osmosis using new plasmonically-enhanced hybrid materials. Classical membrane-based water separation and purification processes such as forward osmosis (FO) is gaining renewed attention as a potentially low-energy alternative technique to energy intensive methods such as distillation, reverse osmosis (RO), multiple effect distillation (MED), etc. Unlike RO, the industry standard for desalination, where energy intensive hydraulic/external pressure drives water flow, here an internal pressure (osmotic) drives flow. It has the characteristics of no/low pressure operation compared to standard RO processes. Consequently, membrane fouling is potentially much less severe and thinner membranes can be used. These advantages make FO extensively applied to a variety of fields to date, which could potentially relieve the stress of freshwater scarcity. As the draw solution is one of the main contributing factors to the FO process, the lack of suitable draw agent has become the obstacle jeopardizing the real application of FO in desalination process. In general, an ideal draw agent needs to provide high osmotic pressure and expel water from itself with minimal energy input. Present FO technology relies on either non-reusable draw agents or draw agents that require complicated process for regeneration. This talk will discuss development of new classes of inorganic/organic hybrid draw agents, which exhibit high osmolalities and easy regeneration process by utilizing industrial waste heat or naturally abundant (solar, geothermal) sources. Results on the design, performance, and integration of these new draw agents will be discussed.

Surfactant-stabilized oil separation from water using ultrafiltration and nanofiltration

The treatment of oily wastewater containing well-stabilized oil emulsions remains a challenge. As gravity-based separation methods cannot effectively remove emulsified oil droplets with sizes below 10µm, water polishing steps need to be applied to reduce the organic load of the treated effluent. Membrane-based separation processes ensure high permeate quality, but are prone to fouling when treating oily wastes. Surfactants play an important role in producing well-stabilized oil emulsions, but there has been limited work on the effect of surfactants on membrane fouling. To fundamentally understand the surfactant effect on fouling, we studied the fouling of model oil (hexadecane) emulsions stabilized by anionic, cationic and nonionic surfactants in a crossflow filtration system using either ultrafiltration (UF) or nanofiltration (NF) membranes. For this, we investigated the impact of membrane surface and emulsion properties on the different fouling mechanisms observed in our experiments. UF filtration experiments revealed that emulsions stabilized with cationic surfactant quickly fouled negatively charged UF membranes due to electrostatic attraction, while anionic and non-ionic surfactants stabilized emulsions experienced less fouling. In NF filtration tests, membranes exhibited exponential fouling when filtrating all types of surfactant stabilized emulsions. Permeate quality confirms that the NF process achieves better rejection of surfactants than the UF process. However, cationic surfactants are able to pass through NF membranes because of their positive charge. When salt is added to the water, electrostatic forces collapse, and the differences between the surfactants are quenched. Our experimental results combined with theoretical calculations reveal that initial membrane fouling by emulsified oil drops is dominated by a cake layer formation. However, once a critical pressure drop across the cake layer is achieved, membrane wetting occurs, which results in irreversible membrane fouling in both UF and NF.

Production of very-high purity succinic acid from fermentation broth using microfiltration and nanofiltration-assisted crystallization

A combined cross-flow microfiltration (MF) and nanofiltration-assisted crystallization technique was successfully employed as a series of purification steps for the production of very-high purity succinic acid from fermentation broth. The membrane fouling mechanism was firstly investigated for MF system during bacterial cells removal. Resistance-in-series model was applied to evaluate the major factors that caused the decline in permeate flux. Experimental results showed that the membrane performance tended to be significantly affected by the adsorption. Separation performance of nanofiltration (NF) process was subsequently investigated for both synthetic solution, and the MF permeate. For the broth, the NF showed its usefulness for removal of impurities including proteins, macromolecules, and especially multivalent ions. In addition, dia-nanofiltration (DNF) was employed for a complete recovery of the succinic acid in the retentate after concentration mode. The removal rates for protein, and magnesium sulfate were reported at 95.61%, and 97.7%, respectively. Finally, crystallization was conducted as the final step to maximize the purity of the bio-based succinic acid product as all other organic acid by-products were presented in the mother liqour. The final purity of the succinic acid crystal was obtained at 99.18% after simple washing with cold water. In conclusion, very high purity succinic acid can be directly obtained from the realistic fermentation broth by the integration of membrane-based separation processes, and crystallization without the need for any auxiliary component.

On the optimal design of membrane-based gas separation processes

Gas-separation processes are of paramount importance for several industrial applications. In this context, membrane-based gas separation has a great innovation potential in term of limiting the energy consumption and simplifying the process operation and control. Much of the research in this field focused on parametric analyses or optimization procedures aimed at the investigation of some performance indicators, such as separation performance, energy consumption, membrane area. This work aims at developing a comprehensive method which provides criteria for the optimal design and operation of membrane gas separation processes. First, a parametric analysis is carried out, resulting in the definition of attainable regions for different process configurations and product specifications. Subsequently, a multi-objective optimization is carried out by employing a genetic algorithm that minimizes the compression energy and the required membrane area by selecting the optimal process layout, operating variables, and membrane materials.

Recent progress in polymeric hollow-fibre membrane preparation and applications

Hollow-fibre membranes are of great commercial interest, with many applications. This article reviews recent progress made – mostly during the last eight years – in polymeric materials for hollow-fibre spinning, the spinning method and the effects of spinning conditions. It was found that amongst the large number of available polymers only a limited number has been used for membrane development. Hollow-fibre surface modification and the incorporation of nanoparticles in mixed-matrix membranes have been attempted to enhance performance. Attempts have also been made to use hollow-fibre membranes in relatively novel membrane-based separation processes, such as membrane distillation and forward osmosis, and in membrane contactors. Progress in these areas is also summarised.

PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes.

A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled “green surface modification”. This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers—ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)—is presented.

ZIF-7/PDMS mixed matrix membranes for pervaporation recovery of butanol from aqueous solution

Abstract In this contribution, zeolitic imidazolate framework (ZIF-7)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) with uniformly dispersed ZIF-7 were fabricated. The homogeneous dispersion of ZIF-7 nanoparticles in PDMS matrix and better interface compatibility were characterized by SEM and EDS. PV performance reveals that the MMMs display increased total flux and the highest separation factor occurs at 20 wt% ZIF-7 loading, which were 1689 g m −2 h −1 and 66 respectively as compared to 1080 g m −2 h −1 and 51 for pure PDMS membrane when separating 1 wt% butanol aqueous solution at 60 °C. The total flux reaches 3496 g m −2 h −1 with 80 wt% butanol in permeate for the enrichment of 5 wt% butanol solution at 60 °C. The enhanced flux may result from enlarged free volume in the polymer matrix caused by the incorporation of ZIF-7 nanoparticles. Moreover, the super-hydrophobic ZIF-7 pore channels and butanol preferential permeation may contribute to the improvement of separation factor. The result also shows that there is a 21.1% reduction of energy barrier for penetrant transportation for 20 wt% ZIF-7 filled PDMS membrane as compared to pristine PDMS membrane. A long period of pervaporation experiment was also carried out to investigate the structure stability of the ZIF-7/PDMS membrane, and the MMM remains intact during the 240 h continuous operation, which is the key to industrial application for membrane-based separation process. All above indicated that ZIF-7 is a good filler to fabricate butanol permselective pervaporation membranes for butanol separation and enrichment.

Mathematical modelling of membrane gas separation using the finite difference method

Membrane gas separation has been recognized as the main technology that is used in chemical engineering for hydrogen recovery, air separation, natural gas sweetening, helium recovery, natural gas dehydration, and so on. Membrane-based gas separation processes have great potential for these industrial applications because of their environmental friendliness, energy efficiency and ease of scale up. Mathematical modelling of the membrane-based gas separation process can be useful to predict the performance of such separation processes. An improved mathematical model has been implemented in this research for the separation of a binary gas mixture using a membrane separator. The finite difference method (FDM) is applied to predict the membrane gas separation behaviour. The method is helpful as it involves the least effort and computational time because algebraic equations are used instead of differential equations. Different configurations, such as single stage and double stage, are used in this study. The results of the FDM simulation are compared with the simulation results of the model and the experimental data of several membrane systems.

Propylene/propane plasticization in polyimide membranes

Polyimides have been considered as attractive polymers to be used in membrane based separation processes to separate propylene/propane mixtures. However, propane and propylene tend to plasticize polyimide membranes. In this study, we used molecular simulation techniques to gain insight on the relationship between molecular structure and plasticization of polyimides due to the sorption of propane and propylene molecules. Three fluorinated polyimides with different backbone rigidities were considered for this purpose: 6FDA–ODA, 6FDA–DPX and 6FDA–DAM (6FDA: 4,4-hexafluoroisopropylidene-diphthalic anhydride; DAM: 2,4,6-trimethyl-m-phenylene diamine; ODA: and 4,4-oxydianiline; DPX: 2,5-dimethyl-p-phenylenediamine). A combination of molecular dynamics and Monte Carlo methods was used to estimate sorption induced changes in the polymer matrices. Structural analyses such as radial distribution function, free volume, and local dynamics analyses were carried out to better understand the plasticization mechanism. Results showed that propane and propylene sorption capacities also depend on the polymer-penetrant interactions in addition to the fractional free volume of the polymer which has been shown as the dominant factor for CO2 sorption on the same polyimides in our previous work. The polymer-penetrant interactions are more dominant for propylene than propane due to high polarizability of propylene resulting from π-electron complexation. The analysis of preferential sorption sites in both single and binary gas adsorption reveals that site preferences are altered in binary gas adsorption due to the competition between propane and propylene molecules. The dianhydride structure contain the most preferential sorption site and hence is plasticized in the single gas adsorption case, whereas, the most preferential sorption site moves to the diamine structure in case of binary sorption, especially in more flexible polyimides such as 6FDA–ODA.

Comparison between Centrifugation and Microfiltration As Primary Clarification of Bottle Gourd (Lagenaria siceraria)Juice

Centrifugation and microfiltration (MF) were used for primary clarification of raw bottle gourd juice. The optimized conditions (time and speed) of centrifugation and those of MF (transmembrane pressure drop [TMP] and cross flow rate) were determined using response surface methodology. Clarified juice was analyzed in terms of clarity, total solids, protein, polyphenol, total soluble solids, sodium and potassium. The performance of both of these methods was compared based on the quality of the clarified juice and power consumption. Microfiltered juice had enhanced clarity (97%), but polyphenol concentration was less (8 mg GAE/100 mL) compared with centrifugation (13 mg GAE/100 mL). Practical Applications Bottle gourd is a traditional medicinal plant. Its juice has tremendous therapeutic qualities including antidiabetic, anticarcinogenic and cardioprotective properties. It is a rich source of various vitamins, minerals like potassium and antioxidants like flavonoids. Therefore, extraction of bottle gourd juice and subsequent clarification followed by fractionation would lead to selective separation of medicinally and nutritionally important bioactive components. This can be attained by a primary clarification to remove undesirable higher sized molecules and suspended materials followed by a more specialized membrane-based separation process. The present work highlights a comparison of the performance of centrifugation and MF as a primary clarification of bottle gourd extract. Thus, this work has direct relevance as an initial step of final scaled up production unit.

Processing of biscuit industrial effluent using thin film composite nanofiltration membranes

Nanofiltration (NF) is a membrane-based separation process having significant potential for the treatment of industrial effluents to enable water reuse. It has the ability to remove low molecular weight trace contaminants from water, which cannot be separated by conventional treatment methods. In the present investigation, a thin film composite polyamide membrane was synthesized by interfacial polymerization technique and evaluated for the treatment of biscuit industrial effluent. The synthesized membrane was characterized using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy to elucidate structure and intermolecular interactions, crystallinity, thermal stability and cross-sectional morphology, respectively. The influence of operating parameters such as feed pressure 0–21 kg/cm2 and total dissolved solids (TDS) of 3160 ppm on water flux and impurity rejection was determined. An average flux of 11.63 L/m2 h was obtained at a constant pressure of 21 kg/cm2. The TDS, chemical oxygen demand (COD), and biochemical oxygen demand (BOD) rejections were found to be 53.62, 80, and 74%, respectively, at a water recovery of 65%. A statistical mechanical model was used to validate the experimental data. Based on this study, a detailed economic estimation for processing biscuit effluent of 1 m3/h feed capacity using commercial NF system is presented. The study revealed that the synthesized NF membrane could be an effective alternative for the treatment of various industrial effluents as well as to reduce the load on reverse osmosis process for desalination of seawater and effluent treatment through high degree of COD and BOD separation.

Minimizing structural parameter of thin film composite forward osmosis membranes using polysulfone/halloysite nanotubes as membrane substrates

Novel forward osmosis (FO) is a membrane-based separation process with significant potentials for low energy desalination. While this technology offers various benefits, overcoming its low water flux performance caused by internal concentration polarization (ICP) of solutes in porous substrates remains a challenge. This study aims at addressing this issue by introducing hydrophilic halloysite nanotubes (HNTs) into substrate made of polysulfone (PSF). The thin film nanocomposite (TFN) membranes suitable for FO applications were prepared via interfacial polymerization on the top surface of PSF-HNT nanocomposite substrates. The results obtained from filtration experiments showed that the TFN membrane prepared with 0.5wt% HNTs (TFN0.5 membrane) demonstrated the most satisfactory results by exhibiting high water permeability and low reverse solute flux. Furthermore, TFN0.5 membrane exhibited remarkably higher water flux than that of control TFC membrane in both FO (27.7 vs 13.3L/m2h) and PRO (42.3 vs 26.0L/m2h) configurations when they were tested with 10mM NaCl as feed solution and 2M NaCl as draw solution. This improvement can be ascribed to the fact that the structural parameter of TFN0.5 is much lower compared to control TFC membrane (0.37 vs 0.95mm), leading to reduced ICP effect.

Synergistic Effect of Combining Titanosilicate and 1-Ethyl-3-Methylimidazolium Acetate in Mixed Matrix Membranes for Efficient C02 Separation

The separation and capture of CO 2 from these sources is becoming important for greenhouse emission. The membrane-based separation process use to remove CO 2 takes advantages in energy efficient and environmentally friendly aspects and has been recognized as an important technology for CO 2 capture and gas separation. The novel mixed matrix membranes (MMMs) were fabricated by incorporating microporous titanosilicate ETS-10 and a highly CO 2 absorbent ionic liquid , [EMIM][Ac] into a Chitosan (CS) matrix to improve CO 2 separation performance, and were prepared, characterized and tested for CO 2 and N 2 . The solubility values show that the CO 2 solubility increases upon addition of ETS-10 particles. The N 2 solubility in the ETS-10/[EMIM][Ac]/CS was reduced, while CO 2 solubility remained constant. FT-IR spectra revealed a good interaction between the components in the MMMs. Subtle differences in the intensity and position of all individual bands, were observed in the region between 3600 and 2700 cm -1 and 1700 and 900 cm -1 . These indicated bonding of the components in the film, confirming the good interaction existing among the components, and that may account for the higher flexibility of the hybrid membrane materials imparted to both CS and ETS-10/CS MMMs, , due to the singular interaction between CS and [EMIM][Ac]. Keywords: CO 2 solubility, CO 2 separation, microporous titanosilicate ETS-10, Chitosan, mixed matrix membranes (MMMs).

Forward osmosis: an alternative sustainable technology and potential applications in water industry

This paper presents an advancing sustainable membrane-based separation process, which is forward osmosis (FO). The review begins with an introduction of the basic principles of the FO process. Then, a comparison to the most currently well-known desalination technology (RO) is presented. Following section summarizes potential applications of FO in the water desalination field, producing either potable water or irrigation water from brackish/saline feeds. Next, two major FO applications in the domain of water reuse are discussed: wastewater and industrial applications. Wastewater applications are such as OSMBR and landfill leachate treatment; and Industrial applications include oil and gas, pharmaceutical, and food and beverage industries. These different FO applications are briefly reviewed and assessed. Although FO has attracted growing attention in many potential applications, it still experiences several considerable limitations, including concentration polarization, membrane fouling, reverse solute diffusion, and need for membrane and draw solution development.

Self-cleaning Metal Organic Framework (MOF) based ultra filtration membranes--a solution to bio-fouling in membrane separation processes.

Bio-fouling is a serious problem in many membrane-based separation processes for water and wastewater treatment. Current state of the art methods to overcome this are to modify the membranes with either hydrophilic additives or with an antibacterial compound. In this study, we propose and practise a novel concept to prevent bio-fouling by developing a killing and self-cleaning membrane surface incorporating antibacterial silver nanoparticles and highly hydrophilic negatively charged carboxylic and amine functional groups. The innovative surface chemistry helps to reduce the contact angle of the novel membrane by at least a 48% and increase the pure water flux by 39.4% compared to the control membrane. The flux drop for the novel membrane is also lower (16.3% of the initial flux) than the control membrane (55.3% of the initial flux) during the long term experiments with protein solution. Moreover, the novel membrane continues to exhibit inhibition to microbes even after 1320 min of protein filtration. Synthesis of self-cleaning ultrafiltration membrane with long lasting properties opens up a viable solution for bio-fouling in ultrafiltration application for wastewater purification.

Temperature effect on ultrasonic monitoring during a filtration procedure

Membranes are used extensively for a wide variety of commercial separation applications including those in the water purification, pharmaceutical, and food processing industries. Fouling is a major problem associated with membrane-based liquid separation processes because it can often severely limit process performance. The use of ultrasonic monitoring technique for the characterization of membranes and membrane processes has been widely used by university researchers and industrial groups for a variety of applications including membrane fouling, compaction, formation, defect detection, and morphology characterization. However, during the industrial application, such as desalination procedure, temperature of the feed liquid is not constant. This change of the temperature brings in the concern that whether the change of the ultrasonic signal is caused by the fouling or by the temperature change. This research is focus on to verify the degree of effect of temperature to ultrasonic signal, and provide a method that calibrate the temperature effect for real applications.

POSS-hybrid membranes for the removal of sulfur aromatics by pervaporation

Membrane-based separations are a promising attempt for desulfurization of fuels in petrochemical industry. The focus on research is to investigate membranes, which are more efficient and show better separation characteristics. Hybrid membranes made of an organic polymer and inorganic compounds combine both in one material and new properties can be realized. Here new hybrid membranes of polyimides and POSS (polyhedral oligomeric silsesquioxane) compounds for desulfurization by the membrane-based separation process pervaporation were investigated. The POSS compounds can act as cross-linking agent between polymer chains through reactive organic side groups, resulting in improved membrane properties.In pervaporation experiments the behavior of glycidyl-POSS hybrid membranes with different amount of POSS as additives have been analyzed for a binary mixture consisting of benzothiophene and n-dodecane in comparison to a native copolyimide membrane. Thereby the concentration of benzothiophene has been varied. The hybrid membranes showed lower fluxes due to cross-linking, correlating with PALS and WAXD results. At higher temperatures also higher selectivity is found. Furthermore in stress strain measurements the glycidyl-POSS hybrid membranes showed improved properties in comparison to a native membrane.