Patent Application
20220105470
The present disclosure relates to liquid mixture separation by a membrane. In particular, the present disclosure relates to an apparatus and method to provide localized induction heating on a ferromagnetic material-coated membrane to achieve efficient liquid mixture separation by pervaporation.
The use of liquid mixtures containing compounds, such as organic compounds, occur throughout various industries. Pervaporation (PV) is a membrane separation process used on liquid mixtures that is a relevant part of processing in environmental, biotechnological, food, petrochemical, chemical, and pharmaceutical industries. Pervaporation separates liquids mixtures by partial vaporization through a non-porous membrane. Typically, the driving force is provided by a chemical potential difference between the liquid feed and vapor permeate at each side of the membrane.
Pervaporation is especially attractive for separation of mixtures that are difficult to separate by distillation. Pervaporation has advantages in the separation of thermally sensitive compounds, close-boiling mixtures, azeotrope mixtures, molecules with similar weight or shape, and removing species present in low concentrations. Separation of components is based on a difference in solubility and diffusion rate of individual components in the membrane.
Compared to other conventional separation processes, pervaporation has the advantages of high separation efficiency and mild operating conditions. Much research into pervaporation processes has been done over the past decades in both the laboratory and in commercial use. However, despite this wealth of research, both in the laboratory and in plant scales, pervaporation processes that are technically and economically competitive with distillation have not been available to date.
Even though energy requirement for pervaporation is lower compared to distillation, continuous external heating of the entire bulk feed streams is required in order to maintain the desired temperature gradient between the two membrane sides to drive effective molecular separation. The cost of bulk feed stream heating is a major contributor to the total cost of a pervaporation process. To make it worse, this conventional heating method inevitably cause unfavorable temperature polarization at the membrane-liquid interface, leading to a decreased thermal efficiency and thus a compromised separation permeability. In conventional heating by either a heating plate or a heat exchanger, the heat transfer reduces the temperature difference across the membrane, resulting in a lower permeate flux across the membrane and thus a lower pervaporation efficiency. Other drawbacks of the conventional heating method include inefficient thermal transfer, the need for heating the entire feed solution, high heating energy consumption and heat loss. This temperature difference or thermal gradient further decreases along the flow direction of the membrane module (e.g., in a cross-flow mode), resulting in a maximal usable length of a single module.
Recent research adopted localized heating with limited success. Localized heating at the feed/membrane interface provides enhanced energy efficiency. It eliminates the requirement of heating the entire input feed stream and reduces the demand for hot feed or the cost to maintain hot feed. It also eliminates the intrinsic temperature polarization existing in the conventional pervaporation process for improved thermal efficiency. The elevated membrane/liquid interfacial temperature enhances the component diffusion coefficient, and potentially increases separation permeability. However, these recent attempts have encountered many drawbacks.
For example, in a recent study a silver nanoparticle had an incorporated polydimethylsiloxane (PDMS) membrane that enhanced ethanol flux and selectivity for water/ethanol separation performance under LED light irradiation. However, the localized heating enabled by light activated or photo-thermal heating is restricted to flat sheet membranes that have low membrane packing density and thus have a potentially high footprint. Moreover, regardless of the use of artificial illumination sources (e.g., LED) or solar irradiation, the heat loss due to the absorption of light energy by the feed liquid is inevitable. In another study that utilized localized heating employed was a microwave to heat the ethanol/water solution for pervaporational separation. However, this method also targeted at the entire feed solution for heating, instead of the membrane-liquid interface, therefore the undesired temperature polarization still negatively affects the separation permeability.
As such, there is a need for effective surface heating methods and integrated systems for pervaporational separation. In this regard, it is important to develop alternative heating methods in a process that enhances heat and mass transfer with low energy consumption.
Disclosed is a newly developed pervaporation system and process that utilizes induction heating in a localized heating manner. Compared to the above prior attempts, the presently disclosed apparatus and method solves the problems of current state of the art, meets the above requirements, and provides many more benefits.
The induction heating process efficiently delivers localized heating on the induction-responsive materials, such as but not limited to ferromagnetic Fe3O4 (Iron(II,III) oxide) nanoparticles, embedded within the selective layer of the pervaporation membrane, or coated on the surface layer of the pervaporation membrane. It will be understood that other induction-responsive materials could be employed. Typically, induction heating involves the heating of a material by inducing an electric current or electron eddy within it. No light or photo-thermal heating is involved in the induction heating and therefore all the drawbacks of the photo-thermal heating technology is avoided. Provided is a pervaporation (PV) system and method that incorporates ferromagnetic materials into the membrane structure and utilizes induction heating as a driving force, which provides unexpectedly enhanced thermal efficiency and separation permeability. This apparatus and process are based on the highly efficient and localized induction heating induced by the ferromagnetic materials, such as the above mentioned Fe3O4 nanoparticles (NPs). The ferromagnetic nanoparticles are embedded within the surface layer of the PV membrane. The localized heating induces in-situ temperature enhancement of the liquid membrane interface. Thus, the enthalpy of evaporation pervaporation can be supplied directly at the membrane surface where the evaporation takes place. This in-situ heating method not only eliminates the intrinsic temperature polarization existed in the conventional PV process but also enhance the component diffusion coefficient, and thus simultaneously improve the thermal efficiency and separation permeability. The localized induction heating process avoids the requirement to heat the entire volume of feed liquid by external means, thus eliminating the substantial power requirements and inherent efficiency limitations of the conventional PV process.
Depending on the embodiment, a PV separation apparatus includes a membrane separation module, an influent side, and permeate side, a membrane, and an induction heating device. During the operation process of the invention, the feed liquid stored in the storage tank is pumped into the influent side of the membrane module by a liquid circulating pump. The feed liquid in the influent side in the membrane module is heated by an induction-responsive membrane that absorb an externally applied electromagnetic induction waves, resulting in promoted driving force for PV separation. In other arrangements, the permeate side in the membrane module may maintain a vacuum by a cascade of a cold trap and a vacuum pump. The cold trap may include, but is not limited to, the following selected from a group consisting of a liquid nitrogen, a dry ice, a dry ice in acetone or a solvent with a boiling point between 40° C.-95° C., or any combination thereof.
The temperature difference and partial vapor pressure difference between the feed side and permeate side cause the liquid components to pass through the functionalized membrane in the present invention. Here, the functionalized membrane can be either hydrophobic or hydrophilic, depending on the hydrophobicity of target separation components, and the target component will be concentrated at the permeate side due to higher selectivity of the membrane towards the target component, and is finally collected in the cold trap.
Depending on the embodiment, an induction-assisted pervaporation apparatus and an interfacial-heating pervaporation membrane module for liquid mixture separation may include an interfacial-heating/separation dual functional pervaporation membrane that incorporates induction-responsive materials into the structure of a conventional pervaporation membrane and utilizes induction heating as the liquid separation driving force. The induction-responsive materials in the pervaporation membrane are in situ excited under an electromagnetic field that is typically characterized by induction field power and field shift frequency. These characteristics of the electromagnetic field is tunable by adjusting the applied electricity, the induction coil shapes or sizes and the membrane-coil distance.
Electromagnetic induction heating provides contactless, fast, efficient, and accurately controlled heating of conductive or ferromagnetic materials that could locally be coated on or blended within the membrane materials. The induction heating is driven by the formation of eddy currents and magnetic polarization effects, when ferromagnetic and conductive materials are exposed to an alternating current electromagnetic field. Since the induction heating is dependent on the conductive and magnetic properties of the material to be heated, the heating process could be made selectively toward specific target materials or regions of the materials without the loss of energy to water heating or others. Various applications of induction heating have been demonstrated, including industrial processes (e.g., forging, melting, welding and annealing), kitchen cooking, and medical applications (e.g., minimally-invasive therapies, sterilization of surgical instruments).
In another implementation, the material of the pervaporation polymer membrane includes, but not limited to, poly(vinyl alcohol), chitosan, cellulose, polydimethylsiloxane, poly(ether amide), poly(1-trimethylsilyl-1-propyne), zeolites, metal-organic frameworks, and any combinations thereof. This is applicable to a wide range of membranes that may be flat, hollow fiber, or tubular.
The membrane could include a hybrid self-heating and separation bifunctional layer and a support layer. In another embodiment, the membrane could include a self-heating layer, the separation layer, and the support layer. In one embodiment, the induction-responsive materials are either incorporated into the selective layer (the separation layer) or coated on the top of the selective layer in the dual functional pervaporation membranes.
Furthermore, the induction-responsive materials-coated interfacial-heating layer can generate heat when exposed to the electromagnetic field. Depending on the embodiment, the induction-responsive materials-coated interfacial-heating layer is associated on the selective layer through cross-linking, coating, grafting, embedding, or other kinds of binding methods such as but not limited to where the induction-responsive materials are disposed in the polymer membrane through cross-linking, surface coating, blending, grafting, or any combination thereof.
The induction-responsive materials-coated interfacial-heating layer is associated on the selective layer through at least one of hydrogen bonds, van der Waals interactions, electrical interactions, and combinations thereof. In addition, the induction-responsive materials include, but not limited to, iron, metal, metal alloys, Fe3O4 nanoparticles, or other ferromagnetic and conductive materials, and a group consisting of iron, metal, metal alloys and their oxides or compounds, Fe3O4 (Iron(II,III) oxide) nanoparticles, Fe2O3 (ferric oxide) nanoparticles, MXene (a ceramic of two dimensional inorganic compounds), ferromagnetic and conductive materials, and any combinations thereof.
The induction-responsive materials in the dual functional pervaporation membrane capable of generating heat may include particles, nanoparticles, composites, or any combination thereof.
In one aspect, a method involves exposing the induction-responsive materials-coated interfacial-heating layer to an electromagnetic field at different frequencies of 0.1 kHz-500 kHz and power supply of 0.1-10 KWh. Further, the electromagnetic field can be provided by single or multiple induction devices or sources. The dual functional membrane can be heated periodically or continuously.
In another aspect, a pervaporation system for liquid mixture separation comprises simultaneous heating and separation of liquid mixture through a dual functional composite membrane to achieve interfacial heating and separation. The dual functional membrane comprises a functionalization capable of generating heat under electromagnetic induction. The heat generated on the surface enhances the separation permeability.
Any combination and/or permutation of the embodiments is envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the present disclosure.
To assist those of skill in the art in making and using the disclosed pervaporation system and method and associated systems and methods, reference is made to the accompanying figures, wherein:
Adverting to the drawings,
During a typical operation, the raw feed stored in the raw feed storage tank 6 is pumped into the influent side 2 of the membrane module 1 by the raw feed circulating pump 7. The raw feed in the influent side 2 in the membrane module 1 of the present invention contacts the locally heated membrane surface under an electromagnetic induction, resulting in the heating of interfacial liquid in the raw feed. Meanwhile, the permeate side 3 in the membrane module 1 in the present embodiment is maintained a high vacuum (4-5 kPa) by a cascade of the liquid nitrogen cold trap 8, the permeate collecting tube 9, and the vacuum pump 10. The purified components from the permeate side 3 is condensed in the liquid nitrogen cold trap 8 and collected periodically from the permeate collecting tube 9.
The temperature difference and vapor pressure difference between the influent side 2 and the permeate side 3 cause the liquid component to permeate through the functional membrane 4 in the present embodiment. The functional membrane 4 will be described in detail in
The middle layer of the membrane is a dense pervaporational separation layer 12, which has perm-selectivity for the feed stream at the influent side 15. The bottom layer is a porous support layer 13 providing mechanical support for the top two layers. The localized heating generated at the interfacial-heating layer 11 promotes the solubility and diffusion of the influent feed 15 in the separation layer 12 and converts to a vapor at the permeate side 14 where a vacuum is maintained. The vapor flows through the channel 14 and is then condensed and collected in the tube 9 shown in
In the embodiment shown in
The materials and the methods of the present disclosure used in examples will be described below. While the examples discuss the use of specific compounds and materials, it is understood that the present disclosure could employ other suitable compounds or materials. Similar quantities or measurements may be substituted without altering the method embodied below.
First, Fe3O4 nanoparticles are synthesized by a modified chemical co-precipitation method. Briefly, 0.99 g FeCl2.4H2O and 2.7 g FeCl3.6H2O are dissolved in 100 ml deionized water in a 250 ml flask with mechanical stirring under nitrogen atmosphere at 80° C.
Then 10 mL NH3.H2O 25% (v %) is dropped at a speed of 1 drop per second into the above solution. The mixture is stirred continuously for 30 min. The obtained black Fe3O4 is washed with deionized water and ethanol under magnetic field and dried in the vacuum oven.
Subsequently, Polyvinyl alcohol (PVA) powder is first dissolved in deionized (DI) water at 90° C. for at least 6 h to obtain a 2 wt. % PVA casting solution. Then, a cross-linking agent of maleic acid (mole ratio of maleic acid:PVA=0.05:1) is added to the PVA solution and further stirred at 90° C. for 12 h. Subsequently, Fe3O4 nanoparticles is added into the PVA casting solution and stir vigorously to obtain a Fe3O4/PVA casting suspension.
The concentrations of PVA and Fe3O4 in the resultant casting solution are both around 5 wt. %, respectively.
Afterwards, the casting suspension is carefully cast on a polyethersulfone (PES) support layer by a casting knife at a casting gate height of 50 and then dried at room temperature overnight to obtain the hybrid Fe3O4/PVA dual functional membrane, whose structure is shown in
First, Fe3O4 nanoparticles were synthesized according to EXAMPLE 1 herein. Then, a PVA/PES membrane was prepared using the following steps: first, a 2 wt. % PVA aqueous solution is prepared by vigorously stirring PVA (polyvinyl alcohol) power in DI (deionized) water at 90° C. for 6 h. Then, the PVA solution is crosslinked by adding a maleic acid (a mole ratio of maleic acid:PVA=0.05:1) for another 12 h at 90° C. Afterwards, the PVA solution is poured into a rectangular container and the PES (polyethersulfone) porous membrane is dipped onto the PVA solution for 5 min and then taken out for drying in room temperature. Four dip-coating cycles are performed, and the resultant PVA/PES pervaporation membrane is dried overnight at room temperature. At the last step, the dried PVA/PES membrane is further cured in an air dry oven at 120° C. for 1 h to ensure complete crosslinking between the maleic acid with the PVA chain.
Subsequently, an interfacial-heating layer is coated through phase inversion method on the PVA/PES membrane prepared above: first, a Fe3O4/PVA casting mixture is first prepared by dispersing Fe3O4 (iron (II,III) oxide) nanoparticles in Milli-Q water under mechanical agitation, which is then added into a crosslinking-treated PVA aqueous solution. The concentrations of PVA and Fe3O4 in the casting mixture are 5 wt. % and 25 wt. %, respectively. Then, the casting mixture is carefully cast on the PVA/PES membrane by a casting knife with a casting gate height of 250 μm. The resultant membrane is immediately immersed into an ethanol coagulation bath at room temperature. After complete solidification, the membrane is taken out and dried at room temperature to obtain the composite multi-layer Fe3O4/PVA dual functional membrane, whose structure is shown in
In this example, the inventors assessed the desalination performance of interfacial-heating/separation dual functional composite membranes by utilizing the bench scale system shown in
While exemplary embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention.
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 63/087,951, filed Oct. 6, 2020, the disclosure of which is hereby incorporated herein by reference.
This invention was made with government support under Agreement No. R19AC00107 awarded by the U.S. Department of the Interior via the Bureau of Reclamation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63087951 | Oct 2020 | US |
