Patent Application
20230173437
The present disclosure relates to membranes and, more particularly, to reverse osmosis membranes.
This section provides background information related to the present disclosure which is not necessarily prior art.
Reverse osmosis membrane water separation is an essential technology necessary in providing today's water demands. Biofilm accumulation due to the presence of microorganisms in the feedwater limits the performance of these essential water separation membranes by reducing flux and rejection performance. To militate against the occurrence of biofouling, mitigation strategies are commonly employed to inactivate the microorganisms, preventing their adsorption. One of the most common known mitigation strategies is the dosing of free chlorine into the feedwater. While effective, free chlorine species have been shown to degrade the polyamide selective layer used in RO membranes.
Research has shown that the interaction with free chlorine results in both irreversible ring chlorination and reversible N-chlorination of the amidic N. The absolute reversibility of the N-chlorination reaction has been disputed, where some studies indicate that chain scission may result under some conditions. Despite this dispute, there is a consistent reporting of correlations between ring chlorination events and performance (i.e. salt rejection and flux) decline. In order to ensure the long-term operability of reverse osmosis membranes without risk of performance decline due to free chlorine exposure new strategies are being explored.
A few known strategies explored focus on the elimination of the need for free chlorine by increasing the surface hydrophilicity of the membrane, disincentivizing foulant adsorption. Undesirably, these approaches often result in significant flux declines. Alternatively, different disinfectants have been explored in efforts to eliminate free chlorine, though most current research suggests that this results in either lessened effectiveness of microorganism inactivation, the formation of harmful byproducts, high operating costs, and the degradation of the PA membrane structure/performance.
Recent research has implemented various strategies in efforts to create a chlorine tolerant membrane. Known methods synthesized reverse osmosis membranes out of graphene-oxide loaded polyimide, resulting in moderate increases in flux and rejection performance which showed little performance loss after 1000 ppm*h exposure to free chlorine under circumneutral conditions. However, extreme chlorine tolerance was not tested. A standard interfacially polymerized membrane can maintain or improve rejection and flux performance up to several thousand ppm*h without much change in performance, so further chlorination studies should be conducted to probe its long-term chlorine resistance. Known systems report the synthesis of a highly chlorine resistant membrane capable of rejections comparable of that of standard network aromatic PA membranes, while maintaining performance up to 100,000 ppm*h free chlorine exposure. While this certainly is a significant step toward achieving a fully chlorine resistant membrane, it is a labor-intensive approach, which employs multiple interfacial polymerization reactions occurring in succession. This complex manufacturing process may hinder the ability to rapidly produce the membranes at scale and require large (double or triple) the volume of organic solvent in making a single standard membrane.
There is a continuing need for a separations membrane system and method that militates against irreversible chlorination from occurring, thereby also militating against long-term performance decline in RO membranes. Desirably, the separations membrane system and method may be more efficiently manufactured compared to known chlorine tolerant membrane synthesis methods.
In concordance with the instant disclosure, an efficient separations membrane system and method which enhance the mass uptake of free oxidants, has been surprisingly discovered. Desirably, the separations membrane system may enable long-term efficacy of reverse osmosis (RO) water separation operations.
The separations membrane system includes a substrate, a microporous layer, and a selective layer. The microporous may be disposed over the substrate. The selective layer may be disposed over the microporous layer, thereby sandwiching the microporous layer between the selective layer and the substrate. In a specific example, the substrate may include a non-woven polyester material. In another specific example, the microporous layer may include a polysulfone material. The selective layer may include a polyamide structure of 2,2-Dimethyl-1,3-propanediamine. In certain circumstances, the polyamide structure may also include 1,3,5-Benzenetricarbonyl chloride.
In another embodiment, the present technology includes methods of manufacturing a separations membrane system. For instance, a method of manufacturing the separations membrane system may include synthesizing a microporous layer on a substrate. The substrate may include a non-woven polyester material. Next, a selective layer may be synthesized over the microporous layer, thus forming a separations membrane. The selective layer may include a polyamide structure of 2,2-Dimethyl-1,3-propanediamine. In a specific example, the polyamide structure of the selective layer may also include 1,3,5-Benzenetricarbonyl chloride. Afterwards, the separations membrane may be cured. For instance, the separations membrane may be heated to around eighty degrees Celsius for curing.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.
The following description of technology is merely exemplary in nature of the subject matter, manufacture, and use of one or more inventions, and is not intended to limit the scope, application, or uses of any specific invention claimed in this application or in such other applications as may be filed claiming priority to this application, or patents issuing therefrom. Regarding methods disclosed, the order of the steps presented is exemplary in nature unless otherwise disclosed, and thus, the order of the steps can be different in various embodiments, including where certain steps can be simultaneously performed.
Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure pertains.
As used herein, the terms “a” and “an” indicate “at least one” of the item is present; a plurality of such items may be present, when possible. Except where otherwise expressly indicated, all numerical quantities in this description are to be understood as modified by the word “about” and all geometric and spatial descriptors are to be understood as modified by the word “substantially” in describing the broadest scope of the technology. “About” when applied to numerical values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by “about” and/or “substantially” is not otherwise understood in the art with this ordinary meaning, then “about” and/or “substantially” as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters. In the present disclosure the terms “about” and “around” may allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range. Likewise, in the present disclosure the term “substantially” can allow for a degree of variability in a value or range, for example, within 90%, within 95%, or within 99% of a stated value or of a stated limit of a range.
Although the open-ended term “comprising,” as a synonym of non-restrictive terms such as including, containing, or having, is used herein to describe and claim embodiments of the present technology, embodiments may alternatively be described using more limiting terms such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting materials, components, or process steps, the present technology also specifically includes embodiments consisting of, or consisting essentially of, such materials, components, or process steps excluding additional materials, components or processes (for consisting of) and excluding additional materials, components or processes affecting the significant properties of the embodiment (for consisting essentially of), even though such additional materials, components or processes are not explicitly recited in this application. For example, recitation of a process reciting elements A, B and C specifically envisions embodiments consisting of, and consisting essentially of, A, B and C, excluding an element D that may be recited in the art, even though element D is not explicitly described as being excluded herein.
As referred to herein, disclosures of ranges are, unless specified otherwise, inclusive of endpoints and include all distinct values and further divided ranges within the entire range. Thus, for example, a range of “from A to B” or “from about A to about B” is inclusive of A and of B. Disclosure of values and ranges of values for specific parameters (such as amounts, weight percentages, etc.) are not exclusive of other values and ranges of values useful herein. It is envisioned that two or more specific exemplified values for a given parameter may define endpoints for a range of values that may be claimed for the parameter. For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that Parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping, or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if Parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, 3-9, and so on.
When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments.
Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below,” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
Lacking from known chlorine resistance studies is the use of ultrathin barrier layers for their ability to slow the diffusion of free chlorine species. While this approach might also have the impacts of reducing flux, the ultrathin nature (<10 nm) of such a modification may limit the effect of flux decline by reducing the diffusion distance water must pass through before reaching the standard membrane chemistry. Conversely, single halogenated aniline endcapping results in significant flux increases, however more rapid performance decline occurs in the presence of free chlorine. This is attributed to the lack of ability of the halogenated anilines have to participate in building a network atop the standard interfacially polymerized membrane, leaving significant amounts of polyamide structure exposed to intruding free oxidant molecules during chlorination. Advantageously, the formation of a pre-chlorinated ultrathin network structure may act as a better system for free chlorine diffusion, while having limited effects on flux.
Methods which employ single interfacial polymerization approaches to synthesize new membrane chemistries enable rapid deployment of chlorine tolerant membranes without large capital costs to membrane manufacturers. Given the irreversible nature of chlorine uptake at the amide-N, polyamide structures lacking these aromatic functionalities are desirable. This requires the replacement of the common monomer m-phenylene diamine (MPD) with an alternative diamine. For instance, 2,2-dimethyl-1,3-diaminopropane (DMDAP) may have similar structural characteristics, given that the methyl functionalities would provide some steric separation within the polyamide (PA) structure, potentially promoting a small increase in free volume to promote water diffusion.
As shown in
In another embodiment, the present technology includes methods of manufacturing a separations membrane system 100. For instance, as shown in
With continued reference to
Provided as a specific, non-limiting example, a quartz crystal microbalance (QCM) was used to probe the rates of mass uptake within model membranes of a standard network aromatic PA with varying degree of halogenated aromatic endcaps (0, 1, 5, and 10 bilayer), and in the separations membrane system 100 synthesized from the reaction of trimesoyl chloride (TMC) and DMDAP. This non-limiting example is provided to show that the separations membrane system 100 having DMDAP containing membranes may successfully militate against irreversible chlorination from occurring, thereby also militating against long-term performance decline in RO membranes.
Prior to QCM analysis, model membranes were deposited by the following method. QCM sensors were first treated in a UV-ozone chamber, commercially available from BioForce Nanosciences, inc., for ten minutes to remove any surface contaminants prior to mLbL deposition.
After model membrane deposition, interaction between the membranes and free chlorine was probed using the QCM. For testing, model membrane samples were placed in the QCM cell and were first equilibrated in water. After mass equilibration in water, 500 ppm aqueous solutions of NaOCl, with pH adjusted to 7.4 using HCl was pumped into the QCM cell at a rate of 1.4 mL/min, and resonant frequency and dissipation factor changes were recorded. Voigt modelling of the recorded response for the selective layer 106 was performed using QTOOLS™ software commercially available from Biolin Scientific AB.
Interfacial polymerization of standard reverse osmosis membranes and DMDAP-containing reverse osmosis membranes 100 was performed for the crossflow characterization and chlorine resistance assessment of bulk scale membranes. Prior to synthesis, membranes were soaked overnight in isopropyl alcohol, then overnight in deionized water to remove any surface-protective layers from the polysulfone. Next, the polysulfone membranes were placed in water-tight frames to house the solutions used during the interfacial polymerization process. After placing membranes in the reaction frame, a 2 wt. % aqueous solution of either MPD or DMDAP was introduced to soak into the polysulfone substrate 102 for 10 minutes. After 10 minutes, the solution was poured off, the surface was dried using a rubber roller, and then a 0.2 wt. % solution of TMC in hexane was placed into the reaction frame for 15 minutes. After 15 minutes of reaction, the TMC solution was then poured off before subsequent rinsing with hexane and drying at 80° C. for 5 minutes. After synthesis, membrane samples were stored in deionized water prior to testing in the crossflow cell.
Chlorine tolerance of interfacially polymerized DMDAP-containing membranes was performed using a CF-042™ crossflow cell commercially available from Sterlitech Corporation. Rejection and flux performance was assessed at 800 psi operating pressure, with a 1 gpm crossflow rate, and 400 ppm NaCl feedwater concentration. Water temperatures were maintained at 28±3° C. using a Polyscience (Niles, Ill.) recirculating chiller. Rejection performance of the membranes was assessed by continually measuring the TDS of the permeate collected in 15 mL aliquots in a scintillation vial until permeate concentration plateaued. Rejection was calculated by equation 6.1, shown below, where Cperm and Cfeed are salt concentrations of the permeate and feedwater, respectively, as measured by TDS measurement.
After rejection plateaued, permeate was mass for thirty minutes to calculate the average flow rate, which was in-turn normalized by the membrane active area to calculate flux (L/(m2d)).
The chlorine response in the first minute of interaction with membranes functionalized using halogenated aminic monomers is shown in
As shown in
Both membrane chemistries displayed similar initial flux, with the standard and DMDAP membranes displaying permeate flux of 27.3 and 28.6 L/(m2h), respectively. This flux performance, however, deviated with increasing free chlorine exposure, with the standard membrane displaying an exponential increase up to four times its initial value. Such an occurrence is associated with the disruption of the PA network as a result of free chlorine interaction, where initial disruption of the network structure nearest the feedwater side lessens the diffusion distance the water must travel before exiting the membrane on the permeate side. This disruption continues deeper into the membrane, continuing to decrease the diffusion distance until a critical flaw is reached, inciting rapid flux increase and rejection decline. Conversely, the DMDAP membrane showed a decline in flux after the initial 1,000 and 3,000 ppm*h doses to 24.3 and 22.9 L/(m2h), respectively. After 10,000 ppm*h exposure, flux was 24.0 L/(m2h), resulting in a flux loss of 2.65×10−4±3.46×10−4 L/(m2 ppm*h2). It is currently unknown whether the small rate of flux performance loss is a real result or an artifact due to differences of operating conditions (variations in water temperature, crossflow rate, etc.). Cyclical mass uptake and mass loss shown through free chlorine introduction and subsequent DI rinsing was attributed to mass changes associated with reversible chlorination. Lacking the aromatic ring necessary for irreversible ring chlorination, continued chlorine exposure appears to have a limited effect on the long-term performance. While the DMDAP membrane in its current form shows significant chlorine tolerance, incremental improvements in rejection may be made to meet the performance of current RO membrane technology, which commonly display rejection performances of 99+%. Also, significant improvements of flux performance to 35-60 L/(m2h) may need to be achieved. Facile surface modification using halogenated anilines, which resulted in a near tripling in flux performance of standard RO membranes could be employed, and has potential to promote such flux increase.
Results showed that these pre-halogenated structures served as a passivation layer capable of slowing chlorine uptake in the underlying PA membrane. Advantageously, the separation membrane having a DMDAP chemistry lacking N-adjacent aromatics was observed to show no evidence of irreversible chlorine uptake. A crossflow characterization of the DMDAP membrane showed no rejection performance decline and negligible flux loss, suggesting the synthesis of a chlorine proof polyamide membrane; the synthesis of which can be immediately deployed in current RO membrane manufacturing facilities.
Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. Equivalent changes, modifications and variations of some embodiments, materials, compositions, and methods can be made within the scope of the present technology, with substantially similar results.
This application claims the benefit of U.S. Provisional Application Ser. No. 63/286,369, filed on Dec. 6, 2021. The entire disclosure of the above application is hereby incorporated herein by reference.
This invention was made with government support under DMR1838513 and CBET1605882 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63286369 | Dec 2021 | US |
