Silica scale inhibitor composition and method for inhibiting silica scale in membrane applications

Abstract

A scale inhibitor composition is provided. The composition has a silica inhibitor composition and a dispersant composition. A method for inhibiting scale formation in a membrane system is provided. The method includes preparing a scale inhibitor composition, the scale inhibitor composition having a silica inhibitor and a dispersant, and adding the scale inhibitor composition to an aqueous stream of a water system.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 62 / 896,939, filed September 6, 2019, which is incorporated herein by reference in its entirety.

[0002] (Technical field) The technology of the present disclosure generally provides compositions and methods for silica scale inhibition in membrane applications, and more specifically, membrane silica scale inhibitors and methods for silica scale inhibition in high silica water membrane applications. [Background technology]

[0003] In the membrane desalination industry, practitioners typically run membrane systems at higher recovery rates to save on operational costs and reduce concentrate disposal. However, this goal is extremely difficult with water containing elevated concentrations of silica. When high concentrations of silica are used, the buildup of silica scale or silica deposits can result in reduced productivity, poor product quality, unscheduled downtime, and frequent membrane cleaning-in-place (CIP) operations. Additionally, once silica scale forms on the membrane surface, it is nearly impossible to remove.

[0004] Silica scaling in membrane systems is very complex and is affected by many factors (e.g., silica level, pH, temperature, other metal ions, system operating conditions, etc.). Among these, silica level and pH are the two most important factors. Broadly speaking, there are two approaches to improving system recovery and reducing concentrate disposal for high-silica water treatment in membrane applications. The first approach is to adjust the feed pH by adding acid. However, adding acid requires additional feed / metering pumps, handling of concentrated acid (potential safety issues), body / skin contact, and vapor inhalation. The second approach is to administer highly effective silica scale inhibitors.

[0005] Therefore, what is needed in the art are compositions and methods for silica scale inhibition in high silica water film applications. Summary of the Invention

[0006] The technology of the present disclosure generally provides compositions and methods for silica scale inhibition in membrane applications, and more specifically, membrane silica scale inhibitors and methods for silica scale inhibition in high silica water membrane applications.

[0007] In one aspect of the disclosed technology, there is provided a scale inhibitor composition, which comprises a silica inhibitor composition and a dispersant composition.

[0008] In some embodiments, the silica inhibitor composition comprises an organophosphate, phosphonate-based compound, or a carboxylic acid sulfonated copolymer. In some embodiments, the organophosphate is 1-hydroxyethylidene-1,1-diphosphonic acid. In some embodiments, the silica inhibitor is present at a concentration of about 5-40% actives.

[0009] In some embodiments, the dispersant composition comprises a sulfonated acrylic acid polymer. In some embodiments, the sulfonated acrylic acid polymer comprises a repeat unit characterized by the following chemical formula:

[0010] [ka] (Chemical formula A)

[0011] where n ranges from about 1 to 100 and Z is H, Na, K, Ca, or NH4.

[0012] In some embodiments, n is about 1 to 20. In some embodiments, Z can be the same or different in c, d, and e. In some embodiments, the molar ratio of c:d:e ranges from about 20:10:1 to 1:1:20.

[0013] In some embodiments, the molecular weight of the sulfonated acrylic acid polymer ranges from about 10,000 to about 30,000. In some embodiments, the concentration ratio of the silica inhibitor composition to the dispersant composition is about 1:2. In some embodiments, the concentration ratio of the silica inhibitor composition to the dispersant composition is about 1:1.6. In some embodiments, the silica inhibitor and dispersant compositions are mixed together.

[0014] In yet another aspect of the disclosed technology, there is provided a scale inhibitor composition comprising a mixture of (i) a silica inhibitor composition comprising 1-hydroxyethylidene-1,1-diphosphonic acid and (ii) a sulfonated / sulfated acrylic acid polymer or terpolymer.

[0015] In some embodiments, the sulfonated acrylic acid polymer or terpolymer comprises a repeat unit characterized by the following chemical formula:

[0016] [ka] (Chemical formula A)

[0017] where n ranges from about 1 to 100 and Z is H, Na, K, Ca, or NH4.

[0018] In some embodiments, the silica inhibitor and dispersant composition are mixed together at about 25°C.

[0019] In yet another aspect of the disclosed technology, a method for inhibiting scale formation in a membrane system is provided, the method comprising: preparing a scale inhibitor composition, the scale inhibitor composition comprising a silica inhibitor and a dispersant; and adding the scale inhibitor composition to an aqueous stream of a water system.

[0020] In some embodiments, the silica inhibitor comprises an organophosphate, phosphonate-based compound or a carboxylic acid sulfonated copolymer. In some embodiments, the dispersant is a sulfonated acrylic acid polymer or terpolymer. In some embodiments, the scale inhibitor composition is a mixture of a silica inhibitor and a dispersant.

[0021] In some embodiments, the silica inhibitor comprises 1-hydroxyethylidene-1,1-diphosphonic acid and the dispersant is a sulfonated / sulfated acrylic acid polymer or terpolymer. In some embodiments, the sulfonated acrylic acid polymer or terpolymer comprises repeat units characterized by the following chemical formula:

[0022] [ka] (Chemical formula A)

[0023] where n ranges from about 1 to 100, and Z is H, Na, K, Ca, or NH4.

[0024] In some embodiments, the aqueous stream comprises a silica content of at least 300 ppm. In some embodiments, the aqueous stream comprises a silica content of about 300 ppm to about 350 ppm. In some embodiments, the aqueous stream comprises a pH of at least 7. In some embodiments, the aqueous stream comprises a pH of about 7.5. In some embodiments, the aqueous stream has a pH of about 7.5 and a silica content of at least 300 ppm.

[0025] In some embodiments, the aqueous system includes a reverse osmosis membrane or a nanofiltration membrane. In some embodiments, the scale inhibitor composition is added to the aqueous stream in an amount of about 1 ppm to about 100 ppm. In some embodiments, the scale inhibitor composition is added to the aqueous stream in an amount of about 3 ppm to about 30 ppm.

[0026] These and other features and advantages of the techniques of the present disclosure are particularly shown, by way of example, in the embodiments now described with reference to the accompanying schematic drawings, including: [Brief explanation of the drawings]

[0027] [Figure 1] 10 is a graph providing results of an exemplary embodiment of the techniques of the present disclosure. [Figure 2] 10 is a graph providing results of an exemplary embodiment of the techniques of the present disclosure. [Figure 3] 10 is a graph providing results of an exemplary embodiment of the techniques of the present disclosure. [Figure 4] 10 is a graph providing results of an exemplary embodiment of the techniques of the present disclosure. [Figure 5A] 1A-1C provide results of an exemplary embodiment of the techniques of the present disclosure. [Figure 5B] 1A-1C provide results of an exemplary embodiment of the techniques of the present disclosure. [Figure 5C] 1A-1C provide results of an exemplary embodiment of the techniques of the present disclosure. [Figure 5D] 1A-1C provide results of an exemplary embodiment of the techniques of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0028] The technology of the present disclosure generally provides compositions and methods for silica scale inhibition in membrane applications, and more specifically, membrane silica scale inhibitors and methods for silica scale inhibition in high silica water membrane applications.

[0029] As used herein, the term "scale inhibitor" refers to a composition / formulation that inhibits (reduces) the formation of silica scale and / or the size and / or shape of solid silica particles.

[0030] It has been surprisingly discovered that a mixture of a silica inhibitor and a dispersant composition exhibits a synergistic effect in silica scale control. The membrane silica scale inhibitor composition described herein has been shown to be effective in treating feed streams containing high silica in membrane applications, such as reverse osmosis (RO) or nanofiltration (NF) systems, under given process conditions. The membrane silica scale inhibitor composition enables plant operation at concentrated silica levels exceeding 300 ppm. This demonstrates the synergistic effect of threshold silica scale inhibition and particle dispersion, increasing membrane system recovery and reducing operating costs.

[0031] In one aspect of the disclosed technology, a scale inhibitor composition is provided. The scale inhibitor composition includes a silica inhibitor composition and a dispersant composition. It has been found that a mixture of the silica inhibitor composition and the dispersant composition as disclosed herein provides an effective treatment for handling high silica aqueous treatments in membrane applications.

[0032] Typically, silica dissolved in feedwater is concentrated several-fold in RO or NF systems. This leads to silica polymerization, which can grow into larger molecules or form colloidal silica and / or particles. In this case, such silica polymerization accelerates with increasing silica levels and pH values. Surprisingly, it has been discovered that a mixture of a silica inhibitor and a dispersant composition allows the silica scale inhibitor composition described herein to postpone silica polymerization and prevent silica particles suspended in the stream from settling on the membrane surface.

[0033] Additionally, the disclosed silica scale inhibitor compositions are non-toxic to the environment (i.e., "green") and can treat high-silica water without the addition of acid, eliminating the need for acid treatment. The silica scale inhibitor compositions described herein avoid the increase in total dissolved solids (or TDS) of water that results from the addition of excess acid, thereby reducing energy consumption and lowering operating costs in water desalination.

[0034] In some embodiments, the silica inhibitor composition comprises an organic phosphoric acid, phosphonic acid-based compound or a carboxylic acid sulfonated copolymer. It is believed that certain anionic groups of the silica inhibitor composition may interact with cations in the feed solution to inhibit precipitation of crystalline inorganic salts, reducing the chance of co-precipitation with silica colloids or particles, thus helping to reduce silica scale formation and minimizing detrimental effects on membrane performance.

[0035] In some embodiments, the organophosphate is 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). In some embodiments, the silica inhibitor of the present technology not only inhibits silica polymerization but also effectively prevents calcium carbonate precipitation. In some embodiments, the silica inhibitor is present at a concentration of about 5-40% actives.

[0036] In some embodiments, the dispersant composition comprises a sulfonated acrylic acid polymer. In some embodiments, the sulfonated acrylic acid polymer comprises a repeat unit characterized by the following chemical formula:

[0037] [ka] (Chemical formula A)

[0038] where n ranges from about 1 to 100, and Z is H, Na, K, Ca, or NH4.

[0039] In some embodiments, n is about 1 to 20. In other embodiments, n is about 10 to 20. In some embodiments, Z can be the same or different in c, d, and e. In some embodiments, the molar ratio of c:d:e ranges from about 20:10:1 to 1:1:20.

[0040] In some embodiments, the sulfonated acrylic acid copolymer, terpolymer, or sulfonated acrylic acid polymer comprising repeating units characterized by Formula A described herein imparts a negative charge to suspended silica particles present in the feed stream, which avoids aggregation and steric hindrance due to enhanced electrostatic repulsion.

[0041] In some embodiments, the molecular weight of the sulfonated acrylic acid polymer ranges from about 10,000 to about 30,000. In other embodiments, the molecular weight of the sulfonated acrylic acid polymer ranges from about 12,000 to about 25,000.

[0042] In some embodiments, the concentration ratio of the silica inhibitor composition to the dispersant composition is about 1:2. In some embodiments, the concentration ratio of the silica inhibitor composition to the dispersant composition is about 1:1.6.

[0043] In some embodiments, the silica inhibitor composition is about 5-25% by weight and the dispersant composition is about 10-40% by weight of the total scale inhibitor composition.

[0044] In some embodiments, the silica inhibitor and dispersant composition are mixed together. In some embodiments, the silica inhibitor and dispersant composition are mixed together at room temperature. In other embodiments, the silica inhibitor and dispersant composition are mixed together at about 25°C. It should be understood that the mixture can be provided by any conventional mixing technique sufficient for the purposes described herein. For example, but not limited to, conventional mixing techniques can include flat baffles, pitched blade impellers, and / or Rushton turbines.

[0045] In some embodiments, the disclosed silica scale inhibitor composition may further include a phosphonic acid-based inhibitor, such as, but not limited to, diethylenetriaminepenta(methylenephosphonic acid) (DTPMP), aminotris(methylenephosphonic acid) (ATMP), hexanediaminetetra(methylenephosphonic acid) (HDTMP), and the like. The presence of a phosphonic acid-based inhibitor may be necessary if or when the feedwater or aqueous stream contains a high potential for CaCO3 precipitation. In such cases, the disclosed scale inhibitor composition may include the addition of a CaCO3 inhibitor.

[0046] In certain embodiments, the scale inhibitor composition comprises a mixture of (i) a silica inhibitor composition, wherein the silica inhibitor composition comprises 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), and (ii) a sulfonated / sulfated acrylic acid copolymer, terpolymer, or sulfonated acrylic acid polymer comprising repeating units characterized by chemical formula A:

[0047] In yet another aspect of the disclosed technology, a method for inhibiting scale formation in membrane systems is provided. The method described herein does not involve acid addition (i.e., allows for the treatment of high-silica water without the need for conventionally used acid addition). This method has been shown to provide synergistic benefits when treating high-silica streams in membrane applications. Furthermore, the method described herein specifically allows for the inhibition of silica scale on membrane surfaces, allowing RO or NF systems to operate at silica levels up to 350 ppm at pH 7.5.

[0048] The method includes providing a scale inhibitor composition including a silica inhibitor and a dispersant, and adding the scale inhibitor composition to an aqueous stream of a water system. In some embodiments, the scale inhibitor composition of the disclosed method is a mixture of a silica inhibitor and a dispersant. As previously mentioned, the mixture can be provided by any conventional mixing technique described herein.

[0049] In some embodiments, the silica inhibitor of the disclosed method comprises an organophosphate, phosphonate-based compound, or a carboxylic acid sulfonated copolymer.

[0050] In some embodiments, the dispersant of the disclosed method is a sulfonated acrylic acid copolymer or terpolymer. In some embodiments, the sulfonated acrylic acid copolymer or terpolymer comprises repeat units characterized by the following chemical formula:

[0051] [ka] (Chemical formula A)

[0052] where n ranges from about 1 to 100, and Z is H, Na, K, Ca, or NH4.

[0053] In some embodiments, the silica inhibitor described in the method comprises 1-hydroxyethylidene-1,1-diphosphonic acid and the dispersant is a sulfonated / sulfated acrylic acid copolymer, terpolymer, or sulfonated acrylic acid polymer comprising repeat units characterized by chemical formula A:

[0054] It is understood that the aqueous systems disclosed herein can be found in, but are not limited to, membrane desalination plants, influents to industrial plants, influents to drinking water plants, etc. In some embodiments, the aqueous systems comprise reverse osmosis (RO) or nanofiltration (NF) membranes.

[0055] In some embodiments, the aqueous stream comprises a silica content of at least 300 ppm. In other embodiments, the aqueous stream comprises a silica content of about 300 ppm to about 350 ppm. In some embodiments, the aqueous stream comprises a pH of at least 7. In some embodiments, the aqueous stream comprises a pH of about 7.5. In other embodiments, the aqueous stream has a pH of about 7.5 and a silica content of at least 300 ppm.

[0056] In some embodiments, the scale inhibitor composition is added to the aqueous stream in an amount of from about 1 ppm to about 100 ppm, hi some embodiments, the scale inhibitor composition is added to the aqueous stream in an amount of from about 3 ppm to about 30 ppm. [Example]

[0057] The present technology is further described in the following examples, which should be considered illustrative and should not be construed to narrow the scope of the technology of the present disclosure or to limit the scope to specific embodiments.

[0058] The scale inhibitor compositions and methods disclosed herein exhibited a synergistic effect when mixed together, demonstrating enhanced performance compared to other targeted silica water treatments. Such synergy is believed to be provided by the threshold silica scale inhibition of the silica inhibitor and the ability of the dispersant to suspend particle dispersions in high silica concentrate feedwater.

[0059] Figures 1-4 provide comparative data on the performance of silica scale inhibitor compositions in Water-A treatment (containing 300 ppm silica, 161 ppm CCPP, and a pH of 7.5). Product A is a phosphonic acid and Product B is a phosphonic acid with a polymer. As shown in Figures 1-4, HEDP is a silica inhibitor and "Formula I" is a sulfonated / sulfated acrylic acid copolymer, terpolymer, or sulfonated acrylic acid polymer containing repeat units characterized by Formula A.

[0060] The results, as shown in Figures 1-4, demonstrate that the presently disclosed scale inhibitor compositions and methods provide silica inhibition for at least two hours before such scale buildup on the membrane surface (i.e., resulting in a loss of permeability) is observed. Therefore, the disclosed scale inhibitor compositions and methods are believed to provide improved performance in field RO / NF systems at 300 ppm silica without added acid. This is in contrast to treatments with other commercially available products (e.g., Product A and Product B), which showed a loss of permeability within the first hour and / or a greater loss of permeability within two hours.

[0061] Referring to Figure 1, the HEDP and Formula I mixture was shown to outperform two other commercial products in treating Water-A. The HEDP and Formula I mixture showed a much lower membrane permeability drop during 6 hours of recirculation. (Note: The HEDP + Formula I permeability observed in Figure 1 is a 10% drop due to the accelerated test mode conditions.)

[0062] Figure 2 illustrates the synergistic effect of the presently disclosed compositions. Specifically, the silica scale inhibitor composition (e.g., a mixture of HEDP and Formula I) demonstrated synergistic effects in Water-A treatment, as it achieved the least membrane permeability reduction than achieved by the individual components alone.

[0063] FIG. 3 provides a repeatability test of the disclosed silica scale inhibitor composition.

[0064] Figure 4 shows the synergistic effect of the presently disclosed composition on a Water-H treatment (containing 350 ppm silica, 369 ppm CCPP, and a pH of 7.5). Specifically, the same synergistic effect of the disclosed scale inhibitor composition was observed with the Water-H treatment, indicating that its silica scale treatment effect is reliable and generally applicable to a variety of water chemistries.

[0065] Figures 5A-D provide SEM and EDS image results of the water-H treatment. As shown in Figures 5A-D, when the disclosed scale inhibitor composition was applied (HEDP and Formula I), a significant reduction in surface deposits was observed, which caused a slight increase in membrane resistance and mitigated the decrease in membrane permeability in a 6-hour recirculation test.

[0066] Figure 5A shows the effect of no treatment, resulting in 4.9% Si and 8% Ca on the membrane surface. Figure 5B shows the effect of HEDP treatment alone, resulting in 8% Si and 0% Ca on the membrane surface. Figure 5C shows the effect of Formula I treatment alone, resulting in 12.3% Si and 0.3% Ca on the membrane surface. Figure 5D shows the effect of HEDP plus Formula I treatment composition, resulting in 2.3% Si and 0% Ca on the membrane surface.

[0067] While embodiments of the technology of the present disclosure have been described, it should be understood that the disclosure is not limited thereto and that modifications may be made without departing from the technology of the present disclosure. The scope of the technology of the present disclosure is defined by the appended claims, and all devices, processes, and methods that come within the meaning of the claims, either literally or by equivalents, are intended to be embraced therein.

Claims

1. A scale inhibitor composition, the composition comprising: a silica inhibitor comprising an organophosphoric acid comprising 1-hydroxyethylidene-1,1-diphosphonic acid, present in an amount of 5 to 25 wt. % based on the total weight of the scale inhibitor composition; 1. A dispersant comprising a sulfonated acrylic acid polymer, said sulfonated acrylic acid polymer having the chemical formula 【Chemical 1】 and wherein the repeat unit is where c, d, and e are repeating units, n ranges from 1 to 100, and Z is H, Na, K, Ca, or NH ４ a dispersant, Including, A scale inhibitor composition, wherein the concentration ratio of the silica inhibitor to the dispersant is 1:

2.

2. The composition of claim 1, wherein n is 1 to 20.

3. 2. The composition of claim 1, wherein Z can be the same or different in c, d, and e, and the molar ratio of c:d:e ranges from 20:10:1 to 1:1:

20.

4. The composition of claim 1, wherein the molecular weight of the sulfonated acrylic acid polymer ranges from 10,000 to 30,000.

5. The composition of claim 1 wherein said silica inhibitor and said dispersant are mixed together.

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