SELECTIVE TREATMENT OF NITRATE FOR BRINE REGENERATION

Abstract

The present disclosure concerns processes for removal of nitrate from nitrate-rich brines, typically selective removal that permits reclaiming the nitrate after such removal.

Claims

1. A process for removal of nitrate from nitrate-containing brine, the process comprising: contacting, in a reactor, said nitrate-containing brine with an active medium, under conditions permitting conversion of said nitrate into nitrogen oxide gaseous products, and removing said nitrogen oxide gaseous products from the reactor, thereby reducing the concentration of said nitrate in the nitrate-containing brine, said conditions being selected to minimize formation of ammonia in the reactor.

2. The process of claim 1, wherein said conditions comprise contacting the nitrate-containing brine with the active medium in an oxygen-devoid atmosphere.

3. The process of claim 1, wherein said conditions comprise maintaining the temperature of the reactor at a range of between about 60 C. and about 99 C.

4. The process of claim 1, wherein said conditions comprise maintaining the reactor at a pH value of below about 3.

5. The process of claim 1, wherein the active medium occupies at least about 30% of the volume of the reactor.

6. (canceled)

7. The process of claim 1, wherein said active medium is activated carbon.

8. The process of claim 1, wherein said active medium is in granular or pellets form, having an average particle size of between about 0.1 mm and about 10 mm.

9. The process of claim 1, wherein the reactor is maintained under sub-atmospheric pressure.

10. (canceled)

11. The process of claim 1, wherein said brine comprises at least 100 ppm of nitrate.

12. The process of claim 1, comprises introducing one or more inert gases into the reactor, for purging said nitrogen oxide gaseous products from the reactor.

13. The process of claim 1, wherein the nitrate-containing brine and the active medium are contacted in an up-flow manner.

14. The process of claim 1, wherein the nitrate-containing brine and the active medium are contacted in a down-flow manner.

15. (canceled)

16. The process of claim 1, comprising pre-treating the nitrate-containing brine before introduction into the reactor to remove volatile contaminants.

17. The process of claim 1, comprising transferring said nitrogen oxide gaseous products to further processing for converting said nitrogen oxide gaseous products into nitric acid or into atmospheric nitrogen (N.sub.2).

18. (canceled)

19. (canceled)

20. (canceled)

21. The process of claim 1, wherein the nitrate-containing brine is circulated through the active medium.

22. The process of claim 1, wherein the nitrate-containing brine is regeneration brine from an ion-exchange system, municipal wastewater, agricultural wastewater, industrial wastewater, waste brine from evaporation ponds, reverse osmosis brine, and spent nitric acid.

23. (canceled)

24. (canceled)

25. A process for recovery of nitrate in the form of nitric acid from nitrate-containing brine, the process comprising: contacting, in a reactor, said nitrate-containing brine with an active medium that comprises activated carbon, under conditions permitting conversion of said nitrate into nitrogen oxide gaseous products, removing said nitrogen oxide gaseous products from the reactor, and treating said nitrogen oxide gaseous products in one or more treatment stages, thereby obtaining nitric acid.

26. The process of claim 25, wherein said one or more treatment stages comprise contacting said nitrogen oxide gaseous products with oxygen.

27. The process of claim 25, wherein said one or more treatment stages comprise contacting said nitrogen oxide gaseous products with water.

28. The process of claim 25, wherein said one or more treatment stages comprise contacting said nitrogen oxide gaseous products by reaction with an alkali or acid solution.

29. The process of claim 25, wherein said one or more treatment stages comprises converting said nitrogen oxide gaseous products into atmospheric nitrogen (N.sub.2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0075] FIGS. 1A-1B are schematic representations of a system for implementing the process according to an embodiment of this disclosure in a down-flow circulation (FIG. 1A) and in an up-flow circulation (FIG. 1B).

[0076] FIG. 2 shows a break-through curve in the Hybrid IX Test.

[0077] FIG. 3 shows the nitrate concentrations in the reactor during the Recovery Tests.

[0078] FIGS. 4A-4B show the change in nitrate (NO.sub.3.sup.) and nitrite (NO.sub.2) in the acid traps (FIG. 4A) and the alkaline traps (FIG. 4B) during the Recovery Tests.

[0079] FIG. 5 shows the % nitrate recovery in the Recovery Tests.

[0080] FIG. 6 shows the NO.sub.3.sup. removal rate (in milligrams of NO.sub.3.sup. per gram of activated per hour) as a function of the amount of removed nitrate for different types of activated carbon.

[0081] FIG. 7A is a schematic representation of a glass column used in the continuous test for assessing the impact of the direction of brine feed.

[0082] FIG. 7B shows removal rates of NO.sub.3 in the continuous tests, as milligrams of NO.sub.3.sup. per gram of AC per hour, as a function of the amount of removed nitrate for up-flow and down-flow configurations.

DETAILED DESCRIPTION OF EMBODIMENTS

[0083] A schematic representation of a process and a suitable system for employing the process of this disclosure is shown in FIGS. 1A-1B. Reactor 100 holds active medium 104, which is selected to provide a reduction reaction of nitrate into NOx under the conditions of the process as described herein. The active medium 104 typically occupies at least 30% of the volume of reactor 100. Nitrate-containing brine is fed into the reactor at through feed inlet 102, and the reactor is maintained under conditions as described herein in order to obtain said reduction reaction. The brine can be circulated via loop 110 through the active medium, e.g. drained from the bottom of the reactor and fed back into the reactor at a top portion 106 (i.e. circulation of the brine in a down-flow manner, FIG. 1A). Alternatively, the brine can be circulated via loop 110 through the active medium in an up-flow manner, as shown in FIG. 1B, e.g. extracted from the top of the reactor and fed back into the reactor at the bottom portion. NOx gaseous products at the headspace 108 formed above the active medium and liquid, can be evacuated and further treated, for example in one or more treatment modules 112 to form subsequent products (such as nitric acid, nitrogen gas and water). The treated brine exists the reactor through outlet 114 and can be further used as regenerated brine.

Example 1: Treatment of Brine from Ion-Exchange Processes

[0084] Hybrid ion-exchange (IX) system are based on traditional IX system that removes nitrate from the water. Once the ion exchange resin is exhausted, the system is regenerated with brine solution containing about 100 g/l of NaCl. The exact concentration depends on the resin type and operational considerations. During regeneration, the Cl exchange the nitrate, as well as other anions, adsorbed on the resin. Consequently, the brine contains all the anions, including the nitrate, that were displaced from the resin by the chloride. Two sets of tests were carried out and will be detailed below: [0085] 1. The Hybrid IX Test-testing whether the process of this disclosure permits obtaining regenerated brine that is suitable for reuse in a hybrid system without significant decrease in the resin performance. [0086] 2. The Recovery Test-demonstrating selective removal of nitrate from used brine and recovering it as nitric acid.

1. Hybrid IX Test

[0087] Cycles of water treatment and regeneration were performed. In each cycle an IX column filled with Purolite A520E was first exhausted with tap water spiked to 100 mg/l of nitrate. Once exhausted the resin was regenerated (with brine) before the next cycle started. The used brine was then treated according to the process of this disclosure for further use in the experiment.

[0088] The tests imitated all the major components of a full-scale system hybrid IX, treating 30 gallons per hour of city water spiked with nitrate to a 100 mg/l nitrate. The spiked water passed through a column containing 9 liters of nitrate selective IX resin. The hybrid IX tests included 42 regeneration cycles. Each cycle was operated for about 72 hours before regenerating the resin. The concentration of nitrate at the outlet of the column followed a typical behavior for these type of resins as the concentration were kept below 10 mg/l for 300-350 BV (bed volumes), before a sharp breakthrough was observed. An example of such breakthrough curve is provided in FIG. 2 for cycles 20 and 41. Comparing the two breakthrough curves demonstrates that no degradation in the IX ability to remove nitrate was observed in the Hybrid IX Tests.

[0089] The Hybrid IX Test clearly shows that the process allows the reuse of the brine for IX regeneration with respect to the IX ability to remove nitrate.

2. Recovery Test

[0090] In these experiments, a synthetic brine (that was similar in its composition to the brine from the Hybrid IX Test) was treated by a process according to this disclosure. The gases emitted during the operation of the process were captured in a series of traps and the recovery of nitrogen, either as nitrate or nitrite, was measured. NOx gases (i.e. NO+NO.sub.2) as well as CO, and SO.sub.2, were measured in the tailing.

[0091] The recovery tests were conducted with synthetic brine containing 20-30 g/l of nitrate and 40-70 g/l of Cl.sup.. This concentration ranges that were observed in the Hybrid IX Tests. In each cycle of the recovery experiment, the reactor treated 6 liters of brine. The concentration of nitrate was measured before and after the treatment in the brine and in the traps that were connected to the gas outlet (FIGS. 1A-1B). The ability of the reactor to remove nitrate is clearly demonstrated in FIG. 3 as the nitrate concentration in the brine dropped to below 4 g/l in all cycles. A target concentration for brine reuse was set to <5 g/l, as it allows to regenerate the IX resin over and over without prolonged degradation in IX capacity. The ability of the system to treat the brine to below 5 g/l suggests that it is possible to use it as part of an IX hybrid system.

[0092] Unlike most suggested hybrid IX, the process and system herein were designed not only to treat the brine but also to recover the nitrate using a NOx convector. The gas outflow from the regeneration process was directed through a series of alkaline and acid traps that absorbed the gases either as nitrite or nitrate. According to the chemistry of the process described hereinabove, nitrite accumulates in the alkaline traps but not in the acid traps (as the pH there can get to <1 which is below the pKa of the nitrous acid, being 3.16). The accumulation of nitrate and nitrite in the acid and alkaline traps is depicted in FIG. 4A-4B respectively. The dominant nitrogen species in the acid traps was nitrate, while in the alkaline traps, nitrite was the dominant species.

[0093] The recovery is the amount of nitrogen that was accumulated in the traps with respect to the amount of nitrogen that was lost from the reactor. The recovery can be calculated by:

[00001]$\begin{array}{cc}\mathrm{Recovery}\left[\%\right]=\frac{.Math.{\mathrm{NO}}_{3\mathrm{traps}}^{-}\left[\mathrm{mol}\right]+{\mathrm{NO}}_{2\mathrm{traps}}^{-}\left[\mathrm{mol}\right]}{{\mathrm{NO}}_{3\mathrm{reactor}}^{-}\left[\mathrm{mol}\right]}100& \left(1.6\right)\end{array}$

[0094] The recovery during the different cycles varies from 30% to over 100% (FIG. 5). This variance is mainly related to technical problems in the system. For example, a leak from the reactor was detected after cycle 6. Once it was fixed, the recovery increased in the following cycles. A recovery rate larger than 100% is related to analytical errors.

[0095] The average recovery in the traps was 79%. This means that about 20% of the nitrogen did not convert to either nitrite or nitrate in the traps and exited the system as gas. The tailing gas analysis showed that an additional 5% of the eliminated nitrate was recorded as NOx. However, it's important to note that this measurement does not include the nitrous acid portion.

Example 2: Effect of Different Carbon Types

[0096] The effect of utilization of different types of activated carbon (Table 1) as active mediums on the efficiency of the process was assessed.

TABLE-US-00001 TABLE 1 Types of activated carbon Batch Type Source A Granular Bituminous B Granular Coconut shell C Granular Coconut shell D Granular Wood/plant E Powder Unknown

[0097] 20 ml samples of activated carbon were batch-tested in 100 ml glass reactors, to which 40 ml of regeneration brine containing about 25 g/l of nitrate were introduced. The samples were tested in 30-40 batch cycles, in every such cycle fresh brine was introduced into the activated carbon and the reactors were heated to 90 C. for about 24 hours. Then the nitrate concentration was measured in each of the reactors. The nitrate removal rate, as milligrams of NO.sub.3.sup. for each gram of AC per hour (mg-NO.sub.3.sup./g-AC/hour), was then calculated. The results are provided in FIG. 6.

[0098] While some differences between the activated carbon types were observed, all tested activated carbon showed ability to remove nitrate from brine in the tested process conditions, with an average rate of 3.36 mg-NO.sub.3.sup./g-AC/hour and a standard deviation of 0.9 mg-NO.sub.3.sup./g-AC/hour. Hence, without wishing to be bound by theory, the process has little sensitivity to the type of activated carbon used.

Example 3: Effect of Brine Feed Flow Direction

[0099] Continuous feed tests were performed a simplified system described schematically in FIG. 7A. A 50 mm glass column (200) was filled with 377 g of granular activated carbon (202). Column 200 included a gas outlet 208, and two brine ports: a top port 204 and a bottom port 206. The system was operated in two modes: Up-Flow mode in which the brine was introduced to the column through bottom port 206 and existed the column through top port 204, and Down-Flow mode in which the brine was introduced to the column through top port 204 and existed the column through bottom port 206. The flow rate ranged from 18-47 ml/hour. The rate of removal of NO.sub.3.sup. in both modes of operation is shown in FIG. 7B.

[0100] As can be seen, similar rates were obtained for both flow modes; the average removal rate was 1.54 mg-NO.sub.3.sup./g-AC/hour with a standard deviation of 0.42 mg-NO.sub.3.sup./g-AC/hour. The tests show that the process can be operated in continuous mode and has little sensitivity to the direction of flow of brine within the reactor.