SI9800182A - Process for treatment with nitrate ion contaminated water - Google Patents

Abstract

The present invention refers to a process of purification of nitrate ion polluted water, including drinking water and technological water, using a combined process of regeneration of nitrate ion saturated ion-exchange resins and catalytic hydrogenation of nitrate ions in a regeneration solution transforming them to nitrogen. By application of the invention which consists of the ion-exchange as physical chemistry method of nitrate ion removal from the polluted water stream, of the regeneration of the saturated or partially saturated ion-exchange resin by means of a water solution of chloride ion, and of the simultaneous removal of the nitrate ion by means of the heterogeneously catalysed hydrogenation carried out in two- or three-phase overflow reactor systems, the nitrate ion concentration in drinking and technological water can be effectively reduced on the legally prescribed value.

Description

Cleaning process for nitrate ion contaminated water

FIELD OF THE INVENTION

The present invention relates to a process for the purification of polluted waters, including drinking water and process water, by a combined process of regeneration with nitrate ions of saturated ion exchange masses and catalytic hydrogenation of nitrate ion in a regeneration solution and its conversion to nitrogen. Using an invention consisting of ion exchange as a physicochemical method of removing a nitrate ion from a polluted stream, regenerating a saturated or partially spent ion exchange mass with an aqueous chloride ion solution, and simultaneously removing the nitrate ion from the latter by heterogeneously catalyzed hydrogenation carried out in two- or three-phase flow reactor systems can effectively reduce the nitrate ion concentration to the statutory value in drinking and process waters.

The problem solved by the invention

Excessive use of natural or artificial fertilizers on agricultural land significantly increases the concentration of nitrate ion in surface water and groundwater, up to 200 mg / L. The use of such waterways to supply the population with drinking water causes carcinogenic diseases and damage to the central nervous system in humans; however, their impact on other living beings and as technological water is problematic.

The state of the art

So far, several methods have been available to remove nitrate ion from aqueous media, for example:

• ion exchange, • ultrafiltration, • reverse osmosis, • biological denitrification, and • heterogeneously catalyzed reduction in the liquid phase.

The disadvantage of the first three physicochemical processes is that they produce waste (secondary) water courses with a very high content of nitrate ion, whose discharge into the environment, especially in continental areas, presents an unacceptable load for the environment. In times of high ecological awareness, only biological denitrification and heterogeneously catalyzed reduction of nitrate ion have such a further perspective, since both techniques allow selective conversion of nitrate ion via intermediates into harmless nitrogen without any wastewater production. The process of biological denitrification also has some drawbacks, which are particularly evident in the slowness and difficulty of managing the reaction. Additional considerations for the introduction of the biological denitrification process in the field of drinking water, however, raise the high likelihood of contamination of the stream of purified water by micro-organisms from the biological denitrification reactor, incomplete consumption of organic compounds added to water (eg methanol, acetic acid) as a carbon source and, consequently, increased consumption of chlorine in the disinfection process as a final cleaning step. Therefore, the heterogeneously catalyzed reduction method, which is still in various developmental stages, is an alternative to biological denitrification, since it is up to 100 times faster.

The process of heterogeneously catalyzed hydrogenation of a nitrate ion, which can be represented by the following chemical reaction:

2NO ₃ + 5H ₂ - _{> Nz + 2QH} - _{+ 4H2} q (i) is carried out in a two- or three-phase reactor system in which the contaminated aqueous phase and the reducing agent (i.e. hydrogen or hydrogen-containing gas mixture) are contacted with a nitrate ion. at the active site of the solid catalyst. Reduction of nitrate ion via intermediate to nitrogen occurs at very mild reaction conditions: temperature up to 298 K and overall pressure from 1 to 10 bar, with partial hydrogen pressure or equal to the whole or substantially lower. Horold et al. (Catal. Today, 17, 21-30 (1993)) used bimetallic catalyst, ie a bimetallic catalyst, in experiments on catalytic reduction of nitrate ion in a slurry reactor. Pd (5% by weight) and Cu (1.25% by weight) metal phase applied to the y-A1 ₂ O3. As can be seen from the results of their work, the catalyst used shows both high activity for hydrogenation of nitrate ion in aqueous solution as well as chemical stability. Its only drawback is the formation of ammonium ion as a by-product of the reaction, which reduces the selectivity of the reaction (82 mol% under the following experimental conditions: reaction temperature: 283 K; hydrogen partial pressure: 1.0 bar; total operating pressure: 1.0 bar; initial nitrate ion concentration: 100 mg / L; catalyst concentration: 1.6 g / L). Pintar and Levec (SI patent, 9500357, January 7 (1998)) have developed a Pd-Cu / y-Al2C> 3 bimetallic catalyst where metal phases are deposited on aluminum oxide by a wet impregnation method in such a sequence that ensures that more than 90 percent of the initial amount of nitrate ion is converted to nitrogen. Pintar et al. (J. Catal.,

174, 72-87 (1998)) have shown that, when removing nitrate ion from aqueous solutions or drinking water containing significant amounts of hydrogen carbonate ion (non-constant hardness), the selectivity of the reaction using the catalyst of the invention discussed in SI 9500357 (1998), significantly deteriorates. Pintar et al. (J. Catal., 174, 72-87 (1998)) also state that it is not possible to directly purify with nitrate ions of contaminated drinking water using the catalytic hydrogenation method, since the concentrations of the formed ammonium ion in the purified water exceed the legal the prescribed value (i.e., 0.5 mg / L NH3).

Of all the industrial processes that effectively remove excess nitrate ion from drinking water, setting up an ion exchange process is the most economically advantageous (Kapoor and Viraraghavan, J. Environ. Eng, 123 (4), 371-380 (1997)). As mentioned above, the drawback of this technique is the formation of a secondary stream of aqueous solution, which as a rule contains very high concentrations of nitrate, sulfate and chloride ions, with its release into the environment being environmentally controversial. Hoek et al. (Water, Air, and Soil Pollution, 37, 41-53 (1988)) and Clifford and Liu (/. 85 (4), 135-143 (1993)) eliminated the disadvantages of the physicochemical ion exchange process by eliminating the column with The ion exchanger is connected to a biological denitrification reactor that enables regeneration with nitrate ions of a saturated or partially exhausted ion exchange mass in a closed circuit. In this way it is possible to drastically reduce the amount of sodium chloride regeneration solution discharged into the surrounding watercourses. Clifford and Liu (J. AWWA, 85 (4), 135-143 (1993)) further state that by using a combined process consisting of an ion exchanger column and a sequential batch reactor containing microorganisms, the amount consumed Sodium chloride is reduced by 50 percent and the amount of regenerative liquor discharged into the environment by 90 percent.

DESCRIPTION OF THE INVENTION

The object of the present invention is a process for purification with nitrate ion of contaminated water, which combines the physicochemical process of ion exchange with the method of heterogeneously catalyzed hydrogenation in such a way that effectively eliminates their disadvantages, ie: (i) formation of secondary water stream with high nitrate content , sulfate and chloride ions; (ii) contamination of purified water with the production of ammonium ions, which is formed due to the unsatisfactory selectivity of PdCu bimetallic catalysts in the presence of hydrogen carbonate ions. Schematically, the combined process of the present invention is presented in Figure 1.

Column (1) contains a layer of strongly basic ion exchange mass (e.g., IMAC HP-555 manufactured by Rohm and Haas Co.) in chloride form. At ambient or medium temperatures and overall pressures up to 10 bar, the contaminated water is pumped into it by nitrate ions so that it passes through the nascent layer of the ion exchanger preferentially from the bottom up, with the linear velocity of the water flow calculated at the empty cross-section of the column , is up to 60 mph. In doing so, the nitrate ion dissolved in water is equimolarly exchanged with the chloride ion entering the solution from the ion exchange mass. Since the maximum permissible concentration for nitrate ion in drinking water is 50 mg / L, only so much of the contaminated water can be led into the ion exchanger column, the remainder flowing through the circulation pipe to the point (2) where the purified stream is combined with the crude, the concentration of nitrate ion in the solution is lower than the maximum allowed. At the moment when the concentration of nitrate ion in the water flow at the site (2) is higher or equal to 50 mg / L, we stop introducing the water stream contaminated with nitrate ions into the column (1), or if more are included in the system. of the ion exchanger columns, switch to another column in which the ion exchange mass is in chloride form.

A reducing agent is introduced into the saturator (3) containing the aqueous sodium chloride solution or the aqueous calcium chloride solution (regeneration solution), where the chloride ion concentration is up to 20 g / L. hydrogen or hydrogen containing gas, the preferential gas mixture H2N2, wherein the concentration of nitrogen in the gas mixture ranges from 5 to 95% by volume. At the same time, we include a pump (4) which draws an aqueous solution of chloride ion through a saturator and a catalytic reactor so that the aqueous solution of chloride ion passes through the catalytic reactor from the bottom up, with its linear velocity up to 0.5 m / s. The saturator is also equipped with a mixing nozzle (3a) which allows the liquid and gas phase to be well contacted. At the same time by activating the pump (4), we also activate the delivery of the neutralizing agent, ie. aqueous hydrochloric acid solution, which ensures that the pH value of the hydrochloride ion aqueous solution ranges from 5.0 to 7.0, preferably in the range from 5.0 to 5.5. When the total system pressure is equal to the setpoint, switch on the pump (5), which draws the aqueous chloride ion solution through the ion exchanger column and the saturator, so that the aqueous chloride ion solution passes through the ion exchanger column, preferentially from top to bottom, with a linear speed of up to 60 mph. In this solution, the chloride ion present in the regeneration solution is equimolarly exchanged with the nitrate ion entering the solution from the ion exchange mass. Due to the constant pumping of an aqueous solution of chloride ion through a catalytic reactor containing a Pd-Cu bimetallic catalyst, the nitrate ion present in the regeneration solution reacts with hydrogen and is converted to nitrogen, and the products of heterogeneously catalyzed reaction are water and equimolar amount of hydroxyl ions. The resulting nitrogen is separated from the hydrogen in the gas mixture by means of a membrane separator (6) and discharged into the environment. When the concentration of nitrate ion in the aqueous chloride ion solution drops below 40 mg / L, stop the regeneration solution being pumped through the column (1). As the ion exchange mass is again in chloride form in the fly, the column (1) can be reused to remove nitrate ions from the polluted water stream. In the meantime, if more than one ion exchanger column is included in the regeneration solution, we begin to pump through the column in which the ion exchanger is in nitrate form. After the regeneration of the saturated or partially exhausted ion exchange mass is completed, the aqueous chloride ion solution does not need to be released into the environment due to its low nitrate content and can be used in further regeneration cycles.

The catalytic reactor may contain a catalyst bed composed of γAI2O3 particles of any shape, on which the Pd and Cu metal phases are deposited in such a sequence that the Pd metal phase overlaps the Cu metal phase, with the concentration of Pd metal phase on the support varying from 0.3 up to 10% by weight, and the Cu metal phase concentration ranges from 0.05 to 5% by weight. A more detailed preparation of Pd-Cu / v-A ^ O bimetallic catalysts used in the present invention is addressed by the SI patent (Pintar and Levec, 9500357, January 7 (1998)).

Monolithic blocks with cross sections of channels of different shapes and effective diameters up to 1 cm on which Pd and Cu metal phases are applied in such a sequence that the Pd metal phase overlaps the Cu metal phase with the concentration of Pd metal phase at the carrier ranges from 0.3 to 10 weight percent, and the Cu metal phase concentration ranges from 0.05 to 5 weight percent. A more detailed preparation of the Pd-Cu bimetallic catalysts used in the present invention is contemplated by the SI patent (Pintar and Levec, 9500357, January 7 (1998)).

In order to maintain electroneutrality, the nitrate ion converted in the catalytic reactor is replaced by a hydroxyl ion, which in turn increases the pH of the aqueous solution when passing through the catalytic layer. In the neutral or basic pH range significant amounts of nitrite ion could accumulate in the aqueous chloride ion solution. In order to avoid this, the saturation vessel is equipped with a pH regulator, which, if necessary, doses the aqueous hydrochloric acid solution into the aqueous chloride ion solution. The added amounts of hydrochloric acid are also sufficient to maintain a constant concentration of chloride ions in the regeneration solution, in other words, to replace the amount of chloride ions consumed in the regeneration process.

A reagent is required for reduction. hydrogen or hydrogen-containing gas, the preferential H2-N2 gas mixture, can be introduced into the saturator, so that the hydrogen or gas mixture H2-N2 injection site is located above the surface of the aqueous chloride ion solution in the saturator. In this case, an aqueous solution containing chloride (and nitrate) ions and dissolved hydrogen flows through the catalytic reactor in a bottom-up direction, the catalytic reactor being considered as a two-phase reactor system.

A reagent is required for reduction. hydrogen or hydrogen containing gas, the preferential H2-N2 gas mixture, can be introduced directly into the catalytic reactor, with the hydrogen or gas mixture site of H2-N2 being located at the bottom of the catalytic layer. In this case, an aqueous solution containing chloride (and nitrate) ions flows through the catalytic reactor in a downstream direction, containing the chloride (and nitrate) ions, and the gaseous phase, with the catalytic reactor being considered as a three-phase reactor system.

EXECUTIVE EXAMPLES

Example 1: Removal of nitrate ion from a stream of aqueous solution by ion exchange method

In a thermostated glass tube with an inside diameter of 0.9 cm there was a solid layer of strongly basic IMAC HP-555 ion exchange mass (Rohm and Haas Co.) in chloride form. A model aqueous nitrate ion solution was introduced into the column using a piston pump (LDC Analytical, model 3200), which was prepared by dissolving a known amount of KNO3 in distilled water. The aqueous nitrate ion solution passed from the bottom upwards through the compacted layer of the ion exchanger. The experimental conditions under which we conducted the physicochemical process of ion exchange, i. The exchange of nitrate ion on the IMAC HP-555 ion exchanger mass is presented in Table 1. The course of removal of the nitrate ion from the aqueous solution was followed by determining the current nitrate ion concentration at the outlet of the ion exchanger layer by flow injection. analyzes (Perkin-Elmer UV / VIS spectrophotometer, Lambda 40P model; Perkin-Elmer FIAS module, model 300). The measurement results are shown in Figure 2 for different concentrations of nitrate ion in the feed solution.

Table 1. Experimental conditions of the nitrate ion exchange process in an IMAC HP-555 condensed ion exchange column.

Temperature, K 298 Total operating pressure, bar 1.0 The mass of the ion exchanger in the compacted layer, g 1.50 Average diameter of ion exchanger grains, mm 0.43 Bulk density of the layer, g / cm ³ 0.32 Porosity of the layer, / 0.43 Input nitrate ion concentration, mg / L 50.0 - 200.0 Liquid phase volume flow, mL / min 9.5 Liquid phase volume flow, BV / h 120 Linear velocity of the liquid phase, m / h 9.0

The mathematical analysis of the data obtained confirms that the amount of exchanged nitrate ion per unit mass of the ion exchange mass does not depend on the concentration of nitrate ion in the feed stream. The capacity of the used IMAC HP-555 ion exchange mass to exchange nitrate ion under the given conditions is 2.86 mmol / g (0.92 eq / liter ion exchange mass). The same result was obtained by determining the capacity of the ion exchanger by the argentometric titration method.

Experiments have also been carried out to determine the influence in aqueous solution of anions present on the exchange capacity of the IMAC HP-555 ion exchanger for nitrate ion. They showed that the capacity of the ion exchanger in the presence of sulfate, chloride and hydrogen carbonate ion decreases in the following order: SO4 ~> Cl “>> HCO3. By analyzing the breakthrough curves obtained from experiments when drinking water was used as the liquid phase instead of distilled, it was found that only the sulphate and chloride ions were affected by the reduction capacity of the ion exchange mass used to exchange the nitrate ion.

Example 2: Regeneration of an ion exchange mass saturated with nitrate ions

A thermostated glass tube with an internal diameter of 0.9 cm contained a compacted layer of strongly basic IMAC HP-555 ion exchange mass (Rohm and Haas Co.) in nitrate form. An aqueous solution of chloride ion was introduced into the ion exchanger column using a piston pump (LDC Analytical, model 3200), which was prepared by dissolving a known amount of NaCl in distilled water. The aqueous chloride ion solution passed from the bottom upwards through the ion exchanger layer. The experimental conditions under which IMAC HP-555 saturated saturated exchange mass was regenerated with nitrate ions are presented in Table 2. The course of exchange of nitrate ions on the exchange mass with chloride ions in aqueous solution was followed by leaving the liquid phase at the exit from the liquid phase. of the ion exchanger layer was determined by the current nitrate ion concentration by flow injection analysis (Perkin-Elmer UV / VIS spectrophotometer, Lambda 40P model; Perkin-Elmer FIAS module, model 300). The results of the measurements are shown in Figure 3 for different volume flows of the regeneration solution with an inlet concentration of sodium chloride, CN _a ci, inlet = 5 g / L.

Figure 3 shows that under the selected conditions of regeneration with nitrate ions, the saturated ion exchange mass IMAC HP-555 using aqueous solution

NaCl sc _Na ci, an inlet-5 g / L during 3.5 - 4 h more than 99 percent of the ion exchanger switches from nitrate to chloride form. Although an aqueous solution with a relatively low concentration of sodium chloride was used in the regeneration of the ion exchange mass in this embodiment, the calculations show that only five to eight percent of it was efficiently consumed through the solidified layer of the ion exchanger by the amount of chloride ion pumped.

Table 2. Experimental conditions of the IMAC HP-555 ion exchange mass regeneration process saturated with nitrate ions.

Temperature, K 298

Total operating pressure, bar 1.0

Mass of the ion exchanger in the compacted layer, g 2.25

Average diameter of ion exchanger grains, mm 0.43

Bulk density of the layer, g / cm ³ 0.32

Layer porosity, / 0.43

Input concentration of chloride ion, g / L 5.0

Volume flow of the regeneration solution, mL / min 3.0 - 7.0

Volume flow of regeneration solution, BV / h 25.6 - 60

Linear velocity of the regeneration solution, m / h 2.8 - 6.6

Example 3: Successive attempts at ion exchange of nitrate ion and regeneration of a saturated ion exchanger

In a thermostated glass tube with an inside diameter of 0.9 cm there was a solid layer of strongly basic IMAC HP-555 ion exchange mass (Rohm and Haas Co.) in chloride form. An aqueous nitrate ion solution was introduced into the ion exchanger column using a piston pump (LDC Analytical, model 3200), which was prepared by dissolving a known amount of KNO3 in distilled water. The aqueous nitrate ion solution passed from the bottom upwards through the compacted layer of the ion exchanger. The experimental conditions under which we studied the physicochemical process of ion exchange, i. nitrate ion exchanges on the IMAC HP-555 ion exchange mass are presented in Table 3.

Table 3. Experimental conditions of nitrate ion exchange in an exchange-regeneration cycle using the IMAC HP-555 ion exchanger.

Temperature, K 298

Total operating pressure, bar 1.0

Mass of the ion exchanger in the compacted layer, g 2.25

Average diameter of ion exchanger grains, mm 0.43

Bulk density of the layer, g / cm ³ 0.32

Layer porosity, / 0.43

Input nitrate ion concentration, mg / L 200

Liquid phase volume flow, mL / min 9.5

Liquid phase volume flow, BV / h 81.1

Linear velocity of the liquid phase, m / h 9.0

The course of removal of the nitrate ion from the aqueous solution was followed by determining the current nitrate ion concentration at the outlet of the ion exchanger layer by flow injection analysis (Perkin-Elmer UV / VIS spectrophotometer, Lambda 40P model; Perkin-Elmer FIAS module, model 300). The results of the measurements are shown in Figure 4 for the various exchange-regeneration cycles. When the concentration of nitrate ion in the flow of aqueous solution at the outlet of the column of the ion exchanger was equal to the concentration of nitrate ion in the feed solution, we replaced the column with a saturated layer of ion exchange mass instead of aqueous solution. of nitrate ion begin to introduce a regeneration solution of sodium chloride with CN _a ci, inlet ⁼ 5 g / L. This was introduced into the ion exchanger column by passing it from the bottom up into the impregnated layer of the ion exchanger. The process of regeneration with nitrate ions of a saturated ion exchanger was carried out for four hours, and the remaining experimental conditions of the regeneration part of the cycle are given in Table 4. After four hours, we began to re-introduce water into the column with the ion exchanger in which it was in chloride form. potassium nitrate solution sc _N0 - _inlet = 200 mg / L.

The process of ion exchange of the nitrate ion and regeneration with the nitrate ions of the saturated ion exchange mass were repeated four times, without changing the ion exchanger.

Table 4. Experimental regeneration conditions with nitrate ions of the saturated IMAC HP-555 ion exchanger in the exchange-regeneration cycle.

Temperature, K 298

Total operating pressure, bar 1.0

Mass of the ion exchanger in the compacted layer, g 2.25

Average diameter of ion exchanger grains, mm 0.43

Bulk density of the layer, g / cm ³ 0.32

Layer porosity, / 0.43

Input concentration of chloride ion, g / L 5,0

Volume flow of the regeneration solution, mL / min 7.0

Volume flow of regeneration solution, BV / h 60

Linear velocity of the regeneration solution, m / h 6.6

Figure 5 shows the capacity of the IMAC HP-555 ion exchange mass as a function of the number of exchange-regeneration cycles. It is evident that under the chosen experimental conditions, despite the use of a relatively low sodium chloride concentration solution, the capacity of the ion exchanger with the number of cycles does not change, which is also confirmed by the independent determination of the exchange capacity of the ion exchange mass after the fifth exchange-regeneration cycle by means of argentometric titration methods.

Example 4: Preparation of catalysts

The Pd-Cu / y-Al2O3 bimetallic catalyst was prepared as follows:

The γ-Αΐ2θ3 beads (NikkiUniversal Co., Ltd., Tokyo, Japan; type NST-5) with an average diameter of 1.7 mm and a specific surface area (BET method) of 171 m ² / g were used as the carrier of the active components. The total pore volume and average pore diameter were 1.02 g / cm ³ and 16.1 nm, respectively. Pd (NO3) 2ŽH2O (Fluka, pa) and Cu (NO ₃ ) 23H ₂ O (Merck, pa) were used as precursors for the formation of Pd and Cu metal phases. The aqueous solution of the salts of each precursor of the metal phase was applied to aluminum oxide by an impregnation method at room temperature. The catalyst was synthesized by first applying copper salt to the support followed by the application of palladium salt. The impregnation of the carrier with aqueous salt solutions was followed by drying of the material at T = 423 K, conversion of nitrates to oxides at T = 773 K, reduction in the flow of pure hydrogen at T = 773 K, and cooling in a nitrogen atmosphere. The catalyst thus produced contains 1.0 wt. % Pd and 0.3 wt. % Cu, with both elements being in metallic state. In further embodiments, this catalyst is designated KAT-1.

Following the wet impregnation process described above, a Pd-Cu / γAI2O3 bimetallic catalyst containing 0.4 wt. % Pd and 0.12 wt. % Cu. In further embodiments, it is designated KAT-2.

Example 5: Reduction of nitrate ion in a Pd-Cu / Y-AJ ₂ O ₃ condensed-flow reactor with a bimetallic catalyst KAT-1

In a thermostated glass tube with a diameter of 2.0 cm there was a solidified layer of Pd-Cu / y-Al2O3 bimetallic catalyst KAT-1, which was synthesized according to the ¹⁵ procedure described in Example 4. In the reactor with a solidified catalyst layer, a piston was used. pumps (LDC Analytical, model 3200) introduced an aqueous nitrate ion solution, which was prepared by dissolving a known amount of potassium nitrate in distilled water. The H2-N2 gas mixture of known hydrogen concentration was prepared by means of electronic mass flow regulators (MKS) and introduced into the catalytic reactor on its underside. The aqueous nitrate ion solution and the H2-N2 gas mixture passed through the nascent PdCu / y-A1 ₂ O ₃ layer of the bimetallic catalyst KAT-1 downstream. The experimental conditions under which the catalytic hydrogenation of aqueous nitrate ion solutions in a three-phase flow reactor was studied are presented in Table 5.

Table 5. Experimental conditions for the nitration ion hydrogenation in a three-phase flow reactor with a solidified layer of Pd-Cu / y-Al2O3 catalyst KAT-1.

Temperature, K 298 Total operating pressure, bar 1.0 Hydrogen partial pressure, bar 0.1 Mass of the KAT-1 catalyst in a compacted layer, g 25 Average diameter of catalyst grains, mm 1.7 Bulk density of the layer, g / cm ³ 0.46 Porosity of the layer, / 0.43 Input nitrate ion concentration, mg / L 70.0 Liquid phase volume flow, mL / min 4.0 - 10.8 Holding time of the liquid phase in the reactor, min 1.3 - 3.5 Gaseous phase volume flow, mL / min 80 pH of the aqueous solution, / 5.3

The course of the destructive reduction of the nitrate ion or its removal from the aqueous solution was followed by determining the current concentrations of nitrate, nitrite and ammonium ion during the liquid phase at the outlet of the catalytic layer by means of flow injection analysis (Perkin-Elmer UV / VIS spectrophotometer, model Lambda 40P; Perkin-Elmer FIAS module, model 300). The results of the experiments on the catalytic hydrogenation of the nitrate ion in the model solutions are shown in Figures 6 and 7 for different liquid phase volumetric flow rates.

Figure 6 shows the conversion of the nitrate ion to the liquid phase at the exit of the catalytic layer as a function of the quotient -. In the area

T t T · C vol., L NOJ, the inlet of the selected liquid phase liquid flow rates with an inlet nitrate ion concentration c _NQ - _inlet = 70 mg / L, the concentration of the latter in aqueous solution at the outlet of the reactor with a solidified catalyst bed was lower than the statutory limit. values (i.e., 50 mg / L). The experiments carried out also confirm that the accumulation of nitrite ion as an intermediate of the reaction is negligible when conducting the catalytic hydrogenation process of the nitrate ion under the conditions described in Table 5.

Figure 7 shows the concentration of ammonium ion as a by-product of the reaction in the liquid phase flow at the exit of the catalytic layer as a function of the quotient

-. The concentration of ammonium ion in aqueous solution is, at all ^ vols, L ^ NOj, the inlet volume flow rates of the liquid phase except at 4> _V oi., L ⁼ 4-0 mL / min, lower than the legal value (i.e., 0.5 mg / L NH3).

Attempts have been made to catalytically hydrogenate aqueous solutions of nitrate ion in a three-phase flow reactor with a solid catalyst bed in which drinking water of the following composition was used as medium instead of distilled water: c (Na ⁺ ): 5.7 mg / L; c (K ⁺ ): 1.5 mg / L; c (Ca ²⁺ ); 105.0 mg / L; c (Mg ²⁺ ); 22.8 mg / L; c (Cl “); 11.5 mg / L; c (NOJ); 47.7 mg / L; c (HCOJ); 316.6 mg / L; c (SO ² ):

36.5 mg / L. Although the initial nitrate ion concentration was lower in these measurements, significant amounts of ammonium ion (1.8 - 4.3 mg) were formed in the presence of the hydrogen carbonate ion in the liquid phase, in contrast to the catalytic hydrogenation experiments performed with potassium nitrate model solutions. / L), which is consistent with the observations reported by Pintar et al. (J. Catal. 174, 72-87 (1998)).

Example 6: Regeneration with saturated ion exchange mass nitrate ions and simultaneous reduction of nitrate ion in a three-phase flow reactor with a solid-state layer Pd-Cu / y-Al2O _{3 of the} bimetallic catalyst KAT-2

This embodiment describes the progress of a combined process of regeneration with the nitrate ions of a saturated IMAC HP-555 ion exchange mass and the simultaneous removal of a nitrate ion from a regeneration solution performed in a laboratory experimental apparatus, schematically shown in Figure 1.

In the thermostated saturator there was a regeneration solution of sodium chloride sc _Na ci = 5.0 g / L. The pH of the regeneration solution was controlled by an autotitrator (Metrohm, model Titrino GPD 751), which, if necessary, dosed with aqueous hydrochloric acid (chci = 0.25 mol / L). The pH of the regeneration solution did not change over time (it ranged from 4.99 to 5.01). The saturator was connected via a piston pump (LDC Analytical model 3200) in Fig. 1 with figures 4 and 5, in closed circuits, connected to an ion exchanger column and a catalytic reactor in closed circuits.

A thermostated glass tube with an internal diameter of 0.9 cm contained a compacted layer of strongly basic IMAC HP-555 ion exchange mass (Rohm and Haas Co.) in nitrate form. By means of a piston pump (5), an aqueous solution of chloride ion contained in the saturator was pumped through the ion exchanger column, the liquid phase flowing from the bottom upwards through the solidified layer of the ion exchange mass. The experimental conditions under which regeneration with nitrate ions of a saturated ion-exchange mass was conducted were recorded in Table 6. By pumping an aqueous solution of chloride ion through an ion exchanger column, the saturator accumulated in it a nitrate ion released from the ion-exchange mass. In order to remove the accumulated nitrate ion in the regeneration solution, the aqueous chloride ion solution was simultaneously passed through a three-phase flow reactor in the manner described in more detail in the following embodiment.

Table 6. Experimental conditions of the combined regeneration process with nitrate ions of saturated ion exchange mass and simultaneous removal of nitrate ions from the regeneration solution using heterogeneously catalyzed hydrogenation in a three-phase flow reactor.

Temperature, K 298

Total operating pressure, bar 1.0

Hydrogen partial pressure, bar 0.5

The mass of the ion exchanger in the compacted layer, g 1.50

Average diameter of ion exchanger grains, mm 0.43

Bulk density of the compacted ion exchanger layer, g / cm ³ 0.32

Porosity of the compacted ion exchanger layer, / 0.43

Volume of the regeneration solution in the saturator, L 1.0

NaCl concentration in the regeneration solution, g / L 5.0

Volume flow of the regeneration solution through a 8.2 ion exchanger column and through a catalytic reactor, mL / min

Mass of the KAT-2 catalyst in the compacted layer, g 25

Average diameter of catalyst grains, mm 1.7

Bulk density of catalytic bed, g / cm ³ 0.46

Catalytic layer porosity, / 0.43

Volume flow of the gaseous phase through the catalytic reactor, 80 mL / min pH value of the regeneration solution in the saturator, / 5.0

In a thermostated glass tube with an internal diameter of 2.0 cm there was a solidified layer of Pd-Cu / y-Al2O3 bimetallic catalyst KAT-2, which was synthesized according to the procedure described in example 4. Through a reactor with a solidified layer of catalyst, a piston pump was used. (4) pumped an aqueous solution of sodium chloride contained in the saturator. The H2-N2 gas mixture with known hydrogen concentration was prepared by means of electronic mass flow regulators (MKS) and introduced into the catalytic reactor on its underside. The regeneration solution and the H2-N2 gas mixture passed through the nascent PdCu / y-Al2O3 layer of the bimetallic KAT-2 catalyst in a downward direction. The experimental conditions in the catalytic reactor, in which the nitrate ion in the regeneration solution was converted to nitrogen in the presence of dissolved hydrogen, are given in Table 6. The course of the destructive reduction or removal of the nitrate ion from the regeneration solution was followed by the aqueous chloride solution. The saturator ions were used to determine the current concentrations of nitrate, nitrite and ammonium ions using flow injection analysis (Perkin-Elmer UV / VIS spectrophotometer, Lambda 40P model; Perkin-Elmer FIAS module, model 300). The results of an experiment of regeneration with nitrate ions of a saturated ion exchange mass and simultaneous removal of a nitrate ion from a regeneration solution by catalytic hydrogenation in a three-phase flow reactor are shown in Figure 8.

Figure 8 shows the time dependences of the concentrations of nitrate, nitrite and ammonium ion in an aqueous solution of sodium chloride contained in the saturator. It is apparent from the present invention that the accumulated amount of nitrate ions can be completely removed from the regeneration solution by the present invention so that it can be reused in subsequent regeneration cycles. Following the completion of the regeneration process of spent ion exchange mass and simultaneous destructive hydrogenation of the nitrate ion, the concentration of the nitrite ion in aqueous sodium chloride solution is lower than the legal value (i.e., 0.02 mg / L). Figure 8 also shows the time dependence of ammonium ion formation as a by-product of the reaction. The final amount of NH ₄ ions formed is negligible compared to the concentration of chloride ion in the regeneration solution and does not affect the exchange capacity of the IMAC HP-555 ion exchange mass.

After completing the experiment of a combined process of regeneration of spent ion exchange mass and simultaneous destructive hydrogenation of nitrate ion in a three-phase flow reactor with a solidified catalyst layer, the IMAC HP-555 ion exchange mass capacity for exchange of nitrate ion was determined using an argentometric titration method. This was equal to the initial capacity and amounted to 2.86 ± 0.01 mmol / g.

The catalysts useful in the present invention and shown in the above embodiments are the subject of SI patent no. 9500357, which is incorporated by reference.

Rohm and Haas Co. manufacturer cited in the description. is the Rohm and Haas Company, Philadelphia, USA.

DESCRIPTION OF THE IMAGES

Figure 1. Schematic illustration of a combined process for the simultaneous removal of a nitrate ion from an aqueous solution of a chloride ion for regeneration with nitrate ions of a saturated ion exchange mass by means of heterogeneously catalyzed hydrogenation in a flow reactor. 1: Ion exchange condenser column; 2: merger point of the purified and untreated liquid phase flow; 3: saturator; 3a: mixing nozzle; 4,5: pump;

6: membrane separator.

Figure 2. Nitrate ion concentration measured in the liquid phase stream at the exit of an ion exchanger column as a function of time for different inlet concentrations of the pollutant.

Figure 3. Nitrate ion concentration, measured in the liquid phase flow at the exit of an ion exchanger column, as a function of time for different volume flows of the regeneration solution.

Figure 4. Nitrate ion concentration measured in the liquid phase stream at the exit of an ion exchanger column as a function of time for several consecutive exchange regeneration cycles.

Figure 5. Ion exchange mass capacity as a function of the number of exchange-regeneration cycles.

Fig. 6. Conversion of nitrate ion measured in the liquid phase stream at the outlet of the reactor with the solidified layer Pd-Cu / y-Al2O3 of the bimetallic catalyst KAT-1, as a function of the l ^ kat ratio - «b-.

ΦνοΙ.Χ ' ^C NO J .input

Figure 7. Concentration of formed ammonium ion, measured in the liquid phase stream at the outlet of the Pd-Cu / y-Al2O3 condensation layer of the bimetallic catalyst KAT-1, as a function of the ratio _ ^m cat. ,

Φ vol.X ® NO

Figure 8. Time dependences of the concentrations of nitrate, nitrite and ammonium ions measured in the regeneration solution during the combined process of regeneration of the ion exchange mass with an aqueous solution of chloride ion and simultaneous reduction of the nitrate ion in a flow reactor with a compacted layer of Pd-Cu / y-Al2O3 bimetallic catalyst KAT-2.

Claims (6)

PATENT APPLICATIONS A process for the purification of nitrate ion contaminated waters, including drinking water and process water, using solid catalysts according to SI patent no. 9500375, characterized in that it consists of: • contacting nitrate ion containing water with ion exchange mass; • regeneration with nitrate ions of saturated or partially used ion exchange mass with aqueous chloride ion solution; and • contacting nitrate ion containing aqueous solution of chloride ion and hydrogen or hydrogen containing gas phase catalysts. Process according to claim 1, characterized in that it consists of: • removal of nitrate ion from the water stream by ion exchange, which takes place in a column with a condensed layer of ion exchange mass at ambient or medium temperature and overall pressure up to 10 bar, with a linear velocity of water flow less than or equal to 60 m / h, aqueous and the solution preferentially passes from the bottom upwards through the compacted layer of the ion exchanger; • regeneration with nitrate ions of a saturated or partially used layer of ion exchange mass by means of an aqueous solution of chloride ion, which in a closed circuit circulates at a linear speed up to 60 m / h through a column with a condensed layer of ion exchanger and saturator, the concentration of chloride ion in a regeneration solution of less than or equal to 20 g / L, while regeneration of the ion-exchange mass takes place at ambient and medium temperatures and overall pressures of up to 10 bar so that the aqueous chloride ion solution passes through the condensed layer of the ion exchanger preferentially from top to bottom; • supplying a reducing agent - hydrogen or hydrogen containing gas - to the “saturator; • simultaneous removal of nitrate ions from an aqueous solution of chloride ion in such a way that it is pumped in a closed circuit at a linear speed up to 0.5 m / s through a catalytic reactor in which the nitrate ion reacts with dissolved hydrogen and is converted to nitrogen, the reaction being carried out at ambient or medium temperature and overall pressure of up to 10 bar, while the aqueous chloride ion solution containing the nitrate ion passes through the catalytic reactor preferentially from the bottom up, • supplying the neutralizing agent - aqueous hydrochloric acid solution - to the saturator, the pH value of the aqueous chloride ion solution ranges from 5.0 to 7.0, preferably in the range from 5.0 to 5.5; • the separation of the resulting nitrogen from the hydrogen in the membrane separator and its release into the environment. Process according to claim 2, characterized in that a H2-N2 gas mixture is fed into the saturator, with the nitrogen content of the mixture ranging from 5 to 95% by volume. Process according to claim 2, characterized in that the hydrogen or the H2-N2 gas mixture is fed directly into the catalytic reactor at its bottom and passes from the bottom to the catalytic layer. Process according to claim 2, characterized in that the source of the chloride ion in the regeneration solution is sodium chloride. Process according to claim 2, characterized in that the source of the chloride ion in the regeneration solution is calcium chloride.