CH660692A5 - METHOD FOR REGENERATING ION EXCHANGERS. - Google Patents

Description

The invention relates to a method for regenerating ion exchangers according to the preamble of patent claim 1.

The ever increasing content of nitrates in natural waters has recently been a serious problem. Nitrates cannot be removed from water using the usual

Water treatment processes are removed because they are under natural conditions, i.e. aerobic, the end product and therefore a stable compound of the conversion of nitrogen compounds in the soil and in the water. The most important of the series of nitrogen sources is the large-area contamination caused by the use of nitrogenous industrial fertilizers in agriculture.

Nitrates cause health damage to fatal diseases in humans and warm-blooded animals. The most well-known is the influence of nitrates on the occurrence of so-called nitrate-alimentary methoglobemia, which can occur in infants up to the age of three months if water containing more than 15 mg is used to prepare the artificial diet. Contains 1 ~ 1 NO3. The Czechoslovakian standard allows up to 50 mg.l NO3. Analog standards also allow higher concentrations than the limit specified for infants. In adults, higher nitrate concentrations in drinking water cause esophageal, stomach and bladder cancer. They can also cause miscarriage in cows and fatal poisoning in artificially fed calves. Nitrates in water also have an unfavorable effect in the food industry (e.g. for malt germination), in the preservation of food and in the production of beverages.

In addition to the nitrates, the hardness components are a maladministration if their content in the treated water exceeds the values given by the drinking water standard. In addition, they are harmful in some food companies, where the greater hardness e.g. Causes the drinks to become cloudy.

One of the ways in which nitrates can be removed from the water is by using ion exchangers. Their common advantage is independence from the water temperature, the corresponding reaction rate, high efficiency and the course of denitrification without the addition of foreign substances and without the need for an anaerobic environment. For the most part, however, the content of the other anion components in the water changes unfavorably. A strongly basic anion exchanger in chloride form is most often used. However, its disadvantage is the high chloride content in the filtrate, because especially at the beginning of the working cycle, the anion exchanger of this type exchanges all the anions present for the chloride anion.

The content of these chlorides in the treated water then exceeds the values determined by the drinking water standard. The filtrate is basically a chloridate that can cause physiological complaints. In contrast, sulfates are removed from the treated water together with the nitrates. In some cases, hydrogen carbonates are also removed, so that the quality of the water is significantly changed. However, the advantage of using this chloride form of the anion exchanger is that it can be regenerated easily. When the filter bed is regenerated, the nitrates are washed out when eight volumes of a 10% sodium chloride solution are used.

The use of the strongly basic anion exchanger alone in the form of hydrogen carbonate is also unfavorable, because of the high hydrogen carbonate content in the filtrate. Hydrogen carbonates replace all anions present in the first half of the sorption phase. It is only in the second third of the sorption phase that the chloride content increases, and in the last third does the chloride concentration significantly outgrow the entry concentration due to its progressive desorption from the ion exchange bed.

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66U 692

However, in the case of inlet water with higher chloride concentrations, this means that the chloride values in the filtrate determined by the standard are exceeded. The sulfates are completely removed and their concentration only increases with the increasing nitrate concentration. Another disadvantage of the strongly basic anion exchanger in hydrogen carbonate form is its difficult regenerability. In the regeneration phase, the nitrates are only washed out after the application of 23 volumes after the anion exchange shear volume of a 10% NaHC03 solution.

The use of regenerated mixed chloride-hydrocarbonate beds of a strongly basic anion exchanger is also known. Your advantage is that chlorides as well as bicarbonates in the filtrate are already at the beginning of the working phase (sorbing phase), i.e. two anion components are included. However, the sulfates are removed together with the nitrates. The filtrate is therefore a chloride hydrocarbonate denaturate. As a result of the desorption of the chlorides in the second half of the working phase, the standardized chloride concentration in the filtrate is exceeded again if higher chloride concentrations are contained in the inlet water (albeit in the norm for drinking water).

Similarly, when removing nitrates via the anion exchanger in the sulfate cycle, all anions are exchanged for sulfate ions at the beginning of the working period.

A weakly basic anion exchanger in hydrogen carbonate form is also used for the denitrification of drinking water. However, this technological process has, besides the excess of hydrogen carbonate ions in the filtrate and the desorption of the chloride ion in the second half of the working cycle and the suppression of the sulfates, further disadvantages. In comparable waters, the denitrification capacity of the weakly basic anion exchanger is only about a quarter of that of strongly basic anion exchangers. If the water to be treated flows through an anion exchanger of this type, the denitrification capacity of which has already been exhausted, the captured nitrates spontaneously wash out of the ion exchanger and the outflowing water is therefore, on the contrary, enriched with nitrates.

Of the previously known methods of nitrate removal by ion exchangers from the water in terms of the efficiency, the type protected by AO No. 200 907 appears to be optimal, as it enables the nitrate to be removed selectively by means of the ion exchanger, the other anion components being retained in the water stay.

»This type uses three forms of the basic anion exchanger, namely the chloride, sulfate and hydrogen carbonate form, which are mixed in a certain ratio. A major disadvantage of this type, however, is that the filter bed obtained in this way cannot be regenerated and all three of the forms of the ion exchanger mentioned have to be produced separately once they have been exhausted. Therefore, this method can only be used in small, single-purpose plants that, for. B. are intended for denitrification of drinking water in the home, usually for the preparation of artificial infant nutrition. When this filter bed is exhausted, it is thrown away.

It follows from the above that processes which are economical, with simple regeneration of the anion exchanger, removing nitrates at the expense of the deterioration in the physiological properties of the water, and on the contrary, the method which selectively removes nitrates cannot be used on a larger scale.

The disadvantages mentioned are solved by the characterizing features of patent claim 1, which make it possible to use the ion exchange bed repeatedly, to selectively remove nitrates and possibly also to remove the hardness components at the same time. The essence of the regeneration process is that the denitrification filter based on a strongly basic anion exchanger or the denitrification filter and softening filter, the denitrification part of which is based on a strongly basic anion exchanger and the softening part is based on a strongly acidic cation exchanger, in the first phase of the regeneration with a solution containing chloride ions , e.g. with a sodium chloride or potassium chloride solution, and in the second phase with a solution containing sulfate ions, e.g. Na or K sulfate solution. In the second phase, the regeneration solution in addition to the sulfate ions, e.g. Sodium or potassium sulfate also hydrocarbonate ions, e.g. Sodium or potassium hydrogen carbonate.

The advantages of this regeneration process are that they make it possible to use strongly basic anion exchangers for the selective removal of nitrates from the water under economically advantageous conditions, while the other anion components and therefore also the physiological values of the water are retained. In view of the relatively simple regeneration process, this process can be repeated and used on a larger scale. In the case of simultaneous denitrification and softening of the water (e.g. for the industrial production of beverages), this process is also economically advantageous in that the solution from the regeneration of the anion exchanger is also used to regenerate the cation exchanger.

In the first phase of the regeneration cycle, there is an effective desorption of the nitrates, which in the previous work cycle are only trapped with a relatively small amount of the solution containing chlorine ions. The anion exchanger is predominantly converted to the chloride form in this phase. In the case of regeneration of the denitrification and softening filter, the regeneration agent from the anion exchanger is used simultaneously to regenerate the cation exchanger, or vice versa. In the further regeneration phase, the strongly basic anion exchanger from the chloride form is transferred to a mixture of different anion exchanger forms and at the same time the last residues of the nitrates from the working cycle are desorbed. The cation component of this second solution can optionally also regenerate the cation exchanger.

Tables 1 and 2 serve to prove the efficiency of the regenerated bed according to the invention. Tab. 1 shows the composition of the filtrate behind the filter bed of the strongly basic anion exchanger, which was regenerated only up to the chloride cycle. The amount of filtrate in the first column is expressed in multiples of the anion exchange volume used in the filter bed.

Table 2 shows the filtrate composition behind the anion exchange bed which was regenerated according to the invention. The amount of filtrate in the first column is expressed as a multiple of the anion exchange content used in the filter bed.

The values in Tab. 1 and 2 show that behind the two filters there is a marked elimination of the nitrates. Behind the second filter (Tab. 2), however, the content of the other anions is relatively evenly represented and in no proportion is the norm for drinking water exceeded. After the first filter, the sulfates are also removed together with the nitrates and in the first half of the process

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Table 1

4th

Table 3

Amount of filtrate

Composition of the filtrate m

V V-1

». VQ

NO "

1 / 2S04 =

HCO "

cr

20th

0

0

0.2

5.8

40

0

0

0.3

5.7

60

0

0

0.3

5.6

80

0

0

0.4

5.6

100

0

0

0.6

5.4

120

0

0

1.1

4.9

140

0.01

0

1.8

4.2

160

0.03

0

2.2

3.8

180

0.07

0

2.4

3.6

200

0.20

0.1

2.3

3.4

220

0.36

0.3

2.0

3.3

240

0.55

0.55

1.8

3.1

entrance

1.53

0.94

1.8

0.8

water

Filter bed: strongly basic anion exchanger of the second type, column height 0.6 m, s = 20 V.Vjj "'. Regenerating with 8 V" a solution with a concentration of 100 g NaCl in liters of distilled water at s = 3 VV ^ 1 h_l. Washed out with 8% distilled water.

V - filtrate volume Vy - anion exchange volume s = specific load

Table 2

Amount of filtrate

Composition of the filtrate nmol. 1

V V-1

v. v0

NO ~

1/2 SO =

HCO "

cr

20th

0

1.3

3.5

1.2

40

0

1.4

3.2

1.4

60

0

2.3

2.3

1.4

80

0

2.8

1.9

1.3

100

0

3.1

1.8

1.1

120

0.01

3.4

1.8

0.8

140

0.05

3.3

1.8

0.8

160

0.12

3.2

1.8

0.8

180

0.24

3.3

1.8

0.8

200

0.40

3.0

1.8

0.8

220

0.52

2.9

1.8

0.8

240

0.66

2.7

1.8

0.8

entrance

1.53

0.94

1.8

0.8

water

Filtrate bed: strongly basic anion exchanger of the second type, with a height of 0.6 m. Simultaneously regenerated with 5 V0 of a solution containing 100 g NaCl in 1 liter of distilled water and then with 5 V0 of a mixed solution containing 85.9 g Na2S04 + 14.1 g NaH-C03 in 1 liter of distilled water at s = 3 V. V ^ 1 h_1. Washed out with 8 V0 distilled water.

V - filtrate volume V0 - anion exchange volume s = specific load during the working cycle also the majority of the hydrogen carbonates. The filtrate is a chloride denaturate: it contains 4 - 7 times more chlorides than the input water and on the whole it does not comply with the norm for drinking water (2.82 nmol.l_I).

Tables 3 to 6 below provide examples of performing the regeneration along with the results obtained on the regenerated bed.

Amount of filtrate Composition of the filtrate nmol. 1 1

V V

v. »0

NO "

1/2 S04 =

HCO3-

cr

20th

0

0.1

1.05

0.50

40

0

0.1

1.0

0.50

60

0

0.15

0.85

0.65

80

0

0.20

0.70

0.80

100

0

0.25

0.55

0.85

120

0.01

0.25

0.50

0.90

140

0.01

0.30

0.45

0.87

160

0.06

0.50

0.40

0.60

180

0.10

0.80

0.40

0.30

200

0.25

0.85

0.40

0.10

220

0.90

0.30

0.25

0.05

260

1.40

0.10

0.10

0

280

1.60

0

0

0

300

1.60

0

0

0

Entrance-

1.60

0

0

0

water

V - filtrate volume V0 - ion exchange volume s - specific load

The results are described in Tab. 3 with the strongly basic anion exchanger of the second type; Filling height 0.6 m, s = 45 V.Vo "1 h-1. This filling was regenerated concurrently with 5 V0 of a solution containing 100 g of chloride in 1 liter of distilled water, and then with 5 V0 of the mixed solution with 85 , 9 g sodium sulfate and 14.1 g sodium hydrogen carbonate in 1 liter of distilled water, washed out with 8% distilled water.

Furthermore, an artificial solution of the input water was prepared, the sodium nitrate in a concentration of 100 mg. Contained 1-1 NOj in distilled water, i.e. without further anion components. Nevertheless in the entrance

Table 4

Amount of filtrate Composition of the filtrate nmol. 1 1

V V

0

NO "

1 / 2S04 =

HCO ~

cr

20th

0

5.8

7.2

1.2

40

0

6.2

6.6

1.5

60

0

6.2

6.3

1.7

80

0

5.9

6.1

2.3

100

0

5.7

6.1

2.4

120

0.01

5.6

6.1

2.5

140

0.01

5.4

6.1

2.6

160

0.02

5.3

6.1

2.8

180

0.05

5.3

6.1

2.8

200

0.10

5.3

6.1

2.7

220

0.15

5.2

6.1

2.7

240

0.20

5.2

6.1

2.7

260

0.24

5.1

6.1

2.7

280

0.38

5.1

6.1

2.7

300

0.49

5.0

6.1

2.65

320

0.61

5.0

6.0

2.60

340

0.61

5.0

6.0

2.60

360

0.61

5.0

6.0

2.60

Input

0.61

5.0

6.0

2.6

water

V - amount of filtrate V0 - ion exchange volume s - specific load s

io

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660 692

Water contains only nitrate salt, the water that has passed through the filter bed according to the invention contains chlorides, sulfates as well as hydrogen carbonates in amounts that would correspond to the Czechoslovakian standard for drinking water, which proves that even in this extreme case, the would not normally occur, the regenerated filter is able to replace the nitrates with the main anion components.

Table 4 describes the results with the strongly basic anion exchanger of the second type, with a filter bed height of 0.6 m, s = 40 V.V0 ~ 'h-1. Simultaneously regenerated with 5% of a solution containing 100 g NaCl in 1 liter of distilled water and then with 5% of the mixed solution containing 85.9 g of sodium sulfate and 14.1 g of sodium bicarbonate in 1 liter of distilled water at s = 3 V.V0 ~ ' Hi. Washed out with 8 V0 distilled water.

The strongly basic anion exchanger regenerated according to the invention (Tab. 4) has a balanced anion composition without extreme values of the individual anions, including sulfates, which is maintained throughout the working phase in concentrations which correspond to the values at the entrance. Table 4 further shows that after the denitrification capacity of the anion exchanger regenerated according to the invention has been exhausted, there is no increase in the nitrate concentration in the filtrate due to spontaneous desorption from the filter bed. This is extremely important for the safety of the operation of the denitrification plant.

Table 5

Amount of filtrate Composition of the filtrate nmol. 1 1

V V-1

y. »0

NO "

1/2 SO =

HCO ~

he

20th

0.006

2.9

7.5

2.7

40

0.006

3.5

6.8

2.8

60

0.010

4.2

6.45

2.6

80

0.010

4.5

6.20

2.6

100

0.016

4.8

6.20

2.5

120

0.018

4.8

6.20

2.3

140

0.025

4.7

6.15

2.3

160

0.050

4.65

6.15

2.3

180

0.096

4.65

6.10

2.2

200

0.150

4.6

6.10

2.2

220

0.180

4.6

6.10

2.2

240

0.250

4.6

6.10

2.2

260

0.320

4.55

6.10

2.2

280

0.43

4.50

6.10

2.2

Entrance-

0.61

4.40

6.00

2.1

water

V - filtrate volume V0 - ion exchange volume s - specific load

In Table 5 the results are described with the strongly basic anion exchanger of the second type, with a filter bed height of 0.6 m, s = 40 V.V0 ~ 1 h_ ', regenerated in the same direction with only 4 V0 of the solution with 100 g NaCl in 1 Liters of the input water and then only with 4 V0 of the mixed solution with 85.9 g sodium sulfate and 14.1 g sodium hydrogen carbonate in 1 liter input water at s = 3 V.'V0 ~ 1 h ~ 1. Washed out with 8 V0 of the input water. This regeneration presents an economically advantageous variant.

Even with this economic regeneration, the composition of the filtrate in all its components corresponds to the norm for drinking water. Compared to the regeneration with 5

Volume of 10% reagents, a somewhat shorter denitrification cycle is achieved. However, the specific costs for removing a nitrate unit are also lower.

In a similar way, denitrification beds can also be regenerated economically with solutions of concentration - for example: with 5 V0 of 8% NaCl + 5 V0 8% mixed regeneration rans, 5 V0 8% NaCl + 4.3 8% Na-, S04 + 0 , 7 V0 8% NaH-C03, or 4 V0 10% NaCl + 4 V010% Na2S04 etc.

Table 6

Amount of filtrate

Composition of the filtrate nn

V V "1

v. • 0

NO "

1/2 S04 =

HCO "

he

20th

0.048

1.00

3.6

2.0

40

0.048

0.90

3.45

2.25

60

0.052

0.90

3.30

2.42

80

0.055

0.90

3.25

2.55

100

0.059

0.95

3.25

2.55

120

0.063

1.05

3.1

2.45

140

0.070

1.25

3.0

2.20

160

0.085

1.60

2.9

2.00

180

0.085

1.80

2.7

1.90

200

0.090

2.00

2.4

1.90

220

0.11

2.25

2.1

1.85

240

0.13

2.35

2.1

1.80

260

0.180

2.40

2.1

1.80

entrance

0.516

2.08

2.05

1.77

water

V - amount of filtrate V0 -

Ion exchange volume

s - specific load

Tab. 6 describes the results with strongly basic anion exchangers of the second type, filter bed height 1.05 m, s = 20 V.V0 ~ 'h_l. Counter-current regenerated with 5 V0 of a solution with 100 g NaCl in 1 liter of inlet water and then 5 V0 mixed solution 85.9 g Na2S04 and 14.1 g sodium hydrogen carbonate in 1 liter of inlet water at s = 3 V.V0 ~ 1 h ~ 1. Washed out with 10 V0 of the input water.

As can be seen from the examples, the method according to the invention can also be used to regenerate in countercurrent, but the denitrification effect of the filter bed regenerated in this way is usually smaller and the difference in the concentration of the other anions in the filtrate can be greater.

When manufacturing the filter bed from a new, unused anion exchanger, the fact is used that the anion exchanger is mostly already supplied in the chloride form. For this reason, the solution with the chloride anions is left out in the first preparation before use and the anion exchanger is only brought into contact with the solution which contains sulfates or sulfates and hydrogen carbonates. As a result, the ion exchanger is prepared for first use and for further regeneration according to the invention.

Tab. 7 describes the results with the strongly basic anion exchanger of the second type; Filter bed height 0.6 m behind which a strongly acidic cation exchanger is placed with a filter height of 0.15 m, s = 20 V.V0 ~ 1 h "', calculated according to the anion exchanger. Regenerated with 5 V0 of a solution containing 100 g Na chloride in 1 liter of distilled water and then with 5 V "of the mixed solution with 85.9 g Na sulfate and 14.1 g Na hydrogen carbonate in 1 liter of distilled water, at s = 3 V.V0_I h_l. Washed out with 8 Vt, distilled What-

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6

Table 7

Amount of filtrate Composition of the filtrate nmol. 1 1

V.V "1 NO ~ 12SO = H CO" Cl- 1 2 To

20th

0

1.3

3.5

1.2

0.02

40

0

1.4

3.2

1.4

0.02

60

0

2.3

2.3

1.4

0.02

80

0

2.8

1.9

1.4

P, 15

100

0

3.1

1.8

1.1

0.24

120

0.01

3.4

1.8

0.8

0.34

140

0.05

3.3

1.8

0.8

0.40

160

0.12

3.2

1.8

0.8

0.70

180

0.24

3.3

1.8

0.8

0.90

200

0.40

3.0

1.8

0.8

1.20

220

0.66

2.7

1.8

0.8

2.40

240

0.66

2.7

1.8

0.8

2.40

Entrance-

153

0.94

1.8

0.8

5.20

water

V - filtrate volume V0 - ion exchange volume s - specific load sers. The cation component also affects a reduction in water hardness. The heavier cation exchanger forms the lower filter layer. The ratio of the anion to the cation exchanger is 4: 1 to 12: 1. In contrast to the use of the cation exchanger in the energy industry, the hardness is reduced in

25 Drinking water is not about the total elimination of calcium and magnesium. The ratio of anion exchanger to cation exchanger is given by the desired degree of hardness reduction, the capacity of the ion exchanger and by the overall composition of the water.

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Claims (9)

660 692 1. A process for the regeneration of ion exchangers for denitrification of water based on a strongly basic anion exchanger, characterized in that in the course of the first regeneration step the strongly basic anion exchanger is brought into contact with a regeneration solution containing chloride ions, in the course of the second regeneration step the mentioned filter bed is brought into contact with a regeneration solution containing sulfate ions. 2. The method according to claim 1, characterized in that in the course of the second regeneration stage, the regeneration solution in addition to the sulfate ions also hydrocarbonate ions, for. B. contains sodium or potassium hydrocarbonate. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that after both regeneration stages, a third regeneration stage by means of a hydrocarbonate, e.g. regeneration solution containing either sodium or potassium hydrocarbonate follows. 4. The method according to claim 1, characterized in that the ion exchange filter serves for denitrification as well as for softening the water and that the filter bed contains, in addition to the strongly basic anion exchanger, a filter bed made of a strongly acidic cation exchanger, the filter beds with a during the first regeneration stage Chloride-containing regeneration solution can be contacted. 5. The method according to claim 4, characterized in that the two filter beds are brought into contact with a regeneration solution containing sulfate ions in a second regeneration stage. 6. The method according to claim 4, characterized in that both filter beds mentioned in a second regeneration stage with a sulfate ion and also hydrocarbonate ions, for. B. sodium or potassium hydrocarbonate containing regeneration solution in contact. 7. The method according to claim 5, where in a third regeneration stage said filter bed with a hydrocarbonate ions, for. B. sodium or potassium hydrocarbonate containing regeneration solution in contact. 8. The method according to claim 4, where the filter bed based on a strongly basic anion exchanger and a filter bed based on a strongly acidic cation exchanger are spatially separated, both of which are first brought into contact with a regeneration solution containing choride ions. 9. The method according to claim 1, characterized in that the ion exchange filter serves for denitrification as well as for softening the water and the filter bed in addition to the strongly basic anion exchanger also consists of a strongly acidic cation exchanger, the regeneration solution serving to denitrify the strongly basic anion exchanger as a regeneration solution is used for the strongly acidic cation exchanger.