FR2580617A1 - Process for the manufacture of potassium sulphate from potassium chloride by means of an ion exchanger - Google Patents

Abstract

a. Process for the manufacture of potassium sulphate from potassium chloride by means of ion exchangers. b. Process characterised in that, as a reaction solution, a saturated potassium chloride solution and, after saturation with potassium sulphate, the exchanger for weakly basic anions, laden with sulphate, are brought into intimate contact, in that separation is again carried out, after which the crystals which have formed therein are separated from this solution, and in that the exhausted anion exchanger is recharged with sulphate ions, by bringing it again into intimate contact with a magnesium sulphate solution. c. The invention relates to a process for the manufacture of potassium sulphate from potassium chloride by means of ion exchangers.

Description

"Process for the production of potassium sulphate
from potassium chloride by means of exchangers
of ions "
It is well known that potassium sulfate and magnesium chloride can be produced by double decomposition of potassium chloride and magnesium sulfate.

 If this double decomposition is carried out according to the prior art and manner, important technical measures must be used to prevent the formation of double salts.

On the other hand, we know from the document
DE-OS 3,331,416, a process by which potassium chloride can be converted to potassium or sodium sulfate by means of ion exchangers under acidic conditions. This process can be represented by the following reaction equations:
Production: 2 KC1 + R2S04 + K2S04 + 2 RC1
Regeneration: 2 RCl + CaS04 + R2 S04 + CaC12
CaS04 + 2 KC1 + K2S04 + CaCl2
A solution of the desired sulphate is obtained here, from which the sulphate is then removed by adding potassium or sodium chloride. The filtrate, separated from the crystals which form, is used for the regeneration of the heat exchanger. anions.

 The essential point for this process is this notion that the solubility of calcium sulphate is greater in a solution of calcium chloride than in water. By this means, the regeneration of the anion exchanger is favored unexpectedly. However, there is, in the regeneration of the ion exchanger with the calcium sulphate suspension, the risk of seeing the calcium sulphate crystals, which deposit on the exchanger particles, strongly affect the regeneration of this exchanger and to be able to remove the calcium sulphate deposited on these exchanger particles only with very important technical measures.

 There therefore arose the problem of developing other possibilities for the production of potassium sulphate in which the defects of the process mentioned above were not encountered.

 A process has been found for the manufacture of potassium sulphate from potassium chloride by means of an anion exchanger charged with sulphate ions.

According to this process, a saturated potassium chloride solution is brought into intimate contact as a reaction solution and, after saturation with potassium sulfate, with the weakly basic anion exchanger, charged with sulfate, which is separated at again after which
the crystals which have formed there are separated from this solution, and the exhausted anion exchanger is recharged with sulphate ions, again placing it in intimate contact with a solution of magnesium sulphate.

 For carrying out the process of the invention, a saturated potassium chloride solution is used as reaction solution, after having dissolved potassium sulfate therein until saturation. The potassium sulphate content of the reaction solution amounts to approximately 5 to 10 X, calculated on the weight of the total of the salts contained in the solution.

 This reaction solution is brought into intimate contact with a weakly basic anion exchanger, charged with sulphates. The sulphate ions of the exchanger will be replaced here by chloride ions of the reaction solution until an equilibrium has been established between the solution and the exchanger as regards the ions exchanged and the exchange is thus finished. Potassium sulfate, which forms under these conditions, crystallizes because the indicated reaction solution is already saturated with potassium sulfate.

 When the exchange is complete, the reaction solution is separated from the anion exchanger. There is an advantage here that the particles of the anion exchanger, preferably used in the form of granules, have a larger diameter than that of the potassium sulphate crystals formed by the exchange in the reaction solution. .

 Tests have shown that the potassium sulphate produced according to the invention has a particle size of less than 0.4 mm. It is then sufficient, for the abovementioned separation operation, that the particle diameter of the anion exchanger amounts to more than 0.5 mm. To separate the anion exchanger from the reaction solution, this exchanger will be retained by a body acting as a sieve, whose mesh size or pore diameter is 0.5 mm, while the solution containing the crystals potassium sulphate, will pass unimpeded through the sieve body, for example a filter cloth with a mesh width apporpriée.

 The potassium sulphate crystals are then separated from the reaction solution, washed with a saturated potassium sulphate solution, then dried.

The separate washing solution can be used again for the preparation of a new reaction solution, as can the reaction solution separated from the potassium sulphate crystals, after saturation with potassium chloride.

 For carrying out the process of the invention, it has also appeared advantageous to keep the potassium chloride concentration of the reaction solution constant during the exchange reaction, by addition of solid potassium chloride, preferably in powder form. It is particularly advantageous to first mix the potassium chloride to be added with a small amount of reaction solution, and to introduce it in this form into this reaction solution. These provisions ensure an increase in the use of the capacity of the exchanger.

 There are three known possibilities for bringing the reaction solution into contact with the weakly basic sulphate-charged anion exchanger <i.

 According to the first possibility, the exchanger can be implemented in the form of a well compacted bed, preferably in a column to which the reaction solution is supplied from above. The exchanger bed will advantageously be placed on a tray with passage openings whose diameter is smaller than the size of the exchanger particles, but larger than the particle size of the potassium sulphate crystals which form in the reaction solution.

By suitable arrangements, for example by passing air, it must be ensured that the exchanger and the reaction solution are thoroughly mixed.

 It is also possible to send the reaction solution to the pressure exchanger bed from below and to take up this reaction solution mixed with the potassium sulphate crystals at the upper end of the exchanger.

 With these arrangements, it is obtained that the compacted exchanger is set into turbulence by the flow pressure of the reaction solution in the latter.

 On the other hand, it is possible to mix the grain exchanger with the reaction solution and to maintain the mixture in a constant movement, for example by shaking or shaking. The exchange is finished after 10 to 20 min, and this mixture can be treated in the manner which has been indicated above.

 It has proved advantageous for the process of the invention to maintain the mixture during this exchange, at temperatures between 10 and 400C.

 With the exchange reaction carried out according to the invention, 80 to 95% of the total capacity of the anion exchanger will be charged with chloride ions.

 To recover, to a large extent, the sulfate ions which would still remain in the exchanger, it may be advantageous to bring the exchanger into contact, intimately, before regenerating it, with a saturated solution of potassium chloride. The solution which remains here, after the separation of the exchanger, contains, next to potassium chloride, the potassium sulphate which has just formed. From this solution, the two salts can be recovered by evaporation and fractional crystallization, in a known manner.

 When the reaction solution is separated from the anion exchanger, the latter is washed with water in the well known manner, before being regenerated by intimate contact with a solution of magnesium sulphate, that is to say that is, to be charged with sulfate ions again. From the regeneration solution which is separated from the regenerated exchanger, and which contains magnesium chloride and magnesium sulphate, these salts can be recovered in a known manner by evaporation and fractional crystallization.

 For the process of the invention, it is particularly advantageous to use weakly basic ion exchangers which consist of polyacrylate with secondary and tertiary amino groups.

 It has also proved advantageous to adjust all the solutions brought into contact according to the invention with these weakly basic anion exchangers beforehand, by adding acids, at a pH of 3 to 6. The solutions which are used for the production of potassium sulphate will advantageously be acidified with sulfuric acid, while the pH of the solutions used for the regeneration of the exchanger will be adjusted with hydrochloric acid.

 The process according to the invention largely avoids the technical difficulties and defects of the processes known from the prior art, and can be carried out with great efficiency without technical difficulties.

Example 1:
Exchange operation with Kastel weakly basic anion exchange resin, in polyacrylate, with dominance of secondary amino groups with 2.2 val / l of total capacity.

 Test with a volume of 500 l of resin in an exchange column.

 Adjustment to pH3 of all solutions with HC1 or H2 S04.

I. Half-cycle of charge exchange of the resin with
SO4-- ions
After performing 4 cycles and adjusting a fixed state, there was obtained, at the end of the half-cycle described under II, a resin bed charged with water which contained small amounts of potassium salts and which was charged
at 86 X of its capacity, of Cl ions and,
at 14% of its capacity, of S04 ions
The following solutions are brought to the bed from above at 250 ° C.
-Al 150 1 with 0.64 val MgCl2 / l and
0.06 val MgSO4 / l
-A2 698 1 with 1.40 val MgS04 / 1
-A3 150 1 with 0.04 val MgCl2 / l and
0.66 val MgS04 / 1
-A4 150 1 water
When bringing solutions A1 to A4, it leaves the column, as eluate
-El 150 1 with 0.13 val KCl / l
0.01 val K2504 / 1
0.10 val MgCl2 / l and
0.01 val MgSO4 / l
-E2 150 1 with 0.64 val MgCl2 / l and
0.06 val MgS04ll
-E3 698 1 with 1.26 val MgCl2 / l and
0.10 val MgSO4 / l
-E4 150 1 with 0.04 val MgCl2 / l and
0.66 val MgS04ll
The eluates El and E3 were taken out of the operation, the eluates E2 and E4 which are identical to Al and
A3 were stored for reuse in the next cycle.

The resin was then loaded
at 94 X of its capacity with S04 ions, and
at 6 X of its capacity with Cl II ions. K2SO4 recovery exchange half-cycle
The following solutions are introduced on this bed, filled with water, which now contains small amounts of magnesium salts.
-A5 150 1 with 0.02 val KCl / l and
0.64 val K2S04 / 1
-A6 150 1 with 0.06 val KCl / l and
1.24 val K2S04 / 1
-A7 150 1 with 4.08 val KCl / l and
0.14 val K2S04 / 1
I1 is at the same time elected:
-ES 150 1 with 0.01 val Mec12 / 1,
0.08 val MgS04 / 1,
0.01 val KCl / l and
0.09 val K2S04 / 1
-E6 150 1 with 0.02 val KCl / l and
0.64 val K2S04 / l
-E7 150 1 with 0.06 val KCl / 1 and
1.24 val K2S04 / 1 E5 is out of the operation, E6 and-E7 are stored to be reintroduced in the next cycle.

Qaund E7 has finished flowing, it is caused by vigorous mixing of the resin and the solution
A7 by blowing compressed air through the holes available on the column.

 While continuing the stirring, a new quantity of 828 l of the solution A7 is brought in.

The solution A7, saturated with KC1 and with K2SO4, reacts here with the resin loaded with SO4 with depletion of KC1, and crystallization of K2 SO4. The reacted solution and the K2 SO4 formed are taken up continuously through the sieving bottom of the column where the sieving openings cannot be crossed by the too large resin grains.

The rest of the reaction solution with the
K2S04 crystallized is removed from the column by means of
A8 150 1 with 2.68 val KCl / l and
0.32 val K2S04 / 1
A7 thus gave in total, the eluate
E8 978 1 with 3.14 val KCl / l and
0.22 val K2S04 / 1 and an amount of crystallized KSS04 of 69.8 kg
Solution A7 is again prepared by saturation of E8 with 68.5 kg KC1, which is used in the following cycle.

At the same time, it still precipitates 6.8 kg of K2SO4, so that the quantity produced amounts to a total of
76.6 kg of K2S04
I1 is then introduced into the column the following solutions
-A9 150 1 with 1.84 val KCl / l and
0.16 val K2S04 / 1
-A10 150 1 with 0.94 vam KCl / l and
0.06 val K2S04 / 1
-All 150 1 water
He is elected
-E9 150 1 with 2.68 val KCl / l and
0.32 val K2S04 / 1
-E10 150 1 with 1.84 val KCl / l and
0.16 val K2S04 / 1
-Ell 150 1 with 0.94 val KCl / l and
0.06 val K2S04 / 1
The solutions E9 to Ell are also stored for reuse in the next cycle.

 After flow of the solution E9 - Ell, the resin is in the same state of charge as at the beginning of the half-cycle described under 1.

Operating performance
S04: 90.1 X
K: 96.1%
(the losses amount to
S04 0.3 X in El
7.0% in E3
2.6 X in E5
K 2.3 X in El
1.6 X in E5)
Example 2
Exchange operation with the weakly basic resin anion exchanger, based on polyacrylate with secondary and tertiary Duolit amino groups with a total capacity of 2.5 val / l
Test with a resin volume of 500 1.

Adjustment of all solutions to pH4 with HC1 or H2S04.

I. Half-cycle of exchange of charge of the resin with 504 ions
After performing 6 cycles and setting a fixed state, at the end of the half-cycle described under II, a resin bed filled with water, which contains small amounts of potassium salts, and which is charged, is obtained. at 93 X of its capacity with Cl ions, and at 7 X of its capacity with S04 ions
On this bed, it is brought, from above, successively, to 600C the following solutions
-Al 150 1 with 0.85 val MgC12 / 1 and
0.12 val MgSO4 / l
-A2 150 1 with 1.58 val MgCl / l and
0.30 val MgS04 / 1
-A3 900 1 with 1.45 val MgCl / 1 and
1.50 val MgSO4 / l
-A4 413 1 with 3.0 val MgS04 / 1
-A5 150 1 with 0.74 val MgCl2 / l and
1.35 val MgS04 / 1
-A6 150 1 with 0.34 val MgCl2 / l and
0.71 val MgSO4 / l
-A7 150 1 water
When solutions Al to A7 are supplied, it leaves the column, as eluates
-El 150 1 with 0.15 val KCl1l
0.01 val K2S04 / 1
0.12 val MgCl2 / l and
0.01 val MgS04 / 1
-E2 150 1 with 0.85 val MgC12 / 1 and
0.12 val MgSO4 / l
-E3 150 1 with 1.58 val MgCl2 / l and
0.30 val MgS04 / 1
-E4 413 1 with 2.33 val MgC12 / 1 and
0.56 val MgSO4 / l
-ES 900 1 with 1.45 val MgCl2 / l and
1.50 val MgSO / l
-E6 150 1 with 0.74 val MgCl2 / l and
1.35 val MgSO4 / l
-E7 150 1 with 0.34 val MgCl2 / l and
0.71 val MgSO4 / l
The eluates El and E4 are removed from the operation, the eluates E2, E3 and E5 to E7, which are identical to Al, A2 and A4 to A6 are stored for reuse in the following cycle.

The resin is now charged at 85 X of its capacity with SO4--, ions, and at 15% of its capacity with Cl II ions. K2S04 production exchange half-cycle
On the bed filled with water, which contains small amounts of magnesium salts, it is then brought to 250C, first the following solutions
-A8 150 1 with 0.03 val KCl / l and
0.61 val K2S04 / l
-A9 150 1 with 0.08 val KCl / l and
1.17 val K2504 / 1
-A10 150 1 with 4.08 val KCl / l and
0.14 val K2S04 / 1 I1 is here eluted
-E8 150 1 with 0.04 val MgCl2 / l
0.10 val MgSO4 / l
<0.01 val KCl / l and
0.08 val K2S04 / 1
-E9 150 1 with 0.03 val KCl / l and
0.61 val K2S04 / l
-E10 150 1 with 0.08 val KCl / l and
1.17 val K2S04 / 1
E8 is output from the operation, E9 and E10 are stored for reuse in the next cycle.

 After E10 has passed quantitatively, the resin which is under A10 receives a new quantity of 300 l of solution A10, in a stirred container, into which is added, at the same time, 75.3 kg of KC1 crystallized.

 In the agitator vessel, the desorption of the SO 4 ions from the resin takes place, and the crystallization of K 2 SO 4 takes place, while, due to the dissolution of KC 1, the KC 1 and K 2 SO 4 concentrations of the solution do not change. Before the end of the reaction, all of the KC1 went into solution.

The contents of the agitator tank are sent to a sieve through which the fine K2SO4 crystals can pass, but not the coarser particles of resin; By rinsing with another 200 l of A10, total separation of the K2SO4 and the resin is ensured. I1 is obtained 84.5 kg of K2S04. Finally, the resin is transferred again to the exchange column, where now the intermediate spaces are filled with 150 l of solution A10. This solution A10 is driven out by the loading solution
All 150 1 with 2.95 val KCl / l and
0.28 val K2S04 / 1
All the A10 solutions (in total of 800 l eluates, which had the composition of the primitive A10, are stored for reuse in the following half-cycle.

I1 is then brought the following solutions
-A12 150 1 with 2.01 val KCl / l and
0.20 val K2S04 / 1
-A13 150 1 with 0.96 val KCl / l and
0.11 val K2S04 / 1
--A14 150 1 water
He is elected
-E12 150 1 with 2.95 val KCl / 1 and
0.28 val K2S04 / 1
-E13 150 1 with 2.01 val KCl / l and
0.20 val K2S04 / 1
-E14 150 1 with 0.96 val KCl! L
0.11 val K2S04 / 1
E12 to E14 are stored to be reused in the next cycle.

 When the solution E14 has completely drained, the resin is again in the state of charge it exhibited at the start of the half-cycle described in 1.

Operating performance
S04: 78.7 X:: 96.4 X (losses
- S04 0.2 X in El
2.2 X in E4
18.9% in E8
- K +: 2.4% in El
1.2% in E8)

Claims (6)

 10) process for the manufacture of potassium sulphate from potassium chloride by means of an anion exchanger charged with sulphate ions, characterized in that one puts in intimate contact, as reaction solutions, a solution saturated with potassium chloride and, after saturation with potassium sulphate, with the weakly basic anion exchanger, charged with sulphate, which is separated again, after which the crystals which have formed there are separated from this solution, and that the exhausted anion exchanger is recharged with sulfate ions, again bringing it into intimate contact with a solution of magnesium sulfate.  20) Method according to claim 1, characterized in that the particles of the anion exchanger have a larger diameter than that of crystals which form in the solution.  30) Method according to one of claims 1 and 2, characterized in that the potassium chloride concentration of the reaction solution is kept constant during the exchange reaction by addition of solid potassium chloride.  40) Process according to any one of claims 1 to 3, characterized in that before regenerating it, the anion exchanger is brought into intimate contact with a saturated solution of potassium chloride and, and separated again.  50) Method according to any one of claims 1 to 4, characterized in that the exchange mixture is maintained during the exchange operation at temperatures between 10 and 400C.  60) Process according to any one of claims 1 to 5, characterized in that, in all the solutions brought into contact with the anion exchanger, the pH is adjusted beforehand to a value of 3 to 6 by addition of 'acid.