DE1567274C - Process for the further purification of technical sugar solutions - Google Patents

Description

35

The inventive method relates to the further purification of technical sugar solutions under Use of strongly basic with weakly acidic cation exchangers, whereby the sugar solution to be purified first percolated over an anion exchanger loaded with sulfate ion with a sponge structure will.

State of the art

45

Since the discovery of ion exchangers based on plastics, especially those that obtained by polymerizing cyclic hydrocarbons with divinyl compounds and are characterized by particular stability in relation to technical sugar solutions, are the processes which deals with the further purification of technical sugar solutions using such ion exchangers deal has become extraordinarily numerous.

The methods proposed so far can be divided into the following groups:

1. Procedure for exchanging the cations:
Exchange of alkali ions and alkaline earth ions using cation exchangers that _{are loaded with NH 4} , Na, Mg ions.

2. Process for decolorizing sugar solutions: For decolorizing technical sugar solutions became the use of weakly basic anion exchangers in the hydroxyl form or of strongly basic anion exchangers, especially those with macroporous ones Nature proposed in the Cl, Br, CH or SOj form.

3. Process for the desalination of technical sugar solutions:

a) Desalination of a technical sugar solution using a strongly acidic cation exchanger in the Η form and one weakly basic anion exchanger in the OH form, said exchangers can be used both as a mixture (mixed bed process) and separately.

b) Desalination of a technical sugar solution using a strongly basic anion exchanger in the OH form and a weakly acidic cation exchanger in the H form.

c) Desalination of a technical sugar solution using a strongly acidic exchanger in the NH ₄ form and a strongly basic anion exchanger in the CH form.

d) Desalination of a technical sugar solution using a strongly acidic exchanger in the NHj form and a strongly basic anion exchanger in the Co ₃ form.

e) Desalination of a technical sugar solution using a combination of two mixed bed exchanger columns, one of which is a mixture of a weakly acidic cation exchanger in the Η form and one weakly basic anion exchanger in the OH form, while the other A mixture consisting of a strongly basic anion exchanger in the column OH form and a weakly acidic cation exchanger in the Η form.

Of the procedures listed so far, in technology only the procedures of groups 1 and 2 enforced, while the procedures of group 3 have only found their way into the sugar industry in the form of the so-called classic desalination process described under 3, a).

All other Group 3 processes are still in the experimental stage or have not been technically tested.

The multitude of proposed procedures suggests this already suggests that the problems to be solved present significant difficulties. These are partly technical, partly of an economic nature. There are four problems in particular that have so far been economically viable Have not found the solution:

1. The formation of invert sugar in the treatment of technical sugar solutions with cation exchangers that are loaded with Η ions, and the associated compulsion, the desalination of the sugar solution at the lowest possible temperature carry out what a cooling of the sugar solution to about 10 to 12 ° C is necessary power.

2. The reduction in capacity of the anion exchangers used, which is caused by components of the technical sugar solution is caused and forces this exchanger after 300

Replace up to 400 cycles with brand new ones, which increases the efficiency of the cleaning process heavily loaded.

3. The elimination of the potassium-containing wastewater heavily contaminated with organic matter,

■ from the regeneration of the exhausted ion exchangers originating waste liquors. · -.

4. The relatively high cost of regeneration the exchanger caused.

The various previously proposed desalination processes now each take into account one or several of the problems identified without being able to solve them in their entirety.

However, the method according to the invention is now able to overcome a large part of the existing difficulties to overcome.

To begin with, a few things should be said about the exchange behavior of weakly acidic exchangers.

All weakly acidic cation exchangers currently on the market have a spectrum of J active groups in the fully activated state, ie in the Η form, the main area of which is between pH 3.0 and. 8.0, but some of the active groups are also able to exchange Η ions for cations at a pH value below 3.0 to about 1.5. This means that if salts of acids with a correspondingly high degree of dissociation are present in a solution, so much of this strong acid is formed through the exchange reaction on this weakly acidic cation exchanger that a pH of 2 to 3 is reached in the solution .

If you now use such a weakly acidic cation exchanger to purify a sugar solution an inversion of this sucrose is inevitable at normal operating temperature (above 60 ° C), because the N ions present in the exchanger are catalytic, depending on their degree of dissociation act, i.e. the Η-ions with the highest degree of dissociation have the greatest catalytic effect on the inversion of sucrose.

The German patent specification 1195 240 should also be mentioned; there will be a method of cleaning proposed technical sugar solutions, which consists in the fact that you first of all the sugar solution to be cleaned passes over a carbonic acid loaded anion exchanger and then a part of this Sugar solution over one laden with ammonium ions Cation exchanger percolates, the parts of the sugar solution are combined again, the ammonium carbonate formed removed, the pH of this solution freed from ammonium carbonate measured and the determined Deviation from a desired setpoint used to control a mixing valve that the Mixing the proportions controls so that a desired pH value in the concentrated sugar solution (Thick juice) is achieved. After during a loading process of the carbonate exchanger with the anions of the technical sugar solution increases the concentration of the alkali carbonate in this solution changes continuously, the mixing ratio must be the same Dimensions can be changed. This not only requires a high-speed evaporator to remove the ammonium carbonate from the sugar solution, but also a considerable amount of electronic control means, which make up a substantial part of the costs of such a desalination plant and beyond are considerably susceptible to failure, with a failure in this control system leading to considerable losses Sugar can cause inversion.

Another disadvantage of this process is that the treated sugar solution in place of the removed ionized impurities contains an equivalent amount of ammonium carbonate, which is only a small part technically can be recovered and the greater part of which is therefore lost. This loss at

xo ammonia or ammonium carbonate pollutes .diejWirt-: economic efficiency of the process. ^ p ^ s> ^ r;

In contrast, in the process according to the invention, the weakly acidic cation exchanger, which is conditioned in a special way, only removes the sum of the alkali carbonates contained in the technical sugar solution treated with the carbonate exchanger by absorbing the alkali ions and splitting off the associated carbonic acid in the form of CO ₂ . It is not necessary to regulate this reaction; This eliminates the need for the entire control device including the flash evaporator, which means a considerable reduction in the construction costs of the desalination plant. Since no ammonium salt is formed when using a cation exchanger in the hydrogen form, the purified sugar solution does not contain any ammonia, so no ammonia is lost with the sugar solution, and the ammonium carbonate cycle for regenerating the carbonate exchanger can

getting closed. . '· · - ·. · ■■ / ;. ·

In summary, it can be said that the investment costs for setting up a desalination plant, which works according to the system of the carbonate process, as well as the ongoing operating costs the method according to the invention greatly reduced

will. · - / "_ ■ --ν ■ ■ · ■ ·

The invention is characterized in that the

Sugar solution pretreated in this way first in a manner known per se over one laden with carbonic acid Anion exchanger with normal pore structure is percolated and then the alkali carbonates formed from this sugar solution by treatment with an extremely weakly acidic cation exchanger in the hydrogen form, which is obtained by using a weakly acidic cation exchanger initially fully loaded with cations and then in an aqueous suspension in motion is treated with a Η-clays containing solution until the solution bypassing the exchanger has a pH of 3.5 to 5.0 after the addition of acid has ended. ... ' V

Further, a preferred embodiment consists of the claimed method is that a weakly acidic cation exchanger is used in the hydrogen form, of up to 5 times 10- ⁴ per MoI at a higher hydrogen ion concentration as a 4 - liter no salt splitting capacity has more.:.

. Example 1 ■ <■ '■; ■ v -': £ i | / ^{^>:.} · '. ■■' ■ "; Activation of the cation exchanger 3

The weakly acidic cation exchanger is first completely with by treatment with NaOH Load cations. Then the soyor-treated Exchanger slurried with water and set in motion by stirring. Now is slowly becoming one diluted mineral acid added and the adjustment of the pH value in the solution waited. The addition of acid is terminated when a pH of about 3.5

Remains 5 minutes after the addition of acid has ended. The exchanger is now activated freed from the surrounding saline solution by washing and is then ready for use.

Treatment of the technical sugar solution with the exchange combination

Two columns are used:.

1. A column with 300 cm ^{3 of} a CO ₃ exchanger.

2. A column with 100 cm ^{3 of} the weakly acidic cation exchanger activated as above and adjusted to pH = 4.0.

A technical sugar solution, pre-cleaned with lime and carbonic acid, was passed through both columns (Thin juice) percolated. Working temperature 90 ° C. -

Length of stay in the columns

CO ₃ column 3 minutes

H column 1 minute

Composition of the thin juice (6.5 1) before the treatment '

Dry matter 15.3%

Sugar: 14.1%

Purity. '. 92.2%

Alkali salts 23.86 meq / 500 ml

Invert sugar 0.119% dry matter

PH value ; 8.35

Composition after "treatment

Dry matter 17.00%

Sugar 16.20%.

Purity 95.30%

Alkali salts 12.33 meq / 500 ml

Invert sugar .ν ....... 0.098 Vo dry

• _ -. .-. ■■ '■■■ - ~ substance

PH value .....,.....:.; 8 ^ 6 ΐ ;: _v

ίο. -. '■ ... -. ■ .. ■ ■ '■ - "' ■

Example 3 (comparative experiment)

The cation exchanger used in Example 1 was fully regenerated in the usual form with excess acid. Combined with a technical sugar solution, it produced a pH of 2.9. .-.--. · A technical sugar solution (thin juice) was then percolated at 90 ° C, as described in Example 1, first over the CO ₃ exchanger, then over the cation exchanger under the same conditions.

Composition of the thin juice ■. before treatment

Dry matter 15.15%

- sugar 13.80%

Purity 91.10%

Alkali salts 23.85 meq / 500 ml

Invert sugar 0.119% dry

. '. substance

PH value ...:. 8.35

Composition of the thin juice after the treatment

Dry matter 14.55%

Sugar 14.04%

Purity 96.5%

Alkali salts 12.90 meq / 500 ml

Invert sugar 0.166% dry matter

pH 5.65

Example 2

Composition of the thin juice.

after treatment

Dry matter. '. . 14.59%

Sugar .... 13.70%

Purity 93.50% '

Alkali salts 13, llmvaI / 500ml

Invert sugar 1.067% dry matter pH 3.65

The following table shows the dependency of the formation of invert sugar on the setting of the pH value in the regeneration of a weakly acidic cation exchanger. . "

The cation exchanger was with a dilute sulfuric acid, which was previously used to regenerate a highly porous anion exchanger, which was used to decolorize a thin juice, in which im Example 1 regenerated manner described. The end point was adjusted to pH 5.0. There were at a working temperature of, 90 ° C 6.0 1 thin juice treated with the following composition.

Composition before treatment

Dry matter ...... ν. ■. .. 15.60%

Sugar 14.35%

Purity 92.00%

Alkalisal / x 25.2 meq / 500 ml

Invert sugar 0.083% dry matter

pH 8.40

PH value
the regeneration solution

Invert sugar content 0.Q0 Q on dry matter

pH 1.0 1.067% pH 2.5 0.285% pH 3.6 : - ■. ■ '- 0.165% pH 4.0. ■ ■■■ 0.163% pH 4.5 0.133% pH 5.0 0.098%

Invert sugar content of the starting solution: 0.085% on T. S.

The technical sugar solution that was used for this determination was a thin juice that was previously treated with a CO., - exchange cr.

The length of time the juice stays in the cation

exchanger was 1.0 minute in all experiments, that is the period of time in which a portion of the juice had passed through the cation exchanger from top to bottom.

The table shows that the treatment of invert sugar with a suitable choice of the cation exchanger and the pH value to be set for the regeneration solution can be prevented almost completely, although the normal working temperature of 90 ° C was used.

The use of the method according to the invention results in the following advantages the previously used procedures:

1. The process can be carried out at 90 ° C without a disturbing inversion of the sucrose to fear. The investment and heat required for cooling and reheating of the thin juice is omitted.

2. The chemical consumption is based on that used to regenerate the decolorization resin Sulfuric acid is reduced as the ammonium carbonate used to regenerate the carbonate exchanger fully recovered by distillation and carbonic acid conversion from the factory will.

3. The one used to regenerate the decolorizing resin and the cation exchanger After regeneration, sulfuric acid falls as a concentrated salt solution with a pH value from 4 to 5, can be easily neutralized and processed on potash salts and so a part to cover the cost of sulfuric acid.

4. There are no concentrated waste liquors that are usually in the form of regeneration Excess caustic soda used can be obtained in sulfuric acid.

209527/108

Claims (2)

Patent claims: 1. Process for the further purification of technical sugar solutions using strongly basic with weakly acidic cation exchangers, with the sugar solution to be cleaned initially is percolated over an anion exchanger loaded with sulfate ions with a sponge structure, characterized in that the sugar solution thus pretreated initially in itself known way via a carbonic acid loaded anion exchanger with normal pore structure is percolated and then the alkali carbonates formed from this sugar solution through Treatment with an extremely weakly acidic cation exchanger removed in the hydrogen form which is obtained by initially using a weakly acidic cation exchanger fully loaded with cations and then in an aqueous suspension in motion is treated with a Η-ion containing solution until the one surrounding the exchanger Solution has a pH of 3.5 to 5.0 after the addition of acid has ended. 2. The method according to claim 1, characterized in that a weakly acidic cation exchanger is used in the hydrogen form, which at a higher hydrogen ion concentration than 4 to 5 times 10 ^-4 moles per liter no salt splitting capacity has more.