DE2164396C3 - Process for the continuous production of calcium sulfite - Google Patents

Description

35

The invention relates to a process for continuous production of crystalline calcium sulfite suitable as a filler for thermoplastics _{and having a grain size of about 5 to about 50 μ by reacting a gas containing SO 2} with milk of lime in several contact zones connected in series at 50 to 100 ^° C.

From US-PS 22 10 405 a process for the continuous production of calcium sulfite in two stages is known. The milk of lime first flows in a cycle through a first stage and, once a predetermined conversion has been reached, in a cycle through a second stage. The _{gas containing SO 2} flows first through the second and then through the first stage. A fine-grained, largely amorphous product with a particle size of about 2 μ is obtained. However, such a fine-grain calcium sulfite is not suitable as a filler for thermoplastics.

If the calcium sulfite formed has a particle size of less than 3μ, then its solubility is quite large in acidic solutions of sulphurous acid. It therefore takes a in acidic solution colloidal form and is difficult to filter.

Thus, it is u to about 50 object of the present invention to provide a process for continuous production of suitable as a filler for thermoplastics crystalline calcium sulfite having a grain size of about 5. To provide.

This object is achieved according to the invention in that a 0.1 to 20 percent by weight and in particular 5 to 10 percent by weight milk of lime together with part of the already converted CaSO-containing circulating suspension is continuously added in a system consisting of at least two contact stages in countercurrent successively to the SO, containing gas in such a way that first a fine-grained CaSO _{3 is} precipitated and the suspension is only brought into contact with new, not yet depleted SO ₂ -containing gas in the last part of the process and that the first contact stage is in the direction of the flow of SO ₂ Gases at a pH of 3 to 6 and all further contact levels at a pH of more than 6.

The milk of lime contains Ca (OH) ₂ and possibly CaSO ₃ and CaCO ₃ . Preferably, exhaust gas or combustion gas containing _{SO 2 is used.} Crystalline hexagonal prismatic calcium sulfite is obtained which, when used as a filler for thermoplastics, gives products with excellent flexural strength and rigidity. The calcium sulfite according to the invention can be used together with other fine-grain fillers.

The invention is explained in more detail below with reference to a drawing. This drawing shows an embodiment of an apparatus which can be used to carry out the method according to the invention. _T. "_.

The reaction apparatus for converting SO ₂

with milk of lime includes a venturi washer (Vl, Vl, V3) and gas-liquid separators (Rl, Rl, R 3). Gas containing SO ₂ is passed from the pipeline 10 through the venturi scrubbers and the gas-liquid separators (Vl - Rl- » Vl-Rl ^ Vl ^ R 3) and sucked in by the fan 12. The exhaust gas escapes through line 11. The milk of lime is transferred from the milk of lime tank 4 into an intermediate tank 5. It is led to the Venturi nozzle 3 and reacts there with the gas containing _{the depleted SO 2.} The milk of lime is then passed through the pump 8 to the venturi nozzle 2 and then through the pump 7 to the venturi nozzle 1. In the Venturi scrubber V 1, the reaction takes place at a pH of 3 to 6, preferably at a pH of about 5, so that unconverted calcium hydroxide or calcium carbonate is completely converted into calcium sulfite. Crystal growth of the fine-grain calcium sulfite obtained with the formation of coarse crystals is achieved in this stage due to the slightly acidic environment.

By means of a pump 9, part of the liquid separated in the gas-liquid separator R 1 is returned to the intermediate tank 5, while the remainder is transferred to a tank 6. There the pH is adjusted to 7 to 9. The product is then filtered off and dried. _{The SO 2} -containing gas used for the process according to the invention can have a high concentration of SO ₂ . It can e.g. B. obtained by burning sulfur. But you can also use a dilute SO ₂ -containing gas, e.g. B. a combustion exhaust, use. Combustion exhaust gases are often contaminated with dust. It is therefore advantageous to collect this dust in dust collectors, e.g. B. in washing towers to remove.

You can use a conventional milk of lime, which is obtained by calcining limestone and

Hydrating the resulting quick lime is obtained. The hydration is usually carried out as 9O ⁰ C for more. The concentration of the milk of lime is 20 to 0.1 percent by weight and preferably 10 to 5 percent by weight. The liquid in the circuit is mixed with this milk of lime.

The following reactions take place in the process according to the invention:

Ca (OH) ₂ + CO, 'CaCO ₃ H ₂ O (1)

CaCO ₃ + SO, + '/, H, O (2)
-CaSO ₃ V ₂ H ₂ O + CO ₂

Ca (OH), + SO, (3)

-> CaSO ₃ · 7, H ₂ O + V ₂ H ₂ O

IO

CaSO ₃ · 7, H, O + SO, + V-. H ₂ O

Ca (HSQ

(4)

'3h

z. B. od with suction filters, rotary kiln dryers.

The CaSO ₃ · '/ 2H ₂ O obtained has a particle diameter of 5 to 50 μm. It is ideal as a filler for polymers, e.g. B. for high density polyethylene. It is incorporated in amounts of 5 to percent by weight. The best way to mix the filler and the polymer is by kneading. Furthermore, the product according to the invention can be used together with other fillers, such as CaSO ₃ · '/ 2H ₂ O with a particle diameter of less than 3 μ, the polymer, e.g. B. a high density polyethylene are incorporated. The total filler material should preferably make up 5 to 90 percent by weight. In this way, the main property, the rigidity of the product, is significantly increased.

The invention is explained in more detail below using an exemplary embodiment.

If the _{gas containing SO 2} contains only a small amount of CO ₂ , the main reactions (3) and (4) take place. If the _{gas containing SO 2} contains a larger amount of CO ₂ , all reactions (1) to (4) take place.

The reaction (1) takes place in an alkaline solution, and the calcium carbonate obtained has a fine particle size of less than 1 μ and is easily converted _{into CaSO 3} · '/ 2H ₂ O _{by SO 2} according to formula (2). During the reaction in stage V 1, the solution turns acidic, and thus the CaSO ₃ V ₂ H ₂ O grows into larger particles with a hexagonal prismatic crystal structure. The reaction (4) then takes place. The reaction (3) takes place in an alkaline medium. The CaSO ₃ · V ₂ H ₂ O obtained in this way consists of fine crystals with a diameter of about 3 μ. Since reaction (4) is an equilibrium reaction, a crystal growth of CaSO ₃ · V ₂ H ₂ O can be brought about by adding Ca (OH) ₂ to Ca (HSO ₃ I ₂ or _{by converting SO 2} from Ca (HSO ₃ J ₂ removed. Reactions (2) and (4) take place under acidic conditions. To increase the reaction rate of reaction (2), it is necessary to work towards fine particles of calcium carbonate with a diameter of less than 1μ and CO ₂ gas, the absorption reaction rate is reduced when the reaction temperature rises from O to 100 ° C. The calcium carbonate obtained in this temperature range has a particle diameter of less than 1 μ. Reaction (2) runs in comparison with reaction (3) very slowly. Thus is obtained upon introduction of SO ₂ gas and CO gas ₃ mainly CaSO ₃ ■ V ₂ H ₂ O. Thus, CaCO _3, which is produced in the reaction (1), and quite useful for producing large crystals of calc ium sulfite, since reaction (2) takes place under acidic conditions.

The apparatus can be arranged horizontally or vertically. The product obtained in the reactions usually has a particle diameter gj of about 5 to 50 μm. The particle size of the product can be controlled by choosing the conditions in the Venturi scrubber VI, in particular the pH and the residence time, ie the recycle ratio. The resulting slurry is neutralized with a small amount of Ca (OH) ₂ , the pH being adjusted to 7 to 9, and the filtering and drying of the slurry can be carried out in a conventional manner, Example A. Temperature of the milk of lime

Vl 98 C Vl 99'C V3 90 C

Temperature of the gas containing _{SO 2}

Vl 42O ⁰ C

Vl 90 ⁰ C

1/3 90 ⁰ C

B. Temperature of calcium hydroxide dispersion

Vl 85 ° C Vl 70 ° C V3 70'C

Temperature of the gas containing _{SO 2}

Fl 100 ° C

Vl 70 ° C

V 3 70 ⁰ C

C. Calcium Hydroxide Dispersion Temperature

Vl 70 ° C Vl 50 ⁰ C V3 50 ° C

Temperature of the gas containing _{SO 2}

Kl 100 ° C

Vl 50 ⁰ C

F3 50 ° C

D. (comparative example)

Calcium hydroxide dispersion temperature

Vl 30 ⁰ C

Vl 2O ⁰ C

V3 20 ⁰ C

Temperature of the gas containing _{SO 2}

Fl 30 ⁰ C

Vl 20 ⁰ C

F3 20 ° C

Composition of the SO ₂ containing gas (M oil percent)

Conc pH 12.3 I. 1.4 ι from SO ₂ Il 13.3 - Vi off III Soft Preparatory work tration 12.3 64.9 78.8 ._ 28.0 Ness bitterness Ca (OH) ₂ KI Vl 12.3 0.3 Vl a 7.9 100.0 0 57.0 (%) 2.1 0 15.0 (mg) 5 5.2 10.0 12.3 31.3 7000 sulfur 0 - 820 Well 10 5.5 10.0 12.3 100.0 6 500 burn up - 810 Well 15th 6.0 8.0 12.3 6000 voltage gas 0 100.0 1 061 out 12.3 Burn 0 draws 5 4.3 7.8 12.3 voltage gas 40,000 0 986 Well 10 4.5 9.5 12.3 35,000 (ppm) 0 796 Well 15th 4.9 11.1 50,000 0 803 Well 5 3.0 9.0 100,000 No 0 932 Well 10 3.5 7.9 70,000 786 Well 15th 3.9 8.8 80,000 900 820 Well 800 700 sulfur 3000 burn up 2,500 voltage gas one difficult 3,500 oil burner 5000 4000 Young Concentration 4,500 module Kl a (kg / cm ² ) O ₂ 28 700 N ₂ 9000 29 600 SO ₂ 9000 38 900 CO ₂ 9000 H ₂ O 82,200 total 79,000 28 100 crowd 79,000 27 100 79,000 27 800 150,000 27 300 150,000 26 400 150,000 A. Conditions of A: gas Type I. I. I. II II II III III III

10

8.5 11.5 12.3

9000

23 500

760 not good

B. Conditions of B:

gas
Type Conc
tration
Ca (OH) ₂ pH
Kl Vl K3 concentration
No from SO ₂
Vl a (ppm)
No K3 off Young
module Soft
Ness Processing
availability (%) (kg / cm ² ) (mg) I. 5 5.2 7.8 12.3 9000 7000 950 0 28 500 724 Well I. 10 5.5 8.5 12.3 9000 6500 870 0 29 200 832 Well I. 15th 6.0 8.8 12.3 9000 6000 730 0 39 900 1 100 out
draws II 5 4.4 10.2 12.3 79,000 45,000 3500 0 37 200 1000 Well II 10 4.7 9.6 12.3 79,000 50,000 4,500 0 27 100 928 Well II 15th 4.9 11.1 12.3 79,000 35,000 2500 0 27 300 865 Well III 5 3.1 8.3 12.3 150,000 110,000 6500 0 29,000 796 Well III 10 3.6 9.5 12.3 150,000 90,000 4,800 0 28 200 782 Well III 15th 4.0 9.9 12.3 150,000 85,000 5000 0 29,000 824 Well

10

9.5 11.8 12.3 79,000

500

24,000

716 not good

C. Conditions of C:

Gas- Conc pH Vl 12.3 Concentration of SO ₂ Vl a (ppm) Vl Young out (kg / cm ² ) Soft Work lyp tration 12.3 module 24 800 Ness baikeil Gi (OH), v \ 7.5 12.3 V I a 6,800 Vi a 0 25,000 (%) 6.8 5,900 0 37 600 (mg) 1 5 5.3 7.3 12.3 9,000 4 900 800 0 728 Well 1 10 5.7 12.3 9,000 780 37 200 786 Well I. 15th 5.9 10.2 12.3 9000 44,000 650 0 29,000 I 046 out 10.0 12.3 49,000 0 28 600 draws 11th 5 4.3 9.9 12.3 79,000 35,000 2,800 0 27 200 989 Well Il IO 4.8 7.8 12.3 79,000 95,000 3,900 0 26,000 908 Well II 15th 5.0 8.2 79,000 89,000 4,200 0 27 200 868 Well IN THE 5 3.3 8.4 150,000 79,000 6,300 0 801 Well III 10 3.6 150,000 5 700 796 Well III 15th 3.8 150,000 4,300 788 Well

10.0 12.0 12.3 150,000 80,000 5,200

24 800

736 not good

D. Conditions of D:

gas
Type Conc
tration
Ca (OH) ₂
(%) pH
v \ Vl VS concentration
V \ a of SO ₂ (ppm)
Vl a Vi a 900
3000
5000 Vi off Young
module
(kg / cm ² ) Soft
Ness
(mg) Processing
availability I.
II
III 10
10
10 5.2
4.5
3.8 10.0
9.5
8.9 12.3
12.3
12.3 9000
79,000
15,000 7,000
40,000
100,000 900 0
0
0 23 800
21 600
23,000 731
718
725 not good
not üiit
not good I. 10 8.8 10.2 12.3 9,000 7,000 1 sheet of drawings 0 22 300 745 not good For this

509 683/196

Claims (3)

Patent claims: 1. A process for the continuous production of crystalline calcium sulfite, which is suitable as a filler for thermoplastics and has a grain size of about 5 to about 50 μ, by reacting a _{gas containing SO 2} with milk of lime in several contact zones connected in series at 50 to 100 ⁰ C, characterized in that 0.1 to 20% by weight, in particular 5 to 10% by weight, milk of lime together with part of the already converted, CaS O ₃ -containing circulating suspension continuously in a system consisting of at least 5 at least two contact stages in countercurrent successively to the SO ₂ -containing gas leads in such a way that first a fine-grained CaSO _{3 is} precipitated and only in the last part of the process the suspension is _{brought into contact with new SO 2} -containing gas which has not yet been depleted and that the first contact stage is in the direction of the flow of the SO ₂ -containing gas to a pH of 3 to 6 and all further contact should be kept at a pH greater than 6 * 5. 2. The method according to claim 1, characterized in that a _{gas containing SO 2} is used with a CO ₂ content. 3. The method according to claim 1 or 2, characterized in that the suspension is conducted in cocurrent with the SO ₂ -containing gas within the individual contact zones.