EP1272427A1

EP1272427A1 - Method for producing precipitated calcium carbonate

Info

Publication number: EP1272427A1
Application number: EP01913859A
Authority: EP
Inventors: Helmut Dillenburg; Kurt Schinninger; Chistoph Nover; Alfred Mattausch
Original assignee: Solvay Soda Deutschland GmbH; Solvay Chemicals GmbH
Current assignee: Solvay Chemicals GmbH
Priority date: 2000-04-06
Filing date: 2001-03-10
Publication date: 2003-01-08
Also published as: DE10017273A1; AU2001239288A1; WO2001077020A1; MY136402A

Abstract

The invention relates to a method for producing precipitated calcium carbonate (CCP) by introducing CO2 into lime milk.According to the invention, the useful properties of CCP can be reproducably controlled within a broad range by specifically adjusting the viscosity of the lime milk used to produce CCP.

Description

Process for the preparation of precipitated calcium carbonate

description

The invention relates to a process for the preparation of precipitated calcium carbonate (CCP) which is suitable as a functional filler and is distinguished by defined properties. A typical application is its use as a filler in e.g. B. Piastisolen, underbody protection for automobiles, sealants and printing inks.

The precipitated calcium carbonate is able to control the flow behavior of the masses. For example, by using the appropriate calcium carbonate materials with very different flow behavior. The yield point according to Bingham in the plasticizer mixture (SEB) is usually given as a typical characteristic of the application suitability of calcium carbonates as fillers. Depending on the application, high, medium or low flowing grass can be desired. The ability of the precipitated calcium carbonate to control the flow limits is influenced, among other things, by the nature of the limestone used for the production of the lime milk, the burning conditions of the limestone and the extinguishing process.

Finely dispersed calcium carbonate is either made from naturally occurring raw materials by mechanical processing or by chemical means, e.g. B. made by precipitation.

Precipitated calcium carbonate is usually produced by introducing C0 ₂ into milk of lime.

Ca (OH) ₂ + C0 ₂ - CaC0 ₃ + H ₂ 0 The properties of the precipitated calcium carbonates are e.g. B. depending on the chemical composition of the limestone used, the firing conditions and the extinguishing conditions.

Limestone of different origins or compositions leads to calcium carbonate with very different application properties. The mechanism of this influence is currently not exactly known. However, it is known that e.g. B. Fe2 ⁺ , Zn 2 ⁺ , Cl ^~ , Mn2 ⁺ and Be2 ⁺ traces interfere with the crystallization of the CCP. In practice you avoid e.g. B. high magnesium content in the limestone when high flow limits are sought.

So-called soft firing is preferably used to produce precipitated calcium carbonate. For this purpose limestone is burned at a temperature of 1,000 to 1,250 ° C.

The burning process is usually carried out in so-called shaft furnaces or in rotary tube furnaces. As a fuel z. B. coke, oil or natural gas can be used. Here, low firing temperatures lead to high lime milk viscosities. The use of this milk of lime for CCP production also leads to small particle diameters of the CCP and high flow limits in the plasticizer mixture. Accordingly, high firing temperatures lead to low lime milk viscosities, coarse CCP particles and low flow limits in the plasticizer mixture. The yield of quicklime is highest at medium temperatures, since not all CaC0 _{3 is converted} to CaO at low temperatures and part of the CaO is overburned at high temperatures, ie it can no longer be extinguished using the usual methods.

The characteristics of quicklime include its ability to react with water. The so-called VEC value (Velocite d'Extinction de Chaux). The heating rate of a defined water / quicklime mixture is measured. Typical VEC values for quicklime, which is suitable for the production of precipitated calcium carbonate, are above 3 ° C / min.

For the production of the milk of lime, the quicklime z. B. reacted with water in an extinguishing drum, forming a Ca (OH) ₂ suspension, the so-called milk of lime. The lime milk usually has a solids content of 70 to 220 g / l of Ca (OH) ₂ , a viscosity of 30 to 2500 mPas and an average particle diameter of less than 50 μm.

Lime milk is e.g. B. to neutralize. Wastewater, used to make soda or precipitated calcium carbonate.

One part of the previously known processes for the production of precipitated calcium carbonate is that its application properties, in particular as a rheology-controlling additive, have so far been insufficiently adjustable.

The object of the invention is the production of precipitated calcium carbonate (CCP) with controllable defined and reproducible properties in a wide range.

According to the invention, the object is achieved in that a lime milk with exactly the viscosity at a given concentration is used for the production of the calcium carbonate with certain rheological properties, which leads to the desired properties of the CCP. The properties of calcium carbonate as a rheology-controlling additive are adjusted by the viscosity of the lime milk.

Depending on the intended use, different flow limits of the CCP are desired. Piastisoles aim for high flow limits. These are achieved by using lime milk with viscosities above 750 Pas. In print ben medium flow limits are sought so that lime milk with viscosities between 100 and 150 mPas is used for this. For highly filled silicone masses, CCP with a low flow limit are used, so that lime milk with a viscosity below 100 Pas is used.

The milk of lime thus produced with the viscosity set is then fed to a reactor, into which gas containing CO ₂ is introduced to precipitate the calcium carbonate and is homogeneously dispersed in the milk of lime.

The precipitated calcium carbonate can be post-treated with fatty acids depending on the intended use.

It has surprisingly been found that the properties of the precipitated calcium carbonate are reproducible and can be varied within a wide range if the viscosity of the lime milk is adjusted and then CO _{2 is introduced} to precipitate the calcium carbonate.

If you compare the processes for the preparation of precipitated calcium carbonate from lime milk of different viscosities, it is noticeable that the viscosity has an influence on the reaction rate, on the average particle diameter of the CaC0 _{3 formed} and on the application properties of the CCP.

It has been found that an increasing viscosity of the milk of lime also leads to a decrease in the mean particle diameter of the primary particles of the CCP.

It has also been found that by controlling the viscosity of the milk of lime, the precipitation time can be reduced by approximately 20%.

By adjusting the viscosity of the milk of lime according to the invention, it is possible to significantly influence the flow limit of the CCP-filled plastisols, ie in a targeted manner adjust. The yield point was found to be a function of the viscosity of the milk of lime at a given concentration. It was therefore found that the properties of the CCP can be reproducibly influenced by the visually adjustable viscosities of the milk of lime.

The undesirable influencing of the properties of the CCP by undefined fluctuations in the quality of the limestone of the burning process and the extinguishing process can, for. B. can be canceled by the defined mixing of different limes, the limes being mixed in the ratio from which the desired lime milk viscosity results after subsequent deletion.

According to the invention, the viscosity can be adjusted by mixing quicklime, which would lead to milk of lime with very different viscosities if used alone, mixed with one another in such a ratio and deleted or deleted together that the desired viscosity of the milk of lime is set. It is also possible to first delete each lime for yourself and then mix the lime milk together. Furthermore, the two limes can be added to the extinguishing apparatus in the specified ratio, where the desired mixture is then formed, from which the desired lime milk viscosity results.

In one embodiment of the invention, the measurement of the viscosity of the lime milk is used to control the mixing ratio of the types of lime milk. The viscosity is easily z. B. to measure continuously, and via a corresponding control loop, the mixing ratio of the two limes and thus the resulting lime milk quality can be controlled very precisely. Examples 1-6:

Quicklime 1 and quicklime 2 are mixed together in different proportions and extinguished in an extinguishing drum:

VEC quicklime 1 4.8 ° C / min.

VEC quicklime 2 9.8 ° C / min.

Denomination in each case: 2 - 5 cm

Calcium carbonate was produced from the lime milk ground in this way by introducing CO ₂ -containing gas:

Fällbedingunαen:

Falling temperature: 18 ° C

C0 ₂ concentration in the precipitation gas: 30 vol .-%

Gas flow: 1 m ³ / h per 10 1 lime milk

Felling time: see table

Aftertreatment: fatty acid treatment with

(0.85 mg stearic acid) /

(m ² CCP surface)

It becomes clear that the viscosity of the lime milk can be controlled in a targeted manner by mixing the limes. As a result, the CCP downtime can be reduced by up to 20%. The particle diameters of CCP are set reproducibly. The flow limit of a mixture of plasticizer and calcium carbonate can be controlled reproducibly. The viscosity of the lime milk can also be controlled by grinding the lime milk. Known mills can be used to grind the milk of lime. Bead mills are preferably used. Zirconium oxide grinding beads with a diameter of 0.4 to 2 mm are particularly suitable as grinding beads. The fineness of the pearls strongly influences the milling result.

The grinding effect is also controlled by the speed of the mill, the dwell time of the lime milk in the mill and the resulting specific energy input.

Examples 7-10:

Slaked lime was extinguished in an extinguishing drum:

Denomination: 1 - 5 cm

VEC: 4.8 ° C / min

The resulting lime milk was ground and characterized:

Solids content: 150 g / 1

milling conditions:

Horizontal agitator ball mill

Grinding chamber voltages 5 1

Motor power 22 kW

grinding media:

Zirconia balls

Diameter 1.0-1.6 mm

Filled volume 4.8 1

The tests are carried out at a constant speed of 1,990 rpm. carried out. Lime milk in the mill was varied. This resulted in various specific energy inputs.

precipitation conditions:

Falling temperature: 18 ° C

C0 ₂ concentration in the precipitation gas: 30 vol .-%

Gas flow: lm ³ / h per 10 l of lime milk precipitation time: see table

Aftertreatment: fatty acid treatment with (0.85 mg stearic acid) / (m ² CCP surface)

It becomes clear that the viscosity of the lime milk and the average particle diameter of the lime milk can be controlled in a targeted manner by the wet grinding. As a result, the CCP downtime can be reduced by up to 20%. The particle diameters of CCP are set reproducibly. The flow limits are increased.

It is also possible to influence the viscosity of the resulting lime milk by varying the firing conditions. It is within the meaning of the invention to vary the firing temperatures in the range from 900 to 1200 ° C. Examples 11-13:

Limestone is crushed to a grain size of <10 mm and then burned for 4 hours at different temperatures. After cooling, the lime is extinguished in a stirred container. This is added to the water in portions. The portions are chosen so that a temperature in the release container does not exceed 95 ° C. A total of 200 g quicklime is added to 1 liter of water. After the reaction is complete, the residue is sieved through a 100 μ sieve and weighed out. The lime milk is diluted to 150 g / 1. CCP is produced by introducing gas containing CO into this milk of lime.

precipitation conditions:

Falling temperature: 18 ° C C0 ₂ concentration in the precipitation gas: 30%

Gas flow: 1 m ³ / h per 10 1 lime milk Post-treatment: fatty acid treatment with 0.85 g stearic acid / m ² CCP surface

It is in the sense of the invention, a lime milk with a viscosity of 20 to ax. 2,500 mPas (measured at 25 ° C). A higher viscosity should be avoided as otherwise the entry of the precipitating gas is not optimally possible.

For the homogeneous dispersion of the precipitation gas, good flowability of the milk of lime is required. Depending on the application, CaC0 ₃ , which is a mixture component with high functionality for z. B. polymers, polymer preparations, plastics, coating compositions, sealants, paper or paints, in particular printing inks is suitable, are provided in consistent quality.

Claims

claims

1. Process for the preparation of precipitated calcium carbonate by introducing C0 ₂ into lime milk, the application properties of the precipitated calcium carbonate being controlled by the viscosity of the lime milk used for the precipitation, by the viscosity of the lime milk

a) separate deletion of quicklime of different quality and subsequent mixing of the lime milk types is set in the ratio from which the desired lime milk viscosity results or

b) is adjusted by mixing quicklime of different quality in the ratio from which the desired lime milk viscosity results after the quicklime mixture is subsequently extinguished, or

c) by separately metering quicklime of different quality directly into the extinguishing apparatus in the ratio from which the desired lime milk viscosity results, or

d) is controlled by grinding the milk of lime or

e) is controlled by varying the firing temperature for producing the quicklime in the range from 900 to 1200 ° C.

2. A process for the preparation of precipitated calcium carbonate according to claim 1, characterized in that the viscosity of the lime milk is set in the range from 20 to 2,500 ps (measured at 25 ° C).

3. Influencing the properties of the precipitated CaC0 ₃ for use as a rheology control additive by targeted adjustment of the lime milk viscosity according to claim 1 and 2.