DE2522005A1 - PROCESS FOR THE PRODUCTION OF ALPHA-HEMIHYDRATE FROM PLASTER - Google Patents

Description

Meissner & Meissner

PATENT AGENCY OFFICE RO

BERLIN - MUNICH

PATENT LAWYERS

DIPL-ING. W. MEISSNER (BLN) DIPL-ING. P. E. MEISSNER (MCHN) DIPL-ING. H.-J. PRESTING (BLN)

1 BERLIN 33, HERBERTSTR. 22nd

Your sign Your letter from Our Sign Berlin, the 15th time in 1975

5o-lo32

Mitsubishi Jukogyo Kabushiki Kaisha, 5-1> Marunouchi 2-chome, Chiyoda-Ku, Tokyo, Japan

Process for the production of α-hemihydrate from plaster of paris

The invention relates to a method for converting a Calcium sulphate dihydrate slurry in a-hemihydrate by means of a water / pressure heat treatment and in particular such a process for continuous implementation.

The a-hemihydrate, which develops a great deal of strength after hydration and setting, is very promising applicable new building material. Because of its negligible expansion and contraction after setting and hardening the hemihydrate is already widely used as a molding material for the manufacture of panels in the automotive and automotive industries Used in aviation industry. As for the manufacture of the hemihydrate, the known methods are inclusive the process carried out under pressure and with aqueous solution and the steam-pressure process, for batches Operations provided; none of these are suitable for mass production.

After an extensive search for ways to technically produce large volumes of the a-hemihydrate in continuous

BORO MÖNCHEN: TELEX: TELEGRAM: TELEPHONE: BANK ACCOUNT: POST CHECK ACCOUNT:

MÖNCHEN 22 1-856 44 INVENTION BERLIN BERLINER BANK AQ. W. MEISSNER, BLN-W

ST. ANNASTR. 11 INVEN d BERLIN 030/885 60 37 BERLIN 31 122 82 -109

TEL .: 089/22 35 44 030/886 23 82 3695716000

609815/1149

Lich operation instead of batch production was now found that uninterrupted production is possible if one uses the crystallization catalyst Sodium citrate limited to Hull or a very small amount compared to the amount in the previous procedures. The invention builds on this finding.

The core of the invention consists in a process for the production of oc-hemihydrate from gypsum by converting a calcium sulfate dihydrate slurry into hemihydrate by means of water / pressure heat treatment, in which the slurry is continuously heat treated with water under pressure and in the presence of sodium citrate in a Amount of from 0.1 to 0.1 % by weight of the total weight of the dihydrate at a temperature not below 14 ° C. for a suitable period of time in the process.

The temperature of the water / pressure heat treatment in the process according to the invention corresponds to the temperature range usually used in technology for such a treatment, but the amount of sodium citrate, limited to zero to 0.1% by weight of the dihydrate, is decisive. If the amount of sodium citrate exceeds the specified range, as the data given later show, conversion to α-Heraihydrate takes place in the conventional preparation process, but the conversion is practically zero or negligibly small when working continuously. In addition, the slurry must be kept in the process of heat treatment with water and under pressure for a sufficient time in order to be converted to oc-hemihydrate. An average residence time of approximately about 1 hour is usually sufficient. If the time is too short, the conversion is incomplete; if the time is too long, one can no longer speak of a continuous, but rather of a batch mode of operation, which makes conversion using the sodium citrate serums in the specified range difficult. For these reasons, the mean residence time of the slurry to c, to 5 for 2 hours is set., Wherein 1 to I ₅ S ¹ hr preferred..

The invention will hereinafter be more fully understood with reference to FIG the attached drawing, in which the only one

609 * 15/11 * $

2 52 200b

FIG. Schematically shows an arrangement for practicing the invention; Lines 1, 2 and 3 are used to feed calcium sulfate dihydrate, sodium citrate and water. Numeral 6 denotes a vessel in which the water / pressure heat treatment is carried out, and numeral 7 a pipe through which a cc hemihydrate slurry is taken out of the vessel 6 under pressure. Calcium sulphate dihydrate, sodium citrate and water are fed via lines 1, 2 and 3 into container 4, where a homogeneous slurry of the dihydrate containing the desired proportion of sodium citrate is produced. (If sodium citrate is not required, the supply via line 2 is blocked). The resulting slurry is transferred via line 5 to the container 4 into the heat treatment container 6, where it is heat-treated with hot water at over 140 ° C. under a suitable pressure. The α-hemihydrate slurry thus obtained _; is continuously removed under pressure via line 7 and at such a rate that the slurry in container 6 is discharged after an average residence time of 1 to 1.5 hours. The oc-hemihydrate slurry is then passed under pressure into a liquid cyclone or thickener 8 for concentration; the concentrated slurry passes through line 9 to dryer 11; the dried product is conveyed via line 12 to a grinder 13 and the end product oc-hemihydrate is drawn off via line 14. The filtrate from the liquid cyclone or thickener

R / 8 in turn becomes the dihydrate '<vufsclammung preparation container via line Io 4 recycled for reuse as batch feed.

To explain the advantages of the invention, the following comparative examples are given in conjunction with exemplary embodiments given the invention.

Comparative example 1

A calcium sulfate dihydrate slurry was made with water / pressure under various conditions as tabulated below heat treated. In the case of partial operation, the corresponding

60981 5 / 1U9

-drawing α-Heraihydrate, when shifting to continuous operation Type II anhydrite was obtained instead of oc hemihydrate,

Temperature slurry sodium citrate residence time concentration conc. Κ

a 14o ^G C Io Wt% 0 , 02 Wt% 1 _ 1 1.5 hours b 14o ° C Io Wt% 0 , 015 Wt% 1 Hours. C. 15o ° C Io Weight - ⁰ I. 0 , 02 Wt% Hours.

^x Based on the total weight of the slurry as in the following examples. This means that, for example, under a) sodium citrate is present in an amount of 0.2% by weight per 100% by weight) of the dihydrate.

Comparative example 2

A calcium sulfate dihydrate slurry was made from among the following Conditions and water / pressure heat treated j when run in batch, some oc hemihydrate was obtained. The crystals however, were in the form of needles, indicating difficulty in driving out the water. The product has been ground, kneaded with water and tested for strength. The measured strength value was low.

Temperature: 14o ° C

Slurry concentration: Io wt% Sodium citrate concentration: ο

Dwell time: 1 hour

Example 1

The procedure of Comparative Example 2 was repeated under exactly the same conditions except that continuously was driven. The obtained oc hemihydrate crystals were no needles, but showed a more developed shape similar to rods. The drainage was relatively easy and the product provided high strength.

609815/1 U9

Example 2

A calcium sulfate slurry was prepared under the following conditions continuously heat treated under water / pressure. Nucleation and crystal growth occurred in cycles of about 2 hours each repeatedly on; rods, platelets and columns of the a-emihydrate were obtained.

Temperature: 14o ° C

Slurry concentration: Io wt% Ilodium citrate concentration: 0.05% by weight Dwell / time: 1 hour

Samples of the oc-hemihydrate obtained in Examples 1 and 2 were dried, ground in a ball mill, kneaded with water and the products obtained are tested for strength and other physical properties. The results are below tabulated.

E.g. med. Standard-Block-Compression-Resistant-Particle-Waterproof strength »s size content

1 25 / U 36 wt% 1.4-3 24o kg / cm ² 64 kg / cm ²

2 55 / U 29 "1.55 27o" 66 "

Wet strength values of hardened test pieces obtained by kneading the α-henihydrate samples with the addition of water in the standard V / water mixing ratio or the gee-even percentages, the mixtures are filled into Gufiforms and the moldings were cured at room temperature and saturation humidity for 7 days.

Claims

609815/1 U9

Claims (2)

Claims 1. Process for the production of oc-hemihydrate from Gypsum converting a calcium sulfate dihydrate slurry in hemihydrate by water / pressure heat treatment, characterized in that the slurry continuously heat treated with water under pressure and the slurry in the presence of for an appropriate period of time Sodium citrate in a range from zero to 0.1% by weight of the Total weight of the dihydrate at a temperature not keeps below 14o ° C in the process. 2. The method according to claim 1, characterized in that that the residence time is 0.5 to 2 hours. IpI.-ing. H. j. Resting Patents 1 sheet of drawing 80981S / 1U9 BORO MONKS: TELEX: TELEGRAM: PHONE: BANK ACCOUNT: CHECK ACCOUNT: 8 MONKS 22 1-856 44 INVENTION BERLIN BERLINER BANK AG. W. MEISSNER, BLN-W ST. ANNASTR. 11 INVEN d BERLIN 030/885 60 37 BERLIN 31 122 82-109 TEL .: 089/22 35 44 030/886 23 82 3695716000