Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Alkaline earth metal
Patent
1982-12-28
1984-07-17
Straub, Gary P.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Alkaline earth metal
423485, 423555, 422189, C01B 708, C01B 718, C01F 1146
Patent
active
044605510
DESCRIPTION:
BRIEF SUMMARY
Synthetic anhydrite is a highly valued raw material in those countries which do not have sufficient gypsum deposits. This substance is an excellent additive in the cement production industry and is also used in the manufacture of floor coverings, together with floorslabs with integral heating coils. For all these applications it is a primary requirement to secure appropriate purity in the produced material, in order to prevent harmful effects to the cement kiln or in the hard-setting process of premixed anhydrous gypsum or to avoid subsequent blooming. However, anhydrites, with slight contamination of fluorides have been found as rather desirable in the cement production processes and for this reason the synthetic anhydrite, which--in addition--can be prepared with simultaneous production of hydrofluoric acid, became a much sought-after substance.
To enable the continuous production of such anhydrite with optimized properties, the present invention proposes a process and associated equipment for a profitable improvement of the hitherto known methods. The methods which are representative of the present state of the art and are to date in actual usage, are described in sufficient detail in the following publications:
Matthes-Wehner: "Inorganic Technological Processes" VEB Verlag Grundstoffindustrie, (1964) pp. 453-455;
Ullmann: "Encyclopaedia of Industrial Chemistry" 3rd Edition, Supplement (1970) pp. 449,450:
Ullmann 4th Edition, Vol. 11. (1976) pp. 599-601 and
Kirk-Othmer: "Encyclopaedia of Chemical Technology" 3rd Edition, Vol. 10 (1980) pp. 742-744.
In all the large industrial processes used to date in trade production, the following common features are applicable: The remaining HF content, originating from the residual gases prior to the aqueous absorption of SiF.sub.4, are scrubbed with cold concentrated sulphuric acid. The so obtained acid mixture of fluorosulphonic acid is intermixed with sulphuric acid and--by the addition of oleum--the residual water is removed. This preliminary process is carried out to enable in the subsequent reaction between fluorspar and sulphuric acid, which has to be carried out at temperatures in excess of approx. 164.degree. C., to separate the fluorosulphonic acid entrained in the recirculation procedure, to liberate therefrom the HF constituent and admit it repeatedly to the prepurifying and condensation treatment. Obviously, this is associated with additional power consumption.
The purpose of the excercise is to produce a synthetic anhydrite, which contains merely the small desirable proportion of CaF.sub.2, whilst the free H.sub.2 SO.sub.4 is completely neutralized, but other desired accelerators will be retained for further usage.
In order to obtain good quality and high grade anhydrite, the reaction between fluorspar and sulphuric acid should be conducted at stochiometric conditions or only with a minute excess of sulphuric acid. A further requirement is that the reaction should be processed at moderate temperatures, in order to prevent the thermal overloading of the precipitated anhydrite.
According to the views of professional experts, the above mentioned requirements are contraindicated, because a relatively fast conversion of CaF.sub.2 +H.sub.2 SO.sub.4 to HF and CaSO.sub.4 can only be obtained at temperatures well beyond 200.degree. C., nevertheless below the decomposition temperature of the sulphuric acid, which is approximately 340.degree. C. This view is apparently confirmed by the overall literature on the subject, as for example, in Kirk-Othmer, 2nd Ed., Vol. 9 (1966) p. 619 is stated, that the conventional reaction time of 30-60 minutes can be obtained at temperatures of 200.degree.-250.degree. C. According to practical experience these data can not be confirmed and the average resindence periods of the material in the reaction zone is frequently much longer, whereby the reactors have to be layed-out with significantly greater dimensions, to meet the requirements.
Should it be attempted to shorten the reaction time, for reasons to increase throughput, by m
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Kaiser Victor, Siedegleichgewichte von Systemen mit Fluorowasserstoff, PhD Dissertation, Von der Eidgenossischen Technischen Hochschule in Zurich, 1964.
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Kirkothmer Encyclopedia of Chemical Technology, 2nd Edition, vol. 9, 1969, p. 619.
Kirkothmer Encyclopedia of Chemical Technology, 3rd Edition, 1980, vol. 10, pp. 742-744.
Ulmans Encyclopedia der Technishen Chemie, 3rd Edition, 1970, Supplemental volume, pp. 449-450.
Boese Dieter
Etter Rene
Buss AG
Saffitz A. A.
Straub Gary P.
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