Chemistry of inorganic compounds – Nitrogen or compound thereof – Carbon containing
Patent
1996-09-11
1998-05-19
Langel, Wayne
Chemistry of inorganic compounds
Nitrogen or compound thereof
Carbon containing
C01C 316
Patent
active
057531994
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a process for the production of calcium cyanamide (lime nitrogen) from urea and a calcium compound containing oxygen.
The large-scale production of lime nitrogen has previously been achieved by azotization of calcium carbide. As an alternative to this, processes are already known which are based on the reaction of urea with compounds containing calcium. Thus a two-step process is known from SU-PS 812 713 in which urea is first reacted with calcium oxide or calcium oxide hydrate at an increased temperature and subsequently the calcium cyanate that is formed is calcined. A disadvantage of this process is the time-consuming purification of the intermediate.
The process according to SU-PS 1 333 638 appears to be much more simple in which the reaction of calcium oxide or calcium hydroxide with urea is carried out at 130 to 220.degree. C. in an inert organic medium. Subsequently the reaction mass is heated at 700.degree. to 900.degree. C. Yields of calcium cyanamide of about 80 to 90% are achieved using this process, the content of cyanamide nitrogen being 28 to 32% N.
Approximately comparable yields are obtained according to the process of the French Patent Application 2 640 610 according to which 1 mole calcium carbonate is reacted with 2 mole urea at a temperature of 135 to 200.degree. C. Subsequently, the reaction mixture is subjected to a further temperature treatment between 300.degree. and 500.degree. C.
It is either very difficult or not possible at all to carry out all these said processes on a technical scale because, in part, very complicated processing steps are necessary which appear to be extremely problematic also with regard to the profitability of these processes.
The object of the invention is therefore to provide a process for the production of calcium cyanamide by reacting urea and an oxygen-containing calcium compound in at least two steps which does not have the said disadvantages of the state of the art but ensures high yields of calcium cyanamide in a technically simple manner.
SUMMARY OF THE INVENTION
The above-stated object is achieved according to the process of the invention wherein: under compression and/or while being revolved or by applying them to a hot surface at temperatures of 120.degree. to 500.degree. C. until a solid is formed and temperatures of 600.degree. to 900.degree. C.
Surprisingly, the process of the invention provides high yields of calcium cyanamide without requiring a complicated processing of the reaction product after the first or second step. In addition high throughputs can be achieved by the process according to the invention due to the short reaction period which was also not foreseeable.
DESCRIPTION OF PREFERRED EMBODIMENT
The process according to the invention includes at least two reaction steps. In the first reaction step urea and the oxygen-containing calcium compound are reacted together at temperatures of 120.degree. to 500.degree. C., preferably 150.degree. to 400.degree. C. In this case burnt lime (calcium oxide (CaO)), calcium hydroxide (Ca(OH).sub.2) or calcium carbonate (CaCO.sub.3) and also calcium alcoholates primarily come into consideration as the oxygen-containing calcium compound. The calcium compound is preferably used with a particle size of 0.1 to 1.0 mm. According to a preferred embodiment calcium carbonate is used in a precipitated form which has a particle size of 1 to 200 .mu.m and has a particularly pronounced reactivity due to being finely divided. It is possible in this case within the scope of the invention to use the precipitated calcium carbonate in an impure form as it for example is formed as a usually non-usable by-product in the further processing of lime nitrogen to cyanamide, dicyandiamide or thiourea. The molar ratio of the oxygen-containing calcium compound to urea can be varied within wide limits, however, it has proven to be particularly advantageous to set this molar ratio to 1:1 to 1:4.
An essential feature of the invention is that the reaction components are
REFERENCES:
patent: 2632687 (1953-03-01), Walter
patent: 3173755 (1965-03-01), Picard et al.
patent: 3235340 (1966-02-01), Kaess et al.
patent: 3499726 (1970-03-01), Scheinost
Graefe Jurgen
Klima Hubertus
Weber Gunter
Wolferstetter Johann
Langel Wayne
SKW Trostberg Aktiengesellschaft
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