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    2.
    发明专利
    未知

    公开(公告)号：DE1204679B

    公开(公告)日：1965-11-11

    申请号：DEB0076110

    申请日：1964-03-28

    Applicant: BASF AG

    Inventor： HAMPRECHT DR GUENTHER ,  FROMM DR DIETER ,  SCHWARZMANN DR MATTHIAS ,  VOGEL DIPL-ING LUDWIG

    IPC: C07C273/16

    Abstract: Urea is recovered from the off-gas obtained in a melamine sythesis from urea in the gas phase and in the presence of catalysts and which has been freed from melamine by fractional condensation at from 150 DEG to 200 DEG C., by bringing said off-gas into intimate contact with a melt of urea or a melt of urea and its thermal decomposition products, both of which are kept up to 50 DEG C. above their melting temperature. Thermal decomposition products which may be present in the urea melt are biuret, triuret, cyanuric acid, ammeline, ammelide, melamine or melamine cyanurate. The presence of 20-25% biuret (obtained by blowing with CO2) is preferred, since this depresses the melting point and allows a very cool melt to be used. Portions of the melt are preferably drawn off after use and passed to the melamine synthesis reactor.

    5.
    发明专利
    未知

    公开(公告)号：DE1212545B

    公开(公告)日：1966-03-17

    申请号：DEB0076407

    申请日：1964-04-20

    Applicant: BASF AG

    Inventor： HAMPRECHT DR GUENTHER ,  ROTHER DR EBERHARD ,  SCHWARZMANN DR MATTHIAS ,  FROMM DR HERMANN DIETER

    IPC: B01J21/04 ,  B01J21/16

    Abstract: Melamine is made by heating urea, and/or its thermal decomposition products, at 300-450 DEG C. in the presence of added ammonia or gas containing ammonia and a catalyst comprising aluminium oxide which has been prepared by calcining bohmite, bayerite, hydrargyllite or a mixture thereof at 700-1000 DEG C. The added ammonia may be in the form of the off-gas containing CO2 which is obtained after removing melamine from the reaction gases. The catalyst may be regenerated by treatment with ammonia at elevated temperatures. The process is effected in a continuous manner. The examples relate to a catalyst obtained by calcining a mixture of bohmite and bayerite.

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