Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2001-12-28
2002-07-09
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C558S351000
Reexamination Certificate
active
06417385
ABSTRACT:
DESCRIPTION
The invention is directed towards an improved process for the continuous production of acetone cyanohydrin from hydrogen cyanide and acetone, whereby hydrogen cyanide in the form of a gas mixture containing inert other gases, in particular in the form of a crude gas arising from the BMA process or the Andrussow process, is employed for the purpose of producing hydrogen cyanide.
Acetone cyanohydrin, that is to say &agr;-hydroxyisobutyronitrile, is the most important initial product for all derivatives of methacrylic acid and, above all, the esters thereof. Technically, acetone cyanohydrin is produced by base-catalysed addition of hydrogen cyanide (hydrocyanic acid) onto acetone. In the neutral range and especially in the alkaline range, acetone cyanohydrin is in equilibrium with its initial components. The commercial processes predominantly utilise liquid-phase processes which are carried out both discontinuously and continuously in the presence of catalysts such as caustic soda solution, caustic potash solution, potassium carbonate, sodium acetate/acetic acid, pyridine/acetic acid as well as anion-exchange resins at temperatures below 40° C. Attention is drawn, in exemplary manner, to the process due to Rohm and Haas (see Ullmann's Encyclopedia of Industrial Chemistry 5
th
Edn. (1985), pages 91-92 [sic]): In this process, liquid hydrocyanic acid, acetone and a basic catalyst are introduced continuously into a reactor and subsequently, after stabilisation with sulfuric acid and filtration of the catalyst by a two-stage distillation, the reaction mixture is freed firstly of unconverted hydrocyanic acid and acetone and then of water. The waste gases from the first distillation stage are recycled into the reactor, pure stabilised acetone cyanohydrin is withdrawn at the bottom of the second distillation stage. A disadvantage of this process is the fact that hydrogen cyanide has to be liquefied from a gas containing hydrogen cyanide, for example a crude gas arising from the BMA process or the Andrussow process for the production of hydrogen cyanide. The technical devices for liquefying gaseous hydrocyanic acid and for storing the liquid hydrocyanic acid give rise to high investment costs and high variable costs of liquefaction, inter alia as a result of the use of cooling brines. A further consideration is that a relatively large stock of liquid hydrocyanic acid conflicts with the Responsible Care Programme.
Instead of liquefied hydrocyanic acid, it is also known to employ a gas mixture containing hydrogen cyanide and inert gases, for example coke-oven gases, in a process for producing acetone cyanohydrin. In the process due to Reinpreussen AG—see Ullmann's Encyklopädie der Technischen Chemie, 4
th
Edition, Volume 7, pages 34-35—coke-oven gases containing hydrogen cyanide are washed continuously, after a potash wash, in countercurrent with acetone which contains 10% water, and the reaction to form acetone cyanohydrin is carried out in the presence of a basic catalyst in two gas-washing columns connected in series; the processing of the reaction mixture containing acetone cyanohydrin encompasses two acetone columns and two columns for purifying the acetone cyanohydrin. Despite the very elaborate plant, it is not possible to avoid a large quantity of the acetone and also some of the unconverted hydrogen cyanide being discharged together with the waste gas emerging from the second gas-washing column.
According to DE-AS 12 57 765 it is possible for acetone cyanohydrin to be obtained from gases containing dilute gaseous hydrogen cyanide arising from the synthesis of hydrocyanic acid from methane and ammonia, i.e. from the crude gas of the BMA process, by the gas being introduced into liquid acetone or into a solution of acetone in an inert solvent such as acetone cyanohydrin at a pH value from 8 to 8.5, by the conversion being carried out at 0 to 25° C. and by the pH value of the reaction mixture being constantly maintained by addition of baryta solution. Together with the inert gases discharged from the reactor, a quantity of acetone corresponding to the phase equilibrium as well as unconverted hydrocyanic acid are also inevitably discharged—as shown by the examples in this document, hydrogen cyanide breaks through in a quantity amounting to approximately 0.5 to 7.2%, relative to the quantity of hydrocyanic acid employed. Accordingly, the embodiments described in this document are hardly suitable for carry-over onto a technical scale or they necessitate at least a subsequent processing of the waste gas with a view to recovering acetone and unconverted hydrocyanic acid. A further disadvantage consists in the fact that the pH value is adjusted by means of baryta solution; accordingly, the liquid phase containing acetone cyanohydrin, after the stabilisation thereof with sulfuric acid prior to the purification by distillation, has to be passed across a filter with a view to separating barium sulfate. In the case of the embodiment described in this document, by virtue of the inert gases that are introduced with the gas mixture containing HCN the equilibrium of the formation of acetone cyanohydrin is steadily shifted in the direction of the initial products, so that a discharge of acetone and hydrogen cyanide is unavoidable. Even if acetone and gas containing hydrogen cyanide are supplied continuously to the circulating reactor which is operated in accordance with the air-lift principle and which is filled with acetone cyanohydrin, the discharge of reactants cannot be avoided, because a pH value of 8 to 8.5 is maintained in the reactor.
The object of the present invention is accordingly to demonstrate an improved process for producing acetone cyanohydrin, in which a gas mixture containing hydrogen cyanide and inert gases is employed, in particular a crude gas arising from the BMA process or the Andrussow process. A process for the continuous production of acetone cyanohydrin has been found, comprising conversion of hydrogen cyanide with acetone in the presence of a basic catalyst and acetone cyanohydrin in a gas/liquid reactor to which acetone and a gas mixture containing hydrogen cyanide and inert gases are supplied continuously and from which a liquid phase containing acetone cyanohydrin and a gas phase containing the inert gases are carried away, and separation of volatile constituents from the liquid phase by distillation, said process being characterised in that the gas phase which is carried away out of the reactor is freed of unconverted hydrogen cyanide and acetone in a gas-washer which is subjected to the action of a solvent boiling at 100 to 200° C. (normal pressure) or of stabilised pure acetone cyanohydrin, and the washed phase which is obtained is supplied to the gas/liquid reactor. The dependent claims are directed towards preferred embodiments of the process according to the invention.
By way of wash liquid, use is made of the gas phase emerging from the gas/liquid reactor, which contains the inert gases of the gas mixture containing hydrogen cyanide that is employed as well as acetone and unconverted hydrocyanic acid, with an inert solvent, in particular a solvent forming azeotropes with water and having a boiling-point above 100° C. (normal pressure). This solvent preferably exhibits a boiling-point in the range from 150 to 200° C., but higher or lower boiling-points are also possible, assuming that the solvent can be separated without difficulty from acetone, on the one hand, and from acetone cyanohydrin, on the other hand. The term ‘inert’ is to be understood to mean that the solvent does not enter into a reaction with hydrogen cyanide, acetone or acetone cyanohydrin under the conditions of operation.
According to an alternative embodiment, stabilised pure acetone cyanohydrin is supplied to the gas-washer by way of wash liquid instead of the stated solvent. A feature essential to the invention is that the stabilised pure acetone cyanohydrin is an acidically stabilised product substantially free of acetone and hydrogen cyanide. In expedient
Börner Walter
Deusser Liane
Marquardt Ralph
Vanheertum Rudolf
Vieweg Karl-Heinz
Degussa - AG
McKane Joseph K.
Smith , Gambrell & Russell, LLP
Wright Sonya
LandOfFree
Method of producing acetone-cyanhydrin does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing acetone-cyanhydrin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing acetone-cyanhydrin will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2853132