Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1997-10-20
1999-07-27
Dentz, Bernard
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C07D32306
Patent
active
059292571
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a practical and economical process for producing trioxane useful as the raw material of polyoxymethylene from an aqueous formaldehyde solution.
BACKGROUND OF THE INVENTION
Trioxane which is a cyclic trimer of formaldehyde is generally prepared by heating an aqueous formaldehyde solution in the presence of an acid catalyst. With respect to this preparation, it is known that the equilibrium concentration of trioxane in the liquid phase is as low as about 2 to 4% by weight to give a large amount of unreacted formaldehyde even when the concentration of the starting aqueous formaldehyde solution is 30 to 70% by weight. Accordingly, it is necessary for the recovery of pure trioxane that the reaction mixture containing trioxane must be first freed from the acid catalyst, followed by the separation of trioxane of pure state from formaldehyde, water and so on.
As a specific process for producing trioxane, JP-B-41-6344 discloses a process which comprises reacting a 30 to 70% (by weight) aqueous formaldehyde solution under heating in the presence of a liquid acid catalyst such as sulfuric acid, distilling the resulting reaction mixture to separate a distillate comprising trioxane, formaldehyde and water from the liquid acid catalyst, and recovering pure trioxane from the distillate by solvent extraction or the like.
However, such a process using a liquid catalyst such as sulfuric acid as the catalyst for the synthesis of trioxane has a problem that the separation of the trioxane-containing component from the catalyst involves an operation necessitating much energy, for example, distillation.
On the contrary, processes using various solid acids, for example, organic solid acids such as a strongly acidic cation-exchange resin or inorganic solid acids such as zeolite have been proposed as processes permitting easy removal of the catalyst from the trioxane-containing reaction mixture to thereby cut down the energy necessary therefor. Further, there have also been proposed economical processes of directly recovering pure trioxane by solvent extraction from the solution obtained by separating the solid acid catalyst from the reaction mixture containing trioxane (JP-A-4-49250 and JP-A-6-73046).
These processes have an advantage in that substantially no energy is necessary for the removal of the catalyst from the reaction mixture.
In the follow-up made by the inventors of the present invention, however, long-term stable operation was substantially impossible when the above process for producing trioxane with a solid acid catalyst was merely applied to a conventional actual plant.
As described above, the equilibrium concentration of trioxane in preparing trioxane from an aqueous formaldehyde solution in the presence of an acid catalyst is low, so that a large amount of unreacted formaldehyde remains in the resulting aqueous solution. In order to produce a desired amount of trioxane, therefore, a large amount of an aqueous formaldehyde solution must be brought into contact with a solid acid catalyst and a large amount of an aqueous solution of unreacted formaldehyde must be recovered and re-used as the starting aqueous formaldehyde solution for the synthesis of trioxane. However, the above processes have a problem that the activity of a solid acid catalyst rapidly lowers in a short period of time and the rate of formation of trioxane lowers with this lowering in the activity, which makes it difficult to produce a desired amount of trioxane constantly. Further, the processes have another problem that increase in pressure loss or channelling occurs in the reactor containing a solid acid catalyst in a short period of time, which makes it difficult to attain the feeding of an aqueous formaldehyde solution at a constant flow rate or the production of trioxane in a constant amount.
SUMMARY OF THE INVENTION
The present invention is embodied a process for producing trioxane from an aqueous formaldehyde solution, characterized by using a production apparatus comprising two
REFERENCES:
Liu et al, Study of Ion-Exchange,etc., Lizi Jiaohuan Yu Xifu, 4(4), pp. 298-304, 1988.
Kirk-Othmer, Encyclopedia of Chemical Technology (4th. Ed.), vol. 14, pp. 737-739,744-745, 760, 761, 764, 766-769, 773, 774 and 778, 1995.
Akiyama Minoru
Kashihara Osamu
Dentz Bernard
Polyplastics Co. Ltd.
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