Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-08-22
2002-09-10
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S868000
Reexamination Certificate
active
06448455
ABSTRACT:
BACKGROUND
The present invention relates to a process for preparing trimethylolpropane with simultaneous formation of a formate salt and to the separation of the formate salt from the reaction mixture, if appropriate, after prior concentration of this reaction mixture by evaporation.
Both trimethylolalkanes, and formate salts are products of industrial interest. Thus, trimethylolpropane is used in the production of surface coating resins, powder coatings, foams and a variety of polyesters. Formate salts can be utilized, for example, for producing formic acid. Calcium formate is particularly versatile and is used commercially in, for example, the following fields: additive in the field of animal nutrition (pig, cattle and turkey feed), use in the building materials industry (improving the curing of cement, gypsum plaster and jointing compositions and also as frost protection agent for mortar), auxiliary in the leather industry, auxiliary in the production of high-gloss papers, treatment of scrubbing water in flue gas de-sulphurization, auxiliary in silage production.
The industrial preparation of trimethylolpropane (TMP) is at present carried out by means of the inorganic Cannizzaro process, a process which simultaneously forms a formate salt. This process makes use of n-butyraldehyde and formaldehyde as starting materials. According to the generally accepted view, 2,2-dimethylolbutanal is initially formed in a base-catalysed aldol reaction via the intermediate 2-methylolbutanal. In the presence of stoichiometric amounts of a base, preferably sodium hydroxide or calcium hydroxide, across-Cannizzaro reaction occurs in the final step to form trimethylolpropane with simultaneous liberation of the corresponding formate salts. For example, calcium formate is formed when calcium hydroxide is used as base.
The formate salts formed have to be removed as completely as possible from the reaction mixture before the work-up by distillation to isolate the trimethylolpropane, since formate salts catalyse the of trimethylolpropane under distillation conditions. Furthermore, the formate salt has to be freed of organic residues and dried so as to be able to be used in a further application. Numerous methods of separating off the formate salt are known.
Thus, according to Ullmann's Encyclopaedia of Industrial Chemistry, 5th Edition 1985, p. 315, trimethylolpropane can be extracted by means of a suitable organic solvent from the reaction solution after the latter has been concentrated. The solvent is subsequently removed under reduced pressure and the crude trimethylolpropane obtained is purified by distillation. Alternatively, the aqueous reaction solution can be evaporated until the formate crystallizes. The mixture is subsequently filtered hot to remove the crystallized material.
DE-B 1 052 383 describes a process in which the trimethylolpropane is separated off by driving off the trimethylolpropane by means of superheated steam in a thin film evaporator. The process is advantageously carried out under reduced pressure and steam temperatures of from 120° C. to 220° C.
DE-A 32 07 746 describes a process for preparing trimethylolpropane using formaldehyde having a particularly low methanol content. To work up the reaction mixture, acid is added to it so as to give a pH of from 5 to 7. Excess formaldehyde is subsequently separated off by distillation. The trimethylolpropane is isolated by distillation or extraction.
The processes mentioned display technological difficulties in respect of the fractionation of reaction mixtures obtained in the preparation of trimethylolpropane by the Cannizzaro process. No optimal solution has yet been found for separating off the formates formed. This can also be seen from the fact that great efforts have been made in recent times to develop or to improve processes for the preparation of trimethylolpropane which proceed without formation of alkali metal formates or alkaline earth metal formates in the product mixture.
According to DE-A 1 952 738, the reaction of n-butyraldehyde and formaldehyde can be carried out in the presence of a lower tertiary amine. An approximately 6-fold excess of formaldyhyde and an approximately 1.5-fold excess of trialkylamine are used. Apart from the desired product trimethylolpropane, the process produces stoichiometric amounts of trialkylammonium formate which can easily be removed from the reaction mixture by distillation. However, unlike alkali metal formates or alkaline earth metal formates, this cannot be used further, so that it is proposed that the trialkylammonium formate be converted into calcium formate in a separate reaction step and the amine liberated in this step be returned to the circuit. This procedure makes the process economically unattractive.
According to DE-A 196 53 093, 2,2-dimethylolbutanal is firstly prepared by condensation of n-butyraldehyde and formaldehyde in the presence of catalytic amounts of a tertiary amine in three steps, with unreacted starting material and by-products formed being recycled and reacted further. The condensation product (2,2-dimethylolbutanal) obtained in this way is subsequently hydrogenated to give trimethylpropane. A usable formate is not obtained in this process.
EP-A 860 419, too, proposes carrying out the preparation of 2,2-dimethylolbutanal from n-butyraldehyde and formaldehyde in a plurality of stages, with the actual reaction occurring in the first stage and the 2-ethylacrolein obtained as by-product being reacted with further formaldehyde in the second stage. The 2,2-dimethylolbutanal prepared in this way can then be hydrogenated to give trimethylolpropane. Once again, no formate is isolated.
The known processes for preparing trimethylolpropane without formation of a formate salt have hitherto been inferior to the inorganic Cannizzaro process. This is firstly because formate salts are interesting and marketable products and secondly because a hydrogenation reaction can only be carried out in expensive equipment designed for this purpose.
It is an object of the present invention to provide a process for the simultaneous preparation of trimethylolpropane and a formate salt and for the effective isolation of both products, which process allows a high space-time yield and gives both products in very pure form. This object is achieved by means of the process of the invention.
SUMMARY
The invention relates to a process for preparing trimethylolpropane with simultaneous formation of formate salts of the formula (I):
M(OOCH)
n
(I),
wherein M is a metal component selected from the group consisting of alkali metals (e.g., lithium, sodium, potassium, rubidium, caesium) and alkaline earth metals (e.g., beryllium, calcium, strontium, barium), and mixtures thereof, wherein n is 1 when M is an alkali metal and n is 2 when M is an alkaline earth metal. The process comprises reacting n-butyraldehyde and formaldehyde by an inorganic Cannizzaro process, forming a reaction mixture, and subjecting the reaction mixture formed to vapor pressure filtration. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DESCRIPTION
The invention provides a process for preparing trimethylolpropane with simultaneous formation of formate salts of the formula
M(OOCH)
n
(I),
where M represents the alkali metals lithium, sodium, potassium, rubidium, caesium and/or the alkaline earth metals beryllium, calcium, strontium, barium and n is 1 when M is an alkali metal and is 2 when M is an alkaline earth metal, characterized in that n-butyraldehyde, formaldehyde and a base are reacted by the inorganic Cannizzaro process and the reaction mixture formed is subjected to vapor pressure filtration.
Distillable constituents may optionally be partly removed in part from the reaction mixture prior to the vapor pressure filtration.
Further purification and drying steps can optionally be carried out after the vapour pressure filtration.
The process of the invention gives good space-ti
Klausener Alexander
Wagner Paul
Barts Samuel
Eyl Diderico van
Henderson Richard E. L.
Price Elvis O.
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