Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-04-20
2002-07-30
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S861000
Reexamination Certificate
active
06426438
ABSTRACT:
The invention relates to a process for the improved preparation of 1,6-hexanediol and 6-hydroxycaproic acid and esters thereof starting from adipic acid or mono- and diesters thereof or hydrocarbon streams which comprise adipic acid or mono- and diesters thereof and 6-hydroxycaproic acid or esters thereof, by catalytic hydrogenation of the acids and/or of the esters and recycling of the dimeric and oligomeric compounds which are formed as the bottom product following distillation of the hydrogenation product.
U.S. Pat. No. 2,066,533 discloses the catalytic partial hydrogenation of dicarboxylic acids and esters thereof to the corresponding hydroxycarboxylic acids or lactones thereof, without producing significant amounts of diols.
EP 724 908 A1 discloses the hydrogenation, on (modified) Raney noble metal catalysts, of adipic acid or esters thereof to 1,6-hexanediol and 6-hydroxycaproic acid or esters thereof.
JP 49 132 003 discloses the hydrogenation of adipic acid on Mo/Co/SiO
2
catalysts to give 1,6-hexanediol and 6-hydroxycaproic acid.
The abovementioned processes have the disadvantage that the product mixtures which are produced during the hydrogenation, ie. alcohols and carboxylic acids, contain dimeric and oligomeric esters.
Esters of adipic acid with hexanediol and hydroxycarboxylic acid and esters of hydroxycaproic acid and hexanediol may be mentioned by way of example (these esters are referred to below as dimers). These esters are unavailable for further use to produce 6-hydroxycaproic acid (6-hydroxycaproate) and 1,6-hexanediol, and have, following removal of the desired products by distillation, to be removed in a further process step, such as eg. hydrolysis with water, which is an equilibrium reaction and does not produce complete conversion. The abovementioned processes are thus only economical to a limited extent.
It is an object of the invention to overcome this prior art disadvantage.
Surprisingly, we have found that it is possible to significantly increase the overall yield of 6-hydroxycaproic acid or esters thereof and 1,6-hexanediol using a process for the preparation of 1,6-hexanediol and 6-hydroxycaproic acid or esters thereof by catalytic hydrogenation of adipic acid, adipic acid monoesters or adipic acid diesters or streams of starting materials which contain adipic acid or esters thereof as essential constituents, if the bottom product which is obtained in the distillation of the hydrogenation product, following removal of the hexanediol and hydroxycaproic acid or esters thereof, and essentially comprises oligomeric esters of 6-hydroxycaproic acid, is recycled to the hydrogenation and the resulting mixture of starting material and recycle stream is reacted at from 100 to 300° C. and at from 10 to 300 bar in the liquid phase and at a molar ratio of carboxyl groups to be hydrogenated to hydrogen in the reactor of from 1:5 to 1:100 on hydrogenation catalysts.
It was surprising that the recycled C
6
-dimers and C
6
-oligomers can be reacted under the reaction conditions of the hydrogenation of the monomeric acids and esters thereof, without a direct increase in the level of dimers, oligomers and byproducts, to give 1,6-hexanediol and 6-hydroxycaproic acid and esters thereof, and that the selectivity of the reaction is not impaired. It was also surprising that the useful life of the catalyst is not impaired by the recycling, since it would have been assumed that some dimeric and oligomeric compounds deposit on the catalyst, impairing its activity and selectivity as a result.
The alcohol component of the esters of adipic acid and 6-hydroxycaproic acid is preferably methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol and n-pentanol. A particular ester of hydroxycaproic acid is the internal ester caprolactone. The starting material used for the hydrogenation is adipic acid or mono- and/or diesters thereof. This starting material may also contain further C
6
compounds, eg. 6-hydroxycaproic acid or esters thereof. It is also possible for further non-C
6
compounds which do not impair the novel process, eg. acids such as glutaric acid or succinic acid or esters thereof, to be present. Such mixtures are described, for example, in DE-A 19 607 953. The novel process may use, for example, the stream from stage 4 or the top product stream from stage 12 from Example 1.c. of the above patent.
The hydrogenation is preferably carried out in the liquid phase. The hydrogenation catalysts generally used in the novel process are heterogeneous catalysts, but it is also possible to use homogeneous catalysts which are suitable for hydrogenating carbonyl groups. They can either be arranged as fixed bed catalysts or be employed in mobile form, for example in a fluidized bed reactor. Examples of hydrogenation catalysts for this purpose are described, for example, in Houben-Weyl, Methoden der Organischen Chemie, Volume IV/1c, pages 16 to 26.
Of the hydrogenation catalysts to be used according to the invention, preference is given to those containing one or more elements from groups Ib, VIb, VIIb and VIIIb, and IIIa, IVa and Va, of the Periodic Table of the Elements, in particular copper, chromium, rhenium, cobalt, rhodium, nickel, palladium, iron, platinum, indium, tin and/or antimony. Particular preference is given to catalysts containing copper, cobalt and/or rhenium.
The catalysts employed in the novel process may be, for example, precipitated catalysts. Catalysts of this type can be prepared by precipitating their catalytically active components from solutions of salts thereof, in particular from solutions of their nitrates and/or acetates, for example by adding solutions of alkali metal hydroxide and/or alkaline earth metal hydroxide and/or alkali metal carbonate and/or alkaline earth metal carbonate, eg. sparingly soluble hydroxides, oxide hydrates, basic salts or carbonates, then drying the resulting precipitates and subsequently converting them by calcination at, in general, from 300 to 700° C., in particular from 400 to 600° C., into the corresponding oxides, mixed oxides and/or mixed valency oxides, which are reduced, and converted into the actual catalytically active form, by treatment with hydrogen or hydrogen-containing gases, generally at from 50 to 700° C., in particular from 100 to 400° C., to give the relevant metals and/or oxides of lower oxidation state. This reduction is generally continued until water is no longer formed. To prepare precipitated catalysts containing a carrier material, the catalytically active components can be precipitated in the presence of the relevant carrier material. However, it is also possible advantageously for the catalytically active components to be precipitated simultaneously with the carrier material from the relevant salt solutions. The hydrogenation catalysts preferably employed in the novel process are those containing the hydrogenation-catalyzing metals or metal compounds deposited on a carrier material. Apart from the abovementioned precipitated catalysts, which also comprise a carrier material in addition to the catalytically active components, suitable carrier materials for the novel process are, in general, those in which the components catalyzing the hydrogenation have been applied to a carrier material, for example by impregnation.
The way in which the catalytically active metals are applied to the carrier is generally not critical and can be brought about in various ways. The catalytically active metals can be applied to these carrier materials for example by impregnation with solutions or suspensions of the salts or oxides of the relevant elements, drying and subsequent reduction of the metal compounds to the corresponding metals or compounds of a lower oxidation state by means of a reducing agent, preferably using hydrogen or complex hydrides. Another potential way of applying the catalytically active metals to these carriers consists in impregnating the carriers with solutions of salts which readily undergo thermal decomposition, eg. with nitrates, or complex compounds which readily undergo thermal decom
Fischer Rolf Hartmuth
Pinkos Rolf
Stein Frank
Barts Samuel
BASF - Aktiengesellschaft
Keil & Weinkauf
Price Elvis O.
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