DE3638168C2 - - Google Patents

Description

The invention relates to a process for the desalination of hydroxypivalaldehyde, that under the catalytic influence of bases from isobutyraldehyde and formaldehyde was obtained. For further processing to pure 2,2-dimethyl-1,3-propanediol, this aldehyde is generally first hydrogenated and the resulting hydrogenation fractionated. At The presence of salts affects both further processing stages negative. While in the first case an assignment of the contact and so that deactivation can be brought about by their presence a more or less strong one when working up by distillation Determine product decomposition.

The aldolization catalysts occur as such interfering compounds even as z. B. their formates, isobutyrates or hydroxypivalates on. The latter are u. a. as a result of Cannizzaro reactions or formed by the action of oxygen on the reaction mixture.

Because of the lability of the crude hydroxypivalaldehyde, the Literature primarily describes processes in which desalination the much more stable system of crude 2,2-dimethylpropane 1,3-diols limited. A major disadvantage of this approach is that the changes in activity caused by salt occupancy the hydrogenation contact can not be compensated for easily can.

The removal of the salts from the hydrogenation discharge using an ion exchanger is set out in DE-PS 9 67 552. After the procedure DE-OS 14 93 048 is an upstream treatment of the NPG raw product proposed by means of a thin film evaporator. In the Description of US-PS 28 95 996 and according to the modified method DE-AS 10 76 655 is the hydrogenation discharge by means of steam distillation  separated from the saline residue and the aqueous Distillate separated in a subsequent work-up step. The Azeotropic distillation of the crude product and subsequent distillations are described in US-PS 28 65 819. According to JP 69/10 767 the hydrogenation discharge first in an extraction stage with z. B. ethers pretreated.

DE-AS 17 93 512 is used for the production of the hydroxypivalaldehyde required catalyst by distillation from the reaction mixture away.

DE-OS 25 47 540 describes a two-stage process for the production hydroxypivalaldehyde; first an aqueous hydroxypi valinaldehyde solution by distilling off the remaining reaction components receive; then the product is crystallized and the Crystals have to be washed with H₂O and dried.

The disadvantages of these methods are the fact that, because of the Lability of the hydroxypivalaldehyde only after its hydrogenation to Neopentyl glycol can be used sensibly and largely system-free Auxiliaries when using energy-intensive multi-stage Equipment systems need. There was therefore an interest in a process in which the reduction in the salt content in the hydroxypivalaldehyde, as in the alkaline catalyzed aldolization of Isobutyraldehyde and formaldehyde are obtained without the addition of extraneous systems Auxiliary substances is made possible.

According to the invention, the resulting task is accordingly Disclosed claims.

Surprisingly, the reduction in the salt content of crude hydroxypivalaldehyde is with a dissolved water content of approx. 5 to 10%, as in the alkaline catalyzed aldolization of isobutyraldehyde and formaldehyde is obtained by treatment with 2 to 8 percent by weight Water possible. The use of larger amounts of water is possible, but also includes undesirably high product losses.  

The water is expediently added after the water has been separated off the aldolization-derived water phase, the dosage in one Step can take place. However, the subdivision is advantageous the total amount of water in several servings. You can reach this A significantly higher degree of desalination with the same amount of water, if after each intensive mixing a separation of the respective Water phase is made.

The water phase is separated according to the prior art, e.g. B. either in appropriate separators or by using Separators.

Due to the density differences required in these separation processes between the organic and the aqueous phase, is by suitable Reaction control to ensure that the density of the organic Phase, for example at 50 ° C, the value of 1.1 g / ml is not exceeds. This can be done in a simple manner, for example Limiting the conversion of isobutyraldehyde or adding a higher excess of isobutyraldehyde during aldolization or by mixing the reaction discharge with slightly water-soluble organic substances such as Isobutyraldehyde and / or isobutanol take place.

When mixing the aldolisate separated from the water of reaction temperatures of 20 to 70 ° C are generally maintained. In addition to reducing the solubility of those present in the aldolisate Salts are unnecessary for setting temperatures lower than 20 ° C Applying energy in the form of cooling. When setting higher Temperature than 70 ° C is associated with increased losses of e.g. B. isobutyraldehyde to be expected if no expensive printing devices are used.

Experimental examples

Raw hydroxypivalaldehyde with a density of 0.96 g / ml and a Salinity of 540 ppm (calculated as NaOOCH) was measured at room temperature the amounts of water shown in the following table  mixed up. In the separating organic phase, the listed salinity calculated as sodium formate.

Water content Salinity

2% 230 ppm 4% 130 ppm 8% 95 ppm

By repeated washing with smaller amounts of water and separation the water phase were based on the same product as above achieved the following values:

Water content Salinity

2 x 2% 40 ppm 3 × 1% 9 ppm

Claims (1)

A process for reducing the salt content of crude hydroxypivalinaldehyde, such as occurs in the alkaline catalytic aldolization of isobutyraldehyde and formaldehyde, characterized in that by limiting the isobutyraldehyde conversion or adding a greater excess of isobutyraldehyde in the aldolization or by adding isobutyraldehyde and / or isobutyraldehyde to the organic phase, a density of at most 1.1 g / mol at 50 ° C., the water phase formed is separated off after aldolization, 2 to 8 percent by weight of water is added to the crude hydroxypivalaldehyde, mixed at 20 to 70 ° C. and then the water phase is separated off again .