CS230823B1 - Method for oxonation of propylene - Google Patents

Abstract

The invention relates to a process for the oxonation of propylene (C) to C. aldehydes at a pressure of 20 to 35 MPa in the presence of a synthesis gas containing carbon monoxide ® hydrogen, which takes place under the catalytic action of cobalt carbonyls prepared in a production facility from oil-soluble cobalt salts and subsequent separation of the oxonation products from heavy fractions, in which these heavy fractions of the oxonation are washed with dilute inorganic acid, preferably 5 to 50% nitric acid, at 20 to 90 °C.

Description

The invention relates to a method for the oxonation of propylene to aldehydes at a pressure of 20 to 35 MPa in the presence of synthesis gas containing carbon monoxide and hydrogen, catalyzed by cobalt carbonyls prepared in an oxonation device from oil-soluble cobalt salts. Various modifications of the oxonation of propylene catalyzed by a cobalt compound are operationally introduced and adopted.

They differ from each other mainly in the way in which the cobalt compounds contained are separated from the oxonation product and in what form the cobalt oxonation catalyst is returned to the oxonation.

During the oxonation of propylene, in which the oxonation catalyst is dosed in the form of an oil-soluble cobalt salt, the obtained oxonation product is freed from the cobalt compounds contained, e.g. by washing with dilute inorganic acids, such as nitric or sulfuric acid. The oxonation product thus decobaltized is subjected to distillation, in which i-butyraldehyde and n-butyraldehyde, alcohols and the solvent used are obtained, the melt heavy portions of the oxonation are removed as a distillation residue. From these heavy portions of the oxonation, the contained organic acid is isolated, e.g. 2-ethylhexanoic acid, which is used to prepare the oil-soluble cobalt salt. The heavy portions of the oxonation, which are removed after the isolation of the contained 2-ethylhexanoic acid, represent a complex mixture of organic substances and their formation cannot be prevented.

They concentrate the higher-boiling fractions formed during oxonation and distillation of the oxonation product, as well as unwashed cobalt compounds. The aldox process is known, according to which aldehydes with twice the number of C atoms are produced by carbonylation and dimerization, in which the residual fractions are washed with an acid solution. However, this is not oxonation itself, and the resulting complex mixture of organic substances differs significantly from the reaction mixture after oxonation.

The method of oxonation of propylene to aldehydes at a pressure of 20 to 35 MPa in the presence of synthesis gas containing carbon monoxide and hydrogen, catalyzed by cobalt carbonyls prepared in a production plant from oil-soluble cobalt salts with subsequent separation of the products of oxosynthesis from the heavy portions of oxonation and isolation of the organic acid contained from these portions consists, according to the invention, in that the heavy portions of oxonation are washed with a dilute inorganic acid, preferably 5 to 50% nitric acid at 20 to 90 ° C. Sulfuric acid can also be used.

The newly incorporated washing of heavy fractions with dilute inorganic acid will allow the recovery of contained cobalt compounds and thus reduce the specific consumption of cobalt required for the production of aldehydes and alcohols from propylene. Furthermore, the recovery of contained 2-ethylhexanoic acid will be facilitated when it is isolated using dilute sodium hydroxide solution and higher yields will be achieved than was the case before the incorporation of washing of heavy fractions of oxonation with dilute inorganic acid.

It has been found that when an inorganic acid is applied to the heavy fractions of the oxonation, the composition of the incoming heavy fractions is partly changed and that the heavy fractions thus treated contain a higher proportion of n-butanol, i-butanol, n-butyraldehyde and i-butyraldehyde. It is advantageous to separate these newly formed alcohol and aldehyde fractions from the treated heavy fractions by distillation or extraction; this reduces the amount of heavy fractions that are discarded, which is economically advantageous. The beneficial effect of the newly incorporated washing of the heavy fractions of the oxonation with dilute inorganic acid is evident from the following examples.

Example 1

0.55 heavy portions of oxonation with a density of 0.875 at 20°C were stirred for 45 minutes with 0.25 m^ of 8% nitric acid while stirring at 50°C.

After separation of dilute nitric acid, the washed heavy portions of the oxonation were used to isolate the contained 2-ethylhexanoic acid using 10% sodium hydroxide solution. The content of cobalt transferred from the heavy portions of the oxonation was determined in the separated 8% nitric acid and, after repeated use, the resulting cobalt nitrate solution was used to prepare the oil-soluble cobalt salt of 2-ethylhexanoic acid. The analytical data obtained were as follows: for comparison, the analytical data obtained during the processing of the heavy portions of the oxonation without the inclusion of washing with dilute nitric acid are also given.

Heavy oxonaee without washing 8% Rys. nitrogen Heavy portions of oxonaee after washing with 8% nitric acid Cobalt content mg/1 273 less than 2 2-ethylhexanoic acid content g/1 45 55 content of 2-ethylhexanoic acid after washing with 10% caustic soda g/1 20 7

Example 2

The heavy fractions of oxonaea washed with 8% nitric acid under the conditions of Example No. 1 were subjected to chromatographic analysis, and the input heavy fractions were similarly analyzed. The following contents of alcohols and aldehydes were found:

Heavy oxonae fractions before washing with 8% nitric acid Heavy oxonae fractions after washing with 8% nitric acid N-butanol % wt. 0.5 6.2 i-butanol % wt. 0.2 9.7 n-butyraldehyde ² .3 8.3 i-butyraldehyde 0.8 3.0

The dilute nitric acid solution intended for washing heavy oxonae fractions can be used once or recirculated. For operational practice, it is more advantageous to work with dilute nitric acid in recirculation and discharge only a smaller part for further processing and replace this part with a fresh solution of dilute nitric acid. As it turned out, about 5 kg of nitric acid, calculated as 100%, is sufficient for 1 heavy oxonae fraction.

The discharged part of nitric acid is enriched not only with cobalt, but also with alcohols and aldehydes dissolved in it. In order to obtain these dissolved alcohols and aldehydes, it is advantageous to strip the discharged part of nitric acid and thus distill off the dissolved components. Similarly, this discharged part of nitric acid can be stripped only after the precipitation of the contained cobalt as cobalt carbonate, but there are other options.

Heavy oxonae fractions with an enriched content of alcohols and aldehydes are suitable raw materials for alcohols and aldehydes. In addition to distillation, it may be advantageous to extract the alcohols and aldehydes contained with water and subject the obtained aqueous solution to stripping.

Claims (2)

THE INVENTION OF THE INVENTION 1. A process for the oxonation of propylene to aldehydes at a pressure of 20 to 35 MPa in the presence of a synthesis gas containing carbon monoxide and hydrogen catalysed by cobalt carbonyls prepared in an oil-soluble cobalt salt production plant and subsequently separating the oxonation products from the heavy fractions. The oxonecs are washed with dilute inorganic acid at 20 to 90 ° C. 2. The process of claim 1 wherein the heavy fractions of oxonation are washed with 5-50% nitric acid.