CS268275B1 - Method for Oxonation of Propylene - Google Patents

Abstract

Method of oxonation of propylene to C aldehydes at a pressure of 20 to 30 MPa in the presence of synthesis gas containing carbon monoxide and hydrogen, catalyzed by cobalt carbonyls prepared in an oxonation device from an oil-soluble cobalt salt with subsequent separation of butyraldehydes and heavy fractions, where the oxonation takes place in two reaction stages arranged in succession, in which a 1.5 to 2.0 times larger amount of propylene is dosed into the first reaction stage than into the second reaction stage. A reduction in the specific consumption of propylene and other advantages is achieved

Description

The invention relates to a process for the oxonation of propylene to C ₄ aldehydes at a pressure of 20 to 30 MPa in the presence of synthesis gas containing carbon monoxide and hydrogen, catalyzed by cobalt carbonyls prepared in an oil-soluble cobalt salt oxonation plant.

Various modifications of propylene oxonation are operationally adopted and introduced. They differ from each other in the reaction conditions and in particular in the way in which the cobalt compounds contained are separated from the oxonation product and in the form in which the oxonation catalyst is returned to the oxonation.

A good method is to wash the oxonation product with a dilute acid, such as nitric acid. The thus decobalted product is subjected to distillation to obtain isobutyraldehyde, n-butyraldehyde, C 1-4 alcohols and the solvent used. 3 so-called heavy oxonation fractions are eliminated as the distillation residue. From these heavy fractions, the contained organic acid is isolated, for example 2-ethylhexanoic acid, which is used to prepare an oil-soluble cobalt salt. Heavy oxonations, which fall off after the isolation of organic acid, represent a complex mixture of organic substances and their formation cannot be completely prevented. In further production steps, part of the n-butyraldehyde is aldolized to 2-ethylhexenal and the aldehydes are hydrogenated separately and, after rectification, the products 2-ethylhexanol, n-butanol and isobutanol are finally obtained.

Although propylene oxonation processes in which rhodium carbonyls are used as complexes as an oxonation catalyst are often preferred in the construction of new oxonation units, the production of oxoalcohols from propylene catalyzed by cobalt carbonyls remains economically interesting and advantageous. This is especially true in the case where the previously built oxonation unit has been intensified without major investment costs and thus increased the production of alcohols. Efforts to increase the yield of aldehydes can be judged on the one hand by the complexity and operability of changes and on the other hand by the conversion of K and the selectivity of S:

The chosen technological and machine concept is difficult to change significantly. Also, increasing the quality of raw materials and reducing the concentration of catalytic poisons has a long-term character. These include limiting concentrations of up to 5 ppm for sulfur compounds, up to 10 ppm for iron and nickel carbonyls, up to 20 ppm for acetylenes and dienes, maintaining the required H ₂ : CO · 0.05 ratio for syngas and minimizing recirculated nitrogen bases in the catalyst. solution. The common disadvantage is the investment intensity. The responses to the change in reaction pressure, temperature and activity of the catalyst, most often given by the cobalt concentration, have a more operative character. The pressure depends on the readiness of the synthesis gas compressors and in order to achieve the highest yield it is desirable to keep it at the maximum allowed in terms of machine layout. The conversion of K can be increased by the reaction temperature and the activity of the catalyst, but at the cost of reducing the selectivity of S. The conversion reduces unreacted propylene P1, which is easily detectable in the off-gas and is, for example, around 1 to 2% by volume at K <98.5 mol. With a series arrangement of 2 oxoreactors, it is necessary to select a higher propylene feed to the 1st reactor to achieve the highest possible conversion, and the propylene feed ratio is then, for example, 2.0: 1.0. The disadvantage of this method is that the yield is not optimal when achieving the highest • conversion. Selectivity S It is reduced by secondary reactions, of which significant application is made: hydrogenation of propylene and aldehydes, formation of acetates, esterification, polymerization of propylene, aldolization and formation of formates. The average molecular weight of the heavy fractions thus formed is close to acetals and is, for example, 200 to 220 and their formation is promoted by elevated temperature, concentrations of cobalt, propylene and butyraldehydes. A characteristic feature of oxonation is that it is not stereospecific and a certain proportion of the undesired branched isomer is always formed. The usual n: iso ratio for cobalt catalysts is 3 to 4: 1, and similar relationships in the description of conversion and selectivity apply. The disadvantage of controlling the oxonation according to the selectivity, which is, for example, S <78 mol%, is the more difficult analytical monitoring and the large time lag between the change in oxonation and the amount of heavy fractions.

CS 26Θ275 Bl

It has now been found that the yield of aldehydes V can be increased and thus the specific consumption of propylene can be reduced. Hitherto, it has been customary to feed propylene into oxonation reactors such that about 2.2 times more propylene is fed to the first reactor than to the second reactor. Principle of the process for oxonation of propylene to C ₄ aldehydes at a pressure of 20 to 30 MPa in the presence of synthesis gas containing carbon monoxide and hydrogen, catalyzed by cobalt carbonyls prepared in an oxonation plant from an oil-soluble cobalt salt followed by separation of butyraldehydes from heavy fractions According to the invention, the propylene is metered in succession with the addition of synthesis gas and catalyst to the 1st reaction stage and the dosing of propylene to both reaction stages in an amount of 1.05 to 2.0 times greater than to the second reaction step. The feed propylene is fed to both reaction stages not only from the bottom, but at least to one further point in the oxonation reaction steps. It was experimentally verified that by reducing the ratio of propylene introduced into the 1st and 2nd reaction stages to 1.05: 1.0, it was possible to increase the yield of aldehydes by 8%, even with increased production. This reduces the formation of heavy fractions and the appropriate part of the reaction space can be used to form the desired butyraldehydes. The suitability of changing the propylene injection ratio increases with the intensification of oxoalcohol production. The reason is that this transfer faces an increased concentration of propylene and butyraldehydes in the 1st reactor, which would otherwise lead to an increase in the rate of heavy formation.

The details are as follows: Oxoalcohol production index % mass 100 210 210 of the total propyl injection is reported in 1. reactor % mass 69 69 52 to the 2nd reactor % mass 31 31 48 the ratio of propylene feed to the 1st and 2nd reactors 1 2.2 2.2 1.1 distribution of propylene to heavy fractions % moth. 9 16 10 to unreacted propylene % moth. 1.0 1.6 3.5 yield of aldehydes % moth. 87 78 83 index of spec. consumption of propylene % mass 100 111 105

. The modified distribution of propylene in both reactors will make it possible to slightly improve the ratio of C ₄ aldehydes produced, resp. alcohols. Previously, it was customary to achieve an n / i ratio of alcohols of 3.255, and according to the new arrangement, a value of 3.3 to 3.35 or 1 higher can be achieved. The specific consumption of propylene per tonne of alcohols produced can be further reduced if the propylene fed to the individual reactors is further divided. In this case, the propylene enters the reactors only from the bottom, but also at least in one further point of the oxonation reactor, preferably in the space between the installed coolers.

One of the important indicators characterizing the Oxonation Unit is the consumption of propylene, calculated for the production of one tonne of alcohol. Consumption of propylene is usually reported as the specific consumption needed to produce one tonne of all oxo alcohols produced.

The efficiency of the actual oxonation reaction, where butyraldehydes are formed from propylene, can be assessed similarly by the yield of aldehydes per unit of propylene entering. The following criteria, expressed in mole fractions or mol%, are further used to control the oxonation.

CS 268275 81 conversion of propylene K ---- p ----- 0. - 0 k in selectivity S «----------,

P - P, vk where P _v , P _{k is the} input and final propylene mass

Oy, 0 _k mass of aldehyde input and final

D, - D kv yield of aldehydes V »KS ---- = ------ The process according to the invention reduces the specific consumption of propylene per tonne of oxoalcohols produced, i.e. 2-ethylhexanol, n-butanol, iso-butanol, large operability of changes made in propylene feed to the 1st and 2nd reactors, which allows continuous optimization of conversion and selectivity to achieve the highest yield of aldehydes. Furthermore, an increase in the n: iso ratio of butyraldehydes produced can be achieved and relative energy savings can be achieved by reducing the formation of heavy fractions.

The production method according to the invention and the effect obtained are demonstrated in the following examples

Example 1

About two flow vertical reactors connected in series with injection! to the 1st reactor, a catalyst solution containing the cobalt salt of 2-ethylhexanoic acid and syngas with a ratio of H 2 CO-1.OS. Propylene was introduced into the bottom of both reactors and the yield of aldehydes was affected by changing the feed ratio. The isothermal course of the reaction was ensured by built-in coolers.

The characteristic data are given in Table 1.

Table 1

Reaction conditions the old way method according to the invention - work pressure MP a 27.5 27.5 - reaction temperature ° C 140 140 - total propyl injection. kmol h 97.9 97.9 - tool ratio propylene to the 1st and 2nd reactors 1 2.06 1.1 - molar ratio of cobalt: propylene 1 _ 2.11.1 ³ 2.11.10 ³ - production of butyraldehydes kmol h 75.3 81.3 - production of heavy shares M.215 ·· 15.8 9.89 - unreacted propylene ·· 1.47 . 3.13 - butyraldehyde ratio n: lso 1 3.20 3.36 - total propyl conversion. K% mol 98.5 96.8 - selectivity of propylene to aldehydes 3 %moth 78.1 65.7 - yield of aldehydes %moth 76.9 83.0 - spec, consumption of propyl, for oxoalcohols t / t 0.792 0.733

CS 26Θ275 Bl

Example 2

Analytical data of the oxonation product and off-gases carried out under the conditions of Example 1 are given in Table 2.

Table 2

component the old way method according to the invention liquid product% wt. Iso butyraldehyde 12.2 13.1 n-butyraldehyde 39.0 44.4 butanols 6.5 5.7 toluene 25, Θ 25.2 heavy shares 16.5 11.6 100.0 ioοο, ο

oxonation off-gas% vol.

Claims (2)

OBJECT OF THE INVENTION A process for the oxonation of propylene to aldehydes at a pressure of 20 to 30 MPa in the presence of synthesis gas containing carbon monoxide and hydrogen, catalyzed by cobalt carbonyls prepared in an oil-soluble cobalt salt oxonation plant, followed by separating butyraldehydes from heavy fractions. sequentially with the addition of synthesis gas and catalyst to the 1st reaction stage and the dosing of propylene to both reaction stages, characterized in that the propylene is metered into the 1st reaction stage in an amount of 1.05 to 2.0 times greater than to the second reaction stage . 2. The process according to claim 1, characterized in that the feed propylene is fed to both reaction stages not only from the bottom, but at least to one further point of the oxonation reaction stages.