DE1518847A1 - Process for the production of isobutyric acid from isobutyraldehyde - Google Patents

Description

Process for the production of isobutyric acid from isobutyraldehyde Es it is already known that isobutyric acid can be obtained by oxidation of isobutyraldehyde can technically win with elemental oxygen. The procedure is multiple carried out without the addition of catalysts; but embodiments are also known where worked in the presence of nanganese, cobalt or iron catalysts will.

It is preferable to work in the presence of excess liquid isobutyric acid, which optionally contains dissolved catalysts and into which the starting materials are introduced will. It is also known that isobutyraldehyde and isobutyric acid as a result the branching of the carbon skeleton on the one adjacent to the functional group Carbon atom through elemental oxygen partially to cc -oxyisobutyraldehyde or CC -oxyisobutyric acid are oxidized. In addition, isobutyraldehyde is formed isopropyl formate in a manner known per se. The three by-products react under the conditions of isobutyric acid production partly continue and lead to further By-products, for example isopropyl isobutyrate, isopropanol, Acetone, formic acid, formaldehyde, water, carbon oxide, carbon dioxide, propane, propylene and others.

The formation of by-products affects the economic efficiency of the process, because they reduce the yield of isobutyric acid, based on the isobutyraldehyde used, limited to 80 to 90%, in unfavorable cases up to 50%.

In contrast, the yields in the production of unbranched Fatty acids from the corresponding aldehydes, for example acetic acid from acetaldehyde, over 90%, in favorable cases up to 97 9S.

It has now been found that isobutyric acid by oxidation of Isobutyraldehyde can advantageously be produced with elemental oxygen if one in the presence of inhibitors containing compounds of zinc and / or cadmium, oxidized.

Suitable compounds of zinc and cadmium are, in particular, salts ; among these are the salts of fatty acids with 1 to 5 carbon atoms, for example the acetates and, above all, the isobutyrates, are preferred. But salts can also be more inorganic Acids, for example the chlorides, sulfates or phosphates, are used. Also basic salts, both those of fatty acids and of inorganic acids, as well as the oxides, hydroxides and hydrated oxides can be used.

The inhibitors can be used in dissolved or solid form. Solid inhibitors can be used as suspensions or as fixed-bed contacts will ; in both cases they can contain support materials, for example Aluminum oxide, aluminum silicate, carbon, silica gel and others. The Content of the inhibitor Zinc and / or cadnium in chemical form Compounds expediently 0.1 to 20 percent by weight. But you can also in the absence work from porters.

Isobutyraldehyde can be used in liquid, dissolved or gaseous form Apply the state of oxidation and the inhibitor. When using fixed One works with inhibitors in the gas phase or in trickles; in last In the case of oxygen and volatile or dissolved iscbutyraldehyde can be in the same or Be stirred countercurrent. When using dissolved or suspended inhibitors it is advisable to work in liquid-filled reaction spaces or in trickle towers.

The preferred solvent for the inhibitors is isobutyric acid; Farther. other fatty acids, such as acetic acid or butyric acid, and water are suitable.

In the case of inhibitor suspensions, it is preferred to use the suspending agent also isobutyric acid, but also isobutyraldehyde itself. You can also use the Suspend inhibitors in reaction-inert liquids, for example in benzine, paraffins with 6 to 18 carbon atoms, benzene, cyclhexane and others.

In many cases the inhibitors initially lie as suspensions, in the later course of the reaction, however, as solutions, for example; if a suspension of the inhibitor in isobutyraldehyde is used; with increasing concentration the inhibitor is then dissolved in isobutyric acid e. This is for example when using of cadmium isobutyrate as an inhibitor.

Solutions and suspensions of the inhibitors expediently contain between 1 and 1000 mmol of zinc and / or cadmium in the form of compounds per liter of solution or Suspension.

Suitable solvents for the isobutyraldehyde to be oxidized are including hydrocarbons such as hexane, gasoline mixtures, benzene, ketones such as Acetone, also water and especially isobutyric acid.

In many cases it is useful in the presence of excess liquid Isobutyric acid to work, both when using dissolved and when Use of suspended or firmly arranged solid inhibitors.

Gaseous feedstocks can be in the form of dilute mixtures. with Oxygen, noble gases, carbon dioxide, methane, ethane, propane, butanes. and others be used. In particular, the oxygen required can be used in the form of air will. Isobutyraldehyde content of other aldehydes, especially n-butyraldehyde. Do not disturb an oxidation; but they will. of course, at least in part, also oxidized to the corresponding acids.

It is expedient to work at temperatures between 0 and 100 ° C., preferably between 0 and 70 ° C, and at pressures, between 0.1 and 20 atm, preferably between 1 and 10 atm.

If you work with dissolved or suspended inhibitors, you can constantly due to the discharge of the liquid reaction products from the reaction chamber one because of the inhibitor lost. This deil becomes after the reaction products have been distilled off. expediently returned to the reactor.

If one works with inhibitor suspensions, one can reduce the inhibitor losses also counteract, for example, from the product mixture in a calming zone lets the suspended inhibitor settle, discharges it and goes to the reaction chamber returns.

In detail one proceeds expediently so that one in the foot of one Reactor, which with the solution or suspension of the inhibitor, expediently in isobutyric acid, is filled and possibly still contains "gaseous" oxygen and introduces liquid, dissolved or gaseous isobutyraldehyde. km head of the reactor you leave the unconverted oxygen and optionally inert gases and gaseous By-products escape which may not have been converted for recovery Isobutyraldehyde are fed to a condensation stage or washing.

In addition, one takes from the top of the * reactor while keeping the Liquid level in the reactor, the solution or suspension of the inhibitor that the contains isobutyric acid formed. The mixture is expediently a distillation column supplied, in the initially unreacted isobutyraldehyde and low-boiling By-products are distilled off. The bottom discharge is passed to a second column to, at the top of which pure isobutyric acid is obtained and its Sunpflauf if necessary contains the inhibitor. If necessary, the bottom drainage is wholly or partially carried out back to the reactor. If used as a solvent or suspending agent for the inhibitor not isobutyric acid but liquids with boiling points below the boiling point which uses isobutyric acid, another distillation may have to be added to the distillation Column are switched on.

In another embodiment, a trickle tower is expediently used, the one with ? ull bodies or the permanently arranged inhibitor is filled. About the Isobutyric acid, optionally with dissolved inhibitor, and / or is left in the filling Isobutyraldehyde, possibly in combination with solvents, trickle down. At the same time, oxygen and, if appropriate, are passed in cocurrent or countercurrent Isobutyraldehyde. The liquid reaction products are withdrawn from the bottom of the reactor and the gaseous products, depending on the circuit, at the foot or head of the Reactor and works it, as indicated above, on. The use of inhibitors, which contain zinc and / or cadmium compounds "yields" compared to the state technology has the advantage of increased yield with practically changed space-time performance.

Example 1 A cooler equipped with a gas inlet pipe and a brine return flow cooler 500 ml round bottom flask is filled with 250 ml isobutyraldehyde and filled with 15 N1 every hour Oxygen is gassed, the contents of the flask being brought to a working temperature by external cooling of 450C. The exhaust gas escaping through the reflux condenser is on his Investigated carbon dioxide content. After 5 hours, the in the stirred flask contained isobutyric acid determined by titration.

In two of a total of three individual experiments, the stirred flask was used Beginning of the experiment 2 g of cadmium acetate dihydrate (experiment Na) or 2 g of zinc acetate dihydrate (Experiment 17 added; no additive was used in comparative experiment 1c.

The result is shown in Table 1. You can see that the., Additions are practically without influence on the amount of isobutyric acid formed and that the the amount of carbon dioxide produced when using the inhibitors is much smaller is than in comparison attempt 1c.

Example 2 The apparatus used for this experiment (see drawing) is a circulating device that works on the principle of the mammoth pump. she consists from a jacketed riser pipe (1) 2400 mm long and 50 mm in diameter, one jacketed downpipe (2) of the same length of 25 mm diameter and a reactor head (3) in the form of a horizontally arranged cylinder 500 mm long and 80 mm in diameter.

Downpipe (2) and riser pipe (1) open at the ends of the reactor head (3) vertically. The downpipe (2) is bent to the horizontal at the lower end and after another turn it merges into the foot of the riser pipe (1).

Gas inlet (4) and isobutyraldehyde inlet (5) are at the foot the riser pipe (1) or the downpipe (2) arranged. At the top of the downpipe # (2) there is a discharge valve 6) for the liquid reaction product. That I Reaction exhaust gas (7) which separates the liquid from the reactor head (3) passes through a Brine cooler set to 1000 (8).

The apparatus is filled with 5.5 l of isobutyraldehyde and heated to 350.degree gassed with an hourly 140 Nl N2 / O2 mixture (62.5% by volume 02). Hourly by titration The increase in the concentration of isobutyric acid is monitored from the samples taken.

After 10 hours, the contents of the reactor are of isobutoric acid approx. 90 percent by weight. 500 ml of isobutyraldehyde are now grounded every hour with the gas supply unchanged fed in continuously at (5). At the same time you take out while holding constant of the total volume of the reactor, the crude acid in (6).

The experiment described was a) with the addition of 25 g of cadmium isobutyrate b) carried out without addition (comparison test).

In) experiment a) the cadmium isobutyrate content was discontinuous topped up every 2 hours by, after distilling off the raw acid removed remaining cadmium isobutyrate was returned to the reactor.

The test results can be seen from Table 2. As you can see, If cadmium isobutyrate is used, the isobutyric acid yield is greater than in comparative experiment 2a, while the conversions are practically the same.

Table 1 (for example 1) Oxidation of 250 ml isobutyraldehyde with 15 Nl oxygen / h at 45 ° C., test duration 5 hours Attempt addition g isobutyric acid g carbon dioxide after 5 h after 5 1a Cd acetate 120 0.7 1b Zn acetate 115 0.9 1c without 108 6.7 (Comparative attempt) Table 2 Conversion, yield and space-time performance in the oxidation of 500 ml = 397 g = 5.51 mol of isobutyraldehyde per hour (see Example 2) Isobutyraldehyde isobutyric acid Attempt additional use conversion% yield on space-time performance Mol / h mol / h mol / h use conversion g / l # h 2a cadmium 5.51 4.40 5.19 94.2 96.1 83.0 iso- butyrate 2b without 5.51 5.42 4.63 84.0 85.4 74.1 (Ver equal attempt)

Claims (6)

Claims 1. Process for the production of isobutyric acid by Oxidation of isobutyraldehyde with elemental or oxygenated oxygen Gases, characterized in that in the presence of inhibitors, the compounds of zinc and / or cadmium are oxidized. 2. The method according to claim 1, characterized in that one inhibitor solutions begins. 3. The method according to claims 1 and 2, characterized in that that zinc and / or cadmium isobutyrate are used. ' 4. The method according to claim 1, characterized in that inhibitor suspensions are used. 5. The method according to claim to, characterized in that nan which uses inhibitors in combination with carrier materials. 6. The method according to claim 1, characterized in that one is in the presence liquid isobutyric acid is oxidized. L e r s e i t e