FR2514345A1 - Isobutyric anhydride prodn. from propylene - by carbonylation in liq. hydrogen fluoride and hydrolysis of prod. - Google Patents

Abstract

Prodn of isobutyric anhydride (I) is carried out by (a) carbonylating propylene in the presence of excess anhydrous liq HF; (b) fractionating the reaction mixt to separate isobutyryl fluoride (II) and recover unreacted HF for recycle; (c) hydrolysing (II) at 0-100 deg C in the presence of an HF acceptor (III) and 0.05-0.5 mole of water per mole of (II), the water being completely consumed in the reaction to form an equilibrium reaction mixt including a liq phase comprising (I) and (II) and a solid phase comprising an HF/(III)complex; and (d) fractionating the liq phase to give a prod fraction comprising (I) and an overhead fraction comprising (II) for recycle to step (c). The process avoids problems associated with the sepn of (I) from HF; recycle HF can be recovered from the HF/(III) complex.

Description

 The present invention relates to a process for the production of isobutyric anhydride.

 The general field to which the invention belongs is the production of a lower carboxylic anhydride from the corresponding monoacyl fluoride.

Olefins are known to readily react with carbon monoxide at low temperatures and under moderately elevated pressures in the presence of a strongly acidic medium, examples of which include anhydrous hydrofluoric acid, concentrated sulfuric acid and the like. anhydrous chlorosulfonic acid. The accepted carbonylation mechanism is classically called the Koch reaction and is described for example in the US Pat.
No. 2,831,877. The main problem with any industrial practice of the Koch reaction to obtain a lower carboxylic acid is the difficulty of recovering the acid catalyst in a form suitable for recycling.

 Komatsu et al. in Bull, Jap. Fart. Inst., 16, 124-131 (1974) discuss this recovery aspect with respect to the Koch reaction using a lower olefin, and describe a process for the recovery of hydrofluoric acid after preparation of pivalic acid, according to Koch's reaction.

Essentially, this process comprises hydrolyzing the reactional carbonylation mixture with an equimolar mixture of hydrofluoric acid and water (54% aqueous hydrofluoric acid) and distillation to recover the anhydrous hydrofluoric acid. Then, the residue is hydrolyzed in the form of an equimolar complex of hydrofluoric acid and pivalic acid, with a minimum of water to obtain two layers: the upper layer consisting of the carboxylic acid product and the other of 54% aqueous hydrofluoric acid recyclable.

 Unfortunately, this method does not apply to a similar process for the preparation of isobutyric acid since this carboxylic acid is soluble in 50% aqueous hydrochloric acid. The only way to achieve phase separation is to dilute the carboxylic acid solution with a large amount of water. The overall result is that in this process one mole of hydrofluoric acid per mole of carboxylic acid is produced. can not be recovered.

 The invention relates to an integral process for the production of isobutyric anhydride by Koch reaction in which liquid anhydrous hydrofluoric acid is used as reaction medium or catalyst. The essential point of the invention is that in the overall process the hydrofluoric acid can be recovered substantially completely in the anhydrous form for recycling.

In the initial phase of the process, propylene is carbonylated in the presence of a large molar excess of anhydrous hydrofluoric acid to convert propylene to isobutyryl fluoride. The unreacted hydrofluoric acid is recovered by distillation for recycling and the residue consisting essentially of isobutyryl fluoride with water is partially hydrolyzed in the presence of a hydrofluoric acid acceptor. The hydrolysis reaction is carried out until the water is completely consumed and an equilibrium mixture consisting essentially of isobutyaryl fluoride, isobutyric anhydride and a hydrofluoric acid complex is obtained. and the acceptor formed during the hydrolysis reaction.After removal of the solid complex, the hydrolysis product is subjected to fractional distillation to obtain an isobutyryl fluoride head fraction which is recycled and a fraction of intermediate mainly composed of isobutyric anhydride. According to another aspect of the invention, the spent acceptor is regenerated to obtain anhydrous hydrofluoric acid and acceptor suitable for recycling.

 The single appended figure is an operating diagram illustrating the production of isobutyric anhydride by carbonylation of propylene in the presence of anhydrous hydrofluoric acid according to the process of the invention with internal cyclic reuse of anhydrous hydrofluoric acid.

 Although the invention is only one aspect of an overall process for the production of isobutyric anhydride corresponding largely to the prior art, its detailed description must necessarily be made in the context of the overall operating scheme envisaged. Referring therefore to the attached figure which first shows a carbonylation reactor 1 in which anhydrous hydrofluoric acid, petroleum-grade propylene and carbon monoxide are reacted to produce isobutyryl fluoride with a selectivity of essentially 100%.

In this respect, the operating conditions must be optimal for a particular structure of the reactor. These conditions may or may not be optimal for a reactor of different structure.

However, the determination of these conditions for a particular structure is within the competence of the specialist.

 The carbonylation reaction is carried out under a pressure of 345 bar created by the carbon monoxide feed stream (11) and a temperature of about 300C. The propylene feed stream (10) is combined with the anhydrous hydrofluoric acid stream (12) to obtain a 1/15 molar ratio in the carbonylation reactor. The residence time in the reactor is 30 min. The effluent stream from the reactor (13) passes through adiabatic expansion valves (not shown) to enter the receiver or primary expansion tank 2 in which the pressure is 20 bar.

 The residual fuel gas (14) of the receiver 2 is passed through the purifier 3, while the condensate composed mainly of isobutyryl fluoride and liquid hydrofluoric acid, forming the stream (16), is introduced into the apparatus of distillation 4 of the hydrofluoric acid. The hydrofluoric acid overhead fraction with makeup hydrofluoric acid constitutes the main hydrofluoric acid feed stream (12) of the reactor. The isobutyryl fluoride residue of the hydrofluoric acid distillation apparatus 4 is introduced into the hydrolysis unit 5 of which it constitutes the main feed (18). The hydrolysis unit is supplied with water from the residual fuel gas scrubber 3 and constitutes the stream (19).

The third feed of the hydrolysis unit is the hydrofluoric acid acceptor which, in the particular example described, is sodium fluoride and constitutes the stream (24).

 The hydrolysis is carried out at a temperature of between about 0.degree. C. and 1000.degree. C. and better still between 0.degree. And 400.degree. C. in the presence of 0.05 to 0.5 mole of water per mole of isobutyryl fluoride present in the reaction mixture. hydrolysis, and more preferably 0.2 to 0.4 mole. It is essential to use the water until exhaustion in the hydrolysis reaction. The product of the hydrolysis reaction obtained is an equilibrium mixture of isobutyric anhydride, isobutyryl fluoride and complexed sodium fluoride. Another feature of the invention is the maintenance of an appropriate amount of isobutyryl fluoride in the equilibrium mixture which has the important role of forming a solvent for isobutyric anhydride. After recovery of the complexed sodium fluoride by filtration as shown or in other suitable manner, for example by centrifugation, the homogeneous phase constituting the stream (20) is introduced into the column 6 of fractional distillation of the product. The isobutyryl fluoride head fraction of column 6 is recycled to the hydrolysis unit 5 and a product fraction consisting of isobutyric anhydride is recovered as a stream (21).

 Although the above description relates to the use of sodium fluoride as a hydrofluoric acid acceptor, various other compounds may be used for this purpose. In the context of the invention, an acceptor is generally a compound which accepts a proton but which, at the same time, does not react competitively with isobutyryl fluoride or isobutyric anhydride. The preferred acceptors are the alkali metal fluorides, especially sodium fluoride taken here as an example. These salts are interesting because they are easily complexed with hydrofluoric acid and are easy to regenerate by heat treatment with simultaneous release of anhydrous hydrofluoric acid. Activated charcoal is another suitable acceptor that can be regenerated by heat. Tertiary amines, basic ion exchange resins, and alkali metal oxides can act as acceptors. However, the regeneration of these latter acceptors is not as easy as that of the preferred acceptors indicated.

 As shown in this regard, the complexed sodium fluoride constitutes the stream (22) of the filter 7 which is fed to the hydrofluoric acid regenerator 8. In this case, the regenerator consists of a simple boiler. The hydrofluoric acid produced is the stream (23) which is combined with the stream (17) of the hydrofluoric acid distillation apparatus 4 to be recycled to the carbonylation reactor 1 with makeup hydrofluoric acid. The regenerated sodium fluoride (2.4) is recycled to the hydrolysis unit 5.

 The invention is illustrated by the following nonlimiting example.

EXAMPLE
The compositions of the various streams shown in the figure of the best embodiment of the invention described above are given below. The indicated values correspond to a unit designed to produce approximately 454 kmol of isobutyric anhydride per hour. The corresponding flows (kmol / h) of the various currents are shown in the following table.

BOARD
Flow rate of currents in the production of isobutyric anhydride.

(Kmol / h)

Current <SEP> n <SEP> 10 <SEP> 11 <SEP> 12 <SEP> 13 <SEP> 14 <SEP> 15 <SEP> 16 <SEP> 17 <SEP> 18 <SEP> 19 <SEP> 20 <SEP> 21 <SEP> 22 <SEP> 23 <SEP> 24
<tb> Propylene <SEP> 99.8 <SEP> 3.0 <SEP> 2.9 <SEP> 2.9 <SEP> 0.05 <SEP> 10.5 <SEP> 0.09 <SEP> 0 09
<tb> Propane <SEP> 42.7 <SEP> 42.8 <SEP> 42.6 <SEP> 40.8 <SEP> 0.14 <SEP> 0.14 <SEP> 0.14 <SEP> 0 14
<tb> Monoxide <SEP> of <SEP> Carbon <SEP> 109.8 <SEP> 13.0 <SEP> 12.6 <SEP> 12.4 <SEP> 0.41 <SEP> 0.41 <SEP > 0.18 <SEP> 0.18
<tb> Acid <SEP> Hydrogen fluoride <SEP> 1497 <SEP> 1400.0 <SEP> 4.5 <SEP> Tr <SEP> 1395.5 <SEP> 1361 (-) <SEP> 4.5 <SEP> 8.3 <SEP> 58.2 <SEP> Tr <SEP> 103.9
<tb> Fluoride <SEP> of isobutyrylate <SEP> 92.0 <SEP> 91.9 <SEP> 2,3 <SEP> 91.0 <SEP> Equil.
<Tb>

<SEP> Isobutyric acid <SEP> 0.9 <SEP> Equil.
<Tb>

<SEP> Isobutyric Anhydride <SEP> Equil. <SEP> 44.5
<tb> Water <SEP> 2.4 <SEP> 46.0
<tb> Heavy <SEP> fluoride <SEP> 4.9 <SEP> 4.9 <SEP> 0.32 <SEP> 4.5
<tb> Fluoride <SEP> of <SEP> sodium <SEP> 103.9
<tb> Complex <SEP> NaHF2 <SEP> 103.9
<Tb>

Claims (5)

 1 - Integral process for the production of isobutyric anhydride, characterized in that it comprises the stages of (A) carbonylation (1) of propylene (10) in the presence of an excess  important anhydrous hydrofluoric acid liquid (12) for  carry out the formation of isobutyryl fluoride; (B) fractionation (4) of the carbonylation reaction mixture  to obtain unreacted anhydrous hydrofluoric acid  that is recycled (17) and isobutyryl fluoride (18); (C) partial hydrolysis (5) of isobutyryl fluoride at a temperature of  between 0 and 100 C, in the presence of a  hydrofluoric acid acceptor and 0.05 to 0.5 mole of water  per mole of isobutyryl fluoride, the water being used up to  depletion in the hydrolysis reaction to obtain  an equilibrium hydrolysis reaction mixture comprising a  liquid phase (20) consisting essentially of iso fluoride  butyryl and isobutyric anhydride; and (D) fractional distillation (6) of said liquid phase of the mixture  hydrolysis reaction to obtain a fraction of  isobutyryl fluoride (18) for recycling into said  hydrolysis stage (5) (C) and a product fraction (21)  isobutyric anhydride.  2 - Process according to claim 1, characterized in that said hydrolysis step (C) is carried out at a temperature between 0 and 400C and in the presence of 0.2 to 0.4 mole of water per mole of fluoride isobutyryl.  3 - Process according to claim 2, characterized in that the hydrofluoric acid acceptor is an alkali metal fluoride.  4 - Process according to claim 3, characterized in that said acceptor is sodium fluoride.  5 - Process according to one of Claims 3 or 4, characterized in that the acceptor complexed with hydrofluoric acid (22) is recovered from the mixture of the hydrolysis reaction of stage (C) and heated ( 8) to obtain anhydrous hydrofluoric acid to be recycled (23) and the regenerated acceptor (24) which is reused in the hydrolysis stage (C).