Method for separating mandelic compounds in salified form and use of same for preparing aromatic aldehyde

Abstract

The invention describes a method for separating a mandelic compound in salified form from an aqueous reaction medium resulting from the condensation reaction of a hydroxylated aromatic compound with glyoxylic acid in a basic medium, said method comprising a) decanting said reaction medium in such a way as to recover an organic phase formed from the excess of said aromatic compound and an aqueous phase formed from said mandelic compound and a quantity of the excess of said aromatic compound and b) bringing said aqueous phase into contact with an adsorbent support, resulting in the selective adsorption of said aromatic compound and the recovery of an aqueous flow comprising said mandelic compound in salified form, which is subjected to an oxidation step before being converted into hydroxyaromatic aldehyde by electrodialysis.

Claims

1. A process for separating at least one mandelic compound in salified form from an aqueous reaction mixture resulting from condensation, in a basic aqueous medium, of at least one aromatic compound bearing at least one hydroxyl group and in which the para position is free with glyoxylic acid, said process comprising: a) decanting said reaction medium to recover an organic phase comprising aromatic compound in non-salified form and an aqueous phase comprising the at least one mandelic compound and an amount of the aromatic compound, each in salified form, b) contacting said aqueous phase with an adsorbent support to selectively adsorb aromatic compound from the aqueous phase on said support and recover an aqueous mixture comprising the at least one mandelic compound in salified form.

2. The process of claim 1, wherein said aromatic compound is selected from the group consisting of phenol and the hydroxylated aromatic compounds corresponding to formula (I): ##STR00004## wherein: at least the position para to the hydroxyl group is free, R represents a hydrogen atom or one or more identical or different substituents, x, the number of substituents on a ring, is a number less than or equal to 4.

3. The process of claim 2, wherein said aromatic compound corresponds to formula (I), wherein R represents a hydrogen atom, an alkyl group containing from 1 to 4 carbon atoms, or an alkoxy group containing from 1 to 4 carbon atoms, and x is equal to 1.

4. The process of claim 1, wherein said aromatic compound is selected from the group consisting of phenol, o-cresol, m-cresol, 3-ethylphenol, 2-tert-butylphenol, guaiacol, and guaethol.

5. The process of claim 1, wherein said organic phase obtained after decantation is recycled into the condensation reaction.

6. The process of claim 1, wherein said step b) is performed co-currently.

7. The process of claim 1, wherein said aqueous stream obtained after said step b) comprises a p-hydroxymandelic compound, an o-hydroxymandelic compound, and a hydroxylated dimandelic compound.

8. The process of claim 1, further comprising desorbing said aromatic compound and recycling desorbed aromatic compound into said condensation reaction.

9. The process of claim 1, further comprising: acidifying said reaction mixture prior to the decanting step, and/or acidifying said aqueous phase prior to contacting the aqueous phase with the adsorbent support.

10. The process of claim 9, wherein acidification of said aqueous phase is effective to lower the pH of said aqueous phase 0.1 to 3 points.

11. The process of claim 9, wherein the acidification is performed by adding strong acid or weak acid or, alternatively, by using CO.sub.2.

12. The process of claim 1, further comprising: c) oxidizing the at least one mandelic compound to at least one alkoxybenzaldehyde hydroxylate compound, and d) converting the at least one alkoxybenzaldehyde hydroxylate compound into at least one hydroxyaromatic aldehyde.

13. The process of claim 12, wherein said step d) comprises neutralizing the at least said alkoxybenzaldehyde hydroxylate compound into the hydroxyaromatic aldehyde and producing a saline hydroxide solution.

14. The process of claim 12, wherein the at least one mandelic compound is selected from the group consisting of p-hydroxymandelic acid salts, 4-hydroxy-3-methoxymandelic acid salts, 3-ethoxy-4-hydroxymandelic acid salts, 4-hydroxy-3-isopropoxymandelic acid salts, and a mixture of 4-hydroxy-3-methoxymandelic and 3-ethoxy-4-hydroxymandelic acid salts.

15. The process of claim 12, wherein said alkoxybenzaldehyde hydroxylate compound comprises a 4-hydroxy-3-methoxymandelic acid salt and the hydroxyaromatic aldehyde comprises vanillin.

16. The process as of claim 12, wherein said alkoxybenzaldehyde hydroxylate compound comprises a 3-ethoxy-4-hydroxymandelic acid salt and the hydroxyaromatic aldehyde comprises ethylvanillin.

17. The process of claim 12, wherein said step d) is performed by electro-electrodialysis using cation-exchange membranes.

18. The process of claim 12, wherein said step d) is performed by electrolyzing using a two-compartment electrolyzer or a three-compartment electrolyzer.

19. The process of claim 12, wherein said step d) is performed by bipolar membrane electrodialysis.

20. The process of claim 19, wherein said step d) is conducted at a temperature of between 45 and 90 C.

21. The process of claim 13, further comprising recycling said saline hydroxide solution into said step c), into said step b), and/or into said condensation reaction.

Description

EXAMPLE

(1) In the example, the degree of conversion and the selectivity obtained are defined.

(2) The degree of conversion (DC) corresponds to the ratio between the number of moles of reagent converted and the number of moles of reagent used.

(3) The selectivity or the yield relative to the converted product (CY) is expressed by the ratio between the number of moles of product formed and the number of moles of reagent converted.

(4) Condensation Reaction

(5) The following are continuously charged into a first 150 mL 316L stainless-steel reactor equipped with a jacket, a mechanical stirrer, a pH electrode, a condenser system and an inert gas inlet: 1.14 kg/h of demineralized water 164 g/h (2.05 mol/h) of an aqueous solution of sodium hydroxide at 50% by weight 178 g/h (1.44 mol/h) of guaiacol (fresh and recycled).

(6) This reaction mixture is maintained at a temperature of 35 C. This preparation is then fed into the first reactor of a system of 3 reactors in cascade, with an aqueous solution of glyoxylic acid at 50% by weight (107 g/h, i.e. 0.72 mol/h).

(7) The 3 perfectly stirred reactors are made of 316L stainless steel and each have a volume of 1.5 L; they operate at 35 C.

(8) The overall residence time is 2.1 hours.

(9) At the outlet of the final reactor, a sample of this reaction medium is taken and the compounds present in the mixture are assayed by liquid chromatography.

(10) The results obtained are as follows: conversion of guaiacol (GA): DC=47% disodium salt of 4-hydroxy-3-methoxymandelic acid (PMA(2Na)): CY(PMA(2Na)/GA)=86% disodium salt of 2-hydroxy-3-methoxymandelic acid (OMA(2Na)): CY(OMA(2Na)/GA)=6% trisodium salt of 2-hydroxy-3-methoxy-1,5-dimandelic acid (DMA(3Na)): CY(DMA(3Na)/GA)=8%

(11) The reaction medium is sent to the decantation/neutralization/adsorption section to separate the excess sodium guaiacolate from the vanillyl-mandelic acid salts.

(12) Decantation/Neutralization

(13) The condensation outlet medium is transferred by pump at a delivery rate of 1.6 kg/h into a 1 L 316L stainless-steel reactor equipped with a mechanical stirrer, a pH electrode and a CO.sub.2 inlet via a gas line immersed at the bottom of the reactor. The CO.sub.2 delivery rate is regulated so that the pH of the reaction medium is neutralized at pH=10.5.

(14) The reaction medium is then transferred into a 2L decanter equipped with a jacket and a temperature maintenance system, and in which the overall residence time is 1.2 hours. Decantation takes place at 35 C.

(15) The decantation produces two streams: The organic layer, withdrawn from the bottom of the decanter, comprising guaiacol, at a delivery rate of 70 g/h. This stream is intended to be recycled directly into the condensation feed. The aqueous layer, the light phase, which contains the vanillyl-mandelic acid salts to be oxidized and 2.9% by weight of sodium guaiacolate.

(16) To optimize the operating conditions of the absorption column, the aqueous phase is again neutralized to pH=10.0 in a 1 L 316L stainless-steel reactor equipped with a mechanical stirrer, a pH electrode and a CO.sub.2 inlet via a gas line immersed at the bottom of the reactor. The CO.sub.2 delivery rate is regulated so that the pH of the reaction medium is neutralized at pH=10.0.

(17) Adsorption

(18) The adsorption of the guaiacol is performed in a glass column equipped with a jacket and a system for maintaining the temperature at 35 C. The adsorbent used is Norit C

(19) Gran active charcoal from the supplier Cabot Norit Activated Carbon: the bed of active charcoal in the column has a volume of 2.0 L.

(20) The various steps of the cycle are controlled by a robot which starts and stops the various feed and collection pumps by interval timing. The time intervals were set beforehand to feed well-defined mass amounts depending on the steps.

(21) The adsorption cycle comprises four steps:

(22) Adsorption:

(23) The decanted and neutralized condensation outlet medium feeds the top of the adsorption column via a peristaltic pump at a delivery rate of 3 L/h. At the column outlet, the stream is directed toward the storage buffer intended to feed the oxidation.

(24) After feeding in 2.9 kg of condensation medium, the robot activates the second step of the cycle.

(25) Start of the Regeneration Cycle:

(26) The column is fed at the top with water and 10% sodium hydroxide via a peristaltic pump at a delivery rate of 3 L/h. At the bottom of the column, the outlet stream continues to be directed toward the oxidation reaction.

(27) When 1.8 kg of water and then 10% of NaOH have been fed into the top of the column, the robot activates the third step of the cycle.

(28) Regeneration:

(29) The column is fed at the top with water via a peristaltic pump at a delivery rate of 3 L/h. At the bottom of the column, the outlet stream is directed toward the storage buffer intended for recycling of the sodium guaiacolate as an aqueous phase into the condensation.

(30) After feeding 1.4 kg of water into the top of the column, the robot activates the fourth step of the cycle.

(31) End of Cycle:

(32) The column is fed at the top with the decanted and neutralized condensation outlet medium, via a peristaltic pump at a delivery rate of 3 L/h. At the bottom of the column, the stream is directed toward the storage intended for recycling of the sodium guaiacolate as an aqueous phase into the condensation.

(33) When 1.0 kg of condensation medium has been fed into the top of the column, the robot activates the first step of the next cycle.

(34) The delivery rate to the oxidation, averaged over the cycle, is 1.9 kg/h, whereas it is 1.0 kg/h for the sodium guaiacolate solution recycled into the condensation.

(35) A sample is taken from each of the two column outlet drums and the compounds present in the mixture are assayed by liquid-phase chromatography.

(36) The results obtained are as follows:

(37) Oxidation Feed Medium:

(38) Sodium guaiacolate (GANa): 1200 ppm

(39) Disodium salt of PMA (PMA(2Na)): 7.0% by weight

(40) Sodium Quaiacolate Recycled into the Condensation:

(41) Sodium guaiacolate (GANa): 3.5% by weight

(42) Disodium salt of PMA (PMA(2Na)): 0.2% by weight

(43) The degree of regeneration of the guaiacol adsorbed onto the column is 100%.

(44) Oxidation Reaction

(45) The 316L stainless-steel oxidation reactor equipped with a self-suction stirrer of cavitation type (cavitator) or of Rushton type and with a jacket for efficient cooling is continuously fed with: the mixture of the catalyst and of the aqueous solution of vanillyl-mandelic acid salts obtained from the adsorption column, i.e.: 1.95 kg/h of condensation reaction medium from which the excess sodium guaiacolate has been separated out (and then recycled) by adsorption on the active charcoal column. This mixture contains about 136 g/h of disodium salt of 4-hydroxy-3-methoxymandelic acid, 9 g/h of disodium salt of 2-hydroxy-3-methoxymandelic acid and 16 g/h of trisodium salt of 2-hydroxy-3-methoxy-1,5-dimandelic acid. 2 g/h of an aqueous solution of CuSO.sub.4 in an amount expressed as molar percentage of metal relative to the molar sum of the vanillyl-mandelic acid salts: 0.04% each. the appropriate amount of an aqueous solution of sodium hydroxide at 50% by weight corresponding at least to the amount required by the stoichiometry of the oxidation reaction. the amount of oxygen at atmospheric pressure sufficient to have a virtually complete conversion of the vanillyl-mandelic acid salts. The oxidizing agent may be oxygen at atmospheric pressure or pressurized air.

(46) This reaction takes place at 80 C.

(47) At the outlet of the reactor, a sample of this reaction medium is taken and the compounds present in the mixture are assayed by liquid chromatography.

(48) The results obtained are as follows: conversion of the disodium salt of 4-hydroxy-3-methoxymandelic acid: DC>99.5% yield of sodium vanillate VANa:

(49) CY(VANa)/PMA=97%.

(50) The solution is stored in a vat before being sent to the electrodialysis section.

(51) Acidification of the sodium vanillate solution after oxidation is performed in batch mode in an electrodialysis pilot which is composed of an electrodialyzer, three hydraulic circuits respectively named electrolyte, salt/acid and base, each comprising a circulation pump and a floating flow meter (rotameter). The circuits are maintained at 53 C. by means of a hot water circulation, supplied by a thermostatically maintained bath, in internal coils. The electrodialyzer, which has a cross section of 0.02 m.sup.2, comprises at each end a support onto which is attached each electrode (nickel anode and cathode), a membrane stack composed of two membranes with cationic ends of Neosepta C6610 type, seven bipolar membranes of Neosepta BP1 type stacked in successive layers alternating with seven Neosepta CMB cationic membranes.

(52) 2448 g of a sodium hydroxide solution at 1 mol/l and 2032 g of a sodium hydroxide solution at 0.5 mol/l are respectively introduced into the electrolyte and base circuits. In parallel, 2256 g of a sodium vanillate solution containing 4.1% of vanillin, 0.1% of ortho-vanillin, 0.6% of sodium hydroxide, 4% of sodium carbonate and 0.5% of vanillylmandelic acid are introduced into the salt/acid compartment. The pH and conductivity measurements are taken by probes dipping into this compartment. The pumps are switched on so as to ensure circulation of the various solutions (300 L/h for the electrolyte solution and 200 L/h for the salt/acid and base solutions) and homogenization of the temperature. The current generator is then switched on and the nominal intensity is set at 15 A by means of the potentiometer, i.e. a current density of 0.75 kA/m.sup.2. The pH decrease is monitored over time. Transfer of sodium ions takes place from the salt/acid solution to the base solution. Substantial evolution of CO.sub.2 is observed at and below a pH in the region of 8, requiring adjustment of the delivery rate of the salt/acid solution. When the pH reaches 5.3 (i.e. after about 50 minutes), the current generator and the circulation pumps are switched off. The solutions in the three compartments are emptied out, weighed and analyzed. The amounts recovered are, respectively, 2448 g of electrolyte solution, 2288 g of base solution and 1980 g of salt/acid solution. The coulombic yield obtained, corresponding to the ratio of the number of moles of elementary electrical charges really transferred to the amount of electrical charges which crossed the stack, is estimated at about 80%. The degree of conversion of the sodium vanillate into vanillin is greater than 95%. Said vanillin is then extracted into organic phase by adding a suitable solvent.