IMPROVED METHOD FOR PREPARING PARA-THYMOL

Abstract

The present invention relates to an improved method for producing 4-isopropyl-3-methylphenol (p-thymol) from distillation residues of thymol production.

Claims

1. A method for producing 4-isopropyl-3-methylphenol from a reaction mixture obtained by reacting meta-cresol with propene in the presence of a catalyst, the method comprising: a) removing thymol and unreacted meta-cresol from the reaction mixture by distillation, to produce a distillation, b) from crystallizing 4-isopropyl-3-methylphenol from the distillation residue remaining according to step a) to form a suspension comprising crystalline 4-isopropyl-3-methylphenol and a liquid phase, and c) separating the crystalline 4-isopropyl-3-methylphenol.

2. The method according to claim 1, further comprising: d) recrystallizing the crystalline 4-isopropyl-3-methylphenol obtained from step c).

3. The method according to claim 1, wherein the separating in step c) is carried out by the effect of centrifugal forces in a centrifuge, preferably in a filter centrifuge, more preferably in a discontinuous filter centrifuge, or preferably in a horizontal centrifuge, particularly preferably in a scraper centrifuge.

4. The method according to claim 1, wherein the method does not include a step.

5. The method according to claim 1, wherein the crystalline 4-isopropyl-3-methylphenol obtained according to step c) has a 4-isopropyl-3-methylphenol content of more than 90% by weight, preferably 91 to 99% by weight, particularly preferably 92 to 99% by weight, and especially preferably 92 to 96% by weight.

6. The method according to claim 1, characterized in that step c) is carried out at a relative centrifugal acceleration from 100 to 1000 g, preferably from 200 to 900 g, particularly preferably from 600 to 800 g.

7. The method according to claim 1, wherein the separation c) comprises separation of the crystalline 4-isopropyl-3-methylphenol from the liquid phase by the effect of centrifugal forces.

8. The method according to claim 1, wherein the crystalline 4-isopropyl-3-methylphenol obtained according to step c) has a 4-isopropyl-3-methylphenol content of 92 to 99% by weight, and especially preferably 92 to 96% by weight

9. The method according to claim 1, wherein: the separation c) comprises separation of the crystalline 4-isopropyl-3-methylphenol from the liquid phase by the effect of centrifugal forces at a relative centrifugal acceleration from 600 to 800 g; and the crystalline 4-isopropyl-3-methylphenol obtained according to step c) has a 4-isopropyl-3-methylphenol content of 92 to 96% by weight.

10. The method according to claim 9, further comprising: d) recrystallization of the crystalline 4-isopropyl-3-methylphenol obtained from step c using methylcyclohexane in the presence of activated carbon to produce 4-isopropyl-3-methylphenol having a purity of 97 to 100% by weight.

Description

EXAMPLES

Example 1

[0054] 21.1 kg of a 60° C. warm, black distillation residue from the production of thymol by reacting m-cresol with propene in the presence of a catalyst, the distillation residue comprising 21.5% by weight thymol, 7.0% by weight 3-isopropyl-5-methylphenol, 25.0% by weight 4-isopropyl-3-methylphenol, 21.5% by weight 2,6-diisopropyl-3-methylphenol, 21.0% by weight 2,4-diisopropyl-5-methylphenol and a sum total of ca. 4% by weight, about 22 different otherwise alkylated cresols, were cooled slowly to room temperature with stirring in a 25-l capacity reactor over 16 hours, whereupon a suspension comprising crystalline 4-isopropyl-3-methylphenol and a liquid phase was formed. The precipitated 4-isopropyl-3-methylphenol was filtered off. 5.26 kg of 4-isopropyl-3-methylphenol were obtained with a purity of 83.4% by weight, which corresponded to a yield of 82.3% by weight of the 4-isopropyl-3-methylphenol present in the distillation residue.

Example 2

[0055] A scraper centrifuge was employed using the following parameters: [0056] Diameter of the drum: 1 m [0057] Filter surface area: 1.57 m.sup.2 [0058] Fill volumes: 172 l [0059] Edge height: 0.125 m [0060] Drum length: 0.5 m

[0061] A suspension was used having the following parameters: [0062] Temperature: 10° C. [0063] Density: 0.97 g/cm.sup.3 [0064] Viscosity: 112.5 mPas

[0065] Concentration of [0066] 4-isopropyl-3-methylphenol: 150 g/l

[0067] The method according to the invention was carried out using the following parameters: [0068] relative centrifugal acceleration: 700 g [0069] suspension feed rate volumes: 120 l/min [0070] suspension feed time: 180 s

[0071] After completion of the suspension feed, the relative centrifugal acceleration of the drum was increased for 900 s to 1000 g. Subsequently, the relative centrifugal acceleration of the drum was lowered to 45 g and the product was discharged using a scraper knife. 63 kg of crystalline 4-isopropyl-3-methylphenol were obtained which had a 4-isopropyl-3-methylphenol content of 96.1% by weight.

Example 3 (Recrystallization)

[0072] 580 g of methylcyclohexane and 5 g of activated carbon were added to 200 g of 4-isopropyl-3-methylphenol from Example 2 and heated under reflux for 10 minutes. The activated carbon is filtered off while hot and the filtrate is cooled to 25° C. with stirring at a cooling rate of 0.5 K/minute.

[0073] The 4-isopropyl-3-methylphenol that crystallizes out is filtered off and the crystals washed once with 100 g of methylcyclohexane on the nutsche filter. The solid filtered off is dried in the vacuum drying cabinet at 40° C./50 mbar. [0074] Yield: 169 g of 4-isopropyl-3-methylphenol [0075] Content: 99.9% by weight [0076] Melting point: 11.5-112.5° C.