# US 8,785,698 B2 · Methods and apparatus for production of natural L-menthol

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- Number: US 8,785,698 B2
- Document ID: US8785698B2
- Status: Granted
- Kind: B2
- Application number: 13/148,929
- Filed: 2010-02-17
- Published: 2011-12-22
- Granted: 2014-07-22
- Earliest claimed: 2009-02-17
- Assignees: Nagaoka & Co., Ltd.
- Applicants: Ryosuke Nagaoka; Hideaki Izukura; Susumu Tokita; Yuri Shibata; Yoshiyuki Nagaoka
- Inventors: Ryosuke Nagaoka; Hideaki Izukura; Susumu Tokita; Yuri Shibata; Yoshiyuki Nagaoka
- Web page: https://patentgrep.com/patent/US8785698B2

## CPC

- B01D 9/0013: {by indirect heat exchange}
- A23L 27/203: {Alicyclic compounds}
- B01D 9/0036: {Crystallisation on to a bed of product crystals; Seeding}
- B01D 9/0063: {Control or regulation (control per se G05)}
- C07C 29/78: by condensation or crystallisation
- C07C 35/12: Menthol
- C11B 9/022: {Refining}
- C07B 2200/07: Optical isomers
- C07C 2601/14: The ring being saturated
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- A23L: FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES, NOT OTHERWISE PROVIDED FOR; PREPARATION OR TREATMENT THEREOF (preservation thereof A23B)
- C07C: ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C11B: PRODUCING, e.g. BY PRESSING RAW MATERIALS OR BY EXTRACTION FROM WASTE MATERIALS, REFINING OR PRESERVING FATS, FATTY SUBSTANCES, e.g. LANOLIN, FATTY OILS OR WAXES; ESSENTIAL OILS; PERFUMES (drying-oils C09F)
- C07B: GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR (preparation of carboxylic acid esters by telomerisation C07C67/47; telomerisation C08F)

## Abstract

Embodiments are provided that provide for efficient production of highly pure natural I-menthol. In some embodiments, a method for preparing natural I-menthol involves providing crude mentha oil in a crystallizer and gradually reducing the temperature of the crystallizer in a step-wise manner, thereby producing highly pure crystals in less than two weeks. The methods disclosed herein are suitable for pharmaceutical GMP.

## Claims

### Claim 1

A method for purifying 1-menthol, comprising:
providing crude mentha oil in a crystallizer, wherein the crude mentha oil is from a mint plant and comprises 1-menthol in the range of about 50% to about 95% by weight, and wherein the crude mentha oil is free of organic solvents;
crystallizing 1-menthol from the crude mentha oil by gradually reducing temperature in the crystallizer from a starting temperature at which the 1-menthol is a liquid to a cooled temperature in the range of −30° C. to 25° C. at a cooling rate in the range of 0.1° C./day to 10° C./day to form 1-menthol crystals;
passing a gas over the 1-menthol crystals to remove residual oil and impurities while gradually elevating the temperature in the crystallizer to a temperature in the range of 30° C. to 40° C., wherein purified 1-menthol crystals of at least 98% purity by weight are obtained;
melting the purified 1-menthol crystals to remove 1-menthol from the crystallizer as a melt; and
cooling the melt into a dried, solid 1-menthol product, wherein the method is performed in a closed system without human contact with the crude mentha oil or the 1-menthol.

### Claim 2 (depends on 1)

The method of claim 1, wherein the 1-menthol product has a purity of at least 99% by weight.

### Claim 3 (depends on 1)

The method of claim 1, wherein the temperature in the crystallizer is gradually reduced to between about 0° C. to about 20° C.

### Claim 4 (depends on 1)

The method of claim 1, further comprising comminuting the solid 1-menthol product into particulate.

### Claim 5 (depends on 4)

The method of claim 4, wherein the particulate are pellets.

### Claim 6 (depends on 1)

The method of claim 1, further comprising introducing seed crystals of 1-menthol into the crystallizer to aid crystallizing 1-menthol.

### Claim 7 (depends on 1)

The method of claim 1, further comprising applying reduced or increased pressure to aid removing residual oils and impurities while gradually elevating the temperature in the crystallizer.

### Claim 8 (depends on 1)

The method of claim 1, wherein the purified 1-menthol crystals are obtained by crystallizing the crude mentha oil only once.