Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-03-30
2001-04-03
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C422S245100, C422S261000
Reexamination Certificate
active
06211404
ABSTRACT:
FIELD OF TECHNOLOGY
This invention relates to a process for purifying benzoic acid.
BACKGROUND TECHNOLOGY
Benzoic acid can be prepared by a process such as oxidation of toluene. For example, there is a report that the liquid phase oxidation of toluene gives benzoic acid in a yield of 40% or so. Benzoic acid obtained by a process such as mentioned above contains a small amount of impurities even after removal of low-boiling substances such as toluene beforehand. The impurities here include benzaldehyde, benzyl alcohol, benzoic acid esters, biphenyls, p-phenylbenzoic acid, phthalic anhydride and toluic acid and, as they cause problems relating to emission of odor and coloration, they should desirably be removed from the product benzoic acid.
The following processes are known for the purification of benzoic acid: treatment with sulfuric acid followed by rectification as disclosed in Japan Kokoku Tokkyo Koho Sho 61-25013 (1986); vaporization in an inert gas followed by crystallization under specified conditions as disclosed in Japan Kokoku Tokkyo Koho Sho 57-11899 (1982); distillation in the presence of aliphatic amines as disclosed in Japan Kokoku Tokkyo Koho Hei 6-43367 (1994); and purification by supercritical extraction as disclosed in Japan Kokai Tokkyo Koho Sho 61-130257 (1986). None of these processes, however, satisfied all the factors involved in purification such as efficiency, equipment, and cost.
A process based on crystallization such as recrystallization is also known for the purification of crystalline solids, but this too faces the aforementioned problems and is not well suited for application on a commercial scale.
An object of this invention is to provide a process for purifying benzoic acid which permits of continuous preparation of high-purity benzoic acid in a relatively simple equipment at high efficiency.
DISCLOSURE OF THE INVENTION
Accordingly, this invention relates to a process for purifying benzoic acid comprising introducing crystals of crude benzoic acid, 0.2 g/cm
3
or more in bulk density and 0.3 mm or more in average particle diameter, into a continuous crystallization apparatus equipped with a stirrer and a heating device from the upper portion of the apparatus, effecting purification by counter-current contact of the crystals of crude benzoic acid falling through the inside of the apparatus with the melt generated by heating with the aforementioned heating device, withdrawing the purified benzoic acid as melt from the lower portion of the apparatus, and withdrawing the mother liquor from the upper portion of the apparatus.
Crude benzoic acid to be purified in this invention is the reaction product of the liquid phase oxidation of toluene from which solids and low-boiling substances such as toluene have been removed, but is not limited to this particular material. Furthermore, the purity of crude benzoic acid is preferably 90% or more, more preferably 95% or more.
Crude benzoic acid is used as crystals with the bulk density controlled at 0.2 g/cm
3
or more, preferably 0.3 g/cm
3
or more, more preferably 0.4 g/cm
3
to 0.8 g/cm
3
. Crystals of such bulk density can be obtained, for example, by melting, crystallizing, and scraping crude benzoic acid in a flaker drum. In addition, the average particle diameter of crude benzoic acid is 0.3 mm or more, preferably 0.5 mm or more, more preferably 1 mm to 10 mm. As the term of average implies here, powders and coarse particles may naturally coexist. Coarse particles with a particle diameter in excess of 30 mm are desirably removed as much as possible, but those with a particle diameter of 100 mm or so may be kept in without harm as long as the thickness is 1 mm or less. This means that the preferable shape is flake.
The bulk density as used in this invention is determined by placing 100 g of crystals of benzoic acid in a 1000 cc measuring cylinder, shaking for 30 seconds by a vibrator, and reading off the graduation of the measuring cylinder. The average particle diamter is determined by picking out some particles of average size, measuring the length (x), width (y) and height (z), calculating (x+y+z)/3, and averaging the calculated values.
A continuous crystallization apparatus equipped with a stirrer to be used in this invention may be any of vertical tower type crystallization apparatuses provided with an opening for introducing raw material and an opening for withdrawing the mother liquor in the upper portion and a heating device and an opening for withdrawing the product in the lower portion. A variety of apparatuses may be used, but an apparatus such as described in Japan Tokkyo Kokoku Koho Sho 58-46322 (1983) and “Aromatics,” Vol. 37 (1985), pages 109-127 or its partially improved version is preferable. Particularly desirable is the aforementioned apparatus from which the cooling device in the upper portion is removed.
REFERENCES:
patent: 3410923 (1968-11-01), Strand et al.
patent: 4004886 (1977-01-01), Thijssen et al.
patent: 4547587 (1985-10-01), Kleintjens et al.
patent: 4588414 (1986-05-01), Takegami et al.
patent: 4652675 (1987-03-01), Goorden et al.
patent: 5466266 (1995-11-01), Griffiths
patent: 5755975 (1998-05-01), Eck et al.
patent: 54-141745 (1979-11-01), None
patent: 56-152702 (1981-11-01), None
patent: 57-99301 (1982-06-01), None
patent: 59-66305 (1984-04-01), None
patent: 61-130257 (1986-06-01), None
patent: 61-25013 (1986-06-01), None
patent: 6-91103 (1994-04-01), None
patent: 6-43367 (1994-06-01), None
Synopsis of Lecture at the Technology Committee, “Present State of the Crystallization Purification Processes,” 9thSymposium on the Industrial Crystallization, Jan. 1985.
Arifuku Yuji
Horibe Kazuyoshi
Kawano Haruki
Kuwahara Hiroyuki
Noma Nobumasa
Birch & Stewart Kolasch & Birch, LLP
Geist Gary
Nippon Steel Chemical Co. Ltd.
Oh Taylor V.
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