Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-06-30
2001-08-07
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06271424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the purification of monotertiarybutyl hydroquinone. More particularly the present invention relates to an improved process for producing food-grade tertiarybutyl hydroquinone.
BACKGROUND OF THE INVENTION
Food-grade tertiarybutyl hydroquinone (“TBHQ”) is useful as a flavor and aroma preservative. Food-grade TBHQ is required by the Food Chemicals Codex Specifications to have at least 99.0% (wt) monotertiarybutyl hydroquinone (“MTBHQ”) on a dry basis and less than 0.2% (wt.) of the major impurity, 2,5-ditertiarybutyl hydroquinone (“DTBHQ”). Additional Food Chemicals Codex Specifications for TBHQ are as follows: 0.2% (wt.) maximum t-butyl-p-benzoquinone, 10 ppm maximum heavy metals, melting range between 126.5° C. and 128.5° C., 0.1% (wt.) maximum hydroquinone, 0.0025% (wt.) maximum toluene, and an ultraviolet absorbance for polynuclear hydrocarbons with maximum absorbances at four different wavelength regions. As a result of such low impurity requirements, the production of relatively pure MTBHQ is essential to the production of food-grade TBHQ.
MTBHQ production is well known in the art. For example, U.S. Pat. No. 2,722,556 to Young, et al., the disclosure of which is incorporated herein by reference in its entirety, discloses a process for producing MTBHQ by reacting hydroquinone with isobutylene or tertiarybutyl alcohol. The crude MTBHQ produced by this process does not meet the TBHQ Food Chemicals Codex Specifications because of high impurity levels. The main impurity in the crude MTBHQ, DTBHQ, is produced in large quantities during the butylation of hydroquinone reaction.
One method of purifying MTBHQ is discussed in the background section of U.S. Pat. No. 5,087,771 to Hilderbrand. This reference discloses purification of crude MTBHQ by dissolving crude, water-wet MTBHQ crystals in toluene, decanting the water, and filtering the hot solution to a crystallizer. The majority of the DTBHQ remains in the toluene mother liquor as the MTBHQ crystallizes. This process is expensive and is very intensive in both labor and equipment, requiring long batch cycle times and specialized equipment.
An alternative method of purifying MTBHQ is taught in U.S. Pat. No. 5,087,771 to Hilderbrand. In this method, crude, water-wet MTBHQ crystals are contacted with a non-polar solvent, such as naphtha, at an elevated temperature. The MTBHQ crystals form a slurry mixture with the non-polar solvent. The temperature of the mixture is lowered and TBHQ is obtained as a solid from the solvent at a temperature above the crystallization point of DTBHQ. The preliminary isolation step required in this process to obtain the crude MTBHQ crystals results in relatively high processing costs, added processing time and extra equipment usage.
JP 62081339 to Hasegawa et al. also describes the purification of crude MTBHQ. In this process, crude, water-wet MTBHQ crystals are purified by forming an extractable eutectic mixture and subsequent solid-liquid extraction. The eutectic mixture is made possible by the unique properties of MTBHQ and DTBHQ: the melting point of a mixture of MTBHQ and DTBHQ is lower than either the melting point of MTBHQ (126° C.) or DTBHQ (216° C.). Although effective, this method requires careful control of temperature, time and flow rate in addition to the high processing costs due to the required preliminary isolation of crude MTBHQ crystals.
In spite of the foregoing, the need still exists for a cost-effective process to produce purified MTBHQ, particularly for removing DTBHQ, such as an in-process purification of MTBHQ.
SUMMARY OF THE INVENTION
The present invention relates to a method of making purified monotertiarybutyl hydroquinone comprised of less than 0.2% (wt.) of 2,5 ditertiarybutyl hydroquinone, wherein the method comprises: a) heating a first composition in a solvent mixture, wherein the first composition comprises monotertiarybutyl hydroquinone and 2,5 ditertiarybutyl hydroquinone and the solvent mixture comprises a polar solvent and a non-polar solvent to substantially strip-off the non-polar solvent; b) solidifying at least part of the 2,5 ditertiarybutyl hydroquinone; c) separating the solidified 2,5 ditertiarybutyl hydroquinone from the non-solidified first composition to form a second composition comprised of the non-solidified first composition and the polar solvent; d) mixing the second composition with a non-polar solvent of the same type as the nonpolar solvent of step (a); e) separating the polar solvent from the non-polar solvent, wherein the polar solvent contains the purified monotertiarybutyl hydroquinone; and f) separating the purified monotertiarybutyl hydroquinone from the polar solvent to produce purified monotertiarybutyl hydroquinone comprised of less than 0.2% (wt.) of 2,5 ditertiarybutyl hydroquinone.
The present invention also relates to a method of making purified monotertiarybutyl hydroquinone comprised of less than 0.2% (wt.) of 2,5 ditertiarybutyl hydroquinone, wherein the method comprises: a) heating a composition in a solvent mixture wherein: (i) the composition comprises monotertiarybutyl hydroquinone and 2,5 ditertiarybutyl hydroquinone, (ii) the solvent mixture comprises a polar solvent and a non-polar solvent, and (iii) the composition and solvent mixture are heated to a temperature at or above the melting point of the composition; b) separating the polar solvent from the solvent mixture at a temperature at or above the melting point of the composition, wherein the polar solvent contains the purified monotertiarybutyl hydroquinone; and c) separating the purified monotertiarybutyl hydroquinone from the polar solvent to produce purified monotertiarybutyl hydroquinone comprised of less than 0.2% (wt.) of 2,5 ditertiarybutyl hydroquinone.
The present invention is further directed to a method of making purified monotertiarybutyl hydroquinone comprised of less than 0.2% (wt.) of 2,5 ditertiarybutyl hydroquinone, wherein the method comprises: a) heating a composition in a solvent mixture wherein the composition comprises monotertiarybutyl hydroquinone and 2,5 ditertiarybutyl hydroquinone, and the solvent mixture comprises a polar solvent and a non-polar solvent, b) separating the polar solvent from the solvent mixture in a liquid-liquid extraction, wherein the polar solvent contains the purified monotertiarybutyl hydroquinone; and c) separating the purified monotertiarybutyl hydroquinone from the polar solvent to produce purified monotertiarybutyl hydroquinone comprised of less than 0.2% (wt.) of 2,5 ditertiarybutyl hydroquinone.
Advantages of the invention will be obvious from the description, or may be learned by practice of the invention. Additional advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory of preferred embodiments of the invention, and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 2722556 (1955-11-01), Young et al.
patent: 3982944 (1976-09-01), Ohi et al.
patent: 4323713 (1982-04-01), Engel
patent: 4323715 (1982-04-01), Engel et al.
patent: 5087771 (1992-02-01), Hilderbrand
patent: 62-81339A (1987-04-01), None
patent: 62-81340A (1987-04-01), None
patent: 32-36340A (1991-10-01), None
Boldea Lucian
Hudnall Phillip Montgomery
Eastman Chemical Company
Graves, Jr. Bernard J.
Shippen Michael L.
Tubach Cheryl J.
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