Distillation: processes – separatory – Adding material to distilland except water or steam per se – Organic compound
Reexamination Certificate
1999-04-26
2001-11-13
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
Adding material to distilland except water or steam per se
Organic compound
C203S060000, C203S063000, C203S064000, C203S065000, C203S099000, C203SDIG001, C203SDIG002, C558S277000, C568S913000
Reexamination Certificate
active
06315868
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of separating dimethyl carbonate and methanol by extractive distillation. The extractive distillation is conducted in the presence of an extractive distillation agent which modifies the azeotropic behavior of the dimethyl carbonate/methanol mixture.
BACKGROUND OF THE INVENTION
Dimethyl carbonate is useful as a starting material in the synthesis of aromatic polycarbonates, as a solvent, and as a reactant in the production of a number of chemical products. Dimethyl carbonate is often present in a mixture with methanol. In various processes to produce dimethyl carbonate, for instance, dimethyl carbonate is obtained in a mixture with methanol. Dimethyl carbonate and methanol form an azeotropic composition having a weight ratio of dimethyl carbonate to methanol of about 30:70 at atmospheric pressure.
It is necessary, therefore, to separate the dimethyl carbonate from the dimethyl carbonate/methanol mixture. Processes used to separate the azeotropic mixture of dimethyl carbonate and methanol include pressure swing distillation, high pressure distillation and extractive distillation.
Extractive distillation is a method to separate components of a mixture that exhibits azeotropic behavior. In an extractive distillation process, an agent, herein referred to as an “extractive distillation agent” is added to mixture of components to be separated in the distillation process, so that the relative volatilities of the components of the mixture are changed. The change in relative volatilities is such that a sufficient difference in volatility of the components results, and effective separation by distillation becomes possible.
U.S. Pat. No. 5,292,917 discloses a process for the extractive distillation of a dimethyl carbonate/methanol mixture by distilling the mixture in the presence of dimethyl oxalate. Two distillation columns are used in series to separate the dimethyl carbonate from the methanol. In the first column, methanol is removed at the top of the column, and the dimethyl carbonate/dimethyl oxalate mixture is fed to the second column. In the second column, the dimethyl carbonate is separated from the dimethyl oxalate.
Japanese Publication 06228026, published on Aug. 16, 1994, discloses a method of extractive distillation of a mixture of methyl carbonate and methanol in the presence of an extractive agent selected from a group of compounds, including anisole.
Japanese Publication 06016596, published on Jan. 25, 1994, discloses a method of separating dimethyl carbonate from methanol by refluxing the dimethyl carbonate/methanol mixture in the presence of an organic solvent, e.g. phenol, and removing methanol as an overhead product and a mixture of the organic solvent and dimethyl carbonate as the bottom product.
Known methods for separating a dimethyl carbonate/methanol mixture involve at least two distillation columns. Therefore, there exists a need for a simplified and more economical process for separating a dimethyl carbonate/methanol mixture.
SUMMARY OF THE INVENTION
The present invention simplifies the process and provides further surprising properties. These and further properties of the invention will be more readily appreciated when considering the following disclosure and appended claims.
The present invention concerns a method of separating dimethyl carbonate and methanol from a mixture comprising dimethyl carbonate and methanol in a single distillation column, the method comprising the steps of:
A) distilling a mixture comprising dimethyl carbonate and methanol in the presence of an extractive distillation agent selected from the group consisting of an aromatic hydroxy compound, an alkyl aryl ether, a dialkyl carbonate, an alkyl aryl carbonate, a diaryl carbonate, an alkylene carbonate and an alicyclic alcohol; and
B) removing a side stream comprising primarily dimethyl carbonate from the distillation column.
The invention further concerns a method for purifying dimethyl carbonate in a single distillation column comprising the steps of:
A) feeding a dimethyl carbonate/methanol feed stream comprising dimethyl carbonate and methanol and a second stream comprising an extractive distillation agent into the distillation column, the dimethyl carbonate/methanol feed stream being fed into the extractive distillation column below the second stream, the extractive distillation agent selected from the group consisting of an aromatic hydroxy compound, an alkyl aryl ether, a dialkyl carbonate, an alkyl aryl carbonate, a diaryl carbonate, an alkylene carbonate and an alicyclic alcohol;
B) distilling the dimethyl carbonate and methanol in the presence of the extractive distillation agent in the distillation column and;
C) removing an overhead product stream, a side product stream, and a bottom product stream from the distillation column, the overhead product stream comprising primarily methanol, the side product stream comprising primarily dimethyl carbonate and the bottom product stream comprising primarily the extractive distillation agent.
In the present invention, a side stream distillation column replaces two distillation columns, each having a reboiler and condenser. The side stream distillation column may be used with a side rectification column if a higher purity product is desired. In the embodiment where a side rectification column is used, the side rectification column is coupled to the side stream distillation column.
REFERENCES:
patent: 4162200 (1979-07-01), Himmele et al.
patent: 4310388 (1982-01-01), Volkamer et al.
patent: 5292917 (1994-03-01), Nishihira et al.
patent: 5426207 (1995-06-01), Harrison et al.
patent: 581115A2 (1994-02-01), None
patent: 6016596 (1994-01-01), None
patent: 6228026 (1994-08-01), None
Patent Abstracts of Japan, vol. 018, No. 222 (C-1193), Apr. 21, 1994.
Chemical Abstracts, vol. 130, No. 1, Jan. 4, 1999.
CN 1 212 172 A (China Petrochemical Corp.) Mar. 31, 1999, Chemical Abstracts, vol. 133, No. 1.
Bouwens Stephan Mathijs
Doherty Michael Francis
Malone Michael Francis
Nisoli Alberto
Caruso Andrew J.
General Electric Company
Ingraham Donald S.
Manoharan Virginia
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