Distillation: processes – separatory – With measuring – testing or inspecting
Reexamination Certificate
1999-02-01
2002-01-08
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
With measuring, testing or inspecting
C159S049000, C203S072000, C203S084000, C203S089000, C203S098000, C203SDIG009
Reexamination Certificate
active
06336997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for refining a heat deteriorative compound, contained in a multi-component liquid mixture, by distillation. More particularly, the present invention relates to a process for refining a heat deteriorative compound, for example, hydroquinone or catechol which are consumed by thermal decomposition, thermal modification or thermal polymerization when heated, and contained in a multi-component liquid mixture, by a specific distillation procedure by which the multi-component liquid mixture is separated, at a temperature lower than the heat deterioration-starting temperature of the heat-deteriorative compound, into a liquid fraction containing a higher boiling temperature component including the heat-deteriorative compound and a vapor fraction containing a lower boiling temperature component which is substantially free from the heat-deteriorative compound and is removed from the multi-component liquid mixture.
2. Description of the Related Art
It is known that a reduced pressure (vacuum) distillation apparatus equipped with a liquid film-falling reboiler attached to a distillation column is advantageous in that the liquid mixture can be distilled even under a reduced pressure, while keeping the temperature of a liquid fraction accumulated in a bottom portion of the distillation column at a relatively low level, and is thus widely utilized for various distillations which must be carried out at a relatively low distillation temperature.
When the conventional distillation apparatus comprising a distillation column, which may be a reduced pressure distillation column and a liquid film-falling reboiler attached to the distillation column, is used to distil, optionally under a reduced pressure, a liquid mixture containing a heat-deteriorative compound, and a liquid fraction generated in the distillation column is fed into the reboiler and falls in the form of liquid films through a plurality of heat-conductive pipes of the reboiler, such a disadvantageous phenomenon that the falling liquid films are broken on portions of the inner surfaces of the heat conductive pipes, and thus the portions of the inner surfaces of the heat conductive pipes are directly exposed to the air atmosphere without being covered by the falling liquid film of the liquid fraction, may occur. When the phenomenon occurs, the portions of the inner surfaces not covered by the falling liquid films are locally over-heated to a higher temperature than the temperature of the other portions of the inner surfaces, and thus portions of the falling liquid films located in boundaries between the liquid film-covered portions and non-covered portions of the inner surfaces of the heat conductive pipes are also locally overheated to a higher temperature than that of the other portions. Accordingly, the heat-deteriorative compound contained in the locally over-heated portions of the falling liquid films is thermally deteriorated to a great extent. Therefore, the heat deteriorative compound contained in the liquid mixture is converted to a high boiling temperature substance (for example, polymer), a thermally decomposed product or a thermally modified product, and consumed in a high proportion during the distillation procedure in the reboiler. In a certain case in which the resultant high boiling temperature substance, for example, a polymeric substance, deposits on and adheres to the inner surfaces of the heat conductive pipes, to form scale, the resultant scale causes the falling of the liquid film along the inner surfaces of the heat conductive pipes to be obstructed and finally stopped, and thus the distilling procedure must be stopped after a short time.
For example, in a conventional process for producing an alkyl ether of an aromatic dihydroxyl compound by an etherifying reaction of an aromatic dihydroxyl compound, for example, hydroquinone or catechol with a lower alkyl alcohol, for example, methyl alcohol or ethyl alcohol, the reaction product liquid comprising a lower boiling temperature component containing the non-reacted lower alkyl alcohol and a higher boiling temperature component containing the non-reacted aromatic dihydroxyl compound and the resultant alkyl ether of the aromatic dihydroxyl compound is distilled by a conventional distillation procedure at a high temperature to collect the target reaction product and to recover the non-reacted compounds. In this conventional distillation procedure, the aromatic dihydroxyl compound which exhibits a high thermal deterioration property is concentrated and thermally deteriorated at the high temperature. The thermal deterioration results in a disadvantageous consumption or loss of the aromatic dihydroxyl compound. Also, in a certain case, the heat-deterioration product deposits and adheres to an inner surface of a heater (or reboiler) of the distillation apparatus and the continuous distilling procedure over a long time is obstructed.
Namely, in the process for producing the alkyl ether of the aromatic dihydroxyl compound, no specific method of refining the target aromatic dihydroxyl compound and of recovering the non-reacted lower alkyl alcohol and aromatic dihydorxyl compound, without heat deterioration of the aromatic dihydroxyl compound has yet been concretely provided.
As mentioned above, the reduced pressure (vacuum) distillation apparatus including the liquid film-falling reboiler attached to a distillation column is advantageous in that the liquid fraction accumulated in the bottom portion of the distillation column can be distilled even under a reduced pressure without a need of heating to a high temperature. Therefore, the reduced pressure distillation apparatus can be used for a distillation procedure for a liquid mixture containing the alkyl ether of aromatic dihydroxyl compound produced by the reaction of the alkyl alcohol with the aromatic dihydroxyl compound.
However, when the distillation procedure is carried out under conventional conditions, the liquid films falling along the inner surfaces of the heat conductive pipes of the reboiler are frequently broken and thus the heat-deteriorative compound contained in the liquid film is thermally deteriorated as mentioned hereinbefore. No specific means for preventing the breakage of the falling liquid films on the inner surfaces of the heat conductive pipes of the reboiler has been known.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for refining a heat-deteriorative compound contained in a multi-component liquid mixture by using a distillation column and a liquid film falling reboiler attached to the distillation column and having a plurality of vertical heat-conductive pipes through which a liquid fraction generated from the liquid mixture in the distillation column and containing the heat-deteriorative compound falls in the form of liquid films along the inner surface of the vertical pipes while being heated and evaporated, in which process, local breakages of the liquid films on the inner surface of the vertical pipes can be prevented, to protect the heat-deteriorative compound in the liquid fraction from heat-deterioration in the reboiler, and thus the heat-deteriorative compound contained in the liquid mixture can be continuously concentrated and refined with a high stability and with a high yield over a long time period.
The above-mentioned object can be attained by the process of the present invention for refining a heat-deteriorative compound, contained in a multi-component liquid mixture, by distillation, which comprises the steps of:
(1) feeding a multi-component liquid mixture comprising a lower boiling temperature component and a higher boiling temperature component containing a heat-deteriorative compound, into a distillation column having a top outlet located in a top portion of the distillation column and a bottom outlet located in a bottom portion of the distillation column, the bottom outlet being connected to a liquid film-failing reboiler having a plurality of h
Fujita Kazunori
Inaba Yukio
Kofuji Hiroshi
Manoharan Virginia
Morgan & Lewis & Bockius, LLP
Ube Industries Ltd.
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