Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-07-13
2002-08-20
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S866000, C568S868000, C568S872000
Reexamination Certificate
active
06437199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for the production of high-purity monoethylene glycol. More particularly, it relates to a method for producing a high-purity monoethylene glycol possessing a fiber-grade quality and excelling in thermal stability by using as the raw material for a hydration reaction an unpurified crude ethylene oxide obtained during the course of producing and purifying ethylene oxide by catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst.
2. Description of the Prior Art:
Among the conventional methods for producing ethylene glycol by using as the raw material for a hydration reaction an unpurified crude ethylene oxide obtained during the course of manufacture of ethylene oxide by catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst, there have been counted (1) a method which as described in JP-B-61-3,772 comprises condensing the vapor emanating from the top of an ethylene oxide stripper in two condensers, refluxing the condensate to the stripper, forwarding the uncondensed gas to a third condenser and condensing the gas therein, forwarding the resultant condensate to a hydration reaction vessel, and carrying out a reaction of conversion to glycol, (2) a method which as described in U.S. Pat. No. 3,904,656 comprises guiding a gas emanating from the top of a stripper to a reabsorption column, performing therein absorption of the gas with an absorbing liquid having water as a main component thereof, forwarding the absorbing liquid having absorbed ethylene oxide to a hydration reaction vessel, and carrying out a reaction of the absorbing liquid, and (3) a method which as described in U.S. Pat. No. 3,964,980 comprises condensing the gas arising from the top of a stripper by a condenser, returning the condensate as reflux to the stripper, guiding the uncondensed gas to a reabsorption column to be absorbed therein, guiding the absorption liquid having absorbed the produced ethylene oxide to a hydration reaction vessel to be subjected to reaction therein.
U.S. Pat. No. 4,349,417 discloses a method for the production of high-purity monoethylene glycol, characterized by adding an aqueous alkalimetal compound solution to the reaction product between a hydration reaction vessel and a monoethylene glycol rectification column adapted to distil monoethylene glycol through the top thereof and effecting this addition of the reaction product in an amount such that the reaction product, while entering the monoethylene glycol rectification column, assumes a pH value in the range of 7-10. In U.S. Pat. No. 4,349,417 mentioned above, in disclosing the invention, makes no mention of the fact that the ethylene oxide (crude ethylene oxide) as the raw material for the hydration reaction incorporates such organic chlorine compounds as ethylene dichloride and ethylene chlorohydrin as extraneous matter. It discloses absolutely no knowledge concerning the technical problem which arises from the use of the raw material for the hydration reaction containing such organic chlorine compounds and the measure for the solution thereof.
We have proposed as in JP-B-61-3,772 a method for producing high-purity monoethylene glycol by using as the raw material for a hydration reaction the unpurified crude ethylene oxide obtained during the course of manufacture of ethylene oxide by catalytic vapor phase oxidation of ethyene with a molecular oxygen-containing gas. This method implements the manufacture of monoethylene glycol without requiring addition of an alkali because the process involved therein has no need for consideration about a measure to cope with the organic chloride compounds arising from the chlorine compound in the crude ethylene oxide.
No method has been heretofore proposed to date which produces high-purity monoethylene glycol by using as the raw material for a hydration reaction an unpurified crude ethylene oxide containing organic chloride compounds. Such is the true state of prior art.
When the hydration reaction is carried out with the liquid which is obtained by condensing the gas arising from the top of an ethylene oxide stripper, refluxing the condensate, and cooling or absorbing the uncondensed gas as contemplated by the conventional method, the ethylene oxide obtained from the uncondensed gas at the first stage does not include most of chloride compounds because the chlorine compounds migrate into the condensate at the first stage or to the bottoms of the column. It may well be concluded, therefore, that the ethylene glycol to be obtained by hydrating this ethylene oxide contains such chlorine compounds only in an amount deserving to be called “trace.”
We, not satisfied with the prior art and with a view to further simplifying the process for the production of monoethylene glycol and saving the energy consumed therein, have studied the feasibility of using as the raw material for the hydration reaction the unpurified crude ethylene oxide obtained without refluxing the top of an ethylene oxide stripper during the manufacture of ethylene oxide by catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst. We have consequently found that when the unpurified crude ethylene oxide is used as the raw material for the hydration reaction, the monoethylene glycol product consequently obtained offers no sufficient stability to withstand the heating and could not afford a fiber grade product.
Specifically, during the manufacture of ethylene oxide by catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst, such organic chloride compounds as ethylene dichloride and ethylene chlorohydrin emanate from the top of an ethylene oxide stripper in conjunction with ethylene oxide and the like. It has been found that notwithstanding such organic chlorine compounds are removed by a subsequent operation of separation by distillation, the monoethylene glycol obtained by using the condensate obtained from the gas emanating from the top of the ethylene oxide stripper in its unmodified form as the raw material for the hydration reaction is destined to entrain as a foreign matter the chlorine compounds in an amount corresponding to 10-20% of the organic chlorine compounds which are present in the raw material for the hydration reaction.
We, therefore, have made a diligent study with a view to elucidating the cause for this persistent adulteration of the monoethylene glycol and have been consequently ascertained that the monoethylene glycol as a finished product has such qualities as thermal stability degraded because the inorganic chlorine originating in the organic chlorine compounds such as ethylene dichloride which are contained in the unpurified crude ethylene oxide (which are added during the process for the production of ethylene oxide by catalytic vapor phase oxidation of ethylene with a molecular oxygen-containing gas in the presence of a silver catalyst) emerges in the hydration reaction solution and, consequently, such impurities as ethylene chlorohydrin are formed during the process of dehydration of ethylene glycol and are suffered to mingle as foreign matter into the rectified monoethylene glycol.
We have studied from various angles the process for the production of monoethylene glycol with a view to simplifying the process of production, saving the energy spent therein, and reducing the cost of production and have been consequently ascertained that in the conventional technique for producing monoethylene glycol by using as the raw material for the hydration reaction of purified ethylene oxide, the objects mentioned above are accomplished by changing the raw material for the hydration reaction from purified ethylene oxide to unpurified crude ethylene oxide but that this measure not merely fails to bring a sufficient reduction in the concentration of heavy aldehyde, particularly glycol a
Furukawa Makoto
Horie Hironori
Oka Yoshihisa
Sugiyama Yutaka
Suzuki Kenji
Barts Samuel
Nippon Shokubai Co. , Ltd.
Price Elvis O.
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