Distillation: processes – separatory – Adding material to distilland except water or steam per se – At least two materials
Reexamination Certificate
1999-05-21
2001-05-08
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
Adding material to distilland except water or steam per se
At least two materials
C203S061000, C203S096000, C203S099000, C203SDIG002, C203SDIG001, C560S248000
Reexamination Certificate
active
06228226
ABSTRACT:
A process for working up crude, liquid vinyl acetate containing acetic acid and water and also ethyl acetate and possible other impurities.
STATE OF THE ART
Processes for preparing vinyl acetate frequently produce a liquid, crude vinyl acetate which essentially consists of acetic acid and water and ethyl acetate and possibly other impurities. A product of this type can be obtained, for example, in the preparation of vinyl acetate by reacting ethylene and acetic acid and oxygen in the gas phase at elevated temperature and atmospheric or elevated pressure in the presence of a catalyst, cooling the gases leaving the reactor and/or scrubbing them with acetic acid. Such a preparation of vinyl acetate is generally carried out with excess acetic acid with the unreacted acetic acid being recirculated to the vinyl acetate preparation.
A workup of crude, liquid vinyl acetate which is accessible from such a preparation process and which still contains acetic acid and water and ethyl acetate and possibly other impurities is described in DE-B 1 768 412. In this process, the crude vinyl acetate is distilled azeotropically, recycling the vinyl acetate obtainable by condensation and phase separation of the overhead product withdrawing overhead the majority of the water together with vinyl acetate and recirculating enough vinyl acetate so that, as bottom product, an acetic acid is obtained which contains about 0.5 to 6% by weight of water. If appropriate, from this distillation, a liquid side stream can be taken off in which ethyl acetate is enriched. The vinyl acetate which is obtainable after condensation and phase separation of the gaseous overhead product contains about 100 to 500 ppm by weight of ethyl acetate.
A further known process for working up crude vinyl acetate is described in DE-C1 282 014 and DE-C1 668 063. In this case, in a first distillation column, the water, as an azeotropic mixture, and the by-product boiling lower than vinyl acetate are distilled overhead and the virtually water-free bottom product is distilled in a second distillation column, vinyl acetate being taken off at the top of the second distillation column, at least the majority of the by-product boiling above vinyl acetate being taken off from one or more enrichment zones between top and bottom and the acetic acid and, if appropriate, the remainder of the by-products, being taken off below the bottom enrichment zone or as bottom product. The vinyl acetate produced in the first column after condensation and phase separation is generally completely recirculated to the first column and vinyl acetate is only taken off from the top of the second column. According to the teaching of DE-C1 668 063, if the pressure in the first distillation column is increased from atmospheric pressure to 1 atm gauge, with about half the reflux rate, the same amount of water is discharged at the top of the second column. No information is given on the water content of the gaseous overhead product of the first column and the ethyl acetate content in the vinyl acetate taken off is about 1000 ppm.
DE-A 2 943 985 describes a process for separating off water from mixtures with vinyl acetate and acetic acid, in which a condensate obtained by cooling the gas mixture exiting from the reaction zone and containing the majority of the acetic acid, the vinyl acetate and the water and which contains a solution obtained by adsorption with acetic acid, which solution contains the non-condensed residual vinyl acetate and water, are applied to various plates in a distillation column. The overhead product can then contain approximately 3 to 5% by weight of water. Whether crude vinyl acetate containing ethyl acetate can be worked up in such a manner and what contents of ethyl acetate are then present in the vinyl acetate taken off is not disclosed in this DE-A.
Finally, DE-B 1 618 240 describes separating off ethyl acetate from vinyl acetate, in which separating an extractive distillation with water as entrainer is carried out. At a weight ratio of water to organic crude charge consisting of 99.8% by weight of vinyl acetate and 0.2% by weight of ethyl acetate, of 0.19:1 and at a reflux ratio of approximately 3:1, an overhead stream of purified vinyl acetate which contains less than 500 ppm by weight of ethyl acetate, based on vinyl acetate, is taken off. However, in this process, the vinyl acetate feed contains no significant quantities of water and/or acetic acid.
Furthermore, U.S. Pat. No. 3,404,177 discloses a process for separating vinyl acetate, water, acetic acid and, if appropriate, acetaldehyde, from gaseous reaction mixtures. Such reaction mixtures also contain ethylene, oxygen and CO
2
. Ethyl acetate and its removal are not disclosed in this publication. Effects accompanied by water feed or azeotrope formation likewise not.
Finally, EP-B-0 072 484 discloses a process for working up by distillation crude, liquid vinyl acetate containing acetic acid and water and also ethyl acetate and possibly small amounts of impurities, an essentially vinyl-acetate- and water-containing mixture being obtained as overhead product, and essentially acetic acid being obtained as bottom product, and a side stream being taken off in which ethyl acetate is enriched, with the overhead product being condensed and, after phase separation, some of the vinyl acetate phase being recirculated as reflux to the distillation, which comprises introducing 0.1 to 5% by weight of water, based on the crude, liquid vinyl acetate feed, into the distillation above the feed point of the crude, liquid vinyl acetate. This known process leads to a sufficient dewatering in the distillation and to a reduction of the ethyl acetate content in the vinyl acetate obtained as overhead product.
DE-A-2 132 299 discloses that liquid vinyl-acetate- and ethyl-acetate-containing mixtures can be subjected to an extractive distillation using acetic acid as entrainer. The disclosed process leads to a reduction in the ethyl acetate content in the vinyl acetate taken off at the column top to approximately 200 ppm by weight. According to the teaching of DE-A-2 132 299, however, 60 g of acetic acid must be fed per 100 g of crude, liquid vinyl acetate used.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an improved process for the purification of crude, liquid vinyl acetate containing acetic acid, water and ethyl acetate.
This and other objects and advantages of the invention will become obvious from the following detailed description.
THE INVENTION
The novel process of the invention for purifying crude, liquid vinyl acetate feed containing acetic acid, water and ethyl acetate and optionally small amounts of other impurities comprises distilling said crude vinyl acetate to remove vinyl acetate and water as overhead product and acetic acid as bottom product while recovering a side stream of enriched ethyl acetate, condensing the overhead product, effecting phase separation and recirculating some of the vinyl acetate as reflux in the distillation column, the improvement comprising introducing into the distillation column above the feed point of the crude, liquid vinyl acetate feed 0.1 to 5% by weight of water and 0.1 to 60% by weight of acetic acid, both based on the crude, liquid vinyl acetate feed.
Surprisingly, it has been found that the ethyl acetate content in the gases leaving the distillation at the top decreases and may be increased in the side stream leaving the distillation and the vinyl acetate discharge via this side stream is decreased if 0.1 to 5% by weight of water, based on the crude, liquid vinyl acetate feed, and 0.1 to 60% by weight of acetic acid, based on the crude, liquid vinyl acetate feed, are introduced into the distillation column above the feed point of the crude, liquid vinyl acetate.
The present invention therefore relates to a process for working up crude, liquid vinyl acetate containing acetic acid and water and also ethyl acetate and possibly small amounts of other impurities by distillation, a mixture essentially consisting of vinyl acetate and water bein
Hess Stefan
Mark Michael
Meilchen Melchior A.
Stamm Johann
Vernaleken Thomas
Bierman, Muserlian and Lucas
Celanese GmbH
Manoharan Virginia
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