Distillation: processes – separatory – With measuring – testing or inspecting – Of temperature or pressure
Reexamination Certificate
2000-10-18
2002-08-20
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
With measuring, testing or inspecting
Of temperature or pressure
C203S014000, C203S071000, C548S552000, C548S555000
Reexamination Certificate
active
06436243
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS
This invention relates to a process for recovering N-vinyl-2-pyrrolidone. N-vinyl-2-pyrrolidone is a useful compound as a raw material monomer for preparing poly-N-vinyl-2-pyrrolidone having wide uses in the fields of medicine, food additives, personal care products, etc.
Prior Art
N-vinyl-2-pyrrolidone has been industrially manufactured by the Reppe process wherein 2-pyrrolidone and acetylene are reacted in a liquid phase under pressure in the presence of an alkali catalyst. However, the Reppe process has various problems, for example that there is a danger that acetylene causes explosion under high pressures, the catalyst preparation step is complicated for preventing the lowering of reaction yield and reaction control such as the control of 2-pyrrolidone conversion is complicated.
Therefore, a preparation process of N-vinyl-2-pyrrolidone not using acetylene as a raw material has been desired, and, for example, various processes have been tried using as a raw material N-(2-hydroxyethyl)-2-pyrrolidone obtained in a good yield by reaction of &ggr;-butyrolactone with monoethanolamine.
For example, there have been proposed a process which comprises dehydrochlorinating N-(2-chloroethyl)-2-pyrrolidone obtained by reaction of N-(2-hydroxyethyl)-2-pyrrolidone with octynyl chloride (U.S. Pat. No. 2,775,599), a process which comprises removing acetic acid from the acetic ester intermediate obtained by reaction of N-(2-hydroxyethyl)-2-pyrrolidone with acetic anhydride, etc. However, since these via intermediate processes have problems that the auxiliary raw material equivalent to N-(2-hydroxyethyl)-2-pyrrolidone is necessary, and more over, intermediate preparation costs a great deal and a large amount of by-products derived from the auxiliary raw material are formed, these cannot be said to be excellent production processes from the industrial viewpoint.
Thus as a process for solving the problems is proposed in Japanese Laid-open Patent Publication No. 8-141402 a process of preparing N-vinyl-2-pyrrolidone by intramolecularly dehydrating N-(2-hydroxyethyl)-2-pyrrolidone in a vapor phase in the presence of a catalyst. In the production process, the raw material N-(2-hydroxy-ethyl)-2-pyrrolidone is easy to get and inexpensive because it is prepared in a good yield by reaction of &ggr;-butyrolactone with monoethanolamine. Further in the production process, no raw material other than N-(2-hydroxyethyl)-2-pyrrolidone is needed, and moreover, the reaction selectivity can be increased by appropriately selecting the kind of catalyst and reaction conditions.
The condensate formed by the reaction in the production process is a mixed liquid having a complicated composition comprising the desired product N-vinyl-2-pyrrolidone, a by-product water, 2-pyrrolidone as a decomposition product of N-(2-hydroxyethyl)-2-pyrrolidone and the unreacted raw material N-(2-hydroxyethyl)-2-pyrrolidone, etc., but there is no disclosure in the above official gazette about a process for recovering N-vinyl-2-pyrrolidone from this mixed liquid in high purity.
Problem to be Solved by the Invention
N-vinyl-2-pyrrolidone is known to be radically polymerized or thermally decomposed by heating and hydrolyzed in the presence of water. Therefore, when N-vinyl-2-pyrrolidone is recovered by a distillation operation from the condensate formed by the reaction in the process of the official gazette, etc., there arises a problem depending on the distillation condition, for example that the recovery percentage of N-vinyl-2-pyrrolidone is lowered by thermal polymerization or thermal decomposition thereof, or polymers are accumulated in the equipment to bring about apparatus troubles.
Thus the object of the invention lies in solving the so far found problem, namely providing a process for recovering N-vinyl-2-pyrrolidone which makes it possible to recover chemically unstable N-vinyl-2-pyrrolidone efficiently and steadily and in high purity by continuous distillation from a mixed liquid having a complicated distillation composition containing N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone and water.
Means for Solving the Problem
The present inventors have vigorously studied for providing a recovery process of N-vinyl-2-pyrrolidone, ans as a result they have found that in recovering N-vinyl-2-pyrrolidone by continuously distilling a mixed liquid containing N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, compounds having a higher boiling point than N-vinyl-2-pyrrolidone and water, thermal polymerization and thermal decomposition of N-vinyl-2-pyrrolidone can be inhibited and N-vinyl-2-pyrrolidone can be recovered efficiently and steadily and in high purity by controlling the temperature of the bottom liquid of the distilling column.
Thus, according to the invention is provided in a process for recovering N-vinyl-2-pyrrolidone by continuously distilling a mixed liquid containing N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, compounds having a higher boiling point than N-vinyl-2-pyrrolidone and water using a distilling column, the improvement comprising carrying out the distillation controlling the temperature of the bottom liquid of the distilling column to 180° C. or less to make water distill as the distillate, and, on the other hand, withdrawing the bottom residue comprising N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone and the compounds having a higher boiling point than N-vinyl-2-pyrrolidone.
It is preferred to continuously distill the bottom residue withdrawn from the distilling column (the first distilling column) using a second distilling column to make N-vinyl-2-pyrrolidone distill as the distillate, and, on the other hand, withdraw the bottom residue comprising N-(2-hydroxyethyl)-2-pyrrolidone and the compounds having a higher boiling point than N-vinyl-2-pyrrolidone.
It is preferred to operate the second distilling column controlling the temperature of the bottom liquid to 230° C. or less.
The process of the invention is particularly useful when the mixed liquid fed for distillation, namely the mixed liquid comprising N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, the compounds having a higher boiling point than N-vinyl-2-pyrrolidone and water is a liquid obtained by cooling collecting the vapor phase dehydration reaction product of N-(2-hydroxyethyl)-2-pyrrolidone.
Mode for Carrying out the Invention
The liquid as the object of distillation operation in the recovery process of N-vinyl-2-pyrrolidone according to the invention is a mixed liquid containing N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, the compounds having a higher boiling point than N-vinyl-2-pyrrolidone and water, as hereinbefore described. Such a mixed liquid can, for example, be obtained readily by the production process disclosed in Japanese Laid-open Patent Publication No. 8-141402 or the like. Specifically, a liquid collected by cooling an N-vinyl-2-pyrrolidone-containing product obtained by intramolecularly dehydrating N-(2-hydroxyethyl)-2-pyrrolidone in a vapor phase in the presence of a catalyst is mentioned, but no particular limitation thereto is made.
As the compounds having a higher boiling point than N-vinyl-2-pyrrolidone, there can specifically mentioned, besides 2-pyrrolidone, tar-like substances such as the dimer of N-vinyl-2-pyrrolidone, but no particular limitation thereto is made.
When the mixed liquid containing N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, compounds having a higher boiling point than N-vinyl-2-pyrrolidone and water is continuously distilled in the first distilling column, it is pertinent that the temperature of the bottom liquid is 180° C. or less, preferably 165° C. or less. In this apparatus, water distills and is removed and N-vinyl-2-pyrrolidone is withdrawn as the bottom residue. Since when the temperature of the bottom liquid is more than 180° C., thermal polymerization or thermal decomposition of N-vinyl-2-pyrrolidone contained in the bottom liquid is accelerated, the recovery percentage of N-vinyl-2-
Kurusu Akira
Shimasaki Yuuji
Yamaguchi Yoshinari
Yano Hitoshi
Manoharan Virginia
Nippon Shokubai Co LTD
Sherman & Shalloway
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