Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-08-27
2004-02-24
Davis, Brian (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S477000
Reexamination Certificate
active
06696610
ABSTRACT:
The invention relates to a continuous process for the preparation of monoethanolamine, diethanolamine and triethanolamine by reacting ammonia in ethylene oxide with liquid phase in the presence of water.
On an industrial scale, ammonia is reacted with ethylene oxide in the presence of water as catalyst to prepare the ethanolamines monoethanolamine, diethanolamine and triethanolamine, referred to below in abbreviated form as MEA, DEA and TEA, respectively, by irreversible reactions according to the following equations
NH
3
+C
2
H
4
O→NH
2
C
2
H
4
OH
Usually, a particularly high proportion of MEA is desired, as is one of DEA, whereas TEA should usually represent the smallest possible proportion of the ethanolamine mixture obtained since there is another more economical preparation route for this. Since the consecutive reactions to DEA and/or TEA each have rate constants which exceed those of the reaction to give MEA by in each case about 10 times, a high ammonia to ethylene oxide ratio in the reaction zone is a prerequisite for a high proportion of MEA in the product mixture of the ethanolamines. A high excess of ammonia, however, has the disadvantage, where it is also retained in the product mixture, that it has to be recovered again, which involves extra expenditure.
According to a known process, a continuously operated tubular reactor is used for the production of ethanolamines. In order to obtain a proportion by weight of MEA in the product mixture of the ethanolamines of 60% by weight, a molar feed ratio of ammonia to ethylene oxide in the reactor feed of 10:1 must be used. To separate the product mixture, at least one distillation column is required to separate off ammonia and a further distillation column is required to separate off water, in each case as overhead take-off. The ammonia/water mixture which forms in high excess, corresponding approximately to three times the product mixture of the ethanolamines, in each case in mass flows, is returned to the tubular reactor. In order to set the monoethanolamine proportion in the resulting ethanolamine mixture to a value in the frequently desired range between 35 and 80% by weight, it would be necessary in this procedure to vary the molar feed ratio of ammonia to ethylene oxide in the range between 5:1 and 30:1. This would require a high flexibility in the ammonia separation, which can only be achieved with high technical complexity.
Japanese laid-open specification JP 2887/77 discloses a process for the preparation of ethanolamines by reacting ammonia with ethylene oxide in the presence of water, a significantly higher ammonia to ethylene oxide ratio in the reaction zone compared with the reactor feed and thus an increased proportion of monoethanolamine in the product mixture of the ethanolamines being achieved by providing gas-liquid contact surfaces (evaporation surfaces) in the reactor, on which the ammonia evaporates as a result of the heat of the reaction, then condenses and the condensate is returned to the reaction zone. The temperature and thus the pressure in the reactor is regulated by the amount of evaporated ammonia. The ammonia:ethylene oxide molar ratio in the reactor feed is, for example, 3.5:1. The reactor is regulated by maintaining the ammonia content at the reactor outlet, based on the ethanolamines, to 30 mol % or more.
The process thus permits an increased proportion of the especially desired MEA in the product mixture of the ethanolamines with a simultaneously lower ammonia excess in the ammonia/ethylene oxide feed stream compared with the known process in the tubular reactor, by utilizing the heat of the reaction for evaporating ammonia. The available heat of the reaction, however, at the same time limits the scope with regard to MEA to DEA to TEA ratio in the product mixture of the ethanolamines. In order to obtain higher proportions of MEA in the product mixture, it is necessary to use an increased ammonia excess in the feed stream, with the disadvantage that the reactor discharge has a relatively high proportion of ammonia and thus the work-up of the reactor discharge with recovery of the ammonia is complex, in particular is not possible in a single atmospheric-pressure column whose head condenser can be cooled with river water. The weight ratio of MEA to DEA to TEA in the product mixture can thus not be regulated as desired.
It is an object of the present invention to provide a process for the preparation of MEA, DEA and TEA which is more economical, in particular requires lower investment costs, and which is more flexible, in particular ensures a change in the relative concentrations of the ethanolamines in the product mixture as required, and where the product discharge can always be adjusted so that the purification of ethanolamine by distillation and ammonia/water recovery are possible in a single distillation column with a cost-effective configuration, i.e. in particular at atmospheric pressure and using river water for the condensation.
We have found that this object is achieved by a continuous process for the preparation of monoethanolamine, diethanolamine and triethanolamine by reacting ammonia with ethylene oxide in the liquid phase in the presence of water as catalyst in a pressure column, where, as a result of the heat of the reaction, some of the ammonia evaporates, condenses at the head of the column and is again charged to the column, the reaction mixture is drawn off at the lower end of the pressure column and is then separated.
The invention involves the pressure column being constructed as a reactive distillation column with evaporator at the bottom and, by means of the input of energy via the evaporator at the bottom, regulating the weight ratio of monoethanolamine to diethanolamine to triethanolamine and, via the ratio of ammonia to ethylene oxide in the feed to the reactive distillation column, regulating the ammonia proportion in the bottom product from the reactive distillation column.
It has been found that, despite the safety problems in the handling of ethylene oxide, the reaction of ammonia with ethylene oxide can be carried out in a reactive distillation column and in this connection, by means of inputting energy via the evaporator at the bottom of the reactive distillation column, it is possible to control the ratio of ethanolamines to one another, it being possible to simultaneously regulate the ammonia content in the bottom product via the ratio of ammonia to ethylene oxide with the feed to the reactive distillation column always in such a way that the separation of the bottom product into the ethanolamines and into ammonia-water is possible in a cost-effective manner in a single distillation column.
With regard to the reactive distillation columns which can be used, there are in principle no limitations; suitable columns are all those in which a chemical reaction and separation by distillation or rectification can be carried out.
The reactive distillation column preferably contains plates as separation-effecting internals; plate columns have the advantage that a sufficiently high hold-up is available for the reaction of ammonia with ethylene oxide.
A feed stream of ammonia and ethylene oxide, preferably in vapor form, is fed to the reactive distillation column, in the upper part thereof, preferably above the uppermost column plate. For a reactive distillation column operating under ideal conditions, the stoichiometric ratio of ammonia to ethylene oxide in the feed stream is to be adjusted to correspond to the desired MEA to DEA to TEA ratio in the product mixture. However, in order to ensure that the highly explosive ethylene oxide does not bleed through into the bottom of the column, ammonia is preferably introduced in a slightly stoichiometric excess, i.e. with a molar ratio toward ethylene oxide in the range from 3:1 to 1.01:1, particularly preferably with a molar ratio of about 1.3:1. The slight excess of ammonia ensures that ethylene oxide is completely reacted.
The stream of vapors from the reactive distillation column is condensed in a condenser at
Bessling Bernd
Hildebrandt Axel
Peschel Werner
BASF - Aktiengesellschaft
Davis Brian
Keil & Weinkauf
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