CS254480B1 - A method for separating water from aqueous morpholine solutions - Google Patents

Abstract

A method of separating water from aqueous solutions of morpholine, in which a significantly higher efficiency is achieved than in rectification, so that the morpholine content in the separated aqueous phase is lower than 0.2% by weight. A mixture containing morpholine and water is azeotropically rectified in the presence of at least one C^ to C? - alcohol. C^ and C^ -alcohols are added in an amount corresponding to their solubility in the water present in the mixture, Cg and C? -alcohols are added in multiple amounts. The vapors from the top of the column are led to a condenser and the condensate is fed to a phase separator, from which the lower layer containing max. 0.2% by weight morpholine is removed and the alcohol phase is fed back to the top of the column as reflux. The distillation residue contains practically all morpholine and max. 2% by weight water. or morpholine and Cg - or C? - alcohol, which is separated into morpholine and alcohol fractions by rectification.

Description

The invention relates to a method for separating water from aqueous solutions of morpholine, possibly also containing non-volatile substances, in which a significantly higher efficiency is achieved than in rectification, so that the morpholine content in the separated aqueous phase is lower than 0.2 wt.

Aqueous solutions of morpholine can be concentrated by rectification, which, however, requires a high-efficiency column and a high reflux ratio, making the process uneconomical. In the German Patent No. 2,405,911, it is therefore recommended to isolate primary or secondary amines, which also include morpholine, from aqueous organic solutions by distillation or extraction in the presence of carbon dioxide. The reaction of carbon dioxide with primary or secondary amines reduces their volatility, while the solubility of water and other organic compounds remains insignificant. Their solubility in organic solvents is also reduced.

Rectification in the presence of carbon dioxide has lower demands on the efficiency of the column and the reflux ratio, but as stated in the patent specification, during separation it is required to blow such an amount of carbon dioxide into the separated mixture that the ratio G„ _n : ' is 1.8 to 2.5,

CUq steam, while the distillate - water contains 0.1% morpholine and the distillation residue 99.2% morpholine. The column has 15 theoretical plates above the CO2 inlet. The disadvantage of this process is the need to circulate a large stream of carbon dioxide, which requires large investments and operating costs.

Carbon dioxide gas also impairs heat transfer during condensation of the distillate.

According to U.S. Patent No. 2,776,972, morpholine is recovered from a dilute aqueous solution by means of an alkali hydroxide, with which, after mixing, two phases are formed, one containing substantially all of the morpholine and the other consisting of a relatively dilute alkali solution. After separation of the phases, the morpholine phase is further processed by distillation and the hydroxide phase is used to neutralize the reaction solution containing morpholine sulfate and sulfuric acid.

When implementing this method for obtaining morpholine from aqueous solutions, a new problem arises: how to process and utilize the relatively concentrated hydroxide solution if there is no use for it. Also, further concentration of the morpholine phase by distillation is not very effective, which is why new and more efficient methods are sought.

The method of production and isolation of morpholine is also the subject of Czechoslovak patent No. 146 401. According to it, morpholine is obtained by condensation reaction of diethanolamine, using excess sulfuric acid. The resulting morpholine, after liberation by neutralization with sodium hydroxide, is isolated by azeotropic distillation using an organic solvent or a mixture of solvents miscible with morpholine and preferably miscible with water, with a boiling point at least 10 °C below the boiling point of morpholine and forming an azeotropic mixture with water, with a boiling point at least 10 °C below the boiling point of the solvent, such as e.g. benzene, cyclohexane, trichloroethylene.

According to the data given in Example 5, the distillation is carried out without a column using an azeotropic attachment. In azeotropic distillation with benzene, the separated water contains about 3% morpholine, in distillation with toluene, up to 10 to 11% morpholine is contained in the separated water, and in distillation with trichloroethylene, the morpholine content in the separated water is 2 to 3%. Such separation of water from morpholine is insufficient, the water cannot be discharged into the wastewater for ecological reasons and also represents a significant loss in production costs.

The above-mentioned shortcomings are eliminated by the method of separating water from aqueous solutions of morpholine, optionally also containing non-volatile substances, according to the present invention, in which the mixture containing morpholine and water is azeotropically rectified in a column in the presence of at least one of up to C _? , alcohols, whereby C ₄ . and C ₅ alcohols are added to the separated mixture in an amount corresponding to the solubility of these alcohols in the water present in the mixture, C ₈ - and C 10 ~ alcohols are preferably added to the separated mixture of morpholine and water in an amount multiple of that corresponding to the solubility in the water present, usually up to 50% of the total amount of the morpholine-water mixture, the vapors from the top of the column are fed to a condenser and the condensate, preferably after cooling, is fed to a phase separator, from which the lower aqueous phase, saturated with alcohol, containing up to 0.2% by weight. morpholine is removed from the system for further processing or use and the alcohol phase is returned to the top of the column as reflux, the bottom product of the column - distillation residue, contains practically all morpholine, and max. 2% by weight of water or morpholine and Cg or C _? - alcohol, which is separated into morpholine and alcohol fractions by rectification.

From the equilibrium data of the liquid-vapor mixture of water-morpholine, it follows that the relative volatility of water decreases with increasing water concentration, and therefore it is more difficult to obtain pure water at the top of the column (or a lower morpholine content in the distillate than 0.1% by weight) during rectification than pure morpholine at the bottom of the column (or a lower water content in the distillation residue than 0.1% by weight). However, for ecological and economic reasons, it is desirable that the distillate, if it is to be discharged into wastewater, contains less than 0.1% by weight of water.

It is known that by adding a third component to the water-morpholine mixture, the relative volatility of water can be increased. This happens, for example, by adding a substance that forms an azeotropic mixture with water. with a min. boiling point. In a homologous group of substances, the influence of the relative volatility of water with respect to morpholine is greater, the lower the boiling point of the added substance /azeotropic medium/. However, this also has a negative consequence, namely, the water content in the vapor phase decreases and the content of the azeotropic medium increases.

Even more than the boiling point of the azeotropic medium, the relative volatility of water is influenced by the nature of the substance, its polarity, ability to form hydrogen bridges, or react with unstable compounds that decompose into the original substances at the boiling point. We have found that alcohols have such properties, of which the most advantageous are those that have limited solubility in water, form an azeotropic mixture with it with a relatively high water content, and by refluxing the alcoholic phase from the condensate of vapors from the column head, ensure good separation of water and morpholine in the column.

The boiling point of alcohols is not decisive for the choice of azeotropic medium. They can be alcohols with a boiling point lower, equal or higher than the boiling point of morpholine. The boiling point of alcohol, or rather its relative volatility with respect to morpholine, is, however, important for the choice of the azeotropic rectification procedure.

Those alcohols which have the same /or close/ boiling point as morpholine or cannot be separated from morpholine by rectification are added as an azeotropic medium to the separated mixture of morpholine and water only in such an amount that they are sufficient to be completely removed from the system in dissolved or even partially emulsifiable form in the aqueous phase, which is taken from the column as distillate. These are C^- and -alcohols which must be added as an azeotropic medium for the separation of the morpholine-water mixture in an amount corresponding only to the amount withdrawn with the distiller-aqueous phase. Then the distillation residue is free of alcohols and can be considered as a product.

Cg-alcohols and higher have a higher boiling point than morpholine, which can be separated from them relatively easily by rectification.

These alcohols form an azeotropic mixture with water with a relatively high water content and a low alcohol content /1-hexanol-water 75% by weight of water, 1-octanol-water 90% by weight of water/, therefore it is more advantageous to add them as azeotropic media to the morpholine-water mixture in a larger amount than corresponds to the solubility in the withdrawal water as a distillate. In this way, during continuous azeotropic rectification, the alcohol flows through the entire column to the reboiler, increasing the rectification effect in the lower part of the column and compensating for the thus reduced effect in the upper part of the column, caused by the reduced reflux of the alcoholic phase. A favorable effect is also manifested in discontinuous azeotropic rectification, since it reduces the relative volatility of morpholine in the reboiler. However, the bottom product of the column /or reboiler/ is not pure morpholine in this case, but a mixture of morpholine and alcohol, which is easily separated by rectification.

The process for separating water from aqueous morpholine solutions according to the invention can be used in a continuous or discontinuous arrangement as illustrated in the following examples.

Example 1 /comparative/

A preheated mixture of 50% by weight water and 50% by weight morpholine is injected into the 4th element of a continuous rectification column, consisting of 8 elements with an internal diameter of 100 mm and a height of 1,000 mm, filled with ceramic Rasohig rings 10 x 10 mm. The heat for distilling water from the mixture is supplied to a circulating reboiler controlled by indirect steam. The vapors exiting the column head are continuously condensed in a backflow condenser and the hot condensate is divided in an electromagnetically controlled reflux divider into distillate and reflux, which is returned back to the column head. The reflux ratio during rectification is 2.3. The distillation residue r.a is continuously removed from the reboiler through a siphon overflow into the distillation residue tank. After the column operation has stabilized, samples of the distillate and distillation residue are taken, which show the following composition: distillate 98.2% by weight of water, 1.8% by weight of morpholine; distillation residue 91.2% by weight of morpholine and 8.8% by weight of water.

Example 2

On the same column as in Example 1, azeotropic rectification is carried out. A mixture of 46 wt. % water, 50 wt. % morpholine and 4 wt. % 1-butanol is sprayed into the column. The condensate formed by condensation of vapor from the top of the column is passed through an aftercooler to a phase separator, where it is separated into a lower aqueous phase and an upper butanol phase. The aqueous phase is continuously discharged to the distillate reservoir and the butanol phase to the top of the column as reflux. The morpholine content in the aqueous phase is 0.02 wt. % and in the distillation residue 99.2 wt.

Example 3

Azeotropic rectification is carried out in a similar manner and on the same apparatus as in Example 2, with the difference that 2-methyl-1-propanol is used instead of 1-butanol. The morpholine content in the aqueous phase is 0.005% by weight and in the distillation residue 99.6% by weight.

Example 4

Laboratory continuous azeotropic rectification of a water-morpholine mixture in the presence of technical 3-methyl-1-butanol. The column has an internal diameter of 30 mm, a height of 2 x 350 mm and is filled with metal spirals of 2.5 mm. The efficiency of the column under load is 20 to 25 theoretical plates. The alcohol used contains 80% by weight of 3-methylbutanol-1 and 20% by weight of 2-methylbutanol-1. The ratio of water to morpholine in the feed is 1:1 and the mixture contains 2.5% by weight of alcohol, calculated on the amount of water. In azeotropic rectification, the mixture of the above composition is preheated to 90 °C and evenly injected into the center of the column. After condensation of the vapor leaving the column head, the aqueous phase is taken as a distillate and the alcoholic phase is returned to the column as reflux. After equilibrium is reached, the distillate contains 0.12% morpholine and the distillation residue contains 99.53% morpholine.

Example 5

On the same column in Example 4, a discontinuous azeotropic rectification of a water-morpholine mixture is carried out in the presence of 1-hexanol as an azeotropic medium. 16.7 wt. % of 1-hexanol is added to the water-morpholine mixture and the mixture in the distillation flask is brought to a boil. The vapors rise through the column, to the top of which the hexanol phase is fed as reflux from the azeotropic distillation head. The aqueous phase - the distillate, is taken from the azeotropic head in fractions in which the morpholine content is determined. After the water has been distilled off and the addition of the aqueous phase has stopped, the azeotropic distillation head is replaced by a normal distillation head with electromagnetic regulation of the reflux ratio.

Rectification is then continued at a reflux ratio of 5:1 and further distillate fractions are taken and analyzed.

The results are as follows:

a/ azeotropic rectification

number, fraction Fraction weight /?/ Contents and morpholine in the fraction! /% wt./ 1 28 0.1 2 24 0.05 3 28 0.02 4 24 0.02 5 24 0.02 6 28 1.00 b/ rectification Numerical fractions Fraction weight Contents morpholine in fractions /9/ /% wt./ 7 10.3 7.24 3 16.5 81.16 ' 9 21.2 97.7 10 34.8 99.9 11 24.4 100.0 12 24.2 99.7 13 5.7 79.3 OBJECT INVENTION

Claims (2)

A method of separating water from aqueous morpholine solutions, optionally containing non-volatile substances, characterized in that the mixture containing morpholine and water is azeotropically rectified in the column in the presence of at least one of the C 1-8 -alcohols, wherein the C 8 -alcohols are added to the split mixture in an amount corresponding to the solubility of these alcohols in the water present in the mixture, Cg and C? the alcohols are preferably added to the divided mixture of morpholine and water in a quantity greater than that corresponding to solubility in direct water, typically up to 50% of the total amount of the morpholino-water mixture, the vapor from the top of the column being fed to the condenser; fed to a phase divider from which the lower aqueous phase saturated with alcohol containing up to 0.2 wt. the morpholine is removed from the system for further processing or use and the alcohol phase is led back to the top of the column as reflux, the bottoms product - a distillation residue containing morpholine and max. 2 wt. water or morpholine and Cg- or C? an alcohol which is separated into the morpholine and alcohol fractions by rectification.