DE1643096C - Process for the purification of crude xylylene diisocyanate obtained by phosgenating xylylene diamine - Google Patents

Description

The invention relates to a process for the purification of ro'-em xylylene diisocyanate (hereinafter referred to as XDI) by fractionation under very specific conditions.

XDI has the formula

OCNCH,

CH, NCO

and is generally prepared by reacting the corresponding xylylenediamine with phosgene. Various by-products are formed in this reaction, e.g. B. Chlorine compounds of the following Formulas (I) to (III) (hereinafter referred to as impurities (I), (II) and (III)):

CH ₇ Cl

CH ₂ Cl

CH,

CH ₇ NCO

Therefore, the XDI formed must be subjected to purification.

XDI is known to have a high boiling point (161 ° C at 10 mm Hg) and is thermally unstable so that it polymerizes when it is heated above 17O ⁰ C. The boiling points of the above-mentioned impurities are very close to the boiling point of XDI, and the boiling point of the impurity (I), which is formed in a larger amount than the other impurities, is closest to the boiling point of XDI. In the purification of crude XDI, the extremely important problem to be solved is to remove these impurities (I) bi ·. (I Il), in particular to effectively remove the impurity (11.

Vacuum distillation has hitherto been used to remove these impurities. At this Method, however, is the connection to be cleaned at the end of a relatively high temperature suspends because a significant temperature rise as a result of a pressure drop inevitably in the vicinity desBodeus of the distillation column takes place. With In other words, this method requires a fractionating column with several tens of trays because of the small difference in boiling points between the impurities and XDI can be used. In addition, the pressure drop in the vicinity of the

At the bottom of the column up to a few 10 mm Hg. Causing the XDI to a temperature of about 180 to 200 C is heated. Therefore, no satisfactory purification of XDI is possible with this method. To the Many attempts have been made to solve this problem

makes the pressure drop in distillation columns largely off, but none of the suggestions made can solve the problem satisfactorily will.

It has now been found that the purification of crude XDI by fractionation without damaging the XDI at low temperature using the usual fractionation columns, e.g. B. tray columns and packed columns, is easily possible if very specific fractionation conditions are applied.

The subject of the invention is accordingly a process, for the purification of crude xylylene diisocyanate obtained by phosgenation of xylylenediamine. which is characterized in that crude xylylene diisocyanate is placed in a fractionating column with superheated steam of an organic solvent boiling at -20 to 150 C 200 mm Hg, namely, an aliphatic hydrocarbon having 2 to 11 carbon atoms, an alicyclic hydrocarbon having 5 to 8 carbon atoms, an aromatic hydrocarbon, a halogenated one aliphatic hydrocarbon having 1 to 6 carbon atoms or a halogenated benzene such conditions that the pressure at the top of the column at 5 to 200 mm Hg and the temperature at the bottom of the column is kept at a maximum of 170 ° C.

According to the invention, the pressure drop at the foot of fractionating columns can be effectively reduced so that raw XDI can be easily and satisfactorily duich fractionation using simple equipment, e.g. B. Tray columns and packed columns, can be purified without decomposition or degradation of the XDI by heating entry.

With the novel process according to the invention for the purification of crude XDI by distillation, the impurities contains, whose boiling point is very close to the boiling point of the XDI, these contaminants will be removed as light cuts from the raw XDI using a simple procedure, with pure XDI that is essentially free of impurities. is obtained in high yield.

The term "xylylene diisocyanate" in this description does not only include the o-, m- and p-isomers individually, but also any mixtures of these isomers. The method according to the invention is suitable thus for the purification of any isomers of

I 643

XDl in the raw state, ie / for purification of raw ₀ _Xvkie: Kliisocyanat, m-Xylylenendiisocyanai. p-xylylene diisocyanal and any mixtures of these compounds.

Xf) I is generally produced by phosgenation of the 5 ^ tjjprcL-hendeP xylylenediamine. The raw phosgenation product as such can be subjected to the invention - to subject it to a simple distillation "in the usual manner and thereby separate the II 'disboiling.
Conventional fractionation columns can be used for the experience according to the invention (ice columns are, for example, testicle columns, such as 15 bell-shaped bottom columns, ballast tray columns -Fill bodies, Palln-.i'jcn, Raschig rings, etc. are filled.

fs -A earth organic solvents -used, the 20 resistant and inert to XDl and to Erhit / c'i are stable and have a boiling point of 20 to 150C at a pressure of 7 (H) 1: 1111 Hg, 30 to 80 C must be required. Examples of suitable * Organic solvents are aliphatic hydrocarbons. /..B. Pentane, hexane, heptane, Octal nonane, decane, undecane, ligroin, alicyclic Hydrocarbons, e.g. B. cyclohexane, methylcyclohexane. Cycloheptane and cyclooctane, aromatic hydrocarbons, e.g. B. benzene, secondary amylben / ol. Toluene, ethylbenzene, xylene, etc., halogenated aliphatic hydrocarbons, e.g. B. chloroform. Dichloi methane, 1,2-dichloroethylene, n-monochlorobutane, Carbon tetrachloride, n-monochlorheptane, n-monochlorhexane, 1,2-dichloroethane, carbon tetrachloride, etc. and halogenated benzenes, e.g. B. monochlorobenzene, !, "■ dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene etc.

Of the solvents mentioned above, cyclohexane, benzene, toluene and Xylene used.

The method according to the invention becomes more superheated Vapor the above organic solvents with crude XDI in a fractionation column brought into contact in direct current. The 4: superheated steam is in practice in a preheater formed in which the organic solvent is at a temperature below the operating temperature the fractionation column heated and an evaporator

is fed. . .

The abovementioned contact in the fractionation column takes place under conditions in which the temperature at the bottom of the column is at most 170 ° C. with a lower limit of about 100 ^° C. and the pressure at the top of the column is 5 to 200 mm Hg, preferably 30 to 100 mm Hg, amounts to. The operating pressure is preferably controlled by an automatic control device, which is arranged in the fractionation system, and the operating temperature by an automatic control device arranged in the evaporator Invention suitable device shows.

Crude XDI is fed to the fractionation column ß through the preheater E. The superheated vapor of the organic solvent, which is formed by heating the solvent S in a heater F , is in the evaporator A and then together with the XDl steam present in the evaporator A; introduced into the fractionation column. The superheated vapor of the solvent flows upwards in fractionation column B with the XDI vapor. In fractionation column B , the crude XDI is separated into light impurities and pure XDI. The light impurities separated in this way are concentrated in the top of the column, while pure XDI is fed into evaporator A. The concentrated light impurities are fed to the partial condenser C together with superheated steam from the top of the column. The temperature of the partial condenser C must be set so that only the light impurities are condensed in it. Part of the condensed light impurities is returned and the other part is collected in a distillate receiver /. The solvent vapor separated off in the partial condenser C is introduced into the total condenser D , where it is collected and fed to the solvent reservoir J for reuse. The XDI collected in the evaporator A is fed to a distillation apparatus G, where it is distilled. The distilled XDI is introduced into condenser H where it is condensed. The pure XDI (P) is drawn from the cooler H al_-. The vacuum connection of the device is indicated by V.

In the following examples, parts are parts by weight unless otherwise specified.

The venanrcu according to the invention can be used in batches or carried out continuously, the continuous procedure being preferred will. To prevent polymerization of the XDI, the fractionation can optionally be carried out in the presence customary polymerization inhibitors are carried out.

example 1

A solution of 200 parts of phosgene in 200 parts of o-dichlorobenzene is mixed at -5 "C with a solution of 68 parts of a mixture of 70 parts of m-xylylenediamine and 30 parts of p-xylylenediamine in 400 parts of o-dichlorobenzene. The mixture is mixed within of 2 hours gradually heated to 170 ° C. while excess phosgene is introduced, with a reaction taking place ^1. After the reaction, nitrogen is introduced into the mixture obtained in order to remove the excess phosgene, whereupon the solvent is distilled off from the mixture thus treated crude XDI is obtained, which contains 3.5 parts of impurities and high-boiling components The crude XDI is subjected to a simple distillation at 135 to 140 ° C./3 mmHg in order to remove the high-boiling components.

The crude XDI treated in this way is fractionated according to the scheme shown in the figure. The following equipment is used:

Fractionation column B: sieve tray column with 40 trays (internal diameter 180 mm, height 4.4 m)

Preheater E: thin-film downdraft

Evaporator

Evaporator A :

Heater F:
Partial capacitor:

Total capacitor:

Jacketed vessel
with gas supply ring

Lamellar heater

Tube bundle exchanger C

Tube bundle exchanger D

As solvent naphtha is used which is heated in the heater F to 160 ⁰ C and l introduced through the evaporator / in an amount of 30400 parts / hour into the fractionation column B. The crude XDI is ^{heated to 160 °} C. in the preheater and introduced into fractionation column B in an amount of 10,000 parts / hour. The operating temperature is set to 160 ^° C. by setting the temperature in evaporator A , and the operating pressure is set to 80 mm Hg by setting the pressure at the top of the column. The crude cXDI is brought into contact with the superheated vapor of the solvent in fractionation column B in cocurrent. The impurities and the heated steam are fed through the top of the column to the partial condenser C, where only the impurities are condensed, while the superheated steam is condensed and collected in the total condenser. The process described above is carried out continuously.

After about 20 hours the fractionation system (reflux ratio about 9.0) has reached steady-state. The XDI collected in the evaporator A is continuously fed to the distillation apparatus G in an amount of 9,000 to 10,000 parts / hour. The XDI is distilled at 140 ° C./2 to 3 mm Hg, purified XDI being obtained in a yield of 95 percent by weight, based on the crude XDI used in the fractionation column. Analysis of the pure XDI obtained in this way gives the following values:

XDI 99.5 percent by weight

Hydrolyzable

Chlorine 0.01 percent by weight

Insoluble in toluene

Ingredients less than

0.02 percent by weight

After the steady state has been reached, the composition of the mixture in evaporator A and of the mixture at the top of fractionating column B is determined. The following results are obtained:

Example 2

Crude XDI prepared in the manner described in Example 1 is purified as follows: Die The apparatus described in Example 1 is used with the difference that a glass column (height 2000 mm, inner diameter 50 mm) is used, which does not contain a sieve bottom, but with MacMahon packings made of stainless steel. When

ίο Solvent, heptane is used. The heptane is heated to 160 ^° C. in the heater and fed into the fractionating column by evaporator A in an amount of 200 parts / hour. The operating temperature is set to 160 C on the reboiler.

The crude XDl (content of impurities (I) about 2%) is heated to 160 ° C. in the preheater and fed to the middle of the column in an amount of 500 parts / hour. The operating temperature is set to 160 ° C by setting the temperature in evaporator A. The operating pressure is adjusted to 30 mm Hg by adjusting the pressure at the top of the column. The crude XDI is continuously brought into contact with superheated Hcp'tandampf in the column for several hours at a reflux ratio of 7.0 under the above-mentioned temperature and pressure conditions in cocurrent.

Purification is carried out in the manner described in Example 1 XDI in a yield of 94 percent by weight, based on the crude XDI used in the column.

receive. The analysis of the pure XDI obtained in this way shows the following composition:

XDI 99.5 percent by weight

Hydrolyzable

Chlorine 0.02 percent by weight

Insoluble in toluene

Ingredients less than

0.02 percent by weight

After the steady state is reached. the composition of the mixture in evaporator A and the composition of the mixture in the top of the fractionating column are determined. The following results are obtained:

Composition of the mixture in the evaporator A 99.7

Composition of the mixture at the top of fractionating column B i 35.0

XDI

Weight percent

Chloromethylbenzyl isocyanate (Pollution

(X)). Weight Pro7enl

0.3

65.0

XDl Weight piwcnt Composition of the Ge mix in evaporator A .. 99.8 Composition of the Ge mix at the head of the frac tioning column B 40.0

Chloromethylbenzyliso anal (impurity

AROUND. Weight percent

0.2

60.0

Example 3

Raw XDI is batch cleaned using an apparatus that includes the following parts:

a glass column (inner diameter 25 mm. height 700 mm), which is made with o ^ -mm MacMahon packing stainless steel and placed vertically on a 500 ml flask with a Entry for raw XDI and one entry for superheated Gas is provided. a partial capacitor and a total capacitor, in this order with are connected to the head of the glass union. The inlet for superheated gas is with a different one

Connected flask in which the solvent evaporates will.

Add 500 parts of crude XDI, which contains approximately 2 parts of impurity (I), to the 500 ml flask. The fractionation is carried out at an operating pressure of 30 mm Hg at the top of the column and at an operating temperature of 165 ° C at the bottom of the column, while superheated xylene vapor in the 500 ml flask in an amount of 0.68 mol / hour through a tube is blown into the flask in which the solvent is evaporated. During the fractionation is carefully the xylene in the on - condensed cooled 20 ⁰ C total condenser and the XDI condensed in the partial condenser is carefully returned as reflux. After 5 hours, a sample is taken from the top of the column and from the flask at the same time. These samples are analyzed by gas chromatography and the following results are obtained:

Composition of the mixture in the flask

Composition of the mixture at the top of the column

XDI

Weight percent

99.8 60.0

Impurity (I), weight percent

0.2 40.0

Example 4

Crude XDI containing 2 parts of impurity (I) is prepared using the method described in Example 3 described apparatus cleaned. The conditions used and the results obtained are in compiled in the following table.

solvent

benzene

toluene

Ethylbenzene

Chlorobenzene

1,2-dichlorobenzene

Dichloromethane

1-chloro-n-butane

1-chloro-n-pentane

1-chloro-n-hexane

chloroform

Carbon tetrachloride ...

n-pentane

η-hexane

n-heptane

n-octane

Ligroin

Cyclohenane

Cyclopentane

Cyclooctane

Methylcyclohexane

*) CBI: chloromethylbenzyl isocyanate (impurity (I)).

Solvent use (mol)

0.98

0.68

1.28

0.68

0.73

0.62

0.65

0.63

0.96

0.63

1.3 '

1.42

1.30

1.01

1.33

0.71

0, b2

0.82

0.52

0.65

) jerk on the

head mm Hg

25th

20th

30th

20th

20th

20th

20th

20th

25th

20th

30th

30th

30th

25th

30th

25th

20th

23

15th

20th

Temperature. ° C

floor
the
column Part-
Condensate
sator 163 10 165 30th 164 55 165 45 163 10 165 0 163 15th 165 20th 165 50 165 10 163 10 165 0 164 0 164 15th 162 45 164 40 164 10 165 25th 163 50 164 15th

Total capacitor

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

-20

Composition of the mixture

Piston CBI *) I XDI

0.3 0.2

0.3

0.2

0.3

0.2

0.2

0.2

0.3

0.3

0.3

0.2

0.3

0.3

0.2

0.2.

0.3

0.3

0.3

99.7

99.8

99.3

99.7

99.8

99.7

99.8

99.8

99.8

99.7

99.7

99.7

99.8

99.7

99.7

99.8

99.8

99.7

99.7

99.7

Column head CBI ·) I XDl

30.2 69.8 32.5 67.5 33, ö 67.0 31.0 69.0 31.6 68.4 31.7 68.3 35.6 64.4 37.1 62.9 36.5 ' 63.5 31.3 68.7 30.6 69.4 31.1 68.9 42.1 57.9 33.6 66.4 31.1 68.9 44.2 55J 40.0 60.0 31.3 68.7 30, V. 69.1 36.3 63.7

1 sheet of drawings

Claims (2)

Patent claims: 1. Process for the purification of crude xylylene diisoeyanate obtained by phosgenation of xylylenediamine. characterized, that crude xylylene diisocyanate in a fractionating column with superheated steam of a at -20 to 150 C 200 mm Hg boiling organic solvent, namely an aliphatic Hydrocarbon with 2 to 11 carbon atoms, an alicyclic carbon hydrogen having 5 to 8 carbon atoms, an aromatic hydrocarbon, a halogenated aliphatic Hydrocarbon with 1 to 6 carbon atoms or a halogenated benzene under such conditions bring together that the pressure at the top of the column at 5 to 200 mm Hg and the temperature at the foot of the column is kept at 170 ° C or less. 2. The method according to claim 1, characterized in that one is used as the organic solvent Cyclohexane. Toluene or ligroin is used.