DE1593712C3 - Process for the continuous production of o-phthalic acid esters - Google Patents

Description

It is known to use phthalic anhydride with high-boiling alcohols in the presence or absence of esterification catalysts to continuously implement with the formation of the corresponding o-phthalic acid ester.

The esterification in the absence of catalysts must take a long time to achieve high conversions Residence times are adhered to, which result in a low space-time yield and very large apparatus require. In addition, high temperatures are necessary in connection with the long Residence times lead to the formation of by-products, for example olefins. This results in a loss of yield and impurities that make it difficult to clean. These disadvantages have led to esterifications in the absence of catalysts in the industry only to a small extent Measures were able to prevail.

The difficulties outlined can be avoided by using catalysts. But one accepts other, equally serious disadvantages for this. Must, for example the catalyst can be removed from the reaction mixture. If this is done by washing or neutralizing, so the crude ester becomes saturated with water. This must be done again in a further step removed. In addition, there are losses of starting products, which reduces the cost-effectiveness of the procedure is called into question.

If, on the other hand, the catalyst remains in the reaction mixture, decomposition genes, no high-quality ester is obtained from the crude ester purification.

In a further procedure in the absence of esterification catalysts, the required Alcohol added gradually. This measure can reduce the residence time of the alcohol Shortened in the course of the reaction and the possibility of the formation of dehydration products restricted will. However, it is not possible to achieve short residence times or high space-time yields achieve.

In addition, in this process, the crude ester must be neutralized unc before further purification getting washed. This makes the implementation of the process more difficult.

A process has now been found for the continuous production of o-phthalic acid esters from Phthalic anhydride and alkanols with 8 to 10 carbon atoms, in the absence of an esterification catalyst and a distillation aid and at a temperature of 180 to 250 ° C. The process is characterized in that the Starting mixture of phthalic anhydride and alkanols, the latter in an excess of 5 to 20% of theory, esterified in two or three stages up to a conversion of 94 to 97% of theory the resulting o-phthalic acid ester by fractionation in a known manner from the unreacted Liquid starting materials are separated and the latter is fed back into the reaction.

Suitable alkanols are alcohols which are stable under the conditions of the process, mi ^; Water does not form a mixture or a hetero-azeotropic mixture and has a boiling point of about 170 to 250 ° C. These are preferably straight-chain or branched-chain octanols-nonanols or decanols.

A temperature of 18Γ to 250 ° C. is advantageous for the esterification. This avoids long residence times and the formation of by-products prevented, which complicate the further work-up.

When carrying out the method, aa ·. Water of esterification is discharged from the reaction mixture by distillation to the extent of its formation, preferably in the form of the corresponding hetero-azeotropic alcohol-water mixture, and the alcohol is circulated after phase separation of the mixture. Therefore, stoichiometric amounts of alcohol are generally sufficient. Surprisingly, however, an improvement in the color quality of the reaction product is achieved in the presence of a slight excess of alcohol. It has therefore proven to be useful to carry out the esterification with an alcohol excess of 5 to 20% of the theory.

The esterification water can particularly advantageously be removed from the reaction mixture if under the conditions of the discharge of the hetero-azeotropic alcohol-water mixture by distillation a gentle stream of inert gas, for example nitrogen, is introduced into the reaction mixture at the same time and the latter in the cycle. The Inertga: can expediently before its introduction be heated by means of a heat exchanger. In this way it succeeds while avoiding high alcohol levels Returns an optionally the azeotropic composition of the predominant alcohol-water Mixture corresponding reactor head product obtained zi.

It also proves to be expedient to carry out the continuous esterification in one apparatus feed, which consists of at least two, preferably three, esterification reactor connected in series ren exists. In this way, backmixing processes can be counteracted.

The process is carried out as follows: Phthalic anhydride is fed to the mixing vessel 3 via line 1 and alcohol via line 2. Phthalic anhydride can be used in liquid or solid form. At a mixing temperature which can be up to 30 ^° C. below the boiling point of the alcohol, and a residence time of about 0.5 hours, phthalic anhydride is quantitatively reacted with the alcohol in the mixing vessel 3 to form the corresponding o-phthalic acid monoester. The resulting homogeneous reaction mixture, which contains excess alcohol in addition to the monoester, is fed to the upper end of the esterification reactor 5 via line 4. To prevent backmixing processes, however, it is expedient for the esterification to be carried out at least in a further esterification reactor 7, but advantageously in a third esterification reactor 9. The esterification reactors 5, 7 and 9 each consist of a tube provided with jacket heating, the height of which is related to the diameter as 30: 1. In addition, at the lower end, in addition to a feed line 20 for the inert gas, it is each provided with a discharge line 6, 8, 21 for the reaction mixture. In addition to the respective feed lines 4, 6, 8 for the reaction mixture and return lines for the alcohol 16, 17, 18, the upper reactor ends each have a riser pipe 10, 11 and 12. The esterification reactors are connected to the phase separators 13, 14 and 15 through the latter. The resulting esterification water is quantitatively driven over to the extent of its formation, mainly in the form of the corresponding hetero-azeotropic alcohol-water mixture, via the riser pipes 10, 11 and 12 into the phase separators 13, 14 and 15. At the same time, by gently blowing inert gas through line 20 into reactors 5, 7 and 9 from bottom to top, with circulation, the removal of water by distillation is supported.

In the phase separators 13, 14 and 15, the alcohol-water mixture is divided into its two components separated. The alcohol reaches the reactors 5, 7 via the return lines 16, 17 and 18 and 9 back. The esterification water is discharged together through line 19.

The hot reaction mixture emerging from the lower end of the esterification reactor 9, the Apart from unreacted alcohol and phthalic anhydride, practically no further impurities contains, via line 21, the upper end of a thin film evaporator operating at 10 to 5 Torr 22 supplied. At the upper end of the thin film evaporator 22, the alcohol falls, the is fed again to the mixing vessel 3 through line 30. At the lower end of the thin film evaporator 22 a practically alcohol-free crude ester is obtained, which via line 23 is hot at the upper end : iner fractionating column 14 operated at 5 to 2 torr is fed. Over the head of this column Unreacted phthalic anhydride is removed through line 31 in the mixing vessel 3 in the form fed in a hot melt. Pure, almost colorless o-phthalic ester falls at the column inlet 25 on.

It is surprising that the esterification to the desired degree of esterification even without catalysts runs just as quickly as in the presence of esterification catalysts. On the other hand was it is not to be expected that, in spite of the incomplete esterification, the resulting crude ester will be obtained solely by distillation Measures can be converted into a high-quality pure ester.

In addition, the process succeeds in a simple manner, avoiding the formation of By-products, phthalic anhydride with practically no loss and under favorable energetic conditions to implement with high-boiling alcohols to very pure and stable o-phthalic acid esters.

example 1

The mixing vessel 3 can be constant by setting conditions which are obtained after a running-in period, hourly via line 1 142.5 parts by weight of phthalic anhydride in the form of about 135 ⁰ C hot melt and via line 2-Hch starts per hour 250.3 parts by weight of 2-ethylhexanol fed. In addition, 61.7 parts by weight of unreacted 2-ethylhexanol per hour and 5.5 parts by weight of unreacted phthalic anhydride (as a hot melt) per hour are fed to it via line 30.

In the mixing tank 3, phthalic anhydride is reacted quantitatively at about 18O ⁰ C and at a mean residence time from about 0.5 hours to mono-2-Äthylhexylphthalat.

460 parts by weight of this reaction mixture are fed via line 4 to the esterification reactor 5 at the top every hour. In addition, the At the same time, 100 parts by volume of nitrogen per hour were introduced into the lower end of the reactor 5 via line 20. The reactor temperature is kept at 210 ° C.

While the reaction mixture in reactor 5

flows from top to bottom and continuously esterifies to di-2-ethylhexyl o-phthalate, the water of esterification formed is discharged to the extent that it is released. The event will supported by the gentle stream of nitrogen. It happens quantitatively and mainly in form of the hetero-azeotropic 2-ethylhexanol-water mixture. The latter is driven over via the riser pipe 10 into the phase separator 13 and there separate layers. 2-Ethylhexanol is returned to the upper part of the reactor 5 via line 16 and the esterification water is discharged via line 19. The divisible from the phase separator 13

So chende nitrogen is via line 20 in the circuit guided.

The reaction mixture obtained at the lower end of the reactor 5 is then added to the same Way via line 6 first through the reactor 7 and then via line 8 through the reactor 9 led. The reaction temperature is 7215 ° C in the reactor and 9220 ° C in the reactor.

The reaction mixture passes through the three reactors within 3.5 hours, so that each Reactor gives a residence time of 1.16 hours. The degree of esterification (based on phthalic anhydride used) after the first reactor 86%, after the second reactor 92.3% and after the third reactor 96.25%. While via line 19 a total of 17.3 parts by weight of water of reaction are obtained, the resulting at the lower end of the reactor 9, crude o-phthalic acid di-2-ethyl ester continuously via line 21 at the

5 Torr operated thin film evaporator 22 is supplied. Over the head of the latter will be hourly 61.7 parts of unreacted 2-ethylhexanol obtained, which is fed to the mixing vessel 3. When A practically 2-ethylhexanol-free falls from the bottom effluent Crude ester, which via line 23 continues to the upper third of the column operating at 4 Torr 24 is supplied. 5.5 parts by weight of unreacted matter per hour are passed over the top of the column 24 Obtained phthalic anhydride. The hourly column effluent 25, which is 375.5 parts by weight is a pure o-phthalic acid di-2-ethylhexyl ester with an APHA value of 40.

The same result is obtained if there is no nitrogen in reactors 5, 7 and 9 via line 20! initiated, but so much heat is supplied via the jacket heating that while increasing the Reflux, the esterification rate per reactor and the space-time yield unchanged remain.

The mean analysis is

Ester content 99.85%

Viscosity 85 ep (DIN 53015)

Special passage resistance about 2.0-10 ⁵ M- cm

Acid number = 0.05

n £ 1,487

Example 2

The procedure is as in Example 1, however

n-Octyl alcohol is used in place of 2-ethylhexanol. The temperature in the mixing vessel 3 is 185 ° C, in reactor 5, it amounts to 225 ⁰ C, in the reactor 7 at 230 ° C and in the reactor 9 to 235 ° C. The total residence time is 3 hours. Via line 25, 375 parts by weight of one per hour

ίο pure, boiling at 228 to 229 ° C (2.5 torr) Obtained o-phthalic acid di - η - octyl ester, the APHA value of which is 35.

Example 3

The procedure is as in Example 1. The mixing vessel 3 receives 141 parts by weight of phthalic anhydride every hour and 301.5 parts by weight of n-decyl alcohol supplied. In the cycle are next to 7.0 parts by weight of unreacted phthalic anhydride, 50 parts by weight of unreacted n-decyl alcohol. The mixing tank temperature is 200 ° C. The temperature in reactor 5 is 225 ° C, the in reactor 7 at 235.degree. C. and that in reactor 9 at 245.degree. The total residence time is 3 hours. 95.3% of the phthalic anhydride used are converted. Via line 25 are per hour 424.3 parts by weight of a pure, at 257 ° C (2.5 torr) boiling o-phthalic acid di-n-decyl ester obtained, the APHA value of which is 40.

1 sheet of drawings

Claims (1)

Claim: Process for the continuous production of o-phthalic acid esters from phthalic anhydride and alkanols with 8 to 10 carbon atoms, in the absence of an esterification catalyst as well a distillation aid and at a temperature of 180 to 250 ° C, characterized in that that the starting mixture of phthalic anhydride and alkanols, the latter in an excess of 5 to 20 ° / o of the theory can be used, which leads to esterification and this in two or three Carries out stages up to a conversion of 94 to 97% of theory, the resulting o-Phthalic acid ester by fractionation in a known manner from the unreacted starting materials liquid separates and the latter supplies the reaction again.