DE1668746C - Process for the production of dimethyl terephthalate - Google Patents

Description

hlossenes reaction vessel to Stachen their overall charged with a slurry of Ϊ Mhalsäure and 1- ^Te 2es of methanol and axi a temperature ^W of 60 to 35O ° C, preferably 150 to 300 ⁰ C, at ^TUR pressure of 1 up to 200 kg / cm'- heated for a period of 30 to 300 minutes in order to initially form approximately equilibrium reaction T, which consists of crude dimethyl terephthalic acid and 5 liters of Zihdkt t

degree of efficiency by em

Α * »unreacted terephtha nmethyl terephthalate as an intermediate ent- io "T d ite stage is not implemented

££ n ™ of a " _{c d2D} kg / cm-

^ Γ ^ ϊΖνΓ ^ Γ dutch the inlet 7 held. ^ "! H ^ eaküonsgef äßes ⁶ blown in at the lower part of the * ^e a * ™ _reaction vessel and with the Rca ^ _{Q d} led in countercurrent from the upper part of the R ^^ ■ ß

moved. ™ " ^d T _atalvsa tor according to the invention. J ^^^^ SzngdLrt. Excess invention for the second: btuu ^ B _reaction formed methanol vapor and the du cn ^

^ S ^^ highly enriched

^ ΑΪ ^^^ ΓώΑ Ge end product at ^el hScent based on terephthalic acid, the i ₅ Das ^{als ^ 5} r, eSenden organic compound adds organic sauna

Je- ^ _{tin salt d}

^V 4 _{is, for} example, a salt of benzoic acid.

_r height dimethyl must for the further

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-D ^ ReakSstemperatur in the esterification in the ride level can be higher than the melting point of Smethylterephthalat, being, however, in Intcr- sm? Aware of a guaranteed by adequate Hießfähigkct smooth reaction process preferably upper-Sb 180 ⁰ C. With regard to the pressure, there is no particular restriction, but in the interests of increasing the concentration of the methanol.

The Tn of the second stage of the esterification «Sand e device can be designed in any way Sern se just a liquid with a gas under the to implement the above-mentioned conditions With a view to simplicity of the device and effective operation, devices from TVO eTnes packed tower, a Fraktion.ersSe with bell bottom, in which the methanol vapor 5 tons of melt are brought into contact in countercurrent or those devices in which Ä-Xnrf are blown into the melt

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catalytically effective Verbmdun _zugegeb s,

system in the second stage of the _{stage of the}

however, d 's also true ™ ^^ _Fa "

Esterification process g ^escne ^ ⁿ , catalyst in these compounds act ^ ^ _wi / _{ksiimkc in} both stages, although «h ^ Sn? not special.c :. in the first stage of Vereswri S _{hsbeispiel 2}

is large, as in the ^"ac hf ^he _s ^nd _k ^ _can ^g _n Of course, also

rei ^B oTern \ e \ rier ^1S lcSlysatorver _bi ndun _g s overall

_mei NSAM apply ffWj. ^.

In the two-stage Verestti ^ " ^s _{duration bycn} acid with methanol, the Verestti ^. ^ The addition of the catalyst ^ '^ ndes ^.

Stage of the esterification reaction after

in accordance with the J ^ J ^ "^" is not just the quality

ethanol was placed in an autoclave and heated at 250 ° C. for 1.5 hours. After evaporation to dryness, a crude dimethyl terephthalate was obtained in which 88.0% of the carboxyl groups had been converted (corresponding to a conversion of 88.0%) Dimethyl terephthalate was mixed with tin (II) formal in varying amounts (percent by weight, based on terephthalic acid), as indicated in Table 1 below, and then ^{heated to melt at 240 °} C. Gaseous methanol was poured from the bottom of the reaction vessel at normal pressure in an amount per hour was blown in which was equal to the amount by weight of the melt, the reaction times given in Table 1. The reaction mixture was then drawn off and analyzed.

Table 1

Comparative example 1

A known esterification catalyst or another compound as indicated below (each 0.5% by weight) was added to a crude dimethyl terephthalate as obtained in Example 1, and the mixture was reacted as in Example 1 for 2 hours. The results obtained are summarized in Table III. It can be seen from it that in each experiment the degree of conversion of the carboxyl groups is below 94% and that the activity of the catalysts is inferior to that of the tin-containing organic compounds as used in Examples 1 and 2.

Tin (ll) formate Reaction time Esterified carboxyl (Weight percent) (Minutes) groups ("/") 0 0 88.0 0 120 91.0 0.01 60 94.8 0.01 120 98.2 0.05 60 97.0 0.05 120 99.8 0.10 60 99.2

Table 111 Esterified
Carboxyl groups ("Aj) catalyst 93.5
93 1 Sulfuric acid .... 92 5 Ferrosulfal 91.5
92 1 Zinc sulfate 91.8
91 5 Cobalt sulfate 92.1 ^a5 cobalt chloride Molybdic acid ... zinc oxide Nickel formate ....

Comparative example 2

Example 2

The procedure of Example 1 was repeated with the modification that different catalysts came into use. The results obtained are summarized in Table 11.

Table 11

catalyst crowd
(Weight Reaction
length of time Esterified
Carboxyl
groups percent) (Minutes) <7n) Tin (ll) acetate ... 0.05 60 97.3 Tin (ll) acetate ... 0.05 120 99.5 Tin (H) acetate ... Q, 02 120 99.3 Tin (H) acetate ... 0.05 120 98.9 Tin butyrate 0.05 120 99.6 Tin succinate .... 0.05 120 97.6 Tin benzoate 0.05 120 98.6 Tin phthalate 0.05 120 99.1 Tin terephthalate 0.05 120 97.6 Triphenyltin hydroxide 0.05 60 96.5 Triphenyltin hydroxide 0.05 120 99.4 Triphenybdenum chloride 0.05 120 99.2 Tin ethoxide 0.05 120 98.5 Tin ethylene glycoxide 0.05 120 98.1 Tin propylene glycoxide 0.05 120 96.9 Tri-lert.-butyl tin phenolate .-. 0.05 120 97.8

F.in parts by weight of terephthalic acid and 4 parts by weight of methanol were heated for 60 minutes in an autoclave after adding 0.5 percent by weight, based on terephthalic acid, of a catalyst according to Table IV. The reaction product was washed with chloroform and the content of dimethyl terephthalate in the former was quantitatively determined by gas chromatography. The results thus obtained are shown in Table IV, from which it can be seen that in the esterification reaction in the first stage, the tin-containing organic compound according to the invention has a comparatively low catalylic activity.

Table IV

catalyst

No cT

sulfuric acid

hydrochloric acid

Zinc sulfate Ferrous sulfate Cobalt chloride Cobalt sulfate Molybdenum acids Nickel formate Ziim (II) -fonniat Zmnäthoxid Triphenyl family hydroxide

Yield of dimethyl terephthalate (%)

6.5 76.3 30.0 70.5 81.0 68.0 69.0 88.0 13.0 10.5 20Y 18.2

Example 3

This example illustrates a continuous fichi Procedure in which a two-wire anti

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Application of the device shown in the drawing was carried out.

A mixture of terephthalic acid with methanol in the weight ratio 1: 4 was continuously fed by means of pump 2 in an amount of 5 parts by weight per hour to the reaction tube 4 (reaction vessel for the first stage), the one through the jacket 3 at 250 ⁰ C and Pressure of 100kg / cm ^{a was} maintained. The reaction mixture from the reaction tube 4 was introduced through the pressure regulating valve 5 into the upper part of the reaction vessel 6 of a fractionating column provided with bubble trays (reaction vessel for the second stage), which was kept at 230 ^° C. and a pressure of 20 kg / cm ² . There the mixture was passed in countercurrent to methanol vapor which was blown into the mixture from the lower part 7 of the reaction vessel at a rate of 0.5 parts by weight per hour.

A catalyst according to Table V below was added to the mixing vessel 1 to the extent of Introduced 0.0002 parts by weight per hour. The respective degree of conversion of the carboxyl groups Sample No. 1 drawn from the pressure regulating valve S and the sample No. 2 drawn from the vent 8 was determined. The results are shown in Table V. It can be seen from her that, although esterification catalysts according to the prior art in the second stage are only unsatisfactory act, the tin-containing organic compounds according to the invention particularly here are effective.

Table V catalyst

None

Tin (II) formate

Tin (II) acetate

Triphenyl tin hydroxide

Ferrous sulfate

Zinc sulfate

Molybdic acid

Esterified carboxyl groups (Vo) sample No. 1 | Sample no.

91.5 92.3 92.1 93.2 95.3 94.8 95.7

93.5 99.6 99.4 99.5 96.1 95.4 96.3

When the catalyst from the top 10 of the reaction vessel 6 in an amount of 0.0002 parts by weight was added per hour, Sample No. 3 withdrawn at 8 showed a degree of carboxyl group conversion according to the following table VI.

Table VI

catalyst Esterified carboxyl
groups C / o)
Sample # 3 None
Tin (II) formate
Tin (II) acetate
Triphenyl tin hydroxide
Tin ethylene glycol oxide 94.8
99.7
99.3
99.6
98.9

1 sheet of drawings

ches
nter

309632/1

Claims (4)

to be hit. In a second stage, therefore, the equilibrium reaction mixture becomes patent claims. (i.e. ^ 5 dimethyl terephthalate, the unreacted terephthalic acid and monomethyl terephthalate 1. Process for the production of dimethyl 5 contains) introduced into an open reaction vessel, terephthalate from terephthalic acid and methanol, after separating off that formed in the first stage characterized in that one has water and excess methanol or already one from the esterification of terephthalic acid with during the separation becomes the molten ReMethanol Melt obtained with a conversion mixture with gaseous methanol in a degree of ventilation of at least 70%> n presence of a 10 running brought under ongoing separation of the Tin-containing organic compound with resulting water will eventually react further esterified with gaseous methanol. brought to the end. 2. The method according to claim 1, characterized in this "two-stage esterification process" signed, that the further esterification with which the two stages differ with regard to the Tin salt of an organic acid, a Sn-C-Or- 15 nature of the reaction vessel and the reacganotin compound, a tin alkoxide or a mixture of ions (a mixture of methanol and terephthalic acid ZinnphenoJnt performs. ■ existing sludge in the first and a mixture 3. The method according to claim 1 or 2, characterized from molten crude dimethyl terephthalate and characterized in that one converts the methanol into the gaseous methanol in the second stage). However blows in melt to be further esterified. 20 no technically satisfactory catalyst is known, 4. The method according to claim 1 or 2, characterized in both the first and the second stage marked that one could be used to further esterify. Melt and the methanol vapor to each other in the case of the reaction in the first stage can known Countercurrent leads. Esterification catalysts can be used, e.g. B. 25 strong acids such as sulfuric or hydrochloric acid; Oxides, chlorides, sulfates and salts of organic acids of Zinc, lead, antimony, cadmium or cobalt. In the second stage in the open reaction vessel, the Reaction temperature higher than the melting point of 30 dimethyl terephthalate, and therefore the concentration of methanol in the crude dimethyl terephthalate melt small amount. Accordingly, after the first stage, the crude dimethyl terephthalate contains only a small amount of compounds containing carboxyl groups 35 Concentration. The esterification reaction is therefore very delayed in the second stage, and the In the last few years the importance of poly- Application of a catalyst is desirable
ethylene terephthalate as a fiber-forming polymer. Since the second stage is also an ordinary Dimethyl terephthalate is an important starting point for this and has been known esterification product; it is mainly used by esterification 40 catalysts, but noted made of terephthalic acid with methanol. that these, with the exception of a few With regard to the achievement of a good yield of organic salts hardly any sufficient effectiveness it is necessary to have dimethyl terephthalate as pure as possible; however, these catalysts underreact to obtain under a high degree of conversion in order to meet the severe reaction conditions, e.g. B. above Loss of residue during fine fractionation, the 45 140 "C, is strongly acidic and therefore leads to a corro for the recovery of dimethyl terephthalate from sion of the reaction vessel. It is therefore convenient "Fiber quality" is essential to reduce. It was impossible to successfully tech such catalysts, however So far not possible to use dimethyl terephthalate in niche. a stage with a higher degree of conversion as an object of the invention is therefore to provide one the one corresponding to the equilibrium, 50 Process for the preparation of dimethyl terephthalate because the boiling point of high purity formed as a by-product through in high yield. Next water is higher than that used as the starting material esterification of an approximately in equilibrium Methyl alcohol. For this reason borrowed reaction mixture of terephthalic acid and is z. B. the so-called »two-stage esterification methanol using a catalyst that procedure «applied. 55 no technically detrimental properties, such as B. In the first stage of this process, a corrosive capacity is obtained. The process for slurrying from excess methanol and solid production of dimethyl terephthalate according to the Er-terephthalic acid in a sealed reactor is characterized in that one is brought out and at high levels Temperatures and pressures of the esterification of terephthalic acid esterified with methanol. The use of a closed melt with a degree of conversion of tion vessel is necessary because methanol _{boils too low at normal pressure of at least 70 ° / 0} in the presence of a pressure containing tin, on the other hand the organic solubility of terephthalic acid with gaseous methanol Too little further esterified in methanol. would. Since there is an equilibrium reaction, in particular, according to the invention, the further the reaction beyond the equilibrium determined by the reaction conditions esterification with the tin salt of an organic acid does not progress beyond a Sn - C organotin compound, a tin step, unless certain measures are taken to alkoxide or a tin phenolate.
Separation of the water formed as a by-product.