DE1220407B - Process for the production of pure phthalic anhydride - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE!

EDITORIAL

Number:
File number:
Registration date:
Display day:

C07c

German KL: 12 ο -14

1220407
B 76154IV b / 12 ο
April 2, 1964
July 7, 1966

It is Z. B. from German patent specification 1144 709 known that in the gas phase oxidation of o-xylene over oxidation catalysts in the presence of Bromine or volatile bromine compounds containing phthalic anhydride. It is also from the USA patent 2,521,466 known that crude phthalic anhydride prepared from o-xylene is fractionated by Can purify crystallization from xylene or by fractional distillation. You get a though analytically pure, but yellowing phthalic anhydride when heated.

It has now been found that pure phthalic anhydride, which does not yellow when heated, is obtained from crude phthalic anhydride, which is obtained by oxidation of o-xylene with oxygen or such gases containing molecular form in the vapor phase at 250 to 600 ^° C. and residence times of 0.5 to 50 Seconds with the use of bromine or a volatile bromine compound on a vanadium oxide-containing catalyst was obtained by purification by distillation or crystallization if the crude phthalic anhydride is first fractionally crystallized from o-xylene and then the separated crystals are fractionated, optionally after washing with xylene distilled and optionally the mother liquor obtained during recrystallization is used as starting material for the production of phthalic anhydride.

Surprisingly, in the order of the cleaning process according to the invention, namely first crystallization from o-xylene and subsequent distillation, a highly pure, non-yellowing Phthalic anhydride is obtained, while in the reverse order, namely first distillation and then crystallization from o-xylene, only a phthalic anhydride which turns yellow on storage is obtained can be.

The production of phthalic anhydride from o-xylene is known. The starting material is used Reia-o-xylene (99.5%) or commercial o-xylene (95%). Man; but can also o-xylene with only 92% o-xylene content use, _ with the remainder mostly from the other xylenes, ethylbenzene and / or naphthalene as well as indane and methylindane.

The phthalic anhydride is separated off from the reaction gases and vapors in the usual way by condensation and then purified. According to the invention, this purification is carried out by recrystallization from o-xylene, 1.2 to 1.8 moles of xylene being used per mole of phthalic anhydride. The recrystallization can be carried out batchwise or continuously. For the separation of the um process for the extraction of pure
Phthalic anhydride

Applicant:

Aniline & Soda Factory in Baden

Aktiengesellschaft, Ludwigshafen / Rhein

Named as inventor:

Dr. Helmut Nonnenmacher,

Dr. Max Appl,

Dr. Jürgen Haug,

Dr. Konstantin Andrussow, Ludwigshafen / Rhine

crystallized phthalic anhydride are common

ao separating devices, e.g. B. Nutsche filters, filter presses, centrifuges, rotary filters or decanters are used. It is expedient to then wash the phthalic anhydride crystals with z. B. 500 to 1200 g pure xylene per kilogram of phthalic anhydride. The washing solution obtained can be used for the next one Use recrystallization approach.

After purification by recrystallization, the phthalic anhydride is expediently after drying, ie after driving off the xylene, for. B. under reduced pressure, fractionally distilled in the usual way, ie at a pressure of 10 to 400 Torr and at temperatures of 134 to 257 ⁰ C using columns with 5 to 30 theoretical plates. It is advantageous to use the mother liquor obtained when the crude phthalic anhydride is recrystallized from o-xylene as the starting material for the production of phthalic anhydride. It also contains the bromine compounds, which are initially contained as impurities in the crude phthalic anhydride. In this case, in the preparation of the phthalic anhydride, a separate addition of volatile bromine compounds can be completely or partially dispensed with.

example

a) recrystallization

9750 g of one in the oxidation of o-xylene with

Air on a catalyst of the composition

so 8.15% V ₂ O ₅ , 1.69% MoO ₃ , 0.16% P ₂ O ₅ , 0.10% Ag ₂ O, 10.4% Na ₂ S ₂ O ₇ , 30.5% K ₂ S ₂ O ₇ and 49.0% SiO ₂ at a temperature of 325 ⁰ C with supply

609 588/428

: i .1J22O 4 & Ψ

of 1.44 g o-Xylolbromid per 100 g o-xylene obtained Rohphthalsäureanhydrids the composition 92 weight percent of phthalic anhydride, 1.2 weight percent maleic anhydride and 0.62 ° / ₀ bromine in bound form are of 11 750 g Waschxylol by heating to 125 ° C and-slow cooling to 10 ° C., recrystallized using washing xylene as solvent, which was obtained after washing and drying a previous crystallization batch. c ■■ ■

On filtering off 11,050 g of filtrate are obtained, the 89 percent by weight of o-xylene, 5.5 percent by weight Contains phthalic anhydride, 0.73 percent by weight maleic anhydride and 0.505 percent by weight bromine. After adding 42 g of o-xylyl bromide, a mixture is obtained which is used as the starting material for the production of phthalic anhydride is suitable. So you get when using this mixture under the reaction conditions given above in this example with a crude phthalic anhydride a composition of 93 weight percent phthalic anhydride, 1.2 weight percent maleic anhydride and 0.68 weight percent bromine in bound form.

The recrystallized phthalic anhydride is washed with 10,000 g of o-xylene, with 10 550 g Waschxylol are obtained: By heating of the phthalic anhydride at 100 ⁰ C for a further 1200 g of o-xylene are aborted. Both liquid fractions can be used to recrystallize crude phthalic anhydride. After washing and drying, 8700 g of phthalic anhydride containing 97 percent by weight of phthalic anhydride, 0.41 percent by weight of maleic anhydride and 0.11 percent by weight of bromine are obtained in the form of organic bromine compounds.

b) distillation

Various crude phthalic anhydrides are made
through fractional. Purified distillation.

The following four tables show the conditions and results for distillations, referring to the distillation of

ba) recrystallized phthalic anhydride, which was obtained according to a), in a 50 cm long, glass Refer to packed column with 5 theoretical plates (Table 1),

bB) reaction product, as it is used as -Rohphthalsäureanhydrid for UmkristaUisation _v,) relate in the same distillation apparatus as described above (Table 2,
bc) Relate reaction products as used for bb) in a 2 m long fine fractionation column with 92 theoretical plates (Table 3), bd) Reaction product as used for bb), which, however, before the distillation with 2, 3 parts of sodium hydroxide to 100 parts of crude phthalic anhydride had been heated to 250 ° C. for 24 hours in order to bind the bromine (Table 4).

relate.

The bromine content of the distillate and the color comparison of the liquefied one serve as purity criteria and 3 hours at 250 ° C tempered distillation fraction with the ASTM standard designation D1209-54 specified color comparison solution H a ζ e η (American Chemical Journal, Vol. 14 [1892], p. 300).

Table 1

Use ..: ......... 1000g

Return ratio 1: 1

as pressure 80 torr

Bromine content

Color comparison Hazenzahl

300 to 350

20 to 60

100 to 150

95 g

Main fraction 730 g
Post fraction 84 g 0.016

Residue 77 g 1.37

*) = The bromine content is below the detection limit of. 0.005%.
... Table 2

Use 1000 g

Return ratio 1: 1

Pressure 80 torr

105 g Bromine content Color comparison 185 g 7o Hazenumber leader 210 g 0.168 > 350 45 1st parliamentary group 195 g 0.37 300 to 350 2nd parliamentary group 200 g 0.34 300 to 350 3rd parliamentary group 90 g 0.26 300 to 350 4th parliamentary group 0.15 300 to 350 Residue 4.6 -

Table 3

Insert 1180 g

Pressure 80 torr

fraction Boiling range Reflux ratio lot Bromine content Color comparison ⁰ C G ° / o Hazenumber 1 181 to 198 1:30 19.4 0.362 > 350 2 198.1 1:20 25.4 0.335 > 350 3 198.1 1:10 77.4 0.210 300 to 350 4th 198.1 1:10 78.6 0.110 300 to 350 5 198.2 1:10 275.3 0.092 250 to 300 6th 198.2 1: 5 469.9 0.076 200 to 250 7th 198.2 1: 3 28.7 0.170 200 to 250 8th 198.1 1: 2 31.2 0.205 > 350 9 198 to 202 1: 1 24.5 0.245 > 350 Residue - - 116 5.3

Tabel

Use 1300 g

Pressure 80 torr

fraction Boiling range Reflux ratio lot Bromine content Color comparison ⁰ C G % Hazenumber 1 180 to 198 1:30 99 0.106 > 350 2 198.0 1:20 231 0.024 200 to 250 3 198.0 1: 5 135 0.019 80 to 100 4th 198.0 1:10 186 0.017 200 to 250 5 198.0 1: 5 155 0.007 150 to 200 6th 198.1 1:10 138 0.022 300 to 350 7th 198.1 1: 5 93 0.010 300 to 350 8th 198 to 204 1: 3 67 0.015 > 350 Residue - - 165 4.5 -,

For comparison, a phthalic anhydride that has been purified by distillation is purified by recrystallization from o-xylene after the distillation. 200 g of the sixth and seventh fractions of the distillate according to example bc) above (Table 3) are recrystallized from 2000 g of o-xylene, then washed at 20 ° C. with 1000 g of freshly distilled o-xylene and at 100 ° C. under a pressure of 0.3 at absolute freed from o-xylene. The bromine content of this phthalic anhydride is 0.105% and the color comparison shows a Hazen number of 300 to 350. Even with subsequent recrystallization with exclusion of air, e.g. B. in a nitrogen atmosphere, no phthalic anhydride is obtained, the
has a better Hazenumber.

one

Claims (3)

Claims: 35 1. A process for the production of pure phthalic anhydride from crude phthalic anhydride, which is obtained by oxidation of o-xylene with oxygen or such gases containing in molecular form in the vapor phase at 250 to 600 ⁰ C and residence times of 0.5 to 50 seconds with the use of bromine or a volatile bromine compound had been obtained on a vanadinoxy-containing catalyst, by purification by distillation or crystallization, characterized in that the crude phthalic anhydride is first fractionally crystallized from o-xylene and then the separated crystals, optionally after washing with xylene, fractionally distilled and optionally the mother liquor obtained during recrystallization is used as a starting material for the production of phthalic anhydride. 2. The method according to claim 1, characterized in that one for fractional crystallization 1.2 to 1.8 moles of xylene are used per mole of phthalic anhydride. 3. Process according to Claims 1 or 2, characterized in that the crystals are washed 500 to 1200 g pure xylene per kilogram Phthalic anhydride is used. 609 588/428 6.66 ® Bundesdruckerei Berlin