AT312896B - PROTECTIVE CAP FOR THE PART OF THE SUPPORT OF A SNOW CATCHER ATTACHED TO THE ROOF - Google Patents

Description

  

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The invention relates to a vcibesscrtes process for the preparation of terephthalic acid dimethyl ester by catalytic air oxidation of p-xylene / p-toluic acid methyl ester mixtures at elevated temperature, optionally elevated pressure, esterification of the acids formed and recycling of the p-toluic acid methyl ester for the oxidation using an oxidation catalyst a combination of cobalt and manganese compounds, according to patent no. 305991. According to the parent patent, the concentrations of Cō¯ and Mn ++ in the reaction medium are between 0.005 and 1% by weight.

   Compared to pure cobalt or pure manganese catalysts, these Co-Mn mixed catalysts result in a higher selectivity of the oxidation and thus also a higher yield of dimethyl terephthalate.



   It has now been found that this increase in yield can also be achieved with significantly lower amounts
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 can.



   In addition, it was found that the addition of manganese also has a beneficial effect on the esterification
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 The addition of manganese has no effect on esterification, however, at the very low manganese concentrations which are favorable for oxidation. It is therefore proposed to carry out the oxidation with low manganese concentrations and to add Mn ++ before the subsequent esterification of the oxidate.



   While aqueous CO ++ and Mn ++ salt solutions can be used for the oxidation, a manganese salt soluble in organic solvents, for example, is recommended for the esterification
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    Manganese initial and final products of the number of stages, the reaction temperature and the reaction pressure in the oxidation and in the esterification. Thus, the manganese concentration in the oxidation can be increased from stage to stage in accordance with the chosen reaction conditions and further Mn catalysts can be added after the oxidation. The further Manganzwatz after the oxidation can also be omitted entirely.



   The advantages of the process according to the invention can be seen from the following examples: With J pie I 1: In a stainless steel reactor with a volume of 1.5 m3 and with an air inlet pipe, heating and cooling system, vapor cooler and reaction water separator, 85 kg / h p- Xylene and 130 kg / h of p-toluic acid methyl ester fed. The level in the reactor is kept at 1 m3. 0.72 l / h of a 3% aqueous Co ++ acetate solution is fed in as a catalyst, so that a concentration of 100 ppm eo ++ is established in the reaction medium. In addition, 60 Nm3 / h of air are blown in.



  The temperature of the reactor is set to 160 ° C. and the pressure to 6 atQ. The concentrations of CO2 and CO in the exhaust gas as well as the concentrations of formic acid acetic acid in the reaction water are continuously analyzed. The evaluation of the analysis data shows the following amounts of by-products:
2, 15 kg / h C02
0.50 kg / h CO
0.14 kg / h formic acid
0.18 kg / h acetic acid
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 cis pie I 2: 1.35 kg / h CO2
0.37 kg / h CO
0.11 kg / h formic acid
0.16 kg / h acetic acid Example 3:

   To esterify the acid mixture obtained according to Example 2, 800 kg of this oxidate are poured into a stainless steel reactor with a capacity of 1.5 m3 and provided with a gas line pipe, heating and cooling system, vapor cooler and receiver, and 100 kg / h of methanol vapor at a temperature of 2000C and a Pressure of 25 atm initiated. When the acid number of the reaction mixture is about 5, the esterification is ended. The distillation of the reaction product gives a residue amount of 6.0%.



   B c) s p) e i 4: An acid mixture obtained from Example 2 is added under the same conditions as in Example 3, but with the addition of 100 ppm of Mn ++ in the form of 3% ethylacetate manganese in p-toluic acid methyl ester. Distillation of the reaction product results in a residue of 4.8%.

 

Claims (1)

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