CS265083B1 - A mixture of inhibitors to prevent the formation of polymers in dehydrogenation products from dehydrogenation of c-tylbenzene to styrene - Google Patents

Abstract

The mixture of inhibitors for preventing the formation of polymers in dehydrogenation products from the dehydrogenation of ethylbenzene to styrene during condensation at temperatures of 90 °C to 140 °C is composed of 0.5 to 1.5 parts by weight of 4-tert.butylpyrocatechin, 1 to 2 parts by weight of diethylhydroxylamine and 1 to 5 parts by weight of B-isopropyl-N '-phenyl-p-phenylenediamine in a total amount of the inhibitor mixture of 5 to 300 ppm based on the styrene content. The inhibitor mixture is added to the vapor phase of the dehydrogenation product.

Description

The invention relates to a mixture of inhibitors for preventing the formation of polymers in dehydrogenation products from the dehydrogenation of ethylbenzene to styrene during condensation at temperatures of 90°C to 140°C.

The unwanted polymer from the dehydrogenation products is formed in the vapor and liquid phases in the heat exchangers. The soluble polymer and the resulting oligomers pass through the rectification columns to the styrene residues. The insoluble polymer accumulates in the exchangers and causes technological problems. After a certain period of time, the exchanger must be shut down and cleaned, which leads to losses in production capacity and unnecessary costs.

However, the problem is to use a suitable inhibitor for this area of the technological process. It must meet the requirements. For the vapor phase area, a volatile inhibitor with a boiling point below 130 °C is the most suitable. When using such an inhibitor, there is a risk of negative effects on the rectification products, since it is impossible to prevent the transfer of the inhibitor to these technological streams. Furthermore, low solubility of the inhibitor in water, hygienic safety, good effectiveness of the inhibitor even in the liquid phase, non-participation in side reactions of the polymerizing product, etc. are required. The requirements of such stabilization cannot be met by a single substance and it is necessary to use a system of compounds so that their quantity and properties minimize the negative impact on the quality of wastewater, returnable ethylbenzene, benzene-toluene fraction, styrene rectification in their overall effect and to ensure sufficient effectiveness.

Currently, a mixture of inhibitors consisting of p-nitrophenol and quinonedioxime is used. The disadvantage of this mixture is the solubility of p-nitrophenol and 'quinonedioxime in water. Also

265 0Q3 4-tert. butylpyrocatechin did not prove to be an inhibitor due to low inhibitory activity and partial transfer of dehydrogenation products into the aqueous layer.

These disadvantages are eliminated by a mixture of inhibitors for preventing the formation of polymers in the dehydrogenation products from the dehydrogenation of ethylbenzene to styrene during condensation at temperatures of 90 °C to 140 °C, which is composed of 0.5 to 1.5 parts by weight of 4-tert.butylpyrocatechin, 1 to 5 parts by weight of N-iso- * propyl-N-phenyl-p-phenylenediamine and 1 to 2 parts by weight of diethylhydroxylamine in a total amount of the inhibitor mixture of 5 to 300 ppm, based on the styrene content. This mixture of inhibitors is added to the vapor phase of the dehydrogenation product.

The advantage of the inhibitor mixture according to the invention is the prevention of the formation of undesirable polymers with a minimized negative impact on the purity of wastewater and the rectification process. If we compare the properties of the individual components, it is clear that the use of a single substance is not suitable. Even while maintaining the same inhibitory effects in the case of diethylhydroxylamine, it would be necessary to use at least seven times the dose, but a small amount of diethylhydroxylamine in the mixture is suitable for maintaining perfect contact of the inhibitor with the vapor phase. N-isopropyl-N-A-phenyl-p-phenylenediamine and 4-tert.butylpyrocatechin guarantee a high inhibitory effect in the liquid phase, while from an ecological point of view it is possible to suppress the amount of 4-tert.butylpyrocatechin to the necessary minimum. N-isopropyl-N-phenyl-p-phenylenediamine is practically insoluble in wastewater with a pH above 3 and passes into styrene residues without affecting their quality.

Given that the most critical point of polymer formation is the condensation region of dehydrogenation products, where the temperature is around 115 °C, the influence on polymer formation was monitored on the lengths of the inhibition or (induction) periods of thermopolymerization of rectified styrene at 115 °C and 125 °C and further on the influence on the growth of the popcorn polymer.

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The effect of the inhibitor mixture according to the invention is described in more detail in the following specific examples.

Example 1

The stabilization efficiency of the inhibitor mixture in comparison with other inhibitors or inhibitor mixtures was verified by a stabilization test at temperatures of 115 °C and 125 °C. A glass apparatus equipped with a reflux condenser was used for the tests. A sample of steel ČSN 11 373 with a surface area of

approx. 20 cm, 18 g of styrene rectified was pipetted off and a 0.2% solution of inhibitor in ethylbenzene was added. The resulting mixture was stirred with an air stream and heated. For the entire series of measurements, rectified styrene was used.

Induction period (h)

At 115 °C and 125 °C at one temperature the same induction periods were used as follows:

Quantity (ppm)

Components

N-isopropyl-N-phenyl-

p-phenylenediamine (AO CD) 200 4 2 4-tert.Butyl Pyrocatechin (TBC) 200 3.5 1.5 diethylhydroxylamine (DEHA) 200 1 0.5 4 J p-Quinonedioxime (CHDGX) 200 5 1 p-nitrophenol (p-N0 ₂ F) 200 up to 0.5 up to 0.5 1 CHDQX + p-N0 ₂ F 100 + 100 3 0.5 AO CD + TB 100 + 100 9.5 4.5 AO CD + DEHA 100 + 100 · 3.5 1.5 TEC + DEHA 100 + 100 3.5 0.5 AO CD + TBC + DEHA 66 + 66 t 66 7 3.5- AO CDX+ TBC + DEHA 99 + 33 + 66 7 2.5 AO CD + TBC + DEHA 50- + 10 + 20 3.5 1.5 AO CD + TBC + DEHA 30+ 10 + 20 3 1 AO CD + TBC + DEHA 15 + 10 + 5 1 —

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Example 2

Furthermore, the effect of the inhibitory systems CHEQX + p-NOgP, TBC + LEHÁ, TBC + AO CL in the amount of 20 + 20 ppm on the styrene content on the growth of popcorn polymer grafted into styrene rectified in the amount of 1 g at a temperature of 90 °C was tested.

Components Quantity Induction period (ppm) (h) AO CD + TB 20 + 20 9.5 TB + DEHA 20 + 20 7 CHDGX + p-NO ₂ F 20 + 20 4

All of the systems mentioned limited the growth of pop black during the period of effectiveness, while with rectified styrene alone, the weight of pop black increased by 10% after one hour and the styrene polymerized strongly.

Claims (1)

Mixture of inhibitors to prevent the formation of polymers in dehydrogenation products from dehydrogenation of ethylbenzene to styrene at condensation at 90 ° C to 140 ° C, characterized in that it consists of 0.5 to 1.5 parts by weight of 4-tert-butylpyrocatechin; up to 2 parts by weight of a diethylhydroxylamine and 1 to 5 parts by weight of N-isopropyl-N- (phenyl-p-phenylenediamine) in a total amount of inhibitor mixture of 5 to 300 ppm, based on the styrene content.