The method of stabilization of the quality of styrene-rectified on the content of oxygen-containing compounds

 

(57) Abstract:

The invention relates to a process for the production of propylene oxide together with styrene and can be used in other petrochemical processes. The proposed method of water condensate obtained after condensation of the contact strip in the process of dehydration methylphenylcarbinol before it is recirculated to the node contact cooling gas, is subjected to vacuum distillation from propanal - source education hexenal, having a boiling point, ulissey to styrene. The technical challenge is to ensure consistent quality of styrene-rectified on the content of oxygen-containing compounds in accordance with GOST in the coproduction of propylene oxide and styrene and reduce the overall costs of raw materials and energy. 1 Il., table 1.

The invention relates to a process for the production of propylene oxide together with styrene and can be used in other chemical processes.

A method of obtaining a styrene-rectifier during its joint production with propylene oxide by the catalytic dehydration of methylphenylcarbinol with subsequent cooling and condensation of the contact gas is hydrated condensate, obtained by condensation of the contact gas is first used for flushing and cooling gas contact, and then fed into the evaporating device for receiving secondary water vapor with subsequent overheating and dehydration. (I. A. Kirpichnikov, etc. Album technologically schemes the main production of the synthetic rubber industry. Leningrad: Khimiya, 1986).

The disadvantage of this method is periodic excess content of high-boiling oxygenated compounds in the styrene-rectified.

Studies have shown, a source of formation of high-boiling oxygenated compounds and hit them with a styrene-rectified are the lungs of oxygen-containing C2-C3(mainly propanal) that getting into the water condensate in an alkaline environment become more "heavy" oxygen, which then accumulate in the circulating water layer, invariably come with the main stream of hydrocarbon rectification (B. P. Serebryakov. New processes of organic synthesis. M.: Chemistry, 1989).

In this case there are almost all oxygenated compounds except hexanes (2-petillant-2-EN-1-Ala), showpad the distillation of hydrocarbon condensate.

The content of propionic aldehyde, the main source of education hexanes in contact with gas ranges from 0.01 to 0.05 wt.%

Periodically, the content of oxygen (hexanes) in the styrene-rectified based on the benzaldehyde reaches of 0.02 - 0.09 wt.%, at a time when this value according to GOST should not exceed 0.01 wt.%. For higher and 0.02 wt.% for first grade.

Tried several ways to purify water of condensation, but none of them by changing the pH or chemical binding, however, as existing at present in industrial production, do not provide stable until receipt of styrene and lead either to increased content of carboxylic acids, or additional costs of raw materials and energy.

The proposed method devoid of the above disadvantages, because it allows to obtain a stable styrene-rectified only the highest and first grade.

The objective of the invention is the provision of quality styrene-rectifier on the content of oxygen-containing compounds in accordance with GOST.

The problem is solved in that the water condensate obtained by condensation of the contact strip, before it is recirculated to the site of ohlazhdeniya of column 620 mm RT. senior - 690 mm RT. Art.

Full cleaning of the condensate from oxygen ensures stable quality of styrene-rectified by hexanal considering getting part of propanal rectification and hydrocarbon condensate.

For the proposed method (see drawing) contact gas after dehydration methylphenylcarbinol in styrene from line 1 enters the foaming device 2 for separation of catalyst dust and temperature decreases from 260 to 120oC.

Chilled contact gas line 3 is fed sequentially in the capacitors 4 and 6, the condensate line 7 flows into the tank 8, where the separation of hydrocarbon and water condensate.

Hydrocarbons from the tank 8 through line 33 are received in the receptacle 34 and thence through line 35 by the pump through line 37 are sent for rectification.

Neskondensirovannyh gas line 38 is fed to the compressor 39 and then through line 40.

Water condensate from the tank 8 through line 9 pump 10 is supplied via line 11 through the condenser 12 through line 13 to column purification from oxygen-containing compounds 14 working under vacuum. The distillate of the column, volatile and water line 15 coming to the capacitor 16. Volatile on line 17 and through the HAC the line 48 is supplied to the cleaning. Its bottom liquid of the column 14 through line 45 by the pump 20 through line 22 is supplied to the heat exchanger 12, where it gives off its heat to the column 14 condensate and thence by line 23 to the foam apparatus 2. In line 23 is supplied via line 32 alkaline solution to neutralize the carboxylic acids.

The condensate from the bottom of column 2 through line 24 by pump 25 is supplied to the heat exchanger 27 where it is heated by the heat of the steam condensate and thence by line 28 evaporating device 29, the heated vapor pressure in the line 41. Obtained from the aqueous condensate water vapor line 31 is returned to the host dehydration methylphenylcarbinol. The residue after evaporation of the condensate, containing high-boiling hydrocarbons and alkali on line 30 will be sent for incineration.

The invention is illustrated by the following examples,

Example 1 (the prototype). Existing industrial way water condensate obtained after condensation and separation of the contact strip in the amount of 30 t/h is sent to the foam machine node contact cooling gas.

The composition of the water coming into the foam apparatus shown in the table of example 2.

The total content of the boiling oxygen-containing sedimentary hexanes.

The content of hexanal in terms of benzaldehyde is with the styrene-rectifier, wt.%:

GOST

Top grade - 0,01

grade 1 - 0.02

Actually - 0,01-0,05

When exceeding the content of hexanes to obtain a styrene-rectifier higher or 1st grade requires re-processing of styrene, accompanied by losses of hydrocarbons and additional energy consumption.

Example 2. The proposed method steam condensate after condensation and separation of the contact gas is fed to the distillation column volatile oxygen-containing compounds, and then sent to the site contact cooling gas in the foam machine.

The material balance of the rectification column steam condensate from oxygen-containing compounds listed in the following table (see the end of the description).

If this is maintained, the following mode of rectification:

Vacuum top - 620 mm RT. Art.

Vacuum bottom - 720 mm RT. Art.

The temperature of the top - 70oC

The temperature of the bottom - 96oC

Reflux the number - 30

After cleaning the water condensate content of hexanal in the styrene-rectified sharply reduced and stabilized in the following limit is - 0.02

Example 3. The distillation column oxygen-containing compounds is fed steam condensate in the amount of 30 t/g and obtained the products listed in the table of example 2.

If this is maintained, the following technological conditions:

Vacuum top - 690 mm RT. Art.

Vacuum bottom - 700 mm RT. Art.

The temperature of the top - 80oC

The temperature of the bottom - 96oC

Reflux the number - 30

The resulting styrene-rectified corresponds to GOST for the highest and first grade.

Thus, the vacuum distillation of volatile oxygenated allows to completely clear them from the water condensate on the cooling node contact strip.

It is noted predominant amount of styrene of the highest quality, and virtually eliminated recycling styrene, leading, naturally, to reduce the overall costs of raw materials and energy.

The method of stabilization of the quality of styrene-rectified on the content of oxygen-containing compounds in the process of obtaining propylene oxide together with styrene by cooling and condensation of gas contact with subsequent separation and distillation of the hydrocarbon condensate and recycling on the foam and the outside, before it is recirculated to the foam apparatus, is subjected to rectification from boiling oxygenated compounds under vacuum the top of the column 620 to 690 mm RT.article

 

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