JPH0370694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for distilling 1,2 dichloroethane (hereinafter referred to as EDC). More specifically, in order to effectively utilize the thermal energy possessed by the EDC gas recovered from the top of the column when EDC containing high-boiling substances is distilled in a high-boiling column, we will discuss an EDC distillation method that skips the heat recovery process. It is something.

Conventionally, the method for distilling EDC has been carried out in the manner shown in FIG. That is, in FIG. 1, crude EDC containing low-boiling point substances and high-boiling point substances is transferred from the dehydration tower and the vinyl chloride tower to conduits 101 and 102.
is fed to the low boiling point column 103, where the low boiling point substances are separated by distillation. Furthermore, the bottoms of column 103 containing high-boilers are fed via conduit 105 to high-boiler column 106 for distillation. tower 103
The heat energy required in the reboiler 104
Supplied by Distillate is collected via conduit 107 and fed to the EDC cracking furnace. While circulating through the conduit 108, the column bottom liquid is reheated in the reboiler 109, rises within the column, and is distilled again.

1,1,2 trichloroethane and 1,1,2,2
EDC containing 5 to 20 mole percent of high-boiling substances such as tetrachloroethane is fed as bottoms to the EDC recovery column via conduit 110. Also, tower 106
Most of the EDC gas, which is discharged from the top of the tower and whose pressure is less than 0.5 Kg/cm ² G, is cooled and condensed in the condenser 111, and then transferred to the gas-liquid separation tank 11.
2, the condensate is separated into a condensate and a non-condensable gas, and the condensate is extracted by a pump 113 and refluxed to the top of the column 106 again.

The EDC gas containing trace amounts of hydrogen chloride and water that is not condensed in the condenser 111 is cooled in the vent condenser 114, and the condensed liquid is extracted from the conduit 115 and the non-condensed gas is extracted from the conduit 116.

However, this conventional method has a drawback in that the thermal energy loss in the condenser 111 is not effectively utilized.

However, in the EDC distillation method, it is not known to recover and utilize the thermal energy loss in the top condenser of the distillation column.

On the other hand, there is a known attempt to recover heat by applying a compression heat pump to propylene and propane distillation columns ('Hydorocarbon
Processing” February 1981 issue, pages 119-126 and 1981
(March issue, pp. 147-151). However, since this method has completely different operating conditions such as pressure conditions and temperature conditions from the EDC distillation method, no method has been known that can be applied to EDC distillation.

Therefore, the present inventors have arrived at the present invention as a result of conducting blunt research on heat recovery conditions for EDC gas recovered from a high-boiling point column in an EDC distillation method.

That is, in the present invention, when EDC containing high-boiling substances is distilled in a high-boiling column, the pressure at the top of the high-boiling column is increased to above atmospheric pressure, and the EDC recovered from the top of the column is compressed. Introduced into the machine, further increase the pressure and temperature by 0.5-7Kg/cm ² and 7-80℃ from the suction pressure and temperature,
The present invention provides an EDC distillation method characterized in that it is used as a reboiler heat source for a high boiler column or a low boiler column.

In the present invention, the top pressure of the high boiler column is operated at above atmospheric pressure, preferably from atmospheric pressure to 1.5 Kg/cm ² G. This is because if a pressure higher than this is selected and the temperature is high, thermal decomposition of high boiling point substances contained in EDC will be promoted, which may cause trouble in the EDC purification process, etc.

In addition, the pressure and temperature increase by the compressor is 0.5 to 0.7Kg/cm ² ,
A temperature of 7 to 80°C is used. If the pressure and temperature are higher than this, not only the energy and equipment costs required for the compressor will increase, but also the thermal decomposition of the compressed EDC gas will be promoted, which may cause trouble in the EDC purification process, etc. Further, if the pressure and temperature are lower than this, the places where the recovered thermal energy can be used will be limited, and the equipment cost required for a heat exchanger for heat recovery will also increase.

According to the present invention, more than 85% of the total heat can be recovered with about 5 to 20% of the energy lost in the overhead condenser of the high boiler column. The heat source recovered here is circulated to a reboiler condenser such as a high boiler column or a low boiler column, and the thermal energy is recovered and used.

The present invention will be explained in more detail below with reference to Examples and Comparative Examples.

Comparative example 1 It is operated according to the flow sheet shown in FIG.

Low boiling point substance 0.7 mol% and high boiling point substance 0.5 mol%
Crude EDC containing 45.2 tons/hour with a heat transfer area of 300 m ²
A low boiler column 103 with 85 sieve trays and a thermosiphon reboiler 104 of
steam was supplied to the reboiler 104 through conduits 101 and 102, and 5.9 tons/hour of steam was supplied to the reboiler 104 for distillation. A high boiler column 106 with 51 sieve trays is further connected from the column bottom via a conduit 105 to the top pressure.
Distillation was carried out by supplying 10.3 tons/hour of steam to the reboiler 109 with a heat transfer area of 600 m ² under the condition of 0.05 Kg/cm ² G.

73.4 tons of EDC gas at 85℃ discharged from the top of the tower/
Time is supplied to condenser 111 via conduit 117, of which 72.8 tons/hour of EDC gas is condensed and refluxed by pump 113. The heat of condensation at this time is 5.64×10 ⁶ Kcal/hour. On the other hand, 0.6 tons of non-condensable EDC gas containing trace amounts of hydrogen chloride and water
At this time, the vent condenser 1 is connected via conduit 118.
14, and after being cooled, it is discharged through conduits 115 and 116. On the other hand, high boiling point substances
3.8 tons/hour of bottoms containing mole % at 95° C. are fed via conduit 110 to the EDC recovery column.

The 85°C liquid purified EDC extracted from the upper part of the column 106 through the conduit 107 contains 0.5 low boiling point substances.
mol% and 0.01 mol% high boiling point substances. In this distillation method, the amount of steam supplied to column 106 was 10.3 tons/hour.

Example It is operated according to the flow sheet shown in FIG.

Bottoms of the low boiler column of Comparative Example 1, composition, temperature,
Crude EDC with the same flow rate is passed through a conduit 201 to a high boiler column 202 having the same structure as in Comparative Example 1.
is supplied to the same distillation stage, and the column top pressure is 0.05Kg/cm ² G.
is distilled in

73.4 tons/hour of 85℃ EDC gas discharged from the top of the tower is 1.41Kg/cm ² G, 131℃ by turbo compressor 203
Of this, 71.3 tons/hour was pumped to conduit 2.
04 to the outside of the tube of a thermosiphon reboiler 205 with a heat transfer area of 1000 m ² . The supplied EDC gas is mixed with the bottom liquid of the column 202 at 95° C. which is circulated through the conduit 206 at a rate of 5.55×10 ⁶ Kcal/
The liquid is condensed through heat exchange and supplied to a gas-liquid separation tank 208 via a conduit 207. On the other hand, in order to maintain the pressure in the column 202, excess thermal energy is cooled and removed in a condenser 210. The result is supplied via conduit 209 to condenser 210;
After condensation, the EDC supplied to the gas-liquid separation tank 208 via conduit 211 was 1.5 tons/hour.

0.6 tons/hour of EDC gas containing trace amounts of hydrogen chloride and water is supplied from the separation tank 208 through a conduit 215.
It is supplied to a condenser 216, cooled, and then discharged.

Liquid EDC at 113.5℃ stored in separation tank 208
is cooled to 85° C. in heat exchanger 212 and then refluxed to the top of column 202 via conduit 214 by pump 213. On the other hand, 3.8 tons/hour of bottoms liquid having the same composition and temperature as in Comparative Example 1 was fed through conduit 217.
Supplied to the EDC recovery tower.

The 85° C. liquid purified EDC withdrawn via conduit 218 from the same distillation stage as column 106 of Comparative Example 1 in column 202 contains 0.5 mol % of bottom boilers and 0.01 mol % of high boilers. Ta.

The power required for the compressor 203 in this operation is
It was 910KWH/hour. In this distillation method,
Column 202, which corresponds to column 106 in the comparative example, did not require steam as a heat source.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing a conventionally known method for distilling 1,2 dichloroethane, and FIG. 2 is a flow sheet showing one embodiment of the present invention. In FIGS. 1 and 2, each symbol indicates the following content. 103...Low boiler column, 104...Reboiler for low boiler column, 106...High boiler column, 109...
... Reboiler for high boiling point column, 111 ... Condenser, 202 ... High boiling point column, 203 ... Turbo compressor, 205 ... Thermosiphon reboiler, 208 ... Gas-liquid separation tank, 210 ... Condenser, 212...Heat exchanger.

Claims (1)

[Claims] 1. When 1,2-dichloroethane containing high-boiling substances is distilled in a high-boiling column, the top pressure of the high-boiling column is distilled under atmospheric pressure or higher, and the 1,2-dichloroethane recovered from the top of the column is Introduce chloroethane gas into the compressor, and further reduce the pressure to 0.5 to 7 Kg/cm ² based on the suction pressure and temperature.
A method for distilling 1,2 dichloroethane, which is characterized in that the pressure and temperature are increased from 7 to 80°C, and the process is used as a reboiler heat source for a high-boiling point column or a low-boiling point column.