JPH0332531B2 - - 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, when EDC containing high boiling point substances is distilled in a high boiling point column, the thermal energy of the EDC gas recovered from the top of the column is effectively utilized, and the thermal efficiency of the EDC distillation process is significantly improved. It is about law.

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-boiling substances are fed via conduit 105 to high-boiler column 106 and distilled. The thermal energy required by column 103 is supplied by reboiler 104. The distillate is fed via conduit 107 to the harvested 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 mol % of high-boiling substances such as tetrachloroethane is fed as bottoms to the EDC recovery column via conduit 110. Also, tower 10
Most of the EDC gas discharged from the top of the column in the gas-liquid separation tank 1 after being cooled and condensed in the condenser 111 and having a pressure of less than 0.5 Kg/cm ² G.
The condensed liquid is separated into a condensed liquid and a non-condensed gas at 12, and the condensed liquid 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.

The present inventors have previously proposed a heat recovery method as shown in the flow sheet shown in FIG.
Although he invented a method for distilling EDC and applied for a patent, this method requires a large amount of equipment cost for the compressor for the EDC gas discharged from the top of the column and the reboiler condenser for the distillation column. Not only does the energy consumption increase, but the thermal energy of the compressed EDC gas is greater than the thermal energy required by the reboiler condenser, so the heat recovery rate is not satisfactory. In addition, since the condensation temperature of the compressed EDC gas in the reboiler condenser becomes low, it is difficult to recover and use the sensible heat energy (thermal energy from the condensation temperature to the top temperature of the high boiling point column) of the condensed EDC. This had some drawbacks, and it was necessary to make further improvements.

The present inventors have arrived at the present invention as a result of intensive research in search of a thermally efficient EDC distillation method that eliminates the above-mentioned drawbacks.

That is, the present invention includes a high boiling point process consisting of a low boiling point distillation step, a high boiling point distillation step, and a heat recovery step of gas recovered from the top of a high boiling point column.
In the EDC distillation method, the top pressure of the high boiling point column is distilled under pressure of 0.5 kg/cm ² G or more, and the EDC gas recovered from the top of the column is further reduced by 0.5 kg/cm 2 G or more by the suction pressure and temperature. Kg/cm ² or more, the pressure and temperature are increased by 10℃ or more, and this is transferred to the reboiler of at least two columns selected from the group consisting of a high boiler column, a low boiler column, a dehydration column, an EDC recovery column, and a vinyl chloride column. The present invention provides a method for distilling EDC, which is characterized in that it is used as a heat source.

In the present invention, the top pressure of the high boiler column is 0.5
Kg/cm ² G or more is sufficient, but 0.5 to 1.5 Kg/cm ² G is usually adopted in order to suppress thermal decomposition of EDC or a high boiling point substance contained in EDC.

In addition, the compression of EDC gas by a compressor is 0.5Kg/
cm ² or more is sufficient, but 0.5 to 2.0 Kg/cm ² is usually adopted in order to suppress an increase in the energy required for pressurization and the equipment cost required for installing a compressor.

According to the present invention, the total amount of heat can be recovered as a heat source for the distillation column reboiler of a vinyl chloride monomer plant including a high boiler column, with approximately 8% of the energy lost in the overhead condenser of the high boiler column. However, the compression energy can be reduced to 8% or less by reducing the pressure loss within the distillation column or by increasing the heat transfer area of the reboiler condenser.

Furthermore, even when comparing the case where the float sheet heat recovery method shown in Fig. 2 is applied to the high boiling point column,
The energy required for the compressor can be reduced to about 1/2, and equipment costs can be significantly reduced.

Furthermore, in order to increase the operating pressure of the high boiler column,
Although the distillate temperature, that is, the purified EDC temperature and the bottom EDC temperature, increases, this increased thermal energy is effectively recovered in the EDC cracking furnace and EDC recovery tower, which are the respective supply destinations.

In addition, since the condensation temperature of EDC is high on the outside of the reboiler tube, it is possible to make the process even more advantageous by recovering the thermal energy from the condensation temperature to the top temperature of the high boiler column. be. For example, it is also possible to reduce the steam requirements of the high boiler column by exchanging heat with the dehydration column bottoms and low boiler bottoms. Yet another example is that the amount of generated steam can be increased by exchanging heat with heated water supplied to a steam generator for removing reaction heat in the oxychlorination reaction zone.

As described above, the present invention is an industrially extremely advantageous method that enables a significant reduction in the energy consumption of a vinyl chloride monomer plant, a significant reduction in equipment costs, and ease of operation.

Next, the present invention will be explained 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 having 51 sieve trays is further connected from the 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/hour of non-condensable EDC gas containing trace amounts of hydrogen chloride and water is supplied to the vent condenser 114 via a conduit 118, cooled, and then withdrawn. On the other hand, 3.8 tons/hour of bottoms at 95°C containing 5 mol% of high boiling point substances are transferred to the EDC via conduit 110.
Supplied to recovery tower.

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 columns 103 and 106 was 16.2 tons/hour.

Comparative example 2 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 2 having the same structure as in Comparative Example 1.
02 is supplied to the same distillation stage, and the top pressure is 0.05Kg/
Distilled in cm ² .

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 supplied 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 low-boiling substances and 0.01 mol % of high-boiling substances. Ta.

The power required for the compressor 203 in this operation is
It was 910KWH/hour.

EXAMPLE One embodiment of the invention operates according to the flow sheet of FIG.

Rough with the same composition, temperature, and flow rate as Comparative Example 1.
45.2 tons/hour of EDC is produced by the low boiler column 303 with the same structure.
were supplied through conduits 301 and 302 and distilled under the same conditions.

The bottoms of the low-boiling column 303 were supplied via a conduit 304 to a high-boiling column 305 having the same structure as in Comparative Example 1, and distilled at a top pressure of 1.0 Kg/cm ² G.

73.4 tons/hour at 106℃ discharged from the top of the tower
The EDC gas was supplied to a turbo compressor 307 via a conduit 306 and compressed to a state of 2.1 Kg/cm ² G and 130°C. The turbo compressor was driven by an electric motor at approximately 3600 revolutions per minute.

42.4 tons/hour of the compressed EDC gas is supplied via conduit 308 to the outside of the tube of a thermosiphon reboiler 309 for a low boiler column with a heat transfer area of 370 m ² and circulated inside the tube via conduit 310. It exchanges heat with the bottom liquid at 95°C, condenses at a temperature of 123°C, and is supplied to a gas-liquid separation tank 312 via a conduit 311.
The amount of heat exchanged in this case is 3.14×10 ⁶ Kcal/hour,
This corresponds to the 5.9 tons/hour of steam required for distillation in the low boiler column 103 in Comparative Example 1.

In addition, the remaining compressed EDC gas (31.0 tons/hour) is supplied via conduit 313 to the outside of the tube of a thermosiphon reboiler 314 for a high boiler column with a heat transfer area of 1000 ^m2 , and is supplied to the inside of the tube via conduit 315. It exchanges heat with the circulating bottom liquid at 115°C, is condensed at a temperature of 123°C, and is supplied to a gas-liquid separation tank 317 via a conduit 316. The amount of heat exchanged in this case is 2.29×10 ⁶ Kcal/
hour, which is equivalent to 4.4 tons/hour of steam. In addition, 6.5 tons/hour of steam was supplied to reboiler 318 with a heat transfer area of 300 m ² . This is 3.4
Equivalent to the amount of heat x10 ⁶ Kcal/hour.

0.3 tons/hour of EDC gas containing trace amounts of hydrogen chloride and water from separation tanks 312 and 317 is transferred to conduit 31.
Discharge via 9.

The 123°C liquid EDC stored in separation tanks 312 and 317 is transferred to heat exchangers 320 and 321 at 106
℃ and refluxed via conduit 324 to the top of high boiler column 305 by pumps 322 and 323.

From the bottom of the high boiler column 305, 3.8 tons/hour of bottoms having the same composition as in Comparative Example 1 and at a temperature of 115°C is poured into the conduit 325.
is supplied to the EDC recovery tower via.

40.5 tons/obtained from the 48th distillation stage from the bottom of the column
At this time, the liquid purified EDC at 106° C. contains 0.5 mol % of low boiling point substances and 0.01 mol % of high boiling point substances and is fed to the EDC decomposition furnace via conduit 326 .

The power required for compressor 307 in this operation is
It was 500KWH/hour. Also, the high boiler column 305
The pressure was increased from Comparative Examples 1 and 2 to 1.0Kg/cm ² G.
As a result, the amount of heat required for EDC decomposition and EDC recovery tower was reduced by 3.1×10 ⁵ Kcal/hour. this is steam
Equivalent to 0.6 tons/hour.

[Brief explanation of the drawing]

1 and 2 are flow sheets showing a method for distilling 1,2 dichloroethane as a comparative example, and FIG. 3 is a flow sheet showing an embodiment of the present invention. In Figures 1, 2 and 3, each symbol indicates the following content. 103...Low boiler column, 104...Thermosiphon reboiler for low boiler column, 106...High boiler column, 109...Thermosiphon reboiler for high boiler column, 111...Condenser, 2
02...High boiler column, 203...Turbo compressor,
205...Thermosiphon reboiler, 20
8... Gas-liquid separation tank, 210... Condenser, 2
12...Heat exchanger, 303...Low boiler column, 30
5... High boiler column, 307... Turbo compressor, 3
09... Thermosiphon type reboiler for low boiling point column, 312... Gas-liquid separation tank, 314... Thermosiphon type reboiler for high boiling point column, 317...
...gas-liquid separation tank, 318...reboiler, 320,
321...Heat exchanger.

Claims (1)

[Scope of Claims] 1. A method for distilling 1,2 dichloroethane containing a high-boiling point substance, which comprises a low-boiling point distillation step, a high-boiling point distillation step, and a heat recovery step for gas recovered from the top of a high-boiling point column. , the top pressure of the high boiler column is 0.5
The 1,2 dichloroethane gas distilled under pressure of Kg/cm ² G or more and recovered from the top of the column is further distilled by a compressor to 0.5 Kg/cm ² or more from the suction pressure and temperature.
The pressure and temperature are increased by 10℃ or more, and this is used as a heat source for the reboiler of at least two columns selected from the group consisting of a high boiler column, a low boiler column, a dehydration column, a 1,2 dichloroethane recovery column, and a vinyl chloride column. A method for distilling 1,2 dichloroethane. 2. The method for distilling 1,2 dichloroethane according to claim 1, wherein the pressure at the top of the high boiler column is 0.5 to 1.5 Kg/cm ² G. 3. The method for distilling 1,2 dichloroethane according to claim 1 or 2, wherein the pressure of the 1,2 dichloroethane gas is further increased by 0.5 to 2.0 Kg/cm ² from the suction pressure using a compressor.