JPH0127052B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat recovery method for recovering heat discarded in a cooling step after partial thermal decomposition of 1,2-dichloroethane and utilizing it as a heat source for a 1,2-dichloroethane distillation column. The. B. F. Gutsudoritsusha's Special Publication 1977-
17205, U.S. Patent No. 3484493 by Kunatsupzatsk Company, and the "Oxychlorination Vinyl Chloride Synthesis Process" published by the Japan Petroleum Institute, 1,2-dichloroethane is usually pressurized to about 40 atmospheres by a pump and passed through a hairpin-shaped stainless steel pipe. The tube is sent to a cracking furnace that connects a large number of tubes, where it is heated to 480
It is heated to 540°C and decomposed into hydrochloric acid and vinyl chloride. These mixtures are sent to a quench tower together with undecomposed 1,2-dichloroethane and cooled to 70°C.
The entire amount of heat lost at this time is discarded to the cooling water side via a heat exchanger. The cooled mixture is sequentially sent to four distillation columns connected in series, and by appropriately selecting operating conditions, hydrochloric acid is produced from the top of the first distillation column, vinyl chloride is produced from the top of the second distillation column, A component with a lower boiling point than 1,2-dichloroethane comes from the top of the third distillation column, and high-purity 1,2-dichloroethane comes from the top of the fourth distillation column, and 1,2-dichloroethane comes from the bottom of the fourth distillation column.
-High boiling components are obtained from dichloroethane. High purity 1,2- recovered from the fourth distillation column
Dichloroethane is recycled to the cracking furnace again, so
Almost all of the 1,2-dichloroethane will be converted to hydrochloric acid and vinyl chloride. Although the above-mentioned known processes or processes based on the same principle are widely practiced industrially, the disadvantage of these processes is that a large amount of heat is wasted in the quenching column, while the distillation column, especially the fourth first, A distillation column (hereinafter sometimes referred to as EDC) for recovering 2-dichloroethane requires a large amount of steam in its bottom heat exchanger. As a result of intensive studies to solve the problems of the conventional technology, the inventors of the present invention recovered the heat of the pyrolysis mixture by flowing hot water through a heat exchanger connected to a quenching tower. It was discovered that it can be used as a heat source for EDC tower heat exchangers. Also, this
EDC towers are normally operated at atmospheric pressure, but the present inventors operated this EDC tower at a reduced pressure below atmospheric pressure to reduce the specific volatility (alpha) of 1,2-dichloroethane and high-boiling components. It has been found that the boiling temperature of the EDC column bottom heat exchanger is lowered and that heat recovery from the hot water is performed economically. Thus, according to the invention, vapor of 1,2-dichloroethane is introduced into a pyrolysis reactor under pressure, and about
Hydrochloric acid, vinyl chloride, and undecomposed 1,2-dichloroethane are generated through partial thermal decomposition at 450 to 650°C, and the mixture is cooled with 1,2-dichloroethane in a quenching tower, followed by a distillation tower connected in series. In the method of sequentially obtaining hydrochloric acid, vinyl chloride, and 1,2-dichloroethane, hot 1,2-dichloroethane from the bottom of the quenching tower is introduced into a heat exchanger connected to the quenching tower, where 1,2-dichloroethane is The heat of 1,2-dichloroethane is recovered from the hot water returned from the distillation column bottom heat exchanger and used as a heat source for the 1,2-dichloroethane distillation column, which is operated under reduced pressure. A method of manufacturing vinyl inexpensively is provided. A preferred embodiment of the present invention using hot water will be described below with reference to FIG. 1,2-dichloroethane is extracted from tank T-1 by pump 2, pressurized to about 35 kg/m ² gauge, and sent to cracking furnace A. The stainless steel pipe inside the decomposition furnace is heated by flame, and the temperature of 1,2-dichloroethane is raised to approximately 500℃ at the outlet, reducing the temperature by 40 to 60%.
is decomposed into hydrochloric acid and vinyl chloride, and undecomposed 1,2
- Enters the quenching tower C via pipe 3 together with dichloroethane. From the top of the quenching tower, it passes through pipe 4 to heat exchanger E-2.
The high-temperature gas from the decomposition furnace into which liquid 1,2-dichloroethane cooled to 40 to 100°C is fed is rapidly cooled. A gas mainly composed of hydrochloric acid and vinyl chloride is discharged from the top of the quenching column and enters the first distillation column C-1 via pipe 5. 100℃~170℃ from the bottom of the quenching tower
A liquid containing 1,2-dichloroethane as a main component at a temperature of
1, where it exchanges heat with hot water, and most of its heat is recovered. The liquid that exits E-1 is then transferred to E
-2, it is cooled by cooling water. A portion of the liquid from the pump 7 directly passes through the pipe 8 and enters the first distillation column C-1. The top pressure of the first distillation column is
It is operated at a gauge of 10 to 18 kg/cm ² and a temperature of -30 to -12°C, and high purity hydrochloric acid is discharged from the top via pipe 9. A mixture of vinyl chloride and 1,2-dichloroethane is discharged from the bottom and enters the second distillation column C-2 via pipe 10. The second distillation column is 4.0-5.0Kg/cm ²
The system is operated at a temperature of 30 DEG to 40 DEG C., and from the top, high purity vinyl chloride, which can be used as a monomer for producing vinyl chloride resins, is obtained via pipe 11. A mixture of 1,2-dichloroethane and a small amount of impurities is discharged from the bottom and enters the third distillation column C-3 via pipe 12. The third distillation column is a column that removes impurities with a boiling point lower than that of 1,2-dichloroethane, and is operated at a top pressure of atmospheric pressure and a temperature of 30 to 40°C, and from the top, a few percent each of chloroprene and 1,1-dichloroethane are extracted. A small amount of 1,2-dichloroethane containing 13
It is then discharged. 1,2-dichloroethane is discharged from the bottom via line 14. Fresh 1,2-dichloroethane is fed through tube 15 and
4 and enters the fourth distillation column C-4 (EDC column).
The fourth distillation column is a 1,2-dichloroethane purification column whose pressure is below atmospheric pressure and whose temperature is 1,2-dichloroethane at that pressure.
- operated at the boiling point of dichloroethane. As shown in Table 1, the specific volatility of 1,2-dichloroethane and impurities with higher boiling points increases as the temperature decreases, so when distilling 1,2-dichloroethane, the temperature must be lowered. It is preferable to do so because the purification operation can be achieved with a small reflux ratio.

[Table] Highly purified 1,2-dichloroethane, which can be used as feedstock for the cracking furnace, is obtained from the top of the EDC tower.
It is sent to tank T-1 via pipe 16. The reflux liquid returns to the top in tube 17. The heat recovered from the pyrolysis gas cooling step, which is the object of the present invention, is utilized in a heat exchanger at the bottom of the EDC tower. In other words, 1,2-dichloroethane containing a small amount of high-boiling point impurities is boiling at the bottom of the column, with a boiling point of 60 to 80°C and a pressure of -360 to -100 mm.
It's an Hg gauge. The hot water from heat exchanger E-1 has a temperature of 90 to 160°C and passes through pipe 18 to heat exchanger E- at the bottom of the EDC column.
3 and gives the heat to 1,2-dichloroethane at the bottom of the column. The hot water discharged from the heat exchanger E-3 is pressurized by the pump 19 and returns to the heat exchanger E-1 via the pipe 20, thereby achieving heat recovery. There may be a plurality of heat exchangers at the bottom of the EDC column, and other heat sources such as steam may be used in combination. Heat exchanger E-4 shows an example in which steam is used in combination. From the bottom of the EDC column, 1,2-dichloroethane containing a small amount of high-boiling components and tar is discharged via pipe 21. Hereinafter, the present invention will be specifically explained by giving examples. Example An example using the apparatus shown in FIG. 1 will be described. 10000 kg/h of 1,2-dichloroethane was fed into decomposition furnace A and thermally decomposed under conditions such that the outlet temperature was 520°C. The outlet pressure was 21 Kg/cm ² gauge. 55% of 1,2-dichloroethane is decomposed, and 2020 kg/h of hydrochloric acid, 3460 kg of vinyl chloride, and 4520 kg/h of undecomposed 1,2-dichloroethane are sent in gaseous form to the quenching tower C, and are fed from the top of the tower. 70℃
The mixture was melted with a liquid containing 1,2-dichloroethane as a main component, cooled to 120°C, discharged from the top, and sent to the first distillation column C-1. This amount is 4900Kg/
It was H. The liquid from the bottom of the quenching tower is drawn out at 130°C, pressurized by pump 7, and sent to heat exchanger E-1. In E-1, it exchanges heat with the hot water returned from the EDC tower bottom heat exchanger E-3, is cooled to 85°C, and is sent to the next heat exchanger E-2. In E-2, it exchanges heat with cooling water, is cooled to 70°C, and returns to the quenching tower again. A portion of the quench bottoms was sent to the first distillation column as well as the gas from the top. This amount was 5100Kg/H. The first distillation column has a top pressure of 12Kg/cm ² gauge and a temperature of -
It was operated at 25°C, and 2020 kg/H of hydrochloric acid was discharged from the top, and 7980 kg/H of a mixed solution of vinyl chloride and 1,2-dichloroethane was discharged from the bottom, which was sent to the second distillation column C-2. The second distillation column has a top pressure of 5.0Kg/ ^cm2 gauge and a temperature of
It was operated at 40°C, and 3460 kg of vinyl chloride was discharged from the top, and 4520 kg/H of a liquid containing 1,2-dichloroethane and a small amount of impurities was discharged from the bottom and sent to the third distillation column C-3. The third distillation column was operated at a top pressure of atmospheric pressure and a temperature of 35°C;
- 110 kg of 1,2-dichloroethane liquid containing 5.0% dichloroethane is discharged, 4410 kg of liquid containing 1,2-dichloroethane and small amounts of high boilers and tar is discharged from the bottom, and 5640 kg of fresh 1,2-dichloroethane/H and was sent to EDC tower C-4. The EDC tower has 30 trays, and the top pressure is -360
mmHg gauge, operated at a temperature of 62°C and a reflux ratio of 0.5;
From the top, 10,000 kg/h of 1,2-dichloroethane with a purity of 99.99% or higher was recovered. The bottom of the tower is -170mm
Hg gauge, can be operated at a temperature of 81℃, 1,
1,2-trichloroethane and tar total approximately 15%
50 kg/h of 1,2-dichloroethane solution containing 1,2-dichloroethane was discharged. Heat exchanger E-3 at the bottom of the column contains 32,200 ml of hot water at 110°C.
Kg/H of steam was supplied, and another heat exchanger E-4 was supplied with 700 Kg/H of steam. Comparative Example An example using the apparatus shown in FIG. 2 is shown. 10000 kg/h of 1,2-dichloroethane was fed into decomposition furnace A and thermally decomposed under conditions such that the outlet temperature was 520°C. The outlet pressure was 21 Kg/cm ² gauge. 55% of 1,2-dichloroethane decomposes, hydrochloric acid 2020Kg/H, vinyl chloride 3460Kg/H
4520 kg/H of undecomposed 1,2-dichloroethane is sent in gaseous form to quenching tower C, where it comes into contact with a liquid containing 50°C 1,2-dichloroethane and vinyl chloride as main components, which is sent from the top of the tower. It was then cooled to 80°C, discharged from the top, and sent to the first distillation column C-1.
This amount was 2000Kg/H. The liquid from the bottom of the quenching tower C is drawn out at 90°C, pressurized by pump 7, and transferred to two heat exchangers E-1 and E-2.
It is then cooled down to 50°C by cooling water and returned to the quenching tower. A portion of the quench tower bottoms was fed into the first distillation column as well as the gas from the top. This amount is 8000Kg/H
It was hot. The operating conditions of the first, second and third distillation columns are as follows:
Since the flow rate and composition are almost the same as those in the example, the explanation will be omitted. EDC column C-4 had 30 plates and was operated at atmospheric pressure at the top, temperature at 83.6°C, and reflux ratio at 1.0, and 10,000 kg/H of 1,2-dichloroethane with a purity of 99.99% or higher was recovered from the top. The pressure at the bottom of the tower is 0.30Kg/
^cm2 gauge and operated at a temperature of 96 °C. From the bottom of the tower is 1,
1,2-trichloroethane and tar total approximately 15%
50 kg/h of 1,2-dichloroethane containing 1,2-dichloroethane was discharged. 2900 kg/H of steam was supplied to heat exchanger E-4 heated by steam at the bottom of the tower.

[Brief explanation of drawings]

The attached FIG. 1 is a flow diagram showing the present invention,
FIG. 2 shows a known flow diagram for comparison. Here, A is a cracking furnace, C is a quenching tower, C-4 is a fourth distillation column (EDC tower), E-1, E-2, E-3,
E-4 each represents a heat exchanger.

Claims (1)

[Claims] 1. 1,2-dichloroethane vapor is introduced into a pyrolysis reactor under pressure, and partially pyrolyzed at about 450 to 650°C to produce hydrochloric acid, vinyl chloride, and undecomposed 1,2-dichloroethane, and a mixture thereof After being cooled with 1,2-dichloroethane in a quenching tower, it is introduced into a series-connected distillation tower where hydrochloric acid, vinyl chloride,
In each method for obtaining 1,2-dichloroethane, hot 1,2-dichloroethane from the bottom of the quenching tower is led to a heat exchanger connected to the quenching tower, where it is returned from the 1,2-dichloroethane distillation tower bottom heat exchanger. Thermal decomposition of 1,2-dichloroethane is characterized in that the heat of 1,2-dichloroethane is recovered by the hot water produced and used as a heat source for a 1,2-dichloroethane distillation column operated under reduced pressure. Heat recovery method in process.