EDC

Introduction to the Oxygen-Chlorination Process for 1,2-EDC Production

1. Process Overview
The 1,2-dichloroethane (1,2-EDC) synthesis technology adopts the ethylene oxychlorination process for producing 1,2-EDC, which is the mainstream, mature, safe and controllable process in China's PVC industry. This process uses ethylene, hydrogen chloride and oxygen as raw materials and copper chloride as the catalyst. The reaction takes place in a fluidized bed reactor to produce 1,2-EDC. This process has the advantages of high conversion, few by-products, low raw material consumption, high product purity and stable operation, and is the preferred process for industrial-scale production of high-purity 1,2-EDC.
1,2-EDC is a colorless transparent liquid, primarily used as a key raw material for ethylene-based VCM plants, and can also serve as a chlorinated solvent, fine chemical intermediate, and pharmaceutical extraction solvent.
The product quality meets the requirements of HG/T 2662-1995 1,2-Dichloroethane for Industrial Use.

2. Reaction Principles
2.1 Hydrogenation Reaction Principle
At 140–180°C, with 0.2% Pd supported on SiO₂ as the catalyst, trace acetylene present in hydrogen chloride is hydrogenated. The acetylene content is controlled to below 50 ppm.
Chemical reactions:

C₂H₂＋H₂→C₂H₄
C₂H₄＋H₂→C₂H₆

2.2 Oxychlorination Reaction Mechanism
Using CuCl2 supported on Al2O3 microspheres as the catalyst, the oxychlorination reaction is carried out at 205–220℃:

C₂H₄+2HCl+½O₂→C₂H₄Cl₂+H₂O+236.55KJ

The reaction proceeds in three steps:

(1)    C₂H₄ + 2CuCl₂ → C₂H₄Cl₂ + Cu₂Cl₂
(2) Cu₂Cl₂ + ½O₂ → CuCl₂·CuO
(3) CuCl₂·CuO + 2HCl → 2CuCl₂ + H₂O

The following side reactions also occur simultaneously, and higher temperatures promote the formation of more by-products.

(1) C₂H₄ + 2O₂ → 2CO + 2H₂O
(2) C₂H₄ + 3O₂ → 2CO₂ + 2H₂O
(3) 2C₂H₄Cl₂ + 2HCl + O₂ → 2C₂H₃Cl₃ + 2H₂O
(4) 2C₂H₃Cl₃ + 2HCl + O₂ → 2C₂H₂Cl₄ + 2H₂O
(5) 2C₂H₂Cl₂ + 4HCl + O₂ → 4CHCl₃ + 2H₂O
(6) CCl₃CHO → CHCl₃ + CO
(7) 2CHCl₃ + 2HCl + O₂ → 2CCl₄ + 2H₂O

If the hydrogenation reactor is not in operation or is out of control, acetylene will undergo the following side reactions:

(8) 2C₂H₂ + 6HCl + 3O₂ → 2CCl₃CHO + 4H₂O
(9) C₂H₂ + 3HCl + O₂ → C₂HCl₃ + 2H₂O
(10) C₂H₂ + 8HCl + 3O₂ → 2C₂Cl₄ + 6H₂O

The extent of the following side reactions depends on various factors:

(11) C₂H₄ + HCl → C₂H₅Cl
(12) 2C₂H₄ + O₂ → 2C₂H₄O
(13) C₂H₄O + HCl → ClCH₂CH₂OH
(14) C₂H₄ + 3HCl + 2O₂ → CCl₃CHO + 3H₂O
(15) CCl₃CHO + H₂O → CHCl₃ + HCOOH

When 20% caustic soda is added from the quench tower, the following reactions occur:

(16) HCl + NaOH → NaCl + H₂O
(17) CO₂ + NaOH → NaHCO₃
(18) NaHCO₃ + NaOH → Na₂CO₃ + H₂O
(19) Na₂CO₃ + 2HCl → NaCl + CO₂ + H₂O
(20) CCl₃CHO + NaOH → CHCl₃ + HCOONa

3. Process Description
3.1 Process Flow Description
The oxychlorination reaction is a process in which ethylene reacts with hydrogen chloride and oxygen to produce EDC and water.
The hydrogen chloride feed, which may contain trace amounts of acetylene, first enters the hydrogenation reactor for acetylene removal. The hydrogen chloride gas and oxygen are then mixed in the O₂/HCl mixer and fed into the reactor through the feed distributor inside the oxychlorination reactor. Ethylene and recycle gas are mixed in the ethylene/recycle gas mixer and introduced into the reactor through the feed distribution plate. The reaction takes place over a CuCl₂ catalyst at a temperature of 210–245°C and a pressure of 0.24–0.32 MPa(g). The reaction produces EDC and water, and the heat of reaction (65 kcal/mol) is removed by hot water circulating through cooling coils, simultaneously generating 1.0 MPa(g) steam as a by-product.
The reaction gas leaves from the top of the reactor and enters the quench tower from the bottom, where it is spray-cooled using the reaction water discharged from the crude EDC decanter. The reaction gas exiting from the top of the quench tower is then sent to the crude EDC condenser for condensation and separation. The condensed liquid stream (mainly consisting of EDC and reaction water) is fed to the CO₂ stripping tower. After condensation and separation, the majority of the gas stream (mainly unreacted ethylene with a small amount of EDC) is recycled to the oxychlorination reactor as recycle gas, while a small portion is sent to the tail gas deep cooler for further cooling. The non-condensable gases are then sent to the incinerator by the tail gas system. The wastewater containing hydrogen chloride, inorganic sodium salts, and organic compounds is discharged from the bottom of the quench tower and sent to the wastewater neutralization and stripping tower for treatment.
Crude EDC is fed into the CO₂ stripping tower from the upper section, where it comes into counter current mass transfer contact with nitrogen introduced from the lower section on the trays. The CO₂ contained in the crude EDC is stripped off from the top of the tower. The purpose of stripping is to prevent corrosion of downstream carbon steel equipment caused by CO₂ in the presence of water, and to reduce caustic consumption in the decantation and caustic washing steps. The overhead off-gas from the stripping tower is sent to the tail gas deep cooling system for treatment. The separated EDC-containing liquid is combined and discharged into the crude EDC decanter, while the non-condensable gases are sent to the incinerator.
The liquid stream after CO₂ removal is discharged from the tower bottom to the crude EDC decanter. Due to the difference in density, water and EDC are separated into two layers in the decanter. The upper water layer is pumped to the quench tower for spray cooling, while the bottom crude EDC layer is transferred to the caustic wash tank by differential pressure.
In the caustic wash tank, impurities such as chloral (trichloroacetaldehyde) and CO₂ generated during the reaction are removed by adding 20% NaOH and water (chloral has a boiling point of 97.8°C and is difficult to remove by distillation; if it enters the cracking unit, it will shorten the decoking cycle of the cracking furnace to a certain extent). During caustic washing, the NaOH mass fraction in the caustic solution is maintained at 1.0%–2.0%, which is mainly achieved by controlling the caustic addition rate and the return water flow from the water wash tank.
The water from the caustic wash tank is ultimately sent to the plant wastewater treatment system, while the EDC is sent to the water wash tank for further treatment.
In the water wash tank, residual dissolved salts from the decantation and caustic washing steps are removed by water washing. After water washing, the EDC becomes essentially neutral and can be sent as the crude product from oxychlorination to the heads tower or to the crude EDC storage tank. Non-condensable gases discharged from the overheads of the caustic wash tank and the water wash tank are sent to the incineration unit for treatment.
The crude EDC produced from oxychlorination enters the heads tower. In the heads tower, water and light-boiling components are removed from the overhead, while EDC and heavy components are taken from the bottom and sent to the heavy-ends tower. In the heavy-ends tower, purified EDC is withdrawn as a side draw from a tray near the top, while heavy components, including solids and high-boiling materials, are continuously discharged from the bottom to the vacuum tower. In the vacuum tower, impurities in the feed EDC are further concentrated to 85%–89% and discharged from the bottom, while purified EDC is taken from the overhead. A vacuum ejector and an EDC circulation system are used to maintain the required vacuum level for the operation of the vacuum tower. During normal operation, the heat required for the heads tower, heavy-ends tower, and vacuum tower is provided by their respective reboilers.
3.2 Process Block Diagram

4. Process Technology Advantages
（1）Reliability: Stable temperature control, excellent heat transfer performance, and uniform temperature distribution within the fluidized bed (no hot spots) ensure more than 99% continuous operation annually. The specially designed feed distribution system enables maintenance-free operation for over two years.
（2）Safety: Oxygen is mixed with anhydrous hydrogen chloride outside the reactor and introduced into the fluidized bed independently of the ethylene feed. The oxygen concentration in the recycle stream is approximately 0.5% by volume, well below the flammable range.
（3）Flexibility: The plant can be operated at loads as low as 40%. The oxychlorination reactor load can be increased from 40% to 100% within 30 minutes, and vice versa. In addition, immediate start-up after shutdown is possible, making operation extremely straightforward.
（4）No hot spots in the reactor eliminate the risk of corrosion, allowing the entire reactor (with the exception of the distribution plate) to be constructed of carbon steel, thereby reducing capital investment.
（5）The plant adopts a pure oxygen fluidized-bed process, with uniform temperature distribution and precise temperature control inside the reactor, minimizing side reactions. As a result, raw material yields are high (ethylene 98.0%, hydrogen chloride 99%, oxygen 93%), and crude EDC purity is high (99.6%).
（6）The highly efficient cyclone system results in extremely low catalyst loss (catalyst loss as low as 20 grams per ton of EDC produced).
（7）The plant is capable of utilizing not only polymerization-grade ethylene and hydrogen chloride generated from the EDC cracking process, but also waste gas streams containing ethylene and/or anhydrous hydrogen chloride — such as ethylene-containing off-gases from direct chlorination and acetaldehyde production, as well as by-product hydrogen chloride from isocyanate plants — thereby achieving resource utilization of by-products.

5. List of Major Equipment

6. Main Consumption Indicators