Ethylene dichloride and vinyl chloride

is the third chapter in a series of three where the products are like pancakes and batter. You can t make pancakes (or vinyl chloride) without maldng batter (or ethylene dichloride) there s not much else you can do with pancake batter (or ethylene dichloride) and you only use pancakes or vinyl chloride to make something else—brealcfast or plastics. Finally, if you ll permit this painfully overbearing analogy to be extended once more, maldng vinyl chloride (or pancakes) from-scratch is a lot easier now than it was 40 years ago. 

The original rnanufacturing route to vinyl chloride (VC) didn t involve ethylene dichloride (EDC) but was the reaction of acetylene with hydrochloric acid. This process was commercialized in the 1940s, but like most acetylene-based chemistry in the United States, it gave way to ethylene in the 1950s and 1960s. The highly reactive acetylene molecule was more sensitive, hazardous, 

Ethylene Hydrogen chloride Oxygen Ethylene dichloride Water 

For Reaction Two, the purified EDC is passed through a dryer to remove water, then fed to a pyrolysis unit. The difference between EDC pyrolysis furnaces and those used for ethylene is the use of a catalyst. 

The tubes in the EDC pyrolosis furnace are packed with charcoal pellets impregnated with ferric (iron) oxide. The EDC is pumped through at about 900—950°F and 50 psi. The conversion of EDC, i.e, how much of.it disappears, is about 50%, and the yield of VC, how much of the disappearing EDC gets converted to VC, is about 95—96%. (See the Appendix if you haven t yet read about the difference between yield and. conversion.) 

---

NOTE - Petrochemical plants also generate significant amounts of solid wastes and sludges, some of which may be considered hazardous because of the presence of toxic organics and heavy metals. Spent caustic and other hazardous wastes may be generated in significant quantities examples are distillation residues associated with units handling acetaldehyde, acetonitrile, benzyl chloride, carbon tetrachloride, cumene, phthallic anhydride, nitrobenzene, methyl ethyl pyridine, toluene diisocyanate, trichloroethane, trichloroethylene, perchloro-ethylene, aniline, chlorobenzenes, dimethyl hydrazine, ethylene dibromide, toluenediamine, epichlorohydrin, ethyl chloride, ethylene dichloride, and vinyl chloride. 

Table 11.4 lists economic data on the main methods for produdng ethylene dichloride and vinyl chloride. Table 11.5 gives data on the three main types of process for manufacturing chlorine by the electrolysis of sodium chloride. 

Figure 22.14 shows an integrated plant for producing ethylene dichloride and vinyl chloride from ethylene, chlorine, and air. In this process, vinyl chloride (VCM) is produced by the thermal cracking of EDC. The feed EDC may be supplied from two sources. In the first source, ethylene and chlorine are reacted in essentially stoichiometric proportions to produce EDC by direct addition. In the second source, ethylene is reacted with air and HCl by the oxychlorination process. Ideally, both processes are carried out in balance, and the oxychlorination process is used to consume the HCl produced in the cracking and direct chlorination steps. The chemical reactions are as follows ... 

Ethylene Dichlonde and Vinyl Chloride. In the United States, all ethylene dichloride [107-60-2] (EDC) is produced from ethylene, either by chlorination or oxychlorination (oxyhydrochlorination). The oxychlorination process is particularly attractive to manufacturers having a supply of by-product HCl, such as from pyrolysis of EDC to vinyl chloride [75-01-4] monomer (VCM), because this by-product HCl can be fed back to the oxychlorination reactor. EDC consumption follows demand for VCM which consumed about 87% of EDC production in 1989. VCM is, in turn, used in the manufacture of PVC resins. Essentially all HCl generated during VCM production is recycled to produce precursor EDC (see Chlorocarbons and Cm OROHYDROCARBONS ViNYLPOLYAffiRS). 

The leading derivative of ethylene dichloride is vinyl chloride [75-01-4] monomer (VCM), which is subsequently used to produce poly(vinyl chloride) and chloriaated hydrocarbons. Viayl chloride is obtaiaed by dehydrochloriaatioa of ethyleae dichloride ia the gas phase (500—600°C and 2.5—3.5 MPa). 

The per pass ethylene conversion in the primary reactors is maintained at 20—30% in order to ensure catalyst selectivities of 70—80%. Vapor-phase oxidation inhibitors such as ethylene dichloride or vinyl chloride or other halogenated compounds are added to the inlet of the reactors in ppm concentrations to retard carbon dioxide formation (107,120,121). The process stream exiting the reactor may contain 1—3 mol % ethylene oxide. This hot effluent gas is then cooled ia a shell-and-tube heat exchanger to around 35—40°C by usiag the cold recycle reactor feed stream gas from the primary absorber. The cooled cmde product gas is then compressed ia a centrifugal blower before entering the primary absorber. 

On November 8, 2000, U.S. EPA listed as hazardous two wastes generated by the chlorinated aliphatics industry.18 The two wastes are wastewater treatment sludges from the production of ethylene dichloride or vinyl chloride monomer (EDC/VCM), and wastewater treatment sludges from the production of vinyl chloride monomer using mercuric chloride catalyst in an acetylene-based process. 

Benzene is a clear, colorless, flammable liquid with a pleasant characteristic odor, bp 80.1°C, flash point -11.1°C, and ignition temperature 538°C. Benzene has been found to be very toxic and is on the list of Known to Be Human Carcinogens published every two years by the Department of Health and Human Services under the National Toxicology Program (NTP). There are four top 50 chemicals on this worst carcinogen list benzene 1,3-butadiene ethylene oxide and vinyl chloride. There are also four chemicals in the top 50 on the Reasonably Anticipated to Be Human Carcinogens list acrylonitrile, ethylene dichloride, formaldehyde, and propylene oxide. 

Multilayered materials can be readily formed using thermoforming including food packaging that may involve inclusion of layers of ethylene-vinyl alcohol copolymers, PS, polyolefins, and/or copolymers of vinylene dichloride and vinyl chloride. Microwavable food trays from (crystallized) PET are manufactured using thermoforming. 

Vinyl chloride (CH2=CHC1) is the second-largest-volume chemical made from ethylene. It is made by adding chlorine to ethylene and then thermally cracking out HC1 from the intermediate, ethylene dichloride. The vinyl chloride is polymerized to polyvinyl chloride (PVC), also called vinyl, which is used to make pipe, floor covering, wire coating, house siding, imitation leather, and many other products. 

Gas exposure times to furnace temperatures are kept short by a direct spray of ethylene dichloride at ambient temperatures onto the exit gases and by an indirect heat exchanger. Hydrogen chloride may be recovered by scrubbing with water, or by some form of fractionation if it is to be fed in anhydrous form to an oxychlorination unit. Many vinyl chloride producers operate an oxychlorination unit solely to convert the by-product hydrogen chloride from the ethylene dichloride cracker to produce additional ethylene dichloride feedstock. Vinyl chloride (b.p. —13.4°C) is almost entirely consumed for the production of poly(vinyl chloride) (PVC). 

These values probably have little meaning in absolute magnitude but in a relative sense they show that the X2 Catalyzed chain reaction should be much faster than the unimolecular thermal decomposition. This prediction is confirmed by the observed catalytic effect of chlorine in promoting dehydrochlorination. Mugdan and Barton reported dehydrochlorination of ethylene dichloride to vinyl chloride and HCl in the presence of per cent chlorine as 30 per cent at 300 C, 50 per cent at 350" C, and 70 per cent at 370 C for a flow rate of 38 g per hr through a 600-mm length of hot zone. In the absence of chlorine, there was only 2 per cent dehydrochlorination at 400 C and 30 per cent at 500" C with the same experimental setup. The mechanism used by Sherman, Quimby, and Sutherland for this catalyzed chain reaction was as follows ... 

A second major use for chlorine derives from its reactivity with organic materials, in particular with hydrocarbons. Two chlorinated hydrocarbons, ethylene dichloride (lUPAC name 1,2-dichloroethane) and vinyl chloride (lUPAC... 

In contrast to this direct chlorination there is the oxychlorination of ethylene using hydrogen chloride and oxygen, the other major method now used. Since the chlorine supply is sometimes short and it is difficult to balance the caustic soda and chlorine demand (both are made by the electrolysis of brine), hydrogen chloride provides a cheap alternate source for the chlorine atom. Most of the ethylene dichloride manufactured is converted into vinyl chloride by eliminating a mole of HCl, which can then be recycled and used to make more EDC by oxychlorination. EDC and vinyl chloride plants usually are physically linked. Most plants are 50 50 direct chlorinationroxychlorination to balance the output of HCl. 

The gaseous products formed on thermal decomposition of ethylene-platinous chloride are ethylene, hydrogen chloride, vinyl chloride, ethyl chloride, ethylene dichloride and ethylidine dichloride. The half life for the decomposition at 130° is 4.5 days, at 172° it is 1.7 hours 98). The hydrolysis of Zeisc s salt K[PtCl3(C2H4)] by water and dilute acids has been studied ... 

The production of ethyl chloride from ethylene and hydrogen chloride, mainly for tetraethyl lead manufacture, is expected to fall rapidly. Ethylene dichloride (1,2-dichloroethane) and vinyl chloride (chloroethene) have already been discussed in section 12.3.3.2. These two materials are also starting points for the production of more highly chlorinated C2 products. The following scheme illustrates routes used for vinylidene dichloride (1,1-dichloroethene) and 1,1,1-trichloroethane (also known as methylchloroform in the U.S.A.) ... 

In the oxychlorination processes a mixture of ethylene, air and hydrogen chloride is passed over a catalyst of cupric chloride on an inert support at 250—315°C. Ethylene dichloride is obtained in about 90% yield and is then dehydrochlorinated (and the hydrogen chloride recycled). In some processes, which operate at higher temperatures, the ethylene dichloride is cracked in situ so that vinyl chloride is obtained in a one-stage operation. The overall oxy chlorination reaction may be represented as follows ... 

As the reaction diagram in Fig. 2 shows, hydrochloric acid and oxygen are used to convert ethylene into ethylene dichloride and then the PVC monomer - vinyl chloride - is produced by means of pyrolysis. At present, this procedure is used to use up waste hydrogen chloride from various chemical processes. An important precondition is that the HCl must be as clean as possible. 

Figure 1.5 Chemical complex erected in Katar by UHDE GmbH, Dortmund, Germany. The chemical complex consists of three main plants for the production of 260000 t/a chlorine, 290000 t/a caustic soda, 175000 t/a ethylene dichloride and 230000 t/a vinyl chloride. The order value was approx. 450 million US. ...

Most of the ethylene dichloride produced is utilized for the manufacture of vinyl chloride, which may be obtained from it by pyrolysis or the action of caustic soda. Large quantities are also used in anti-knock additives for gasoline. As a solvent It has been displaced by trichloroethylene and tetrachloroelhyJene. U.S. production 1978 4-75 megatonnes. 

---