vcm

PRODUCTION OF VINYL CHLORIDE FROM ETHYLENE DICHLORIDE BY PYROLYSIS Aspen Model Documentation

Index •

Process Summary

•

About This Process

•

Process Definition

•

Process Conditions

•

Physical Property Models and Data

•

Chemistry/Kinetics

•

Key Parameters

•

Selected Simulation Results: Blocks Streams

•

References

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20 Sep 1999

Process Summary This Aspen Plus model simulates the production of vinyl chloride monomer (VCM) from ethylene dichloride (EDC) by pyrolysis. The process is based on the dehydrochlorination of EDC in a gas-phase reaction. Our evaluation of this process is based on a production capacity of 500 million lb/yr (227,000 metric ton/yr) of VCM at 0.9 stream factor. The process consists of the dehydrochlorination and VCM recovery sections. Results from the Aspen Plus simulation shows that the purity of VCM obtained is 99.97%. Byproducts contains 77.8wt% EDC, at 4,575 lb/hr. Other gaseous by-product from the HCl column is obtained at 37,240 lb/hr, 99.8% HCl mass purity.

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About This Process Previously, the dehydrochlorination process is carried out in a liquid phase with alkali. Today, gas-phase dehydrochlorination is used exclusively: thermal (favored method) and catalytic (infrequent; e.g. SBA process, Wacker process). The manufacture of VCM from EDC involves cracking of the EDC, and subsequent cooling and rectification of the reaction product mixture. Deposits of carbon black and coke in the reaction furnace often require a shutdown of the furnace at intervals of some months for decoking operations. The formation of  by-products is partly attributable to the fact that attempts have been made to use very pure EDC. Another cause is that the reaction products are thermally unstable at the required high temperature and undergo decomposition to carbon in a series of further reactions. Selectivity to VCM is favored by high flow rate, exact temperature control, careful purification of EDC, and limitation of conversion of EDC. A recent Hoeschst patent (643035) permits the exact measurement of the conversion rate, thus effects a more reliable suppression of by-product formation. The important aspects of the process are discussed below.

Feeds The feed should be pure EDC. Impurities increase coking, and thereby shorten the operating time between decokings. A high purity feed may also minimize the formation of troublesome impurities in the product and simplify the recovery procedures. The desired minimum purity often quoted is 99.5% (Industrial Organic Chemistry, 1993). One analysis given in a patent is shown in Table 1 (481370). Table 1. EDC FEED COMPOSITION Components

Percent

1,2-EDC

99.51

Vinyl chloride

0.1

Benzene

0.159

Ethyl chloride

0.004

1,2-Dichloroethylene

0.014

2-Chlorobutadiene-1,3

0.034

l,l-Dichloroethane

0.052

Carbon tetrachloride

0.044

Chloroform

0.011

1,1,2-Trichloroethylene

0.044

l,l,P-Trichloroethane

0.004

Ethylene chlorohydrin

0.002

Unknown

0.053

One U.S. plant uses 99.8% EDC (private communication). However, a patent (643007) advocates the addition 0.001-5% by weight of trichloroacetyl chloride to reduce the cleavage temperature of EDC at the same conversion or increase conversion at the same cleavage temperature, and at the same time reduce by-products formation. A Hoeschst patent (643023) uses 250 ppm of benzotrichloride to increase VCM yield; another patent (643068) uses hexachloroacetone at a weight ratio of promoter to EDC in the range from about 0.00001:1 to about 0.01:1also to increase VCM yield. PEP Process Module

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Patent 643094 advocates the addition of  20 Sep 1999

carbontetrachloride (0.1-0.15% by weight of carbontetrachloride based on EDC), while limiting the trichloromethane content to less than 200 ppm.

Reactor Pyrolysis of EDC in the gaseous phase is the most widely used industrial process for the production of  VCM. According to this process, the reactor is a direct-fired tubular furnace (643032, 643005). Some of the tubes are made of Inconel, when fuel oil is burned. Stainless steel 316 can be used exclusively when the fuel is natural gas, provided precaution is taken on shut-down, to guard against the entry of moisture into a reactor containing HCl gas.

It has now unexpectedly been determined that EDC can be heated to an elevated

temperature by intimately admixing it with a very hot fluid or solid particles (643032). This markedly differs from the process in which liquid EDC is heated in the tubes of a reactor furnace.

Heat Recovery Some patents advocate the recovery of heat from the reaction product by indirect cooling to generate steam, to preheat the feed, or to preheat air needed in the furnace (643013, 643005, 643087, 643077, and 643089). Patent 643087 also applies partial utilization of the heat content of the flue gases from the pyrolysis furnace firing to preheat liquid EDC almost to its boiling point, utilizing the flue gas waste heat to generate steam.

A patent (643003) applies direct cooling of the pyrolysis product immediately after leaving the

pyrolysis step down to about 150-2500C, recovering the vapors from the head of the quench column, and indirectly cooling the same by heat exchange to at least its condensation point, thereby recovering some thermal energy.

Such procedures, however, causes tar formation and plugging; it is not practiced in

commercial operations. A recent Tosoh Corp. patent (643013) endeavors to minimize the problem by careful cooling. Another patent (481370) applies indirect and then direct cooling, with the intention to avoid an essential portion of the equipment and machinery required for purely direct cooling where large quantity of  recycle coolant is required.

Nevertheless, quenching the product mixture with cold EDC or cooled, condensed portions of the reaction mixture, and recycling the EDC back to the dehydrogenation step after separation of the VCM by distillation is the procedure commonly used (643076, Industrial Organic Chemistry, 1993). The disadvantage of this method, however, is the high-energy demand for pumping the recycle flow of reaction product and the complete loss of  the heat supplied to the reaction furnace (481370).

Separation The product from the reactor is mainly VCM, HCl, and unreacted EDC, conversion being generally 50%65%. These are often separated according to their relative volatility; HCl is first separated, and then VCM. VCM thus recovered is degassed to remove residual HC1. The above procedure (US 3,843,736) is the one generally followed. Separation by freezing or adsorption is not used commercially. PEP Process Module

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However, the known process is disadvantageous if the VCM fed to the degassing zone still contains small amounts of water unavoidably introduced during interruptions in operation.

In practice, therefore, the

degassing zone is then operated in such a way that the water is separated off via the bottom of the degassing column, together with HCl, for which purpose the towers filled with sodium hydroxide is required. If this separation is not carried out, water would be circulated together with the recycled EDC and cause corrosion. Patent 643033 states that the towers filled with sodium hydroxide can be omitted if the degassing column is operated in such a way that the major part of the water is taken off at the top and removed, advantageously by drying.

Purification of VCM Several patents aim at removing butadiene from VCM (90616, 90303, 481106, 481206, 481208). References 90560, 90591, and 311728 also deal with removal of butadiene from the reaction product, before the separation of VCM. However, it seems that if the feed to the reactor is 99.8% or purer EDC, the VCM produced contains butadiene in an amount below 8 ppm, which is allowable for polymerization. Another possible impurity in VCM is HCl. The conventional way to remove HCl is by degassing, followed by a caustic treatment or contacting with zinc (481110) to remove residual HCl. Reference 90617 suggests a method using an alcohol treatment, and distillation.

Purification of EDC EDC separated from VCM contains numerous impurities, as discussed under the section on chemistry. Trichloroethane, perchloroethane, perchloroethylene, and polychlorinated C-4 compounds are separated as heavy ends. Ethyl chloride, methyl chloride, chloroform, carbon tetrachloride, l,l-dichloroethane, and dichloroethylene (cis and trans) are separated as light ends.

Trichloroethylene itself boils at a higher

temperature than EDC does but it forms a minimum boiling point azeotrope with EDC (normal bp 82.1°C, EDC bp 83.7°C) and is extremely difficult to separate from EDC.

To minimize the accumulation of 

trichloroethylene in the recycled EDC, one has to allow some EDC to go into the light ends, together with the azeotrope of trichloroethane/EDC. Chloroprene, which if accumulated in large amounts may polymerize and lead to plugging. It seems that if high purity EDC is used, chloroprene does not accumulate to a troublesome degree. Both the light ends and heavy ends contain EDC and can be used as feed for making chlorinated solvents. In an integrated operation, the light ends may be added to the chlorination unit, where dichlorinated compounds and trichloroethylene convert to trichloroethane and perchlorinated compounds and become heavy ends. If there are not such outlets, the light ends and heavy ends have to be incinerated.

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Process Definition The Aspen Plus model simulate the steady-state production of VCM from EDC. The process is based on the dehydrochlorination of EDC in a gas-phase reaction.

Our evaluation of this process is based on a

production capacity of  500 million lb/yr (227,000 metric ton/yr) of VCM at 0.9 stream factor. The design bases and assumptions are summarized in the following section.

In the Aspen model, Radfrac models are used to represent the distillation columns. Due to insufficient kinetics information, Aspen Plus RYIELD reactor models are used to represent R-101A and B. The reactor is considered to have two valid phases; vapor and liquid phases.

Purified ethylene dichloride is preheated and vaporized by steam in vaporizer E-101. EDC vapor is heated to decomposition in the tubes of furnace R-101, where about 60% are converted to vinyl chloride. The conditions are controlled at 930F and 210-230 psig. The reaction gas emerging from the furnace flows to quenching tower, C-101, where the gas temperature is reduced to 287F. In cooler E-102 most of the EDC is condensed. The bottom stream from C-101 is filtered to remove carbon and tars, and recycled to the top of the column.

Condensate and gases from E-102 are fed to hydrogen chloride fractionating column C-102.

The

overhead from the hydrogen chloride fractionating column is hydrogen chloride gas, which is available for use in hydrochlorination or other uses. The bottom product from C-102 is fractionated in VCM column C-103. Vinyl chloride recovered from C-103 contains about 300-500 ppm hydrogen chloride. In degassing column C107, HCl together with some VCM is removed and recycled to C-102. Vinyl chloride from the bottom of C107 still contains about 10 ppm HCl, which is removed by contacting with solid caustic soda pellets in V-112. When the caustic soda is used up, V-112 is flushed with water. Vinyl chloride thus obtained has an acidity below 0.1 ppm.

The bottom product from C-103 is unconverted EDC with impurities. It is pumped to column C-104, where light ends, together with some EDC are removed as a distillate to column C-108, where light ends are then removed as a distillate. The bottom product from C-104 is pumped to heavy ends column C-105. The distillate is EDC with a purity of 99.9% or higher. The bottom product from C-105 is further distilled in vacuum column C-106 to recover more EDC, which is recycled to the pyrolysis furnace R-101.

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Process Conditions Table 2 provides the list of important blocks, design bases and assumptions for the process: TABLE 2. VCM FROM EDC BY PYROLYSIS DESIGN BASES AND ASSUMPTIONS Capacity: 500 million lb/yr (227,000 t/yr) VCM at 0.90 stream factor References

Reactor Reactor temperature ( 0C) Reactor pressure (psig) EDC Conversion (%) Selectivity to VCM (%) Column internals C-101, Quenching Column

Industrial Organic Chemistry (1993), 643076, 643003, 643087

930°F (5000C) 210-230 psig 60 99

Sieve trays No design spec

C-102 HCl Column

Valve trays Design specs: 99.99mol % recovery of HCl in the overhead. Design variables: Bottom to feed ratio.

C-103 VCM Column

Valve trays Design spec: 99.7 mass % recovery of VCM in the overhead. 99.7 mass % recovery of EDC in the bottoms. Design variable: Bottom to feed ratio. Reflux ratio.

C-104 Light Ends Column

Valve trays Operation specs: Distillate to Feed ratio=0.3 Reflux Ratio=5 No design spec Valve trays Operation specs: Bottom to Feed ratio=0.1 Reflux Ratio=3 Design specs: 98 mol % recovery of EDC in the overhead. Design variables: Bottom to feed ratio. Sieve trays Operation specs: Bottom to Feed ratio=0.015 Reflux Ratio=2 No design spec

C-105 Heavy Ends Column

C-106 Vacuum Column

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C-107 Degassing Column

Valve trays Operation specs: Distillate rate=3321 lb/hr Reflux Ratio=3 Design specs: 98 mol % recovery of VCM in the bottoms. Design variables: Distillate rate.

C-108 EDC Recovery Column

Valve trays Operation specs: Bottom to Feed ratio=0.965 Reflux Ratio=3 No design spec

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Physical Property Methods and Data The Aspen Plus simulation uses the NRTL-RK physical property method. The NRTL model can describe VLE and LLE of strongly nonideal solutions. The NRTL model requires binary parameters. Many binary parameters for VLE and LLE, from literature and from regression of experimental data, are included in the ASPEN PLUS databanks.

Separate data sets can be used for the NRTL binary parameters to model properties or equilibria at different conditions. The NRTL model can also handle any combination of polar and non-polar compounds, up to very strong non-ideality. Parameters should be fitted in the temperature, pressure, and composition range of  operation. No component should be close to its critical temperature.

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Chemistry/Kinetics  Reactors

Ethylene dichloride decomposes on heating, to vinyl chloride and hydrogen chloride: C 2 H 4Cl 2 → C 2H 3Cl + HCl ΔH r

=

16.66 kcal/gmol (endothermic)

The mechanism is a thermal chain reaction, initiated by a chlorine free-radical that splits from C 2H4Cl2 on heating.

(PEP Report 5, pp. 17-18.)

Numerous by-products such as trichloroethane, tetrachloroethane,

pentachloroethane, perchloroethane, dichloroethylene, trichloroethylene, and perchloroethylene are formed through chlorination and dehydrochlorination. CH 2

=

Cl

CHCl ⎯   ⎯→ CHCl 2 − CH 2Cl ↓Δ

CHCl

=

CHCl + HCl

↓ Cl

CHCl 2 − CH 2Cl ↓Δ

CCl2

=

CHCl + HCl

↓ Cl

CCl3 − CHCl 2 ↓Δ

CCl2

=

CCl2

+

HCl

↓ Cl

CCl3 − CCl3

1,1-Dichloroethane may form from vinyl chloride and HCl (481104): C 2H 3Cl + HCl ⇔ CH 3CHCl 2

Small amounts of coke and acetylene are formed: 2C2H 4Cl2 → C2H 4 + 4HCl + 2C 2C2H 4 → 2CH4

+

2C

C2H 3Cl → HCl + C2H 2 Other impurities also found in the cracking product are benzene, hydrogen, ethylene, chloroprene, butadiene, polychlorinated C-4 compounds, methyl chloride, chloroform, carbon tetrachloride, ethyl chloride, and polymeric solid. The decomposition to vinyl chloride is accelerated by the presence of a small amount of initiator such as tetrachloride or chlorine, but it is inhibited by ethylene olefins or impurities such as ethylene chlorohydrin (481322).

Oxygen also accelerates the decomposition, but leads more to the formation of by-products.

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0

Catalytic cracking at 300-400 C on pumice (SiO2, Al2O3, alkalis) or on charcoal, impregnated with BaCl 2 or ZnCl2, has not found more widespread application due to the limited life of catalysts.

The yields used to model the RYIELD reactor R-101A and B in the Aspen Plus model are as follow:

Components

Yields Per Unit Mass of Non-Inert Feed (Not normalized)

PEP Process Module

H2

9

HCl

37,165

ACETYLE

26

ETHYL-01

33

VCM

63,634

1,2-B-01

0.49

CIS-1-01

42

CHLORPR

82

Benzene

99

EDC

66,187

TRICH-01

49

1,1,2-01

304

TETRA-01

94

P-TER-01

185

Carbon

251

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References Reference Number  (Patent) 481370 (US 4,324,932)

Assignee

Earliest Date Shown

Link, G., et al.

7/17/80

Catalyst

Feed

Reaction Temperature (°C)

Reaction Pressure (psia)

Residence Time (seconds)

EDC Conversion (%)

Selectivity to VCM (mol%)

None

EDC

480-560

203-348

4

55

N/A

The hot gas mixture leaving the reaction furnace is cooled to the inlet temperature of the column in which HCl is separated from the products of  the thermal cracking of EDC. Within the range of 560-490 oC and 220-120 oC, one or more cooling stages are applied through which the reaction gas mixture passes at high flow velocity, the cooling device being preferably a single-tube cooler. Starting from about 220 oC, a liquid substantially consisting of EDC may be added intermittently. The heat transferred to the coolant in the stages of indirect cooling is preferably reused within the VCM manufacturing process, utilizing valuable thermal energy that is lost through purely direct cooling.

643093 (US 4,960,963)

Tosoh Corp., Shinnayo

11/25/87

None

EDC

500

338

N/A

58.8

N/A

There is a heat exchange between a high temperature cracked gas produced and the EDC to be introduced into the pyrolysis furnace. The cracked gas is cooled down to 180-350 oC, and with the flow rate of the cracked gas being equal to or more than 5 m/s but less than 20 m/s, preferably 9.213.8 m/s. As a result, the pressure drop in the heat exchanger in which EDC introduced in the pyrolysis furnace is preheated and evaporated is minimized. Coke formation is also reduced.

643035 Hoeschst (US 5,545,780) Aktiengesellschaft

2/8/95

None

EDC

N/A

N/A

N/A

60

N/A

The patent describes the determination of the conversion rate in the preparation of VCM by thermal cracking of EDC by measuring the absorption of high-energy radiation, pressure, and temperature of the gases issuing from the cracking furnace. The objective is to keep the conversion rate as constant as possible, and as a result, suppress the formation of by-products, in particular, coke formation, which in turn leads to considerably increased service lives of the entire plant.

10/9/92 643023 Hoeschst (US 5,210,345) Aktiengesellschaft

None

EDC

300-600

145-580

N/A

76

N/A

An addition of benzotrichloride produces a significantly higher yield of VCM in the thermal cleavage of EDC. For example, 250 ppm of  benzotrichloride increases the VCM yield from 52% (feed EDC without additive) to about 76%.

643068 (US 4,584,420)

PPG Industries, Inc.

6/25/84

None

EDC

500

26-305

0.1-30

62-64

N/A

The patent describes the use of a compound with chemical formula CX 3COCX 3, wherein each X is independently chloro or bromo, as a pyrolysis promoter in the pyrolysis of EDC to VCM. Hexachloroacetone is the particularly preferred promoter. The promoter is introduced at a weight ratio of promoter to EDC in the range from about 0.00001:1 to about 0.01:1, to increase VCM yield.

12/7/94 643033 Hoeschst (US 5,507,920) Aktiengesellschaft

None

EDC

450-650

118-588

N/A

N/A

N/A

The patent describes the three distillation stages used in the preparation of VCM by pyrolysis of EDC. The first step involves the distillation of  HCl, then VCM and finally entrained HCl with VCM. If in the last stage, entrained water is not drawn off via the bottom, it is re-circulated with the top product to the first stage and causes corrosion. Removal of water at the top of the third distillation stage by drying with molecular sieve or silica gel prevents the corrosion. The dried mixture of VCM and HCl is then re-circulated back into the first distillation zone.

643032 (US 5,488,190)

Elf Atochem S.A.

4/21/93

None

EDC

662

22

0.089

77

95.5

VCM is prepared by intimately contacting, in the absence of steam, a feedstream of EDC with a flow of fluid or solid particulates heated to such elevated temperature and for such small period of time, i.e. 0.01-0.5 second, as to transfer a dehydrochlorinating amount of thermal energy to the EDC and thereby ultrapyrolyzing EDC into VCM and HCl.

643007 (US 4,851,597)

Hoeschst Aktiengesellschaft

PEP Process Module

8/6/84

None

EDC

27

350-550

145-580

4-40

50-60

20 Sep 1999

N/A

The patent describes the addition of 0.001-5% by weight of trichloroacetyl chloride or a compound which contains 3 carbon atoms and, for each carbon atom bonded to the latter, 0-1 hydrogen atom, is added to it. The compounds are added into liquid EDC before thermal decomposition. The advantage of the invention is to make it possible to reduce the cleavage temperature of EDC at the same conversion or increase conversion at the same cleavage temperature, at the same time reduce by-products formation.

643005 (US 4,843,182)

Snamprogetti, S.p.A.

7/24/78

None

EDC

450-550

N/A

N/A

N/A

N/A

The invention relates to a process for the production of VCM by starting from EDC is heated without being vaporized in the convective section of  the oven. It is then vaporized by indirect heat exchange with air or another fluid, which is heated in its turn by the heat of the cracking products leaving the oven. EDC, as vapor is then introduced into the radiant section of the oven, whereby it undergoes cracking to give VCM.

643003 (US 4,822,932)

Wacker-Chemie GmbH

4/7/88

None

EDC

512

181

N/A

60

N/A

The patent describes a method in the production of VCM by pyrolysis of EDC, with multiple stage cooling and distillation to separate the reaction product, and recycle the unreacted EDC to the pyrolysis step. This method applies direct cooling of the reaction product immediately after leaving the pyrolysis step, within 1 second from a temperature of 480-540 oC down to 150-250 oC. The cooled product is charged into a quench column, recovering the vapors from the head of the quench column, and indirectly cooling the same by heat exchange to at least its condensation point. The heat exchange media could be (a) EDC to be fed to the pyrolysis unit, (b) air used as combustion air to fire the pyrolysis unit, (c) the sump of  the HCl column, (d) liquid HCl to be evaporated, and (e) water to dissipate heat. This invention partially recovers the energy expended from the pyrolysis and avoids large pressure loss in the heat exchanger.

10/8/87 643089 Hoeschst (US 4,798,914) Aktiengesellschaft

None

EDC

533

537

N/A

65

96

Hot product gas leaving the cracking furnace heat liquid EDC in a first container to almost its boiling point, and the EDC is transferred into a second container in which it is partly evaporated under a lower pressure than the first container. The evaporated EDC is fed into the cracking furnace and the non-evaporated EDC is fed back into the first container. By supplying pre-warmed EDC into the second container, the amount of  product evaporated therein is replaced, the pre-warming being regulated by the level of the liquid EDC in the second container. The pre-warming of the EDC can take place in the convection zone of the furnace or by steam, which has been heated in the convection zone of the furnace. The process provides higher cracking conversions and more favorable energy utilization.

643087 Wacker(US 4,788,357) Chemie GmbH

7/16/87

None

EDC

507

145-522

N/A

61.2

99

EDC is thermally cracked with partial utilization of the heat content of the flue gases from the pyrolysis furnace firing to preheat liquid EDC almost to its boiling temperature, utilizing the flue gas waste heat to generate steam. The pyrolysis gas mix is cooled in several stages. HCl is separated from the pyrolysis gas mix in a HCl column and VCM is separated from the gas mix in a VCM column. It is an object of this invention to increase flue gas temperature in combination with another measure so that the heat recovery is economically feasible.

643094 Wacker-Chemie 10/27/86 (US 4,746,759) GmbH

None

EDC

497

145-232

10-15

64

N/A

This patent describes a process for the preparation of VCM from EDC wherein 0.10-0.15% by weight of CCl 4 based on EDC, is used as a promoter and the CHCl 3 content is limited to less than 200 ppm. Before being fed to the cracking zone, EDC is brought almost to the boiling point at 15-31 bar, and then expanded to 10-16 bar. The EDC vapors is flashed and the fraction which remained as liquid is vaporized externally. The combined EDC gas streams are then fed into the cracking furnace. The energy required for cracking is already supplied in the first 75-85% of the reaction zone, whereby a conversion of 60-70% is obtained at residence time from 10-25 seconds. The exit temperature of the reaction zone is 485-510oC. It is an object of the invention to substantially reduce the specific consumption of utilities for the process steps of purifying unconverted EDC and vaporizing purified EDC in the cracking furnace.

10/9/84 643076 BASF (US 4,720,599) Aktiengesellschaft

None

EDC

450-500

218

N/A

N/A

N/A

The patent describes a process for the preparation of VCM by vaporizing liquid EDC, thermally cracking the EDC and cooling the hot reaction mixture by means of cooled and condensed portions of the reaction mixture. A defined amount of the EDC is taken off as liquid in or downstream of the vaporizer and mixed with a defined amount of the cooled liquid portion of the reaction mixture. The mixture is distilled and the constituents taken off the top of the distillation column are recycled to the liquid EDC upstream of the vaporizer. The constituents taken off the bottom of the distillation column are worked up by distillation. The objective of this invention is to reduce the losses of useful products.

643077 (US 4,721,604)

Snamprogetti S.p.A.

8/15/86

None

EDC

450-550

N/A

N/A

N/A

The patent describes the thermal cracking furnace for the production of VCM from EDC. EDC is heated, without being vaporized, in the convective section of an oven. It is then vaporized by indirect heat exchange with air or another fluid, which is heated in its turn by exploiting the

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N/A

heat of the cracking products leaving the oven. EDC vapor is introduced into the radiant section of the oven, wherein it undergoes cracking and forms VCM. The enthalpy of the products is thus recovered.

643074 Stauffer Chemical (US 4,665,243) Company

12/8/82

None

EDC

185

157

N/A

N/A

N/A

The energy requirements for preparing VCM can be reduced by a process, which includes the steps of purifying by distillation EDC, compressing EDC vapor from the distillation column to a temperature and pressure sufficient for direct feed to a pyrolysis furnace. Up to 80% of the heat presently used after distillation and before pyrolysis can be saved. The compressor can be any mechanical compressor that is adapted for gas compression; insulated and provided with proper temperature control means such as heating fluids in a jacket to prevent condensation. Further heating can also be applied beyond the compressor and before the pyrolysis furnace if necessary.

11/23/84 643071 PPG (US 4,590,318) Industries, Inc.

None

EDC

517

116-174

3-15

60

In the pyrolysis of EDC to VCM, the stream removed from the furnace is introduced to essentially unheated conduit means. Pyrolysis promoter is introduced to the stream in the conduit means and sensible heat of the stream is utilized in the conduit means to pyrolyze further amounts of EDC and to increase the yield of VCM. Molecular chlorine is the preferred promoter. The promoter preferably, is introduced to the stream at a weight rate ratio of the promoter to the stream from about 0.001:1 to about 0.0015:1. The residence time of the stream in the conduit means range from about 0.15-2 seconds.

Report by: Noni Lim September 20, 1999

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99