Production of 200,000 tons/a Vinyl Chloride Monomer via direct chlorination and oxychlorination

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Delft

Technische Universiteit Delft

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Conceptual Process Design

Chemical Process Technology

Subject

Production of 200,000 tons/a Vinyl Chloride

Monomer via direct chlorination and

oxychlorination

Authors

A.E.

Koren

lC

.

M

.

van Leeuwen

R.A.

Spruijt

J.

Weststrate

Keywords

TelepllOne

078-6187902

015-2573800

015-2622241

015-2126249

VCM; vinyl chloride; EDe; 1,2-ethylenedichloride; direct chlorination; oxychlorination

Assignment issued

Report issued

Assessment

: 4

th

_{March 1998}

: 26

th

June 1998

Faculteit Technische Natuurwetenschappen Scheikundige Technologie en Materiaalkunde

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Summary

The assignment received was to design a process for the producti n of 200,000 tons/a Vinyl Chloride Monomer (VCM). The plant should at least contain a di ect/'hlorination unit and an oxy-~hlorination unit, the so called b~lanced proc~ss. The main ~ ma~erials us~d in the vinyl chlonde.process are: Ethylene, Chlon~e and Oxygen. The ~reac~-equat1o~n ofthe -)

process 1S:

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2 C2H4 +C12 + 1/2 O2 H20 2 H2C- - I (VCM)

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VCM is rnainly used for the pro 0 VC (Polyvinyl chloride). With the information ~.

found in the literature, a block-scherne was created which consisted of~ units: / (]

oxychlorination (U20Q), direct cJ:llorination _{' .}

_{. , . . .}

300 EDc..pJllificà.tion.

_.

.{U.4üO), pyrolysis (

(U500), VCM p4,rification {U600) and th hydrogenation and Catalytic Oxidation (U700) An extra unit, the feed-pretreatrnent-unit (UIOO) was a e ater. was eC1 e öproouce VCM ofrnonorner-grade level purity, which is 99.98 Wllo pure. The location chosen to build

this plant is the Delfzijl industrial area.

-=

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The process was simulated with ChemCad and the process-flowsheet was developed. The

proc~ss-control has been basically designed (configuration ofthe control). Heat integration has also takeri place, using pinch-technology. All heat-exchangè~-du ~ndatrïms

.al

reboiler- and condenser:-duties were used in the heat integration. NFPA hazard s been carried out in or~er to identifY a unit operation which could be state ,critical. urnt. The pyrolysis reactor turned out to be the critical unit operation and was subjected to a short HAZOP;·analysis.

Also

an economical analysis was done. The process developed does not have good economical perspectives: big losses are to be expected when this process will be exploited. The rnain reason for this is that the market for VCM and PVC is currently tight. The conceptual process developed for the production ofVCM meets the requirements. It is able to produce 200,000 tons/a VCM at 99.98 Wllo purity. It also contains a direct chlorination and an oxychlorination unit. Though, it would not be advisable to build this plant for it will not make any profit, only loss.

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Contents

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1.

~ntroduction

. . . . • . . . .. 5

11. Basic Assumptions ... 7

11.1 Reaction equations and conversions . . . 7

11.2 The process-block-scheme ... .. ... ... .. ... ... .... . .... .. 7

\

11.3 Streams at Battery Limits . ... ... .... .. ... ... .. ... .. 8

11. 4 Utilities at Battery Limits . . . .. 10

11. 5 Annual production and annual production hours .... ... .. .. .. .... . . ... . 10

11.6 Location . . . .. 11

11.7 Components . .... .... .. ... .. .. .... . .. .... ... ... ... .. 11

11

Process-structure and process-flowsheet . . . .. 12

111.1 Unit 100 (feedstock pretreatment) ... .... ... ... . ... .. .. .. ... 12

111.2 Unit 200 (Oxychlorination) ... ... ... ... .. ... . .... .. .. .. 12

111.3 Unit 300 (Direct Chlorination) . . . .. 13

111.4 Unit 400 (EDC-purification) ... .... .. .. .... ... ... . .... ... 14

111.6 Unit 600 (VCM-purification) ... .. ... . .. .. ... ... .. .. .. 15

111.7 Unit 700 (Catoxid and hydrogenation) .... .... .. ... . .... .. .. .. 16

111.8 Thermodynamics .... .. . ... .. ... . .. .. .. ... ... .... . .. 16

IV. Process-flowsheet and equipment calculations ... 19

VI. 1 Reactors . . . .. 19

IV.2 Towers/columns .... ... ... ... ... .. .. .... . ... . .. ... .. ... .. 23

IV.3 Separators . .. .. ... .. .. ... .. .. ... .. . .. ... ... .. ... .. . ... . 28

IV.4 Heat exchangers ... .... .. ... .. ... .. .. .... . 28

IV.5 Pumps, compressors and expanders .. .... ... . ... . 29

IV.6 Closing ofthe recycIes . ... . .... ... .. ... .. 29

V. Design of major equipment ... 30

V.I Reactors ... .. .... ... ... ... ... ... ... . . 30

V.2 The design ofthe towers .... .. ... ... ... ... ... ... .. . . .... 33

V.3 Design ofthe heat exchangers .. ... ... ... . .. .. . .. .. 34

VI. Heat aod mass balance . . . .. 36

VII. Heat integration . . . .. 45

VII. 1 Composites ... .... ... .. ... ... .. . ... ... . ... .. .. 45

VII.2 First law . . . 45

VII.3 Second law ... .. ... . ... ... .. ... 45

VII.4 Grand composite ... .... ... . ... ... . ... .... 45

VII.6 Match above pinch temperature ... .. .. .. . . .. .... ... .... 45

VII. 7 Match below pinch temperature ... .... ... . ... . .. .. .. ... 46

VII.8 Utilities ... ... .. .. .. . ... .. . ... .. ... .... . ... .. . .. ... . 46

VIII. Specification Sheets . . . 47

IX. Process-control . . . .. 53

IX.l Overall mass balance ... ... ... ... . ... .. .. 53

IX.2 Unit 100 (feed-pretreatment) .... .... . ... ... .. .... .... .. ... 53

IX3 Unit 200 (oxychlorination) IX.4 Unit 300 (Direct chlorination) .. .... ... .... ... . ... 55

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IX.5 Unit 400 & 600 (EDe and VCM purification) .. ... : .. ... .. ... 55

IX.6 Unit 500 (pyrolysis) ... ... .. . . ... ... . ... 56

IX.7 Unit 700 (Catoxid and hydrogenation) ... .... .. .. .... .. . 57

X. Process Safety . . . .. . . .. 58

X.l Introduction .... .. .... ... .. ... ... .. ... .. ... ... 58 X.2 Air emission <223> ... 58 X.3 Water emission <226> . . . 59 X.4 Tar bleed <702> ... . . . 60 X.5 NFP A hazard rating . . . 60

X.6 HAZOP ofthe pyrolysis reactor ... ... .. ... ... 61

XI. Economic Evaluation ... 67

XI.l Followed method ... 67

XI.2 Main equipment costs ... ... 67

XI.3 Fixed capital costs and total investment costs ... .. ... .... ... 68

XI.4 Raw material costs . . . 68

XI.5 Utility costs ... . .. ... ... 68

XI.6 Annual costs ... ... 69

XI.7 Economic prognoses ... . ... ... ... . ... . ... .. 69

XI.8 Sensitivity analysis . . . 69

XI.9 Economic conclusions ... ... .. ... .. ... ... ... .. 70

XII. Conclusions and recommendations . . . 71

XII. 1 Conclusions .. ... .. ... ... .... ... .. ... ... 71

XII.2 Recommendations ... .... ... .. .. .. . .. ... . ... 72

XIII. List of sym bols . . . .. 74

XIV. References ... 76

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Appendices:

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A.

B.

C.

D.

E.

F.

Calculations Figures Process Flowsheet Economics

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Stream Summaries Equipment Surnrharies ,

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I. Introduction

The assignme

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was to design a chemical plant, which cao produce200,OOO ton I <../.' .•

Vmyl

Chlond~:~:~v~VCM)

Re year. The plant should at least contam a direct

)7

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chlorination unit and an oxy-chl,9 nation unit, the so called balanced process. Tbis process

mainly uses three raw material~, these are Chlorine, O~n and Ethylene. The first industrial

process for the manufac~ e of VCM is

-n

the addition of hydrogen chlori~e (HCI) on ~ acetylené. Due to the Jarge presellce 0 ethylene as a çheaper f~edstoçk

dus

process was ~

aboundeçI in the end ofthe eighties. To ' is almost .exêt~~ely manufacturèd by the thermal c1eavage of 1,2-dichloroèthane (ED~). With t~s cleavage )rCM and HCI are created. Tbis EDC can be produced by two routes. The first is tn additi nlof ~hlorine to ethylen~. The second, more modem, process is the oxy-chlorination of èthylene with hydrogen chloride (!nd oxygen (or air). Often a combination of these processes is used: the'balanced pro'cess, where the HCI formed in the thermal cracking (pyrolysis) ofEDC to VCM is feedstock for the

oxychlorination. Some processes have been developed to. convert the

Hci

created by the )

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\) thermal cracking of EDC into Chl?rine. é

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raw mat fials are used in many-c cal processes and c; urchased easily. (/,t"

xygen . i s a r o u n ä the world

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0xy;~en

The ethylene in

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Europe I created ostly by large

Naph~ers.

In Rotterdam th a large network

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wbic . , 0 ,s s eral producèrs and u;ers of ethyl ene. The t.lijLd mostly used, raw

material is 'ne Chlorine s created for example by AKZO-NOBEL in the Netherlands by

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electroly~i ~ So' e ",~t should be lpc!ted near a Chlorinè pr.?ducing facility. '

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The VCM product is mainly used in the plastic industry, wh ere 95% is polymerised ,to form Polyvinyl chloride (PVC). For tbis reason it was decided that the VCM produced by tbis plant should be polymer-grade. The rest 'is used in co-polymers and a small amount is used as a precursor in the manufacture of chlorine deriv!ltes. PVC is used all over the world" in'cars, houses ~md the chemical industry. Th'e PVC market is one ofthe largest chemical markets of

the world.

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In the Netherlands the main-producer ofVCM is ROVIN. ROVIN is a 50/50 joint-venture of AKZO-NOBEL chemicals and Shell Nederland Chemie. It is located ip Rotterdam and also uses direct chlorination and oxy-chlorination. It receives it's ethylene trom the ethylene grid and it's chlorine trom AKZO-NOBliL: ROVIN, wbich is the fourth largest VCM producer in Europe (ref 46), has an a~nual production èapacity ot5'20,OOÖ ton. The largest producer in Europe is the European Vinyls Corporation (EVC). They have an annual production of

,1,200,000 tQ!l. The total production in Western Europe is 5,400,000 ton. World-wide in 1994 the VCM production was 20,000,000 ton. So the proposed plant should add 1% to the world-wide annual pro~tion. According to ref45 the production of PVC is not profitable. '

According to e~the current market is not very much demanding and the ROVIN-plant is working on 60-70% ofit's maximum capacity. '

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VCM can be stored in two ways. The first method is under bigh pressure in liquid state. The

~ second method is in a large tank where it is cooled

bel

ow it's boiling point'(-13°C). ROVIN

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uses both storage methods and has a cooled tank with a capacity of 10,000 ton. All tbis VCM

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can be transported across the ocean by one ship.

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VCM i,s a

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hydro on, which are considered hazardous to the environment. It's main product ~ PVC is non-bio-degradable.

~CM

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con~ed

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non-sustaina~le

product.. But sin ce no alt/matives for PVC are yet c?mmerciall~the production will continue. JkéVCM is also considered a carcinogenic ubstance. Tlie efor strict ernission lirnits must be followed (ref.41).

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11. Basic Assumptions

III Reaction equations and conversions

The main process consists of a direct chlorination, an oxy-chlorination and a pyrolysis step.

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The reactions taking place are:

Oxy-Chlorination: }

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C₂H₄ +C1₂ ~ C2H4Cl2 (11.1) (11.2) Pyrolysis:

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(IA.v' C₂H₄Cl₂ ~ H₂C=CHCI + HCI (11.3)

Overall reaction equation:

2 C2H4 +C12 + 1/2 02~ H20 + 2 H2C=CHCI (VCM) (11.4)

The conversion in the first two steps (oxy-chlorination and direct chlorination) is more than

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The conver,sion in.the pyrolysis is 55%-60% once through.J6' it is necessary to use a

~le over the pyrolysls.reactor. ' ~~

IL 2 The process-block-scheme

The first decision was to design a continuous process. Ihis is necessary because the desired production is 200 ktons per annum. In paragral1h lI.5 ore will be said concerning the annual production anä the production hour.s per year.

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So the process now consists ofthree main production steps which can be seen in figure Il.l (on the left page). This figure shows the six Units which form the total process. Unit 100 is not shown because it consists only ofpr~-treatment ofthe feed-st,reams. Umt 200, the oxy-chlorination and Unit 300, the direct oxy-chlorination, both pro duce the intermediate EDe. The streams leàving these Uruts enter Unit 400:the EDC-purification. A iight ends and a heavy ends stream leave Unit 400. This EDC-purification Unit àlso produces a EDC-stream which is

>99.95 wOlo pure. This EDC-stream enters Unit 500, the EDC-pyrolysis, where reaétion Il.3 takes place. The stream leaving Unit 500, consisting mainly ofVCM, HCI and EDC, enters Unit ~, the VCM-purification. From this Unit three streams are shown, a HCl-recycle stream, a EDC-recycle stream and a VCM-product stream.

The EDC-recycle strea cont-a' s some by-products which are not easily removed in the towers of Unit 400. S Unit 400 lso contains a chlorination reactor which chlorinates these Qy-products. The chlor.i!L- y-products can be easily removed by a heavy-~ower. The HCl-recycle stream contams acetylene, which should be converted before entering the oxy-chlorination unit. This is done by a hydrogenation reactor in Unit 700,. the hydrogènation and

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Catalytic Oxidation. The CaS&Jytic Oxidatipn oxidizes all ~hlorinated _{by-products to HCI, H 20}

and C~02' The stream leaving the Unit 700 enters Unit 200 as ~eedstOCk~" <:. '~

Two streams are nol yel men ioned bul are a1sorelevant. The tirsl is

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feed

0 Unil 700 which is required i ' er to oxidize e chlorinated by-products catalytic ~ e second is the stream labelled aste water/purgt:. n the oxy:.·chl~rination unit 'wa~er is produced

(Eq .Il.l) this is cón,' red waste 'w . Th~m should be used to remove GO/C0_2, N2 and other inert gasses from the process, This stream p~ób~ly contains some chlorinated 'j)roducts. Therefor 'it should 'go to a' speèial incinerator àîsênarge and cannot be vented, The

purge-stream and waste water stream are sent outside the battery limits where they càn be treated further. The VCM-product stream is, as already mentioned, u,sed}rt the fabriea'ûon, of

PVC }S6:'it is made at, monomer-grade (polymer-grade) quality. ~ ,tu~

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IL3 Streams at Battery Limits

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The process uses several feed stocks, namely:

Chlorine, Ethylene, _0 -gen, Hydrogen, Air, NaOH and process water. :) ><.

The process pr~ , uces tfiree prodÛêt streams, thêy ar~:

-VCM-product, Purge and waste water. '

Much effort was tàken to obtain èommercial specifications ofthe feed stocks. Unfortunately most companies kept most of the specifications a secret. Concerning the' qualÏiy of VCM at

monomer grade more information was found. All the information which could be retrieved is

f

summarised in tables. ' ,

Table 11.1 Conditions ofthe feed stocks

P [bar] lTemp [I<] Phase Purity Design

Chlorine 7 20'" 293 L >99.8w% 99.8w% Ethylene 80 293 V >99.8'1% 99.8'1% Oxygen 14 293 V >99.5'1% 99.62V% Hydrogen 25 293 V >99.995VOIo 100% Air 1 293 V - -NaOH 1 293 S >99.9w% 100%' Proc. Wat. 5 '2~" 298 L >99w% 100% 8

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Chlorine Ethylene NaOH Proc. Wat. ?

As can be seen in table II.1yod--t .2 in the last column the percentages are displayed with which ChemCad was rrr60elled. Chlorine impurities are kept a secret and so it was decided to assume ~ purity for ~hloririe. Ethylene has two main imp'}r-it1~h with Cl: maxim~-m of

/ ,2.1 yOlo~ was decided to take this percentage as impurit)(. Oxygen IJas a li-st ofimpurities

/ with ~gon as the main impurity. Because Argon is an inert ga 'u-snîsNitrogen, Nitro8en was

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n as e only impurity. With this decision, adding another component could be,avOlded. Hydrogen as a ~ high urity so it was decided to as su me 100 % purity. Some ofthe

~@fitain water which coul cause a problem in the p~Q1~ut since they do not enter this Unit this water content could be negl~cted. Concernin~ NaOH jnd the process water little is known. They mix together and enter the Unit 200 in ord~act by-products and then it leaves Unit 200 as waste water. So the impurities are less relevant and they are assumed absent.

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onomer Grade Vinyl Chloride (ref 2)

~~----~--~--~----~~---, Im uri acetylene acidity by wt acetaldehyde alkalinity by wt 1,3-butadiene ethyl chloride EDC iron bywt methyl chloride inyl acetylene ater 10 ppm 70 ppm

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chl

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and 1,3-butadiene) have a concentration below the design concentration (1 70 ppm) all other requirements are met. The calculated VCM concentration was 99.9 tnol%. ~

lI4 Utilities at Battery Limits

In the process several utilities are used. They are summarised in table Il.4. Table HA Utilities

Tcond.[°C] Hcond kj/kg references

Steam (18 bar) 205 2200

Steam (25 bar) 225 2200 47

Tin (0C) Tout (0C) Cp [kJ/kg°C]

Cooling Water 25 max40 4.18 47

Energy MJ/m3 mol Weight Dens. [kgINm3

] ~

Fuel 31.65 18.6 0.84 48

Electricity 220/380/10,000 Volt 49

lIS Annual production and annual production hours

As already mentioned in paragraph Il.2 a continuous process was chosen because ofthe large production which is required. At first it was decided to assume 8000 production hours per annum. This would require the plant to remain in production mode for at least 11 months

_.

_-===-

. One month per year would be available for maintenance, coke burning ànd refilling of catalyst. The

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Table 11.5 Pure component properties

PURE COMPONENT PROPERTIES

Component Name Technoloaical Data Medical Data

Formula Mol. Weight Boiling Point Melting Point Density of MACvalue LD500rai

at 101.3 kPa at101.3kPa Liquid (1) (2)

Design Svstematic g/mol °C °C kg/m"3 mg/m"3 g

Hydrogen Hydrogen H2 2.02 -252.9 -259.3 *0.088 n.a. n.a.

Nitrogen Nitrogen N2 28.01 -195.8 -210.0 1.2 n.a. n.a.

Oxygen Oxygen 02 32.00 -183.0 -218.8 *1.404 n.a. n.a.

Ethylene Ethene C2H4 28.05 -103.7 -169.0 567.8/-104°C n.a. n.a.

C)

Hydrogen Chloride Hydrogen Chloride Acetylene Ethyne HCI C2H2 36.46 26.03 -84.7, sub!. pt. -80.7, trip. pt. -85.0 -114.2 *1.600 *0.377 n.a. 8 n.a. n.a.

Chlorine Chlorine CI2 70.91 -34.0 -101.5 *3.111 3 n.a.

<IV

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Methyl Chloride Chloroacetylene Chloromethane Chloroethyne C2HCI CH3CI '- 50.49 60.48 -30.0 -24.0 -126.0 -97.7 *911.0 n.a. n.a. 52 1n.a. .26

Methyl Acetylene Propyn C3H4 40.06 -23.2 -102.7 *607.0 1650 n.a.

Vinyl Chloride Chloroethene C2H3CI . 62.50 ) -13.3 _{-153.7 910.6 3ppm 0.35}

Butadiene 1,3-Butadiene C4H6 54.09 -4.4 -108.9 *614.9 46 3.84

Vinylacetylene 1-Buten-3-yne C4H4 52.08 5.1 n.a. 709.4/0°C n.a. n.a.

Ethyl Chloride Chloroethane C2H5CI 64.51 12.3 -138.70 *890.2 2600 n.a.

Benzene Benzene C6H6 78.11 80.0 5.5 876.5 3 2.31

Ethylene Dichloride 1,2-Dichloroethane C2H4CI2 98.96 83.5 -35.5 1235.1 200 0.78

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Trichloroethylene Trichloroethene

C2HCI3 131.39 87.2 -84.7 1464.2 190 3.36

Chloral Trichloroethanal C2HCI30 147.39 97.8 -57.5 1512.0 n.a. n.a.

3)

..

_{Water Dihydrogenoxide H20 18.02 100.0 0.0 997.0 n.a. n.a.}

Trichloroethane 1,1,2-Trichloroethane C2H3CI3 133.40 113.8 -36.6 1439.7 45 0.59

Chlorobenzene Chlorobenzene C6H5CI 112.56 131.7 -45.2 1105.8 230 1.60

Notes:

(1) Density at 20°C, unless specified otherwise

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* Density at 25°C , . b d LD50 (mg/kg) for rat, orally administrated, with safety factor 100

(2) Oral for a male of 70 kg s welght, ase on . .

(3) Based on LD50 (mg/kg) for mouse, orally admlnlstrated

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tons/hour and thisJ<intfof stream hours is only feasible in a

~

continuous process. According to ref 46 the ROVIN-plant is shut down once in two years for

Q

maintenance. This means that the initial decision of 8000 production hours per annum is

correct. The Shut-Down occurs in the Spring in order to avoid freezing ofpipes and to avoid w

... ' , . ~ .~

working in the hottest time of year. -

~...-~~arpro

'

uctl~ld

be

accordin~

to our assignment 200,000 ton/annum. Ip...erder to 6-)

r

be flexible and compensate for the fact that maintenance may only occur once .iRtwo years it ~ ,

was decided to design the plant with a slight over-capacity. This is a

over

~

~

t.

~

which would all ow the plant to produce 200,000 ton/annum ifthe plant can only be in

~

.

production mode for 1

°

month~ instead of 11 m,ont~s. This would be the fa~t in a year in I(

which fl?aintenance would be

r~quired

.

~

~

116 Location

~

4

As mentioned above, Chlorine and Ethylene are main raw materials and alocation should be chosen in the vicinity of suppliers of these materiais. According to reference 1 the industrial area of Delfzijl in Groningen, The Netherlands, could provide enough Chlorine (90-150.000

ton) when a plant for the production of Magnesium is installed. At this moment, Delfzijl is not

"k1t-

é.p

connected to the international network ofEthylene-pipelines, but the Dutch

an~

local

zr::;.;.:;e

governments are prepared to invest ,250-300

*

106 Dutch .Qorins in tbis.-fa:c~lity ifthere are :1e~ sufticient industrial investments in the Delfzijl area. Also, a co srcre;.able amount of Oxygen is

~

1.<.d

needed for which an air separation plant should be availabl . H~rogen could be supplied by a 6/~< steam reforming plant or lt could be purèhased in large c inders. Nat~ral gas resource's are () ~

extensively available in the area (Slochteren). Sin~ VCM produced is used in the

Y

h ,(,,_

manufacture ofPoly Vinyl Chloride, it would be convenient to install such a plant nearby for .,./

?-the reason of low transportatio~ costs. Together with already existing plants in the Dèlfzijl

'?

Ó

IJ;

~

area the plants mentioned above are of great importance for the industrial developmeilt in x t.._

Groningen. Concerning environmental issues it should be. realised that this location is near the ~ ~ (o~

"Waddenze~"

and that environmental restrictions could be more severe than in the rest

Of

the

2

dO

~

Netherlands. But assuming that ref 1 is correct this area would welcome extra investments

and these environment al restrictions should not cause large problems.

11 7 Components

On the left a list of components has been added (tabie 11.5 on the left). This list contains all components which have been used in modelling towers in ChemCad. The stated components and their boiling points were used in the design of the towers in the process. Also all

components which are crucial in the main production route have been entered. These ( )

components are considered most important for the design procedure or the modelling in

ï

ChemCad. In ChemCad even more c n used but they are left out in table

11.5 so that the reader is not suppli with an exce.ss . ormation. ...--) .Q

In ChemCad a new component was peci led, the heavy C4-lump.:.. This is the product ofthe chlorination of unsaturated hyd~carbons in the chlorinat!on r~actor. Because of the .

uncertainties on the exact pr~ucts it w~s decided to represent chlorination products wit~ one component. !his compon~{ h~s as, formula

C

4

H

s

3.

It's properties are calculated by

ChemCad wlth the gro~ contnb~tIon met~lOd, .

c;

The stmcture w7 sento

be

:

1

1\~~

c

~,

C~

!~

C

r

C

7

ClH

1

~

I (

.f{,t

. 1 .A~~

~

},11 I .

l4

~

('~

crt.

ce

ct i.If.A., ... -

I~

d

~

"

/<hU-

U-

~~~

Ir

f )

')

()

P

!ko{

~ ~

K

,

ç-.

~

~

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_?

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9

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-111

Process-structure and process-flowsheet

In this chapter the process-structure, as is seen in the process-flowsheet (appendix C), is discussed and motivated. Per unit the main unit-operations are discussed. In the last paragraph some attention is paid to

t~~ynamic

aspects ofthis process, e.g.

T~~ots

and

~

of reaction.

j(~~~

lIlJ Unit J 00 (feedstock pretreatment)

~ fl~ ~=::~~.:::?----

-

1

Because the feedstocks ethyl ene, chlorine and oxygen do not have

~

right pressure and temperature when they enter the battery limit, they have to be brought to the right process conditions. is delivered at~ar and ambient temperature and has to be brought to a

1. 5 bar. his is done with four expanders (E 10 1, El 06, El 09 and E 111) with heat

exchang H 17, H636) between them. These heat exchangers are necessary to

prevent the ethylene from condensing in the expanders. For the same reason and because of capacity-limitations, four expanders are needed.

The ~Jori.Qe is delivered at 7 bar and ambient temperature and is in the liquid phase. Because

chlorine-gas is needed in the direct chlorination, it has to be evaporated. This is done i

-heated flash column (MI04). The pressure ofthe gas coming out ofthis flash colu

10 bar

This is the ressure needed for the chlorination-reactor. The chlorine gas needed D r the dir

c orination is brought to 1.5 ar operating pressure ofthe reactor) with expander 8. f) Some

0wen

is mixed with tbis chlorine because that would improve the

s~lectivity

of the

~

~

direct chlorination reaction. In heat-exchanger H620 this chloririe stream is brought to ~

reaction temperature.

The ~n has a pressure of 14 bar at the battery limit. The oxygen is expanded to a pressure of

1.5

6afin expander El07 (the pressure in the oxychlorination). Before expanding the oxygen is heated to ma!.ce sure it will not condense in the expander. This is done with heat-exchangers H626 and HI05: After expa ding the oxygen is heated again with HIIO and H710

till the oxychlorination-reaction tempe ture is reached. ~

-

--

_.-

..

----

.

Hydrogen comes from a cylinder and is supposed to be at the right pressure (25 bar) already.

Process-water is pumped by P102 and air is compressed by CI03. ' \

~

.

/

~H---lIl2 Unit 200 (Oxychlorination)

In the oxychlorination reactor (R20 1) ethyl ene . erted with HCI and oxygen to form EDC. The feedstreams are preheated in unit 10 so hey are on. reactiori temperature when they enter the reactor. The oxychlorination re ac is a fluidizèd bed reactor. This type of reactor is chosen instead of a fixed bed reactor,

becaus~orination

is a very

exothermic reaction and in a fluidized bed the temperature is easier to control. In a ~d bed reactor hot spots can occur, which could be dangerous. In a fluidized bed reactor the solids are weIl mixed, so hot spots will not occur. The operating temperature is 245°C and the

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/~~

if'~~ ~

(.

operating pressure

e

ar

(as found in referenees 2, 9 and 10).

After the oxy-reaetor the reaetor-exit-gases are brought to a uressure of 6 bar by

eompressor

~

!

C206 to have the right pressure for entering the quench tower (T208). In this quench tower ~ the hot gases are guenched with cold water and the EDC and water are condenSeil. The hot

gases enter the quench tower at the bqttom and the water is sprinkled from'th~ top. Because

CJAû

_ ,

the water can not be cold enough to cool the gases properly, a condenser

(tt

·

-i ed on r "1.

~

top of this tower. The hot gases act like areboiler, delivering the eiiergy fa separation. ases

re

~

I

like ethyl ene, carbon dioxide, carbon monoXIde and nitrogen e n onde . d-Ie ve the ~ . quench tower as a vent <215>. The quench tower operate at 5.8 b top-pressure. After the ~ ,

quench tower the EDC is separated from the water in a LIL- rator (V214). The 0 ratin

pumped out oft e separator LsiJartially recyc1ed to the quench tower and is coole' IJ/ -,

o-i./;f;:

pressure is 5 bar~so h~oes not have to be pumped to the separator. The water-ph ase

and H218 before Rftg-' . The part ofthe

~ater

that is oot recyèle.d is waste waterTndgoes to a waste water treatment (outside battery lirilit). The vent <216> coming from V214 is very smalt' and is mixed with the vent coming from the quench tower.

~""'j;:)C~

Thei ...

~

-

g

-

aru

-

·

-

c

-

p

-

h

-

a

..:

se

::;.\

is

pumped from V214 to a reactor-vessel (R207) in which it is mixed with a caustlc solution to remove chloral from the EDC. The pressure is 5 bar and the temperature is 107°C. The NaOH-solution is made in a vesselJtank (V204) with solid NaOH coming from M202 and process water <110> and pumped to R207. From R207 the mixture is pumped to a settler (V215) in which the two phases separate (P=5 bar, T=I07 °C). For pressure-control reasons a small vent <227> is drawn in the flowsheet. The water phase is pumped out of V215 by P219 and mixed with the ste water. The organic phase is pumped with P220 to the LE-column in unit 400.

IJl3 Unit 300 (Direct Chlorination)

In the direct chlorination reactor (R303) ethylene is directly chlorinated with Cl2 to form EDe.

This reaction takes place in a boiling reactor with a distillation-çolurnn on top of it. The reason for choosing a boiling reactor is that the temperature is constant in such a reactor, the heat of r~eaction is easily removed by evaporation ofE:pC and the heat ofreaction is directly u'sed for separatlOn of the EDC from the other components present. Chlorine and ethyl ene (both gases) are bubbled through liquid EDC. Before entering the reactor the feed-s re am <302> is heated

with heat exchangers H301 an1 l3 02. The EDC, which is at it's b . i g

poin

~

aporates due \, -LU

to the heat of reaction release . It partially condenses in the colu on top

o

~

.

he . t

r

./

unreacted gases and the vapou DC go over the top to a condens In this . lal condenser /

almost all ofthe EDC is condensed. The gases (mainly ethylene, chlorine and hY2r0~en

chloride) are recyc1ed and mixed with the reactor-feed and a small part ofthem is purged to the catoxid reactor (R704). A part ofthe condensed EDC goes to a boffeftank (V50I) in the pyrolysis section (U500), from which it is pumpedto the pyrölysis

re~ctor

(R506) and the rest goes back into the column. The butfertank is placed there to be able to control the amount of EDC going into the pyrolysis reactor. From the lowest tray ofthe reactor/column EDC is pumped (P305) to the light ends column (T403). A coil immersed in the liquid EDC in the reactor takes care ofthe cooling ofthe reactor-contents ifnecessary. The temperature in the reactor is 90°C and the pressure is 1.5 bar. The top-temperature ofthe column is 64°C and

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the temperature on the lowest tray is 82°C.

IIl4 Unit 400 (EDC-purification)

The EDC recycle stream contains some impurities of which a few can cause trouble further on in the process. Com ents like benzene and trichloroethylene are hard to separate from EDC ~ and thus wiII a mulate in e prócess and ,iQillhe EyrolY;is::.eactor if they are not removed

by some mean . Chloroprene r adily polymenzes In

lM

hghl ends column and thus has to be

removed. The c onents al ave double bonds so the addition of chlorine to these components is possib e, at ough benzene is somewhat harder to chls a because ofit's stabilized bonds. By chlorinating these components they become hea ier a d wili .be removed in the heavy ends column. In the chlorination reactor (R401) chlorin IS bubbled through

the EDC. The pressure in the reactor is 5 bar and the temperature is about 130 oe.

:;;;;:=-- 'cF: ...

The EDC-stream coming trom the oxychlorination and the EDC recycle stream coming from the chlorination reactor (both the gaseous and the liquid-stream) both ar tripped offlight ends in the light ends column (T403). Water forms an azeotrope wit EDC This azeotrope has a lower boiIing point (140 oe at 5 bar) than EDe an us WI eave t e column over the

top. The EDC-stream coming trom the direct chlorination (R303, trom the lowest tray) does not contain any lights (or at least very littIe) and therefore does not need to go through the light ends column. The light ends column operates at a pressure of 5 bar. The top temperature is 134°C and the temperature at the bottom is 146 oe.

IIl5 Unit 500 (Pyrolysis)

The EDC pumped out ofbuffertank V501 by pump P502 is first evaporated and preheated in vaporizer F503. The purified EDe co ming from the heavy ends column (T408) is already preheated in unit 400. Then these two streams are mixed and brought to pressure with a comRressor (C504). In the pyrolysis-reactor (R506) the EDC is cracked and VCM anä=R.Cl are formed. It is an endothermic reaction, so the pyrolysis reactor is a furnace with coils in it through which the gas flows. The temperature in this reactor is 500°C and the pressure is 25 bar. The conversion is 60~. The conversion is kept low to minimize the formation

ofby-products.

;?'J>

ct

f

'

e reaction roduct has to be cooled quickly to stop the reaction. This is done in a 9uench tower (T50?) The reaction-gases enter at the bottom ofthe tower. The cooled reactIOn

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product/unconverted EDC is partly used for quenching and enters the tower at the top after it has been cooled in a train of heat exchangers (H415, H420, H418, Hi01 and H505). Also a (partial) condenser (H508) is placed at the top ofthe column for additional cooling. The bottom temperature is 211°C and the top temperature is 141

oe.

The pressure in this quench-tower should be somewhat less than 25 bar, so no compressor between the pyrolysis reactor and the quench tower is needed. The distillate (vapour) is c.Oinpressed~to a pressure of 50 bar and then goes to unit 600 for purification. The bottom stream is partia recycled for

I

quenching and the rest is pumped (p513) to unit 600 for purification.

iJl)JJ

I

(J,....

{y. ..

I'

K"

1 [ .

lIJ. 6 Unit 600 (VCM-purification)

/

.

/

The top- and bottom stream commg.tfrom the quench tower (T507) are both led to the HCI-recovery tower (T601). Here the xtCM is separated from the HCI formed in the pyrolysis-reaction. This HCI is going to b recycled to the oxychlorination (unit 200) after treatment in unit 700. The HCI (and

s~m

-'-~

ther

lights like methane, ethylene and acetylene) leave the HCI-column o~r·lJ-iëTOJ>\and yte VCM, EDC and heavies leave at the bottom. The

column-pressure ,~ 50 ba~6 b th streams are first brought to pressure (this is done in unit 500). This pressure i~hes6 to void cooling at very low temperatures. The temperature at the top is 38 °C and the te era r at the bottom 182

oe.

The distillate, the HCI recycle, is expanded from ~ to ~ bar· E611, b cause the hydrogenation reactor operates at ~5 ar. Before this

expansIOn the s heated in H607 and H608 to prevent conden . . After the expansion the recycle HCI stream is heated again to reaction temperature wlth H61 and H615.

a~

In the second distillation tower, the EDC recycle tower (T609), the VCM is separated from the unconverted EDC. The VCM leaves the tower over the top and the EDC (together with some heavies) over the bottom. The pressure in this tower is 50 bar. The temperature at the top is 149°C and the temperature at the bottom 282

oe.

The EDC is cooled wlth the heat exchangers H615, H608, H616, H411, H620 and H302 and expanded in E634 be~re going to

the chlorination reactor (R401). ~ ~~ -h:. ~~C· ~~"t

. ~

~

Because the VCM leaving the top of tower T609 does not meet the specifications for

I~

' )

polymer-grade VCM, two extra

towe~e

needed. In the first tower (T618) lights like

~

•

chlorine and methyl chlonde are remöVed. The pressure in this tower is 47.5 bar, somewhat less than in the previous towers. The top-temperature is 134°C and the bottó tempera e is

146

oe.

The distillate of this tower is led to the catmcid reaiaor. Thii stream . s expanded '.:'--...

(E628) from 47.5 to 2 bar (that is the catoxid-pressure) and before that it is ate· 621

~

O.Ct

~

and H625 to avoid condensation. " __

p

f)

S

(

(r~;,

':j,) -- t}

~

oP

In the last distillation

tow

~

ts

like 1,3-butad e and vinyl acetylene are ' moved

AJ

f) I

P

from the VCM. The VCM ofthe right purity, 99.98 w%, is

op-

~r

oduc

r

:

-

e top ")

temperature is 142.5 °C and the bottom temperature is 144.3

oe.

Condenser H630 is a total condenser. The pressure in this column is 45 bar, again somewhat less than in "the previous tower. The condenser ofthis column is replaced by a train ofhèat-e~changers (H626, H607, H629, H635) and a condenser (H630) (with water). The

top-pr

~~

~t

:

VCM, is cooled to 60 °C with heat exchangers: H617, H636 and H637. The bottom- tream is led to unit 700 ( catoxid reactor).

Temp [Kl 420 415 410 405 400 395 Temp [Kl 405 400 395 390 385 380 375 Figure lIl. I

U.

L

Chloroform , 'W

~~f>~

1,2-DiC1-Ethane

I

><---*-->< Xl

C'"

Y1 ... , ... ! ... , ... -'W _,: :. , ,

·

·

'

·

~

"

i.

.

...

..

...J

~ i

i~

_i

_~

_,

;"",:,! i ... ···f ... ~ i __ ... ;.: j ... ; ... "' ... j .'i( ... . . . ; .... . ... ! I

..

_..

_;

--

I

.

•

1··· ... -+ ... j ... )(;: ...•... ...• .... .... ... ;

...

.

.

..

.

...

...

.

.1

•

• •

_•

>~~.

···

···I~{

L -_ _ _ _ _ _ ~ _ _ _ _ _ _ ~ _ _ _ _ _ _ _ _ ~ _ _ _ _ _ _ ~~~~~ 0.2 0.4 0.6 0.8 1.0 Xl 1 Yl Mole Frac

Figure III.2 1.2-DiCI-Ethane I 1. 1. 2-3CI-Ethane at

I ><---*-->< Xl __ .... Y1 -. ... , ... ... , ... . ! ... '=====::;======" ;

-.

,

... ! ... :'11, ... . . j ... ; ... ,

-.

,

-.

,

... , ... ! .. . ... + .... 0.2 0.4 0.6 0.8 1.0 Xl 1 YI Mole Frac

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+-

~tJf~

(

. . .J .JA~ f. llJ:L1J/l--~ ~

ty

~

-

~~-~

~

"

JlI.7 Unit 700 (Catoxid and hydrogenation) \

In order to recover chlorine trom cWorinated byproduçts and to mI_'_n.,.i ~e--:-_~...-~

chlorine-containi

~

g

compounds, the catmcid .reactor

(R

7

'Q

~

has

be~

develo fluidized bed reactor chlorinated hydrocarbons are catalyticàl~nci te

HCI, CO/CO ançl H20, Again a fluidized bed reactor is chosen ~eaus.e..J) 't's u " rm temperature profile. The top stream trom the light ends column (T403), the bottom stream trom the heavy ends column (T408), the top stream trom the first VCM purification column (T618), the bottom stream from the second VCM purification column (T627) and the vent

trom the direct chlorination (R303) D-the-Gat-e~~~tor to be incinerated, Because the

n

chlorine content exceeds 70.W% auxilia fuel is eedçd)rhe catoxid reactor operates at 2 )

~k

r

bar and ±450°C. This ' tem e a ' ra e because high pressure steam can'be ~

generated with th eat released in the reacto , The heavy ends stream trom T408 is flashed ~ ~ .

(M70 1) before enten ~moxi reactor to remove some tars, This small stream of tars trom the flash that does not evaporate has to be treated (burned) elsewhere, The stream coming trom the second VCM purification tower (T627) is also flashed first in M702 to bring it to a pressure of2 bar, resulting in one vapour and one liquid stream (cold), This liquid stream first has to be evaporated and this is done in F705, The stream coming out of the catoxid reactor mainly contains HCI, N_2, CO/CO and H₂0 and is, after expansion to 1.5 bar (E706), mixed with the HeI-recycle stream.

The hydrogenation reactor (R 707) is placed in the process to convert the acet,ylene present in the HCI recycle, formed in the pyrolysis. Acetylene will cause increased formation of

byproducts in the oxychlorination if it is not removed. In the hydrogenation reactor the

?

acetylene is hydrogenated selectively to ethyl ene (and some ethane). The hydrogenation

lf.e:..c.

reactor is an adiabatic fixed bed reactor. The pressure is 25 bar .and the temperature is 197 °C

at the entrance and 263 °C at the exit ofthe reactor. The reactor-exit gases are expanded to 1,5 bar (E708) and mixed with the catoxid-stream. This mixed stream is first cooled with several heat exchangers (H625, H709, H710, H711 ànd H421) and then led to the oxychlorination reactor. The HCI is converted there and the other gaseous components

~ormed in or coming trom the catoxid reaçtor) are vented trom the guench column

o ndleavetheprocessthere. <1l~> ~

lIL 8 Thermodynamics

Enthalpies of process-streams are ca1culated by ChemCad. AJso specific heats and other thermodynamic properties of components are in ChemCad' s databank and are used for

calculations. The TXY -plots of the key-èomponents of the main separations in this process are printed on the left. Figure' lIl. 1 shows the ~h]oroformlEDC curve at 5 bar (these are the

key-I

~{)$

components in the Light en9s t6wer) Figure

III

.

~

shows the TXY-plot ofEI?C and 1,

1,2-1~ trichloroethan~ at 1.5 bar; the key-co ponents in the H~avy ~nds tower. The TXY-plot ofthe

I

'Ls:J/

key-componenkey-components in t fs in the HCI-Tower ( èthyC-towe ( CM and butadiene at 50 bar) are not printed,l cWorideNCM a~ 50 bar) and the TXY-plot ofthe . These two

~r

plots did not show nice' rve, 'I several thermo-modéls were tried. The simulation was

I

done wit tee oic ert s stem of ChemCad: ~ggac, The' last two towers have the

16

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Temp [Kl 426 424 422 420 418 416 Figure III.3

..

_\ \ \ \ \ 0.2

..

_\

,

1,2-DiCl-Ethane / Water at 5.00 bar By UNQC

~ '0

4

L

<65

... ! ... ··· .. · .... ···7/'····' ~

,'ir·

0.4 0.6 0.8 1.0 Xl / YI Mole Frac

\

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sa e key-components s the HCL- and EDC-tower respectively at nearly the same pressures, so di e also not printed.

Azeotrope of EDe and water

In the literature it was found that EDC forms an azeotrope with water (ref. 2, 10). It was tried to find thisazeotrope in one of the thermodynamic models in ChemCad and was found in only two models. Those two thermodynamic models were "uniguac/unifac" and "BWRS" , but since the last model is mainly used to. describe hydrocarbon-hydrocarbon systems, uniquaclunifac was thought to give a more reliable r~sult. Fi~re liL3 shows the'T -x/y diagram at 5 bár. The azeotrope exists at about the .5,0%/50% mixture'ofEDC and water and hàs a boiling point that

is lower thati th. boiling point ofEDC. {~?

Thermodynamie models used

The main thermodynamic model used in the ChemCad simulation ofthe process is Yf!fac. For several unit-operations th~ uniqu~c:..model is used. ~hese two theimodynamic mode s are listed below together with ~ short descnption of each of them.

Unifac: Thermo-model for chemicais, systems with two liquid phase~ no -ideal sstems. This

model uses gI:..oup-contributions for caleU'latro~ was recornmended by the expe~ system (of ChemCad) for modelling th irect G chlorinat~_ _ _ ~ •

Uniquac: Therm9-model for chemicais, systems with two li uid hases, higl)Jy nOD ideal

systems. This model was chosen for the

~

hlorinatio

ecause the system was highly non-ideal due to the presence of w~r and it I~ e'1'hoel most similar to 'uac/l}nifac. The uniquac/unifac model showed the azeotrope, but made th _{. , " ,} Imulation difficu _.., convergence).

An electrolyte model is also used_~ . The main reason for this was to let ChemCad simulate that _, HCI (and NaOH) dissolves in 'water. The model used was the ideal electrolyte model. The

1 4

components for which electrolyte-'caJculations we re done, are: H20, HCI, CO2 and NaOH.

~

Reaction mechanisms and enthalpies

Although in most of the cases reaction enthalpies were caJculated by ChemCad, the reaction enthalpies found in the literature for the several reactions are listed below, together with the _,

' reaction-equations. Oxy-Chlorination: C2H4

+

2 HCI

+

1/202 ... C2H4Cl2

+

H20 ~RH298= -295 kJ/mol " ' Direct Chlorination C2H4 +CI2 ... C2H4Cl2 ~ R H298= -220 kJ/mol Pyrolysis: C2H4Cl2 4 H2C=CHCI + HCI ~RH298= +71 kJ/mol , , (D.I) (D.2) (D.3) 17

/

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For the oxychlorination the reaction-mechanism is known (with catalyst CuC12):

'"

,

~

C,2H4 +2 CUQ2 ... ,CIÇH2CH2Cl ~ 2CuCI

+

0.5 O2 ' ' ' CuOCliC12 CuOCuC12

+

2H~1 ... H20

+

2 CuC12 (m.l) (m.2) (m.3) 18

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IV. Process-flowsheet and equipment calculations

Vl.1 Reactors

Oxychlorination reactor (R201)

The oxychlorination-reaction is modelled in ChemCad by the use of two stoichiometric ..

reactors. All reactions related to the C(onversion of ethyl ene arè modelled in the ~t ~eactor

and in the second the conversion of vinyl chloride is modelled, which is presentm small amounts. The reaction equations used are (with selectivities) : .

Main reaction: Oxidation reaction: Addition ofHCl: Formation ofTCE: Formation of chloral: C2H + 0.5 O2 + 2 HCI ~ _{C2H4Cl2 + H20} (0.972~) C2H4 + 2.8 O2 ~ _{2 H2}0 + 0.4 CO + 1._{6 CO2} (0.0068) Ç2H4 + I:ICI ~ Ç₂

B

_sCI (0.015) C2H4 + 3 HCI + O2

4

C2~3C13 _{+ 2 H2}0 (0.0008) I C2H4 + 3 HCI + 2 O2 ~ è2H,Ç130 + 3 H20 (0.0023) I ' .

Formation of chloroform:

i

~2H4;+ 6 HCI + 2 O2 ~ 2 HeCl3 + 4 H20 (0.0023)

(IT. I) (IV.I) (IV.2) (IV.3) (IV. 4) (IV. 5) L---'- I .0000

Using the selectivities mentioned in reference 14, the Q-yerall reaction (mole-based) is

calculated to be:

-.::::::::-1 _{C2H4 + 0.515 O2 + 1.9837 HCI} ~ 0._{9728 C2H4Cl}2 + 0.015 C2HsCI +

0.0008C2H3C13 + 0._{0023 C2HCl3}0 + 0._{0046 HCCl3 + 1.0041 H2}0 + 0.00272 CO + 0.0109 CO2

(IV.6)

The assumptions made are: _")

__ o.c:1(t-")g

.

-The ethylene-conversion is ~8.%.

-The factor 'other componertts' in the table with selectivities to ethylene in ref.14 is divided in two parts: chloral and chloroform (both an equal' share). Çhioral is chosen becau'se it was mentioned several times in literature that it shpuld be washed out and chloroform because it _,

~ <

was one ofthe major waste roducts according to ref. 16.

-Light ends such as ~ane are Qqt con~erted in the o~chlorination reactor.

- VC entering the reactor

,will

onl~ be conVêrt;ed to 1, 1 ,2-t~chloro'ethane, follo,wing the same reaction mechanism as ethyl ene (reaction equation from ref. 16.)

-The ratio CO2:CO formed is 4: 1, this is abbreviatèd from the' mass balance in ref. 2.

-Selectiviti~ do not change when using a' tluidized bed reactor in 'stead of a fÎxed bed reactor.

ehloral removal reactor (R207)

The reactor vessel in which chloraLis removed by washingthe oxy~EDC with a

NaOH-- , . ' ~

s~n is modelled in ChemC;ad with a stoichiometric reactor. The reaction thai takes place

IS: C2HCI3.O + H29

-+

Cf!CI~ + CH20 2 fot

~CR.

C~

~

(IV.7) 19 I Ce..

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The following assumptions are made:

•

•

•

•

it is an isothermal reactor

the chl~ral is convefsed for 90%

the NaOH is there as a c . s t for the reaction the NaOH is used to neutralise the fl.Yid

Direcd ûorination reactor (R303)

-The direct chlorination reactor is a boiling liguid reactor with several trays in it. In ChemCad this kind of reactor is not available so a combination of a rea and a tower had to be used.

The problem was'that the .gas leaving the r~lf ~ft e DC reactQr:. cond~nses in the separation-half and flows back in the reactor-half as a liquid. econd problem was the fact that ChemCad had probie s modelling e mixed phase in the DC-~eactor.

For the reactor-half kinetic reactor was used with two reactions

_.

_{. .} :

C2H4 +C12 ~ C2H4CI~ (11.2)

RI=kRI *[C2H4]*[CI2] kRI=0.132 [m3_,mol-1 _{S-I] (IV.S)}

J..I:s

C2H4Cl2 + Cl2 ~ CÀCl₃ + HCI

. . '\. .... " '" ' , ~ (IV.9)

(IV.lO)

These kinetics (ref 7 and 8) have been entered into ChemCad and further assumptions have been made:

•

•

•

•

•

Reaction temperature is 363 K constant Reaction phase is liquid

~

°C

I

It is a CSTR-reactor

or

O

The pressure in the reactor is 1.5 bara..,.... •

The once-through conversion of ethylene is 75%

.~

The stream leaving the reactor enters the tower which in reality ~hould be i

reactor. Naturally in order to reflect reality the feed tray oftbjs tower i _, ra .

Secondly the reboiler duty is taken the same as the reaction energy which i released' e kinetic reactor. The assumption w a e at this tower should be able to separate in such a manner that 1% ofthe byproduc CiH4CI aves the tower with the distillate_. . The tower than -has 15 trays. On the top tray the - Oricentiation was high enough to use this EDC directly for the pyrolysis. In ChemCad this w

s

modeIted usin a li uid 'withdrawal. .

The top stream leaving the tower is vided with' a 99 1. r~Jio . .

l~

g/f~ee~!

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Chlorination reactor (R401)

The chlorination reactor is modelled in ChemCad using six stoichiometrie reactors. These reactors are all adiabatic because there is no cooling. Each reactor in ChemCad represents one chemical reaction. Each reaction has it' s own conversion, the used reactions are;

C4~ _{+ Cl2} -t C4~C12 C4H4 + 1.5 Cl2 _'. -t

C

₄

H

_{4Cl3 ..} C4HsCI + CI2'-t C4HsCl3 C₂HCl3

+

Cl2 -t C2HCIs C₂H₃CI + Cl2 -t C2H3Cl3 C6~ _{+ Cl2} -t _C6HsCI + HCI ç=0.99

*

J

ç=0.99

*

ç=0.99

*

ç=0.95 ç=0.95 ç=0.90 (IV.H) (IV. 12) (IV. 13) (IV. 14) (IV.IS) (IV.16)

In order not to use to many components it was decided to create the, heavy C4-lump which has been discussed earlier. All _{reaction-products (and ot hers such as C4H4Cl4 ) marked with an}

\ .

.

asterisk have been replaced by this lump. The pressure in the chloriniltion reactor was taken 5 bar and the temperature'arounq 130o

e

:'"

.

The reactor also requires a catalyst and this could be according to ~ference 2 a ferric halide on a carrier, for example FeCl₃ on silica. According to'referencè 56 this should be possible at

" ' J

the chosen pressure and temper~ture. This would make the reactor a~fixed bed.leactor.

Pyrolysis reactor (R506)

The pyrolysis reactor is modelled in ChemCad using a stoichiometrie reactor. In this reactor the reaction is taken from a table in re(erence 17. EDC was taken as a key component and it's conversion is taken from this table ás'ç=0.6002. The heat ofreaction has been calculated by ChemCad. Further assumptions and inputs are:

,

.

• T emperature is taken 773 K

• Pressure is taken 25 bar

The stream leaving this reactor enters the pyrolysis quench tower.

Catoxid reactor (R704) .

Y

1

The catmcid reactor is modelled in ChemCad ",th 23 st ichiometric reactors. For each 0

dJl.

reaction equation one reactor is used. The rea tions represent the catàlytic oxidation of ., •

(chlorinated) hydrocarbons to give HCI, COz, _{and H2}0. The reaction-equations used are:

C2Cl2H4

+

2.3 O2 C₂CI₃H3

+

1.8 O2 C2H4

+

2.8 O2 C₂H₂ + 2.3 O₂ C4HsCI + 4.6 O2 CC1H3

+

1.4 O2 1.6 CO2

+

2 HCI

+

1 H20

+

0.4 CO 1.6 CO2 + 3 HCI + 0.4 CO 1.6 CO2

+

2 H20

+

0.4 CO 1.6 CO2

+

0.4 CO

+

H20 3.2 CO2 + 0.8 CO

+

HCI _{+2 H20} 0.8 CO2

+

0.2 CO

+

HCI + H20 (IV.17) (IV.18) (IV. 19) (IV.20) (IV.21) (IV.22) 21

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C_3H4 + 3._{7 O2 2.4 CO2} + 0.6 CO + _{2 H20} C2H3CI + 2.3 O2 1.6 CO2 + 0.4 CO + HCI + H20 C4~ + 5._{1 O2 3.2 CO2} + 0.8 CO + 3 H20 C4H4 + 4.6 O2 3.2 CO2 + 0.8 CO + 2 H20

C2H sCI + 2.8 O2 1.6 CO2 + 0.4 CO + 1 HCI + 1 H20

C6~ + _{5.7 O2 4.8 CO2} + 1.2 CO + _{3 H2}0 C2HCl3 + 1.3 O2 + 1 H20 1.6 CO2 + 0.4 CO + 3 HCI C2H2Cl20 + 1.3 O2 1.6 CO2 + 0.4 CO + 2 HCI C2H2Cl2 + _{1.8 O2 1.6 CO2} + 0.4 CO + 2 HCI (2x) C4Cl3Hs + 4.1 O2 2 CO2 + 0.8 CO + 3 HCI + 1 H20 HCCl₃ + 0.4 O₂ + 1 HO 0.8 CO2 + 0.2 CO + 3 HCI C2H3Cl30 + 1.3 O2 1.6 CO2 + 0.4 CO + 3 HCI C2HCIs + 0.8 O2 + 2 0 1.6 CO2 + 0.4 CO + 5 HCI C6HsCI + 6.4 O2 4.8 CO2 + 1.2 CO + 1 HCI + 2 H20 C2~ + _{3.3 O2} 1.6 CO2 + 0.4 CO + 3 H20 Assumptions:

-All chlorinated hydrocarbons can be catalytically burned in the catoxid reactor

( . ~

-The only reaction-products formed are CO2; CO, H20 and HCI

-All Cl-atoms react with H-atoms to give BCI

(IV.23) (IV.24) (IV.25) (IV.26) (IV.27) (IV.28) (IV.29) (IV.30) (IV.31) (IV.32) (IV.33) (IV.34) (IV.35) (IV.36) (IV.37)

-Ifthere are more Cl-atoms than H-atoms present in a molecule, then H-atoms from another molecule are used for the reaction (e.g. a water-molecule).

-The ratio CO2:CO is 4: 1 (mole-based) (ref 2) -The conversion is 99% for all reaetants

Hydrogenation reactor (R707)

_.

The hydrogenation reactor was modelled using a stoichiometrie reactor. For the reactions and conversions reference 15 was used. Reactions are:

C_2H2 + H₂ ~ _C2H4

C2H4 + H2 ~ C2~

In ChemCad this reaction equation was used:

1.01 H_. 2 + 1 C2H_. 2 -t 0.99 C2H4 + 0.01 C2H6

Further assumptions made are:

•

•

•

•

Conversion taken as 1;=0.99 (based on C2H2)

Adiabatic reactor (no cooling) Pressure taken 25 bar .

The heatof reactièn was calculated by ChemCad

(IV.38) (IV.39)

(IV.40)

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IV,2 Towerslcolumns

Quench column after oxychlorination (T208)

In Quench column T208 the reaction mixture from the oxychlorination is quenched. This stream of hot gases enters at the bottom of the column and cold water is sprinkled from the top. The aim is to cool the reaction mixture and to condense the EDe.

This tower is modelled in ChemCad with a "SCDS-tower". This is done because this is the onIy tower-model in ChemCad that is compatible with an electrolyte-mndel. The use of an electrolyte model was necessary in order to sim~late that the ijCI dissolves in the water. The electrolyte-model us.ed was the "i~eal" model, because this model had the shortest calculation time and the least convergence-probl.ems (other models like NRTL tooktoo much calculation-time). The type of simulati<?n of electrolyt,es used was thè "apparent s~cies". This type had to be used i~ order to be able to calculate with two liquid.phases. UnIike the "tr:ue species" type, this type does not show ions, onI}: the ~lts. The thermo-model used was "unigyac" beèause this model describes two-phase systems like water/hydrocarbon systems and in this column mainly EDC and water are present.

J

'

Jo." " , ' _ ~ 1_

o.'S~+-~ t7-U~~~

Because th ortcut col could not be use<! for simulation llnd calculation of t~e number

of stage withthe scds-tower. A number of stages of 15 was chosen, which is

not to 1 number. First a calculation with only one phase in the ,Scds-tower was done. Aft~;)rus the results were used for a calc~lation of the scds-tower but now wit? two phases in tbe column: the water and the or anic phase. Finally also the ele oly!e od was activated

/ during the

calc

~

0 in three

step~

t s equipment could be

calculc~.ted

.

The reboiler mode was s~t to: "no reboiler" (after all this is a qu~nch tower). After the first estimations with the shortcut cÓlumn it became evident that a condenser was necessary in addition to thè quench water' to condense the EDÇ. The pressure in !he column was chosen to be ~r, because at this pressure onIy a minimum amount

$

--

ould go alçmg with the vent and t~e temperature at the top would not b~ lower th ' room-te perature.

\

The condenser type was set to partial, because of the low-boiling ventgases, like N_2, from the catoxid reactor which would makê the distillate-temperature ve~ low. The condenser mode chosen was "distillate coml2onent fraction' recoverY" and the specification put on tbe system was that no more'than 4% ofthe EDC was alfowed to go wit)l/the vent (distillate). The temperature

esti

~

~

s

w

~

e

~

: 300K,

botto~

:

370 K. Apd the calculated top and bottom temperatures arr 29 an 1 3 8~ . The specification for tJ<e distillate was' ~lo~ly increased until the final specifica 'on of C in the distillate wasr.lchieved. Efforts to get even less EDC in the distillate result.ed in a top-teml2er:.!lt!Jle that

w

is

~

w

(and the cooling duty raised

more than proportional), I /

/

/