Epichlorohydrin

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Technische Universiteit Delft

Third and Final

Report

EPICHLOROHYDRIN

,_ V

EITROUWEUJk

June 1992

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Delft Technical University

Department of Otemical Engineering and Material Science

Julianalaan 136 2628BLDelft Thc Netherlands

EPICHLOROHYDRIN

A.E. van Diepen JJ. Feddes R.P.A. Hartman J.P.F.M. van Hertrooij R.R.P.T. Korver E.T. de Leeuw J.G. Reinkingh J .L.B. van Reisen

CONFIDENTIAL

Third and fmal report of the joined design project EPICHLOROHYDRIN by order of Comprimo B.V .• Amsterdam.

Supervisors Delft TU:

Comprimo:

prof.

ir.

1.

Grievink prof.

ir.

A.G. Montfoort

drs. F.A. Meijer dr.ir. P,J.T. Verheijen

dr.ir. F.P.M. Kerkhof

ir.

R. Dobbelaar

r ' r ' , 1 , ~ Confidential

SUMMARY

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-In this

third and final report tbc results of thc design projeCt, as part of thc two year graduate _~ll':J_:' -J.o"'J(.ï."~"': ' .". -."'} . ," . . '~. ' " . "

program

'~pp~~~~~ ~gn' a~

Delft

~ni!~~ of Tèèhnology, are presented. Tbc

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~pichloroiiydrin

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(BCH)

'md waS

realized

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cooperation

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In

the

fust

progressreport (1991) comprèhcnsive studies were made of thc market prospects of ECH and epoxy resins and of all possible process routes for the production of ECH. It was found that the ECH market is still expanding significandy and this growth is expected to continue

in

the future. Consequendy further investigation for process optimization and improvement was considered relevant. Based on the extensive literature survey, all potential process routes were compared and scrutinized. Out of several recommended subjects it was decided, in consultation with Comprimo, to proceed with the following topics:

• improvement of the allyl chloride reactor, as currendy operating in the Spolek/Compri-mo process;

• conversion of propene and hydrogen chloride to allyl chloride by oxychlorination; • improvement of the dichlorohydrin reactor;

• investigation of the alternative route for the production of ECR as described in the patent of Showa Oenko.

The majority of the results, with respect to process improvements or new process units, was treated in the second progress report.

In this report the refined, adjusted and/or new results of the four topics are presented. In addition cost price calculations were made for each process improvement or new process unit, as also for the current Comprimo/Spolek process.

For the allyl chloride reactor it was found that the highest selectivities can he reached in a

tank reactor in series with a plug flow reactor. The total reactor volume was calculated to be two times smaller than the reactor volume in the Spolek/Comprimo process. Due to uncertainties in the reaction kinetics it was only possible to indicate a selectivity range in which the highest attainable selectivity win lie (84 to 96%).

The alternative way of producing allyl chloride by oxychlorination, according to a modified Monsanto process, seems to be a technologically feasible process, although the theoretical basis is rather weak:. Opposed to this, it was conc1uded that the technological feasibility of the manganese dioxide process is rather uncertain, and further studies were omitted.

With respect to the dichlorohydrin production a new reactor system has been proposed. Four reactor set-ups were presented, OCHl to DCH4, in which higher selectivities can be reached and the effluent stream is highly diminished. DCH2 was found to be the most favourable with respect to the Spolek/Comprimo dichlorohydrin reactor.

+H

IL1 _

Confidential The altemative production process of epichlorohydrin has been developed based on patents by Showa Denko, Bayer

and

Hoechst. This process appears to have several important advantages compared to the Spolek/Comprimo process, like higher overall selectivity, limited chlorine cons~tion, reduction of waste water streams and of o~anic waste gases. However,

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has been calculated. Thc producuon cost pitce in thc Coïnprimo/Spolck proccss;"producing 24 kton

ECH

per

year, was

calcul~tcd

to

79.S

·'

8Q3k

f/Yr

c~rfêsp;;ndirig

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to

iH4

f/ton

ECH.

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In comparison with the Comprimo/Spolc:k process, the lowest production cost price of ECH was calculated for the modified MonsantD process in combination with the DCH2 set-up, namely only 79% of the Comprimo/Sp ek production cost price. The uncertainties in both the modified Monsanto and DCH2 units are considerable, since the former is not founded on a strong theoretical basis, while the for tbe latter tbere is no industrial experience. However, it is desirabie and recommended to investigate the proposed DCH2 unit further, since this adjustment may yield in significant savings in the conventional process.

The ECH production cost price in tbe Showa Denko process was calculated to be 81 % of the Comprimo/Spolek cost price. The Showa Denko process is currently implied in industry and does not suffer from uncertainties like the modified Monsanto process unit and DCH2 unit. lt was therefore concluded that the Showa Denko process is superior to the other processes with respect to the production co st price of ECH. In addition to this, the process effluent stream is considerably less than in the Comprimo/Spolek process, which presumably

will

become more important as environmental regulations

will

be tightened in the future.

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Contents

1 INTRODUCTION 1

2 COSt PRICE CALCULATION FOR THE COMPRIMO BASE CASE. . . . . . . . . . . 5

S1Jmm.ary

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.

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5

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1.1 The production dependent costs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1.2 Labour costs . . . 8

2.1.3 The fixed capital costs . . . 9

2.2 The Comprimo/Spolek process . . . 10

2.2.1 Production dependent costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.2 Labour co st calculations . . . 11

2.2.3 Capital invesbnent calculations . . . 12

2.2.4 Variation of the number of functional units. . . . . . . . . . . . . . . . . . . . . . . 17

2.3 Results for the Comprimo base case . . . 17

2.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.5 Nomenclature 20 3 THE ALL YL Clll..ORIDE REACTOR .. . . 21

Summary 3.1 Introduction 21 22 3.2 The current Spolek/Comprimo reactor . . . 22

3.2.1 The chlorination of propene . . . 22

3.2.2 Configuration . . . 23

3.3 Model calculations of the allyl chloride reactor . . . . . . . . . . . . . . . . . . . . . . . 23

3.3.1 Previous work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.3.2 The consecutive reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.3.3 Comparison of Wermann with and without Biegler's rate equation ... 28

3.4 Sensitivity analysis . . . .. . . 29

3.5 Cost price calculations: the allyl chloride reactor. . . . . . . . . . . . . . . . . . . . . . 31

3.5.1 The influence of selectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.5.2 The influence of the propene chlorine feed ratio . . . 32

3.5.3 Optimal propene chlorine feed ratio . . . . . . . . . . . . . . . . . . . . . 33

3.6 Conclusions 3.7 References 3.8 Nomenclature 36 37 38 4 OXYCHLORINATION OF PROPENE . .. ... ... .. . . 39 Summary 39 4.1 Description Monsanto process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5

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Confidential 4.2 Mass balances and Aspen plus simulllions . . . .

4.2.1 Mass balances ...•• . . .

4.22

~ simulatiollS ••••••• _ •••••••••••••••••••••••.•.••••••

4.3 Heat balance and Refrigeration cycle design . . . • . . . . 4.3.1 Heat balance ...•••••••• •••••.••.•••••.••••••... . •.•.

4.3.2 Refrigeration cycle design .. ••. . .

4.4 AW~ ~~gIl ~~ ,: ••

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4.4.1 AC-reactor . . . ••. . . • • . • . . . 4.4.2 Regeneration . . . .. '. . . . . . . . . . . . . . . '. :" ... . 4.5 Costs calculations . . . ... . . . 4.5.1 Labour costs . . . .... . . . 4.5.2 Production costs . . . ... . . . 4.5.3 Investtnents . . . .. . . . 4.5.4 Results . . . ... . . . 4.6 SWOT -analysis . . . .. . . . 4.7 Manganese dioxyde process ... .. . . . 4.7.1 Process description ... .. . . . 4.7.2 SWOT analysis . . . .. . . . 4.8 Conclusions

4.9 References

4.10 Nomenclature . . . ... . . .

THE DICHLOROHYDRIN REACTOR SYSTEM .. . . .

Sununary 5.1 Introduction 42 42 44 45 45

46

48 48 51 52 52 53 53 55 58 60 60 61 63 63 64 67 67 68 5.2 Mechanisms of addition of hypochlorous acid to ally1 chloride . . . 68 5.3 The hypochlorous acid production process . . . 70 5.3.1 Introduction . . . . . . . . . . . . 70 5.3.2 Reactions . . . .. ... .. . . ... . 71 5.3.3 The hypochlorous acid reactor system . . . 72 5.4 The dichlorohydrin reactor system . . . .

5.4.1 The production set-up .. ... . . .. . . . 5.4.2 A quantitative analysis of the production process . . . . 5.5 An economie analysis of the different production set-ups . . . . 5.6 SWOT analysis . . . .. . . . 5.7 Recommendations . . . .... . . .. 5.8 Conc1usions ... . . . .. . . .. . . . 5.9 References ... ... . . . . 5.10 Nomenclature ... .. ... .. ... .... . . ... .. .... .

THE SHOW A DENKO PROCESS .. .... .. . . . Summary 6.1 Introduction 75 75 79 79 84 86 87 89 90 91 91 92 .1

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6.2

Process description ....•..•...

6.2.1 Allyl alcohol production . . . • • • . . . • . .

6.2.2

OIJorination . .•...•...••••.•. .

623

S~fication ...•••...•..•...•..•...

6.3 Process

flow

sctIe:IIle ...•..•...•••..•..•••••••....•.•....

6.3.1 11Je allyl acetate unit ..••...•..••••••..••••••....••• " .••..

6.3.2

Allyl alcohol unit . . . • . • • • • . . . . . • • . • • • • • . • • • . • • • . . . . . • . . • • •

6.3.3

OIJorination unit . . . • . . . 6.3.4 Saponification unit . . . • . ••. . . 6.4 Waste streams . . . . 6.5 Cost estimate 6.5.1 Capital investtnent . . . .... . 6.5.2 Production dependent casts ... ... . . . ... . . .

6.5.3

Tatal casts . . . .. . . . 6.5.4 Sensitivity analysis . . . . 6.6 SWOT analysis ... .. . . .. . . ... . 6.7 Canclusians 6.8 References 6.9 Narnenclature 92 94 94

95

95

97 98 99 100 101 102 102 103 104 106 109 110 111 112 7 PROCESS COMPARISON . ... . . 113

7.1 Raw material cansurnptian . . . .. . . ... .. . . 114

7.2 Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

7.3 Waste strearns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

7.4 Capital & labour casts .. .. . . 117

7.5 Design reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

7.6 Tatal cast price, averall carnparisan . . . . . . . . . . . . . . . . . . . . . 119

8 CONCLUSION 121

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Confidential

APPENDICES

:ffi::.~ _.: '

Contents:

A A SWOT analysis of the Co rimo/Spolek process

B Spreadsheet for the calculation of the Comprimo base case and variations C AC reactor kinetics discrimiDation

D AC reactor kinetics combinad

E Chlorinated by-products

F Spreadsheet for the cost price calculation for AC reactor related variations

G Stream report of the Aspen Plus simulation of the Monsanto oxychlorination process H Design sheets for compressors and columns of the Monsanto process

I Costs calculation sheet for the Monsanto process

J The hypochlorous acid reactor system K The chlorohydrin productim set-ups L Spreadsheet costs calculation

M Mass balances for the Showa Denko process N Utilities

o

Co st price calculation Vl .1 T

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1 INTRODUCTION

. -;:... , .

As part of the two year graduate program' Apparatus and Process Design' at Delft University of Teclmology, a joined design project bas to be carried out. This year's project is realized in cooperation with Comprimó B.V., Amsterdam. . ... __ . -..--:-._. ' - -_'_''''--''-'._ .. __ .-. The subject of thèproject is the production of epichlorobydriD. This report is the third and final

report. ·!3JOJi::.~A

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-In the fust progress report (december 1991) comprebensive studies were made of: • the market prospect of epichlorohydrin and its derivative epoxy resins; • all possible process routes for the production of epichlorohydrin.

In the first report it was concluded that the market for epichlorohydrin is still expanding

significantly with an annual growth of 1 to 2 percent per year and that this growth is expected to continue in the future. The market for epoxy resins, the main consumer of epichlorohydrin, is expected to grow at 4 percent per year. Therefore, it was concluded that further investigation for process optimization and improvement is still attractive. A SWOT analysis of the Comprimo/ Spolek epichlorohydrin process can be found in appendix A.

Based on an extensive literature survey all potential process routes were compared and scrutinized. All synthesis routes found in literature, are presented in figure 1.1. Nearly all process routes use propene as a starting material. Each route proceeds through one of the following intermediates:

• allyl chloride • allyl alcohol

• dichloropropyl acetate

Qnly two processes were found to operate on an industrial scale, namely the conventional process through allyl chloride and the Showa Denko process through allyl acetate and allyl alcohol. The final step in both processes is the reaction between dichlorohydrin and Ca(OH},z to epichloro-hydrin.

In the first report, the following subjects were recommended for further investigation: • oxychlorination of propylene to allyl chloride in two steps (Monsanto Company); • waste water treatment (e.g. by usage of electrolysis);

• production of epichlorohydrin from allyl chloride by electrolysis (Shell);

• co st price estimation and comparison of Spolek/Comprimo and Showa Denko process; • recycling of by-products from the allyl chloride reactor;

• alternative design for the allyl chloride reactor;

• alternative design for the dichlorohydrin reactor system in order to diminish waste water formation;

• specific bottle-necks in relation with the Spolek/Comprimo process.

2 ~~OPANE CH3-CH2-CH3 .' > HCI + ~ ALL YL CHLORIDE CH2-CH-CH2CI oxidation HCI HOCI j r ; _ PR! fYLENE . --J~. . ... • •. , ... iitt\. ",-- " CiG-CH-CH2

Confidential

ACROLEIN

CH2-CH-CHO + PROPYLENE OXIDE H2C-CH-CH3 ALLYL ACETATE , CH2-cH-CH2-0-Çf-CH3

o

DICHLOROPROPYL ACETATE CH2CI-ÇHCI-CH20Ac CH2CI-CHOAo-CH2CI DICHLOROHYDRIN (OCH) CH2CI-CHCI-CH20H CH2CI-CHOH-CH2CI Ca(OH)2

-

liet.

EPlCHLOROHYDRIN (ECH) H2~H-CH2CI

'd

ALL YL ALCOHOL CH2-CH-CH20H

Figure 1.1 Synthesis routes to epichlorohydrin

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In consultation with Comprimo B.V. and taking into account the relevance of the topics in relation

with the educational program, the following subjects were chosen for ftlrther investigation:

• improvement of the allyl chloride reactor, as currently operating in the SpolekiComprimo

process;

• convers ion of propene

and

hydrogen chloride to allyl chloride by oxychlorination;

• improvement of the dichlorohydrin process;

• investigation of the alternative route for the production of epichlorohydrin as described

in

the

patent of Showa Denko.

The results of this investigation were presented in the second progress report. In this third and

final report the results of the second progress report are further developed into process designs.

The new process designs are compared with the conventional Comprimo process on an economical

basis and by means of a SWOT analysis (Strengths, Weaknesses, Opportunities and Threats).

Finally conclusioos are drawn regarding the position of the Comprimo process and

recomrnenda-tioos are given for improvements of the present process and for further experimental

investiga-tioos

.

-Confidential ... , . -~ .... --, 4

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2 COST PRICE CALCULATION FOR THE COMPRIMO

BASE CASE

Summary

In this chapter a cost price calculation is set up, for the Comprimo base case. The model used for the calculations is given by Montfoort (1988) and consists of three major elements:

• production dependent costs; • capital investment related costs; • labour costs.

The production dependent costs include raw material and utility costs as weil as penalties for generated waste streams.

Input data for the Comprimo base case are:

• annual production of 24,000 ton epichlorohydrin; • productivity of 8,000 hours per year.

The production dependent costs were determined using the energy and mass balances provided by Comprimo B.V .. Capital investment was calculated only for on site battery limits investment using a modified Zevnik-Buchanan method. The modification imp lies that each functional unit is

regarded individually concerning capacity and complexity. The labour costs were calculated with the Wessel equation.

Other data like raw material and utility costs and information concerning waste streams were all provided by Comprimo B. V.

In determining the capital investment related costs, two variations on the base case were

considered. For the base case, the number of functional units was set to 16. The variation consists of an upper and lower boundary for the number of functional units (14 and 18 units) and an upper and lower boundary tor capacities of specitic units (distillation columns and reactor systems with large recycles).

-Confidential

The calculated costs are:

total costs per year % costs per ton ECH

[kflyr] [{Iton ECH]

production dependent costs 49139.19 61.79 2047.47

capital charge (13 %) 12132.18 15.25 505.51

depreciation and interest (16 %) 14931.92 18.78 622.16

labour costs 3325.94 4.18 138.58

I

total

I

79529.23 100 3313.72

114

units

I

77796.17 -2.18 3241.51 83412.75 +4.88 3475.53 18 units min. capacity 75080.83 -5.59 3128.37 max capacity 100026.96 +25.77 4167.79 6

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Confidential

2.1 Introduction

In the cost price build-up of epichlorohydrin (ECH), the following categories can be recognized: • production dependent costs;

• labour costs;

• fixed capital related costs.

The total costs per year for producing epichlorohydrin is the sum of the costs mentioned above, all multiplied by a model factor:

Il.I in which:

a

Kp d L f

= total costs per year

= model parameter

= production dependent costs per year

=

model parameter

[kj/yr]

[-]

[kj/ton ECH]

= labour costs per year

=

capital charge

=

depreciation and interest

[-]

[kj/yr] [%/yr] [%/yr]

=

on site investment of battery limits [kj] The factor a stands for the non calculated production dependent costs such as transport, storage etcetera, and equals 1.13, All labour dependent costs are calculated as a multiple (d) of the labour

costs (L); d equals 2.6. Amongst others, d stands for supervision, payroll- and general office

overhead. The capital charge f equals 0.13 and consists of:

• maintenance; • insurance; • overhead;

• indirect production costs; • etcetera.

The values for

a,

d and f are taken from Monttoorts best model (1988), Depreciation and interest, i, is set to 16 % of the capital investment.

I!

-2.1.1 The production dependent

costs

The production dependent costs cao be di ed into three classes:

• raw material costs (propene, chlorine, etc.);

• utility costs (steam, electricity, etc.);

• penalties (waste water, chlorinated by-products)

The costs per year (Kp) for these classes are calculated by:

in which:

vI ·

Kp = Icp'P = P·L(vj.qj)

= casts per ton epichlorohydrin

=

costs per ton raw material. utility or penalty

=

ton materia! or utility used or ton waste produced per ton ECH

Confidential

11.2

[kj/ton ECR] [kj/ton mat.] [ton mat./ton ECR]

Thus the tata! costs per yeaf of production dependent casts (Kp), are calculated by multiplying the

costs per ton ECH (kp) with the total production of ECH per year (P). The costs fOf the utilities

and raw materials are also multiplied by a (see equation 1I.l) to account for not calculated

production dependent casts (storage, transport etc.). The penalties are also calculated by equation

11.2, but they are not multiplied with

a.

2.1.2 Labour costs

The labour casts per year (L) are related to the number of man hours per ton product. The

number of man hours per ton ECR is calculated using the Wessel equation, namely:

in which: MR k S C MH = k _S_ CO.76

=

the number of man hours per ton product

=

model parameter

= the number of process steps

= the capacity of ECH per day

11.3

[# of hrs/ton ECR]

[-]

[# of steps] [ton ECR/day]

The value of k is of major importanee. In 1952 k was given tor a continuous process to be 10.

With the use of function places, the labour casts per year can be calculated from the number of

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Confidential man hours per ton product through equation 11.4. Each function place stands for 24 man hours a day and costs about 400 kj per year (extrapolation, Montfoort 1988), so the totallabour costs in

kj per year are given by:

2.1.3 The iIXed

capital

cost

400 d·L

=

d·MH·C·-24

11.4

For the calculation of the battery limits investment (Is), a modified Zevnik-Buchanan method was used. This method (without the modification) is based on the fact that investments are a function of process capacity and process complexity. Other forms of investments are not taken inta account, except for investment related costs for utilities. These are however covered in the production dependent costs of the utilities. For the calculation of the battery limit investment only the following four basic data have to be known:

• capacity of the plant;

• the number of functional units; • a complexity factor;

• a construction cost index.

Expression 11.5 gives the battery limits investment in k$:

in which:

= the number of functional units

=

the camplexity factor

=

the Chemical Engineering Plant Cast Index = model parameter

11.5

The complexity factor is a function of the highest temperature and pressure reached in the plant, and of the material necessary tor construction.

[I]

[ -]

[-]

[-]

The parameter m depends on the capacity, but tor capacities greater than 4.5 kton per year, equals 0.6 (Montfoort 1988).

The advantage of this method is its simplicity , this however at the expense of accuracy. The major difficulty for this method lies in determining the number of functional units.

The modification as used by lansen (described in Montfoort 1988), means that tor each functional unit individually, a complexity factor is calculated and a separate capacity is used. In this way the effect of recycle streams and specitic complexities like high temperatures or corrosive media can

t'

-Confidential be accounted for. Equation 1I.5 then becomes:

11.6

2.2 The Comprimo

I

Spol

process

In this paragraph the cost price calculatio for the Comprimo base case are carried out. Also the influence of upper and lower boundaries both for capacities of specitïc functional units and for the number of units is investigated. The basic preconditions are:

• an annual production of epichlorohy rin of 24,000 ton; • 8,000 production hours per year.

2.2.1 Production dependent costs

In table 2.1 the costs of raw materials, utilities and penalties are given, together with the amount used or produced (penalties) in the Comprimo process. All data for this base case have been provided by Comprimo B. V. ex cept for the amount of electricity used. The electricity post is governed here exclusively by the work tequired by the propene recycle compressor, and is calculated, based on data given by Comprimo B.V. with the ASPEN Plus package.

Table 2.1 Prices and quantities of production dependent streams

raw material v· _I Q;

~

rf/unit] [unit/ton ECH] rf/ton ECH]

propene 620.00 0.63 388.95 chlorine 250.00 2.09 521.42 Ca(OHh 75.72 0.95 72.11 AI:P3 1670.00 0.00 0.50 caustic 470.00 0.01 3.45 industrial water 0.20 32.67 6.53

boiler feed water 0.50 0.27 0.13

10

, 1

I ...

Confidential

nitrogen 0.30 0.33 0.10

utilities vi

_<Ii

ie.,

coaling water 0.08 560.33 44.83 chilled water 0.15 248.00 37.20 L.P. steam 25.00 4.74 118.57 M.P. steam 27.50 1.06 29.17 H.P. steam 30.00 0.92 27.62 electricity 0.12 460.00 55.20 fuel 300.00 0.09 27.70

I

penalties

I1

v· I

I

qj

I

~

I

effluent water 10.00 38.44 384.40 organics to incineration 500.00 0.31 156.25 total production costs (a· ~. P) [kf/yr]

materials 26935.15

utilities 9228.44

penalties (~. P) 12975.60

total 49139.19

2.2.2 Labour cost calculations

To be perfectly clear, the number of process steps (S) used in the Wessel equation, does not equal the number of functional units in the capital investment calculations. The number of process steps is taken to be five, namely:

1. allyl chloride reactor

+

quench column;

2. allyl chloride and hydrogen chloride processing; 3. hypochlorous acid and dichlorohydrin system: 4. saponitication step;

5. epichlorohydrin work up.

" r H _

Confidential

As mentioned earlier, k had a value of 10

in

1952. To compensate for production increase, we

calculate a new

k,

based on the one from 1952. If we use a production increase of 2 % per year

(Dobbelaar 1991), the value of kin 1992 5.5.

However, if we use the productivity iner of 6 % per year given by Montfoort (1988), k

becomes 1.7. This would lead to unrealistic low labour costs. As the epichlorohydrin plant is

relatively small but complex, a figure of ' ee function places seem to be appropriate in

ca1culat-ing the labour costs. In the spreadsheets used, the labour costs are still ca1culated using the Wessel

relation with k equals 5.5, leading to 3.2 function places (see table 2.2).

Table 2.2 Labour costs calculations

capacity ECH per day 72 [ton ECH/day]

number of process steps 5

_H

k 5.5 [-]

number of man hours per ton ECH 1.07 [hrs/ton ECH]

number of function places 3.20 [-]

costs per function place per year 400 [kf/yr]

labour costs (L) per year 1279.21 [kf/yr]

d·L 3325.94 [kf/yr]

2.2.3 Capita) iovestmeot calcu

t

ioos

The number of functional units in the Comprimo/Spolek proeess is determined based on the flow

seheme provided by Comprimo B.V. (Comprimo (991). The Comprimo/Spolek proeess is divided

into 16 functional units, see figure 2.1 Cor a tlow scheme with all units appointed. The 16 units

are:

1. prop ene recycle compressor; 9. AC topping column;

2. propene drier and vaporiser; 10. AC tailing column;

3. propene oven; 11. HOCI column;

4. allyl chloride and quench; 12. wash column;

5. quench column; 13. dichlorohydrin reactor;

6. allyl chloride propene splitter; 14. dichlorohydrin column;

7. HCI absorption column; 15. ECH/water column;

8. wash column; 16. ECH end column.

l r L .-W

~

_l:: ~ !'> ...

~

~

'"

~ ~ !1> ~ §: ~

:g

c :;

-~

'?

::I ~

ë-~

l:: ::

a-""""

_o

~

~

-~

\)-~ !1>

§

~ propyllnl AC-loPPlng column 1 prop)",n. dri., AC-rl,lin; column ( HOCI column plopyllnl oVln 3 wnh column (ignt .nd.

.---~ I 110 h .. ..,.,. Indl c.(OH). ehlOlin. (9''''1 .p.nl "u.lu: AC ,..CIO' dichlotohydtinl "":101 syarem qUlnch column unling IAnk orgln'CI to ,.·di.lillallon Ol incinwaaon AC/Plopytono HCl oblotphon .~in.r Column dOhydrodllOlin.1Ion column wo'" column Plopyleno

'.-w.ter ECH/w.ter COIumII w ...

'OUSII(

-

/ ~ _ _ J lpenl ca<olllC ECH .nd COIuIM ... ca 10

,.

·

cIieIoII • ...,.

..

~ () o

~

CII

sa

ëI

-The complexity factor in equation 11.5 is calculated as follows:

in

which:

=

temperature factor = pressure factor = material factor 0.018- (

T~~O]

ij T

>

290K -0.20- [T-290] ij T

<

290K 100 0.1 -log [

P;:

1

if

P

mu.

>

Po

0.1 -log [ Po

1

ij P min

<

Po Pmm

The material factor is taken from table 2.3.

Table 2.3 The material factor Fm

construction material

Cast iron, carbon steel, wood

Aluminium, copper, brass, stainless steel (400 series)

Monel, nickel, inconel stainless steel (300 series) Hastelloy, etc. Precious metals

Fm

0.0 0.1 0.2 0.3 0.4

In table 2.4, the complexity factor is calculated for each functional unit.

14 Confidential 11.7 11.8 [-] [-] [ -] 1l.9

Confidential

Table 2.4 The calculation of the complexity factor

no. T Ft p F_p Fm Cf [0C] [bar] 1

136

0.02142 20 0.13010 0.1 3.56905 2 23 0.00108 19.5 0.12900 0.1 3.39714 3 380 0.06534 6 0.07781 0.1 3.50094 4 500 0.08694 2 0.03010 0.2 4.15023 5 40 0.00414 1.6 0.02041 0.2 3.35414 6 59 0.00756 1.5 0.01760 0.2 3.35891 7 48 0.00558 1.3 0.01139 0.2 3.29613 8 20 0.00054 1.2 0.00791 0.1 2.56736 9 95 0.01404 3.8 0.05797 0.1 2.97199 10 98 0.01458 l.7 0.02304 0.1 2.74571 11 27 0.00180 l.1 0.00413 0.2 3.21343 12 30 0.00234 1 0 0.1 2.53145 13 27 0.00180 3.7 0.05682 0.1 2.88170 14 92 0.01350 3 0.04771 0.1 2.89895 15 141 0.02232 l.8 0.02552 0.1 2.81110 16 134 0.02106 0.3 0.05228 0.1 2.98110

For each functional unit, the capacity has to be determined. Some units have large intern al

recycles, such as the quench column, the dichlorohydrin reactor system and most of the distillation columns. For several units an upper and lower capacity is given, depending only on the internal recycles. For the Comprimo base case, only internal recycles of distillation columns are used in the calculations. The large recycles for the two reactor systems mentioned above are not regarded in the base case, since they lead to enormous (unrealistic) investments. Both for the base case and the upper and lower limit for the capacities, the capital investment for the functional units are listed in table 2.5. To convert American dollars to Dutch tlorins, an exchange value of 1.87 was used.

--- - - - -

-Confidential Table 2.5 Capital investment as a CunctioD of capacity Cor each Cunctional unit

DO

cap.

Ia [k.$] Ia

f1

cap.

Ia [kJ]

cap.

Ia [kJ]

b.c.1 (min) (mu) 1 120 2279.97 4263.55 4263.55 4263.55 2 134 2318.70 4335.97 4335.97 4335.97 3 86 1831.27 3424.47 3424.47 3424.47 4 112 2543.73 4756.78 112 4756.78 752 14911.22 5 112 2055.80 3844.35 112 3844.35 2400 24177.88 6 225 3128.79 5850.84 5850.84 5850.84 7 187 2747.75 5138.29 5138.29 5138.29 8 172 2035.51 3806.40 3806.40 3806.40 I -9 498 4459.17 8338.65 28 1482.70 498 8338.65 10 94 1514.95 2832.96 27 1340.24 94 2832.96 11 771 6267.15 11719.56 11719.56 11719.56 I -12 69 1160.24 2169.65 5 449.22 69 2169.65 13 792 5711.54 10680.58 792 10680.58 10680 50874.77 14 1030 6726.86 12579.23 12579.23 12579.23

-15 90 1511.09 2825.74 2825.74 2825.74 16 349 3613.61 6157.45 28 1487.24 349 6757.45

Sum: 4.99E+04 9.33E+04 7.80E+04 1.64E+05

f· Ie [kJ/yr] 12132.18 10138.07 21320.86

i'Ie [kJ/yr] 14931.92 12477.63 26241.06

l)base case

Confidential

2.2.4 Variation of the number of functional units

Ta get an idea of the intluence of the number of functional units on the total costs, the epichloro-hydrin cost price was calculated for an upper and lower limit of the number of functional units. For the lower limit, the two wash columns (units no. 8 and 12) were not considered; for the upper limit, two units were split up, namely the

propene drier and vaporiser

(unit 2) into

propene drier

and

propene vaporiser

and the

dichlorohydrin reactor

(unit 13) into

dichlorohydrin reactor

and

dichlorohydrinfinaJ reactor.

In bath cases, new capacities and complexity factors were calculated for the new units. In table 2.6 the values for the tota! investment, the capita! charge and the expense for depreciation and interest are listed' for the base case, as weil as for the upper and lower limit of the number of functional units.

Table 2.6 The influence of the number of functional units

I

I1

base case

I

14 units

I

18 units

IB 93324 87348 (-6.4 %) 106716 (+ 14.35 %)

[kJ]

[kf/yr] [f/ton ECR] [kf/yr] [f/ton ECR] [kf/yr] [f/ton ECR]

f·IB 12132.18 505.51 11355.29 473.14 13873.07 578.04 i • IB 14931.92 622.16 13975.75 582.32 17074.55 711.44

As can be seen from table 2.6, the intluence of the two extra units on the capital investment is much larger than for the 14 units option. This depends of course on the capacities and complexity factor used for these specitic units. In appendix A, a listing of the spreadsheet used for these calculations is given.

2.3 Results for the Comprimo base case

In tigure 2.2 the co st price build-up for epichlorohydrin (ECR) is shown. From this tigure it can be seen that the cost price tor ECR without penalties is about

f

2800.- per ton ECR. The total

costs per year are kf 79529.23.

Since the cost price evaluation is mainly intended for comparison between the Comprimo base

case, the Showa Denko process and modifications to the Comprimo process, no conc1usions are

drawn here concerning this cost price calculation.

However, compared to the calculations performed by Dobbelaar (Comprimo B.V. 1991), the

calculated cost price tor epichlorohydrin is about 18 % higher. This is mainly caused by the

I

-Confidential penalty on the effluent water (19 %) which

was

not taken into account by Dobbelaar, and the fact that the capital related cost tumed out to be igher due to a higher capital investment (93.3 versus 80.0 M.n.

18

Compri

0

base case

cost price

E

CH: 3313.72 f/tan

raw materlals (34%)

depr & Interest (19%)

utilltles (12%)

capitaI charge (15%)

labour (4%)

Figure 2.2 The co st price build-up fot EeR

I

~,

I

J

"]

]

]

]

r

[ t

r'

r

.

Confidential

2.4 References

Chemical Engineering, april 1992

Comprimo B.V., 'The SpoleklComprimo Epichlorohydrin process' , Comprimo B.V. (1991) Montfoort, A.G., 'De Chemische Fabriek deel 11 (st44)', Delft University of Technology (1988)

-Confidentia!

2.5 Nomenclature

a model parameter 1.13 [-]

Cf the complexity factor [-]

Cf· ,1 complexity factor for functioual unit i [-]

Cl the Chemica! Engineering Plant Cost Index 361.3 [-] C the capacity of ECH per day 72 [ton ECH/day]

d model parameter 2.6 [-]

f capital charge 0.13 [%/yr]

Fm

materia! factor [-]

l

F_p pressure factor [ -]

Ft temperature factor [ -]

depreciation and interest 0.16 [%/yr]

1

Is on site investment of battery Iimits [kJl

k model parameter 5.5 [-]

J

Kp production dependent costs per year [kj/ton] kp production dependent costs per ton product [kJ/ton ECR]

~ tota! costs per year [kj/yr]

f

L labour costs per year [kj/yr]

m model parameter 0.6 [ -]

MR number of man hours per ton product [# of hrs/ton ECR]

r

N nu mb er of functional units

[I]

P total production of ECR per year [ton ECR/yr]

Pi capacity for functiona! unit i [kton ECR/yr]

r-qi ton material or utility used per ton ECR [ton mat./ton ECR]

S number of process steps 5 [# of steps]

r-v_I · costs per ton raw material or utility used or waste produced [kj/ton mat.]

Abbreviations

AC a!lyl chloride ECR epichlorohydrin

---

~--• 1

Confidential

3 THE ALL YL CHLORIDE REACTOR

Summary

The allyl chloride reactor in the SpoleklComprimo process was modelled by a tank reactor in

series with a plug flow reactor. In the previous work (chapter 2, Second Progress Report (1992» this was performed using Wermann's rate expressions for the main reaction and a parallel

reaction. For this report Biegier and Hughes' rate equation for the consecutive reaction was added to the model to gain insight of the influence of this reaction.

Calculations made with Biegler's original rate expression resulted in selectivities lower than currently achieved in the SpoleklComprimo reactor. Therefore also model calculations were made with Biegler's expression divided by two and four.

It was found again, that a tank reactor in series with a plug flow reactor is a better configuration. However, the optimal tank volume is signit1cantly smaller when the consecutive reaction is taken into account.

The total reactor volume is calculated to be in the range of 0.6 to 1.0 m3, at least two times smaller as the current reactor volume in the Spolek/Comprimo process (::::: 2 m3).

The values of the selectivity towards allyl chloride calculated with the model vary significantly depending on wh ether the consecutive reaction is taken into account or not. As long as the kinetics of the reactions in the allyl chloride reactor are not known any better, it is only possible to

indicate a selectivity range of 84 % to 96 %, in which the highest attainable selectivity will !ie. In the final paragraph the co st price for epichlorohydrin is computed for variations concerned with the allyl chloride reactor, namely:

• the selectivity towards allyl chloride; • the prop ene chlorine feed ratio.

The selectivity affects the amount of propene and chlorine needed, and the amount of chlorinated byproducts formed. The propene chlorine feed ratio intluences the propene recycle compressor duty, and the capacity of some functional units, thus capital investment.

From the computations it becomes clear that a lower propene chlorine feed ratio is economically more favourable despite loss of selectivity, for all evaluated rate equations.

- - - -_ _ _ _ _ ~.LI ... , ,...LI,'--.-_______ __ __

Confidential

3.1 Introduction

In the second progress report (1992) a study was made of the allyl chloride reactor. Several potential improvements were considered aod investigated. Obviously the reaction kinetics and the configuration of the reactor play a key role. In this chapter some of the previous work will be discussed and extended.

In

the final paragr,aph the influence of the selectivity in the allyl chloride reactor and the propene chlorine feed ratio on the cost price of epichlorohydrin is investigated.

3.2 The current Spolek/Comprimo reactor

3.2.1 The chlorination of prope

e

The allyl chloride reactor is the tirst reactor in the epichlorohydrin (ECH) production process. In this reactor propene is converted into allyt chloride at an elevated temperature in the gas phase. Besides the desired allyl chloride, sever mono-, di- and trichloro substituted products are formed. The three main byproducts are 1,2-dichloropropane, 1,3-dichloropropene and

l-chloropropene. In literature three reactions are generall y mentioned in the process of prop ene chlorination.

CH₂=CH-CH₃

+

Cl₂ > _{CH2 = CH -CH2}Cl

+

HCI (3.1)

propene allyl chloride

CH₂=CH-CH₃

+

CI₂ > _CH

2CI-CHCI-CH3 (3.2)

propene 1,2-dichloropropane

CH₂=CH-CH₂CI

+

CI₂ > _CHCl=CH-CH

2Cl

+

HCI (3.3)

allyl chloride 1,3-dichloropropene

In the Spolek/Comprimo process the reaction is executed in an adiabatic reactor. The reactions are exothermic and the temperature rises trom about 370 to 500 °C. Temperatures above 500 °C are very unfavourable, because coke formation will increase rapidly. On the other hand the reactor temperature should not be lower than 300 °C, since at that temperature the main product will be

1,2-dichloropropane.

In order to prevent the reaction temperature from becoming too high, an excess amount of propene is fed to the reactor. In the Spolek/Comprimo process the prop ene chlorine feed ratio is 5.5.

In the Spolek/Comprimo reactor a seJectivity towards allyl chloride of 84.1 %, based on chlorine, is achieved, while the selectivity is

86.

9

% based on propene.

22

1

1

- - -

-Confidential

3.2.2 Configuration

The reactor, as currently operated in the SpolekiComprimo process is a cyclone reactor with eigbt tangential inlet nozzles (Dobbelaar 1991). The reactor has an annular form and is expected to perform as a plug flow reactor with very little backmixing. The reaction mixture is immediately quenched to 90

oe

when it leaves the reactor to stop all reactions. The space time of the mixture is about 1.8 seconds.

In the reaction scheme equation 3.1 represents the main reaction (substitution), equation 3.2 the parallel reaction (addition) and equation 3.3 the consecutive reaction (substitution). The selectivity towards allyl chloride is 86.9 %, the parallel and the consecutive reactions cover about 3.9 % and 4.5 % respectively. The remaining 4.7 % consists of 3.9 % l-chloropropene and 0.8 % others, all based on propene. In literature no information was found concerning the reaction kinetics of the formation of the latter by-product. Hence, the reaction towards l-chloropropene will not be taken into account in this studies.

The reactions were studied extensively by Groll and Hearne (1939) from whose article Smith

(1959) derived the rate equations tor the tirst two reactions. Later on the kinetic relation tor the third reaction was added by Biegier and Hughes (1982). Wermann (1970) also derived rate expressions for the main and the parallel reaction based on experiments in an adiabatic pilot reactor.

The parallel reaction is favoured by lower temperatures with respect to the main reaction. Theretore it is important that the reactor temperature is higher than 300 °C. The consecutive

reaction in fact proceeds more rapidly than the main reaction at the prevalent temperature,

according to Biegier and Hughes. However its rate depends on the concentration of allyl chloride. To suppress this reaction it is preferred to pertorm the reaction in an ideal plug tlow reactor. The moment the concentration of allyl chloride becomes significant the chlorine concentration will already be smal!. In a tank reactor the concentrations of both allyl chloride and chlorine will be higher which will increase the dichloropropene formation and is theretore undesirable.

The current reactor in the Spolek/Comprimo process is meant to operate as an ideal plug flow reactor, conciliatory the reaction kinetics discussed above.

3.3 Model calculations of the allyl chloride reactor

3.3.1 Previous work

In paragraphs 2.3.2 and 2.3.3 of the second progress report (1992) the rate equations for the above mentioned reactions were discussed and investigated. Smith (1959) was the flrst to derive rate equations for the main and the parallel reaction based on Groll and Hearne's work (1939).

Later on Wermann derived expressions tor the same reactions based on his own experiments. It was shown (Second progress report, (1992)), that the reaction rate equations proposed by

Wermann appeared to describe the overall kinetics in the allyl chloride reactor better than Smith.

- - - -_ _ _ ...w.--i...i •• ~ _ _ _ _ _ _ _ _ _ _ _ _

Confidential In appendix C a summary of the studies' the second progress report is given.

The allyl chloride reactor was modelled as a tank reactor (CSTR) in series with an ideal plug flow reactor (pFR). For this reactor configuradon conversions and selectivities were calculated using Wermann kinetics, varying the tank volu and the propene chlorine feed ratio. In table

3.1

a summary is given of the generated data ( table 2.6 in second progress report (1992) for more data).

It is clear from the calculated data tbat tb ideal reactor configuration would be a tank reactor followed by a smaller plug flow reactor to complete the conversion of chlorine. For tbis configuration top selectivities towards all chloride of about 96% were calculated. Further it seems possible to operate with a smaller propene chlorine feed ratio. A plug flow reactor only, leads to selectivities that are considerably ower than those reached in a tank reactor in series with a plug flow reactor. The selectivity towards allyl chloride was independent of the propene chlorine feed ratio for tank volumes of 0.4 m3 or ger. The propene chlorine feed ratio was varied from 3.5 to 7.5. The lower I imit is determined by the fact that the inlet temperature cannot be too low, because of high dichloropropane formatioD. It should be noted here that the inlet temperature can be lower than 300 °C as long as the temperature in the reactor is higher. However, if the inlet temperature is too far below 300°C, it is likely that inlet effects will occur.

Table 3.1 Summary of calculated val of selectivities taken from table 2.6 second progress report (Selectivities are based on propene)

CSTR in series with PFR, Pe/CI₂

=

5.5

Tank Volume (m3) Total Volume (m3) Selectivity

0.2 0.57 95.9

0.4 0.73 96.6

0.6 0.97 96.7

0.8 1.12 96.9

PFR only (V CSTR = 0)

Pe/CI:! Total Volume Selectivity (m3) 3.5 1.03 72.6 4.5 0.72 84.2 5.5 0.62 89.5 6.5 0.62 91.5 7.5 0.62 92.6 24 l.

1

1

~ I

r

r

T

T

1

Confidential

3.3.2 The consecutive reaction

In the previous work (Second Progress Report, 1992) it was decided to use Wermann kinetics, because it was shown that it describes the overall reaction kinetics of the allyl chloride reactor better than Smith's rate equations. However, both Wermann and Smith gave rate expressions only for the main reaction and the parallel reaction, although they were both weil aware of the third, consecutive reaction.

Biegier and Hughes (1982) came up with a rate expression for the consecutive reaction, based on Smith and the experimental data from Groll and Hearne (1939).

Wermann (1970) derived his rate expressions from experiments performed by himself. As mentioned in the second progress report (1992) it is not clear whether or not corrections have been made for side reactions in the rate equations. Hence, Wermann's two rate equations and Biegler's equation for the consecutive reaction seem to be incompatible.

Nevertheless, in order to obtain a better insight in the intluence of the consecutive reaction, the expression given by Biegier and Hughes was added to the model. In appendix D the rate constants of the different reaction rates as a function of temperature are shown. The results of the

calculations are given in table 3.2.

Table 3.2 Calculated values of temperatures, volumes and product compositions in the CSTR in series with a PFR af ter optimizing the CSTR volume. The rate expression for the consecutive reaction (k3) is given by Biegier and Hughes.

k3 [V in m3, T in 0c]

Pe/C1₂ V_CSTR V_{PFR V tolal Tin T CSTR Tout}

4.5 0.175 0.528 0.703 250 342.8 500.0

5.5 0.125 0.619 0.744 290 353.2 494.0

6.5 0.100 0.627 0.727 330 393.8 500.1

7.5 0.070 0.716 0.786 352 392.2 499.5

Product composition in mole %

CSTR Overall

Pe/C1₂ C1₂ AC DCP DCPe AC DCP DCPe

4.5 63.79 29.18 5.81 1.22 76.73 10.29 12.11

5.5 69.78 25.12 4.28 0.81 79.78 9.00 10.48

6.5 62.59 32.37 3.25 1. 78 82.02 6.37 10.83

7.5 72.94 23.85 2.42 0.80 83.68 6.15 9.50

- -~-

--

---__________________________________________________________ C_o_nfi __ d_eo_t __

iru

1

-]

k3/2 [V in m3, T in 0c]

Pe/CI2 V_CSTR V_PFR

v

...

_Tin T_{CSTR Tout}

3.5 0.255 0.433 0.688 197 417.42 497.5 4.5 0.18 0.526 0..706 265 418.42 500.5

5.5 0.15 0.535 0.685 305 418.69 499.1 6.5 0.11 0.624 0~134 335 410.80 500.3

7.5 0.085 0.711 0.796 355 407.14 498.9

Product composition in mole %

CSTR Overall

Pe/Cl₂ Cl₂ AC OCP DCPe AC DCP DCPe

3.5 26.67 60.33 4.88 8.58 80.30 6.01 13.23 4.5 34.92 55.51 4.23 5.35 83.43 5.71 10.15 5.5 41.58 51.08 3.83 3.52 85.68 5.63 8.11 6.5 54.50 40.56 3.29 1.66 87.32 5.79 6.43 7.5 64.19 32.24 2.71 0.85 88.43 5.77 5.42 k3 /4 [V in m3 , T in 0c]

Pe/Cl₂ V_CSTR V_PFR V_{tota1 Tin} T_{CSTR Tout}

3.5 0.22 0.515 0.735 208 397.53 502.1 4.5 0.19 0.524 0.714 270 428.78 499.4 5.5 0.15 0.611 0.761 310 425.37 500.1 6.5 0.12 0.621 0.741 338 422.33 500.3 7.5 0.09 0.709 0.799 358 415.11 499.8

Product composition in mole %

CSTR Overall

Pe/C1₂ C1₂ AC DCP DCPe AC DCP DCPe

3.5 36.17 55.66 5.43 2.85 86.18 7.21 6.29 4.5 31.03 61.33 4.07 3.57 88.22 5.36 5.99 5.5 39.68 54.49 3.73 2.11 89.71 5.42 4.56 6.5 48.50 46.95 3.31 1.24 90.67 5.42 3.65 7.5 60.30 36.35 2.77 0.58 91.30 5.53 2.96

26

• 1

I

Confidential The SpolekJComprimo allyl chloride production unit has three reactors, two operating aod one spare. The two operating reactors produce

23760

tODDes allyl chloride (AC) per year. Each reactor has a volume of about 2 m3 and is fed with

6.381

moles chlorine (CI~ and

35.093

moles propene (Pe) per second. The propene chlorine feed ratio (Pe/Cl₂₎ is 5.5. In the model

calculatioDS the chlorine feed was taken 6.381 molesIs and the propene feed was varied corresponding with the propene chlorine feed ratio.

The calculatiODS were performed using the original rate expression for the consecutive reaction as given by Biegier and Hughes. This reaction rate seems very fast with respect to the main and the parallel reaction (Dobbelaar 1991) and therefore the calculatioDS were also carried out for k3 divided by two and four. All data in table 3.2 were generated after optimization of the tank volume (V CSTR) with respect to the overall selectivity towards allyl chloride based on chlorine. This was done in a more or less random way. It was found that at low propene chlorine feed ratio's the system was very sensitive to the inlet temperature.

Note that Tin is not the temperature in the reactor, but of the inlet feed stream.

In general it cao be concluded from table 3.2 that it is preferabie to operate at a higher propene

chlorine feed ratio. The total volume of the reactor is found to be in between 0.7 m3 and 0.8 m3;

then all the chlorine has reacted.

The overall product composition corresponds with the selectivities towards allyl chloride (AC), dichloropropane (DCP) and dichloropropene (DCPe), all based on propene. The selectivity to allyl

chloride varies from 76.7 % to 91.3 % depending on k3 and on the propene chlorine feed ratio. In

table 3.3 the calculated data are shown for the allyl chloride reactor consisting of a single tank or plug tlow reactor. It can be seen that a reactor contiguration of a CSTR in series with a PFR results in higher selectivities than can be reached in a plug t10w or tank reactor alone. The calculated selectivities (based on propene) in a CSTR and a PFR are 77.3 % and 84.4 % respectively, while in a CSTR in series with a PFR this is 85.7 % (k₃/2, propene chlorine feed ratio = 5.5).

Table 3.3 Data calculated for a tank reactor and for a plug flow reactor alone, to be compared with a tank and plug flow reactor in series

I

k312, Pe/CI₂

=

5.5

CSTR products (%) PFR products (%)

V_CSTR 2.06 Cl₂ 1.70 V_CSTR 0 Cl₂ 0.00

V_pFR 0 AC 77.34 VpFR 0.824 AC 84.42

Vtotal 2.06 DCP 2.40 _Vtotal 0.824 DCP 9.34

Tin 310 DCPe 18.56 Tin 298 DCPe 5.83

T_CSTR 501 SAC 77.3 Tout 498.9 SAC 84.4

I

- - _.

_---_._---~----Confidential

3.3.3 Comparison of Wermann ith and without Biegler's rate equation

For the previous report model, calculati were made using the kinetic equations provided by Wermann, for here called the

Wennann

Mly

case. For the current report Biegier and Hughes' rate expression was added to the model, the

'e

nnann

&

Bleg/er

case. As discussed before it doesn't seem reasonable to draw any rigorous co . usions from either one of these cases. However, it is possible to indicate some upper and lower limits together with some trends.

In all cases the total reactor volume was calculated to be much smaller than currently used in the SpoleklComprimo process. In the

Werm

ann

only

case most of the calculated reactor volumes are in between 0.6 and 1.0 m3. For the

Wermann

&

Bieg/er

case this is in between 0.7 and 0.8

of.

The current SpoleklComprimo reactor has

a

volume of 2 m3 and is therefore probably two times larger than necessary. It is presumably uafavourable that the reactor volume is too large. All the chlorine has already reacted when the reaction mixture is only halfway through the reactor. From here the reactor now holds the reaction mixture, containing AC, DCP, DCPe, HCI and a few ather products at about 500°C. It is not unlikely that some of the products, also allyl chloride, will react with hydrogen chloride, resulti g in a decrease of the selectivity.

The difference in selectivities reached in the two cases is large. Obviously, the selectivities in the

Wermann

&

Bleg/er

case are lower than in the

Wermann only

case. In table 3.4 the calculated selectivities for both cases (at a propene chlorine feed ratio of 5.5) can be compared.

Table 3.4 Selectivities for both the Wennann only case and the Wennann & Bieg/er case

Wermann on

ly

Wermann

&

Biegier

k3 k3/2 _k3/4

S 0.966 0.798 0.857 0.897

The intluence of the cansecutive reaction seems signiticant and causes a considerable decrease in the selectivity. Since in the current SpoletJComprimo reactor a selectivity of 86.9 % is reached, it is clear that

Wermann

&

Blegler

with the original expression of Biegier (S =:: 80 %) does not describe the system adequately. In case Biegler's expression is divided by two (k₃/2) the calculated selectivity is 85.7 % (Pe/CI₂

=

5.5), still somewhat lower with respect to the selectivity reached in the Spolek/Comprimo reactor. The rate expression tor the consecutive reaction proposed by Biegier and Hughes seems to be somewhat fast in accordance with the kinetic equations of Wermann. In the second progress report (1992) Wermann kinetics were found to be six times faster than Smith 's rate equations. This signities that model calculations using a combination of Smith and Biegier would result in even lower values for the selectivity to allyl chloride than now tound with combining Wermann and Biegler's rate expressions (see appendix

0). As long as the kinetic equations of the reactions in the allyl chloride reactor are not known any better, it is difficult to draw any conclusions. The selectivity will however lie in between 86.9 % and 96 %. Including the consecutive reaction in the model results in a smaller optimal tank volume. In the

Wermann

on/y

case the tank volume seems less critical, as long as it is 0.2 m3 or larger. 28 .l

1

I

l

. J

,

.

r

• 1

Confidential

3.4 Sensitivity

analysis

So far several reaction rate equations have been discussed. It has been pointed out that none of the equation found in literature cao be considered more or less accurate. Hence, the sensitivity of the selectivity was investigated by varying the reaction rates. For the main and the parallel reaction, kt and k₂ (Wermann) were varied

±

10 %. In case ofthe consecutive reaction, the results were already calculated for the original rate expression, and for k3 divided by two and four.

In

table 3.5 the variations in the rate equations are summarized.

Table 3.5 Variations in the rate expressions in the sensitivity analysis

1

Z.

0.92

.;; -..= ü Q) Q) Cf) kt k" k3

±

10% ma in reaction

±

10% parallel reaction k3/2, k3/4 consecutive reaction - - - - -- -- - -_._- ... -

--_._._

...

_-_

.

-10%

o

k1

+

10 %

Fi!:ure 3. j Seflsitiviry of rhe selectiviry as Cl fUflctiofl of kj mul k2

±

JO %

-

- -

-Confidential Some of the results are shown in figure 3.1, where the selectivities are calculated with Wermann kinetics only in an ideal plug flow reactor. In figure 3.2 the selectivity as a function of kt and ~

±

10 % is given for two different rates of k3 for an ideal plug flow reactor.

The uncertainty in kt and

k-z

of

±

10 ~ results in an variation of the selectivity of

±

2 %.

The selectivity towards allyl chloride increases from 80.1 _{% for the original k3, to} 85.3 % for k312 and 88.3 % for k3/4.

It seems that the overall uncertainty in e reaction kinetics is much larger than the

±

10 % in kt and ~ may cause.

è

'S ~ ü Q) Q) Cl)

0.9

0.88

0.86

0.84

0.82

0.8

0.78

0.76

0.74

0.72

0.7

-10%

o

k1

~

k2-10%, k3/2 _

k

2,

k3/2

!mi

k2-10%, k3

I

;<~/;q

k

2,

k3

+

10%

_

k2+10%, k3/2

r

:::::<>

!

k2 + 10%, k3

Figure 3.2 The selectivity as afullctioll of kj (lJul k"] ± 10 % for k3 alld k/2

30

r

r

T

1

1

1

l

~ . (

I

1

r

r

T

- - - -

-Confidential

3.5 Cost price calculations: the

allyl

chloride reactor

In this paragraph the influence on the cost price of epichlorohydrin (ECR) of variations for the allyl chloride (AC) reactor are described. These variations are:

• changes in selectivity towards allyl chloride; • changes in the propene chlorine feed ratio.

The selectivity towards allyl chloride in the AC reactor determines the use of propene, and to some extent the use of chlorine. Also the major part of all chlorinated byproducts is formed in the AC reactor which, of course, is also influenced by the selectivity.

Changes in the propene chlorine feed ratio, affect the amount of work needed for the recycle

compressor and the capacity of several functional units, thus capital investment.

3.5.1 The influence of selectivity

The amount of propene and chlorine necessary for the 24 kton epichlorohydrin per year

production as a function of the selectivity towards allyl chloride in the AC reactor, can easily be calculated.

In appendix E a list of chlorinated byproducts is given, as formed in the Comprimo process (base case). The assumption is that only the top four byproducts are intluenced by the selectivity in the AC reactor, and that their relative ratios are independent of this selectivity. The byproducts and their fractions are:

• monochloropropane • monochloropropene • dichloropropane • dichloropropene 3.4 mole%; 29.5 mole%; 29.5 mole%; 35.6 mole%.

The calculations were based on the Comprimo base case; a I isting of the spreadsheet used, can be found in appendix F.

In figure 3.3 the relative gain in cost price and total co st is given. For example, to calculate the cost price of ECR for a selectivity of 100 %, multiply the cost price tor the base case with 1 minus the relative gain. Thus:

cost price EeR = 3313.72· (1 - 0.0608) = 3112.25

(100 % selectivity) lIl. 1

From tlgure 3.4 it can be seen that an increase of one percent in the selectivity, results in a decrease of the cost price of epichlorohydrin of a little less than one half percent.