A Multi-purpose Esterification plant for the production of Acetates from Methyl Proxitol (25 kt/a), Ethyl Proxitol (17 kt/a), Butyl Oxitol (7.5 kt/a) and Butyl Di-oxitol (7.5 kt/a)

(1)

.~i

· T

U

Delft

CPD No.

Conceptual Process Design

Chemical Process Technology

Confidential

Subject

A Multi-purpose Esterification plant for the production of Acetates from Methyl Proxitol (25 kt/a), Ethyl Proxitol (17 kt/a), Butyl Oxitol (7.5 kt/a) and Butyl Di-oxitol (7.5 kt/a)

Authors

L. Bode

E.S. Koppendraaier

A.D. Minnigh

J.P.A

.

Monod de Froideville

Keywords

Telephone

015-215 8449

015-215 85 14

015-257 82 70

015-2135351

Esterification, glycol ether esters, multi purpose, entrainer

selection

Assignment issued

Report issued

Assessment

January 14

th,

1999

Apri120

th,

1999

May 4

th,

1999

Faculteit Technische Natuurwetenschappen Scheikundige Technologie en Materiaalkunde

(2)

I 4100 I I 4200 I I 4300 I L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ JL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ J LP ,team

---,

U

CW

~01

r-....o I I I

~CW

[

.-CW

r-.--t

· w

u: I I P4205 : L ____________ _ P4312 Process

C~201 Elter Iwater spUtter E4205 : C~201 .. boA er E421~ : Product cooler C4202 Roactanto recovery E4206 : C4201 roboner E4215 : Product cool ...

I

f

E

W

~I

.201

Equipment Summory

E4323 : Woter cooler P4208 : Pump

E4324 Wat ... cooler P4209 : Pump

T C4203 UCW

~212

r---, I I P4315 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ J Designers

P4317 Pump V4304 C4304 reftu. occu _{L Bode} P4318 Pump V4305 Oeconter T C4304 Project I I I I I I I I I B C4305

i

[ 4l2O CW I P4318 I L ____________ _ Process Flow

U

CW

~323

....

---,

Waste

BDGA

Scheme

Productlon of But)! 0191)'<:01 Acetot. In a loIuIU-P"'l'ol' [It ... lflcotlon plant

(3)

1 4100 11 4200 11 4300 I L ____________________________________ ~ L _______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ JL __________________________________ ---~

P4312

C4201 E.I.,. Iwaler oplltler C4202 Reactant. recovery C4203 Producl purlflcaUon C4304 Reactant. recovory C4305 Rloctonts/entrolner recovery E4101 Reactanb cool.r

---ï kjCW

~OI

E4205 : E4206 : E4207 : E4208 : E4209 : E4210 C4201 re bon er C4201 reboner C4202 eonden.er C4202 eonden.er C4203 robollor C420J condens.r I I

~CW

[ 4_ CW P4205 Process

E4214 : Product cooler

E4215 : Producl cool er E4316 : C4304 conden.er E4317 : C4304 reballer E4J18 : Wast. CO~.,

[4319 : C4J05 condenair

~CW

r - - - ----i~~ I I I I I P4208 Equipment Summory

E4323 : Water cooler

E4324 : Water cooler

P4101 Pump P4102 : Pump P4103 : Pump P4204 : Pump P4208 : Pump P4209 : Pump P4210 Pump P4211 Pump P4212 Pump P431J Pump T C4202 P4211 T C4203

î--1

I I I I I P4315 I __________ J I I ~ ______________________________________________ J Designers

P4317 Pump V4304 C4304 reftux accu _{L Bod,}

P4318 Pump V4305 Deconter

P4319 Vocuum pump V4306 C4305 ronu. accu LS. Koppendraalor P4320 : Vocuum pump cw coollnQ waler

P4321 Vocuum pump lp .teom light pr •• au,. ,teom A.D. IoIlnnlQh

R4101 : Reactor mp ,team medium pr ... ur. .teom _J_._P_._{A. loIonod do 'ro}_l_dovili.

B C4305 B C4304

~CW

[ 4J2I) CW

r-

-

---I I I I I I kjCW

~323

-., 1'---, ~~~~~~~_, I I I I I [4.122 : I I P4318: L ____________ "

Process Flow Scheme

BGA

Projecl Producllon of Bul)4 Glycol Acelalo In a loIultl-purpo .. E.lorlRcaUon plonl Pro jecl 10 number CP03229

Compl.Uon Dal. April 20th. 1999

I I I I

(4)

I 4100 I I 4200 I I 4300 I

L ____________________________________ J l _______________________________________________________________________ JL _________________________________________________________________________ J

P4312

C4201 E.ler /woler spIlIter C4202 Reactant. recovery

WLP

,Ieom

\:;{,02

CW

---,

H205 : C4201 rebon ... E4206 : C4201 rebon.,. I I I I I : P4205: L ____________ j Process H214 Product cooler H215 Product cooler

~CW

[ 4200 P4208 ---' Equipment Summary

HJ2J : Wot.,. cooler P4208 : Pump E4J24 : Waler cooler P4209 : Pump

T C4202 r---, I I I I I I P4J17 Pump P4JI8 Pump B C4305 B C4304 kjCW Y.212

r---,

W

CW Y.318 I P4315 I P4318 __________ J ~--I ~---,

~~-I--\---'{---'~

· ~~ ~:

l __

-{~~---'-Hc.:....:....eaV.;"":,,.,:..ies_____..;:

~.

_______________________________

,.;E

__

P_A

... _ ..

-~

Designers Process Flow Scheme

V4J04 CU04 renu. accu _{L Bode} Projecl ProductIon of Eth)l Proxllol Acelole Ino V4J05 Oeconter t.lultl-purpoll E.lorlflcollon plonl

(5)

I 4100 I I 4200 I I 4300 I

L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ~ L _______________________________________________________________________ JL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ J

---

-

--,

C4201 E.ler /waler opUlter E4205 : C4201 rebaner C4202 Reactant. recovery E4206 : C4201 reboRer C4203 Product purlf1cotlon E4207 : C4202 condensor

C4J04 Reactant. recovery E4208 : C4202 conden.er CU05 Raoctonta/enlrolnar recovery E4209 : C4203 reboller E4101 Rlactonta cooler E4210 C420J conden •• r

~CW

[ 420+

CW

P4205

Process

E4214 Product cooler E4215 Product cooler E4316 C4J04 condenser

E4317 C4304 reboner E4318 Wast. cooler

[4319 C4J05 condensor

P4208 _ _ ___ _ _ _ __ _ _ .J

Equipment Summary

E4323 : Waler cooler P4208 : Pump E4324 : Water cooler P4209 : Pump

P4101 Pump P4210 Pump P4102 : Pump P4211 Pump P4103 : Pump P4212 Pump P4204 : Pump P4J13 Pump B C4304 T C4202 Waste water

r---

-

---..,

kjCW Y.212

U

CW Q 3 1 8 I P4211 __________ J P4315 I P4318

1 ~

· 2 2L_I_~[_~=_~[

.

_________________________________________

_ _

-(~~---M-P--A---:.~

8 _ _

__...

Heavies

Designers Process Flow Scheme

P4317 Pump V4304 C4304 renux accu L Bode Project ProductIon 0' lAoth)l ProxltDl Acetale In a

P4318 Pump V4305 Oecanter lAulti-purpo •• E.t",lflcollon plant

P4J19 Vocuum pump V4306 C4305 renux accu E.S. Koppendrooier

Pro jee I 10 numb ... CPD3229 P4J20 : Vocuum pump cw coollng wol.,

P4J21 Vocuum pump lp .teom light preuur • • teom A.D. Mlnnlgh

(6)

CPD 3229, Confidential Summary

Summary

It is possible to produce 25 kt/a of methyl proxitol.acetate (MPA), 17 kt/a ethyl proxitol acetate (EPA), 7.5 kt/a butyl glycol acetate (BOA) and 7.5 kt/a butyl diglycol acetate (BDOA) out of respectively methyl proxitol (MP), ethyl proxitol (EP), butyl glycol (BO), butyl diglycol (BDO) and acetic acid (AA) in a multi purpose plant. These glycol ether esters are used as additives in water based paints and have a high water solvent power and relatively low volatility. The low volatility can be a great advantage in case of new legislation with respect to volatility of paint additives.

In

the following table the market prices of reactants and products are shown.

DEM/t DEM/t DEM/t DEM/t

MP 1400 EP 1700 BG 1300 BDG 1300

AA 1000 AA 1000 AA 1000 AA 1000

MPA 2100 EPA 2700 BGA 2000 BDGA 2000

Margin 691 1078 666 674

The economie margin on EP A is the biggest and therefore it is the most interesting process. MP A has the largest market share but operates with a loss when produced in

a single purpose plant. In a multi purpose plant this conceptual process design will become economically interesting when the precentage of chlorinated organic

components in the MP A wastewater stream is reduced. When the raw material prices decrease with 12.6% the multi purpose plant becomes profitable (NPV=O).

The process is designed to operate 305 days a year, consisting of 166 days for MP A production, 71 days for EPA production, 39 days for BOA production and 29 days for BDGA production. The remaining 60 days are used for c1eaning between runs and catalyst regeneration.

The advantage of a multi purpose plant is the high flexibility to adapt to changing market situations. Future legislation could lead to a higher demand for BOA and BDGA.

To improve the design of this multi purpose plant for glycol ether esters the following research is suggested. In the first place thorough laboratory test should be conducted to obtain accurate kinetic data and thermodynamic properties. Secondly, extensive research should be done to find an entrainer with lower SHE impact and equal or better entrainer properties than 1,2-dichloro ethane.

(7)

CPD 3229, Confidential Acknowledgements

Acknowledgements

We would like to thank the following persons for their assistance and support:

Drs.

A.

Beers, Prof

.

dr. ir. H. van Bekkum, Corry

&

Mary, Dr. ir. H.J. van der Kooi,

Liang Wu,

Ir. e.P. Luteijn,

Ir.

R.M. MooIdijk,

Ir.

B. Ramakers,

"

Jullie hoeven je collegekaart niet meer te laten

zien,

ik ken jullie nu wel"

Nachtportier

"

Ik dacht al tijdens de reviewmeeting, dit had best een afstudeerproject kunnen

zijn"

CPL

"Havefun"

RM

"Anders doe je

gewoon

de reflux ratio

omhoog"

RM

"Voor

mij hoef je de recycle niet te sluiten"

RM

"m%

is toch mol procent?!"

CPD3229

"Sorry,

Aspen Plus license

validation/chechkoutfailure.

Aspen will shutdown and

reinitialize again

!oKB"

(8)

CPD 3229, Canfidential Table af cantents

Appendices

1. Process flow schemes

1.1 Process flow scheme MP A

1 .

2 Process flow scheme EPA

1.3 Process flow scheme BGA

1.4 Process flow scheme BDGA

2. Blockschemes

2.1 Block scheme MP A

2.2 Block scheme EP A

2.3 Block scheme BGA

2.4 Block scheme BDGA

3. Basis of design

3.1 Pure component properties

3.2 Reaction schemes

4 .

Stream summaries

4.1 Stream summary MP A

4.2 Stream summary EPA

4 .

3 Stream summary BGA

4.4 Stream summary BDGA

5. Utility summaries

5 .

1 Utility summary MPA

5.2 Utility summary EPA

5 .

3 Utility summary BGA

5.4 Utility summary BDGA

6 .

Mass balances

6.1 Mass balances MP A

6.2 Mass balances EP A

6.3 Mass balances BGA

6.4 Mass balances BDGA

7 .

Equipment calculations

7 .

1 Calculations of the distillation column dimensions

7.2 Calculations of the decanter dimensions

8 .

Equipment

8.1 Equipment summaries sheets

8.2 Equipment specification sheets

9. Liquid waste streams for the MPA

,

EPA, BGA and BDGA process

10 .

Process safety

10.1 The HAZOP study

10 .

2 Dow Fire and Explosion index ca1culation

11. Economic analysis

(11)

CPD 3229, Confidential 1 Introduction

1 Introduction

The main objective of this conceptual process design is to evaluate whether it is

possible to produce methyl proxitol acetate (25 kt/a), ethyl proxitol acetate (17 kt/a),

butyl glycol acetate (7.5 kt/a) and butyl diglycol acetate (7.5 kt/a) from acetic acid

with respectively methyl proxitol, ethyl proxitol, butyl glycol and butyl diglycol

in a

multi purpose esterification plant.

1. 1

Reaction

produets

Glycol ether esters are used as additives in water based paints and are specialty

products. Adding the glycol ether ester to the paint can increase the solubility of water

in paint. The four glycol ether esters mentioned above are characterised by their high

solvent power and relatively low volatility. The low volatility can be a great

advantage in case of new legislation with respect to volatility of paint additives, BGA

and BDGA being the most interesting with respect to the volatility. Por more detailed

component properties, see Appendix 3.1.

1.2 Market situation

The process design is based on the production of methyl proxitol acetate, this being

the product with the highest market share. At this moment the financial margin on the

production of methyl proxitol acetate is very low. Por the process concept chosen in

this process design the MP A process will not be profitable, unless

it

is produced in a

multi purpose plant, see Chapter 11 for more details.

The current situation is that a plant in Belgium produces methyl proxitol acetate for

Shell and Arco Chemicals on the European market. The other three glycol ether esters

are produced in very small quantities; their market shares are still small.

If

in the

future legislation on the volatility of paint additives will be introduced, these market

shares may grow.

1.3 Process

Por esterification processes, many processes are available. Because the main objective

is to design a multi purpose esterification plant, the most flexible process concept is

the best option. This process concept consists of a fixed bed tubular reactor, with

catalyst Duolite ES-276. The reactor is followed by

a

distillation column to separate

the produced water from the glycol ether ester. The unconverted reactants will be

recovered from the top water stream (for the MP A process the azeotropic agent

1,2-dichloro ethane is used to separate the reactants from water) and the bottom product

stream. The bottom product stream will be purified by distillation. Por the MPA

process a decanter is used to separate the water phase from the entrainer phase.

With esterification processes, one mole of water will be formed for each mole product

formed. Therefore the largest waste

stream

is a wastewater stream, which will be

contaminated with organic compounds (reactants, lights and product). Por each

process, acetic acid is used in high concentrations as a reactant. Acetic acid is very

toxic and introduces a serious hazard.

It will also be present in the waste streams. Por

the production of methyl proxitol acetate the use of an azeotropic agent, 1,2-dichloro

ethane, is necessary to separate water from the reactants. In the wastewater stream for

this process, the chlorinated organic compound 1,2-dichloro ethane will be present.

(12)

CPD 3229, Confidential 1 Introduction

Also an additional waste stream of 1,2-dichloro ethane with light ends will exit the

process. The azeotropic agent is toxic and is highly flammable (see Chapter 10

.

2)

.

1.4 Availability of physical data

The four processes were simulated in Aspen Plus 10.0. All physical data necessary for

the simulations were taken from literature, supplied by the database of Aspen Plus

10 .

0 or estimated by Aspen Plus 10.0. The components ethyl proxitol, ethyl proxitol

acetate and by-product propylene glycol diacetate were not available in the Aspen

database

.

Therefore all physical data for these three components were estimated by

(13)

CPD 3229, Confidential 2 Process options & selection

2 Process options

&

selection

2. 1 Process concept chosen

The formation of glycol ether acetates from glycol ethers is an esterification/

equilibrium reaction. These types of reactions are slightly exothermal and have a high

selectivity in the main esterification reaction. A disadvantage is the equilibrium; in

such cases often one product is removed in order to make the inverse reaction

impossible. Another possibility to reach an acceptable overall convers ion is a large

recycle of reactants (with a relatively small amount of product). More detailed process

options are described below.

It

tumed out that the choice for a process design depends

strongly on the multi purpose aspect.

2.1.1 Tubular reactor and separate distillation section

The reaction takes place in a tubular reactor, because of the high selectivity towards

the favourable reaction. The effluent of the reactor is purified in two distillation

sections. The first section contains a column for water removal and, depending on the

product

,

several columns for reactant recycle and product purification

.

The second

section is used for the recovery of reactants from the wastewater stream.

The process for the production of MP A needs an entrainer for the water removal. The

second section starts with a column using an entrainer.

2.1.2 Reactive distillation [1,2,3]

In this process reaction and distillation are combined in one column. This process will

give good results for slow equilibrium reactions. The reaction takes place in the

distillation column. The location of the reaction section in the reactive distillation

column depends on the concentration profiles of the components in the column. These

concentration profiles depend on the substances involved. In a multi purpose plant,

four different types of component systems exist. Therefore reactive distillation is not

an option for a multi purpose plant.

2.1.3 Distillation with external reactors [4]

Reaction and distillation can also be combined without actually integrating both in

one column. Use of a mineral acid can be avoided by applying heterogeneous instead

of homogeneous catalysis, employing a strongly acidic ion exchanger. For practical

purposes, it is favourable to arrange the ion exchange beds in extemal reactors. As for

reactive distillation

,

the location of the reaction section in the distillation column

depends on the concentration profiles of the components in the column

.

2.1.4 Reaction with membrane separation

Another possibility is to use a membrane after the reactor. The water formed during

the reaction is taken out before the stream is sent to the distillation columns. The

membranes needed for this process cannot separate all the water from the reaction

mixture. Also other components of the reaction mixture could interact with the

membrane and make the separation impossible.

(14)

CPD 3229, Confidential 2 Process options & selection

2.1.5 Distillation column with reactor in reboiler section [5,6]

Again reaction and distillation are combined. The reboiler section of the distillation

column is used as the reaction section. The distillation column continuously strips

water from the main stream with the use of an inert water azeotropic agent. Water and

the entrainer can be separated physically.

The first process option will be developed further because of the following reasons:

1. Reactive distillation (internal and external) is not an option for a multi purpose

plant because of the delicate choice of the reaction section.

2. A membrane is not capable of removing all the water formed in the reactor and it

is not very selective.

3. Because of the difference in boiling points of reactants and products in the four

processes it is very difficult to operate a distillation column with reaction in the

reboiler section.

4.

In

a process with separate reaction and distillation section it is possible to differ

conditions for each process.

It

also leaves the possibility to vary the sequence of

the columns.

Block schemes of the chosen process concepts can be found in Appendix 2

.

2.2 The entrainer

Af ter the reaction section it is necessary to remove the water in the reaction mixture.

Unfortunately in the MPA process, water forms azeotropes with reactants in the

mixture. Therefore an entrainer is used to separate the water from the other

components. Such an entrainer should be capable of [7]:

• Removing as much water as possible (the amount of entrainer should be as small

as possible).

• Af ter the distillation the entrainer/water stream must split up in two phases

.

Both

must contain as little other compound as possible.

• The azeotropic boiling point and the boiling point of the entrainer should be lower

than the boiling points of the other components, because the top stream should

contain little product and reactants.

• The entrainer must not react with the product or the reactants.

• The entrainer must be HSE acceptable if possible.

In literature [8,9,10,11] tetrahydrofuran and diisopropyl ether and butyl acetate are

suggested as entrainer. All comply with the stated demands.

In

the manufacturing of

MP A with the AKZO trial plant [7] also 1,2-dichloro ethane (DCE) is used as

entrainer. A disadvantage of DCE is its low HSE acceptance.

Af ter a closer examination in Aspen, DCE is the only entrainer with reasonable

results. The butyl acetate/water mixture does not split up in two phases in the decanter

due to a large amount of reactants. The use of cyclohexane leads to the loss of

reactant in the water phase. Isopropyl ether leads to unacceptable entrainer waste.

That leaves DCE as only possible entrainer.

(15)

CPD 3229, Confidential 3 Basis of design

3 Basis of design

3. 1

Description of the design

The main objective of this conceptual process design is to evaluate whether it is

possible to produce methyl proxitol acetate, ethyl proxitol acetate, butyl glycol acetate

and butyl diglycol acetate out of respectively methyl proxitol, ethyl proxitol, butyl

glycol, butyl diglycol and acetic acid in the same plant.

As target the following production is proposed:

Table 3.1 Target production

Methyl proxitol acetate Ethyl proxitol acetate Butyl glycol acetate Butyl diglycol acetate

Purity wt%· 99.5 99.0 99.0 99.0 Prodriêtion (kt/y) 25 10 7.5 7.5

Initially the MPA process is chosen as base case because of the largest production

capacity needed. The other processes are designed with the restriction that they use

the same equipment as the MPA process; the detailed sizing is based on the most

extreme conditions in the particular unit.

The volume of the streams in all processes is kept in the same order. This assumption

is the basis for scheduling of all processes.

3.2 Process definition

3.2.1 Components and reactions

All components that are assumed to play a role in the systems are presented in

Appendix 3 .

1 (Pure components properties).

It

should be noted that ethylene glycol,

propylene glycol and the diacetates are heavy by-products, all other by-products are

light ends.

Methyl diproxitol acetate, ethyl diproxitol acetate, butyl dioxitol acetate and butyl

trioxitol acetate are heavy by-products in respectively the MPA, the EP A, the BGA

and the BDGA process that are not modelled in Aspen. They are formed in very little

amounts. To create

areasonabie

simulation a suitable kinetic model is needed. It is

very difficult to fit these heavies in the model and because of the small amounts they

can be neglected. Moreover, all these by-products are not present in the Aspen

databases. Creating them would be introducing new uncertainties.

In further investigations of the BDGA process one should keep in mind that there

might occur

a

formation of dioxan

,

a very stabie compound.

The reactions that take place in the reactor for the MP A process are graphically

displayed in Figure 3.1. The reaction schemes of the other processes are similar and

are provided in Appendix 3.2.

(16)

°

O.-H

) l o

o~

_{H.-O .... H}

/o~

+

I ----..::..

/o~

+

H

...--

Water MP AA MPA O.-H H.-O .... H O.-H /O .... H

/o~

+

_Water

-

~O""H

+

_MeOH

MP Pglyc

°

)lo

_{/O .... H} ----..::..

/Oy

H.-O .... H I

₊

H MaOH

...--

0 Water MA AA .... H ₀ 0

~O""H

-

Ä

+

H.-O .... H _Water

Pglyc Propanal

°

.... H

) l o

o~

0 H.-O .... H

~O

.... H

+

2 _HI

...--

----..::..

~OIO

+

2 _Water Pglyc AA PGDA Figure 3.1 Reaction scheme MP A process

As shown in the reaction schemes each system consists of three (equilibrium)

esterification reactions, an ether cleavage and a dehydration readion. The mechanism

of the esterification is a nucleofilic substitution although it cannot be referred to as a

Sn 1 or Sn2 reaction. This equilibrium reaction is characterised by

a

temporary

addition to the carboxylic group followed by elimination

and

therefore called

nucleofilic substitution trough addition-elimination.

Esterification reactions are catalysed by strong acids.

In literature the following

categories of acidic catalysts are suggested: homogenous catalysts, divided in small

molecules like sulphuric acid and Lewis acids and large molecules like para-toluene

sulfonic acid and heterogeneous catalysts. The advantages and disadvantages are

tabulated in Table 3.2.

(17)

CPD 3229, Confidential

Table 3.2 Catalyst selection

Catalyst Sulphuric acid, Lewis minerals Para-toluene sulfonic acid Pro • Cheap • A lot of experience • Possibility of recycling • A lot of experience

Heterogeneous acid • No need for catalyst recycling

• High activity

• Reaction only occurs in the reactor

• Regeneration is possible during shut down periods

3 Basis of design

Conti-à

• Corrosive

-. Difficult to recycle -7 it leaves with water

• Present in a large part of the process • Possibility of reaction outside the

reactor • Corrosive

• Present in a large part of the process • Possibility of reaction outside the

reactor

• Expensive

• Possibility of hot spots

Based on Table 3.2 a heterogeneous catalyst is chosen. Anormal disadvantage of a

heterogeneous catalyst is the regeneration period. In a multi purpose plant one can use

the time between two runs (needed for cleaning, etc.) to regenerate the catalyst.

Literature provides kinetic data on some of the processes for several catalysts. Duolite

ES-276 tums out to have the highest activity and is chosen as catalyst for all

processes.

The kinetic data for this catalyst are derived from data generated in a MP A trial run

[7] and from kinetic data on a zirconium based heterogeneous catalyst [12, 13, 14].

From the trial run the following parameters were known: In- and out-going

component mole flows, residence time, reactor type (batch loop), reactor volume,

catalyst load, kinetic parameters for the esterification of MP and the esterification

equilibrium constant. The kinetic constants for the other reactions in the MP A system

can be estimated from these data combined with mass balances over the reactor.

The other processes are related by the kinetic data for the main esterification reaction

on a zirconium-based catalyst. Three additional assumptions are made:

• The ratios of all reaction rates in the other systems are the same as the ratios in the

MPA system

.

• Each system reacts in a similar way on Duolite as on a zirconium-based catalyst.

These ratios do not change with temperature. This assumption can be made

because all reactions have a small temperature effect.

• The reaction rate of the formation of ethoxy ethyl acetate is approximately the

reaction rate of the fonnation of MP

A.

This assumption can be made since ethoxy

ethyl acetate and methyl proxitol acetate have a similar structure and mole mass.

3.2.2 Processes

In order to be able to operate four processes in one plant a separate reactor and

distillation section is chosen. This choice is explained in Chapter 2

.

(18)

The main objective of the process is to produce as much ether ester as possible in relation to the by-products formed in a tubular reactor. For the esterification process is an equilibrium reaction, the unreacted reactants must be recycled after the separation from the products.

Appendix 2 provides block schemes of each process.

The plant is divided in three sections: reactor section (4100), product purification (4200) and reactants recovery (4300). All unit and stream numbers begin with the number of the section and end with their unique identity, so stream 4101 does exist and stream 4301 does not exist, since a stream '1' is already present. The advantage of this numbering is that a stream can be detected in two ways: by searching for its section and by searching for the sequence of streams.

The operating window of all processes is between 30°C and 160°C and between 0.01 bara and 1 bara. The thermodynamic properties and models are described in Chapter 4.

The pure component properties are presented in Appendix 3.1.

In some of the processes azeotropes occur. The MP A system is the only system in which azeotropes influence the process significantly resulting in the use of an entrainer. As entrainer in the MP A process the use of cyclohexane, butyl acetate, isopropyl ether and 1 ,2-dichloro ethane (DCE) is simulated in Aspen. In Chapter 2 the choice of the entrainer is described in more detail.

3.3 Basic assumptions

3.3.1 Plant location and capacity

The esterification plant will be situated on the existing Shell site in Rotterdam Pemis, the Netherlands. The advantage is that the plant can use all existing administrative and emergency services. For wastewater treatment biotreaters are also available on the site.

The production of the plant is shown below.

Table 3.3 Production capacity

Product

Methyl proxitol acetate Ethyl proxitol acetate Butyl glycol acetate Butyl glycol diacetate Not in use Production [kt/a] 25 17 7.5 7.5 Production per cycIe [kt] 5 3.4 1.5 l.5 Runt!me [hrs/a] 3984 1704 936 696 1440

During the sizing of the flows in all processes, the target production as mentioned in Table 3.1 was obtained in a shorter period than initially planned. Since the EPA process is most profitable, the remaining time is allocated to the production of EP A. As can be seen in Table 3.3 the total production time is set to 7320 hrs/a. The

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production in a run is 1.5 kt, which results in 5 runs for BGA and BDGA. This is applied to the other products, sa a year consists of 5 cycles of 4 runs (1 run for each product).

The total production is divided in 5 cycles. For each switch 3 days of cleaning is needed, resulting in 12 non operating days per cycle and 60 non operating days a year. The design production is set to 0.16 kt/day (365/305*50 kt/a).

3.3.2

Battery

limit

In the design of the esterification plant an imaginary fence is set around the care of the process: It is assumed that all incoming streams as weIl as all outgoing streams are

actual streams. Storage (reactants and products), cleaning of waste streams and fueIling of lights and heavies are left outside the battery limit. The utilities are assumed to be available in an existing piping system. Equipment for utilities is not induded in this design. Also the regeneration of the catalyst is not taken into account. In Table 3.4 to Table 3.11 all incoming and outgoing streams are defined for each process. In general can be noted that all incoming streams enter the process in pipes at

2SOC

and 1 bara as a liquid and that all outgoing streams leave the plant in pipes at a

maximum temperature of 40°C and 1 bara. These streams are liquids as weIl.

Methyl proxitol acetate in- and outgoing strearn

Table 3.4 Incoming stream MPA process

s

tream name A ce IC aCI f ·df d ee M th I e lYI prma 0 ee ·t 1 f d D· hl IC oro e th ane ee f d

Stream number <4101> <4102> <4340> Consumption [kt/a] 12.05 19.08 2.01

Costs [EURJt] 511 652 161

Commercial AA 99.0 MP 99.5 DCE specifications [wt%] Water 0.1 Water 0.1 Design specifications AA 99.5 MP 99.8 DCE

[wt%] Water 0.5 Water 0.2

Temperature [0C] 25 25 25

Pressure [bara] 1 1 1

Phase Liquid Liquid Liquid

Transport to plant Pipe Pipe Pipe

In both feed streams impurities other than water are neglected because of their assumed inertness. Therefore the design purity of the streams is higher than the commercial specifications. In further investigations one should simulate with the actual impurities.

100 100

In the DCE stream impurities were not taken into account since specifications could not be supplied (DOW chemicals Benelux).

In

further process development it is likely to as su me that the impurities are lights or water. The amounts will be small and will not influence the results significantly.

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GPD 3229, Gonfidential 3 Basis of design

Table 3.5 Outgoing streams MPA process

Stream namë". MPA (product) Wastewater Lights Heavies.

Stream number <4237> <4347> <4361> <4234>

Production [kt/a] 25.10 6.02 1.72 0.34

Price [EUR/t] 1181 -376 -2189 107

Commercial specifications MPA 99.5 DCE <10%

[wt%] Water 0.03

Design specifications [wt%] MPA 99.9 MP 24.3 DCE 89.0 Pglyc 63.3

Water

-

Water 56.3 Water 4.3 PGDA 2.7

Pglyc 0.1 AA 10.4 MP 5.0 MPA 34.0

DCE 7.1

Temperature lOC] 35.4 34.2 40 39.2

Pressure [bara] 1 1 1 1

Phase Liquid Liquid Liquid Liquid

Transport from plant Pipe Pipe Pipe Pipe

If the waste streams contain less than 10 wt % of chlorinated compounds a low fee is to be paid for incineration (Wastewater treatment company AVR, The Netherlands). The light ends unfortunately contains more than 10 wt %, making a special expensive treatment necessary (Appendix 11).

Ethyl proxitol acetate in- and outgoing streams

Table 3.6 Incoming streams EPA process

S treamname A ti ce c aCI "d ~ ee d Eth I lyl proXi ï 0 If d ee

Stream number <4101> <4102> Consumption [kt/a] 7.24 12.58 Costs [EUR/t] 511 818 Commercial specifications AA 99.0 EP 99.0 [wt%] Water 0.1 Water 0.1 Design specifications [wt%] AA 98.9 EP 98.9 Water 1.1 Water 1.1 Temperature lOC] 25 25 Pressure [bara] 1 1

Phase Liquid Liquid

Transport to plant Pipe Pipe

To be on a safe side in the simulations - water has a negative effect on the equilibrium reaction - all impurities in the feed streams are assumed to be water. In the MP A process this assumption is not made due to the unwanted effect on the entrainer column.

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CPD 3229, Confidential _{3 Basis of design}

Table 3.7 Outgoing streams EPA process

, Sti'eamname j~ ~:~, "1'EPA (product) ".~."

Wastewáter1':i!;: Hèävies ' ,,..

",' _"9C Stream number <4236> <4361> <4235> Production [kt/a] 17.30 2.45 0.08 Price [EURJt] 1519 -256 107 Commercial EPA 99.0 specifications Water 0.1 [wt%]

Design EPA 99.8 Water 94.7 Pglyc 99.5

specifications Water - AA 2.7 PGDA 0.5

[wt%] AA 0.1 EtOH 2.5

Pglyc 0.1

Temperature [0C] 37.9 40 40

Pres su re [bara] 1 1 1

Transport from Pipe Pipe Pipe

plant

The wastewater stream is treated on site. No fees are paid for treatment of streams

containing less than 500 ppm of organic compounds. Unfortunately this is not the

case. In Chapter 11 the economie aspects of the wastewater treatment are discussed.

The heavyends can be used as fuel elsewhere on site.

Butyl glycol acetate in- and outgoing streams

Table 3.8 lncoming streams BGA process

s

treamname A f ce IC aCI 'd~ ee d B t l l otyl glyco ee l f d Stream number <4101> <4102> Consumption [kt/a] 3.13 6.17 Costs [EURJt] 511 652 Commercial specifications AA 99.0 BG 99.0 [wt%] Water 0.1 Water 0.1 Design specifications AA 99.0 BG 98.9 [wt%] Water 1.0 Water 1.1 Temperature [0C] 25 25 Pressure [bara] 1 1

Phase Liquid Liquid

Transport ta plant Pipe Pipe

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CPD 3229, Canfidential 3 Basis of design

Table 3.9 Outgoing streams BGA process

Stream name:' .' ." .. BGA (product) Wastewater . Puree

Stream number <4235> <4361> <4239> Production [kt/a] 7.58 1.02 0.66 Price [EURlt] 1125 -256 107 Commercial BGA 99.0 specifications Water 0.1 [wt%]

Design BGA 99.8 Water 96.3 BGA 54.7

specifications Eglyc 0.2 Ethanal 3.4 BG 28.7

[wt%] AA 13.4

BuOH 2.5

plant

See the notes on EP A for the destination of the waste streams.

Butyl di glycol in- and outgoing streams

Table 3.10 Incoming streams BDGA process

s

treamname A cetIc aCI 'df d ee

Stream number <4101> Consumption [kt/a] 2.33 Costs [EURlt] 511 Commercial specifications

AA

99.0 [wt%] Water 0.1 Design specifications [wt%] AA 98.9 Water 1.1 Temperature [0C] 25 Pressure [bara] 1 Phase Liquid

Transport to plant Pipe

B utyl 19lyco eed ldil lf

<4102> 6.29 652 BDG 99.0 Water 0.15 BDG 98.9 Water 1.1 25 1 Liquid Pipe

See the notes on EP A for the large water impurities in the feeds.

Table 3.11 Outgoing streams BDGA process

s

tream name BDGA( (pro oct d

w

astewater , aste

Stream number <4235> <4361> <4353> Production [kt/a] 7.51 0.80 0.28 Price [EURlt] 1125 -256 107 Commercial BDGA 99.0 specifications Water 0.1 [wt%]

Design BDGA 100 Water 91.0 BDG

specifications Water - BuOH 6.7 AA

[wt%] Ethanal 1.3 Eglyc

BuOH EGDA

plant .! 36.7 27.2 31.2 2.7 2.2

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CPD 3229, Confidential

All utility requirements for each process are presented below.

Table 3.12 Utility requirements

: ~t>'Y~',

C

00 lOg

r

wa er . t ....

LP

_{steam ;'} _MP_steam

Conditions 20°C, 1 bara 190°C, 3 bara 220°C, 10 bara Costs per unit 0.05 0.68 13.61 [EUR/t],

[EURIkWh]

MPA process 3426 20.6 94.2

[kt/a], [kWh/a]

EPA process [kt/a], 2353 36.5 47.3 [kWh/a] BOA process 810 19.1 15.5 [kt/a], [kWh/a] BDOA process 407 13.8 7.0 [kt/a], [kWh/a] 3 Basis of design EI ectnclty .. , 220V 0.06 25.0 20.0 20.0 25.0

Most of the utilities are used at their maximum limits meaning that the cooling water

leaves the plant at 40°C and that the low pressure and high pressure steam is

condensed, leaving the process at respectively 133

.

5°C and 180°C.

The last requirement is the catalyst: Duolite ES-276. Table 3.13 displays details

.

The

catalyst is regenerated with an acid during the period between two runs.

Table 3.13 Catalyst requirements Catalyst

Requirement [tonnes] Costs [EUR/t] Life time [years]

Duolite ES-276

15 26000

4

3.4 Determination of the margin and maximum allowable investment

3.4.1 Calculation of the margin

The maximum margin on the four produets MPA, EPA

,

BGA and BDGA was

ca1cu!ated by assuming that 1 mole of MP

+

1 mole of AA is used to make 1 mole of

MPA with 100% overall conversion. For EPA

,

BGA and BDGA similar assumptions

have been made. The results are shown in Table 3.14

.

It is c1ear that the real margin

on MPA will have to be corrected for the use of entrainer

,

product conversion and

utilities. Also for the ca1culation no costs for wastewater treatment have been

inc1uded

.

Detailed ca1culation of the real margin is supplied in Chapter 11.

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Table 3.14 Maximum margins on MPA, EPA, BGA and BDGA

EP AA EPA 104.15 60.05 146.14 162.23 60.05 204.27 1300 1000 2000 1.30 210.90 1.00 60.05 2.00 408.54

3.4.2 Calculation of the maximum allowable investment

For all calculations the Shell market prices have been used. To determine the margin per year these values have to be multiplied by the number of production days. The margin as show in Table 3.16 is 23.56 Million EURO. Correcting this value with an Earning power of 15% with a plant life of 10 years and 2 construction years, the maximum allowable investment is 102.82 Million EURO. A detailed calculation is shown in Table 3.15.

Table 3.15 Margins

PROFIT MARGIN DISCOUNTED PROFIT MARGIN Annual Year MEURO Construction Construction 2 Production 3 23.56 Production 4 23.56 Production 5 23.56 Production 6 23.56 Production 7 23.56 Production 8 23.56 Production 9 23.56 Production 10 23.56 Production 11 23.56 Production 12 23.56 TOTAL 235.60

Table 3.16 Margin per annum Raw materiarprofit .

Production days

Production (kt/a)

Profit per annum (M DEM)

Profit per annum (M EURO)

3.4.3 Conclusion

Accumulative Factor Annual Accumulative MEURO 0.15 MEURO MEURO

1.000 0.870 23.56 0.756 17.81 17.81 47.12 0.658 15.49 33.31 70.68 0.572 13.47 46.78 94.24 0.497 11.71 58.49 117.80 0.432 10.19 68.68 141.36 0.376 8.86 77.53 164.92 0.327 7.70 85.23 188.48 0.284 6.70 91.93 212.04 0.247 5.82 97.76 235.60 0.215 5.06 102.82 102.82

MPA"EPA BGA BDGA TOTAL

166 71 39 29

25.10 17.30 7.58 7.51

17.33 18.64 5.05 5.06 46.08 8.86 9.53 2.58 2.59 23.56

Looking at the raw margins on the products the margin for EP A is the most interesting. Especially wh en taking into account that MPA will have additional

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the waste streams

. Unfortunately the European market for EPA (4 kt/a) compared to

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CPD 3229, Confidential 4 Thermodynamic properties and reaction kinetics

4 Thermodynamic properties and reaction kinetics

For the design of the multi purpose plant several th.ermodynamic properties and reaction constants were found in literature [17][18], however most of the

thermodynamic properties are taken from the Aspen Plus 10.0 databanks. In this chapter the validity of the parameters is checked within the operating window. Also the reaction rates are discussed.

4.1 Thermodynamic properties

4.1 .1

Operating window

Comparing the four processes, the equipment for reaction and distillation is the same but the temperatures and pressures are different. For each process and each unit the operating window is determined (TabIe 4.1 & Table 4.2).

Table 4.1 Operating windows temperature (0C)

UNIT MPA P EPA P BGA P BDGA - P

Min Max top Min Max top Min Max top Min 0< iMáx top

R4101 80.0 92.9 1 ₃₅ _4L5 I _80.0 ₈₈_.₇ I _80.0 _95.0 I C4201 105.2 140.0 I ₁₀₀_.₃ _141.0 I ₁₀₃_.₉ ₁₂₉_.₀ 1 _93.8 _156.5 I C4202 138.9 145.4 I ₁₃₂_.₉ ₁₅₇_.₈ I ₉₅_.₇ _148.0 0.5 _56.4 _164.5 0.1 C4203 35.4 39.2 0.01 _37.9 _79.1 0.01 ₄₃_.₆ ₆₀_.₅ 0.01 _107.3 _116.7 0.01 C4304 34.7 91.2 I _63.4 _72.9 I ₆₅_.₅ ₇₇_.8 0.25 _40.7 ₇₄_.₉ 0.05 C4305 67.6 83.6 I ₉₇_.₀ _119.6 1 _98.6 ₁₁₇_.₆ I ₉₂_.₅ _100.2 I

The maximum operating window is from 35°C to 164.5 °C and from 0.01 to 1 bara.

Table 4.2 Operating window pressure (bara)

UNIT MPA EPA BGA BDGA

Bottom To Bottom To Bottom To Bottom

1.17 1.00 1.37 1.00 1.14 1.00 1.15 1.88 1.00 1.43 0.50 1.36 0.10 0.58 0.14 0.01 0.24 0.01 0.29 0.01 0.33 0.42 0.25 0.39 0.25 0.47 0.05 0.51 1.27 1.00 1.44 1.00 1.29 1.00 1.20

4 .

1.2 Component properties

Due to the fact that only a few literature values were found, most of the properties were taken from Aspen databanks. The properties that were not present were estimated with the UNIF AC group contribution method. All the components were present in the databank except EP, EP A and PGDA. Of those components the

molecular weight, boiling point and molecular structure from literature were used for estimation by UNIF AC and for the estimation of the vapour pressure by the Riedel estimation method.

4.1 .

3 Thermodynamic models

This process consists of polar components, which are non-electrolytes. The applied pressure is smaller than 10 bar, interaction parameters are known (Aspen) and the

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CPD 3229, Confidential 4 Thermodynamic properties and reaction kinetics

Wilson model cannot be used. As stated in the Basis of design, chapter 3, the Non

Random Two Liquid (NRTL) model was used for all the process simulations. This

model is used for vapour-liquid-liquid equilibria. To incorporate the chemical theory of dimerisation (for acetic acid) and to account for strong association and solvation effects, the Hayden-O'Connell (HOC) and Nothnagel (NTH) variants of above model were used. For the MP A, BGA and BDGA process the HOC model was used. Since the HOC model was not able to give proper results due to missing dipole moments the NTH model was applied to the EP A process.

4.1.4 Azeotropes

In

some of the processes azeotropes occur. They are tabulated in Error! Reference

souree not found .. The MP A system is the only system in which azeotropes influence the process significantly resulting in the use of an entrainer. This is due to the fact that the boiling points of the relevant components are very closely related.

In

the other systems the boiling points differ more substantially. A reduction of pressure in the second column solves the azeotropic problem. In Appendix 12 T,x,y-plots of all possible binary azeotropes in the four systems are supplied. As entrainer in the MPA

process the use of cyclohexane, butyl-acetate, isopropyl ether and 1,2-dichloro ethane

(DCE) was simulated in Aspen. DCE is the only entrainer with reasonabie results. In Chapter 1.2 the choice of the entrainer is described in more detail.

Table 4.3 Azeotropes in the process

MPAPROCESS

Compound AzeotrClQes with ...

Methyl proxitol Water, acetic acid

Methyl proxitol acetate Acetic acid

EPA PROCESS

Ethyl proxitol Water, acetic acid

Ethyl proxitol acetate

-BGA PROCESS

Butyl glycol Water

Butyl glycol acetate

-BDGA PROCESS

Compound Azeotropes with ...

Butyl diglycol

-Butyl diglycol acetate

-4.1.5

Data accuracy and validation

Unfortunately the number of literature values of the pure components is very limited. The only values found are presented in the pure component list (Appendix 3.1). These literature parameters are verified with the values in the Aspen database. Since these

values were practically identical, the assumption was made that the thermodynamic parameters were correct. In spite of this verification the thermodynamic properties could not be validated. Due to the use of data supplied by the Aspen databanks serious uncertainty is introduced to the simulations which can only be reduced by laboratory testing.

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CPD 3229, Confidential _{4 Thermodynamic properties and reaction kinetics}

4.2 Reaction kinetics

The method of obtaining the reaction kinetics is explained in Chapter 3. This will be

summarised here. From a trial run all data on the catalyst Duolite ES 276 are known

for the esterification of MP to MP

A. Also the amount of by-products is known.

The first step was to develop a plausible reaction scheme (Appendix 3.2); the result

consists of 8 reactions. Then mass balances over the reactor for each component were

set up. Every reaction is assumed to be first order in all reactants. By trial and error in

an Ordinary Differential Equation (ODE) solver the overall reaction constants

(including the influence of the catalyst) we re obtained.

The amount of by-products formed is insignificantly small. Therefore the ratios of the

reaction rates for the formation of by-products and the reaction rate of the main

reaction are assumed to be constant for all four processes, independent of temperature.

For the MP A process this leads to the following overall constants:

Table 4.4 Reaction rates MP A process

Reaction MP + AA -7 MPA + H20 MP A + H20 -7 MP + AA MP + H20 -7 Pglyc + MeOH AA + MeOH -7 MA + H20 MA + H20 -7 AA + MeOH Pglyc ~ Propanal + H20 Pglyc + 2 AA -7 PGDA + 2 H20 PGDA + 2 H20 -7 Pglyc + 2 AA

Overall reaction rateconstant at 80°C 8.73.10-4 [m3j(kmol·s)J 4.22.10-4 [m3_j(kmol·s)J 2.03.10-6 [m3j(kmol·s)J 1.52.10-6 _[m3_j(kmol·s)J 3.42.10-5 [m3j(kmol·s)J 3_25.10-5 [lIsJ 2.03.10-6 [m6j(kmofs)J 7.12.10-6 [m6j(kmoe·s)J

The kinetic data for the other processes are deduced from a comparison of the MP A

kinetics on two catalysts: Duolite and Zirconium base catalyst [12, 13, 14] (See

Chapter 3).

This comparison results in the following kinetic constants for the other processes.

Table 4.5 Reaction rates EPA process

Reaction EP + AA -7 EP A + H20 EPA + H20 -7 EP + AA EP + H20 -7 Pglyc + EthOH AA + EthOH -7 EA + H20 EA + H20 -7 AA + EthOH Pglyc ~ Propanal + H20 Pglyc + 2 AA -7 PGDA + 2 H20 PGDA + 2 H20 -7 Pglyc + 2 AA

Overall reaction rate constant

" at 35°C ' 1.82·10-4 [m3j(kmol·s)J 8.80.10-5 [m3j(kmol·s)J 4.24.10-7 [m3j(kmol·s)J 3.18.10-7 [m3j(kmol·s)J 5.54.10-6 [m3j(kmol·s)J 2.26.10-6 [lIsJ 1.41.10-7 [m6j(kmoI2·s)J 4.95.10-7 [m6j(kmoI2s)J

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CPD 3229, Confidential

Table 4.6 Reaction rates BGA process

BG + AA -7 BGA + H20 BGA + H20 -7 BG + AA BG + H20 -7 Eglyc + BuOH AA + BuOH -7 BA + H20 BA + H20 -7 AA + BuOH Eglyc -? Ethanal + H20 Eglyc + 2 AA -7 EGDA + 2 H20 EGDA + 2 H20 -7 Eglyc + 2 AA

4 Thermodynamic properties and reaction kinetics

Overnllreaction iàte constánt

--.. ~i,/

at

80

0

ë

it ,:" . 1.31.10-3 [m3/(kmol's)] 6.33·10-4 [m3/(kmol·s)] 3.05.10-6 [m3/(kmol·s)] 2.28-10-6 [m3/(kmol·s)] 2.77.10-5 [m3/(kmol·s)] 3.25-10-5 [l/s] 2.03.10-6 [m6_/(kmofs)] 7.12.10-6 _[m6_/(kmoI2 ·s)]

Table 4.7 Reaction rates BDGA process Reactión BDG + AA -7 BDGA + H20 BDGA + H20 -7 BDG + AA BDG + 2 H20 -7 2 Eglyc + BuOH AA + BuOH -7 BA + H20 BA + H20 -7 AA + BuOH Eglyc -? Ethanal + H20 Eglyc + 2 AA -7 EGDA + 2 H20 EGDA + 2 H20 -7 Eglyc + 2 AA

Overall reaction rateconstant at 80°C 1.05.10-3 [m3/(kmol's)] 5.06.10-4 [m3/(kmol·s)] 1.45.10-6 [m6/(kmofs)] 1.83.10-6 [m3/(kmol·s)] 2.22.10-5 [m3/(kmol·s)] 3.25.10-5 _[1/s] 2.03.10-6 [m6_/(kmoI2 ·s)] 7.12.10-6 _[m6_/(kmoI2_·_s)]

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CPD 3229, Confidential 5 Process structure and selection

5 Process structure and selection

5.1 Design criteria and unit selection

The multi purpose plant is designed on the production of MP A. This process has to operate the main part of the year besides that it is the most difficult process due to the need for an entrainer. Af ter the plant lay out and the determination of the number of trays per columns were known the other three processes were designed. The only restrictions for the design of the processes for EP A, BGA and BDGA are the nu mb er of columns and trays. The overall design was optimised by trial and error methods in all processes. The detailed design of the equipment is based on the extreme values in all processes.

Overall criteria are the temperatures, which are not allowed to be higher than 165DC or lower than 30DC in order to be able to use normal cooling water for cooling and low and medium pressure steam for heating.

In the following subsections the selections made in each process will be explained.

5.1.1 Design of the methyl proxitol acetate process

The basic block scheme as provided in Appendix 2 consists of a reaction section, a product purification section and a reactant recovery section. As design specification all reactants recovered anywhere in the process are fed back to the reactor to obtain the highest possible overall conversion.

As reactor a fixed bed tubular adiabatic reactor is taken, because the main reaction is first order in both reactants. Therefore the concentration of these reactants will have to be kept as high as possible. The kinetics of all reactions are provided and explained in Chapter 4. To be able to use this kinetics the fluids in the reactor have to be in the liquid phase. As design temperature 80DC is taken; the reaction is reasonably fast, there are no gases present (water boils at 100DC) and the formation of by-products is limited. The diameter length ratio of the reactor is set to

Ik

With these criteria the reactor size is optimised in Aspen Plus, resulting in a length of 8.5 meters and a diameter of 2.2 meters.

The task of column C4201 is to remove all the water from the product (MP A) and to get as little reactants as possible over the top. In the first simulations the dichloro ethane entrainer was added in this column, but the simulations proved that by adding the azeotropic agent to the next column better results could be obtained. When the entrainer was added in C4201, the large amounts of methyl proxitol caused serious problems with the phase split in the decanter. With these boundary values the C4201 column was simulated and optimised in Aspen Plus.

The bottom of C4201 is the feed of C4202. The purpose of this column is to recover all reactants in order to recycle them. A design criterion is that all reactants and as little product as possible must go over the top.

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CPD 3229, Confidential 5 Process structure and selection

In order to recover the reactants from the top stream of C4201 a distillation (C4304) with an azeotropic agent will have to be performed. In Chapter 2 the choice for dichloro ethane is explained. A design criterion is that all dichloro ethane willieave C4304 over the top and as much reactants as possible through the bottom. The separation is optimal at high vacuum with the restriction that the top temperature cannot be lower than 30°C. This leads to a column pressure of 0.25 bara. The top stream is led to a decanter. Here the resulting water stream may hardly contain any reactants or dichloro ethane. The top stream of C4304 is 34.7°C and will not further be cooled or heated.

In the last column (C4305) dichloro ethane has to be recovered. Section 4300 is optimised for the amount of entrainer feed. The less fresh entrainer feed is added the less dichloro ethane will be present in the waste streams. The entrainer flow in the recycle is kept at 45 kmol/hr, setting it as a design specification in Aspen, because this molar flow turned out to be the optimal amount. The 45 kmol/hr is maintained by varying the distillate to feed ratio in C4305.

5.1.2 Design of the ethyl proxitol acetate process

As mentioned before the EP A process is designed within the hardware limits set by the MP A process. All processes were initially designed with a 70 kmol/hr feed stream. Later on this is reduced to the molar flow necessary for the target production (50 kmollhr) except for the EPA process. Here the feed streams are kept at 70 kmol/hr since this is the most profitable process.

The reaction mixture in the EP A process is cooled to 35°C to ensure a high selectivity towards the main esterification reaction. This was not needed in the other processes.

Varying the reflux ratios and the distillate to feed ratios optimises the columns C4201, C4202 and C4203. The reactants recovered in C4202 are recycled.

Contrary to the MPA process in the EPA process no entrainer (and thus no decanter) is required to recover all reactants. Again the design variables were the reflux ratio and the distillate to feed ratio.

It

was not possible to regain all reactants in one column, so C4305 is used to recover the last bit of reactants. All reactants (bottom streams of C4304 and C4305) are recycled.

5.1.3 Design of the butyl glycol acetate process

In the EGA process it is possible to operate the reactor at 80°C without loss of selectivity.

In section 4200 the columns are optimised in the same way as in the EP A process: by varying the reflux ratios and the distillate to feed ratios. In column C4203 a problem occurs: The bottom stream contains all EGA and in the top stream that has to be recycled, too much butanol is present. This butanol would cause accumulation in the process, so a purge is required. The top stream of C4202 and the main part of the top stream of C4203 are recyc1ed to the reactor. This recycle system is optimised by reducing the purge stream.