Modeling of Reactive Distillation

Modeling of Reactive Distillation

John Schell

Dr. R. Bruce Eldridge

Dr. Thomas F. Edgar

OutlineOutline

• Overview of Reactive Distillation

• Project Overview– Tower Design

– Steady-State Models

– Dynamic Models and Control

• Individual Work– Column Design and

Operation

– Validation of Models

– Preliminary Dynamics and Control Studies

• Future Work

Reactive DistillationReactive Distillation

• Homogeneous or Heterogeneous/ Catalytic Distillation

• First Patents in 1920s• Applied in 1980s to

Methyl Acetate• Common applications:

– Ethylene Glycol– MTBE, TAME, TAA

Favorable ApplicationsWesterterp (1992)

Favorable ApplicationsWesterterp (1992)

• Match between reaction and distillation temperatures

• Difference in relative volatility between product and one reactant

• Fast reaction not requiring a large amount of catalyst

• Others: liquid phase reaction, azeotrope considerations,exothermic reactions

Subawalla Approach (Dissertation)Subawalla Approach (Dissertation)

1. Decide on a Pre-reactor- Rate of reaction

- >1/2 of initial reaction rate at 80% of equilibrium conversion

2. Pressure

3. Location of Zone

4. Estimate Catalyst- Isothermal Plug-flow reactor

with ideal separators

5. Design Tower- Size reaction zone

• Catalyst requirements• Column diameter

- Determine reactant feed ratio

- Feed location- Reflux ratio

• High reflux rate - 2-3 times non-rxtive column

- Diameter• Through-put• Catalyst density

Project Overview

• Design and Construct TAME Column

• Validate Steady State Models

• Develop Dynamic Models

• Test Control Algorithms

TAME ChemistryTAME Chemistry

• Exothermic• Equilibrium Limited

– 45-62% at 50-80 C

• Azeotropes• Catalyst: Amberlyst-15

• Methanol can inhibit rates.

• Rihko and Krause (1995)

MeOHSa MeOH Sa

TAMES a KB1

KB2

MeOHSa 2M1B

TAMES a KB3

KB4

MeOHSa 2M2B

TAMES a TAME Sa

2M2BKB5

KB62M1B

Sa is a vacant adsorption site.

Pilot Plant (SRP)Pilot Plant (SRP)

• 0.152-meter diameter column

• Finite reflux

• 7 meters of packing in 3 sections

• Fisher DeltaV Control

• Koch’s Katamax packing

Makeup MeOH

C5 from Cat

Cracker Pre-Reactor

ReactiveDistillation

Column

Mixing Tank

Back - CrackingReactor

Recycle

TAME

Unreacted C5, MeOH

3.7 atm

SRP Pilot PlantSRP Pilot Plant

•Koch – Spool section, Katamax, Catalyst

•SRP - $145K

Steady-State MultiplicitySteady-State Multiplicity

• Bravo et al. (1993)– Observed multiple steady-states in TAME CD

• Hauan et al. (1997)– dynamic simulation provided evidence in MTBE

system

• Nijuis et al. (1993)– found multiplicity in MTBE system

• Jacobs and Krishna (1993)– found multiplicity in MTBE system

Steady-State Distillation ModelsSteady-State Distillation Models

Trayed Tower:

Equilibrium Model

Rate Model

Packed Tower:

Continuous Model

ii

jijijjij

jijjij

Kxy

RyVxL

yVxL

,,,

1,11,1

Li

Vi NN

kkLi

Lii RAANLx

z

TAME Reaction RatesTAME Reaction Rates

Comparison of Reaction Rates

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Stage (Condenser=1)

Rea

ctio

n R

ates

(lb

mol/h

r)

RADFRAC

RateFRAC

TAME Concentration ProfileTAME Concentration Profile

Comparison of TAME Profiles

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Stage (Condenser=1)

Mole

Fra

ctio

n

RADFRAC

RateFRAC

Effective Reaction RateEffective Reaction Rate

• Traditionally simulations use intrinsic reaction rate.

• Effective rate is a function of intrinsic rate and diffusion limitations. Molefraction

Eff

ecti

ve R

ate

Control for TAME TowerControl for TAME Tower

• Fisher DeltaV– Visual Basic

– Matlab, Visual Studio

• State Estimation– Temperature Profiles

– Online Analyzers

• Control Algorithms– PID

– Linear MPC

– Non-Linear MPC

Individual Work

• Design and Construct RD Column for Novel System

• Steady State Model Validation

• Dynamic Models and Control Study

Novel System

• Kinetic Reaction– Not Equilibrium limited

– Equilibrium Isomers

• Exothermic

• Kinetics from CSTR Experiments

• Feed is dominated by inerts

• Replace hazardous heterogeneous catalyst

A + B C1

C1 C3C2Isomer Distribution for Reactive Systems

0

5

10

15

20

25

30

35

40

45

50

1 2 3 4 5

Isomer

Mo

le %

Plug-flow Reactor

CD Column

Novel System DataNovel System DataStandard Conditions at 50 psig Over 26 Experiments

OverheadVaporTemp

DA-220-1 DA-220-2 DA-220-3 DA-220-4 TI-215 DA-210-1 DA-210-2 DA-210-3 DA-210-4 ReboilerTemp

Te

mp

era

ture

(C

)

0

5

10

15

20

25

High

Low

Average

Standard Deviation

Reactive Zone

Novel System DataNovel System DataProfiles for 35 psig at Standard Conditions

OverheadVapor Temp

DA-220-1 DA-220-2 DA-220-3 DA-220-4 TI-215 DA-210-1 DA-210-2 DA-210-3 DA-210-4 ReboilerTemp

Tem

per

atu

re (

C)

0

5

10

15

20

25

Hi

Lo

Average

Stnd Dev

Reactive Zone

Simulation Validation - 50 psigSimulation Validation - 50 psigColumn Data and Simulation for Standard Flows at 50 psig

0 5 10 15 20 25

Tem

per

atu

re (

C)

Simulation Validation – 35 psi

Simulation and Data for Standard Flows at 35 psig

0 5 10 15 20 25

Tem

per

atu

re (

C)

Effect of PressureEffect of Varying Pressure

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Tem

per

atu

re (

C)

25 psig

35 psig

50 psig

75 psig

Effect of Varying Feed RateEffect of Varying Reactant Feed Rates

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Tem

per

atu

re (

C)

25 g/min A and 10 g/min B

75 g/min A and 10 g/min B

100 g/min A and 10 g/min B

150 g/min A and 20 g/min B

Dynamic Modeling and Control Study

• Aspen Custom Modeler/ Aspen Dynamics– Validate Steady State

Solution

– Validate Dynamic Studies

• Develop Control Algorithms– PID

– Linear MPC

– NLMPC

Aspen Custom ModelerAspen Custom Modeler• Formerly Speed-Up

and DynaPlus• Equation Solver• Aspen Properties Plus• Tear Variables

automatically selected• Solves Steady-State

and Dynamic• Dynamic Events and

Task Automation

1 2 3 4 5 6 7 8 9 10

1 X X

2 X X

3 X X T T

4 X X T T

5 X X T T

6 X X T T

7 T T T T T T

8 T T T T T T

9 X

10 X

Equations vs. Variables

Validation of Dynamic SimulatorValidation of Dynamic SimulatorComparison of ACM and Aspen Plus Radfrac Results

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Tem

per

atu

re (

C)

ACM w/Tear

Aspen Plus

Feed Disturbance With Manual ControlFeed Disturbance With Manual Control

Stream Results

Time Hours0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3

Pre

ssur

e N

/m2

Tem

pera

ture

K

Mol

ar F

low

rat

e km

ol/s

3500

0036

0000

520

540

560

2e-5

2.5e

-53e

-53.

5e-5

C - Production

Time Hours0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

B-F

eed

Rat

e

B-P

rodu

ctC

1.5e

-52e

-52.

5e-5

3e-5

-0.0

50

0.05

0.1

0.15

0.2

Control of Reactive DistillationControl of Reactive Distillation

• Configurations– DB

– LV

– BV, LB…

• Goals– Conversion

– Product Purity

F

R

D

B

VL

Duty

Control of Reactive DistillationControl of Reactive Distillation

• Bartlett and Wahnschafft (1997)– Simple Feed-Forward/

Feed-Back PI Scheme

• Sneesby et al. (1999)– Two point control with

linear conversion estimator

• Kumar and Daoutidis (1999)– Showed linear

controllers unstable for ethylene glycol systems

– Demonstrated possible Nonlinear MPC scheme

Dependency of Conversion on Reboiler Duty and Reflux RatioDependency of Conversion on Reboiler Duty and Reflux Ratio

Conversion vs Reboiler DutyConversion vs Reboiler Duty

Conversion of Olefin for Molar Reflux Ratio of 1.9

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Reboiler Duty (MMkcal/hr)

Convers

ion

Single Tray Conversion Estimation

Dependency of Conversion on Temperature

0

50

100

150

200

250

300

350

400

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Conversion

Tem

per

ature

(C

)

T8

T6

Single Tray Conversion Estimation

Single Tray Purity Estimation

Purity of Alkylate

230

235

240

245

250

255

260

265

0.00

000E

+00

5.00

000E

-08

1.00

000E

-07

1.50

000E

-07

2.00

000E

-07

2.50

000E

-07

3.00

000E

-07

3.50

000E

-07

4.00

000E

-07

4.50

000E

-07

5.00

000E

-07

Benzene Concentration

Tem

per

ature

(C

) T6

T7

T8

Single Tray Purity Estimation

Feed Disturbance With Manual ControlFeed Disturbance With Manual Control

Stream Results

Time Hours0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3

Pre

ssur

e N

/m2

Tem

pera

ture

K

Mol

ar F

low

rat

e km

ol/s

3500

0036

0000

520

540

560

2e-5

2.5e

-53e

-53.

5e-5

C - Production

Time Hours0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

B-F

eed

Rat

e

B-P

rodu

ctC

1.5e

-52e

-52.

5e-5

3e-5

-0.0

50

0.05

0.1

0.15

0.2

Feed Disturbance with Simple PID Control

Feed Disturbance with Simple PID Control

S trea m R esu lts

T im e H o u rs

0 0 .2 5 0 .5 0 .7 5 1 1 .2 5 1 .5 1 .7 5 2 2 .2 5 2 .5 2 .7 5 3

Pressu

re N/m

2

Tem

pera

ture K

Mo

lar F

low

rate k

mo

l/s

37

00

00

38

00

00

52

05

40

56

05

80

1.5

e-52

e-52

.5e-5

3e-5

3.5

e-5

C-Production

Time Hours0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

B-F

eed

Rat

e

B-P

rodu

ctC

1.5e

-52e

-52.

5e-5

3e-5

-0.0

50

0.05

0.1

0.15

Conclusion and Future WorkConclusion and Future Work

• TAME Tower– Collect Data– Validate Models– Developing Advanced

Models– Improvements

• New chemical system• Adjust for better dynamic

studies

• Novel System– Validate Dynamic Models– Develop Control

Algorithms

Comparison of Reaction Rates

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Stage (Condenser=1)

Rea

ctio

n R

ates

(lb

mol/h

r)

RADFRAC

RateFRAC

C-Production

Time Hours0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

B-F

eed

Rat

e

B-P

rodu

ctC

1.5e

-52e

-52.

5e-5

3e-5

-0.0

50

0.05

0.1

0.15