C APEC
Design of Environmentally
Benign Processes: Integration
of Solvent Design & Separation
Process Synthesis
Peter M. Harper, Martin Hostrup, Rafiqul Gani
CAPEC
Dept. of Chem. Eng., Tech. Univ. of Denmark
http://www.capec.kt.dtu.dk
Overview
• Introduction
• Methodology
– Problem Formulation
– Solution Approach
– Tools needed
• Application examples
• Conclusions
Clean Products and Processes II 2
Introduction-I: Definitions
• Environmentally Benign Process
– All environmental aspects have been
considered.
– The process complies (AT LEAST) with all
regulatory requirements.
• Pollution
– Causes
• Solvents, energy use, by-products in effluent
streams.
– Prevention, Treatment & Cure
Clean Products and Processes II 3
Introduction -II: Integration
Integration of
synthesis, design, Separation Solvent
synthesis Reactor design
pollution design
prevention, etc.,
means solving Equipment
Flowsheet Optimization
various design
generation
problems
simultaneously Property
Impact estimation
Simulation
analysis
Objective: Develop a combined methodology in
order to determine (interactively), optimal,
environmentally benign processes
Clean Products and Processes II 4
Superstructure representation
Y18
DEC Y19
Y20 Y13
Y21 Y14
Y22 Y15
Y23 P1
Y6
Y8
Y1 Y9
D2
Y2 Y7
Feed
D1
Y3
Y10
Y11
Y12 Y16
Y4
Y17
EX
Y5 P2
Y24
Solvent1 Y25+1 Y25
Solvent make up Solvent2 Y25+2
.
.
.
SolventN
Y25+N Clean Products and Processes II 5
Methodology-I: Problem Formulation
• New process (pollution prevention)
FOBJ = min { CT y + f(x)}
s.t.
h1 (x) = 0 Process model
h2 (x) = 0 Process constraints
g1 (x) 0
g2 (x) 0 Environmental constraints
By+ Cxd Solvent alternatives
• Existing process (treatment/cure)
– Variables are fixed
– Problem more constrained (less degrees of freedom)
– More difficult to solve
Clean Products and Processes II 6
Problem Formulation Steps
1. Analyse process, divide into reaction & separation blocks.
2. List separation techniques to be considered.
3. External mediums? Eliminate if none found.
4. Screen out infeasible separation techniques.
5. Binary mixture analysis: Azeotropes, miscibility, …
6. Generate solvent alternatives.
7. Multicomponent mixture analysis: Separation boundaries, etc.
8. Check separation stream for reactants. Recycle?
9. Formulate optimization problem in terms of superstructure,
objective function, constraints, etc.
Clean Products and Processes II 7
Methodology-II: Solution Approach
Sub-Problems
Process Design
Solvent Design/Selection
Material Design/Selection
Waste/Energy Aspects
Clean Products and Processes II 8
Sub-Problems: Process Design
* Conditions of operation
– Temperature / Pressure
* Separation unit (distillation column) design
– Separation efficiency curves
– Product specifications
– Design parameters (feed location, reflux, …)
* Reaction synthesis and optimization
– Volume / Residence time
– Temperature profile
* Operational constraints
– Separation boundaries
* Solvent/material design (selection)
& waste
* Energy consumptionProducts and Processes II
Clean 9
Process Design: Separation techniques
Separation technique Class Phases involved
Absorption Solvent-based Gas-Liquid
External material-based Gas-Gas
Adsorption External material-based Gas-Liquid
Pervaporation External material-based Vapour-Liquid
Filtration External material-based Solid-Liquid
Crystallisation Property difference Solid-Liquid
Distillation Property difference Vapour-Liquid
Distillation plus decanter Property difference Vapour-Liquid plus Liquid-Liquid
Extractive distillation Solvent-based Vapour-Liquid
Azeotropic distillation Solvent-based Vapour-Liquid-Liquid
Liquid-Liquid extraction Solvent-based Liquid-Liquid
Super-critical extraction Solvent-based Fluid-Vapour-Liquid
• Need for (appropriate) thermodynamic models.
Thermodynamic Model Selection
• Need for Properties (Database/Property
prediction)
Clean Products and Processes II 10
Sub-Problems: Solvent Design/Selection I
• Find compounds Start
matching desired
properties No s ui table
• Performs database
s ol utions (due to
performanc e,
Candidate economic or
se lection s afety c onc erns)
Proble m
search (final v erif ication/
comparison
form ulation
• Generates missing
(identify the
using rigorous
goals of the
simulation and
Promis i ng design operation)
experimental
data procedures)
c andidates have
been i denti fied
• Based on properties Re sult Method and
controlling the analysis and
verification
constraint
se lection
search/design Finish (analy se the (specify the
suggested design criteria
operation compounds
using external
based on the
problem
• Ability to identify
tools) f ormulation)
novel compounds CAMD
Solution
• Suitable for (identify
compound
substitution hav ing the
desired
problems Clean Products and Processes II properties) 11
Molecule Generation
• Multilevel Approach
– All generation is rule-based (feasibility, method considerations).
– Increasing complexity on the generated molecular descriptions.
– Output from previous level is used as input for the next next level.
Level 3/4
O
Level 2 - A
CH3 CH2 CH2 CH3C=O CH=CH
CH3 0 1
CH2 1 0 1
CH2 1 0 1
Level 1 CH3C=O 0 1
CH=CH 1 1 0
1 CH3
2 CH2 O
1 CH3C=O Level 2 - B
1 CH=CH
CH3 CH2 CH2 CH3C=O CH=CH
CH3 0 1
CH2 0 1 1
CH2 1 0 1
CH3C=O 1 0
CH=CH 1 1
Clean Products and Processes II 0 12
Generation criteria/properties
Pure component non temperature dependant properties
• Group Molecular weight Critical pressure
contribution Critical temperature Critical volume
Acentric factor Boiling point
• Correlation Melting point
Enthalpy of formation
Gibbs energy of formation
Enthalpy of vaporisation
• EOS Liquid molar volume (@298K)
Closed cup flash point
Liquid molar volume (@TBoil)
Open cup flash point
• UNIFAC Hansen solubility parameters (H, D & P)
Surface tension composition
Total solubility parameter
Log(Water solubility)
• Rigorous Octanol solubility
Refractive index
Octanol/Water partition coefficient (logP)
Molecular refractivity
phase Dipole momentum Henry’s Law constant
Biodegradability
calculations
Pure component temperature dependant properties
• Link to Liquid density Viscosity
database Diffusion coefficient in water Vapour pressure
Thermal conductivity
• Calculation Mixture properties
order Solvent power Selectivity
Distribution coefficient Solvent loss
optimised Separation factor Solute loss
Selectivity based on feed composition Solvent capacity
for speed Mixture viscosity
Special
Clean
Miscibility CalculationsProducts and Processes II
Azeotrope Calculations 13
SLE Calculations
Sub-Problems: Material Design/Selection
• Designing or selecting the most appropriate
membrane material for a particular
application.
• Computer Aided Membrane Design still an
emerging field.
• Database approach combined with shortcut
simulations:
– Allows for realistic input data to be used in the
selection process.
– The choice of material can change the efficiency of a
process by several orders of magnitude.
Clean Products and Processes II 14
Sub-Problems: Waste/Energy Aspects
• Local (process-wide) energy aspects can be
addressed using the simulation engine.
• Off-process energy requirements must be
handled using LCA techniques - taking local
conditions into account.
• Waste/effluent minimisation can (in part) be
handled using the simulator/optimiser.
• Impact assessment tools must be used……...
Clean Products and Processes II 15
Methodology- III: Problem Solution
• Flexible & interactive solution of the problem
• Rigorous models used in the NLP-step
• Linear model generated for the MILP-step
• Any sub-problem can also be solved independently
Linearized ICASSim
model Process Simulator
NLP
Binary variables
optimizer
MILP
optimizer
Contineous variables
Clean Products and Processes II 16
Methodology - IV: Tools Needed
• Process Simulator (steady state, dynamic) &
Modelling tool
• Solvers (NLP, MINLP, AE, DAE, etc.)
• Flowsheet generation tool (process synthesis)
• CAMD (solvent selection/design)
• Physical properties database (> 13000 compounds)
• Environmental properties database
• Materials database
• Properties estimation tool (Pure component &
mixture properties)
• Impact Assessment tools
Clean Products and Processes II 17
Application Examples
* Solvent Design/Selection: Sub-problem
- Replacement solvent (Isoamyl acetate) for
extraction of acetic acid from water
* Process Flowsheet Synthesis: Integrated
problem
- Separation of acetone and chloroform
Clean Products and Processes II 18
Example-I: Design criteria
• Compound type: Acyclic alkanes, ethers, esters,
aldehydes, ketones and acids.
• Pure component properties:
– Tflash > 310 K, Tboil > 421 K ; Tmelt 0.1 ; > 7 ; B > 1
– Solvent must not form azeotrope with acetic acid
– Liquid-liquid phase behaviour at 298 K
1 B,S
A, B MWB
x A, S
Sl m B
x
A, S
A, S A, S MWS B,S 2 phaseequilibria
Clean Products and Processes II 19
Example-I: Results & performance
• 2332 Alternatives were found
• Candidates sorted using m* as ranking criteria
• Structure analysis/matching to identify CAS-NO
CAS-NO Tboil Tmelt Sl m
5-Nonanone 502-56-7 476 248 7.8e-5 20.3 0.28 1.52
Ethylhexaldehyde 123-05-7 447 228 2.4e-4 19.8 0.23 1.51
Diisobutyl Ketone 108-83-8 462 227 7.8e-5 20.3 0.28 1.52
Nonyl acetate 143-13-5 506 254 6.2e-6 7.9 0.13 1.56
2-Ethylhexyl Acetate 103-09-3 483 236 1.8e-5 7.5 0.14 1.45
Heptyl acetate 112-06-1 472 237 5.4e-5 7.0 0.16 1.34
Methyl decanoate 110-42-9 501 245 3.6e-6 9.3 0.11 1.81
1-Nonanol 143-08-8 499 250 1.1e-4 7.1 0.50 0.77
Decanoic Acid 334-48-5 541 304 7.9e-5 4.1 0.29 0.72
Isoamyl Acetate 123-92-2 421 202 4.7e-4 6.0 0.20 1.07
Clean Products and Processes II 20
Example-I: Environmental Aspects
CAS-NO RTECS Class Assessment Comments
5-Nonanone 502-56-7 D Highly Toxic
Ethylhexaldehyde 123-05-7 S Hazardous Causes skin
burns on
contact
Diisobutyl Ketone 108-83-8 S Low hazard
Nonyl acetate 143-13-5 - Limited data
2-Ethylhexyl Acetate 103-09-3 S Some hazard
Heptyl acetate 112-06-1 S Low hazard
Methyl decanoate 110-42-9 - Limited data
1-Nonanol 143-08-8 T Some hazard High aquatic
toxicity
Decanoic Acid 334-48-5 M+S Toxic Causes skin
burns on
contact
Isoamyl Acetate 123-92-2 C Hazardous
• D = Drug, S = Primary Irritant, T = Reproductive-Effector, M = Mutagen, C= Tumorigen
Clean Products and Processes II 21
Example-II: Integrated Problem
Problem: A process stream of 50 mole% Acetone and 50
mole% Chloroform at 300K, is to be separated.
Separation techniques considered: No external medium known
Adsorption (liquid, gas) Binary ratios of properties
Crystallization identify the following
Desublimation alternatives
Distillation – simple
Distillation – extractive
Distillation with decanter Separation techniques:
Liquid-liquid extraction Distillation – simple
Flash/evaporation Distillation – extractive
Membrane (gas, liquid) Distillation – azeotropic
Microfiltration Liquid extraction
Partial condensation Pressure swing
Note: Acetone-chloroform forms a high boiling azeotrope
that is pressure sensitive 22
Pressure dependence
Clean Products and Processes II 23
Pressure dependence
Clean Products and Processes II 24
Solvent design sub-problem
• CAMD problem:
• 340 3.5
1-Hexanal
• Solvent power> 2.0
Methyl-n-pentyl ether
• No azeotropes
(Benzene)
• Number of compounds designed: 47792
Number of compounds selected: 53
• Number of isomers designed: 528
Number of isomer selected: 23
• Total time used to design: 57.01 s
Clean Products and Processes II 25
Phase behaviour
Clean Products and Processes II 26
Phase behaviour
Clean Products and Processes II 27
Problem formulation & Solution
Objective function:
Maximize
Profit = Earnings
– Solvent cost
– Energy costs
Constraints:
Acetone purity > 0.99
Chloroform purity > 0.98
Results:
Solvent Solvent Reflux Reflux Objective
flow rate Reb. 1 Reb. 2 function
1-hexanal 0.082 kmol/hr 0.45 0.65 2860.51 $/hr
Clean Products and Processes II 28
Conclusions
• A systematic, knowledge intensive framework
for design for the environment on the process
level.
• Pollution prevention
– Use of thermodynamic knowledge
– Synthesis of flowsheets
– Optimizes operational parameters
• Cure/Treatment
– Verification by simulation
– Uses existing operational constraints
– Identifies needed changes in operational parameters
• Use of rigorous models
Clean Products and Processes II 29
More information ?
• CAPEC Web-Sites
– www.capec.kt.dtu.dk (Primary site)
– www.capec.kt.dtu.dk/eurecha (EURECHA inf. site)
– www.escape11.kt.dtu.dk (European Symposium on
Computer Aided Process Engineering - 11, May 2001
Denmark)
Clean Products and Processes II 30