Design of Environmentally Benign Processes: Integration of Solvent Design

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Design of Environmentally Benign Processes
Integration of Solvent Design Separation
Process Synthesis
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• Peter M. Harper, Martin Hostrup, Rafiqul Gani
• CAPEC
• Dept. of Chem. Eng., Tech. Univ. of Denmark
• http//www.capec.kt.dtu.dk

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Overview

• Introduction
• Methodology
• Problem Formulation
• Solution Approach
• Tools needed
• Application examples
• Conclusions

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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

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Introduction -II Integration
Integration of synthesis, design, pollution
prevention, etc., means solving various problems
simultaneously

• Objective Develop a combined methodology in
  order to determine (interactively), optimal,
  environmentally benign processes

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Superstructure representation
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Methodology-I Problem Formulation

• New process (pollution prevention)
• Existing process (treatment/cure)
• Variables are fixed
• Problem more constrained (less degrees of
  freedom)
• More difficult to solve

Process model Process constraints Environmental
constraints Solvent alternatives
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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.

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Methodology-II Solution Approach
Sub-Problems Process Design Solvent
Design/Selection Material Design/Selection Waste/E
nergy Aspects
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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)
• Energy consumption waste

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Process Design Separation techniques

• Need for (appropriate) thermodynamic models.
  Thermodynamic Model Selection
• Need for Properties (Database/Property
  prediction)

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Sub-Problems Solvent Design/Selection I

• Find compounds matching desired properties
• Performs database search
• Generates missing data
• Based on properties controlling the search/design
  operation
• Ability to identify novel compounds
• Suitable for substitution problems

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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
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Generation criteria/properties

• Group contribution
• Correlation
• EOS
• UNIFAC
• Rigorous phase calculations
• Link to database
• Calculation order optimised for speed

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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.

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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...

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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

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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 (gt 13000 compounds)
• Environmental properties database
• Materials database
• Properties estimation tool (Pure component
  mixture properties)
• Impact Assessment tools

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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
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Example-I Design criteria

• Compound type Acyclic alkanes, ethers, esters,
  aldehydes, ketones and acids.
• Pure component properties
• Tflash gt 310 K, Tboil gt 421 K Tmelt lt 310 K
• Mixture properties
• Sl lt 0.01 m gt 0.1 ? gt 7 B gt 1
• Solvent must not form azeotrope with acetic acid
• Liquid-liquid phase behaviour at 298 K

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Example-I Results performance

• 2332 Alternatives were found
• Candidates sorted using m? as ranking criteria
• Structure analysis/matching to identify CAS-NO

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Example-I Environmental Aspects

• D Drug, S Primary Irritant, T
  Reproductive-Effector, M Mutagen, C Tumorigen

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Example-II Integrated Problem
Problem A process stream of 50 mole Acetone and
50 mole Chloroform at 300K, is to be
separated.
No external medium known Binary ratios of
properties identify the following alternatives
Note Acetone-chloroform forms a high boiling
azeotrope that is pressure sensitive
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Pressure dependence
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Pressure dependence
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Solvent design sub-problem

• CAMD problem
• 340 lt Tboil lt 420
• Selectivity gt 3.5
• Solvent powergt 2.0
• No azeotropes
• Number of compounds designed 47792Number of
  compounds selected 53
• Number of isomers designed 528 Number of
  isomer selected 23
• Total time used to design 57.01 s

Solution 1-Hexanal Methyl-n-pentyl
ether (Benzene)
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Phase behaviour
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Phase behaviour
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Problem formulation Solution
Objective function Maximize Profit
Earnings Solvent cost Energy
costs Constraints Acetone purity gt
0.99 Chloroform purity gt 0.98
Results
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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

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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)