Lida Simasatitkula, Rafiqul Ganib, Amornchai Arpornwichanopa
a Department
b Chemical
of Chemical Engineering, Faculty of Engineering, Chulalongkorn University,
Bangkok 10330, Thailand
& Biochemical Engineering, Technical University of Denmark, Soltofts Plads,
Building 227, DK-2800 Lyngby, Denmark
Introduction
Objective
Methodology
Results and discussions : Case study
Conclusion
Due to a limited availability of fossil fuels and an increased price
of petroleum diesel, biodiesel (a fatty acid alkyl ester) has become
an important alternative fuel.
Transesterification reaction
1
2
Triglyceride + CH3OH 
 Diglyceride + RCOOCH3
k and k
3
4
Diglyceride + CH3OH 
 Monoglyceride + RCOOCH3
k and k
5
6
Monoglyceride + CH3OH 
 Glycerol + RCOOCH3
k and k
Esterification reaction
RCOOH  CH3OH  RCOOCH3  H2 O
Reactive distillation can improve the conversion of reversible
reactions.
Separation task
Reaction task
Separation task
Advantages of reactive distillation:
- Improve process performance
- Reduce energy consumption
- Improve process economic
Reactive distillation is considered a process intensification that
combine reaction and separation tasks.
• Energy consumption of reactive distillation for
heterogeneous catalyzed processes is high.
• A heat-integrated reactive distillation has been proposed
with different designs, e.g., a petlyuk reactive distillation, a
thermal coupling reactive distillation and an internal heat
integrated reactive distillation.
• Caballero and Grossman (2008) proposed a design
methodology for the sequence of distillation column and
thermally coupling distillation.
Introduction
Objective
Methodology
Results and discussions : Case study
Conclusion
• To develop a systematic design of a heat integrated
reactive distillation for biodiesel production.
Distillated methanol
Water
Crude
biodiesel
Trilinolein
Methanol
Water
Vapor
methanol
Methyl oleate+
methyl
linoleate
L
Waste
Methyl oleate+methyl
linoleate+Glycerol
Water+Glycerol
Introduction
Objective
Methodology
Results and discussions : Case study
Conclusion
Step 1: Define problem
Step 2 : Analyze conventional
reactive distillation
Step 3 : Identify heat integrated reactive
distillation (generate superstructure)
Step 4 : Screen the number
alternatives
Step 5 : Minimize objective
function
Step 1: Define problem
-The starting point is
problem definition.
- The minimization of a
total annual cost is set as a
target for process design.
Step 1: Define problem
Step 2: Analyze a conventional
reactive distillation
Step 2.1: Identify limitation of
reactive distillation
Step 2 : Analyze conventional
reactive distillation
Step 3 : Identify heat integrated reactive
distillation (generate superstructure)
Step 2.2 : List all component and
define product specification
Step 2.3 : rank the boiling point of
components
Step 4 : Screen the number
alternatives
Step 2.4 : Find the component at the
top and bottom of column
Step 5 : Minimize objective
function
Step 2.5 : Compute the ratio of
properties
Step 2.6 : If the ratio is equal to 1, solvent
selection is needed; otherwise skip this step.
Step 1: Define problem
Step 2 : Analyze conventional
reactive distillation
Step 3 : Identify heat integrated reactive
distillation (generate superstructure)
Step 4 : Screen the number
alternatives
Step 5 : Minimize objective
function
Step 3: Identify heat
integrated reactive
distillation
The objective of this step is
to generate a full set of
heat integrated reactive
distillation columns.
Step 4: Screen the number of
alternatives
Criteria
Step 4.1: Fast screen the
number of alternatives
Step 4.2 : Reduce the number of
alternatives from ratio of boiling
point of key components
Step 4.3 : Reduce the number of alternatives from key
components
- The lightest key component/light key component
- Light key component/heavy key component
Purity of key components
Ratio of boiling point of key
component
Type of key components
Step 1: Define problem
Step 2 : Analyze conventional
reactive distillation
Step 3 : Identify heat integrated reactive
distillation (generate superstructure)
Step 4 : Screen the number
alternatives
Step 5 : Minimize objective
function
Step 5: Minimize
objective function
The objective function, a
total annual cost, is
minimized in order to find a
feasible one.
Introduction
Objective
Methodology
Results and discussions : Case study
Conclusion
Configuration of a conventional reactive distillation for
biodiesel production using heterogeneous acid catalyzed.
Distillated
methanol
Water
Vapor methanol
Crude biodiesel
Trilinolein
Methanol
Distillated
methanol
Methyl oleate+
methyl linoleate
Water
L
Waste
Methyl oleate+methyl
linoleate+Glycerol
Water+Glycerol
Application of the methodology for a heat integrated reactive distillation
Step 1 : Define problem for design of a heat integrated reactive
distillation
min TAC = Operating cost +
Capital cost
3
Step 2 : Analyze a conventional reactive distillation
Conventional reactive
distillation using
heterogeneous acid
catalyzed
Conventional reactive
distillation using alkali
catalyzed
P (atm)
Performance
conversion
Energy (Btu/h)
5.5
97.1%
1.78e7
1
98.52%
1.0e7
Step 2 : Analyze a conventional reactive distillation
Component
Ratio of boiling point
Methanol/water
1.45
Water/glycerol
2.85
Glycerol/methyl oleate
1.1
Methyl oleate/oleic acid 1.03
Oleic acid/trilinolein
1.45
It is found that a binary ratio of the boiling point of water and
glycerol is the highest value. So water can be separated from
glycerol.
Step 3 : Identify heat integrated reactive distillation
1.
2.
3.
4.
5.
6.
7.
8.
9.
HiRDC without heat exchanger
HiRDC with heat exchanger
Petyuk RD
Feed split multi-effect RD
HiRDC with distillation column
without heat exchanger
HiRDC with distillation column
with heat exchanger
Thermal coupling indirect RD
integrated with distillation column
Thermal coupling direct sequence
RD integrated with distillation
column
Multi-effect indirect split
arrangement RD integrated with
distillation column.
Step 4 : Screen the number of alternatives
1st criteria
Purity of water is not mentioned.
2nd criteria
Ratio of the boiling point is used as
criteria.
1.
2.
3.
4.
5.
6.
7.
3rd criteria
Type of key component
(water/glycerol)
8.
9.
HiRDC without heat exchanger
HiRDC with heat exchanger
Petyuk RD
Feed split multi-effect RD
HiRDC with distillation column
without heat exchanger
HiRDC with distillation column
with heat exchanger
Thermal coupling indirect RD
integrated with distillation column
Thermal coupling direct sequence
RD integrated with distillation
column
Multi-effect indirect split
arrangement RD integrated with
distillation column.
Step 4 : Screen the number of alternatives
Step 1: Define problem
Step 2 : Analyze conventional
reactive distillation
Step 3 : Identify heat integrated reactive
distillation (generate superstructure)
Step 4 : Screen the number
alternatives
Step 5 : Minimize objective
function
Step 5 : Minimize objective function
Multi-effect indirect split arrangement reactive distillation
Excess methanol
Trilinolein
Reflux
Methanol
Boilup
Methyl ester+Glycerol
Waste water
Step 5 : Minimize objective function
Indirect thermal coupling reactive distillation
Trilinolein
Methanol
Methyl ester+Glycerol
Step 5 : Minimize objective function
Heat integrated reactive distillation without heat exchanger
(HiRDC without heat exchanger)
Stripping section
Rectifying section
Trilinolein
Methanol
Methanol
Waste water
Methyl ester+Glycerol
Step 5 : Minimize objective function
Heat integrated reactive distillation with heat exchanger
(HiRDC with heat exchanger)
Stripping section
Rectifying section
Methanol
Trilinolein
Methanol
Methanol+water
Methyl ester+Glycerol
Base multi-effect Thermal
case indirect splitRD
design arrangeme
nt RD
Pressure of reactive distillation column(bar) 5.5
Pressure of distillation column
1
11
Reaction stage of reactive distillation
Total stage of distillation column for separation9
water and methanol
Reboiler duty of reactive distillation (Btu/h)
1.82e7
Reboiler duty of distillation for separation
7.98e6
methanol from water (Btu/h)
Condenser duty of reactive distillation (Btu/h) 7.46e5
8.07e6
Condense duty of distillation for separation
methanol from water (Btu/h)
1e6
TAC of reactive distillation ($/year)
5.6e5
TAC of distillation for separation methanol
from water($/year)
Cost saving (%)
6
1
3
4
6
1
9
10
heat
heat
integrated integrated
RD withoutRD
with
heat
heat
exchanger exchanger
6
6
23
23
8
8
10
10
1.88e7
-
1.88e7
1.47e2
1.92e7
-
1.87e7
-
1e6
8.9e5
1.76e6
8.44e5
1.05e6
1.07e6
1.17e6
1.107e6
22.35
21.95
17.3
20.17
Introduction
Objective
Methodology
Results and discussions
Conclusion
• Design methodology for a heat integrated reactive distillation was
proposed.
• The full set of alternatives was generated from a generic superstructure
and the number of alternative is reduced through criteria.
• By performing an economic analysis in terms of total annual cost, a
multi-effect indirect split arrangement reactive distillation is a feasible
one because of the minimum energy consumption and total annual cost.
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