Introduction to Coiled Flow Inverter (CFI) Photocatalytic Reactor. Many research has shown that a CFI reactor is capable at increasing the yield of the reaction as compared to straight tubular reactor and helical tubular reactor.
Introduction to Coiled Flow Inverter (CFI) Photocatalytic Reactor
1. Synthesis ofAnisaldehyde
in CFI Photocatalytic Reactor
and its CFD Simulation
Asia-Oceania Top University League on Engineering (22 November 15th, 2018)
Tokyo Institute of Technology
Department of Chemical and Science Engineering
ONG, Hui Yang (M1) 1
2. Organic Substance
2
[1] D. Heggo, et al., Process Intensication of Photocatalytic p-Anisaldehyde Synthesis by Using Mini Batch Reactor and UV-LED, Journal of Chem.
Eng. of Japan, 49, 130-135 (2016)
โข One of the intermediates used in pharmaceutical and
perfumery industries.
What is anisaldehyde?
Drawbacks of the conventional reaction:
๏ถHigh temperature
๏ถToxic oxidizer / costly synthesized catalysts
Photocatalytic oxidation with TiO2
3. Photochemical Transformation
3
[1] Jagan M. R. Narayanam, Corey R. J. Stephenson, Visible light photoredox catalysis: applications in organic synthesis, Chem. Soc. Rev., 40,
102-113 (2011)
Substitute of
thermochemical and
electrochemical
activation
Traceless and โgreenโ
Advantages
Complex reactor design
and modeling
Difficult โscale-upโ
strategy
Challenges
Certain light source is
only compatible with
certain solvent
Microreactor
technology
4. Microreactor Technology
4
Smaller
Size
Up to few
meters
height and
width
Larger
Specific
surface area
100~500
m2/m3
Petrochemical,
biomass conversion
and acid producing
etc.
Conventional Batch Process Reactor
Low mixing
efficiency
Low penetration
of light source
Higher safety
hazards
Less than
1mm in
diameter
10,000 ~
50,000 m2/m3
Continuous Flow Microreactor
Medicine and fine
chemicals etc.
Enhanced mass and heat
transfer
Radiation homogeneity
Ease of numbering-up and
reduced safety hazards
Efficient
Simple
Safe
5. Process Intensification
5
[1] D. Heggo, et al., Process Intensification of Photocatalytic p-Anisaldehyde Synthesis by Using Mini Batch Reactor and UV-LED, Journal of Chem.
Eng. of Japan, 49, 130-135 (2016)
Important factors in anisaldehyde photocatalytic reactor design:
Large catalyst
surface area
Sufficient UV
light intensity
Absorption of
oxygen
โข Using smaller tubular
reactor
Shorter light pass enables light
penetration through the whole
reactor volume
โข Suspension contains
fine solid particles of
photocatalyst (slurry
containing TiO2)
โข TiO2: Surface area of
50m2/g (BET)
โข High oxygen flow rate
โข Internal circulation
within the slug flow
caused by shear
forces enhance
absorption
6. CFI Reactor
6[1] Nikhil Kateja, Anurag Rathore, A Coiled Flow Inversion Reactor Enables Continuous Processing, BioPharm International, 29, 32-35 (2016)
A:
Straight helical
reactor
B:
Coiled flow
inversion (CFI)
reactor with 90
degree bend
Why use helical
reactor instead of
normal tubular
reactor?
Secondary flow patterns (Dean vortices)
are formed due to centrifugal force
โ Enhances radial mixing
โ Narrows residence time distribution (RTD)
Equidistant right angle bends change the
direction of the centrifugal force
โ New Dean vortices formed further
enhances mixing
โ Further narrows RTD
Why use B instead of A?
7. 1st Centrifugal
force
7
[1] Subhashini Vashisth, K.D.P. Nigam, Experimental investigation of void fraction and flow patterns in coiled flow inverter, Chemical Engineering
and Processing, 47, 1281-1291 (2008)
A: Straight helical reactor
Inner
wall
Outer
wall
Centrifugal
force
B: CFI reactor with 90ยฐ bend
Inner wall
Outer wall 2nd Centrifugal
force
Sudden
shift in the
direction of
centrifugal
force
CFI Reactor
Internal circulation as a result of
shear forces within a tubular reactor
Flow direction
8. Research Objective
8
To study how a secondary Dean vortex caused by
changing of direction of the centrifugal force between
two helical structure with 90 degree bend in CFI reactor
can enhance the circulation flow
To obtain a higher generation rate of synthesis of
anisaldehyde
1) CFD Simulation 2) Experiment
9. 9
Various Reactor Designs
Mini Batch Reactor
1cmร1cm ร4.5cm quartz cell
UV LED Lamp
1
Straight Microtube Reactor
1m length and 1mm diameter of PTFE tube
Black light lamp
Flow direction
2
Straight Helical Reactor
10m length and 1mm diameter of
PTFE tube
3
CFI Reactor
10m length and 1mm
diameter of PTFE tube
4
10. Diffusion of Oxygen
10
[1] D. Heggo, et al., Process Intensification of Photocatalytic p-Anisaldehyde Synthesis by Using Mini Batch Reactor and UV-LED, Journal of Chem.
Eng. of Japan, 49, 130-135 (2016)
Important factors in anisaldehyde photocatalytic reactor design:
Large catalyst
surface area
Sufficient UV
light intensity
Absorption
of oxygen
โข Using smaller tubular
reactor
Shorter light pass enables light
penetration through the whole
reactor volume
โข Suspension contains
fine solid particles of
photocatalyst (slurry
containing TiO2)
โข TiO2: Surface area of
50m2/g (BET)
โข High oxygen flow rate
โข Internal circulation
within the slug flow
caused by shear
forces enhance
absorption
12. Volumetric Mass-Transfer Coefficient
๐ ๐
๐ ๐
=
๐ซ ๐ณ
๐ณ
๐ (๐ช ๐บ โ ๐ช)
Symbols
Cs : saturated concentration of O2 in liquid phase [mol/m3]
C : concentration of dissolved O2 in liquid phase [mol/m3]
L : thickness of liquid film [m]
A : gas-liquid contact area [m2]
DL : molecular diffusion coefficient [m2/s]
dm / dt : oxygen transfer rate [mol/s]
V : slug volume [m3]
a : A / V
kLa : volumetric mass-transfer coefficient [1/s]
๐ ๐
๐ ๐
= ๐ ๐ณ ๐ (๐ช ๐บ โ ๐ช)
๐ ๐ช
๐ ๐
=
๐ ๐
๐ ๐
โ
๐
๐ฝ
= ๐ ๐ณ
๐จ
๐ฝ
(๐ช ๐บ โ ๐ช)
๐ ๐ช
๐ ๐
= ๐ ๐ณ ๐ (๐ช ๐บ โ ๐ช)
๐ ๐ณ ๐ =
๐๐(
๐ช ๐บ โ ๐ช ๐
๐ช ๐บ โ ๐ช ๐
)
๐ ๐ โ ๐ ๐
Liquid
slug
Gas
phase
Gas
phase
Diffusion of Oxygen Diffusion of Oxygen
Important indicator for
โข Evaluation of reactor design
โข Process optimization
13. 0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0 2 4 6 8 10
kLa[1/s]
ConcentrationofOxygen[mol/dm3]
Time [s]
Without Addition of Force (0.1m/s, 1mm)
Concentration of Oxygen
kLa
Relationship of Concentration of Oxygen and kLa
As time passes by,
mass transfer of
oxygen into the liquid
slug increases.
As time passes by,
the kLa value
decreases to a
certain value and
remain unchanged.
14. Simulation Specification
CFI
x momentum
y momentum
Momentum
equation
๐
๐๐
๐๐ + ๐ โ ๐๐๐ = โ๐๐ + ๐ โ ๐ + ๐๐ + ๐ญ
Straight microtube
x
y
A
x momentum
Straight helical
B C
B C ๐ญ =
๐(๐ ๐ + ๐ ๐๐๐๐ ) ๐
๐น + ๐
A ๐ญ = ๐
density
stress
tensorstatic pressure
external
body
force
15. Time Step Size and Mesh Independence
Time step size: 0.01 [s]
No. of element:
129300
Increased accuracy
Increased simulation cost
Increased accuracy
Increased simulation cost
16. Length and Speed of Slug
โข Shorter slug can increase mass transfer of
oxygen significantly due to its increased
contact area per volume.
โข Higher speed can increase mass transfer of
oxygen due to its increased internal flow
circulation.
0.1
0.15
0.2
0 1 2 3 4 5 6 7 8 9 10
kLa[1/s]
Time [s]
Speed Comparison (With Centrifugal Force)
D=1.81E-6 [kg/ms]
0.12m/s, 5mm
0.10m/s, 5mm
0.08m/s, 5mm
17. Diffusion Coefficients
0
0.05
0.1
0.15
0.2
0.25
0.3
0 1 2 3 4 5 6 7 8 9 10
kLa[1/s]
Time [s]
Comparison Between Different Diffusion Coefficients
(With and Without Centrifugal Force)
with centrifugal force, D=3.11E-06 [kg/ms]
w/o centrifugal force, D=3.11E-06 [kg/ms]
with centrifugal force, D=1.81E-06 [kg/ms]
w/o centrifugal force, D=1.81E-06 [kg/ms]
with centrifugal force, D=4.50E-07 [kg/ms]
w/o centrifugal force, D=4.50E-07 [kg/ms]
โข Higher diffusion
coefficient induces
higher mass transfer of
oxygen into the liquid slug.
โข Different diffusion
coefficients have
different impacts on the
effect of centrifugal
forces.
โข The lower the diffusion
coefficient, the less the
significance of adding
centrifugal force.
18. My Next Move
18
To conduct a detailed CFI simulation
โข I have already started the simulation, but since the result
did not fulfil my expectation, I would like to check it again
with finer meshing and perhaps smaller time step size.
โข The present simulation took more than 3 hours to
complete. I would move the simulation into Tsubame 3.0.
I would love to hear any advice regarding how to incorporate
UDF into Fluent in Tsubame 3.0.
19. My Next Move
19
To conduct a detailed CFI simulation
โข I have already started the simulation, but since the result
did not fulfil my expectation, I would like to check it again
with finer meshing and perhaps smaller time step size.
โข The present simulation took more than 3 hours to
complete. I would move the simulation into Tsubame 3.0.
I would love to hear any advice regarding how to incorporate
UDF into Fluent in Tsubame 3.0.
Editor's Notes
Anisaldehyde (4-Methoxybenzaldehyde) is one of the intermediates in pharmaceutical and perfumery industries.
It is a clear liquid with strong aroma, provides sweet, flora and aniseed odor.
Synthetic routes to anisaldehyde usually involve oxidation of methoxytoluene in the presence of catalyst at high temperatures.
The use of the catalyst was also not wise in terms of costs and environmental health.
Photochemical transformations utilize photons to provide sufficient energy to overcome activation barriers.
Light activation of organic molecules facilitates remarkable reaction pathways that are otherwise difficult to reach by thermochemical or electrochemical activation.
Consequently, synthetic routes can be significantly shortened making photochemistry popular in a variety of applications.
Another reason for its popularity can be found in the fact that light can be considered as a traceless and โgreenโ reagent.
In the absence of any reaction, the starting material can often be recuperated since the molecule can return to its ground state by releasing the energy by radiative or nonradiative pathways.
However, process complexity associated with photochemical processes leads to significant challenges for the proper reactor design and its modeling.
Compatibility aspects of the reactor with the light sources and solvents should be taken into consideration when designing an efficient photochemical process.
The scale-up strategy is one of the major challenges for the transfer of photochemical processes from laboratory to production scale.
These limitations, which are associated with photochemical transformations in batch reactors, might be overcome by utilizing microreactor technology.
Conventional batch process reactor is usually a large-scale production equipment that requires a huge building and is suitable for large volume production.
Continuous Flow Microreactor, is mainly used in the fields of medicine and fine chemicals.
Microreactor technology allows a high degree of control over photochemical transformations compared with conventional batch processing, for example, continuous-flow operation, large specific surface area, enhanced heat, and mass-transfer rates, reduced safety hazards and the ease of increasing throughput by numbering-up etc.
Furthermore, extremely small characteristic dimensions of microreactors ensure excellent light irradiation of the entire reaction medium and thus increased radiation homogeneity, resulting in higher reaction selectivity, shorter reaction times and lower catalyst loadings.
Here are some important factors in anisaldehyde photocatalytic reactor design.
Suspension contains fine solid particles of photocatalyst Titanium dioxide which have a surface area of 50m2/g.
Sufficient light intensity which is also important can be achieved by using smaller tubular reactor as shorter light pass enables light penetration through the whole reactor volume.
Higher absorption of oxygen can be achieved with high oxygen flow rate and internal circulation within the slug flow caused by shear forces also enhance absorption.
You might wonder why it is better to use helical reactor instead of normal tubular reactor.
This is because helical structure induces secondary flow pattern (Dean vortices) due to centrifugal force and hence enhances radial mixing.
It narrows residence time distribution (RTD) even under laminar flow.
On the other hand, CFI is a combination of helical structures incorporated at equidistant right angle.
When the equidistant right angle bends change the direction of the centrifugal force, the sudden shift in the direction of centrifugal force causes new Dean vortices to form, as shown as the blue arrows. As a result, it further enhances radial mixing, and further increase rate of reaction.
Dissolved oxygen (DO) is often the limiting substrate in fermentation and cell-culture systems. For bacteria and yeast cultures, the critical oxygen concentration is usually 10โ50% of air saturation. Above that critical level, the oxygen concentration
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no longer limits growth. For optimum growth, it is therefore important to maintain DO levels above the critical value by sparging (bubbling gas through) the bioreactor with air or pure oxygen. Of course, to be effective, the mass transfer rate of oxygen to the liquid broth must equal or exceed the rate at which growing cells take up that oxygen.
The computational toolโs accurate prediction of the fluent may be difficult due to the difficulty of obtaining the accurate values for lamp efficiency, the quartz sleeve transmittance, and the reactor wall reflection rate. But those parameter uncertainties have much less influence on the radiant exposure (fluence). The distribution of fluence is highly determined by the flow pattern inside the tube and by the lamp numbers and location inside the reactor.
The geometry of liquid slug can be assumed as a normal cylindrical model.
Measurements of kLa provide important information about a bioprocess or bioreactor. These determinations ensure that processing conditions are such that an adequate supply of oxygen is available for oxidation. The kLa value can also be used to optimize control variables over the lifecycle of a bioprocess. Such optimization would be based on the oxygen demand at various points in the process and growth phase of the biological. Criteria for optimization may be product yield, power consumption, or processing time. Measurements of kLa are made when evaluating new reactor designs, new gas sparging equipment, and/or operating conditions. The goal in each case is to confirm that reactor conditions can support a system being processed at each point in its lifecycle. Measuring kLa is also critical during process optimization. In scale-up and manufacturing situations, fine-tuning bioreactor performance assumes greater significance. Measuring kLa is key to controlling oxygenation at the optimal rate (1).
The computational toolโs accurate prediction of the fluent may be difficult due to the difficulty of obtaining the accurate values for lamp efficiency, the quartz sleeve transmittance, and the reactor wall reflection rate. But those parameter uncertainties have much less influence on the radiant exposure (fluence). The distribution of fluence is highly determined by the flow pattern inside the tube and by the lamp numbers and location inside the reactor.
The computational toolโs accurate prediction of the fluent may be difficult due to the difficulty of obtaining the accurate values for lamp efficiency, the quartz sleeve transmittance, and the reactor wall reflection rate. But those parameter uncertainties have much less influence on the radiant exposure (fluence). The distribution of fluence is highly determined by the flow pattern inside the tube and by the lamp numbers and location inside the reactor.
The computational toolโs accurate prediction of the fluent may be difficult due to the difficulty of obtaining the accurate values for lamp efficiency, the quartz sleeve transmittance, and the reactor wall reflection rate. But those parameter uncertainties have much less influence on the radiant exposure (fluence). The distribution of fluence is highly determined by the flow pattern inside the tube and by the lamp numbers and location inside the reactor.
The computational toolโs accurate prediction of the fluent may be difficult due to the difficulty of obtaining the accurate values for lamp efficiency, the quartz sleeve transmittance, and the reactor wall reflection rate. But those parameter uncertainties have much less influence on the radiant exposure (fluence). The distribution of fluence is highly determined by the flow pattern inside the tube and by the lamp numbers and location inside the reactor.
The computational toolโs accurate prediction of the fluent may be difficult due to the difficulty of obtaining the accurate values for lamp efficiency, the quartz sleeve transmittance, and the reactor wall reflection rate. But those parameter uncertainties have much less influence on the radiant exposure (fluence). The distribution of fluence is highly determined by the flow pattern inside the tube and by the lamp numbers and location inside the reactor.
Depleting fossil fuel and greenhouse effect have driven the people to find a new way to make use of lignocellulosic biomass as a source for generating energy and producing useful chemical substances such as furfural.
Depleting fossil fuel and greenhouse effect have driven the people to find a new way to make use of lignocellulosic biomass as a source for generating energy and producing useful chemical substances such as furfural.
![Organic Substance
2
[1] D. Heggo, et al., Process Intensication of Photocatalytic p-Anisaldehyde Synthesis by Using Mini Batch Reactor and UV-LED, Journal of Chem.
Eng. of Japan, 49, 130-135 (2016)
โข One of the intermediates used in pharmaceutical and
perfumery industries.
What is anisaldehyde?
Drawbacks of the conventional reaction:
๏ถHigh temperature
๏ถToxic oxidizer / costly synthesized catalysts
Photocatalytic oxidation with TiO2](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)