Evaluation and performance comparison of micro-flow reactors

for visible light photo-catalysis

Master Thesis – Sylvain GROS

Supervisors: Prof. Albert Renken Dr. Thomas H. RehmDr. Patrick Löb

Mainz, 23rd of September 2015

• Introduction

• Theoretical Part

• Results

• Conclusions

Outline

2

• Study of the photosensitised oxygenation of1,5-dihydroxynaphtalene (DHN) to Juglonewith 2 dyes.

• Performance comparison of falling-film microreactors (FFMR) and the Taylor-flowcapillary reactor developped by Fraunhofer ICT-IMM.

IntroductionGoals of the thesis

3

IntroductionPhotocatalysis

Indirect reaction via a sensitizer

3𝑂2

1𝑂2∗

Collision+Quenching

hν

1𝑆

1𝑆∗E

3𝑆∗

Intersystem crossing (ISC)

+ R → 𝑃

𝑆𝐿𝑖𝑔ℎ𝑡

𝑆∗→𝑂2 1𝑂2→

𝑅𝑃

Karl-Heinz Pfoertner, Thomas Oppenländer, éds. (2000) Photochemistry. Ullmann's Encyclopedia of Industrial Chemistry.

Weinheim, Germany

4

Photocatalytic cycle

IntroductionMicro-flow reactors for gas-liquid photochemical reactions

𝑰 = 𝑰𝟎 ∙ 𝒆𝒙𝒑(−𝜺𝝀 ∙ 𝑪 ∙ 𝐬 ∙ 𝐥𝐧 𝟏𝟎)

Typical micro-channels diameter: 10 - 1000 µm vs Typical batch immersion well diameter: 20 - 40 mm

Photochemical Reactors LTD, Model 3309

0

50

100

150

200

250

300

350

400

0 200 400 600 800 1000

Inte

nsi

ty [

W m

-2]

Path length, s [µm]

TcPP-violet

RB-green

With C = 0.5 mM, Pel = 2.2 W, A = 15.7 cm2

5

Reaction plate of the falling-film microreactorDevelopped by Fraunhofer ICT-IMM

More efficient and uniform irradiation profile.

Controlled irradiation time with Plug-Flow Reactor (PFR) types.

Improved gas-liquid mass transfer with interfacial area (a) increased by 10 - 100.

? Productivity

IntroductionMicro-flow reactors for gas-liquid photochemical reactions

Knowles, Jonathan P.; Elliott, Luke D.; Booker-Milburn, Kevin I. (2012) Flow photochemistry: Old light through new windows. In : Beilstein

Journal of Organic Chemistry, vol. 8, p. 2025–2052.6

Theoretical Part

1. Photo-excitation and ISC:

𝐒𝒉𝝂 𝟏𝑺∗

𝑰𝑺𝑪 𝟑𝑺∗

2. Oxygen mass transfer in 2-propanol:

𝑶𝟐(𝑮) → 𝑶𝟐(𝑳)

3. Quenching of sensitizer triplet state: 𝟑𝑺∗ + 𝟑𝑶𝟐 →

𝟏𝑶𝟐

4. Chemical reaction:

𝟏𝑶𝟐 +𝐌→𝒌𝒓𝑴𝑶𝟐

5. Quenching by solvent:

𝟏𝑶𝟐 + 𝒔𝒐𝒍𝒗𝒆𝒏𝒕𝒌𝒅 𝟑𝑶𝟐

6. Physical quenching:

𝟏𝑶𝟐 +𝑴→𝒌𝒒 𝟑𝑶𝟐 +𝑴

7. Phosphorescence:

𝟏𝑶𝟐

𝒌𝒑 𝟑𝑶𝟐 + 𝒉𝝂

Rose Bengal (RB) & meso-tetra-carboxy-phenylporphyrin (TcPP)

1𝑂2 lifetime: corresponds to 1

𝑘𝑑= 22 ns

Theoretical PartProposed mechanisms for the synthesis of Juglone

S. Croux, Kinetic Parameters of the Reactivity of Dihydroxynaphthalenes with Singlet Oxygen, New

Journal of Chemistry 14 (1990) 161–167.

F. Wilkinson, W.P. Helman, A.B. Ross, Rate Constants for the Decay and Reactions of the Lowest Electronically Excited

Singlet State of Molecular Oxygen in Solution, J. Phys. Chem. Ref. Data 24 (1995) 663. 8

Theoretical PartAbsorption spectra

9

Plate

Channel

width (W)

[mm]

Channel

height (H)

[mm]

Number of

channels

(N)

Illuminated length

(Lill)

[mm]

Illuminated surface area

(window) (Aill)

[cm2]

(B) FFMR-S_plate 600 0.6 0.2 32 54 15.7

(C) FFMR-S_plate 1200 1.2 0.4 16 54 15.7

(E) FFMR-L 1.2 0.4 50 212 218.3x 3.1 x 3.9 x 14

A B C

D E C

Theoretical PartReactors - Falling-film microreactor (FFMR)

A: FFMR-Standard D: FFMR-Large

10

0

0.2

0.4

0.6

0.8

1

350 450 550 650 750

Re

lati

ve r

adia

nt

po

we

r [-

]

Wavelength [nm]

Violet (410 nm)

Royal blue (455 nm)

Green (520 nm)

Cold White

Theoretical PartReactors - Falling-film microreactor (FFMR): Light sources

11

At 350 mA: 2.2 W At 350 mA: 11 W

Theoretical PartReactors – Taylor-flow capillary reactor

Fluorinated ethylene propylene tubing:Length (L): 27.96 mDiameter (d): 0.8 mmReactor volume (VR): 14 mLIlluminated surface area: 475 cm2

T-mixer junction

Dispersed-phase flow: Light sources:

Royal blue (455 nm) and green (520 nm)

12

Gas and liquid slugs2-propanol: 0.6 mL min-1

Air: 0.48 mL min-1

2-propanol: 𝑉𝐿= 0.40 mL min-1

Air: 𝑉𝐺= 0.31 mL min-1

Taylor-flow capillary reactor- Example with Air

13

Supply power

Optical power

Effective power

Intensity at the surface

Mean intensity

Mean absorbed

power

Flow of photons

absorbed

Wavelengths dependency

Theoretical PartQuantification of absorbed photons: MethodM. Roger, J. Villermaux, Modelling of light absorption in photoreactors Part I. General formulation based on the laws of photometry,

The Chemical Engineering Journal 17 (1979) 219–226.

14

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

400 450 500 550 600 650 700 750

rela

tive

rad

ian

t p

ow

er

[-]

Wavelength [nm]

Cold-white LED

Results

Study of the reaction in the FFMRs

0

1E-09

2E-09

3E-09

4E-09

5E-09

6E-09

7E-09

380 580 780

[mo

l s-1

]

Wavelength [nm]

Absorbed photon flow

ResultsFFMR-S_1200: Influence of light source for Rose Bengal (0.5 mM)

10 mM DHN in 2-propanol; 20°C, 101 kPa, 𝑉𝐿= 0.16 mL min-1; O2, 𝑉𝐺= 100 mL min-1

LED array

(350 mA)

Electrical-

power

[W]

Photons at the structured

illuminated surface per

residence time

[µmol]

Absorbed photons by

the solution per

residence time

[µmol]

Quantum

yield of the

reaction, Φ

[-]

Violet 2.3 24.8 0.2 0.11

Royal blue 2.2 25.8 0.3 0.18

Green 2.2 31.2 4.9 0.03

Cold white 2.2 35.1 3.6 0.06

X = Conversion of DHN

S = Selectivity to Juglone

Y = Yield of Juglone with respect to DHN

Φ = Quantum yield of the reaction = moles of Juglone produced

moles of photons absorbed

16

0

1E-08

2E-08

3E-08

4E-08

5E-08

380 480 580 680

[mo

l s-1

]

Wavelength [nm]

Absorbed photon flow

Cold White

Green

Violet

Royal Blue

ResultsFFMR-S_1200: Influence of light source for TcPP (0.5 mM)

LED array

(350 mA)

Electrical-

power

[W]

Photons at the structured

illuminated surface per

residence time (19.3 s)

[µmol]

Absorbed photons by

the solution per

residence time

[µmol]

Quantum

yield of the

reaction

[-]

Violet 2.3 24.8 15.9 0.02

Royal blue 2.2 25.8 1.5 0.05

Green 2.2 31.2 2.5 0.04

Cold white 2.2 35.1 2.1 0.06

X = Conversion of DHN

S = Selectivity to Juglone

Y = Yield of Juglone with respect to DHN

Φ = Quantum yield of the reaction = moles of Juglone produced

moles of photons absorbed

17

10 mM DHN in 2-propanol; 20°C, 101 kPa, 𝑉𝐿= 0.16 mL min-1; O2, 𝑉𝐺= 100 mL min-1

LEDs

Electrical

-power

[W]

Photons at the structured

illuminated surface per residence

time (19.3 s)

[µmol]

Absorbed photons

per residence time

(19.3 s)

[µmol]

Quantum yield

of the reaction

[-]

Green

1.1 14.8 2.3 0.05

2.2 31.2 4.9 0.03

3.6 49.9 7.8 0.02

ResultsFFMR-S_1200: Influence of photon flux (0.5 mM Rose Bengal)

X = Conversion of DHN

S = Selectivity to Juglone

Y = Yield of Juglone with respect to DHN

Φ = Quantum yield of the reaction = moles of Juglone produced

moles of photons absorbed

18

10 mM DHN in 2-propanol; 20°C, 101 kPa, 𝑉𝐿= 0.16 mL min-1; O2, 𝑉𝐺= 100 mL min-1

ResultsFFMR-L: Selectivity versus conversion

10 mM DHN, 0.5 mM Dye in 2-propanol; 20 °C, 101 kPa; 𝑉𝐺= 100 mL min-1

Higher selectivity with oxygenHighest selectivity with TcPP-violetRB: green LED more selective than cold white

19

Results

Taylor-flow capillary reactor

ResultsCapillary reactor: Conversion and selectivity as function of residence time with air and pure oxygen

10 mM DHN, 0.5 mM Rose Bengal in 2-propanol illuminated by green LEDs (350 mA)

21

Results

Performance comparison

0.88

0.05

0.26

0.10 0.070.04

0.45

0.03

0.89

0.04 0.03

0.19

0.03

0.22

1.13

0.02

0.8

0.06

0.61

0.01

0.17

0.36

0.050.06

0

0.2

0.4

0.6

0.8

1

1.2

S[-]

φ[-]

Productivity[mmol/h ]

Space timeyield

[mol/(s m^3)]

Energyefficiency

[10^-7 mol/J]

Energyefficency

/Illuminatedsurface area[10^-5 mol/(J

m^2)]

Absorbedpower density

[W/m^3]

Absorptionpower

efficiency[-]

RB-green LED (350 mA), O2, X = 0.67

FFMR-L FFMR-S_600 Capillary

ResultsPerformance comparison of the three reactors

23

Productivity: molar quantity of Juglone produced per unit of timeSpace time yield: productivity / liquid volumeEnergy efficiency: productivity / electrical-powerPower absorption efficiciency: absorbed power / electrical-power

Investigation of DHN photo-oxygenation in FFMR-S & FFMR-L:

• Higher light absorption → higher product yield.

appropriate LED (e.g. violet with TcPP), or by increasing the LED power.

• Yields improved with pure oxygen.

Comparison of FFMR-S_600, FFMR-L & Capillary:

• Capillary reactor → highest productivity and energy efficiencies.

• FFMR-S successfully scaled-up with FFMR-L (productivity x 9).

• Space time yields: 1 order of magnitude higher with FFMRs vs capillary.

Conclusions

24

Further improvements:

• Increase the pressure → increase oxygen saturation concentration.

→ Working at higher concentrations for industrial purposes.

• Prof. Albert Renken

• Dr. Patrick Löb

• Dr. Thomas H. Rehm

• Dorothee Reinhard

• Christian Hofmann

• Fraunhofer ICT-IMM

Acknowledgements

25

QUESTIONS

26