Spinning Disc Reactor: Basic Principles and Applications

Dr Kamelia BoodhooSchool of Chemical Engineering & Advanced MaterialsNewcastle UniversityUnited Kingdom

Outline

Operating Principles of SDRCharacteristic features of thin film flow

Exploiting SDR characteristics: case studies of SDR application

Spinning Disc Reactors

200 mm diam. smooth stainless steel disc

Feed pipes

Water cooled jacket

100 mm disc surface

Characteristics features of SDR

Rotation of disc surface creates high centrifugal fields which promote thin film flow

Centrifugal acceleration (=ω2r) as high as 1000gFilm thickness typically 50-500 μm

Films are highly sheared and have numerous unstable surface ripples

Various disc configurations may be used for enhanced performance

SmoothMetal sprayedGrooved

liquid feed

Liquid film

Disc surface

ω

Stationary feed pipe

Centrifugal force

Thin film flow on a spinning disc

Water like liquid on disc rotating at 400 rpm

Wave formation in water-like fluid on rotating disc

(Source: Aoune & Ramshaw, Int. J. Heat & Mass Transfer, 42, 2543-2556 (1999))

Mass flowrate of liquid= 0.013-0.019 kg/s

ω=10 s-1

Spiral waves

ω=20 s-1

Irregular surface ripples

ω=40 s-1

ω=60 s-1

whereQ: feed flowrateν: kinematic viscosity (=η/ρ)ω: rotational speed (= 2πN/60)r: radial distance across disc surface

Parameters of interest in SDR based on centrifugal model

δπ

νω

= 3

2 Q

r2 2⎛⎝⎜

⎞⎠⎟

13

Film thickness:

( )t = 81

Q r rres

2

2 2

13

o iπ νω16

43

43

⎛⎝⎜

⎞⎠⎟ −Residence time:

31

2

42

0. 18

5.12

v⎟⎟⎠

⎞⎜⎜⎝

⎛===

= πνω

νδωγ rQr

dzd

z

rave&Shear rate:

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 200 400 600 800 1000 1200

Disc rotational speed (rpm)

Mea

n re

side

nce

time

in

SDR

, tre

s (s

econ

ds)

0

25

50

75

100

125

150

175

200

225

Mea

n fil

m th

ickn

ess

(m

icro

ns)

5 ml/s

5 ml/s

1 ml/s

Disc diameter: 0.2 mData based on viscosity and density of n-butyl acrylate at 40oC

Mean residence time and film thickness profiles in SDR

Thin film flow regime in SDR

Reynolds number:

Various flow regimes observed:Re<16: smooth laminar flow16≤ Re< 40: Small amplitude waves40≤ Re< 80: Sinusoidal and regular wavesRe>80: Random surface waves

Waves greatly influenced by disc speed

DQ

πν4Re =

Heat transfer characteristics of thin film

Overall heat transfer coefficient U as high as 4 kW/m2K can be achieved using this system under optimised conditions

Coolant IN

Coolant OUTHollow drive shaft

Internal baffled plate

Process liquid

Disc surface

Internal cooling/heating system in SDR

0

2

4

6

8

10

12

14

16

0 200 400 600 800 1000

Rotational Speed (RPM)

Ave

rage

Hea

t Tra

nsfe

r Coe

ff. (k

W/m

2 K

)

Normal Groove Disc

Metal Sprayed Disc

Smooth Disc

Convective heat transfer characteristics of films on rotating disc surfaces

Effect of rotational speed on local mass transfer coefficients in SDR film

water flowrate: 30 cm3/s smooth disc

(Source: Aoune & Ramshaw, Int. J. Heat & Mass Transfer, 42, 2543-2556 (1999))

Summary of characteristics of thin film flow in SDR

Vigorous mixing characteristics at film surface (waves) and within film (high shear)High heat and mass transfer ratesShort and easily controllable residence times

Extremely short path lengths for efficient UV penetration in photo-reactions

These characteristics make the SDR particularly suitable for reactions that are:

• Highly exothermic• Inherently fast

Reactions/processes for potential SDR application (1)

Inherently fast, highly exothermic reactionsAcid-base neutralisationSulphonationPolymerisations

• Free-radical polymerisations• Chemical initiated• UV-initiated (photopolymerisation)

• Cationic polymerisation• Step-growth polymerisations

• Polyesterifications

Reactions requiring rapid mixingCrystallisations for narrow distribution of particle sizeOrganic, competitive reactions for high selectivity or high yield of desired product

Processes involving heat sensitive materialsPolymer processing at high temperatures Food processing

• Short residence times in SDR gives minimal risk of degradation of product

Reactions/processes for potential SDR application (2)

Case study 1

SDR applications to mixing/mass transfer limited processes in pharmaceutical industry

Rate limiting step: mass transfer across immiscible phases

Batch Process SDR process(4500 rpm)

Conversion 100% 90%Reaction time 1 hr <1 sReaction temp. 0oC 20oCImpurity level 1.5% 0.1%Reactor volume 100 (arbitrary units) 1Production capacity 8 tonnes/yr 8 tonnes/yr

Source: Oxley, P. et al. “Evaluation of spinning disc reactor technology for the manufacture of pharmaceuticals”, Ind. Eng. Chem. Res., 39, 2175-2182 (2000)

Example 1: Phase transfer catalysed reaction- Darzen process

Crystallisation in SDR

Rapid micromixing in the SDR film at high supersaturation

Homogeneous nucleation

Smaller crystal sizes with tighter distribution

Rate limiting step: mixing (hence mass transfer)

Source: Oxley, P. et al. “Evaluation of spinning disc reactor technology for the manufacture of pharmaceuticals”, Ind. Eng. Chem. Res., 39, 2175-2182 (2000)

Example 2: Recrystallisation of an API

Micromixing: SDR vs STR

0.01

0.10

1.00

10.00

100.00

0 1 10 100 1000 10000

Specific Power Dissipation(w/kg)

tm(m

s)

(SDR)Q=1ml/sec

(SDR)Q=3mil/sec

(SDR) Q=5mil/sec

(STR) Injection Point close to impeller

(STR) injection Point away from impeller

tm = 2(ν/ε)0.5 arcsinh (0.05ν/D )

( SDR - Molecular Diffusion Model )

tm = 17.2(ν /ε)½

( STR – Baldyga and Bourne Model)

Case study 2

Application of SDR to organic catalytic reaction using immobilised catalyst

ACatalyst

BA – α-pinene oxide, B – campholenic aldehyde

Process chemistry

Homogeneous catalyst used in current industrial process

Low selectivity due to many side reactions

OH

trans-Pinocarveol

trans-Sobrerol

OH

OH

OH

trans-Carveol

p-Cymene

O

Pinol

O

α-pinene oxide

O

campholenic aldehyde(2,2,3-trimethyl-3-cyclopentenacetaldehyde)

H +H2O/H +

- H2O- 2 H2O

N(Et)2

via cis-Sobrerol

Desired product

8

ReactantCatalyst

Catalyst separation

Product

Current industrial process

Batch process where processing time is typically very high (order of hours)

Need to separate catalyst from product using large amounts of solvent in downstream separation process

Environmental considerations of waste disposal

Objectives of studyEasier catalyst separation

Development of heterogeneous catalysts Immobilisation on reactor surfaceRe-usable

Improve selectivity towards campholenicaldehyde using heterogeneous catalysis and intensified continuous processing

SDR processing:Continuous processProcessing time of the order of secondsCatalyst fixed to rotating surface

Reactant

ProductCatalyst

STR data for benchmarking

0

20

40

60

80

100

0 5 10 15 20 25 30

Reaction Time (min)

Con

vers

ion

(%)

0

20

40

60

80

100

Sele

ctiv

ity (%

)

ConditionsT = 850C

Catalyst: 0.05 mmolg-1 Zn(OTf)2/SiO2

B40% Selectivity

A

Effect of SDR residence time on conversion

70

75

80

85

90

95

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Residence Time (s)

Con

vers

ion

(%)

Flow rate = 4 cm /s Flow rate = 5 cm /s Flow rate = 6 cm /s

ConditionsDisc Temperature = 850C

Catalyst: 0.05mmolg-1 Zn-triflate/SiO2

333

M. Vicevic, K.V.K. Boodhoo and K. Scott, Catalytic Isomerisation of alpha-pinene oxide to campholenicaldehyde using silica supported zinc triflate catalysts: II. Performance of immobilised catalysts in a continuous Spinning Disc Reactor. Chem. Eng. J. 133(1-3), 43-57 (2007).

Effect of SDR residence time on selectivity

0

20

40

60

80

100

0 0.2 0.4 0.6 0.8 1 1.2

Residence Time (s)

Sele

ctiv

ity (%

)

Flow rate = 4 cm /s Flow rate = 5 cm /s Flow rate = 6 cm /s

ConditionsDisc Temperature = 850C

Catalyst: 0.05mmolg-1 Zn-triflate/SiO2

333

M. Vicevic, K.V.K. Boodhoo and K. Scott, Catalytic Isomerisation of alpha-pinene oxide to campholenicaldehyde using silica supported zinc triflate catalysts: II. Performance of immobilised catalysts in a continuous Spinning Disc Reactor. Chem. Eng. J. 133(1-3), 43-57 (2007).

Summary of resultsReaction completed within 0.5 s in one SDR pass compared to a timescale of at least 5 min in the batch process

Improved mixing and mass transfer rates in the thin film formed on the rotating disc surface allows the catalytic reaction to proceed at its inherent rate in SDRReaction slower in batch due to mixing limitations

High selectivity in the SDR is encouraged by the short and controllable residence times achieved on the disc

High catalyst activity can be maintained in SDR over long periods of time as shown by re-use studies

Demonstrated benefits of SDRFaster reaction rates

Reduced processing timeImproved product quality

Better control of molecular weight properties in polymerisationsTighter particle size distribution in crystallisations

Improved selectivityLess unwanted by-productsGreener/cleaner technology since reduced downstream processing required

Improved intrinsic safetyLow volumes of materials processed