CHE 309: Chemical Reaction EngineeringCHE 309: Chemical Reaction Engineering

LectureLecture--22--11

Special Module: Special Module: Fluidized Bed Coating

Contents

Introduction

Principle of fluidized-bed coating

Batch type fluidized-bed coater

Continuous fluidized-bed coater

Industrial application

Conclusions

History of powder coating

The history of coating in the pharmaceutical industry dates back

over 1000 years. The first coating of pills was recorded in the

drug literature of early Islam.

The pills were coated in rotating pans until the 19th century

Fluidized bed coater was invented by Dr. D. Wurster at 1959,

and it is applied in the field of pharmaceutical industry [US

patent 2,799,241].

Fluidized process was considered a revolutionary technique.

- Uniform coatings in short operating time

Fluidized Bed Coating

Bed Particles Solid Objects

Metal Coatings

(Immersed into a

bed of coating

material)

Pharmaceutical

Agricultural

Chemical

Catalytic Reactions

production of Polyolefin

Sustained release coatings

Enteric & Barrier coatings

Cosmetic coatings

Metal Coatings

Solventless

coatings

Surface

treatments

buoyant + frictional force

Fluidization (Gas suspension)

Umf; particles are just suspended in upward flow gas

(Expanded bed)

gravity force

The compressive force between

adjacent particles disappeared

Pressure drop through any

section of bed equals weight of

fluid and particles

2

3

5

7

B

D

Density difference (g/cm3)

Powder classification diagram for fluidization

by air-ambient conditions (from Geldart)

Group A: aeratable , these solids

fluidize easily

Group B: sandlike, these solids

fluidized well with vigorous

bubbling action and bubbles grow

- relative fluidization properties for materials of various particle sized and densities

20 50 100 200 500 1000 2000

0.2

0.5

1

2

CA

Mean particle size (m)

Density difference (g/cm

bubbling action and bubbles grow

large

Group C: generally cohesive and

difficult to fluidize. It easily gives

rise to channeling

Group D: spoutable, or large

dense particles, giving large

exploding bubbles or severe

channeling

Advantages of Fluidized-beds

The smooth, liquidlike of flow of particle allows

continuous automatically controlled operations with

ease of handling

The rapid mixing of solids leads to nearly isothermal

conditionsconditions

It is suited large-scale operation

Heat and mass transfer rate between gas and

particles are high

Disadvantages of Fluidized-beds

In efficient contacting system: especially serious

when high conversion of gaseous reactant is required

Nonuniform residence times of solids in the reactor

Friable solids are pulverized and entrained by gas

Erosion of pipes and vessels from abrasion by

particles can be serious

The movement of particle in the spray zone

for fluidizied bed coating

Fluidized Particle

Partial Coating of Particle

Droplet Coalescence

Atomized Liquid Droplet

Solvent Evaporation

Fluidized Particle Movement through Spray Zone

Atmomizing Nozzle

Liquid spray impinges on the solid bed

material as it move through spray zone

The repeated motion of particles

through the spray zone smooth and uniform coating

Spraying Wetting Solidifying

Coating procedure on the suface of suspened particle

Essential for uniform coating

coating droplets

particle coated particle

Droplet is not wet but bead up the resulting coating may be discontinuous layer of tiny sphere of solute

Use of surfactant or plasticizer improvement of spreading or wetting of liquid on surface of particle

Fluized-bed Coating Processes

Batch type fluidized-bed

1) Top-spray using a conventional fluidized-bed

2) Bottom-spray with a partition

3) Tangential-spray with a rotor 3) Tangential-spray with a rotor

Continuous type fluidized bed

1) Countercurrent contacting type

2) Crosscurrent contacting type

Batch type fluidized-bed process

Rotor spray

Particles move up first inside

of partition, then move down

to the annulus

repeated circulation of

particle uniform coating

The disc height is adjustable

silt width air volume, drying rate, spray rate, expanded

fluidization pattern - spiraling helix

Spray nozzle is located above

the distributor

product container/expansion

chamber

Batch type fluidized-bed process-Top spray

Advantages

Largest batch capacity

Simple set-up

Short time between batches Short time between batches

Disadvantages

Narrow application range

Often minor agglomeration can not be avoided

especially with smaller particles

Fluidization quality is not good with larger

denser particles

Batch type fluidized-bed process-Bottom spray (Wurster type)

Advantages

Best film characteristics - uniform in

distribution due to good mixing; good quality

due to concurrent sprayingdue to concurrent spraying

Widest application range - all film properties-

Moderate batch size

Disadvantages

The process should be tailored to the products

being made (Orifice plates may need to

changed

Batch type fluidized-bed process-Rotor spray

Advantages

Good film characteristics due to minimization

of distance between product and nozzle

Easy to set up and operate Easy to set up and operate

Disadvantages

Mechanical stress on the product

M

PDI

PDI

TIS+

spraying solvent

exhaust air

n~

2 7 8

Basic installation

1 fluid bed unit2 control flaps3 prefilter4 posifilter5 heater6 dosing pump

Schematic diagram of fluidized-bed spray coating system

M

PDIFI

TIS+PDIA+

TIC

PDIA+ FIC

heating medium

drain

H

n~

inlet air

1

2

2

2

234 5

67 vacuum pump8 silencer

Major parts for fluidized-bed coater

Continuous type Fluidized bed Process

- Crosscurrent contacting type -

Continuous type of multi-stage fluidized-bed

Smooth, and liquid like flow characteristics of particles in fluidized-bed allows continuous

automatically controlled operations with ease of handling

Countercurrent contacting type Crosscurrent contacting type

In a single stage of fluidized-bed, a significant of

portion of feed particles stays in a vessel for a very short

time, consequently, a very large reactor is needed to

achieve high conversions.

Multistage for the particle coating, either by

Advantages of multi-stage fluidized-bed

Multistage for the particle coating, either by

countercurrent or crosscurrent flow reduces this by

passing and gives a distribution of residence times

approaching plug flow and size of reactor needed.

Improvement of throughput for multi-stage

fluidized-bed coater

* coating loss 1%

negligent back-mixing

the same residence time

*N=2 Fo =5.6

N=3 Fo =20.8

expansion chamberwith internal filter

Major Parts for Continuous Fluidized bed Process

dischargeshute

inlet air plenum

processing chamber

bottomscreen

inletshute

solid raw

exhaust air

Operating Principle for Continuous Fluidized bed Process

solid rawmaterial

product

liquid rawmaterial

process air

Application - Coating, Granulation, Agglomeration

solid material *binder *coating liquid

AgglomerationCoatingCooling

e.g. suger

Design variables Process variables Formulation variables

Type of equipment Temp. of the Uf Solvent(water/organic)

Type of nozzle Spray rate Coating solution composition

Variables involved in a fluidized-bed coater

Type of distributor Atmoization pressure Particles properties

Diameter of insert Batch size

Distance of insert

above distributorUf (inside/outside)

Height of insert

Coating materials

1) Cellulose derivatives, e.g. methyl cellulose, hydroxyethyl

cellulose, ethyl cellulose

2) Polymethylacrylate copolymer, e.g. Eudragit E, Eudragit series

3) Other polymers, e.g. polyvinyl pyrrolidone, polyvinyl acetate

phthalate, latex, shellac

4) Metal salts4) Metal salts

1) water-based coating

2) solvent based coating

3) hot melts

4) coating emulsions

Due to strict air-pollution control and high cost of solvents, water-based and other solvent free coatings are of increasing interest

Typical capacities of fluidized bed coaters with draft tubes

- bottom spray -

Bed diameter

(mm)

Number of

draft tube

Height of draft tube

(mm)

75

Draft tube diameter

(mm)

150 225 1

Approximate

batch size

(kg)

0.5-2

1300 375

1

150

225 300112

12-20

7-10

3800 750

225

1

225

450 600

1150

225

900 7

200-275

35-55

400-575

Fluidized-bed coating

Industrial applicationIndustrial application

Snack

Protective coating

& taste masking

Lithium ion battery

Fertilizer

Detergent

Enteric coatings

Sustained

Controlled released

coating

Control of site of

drug release

Delay absorption of

drug component by

retarding release of

drug

Purpose of fluidized-bed coating for industrial application

Pharmaceutical industry: masking unpleasant taste; enteric and

stained release coating; improve appearance

Agricultural industry: sustained controlled release fertilizer or

insecticide

Detergent: protect active components from atmospheric Detergent: protect active components from atmospheric

degradation (e.g., sodium percarbonate is used as an active oxygen component in cleaning agents/unstable against moisture /used as a sodium sulphate decahydrate as coating

component)

Food industry: improve taste (sugar coating)

Battery industry: surface modification of active materials of

electrode

Samil Pharm. Co.

Capa. : 120kg/batch

use: drug coating

Fluidized-bed systems

employed for various industry

in Korea

Oriental Fine Chemicals

Capa.: 900kg/batch

use: moisture barrier coatinguse: drug coating

Boehringer Ingelheim Pharm. Co.

Capa. : 120kg/batch

use: powder granulation

Chosun Chemicals

Capa. : 500kg/batch

use: sustained release coating

Dae-woong Phar. Co.

Capa.: 120kg/batch

use: taste masking

use: moisture barrier coating

Example I- Electrochemical application

LiCoO2~5 m

Graphite6~10 m

LiMOx or C

O

Mn

Li

c

a b

LiMn2O4 Unit Cell

O

Mn

Li

c

a b

c

a b

LiMn2O4 Unit Cell

LiMn2O48~10 m

Improvement

Performance

Rate capability

Stability

MOyM

x

Coating materials

Al, Mg, Ag, Cu, Sn etc.

1-300nm

Example IIFormation of electromagnetic shielding film

Carbon fiber

~10-30 m

C

conductive filler

x

Carbonblack< 1m

M MAg/Cu

conductive metalsFerric metals

EMI

x

Example III-New drugs-

Aspirin: anti-inflammatory~20 m

Water soluble vitamin

Fluid suspension coating

COOH

OCOCH3

Water soluble vitamin

PMA coating

rumatism, cerebral arteriosclerosis

and heart disease : prevent and

curing; long term dosage is required

(side effect:: stomach

discomfort, stomach ulcer,

coagulation problem and

possible bleeding)

(release effect of labor pains)

New drug having Synergy effect

Low

Value

High

Value

Thermo

dynamics Cosmetics

Detergent

Fluidized-bed

Process

designTransport

phenomena

Value

limited

Use

Value

New

Function

Hydro

dynamics

Process

controlInterfacial

phenomena

Food

Drugs

Fertilizer

Fluidized-bed

coating

Conclusions

Fluidized coating Technology is very interesting and

useful for various industrial fields.

It can be possible low value of basic materials which

applied to limited use can be changed to high priced

products with multi-functional use. products with multi-functional use.

To understand the basic principle of fluidized-bed, the

learning of transport phenomena, process design,

thermodynamics, interfacial phenomena, process control

are required.

1. Please describe the meaning of minimum fluidization ?

2. Can you drive the pressure drop of fluidization at minimum fluidization

condition?

CHE 309 Intensified study 1)

condition?

Ref. Daizo Kunii & Octave Levenspiel,

Fluidization Engineering, John Wiley & Sons, Inc.