Christ Theorie Katalog en Web

8/22/2019 Christ Theorie Katalog en Web

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Smart Freeze Drying

Basic principles, optimum procedures

and applications


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Contents

1 Introduction 4

2 Basic principles 6

3 Freeze Dryer Design 84 Procedures 10

4.1 Overview 10

4.2 Freezing 12

4.3 Primary drying and secondary drying 16

5 Practical aspects 24

5.1 Warm up / Cool down 24

5.2 Shell-Freezing and Spin-Freezing 24

5.3 Achievable vacuum values 25

5.4 Determining the end o drying / PAT 26

6 Summary of procedures 30

7 Further literature 32

Some examples of freeze drying applications 34

Impress 52


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Freeze-drying or lyophilisation is an eective way o drying

materials without harming them. It makes use o the physical

phenomenon o sublimation, which involves the direct

transition between the solid state and the gaseous state

without passing through the liquid phase. To achieve this, the

rozen product is dried under vacuum, without being allowed

to thaw out. The process is suitable or a wide range o

applications:

or preserving the characteristics o the initial substance

(e. g. pharmaceutical products, milk)

or or preserving the initial orm (e. g. taxidermy,

or conserving archaeological nds or fowers)

or conditioning materials (e. g. reeze-dried ruit in yoghurt)

or chemical analyses (e. g. investigating trace organic

substances in oodstus, slurries, soils)

Freeze drying is used or more than 30 categories o

substances or materials. The most important markets are the

pharmaceutical industry and biotechnology as well as the

ood industry.

In general, a distinction is made between reeze-driers

used only in batch procedures, and continuously operating

systems. Non-continuous systems are available to processes

loads rom 2 kg up to approximately 1000 kg. We specialise

in this product group, and we are the only manuacturer

worldwide to oer a complete range rom laboratory bench-

top systems and pilot reeze-dryers through to large-scale

production machines:

1 Introduction

The food industry accounts or the largest volumes o reeze-dried

products, such as instant coee, but biotechnology and pharma-

ceutical products, e. g. vaccines, require systems which meet the

highest quality standards

i n t r o d u c t i o n


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Laboratory reeze-drying equipment

Ice condenser capacity rom 2 to 24 kg

Mostly air-cooled rerigeration system

Broad range o accessories or

wide-range applications

Pilot reeze-drying systems

Ice condenser capacity rom 6 to 16 kg

Air- or water-cooled rerigeration systems

Freezing and drying in the drying chamber

on liquid-controlled shelves

Production reeze-dryers

Ice condenser capacity rom 20 to > 1000 kg

Water-cooled rerigeration systems

Freezing and drying in the drying chamber

on liquid-controlled shelves

SIngle-or-double chamber systems

Customized project engineering

SIP / H2O

2disinection, CIP, IQ / OQ,

Process integration (loading systems,additional equipment)

i n t r o d u c t i o n


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E I N F H R U N G

2 Basic principles

The principle o sublimation can be explained with reerence

to a phase diagram (= vapour-pressure diagram). The process

is usually carried out with aqueous systems, although in recent

years reeze drying o solutions with special solvents have

become increasingly important.

The vapour-pressure diagram shows the phase transition

o the substance in a graph o pressure and temperature.

For example, it shows the boiling point o water at precisely

100 C at normal atmospheric pressure. At lower pressures,

the boiling point is reduced (the principle on which vacuum

distillation is based), and conversely, at higher pressures

the boiling point is raised (which is the principle on which

a pressure cooker operates).

Figure 2.1 Phase diagram o water [1]

I the pressure is higher than 6.11 mbar, H2O passes through

all three states (solid, liquid, and gaseous) as the temperature

increases or decreases. Below this point however, i. e. i the

pressure is less than 6.11 mbar, it passes directly rom the solid

to the gaseous state. At exactly 6.11 mbar the melting-point

curve, vapour-pressure curve and sublimation-pressure curve

meet at the so-called triple point. At the triple point all three

phases can coexist.

Freeze drying under atmospheric conditions is widely believed to have been

irst developed by the aboriginal peoples living and hunting in the Arctic

Circle, but this is a myth. In act when they dry ood it passes through a series

o melting and evaporation processes, but the evaporation is so rapid that it

is not possible to see any liquid phase orming.

b a s i c p r i n c i p l e s

liquid

triple point

critical point

solid

gaseous

0 100 200 300 400

t temperature in C

10-5

10-4

10-3

10-2

10-1

1

10

102

II

102

104

H2O

III

I

p pressure in bar


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E I N F H R U N G

The ollowing table contains values or part o the

ice-pressure curve:

For the conversion o units:

C = mbar C = mbar C = mbar C = mbar

0 6.110 -20 1.030 -40 0.120 -60 0.011

-1 5.620 -21 0.940 -41 0.110 -61 0.009

-2 5.170 -22 0.850 -42 0.100 -62 0.008

-3 4.760 -23 0.770 -43 0.090 -63 0.007

-4 4.370 -24 0.700 -44 0.080 -64 0.006

-5 4.020 -25 0.630 -45 0.070 -65 0.0054

-6 3.690 -26 0.570 -46 0.060 -66 0.0047

-7 3.380 -27 0.520 -47 0.055 -67 0.0041

-8 3.010 -28 0.470 -48 0.050 -68 0.0035

-9 2.840 -29 0.420 -49 0.045 -69 0.0030

-10 2.560 -30 0.370 -50 0.040 -70 0.0026

-11 2.380 -31 0.340 -51 0.035 -71 0.0023

-11 2.170 -32 0.310 -52 0.030 -72 0.0019

-13 1.980 -33 0.280 -53 0.025 -73 0.0017

-14 1.810 -34 0.250 -54 0.024 -74 0.0014

-15 1.650 -35 0.220 -55 0.021 -75 0.0012

-16 1.510 -36 0.200 -56 0.018 -76 0.0010

-17 1.370 -37 0.180 -57 0.016 -77

-18 1.250 -38 0.160 -58 0.014 -78

-19 1.140 -39 0.140 -59 0.012 -79

1 mbar = 100 Pa = 1 h Pa

1 Pa = 0,010 mbar

T = thermodynamic temperature K (Kelvin)

t = Celsius temperature C

tF

= Fahrenheit temperature F

Temperature

T = t + 273

t = T 273

tF= 1.8 x t + 32

t =tF 32

1.8

Pressure

b a s i c p r i n c i p l e s


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3 Freeze Dryer Design

The basic components o a reeze dryer are:

a) Vacuum drying chamber (see accessories

catalogue, Section 3.1)

b) Vacuum pump to extract air rom

the drying chamber (gas pump)

c) Ice condenser operating at temperatures

rom - 55 C to -105 C (depending on

the type o system) to extract water vapour

rom the chamber (vapour pump)

d) Heated or unheated shelves or drying in dishes

(see accessories catalogue, Section 3.3 and 3.4)

e) Shelves with sealing device or drying in vials

(see accessories catalogue, section 3.2)

) Rubber valves or the connection o round-bottomed

fasks, wide-necked fasks, etc. (see accessories

catalogue, section 4.4)

g) Maniolds or connection o round-bottomed fask,

wide-necked fasks etc. (see accessories catalogue,

section 3.5.)

Figure 3.1 Freeze dryer with acrylic glass drying chamber (a)and rubber valves ()

Figure 3.2 Freeze-dryer with sealing device or drying in vials (e)

(placed inside during operations)

For both the laboratory reeze-dryers and the production-scale

systems a distinction is made between single-chamber and

double-chamber systems. Only the laboratory systems are

presented here:

Generally, a lyophilisator consists o a recipient (product chamber) in

which the substance is placed, an ice condenser, and a vacuum pump.

However, various technical developments have been made, and these

are now incorporated in a wide range o available systems.

f r e e z e d r y e r d e s i g n


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Figure 3.3 Laboratory system shown in single chamber operation

As shown in Figure 3.3, in the single-chamber system the

reezing and then the drying o the product are carried out in

the ice condenser. The reezing o the sample results rom the

low temperature o the ice condenser (- 55 C or the single-

compressor system or - 85 C or the double-compressor

system). The interior can then be cooled down to about - 20 C

or - 40 C, respectively. Using a an during the reezing phase

proves to be very eective or transerring energy betweenthe sample and the ice condenser (see Article no. 121423).

During the primary drying phase it is necessary to introduce a

moderate amount o energy to the rozen sample and this is

provided rom the heated shel. The attachment unit shown in

Figure 3.2 (see Article no. 121009) makes it possible ater

the completion o drying to close the injection vials under

vacuum or inert gas, so that the reeze-dried sample is also

vacuum-sealed.

In the array shown in Figure 3.4 the rack with shelves is

under an acrylic glass cover outside the ice condenser, so that

this is reerred to as a two-chamber system. The advantage othis is that it oers a much greater product capacity or the

same ootprint area. Furthermore, by separating the product

chamber o rom the ice condenser (by means o the inter-

mediate valve shown in the sketch) it is possible to carry out

a so-called pressure-increase test to determine the end o the

drying process. This is explained on page 27. The disadvantage

is that it requires additional handling o the samples, which

have to be rozen externally in advance, e. g. in a rerigerator

or reezer. Ater transer to the reeze-drier, the acrylic

chamber is put in place and the sublimation itsel is started.

All laboratory systems rom Christ which are equipped with

shel temperature control can be operated either as a single-chamber or double-chamber system as required.

Figure 3.4 Laboratory system with two chambers

f r e e z e d r y e r d e s i g n


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4.1 Overview

Beore loading a new product, it is important to remove any

water rom the previous batch that remains in the ice condens-

er chamber. When this has been done the outlet valve and the

ventilation valve are closed. The product should only orm a

layer o 12 cm, because i it is too thick this will have a

detrimental eect on the drying time.

As shown in Figure 4.1, the reeze-drying process can be

controlled by the selection and alteration o only two master

parameters in the system:

Figure 4.2 shows a record o the reeze-drying process or a

ceramic suspension. Because it has a reezing point near 0 C

and no dicult product properties, this can be reeze-dried

already at a pressure o 1 mbar and with a shel temperature

o + 40 C. As the drying reaching completion, the temperature

sensors in the 3 cm-thick layer o the suspension (yellow, green

and blue lines) reach values close to the shel temperature.

Beore this, a mixed temperature is measured combining

the sublimation temperature and the temperature o the dried

cake. The ice condenser temperature (black line) rises at the

start o primary drying rom - 83 C to about - 70 C, because

large quantities o water vapour have to be rozen out. Ater

about 20 hours this eect has declined to some extent so that

the ice condenser again reaches a temperature o about - 85 C.

4 Procedures

Figure 4.1 Vacuum and shel temperature

Figure 4.2 Process graph or the reeze-drying o a ceramic

suspension

Freeze-drying process

Two key parameters o the system Vacuum p = (fd-step) Shel temp. t = (process time)

p r o c e d u r e s

Vacuum Lyo RxShel Icecond. Product 1 Product 3 Lyo Temp

-10000 4020 6010 5030 705 4525 6515 5535 75

0,001

0,001

0,100

1.000

10.00

100.0

Atm.(mbar)

-905

-4030

1055

6080

-8010

-3035

2060

7085

-7015

-2040

3065

8090

-6020

-1045

4070

90

(C)

100

95

(%)

100

-5025

050

5075


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As a rule, the product is rozen under atmospheric conditions,

analogous to a conventional reezer.

As already explained, the substance is rozen in small

amounts in the ice condenser chamber (process A) or separate-

ly in the laboratory in conventional reezer unit (process B).

A rozen product in round-bottomed fasks or wide-necked

lter fasks is oten preerred or drying because the fasks canbe attached and removed separately, without aecting the

drying process o the other fasks. As explained in Chapter 5.2,

the time required or the drying is aected by the thickness o

the layer, which can be considerably reduced by reezing under

rotation rather than using conventional stationary reezing.

The rotation leads to the ormation o a uniorm ice layer

inside the glass vessel.

When reezing in a separate process it is advisable,

particularly with small charges, to cool the shel so as to avoid

a partial melting during the evacuation process.

Ater the reezing, the system should then be taken

through a warm-up / cool-down phase. The vacuum pump can

warm up with the pressure control valve closed, and in this

way improve its perormance and its ability to withstand water

vapour. At the same time the ice condenser is pre-cooled, so

that it will be able to cope with the water vapour rom the

primary drying step. The preparation phase should take

between 15 and 30 minutes.

In order to start the sublimation process, the pressure

control valve to the vacuum pumps is opened so that the

pressure drops. The primary drying is started.

The optional secondary drying involves reducing the pressure

as low as possible in connection with a slightly elevated shel

temperature (both o these measures improve the desorption).

This desorption phase is subject to dierent thermodynamic

laws than the actual sublimation.

Ater the end o the process the drying chamber is

aerated through a rubber valve or the ventilation valve. It isalso possible to introduce nitrogen or an inert gas through

the aeration valve. The system can then be switched o and

the product taken out.

The ice condenser can be allowed to derost at room

temperature, or warm water can be used to speed up the

process i necessary. The ice condenser chamber should not be

more than hal ull o water. When derosting the ice condens-

er in this way it is important to make sure that no water nds

it way into the connecting pipes to the vacuum pump and the

pressure gauge!

Condensation and derosted water is drained o into a

container through the drain valve. Beore starting a new

process any residual water in the system should be removed.

The drain valve and aeration valve are then closed and the

system can be loaded with the next batch.

p r o c e d u r e s


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4.2 Freezing

The reezing phase determines the microstructure ormed by

the solidied solution and thus also that o the dried product.

A distinction is made between two dierent structures o

rozen materials: the crystalline orm is characterised by the

presence o ice crystals with denite crystal boundaries. This is

the case or most aqueous solutions with a low proportion osugars or proteins. I the reezing is carried out slowly enough

the mixture will separate out gradually until the nal drop o

liquid solidies at the lowest possible temperature, the

so-called eutectic temperature. In many cases the system does

not keep to the thermodynamic equilibrium and the liquid

becomes supercooled, possibly by as much as 1020C.

Crystallisation can then be initiated suddenly by shaking or

the introduction o a nucleus o crystallisation, and in this case

the solid phase will not have a eutectic composition.

In contrast, amorphous substances do not have any crystal

boundary, similar to a supercooled melt, e. g. window glass.

Heating such a congealed solution does not lead to a sudden

melting, but rather the material which has become soter

begins to fow away. This is thereore reerred to as the

collapse temperature TC. The glass transition temperature T

G

reers to the solidication point rom the liquid to the

amorphous and is usually a ew Kelvin lower than thecollapse temperature.

In the pharmaceutical industry amorphous matrices are

preerred or embedding sensitive biomolecules because the

active substance can be stabilised better. Conversely, crystalline

products can be reeze-dried quicker and more easily because

the grain boundaries avour the transport o water vapour.

While the melting o a crystalline product during drying can

lead to spattering and the risk o cross-contamination, with

amorphous, honey-like substances there is at rst only a loss

o structure. Although the product may not be impaired, anycustomer would object to being oered sticky crumbs. Many

substances in the pharmaceutical sector have a longer shel

lie i they are embedded in an amorphous matrix.

The key aspect when determining the necessary shel

temperature and pressure during primary drying is the

solidication temperature (= reezing point) o the material

being dried. In addition to being dependent on the product

in question, this is also dependent on the rate o reezing.

As an example, the table in Figure 4.4 shows the wide range

o eutectic points o microbiological culture media.

The eutectic point is the point in a constitutional diagram

at which an homogeneous eutectic alloy or mixture solidiies

directly rom liquid to solid state without orming a mix

o phases.

Figure 4.3 Determining the reezing point with CHRIST Lyocontrol

10-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

C

2 3 4 5

Shel 1

Product 1

Product 2

Lyo Temp

Shel 2

Icecondenser

Stopper

Sensor

Product

CHRIS-Lyocontrol LC-1

Freezing point

Rx

t / h

p r o c e d u r e s


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Sample Eutectic Temperature/C

Tab water -1.0

Super pure water 0.0

UHT-Milk -11.7

Skim-Milk -11.0

Lactose 5 % -1.0

Lactose 10 % -2.0

mod. pc-med. (3 % NaCl) -45.0

Litmus milk -12.0

Hgl -12.0

ba bouillon -29.0

Glucose bouillon -6.5

Malt extract bouillon -6.5

Yeast water -1.5

ygc -15.0

Mrs bouillon -20.0

M 17 -15.5

Basic medium streptococcus -15.0

Figure 4.4 Eutectic point o various nutrient

media [1]

Figure 4.5 With a less rapid rate o increase o the Rx-value during

solidiication, the solidiication point should be taken as the product

temperature determined according to this igure.

The reezing point can be determined by means o

the theoretical thermodynamic value

(source: chemistry manuals, technical literature

[e. g. VDI Thermal Atlas], reerences)

Cryo-microscope

DSC (Dierential Scanning Calorimetry)

measurement o temperature and resistance

during the reezing phase

The electric resistance o the product being dried almost

always rises dramatically with the transer rom the liquid to

the solid state due to the reduced mobility o the ions and

electrons. This means that by measuring the product

temperature and electrical resistance at the same point it

is possible to determine the reezing point.

Because there is usually a very abrupt rise in resistance,

the intersection o the Rx- and T-curves can be taken as the

reezing point with a very high level o accuracy. This has been

conrmed by numerous measurements with various solutions.

p r o c e d u r e s

Lyo product Calc.-Tmp.

Freezing point -21.6 C

Pressure according to vapour-pressure 0.884 mbar

Proposed drying pressure 0.538 mbar

0

10

20

30

40

50

60

70

80

90

100

(%)

00:25 00:26 00:27 00:28 00:29 00:30 00:31 00:32 00:33 00:34 00:3509:24 09:25 09:26 09:27 09:28 09:29 09:30 09:31 09:32 09:33 09:34

-100

-100

-80

-70

-60

-50

-40-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

(C)

Duration

Upper Rx-asymptote 96.9 %

Point o infection Rx 40.4 %

Freezing point -21.6C

Lower Rx-asymptote 96.9 %

Intersection with asymptote -96.9 %

Lyo Rx Lyo RxCalc Tangent Limits


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With Christ pilot and production systems it is possible to

speciy an Rx minimum value in advance. Below this, the

systems reverts to reezing mode, so that any o the product

which has thawed out will be rozen again. The Lyo-Control

System is able to accurately detect the reezing point o the

solutions which solidiy in a crystalline orm, but is less good

at reading o the collapse temperature o the amorphous

substances used in the pharmaceutical sector. The rate o

reezing has a considerable impact on the morphology o

crystalline systems (see Figure 4.8).

Figure 4.6 Plot o Lyo-Rx or a non-sensitive product

Figure 4.5 shows the determination o the eutectic point or

more generally the reezing point. For a less steep rise o the

Rx-value during the solidication then the solidication point

should be taken as the product temperature at which the

Lyocontrol resistance no longer changes.

The resistance is recorded as a percentage because it

can vary over several orders o magnitude and the actual

Ohm-value is not relevant or determining the reezing point.

A urther advantage o the Christ Lyocontrol system it the

opportunity it oers to monitor the process. During primary

drying the product can melt, leading to splattering, cross-

contamination and possibly the loss o the batch, but this can

be avoided by checking the Lyo-Rx level. The resistance can

break down i the product is heated up too quickly. Figure 4.6

and Figure 4.7 show graphs or a non-sensitive product

(resistance value always near 100 %) and or a very sensitive

product which thawed out ater only a ew hours o primary

drying.

Amorphous substances e. g. glass have no crystalline boundary

and behave like a rozen liquid. At the glass transition temperature TG,

the product starts to behave like elastic rubber and urther begins

to low (collapse temperature TC).

Figure 4.7 Plot o Lyo-Rx or a sensitive product which thaws out

in the course o primary drying

-1000

0 402010 305 452515 35 (h)

0.001

0.001

0.100

1,000

10,00

100,0

Atm.(mbar)

-905

-4030

1055

6080

-8010

-3035

2060

7085

-7015

-2040

3065

8090

-6020

-1045

4070

90

(C)

100

95

(%)

100

-5025

050

5075

-1000

0 4020 6010 5030 705 4525 6515 5535 75 (h)

0.001

0.001

0.100

1,000

10,00

100,0

Atm.(mbar)

-905

-4030

1055

6080

-8010

-3035

2060

7085

-7015

-2040

3065

8090

-6020

-1045

4070

90

(C)

100

95

(%)

100

-5025

050

5075



p r o c e d u r e s


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Crystal ormation at -2 C

Freezing too rapidly and to a too low temperature leads to a changed

drying rate (lower pore diameter, crack-ree surace structure)

longer primary drying

Figure 4.8 Crystal ormation (vertical cross-section)

when reezing 100% mannitol solution [3]

Fast freezing

(in liquid nitrogen LN2,

cooling rate approx.

50 C / min)

Slow freezing

(cooling rate

approx. 0.14 C / min)

Moderate Freezing

(e. g.: cooling rate

11.5 C / min)

Annealing

(e. g.: cooling rate

approx. 1.5 C / min,

5 h storage at -10 C)

Crystal morphology (vertical cross-section) 10 % mannitol

Crystal ormation at - 8 C

On the let a 10 % mannitol solution was slowly cooled

to - 2 C, and then crystallised out. The section on the right

show the result o rapid cooling with crystallisation at -8 C.

Rapid reezing leads to a longer primary drying duration due

to the lower pore diameter with ewer ssures in the surace

structure. Slow reezing (classication see Figure 4.8) leads

to so-called reezing concentration.

- 40C

t

+10C

Figure 4.9 Classiication o possible cooling rates [4]

As an example, a sodium chloride solution orms two separate

types o crystal during reezing, namely an NaCl-poor ice phase

and a second, highly NaCl enriched phase. The last drop

solidies at the lowest possible temperature, the so-called

eutectic temperature.

For practical purposes, a rate o reduction o temperature

o 12 Kelvin per minute (moderate reezing) is best or

avoiding reezing concentration on the one hand, while on

the other hand allowing the ormation o suitable crystal

structures.

A starting material containing solvent, or a material with

high salt concentration may thaw during the drying process

(usually clearly visible because o oaming). It is then necessary

to reeze the material to the lowest possible temperature, e. g.

in liquid nitrogen.

I the starting material has a high solvent concentration or

contains acidic material it cannot be dried without protective

measures and special apparatus, e. g. additional LN2

cooling

traps to protect the vacuum pump (in case o doubt consult

us). Alternatively, Vacuum Hybrid pumps (e. g. RC-6) can be

used which are resistant to chemicals.

p r o c e d u r e s


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E I N F H R U N G

Sublimation in thermodynamics is when a substance transers

directly rom the solid to the gaseous state without the

intermediate ormation o a liquid.

Ideal gas law

p x V = m x Rm

x T = const.

p = gas pressure [Pa], 105 Pa = 1 bar

V = volume [m3]

m = mass [kg]

rm

= r / M, r = ideal gas constant = 8.314 J / mol x K,

M = mol mass [g / mol], M(H2o) = 18 g / mol

t = temperature [K]

1.0 gram o ice at a pressure o

1.0 mbar produces 1 m3 o water vapour



P = 10 5 Pa = 1bar P = 10 4 Pa = 0,1bar

A very low pressure would lead to the production o an enormous

volume o water vapour, but not necessarily to a rapid reduction in

the water content o the sample!

However, i the pressure is too low this is counterproductive:

It is very important to select the correct pressure.

This can be explained with reerence to the ideal gas law:4.3 Primary drying and secondary drying

Following on rom the necessary warm-up / cool-down

phase already mentioned (warming up the vacuum pump

and cooling the ice condenser) the pressure in the system is

reduced to a specied working vacuum, and this is then

generally maintained during the primary drying. As soon

as the sublimation o the ice in the rozen material begins,heat energy is extracted rom the material and it is thereore

urther cooled.

At the same time the stepwise increase o the shel

temperature supplies the necessary sublimation energy to

the product.

The duration o the reeze drying process can range rom at

least 12 hours or simple products through to several days

or products which are more dicult to dry, such as a vaccine

with a low solidication temperature. Drying voluminous

archaeological nds may take weeks.

The vapour extracted when drying under vacuum reezeson the suraces o the very cold ice condenser, so that the ice

condenser eectively acts as a vapour pump. The vacuum

pump serves only to extract the air rom the drying chamber,

but not to pump out the water vapour (gas pump).

p r o c e d u r e s


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E I N F H R U N G

Figure 4.10 Inluence o the working pressure

on the rate o sublimation [5]

-1.0

0:00 5:00 10:00 15:00 20:00 25:00 30:00 35:00 40:00 45:00

0,0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Rate o sublimation [mg / min]

Protein solution

Time (hh:mm)

Rate o sublimation with shel temperature -10 C and 0.1 mbar

Rate o sublimation with shel temperature 0 C and 0.1 mbar

Rate o sublimation with shel temperature 0 C and 0.05 mbar

The longer drying times or very low pressures deduced rom

the vapour-pressure curve and the ideal gas law have been

conrmed in many experiments. For example. Fig. 4.10 shows

the rate o sublimation which can be achieved or various

chamber pressures and shel temperatures [This result was

obtained using a Christ micro-balance].

p r o c e d u r e s


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18

Example

Eutectic temperature teu

= -10C

Drying temperature tdry

= -20C

Drying vacuum pdry

= 1.030 mbar

Saety temperature tsae

= -15C

Saety vacuum psae

= 1.650 mbar

Alarm temperature talarm

= -13 C

Alarm vacuum palarm

= 1.980 mbar

Figure 4.11 Freeze drier with saety pressure unction

Figure 4.12 Freeze dryer with additional alarm pressure unction

In view o the dominant infuence o the apparatus

vacuum on the product temperature, CHRIST has integrated a

so-called saety-pressure unction to protect the products. I

the pressure in the drying chamber rises until it exceeds thesaety pressure limit, then the energy supply to the shel is

interrupted and the sublimation process slows down. This

prevents the product rom melting and avoids the risk o

cross-contamination and the alteration o the product

properties. The saety temperature should be 5 C below the

melting point, i. e. between the drying temperature and the

melting point:

Example

Eutectic temperature teu

= -10 C

Drying temperature tdry

= -20 C

Drying vacuum pdry

= 1.030 mbar

Saety temperature tsae

= -15 C

Saety vacuum psae

= 1.650 mbar

In larger units with liquid temperature control or the shel

it is possible to work with an additional alarm pressure. I the

pressure in the drying chamber rises to a selected alarm value

despite the energy supply being interrupted, the shel is

cooled down as quickly as possible to the reezing tempera-

ture. The alarm temperature should be about 3 C below

the melting point.

The comparison o the red and blue curves shows that even a

slight increase in the pressure rom 0.05 mbar to 0.1 mbar with

the same energy supply can lead to a signicant increase in the

sublimation rate, with the result that the primary drying phase

is about 4.5 hours shorter. This phenomenon is also used in

industrial reeze drying. For example, when reeze drying

ceramic suspensions, which have a reezing point near 0C,

a pressure o 2 to 4 mbar is used, that is near the triple pointo water, but producers o vaccines operate at 0.04 to

0.12 mbar. This is because the reezing point o such solutions

is oten very low.

Another inhibiting actor in the pharmaceutical sector

is the amorphous structure o the materials (no crystal

boundaries or water vapour transport).

p r o c e d u r e s


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19

Figure 4.13 Production unit with so-called liquid-controlled shel

temperature (with silicone oil) and alarm pressure unction

The secondary drying is an option which can be used i the

goal is to retain the minimum amount o residual moisture.

This in act involves the physical process o desorption, i. e.

the removal o absorbed residual solvent. An ice phase should

not longer be present. The secondary drying is carried out at

the lowest possible nal pressure in the system, as a rule

supported by a raised shel temperature (e. g. rom +20 C to

+30 C) in order to make it easier to outgas the thin layers o

solvent molecules on the pore suraces.

The lowest-possible nal pressure in the drying chamber

or the most eective desorption depends on the ice condens-

er temperature in accordance with the vapour-pressure curve

over ice and the rating o the vacuum pump.

In order to be certain o avoiding a melting o the product

during the drying, we recommend working at approx. 10 C

below the solidication temperature (eutectic point or

glass-transition temperature). This approach is described

in more detail on page 18.

Where eciency and speed are key production actors, e. g.

or active pharmaceutical substances, then the aim is usually to

work as closely as possible to the solidication point (perhaps

only 2 C below this). These processes require good knowledgeo the product and extensive pilot tests as preparation.

In order to start the sublimation process, the energy must

be provided or the product in some orm. Energy is received

rom the much warmer surroundings (direct contact heat)

when drying in round-bottomed fask, wide-necked fasks, etc,

or by ambient thermal radiation in the case o an unheated

shel, or directly rom a temperature-controlled shel.

Figure 4.14 Properly dried product (let) and melted, splattered product

(right)

p r o c e d u r e s


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20

Figure 4.15 Temperature proile in a beaded-rim lask

during primary drying

melting

triple point

evaporationsolid

gaseous

10-5

100 -80 -60 -40 -20 0 20 40 60 80 100 C

p

10-4

10-3

10-2

10-1

100

101

102

103

sublimation

solidiication point tr

= -15 C

drying temp. tdry

= -25 C

drying vacuum pdry

= 0.630 mbar

temperature C

-25 -15 -5 +5 +15 +25

heated shel

radiation heat

stopper not tight

dried layer

rozen layer

sublimation ront

thermal transmission

and convection

Figure 4.15 shows the temperature prole at a

beaded-rim fask during primary drying.

The thermal insulation provided by the vial material and the

geometry o the base o the vials lead to a very high tempera-

ture drop rom + 25 C on the shel to -15 C at the base o the

vessel and the rozen product on it. The comparatively good

thermal conductivity o the rozen solid leads to a lower

temperature gradient rom the fask base to the sublimation

ront. The heat transer is given by the equation:

This provides a direct relation to the heat transported

to the ice surace where it is required or sublimation.

The ice temperature at the sublimation ront is determined

by the water vapour pressure curve o the material, which

is ideally aqueous. The temperature gradient in the dried prod-

uct cake above this is determined by the radiant heat and by

the cooling eect o the water vapour fowing through it.

Lyophilisation can be described mathematically as a complex

heat and material transport problem. This can only be solved

by making certain simpliications.

Q = Q = k A T

Q: heat low [W = J ]

Q: heat quantity [J]

t: time [s]

k: heat transport resistance [ W ]

A: cross-sectional area or the heat transport [m 2]

T: temperature dierence [K]

t

.

.

S

m2K

p r o c e d u r e s


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21

Figure 4.16 Freeze drying process in a product dish

shel

contact:

heat transer

product

sublimation zone

t < collapse

temperature

vessel

ice core

thermal radiation

thermal radiation

water vapour

~ + 30C

The second way to infuence the speed is using the tempera-

ture-control o the shel. Figure 4.17 presents the results o

a laboratory drying experiment using pure water with and

without shel heating. In practical application the shel

temperature has less infuence because the pressure will oten

be lower and normally a product matrix will impede the water

vapour fow and reduce the rate o drying.

- 30

- 25

- 20

- 15

- 10

- 5

- 0

- 5

10

15

20

25

30

product temperature in C

time / h

heated shelves (T = 20 C)

unheated shelves

drying time = (T)

product quantity: 5 x 200 ml water

layer thickness: 0.8 cm

vacuum: 1.03 mbar

end o drying end o drying

0 5 10 15 20 25

The reeze-drying o rozen liquids, slurries, suspensions etc.

in dishes should be carried out in systems with heated shelves.

But this is not necessary with materials in pieces or irregular

orms, e. g. plants, ruits, archaeological nds, because the

contact area or heat exchange would be in any case too small.

As in the case o fask drying, the necessary energy here is

provided by ambient thermal radiation through the trans-

parent plexiglass hood. It is hardly possible to regulate the

energy supply. I the product begins to melt (= too much

radiation) then the hood or glass fask can be insulated,

e. g. with aluminium oil.

Figure 4.17 Inluence o shel heating on the

drying rate (pure water) [6]

p r o c e d u r e s

The situation in practice is illustrated in the ollowing

graphic.


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22

In summary, the product temperature during the drying is

mainly determined by the vacuum level which is chosen, and

less by the shel temperature.

In the rst quarter o the primary drying accounts or 50 % o

the water content, the next quarter or 50 % o the remaining

water content, and so on until the drying curve asymptotically

approaches the time axis. This is due to the act that the

sublimation level withdraws into the product and the water

vapour then has to nd its way through the dry layers and the

resistance becomes increasingly greater. The drying process is

determined mainly by the supply o sublimation heat and therate o transport o water vapour. In order to increase the

special thermal conductivity o the material to be dried and

to generate the smallest possible volumes o water vapour,

the drying should be carried out as near as possible to the

solidication point (eutectic temperature or glass transition

temperature).

The closer the pressure is to the solidication point

according to the vapour-pressure curve over ice then the

shorter is the primary drying time.

Figure 4.18 Asymptotic drying

0

0

50

100

10 20 3024

time (h)

water (%) primary drying secondary drying

The drying o a substance with a solids content o approx. 10 %

is shown in gure 4.18.

p r o c e d u r e s


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23

p r o c e d u r e s


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24

A virtual leak is a phenomenon whereby liquid which has remained

in a reeze drier rom the previous drying process gradually evaporates,

so that (as with a real leak) the pressure does not all as low as would oth-

erwise be possible.

5 Practical aspects

5.1 Warm up / cool down phase

With systems tted with a pressure control valve, the

opportunity should be used to warm up the vacuum pump.

It is better or the working lie o the vacuum pump i this is

only subjected to the vapours ater the operating temperature

o the pump has been reached, to avoid condensation.

The vacuum pump can be started up during the reezing

and the pressure control valve kept closed. The vacuum pump

should be allowed to warm up or at least 15 minutes, or be

switched on beore the start o primary drying.

In some cases, it is possible that during the primary drying

the pressure in the ice condenser chamber or in the drying

chamber will drop (e. g. rom 0.63 mbar to 0.47 mbar), even

though the valve to the vacuum pump has been closed.

This is due to the pumping eect o the ice condensers

(Cryo-Pumping Eect).

5.2 Shell-reezing and spin-reezing

I liquids are to be dried in fasks in a layer more than 1 cm

thick, then we recommend using a shell- or spin-reezing

arrangement (see Figure 5.2) in a cooling bath. The rotation

spreads the liquid on the inner walls o the fask where it

reezes. The reezing process produces a thinner layer

and increases the potential area or sublimation, which

considerably reduces the overall drying time.

Figure 5.2 Spin-reezing in an inusion lask

Figure 5.1 Shell-reezing in a round-bottomed lask

Layer thickness 70 mm

Surace area 38.5 cm2Layer thickness 9 mm

Surace area 253.3 cm2

70mm

As an example, i 250 ml o substance is introduced in

a 500 ml blood plasma fask, the resultant layer would be

approx. 70 mm thick. By rotating the fask in an upright

position at approx. 1000 rpm, the rozen product liquid is

spread evenly on the inner walls o the fask, so that the

maximum thickness o the layer is approx. 9 mm.

The fask is rotated in a cooling bath. Spin reezing

produces an even, homogeneous layer. Concentration

increases, volume changes and the ormation o varying

crystals o the substances are largely excluded.

155mm

9 mm

p r a c t i c a l a s p e c t s


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25

Figure 5.3 Cooling bath or reezing round-bottom lasks

or wide-necked lasks under rotation (let) and drying lasks

in a laboratory dryer (right)

5.3 Achievable pressure values

The vapour-pressure graph above ice that is the relationship

between ice temperature and the vapour pressure above

this has consequences or daily operations. With single-

stage cooling systems (e. g. ALPHA 14, DELTA 124) the

lowest possible pressure is only 0.021 mbar, because

the ice condenser has a temperature o - 55 C.

The attempt to reduce the pressure urther, e. g. to

0.01 mbar, would be thwarted by the sublimation o ice

rom the ice condenser (secondary vaporisation).

In comparison, the lowest possible pressures with a

two-stage cooling system (e. g. GAMMA 216, EPSILON 26D)

is limited by the nal vacuum o the rotary vane pump which

is usually used this is about 0.005 mbar. The vapour pressure

over the ice condenser at about - 85 C would be an order

o magnitude lower, at 0.0005 mbar.

The theoretical values given here could only be achieved

with a completely dry system. Any residual moisture, e. g. in

an outlet, would increase the achievable nal pressure as a

result o secondary evaporation (virtual leak).



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26

A rough statement about the end o drying can be made on

the basis o the pressure and the ice condenser temperature.

Is the ice condenser not longer burdened, it reaches its nal

temperature o approx. - 55 C or -85 C.

The pressure in the drying chamber alls in accordance

with the ice condenser temperature.

Figure 5.4 shows an example o the placement o producttemperature sensors. The drying is also at an end when sample

temperature and shel temperature are well into the positive

range (15 20 C) and do not dier rom one another by more

than 5 K. This indication is more reliable than the observation

o pressure and ice condenser.

Figure 5.5 shows the extent to which the position o the

sensor in the vial infuences the recorded product temperature.

Figure 5.4 Product sensors in a 1 cm high beaded-rim lask illed with an

active substance and in a spongy product

5.4 Determining the end o drying / PAT(Process Analytical Technologies)

The residual moisture in the substance being dried is mainly

dependent on the temperature o the substance during the

secondary drying and the nal pressure achieved during

secondary drying.

The end o the primary drying phase is reached whenthe product temperature and shel temperature are approxi-

mately the same (temperature dierence between shel

and product about 3 K to 5 K). I the absorbed water is to be

removed rom the product, it is then possible to proceed to

the secondary drying phase.



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27

A sample can be assumed to dry rom top to bottom, as a

rst approximation, and the upper o the three temperature

sensors shows a rise in product temperature already ater

approx. 7 hours. Due to the cooling eect o the vapour romthe sublimation boundary, the product temperature at the

sensor takes approx. 20 hours to rise above 0. The lowest o

the three sensors shows the most correct value, because it is

directly above the base o the vial or dish where the material

will dry last. The box symbols in the graph show the product

temperatures at the sublimation ront determined using the

relatively new, so-called barometric temperature process o

measurement, a special process which operates with quickly

opening and closing intermediate valves.

In contrast, the pressure increase tests, which have been

in practical use or some time, operate with longer closingperiods or the valve (see Figure 5.6). The principle is based on

a separation o the product chamber rom the ice condenser,

so that the water vapour rom the sublimation cannot escape.

This results in an increase in pressure in the product chamber,

which can be measured. But once the product is completely

dry there will be little or no increase in the pressure.

Figure 5.5 Inluence o the positioning o a temperature

sensor in the product [4]

0 5 10 15 20 25

-30

-20

-10

0

10

20

30

40

T (C)

Time (h)

PT 100

BTM TICE

Figure 5.6 Principle o the pressure increase test

This process is in wide practical use, wherever the reeze dryer

is regularly operated with the same load (number and type o

vials or dishes). The pressure increase test is requently used as

a criterion or switching automatically between primary andsecondary drying as well as or recognising the end o the

drying process.

With sensitive products, the valve must not be kept closed

or very long, i. e. only or a ew seconds, in order to prevent

the rozen material rom collapsing or melting.

The CHRIST microbalance is a unique tool or process

development and optimization in pilot plants.

Flow ovapour romthe sampleto the icecondenser

Vapourenclosed inthe productchamber

Valve open Valve closed

Vacuumpumps

Vacuumpumps

Ice condenser Ice condenser

Productchamber

Productchamber



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28

Figure 5.7 The microbalance rom Christ or measuring

vials and small dishes

Figure 5.8 Spectroscopic measurement o the end o drying by recording

the proportion o water vapour in the gas low to the ice condenser

(creating a cold plasma) [7]

Figure 5.9 Principle o the pressure measurement with the

Pirani gauge (let) and with a capacitive sensor (right)

The microbalance works on the principle o electromagnetic

orce compensation. At periodic intervals pre-selected by the

customer, the micro-balance lits the vial and generates a

weight reduction curve with an accuracy o 0.001 g, which

indicates the completion o drying.

The drying process itsel is not interrupted, and thebalance can be placed at any position on the trays in the

chamber. But the shel where the balance is located cannot

be used or sealing. Furthermore, the microbalance cannot

be autoclaved. A dish is provided or the simulation o

bulk-drying.

Lyotrack, developed by Alcatel / Adixen, France does not

examine individual products but monitors the progress o

drying indirectly. At a dened measuring point between the

product chamber and ice condenser, a sample o the vapour

fow is extracted and placed in a so-called Cold Plasma using

a special method. A spectrometric analysis o the radiationreleased provides the ratio o nitrogen to water vapour in the

mixture on its way to the ice condenser at the time o meas-

urement. The urther the drying proceeds, the lower the

proportion o water vapour becomes. Reerence measurements

in comparison with the microbalance show that the Lyotrack is

so sensitive that it not only determines the end o the primary

drying, but can also track the release o water vapour in

secondary drying (desorption).

The composition o the gas fow is also used in methods based

on process monitoring with simultaneous measurement o the

pressure using a Pirani gauge and with the capacitive sensor

(comparative pressure measurement). Figure 5.9 shows both

operational principles.

1

Electrode

Diaphragm

xxxx1

2

3

4

12:00 13:00 14:00 15:00 16:00 17:00 18:00

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Duration o reeze drying (hh:mm)

Plasma versus temperature sensor

Plasmasignal

relativetosaturation

Temperatureof

shelves-/product(C)

-35

-30

-25

-20

-15

-10

-5

0

12:00 18:00 0:00 6:00

Duration o reeze-drying (hh:mm)

Lossofweightmeasured

withthemicro-balance

Plasma versus microbalance

Plasmasignal

relativetosaturation

0 0

0.20.4

0.60.8

1

1.21.4

1.61.8

2

0.10.20.30.40.50.60.70.80.9

11.1



30/54

29

0:00 5:00 10:00 15:00 20:00

Time (hh:mm)

Temperature(C)

Pressure(mbar)

Temperature sensor End primary drying

End primary drying

MKs sensor

Pirani gauge

25:00 30:00 35:00 40:00

0.001

0.01

0.1

1

10

100

-100

-80

-60

-40

-20

0

20

40

The Pirani sensor consists o a single wire which loses heat

depending on the pressure o the surrounding gas. The change

o temperature o the wire alters its electric resistance and

thus the current I fowing under a constant voltage V (I = V / R).

The indirect relationship between current and pressure,

I = (pressure) is established by calibration. The heat loss also

depends on the type o gas, and is higher i there is a large

proportion o water vapour.The capacitive sensor is based on the pressure-dependence

o the defection o the membrane o an electrical capacitor,

which is not dependent on the composition o the medium.

Since the Pirani gauge readings are dependent on the type

o gas, and in particular measurements are too high at the

start o drying when a higher proportion o the mixture is

water vapour, whereas the capacitive sensor measurements are

independent o the nature o the gas, when the two measure-

ment curves meet this indicates the end o the primary drying.

Figure 5.10 Pressure measurement with the Pirani gauge and

with a capacitive sensor [5]



31/54

30

E I N F H R U N G

The temperature o the rozen product beore the start o

sublimation should be approx. 10 C below the solidication

temperature. The pressure value or the 10 C lower value

should be chosen using the ice pressure curve.

During the primary and secondary drying, the shel is

heated to provide the necessary energy, but the shel

temperature prole can as a rule only be determinedempirically.

Figure 6.2 shows how the rate o sublimation depends

on both, the pressure and the shel temperature.

This gure only applies or a time point t, because the array

o curves changes with the development o a dried, porous

layer (increasing pressure loss or vapour fow). The determi-

nation o the suitable temperature prole o the shel heating

involves a very complex thermodynamic heat and material

transport problem. In this case, some empirical tests with

temperature sensors and Lyocontrol are preerable to

time-consuming theoretical calculations. Christ provides

recommendations or product applications on its web site

(www.martinchrist.de) and in the ollowing part o this

brochure.

s u M M a r y o f p r o c e d u r e s

Figure 6.2 Dependence o the rate o sublimation on pressure p and

the shel temperature T with the corresponding isotherms o the

product temperature [19]

+30 C

6 Summary o procedures

Figure 6.1 gives an overview o the master parameters or the

design o a reeze drying cycle.

Figure 6.1 Key relationships or the reeze-drying

A key actor is the solidication temperature o the product

in question. As an approximation, it is possible to record the

cooling temperature in the reeze dryer. At the reezing point,

the curve will have a plateau, i. e. the product only cools

urther when the last liquid drop has solidied (Gibbs'

phase rule). Alternatively, the solidication temperature

can generally be determined reliably with the Lyocontrol.

However, this process is less accurate when used withamorphous structures. When such substances are being

handled, or example in the pharmaceutical industry, then

it is better to use other procedures such as dierential

scanning calorimetry (DSC) or cryo-microscopy.

Freezing temperature= (solidiication temperature)

Vacuum = (solidiication temperature)

Lyo-Rx, T-curve, DSC, Lyo-microscope

Shelf temp. primary drying = (time, vacuum)

T-sensor, Lyo-Rx, some tests, Christ application instructions

Process end of primary and secondary dr ying

T-sensor, pressure-rise test, sample thie, micro balance

comparative pressure measurement (igure 5.10)

Pressure p (primary drying)

Product temperature

ShelftemperatureT(primarydrying)

Rateofsubli

mation

-10 C

-40 C

-35 C

-30 C

-25 C

-20 C

0 C

+10 C

+20 C


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31

E I N F H R U N G

The end o the primary drying process can be determined

by a temperature sensor, the pressure rise test or the micro-

balance. In order to determine the end o secondary drying,

the pressure rise test is a suitably sensitive process and is

preerable because the product temperature no longer

changes and the balance is not always sensitive enough or

measurements during desorption. Alternatively the detection

o the residual water vapour in the chamber is a suitablemethod (Lyotrack by Adixen). O course it is also possible to

use manipulators or sampling equipment to take samples

during the process or the chemical analysis o the residual

moisture content.

s u M M a r y o f p r o c e d u r e s


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32

f u r t H e r l i t e r a t u r e

7 Further literature

1 Bockelmann, WilhelmGeriertrocknung und Lagerung

von Mikroorganismen. Christ-Geriertrocknungsseminar,

3rd 4th o march 2009, Osterode.

2 Hudel, Klaus Probetrocknung im Versuchslabor der

Fa. Christ, 12 / 2006.

3 Gieseler, H.; Lee, G.Inuence o Dierent Cooling

Rate on Cake Structure o Freeze Dried Samples Measured

by Microbalance Technique. Poster presentation, Controlled

Release Society German Chapter Annual Meeting,

Mnchen (2003).

4 Gieseler, HenningGeriertrocknung von Pharmazeutika

Grundlagen der Formulierungs- und Prozessentwicklung.

Christ-Geriertrocknungsseminar, 25th o june 2003.

5 Presser, IngoGeriertrocknung von Pharmazeutika

Stabilisierungsverahren r empfndliche Arzneistoe.

Christ Seminar Geriertrocknung mit System,

23rd o november 2005.

6 Knerr, Petra Probetrocknung im Versuchslabor der

Fa. Christ, 3 / 2008.

7 Diverse Lyotrack presentation or reeze drying, given

at company Martin Christ, Alcatel / Adixen 8 / 2006.

8 Franks, FelixFreeze-drying o bioproducts: putting

principles into practice. European Journal o Pharmaceutics

and Biopharmaceutics 45, 221229 (1998).

9 Mi, J. Protection Mechanisms o Excipients on Lactat

Dehydrogenase during Freeze-Thawing and Lyohilisation.

Doctoral Dissertation (2002).

10 Allison, S. D.;Chang B.; Randolph T.; Carpenter, J.

Hydrogen bonding between sugar and proteins is responsible

or inhibition o dehydration-induced protein unolding,

Arch. Biochem. Biophys., 365, 289298 (1999).

11 Cleland & Langer Formulation and Delivery o Proteins

and Peptides, Chapter 8, Freeze Drying o Proteins by

Pikal M, American Chemical Society, 120133 (1994).

12 Oetjen, G. W.Lyophilisation. Wiley-VcH ,

isbn 3-527-29571-2 (1999).

13 Kramer, M.Innovatives Einrierverahren zur Minimierung

der Prozezeit von Geriertrocknungszyklen Dissertation

Universitt Erlangen (1999).

14 Ramott, R.; Rambhatla, S.; Pikal, M.; The Eect o

Nukleation Temperature on the Process o Lyophilisation.

Oral Presentation at the University o Connecticut School

o Pharmacy (2002).

15 Searls, J.; Carpenter, J.; Randolph, T.Annealing to

Optimize the Primary Drying Rate, Reduce Freeze-Induced

Drying Rate Heterogeneity, and Determine Tg in

Pharmaceutical Lyophilisation, J. Pharm. Sci., Vol. 90,

Nr. 7, 872887 (2001).

16 Milton, N.Evaluation o Manometric Temperature

Measurement as a Method o Monitoring Produkt

Temperature During Lyophilization, J. Pharm. Sci.

and Techn., 57, 716 (1997).

17 Roth, C.; Winter, G.; Lee, G.;Continuous Measurement

o Drying Rate o Crystalline and Amorphous Systems during

Freeze-Drying Using an In Situ Microbalance Technique.

J. Pharm. Sci., Vol. 90, No. 9, 13451355 (2001).

18 Bedienungsanleitung WgesystemcWs 40, Fa. Christ

Geriertrocknungsanlagen, 10 / 1997, 03 / 2000.

19 Pikal, M.; Nail, S. and Tang, XiaolinAutomated Process

Design Through Manometric Temperature Measurement

Design o a Smart Freeze Dryer. Conerence Presentation,

Freeze Drying o Pharmaceuticals and Biologicals,

Breckenridge, CO (2001).


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33

f u r t H e r l i t e r a t u r e

20 Pikal, M.Lyophilisation. In: Decker, M. ed. Encyclopedia

o Pharmaceutical Technology. 2001: 1299Y1326

21 Fonseca, F.; Passot, S.; Trelea, C.; Marin, M.Impact o

physical properties o bioproducts on ormulation and on

reeze-drying cycle development. Vienna Congess ispe,

Sept 2006

22 Jiang, G.; Akers, M. et al.Mechanist Studies o Glass Vial

Breakage or Frozen Formulations I. Vial Breakage Caused

by Crystallizable Excipient Mannitol. PDA Journal o Pharma-

ceutical Science and Technology. Vol. 61, No. 6, NovDec 2007

23 Jiang, G.; Akers, M. et al. Mechanist Studies o Glass Vial

Breakage or Frozen Formulations I. Vial Breakage Caused

by Amorphous Protein Formulations. PDA Journal o Pharma-

ceutical Science and Technology. Vol. 61, No. 6, NovDec 2007

24 Tang, X.; Pical, M. J.Design o reeze drying or pharma-

ceuticals: practical advice. Pharm. Res., 21(2): 191200 (2004)

25 Carpenter, J. F.; Pikal, M. J.; Chang, B. S.; Randolph, T. W.

Rational design o stable lyophilized protein ormulations:

some practical advice. Pharm. Res. 1997; 14:969Y975.

26 Tang, X. C. M.; Nail, S. L .; Pikal, M. J. Evaluation o

Manometric Temperature Maesurement, a Process Analytical

Technology Tool or Freeze-drying: PartII Measurement o

Dry-layer Resistance. PharmaSciTech 2006; 7(4) Article 93.

27 Chang, B. S.; Fischer, N. L. Development o an Efcient

Single-step Freeze-Drying Cycle For Protein Formulations.

Pharmaceutical Research, Vol. 12, No. 6, 1995.

28 Presser, I.; Denkinger, N.; Hoermann, H.; Winter, G.

New methods in the monitoring o reeze drying processes:

Validation o the microbalance. Central European Symposium

Pharmaceutical Technology Conerence, Vienna 2001

29 Presser I, Denkinger N, Hoermann H, Winter G

New methods in the monitoring o reeze drying processes:

near inrared spectroscopy determination o residue

moisture during reeze drying. Protein Stability Conerence,

Breckenridge, Colorado 2002


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a p p l i c a t i o n s o f f r e e z e d r y i n g

Algae

Procedure (Overview)

Freezing Solidication range,

Solidication point

Container or FD Process

A / B / C *

Vacuum primary drying

-35 C, reezing in LN2

is

convenient

-15 to -25 C wide-necked fasks, dishes A and C TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 0.630 0.220 mbar

Temp. o the shelves during

primary drying (TSF

/ t)

Duration o primary drying Vacuum or secondary drying

-10 C / 4 h, 0 C / 4 h, +10 C / 4 h, +20 C / 1224 h 624 h not necessary

Special eatures

watery material (not de-watered or pre-treated),

straggly consistency

very hygroscopic

resh water and sea-water species

have dierent reezing points

Short description o market

Uses o the reeze-dried products /

Typical users

Food industry (inclusion as favour

carrier, protein-rich)

Cosmetics

* Comments

Process A (Freezing and) drying in the ice condenser chamber

Process B Freezing separate (e. g. rerigerator), drying outside the ice condenser,

e. g. with plexiglass hood

Process C Freezing (on liquid-cooled shelves) and drying outside the ice condensers,

e. g. with plexiglass hood or steel chamber (like EPS ILO N-systems)

EPSILON system with rectangular product chamber, ront loader

It is very diicult to model the processes involved in reeze-drying,

because the transport o heat energy and mass involve very

complex phenomena.


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Books, archaeological nds



Solidication point


A / B / C *


books: reezing in the

deep reezer at -10 C,

arch. nds: -30 C

approx. 0 C to -3 C steel cabinet / chamber,

plexiglass tubes

B or C (tempered stainless

steel tubes)

TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 2.560 1.980 mbar


primary drying (TSF

/ t)


-30 C / 10 h, increase by 5 C every 10 h, i shel

heating is not possible, inrared heating may

be possible (no reports available). Do not dry

too much, books are then placed in the climate

chamber

t = 38 days per object, (or archaeological

nds also some weeks)

end o drying by measuring pressure increase

or weight loss

or books no secondary drying

Special eatures

Books must stand vertically (rack), because

otherwise water vapour cannot escape

Heat transport also possible in sae,

operate close to the eutectic point!

Heating is bad or books (deormation

due to uneven drying because the book

is only warm at the bottom), inrared heating

would be possible (heater at the back o the cabinet)

As ar as possible, objects should be o similar size

so that they dry at the same rate (or example arch les)No temperature prole necessary and not

possible without heated shel

Other application in a vacuum cabinet

(pharmaceutical industry):

Aventis Pharma, Frankurt reeze dries Erlenmeyer

fasks in such cabinets with heated shelves,

giving even heat transer!

Uses o the reeze-dried products

Restoration, or example: wet planning

permission documents ater a food

Typical users

Libraries, museums, public authorities

e. g. wood, textiles, leather

Freeze-dryer or book drying with

2 rerigeration units and heated shelves

Special dryer or archaeological

inds, here treating a Viking boat

It is usually advisable to carry out optimization tests with a

product irst. Some examples o applications ollow to oer

a basis or this.


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Bacteria, viruses, ungi, vaccines


Solidication point


A / B / C *


-50 C and below -40 C and lower beaded-rim fasks, vials,

ampoules, dishes

A or EPSILON (process C) in

the production range

TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 0.040 mbar and below


primary drying (TSF

/ t)


-50 C / 5 h, increase every 5 h by 5 C (4 or

5 times), then reduce to time interval to 3 h

and 1.5 h, Lyocontrol highly recommended

2448 h only in exceptional cases

Special eatures

In laboratories: Disinection and gas sterilisation possible:

Ethylene oxide (highly toxic, outdated), paraormaldehyde,

H2O

2, (increasingly common)

Chemically-resistant CHRIST systems can be provided

Disinection / decontamination: Liquid cleaning (alcohol, etc.),

germs may still be present, special cleaning agents are

recommended or plexiglass (e. g. Incidur)

It is usually necessary to steam-sterilise systems

or production purposes

Sterilisation: with steam > 121 C, complete elimination o germs

Operating in accordance with GMP (Good Manuacturing Practices)and FDA (Food and Drug Administration) requirements


For human and veterinary vaccination

Ampoules are sealed under vacuum

Vials are closed under vacuum or N2-atmosphere

using special accessories

(pressure o 800 mbar avoids excessive air

diusion into the closed vial in storage and

is enough to keep the sample sterile)

Various bacteria cultures under

vacuum in tightly-sealed

injection vials




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Plants, sh


Solidication point


A / B / C *


reezer: -35 C,

eutectic range can

only be determined ater

homogenization

to -15 C see books,

large chambers

B TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 0.630 mbar


primary drying (TSF

/ t)

Duration o primary drying Vacuum or secondary drying Duration o secondary drying

not applicable, see books 1 d to 1 week (depending on

object dimensions)

minimal 3 h10 h

Special eatures

No temperature-prole requiredFish: remove sh entrails in order to reduce

the layer thickness

Flowers: hang upside down in holders

Note: tissue (bodily fuids) o aquatic animals

contains CaCl2

and so the reezing points are very low

Specialist publication Restoration available rom us



Fish: anglers, works o art, teaching demonstrations

Plants with very high water content (aquatic plants)or decoration purposes

Typical users

Fish: taxidermists, anglers

Flowers: Garden centres, biological institutes,

generally smaller companies

Freeze-dried sh with a protective

surace coating

Flower seeds ater reeze drying




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Collagen, tissue samples, thymus


Solidication point


A / B / C *


pre-cooled in LN2

or

on the shel

Collagen: -45 C

Collagen: about -35 C,

Tissue samples: -56 C

(contain CaCl2)

special dishes,

Special ormats

(L x W, indentation)

A and C TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 0.070 mbar to

0.0047 mbar


primary drying (TSF

/ t)


-30C / 5 h, increasing rst by 5 C every 5 h

(56 x), then reduce the time interval to 2 h

36 h necessary to remove capillary water,

lowest pressure o pump (10-3mbar)

Special eatures

Rate o rerigeration 1 C / min

Avoid damage to cell walls with non-reezing mixture

(cryo protectants, displace water in the cell wall

and prevent denaturation)

Only heat moderately so that cells do not derost and burst



Collagen or skin cosmetics (moisturiser, cell rejuvenation)

Cell tissue, bone, arteries, scalp tissue, or aorta valves or

transplantation can be lyophilised

Typical users

Doctors, clinics, increasingly also beauty arms

Collagen plate during test drying




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Fruits, vegetables, meat


Solidication point


A / B / C *


ruits, vegetables: -35 C;

meat: -40 C

-25 C dishes B TICE

= TEP

-10 C (= -35 C)

pHT

= (TICE

)

ice pressure curve

= 0.220 mbar


primary drying (TSF

/ t)


ruits, vegetables:

0 C / 4 h, 10 C / 4 h, 20 C / 1624 h)

meat:

-10 C / 4 h, 0 C / 4 h, +10 C / 4 h,

+ 20 C / 1224 h

2436 h a question o cost, not usually

needed

optional

Special eatures

Meat is diced with a side length o about 1 cm

The packaging or reeze-dried products must be

impermeable to air, water vapour and gases

Additional inormation

Freeze drying is viable i the price is more

than Euro 10 / kg (market price)

Freeze-drying plants have an amortisation

period o at least ten years

Doubling the capacity reduces specic

production costs by 10 to 20 percent

A reeze dried product has ten times the aroma

intensity o the same amount o resh product


Fruits: Baby ood, milk industry

(adding aroma to milk products),

Vegetables: Kitchen herbs

Meat: only as favour carrier (deep-rozen

granules, or ground in a mill)

Typical users

Food industry

Drying specialists

Freeze-dried tropical ruits Arillen

External reezing o trufes

in a reezer

A wide range o oodstus

can be reeze-dried




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Gelatine


Solidication point


A / B / C *


-25 to -30 C below -20 C dishes A TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= less than 0.370 mbar


primary drying (TSF

/ t)


sensitive, stepwise warming needed -10 C / 4 h,

0 C / 4 h, + 10 C / 4 h, + 20 C / 1224 h

2448 h no

Special eatures

Viscous material, can orm skin,

aecting process

Hygroscopic

The resultant cake is ground



Typical users

Intermediate products or the pharmaceutical

industry (carrier, ller), oodstus sector

(binding agent)

Freeze-drying o Lecithin with

tendencies o orm surace skin




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Royal jelly, honey


Solidication point


A / B / C *


process A or C,

pre-cooled shel,

shock reezing

usually at -40 C

to -40 C dishes A, C TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= to 0.040 mbar


primary drying (TSF

/ t)


-30 C / 5 h, rst increase by 5 C every 5 hours

(5 to 6 x), then reduce the interval to 2 hours

2436 h as appropriate

Special eatures

Product is very hygroscopic, must be packed quickly

Substances containing aroma additives and sugar

tend to orm skin during the drying process



Drugs, ood additives

Typical users

Pharmaceutical companies, private companies




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Ceramic powders


Solidication point


A / B / C *


to -20C, separately or in

system

below -10 C

(that is 0 to -10 C)

dishes or modules A TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 1.030 mbar


primary drying (TSF

/ t)


-10 C / 4 h, 0 C / 4 h, +10 C / 4 h, +20 C /

1224 h, stepwise, rapid drying

possible up to +80 C

224 h no

Special eatures

Initial material is ceramic powder and binding agent

(coating grains), this binder is preserved by reeze-drying,

it would be broken up by thermal drying)



Typical users

Use as ceramic base structure or compound materials

Small-scale (Lab): KFA Jlich (Inst. For Materials Testing),

BAM, Berlin

Cylinder rom porous special

ceramics (not a nished product)




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Sewage sludge, soil samples


Solidication point


A / B / C *


at about -35 C -25 C dishes, with sieves to hold

back very ne silt particles

A, B, C possible TICE

= TEP

-10 C (= -35 C)

pHT

= (TICE

)

ice pressure curve

= to 0.220 mbar


primary drying (TSF

/ t)


0 C / 6 h, 30 C / 18 h slurry: 24 h

soils: 2436 h

not necessary not applicable

Special eatures

Material o dishes: Aluminium (less rigid) or stainless steel,

can be tefon-coated or heavy-metal analysis

Product sieve or ne-grained soils

German standard DI N 3841 4/22 (Sample preparation)

gives details o eective working pressure, sae pressure,

the pressure control valve, the heatable shel and

sample preparation)



Analytical laboratories, environmental

departments o industrial companies

Assessing soil contamination levels

Typical users

Environmental oces, analytical laboratories,

sewage treatment plant, water management associations

Lab reeze-drier or up to 4 litres

o slurry or soil samples




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Microbiological products, ermented products


Solidication point


A / B / C *


200500 ml spin reezing

(in vertical fasks, with

corresponding cooling

baths

-13 to -35 C 5500 ml fasks,

dishes (albumin)

A and C,

EPSILON systems

(Soletemp.)

TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= to 0.770 0.070 mbar


primary drying (TSF

/ t)


-30 C / 5 h, increase temperature

initially by 5 C every 5 h (e. g. 3 x),

then reduce the time interval to

2 h

24 h (at 1 cm) not at max. vacuum; set or

residual moisture content o

25 %, (customer expertise)

24 h

Special eatures

Lyo-Control recommended or reezing process,

Max. product temperature 30 C (denaturation above 37 C),

Close under vacuum, but risk o air diusion internally

(better to close in an N2atmosphere)



Blood derivatives or injection purposes, now used instead o ull

plasma transusions (blood substitute = saline solution and plasmacomponents dissolved in bi-distilled water; allows aster uptake o

key components)

Typical users

Red Cross, pharmaceutical companies

e. g. proteins, enzymes, blood serum, plasma, other blood derivatives (albumin, fbrinogen, actor 8 and 9).

Freeze-dryer with temperature-

regulated shel and system or

closing fasks under vacuum




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Milk products


Solidication point


A / B / C *


Shell-reezing (round-bot-

tomed fask) Spin-reezing

(cylindrical fasks),

minimum -25 C

-13 C (cow's milk) dishes,

round-bottomed fask,

wide-necked fasks

B, possibly C TICE

= TEP

-10 C (= -23 C)

pHT

= (TICE

)

ice pressure curve

= 0.770 mbar


primary drying (TSF

/ t)


0 C / 5 h, then increase to between

+25 and + 30 C

24 h not necessary

Special eatures

non-sensitive product,

Single-chamber systems highly suited or

production applications



Mare's milk (health ood, valuable vitamins),

goat's milk, camel milk (Emirates), mother's milk

Typical users

Mare's milk arms, pharmacists who wish to

supply to wider areas (rozen then not possible,

thereore reeze-dried); mare's milk goes o

very easily i not reeze dried

Drink yoghurt and reeze-dried

yoghurt

Drying yoghurt in stainless

steel trays




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Nucleic acids, peptides


Solidication point


A / B / C *


to -40 C to -30 C nucleic acids: fasks

peptides: dishes, fasks,

vials, ampoules

A (nucleic acids)

A and B (peptides)

TICE

= TEP

-10 C

pHT

= (TICE

)

ice pressure curve

= 0.120 mbar


primary drying (TSF

/ t)


-30 C / 5 h, increase temperature by 5 C every

5 h (56 x), then reduce the time interval to 2 h,

more rapid heating oten possible i no

problems are encountered

2436 h as required

Freeze-dried peptides in

injection vials



Special eatures

Material is hygroscopic

In production plant with automatic cleaning (CIP),

steam sterilisation in some cases



Typical users

Pharmaceutical companies (additives)


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Organic solvent


Solidication point


A / B / C *


rst evaporate solvent

with RVC

below -50 C possible dishes

in part also fask drying

(particularly ACN-water

mix)

A corresponding to the xed

point (Ice pressure curve

or water not applicable)


primary drying (TSF

/ t)


TFp.

-10 C, note: avoid partial derosting

i the pore structure o the sample is important

must be determined experimentally or

a wide range o substances (see below)

depends on product

Special eatures

Examine vapour-pressure curve o the solvent,

Ice pressure curve or water is oten not applicable

An indication o the drying time relative to water (1 cm layer

o ice in 24 h) is given by comparing the vapour pressure

or better sublimation pressure o the substance with that o H2O

Check state o system (rubber seals, acrylic doors / hoods)

With processes A and C, reeze-drying systems can also

be used or vacuum drying or conditioning processes

(creating a product oam). At a low pressure, careul increase

o the heating temperature causes a controlled boiling process.


Uses or the reeze-dried products

Special market, preparation processes in the

pharmaceutical industry, extracting natural substances

Solvents with high-boiling points can also be used

(the key is the solubility o the relevant substances)

Typical users

Chemical and pharmaceutical industry, growing

markets or special applications

Comments

A special presentation is available on this

with details o applications

Laboratory system or fask drying

rom solvent

Rack with sieve cover or drying

rom solvent (avoidance o

cross-contamination)




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Vegetable materials


Solidication point


A / B / C *


-10 C (sometimes down

to -40 C) A and C, reezer

cabinet, rarely with LN2

-10 C (in some cases

to -30 C)

dishes, shelves A and B

TICE

= TEP

-10 C

pHT

= (TIC

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