Chapter 8 Crystallization

7/24/2019 Chapter 8 Crystallization

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MISS. RAHIMAH BINTI OTHMAN

(Email: [email protected])

Chapter 6:Chapter 6:cRYSTALLIZATIONcRYSTALLIZATION


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COURSE OUTCOMESCOURSE OUTCOMES

CODESCRIBEthe basic

principles andapplications of

crystallization process.

CALCULATE the yields,aterial and ener!ybalance in crystallization.


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Basic principlesand applicationsof crystallization

process.CALCULATI"# of

yields, aterialand ener!ybalance in

crystallization.

OUTLINESOUTLINES


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Process ofproducing crystals from ahomogeneous phase which is obtained from asolution.

Capable of producingbioproductsat very highpurity and considered to be a polishing step and apurification step

Two different application of crystallization:

i. Crystallization for polishing and purification

ii. Crystallization for crystallography

CRYSTLLI!TIONCRYSTLLI!TION


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COMPARISON OF CRYSTALLIZATIONCOMPARISON OF CRYSTALLIZATION

AND PRECIPITATIONAND PRECIPITATION

Desrip!i"n #rys!alli$a!i"n %reipi!a!i"n

Solubility Wide range, usuallymedium to high

Sparingly soluble

Relative

supersaturation

Low High

Product morphology Well-defined Ill-defined

Product crystal sie Large Small

!ucleation

mechanism

Secondary Primary

!ucleation rate Low High

"rowth Rate Wide Range Low

#ontrollability #ontrollable $ifficult to control


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CRYSTLLI!TION "ROM

SU#ERSTURTE$ SOLUTIONS O"

SO$IUM CETTE

Description$A supersaturated solutionofsodium acetate is crystallied !y pourin" it

onto a seed crystal# formin" a stala"mite$li%e solid& 'eat is radiated from the solid&

So%rce$Sha%hashiri# (&Z& Chemical )emonstrations: A'and!oo% for Teachers of Chemistry


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CRYSTALLIZATION PRINCIPLESCrystals Can appear as polyhedrons# or solids formed !y plane

faces *hen allo*ed to form freely&

Anglesmade !y the correspondin" faces of the samematerial do not +ary , can !e classi-ed !y thischaracteristics&

Relati&e sizes of the faces of a crystal in a particularsystem can +ary considera!ly , res%ltin! in a &arietyof crystal shapes& This +ariation is called a habit&

Crystal habit is in.uence !y the conditions of

crystalliation# particularly !y the impurities presentand !y the particular sol+ent or sol+ents used&

Impurities can stunt the "ro*th of a crystal in certaindirections&


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%O&'HEDRONS SHA%E


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TAB&AR

%oo&-li&e 'tablets( that are thic&er than pla!y

but not as longated as laded.*ul+eni!e

forms crystals that are a good e)ample of

tabular crystals*

%RISMATI#

+ne of the most common of crystal habits*

Prismatic crystals are pencil-like, elongatedcrystals that are thic&er than needles 'see

aiular(* Indi"li!e'a variety of elai!e( forms

good e)amples of prismatic crystals*

A#I#&AR

Long and needle-li&e, thinner than

prisma!ibut thic&er than +ir"us.Na!r"li!e

crystals can be good e)amples of acicular

crystals*


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CRYSTLS %RO&

IN ' STE#S(

'. #%cleation ( )rsta!!re!ation.

*. +roth. Therodynaicallydistinct

-ant a fe n%clei to

!ro bi! Use therodynaicsto %nderstand there%ired conditions


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#%cleation

The "eneration of %ltraicroscopic particles in the processof nucleation is the sum of contri!utions !yprimary nucleationand second nucleation.

/riary n%cleation: occurs in the a!sence of crystals#secondary n%cleation: attri!uted to the in.uence of e/istin"crystals

/riary n%cleation can !e either homo"eneous 0no forei"nparticles are present1 or hetero"eneous 0forei"n particlespresent durin" hetero"eneous nucleation1

Rate of primary nucleation has !een modeled !y the follo*in"po*er la* e/pression:

#rys!alli$a!i"n %riniples#rys!alli$a!i"n %riniples

'(

B. number of nuclei formed per unit volume per unit time/

N. number of nuclei per unit volume/ kn. rate constant/

c. instantaneous solute concentration/c0. solute

concentration at saturation* 'c-c0( term . supersaturation,

the e)ponent of ncan range up to 1 but typically is in

the range of 2 to 3*

RY T LLIZ TI N


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RY T LLIZ TI N

PRINCIPLESPRINCIPLES T*o types of secondary nucleation : shear

nucleation 0occurs as a result of .uid shear on"ro*in" crystal faces1# contact nucleation0 happens !ecause of crystals collidin" *ith eachother and *ith the impeller and other +esselinternal surfaces&

Rate of secondary nucleation in crystalliation isthe follo*in":

'4(

k. rate constant/ MT. suspension density, b. can

range up to 5 but has a most probable value of 4/

j. ranges up to *5 with being the most probable value

C


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Crystallization PrinciplesCrystallization Principles

,i-ure :6ypical phase diagram* 6he

components in solution consist of the product

'ordinate( and the precipitating reagent

'abscissa(* 6he lines with arrows out line one

possible way of performing the crystalliation*

- 6he supersaturation must be above the a

certain value before nucleation will begin

- 7etastable region . the supersaturation islow that nucleation will not start

- +nce the supersaturation has been

raised enough to be in the labile region,

nucleation can begin*

- A! !his p"in!, crystals begin to grow, andthe supersaturation decreases

- If the supersaturation becomes too high,

the nucleation rate will be too great, and

amorphous precipitate will result*


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#rys!alli$a!i"n %riniples#rys!alli$a!i"n %riniplesNulea!i"n


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SupersaturationSupersaturationPHASE DIAGRAMSPHASE DIAGRAMS

Precipitatant concentration (salt, PEG etc.)

Pr

otein

conce

ntration

Under-saturation(protein remains soluble; crystals dissolve)

Nucleation zoneNucleation zone

Precipitation zonePrecipitation zone

Solubility

curve

Metastable zoneMetastable zoneCrystals grow, butCrystals grow, but

Nuclei form onlyNuclei form onlyinfinitely slowlyinfinitely slowly

COURSE OF CRYSTALLIZATIONCOURSE OF CRYSTALLIZATION


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COURSE OF CRYSTALLIZATIONCOURSE OF CRYSTALLIZATION

EXPERIMENTEXPERIMENT

[Precipitatant]

Pr

otein

conce

ntration

NucleationNucleation

PrecipitationPrecipitation

MetastableMetastable

Start w/soluble protein(undersaturatedor metastable)

NucleatesNucleatesherehere

Incr

ease

[pr

otein],

[pr

ecipit

ant]

Crystal growsCrystal growsSequesters proteinSequesters protein

[protein] rops[protein] rops

Crystal stops growing !Crystal stops growing !

solubility cur"esolubility cur"e

#$pt incr% [protein], [precipitant]&tl grows again, until hits cur"e

'epeats as follows solubility cur"e

C lli i P i i lC t lli ti P i i l


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Crystal +roth

2ost nucleation process in *hich molecules in solution are

added to the surface of e/istin" crystals

The rate of mass deposition Rdurin" crystal "ro*th is:

O+erall linear "ro*th rate can also !e e/pressed as:

L: characteristics sin"le dimension of the crystal# such as len"th

Crystallization PrinciplesCrystallization Principles

'2(

'3(

W: mass of crystals per volume of solvent/

A: the surface area of crystals per volume of

solvent/kG: overall mass transfer coefficient 'depends

on temperature, crystal sie, hydrodynamic

conditions, the presence of impurities(/

g: usually 1 and 4*5


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CRYSTALLIZATIONCRYSTALLIZATION

PRINCIPLESPRINCIPLES

Crystal !roth is a process that consists oft*o steps in series , di3usion and surfaceinte"ration

4hen the e/ponents are unity# com!inin"5uation 7# 8# 6 "i+es

'5(

ci. concentration at the interface between the li8uid

and solid phase/kdand kr. mass transfer

coefficients

'9(

':(

6hus, if surface integration is very fast

compared with bul& diffusion, then kr;; kd,

and kG , &d*


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YIELDS AND HEAT AND MATERIALYIELDS AND HEAT AND MATERIAL

BALANCES IN CRYSTALLIZATIONBALANCES IN CRYSTALLIZATION 0ields and aterial balance in crystallization

The sol%tion 1other li%or2 and the solid crystals are incontact for enou"h time to reach euili!rium& 'ence# themother liuor is saturated at the -nal temperature at the-nal temperature of the process# and the -nal process# andthe -nal concentration of the solute in the solution can !eo!tained from the solu!ility cur+e&

The yield can !e calculated 3noin! the initialconcentration of sol%te, the )nal teperat%re, andthe sol%bility at this teperat%re.

In ma%in" the material !alances# the calculations arestrai"htfor*ard *hen the solute crystals are anhydrous&Simple *ater and solutematerial !alances are made& 4henthe crystalliations are hydrated# some of the *ater insolution is remo+ed *ith the crystals as a hydrate.

EXAMPLE 1EXAMPLE 1


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EXAMPLE 1EXAMPLE 10ield of a Crystallization /rocess

A salt solution *ei"hin" 9 %" *ith 7 *t ; Na


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EXAMPLE 1EXAMPLE 1Sol%tion

The molecular *ei"hts are 96& for Na


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Example 1Example 1Ea%in" a !alance for Na


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8eat e9ects and heat balances in crystallization

4hen a compound *hose solu!ility increases astemperature increases dissol+es# there is an a!sorption ofheat# called the heat of solutionoccurs *hen thesolu!ility decreases as the temperature increases

At e%ilibri%the heat of crystalliation is eual to the

ne"ati+e of the heat of solution at the same concentration insolution&

The enthalpy H9of the enterin" solution at the initialtemperature is read o3 the chart# *here H9is % for the totalfeed& The enthalpy H


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EXAMPLE 2EXAMPLE 2

8eat Balance in

CrystallizationA feed solution of


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EXAMPLE 2EXAMPLE 2

Sol%tion

Ea%in" a *ater !alance and a !alance for E"SOH

usin" euations similar to 0971 and 09H1 in

5/ample 9# C F 696&= %" E"SOH@G'


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Example 2Example 2The heat of solution is $097&79/971


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CRYSTALLIZATIONCRYSTALLIZATIONTank Crystallization

'ot saturated solutions are allo*ed to cool in opentan%s

After a period of time# the mother liuor is drained andthe crystals remo+ed

Nucleation and the sie of crystals are diKcult tocontrol

La!or cost are +ery hi"h

'as limited application used to produce certain -nechemical and pharmaceutical products&

E i t ! C t lli tiEqipment !or Crystallization


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Scraped s%rfacecrystallizers

One type of scraped surfacecrystallier is the Senson(-al3er crystallizer# *hichconsists of an open trou"h 6.: ide *ith a semicircular

!ottom ha+in" a coolin" Mac%etinside&

Slo(speed spiral a!itatorrotatesand suspendsthe"ro*in" crystals on turnin"&

(lades pass close to the *alland !rea% o3 any deposits ofcrystals on the cooled *all&

sed in crystallizin! icecrea and plasticizin!ar!arine&

Eqipment !or CrystallizationEqipment !or Crystallization

E i t ! C t lli tiEqipment !or Crystallization


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Circ%latin!(li%id e&aporated(crstallizer

S%persat%rationis "enerated !y

e+aporation& Circulatin" liuidis dra*n !y the scre*

pump do*n inside the tu!e side ofcondensin" steam heater

8eated li%id then .o*s into the+apor space# *here .ash e+aporation

occurs# "i+in" some supersaturation& The +apor lea+in" is condensed& The supersaturated liuid .o* do*n

the do*n.o* tu!e and then upthrou"h the !ed .uidied and a"itatedcrystals# *hich are "ro*in" in sie&

The li+in" saturated liuid then "oes!ac% as a recycle stream to the heater#*here it is Moined !y the enterin" feed&

The lar"er crystals settle out and aslurry of crystals and mother liuor is*ithdra*n as product&

Also called "slo crystallizer.




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Circ%latin!(a!a&ac%% crystallizer

The ma"ma or suspension of crystalsis circulated out the main !ody throu"ha circulatin" pipe !y a scre* pump

Ea"ma .o*s throu"h a heater# *hereits temperature is raised &

The heated liuor then mi/es *ith!ody slurry and !oilin" occurs at liuidsurface

This cause supersaturation in thes*irlin" liuid near the surface# *hich

results in deposits on the s*irlin"suspended crystals until they lea+ea"ain +ia the circulatin" pipe

The +apors lea+e throu"h the top

A steam$Met eMector pro+ides the+acuum



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Chapter 8 Crystallization