THE PEOPLE
BEHIND SUGAR
Presents a Technical Paper to BSST 11/10/2012
Decolourisation Techniques used in Sugar Refining
What is Refined Sugar?
THE PEOPLE BEHIND SUGAR
Early Sugar Refining in London
Bone Char Treatment
Taylor Filters
The Wash Floor
What is Refined Sugar?
Typical Refined Sugar Colours
EEC Grade I 20 IU colour
Bottlers Grade 35 IU colour
EEC Grade II 45 IU colour
EEC Grade III 60 IU colour
White Sugar
<100 IU colour (typical)
What is Refined Sugar?
Other Typical Refined Sugar Requirements
Filtered (as a dissolved solution)
Suspended solids less than 2ppm
Pol 99.9 minimum
Ash 0.015% maximum
Invert 0.020% maximum
Other The full list of requirements for refined sugar may vary from one
grade of sugar to another and these are often on a sliding scale as in the
case of EEC Sugars. However, the important parameters listed above
along with sugar colours are typical specifications for refined sugars.
Sugars such as bottlers grade may be subject to individual purchasers
specifications, and the likes of the international Cola beverage companies
have their own world standards for acceptable sugars for their drinks
formulations.
What is Refining?
A series of steps for removing
impurities and Colour
Affination
Melting
Clarification
Phosphotation or
Carbonatation
Filtration
Pressure Filtration or
Deep Bed Filtration
Decolorisation
Ion Exchange Resin ,
Powdered Activated
Carbon or Granular
Activated Carbon
Primary Decolourisation
Phosphatation
Carbonatation
Evaporation
Crystallisation
Drying
Conditioning
Bagging and
packing
3 , 4 or 5 boiling or
backboiling
Secondary Decolourisation
Ion Exchange Resin
Powder Activated Carbon
Granular Activated Carbon
Types of Colorants in Raw Sugar
Types of Colorants in Raw Sugar
Indicator Value = Colour pH9 / Colour pH4
Origin of Colorants in Raw Sugar
Colour Profile in Raw Sugar
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
A
E
5.0
0.0
0.0
5.0
High
10.0
15.0
20.0
25.0
Molecular Weight
30.0
35.0
40.0
Low
Colours after Affination
Process
45.0
Percent Removed
C
A
40.0
Affination
56%
43%
34%
35.0
30.0
B
25.0
20.0
15.0
D
10.0
5.0
0.0
0.0
5.0
High
10.0
15.0
20.0
25.0
Molecular Weight
30.0
35.0
40.0
Low
34%
34%
Colours after Carbonatation
Process
45.0
Percent Removed
C
A
56%
43%
34%
34%
34%
Carbonatation 80%
50%
50%
50%
20%
40.0
Affination
35.0
30.0
B
25.0
20.0
15.0
D
10.0
5.0
0.0
0.0
5.0
High
10.0
15.0
20.0
25.0
Molecular Weight
30.0
35.0
40.0
Low
Colours after Ion Exchange Resin
Process
45.0
Percent Removed
C
A
Affination
56%
43%
34%
34%
34%
Carbonatation
80%
50%
50%
50%
20%
0%
92%
67%
93%
50%
40.0
35.0
Acrylic
30.0
B
25.0
20.0
15.0
D
10.0
5.0
0.0
0.0
5.0
High
10.0
15.0
20.0
25.0
Molecular Weight
30.0
35.0
40.0
Low
Colours after Carbon
Process
45.0
Percent Removed
C
A
Affination
56%
43%
34%
34%
34%
Carbonatation
80%
50%
50%
50%
20%
Acrylic
0%
92%
67%
93%
50%
Carbon
33%
40%
50%
72%
50%
40.0
35.0
30.0
B
25.0
20.0
15.0
D
10.0
5.0
0.0
0.0
5.0
High
10.0
15.0
20.0
25.0
Molecular Weight
30.0
35.0
40.0
Low
Decolourisation Systems Comparison
20.00
18.00
16.00
14.00
12.00
10.00
8.00
6.00
4.00
2.00
0.00
10
15
20
25
Resin/Granular Carbon
30 5
35 10
40 15
20
Bone Char
25
Processing Choices
COLOUR
REMOVAL
ACROSS
PROCESS
50%
50%
50-80%
90%
IER
CARBONATATION
CRYSTALLISATION
RAW
SUGAR
GAC
AFFINATION
&
CENTRIFUGAL
SEPARATION
PHOSPHATATION
PAC
REFINED
SUGAR
Removal Chart
How do they Work?
Affination
Raw
Sugar
Bin
Syrup
Overflow to
Recovery
Steam
Weigher
44oC
Wash
Water
To Melter
Syrup
How do they Work?
Affination
A large proportion of the Raw Sugar Colour is on the
surface syrup layer and the rest is included in the Crystal
It is easy in Affination to OVERWASH and dissolve
crystal rather than just remove surface syrup
Only two Variables that can be controlled by the Affination Process:
Magma Temperature
Wash Water Addition
How do they Work?
Affination
Magma Too Hot Too Much Crystal will be dissolved
Magma Too Cold Impurity not removed from Surface of Crystal
Magma Temperature Just Right All Surface Impurity Removed and
No Crystal Dissolved
Around 44C is correct Magma Temperature
Magma Temperature needs to be measured not Green Syrup
Temperature
How do they Work?
Affination
Syrup is a closed circuit with just an overflow to Recovery
The only way Impurity or Crystal can be dissolved is by the
addition of Water at the Centrifuge
Typically aim for 72 brix and 84-88 purity to give 7% of Raw
Sugar going into Green Syrup
How do they Work?
Carbonatation
How do they Work?
Carbonatation
CAPTURE of impurities so that they can be
filtered out of the syrup
REMOVAL of impurities by filtration
Note: In carbonatation the CaCO3 that is
formed is the filter aid
A SIMPLE SERIES OF REACTIONS:
CaO + H2O
Ca(OH)2 + CO2
Ca 2+ + imps
Ca(OH)2 + CO2 + Imps
Ca(OH)2
CaCO3
Ca(imps) 2+
CaCO3(Imps)
How do they Work?
Carbonatation
Liquor is a
concentrated solution
There is barely enough
water to dissolve the
sucrose so not much
is left over to dissolve
anything else
Some impurities are
already out of solution
(turbidity) or close to
precipitation
Adding lime into the syrup does three things:
o Raises the pH
o Changes the ionic strength of the solution
o Changes the ionic environment of the impurities
The local environment of any dissolved species is significantly disturbed.
Many species are no longer soluble (or as soluble as they were)
Bubbling CO2 into the mixture causes precipitation of CaCO3 to occur
These crystallites provide nucleation sites for the co-precipitation of some of the
impurities
Many of the high Mw species are acids at the higher pHs seen in carb they form
anions which can then complex with Ca 2+
How do they Work?
Carbonatation
Filterability vs % Lime
4.50E-07
4.00E-07
3.50E-07
3.00E-07
2.50E-07
2.00E-07
1.50E-07
1.00E-07
5.00E-08
0.00E+00
Final colour
Quality
Amount added
Method of addition
Lime
Final colour vs % LIme
950
900
850
800
750
700
650
600
0.4
0.4
0.5
0.6
0.7
0.8
0.9
1.1
0.5
1.2
0.7
0.8
Colour (RL)
F (Powd Lime)
CO2
Gassing rate
Bubble size
Kinetics of absorption
Large bubbles
Small bubbles
Slower kinetics
Poor mixing
Less crystallites but larger
0.9
% Lime
Amount of lime (% CaO on brix)
F (Rock Lime)
0.6
Faster kinetics
Propensity to form Foam
Lots of crystallites
Colour (PL)
1.1
1.2
How do they Work?
Carbonatation
Mixing
Rate determining step is the transfer of
Ca(OH)2 to the surface of the gas bubbles
Phase boundary
layer
Transfer of CO2 through the phase boundary
layer can become rate limiting
CO2 concentration and pressure of the gas can
influence the CO2 absorption efficiency
CO2
GAS
pH
We are titrating a basic solution with an acidic
gas.
Our reactor is continuous so every stage of
the titration is represented within the vessel
Ca 2+
LIMED SYRUP
How do they Work?
Carbonatation
How do they Work?
Phosphatation
How do they Work?
Phosphatation
3Ca(OH)2 + 2 H3 PO4 = Ca3(PO)4 + H20
There are two steps in the process: Floc Formation and Floc Separation.
Mechanism;
Precipitate formation: Phosphoric acid and Lime reacts to produce a
large amount of calcium phosphate crystals.
Those crystals adsorb in their surface the colloids in suspension
producing a primary floc.
A cationic decolorant (high molecular cationic polymer) can be used to
capture negative charged colorants
Flocculant (high molecular anionic polymer) is added to coagulate
primary flocs into bigger secondary flocs.
How do they Work?
Phosphatation
Liquor
Heating
Chemical
Addition
Ph
FC
Flocculant
FC
Lime
Acid
Decol.
Air
FC
Reaction
Primary
Floc
Formation
Aeration
FC
Flocculant
Addition
TC
Secondary
Floc
Formation
Steam
Raw Liquor
Scums
Clarified
Liquor
How do they Work?
Phosphatation
The more air in the system the better the
performance of the clarifier.
Cavitation:
A disc at the end of a hollow shaft rotates in the liquor
producing microscopic air bubbles.
Dissolved air: (Scum Desweetening)
Compressed air is fed into the eye of the aeration
pump impeller. The air blends with the liquor and
dissolves under the pressure. It requires an aeration
chamber or a pressurized tank that provides time for
the air to dissolve. The pressure should be 70 to 100
psig. When the pressure is released the air comes out
of solution in the form of microscopic bubbles.
How do they Work?
Phosphatation
The thickness and consistency of the scums bed is
controlled by:
The weir box setting that regulates the level of
liquor.
The speed of the scums rake that controls the
scums removal.
Self Draining
How do they Work?
Phosphatation
Temperature : 85oC (176oF).
Lower temperatures increases the viscosity of the liquor.
Higher temperatures favours inversion and color formation.
Liquor Concentration: 63 to 65 brix.
Acid dose: 150 to 500 ppm P2O5
Ph on reaction tank: 7.0 to 7.5 Controlled by the addition of lime
Cationic Decolorant: 100 to 300 ppm active ingredient.
Flocculant: Max 10 ppm
How do they Work?
Phosphatation
How do they Work?
Activated Carbon
How do they Work?
Activated Carbon
Macroscopic
Crack / Crevice
Graphitic Crystallite
Graphite
plate
10 millimetres
Coal Particulates
1 millimetre
1000 angstroms
Macroscopic Crack
How do they Work?
Activated Carbon
pH
Non-dissociated form is more strongly adsorbed.
Dissociated form behaves as competitor for adsorption space.
Temperature
As temperature increases, capacity decreases
This may reduce capacity for the most volatile compounds 10-20%.
Particle Volume
Pore size distribution has a dramatic influence on adsorptive performance. Removal of trace
levels of contaminants requires an extensive micropore volume.
Bed Depth
Increasing bed depth means the Mass Transfer Zone is a smaller percentage of the bed.
Flow Rate
Increasing the flow rate does reduce the efficiency.
How do they Work?
Activated Carbon
PAC
GAC
Rely on external surface area
Rely on internal surface area
Cannot normally be reactivated
Can be thermally or chemically re-activated
Requires a precoat filter to be removed
Requires on site regeneration
Varying Quality of feed is accommodated
Varying Quality of feed is NOT accommodated
Low Capex, high opex option
Requires large inventory of GAC
Typical dose 0.05 to 0.5% on Sugar Solids
Typical burn rate 0.5 to 0.8% on Sugar Solids
Contact time 20-30 mins
Contact time 2-5 hrs
Solid effluent
Liquid and Gaseous effluents
How do they Work?
Activated Carbon
USCE - Egypt
How do they Work?
Ion Exchange Resins
How do they Work?
Ion Exchange Resins
Colour
Colour
Cl-
Colour
SUGAR
SYRUP
Cl-
Resin
Resin
+
Cl-
Colour
Colour
SUGAR
SYRUP
Colour
Ion exchange: The colorants exhibit mostly an anionic behavior at
alkaline pH and thereby they can be exchanged against the mobile
chloride ions. However this mechanism is not the only one in color
removal.
Colorant molecular weight
Charge density
Type of charge
Degree of hydrophobicity
pH
Ionic strength of the medium.
How do they Work?
Ion Exchange Resins
Steric effect
Porosity of the decolorizing media is a key parameter.
This illustrates why the decolorization of sugar juices is
carried on at relatively low flow rate.
Hydrophobic effect
Polymeric adsorbents have a polarity. The colorants are
basically hydrophobic (not highly soluble in water) and will
tend to be adsorbed on the hydrophobic part of the
adsorption media.
Van der Waals forces effect
These are attractive forces between chemical groups in
contact. They result from a temporary dipole formation.
Hydrogen bonds
It is an electrostatic attraction that occurs between
molecules in which hydrogen is in a covalent bond with a
highly electronegative element.
How do they Work?
Ion Exchange Resins
Anionic Resins used in sugar have usually a quaternary ammonium functional
group and are in Chloride form.
Styrenic
Has aromatic groups in the structure
Selective for colour but low regeneration
efficiency
Acrylic
Is mostly aliphatic
Less selective but easier
regeneration
Acrylic Macroporous
Styrenic Macroporous
Typical Decolorization
50-60%
65-75%
Regeneration Efficiency
Excellent
Good
10% NaCl
10% NaCl + 0.5% NaOH
Aliphatic
Aromatic
Max Feed Colour IU
2500
800
Colour Loading BVIUs
35000
25000
High
Medium
Regenerant
Matrix
Cost
How do they Work?
Ion Exchange Resins
LARGE EFFLUENT VOLUME
Volume
BV
Flow
(BV/hr)
Temperature
(C)
Material In
Material Out
Sweet off 1
2-4
60-80
Hot Water
Liquor Feed Tank
Sweet off 2
2-4
60-80
Hot Water
Sweetwater Tank
Backwash Lower Bed
1.25
2-4
60-80
Recovered Water
Effluent
Backwash Top Bed
1.25
2-4
60-80
Recovered Water
Effluent
Caustic Regen 1
0.64
1-2
60-80
Reclaimed/Fresh Brine
Reclaim Water Tank
Caustic Regen 2
0.58
1-2
60-80
Reclaimed/Fresh Brine
Effluent
Caustic Regen 3
0.43
1-2
60-80
Reclaimed/Fresh Brine
Effluent
Rinse 1
60-80
Reclaim Water
Effluent
Rinse 2
1.5
60-80
Fresh Water
Effluent
Rinse 3
1.5
60-80
Fresh Water
Reclaim Water Tank
Sweet On 1
0.6
2-4
70-80
Feed Liquor
Reclaim Water Tank
Sweet On 2
2-4
70-80
Feed Liquor
Sweetwater Tank
2-4
70-80
Step
Service
How do they Work?
Ion Exchange Resins
OP TIM UM REM OVAL P ROFILE
14
12
DS
NaCl
Other (COLOUR)
10
0
30
-2
40
50
60
70
80
90
100
110
120
How do they Work?
Brine Recovery
What does Nanofiltration do?
It removes colour from the regeneration effluent (brine) in order to
reuse it.
Why is that important?
To save money: reduce Salt, Caustic and water consumption.
Reduces Chloride to effluent
Key NF figures:
Typical: 75 % decolourisation, 85 % recovery
Concentrate
Feed
Membrane
Permeate
How do they Work?
Brine Recovery
How do they Work?
Brine Recovery
Regeneration Effluent
Colour
-Charged
Na+
Nanofilter
Na+ ClColour
-Charged
Na+
Na+ Cl-
Na+ Cl-
Na+ Cl-
Na+ ClNa+ Cl-
Na+ ClNa+ Cl-
Na+ Cl-
Na+ Cl-
Colour
Na+ -Charged
Feed & Concentrate
mixture
High pressure side
Reclaimed Brine
Nanofilter
Trans Membrane Pressure
(TMP)
Permeate
Low pressure side
How do they Work?
Brine Recovery
How do they Work?
Brine Recovery
How do they Work?
Primary Decolourisation Comparisons
Phosphatation operates at higher Brix (65) compared to Carbonatation, so
less steam used, and less combustible fuel
Carbonatation requires double filtration, phosphatation does not
Phosphatation uses less power than carbonatation
Phosphatation is more flexible than carbonatation, especially on flow
capacities
Carbonatation has a more capital intensive cost
Docolourisations similar percentage
Operational costs similar
How do they Work?
Secondary Decolourisation Comparisons
Some Key Points
Carbon decolourisers are superior in removing impurities & flavenoids
GAC & Bone Char have air emissions
IER has waste water emissions
GAC has traditionally had the lowest operating cost
GAC & PAC do not have de-ashing capabilities
IER and Bone Char do have de-ashing capabilities
Bone char uses 90% more energy than GAC for the same decolourisation
IER has the option of membrane treatment to recover 90% of the salt and
drastically reduce waste emissions
Conclusions
Summary of Decolourisation Process Options
Phosphatation + IER Low Capex & Low Opex
Phosphatation + GAC Low/High Capex & Low Opex
Phosphatation + PAC Low Capex & High Opex
Carbonatation + IER Mid Capex & Low Opex
Carbonatation + GAC High Capex & Low Opex
Carbonatation + PAC High Capex & High Opex
References
Brad Ahlgren, Calgon Carbon Corp. - Carbon 101.ppt
T&L HydraCoRe 70pHT Presentation, Thames Jan 2006.ppt
Robert Albright, Albright Consulting - Architecture and App.ppt
Cane Sugar Refining
with Ion Exchange Resins - Purolite
Colour
Norit - Introduction to the purification of
liquid
sugar with Norit Activated Carbon
1) The chemistry of colour removal: a processing perspective SB Davis Proc
S Afr Sug Technol Ass (2001) 75
2) Separation and identification of sugar colourant (TM Letcher and PG
Whitehead ) Proc S Afr Sug Technol Ass (1996) 70
Comparison of methods
1) A Comparative evaluation of Carbonatation and Phosphatation (AS
Vawda) SIT 940
2) Pros and Cons of various decolorisation processes for production of
refined sugar SIT Savannah May 2010
3) Removal of colour in sugar cane juice clarification by defecation, sulfiation
and carbonation
4) Analysis of Refinery Clarification Processses (TLPT) July 2004
THE PEOPLE
BEHIND SUGAR
Thank You!
To ensure the most efficient and effective
refinery, with maximum output and minimized
energy use and environmental impact, or just to
get the best out of your upgrade and refit, talk
to the people behind sugar.
THE PEOPLE BEHIND SUGAR
