Note: Descriptions are shown in the official language in which they were submitted.
113~4
- 1 - DN 79-37
DECATIONISATION OF AQUEOUS -SUGAR SOLUTIONS
This lnvention is concerned with the decationisation
of (i.e. complete or partial removal of cations from)
S aqueous sugar solutions.
The field t~ which the invention relates is the
purification of solutions in sugar refineries or mills
which are at least decationised and possibly also deanion-
ised and/or decolorised using ion exchange resins.
In conventional ion exchange processes for the
decationisation of aqueous sugar solutions, the solution
is passed in a fixed bed process, through a bed of ion
exchange resin containing strong acid cationic exchange
resin in the hydrogen form. However, it has been necessary
to cool the sugar to minimise inversion which takes place
when sugar is subjected to a low pH, as is inevitable at
the exchange sites in a strong acld cation exchange resin,
for the time required for the sugar solution to pass
through the bed within acceptable hydraulic parameters,
that is to say without an unacceptable pressure drop.
Since cooling down to about 10C is needed, this signifi-
cantly increases the viscosity of the sugar solution and
so the problem is compounded, and the sugar solution has
usually been diluted to offset this effect, at least in
part. The diluted solution has eventually to be
reconcentrated and this, of course, is wasteful in power
consumption.
It is known from Italian Patent 641205 to treat sugar
solutions in a batch process with ion exchange resins.
30 Batch treatment, wherein sugar solution and ion exchange _ --
resin are- -- - ------~~~~ ~-~~~~~~~~~~~~~
... . . , _ . .
'
`''
4L~
mechanicall~ ag tatsd together does not demand that the sugar
solution bs 2S low in viscosity as in a process wherein the
sugar solution must flow through a fixed bed of resin. This
specification, however, does not teach how to avoid inversion
of raw sugar solution which is contacted with strongly acid
cation exchange resin in the hydrogen form other than in a
mixed bed of anion and cation exchange resins. Furthermore,
the teaching is wholly silent as to the nature o~ the resins
used, for example whether they are strong or weak electrolyte
resins
We have now unexpectedly found that raw sugar solution
can be successfully decationised without the conventional
degree of cooling and therefore without the need to dilute
as much, or at all, in a batch process by contacting it with
a strong acid cation exchange resin in the hydrogen form under
closely defined time and temperature conditions without an
unacceptable level of inversion taking place. Furthermore,
we have found that inversion can be kept within acceptable
- limits and deionisation and some decolouration can be achieved
by using, in a batch operation, strong or weak cation exchange
resins in a mixed bed with anion exchange resin, usually in
the hydroxide or free base form, at temperatures higher than
have, as described above,conventionally been used with a
fixed resin bed.
Accordingly this invention provides a process for the
- decationisation of an aqueous sugar solution wherein the
solution is passed into contact with ion exchange resin in i~ a batch reaction, agitated therewith and separated therefrom~
and wherein the resin (a) comprises strong acid cationic
exchange resin in the hydrogen form, the temperature is from
20 to 40C, preferably 25 to 30C~and the contact time
between the sugar solution and the resin is at most 20 minutes~
or (b) comprises a mixture of weak acid cation exchange resin
in the hydrogen form and an anion exchange resin, the tempera-
ture is 20 to 90 C preferably 40 to 90C, most preferably
50 to 65C, and the contact time between the resin and the
sugar solution is at most 90 minutes.
Any strong acid cation exchange resin is useful in resin
113~4~g
(a) in the process of the invention. Preferred resins are
macroreticular styrene/divinylbenzene resins, such as"Amber-
lite 200"or"Amberlite 252"~r the highly crosslinked gel resins,
such as"Ar.berlite IR-122" nd"Amberlite IR-124"commercially
available from Rohm and Haas Company.
Any weak acid cation exchange resin can be used in
admixture with the anion exchange resin in the deionisation
and decolourisation process of the invention. The most
preferred are acr~lic acid/divinylbenzene resins such as
"Amberlite IRC-84"or methacrylic acid/divinylbenzene resins
- such as"Amberlite IRC-50"also commercially available from
Rohm and Haas Company.
The strong acid cation exchange resins can, and the
weak acid cation exchange resins should, be used in the
process of the invention in a mixed bed of resins containing
anion exchange resins whereupon deionisation and removal of
some colour bodies can be achieved. Any anion exchange resin
can be used for this purpose. However, it is preferred to
use acrylic anion exchange resins such as the macroreticular
resin Amberlite IRA-35 and the gel resin Amberlite IRA-68
(both commercially available from Rohm and Haas Company)
since these afford minimal regenerant requirement and optimal
decolourisation efficiency.
` The sugar solutions capable of being treated by the
- 25 process of the invention may be any aqueous solution of sugar
(including molasses) to be found, or which can be made up,
in a sugar mill or refinery operation. The impurities
generally contained in such solutions are those organic and
mineral salts found in the sugar beet and sugar cane, such
as betaine, pyrrolidone carboxylic acid, amino acids and
sodium and potassium salts.
On contacting the cation exchange resin, either alone
or in the mixed bed, the cations in these impurities will be
exchanged for hydrogen ions and the exhausted resin will
consequently need to be regenerated to remove the cations
with which it is loaded.
It is surprising that a weak acid cation exchange resin
can remove the indicated cations within the time and
1 - 8 inclùsive. The terms bearing these superscript numerals
are trademarks.
--4--
temperature constraints definQd.
The anion exchange resin, when used, will partially or
completely deionise the solution by removing the mineral
and/or organic acids resulting from the cation exchange to
liberate water, the anion exchange resin being in the hydroxyl
(in the case of strong electrolyte anion exchange resins) or
free base (in the case of weak electrolyte anion exchange
resins) form. The exhausted ion exchange resin will therefore
need to be regenerated to remove the exchanged ions and
reconvert it to hydroxyl functionality or free base form.
Additionally, the anion exchange resin will remove colour
bodies usually present in the sugar solution and these can be
eluted from the resin along with the exchanged ions during
regeneration.
Regeneration of the cation exchange resin can be effected
in known manner by contacting the exhausted resin with strong
mineral acid.
Regeneration of the anion exchange resin, and removal of
colour bodies therefrom, can conveniently be achieved by
contacting the resin with a solution of strong base, in the
case of a strong electrolyte resin, or with ammonia or a
solution of a strong base in the case of a weak electrolyte
resin.
The concentrations of solutions which can be treated by
the process of this invention may be as high as 88 Brix. This
is of course much higher than the concentrations treatable
by prior art fixed bed processes. The solutions treated may
already be present in the sugar mills or refineries at the
indicated concentration or any existing refinery or mill
streams which have lower Brix values can be concentrated, for
example by evaporation or mixing to increase their Brix values.
Thus, the invention can be used to treat standard syrup, poor
strike machine syrups and molasses.
The proportions of resin to sugar which would effectively
decationise and deionise the sugar solution depend, amongst
other things, on the level and nature of the impurities, the
resin chosen, the temperature, concentration and time of
contact and will optimised by trial-and-error experimentation
in any particular case. The ratio may be expressed as
a ratio of resin volume (mls) to weight of non-sugar (grams)
impurities. Depending on the operating conditions, this
ratio would generally be l.0 to 3 0, most usually 1.2 to
1.6, for decationisation alone.
For deionisation in a mixed bed of weak electrolyte
resins, from 35 to 75 grams of non-sugar per litre of mixed
resin can be removed from the sugar solution in a bed con-
taining a ratio of cationic to anionic resin of 1:1.5 to
1:5, in 0.5 to 1.5 hours.
As to the conditions used in the process of the
invention, for decationisation alone we prefer to operate
at a temperature of from 20 to 40C~preferably 25 to 35C~
using a contact time of 3 to 15 minutes, preferably 5 to
10 minutes. Under these conditions solutions having a
concentration of 60 to 78 Brix can effectively be treated.
For deionisation using a mixed bed containing strong
cation and, usually weak, anion exchange resins we prefer
to use the same temperaturesand a contact time of 5 to 20
minutes, preferably lO to 20 minutes, more preferably lO
to 15 minutes; We also prefer a cation to anion exchange
resin ratio from 1:1 to 1:5.
For deionisation using a mixed bed of weak electro-
lyte resins we prefer to use temperatures from 20 to 90C,
25 more preferably 40 to 90C, most preferably 50 to 65C,
and a contact time of 60 to 90 minutes. Under these
conditions solutions up to 88 Brix can be treated.
Some preferred embodiments of the invention will now
be described for the purposes of illustration only, in the
following Examples in which all percentages are by weight
unless otherwise specified.
Example l - Decationisation
_
250 grams of poor strike machine syrup were stirred
for 10 minutes, at 30C and in a 500 ml beaker with 52 ml
of AMBERLITE 252 in its H form (a macroreticular strong
cation resin). The mixture was then transferred to a
sintered glass
--rJ--
~ilter and the trea~,_d syrup waC; analysed, after filtration,
giving the ~ollowing results:
Poor Strike
Machine syrup Treated syrup
Brix 69.1 ' 65.1
Sugar % 53~5 50.6
Purity 77-4 77~7
Non sugar 15.6 14.5
pH 7.0 3.7
K+ (%) 1.58 0.67
K (% Brix) 2.29 1.03
K removed (%) 55-
Percent Inversion - none
Example 2
Deionisation using a Strong_Acid/Weak Base,Monobed
200 grams of sugar syrup were stirred for 20 minutes,
at 30C and in a 500 ml beaker with a mixed bed of resin
comprising 41 ml of AMBERLITE 252 and 78 ml of AMBERLITE
IRA-68, in the H+ and free base form respectively. The
mixture was then transferred to a sintered glass filter and
the treated syrup was analysed after filtration giving the
following results:
Raw syrup 'Treated_syrup
Brix 69.0 60.2
Sugar % ,' 63.7 58.9
Purity 92.3 97.8
Non sugar % 5.3 1.3
pH , 8.8 5.7
Colour (% Brix) 1670 150
K+ (%) 0.58 traces
Na (%) 0.09 traces
Percent Inversion - none
' Example 3
Deionisation Using a Weak Acid/1~leak Base Monobed
250 grams of a mixture of sugar syrup and poor strike
.. . _ . . .. . . .
11 38~9L4
machine syrup were stirred for 90 minutes at 60C and in
a 500 ml beaker with a mixed bed of resin comprising 41
ml of AMBERLITE IRC-84 and 78 m:L of AMBERLITE IRA-35, in
the H+ and free base form respectively. The mixture was
then transferred to a sintered glass filter and the treated
syrup analysed, giving the following results:
Mixture
of syrupsTreated syrups
Brix 68.6 64.7
Sugar % 61.7 61.1
Purity 90.0 94.4
Non sugar (%) 6.9 3.6
pH 8.7 6.6
Colour (% Brix) 2420 310
K+ (~) 0.61 0.13
Na (%) 0.24 0.05
Percent Inversion - none
Example 4 - Deionisation using Weak Acid/Weak Base Monobed
In to a column 5.1 m high and 0.3 m diameter were
placed a mixture of 28.5 1 of AMBERLITE IRC-84 and 57.0 1
of AMBERLITE IRA-35 accounting for 40 cm and 88 cm of bed
height respectively. 53 cycles of loading and regeneration
were carried out treating a 69.7 Brix sugar solution
containing 91.5% by weight sucrose and 8.5% by weight
non-sucrose on a solids basis. The non-sucrose was
predominantly amino acids, other acids, colour bodies,
sodium and potassium salts. In each loading cycle the
resin was agitated (by passage upflow of preheated air)
for 80 minutes at a temperature of 65C with the sugar
solution. After loading the resins were separated by
upflow of very dilute sugar solution, rinsed with deionised
water and regenerated with dilute sulphuric acid and
ammonium hydroxide by standard procedures. Before the
next loading cycle the resins were re-mixed.
The purity of the treated sugar was increased to 94.5%
1 13~
(from 91.5%) and 75% of the colour bodies were removed
as was 62% of the potassium. The sucrose yield is
increased by 1.5 times the weight of non-sucrose removed.
Comparative Calculation
Extrapolating these results to compare a conventional
system (fixed bed with strong sulfonic acid resin and
weak carboxylic resin) with a system operated according
to Example 4 gives the following comparison. In order
to obtain a direct comparison certain fundamental assump-
tions common to both systems have to be made. In this
case we have assumed that sugar solution (syrup) to be
treated is the product of the processing of 9,500 Tonnes
per day of beet and that it has been decided to remove
44.2 Tonnes per day of non-sucrose from that solution.
System operated
Conventional according to
IER System Example 3
Percent total syrup treated 30 - 40 100
Influent syrup purity91.5% 91.5
(sucrose content) ;
Total resin volume (M3) 253 105
Cation resin volume (M3) 143 35
Anion resin volume 110 70
Total no. of columns 24 8
Total3vol. spent regenerant 1523 820
(M /day) (sulphuric acid
and ammonia)
Water used and to be evap- 888 473
orated in reconcentration
of syrup (Tonnes/day)
Sulphuric acid regenerant 30.586 17.857
(Tonnes/day)
Ammonia regenerant6.718 7.514
(Tonnes/day)
Percent Decolourisation 20 - 24 75
It can be seen therefore that capital and operating
costs using the system of the invention can be much reduced
1 ~3~4~
over those of the prior art, and there is an additional
advantage in the decolourisation achieved. Of course if
the basic assumptions are changed the benefit may be
obtained in terms of greater non-sucrose removal, and
therefore sucrose yield, at the expense of some of the
capital and operating cost savings.
"Amberlite" and "Monobed" are trademarks of Rohm and
Haas Co., Philadelphia, United States of America.
Amberlite 252 is a macroreticular styrene/divinyl-
benzene strong acid cation exchange resin used in the H+form.
Amberlite IR~-35 is a macroreticular acrylic weak
base anion exchange resin.
Amberlite IRA-68 is a gel acrylic weak base anion
exchange resin.
Amberlite IRC-84 is a gel acrylic acid weak cation
exchange resin.
