Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
SWEETENER SOLUTION PURIFICATION PROCESS
BACKGROUND OF THE INVENTION
Ion-exc~ange resins may be poisoned by t~e
adsorption of substances tbat are either very
difficult to remove or are very easily removed from
th~ polymeric structure of the resin. A guard
chamber containing activated carbon has been employed
for the protection of an anion exchange resin column
used in the purification of uranium values. This
system operates in a pH range of 5-lû. See, U.S.
Patent No. 4,296,075.
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Cation and anion exc~ange resin pairs (or
systerns) are used extensively in the purification of
sweetener solutions, for exarnple, corn syrups, cane
syrups, beet syrups and in other s~/eetener
applications. These ion~exchanye resin systems are
especially useful in purif`ying dextrose syrups for
the production of high fructose corn syrups (HFCS).
These resins are employed for the removal of ash,
specifically conductometric ash as measured by the
beverage industry. A key cause of unwanted syrup
conductance is the presence of salts resulting from
neutralization reactions during the processing of the
syrup. While the cation and anion exchange resins are
effective in removing these salts, other components
present in crude sweetener solution also contribute
to this undesirable syrup conductivity. These other
components are generally weak organic acids, generated
by the breakdown of starches or proteins. These acids
include citric, glutamic, lactic, tartaric and others.
Generally, the specific acids are not identified.
Rather, the mixture of acids in the syrup are termed
"titratable acidity". These weak organic acids are
removed by the anion exchange resin as negatively
charged organic anions. However, due to the low
charge density of some of these acids, they are
easily displaced from t~ne anion exchange resin. T~is
results in an early rollover of the organic acids
from the anion exchange resin causing an unacceptable
rise in syrup conductance. This rollover or bleed of
organic acids into the syrup triggers a need for
regeneration of the anion exchange resin before it
has been fully utilized. Others of these acids will
not be readily displaced and will occupy exchange
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sites which are then unavailable to the inorganic ash
constituents -thereby also shorteniny the useflJl resin
cycle. Such exchanye resin system downtirne is
wasteful bot~ from a processing (tirne) standpoint and
an economic standpoint.
It ~as been discovered, that the
ion-exchanye system downtime can be reduced, and
~ence, overall process efficiency increased, if the
weak undissociated acids in the sweetener syrup are
removed before -they enter the anion exchange resin.
These acids are adsorbed on a properly posi-tioned
microporus adsorbent within the ion exchanye resin
system.
SUMMARY OF T~IE INVENTION
Under low pH conditions present in a
sweetener purification process, the weak organic
acids contributiny to t~e titratable acidity of the
syrup can be removed from the system by a microporous
adsorbent. From this discovery, it has been
theorized that numerous other applications are
possible for t~e use of microporous adsorbents such
as activated carbon for the protection of ion
exchanye resins. These other applications are
described in greater detail herein below.
Thus t~ere is provided an improved sweetener
solution purification process which comprises: (a)
passiny crude sweetener solution t~rough a bed
containing a cation exchange resin,
thereby loweriny the syrup pH; (b) passing the
effluent of said cation exc~anye resin t~roug~ a bed
containing a microporous adsorbent, thereby adsorbing
weak oryanic acids contributiny to titratable
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acidity; and (c) passing the effluent -frorn said
microporous adsorbent t~roug~ a becl containing ar-
anion exchange resin.
BRIEF DESCRIPTIûN OF THE DRAWINGS
FIG. I describes a converltional process
scheme For generating ~lg~ fructose corn syrup
(HFCS). Sections A-D represent t~e dextrose side and
Sections E-I represent t~ fructose side.
FIG. II details one embodiment of t~e
present inventi.on, namely t~e placement of a
microporous adsorbent (MPA) between t~e cation-anion
exchange resin pair used to purify sweetener
solutions. The solid lines represent conventional
solution flow directions, t~e broken lines show
alternative flow directions.
FIG. III is a conductance breakt~roug~ curve
s~owing improved ion exc~ange resin system
performance for carbon treated dextrose syrup (curve
8) over untreated dextrose syrup (curve A).
FIG. IV is a conductance breakt~roug~ curve
s~owing improved ion exc~ange resin system
performance for regenerated carbon treated dextrose
syrup (curve C) over virgin carbon treated syrup
(curve B) over untreated syrup (curve A).
FIG. V is a conductance breakt~roug~ curve
s~owing improved ion exc~ange resin sys-tem
performance for carbon treated fructose syrup (curve
E) over untreated fructose syrup (curve D).
DETAILED DESCRIPTIûN ûF THE INVENTIûN
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T~e present invention involves t~e use of a
microporous adsorbent in a sweetener solution
refining process to protect t~e anion resin o-f t~e
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cation-anion exchange resin system. The terms
"sweetener solution" are intended to inc1ur~e t~ose
crude sugar solutions recognized in the art as common
"sweeteners", for example, corn SyIup, cane syrup,
beet syrup, ~ig~l fructose syrup, h19h dextrose syrup,
sorbitol and the like. The terms "rr;lcroporous
adsorbent" are intended to include those comrnon
adsorbents having microporous intersticies (pore
volume) of more t~an 0.1 cc/gram in pores of lOOA or
less, including activated carbon, alumina, silica,
Ambersorb type macrorecticular resins, zeolites,
microporous clays and the like. The preferred
microporous adsorbent is activated carbon. Activated
carbon may be employed in any convenient form,
granular, powder, or a mixture of both.
It has been discovered t~at the acids w~ich
contribute to titratable acidity in crude sweetener
solutions are effectively adsorbed by microporous
adsorbents such as activated carbon w~en in the
undissociated form. To obtain a hig~ degree of
undissociated acids, a pH of from about 2 to 2.5 is
necessary. Two locations in a sweetener solution
purification process where pH is this low are (1)
wit~ln the cation exchange resin bed and (2) directly
following t~e cation exc~ange resin bed, including
for a short time within the anion exchange resin
bed. Ot~er sweetener solution impurities, some of
which are generated in t~e cation resin bed, such as
proteins, hydroxy methyl furfuryl, fragments of the
cation resin and unidentified organics not
contributing to titratable acidity, are rendered less
soluble at low prl and will also be adsorbed by a
properly positioned microporous bed.
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A conventional high ~ructose co:rn syrup
purification process is described in FIG. I. The
process is generally divided into two areas; dextrose
purification and fruc-tose puri,fication. '~Ihi],e this
general description is directed to a colurmn
operation, it is anticipated -that a batch processing
operation will derive a similar benefit frorn -the
present invention.
Referring to Figure I in detail, raw
materials are ground into a pulp, are washed and
starches are separated (Section A). This is followed
by conversion of the crude materials either by
chemical conversion (acid~ or by enzymatic conversion
of the starch slurry to a high dextrose equivalent
syrup (Section B).
Th~ dextrose syrup is passed through a
column of activated carbon (Section C) for
decolorization and removal of some impurities. The
syrup pH at this poin-t is about 3.5-5.0 and it has
been found that many weak organic acids contributing
to titratable acidity are not effectively adsorbed by
this activated carbon.
The carbon treated syrup passes next to tbe
cation-anion exchange system (Sec-tion D) wherein
first a cation and second an anion exchange resin
remove salts and ot~er impurities. The syrup exiting
the cation exchange resin has a pH below 3.0
(preferably 2.5 or less). The syrup exiting the
anion exchange resin has a pH of frorn 3.5 -to 5Ø
T~e use of a microporous adsorbent in this ion
exchange system would delay the organic acid rollover
from the anion exchange resin and thus improve the
overall process efficiency.
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The purified dextrose syrup is tben
converted into big~ fructose corn syrup (IIFCS) by
enzymatic conversion (Section E).
Activated carbon is again ernployed to
decolorize t~e syrup and adsorb impurities (Section
F). T~e syrup pl-l is between 4.0 and 5.0 enterirlg anrJ
exiting t~is carbon bed and it has been found that
any remaining weak organic acids are not adsorbed.
T~e fructose syrup is t~en passed t~rough an
ion-exchange system (Section G~ to remove salts and
ot~er impurities remaining in the syrup. Tbe use of
a microporous adsorbent in t~is ion-exc~ange system
will agaln delay t~e rollover from t~e anion exchange
resin and t~us improve t~e overall process efficiency.
The purified syrup is t~en eit~er
concentrated by evaporation (Section H) or again
passed t~rougb a cation excbange resin to upgrade the
syrup from 42% HFCS to 55% HFCS (Section I).
The instant invention, wbile described in
t~e examples tbat follow by a preferred embodiment,
is not intended to be limited to t~e use of activated
carbon. For example, using adsorbents otber t~an
activated carbon at the low pH ion-exc~ange sites may
also prevent t~e premature need for regenerating t~e
anion excbange resin. Examples of other microporous
adsorbents capable of adsorbing -tbe acids responsible
for titratable acidity and ot~er solution impurities
include: Ambersorb Macrorecticular Resins (Ro~m &
Haas Co.), Fuller's Eart~ and other microporous clays,
zeolite sieves, silica gel, alumina~ and tbe like.
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EXAMPLE 1
A two inc~ diameter bed containing 12 9 of'
acid washed PCB activated carbon (available From
Calgon Corporation, Pi-ttsburgh, Pa.) was inserted
between a cation and anion exchange resin pair (see
FIG. II).
Untreated dextrose syrup was run t~rough the
carbon containing system and t~le conductance
breakthroug~ of t~e system was measured. Conductance
of the solution was measured in lOO ml increments on
a Cole-Parmer Model 1481-OO conductivity meter. The
unit of conductance generally used in the sweetener
industry are microm~os. Thus the condu'ctance
breakt~rough plots s~ow when (in terms of volurrle
treated) an ion exc~ange resin system has ceased
adsorbing ionic species contributing to solution
conductivity. This conductance breakt~roug~ was
plotted against t~e conductance breakthroug~ of the
same ion-exc~ange resin system without the carbon bed
inserted. FIG. III s~ows t~ese two curves. Curve A
represents the untreated (no carbon) syrup w~ile
curve B represents the treated syrup. Assuming an
arbitrary breakt~roug~ point of lOO micromhos, an
extension of anion resin lifetime of about 30 percent
was shown as measured by t~e increased volume of
syrup treated by the carbon containing system.
_~MPLE 2
The carbon bed employed in Example 1 was
regenerated using conditions conventionally used for
regeneration of the anion exchange resin, i.e.,
caustic (NaOH) was~ (about 2 wt%) followed by water
rinse (to a pH of about 9.O). T~e conduct3nce
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breakt~rough test was repeated, as in Exarnple I,
using the regenerated PCB activated carbon and fresh
supplies of cation and anion excharlge resins. T~e
conductance breakthrough curves shown in FIG. IV s~ow
an extension of anion resin of about ~19% lb;s
lmprovement over t~e virgin carbon is probably due to
better wetting of t~e carbon bed following t~e
caustic regeneration. Curve A represents an
untreated (no carbon) system, curve B represents a
virgin carbon system and curve C represents a
regenerated carbon breakthroug~ cycle.
In addition to t~e two weigbt percent
caustic was~ employed in this Example, ot~er caustic
solutions such as NH40H, KOH, Na2C03, NaHCû3,
Ca(OH)2, Mg(OH)2 and the like, may be employed so
long as a high pH is attained. In addition to the
water rinse described above, an acid rinse
(neutralization) could be employed or a series of
acid-water rinses or water-acid rinses could be
employed.
EXAMPLE 3
Following the successful extensions of anion
exchange resin lifetime on t~e dextrose side of tbe
HFCS purification system, a similar experiment was
run on the fructose side. T~e same conditions as
used in the preceeding examples were used. FIG. V
shows t~e breakthroug~ curves D, for the untreated
anion effluent and E, for the carbon treated
effluent. T~a extension factor ~ere is smaller t~an
t~at seen on t~e dextrose side of the process because
most of t~e organic acids likely to in-terfere with
the fructose side anion exc~ange resin bave already
been removed earlier in t~e processing.
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Tbe examples dernonstrate tbe userulness of
-the present inventlon. Uslng tbe flgures showrl on
t~e conductance breakt~rough curves as guides,
expected extension of anion excbange resin lifetime
for tbe dextrose side of a HFCS proc:ess woulcl be on
t~e order of about 25 to 50% or ~igher.
As described above, adsorption of t~le weak
organic acids contributing to titratable acidity by
microporous adsorbents will occur best at low pH.
Low pH conditions exist wit~in t~e cation excbange
resin bed. Tberefore a mixture of t~e cation
exchange resin and ac-tivated carbon or another
microporous adsorbent would also be expected to delay
prema-ture exhaustion of the anion exchange resin as
does carbon treat~ent of t~e cation exc~ange resin
effluent. Finally, a low pH condition also exists
initially ln t~e anion exchange bed. After some time
passes, ~owever, the anion excbange process raises
the pH of the syrup within tbis anion bed. However,
one could mix a microporous adsorbent wit~ tbe anion
exc~ange resin for additional protection of t~e anion
bed. T~ls placement would be tbe least desirable of
t~ose described, but, t~e concept would still apply.
Mixtures of ion exc~ange resin (cation or anion) witb
the microporous adsorbent may vary from 1 percent by
volume microporous adsorbent to 99 percent by volume
microporous adsorbent. T~e quality of t~e adsorben-t,
- tbat is, its adsorptive capacity will be a
determinatlve factor. For activated carbons a
preferred amount in a mixture wit~ an ion exchange
resin would be from 10 percent to 50 percent by
volume carbon. T~e addition of acids (e.g., HCl,
H2S04, etc.) to t~e syrup to acbieve a low pH
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condition is not generally a desirable alternative
because the acid counter--ions would necessarily have
to be rernoved by the anion exchange resin. This
would reduce or eliminate the at-tempted ex-tension of
that resin's useful lifetime. HoweverJ in -those
cases where the impurities to be removed are of the
highly pH ,ensitive type, the addition of an aqueous
mineral acid (e.g. HCl, H25û4, H3P0~, HN03
and the like) mlght be advanteagous. Such a case
would be the irnproved purification of the sweetener
solution in which the pH shift through a cation resin
would be insuf~icient to achieve significantly
enhanced adsorption of pH sensitive species, or when
practical engineering considerations preclude the use
of a cation bed to lower the pH. This improved
sweetener purification process ernploying the addition
of acid is illustrated in Table I.
Table I
25~ nm U.V. impurity Removal Efficiency
from Dextrose Syrup
Column Brea~t~rough at 0.25 lbs. of carbon/100 lbs of
sugar.
pH Percentage of Impurity removed
4.6 26%
*3.0 39~0
*2.5 51%
*2.0 60%
-~Ajusted with (12.0 molar) HCl.
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A microporous adsorben-t placed followlny a
cation exchange resin could also precede a In.ixed
cation/anion resln bed and serve as a useful adsorber
of undesirable contaMinants. For example, sweetener
solution refineries may errlploy rnixed cation/anion
resin beds in tbeir refining process. T~le use of a
cation resin bed, fol].owed by, for exarnple, an
activated carbon bed, would improve t~e sweetener
solution purification by removing organics not
adsorbed earlier in t~e processing, tbus extending
the lifetime of t~e mixed cation/anion resin system.
8ased on t~e improved anion resin
performance for sweetener applications, it is
anticipated t~at under ot~er conditions, a properly
positioned microporous adsorbent could be used to
enhance t~e performance oF a cation exc~ange resin.
For example, ion exchange resins used in t~e
treatment of condensate water systems (boiler
corrosion prevention) rely on a cation resin to
remove weak organic bases from aqueous solutions and
retain them as -tbe positively charged species.
Examples of typical weak organic bases include
aniline, purine, pyridine, toluidine, quinollne and
ot~er common organic amines wi-t~ PKa of greater
than 7. T~ese weak organic bases become less water
soluble at ~ig~ pH. T~us, at a systern pH of at least
lû, these bases could easily be removed by a
microporous adsorbent, tbus reserving the cation
exchange resin for t~ose materials not adsorbed,
t~ereby extending its useful lifetime. To accomplis~
this extension, t~e solution being purified would
initially enter an anion exc~ange resin, exiti.ng at a
~igb pH and t~en pass to t~e cation exc~ange resin.
As described above, the microporous adsorbent could
be (l) rnixed witb eitber of t~e ion-excbange beds or
(2) placed between the beds as a separate adsorber.
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