Note: Descriptions are shown in the official language in which they were submitted.
~ 2~97~
FIELD OF THE INVENTION
The present invention relates to a process and
apparatus for removing undesired components and especially
organic acids from aqueous feedstocks containing them.
BACKGROUND OF THE INVENTION
It is frequently desired to separate organic acids from
feedstocks containing them. The term "feedstocks" as used herein
is intended to denote aqueous media generally, whether solutions
or suspensions, which have an undesired content of organic acids.
Such media include, for example, process liquids and waste
streams from the food industry, or from chemical production
plants utilizing synthetic or extractive methods, or
biotechnological methods. In the known art, the following
technigues have been used to effect such separations, namely, ion
exchange, solvent extraction, absorption with selective resins,
extraction with supercritical gases, and the action of membranes.
When effecting such separations, it is often desired to
otherwise maintain the composition of the aqueous feedstocks
substantially unchanged. By way of example, it may be noted that
absorptive processes in which citrus juices were contacted with
ion exchange resins, have been used to remove citric acid and the
bitterness due to limonin, therefrom (Johnsson and Chaundler,
CSIRO Food Res. Q. 1985: 4525-32); most of the absorbents used in
these processes did not absorb juice sugars, had no adverse
effect on the fruit character of the juices and in particular did
. .
'``"` 2~17~8
not introduce objectionable ofP Plavors. The main problem
observed during the processing oP orange juice related to the
slight loss oP vitamins, minerals and amino acids; see Assar,
Minute Maid Reduced Acid, FCOJ, 19th annual short course for the
food industry, 1979. Moreover, adsorption processes require
regeneration oP the absorbent, resulting in the use oP chemicals,
consumption oP energy and a waste disposal problem for the
regenerating chemicals.
Selective separations using membranes ofPer
considerable advantages over~other known separation processes.
Thus, they can readily be adapted to a commercial scale and to
,
contlnuous operation, they do not require the use oP regenerating
chemicals and oPPer substantial economic advantages. For these
reasons, conventional separation techniques are being
increas~ingly replaced by technigues utilizing selective
membranes. Such techniques include reverse osmosis (RO),
ultrafiltration (UF) and microPiltration (MF), all o~ which are
pressure~ driven, and electrodialysis (ED), which as the name
implies is electrically driven.
,;
In RO, UF and MF, a liquid stream containing soluble
and suspended matter is circulated parallel to the membrane
surPace~(cross flow)~and pressurized simultaneously. Water and
some soluble substances~ are transported across the membrane,
while the retained soluble and suspended substances are
concentrated. These processes differ in the dimensions of the
membrane pores: in UF membranes they may range from 1.5 to 1~
nanometers, in MF membranes from ~.~5 microns to 1~ microns,
~ :`` 2~ g7~3
while in RO membranes they may range from 0.1 to 1.0 nanometers.
Thus UF is basically a sieving process - the small molecules are
responsible for the established osmotic pressure but are not
retained by the membrane, the applied hydraulic pressures are
thus not high; they may be of the order of about 5 bars, as
compared with the higher pressures of say 10 to 100 bars in the
case of RO.
Diafiltration (DF) is a modification of pressure driven
processes (mainly UF and MF) in which water is added to the feed,
to maintain its volume constant. As filtration proceeds, the
components are effectively washed out from the feed and pass
through t~e membrane, the rate of adding water ~o the feed equals
the rate of permeate removal. The diluted permeate stream is
regarded as waste and is often discarded.
In ED, a feed containing ionized species is circulated
in a stack of alternating cation and anion exchange membranes
under an applied electric field, so that the ionized species are
transported from the feed into the adjacent compartments. Ion
exchange membranes have pores of the order of inorganic and
relatively small organic ions; inorganic ions in particular can
be effectively removed by this process. In the case of small
organic ions having a molecular weight below 2~0, these can also
be readily removed by means of ED in the absence of fouling
agents, but if large organic ions above 4~0 daltons are present
they plug the membrane pores with the result that the process
becomes very inefficient. Thus, there are relatively few
successful commercial applications of ED where organic ions are
involved.
, . . . . .
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i:, .,, .":: . :. : . ,
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As indicated above, unit separation processes such as
UF, MF and RO are being increasingly applied in the food
industry, e.g. for concentrating liquid products. Such processes
are especially beneficial for products which would be adversely -
affected by high temperatures, and are also energy efficient. In -
this connection, reference may be made, for example, to "Water ; ~
and ion flow-through imperfect osmotic membranes", Breton E.J., ~-
-,
Dissertation Abstr. 18: 822 (1958). Applications of UF and RO
for concentrating liquid food products were initiated in the
:, :::
dairy industry in the 1960s. Marshall et al in Food Technol. 22:
969 (1968), studied the concentration of cottage cheese whey
solids by RO as an alternative to whey disposal. Industrial scale
applications of UF and RO in the dairy industry are summarized by
Glover, National Institute for Dairying, Reading, England, 1985.
Other studies described UF and RO concentrating techniques for
concentrating various liquid food products such as maple syrup,
egg white, fruit and vegetable juices, and plant pigments such as
anthocyanins. In general, these researches concluded that such
techniques, modified as necessary, could be applied to the food
industry.
A combined UF and RO process is also known in the
literature for the preparation of purified beet color extracts,
which were separated from soluble solids originally present in
the feed. The juices were prefiltered, enzymated and subjected
to a two stage UF process, using in sequence UF membranes with
20000 and 60~0 molecular weight cutoff, in order to remove
soluble materials of high molecular weight. Such materials, if
: ` 2 ~ 7 ~ ~ ~
present in a stream contacting RO membranes, would plug the pores
and therefore reduce the throughput rates and recovery of the
natural color. In order to recover as much as possible of the
natural color in the permeate of each UF step, the feed was
repeatedly diluted and washed out with fresh water. In the
subsequent RO step, the solution was subjected to combined
concentration and purification, the RO membrane being endowed
with high retention of the color, while allowing inorganic salts,
sugars and beet taste co=ponents to permeate. A highly
concentrated beet color product with improved sensory properties
was thus obtained. In this example, UF and RO membranes were
used to fractionate a selected component from an aqueous stream;
all fractions except the color were of minor value and could be
discarded. It is to be noted that large quantities of rinsing
water were used for extracting the color while removing high
molecular weight contaminants ln the UF steps, without losing the
color when low molecular weight contaminants were being removed
in the subsequent RO step. In such a process, the high dilution
of the permeate solubles means that their recovery is not usually
economic and they =re lost in the discarded waste stream.
UF membranes have also been used for the preparation of
protein concentrates having reduced lactose content, from skim
milk. Simple UF concentrates the protein, but leaves a product
containing some lactose and salts, the content of which may be
reduced by DF (see Ultrafiltration and Reverse Osmosis for the
Dairy Industry, National institute for Dairy Research, Reading,
England, 1985, p. 10~). In the DF step, water is added at a rate
,. ., , '
~ 7t~
which keeps protein concentration constant; it is undesirable to
add water at a greater rate, because by keeping the lactose
concentration high in the feed, it is removed at a relatively
faster rate. In this example also, the permeating substances are
of low value and can be discarded.
In many cases, it is desired to remove selected
substances from an aqueous stream, while imparting minimal
changes to the remaining composition of the feed. However, the
use of a washing/DF step in conjunction with selective, pressure
driven process utilizing membranes has the drawbacks that large
quantities of rinse water are required and that almost inevitably
large quantities of feed components are lost through the
selective membranes, and are not economically recoverable. Also,
membranes with sharply defined selectivities are not available
for many applications, while the use of less selective membranes
tends to accentuate the losses of valuable solids.
Ionized organic substances can generally be removed
from feeds by ED, of which examples are as follows:
(1) Smith et al (R & D Associates Convenience Food
Conference, Philadelphia, 1964) reported the removal of citric
acid from citrus juices and improvement of their organoleptic
properties by ED; other workers reported similarly on the removal
of a variety of organic acids from apple and citrus juices and
from wines.
(2) Malic acid effluent containing less than 1~% malic acid
alone or in admixture with maleic and fumaric acids, when treated
by ED, produces two streams, one of about 3~% acid and the other
i . . ,
-: . , -. .: - : ,
-" 2~
less than about ~.3% (U.S. Patent No. 3752749). In this case,
the separation and concentration of acids is non-selective and
the feed is relatively clean, being free of fouling agents which
can clog the membranes and thus interfere with the separation
process.
(3) The separation by ED of organic amino acid esters from
admixtures with amphoteric amino acids is described in Israel
Patent Nos. 52686 and 52687. In this case also, the feed is free
of fouling agents.
Many industrial feed or waste streams may contain
suspended or soluble substances which either adhere to the
membrane pores or accumulate therein and thereby prevent
efficient ion transfer. The problem of ED membrane fouling
arises, for example, in demineralization of cheese whey (fouling
by proteins~, deacidification of citrus juices (fouling by high
MW pectic substances) and demineralization of sugar molasses
(fouling by proteins). Further, fouling may arise due to the
presence of low and medium size molecules which adsorb strongly
on and in the ED membranes; e.g., whereas organic anions MW <
about 2~ daltons are readily transported across anion exchange
membranes, larger organic ions MW > about L~5~ are usually very
problematic. Thus, the biodegradation product humic acid is
present in most natural waters as colloidal negatively charged
matter, and during ED such ions accumulate progressively on and
in the membrane, and the electrical resistance of the ED stack is
raised to the point where operation becomes uneconomical.
7 ~
Various attempts have been made to overcome such
difficulties, which would otherwise tend to delay or even prevent
the penetration of ED technology into industrial and waste
treatment fields.
Thus, in U.S. Patent No. 4554076 there is described a
method of modifying the surface of anion exchange membranes by
coating with oriented layers of amphiphilic surface active
molecules thaving one polar and one hydrophilic end). This
method does not have appeared to have been used on an industrial
scale. Japanese Patent No. 1014234 (198~) describes the
difficulties encountered in attempting to desalt sugar molasses
streams, due to fouling of the (otherwise efficient) anion
exchange membranes, and a solution of the problem by replacing
the latter with a neutral porous layer of PVA, which reduces the
efficiency of the process.
It is also known to pretreat the feeds to remove
fouling substances, e.g. by use of UF to remove proteins and
other contaminants prior to an ED step, but such processes have
the following drawbacks:
(a) High extraction recoveries require high volumetric
efficiencies of the UF/MF/RO step, which in -turn means operation
at high concentrations of fouling substances, i.e. low flux.
(b) If it is attempted to increase recovery without
excessive concentration of the foulants, diafiltration or washing
steps may be introduced. However, this leads to a diluted
permeate, so that the economy of the subsequent ED step is
impaired.
:, ' ' ,' ,, . , ,; ,: . . . . ..
9 7 ~ ;~
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to
provide an efficient process and system for the removal of at
least one organic acid from aqueous feed streams.
It is also an object of the present invention to
provide the aforementioned process and system which would leave
the ingredients of such aqueous feed streams subs-tantially
unchanged apart from the fact that at least one organic acid will
have been removed.
It is still a further object of the present invention
to provide a process and system of the type described in which
the removal of at least one organic acid is effected by use of at
least one electrodialysis membrane.
Yet another object of the invention relates to the use
of electrodialysis membranes in the process and system of the
type described in which such membranes are much less susceptible
to fouling than in the comparable prior art.
Further objects of the invention will appear from the
description which follows.
The present invention thus provides in one embodiment,
a batch or continuous process for removing at least one organic
acid from an aqueous feedstock comprising such acid, and for
interim removal of at least one ingredient known to foul
electrodialysis membranes, which comprises the steps of: ;
(i) subjecting the feedstock under superatmospheric
pressure to the action of at least one selective non-
electrodialysis membrane adapted to retain the at least one
fouling ingredient, the at least one selective non-
electrodialysis membrane being selected from the group consisting
of selective ultrafiltration, microfiltration and reverse osmosis
membranes, thereby to obtain (a) treated feedstock and ~b) a
permeate having a significantly reduced content of the at least
one fouling ingredient and a substantially unchanged content of
the at least one organic acid;
(ii) subjecting the permeate to treatment with at least one
electrodialysis membrane, thereby to obtain (c) treated permeate
from step ~i) now having a significantly reduced content of the
at least one organic acid, compared with such content of the
initial aqueous feedstock, and (d) effluent; and
(iii) combining fractions (a) and (c) to give a product in
which the content of water-soluble and water-insoluble
ingredients is substantially unchanged, other than Por the at
least one organic acid.
It is preferred to operate the inventive process
according to this embodiment, in such a manner that at least a
part of (and more preferably, substantially the whole of) treated
permeate (c) from step (ii) is recirculated so as to repeat at
least step (ii) until stream (c) contains a concentration of the
at least one organic acid which lies within a preselec-ted range.
In this prePerred embodiment, recirculated treated permeate may
be combined with fresh feedstock and the thus modified feedstock
1~
: :`` 2~7~3~
may be subjectad to both steps (i) and (ii).
The process of the invention in this embodiment may for
example be applied to the removal of at least one organic acid
from citrus juices, or the removal of at least one organic acid
comprising e.g. malic acid from green coffee extracts and other
coffee streams.
In accordance with another embodiment, the present
invention provides a continuous process for removing at least one
species from an aqueous feedstock comprising such species,
including contacting the feedstock with separation apparatus of
firsk and second types, respectively, which comprises the steps
of:
(i) subjecting the feedstock under superatmospheric
pressure to the action of separation apparatus of a first type
constituted by at least one selective reverse
osmosis/ultrafiltration/microfiltration membrane adapted to
retain at least one ingredient known to foul the second type of
separation apparatus, thereby to obtain (a) treated feedstock and
(b) a permeate having a significantly reduced content of the at
least one ingredient and a substantially unchanged content of the
at least one species;
(ii) subjecting the permeate to contact wi-th the second
type of separation apparatus adapted to remove the at least one
species from the aqueous feedstock, thereby to obtain (c) treated
permeate from step (i) now having a significantly reduced content
of the at least one species, compared with such content of the
,: ,
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2 ~
aqueous feedstock and (d) effluent;
(iii) continuously recirculating substantially the whole
of treated permeate (c) from step (ii) so as to repeat at least
step (ii) until stream (c) contains a concentration of the at
least one species which lies within a preselected range; and
(iv) combining fractions (a) and (c) to give a product in
which the content oP water-soluble and water-insoluble
ingredients is substantially unchanged, other than for the at
least one species.
This process embodiment may for example be applied to
the removal of bitter components from fruit ~uice, so that
recirculation step (iii) is repeated for the requisite number of
times prior to step (iv), until the effluent (d) contains a
concentration of the bitter components which lies within a
preselected range. Moreover, this embodiment of the process of
the invention may for example be applied also to the removal of
at least one organic acid comprlsing e.g. malic acid from green
coffee extracts and other coffee streams.
The invention further provides in accordance with
another embodiment, a system for removing at least one species
from an aqueous feedstock comprising such species, including
contacting the feedstock with separation apparatus of first and
second types, respectively, which comprises in operable
combination: inlet feed apparatus for -the feedstock; apparatus
for pressurizing the feedstock to a superatmospheric pressure;
apparatus for contacting the pressurized feedstock with
separation apparatus of a first type constituted by at least one
; ` 2~97
,
selective revers: osmosis/ultrafiltration/microflltration
membrane apparatus adapted to retain at least one ingredient
known to foul the second type of separation apparatus; apparatus
for removing treated pre:surized feedstock from the membrane
apparatus; ~ apparatus for removing permeate from the membrane
.
apparatus and for contacting it with the second type of
separation~apparatus ad:pted to remove the at least one species;
apparatus~ for removing treated permeate from the second type of
separation apparatus; apparatus for removing effluent from the
second type of separation apparatus; and apparatus for combining
the pressurized treated feedstock with the treated permeate.
The system of- the; invention preferably comprises
additlonally apparatus for recirculating at least a part of the
treated permeate. ~ Preferably also the system of the invention
comprises monitoring apparatus for determining when the
:: :
concentration of the at least one, species lies within a
preselected range, a: well as control apparatus for terminating ,~
operation of the recirculating apparatus when the concentration
of the undesired at least~one :peci:s lies within a preselected
range. The second type ,of~separation apparatus ~ay, e.g.,
comprise electrodialysis membrane apparatus, or it may comprise, ~'
e.g., ion exchange or absorption apparatus. ~,
,
:~ : :
BRIEF DESCRIPTION OF THE DRA~INGS
Fig. 1 illustrates a particular embodiment of the ~
present process and system. ~,
::
13 ~'
2~7~i3 :
DETAILED DESCRIPTION OF' THE INVENTION
In accordance with the present process, it will be
appreciated that it is possible to mix incoming fresh feedstock
with a relatively acid free stream from the electrodialysis step,
thereby in efPect obtaining a benefit of diafiltration without
however diluting the feed and thus obviating an additional
concentration step which would detract from the overall
efficiency and economy of the process.
Thus in accordance with a particularly preferred
embodiment of the invention, a continuous process for removing at
least one organic acid from an aqueous feedstock comprising such
acid, and for interim removal of at least one ingredient known to
foul electrodialysis membranes, comprises carrying out the above-
stated steps (i) and (ii), recirculating substantially the whole
of the treated permeate (c) from step (ii) so as to be mixed with
untreated aqueous feedstock and -thus giving a modified aqueous
feedstock which may be repeatedly subjected to steps (i) and (ii)
until the concentration of the at least one organic acid in the
thus-treated modified feedstock has fallen to a preselected
level.
- .. :, . , - . ,
7 ~ ~
It will also be appreciated that since it is a general
objective of the invention~to recover the feedstock substantially
unchanged apart from a significant reduction in the acid content,
the ingredients which tend to foul the electrodialysis membrane
are not undesirable in other respects and are not usually removed
from the system as a whole, but rather they may be mixed with the
other components of the system.
The selective membranes used to separate ED fouling
ingredients may have~sharp separation characteristics, which
enable them to discriminate between molecules of rather close MW.
For example, permeable species may have a MW of about 1~-3~,
while the retained substances (including fouling ingredients) may
have a MW of about 36~-5~, or higher.
In certain cases~the separation between such closely
related species to be separated can be sharpened by maintaining
optimal pH in the feed. In one specific case of treating green
:
coffee extracts (GCE) low MW organic acids such as citric acid
(MW -~21~) and malic acid (MW = 134) have to be extracted in the
presence of another low MW foulant of ED, the chlorogenic acid
(CAC), MW 36~. The latter is a very strong foulant of anion
exchange membranes assembled in the ED apparatus. Effective
removal of ~:.g.) malic acid can be readily achieved by ED (see
U.S. Patent No. 3752743), provided that the stream does not
contain foulants; in the case of GCE, this removal can only be
effectively achieved if CAC and other high and low MW foulants
are eliminated from the stream to be contacted with the ED
membranes. :~
2~ 97~8
By using selective reverse osmosis membranes ("SELRO")
it is possible to effect a transport of organic acids such as
malic acid into the permeate, The separation characteristics of
the selective membranes can be imparted during the production of
these membranes, but they may also be formed in situ by
depositing from the feed a dynamic layer of artificially added or
naturally existing poIyelectrolytes during the RO step. It
should be noted that the separation step at the RO membrane is a
kind of diaextraction, inso~ar as the extraction may be regarded
as being driven by diafiltration using internally recirculated
permeate from the ED step. Use of a selective RO membrane is
highly advantageous in comparison with the use of UF membranes,
because in the latter case high MW species (which in any event
will not be transported across the ED membrane) are mainly
retained, whereas all the low MW species such as sugars, amino
acids and vitamins are transported across the UF membranes and
may be partially lost in the ED step. By contrast, since -the
selective RO membrane retains these low MW species to a certain
degree, their loss in the ED step is minimized.
,
It is also to be stressed once again, that employment
of a conventional dia~iltration mode at the first (RO/UF/MF) step
would unduly dilute the permeate to be treated at the ED step,
and make the removal of organic acids therefrom very difficult,
if not impossible.
On the other hand, in accordance with an embodiment of
the present invention, a selective diaextraction process is
16
2~ 9 '7~8
combined with continuous removal of organic acids. In the
example of the removaI of malic acid from GCE, a portion of the
feed is contacted with a SELRO membrane which has tailor-made
characteristics enabling retention of most of the CAC and a
substantial proportion of the sugars; the permeate from which
high and low molecular welght ED foulants have been removed is
processed in the ED unit until the organic acid concentration has
been reduced to a satisfactory (preselected) level. The
thus-treated feed of the ED unit, from which most of the organic
acid content has been removed, is continuously recycled into the
feed of the S~LRO unit so as to carry out what has been termed
herein diaextraction, which~is continued until it is feasible to
withdraw a product in which the organic acid content has been
reduced to an acceptable level.
As has already been intimated, the present invention is
not limited to the use oP ED; another selective process such as
ion exchange or absorptlon may be used to permanently remove an
undesired species from an aqueous feedstock. The permeate from
the selective RO/UF/MF step, after treatment for permanent
removal of the undesired species, may be continuously recycled to
~,
effect further extraction of undesired species into the permeate. ~ ~ -
1: ~ I ~ :
For example, a continuous debittering process can be
effected, in which a Pirst RO/UF/MF step transforms a fraction ~ ~
of the feed volume into a foulant-free and depulped permeate, the ;~; -
permeate is subjected to a debittering process with resin-filled
column, and the treated feed is continuously recycled back to the
17
~ ~ 2 ~
RO/UF/MF unit to effect further debittering. This process offers
substantial advantages over the conventional process in which the
whole juice volume is subjected to simple depulping, in order to
minimize plugging of the absorption columns. Thus in the present
process, there are no losses of the solubles beyond the amount of
material which is adsorbed on the column, and since the latter is
minimized as a result of retention of these substances in the
preceding SELRO step, the total solute losses are minimized.
Furthermore, the pulp composition which imparts to the juice its
natural appearance is maintained unchanged, in the present
process.
As previously noted generally, it is possible in this
case to replace the SELRO membrane by selective UF or MF
membranes, which would mainly effect depulping and removal of
high MW solubles, thus facilitating debittering of the permeate
ln the subsequent absorption columns.
The advantages of the present invention will now be
illustrated in the following non-limiting Examples.
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Example I: Removal of malic acid from aqueous streams in absence
of fouling.
_________________________________________________________________
An electrodialysis experiment was performed in a
laboratory scale ED unit using an ED stack equipped with-8 anion
exchange membranes Selemion from Asahi Glass, each of area 1~ x 3
cm.Z. One liter oP approx. 4% aqueous malic acid solution was
processed in this unit by applying a current of 5~ milliamperes
at an established voltage of 3~-4~ volts, i.e. a voltage drop of
approximately 3.5-5 volts/cell pair. The results are shown in
Table 1; Table 2 shows results for a similar experiment where the
initial malic acid concentration was ~.36%
T~bl-2 ~
time (mins.) current (mA) voltage (volts) pH malic acid (%)
: .
5~ 27 2.~ 4.2
15 5~ 32 2.~ 3-5 ~ -
- , - .,
3~ 5~ 4~ 2.~ 2.7 ;
6~ 5~o 4~ 2.~ 2.5
Table 2.
time (mins.) current (mA) voltage (volts) pH malic acid (%) ~-
_________________ _____________________________________________ .
3~ 32 2.5 ~.36
3~ 47 3-~ ~.12
6~ 3~ 57 ~ 3
_____ _ _ _ _ _____ _ __ _ _
These results show that the concentration of malic acid
can be readily reduced to 30~ ppm in absence of fouling agents.
19
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2 ~
Example II: Behavior of chlorogenic acid (CAC).
________________________________________________
An experiment was carried out under similar conditions
to Fxample I, but substituting CAC for malic acid. The results
are given in Table 3.
Table ~.
time (mins.) current (mA) voltage (volts) CAC (%)
__________ ______ __ __ __ _________________________
~ 5~ 58 1.25
6~ ô~ 5~ 1.18
12~ 58 1.18
18~ 58 1.18
3~ 58 1.18
____________________ __________________________________________
These results show that introduction of CAC into the ED
stack causes the voltage to increase to the limit o~ the current
supply (58 volts), the current declines substantially, i.e. the
resistance of the ED membranes is increasing as a resul-t of
poisoning by CAC. The latter cannot be removed from the feed by
ED.
-- . - : ,
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: : .. .. .
Example III: Malic acid removal in presence of chlorogenic acid.
_______________________________________________________________ ,
An experiment was carried out under similar conditions
to Example I. There were used one liter of aqueous solution
containing malic acid (a) in absence of CAC and (b) in presence
of 2.5% CAC. The results are given in Table 4.
~ able 4.
(a): in absence of CAC
time (mins.) current (mA) voltage (volts) pH malic acid (%)
_____ ______________ :
~ 3~ 38 2.~ ~.54
3~ 54 2-5
3~ 3~ 54 3.~ ~.28 ;~
___________ ___________________________________________________ .
change of malic acid concentration : ~.26%
electrical efficiency of malic acid removal: 85%
(b): in presence of 2.5y CAC
time (mins.) current (mA) voltage (volts) pH malic acid (%)
________________________ ~ :
~ 25~ 58 2.5 ~.38
15 22~ 58 2.~ ~.28
3~ ~ 22~ 58 2.5 ~.19
__ ___________ :
change of malic acid concentration : ~.19%
electrical efficiency of malic acid removal: 45%
The resul-ts demonstrate that in the presence of CAC the - -
efficiency of malic acid removal is reduced almost by a factor of
2, and the resistance of the ED membranes increases (higher
voltage at smaller current).
21
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:~ 2 ~ 8
Example IV: Malic acid removal from crude Green Coffee Extract.
______________________________________________________________
An experiment was carried out under similar conditions
to Example I. There was used one liter of green coffee extract
(GCE) prepared by mixing green coffee beans for a period of 1-2
hours with deionized water at 8~C. The GCE was then subjected
to ED deacidification. The results are given in Table 5.
Table ~.
time (mins.) current (mA) voltage (volts) malic acid (%)
_________________________ _________________________________
~ 25~ 48 ~.5~
18~ 58 ~.5
3~ 17~ 58 ~.50
6~ 15~ 58 ~.5
9~ 15~ 58 ~-5
15~ 15~ 58 ~-5
____ _____________________ __ _________________________________
The results demonstrate that there is no removal of
malic acid from the crude GCE stream despite the fact that it
could readily be removed from corresponding non-fouling aqueous
streams.
,
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Example V: Malic acid removal from crude Green Coffee Extract
after pretreatment with a selective membrane.
_________________________________________________________________
An experiment was carried out under similar conditions
to Example I. The feed for the ED membrane was in this instance a
stream obtained as permeate by contacting green coffee extract
(GC~) with a SELRO membrane in a RQ apparatus. The
characteristics of the SELRO membrane, which in a separate
experiment (see Example 6, infra) is demonstrated to be capable
of selectively transporting malic acid from an aqueous stream
while retaining the CAC, are as shown in Table 6. -
Table 6. ~ . -
solute concentration MW rejection :
____ _______________ _ ___________________________________
sodium chloride 500ppm 58 2
sodium chloride 5% 58 ~ :
sodium sul~ate 5% 142 35
sucrose 1% 360 95 :
glucose 1% 18~ 70
fructose 1% 180 70
chlorogenlc acid 1% 360 98
anthocyanin (grape red color) 1% 900 99
betaxanthlne (red beet color) 1~ _ 98 :
sulfonated aromatics 1% 25~ 85 ~ ~
sulfonated aromatics 1% 400 92 ~ :
sulfonated aromatics 1% 70~ 99
sulfonated aromatics 1% 10~0 99.99
The results of the ED experiment with the permeate o~ :~
this SELRO membrane are given in Table 7.
23 .~ -~
3 9 7 ~
Table ~.
time (mins.) current (mA) voltage (volts) pH malic acid (X,)
_______________________________________________________________
~ 2~ 56 6.~~.17
3~ 17~ 56 6.~~.14
6~ 15~ 58 5-5 ~-~9
9~ 15~ 58 5-~ 7
12~ 15~ 58 5~ 5
15~ 15~ 58 4-5 ~-~3
:
It is observed that more than 80% of the malic acid
could be removed from the GCE after treatment with SELRO
membrane. For comparlson, the results of an ED experiment
conducted with the permeate obtained after treatment with a UF
membrane instead of SELRO, are given in Table 8. It is to be
noted that in this case the process prac-tically stops after the
removal of 45% of the malic acid; also, the lowest value for
malic acid concentration is ~.14%, compared with ~.~3% for the
SELRO permeate.
Table 8.
time (mins.) current (mA) voltage (volts) pH malic acid (%)
___________ _____ ____ _ ______________________________________
3~ 12 L~ . ~ Q . 25
3~ 3~ 2~ L, . 5 ~.16
6~ 3~ 2~ 4.5 ~.17
9~ 3~ 2~ 4.~ ~.14
12~ 30~ 2~ 4.~ ~.14
150 3~ 2~ L~ .14
2L~
:` ?, ~
Example VI: Selectivity of SELRO membrane towards malic acid and
chlorogenic acid as a function of pH.
_________________________________________________________________
A membrane of area 8 cm.2 was installed in a laboratory
scale, magnetlcally stirred cell, filled with 15~ ml. of
deionized water containing ~.2% w/v each of analytical grade
chlorogenic acid and malic acid. The pH of the solution was
adjusted to different levels in the range of pH 2-5 by adding
hydrochloric acid. The cell was pressurized by applying nitrogen
at 25 atm., and 15 ml. permeate was collected, and analyzed by
HPLC. The re~ection values of the membrane for each solute were
calculated from the measured concentration values in the permeate
and the feed by the following equation:
R(%) = (l-Cp/Cf) x 1~.
The results are summarized in Table 9, below. It will be
observed that the relative transport of malic acid vs.
chlorogenic acid is pH dependent and the diafiltration at an
optimal point will enable the recovery of most of the malic acid
(MA), with minimal losses of chlorogenic acid (CAC) into the
permeate.
Table ~.
____________________________________________________
relative permeation:
pH ~ R(%) CAC R(%) MA 100-R (MA)/l~-R (CAC)
_____________________________________________________
5 89 6~.9 3.6 ~' -
4 9~ 62-5 3.8
3 79.5 61.6 1.9
2 77.5 40~Ll 2.6
_____________________________________________________
'.: ' : - , ' .:
: 2~7~
Example VII: Deacidification of citrus juices using
"diaextraction".
_________________________________________________________________
The diaextraction system illustrated schematically in
Fig. 1, in which liquid is circulated in the direction indicated
by the arrows, was used for the deacidification of orange juice.
Whole orange juice containing 12% pulp, 11 Brix sugar and 1.5%
acids was fed at an exemplary rate of 1~ l./hr. via inlet
conduit 1~ and valve 12 into feed tank 14 (vented to atmospheric
pressure at 16); the juice was circulated from feed tank 14 via
conduit 18 and thence through conduit 22 by means of centrifugal
pump 2~ to microfiltration module 24 containing a microfiltration
(MF) membrane 26 of area 1 m. 2 at a linear velocity of 4 m./sec.
The MF membrane had 5 micron pores. Treated feedstock may be
removed from the module via exit conduit 3~ and valve 32, and may
be bled from the system (if desired) by conduit 34. The
clarified permeate issues from module 24 via conduit 28; it had a
soluble solids content close to that of the original feed juice,
but its pulp content was below 0. 5% . This depulped juice was fed
first to tank 36 which is vented to atmospheric pressure at 38,
and from there via conduit 4~, pump 42 and conduit 44 to be
deacidified in unit 46 which contains ED membranes 48. Citric
acid is removed from the unit 46 via exit conduit 5~. The
concentration of citric acid in the depulped juice, measured in
tank 36 declined with time as shown in Table 1~. It will be
appreciated that in general, progressively deacidified juice,
previously depulped, may be withdrawn from unit 46 via conduit 52
and valve 54, and recirculated to tank 36 for further treatment
26
.... . , .. ` ,, ~ . ~ . .
.. ~ - ;
, .. .
7 ~ ~
.
at the ED membranes until a preselected level of acidity is
reached.
Table 1~.
time (mins.) citric acid (%)
_____________________________
~ 1-5
3~
6~ ~-7
9~ ~.3
12~ ~.2
After reaching a citric acid concentration of ~.2%, the depulped
and deacidified stream was withdrawn from the ED unit 46 via
conduit 52, valve 54 and conduit 56 to intermediate tank 62,
there to be mixed with treated feedstock from microfiltration
module 24, which reaches the intermediate tank via conduit 3~,
valve 32 and conduit 6~. From the intermediate tank, the mixture
which is effectively reconstituted deacidified juice may be
withdrawn from the system if desired, via conduit 8~, but in the
present example it is recirculated via conduit 64 and valve
66 into feed tank 14, at a flow rate which was identical to the
permeate flow rate of ~5~ l./hour. After about 6~ minutes the
acid concentration in the feed tank had reduced from 1.5% to
.5%, thus improving the brix to acid value from 7.3 originally,
to 22. At this point, a continuous supply of fresh orange juice
is fed into tank 14 via conduit 1~ and valve 12, at a rate of 2~0
l. per hour and simultaneously, deacidified but otherwise
reconstituted juice (with the original pulp content) is bled from
the system via conduit 68 and valve 7~.
'''''' ' , ' ' ~
` ` 2 ~ 8
. ~. .
It will be appreciated that the rate of feeding and
mixing of the various fractions of juice may be controlled in a
=anner known ~ se. Thus, Por example, the amounts of liquid
passing through valves 12, 66 and 70, and pump 20, may be
monitored at control~ box 72 which may include (e.g.) a
microprocessor (not shown),~ by information fed through two-way
~ ,
conductive lines 74, 76, 78 and 82, respectively, and the control
box may output through these lines to control the amounts of the
respectlve liquids~ p~assing ~through these valves and pump 20.
Thus, by way of example, control box 72 may be preset to keep the
:
liquid level in tank 14 constant, i.e. the total volume of liquid
:: :
per unit time passlng through valves 12 and 66 into the tank may
substantially equal the total volume of liquid per unit time
~ .
withdrawn from the tank vla v~alve 68 and conduit 18. Of course,
the water removed with the undesired acid content oP the juice
via conduit 5~ may be compensated for by addition of a similar
~amount of water to tank 14, by means not shown; and the amount of
.
water thus added ~may be controlled from box 72 by means not
depicted in the figure, and therefore may be accounted for in the
liquld balance of the overall operation, if desired.
Those skilled in the art will appreciate that many
modifications and varlations may be effected in the practice of
the invention, and therefore the latter is not to be regarded as
limited to the methods of operation particularly described.
Rather, the scope of`the invention will be defined with reference
to the claims which follow.
.
28
