Note: Descriptions are shown in the official language in which they were submitted.
363~
IMPROVED METHOD OF RECOVERING SUCROS~
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The present invention generally relates to sugar refining
and, more particularly, to an improved method of recovering sucrose
from an aqueous solution.
In the conventional purification of sugar beet juices and
the recovery of sucrose contained in the juices, milk of lim~ is
added to the diffusion juice from the beets and is then precipitated
from the solution with carbon dioxide. The physical and chemical
changes caused by the addition of milk of lime and carbon dioxide,
and the subsequent settling or filtration of the precipitated
calcium carbonate, effect removal of betw en 20 and 40% of the
impurities present in the juice. This purification step is known as
first carbonation. The amount of carbon dioxide and lime used is
selected to achieve an optimal removal of color and other impurities
and achieve an optimal filtPrability of sludge produced. The usual
alkalinity range for this process is 0.065 to 0.140% CaO. First
carbonation is followed by second carbonation. The purpose Qf
second carbonation is to minimize the amount of dissolved calcium
(lime salts~ remaining in the juice. This is done to minimize
scal1ng in the equipment~and lines in the process, as well as to
20 remove the calcium ion which would otherwise contribute to the
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formation of molasses.
There are many process variations known and practiced for
the purification of sugar beet juices that employ lime and lime plus
magnesium oxide or magnesium carbonate. These include variations
employed in both the first and second carbonation steps. Some of
~ the process variations are:
a) Preliming with carbonation;
b) Preliming without carbonation;
c) Defeco-carbonation;
d) Separation of prelime sludge;
e) Separation of precarbonated sludge;
f) Recycle of spent lime from first carSonation;
g) Intermediate liming;
h) Main liming;
i) Main carbonation;
j) Over-carbonation prior to main liming;
k) Over-carbonating second carbonation, followed by
realkalization with magnesium oxide; and
13 Carbonating second carbonation to its optimum
alkalinityr followed by the addition of freshly prepared magnesium
carbonate.
The ability of the refining process to recover white sugar
- from sugar beets is dependent on the extent of process losses.
These include pulp loss from diffusion, lime flume loss, inversion
in the process, uncontrolled leakage, and loss of the sugar
contained in the molasses produced by the process. The largest loss
is sucrose in the molasses and the amount of sugar contained in
molasses is heavily dependent on the efficiency of impurity removal
by carbonation in the process. --~
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Several processes have been developed and employed to
enhance the recovery of sucrose from sugar beets. The most common
process for selectively recovering sucrose from molasses is the
Steffens process, which employs lime at low temperatures to
precipitate sucrose. A similar process employs barium hydroxide to
precipitate sucrose. Sucrose may also be separated
chromatographically on ion exchange columns. Another major
technique involves the modification of the juice composition by ion
exchange. One approach is the Quentin process, where cations are
r~ mc~ es~
A 10 selectively exchanged for ~ e~H~h~. Another approach is the
partial or complete removal of ionic impurities to decrease or
eliminate molasses production.
Another method of reeovering sucrose from sugar beet
molasses involves concentrating molasses to a very high dry
substance and then mixing it with solvents. The result is a
precipitation of sucrose, while essentially all impurities remain in
solution. Work on this method continued through the 1920's, but
commercial exploitation was never realized. The method was never
applied to substrates other than molasses.
Z0 Two phase solvent extractor systems have also been devised
to recover sucrose. For example, in one known process sugar juice
is eountercurrently contacted with an immiscible solvent comprising
two mutually insoluble phases. Acid addition is required to control
pH to 1.3-1.5, a range which greatly accelerates inversion of
25 suerose and thus reduces the amount of sucrose recovered. The
process has never been commercially employed.
Juices extraeted from sugar cane must also be treated with
one, or a combination of several, processes for the production of
either white or raw sugar. Lime or magnesia is a usual purification
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agent used, and the treatm~nt step is termed defecation. Other
steps employed may include treatment with sulfurous acid
(sulfitation), phosphoric acid (phosphatation), and carbon dioxide
(carbonitation). Processes are also employed that use flocculating
or foaming agents to remove coloring matter.
All of th~ methods employed for purification in the cane
sugar industry are chemically gentle. This is required ~or economic
and quality reasons, because the aggressive chemical conditions
required for beet sugar production would lead to the destruction of
invert sugar and the creation of large quantities of colored
impurities in the cane sugar refining process. Invert sugars in
that process are beneficial because they lower the solubility of
sucrose in the final molasses, and coloring matter is detrimental
because it lowers the quality o sugar produced. However, the
gentle conditions are not capable of removing significant amounts of
impurities and the improvement is generally in the range of .5 to 2
purity points. The recovery of sucrose from cane juices is thus
limited. The removal of impurities in cane sugar processing is
significantly less than the impurity removal in beet processing, but
the ability to crystallize sucrose to produce a low purity molasses
in cane sugar processing compensates for the lower impurity removal.
The method of the present invention comprises contacting a
- concentrated (about 55-96 Brix) aqueous solution of sucrose with
selected aliphatic carboxylic acid having an average carbon chain
25 length of about 2~6 preferably by rapidly adding the solution to and
rapidly dispersing it in the acid, in order to assure rapid maximum
growth of large sucrose crystals ~o facilitate their selective
recovery. The weight ratio of water in the solution to acid is
about 0.02-0.2:1. The solution also usually contalns non-sugar
solids in a weight ratio to the acid of about 0.1-1:1. The sucrose
precipitate is then separated from the solution, as by filtration,
centrifugation or the like, and recovered in purified form. The
sucrose-stripped carboxylic acid-containing solution can be
recycled, if desired, or stripped of its carboxylic acid.
The fundamental principle of the present invention is the
precipitation of sucrose by making a solvent change. Sucrose and
the non-sugars present in sugar-containing juices have different
solubilities in different solvents. In the normal a~ueous system,
all impurities, as well as the sucrose, are highly soluble. If a
solvent change is made to sufficiently reduce the solubility of
sucrose, sucrose will precipitate from solution. Aliphatic
carboxylic acids having an average carbon chain of about 2-6 have
excellent characteristics for this purpose in that sucrose has a
very low solubility in them, while all impurities normally
associated with sucrose-containing plant juices are highly soluble
in such acids. In contrast, sucrose is highly soluhle in formic
acid. Co-precipitation of impurities with sucrose is undesirable
because it results in a lowered recovery of the sucrose in
subsequent steps in the refining process. In the case of the
selected carboxylic acid, potentially saleable sucrose can be
produced directly from the prelimed concentrated diffusion juice.
The solvent change is accomplished in juice which first has
been concentrated to a high solids content. The solvent system may
consist of pure or somewhat diluted selected acid, a recycled
solvent stream, or a mixture of the two. Such acid preferably is
acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic
acid or mixtures thereof. It will also be understood that the
selected acid can be a mixture which includes aliphatic carboxylic
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acids having a carbon chain length in excess of 6 or less than 2,
provided that the average carbon chain length of the mixture is
about 2~6. Thus, formic acid can be presen-t, buL only in mixture
with other aliphatic carboxylic acid so that the average sucrose
S solubility of the acid mixture is acceptably low.
The purity of the sucrose produced by the contacting of the
solution with the acid may be enhanced by pre-treatment steps such
as those normally employed with sugar juices. The sucrose
crystallization with selected acid solvent precipitation is greatly
improved, compared to aqueous systems, and equilibrium is closely
approached at room tempera~ure in less than two hours under most
laboratory conditions.
In the case of a sugar juice purified by conventional
techniques, as previously described, the juice is concentrated to a
high percent of solids in the range of 55 to 96 Brix. The
concentrated a~ueous solution is then fed into, for example, acetic
acid or recycled acetic acid-containing solution wherein the sucrose
precipitates out in high yield and high purity. The slurry of
crystals and solution is very low viscosity and the crystals may be
recovered by conventional filtration techniques, such as a rotary
vacuum filter~ The mother liquor resulting from the separation
contains dissolved sucrose in low amounts, the sucrose concentration
being a function of the water content, the impurity content/ and the
acetic acid concentration.
The weight ratio of the water to the selected carboxylic
acid in the contact zone is usually in the range of .02 to .2:1 and
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the non-sugar to selected acid weight ratio is usually in the range
of .1 to l.0:1.
The selected acid must be recovered for most economical
operation of the sugar refining process. Care must be taken in the
case of acetic acid because dehydration of the acetic acid solution
by boiling tends to result in a significant loss of acetic acid by
decomposition so that the process must operate under conditions
insuring adequate water to minimize such loss. Alternative
techniques may be employed, such as recovery via solvent extraction,
utilizing liquid carbon dioxide or some other solvent in which the
carboxylic acid has a high solubility.
Significantly more rapid and larger sucrose crystal growth
control may be obtained by adding the aqueous sucrose-containing
solution to the selected acid, followed by rapid dispersion into the
acid. Slow dispersion of the sucrose-containing ~solution in the
acid or addition of the acid to the aqueous solution will resul~ in
localized supersaturation and result in the formation of small
crystals of sucrose, rendering sucrose recovery more difficult.
In the case where conventional solution purification is not
practiced prior to the contacting, a significant economic gain is
achieved for several reasons. First, the cost of conventional
purification is eliminated from the economics of sugar production;
~ second, the production of non-sugars for sale increases up to 50%;
and third~ the extraction is significantly improved because only low
levels o~ sucrose remain in the resulting molasses.
Significant reductions in energy requirements are possible
in the case where sucrose is sold as produced or where it is
dissolved and sold as a liquid. If conventional granular sucrose is
desired, the energy requirements are still diminished becaùse the
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intermediate and raw sides of the sugar refining process are not
needed in their present form due to the high purity of the sugar and
the ability to return to the processing plant low purity syrups that
will eventually be produced to the solvent precipitation step.
The process may be applied at a variety of alternative
points in a beet sugar factory, depending upon the grade of sugar
desired and the impurity production desired~ Examples of those
possibilities are set forth below.
~lternative 1
Conventional untreated beet sugar diffusion juice is
concentrated to between 55 and 96 Brix, while controlling pH. The
juice is then fed to the selected carboxylic acid contacting zone
where the sucrose precipitates from solution. The sucrose is
separated and recovered by filtration or other solids separation
techniques. The separated sugar contains suspended solids and some
colloidal material present in the diffusion juice.
Alternative 2:
_. .
Conventional beet sugar juice is treated by a preliming
technique or predefecation technique to remove suspended solids and
proteinaceous material and to clarify and stabilize the juice. The
- juice is then concentrated under controlled pH conditions to 55 to
96 Brix and fed to the selected carboxylic acid-contacting zone
where the sucrose is separated from the mother liquor. In this
case, with careful control of the conditions involved in solvent
precipitation, a high purity sucrose can be produced for sale
directly. The sucrose may be separated from t~e mother liquor by
filtration or other techniques, and the residual acetic acid removed
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by air drying, solvent extraction, or another technique.
Alternative 3:
Beet sugar diffusion juice is first purified by conventional
means and then concentrated to 55 to 96% (Brix) solids. The
resulting juice is fed to the selected carboxylic acid contacting
zone where sucrose is separated from the mother liquor. In this
case, with careful monitoring of the conditions involved in solvent
precipitation, a high purity sucrose can be produced for sale. The
sucrose may be separated from the mother liquor by filtration or
another solid-liquid separation technique and the residual acetic
acid removed by air drying, solvent extraction, or another
techniqueO
Alternative 4-
The sugar factory may be run in a conventional fashion up to
the raw sîde operation. In this case, the raw pan fillmass is
concentrated to as high a Brix as can be handled and the material is
subsequently fed to the selected carboxylic acid contacting zone
where the sucrose is precipitated from the mother liquor. The
precipitated sucrose is returned in a conventional fashion to the
high melter where it is used in a conventional fashion to produce
- white sugar.
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Alternative 5-
In production of cane sugar, the juice, at any stage of
processing analogous to those listed in Alternatives 1, 2, 3 and 4,
is concentrated to 55 to 96 Brix and fed to the selected carboxylic
acid contacting ~one, where sucrose precipitates from solution and
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is recovered either for sale or for subsequent reprocessing.
_lternative 6:
Raw cane sugar is dissolved in water to produce a solution
of between 55 and 96 Brix and is subsequently fed to the selected
carboxylic acid contacting zone where sucrose is separated from the
mother liquor as previously described.
Alternative 7:
Certain waste flows containing sucrose, such as are involved
in canning operations, are concentrated with pH control to between
55 and 96 Brix and fed to the selected carboxylic acid contacting
zone as described above, to precipitate the sucrose therefrom.
The following specific Examples further illustrate certain
features of the present invention:
Exam~le l - Recovery of Sucrose from Diffusion (Raw) Juice
A 1,700 ml. sample of diffusion juice (13.87% by weight
solids, 86.7% by weight purity) was treated with 35 ml. of
approximately 30 Brix milk of lime so that the pH was brought to
10.3 at 50C. The sludge that separated was removed by filtration
and the filtrate was conventionally carbonated to a pH of 7.6 at
35C. The filtrate was then heated to 90 and filtered to remove
calcium carbona~e.
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A 745.0 g. sample of treated juice, obtained as described
above, was placed in a tared 2 liter filter flask equipped with an
air delivery tube and the water in the juice sample was evaporated
under an air stream. Heat was provided by a water bath. After the
residual syrup had reached 89~0% by weight solids, the flask was
removed from the water bath, disconnected from the air supply and
127 ml. of glacial acetic acid was added to the hot syrup. Sucrose
precipitated immediately. The solution was allowed to cool to room
temperature and the product was collected by suction filtration.
The filter cake was washed with three 30 ml. portions of glacial
acetic acid and four 25 ml. portions of acetone and then dried at
80C for one hour. The yield was 81.7 9. sucrose with a pol of
97.9S. The yield, based on sucrose taken and corrected for product
purity, was 89.3%. Accordingly, the present method was shown to be
rapid, efficient and practical, providing for a large immediate
recovery of sucrose from a sugar refining stream.
Example 2 - Recovery of Sucrose from Thin Juice
The apparatus employed in this run was iden~ical to that
20 used in Example l. A 677.2 9. portion of thin juice (13.08% by
weight solids, 88.8% by weight purity) was placed in a tared 2 liter
filter flask and water was removed until the solids content of the
~ syrup reached 89.9% by weight. A llO ml. por~ion of glacial acetic
acid was added to the hot syrup and sucrose precipitated promptly.
25 Washing and drying were carried out as in Example l. A total of
71.39 g. of 97.7S pol sucrose was obtained. The yield, based on
sucrose taken and corrected for product purity, was 8806% by weight.
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Example 3 - Recovery of Sucrose from Thick Juice
A 205.0 g. portion of thick juice (67.72% by weight solids,
87.4% by weight purity) was placed in the evaporation apparatus
described in Example 1 and water was removed in the usual fashion.
S When the solids content reached 91.0~ by weight, acetic acid (170
ml.) ~as added to the hot syrup and sucrose precipitated promptly.
Isolation of the product in a manner analogous to the procedure of
Example 1 gave 112.61 g. of 98.0S pol sucrose. The yield, based on
sucrose taken and corrected for product purity, was 90.9% by weight.
Exam~le 4 - Purification of Cane Raw ~
A 100.0 g. sample of cane raw sugar (96.3S pol) was mixed
with a 25.0 g. portion of water and water was evaporated until the
solids content had reached 88.5~ by weight. A 125 ml. portion of
glacial acetic acid was added to the hot slurry of crystals and
syrup and the sucrose precipitated in the usual fashion. A total of
88.63 g~ of 97.2S pol sugar was obtained. The yield, based on
sucrose taken and corrected for product purity, was 89.4% by weight.
20 Example 5 - Recovery of Sucrose from 55 Brix Carbonated Beet Juice
A 250.00 g. sample of carbonated beet juice (55.0% by weight
solids, 8700% by weight purity) was mixed at 25 C with a 1750 g.
~ _ portion of glacial acetic acid and crystallization was allowed to
proceed at 25 C. After an initial induction period of 0.5 hour,
sucrose precipitated as small crystals. The crystals were isolated,
washed and dried in the usual fashion to give 83.22 g. of 97.6S pol
sugar (67.3% recovery corrected for pol).
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Example 6 - Recovery of Sucrose from 96 Brix Massecuite (Mixture of
Mother Li~uor and Crystals)
A 100.20 g. portion of massecuite (96.0 weight percent
solids, 89.6 weight percent purity) was heated on a water bath and
mixed with 129.00 g. of hot (approximately 100 C) glacial acetic
acid. Sucrose precipitated promptly. After cooling, the product
was collected and washed in the usual fashion to give 77.53 9. of
99.4S pol sugar (88.2% recovery corrected for pol).
10 Example ? - Recovery of Sucrose from Thick Juice with Propanoic Acid
A 200.13 g. portion of beet-derived juice (65.4% solids,
90.8% purity) was placed in a 1 liter flask and water was evaporated
under an air stream until the solids content reached 88.4%. A
15 253.44 9. portion of n-propanoic acid was heated to about 100 C and
then added all at once to the hot concentrated juice with stirring.
Within 45 seconds sucrose began to crystallize. After cooling,
filtration and washing with four 150 ml. portions of methanol, the
product was dried in an oven. The yield was 109.0 g. (99.0S pol)
20 sucrose (91.7% recovery corrected for pol).
Example 8 - Recovery of Sucrose from Thick Juice with n-Butanoic
~ Acid
A 141.84 9. sample of thick juice (67~4% solids, 90.5%
25 purity? was treated in the same manner as in Example 7. A 193.00 g.
portion of n-butanoic acid at 100 C was added all at once to the
hot concentrated juice t90.0% solids). After cooling, filtration,
washing and drying, the sucrose yield was 79.56 g. and the pol was
95.6S (91.9% recovery corrected for pol).
14
rn a parallel run, formic acid was substituted for the
n-butanoic acid. However, no sucrose precipitated. The form;c acid
kept the sucrose in solution.
Example 9 - Recovery of Sucrose from Thick Juice with Mixed Acid.
A 200.00 g. sample of thick juice (68.06% solids, 90.0%
purity) was heated on a water bath while water was evaporated under
an air stream to reduce it to 150041 g. ~136.12 9. solids). It was
then contacted with a 100 C mixture of 120.10 g. acetic acid and
144.16 g. n-propanoic acid (less a 15~00 9. portion of the acid
mixture which had been discarded before the contacting), the acid
being added all at once to the sugar solution, with stirring. The
resulting mixture wa~ then cooled to room temperature. The
precipated sucrose product was collected by filtration and was
washed with 75 ml. n-propanoic acid and then methanol and then was
dried. The dried product weighed 105.40 g. to provide a 86.0% yield
(99.0S pol).
Examples 1 through 9 clearly illustrate that when a beet
20 sugar raw (diffusion) juice, thin juice or thick juice or a raw cane
sugar solution is concentrated to about 55-96 Brix, then contacted
with a selected aliphatic carboxylic acid of 2-6 carbon chain
length, such as acetic a~id, propanoic acid, butanoic acid or a
mixture thereof, sucrose immediately precipitates in very high yield
therefrom and is recovered easily from the juice by filtration,
centrifugation or the like. Similar results have been obtained with
cane sugar juice~ In contrast, formic acid solubilizes the sucrose.
Parallel tests have shown that juices and other solutions
containing sucrose such as are described in Alternatives 1-7 above,
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which solutions have been concentrated to about 55-96 Brix, can be
readily precipitated by contacting with acetic acid, propanoic acid,
butanoic acid, pentanoic acid, hexanoic acid, or a mixture of
aliphatic carboxylic acid having an averaye carbon chain length of
about 2-6, in a concentration sufficient to provide a weight ratio
oE water to selected carboxylic acid of about 0.02-0.2:1. After
precipitation and recovery of the sucrose, the selected carboxylic
acid solution can be recycled per se or the selected carboxylic acid
therein can be recovered by various ~neans for reuse.
