Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1133881
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"ADMIXTURES OF GRANULAR ACTIVATED CARBON AND
BONE CHAR WHICH OFFER ENHANCED CAPABILITIES
FOR RE~OVAL OF COLOR BODIES FRO~ CANE SUGAR
LIQUORS"
,
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^ Disclosure of the Invention
'"^
This invention relates to admixtures of granu-
lar activated carbon and bone char which may be
^ utilized for decolorizing and deashing cane sugar
liquors. More particularly, this invention pertains
to a new adsorption media and an improved process
for decolorizing cane sugar li~uors and a new process
for thermally regenerating the spent admixture.
.,
The process of refining cane sugar may be sub-
divided into the following unit operations and
unit processes. From a storage facility within a
sugar refinery, raw cane sugar is transformed in
bulk quantities to a raw sugar bin. The first step
in xefining is "affination" wherein the raw sugar
crystals are treated with a heavy syrup in order to
remove the ~film of adhering molasses. The resulting
syrup is r moved by a centrifuge and the sugar
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crystals are sprayed with water. The washed crystals
are dumped into a "melter" wherein they are dissolved
in about half their weight of hot water and/or sweet
water. The second stage is "defecation" wherein the
raw liquor is prepared for filtration and clarifica-
tion by removing solid impurities. During this opera-
tion, a flocculent precipitate is formed on addition
of lime and either carbon dioxide or phosphoric acid.
This precipitate entangles the suspended and/or col-
loidal matter and thereby allows removal of thismatter from the process by filtration. The resulting
effluent, which is now free of insoluble materials,
is then passed through an adsorbent media which re-
, moves significant amounts of dissolved impurities
(i.e., color bodies and ash constituents). Tradi-
tionally, the adsorbent media utilized for this
application has been bone chax. Bone char was
employed extensively in past times because it was
the first material available in bulk quantities as
are required for this application, because of well-
established process concepts deeply implanted within
existing refinery operations and because bone char
provided purification (i.e., decolorization and
deashing) required to yield a clarified liquor from
which may be crystallized a final product of accep-
- table quality.
Many present day refineries still employ the
classic process of simultaneously decolorizing and
deashing cane liquor by passing the liquor through
bone char. The bone char is regenerated by washing
the media sufficiently well with water followed by
heating at temperatures of 900F. to 12~0F in a
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; controlled atmosphere to maintain its carbon content.
The color removal capacity of bone char is
~; generally the limiting factor determining its service
life. If service life could be extended, there would
be realized a great saving in labor and other pro-
- cessing costs.
~.,
Heretofore, bone char and activated carbon were
: not directly combined as such for use in a single
bed. It was generally believed that conditions
necessary for the regeneration of bone char were
insufficient to regenerate the activated carbon and
- that conditions that were sufficient to regenerate
the activated carbon would destroy the bone char.
Thus, it was not thought that a spent admixture of
bone cnar and activated carbon could be regenerated
concomitantly as a composite without first separa-
ting them into their component parts. Additionally,
there was concern about the handling of the admixture
in the e~uipment presently used in bone char refiner-
ies.
; While others have attempted to combine a so-
called bone char skeleton with activated carbon,
spent activated carbon was separated from bone char
in the admixture prior to reactivation. In U.S.
25 Patent No. 2,209,069, a charred form of a spent bone
char was combined with powdered activated carbon and
after exhaustion, the activated carbon was separated
by a hydraulic mechanism from the bone char.
In this invention, granular activated carbon
and bone char are combined to provide a decolorizing
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and a deashing medium for processing of white cane
sugar liquors and other feed liquors for yellow
sugar production. This admixture does not require
separation during the regeneration cycle. Such a
process modification provides several benefits to
the refinery whereby significant savings in the
operating costs could be realized. These benfits
, include (a) significant reduction in the amounts of
process water required and sweet water produced;
(b) increase in the melt capacity of a refinery
where decolorization is a bottleneck; (c) reduced
energy consumption associated with the reduction
- in regeneration requirements of the mixture because
of extended service life and, also, hot process
water requirements; (d) reduced labor costs; (e)
better overall process control; and (f) improved
quality of sweet water produced.
Through this invention, the deashing capacity
of the admixture and its decolorizing capacity can
be balanced so that both parameters become more or
less simultaneously exhausted. To this end, a
plausible substitute for conventional bone char in
the usual refinery bed is an admixture of bone char
and granular activated carbon in which greater than
10 perrent by weight of activated carbon is employed,
; but the mixture may be comprised of activated carbon
composition from 10 percent to 50 percent by weight.
The most preferred compositions include from 10 per-
cent to 30 percent by weight activated carbon. The
remainder of the composition consists essentially
of bone char, but there can be included, if desired,
from 3 percent to 8 percent by weight based on the
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weight of activated carbon of a pH control agent
such as magnesium oxide, so-called dead burned
magnesite which may inhibit undesired pH shifts in
the sugar syrup and consequent inversion (hydrolysis)
of the sugar content on processing of the syrup.
While this agent or other suitable material can be
randomly added to the composition of this invention,
it is highly preferred that the agent is an impreg-
nant of the activated carbon.
This admixture can be used in place of the
bone char in any of the char cisterns presently em-
ployed to contain the adsorption media such as, but
without limitation, fluidized and other expanded
beds, and the admixture can be suitably handled in
the equipment presently used for bone char, thereby
eliminating or minimizing the need for new capital
investment. Furthermore, the mixture can be pre-
wetted by standard methods used for bone char in the
refineries whereby the amount of sweet water produced
will be very similar to the amounts presently pro-
duced in bone char operations.
- While the balancing of the deashing and decolor-
izing capacity of bone char is not a newly discovered
goal, the discovery of accomplishing it by adding
granuïar activated carbon is unique since until now,
it was not appreciated that the two could be regen-
erated as a composite without first separating the
admixture and regenerating each component individu-
ally at its optimum conditions. We have found that
the mixture of granular activated carbon and bone
char may be regenerated and used through a minimum
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of five cycles without any appreciable loss of capa-
city.
.,
In the process of regeneration, the existing
equipment, such as Herreshoff kilns and retort-type
kilns, already installed for regenerating bone char
may be employed. In regeneration, the spent bed is
washed to remove sugar liquors and to regenerate
deashing capacity. The spent bed is then unloaded
from an adsorber vessel and the excess wash water
drained off from the adsorption media. The damp
admixture is then placed in the regeneration kiln.
The temperature may be raised to an operating value
within the limits of 900F. and 1200F.
The regeneration of the mixture should be
performed in a gas atmosphere containing controlled
levels of oxygen usually between 0.5 to 2 percent.
The controlled atmosphere can be maintained by re
placing the oxygen normally found in air with com-
bustion gas and/or steam. While the wet or damp
admixture is being heated in the furnace, an auxi-
liary source of steam into the regeneration zone may
be added.
::
The regeneration conditions are such that at
least 90 percent of the original decolorization
capacity of the mixture is restored upon regenera-
tion. Usually, a period of up to four hours is
sufficient in a multiple hearth furnace operating
at temperatures in the range of 900F. to 1200F.
However, at lower temperatures, a longer time period,
up to nine hours, might be required.
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The following experimental results illustrate
the utility and performance of the admixture of this
invention.
Two parallel one-inch diameter and 20.4 feet
bed depth column studies with bone char and bone
char/virgin granular activated carbon mixture were
conducted. The effluent sugar solution from the
columns was analyzed for color by utilizing spectro-
photometry for absorbance at 420, 560 and 720 nm, pH,
brix and conductometric ash. These tests were con-
ducted by following accepted analytical techniques
in the sugar industry. In cycle 1, service bone
char and virgin granular activated carbon were used
for the mixture. At 20.4 feet bed depth, bone char
and granular activated carbon mixtures outperformed
the bone char system for color removal at all times.
Up to approximately 20 percent color breakthrough
level, the bone char/granular activated carbon mix-
ture generated an effluent color quality equivalent
to that obtained by bone char alone over a service
time of approximately two (2) times that afforded
by bone char. For ash removal (measured conducto-
; metrically), bone char columns outperformed bone
; char/granular activated carbon mixtures above 40
percent ash removal. The calcium levels, in parti-
cular, of the effluent sugar solution at 20.4 feet
bed depth were also measured. Even at 140 hours of
column run, bone char columns were removing only 7
percent more calcium in comparison with bone char/
granular activated carbon columns.
.
The spent bone char and bone char/granular
acti~ated car~on mixtures were sweetened off following
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standard procedures used in sugar refineries and
were subsequently regenerated using typical bone
char regeneration conditions at 1000F. (additional
details are described later in the text). The col-
umn studies were repeated using regenerated bonechar and bone char/granular activated carbon mixtures.
- In these studies, no make-up bone char or bone char/
granular activated carbon mixtures were used. As a
result of handling and regeneration losses, the total
bed depth decreased from 20.4 feet in the first cycle
to 19.4 feet in the second cycle for both the bone
char and bone char/granular activated carbon systems.
Even with this reduced bed depth, the bone char/granu-
lar activated carbon admixture provided an effluent
color quality equivalent to that obtained by bone char
; alone over a service time of approximately 1.9 times
that afforded by bone char. These results showed
that the spent mixture could be regenerated to re-
cover at least 9S percent of the original decoloriza-
tion capacity.
The aforementioned results clearly showed that
for sugar decolorization, bone char/granular activated
carbon mixture performed significantly better than
bone char alone. Although bone char columns were
;25 bettex for ash xemoval than the mixture, the calcium
removal was only slightly better.
The laboratory regeneration of the admixture of
this invention is preferably accomplished in accor-
dance with the following procedure.
The spent bone char/granular activated carbon
- mixture was sweetened off with water following
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standard industrial procedure. The admixture is
then dried in air at room temperature overnight.
The admixture was regenerated in a furnace which
- simulates a Herreshoff furnace. The furnace was
maintained at 1000F. As the admixture is intro-
duced into the furnace, the temperature drops from
1000F. to 600F. The time for bringing the furnace
back to the preferred temperature of 1000F. was
approximately 20 minutes. The mixture was regener-
ated at 1000F. for 25 minutes. During the entire
: process, a controlled oxygen atmosphere was maintained.
A 3 liters/minute gas (0.5 percent 2 in N2) flow
rate was used. After regeneration, the admixture was
removed from the furnace and placed in a closed con-
tainer to minimize exposure to air. After cooling to
room temperature, the material is stored for reuse in
the process of this invention.
The granular activated carbon/ like the bone
char employed in this invention, is suitable 8 x 50
mesh and preferably an 8 x 35 mesh. By that term, it
is meant that from 0 percent to 5 percent by weight
of the granular material is retained by the larger
U.S. Standard Sieve, and from 0 percent to 5 percent
by weight is passed by the smaller sieve of the range.
Generally, any granular size is satisfactory,
as lo~g as it is not so samll as to become suspended
in the filtrate and carried from the bed, nor so
large as to seriously limit the surface area exposed.
Those skilled in the art have been using granular
bone char routinely for sugar liquor filtration and,
generally, the granular activated carbon should have
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an equivalent size range to that of the bone char
employed therewith.
The preferred activated carbon is one impreg-
nated with magnesium oxide and available under the
trademark, CANE-CAL~.
