Note: Descriptions are shown in the official language in which they were submitted.
106~275
The present invention relates to a process for
fluidization, and more particularly, to a process for
fluidization of materials which are difficult to fluidize.
Various types of fluidization processes have been
` used for many years for a number of different unit operations
and/or unit processes, including chemical reactions and
drying operations. In the usual fluidized system, a solid
phase is suspended in an upwardly moving fluid stream,
usually a gas stream, whereby the mass of solid particles
have the appearance of a boiling liquid. The solid phase
may be a catalyst to promote a chemical reaction, with the
reactants being contained in the fluidizing gas, or the solid
phase may be a material which is reactive with the fluidizing
gas. Alternatively, the solid phase may be a material which
is treated by the fluidizing gas as in the case of fluidized
- ~ drying.
One of the primary advantayes of fluidized bed
systems resides in the fact that the high turbulence
existing in a fluidized bed provides high heat transfer
characteristics. In addition, that turbulence in the fluid
;~ bed causes complete mixing of the solids with the fluidizing
gas to form a relatively homogeneous gas-solid system.
:
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~(:36~Z75
Fluidized bed systems are, however, not without
some disadvantages. As is now well known to those skilled
in the art, the use of fluidized C;ystems frequently results
in channeling, a phenomenon causecl by the formation of
pockets in the solid phase which ;n turn results in the
passage of gas through the solids forming the bed without
intimate contact with the solid phase.
The problem in channeling in a fluidized bed system
can be partially minimized by the use of a plurality of
tubular zones through which the fluidizing gas is passed
in contact with the solid phase. Each tube thus operates
as an individual fluidized bed having a much smaller cross
sectional area. Such tubular bed systems have even greater
heat transfer characteristics because the plurality of tubular
zones increase the surface available for heat transfer.
Howeyer, the use of a plurality of tubular zones,
has not found acceptance in the fluidization of materials
which, because of their cohesive characteristics, tend to
form aggregates and are consequently difficult to fluidize.
The difficulty in fluidizing such materials has been explored
by Gelhart in "Types of Gas Fluidization", Powder T0chnolo~y, -~
7, pp. 285-292 (1973). In that publication, the author
classifies solids into groups A through D, inclusive,
;~ characterizing materials having a small mean size and/or
a particle~ density 10ss than 1.4 g/cm3 as group A materials.
~ ' ~
''~ ' -' ''
,.
.,
~ 2 -
. .
69Z75
Group B materials are described as having a mean size ranging
from 40 ~m to 500 ~m and a density ranging from 1.4 to 4
g/cm . Materials of the groups A and B do not present
unusual problems from the standpoint of fluidization.
Groups C and D, on the other hand, present the most severe
fluidization problems, the group C materials being cohesive
and as a result, tending to plug small diameter tubes.
Gelhart points out that fluidization of such
materials can be made possible or improved by the use of
mechanical stirrers or vibrators to minimize channeling
in the fluid bed. However, the author points out that
one of the more effective means to avoid difficulties with ~ ;
such materials is the addition of extraneous solids to the
system.
There are a number of solid materials which fall
into the groups C and D categories as outlined above.
~, ~ ,. .
Starch is one example of a group C material since starch
tends to be quite cohesive, and thus tends to plug small ~
diameter tubes. Attempts have been made in the prior art ~ `
to process starches in a fluidized bed system. For example,
in U. S. Patent ~o. 2,845,368, there is described a process
~ ~ ,
for the conversion of starch to dextrin in a fluidized bed
system in which the fluidized reactor includes a plurality
of heat ~ansfer tubes contained in the reactor to supply
heat to the starch undergoing conversion. One of the primary
diffLculties wi`th a system of the type described in the
foregoing patent LS that the starch, when contacted with
~6927S
an acid catalyst, tends to form lumps or agglomerates
within the fluidized bed reactor to an even greater extent
Thus, the inherent cohesiveness of starch coupled with the
increased tendency for starch to agglomerate when contacted
with a catalyst results in severe channeling. Channeling,
in turn, results in incomplete conversion of the starch to
dextrin.
In addition, reactors used in the dextrinization
of starch are frequently characterized by a "dead zone" at
the upper portion of the reactor where the starch may lay
and be subjected to high temperatures for extended periods
Auto ignition can occur, causing fire and/or explosions.
This problem can be particularly aggravated in apparatus
of the type taught by the foregoing patent for the heat
transfer surfaces present in the fluidized bed reactor,
when prssent in sufflcient surface area to provide the
necessary heat exchange, disrupts the fluid flow within
the reactor to cause the formation of such "dead zones".
It iS accordingly an object of this invention to
provide a process for the fluidization of solids difficult
:
to fluidize which overcomes the foregoing disadvantages.
It is a more specific object of the invention to
provide a process for the fluidization of solids dlfficult
to fluidize whlch is characterized by the absence of "dead
zones", improvecl homogeneity and improved heat transfer
characteristics.
~; ~ ~ 4 ~
, :
. ~ I
- ~ ~
~069275
It is a further object of the invention to provide a
process for fluidization of starches in the production of starch
conversion products by processes wherein the starches are -
efficiently converted with relatively short residence times
while minimizing thermal degradation and risks of explosion
and/or fire.
These and other objects and advantages of the inven-
tion will appear more fully hereinafter, and, for purposes of
illustration but not of limitation, an embodiment of the inven-
tion is-shown in the accompanying drawings as described here-
inafter.
The present invention is directed to a process for
the fluidization of solid materials difficult to fluidize,
particularly solid particulate materials which have a tendency
to adhere or agglomerate to form cohesive masses. The present
invention contemplates chemical and/or physical processes in
.~ I .
which such particulate materials are fluidized and subjected to
heat transfer during fluidization, usually to supply heat thereto.
In~accordance with the practice of the invention, use
is made of a fluidization system including an upper, agitated
fluidized zone and~a lower, agitated fluidized zone, with an
intermediate fluidized æone formed of a plurality of tubular
zones communicating with~each of the upper and lower fluidized
zones whereby fluldi~zLng~gas~may~be passed upwardly through the
lower, agitated fluidized~;zone, through the intermediate zone
and into~the upE~er,~agitated fluidized zone to fluidize the
solids~Ln~each of~the~three~zones.
The heat~transfer to Qr~from the fluidized system
takes~place preclominantly~i`n~the~intermediate zone. The small
~ dl~ameter tubular~zones~ forming the intermedlate zone is pro-
vided with~heat exchsnge~mesns, and the ~maLl diameters of the
plur~li V ~Oe ~ubulsr zoAos~provide high heat transfer area.
~06~32'75
The fluidization process of the present invention i~
particularly well suited to the processing of starches, includ-
ing starch dextrinization, starch oxidation, etc., since starches
are cohesive and thus are difficult to fluidize. The invention
also contemplates physical as well as chemical processes, such
as drying. Starches can be effectively dried in the practice
of the invention. In addition, other physical and/or chemical
processes can be carried out on other solids difficult to
fluidize including coal, etc.
Broadly, the invention comprises a fluidization pro-
cess for fluidizing solids with a fluidizing gas in a vertically
disposed fluidizing chamber having a first end and a second end
fluidizing zone, comprising (a) introducing the solids into
said first end fluidizing zone while continuously subjecting
said solids to mechanical agitation, (b) passing the agitated,
; fluidized solids in the fir t end fluidizing zone toward said
second end fluidizing zone, and through a plurality of tubular
fluidizing zones into said second end fluidizing zone while
.
mechanically agitating the fluidized ~olids in the second end
fluidizing zone, and (c) contacting the tubular fluidizing zones
with heat exchange media and effecting heat transfer with the
fluidized solids in the tubular ~luidizing zones.
The first~end zone may be an upper zone in which case
the second end zone is a lower zone; or the first end zone may
; be a~lower~æone in which;case the second end zone is an upper
zone. The solids may thus be fed to the upper zone or to the
lower zone in practising~the process of the invention.
FIGURE l~is a~sectional view of a fluidized bed re~
actor suitable for use;in the process of the invention;
~`~;30 ~ FIGURE' 2 ls a sectional view taken along linea 2-2 in '~
FIGURE 1~; and, illustrating;a larger number of tubes than in
; Figure 1 ~where only four tubes are chosen for purposes of ~-
illus~rative~simplicity. ~ -~
~69275
FIGURE 3 is a schematic illustration of the process
of the invention.
In accordance with one embodiment, the concepts of
the present invention are applied in converting starch to
dextrin in an acid catalyzed reaction at an elevated
temperature wherein the starch is introduced to a fluidized
zone which is continuously agitated. From that fluidized
zone, the starch is passed, either concurrently or preferably
countercurrently, with the fluidizing gas through a plurality
of tubular fluidized zones and into another fluidized zone
which i9 likewise subjected to agitation.
In the preferred practice of the invention, the
starch is introduced to an upper fluidized zone and is
continuously agitated in that upper fluidized zone. From
the upper fluidized zone, the starch is passed downwardly
countercurrently with the fluidizing gas through the
plurality of tubular fluidized zones into a lower fluidized
zone which is likewise agitated. The product formed is
removed fro~ the lower fluidized zone. -~
One of the important features of the process of
this invention is that both the upper and lower fluidized ~ -
zones are vigorously agitated to insure complete mixing in
both the upper and lower zones. That agitation not only
serves to preveot channeliog and thus avoid incomplete
conyersion of the~starch, it also operates to prevent the
buildup of so-called~"dead~zones" in the reaction vessel
,: ~ : : . . -
~ 7 - --
1~69;~75
and thereby avoid scorching and undesirable thermal
degradation of the starch.
As is well known to those skilled in the art,
dextrins are the products of starch degradation obtained
by heating starch in a relatively dry state in the presence
or absence of an acid. Normally, corn starch contains from
about l~/o to about 12% by weight moisture; during the dry
heating of naturally dry starch, that moisture is removed,
whereupon dextrinization and branching commences. During
the dextrinization reaction, both hydrolysis and condensation
are effected. Branching occurs as a result of repolymerization
of partially hydrolyzed starch when the moisture in the starch
~ is below about 3% by weight.
; The term dextrose equivalent value (D.E.) is used
herein to refer to the reducing sugars content of the
dissolved solids in a starch hydrolysate or dextrin
expressed as percent dextrose as measured by the Schoorl
: ~ :
method (Encyclopedia of Industrial Chemical AnalYsis, Vol.
11, pp. 41-42). Starch dextrins generally have a dextrose
equivalent value of less than about 7, and most frequently,
in the range from about L to 7.
, : .
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8 -
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~ 5
Untreated starch normally has a degree of branching
of about 3.6%. Dextrins, on the other hand, usually have a
degree of branching of at least 7%, usually 7% to 16%.
The degree of branching in a dextrin is determined by
three types of analyses, i.e., dextrose equivalent value
(Schoorl's D.E. discussed hereinabove), dry ~ubstance, and the
amount of formic acid formed on periodate oxidation The
latter analysis, also known as formic acid value (FAV) expres~ed
as milliequivalents of formic acid per gram dry substance, i~
determined by low temperature oxidation (2C) with sodium meta-
periodate under rigidly controlled conditions. This method
iq more fully de~qcribed by R. W. Kerr and F. C. Cleveland,
J. Am. ChemO Soc., 74, 4036-4039 (1952) and by the same
author~ in Die Starke, 5, 261-266 (1953).
Periodate oxidation produce~ one molecule of formic
acid from each non-reducing terminal glucose unit and two
molecules of formic acid from each reducing texminal gluco~e
.:
~ unit. ~hu~, changes in tha FAV when calculated on a mole -
::
baqis indicate degree of branching in dextrin. From the fore-
going three (3) analyses, the degree of branching is
calculated as follows:
; ~1. Calculated number average molecular weight (Mn):
Mn - 20~500
D.E.
~ Note: Correction of D.E. for dextrose in
:!
dextrin i3 disregarded because the
amount of dextrose pxe~ent in dextxins
! :
negligible.
~ : ~ : : :
.
~.: :
.
3~06~75
2. Convert formic acid value (FAV) from mille-
equivalents per g.d.s. to equivalents per mole:
FAV, eq/mole = FAV, meq/g.d.s. x Mn
1, 000
3. Calculate number of branches per mole;
Branches/mole = FAV, eq/mole -3
~ote: Periodate oxidation produces one formic
acid molecule from each non-reducing
end group and two molecules of formic
acid from each reducing end group.
4. Calculate total linkages per mole
Linkages/mole = Mn - 18 1
162
5. Calculate degree of branching:
Branching, % = Branches/mole x 100 ;
Linkages mole
;;~ The formula for starch dextrin can be written as
.- . . .
(C6H1005)n, where n is a variable (rather than a mathematical ,,!~'." '"
~ constant) and smaller than the value for n in starch.
;~ Dextrins are obtained in several different~grades by
heating starch for varying lengths of time at temperatures
ranging~up to~about 240C. The amylodextrin, erythrodextrln, -~
20~ ~ ~achrodextrin, and~ao forth, produced by thls means may be
graded~roughly as to molecular size by the standard iodine
~069Z75
The dextrinization reaction can be catalyzed by
treating the naturally dry starch with an acid either
before or during the heating of the starch. Any acid may
be utilized for this purpose, such as sulfuric acid, sulfurous
acid, hydrochloric acid, and the like. Preferably, aqueous
dilute hydrochloric acid or anhydrous hydrogen chloride gas
is sprayed onto the starch particles before or during the
heating process. Other chemicals, such as Borax, may also
be incorporated into the starch during the dextrinization
process.
Referring now to the practice of this invention,
there is shown in Figure 1 in detail a cross sectional view
of the fluidized apparatus preferably used in the practice
of this invention. The apparatus includes an elongate ;
vertical housing designated as 10 which defines in its
upper portion, an upper chamber 12 having inlet means 14
to supply the starch. The housing 10 also defines a lower
chamber 16 positioned at substantially the bottom. Both
of the upper chamber 12 and the lower chamber 16 include
agitator means 18 and 20, respectively. The agitator means
:
18 includes a shaft 22 mounted for rotation within the upper
chamber 12. Mounted on shaft 22 for rotation therewith are
a plurality of impellers~24 which may be in the form of
flat paddles rotatable~with the shaft 22. The agitator
means 20 in the lower chamber 16 similarly includes a
rotatable shaft 26 having~lmpellers 28 mounted for rotation
therewith.
::: :
1(~6~75
In the preferred practice of this invention, the
agitating means 18 is formed with multi-bladed upthrust
impellers 24 at staggered locations, with additional impellers
30 being mounted at a 90 angle between each of the impellers
24 when two-bladed impellers are used. The agitating means
20 in the lower chamber 16 preferably has a similar confi~
guration. If desired, some or all of the impellers can be
disposed at angle with respect to those illustrated depending
on the number of blades per impeller.
Positioned in the housing 10 in an intermediate
section 32 are a plurality of tubes 34 having an upper end ; ;
36 communicating with the upper chamber 12 and a lower end
38 communicating with the lower chamber 16. In this way,
starch introduced to the inlet 14 flows by gravity downwardly
through the upper cham~er 12 through the plurality of tubes
34 and into the lower chamber 16. The lower chamber 16
also includes outlet means 40 to withdraw starch dextrin
therefrom.
. ...
Positioned below the lower chamber 16 is a housing
42 defining a plenum chamber 44. Fluidizing gas is intro-
duced to the plenum chamber through~fluidizing gas inlet
means 46, and passes through an opening 48 into the lower
chamber 16.
The arrangement of the tubes in the intermediate
;~ section 32 can be varied considerably. One suitable arrange-
ment ~or the tu~jes 34 ln the section 32 is shown in Figure 2
of the drawing, As shown in this ~igure, the tubes 34 are
arranged~in a pattern about the center of the section 32.
:
.: ~ : '
~ 12 -
~ :
~69Z7S
At least the tubular section is provided with means
to supply and/or remove heat therefrom. For this purpose,
the section 32 preferably defines a jacket for heat exchange
media which can be supplied to the section 32 by inlet means
49 and removed from the section or jacket 32 by outlet means
50 as shown in Figure 1. It is also desirable in many
instances to employ heat exchange means with the upper and
lower chambers. For this purpose, it is generally sufficient
to provide a jacket 52 surrounding the upper chamber 12, with
the jacket 52 including inlet means 54 to supply heat exchange
media to the jacket 52 and outlet means 56 to remove heat
exchange media from the jacket 52.
-~ As is shown in Figure 1 of the drawing, it may be
sufficient that the heat exchange jacket 52 for the upper
chamber 12 extend only up to the inlet means 14, or it may
be desirable to jacket the entire upper section to prevent
~`~ condensation. However, it is generally preferred that the
upper chamber 12 include a dome portion 58 integral therewith
`~ from which the fluidizing gas may be removed from the reactor
-~ 20 by means of outlet means-60.- As will be appreciated by those
skilled in the art, not only is the fluidizing gas removed
from the outlet means 60, but any "fines" entrained in the
fluidizing gas àre carried out with it through the outlet ;~
means 60. As wiIl be~appreciated by those skilled in the
art, it is possible, and~sometimes desirable, to form the
upper chamber with an increased sectional area to reduce
the linear velocity of~the fluidizing gas to thereby assist
in the separation of entrained particles of the solid phase.
`~ The cross sectional srea of the dome itself may be increased,
~;30 ~or, the cross sec~tional~area of the entire chamber 12 may be
increased for this purpose.
.; :
~ 13 - ~
3L0~9275
The lower chamber 16 may likewise be provided with
heat exchange media, preferably in the Eorm of a jacket 62,
to which heat exchange media is supplied through inlet
means 64 and from which the heat exchange media can be
removed from outlet means 66.
The process for the conversion of starches to dextrin
- is illustrated in Figure 3 of the drawing. AS shown in this
figure, the supply of starch, preferably containing an acid
catalyst,.is fed from a hopper 70 to the inlet means 14 for
introduction to the upper chamber 12. In the preferred prac-
tice of the invention, steam is introduced through lines 72
and 74 into the heat exchange jacket 52 to supply heat to
the upper chamber. The shaft 22 of the agitating means 18
can be driven by suitable means 76 as shown in Figure 3.
` The catalyst-containing starch i9 fluidized by
humid air introduced to the plenum chamber 44 through the
inlet means 46 and passes upwardly through the lower chamber
..
~ 16, through the tubes 34 in the intermediate section 32 and
-~; into the upper chamber 12. Steam as a heat exchange medium
. ~ : . .
20~ is also supplied through lines 78 to the jacket of section
32, and also through line 80 to the jacket 62 surrounding
the lower chamber 16. In this way, the upper and lower
. ~ ~ ~: : : - . ..
chambers as well as~the tubular section are supplied with
steam to heat~the~starch passing therethrough.
Thus,~the ac1dified starch supplied to the inlet
means 14 i5 immediately fluidized in the upper chamber 12
while the~upperchamber~l2~is continuously agitated against
the action;of bhe~fluidizing medium downwardly through the
upper chamber w~1le~subjected to agitation~ The acidified
.,: ~ : : .
.: : : : : , ~ .
. .
-
~69;~'75
starch continues its downward flow by gravity against the
suspending action of the air through the tubes 34 in which
there is no agitation, except for that which occurs naturally
due to the inherent turbulence in the tubes containing the
fluidized starch. After descending through the tubes 34,
the starch, at least partially converted to dextrin,
continues its descent into the lower chamber 16 against the
action of the fluidizing gas, and it is removed from the low-
er chamber 16 through the outlet means 40.
In one embodiment of the practice of this invention,
the product removed through line 40 is passed through a
rotary air lock 82 into a pneumatic cooling tube where the
temperature of the product is lowered to below 150F. For
this purpose, the product is discharged through the rotary
air lock 82 into the cooling tube 84 and to collection
- equipment through line 86. Dust or fines discharged through
the discharge means 60 is removed by means of a cyclone 88, ;~
: ~
and is thus transported by dust discharge line 90 to the
collection equipment through line 86.
~20 The starch which is dextrinized in accordance with
the process of this invention may be derived from a variety
of starchy materials,~including cereal starches, wa~y
starches and/or root starches. Typical of such starch
materials are non-waxy cereal starches (i.e., corn starch
and wheat starch~, potato starch, tapioca starch, grain
sorghum starch, rice~starch, waxy starches (i.e., waxy milo
starch, waxy maize starch)~, etc.~ The non-waxy cereal starches `-
:
~ are preferred, with corn~starch being particularly preferred. ~ ~
: : ~::: : : : :
~69Z75 :
In the preferrred practice of the invention, the
starch is blended with an acid catalyst prior to introduction
to the agitated fluidized bed. Hydrogen chloride or hydro-
chloric acid are preferred, although any acid may be used
for this purpose, including sulfuric acid, sulfurous acid
and the like. The acid is blended with the starch, preferably
by spraying a weighed amount of acid on a bed of starch while
continuously blending the starch to provide a homogeneous
acidified starch mixture. The use of a ribbon blender has
been found to be particularly well suited for this purpose.
The amount of acid blended with the starch is not
critical and can be varied within wide limits, depending in
part on the type of starch employed and the type of dextrin
produced. In general, amounts of an acid corresponding to
the range of 0.01 to 10 parts by weight of 20 Be' HCl per `i
1000 parts by weight of starch c.b., corresponding approxi-
mately to average past acidities expressed as millequivalents
of acid per gram of starch (dry basis) of 0.001 to 0~10.
The acidified starch is then passed through the
~20 apparatus described hereinabove while maintained at a
temperature which is dependent somewhat on the type of
dextrin to be produced. In general, the starch is maintained
at a temperature within the range of 125-380F, and pre-
; ferably 170-375F~in the fluidized bed reactor. In general,
the residence time of the starch in the fluidized bed
~ : ~
reactor oE th1s;invention lS less than one hour, and most
frequently ranges from~lO to 30 minutes, although longer
or shorter residence~times may be employed depending somewhat
on the grade of dextrin desired and the degree of conversion
30~ sought.~ ~
~ ~ .. :. . ..
~6~2~7~
If desired, the air as the fluidizing gas may be
heated externally, depending on the grade of dextrin to be
produced, although there is frequently little advantage in
doing so. In general, the fluidized bed can be heated to
a temperature within the range from 85-350F. For example,
when canary dextrin is to be procluced, temperatures within
the range of 225-335F are usual]y preferred. The air sup-
plied as the fluidizing gas preferably contains moisture to
more efficiently promote the conversion reaction.
As will be appreciated by those skilled in the art,
other fluidizing media can be used. For example, steam or
inert gases such as argon, nitrogen, carbon dioxide, etc.,
preferably containing some moisture can be used. In addition,
flue gases from combustion operations can similarly be used as
the fluidizing medium, if desired. It is not essential that
the fluidizing medium add any sensible heat to the starch
undergoing dextrinization since the tubular section of the
reactor employed with the concepts in the practice of this in-
vention in the dextrinization of starches is capable of pro-
2~0 viding all of the heat necessary to eficiently effect the re-
:
action. ~ -~
In accordance with another embodiment o~ the inven-
tion, the fluidization process described herein can also be
employed in the treatment of starches to produce bleached
starches and oxidized starches. ~s is now well known to
those skilled in the art,~bleached starches are starches pro-
duced by oxidative treatment which leads~to a marked whitening
of the starch~ In general, the severity of the oxidation
. ~ :
~ 17 -
~ ,
106927~i
treatment is controlled so that the carotene, xanthophyll and
related pigments occurring naturally in the starch are ef-
ficiently oxidized to colorless compounds while the starch
produced is only slightly oxidized (D.S. < 0.1) as later de-
fined (if at all). Bleaching is preferably carried out in a
dry state, and accordingly, a wide variety of oxidizing agents
may be used, provided that the oxidizing agent is one which is
mild enough under the reaction conditions so as to avoid exces-
sive oxidation of the starch but strong enough to insure that
the pigments themselves will be effectively oxidized. Examples
of usable bleachable agents include, without limitation,
chlorine, bromine, alkali metal hypochlorites, alkali metal
permanganates, ozone, alkali metal chlorites or alkali metal
chlorites in combination with alkali metal persulfates. Methods
of bleaching starches are discussed in greater detail in
"Chemistry and Industries of Starch", Second Edition, R.W. Kerr,
Editor, Academic Press, Inc., New York, ~ew York (1950).
Oxidized starches are starches produced ~rom the
~; oxidative treatment of the starch which leads to chemical
changes in the starch. For example, oxidation of primary
:: :
alcohol groups to carboxyl groups, of aldehyde groups to
carboxyl groups, of secondary alcohol groups to ketone groups,
and of glycol groups to carboxyl groups occur. The oxi-
dation of starch leads to a starch product which is more
~ : :
easily solubiliæed and which exhibits a lower viscosity when
solubillæed in watèr. OxLdation may be carried out by
utiIizing any oE a number of oxidizing agents. Often the
: : . .
-
: ~ . .
~ 18 -
.
~(~6927S
oxidizing agents used to form oxidized starch are the same
agents that are used to bleach starch. Harsher reaction
conditions such as higher temperatures, longer contact times,
different pH, etc., are used to cause these agents to react
with the starch molecules rather than just the carotene,
etc. Reagents used in the oxidation of starch include,
but are not limited to air, bleaching powder, halogens,
chloramines, chloric acid, chlorates, chromic acid, ferric-
chloride, hydrogen peroxide, hypochlorite, manganese dioxide,
nitric acid, nitrogen dioxide, perborates, periodic acid,
persulfates, potassium dioxide, potassium permanganate,
silver oxide, p-toluene sulfochloramide and zinc oxide.
Methods of oxidizing starch are also disclosed in more detail
in the previously cited text, "Chemistry And Industry of
Starch".
The repeating anhydroglucose units in starch may
have different degrees of substitution (D.S.), i.e., from
one to three, and starch deri`vatives are generally categorized
in terms of their D.S. In a given quantity of a starch
derivative, there will generally be some anhydroglucose
.~ .
units that are not substituted at all (i.e., D.S. < 0),
together with other anhydroglucose units that have different
degrees of substitution, from 1 to 3. A statistical average
is employed to characterize the average D.S. of the entire
.. . ..
quantity, although the figure is ordinarily stated as the
D.S. rather than the average D.S. The oxidized starch
treated according to this invention may have a varying range
of D.S. (carboxyl substitutionj which may be as little as
0.0001, up to the maximum level of 3Ø Irrespective of the
:~ : .'' ,'.
: ' ~ ' ''
19- -:
~ .
~06gZ75
numher of molecules of ~tarch which are reacted, or the actual
sequence of substitution, or the number of anhydroglucose
units involved, the general formula is intended to represent
products where the substitution may occur to various degrees
of substitution at all or less than all anhydroglucose units
in all or less than all starch molecules.
The di~tinction between oxidized and bleached
starche~ is now well known to those skilled in the art,
particularly the corn wet milling industry. Such a di~tinction
is described in U.S. Patent 3,598,622~
In general, the distinction between the oxidation
of starch and the bleaching of starch is directly related to
the severity of the reaction conditions. It has been found
; that oxidation of the starch generally occurs where the
temperature of the starch undergoing conversion was maintained
at tamperatures higher than 200F. While the conversion is ~lso
related to the amount of oxidizing agent employed, it has bean
found that the reaction temperature largely dictates whether
the reaction i~ a bleaching reaction or an oxidation reaction,
.
~20 However, to effect oxidation, it is preferable to employ an
oxidizing agent in an amount within the range of from 0.5 to 5%
of oxidizing agent based~on the weight of the starch, dry ba~
At temperature~ below 200F., the reaction is predominantly
a bleaching reaction, and the starch is affected to a minimal
extent. In general, bleaching of starch is carried out at
a reaction ~emE~erature of at least 80F, and preferably 80-
220F, w1th an amount~of~oxidizing agent ranging from .05 to
~/O~ ba~ed upon;~the weight of the starch, dry basis. -
`~ ~ , .-.
~: ,: , : ~ : .: .
~ ' 20 -
. .
1~;9275
In carrying out the fluidization proces~ of this
invention for the oxidation or bleaching of ~tarch, it i~
generally preferred to introduce the starch, which has been
blended with the oxidizing and/or bleaching agent, into
the upper agitated fluidized zone, from which the ~tarch
is allowed to pass downwardly from the upper, agitated
fluidized zone against the fluidizing gas through a plurality
of tubular fluidized zones into a lower fluidized zone while
the starch is being agitated in both the upper and lower
fluidized zones. The oxidized or bleached ~tarch is thus
recovered from the lower fluidized zone. As in the case
of dextrinization, the vigorous agitation in the upper and
lower fluidized zones serves not only to prevent channeling
and thus avoids incomplete conver3ion of the starch, it al~o
operates to prevent the buildup of so-called "dead zones" in
the reaction vessel to thereby avoid scorching and undesir-
able thermal degradation of the starch.
Alternatively, the starch, blended with the oxidizing
or bleaching agent, can also be supplied to the lowar
fluidized zone whereby the s~arch is passed upwardly from
the lower fluidized zone through the tubular zones and into
the upper fluidized zones concurrently with the fluidizing
gasn In tha practice of this invention, the oxidized or
; bleached ztarch~is thus recovered from the fluid sy~tem
from the upper;fluidized zone
The heat zupplied to the bleaching or oxidizing
reaction is supplied through the heat exchange media
surrounding the tubular zones. Because of the high ~urface
~ area for heat tran~fer afforded to the tubuIar zones, it i3
; ~ : ~ `: : `.
~ 21 -
.: : :~ ~ : , , ., ;
~: : ,: ~ : :: : : . .. .
~CI 69Z75
unnecessary to heat either the upper or lower agitated
fluidized zones.
In general, the re~idence time of the starch in
the fluidized bed reactor is less than one hour, both for
the production of oxidized starches and the production of
bleached starches. Most frequently, the residence time
ranges from 10 to 30 minutes, depending upon whether oxi-
dation or bleaching is desired.
In accordance with another embodiment of this
invention, the fluidization process can also be uqed in the
drying of starch or like cohesive solid particles. It has
been found that the fluidization process of this invention
i9 capable of use in the drying of starches and like mater-
ials which are cohesive in character and consequently dif-
ficult to fluidize. The ~luidization process of the present - :
invention provides remarkable energy and cost reductions
over drying processes ~or starch now in use.
As is well known to those skilled in the art, flash
drying is a method for drying starches at low cost because
it minimizes the residence of starch to heat transfer.
However, one o the~signlficant disadvantages of fla~h drying
as applied to starch~or any other material is that a high ~T
or driving force or heat transfer is required because all
of the energy for drying~must enter with the gas or superheated
vapor. In the~flash drying of starches, it has generally
been the practice to employ hot air with inlet temperatures
ranging from 350F-500F, that heated air serves as the source
` o heat as well as~the carrier or the exit moisture.
22 -
~69;~7S
The process of the present invention overcomes
the disadvantages of flash drying since the fluidization
process of the present invention is capable of providing
extremely high surface area for heat transfer as wall as
high heat transfer coefficients due to the turbulence in
the intermediate tubular zones of the fluidized system.
At the same time, the process of this invention does not
necessitate the use of a high ~T as required in flash drying
since the.driving force needed to effect the desired degree
of drying can be supplied by a heat transfer fluid in
contact with the intermediate tubular fluidized zones.
In fact, it has been found that the fluidization
process of this invention can be used in the drying of
starch, using as the heat transfer fluid waste steam from
turban-driven generators used to generate electrical power.
Such steam is usually saturated at a pressure of only a
few p.s.i. The ability to use exhaust steam in the drying
of starch represents a s ignificant economic advantage for
.
; it avoids the use of extremely high air temperatures
characteristic of flash drying while fully utilizing low
:
energy, exhaust~steam.
.. . .
In the pract~ice of the fluidization process of this
invention for drylng, the starch or like material can be
supplied either to the upper agitated fluidi~ed zone or the
::: : .
lower agitated fluidized zone, and the dried starch recovered
from the opposite zone. The fluidizing gas can be any of
the fluldizing gases de;scribed above, althoùgh it is
generally mo9t econ~omical~ to Use air. Heat for the drying
; ' ~ ~ .: : - :"
23 -
1069Z~5
operation can be supplied solely by the heat exchange medium
surrounding the intermediate, tubular zones which provide a
high surface area for heat transfer, while at the same time
providing high heat transfer coefEicients due to the turbu-
lence of the fluidized starch in the plurality of tuhular
zones. In general, use can be made of heat transfer media
having temperatures ranging from L00-500~F, depending upon
the material being dried and the amount of moisture present.
The present invention, having been described in
detail, the following specific examples are presented to
illustrate additional embodiments of the process and the
product thereof. It is to be understood that the examples
are given for illustrate purposes only and not by way of
limitation.
EXAMPLE 1
This example illustrates the use of an agitated
fluidized bed reactor of the type illustrated in Figures
1 and 3 of the drawing, having 7 tubes in the intermediate
section in the dextrinization of starch.
An acidified s~arch is prepared by feeding raw
~: -,
starch to a covered ribbon blender to which gaseous hydro-
chloric acld i3 subsequently added. The amount of hydro-
chloric acid added is determined by titration and it is
~ reported as a titer which represents the milliliters of 0.1
`; ~ N NaOH required to bring 20 grams of starch slurried in 100
milliliters of clistilled~water to a p~ of 6. The acidified
starch is introaiuced to the fluidized bed through the inlet
means 14, and air i9 introduced to the plenum chamber 44.
~. :
:;
: ,
- - -
:
~ 24 -
~69;~75
Dextrins may be characterized as either white dextrin~
or canary dextrins. Further white dextrins may be either high
solubles or low solubles. Solubles are reported a~ per cent,
and represent~ the amount of a 2-gram sample which dissolves
after being suspended in 250 milliliters of water at 25C
and shaken for 1 hour.
Canary dextrins are classified as either thick (high
viscosity) or thin (low viscosity). Dextrin viscosity is
normally reported as fluidity. For example, a 3:4 fluidity,
suCh as for Test 4050 in the table below, represents the
following. Three parts by weight of dextrin sample are mixed
with four parts by weight of water, heated in a steam bath for
30 minutes, then cooled to 25C. Any evaporation
of water, as determined by weighing, is compensated for by
addition of water. The material is then strained through a
No. 5029 nylon* into a glass beaker and held at 25C for a
total cooling time of 1 hour. The material is then placed
in a standard funnel at 25C. Fluidity i9 normally reported
in unit~ of milliliters and represents the amount of material
that flows out of the standard funnel in exactly 70 seconds. -~
The borax fluidlty method is the aame as ~hat described above,
except that l~/o;~ by weight of the sample is substituted with
borax (~a2B47-1H2~
A3 shown in the t~ab~le below, a hig~ soluble white
dextrin (~est 4050); a low soluble white dextrin ~Test 4060),
a thin~canary dextrin (Test 4064) and a thick canary dextrin
(Test 4074~werlC produced:
*manufacturer',3 designation~
1~69Z7~
Test 4050 4060_064 4~74
Starch moisture, % 10.7 10.7 10 11
Starch titer, ml 4.6 4.2 5.3 4.
Operating temperature, F 275 200310 325
Nominal retention time,
minutes a) 15.3 14.8 13.3 12.6
Air rate/tube, scfm /tub~) 5.5 5.5 5.5 5.5
Air velocity, feet/second 2.1 2.1 2.1 2.1
Jacket steam pressure, psig 55 5 112 150
Product moisture, % 2.5 5.0 2.2 1.9
Product solubles, % 94.5 19.8 98.197~9
Product fluidity, ml 22C) 25d' l6e)36~)
,
a) scfm - standard cubic fee per minute.
b) Based on inside tube diameter of 2.834 inches.
c) 3:4 fluidity, as is.
d) 1:3 l~/o borax fluidity, as is.
e) 2:3 l~/o borax fluidity, as is.
f) 1:2 l~/o borax fluidity, as is.
The fluid bed apparatu~ contained 7 tubes, the tubes
having an inside diameter of 2.834 inches. The height of
each tube was 5 feet.
EXAMPLE 2
-~ This example illustrates another dextrinization
reaction carried out in a fluidized bed system similar to
that described in Example 1. The reactor employed is of the
;~ same type illustrated in Figures 1-3 of the drawing, and
: ~
has 7 tubes in the intermediate section.
~ Using the procedure described in Example 1, an
- ~ acidified starch is prepared by feeding raw starch to a
blender along with gaseous hydrochloric acid as set forth
; ~ in the following table. The amount of hydrochloric acid
added is determined in the same manner as described in
:
~ Example 1.
: : .
~ - 26 - ~ -
, ~
: . -
~69Z75
The acidified Qtarch is then introduced to the
fluidized bed through the inlet means 14 and air is intro-
duced to the plenum chamber 44.
As is shown in the table, a highly soluble white
dextrin (Test 5170), a low soluble white dextrin (Test
5268), a thin canary dextrin (Test 5199) and a thick canary
dextrin (Test 5198) were produced.
Test 5170 52685199 5198
Starch moisture, % 9.9 12.011.3 12.3
Starch titer, ml 4.3 4.5 5.0 4.7
Operating temperature, F278 214 323 321
Nominal retention time,
minutes 12.0 9.823.2 21
Air rate/tube, scfma)/tub~ 3.3 3.6 3.1 3.1
Air velocity, feet/second ) 2.0 2.0 2.0 2.0
Jacket steam pressure, psig 68 14 120 117
Upper agitator rpm (15" diam)g) 42 42 42 42
Lower agitator rpm (10" diam~h) 66 66 66 66
Product moisture, % 2.0 5.7 1.9 1.5
Product solubles, % 98.3 17.498.9 98.5
Product fluidity, ml 27C) 23d)18e) 42f)
,
a) scfm = standard cubic feet per minute.
b) Based on inside tube diameter of 2.8 inches.
~ .
c) 3:4 fluidity, as is.
d) 1:3 10% borax fluidity, as is.
e) 2:3 10% borax fluidity, as is.
f) 1:2 l~/o borax fluidity, as is.
g) Two 4 bladed upthrust impellers
h) Three 4 bladed upthrust impellers
The fluid bed~apparatus contained 7 tubes, the tubes ~ -
having an inside~dlameter~of 2.8 inches. The height of
each tube was 5 feet.
~: : '
, .:
; . . .~:
.:
: :
~ 27 - -
.~ l
-,
1~6~Z75
EXAMPLE 3
Thi~ example illustrates the use of the fluidization
process of this invention in the drying of starch,
Using the equipment described in Example 1, starch
having a moisture content of 12% by weight based on the
weight of the starch, dry basis, is supplied to the inlet
14, and ambient dry air is introduced as the fluidizing gas.
Heat for the drying operation i9 supplied by
feeding to the jacket 32 steam at 147 psig. The starch
is fluidized for an average residence time of 15 minutes,
and is dried to a moisture content of 3 . ~/o by weight, dry
ba~is.
The foregoing examples illustrate the use of the
process of this invention in the dextrinization of starch
and in the drying of starch. While Example 3 above
;~ illu~trates ~hat is known in the art as secondary drying of
starch, that is reducing the moisture content of starch
from about 10 to about 14% to 3 to about 5%, the process `
of this invention can also be employed in the drying of starch
containing greater amounts of moisture. For example, the
process of the invention can be employed ln the drying of
starch containing about 35% by weight moisture on a weight
basis. In addition to starch, the process of this invention
` may also~be employed~in the drying of gluten, germ, corn
syrup solids or~sugars, dextrose, etc.
The process of~this invention is likewise well
suited for use in the~preparation of starch derivatives.
28 ~
: ` ~ :~ : : -
1~69Z75
Such derivatives are formed by reaction of starch, containing
up to 35% moisture on a dry basis with a variety of reagents
in accordance with now well known reactions. Such deriva-
tives are formed by reaction of starch as represented by
CH2H Ç 2 I CH2H
H~H I H~'~H 1 ~Ih~H
11~ ~-- ~ H o~
I___ In
with a number of reagents whereby the starch molecule is
substituted at either the primary and/or secondary hydroxyl
groups. For example, starch phosphates can be prepared by
reaction of starch with an alkali metal tripolyphosphate
~ 10 whereby the starch forms a starch phosphate ester. In
;~ addition, cationic starches can be produced by reaction of
starch with glycidyltrialkylammonium halides, preferably
those having the structural formula
CH2 ~CH2 - ~ CH2 -- ~ ( R ) 3 X
`: : o
wherein R represents a lower alkyl group such as methyl,
ethyl, propyl, etc. and X represents a halide ion. In
addition, use can be made of other reagents to produce
cationic starches, such as beta-halogenated amines including
2-dimethylaminoethyl chloride, 2-diethylaminoethyl chloride, -~
2-dimethylaminoi,sopropyl chloride, 2-di~allylaminoethyl ~-
chloride, 2-diisopropylaminoethyl chloride, etc.
:
29
~ : .: l : :: . ,
~: : : : ~ : ,.
~06~Z75
Anionic ~tarch derivatives can be produced in the
practice of this invention by reaction of starch with an
alkali metal salt of an omega-halogenated substituted
carboxylic acid. Preferred reagents for use in the pre-
paration of anionic starches include sodium chloroacetate,
sodium 2,3-epoxypropyl sulfonate, sodium 3-chloro-2-hydroxypropyl
~ulfonate or propiolactone. In the reactions as described
above to produce anionic starches, the starch is contacted
with the reagent in the presence of a basic cataly~t to
promote the reaction, a~ is well known to those skilled
in the art.
Another reaction to which the process of this
invention is ideally suited is the preparation of starch
carbamate. In this reaction, urea is reacted with starch
whereby the starch becomes substituted with carbamate
group9 O
O ~ H2
Other starch ethers can also be produced in the
process of this invention in accordance with well known
reactions. In such reactions, starch is reacted with,
for example, acrylonitrile, acrylamide, methacrylamide,
dialkylmethacrylamides, etc.
In carrying out each of the above-described
reactions, it has generally been found preferred to contact
(,
~ ` 9tarch, containing from 3 to about 35% moisture by weight,
: ;: :
~ with the reagent to be employed in the manufacture of the
~ ; derivative to insure lntimate admixture of the starch with
9uch reagent. q'he~9tarch containing the desired reagent
is then suppIiedL to the ~fluidized bed system in the practice
of thi9 invention, either to the upper fluidized zone or
, ~ .
', : :
: : ~ :: .-'
- 30 -
~ ~ :
. ~ : ..
9Z75
the lower fluidized zone as described above, and the reaction
carried out as described in the examples to produce the
desired starch derivative. In the practice of this inven-
tion, the desired conversion of the starch to the starch
derivative is completed in a relatively short period of
time, generally from 5 to 30 minutes in the fluidized
system, while avoiding undesirable thermal degradation of
starch as well as minimizing risks of fire and/or explosion
as a resu~t of overheating in the fluidized reactor system.
As illustrative of typical reactions, starch
can be oxidized by blending the starch with a suitable
oxidizing agent (NaOCl) in a ribbon blender in an amount
sufficient to`provide starch containinq l.~/o oxidant
expressed as chlorine on a dry solids basis. The re9ultant
blend of starch and oxidant is then introduced to the fluidized
bed through the inlet 14, and a suitable fluidizing gas,
preferably air, is introduced to the plenum chamber 44.
The necessary heat to promote the oxidation reaction
is supplied by contac~ting the plurality of tubular zones with
a suitable heat exchange medium, such as steam, to heat the
fluidlzed bed to the desired reaction temperature. The ~-
resulting oxidizinq starch is then removed from the lower
~; fluidized zone, having à Scott viscosity (I00 g) of about 47
and a carboxyl value of 0.65.
It will be ;understood that the process of the
present invention~provides a slgnificant improvement in the
:
fluidization o materials which tend to be cohesive, and
thus are difficult to fluidize. The process of the present -~
31 -
275
invention is particularly well suited for the treatment of
starch for the use of an agitated fluidized bed system
including upper and lower mechanically agitated zones which
serves to maintain homogeneity in the fluidi.zed bed and
to prevent scorching of the starch as it is passed through
the tubular zones of the reactor. The process includes
the use of an intermediate constr:icted heat exchange zone
between the upper and lower agitated fluidized zones through
which the.starch undergoing processing is rapidly passed
to prevent scorching of the starch.
It will also be understood by those skilled in the
art that the process of the present invention is not limited
to the process of starch. On the contrary, the process of
the invention can be used in the treatment of various other
~ materials which tend to be cohesive, and are thus difficult ~
to fluidize. - ~:
While the invention has been descrlbed in connection
.~ with specific embodiments thereof, it will be understood that
it is capable of further modification, and this application
is intended to cover any variations, uses or adaptations of
the invention following, in general, the principles of the -:
;: invention and including such departures from the present - :
'~ ~ disclosure as come within the known or customar~ practice . -
. . . ..
~ in the art to which the invention pertains and as may be
: :. . ,
applied to the essential features hereinbefore set forth,
and as falls within the~scope of the invention. ~ .'
':'
~: :
:
,
~ 32
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