Note: Descriptions are shown in the official language in which they were submitted.
~'~23~
A PROCESS FOR MAKING CATIONIC STARCH
The preparation of cationic starch is a well
known commercial process. The basic water-slurry
process for the quaternization of starch employing the
reaction product of epichlorohydrin and an amine is
taught in U.S. patent 2,876,217. The art also teaches
that in such a process an alkali metal salt, e.g. NaCl
or Na2S04 should be used to inhibit gelatinization.
The starch is usually slurried in water at a dry weight
(d.b.) of from about lO to about 4~ percent. Reaction
times are generally from 12 to 20 hours, the slurry is
maintained at a pH between 11 and 12 and the temperature
must be low to prevent gel~tinization during the process,
generally from room temperature up to 50C. The reaction
product must then be neutralized and washed to remove
1~ salts. According to teachings of U.S. 3,422,087 cationic
starch products can be made in the absence of alkali
and at temperatures much higher than normal, up to just
under 200C, which is the browning temperature of the
polysaccharide.
30,578-F
3870
This invention is directed to a process for
preparing cationic starch by reacting in an agueous
medium said starch with a halohydrin quaternary amine
in the presence of an alkaline catalyst characterized
by (1) initiating said reaction with an alkali metal
oxide or hydroxide and (2) thereafter adding an alkaline
earth metal oxide or hydroxide to complete the reaction.
The use of a combination of an alkali metal
oxide or hydroxide and an alkaline earth metal oxide or
hydroxide as catalysts in a particular order in the
reaction for making cationic starch reduces viscosity
and permits use of starch solids up to 46 percent
(d.b.) which results in superior yield of desired
product compared to the use of either an alkali metal
oxide, a hydroxide or an alkaline earth metal oxide or
hydroxide alone. When the halohydrin guaternary amine
is reacted with the alkali metal oxide or hydroxide, an
epoxide gxoup is formed from the halohydrin group.
The catalyst of the present invention is a
combination of an alkali metal oxide or hydroxde and an
alkaline earth metal oxide or hydroxide employed in
sequence, the latter being added after the reaction has
been initiated by the former. The alkali metal oxide
or hydroxide catalyst is employed at a concentration of
from 0.35 to 1.2 percent by weight and preferably from
0.6 to 1.0 percent; while the alkaline earth metal
oxide or hydroxide is employed at a concentration of
from 0.15 to 0.8 percent by weight, preferably from 0.3
to 0.6 percent. The use of less than the indicated
amount of either catalyst will give low yields and, in
the case of adding insufficient lime, gelation can
occur. Too much of either is uneconomical and mixing
30,578-F -2-
,
~ 387~
3-
the slurry of reactants becomes difficult with too much
alkaline earth metal oxide or hydroxide and filtering
is difficult with too much alkali metal oxide or hydroxide.
Preferably, the alkali metal is sodium or potassium and
the alkaline earth metal is calcium or barium.
Preferably, the halohydrin quaternary amine
has the formula
OH ~+R1
X-cH2cH(cH2)n A wherein A is -N -R2 X
X is chlorine or bromine, R1, R2 and R3 are independently
selected from the group of C1-C4 straight or branched
alkyl radicals with the proviso that the total number
of carbon atoms in R1, R2, and R3 does not exceed 8,
and n is 1-3. Thus, for example, starch is reacted
with 3-chloro-2-hydroxypropyltrimethylammonium chloride
according to the method of the present invention by
employing an aqueous starch slurry of 40 to 46 percent
by weight of dry starch with from 2 to 4 percent by
weight of 3-chloro-2-hydroxypropyltrimethylammonium
chloride in the presence of 0.5 to 2.0 percent by
weight of a gelatinization inhibitor, all based on
total reaction mixture. At lower temperatures, which
reduce the rate of gelatinization, the use of a gelatin-
ization inhibitor can be omitted, but in order toshorten the time of reaction the temperature should be
increased and a gelatinization inhibitor used. Even at
lower temperatures it is preferred to use a gelatin-
ization inhibitor since this, of itself, increases the
rate of reaction.
30,578-F -3-
3870
-
-4-
Below 40 percent starch in the slurry the
yields become unacceptably low, whereas above 46 percent
stirring of the reactants becomes difficult and gelatin-
ization is likely to occur. When the cationic rea~ent
is employed at less than the lower operable limit the
product becomes less effective as a paper additive.
More than the indicated operable amount is uneconomical
and of no additional benefit. More than the operable
level of gelatinization inhibitor is likewise uneconom-
ical and of no further benefit.
The time of reaction is ~rom 4 to 14 hours,
depending upon the temperature, and preferably from 7
to 10 hours. Temperatures in the range of from 35 to
60C are employed and preferably from 45 to 55C.
The yields of the process of the present
invention are from 70 to 85 percent. This compares to
yields in the range of 55 percent to 60 percent known
and practiced in the prior art. In addition to the
yield advantage, shorter reaction times and reduction
in waste effluents are achieved.
Although corn starch is exemplified in the
following experiments, wheat, rice, potato and (waxy)
maize starches can also be employed in the present
process.
Suitable gelatinization inhibitors include,
for example, Na2SO4, NaCl, KCl, K2SO4, Na2CO3 and
K2CO3. The sulfates are preferred.
After the reaction is complete, the resultant
cationic starch is ordinarily neutralized with an acid,
30,578-F -4-
~ 38'70
--5
such as, for example, hydrochloric, citric, nitric,
phosphoric, or adipic, to a pH of neutral or below,
usually about 6. After neutralization, the product is
usually filtered and washed. The product obtained
normally is dried before use.
The following experiments are representative
of the invention and of the known art for comparison.
Examples 1 Through 12 and ComParative Runs A Throuqh D
For Example 1, a 500 ml round bottom flas~,
equipped with stirrer and placed in a 50C constant
temperature bath. To the flask was added 15.4 g of a
50 percent solution of 3-chloro-~-hydroxypropyltrimethyl-
ammonium chloride plus a caustic solution made of 2 g
NaOH diluted with 97 g of water. The contents was
stirred and after formation of the epoxide which was
determined by a drop of the pH from 13.2 to 12.3
(approximately 2 minutes), 121.74 g of corn starch
mixed with 2.7 g of Na2SO4 was fed into the pot at a
rate insuring uniform dispersion (10-15 minutes). This
mixture was heated with stirring at 50C for 10 minutes,
during which time the pH dropped to about 10. Then a
slurry of 1 g CaO in 3 g of water was added, increasing
the pH from 10.0 up to 11.4. The mixture of reactants
was maintained at that temperature with stirring for 8
hours. At the end of this reaction period, 10 ml of
water was poured in to further reduce the viscosity.
Then the pH was lowered to 6.5 by neutralizing with lN
HCl. The starch slurry was filtered and washed four
times with 100 ml quantities of water. A nitrogen
content of 0.463 percent was obtained for this run
which was a 79 percent yield based on the 3-chloro-
-2-hydroxypropyltrimethylammonium chloride reactant.
30,578-F -5-
~ 3870
-6-
Examples 2 through 12 and Comparative Runs A
through D were conducted in a similar manner. The
addition order (except where noted) was always (1)
sodium hydroxide, (2) water, (3) chlorohydrin quaternary
amine salt, (4) starch + salt inhibitor and (5~ calcium
oxide.
The temperature at which the reactions were
conducted were: Examples 2-6 and Comparative Run D
(45C); Examples 7-12 and Comparative Runs A through C
(50C). The times of reaction were all 8 hours.
The amounts of catalysts (a) NaOH and (b) CaO
are given for each example and comparative run as are
the amounts of quaternary salt (quat), water, starch
and inhibitor salt (Na2SO4).
A11 samples were neutralized to pH 6 at the
end of the reaction, filtered and washed four times
with 100 ml or 10 ml of water depending upon size of
reaction. Yield was measured by the increase of nitrogen
as analyzed by the K~eldahl method.
30,578-F -6-
3870
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