Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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POLYASPARTIC ACID MANUFACTURE
Cross-Reference to Related Application
This application is a continuation-in-part of
co-pending application U.S. Serial No. 07/660,355, filed
on 22 February 1991.
Field of the Invention
The present invention relates to a method
of polymerizing aspartic acid and to polysuccinimides
and polyaspartic acids prepared by such method.
Background of the Invention
Polyaspartic acids have utility as
calcium carbonate and calcium phosphate inhibitors.
Their biodegradability makes them particularly valuable
from the point of view of environmental acceptability
and waste disposal.
Anhydropolyaspartic acids (i.e.,
polysuccinimides) are the anhydrous forms of
polyaspartic acids.
Thermal condensation of aspartic acid to
produce polyaspartic acid is taught by Etsuo Kokufuta,
et al., "Temperature Effect on the Molecular Weight and
the Optical Purity of Anhydropolyaspartic Acid Prepared
by Thermal Polycondensation," Bulletin of the Chemical
Society Of Japan 51(5):1555-1556 (1978). Kokufuta et
al. teach that the molecular weight of the polyaspartic
acid produced by this method increases with increased
reaction temperature. Moreover, the suggested maximum
percent conversion of the aspartic acid to
anhydropolyaspartic acid is no more than 68% using oil
bath temperatures of between 325°F and 425°F.
A more recent work by Brenda J. Little et al.,
"Corrosion Inhibition By Thermal Polyaspartate" Surface
Reactive Peptides and Polymers, pp 63-279, American
Chemistry Society Symposium Series 444(1990), cites
Kokufuta et al. Oil bath temperatures of 374°F were
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reportedly used to produce anhydropolyaspartic acid from
powdered aspartic acid over a period of 24 to 96 hours.
The reported results were no better than those reported
by Kokufuta et al., however.
Summary of the Invention
The method of the present invention provides a
much higher conversion of L-aspartic acid to
polysuccinimide and polyaspartic acid than has been
taught or suggested by the prior art. Moreover,
contrary to the teachings of the prior art, the
molecular weight of the polyaspartic acid produced by
our method does not increase with the reaction
temperature.
We have discovered that the thermal
condensation of powdered L-aspartic acid to produce
polysuccinimide in relatively high yields optimally
occurs above the initiation temperature of about 370°F,
and preferably occurs above about 420°F, and most
preferably occurs above about 440°F.
While a reactant temperature of less than
about 370°F may produce polysuccinimide over a period of
many hours, the theoretical yields will be low. The
conversion of the L-aspartic acid to polysuccinimide is
likely to be less than 70~ over a period of many days.
On the other hand, as the reactant temperature
is increased above 370°F, the percent conversion
increases to greater than 90~, and the reaction times
are greatly reduced.
The thermal condensation of L-aspartic acid to
polysuccinimide according the method of our invention
produces a characteristically shaped "temperature vs.
time" reaction curve. The curve is characterized by an
initial, rapid rise in reactant temperature, followed by
an endotherm signaling the beginning of the reaction.
Immediately following the onset of the endotherm there
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is evaporative cooling, followed first by a temperature
' rise, and then by a second endotherm, which is followed
by an evaporative cooling plateau. The temperature then
rises to a substantially constant plateau. The
condensation reaction has gone to at least 95%
conversion at a temperature approximately midway between
the final plateau and the time the temperature begins to
rise to that plateau.
Polyaspartic acid is produced from the
polysuccinimide by base hydrolysis of the
polysuccinimide.
The produced polyaspartic acid has a weight
average molecular weight of 1000 to 5000. This molecular
weight range is uniform regardless of the percent
conversion.
The percent conversion of the L-aspartic acid
to the polysuccinimide can be increased in reduced time
periods by increasing the temperatures used.
Where the thermal fluid used to heat the L-
aspartic.acid is brought to 500°F in a reasonable time
period, at least 90o conversion can be effected within 4
hours.
Where the thermal fluid used to heat the L-
aspartic acid is brought to a maintenance temperature of
at least 550°F within a reasonable time period, at least
90~ conversion can be effected within 2 hours.
Continuous as well as batch processes can be
used. The process can be carried out in a fluidized
bed; in a stirred reactor; in an indirectly heated
rotary drier, in an indirectly heated plate drier, and
' the like.
Brief Description of the Drawincrs
FIGURE 1 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction mixture temperature.
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FIGURE 2 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction mixture temperature.
FIGURE 3 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction mixture temperature.
FIGURE 4 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction temperature.
FIGURE 5 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction temperature.
FIGURE 6 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction mixture temperature.
FIGURE 7 depicts a temperature versus time
reaction curve. Series 2 is the oil temperature.
Series 1 is the reaction mixture temperature.
Description of Preferred Embodiments
A series of experiments were conducted to
thermally polymerize solid phase L-aspartic acid to
polysuccinimide. In each instance, the powdered L-
aspartic acid was added to a reaction vessel and heated.
Samples-were taken throughout the course of the
polymerization reaction. Those samples were analyzed
for percent conversion to the product, polysuccinimide.
The color and temperature of the samples were noted as
well. The produced polysuccinimide was then hydrolyzed
to produce polyaspartic acid. Activity tests were
conducted on the polyaspartic acid.
Each of these, conversion, color, production
of polyaspartic acid, and activity are described below.
The following procedure was utilized to
determine the percent conversion of the L-aspartic acid
to the product, polysuccinimide:
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THE DETERMINATION OF CONVERSION OF
L-ASPARTIC ACID TO POLYSUCCINIMIDE
A specific amount of the reaction mixture or
product was dissolved in an aliquot of dimethylformamide
(DMF). The dissolution was allowed to proceed for 4 to
5 hours until all of the polysuccinimide dissolved in
the DMF, leaving unreacted L-aspartic acid which was
filtered out. The amount of unreacted L-aspartic acid
was determined and used in the following formula:
A - B
CONVERSION = * 100
A
Where: A = weight of initial sample
B = weight of residue (unreacted L-aspartic
acid)
COLOR
The color of each product sample was noted.
The color of L-aspartic acid is white. The samples
containing polysuccinimide varied in color according to
the temperature of the sample taken from the reaction
mixture. From low temperature to high, the colors
varied as follows: light pink, to pink, to tannish pink,
to tan, to light yellow, to yellow, respectively. These
colors generally corresponded to the percent conversion
of the L-aspartic acid, in the same order with light
pink indicating the lowest percent conversion and yellow
indicating the highest percent conversion. The pink
colors had less than 70 conversion. The literature has
never reported any other color but pink.
POLYASPARTIC ACID
Polyaspartic acid was produced from
polysuccinimide using the following hydrolysis
procedure:
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Hydrolysis Procedure for Making
Polyaspartic Acid from Polysuccinimide .
A slurry was made from a measured amount of
polysuccinimide and distilled water. Sodium hydroxide
was added dropwise to hydrolyze polysuccinimide to
polyaspartic acid. Complete hydrolysis was attained at
pH 9.5.
Bases other than sodium hydroxide can be used
for hydrolysis. Suitable bases include ammonium
hydroxide, potassium hydroxide, and other alkaline and
alkaline earth hydroxides.
Generally, the base is added to the
polysuccinimide slurry until the pH value thereof
reaches about 9.5, and a clear solution has been formed.
ACTIVITY TEST
Polyaspartic acid was produced from the
samples of polysuccinimide. The activity of the
polyaspartic acid as an inhibitor for preventing the
precipitation of calcium carbonate was determined as
described in the test below:
A standard volume of distilled water was
pipetted into a beaker. Inhibitor (polyaspartic acid)
was added after the addition of a calcium chloride
solution, but prior to the addition of a solution of
sodium bicarbonate. Sodium hydroxide was then added to
the solution until there was an apparent and sudden
calcium carbonate precipitation evidenced by the
cloudiness of the solution.
At this point the pH dropped, the addition of
the sodium hydroxide was stopped, and the pH was
recorded. The volume of sodium hydroxide consumed was
noted. The pH drop after ten minutes was recorded.
The amount of inhibitor used was adjusted to
provide a constant weight of polyaspartic acid in each
of the tests.
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The activity of the inhibitor was judged by
the volume of sodium hydroxide consumed and by the pH
drop. The greater the amount of sodium hydroxide
needed, the greater the activity of the product as an
inhibitor. The smaller the pH drop, the greater the
activity of the product as an inhibitor.
MOLECULAR WEIGHT DETERMINATION
Gel permeation chromatography was utilized to
determine the molecular weights of the polyaspartic acid
produced. The molecular weight determinations were made
on the polysuccinimide that was hydrolyzed using the
hydrolysis procedure described herein.
Rohm & Haas 2000 Mw polyacrylic acid and Rohm
& Haas 4500 Mw polyacrylic acid were utilized as
standards. The molecular weights provided for the
polyaspartic acid produced according to this invention
are based on these standards unless otherwise noted, and
are reported as weight average molecular weights,(Mw).
This is because molecular weights based on gel
permeation chromatography can vary with the standards
utilized.
It was found that the molecular weight for the
polyaspartic acid produced fell within the range of 1000
Mw to 5000 Mw, regardless of percent conversion.
The term polyaspartic acid used herein also
includes salts of polyaspartic acid. Counterions for
polyaspartate include cations such as Na+, K", MgT, Li',
Ca'+, Zn'+, Baf+, Co'+, Fe++, Fe*+', and NH4+.
Polysuccinimide is the imide form of
polyaspartic acid and is also known as
anhydropolyaspartic acid.
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Conversion is defined to be the degree to
which L-aspartic acid has formed polysuccinimide by
thermal condensation.
Equilibrium temperature is defined to be the
temperature of the product upon completion of the
reaction.
EXPERIMENTS
Reported below are examples of the production
of polysuccinimide and polyaspartic acid.
Laboratory Experiment 1
A "time vs. temperature" plot of the following
reaction is depicted in Figure 1.
A 500-ml covered, stainless steel beaker
charged with 400 grams of powdered L-aspartic acid was
placed in an oil bath. The oil bath was quickly heated
to a 425°F maintenance temperature. The sample was
stirred throughout the experiment.
At 40 minutes, the reaction began when the
first endotherm was reached. The first endotherm of the
reaction mixture peaked at 390°F at an oil temperature
of 425°F which was the maintenance temperature.
Evaporative cooling immediately followed this
first endotherm. Water loss was evidenced by the
evolution of steam. The reaction mixture temperature
dropped to a low of 360°F during this period. Following
the temperature drop, the reaction mixture began to heat
up. At 2.75 hours, the reaction mixture attained a
plateau temperature of 400°F. At the end of 6.88 hours,
42 percent conversion had been attained. Steam coming
from the system evidenced water loss throughout the
entire endothermic reaction. Evaporative cooling still
continued to take place. The experiment was concluded
after seven hours.
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Table 1 below provides data developed during
this experiment. Samples were taken at the times
indicated and analyzed for percent conversion to
polysuccinimide.
The relative activity of polyaspartic acid
produced from the product polysuccinimide was determined
by the activity test described above. Activity is
reported in terms of pH drop (8pH) and milliliters (ml)
of sodium hydroxide, as described in the Activity test.
The color of the reaction mixture is provided.
Color was observed to vary with product temperature.
TABLE 1
POLYMERIZATION ACTIVITY
TEST
Time. hr. Product. Oil. Conv. NaOH, SpH Color
F F % ml
0.0 250 270 0 0.95 1.47 LP
1.0 386 430 5 --- ___ Z,p
1.7 385 425 13 1.75 0.56 P
3.4 401 425 26 1.75 0.56 P
2 0 5.0 400 424 27 1.75 0.56 P
6.9 400 425 42 1.80 0.57 P
The following definitions apply through out this
writing:
2 5 LP = 1 i ht
g pink
LY = light yellow
P = Pink
T = Tan
W = White
30 Y = Yellow
Conv. - Conversion
8pH = activity test pH drop
hr = hours
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Laboratory Experiment 2
A "time vs. temperature" plot of the following
reaction is depicted in Figure 2.
A 500-ml covered, stainless steel beaker
charged with 400 grams of powdered, L-aspartic acid was
placed in an oil bath. The oil bath was quickly heated
to a 450°F maintenance temperature. The sample was
stirred throughout the experiment.
At 30 minutes, the reaction began when the
first endotherm was reached. The first endotherm of the
reaction mixture peaked at 395°F at an oil temperature
of 439°F.
Evaporative cooling immediately followed this
first endotherm. Water loss was evidenced by the
evolution of steam. The reaction mixture temperature
dropped to a low of 390°F during this period and the oil
temperature rose to the 450°F maintenance temperature.
Following the temperature drop, the reaction
mixture began to heat up. At 1.67 hours, a second
endotherm occurred. At this endotherm, the reaction
mixture temperature was 420°F and the oil temperature
was 450°F. Steam coming from the system evidenced water
loss.
Evaporative cooling continued to take place
until the conclusion of the second endotherm. Water
loss was evidenced by the evolution of steam. At the
conclusion of this period, the reaction mixture was then
heated up and maintained at an equilibrium temperature
of 434°F.
Table 2 below provides data developed during
this experiment. Samples were taken at the times
indicated and analyzed for percent conversion to
polysuccinimide.
The relative activity of polyaspartic acid
produced from the product polysuccinimide was determined
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by the activity test described above. Activity is
reported in terms of pH drop (8pH) and milliliters (ml)
of sodium hydroxide, as described in the activity test.
The color of the reaction mixture is provided.
Color was observed to vary with product temperature.
TABLE 2
POLYMERIZATION ACTIVITY TEST
Time, hr. Product. °F Oil. °F Conv. % NaOH. ml 8nH Color
0.0 340 345 0 0.95 1.47 W
0.5 400 440 22 --- --- Lp
1.1 396 45I 23 1.75 0.59 LP
1.7 422 457 32 1.80 0.57 P
4.2 416 451 58 1.81 0.61 P
5.5 420 452 81 1.80 0.63 T
7.1 430 454 97 1.75 0.69 T
Laboratory Experiment 3
A "time vs. temperature" plot of the following
reaction is depicted in Figure 3.
A 500-ml covered, stainless steel beaker
charged with 400 grams of powdered, L-aspartic acid was
placed in an oil bath. The oil bath was quickly heated
to a 500°F maintenance temperature. The reaction mixture
was stirred throughout the experiment.
At 30 minutes, the reaction began When the
first endotherm was reached. The first endotherm of the
reaction mixture peaked at 405°F at an oil temperature
of 4 65 °F .
Evaporative cooling immediately followed the
first endotherm. Water loss was evidenced by the
evolution of steam. The reaction mixture temperature
dropped to a low of 390°F during this period, and the
oil temperature rose to 490°F.
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At 1.25 hours, a second endotherm occurred.
At this second endotherm, the reaction mixture
temperature was 438°F and the oil temperature was 495°F.
Evaporative cooling continued to take place
until the conclusion of the second endotherm. Water
loss was evidenced by the evolution of steam. The
reaction mixture temperature dropped to a low of 432°F
during this period and the oil temperature rose to
499°F.
A diminution in evaporative cooling was
evidenced by a steady rise in reaction mixture
temperature between approximately 2.65 hours and °sl~,
hours. At 3.17 hours a temperature plateau was
attained. No further increase in conversion was noted
beyond that point.
Table 3 below provides data developed during
this experiment. Samples were taken at the times
indicated and analyzed for percent conversion to
polysuccinimide.
The relative activity of polyaspartic acid
produced from the product polysuccinimide was determined
by the activity test described above. Activity is
reported in terms of pH drop (8pH) and milliliters (ml)
of sodium hydroxide, as described in the activity test.
The color of the reaction mixture is provided.
Color was observed to vary with product temperature.
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TABLE 3
POLYMERIZATION ACTIVITY TEST
Time, hr. Product. F Oil, F Conv. NaOH, ml SpH Color
%
0.0 256 316 0 0.95 1.47 W
0.5 406 464 7 ___ ___ I,p
1.3 437 496 43 1.80 0.56 P
2.3 438 497 81 1.80 0.56 P
3.1 470 499 90 1.80 0.67 TP
3.8 476 500 95 1.80 0.63 TP
6.0 476 502 98 1.80 0.63 LY
Laborator y Experiment 4
A "time vs. temperature" plot of the following
reaction is depicted in Figure 4.
A 500-ml covered, stainless
steel beaker
charged w ith 400 grams of powdered,L-aspartic acid was
placed in an oil bath. The oil bat h was quickly heated
to a 550F The sample was
maintenance
temperature.
stirred throughout
the experiment.
At 24 minutes, the reacti on began when the
first endotherm irst endotherm of
was reached. the
The f
reaction an oil temperature
mixture
peaked at
410F at
of 470F.
Evaporative cooling immediately followed the
first endotherm. Water loss was evidenced by the
evolution of steam. The reaction mixture temperature
dropped to a low of 395°F during this period.
A second endotherm occurred at 1 hour at a
reaction mixture temperature of 442°F.
Evaporative cooling continued to take place
until the conclusion of the second endotherm. The
. reaction mixture temperature dropped to a low of 440°F
during this period.
A diminution in evaporative cooling was
evidenced by a steady rise in reaction mixture
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temperature between approximately 1.5 hours and 2.06
hours. At 2.06 hours a temperature plateau was
attained. No further increase in percent conversion was
noted beyond 1.95 hours.
Table 4 below provides data developed during
this experiment. Samples were taken at the times
indicated and analyzed for percent conversion to
polysuccinimide.
The relative activity of polyaspartic acid
produced from the product polysuccinimide was determined
by the activity test described above. Activity is
reported in terms of pH drop (8pH) and milliliters (ml)
of sodium hydroxide, as described in the activity test.
The color of the reaction mixture is provided.
Color was observed to vary with product temperature.
TABLE 4
POLYMERIZATION ACTIVITY
TEST
Time, hr. Product. Oil, Conv. NaOH, SvH Color
F F % ml
2 0 0.0 330 348 0 0.95 1.47 W
0.5 405 470 11 --- --- LP
~
1.0 436 520 36 1.80 0.60 LP
1.4 439 536 66 1.80 0.67 P
1.8 462 540 92 1.80 0.58 TP
2 5 2.0 495 544 94 1.75 0.64 TP
2.4 510 547 96 1.75 0.58 LY
3.4 512 548 98 1.80 0.63 Y
Production scale product runs were conducted
30 as follows:
Pilot Plant Test Run #1
A "time vs. temperature" plot of the following
reaction is depicted in Figure 5.
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A DVT-130 drier-mixer manufactured by
Littleford Brothers, Inc., of Florence, Kentucky was
used. The jacketed drier utilizes oil as a thermal
fluid and a plough blade impeller. The drier-mixer had
a stack open to the atmosphere and a heat transfer area
of 10 ft2. The reactor's oil reservoir was preheated to
550°F to provide an oil inlet temperature of about
500°F.
The reactor was charged with 110.4 lb of
powdered, L-aspartic acid. Hot oil began to flow through
the jacket, and the impeller speed was set at 155 rpm.
Both the product and oil temperatures rose steadily. At
a product temperature of 390°F, there was a sudden,
endothermic reaction which caused the product
temperature to drop (see Fig. 5). Water loss was
evidenced by the evolution of steam. A sample taken
revealed that the powder had changed from white to pink.
Three percent of the material was converted to
polysuccinimide.
Thereafter, product temperature began to rise
steadily until it reached a plateau at 928°F which
continued for an hour. Throughout this whole reaction,
steam evolved, and the conversion increased in a linear
fashion. At the end of the hour, the product
temperature rose to 447°F at which time the reaction
underwent a second endotherm. Immediately after this
endotherm, steam ceased to evolve. Shortly after this
point, the reaction was at least 88$ complete.
Following the second endotherm, the product slowly
changed from a pink to a yellow color. The final
conversion was measured at 97~. Table 5 below provides
data developed during this experiment. Samples were
taken at the times indicated and analyzed for percent
conversion to polysuccinimide.
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TABLE 5
POLl'NIERIZATION
Time, hr. Product. °F Oil, °F Conv. %
0.0 70 375 0
0.8 390 394 3
1.1 396 504 15
1.5 423 501 24
2.0 430 500 41
2.6 430 506 61
3.6 444 505 84
4.5 471 508 88
5.8 466 506 97
Pilot Plant Test Run #2
A "time vs. temperature" plot of the following
reaction is depicted in Figure 6.
A Littleford DVT-130 drier-mixer with w heat
transfer area of 10 ftZ, was charged with 110.4 lb of
powdered, L-aspartic acid, and the oil reservoir was
preheated to 525°F.
At the start up, hot oil began to flow through
the jacket, and the impeller speed was set at 155 rpm.
Both the product and oil temperatures rose steadily.
The product temperature rose to 393°F whereupon a
sudden, endothermic reaction caused the product
temperature to drop (see Fig. 6) and steam began to
evolve. A sample taken revealed that the powder had
changed from white to pink. Four percent of the
material was converted to polysuccinimide. Thereafter,
product temperature began to rise steadily until it
reached a plateau at 427°F which continued for one and a
half hours. Throughout this whole reaction, steam was
evolved, and the conversion increased in a linear
fashion. At the end of this time, the product
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temperature rose to 444°F until the reaction underwent a
second endotherm. Immediately after this second
endotherm, steam ceased to evolve. Shortly after this
point, the reaction was at least 94~ complete.
Following the second endotherm, the product slowly
changed from a pink to a yellow color. The final
conversion was measured at 98~s. Table 6 below provides
data developed during this experiment. Samples were
taken at the times indicated and analyzed for percent
conversion to polysuccinimide.
TABLE 6
POLYMERIZATION
Time. hr. Product.
F Oil. F Conv.
0.0 70 4pp 0
1.0 393 488 5
1.3 400 476 18
2.0 428 475 20
3.9 441 480 66
2 4.4 450 477 85
0
5.1 456 476 94
6.1 457 484 98
Pilot Plant Test Run #3
A "time vs. temperature" plot of the following
reaction is depicted in Figure 7.
A "B" blender, manufactured
by J.H. Day of
Cincinnati, Ohio was charged with 110.4 lb of powdered,
L-aspartic acid. The unit was a trough-shaped blender
with a plough-bladed impeller and a heat transfer area
of approximately 8 ft z. The reactor was wrapped in
fiberglass insulation because the oil heater was
undersized. The reactor
also had a large funnel
in a
top port open to the atmosphere. The oil reservoir was
preheated to 500F. At
the start up, hot oil
began to
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flow through the jacket, and the impeller began to
rotate at 74 rpm. Both the product and oil temperatures
rose steadily. The product temperature rose to 377°F
whereupon a sudden, endothermic reaction caused the
product temperature to drop (see Fig. 7) and steam
began to evolve. A sample taken revealed that the
powder had changed from white to, pink. Thirteen percent
of the material was converted to polysuccinimide.
Thereafter, product temperature began to rise steadily
until it reached a plateau at 416°F which continued for
3.75 hours. Throughout this whole reaction, steam was
evolved, and the conversion increased in a linear
fashion. Due to the heater being undersized, it took a
longer time for the product temperature to rise. At the
end of this time, the product temperature rose to 435°F.
The reaction was at least 88$ complete. Due to time
limitations, the reaction was stopped when the product
temperature reached the plateau. At this point, the
final conversion was measured at 90~. Table 7 below
provides data developed during this experiment. Samples
were taken at the times indicated and analyzed for
percent conversion to polysuccinimide.
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TABLE 7
POLYMERIZATION
Time, hr. Product. F Oil. F Conv.
%
0.0 55 390 0
1.0 370 420 0
2.3 377 448 13
3.0 403 455 21
3.5 416 460 26
4.0 417 469 32
4.5 416 471 38
5.0 416 472 45
5.5 415 460 52
6.8 413 446 64
7.3 414 448 70
7.8 418 451 74
8.3 422 455 81
9.3 433 460 88
9.8 435 460 90
These experiments show that
degree of
conversion of L-aspartic ac id and the me required for
ti
conversion are related to t he temperature
of the
reaction mixture.
The higher the te mperature the thermal
of
fluid used to heat the reac tion mixture,the higher the
degree of polymerization an d the faster the rate of
conversion.
Because of normal heat losses the temperature
of the thermal fluid will a lways be higher than the
temperature of the reaction mixture. It is known that
increasing the temperature of the thermal fluid will
increase the driving force of the reaction. Assuming
that the thermal fluid temp erature will be raised to
its
maintenance temperature in a reasonably short period
of
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time, we have found that generally the following has
held true:
Where the oil maintenance temperature was
425°F, at the end of 5 days only 60% conversion was
achieved. The equilibrium temperature of the reaction
mixture appeared to be 400°F.
Where the oil maintenance temperature was
450°F, 90~ conversion took place within 7 hours. The
equilibrium temperature of the reaction mixture is not
known.
Where the oil maintenance temperature was
500°F, 90% conversion took place within 4 hours. The
equilibrium temperature of the reaction mixture was
477°F.
Where the oil maintenance temperature was
550°F, 90% conversion took place within 2 hours. The
equilibrium temperature of the reaction mixture was
510°F.
The difference between the maintenance
temperature and the reaction temperatures provides the
driving force. Different means for providing the
thermal energy can result in different driving forces.
Thus, although the relations derived here are
qualitatively valid, there may be some quantitative
differences found in different systems. Different
thermal resistances will result in a shift in
temperature and/or time requirements.
The systems tested here tend to have high
thermal resistance. For systems with less thermal
resistance, lower source temperatures will suffice to
provide equivalent results.
The data indicates that continuous as well as
batch processes can be used. The relationships
discussed above are equally valid for both. Based on
the data presented herein, a number of different
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reactors can be used. Examples of these include, but
are not limited to a heated rotary drier; a thin-layer
plate reactor; a stirred reactor; a fluidized bed and
the like. The reaction can be carried out at ambient
pressure or under a vacuum, as desired. The reaction
can occur in air or a variety of atmospheres, inert or
otherwise. As a further example, an indirectly heated
rotary drier providing the same residence time as the
DVT 130 drier-mixer provides similar results under the
same operating conditions.
THERMAL CONDENSATION IN A STIRRED REACTOR
Apparatus: a hollow, cylindrical, stainless
steel, jacketed vessel in the form of a pan with a
height of approximately 150 mm and a diameter of 400 mm.
The vessel was fitted with four arms, each with several
attached plows. Thermal fluid was used to heat the
vessel.
Procedure: The vessel was preheated to the
desired temperature. A layer of L-aspartic acid was
deposited in the pan and spread evenly across the pan.
Samples were taken periodically to measure extent of
reaction and conversion to polysuccinimide. Evolved
steam was condensed. The observed results are set forth
in Table 8, below.
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TABLE 8
Plate Layer
Test Temp. Sample ConversionTime Plow Depth
No. ~F No. (%) min Tvpe1 (mm Comments
1 500 1 33.88 20 Standard13
2 95.18 60
3 100.00 90
180
2 400 1 1.8 40 Window 18
2 8.4 70
80
3 430 1 2.1 10 Window 18
2 3.3 20
3 7.7 30
4 12.5 40
5 19.5 50
6 22.8 60
4 500 1 27S 10 Window 18 Cont. of
No. 3
2 512 30
2 0 3 76.6 50
4 97.0 70
80
5 430 1 .2 10 Window 17
6 500 1 16.1 15 Window 18 Cont. of
No. 5
2 5 2 28.9 30
7 430 1 5.1 20 Window 18
20
8 500 1 242 15 Window 18 Cont. of
No. 7
2 39.5 30
3 0 9 430 1 25.2 - Standard15
15
10 500 1 37.3 - Standard15 Cont. of
No. 9
2 66.9 -
3 91.0 -
3 5 4 99.6 -
5 99.5 -
110
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Plate Layer
Test Temp. Sample ConversionTime Plow Depth
No. ~F No. (%) - min T~ mm Comments
,
11 500 1 10.2 - Serrated15
2 30.7 -
3 40.6 -
4 54.4 -
5 71.9 -
6 882 -
60
12 455 1 6.7 - Standard15
2 13.2 -
15
13 464 1 8.1 - Standard15
2 15.2 -
15
14 500 1 18.3 - Standard15 Cont of No.
13
2 433 -
3 73.9 -
4 95.9 -
5 99.2 -
60
2 0 1 S 474 1 26.6 - S tandard15
20
16 500 1 52.3 - Standard15 Cont of No.
15
2 85.3 -
3 98.6 -
2 5 4 99.4 -
5 99S -
75
' In the above table, "standard" denotes a 90 mm solid plow; "window"
indicates that the center portion
3 0 of each plow has been cut-out; and "serrated" denotes a plow in which the
bottom of the plow has teeth.
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THERMAL CONDENSATION ON A PLATE DRIER
Pilot plant scale tests were performed in a -
Krauss Maffei VTA 12/8 plate drier having eight
stainless steel plates with a diameter of 1200 mm. The
drier was operated in ambient atmosphere. The first two
plates were maintained at a relatively lower temperature
than the next five. The last plate was not utilized due
to temperature control problems. Each plate has 0.35m2
of heat transfer surface and four arms of plows. Except
for the first plate, the fourth arm of each plate had
the plows moving in reverse in order to increase the
retention time and the turnover rate.
L-aspartic acid powder was delumped and then
fed to the first plate of the drier. The plows evenly
distributed the deposited L-aspartic acid until thin
ridges covered the plate. The deposited powder followed
a spiral across the plate until it was pushed off the
edge onto the next plate. There the process was
repeated until the powder was swept off the center of
the plate. Once process conditions stabilized, samples
were taken from each plate to measure extent of
reaction. The conversion of L-aspartic acid to
polysuccinimide could be followed by noting the color
change of the powder by plate. The powder on the
initial plates was observed to be light pink, on the
middle plates a yellowish salmon, and on the final
plates yellow-tan.
The observed results are compiled in Table 9,
below.
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TABLE
9
Plate Air Residence
Test Temp. Air FlowTemp. ConversionTime=
No. ~F tt/min ~FZ Plate ~ fmin
No,
A 435 19 485 1 9.76 68.5/65.6
2 12.38
480 3 34.85
4 62.24
66.78
6 91.30
7 98.63
discharge
B 430 17 460 1 4.93 68.5/69.2
2 16.44
495 3 26.47
4 50.94
5 66.90
6 80.35
7 96.50
2 0
discharge90.97
C 430 17 460 I 61.8/-
2
495 3
4
5
6
7 98.72
discharge
D 440 17 462 1 19.71 61.8/42.1
3 0
2 35.39
511 3 39.01
4 89.52
5 99.01
6 99.03
3 5
7 99.40
discharge99.67
i Total ated
time time
spent based
in reactor/Calcul on
9890
conversion
.
' Includes
by-pass
from
feeder.
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Polysuccinimide produced in the foregoing
manner can be readily converted to polyaspartic acid by
base hydrolysis.
