CA1095050A - Method of promoting the crystallization of picloram - Google Patents
Method of promoting the crystallization of picloramInfo
- Publication number
- CA1095050A CA1095050A CA312,683A CA312683A CA1095050A CA 1095050 A CA1095050 A CA 1095050A CA 312683 A CA312683 A CA 312683A CA 1095050 A CA1095050 A CA 1095050A
- Authority
- CA
- Canada
- Prior art keywords
- picloram
- weight
- sulfuric acid
- flocculating agent
- solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT
A process for promoting the spherical crystal-lization of picloram (4-amino-3,5,6-trichloro-2-picolinic acid), wherein an anionic polymeric acrylamide flocculating agent, when combined with a solution of picloram in an aqueous sulfuric acid medium, serves to promote the formation of polycrystalline picloram spheres and to greatly reduce the formation of fines.
18,299-F
A process for promoting the spherical crystal-lization of picloram (4-amino-3,5,6-trichloro-2-picolinic acid), wherein an anionic polymeric acrylamide flocculating agent, when combined with a solution of picloram in an aqueous sulfuric acid medium, serves to promote the formation of polycrystalline picloram spheres and to greatly reduce the formation of fines.
18,299-F
Description
10~50~i~
METHOD FOR THE CRYSTALLIZATION OF PICLORAM
This invention is concerned with an improved method of promoting the spherical crystallization of picloram, which is the common name for 4-amino-3,5,6-trichloro-2-picolinic acid.
In conventional preparative and purification proce-dures where picloram is crystalli zed by altering the acidity and/or temperature of an aqueous solution, picloram tends to - crystallize primarily as small needle-like fines, i.e., particles less than 105 microns in diameter, which tend to form a mush in the mother liquor. Centrifuging and washing of this mush is time consuming and may result in a significant loss of the final product through the centrifuge screen.
One advantage, therefore, of the method of the present invention is that it reduces the amount of fines and promotes the crystallization of picloram as dense poly- -crystalline spheres which are gxeater than 105 microns in diameter. These spheres can be readily washed free of the mother liquor without an undue loss of the final product.
This invention provides a method for promoting the spherical crystalliæation of picloram, which comprises combining an anionic polyacrylamide flocculating agent, picloram, and an aqueous sulfuric acid medium, wherein the flocculating agent is present in an amount of at least 10 ..g~
parts by weight of the flocculating agent per million parts by weight of the combined weight of the picloram and the aqueous sulfuric acid medium.
In the process of the present invent7on, anionic polymeric acrylamide flocculating agents are utilized to promote the spherical crystallization of picloram, from an aqueous sulfuric acid solution. This process also serves to reduce the formation of fines.
The flocculating agent is generally added to the dilution water which is metered together with a solution of picloram in aqueous sulfuric acid into a stirred ~essel.
However, depending on the ne~ds of the individual practitioner of this invention, the flocculating agent can be present in the vessel before the addition of the picloram is begun, or the flocculating agent can be added to the vessel in incre-ments during the crystallization period. As the addition of the dilution water and of the solution of picloram in sulfuric acid proceeds, crystallization and orientation of the picloram crystals from a limited number of sites occur to form large masses of crystals bonded together in spherical shapes Upon drying, these larger crystal masses remain intact. Apparently, the crystals bond together in a mass radiating from a center which results in the formation of dense polycrystalline balls.
The sulfuric acid solution of picloram, flocculating agent, and dilution water can be combined in any manner that is convenient to the individual practitioner of this invention.
For example, a batch or semi batch process may be used where the flocculating agent is added to the heel from a previous batch before the addition of the picloram solution and dilution water is begun. Alternately, a continuous process may be used where the dilution water containing the floccu-lating agent is metered simultaneously with the picloram 18,299-F
lO~S~50 solution into the stirred vessel and a slurry of the crystallized picloram removed at a rate to maintain a level in the vessel. Other variations which are obvious to those skilled in the art are intended to be within the scope of the present invention.
Flocculating agents which may ~e employed in the improved method of the present invention are water soluble, anionic acrylamide polymers such as, for example, Purifloc~
A22, Purifloc~ A23, and Purifloc~ A25 flocculants, which are well known to the art-skilled persons.
During the polymerization of acrylamide, there is some degree of hydrolysis of the -CONH2 groups to -~OOH. As used herein, the term "anionic" refers to those acrylamide polymers which contain greater than one percent of carboxyl or which will hydrolyze in aqueous sulfuric acid to form greater than one percent of carboxyl.
The optimum amount of anionic polyacrylamide flocculating agent to be employed in combination with the picloram-aqueous sulfuric acid medium solution will be dependent upon such variable factors as the temperature of the solution, the acidity of the aqueous acid medium, the purity of the picloram, and the particular flocculating agent utilized. Generally, an effective crystallization-promoting amount is at least 10 parts by weight of the floccu-lating agent per million (1 000 000) parts (ppm) by weight of the solution and usually an amount from 20 ppm to 40 ppm is suitable. It is understood that the weight of the solution is equivalent to the combined weight of the picloram, the dilution water, and the aqueous sulfuric acid medium. Ordinarily such solutions will contain from
METHOD FOR THE CRYSTALLIZATION OF PICLORAM
This invention is concerned with an improved method of promoting the spherical crystallization of picloram, which is the common name for 4-amino-3,5,6-trichloro-2-picolinic acid.
In conventional preparative and purification proce-dures where picloram is crystalli zed by altering the acidity and/or temperature of an aqueous solution, picloram tends to - crystallize primarily as small needle-like fines, i.e., particles less than 105 microns in diameter, which tend to form a mush in the mother liquor. Centrifuging and washing of this mush is time consuming and may result in a significant loss of the final product through the centrifuge screen.
One advantage, therefore, of the method of the present invention is that it reduces the amount of fines and promotes the crystallization of picloram as dense poly- -crystalline spheres which are gxeater than 105 microns in diameter. These spheres can be readily washed free of the mother liquor without an undue loss of the final product.
This invention provides a method for promoting the spherical crystalliæation of picloram, which comprises combining an anionic polyacrylamide flocculating agent, picloram, and an aqueous sulfuric acid medium, wherein the flocculating agent is present in an amount of at least 10 ..g~
parts by weight of the flocculating agent per million parts by weight of the combined weight of the picloram and the aqueous sulfuric acid medium.
In the process of the present invent7on, anionic polymeric acrylamide flocculating agents are utilized to promote the spherical crystallization of picloram, from an aqueous sulfuric acid solution. This process also serves to reduce the formation of fines.
The flocculating agent is generally added to the dilution water which is metered together with a solution of picloram in aqueous sulfuric acid into a stirred ~essel.
However, depending on the ne~ds of the individual practitioner of this invention, the flocculating agent can be present in the vessel before the addition of the picloram is begun, or the flocculating agent can be added to the vessel in incre-ments during the crystallization period. As the addition of the dilution water and of the solution of picloram in sulfuric acid proceeds, crystallization and orientation of the picloram crystals from a limited number of sites occur to form large masses of crystals bonded together in spherical shapes Upon drying, these larger crystal masses remain intact. Apparently, the crystals bond together in a mass radiating from a center which results in the formation of dense polycrystalline balls.
The sulfuric acid solution of picloram, flocculating agent, and dilution water can be combined in any manner that is convenient to the individual practitioner of this invention.
For example, a batch or semi batch process may be used where the flocculating agent is added to the heel from a previous batch before the addition of the picloram solution and dilution water is begun. Alternately, a continuous process may be used where the dilution water containing the floccu-lating agent is metered simultaneously with the picloram 18,299-F
lO~S~50 solution into the stirred vessel and a slurry of the crystallized picloram removed at a rate to maintain a level in the vessel. Other variations which are obvious to those skilled in the art are intended to be within the scope of the present invention.
Flocculating agents which may ~e employed in the improved method of the present invention are water soluble, anionic acrylamide polymers such as, for example, Purifloc~
A22, Purifloc~ A23, and Purifloc~ A25 flocculants, which are well known to the art-skilled persons.
During the polymerization of acrylamide, there is some degree of hydrolysis of the -CONH2 groups to -~OOH. As used herein, the term "anionic" refers to those acrylamide polymers which contain greater than one percent of carboxyl or which will hydrolyze in aqueous sulfuric acid to form greater than one percent of carboxyl.
The optimum amount of anionic polyacrylamide flocculating agent to be employed in combination with the picloram-aqueous sulfuric acid medium solution will be dependent upon such variable factors as the temperature of the solution, the acidity of the aqueous acid medium, the purity of the picloram, and the particular flocculating agent utilized. Generally, an effective crystallization-promoting amount is at least 10 parts by weight of the floccu-lating agent per million (1 000 000) parts (ppm) by weight of the solution and usually an amount from 20 ppm to 40 ppm is suitable. It is understood that the weight of the solution is equivalent to the combined weight of the picloram, the dilution water, and the aqueous sulfuric acid medium. Ordinarily such solutions will contain from
2 to 19 weight percent of picloram and from 30 to 80 weiqht ~5 percent sulfuric acid.
18,299-F
The operable crystallization temperature will vary from 20C to 90C. Generally, however, any temperature at which the picloram will crystallize from an aqueous sulfuric acid medium is suitable for the purposes of this invention. The acceptable amount of crystallization will be determined by the individual practitioner of this invention. At temperatures above 90C, a significant amount of picloram tends to remain in solution. Thus, the individual may choose to maintain the solution temperature at that range in which solubility losses will be minimized.
Generally, the preferred temperature range is from 40~C to 75C.
EXAMPLES
-The following examples are given for the purpose of illustration.
A laboratory crystallizer consisting of a baffled one-liter round bottom flask was charged with 100 ml aqueous 30 weight percent sulfuric acid containing 20 ppm by weight Purifloc~ A23 flocculating agent. The solution was heated to 60C and stirred. A solution containing 105 gm picloram in 395 gm aqueous 75% by weight sulfuric acid at 120C was fed into the crystallizer simultaneously with an aqueous solution containing 36 ppm by weight Purifloc~ A23 at 25C.
The mixture in the crystallizer was stirred at a rate to keep the crystallized picloram suspended throughout the solution.
The feed rates were adjusted to maintain the aqueous phase in the crystallizer at about 30~ to 35~ by weight sulfuric acid. Thus, about 20 ppm by weight Purifloc~ ~23 was main-tained in the crystallizer throughout the crystallization.
The mixture in the crystallizer was kept at 60-70C through-out the crystallization, about one hour. The crystallized product was filtered on a Buchner funnel and washed with 18,299-F
'~
~10~050 about 300 ml distilled water. After drying the picloram solids in a fa~-forced oven at 80~C, a particle size distri-bution was determined using standard mesh screens. Table I
shows the percent of particles in each size range. Even particles hel~w 105 microns in diameter are spherical and not needle-like as in the prior art.
IrA13LE 1 Particle Size Distribution Particle Size _Diameter in Microns) Percent >841 0.15 ~41-5~5 1.1 250-177 6.75 177-1~9 1.1 149-105 0.6 <105 0.3 rrhe experiment was repeated with 30 ppm of Purifloc'~
A23 maintailled in the crystallizer.
Table 2 shows the results of the particle si~e distribution determination.
Particle Size (Diameter in Microns~ ercent ~41 *
595-250 21.1 ~50-177 48.7 177-1~9 18.
149-105 10.4 <105 0.6 35*less than 0.1 percent 1~,29g-~
:
.
.
5al ilhe experiment was repeated with 10 ppm ofPurifloc~ A23 mainlained in the crystallizer.
Table 3 shows the results of the particle size distribution determination.
Particle Size ( amete. in Microns) Percent >~41 0.15 595-250 6.79 250-177 10.24 177-149 9.97 149-lOS 12.95 <105 55.22 The experiment was repeated with no Puri10c~ A23 ~eing used in ~he crystallizer. A mush was formed composed of needle-like cr~stals of picloram <lOS microns in size suspended in the a~ueous sulfuric acid medium with no evidence of dense polycrystalline balls being formed. Drying of the picloram product produced a cake that cou'd not be screened without crushing.
2~
The experiment was repeated except that a second lot of picloram was used to prepare the 105 gm picloram-395 gm 75~ aqueous sulfuric acid feed solution and with 40 ppm of Purifloc~ A23 maintained in the crystallizer.
Table 4 shows the results of the particle size distribution determination.
].8,~99-F
`` ~ s~
Particle Size tDiameter in Microns ~ Percent .
~841 0.~2 841-59S ~.12 595-250 ~8 . 77 Z50-177 32 . 87 177-149 ~~. 05 149~105 ~ 4 . 76 ~.05 5 . ~5 :
- : : :
.
':
:
:, :
~ ~ , : : : : :
.:
~ : 1 8, 2 9 9-F
~ :
18,299-F
The operable crystallization temperature will vary from 20C to 90C. Generally, however, any temperature at which the picloram will crystallize from an aqueous sulfuric acid medium is suitable for the purposes of this invention. The acceptable amount of crystallization will be determined by the individual practitioner of this invention. At temperatures above 90C, a significant amount of picloram tends to remain in solution. Thus, the individual may choose to maintain the solution temperature at that range in which solubility losses will be minimized.
Generally, the preferred temperature range is from 40~C to 75C.
EXAMPLES
-The following examples are given for the purpose of illustration.
A laboratory crystallizer consisting of a baffled one-liter round bottom flask was charged with 100 ml aqueous 30 weight percent sulfuric acid containing 20 ppm by weight Purifloc~ A23 flocculating agent. The solution was heated to 60C and stirred. A solution containing 105 gm picloram in 395 gm aqueous 75% by weight sulfuric acid at 120C was fed into the crystallizer simultaneously with an aqueous solution containing 36 ppm by weight Purifloc~ A23 at 25C.
The mixture in the crystallizer was stirred at a rate to keep the crystallized picloram suspended throughout the solution.
The feed rates were adjusted to maintain the aqueous phase in the crystallizer at about 30~ to 35~ by weight sulfuric acid. Thus, about 20 ppm by weight Purifloc~ ~23 was main-tained in the crystallizer throughout the crystallization.
The mixture in the crystallizer was kept at 60-70C through-out the crystallization, about one hour. The crystallized product was filtered on a Buchner funnel and washed with 18,299-F
'~
~10~050 about 300 ml distilled water. After drying the picloram solids in a fa~-forced oven at 80~C, a particle size distri-bution was determined using standard mesh screens. Table I
shows the percent of particles in each size range. Even particles hel~w 105 microns in diameter are spherical and not needle-like as in the prior art.
IrA13LE 1 Particle Size Distribution Particle Size _Diameter in Microns) Percent >841 0.15 ~41-5~5 1.1 250-177 6.75 177-1~9 1.1 149-105 0.6 <105 0.3 rrhe experiment was repeated with 30 ppm of Purifloc'~
A23 maintailled in the crystallizer.
Table 2 shows the results of the particle si~e distribution determination.
Particle Size (Diameter in Microns~ ercent ~41 *
595-250 21.1 ~50-177 48.7 177-1~9 18.
149-105 10.4 <105 0.6 35*less than 0.1 percent 1~,29g-~
:
.
.
5al ilhe experiment was repeated with 10 ppm ofPurifloc~ A23 mainlained in the crystallizer.
Table 3 shows the results of the particle size distribution determination.
Particle Size ( amete. in Microns) Percent >~41 0.15 595-250 6.79 250-177 10.24 177-149 9.97 149-lOS 12.95 <105 55.22 The experiment was repeated with no Puri10c~ A23 ~eing used in ~he crystallizer. A mush was formed composed of needle-like cr~stals of picloram <lOS microns in size suspended in the a~ueous sulfuric acid medium with no evidence of dense polycrystalline balls being formed. Drying of the picloram product produced a cake that cou'd not be screened without crushing.
2~
The experiment was repeated except that a second lot of picloram was used to prepare the 105 gm picloram-395 gm 75~ aqueous sulfuric acid feed solution and with 40 ppm of Purifloc~ A23 maintained in the crystallizer.
Table 4 shows the results of the particle size distribution determination.
].8,~99-F
`` ~ s~
Particle Size tDiameter in Microns ~ Percent .
~841 0.~2 841-59S ~.12 595-250 ~8 . 77 Z50-177 32 . 87 177-149 ~~. 05 149~105 ~ 4 . 76 ~.05 5 . ~5 :
- : : :
.
':
:
:, :
~ ~ , : : : : :
.:
~ : 1 8, 2 9 9-F
~ :
Claims (4)
1. A method for promoting the spherical crystal-lization of picloram, which comprises combining an anionic polyacrylamide flocculating agent, picloram, and an aqueous sulfuric acid medium, wherein the flocculating agent is present in an amount of at least 10 parts by weight of the flocculating agent per million parts by weight of the com-bined weight of the picloram and the aqueous sulfuric acid medium.
2. The method of Claim 1 wherein the amount of flocculating agent ranges from 20 to 40 parts by weight of the flocculating agent per million parts by weight of the combined weight of the picloram and the aqueous sulfuric acid medium.
3. The method of Claim 1 wherein the aqueous acid medium is 30% to 35% H2SO4 by weight.
4. The method of Claim 1 wherein the crystalli-zation temperature is maintained at from 40°C to 75°C.
18,299-F
18,299-F
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA312,683A CA1095050A (en) | 1978-10-04 | 1978-10-04 | Method of promoting the crystallization of picloram |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA312,683A CA1095050A (en) | 1978-10-04 | 1978-10-04 | Method of promoting the crystallization of picloram |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1095050A true CA1095050A (en) | 1981-02-03 |
Family
ID=4112527
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA312,683A Expired CA1095050A (en) | 1978-10-04 | 1978-10-04 | Method of promoting the crystallization of picloram |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1095050A (en) |
-
1978
- 1978-10-04 CA CA312,683A patent/CA1095050A/en not_active Expired
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