PHOSPHORIC ACID PRODUCTION GYPSUM FILTRATION FLOCCULANT PREDILUTION
(MAKE DOWN) WITH POST-FILTRATION PHOSPHORIC ACID
FIELD OF THE INVENTION
The present invention is in the technical field of the wet process production of phosphoric
acid and additives therefor, and in particular the present invention is a method to make down
additives using crude phosphoric acid filtrate as the diluent.
BACKGROUND
Phosphoric acid is generally produced by the digestion of phosphate rock with
concentrated sulfuric acid in a slurry of recycled phosphoric acid. This reaction also generates
solid gypsum (CaS0 ) particles, which are typically removed by filtration. In subsequent steps
the phosphoric acid is clarified and concentrated by thermal evaporation to drive off more than
half the water from the crude filtrate.
Flocculants are added to the crude phosphoric acid gypsum slurry to increase particle
size, which improves settling and filtration rate. Traditional flocculants used for this application
are supplied as a liquid concentrate or dry powder. The dissolution kinetics of traditional
powders and the emulsion inversion kinetics of liquid concentrates prevent their direct feed to the
crude slurry. A crude phosphoric acid gypsum slurry reaches the filtering stage in tens of
seconds to a few minutes after the flocculant feed point, while emulsions and powders require
tens of minutes to a few hours for dissolution or inversion. Thus, a concentrate or powder
flocculant is diluted with water at the site to yield a working solution (typically containing 0.5%
to 1% of the concentrate) that is subsequently fed into the process stream. Traditional flocculant
make-down systems consist of a mixing tank to which concentrate or powder is added with
water. After sufficient mixing the dilute flocculant is transferred to a storage tank from which
the dilute solution is fed to the process. Use of traditional dilute flocculant solution accounts for
about 0.5% to 1% of the total volume of water present in the crude phosphoric acid slurry. A
typical phosphoric acid production facility will use 5-10 million gallons of water per year for
flocculant make-down. After addition, this water must be removed by thermal evaporation in
subsequent processing stages requiring use of substantial thermal energy.
Polymer conformation is highly influenced by solution composition. Turro and Arora (J.
Phys. Chem. B, Vol. 09 No. 44, 2005, 20714 - 20718) note that an acrylic acid polymer is
tightly coiled at low H, but raising the pH ionizes the carboxylic acid groups and leads to
stretching or swelling of the polymer. The sensitivity of polymer conformation to the presence of
dissolved ions is well known, as is the tendency of polymers to bind to the surface of suspended
particles. Thus, to ensure that polymers are in a predictable and optimal conformation,
traditional polymeric flocculants are made down with raw water rather than low pH process
water containing relatively high levels of dissolved solids and suspended particles.
U.S. Patent No. 4,263,148, to Symens et al., discloses a process for removing colloidal
and non-colloidal humic matter from an aqueous solution of phosphoric acid. The process
includes the step of treating the phosphoric acid with a flocculant. The disclosure requires that
the flocculant first be made down with water to a concentration of 0.1% to 0.5% prior to its
further dilution with phosphoric acid to about 0.05% and subsequent addition to the phosphoric
acid production process.
In contrast to traditional flocculants, quick inverting flocculant emulsions {e.g., Nalco
Pol-EZ) can be added directly to the crude phosphoric acid slurry without the need for dilution.
These products offer the advantage of eliminating traditional flocculant dilution water as well as
the complicated expensive feed systems that are also associated with traditional flocculants. In
some cases, for example, when the required feed point is too near the slurry discharge to the
filter, the time is insufficient to allow these emulsions to undergo rapid inversion and adoption of
an optimal polymer conformation within the process. As a result, the emulsion may not
completely invert or the polymer may be trapped in a poor performing conformation when it
binds to the gypsum surface. This results in less than optimal flocculant performance.
Accordingly, there is a need for optimizing the addition of flocculant to the phosphoric
acid production process. Desirably, the addition of flocculant will minimize the introduction of
water into the phosphoric acid production process. More desirably, the flocculant will be added
to the phosphoric acid production process by mixing the flocculant with clarified phosphoric acid
that is recycled from the phosphoric acid production process.
SUMMARY OF THE INVENTION
The present invention is directed toward a method of adding an effective amount of a
flocculant to a phosphoric acid production process. The method comprises the steps of providing
phosphoric acid; injecting the effective amount of flocculant directly into the phosphoric acid;
mixing the effective amount of flocculant and the phosphoric acid, which creates a flocculantacid
substance; and introducing the flocculant-acid substance into the phosphoric acid production
process.
The present invention is alternately directed toward a method of improving solids
separation performance in a phosphoric acid production process. The method comprises the
steps of providing phosphoric acid; introducing an effective amount of flocculant directly into the
phosphoric acid; mixing the effective amount of flocculant and the phosphoric acid, which
creates a flocculant-acid substance; and adding the flocculant-acid substance to the phosphoric
acid production process.
The present invention minimizes the introduction of additional water to the phosphoric
acid production process by substituting phosphoric acid when making down the flocculant.
These and other features and advantages of the present invention will be apparent from the
following detailed description, in conjunction with the appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VrEWS OF THE DRAWINGS
The benefits and advantages of the present invention will become more readily apparent
to those of ordinary skill in the relevant art after reviewing the following detailed description and
accompanying drawings, wherein:
FIG. 1 is a graph that illustrates experimental results for experiments employing
Compound A as the flocculant;
FIG. 2 is a graph that illustrates experimental results for experiments employing
Compound B as the flocculant;
FIG. 3 is a graph that illustrates experimental results for experiments employing
Compound C and Compound D as flocculants; and
FIG. 4 is a graph that illustrates experimental results for experiments employing
Compound E at two concentrations as the flocculant.
DETAILED DESCRIPTION OF THE INVENTION/PREFERRED EMBODIMENT
Definitions:
For purposes of this patent application, the following terms have the definitions set forth
below:
"Clarification operation" is any unit operation(s) of a chemical process that decreases the
level of cloudiness of a liquid.
"Clarified crude phosphoric acid" is any filtered phosphoric acid ( i.e., not digestion
slurry) that is not of a quality that is typical of a final product, but that has been treated by a
clarification operation.
"Clarified phosphoric acid" is any phosphoric acid that has been treated by a clarification
operation, which may include phosphoric acid of a quality that is typical of a final product.
"Crude phosphoric acid" is any filtered phosphoric acid (i.e., not digestion slurry) that is
not of a quality that is typical of a final product.
"Digestion slurry" is the product (intermediate or otherwise) of digesting phosphate rock
with sulfuric acid. A typical digestion slurry contains solids in a strong acidic solution.
"Directly" is used to describe the addition of a first substance to a second substance
without diluting the first substance with water. Flocculants are typically diluted (made down)
with raw water prior to their addition to a phosphoric acid digestion slurry. The term "directly"
is used to describe such an addition without dilution with raw water.
"Effective amount" means any dosage of any additive that aids desired performance when
compared to an untreated control sample.
"Final product" describes a substance or item of a quality such that the substance or item
is shipped from a production facility. A final product as related to phosphoric acid is one that has
been processed to concentration and clarity specifications that are commonly produced by a
phosphoric acid production process and may be shipped to another location for further
concentration.
"Flocculant" is a chemical substance that aids filtration or clarification of a liquid by
binding to the surface of several small particles to create a larger particle.
"Flocculant-acid substance" is a substance that comprises phosphoric acid and a
flocculant.
"Inline blending" is a method of mixing a plurality of substances without using a separate
vessel.
"Make down" is the term commonly used to describe the dilution of a flocculant in order
to prepare a rapidly active flocculant working solution prior to its addition to a substance.
"Mixing vessel" is anything that is capable of retaining and blending a substance or
substances. A mixing vessel may be a tank equipped with an agitator, a tank with a recirculation
circuit, or anything else capable of retaining and blending a substance or substances.
"Phosphoric acid production process" is a circuit or series of circuits used for the
production of phosphoric acid. A phosphoric acid production process may produce crude
phosphoric acid, phosphoric acid of a quality that is typical of a final product, or any other grade
or quality of phosphoric acid. A typical phosphoric acid production process includes several
interconnected circuits that produce or concentrate phosphoric acid.
"Solids separation operation" is any process of separating solid matter from a fluid.
"Water" and "raw water" are used interchangeably to describe water that contains
substantially no phosphoric acid.
While the present invention is susceptible of embodiment in various forms, there is
hereinafter described a presently preferred embodiment with the understanding that the present
disclosure is to be considered an exemplification of the invention and is not intended to limit the
invention to the specific embodiment illustrated.
It should be further understood that the title of this section of this specification, namely,
"Detailed Description of the Invention," relates to a requirement of the United States Patent
Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein.
The invention relates to the use of crude phosphoric acid, either clarified or unclarified, as
a dilution liquid for gypsum flocculants. Flocculants of the invention can be traditional
concentrated emulsions or dry polymer products, or they can be quick inverting polymer
emulsions. In the case of traditional flocculants, the materials are made down using crude
phosphoric acid filtrate as the diluent in place of raw water. In the case of quick inverting
polymer emulsions, inline blending of the flocculant with crude phosphoric acid can be used to
provide the necessary time for the emulsions to invert and for the polymer to adopt an optimal
conformation before introduction to the gypsum slurry. Tn either case, make-down of flocculants
in crude phosphoric acid eliminates the addition of raw water to the phosphoric acid production
circuit and allows the manufacturer to produce a higher quantity of final product using the same
water and energy resources.
The present invention is directed toward a method of improving filtration and clarification
performance in a phosphoric acid production process. The method comprises the steps of
providing phosphoric acid; introducing an effective amount of flocculant directly into the
phosphoric acid; mixing the effective amount of flocculant and the phosphoric acid, which
creates a flocculant-acid substance; and adding the flocculant-acid substance to the phosphoric
acid production process.
The present invention is also directed toward a method of adding an effective amount of a
flocculant to a phosphoric acid production process. The method comprises the steps of removing
crude phosphoric acid from the phosphoric acid production process; injecting the effective
amount of flocculant directly into the crude phosphoric acid; mixing the effective amount of
flocculant and the crude phosphoric acid, which creates a flocculant-acid substance; and
introducing the flocculant-acid substance into the phosphoric acid production process.
For purposes of this patent application, the following table illustrates the various
compounds that are discussed.
In an effort to minimize the addition of water to the phosphoric acid production process, it
has been discovered that crude phosphoric acid can be used as dilution liquid to make down
concentrated or dry flocculant polymer products. Such use of crude phosphoric acid requires
using pumps, mixers, transfer lines and storage containers compatible with phosphoric acid.
Clarified or unclarified crude phosphoric acid filtrate can be used as a dilution fluid.
In an effort to allow time for a flocculant to completely invert, to achieve an optimal
conformation prior to application, and to eliminate the addition of undesirable dilution water to
the process, it has been discovered that crude phosphoric acid filtrate can be used as a quick
inverting flocculant ("QIP" for "quick inverting polymer") diluent. Crude phosphoric acid
diluent can be used to provide time for quick inverting polymer activation prior to introduction
into the process. Inline blending of a QIP solution into a crude phosphoric acid filtrate stream
offers a simple and inexpensive flocculant feed system. With such dilution, soon after the
flocculant feed system begins operation, a steady state will be achieved wherein the phosphoric
acid content of the crude gypsum slurry filter feed liquid is essentially equivalent to the
phosphoric acid content of the crude acid slurry prior to flocculant addition. Virtually no dilution
of the crude phosphoric acid will occur with flocculant addition. By comparison, a traditional
flocculant feed system accounts for approximately 0.5% to 1.4% of the total volume of the crude
phosphoric acid gypsum slurry. Clarified or unclarified crude phosphoric acid filtrate can be
used as a dilution fluid.
Using slurry filtration tests, it has been discovered that the performance of some
flocculants suffer when crude phosphoric acid diluent is used, while other flocculants exhibit the
same or nearly the same performance when diluted with crude phosphoric acid. In a slurry
filtration test, a desired amount of a pre-diluted (1% by weight) flocculant solution is added with
stirring to 250 mL of freshly collected phosphoric acid digestion slurry containing gypsum solids.
The mixture is then stirred for 30 seconds and delivered to a Millipore vacuum (18 psi) filtration
apparatus. A timer is started when the slurry enters the filter unit and the time required for the
liquid portion of the slurry to pass through the filter wherein the liquid just passes from the edge
of the filter cake is recorded as the filtration time. As shown in Figure 1, quick inverting
flocculant formulation Compound A displays a poorer filtration performance profile when prediluted
in clarified crude phosphoric acid filtrate. However, as illustrated in Figure 2, Compound
B yields approximately the same performance when pre-diluted with clarified crude phosphoric
acid filtrate. These results may be due to the crude acid filtrate altering the Compound A
polymer conformation in solution relative to raw water, slow Compound A conformation kinetics
preventing the formation of the optimal conformation prior to testing and/or the additional
polymer demand resulting from the presence of residual gypsum particles present in the clarified
crude acid solutions.
Pre-dilution of Compound B with unclarified crude phosphoric acid filtrate reduces
filtration performance relative to clarified crude acid, also shown in Figure 2. This is likely due
to presence of residual gypsum particles that are expected to provide polymer binding sites and
effectively reduce the concentration of available flocculant. As shown by the trend in filtration
time as dosage is increased, adjusting polymer dose compensates for this additional polymer
demand and can allow unclarified crude phosphoric acid filtrate to act as an acceptable flocculant
dilution liquid.
Phosphoric acid settling tests reveal that Compound C performs well when made down in
unclarified 28% phosphoric acid. In a phosphoric acid settling test a freshly collected sample of
44% crude phosphoric acid is dosed with a desired amount of pre-diluted (1% by weight)
flocculant in a 1000 mL graduated cylinder. The cylinder is immediately inverted 4 times and a
timer started. The rate at which the flocculated gypsum particulates settle is recorded over a
period of several minutes. As shown in Figure 3, Compound C yields approximately the same
gypsum settling rate when pre-diluted with 28% unclarified acid as when pre-diluted with water.
Compound D, in contrast, displays much slower settling when made down in 28% unclarified
phosphoric acid.
Quick inverting flocculant formulation Compound E displays no decrease in digestion
slurry filtration performance when pre-diluted with unclarified 28% phosphoric acid, as shown in
Figure 4. As seen in the figure, at 50 ppm and at 00 ppm Compound E yields filtration times
that are no slower than when pre-diluted with water.
Due to the higher polymer demand of unclarified phosphoric acid filtrate, clarified crude
acid obtained from a later stage of the phosphoric acid production process is a generally more
desirable diluent source due to its lower level of suspended solids and corresponding lower
polymer demand.
In an embodiment, the present invention may employ crude phosphoric acid, clarified or
unclarified.
In an embodiment, the phosphoric acid may be recycled from a single production circuit
in a phosphoric acid production process, another circuit within the phosphoric acid production
process, an entirely separate phosphoric acid production process, or by other means known to one
skilled in the art.
In an embodiment, the flocculant-acid substance may be created and/or mixed via inline
blending, mixing in a vessel, or by other means known to one skilled in the art.
In an embodiment, the flocculant-acid substance may be added to the phosphoric acid
production process prior to a solids separation operation.
In an embodiment, the flocculant may be an anionic, cationic, amphoteric, or non-ionic
polymer.
In an embodiment, the flocculant in this invention may be comprised of a substance
selected from the group a vinyl containing functional monomer, a styrene containing functional
monomer, an ethylene oxide containing functional monomer, and combinations thereof.
n an embodiment, the flocculant in this invention may be selected from the group
copolymers, homopolymers and terpolymers comprising from 0.01 to 100 mole percent of a
vinyl-containing functional monomer.
In an embodiment, the flocculant in this invention may be selected from the group
copolymers, homopolymers and terpolymers comprising: APTAC (acrylamide propyl trimethyl
ammonium chloride), MAPTAC (methacrylamide propyl trimethyl ammonium chloride),
DMAEA-MCQ (dimethylaminoethylacrylate methyl chloride quaternary salt), DMAEA-BCQ
(dimethylarninoethylacrylate benzyl chloride quaternary salt), DMAEM-MCQ
(dimethylaminoethylmethacrylate methyl chloride quaternary salt), DADMAC
(diallyldimethylammonium chloride), vinylamine, vinylformamide, ethylenedichloride, and
combinations thereof.
In an embodiment, the flocculant may be comprised of a substance selected from the
group homopolymers, copolymers, terpolymers comprising: acrylamide, acrylic acid, partially
hydrolyzed acrylic acid, partially hydrolyzed acrylamide, 2-acrylamido-2-
methylpropanesulfonate, 2-acrylamidoethanesulfonate, styrenesulfonate, ethylene oxide, vinyl
alcohol, a ky hydroxamate, methacrylate, itaconic acid, fumaric acid , crotonic acid, maleic acid,
itaconic acid esters, fumaric acid esters, maleic acid esters, alpha-haloacrylic acid, vinylacetic
acid, allylacetic acid, beta-carboxyethylacrylate, sulfoalkyl acrylate, sulfoalkyl methacrylate,
allylsulfonic acid, methallylsulfonic acid, N-sulfohydrocarbon-substituted acrylamide (e.g.
sulfomethylated acrylamide), and combinations thereof. The flocculant may take the form of one
or more anionic polymers, as the salt of one or more anionic polymers, as one or more neutral
polymers or as one or more cationic polymers, The counterions of the salt of the anionic
polymers and the cationic polymers can have a wide range of composition as known to those
skilled in the art.
All patents referred to herein, are hereby incorporated herein by reference, whether or not
specifically done so within the text of this disclosure.
In the present disclosure, the words "a" or "an" are to be taken to include both the
singular and the plural. Conversely, any reference to plural items shall, where appropriate,
include the singular.
From the foregoing it will be observed that numerous modifications and variations can be
effectuated without departing from the true spirit and scope of the novel concepts of the present
invention. It is to be understood that no limitation with respect to the illustrated specific
embodiments or examples is intended or should be inferred. The disclosure is intended to cover
by the appended claims all such modifications as fall within the scope of the claims.
CLAIMS
We claim:
. A method of adding an effective amount of flocculant to a phosphoric acid production
process, the method comprising the following steps:
providing phosphoric acid;
injecting the effective amount of flocculant directly into the phosphoric acid;
mixing the effective amount of flocculant and the phosphoric acid to create a
flocculant-acid substance;
introducing the flocculant-acid substance into the phosphoric acid production process.
2. The method of claim 1, wherein the phosphoric acid is crude phosphoric acid, the crude
phosphoric acid removed from the phosphoric acid production process.
3. The method of claim 1, wherein the introducing step takes place prior to at least one
solids separation operation.
4. The method of claim 1, wherein the crude phosphoric acid is removed after at least one
clarification operation of the phosphoric acid production process.
5. The method of claim 1, wherein the the mixing step is achieved via inline blending.
6. The method of claim 1, wherein the mixing step is achieved via a mixing vessel.
7. The method of claim 1, wherein the flocculant is comprised of a substance selected from
the group homopolymers, copolymers, terpolymers comprising: a vinyl containing
functional monomer, a styrene containing functional monomer, an ethylene oxide
containing functional monomer, and combinations thereof.
8. A method of improving solids separation performance in a phosphoric acid production
process, the method comprising the following steps:
providing phosphoric acid;
introducing an effective amount of flocculant directly into the phosphoric acid,
mixing the effective amount of flocculant and the phosphoric acid, the mixing
forming a flocculant-acid substance; and
adding the flocculant-acid substance to the phosphoric acid production process.
9. The method of claim 8, wherein the phosphoric acid is a crude phosphoric acid.
10. The method of claim 9, wherein the crude phosphoric acid is clarified crude phosphoric
acid.
11. The method of claim 10, wherein the clarified crude phosphoric acid is recycled from the
phosphoric acid production process.
12. The method of claim 8, wherein the mixing step is achieved via a mixing vessel.
13. The method of claim 8, wherein the mixing step is achieved via inline blending.
1 . The method of claim 8, wherein the adding step is performed prior to at least one solids
separation operation of the phosphoric acid production process.
5. A method of improving solids separation performance and minimizing the introduction of
additional fresh water in a phosphoric acid production process, the method comprising the
following steps:
providing phosphoric acid;
introducing an effective amount of flocculant directly into the phosphoric acid;
mixing the effective amount of flocculant and the phosphoric acid, the mixing
forming a flocculant-acid substance; and
adding the flocculant-acid substance to the phosphoric acid production process;
wherein
the phosphoric acid is a clarified crude phosphoric acid, the clarified crude phosphoric
acid recycled from the phosphoric acid production process;
the flocculant is comprised of a substance selected from the group homopolymers,
copolymers, terpolymers comprising: a vinyl containing functional monomer, a
styrene containing functional monomer, an ethylene oxide containing functional
monomer, and combinations thereof;
the mixing step is achieved via inline blending; and
the adding step is performed prior to at least one solids separation operation of the
phosphoric acid production process.