DUAL INJECTION OF TWO POLYMERIC FILTRATION AIDS FOR GYPSUM REMOVAL FROM PHOSPHORIC ACID/GYPSUM SLURRY

BACKGROUND OF THE INVENTION

1. Field of the invention.

The present invention relates, generally, to filtration aids. A process has been developed to improve polymeric filtration aid performance in the removal of gypsum from phosphoric acid/gypsum slurry.

2. Description of the related art.

During the process of producing phosphoric acid (for fertilizer), gypsum is formed as a by-product in the 25-45% phosphoric acid solution. This gypsum is filtered out with various types of vacuum filters. Polymeric filtration aids have been used to enhance filtration time for faster production and higher recovery of the phosphoric acid.

The polymeric filtration aids are high molecular weight polymers, of various chemistries and molecular weights specific for various phosphate ores. The chemical class of the polymers that have been used is classified as non-ionic, anionic or cationic in nature.

The normal application of the polymers is by making a 0.5-3% polymer solution and injecting this into the gypsum/phosphoric acid slurry prior to filtration (by vacuum filter). The amount of polymer filtration aid for maximum performance varies with each production facility and ranges from 5-150 ppm (via volume of slurry). The amount of performance improvement by the filtration aid varies typically from 5-70%.

SUMMARY OF THE INVENTION

The present invention is both a chemical and physical process to improve the polymeric filtration aid performance used in removal of gypsum from phosphoric acid/gypsum slurry. A synergistic effect has been observed by using a dual injection method (physical process); specifically when using two polymers of different chemistry (chemical process) and injecting into the slurry at a different time, the polymer usage is reduced by around 50% and performance improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. IA is a chart depicting an example of a single versus dual injection polymer performance;

Fig. IB is a chart depicting an example of the actual filtration rate in seconds using a filtration aid as in Fig. IA;

Fig. 2 is a chart, which shows the percent of filtration rate improvement with filtration aid where the test data indicates the standard type polymeric filtration aid N-3 as a dual injection is inferior to the two-polymer system with dual injection and the two polymers, S4220 + N-3, performs best when injected separately versus at same time or as a preblended solution;

Fig. 3 is a chart, which shows the percent of filtration rate improvement with filtration aid where the test data indicates the mix time of the two polymers for the dual injection is important for maximum performance;

Fig.4 is a chart, which shows the percent of filtration rate improvement with filtration aid where the test data indicates that a variety of sulfonated polymers (plus N-3 Non-ionic) perform well for the dual injection, with most showing low dosage and better performance than single Polymer N-3; and

Fig. 5 is a chart, which shows the percent of filtration rate improvement with filtration aid where the test data indicates that a variety of non-ionic polymers (plus Sulfonated S4227) perform well for the dual injection, showing polymer type not as important as dual injection. DETAILED DESCRIPTION OF THE INVENTION

Various anionic, non-ionic, cationic and sulfonated polymers have been used as filtration aids for gypsum from phosphoric acid. Each ore and its phosphoric acid slurry are specific to which polymer performs best and determines what polymer dosage is required. When western (Idaho and Wyoming) phosphate ore are used for the phosphoric acid/gypsum slurry, the polymeric filtration aid can improve performance by up to 70%; however the filtration aid usage can be as high as 150 ppm (via volume of slurry).

A synergistic effect has been observed by using a dual injection method. More specifically, when using two polymers of different chemistry (A & B) and injecting into the slurry at a different time, the Polymer usage is reduced by around 50% and performance improved.

The polymer chemistry of filtration aid "A" could be non-ionic, anionic, or cationic depending on the phosphate ore used to make the phosphoric acid. The polymer chemistry of filtration aid "B" should be a sulfonated polymer. The best results observed for western ore have been non-ionic "A" + sulfonated "B" filtration aid. Results could vary depending on the ore type.

Furthermore, to achieve the lowest usage, a combination of sulfonated + non-ionic polymer in a specific ratio is required. The type of sulfonated polymer or type of non-ionic polymer is not as critical as the A & B proportions, or more importantly the dual injection.

lhis process works best via a separate polymer injection with a minimum of 5 seconds between the two polymers, whereas simultaneous injection or premising of polymer solutions (A & B) is not as effective. It is preferred that the intervals between the injections be about 5 to 15 seconds. Best results have been achieved when using the sulfonated "B" polymer first. EXAMPLES

The following examples serve to provide further appreciation of the invention and are not meant in any way to restrict the effective scope of the invention. Example #1 - Single versus Dual Injection polymer performance

Fig. IA shows a chart of the percent of filtration rate improvement with filtration aid. This test data indicates the standard type polymeric filtration aid N-3, single injection and single polymer, requires a 100-ppm dosage for maximum performance. However, a dual injection with two polymers, S4220 + N-3 requires only 25 PPM each (or 50 PPM total) to obtain the maximum performance. The performance for the slurry filtration section is also better for increased production rate.

Polymer S4220 is a high molecular weight Sulfonated polymer, produced from the two monomers ATBS (Acrylamide Tertialy-Butyl Sulfonic acid) and Acrylic Acid. Polymer N-3 is a low molecular weight Non-ionic Polymer, produced from the monomer Acrylamide.

Fig. IB is a chart that shows an example of the actual filtration rate in seconds using a filtration aid. This test data indicates the standard type polymeric filtration aid N-3, single injection and single polymer, requires 100 ppm dosage for a minimum filtration time of 70 seconds. However, a dual injection with two polymers, S4220 + N-3 requires only 25 ppm each (or 50 ppm total) to obtain a lower minimum filtration time of 68 seconds. Example #2 - Dual Injection Method — Single versus Two Polymers:

Fig. 2 shows the percent of filtration rate improvement with filtration aid where the test data indicates the standard type polymeric filtration aid N-3 as a dual injection is inferior to the two-polymer system with dual injection. The two Polymers, S4220 + N-3, perform best when injected separately versus at same time or as a preblended solution. The dual injection/dual polymer system continues to show 50% lower dosage. Example #3 - Dual Injection Method - Mix Time:

Fig. 3 shows the percent of filtration rate improvement with filtration aid where the test data indicates the mix time of the two polymers for the dual injection is important for maximum performance. Example #4 - Dual Injection Method - Various Sulfonated Polymers:

Fig. 4 shows the percent of filtration rate improvement with filtration aid where the test data indicates that a variety of sulfonated polymers (plus N-3 Non-ionic) perform well for the dual injection, with most showing low dosage and better performance than single Polymer N-3. Example #5 - Dual Injection Method - Various Sulfonated Polymers:

Fig. 5 shows the percent of filtration rate improvement with filtration aid where the test data indicates that a variety of non-ionic polymers (plus Sulfonated S4227) perform well for the dual injection, showing polymer type not as important as dual injection. Polymer S4227 is a low molecular weight Sulfonated polymer, produced from the two monomers ATBS (Acrylamide Tertialy-Butyl Sulfonic acid) and Acrylamide.

For additional explanation of the polymers noted on the drawings, polymer S4220, S4221, S4223 are sulfonated co-polymers, produced from the two monomers; ATBS (Acrylamide Tertialy-Butyl Sulfonic acid) and Acrylic Acid of various ratios and polymerized in various molecular weights.

Polymers S4227, S4226, S4229, Sl 18, S125L are sulfonated co-polymers, produced from the two monomers; ATBS (Acrylamide Tertialy-Butyl Sulfonic Acid) and Acrylamide of various ratios and polymerized in various molecular weights.

Polymers N-3, N920M, and N920S are non-ionic polymers, produced from the monomer acrylamide and polymerized in various molecular weights.

Polymers N-903, N903M are non-ionic/anionic co-polymers, produced from the monomers acrylamide and acrylic acid of various ratios and polymerized in various molecular weights.