Chemistry: fertilizers – Processes and products – Organic material-containing
Reexamination Certificate
1999-07-16
2002-05-28
Langel, Wayne (Department: 1754)
Chemistry: fertilizers
Processes and products
Organic material-containing
C071S064100, C071S903000, C428S402000, C524S401000, C524S423000, C524S428000, C524S555000, C526S310000
Reexamination Certificate
active
06395051
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to methods of producing flowable, small-particle size, high molecular weight, water-soluble polyacrylamide from larger size particles, improved methods for making solutions of the polyacrylamide, and their uses for soil conditioning.
Water-soluble polyacrylamide (PAM) and other water soluble polymers are used as soil conditioners because they help form and protect soil aggregates by binding to clay particles in the soil. Among the benefits, this property helps to control wind and water erosion, improve water infiltration and retention, improve soil aeration, and inhibit crusting or sealing. One use is in forestry, wherein granules of PAM are mixed into soil into which seedlings are planted. Water-soluble PAM is a long-chain molecule, which is distinguished from an insoluble cross-linked form of PAM that is used for different purposes. This disclosure relates to the water-soluble variety of PAM, which will also be referred to herein simply as PAM.
Water-soluble PAM with the most desirable properties for soil conditioning has a molecular weight of about 15-22 million a.u. (atomic units), and is about 20% anionic. Water-soluble PAM of this molecular size is commercially available in granule sizes of about +60, −25 mesh (between 250 and 600 &mgr;m), and, more typically, essentially not smaller than +40 mesh (>450 &mgr;m) sizes. PAM of this type, which comprises an anionic linear copolymer of acrylamide and sodium acrylate, is available under the trade name FLOBOND A30 from Chemtall, Inc. of Riceboro, Ga. The water-goluble granules appear to be aggregates of many molecules and have a very irregular shape, as shown in FIG.
1
A. Under an optical microscope, flat crystal faces are visible, and the particles appear translucent. Some small portions of the granules, e.g. dark areas in
FIG. 1A
, appear transparent. The granules are probably not entirely clear because of included fractures and other defects, which will scatter light.
Severe barriers exist to more widespread use of water-soluble PAM in soil. When dry granules of PAM of standard commercial sizes are applied to agricultural soil at reasonable economic rates, the soil typically is nonuniformly conditioned because the dry granules are too far apart to fully condition soil. For example, when 10 pounds (4.5 kg) of the standard size water-soluble PAM are mixed into an acre of soil to a uniform depth of six inches (15 cm), each pound (0.45 kg) of soil will contain on average only about 22 particles of water-soluble PAM. Each ounce (28.4 grams) of soil would contain only about 1-2 particles.
Applying water-soluble PAM in solution is more effective than dry granule application because it produces a more uniform spatial distribution of the PAM in the soil. Therefore, solution application requires less PAM than does application of granules for favorable results. Another benefit of using a solution of PAM is that it can be applied to soil through standard irrigation systems. However, the commercially available PAM granules have a slow and low solubility in water. These solubility charateristics make it difficult to obtain sufficiently concentrated stock solutions of water-soluble PAM to be economically useful when injected into irrigation lines. Full solution time for standard sized granules can be an hour or more but many dealers and manufacturers say that it is best to allow the water-soluble PAM to sit overnight in water to fully dissolve in a stock solution. This is too long to be practical for most large scale agricultural purposes.
Generally, stock solutions of around 2,000 to 3,000 parts per million (ppm) by weight (mg/liter) water-soluble PAM in water are the most concentrated that can be conveniently made with conventional procedures. When fertilizer salts are included, somewhat higher concentrations, e.g. up to about 12,000 ppm, are possible. The presence of fertilizer solutes will also help PAM go into solution somewhat more rapidly. For example, solution concentration can be improved by disssolving PAM in various fertilizer salt solutions, as described in U.S. Pat. No. 4,797,145, to Wallace, et al. However, the solution rate generally remains slower than desirable because of the large particle sizes. An hour or more is typically required to achieve the higher concentrations even with the use of fertilizer salts.
Co-application of dry PAM with some divalent calcium helps the water-soluble PAM to bridge with or react with clay to add stability to soil aggregates, as described “Need for Solution or Exchangeable Calcium and/or Critical EC Level for Flocculation of Clay by Polyacrylamides,” by Wallace and Wallace, in “Proceedings: Managing Irrigation-Induced Erosion and Infiltration with Polyacrylamide,” Univ. Idaho Misc. Pub No. 101-96, pp. 59-63, 1996. This enhances the soil conditioning value. To achieve this, solution-grade gypsum of −200 mesh particle size (<75 &mgr;m), which is typically composed mostly of calcium sulfate dihydrate, can be applied to soil before addition of water-soluble PAM, or gypsum and water-soluble PAM are applied together in solution after each is dissolved separately. But gypsum also has a low solubility, which limits its use.
Using water-soluble PAM in solution for liquid application to soil entails high handling costs. It generally requires bulk equipment that is not easily portable to fields because large volumes of stock solution are needed for large fields. The PAM granules of the size used commercially take too much time to go into solution. Because low PAM concentrations of stock solution are the rule, large amounts of stock solution are needea for each application. Dissolving standard-sized polymers requires considerable experience. Training is often required to become proficient in getting water-soluble PAM particles into solution. When directions are not followed, failed applications result. If the PAM is not completely dissolved, particles of PAM tend to clump together in agglomerations. These large undissolved clumps make using solutions of PAM in sprinkler irrigation systems very difficult, as the clumps tend to clog the sprinkler lines and nozzles.
One approach to the time and concentration problems has been to use mechanical devices that meter the water-soluble PAM into a stream of irrigation water. A residence time in a tank of one hour or more before applying the solution to fields is realistic and common. For example, U.S. Pat. No. 5,450,985, to Meuleman, discloses a device that delivers dry water-soluble PAM into a canister and from there into an irrigation water stream, such as an irrigation ditch or canal, after a time period. This system does not produce PAM solutions for injection into sprinkler irrigation systems. Pat. No. 5,580,168, to Alireza, et al., discloses a venturi system for injecting water-soluble PAM first into a dispersion tank and then into an aging tank, which is further agitated before injecting the stock solution into an irrigation system. Solution time for both systems is much too slow for convenience. The size of the granules of water-soluble PAM that are used commercially is too large to allow faster solution times.
U.S. Pat. No. 5,548,020, to Santini et al., discloses an alternative procedure for putting water-soluble PAM into irrigation lines. A 30 percent concentrated emulsion product is prepared with kerosene or oil. The flow rate of this product is relatively slow, which decreases its usefulness for sprinkler irrigation systems. Also, this form of PAM flows into water like a semi-stiff string that requires considerable mechanical turbulence by a machine to put into solution. The kerosene or oil adds expense and appears to decrease the effectiveness of the soil conditioning properties of the PAM, and they are environmentally undesirable. The water-soluble PAM in the concentrated 30 percent solution-emulsion is considerably more expensive than granular or powder forms of water-soluble PAM to further detract from any advantage it may have.
Water-soluble polymers also have u
Arnold Charles A.
Wallace Arthur
Langel Wayne
Soil Enhancement Technologies LLC
Wainer Jonathan
LandOfFree
Small particle polyacrylamide for soil conditioning does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Small particle polyacrylamide for soil conditioning, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Small particle polyacrylamide for soil conditioning will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2822014