Abstract:
A method of hydrating a dry powdered viscosifier such as a powdered polymer is disclosed. The method includes mixing the powdered viscosifier with a solvent such as water to form a mixture; moving the mixture through a cavitation zone; inducing energetic shock waves and pressure fluctuations in the mixture by mechanically inducing cavitation events within the mixture, the shock waves and pressure fluctuations untangling, separating, and straightening polymer molecule chains and distributing the chains throughout the mixture, and extracting the resulting hydrated viscosifier from the cavitation zone.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    Priority is hereby claimed to the filing date of U.S. provisional patent application 62/152,604 entitled Method of Enhancing Hydration of Viscosifiers Using Controlled Mechanically Induced Cavitation and filed on Apr. 24, 2015, the content of which is incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to hydration of natural and synthetic polymers, gums, and other viscosifiers and more specifically to enhancing or increasing the efficiency and effectiveness of such hydration using controlled mechanically induced cavitation. 
       BACKGROUND 
       [0003]    Viscosity increasing agents are used in many industries from personal care products, to food, to waste treatment, to fossil fuel (oil) drilling muds. Such agents when mixed with a working fluid function to increase or otherwise affect the viscosity or flow characteristics of the fluid so that the fluid is better suited for an intended use. For example, when preparing drilling mud for use in oil drilling operations, a specific viscosity of the mud is desired to maximize the ability of the mud to, for instance, provide a desired hydrostatic pressure; cool and lubricate the drill head assembly; suspend, carry away, and release cuttings; and other functions. 
         [0004]    Dry or powdered viscosifiers, which may be natural or synthetic, commonly are used in many industries to prepare viscosity increasing agents. In most cases, a dried polymer powder is used. A small amount of polymeric powder such as guar, starch, cellulose, carageenan, xanthan, or acrylic is first hydrated before being used to thicken a fluid. Polymer powder consists of small powder particles wherein the individual polymer molecule chains are often tangled, folded, and compacted together. Hydration of the powdered polymer is nothing more than mixing the powdered polymer thoroughly with water to expand, separate, untangle, and solubilize the polymer chains. As the polymer hydrates, its molecules unfold into long chains, which increase fluid viscosity. It is important to hydrate the polymer completely without breaking or damaging the polymer chains with excess shear forces in the mixing process in order to achieve maximum viscosity improvement and product quality at minimum cost. 
         [0005]    Conventional technologies for hydrating polymers to produce viscosifiers generally include mixing powdered polymer with water in a bulk mixer and then allowing the mixture to age in an ager before being added to a fluid to be viscosified. Traditional mixers used for this process often expose the polymer molecules to high shear stresses, which can damage and break apart a significant portion of the polymer molecule chains. To address this problem, traditional polymer hydrators often attempt reduce polymer chain damage using additional process steps such as, for instance, conducting hydration at elevated temperatures, mixing more slowly for long periods of time, adding secondary solvents to the mixture, or simply adding excess polymer to make up for damage and consequent incomplete hydration. Conventional hydration processes also can result in inferior end product quality in the form of a liquid having lumps of un-hydrated powder surrounded by hydrated powder referred to as “fish eyes” in the industry. Such fish eyes are detrimental in many ways, including waste of polymer not contributing to viscosity, cleaning issues, and lack of homogeneity in the final product. 
         [0006]    A need exists for an improved method and apparatus for hydrating or activating powdered polymers in the production of viscosifiers that produce an extraordinarily homogeneous and high quality end product with minimum clumping and minimum polymer chain damage, and all without adding cost or process steps to the method. It is to the provision of such a method and an apparatus for carrying out the method that the present invention is primarily directed. 
       SUMMARY 
       [0007]    Briefly described, an improved method is disclosed for hydrating or activating a viscosity enhancing substance such as a powdered polymer to produce a more effective viscosifier. The method includes subjecting a mixture of polymer powder and water or other solvent to intense cavitation-induced pressure fluctuations in a very low shear controlled cavitation environment. This greatly improves the completeness of hydration and results in minimum damage to the resulting hydrated polymer chains. The cavitation induced pressure fluctuations serve to straighten, untangle, and stretch the polymer chains more fully, resulting in more complete hydration and viscosity development when compared to conventional shear mixing. The very low shear forces results in far less polymer chain breakage and damage than conventional hydration techniques thereby increasing the viscosity enhancing efficiency of the finished viscosifier. Also, the method is carried out without heating or adding secondary solvents and can be carried out at commercial flow rates in a continuous process. The result is a very high quality homogeneous viscosifier produced for low cost in commercially usable volumes. An apparatus for carrying out the method also is disclosed. 
         [0008]    These and other aspects, features, and advantages of the invention disclosed herein will become more apparent upon review of the detailed description set forth below taken in conjunction with the accompanying drawing figures, which are briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic illustration showing one embodiment of an apparatus that can be used for carrying out improved hydration according to the method of the present invention. 
           [0010]      FIG. 2  is a schematic illustration of how polymer chains of a polymer powder are detangled, separated, and relaxed during the hydration methodology of the present invention. 
           [0011]      FIG. 3  is a photomicrograph comparing the homogeneity or quality of a hydrated polymer resulting from a traditional hydration method with the homogeneity of the same hydrated polymer using the improved method of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  illustrates one embodiment of a controlled cavitation reactor suitable for carrying out the method of the present invention. The structure of the reactor is described in detail in U.S. Pat. No. 7,360,755; and that detailed description as well as the entire contents of the &#39;755 patent is hereby incorporated by reference. The reference numerals in  FIG. 1  are referred to in the incorporated &#39;755 patent and need not be referred to again here. With the description of the apparatus of  FIG. 1  from the &#39;755 patent in mind,  FIG. 1  illustrates that water is fed to the controlled cavitation reactor through a port that, in this case, is shown at the bottom of the drawing. While water is the most common substance used in hydration, it will be understood that the present invention is not limited to water but is intended to encompass other hydrating fluids, solvents, and mixtures thereof according to the demands of a particular application. With continued reference to  FIG. 1 , a powdered viscosifier is fed to the water flow through another port, which in  FIG. 1  is shown at the bottom right of the figure. The powdered viscosifier, commonly a powdered or dehydrated polymer, mixes with and becomes entrained in the flow of water and the mixture enters the controlled cavitation reactor. The mixture flows from the sides of the spinning rotor in the reactor shown in  FIG. 1  and through the space between the peripheral surface of the rotor and the cylindrical outer wall of the housing. This space is referred to the cavitation zone or the reaction zone. 
         [0013]    As the rotor spins, highly energetic cavitation events are created in the mixture within the bores of the rotor and are continuously replenished within the bores. In a cavitation event, a low pressure zone forms a cavitation bubble in the mixture within a bore, and the bubble then collapses and releases a highly energetic shockwave. These shock waves propagate from the bores through the mixture as the mixture flows through the cavitation zone of the controlled cavitation reactor. This in turn sets up high energy microscopic and macroscopic pressure fluctuations within the mixture. The shockwaves and pressure fluctuations first separate and disperse individual particles of powder within the mixture allowing solvent (H 2 O molecules) to contact the powder particles on all sides. This maximizes the surface area contact between solvent molecules and polymer chains. As the polymer chains in the particles begin to hydrate with solvent, the pressure fluctuations drive the water molecules into and out of the particles. This, in turn, detangles, releases, separates, and straightens the individual polymer molecule chains found in each particle of the powder. 
         [0014]    Cavitation pressure fluctuations are controlled by controlling the rotation rate of the rotor and other variables so that maximum straightening, separation, and untangling of polymer chains occurs without covalent bond breakage and polymer chain cision. Virtually complete separation and straightening of the polymer chains is achieved with minimum damage to the chains, resulting in maximum viscosity development. In addition, the low shear environment within the cavitation zone compared to conventional hydration mixers greatly reduces polymer chain breakage. This results in a maximum number of longer polymer chains within the resulting viscosifier, which in turn improves the viscosity enhancing properties of the viscosifier with a minimum use of powder.  FIG. 2  illustrates the hydration process schematically. On the left, H 2 O molecules are seen surrounding a particle of polymer powder. As mentioned above, the particle has been separated and segregated from other powder particles by high energy pressure variations in the cavitation zone so that the H 2 O molecules can surround the particle completely. The polymer chains within the particle are bunched together, folded and convoluted, and entangled with each other. As the mixture is exposed to cavitation induced pressure fluctuations, the H 2 O molecules are forced by the fluctuations and shock waves into and out of the bunched up polymer chains within the powder particle. This very efficiently untangles and separates the polymer chains, straightens them, and disburses them through the mixture. This result is illustrated on the right in  FIG. 2 . As mentioned, the untangling, separation, and straightening resulting from the method of the present invention is substantially more effective than prior art hydration techniques. The inherently low shear environment within the cavitation zone minimizes polymer chain breakage. 
         [0015]    Conventional hydration can also result in inferior product quality with lumps of un-hydrated powder surrounded by hydrated powder referred to as “fish eyes” in the industry. These are detrimental in many ways including waste of polymer powder not contributing to viscosity, cleaning issues, and lack of homogeneity in the final product. With the method of the present invention “fish eyes” are obliterated by the highly energetic shock waves and pressure fluctuations within the cavitation zone, allowing for separation, disbursement, and hydration of the powder and chains within the fish eyes. Thus, lost viscosity due to fish eye formation and the general lack of homogeneity resulting from traditional hydration techniques is eliminated. 
         [0016]      FIG. 3  shows two photomicrographs of a hydrated polymer. The image on the left in  FIG. 3  shows a hydrated polymer resulting from a traditional mixing and aging technique commonly used for achieving hydration. It is clear in this image that the resulting viscosifier product lacks homogeneity and contains un-hydrated fish eyes that detract from the effectiveness of the product. Not visible in the left image are the broken and damaged polymer chains that have resulted from the relatively high shear forces to which the mixture is subjected in a traditional hydration mixing process. The image on the right in  FIG. 3  is a photomicrograph of the end product hydrated in a controlled cavitation reactor according to the method of the present invention. The product is seen to be far more homogeneous than the product in the left image with very few if any clumps and fish eyes to detract from the effectiveness of the product. Also not visible in the right image are the straight, separated, and uniformly disbursed polymer chains that exhibit very little damage and breakage due to shear forces. 
         [0017]    In commercial use, the controlled cavitation reactor of this invention can be attached as a side stream of an already existing batch hydration process. Alternatively, it can be part of a continuous hydration process acting upon dry powders mixed with water or another solvent or slurries of polymers and other viscosity inducing agents. One advantage of the present invention is that the requirement of aging after mixing that is an integral part of many traditional hydration techniques is eliminated. With the present invention, the end product emerges directly from the controlled cavitation reactor fully hydrated and ready to use. 
         [0018]    Lab results have shown an increase in hydration yield of 20-30% with the method of the present invention over traditional hydration techniques. Contact time between particles of powder and the energy applied (which is directly proportional to the rotation rate of the rotor) have proven to be critical factors. Fortunately, the cavitation reactor of the present invention can be controlled precisely and easily to establish and maintain virtually any dwell time and energy input for maximizing the hydration process. 
         [0019]    Using the microscopic and macroscopic pressure fluctuations of cavitation according to the method of this invention allows for many benefits in hydration. Some of these benefits include:
       Cost reduction and/or increased viscosity due to higher hydration yield   Elimination or reduction of the need for costly secondary solvents   Reduced temperatures required for complete hydration   Less shear damage due to the low shear environment of the cavitation zone   Improved homogeneity and thus quality of the final product       
 
         [0025]    Many parameters may be varied during the process described above to control the rate of hydration. For example, temperature may be varied as well as rotor speed and concentration of powder within the mixture. It has also been found that gum powder particulate grind size also can be varied and that such variations affect the rate at which viscosifiers are hydrated. 
         [0026]    The invention has been described herein in terms and within the context of preferred embodiments and methodologies considered by the inventor to represent the best modes of carrying out the invention. It will be clear to the skilled artisan, however, that a wide gamut of additions, deletions, and modifications both subtle and gross might be made to the illustrative embodiments presented herein without departing from the spirit and scope of the invention.