Abstract:
Systems and methods for plasma sterilization are described. The sterilization method includes placing a substance to be sterilized into a rotating chamber and irradiating the substance with plasma. An RF generator is used to produce the plasma from a gas. The gas has a concentration of at least 85% N 2  and less than 15% O 2 . The plasma includes a NOx species that is effective in killing microbial organisms in the substance.

Description:
[0001]    This application claims priority to U.S. provisional patent application No. 61/718,493 filed on Oct. 25, 2012, U.S. provisional patent application No. 61/569,485 filed on Dec. 12, 2011, and U.S. provisional patent application No. 61/569,449 filed on Dec. 12, 2011. This and all other referenced extrinsic materials are incorporated herein by reference in their entirety. Where a definition or use of a term in a reference that is incorporated by reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein is deemed to be controlling. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention is plasma sterilization. 
       BACKGROUND 
       [0003]    The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art. 
         [0004]    While numerous sterilization processes and devices are known, most are not well suited for sterilizing food powder and other food-based materials. This is due, in part, to the fact that food material is sensitive and easily damaged (e.g., its composition can be easily changed). 
         [0005]    U.S. Pat. No. 4,133,638 to Healey discloses sterilization of powders, such as talc, by fluidizing a bed of the powder with a sterilizing stream of gas. A commonly used sterilizing agent is ethylene oxide, but because of its inflammatory and explosive nature it is often mixed with a compound, usually a fluorinated hydrocarbon, to render it is less dangerous. A major problem, however, is that purchasing and transporting sterilization gases can be expensive. 
         [0006]    U.S. patent application Ser. No. 10/585,088 to Arnold et al. (published as US2008/0317626) describes systems and methods that generate NO or a mixture of NO and NO 2  as sterilization gases in situ, using a carbon-based diazeniumdiolate compound and a powdered acid. That process, however, is inconvenient and expensive. 
         [0007]    Given the state of the art, there is still a need for improved gases for sterilization processes. 
       SUMMARY OF THE INVENTION 
       [0008]    The inventive subject matter provides apparatus, systems and methods in which a sterilization apparatus employs reactive nitrogen species (RNS) to sterilize a substance (e.g., food powder, food-based materials, pharmaceutical compounds, etc.). The RND is produced in situ using a radio frequency (RF) generator. The RF generator converts a gas into plasma having the RNS, which is then mixed with a substance to be sterilized. In some embodiments, the mixing occurs in a rotating chamber (e.g., drum). 
         [0009]    In a preferred embodiment the RNS comprises one or more NO x  species, especially mono-nitrogen oxides NO and NO2 (nitric oxide and nitrogen dioxide), where the Nitrogen and Oxygen are derived from ambient air. 
         [0010]    From a methods perspective the inventive subject matter includes the steps of placing the substance in a rotating chamber, using an RF generator to produce a plasma, and subjecting the substance to the plasma (e.g., allowing the plasma to mix with the substance inside the rotating chamber). In a preferred embodiment the plasma includes an RNS such as a NO x  species. 
         [0011]    Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a drawing of one embodiment of a sterilization system. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed. 
         [0014]      FIG. 1  shows a sterilization system  100 . System  100  comprises a reactor  101  and an RF generator  102 . Reactor  101  is a drum that has an internal chamber with a substance  103  disposed inside. Substance  103  can comprise any substance that a user desires to sterilize via a plasma sterilization process. In some embodiments substance  103  is a food-based material such as a food powder. 
         [0015]    Reactor  101  has a porous wall  104  through which gas  160  passes to enter the internal chamber of reactor  101 . Once inside the chamber, gas  160  is converted into plasma  106  by RF generator  102  and coils  150 . As reactor  101  rotates in direction  110 , plasma  106  and substance  103  mix. Reactive groups in plasma  106  are effective in killing microbial organisms in substance  103 . 
         [0016]    Plasma production and plasma sterilization processes are discussed in further detail in U.S. Pat. No. 4,756,882 and co-pending application Ser. No. 13/711,867 (filed on Dec. 12, 2012), which are incorporated herein by reference. 
         [0017]    In some embodiments, plasma  106  includes a NO x  species at a concentration of at least 5%-10%, inclusive. 
         [0018]    Gas  160  can comprise any gas suitable for plasma sterilization. In some embodiments, gas  60  can comprise air. In especially preferred embodiments, the gas  160  contains 85%-90% N 2  and between 10%-15% O 2 , or between 87%-93% N 2 , and between 13%-7% O 2 . Since dry air contains roughly (by volume) 78% nitrogen, 21% oxygen, additional nitrogen can be provided to air from an external source such as a bottle containing compressed nitrogen. 
         [0019]    Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary. Still further, unless the context dictates the contrary, all concentration percentages are to be interpreted as wt %. 
         [0020]    In some embodiments, RF generator  102  is operated at powers from 100 Watts to 5 kW, using a basic frequency of 13.56 MHz, while gas  160  comprising 90% N 2  and 10% O 2  is supplied to reactor  101  at a total gas flow from 250 cc/m to 2000 cc/m, with reactor  101  having a chamber pressure in the range of 100 mTorr to 5 Torr. 
         [0021]    As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously. 
         [0022]    As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
         [0023]    The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention. 
         [0024]    Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. 
         [0025]    It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.