Method for cooling microwave plasma and system for the selective destruction of chemical molecules using said method

Abstract

The invention relates to a method for cooling a plasma processing system for processing a mixture of particularly gaseous fluids, which comprises a means for coupling a source of microwave power to a mixture of particularly gaseous fluids flowing in a dielectric tube at the level of the coupling means adapted for transferring a portion of the microwave energy to the fluid mixture in order to generate therein a plasma for initiating the breaking of at least some chemical bonds of the fluid molecules, wherein said dielectric tube is at least partially cooled down by a coolant flow in thermal contact with the outer wall of the tube to be cooled. According to the invention, on the one hand, the coolant flow in thermal contact with the dielectric tube flows in a direction opposite to that of the fluid or fluid mixture in the dielectric tube and, on the other hand, the coolant includes at least one oil selected from linear alpha-polyolefins having a carbonated chain of at least ten carbon atoms and/or perfluorocarbonated liquids having a dielectric constant ∈ lower than 2.5, a microwave absorbance tan δ of between 10 −2 and 10 −4 , and a specific heat Cp<0.6 g. cal/g. ° C.

1 - 6 . (canceled) 
     
     
         7 . A method for cooling a plasma treatment system (A) for treating an especially gaseous fluid or fluid mixture, the system comprising means ( 7 ,  8 ) for coupling a microwave power source ( 1 ) to the fluid or fluid mixture flowing in a dielectric tube ( 16 ) past the coupling means that transfer a part of the microwave energy to the fluid or fluid mixture in order to create therein a plasma that causes at least some chemical bonds of molecules in the fluid or fluid mixture to break, the method comprising:
 At least partially cooling said dielectric tube ( 16 ) by thermally contacting a coolant with an external wall of the dielectric tube ( 16 ) by flowing said coolant cocurrently to the fluid or fluid mixture in the dielectric tube ( 16 ), the coolant comprising at least one oil selected from the group consisting of linear alpha-olefins having a carbon chain of at least ten carbon atoms, perfluorocarbon liquids having a dielectric constant ∈ lower than 2.5, a loss tangent tan δ of between 10 −2  and 10 −4  and a specific heat Cp<0.6 g.cal/g.° C., and mixtures thereof.   
     
     
         8 . The method of  claim 7 , wherein the oil is selected from the group consisting of a C 14  linear alpha-olefin, 1-tetradecene, and a perfluorocarbon (PFC) fluid having a dielectric constant ∈<2 and/or a loss tangent tan δ<10 −3  and/or a specific heat Cp≦0.3 g.cal/g.° C. 
     
     
         9 . The method of  claim 7 , characterized in that the fluid or fluid mixture to be treated in the tube is injected at atmospheric pressure or at a pressure near atmospheric pressure. 
     
     
         10 . The method of  claim 7 , further comprising injecting the fluid or fluid mixture and/or a complimentary inert gas into the dielectric tube ( 16 ) in a form of a vortex. 
     
     
         11 . The method of  claim 7 , characterized in that the fluid or fluid mixture and the coolant flow from top to bottom. 
     
     
         12 . A plasma treatment system (A) comprising:
 a) means ( 19 ) for injecting a fluid and/or a gas;   b) a dielectric tube ( 16 ) that receives the fluid and/or the gas;   c) a microwave generator ( 1 );   d) means ( 7 ,  8 ) for coupling microwaves to the fluid and/or the gas so as to create a plasma in the dielectric tube ( 16 );   e) means for cooling the dielectric tube using a coolant ( 19 ), said means being placed outside the dielectric tube ( 18 );   f) a source of linear alpha-olefin and/or of perfluorocarbon fluid connected to the means for cooling the dielectric tube ( 16 ); and   g) means for making the coolant flow cocurrently to the fluid and/or gas.