In general, chemical processes are affected when appropriate local environmental conditions are modified. For example, the rate of the reaction may increase, the selectivity may increase, and/or reactions that would otherwise have low yield or be prohibitively expensive might thus become commercially feasible.
Catalysts and enzymes substantially increase the rate of a reaction even if present in small concentrations. The mechanism for this enhancement is usually expressed in terms of reducing the activation energy of the reaction. Of course, not all chemical reactions are so enhanced and still other reactions are enhanced often only under a limited set of conditions.
Often, increasing the temperature or pressure enhances reactions. The mechanism for this enhancement is usually expressed in terms of increasing the likelihood of overcoming the activation energy. However, this type of an enhancement often has undesirable aspects.
Externally applied electric fields are known to affect physical processes in electrorheological fluids, such as slurries, and are used in electrophoresis and field-flow fractionation to separate phases. Further, reaction rates of many chemical processes are affected by the application of an electric field, as in Friedel-Crafts, decomposition, proton-transfer reactions, and field-induced effects at surfaces.
However, these applications all involve high electric field strengths of at least 1000 V/cm or even as high as several V/Å. In general, it is undesirable to use high voltage DC electric fields because they cause unwanted ionization, such as hydrolysis, or other unwanted reactions to occur.
In electrolysis, electron transfer is a critical reaction step. Electrons are provided or removed at appropriate electrodes. Conventional electrolysis is typically carried out in media with high ionic strength, usually provided by electrolytic solutions or molten salts and with low applied voltages, typically less than 2 volts. The concentration of ions and salts might be higher than that of reactants, thereby limiting desired reaction paths or providing additional unwanted reaction paths. Furthermore, the limited voltage window in electrolysis due to the high ion and salt concentration often blocks desired reaction paths that correspond with larger voltage fields. As such, certain reactions are unreachable with conventional electrolysis.
In dispersion electrolysis, metal spheres or supported-metal particles are suspended in a high-impedance medium between feeder electrodes. Due to the small size of the metal spheres and supported metal clusters, the unique properties of microelectrodes apply—electrolysis of small amounts of material in the absence of supporting electrolyte salt. However, the suspension provides for a large number of particles so that the resulting macroscopic electrode area is large; this makes it possible to electrolyze relatively large quantities of material at the ensemble of microelectrodes. Since dispersion electrolysis is a form of electrolysis, electron transfer is a critical reaction step.
U.S. Pat. Nos. 5,296,106 and 5,397,447 in the name of Rolison et al. disclose a system and method for enhancing chemical reactions using a constant DC field to assist in chemical reactions. Specifically, a reactant is brought in contact with a stable, non-soluble, porous, and electronically non-conductive solid (reaction enhancer) in a fluidic medium to form a reaction mixture of low ionic strength. The reaction mixture so formed is then subjected to an electrifying force thereby enhancing the chemical reaction.
In U.S. Pat. No. 5,137,607 issued Aug. 11, 1992 to Anderson et al. variable DC voltage is suggested to vary voltage and polarity over time, to change the Fermi level of the membrane relative to the electrode to create a favorite condition for a certain reaction or reaction direction to occur. However it is understood that very low frequency varying voltage of less then one Hz is required for this to occur.
GB Patent Number 1,208,163 discloses a method and apparatus for the manufacture of phenols. A gaseous mixture of an aromatic hydrocarbon and an oxygen containing gas is introduced into a reaction chamber wherein the gaseous mixture is subjected to a silent electric discharge having a carrying frequency in the range of 30 Hz to 2 MHz and a field strength of 20-150 kV/cm. Of course, the field strength that is required to induce silent discharge in a gas is approximately invariant as a function of the carrying frequency. That said, one of skill in the art would not use high frequency electric fields, such as for instance up to 100 GHz, because high frequency and high power is hazardous.
Moreover, as is well known in the power industry, low frequency electric fields in the range of 60 Hz assist in the timely unwanted breakdown of liquid insulators. This problem, which has plagued the electric power industry for decades constitutes a phenomenon that has not been taken advantage of. Specifically, although the dielectric breakdown of liquids used as insulators with low frequency electric fields is known, to the best knowledge of the inventors of the present invention, high frequency electric fields have not been used to assist chemical reactions in liquids as a result of this breakdown phenomenon.
It is an object of the present invention to provide an apparatus and method that uses high frequency electric fields to initiate and/or enhance a chemical reaction in liquid continuous media at dielectric breakdown or pre-breakdown conditions.