Abstract:
A method for producing hydrogen from raw feed gases. The method comprises providing a reactor, positioning reactor walls within the reactor, introducing the raw feed gases into the reactor, and reacting the raw feed gases within the reactor to produce hydrogen. An apparatus for the production of hydrogen using a reactor is also provided.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to the production of higher C 2  and C 3  hydrocarbons and to the production of elemental sulfur, accompanied by the simultaneous recovery of hydrogen, from feedstreams containing methane and hydrogen sulfide and, more particularly, it describes a new process for the production of acetylene from methane and the production of hydrogen and elemental sulfur from hydrogen sulfide in silent and pulsed corona discharge reactors by continuously recovering hydrogen from the gaseous mixture of products and reactants through a membrane wall.  
           [0003]    2. Description of the Prior Art  
           [0004]    The principal impetus behind the synthesis of acetylene arises from its value as a chemical intermediate. In the early 1900&#39;s, acetylene was used as a raw material in the production of chlorinated solvents, acetic anhydride, and acid, as well as acetone. Starting in 1930&#39;s, acetylene was also used as the starting material for a variety of polymers such as synthetic rubbers, vinyl acetate and vinyl chloride monomers required for PVA and PVC, water-base paints, dry-cleaning solvents, and aerosol insecticides.  
           [0005]    Two principal routes have been described in the literature for the commercial production of acetylene:  
           [0006]    Hydrolysis of calcium carbide formed from the reduction of lime with carbon  
           [0007]    Calcium oxide is one of the most stable metal oxides. Production of calcium carbide using the following reaction, then, requires significant expenditure of energy.  
         CaO   +     2      C     +       1   2          O   2         -&gt;       2      CO     +     CaC   2                             
 
           [0008]    Not surprisingly, the majority of earlier technological improvements related to the development of the reduction furnace. The hydrolysis reaction:  
           CaC 2 +H 2 O→CaO+C 2 H 2    
           [0009]    is highly exothermic. Temperature control is vital to prevent decomposition of acetylene.  
           [0010]    Cracking of hydrocarbons, in particular methane, at high temperatures  
           [0011]    More recently, cracking processes for producing acetylene have received significant attention. Methane is used, most often, as the feedstock; other hydrocarbon sources are not available as readily. Several techniques have been described in the literature; however, two key limitations appear to be common to most of these methods. First, acetylene is diluted considerably by reaction products. For example, consider the reaction:  
           2CH 4 →C 2 H 2 +3H 2    
           [0012]    The maximum possible concentration of acetylene, at 100% conversion of methane, is twenty-five (25 vol. %) volume percent. Second, for acetylene production to be favored thermodynamically, the reaction temperature should be greater than about two thousand (2000° K.) degrees Kelvin. At this temperature, conversion to acetylene is rapid; however, sequential decomposition of acetylene to carbon and hydrogen is rapid as well. Clearly, recovery of the acetylene intermediate requires rapid quenching of the product gases. This is difficult in practice since the thermal capacity of gases is low.  
           [0013]    The several thermal methods described in the literature for cracking of hydrocarbons to produce acetylene include the following:  
           [0014]    Electric arc: This method provides comparatively easy heating of gases to the appropriate reaction temperature. The hot zone, however, can be spatially irregular leading to excessive product decomposition.  
           [0015]    Partial oxidation: The raw material is combined with just sufficient oxidizing gas to release the thermal energy required for achieving and maintaining the desired reaction temperature. Quenching of gases remains difficult though product dilution can be minimized by use of oxygen.  
           [0016]    Regenerative pyrolysis: In this method, a structure of refractory shapes is heated through intermittent flow of oxidizing gas. In between the periods corresponding to oxidizing gas flow, hydrocarbons contact the heated surfaces and undergo endothermic pyrolytic cracking.  
           [0017]    Submerged flame: A flame is propagated in within the bulk of a liquid hydrocarbon. The high temperature required for reaction is achieved in the flame region. Quenching is rapid.  
           [0018]    Other thermal methods—for example, triboelectric discharge and laser irradiation—have also been described more recently in the patent literature. Expensive and potentially corrosive reaction chamber is necessary for laser irradiation; and triboelectric discharge involves potentially dangerous pressure changes.  
           [0019]    Non-thermal discharges have attempted to overcome the shortcomings of thermal methods. Such non-equilibrium plasmas have been divided into five distinctive groups depending on the mechanism used for their generation, applicable pressure range, and electrode geometry. These are as follows:  
           [0020]    Glow discharge: This is an essentially low-pressure phenomenon usually between flat electrodes. The low pressure and mass flow severely restrict chemical industrial application.  
           [0021]    Corona Discharge: Use of inhomogeneous electrode geometries permits stabilization of discharges at high pressure. Several specific regions of operation—for example, ac or dc, and pulsed—have been described in the literature for applications involving, most often, cleanup of flue gas and atmospheric pollutants. The use of dc corona discharges for the production of acetylene from methane has been described. The AC/DC corona discharges, however, are inefficient in their higher energy consumption. The use of pulsed corona discharges for the production of acetylene from methane is one of the embodiments of the present patent application.  
           [0022]    Silent Discharge: In this operational regime, one or both of the electrodes are covered with a dielectric layer. Application of a sinusoidal (or other time-varying) voltage, then, leads to pulsing electric fields and microdischarges similar to those observed in pulsed corona discharge systems.  
           [0023]    RF Discharge: In such systems, the electrodes are not an integral part of the discharge volume. Non-thermal (or non-equilibrium) conditions are expected only at low pressures whereas thermal plasmas, with the limitations discussed earlier, can be expected at high pressures—and larger production rates—of interest in the chemical process industry.  
           [0024]    Microwave Discharge: Here, similar to RF discharge systems, the electrodes are not an integral part of the discharge volume. The wavelength of the applied electromagnetic field becomes comparable to the dimensions of the discharge volume and necessitates other coupling mechanisms. Several patents have been issued on the use of microwave energy for the production of acetylene from methane. Used metal/non-metal composites (elongated structural construction) within the discharge volume and a pulsating microwave energy source have been described. Using similar internals in the discharge volume but with a continuous microwave energy source has also been described. Other catalytic materials have also been used within the discharge volume. The use of activated charcoal as catalyst/reactant within the discharge volume has been described. The use of catalytic pellets within the discharge volume can lead to deposition of carbon on the internal surfaces and, therefore, intermittent operation. Others have, consequently, generated plasma using microwave energy; this plasma was introduced into a reactor loaded with catalyst.  
           [0025]    In comparing these non-thermal plasmas, it must be noted that in a glow discharge, the electrons gain energy from the applied field. Due to low pressures, collision with neutral species is infrequent. Propensity for the creation of reactive ions and chemical species is limited. Steady state operation is governed, primarily, by loss of energy incurred by the electrons on enclosure walls and other surfaces within the reactor. The situation is similar in RF and microwave discharges. In corona and silent discharges, the situation is entirely different; these are the operating regimes that are embodied in the present patent application. The fast electrons do indeed transfer energy to other molecules in the system. Electrode geometry and construction prevent sparking or arcing. Propensity for the creation of reactive ions and chemical species is very high.  
         SUMMARY  
         [0026]    The present invention is a method for the production of acetylene. The method comprises providing raw feed gases consisting of methane, introducing the raw feed gases into a reactor, positioning reactor walls within the reactor, and reacting the raw feed gases within the reactor with the following reaction:  
           2CH 4 →C 2 H 2 +3H 2 .  
           [0027]    The present invention additionally including an apparatus for the production of acetylene. The apparatus comprises raw feed gases consisting of methane, a reactor for reacting the raw feed gases within the reactor, and reactor walls positioned within the reactor wherein the following reaction occurs:  
           2CH 4 →C 2 H 2 +3H 2 .  
           [0028]    The present invention further includes a method for producing hydrogen from raw feed gases. The method comprises providing a reactor, positioning reactor walls within the reactor, introducing the raw feed gases into the reactor, and reacting the raw feed gases within the reactor to produce hydrogen.  
           [0029]    The present invention further still includes a method for the production of hydrogen and elemental sulfur. The method comprises providing raw feed gases consisting of hydrogen sulfide (H 2 S), introducing the raw feed gases into a reactor, positioning reactor walls within the reactor, and reacting the raw feed gases within the reactor with at least one of the following reactions:  
           H 2 S→H+SH  
           H+SH→2H+S  
           2H→H 2    
           H 2 S+H→SH+H 2 .  
           [0030]    The present invention further yet includes an apparatus for the production of hydrogen and elemental sulfur. The apparatus comprises raw feed gases consisting of hydrogen sulfide (H 2 S), a reactor for reacting the raw feed gases within the reactor, and reactor walls positioned within the reactor wherein at least one of the following reactions occur:  
           H 2 S→H+SH  
           H+SH→2H+S  
           2H→H 2    
           H 2 S+H→SH+H 2 .  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    [0031]FIG. 1 is a schematic view of the apparatus and method for the conversion of methane in non-thermal silent and pulsed corona discharge reactors, constructed in accordance with the present invention; and  
         [0032]    [0032]FIG. 2 is a schematic view of the apparatus and method for the conversion of hydrogen sulfide in non-thermal silent and pulsed corona discharge reactors, constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    The present invention concerns utilizing either a non-thermal pulsed plasma corona reactor or a silent barrier reactor having membranes positioned therein and receiving co-axial or other gas flow patterns. The present invention permits collection of purified hydrogen and provides significant energy and conversion advantages.  
         [0034]    As illustrated in FIG. 1, the present invention is an apparatus and method, indicated generally at  10 , for the production of acetylene  11  (and other C 2  and C 3  hydrocarbons), using methane as a raw feed gas  12 , and for the production of elemental sulfur and hydrogen using hydrogen sulfide (H 2 S) as a raw feed gas  12 , both in a silent discharge and non-thermal pulsed plasma corona reactor  14 . It should be noted that the present invention can utilize either a silent discharge reactor or a non-thermal pulsed corona reactor.  
         [0035]    The raw feed gas  12  is available in sour natural gas streams and the production facility for producing the acetylene  11  and the hydrogen and elemental sulfur can be sited, to advantage, near such gas fields. The principal overall reaction for production of the acetylene  11  within the non-thermal pulsed plasma corona reactor  14  is as follows:  
         2CH 4 →C 2 H 2 +3H 2   (A)  
         [0036]    Within the non-thermal pulsed plasma corona reactor  14 , conversion is expected to proceed through the dissociation of methane and hydrogen sulfide by energetic electrons according to the following:  
         CH 4 →CH 3 +H  (B)  
         CH 3 →CH 2 +H  (C)  
         CH 2 →CH+H  (D)  
         CH→C+H  (E)  
         [0037]    The recombination of the radical species leads to the following:  
         CH 3 +CH 3 →C 2 H 6   (F)  
         CH 2 +CH 2 →C 2 H 4   (G)  
         CH+CH→C 2 H 2   (H)  
         H+H→H 2   (I)  
         [0038]    High voltage pulses in the non-thermal pulsed plasma corona reactor  14  produce short-lived microdischarges that preferentially accelerate the electrons without imparting significant energy to the ions. The high voltage pulses within the non-thermal pulsed plasma corona reactor  14  lowers power consumption. In addition, most of the energy applied goes to accelerating the electrons rather than the comparatively massive ions. Larger reactor volumes are consequently possible.  
         [0039]    The non-thermal pulsed plasma corona reactor  14  has reactor walls  16  constructed from membrane materials—for example, palladium coated substrates, carbon among others—which permit selective permeation of hydrogen  18 . Continuous removal of hydrogen  18  through the reactor walls  16  pushes reaction A towards completion. The membrane materials can be coated with a corrosive resistant material such as platinum or the like.  
         [0040]    A schematic diagram illustrating the apparatus and method of the present invention is illustrated in FIG. 1. It should be noted, however, that alternative arrangements devised to exploit the process concept more advantageously are within the scope of this invention.  
         [0041]    As illustrated in FIG. 2, and as described above, the present invention further includes the conversion of hydrogen sulfide  13  to elemental sulfur  13  and hydrogen  18  in a non-thermal pulsed corona reactor  14 . The H 2 S, CO 2 , and CH 4  from a regenerator (not shown) will form the primary feed to the non-thermal pulsed corona reactor  14 . Recovery of elemental sulfur  22  and hydrogen  18  from H 2 S in the non-thermal pulsed corona reactor  14  is based, primarily, on the following reactions:  
         H 2 S→H+SH  (6)  
         H+SH→2H+S  (7)  
         2H→H 2   (8)  
         H 2 S+H→SH+H 2   (9)  
         [0042]    The emphasis is on the dissociation of H 2 S according to Reaction (6). Formation of sulfur occurs by Reaction (7). Reactions (8) and (9) are responsible for the formation of hydrogen. Since the feed gas stream to the non-thermal pulsed corona reactor  14  consists of H 2 S and CO 2 , the following reaction can also take place:  
         H 2 S+CO 2 →H 2 O+CO+S  (10).  
         [0043]    The approach herein has a distinct advantage in that the fuel value of H 2 S is transformed to CO and H 2 ; this synthesis gas can actually be burnt to meet the energy requirements of the process. While CO 2  also leads to the formation of COS, its production can be minimized by choice of proper operating conditions.  
         [0044]    The reactions and processes described herein can also be viewed as a substitute for the Claus chemistry and operations used widely for sulfur recovery from streams containing hydrogen sulfide.  
         [0045]    The advantages of the apparatus and process  10  of the present invention are clear:  
         [0046]    The present invention permits the production of acetylene (and other C 2  and C 3  hydrocarbons)  11  and elemental sulfur  22  and hydrogen  18  from relatively inexpensive feedstock. Expensive preheating and pressurization of the feed gases  12  is also not required. The hydrogen  18  separation is relatively simple.  
         [0047]    The present invention permits simultaneous production of hydrogen  18 . The fuel value of methane is recovered in the form of cleaner-burning hydrogen. The hydrogen  14  can find use within the petroleum refinery if the process is used in conjunction with a desulfurization unit. Alternatively, hydrogen  14  can be used to generate clean electricity using fuel-cell technology.  
         [0048]    The present invention can be utilized for methane, hydrogen sulfide, or mixtures thereof, along with other gases. The products, besides the hydrogen, will vary with operating conditions and feed mixture composition. Also, the present invention can be integrated readily into fuel cell applications.  
         [0049]    The foregoing exemplary descriptions and the illustrative preferred embodiments of the present invention have been explained in the drawings and described in detail, with varying modifications and alternative embodiments being taught. While the invention has been so shown, described and illustrated, it should be understood by those skilled in the art that equivalent changes in form and detail may be made therein without departing from the true spirit and scope of the invention, and that the scope of the present invention is to be limited only to the claims except as precluded by the prior art. Moreover, the invention as disclosed herein, may be suitably practiced in the absence of the specific elements which are disclosed herein.