Patent Abstract:
The present invention relates to a process for the preparation of synthesis gas (i.e., a mixture of carbon monoxide and hydrogen), typically labeled syngas. More particularly, the present invention relates to a regeneration method for a syngas catalyst. Still more particularly, the present invention relates to the regeneration of syngas catalysts using a re-dispersion technique. The re-dispersion technique involves the formation and removal of carbonyls with the active metals. The carbonyl formation and removal effectively re-disperses the catalyst metal.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to a process for the preparation of synthesis gas (i.e., a mixture of carbon monoxide and hydrogen), typically labeled syngas. More particularly, the present invention relates to novel methods of regenerating a partial oxidation catalysts via chemical re-dispersion of the catalytic metals. In addition, the present invention can be used for in-situ regeneration of a partial oxidation catalyst without any downtime in production. 
     BACKGROUND OF THE INVENTION 
     Catalysis is literally the lifeblood for many industrial/commercial processes in the world today. The most important aspect of a catalyst is that it can increase the productivity, efficiency and profitability of the overall process by enhancing the rate, activity and/or selectivity of a given reaction. Many industrial/commercial processes involve reactions that are simply too slow and/or inefficient to be economical without a catalyst present. For example, the process of converting natural gas or methane to liquid hydrocarbons (an extremely desirable process) necessarily involves several catalytic reactions. 
     The conversion of methane to hydrocarbons is typically carried out in two steps. In the first step, methane is catalytically converted to carbon monoxide and hydrogen (i.e., synthesis gas or syngas). In a second step, the syngas intermediate is catalytically converted to higher hydrocarbon products by processes such as the Fischer-Tropsch Synthesis or to other chemicals by processes such as an alcohol synthesis. For example, fuels such as hydrocarbon waxes and liquid hydrocarbons comprised in the middle distillate range, i.e., kerosene and diesel fuel, may be produced from the synthesis gas. 
     Current industrial use of methane as a chemical feedstock for syngas production proceeds by the initial conversion of methane to carbon monoxide and hydrogen by either steam reforming or dry reforming. Steam reforming currently is the major process used commercially for the conversion of methane to synthesis gas, the reaction proceeding according to Equation 1.
 
CH 4 +H 2 O           CO+3H 2   (1)

     The catalytic partial oxidation (“CPOX”) of hydrocarbons, e.g., methane or natural gas, to syngas has also been described in the literature. In catalytic partial oxidation, natural gas is mixed with air, oxygen-enriched air, or oxygen, and introduced to a catalyst at elevated temperature and pressure. The partial oxidation of methane yields a syngas mixture with a more preferable H 2 :CO ratio of 2:1, as shown in Equation 2:
 
CH 4 +1/2O 2             CO+2H 2   (2)

     The H 2 :CO ratio for this reaction is more useful for the downstream conversion of syngas to fuels or to chemicals such as methanol than is the H 2 :CO ratio from steam reforming. However, both reactions continue to be the focus of research in the world today. 
     As stated above, these reactions are catalytic reactions and the literature is replete with varying catalyst compositions. The catalyst compositions typically are comprised of at least one catalytically active metal, such as a Group VIII metal. Many catalyst compositions also have other promoters present. Catalytic metals are typically selected based on their activity and selectivity towards a particular reaction. Further, the catalyst compositions typically include particular support materials such as alumina, silica, titania, etc., that can also enhance the catalyst activity. 
     After a period of time in operation, a catalyst will become deactivated, losing its effectiveness for catalyzing the desired reaction to a degree that makes the process uneconomical at best and inoperative at worst. This process is generally known as “aging.” The more aged a particular catalyst the less efficient the catalyst is at enhancing the reaction, i.e., less activity it has. At this point, the catalyst can be either replaced or regenerated. However, replacing a catalyst typically means discarding the deactivated catalyst. Even if a fresh replacement catalyst is ready and available, a single syngas reactor will typically have to be shut down and offline for days to weeks. The time delay is due at least in part to the time required for simple cooling and heating of the reactor. 
     In addition, a discarded catalyst represents a loss of expensive metals. Alternatively, the user may send the catalyst back to the supplier for recovery of expensive metals, such as Rh, Pt, Pd, etc. However, the recovery process involves dissolving the multi-component catalyst and subsequent separation of the active components from the mixed solution. The chemistry is complex and costly, more importantly, it involves bulk amounts of harsh chemicals that ultimately must be discarded and the use of landfills for such disposal is problematic. For example, the environmental protection agency (EPA) “Land Ban” imposes restrictions on disposal because these harsh chemicals can release toxins into the environment. For all of these reasons, regeneration is preferred over replacement. 
     However, regeneration has problems as well. Like replacement, regeneration typically requires some downtime resulting in a decrease in production. In addition, regeneration may not be available for every deactivated catalyst. Catalyst systems can become deactivated by any number of mechanisms. Some of the more common deactivating mechanisms include coking, sintering, poisoning, oxidation, and reduction. The process chiefly responsible for deactivation varies among catalyst systems. Some catalysts that have been deactivated can be regenerated and/or the deactivation reaction can be reversed. However, many regeneration processes are not economically feasible. 
     Sintering as a cause of deactivation traditionally has been viewed as a non-reversible phenomenon, since a sintered catalyst is particularly difficult to regenerate. In terms of synthesis gas catalysts, sintering is usually the result of the high temperatures within the catalyst bed. The syngas reactions achieve very high temperatures during operation. Temperatures within a syngas catalyst bed typically reach temperatures in excess of 1000° C. Sintering for syngas catalysts is therefore practically unavoidable. There are similarly potential deactivation issues with other catalytic partial oxidation reactions that take place at high temperature. 
     Because regeneration has traditionally been so difficult, the active metals are typically dissolved and recaptured for use in new catalyst batches. However, research is continuing on the development of more efficient syngas catalyst systems and catalyst systems that can be more effectively regenerated. To date there are no known methods that are economically feasible for regenerating a partial oxidation catalyst, such as a syngas catalyst. 
     Hence, there is still a great need to identify new regeneration methods, particularly methods that are quick and effective for regenerating deactivated partial oxidation catalysts without having to dissolve the catalyst components and without significant downtime or loss of production. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a process for the preparation of synthesis gas (i.e., a mixture of carbon monoxide and hydrogen), typically labeled syngas. More particularly, the present invention relates to novel methods of regenerating partial oxidation catalysts via chemical re-dispersion of the catalytic metals. In addition, the present invention can be used for in-situ regeneration of a partial oxidation catalyst with little to no downtime in production. 
     The regeneration of the partial oxidation catalysts is accomplished by passing a gas over a deactivated catalyst that restores the catalytic metal to its active form and/or restores active surface area of the catalytic metals lost from deactivation phenomenon. Suitable regeneration gases include but are not limited to carbon monoxide, hydrogen, oxygen, syngas and steam. The present invention is primarily directed towards partial oxidation catalysts used preferably in partial oxidation reactions of hydrocarbons or hydrogen sulfide or combinations and even more preferably used in syngas catalysts that contain Group VIII, noble metals or combinations thereof. 
     Sometimes it may be necessary or just advantageous to use a multiple step regeneration process in which the deactivated catalysts are exposed to more than one type of gas in a stepwise fashion. For example, one embodiment of the present invention would be to expose the deactivated partial oxidation catalyst to an oxidizing gas followed by a reducing gas. 
     In yet another preferred embodiment of the present invention, a synthesis gas reaction is carried out producing primarily hydrogen and carbon monoxide, i.e., syngas. A slip stream of the syngas product is removed, resulting in a primary syngas product stream and a small secondary syngas stream, the slip stream. The slip stream is separated to produce a hydrogen rich stream and a carbon monoxide rich stream. The hydrogen rich stream can then be used for in-situ regeneration or activation of a second partial oxidation catalyst. The excess hydrogen rich gas from the regeneration or activation process can be re-introduced into the primary syngas stream from the first reactor along with the carbon monoxide rich stream. The primary syngas stream can then be introduced into a Fischer-Tropsch reactor to produce liquid hydrocarbons. 
     In the most preferred embodiment of the present invention, more than one partial oxidation reactor is used, allowing continuous production even during the regeneration process. For example, one syngas reactor produces syngas, which in turn is partially used to obtain a hydrogen rich regeneration gas. The hydrogen rich gas is passed over the deactivated catalyst in a second syngas reactor for regeneration. When the catalyst in the first syngas reactor is deactivated, the process can be reversed. The second syngas reactor produces the syngas and thus hydrogen rich gas. The hydrogen rich gas is then used to regenerate the catalyst in the first syngas reactor. This type of cycle can be repeated indefinitely or until the catalyst can no longer be regenerated. 
     These and other embodiments, features and advantages of the present invention will become apparent with reference to the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed description of the preferred embodiment of the present invention reference will now be made to the accompanying Figures, 
         FIG. 1  is a block flow diagram of a hydrocarbon gas to liquid conversion process in accordance with one embodiment of the present invention; and 
         FIG. 2  is a block flow diagram of a hydrocarbon gas to liquid conversion process in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     There are shown in the Figures, and herein will be described in detail, specific embodiments of the present invention, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. The present invention is susceptible to embodiments of different forms or order and should not be interpreted to be limited to the particular structures or compositions contained herein. In particular, various embodiments of the present invention provide a number of different configurations of the overall gas to liquid conversion process. 
     The regeneration of a partial oxidation catalyst is accomplished by passing a gas over a deactivated catalyst that restores the catalytic metal to its active form and/or restores active surface area of the catalytic metals lost from deactivation phenomenon. The present invention is primarily directed towards partial oxidation catalysts used in partial oxidation reactions of hydrocarbons or hydrogen sulfide or combinations thereof and even more preferably towards catalysts that contain Group VIII or noble metals that are used in partial oxidation reactions of natural gas or methane to produce syngas. The partial oxidation catalyst preferably contains one or more of the following metals: rhodium, ruthenium, platinum, palladium, iridium, nickel, cobalt, with optional promoters. 
     According to the present invention, a syngas reactor can comprise any of the synthesis gas technology and/or methods known in the art. The hydrocarbon-containing feed is almost exclusively obtained as natural gas. However, the most important component is generally methane. Methane or other suitable hydrocarbon feedstocks (hydrocarbons with four carbons or less) are also readily available from a variety of other sources such as higher chain hydrocarbon liquids, coal, coke, hydrocarbon gases, etc., all of which are clearly known in the art. Similarly, the oxygen-containing gas may come from a variety of sources and will be somewhat dependent upon the nature of the reaction being used. For example, a partial oxidation reaction requires diatomic oxygen as a feedstock, while steam reforming requires only steam. According to the preferred embodiment of the present invention, partial oxidation is assumed for at least part of the syngas production reaction. 
     Regardless of the source, the hydrocarbon-containing feed and the oxygen-containing feed are reacted under catalytic conditions. The catalyst compositions useful for synthesis gas reactions are well known in the art. They generally are comprised of a catalytic metal that has been reduced to its active form and one or more promoters on a support structure. The most common catalytic metals are Group VIII metals or noble metals. The support structures may be monoliths, wire mesh or particulates. Often, the support selected will dictate the type of catalyst bed that must be used. For example, fixed beds are comprised of monoliths and large particle sized supports. Supports comprised of small particles tend to be more useful in fluidized beds. The support matrix is usually a metal oxide or mixture of metal oxides, such as alumina, titania, zirconia, or the like. 
     The synthesis gas feedstocks are generally preheated, mixed and passed over or through the catalyst beds. As the mixed feedstocks contact the catalyst, the synthesis reactions take place. The synthesis gas product contains primarily hydrogen and carbon monoxide, however, many other minor components may be present including steam, nitrogen, carbon dioxide, ammonia, hydrogen cyanide, etc., as well as unreacted feedstock, such as methane and/or oxygen. The synthesis gas product, i.e., syngas, is then ready to be used, treated, or directed to its intended purpose. For example, in the instant case some or all of the syngas may be used to prepare regeneration gases for the present invention or may be used as a feedstock for a Fischer-Tropsch process or an alcohol synthesis plant. 
     The syngas-containing stream when leaving a syngas reactor is typically at a temperature of about 600–1500° C. The syngas must be transitioned to be useable in synthesis reactor downstream of the syngas reactor such as a Fischer-Tropsch or other synthesis reactors e.g. an alcohol synthesis reactor, which operate at lower temperatures of about 200° C. to 400° C. The syngas is typically cooled, dehydrated (i.e., taken below 100° C. to knock out water) and compressed during the transition phase. Thus, in the transition of syngas from the syngas reactor to a synthesis reactor, the syngas stream may experience a temperature window of 50° C. to 1500° C. 
     Several reactions have been discovered that can restore the activity to a deactivated syngas catalyst depending on the deactivation phenomenon. The applicants believe that the methods disclosed herein to regenerate a syngas catalyst are applicable to any partial oxidation catalyst, which loses its activity due to the same or similar deactivation mechanisms. For example, catalytic metals are often oxidized as a result of the syngas reaction, which results in at least two problems, namely, the loss of the “active state” (reduced) of the catalytically active metals, and the loss of catalytically active surface area. Noble metals are preferred as the primary catalytic metals for syngas catalyst compositions. Noble metals form metal oxides under syngas reactor conditions. In addition, the preparation of a noble metal-containing syngas catalyst often includes at least one calcining step that will oxidize the noble metal. Calcination results in metal oxides. Thus, sometimes the catalytic metals are not in the fully active form even before exposure to the syngas reactions. In any event, the noble metal oxides will still catalyze the syngas reaction, however, the activity of the reduced metal, generally considered the active species, is greatly preferred. 
     Also, oxidation of the syngas catalytic metals can result in the loss of catalytically active surface area. As the noble metal oxides are formed, other oxides can be forming simultaneously, i.e., oxides of secondary catalytic metal or promoter metal. Due to the mobility of these metal particles, the noble metals are often physically “covered” by other metal oxides, further decreasing the amount of active surface area available for catalytic participation. 
     Thus, according to one embodiment of the present invention, a hydrogen-rich gas is passed over deactivated syngas catalysts as the primary regeneration gas. It is believed that the hydrogen exposure results in at least one of two phenomena that can help restore the activity back to the overall catalyst composition. First, the oxidized noble metal particles are “uncovered” or brought back toward to the surface of the support. “Surface” in this context is intended to mean the place where the metal particle will have exposure to the reactant gases. In other words, surface is not limited to the outer surface of a spherical support particle, and could also be the inner surface of a pore or microfracture within the support particle or structure such that the syngas reactants could be exposed to the particle and react. The catalytic metals tend to migrate towards the surface and are reduced under the hydrogen gas. Second, as the hydrogen reduction reaction reduces the metal particles they re-disperse. Thus, more of the noble metal particles are reduced to the more active form and dispersed on and through the support to achieve the high amount of surface area needed for the syngas reaction. 
     The hydrogen rich gas may be obtained or produced from any available source including, but not limited to, recycled gas streams, bottled gas, produced syngas, Fischer-Tropsch tailgas, hydroprocessing tailgas, hydrogen-rich streams from an alcohol synthesis plant, an olefin synthesis plant, a carbon filaments/carbon fibers synthesis plant, an aromatic synthesis plant, or the like. The purity of the hydrogen rich gas is not critical, but it is preferred that the hydrogen rich gas be oxygen free. A secondary preference is that the hydrogen rich gas be also carbon free. It will be understood by those skilled in the art that gases cannot ever be absolutely free of impurities, including oxygen or carbon. Likewise, the present invention does not assert or contemplate such an extreme position. It is intended that these impurities are substantially eliminated to the point that side reactions associated with their presence do not significantly alter or inhibit the effective regeneration of the catalyst metal according to the present invention. 
     According to another embodiment of the present invention, a hydrocarbon-rich gas is passed over deactivated partial oxidation catalysts as the primary regeneration gas. Preferably the hydrocarbon-rich gas is natural gas, mixtures of C 1 –C 10  hydrocarbons, methane, or combinations thereof. It is believed that the hydrocarbon-rich gas creates a reducing environment thereby reducing the metal particles. 
       FIG. 1  shows a block flow diagram in accordance with one preferred embodiment of the present invention. The flow diagram is of a gas to liquid conversion process that includes a method for in-situ regeneration or activation of a syngas catalyst. Syngas can be generated by a catalytic reaction between a hydrocarbon-containing gas and an oxygen-containing gas and optionally steam. The hydrocarbon containing gas can be any hydrocarbon containing gas in which the hydrocarbon content is substantially C 4  or less. The more preferred hydrocarbon containing gases are natural gas or methane. The oxygen containing gas can be air or oxygen and is preferably oxygen. 
     The hydrocarbon containing gas and oxygen containing gas (collectively “syngas feedstock”) are introduced into a first syngas reactor  100  through line  105 . It should be appreciated that these gases are typically mixed very near in time to exposure to the syngas catalyst.  FIG. 1  is intended merely as a flow diagram and not intended to disclose these kinds of details that are well known in the art and by those of ordinary skill. The syngas feedstocks are catalytically reacted in a first syngas reactor  100  to produce primarily hydrogen and carbon monoxide, i.e., syngas. 
     The produced syngas exits through line  110  and is then passed to a Fischer-Tropsch reactor  145  via line  120 . Again, it should be appreciated that other details such as preparation of the syngas as a Fischer-Tropsch feedstock in terms of temperature, pressure, water knock-out, etc., are presumed to be understood by those of ordinary skill in the art. 
     A slip stream of syngas is removed from line  110  and passed into a gas separation unit  125  through line  115 . The type of separation used in unit  125  is not critical to the present invention and may include any physical and/or chemical means of separation such as membranes, adsorption-desorption techniques, water gas shift reactors, and the like. In the most preferred embodiment, gas separation unit  125  comprises a membrane separator. Membranes are well known in the art to be highly selective to hydrogen, typically greater than 70%. With the hydrogen removed, the remaining syngas will be carbon monoxide rich. Thus, the gas separation unit  125  produces a hydrogen rich permeate stream and a carbon monoxide rich stream. 
     The carbon monoxide rich stream exits the gas separation unit  125  through line  135 . The carbon monoxide rich stream can be sent to flare, used as a feedstock or reactant for various reactions, but is preferably re-introduced into line  120 . 
     In accordance with the most preferred embodiment of the present invention, the hydrogen rich permeate stream is removed and introduced into a second syngas reactor  150  via line  130 . The hydrogen rich gas is passed over a syngas catalyst located within second syngas reactor  150  for regeneration or activation of the syngas catalyst. The excess hydrogen rich gas will pass through the second syngas reactor  150  and exit though line  140 . The excess hydrogen rich gas will then preferably be re-introduced into line  120 . 
     Regulation of lines  135  and  140  can be used to adjust the hydrogen to carbon monoxide molar ratio in primary syngas stream  120  prior to introduction into the Fischer-Tropsch reactor  145 . For example, if more hydrogen is needed in the primary syngas stream  120 , the carbon monoxide rich gas  135  will be decreased by lowering the flow rate, sending some or all to flare, or simply redirecting the gas for other purposes. As the flow rate of carbon monoxide stream  135  is decreased, the flow rate of hydrogen rich stream  140  will be increased as needed to achieve the desired ratio. Likewise, more carbon monoxide can be added from line  135  and less hydrogen from line if the reverse situation is desired. By re-introducing the carbon monoxide and hydrogen rich streams  135  and  140 , respectively, the present invention has the advantage of regenerating the deactivated catalyst using readily available in-house gases while losing very little in terms of final products. 
     According to the present invention, the time necessary for in-situ regeneration of the syngas catalyst in reactor  150  will be primarily dependent on the volume of catalyst and flow and concentration of hydrogen passing over the catalyst. Under normal operating conditions, i.e., the space velocities for the gas flow, stated as gas hourly space velocity (GHSV), are from about 20,000 to about 100,000,000 hr −1 , preferably from about 100,000 to about 25,000,000 hr −1  a temperature of about 25° C. to about 1500° C., preferably less than 1000° C., more preferably less than 600° C., and a pressure of about 25 psig to about 250 psig, it is anticipated that the time necessary to regenerate a catalyst bed of less than 1 foot in length will be less than 24 hours. Once regenerated, the second syngas reactor  150  can be used to produce syngas for the regeneration of the catalyst in the first syngas reactor  100  when the catalyst becomes deactivated. The process described above is simply reversed as described below. 
     The syngas feedstocks are introduced into the second syngas reactor  150  through line  155 . The syngas feedstocks are catalytically reacted in syngas reactor  150  to produce syngas. The produced syngas exits through line  160  and is then passed to a synthesis reactor  195  via line  170 . A slip stream of syngas is removed from line  160  and passed into a regenerating gas recovery separation unit  175  through line  165 . Again, the type of separation and/or purification used is not critical to the present invention and may include any physical and/or chemical means of separation such as membranes, adsorption-desorption techniques, water gas shift reactors, and the like. Thus, the gas separation unit  175  will produce a hydrogen rich permeate stream and a carbon monoxide rich stream. 
     The carbon monoxide rich stream exits the gas separation unit  175  through line  185 . The carbon monoxide rich stream can be sent to flare, used as a feedstock or reactant for various reactions, but is preferably re-introduced into line  170 . 
     In accordance with the most preferred embodiment of the present invention, the hydrogen rich permeate stream is removed and introduced into the first syngas reactor  100  via line  180 . The hydrogen rich gas is passed over a syngas catalyst located with the first syngas reactor  100  for regeneration or activation of the syngas catalyst. The excess hydrogen rich gas will pass through the first syngas reactor  100  and exit though line  190 . The excess hydrogen rich gas will then preferably be re-introduced into line  170 . 
     As before, regulation of lines  185  and  190  can be used to adjust the hydrogen to carbon monoxide molar ratio in the primary syngas stream  170  prior to introduction into the synthesis reactor  195 . For example, if more hydrogen is needed in the primary syngas stream  170 , the carbon monoxide rich gas  185  will be decreased by lowering the flow rate, sending some or all to flare, or simply redirecting the gas for other purposes. As the flow rate of carbon monoxide stream  185  is decreased, the flow rate of hydrogen rich stream  190  will be increased as needed to achieve the desired ratio. Likewise, more carbon monoxide can be added from line  185  and less hydrogen from line  190  if the reverse situation is desired. 
     The synthesis reactor  145  or  195  can comprise any of the Fischer-Tropsch technology and/or methods known in the art. The Fischer-Tropsch feedstock is hydrogen and carbon monoxide, i.e., syngas. The hydrogen to carbon monoxide molar ratio is generally deliberately adjusted to a desired ratio of approximately 2:1, but can vary between 0.5 and 4. The syngas is then contacted with a Fischer-Tropsch catalyst. Fischer-Tropsch catalysts are well known in the art and generally comprise a catalytically active metal, a promoter and a support structure. The most common catalytic metals are Group VIII metals, such as cobalt, nickel, ruthenium, and iron or mixtures thereof. The support is generally alumina, titania, zirconia or mixtures thereof. Fischer-Tropsch reactors use fixed and fluid type conventional catalyst beds as well as slurry bubble columns. The literature is replete with particular embodiments of Fischer-Tropsch reactors and Fischer-Tropsch catalyst compositions. As the mixed feedstocks contact the catalyst the hydrocarbon synthesis reactions take place. The Fischer-Tropsch product contains a wide distribution of hydrocarbon products from C 5  to greater than C 100 . 
     The Synthesis reactor  145  or  195  can comprise any of the reactors known in the art, which produce alcohols, particularly methanol when using syngas as feedstock. 
     It should be appreciated that other suitable reducing gases, such as methane, natural gas, light hydrocarbons, can be used to perform the regeneration step. If methane were the regeneration gas selected, the oxygen feedstock would be reduced or eliminated to create a substantially methane stream into the deactivated syngas catalyst bed. Alternatively, the methane may come from stored gas, bottled gas or a slip stream of methane gas from some other source, such as a separate feedstock stream from a second syngas reactor. Also, unreacted methane may be recovered and used from tail-gas of any available process. 
     In another embodiment of the present invention, the regeneration process described above may use oxidative gases for regeneration rather than reducing gases, such as oxygen, steam or air, with or without other inert gases for safety/dilution purposes. Referring now to  FIG. 2 , an in-situ process using oxygen would be possible in which a hydrocarbon containing gas and oxygen containing gas are introduced into a first syngas reactor  200  through line  205 . The syngas feedstocks are catalytically reacted in a first syngas reactor  200  to produce primarily hydrogen and carbon monoxide, i.e., syngas. 
     The produced syngas exits through line  210  and is then passed to a synthesis reactor  245  via line  220 . At least a portion of the syngas, preferably the entire stream, is passed into a gas separation unit  225 . The type of separation used in unit  225  is not critical to the present invention and may include any physical and/or chemical means of separation such as oxygen selective membranes and any other techniques known or used in the art. In the most preferred embodiment, gas separation unit  225  comprises a membrane separator. Membranes are well known in the art to be highly selective to oxygen, typically greater than 70%. Thus, the gas separation unit  225  produces an oxygen rich stream  230  and a secondary syngas stream  235 . The secondary syngas stream exits the gas separation unit  225  through line  235  and is sent to the synthesis reactor  245 . 
     In accordance with the most preferred embodiment of the present invention, the oxygen rich stream is removed and introduced into a second syngas reactor  250  via line  230 . The oxygen rich gas is passed over a syngas catalyst located within second syngas reactor  250  for regeneration or activation of the syngas catalyst. The excess oxygen rich gas will pass through the second syngas reactor  250  and exit though line  240 . The excess oxygen rich gas can be recycled and used as syngas feedstock, sent to flare, or released into the atmosphere. 
     According to the present invention, the time necessary for in-situ regeneration of the syngas catalyst in reactor  250  will be primarily dependent on the volume of catalyst and flow and concentration of hydrogen passing over the catalyst. Under normal operating conditions, i.e., the. space velocities for the gas flow, stated as gas hourly space velocity (GHSV), from about 20,000 to about 100,000,000 hr −1 , preferably from about 100,000 to about 25,000,000 hr −1  a temperature of about 25° C. to about 1500° C., preferably less than 1000° C., more preferably less than 600° C., and a pressure of about 25 psig to about 250 psig, it is anticipated that the time necessary to regenerate a catalyst bed of less than 1 foot in length will be less than 24 hours. Once regenerated, the second syngas reactor  250  can be used to produce syngas for the regeneration of the catalyst in the first syngas reactor  200  when the catalyst becomes deactivated. The process described above is simply reversed as described below. 
     The syngas feedstocks are introduced into the second syngas reactor  250  through line  255 . The syngas feedstocks are catalytically reacted in syngas reactor  250  to produce syngas. The produced syngas exits through line  260  and is then passed into a gas separation unit  275 . Thus, the gas separation unit  275  will produce an oxygen rich stream  280  and a secondary syngas stream  285 . The secondary syngas stream exits the gas separation unit  275  through line  285  and is sent to the synthesis reactor  295 . 
     The oxygen rich stream is removed and introduced into the first syngas reactor  200  via line  280 . The oxygen rich gas is passed over a syngas catalyst located with the first syngas reactor  200  for regeneration or activation of the syngas catalyst. The excess oxygen rich gas will pass through the first syngas reactor  200  and exit though line  290 . The excess oxygen rich gas can be recycled and used as syngas feedstock, sent to flare, or released into the atmosphere. 
     The synthesis reactor  245  or  295  can comprise any of the Fischer-Tropsch technology and/or methods known in the art as described above with respect to the regeneration embodiment using hydrogen. 
     Alternatively, the regeneration process may be carried out with a single syngas reactor design. For example, in another embodiment of the present invention, a single syngas reactor can be operated in cyclic mode in which the reactor simply alternates between reaction and regeneration operating conditions. The regeneration gas needed for the process may come from bottled gas or other suitable regeneration gases available from other plant processes on site. Once deactivation of a catalyst is detected, the syngas reactant feedstocks would be replaced with the available regeneration gas for a period of time sufficient to restore some or all of the activity to the deactivated catalyst. It should be appreciated that with a given volume, type and composition of catalyst, the necessity for a regeneration cycle can become quite predictable. Thus, no actual detection of deactivation is necessary, simply the understanding that at some given point in time a regeneration cycle is warranted and can be carried out. It is believed that this process would be necessary only on a weekly if not longer basis, resulting in very little down time for syngas production. In addition, depending upon the flow rates and volume of the syngas catalyst bed, the downtime should be insignificant against the total time for available for production. For example, a regeneration cycle may constitute only a three-hour period of time in an entire week. 
     In another embodiment of the present invention, a multiple step regeneration process may be used. Preferred steps would be to subject the deactivated catalyst first to oxidation by exposure to an oxidizing gas, such as water, steam, oxygen, air, etc., followed by a reduction step by exposure to a reducing gas, such as methane or hydrogen. Air and methane are the preferred gases due to their low cost and availability. This type of multiple step regeneration can be performed under the multiple reactor design or when using a single reactor in cyclic mode. In addition, one of ordinary skill in the art could easily apply the spirit of the embodiments as described in connection with the flow diagrams of  FIGS. 1 and 2  to produce a combined process for in-situ multiple step regeneration. For example, the syngas lines exiting the syngas reactors could have a valve that allowed the syngas product to be sent either to a hydrogen separation unit or an oxygen separation unit such that the appropriate regeneration gas could be obtained for the process. 
     The present invention will be more easily and fully understood by the following example. The example is representative of the regeneration process in accordance with one embodiment of the preferred present invention. 
     EXAMPLE 
     A 4 wt % Rh/4 wt % Sm catalyst was tested at a natural gas:oxygen ratio of 1.82:1 at weight hour space velocities (WHSV) of 530 and 940 hr −1  and pressures of 45 and 90 psig (412 and 722 kPa), respectively. The weight hour space velocity is defined by the weight of reactant feed per hour divided by the weight of catalyst. The partial oxidation reaction was carried out in a conventional flow apparatus using a 12.7 mm I.D. quartz insert embedded inside a refractory-lined steel vessel. The quartz insert contained a catalyst bed containing a 9.5 mm catalyst bed held between two inert 80 ppi alumina foams. The reactor effluent was analyzed using a chromatograph equipped with a thermal conductivity detector. 
     The catalyst was tested for 24 hours at 45 psig (412 kPa), after which a pressure drop of 3.3 psi was observed. The pressure was then increased to 90 psig (722 kPa) for 1.5 hours and an increase in pressure drop to 6.2 psi was observed, as shown in Table 1. An increase in pressure is indicative of at least one deactivation phenomenon, i.e., carbon deposition. Consequently, at the point of the increase in pressure drop, the methane conversion as well as the CO and H 2  selectivity values were decreasing. The reaction was quenched. The catalyst was then treated with 18% molar oxygen in nitrogen for 1-hour at 300° C. and the syngas reaction was re-initiated at a pressure of 90 psig. A pressure drop of 4.0 psi was observed immediately upon re-initiation. After 19 hours of syngas production, the pressure drop had leveled out at 2.5 psi, indicating that the syngas reactant feeds were able to continue the process of improving pressure drop and methane conversion that was initiated by the 1-hour oxygen treatment. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Pressure 
                 CH 4   
                 Selectivity 
                   
               
             
          
           
               
                   
                 Drop (psi) 
                 Conv. 
                 CO 
                 H 2   
               
               
                   
                   
               
             
          
           
               
                 After 24 hours at 45 psig 
                 3.3 
                 86.1 
                 92.9 
                 89.6 
               
               
                 After an additional 1.5 
                 6.2 
                 84.5 
                 91.1 
                 86.7 
               
               
                 hours at 90 psig 
               
               
                 Reaction quenched 
                 — 
                 — 
                 — 
                 — 
               
               
                 Upon re-initiation of syngas 
                 4.0 
                 85.5 
                 92.6 
                 88.4 
               
               
                 production after 1 hour O 2   
               
               
                 treatment 
               
               
                 19 hours after re-initiation 
                 2.5 
                 87.1 
                 94.1 
                 90.5 
               
               
                 of syngas production 
               
               
                   
               
             
          
         
       
     
     The data presented herein shows that the present invention is an improved process for the optimal production of a partial oxidation reactor. The data conforms to one of the preferred embodiments for optimizing a partial oxidation process. The optimization process comprises operating a partial oxidation reactor such that: (a) for some time, t 1 , the reactor is fed a gas comprising hydrocarbon and oxygen and produces a product comprising synthesis gas at a pressure greater than or equal to at least two times ambient pressure, and (b) for some time, t 2 , the catalyst in the reactor is regenerated using a regeneration gas, wherein the optimum operation occurs where t 1  is greater than or equal to twice t 2  and t 1  is greater than or equal to 24 hours. All other parameters are consistent with the preferred embodiments described herein. For example, the regeneration gas for the optimization process comprises one or more gases selected from the group consisting of oxygen, carbon monoxide, hydrogen and hydrocarbons. 
     It should be noted that the invention further includes an arrangement where at least a portion of any unused or produced gas from the regeneration reaction may be recycled into the syngas produced by a syngas reactor. 
     While preferred embodiments of this invention have been shown and described, modification thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. For example, while syngas and Fischer-Tropsch reactions are explicitly referred to as part of the preferred embodiments, it is clear that any partial oxidation catalyst reactions and hydrocarbon or alcohol reactions, respectively, may be substituted without departing from the spirit of the invention. Many other variations and modifications of the system and apparatus are possible and are within the scope of this invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims, which follow, the scope of which shall include all equivalents of the subject matter of the claims. In particular, unless order is explicitly recited, the recitation of steps in a claim is not intended to require that the steps be performed in any particular order, or that any step must be completed before the beginning of another step.

Technology Classification (CPC): 8