Method of enhancing an aromatization catalyst

A hydrocarbon aromatization process comprising adding a nitrogenate, an oxygenate, or both to a hydrocarbon stream to produce an enhanced hydrocarbon stream, and contacting the enhanced hydrocarbon stream with an aromatization catalyst, thereby producing an aromatization reactor effluent comprising aromatic hydrocarbons, wherein the catalyst comprises a non-acidic zeolite support, a group VIII metal, and one or more halides. Also disclosed is a hydrocarbon aromatization process comprising monitoring the presence of an oxygenate, a nitrogenate, or both in an aromatization reactor, monitoring at least one process parameter that indicates the activity of the aromatization catalyst, modifying the amount of the oxygenate, the nitrogenate, or both in the aromatization reactor, thereby affecting the parameter.

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

The disclosure generally relates to aromatization of hydrocarbons with an aromatization catalyst. Specifically, the disclosure relates to a method for activating and/or enhancing an aromatization catalyst by the addition of an oxygenate, a nitrogenate, or both.

The catalytic conversion of hydrocarbons into aromatic compounds, referred to as aromatization or reforming, is an important industrial process. The aromatization reactions may include dehydrogenation, isomerization, and hydrocracking the hydrocarbons, each of which produces specific aromatic compounds. These reactions are generally conducted in one or more aromatization reactors containing an aromatization catalyst. The catalyst may increase the reaction rates, production of desired aromatics, and/or the throughput rates for the desired aromatic compounds. Given their commercial importance, an ongoing need exists for improved methods and systems related to aromatization processes and catalysts.

SUMMARY

In one aspect, the disclosure includes a hydrocarbon aromatization process comprising adding a nitrogenate, an oxygenate, or both to a hydrocarbon stream to produce an enhanced hydrocarbon stream, and contacting the enhanced hydrocarbon stream with an aromatization catalyst, thereby producing an aromatization reactor effluent comprising aromatic hydrocarbons, wherein the catalyst comprises a non-acidic zeolite support, a group VIII metal, and one or more halides.

In another aspect, the disclosure includes a hydrocarbon aromatization process comprising adding a nitrogenate, an oxygenate, or both to a hydrocarbon stream to produce an enhanced hydrocarbon stream, to a hydrogen recycle stream to produce an enhanced recycle stream, or to both, contacting the enhanced hydrocarbon stream, enhanced recycle stream, or both with an aromatization catalyst in an aromatization reactor to produce an aromatization reactor effluent comprising aromatic hydrocarbons, and controlling the addition of the nitrogenate, the oxygenate, or both to the enhanced hydrocarbon stream, the enhanced recycle stream, or both in order to maintain one or more process parameters within a desired range.

In yet another aspect, the disclosure includes a hydrocarbon aromatization process comprising monitoring the presence of an oxygenate, a nitrogenate, or both in an aromatization reactor, monitoring at least one process parameter that indicates the activity of the aromatization catalyst, modifying the amount of the oxygenate, the nitrogenate, or both in the aromatization reactor, thereby affecting the parameter.

DETAILED DESCRIPTION

Novel methods and systems for aromatizing hydrocarbons and/or activating, preserving, and/or increasing the productivity of an aromatization catalyst are disclosed herein. Generally, it has been thought that water and impurities that can be converted to water are detrimental to aromatization catalysts, causing sintering of the platinum, thereby damaging the catalyst. Thus, the conventional wisdom is that water, oxygenates, or nitrogenates should be rigorously purged from the aromatization system. For example, it has generally been considered advantageous to substantially reduce or eliminate the presence of water and oxygen in the hydrocarbon feed to the aromatization system and/or a hydrogen recycle stream within the aromatization system when using the catalysts described herein. Specifically, water levels as low as a half part per million by volume (0.5 ppmv) in the feed and the hydrogen recycle have been desirable. Such generally accepted wisdom is evidenced by the presence of hydrotreaters and dryers in the feed stream and dryers in the hydrogen recycle stream of conventional aromatization processes. Contrary to such commonly accepted wisdom, the inventors have found that some water is beneficial in activating, preserving, and/or increasing the productivity of certain types of aromatization catalysts. Specifically, an oxygenate, a nitrogenate, or mixtures thereof may be inserted into the aromatization system at various times, in various locations, and in various manners, thereby causing a specific amount of water and/or ammonia to be present in one or more aromatization reactors during the aromatization process. In an embodiment, the presence of the specific amount of water and/or ammonia in the aromatization reactor activates or enhances the aromatization catalyst.

FIG. 1illustrates one embodiment of a catalytic reactor system100suitable for use in an aromatization system and process as described herein. In the embodiment shown inFIG. 1, the catalytic reactor system100comprises four aromatization reactors in series: reactors10,20,30, and40. However, the catalytic reactor system100may comprise any suitable number and configuration of aromatization reactors, for example one, two, three, five, six, or more reactors in series or in parallel. As aromatization reactions are highly endothermic, large temperature drops occur across the reactors10,20,30, and40. Therefore, each reactor10,20,30, and40in the series may comprise a corresponding furnace11,21,31, and41, respectively, for reheating components back to a desired temperature for maintaining a desired reaction rate. Alternatively, one or more reactors10,20,30, and40may share a common furnace where practical. All of the reactors10,20,30, and40, furnaces11,21,31, and41, and associated piping may be referred to herein as the reaction zone.

InFIG. 1, the hydrocarbon feed101is combined with recycle stream119to form combined feed stream102, which is fed into purification process80. The purification process80employs known processes to purify the hydrocarbon feed, which may include fractionation and/or treating the hydrocarbon feed. As used herein, the term “Fractionation” includes removing heavy (e.g., C9+) hydrocarbons and/or light (e.g., C5−) hydrocarbons. As used herein, the term “Treating” and “Removing” refer interchangeably to removing impurities, such as oxygenates, sulfur, and/or metals, from the hydrocarbon feed. The resulting purified feed103may be combined with a dry hydrogen recycle116to produce hydrogen rich purified feed104, which may then be combined with the oxygenate and/or the nitrogenate105to produce a reactor feed stream106. Oxygenate and/or nitrogenate may be fed to the reactor system100at one or more locations in addition to stream105or as an alternative to stream105, as will be described in more detail herein.

The reactor feed stream106is pre-heated in a first furnace11, which heats the hydrocarbons to a desired temperature, thereby producing a first reactor feed107. First reactor feed107is fed into reactor10, where the hydrocarbons are contacted with an aromatization catalyst under suitable reaction conditions (e.g., temperature and pressure) that aromatize one or more components in the feed, thereby increasing the aromatics content thereof. A first reactor effluent108comprising aromatics, unreacted feed, and other hydrocarbon compounds or byproducts are recovered from the first reactor10.

The first reactor effluent108is then pre-heated in the second furnace21, which heats the hydrocarbons to a desired temperature, thereby producing a second reactor feed109. Second reactor feed109is then fed into reactor20, where the hydrocarbons are contacted with an aromatization catalyst under suitable reaction conditions for aromatizing one or more components in the feed to increase the aromatics content thereof. A second reactor effluent110comprising aromatics, unreacted feed, and other hydrocarbon compounds or byproducts are recovered from the second reactor20.

The second reactor effluent110is then pre-heated in the third furnace31, which heats the hydrocarbons to a desired temperature, thereby producing a third reactor feed111. Third reactor feed111is then fed into reactor30, where the hydrocarbons are contacted with an aromatization catalyst under suitable reaction conditions for aromatizing one or more components in the feed to increase the aromatics content thereof. A third reactor effluent112comprising aromatics, unreacted feed, and other hydrocarbon compounds or byproducts is recovered from the third reactor30.

The third reactor effluent112is then pre-heated in the fourth furnace41, which heats the hydrocarbons to a desired temperature, thereby producing a fourth reactor feed113. Fourth reactor feed113is then fed into reactor40, where the hydrocarbons are contacted with an aromatization catalyst under suitable reaction conditions for aromatizing one or more components in the feed to increase the aromatics content thereof. A fourth reactor effluent114comprising aromatics, unreacted feed, and other hydrocarbon compounds or byproducts is recovered from the fourth reactor40.

The fourth reactor effluent114is then fed into a hydrogen separation process50that uses a number of known processes to separate a hydrogen recycle115from a reformate117. The reformate117comprises the aromatization reaction products from reactors10,20,30, and40(e.g., aromatic and non-aromatic compounds) in addition to any unreacted feed and other hydrocarbon compounds or byproducts. The hydrogen recycle115may be dried in a dryer60, thereby forming dry hydrogen recycle116, which may then be recycled into the purified feed103. The reformate117goes to a purification-extraction process70, which separates the raffinate recycle119and reactor byproducts (not shown) from the aromatics118. The hydrogen separation processes50and the purification-extraction processes70are well known in the art and are described in numerous patents, including U.S. Pat. No. 5,401,386 to Morrison et al. entitled “Reforming Process for Producing High-Purity Benzene”, U.S. Pat. No. 5,877,367 to Witte entitled “Dehydrocyclization Process with Downstream Dimethylbenzene Removal”, and U.S. Pat. No. 6,004,452 to Ash et al. entitled “Process for Converting Hydrocarbon Feed to High Purity Benzene and High Purity Paraxylene”, each of which is incorporated herein by reference as if reproduced in its entirety. The raffinate recycle119is then recycled into the feed101and the aromatics118are sold or otherwise used as desired. For the sake of simplicity,FIG. 1does not illustrate the byproduct streams that are removed from the catalytic reactor system100at various points throughout the system. However, persons of ordinary skill in the art are aware of the composition and location of such byproduct streams. Also, whileFIG. 1shows the oxygenate and/or nitrogenate105being added to hydrogen rich purified feed104, persons of ordinary skill in the art will appreciate that the oxygenate and/or nitrogenate may be added to any of process streams101,102,103,104,106,107,108,109,110,111,112,113,114,115,116,117,119, or various combinations thereof.

In various embodiments, the catalytic reactor system described herein may comprise a fixed catalyst bed system, a moving catalyst bed system, a fluidized catalyst bed system, or combinations thereof. Such reactor systems may be batch or continuous. In an embodiment, the catalytic reactor system is a fixed bed system comprising one or more fixed bed reactors. In a fixed bed system, the feed may be preheated in furnace tubes and passed into at least one reactor that contains a fixed bed of the catalyst. The flow of the feed can be upward, downward, or radially through the reactor. In various embodiments, the catalytic reactor system described herein may be operated as an adiabatic catalytic reactor system or an isothermal catalytic reactor system. As used herein, the term “catalytic reactor” and “reactor” refer interchangeably to the reactor vessel, reactor internals, and associated processing equipment, including but not limited to the catalyst, inert packing materials, scallops, flow distributors, center pipes, reactor ports, catalyst transfer and distribution system, furnaces and other heating devices, heat transfer equipment, and piping.

In an embodiment, the catalytic reactor system is an aromatization reactor system comprising at least one aromatization reactor and its corresponding processing equipment. As used herein, the terms “aromatization,” “aromatizing,” and “reforming” refer to the treatment of a hydrocarbon feed to provide an aromatics enriched product, which in one embodiment is a product whose aromatics content is greater than that of the feed. Typically, one or more components of the feed undergo one or more reforming reactions to produce aromatics. Some of the hydrocarbon reactions that occur during the aromatization operation include the dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, dehydrocyclization of acyclic hydrocarbons to aromatics, or combinations thereof. A number of other reactions also occur, including the dealkylation of alkylbenzenes, isomerization of paraffins, hydrocracking reactions that produce light gaseous hydrocarbons, e.g., methane, ethane, propane and butane, or combinations thereof.

The aromatization reaction occurs under process conditions that thermodynamically favor the dehydrocyclization reaction and limit undesirable hydrocracking reactions. The pressures may be from about 0 pounds per square inch gauge (psig) to about 500 psig, alternatively from about 25 psig to about 300 psig. The molar ratio of hydrogen-to-hydrocarbons may be from about 0.1:1 to about 20:1, alternatively from about 1:1 to about 6:1. The operating temperatures include reactor inlet temperatures from about 700° F. to about 1050° F., alternatively from about 900° F. to about 1000° F. Finally, the liquid hourly space velocity (LHSV) for the hydrocarbon feed over the aromatization catalyst may be from about 0.1 to about 10 hr−1, alternatively from about 0.5 to about 2.5 hr−1.

The composition of the feed is a consideration when designing catalytic aromatization systems. In an embodiment, the hydrocarbon feed comprises non-aromatic hydrocarbons containing at least six carbon atoms. The feed to the aromatization system is a mixture of hydrocarbons comprising C6to C8hydrocarbons containing up to about 10 wt % and alternatively up to about 15 wt % of C5and lighter hydrocarbons (C5−) and containing up to about 10 wt % of C9and heavier hydrocarbons (C9+). Such low levels of C9+and C5−hydrocarbons maximize the yield of high value aromatics. In some embodiments, an optimal hydrocarbon feed maximizes the percentage of C6hydrocarbons. Such a feed can be achieved by separating a hydrocarbon feedstock such as a fill range naphtha into a light hydrocarbon feed fraction and a heavy hydrocarbon feed fraction, and using the light fraction.

In another embodiment, the feed is a naphtha feed. The naphtha feed may be a light hydrocarbon, with a boiling range of about 70° F. to about 450° F. The naphtha feed may contain aliphatic, naphthenic, or paraffinic hydrocarbons. These aliphatic and naphthenic hydrocarbons are converted, at least in part, into aromatics in the aromatization reactor system. While catalytic aromatization typically refers to the conversion of naphtha, other feedstocks can be treated as well to provide an aromatics enriched product. Therefore, while the conversion of naphtha is one embodiment, the present disclosure can be useful for activating catalysts for the conversion or aromatization of a variety of feedstocks such as paraffin hydrocarbons, olefin hydrocarbons, acetylene hydrocarbons, cyclic paraffin hydrocarbons, cyclic olefin hydrocarbons, and mixtures thereof, and particularly saturated hydrocarbons.

In an embodiment, the feedstock is substantially free of sulfur, metals, and other known poisons for aromatization catalysts, and is initially substantially free of oxygenates and nitrogenates. If present, such poisons can be removed using methods known to those skilled in the art. In some embodiments, the feed can be purified by first using conventional hydrofining techniques, then using sorbents to remove the remaining poisons. Such hydrofining techniques and sorbents are included in the purification process described below.

In an embodiment, an oxygenate, a nitrogenate, or both may be added to one or more process streams and/or components in the catalytic reactor system100. As used herein, the term “oxygenate” refers to water or any chemical compound that forms water under catalytic aromatization conditions, such as oxygen, oxygen-containing compounds, hydrogen peroxide, alcohols, ketones, esters, ethers, carbon dioxide, aldehydes, carboxylic acids, lactones, ozone, carbon monoxide or combinations thereof. In one embodiment, water and/or steam is used as the oxygenate. In another embodiment, oxygen may be used as the oxygenate, wherein such oxygen converts to water in situ within one or more aromatization reactors under typical aromatization conditions or within one or more hydrofining catalyst or sorbent beds under normal hydrofining conditions. Furthermore, the oxygenate may be any alcohol-containing compound. Specific examples of suitable alcohol-containing compounds are methanol, ethanol, propanol, isopropanol, butanol, t-butanol, pentanol, amyl alcohol, hexanol, cyclohexanol, phenol, or combinations thereof.

As used herein, the term “nitrogenate” refers to ammonia or any chemical compound that forms ammonia under catalytic aromatization conditions such as nitrogen, nitrogen-containing compounds, alkyl amines, aromatic amines, pyridines, pyridazines, pyrimidines, pyrazines, triazines, heterocyclic N-oxides, pyrroles, pyrazoles, imadazoles, triazoles, nitriles, amides, ureas, imides, nitro compounds, nitroso compounds, or combinations thereof. While not wanting to be limited by theory, it is believed that the ammonia will improve catalyst activity in much the same way as the water. Additionally, all the methods of addition and control for oxygenates described herein can also be fully applied additionally or alternatively to the methods of addition and control for nitrogenates.

Persons of ordinary skill in the art will appreciate that any of the oxygenates, nitrogenates, or mixtures thereof described herein may be used alone, in combination, or further combined to produce other suitable oxygenates or nitrogenates. In some embodiments, the oxygenate and nitrogenate may be contained within the same bifunctional compound. The oxygenate and/or nitrogenate may be added in any suitable physical phase such as a gas, liquid, or combinations thereof. The oxygenate and/or nitrogenate may be added to one or more process streams and/or components via any suitable means for their addition, for example a pump, injector, sparger, bubbler, or the like. The oxygenate and/or nitrogenate may be introduced as a blend with a carrier. In some embodiments, the carrier is hydrogen, a hydrocarbon, nitrogen, a noble gas, or mixtures thereof. In a preferred embodiment, the carrier is hydrogen.

The oxygenate and/or nitrogenate may be added at various locations within the aromatization system described herein. For example, the oxygenate and/or nitrogenate may be added to one or more process streams in the catalytic reactor system100, to one or more equipment components or vessels of the catalytic reactor system100, or combinations thereof. In an embodiment, the oxygenate and/or nitrogenate may be added at one or more locations within a reaction zone defined by the reactor system100, wherein the reaction zone comprises process flow lines, equipment, and/or vessels wherein reactants are undergoing an aromatization reaction. In one embodiment, the oxygenate and/or nitrogenate is added between the purification process80and the first furnace11, either before the addition of the dry hydrogen recycle116, or after the addition of the dry hydrogen recycle116as depicted inFIG. 1. Alternatively, the oxygenate and/or nitrogenate may be added within the purification process80. However, it is also contemplated that the oxygenate and/or nitrogenate can be added at various other locations within the catalytic reactor system100. For example, the oxygenate and/or nitrogenate can be added to the feed101, the combined feed102, the first reactor feed107, the first reactor effluent108, the second reactor feed109, the second reactor effluent110, the third reactor feed111, the third reactor effluent112, the fourth reactor feed113, or combinations thereof. In addition, the oxygenate and/or nitrogenate could be added to the fourth reactor effluent114, the hydrogen recycle115, the dry hydrogen recycle116, the reformate117, the raffinate recycle119, or combinations thereof. Furthermore, the oxygenate and/or nitrogenate can be added to any combination of the aforementioned streams, directly to any of the reactors10,20,30, or40, directly to the furnaces11,21,31,41, or combinations thereof. Likewise, the oxygenate and/or nitrogenate can be added directly to any other process equipment or component of the catalytic reactor system100such as a pump, value, port, tee, manifold, etc. Finally, it is possible to add the oxygenate and/or nitrogenate to any process equipment or component upstream of the catalytic reactor system100such as a tank, pump, value, port, tee, manifold, etc. that supplies the feed101to the catalytic reactor system.

The oxygenate and/or nitrogenate may be added to the aromatization process at any time during the service life of the aromatization catalyst. As used herein, the term “time” may refer to the point in the service life of the aromatization catalyst at which the oxygenate and/or nitrogenate is added to the catalyst. For example, the oxygenate and/or nitrogenate may be added at the beginning of the life of the aromatization catalyst, e.g. when or soon after a new batch of catalyst is brought online. Alternatively, the oxygenate and/or nitrogenate may be added to the catalyst close to or at the end of the catalyst run. The end of the catalyst run may be determined using any of the methods described herein and known in the art, such as a time-based lifetime such as 1,000 days online, or a temperature-based lifetime exceeds a defined value, e.g., 1000° F., which often is based upon process limitations such as reactor metallurgy. Further, the oxygenate and/or nitrogenate may be added continuously during the lifetime of the catalyst, e.g. from when the catalyst is brought online to when the catalyst is taken offline. Finally, the oxygenate and/or nitrogenate may be added to the aromatization catalyst at any combination of these times, such as at the beginning and at the end of a catalyst lifetime, but not continuously.

In addition, the oxygenate and/or nitrogenate may be added to the aromatization process in any suitable manner. As used herein, the term “manner” may refer to the addition profile of the oxygenate and/or nitrogenate, for example how the addition of the oxygenate and/or nitrogenate to the catalyst changes over time.FIGS. 2A,2B,2C, and2D illustrate four manners in which the oxygenate and/or nitrogenate may be added to the aromatization catalyst. Specifically,FIG. 2Aillustrates the case where the oxygenate and/or nitrogenate is added as a constant-level step increase. Such would be the case when the oxygenate and/or nitrogenate is increased from about 2 ppmv to about 10 ppmv during the catalyst life. The step may be an increase or a decrease in oxygenate and/or nitrogenate levels.FIG. 2Billustrates the case where the amount of oxygenate and/or nitrogenate is increased a step change and then at a steady rate (e.g., constant slope) over time. Such would be the case when the oxygenate and/or nitrogenate is increased from 0 to 2 ppmv at a start point, and thereafter at a rate of 0.2 ppmv/day. In such an embodiment, the increase in oxygenate and/or nitrogenate at a steady rate may be preceded by an initial step, as shown inFIG. 2B, or may lack the initial step (i.e., may start at 0 ppmv).FIG. 2Cillustrates the case where the amount of oxygenate and/or nitrogenate is decreased at a steady rate over time. Such would be the case when the oxygenate and/or nitrogenate is decreased at a rate of 0.2 ppmv/day. In such an embodiment, the increase in oxygenate and/or nitrogenate may be preceded by an initial step, as shown inFIG. 2C, or may lack the initial step, such as when it is desirable to reduce the oxygenate and/or nitrogenate levels.FIG. 2Dillustrates the case where the oxygenate and/or nitrogenate is added as a pulse. Such would be the case when the oxygenate and/or nitrogenate is increased from about 2 ppmv to about 10 ppmv for two days, then returned to 2 ppmv. The oxygenate and/or nitrogenate may be added in multiple pulses, if desired.

While the addition profiles illustrated inFIGS. 2A,2B,2C, and2D are shown near the end of the catalyst life, those addition profiles may be implemented at any point during the catalyst life. Specifically, the addition profiles illustrated inFIGS. 2A,2B,2C, and2D may be implemented at the beginning of the catalyst life, shortly after the beginning of the catalyst life, at any point during the catalyst life, or at the end of the catalyst life. In addition, the oxygenate and/or nitrogenate may be added in any combinations of the above manners, such as two pulses followed by an increasing amount of oxygenate and/or nitrogenate at a constant rate.

The addition of the oxygenate and/or nitrogenate to the aromatization process may be a function of any of the aforementioned locations, times, and/or manners. For example, the sole consideration in adding the oxygenate and/or nitrogenate to the aromatization process may be the time when the oxygenate and/or nitrogenate is added to the aromatization process, the location where the oxygenate and/or nitrogenate is added to the aromatization process, or the manner in which the oxygenate and/or nitrogenate is added to the aromatization process. However, the oxygenate and/or nitrogenate will typically be added to the aromatization process using a combination of these considerations. For example, the oxygenate and/or nitrogenate may be added in a combination of times and locations irrespective of manner, times and manners irrespective of locations, or locations and manners irrespective of times. Alternatively, the time, location, and manner may all be considerations when adding the oxygenate and/or nitrogenate to the aromatization system.

In an embodiment, the addition of oxygenate and/or nitrogenate to the catalytic reactor system100as described herein functions to activate the aromatization catalyst, wherein such catalyst might otherwise be inactive or display insufficient activity in the absence of the addition of oxygenate. For example, certain types of aromatization catalysts such as L-zeolite supported platinum containing one or more halogens such as F and/or Cl may not activate or may have inadequate activity where the feed to the reactors, e.g.,10,20,30,40, is substantially free of oxygenate, for example containing less than about 1 ppmv total oxygenate and/or nitrogenate, alternatively less than about 0.5 ppmv total oxygenate and/or nitrogenate in the hydrogen recycle stream115. Thus, in some embodiments, the addition of oxygenate and/or nitrogenate as described herein may serve to activate and maintain such catalysts resulting in desirable conversion rates of reactants to aromatics as well as other benefits such as improved fouling characteristics and catalyst operating life as described herein. Thus, catalyst activity or activation may be controlled with addition or removal of an oxygenate and/or nitrogenate. In an additional embodiment, a nitrogenate may similarly be added to the catalytic reactor system100and function to activate the aromatization catalyst, wherein such catalyst might otherwise be inactive or display insufficient activity in the absence of the addition of nitrogenate.

In an embodiment, the addition of the oxygenate and/or nitrogenate increases the useful life of the aromatization catalyst. As used herein, the term “useful life” may refer to the time between when the aromatization catalyst is placed in service, and when one or more parameters indicate that the aromatization catalyst should be removed from service (e.g., reaching a Teqmaximum or limit). While the time, location, and manner of oxygenate and/or nitrogenate addition can affect the useful life of the aromatization catalyst, in embodiments the addition of the oxygenate and/or nitrogenate can increase the useful life of the catalyst by at least about 5 percent, at least about 15 percent, or at least about 25 percent. In other embodiments, the addition of the oxygenate and/or nitrogenate can increase the useful life of the catalyst by at least about 50 days, at least about 150 days, or at least about 250 days.

In an embodiment, the addition of the oxygenate and/or nitrogenate increases the selectivity and/or productivity of the aromatization catalyst. As used herein, “selectivity” may refer to the ratio of aromatic products produced by the aromatization catalyst for a given set of reagents. As used herein, “productivity” may refer to the amount of aromatic products produced by the aromatization catalyst per unit of feed and unit time. When the oxygenate and/or nitrogenate is added to the aromatization catalyst, an increased amount of one or more aromatic compounds may be produced. Specifically, the addition of the oxygenate and/or nitrogenate to the aromatization catalyst may increase the amount of aromatics in the effluent by at least about 20 percent, at least about 10 percent, at least about 5 percent, or at least about 1 percent over pre-addition levels. Also, the addition of the oxygenate and/or nitrogenate to the aromatization catalyst may increase the catalyst selectivity to desirable aromatics, such as benzene. In an embodiment, the addition of the oxygenate and/or nitrogenate to the aromatization catalyst may increase the catalyst selectivity to desirable aromatics by at least about 20 percent, at least about 10 percent, at least about 5 percent, or at least about 1 percent over pre-addition levels. In a specific example, benzene production may be increased from about 40 weight percent to about 48 weight percent of the effluent, without decreasing the production of any of the other aromatics. Such would indicate an increase in catalyst production and selectivity. In some embodiments, such effects may be independent of each other such as when benzene production is increased with no increase in overall aromatic production.

In an embodiment, the methods described herein may yield alternative benefits. For example, if the aromatic production level is maintained at a specified level, then the reactors may be operated at lower temperatures, which results in a longer catalyst life. Alternatively, if the reactor temperatures are maintained at a specified level, then the space velocity within the reactors may be increased, which produces additional amounts of aromatic products. Finally, the methods described herein may yield additional advantages not specifically discussed herein.

In an embodiment, the effects of the addition of the oxygenate and/or nitrogenate are fast and reversible. For example, when the oxygenate and/or nitrogenate is added to the aromatization catalyst, the oxygenate and/or nitrogenate begins to affect the aromatization catalyst (e.g., increases activity) within about 100 hours, within about 50 hours, within about 10 hours, or within about 1 hour. Similarly, once the oxygenate and/or nitrogenate is removed from the aromatization catalyst, the aromatization catalyst may revert to the catalyst activity, aromatics yield, or aromatics selectivity seen prior to the addition of the oxygenate and/or nitrogenate within about 500 hours, within about 100 hours, within about 50 hours, or within about 10 hours.

In an embodiment, the existing oxygenate and/or nitrogenate content of a stream to which the oxygenate and/or nitrogenate is to be added is measured and/or adjusted prior to addition of the oxygenate and/or nitrogenate. For example and with reference toFIG. 1, one or more feed streams such as hydrocarbon feed101, recycle stream119, combined feed stream102, hydrogen recycle116, or combinations thereof may be measured for oxygenate and/or nitrogenate content and the oxygenate and/or nitrogenate content thereof adjusted prior to the addition of the oxygenate and/or nitrogenate. Likewise, the same streams may be measured for nitrogenate content and/or the nitrogenate content thereof adjusted prior to the addition of the nitrogenate. Generally, a raw or untreated feed stream such as hydrocarbon feed stream101may contain some amount of oxygenate or nitrogenate when it enters the catalytic reaction system described herein. In addition, depending on the plant configuration, the duration of feed storage and weather conditions, the feed may absorb oxygenates or nitrogenates from the air. In order to accurately control the amount of oxygenate or nitrogenates entering one or more of the aromatization reactors (e.g., reactors10,20,30,40), the amount of oxygenate and/or nitrogenate in one or more feed streams to the reactors may be measured, adjusted, or both.

In an embodiment, the oxygenate and/or nitrogenate content of a given stream such as a feed stream may be measured, for example with a real-time, in-line analyzer. In response to such measurement, the oxygenate and/or nitrogenate content of the stream may be adjusted by treating and/or adding oxygenate and/or nitrogenate to the stream to obtain a desired amount of oxygenate and/or nitrogenate therein. In an embodiment, a control loop links the analyzer to a treater and an oxygenate and/or nitrogenate injector such that the amount of oxygenate and/or nitrogenate in one or more streams is controlled in response to an oxygenate and/or nitrogenate set point for such streams. In an embodiment the measuring and/or adjusting of the oxygenate and/or nitrogenate content and associated equipment such as treaters and/or chemical injectors are included as part of the purification process80. The oxygenate and/or nitrogenate treaters vary based on the type and amounts of oxygenate and/or nitrogenate. In embodiments where the oxygenate comprises water, beds of sorbent materials may be used. These sorbent beds are commonly known as driers. In embodiments where the oxygenate comprises oxygen, the use of treaters which convert the oxygen to water can be used in combination with driers. In further embodiments where the nitrogenate comprises a basic chemical, beds of sorbent materials may be used.

In an embodiment, one or more streams such as hydrocarbon feed101, recycle stream119, combined feed stream102, hydrogen recycle116, or combinations thereof are treated prior to the addition of oxygenate and/or nitrogenate thereto. In such an embodiment, measuring the oxygenate and/or nitrogenate content of the streams before such treated may optionally be omitted. If there is no apparatus for readily measuring the oxygenate and/or nitrogenate content of the feed, then it is difficult to reliably maintain a desired level in the aromatization reactors.

Treating one or more streams prior to the addition of the oxygenate and/or nitrogenate may aid in the overall control of the amount of water and/or ammonia in one or more streams entering the aromatization reactors by removing variability in the oxygenate and/or nitrogenate content in such streams. Treating such streams provides a consistent, baseline amount of oxygenate and/or nitrogenate in such streams for the addition of oxygenate and/or nitrogenate to form an oxygenated stream such as reactor feed stream106. When the reactor feed is sufficiently free of oxygenates and/or nitrogenates, precise quantities of the oxygenate and/or nitrogenates can be added to the reactor feeds such that the amount of oxygenate and/or nitrogenates in the reactors may be reliably maintained. In an embodiment, the purification process80may include a hydrocarbon dryer that dries the hydrocarbon feed (e.g., streams101,119, and/or102) to a suitable water level. In other embodiments, the purification process80may include a reduced copper bed (such as R3-15 catalyst available from BASF) or a bed of triethyl aluminum on silica for use in removing oxygenates. In still further embodiments, the reduced copper bed (such as BASF R3-15 catalyst) or a bed of triethyl aluminum on silica is used in combination with the hydrocarbon dryer. Similarly, the dryer60can be used to dry the hydrogen recycle and/or other process streams such as101,119, and/or102to a suitable water level. In an embodiment a suitable oxygenate level in one or more streams such as hydrocarbon feed101, recycle stream119, combined feed stream102, hydrogen recycle116, is such that the combination thereof produces less than about 1 ppmv, alternatively less than about 0.5 ppmv, or alternatively less than about 0.1 ppmv of water in the untreated hydrogen recycle stream115. In an embodiment, one or more streams fed to the aromatization reactors such as hydrocarbon feed101, recycle stream119, combined feed stream102, hydrogen recycle116, or combinations thereof are substantially free of water following drying thereof. In an embodiment, the precise amount of the oxygenate and/or the nitrogenate may be added by partially or fully bypassing such treatment processes. Alternatively, the precise amount of the oxygenate and/or the nitrogenate may be added by partially or fully running the hydrogen recycle stream through a wet, e.g. spent, mole sieve bed.

In one embodiment, the amount of oxygenate added to the aromatization process may be regulated to control the water content in the hydrogen recycle stream115. Specifically, the amount of oxygenate present in one or more of the reactors10,20,30, and40may be controlled by addition of the oxygenate as described and monitoring the amount of water exiting the last reactor, for example the amount of water in effluent stream114, the hydrogen recycle115(upstream of dryer60), or both. Having a sufficient water level present in the hydrogen recycle115indicates that sufficient oxygenate is present in the reactors10,20,30, and40so that the catalyst is activated as described herein. However, the water level in the hydrogen recycle stream115should also be limited because excess water can decrease the useful life of the catalyst. Specifically, the upper limit of water addition should be determined based on the long-term catalyst activity. In various embodiments, the amount of oxygenate added to the catalytic reactor system100is controlled such that the hydrogen recycle stream115contains from about 1 ppmv to about 100 ppmv, alternatively from about 1.5 ppmv to about 10 ppmv, or alternatively from about 2 ppmv to about 4 ppmv of water. In related embodiments, the amount of nitrogenate added to the aromatization process may be regulated to control the ammonia content in the hydrogen recycle stream115in many of the same ways used for the oxygenate.

In another embodiment, the amount of oxygenate and/or nitrogenate added to the aromatization process may be regulated to control the catalyst activity or to preserve the useful life of an aromatization catalyst. The catalyst activity can be measured by a number of methods including the endotherm, or ΔT, across one or more reactors or alternatively Teq. Measurements of activity such as reactor temperature, inlet temperature, yield-adjusted temperature, fouling rate, etc. compare activities at a given conversion of reactants in the reaction zone. As used herein, the term “yield-adjusted temperature” or “Tyld” refers to the average catalyst bed temperature in a lab-scale reactor system which has been adjusted to a specified yield (conversion) level. As used herein, the term “Teq” refers to the equivalent reactor weighted average inlet temperature (WAIT) that would be required to run a catalytic aromatization reaction to a specified conversion at a standard set of reactor operating conditions such as hydrocarbon feed rate, recycle hydrogen-to-hydrocarbon molar ratio, average reactor pressure, and concentration of feed-convertible components. Teqcan either be established by running at standard conditions or by using a suitable correlation to estimate Teqbased on measured values of reactor variables. As used herein Teqparameters include running the catalytic aromatization reaction to about 88 wt % conversion of C6convertibles at a hydrogen-to-hydrocarbon ratio of about 4.0, a space velocity of about 1.2 hr−1, in a six adiabatic reactor train with the inlet pressure to the last reactor at about 50 psig, with a feed composition comprising a C6fraction greater or equal to 90 wt %; a C5fraction less than or equal to 5 wt %; and a C7+fraction less than or equal to 5 wt %. As used herein, the conversion of C6convertibles refers to the conversion of C6molecules with one or fewer branches into aromatic compounds. In various embodiments, the amount of oxygenate and/or nitrogenate added to the catalytic reactor system100is regulated such that the Teqis from about 900° F. to about 1000° F., from about 910° F. to about 960° F., or from about 920° F. to about 940° F. Furthermore, because any increase in catalyst activity is evidenced by a decrease in Teq, the increase in catalyst activity can also be measured as a percentage decrease in the Teqof an equivalent reactor system running an equivalent dry hydrocarbon feed. In various embodiments, the amount of oxygenate added to the catalytic reactor system100is controlled such that the Teqis from about 0 percent to about 25 percent, alternatively from about 0.1 percent to about 10 percent, or alternatively from about 1 percent to about 5 percent less than the Teqof an equivalent reactor system running an equivalent substantially dry hydrocarbon feed, for example resulting in less than about 1 ppmv water in the hydrogen recycle stream115, alternatively less than about 0.5 ppmv total water. In related embodiments, the amount of nitrogenate added to the aromatization process may be regulated to control the catalyst activity in many of the same ways used for the oxygenate.

Furthermore, the use of the oxygenate and/or nitrogenate in the catalytic reactor system may have a beneficial effect on the fouling rate of the catalyst. Catalysts may have a useful life beyond which it is no longer economically advantageous to use the catalyst. A commercially valuable catalyst will exhibit a relatively low and stable fouling rate. It is contemplated that the use of the oxygenate and/or nitrogenate as described herein increases and maintains the potential life of the catalyst when operating under conditions substantially free of these chemicals, for example, containing less than about 1 ppmv total oxygenate in stream107alternatively less than about 0.5 ppmv total oxygenate in stream107.

Various types of catalysts may be used with the catalytic reactor system described herein. In an embodiment, the catalyst is a non-acidic catalyst that comprises a non-acidic zeolite support, a group VIII metal, and one or more halides. Suitable halides include chloride, fluoride, bromide, iodide, or combinations thereof. Suitable Group VIII metals include iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Examples of catalysts suitable for use with the catalytic reactor system described herein are the AROMAX® brand of catalysts available from the Chevron Phillips Chemical Company of The Woodlands, Tex., and those discussed in U.S. Pat. No. 6,812,180 to Fukunaga entitled “Method for Preparing Catalyst”, and U.S. Pat. No. 7,153,801 to Wu entitled “Aromatization Catalyst and Methods of Making and Using Same”, each of which is incorporated herein by reference as if reproduced in their entirety.

Supports for aromatization catalysts can generally include any inorganic oxide. These inorganic oxides include bound large pore aluminosilicates (zeolites), amorphous inorganic oxides and mixtures thereof. Large pore aluminosilicates include, but are not limited to, L-zeolite, Y-zeolite, mordenite, omega zeolite, beta zeolite and the like. Amorphous inorganic oxides include, but are not limited to, aluminum oxide, silicon oxide, and titania. Suitable bonding agents for the inorganic oxides include, but are not limited to, silica, alumina, clays, titania, and magnesium oxide.

Zeolite materials, both natural and synthetic, are known to have catalytic properties for many hydrocarbon processes. Zeolites typically are ordered porous crystalline aluminosilicates having structure with cavities and channels interconnected by channels. The cavities and channels throughout the crystalline material generally can be of a size to allow selective separation of hydrocarbons.

The term “zeolite” generally refers to a particular group of hydrated, crystalline metal aluminosilicates. These zeolites exhibit a network of SiO4and AlO4tetrahedra in which aluminum and silicon atoms are crosslinked in a three-dimensional framework by sharing oxygen atoms. In the framework, the ratio of oxygen atoms to the total of aluminum and silicon atoms may be equal to 2. The framework exhibits a negative electrovalence that typically is balanced by the inclusion of cations within the crystal such as metals, alkali metals, alkaline earth metals, or hydrogen.

L-type zeolite catalysts are a sub-group of zeolitic catalysts. Typical L-type zeolites contain mole ratios of oxides in accordance with the following formula:
M2/nO.Al2O3.xSiO2.yH2O
wherein “M” designates at least one exchangeable cation such as barium, calcium, cerium, lithium, magnesium, potassium, sodium, strontium, and zinc as well as non-metallic cations like hydronium and ammonium ions which may be replaced by other exchangeable cations without causing a substantial alteration of the basic crystal structure of the L-type zeolite. The “n” in the formula represents the valence of “M”, “x” is 2 or greater; and “y” is the number of water molecules contained in the channels or interconnected voids with the zeolite.

Bound potassium L-type zeolites, or KL zeolites, have been found to be particularly desirable. The term “KL zeolite” as used herein refers to L-type zeolites in which the principal cation M incorporated in the zeolite is potassium. A KL zeolite may be cation-exchanged or impregnated with another metal and one or more halides to produce a platinum-impregnated, halided zeolite or a KL supported Pt-halide zeolite catalyst.

In an embodiment, the Group VIII metal is platinum. The platinum and optionally one or more halides may be added to the zeolite support by any suitable method, for example via impregnation with a solution of a platinum-containing compound and one or more halide-containing compounds. For example, the platinum-containing compound can be any decomposable platinum-containing compound. Examples of such compounds include, but are not limited to, ammonium tetrachloroplatinate, chloroplatinic acid, diammineplatinum (II) nitrite, bis-(ethylenediamine)platinum (II) chloride, platinum (II) acetylacetonate, dichlorodiammine platinum, platinum (II) chloride, tetraammineplatinum (II) hydroxide, tetraammineplatinum chloride, and tetraammineplatinum (II) nitrate.

In an embodiment, the catalyst is a large pore zeolite support with a platinum-containing compound and at least one organic ammonium halide compound. The organic ammonium halide compound may comprise one or more compounds represented by the formula N(R)4X, where X is a halide and where R represents a hydrogen or a substituted or unsubstituted carbon chain molecule having 1-20 carbons wherein each R may be the same or different. In an embodiment, R is selected from the group consisting of methyl, ethyl, propyl, butyl, and combinations thereof, more specifically methyl. Examples of suitable organic ammonium compound is represented by the formula N(R)4X include ammonium chloride, ammonium fluoride, and tetraalkylammonium halides such as tetramethylammonium chloride, tetramethylammonium fluoride, tetraethylammonium chloride, tetraethylammonium fluoride, tetrapropylammonium chloride, tetrapropylammonium fluoride, tetrabutylammonium chloride, tetrabutylammonium fluoride, methyltriethylammonium chloride, methyltriethylammonium fluoride, and combinations thereof.

In an embodiment, the organic ammonium halide compound comprises at least one acid halide and at least one ammonium hydroxide represented by the formula N(R′)4OH, where R′ is hydrogen or a substituted or unsubstituted carbon chain molecule having 1-20 carbon atoms wherein each R′ may be the same or different. In an embodiment, R′ is selected from the group consisting of methyl, ethyl, propyl, butyl, and combinations thereof, more specifically methyl. Examples of suitable ammonium hydroxide represented by the formula N(R′)4OH include ammonium hydroxide, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and combinations thereof. Examples of suitable acid halides include HCl, HF, HBr, HI, or combinations thereof.

In an embodiment the organic ammonium halide compound comprises (a) a compound represented by the formula N(R)4X, where X is a halide and where R represents a hydrogen or a substituted or unsubstituted carbon chain molecule having 1-20 carbons wherein each R may be the same or different and (b) at least one acid halide and at least one ammonium hydroxide represented by the formula N(R′)4OH, where R′ is hydrogen or a substituted or unsubstituted carbon chain molecule having 1-20 carbon atoms wherein each R′ may be the same or different.

The halide-containing compound may further comprise an ammonium halide such as ammonium chloride, ammonium fluoride, or both in various combinations with the organic ammonium halide compounds described previously. More specifically, ammonium chloride, ammonium fluoride, or both may be used with (a) as described previously, a compound represented by the formula N(R)4X, where X is a halide and where R represents a hydrogen or a substituted or unsubstituted carbon chain molecule having 1-20 carbons wherein each R may be the same or different and/or (b) as described previously, at least one acid halide and at least one organic ammonium hydroxide represented by the formula N(R′)4OH, where R′ is a substituted or unsubstituted carbon chain molecule having 1-20 carbon atoms wherein each R′ may be the same or different. For example, a first fluoride- or chloride-containing compound can be introduced as a tetraalkylammonium halide with a second fluoride- or chloride-containing compound introduced as an ammonium halide. In an embodiment, tetraalkylammonium chloride is used with ammonium fluoride.

EXAMPLES

Having described the methods for activating and enhancing the aromatization catalyst with an oxygenate and/or nitrogenate and controlling the amounts thereof by monitoring process parameters, the following examples are given as particular embodiments of the method disclosed and to demonstrate the practice and advantages thereof. For the following examples, water or oxygen was injected into the aromatization feed prior to the first reactor as shown inFIG. 1and described herein, unless otherwise described in the examples. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.

In a first example, the water in the recycle hydrogen was maintained below about 1 ppmv. The experiment was conducted in a series of 6 adiabatic reactors operating at a liquid hourly space velocity of about 0.8 to about 1.2 hr−1, a hydrogen-to-hydrocarbon ratio of about 3 to about 6, and a sixth reactor inlet pressure of about 50 psig. Each individual reactor was a radial flow reactor with an internal diameter of between about 3 and about 10 feet. The feed was treated prior to use such that less than about 1.0 ppmv of oxygenates were present. Thus, this configuration does not contain any added oxygenate and/or nitrogenate and can be used as a reference.

The process of example 1 was repeated except that the water in the recycle hydrogen was varied from about 2 to about 9 ppmv through the addition of water to streams107or109ofFIG. 1.FIGS. 3A and 3Billustrate the effect that the presence of water as an oxygenate has on the Teqfor the catalyst activity in examples 1 and 2. Specifically,FIG. 3Adepicts the amount of water present in parts per million in the hydrogen recycle gas stream115for example 1 and example 2, whereasFIG. 3Bdepicts the Teqin degrees Fahrenheit for the same two examples. The hollow diamonds inFIGS. 3A and 3Bare data from Example 1, run under substantially dry conditions, that is without the addition of any water to the system. The solid squares inFIGS. 3A and 3Bare data from Example 2, the experiment in which the oxygenate was added to the system prior to the first aromatization reactor. As can be seen inFIGS. 3A and 3B, when the system was run under substantially dry conditions, the catalyst activity continually decreased, as represented by a continuous increase in Teqfor the aromatization reactors. In contrast, when the same process used the same catalyst but with the addition of the oxygenate prior to the first aromatization reactor, the catalyst maintained its high initial activity as represented by the low and relatively constant Teqshown at the bottom ofFIG. 3B.

The relationship between the water content of the hydrogen recycle stream and the catalyst activity may also be reversible. On about day 6 of the oxygenated run (Example 2) the addition of water to the system ceased, as shown by the reduced water in the hydrogen recycle onFIG. 3A. Starting at day 6, the catalyst activity decreased as evidenced by the increased Teqshown inFIG. 3B. By about day 10, the amount of water in the hydrogen recycle was about 2 ppmv, a level approaching the levels seen at the beginning of the substantially dry run, about 1.5 ppmv. When the addition of oxygenate resumed on day 10, the catalyst activity returned to its previous levels as evidenced by the decreased Teqshown inFIG. 3B. This increase and decrease in Teqforms a slight hump in the graph for Example 2 at the bottom ofFIG. 3Bbetween days 6 and 12.

The relationship between the water content of the hydrogen recycle stream and the catalyst activity may also be catalyst specific as shown in this example. An experiment was conducted to determine the short-term affect of oxygenate addition on aromatization catalyst activity for two different catalyst formulations. The first catalyst was comprised of L-zeolite, impregnated with platinum, which had not been further impregnated with the halogens chloride, and fluoride (Pt/L-zeolite). The second catalyst was comprised of L-zeolite, impregnated with platinum, along with the halogens chloride, and fluoride (Pt/Cl/F/L-zeolite). In this example, the two catalysts were first brought to stable operating conditions without the addition of an oxygenate at about 3.0 liquid hourly space velocity (LHSV); about 140 psig; about 3.0 H2/hydrocarbon feed ratio; at a temperature that achieved a significant aromatic yield. Once stable operations had been established the processes were then perturbed by the addition of equal amounts of oxygenate, specifically a trace amount of O2in the hydrogen feed, for a period of about 24 hours. The oxygenate addition was measured as water in the off-gas from the reactor. During these short-term perturbation tests, the catalyst bed temperatures were held constant. The response of the catalyst activity to the addition of oxygenate, and the subsequent cessation of oxygenate addition, was measured using the Tyld.

As shown by the steady plot for TyldinFIG. 4, the presence of the oxygenate did not have an affect on the activity of the Pt/L-zeolite catalyst. Similarly, the removal of the oxygenate did not have an affect on the activity of the Pt/L-zeolite catalyst either, as the plot of TyldinFIG. 4remained steady before, during, and after the oxygenate injection. In contrast,FIG. 5shows that the addition of the oxygenate increased the activity of the Pt/Cl/F/L-zeolite catalyst, as evidenced by the decrease in the Tyldfor the aromatization reactor during the interval of oxygenate injection. Moreover, when the oxygenate addition was terminated, the Tyldreturned to its previous, higher levels. As noted previously, for an endothermic aromatization reaction as carried out in the Examples, a higher Tyldis associated with a lower catalyst activity and vice-versa.

This example further exemplifies of the use of oxygenates to improve and control catalyst activity. In this example a feed of having a C6concentration of less than or equal to about 63 wt %; a C5concentration of less than or equal to about 5 wt %; a C7concentration of less than or equal to about 27 wt % C7; and a C8+concentration of less than or equal to about 10 wt % was fed to a single reactor. The single reactor was operating at a pressure of about 65 psig, with a hydrogen-to-hydrocarbon molar ratio of about 2.0 and a liquid hourly space velocity of about 1.6 hr−1. The downflow reactor was a packed bed reactor with an internal diameter of about 1.0 inch. The feed was pretreated using a combination of Type 4A molecular sieves and reduced BASF-R3-15 (40 wt % copper) to less than about 1.0 ppmv oxygenate. During the run of this example, the amount of oxygenate in the reactor feed was varied by adjusting the flow rate of O2in a carrier gas of hydrogen being injected into the feed stream. The results of this example are presented inFIG. 6. As shown, the substantial variation in Tyldcorresponds to variations in the measured water in the recycle hydrogen stream.

This experiment illustrates the effect that water has on the life of an aromatization catalyst. In this example, two side-by-side laboratory scale isothermal reforming reactor systems were started under the same process conditions, both using the same halogenated Pt/K-L zeolite catalyst. Both reactors exhibited the typical spike in water (measured in the reactor product gas) during the initial 4 to 6 hours of operation, which subsequently decayed for the remainder of the 50 hour low severity “break-in.” Low severity conditions were 3.0 LHSV, 3.0 H2/hydrocarbon, 140 psig, with 60% aromatics in the liquid product. At 50 hours on stream (HOS), both reactors were set to high severity. High severity conditions were 3.0 LHSV, 0.5 H2/hydrocarbon, 140 psig, with 76% aromatics in the liquid product. Both reactors exhibited the typical spike in water in transition to high severity, which subsequently decayed. For the first 100 HOS, both reactors were subject to the same experimental conditions and both reactors had comparable performance.

Run 1 was continued from 50 to about 1600 HOS without the addition of water, e.g. was run substantially dry. Run 1 leveled off at about 2 ppmv of water in the off-gas by about 500 HOS. The water level in Run 1 stayed at about 2 ppmv through about 1600 HOS. In contrast, water was added to Run 2, the substantially wet run. Specifically, at 100 HOS the water level was increased in the second reactor, e.g. the reactor associated with Run 2, via controlled addition of trace oxygen in the hydrogen feed. The Run 2 moisture level reached about 8 ppmv water by 500 HOS, where it stayed through about 1600 HOS.

In this example, the Start of Run (SOR) yield-adjusted reactor temperatures for both Run 1 and Run 2 were about 940° F. The End of Run (EOR) temperature for this example was defined as 1000° F. At about 1600 HOS, the yield-adjusted reactor temperature for both runs is about 985 to 990° F., and thus both runs are approaching the EOR temperature. Consequently, at about 1600 HOS the water level in both Run 1 and Run 2 was increased by about 5 to 6 ppmv water, so that the Run 1 reactor off-gas increased to about 8 ppmv water and the Run 2 reactor off-gas increased to about 13.5 ppmv water. The Run 2 reactor continued to deactivate at the same rate. That is the increase from 8 to 13.5 ppmv water did not change the fouling rate or the catalyst activity. In contrast, the catalyst activity in the Run 1 reactor increased substantially when the water in the off-gas changed from 2 to 8 ppmv, as seen by the decrease in the reactor yield-adjusted temperature from 1600-1750 HOS. At about 1750 HOS, the Run 1 reactor activity began to decay again, but at a lower decay rate than prior to the water increase.

FIG. 7illustrates the results of this example. No data is plotted during the first about 50 HOS ofFIG. 7which represents the start-up period in which the reactors are operated under non-standard operating conditions. Run 1 was used to predict point A and determine point C, whereas Run 2 was used to determine point B. The substantially dry run, Run 1, is predicted to reach EOR at point A. The substantially wet run, Run 2, which had about 8 ppmv of water for most of the run, had an EOR at about point B. However, the best run length is achieved by operating at moderately-low water (e.g. 2 ppmv) through most of the cycle and then adding water to the feed to achieve 8 ppmv water in the off-gas just prior to reaching the EOR temperature. This approach is better than the two previous, and results in endpoint C. The difference between points A and B is about 200 hours, which is an increase of about 10% over point A, and the difference between points B and C is about 200 hours. Thus, a late addition of water to the catalyst system can result in about 400 more hours of useful catalyst life, which is an increase of about 20% over the dry run.

An experiment was conducted on a full-scale reactor system similar to the one described inFIG. 1. Specifically, the aromatization process was run under normal conditions to develop a baseline for the trial.FIGS. 8A-8Dillustrate the reactor history and performance.

On day 623, water injection was started at stream107inFIG. 1at a rate of 12 milliliters per minute to produce an estimated water content in the recycle gas of 5 ppmv. The water content in the recycle gas stream (stream115inFIG. 1) increased from 1.2 ppmv to 4 ppmv. On day 624, an increase in catalyst activity was observed, and the WAIT was decreased by 1.5° C. to 530° C., and the reactor space velocity (hr−1) was increased by 0.75%. On day 625, the water injection rate was reduced from 12 ml/min to 6 ml/min to control catalyst activity increase and to improve H2production purity. The WAIT was decreased from 529° C. to 528.5° C., and the reactor was maintained at the higher space velocity. After day 626, the catalyst activity was expected to follow the activity decay of the previous catalyst charge, thus yielding an estimated additional about 150 days on stream. Table 1 shows the results:

The results reported in examples 7 and 8 were obtained using experimental units such as those described in examples 5 and 6 of U.S. Pat. No. 6,190,539 to Holtermann and entitled “Reforming using a bound halided zeolite catalyst.” In this example and the following example, the experimental equipment was routinely operated with less than 1 ppmv H2O in the recycle hydrogen. The experimental equipment was modified so that oxygen could be added to the recycle hydrogen stream. This oxygen was then converted to water as it passed through the catalyst within the hydrofining section. The oxygen addition was then controlled by measuring the water level in the recycle hydrogen. In this example, oxygen was injected into the recycle and the resulting yield-adjusted catalyst average temperature was plotted inFIG. 9. Furnace temperature was held constant and changes in catalyst activity were monitored by measuring changes in the yield-adjusted catalyst temperature. Specifically, about 400 ppmv of O2in H2was added at a rate of 0.08 cubic centimeters per minute per gram of catalyst (cc/min·gcatalyst) starting about 14,100 hours. The oxygen addition rate was increased to about 0.17 cc/min·gcatalystat about 14,300 hours, and oxygen addition ended at about 14,800 hours. Linear regression of the temperature before injection, during injection, and after injection was conducted for the temperature values. As shown, the slope was lower during O2injection, indicating a lower deactivation rate during O2injection, compared to before and after the O2injection. Specifically, the fouling rate of the catalyst before the water addition was 0.13° F./day. The fouling rate of the catalyst during the water addition was 0.05° F./day. Finally, the fouling rate of the catalyst after the water addition was 0.28° F./day.

In this example, furnace temperature was again held steady so that reactor endotherms could be monitored precisely with time and water content. This run operated at 65 psig, 1.6 LHSV, 2.0 H2/hydrocarbon mole ratio.

From the outset, there was low water concentrations (<2 ppmv, with levels reaching <1 ppmv at times) in the recycle hydrogen and the result was decreasing catalyst activity almost immediately following the extended reactor idle time at about 500 HOS. As shown inFIG. 10, when water was added to the reactor system via oxygen addition to the recycle gas at 1,600 HOS and activity was restored. When water addition to the aromatization reactor was stopped, the activity decayed once again in the period between 2,000 and 3,100 HOS. Subsequently, increasing water levels via oxygen addition caused an increase in the catalyst activity up to about 4 or 5 ppmv water. Further increases in water did not raise activity further. When water addition was stopped at 3,900 HOS, catalyst activity started to fall again immediately.

The oxygen (O2) addition was initiated upstream of the hydrofining system at 3,900 HOS. The reaction rate in the aromatization reactor started to increase in a (top down) wave through the reactor about 11 hours prior to the detection of increased water in the effluent hydrogen from aromatization reactor at 1,650 HOS. The increased reaction rate is indicated by the increase in the reactor endotherm (reduction in thermowell temperatures by as much as 10° F.). InFIG. 11, the internal thermowell temperatures during the run are plotted between 1,600 and 1,700 HOS during the time period of the first oxygen addition. It can be seen (inFIG. 11) that the reactor internal temperatures started to move (temperatures decreased, which indicates an increase in the reactor endotherm, and catalyst activity) about 11 hours prior to detection of water in the reactor outlet.

During periods of low moisture operation, only the conversion to benzene was adversely affected. The conversions to toluene and xylenes remained invariant. This behavior is illustrated inFIG. 10. When moisture levels were increase via oxygen addition at about 1,600 HOS, the benzene concentration in the effluent increase about 8% from 40% to 48%.