Abstract:
Methods and processes for reducing alkylation catalyst poisoning are described herein. Such methods generally include contacting ethylbenzene with a dehydrogenation catalyst to form a dehydrogenation output stream within a dehydrogenation system and passing at least a portion of the dehydrogenation output stream to an alkylation system, wherein the at least a portion of the dehydrogenation output stream contacts an alkylation catalyst. The at least a portion of the dehydrogenation output stream includes a level of impurities resulting from offtest and wherein the level of impurities is sufficiently low to result in essentially no observed effect on the alkylation catalyst life in comparison with an alkylation system feed absent offtest.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/656,464, filed Feb. 25, 2005. 
     
    
     FIELD  
       [0002]     Embodiments of the present invention generally relate to minimizing alkylation catalyst poisoning.  
       BACKGROUND  
       [0003]     In many processes, benzene and toluene are recovered from catalytic dehydrogenation systems and fed to alkylation/transalkylation processes. However, nitrogen compounds and other compounds present in the recovered benzene may poison the alkylation catalyst, therefore requiring more frequent regeneration and/or replacement of such catalyst.  
         [0004]     Therefore, a need exists to utilize the recovered benzene and toluene in alkylation processes while reducing the poison effect of the nitrogen containing compound(s) and impurities on the alkylation catalyst.  
       SUMMARY  
       [0005]     Embodiments of the present invention generally include a dehydrogenation process. The dehydrogenation process generally includes introducing an alkyl aromatic hydrocarbon into a dehydrogenation system, contacting the alkyl aromatic hydrocarbon with a dehydrogenation catalyst to form a dehydrogenation output stream including a vinyl aromatic hydrocarbon, passing at least a portion of the dehydrogenation output stream to a separation system, wherein the separation system includes a first separation column and at least one additional separation column and withdrawing offtest from the dehydrogenation process. The process further includes introducing the offtest into at least one of the additional separation columns.  
         [0006]     One or more embodiments further include a method for reducing alkylation catalyst poisoning. Such method generally includes contacting ethylbenzene with a dehydrogenation catalyst to form a dehydrogenation output stream within a dehydrogenation system and passing at least a portion of the dehydrogenation output stream to an alkylation system, wherein the at least a portion of the dehydrogenation output stream contacts an alkylation catalyst. The at least a portion of the dehydrogenation output stream includes a level of impurities resulting from offtest and wherein the level of impurities is sufficiently low to result in essentially no observed effect on the alkylation catalyst life in comparison with an alkylation system feed absent offtest. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]      FIG. 1  illustrates a conventional dehydrogenation system.  
         [0008]      FIG. 2  illustrates an embodiment of a dehydrogenation system. 
     
    
     DETAILED DESCRIPTION  
       [0000]     Introduction and Definitions  
         [0009]     A detailed description will now be provided. Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims. Each of the inventions will now be described in greater detail below, including specific embodiments, versions and examples, but the inventions are not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the inventions when the information in this patent is combined with available information and technology.  
         [0010]     Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents. Further, unless otherwise specified, all compounds described herein may be substituted or unsubstituted and the listing of compounds includes derivatives thereof.  
         [0011]      FIG. 1  (Prior Art) illustrates an embodiment of a catalytic dehydrogenation/purification process  100 . Such dehydrogenation processes generally include contacting an alkyl aromatic hydrocarbon with a dehydrogenation catalyst to form a vinyl aromatic hydrocarbon. A variety of catalysts can be used in the catalytic dehydrogenation process and are known to one skilled in the art, such as potassium iron oxide catalysts and cesium iron oxide catalysts, for example.  
         [0012]     In  FIG. 1 , an input stream  102  is supplied to a dehydrogenation system  104 . As used herein, individual streams will be denoted with a number, but it is generally known that such streams flow through conduits, such as pipes. The input stream  102  includes an alkyl aromatic hydrocarbon, such as ethylbenzene, for example. Steam may further be added to the input stream  102 . The steam may be added to the input stream  102  in any manner known to one skilled in the art. Although the amount of steam contacting the input stream  102  is determined by individual process parameters, the input stream  102  may have a steam to alkyl aromatic hydrocarbon weight ratio of from about 0.01:1 to about 15:1, or from about 0.3:1 to about 10:1, or from about 0.6:1 to about 3:1, or from about 1:1 to about 2:1, for example.  
         [0013]     The dehydrogenation system  104  may include any reaction vessel, combination of reaction vessels and/or number of reaction vessels (either in parallel or in series) known to one skilled in the art for the conversion of an alkyl aromatic hydrocarbon to a vinyl aromatic hydrocarbon. For example, the one or more reaction vessels may be fixed bed vessels, fluidized bed vessels and/or tubular reactor vessels.  
         [0014]     The dehydrogenation processes discussed herein are generally high temperature processes. As used herein, the term “high temperature” refers to process operation temperatures, such as reaction vessel and/or process line temperatures (e.g., the temperature of the input stream  102  at the vessel inlet) of from about 150° C. to about 1000° C., or from about 300° C. to about 800° C., or from about 500° C. to about 700° C., or from about 550° C. to about 650° C., for example. The reaction vessel inlet will vary depending on the type of vessel.  
         [0015]     The output  106  from the dehydrogenation system  104  (e.g., ethylbenzene and styrene) may be supplied to a first column  200  for benzene recovery. A first portion (overhead fraction)  106   b  (e.g., benzene and toluene) may be removed for further processing, such as alkylation/transalkylation or separation, for example. The first column  200  may include any vessel, combination of vessels and/or number of vessels (either in parallel or in series) known to one skilled in the art for the recovery of benzene from a mixed input stream. For example, the first column  200  may include one or more distillation columns.  
         [0016]     The second portion (bottoms fraction)  202  (e.g., ethylbenzene and styrene) is sent to a second column  204  for ethylbenzene recovery. Ethylbenzene  106   a  is recovered from column  204  and may be recycled back to the dehydrogenation system  104  (not shown) or used for any other purpose. Line  106   a  may be fed to the dehydrogenation system  104  via a variety of methods, such as combination with line  102  or by directly feeding line  106   a  into the dehydrogenation system  104 . The second column  204  may include any vessel, combination of vessels and/or number of vessels (either in parallel or in series) known to one skilled in the art for the recovery of ethylbenzene from a mixed input stream. For example, the second column  204  may include one or more distillation columns.  
         [0017]     A bottoms fraction  206  (e.g., styrene and “heavies”) may be transferred from column  204  to a third column  208  for styrene separation. Styrene  110  may be recovered and used for any suitable purpose, such as the production of polystyrene, for example. The third column  208  may include any vessel, combination of vessels and/or number of vessels (either in parallel or in series) known to one skilled in the art for the recovery of styrene from a mixed input stream. For example, the third column  208  may include one or more fractionation columns.  
         [0018]     The bottom fraction  210  (e.g., styrene, polymer and heavies (high boiling point compounds)) may be removed and further processed, not shown. As used herein, the term “heavies” refers to higher boiling point compounds, such as indene and indane (e.g., TAR).  
         [0019]     Offtest is generally recovered from various locations within the process  100  and may be sent to storage (not shown) prior to further processing. As used herein, the term “offtest” refers to products, such as styrene, that do not meet further processing specifications and other compounds, such as impurities having a boiling point similar to that of benzene. Generally, offtest is fed, either continuously or generally intermittently as needed, to column  200 . However, such impurities often pass through line  106   b  to the alkylation process.  
         [0020]     In addition, dehydrogenation processes may include the addition of nitrogen containing compounds (not shown) and other additives. The nitrogen containing compounds, such as amines, may be added to the dehydrogenation process for a variety of purposes, such as polymerization inhibitors and/or neutralizers, for example. In many processes, the recovered benzene and toluene, e.g., line  106   b,  are fed to an alkylation/transalkylation process. However, the nitrogen compounds and the other compounds present in the recovered benzene may poison the alkylation catalyst, therefore requiring more frequent regeneration and/or replacement of such catalyst. Embodiments of the present invention seek to reduce the poison effect of the nitrogen containing compound(s) and impurities on the alkylation catalyst.  
         [0021]     Referring to  FIG. 2 , the offtest  218  is fed to the second column  204 , rather than back to the first column  200 . The offtest  218  may be fed to column  204  via a variety of methods, such as combination with line  202  (shown) or by directly feeding line  218  into the second column  204  (not shown). Such an embodiment significantly reduces that amount of catalyst poisons passing from the first column  200  to the alkylation system. In one embodiment, the poisons pass through the second column  204  and may be recycled via line  106   a  back to the dehydrogenation system  104 . The poisons then may burn during such reaction and not exit the system  104  via line  106 . As a result, a minimal amount of impurities pass from the first column  200  to an alkylation system.  
         [0022]     Although not shown in the Figures, additional process equipment, such as heat exchangers, may be employed throughout the process shown above and such placement is generally known to one skilled in the art.  
         [0023]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof and the scope thereof is determined by the claims that follow.