Abstract:
The processes and systems disclosed herein relate to the removal of contaminants from the effluent of an oxygenate removal unit (ORU). More particularly, the processes and systems disclosed herein relate to the removal of contaminants resulting from the regeneration of adsorbers in an ORU. Processes and systems are provided for regeneration of an adsorber in an oxygenate removal unit comprising: (a) providing an oxygenate removal unit comprising at least one adsorber, wherein the at least one adsorber comprises a feed end and an effluent end; (b) passing a liquid hydrocarbon feedstock to the feed end of the at least one adsorber and removing an effluent stream from the effluent end of the adsorber; (c) isolating the at least one adsorber for regeneration by terminating passage of the liquid hydrocarbon feedstock to the feed end of the adsorber; (d) removing substantially all of the effluent stream from the adsorber; (e) regenerating the adsorber with a regeneration gas; (f) refilling the adsorber with an inventory liquid; and (g) purging the regenerated adsorber with a slipstream of liquid hydrocarbon feedstock to displace the inventory liquid.

Description:
TECHNICAL FIELD 
       [0001]    The processes and systems disclosed herein relate to the removal of contaminants from the effluent of an Oxygenate Removal Unit (ORU). More particularly, the processes and systems disclosed herein relate to the removal of contaminants resulting from the regeneration of adsorbent in an ORU. 
       BACKGROUND 
       [0002]    Light olefins and other related hydrocarbons serve as feeds for the production of numerous chemicals. Light olefins have traditionally been produced from petroleum sources. However, oxygenates such as alcohols, particularly methanol, ethanol, and higher alcohols or their derivatives, are used as alternative materials for light olefin production. These alcohols may be produced by fermentation or from synthesis gas. Oxygenates are particularly attractive because they can be produced from such widely available materials as coal, natural gas, recycled plastics, various carbon waste streams from industry and various products and by-products from the agricultural industry. 
         [0003]    Although many oxygenates have been discussed in the prior art, the principal focus on producing the desired light olefins has been on methanol conversion technology, primarily because of the availability of commercially proven methanol synthesis technology. Various methanol to olefin (MTO) procedures for catalytically converting methanol into the desired light olefin products have been developed. 
         [0004]    The product stream from MTO process is generally a raw product stream containing impurities. For example, a product stream from an MTO process typically contains light olefins, oxygenates, and water. The product stream undergoes a process to remove the impurities and separate the light olefins. 
       SUMMARY 
       [0005]    The processes and systems disclosed herein relate to the removal of impurities and separation the light olefins from an MTO product stream. Specifically, Oxygenate Removal Units (ORUs) are often incorporated into processes and systems for the treatment of MTO product streams to remove oxygenates. The processes and systems disclosed herein relate to the removal of contaminants from the effluent of an ORU. More particularly, the processes ad systems disclosed herein relate to the removal of contaminants resulting from the regeneration of adsorbers in an ORU. 
         [0006]    In one aspect, process is provided for regeneration of an adsorber in an oxygenate removal unit comprising: (a) providing an oxygenate removal unit comprising at least one adsorber, wherein the at least one adsorber comprises a feed end and an effluent end; (b) passing a liquid hydrocarbon feedstock to the feed end of the at least one adsorber and removing an effluent stream from the effluent end of the adsorber; (c) isolating the at least one adsorber for regeneration by terminating passage of the liquid hydrocarbon feedstock to the feed end of the adsorber; (d) removing substantially all of the effluent stream from the adsorber; (e) regenerating the adsorber with a regeneration gas; (f) refilling the adsorber with an inventory liquid; and (g) purging the regenerated adsorber with a slipstream of liquid hydrocarbon feedstock to displace the inventory liquid. In at least one embodiment, the process further includes (h) transferring the displaced inventory liquid to an upstream operation unit that is upstream of the oxygenate removal unit. 
         [0007]    In another aspect, a system is provided for regeneration of an adsorber in an oxygenate removal unit comprising: (a) an oxygenate removal unit comprising at least one adsorber, wherein the at least one adsorber comprises a feed end and an effluent end; (b) a supply of a liquid hydrocarbon feedstock that is fed to the feed end of the at least one adsorber; (c) an effluent stream that is removed from the effluent end of the adsorber; (d) a device that isolates the first adsorber from the system by terminating passage of the liquid hydrocarbon feedstock to the feed end of the first adsorber; (e) an effluent line operatively connected to the effluent end of the first adsorber that provides for removal of the effluent stream from the effluent end of the first adsorber; (f) a regeneration gas supply operatively connected to the adsorber that supplies regeneration gas to regenerate the adsorber; (g) an inventory liquid supply operatively connected to the adsorber that refills the adsorber with an inventory liquid; and (h) a slipstream supply operatively connected to the adsorber that supplies a slipstream of hydrocarbon feedstock to displace the inventory liquid. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0008]      FIG. 1  is a representative process for regeneration of an adsorber in an oxygenate removal unit. 
           [0009]      FIG. 2  is a representative process for regeneration of an adsorber in an oxygenate removal unit. 
           [0010]      FIG. 3  is a representative process for regeneration of an adsorber in an oxygenate removal unit. 
           [0011]      FIG. 4  is a representative system for regeneration of an adsorber in an oxygenate removal unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    One example of a process for the removal of impurities and the separation of light olefins from an MTO product vapor stream is illustrated in  FIG. 1 . An MTO product vapor stream typically contains light olefins, oxygenates, and water. For example, an MTO product vapor stream can contain unreacted methanol, dimethyl ether intermediate, ethylene, propylene, C 4  to C 6  olefins, and minor amounts of other hydrocarbons and oxygenates. As illustrated, the product vapor stream  102  from the MTO process goes from the MTO process  100  to a compressor  104 . The product vapor stream undergoes compression in the compressor  104 , and the pressure of the vapor stream is increased. In at least some instances, liquid can be formed during compression, and is recycled upstream in the MTO process (not shown). The vapor stream exits the compressor  104  at increased pressure, and goes to an oxygenate absorber  106  and a scrubber  108 . In the absorber  106 , the vapor stream is contacted with a solvent such as, for example, water, to remove at least some oxygenates. In the scrubber  108 , the vapor stream undergoes caustic scrubbing for bulk removal of carbon dioxide. 
         [0013]    After undergoing caustic scrubbing, the vapor stream goes to a dryer  110 , where moisture is removed from the vapor stream. The dried vapor stream then undergoes cooling  112  and is put through a distillation sequence  114  that results in the vapor stream becoming a liquid hydrocarbon feedstock  116 . As further illustrated in  FIG. 1 , the liquid hydrocarbon feedstock goes to a deethanizer  118 , which separates the C 1  and C 2  olefins from the olefins comprising C 3  or greater. 
         [0014]    The feedstock  120  containing C 1  and C 2  hydrocarbons is sent from the deethanizer  118  to a demethanizer  122 , where methane (C 1 )  124  and other light impurities are removed. The resulting C 2  hydrocarbon feedstock  126  then goes to a C 2  splitter  128  that separates out ethylene  130  and ethane  132 . 
         [0015]    The feedstock  134  containing C 3  or greater hydrocarbons is sent from the deethanizer  118  to a depropanizer  136 , where the C 3  fraction is removed from the remaining hydrocarbon feedstock  138  containing C 4  or greater hydrocarbons. The hydrocarbon feedstock  140  containing C 3  hydrocarbons goes to an oxygenate removal unit (ORU)  142 . The oxygenate removal unit removes oxygenates such as, for example, dimethyl ether. The resulting product stream  144 , sometimes referred to herein as the “effluent stream,” goes to a C 3  splitter  146 , where propylene  148  and propane are separated  150 . 
         [0016]    A second example of a process for the removal of impurities and the separation of light olefins from an MTO product vapor stream is illustrated in  FIG. 2 . This process is similar to the process illustrated in  FIG. 1 , in that an MTO product vapor stream  202  goes from the MTO process  200  to a compressor  204 . The product vapor stream undergoes compression in the compressor  204 , and the pressure of the vapor stream is increased. The vapor stream exits the compressor  204  at increased pressure, and goes to an oxygenate absorber  206  and a scrubber  208 . In the absorber  206 , the vapor stream is contacted with a solvent such as, for example, water, to remove at least some oxygenates. In the scrubber  208 , the vapor stream undergoes caustic scrubbing for bulk removal of carbon dioxide. 
         [0017]    After undergoing caustic scrubbing, the vapor stream goes to a dryer  210 , where moisture is removed from the vapor stream. The dried vapor stream then undergoes cooling  212  and is put through a distillation sequence  214  that results in the vapor stream becoming a liquid hydrocarbon feedstock  216 . 
         [0018]    In contrast to  FIG. 1 , the liquid hydrocarbon feedstock  216  illustrated in  FIG. 2  goes from the distillation sequence  214  to a demethanizer  218 , which separates the C 1  hydrocarbons  220  from the remaining feedstock containing hydrocarbons comprising C 2  or greater  222 . 
         [0019]    The remaining feedstock  222  is passed from the demethanizer  218  to a deethanizer  224 , where the ethane (C 2 ) fraction  226  is separated from the remaining feedstock containing hydrocarbons comprising C 3  or greater  228 . The ethane fraction  226  is passed to an ethane/ethylene splitter column (C 2  splitter)  230  that separates out ethylene  232  and ethane  234 . 
         [0020]    The feedstock containing C 3  or greater hydrocarbons  228  is sent from the deethanizer  224  to a depropanizer  236 , where the C 3  fraction is removed from the remaining hydrocarbon feedstock containing C 4  or greater olefins  238 . The hydrocarbon feedstock containing the C 3  fraction  240  is passed to an oxygenate removal unit (ORU)  242 . The oxygenate removal unit removes oxygenates such as, for example, dimethyl ether. The resulting product stream  244 , sometimes referred to herein as the “effluent stream,” goes to a C 3  splitter  246 , where propylene  248  and propane  250  are separated. 
         [0021]    A third example of a process for the removal of impurities and the separation of light hydrocarbons from an MTO product vapor stream is illustrated in  FIG. 3 . This process is similar to the process illustrated in  FIGS. 1 and 2 , in that an MTO product vapor stream  302  goes from the MTO process  300  to a compressor  304 . The product vapor stream undergoes compression in the compressor  304 , and the pressure of the vapor stream is increased. The vapor stream exits the compressor  304  at increased pressure, and goes to an oxygenate absorber  306  and a scrubber  308 . In the absorber  306 , the vapor stream is contacted with a solvent such as, for example, water, to remove at least some oxygenates. In the scrubber  308 , the vapor stream undergoes caustic scrubbing for bulk removal of carbon dioxide. 
         [0022]    After undergoing caustic scrubbing, the vapor stream goes to a dryer  310 , where moisture is removed from the vapor stream. The dried vapor stream then undergoes cooling  312  and is put through a distillation sequence  314  that results in the vapor stream becoming a liquid hydrocarbon feedstock  316 . 
         [0023]    In contrast to  FIGS. 1 and 2 , the liquid hydrocarbon feedstock  316  illustrated in  FIG. 3  goes from the distillation sequence  314  to a deproanizer  318 , where the C 4  fraction  320 , containing hydrocarbons of C 4  or greater, is removed from the remaining hydrocarbon feedstock  322 , containing the hydrocarbons of C 3  or lighter. 
         [0024]    The hydrocarbon feedstock  322  containing the hydrocarbons of C 3  or lighter is passed to a deethanizer  324 , where the hydrocarbons containing C 2  or lighter are separated from the hydrocarbon feedstock containing the C 3  hydrocarbons. The feedstock containing the C 2  or lighter olefins  326  is passed to a demethanizer  328 , which separates the C 1  hydrocarbons  330  from the remaining C 2  hydrocarbons feedstock  332 . The C 2  hydrocarbons feedstock  332  is passed to an ethane/ethylene splitter column (C 2  splitter)  334  that separates out ethylene  336  and ethane  338 . 
         [0025]    The hydrocarbon feedstock  340  containing the C 3  hydrocarbons is passed to an oxygenate removal unit (ORU)  342 . The oxygenate removal unit  342  removes oxygenates such as, for example, dimethyl ether. The resulting product stream  344 , sometimes referred to herein as the “effluent stream,” goes to a propylene/propane splitter column (C 3  splitter)  346 , where propylene  348  and propane are separated  350 . 
         [0026]    In the processes and systems disclosed herein, the oxygenate removal unit (ORU) has at least one adsorber, and preferably has a plurality of adsorbers, to remove oxygenates.  FIG. 4  illustrates a particularly preferred system for regeneration of an adsorber in accordance with the process described above. As illustrated in  FIG. 4 , the ORU has a first adsorber  402 , a second adsorber  404 . Each adsorber has a feed end and an effluent end. For example, as illustrated in  FIG. 4 , first adsorber  402  has feed end  406  and effluent end  408 , and second adsorber  404  has feed end  410  and effluent end  412 . Additionally, each adsorber includes an adsorbent bed that contains a solid adsorbent capable of selectively adsorbing trace amounts of oxygenates. For example, the first adsorber  402  has adsorbent bed  414 , the second adsorber  404  has adsorbent bed  416 . 
         [0027]    A supply of a liquid hydrocarbon feedstock is fed to the feed end of at least one adsorber. As illustrated in  FIG. 4 , a feedstock line  418  passes a liquid hydrocarbon feedstock to the feed end  406  of adsorber  402 . An effluent stream is removed from the effluent end of at least the first adsorber through outlet piping  420 . In preferred processes and systems, the liquid hydrocarbon feedstock is a product stream from an MTO process that contains propylene. 
         [0028]    Adsorbers require regular, independent regeneration. Regeneration of one adsorber can begin by isolating, for example, first adsorber  402  for regeneration by terminating passage of the liquid hydrocarbon feedstock to the feed end  406  of the adsorber. There is a device  422  that isolates the first adsorber from the system by terminating passage of the liquid hydrocarbon feedstock to the feed end  406  of the first adsorber  402 . The device  422  may be a valve that can be closed to prevent the flow of liquid hydrocarbon feedstock into the first adsorber. 
         [0029]    Preferably, once the first adsorber  402  is isolated, it is drained by removing substantially all of the effluent stream from the adsorber. An effluent line  424  operatively connected to the effluent end of the first adsorber that provides for removal of the effluent stream from the effluent end of the first adsorber. It is particularly preferred that substantially all of the removed effluent stream be transferred from the adsorber  402  to another adsorber such as, for example, adsorber  404 . The term “substantially all” is used in this context to indicate that a residual amount of effluent stream tends to remain within the first adsorber, as well as within the outlet piping at the effluent end of the first adsorber. The adsorber to which the effluent stream, is transferred is preferably an adsorber that has undergone regeneration immediately prior to receiving the effluent stream from the first adsorber  402 , and is in the process of coming back on-stream. The effluent stream from the first adsorber  402  is preferably used to fill the adsorber coming back on-stream prior to re-initiating the flow of hydrocarbon feedstock the adsorber coming back on-stream. 
         [0030]    After the removal of substantially all of the effluent stream from the adsorber that has been isolated for regeneration, the adsorber can be regenerated with a regeneration gas. There is a regeneration gas supply  426  operatively connected to the adsorber that supplies regeneration gas to regenerate the adsorber. In at least some instances, nitrogen or methane is utilized as the regeneration gas. Preferably, in some instances, the overhead distillate vapor from the upstream demethanizer is utilized as the regeneration gas. The overhead distillate vapor from the upstream demethanizer, however, can be contaminated with light olefins such as, for example, methane and ethylene. 
         [0031]    In preferred processes, the regeneration gas is passed to the adsorbent bed of the adsorber at a temperature effective to desorb oxygenates from the solid adsorbent and recover the oxygenates from the adsorbent bed in a spent regenerant vapor stream. Upon regeneration of the adsorber with the regeneration gas, at least some residual regeneration gas tends to remain in the adsorber. 
         [0032]    After regeneration of the adsorber with the regeneration gas, the regenerated adsorber is refilled with an inventory liquid. Accordingly, the system illustrated in  FIG. 4  has an inventory liquid supply  428  operatively connected to the adsorber that refills the adsorber with an inventory liquid. The inventory liquid preferably comprises hydrocarbons, such as propylene. More preferably, the inventory liquid is effluent stream that has been removed from another adsorber such as, for example, second adsorber  404 , that is beginning to undergo regeneration as described herein with respect to the first adsorber  402 . 
         [0033]    As the adsorber is refilled, residual regeneration gas is absorbed into the inventory liquid. Any contaminates in the residual regeneration gas are thus also absorbed into the inventory liquid. It is preferred that the regenerated adsorber be purged with a slipstream to displace the inventory liquid. The slipstream is preferably liquid hydrocarbon feedstock. Accordingly, a slipstream supply is preferably operatively connected to the adsorber that supplies a slipstream of hydrocarbon feedstock to displace the inventory liquid. As illustrated in  FIG. 4 , the slipstream supply is preferably the hydrocarbon feedstock supply  418 . The displaced inventory liquid is then preferably transferred to an upstream operation unit  430 , and the regenerated gas, as well as the contaminates therein, that dissolved in the inventory liquid during refilling of the adsorber can be removed as the inventory liquid proceeds through the system from the upstream unit. If not displaced and transferred upstream, the inventory liquid would be passed to the propylene/propane splitter as effluent stream, thus contaminating the propylene and/or propane products. In order to avoid having a significant affect on the upstream operation unit, the slipstream is from about 10% to about 20% of the volume of influent to the upstream operation unit from any other process steps. 
         [0034]    For example, with respect to the process illustrated in  FIG. 1 , the displaced inventory liquid  152  is transferred from the oxygenate removal unit  142  to the deethanizer  118 . To accomplish this transfer, there is preferably a transfer line operatively connected to the regenerated adsorber to transfer the displaced inventory liquid to the deethanizer. 
         [0035]    As another example, with respect to the process illustrated in  FIG. 2 , the displaced inventory liquid  252  is transferred from the oxygenate removal unit  242  to the demethanizer  218 . To accomplish this transfer, there is preferably a transfer line operatively connected to the regenerated adsorber to transfer the displaced inventory liquid to the demethanizer. 
         [0036]    As a third example, with respect to the process illustrated in  FIG. 3 , the displaced inventory liquid  352  is transferred from the oxygenate removal unit  342  to the depropanizer  318 . To accomplish this transfer, there is preferably a transfer line operatively connected to the regenerated adsorber to transfer the displaced inventory liquid to the depropanizer. 
         [0037]    From the foregoing, it will be appreciated that although specific representative structures and processes have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of the disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the disclosure subject matter.