Abstract:
The invention described herein is a method for selectively removing mercaptans such as methyl mercaptan from dry gas mixtures containing high concentrations of carbon dioxide. In the method, the carbon dioxide-rich gas (sour gas) is passed through an absorption vessel or distillation column in which it is contacted with an absorbent such as liquid carbon dioxide in order to selectively absorb the mercaptans. The treated gas, which is now free of mercaptans, leaves the top of the vessel as a sales gas suitable for use in enhanced oil recovery applications. Preferably, a portion of the carbon dioxide in the sales gas is condensed and the liquid is returned to the absorber or distillation column as the scrubbing agent. At least part of this scrubbing agent leaves the bottom of the absorber or distillation column enriched in methyl mercaptan and other sulfur compounds. The stream from the absorption vessel containing the mercaptans can be incinerated or otherwise processed to utilize or dispose of the methyl mercaptan.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention generally relates to methods for purifying carbon dioxide gas streams, and more particularly to methods for reducing the concentration of mercaptans in gas mixtures containing high concentrations of carbon dioxide.  
         [0002]     Oil-field-grade carbon dioxide (CO 2 ), such as is produced from lignite coal gasification, is generally contaminated with a variety of fuel gas and sulfur compounds. The contaminants include hydrogen sulfide (H 2 S), carbonyl sulfide (COS), methyl mercaptan (CH 3 SH), and C 2 - and C 3 -hydrocarbons, along with numerous other minor constituents. When oil-field-grade carbon dioxide is used for enhanced oil recovery projects, the methyl mercaptan, along with some of the other sulfur compounds, is of concern because it leaves the gas handling equipment and piping with an unpleasant and lingering odor. Furthermore, it is believed that the methyl mercaptan and other sulfur compounds might react with the crude oil to effectively increase its sulfur content and thus reduce its quality and sales value. It would be useful to develop a process for selectively removing mercaptans, such as methyl mercaptan, and certain other organic sulfur compounds from dry gas mixtures rich in CO 2  and concentrating them into a smaller stream for efficient processing or disposal.  
       SUMMARY OF THE INVENTION  
       [0003]     It is an object of the invention to provide a method of purifying a carbon dioxide gas stream to render it useful in a variety of ways, including in enhanced oil recovery projects.  
         [0004]     Another object of the invention is to provide a dry gas stream that can be used to recover oil and that does not leave the gas handling equipment and piping with lingering and unpleasant odors.  
         [0005]     A further object of the invention is to provide a continuous flow process for purifying a carbon dioxide gas stream which has varying mercaptan impurity levels.  
         [0006]     Yet another object of the invention is to provide an efficient method of producing a mercaptan-free carbon dioxide gas stream as a by-product of lignite coal gasification.  
         [0007]     The invention in a preferred form is a method of removing methyl mercaptan from a carbon dioxide gas stream, comprising the steps of: (a) obtaining a first gas stream comprising at least 80 volume percent carbon dioxide and up to 500 parts per million based on volume of methyl mercaptan, and (b) contacting the first gas stream with a liquid carbon dioxide stream under conditions sufficient to produce a first liquid stream containing at least 85 weight percent of the methyl mercaptan from the first gas stream and a second gas stream containing at least 90 weight percent of the carbon dioxide from the first gas stream.  
         [0008]     Preferably, the contacting step takes place in an absorber or a distillation column. The column generally has a reflux ratio of at least eight pounds of liquid carbon dioxide per 100 pounds of the first gas stream. The first gas stream is usually compressed and cooled prior to being contacted with the liquid carbon dioxide stream. Optionally, the first gas stream is dehydrated prior to being contacted with the liquid carbon dioxide stream.  
         [0009]     In one preferred form of the invention, at least a portion of the second gas stream is condensed to form the liquid carbon dioxide stream. Preferably, at least a portion of the second gas stream is condensed and used to cool the first gas stream. Furthermore, at least a portion of the first liquid stream can be used to cool the first gas stream. The contacting step preferably takes place in a column having an operating pressure in the range of 280 to 360 psig and a temperature in the range of −5 to 15° F. at the top of the column. The column preferably has a reflux ratio in the range of 8-16 and more preferably 10-14 pounds of liquid carbon dioxide per 100 pounds of the first gas stream. At least a portion of the second gas stream can be cooled by conventional refrigeration or autorefrigeration. Autorefrigeration preferably takes place in an absorption column or a heat exchanger.  
         [0010]     In one form of the invention, the methyl mercaptan content of the second gas stream is no more than 20 parts per million based on volume (ppmv), and more preferably is no more than 10 ppmv. The second gas stream preferably contains at least 90 weight percent, and even more preferably at least 95 weight percent of the total gas components from the first gas stream. The second gas stream desirably contains at least 99 weight percent of the total gas components from the first gas stream.  
         [0011]     In one embodiment, the method further comprises the step of (f) concentrating the methyl mercaptan in the first liquid stream by reboiling the first liquid stream to evaporate a portion of the carbon dioxide therein and recycling the evaporated carbon dioxide to step (b).  
         [0012]     Another preferred form of the invention is a method of removing methyl mercaptan from a carbon dioxide gas stream, comprising the steps of: (a) obtaining a first gas stream comprising at least 80 volume percent carbon dioxide and up to 500 parts per million based on volume of methyl mercaptan, (b) compressing the first gas stream to a pressure of 70 psig to 1100 psig, (c) cooling the first gas stream to a temperature of −60° F. to 90° F., and (d) contacting the first gas stream with an absorbent to produce a first liquid stream containing at least 85 weight percent of the methyl mercaptan from the first gas stream and a second gas stream containing at least 90 weight percent of the carbon dioxide from the first gas stream. Usually, at least a portion of the first liquid stream cools the first gas stream. The contacting step preferably takes place in a column having a reflux ratio of at least eight pounds of liquid carbon dioxide per 100 pounds of the first gas stream and preferably about twelve pounds of liquid carbon dioxide per 100 pounds of the first gas stream. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Other features and advantages of the invention are further described in the following detailed description of preferred embodiments of the invention, considered in conjunction with the drawings, in which:  
         [0014]      FIG. 1  is a general schematic flow diagram for using a reboiled absorber according to the invention to remove methyl mercaptan from a sour CO 2 -rich feed gas, with conventional refrigeration being used for cooling and condensing the carbon dioxide;  
         [0015]      FIG. 2  is a general schematic flow diagram for using a simple absorber according to the invention to remove methyl mercaptan from a sour CO 2 -rich feed gas, with conventional refrigeration being used for cooling and condensing the carbon dioxide;  
         [0016]      FIG. 3  is a general schematic flow diagram for using a reboiled absorber according to the invention to remove methyl mercaptan from a sour CO 2 -rich feed gas with autorefrigeration being used for cooling and condensing a portion of the purified CO 2  gas stream; and  
         [0017]      FIG. 4  is a general schematic flow diagram for using a simple absorber according to the invention to remove methyl mercaptan from a sour CO 2 -rich feed gas with autorefrigeration being used for cooling and condensing a portion of the purified CO 2  gas stream. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The present invention provides a highly effective and efficient method of removing mercaptans and similar odorous substances from a sour CO 2 -rich gas stream. The sweetened or treated CO 2 -rich gas can be used for enhanced oil recovery operations such as tertiary oil recovery, thereby increasing the overall percentage of oil that can be recovered from a particular well in an economical manner. The process of the invention preferably involves scrubbing a sour CO 2 -rich gas stream such as oil-field-grade gas with liquid carbon dioxide (CO 2 ), however, the same effect can be achieved by configuring the process for distillation. The process is continuous and preferably starts by first compressing the dry, sour, CO 2 -rich gas stream to a pressure in the range of 70 psig to 1100 psig, more preferably between 280 psig and 360 psig, with the range of 280 psig to 300 psig being most preferred. Some cooling can take place before compression if the gas stream is hot. After compression, the sour CO 2 -rich gas stream is cooled first to remove the heat of compression and then to lower its temperature to the condensation point of carbon dioxide at the operating pressure employed. The sour CO 2 -rich feed preferably is cooled in one or more cooling stages to a temperature in the range of −60° F. to 90° F., more preferably −5° F. to 15° F., and most preferably −5° F. to 5° F. Next, the cooled gas is passed upwardly through a tray or packed column, where it is brought into contact with a counter flowing stream of liquid carbon dioxide. The methyl mercaptan in the sour carbon dioxide-rich gas stream is physically absorbed by the liquid CO 2 , and is removed from the upwardly flowing gas. Of the treated gas that leaves the top of the column, a portion is further refrigerated and condensed to produce liquid CO 2  for scrubbing and cooling the fresh sour gas that enters the system. The remainder of the treated gas is further compressed and transported or piped to the oil fields for underground injection, or to another site where it is to be further processed and/or used.  
         [0019]     The liquid CO 2  containing the methyl mercaptan is collected in the bottom of the column and preferably is further concentrated by evaporation of the excess CO 2 . The evaporated excess CO 2  passes upwardly through the column, where it mixes with fresh sour feed. This concentration step is done using either a conventional reboiler (distillation or reboiled absorption) or through direct heat exchange by commingling with the warm sour feed gas (simple absorption). The concentrated methyl mercaptan stream is then removed from the bottom of the column and incinerated or processed further for recovery of the CO 2  and absorbed components. In the process of the invention, the loss of CO 2  with the methyl mercaptan and other sulfur compounds typically is no more than 5 weight percent of the CO 2  in the feed gas, and preferably is no more than 3 weight percent of the CO 2  in the feed gas.  
         [0020]     Refrigeration for the process can be accomplished either by conventional refrigeration techniques using ammonia or another suitable refrigerant, or by autorefrigeration using some of the treated gas. Wet CO 2 -rich feed streams may be capable of being processed through the methyl mercaptan removal system if the operating pressure and temperature are sufficiently high to prevent freezing of water, or if they are first processed through a dehydrator to remove the moisture.  
         [0021]     Typical sources of CO 2 -rich gas that may be contaminated with mercaptans include by-product CO 2  streams from lignite, subbituminous coal, and biomass gasification plants, fermentation plants, direct coal liquefaction plants and underground coal gasification facilities. In addition, some natural sources of CO 2  may also contain mercaptans, as may the CO 2  effluent from natural gas sweetening plants and other processes when Rectisol® or similar absorption steps are used to remove and concentrate acid gases. The sour feed stream typically has a CO 2  content of at least 80 volume %, more preferably at least 85 volume %, and most preferably at least 90 volume %. The methyl mercaptan content of the sour feed stream generally is no more than 500 ppmv, preferably is 50 to 400 ppmv, and usually is in the range of 100-350 ppmv.  
         [0022]     With reference to  FIG. 1 , a gas stream in conduit  110  from a coal gasification operation or from a gas purification process, such as Rectisol®, containing a high concentration of carbon dioxide along with sulfur compounds such as methyl mercaptan, hydrogen sulfide, dimethyl disulfide, ethyl mercaptan, propyl mercaptan, dimethyl sulfide and the like is conveyed to a compressor  112  for pressurization and further treatment according to the invention. The pressurized gas is conveyed through conduit  114  to a cooler/evaporator  116  which cools the compressed gas while also evaporating liquid waste-gas in conduit  125 , which is under the control of level valve  143 . The evaporated waste-gas leaves the unit through conduit  115  and is disposed of by incineration or is processed using other treatment methods. The cool compressed gas leaves the cooler/evaporator  116  through conduit  118 . A portion of the gas in conduit  118  is routed through conduit  120  and into a reboiler  122  where it is used to concentrate the liquid waste-gas in conduit  124  by evaporating a portion of it. The evaporated waste-gas leaves the reboiler  122  in conduit  126  and returns to the absorber  130 . The compressed gas used in the reboiler leaves in conduit  132  and blends back with the compressed gas from conduit  133  in conduit  134 . The temperature valve  135  in conduit  133  controls the amount of heat applied to the reboiler  122  so that the correct bottoms flow is obtained from the column in conduit  124 . Conduit  134  conveys the compressed gas to cooler/evaporator  136  where the compressed gas is cooled to near its condensation temperature by evaporating liquid ammonia or some other refrigerant.  
         [0023]     The refrigerant enters the cooler/evaporator  136  as a liquid through conduit  138  and leaves the cooler/evaporator as a vapor in conduit  140 . The cold compressed gas is conveyed in conduit  142  to the absorber  130 . The cold compressed gas flows upwardly through the absorber  130  where it is contacted with a downwardly flowing stream of liquid carbon dioxide. The liquid carbon dioxide absorbs methyl mercaptan along with various amounts of other sulfur compounds and collects in a sump  131  at the bottom of the absorber  130  to form a liquid waste-gas. The liquid waste-gas leaves the sump  131  at the bottom of the absorber  130  through conduit  124  and is heated and evaporated as explained previously. Treated gas leaves the top of the absorber  130  through conduit  144  and is conveyed to condenser/evaporator  146 , where a portion of the treated gas is condensed by evaporating a refrigerant. Liquid refrigerant in conduit  156  enters the bottom of the condenser/evaporator  146  and leaves as a vapor in conduit  158 . The non-condensed treated gas leaves the condenser/evaporator  146  in conduit  148  and is conveyed to a compressor  150  where it is further pressurized for export in conduit  152  to the consumer. The portion of the treated gas which is condensed in the condenser/evaporator  146  returns to the top of the absorber  130  in conduit  154  under flow control through flow valve  155  and flows downwardly through the absorber  130  to scrub and cool the gas which enters the absorber  130  in conduit  142 .  
         [0024]     With reference to  FIG. 2 , a gas stream in conduit  210  from a coal gasification operation or from a gas purification process, such as Rectisol®, containing a high concentration of carbon dioxide along with sulfur compounds such as methyl mercaptan, hydrogen sulfide, dimethyl disulfide, ethyl mercaptan, propyl mercaptan, dimethyl sulfide and the like is conveyed to a compressor  212  for pressurization and further treatment according to the invention. The pressurized gas is conveyed through conduit  214  to a cooler/evaporator  216  which cools the compressed gas while also evaporating liquid waste-gas. The evaporated waste-gas leaves the unit through conduit  218  and is disposed of by incineration or is processed using other treatment methods. The cool compressed gas leaves the cooler/evaporator  216  through conduit  220 . Conduit  220  conveys the compressed gas to the absorber  226  where the compressed gas is cooled to near its condensation temperature by evaporating some of the liquid carbon dioxide that is flowing inside the absorber. The cold compressed gas flows upwardly through the absorber  226  where it is contacted with a downwardly flowing stream of liquid carbon dioxide. The liquid carbon dioxide absorbs methyl mercaptan along with various amounts of other sulfur compounds and collects in a sump  227  at the bottom of the absorber  226  to form a liquid waste-gas. The liquid waste-gas leaves the bottom of the absorber  226  through conduit  224  under the control of level valve  243  and is heated and evaporated as explained previously. Treated compressed gas leaves the top of the absorber  226  through conduit  228  and is conveyed to condenser/evaporator  238 , where a portion of the treated gas is condensed by evaporating a refrigerant. Liquid refrigerant in conduit  234  enters the bottom of the condenser/evaporator  238  and leaves as a vapor in conduit  236 . The non-condensed treated gas leaves the condenser/evaporator  238  in conduit  230  and is conveyed to a compressor  242  where it is further pressurized for export in conduit  240  to the consumer. The portion of the treated gas which is condensed in the condenser/evaporator  238  returns to the top of the absorber  226  in conduit  232  under the control of flow valve  255  and flows downwardly through the absorber  226  to scrub and cool the gas which enters the absorber  226  in conduit  220 .  
         [0025]     With reference to  FIG. 3 , a gas stream in conduit  308  from a coal gasification operation or from a gas purification process, such as Rectisol®, containing a high concentration of carbon dioxide along with sulfur compounds such as methyl mercaptan, hydrogen sulfide, dimethyl disulfide, ethyl mercaptan, propyl mercaptan, dimethyl sulfide and the like is admixed with recycle gas in conduits  364  and  390  and is conveyed via conduit  310  to a compressor  312  for pressurization and further treatment according to the invention. The pressurized gas is conveyed through conduit  314  to a cooler/evaporator  316  which cools the compressed gas while also evaporating liquid waste-gas in conduit  325 , which is subject to the control of level valve  343 . The evaporated waste-gas leaves the unit through conduit  326  and is disposed of by incineration or is processed using other treatment methods. The cool compressed gas leaves the cooler/evaporator  316  through conduit  318 . A portion of the gas in conduit  318  is routed through conduit  320  and into a reboiler  322  where it is used to concentrate the liquid waste-gas in conduit  324  by evaporating a portion of it. The evaporated waste-gas leaves the reboiler  322  in conduit  328  and returns to the absorber  330 . The compressed gas used in the reboiler leaves in conduit  332  and blends back with the compressed gas from conduit  333  in conduit  334 . The temperature valve  335  in conduit  333  controls the amount of heat applied to the reboiler  322  so that the correct bottoms flow is obtained from the column in conduit  324 . Conduit  334  conveys the compressed gas to cooler/evaporator  336  where the compressed gas is cooled to near its condensation temperature by evaporating liquid carbon dioxide.  
         [0026]     Treated carbon dioxide enters the cooler/evaporator  336  as a liquid through conduit  384  and leaves the cooler/evaporator as a vapor in conduit  386 . The cold compressed sour feed gas is conveyed in conduit  342  to the absorber  330 . The cold compressed sour feed gas flows upwardly through the absorber  330  where it is contacted with a downwardly flowing stream of liquid carbon dioxide. The liquid carbon dioxide absorbs methyl mercaptan along with various amounts of other sulfur compounds and collects in a sump  331  at the bottom of the absorber  330  to form a liquid waste-gas. The liquid waste-gas leaves the bottom of the absorber  330  through conduit  324  and is heated and evaporated as explained previously. Treated compressed gas leaves the top of the absorber  330  through conduit  344  and is conveyed to a compressor  350  where it is further pressurized for export in conduit  352 . Before leaving the process, a slip stream of the high pressure gas is taken from conduit  352  in conduit  356  and across level valve  357  where a portion of the treated carbon dioxide gas is condensed by expansion at a lower pressure in flash vessel  358 . That portion of the gas that is liquefied is used as both scrubbing liquor and refrigerant. The portion of the product or purified gas which is not used for refrigeration is exported to the consumer in conduit  354 . The scrubbing liquor portion is withdrawn from vessel  358  in conduit  372  and fed under flow control through valve  374  into absorber  330 . The refrigerant portion of the liquid carbon dioxide in vessel  358  is withdrawn through conduit  380  under control of valve  382  and fed into the cooler/evaporator  336  via conduit  384 . Liquid refrigerant in conduit  384  enters the bottom of the condenser/evaporator  336  and leaves as a vapor in conduit  386  under the influence of pressure valve  388  and is recycled by means of conduit  390  to the inlet line  310  of compressor  312 . The non-condensed portion of the gas in flash vessel  358  is withdrawn through conduit  360  under the influence of pressure valve  362  and recycled by means of conduit  364  to the inlet line  310  of compressor  312 . Alternatively, under the appropriate operating conditions, the non-condensed portion of the gas can be recycled by means of conduit  366  to the inlet line  344  of compressor  350  and recompressed as sales gas.  
         [0027]     With reference to  FIG. 4 , a gas stream in conduit  410  from a coal gasification operation or from a gas purification process, such as Rectisol®, containing a high concentration of carbon dioxide along with sulfur compounds such as methyl mercaptan, hydrogen sulfide, dimethyl disulfide, ethyl mercaptan, propyl mercaptan, dimethyl sulfide and the like is admixed with recycle gas  454  and conveyed in conduit  412  to a compressor  414  for pressurization and further treatment according to the invention. The pressurized gas is conveyed through conduit  416  to a cooler/evaporator  418  which cools the compressed gas while also evaporating liquid waste-gas. The evaporated waste-gas leaves the unit through conduit  426  and is disposed of by incineration or is processed using other treatment methods. The warm compressed gas leaves the cooler/evaporator  418  through conduit  420 . The warm compressed gas is conveyed in conduit  420  to the absorber  422 . The warm compressed gas flows upwardly through the absorber  422  where it is contacted with a downwardly flowing stream of liquid carbon dioxide. The liquid carbon dioxide both cools the compressed gas and absorbs methyl mercaptan along with various amounts of other sulfur compounds. The liquid carbon dioxide collects in a sump  423  at the bottom of the absorber  422  to form a liquid waste-gas. The liquid waste-gas leaves the bottom of the absorber  422  through conduit  424  under the control of level valve  425  and is heated and evaporated as explained previously. Treated compressed gas leaves the top of the absorber  422  through conduit  430  and is conveyed to a compressor  432  where it is further pressurized for export in conduit  434 . Before the product or purified gas from the process is exported to the consumer in conduit  436 , a slip stream of the high pressure gas is taken from conduit  434  in conduit  438  and across level valve  440  where a portion of the treated carbon dioxide gas is condensed by expansion at a lower pressure in flash vessel  442 . That portion of the gas that is liquefied is used as scrubbing liquor. The scrubbing liquor is withdrawn from vessel  442  in conduit  444  and fed under flow control through flow valve  446  into absorber  422 . The non-condensed portion of the gas in flash vessel  442  is withdrawn through conduit  450  under the influence of pressure valve  452  and recycled by means of conduit  454  to the inlet line  412  of compressor  414 . Alternatively, under the appropriate operating conditions, the non-condensed portion of the gas can be recycled by means of conduit  456  to the inlet line  430  of compressor  432  and recompressed as sales gas.  
         [0028]     The following non-limiting example demonstrates various aspects of the invention.  
       EXAMPLES 1-53  
       [0029]     A 2200 lb/hr slip stream of a contaminated CO 2 -rich off gas from a Rectisol® Unit inside a North Dakota coal gasification plant, having an average (but also highly variable) methyl mercaptan content of about 200 ppmv and containing 1.1 mole percent hydrogen sulfide, 95 ppmv carbonyl sulfide, 3 ppmv dimethyl disulfide, 1 ppmv ethyl mercaptan and trace amounts of carbon disulfide, propyl mercaptan and dimethyl disulfide, was processed in a continuous flow pilot plant. The pilot plant consisted of two CO 2  gas compressors in series, five heat exchangers, a packed absorption/distillation column, and an on-line analyzer for methyl mercaptan analysis. The pilot plant was operated over a range of conditions such that the raw feed gas was first compressed to between 280 psig and 360 psig. The compressed gas was then cooled either prior to the absorber or inside of it depending upon the mode of operation. The absorber operating temperature ranged between minus 3° F. and plus 13° F. depending on the pressure of operation, with the lower temperatures corresponding to the lower operating pressures. The cold feed gas was allowed to flow upwardly through the absorber where it was contacted with a downward flow of liquid carbon dioxide. The flow of liquid carbon dioxide was varied over a range of rates corresponding to 4 (Table 1, Example 40) to 25 (Table 1, Example 20) weight percent of the feed gas mass flow rate, resulting in an L/G ratio or reflux ratio in the range of 4 to 25 pounds of liquid carbon dioxide per 100 pounds of sour feed gas. Liquid carbon dioxide was collected in the sump at the bottom of the absorber, where the methyl mercaptan was concentrated by evaporating some of the carbon dioxide from the liquid using either warm feed gas or an electric reboiler as the heat source. This method of concentration typically reduced the bottoms flow of liquid to within the range of 1 to 5 weight percent of the weight flow of fresh feed gas. The evaporated gas from the concentration step was returned to the absorber for reprocessing. The liquid containing the methyl mercaptan was withdrawn from the bottom of the absorber and then vaporized using steam heat, after which it was fed into the combustion zone of a steam boiler for incineration and later recovery of the sulfur using a wet scrubber to produce ammonium sulfate fertilizer. The purified gas was withdrawn from the top of the absorber and a portion (4 to 25 weight percent of the feed gas mass flow rate) was condensed and returned to the absorber as scrubbing liquor. The remaining treated gas was removed from the pilot plant as product. The results are shown on Table 1.  
         [0030]     The data in Table 1 shows that a significant reduction in methyl mercaptan was obtained by treating contaminated carbon dioxide gas with liquid carbon dioxide at pressures ranging from about 280 psig to 360 psig and at temperatures from about minus 3° F. to plus 13° F. Under some of the best conditions, such as were used in Runs 3, 19, 20, 33, 34 and 45, more than 99.5 percent of the methyl mercaptan was removed from the feed gas.  
                                                                                                                                     TABLE 1                                                                       CH3SH Removal   CH3SH Removal                                                           From the   From the                   Column                   Reflux or   Total               Final Protect   Final Protect                   Configuration           Average   Average   Wash   Liquid CO2       Conc. of   Conc. of   Based on the   Based on the                   Feel of           Column   Overall   Rate,   Produced,   Conc. of   CH3SH   CH3SH   Concentration   Concentration   Final Protect           Process   Packing   Operating   Feed Gas   Top   Column   Wt % of   Wt % of   CH3SH   in Column   in Final   Leaving the   Leaving the   Recovery as           Configu-   above Feed   Pressure,   Temperature   Temperature,   Temperature   Feed Gas   Feed Gas   in Feed gas   Ovrhd Gas   Protect Gas   the Absorber   the Process   wt % of       Test No.   ration   Point   Psig   deg F.   deg F.   deg F.   Rate   Rate   ppm/   ppm/   ppm/   %   %   Feed Gas                                 1*   Absorber   15   321   82   7.0   11.7   17.9%   39.0%   196   150.0   65.0   23.5%   68.8%   99.0%        2   Absorber   15   321   85   6.2   9.2   19.8%   54.6%   198   5.2   0.0   97.4%   100.0%   97.9%        3   Absorber   15   321   84   5.6   7.5   21.8%   25.8%   210   0.4   0.0   99.8%   100.0%   95.7%        4   Absorber   15   321   85   6.5   10.5   18.9%   28.0%   186   9.0   4.0   95.2%   97.8%   98.7%        5   Absorber   15   321   57   5.9   7.9   16.8%   24.4%   196   11.0   5.0   94.4%   97.4%   96.9%        6   Absorber   15   321   53   6.1   7.9   12.6%   33.5%   178   70.0   17   60.7%   90.4%   98.0%        7   Absorber   15   321   59   6.0   7.7   14.4%   19.1%   145   21.0   7.6   85.5%   94.8%   97.5%        8   Absorber   15   321   77   5.8   8.0   18.7%   37.4%   145   2.9   0.9   98.0%   99.4%   97.3%        9   Absorber   15   361   69   13.1   15.4   15.9%   25.8%   186   28.3   12.4   84.8%   93.3%   97.2%       10   Absorber   15   281   75   −3.0   0.3   19.2%   23.6%   134   2.0   0.9   98.5%   99.3%   97.8%       11   Absorber   15   300   70   1.0   4.1   17.6%   28.5%   144   4.0   1.7   97.2%   98.8%   97.7%       12   Absorber   15   320   68   4.7   7.1   17.2%   61.2%   195   15.0   0   92.3%   100.0%   97.0%       13   Absorber   15   340   68   8.3   10.6   16.2%   24.4%   140   9.8   4.1   93.0%   97.1%   97.3%       14   Absorber   15   360   71   11.7   14.2   16.2%   33.9%   119   17.4   7   85.4%   93.6%   97.8%       15A   Distillation   15   360   12   11.0   12.5   21.1%   29.7%   176   3.0   1   98.3%   93.8%   97.7%       15B   Distillation   15   360   12   11.0   12.5   19.8%   34.4%   210   7   2   96.7%   99.0%   97.0%       16   Distillation   15   339   8   7.4   8.8   19.6%   26.0%   210   4   2   98.1%   99.0%   97.2%       17   Distillation   15   320   5   3.9   5.4   20.0%   NA   200   4   2   98.0%   99.0%   96.8%       18   Distillation   15   300   2   0.3   1.8   19.4%   28.3%   153   1.5   0.5   99.0%   99.7%   98.0%       19   Distillation   15   300   2   1.0   2.0   20.7%   32.0%   181   0.7   0.7   99.6%   99.6%   98.0%       20   Distillation   15   299   2   0.8   1.9   24.7%   26.9%   212   0   0   100.0%   100.0%   97.8%       21   Distillation   15   300   3   1.2   2.2   16.5%   27.1%   193   5.1   2.1   97.4%   98.9%   97.1%       22   Distillation   15   300   3   1.4   2.4   14.4%   33.9%   205   10   2.9   95.1%   98.6%   97.2%       23   Distillation   15   300   3   1.4   2.4   12.6%   31.9%   180   21.2   5.5   88.2%   96.9%   97.9%       24   Distillation   15   300   3   1.4   2.4   14.6%   23.2%   203   11.5   3.9   94.3%   98.1%   97.3%       25   Distillation   15   300   3   1.5   2.5   11.4%   32.4%   200   48   13   76.0%   93.5%   97.7%       26   Distillation   15   300   3   1.3   2.3   17.7%   26.7%   248   4.3   1.6   98.3%   99.4%   96.0%       27   Absorber   27   290   71   −0.1   3.0   18.0%   31.5%   197   4   1   90.0%   99.5%   97.7%       28   Absorber   27   290   60   0.0   2.4   15.8%   26.7%   187   7.2   2.7   96.1%   98.6%   97.4%       29   Absorber   27   290   74   −0.1   2.6   19.4%   NA   186   2   1.9   98.9%   99.0%   97.1%       30   Absorber   27   290   55   0.0   2.3   15.6%   44.9%   211   19   5   91.0%   97.6%   96.6%       31   Absorber   27   290   46   0.1   2.1   13.4%   20.3%   222   25.6   9.8   88.5%   95.6%   96.9%       32   Absorber   27   290   20   0.0   1.4   7.1%   NA   182   75   38.1   58.8%   79.1%   97.6%       33   Absorber   27   290   78   −0.3   0.3   18.4%   22.3%   138   0.1   0   99.9%   100.0%   98.8%       34   Absorber   27   290   54   −0.4   0.0   15.2%   16.8%   154   0.3   0   99.8%   100.0%   96.7%       35   Absorber   27   290   37   −0.4   −0.1   12.5%   20.4%   209   5.4   1.9   97.4%   99.1%   95.7%       36   Absorber   27   290   15   −0.5   −0.2   10.8%   15.1%   244   12   5   95.1%   98.0%   92.6%       37   Absorber   27   290   44   −0.5   −0.1   14.1%   NA   245   2   0   99.2%   100.0%   95.6%       38   Absorber   27   290   23   −0.3   0.0   11.0%   25.4%   289   47.4   12.7   83.6%   95.6%   94.0%       39   Absorber   27   290   15   −0.2   0.1   7.5%   20.7%   284   139   53   51.1%   81.3%   95.8%       40   Distillation   27   290   1   0.0   0.1   4.3%   NA   267   258   166   1.4%   37.8%   99.9%       41   Distillation   27   290   1   −0.4   −0.2   10.3%   23.8%   329   39.4   13.6   88.0%   95.9%   97.0%       42   Distillation   27   290   4   −0.4   −0.2   8.4%   39.5%   238   76   18   68.1%   92.4%   97.7%       43   Distillation   27   290   4   −0.6   −0.4   11.3%   28.0%   247   19   5.7   92.3%   97.7%   96.8%       44   Distillation   27   290   4   −0.7   −0.4   13.7%   37.0%   251   2   0   99.2%   100.0%   97.2%       45   Distillation   27   290   4   −0.7   −0.3   15.2%   NA   200   0.7   0.5   99.7%   99.8%   97.4%       46   Distillation   27   290   4   −0.4   −0.2   8.5%   NA   220   78   15   64.5%   93.2%   98.1%       47   Distillation   27   290   4   −0.6   −0.4   12.9%   18.0%   225   5.2   2.1   97.7%   99.1%   97.2%       48   Distillation   27   300   6   1.5   1.7   8.5%   33.0%   205   58   15   71.7%   92.7%   98.1%       49   Distillation   27   300   6   1.3   1.5   12.1%   32.0%   177   10   3   94.4%   98.3%   97.7%       50   Distillation   27   300   6   1.4   1.6   10.3%   36.7%   198   56   11   71.7%   94.4%   98.2%       51   Distillation   27   300   6   1.2   1.4   14.2%   33.9%   175   3.2   0.9   98.2%   99.5%   97.7%       52A   Distillation   27   300   6   1.2   1.4   12.2%   34.6%   171   18.4   4.1   89.2%   97.6%   97.6%       52B   Distillation   27   300   6   1.3   1.5   12.0%   NA   154   21   12   87.2%   92.7%   97.9%       52C   Distillation   27   300   6   1.3   1.5   12.6%   24.9%   157   12   5   92.4%   96.8%   97.9%       52D   Distillation   27   300   6   1.4   1.6   11.4%   23.7%   148   19   8   87.2%   94.6%   98.5%       53   Distillation   27   300   6   1.4   1.6   9.8%   20.3%   159   38   15   76.1%   90.6%   98.1%                 NA = Not Available            *low CH3SH removal attributed to start-up conditions             
 
         [0031]     Having now described and illustrated the preferred embodiments of the invention, it will be appreciated by those of appropriate skill that various modifications, rearrangements and substitutions may be made to the invention within the spirit and scope of the appended claims.