Patent Publication Number: US-2022236216-A1

Title: Systems and related methods for analyzing a gas

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 63/141,548, having a filing date of Jan. 26, 2021, and Canadian Patent Application No. 3,141,116, having a filing date of Dec. 6, 2021, the entire contents both of which are incorporated herein by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The following relates to gas analysis. More particularly, the present disclosure relates to systems and methods for analyzing sulfur compounds in hydrocarbon gas. 
     BACKGROUND 
     Hydrocarbon gases including natural gas, liquid petroleum gas, and propane are colorless and odorless. Organosulfur compounds are typically used to odorize hydrocarbon gases, allowing humans to detect leakage of these hydrocarbons before they reach their lower explosion limit. Organosulfur compounds commonly used as gas odorants include tetrahydrothiophene (THT), tert-butyl mercaptan (TBM), ethyl mercaptan (EM), sec-butyl mercaptan (SBM), methyl ethyl sulfide (MES), n-propyl mercaptan (NPM), isopropyl mercaptan (IPM), diethyl sulfide (DES), and dimethyl sulfide (DMS). In North America, a widely used natural gas odorant is a blend of TBM and MES. 
     Natural gas distributors typically analyze and maintain the concentration of the odorants throughout their distribution network on a regular basis. This process is conventionally done by sampling natural gas samples from the field and sending each sample to a gas chromatography laboratory for analysis. An example of natural gas odorant analysis method with gas chromatography can be found in Macak et al. “Determination of sulphur compounds in natural gas by gas chromatography with a flame photometric detector”, Journal of Chromatography, 286 (1984), pp. 69-78. However, such methods can be time-consuming and expensive. 
     U.S. Pat. No. 4,526,755 to Vincent et al. teaches an alternative approach to natural gas odorant analysis in which natural gas passes through bubblers followed by analysis by coulometric titrators. The bubblers contain aqueous solutions to remove specific compounds from the natural gas: e.g., a 1.0% CdSO 4  and 2.0% H 3 BO 3  solution (to remove H 2 S), a 10.0% NaOH solution (to remove mercaptans), and a 0.5% AgNO 3  water solution (to remove sulfides). Although this approach may be suitable for laboratory use, it is not suitable for field deployment as the aqueous bubbling solutions may freeze if the environmental temperature drops below their freezing point. The concentration of the bubbling solutions may also need to be frequently compensated due to evaporation. Furthermore, additional moisture in the processed gas can also influence the performance of the sensors positioned downstream of the bubblers. 
     Another possible approach for the analysis of odorants in natural gas involves the use of electrochemical cell gas sensors, also known as electrochemical sensors. Electrochemical sensors are widely used and their selectivity has improved greatly over in recent years (Guth et al. “Recent developments in electrochemical sensor application and technology—a review”, Measurement Science and Technology, 20 (2009), 042002); however, they still suffer from cross-sensitivity issues. For example, an electrochemical sensor designed for sensing methyl mercaptan (MM) will also respond to other sulfur-containing molecules (including TBM, MES, and H 2 S), triggering a false positive when MM is not present. Thus, electrochemical gas sensors alone are not able to analyze the concentrations of individual odorants when two or more sulfur compounds are present in an analyte gas. As a result, commercial electrochemical gas sensors designed for natural gas odorant analysis typically only provide estimated total odorant concentration. In addition, these sensors may be affected by cross-sensitivity to H 2 S that naturally exists in natural gas. 
     European Patent Publication No. EP0445927 to Willance et al. describes an odorant analyzer system to address the cross-sensitivity issue. The system utilizes a gas chromatography column to separate the sulfur compounds present in a natural gas sample before analysis by an electrochemical gas sensor. However, this system is large and complex with considerable electronic requirements, which would be difficult to implement for field deployment in hazardous locations. 
     SUMMARY 
     An aspect relates to a system for analyzing a gas, the system comprising: at least one scrubber comprising a non-aqueous scrubber material that removes at least one sulfur compound from the gas to produce a scrubbed gas; and at least one gas sensor in fluid communication with the at least one scrubber, the at least one gas sensor sensing at least one remaining sulfur compound in the scrubbed gas. 
     In some embodiments, the scrubber material comprises an alkali metal hydroxide, an alkaline earth metal hydroxide, a carbonate salt, a bicarbonate salt, an iodate salt, a metal oxide, an amine, or a combination thereof. 
     In some embodiments, the at least one scrubber comprises a first scrubber and a second scrubber, the first scrubber comprising a first scrubber material and the second scrubber comprising a second scrubber material. 
     In some embodiments, the first scrubber material is a liquid-phase scrubber material and the second scrubber material is a solid-phase scrubber material. 
     In some embodiments, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt. 
     In some embodiments, the at least one gas sensor comprises a first gas sensor and a second gas sensor, the first gas sensor fluidly connected to the first scrubber and the second gas sensor fluidly connected to the second scrubber. 
     In some embodiments, the system further comprises a valve in fluid communication with the first and second scrubbers and the at least one gas sensor, the valve selectively movable between a first position in which a first gas stream flows from the first scrubber to the at least one gas sensor and a second position in which a second gas stream flows from the second scrubber to the at least one gas sensor. 
     In some embodiments, the system further comprises at least one pump operable to move the scrubbed gas from the at least one scrubber to the at least one gas sensor. 
     In some embodiments, the system further comprises a processor that processes sensor output of the at least one gas sensor to determine a concentration of the at least one remaining sulfur compound. 
     In some embodiments, the at least one gas sensor comprises one or more electrochemical cells. 
     In another aspect, there is provided a method for analyzing a gas, the method comprising: contacting the gas with a non-aqueous scrubber material that removes at least one sulfur compound to produce a scrubbed gas; and sensing at least one remaining sulfur compound in the scrubbed gas. 
     In some embodiments, the scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine. 
     In some embodiments, sensing the at least one remaining sulfur compound comprises sensing at least one of tetrahydrothiophene (THT), tert-butyl mercaptan (TBM), methyl ethyl sulfide (MES), n-propyl mercaptan (NPM), isopropyl mercaptan (IPM), dimethyl sulfide (DMS), sec-butyl mercaptan (SBM), diethyl sulfide (DES), and ethyl mercaptan (EM). 
     In some embodiments, sensing the at least one remaining sulfur compound comprises sensing a first sulfur content of the scrubbed gas. 
     In some embodiments, further comprising sensing a second sulfur content of an unscrubbed stream of the gas and determining an H 2 S concentration based on the difference between the first sulfur content and the second sulfur content. 
     In some embodiments, the scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt. 
     In some embodiments, sensing the at least one remaining sulfur compound comprises sensing at least one of MES, DMS, DES, and THT. 
     In some embodiments, the at least one remaining sulfur compound is sensed by at least one gas sensor, the at least one gas senor comprising one or more electrochemical cells. 
     In another aspect, there is provided a method for analyzing a gas, the method comprising: separating the gas into a first gas stream and a second gas stream; contacting the first gas stream with a first non-aqueous scrubber material to produce a first scrubbed gas stream; contacting the second gas stream with a second non-aqueous scrubber material to produce a second scrubbed gas stream; sensing at least one first remaining sulfur compound in the first scrubbed gas stream; and sensing at least one second remaining sulfur compound in the second scrubbed gas stream. 
     In some embodiments, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt. 
     Other aspects and features of the present disclosure will become apparent, to those ordinarily skilled in the art, upon review of the following description of the specific embodiments of the disclosure. 
    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein: 
         FIG. 1A  is a schematic diagram of an example one-scrubber-one-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 1B  is a functional block diagram of the system of  FIG. 1A ; 
         FIG. 2  is a schematic diagram of another example one-scrubber-one-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 3  is a schematic diagram of another example one-scrubber-one-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 4  is a flowchart of an example method for analyzing a gas, according to some embodiments; 
         FIG. 5  is a schematic diagram of an example two-scrubber-two-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 6A  is a schematic diagram of another example two-scrubber-two-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 6B  is a schematic diagram of another example two-scrubber-two-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 6C  is a schematic diagram of another example two-scrubber-two-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 6D  is a schematic diagram of another example two-scrubber-two-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 7  is a schematic diagram of an example two-scrubber-one-sensor system for analyzing a gas, according to some embodiments; 
         FIG. 8  is a flowchart of another example method for analyzing a gas, according to some embodiments; 
         FIG. 9  is a schematic diagram of another example one-scrubber-one-sensor system, according to some embodiments; 
         FIG. 10  is a flowchart of another example method for analyzing a gas, according to some embodiments; 
         FIG. 11  is a schematic diagram of an experimental system for analyzing a gas; 
         FIG. 12  is a line graph showing electrochemical sensor output in response to varying concentrations of TBM; 
         FIG. 13  is a line graph showing electrochemical sensor output in response to varying concentrations of MES; 
         FIG. 14A  is a line graph showing electrochemical sensor output in response to TBM, with and without a pre-treatment step with NaOH and Ca(OH) 2  scrubber material; 
         FIG. 14B  is a line graph showing electrochemical sensor output in response to H 2 S with and without a pre-treatment step with NaOH and Ca(OH) 2  scrubber material; 
         FIG. 14C  is a line graph showing electrochemical sensor output in response to MES with and without a pre-treatment step with NaOH and Ca(OH) 2  scrubber material; 
         FIG. 15A  is a line graph showing electrochemical sensor output in response to H 2 S, with or without a pre-treatment step with CaCO 3  scrubber material and MDEA scrubber material, respectively; 
         FIG. 15B  is a line graph showing electrochemical sensor output in response to H 2 S, with or without a pre-treatment step with CaCO 3  scrubber material and MDEA scrubber material, respectively; and 
         FIG. 16  is a line graph showing electrochemical sensor output in response to a gas sample comprising TBM, MES, and H 2 S following a pre-treatment step with NaOH and Ca(OH) 2  scrubber material (first peak) or MDEA scrubber material (second peak). 
     
    
    
     DETAILED DESCRIPTION 
     Generally, the present disclosure provides a system for analyzing a gas. In some embodiments, the system comprises: at least one scrubber comprising a non-aqueous scrubber material that removes at least one sulfur compound from the gas; at least one gas sensor in fluid communication with the at least one scrubber, the at least one gas sensor sensing at least one remaining sulfur compound in the scrubbed gas. Related methods for analyzing a gas are also provided. 
     As used herein, “upstream” and “downstream” refer to the direction of flow of a gas stream through embodiments of the systems described herein. Under normal operating conditions, the gas stream flows from an upstream position to a downstream position. 
     The systems and methods disclosed herein may be used to analyze a gas. In some embodiments, the gas is a hydrocarbon gas. As used herein, the term “hydrocarbon gas” refers to any gas comprising at least one hydrocarbon component. Non-limiting examples of hydrocarbon gases include natural gas, liquefied petroleum gas, and propane. In some embodiments, the gas further comprises one or more native sulfur compounds that are naturally present in the gas. In some embodiments, the native sulfur compounds comprise hydrogen sulfide (H 2 S) and/or one or more mercaptans. 
     The gas may further comprise one or more odorants. In some embodiments, one or more of the odorants comprises a sulfur compound. In some embodiments, the sulfur compound is an organosulfur compound. Non-limiting examples of organosulfur compounds include (THT), tert-butyl mercaptan (TBM), ethyl mercaptan (EM), sec-butyl mercaptan (SBM), methyl ethyl sulfide (MES), n-propyl mercaptan (NPM), isopropyl mercaptan (IPM), diethyl sulfide (DES), and dimethyl sulfide (DMS). In some embodiments, the gas comprises a blend of two or more odorants including, but not limited to, an organic sulfide and a mercaptan (e.g., TBM/MES blends or TBM/THT blends). In some embodiments, the gas to be analyzed comprises between about 0 and about 10 ppm of each odorant. 
       FIG. 1A  is a schematic diagram of an example system  100  for analyzing a gas, according to some embodiments. The system  100  may comprise at least one scrubber and at least one gas sensor. The system  100  in this embodiment comprises a scrubber  102  and a gas sensor  104 . The system  100  may therefore also be referred to herein as a “one-scrubber-one-sensor” system. 
     As used herein, “scrub” or “scrubbing” refers to removing at least one chemical component of the gas and a “scrubber” refers to an apparatus or device that comprises a material capable of scrubbing (the “scrubber material”). The scrubbing may involve one or more physical and/or chemical processes to remove the chemical component(s) from the gas. Physical processes may include adsorption and/or absorption. Chemical processes may include one or more chemical reactions between the chemical component and the scrubber material that convert the chemical component into one or more different chemical entities. Scrubbing may fully or partially remove the chemical component(s) from the gas. 
     The scrubber material may have selectivity for at least one pre-defined chemical component of the gas. As used herein, “selectivity” or “selective removal” refers to relatively strong physical or chemical interaction with the pre-defined chemical compound(s) and relatively weak interaction (or no interaction) with any other components of the gas. In some embodiments, the scrubber material has selectivity for at least one sulfur compound. 
     The scrubber material may be a non-aqueous material. As used herein “non-aqueous” refers to a material that is substantially free of water, although it may contain trace amounts of water as an impurity. In some embodiments, the scrubber material may also be substantially free of other solvents, carriers, and the like. In some embodiments, the scrubber material comprises a substantially pure chemical compound. As used herein, “purity” refers to the amount of a chemical compound in a given substance and a “substantially pure” chemical compound refers to a substance in which at least about 50% of the total composition of the substance is the compound of interest. In some embodiments, the purity of the chemical compound of the scrubber material is at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 98%, or at least about 99%. In some embodiments, the scrubber material may be a single substantially pure chemical compound or a mixture of two or more substantially pure chemical compounds. In other embodiments, the scrubber material may have a lower purity if none of the other components interfere with the interaction between the scrubber material and the sulfur compounds in the gas being analyzed. 
     In some embodiments, the scrubber material is a solid material that selectively removes at least one chemical component of the gas (a “solid-phase scrubber material”). The solid-phase scrubber material may be in the form of powder, pellets, or any other suitable solid form. 
     In some embodiments, the solid-phase scrubber material comprises a solid form of a carbonate salt, a bicarbonate salt, a metal oxide, or a combination of one or more carbonate salts, bicarbonate salts, and/or metal oxides. In some embodiments, the carbonate salt, bicarbonate salt, or metal oxide is substantially pure. Non-limiting examples of carbonate and bicarbonate salts include Na 2 CO 3 , CaCO 3 , K 2 CO 3 , NaHCO 3  and KHCO 3 . Non-limiting examples of metal oxides include CaO and ZnO. The solid-phase scrubber material may selectively remove H 2 S from the gas. In some embodiments, H 2 S reacts with the scrubber material. Non-limiting examples of possible reactions between H 2 S and the scrubber material are provided below: 
         x H 2 S+M 2 (CO 3 ) x =M(HS) x +M(HCO 3 ) x    
         x H 2 S+2M(HCO 3 ) x =M 2 S x +2 x H 2 O+2 x CO 2    
         x H 2 S+M 2 O x =M 2 S x   +x H 2 O         where M is a metal atom and x is equal to its oxidation number.       
     In other embodiments, the solid-phase scrubber material comprises a hydroxide-based scrubber material. In some embodiments, the hydroxide-based scrubber material comprises a solid form of an alkali metal hydroxide, an alkaline earth metal hydroxide, or a combination of one or more alkali metal hydroxides and/or one or more alkaline earth metal hydroxides. In some embodiments, the alkali metal hydroxide and/or alkaline earth metal hydroxide is substantially pure. The alkali metal hydroxide may comprise NaOH, LiOH, KOH, RbOH, or CsOH. The alkaline earth metal hydroxide may comprise Ca(OH) 2 , Ba(OH) 2 , and Sr(OH) 2 . The hydroxide-based scrubber material may selectively remove H 2 S and mercaptans (e.g., TBM) from the gas. Where the gas to be analyzed comprises natural gas, the scrubber material may also remove other mercaptans that are naturally present in the natural gas. In some embodiments, H 2 S and mercaptans reacts with the scrubber material. Non-limiting examples of possible reactions between H 2 S and mercaptans and the scrubber material are provided below: 
         x H 2 S+2M(OH) x =M 2 S x +2 x H 2 O 
         x RSH+M(OH) x =M(SR) x   +x H 2 O         where M is an alkali metal atom or alkaline earth metal atom, x is equal to the oxidation number of the metal atom, and R is an alkyl group       
     In other embodiments, the solid-phase scrubber material comprises an iodate-based scrubber material. In some embodiments, the iodate-based scrubber material comprises a solid form of an iodate salt, or a combination of one or more iodate salts and one or more alkali metal hydroxides or alkaline earth metal hydroxides. In some embodiments, the iodate salt is substantially pure. The iodate salt may comprise NaIO 3 , KIO 3 , Ca(IO 3 ) 2 , or Mg(IO 3 ) 2 . The iodate-based scrubber material may selectively remove H 2 S and mercaptans (e.g., TBM) from the gas. Where the gas to be analyzed comprises natural gas, the scrubber material may also remove other mercaptans that are naturally present in the gas. 
     In other embodiments, the solid-phase scrubber material comprises any other suitable solid material that is capable of scrubbing at least one sulfur compound from a gas. 
     In other embodiments, the scrubber material is a liquid material that selectively removes at least one chemical component of the gas (a “liquid-phase scrubber material”). The liquid-phase scrubber material may comprise an organic, non-aqueous liquid. In some embodiments, the liquid-phase scrubber material comprises an amine or a mixture of two or more amines. In some embodiments, the amine is substantially pure. Non-limiting examples of amines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), and diglycolamine (DGA). The amine-based scrubber material may selectively remove H 2 S from the gas. In some embodiments, H 2 S reacts with the scrubber material. Non-limiting examples of possible reactions between H 2 S and the scrubber material are provided below: 
       RNH 2 +H 2 S=RNH 3   + +HS—
 
       RR′NH+H 2 S═RR′NH 2 ++HS—
 
       RR′R″N+H 2 S═RR′R″NH++HS—
         where R, R′, and R″ are alkyl or alkanol groups.       

     In embodiments in which the scrubber material is solid-phase, the scrubber  102  may comprise a dry scrubber, a filter, or any other suitable apparatus configured to contain the solid-phase scrubber material. In embodiments in which the scrubber material is liquid-phase, the scrubber  102  may comprise a wet scrubber. The wet scrubber may comprise a bubbler, a spray tower, or any other suitable apparatus configured to contain the liquid-phase scrubber material. As used herein, a “bubbler” refers to any system in which a stream of gas is directed (i.e., “bubbled”) through the liquid-phase scrubber material, while a “spray tower” is any system in which the liquid-phase scrubber material is sprayed through or into the gas. 
     The gas sensor  104  is configured to sense at least one remaining sulfur compound in the gas scrubbed by the scrubber  102 . In this embodiment, the gas sensor  104  comprises an electrochemical sensor having one or more electrochemical sensor cells (hereafter also referred to as simply “electrochemical cells”). Electrochemical sensors have several advantages including low cost, low power consumption, and high sensitivity. Electrochemical sensor cells operate by reacting an analyte on the surface of a working electrode, generating an electrical signal that is linearly proportional to the concentration of the analyte. Each sensor cell may comprise a working electrode and a counter electrode (two electrode cell) and optionally a reference electrode (three electrode cell). In some embodiments, the gas sensor  104  comprises two or more electrochemical sensor cells placed in series or parallel with one another. 
     In other embodiments, the gas sensor  104  comprises a portable gas chromatograph, a UV-Visible spectrophotometer, a stain tube detector, or any other suitable gas sensing device. In alternative embodiments, the gas sensor  104  may be replaced by an individual performing a “sniff” test. 
     The gas sensor  104  may be in fluid communication with the scrubber  102 . In this embodiment, the gas sensor  104  is positioned downstream of the scrubber  102  and fluidly connected to the scrubber  102  by a first fluid conduit  103 . As used herein, “fluid conduit” will be understood to include one or more pipes, hoses, ducts, tubes, channels, or the like, in any suitable size, shape, or configuration. Embodiments are not limited to any specific type, number, or structure of fluid conduit. 
     The system  100  may further comprise a pump  106 . The term “pump” in this context refers to any device that moves fluids, including but not limited to pumps, aspirators, etc. The pump  106  may be any suitable type of pump capable of pumping a gas stream. In this embodiment, the pump  106  is positioned upstream of the scrubber  102  and is fluidly connected to the scrubber  102  by a second fluid conduit  105 . 
     In operation, the pump  106  receives a gas stream via an inlet  107  and pumps the gas stream through the second fluid conduit  105  to the scrubber  102 . As the gas stream passes through the scrubber  102 , one or more sulfur compounds are removed from the gas. The gas sensor  104  then receives a stream of scrubbed gas via the first fluid conduit  103  and the gas sensor  104  senses one or more of the remaining sulfur compounds in the scrubbed gas. In this embodiment, the electrochemical cell of the gas sensor  104  outputs an electrical signal linearly proportional to the concentration of the one or more remaining sulfur compounds. 
     In some embodiments, the system  100  further comprises a control module  108 . The control module may be operatively connected to one or both of the pump  106  and the sensor  104 . As shown in  FIG. 1B , the control system  108  may comprise at least one processor  110 , a memory  112 , a transceiver  114 , and a user interface  116 . 
     The processor  110  is operatively connected to the memory  112 , the transceiver  114 , and the user interface  116 . The memory  112  stores processor-executable instructions therein that, when executed, cause the processor  110  to implement one or more methods described herein. 
     The transceiver  114  may be configured to send and receive communications over a communication network such as the Internet. The communication network may be a wired or wireless network. In some embodiments, the transceiver  114  comprises both a transmitter and receiver sharing common circuitry. In other embodiments, the transceiver  114  comprises a separate transmitter and receiver. 
     In some embodiments, the control module  108  is in communication with one or more remote devices via the communication network. The remote device may comprise, for example, a client computer or server. In some embodiments, the remote device comprises a mobile communications device such as a smartphone or tablet. 
     The user interface  116  may be configured to display information to a user and/or to receive user input. In some embodiments, the user interface  116  comprises at least one output component and at least one input component. The output component may comprise, for example, at least one of a display screen, a display panel, one or more lights, an audio output device, etc. The input component may comprise, for example, one or more buttons, a touchscreen, keyboard, keypad, trackpad, mouse, microphone, etc. 
     The processor  110  may be operatively connected to the sensor  104  and may be configured to receive and process sensor output therefrom. For example, the processor  110  may calculate the concentration of one or more sulfur compounds based on the electrical signal generated by the sensor  104 . The calculated concentration(s) may be displayed to the user via the user interface  116  and/or may be transmitted to a remote device via the communication network. 
     The processor  110  may also be operatively connected to the pump  106 , for example, via the pump&#39;s power source (not shown). The processor  110  may run a program stored in the memory  112  to control the operation of the pump  106 . Alternatively, or additionally, the processor  110  may receive user input via the user interface  116  to start, stop, or adjust the operation of the pump  106 . In some embodiments, the processor  110  is operable to receive input via a remote device via the communications network. In other embodiments, the pump  106  may be operated manually and the connection between the processor  110  and the pump  106  may be omitted. 
     In some embodiments, the system  100  further comprises one or more additional components. For example, one or more valves (not shown) may be provided in fluid communication with one or more of the fluid conduits  103 ,  105 ,  107  to control the flow of fluid therethrough. In some embodiments, the processor  110  of the control module  108  is operatively connected to the valve(s) to control their operation. 
     In embodiments in which the gas sensor  104  comprises an electrochemical sensor cell, the system  100  may further comprise an air pump (not shown) and an air purging line (not shown) upstream and in fluid communication with the gas sensor  104 . Although electrochemical sensor cells operate normally in hydrocarbon gas (generally a low-humidity and low-oxygen environment) for a short period of time (several minutes to hours), maintaining the cells in a humid (e.g., approximately 10-90% relative humidity) and oxygen-rich environment may improve performance. In these embodiments, ambient air may be pumped through the gas sensor  104 , via the air pump and air purging line, to purge the gas sensor  104  between readings and thereby maintain a suitable humid and oxygen-rich environment. Optionally, the system  100  may further comprise a humidity and temperature sensor (not shown) to monitor the gas flowing into or out of the gas sensor  104 . In other embodiments, where the gas sensor  104  comprises a different type of sensor (e.g., a portable gas chromatograph, a UV-Visible spectrophotometer, or a stain tube detector), the air pump, air purging line, exhaust line, and humidity and temperature sensor may be omitted. 
     In some embodiments, the system  100  comprises a single housing (not shown) that encloses all of the components described above. In other embodiments, the system  100  may comprise two or more separate housings, each housing enclosing one or more individual components. 
       FIG. 2  is a schematic diagram of another example system  200  for analyzing the gas. The system  200  is an alternative embodiment of a one-scrubber-one-sensor system. As shown in  FIG. 2 , the system  200  comprises a scrubber  202 , a gas sensor  204 , and a pump  206 . In this embodiment, the gas sensor  204  is positioned downstream of the scrubber  202  and the pump  206  is positioned downstream of the gas sensor  204 . 
       FIG. 3  is a schematic diagram of another example system  300  for analyzing a gas. The system  300  is another alternative embodiment of a one-scrubber-one-sensor system. As shown in  FIG. 3 , the system  300  comprises a scrubber  302 , a gas sensor  304 , and a pump  306 . In this embodiment, the pump  306  is positioned between the scrubber  302  and the gas sensor  304 . 
     The system  200  and  300  may each further comprise a control module (not shown) similar to the control module  108  of the system  100  of  FIGS. 1A and 1B . The systems  200  and  300  may also comprise any of the other optional components of the system  100  as described above. 
       FIG. 4  is a flowchart of an example method  400  for analyzing a gas, according to some embodiments, that may be implemented using the systems  100 ,  200 , and  300  of  FIGS. 1A-1   i ,  2 , and  3 . The method  400  may be used to analyze a gas containing one odorant such as, for example, THT, TBM, MES, NPM, IPM, DMS, SBM, DES, or EM. 
     At block  402 , a gas is contacted with a scrubber material. The term “contact” in this context is intended to include any means by which the gas is brought into contact with the scrubber material. For example, in embodiments in which the scrubber material is solid-phase, the gas may be flowed through the scrubber material. In embodiments in which the scrubber material is liquid phase, the gas may be bubbled through the scrubber material, or the scrubber material may be sprayed into or through the gas. As discussed above, at least one sulfur compound in the gas may react with the scrubber material. In some embodiments, the reaction is instantaneous or near instantaneous such that there is little to no retention time of the gas in the scrubber material. 
     Contacting the gas with the scrubber material scrubs the gas to remove at least one sulfur compound and thereby produce a scrubbed gas. The gas may be contacted with the scrubber material in the scrubber  102 ,  202 , or  302  of the system  100 ,  200 , or  300  described above. In some embodiments, at least one sulfur compound is completely removed from the gas by the scrubber material such that the compound(s) are no longer present in the scrubbed gas. In other embodiments, at least one sulfur compound is partially removed from the gas such that the concentration of the compound(s) in the scrubbed gas is significantly reduced but small quantities may still be present. 
     In some embodiments, the scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine. In these embodiments, the scrubbing (or “pre-treatment”) step removes H 2 S from the gas. In other embodiments, the scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt. In these embodiments, the scrubbing step removes H 2 S and one or more mercaptans (e.g., TBM). Where the gas to be analyzed comprises natural gas, the scrubbing step may also remove one or more native mercaptans that are naturally present in the natural gas. 
     The scrubbing step at block  402  may be performed under any suitable conditions. In embodiments in which the scrubber material is one of the solid-phase scrubber materials, the scrubbing step may be performed at any ambient temperature, including a wide range of temperatures in the field such as between about −50° C. and about 50° C. In embodiments in which the scrubber material is a liquid-phase material, the scrubbing step may be performed at suitable temperature to maintain the viscosity of the liquid. For example, a scrubbing step with an amine-based scrubbing material may be performed at about 0° C. or higher. 
     At block  404 , at least one remaining sulfur compound in the scrubbed gas is sensed. As used herein, “sensing” refers to detecting, measuring, or otherwise acquiring data or information related to at least one sulfur compound in the gas. The sulfur compound(s) may be sensed using any embodiment of the sensors  104 ,  204 , or  304  described above. In some embodiments, the sulfur compound(s) are sensed by an electrochemical sensor that generates an electrical signal, which is linearly proportional to the concentration of the sulfur compound(s). 
     In some embodiments, the method  400  further comprises calculating a concentration of at least one sulfur compound based on a sensor output. In embodiments in which the sensor is an electrochemical sensor, the sensor output is an electrical signal (I), and the concentration of the sulfur compound can be calculated by dividing the signal by a linear coefficient as shown in Equation 1: 
         C=I/a   (Eq. 1)
         where a is the linear coefficient.       

     The concentration may be expressed in ppm or any other suitable unit. In some embodiments, the calculation step is performed by the processor  110  of the control module  108  (or similar control modules of the systems  200  or  300 ). In other embodiments, the sensor output is transmitted to an external device to perform the calculation or to display the sensor output to a user to perform the calculation manually. 
     As one specific example of the implementation of the method  400 , the gas to be analyzed is natural gas containing TBM as an odorant along with native H 2 S. At block  402 , the scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the scrubbing step removes H 2 S from the gas. At block  404 , the TBM in the gas is sensed by an electrochemical sensor and the sensor output is used to determine the concentration of TBM in the gas. THT, MES, NPM, IPM, DMS, SBM, DES, or EM can also be analyzed in a similar manner. 
     As another example, the gas to be analyzed is natural gas containing THT as an odorant along with native H 2 S and one or more mercaptans. At block  402 , the scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt, and the scrubbing step removes H 2 S and one or more mercaptans. At block  404 , the THT in the gas is sensed by an electrochemical sensor and the sensor output is used to determine the concentration of THT in the gas. MES, DES, and DMS can also be analyzed in a similar manner. 
       FIG. 5  is a schematic diagram of another example system  500  for analyzing a gas, according to some embodiments. The system  500  in this embodiment comprises a first scrubber  502 A, a second scrubber  502 B, a first gas sensor  504 A, and a second gas sensor  504 B. The system  500  may therefore be referred to herein as a “two-scrubber-two-sensor” system. 
     The first scrubber  502 A may comprise a first scrubber material and the second scrubber  502 B may comprise a second scrubber material. In this embodiment, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt. 
     In this embodiment, the first and second sensors  504 A and  504 B each comprise an electrochemical sensor comprising one or more electrochemical cells. In other embodiments, the first and second sensors  504 A and  504 B comprise any other suitable type of sensor including any of the sensors described above for the sensor  104  of the system  100 . The first and second sensors  504 A and  504 B may be the same type of sensor or different types of sensors. 
     The first sensor  504 A may be in fluid communication with the first scrubber  502 A and the second sensor  504 B may be in fluid communication with the second scrubber  502 B. In this embodiment, the first sensor  504 A is downstream of the first scrubber  502 A and is fluidly connected to the first scrubber  502 A by a first fluid conduit  503 A. The second sensor  504 B is downstream of the second scrubber  502 B and fluidly connected to the second scrubber  502 B by a second fluid conduit  503 B. 
     The system  500  may further comprise at least one pump. In this embodiment, the system  500  comprises a pump  506  upstream of both the first and second scrubbers  502 A and  502 B. The pump  506  may be fluidly connected to the first and second scrubbers  502 A and  502 B via a branched fluid conduit  505 . The fluid conduit  505  may comprise a junction  508  that splits the fluid conduit  505  into a first branch  509 A and a second branch  509 B. The first branch  509 A may fluidly connect to the first scrubber  502 A and the second branch  509 B may fluidly connect to the second scrubber  502 B. 
     The system  500  may operate as follows. The pump  506  receives a gas stream via an inlet  507  and pumps the gas stream through the branched fluid conduit  505 , where it is split at the junction  508  into a first gas stream and a second gas stream. The first gas stream flows through the first branch  509 A to the first scrubber  502 A and the second gas stream flows through the second branch  509 B to the second scrubber  502 B. 
     As the first gas stream passes through the first scrubber  502 A, one or more sulfur compounds are removed from the gas to produce a first scrubbed gas. The first scrubbed gas is received by the first gas sensor  504 A via the first fluid conduit  503 A and the first gas sensor  504 A senses one or more of the remaining sulfur compounds in the first scrubbed gas. In this embodiment, the electrochemical cell of the first gas sensor  504 A outputs an electrical signal linearly proportional to the concentration of the one or more remaining sulfur compounds. 
     As the second gas stream passes through the second scrubber  502 B, one or more sulfur compounds are removed from the gas to produce a second scrubbed gas. The second scrubbed gas is received by the second gas sensor  504 B via the second fluid conduit  503 B and the second gas sensor  504 B senses one or more of the remaining sulfur compounds in the second scrubbed gas. In this embodiment, the electrochemical cell of the second gas sensor  504 B outputs an electrical signal linearly proportional to the concentration of the one or more remaining sulfur compounds. 
     The system  500  may comprise a control module (not shown) similar to the control module  108  of the system  100  of  FIG. 1B . In some embodiments, where at least one of the gas sensors  504 A and  504 B comprises an electrochemical sensor cell, the system  500  may comprise an air pump, air purging line, exhaust line and, optionally, a humidity and temperature sensor (all not shown) as described above with respect to the system  100 . 
       FIGS. 6A, 6B, 6C, and 6D  are schematic diagrams of additional example systems  600 ,  620 ,  630 , and  640 , respectively, for analyzing the gas. The systems  600 ,  620 ,  630 , and  640  are alternative embodiments of two-scrubber-two-sensor systems 
     As shown in  FIG. 6A , the system  600  comprises a first scrubber  602 A and a second scrubber  602 B, a first gas sensor  604 A and a second gas sensor  604 B, and a pump  606 . The first and second scrubbers  602 A and  602 B and the first and second gas sensors  604 A and  604 B may be similar to the first and second scrubbers  502 A and  502 B and the first and second gas sensors  504 A and  504 B, respectively, of the system  500  as described above. A first branched conduit  605  may be fluidly connected to the first scrubber  602 A and the second scrubber  602 B. 
     In this embodiment, the pump  606  is positioned downstream of the first and second gas sensors  604 A and  604 B. The pump  606  is fluidly connected to the first and second gas sensors  604 A and  604 B by a second branched conduit  610 . 
     The system  600  may operate in a similar manner to the system  500  as described above. Briefly, the gas may be received by the first branched fluid conduit  605  and split into a first fluid stream and a second fluid stream. The pump  606  may draw the first gas stream through the first scrubber  602 A to the first gas sensor  604 A and draw the second gas stream through the second scrubber  602 B to the second gas sensor  604 B. The first and second scrubbed gas streams may be combined downstream of the first and second gas sensors  604 A and  604 B in the second branched conduit  610 , from which they are pumped out of the system  600 . 
     As shown in  FIG. 6B , the system  620  comprises a first scrubber  622 A, a second scrubber  622 B, a first sensor  624 A, and a second sensor  624 B. In this embodiment, the system  620  further comprises a first pump  626 A and a second pump  626 B. The first pump  626 A is positioned downstream of the first sensor  624 A and the second pump  626 B is positioned downstream of the second sensor  624 B. 
     As shown in  FIG. 6C , the system  630  comprises a first scrubber  632 A, a second scrubber  632 B, a first sensor  634 A, a second sensor  634 B, a first pump  636 A, and a second pump  636 B. In this embodiment, the first pump  636 A is positioned between the first scrubber  632 A and the first sensor  634 A and the second pump  636 B is positioned between the second scrubber  632 B and the second sensor  634 B. 
     As shown in  FIG. 6D , the system  640  comprises a first scrubber  642 A, a second scrubber  642 B, a first sensor  644 A, a second sensor  644 B, a first pump  646 A, and a second pump  646 B. The first pump  646 A is positioned upstream of the first scrubber  642 A and the second pump  646 B is positioned upstream of the second scrubber  642 B. 
     The systems  620 ,  630 , and  640  may otherwise operate in a similar manner to the systems  500  and  600  as described above. 
       FIG. 7  is a schematic diagram of another example system  700  for analyzing a gas. The system  700  in this embodiment comprises a first scrubber  702 A, a second scrubber  702 B, a gas sensor  704 , and a pump  706 . The system  700  may also be referred to herein as a “two-scrubber-one-sensor” system. The system  700  is a simplified embodiment of the two-scrubber-two-sensor systems described above. 
     The first and second scrubbers  702 A and  702 B may be similar to the first and second scrubbers  502 A and  502 B, respectively, of the system  500  as described above. In this embodiment, the pump  706  is upstream of the first and second scrubbers  702 A and  702 B and is fluidly connected to the first and second scrubbers  702 A and  702 B via a branched fluid conduit  705 . 
     The system  700  in this embodiment further comprises a three-way valve  712 . The valve  712  is in fluid communication with the first and second scrubbers  702 A and  702 B and the gas sensor  704  and is positioned downstream of the first and second scrubbers  702 A and  702 B and upstream of the gas sensor  704 . The valve  712  in this embodiment is fluidly connected to the first scrubber  702 A via a first fluid conduit  711 , to the second scrubber  702 B via a second fluid conduit  713 , and to the gas sensor  704  via a third fluid conduit  714 . 
     The system  700  may operate as follows. The pump  706  receives a gas stream via an inlet  707  and pumps the gas stream through the branched fluid conduit  705  where it is split into a first gas stream and a second gas stream. The first gas stream flows through the first scrubber  702 A and the second gas stream flows through the second scrubber  702 B. A first scrubbed gas flows through the first fluid conduit  711  and a second scrubbed gas flows through the second fluid conduit  713 . 
     The valve  712  may be selectively movable between a first position and a second position. When the valve  712  is in the first position, the first fluid conduit  711  is in fluid communication with the third fluid conduit  714  and the gas sensor  704  receives the first scrubbed gas. When the valve  712  is in the second position, the second fluid conduit  713  is in fluid communication with the third fluid conduit  714  and the gas sensor  704  receives the second scrubbed gas. Thus, the gas sensor  704  may alternate between sensing one or more sulfur compounds in the first scrubbed gas and one or more sulfur compounds in the second scrubbed gas. 
     Alternatively, instead of a three-way valve  712 , the system  700  can comprise two one-way valves (not shown). A first one-way valve may be in fluid communication with the first fluid conduit  711  to control the flow of the first scrubbed gas and a second one-way valve may be in fluid communication with the second fluid conduit  713  to control the flow of the second scrubbed gas. In other embodiments, the three-way valve  712  (or two one-way valves) may be positioned upstream of the first and second scrubbers  702 A and  702 B to alternate the flow of gas into the first scrubber  702 A and the second scrubber  702 B, thereby alternating the generation of the first gas stream and the second gas stream. 
     The system  700  may further comprise a control module (not shown) similar to the control module  108  of the system  100  of  FIG. 1B . The control module may be operatively connected to the three-way valve, or two one-way valves, to control operation thereof. 
       FIG. 8  is a flowchart of an example method  800  for analyzing a gas, according to some embodiments. The method  800  may be implemented by embodiments of the systems  500 ,  600 ,  620 ,  630 ,  640 , and  700  of  FIGS. 5, 6A, 6B, 6C, 6D and 7 , respectively. For simplicity, only systems  500 ,  600 , and  700  will be referred to in the description of the method  800  below. The method  800  will be described using natural gas as the gas to be analyzed, wherein the natural gas contains two odorants (TBM and MES) along with native H 2 S and mercaptans. However, it will be understood that the method  800  may be adapted to analyze any other gases comprising two or more odorants such as sulfur compounds. 
     At block  802 , the gas is separated into a first gas stream and a second gas stream. In some embodiments, the gas is separated by pumping the gas through a branched fluid conduit such as the branched fluid conduit  505 ,  605 , or  705  of the system  500 ,  600 , or  700 . 
     At block  804 , the first gas stream is contacted with a first scrubber material. Contacting the first gas stream with the first scrubber material scrubs the gas to remove at least one sulfur compound and thereby produce a first scrubbed gas stream. The first gas stream may be contacted with the first scrubber material by the first scrubber  502 A,  602 A, or  702 A of the system  500 ,  600 , or  700 . In this embodiment, the first scrubber material comprises at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine, and the scrubbing step removes H 2 S from the first gas stream. 
     At block  806 , a second gas stream is contacted with a second scrubber material. Contacting the second gas stream with the second scrubber material scrubs the gas to remove at least one sulfur compound and thereby produce a second scrubbed gas stream. The second gas stream may be scrubbed by the second scrubber  502 B,  602 B, or  702 B of the system  500 ,  600 , or  700 . In this embodiment, the second scrubber material comprises at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an iodate salt, and the scrubbing step removes H 2 S, TBM, and native mercaptans from the second gas stream. 
     At block  808 , at least one remaining sulfur compound in the first scrubbed gas stream is sensed. The sulfur compound(s) may be sensed by the first sensors  504 A or  604 A of the systems  500  or  600 , respectively, or by the sensor  704  of the system  700  when the valve  712  is in the first position. A first sensor output may be generated by the first sensor  504 A or  604 A or the sensor  704 . In this example, both TBM and MES are sensed in the first scrubbed gas stream and the first sensor output is a total electrical signal (I A ) induced by TBM and MES. 
     At block  810 , at least one remaining sulfur compound in the second scrubbed gas stream is sensed. The sulfur compound(s) may be sensed by the second sensors  504 B or  604 B of the systems  500  or  600 , respectively, or by the sensor  704  of the system  700  when the valve  712  is in the second position. A second sensor output may be generated by the second sensor  504 B or  604 B or the sensor  704 . In this example, MES is sensed in the second gas stream and the second sensor output is an electrical signal (I B ) induced by MES. 
     In some embodiments, the steps at blocks  804  and  808  are performed approximately simultaneously as the steps of blocks  806  and  810 . In other embodiments, the steps at blocks  804  and  808  can be performed before or after the steps of blocks  806  and  810 . 
     The method  800  may further comprise calculating a concentration of at least one sulfur compound based on the first and second sensor output. In this example, the concentrations of TBM (C TBM ) and MES (C MES ) can be computed by Equation 2 as follows: 
     
       
      
       C 
       MES 
       =I 
       B 
       /a  
      
     
         C   TBM =( I   A   −I   B )/ b   (Eq. 2)
         where a and b are the linear coefficients.       

     Thus, the method  800  can be used to determine the concentrations of two different sulfur-based odorants within a hydrocarbon gas. It will be understood that the method  800  may be adapted for other types of gases and other combinations of odorants. For example, the method  800  may be adapted to determine the concentrations of an odorant blend comprising an organic sulfide and a mercaptan (e.g., TBM/MES blends or TBM/THT blends). Embodiments are not limited to the specific odorants described herein. 
       FIG. 9  is a schematic diagram of another example system  900  for analyzing a gas, according to some embodiments. The system  900  comprises a scrubber  902 , a gas sensor  904 , and a pump  906 . The system  900  is an alternative embodiment of a one-scrubber-one-sensor system that may be used to determine H 2 S content in a hydrocarbon gas. 
     The scrubber  902  may comprise a scrubber material that selectively removes H 2 S from the gas. For example, the scrubber material may comprise at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine. The gas sensor  904  in this embodiment comprises an electrochemical sensor comprising one or more electrochemical cells. In other embodiments, the gas sensor  904  comprises any other suitable type of gas sensor. 
     The system  900  may further comprise a three-way valve  912  between the scrubber  902  and the sensor  904 . The valve  912  may be fluidly connected to the scrubber  902  by a first fluid conduit  908  and fluidly connected to the sensor  904  by a second fluid conduit  909 . The system  900  may further comprise a control module (not shown) operatively connected to the three-way valve  912  to control operation thereof. 
     The pump  906  in this embodiment is positioned upstream of the scrubber  902  and is fluidly connected to the scrubber  902  via a branched fluid conduit  905 . The branched fluid conduit  905  may comprise a first branch  910  and a second branch  911 . The first branch  910  may be fluidly connected to the scrubber  902  and the second branch  911  may be fluidly connected to the three-way valve  912 . 
     In operation, the pump  906  receives a gas stream via an inlet  907  and pumps the gas stream through the branched fluid conduit  905 , where it is split into a first gas stream and a second gas stream. The first gas stream flows through the first branch  910  to the scrubber  902  where it is scrubbed to produce a scrubbed gas stream. The scrubbed gas stream flows through the first fluid conduit  908  to the valve  912 . The second gas stream is an “unscrubbed” stream of the gas that flows through the second branch  911  directly to the valve  912 . 
     The valve  912  may have a first position and a second position. When the valve  912  is in the first position, the first fluid conduit  908  is in fluid communication with the second fluid conduit  909  and the gas sensor  904  receives the scrubbed gas stream from the scrubber  902 . When the valve  912  is in the second position, the second branch  911  of the branched fluid conduit  905  is in fluid communication with the second fluid conduit  909  and the gas sensor  904  receives the unscrubbed gas stream from the pump  906 . Thus, the gas sensor  904  may alternate between sensing total sulfur content of the unscrubbed gas and sensing total sulfur content of the scrubbed gas (from which H 2 S has been removed) depending on the position of the valve  912 . As described in more detail below with respect to the method  1000 , the system  900  may thereby be used to determine the H 2 S concentration of the hydrocarbon gas. 
     In some embodiments, the system  900  may be integrated with one of the systems  100 ,  200 ,  300 ,  500 ,  600 ,  700  described above by connecting a fluid conduit for unscrubbed gas to one of the sensors in the system and providing a valve in fluid communication with the fluid conduit to control the flow of unscrubbed gas therethrough. 
       FIG. 10  is a flowchart of an example method  1000  for analyzing a gas, according to some embodiments, that may be implemented using the system  900 . The method  1000  may be used to analyze H 2 S in a hydrocarbon gas. 
     At block  1002 , a first sulfur content of the gas is sensed. As used herein “sulfur content” refers to the total content of sulfur compounds in the gas. The first sulfur content may be sensed by the sensor  904  of the system  900  when the valve  912  is in the second position such that unscrubbed gas is received by the sensor  904 . A first sensor output may be generated by the sensor  904 . In this example, the first sensor output is a total electrical signal (I C ) induced by the sulfur compounds in the unscrubbed gas. 
     At block  1004 , the gas is contacted with a scrubber material. Contacting the gas with the scrubber material scrubs the gas to remove H 2 S and thereby produce a scrubbed gas. The gas may be scrubbed through the scrubber  902  with a scrubber material comprising at least one of a carbonate salt, a bicarbonate salt, a metal oxide, and an amine. 
     At block  1006 , a second sulfur content of the scrubbed gas is sensed. The second sulfur content may be sensed by the sensor  904  when the valve  912  is in the first position such that scrubbed gas is received by the sensor  904 . A second sensor output may be generated by the sensor  904 . In this example, the second sensor output is a total electrical signal (I A ) induced by the remaining sulfur compounds in the scrubbed gas. 
     At block  1008 , an H 2 S concentration of the gas is determined based on a difference between the first sulfur content and the second sulfur content. The H 2 S concentration may be calculated using Equation 3 as follows: 
         C   H2S =( I   c   −I   A )/ c   (Eq. 3)
 
     where c is the linear coefficient of H 2 S concentration to the first sensor output. 
     In some embodiments, the method  1000  may be combined or performed in parallel with the method  400  or  800  described above. Thus, the concentration of H 2 S in a gas can be determined along with the concentration of one or more odorants. 
     Therefore, embodiments of the systems and methods described herein may be used to analyze odorants in a gas with high accuracy and sensitivity, while reducing or eliminating the cross-sensitivity issues of conventional electrochemical sensor-based approaches. Some embodiments of the systems and methods allow the concentrations of individual odorants to be determined in a blend of two or more odorants. 
     The systems described herein may be relatively inexpensive and may be deployed as automated field sensors in some embodiments. This unmanned approach may also allow for faster sampling (e.g., on a daily or hourly basis) resulting in near real-time analysis of odorants in natural gas pipelines and substations. 
     Moreover, embodiments of the disclosed systems are compact and require few electronic parts and may therefore be suitable for analyzing odorants in hazardous locations. Further, by using non-aqueous material as the scrubber material, the systems may avoid the need for additional filtration or moisture trapping between the scrubber(s) and the sensors(s), while maintaining performance of the sensor(s). The non-aqueous scrubber materials may also allow the systems to be used in the field across a wide temperature range without risk of freezing the scrubber material and/or requiring the concentration of the scrubber material to be compensated due to evaporation. 
     Other variations of the systems and methods described herein are also possible. As discussed in the Examples below, when the hydrocarbon gas to be analyzed by the system is already pressurized, alternative embodiments may also be provided in which the pump(s) are omitted, and the system instead comprises a pressure regulator and flow meter. It will also be understood that although particular configurations of the systems  100 ,  200 ,  300 ,  500 ,  600 ,  620 ,  630 ,  640 ,  700 , and  900  are shown in  FIGS. 1A-1B, 2, 3, 5, 6A-6D, 7, and 9  described above, other configurations are possible and embodiments are not limited to the specific configurations provided herein, including the specific number and placement of fluid conduits, valves, etc. 
     Examples 
     Experiments were performed using an experimental system  10  as shown in  FIG. 11 . The experimental system  10  is similar to the system  700  of  FIG. 7  with two scrubbers and one electrochemical sensor. 
     As shown in  FIG. 11 , the experimental system  10  comprises a first scrubber  12 A and a second scrubber  12 B in fluid communication with an electrochemical sensor  14 . The first scrubber  12 A contains CaCO 3  or MDEA as a first scrubber material (to remove H 2 S) and the second scrubber  12 B contains a mixture of NaOH and Ca(OH) 2  as a second scrubber material (to remove H 2 S and mercaptans). A first on/off valve  16 A is provided between the first scrubber  12 A and the sensor  14  and a second on/off valve  16 B is provided between the second scrubber  12 B and the sensor  14 . 
     In the experimental system  10 , a natural gas sample is drawn from a pressurized pipeline and the sensing tests are performed at ambient pressure. Thus, in the experimental system  10 , a combination of a pressure regulator  18  and a flow meter  20  is used instead of a pump. A coalescing filter  22  is provided between the pressure regulator  18  and the flow meter  20 . 
     In addition, the experimental system  10  includes an air pump  24  and an air purging line  26  to purge the electrochemical sensor  14  with ambient air between the sensing tests. A check valve  28  is in fluid communication with the air purging line  26  to control the flow of air therethrough. 
     In operation, a sample inlet  30  receives a pressurized natural gas stream, which flows through the pressure regulator  18 , coalescing filter  22 , and flow meter  20  before being split into a first gas stream and a second gas stream via a branched conduit  32 . The first gas stream flows through the first scrubber  12 A to produce a first scrubbed gas and the second gas stream flows through the second scrubber  12 B to produce a second scrubbed gas. 
     When the first on/off valve  16 A is on (i.e., open) and the second on/off valve is off (i.e., closed), the first gas stream will flow to the electrochemical sensor  14  to allow the sensor  14  to sense at least one remaining sulfur compound in the first scrubbed gas. When the first on/off valve  16 A is off (i.e., closed) and the second on/off valve is on (i.e., open), the second gas stream will flow to the electrochemical sensor  14  to allow the sensor  14  to sense at least one remaining sulfur compound in the second scrubbed gas. The air pump  24  and the air purging line  26  are used to purge the sensor  14  between readings and the purged air flows out of an exhaust line  34 . 
     Gas samples with varying concentrations of TBM and MES were tested using the experimental system. As shown in  FIGS. 12 and 13 , the voltage signals from the electrochemical sensor are linearly proportional to the concentrations of TBM and MES, respectively. 
       FIGS. 14A to 14C  show the sensor response (voltage) over time to gas samples containing TBM, H 2 S, and MES, respectively, with and without a scrubbing (pre-treatment) step with the NaOH and Ca(OH) 2  scrubber material. As shown in  FIGS. 14A and 14B , both TBM and H 2 S are substantially removed from the gas by the scrubbing step. As shown in  FIG. 14C , MES remains in the gas following scrubbing and little to no MES is lost during the scrubbing step. Thus, the experimental system was able to provide an accurate concentration of the MES present in the gas. 
       FIGS. 15A and 15B  show the sensor response (voltage) over time to a gas sample comprising H 2 S, with or without a scrubbing step with the CaCO 3  scrubber material and with or without the scrubbing step with the MDEA scrubber material, respectively. As shown in  FIGS. 15A and 15B , the H 2 S is substantially removed by the scrubbing step with the CaCO 3  scrubber material and completely removed with the MDEA scrubber material. 
       FIG. 16  shows the sensor response (voltage) of the system described in  FIG. 11  in sensing the TBM and MES content of a gas sample containing TBM, H 2 S, and MES. The sensing peak at 16-28 min is the MES response, where the sample gas is scrubbed with the NaOH and Ca(OH) 2  scrubber material, and the sensing peak at 36-50 min is the total response of MES and TBM, where the sample gas is scrubbed by the MDEA scrubber material. Thus, the experimental system  10  can be used to determine the concentrations of both MES and TBM in a gaseous mixture. 
     Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
     For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.