Monetizing stranded gas: Difference between revisions

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===Gas to liquids (GTL)===
===Gas to liquids (GTL)===
In contrast to the GTG and GTS gas monetization options, which are based on a physical conversion process, [[Natural gas utilization: Gas to liquids (Fischer-Tropsch route)|gas to liquids (GTL)]] is a chemical conversion route involving rearrangement of molecules. GTL processes are classified into direct and indirect processes.  
In contrast to the GTG and GTS gas monetization options, which are based on a physical conversion process, [[gas to liquids (GTL)]] is a chemical conversion route involving rearrangement of molecules. GTL processes are classified into direct and indirect processes.  


====Direct GTL processes====
====Direct GTL processes====
Considerable research is ongoing worldwide on direct routes of converting gas into a liquid;<ref name="r1" /> <ref name="r2" /> <ref name="r3" /> <ref name="r4" /> <ref name="r5" />however, these routes have not yet been commercialized. Methane is a molecule in which one carbon atom is bound to four hydrogen atoms by strong chemical bonds. Hence, the chemical reactivity of methane is low, making it difficult to directly convert to a liquid. Direct conversion processes have the potential for achieving a higher efficiency than indirect (syngas-based) processes. However, the key issue with these processes is poor selectivity or conversion leading to low yields of the desired products. Some of the direct GTL routes being explored include the following.  
Considerable research is ongoing worldwide on direct routes of converting gas into a liquid;<ref name="r1" /> <ref name="r2" /> <ref name="r3" /> <ref name="r4" /> <ref name="r5" />however, these routes have not yet been commercialized. Methane is a molecule in which one carbon atom is bound to four hydrogen atoms by strong chemical bonds. Hence, the chemical reactivity of methane is low, making it difficult to directly convert to a liquid. Direct conversion processes have the potential for achieving a higher efficiency than indirect (syngas-based) processes. However, the key issue with these processes is poor selectivity or conversion leading to low yields of the desired products. Some of the direct GTL routes being explored include the following.  


=====Cold Flame Oxidation=====
=====Cold Flame oxidation=====
Cold flame oxidation involves the conversion of a pressurized mixture of methane and oxygen at moderate temperatures. The main reaction is the oxidation of methane to methanol; however, further oxidation of methanol to formaldehyde often takes place simultaneously.  
Cold flame oxidation involves the conversion of a pressurized mixture of methane and oxygen at moderate temperatures. The main reaction is the oxidation of methane to methanol; however, further oxidation of methanol to formaldehyde often takes place simultaneously.  


=====Direct Oxidation=====
=====Direct oxidation=====
Direct oxidation involves the catalytic coupling (oxidative coupling) of methane and an oxidant in the presence of a catalyst at moderate temperatures and approximately atmospheric pressure to produce C<sub>2</sub>+ hydrocarbons.  
Direct oxidation involves the catalytic coupling (oxidative coupling) of methane and an oxidant in the presence of a catalyst at moderate temperatures and approximately atmospheric pressure to produce C<sub>2</sub>+ hydrocarbons.  


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Oxychlorination involves the catalytic reaction of methane with a mixture of hydrogen chloride and oxygen to produce methyl chloride. The methyl chloride is then reacted over a zeolite catalyst to produce a mixture of aliphatic and aromatic hydrocarbons.  
Oxychlorination involves the catalytic reaction of methane with a mixture of hydrogen chloride and oxygen to produce methyl chloride. The methyl chloride is then reacted over a zeolite catalyst to produce a mixture of aliphatic and aromatic hydrocarbons.  


=====Indirect Oxidation=====
=====Indirect oxidation=====
This process involves indirect oxidation of methane to ethylene at high temperatures with the use of various reducible metal oxides as oxygen carriers as well as catalysts.  
This process involves indirect oxidation of methane to ethylene at high temperatures with the use of various reducible metal oxides as oxygen carriers as well as catalysts.  


=====Catalytic Pyrolysis=====
=====Catalytic pyrolysis=====
Direct methane conversion through catalytic pyrolysis involves contacting methane with a catalyst at a relatively high temperature to form ethylene.  
Direct methane conversion through catalytic pyrolysis involves contacting methane with a catalyst at a relatively high temperature to form ethylene.  


====Indirect GTL Process====
====Indirect GTL process====
'''Fig. 2''' shows the indirect GTL routes to gas monetization. These routes involve the conversion of natural gas to synthesis gas (also called syngas), which is primarily a mixture of carbon monoxide and hydrogen. The syngas is then converted to liquid products such as methanol, dimethylether (DME), and Fischer-Tropsch (FT) liquids. The conversion of natural gas to syngas could be catalytic or noncatalytic. There are various technologies available for the conversion of natural gas to syngas. Several publications <ref name="r6" /> <ref name="r7" /> <ref name="r8" /> <ref name="r9" /> <ref name="r10" />cover these technology options extensively. The key parameters in the selection of a suitable syngas generation process are H<sub>2</sub>:CO ratio in the syngas, O<sub>2</sub> /feed-gas ratio, methane slip, steam/carbon ratio, CO<sub>2</sub> production, uses integration options and capital, and operating costs.  
'''Fig. 2''' shows the indirect GTL routes to gas monetization. These routes involve the conversion of natural gas to synthesis gas (also called syngas), which is primarily a mixture of carbon monoxide and hydrogen. The syngas is then converted to liquid products such as methanol, dimethylether (DME), and Fischer-Tropsch (FT) liquids. The conversion of natural gas to syngas could be catalytic or noncatalytic. There are various technologies available for the conversion of natural gas to syngas. Several publications <ref name="r6" /> <ref name="r7" /> <ref name="r8" /> <ref name="r9" /> <ref name="r10" />cover these technology options extensively. The key parameters in the selection of a suitable syngas generation process are H<sub>2</sub>:CO ratio in the syngas, O<sub>2</sub> /feed-gas ratio, methane slip, steam/carbon ratio, CO<sub>2</sub> production, uses integration options and capital, and operating costs.  


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