''CO2 selectivity'' calculation from the GC analysis data for Low temperature Water Gas Shift (LT-WGS) reaction.
Established Cu based LTS catalysts used in ammonia and older hydrogen plants take the WGS reaction to equilibrium at a little above 200oC. The reaction is CO + H2O CO2 + H2 with minimal by-product formation (
The CO2 selectivity for the Low temperature Water Gas Shift (LT-WGS) reaction can be calculated using the following equation:
CO2 selectivity = (moles of CO2 produced / moles of CO consumed) x 100%
To determine the moles of CO2 produced and moles of CO consumed, you will need to measure the initial and final concentrations of CO and CO2, as well as the total gas flow rate, temperature, and pressure.
Here are the steps to follow:
Note that LT-WGS is typically performed over a catalyst, so the selectivity may be influenced by the catalyst type and its properties, as well as the reaction conditions.
Building on Amit's answer, established commercially available LTS catalysts are typically used in ammonia and older hydrogen plant flowsheets downstream of the steam reforming and HTS converters. The catalysts are based on Cu/ZnO/alumina, operate at approximately 200oC and usually 30 - 40 bara. CO2 selectivity is very high but these catalysts do produce low level by-products, mainly MeOH and lower levels of other oxygenate compounds. From memory (so this should be confirmed as it's a while since I have worked on LTS Catalysts), the level of these by-products is typically 200 - 1000 ppmv (dry gas basis). Most LTS catalysts contain low level additives (usually Cs2O &/or K2O) to inhibit the MeOH and other oxygenate formation to the lower end of this range.
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