Approaching complete CO conversion and total H2 recovery for water gas shift reaction in a high-temperature and high-pressure zeolite membrane reactor

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

“…During the MR operation, the P r,ex was maintained at each preset value while the pressure of feed entrance (P r,in ) was elevated to keep the GHSV constant when the resistance to gas flow in the catalyst bed increased continually by the accumulating carbon deposits. Figure 1a shows that P r,ex was able to stabilize to below 15 bar without large adjustments for P r,in , indicating that carbon deposition was insignificant or very slow under relatively low reaction pressures, which is consistent with the findings on similar Cr-doped ferrite catalysts [5,11]. However, when the P r,ex reached~20 bar, where χ CO exceeded 99.5% at R H 2 of~99%, the P r,in rapidly increased in order to keep GHSV unchanged.…”

“…Recently, we demonstrated a modified MFI-type zeolite membrane with long-term stability and a high H 2 /H 2 S separation factor for WGS MR operation at high temperature and pressure [3,4]. The combination of the ferrite-based catalysts with the H 2 -permselective zeolite membrane was able to achieve near-complete CO conversion (χ CO > 99.5%) under high reaction pressure (>15 bar) and temperature (~500 • C) with and without high H 2 S content (>400 ppm) in the feed [5]. The high-temperature and high-pressure (HTP) conditions on the reaction side elevate the H 2 partial pressure on the reaction side (p H2,r ) that, with near-zero H 2 partial pressure on the permeate side (p H2,p ), maintains the driving force (i.e., ∆p H2 = p H2,r − p H2,p ) for maximum removal of H 2 through membrane permeation, which is necessary for approaching complete CO conversion [5].…”

“…The combination of the ferrite-based catalysts with the H 2 -permselective zeolite membrane was able to achieve near-complete CO conversion (χ CO > 99.5%) under high reaction pressure (>15 bar) and temperature (~500 • C) with and without high H 2 S content (>400 ppm) in the feed [5]. The high-temperature and high-pressure (HTP) conditions on the reaction side elevate the H 2 partial pressure on the reaction side (p H2,r ) that, with near-zero H 2 partial pressure on the permeate side (p H2,p ), maintains the driving force (i.e., ∆p H2 = p H2,r − p H2,p ) for maximum removal of H 2 through membrane permeation, which is necessary for approaching complete CO conversion [5]. In this case, the HTP reaction conditions may create extremely H 2 -lean gas environments that are fundamentally different from that in the conventional packed bed WGS reactors or in most of the reported WGS MRs where H 2 removal is often far from completion.…”

“…The χ CO of the MR increased continuously with reaction side pressure while the permeate side sweep flow remained at atmospheric pressure. Such a χ CO dependency on the reaction pressure can be attributed to the prolonged residence time, accelerated reaction rate, and enhanced H 2 membrane permeation rate under increased reaction pressures at a fixed gas hourly space velocity (GHSV) [4,5]. At GHSV = 7500 h −1 and steam-to-CO ratio R S/CO = 3.5, the MR achieved CO conversion χ CO > 99.5% when operating at reaction side exiting pressure P r,ex of >15 bar.…”

“…The rapid decline of CH 4 content upon carbon formation in the WGS MR at 20 bar, as shown in Figure 1b and Figure S1, may be attributed to sudden catalyst deactivation by the fast carbon deposits. Although the catalytic methane decomposition could involve complicated serial reaction steps [24], the whole process of carbonization via the routes of methanation and CH 4 decomposition must have overall stoichiometric mass balance and overall energy effect the same as the CO disproportionation Reaction (2) when WGS Reaction (1) is the H 2 source for Reactions (4) and (5).…”