## 3 Results
### Smr vs. SE-SMR: Sensitivity Analysis
Moving from 1 to 10 to 20 bar maps, both a gradual shift upwards and a shrinking of the maximum zone (red zone) occurs, i.e., higher temperatures are needed to reach equally high values, all the other parameters being the same. Although carbonation is favored by the increase of pressure, the deterioration on the reforming process determines the overall effect. In Figure 3, where the CH4 conversion maps are reported, the above-mentioned results are also confirmed. The qualitative pattern of the 1 bar CH4 conversion maps (Figure 3, upper maps) is different from that of the dry hydrogen concentration maps (Figure 2). In the case of Figure 3, the 1 bar map shows a'sigmoid' pattern for high temperatures and low S/C ratios (S/C = 1-2). In these zones, XCH4 reaches very high values, being conversion favored by high temperatures and atmospheric pressure. However, given the stoichiometric deficiency of H2O, the CO produced by the reforming reactions cannot be further consumed by the WGS reaction to produce CO2 (and consequently a stream with a higher H2 purity); this is confirmed by the high levels of CO leaving the reactor under these operating conditions, reaching a dry concentration of 30% for S/C = 1 and 725 \({}^{\circ}\)C. The increase in H2 purity under SE-SMR conditions is indeed essentially due to the CO2 removal from the outgoing gas; the CO2 molar fraction (on dry basis) reached values as low as 0.25%, compared with the typical values under SMR conditions around 12-13%. Finally, as for the yield trend (Figure 4), the behavior at 10 and 20 bar reproduces that of XCH4. The profile slightly differs at 1 bar, due to the occurrence at low S/C ratios and high temperatures of the reverse-WGS reaction, leading to a reduction in \(\eta_{\rm CH4}\). When considering the effect of the CaO/CH4 ratio, namely moving from left to right at fixed pressure, improvements are observed with a significant expansion of the area of the map characterized by high values (orange and red colors) of the performance indicators, all the other variables being the same. Thus, as expected, a higher CaO/CH4 ratio allows greater capture of the produced CO2, resulting in a performance improvement due to the chemical reaction shift. For example, by setting a reasonable feed ratio of S/C = 3, a temperature of 650 \({}^{\circ}\)C and a pressure of 1 bar, the H2 dry concentration goes from 86.6% for CaO/CH4 = 0.5 to 94% for CaO/CH4 = 1, the CH4 conversion from 89.1% to 92.7%, while the H2 yield from 83.6% to 90.4%. At a pressure of 20 bar, on the other hand, \(J_{H_{2}}^{dry}\) improves from 80.5% to 87.7%, XCH4 from 52.2% to 64.5%, and \(\eta_{\rm H2}\) from 52% to 64.4%. These results suggest that the use of CaO for the sorption-enhanced process may partly counterbalance the negative effect of a pressure increase and improve operation in industrially relevant conditions, which often involve pressures higher than the atmospheric one. This counterbalancing effect is only partial, since, moving from SMR at 1 bar to SE-SMR at 10 bar, for example, only yH2 showed an increase of +20%, while XCH4 and \(\eta_{\rm H2}\) still showed a \(-14\%\) and \(-4\%\) decrease. Lastly, to quantify the SE effect, the percentage increase of performance under the sorption-enhanced process conditions with respect to the traditional SMR, fixing all the other variables, was evaluated and reported in Table 1 for the three parameters investigated. By passing from SMR to SE-SMR at 1 bar and CaO/CH\({}_{4}\) = 1, y\({}_{\text{H2}}\), X and \(\eta\) increased by +25, +8, and +15%, respectively, while at 10 and 20 bar, y\({}_{\text{H2}}\), X and \(\eta\) increased by +44, +54, and +65% and by +54, +80, and +90%, respectively. It should be noted that, being a percentage variation, although this is clearly higher where the traditional SMR process conditions are unfavorable and thus characterized by low performance values, the best overall operating conditions of the SE-SMR process are still those corresponding to high temperatures and the lowest pressure.