*3.5. Sensitivity and Scenario Analysis*

To investigate key economic parameters in each system and the possibility of the commercialization of each system, sensitivity and scenario analyses were conducted. In this study, one economic parameter was varied in the range of ±20% with the remaining parameters fixed, and variations of unit H2 production cost for each system were obtained with key factors showing high variation remarked. Figure 8a,b reveal the economic importance of C selling price in both TMP-S1 and CMP-S2 showing very high variations of 19.1% and 11.1%, respectively. Costs of the MP reactor and reactant were also figured out as the next influential parameters showing variations of 12.1% and 10.9%, and 7.2% and 6.9% for TMPG-S3 and CMPG-S4, respectively. For TMPG-S3 and CMPG-S4, where all C is combusted leading to no profits from the selling of C, the same economic parameters of costs of the MP reactor and reactant were reported as the most influential factors with variations of 6.0% and 3.9%, and 5.6% and 3.9%, respectively (Figure 8c,d).

**Figure 8.** Results of sensitivity analysis for methane pyrolysis (MP) systems of (**a**) thermal methane pyrolysis (TMP-S1), (**b**) catalytic methane pyrolysis (CMP-S2), and the systems with additional gasification and WGS reaction of (**c**) TMPG-S3 and (**d**) CMPG-S4.

On the other hand, the scale of certain chemical engineering processes is also known to be a very influential factor to determine their economic feasibility [65]. Therefore, a scenario analysis for H2 production scale, which can lead to a cost reduction in capital cost as reported [66], and the different C selling price in the system of TMP-S1 and CMP-S2, which is a very crucial economic factor as reported by the sensitivity analysis, to reflect a pessimistic price fluctuation and low product quality of C, was conducted and compared to conventional H2 production methods of SMR (USD 0.94–1.78 kgH2 <sup>−</sup>1) and SMR with CCS (USD 1.45–2.38 kgH2 <sup>−</sup>1) [67] (Figure 9). As shown in Figure 9, there was a clear cost reduction as the H2 production scale increased due to the economics of scale. For CMPG-S4, unit H2 production cost decreased from USD 3.82 to 1.99 kgH2 <sup>−</sup><sup>1</sup> (−47.9%) proving it can compete in price with SMR+CCS but not with SMR. Similarly, larger cost reductions of 51.6% and 60.7% were obtained for TMP-S1 and CMP-S2, respectively, with no C selling

price assumed (represented by USD 0 ton<sup>−</sup>1), which are still not enough to compete with conventional H2 production methods of SMR.

**Figure 9.** Results of scenario analysis up to 1000 Nm<sup>3</sup> h−<sup>1</sup> for methane pyrolysis (MP) systems of (**a**) thermal methane pyrolysis (TMP-S1), (**b**) catalytic methane pyrolysis (CMP-S2), and the systems with additional gasification and WGS reaction of (**c**) TMPG-S3 and (**d**) CMPG-S4 with comparison to systems of steam methane reforming (SMR) of USD 0.94–1.78 kgH2 <sup>−</sup><sup>1</sup> and SMR with carbon capture and storage (CCS) of USD 1.45–2.38 kgH2 <sup>−</sup>1.

However, for TMP-S1 and CMP-S2, with a C selling price of EUR 250 ton−<sup>1</sup> (−50% of the assumed C selling price) and for TMPG-S3, with unit H2 production costs decreased from USD 3.16 to 1.00 kgH2 <sup>−</sup>1, USD 4.68 to 1.22 kgH2 <sup>−</sup>1, and USD 3.53 to 1.60 kgH2 −1 showing reductions of 68.3%, 73.9% and 54.8%, respectively, proving their economic competitiveness with conventional commercialized H2 production methods of SMR and SMR with CCS.

In short, the key economic parameters of C selling price and costs of MP reactor and reactant were calculated and the future economic competitiveness for all systems with high H2 production scales and C selling prices, even pessimistic prices, was confirmed.
