*3.1. H2 and C Production Rates*

Based on the result of the process simulation, H2 and C production rates for each MP system with a feed CH4 rate of 1 kmol h−<sup>1</sup> were obtained at the different operating temperatures of 1073–1373 K for TMP-S1 and TMPG-S3 and 1023–1173 K for CMP-S2 and CMPG-S4, with the ratio of H2 combusted of 0%–100%, and the ratio of reactants composed of C, Air, and H2O (Figure 4).

**Figure 4.** Technical performance for methane pyrolysis (MP) systems of (**a**) thermal methane pyrolysis (TMP-S1), (**b**) catalytic methane pyrolysis (CMP-S2), and systems with additional gasification and WGS reaction of (**c**) TMPG-S3 and (**d**) CMPG-S4.

For TMP-S1 (Figure 4a), net H2 production rates of 0–0.17, 1.56–1.93, 1.32–2.00, and 1.28–2.00 kmol h−<sup>1</sup> and C production rates of 0.08, 0.97, 1.00, and 1.00 kmol h−<sup>1</sup> were obtained at a temperature of 1073 K, 1173 K, 1273 K, and 1373 K, respectively. As reaction temperature increased, the range of net H2 production rate was highly dependent on the ratio of H2 combusted due to the large amount of heat required and the different thermodynamic properties of each fuel, and produced C was maximized from 1173 K, not even the maximum investigated temperature.

For CMP-S2 (Figure 4b), 0.00–0.12, 0.08–0.33, 0.49–0.87, and 1.25–1.85 kmol h−<sup>1</sup> for net H2 production rates and 0.06, 0.17, 0.43, and 0.93 kmol h−<sup>1</sup> for C production rates were obtained at temperatures of 1023 K, 1073 K, 1123 K and 1173 K, respectively. Even though an increasing trend of H2 and C production rate and a high dependence of the ratio of H2 combusted was shown, which are similar to the results from TMP-S1, no theoretical maximum amounts of H2 and C (2 and 1 kmol h<sup>−</sup>1, respectively) were produced.

For TMPG-S3 (Figure 4c), even with the various ratios of C, Air, and H2O for the gasification unit, very low H2 production rates of 0.00–0.29 kmol h−<sup>1</sup> were obtained at 1073 K. That poor technical performance, lower than the theoretical H2 production rate of 2 kmol h−<sup>1</sup> for the previous system of TMP-S1, was raised by higher reaction temperatures of MP, leading to the improved technical performance of 2.00–3.49 kmol h−<sup>1</sup> H2 production rates at 1173–1373 K. For the ratio of reactants in the gasifier, H2 production rates at 1373 K dramatically increased 2.02–2.89 kmol h−<sup>1</sup> for a 1:1:1 ratio to rates of 2.10–3.49 kmol h−<sup>1</sup> for a ratio of 1:1:3, proving the importance of H2O in the additional H2 production processes of C gasification and the WGS reactor. Compared to the effect of H2O on net H2 production rates, an opposite effect of air was shown with decreased maximum H2 production rates of 2.81 and 2.61 kmol h−<sup>1</sup> for the ratios of 1:2:1 and 1:3:1, respectively, down from 2.89 kmol h−<sup>1</sup> for a 1:1:1 ratio, thereby identifying its disadvantage in technical performance.

For CMPG-S4 (Figure 4d), lower H2 production rates of 0.00–0.20, 0.19–0.58, and 0.78–1.52 kmol h−<sup>1</sup> were obtained than those from TMPG-S3 in a range of similar investigated temperatures (1073–1273 K). Even though the technical performance was improved at a higher reaction temperature of 1173 K showing H2 production rates of 1.86–3.23 kmol h<sup>−</sup>1, this is still lower than those from TMPG-S3. For the effect of air and H2O on H2 production rates, similar trends to those for TMPG-S3 of increased rates from 1.86–2.63 kmol h−<sup>1</sup> (1:1:1) to 1.99–3.23 kmol h−<sup>1</sup> (1:3:1) and decreased rates from 2.19–2.63 kmol h−<sup>1</sup> (1:2:1) to 2.39–2.44 kmol h−<sup>1</sup> (1:3:1).

As a result, through the trends of H2 and C production rates obtained from the process simulation, the detailed effects of temperature, the ratio of H2 combusted, and the ratio of reactants entering the gasifier were confirmed.
