## 4 Experimental Results
### Desulfurization Tests  
The sulfur capacity of the Cu-based COS absorbent was determined by measuring the COS concentration at the outlet of the packed bed reactor with respect to the time evolution. As shown in Figure 9a, when approximately 1.0 g of a powder type absorbent with approximately 15 wt % CuO was charged, and approximately 5000 ppmv COS was supplied at a flow rate of about 150 mL/min, the COS breakthrough time with CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\) and CuO/macro-porous Al\({}_{2}\)O\({}_{3}\) were 35 min and 40 min, respectively. The sulfur capacity of the CuO/\(\gamma\)-alumina and CuO/macro-porous alumina absorbed to the breakthrough time, in which COS was detected in the reactor outlet, was 37.5 mgS/g-sorbents and 42.9 mgS/g-sorbents, respectively. The sulfur capacity of the CuO/macro-porous alumina was higher than on CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\), and a difference in the slope of the breakthrough curve was observed. The slope of the CuO/\(\gamma\)-alumina increased more rapidly than the slope of the CuO/macroporous alumina. A short breakthrough time and a sharp rise in the slope of the breakthrough curve indicated that the sulfur absorption performance of the absorbent (CuO/\(\gamma\)-alumina) decreased rapidly. The low performance of CuO/\(\gamma\)-alumina can be attributed to the high gas diffusion resistance to the pores in the relatively high-density \(\gamma\)-alumina. Figure 9b presents the breakthrough curve according to the sulfur absorption of the pellet-type absorbent. These COS absorption tests of the samples (peltelt type) of two absorbents with a CuO loading (approximately 15 wt %) were carried out under the experimental condition, in which approximately 3000 ppmv COS was supplied to the reactor at 130 mL/min. The sulfur capacity of \(\gamma\)-alumina at the breakthrough time was approximately 36.2 mgS/g-sorbents, and the sulfur capacity of macro-porous alumina showed a significant difference of approximately 50.1 mgS/g-sorbents. The gas diffusion resistance into the sorbent was higher for the pellet-shaped absorbent than the powder-type sorbent because the pellet-shaped absorbent has a large particle size. Table 2 lists the sulfur adsorption capacity of the absorbents with \(\gamma\)-alumina support and macro-porous alumina support with varying amounts of CuO. The sulfur adsorption capacity increased with increasing CuO content, but the sulfur capacity did not increase linearly with increasing CuO content. XRD and SEM showed that the crystal growth of CuO influenced these results because CuO crystal growth leads to a decrease in the surface area of CuO that can participate in the reaction. CO production was observed during the sulfur absorption test of the Cu-based absorbent, as shown in Figure 10. The concentration of CO in the reactor outlet increased to approximately 1900 ppmv after the start of the COS absorption test and was maintained at approximately 1200 ppmv as the reaction proceeded. After COS was detected at the reactor outlet, the CO concentration decreased with increasing COS concentration in the reactor outlet. This result differed from the known conversion of oxygen in the metal oxide and sulfur in COS to metal sulfide and carbon dioxide. This suggests that the COS dissociation reaction occurs along with the sulfur absorption by the gas-solid reaction of the metal oxide and COS. In addition, the concentration of COS was maintained without increasing rapidly to the initial concentration after the breakthrough time of COS. This was attributed \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multirow{2}{*}{**Amounts of CuO, wt \%**} & **Sulfur Capacity,** \\  & & **mgS/g-Sorbent** \\ \hline \multirow{3}{*}{CuO/\(\gamma\)-Al\({}_{2}\)O\({}_{3}\)} & 5.0 & 19.5 \\ \cline{2-3}  & 10.0 & 43.2 \\ \cline{2-3}  & 15.0 & 36.2 \\ \hline \multirow{3}{*}{CuO/macro-porous-Al\({}_{2}\)O\({}_{3}\)} & 5.0 & 26.5 \\ \cline{2-3}  & 10.0 & 48.8 \\ \cline{2-3}  & 15.0 & 50.1 \\ \hline \hline \end{tabular}
\end{table}