1.2.1. Catalyst Evaluation in a Two-stage Fixed-bed Reactor

Figure 9 illustrates the gas yield and the biomass carbon balance of woody red pine pyrolysis in a two fixed-bed quartz reactor. In the case Ni/BCC catalyst, total gas yield increased drastically at a catalyst bed temperature of 923 K, at which the yield of CO and H2 achieved was 21.2 and 29.5 [mmol/g-sample daf], respectively, approximately three and six times in comparison to sand (Figure 9(a)). It was considered that tarry material was efficiently decomposed by the Ni/BCC catalyst. If we consider the effect of catalytic pyrolysis temperature on gas yield, Figure 9 (a) also shows that the gas yield increased by increasing temperature from 823 to 923 K, thus suggesting tar decomposition can be controlled by chemical kinetics.

Although there was no direct measurement of tar, we have the biomass carbon balance, which is illustrated in Figure 9(b). Among total carbon in biomass, percentages of carbon in product gas (C_ gas) and carbon in char (C_char) could be obtained by analyzing product gas and product char, respectively. Carbon in tar (C_tar) was estimated fairly by a different method: C_tar = 100 — (C_ gas + C_char). In the case of Ni/BCC, we could assume that the total carbon of product gas was released from biomass pyrolysis because the pyrolysis time

of 90 min was enough to release most releasable carbon in Ni/BCC at 923 K. The amount of C_chars was almost constant in all cases, because the char is accumulated in the first bed without contacting the catalyst particles at the same temperature of 1173 K. In the case of catalytic tar decomposition, the amount of C_gas increased drastically compared to no catalyst at 923 K. That is to say, the tar was decomposed over Ni/BCC catalyst by Equation, Tar ——CO + H2 + CO2 + CH4 + C2H4 + other hydrocarbon.

When using Ni/BCC catalyst, C_tar approaches zero at 923 K. Moreover, we did not observe tar adhered on the reactor. Thus, it suggests almost all of the tar was decomposed at 923 K under the pyrolysis experimental conditions.