## 3 Results and Discussion
### Structural Variation of Treatment Samples  
Figure 2 shows that the pore size distributions at all regions using the BET method were based on the results of nitrogen sorption analyses of PSD samples and Kenaf samples after grinding. The porous structures are divided according to the pore diameter into micropores (those with a diameter \(<\)2 nm), mesopores (diameters 2-50 nm), and macropores (diameters \(>\)50 nm) [24]. Table 2 shows the quantitative values for pore volume and surface area for PSD samples and Kenaf samples divided by the pore diameter based on the BET results. Following the torrefaction and ashless processes, the cumulative pore volume and surface area of T. [PERSON] and A. PSD became larger than that of R. PSD. T. PSD showed a pore distribution similar to A. PSD. However, the A. PSD micropores are larger than those of the T. PSD. Further, the micro- and macropores of the T. A PSD became largeR. For R. Kenaf, only torrefaction was performed and a similar pore volume and surface area were observed. However, the ashless process greatly increases the distribution of the pore sizes by more than 50 nm. After torrefaction, T. Kenaf and T. A Kenaf macropores became smaller while the micro- and mesopore areas were largeR. This indicates that woody and herbaceous biomasses were influenced differently by the ashless and torrefaction processes. Figure 1: Van Krevelen diagram showing properties of raw and pretreated biomasses. Figure 2: Pore size distribution of PSD samples (**a**) and kenaf samples (**b**) at all regions by nitrogen sorption analysis. The herbaceous biomass had about twice as much the pore distribution as the woody biomass and the ashless process generated more pores in all regions of the samples, with an increase in macropores in particulaR. Torrefaction, in the case of PSD, showed an increase in pore sizes at all regions, including macropores. In contrast, the macropores in Kenaf were reduced while the micro- and mesopore regions were enlarged. The different pore size distributions of woody and herbaceous biomasses can be explained by the results of [PERSON] et al. [10]. They indicated that the degradation of agricultural residues is greater than that of ligneous plants because of the higher volatile and hemicellulose contents in herbaceous residues; they also showed that the weight loss of herbaceous biomass with a higher xylan content is more likely to occur compared to woody biomass owing to the different chemical structure. Xylan is more reactive and can break down more easily at a low temperature compared to glucomannan [25]. In addition, the rapid release of volatile matter can open and link the blind and closed pores during torrefaction and create new cracks, micropores, and mesopores, which can lead to a significant increase in porosity in case of woody biomass. In contrast, a greater amount of degradation of hemicellulos in the case of herbaceous biomass leads to a decrease in macropores. SEM images of particles were taken and measured to observe these differences between PSD and kenaf more clearly. SEM images of PSD and kenaf showed that the torrefaction and ashless processes had differing degrees of influence (Figure 3). Within R. PSD, very strong, bulky xylem tissues were observed. Following torrefaction, PSD began to lose it bound, fibrous structure, and cracks and large pores became more obvious in the particles. The structure of A. PSD by the ashless process appeared to be more broken, and the T. A PSD by torrefaction further facilitated this phenomenon. The kenaf images contained a different microstructure and morphology compared to PSD. Particles from torrefied kenaf had smoother and cleaner surfaces compared to those from R. Kenaf. Additionally, T. A Kenaf contained a greater degree of decomposition and cracking in the particles. Thus, kenaf particles appeared to lose their characteristic fibrous structure and became smoother compared to PSD after the torrefaction and ashless processes, as confirmed by the BET results.