Improving the Understanding of the Bonding Mechanism of Primary Components of Biomass Pellets through the Use of Advanced Analytical Instruments

Figures & data

TABLE 1. Pelleting conditions of industrial spruce pellets and some physical properties before and after pelleting.

Parameter		Pelleting conditions
Temperature		100 °C
Minimum compression force		16.0 MPa
Maximum compression force		40.5 MPa
Die configuration		8 L/D
Holding time		15 s
Additives		No
Sample physical properties before and after pelleting
Property	Value
Moisture content	10% and 6%
Particle size	<5 mm and 6 mm (D)
Bulk density	103 kg/m^3 and ca. 650 kg/m^3

L, die length; D, die diameter.

Figure 2 Thermogram of industrial spruce pellet showing modification range temperatures.

TABLE 2. Primary organic and elemental constituents of industrial spruce pellet.

Primary organic components	(%)	Standard deviation
Cellulose	42.3	—
Hemicellulose	23.2	—
Lignin	30.6	—
Primary elemental constituents	Wt.% (db)	Standard deviation
C	48.9	±0.93
H	5.9	±0.24
O	43.6	±0.77

Figure 1 FT-IR spectrum of industrial spruce pellet showing absorption bands that qualitatively identifies primary functional groups.

TABLE 3. FT-IR absorption bands of industrial spruce pellet and assignment of functional groups.

Wavenumber (cm^−1)	Number in Figure 1	Peak assignment
808	1	Corresponding to mannan in hemicellulose
870	2	Glucomannan in hemicellulose
897	3	α-β-bonds corresponding to cellulose
1028	4	C–O str. in cellulose and hemicellulose
1160	5/6	C–O–C str. in cellulose and hemicellulose
1235	7	C–O str. in xylan and lignin
1370	8	C–H bend (uronic acid in hemicellulose)
1508	9	Aromatic skeletal vibration in lignin
1600	10	C=O str. due to aromatic ring breathing in lignin
1731	11	C=O str. Due to xylan in hemicellulose
2855	12/13	C–H str. of methyl group connected to lignin
3335	14	O–H str. vib. linked to all primary components

Str, stretching; Vib, vibration.

Figure 3 Confocal images of industrial spruce pellet showing: (a) internal structure from a section of the pellet; (b) surface structure from the same section as the previous; (c) internal structure from a different part of the pellet; (d) surface structure from same part as c. The color interpretation of the images is such that deep blue indicates the presence of cellulose, yellowish-green depicts hemicellulose, and reddish coloration implies the presence of lignin.

Figure 4 SEM images of industrial spruce pellet obtained at different magnifications: (a) ×100; (b) ×200; (c) ×500; (d) ×1000. The images reflect internal and surface morphology taken from different parts of the pellet.