The effect of heating rate on both the yields and the distribution of the oil products obtained from the pyrolysis of pubescen was studied. The molecular weight of the liquid products was mainly distributed in the range 200–500 Da [about 77 % from gel‐permeation chromatography (GPC)]. At 15 °C min−1, the total yield of small‐molecular products from degradation of carbohydrate was 9.53 wt % and the total yield of identified monophenols reached a maximum of 3.57 wt %. Thus, the liquid products were predominantly present as oligomers. Lignin in pubescen was degraded to stable tetramers. The formation of monophenols and/or oligophenols mostly involved the cleavage of the C−C (Cα−Cβ, Cβ−Cϒ, C1−Cα) and C−O bonds (β−O−4, β−O−5, Cα−O, Cϒ−O, and 4‐aryl ether linkages). Carbohydrate‐derived species interacted with each other and then produced oligomers, the formation pathways of which are explained. A decrease of relative content of the species with molecular weight Mn=200–500 Da and an increase of relative content of the species with Mn=500–1000 Da were observed as the heating rate was increased from 2.5 to 15 °C min−1. With further increasing the heating rate from 15 to 25 °C min−1, the molecular‐weight distribution remained almost unchanged. Increase of the heating rate promoted the cleavage of C1−Cα bonds, Cβ−Cϒ bonds in lignin, and the dehydration of Cα−OH units of lignin into Cα=Cβ.
Pd/NbOPO
4
multifunctional catalyst was prepared and
used for catalytic hydrotreatment upgrading of bio-oil, which was
obtained from low-temperature torrefaction (LTT) of pubescens and
contained mainly lignin oligomers. The upgrading temperatures were
investigated at 220–280 °C. Pd/NbOPO
4
exhibited
good performance for the effective depolymerization of oligomers with
increasing temperature. It was revealed that both Brönsted
acid sites and Lewis acid sites existed on NbO
x
, which contributed to the cleavage of the C–O–C
bond. Furthermore, esterification, hydrogenation, and O-alkylation
of monomeric derivatives also occurred simultaneously during the depolymerization
process. After hydrotreatment upgrading, the average molecular weight
of bio-oil decreased from
M
w
= 320 Da
(
M
n
= 298 Da) to
M
w
= 273 Da (
M
n
= 254 Da) and the
bio-oil quality was improved dramatically. The oxygen content decreased
from 29.53 to 9.78 wt %. The upgraded bio-oil obtained at 280 °C
had a heating value of 40.48 MJ kg
–1
, which was
much higher than that of the original bio-oil (26.96 MJ kg
–1
).
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