posted on 2024-01-17, 12:08authored byJialiang Zhang, Zhi Yang, Aditya Ponukumati, Manjula Senanayake, Sai Venkatesh Pingali, Marcus Foston
A fundamental understanding of the solution behavior
of lignin
under reaction conditions is required for the rational design of
porous heterogeneous catalysts that minimize the mass-transfer limitations
on lignin depolymerization kinetics. In situ and ex situ small-angle
neutron scattering (SANS) methods were used to study the structural
changes of lignin during non-catalytic solvolysis reactions in deuterated
methanol (MeOH-d4) and catalytic reactions
in the presence of copper-containing porous metal oxide (CuPMO) and
MeOH-d4. The results indicate that at
room temperature, lignin adopted a rigid and stretched conformation
that becomes more spherical, flexible, and folded when heated to the
reaction temperature of 250 °C. In the presence of CuPMO, the
volume fraction of small lignin particles (<50 Å) in the reactor
is higher than under solvolysis conditions, while the median radius
of this fraction of lignin particles is smaller. The SANS data were
analyzed using a population balance model and found that two reaction
processes dominate: disassembly of large lignin aggregate particles
(>50 Å) and condensation of small lignin particles (<50
Å).
The study also suggests that the cooling and quenching step in the
ex situ experiments alters the small lignin (<50 Å) particle
size distribution.