4 research outputs found
Reply to âComment on 'Instantaneous Dissolution of Cellulose in Organic Electrolyte Solutions'â
Reply to âComment
on 'Instantaneous Dissolution
of Cellulose in Organic Electrolyte Solutions'
Liquid-Phase HâTransfer from 2âPropanol to Phenol on Raney Ni: Surface Processes and Inhibition
Raney
Ni is perhaps the most widely used catalyst for the transformation
of biogenic molecules in industrial practice (e.g., as in the production
of sugar alcohols and hardening of vegetable oils). Currently, Raney
Ni has found another key application; the catalytic upstream biorefining
(CUB) of lignocellulose in which the soluble products released from
the lignocellulosic matrix undergo reductive processes, rendering
depolymerized lignin oils in addition to high-quality holocellulosic
pulps. Despite the industrial importance of Raney Ni, its surface
chemistry is poorly understood. In this study, using the H-transfer
reaction between 2-propanol (2-PrOH) and phenol as a model reaction,
we studied the influence of various alcohols on the catalytic performance
of Raney Ni. For the H-transfer hydrogenation of phenol to cyclohexanol,
the inhibition of the catalyst increases in the order of secondary
alcohols < primary alcohols < polyols at 130 °C. To better
understand the observed inhibition, we also studied the molecular
interactions of the various alcohols at the catalytic solidâliquid
interface using in situ attenuated total reflection infrared (ATR-IR)
spectroscopy. The in situ spectroscopic data revealed that 2-PrOH
adsorbs on at least two chemically different sites on the surface
of Raney Ni. One of these two adsorption sites was attributed to the
Ni site responsible for the saturation of the phenolic ring. The ATR-IR
spectroscopic data also shows that the adsorption of phenol involves
its hydroxyl group. Notably, the phenolic ring was found to be tilted
with respect to the surface. Competitive adsorption of various other
alcohols was also investigated at the catalytic solidâliquid
interface. The presence of methanol inhibited the adsorption of 2-PrOH
to a significantly greater degree than phenol. Therefore, it is proposed
that hydrogen transfer hydrogenation of the phenolic ring is inhibited
in the presence of additional alcohols mainly due to the competitive
adsorption with 2-PrOH. Several polyols were found to interact through
a bidentate interaction with the catalyst surface, which explains
their stronger inhibition compared to primary alcohols. In a broader
context, this study proposes the effect of hemicellulose sugars and
sugar alcohols, formed in the CUB process, upon the product selectivity
of CUB catalyzed by Raney Ni and using 2-PrOH as an H-donor
Mechanocatalytic Depolymerization of Lignocellulose Performed on Hectogram and Kilogram Scales
Mechanocatalytic depolymerization
of lignocellulose constitutes
a new frontier in biorefining. In a one-pot process, the combination
of mechanical forces and acid catalysis leads to the full conversion
of (dried) lignocellulose into water-soluble products (oligosaccharides
and lignin fragments). In solution, these products undergo hydrolysis
and other reactions, rendering high yields of monosaccharides along
with precipitation of a sulfur-free lignin. Therefore, the water-soluble
oligosaccharides may serve as a unique replacement for glucose and
xylose for the production of platform chemicals. In this work, we
report the results obtained from mechanocatalytic depolymerization
of α-cellulose, beechwood, and poplar wood performed in Simoloyer
mills operating on hectogram and kilogram scales. Irrespective of
the process scale, full conversion of the substrate into âwater-soluble
(ligno)Âcellulosesâ, within milling durations of 1â3
h, is achieved. A phenomenological analysis of parameters for the
process upscaling is provided. Moreover, the energy consumption of
the process on different scales is assessed. Remarkably, energy consumption
significantly decreases (from ca. 200 MWh·t<sup>â1</sup> to 9.6 MWh·t<sup>â1</sup>) with upscaling of the experiment
from 1 g (planetary mill) to 1 kg. This increase in energy efficiency
constitutes key evidence for the feasibility of the mechanocatalytic
depolymerization on a large scale
Mechanocatalytic Depolymerization of Dry (Ligno)cellulose As an Entry Process for High-Yield Production of Furfurals
Driven by mechanical forces, the
acid-catalyzed depolymerization of solid biomass completely overcomes
the problems posed by the recalcitrance of lignocellulose. The solid-state
reaction leads to water-soluble oligosaccharides, which display higher
reactivity than cellulose and hemicellulose. Here, we show that water-soluble
oligosaccharides are useful feedstock for the high-yield production
of 5-hydroxymethylfurfural (HMF) and furfural in biphasic reactors.
This is because they readily undergo hydrolysis upon microwave heating,
selectively forming monosaccharides as intermediates in the aqueous
phase. Short reaction times are possible with the use of microwave
heating and limit the extent of degradation reactions. This work provides
an ionic-liquid-free approach to process lignocellulosic substrates
into HMF and furfural with high yields. In fact, starting this novel
approach with α-cellulose, yields of HMF of 79% and furfural
of 80% at 443 K for 9 min were obtained. The processing of real lignocellulose
(e.g., beechwood and sugar cane bagasse) also achieved high yields
of HMF and furfural. Thereby, the current results indicate that the
process limitation lies no longer in the recalcitrance of lignocellulose,
but in the extraction of highly reactive HMF and furfural from the
aqueous phase in the biphasic reactor