Chemical Engineering July 2022 - 6

ergy required for the process
to be derived from
the process byproducts,
such as insoluble lignin.
DELIGNIFICATION
Researchers from Washington
State University
(Pullman; www.wsu.edu)
and the U.S. Dept. of
Energy's Pacific Northwest
National Laboratory
(PNNL; Richland, Wash.;
www.pnnl.gov) have developed
an artificial enzyme
that digests lignin,
which has stubbornly resisted
previous attempts
to develop it into an economically
useful energy
source. " This is the first
nature-mimetic
enzyme
that we know can efficiently
digest lignin to
produce compounds
that can be used as biofuels
and for chemical
production, " according
to Chun-Long Chen, a
corresponding author, a
PNNL researcher and affiliate
professor in chemical
engineering and
chemistry at the University
of Washington.
Enzymes offer a much
more environmentally benign
process than chemical
degradation, which
requires high heat and
consumes more energy
than it produces. In nature,
fungi and bacteria
are able to break down
lignin with their enzymes,
but natural enzymes degrade
over time, which
makes them hard to use
in an industrial process.
They're expensive, too.
In the current study, the
researchers replaced the
peptides that surround
the active site of natural
enzymes with protein-like
molecules called peptoids.
These peptoids
then
self-assembled
into nanoscale crystalline
tubes
and sheets
that have a high density
of active sites. " We can
precisely organize these
active sites and tune their
local environments for
catalytic activity, " says
Chen. The new enzymes
can also work at higher
(Continues on p. 7)
6
Boosting methane yields in biogas plants
IMM
B
iogas plants play an important role
in defossilization - anaerobic bacteria
in these plants break down
biomass to form biogas which, on
average, comprises up to 60% methane and
more than 40% CO2. While the biogas is
used to generate electricity and heat in combined
power-and-heating (CPH) units or can
be upgraded to natural gas quality and fed
into the natural gas network, the CO2 has not
been utilized to date. Instead, it is typically released
to the atmosphere. Now, as part of
the ICOCAD projects, researchers from the
Fraunhofer Institute for Microengineering and
Microsystems (IMM, Mainz, Germany; www.
imm.fraunhofer.de) are developing a way to
convert CO2 into additional methane.
The underlying chemical reaction - the
Sabatier process; CO2 + 4H2 → CH4 +
2H2O - was discovered more than a hundred
years ago, but to date it has not been
used for direct upgrading of biogas. This endothermic
reaction requires a high temperature
(around 400°C), which not only reduces
the maximum CO2 conversion through thermodynamic
equilibrium, but also favors the
undesired competing reverse water-gas shift
reaction. Also, sulfur compounds generated
in the biogas plant can poison the catalyst.
The goal of the ICOCAD I project was to
improve the catalyst stability against small
amounts (below 1 part per million (ppm)) of
sulfur remaining after the sulfur-removal trap,
as well as reducing other deactivation processes,
such as coking and sintering. Nickel
and ruthenium-based catalysts were studied,
both in fixed-bed and microchannel reactors
(photo). The selected catalyst achieved constant
CO2 conversion and CH4 selectivity in
long-term (1,000 h) durability tests. When exposed
to H2S in the feed, the nickel-containing-catalyst
formulation showed improved
stability, as it served as a sulfur trap.
The plant concept consists of a two-step
methanation with a first adiabatic reactor
stage, followed by a plate heat-exchanged
reactor with integrated cooling. Such a system
achieved more than 97% CO2 conversion.
In the ICOCAD I project, a pilot plant
was built that converts 1 m3/h of biogas into
1 m3/h of CH4, using a 10-kW electrolyzer
to supply the H2. In a follow-up project, ICOCAD
II, the researchers are scaling this up
by a factor of five, and plan to have this operating
by 2023. Scaleup to 500-kW is envisioned
by 2025, and to 2-MW by 2026.
A 'liquid' platinum catalyst outperforms solids at
low temperature
P
latinum is widely used for many catalytic
reactions, and because the
precious metal is so expensive, efforts
have been ongoing to reduce
the amount of Pt required to perform reactions.
Among these efforts are the use of
nano-dispersions, clusters and even single
atoms on different supports. Now, researchers
from the University of New South Wales
(UNSW; Sydney, Australia; www.unsw.edu.
au), in collaboration with scientists from the
Royal Melbourne Institute
of Technology
(RMIT; Australia), Deakin University (Victoria,
Australia) and the University of California
at Los Angeles, have demonstrated, for
the first time, a new way to support platinum
catalysts that significantly reduces the
amount of Pt required to catalyze reactions
- even at low temperature.
The concept - described in a June issue
of Nature Chemistry - is to dissolve traces
of liquid Pt into a solvent-like gallium matrix.
Because Ga melts at around 30°C, this
liquid-supported Pt catalyst can be used
at low temperatures. The Pt atoms in the
Pt-Ga system were shown to remain atomically
dispersed without segregation, as well
as being free to move through the liquid via
diffusion. This dynamic property of the Pt in
Ga was demonstrated, both by simulations
and by experiments in which deactivation
was found to be negligible. Alternative support
systems that fix the Pt in place make
the active sites prone to deactivation once
the reaction is running.
To make the catalyst system, Pt beads
are dissolved in molten Ga at around 400°C,
then cooled to the operating temperature of
the reaction (typically 40-80°C). In one (of
several) reaction studied, the electrochemical
oxidation of methanol using the Pt-Ga
system as the anode was shown to have
an activity of around 2.8 × 107 milliamp per
milligram of platinum, which is three orders
of magnitude higher than existing solid platinum
catalysts.
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JULY 2022
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Chemical Engineering July 2022

Table of Contents for the Digital Edition of Chemical Engineering July 2022
