Chemical Engineering March 2019 - 11

Accelerated electrons unlock sugars from
cellulosic biomass
O
btaining sugars from
cellulosic biomass
cost-effectively is
difficult because the
predominant biopolymers in
plant material evolved to protect
these sugars. A process
currently being scaled up for
obtaining sugars from waste
agricultural biomass employs
beams of accelerated electrons
to fracture chains of
cellulose and hemicellulose,
allowing dramatically improved enzymatic
hydrolysis in subsequent process steps.
Xyleco, Inc. (Wakefield, Mass.; www.
xyleco.com) is building a commercial-scale
demonstration plant in Moses Lake, Wash.
to make several end products at 10 times
the volume of its initial pilot plant. The process
consists of three major steps. First,
waste agricultural biomass, such as corn
cobs, corn stover, sugarcane bagasse and
others, are milled to a particular particlesize
range, depending on the feedstock
used. Next, the biomass is passed below a
beam of accelerated electrons, which collide
with the atoms of the biomass, causing
electrons to be ejected from the plant material
(diagram).
Biomass
Conveyor
Electron beam
" The collisions, and subsequent ejection
of electrons leave the material in an ionized
state, " explains Craig Masterman, Xyleco's
chief technology officer. " This charged state
is unstable, so the long chains that make up
the polymer strands of the biomass fracture
and break apart. "
The molecular weight of the polymers
is reduced in this way by 95% or more,
Masterman says, although to the naked
eye, the processed material appears idenXyleco
Hopper
containing
biomass
Electron
accelerator assembly
Whey coordinator Glanbia Ireland
(Kilkenny; www.glanbia
ireland.com), in collaboration
with University College Dublin
and Trinity College Dublin.
SOLVENT FILTRATION
tical to the starting biomass. Because
the biopolymers are broken down by the
electron beam, the third stage of the process
- an enzymatic hydrolysis step with
a proprietary mix of enzymes that yields
sugars - is more efficient by a factor of
10 compared to untreated biomass and
significantly more productive than biomass
treated with acids. The predominant sugars
obtained are xylose and glucose, which
can be fermented or otherwise chemically
transformed into a range of products, including
ethanol, polylactic acid, succinic
acid and others.
The key advantages of the process include
relatively low-cost process equipment (no
high temperatures or pressures are required),
low water use and waste production, fast processing
times for the electron pre-treatment
(a few seconds), and generation of products
that are well suited to downstream processing.
Masterman points out, for example, that
acid pre-treatment generally destroys most
of the xylose contained in the biomass (about
40% of the total sugars) and produces toxic
compounds, such as hydroxymethylfurfural
(HMF), which inhibit downstream processing,
including fermentation.
Organic solvent nanofiltration
typically involves polymerbased
membranes that feature
tiny pores, but form dense
and amorphous networks.
Well-ordered microporous
materials, such as zeolites and
metal-organic frameworks
(MOFs), perform significantly
better than these conventional
membranes in various separation
processes, but they are
not suitable for extensive use
in liquid separation because
of their poor structural and
chemical stability in liquids.
Now, researchers from King
Abdullah University of Science
and Technology (KAUST; Thuwai,
Saudia Arabia; https://
kaust.edu.sa) have developed
a synthetic approach that
produces well-ordered microporous
materials that are
stabilized by covalent keto-
enamine linkages.
The new membranes, described
in a recent issue of J.
Am. Chem. Soc., are said to
outperform amorphous analogues
and the best polymerbased
systems. The organic
solvent
permeability of the
new membranes is almost
an order of magnitude higher
than that of the best-reported
polymer membranes, says
KAUST. The membranes are
said to be more stable than
MOFs and more cost-effective
than inorganic membranes. ❑
Making formaldehyde from methane, without generating CO2
R
esearchers from South Korea
have discovered a highperformance
catalyst for the
selective oxidation of methane
to formaldehyde. The study was
conducted by staff from Ulsan National
Institute of Science and Technology
(Ulsan; www.unist.ac.kr), Ajou
University (Suwon; www.ajou.ac.kr)
and Hanyang University (Seoul; www.
hanyang.ac.kr), and led by Ulsan's
professor Kwang-jin Ahn.
Methane is very stable and does not
react easily with other substances.
Temperatures above 600°C are required
for a reaction that changes the
chemical structure of methane. Vanadium
oxide (V2O2) and molybdenum
oxide (MoO3) were known to be the
best catalysts, but the conversion of
methane to formaldehyde is low (less
than 10%).
The catalyst developed by the
Korean team has a core-shell structure
consisting of vanadium oxide
nanoparticles surrounded by a thin
aluminum film. The shell protects the
grain and keeps the catalyst stable
and maintains stability and reactivity
even at high temperatures. The
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
MARCH 2019
team utilized hydrothermal synthesis
followed by atomic layer deposition
to prepare the catalyst based on the
novel SiO2@V2O5@Al2O3 core@shell
nanostructures. The thickness of
Al2O3 shells over SiO2@V2O5 cores
can be tuned by controlling the number
of atomic layer deposition cycles.
With this catalyst the efficiency of
conversion of methane to formaldehyde
increased by more than 22%.
Ahn says the team plans to further develop
the catalyst manufacturing technology
and the catalytic action in order
to move to industrial application. n
11
http://www.glanbia http://www.ireland.com http://www.xyleco.com http://https:// http://kaust.edu.sa http://www.unist.ac.kr http://www.ajou.ac.kr http://hanyang.ac.kr http://WWW.CHEMENGONLINE.COM
Chemical Engineering March 2019

Table of Contents for the Digital Edition of Chemical Engineering March 2019
