Chemical Engineering July 2017 - 7

Chementator
Low-cost water treatment uses CO2 to remove
particles without membranes
Air
R
esearchers at
Princeton University
(Princeton,
N.J.; www.
Waste
particle
RECYCLING SACHETS
Particle
princeton.edu) have developed
a water treatment
technique that injects
carbon dioxide gas into a
stream of water to separate
suspended particles
that would be difficult to
remove by sedimentation
or by microbes. The system,
built initially at laboratory-scale,
removes suspended
particles 1,000
times more efficiently than conventional
filtration units, and does not require membranes,
the research team says.
The low-cost, low-energy system could
be used as a replacement to microfiltration
and ultrafiltration, or as an adjunct to conventional
filtration, protecting membranes
from fouling. The system could also be used
to separate waterborne bacteria and viruses
without chlorination or treatment with ultraviolet
light, the researchers say.
suspension
Filtered water
C02
Particle
suspension
C02
Princeton University
The system works by taking advantage of
a principle called diffusiophoresis, whereby
the movement of solid particles in water is
induced by an ion concentration gradient.
The ion gradient is set up by dissolving CO2
gas in water, forming carbonic acid. The acid
dissociates into hydrogen ions and HCO3
-
ions, similar to the chemistry that occurs in
carbonated beverages. Large differences in
the diffusivities of H+ and HCO3
- ions create
a diffusion potential, which can be exploited
to move suspended particles (which have
significant surface charges) by diffusiophoresis,
the researchers say.
The solids-containing water travels through
a gas-permeable material (polydimethylsiloxane)
and the ion gradient induces particle
motion transverse to the flow direction. The
particles then accumulate in one side of the
channel, where they can be separated by
splitting the water stream (see figure).
The research project was carried out in
the Princeton laboratory of Howard Stone
by post-doctoral researcher Sangwoo Shin,
an engineering professor at the University
of Hawaii at Manoa, and Orest Shardt, a
former Princeton scientist now at the University
of Limerick (Ireland). The research
was described in a recent issue of Nature
Communications. The team plans to scale
up the technology.
Commercial debut for a process that
captures CO2 directly from air
O
n May 31, Climeworks (Hinwill/
Zurich, Switzerland; www.climeworks.com)
inaugurated its -
and the world's - first commercial
plant that captures CO2 directly from
air. The Direct Air Capture (DAC) facility,
located at the waste-utilization plant of
KEZO in Hinwill, Switzerland, will supply up
to 900 metric ton per year (m.t./yr) of CO2
to a nearby greenhouse-cultivation company,
Gebr. Meier Primanatura AG, which
previously had to purchase CO2 delivered
by trucks. CO2 is used in greenhouses for
increasing the growth of vegetables, such
as tomatoes and cucumbers.
The DAC plant uses an air-filtration system
that the company's founders first began
developing while engineering students at
the Swiss Federal Institute of Technology in
Zurich (ETH; www.ethz.ch). The facility has
18 collectors, each equipped with a fan and
a filter. The fans blow air through the filters,
which are porous granulates modified with
amines that absorb CO2 from air. After a
few hours, the filter becomes saturated. The
captured CO2 is then released by heating
to 100°C using waste heat from the wasteutilization
plant. The CO2 is then pipelined to
the greenhouses located 400 m away.
The plant will operate as a three-year
demonstration project in cooperation with
partners Gebr. Meier and KEZO, and with a
contribution toward non-amortizable costs
by the Swiss Federal Office of Energy.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2017
Later this year, Unilever (London,
Air
U.K.;
www.unilever.
com) plans to open a pilot
plant in Indonesia to test the
long-term viability of its new
technology for recycling plastic
sachet (small bags) waste.
The process, called CreaSolv,
has been developed in cooperation
with the Fraunhofer
Institute for Process Engineering
and Packaging (IVV;
Freising, Germany; www.ivv.
fraunhofer.de). The technology
has been adapted from
a method IVV developed to
separate brominated flame
retardants from waste electrical
and electronic equipment.
The pilot plant will enable the
recovery of 6 kg of pure polymers
using the same energy
needed to produce 1 kg of
virgin monomer, says IVV.
Today, only 14% of all plastic
packaging is recycled globally,
says Unilever. Sachets
are widely used in developing
and emerging regions of the
world because they enable
low-income consumers to
purchase small amounts of
products. In Indonesia, some
64 million m.t./yr of waste
is generated, with 1.3 million
m.t./yr ending up in the
ocean. Unilever has pledged
to make 100% of packaging
recyclable, reusable or compostable
by 2025.
UREA + SULFUR
Building on years of joint
experience in the field of
sulfur
granulation, Sandvik
Process Systems (Fellbach,
Germany; www.processsystems.sandvik.com)
and
Shell joined forces and
successfully demonstrated
the integration of the Shell
Thiogro (www.shell.com/
sulphur/thiogro) Urea-ES
technology
and
Sandvik
Rotoform equipment during
a series of continuous plant
trials at Sandvik's productivity
center in Fellbach. Shell's
unique technology and
(Continues on p. 8)
7
Edited by:
Gerald Ondrey
http://www.princeton.edu http://www.unilever http://www.ivv http://www.fraunhofer.de http://www.clime http://www.works.com http://www.ethz.ch http://www.process http://systems.sandvik.com http://www.shell.com/ http://WWW.CHEMENGONLINE.COM
Chemical Engineering July 2017

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