Chemical Engineering February 2016 - 8

to methylcyclohexane, and
then releases H2 when
needed. Now, a promising
alternative H2 carrier, based
on formic acid, is being developed
by the group of Hajime
Kawanami at the Research
Institute for Chemical Process
Technology, National
Institute of Advanced Industrial
Science and Technology
(Sendai City, Japan; https://
unit.aist.go.jp/cpt/034_
cpt-mfc_en.html). The researchers
have developed a
catalyst, based on an iridium
complex, that selectively
decomposes formic acid at
a temperature of less than
100°C, to produce H2 at very
high pressure (greater than
120 MPa). This temperature
is significantly lower than the
200°C needed to generate
H2 from cyclohexane-based
H2 carriers, and the formation
of pressurized H2 is advantageous
in refueling vehicles.
The catalyst has a high turnover
frequency (1,800 h-1) at
40 MPa, and generates H2
and CO2 at a very fast rate (1.2
MPa/s per gram of metal). The
H2 can easily be recovered
by a simple gas-liquid separation
at -10°C to give 85%
H2. Further cooling to -50°C
removes the remaining CO2,
and the product H2 has less
than 6 parts per million (ppm)
by volume CO.
Water purification
University of Cornell researchers,
led by Will Dichtel,
associate professor
of chemistry and chemical
biology, have invented a
porous form of cyclodextrin
that adsorbs pollutants from
wastewater at rates vastly
superior to traditional activated
carbon - 200 times
greater in some cases. This
fast adsorption rate means
the material has the potential
for very low energy, flowthrough
water purification
applications, says Dichtel.
The cyclodextrin-containing
polymer has a cup shape,
which gives it a large surface
area. It features easier, lessexpensive
regeneration, so
it can be reused many times
with no loss in performance,
says Cornell.
❐
8
Using air and hydrostatic pressure to
store energy underwater
C
onsisting of a landbased
mechanical
facility and underwater
pipelines and
Air In
Motor
accumulators, the underwater
compressed-air energystorage
(UCAES) system
from Hydrostor Inc. (Toronto,
Ont., Canada; www.
hydrostor.ca) takes electricity
(potentially excess solar
or wind energy) and uses it
to run a compressor, which
pressurizes atmospheric air,
while also enabling the capture of the heat
of compression. Once the pressure of the
air is equal to the hydrostatic pressure of
the nearby body of water where the accumulators
are located, the air is sent through
the pipeline to the accumulators, where it
is stored until the UCAES system needs
to produce energy. At this time, a valve is
opened, allowing the weight of the water to
push the air back through the pipeline to a
network of heat exchangers, an expander
and eventually a generator. Since the direction
of airflow is controlled by simply opening
a valve, this allows for " black start " -
the system can be started without using
additional power from the grid.
The systems are designed for a specific
application's needs. A balance between
water depth and the installation's distance
from land is key in selecting the best sites
Air out
Comp
Expander
Gen
Cold
tank
Hot tank
HXer
Accumulator
Thermal enhancement option
(concentrated solar, photovoltaics,
natural gas, diesel, and others)
and sizing the compressor and turboexpander,
explains Hydrostor CEO Curtis
VanWalleghem. The systems use standard
12-in. pipelines, and multiple lines can be
installed in parallel based on pressure-drop
requirements. The amount of storage capacity
required determines the required number
of accumulators, which are available in either
a flexible, balloon-like version or a rigid cement
version. The mechanical nature of this
energy-storage technique leads to a much
longer lifetime and lower costs than batterybased
technologies, says VanWalleghem
After four months of construction, the
company commissioned its first installation
of a UCAES system in Toronto in November
2015. In the coming months, Hydrostor
expects to announce a partnership with a
global engineering, procurement and construction
(EPC) company.
Removing harmful metals from wastewater
with crab shells
C
opper and cadmium exist naturally
in the environment, but human activity
can increase their concentrations
to a point where they become
a health hazard. Conventional wastewater
treatment to remove those metals includes
chemical precipitation, coagulation, flocculation,
ion exchange, membrane filtration,
activated carbon, and the use of carbon
nanotubes. However, naturally occurring biosorbents
can clean up contaminated water
at the same efficiency, and with little impact
on the environment and on human health.
Crab shells from Scylla serrata (mud crab)
proved to be a good biosorbent for removing
copper and cadmium from industrial
wastewater by researchers from the Universiti
Putra Malaysia (Serdang, Malaysia; www.
upm.edu.my). The researchers chose crab
shells due to their abundance and ready
availability as waste products. The crushed
crab shells were able to remove up to 94.7%
of copper (5 mg/L initial concentration), and
85.1% of cadmium (1 mg/L initial concentration).
The conditions (pH = 6, T = 25°C)
closely matched the wastewater effluent
characteristics from industrial mining and
metal refining.
Crab shells consist of calcium carbonate
and protein (29.19%), ash (40.60%), lipids
(1.35%), and chitin (26.65%) on a dry weight
basis. The researchers say the calcium carbonate
and chitin in the crab shells are found
to be the most effective in removing heavy
metals, especially copper and lead. This is
because calcium carbonate forms strong
copper-carbonate and lead-carbonate bonds
when reacting with copper and lead, while
chitin acts as an adsorbent for precipitation in
the presence of those metals, they say.
ChemiCal engineering www.Chemengonline.Com february 2016
http://https:// http://unit.aist.go.jp/cpt/034_ http://www.hydrostor.ca http://upm.edu.my http://www.Chemengonline.Com
Chemical Engineering February 2016

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