Chemical Engineering March 2012 - 13

Know-how
for Your Success
Composites that can enhance
forward osmosis
esearchers from the Dept. of Chemical Engineering,
Monash University (Clayton, Victoria, Australia; www.
monash.edu), have reported on a new composite polymer
hydrogel with light-absorbing particles incorporated
within it, that can be used as draw agents in the forward
osmosis (FO) process of desalination.
The researchers, led by professor Huanting Wang,
R
aimed to develop new " draw agents " capable of meeting
the following requirements: low-energy consumption for
regeneration, complete separation from the fresh water
product, low toxicity and chemical inertness with polymeric
membranes.
They have previously shown that hydrogel particles are
able to draw pure water through FO membranes. The water
can then be removed by pressure or heating, or both. The
incorporation of light-absorbing particles leads to natural,
enhanced heating and dewatering of the composites, as
compared with pure hydrogels under irradiation with light.
Another advantage of composite polymer hydrogels is that
they exhibit higher swelling ratios, thus producing higher
water fluxes in the FO process. With increasing loading of
carbon particles, the water recovery rates from the swollen
composite hydrogels are greatly enhanced.
The hydrogels are synthesized by free-radical polymerization
of different monomers (such as sodium acrylate, Nisopropylacrylamide)
and the crosslinker N,N'-methylenebisacrylamide,
with light-absorbing carbon particles.
Very rapid cooling enables
a new way to produce magnesium
A
carbothermal process for obtaining magnesium - developed
by CSIRO (www.csiro.au) Light Metals Flagship
(South Clayton, Victoria, Australia) - overcomes previous
limitations to commercial viability. For several years, magnesium
has been produced mainly by electrolytic routes,
from magnesium chloride sources such as seawater and
natural brines. More recently, world production has been
mainly in China, using the Pidgeon process, where ferrosilicon
reduces magnesia from calcined dolomite under
vacuum. One of the main problems with those methods is
the reversion of Mg and CO2 to magnesium oxide and carbon
as the vapors cool.
The CSIRO process, called MagSonic, uses shock-quenching
to achieve extremely rapid cooling - up to 106 °C/s
- of the gaseous reaction products and prevent the back
reaction. According to CSIRO, carbothermic reduction is a
much cheaper reduction than ferrosilicon, and there is significant
potential for reduction in equipment size, capital
costs, and productivity over electrolytic routes.
In the MagSonic process, magnesia and carbon (graphite)
react above 1,700°C to produce Mg vapor and CO gas.
The equilibrium total pressure of the products is 1 atm at
1,764°C. In CSIRO's experimental work, a charge of up to
2,500 g of briquettes of MgO and graphite were heated under
inert gas at atmospheric pressure. The gas phase was shock(Continues
on p. 14)
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Chemical Engineering March 2012

Table of Contents for the Digital Edition of Chemical Engineering March 2012
