Chemical Engineering February 2016 - 9

A 'greener' route for making red pigments
E
arly this year, Lanxess AG (Cologne, Germany;
www.lanxess.com) will start production of bright
red iron-oxide pigments at its Ningbo, China
production site. The production facility will utilize
- for the first time - the Ningbo Process, a highly
sustainable production process that the company has
developed in a test reactor at its Krefeld-Ürdingen, Germany
site. Compared to the traditional Penniman production
process, which is already widely used in China
for making yellowish-red pigments, the new Lanxess
technology ensures substantial improvements in terms
of sustainability. The new plant for iron-oxide red pigments
in Ningbo is being designed for an initial synthesis
capacity of 25,000 m.t./yr.
The Penniman process is one of four routes that are
used for making pigments of various shades of red. The
Penniman red process produces particularly yellowish-red
pigments. However, the process generates oxides of nitrogen
(NOx) and wastewater that contains dissolved ammonium
nitrate. While developing a " cleaner " and more
sustainable process, Lanxess also discovered that the
conventional route also produced significant quantities of
nitrous oxide - a greenhouse gas (GHG) with a globalwarming
potential that is 300 times higher than that of
CO2, as well as being an ozone-depleting compound.
In the conventional process, hematite seeds are first
produced by the reaction of scrap iron with HNO3 at a
temperature of over 90°C. The hematite seeds, together
with the scrap iron and ferrous nitrate, are then developed
into pigments at temperatures of 70-95°C under aeration.
After the pigments are formed, they are filtered, washed,
dried and (if required) milled to the desired size.
The Ningbo Process ensures NOx emissions are reduced
by over 90%, while also reducing energy consumption
by 80%. Significantly less Fe(NO3)2 is required,
which minimizes the amount of dissolved nitrates in the
wastewater. Residual NOx is removed in a nitric-acidrecovery
plant, with the recovered acid reused in the
process. The N2O, which cannot be removed by scrubbing,
is catalytically converted into N2, O2 and H2O. Heat
from this exothermic reaction is recovered and used in
the process. Finally, a multistage wastewater-treatment
process, including sedimentation, biological denitrification,
ultrafiltration and reverse osmosis, produces water
that can be reused as process water.
Coral enhances the removal of
mercury from wastewater
A
convenient route for the fabrication of a bio-mimetic,
coral-like nanoporous γ-Al2O3 with a higher
capacity to adsorb Hg(II) in aqueous solution than
those of commercial Al2O3, has been reported by
a research group from Anhui Jianzhu University (Hefei City,
China; www.ahjzu.edu.cn), the Chinese Academy of Sciences
(Hefei, China; www.cas.ac.cn), and Monash University
(Melbourne, Australia; www.monash.edu).
Generally, nanosized γ-AlOOH (boehmite) or γ-Al2O3
adsorbents have been used to remove heavy metals,
such as mercury from water due to their high surface area
and the existence of rich adsorption sites. However, those
adsorbents tend to aggregate in solution during the adsorption
process, resulting in a decrease of adsorption efficiency.
Also, they require centrifugation to separate the
heavy metals from water, which limits their large-scale industrial
application. Coral-like adsorbents might overcome
this problem due to their hierarchical micro/nanostructure.
The microsized units are composed of curled nano-sized
units that can resist aggregation, maintain high exposed
surface area, and they can be easily separated, leading to
high adsorption efficiency. Therefore, coral-like aluminumbased
materials should be high efficiency adsorbents.
The researchers fabricated the nanoporous γ-Al2O3 by
annealing coral-like γ-AlOOH based on an ethylene-glycol
driven self-curled assembly process. In this process
the ethylene-glycol works as a capping agent for the
self-curled process of the layered structure of γ-AlOOH
nanoplates, and also as a driving force for their assembly
through a charge shielding effect.
The γ-Al2O3 unit (approx. 1.5 µm) obtained by the
group is composed of curled porous (2.5-nm-dia.
pores) γ-Al2O3 nanoplates. The material obtained has
a Hg(II) removal capacity 2.5 times higher than that of
commercial Al2O3 nanoparticles and 2.7 times the removal
capacity of hollow structured γ-Al2O3 prepared
without ethylene glycol.
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Chemical Engineering February 2016

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