Chemical Engineering May 2013 - 11

Edited by Gerald Ondrey
Air Products Recovery System
PSA
A waste-free monomer
recovery process is licensed
L
ast month, Air Products (Allentown, Pa.;
www.airproducts.com) announced that
it has licensed its proprietary adsorptionbased,
monomer recovery process to custom
process equipment supplier Cryo Technologies
(Allentown, Pa.; www.cryotechnologies.
com). The hybrid Air Products technology
combines a partial condensation unit with
a pressure-swing adsorption (PSA) process
to recover unreacted ethylene and propylene
coming from the degassing step at a
polyolefin production plant. The recovery
technology reduces production costs by $10
per metric ton (m.t.) by recovering valuable
olefins, solvents and nitrogen and leaving no
waste. " The process can achieve essentially
100% recovery of unreacted hydrocarbons,
so no flaring is required, " says Jeffrey Knopf,
Air Products licensing and technology transfer
manager. Also, the recovery process recaptures
high-purity nitrogen gas that was
originally used in the degassing step and
that can be re-used for further degassing.
After compressing the unreacted monomer-laden
nitrogen gas stream to 200 to
300 psi, the compressed stream is cooled
in a partial condensation unit, condensing
the majority of the unreacted hydrocarbons.
The remaining hydrocarbons flow with
CW
Water
wash
scrubber
Mechanical
refrigeration
unit
Mechanical
Feed
refrigeration
unit
Water discharge
To water wash scrubber
To water wash scrubber
the nitrogen gas into the PSA unit, where
more hydrocarbons are removed, leaving a
nitrogen gas stream with 50 to 1,000 ppm
hydrocarbons by weight, the company says.
Hydrocarbons recovered from the PSA are
recycled in a low-pressure tailgas stream to
the feed compressor.
Air Products' monomer recovery technology
was originally developed with a grant
from the U.S. Dept. of Energy's Industrial
Technologies Program, and was installed
in three commercial polyolefin facilities in
the mid-2000s by Air Products before the
company placed its focus elsewhere, Knopf
explains. Now, Cryo Technologies will offer
the technology to polyolefin makers around
the world.
Gas-phase option for NOx abatement
T
he first commercial application of a newly
developed process for the treatment of oxides
of nitrogen (NOx) waste gas has been
established at a milling operation in Los
Angeles, Calif. Developed by Pacific Rim Design
and Development (PRDD; Reno, Nev.;
http://prdd.net), along with DuPont (Wilmington,
Del.; www.dupont.com), the process
uses gas-phase chlorine dioxide to react
with both NO and NO2 to form nitric and
hydrochloric acids.
Because of the low solubility of NO,
traditional liquid-phase scrubbers need
to employ multiple stages to convert the
NO to NO2 and then to react the NO2.
" Carrying out the reactions in the gas
phase allows high removal efficiencies
with short residence times, " says Robert
Richardson, president of PRDD. The reaction
speeds make it possible to elimiNote:
For more information, circle the 3-digit number
on p. 72, or use the website designation.
Temperature-swing
adsorption dryer
Propylene
product
May 2013
Nitrogen
nate a stage from the process and reduce
equipment costs.
The major innovation of the technique is
the proprietary method for mixing the ClO2,
which is generated onsite via several possible
routes, with the waste gas. The ClO2
reacts with NO to form NO2 and with NO2
to form nitric and hydrochloric acids. The
mixed acid waste can be used for neutralizing
high-pH solutions, Richardson notes.
The gas-phase scrubbing technique can
work with existing air-pollution control processes
as either a pre- or post-treat option.
The lighter equipment loads mean that such
a process could be mounted on the roof or
in the rafters of a building, rather than requiring
ground space. Richardson says the
method can be used in chemical milling,
etching, aluminum brightening and pickling
applications, among others.
Heap-leaching for REs
Studies conducted by Texas
Rare Earth Resources Corp.
(Sierra Blanca, Tex.; www.trer.
com) indicate that heap leaching
with 15% (~150 g/L) sulfuric
acid has the potential to
dissolve minerals containing
rare-earth (RE) elements from
host rock at an RE mineral site
near El Paso, Texas. Research
conducted by the heavy RE
exploration company on the
minerology, geochemistry and
kinetics of direct-acid leaching
demonstrated that this technique
is effective at recovering
more than 80% of targeted
heavy RE elements from
host rock. If further technical
results and economic assessments
prove favorable, the
company says that combining
open-pit mining and heap
leaching could significantly
reduce capital and operating
costs for a heavy rare-earth
facility. Texas Rare Earth is investigating
different host-rock
particle sizes, as well as acid
strengths to further optimize
the extraction method.
Anti-scalant
BWA Water Additives Ltd.
(Manchester, U.K.; www.
wateradditives.com) introduced
a biodegradable antiscalant
product for reverse
osmosis (RO) membranes
that prevents common inorganic
deposits from forming
(Continues on p. 12)
ChEMICAL EngInEERIng WWW.ChE.COM MAy 2013 11
http://www.airproducts.com http://www.cryotechnologies http://www.trer http://www.prdd.net http://www.dupont.com http://www.wateradditives.com http://WWW.ChE.COM
Chemical Engineering May 2013

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