Chemical Engineering June 2016 - 49

SiLT denSiTy index
Silt density index (SdI) is a sensitive method for determining the ability of a filter to remove
colloidal particles. SdI is used extensively as a criterion in minimizing fouling of reverse
osmosis membranes. The lower the SdI value, the cleaner the stream. EPFs can be used
to pretreat water before it enters Ro membranes. Pretreatment with EPF reduced nanoparticle
fouling of microfiltration (MF) membrane by about 2% (with pretreatment), as compared
to 80% (with no pretreatment) [6].
Manufacturers of Ro membranes recommend that the stream be prefiltered so that it has
an SdI factor less than 3.0. Typically " 1-μm absolute " [14] filters have an SdI of about 4 to 5.
Manufacturers of hollow fiber membrane filters claim SdIs in the range of 1.75 to 2.25. SdI
measurements of effluents from the media with nanoscale alumina features media range
from 0.5 to 1.0. Turbidity as well as SdI tests have confirmed that the extent of shedding of
nanoscale particles from the nano-alumina-type filters into effluent streams is minimal.
the media thickness is 0.8 mm.
The high surface area of the nanoscale
alumina fibers, plus their high
zeta potential, produce strong electrostatic
and electrokinetic fields
that influence the flow of particles
as far as 1 µm away from the surface
of the media. zeta potential is
a measure of the magnitude of the
electrostatic attraction or repulsion
between particles. The field therefore
overlaps the flow channels of
the 2-µm-pore-size media. Since
the particle flows through a tortuous
path of approximately 400 pores
across the media, there is a high
probability of particle capture.
Since the electropositive nanoAl
fibers are dispersed and fixed in
place via electroadhesive forces,
particles have easy access to the
charged surface. Powdered activated
carbon (Figure 1, center) or
nanoparticles such as nano-silica
can be retained in the nanoAl structure.
The pore size of the non-woven
media is 2 μm, yet the filter can remove
suspended solids as small as
GET ME A CHECK-ALL®
SILENT OPERATION!
Check-All®
valves close
quickly and smoothly to
minmize hammer noise.
UPSTREAM TRIM!
The upstream trim is
protected from corrosive
media mixing; thereby,
extending valve service life.
Spring-Loaded check valves
assembled to your exact needs.
Most lead times are less than
one week!
®
TM
SINCE 1958
515-224-2301
Manufactured in West Des Moines, Iowa, USA
www.checkall.com  sales@checkall.com
Circle 05 on p. 74 or go to adlinks.chemengonline.com/61496-05
ChemiCal engineering www.Chemengonline.Com June 2016
m
s
miller-stephenson chemical company, inc.
Connecticut - Illinois - California - Toronto
800.992.2424 Technical Service
miller-stephenson.com support@mschem.com
Krytox™, Vertel™and Vazo™ are registered trademarks of The Chemours Company FC, LLC
Circle 19 on p. 74 or go to adlinks.chemengonline.com/61496-19
49
Miller-Stephenson Offers a Wide Range
of Chemicals for Industry
* PTFE Dry Lubricants
* KrytoxTM
Lubricants
* Solvent Cleaners
* Contact Cleaners
* VertrelTM
Solvents
* Connector Lubricants
* Aero-Duster®
* Adhesives and Sealants
* Epoxy Resins
* VazoTM
!
viruses (typically 20-30 nm in diameter)
and does so at high flowrates
and at salinity values up to 3.4 M
of naCl (near saturation at 300,000
ppm) and at pH values in the range
from 4 to 10.
Filtering bacteria and viruses
The removal of bacteria and viruses
from water in CPI applications is important
for several reasons. Aside
from being potentially pathogenic
contaminants, microbes are also
foulants in HvAC (heating, ventilation
and air conditioning) and other systems.
Bacteria can also play a role in
corrosion (Thiobacillus ferrooxidans
is known to feed on iron and cause
corrosion, for example). Microbes
also have a tendency to attach to
surfaces and form biofilms, which
may not be affected by disinfecting
efforts, such as the use of free chlorine,
even at concentrations of several
ppm [13].
EPFs can offer a means of effecCHEM
ENG - Biullet 1/4pg 2016 A.qxp_EP&T Ad Electronic 1/4pg 2014 4/7/16
tively removing bacteria and viruses
Free Radical Sources
Low Global Warming Formulations and nPB & HCFC 225
Replacements Available

http://www.miller-stephenson.com http://www.checkall.com http://adlinks.chemengonline.com/61496-05 http://adlinks.chemengonline.com/61496-19 http://www.Chemengonline.Com

Chemical Engineering June 2016

Table of Contents for the Digital Edition of Chemical Engineering June 2016