Selection of Filter Media

DIFFERENT TYPE OF FIBERS


FIBER TYPE -- THERMOPLASTIC -- HYDROLYSIS

Polypropylene - Yes - No
Polyester - Yes - Yes
Co-Polymer - No - No
Homo Polymer - No - No
Nylon - No - Yes
Nomex / Conex - No - Yes
Rayton - Yes - No
P-84 (Polymide) - No - Yes
Glass - No - No
Teflon - No - No
Huyglass - No - No

FIBERS WHERE USED / WHERE NOT USED

Polypropylene :

Polypropylene is used exclusive in application where moisture is clearly a problem. It is limited by its low temperature resistance. At elevated temprature, rayton is selected for these same moist application

Polyster :

When Hydrolysis attack polyster it will weaken the media overall. Polyster is suitable when moisture is low.

Homopolymer :

Demonstrate good resistance to solvents, oxidizing agents, acid where the temperature is below 125-130 deg. cen. When moisture and chemistry attack polyster media, it looses its strength mainly due t break down of molecular structure of the polyster through hydrolysis.

Rayton :

Rayton fiber is problem solving material is high temprature application. It replaces Nomex when it fails due to Hydrolysis. This fiber can operate satisfactorily a elevated temperature . This can also replace Fiber glass some times when FG fails due to flex abrasion .This can also replace other material which can not withstand high temperature or chemistry /moisture.

Nomex :

Nomex is used in high temperature ( 204 deg.cen.) but in dry conditions Nomex is subject to Hydrolysis and will fail quickly in the presence of chemistry and moisture at elevated temprature.It s especially subjected to attack by sulfur oxides.

P-84 ( Polyamide ) :

P-84 is used I high temprature application ( 240 C ) but again dry condition .This s again subjected to hydrolysis .P-84 susbstituted fr fiber glass which can not take abrasion of continuous pulsing .It works better when there is no moisture and chemistry.

PTFE :

This is used when chemicals conditions are sever ,temprature resistance is also very good ( 240 C ) .PTFE does not have high level of abrasion resistance.

Glass :

This material offers outstanding performance in high temperature application ( 260 C ) . It is also resistant to most of the acid with major application being Hydrofluoric acid. Fiber glass has very poor flex abrasion resistance and it subject to quick failure if pulsed or cleaned vigorously.


FIBER -- CONT . OP. TEMP. - RESIST. TO ACIDS - RESIST. TO ALKALI - TENSILE STRENGTH
ABRASION RESISTANCE
Polypropelene - 90 - Excellent - Excellent - Excellent -
Good

Nylon - 110 - Fair - Excellent - Excellent
Excellent

Polyester - 150 - Good - Fair - Excellent
Excellent

Co-Polymer - 125 - Good - Fair - Good
Good

Homopolymer - 135 - Excellent - Fair - Good
Good

Nomex - 204 - Fair - Excellent - Excellent
Excellent

PPS (Ryton) - 190 - Excellent - Excellent - Poor
Excellent

Polymide - 200 - Fair - Excellent - Excellent
Excellent

Teflon - 260 - Excellent - Excellent - Fair
Poor

Cotton - 80 - Poor - Excellent - Good
Fair

Wool - 90 - Fair - Poor - Poor
Fair

Glass Fiber - 260 - Excellent - Fair - Excellent
Poor

Huyglass - 270 - Excellent - Fair - Excellent
Fair

Evaluating Filtration Media - A Comparison of Polymeric Membranes and Nonwovens

In early 1998, DuPont introduced an improved version of T-980, marketed under the name Tyvek® SoloFlo™
filtration medium. Engineered for a better balance of filtration properties, Tyvek® SoloFlo™ is made with a new
spinning technology (patent pending) that produces a reduced average fiber size and more even fiber size
distribution. The smaller fibers result in sheet layers with fewer thicker portions and a larger number of smaller
pores. A less cohesive structure, with larger void spaces between the layers in the plane of the sheet, allows more
gas and vapor to pass through the material. This gives Tyvek® SoloFlo™ a more open structure with a higher
porosity, significantly improved permeability and a 50% greater dirt-holding capacity (or filter life) than the
earlier T-980 style.

A Comparison of Filtration Media

At their simplest, filtration processes must meet objectives and be the most economical. Most processes are
chosen based on initial capital investment alone, with operating costs ignored. However, filtration media can
greatly affect the efficiency of any filtration process, as well as filtration cost. Therefore, filtration media should
be closely examined -- and evaluated -- before processes are chosen.
When choosing filtration media, end-users should first define their individual problems as carefully as possible,
particularly the desired flow (batch or continuous), required level of filtration, desired end-product (i.e., fluid,
solids or both), anticipated solids level(s), variability and operating conditions. Only after the process has been
defined and a filtration device has been selected, can the media selection begin. This requires both careful
planning and rigorous testing.
Filtration media can be evaluated against many criteria, but the four key criteria are: permeability, filtration
efficiency, filtration capacity (or life) and filtration costs.
Permeability
Meltblown nonwovens are considered the most permeable of today's filtration media, while microporous
membranes and spunbonded media (including Tyvek®) have decreased permeability. However, Tyvek®
SoloFlo™ exhibits air and water flow rates comparable to microporous membranes and begins to approach the
rates exhibited by typical meltblown media. The more open depth, finer fibers and asymmetrical structure of
Tyvek® SoloFlo™, as seen in scanning electron photo micrographs (SEMs), account for the material's high level
of permeability (see Figure 1: Top and cross-sectional views of Tyvek® SoloFlo™ at 200X magnification).
Figure 1: Top and cross-sectional views of Tyvek® SoloFlo™ at 200X magnification
Filtration Efficiency
When the filtration efficiency of media is compared, the positions of meltblown nonwovens and
microporous/PTFE membranes reverse, with membranes proving to be the most efficient, and meltblowns the
least efficient in a variety of applications. Typically, mean flow pore size (as determined by Coulter Porometer™
or Porous Materials Inc. Capillary Flow Porometer) can serve as an indicator of filtration efficiency, as in the
case of membranes versus most nonwovens.
Evaluating Filtration Media - A Comparison of Polymeric Membranes and Nonwovens
Submitted to Filtration & Separation Journal, Volume 35 No. 10, December 1998
Page 3 of 6
However, this principle does not hold true with Tyvek® SoloFlo™. Even though its mean flow pore size is close
to 5 microns, Tyvek® SoloFlo™ has demonstrated a high liquid efficiency at a nominal rating of 1 micron due to
the tortuous path of its fibers. In fact, AC Fine Test Dust (ACFTD) full-scale challenge tests have confirmed that
Tyvek® SoloFlo™ has higher Beta ratios (and therefore, higher efficiencies) than both meltblown and
spunbonded media, and approaches that of the 0.5-micron PTFE membrane laminate (see Figure 2: Results of
ACFTD testing on an Oberlin 2.4 ft2 production automatic pressure filter). Figure 3 shows that Tyvek®
SoloFlo™ approaches the efficiency of a 0.45-micron microporous membrane at about 4 microns, but is inferior
to an older version 0.5-micron PTFE laminate (which had a lower permeability than the grade presently
manufactured). Note that these IBR data were collected in discrete intervals with a HIAC/ROYCO 8000A
automatic particle counter and averaged, while the Oberlin data were measured with a Particle Measuring System
(PMS) instrument over the whole cycle (see Figure 3: Results of lab-scale ACFTD testing conducted by Inter
Basic Resources, Inc., Grass Lake, MI, USA).
Filtration Capacity (or Life)
The third property of filtration media that most end-users need to evaluate is filtration capacity (or life). In
ACFTD challenge tests conducted on both the Pall 47-mm disc filterability kit and the full-scale Oberlin 2.4 ft2
HA filter, meltblown media were demonstrated to have the longest life at 600 ppm. However, these media were
not shown to have a substantially longer life than microporous membranes -- and their filtrate quality is marginal,
at best. Tyvek® SoloFlo™ was shown to have approximately 80% of the life of the 0.45-micron microporous
membrane at 60 ppm ACFTD and approximately 85% at 600 ppm ACFTD, largely due to the lower permeability and porosity.
Although this is a moderate difference, the much lower cost of Tyvek® SoloFlo™ more than compensates for its
shorter life. Tyvek® SoloFlo™ also compared favorably to spunbonded and meltblown media in real-life
situations.

Filtration Costs

All too often when filtration media are purchased, only the initial cost is considered. But, for a true estimation of
"cost," several other factors should be considered. Generally speaking, the purchase costs of filtration media
range from microporous and PTFE membranes at the high end to meltblown media at the other end of the
spectrum. The purchase costs for flash-spun Tyvek® SoloFlo™ and other spunbonded media fall between these
two.
However, in typical wastewater applications (based on cents per gallon filtered), the actual costs of these products
become more apparent. The difference in purchase price vs. actual cost is most dramatic when comparing
microporous/PTFE membranes and meltblown media with Tyvek® SoloFlo™. Because Tyvek® SoloFlo™ can
be used as a single layer without support structures and can be reused in many wastewater applications -- unlike
most microporous/PTFE membranes and meltblown media -- its overall cost is half that (or less) of comparable
(1-micron) meltblowns and a fraction (5% or less) of the cost of microporous and PTFE membranes (see Table
1: Media Costs per Gallon Waste Filtered).
While Tyvek® SoloFlo™ exhibits only a slight deterioration in filtrate quality in comparison to microporous
membranes, it exhibits far better filtrate quality and superior strength than the low-cost meltblown media. And,
because of its much smoother surface, Tyvek® SoloFlo™ provides easy, dry cake release for more cost-effective
disposal.
Evaluating Filtration Media - A Comparison of Polymeric Membranes and Nonwovens
Submitted to Filtration & Separation Journal, Volume 35 No. 10, December 1998
Page 4 of 6
Evaluating Filtration Media - A Comparison of Polymeric Membranes and Nonwovens
Submitted to Filtration & Separation Journal, Volume 35 No. 10, December 1998
Page 5 of 6
Evaluating Filtration Media - A Comparison of Polymeric Membranes and Nonwovens
Submitted to Filtration & Separation Journal, Volume 35 No. 10, December 1998
Table I: Media Costs Per Gallon Waste Filtered
Actual Costs/Gallon Filtrate (cents/gal)*
Media Nominal
Rating (mm)
General Filtrate
Quality
60 ppm
ACFTD**
600 ppm
ACFTD**
2000 ppm
Lead-bearing
Waste Water
Microporous Membrane 0.45 Excellent 11 48 23
PTFE Membrane Laminate 0.5 Very Good 8.9 45 13
DuPont SoloFlo. 1 Very Good 0.5 1.3 0.3
DuPont style T-980 1 Very Good 0.8 2.1 0.5
Meltblown Polypropylene 1 Good 1.1 3.8 2.0
Meltblown Polypropylene 5 Poor 0.5 2.5 1.3
* Based on actual media costs, flux rates, and measured life cycles.
** AC Fine Test Dust (ACFTD) challenge testing.

Conclusion

To choose the appropriate filtration media for each application, purchase costs cannot be the sole determining
factor. Extensive research, testing and evaluation are required to make the proper selection. Based on the four
major criteria detailed in this article, Tyvek® SoloFlo™ from DuPont has been determined to be the most
economical for typical wastewater applications (based on cents/gallon filtered). Third-party challenge tests also
have confirmed that Tyvek® SoloFlo™ is quite efficient at low-micron ratings, approaching typical microporous
membranes in performance. In addition, Tyvek® SoloFlo™ compares favorably to PTFE membrane laminates at similar permeabilities and proves far superior to both spunbonded and meltblown media.
In recent years, innovations such as Tyvek® SoloFlo™ have expanded the role of nonwovens in filtration
applications. DuPont is continuing its research into alternative polymers for its flash-spinning process to provide
new alternatives to the filtration industry.