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Ntitornai OtlenseU De'ence air1!

CHEMICAL EFFECTS IN PARTICULATE FILTRATIONI. THE SIZE RANGE 0.1-0.3 pm [U)

.

bv

ýJR. Coleman

v* JA . .6.1988.

DEFNCERESEARCH ESTABLISHMENT OTTAWA'.

July 1987_______________________Ottawa

_88 1. 2 0 U48

I*National DibtenseDefence nationale

CHEMICAL EFFECTS IN PARTICULATE FILTRATIONI.THE SIZE RANGE 0.1 0.3 pm (U)

by

J.R. ColemanChemical Protection Section )Protective Sciences Division A so o

?ITIS GR&

Distribut lon/

Avlabilit y CodesAva I1-ýý/, r

DEFENCE RESEARCH ESTABLISHMENT OTTAWAU

TECHNICAL NOTE 87-16

PCN ~July 1987NI051LB13 --- - --. OttawaV.

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ABSTRACT

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_Aerosols were prepared from sixteen mnteria~s, ' iquit and solid.These were used, over the size range 0.01/1.30(T3 , to •hallenge a standardfilter paper. Penetration was nearly in ependent of the chemical nature ofthe aerosol in the size range 0.10-0.30(ý,. Below 0.10 o3, oenetrationvaried widely from challenge to challenge.

RESUME

Des a6rosols ont 6t6 pr6pares • partir de seize substances,liquides et solides, dans la plague de diamýtres de o,01 A 0,30 um, pour6preuver un papier-filtre standard. Le p~n6tration est oresqueind~pendante de la composition chimique des a~rosols dans cette plage. Endeq9 de 0,10 ýim, la p6n~tration varie beaucoup d'une 6preuve l l'autre.

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TABLE OF CONTENTS

Page

ABSTRACT/RESUME. ............ ....... . . . . . . . . . . . . . . ii

1.0 INTRODUCTION . ........... . . . . . . . . . . . . . 1

2.0 EXPERIMENTAL .. ...................................... . . . 2

2.1 Apparatus............ . .... a. 4. .... . . . 600 . 2

2.2 Challenge Materials .. ................... . . . . . 32.3 Filter Paper .. .......... .............. . .* . . 52.14 Procedure. ............ .............. * . * 6 * . 5

3.0 RESULTS AND DISCUSSION . . . . . . . . . . .. .. .. . .. 5

3.1 Modification of Filter Paper. .. ....... . .. . . 8

14.0 CONCLUSIONS .. ...... ........... . . . . . . . . . . . ... 10

5.0 BIBLIOGRAPHY .. ............................................ 12

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1.0 INTRODUCTION

Present-day theories of particulate filter action attributecapture to mechanisms of interception and impaction, and to settling undergravity at larger size, with diffusion (Brownian motion) becoming animportant factor in the submicron range. Additionally, electrostatic modesof capture operate when either the particle or the filter medium ischarged. For a given filter and air flow rate, only geometric factors(particle size and shape) are considered, it being assumed that thechemical nature of the medium or aerosol does not enter into account.

With instrumentation developed in recent years one can surveyaerosols from different materials t-1 test the correctness of thisassumption. The electrostatic fier (1) can select from aheterogeneous aerosol particles c., -oplets of narrow'y defined size, tochallenge the filter. Any suffic.iently involatile liquid or solid forwhich a compatible volatile solvent can be found, can be used as a sourceof aerosol. The resulting concentrations upstream and downstream cf thefilter can be measured by the condensation nucleus counter (CNC) (2).

In the present work sixteen substances were employed. The testmedium was a filter paper available in quantity, whose characteristics werefound to be uniform from sample to sample.

In summary, it was found that, between a particle/droplet size of0.10 and 0.30 •m, filter penetration was nearly independent of material, inaccordance with expectations. A plot of per cent penetration vs diameterresults lay for the most part in a narrow band with only a few outliers.However at sizes ý 0.05 pm penetration varied markedly on passing from onechallenge material to another. This phenomenon, and other observationsmade with small particle sizes are -he subject of a separate note.

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2.0 EXPERIMENTAL

2.1 Apparatus

The filter test system FTS 4001 has been described (3). Inaddition to the classifier-CNC combination for use in the submicron region,it incorporates a method, not used here, for generating aerosols in thesize range 0.5 - 10 pm.

Aerosol is generateu in one of several atomizers which aresupplied from stock bottles containing solutions of the involatilechallenge. The atomizer spray dries to leave a heterodisperse aerosol ofdroplets or particles. In the classifier a single narrowly defined size isselected on the basis of the electrical mobility of singly chargedparticles. The monodisperse aerosol after introduction of dilution airpasses to the test chamber containing the filter under examination, andthenue by separate upstream and downstream sampling paths to the CNC.

The system was originally designed to produce two standardchallenges - sodium chloride (NaCI) from water, and dioctyl phthalate (DOP)from isopropanol (IPA). Three aqueous solutions of NaCl (0.01, 0.1,1.0% w/v) were used with three atomizers, to match concentration to therequired particle size, in the ranges < 0.02 um, 0.02 to < 0.10 um, and0.10-0.31 !im. A computer program activates the correct atomizer. ExcessNaCl is returned from the atomizer to the stock bottle in a recirculatingsystem. With DOP in isopropanol, the solvent evaporated too rapidly in theatomizer, leading to excessive concentration of DOP in the stock; thereforesolutions were discarded after one passage through the atomizer. Twoconcentrations (0.05% w/v and 0.2% w/v) were employed, covering the sizedomain up to 0.05 um, and above this size. A second program is providedfor testing with DOP.

In the work described here the same arrangement is used, withthree solution concentrations and the original FTS program forwater-soluble materials; and for non-aqueous solvents the DOP rrogram, andtwo concentrations, the solutions again being discarded atter one passagethrough the atomizers. Some preliminary trial and error was necessary inarriving at suitable stock solution concentration, Earlier observations

A product of TSI Inc, St. Paul, Minnesota, USA

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have shown however that results, as judged by measured per cent penetrao

of a standard filter, were not very sensitive to concentrations, unless o.

these were grossly out of line. As per cent penetration is a ratio of twc

measurements en downstream and upstream aerosol, perturbing factors largely

cancel out.

In this work a radioactive tLtatrallzer (TSI 3077) is installed in

the line downstream from the classifier, to reduce measurement errors atsmall particle size, as described in earlier work (4).

2.2 Challenge Materials

These are listed below, grouped under their solvents used toprepare solutions for atomization. A few notes on chemical/physical

properties are added. The two (or three) numbers following each entry arethe concentrations in g/1000 ml of the stock solutions.

TABLE I

Material _ eiMaterial m.p. b.p. weightl Remarks

-- WATER --

NaCl(0.1, 1.0, 10.0) 801 - 58

Glycerol 290 92 polyalcoholDextrose 148-150 180 monosaccharideGlycine 232-6 75 amino acidUrea 133 60Sodium potassium tartrate -100 282 tetrahydrateCitric acid 153 210 monohydrate ZPolyethylene' glycol -400Triethylene glycol 150 liquid dialcohol(0.2, 2.0, 12.0)

Oxamide 2 417-419 88 diamide; highly insoluble(0.095, 0.142, 0.190)

Aldrich Chemical Co 20,239-8, PEG 400, average molecular weight OO.0(i.e. nine ethylene glycol units on average)

2 The extremely low solubility of this compound necessitated using

slightly undersaturated solutions. Saturation at 20 0 C is about .275g/1000 ml H20. Complete saturation was avoided, since evaporationmight lead to clogging of the atomizer nozzles.

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T'ABLE I (cornt'd)

Material JM.P. jb.p. Iw~eiglht JRemarks-ISOPROPANOL --

Dioctyl phthalate Ij358 jrmtcdiester(0.5, 2.0) 1 1

-ETHANOL --

Silicone oil3 of general form: CH,1(CH 3)2 S1O 2 1n Si(CH,)3

Oleic acid 16 285-6/ 282 long chain unsaturated(0.5, 2.0) 100 mm fatty acid

Phthalic anhydride 131 1148(0.5, 5.0)

-- ISOOCTANE -

Paraffin o414 comparable to light machine(0.5, 2.0) 1 J oil

TOLUENE -XYLENE (3:1 ) --

Anthracene 217 1 3~40 1 178 1polynuclear aromatic(0.5, 2.0) I

'Aldrich Chemical Co, 17,563-3 silicone oil, high temperature.

Fisher Scientific Co,' 0-119, paraffin oil, light, white, domestic.

This range of compounds was chosen so as to Include iiquid andsolid, organic and Inorganic, ionic and covalent, and polar and non-polarmaterials. Solvet.ts and their solutes had to be non-corrosive andIcompatible with components that they could encounter in the FTS 400. Whenchanging from one material to the next the system was purged with mutuallycompatible solvents to avoid precipitating materials that might blocknozzles or lines.

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2.3 Filter Paper

A high efficiency filter paper produced by Hollingsworth andVose, (East Walpole, Mass. U.S.A.), was used. The DREO designation for thepaper was HV4A.

2.4 Procedure

Sheets of HV4A were run in quadruplicate. The flow rate was 16LPM, which for the 44" diameter circular test area corresponds to the 32 LPMin certain standard tests used at DREO. Using the FTS or FTS DOP programas appropriate, penetration was measured at seven sizes between 0.01 and

0.30 um.

3.0 RESULTS AND DISCUSSION

Experimental results are collected in Table II, as percentpenetration with standard deviation. To facilitate comparison, from thesixteen materials eight were selected whose penetrations in the sizeinterval 0.10 to 0.30 pm were judged to lie in the mainstream or "normal"range. Their average penetrations and standard deviation are plotted inFigure 1. The remaining eight, deemed somewhat arbitrarily to be "high" or"low" are plotted individually. To avoid complicating the figure theselatter results are plotted only down to 0.05 ýim.

It is evident that above 0.1 Wm the assumption that filterbehaviour is not dependent on the chemical nature of the particle issupported. Three materials, DOP, silicone oil and oleic acid were placedin the high penetration category, but all penetration results were lessthan twice the average for- the normal materials, most of them considerablyless. These three might ireed plausibly have been included amn-r thenormal maF, -i;- F w rials werc .-- zed as having lowore of these (phthalic anhydrtde) rather dubiously so. DeviatiOc : hori,.gative are greater than those in the positive direction. Results for oneof these materials, oxamide, were considered questionable because of thelow concentrations of its stock solutions (Table I). However, per cent

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TABLE II

PER CENT PENETRATION OF HV4A PAPER BY VARIOUS MATERIALS

Diameter (un)Material

0.01 0.02 0.05 0.10 0.15 0.20 0.30

NaCl .0068 .00016 .0043 .030 .035 .029 .00751.0045 1.00007 1.0008 ±.003 ±.006 ±.004 ±.0006

Glycerol .0059 .00038 .0016 .012 .020 .029 .0231.0033 1.00017 t.0002 i.001 t.005 ±.003 ±.003

Dextrose .011 .0075 .012 .032 .035 .031 .010±.0006 ±.011 ±.002 ±.002 ±.006 ±.004 ±.002

Glycine .011 .0076 .011 .X25 .028 .026 .011i.001 t.001 ±.002 ±.002 ±.001 ±.003 ±.005

NaK .0097 .00074 .0043 .029 .033 .032 .012Tartrate t.0016 ±.00006 ±.0006 1.004 ±.004 ±.004 1.003

Citric Acid .010 .00091 .0061 .029 .033 .032 .010±.002 t.00022 ±.0014 1.004 ±.004 ±.002 1.0003

Phthalic .00094 .00010 .0018 .019 .024 .025 .012Anhydride 1.00054 ±.00065 ±.0002 ±.003 ±.003 ±.004 ±.001

Dioetyl .048 .010 .0029 .035 .045 .038 .0106Phthalate 1.015 ±.002 ±.0006 ±.002 1.004 ±.005 ±.0009

Oleic Acid .047 .00044 .0041 .025 .038 .043 .01331.018 ±.00013 ±.0004 1.003 ±.004 ±.003 ±.0003

PEG 400 .024 .0047 .013 .024 .1130 .023 .0087±.015 ±.0003 ±.002 ±.001 t.003 1.004 t.0003

Paraffin .045 .00027 .0016 .024 .0311 .0313 .015Oil t.010 ±.00013 :.0003 ±.002 ±.0002 t.0008 t.003

Anthracene .0014 .000036 .00047 .0067 .012 .012 .0048±.0008 ±.00002.4 ±.00019 ±.0010 :.001 ±.001 ±.0015

Silicone .051 .00029 .0026 .030 .045 .050 .018Oil t.009 t.00009 ±.0007 ±.003 t.004 t.006 ±.001

Urea .0018 .0022 .0068 .017 .029 .031 .011±.0004 ±.0012 ±.0010 t.001 t.002 t.004 t.002

Oxamide .057 .0014 • .0021 .01,1 .0113 .0066 .0039t.026 ±.0005 ±.0005 ±.0007 t.0009 ±.0006 ±.0026

Triethylene .0079 .000068 .00050 .0031 -.0052 .0082 .0131Glycol ±:.0022 t.000027 ±.00002 *.0003 t.0006 1.0004 ±.0009

.01

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.NORMAL HIGH LOW

.NCJ -0 QOP -0 GLYCEROLDEXTROSE 8 SILICONE OIL - -A ANTHRACENEGLYCINE --- 0 OLEIC ACiD - -P PHTHALIC ANHYDRIDE

.CITRIC ACID .... OX OXAMIDENAIC TARTRATE - T TRIETHYLENE GLYCOLPEG 400PARAFFINUREA

A)00010.1 0,2 0.3

DIAMETER (mm)

Figure 1 Penetration of HVJ4A paper by sixteen aerosol challenges. - - -

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penetration results on HV4A using NaCl solutions of the same concentrationlay again In the normal range, so that this appears to be an intrinsicproperty of oxamide.

DOP, silicone and oleic acid, the high penetrants are allliquids; ho'ever glycerol and triethylene glycol, also liquids, are in thelow category, while paraffin oil and PEG 400 are nornal. Consideringmaterials of closely related chemical nature, triethylene glycol (threeglycol units) is low, PEG 400 (with approximately nine glycol units) isnormal; urea, a diamide, is normal, cxamide, also a diamide, is low.Citric acid is normal, phthalic anhydride low. No distinction based onpresence or absence of polar, or ionizable groups is discernible. In shortthese relatively small differences in penetration are not relatable to anychemical property of the materials.

One factor not considered is particle shape. In the operation ofthe classifier it is assumed that spherical, singly charged aerosolparticles had been formed, whose motion in an electric field is governed byStokes law with corrections appropriate to the submicron size range.Particles result in fact from forced evaporation of small droplets producedin the atomizers, and their shape cannot be predicted. Deviation fromsphericity can have two effects a) a slight displacement in the sizeselected by the classifier b) particle shape could directly affectefficiency of capture in the filter. To clarify this point directexamination by electron microscopy is required. This has not yet beenpossible. Particle shape, if It is a factcr, is not the only one; there isconsiderable variation in penetration among liquid penetrants which are allspherical.

At small particle size the minimum in penetration near 0.02 pm isagain noted (4), urea being the only material that did not display it.Penetration-size relationships vary greatly in detail from one material toanother, and no correlation could be found between behaviour in this sizeregion, and the division into low, normal and high penetrants at largersizes. The point is illustrated in Figure 2, using data from Table II.The extreme broadening of the hatched area, representing the standarddeviation, at sizes less than 0.1 pm, in Figure 1, is another indication ofvariability of results even among substances that behave very similarly atlarger size.

3.1 Modification of Filter Paper

In the previous work the challenge was varied but the same HV4Apaper was used. In a few miscellaneous experiments the procedure wasreversed; the effect of chemical modification of the paper surface wasdetermined, using the same challenge.

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b / +

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I .0001X DO

+

0.1 0.2 0.34 DIAMETER (Mum)

~~ Figure 2 Detail of HVJ4A penetration, four cases showing extremes inbehaviour.

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HV4A paper was soaked in silicone oil dissolved in alcohol, orparaffin in isooctane (0.5 g/60 ml) and after drying tested for penetrationwith NaCI. Several obvious interferences oust be considered:

a) Physical blockage of the filter by the impregnant. At the dilutionsemployed, the volume fraction of silicone or paraffin deposited in thefilter paper should not be significant. The only information on thissubject comes from pressure drops measured during the testing. Theseare unchanged: 14.0 ± 0.7 mm HI O for the original HV4A, 14.4 ± 0.3for paraffin-treated and 13.9 t 0.5 for silicone-treated HV4A.

b) Swelling or shrinking of the filter-paper by the solvent (ethanol orisooctane) not reversed on subsequent drying. NaCi penetration testswere conducted on HV4A paper soaked in the solvents above and thendried. These gave results closely similar to those for NaClpenetration of the original HV4A (Table II, first entry). All theresults, including the check for solvent swelling, are listed inTable III. It cannot be claimed with certainty that all sources oferror (physical modification of filter paper) are eliminated fromconsideration by the checks described above; yet there is a strongindication that surface modification of the filter fibres bydeposition of a deposit has increased penetration by, in some cases, afactor of two or three.

4.0 CONCLUSIONS

1. Chemical effects play only a second-order role in the filteringof particles in the submicron range down to about 0.10 um.

2. Surface modification of the filter paper by soaking treatments invarious chemicals either had no effect or increased the NaCl penetration.

TADLEE III

PER CENT 'ENETRATION OF HV4A PAPER BY NaCi AS FUNCTION OF PRE-TREATMENT

I ~Diameter (uim)Treatment

0.01 0.02 0.05 0.10 0.4.5 0.20 0.30

None .0068 .00016 .OO03 .030 .035 1.029 .00T51.0045 ±.00007:' ±.00082 ±.0034 1.0061 1.0037 ±.0006

Isooctane .0098 .00019 .0037 .027 .031 .028 .0083Washed

Paraffin .00018 .00028 .0088 .055 .068 .069 .0215Treated ±.000089 ±.00017 ±.03 t 5 ±.014~ 1.01~4 ±0

EtOH .0070 .00017 .0050 .034 .038 .033 .013Washed

Silicone .00023 .00019 .0070 .042 .051 .0146 .017Treated t-00011 t.00006 t.0012 ±.005 ±.008 ±.005 t.002

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5.0 BIBLIOGRAPHY

1. B.Y.H. Liu and D.Y.H. Pui, J. Colloid. Interfac Si. 147' 155 (19714).

2. J.K. Agarwal and G.J. Semr, J. Aerosol Sot. 11 3413 (1979).

3. J.R. Coleman, Observations on the Use of the FTS 4100 (U), DREOTechnical Note in preparation.

14. J.R. Coleman, Observations on Electrostatic Effects in a Filter TestSystem, DREO Technical Note In preparation.

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CHEMICAL EFFECTS IN PARTICULATE FILTRATION. I: THE SIZE RANGE 0.1 - 0.3 um (U)

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Aerosols were prepared from sixteen materials, liquid and solid. These

were used, over the size range 0.01-0.31 um, to challenge a standard filter -.-

paper. Penetration was nearly independent of the chemical nature of the aerosol

in the size range 0.10-0.30 vm. Below 0.10 pm, penetration varied widely from

challenge to challenge.

'-S

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FITTER TEST SYSTEMAEROSOLSFIBROUS FILTERSPENETRATIONSIZE EFFECTS p.

SODIUM CHLORIDEDIOCTYL PHTHALATEORGANIC COMPOUNDSINORGANIC COMPOUNDS

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