Pro-static Agents in Jet Fuels · PRO-STATIC AGENTS IN .YET FUELS , INTRODUCTION Over the past 15 years, there have been at least 116 reported fires or explosions attributed to static

U.S. DEPARTMENTY Of COMMERCNOt"a Technca Iftmu Senic

Best Available CopyAD-A029 382

Pro-static Agentsin Jet Fuels

Naval Research Lab.

August 16 1976

Q4Y&8

A 254101

NRL Report 3021

Pro-static Agents in Jet Fuels

J. T. LiEONAJD AND H. F. BOGAWDUS

Chemical Dynamics BranchChemistr Niison

-€: i6

* August 16, 1976

.!7 f V

ktPROOUCED By I

NATIONAL TECHNICAL, INFORMATION SERVICE

I U S. DIPAITMENT 0F CO M P*'." l 5PIMF!LD. YA, 221Wd

NAVAL RESARCH LABORATORY,MmW . D.C.

Approvej tor pub rMeme: &Nrk.rth;4m ukwmied.

-- .lol .

SECURITY CLASSIFICATION OF THIS PAGE (UWhln Dae Enilered)

REPORT DOCUMENTATION PAGE READ INSTRUCTIONSR NBEFORE COMPLETING FORM

I. REPORT NUMBER 2. GOVT ACCESSION NO 3. RECIPIENT*S CATALOG NUMNER

NRL Report 80214. TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED

Final report on one phase of aPRO-STATIC AGENTS IN JET FUELS ontinuing NRL Problem.

S. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(*) S. CONTRACT OR GRANT NUErP,(e)

J. T. Leonard and H. F. Bogrdur

S. PERFORMING ORGANIZATION NAME AND ADDRESS 10. ROGRAM ELEMENT. PROJECT. TASKAREA a WORK UNIT NUMBERS

Naval Research LaboratoryWashington, D.C. 20375 C05-19A

I t. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATEAmerican Petroleum Institute August 16, 19761801 K Street, NW. 1i. NUMBER OF PAGESWashington, D.C. 20006 37

14. MONITORING AGENCY NAME & AOORESS(I1 dliffrent b Cmntoilind Office) IS. SECURITY CLASS. (of thls toport)

Unclassified

IS&. DECL ASSIFI CATION/DOWNGRADINGSCHEDULE

IS. OISTRIBUTION STATEMENT (of tis Depott)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abstract enteod in Block 20, it different 1e Repld)

IS. SUPPLEMENTARY NOTES

19. KEY WOROS (Conthnu on ,eemrse ele If neceoensy .nd Identify by block nimmber)

Static electricityCharge generationJet fuelsElectrical conductivity

20. ABSTRACT (Contlnue m revers el d If neceeery and Identify by block niumber)

The effects of a wide variety of polar compounds and fuel additives on both the electricalconductivity and electrostatic charging tendency of both silica gel treated n-heptane and Jet A fuelshave been examined. Conductivity was determined by ASTM D3114 and charging tendency bymeasuring the current developed as the hydrocarbon liquid passed through an electrically Isolatedfilter holder containing a paper, fiberglass or teflon screen filter.

(Continued)

DD Fo AN 7 1473 EDITION OF I NOV S is OBSOLETES/N, 01o2-oI4- 5601 ISECURITY CLASSIFICATION OF THIS PAGE (ten Dete beefto

20. (Continuea)

Of all the compounds and additives tested, water carne closest to fulfilling the definilion of anIdeal pro-static agent, viz, a compound that greatly increaser t e charging tendency of a fuel withoutuwreasing its conductivity. After saturation with water, the charge density of clay-treated Jet A fueltltcreased by a factor of 2 # and that of an untreated let A by a factor of 7. The conductivities ofboth fuels remained essentially the same. Since water did not increase the charging tendency orconductivity of silica gel-trea~ed n-heptane it was concluded that it is not water per _-e, but rather itsintera.tion with some constituent in the jet fuel that is responsible for its pro-static effect.

Ii _________

p -

CONTENTS

INTRODUMCI ION .................................... 1

EXPERIMENTAL PROCEDURE ........................ 1

Screening of Potential Pro-Static Agents in n-Heptane ..... 1Evaluation of Pro-Static Agonts in Clay-Treated and

Untreated Jet A Fuels ......................... 2

RESULTS AND DISCUSSION ........................... 4

Screening of Potential Pro-Static Agents in nr-ieptane ..... 4Selection of Potential Pro-Static Agents ............... 10Evaluation of Potential Pro-Static Agents in Clay-Treated

Jet A Fuels ................................. 11Evaluation of Pro-Static Agents in Untreated Jet A Fuels . . 15

EFFECT OF MOISTURE .............................. 24

SUMMARY AND CONCLUSIONS ....................... 27

ACKNOW LEDGMENTS ............................... 28

R EFER EN CES ...................................... 29

APPENDIX A - Compounds and Additives Selectedfor Screening ........................... 30

lit

PRO-STATIC AGENTS IN .YET FUELS ,

INTRODUCTION

Over the past 15 years, there have been at least 116 reported fires or explosionsattributed to static electricity generated by fuel while loading tank tracks and refuelers.and 3 incidents while fueling commercial jet aircraft [1]. In most of these cases, thefueling operations were being carried out in the same fashion as they has been in the pastwhen there was not an incident. In a number of instances, a second static-induced igni-tion occurred within a day or so following the first. In an attempt to account for theseunusual occurrences, it has been postulated that, at the time of the explosion, the fuelwas unusually electrostatically active, or "hot," as a result of contamination by traceamounts of pro-static agents. However, attempts to identify such agents in the fuelsamples acquired from a number of these explosions were not successful. Therefore, thepresent study was initiated to determine if, by screening a wide variety of polar and ioniccompounds and fuel additives, it would be possible to identify the types of compoundsresponsible for unusually high electrostatic activity in hydrocarbon fuels.

EXPERIMENTAL PROCEDURE

Screening Of Potential Pro-static Agents in n-Heptane

In the first phase of this study, 39 compounds and 24 fuel additives were screenedfor possible pro-static activity by measuring the effect of these materials on both theelectrical conductivity and charging tendency of silica-ge!,-treated n-heptane. The com-pounds and additives selected for screening are identified in Appendix A. Most of theadditives are approved for use in turbine fuels [21, although not all are listed in the cur-rent Qualified Products List [3). Electrical conductivity was measured by the AmericanSociety for Testing and Materials (ASTM) method [41 and charging tendency by theExxon Mini-Static Test procedure [5].

The apparatus used for the Mini-Static Test is shown in Fig. 1. In this test, thecurrent is measured as a 50 cm 3 sample of fuel is passed at a constant flow rate throughan electrically isolated filter holder containing a 1.3-cm (1/2-h.) diameter filter. Thefilter current is multiplied by the flow velocity to exprc s the charging tendency of thefuel in terms of charge density in microcoulombs per cubic meter. Both the ASTM con-ductivity method and the Mini-Static procedure were used to evaluate samples taken in arecent survey of jet fuels at 10 airports and 3 military bases in the United States [6].Consequently, the results of the present study can be directly related to actual fieldexperience. Prior to use, the n-heptane (Phillips Pure Grade, 99 mol %) was passed througha column containing Drierite and silica gel to remove moisture and polar contaminantsthat might interfere with the compound or additive being screened. This treatment

Manuscript submitted June 1, 1976.

-7

LEONARD AND BOGARDUS

---- SYRINGE DRIVE

SCLAMP

SAMPLE-SYRINGE (Poly.thylmne, SO ml)

, 5 -- FARAOAY CAGE

TO RECOROER

VALVE .. .

FILTER "OLDER . _

RECEIVER

TEFLON PAD 'j-I

ELECTROMETER

Fig. I - Exxon Mini-Static Tester

lowered the electrical conductivity from about 5 to 0.05 pS/m and the charging tendencyfrom about 80 to 2 pC/rm3 depending on the batch of n-heptane'.

The polar compounds were tested at concentrationis of 100 and 1000 ppm (wt/vol),or at saturation, if the solubility was limited. The fuel additives were also tested at 1000ppm, except for the static dissipator additives and the sodium sulfonates, which, becauseof their exceptional activity, had to be evaluated at 1 ppm.

Evaluation of Pro-static Agents in Clay-Treated and Untreated Jet A Fuels

In the second phase, the 20 most active compounds from the screening study wereselected for further testing in clay-treated Jet A turbine fuel. The available inspectiondata on this fuel are given in Table 1.

2

NRL REPORT 8021

Table I - Inspection Data On Jet A Fuels

Type of Jet A FuelProperty

Clay-Treated Jet A Untreated Jet A

Composition:Sulfur, mercaptan (ppm) < 1 1Sulfur, total (wt-%) 0.03 0.04

Volatility:Distillation:

Initial boiling point (C (F)) 169 (336) 166 (330)10% reclamation (C (F)) 169 (336) 185 (365)50% reclamation (C (F)) 208 (407) 212 (414)90% reclamation (C (F)) 249 (480) 238 (460)Final boiling point (C (F)) 289 (552) 282 (539)

Flash point (C (F)) 54(130) 49(120)

Fluidity: freezing point (C (F)) -41.4 (-42.5) (-40.8) -41.6

Corrosion: copper strip* 1A 1A

Conductivity:At refinery (pS/m) 0.38 0.32At start of tests (pS/m) 0.10 0.16

*2 hr at 100*C (212F).

In addition to the single paper filter used in the screening tests, charging tendency inthis phase was evaluated on four other paper filters and on a Teflon® screen, all of whichwere cut from production model separator elements, and on a Fiberglas® and a paperfilter from a coalescer element. The types of filter elements used, the manufacturers, anddescriptions are as listed below.

Type of Filter Manufacturer Description of Filter Medium

CC-15-1 Fram* Pleated Fiberglas® paper (2 layers)tPleated papertBonded Fiberglas®tWhite polyestertWhite sock t

CS-58-10 Fram* Pleated paper, high charging, obsoleteCS-61 F Pleated paper, ASA 3 ratedCS-64 Unpleated paperA-3061 Keene* Pleated paper plus

Teflon) screen


Type of Filter Manufacturer Description of Filter Medium

S0616 PLF Velcon I Pleated paper plusunpleated paper

Type CC-15-1 is the coalescer element; the others are separator elements.

Fram Corp., Industrial Divisions, Tulsa, Okla."Only the bonded Fibergas and the pleated paper were used in the present study of this coaleserelement.

*Keene Corp., LA Grange, Ga.1Velcon Filters Inc., San Jose, Calif.

The elements shown in Fig. 2, are representative of the types employed to filter jetfuels when loading tank trucks and refuelers and during aircraft servicing. In this type offiltration, which is illustrated in Fig. 3, the fuel passes through two sets of elements; inthe first set, called the coalescer elements, particulate matter is removed and undissolvedwater droplets are coalesced; in the second set, the separator elements, coalesced dropletsare separated from the fuel. Because the shorter relaxation volume downstream of theseparator elements (4 vs 13 s for the coalescer), it is believed that the separator stage isthe primary electrostatic charge generator in fuel handling.

Fuel samples were stored in epoxy-lined cans at least 2 days before testing. Chargingtendency measurements were made immediately after the fuel conductivity tests.

In the third phase of this study, untreated Jet A Fuel was substituted for the clay-treated fuel in phase 2, and the entire test sequence was repeated. The inspection dataon this fuel are given in Table 1. Because of the interest generated by the behavior ofthe sodium sulfonates, an additional five compounds were included in this phase of test-ing.

RESULTS AND DISCUSSION

Screening of Potential Pro-static Agents in n-Heptane

The effects of various polar compounds (acids, alcohols, aldehydes, amines, esters,and ketones) on the electrical conductivity and charging tendency of silica-gel-treatedn-heptane are shown on Fig. 4 and 5. For each type of functional group represented inthis series, a low and a high molecular weight compound and an aromatic analog areincluded. The results show that for the acid and the amine, increasing the length of thealiphatic chain from 2 to 10 carbon atoms definitely increases the effect that the mole-cule has on the electrical conductivity of n-heptane. However, the reverse is true for thealcohol, aldehyde, and ester derivatives. Also, the aromatic analogs of the acid, alcohol,aldehyde, amine, ester, and ketone have very little effect on electrical conductivity. Theresults demonstrate that, contrary to widespread opinion, trace amounts of many polarcompounds have little effect on the electrical conductivity of hydrocarbon liquids. Evenat a concentration of 1000 ppm, the most active compound tested (decylamine) did not

4

Platte ftF4 v-v -~fAsts.u at. pas lgpst e

aA' d.,\, 'K

- *A. L

Lm~v


n , lMptofle Filter Type t0

f1 n-Heptone * Additive Additive Cone. fOO ppm

ACETIC ACID

DECANOIC ACID

. ENZOIC ACID

/ 7'-'-ETHYL ALCOHOL

DECYL ALCOHOL

AC TALOE4YOE

% LAUMALDE HYDE1- EZALCHYoDE

NEYLALOINE

OI.T.YLAMINE

TIETHYL AMINE

DECYLAMINE

ANILINE

ETHYL ACETATE

METHYL UNDECONATE

METHYL SENZOATE

ACETONE

ACETOPHENONE

0000 0.01 0.10 1.0 to

CONDUCTIVITY (pS/rn)

Fig. 4 - Effect of polar compounds on electrical conductivity of silica-gel-treated n-heptane

raise the conductivity of silica gel-treated n-heptane to the lowest level (0.09 pS/m) foundin a recent survey of jet fuels [6].

The effect of the same polar compounds on the charging tendency of n-heptane isshown in Fig. 5. Just as with conductivity, most of these compounds had little effect onthe charging tendency of n-heptane at a concentration of 1000 ppm. Some; e.g., aceticacid, decyl alcohol, and acetone, actually lowered it.

A number of higher molecular weight polyfunctional compounds were also tested(Fig. 6 and 7). Because of their limited solubility, these compounds were tested assaturated solutions. As indicated in the figures, none of these compounds has an appreci-able effect on either electrical conductivity or changing tendency.

Ferrocene was tested because it is a fuel additive (though not for turbine fuels) andbecause iron compounds were identified in the fuel recovered from we least one electro-static incident. However, ferrocene was found to be inactive.

NRL REPORT 8021

.-. n-Hptane Filter Type 10

-n-Heptoali Additive Additive Co¢ 1000ppm

ACETIC ACD

OECANOIC ACID

BENZOIC ACID

ETHYL ALCOHOL

DECYL ALCOHOL

PHENOL

ACE TALDEHYDE

LAURALDEHYDE

OENZALOEHYOE

E rHYLAMINE

DIETHYLAMINE

TftIFTHYL AMINE

DEC YLAINE

ANILINE

ETHYL ACETATE

METHYL UNDECONATE

METHYL BENZOATE

ACETONE

ACETOPHE NONI-

1O .00 1000 10,000

CHARGE DENSITY (juC/ms)

Fig. 5- Effect otpolar compounds on charging tendency of silica-gel-treated n-heptane

Naphthenic acid is neither a fuel additive nor a pure compound. It' does increase bothfuel conductivity and charging tendency, but it is not certain whether the increase resultsfrom the acid or from the impurities.

The effects of the antioxidants and the metal deactivator additives are shown in Fig.8 and 9. Antioxidants Nos. 22 and 23 are higher molecular weight substituted aminesand, in agreement with the data in Figs. 4 and 5, these compounds do increase conduc-tivity and charging tendency. The other two antioxidants, Nos. 30 and 31, are substitutedphenols, and, as does the parent compound shown in Fig. 4 and 5, these additives hadlittle or no effect on conductivity or charging tendency. The metal deactivator, anothersubstituted amine, only slightly increased conductivity and charging tendency.

All of the corrosion inhibitors and the thermal stability additive increased both theconductivity and charging tendency of n-heptane, as shown in Figs. 10 and 11. Three ofthe corrosion inhibitors increased the conductivity of the n-heptane above 10 pS/rn: Gulf178. 17.2 pS/in; Hitec E 515, 48.5 pS/in; and Na-Sul.LP, 393 pS/m. Gulf 178 alsoproduced the highest cliarging tendency (8546 pC/rn3 ) of any of the corrocion inhibitors.

7


ft - Heplne Iroller Type 10

' - Hepfgne + Add,' ve Additsve Cone : 1000ppm or 5efgrteo d(. -Setvroted)

ALi7ARIN

CARM YIC AC;ID*

FERRQIC OENZOYLACETONLTE

FLU0RESCriN

ROSANILINE HY'DROCHLORIDE

PHENrCL P NTHALEIN

MISCELLANEOUS COMPOUNDS

- - ~NAPHTHENIC ACDO-l -i

0001 001 0 I0 0

CONDUCTIVITY (pS/m)

Fig. 6 - Effect of higher molecular weight polar and miscellaneous compounds on electrical conductivityof silica-gel-treated n-heptane

The response of the anti-icing additive was just the opposite of what was being sought ina pro-static agent-it increased conductivity but had very little effect on chargingtendency.

The static dissipator additives were compared at a concentration that is considerablylower than the recommended dosage for two of the additives, Stadis 125 and Ethyl DCA48, but close to the range for the other two additives, Statis 450 and ASA-3. (SeeAppendix A). The effects that these additives had on the conductivity of n-heptane at aconcentration of 1 ppm (Fig. 12) are in keeping with the recommended dosages; e.g.,ASA-3, which has a recommended dosage of 0.6 ppm, had the greatest effect, whereasDCA 48, with a recommended dosage of 7 ppm, had the least effect. As with the anti-icing additive, DCA 48 and Stadis 125 had little or no effect on charging tendency. Con-trarily, Stadis 450 and ASA-3 had a considerable effect.

Because some of the corrosion inhibitors and the static dissipator additive that hadthe greatest effect on the charging tendenry of n-heptane (ASA-3) contain salts of varioussulfonic acid derivatives, these types of compounds were examined further.

8

rm- .-. .

NRL REPORT 8021

n n-Hept@ne Filter Type 10

C:) n-Hoplans * Additive Addltlvc Conc 1000 ppm or saturated Ie Setaewd)

AL IZARIN*

CARMINIC ACID'

FERRIC SENZOYLACETONATE

FLUORESCEIN*

ROSANILINE HYDROCHLORIOE

1IIrENOLPHTHALEIN.

MISCELLANEOUS COMPOUNDS

FERROCENE

~~NAPTNENIC ACID

10 100 000 10,00

CHARGE DENSITY (pC/m)

Fig. 7 - Effect of higher molecular weight polar and miscellaneous compounds on charging tendencyof silica-gel-treated n-heptane

The results obtained with the sodium dialkyl sulfonsuccinates are shown in Figs. 13and 14. With the exception of the di-n-dodecyl compound, all of the higher molecularweight derivatives have about the same effect on the conductivity of n-heptane, but onecompound, the diamyl derivative, was particldarly effective in increasing the chargingtendency of n-heptane. On the other hand, the inactivity of the lower molecular weightderivatives (diethyl and di-isopropyl) is difficult to explain, in view of the greater mobilityof the lower molecular weight compounds.

Although the petroleum-derived sodium sulfonates have about the same molecularweight as the higher molecular weight dialkyl sulfosuccinates, they differ in structure inthat the petroleum derivatives are basically aromatic rather than aliphatic compounds.Two of the petroleum derivatives, Petrosul 750 and Bryton 445, were particularly effec-tive in increasing conductivity, but none of the three increased the charging tendencysignificantly.

9


n - Hoptone rilter Type 10

C3 i-Heptane + Addtlv Addtive Conc.. 1000 ppm or seturoled (* saturoted)

ANTIOXIDANTS

J*22

#31

METAL DEACTIVATOR'

CONDUCTIVITY (pS/m)

Fig. 8- Effect ofantioxidants and metal deactivator on electrical conductivity of silica-gel-treated n-heptare

Selection of Potential Pro-static Agents

All of the compounds that, at a concentration of 1000 ppm, increased the chargingtendency of silica-gel-treated n-heptane above 100 yC/m 3 were selected for evaluation aspotential pro-static agents in Jet A fuel. In addition, the static dissipator additives andthe more active sodium sulfonates were also included, although some of these materialsfor example, (ASA-3 and Stadis 450) also produce rather dramatic increases in conduc-tivity at a concentration of 1 ppm or less. It is recognized that if the conductivity of ahydrocarbon liquid exceeds 50 pS/m, the charge dissipates almost as quickly as it isgenerated. Consequently, compounds that increase conductivity above 50 pS/m are notpro-static agents in the sense implied here. Nevertheless, a number of compounds andadditives that increased the conductivity of silica-gel-treated n-heptane above 50 pS/mwere included in the tests with Jet A fuels because these compounds also have thegreatest impact on the charging tendency.

10

NRL REPORT 8021

n - Hiptone ropler Type 10

n - HOapOIIe * Addielve Addihve Con¢ 1000 opm or eofursted I. -SOturoted)

ANTIOXIDANTS

A0. - . 23

METAL OEACTIVATOR

. . . . . . I . . . . . I . . . .

0 00 1000 10,000

CHARGE DENSITY (pC/m)

Fig. 9 - Effect of antioxidants and metal deactivator on charging tendency of silica-gel-treated n-heptane

Evaluation of Potential Pro-static Agents in Clay-Treated Jet A Fuels

The effects of the potential pro-static agents on the electrical conductivity andcharging tendency of clay-treated Jet A fuels are given in Tables 2 to 4. To evaluate thedata, requires some idea of what constitutes high charging. In a recent survey of Jet Afuels from 10 airports in the United States, it was found that only one sample in 338 hada charge density above 4000 pC/m3 when tested on Type 10 paper. It would seem thenthat 4000 pC/m3 is a reasonable value for a threshold of high charging. However, asindicated, if the conductivity of the fuel is greater than 50 pS/m, the charge dissipatesalmost as quickly as it is generated. As the conductivity decreases below 50 pS/m, theprobability that charges will accumulate increases, reaching a maximum in the range of 1to 10 pS/m, depending upon the system. In view of these considerations, the followingcriteria were used to evaluate pro-static effects in this work:

1. The charge density must exceed 4000 pC/m3 when measured on Type 10 paper.

2. The conductivity must be less than 50 pS/m.

11


S- Mepiane Filter Type 10

J'--M opfene * Additive Additive Con, 1000 pPm

CORROSION INHIBITORSUNiCOrn J

COPIOCO T- 60

LU$RIZOL 541

TOLAD 245

OCI 4A] PRO ig., NALCO 5400

TOLAD 244

, MALCO 5402

GULF 170 "Y2

HITEC E515 464S

/ NASUL LP33

ANTI -ICING ADDITIVE

/,PFA ",M

THERMAL STABILITY ADDITIVE

JFA--I

0001 0.01 0.10 1.0 10

CONDUCTIVITY (pS/m)

Fig. 10 - Effect of corrosion inhibitors, anti-icing, and thermal-stability additives on electrical conductivityof silica-gel-treated n-heptane

Applying these criteria to the data in Table 2 shows that pro-static effects were exlhibitedby three additives at a concentration of 100 ppm: Hitec E 515, Antioxidant No. 23, andGulf 178. None of the other additives had a significant effect on either conductivity orcharging tendency of clay-treated Jet A fuel at this concentration except Na-Sul-LP, whichincreased the conductivity to 52 pS/m without having a significant effect on the chargingtendency. Nalco 5402 actually decreased the charge density while increasing the conduc-tivity by a factor of 12. The charge densities measured with the other separator papersare all considerably lower than the values obtained with the Type 10 paper. The highestvalue, 4450 pC/m3 , was obtained with Gulf 178 on CS 61F paper. This was less than athird of the corresponding value obtained with the same additive on Type 10 paper. Gulf178 also exhibited high charging on both the paper and Fiberglas ® media of the coalescerelement.

When the same additives were evaluated at a concentration of 1000 ppm (Table 3),pro-static effects were exhibited by an additional three additives: JFA-5, Nalco 5400,and AFA-1. Both Gulf 178,and Antioxidant No. 23 showed high charging on the Velcon

12

NRL REPORT 8021

0, . Hoptene Fillr Type 10

n -Hplane 4 Additive Addstlve Cone 1000 ppm

CORROSION INHIBITORS

..." !': U"Icolt i,ii~ 7-4c,0

LUBRIZOL 541

TOLAD 245

ANTI-ICING A2DITIVE

THERMAL STABILITY ADDITIVE

A FA - II

0 to o000 10,000

CHARGE DENSITY (pC/ms )

Fig. 11 - Effect of corrosion inhibitors, anti-icing, and thermal-stability additives on charging tendency ofsilica-gel-treated n-heptane

papers, as well as on the coalescer paper and Fiberglas® media. However, the conductivi-ties achieved with both of the additives at this concentration (Gulf 178 conductivity is54.8 pS/m and AKtioxidant No. 23 conductivity is 103 pS/m) were above 50 pS/m, andhence, the high charging with either sample cannot be considered a true pro-static effect.High charging on filter media other than Type 10 was experienced with only one otheradditive (Na-Sul-LP on Fiberglas® ), but again the conductivity was sufficiently high (414pS/m) that this cannot be considered a prostatic effect either.

As shown by the data in Tables 2 and 3, charge densities obtained with the otherfilter media are considerably lower than the values obtained with the Type 10 paper.The data obtained with the two other types of Fram paper, CS-61F and CS-64, aregenerally quite similar and consistently higher than the values obtained with the other-filter media (except Type 10). The Teflon ® screen has the lowest available surface areaof all of the filter media tested and, consequently, the lowest charge densities were ob-tained when this filter was used. Charging on FiberglasO was less consistent: Usually ifthe conductivity was high (for example, with Na-Sul-LP and Gulf 178) the charge density

13


M R Neptene filter Type Ir n-Meptone + Additive Additive Conc. I ppo

STATIC DISSIPATOR ADDITIVES

- 0'A 48

/STACIS 125

* / STADIS 450 u

'7' / ASA 3 0

-~.. .. I ... • i -. I i I i• *1 I II*• .

001 0.01 0.10 1.0 IO

CON DUCTIVITY pS/m)

OCA 43

STACIS 125

'4' STADIS 450

K.,.,ASA-3

10 200 1000o 10,000

CHARGE DENSITY (uC/mll)

Fig. 12 - Effect of static-dissipator additives on electrical conductivity and charging tendency ofsilica-gel-treated n-heptane

was higher on Fiberglas® than on Type 10 paper. Otherwise the charging on Fiberglas®

was generally lower on Fiberglas® than on Type 10 paper.

The maximum allowable concentrations for the additives listed in Tables 2 and 3 areless than 50 ppm (16.8 lb/1000 bbls). (See Appendix A). The data indicate that noneof these additives would exhibit pro-static effects at this concentration. However, if afuel were overdosed with certain of these additives, particularly Gulf 178 or AntioxidantNo. 23, then pro-static effects would be expected.

The effects of the static dissipator additives are compared in Table 4. At 1 ppm,Stadis 125 slightly increases the charging tendency (on Type 10 paper), whereas DCA 48actually decreases the charging tendency of clay-treated Jet A fuel by about 50%. Noneof the static dissipator additives exhibited high charging on any of the other filter mediaexcept for Stadis 125 and 450 on Fiberglas® and Stadis 125 on the coalescer paper. Inthe case of Stadis 125, this was definitely a pro-static effect on Fiberglas® at a concentra-tion of 1 ppm. The values obtained for this additive at 5 ppm (4730 pC/ms on TypeCC-15 paper and 9300 pC/Im3 on Fiberglas ® are the highest values obtained on any filter

14

NRL REPORT 8021

C - Neptune riIter Type 10

n- Heptune Additfve Additive Conc. Ippm

K . .SODIUM DIALKYL SULFOSUCCINATF.S

DIE THYLf _IISOPROP

DIAMYL

Q -2 ETNYLHEXYL

_______ Ojn- OLTsL

- DECYL

f O,-n-OODECYL

OTHER AEROSOL SURFACTANTS

- jJA 196

PETROLEUM -DERIVED SODIUM SULFONATES

'/L //. " TROSUL 742

, ,:... ' : ;QYTON -.;

0001 001 010 10 o

CONDUCTIVITY (pS/m)

Fig. 13 - Effect of sodium sulfonates on electrical conductivity of silica-gel-treated n-heptane

media except Type 10 paper with a sample conductivity less than 50 pS/m. As shown inTables 2 and 3, there were only four other cases in which Fiberglas0 gave higher charg-ing than Type 10 paper with clay-treated Jet A fuels, namely, Na-SuI-LP and Gulf 178at 100 and 1000 ppm.

The data for the sodium sulfonates are also given in Table 4. As expected, thecharge densities and conductivities obtained with these additives are somewhat higherthan were obtained at 1 ppm in silica-gel-treated n-heptane (Figs. 13 and 14). The onl,pro-static effect attained in clay-treated Jet A fuel with the sodium sulfonates on any ofthe filter media was with Aerosol OT on Fiberglas 0 . High charging was also found at aconcentration of 1.6 ppm fo-, Bryton 430 and Petrosul 742 on Fiberglas 0 , but onceagain, the conductivity was too high for this to be a pro-static effect.

Evaluation of Pro-static Agents in Untreated Jet A Fuels

The results obtained when the same additives were tested in untreated Jet A fuel aregiven in Tables 5 and 6. Although the conductivity and charging tendency of the neat

15


n - "*plane Filter Type 10

0- n Heptn: + Additlv¢ Additive Cen.: I ppm

SODIUM DIALKYL SULFOSUCCINATESDIETHYL

jJOIISOPROPYL

DIAMYL

01 D -2- ETHYLNEXYL

01-o-OCTYL

L/ 0-e-OECYL

0,-n-DOOECYL

OTHER AEROSOL SURFACTANTS

7 Os

PETROLEUM - DERIVED SODIUM SULFONATES

I tO 100 00 0000

CHARE DENSITY (pC/aml )

Fg. 14 - Effect of sodium sulfonates on charging tendency of silica-gel-treated n-heptane

untreated Jet A fuel was slightly higher than the neat clay-treated fuel (compare Tables 2and 5), the untreated Jet A fuel was less responsive to most of the additives than was theclay-treated fuel; i.e., except for Nalco 5402 and JFA-5, both'the conductivity and charg-ing tendency in the untreated Jet A were lower than in clay-treated fuel (see Figs. 15 and16). However, pro-static effects were obtained at 100 ppm for the same two additives(Gulf 178 and Antioxidant No. 23) in untreated Jet A fuel (Table 5) and with the clay-treated fuel (Table 2). Only one instance of high charging was found on any of the otherfilter media besides Type 10, namely, for Gulf 178 on Fiberglas® . In all other cases, thecharge densities were remarkably low. As with the clay-treated fuel, the charge densitiesobtained with the CS-61F and CS-64 papers were consistently higher than with the otherpapers (except Type 10). Also, the Teflon ® screen consistently gave the lowest chargedensities of all the filter media.

The data obtained with the static dissipator additives and the sodium sulfonates inuntreated Jet A fuel are given in Table 6. Stadis 125 decreased the charge density onType 10 paper by about 50% at a concentration of 1 ppm, whereas DCA 48 only slightlydecreased the charging tendency at the same concentration. Both Stadis 450 and ASA-3increased the charging tendency of the untreated Jet A fuel to a greater extent than the

16

NRL REPORT 8021

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NRL R1EPORT 8021

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23


clay-treated fuel, but both additives were less effective conductivity improvers in theuntreated Je. A fuel. These variations in response to specific additives highlight the roleof trace contaminants in jet fuels that react synergistically with certain additives and notat with others.

Aerosol AY and Aerosol OT had about the same effect on both the conductivityand charging tendency of the untreated Jet A fuel as on the clay-treated fuel, althoughthe high charging with the Fiberglas ® filter that was found with the clay-treated Jet Afuel (Table 4) was not found with the untreated fuel. What is perhaps more interestingabout these two sulfonates is that the mere removal of six CH 2 groups (three from eachoctyl substituent of Aerosol OT) to produce the diamyl derivative (Aerosol AY) causesthe charging tendency on Type 10 paper to double in jet fuel (Table 4 and 6) and qua-druple in n-heptane (Fig. 14). Yet, removal of six more CH2 groups to produce thediethyl derivative (Fig. 14) does not increase, but rather lowers, the charging tendency.The results underscore the sensitivity of the charging mechanism to the molecular struc-ture of the charge-promoting species in the fuel. For example, introducing a substitutedbenzene ring, as in Sul-fon-ate AA 10 (sodium dodecylbenzenesulfonate) markedlyincreases the effect of the sulfonate on both the conductivity and charging tendency.(Note that Sul-fon-ate AA 10 and Aerosol AY have practically the same molecular weight.Sul-fon-ate AA 10 has a molecular weight of 348; Aerosol AY has a molecular weight of360. However, Aerosol AY is strictly an aliphatic compound.)

Three of the petroleum-derived sulfonates, Acto 630, Petrosul 742, and PurifiedSulfonate L, exhibited pro-static effects at a concentration of 1 ppm. Obviously, theother two, Bryton 430 and Petrosul 745 would show pro-static effects at a slightly lowerconcentration. Bryton 430, Petrosul 742, and Petrosul 745 also showed high charging onmost of the other filter media. This is particularly evident in the data obtained at thehigher concentration (1.6 ppm, see Table 6). It is also apparent from these data, asshown in Fig. 17, that charging tendency of the Petrosul compounds decreases withincreasing molecular weight.

EFFECT OF MOISTURE

All of the fuel conductivity and charging tendency measurements were made underambient conditions of 22.20 C (72"F) and 47% ± 11% relative humidity (RH). However,it is recognized that moisture can effect both properties. In a recent survey conductedby the Coordinating Research Council [6], fuel conductivity and charging tendencymeasurements were made on 93 samples of Jet A fuel under laboratory conditions(about 50% RH) and after conditioning at 100% RH. It was found that moisture had anunpredicable effect on fuel conductivity; with some samples it increased the conductivity;with others, it decreased the conductivity; and in some cases, moisture had no effect onthe conductivity. However, for 85 of the samples, moisture increased the chargingtendency by as much as 9.5 times depending on the fuel. The survey data for thosesamples for which the charge density exceeded 4000 pC/m 3 after being conditioned at100% RH are reproduced in Table 7. For all but three of these samples, the conductivitydecreased after conditioning at 100% RH, and the charging tendency increased on theaverage by a factor of 6.4. Mora. significantly from the stand-point of pro-static effects,the maximum conductivity after conditioning at 100% RH was only 5.4 pS/m, and for10 samples the conductivity was less than 1.0 pS/m. None of the 63 compounds and

24

NRL REPORT. 8021

10,000

CONCENTRATION OF PETROSUL * .6 ppm

CPETROSUL 742

A PETROSUL 744 LC

v PETROSUL 745

# PETROSUL 7501 6,000

14,000 A

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Z 10,000

hi

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AVERAGE MOLECULAR WEIGHT

F1g. 17 - 1Vffect of molecular weight of PetroI ul conipoundsion charging tendency

of untreated Jet A fuel.

25


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NRL REPORT 8021

Table 8 - Effect of Moisture on Fuel Conductivity and Charging Tendency

Conductivity (pS/m) j Charge Density (uC/m 3 )

Fuel Before Shaking After Shaking Before Shaking After Shaking

With Water* With Water With Water* With Water

Clay-treated Jet A 0.060 0.070 140 3170

Untreated Jet A 0.313 0.126 390 2960

Silica Gel Treatedn-Heptane 0.005 0.011 3 2

*These measurements were made approximately 6 months after the fuel conductivity and charging tendencymeasurements given in Tables 2 to 6. During this period, the conductivity of the clay-treated Jet A fueldecreased and the conductivity of the untreated fuel increased. The charging tendency of both samples de-creased markedly over the same period.

additives tested in the present study produced this unique combination of effects; i.e.,none of these compounds or additives were able to increase the charging tendency of thefuel without simultaneously increasing its conductivity. Thus, in some fuels, dissolvedwater is the most powerful pro-static agent identified to date.

In the present study both the untreated and the clay-treated Jet A fuels and silica-gel-treated n-heptane were shaken with distilled water (5 drops of distilled H2 0/1000 cm3

of fuel) and allowed to stand overnight. As indicated in Table 8, increasing the moisturecontent had little effect on the conductivity of either fuel or of the n-heptane. However,water did increase the charge density of both fuels, by a factor of 23 in the case of theclay-treated fuel, and by a factor of 7.6 for the untreated fuel. On the other hand, waterhad no effect on the charge density of the silica-gel-treated n-heptane, indicating that itis not water per se, but rather its interaction with some constituent of the fuel that isresponsible for its pro-static effect in fuels.

SUMMARY AND CONCLUSIONS

At concentrations up to 1000 ppm, simple polar compounds (acids, alcohols,aldehydes, amines, esters, and ketones) do not significantly increase the electrical conduc-tivity or charging tendency of silica-gel-treated n-heptane.

Certain fuel additives (corrosion inhibitors, an antioxidant, and a thermal-stabilityadditive) at concentrations exceeding the maximum allowable values in fuels can have apro-static effect on jet fuels when Type 10 paper is used.

Two of the static dissipator additives (DCA 48 and Stadis 125) have very little effecton the charging tendency on any of the separator media. However, Stadis 125 in clay-treated Jet A fuel does have a pro-static effect on both the paper and Fiberglas' mediaof the coalescer element. The other two static dissipator additives, Stadis 450 and ASA-3,

27


gave very low charging on all of the separator media except Type 10 paper. However,Stadis 450 gave high charging on the Fiberglas ® coalescer medium.

The most electrostatically active compounds found in this study were the sodiumsulfonates, particularly those derived from petroleum. Two of these compounds, Acto630 and Purified Sulfonate L, gave charge densities in excess of 4000 pC/m 3 at conduc-tivities of less than 50 pS/m 3 and, hence, qualified as pro-static agents according to thedefinition adopted for this study. Other petroleum sulfonates and at least one syntheticsodium sulfonate (Sul-fon-ate AA 10) would probably be classified as pro-static agents atconcentrations of less than 1 ppm.

Electrostatic activity is highly dependent on molecular structure. Within a givenhomologous series, such as the sodium diakyl sulfosuccinates, addition or subtraction ofa few CH 2 groups can markedly change the effect that a given compound can have on thecharging tendency of a hydrocarbon fuel. Also, a definite correlation between molecularweight and charging tendency was found for the Petrosul compounds with the maximumeffect being shown by the material of the lowest molecular weight.

One type of filter media, the obsolete Type 10 paper, gave consistently higher chargelevels than any of the other paper media tested regardless of the fuel sample. Of theseparator elements in current use, two types of paper, Fram CS-61F and CS-64, gavehigher values than the other three types. The lowest levels of charge were obtained withthe Teflon ® screen. With only the sample, 1000 ppm Gulf 178 in clay-treated Jet A fuel,was a charge density in excess of 300 pC/m 3 obtained with Teflon ® . Charging onFiberglas® was irregular, sometimes exceeding that of Type 10 paper and at other timesas low as that of low-charging papers.

A comparison of the results of the present study with available literature dataindicates that water is an ideal pro-static agent. In one study it was found that increasingthe moisture content of most fuels increased the charging tendency by as much as 9.5times while decreasing fuel conductivity. In the present study it was found that satura-tion with water had little effect on the conductivity of either fuel or of silica-gel-treatedn-heptane. However, water did increase the charge density of clay-treated Jet A by afactor of 23 and of untreated Jet A by a factor of 7.6. On the other hand, water had noeffect on the charge density of the n-heptane, indicating that it is not water per se, butrather its interaction with some constituent of the fuel, that is responsible for its pro-static effect in fuels.

Finally, as demonstrated by the effect of moisture on conductivity and chargingtendency, fuels vary in their response to additives. Similar charge-enhancing effects wouldbe expected if the pro-static agents tested in this program were added to other jet fuels,but the magnitude of the charge would not necessarily be the same.

ACKNOWLEDGMENTS

In addition to the American Institute, which sponsored this research, the authorwishes to express his gratitude to the following: V. Laucius and W.G. Dukek of Exxonfor supplying Type 10 filter paper for the Mini-Static Tester, D. Rhynard of Mobile

28

NRL REPORT 8021

Research and Development Corp., for supplying both the clay-treated and untreated Jet Afuel, and A. Matthews of Fram Corp., S. Loftis of Keene Corp., and B. Sand of VelconFilters, Inc., for supplying filter elements for tests.

REFERENCES

1. J.T. Leonard, "Principles of Electrostatics in Aircraft Fuel Systems," in "Lightningand Static Electricity Conference Papers," Air Force Avionics Laboratory, Wright-Patterson AFB, Ohio, Dec. 19, 1972, p. 415.

2. "Jet Fuel Specifications," Exxon Corporation, New York, N.Y., 1973.

3. "Qualified Products List of Products Qualified Under Military Specification MIL-I-25017, Inhibitor, Corrosion, Fuel Soluble," QPL-25017-11, 24 June 1975, Air ForceAero Propulsion Laboratory (SSF), Wright Patterson AFB, Ohio.

4. "Standard Method of Test for D.C. Electrical Conductivity for Hydrocarbon Fuels,ASTM Designation D 3114-72," in Annual Book of ASTM Standards - Part 17,American Society for Testing and Materials, Philadelphia, Pa., 1972, p. 1119.

5. D.A. Young, "Mini-Static Test Procedure," Exxon Research and Engineering Co.,Linden, N.J., June 1972.

6. "A Survey of Electrical Conductivity and Charging Tendency Characteristics of Air-craft Turbine Fuels," CRC Report No. 478, Coordinating Research Council, NewYork, N.Y., April 1975.

7. "Specifications for Aviation Fuels," du Pont Chemicals Tech Memo No. 10, 001-74-2,E.I. du Pont de Nemours and Co., Wilmington, Del., 1974.

8. "Ethyl Distillate Conductivity Additive 48--Conductivity Improver," Ethyl Corpora-tion, Houston, Tex., June 1971.

9. R.G. Davies and R.W. Knipple, "Experience with Static Dissipator Additives inAviation Fuels," SAE Paper No. 700278, Society of Automative Engineers, Inc., NewYork, N.Y., April 1970.

10. "Stadis 125 - Antistatic Additive," du Pont Petroleum Chemicals, Wilmington, Del.,Sept. 1972.

11. "Stadis 450 - Antistatic Additive," du Pont Petroleum Chemicals, Wilmington, Del.,Jan. 1975.

29

Appendix ACOMPOUNDS AND ADDITIVES SELECTED FOR SCREENING

The polar organic compounds with their purity and suppliers are as follows:

Polar Organic Compounds Purity Supplier

Acetic acid Reagent ACS Fisher*Decanoic acid 96% minimum EastmantBenzoic acid Reagent ACS EastmantEthyl alcohol 200 proof U.S. Industrial Chemicals*Decyl alcohol Melting poing:

-14.720- -14.27'OC (5.5c-650 F) EastmantPhenol Reagent ACS Allied Chemical'Acetaldehyde Boiling point:

-6.670- -5.56*C (200-22*F) Eastmant

lAuraldehydr- Boiling point:8500 (1850 F) at 13.3 kPa Aldrich Chemnical1

Benzaldehyde 99% minimum Eastman t

Ethylamine Anhydrous Eastmant

Diethylamine Reagant grade Fisher*Triethylamine 98% minimum Eastmar t

Decylamine Practical Eastma'.;Aniline Certified ACS Fisher*Ethyl acetate NF Baker**Methyl undeconate Spec grade Baker**Methyl Benzoate Reagent grade Fisher*Acetone Certified ACS, Fisher*Acetophenone Certified ACS Fisher*

Other miscellaneous organic compounds are as follows:

Compound Purity Supplier

Alzarin Not available Fisher*Carr"'nic acir! Not available Fisher*Ferr~c benzoylacetonate Not available Fisher*Ferrocene Practical Eastman t

Fluoroscein Practical EastmantIndigo Not available EastmantNaphthenic acids Practical Eastman t

30

NRL REPORT 8021

Compound Purity Supplier

Pararosandinehydrochloride Not available Eastmant

Phenolphthalein Not available Fisher*

*Fisher Scientific Co., Fairlawn, N.J.1'Eastman Organic Chemicals, Rochester, N.Y.SU.S. Industrial Chemicals, New York, N.Y.tAllied Chemical Corp., New York, N.Y.SAldrich Chemical Co., Milwaukee, WVis.

**J.T. Baker, Phillipsburg, N.J.

Table Al gives the suppliers, composition, and allowable concentrations; of the fueladditives selected for this study. It also gives the supplier of each additive.

The Composition and Suppliers of the sodium sulfonates selected for this studyfollow:

MolecularName Composition Weight- Supplier

Sodium diethyl sulfosuccinate 276 American Cyanamid*Sodium di-isopropyl sulfosuccinate 304 American Cyanamid*

Aerosol AY Sodium diamyl sulfosuccinate 360 American Cyanamid*Aerosol OT Sodium di-2-ethylhexyl sulfosuccinate 444 American Cyanamid*

Sodium di-n-octyl sulfosuccinate 444 American Cyanamid*Sodium di-n-decyl sulfosuccinate 500 American Cyanamid*Sodium di-n-dodecyl sulfosuccinate 556 American Cyanamid*

AerosolA 196 Sodium dicy clohexyl sulfosuccinate 386 American Cyanamid*

Aerosol OS Sodium isopropyl naphthalene sulfonate 272 American Cyanamid*Sul-f on-ate

AA 10 Sodium dodecyl benzene sulfonate 348 Tennessee Corp.t

*American Cya namid, Stanford, Conn.tTennessee Corp., Atlanta, Ga.

31


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NRL REPORT 8021

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33


The name, molecular weight, and suppliers of the petroleum sulfonates follow:

Name Molecular Weight Supplier

Acto 425 Hlumble*Bryton 430 435 Bryton Chemicaltlryton 445 450 lDryton I," - icnltPetrosul 742 423 Pennsylvania RefiningtPetrosul 744 LC 445 Pennsylvania RefiningtPetrosul 745 468 Pennsylvania Refining*Petrosul 750 513 Pennsylvania RefiningtPurified Sulfonate 420 Chevron'

The composition of the petroleum sulfonates is-62% sulfonates (typical formula-024 H38 SO3 Na), 33% mineral oil, 4.5% water, 0.5% Inorganic salt.

*Humble Oil and Refining Co., Linden, N.J.tBryton Chemical Corp., Saddle Brook, N.J.tPennsylvania Refining Corp., Butler, Pa.IChevrcn Research Co., San Francisco, Calif.

34

Documents

Pro-static Agents in Jet Fuels · PRO-STATIC AGENTS IN .YET FUELS , INTRODUCTION Over the past 15 years, there have been at least 116 reported fires or explosions attributed to static