Deposit Formation from Deoxygenated Hydrocarbons. II. Effect of

The effect of trace impurity sulfur compounds on the rate of deposit formation in deoxygenated jet ... Markedly higher deposit formation rates were ob...
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Deposit Formation from Deoxygenated Hydrocarbons. II. Effect of Trace Sulfur Compounds Willlam F. Taylor Exxon Research and Engineering Company, Government Research Laboratory, Linden, New Jersey 07036

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The effect of trace impurity sulfur compounds on the rate of deposit formation in deoxygenated jet fuel range hydrocarbons was investigated. The change in the deposit formation rate following the addition of 3000 ppm of S to a stable jet fuel using representative sulfur compounds from the classes including thiols, sulfides, condensed thiophenes, disulfides, and polysulfides was determined at temperatures up to 54OoC and with the molecular oxygen content reduced to below l ppm. Markedly higher deposit formation rates were observed with added sulfides, disulfides, polysulfides, and a thiol. In contrast, the addition of condensed thiophene compounds did not increase the rate of deposit formation. The results confirm that the ability of rigorous deoxygenation per se to suppress the deposit formation process depends on the type and level of the trace impurity sulfur compounds which are present in the fuel,

Introduction The deposit formation tendencies of jet fuel range hydrocarbons has been the subject of considerable interest, in order originally to investigate storage stability characteristics and subsequently to investigate the stability of such fuels a t higher temperatures when used in high speed supersonic aircraft (Nixon, 1962; Churchill, 1966). The majority of such studies were carried out with fuels saturated with molecular oxygen via exposure to air. This laboratory completed an extended study of the variables which control the kinetics of the deposit formation process in air saturated jet fuels a t temperatures up to 25OOC at reduced pressures (Taylor and Wallace, 1967, 1968; Taylor, 1968a,b, 1969a,b). We are now extending our study of the kinetics of deposit formation to deoxygenated jet fuel range hydrocarbons (i.e., fuel in which the molecular oxygen content has been drastically reduced). We initially reported the effect of variables such as fuel type, temperature, pressure, and molecular oxygen content on the rate of deposit formation from jet fuel range hydrocarbons a t temperatures up to 649OC and pressures up to 69 atm (Taylor, 1974). With most fuels, removal of molecular oxygen markedly lowered the rate of deposit formation. However, the poorest quality fuel tested did not exhibit lower deposit formation rates with deoxygenation. This surprising result suggested the need for a detailed study of the effect of trace impurity compounds in a deoxygenated fuel. This paper discusses the effect of trace impurity sulfur compounds on the rate of deposit formation in a deoxygenated jet fuel. Subsequent work will discuss the effect of trace impurity organic nitrogen and oxygen compounds on deposit formation in deoxygenated fuels. Experimental Section Apparatus. A schematic of the Advanced Kinetic Unit used to measure the rate of deposit formation was shown previously (Taylor, 1974). The molecular oxygen content of the fuel to be tested is adjusted in a fuel treatment vessel by sparging the fuel at an atmospheric pressure using either helium or air. Following this, the treated fuel is passed through an oxygen sensor cell and delivered to a double piston fuel delivery cylinder. The oxygen sensor cell contains a polarographic sensor and the oxygen content of the total fuel is monitored. Oxygen analyses were also made on selected samples using a thermal conductivity gas chromatographic analyzer. The fuel is delivered to the unit by 64

Ind. Eng. Chem., Prod.

Res. Dev., Vol.

15, No. 1, 1976

means of high-pressure nitrogen. The treated fuel is separated from the nitrogen drive gas by use of two individual pistons, separated by a small water layer. The fuel then passes through a heated tubular reactor section consisting of a 0.25-in. o.d., 0.083-in. wall S.S. 304 tube which is contained inside of four individually controlled heaters. Each heater zone is approximately 12 in. in length and is controlled by a proportional temperature controller. Unit pressure is controlled by means of a MITY-MITE type of pressure controller releasing to vent. The rate of deposit formation is measured after a 4-hr run. The reactor tube is cut into 16 sections, each 3 in. long (4 sections per reaction zone), and the tube sections are analyzed for carbonaceous deposits using a modified LECO low carbon analyzer system previously described (Taylor, 1974). The analytical system was calibrated against known standards. The deposit formation rate is obtained by dividing the net carbon production per section by the corresponding inner surface area and expressed as micrograms of carbon per cm2 per 4-hr reaction time. Reagents. The jet fuel employed was a JP-5 (MIL-T5624H) whose properties were previously reported (Fuel A in Table I; Taylor, 1974). The fuel contained 234 ppm of total sulfur and less than 1 ppm of thiol sulfur. The fuel was additive free and was obtained in 1971 from the Baton Rouge refinery of the then Humble Oil and Refining Company (now Exxon Company, U.S.A.). The tubing employed in the reactor section of the Advanced Kinetic Unit was 0.25-in. 0.d. X 0.083-in. wall stainless steel type 304. Prior to use, the tubing is cleaned inside and out with acetone and chloroform and blown dry with nitrogen. Pure sulfur compounds of the highest quality available were obtained and employed as received. Ditertiary dodecyl disulfide and ditertiary butyl disulfide were obtained from Phillips Petroleum Co., Bartlesville, Okla. Di-n-hexyl sulfide, phenyln-propyl sulfide, diphenyl sulfide, phenyl benzyl sulfide, and phenyl methyl sulfide were obtained from Wateree Chemical Co., Lugoff, S.C. Ditertiary nonyl polysulfide, dibenzyl disulfide, 1-decanethiol, benzo(b) thiophene and dibenzothiophene were obtained from Matheson Coleman and Bell, East Rutherford, N.J.

Results The source of petroleum is believed to be the remains of marine animal and vegetable life deposited with sediment in coastal waters (Hodgson, 1971). Bacterial action evolves

Table I. The Effect of Individual Sulfur Compounds on Total Deposit Formation in a Deoxygenated Jet Fuel Total carbonaceous .depositsa

Class of added sulfur compound Polysulfide Disulfide

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Sulfide

Thiol Condensed Thiophene

__

Added compound

oxygen As content, Micro- ppm PPm grams based on of of fuel 0, carbon

__________

Ditertiary nonyl polysulfide Ditertiary dodecyl disulfide Dibenzyl disulfide Ditertiary butyl disulfide Di-n-hexyl sulfide Phenyl-n-propyl sulfide Diphenyl sulfide Phenyl benzyl sulfide Phenyl methyl sulfide Thiocyclohexane 1-Decanethiol Benzo (b) thiophene Dibenzothiophene Base Fuel

.\

-

100

't

________

0.4

7 450

3.85

0.9

7 295

3.76

0.2

6 691

3.45

0.2 10 659 5 739 0.3 3 020 0.3 4 503 0.3 0.2 1 2 253 2 190 0.1 0.2 2 788 3 909 0.3 1 351 0.9 0.7 981 1 485 0.4

5.51 2.96 1.56 2.32 6.33 1.14 1.44 2.02

N O A D D E D SULFUR

0.70

0.51

-

,

10

5.0

1.20

1.10

1.30

1.40

1.50

1.60

70

1000PK

Figure 1. Deoxygenated fuel (0.4 ppm of 02)with added ditertiary nonyl polysulfide at 69 atm.

0.77

a Cumulative deposits produced in 4 hr in the Advanced Kinetic Unit. Conditions: 69 atm, zone 1, 371"C, zone 2, 427" C, zone 3, 482" C, zone 4, 538" c.

sulfur, oxygen, and nitrogen as volatile compounds. These, however, are never completely eliminated despite the everincreasing pressure of sediment. The result of this is that crude oil is a mixture of hydrocarbons containing varying quantities of sulfur, nitrogen, and oxygen compounds. The total sulfur content of crude oil varies from practically zero to as much as 14%. Sulfur compound classes identified in crude oil include thiols, sulfides, and thiophenes. In a review of the Bureau of Mines-API Project 48 work, it was stated that no disulfide has been conclusively identified as present in virgin crude oil (Rall, 1962). Subsequent extensive work appears to have identified a single disulfide in crude oil (Coleman, 1970). Sweetening processes which may be employed to convert odorous thiols in a jet fuel fraction to nonodorous disulfides generally leave the resultant disulfides in the fuel. In addition, sweetening processes which employ elemental sulfur (e.g., Doctor Sweetening) rather than molecular oxygen can inadvertently form polysulfides which would remain in the jet fuel (Thompson, 1949; Walker, 1956). Thus, a jet fuel can contain sulfur compounds from the classes including thiols, sulfides, condensed thiophenes, disulfides, and polysulfides. The effect of various trace sulfur compounds was investigated directly by adding 3000 ppm of S to a highly stable JP-5 fuel and measuring the effect of this addition on the rate of deposit formation in a rigorously deoxygenated system (Le., less than 1 ppm of 0 2 ) . The base fuel contained 234 ppm of S so that the total sulfur content of the fuel with the added sulfur was still below the MIL-T-5624H specification of 4000 ppm of S. Sulfur compounds representative of all of the major classes potentially present in jet fuel were employed. Since the added sulfur content was set on a fixed weight basis, the addition of sulfides, condensed thiophenes, and thiol compounds resulted in a higher molar concentration than the addition of disulfides and polysulfides. The rate of deposit formation was measured in the Advanced Kinetic Unit at 69 atm with the temperature zones at 371-54OOC and with the fuel's molecular oxygen content

Y

c e

z p c

B -c

1J

Y

NO

ffl

0

0 Y

t

lo

1000/'K

Figure 2. Deoxygenated fuel a t 69 atm: 0 , with added dibenzyl disulfide 0.2 ppm of 0 2 ) ; A, with added ditertiary dodecyl disulfide (0.9 ppm of 0 2 ) ; H, with added ditertiary butyl disulfide (0.2 ppm of

02).

reduced to below 1ppm. Results with the base J P - 5 fuel on a deoxygenated basis were previously reported a t 69 atm over the range of 150-649OC (Taylor, 1974). The individual sulfur compounds evaluated are shown in Table I, along with the total deposits formed in each run. Representative Arrhenius plots of the rate of deposit formation are shown in Figures 1to 5. It can be seen that the effect of individual sulfur compounds in a deoxygenated fuel is complex. In general, the addition of the polysulfide, disulfides, sulfides, and thiol all resulted in an increase in the rate of deposit formation. As can be seen from the Arrhenius plots, however, the magnitude of this increase a t a given temperature varied considerably. In contrast, the condensed thiophene compounds evaluated did not increase the rate of deposit formation, and actually appeared to inhibit the deposit formation process to some extent. The effect of sulfur compound concentration in a deoxygenated fuel was investigated using both a sulfide (phenyl Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, 1976

65

4

q

i

4 1

8

4

c

1J

1'

L

t

:

TkG-

ih4--A7G

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1000

O K

Figure 3. Deoxygenated fuel a t 69 atm: 0 , with added diphenyl sulfide (0.3 ppm of 0 2 ) , A, with added phenyl benzyl sulfide (0.2

I '1 1 0

120

130

1 " 40

150

160

1l 7 0

1000/'K

Figure 4. Deoxygenated fuel (0.3 ppm of anethiol a t 65 atm.

02)

with added l-dec-

ppm of 02).

markedly increase the rate of deposit formation of a fuel Table 11. Effect of Sulfur Compound Concentration on Deposit Formation in a Deoxygenated Jet _ Fuel_ _ _ _ ~ even when it is rigorously deoxygenated. Of the five major classes of sulfur compounds potentially Concn of Oxygen present in jet fuel, only condensed thiophene compounds added sulfur content, Relative total did not increase the rate of deposit formation in a deoxyCompound compound, ppm of carbonaceous genated system. 0, deposits0 added ppmof S The formation of deposits from jet fuel range hydrocarPhenyl benzyl bons involves complex chemical and physical processes, sulfide 3 000 0.2 8.22 whose exact nature have not been elucidated. In air-satu300 0.3 3.56 rated systems a t temperatures below the pyrolysis range, it 0 0.4 1 .00 (base) is clear that deposits form as the end result of free radical Ditertiary dodecyl disulfide 3 000 0.9 4.88 chain reactions involving molecular oxygen. Deposit char300 0.2 2.36 acterization studies indicate that typically such deposits 0 0.4 1.00 (base) contain high concentrations of oxygen and lesser but signifa Relative cumulative deposits produced in 4 h r in the icant amounts of sulfur and nitrogen in a relatively low moAdvanced Kinetic Unit. Conditions: 69 atm, zone 1, 371" C, lecular weight species which collects into microspherical zone 2, 427"C, zone 3, 482'C, zone 4, 538°C. particles of an approximate 1000 A diameter. This suggests that in liquid phase autoxidative deposit formation it is the change in solvent character resulting from the incorporabenzyl sulfide) and a disulfide (ditertiary dodecyl disulfide). Results are summarized in Table TI. In both cases tion of oxygen, nitrogen, and sulfur into the deposit species which is important rather than an increase in molecular higher levels of added sulfur compounds resulted in higher levels of deposit formation. The deposit formation level, weight per se. As reported previously, in general, deoxygehowever, did not increase linearly with added sulfur comnation greatly reduced low-temperature, liquid phase depound level. In both cases, increasing the added sulfur level posit formation rates, and significant rates of deposit forby a factor of 10 (Le., from 300 to 3000 ppm) approximatrely mation did not occur until higher temperatures were doubled the level of total deposits. reached. At higher temperatures new hydrocarbon reactions begin Discussion to assume importance. Jet fuel range hydrocarbons start to exhibit measurable rates of pyrolysis a t temperatures The most striking feature of the results of our initial above approximately 35OoC (Fabuss et al., 1965). The prestudy of the deposit formation tendencies of deoxygenated dominate products from pyrolysis reactions have molecular jet fuel range hydrocarbons was that not all fuels exhibited weights equivalent to or less than the parent hydrocarbons, lower deposit formation rates with rigorous deoxygenation. although higher molecular species have been reported (FaNumerous studies had shown that deposits in air-saturated buss et al., 1965). The catalytic effect of surfaces would also hydrocarbons form as the end result of complex free radibe expected to increase in importance with increasing temcal, chain reactions involving molecular oxygen (Nixon, perature. Surfaces are known to exert catalytic effects in 1962, Boss and Hazlett, 1969). Thus, a priori, it would be so-called "homogeneous" pyrolysis reactions. In addition, expected that the rigorous exclusion of molecular oxygen a t higher temperatures where a vapor phase rather than a would suppress autoxidative reactions and result in a reliquid phase would be present it would be expected that duction in deposit formation. At the time of the initial changes in the molecular weight of deposit precursors study, it was postulated that the anomalous behavior of the would be more important than their liquid phase solvent fuel which failed to respond to deoxygenation was caused properties. As previously reported (Taylor, 1974), the analby the presence of disulfides. The present study has clearly ysis of deposits formed from a deoxygenated fuel indicated demonstrated that the presence of trace levels of not only that its composition is different from deposits formed in a disulfides, but sulfides and a polysulfide and a thiol can _ I . -

_

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.

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~

Ind. Eng. Chem., Prod. Res. Dev., Vol. 15,No. 1, 1976

Table 111. Relative Effect of Sulfides in a Deoxygenated vs. an Air Saturated System Rate of deposit formation relative to that of base fuel Sulfur compound added to base fuel Methyl phenyl sulfide ..,-Sa

20.0

Deoxygenatedb 1.9

-

n-Propyl phenyl sulfide C,H.-S-(-J

Airsaturated0

1000

i) i 0

YI ir 0 3

1

9

< u 8

100

0.

Y

r

8.9

2.9

a c z

-r 0

a

-

\

a D!

L 0

Benzyl phenyl sulfide

1.3

15.3

(-+-sa

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Base fuel with no added sulfur 1.0 (base) 1.0 (base) a Sulfur compound added to base fuel (P&W 523) to the 1000 ppm of S level. Rates measured at 177" C and 0.2 atm (Taylor and Wallace, 1968). b Sulfur compound added to base fuel ( J P - 5 ) to the 3000 ppm of S level. Rates measured at 427°C and 69 atm. typical air-saturated fuel. This suggests that deposits are formed as a result of different chemical and physical processes in a deoxygenated environment than in an air-saturated environment. In a previous study of the effect of sulfur compounds on the deposit formation rate in an air-saturated system, it was observed that the addition of equal quantities of different sulfides to a stable fuel resulted in markedly different changes in the rate of deposit formation (Taylor and Wallace, 1968). In the present study in a deoxygenated system marked differences among the effect of various sulfide compounds were also observed. In Table I11 is shown a comparison of the effect of the addition of the same sulfide compounds on the deposit formation rate in a deoxygenated versus air saturated system. The rates are compared on a relative basis since the base fuels and conditions employed vary between the two studies. I t can be seen that the relative effects of the addition of the same sulfide compound differed greatly between the low-temperature airsaturated environment and the higher temperature deoxygenated environment, again suggesting that different deposit formation processes are involved. Sulfur compounds are known to pyrolyze via a homogeneous free-radical process; e.g., phenyl methyl sulfide was shown to decompose to phenyl thiyl and methyl radicals (Back and Sehon, 1960), benzyl methyl sulfide decomposed to benzyl and methyl thiyl radicals (Braye et al., 1955), and various thiols decomposed via rupture of the C-S bond to alkyl and hydrosulfide radicals (Sehon and Darwent, 1954). The weakest bond in disulfides and polysulfides is usually the S-S bond, and disulfides have been used to initiate free radical, chain reactions in the same manner that peroxides are employed (Pryor, 1962). The heterogeneous decomposition of thiols occurs readily and usually yields olefins, sulfides, and hydrogen sulfide (Reid, 1958). Sulfides and disulfides both (Reid, 1960a,b) undergo a complex heterogeneous decomposition a t temperatures above 200OC. Rudenko and Gromova (1951) passed a series of sulfur compounds over iron and reported the minimum temperature a t which decomposition became significant as evidenced by evolution of hydrogen sulfide. Thiols, disulfides, and dialkyl sulfides readily decomposed a t temperatures above 15OOC. Diary1 sulfides decomposed a t 449OC, but thiophene was stable a t 5OOOC. Fabuss et al. (1965) have shown that ti-ace quantities of sulfur com-

NO ADDED SULFUR

r -

s 0 0 Y

IC

5.c

0

1.20

1.30

1.40

1.50

1.60

1.70

1000PK

Figure 5. Deoxygenated fuel at 69 atm: 0 , with added benzo(b)thiophene (0.9 ppm of 0 2 ) ; B, with added dibenzothiophene (0.7 ppm of 0 2 ) .

pounds can either increase or decrease the rate of thermal pyrolysis of various hydrocarbons. In the present study condensed thiophene compounds were found not to increase the rate of deposit formation in a deoxygenated system. This presumedly reflects the relative strength of the aryl C-S bond in these compounds. A similar effect was previously observed in an air saturated environment (Taylor and Wallace, 1968). The other deleterious sulfur compounds contain weaker s-S bonds and alkyl C-S bonds which presumedly undergo pyrolysis and/ or surface catalyzed decomposition reactions a t milder conditions than the bonds present in pure hydrocarbons and whose products ultimately lead to the acceleration of the deposit formation processes. The various deleterious sulfur compounds evaluated in the present study often produced maximum increased deposit formation rates a t different temperatures. This presumably reflects the effect of the variation in bond strength between S-S bonds and the various alkyl C-S bonds (Pryor, 1962), which would cause these compounds to exhibit scission of these bonds at different temperatures. In the present study added sulfur compounds in a deoxygenated system exhibited a less than linear effect on the increase in the level of deposits formed. A similar effect was found previously in a study of the effect of added sulfur compounds in an air-saturated system (Taylor, 1974).

Acknowledgments Helpful discussions with C. J. Nowack, L. Maggitti, Jr., and J. R. Pitchtelberger are gratefully acknowledged. Literature Cited Back, M. H.. Sehon, A. H., CanJ. Chem., 38, 1076 (1960). Boss, 5. D., Hazlett, R. N., Can. J. Chem.. 47, 4175 (1969). Braye, E. H., Sehon, A. H., Darwent, B. de B.,J. Am. Chem. SOC.,7, 5282 (1955). Coleman, H. J.. Hopkins, R. L.. Thompson C. J., Am. Chem. SOC. Div. Pet. Chem. frepr., 15, (3),A17 (1970). Churchill, A. V., Hager, J. A., Zengel, A. E., S.A.E. Trans.. 74, 641 (1966). Fabuss, E. M., Duncan, D. A.. Smith, F. O., Satterfield, C. N., Ind. Eng. Chem., Process Des. Dev., 4, 117 (1965). Hodgson, G. W., Adv. Chem. Ser., No. 103 (1971). Nixon. A. C., in "Autoxidation and Antioxidants," Vol. 11, W. 0. Lundberg, Ed., Interscience, New York, N.Y., 1962. Pryor. W. A,, "Mechanisms of Sulfur Reactions," McGraw-Hill, New York. N.Y.. 1962.

Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, 1976

67

Rall, H. T., Thompson, C. J., Coleman, H. J., Hopkins, R. L.. Roc. Am. Pet. lnst., 42, Sect. VIII, 19 (1962). Reid, E. M.. "Organic Chemistry of Bivalent Sulfur," Vol. I, p 1IO, Chemical Publishing Co., New York, N.Y.. 1958. Reid, E. M., "Organic Chemistry of Bivalent Sulfur," Vol. 11, p 60, Chemical Publishing Co., New York, N.Y., 1960a. Reid, E. M., "Organic Chemistry of Bivalent Sulfur," Vol. Ill, p 369, Chemical Publishing Co., New York, N.Y. 1960b. Rudenko, M. G., Gromova, V. N., Dokl. Akad. Nauk, SSSR, 81, 297 (1951). Sehon, A. H.,Darwent, B. de B., J. Am. Chem. SOC.,78, 4806 (1954). Taylor, W. F., J. AppI. Chem., 18, 251 (1968a). Taylor, W. F., SA€ Trans., 78, 281 1 (1968b). Taylor, W. F., J. Appl. Chem., 19, 222 (1969a). Taylor, W. F., Ind. Eng. Chem., Prod. Res. Dev., 8, 375 (1969b).

Taylor, W. F., Ind. Eng. Chem., Prod. Res. Dev., 13, 133 (1974). Taylor, W. F., Wallace, T. J., lnd. Eng. Chem., Prod. Res. Dev., 6, 258 (1967). Taylor, W. F., Wallace, T. J.. Ind. Eng. Chem.. Prod. Res. Dev.. 7, 198 (1968). Thompson, R. B., Druge, L. W., Chenicek, J. A,, lnd. fng. Chem., 41, 2715 ( 1949). Walker, H. E.,Kenney, E. B., Pet. Process., 11, 58 (1956).

Received for review June 5, 1975 Accepted August 14,1975 This work was sponsored by the Department of the Navy under Contracts N00019-71-C-0463and N00140-72-C-6892.

Analyzing Cetyldimethylbenzylammonium Chloride by Using Ultraviolet Absorbance Downloaded by UNIV OF WINNIPEG on September 12, 2015 | http://pubs.acs.org Publication Date: March 1, 1976 | doi: 10.1021/i360057a012

Lawrence K. Wang,' Donald B. Aulenbach, and David F. Langley Department of Chemical and EnvironmentalEngineering, Rensselaer Polytechnic Institute, Troy, New York 72 78 7

The engineering significance of cetyldimethylbenzylammoniumchloride is described. The compound in distilled water in the range of 1.0 to 5.0 mg/l. can be rapidly measured by a uv method at 210 nm with less than 8 % relative standard deviation and relative error.

Introduction Quaternary ammonium compounds are widely used for: (a) fabric antistatics and softening (cationic quaternary ammonium compounds can eliminate the normal buildup of static electrical charges of plastics and synthetic fibers when dried in a mechanical drier, and the quaternary ammonium compounds with two long alkyl chains also have excellent softening properties when used in conjunction with common synthetic detergents for cleaning fabrics and clothes); (b) corrosion inhibition in flue gas scrubbers, acid pickling baths, and petroleum pipelines; (c) emulsion compounding (they have the special property of being substantive, that is, causing the oil phase of an emulsion to plate out on such surfaces as textile fabrics, metals, glass, plastic, wood, and foliage); (d) pigment treatment; and (e) ore flotation (separation of certain minerals from low grade ores can best be accomplished using quaternaries). For water pollution control, the release of such cationic surfactants to water resource systems should be monitored and controlled. Recently environmental engineers have been researching the use of quaternary ammonium compounds for water treatment (Grieves and Schwartz, 1966; Grieves and Conger, 1969; Grieves et al., 1970; Wilson, 1969; Wang, 1972; Wang and Peery, 1975), wastewater treatment (Wang et al., 1974a; 1974b; Wang, 1973a, 1973b), and sludge treatment. Therefore, the development of effective analytical techniques for determining the initial and residual concentrations of quaternary ammonium compounds is necessary. For general analysis of quaternary ammonium compounds in aqueous solution, the presently accepted method is the two-phase titration method (Wang, 1973c; Wang et al., 1974b), which can measure the concentrations of quaternaries at a range of l to 30 mg/l. More recently, Wang and Langley (1975) developed a methyl orange method for more accurate determination of cationic surfactants (in68

Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, 1976

cluding quaternaries) at the concentration range of 0.1 to 4.5 mg/l. Either the two-phase titration method (Wang 1973c; Wang et al., 1974b) or the methyl orange method (Wang and Langley, 1975) is applicable to the quantitative measurement of a single type of cationic surfactant in water. Neither method can differentiate between two quaternary ammonium compounds, between two amines, or between a quaternary ammonium compound and an amine compound. Nevertheless, the two methods are effective for chemical engineering processes control in which the specific cationic surfactant used is known, and for environmental water quality control in which only the residual concentration of a group of contaminants, such as cationic surfactants, is of particular concern. The objective of this paper is to introduce an ultraviolet spectrophotometric method for rapid analysis of a specific cationic surfactant (quaternary ammonium compound), cetyldimethylbenzylammonium chloride (CDBAC). Its molecular structure is shown in Figure l. Since CDBAC is an approved germicide (U.S.D.A. Regulation No. 1457-16), it may be used in throat lozenges, provided the individual lozenge contains not more than 5 mg of CDBAC and that the directions for use do not provide for consumption of more than 8 lozenges in 1 day. CDBAC is also generally used in mouth washes in a concentration of 1:4000. In the field of environmental engineering, CDBAC is a highly effective sanitizer (Ehlers and Steel, 1958; Fine Organics Inc., 1970), flotation agent (Wilson, 1969; Grieves and Conger, 1969; Grieves et al., 1970; Wang, 1972), and disinfectant (Wang and Peery, 1975). Many research projects are presently being conducted for the exploration of other applications and recovery techniques. The proposed uv method provides direct measurement ( 3 0 solvent extraction is involved), thereby significantly reducing the time for analysis and eliminating possible health hazards from toxic solvent vapors, such as chloroform.