Petroleum Marker Dyes Synthesized from Cardanol and Aniline

These synthetic dyes were found to be stable in fuel oils up to at least 3 ... that these marker dyes could be readily applied as markers for commerci...
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Ind. Eng. Chem. Res. 2004, 43, 4973-4978

4973

APPLIED CHEMISTRY Petroleum Marker Dyes Synthesized from Cardanol and Aniline Derivatives Somsaluay Suwanprasop,† Thumnoon Nhujak,‡ Sophon Roengsumran,†,‡ and Amorn Petsom*,†,‡ Program of Petrochemistry and Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

Marker dyes 1-15 for petroleum products were synthesized by coupling reaction of a naturally occurring n-alkylphenol, cardanol, with aniline and its derivatives. These synthetic marker dyes provided invisible color in gasoline and high-speed diesel fuel at an effective usable level (2-5 ppm), but gave visible colors when detected by extraction with 50% (v/v) 1,2-diaminoethane in a solution containing ethane-1,2-diol and methanol (1:1, v/v). Dye contents in fuel oils could be simply quantified with a vis spectrophotometer. The ASTM test methods revealed that the general physical properties of the dyed fuel oils were similar to those of the undyed fuel oils. These synthetic dyes were found to be stable in fuel oils up to at least 3 months, suggesting that these marker dyes could be readily applied as markers for commercial fuel oils. I. Introduction The fuel oil industry is one of the world’s largest businesses. Fuel oils are taxed according to government rates, which are dependent on the types of fuel oils as well as their application purposes (the same fuel used for different purposes, thus having different tax rates). This causes the government many problems such as adulteration of the higher-priced product with lowerpriced material, for example, the addition of a regulargrade gasoline to a premium-grade gasoline; mixing of hydrocarbon solvents to fuel oils; and the addition of low-taxed light heating oil to high-taxed diesel fuel. For these reasons, it is essential to develop methods of marking and identifying petroleum products so as to distinguish varieties of fuel oils available in the market. Marker systems for fuel oils and petroleum products have been reported and used for a long time.1 Some marker dyes have drawbacks that hinder their effectiveness; examples include quinizarin and diphenylamine (poor solubility in nonpolar materials) and furfural (unstable in certain oils). Several studies on the synthesis of alternative marker dyes have been performed, and those marker dyes that were successfully established are as follows: anthraquinones such as substituted 1,4-dihydroxyanthraquinones,2 azo compounds such as derivatives of phenylazophenol and phenylazonaphthol,3,4 and fluorescent markers such as phthalocyanines and naphthocyanines.5-7 As part of our continuing search for novel marker dyes for petroleum products,8 we prepared new markers by coupling a naturally occurring reaction of n-alkylphenol, cardanol, with aniline and its derivatives. Cardanol * To whom correspondence should be addressed. Tel.: +662218-8051. Fax: +662-253-3543. E-mail: [email protected]. † Program of Petrochemistry. ‡ Department of Chemistry.

Figure 1. Structure of cardanol.

(Figure 1) is obtained from cashew nut shell liquid (CNSL), which is an agricultural byproduct from the manufacturing of cashew nuts and commercially available in the southern part of Thailand. CNSL is a rich source of anacardic acid,9 which is easily decarboxylated to give the oil-soluble n-alkylphenol cardanol. We report herein the synthesis of petroleum fuel markers from the naturally occurring substrate (cardanol) and the method for detecting these synthetic dyes when marked in fuel oils. II. Experimental Section Material and Methods. Cashew nut shells were obtained from the cashew nut factory in Phuket, Thailand. All reagents were of analytical grade from Fluka. The infrared spectra were recorded on a Nicolet (Impact 410) FT-IR spectrophotometer. The 1H NMR spectra were obtained with a Bruker (DRX 400) NMR spectrometer operating at 400.1 MHz. Electrospray ionization time-of-flight (ESITOF) MS were obtained with a Micromass (LCT) mass spectrometer. The vis spectra and quantities of marker dyes in fuel oils were measured using a Perkin-Elmer (Lambda 2) UV/vis spectrophotometer. The kinematic viscosities of dyed and

10.1021/ie030739s CCC: $27.50 © 2004 American Chemical Society Published on Web 07/02/2004

4974 Ind. Eng. Chem. Res., Vol. 43, No. 17, 2004

undyed diesel fuels were measured in a Cannon viscometer. The flash points (Pensky-Martens) of the dyed and undyed diesel fuels were measured using an ISL (PMFP93) flash-point analyzer, and the pour points of the dyed and undyed diesel fuels were recorded on an ISL (CPP92) pour-point analyzer. The sulfur contents of the dyed and undyed diesel fuels were determined employing an Outokumpu (X-MET820) X-ray diffraction spectrometer. The distillations of the dyed and undyed diesel fuels were performed with a Herzog (MP626) distillation apparatus, and the distillations of the dyed and undyed gasoline were measured in an ISL (AD865G) distillation apparatus. The total acidities of the dyed and undyed fuel oils were evaluated with a Metrohm 665 total acid number analyzer, and the colors of the dyed and undyed fuel oils were observed with a Lovibond (PFX990/P) petrochemical tintometer. The octane numbers of the dyed and undyed gasoline were recorded on a CFR research octane number analyzer, and the Reid vapor pressures of the dyed and undyed gasoline were obtained with a Grabner Reid vapor pressure analyzer. Decarboxylation of CNSL. Cashew nut shells (500 g) were extracted with n-hexane (1 L). The extract was evaporated to dryness to yield a brown viscous liquid of CNSL (215 g). The CNSL (100 g) was mixed with toluene (200 mL) in a 1000-mL round-bottom flask and refluxed for 3 h. The decarboxylated product, cardanol, was characterized by analyses of FT-IR, ESITOF MS, and 1H NMR spectral data. Purification of Cardanol.10 Decarboxylated CNSL (60 g) and methanol (200 mL) were placed in a 500-mL round-bottom flask. Then, 18.0 mL (0.24 mol) of 40% formaldehyde solution and 2.7 mL (0.025 mol) of bis(2aminoethyl)amine were added into the solution. This mixture was heated until boiling under reflux for 2 h. After the solution was allowed to reach room temperature, a phase separation occurred, showing a slightly reddish upper solution, and a dark brown solidified lower phase. The upper phase was subsequently decanted, and treated with distilled water (40 mL) followed by petroleum ether. The petroleum ether layer was evaporated to dryness, yielding a reddish residue of cardanol, which was characterized by analyses of FT-IR, ESITOF MS, and 1H NMR spectral data. Cardanol: viscous liquid; IR (KBr) υmax (cm-1) 3354 (OH), 3010, 2921, 2859, 1598, 1457, 1369, 1264, 1155; ESITOF MS 297 [(M - H)- of cardanol d], 299 [(M - H)- of cardanol c], 301 [(M - H)- of cardanol b], 303 [(M - H)- of cardanol a]; 1H NMR (400 MHz, CDCl3) 7.16 (t, J ) 7.5 Hz, H-5), 6.80 (d, J ) 7.5 Hz, H-4), 6.72 (br s, H-2), 6.68 (d, J ) 7.5 Hz, H-6), 5.86 (m, olefinic proton), 5.42 (m, olefinic proton), 5.09 (m, CHdCH2), 2.85 (m, dCHCH2CHd), 2.67 (t, J ) 7.5 Hz, H-7), 2.10 (m, dCH-CH2), 1.62 (m, -CH2-), 1.35 (m, -CH2-), 0.92 (m, -CH3). Preparation of Marker Dyes. Aniline and its derivatives employed were aniline, 4-nitroaniline, 3-nitroaniline, 2-nitroaniline, 4-chloroaniline, 3-chloroaniline, 2-chloroaniline, 2-chloro-4-nitroaniline, 2-chloro5-nitroaniline, 4-chloro-2-nitroaniline, 4-chloro-3-nitroaniline, 4-methylaniline, 3-methylaniline, 2-methylaniline, and 2-methoxy-4-nitroaniline. Aniline or a derivative (0.01 mol) was added to a mixture of 3 mL of concentrated hydrochloric acid and 3 mL of distilled water. The mixture was stirred vigorously while being cooled to -2 to 0 °C. When the solution was cold, a solution of sodium

nitrite (0.69 g, 0.01 mol) in distilled water was added dropwise to the reaction mixture while the temperature of the reaction was kept below 0 °C. When the pale yellow solution of benzenediazonium was obtained, this solution was added dropwise into n-alkylphenolate ion solution while the temperature of the reaction mixture was controlled below 0 °C. The solution of n-alkylphenolate ions was prepared by dissolving potassium hydroxide 0.56 g (0.01 mol) in 5.0 mL of methanol, then cooling the solution to 0 °C, and adding 3.0 g of cardanol with continuous stirring to give a reddish-brown oil. The reaction mixture was left stirring at a temperature below 0 °C for 1 h. The marker dye product was extracted from the reaction mixture by treatment with methylene chloride. The methylene chloride layer was washed repeatedly (3-4 times), each time with 20 mL of distilled water, and then evaporated to dryness, yielding a dye product. The common yield of each dye was 80-85% (w/w). Marker dyes were individually characterized by spectroscopic techniques (FT-IR, ESITOF MS, and 1H NMR). Assignments of proton (1H) NMR spectra of marker dyes 1-15 are provided in the Supporting Information. Suitable Extraction System for the Detection of Marker Dyes in Fuel Oils. To determine the suitable extraction system for the detection of marker dyes, the dye 4-(2-chloro-4-nitrophenylazo)-cardanol (8) was used as a dye model because its color in the extracted phase was purple to violet, which is easily observed. Gasoline containing 2 ppm of 4-(2-chloro-4-nitrophenylazo)-cardanol (8) was used for the determination of a suitable extraction system. The dyed gasoline (30 mL) was pipetted into a 50-mL screw cap vial. Then, 6 mL of each extraction system was added into separate vials, each of which was then capped and shaken for 30 s. The extraction systems used were 10-50% (w/v) potassium hydroxide, 10-50% (v/v) 1,2-diaminoethane, and 1050% (v/v) bis(2-aminoethyl)amine in a solution containing ethane-1,2-diol and methanol (1:1, v/v). The mixtures were left at room temperature until two phases were observed. The lower phase, which developed color, was drawn off for recording of the maximum absorption in the visible region for λ ) 350-750 nm using a vis spectrophotometer. The extraction system that gave the highest absorption at its maximum wavelength (λmax) was regarded as the suitable extraction system. Effects of Marker Dyes on the General Physical Properties of Dyed Fuel Oils. The study on the effects of marker dyes on the general physical properties of dyed fuel oils was conducted according to ASTM methods, employing 2 ppm of 4-(2-chloro-4-nitrophenylazo)-cardanol (8) as a dye model. Stability of Marker Dyes in Fuel Oils. The quantity of each marker dye in fuel oils was determined monthly for 3 months by the following procedure. The selected marker dyes, namely, 4-(4-nitrophenylazo)cardanol (2) (2 ppm), 4-(2-chloro-4-nitrophenylazo)cardanol (8) (2 ppm), and 4-(2-methoxy-4-nitrophenylazo)cardanol (15) (5 ppm), were the dye models in this experiment; each was dissolved separately in gasoline and diesel fuel. The dyed fuel oils (30 mL) were separately pipetted into individual vials, and 6 mL of 50% (v/v) 1,2-diaminoethane in a solution containing ethane-1,2-diol and methanol (1:1, v/v) was added to each. Each reaction vial was capped and shaken for 30 s. The vis absorption (at λmax of the extraction system) of the lower phase was measured, and the determination

Ind. Eng. Chem. Res., Vol. 43, No. 17, 2004 4975 Table 1. Vis Absorbance of the Alcohol Part from the Extraction of Marker Dye 8 with Various Solvent Systemsa extraction system

absorbanceb

λmax (nm)

ease of separation

visual color

A1 A2 A3 A4 A5

1% KOH in EDc/MeOH (1:1, v/v) 2% KOH in ED/MeOH (1:1, v/v) 3% KOH in ED/MeOH (1:1, v/v) 4% KOH in ED/MeOH (1:1, v/v) 5% KOH in ED/MeOH (1:1, v/v)

System A 528.5 528.2 527.7 528.0 528.9

0.3993 ( 0.0003 0.3895 ( 0.0005 0.3969 ( 0.0007 0.3841 ( 0.0003 0.3654 ( 0.0003

purple purple purple purple purple

easy easy easy easy easy

B1 B2 B3 B4 B5

10% DAEd in ED/MeOH (1:1, v/v) 20% DAEin ED/MeOH (1:1, v/v) 30% DAE in ED/MeOH (1:1, v/v) 40% DAE in ED/MeOH (1:1, v/v) 50% DAE in ED/MeOH (1:1, v/v)

System B 540.5 547.3 554.8 562.1 568.4

0.3475 ( 0.0005 0.4073 ( 0.0004 0.4263 ( 0.0004 0.4643 ( 0.0002 0.4727 ( 0.0003

purple purple violet violet bluish-violet

easy easy easy easy easy

C1 C2 C3 C4 C5

10% BAAe in ED/MeOH (1:1, v/v) 20% BAA in ED/MeOH (1:1, v/v) 30% BAA in ED/MeOH (1:1, v/v) 40% BAA in ED/MeOH (1:1, v/v) 50% BAA in ED/MeOH (1:1, v/v)

System C 538.9 547.0 554.0 561.1 568.6

0.3378 ( 0.0004 0.4046 ( 0.0002 0.4101 ( 0.0003 0.4352 ( 0.0004 0.4584 ( 0.0003

purple purple violet violet bluish-violet

easy easy easy easy easy

a Marker dye 8 in gasoline (2 ppm) was a dye model. b Average ( Standard deviations, n ) 3. c Ethane-1,2-diol (ED). (DAE). e Bis(2-aminoethyl)amine (BAA)

Figure 2. Structures of marker dyes 1-15.

of the quantity of marker dyes in the fuel oils was performed by comparing the absorbance with the calibration curve. III. Results and Discussion Suitable Extraction System for the Detection of Marker Dyes in Fuel Oils. Marker dyes 1-15 (Figure 2) were successfully synthesized by coupling aniline and its derivatives with cardanol. All synthetic dyes were either yellowish-brown or reddish-brown, which were regarded as appropriate colors that would not interfere with the color of petroleum oils.

d

1,2-Diaminoethane

To assess the method of the detection of marker dyes in fuel oils, various extraction systems were designed: system A contained 1-5% (w/v) of potassium hydroxide in a solution containing ethane-1,2-diol and methanol (1:1, v/v), system B was 10-50% (v/v) of 1,2-diaminoethane in a solution containing ethane-1,2-diol and methanol (1:1, v/v), and system C was composed of 1050% (v/v) of bis(2-aminoethyl)amine in a solution containing ethane-1,2-diol and methanol (1:1, v/v). The dye 4-(2-chloro-4-nitrophenylazo)-cardanol (8) (2 ppm) was a dye model. The vis absorbances of the colors developed in extraction systems A, B, and C are shown in Table 1. The solvent system of ethane-1,2-diol and methanol (1:1, v/v) for systems A-C was well separated from an oil phase after vigorously shaking, and this result could be due to ethane-1,2-diol, which itself could act as a phase separation enhancer.2 The extraction system A, employing a strong alkali (potassium hydroxide) to react with the marker dyes, developed unstable colors that resulted in errors during the quantitative determinations of the marker dyes. This system was therefore not suitable for the extraction of the marker dyes, although its cost was the lowest when compared with extraction systems B and C. Extraction systems B and C were weak alkali solutions of 1,2-diaminoethane, and bis(2-aminoethyl)amine, respectively. Both systems gave clearly defined and deep colors with high absorbance at the maximum wavelength of the developed colors in an extracted phase. However, when comparing their costs, that of 1,2diaminoethane was lower than that of bis(2-aminoethyl)amine. Thus, extraction system B was the better choice system for the extraction of marker dyes from fuel oils. The percentages of 1,2-diaminoethane in the system B were found to affect the maximum wavelength: when the percentage of base was increased, the maximum wavelength of the developed color would shift to longer wavelength, which is commonly known as a “bathochromic shift” or “red shift”. This bathochromic shift presumably resulted from a reduction in the energy level of the excited state accompanying dipole-dipole interaction and hydrogen bonding between 1,2-diaminoethane and marker dyes. It was found that extraction system B5 [50% (v/v) of 1,2-diaminoethane] gave the highest absorbance at the maximum wavelength

4976 Ind. Eng. Chem. Res., Vol. 43, No. 17, 2004

Figure 3. Complexation reaction of 1,2-diaminoethane and marker dye. Table 2. Percentage Yields from the Syntheses of Marker Dyes 1-15 and Visual Colors in the Extracted Phase of Marker Dyes 1-15 in Gasoline and Diesel Fuel (Each with 5 ppm) When Using Extraction System B5 gasoline marker yield λmax dye (%) (nm) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

83 76 81 75 74 82 76 79 70 74 71 73 70 69 70

418.1 537.5 470.3 479.1 418.3 432.4 434.2 567.7 490.2 495.2 480.9 407.3 407.8 407.4 546.3

diesel fuel

visual color

λmax (nm)

visual color

yellow purple yellowish-orange orange yellow yellow yellow bluish-violet orange reddish-orange orange yellow yellow yellow purple

424.0 538.2 471.2 483.0 454.0 450.4 462.5 569.8 495.6 500.6 495.3 420.7 420.9 421.3 550.8

yellow purple yellowish-orange orange yellow yellow yellow bluish-violet orange reddish-orange orange yellow yellow yellow purple

(Table 1). Extraction system B5 was therefore regarded as the most appropriate extraction system for marker dyes in this paper. The synthetic marker dyes (each with 5 ppm) were dyed in gasoline and diesel fuel. They were subsequently extracted with system B5, and their visual colors were observed as shown in Table 2. The colors of the marker dyes were visible because of the complexation reaction of 1,2-diaminoethane and marker dyes, as shown in Figure 3. These reactions resulted in the oil-soluble marker dyes being rendered soluble in an aqueous medium and thus extractable into an aqueous phase. From this mechanism, the negative charge would appear in the positions para and ortho to the azo group. If the positions para and ortho to the azo group are occupied by an electron-withdrawing moiety, such as chloro and nitro groups, the structure is stabilized by an inductive effect. Moreover, if the substituent at the

positions para and ortho to the azo group is the nitro group, the structure is stabilized not only by the inductive effect but also by the resonance effect, because the nitro functionality could delocalize the negative charge through its structure. From Table 2, the color in the extracted phase of 4-(4nitrophenylazo)-cardanol (2) was purple, whereas the color in the extracted phase of 4-(2-nitrophenylazo)cardanol (4) was orange. Both ionized structures were stabilized by the inductive and resonance effects, but the differences in colors supported that the substitution of the electron-withdrawing group at the ortho position was less effective than that at the para position to the amino moiety. For the above reasons, the best dye exhibiting the highest maximum wavelength should be substituted with electron-withdrawing groups at 2′ and 4′. Among the marker dyes synthesized, 4-(2-chloro-4nitrophenylazo)-cardanol (8) therefore exhibited the highest maximum wavelength (569.8 nm). Even though each synthesized marker dye was a mixture of four different compounds, these compounds were different only in the number and position of double bonds in their alkyl side chain. They still had the same azo chromophore, so, their vis spectra were very similar and would not cause any deviation in quantitative analysis. Effects of Marker Dye on the Physical Properties of Dyed Fuel Oils. The general physical properties of the dyed and undyed gasolines, when using 4-(2chloro-4-nitrophenylazo)-cardanol (8) (2 ppm) as a dye model, are shown in Table 3. The physical properties of the dyed gasoline were not significantly different from those of the undyed gasoline. Both dyed and undyed gasoline gave similar specific gravities, research octane numbers, Reid vapor pressures, distillation properties, and colors. The physical properties of the dyed and undyed diesel fuels are listed in Table 4. The physical properties of

Table 3. General Physical Properties of Dyeda and Undyed Gasolines

c

physical property

method (ASTM)b

API gravity at 15.6 °C specific gravity at 15.6/15.6 °C research octane number Reid vapor pressure at 37.8 °C (kPa) copper strip corrosion (3 h, 50 °C) distillation: IBPd (°C) 10% (v/v) evaporated (°C) 50% (v/v) evaporated (°C) 90% (v/v) evaporated (°C) end point (°C) recovery (% v/v) residue (% v/v) total acid number (mg of KOH/g) color

D-1298 D-1298 D-2699 D-5195 D-130 D-86

D-974 D-1500

undyedc

dyedc

58.5 ( 0.0 0.7447 ( 0.0 95.1 ( 0.1 60.2 ( 0.2828 no. 1

56.3 ( 0.0 0.7455 ( 0.0 95.4 ( 0.1 59.4 ( 0.1414 no. 1

34.4 ( 0.4950 53.4 ( 0.2121 87.6 ( 0.1414 153.8 ( 0.2828 181.4 ( 0.2121 97.6 ( 0.2828 1.1 ( 0.1414 0.0035 ( 0.0007