EXPERIMENTALNOTES Spectrum Two™

Determination of Aromatic, Paraffinic and Naphthenic Carbon In Mineral Base Oils Using FTIR

Experimental

1 mm Syringes with appropriate fittings were used to transfer the oil samples into the cell. Moisture free solvent was used for cleaning. The spectra for oil samples were recorded from 2000 cm-1 to 450 cm-1 using 0.1 mm KBr fixed path length cell.

Sample preparation

Using a syringe, the cell is filled with the sample to ensure that there are no entrapped air bubbles and that the exterior of the cell does not get contaminated. Place the PTFE stopper and place cell in FTIR.

Instrumental conditions

Spectrum Two FTIR Experimental Conditions

Background Air

Scan range 2000cm-1 to 450cm-1

Resolution 4cm-1

No. of scans 4

Path-length Used 0.1mm

Cell Used KBr Fixed Path-length Cell

Abstract

This experimental note presents the method for the determination of Aromatic (CA), Paraffinic (CP), and Naphthenic (CN) carbon in mineral base oils, based on the Indian Standard 13155:1991. The presence of one type or the other of these determines some of the physical properties of the lubricants i.e. pour point, viscosity index, pressure-viscosity characteristics, etc. They originate from crudes from different sources and correspond to an exact chemical type. Paraffinic implies straight chain hydrocarbons; naphthenic means cyclic carbon molecules with no unsaturated bonds and aromatic oils contain benzene type compounds. Oils are distinguished based on their relative proportions of Paraffinic, Naphthenic and Aromatic Components present (reference 1).

Author

Jui Kuse and Afshan SayedTechnical Specialist-Product-Application-Material charachterizationCustomer Knowledge Centre for Analytical Sciences PerkinElmer (India) Pvt. Ltd. Thane – 400 615 India. Email: application.india@perkinelmer.com

FTIR - PETROCHEMICAL

Analytical results & conclusions

Figure 2. shows the Spectrum for fresh oil sample in the 2000-450 cm-1 range. The calculation can be performed either manually or using software calculations (as shown in Figure 3.) Then tangents are drawn across the transmission maxima on either side of the peak being measured, as shown in fig.3, and a vertical line is drawn through the peak minimum. The intersection of these lines gives the value of intensity Io and the intersection of the vertical with the peak minimum gives value of I. The values are to be read of Io and I for CA (1600 cm-1) and CP (720 cm-1). CN is calculated from the difference.

Figure 2: IR spectrum of sample showing peaks at 1600cm-1 and 720cm-1

Figure 3: IR spectrum of sample showing I0 and I

Calculations:

Formulae

For CA:

E = [Log Io/ I ] / cd

CA = 1.2 + 9.8 E

For CP :

E = [Log Io/ I ] / cd

CP = 29.9 + 6.6 E

Where: c = Concentration factor (1 for undiluted oil)

d = path length

For CN :

CN = 100 - (CA + CP)

e.g. The calculations for the above example (from Figure 3) are as follows:

For CA: at 1600cm-1

E = [Log ( 72.03/ 66.49) ] / 1 x 0.1= 0.3475

CA = 1.2 + (9.8 x 0.3475) = 4.6055

For CP: at 720cm-1

E = [Log ( 74.32/19.62 ) ] / 1 x 0.1= 5.7840

CP = 1.2 + (9.8 x 5.7840) = 57.8832

For CN: from CA and CP values

CN = 100 – (4.6055 + 57.8832) = 37.5113

Conclusion:

FT-IR is very simple and rapid technique to perform this analysis. It does not require complex sample preparation. Spectrum TwoTM gives us the flexibility to run the samples in liquid phase with 0.1mm path length cells. This application is useful in oil or petroleum segment wherein we need to check the quality of oil on the basis of carbon type.

Note: If sample has a large aromatic content (approximately 20 %) the paraffinic peak may become masked by adjacent peaks, making accurate measurement difficult.

References:

1- G.W. Stachowiak, A.W. Bachelor, Engineering Tribology, “Chapter 3: Lubricants and their compsotion”, Elsevier