Industry application scheme
Industry application scheme
Abstract: The content of petroleum pollutants in environmental water is one of the indicators reflecting water quality. This paper adopts a three-wavelength quantitative test for oil content in water, featuring convenient sample testing and accurate data. Petroleum substances in water come from industrial wastewater and domestic sewage pollution. Oil forms an oil film on the water surface, affecting gas exchange between air and water; oils dispersed in water, adsorbed onto particles, or existing in water in an emulsified state consume dissolved oxygen when decomposed by microorganisms, easily deteriorating water quality. Mineral oil is a mixture composed of alkanes, cycloalkanes, and aromatic hydrocarbons.
This paper refers to "HJ 637-2018 Water Quality - Determination of Petroleum and Animal and Plant Oils - Infrared Spectrophotometry" and selects the three-wavelength infrared spectroscopy method for measuring surface water, with accurate measurement results, avoiding the use of "standard oil".
Keywords:Infrared Spectroscopy Method, Oil in Water, Quantitative Detection
Principle:
Oil substances in water are mixtures of alkanes, cycloalkanes, and aromatic hydrocarbons, which can be extracted using carbon tetrachloride (CCl4), measuring total extractables. Then, the extract is adsorbed by magnesium silicate to remove polar substances such as animal and plant oils, after which the petroleum content is measured. Petroleum and animal and plant oils exhibit absorption at 2930 cm-1, 2960 cm-1, or 3030 cm-1 in the infrared spectrum, and their content can be calculated based on the absorbance values at these three wavenumber positions.
Experimental Conditions:
Instruments and Accessories:
FTIR-650 Fourier Transform Infrared Spectrometer
4cm Quartz Stoppered Cuvette
Reagents:
Tetrachloroethylene (C2Cl4): Environmental grade
n-Hexadecane [CH3(CH2)14CH3]: Analytical grade
Pristanne (2,6,10,14-tetramethylpentadecane):Analytical grade
Toluene (C6H5CH3): Analytical grade
Anhydrous Sodium Sulfate (Na2SO4): Analytical grade
Sodium Chloride (NaCl): Analytical grade
Hydrochloric Acid (HCl): Analytical grade
Sample Pretreatment:
Transfer the water sample entirely into a separatory funnel, wash the sampling bottle with 20ml of tetrachloroethylene, combine the washing liquid with the separatory funnel, adjust pH ≤ 2, add 20g of sodium chloride, shake thoroughly for 2 minutes, then let it stand fully. Pass the extract through a glass sand core funnel lined with 10mm anhydrous sodium sulfate, collecting the filtrate in a volumetric flask. Extract again with 20ml of tetrachloroethylene and wash the glass sand core funnel with an appropriate amount of tetrachloroethylene, combining the extracts and washings in the volumetric flask. Dilute to the mark with tetrachloroethylene and mix well.
Measurement Results:
1. Determination of Calibration Coefficients:
Using tetrachloroethylene as the solvent, prepare solutions of 100mg/L n-hexadecane, 100mg/L pristanne, and 400mg/L toluene separately. Using tetrachloroethylene as the reference solution, measure the absorbances A2930, A2960, and A3030 at 2930 cm-1, 2960 cm-1, and 3030 cm-1 respectively using a 10mm x 10mm cuvette. The absorbance of these three solutions satisfies the formula:
C = X•A2930 + Y•A2960 + Z(A3030 - A2930/F),
where:
C - compound content in the extraction solvent, mg/L;
A2930, A2960, A3030 - absorbance values measured at each corresponding wavenumber;
X, Y, Z - correction coefficients corresponding to the absorbance of each C-H bond;
F - correction factor for aliphatic hydrocarbons relative to aromatic hydrocarbons, i.e., the ratio of absorbance of n-hexadecane at 2930 cm-1 and 3030 cm-1;
For n-hexadecane (H) and pristanne (P), since they contain no aromatic hydrocarbons, i.e., A3030 - A2930/F = 0, F = A2930(H)/A3030(H);
C(H) = X×A2930(H) + Y×A2960(H);
C(P) = X×A2930(P) + Y×A2960(P);
From this, the values of X, Y, F can be obtained.
For toluene (T), there is: C(T) = X•A2930(T) + Y•A2960(T) + Z[A3030(T) - A2930/F], from which the value of Z can be derived.
The calculated correction coefficients X, Y, Z, F are 126.6, 242.5, 1575, and 63, respectively.
2. Verification of Correction Coefficients:
Mix hydrocarbons in a volume ratio of 5:3:1 of n-hexadecane, pristanne, and toluene. Accurately weigh an appropriate amount of mixed hydrocarbons to prepare a series of solutions of different concentrations, measure their absorbances at A2930, A2960, A3030 (see Figure 1) and calculate the concentration of the mixed hydrocarbons, recovery rate (results see Table 1).
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