The steps of detecting petroleum content in industrial wastewater by infrared spectrophotometry

  Generally, most of the oil in industrial wastewater comes from industries such as refineries, petrochemicals, and oil extraction. Before, we introduced the steps of using fluorescence method to detect oil in surface water, but this method is not suitable for complex water bodies such as industrial wastewater or domestic sewage. Today we want to understand how to use infrared spectrophotometry to detect the oil content in industrial wastewater.

  The detection principle of this method is to extract the water sample with tetrachloroethylene under the condition of pH≤2, and then determine the oil; after the extract is adsorbed with magnesium silicate to remove polar substances such as animal and vegetable oils, the petroleum is determined. The contents of oil and petroleum are determined by wavenumbers of 2930 cm-1 (stretching vibration of C—H bond in CH2 group), 2960 cm-1 (stretching vibration of C—H bond in CH3 group) and 3030 cm, respectively. Absorbance A2930, A2960 and A3030 at -1 (stretching vibration of C—H bond in aromatic ring), calculated according to correction factor;

Reagents required for testing

1. Hydrochloric acid: 1.19g/ml, excellent grade.
2. Hydrochloric acid solution: 1+1.
Prepared with hydrochloric acid.
3. Tetrachloroethylene
Using a dry 4cm empty quartz cuvette as a reference, use a 4cm quartz cuvette to measure tetrachloroethylene between 2800cm-1-3100cm-1. The absorbance at 2930cm-1, 2960cm-1 and 3030cm-1 should not exceed 0.34, 0.07, 0.
4. n-hexadecane: chromatographically pure.
5. Isooctane: chromatographically pure.
6.6 Benzene: chromatographically pure.
7. Anhydrous sodium sulfate.
It was placed in a muffle furnace and heated at 550 °C for 4 hours, and then put into a ground glass bottle after cooling slightly, and stored in a desiccator.
8. Magnesium silicate: 150um-250um (100-60 mesh).
Take magnesium silicate in a porcelain evaporating dish, heat it in a muffle furnace at 550°C for 4 hours, cool it a little, and then transfer it to a desiccator to cool to room temperature. Weigh an appropriate amount of magnesium silicate into a ground glass bottle, add an appropriate amount of distilled water at a ratio of 6% (m/m) according to the quality of magnesium silicate, seal it tightly and shake it fully, and place it for 12 hours before use. Store in bottle.
9. Glass wool
Before use, soak and wash glass wool in tetrachloroethylene and dry it for later use.
10. Standard stock solution of n-hexadecane: 10000mg/L.
Weigh 1.0g (accurate to 0.1mg) of n-hexadecane in a 100ml volumetric flask, dilute to volume with tetrachloroethylene, and shake well. Refrigerated at 0℃-4℃ and protected from light, it can be stored for 1 year.
11. Standard solution of n-hexadecane: 1000mg/L.
Dilute the standard stock solution of n-hexadecane with tetrachloroethylene into a 100ml volumetric flask.
12. Isooctane standard stock solution: 10000mg/L.
Weigh 1.0g (accurate to 0.1mg) of isooctane in a 100ml volumetric flask, dilute to volume with tetrachloroethylene, and shake well. Refrigerated at 0℃-4℃ and protected from light, it can be stored for 1 year.
13. Isooctane standard solution: 1000mg/L.
Dilute the isooctane standard stock solution with tetrachloroethylene in a 100ml volumetric flask.
14. Benzene standard stock solution: 10000mg/L.
Weigh 1.0g (accurate to 0.1mg) of benzene in a 100ml volumetric flask, dilute to volume with tetrachloroethylene, and shake well. Refrigerated at 0℃-4℃ and protected from light, it can be stored for 1 year.
15. Benzene standard solution: 1000mg/L.
Dilute the benzene standard stock solution with tetrachloroethylene to a volume of 100ml in a volumetric flask.
16. Petroleum standard stock solution: 10000mg/L.
According to the ratio of 65:25:10 (V/V), measure n-hexadecane, isooctane and benzene to prepare a mixture. Weigh 1.0g (accurate to 0.1mg) of the mixture in a 100ml volumetric flask, dilute to volume with tetrachloroethylene, and shake well. Refrigerated at 0℃-4℃ and protected from light, it can be stored for 1 year.
17. Petroleum standard liquid: 1000mg/L.
Dilute the petroleum standard stock solution with tetrachloroethylene to a volume of 100ml in a volumetric flask.
18. Adsorption column
Fill a small amount of glass wool at the outlet of the glass column with an inner diameter of 10mm and a length of about 200mm, slowly pour the magnesium silicate into the glass column, tap gently while pouring, and the filling height is about 80mm.

Testing Equipment

1. Infrared oil meter or infrared spectrophotometer: can measure absorbance at 2930cm-1, 2960cm-1, 3030cm-1, and is equipped with a 4cm quartz cuvette with a lid.
2. Horizontal oscillator.
3. Sampling bottle: 500ml wide-mouth glass bottle.
4. Glass funnel.
5. Triangular bottle: 50ml, with stopper and ground mouth.
6. Colorimetric tube: 25ml, 50ml, with stopper and ground mouth.
7. Separation funnel: 1000ml, with PTFE stopper.
8. Graduated cylinder: 1000ml.
9. Common laboratory utensils and equipment.

water sample preparation

Preparation of oil samples

  Transfer the sample to a 1000ml separatory funnel, measure 50ml of tetrachloroethylene to wash the sample vial, transfer all of it to the separatory funnel, shake it for 2 minutes, open the cock frequently to exhaust, and let it stand for stratification; use tweezers to take the glass Put the cotton on the glass funnel, spread an appropriate amount of anhydrous sodium sulfate on it; open the cock of the separatory funnel, put the lower organic phase extract into a 50ml colorimetric tube through the glass funnel filled with anhydrous sodium sulfate, and use an appropriate amount of four. The glass funnel was rinsed with vinyl chloride, the rinse solution was combined into the extract, and the volume was adjusted to the mark with tetrachloroethylene. The entire upper aqueous phase was transferred to a graduated cylinder, and the sample volume was measured and recorded.

Preparation of petroleum samples

Oscillation adsorption
  Take 25ml of the extract, pour it into a 50ml conical flask containing 5g of magnesium silicate, place it on a horizontal shaker, shake continuously for 20min, let it stand, put the glass wool in a glass funnel, pour the extract into the glass funnel and filter to 25ml Colorimetric tubes for the determination of petroleum.

adsorption column method

  Take an appropriate amount of the extract and pass it through a magnesium silicate adsorption column, discard the first 5ml of the filtrate, and connect the remaining part to a 25ml colorimetric tube for the determination of petroleum.

Preparation of blank samples

  Use experimental water to add hydrochloric acid solution to acidify to pH≤2, and prepare blank samples according to the same steps as sample preparation.

Detection steps

calibration
  Measure 2.00ml of n-hexadecane standard solution, 2.00ml of isooctane standard solution and 10.00ml of benzene standard solution in three 100ml volumetric flasks, make up to the mark with tetrachloroethylene, and shake well. The concentrations of standard solutions of n-hexadecane, isooctane and benzene were 20.0 mg/L, 20.0 mg/L and 100 mg/L, respectively.
  Using a 4cm quartz cuvette to add tetrachloroethylene as a reference, measure the absorbance A2930, A2960 and A3030 of the standard solutions of n-hexadecane, isooctane and benzene at 2930cm-1, 2960cm-1 and 3030cm-1 respectively. The absorbance of n-hexadecane, isooctane and benzene standard solutions at the above-mentioned wavenumbers are simultaneously equations according to the formula, and the corresponding correction coefficients X, Y, Z and F are obtained respectively after solving.
Determination
Determination of oils
  Transfer the extract to a 4cm quartz cuvette, and measure its absorbance A2930, A2960, A3030 at 2930cm-1, 2960cm-1, 3030cm-1 with tetrachloroethylene as a reference.
Determination of Petroleum
  The extract after adsorption by magnesium silicate was transferred to a 4cm quartz cuvette, and the absorbance A2930, A2960 and A3030 were measured at 2930cm-1, 2960cm-1 and 3030cm-1 with tetrachloroethylene as a reference.
The concentration of petroleum in the final water sample can be calculated according to the relevant formula.