Method for determining oil content in water, oil and surfactant three-phase system

Abstract

The invention discloses a method for measuring oil content in a water, oil and surfactant three-phase system, which comprises the following steps: collecting a water sample to be measured of the water, oil and surfactant three-phase system, recording the total amount of the water sample to be measured, and adding an extraction agent into the water sample to be measured to form an extraction system; adding anhydrous sodium sulfate and anhydrous magnesium sulfate into the extraction system, oscillating and uniformly mixing, then standing to form a layer, and taking an upper-layer extraction liquid phase; and determining the weight or concentration of the oil in the extract liquid phase by adopting a drying gravimetric method or an infrared oil meter, and calculating to obtain the oil content in the water sample to be detected. The method solves the problem that when the oil content of a water body containing a three-phase system of water, oil and a surfactant is measured, the surfactant seriously interferes with the water body and cannot accurately measure the oil content, and achieves the effect of accurately measuring the real value of the oil content in the water.

Description

Technical Field

[0001] The present invention belongs to the field of sewage analysis, and particularly relates to a method for determining the oil content in a three-phase system of water, oil, and surfactant. Background Art

[0002] Surfactant, also known as interfacial active agent, is a compound that can significantly reduce the surface tension or interfacial tension between two liquids, between a liquid and a gas, or between a liquid and a solid. Due to its existence, during the extraction process for measuring the oil content in water in the prior art, it is easy to produce an emulsified state in the extraction liquid, bringing in some surfactants, thus affecting the true value of the oil content in water and causing a large deviation in the result.

[0003] Chongqing Environmental Science published an article titled "Improvement of the Method for Measuring Oil Content in the Water-Oil-Surfactant System". It uses tannic acid for pretreatment to eliminate the influence of surfactants on the determination of oil content in water. However, the dosing node is difficult to control and the operation is complex. Summary of the Invention

[0004] In view of the problems in the above-mentioned prior art, the present invention provides a method for determining the oil content in a three-phase system of water, oil, and surfactant. This method can make the surfactant in the three-phase system of water, oil, and surfactant stably layer with the extraction liquid, obtain an accurate oil extraction layer, and thus obtain an accurate determination result.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A method for determining the oil content in a three-phase system of water, oil, and surfactant, comprising the following steps: (1) Collect a water sample to be measured in the three-phase system of water, oil, and surfactant and record the total amount of the water sample to be measured. Add an extractant to the water sample to be measured to form an extraction system; (2) Add anhydrous sodium sulfate and anhydrous magnesium sulfate to the extraction system, shake and mix evenly, and then let it stand to form a layer. Take the upper extraction liquid phase; (3) Use the drying weight method or an infrared oil analyzer to measure the weight or concentration of the oil in the extraction liquid phase, and calculate the oil content in the water sample to be measured.

[0006] Preferably, the oil content in the water sample to be measured is above 0.06 mg / L.

[0007] More preferably, when the oil content in the water sample to be measured is between 0.06 mg / L and 10 mg / L, in step (3), an infrared oil analyzer is used for measurement; when the oil content in the water sample to be measured is above 10 mg / L, in step (3), the drying weight method or an infrared oil analyzer is used for measurement.

[0008] Preferably, the extractant described in step (1) is petroleum ether or tetrachloroethylene.

[0009] More preferably, when the extractant described in step (1) is petroleum ether, the drying weight method is used for determination in step (3); when the extractant described in step (1) is tetrachloroethylene, an infrared oil analyzer is used for determination in step (3).

[0010] Preferably, the pH of the water sample to be measured in step (1) is below 2.

[0011] Preferably, based on the volume of the water sample to be measured in step (2), the addition amount of anhydrous sodium sulfate is 56 g / L, and the addition amount of anhydrous magnesium sulfate is 24 g / L.

[0012] Preferably, in step (3), when using an infrared oil analyzer for determination, the absorbances are measured at wavelengths of 2930 cm -1 , 2960 cm -1 , 3030 cm -1 respectively, and the concentration of oil in the extraction liquid phase is calculated according to the correction coefficient (HJ 637-2018).

[0013] Preferably, in step (3), when using the drying weight method for determination, the extractant is removed by rotary evaporation from the extraction liquid, and then the remaining weight is measured, which is the weight of the oil (Fourth Edition of the Monitoring and Analysis Methods for Water and Wastewater).

[0014] The beneficial effects of the present invention are as follows: The present invention solves the problem that when measuring the oil content in a water body containing a three-phase system of water, oil, and surfactant, the surfactant seriously interferes with the measurement and the accurate measurement cannot be achieved, and achieves the effect of accurately measuring the true value of the oil content in water.

[0015] The present invention utilizes the strong water absorption and high ionization characteristics of the sodium-magnesium mixture to destroy the potential bridge balance between the surfactant and the oil substances, and absorb the excess water carried by the surfactant, so as to achieve the purest oil extraction layer. Description of the Drawings

[0016] Figure 1 It is the appearance diagram of the sample in Example 1, where the left figure is the original water sample to be measured, the middle figure is the petroleum ether extraction system, and the right figure is the tetrachloroethylene extraction system.

[0017] Figure 2 It is the appearance diagram of the two-phase system in Example 1.

[0018] Figure 3 It is the photo of the white substance obtained after treating Sample 1 in Example 1.

[0019] Figure 4 It is the layered appearance diagram of the samples in Example 1, where the left figure is sample 6 and the right figure is sample 8.

[0020] Figure 5 It is the layered appearance diagram of sample 2 in Example 1. Detailed implementation manners Example 1

[0021] (1) Taking the drainage water at the project site as the sample to be measured, the oil content is theoretically calculated based on the loss amount of oil at the site and the total generated water volume, and the calorific value calculated by the combustion method in the subsequent process also verifies that the oil content in this water body conforms to the theoretical value.

[0022] The water sample to be measured is divided into 8 parallel samples, and the volume of each sample is recorded as 100 ml. Then, petroleum ether (sample 1), petroleum ether (sample 2), petroleum ether (sample 3), tetrachloroethylene (sample 4), tetrachloroethylene (sample 5), petroleum ether (sample 6), petroleum ether (sample 7), and petroleum ether (sample 8) are added respectively to form an extraction system, and the added amount of tetrachloroethylene in each sample is recorded.

[0023] The appearances of the original water sample to be measured, the extraction system with petroleum ether added, and the extraction system with tetrachloroethylene added are as Figure 1 shown.

[0024] Using the petroleum ether layer and the water layer that absorb oil substances to configure a two-phase system, it can be seen from Figure 2 that in the two-phase system without surfactant, the water and oil layers can form a transparent and clear layer. While in the three-phase system of water, oil, and surfactant, the extraction liquid is in an emulsified state and cannot form a clear layer.

[0025] After sample 1 is shaken and extracted with petroleum ether, the lower water layer is removed, and the upper emulsified petroleum ether extraction layer is taken. After dehydration with anhydrous sodium sulfate, filtration, evaporation, and drying, a solid-like substance appears at the bottom of the beaker, as Figure 3 shown, which is surfactant rather than oil substances. After the oil substances are dried, they should be in a flowing and thick state.

[0026] This is because one end of the surfactant is a hydrophilic polar group and the other end is a lipophilic non-polar group, which can reduce the oil-water boundary and promote the uniform dispersion and mutual solubility of water and oil.

[0027] The extractants tetrachloroethylene and petroleum ether can both form stable emulsions or dispersions with some surfactants. If an emulsified state is formed, it indicates that the surfactant in this water sample can be extracted by this extractant, and there is interference in the extraction process.

[0028] The residue after drying after treatment with the emulsified extract also demonstrated the influence of surfactants in the extraction process, resulting in significantly higher apparent oil content data.

[0029] (2) Add 5.6 g and 6.4 g of anhydrous sodium sulfate and 2.4 g and 1.6 g of anhydrous magnesium sulfate to Samples 2 and 4, respectively; add 6.5 g of anhydrous sodium sulfate to Samples 3 and 5, respectively; add 2.4 g of tannic acid to Sample 6; add 6 g of anhydrous calcium chloride to Sample 7; and add 8 g of anhydrous magnesium sulfate to Sample 8. Then, shake to mix and allow to stand to separate into layers.

[0030] (3) For samples 2, 3, 6 to 8, the weight of the oil was determined using the drying weight method. The weight of the oil was then substituted into the recorded amount of the water sample to be tested to obtain the oil content.

[0031] The oil concentration of samples 4 and 5 was measured using an infrared oil meter, and the amount of tetrachloroethylene used and the amount of water sample to be tested were substituted to perform the technique to obtain the oil content.

[0032] The measurement results are shown in Table 1:

[0033] Sample Oil content (mg / L) Theoretical value 2,103 Sample 5 (Infrared method, monosodium) 27,247 Sample 3 (Gravimetric method, monosodium) 16,391 Sample 4 (Infrared method (treatment of sodium-magnesium mixture)) 2,174 Sample 2 (Gravimetric method (treatment of sodium-magnesium mixture)) 2,257 Sample 6 (Gravimetric method (treatment with tannic acid)) 1,870 Sample 7 (Gravimetric method (treatment with anhydrous calcium chloride)) It is impossible to clearly layer to obtain the extract Sample 8 (Gravimetric method (treatment with anhydrous magnesium sulfate)) 379 From Table 1, Figure 4 It can be seen that when the infrared method is used to determine the oil content of the water sample and only anhydrous sodium sulfate is used for water absorption treatment, the data is high due to the emulsification of the extraction layer during the extraction process.

[0034] When the gravimetric method is used to determine the oil content of the water sample and only anhydrous sodium sulfate is used for water absorption treatment, there is also an emulsification phenomenon in the extraction layer during the extraction process, and after evaporation and drying, there is a solid substance similar to salt accumulation remaining, resulting in a higher oil content data.

[0035] like Figure 4 , 5 As shown in the figure, if tannic acid is added to the extract, the emulsified state of the extraction layer can be destroyed, forming a stratified state; magnesium sulfate treatment has a certain separation effect, but the effect is poor, and there is very little extract in the upper layer of the stratification, resulting in a low result; adding anhydrous sodium sulfate and anhydrous magnesium sulfate to the emulsified extract at the same time and shaking it appropriately can also achieve the effect of destroying the emulsified state of the extraction layer and forming a stratified state.

[0036] For wastewater in the three-phase system of water, oil and surfactant, during the determination of oil content, the surfactant it contains will cause abnormal extraction phenomena in both the infrared method and the weight method, making the results biased high.

[0037] In the treatment of emulsified petroleum ether extraction liquid, both tannic acid and sodium-magnesium mixture can cause the petroleum ether to layer again. The upper layer is the clear liquid extracted by petroleum ether, and the lower layer is the surfactant layer. The upper clear liquid can be separated and taken for determination by gravimetry or infrared method to obtain the oil content.

[0038] During the pretreatment process, the operation of treating with sodium-magnesium mixture is more simple and rapid than that with tannic acid. Moreover, the flocculent layer formed by tannic acid is thicker, which easily leads to incomplete extraction of the petroleum ether layer and results in a lower result.

Claims

1. A method for determining the oil content in a three-phase system of water, oil and surfactant, characterized in that: The steps include: (1) collecting a water sample to be tested of a three-phase system of water, oil and surfactant and recording the total amount of the water sample to be tested, and adding an extractant to the water sample to form an extraction system; (2) adding anhydrous sodium sulfate and anhydrous magnesium sulfate to the extraction system, oscillating and mixing, and then standing to form layers, and taking the upper layer of the extract; (3) The weight or concentration of the oil in the extract phase is measured by a drying weight method or an infrared oil measuring instrument, and the oil content in the water sample to be tested is calculated.

2. The measuring method according to claim 1, characterized in that The oil content in the water sample to be tested is above 0.06 mg / L.

3. The measuring method according to claim 2, characterized in that When the oil content in the water sample to be tested is between 0.06 mg / L and 10 mg / L, an infrared oil measuring instrument is used for determination in step (3); when the oil content in the water sample to be tested is above 10 mg / L, a drying weight method or an infrared oil measuring instrument is used for determination in step (3).

4. The measuring method according to claim 1, characterized in that The extractant in step (1) is petroleum ether or tetrachloroethylene.

5. The measuring method according to claim 4, characterized in that When the extractant described in step (1) is petroleum ether, the drying weight method is used in step (3); when the extractant described in step (1) is tetrachloroethylene, the infrared oil measuring instrument is used in step (3).

6. The measuring method according to claim 1, characterized in that The pH of the water sample to be tested in step (1) is below 2.

7. The measuring method according to claim 1, characterized in that In step (2), based on the volume of the water sample to be tested, the amount of anhydrous sodium sulfate added is 56 g / L, and the amount of anhydrous magnesium sulfate added is 24 g / L.

8. The measuring method according to claim 1, characterized in that In step (3), when using an infrared oil meter to measure, the wavelength of 2930cm -1 、2960cm -1 、3030cm -1 The absorbance of each is measured, and the concentration of the oil in the extract phase is calculated based on the correction factor.

9. The measuring method according to claim 1, characterized in that In step (3), when the drying weight method is used for determination, the extract is evaporated to remove the extractant, and then the remaining weight is measured, which is the weight of the oil.

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