An extraction method capable of removing elemental sulfur from oils in marine sediments

Abstract

The present invention relates to an extraction method capable of removing elemental sulfur from oil in marine sediments, which includes: weighing 1 g - 2 g of air-dried or freeze-dried marine sediment samples and adding them into a brown screw-cap glass bottle, adding copper powder, anhydrous sodium sulfate, and 20 mL of n-hexane, and sealing the brown screw-cap glass bottle with a polytetrafluoroethylene gasket; after vortex mixing, ultrasonically treat it in a water bath for 20 min, take it out and vortex mix it, vortex mix it again after an interval of 1 h, and perform the operation continuously for 4 times, then let it stand for 19 - 24 h, vortex mix the solution after standing again, after centrifugation, take the supernatant and directly detect it by ultraviolet spectrophotometry. In this application, a polytetrafluoroethylene solid is used as a gasket for sealing. On the basis of avoiding contamination, the volatilization of n-hexane is controlled, which is beneficial to long-term extraction without volume correction, can remove the influence of elemental sulfur in a short time, and at the same time improves the single extraction efficiency of oil, ensures the synchronous development of the removal of elemental sulfur in sediments and the extraction of oil, and improves work efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of marine environmental detection, and particularly relates to an extraction method capable of removing elemental sulfur in marine sediment oil. Background Art

[0002] The detection of oil in marine sediments is an important indicator in the evaluation of the environmental quality of marine sediments, and the detection results reflect the impact of human activities on the marine environment. The three current determination methods for oil in the "Marine Monitoring Specifications - Part 5: Sediment Analysis" (GB 17378.5 - 2007) are: fluorescence spectrophotometry, ultraviolet spectrophotometry, and gravimetry.

[0003] Fluorescence spectrophotometry is the arbitration method. It utilizes the fluorescence emission characteristics of the aromatic components of oil. The fluorescence intensity excited at 310 nm and emitted at 360 nm is proportional to the concentration of the extract. This method has high sensitivity and good selectivity, but the disadvantage is that the universality of the instrument is relatively low, and the types of oils that can be determined are limited.

[0004] Both ultraviolet spectrophotometry and gravimetry use n - hexane to extract oil in sediments. Ultraviolet spectrophotometry utilizes the fact that the absorbance of aromatic components in sediments at 225 nm is proportional to the aromatic content, and uses standard oil as a reference to calculate the oil content; gravimetry is to calculate by weighing after distilling off n - hexane. This method has cumbersome operations, low sensitivity, and a high detection limit (>20 mg / kg). Therefore, ultraviolet spectrophotometry is often used for the detection of oil in sediments in marine environmental monitoring.

[0005] There is an extremely complex sulfur cycle process in marine sediments, which is driven by the anaerobic microbial sulfate reduction process. The first - reduced sulfide generates relatively stable elemental sulfur intermediate products in a series of oxidation processes, resulting in the widespread presence of elemental sulfur in the anaerobic sediment environment. The content of elemental sulfur is generally higher than 100 mg / kg in productive sea areas. The n - hexane used for the extraction of oil in marine sediments can quickly dissolve elemental sulfur in sediments, and elemental sulfur has a strong absorption at 225 nm and a response sensitivity nearly twice that of the HJ oil standard, as shown in Figure 1 shown. Therefore, when conducting oil detection in an unpolluted marine environment, the presence of elemental sulfur significantly affects the determination of oil, as shown in Figure 3 shown. Summary of the Invention

[0006] To overcome the above - mentioned deficiencies, the purpose of the present invention is to provide an improved extraction method for marine sediment oil that can eliminate the influence of elemental sulfur, and solve the problem that the elemental sulfur, which is an intermediate product generated by the sulfur cycle process in marine sediments, has a significant impact on the ultraviolet detection method for oil content.

[0007] The technical solution adopted by the present invention to solve its technical problems is: an extraction method capable of removing elemental sulfur in marine sediment oil, including:

[0008] Step 1: Weigh 1 g - 2 g of air-dried or freeze-dried marine sediment sample and add it to a brown screw-cap glass bottle. Add copper powder, anhydrous sodium sulfate, and 20 mL of n-hexane, and seal the brown screw-cap glass bottle with a polytetrafluoroethylene gasket.

[0009] Step 2: After vortex mixing, ultrasonicate in a water bath for 20 min. Take it out and vortex mix. After an interval of 1 h, vortex mix again. Operate continuously 4 times, and then let it stand for 19 - 24 h.

[0010] Step 3: Vortex mix the solution after standing again. After centrifugation, take the supernatant and directly detect it by ultraviolet spectrophotometry.

[0011] Specifically, in Step 1, using a 1-mm-thick polytetrafluoroethylene solid as a gasket for sealing can ensure the control of n-hexane volatilization within 90 days without volume correction. In the actual experimental process, experiments were continuously carried out for 90 days, and finally the n-hexane volatilization was less than 0.5%.

[0012] Specifically, in Step 1, add 0.1 g of copper powder. The copper powder is 200 - 300 mesh, and the amount of copper powder can eliminate the influence of elemental sulfur with a content of less than 2000 mg / kg in the sediment.

[0013] Specifically, in Step 1, add 0.5 g of anhydrous sodium sulfate. Anhydrous sodium sulfate can catalyze the reaction between unactivated copper powder and elemental sulfur, and can also remove the moisture in the reaction bottle.

[0014] Specifically, in Step 2, vortex mix from time to time within the first 5 h to mix the sample, which is beneficial to the uniform mixing and reaction of copper powder and elemental sulfur in the sediment, is also beneficial to the reaction of copper powder and elemental sulfur dissolved in n-hexane, and is also beneficial to improving the oil extraction efficiency.

[0015] Specifically, in Step 2, let it stand for 19 - 24 h, which helps the copper powder continue to react with the remaining elemental sulfur until there is no influence on ultraviolet absorption, and is also beneficial to improving the oil extraction efficiency.

[0016] Specifically, in Step 3, centrifuging at 2500 rpm for 5 min can reduce the influence of sediment and copper powder particles on the absorbance measurement and avoid glass breakage caused by too high a centrifugation rate.

[0017] The beneficial effects of the present invention are as follows: the polytetraethylene entity is used as a gasket for sealing in the present application, and the volatilization of n-hexane is controlled on the basis of avoiding pollution, which is conducive to long-term extraction without volume correction; the unactivated copper powder can accelerate the reaction with sulfur element in n-hexane solvent under the catalysis of solid salts such as anhydrous sodium sulfate; the water bath ultrasound, occasional stirring within the first 5 hours and long-term static effect are fully utilized to eliminate the influence of sulfur element within 24 hours; at the same time, the single extraction efficiency of oil is also improved, ensuring that the removal of sulfur element in sediments and oil extraction are carried out simultaneously, thereby improving work efficiency and enabling large-scale batch detection of samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the ultraviolet absorption spectrum of n-hexane solution of sulfur and HJ oil standard at 200nm~400nm, where the solid line is 10mg / L HJ oil standard solution and the dotted line is 10mg / L sulfur solution.

[0019] Figure 2 Schematic diagram of three typical sea area sample sampling stations of the present invention.

[0020] Figure 3 It is a gas chromatography detection spectrum of sulfur element in n-hexane extract in the prior art, wherein spectrum a is a 10 mg / L high-purity sulfur element solution; and spectra b and c are extracts with high oil content in the original extraction method in Xinghua Bay and Minjiang Estuary, respectively.

[0021] Figure 4 This is a comparative schematic diagram of the determination of the oil content in sediments in the northern waters of Dayushan Island using different extraction methods in the examples.

[0022] Figure 5 The figure is a comparative schematic diagram of the oil content in the sediments of the Minjiang Estuary using different extraction methods in the examples.

[0023] Figure 6 This is a comparative schematic diagram of the oil content in sediments of Xinghua Bay using different extraction methods in the examples. DETAILED DESCRIPTION

[0024] The present invention will now be described in further detail with reference to the accompanying drawings.

[0025] 1. Material preparation

[0026] 1.1 Reagents: high-purity sulfur (Sinopharm Chemical Reagent Co., Ltd.), anhydrous sodium sulfate (analytical grade, Sinopharm Chemical Reagent Co., Ltd.), n-hexane (chromatographic grade, Sigma-Aldrich), copper powder (200 mesh, analytical grade, Sinopharm Chemical Reagent Co., Ltd.).

[0027] 1.2 Standard Substance: GBW(E)080913 HJ Oil Standard (National Marine Environmental Monitoring Center).

[0028] 1.3 Main Instruments and Equipment for the Experiment: EYEL4 MMV-1000W Extraction Oscillator; Shumei KQ-1500E Ultrasonic Cleaner; Leici HY-2 Vortex Mixer; Xiangyi TG16-WS Desktop High-Speed Centrifuge; Shimadzu UVmini-1280 UV-Visible Spectrophotometer; Agilent 6890N Gas Chromatograph (μECD Detector).

[0029] 2. Sample Collection and Preparation

[0030] During October 2021, surface marine sediment samples were collected from 60 stations in the northern waters of Dayaoshan Island (22 stations), the Minjiang Estuary waters (13 stations), and the Xinghua Bay waters (25 stations) (see the sampling station schematic diagram in Figure 2 ). The samples were spread out on ceramic plates, air-dried for 5-6 days under natural conditions, ground, and passed through an 80-mesh sieve, and then reserved for use as test samples.

[0031] 3. Oil Extraction Method in Samples

[0032] 3.1 According to the original extraction method in the ultraviolet spectrophotometry method in "Marine Monitoring Specifications - Part 5 Sediment Analysis (GB 17378.5-2007)", the specific steps are as follows:

[0033] Weigh about 1.0 g (accuracy 0.0001 g) of the sample, add it to a 50 mL glass colorimetric tube, add 10 mL of chromatographic pure n-hexane, oscillate and extract for 2 min, then let it stand for layer separation. The upper extraction solution is transferred to a 125 ml separatory funnel containing 20 mL of 30 g / L Na2SO4 solution; repeat the extraction once and combine the extraction solutions; finally, add 10 mL of 30 g / L Na2SO4 solution to the sediment, let it stand for layer separation, and transfer the separated extraction solution to the separatory funnel.

[0034] The extraction solution in the separatory funnel is oscillated for 2 min and then allowed to stand for layer separation, and the aqueous phase is discarded; then the extraction solution is repeatedly washed 2 times with 20 mL of 30 g / L Na2SO4 solution, and then the extraction solution is transferred to a 25 mL graduated colorimetric tube and made up to 20 mL; during the sample extraction process, a reagent blank is prepared simultaneously.

[0035] 3.2 Extraction method of the improved ultraviolet detection method for oils in marine sediments, the specific steps are as follows:

[0036] Weigh about 1.0 g (with an accuracy of 0.0001 g) of the sample and add it to a 30 mL screw-cap glass tube. Then, weigh 0.1 g of 2.7N 200-mesh copper powder of the Shanghai Test brand from the Sinopharm Chemical Reagent Co., Ltd. and 0.5 g of analytical pure anhydrous sodium sulfate respectively and add them to the 30 mL screw-cap glass tube. Subsequently, use a burette dispenser to add 20 mL of n-hexane solution that has been subjected to de-aromatization treatment. Finally, use a 1 mm thick polytetrafluoroethylene solid as a gasket to seal the screw-cap glass tube, and at the same time, use a sample that has been ashed at 500 °C for 3 h to replace the sample to prepare a reagent blank.

[0037] Use a vortex mixer to mix the sample evenly, and then place it in a water bath and ultrasonicate for 20 min. After the ultrasonication is completed, take out the sample, use a towel to remove the moisture on the outer wall, vortex mix it again, and then let it stand. Mix it once every 1 h and then let it stand, and operate continuously 4 times. Finally, let it stand for 16 - 21 h.

[0038] After the oil is extracted by ultrasonic, vortex mixing, and standing for about 24 h, vortex mix it once again, centrifuge at 2500 rpm for 5 min, and the supernatant is the extract.

[0039] 4. Determination of oil in the sample

[0040] Respectively pipette 0 μL, 40 μL, 80 μL, 120 μL, 160 μL, 200 μL of the HJ oil standard, and make up the volume to 20 mL with n-hexane to obtain the HJ oil standard working series of 0 mg / L, 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, 10 mg / L. The absorbance of the standard solution and the sample extract is measured at 225 nm using a 1 cm cuvette.

[0041] Evaluate the oil extraction coefficient for the original extraction method and the improved extraction method respectively. Weigh 9 portions of 1.0 g of the sample not contaminated with oil for each method, add 100 μL of the HJ oil standard to 6 of them, and carry out sample extraction and determination. Determine the oil extraction efficiency coefficient through the ratio of the measured value to the theoretical value after adding the standard.

[0042] Under the conditions of considering the moisture content of the air-dried sample and the oil extraction efficiency coefficient, calculate the oil content in the dry sample of the sample according to formula (1).

[0043]

[0044] In the formula:

[0045] ω oil —— Oil content in the dry sediment sample (unit: 10-6);

[0046] ρ —— Oil content in the extract (unit: mg / L);

[0047] V—the volume of the extractant (unit: mL);

[0048] K—the extraction efficiency coefficient;

[0049] M—the weighed sample amount of the sediment (unit: g);

[0050] —the moisture content in the air-dried sample.

[0051] 5. Qualitative detection of sulfur in the extractant of the original extraction method

[0052] Use n-hexane to dissolve high-purity sulfur and prepare a sulfur standard series of 0.0 mg / L, 5.0 mg / L, 10.0 mg / L, 20.0 mg / L, and 30.0 mg / L; detect the sulfur standard and the sample extractant using gas chromatography.

[0053] The gas chromatography conditions are as follows: inject 1 μL, the injection port temperature is 180 °C, splitless injection; HP-5 (30 m × 0.32 mm, 0.25 μm) quartz capillary column, carrier gas (high-purity nitrogen) 70 mL / min, column head pressure 28 psi; the column temperature is 100 °C, hold for 0.5 min, rise to 180 °C at 40 °C / min, and hold for 7 min; the detector temperature is 250 °C.

[0054] 6. Results

[0055] The following table shows the comparison of the results obtained after treating samples of oils in sediments from 3 typical sea areas in the coastal waters of Fujian using the original extraction method and the improved extraction method of the present invention by ultraviolet spectrophotometry.

[0056]

[0057]

[0058] As can be seen from the above table, the improved extraction method of the present invention has little influence on the extraction efficiency coefficient of oils, but can significantly reduce the influence of sulfur in sediments on the determination of oils, resulting in an average reduction in the oil content between 91.2% and 98.6%.

[0059] Sulfur is produced during the anaerobic degradation of sediment organic matter and widely exists in muddy sediments. It is clearly found through gas chromatography detection that sulfur widely exists in the extractant of the original extraction method, especially in samples with high crude oil content, where the sulfur content is the highest, approaching 30 mg / L (as Figure 3 shown).

[0060] By comparing the oil content distributions of the two methods, it can be seen that the present invention can more effectively evaluate the oil pollution area and pollution amount, such as Figure 4 , 5, as shown in Figure 6, is a comparative schematic diagram of measuring the oil content in sediments in the northern sea area of Dazhushan Island, the Minjiang Estuary sea area, and the Xinghua Bay sea area using different extraction methods.

[0061] The present invention is not limited to the described embodiments. Any person should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, fall within the protection scope of the present invention.

[0062] The technologies, shapes, and structures not detailedly described in the present invention are all well-known technologies.

Claims

1. An extraction method capable of removing elemental sulfur from oil in marine sediments, characterized in that: Including: Step 1: Weigh 1 g - 2 g of air-dried or freeze-dried marine sediment samples and add them into a brown screw-cap glass bottle. Add 0.1 g of copper powder, 0.5 g of anhydrous sodium sulfate, and 20 mL of n-hexane. The copper powder is of 200 - 300 mesh and the brown screw-cap glass bottle is sealed with a PTFE gasket; Step 2: After vortex mixing, ultrasonicate in a water bath for 20 min. Take it out and vortex mix. Vortex mix again after an interval of 1 h, and perform the operation continuously for 4 times. Then let it stand for 19 - 24 h; Step 3: Vortex mix the solution after standing again. After centrifugation, take the supernatant and directly detect it by ultraviolet spectrophotometry.

2. The extraction method for removing elemental sulfur from oil in marine sediments according to claim 1, characterized in that: In Step 1, a 1-mm-thick PTFE solid is used as the gasket for sealing.

3. An extraction method capable of removing elemental sulfur from oil in marine sediments according to claim 1, characterized in that: In Step 3, the parameters of the centrifugation treatment are 2500 rpm and centrifugation for 5 min.

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