A method for determining chlorinated terphenyls in heavy oil products

Abstract

The present invention relates to a method for determining chlorinated terphenyls in heavy oil products, the method comprising the following steps: S1. performing vacuum distillation on the heavy oil products to collect light components; S2. the light components collected in step S1 are passed through a solid phase extraction column, eluted with a petroleum ether 60-90 / cyclohexane mixed solution, and then eluted with a toluene / dichloromethane mixed solution to obtain a sample to be tested; S3. based on an internal standard method, nickel is used as a catalyst, online catalysis is used to dechlorinate and hydrogenate the sample to be tested, and gas chromatography-tandem mass spectrometry is used for analysis to obtain the content of chlorinated terphenyls in the heavy oil product. The method can detect chlorinated terphenyls in heavy oil products without using high-resolution mass spectrometry, with high sensitivity, accuracy, stability and precision.

Description

Technical Field

[0001] The invention relates to the field of detection technology, and more specifically to a method for determining chlorinated terphenyls in heavy oil products. Background Art

[0002] A certain amount of chlorinated aromatics may be present in heavy oil products such as diluted asphalt and residual fuel oil. The reason is that mineral fuel oil contains chlorinated chemical additives, which may be partially converted into chlorinated aromatics during the distillation and catalytic cracking of mineral fuel oil and remain at the bottom of the kettle. After being diluted with solvents, they migrate to heavy oil products such as diluted asphalt or residual fuel oil. On the other hand, chlorinated aromatics have long been widely used in insulation and flame retardant fields such as electricity, chemicals, plastics, and printing, and are often used as insulating oils and flame retardants. This also leads to a certain amount of chlorinated aromatics in heavy oil products such as diluted asphalt and residual fuel oil.

[0003] Chlorinated aromatic hydrocarbons are a general term for organochlorine aromatic hydrocarbons formed by replacing several hydrogen atoms on the benzene ring of aromatic hydrocarbons with chlorine atoms. They are a type of artificially synthesized persistent organic pollutants. So far, many isomers have been found. As the number of carbon atoms or benzene rings continues to increase, the number of chlorine-containing isomers increases dramatically, making it difficult to find accurate standard substances for corresponding measurements.

[0004] Chlorinated terphenyls are one type of chlorinated aromatic hydrocarbons, which not only easily cause corrosion risks to engines, but are also stable and difficult to decompose. They degrade slowly in nature and will eventually remain in various environmental media. Moreover, they are easily accumulated in adipose tissue, have the characteristics of high enrichment, high carcinogenicity and high teratogenicity, and have obvious toxic effects on the human body. They have obvious adverse effects on children's growth and neurological development. Therefore, it is necessary to detect chlorinated terphenyls in heavy oil products.

[0005] At present, the analysis of chlorinated aromatics reported at home and abroad is mainly determined by reference to standard substances. However, due to the wide variety of target homologues, there are certain challenges in both the qualitative determination of the target and the search for corresponding isomer compounds. In terms of pretreatment, different sample matrices are involved, and the pretreatment methods used are different in purification and extraction. However, there are no reports on the detection methods of chlorinated terphenyls in heavy oil products such as diluted asphalt and residual fuel oil. From the perspective of instrumental analysis methods, the most commonly used instrumental methods for the detection of chlorinated aromatics are gas chromatography, liquid chromatography, gas chromatography-quadrupole mass spectrometry, etc. Some researchers also use comprehensive two-dimensional gas chromatography, quadrupole time-of-flight mass spectrometry, ion trap tandem mass spectrometry and other high-resolution mass spectrometry to carry out detection research, mainly for highly toxic polychlorinated biphenyls or polychlorinated naphthalenes, and have achieved good results. Generally speaking, gas chromatography is the most popular method and can be used by most laboratories. However, it has the disadvantages of relatively high detection limit and insufficient precision. The chromatogram obtained after detecting polychlorinated biphenyl mixture (including chlorinated terphenyls) is as follows: Figure 1 As shown; the resolution of conventional gas chromatography-mass spectrometry techniques such as gas chromatography-quadrupole mass spectrometry is still insufficient, and the interference of other chlorinated hydrocarbons on chlorinated terphenyls cannot be ruled out, and the chlorinated terphenyls in heavy oil products cannot be accurately determined. The chromatogram obtained after the conventional gas chromatography-mass spectrometry technique is used to detect polychlorinated biphenyl mixtures (including chlorinated terphenyls) is as follows Figure 2 As shown; high-resolution mass spectrometry techniques such as ion trap tandem mass spectrometry and quadrupole time-of-flight mass spectrometry may be able to accurately determine chlorinated terphenyls in heavy oil products, but the requirements for instruments and equipment are high and it is difficult for general laboratories to meet them.

[0006] Therefore, there is an urgent need to develop a detection method that can detect chlorinated terphenyls in heavy oil products without using high-resolution mass spectrometry. Summary of the invention

[0007] The primary purpose of the present invention is to overcome the problem that there is still a lack of existing detection methods for chlorinated terphenyls in heavy oil products without using high-resolution mass spectrometry, and to provide a method for determining chlorinated terphenyls in heavy oil products. The method can detect chlorinated terphenyls in heavy oil products without using high-resolution mass spectrometry, with high sensitivity, accuracy, stability and precision.

[0008] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0009] A method for determining chlorinated terphenyls in a heavy oil product comprises the following steps:

[0010] S1. Vacuum distillation of heavy oil products to collect light components;

[0011] S2. The light component collected in step S1 is passed through a solid phase extraction column, washed with a 60-90% petroleum ether / cyclohexane mixed solution, and then eluted with a toluene / dichloromethane mixed solution to obtain a sample to be tested;

[0012] S3. Based on the internal standard method, nickel was used as a catalyst, and the sample to be tested was dechlorinated and hydrogenated using online catalysis, and analyzed by gas chromatography-tandem mass spectrometry to obtain the content of chlorinated terphenyls in the heavy oil product;

[0013] The temperature of the online catalysis is 200-245°C.

[0014] The method of the present invention adopts vacuum distillation-solid phase extraction-nickel-based online catalysis-gas chromatography-tandem mass spectrometry technology to measure the chlorinated terphenyls in the heavy oil product. Among them, the chlorinated terphenyls can be effectively separated from the heavy oil product by the combination of vacuum distillation, solid phase extraction, specific eluent and eluent. Then, dechlorination and hydrogenation are carried out under nickel catalysis and a specific temperature to convert the chlorinated terphenyls into characteristic dicyclohexylbenzenes (including 1,4-dicyclohexylbenzene and 1,3-dicyclohexylbenzene) through online dechlorination and hydrogenation, and then the content of chlorinated terphenyls (including chlorinated p-terphenyl and chlorinated m-terphenyl) in the heavy oil product is obtained after analysis by gas chromatography-tandem mass spectrometry. This method can detect chlorinated terphenyls in heavy oil products without using high-resolution mass spectrometry, and has high sensitivity, accuracy, stability and precision. Specifically, the linear correlation coefficients of the targets are all greater than 0.9955, which can well meet the needs of testing work. The detection limit can reach 0.3 μg / mL, the quantification limit can reach 1.0 μg / mL, the spiked recovery rate is between 93.7% and 108.6%, and the relative standard deviation is less than 6.3%.

[0015] Among them, the inventor of the present invention has found that the catalyst selected during online catalysis and the temperature of online catalysis are very critical, because chlorinated terphenyl can be mainly reduced to dicyclohexylbenzene with nickel as catalyst at a specific catalytic temperature, so that the determination target is changed from the isotope ions dispersed by polychlorinated hydrocarbons to concentrated high-response alkanes and aromatic hydrocarbon ions, further reducing interference and improving the detection limit. If other catalysts (such as palladium catalysts) are used, chlorinated terphenyl will crack to produce more bicyclohexane and phenylcyclohexane, which is difficult to distinguish from the reduction products of other non-target objects, thereby the chlorinated terphenyl in the sample cannot be detected. If the catalytic temperature is not suitable, chlorinated terphenyl will also crack to produce bicyclohexane and phenylcyclohexane, interfering with the quantitative determination of chlorinated terphenyl.

[0016] Preferably, in step S1, the temperature of the reduced pressure distillation is above 400°C; more preferably, 400-450°C.

[0017] Preferably, in step S1, the pressure of the reduced pressure distillation is 5 to 7 mbar.

[0018] In the present invention, petroleum ether 60-90 means that the initial distillation point of petroleum ether is not less than 60 degrees Celsius and the final distillation point is not higher than 90 degrees Celsius.

[0019] Preferably, in step S2, the volume ratio of petroleum ether 60-90 to cyclohexane in the petroleum ether 60-90 / cyclohexane mixed solution is 1:(0.8-1.2); more preferably 1:1.

[0020] Preferably, in step S2, the volume ratio of toluene to dichloromethane in the toluene / dichloromethane mixed solution is 1:(0.8-1.2); more preferably 1:1.

[0021] Preferably, in step S2, the solid phase extraction column is at least one of a silica gel solid phase extraction column or a silver nitrate-alumina solid phase extraction column.

[0022] Preferably, in step S3, the temperature of the online catalysis is 200-240°C.

[0023] Preferably, in step S3, the catalyst is a glass bead-supported nickel (metal) catalyst.

[0024] The use of glass bead-supported nickel catalysts can increase the specific surface area of ​​the active component (nickel) and improve the catalytic efficiency.

[0025] More preferably, the glass bead-supported nickel catalyst is prepared by the following method: nickel acetate is added to a solvent to dissolve to obtain a nickel acetate solution, the nickel acetate solution is mixed with dried activated glass beads, the solvent is volatilized, and then the nickel acetate is reduced to metallic nickel under hydrogen at 230 to 250° C. to obtain the glass bead-supported nickel catalyst.

[0026] Preferably, in step S3, the chromatographic column of the gas chromatography in the gas chromatography-tandem mass spectrometry is a medium polarity (DB-5MS, DB-35MS) or weak polarity chromatographic column (DB-17MS).

[0027] More preferably, in step S3, the conditions of gas chromatography in the gas chromatography-tandem mass spectrometry include: the carrier gas is hydrogen; the collision gas is nitrogen; the chromatographic column flow rate is 1.0-1.5 mL / min; the inlet temperature is 240°C; the split ratio is 1:(1-10); the heating program: 40-45°C (maintained for 2-5 min), heating to 240-260°C at 15-20°C / min (maintained for 1-5 min), and finally rapidly heating to 300-320°C at 30°C / min.

[0028] More preferably, the flow rate of the hydrogen is 1.0-1.8 mL / min.

[0029] Preferably, in step S3, the mass spectrometry conditions in the gas chromatography-tandem mass spectrometry are: electron bombardment ion source, energy 70eV; transmission line temperature: 300-320°C; ion source temperature: 230°C; the mass analyzer is a quadrupole, quadrupole temperature: 150°C; multiple reaction monitoring negative ion mode, solvent delay 3-5min.

[0030] Preferably, in step S3, the internal standard substance selected for the internal standard method is dodecylbenzene.

[0031] Preferably, the chlorinated terphenyl is at least one of chlorinated p-terphenyl or chlorinated m-terphenyl.

[0032] Preferably, the number of chlorine atoms substituted in each molecule of the chlorinated terphenyl is 1 to 14.

[0033] Preferably, the chlorinated terphenyl is at least one of pentachloro-p-terphenyl, tetradecachloro-m-terphenyl, Aroclor 5460, Aroclor 5442 or Aroclor 5432.

[0034] Preferably, the heavy oil product is at least one of diluted asphalt or residual fuel oil.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The method of the present invention adopts vacuum distillation-solid phase extraction-nickel-based online catalysis-gas chromatography-tandem mass spectrometry technology to determine the chlorinated terphenyls in heavy oil products. The method can detect the chlorinated terphenyls in heavy oil products without using high-resolution mass spectrometry, with high sensitivity, accuracy, stability and precision; specifically, the linear correlation coefficients of the target objects are all greater than 0.9955, which can well meet the needs of the test work; the detection limit can reach 0.3μg / mL, the quantitative limit can reach 1.0μg / mL, the spike recovery rate is between 93.7% and 108.6%, and the relative standard deviation is less than 6.3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The chromatogram is obtained by analyzing a polychlorinated biphenyl mixture (including chlorinated terphenyls) using the existing gas chromatography method.

[0038] Figure 2 It is a total ion current chromatogram obtained after analyzing a polychlorinated biphenyl mixture (including chlorinated terphenyls) using existing gas chromatography-quadrupole mass spectrometry.

[0039] Figure 3 This is the total ion current chromatogram of the online catalytic chlorinated terphenyl compounds of Example 1 using gas chromatography-tandem mass spectrometry multiple reaction monitoring.

[0040] Figure 4 This is a graph showing the effect of reduced pressure distillation temperature on the total extraction efficiency of polychlorinated terphenyls 5460.

[0041] Figure 5 This is a graph showing the effect of online catalytic temperature on the content of catalytic products from dechlorination and hydrogenation of chlorinated terphenyls.

[0042] Figure 6 This is the full scan mass spectrum of dicyclohexylbenzene.

[0043] Figure 7 This is the full scan mass spectrum of the internal standard (dodecylbenzene). DETAILED DESCRIPTION

[0044] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0045] The information of the instruments and reagents used in each embodiment of the present invention is as follows:

[0046] (1) Instruments and reagents (all reagents were of analytical grade unless otherwise specified)

[0047] Gas chromatography tandem mass spectrometer: Agilent 7890B-7000C triple quadrupole tandem mass spectrometer;

[0048] Single cone liner: inner diameter 4mm;

[0049] Silica gel solid phase extraction cartridge: RIPP, (6 mL, 1 g): Activate with 0.5 mL of n-hexane before use and keep moist;

[0050] Glass beads: 60~80 mesh;

[0051] Chlorinated terphenyl standard stock solution: 1000 μg / mL, Aroclor 5460;

[0052] 1,4-Dicyclohexylbenzene standard: purity ≥95%;

[0053] 1,3-Dicyclohexylbenzene standard: purity ≥95%;

[0054] Dodecylbenzene standard: purity ≥99%

[0055] n-Hexane: pesticide residue grade; acetone: analytical grade; ether: analytical grade; toluene: chromatographic grade; nickel acetate: chromatographic grade; calcium carbonate: chromatographic grade.

[0056] (2) Standard working solution

[0057] 1) Internal standard intermediate solution: a) Accurately weigh an appropriate amount of dodecylbenzene standard, prepare an internal standard stock solution of 100 μg / mL with toluene, store below 4°C for later use. b) Accurately weigh an appropriate amount of internal standard stock solution, prepare an intermediate solution of 10 μg / mL with toluene, store below 4°C for later use.

[0058] 2) Chlorinated terphenyl standard working solution: a) Accurately measure an appropriate amount of chlorinated terphenyl standard stock solution, prepare a 100μg / mL chlorinated terphenyl standard intermediate solution with toluene, and store it below 4°C for later use. b) Accurately pipette an appropriate amount of chlorinated terphenyl standard intermediate solution and internal standard intermediate solution, dilute to the mark with toluene, and prepare a 10μg / mL standard working solution, in which the internal standard content is 1μg / mL.

[0059] 3) Dicyclohexylbenzene standard working solution: a) Accurately measure an appropriate amount of dicyclohexylbenzene standard stock solution, and prepare a dicyclohexylbenzene standard intermediate solution with a concentration of 100 μg / mL with toluene, and store it below 4°C for later use. b) Accurately pipette an appropriate amount of dicyclohexylbenzene standard intermediate solution and internal standard intermediate solution, dilute to the scale with toluene, and prepare standard working solutions with concentrations of 1 μg / mL, 2 μg / mL, 5 μg / mL, 10 μg / mL, and 20 μg / mL, and the internal standard content is 1 μg / mL.

[0060] Unless otherwise specified, the operating conditions in the embodiments and comparative examples of the present invention are as follows:

[0061] (1) Preparation of catalyst and reaction liner

[0062] 1) Preparation of nickel / glass bead catalyst precursor:

[0063] Weigh 2 g of glass beads into a headspace bottle, add 10 mL of 0.1 mol / L hydrochloric acid solution, stir thoroughly and ultrasonicate for 10 min, then wash with deionized water, filter and dry at 100 °C to obtain activated glass beads, place in a desiccator for standby use.

[0064] Weigh 0.01g of nickel acetate into a headspace bottle, add 10mL of acetone and stir ultrasonically to dissolve, and set aside. Transfer the dried activated glass beads obtained above to an 80mm watch glass, add the nickel acetate solution dissolved in acetone, place in a 50°C water bath, stir continuously to evaporate the acetone to dryness, add an appropriate amount of acetone again to dissolve the nickel acetate, continue stirring to make it uniform and evaporate to dryness, and the glass beads will become uniformly light green. At this time, nickel acetate is evenly covered on the surface of the glass beads. Continue to dry the glass beads with nickel acetate attached to the surface for later use, and obtain the nickel / glass bead catalyst precursor.

[0065] 2) Preparation of reaction liner

[0066] Take a non-split single-taper liner, fill the bottom with deactivated glass wool, then add 1mm high calcium carbonate, 2mm high deactivated glass wool and 10mm high nickel / glass bead catalyst precursor from bottom to top, and finally cover it with a layer of about 2mm high deactivated glass wool. Install the liner into the gas chromatography injection port, activate it with hydrogen as carrier gas at 240℃ for 3h to obtain a reaction liner.

[0067] (2) Gas chromatography-tandem mass spectrometry conditions

[0068] Gas chromatography: chromatographic column: DB-5MS quartz capillary column specifications (30cm×0.25mm, 0.25μm); carrier gas: high-purity hydrogen; collision gas: high-purity nitrogen; column flow rate: 1.5mL / min; inlet temperature: 240℃; heating program: 45℃ (maintained for 2min), heated to 250℃ at 15℃ / min (maintained for 1min), and finally rapidly heated to 300℃ at 30℃ / min (maintained for 7min); injection volume: 1μL; injection mode: split injection, split ratio of 1:1; septum purge flow / mode: 3mL / min switch.

[0069] Mass spectrometry: electron impact ion source (EI), ion source temperature: 230°C, ionization energy: 70 eV; transfer line temperature: 300°C; ion source temperature: 230°C; mass analyzer is quadrupole, quadrupole temperature: 150°C; multiple reaction monitoring negative ion mode (MRM), solvent delay 5 min; run time: 25 min (post-run 0 min).

[0070] (3) Calculation method

[0071] The conversion factor of chlorinated terphenyl to dicyclohexylbenzene is calculated according to formula (1):

[0072]

[0073] In formula (1):

[0074] k – conversion factor;

[0075] X——molecular weight of dicyclohexylbenzene;

[0076] Y——molecular weight of chlorinated terphenyl;

[0077] z——chlorine content of chlorinated terphenyl (%);

[0078] 1.05——Correction factor.

[0079] The catalytic efficiency of chlorinated terphenyl in the sample was calculated according to formula (2):

[0080]

[0081] In formula (2):

[0082] r——catalytic efficiency (%);

[0083] C i ——The content of dicyclohexylbenzene in the quality control sample after catalysis, in micrograms per milliliter (μg / mL);

[0084] C s ——The concentration of the target compound in the sample is in micrograms per milliliter (μg / mL);

[0085] k – conversion factor;

[0086] The correction factors of two dicyclohexylbenzenes to the internal standard were calculated according to formula (3):

[0087]

[0088] In formula (3):

[0089] f——Correction factors of various dicyclohexylbenzenes to internal standards;

[0090] A i ——Peak area of ​​internal standard in standard working solution;

[0091] C i ——Concentration of internal standard in standard working solution, in milligrams per liter (μg / mL);

[0092] A s ——Peak areas of various dicyclohexylbenzenes in standard working solutions;

[0093] C s ——Concentration of various dicyclohexylbenzenes in the standard working solution, in milligrams per liter (μg / mL).

[0094] Calculate the content of chlorinated terphenyl in the sample according to formula (4):

[0095]

[0096] In formula (4):

[0097] X——the content of chlorinated terphenyls in the sample, in milligrams per kilogram (mg / kg);

[0098] f——Correction factor of target compound to internal standard;

[0099] C i ——The concentration of dicyclohexylbenzene in the sample, in micrograms per milliliter (μg / mL);

[0100] C i0——The concentration of dicyclohexylbenzene in the blank sample, in micrograms per milliliter (μg / mL);

[0101] V——sample solution fixed volume, in milliliters (mL);

[0102] DF——sample dilution factor;

[0103] M——sample mass, in grams (g);

[0104] k – conversion factor.

[0105] Example 1

[0106] This embodiment provides a method for determining chlorinated terphenyls in a heavy oil product, comprising the following steps:

[0107] 1) Vacuum distillation: Weigh 500.0 g of residual fuel oil products and carry out vacuum distillation in a 500 mL distiller to collect light components; the vacuum distillation temperature is 400° C. and the pressure is 5 mbar.

[0108] 2) Purification and elution: Take 50mL of the sample solution in step 1) and pass it through a silica gel solid phase extraction column. After it is fully absorbed by the column, add 2mL of a mixed solution of petroleum ether 60-90 / cyclohexane (volume ratio 1:1) to elute it. When the solution has completely passed through the extraction column sieve plate, discard the filtered eluent and replace the receiving bottle. Continue to add 5.0mL of a mixed solution of toluene / dichloromethane (volume ratio 1:1) to the solid phase extraction column for elution, collect the above eluent and transfer it to a headspace bottle, blow it almost dry with nitrogen, add 0.1mL of the internal standard intermediate solution, and dilute to toluene to obtain the test solution for determination.

[0109] 3) Using nickel / glass bead catalyst as catalyst, dechlorination and hydrogenation of the test solution in step 2) are performed by online catalysis (online catalytic temperature is 230°C; catalyst dosage is 2g; hydrogen flow rate is 1.5mL / min), and the test solution and standard working solution are measured by gas chromatography-mass spectrometry / mass spectrometry conditions. If the retention time of the mass chromatographic peak of the test solution is consistent with that of the standard, and all selected ion pairs should appear, then positive confirmation is performed based on the type of qualitative selected ion pairs and their relative abundance ratio. In qualitative analysis, if the relative abundance allowable deviation does not exceed the range specified in Table 1, it can be determined that the corresponding analyte exists in the sample.

[0110] Table 1 Maximum allowable deviation of relative ion abundance ratios for confirmation of positive results

[0111] Relative ion abundance / % >50 >20～50 >10～20 ≤10 Allowable relative deviation / % ±20 ±25 ±30 ±50

[0112] The blank test solution and method blank sample were injected in sequence, and after deducting the blank background, the chromatographic peak area of ​​chlorinated terphenyl compounds was obtained. Each solution was injected twice in parallel, and the average peak area was calculated. The operating conditions were ensured to be consistent throughout the determination process of the sample and the standard working solution, and the internal standard method was used for quantification.

[0113] Under the above experimental conditions, the total ion current chromatogram of the online catalytic chlorinated terphenyl compounds by gas chromatography-tandem mass spectrometry multiple reaction monitoring is shown in Figure 3 shown.

[0114] Example 2 Optimization of conditions

[0115] 1) Temperature of vacuum distillation

[0116] Weigh 500.0 g (accurate to 0.01 g) of heavy oil product in a 500 mL distiller, examine the reduced pressure temperatures of 300°C, 350°C, 400°C, and 450°C and record the evaporated mass. The total extraction efficiency of PCT 5460 is as follows: Figure 4 As shown. Figure 4 It can be seen that as the vacuum temperature increases from 300°C to 450°C, the extraction efficiency of the target product is significantly improved. When the temperature is 400°C, the recovery rate remains basically unchanged, and the recovery increase rate slows down. When the temperature continues to rise, the extraction recovery rate remains basically unchanged and reaches equilibrium. Therefore, 400°C is selected as the optimal vacuum distillation temperature.

[0117] 2) Optimization of purification and elution conditions

[0118] The presence of mineral oil, aliphatic hydrocarbons and other substances in the light components after vacuum distillation will interfere with subsequent detection. The experiment used a silica gel solid phase extraction column as a purification column, and selected four solvents: dichloromethane, toluene, cyclohexane, n-hexane, and petroleum ether 60-90 / cyclohexane (1+1) as eluents. The experiment used 1mL, 1.5mL, 2mL, 2.5mL, and 3mL of eluents to study the effect of elution degree. The results showed that dichloromethane and toluene were both highly polar, and they were easy to wash out the target and some polychlorinated compounds, so they were not suitable as eluents; the elution efficiency of n-hexane was low, and only some long-chain hydrocarbons could be washed out, and the elution of aromatic hydrocarbons was not sufficient; the elution efficiency of cyclohexane was higher than that of n-hexane, and some C8-C10 aromatic hydrocarbons could be washed out when eluted with the same volume, but the elution efficiency of cyclohexane for long-chain normal alkanes or long-chain base substances was lower than that of normal alkanes. Petroleum ether 60-90 / cyclohexane (1+1) has the best elution effect. It can not only wash out aliphatic saturated hydrocarbons and long-chain aromatic hydrocarbons, but also retain polychlorinated terphenyls in the purification column. Therefore, petroleum ether 60-90 / cyclohexane (1+1) was finally selected as the eluent.

[0119] After the sample is purified by eluting with petroleum ether 60-90 / cyclohexane (1+1), the target substance remaining on the extraction column needs to be eluted with a suitable elution solvent. Chlorinated aromatic hydrocarbons have a certain polarity due to the different chlorination positions on the carbon skeleton and can be eluted by chlorinated hydrocarbons, lipids, ethers, etc. Therefore, a mixed solvent (toluene / dichloromethane = 1+1 (V / V), toluene / ethyl ether = 1+1 (V / V), toluene / ethyl acetate = 1+1 (V / V) is selected as the elution solvent, and different volumes (1.5mL, 2mL, 2.5mL, 3mL, 3.5mL) of elution solvent are selected for the test. The recovery rate is measured using the above-mentioned chlorinated terphenyl standard working solution. Test. Two tests were conducted for each condition. The results showed that when the same volume of elution solvent was added, the elution effect of toluene / ethyl acetate mixture was average, with an average recovery rate of about 85%; the elution effect of toluene / ether mixture on chlorinated alkanes was better, reaching more than 90%, but the elution effect on chlorinated aromatics was average; and the recovery rate of toluene / dichloromethane mixture on chlorinated aromatics reached more than 95%. Finally, 2mL of toluene / dichloromethane (1:1) mixed solution was selected as the elution solvent.

[0120] 3) Effect of temperature on online catalytic efficiency

[0121] In order to explore the effect of injection port temperature on catalytic efficiency, the standard working solution of chlorinated terphenyl was tested at selected temperatures of 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, and 270℃. The experimental results are shown in Figure 2. Figure 5As shown in the figure, two kinds of polychlorinated terphenyls were reduced at different temperatures. From the relationship between the response peak area of ​​the reduction product and the catalytic temperature, it can be seen that the response of the chlorinated hydrocarbon product increases with increasing temperature, and the peak area is the highest at around 200-230℃. When the temperature is higher than 240℃, the peak area decreases. The reduction products of chlorinated terphenyl are relatively complex. In addition to being dechlorinated and hydrogenated to terphenyl and dicyclohexylbenzene, chlorinated terphenyl can also be further reduced to generate tercyclohexane. The reduction products of chlorinated terphenyl in the range of 200-240°C are tercyclohexane and dicyclohexylbenzene, with dicyclohexylbenzene being the main component (wherein, for tercyclohexane, whether it is para-tercyclohexane or meta-tercyclohexane, standard products of such compounds are not available on the market for the time being, which is not convenient for detection and calculation. Therefore, the content of chlorinated terphenyl is calculated through dicyclohexylbenzene based on the internal standard method). The peak area of ​​the reduction product is first directly proportional to the temperature; after exceeding 240°C, it becomes inversely proportional, because further increase in temperature will inhibit the formation of the reduction products tercyclohexane and dicyclohexylbenzene. When the temperature is around 250-270°C, it is further broken down and reduced to bicyclohexane and phenylcyclohexane. The peak area of ​​the reduction product is proportional to the temperature. The original content of reduced compounds such as tercyclohexane and dicyclohexylbenzene that retain the original carbon skeleton structure decreases rapidly. If it is reduced to bicyclohexane and phenylcyclohexane, since bicyclohexane and phenylcyclohexane can also be obtained by reducing chlorinated biphenyls, it is not possible to infer that the unknown sample contains chlorinated terphenyls through bicyclohexane and phenylcyclohexane.

[0122] 4) Effect of hydrogen flow rate on catalytic efficiency

[0123] The carrier gas is used as the source of reducing hydrogen to catalytically reduce the chlorinated hydrocarbons in the sample under a hydrogen atmosphere. The flow rate of hydrogen has a certain influence on the catalytic efficiency of the catalyst. The standard solution of chlorinated terphenyl was tested by setting different hydrogen flow rates (1.0, 1.2, 1.4, 1.6, 1.8 mL / min). The results showed that when the hydrogen flow rate increased from 1.0 to 1.8 mL / min, the retention time of the reduction product gradually decreased and the peak area slowly increased. This may be because at a relatively high hydrogen flow rate, the injection port pressure increased, and the target substance was in more complete contact with the catalyst. When the hydrogen flow rate was around 1.4-1.6 mL / min, the catalytic efficiency tended to be stable.

[0124] 5) Effect of chlorination degree on catalytic efficiency

[0125] Stock solutions of pentachloro-p-terphenyl and tetradecachloro-m-terphenyl were selected and prepared into working solutions with a concentration of 10 μg / mL. Dechlorination hydrogenation reduction experiments were carried out under the above instrumental analysis conditions. The corresponding catalytic efficiency results showed that the catalytic efficiencies obtained in the experiments were all greater than 95.1%. It can be seen that the catalytic efficiency of the catalyst for pentachloro-p-terphenyl and tetradecachloro-m-terphenyl remained basically unchanged, indicating that the chlorine content has little effect on the catalytic efficiency of the catalyst.

[0126] 6) Catalyst selection

[0127] When palladium catalyst is used, chlorinated terphenyl will be reduced and cracked more obviously, producing terphenylcyclohexane, bicyclohexane and cyclohexylbenzene substances. For terphenylcyclohexane, standard products of such compounds are not available on the market, which brings inconvenience to detection. Bicyclohexane and phenylcyclohexane may be obtained by reducing chlorinated biphenyl, so it is not possible to infer that the unknown sample contains chlorinated terphenyl through bicyclohexane and phenyl ring. Therefore, nickel catalyst is finally selected as the catalyst for online catalysis.

[0128] 7) Selection and optimization of catalytic parameters

[0129] Pentachloroterphenyl was used as a representative substance of chlorinated aromatics, and the response surface model was used to confirm the optimal parameters through experiments and statistical methods. The degree of chlorination has little effect on the catalytic efficiency. Therefore, the four parameters of catalytic temperature (A, ℃), hydrogen flow rate (B, mL / min), concentration of compounds that may affect the catalytic efficiency (C, μg / mL), and catalyst dosage (D, g) were selected as variables. A fuel oil raw material spiked sample was used for the experiment. Each variable was set at 3 levels. The catalytic efficiency of chlorinated aromatics in the test solution was the response value. According to the Box-Behnken central composite experimental design principle, 4 factors and 3 levels were used for a total of 29 experiments. The regression model equation of chlorinated aromatics was obtained: catalytic efficiency = 73.60-14.67A + 2.25B-1.00C + 1.75D + 1.75AB + 0.50AC-0.25AD-0.25BC-4.74BD-3.25CD-7.34A 2 +0.03B 2 +0.66C 2 -2.47D 2 .

[0130] The above experimental results were subjected to variance analysis. It can be seen from Table 2 that the F value of the model is 19.76, and the model probability P value is less than 0.05, indicating that each influencing factor has a significant effect on the catalytic efficiency. The adjusted correlation coefficient is 0.9518, and the model fit is good, indicating that the correlation is good, and 95.18% of the response value changes of the model can be analyzed. This model can be used to analyze the catalytic efficiency of chlorinated aromatics in fuel oil. Comprehensive test results show that the first-order term A of the model has a very significant effect, and C has an insignificant effect. The order of influence of single factors on the recovery rate is A>B>D>C, and the catalytic reaction temperature is the most significant, followed by the hydrogen flow rate. The quadratic terms A2 and D2 of aromatic chlorinated hydrocarbons have significant effects, while C2 and B2 have insignificant effects. Combined with the actual sample processing and catalytic efficiency analysis, the optimal parameters were obtained through response surface model analysis, and the experimental parameters were obtained as catalytic temperature of 220-250°C, hydrogen flow rate of 1.5mL / min, and catalyst dosage of 2g. To further verify the reliability of the data, the above optimal conditions were used to conduct a catalytic efficiency test on a mixed solution of pentachloroterphenyl and tetradecachloroterphenyl with known concentrations. The test was repeated three times and the catalytic efficiencies were 97.3% and 92.1%, which were comparable to the theoretical values. Therefore, the above conditions were finally used for the test.

[0131] Table 2 ANOVA results of Box-Benhnken central composite design

[0132]

[0133]

[0134] 8) Selection of mass spectrometry conditions

[0135] The standard solutions of the two chloroaromatic reduction products were scanned one by one in the EI full scan mode with the same ionization energy. The results showed that aromatic substances tend to form molecular ion peaks [M] + , such as [C 18 H 32 ] + (tricyclohexane, M = 248.1) and [C 18 H 26 ] + (dicyclohexylbenzene, M = 242.1), [C 18 H 30 ] + (dodecylbenzene, M = 246.1) and other molecular ion peaks. The above dicyclohexylbenzene and dodecylbenzene molecular ions were scanned in product ion mode at a collision energy of 0 to 60 eV. The full scan mass spectrum of dicyclohexylbenzene is as follows Figure 6 As shown, the full scan mass spectrum of the internal standard (dodecylbenzene) is as follows Figure 7The results show that aromatic hydrocarbons are prone to form characteristic peaks of benzene ring structures with hydrocarbon substitution, such as [C9H9] + (α-methylstyrene, M=116.9), [C8H8] + (styrene, M = 104.2), [C 12 H 15 ] + (phenylcyclohexane, M = 159.1),

[0136] [C7H7] + (Toluene, M = 91.1) molecular ion peak.

[0137] The optimized GC-MS / MS conditions are as follows:

[0138] Gas chromatography: chromatographic column: DB-5MS quartz capillary column specifications (30cm×0.25mm, 0.25μm); carrier gas: high-purity hydrogen; collision gas: high-purity nitrogen; column flow rate: 1.5mL / min; inlet temperature: 240℃; heating program: 45℃ (maintained for 2min), heated to 250℃ at 15℃ / min (maintained for 1min), and finally rapidly heated to 300℃ at 30℃ / min (maintained for 7min); injection volume: 1μL; injection mode: split injection, split ratio of 1:1; septum purge flow / mode: 3mL / min switch.

[0139] Mass spectrometry: electron impact ion source (EI), ion source temperature: 230°C, ionization energy: 70 eV; transfer line temperature: 300°C; ion source temperature: 230°C; mass analyzer is quadrupole, quadrupole temperature: 150°C; multiple reaction monitoring negative ion mode (MRM), solvent delay 5 min; run time: 25 min (post-run 0 min).

[0140] Example 3 Methodology Verification

[0141] 1) Linear range

[0142] Chlorinated terphenyl is converted into dicyclohexylbenzene by online catalysis. Accurately pipette an appropriate amount of dicyclohexylbenzene standard intermediate solution and internal standard intermediate solution, dilute toluene to scale, and prepare a standard working solution with a concentration of 1 μg / mL, 2 μg / mL, 5 μg / mL, 10 μg / mL, and 20 μg / mL, and the internal standard content is 1 μg / mL. According to the experimental conditions of step 3), the standard working solution prepared above is detected, and a standard working curve is drawn to obtain a linear equation and a correlation coefficient, as shown in Table 3. As can be seen from Table 3, the linear range of the reduction product of chlorinated terphenyl compounds is wide, and the linear correlation coefficient of all substances is greater than 0.9955, which can well meet the needs of testing work.

[0143] Table 3 Linear relationship table of reduction products of chlorinated terphenyl compounds

[0144] Target compound Linear range (μg / mL) Linear equations <![CDATA[Coefficient of correlation r 2 > 1,4-Dicyclohexylbenzene 1.0～20 Y=0.106821X+0.154244 0.9977 1,3-Dicyclohexylbenzene 1.0～20 Y=0.065690X+0.131371 0.9982

[0145] 2) Limit of detection and limit of quantification

[0146] A series of standard solutions with a concentration of 1.0 to 20 μg / mL were prepared using a blank sample solution with a matrix. The minimum detection limit was 3 times the signal-to-noise ratio (S / N) and the detection limit concentration was verified by the standard deviation of 7 repeated tests SMDL × coefficient T (n-1, 1-α = 0.99) (when the number of repetitions was 7 and the confidence level was 99%, T was 3.143, and the calculated value was ≤ the detection limit obtained by the signal-to-noise ratio). The minimum quantification limit was 10 times the signal-to-noise ratio (S / N) and the applicability of the instrument in actual detection and the universality of the influence of different fuel oil matrices were considered. Finally, the detection limits of 1,4-dicyclohexylbenzene (corresponding to polychlorinated p-terphenyl compounds) and 1,3-dicyclohexylbenzene (polychlorinated m-terphenyl compounds) were 0.3 μg / mL and the quantification limits were 1.0 μg / mL.

[0147] 3) Recovery and precision

[0148] The recovery test of common chlorinated terphenyl compounds was carried out by adding a blank sample. Common chlorinated terphenyl compounds were added to blank fuel oil samples that did not contain chlorinated terphenyl compounds, and three concentration levels (1.0μg / mL, 5.0μg / mL and 20.0μg / mL) were prepared and measured. Each concentration level was measured 6 times, and the recovery and precision tests were carried out. The recovery and precision test results are shown in Table 4. It can be clearly seen from the data in Table 4 that the spiked recovery of chlorinated terphenyl compounds in fuel oil determined by this method is between 93.7% and 108.6%, and the relative standard deviation is less than 6.3%, indicating that this method has good recovery and precision.

[0149] Table 4 Recovery and precision test of chlorinated terphenyl compounds

[0150]

[0151] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for determining chlorinated terphenyls in heavy oil products, characterized in that: The following steps are involved: S1. Vacuum distillation of heavy oil products to collect light components; S2. The light component collected in step S1 is passed through a solid phase extraction column, washed with a 60-90% petroleum ether / cyclohexane mixed solution, and then eluted with a toluene / dichloromethane mixed solution to obtain a sample to be tested; S3. Based on the internal standard method, nickel was used as a catalyst, and the sample to be tested was dechlorinated and hydrogenated using online catalysis, and analyzed by gas chromatography-tandem mass spectrometry to obtain the content of chlorinated terphenyls in the heavy oil product; The temperature of the online catalysis is 200-245°C.

2. The method according to claim 1, characterized in that: In step S1, the temperature of the reduced pressure distillation is above 400°C.

3. The method according to claim 1, characterized in that: In step S2, the volume ratio of petroleum ether 60-90 to cyclohexane in the petroleum ether 60-90 / cyclohexane mixed solution is 1:(0.8-1.2).

4. The method according to claim 1, characterized in that: In step S2, the volume ratio of toluene to dichloromethane in the toluene / dichloromethane mixed solution is 1:(0.8-1.2).

5. The method according to claim 1, characterized in that: In step S2, the solid phase extraction column is at least one of a silica gel solid phase extraction column or a silver nitrate-alumina solid phase extraction column.

6. The method according to claim 1, characterized in that: In step S3, the catalyst is a glass bead-supported nickel catalyst.

7. The method according to claim 1, characterized in that: In step S3, the chromatographic column of the gas chromatography in the gas chromatography-tandem mass spectrometry is a medium polarity or weak polarity chromatographic column.

8. The method according to claim 1, characterized in that: In step S3, the mass spectrometry conditions in the gas chromatography-tandem mass spectrometry are: electron bombardment ion source, energy 70eV; transmission line temperature: 300-320°C; ion source temperature: 230°C; mass analyzer is a quadrupole, quadrupole temperature: 150°C; multiple reaction monitoring negative ion mode, solvent delay 3-5min.

9. The method according to claim 1, characterized in that: The chlorinated terphenyl is at least one of chlorinated p-terphenyl or chlorinated m-terphenyl.

10. The method according to claim 1, characterized in that: The heavy oil product is at least one of diluted asphalt or residual fuel oil.

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