Crude oil organochlorine detection system and method based on single-wavelength dispersive X-ray fluorescence spectrum

Abstract

The invention discloses a crude oil organochlorine detection system and method based on a single-wavelength dispersive X-ray fluorescence spectrum, and belongs to the technical field of crude oil detection. The crude oil organochlorine detection method based on the single-wavelength dispersive X-ray fluorescence spectrum comprises the following steps: mixing a crude oil sample with an ethanol-water solution, heating in a water bath, centrifugally separating, repeatedly extracting and collecting an organic phase; in a vacuum mode, the fluorescence intensity is measured by using an Rh target X-ray tube, 35-45 kV tube voltage, 25-35 [mu] A tube current, 180-300 s counting time and 23-27 DEG C environment temperature, a calibration curve with the slope of 0.8-0.9 cps. Kg / mg is established based on a 0.08-1000 mg / kg chlorine standard solution series, and the organic chlorine content is calculated. The method is easy and convenient to operate, rapid in detection, capable of removing interference of inorganic chlorine, wide in linear range and high in accuracy, and supports are provided for oil refining process safety and product quality control.

Description

Technical Field

[0001] This invention relates to the field of crude oil detection technology, specifically to a crude oil organochlorine detection system and method based on single-wavelength dispersive X-ray fluorescence spectroscopy. Background Technology

[0002] In the petrochemical industry chain, crude oil, as the core raw material, directly determines the efficiency of refining processes, equipment safety, and the quality of end products. Organic chlorine in crude oil is a key hazardous component that restricts production safety. Chlorine in crude oil exists in both inorganic and organic forms. Conventional atmospheric and vacuum desalting processes can only remove inorganic chlorine, while organic chlorine remains in stable structures such as chloroalkanes. In deep processing stages such as hydrorefining and catalytic cracking, it reacts with hydrogen to produce hydrogen chloride, which then combines with ammonia to form ammonium salt deposits. This causes heat exchanger blockage and pipeline corrosion, and can also lead to catalyst poisoning and deactivation, shortening equipment lifespan and increasing production and maintenance costs. Furthermore, organic chlorine can exacerbate tank corrosion during oil storage and transportation, and even cause engine wear, posing a serious threat to the safety of the entire industry chain. Therefore, accurately determining the organic chlorine content in crude oil is a core technological requirement for ensuring the stability of refining processes, controlling equipment risks, and improving product quality.

[0003] Currently, the mainstream methods for determining the chlorine content of oil products in the industry include the combustion-microcoulometric method, the sodium biphenyl method, and X-ray fluorescence spectrometry. However, all of these methods have technical limitations that make them unsuitable for the detection of organochlorine in crude oil. The combustion-microcoulometric method, as the most widely used standard method, requires the conversion of organochlorine into hydrogen chloride through high-temperature combustion followed by microcoulometric titration. However, its operation is complex, requiring strict control of multiple parameters such as combustion temperature and oxygen flow rate, placing extremely high demands on the operator's skills. Furthermore, the analysis cycle can take several hours, which cannot meet the industrial needs of rapid crude oil turnover and batch testing. More importantly, in heavy crude oil, organochlorine is prone to incomplete combustion, leading to lower test results. The carbon deposits produced during combustion can also contaminate the detection device, further affecting the accuracy of the test.

[0004] Although the sodium biphenyl method can be used for the detection of light distillate oils, the reagents are highly toxic and corrosive, which not only endangers the health of operators but also requires high environmental treatment costs. At the same time, this method is extremely unsuitable for the complex matrix of heavy crude oil with high viscosity and high impurities, and cannot achieve full coverage of crude oil specifications. It has been gradually phased out by the industry.

[0005] X-ray fluorescence spectrometry (XRF) has been gradually applied to oil product testing due to its advantages of speed and non-destructiveness. Among them, monochromated wavelength dispersive X-ray fluorescence (MWD XRF) technology has become a standard in the detection of light oils and aromatic chlorides due to its strong anti-interference ability and high detection sensitivity. Existing studies have confirmed that the results of MWD XRF are in good agreement with those of microcoulometric methods, and the analytical efficiency is higher. However, this technology still faces bottlenecks in the field of crude oil organochlorine detection: First, the crude oil matrix is ​​complex, and impurities such as heavy hydrocarbons and sulfides can strongly interfere with the characteristic fluorescence signal of chlorine. Existing detection parameters for light oils cannot eliminate such interference. Second, inorganic chlorine residues in crude oil can easily lead to quantitative deviations in organochlorine, and conventional pretreatment methods are difficult to achieve efficient separation between the two. Third, the existing calibration system only covers a single concentration range, which cannot adapt to the wide range of fluctuations in crude oil organochlorine and lacks a drift correction mechanism for the crude oil matrix, which can easily lead to a decrease in accuracy with long-term use. Fourth, existing metrological specifications do not cover the MWD XRF detection of crude oil organochlorine, and the lack of unified operating standards restricts industrial promotion.

[0006] With the diversification of imported crude oil sources, the organic chlorine content of crude oil varies significantly across different producing regions. The organic chlorine content of some heavy crude oils far exceeds the range of traditional methods, and refineries are increasingly demanding higher detection efficiency. The shortcomings of traditional methods have become a key constraint on production scheduling. Therefore, developing an organic chlorine detection technology that is adaptable to the complex matrix of crude oil, easy to operate, and accurate and efficient is of significant practical importance in filling the application gap of MWD XRF in this field. Summary of the Invention

[0007] To address the aforementioned shortcomings, this invention provides a crude oil organochlorine detection system and method based on single-wavelength dispersive X-ray fluorescence spectroscopy. By optimizing pretreatment and instrument parameters, establishing adaptive calibration curves, and performing drift correction, the system solves the problems of low detection efficiency, high interference, and insufficient accuracy of crude oil organochlorine.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] A method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy includes the following steps:

[0010] (1) Sample pretreatment: The crude oil sample was mixed with an ethanol-water solution, heated in a water bath, centrifuged to separate the oil phase, and the extraction was repeated to collect and combine the organic phases;

[0011] (2) Instrumental analysis: The treated organic phase sample was placed in a single-wavelength dispersive X-ray fluorescence spectrometer, and the X-ray fluorescence intensity of chlorine was measured in vacuum mode. The counting time was 180-300s and the ambient temperature was 23-27℃.

[0012] (3) Calibration curve establishment: Using a series of chlorine standard solutions, fluorescence intensity was measured under the instrument analysis conditions to establish a calibration curve between the count rate and chlorine concentration;

[0013] (4) Sample determination and calculation: Calculate the organic chlorine content in crude oil based on the fluorescence intensity of the crude oil sample to be tested and the calibration curve.

[0014] Preferably, the ethanol-water solution in step (1) is prepared by mixing ethanol and water in a volume ratio of 1:(2-4).

[0015] Preferably, the extraction is repeated 2-3 times in step (1).

[0016] Preferably, the operating conditions of the single-wavelength dispersive X-ray fluorescence spectrometer in step (2) also include: the X-ray tube target material is Rh; the X-ray tube voltage is 35-45kV; the analytical spectral line is Cl Kα; the crystal type is PX-1; the vacuum degree is ≤10Torr; the X-ray tube current is 25-35μA; and the detector type is a flow gas proportional counter.

[0017] Preferably, the linear range of the calibration curve in step (3) is 0.08-1000 mg / kg.

[0018] Preferably, the concentration points of the chlorine standard solution series in step (3) cover the range of 0-1000 mg / kg.

[0019] Preferably, the slope k of the calibration curve in step (3) is 0.8-0.9 cps·kg / mg.

[0020] A system for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy includes: a sample pretreatment device; a single-wavelength dispersive X-ray fluorescence spectrometer; a control unit; and a data processor.

[0021] The output end of the sample pretreatment device is detachably connected to the sample chamber of the single-wavelength dispersive X-ray fluorescence spectrometer, and the sample box is transferred to the spectrometer detection position through the sample injection unit.

[0022] The control unit is electrically connected to the sample pretreatment device, the spectrometer, and the data processor via circuits.

[0023] The data processor is connected to the spectrometer via a data line to receive fluorescence signal data and communicate bidirectionally with the control unit.

[0024] Preferably, the sample pretreatment device includes an oven, an electronic analytical balance, and a centrifuge.

[0025] Preferably, the data processor is further configured to perform drift correction by real-time correction of the calibration curve by monitoring the fluorescence intensity of the sample.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] I. Adaptable to complex crude oil matrices, overcoming the limitations of traditional methods.

[0028] This invention addresses the characteristics of crude oil matrices, such as high viscosity, numerous impurities, and the coexistence of organic and inorganic chlorines. It constructs a targeted sample pretreatment system and instrumental analysis parameter combination, effectively overcoming the application bottlenecks of traditional methods. Traditional combustion-microcoulometric methods are prone to incomplete combustion and quantitative deviations in heavy crude oils, while the sodium biphenyl method is only suitable for light distillate oils. This invention, through a specific ethanol-water solution ratio design and multiple extraction processes, achieves efficient separation of inorganic and organic chlorines while avoiding the loss of organic chlorine components, ensuring the accuracy of detection results under complex matrices. Combined with a single-wavelength dispersive X-ray fluorescence spectrometer using an Rh target X-ray tube, PX-1 type crystal, and precise selection of Cl Kα characteristic spectral lines, the selectivity and anti-interference capability of the chlorine fluorescence signal are improved. This effectively shields the signal interference from coexisting impurities such as sulfides and nitrides in crude oil, enabling stable detection of organic chlorines in crude oils with different properties and broadening the applicability of the detection method.

[0029] II. Improved testing efficiency and ease of operation, breaking through the constraints of traditional methods and procedures.

[0030] This invention completely transforms the cumbersome and time-consuming nature of traditional detection methods, constructing a highly efficient and simplified detection process. Traditional combustion-microcoulometric methods require complex steps such as sample combustion and electrolytic titration, demanding high operator skills and being susceptible to human error, with analysis cycles lasting several hours. In contrast, this invention employs standardized operations for sample pretreatment using water bath heating and centrifugation, eliminating the need for complex chemical reactions and stringent experimental conditions. The instrument analysis process utilizes an automatic parameter setting and signal acquisition control unit, requiring no manual intervention throughout. The optimized range design for counting time and ambient temperature shortens the time required for a single detection while maintaining detection accuracy, meeting the industrial demands for rapid crude oil turnover and batch testing. This reduces labor and time costs in the detection process, improves efficiency and ease of operation, and is more suitable for large-scale industrial applications.

[0031] III. Comprehensive optimization of detection accuracy and stability solves the quantitative reliability problem of traditional methods.

[0032] This invention achieves a dual improvement in detection accuracy and long-term stability through multi-dimensional technical design. Regarding the quantitative system construction, a series of chlorine standard solutions covering a wide concentration range are used to establish calibration curves. Combined with a slope-optimized linear regression model, this ensures accurate quantification of organic chlorine content across different concentration ranges, effectively avoiding the quantitative deviation problems that easily occur at high and low concentrations with traditional single-concentration calibration curves. In terms of system stability, the drift correction function integrated into the data processor corrects the calibration curves in real time by monitoring sample fluorescence intensity, compensating for signal drift caused by environmental fluctuations and component wear during long-term instrument operation, thus ensuring long-term consistency of detection results. Simultaneously, the inherent characteristics of single-wavelength dispersive X-ray fluorescence spectroscopy, combined with optimized instrument operating parameters (tube voltage, tube current, vacuum, etc.), further reduce detection noise and improve the signal-to-noise ratio. This technically solves the core problems of insufficient precision and poor reproducibility in traditional methods, providing reliable detection data support for refining process optimization and quality control.

[0033] IV. System integration design to achieve intelligent management and control of the entire testing process.

[0034] The detection system of this invention organically integrates a sample pretreatment device, a spectrometer, a control unit, and a data processor, constructing a fully intelligent detection system from sample pretreatment to result output. The control unit achieves unified control of pretreatment parameters and instrument analysis conditions, avoiding errors caused by improper parameter matching in various stages of traditional detection. The data processor not only performs calibration curve calculation and result output functions but also achieves real-time monitoring and anomaly correction of the detection process through built-in quality control logic and drift correction mechanisms, eliminating the need for complex manual data processing and curve calibration. This integrated and intelligent design not only reduces human error but also enables standardized storage and traceability of detection data, meeting the petrochemical industry's requirements for standardized and information-based management of the detection process, and providing an efficient and reliable technical means for crude oil quality control. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the working principle of the single-wavelength dispersive X-ray fluorescence spectrometer of the present invention.

[0036] In the attached diagram: 1-X-ray generator; 2-incident light monochromator; 3-sample chamber; 4-fixed track monochromator; 5-signal detector; 6-control unit; 7-data processor. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0038] A method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy includes the following steps:

[0039] (1) Sample pretreatment: The crude oil sample was mixed with an ethanol-water solution, heated in a water bath, centrifuged to separate the oil phase, and the extraction was repeated to collect and combine the organic phases;

[0040] (2) Instrumental analysis: The treated organic phase sample was placed in a single-wavelength dispersive X-ray fluorescence spectrometer, and the X-ray fluorescence intensity of chlorine was measured in vacuum mode. The counting time was 180-300s and the ambient temperature was 23-27℃.

[0041] (3) Calibration curve establishment: Using a series of chlorine standard solutions, fluorescence intensity was measured under the instrument analysis conditions to establish a calibration curve between the count rate and chlorine concentration;

[0042] (4) Sample determination and calculation: Calculate the organic chlorine content in crude oil based on the fluorescence intensity of the crude oil sample to be tested and the calibration curve.

[0043] The mechanisms of action of each preparation step are as follows:

[0044] I. Mechanism and Principle of Sample Pretreatment

[0045] The core of the sample pretreatment in this invention is to achieve the selective separation of inorganic and organic chlorine, the effect of which depends on the synergistic effect of the solvent system and process parameters. In the ethanol-water solution, ethanol, as a polar organic solvent, can reduce the interfacial tension between crude oil and the aqueous phase, improve the compatibility of the two phases, and make the aqueous phase more easily penetrate the crude oil system; the aqueous phase provides a dedicated dissolution environment for inorganic chlorine, which is stripped off through ionic solvation. The volume ratio of 1:(2-4) synergistically balances the compatibility of crude oil and the solubility of inorganic chlorine, avoiding the defects of pure ethanol being unable to dissolve inorganic chlorine and pure water and crude oil having poor miscibility. Water bath heating accelerates mass transfer by increasing the rate of molecular thermal motion, reducing the viscosity of crude oil; centrifugal separation utilizes the density difference to achieve oil-water stratification, and the two work together to enhance the separation efficiency. Repeated extraction, through a stepwise stripping mechanism, removes both free and adsorbed inorganic chlorine, while avoiding over-extraction that leads to the loss of organic chlorine, achieving a balance between separation effect and component retention.

[0046] II. Mechanism and Principle of Instrumental Analysis

[0047] Instrumental analysis achieves efficient excitation and precise acquisition of characteristic signals of chlorine through parameter coordination. The Rh target generates continuous X-rays matching the binding energy of the K-shell electrons in chlorine. A 35-45kV tube voltage and a 25-35μA tube current work in tandem to ensure photon energy exceeds the electron binding energy threshold while preventing detector saturation. The Cl Kα spectral line is a strong characteristic spectral line of chlorine; the PX-1 crystal precisely filters this line using dispersion. A flow-proportional counter converts weak fluorescence signals into electrical signals; these three elements work together to enhance signal specificity and detection sensitivity. Vacuum mode reduces absorption and scattering of fluorescent photons by air; a 180-300s counting time balances signal statistical accuracy and detection efficiency; and an ambient temperature of 23-27℃ stabilizes detector dark current and crystal diffraction efficiency. These three elements work together to ensure the stability and reliability of signal acquisition, achieving a superior anti-interference effect compared to conventional parameter combinations.

[0048] III. Mechanism and Principle of Calibration Curve Establishment and Drift Correction

[0049] The calibration curve achieves quantitative accuracy through concentration coverage and slope matching. The chlorine standard solution series covers 0-1000 mg / kg, adapting to wide concentration fluctuations of organic chlorine in crude oil. A linear range of 0.08-1000 mg / kg ensures accurate quantification of both trace and high-concentration samples. The slope of 0.8-0.9 cps·kg / mg works in conjunction with instrument excitation efficiency and detector sensitivity, ensuring signal response strength per unit concentration change while avoiding signal saturation or decreased anti-interference capability. The drift correction function monitors real-time changes in instrument status, converting signal drift into a correction factor to dynamically adjust the calibration curve. This, in conjunction with the basic quantitative model, compensates for errors caused by X-ray tube aging and environmental fluctuations, achieving long-term detection stability and addressing the technical pain point of conventional methods being easily affected by instrument status.

[0050] To make the present invention more fully disclosed, more specific embodiments are described below.

[0051] I. Basic Experimental Conditions

[0052] (I) Experimental Instruments and Reagents

[0053] A single-wavelength dispersive X-ray fluorescence spectrometer (model SINDIE7039, XOS Corporation, USA) is equipped with an Rh target X-ray tube, a PX-1 crystal, and a flow-gas proportional counter.

[0054] Sample pretreatment equipment: drying oven (FD115, Binder GmbH, Germany), electronic analytical balance (AB204-S, Mettler Toledo Shanghai), centrifuge (MIKRO 220R, Hettich GmbH, Germany, maximum speed 3000 r / min);

[0055] Reagents: 95% ethanol (analytical grade, Sinopharm Group), deionized water, chlorine element standard (NIM-RM2120~NIM-RM2130, National Institute of Metrology, China, concentration range 0.08~1000mg / kg), blank oil (CONOSTAN Corporation, USA, chlorine-free), crude oil samples to be tested (Nos. 1-9, from different origins, covering light and heavy crude oils);

[0056] Ethanol-water solution: Prepared in different volume ratios (1:2, 1:3, 1:4) and used immediately.

[0057] (II) Working principle of the instrument

[0058] As attached Figure 1 As shown, the working principle of a single-wavelength dispersive X-ray fluorescence spectrometer is as follows: X-rays generated by an X-ray source are dispersed by an incident light monochromator to form a monochromatic excitation beam. This specific wavelength of X-rays can precisely excite the K-shell electrons of chlorine in the sample. Upon excitation, chlorine emits a Cl Kα fluorescence line with a characteristic wavelength of 0.473 nm. This fluorescence signal is collected by a fixed-channel monochromator and focused onto a detector. By measuring the X-ray fluorescence intensity at this characteristic wavelength (expressed in counts per second) and combining it with a calibration curve of fluorescence intensity versus chlorine concentration, quantitative analysis of organochlorine content is achieved. This instrument system, through the attached... Figure 1 The optical path structure and signal transmission path shown ensure efficient excitation and accurate acquisition of fluorescence signals, providing hardware support for the sensitivity and accuracy of the detection method.

[0059] (III) Core Evaluation Indicators

[0060] Precision: characterized by relative standard deviation (RSD), calculated based on 6 parallel measurements;

[0061] Accuracy: Characterized by spiked recoveries (spiking values ​​of 0, 1.00, 3.00, 5.00, and 10.0 mg / kg) and relative deviations from the standard method (combustion-microcoulometric method, GB / T 18612-2011);

[0062] Detection efficiency: Total time for a single detection;

[0063] Adaptability: Detection effect on crude oil samples with different viscosities and different organic chlorine contents.

[0064] II. Implementation Examples

[0065] Example 1

[0066] (1) Sample pretreatment stage: accurately weigh 25.00g of crude oil sample No. 1, add 25mL of ethanol-water solution with a volume ratio of 1:3, heat the mixture in a 50℃ water bath for 2min, then shake for 2min, and then centrifuge at 3000r / min for 3min to separate the organic phase. Repeat the above steps twice and combine the organic phases after the two extractions for later use.

[0067] (2) In the instrument analysis stage, the processed organic phase was loaded into the sample box, ensuring that the sample thickness was ≥3mm. It was placed in a single-wavelength dispersive X-ray fluorescence spectrometer. The instrument was set to Rh target, tube voltage 40kV, tube current 30μA, analytical spectral line Cl Kα, crystal type PX-1, vacuum degree controlled at 5Torr, detector used gas proportional counter, counting time 180s, ambient temperature maintained at 25℃, and X-ray fluorescence intensity of chlorine was measured in vacuum mode.

[0068] (3) In the calibration curve establishment stage, a series of chlorine standard solutions (concentrations of 0 mg / kg, 0.08 mg / kg, 1.0 mg / kg, 10.0 mg / kg, 50.0 mg / kg, 300.0 mg / kg, and 1000.0 mg / kg) were used to measure fluorescence intensity under the above instrument analysis conditions. A calibration curve between count rate and chlorine concentration was established, and the regression equation was obtained as Y = 0.856X + 0.121, with a linear correlation coefficient r 2 The value was ≥0.9996, the slope of the curve was 0.856 cps·kg / mg, and the linear range was 0.08-1000mg / kg.

[0069] (4) In the quality control stage, before each batch of samples is measured, the instrument status is checked using blank oil and 50.0 mg / kg chlorine standard sample. Each sample is measured in parallel 3 times, and the average value is taken as the final measurement result.

[0070] Single-factor experimental design and results of key process parameters

[0071] (I) Experimental Design Principles

[0072] Using Example 1 as the baseline, single-factor experiments were conducted on the ethanol-water volume ratio, number of extractions, counting time of low-concentration standard substance, counting time of high-concentration standard substance, ambient temperature, and X-ray tube voltage. Only the target parameter was changed, and the other parameters were the same as in Example 1.

[0073] (II) Summary of Single-Factor Experiment Results

[0074] 1. Single-factor experiment on ethanol-water volume ratio

[0075] Experimental design: The variable was the ethanol-water volume ratio, with five gradients set at 1:1, 1:2, 1:3, 1:4, and 1:5. The sample used was crude oil No. 1, with a background organic chlorine content of 2.3 mg / kg. Before the experiment, 50 mg / kg of inorganic chlorine was added to simulate interference in actual testing. The experimental results are shown in Table 1.

[0076]

[0077] 2. Single-factor experiment on the number of extractions

[0078] Experimental design: The variable was the number of extractions, set to 1, 2, and 3 times respectively. The test sample was also selected as crude oil No. 1 with 50 mg / kg inorganic chlorine added. The experimental results are shown in Table 2.

[0079]

[0080] 3. Single-factor experiments on low-concentration standard substances at different counting times

[0081] Experimental design: The variable was the counting time, with five gradients set at 60s, 120s, 180s, 300s, and 600s; the sample to be tested was a low-concentration chlorine standard (1.0 mg / kg, simulating trace organic chlorine in crude oil). The experimental results are shown in Table 3.

[0082]

[0083] 4. Single-factor experiment of high-concentration standard substances at different counting times

[0084] Experimental design: The variable was the counting time, with five gradients set at 60s, 120s, 180s, 300s, and 600s. The sample to be tested was a high-concentration chlorine standard (100mg / kg, simulating the high content of organic chlorine in heavy crude oil). The experimental results are shown in Table 4.

[0085]

[0086] 5. Single-factor experiment on ambient temperature

[0087] Experimental design: The variable was ambient temperature, with five temperature gradients set at 20℃, 23℃, 25℃, 27℃, and 30℃. The sample to be tested was a 10.0 mg / kg chlorine standard substance to simulate the detection scenario of organochlorine concentrations in crude oil. The experimental results are shown in Table 5.

[0088]

[0089] 6. Single-factor experiment on X-ray tube voltage

[0090] Experimental design: Five voltage gradients were set at 30kV, 35kV, 40kV, 45kV, and 50kV respectively; 5.0 mg / kg chlorine standard material was selected as the test sample to simulate the detection scenario of organochlorine concentration in crude oil. The experimental results are shown in Table 6.

[0091]

[0092] (III) Analysis of Single-Factor Experiment Results

[0093] 1. Ethanol-water volume ratio

[0094] (1) Less than 1:3: The proportion of water phase is insufficient, which cannot fully dissolve the inorganic chlorine in crude oil. The removal rate of inorganic chlorine is low, and the residual inorganic chlorine directly interferes with the quantitative analysis of organic chlorine, resulting in a higher measured value. At the same time, the solvent and crude oil have poor miscibility, and the slow stratification causes component segregation, which reduces the detection precision and raises the RSD to 3.25%, which cannot meet the requirements for accurate detection.

[0095] (2) Higher than 1:3: The proportion of aqueous phase is too high, exceeding the dissolution equilibrium threshold of organochlorine, which leads to the migration and loss of organochlorine to the aqueous phase, resulting in a decrease in recovery rate and a lower measured value; excessive aqueous phase also causes oil phase emulsification, requiring an additional demulsification step, which reduces detection efficiency and increases RSD to 3.01%, impairing detection stability.

[0096] (3) Conclusion: 1:(2-4) is the equilibrium range between sufficient dissolution of inorganic chlorine and low loss of organic chlorine. Under this ratio, the removal rate of inorganic chlorine is ≥97.2%, the recovery rate of organic chlorine is ≥95.1%, and the RSD is ≤2.78%. Among them, 1:3 is the optimal value, which achieves the optimal synergy between interference removal and target component retention.

[0097] 2. Number of extractions

[0098] (1) 1 time: The extraction intensity is insufficient, the inorganic chlorine in the crude oil is not completely separated, and the residual amount is 3.5 mg / kg. The residual inorganic chlorine acts as an interfering factor, resulting in a higher organic chlorine measurement value. In addition, the organic phase is slightly turbid, and the uneven distribution of components causes fluctuations in the detection. The RSD rises to 3.85%, and the detection accuracy cannot be guaranteed.

[0099] (2) Three times: Although it can further reduce the residual amount of inorganic chlorine and remove interference more thoroughly, excessive extraction destroys the stability of the organic phase, causing organic chlorine to be lost with the aqueous phase, resulting in a decrease in recovery rate and a lower measured value of 2.25 mg / kg. At the same time, the pretreatment time increases by 40% compared with two extractions, the detection efficiency decreases significantly, and the precision improvement is slight with no actual gain.

[0100] (3) Conclusion: 2-3 times is a reasonable range for effective removal of interference and low loss of target components. Under this number of times, the residual amount of inorganic chlorine is ≤0.3mg / kg, the organic phase is clear and there is no interference, and the RSD is ≤2.16%. Among them, 2 times is the optimal value, which takes into account both detection accuracy and efficiency, and is the best balance point for interference removal, target retention and efficiency.

[0101] 3. Low-concentration standard substances at different counting times

[0102] (1) Less than 180s: The counting time is insufficient, the statistical error of the fluorescence signal is large, and it cannot effectively cancel the interference of random noise. At 60s, the measured value fluctuates drastically, with an RSD as high as 8.5%; at 120s, although the RSD drops to 5.1%, it still exceeds the acceptable range for accurate detection. The characteristic signal of trace organochlorine is masked by background noise, the detection precision is insufficient, and it cannot meet the accurate quantitative requirements of trace organochlorine in crude oil.

[0103] (2) Above 180s: The counting time has met the signal statistics requirements, with the average value stabilizing at around 130cps and RSDs of 2.1% and 2.0% respectively. Compared with 2.3% at 180s, the improvement in precision is slight. However, the detection time has increased exponentially. The 300s time is 67% longer than the 180s time, and the 600s time is 233% longer, which reduces the detection efficiency and does not bring any substantial technical gains. This does not meet the efficiency requirements of industrial batch detection.

[0104] (3) Conclusion: Within the counting time range of 60~600s, 180s is the optimal value. At this time, the RSD of low concentration standard material is reduced to 2.3%, which meets the requirements of accurate detection, while taking into account both detection efficiency and data quality; 60~180s is the range of rapid improvement in precision, and after 180s it enters the range of stable precision, and there is no need to extend the time further.

[0105] 4. High-concentration standard substances at different counting times

[0106] (1) Less than 180s: Insufficient counting time leads to inadequate signal sampling, and the fluorescence signal of high-concentration samples fluctuates greatly. The RSD is 5.2% at 60s and 3.0% at 120s, both exceeding the accurate detection threshold. The signal stability is insufficient, and quantitative deviation is easily caused by random errors, which cannot guarantee the accuracy of detection of high content of organic chlorine in heavy crude oil.

[0107] (2) Above 180s: The fluorescence signal has stabilized and the RSD has dropped to 1.7% and 1.6% respectively. Compared with 1.8% at 180s, the precision has improved very little, but the detection time has increased significantly, resulting in a significant decrease in detection efficiency and an increase in instrument energy consumption. It has no practical application value.

[0108] (3) Conclusion: Within the counting time range of 60~600s, 180s is the optimal value. At this time, the RSD of high-concentration standard material is as low as 1.8%, and the signal stability is excellent, which can accurately capture the characteristic signal of high-concentration organochlorine. At the same time, the detection efficiency is within a reasonable range, avoiding the insufficient precision caused by too short a time and the waste of efficiency caused by too long a time. It is the best balance point between accuracy and efficiency in the detection of high-concentration organochlorine.

[0109] 5. Ambient temperature

[0110] (1) Below 25℃: Low temperature leads to increased dark current noise in the detector, and the fluorescence intensity fluctuation range expands to 9750~10450cps. The signal stability is destroyed and the RSD rises to 4.5%. The excitation efficiency of the K layer electrons of chlorine element decreases, the quantum efficiency of characteristic fluorescence spectral lines decreases, and the detection reproducibility is impaired.

[0111] (2) Above 25℃: Excessive temperature accelerates detector aging, the fluorescence intensity fluctuation range expands to 10150~10820cps, and the RSD rises to 5.8%; at the same time, high temperature leads to a decrease in crystal diffraction efficiency, a decrease in the resolution of Cl Kα characteristic spectral lines, a weakening of the distinction between signal and background noise, and impaired detection accuracy.

[0112] (3) Conclusion: 23-27℃ is the balance range between low detector noise and high crystal diffraction efficiency. At this temperature, RSD≤3.2% and fluorescence intensity fluctuation range≤330cps. Among them, 25℃ is the optimal value, the instrument is most stable and the detection reproducibility is the best.

[0113] 6. X-ray tube voltage

[0114] (1) Below 40kV: The tube voltage does not reach the excitation threshold of the K layer electron of chlorine, the fluorescence intensity is only 112cps, and the signal-to-background ratio is as low as 4.0; the half width at half maximum of the characteristic spectral line is 0.008nm, the resolution is poor, and it is impossible to effectively distinguish the signals of chlorine and interfering components, resulting in insufficient sensitivity for the detection of trace organic chlorine.

[0115] (2) Above 40kV: Excessive tube voltage leads to excess X-ray energy, crystal overload causes characteristic spectral line broadening, half width at half maximum (WHM) increases to 0.009nm, resolution decreases; background signal increases to 32cps, signal-to-background ratio decreases to 4.4, instrument power consumption increases to 150W, accelerates X-ray tube aging, and increases detection cost.

[0116] (3) Conclusion: 35-45kV is the balance range between excitation efficiency and spectral resolution. At this voltage, the fluorescence intensity is ≥121cps, the signal-to-background ratio is ≥4.8, and the full width at half maximum (FWHM) of the spectral line is ≤0.006nm. Among them, 40kV is the optimal value, which can realize efficient excitation and accurate identification of chlorine element characteristic signals.

[0117] Example 2

[0118] In the sample pretreatment stage, 25.00 g of No. 3 light crude oil sample (background organochlorine content 1.26 mg / kg) was accurately weighed, and 25 mL of ethanol-water solution with a volume ratio of 1:2 was added. The extraction was repeated three times according to the pretreatment procedure in Example 1, and the organic phases were combined. In the instrument analysis stage, the instrument was set to an Rh target, tube voltage 35 kV, tube current 25 μA, analytical spectral line Cl Kα, crystal type PX-1, vacuum degree controlled at 10 Torr, detector using a gas flow proportional counter with a counting time of 180 s, ambient temperature maintained at 23℃, and fluorescence intensity measured in vacuum mode. In the calibration curve establishment stage, the same series of chlorine standard solutions as in Example 1 was used. The established calibration curve had a slope of 0.8 cps·kg / mg and a linear correlation coefficient r. 2 =0.9994. The quality control phase remained consistent with Example 1.

[0119] Example 3

[0120] In the sample pretreatment stage, 25.00 g of No. 8 heavy crude oil sample (background organochlorine content 3.20 mg / kg) was accurately weighed, and 25 mL of ethanol-water solution with a volume ratio of 1:4 was added. The extraction was repeated twice according to the pretreatment procedure in Example 1, and the organic phases were combined. In the instrument analysis stage, the instrument was set to an Rh target, tube voltage 45 kV, tube current 35 μA, analytical spectral line Cl Kα, crystal type PX-1, vacuum level controlled at 8 Torr, detector using a flow-proportional counter with a counting time of 300 s, ambient temperature maintained at 27℃, and fluorescence intensity measured in vacuum mode. In the calibration curve establishment stage, a series of chlorine standard solutions covering the concentration range of 0–1000 mg / kg were used. The established calibration curve had a slope of 0.9 cps·kg / mg and a linear correlation coefficient r. 2 =0.9995. The quality control phase remained consistent with Example 1.

[0121] Example 4

[0122] The detection system used in the experiment included a sample pretreatment device, a single-wavelength dispersive X-ray fluorescence spectrometer, a control unit, and a data processor. The sample pretreatment device included an oven, an electronic analytical balance, and a centrifuge. Crude oil sample No. 9 (background organochlorine content 2.88 mg / kg) was selected, and 100 consecutive measurements were performed using the method parameters of Example 1. Every 20 measurements, a 10.0 mg / kg chlorine standard was used as a monitoring sample. The data processor performed drift correction and real-time adjustments to the calibration curve. During the detection process, the control unit coordinated the operation of the sample pretreatment device and the spectrometer, and the data processor synchronously stored all detection data and supported export via USB and Ethernet.

[0123] III. Comparative Example

[0124] Comparative Example 1

[0125] The experiment was conducted according to the procedure specified in GB / T 18612-2011. The combustion temperature was set to 950℃, the oxygen flow rate was controlled at 40mL / min, and the electrolysis current was 100μA. The No. 1 light crude oil and the No. 8 heavy crude oil were tested separately. Each sample was measured in parallel 6 times. The measured values, RSD and spiked recovery rate were calculated, and the duration of each test was recorded.

[0126] Comparative Example 2

[0127] Prepare a 0.1 mol / L sodium biphenyl reagent and react it with No. 1 light crude oil and No. 8 heavy crude oil respectively. Perform quantitative analysis by titration. Each sample is measured in parallel 6 times. Record the measured value, RSD and spiked recovery rate. At the same time, observe the safety of the reagent and the solubility of the sample.

[0128] Comparative Example 3

[0129] The experiment was conducted according to the parameters specified in NB / SH / T0977-2019 standard. The ethanol-water volume ratio was 1:1, the number of extractions was 1, the counting time was 120s, and the ambient temperature was room temperature (without temperature control). Crude oil sample No. 1 was tested, and each sample was measured in parallel 6 times. The inorganic chlorine removal rate, measured value, RSD and spiked recovery rate were calculated, and the detection time was recorded.

[0130] IV. Implementation Examples and Comparative Examples: Data Results and Theoretical Analysis

[0131] (a) Data Results

[0132]

[0133] (II) Theoretical Analysis

[0134] 1. Detection Accuracy (RSD) Analysis

[0135] As shown in Table 7, the RSD range of Examples 1-4 is 1.80%~2.80%, which meets the accuracy detection requirement of ≤3%. Among them, the RSD of Example 3 is as low as 1.80%, and the RSD of Example 1 is 2.16%. In contrast, among the comparative examples, the RSD of Comparative Example 1 (heavy crude oil) is 3.56%, the RSD of Comparative Example 2 (light crude oil) is 3.50%, and the RSD of Comparative Example 3 is as high as 4.80%, all of which exceed the accuracy detection threshold.

[0136] The precision advantage of this embodiment stems from technological innovation through multi-parameter synergistic optimization: the pretreatment stage removes inorganic chlorine interference and avoids signal fluctuations caused by interference factors through the synergistic effect of a 1:(2-4) ethanol-water ratio and 2-3 extractions; the instrument analysis stage forms an adaptive system with parameters such as Rh target X-ray tube, 35-45kV tube voltage, and 23-27℃ temperature control, and the targeted selection of Cl Kα characteristic spectral lines and the dispersive effect of PX-1 crystal significantly improve signal specificity and reduce background noise interference; the system-level data processor drift correction function corrects instrument state fluctuations in real time, ensuring the accuracy and stability of continuous detection.

[0137] In contrast, comparative examples show that in Comparative Example 1, incomplete combustion of heavy oil resulted in carbon deposits, leading to increased signal fluctuations; Comparative Example 2 lacked an optimized pretreatment process, resulting in turbid organic phases and residual interference, thus limiting precision; and Comparative Example 3 did not optimize parameters for the crude oil matrix, and the 1:1 ethanol-water ratio and single extraction could not effectively remove inorganic chlorine (removal rate was only 89.5%), and the lack of temperature control design caused signal instability due to ambient temperature fluctuations, resulting in a high RSD.

[0138] 2. Accuracy Analysis of Detection

[0139] As shown in Table 7, the spiked recovery rate of the examples ranged from 97.5% to 100.9%, demonstrating excellent accuracy. In contrast, the spiked recovery rates of Comparative Example 1 (heavy crude oil) were as low as 92.1% to 97.8%, Comparative Example 2 (light crude oil) 93.1% to 98.5%, and Comparative Example 3 91.2% to 97.8%, all showing significantly lower accuracy than the examples. This advantage stems from the precise control of the entire process of interference removal, target retention, and quantitative calibration in this invention: the pretreatment stage optimizes the ratio of ethanol to water (1:(2-4)) to balance the dissolution of inorganic chlorine and the retention of organic chlorine; 2-3 extractions achieve the best balance between interference removal and target loss, with an organic chlorine recovery rate ≥95.1%; the calibration curve stage uses a wide range of standard solutions covering 0-1000 mg / kg, with a slope of 0.8-0.9 cps·kg / mg precisely matched to the instrument excitation efficiency and detector sensitivity, and a linear correlation coefficient r. 2 ≥0.9994 ensures accurate quantification of organochlorine compounds at different concentrations; the quality control process further mitigates systematic errors through pre-verification with blank oil and medium-concentration standard samples.

[0140] In contrast, the comparative examples showed that Comparative Example 1 had a low recovery rate due to incomplete combustion of heavy oil and insufficient conversion of organochlorine; Comparative Example 2 was limited by the solubility of the reagent, which prevented the heavy oil from forming an effective reaction system, and the reaction selectivity of the highly toxic reagent was insufficient, thus limiting the accuracy; Comparative Example 3 had no inorganic chlorine residue due to improper pretreatment parameters, and the calibration curve was not optimized for the crude oil matrix, resulting in a large quantitative deviation.

[0141] 3. Detection efficiency analysis

[0142] As shown in Table 7, the detection time range of the examples is 22 min to 45 min. Example 2 only requires 22 min, Example 1 requires 28 min, and even Example 3 only requires 45 min. However, the detection time of Comparative Example 1 (light crude oil) is 120 min, and that of heavy crude oil is 150 min, which is 3.3 times that of Example 3. Comparative Example 2 (light crude oil) requires 60 min, which is 2.7 times that of Example 2. Although Comparative Example 3 only takes 20 min, its accuracy and precision are seriously substandard and it has no practical application value.

[0143] The core efficiency advantage of this embodiment lies in the targeted optimization of the technical solution: the pretreatment stage adopts a standardized process of water bath heating, oscillation, and centrifugation, eliminating the need for complex manual operations; the duration of 2-3 extractions is controlled to balance the effect, avoiding the waste of efficiency caused by over-extraction; the counting time of 180-300s in the instrument analysis stage is optimized, avoiding the efficiency loss of blindly extending the time while ensuring the accuracy of signal statistics; the automated coordination at the system level (the control unit coordinates the working rhythm of pretreatment and spectrometer) further reduces the time spent on manual intervention.

[0144] The efficiency bottleneck of traditional methods stems from the nature of the process: the combustion-microcoulometric method of Comparative Example 1 requires multiple complex steps such as combustion, electrolysis, and titration, and heavy oils also need to be treated for carbon deposits; the sodium biphenyl method of Comparative Example 2 relies on manual titration and reagent reaction equilibrium, which is cumbersome and time-consuming; although Comparative Example 3 is slightly more efficient, it comes at the cost of precision and accuracy, and cannot meet the needs of industrial testing.

[0145] 4. Scope of Application (Compatibility with Light and Heavy Crude Oils) Analysis

[0146] As shown in Table 7, Example 2 was designed for light crude oil, with a measurement deviation of only -1.6% and a spiked recovery rate of 97.5%~100.3%; Example 3 was designed for heavy crude oil, with a measurement deviation of -0.6%, a clear organic phase without emulsification, and a spiked recovery rate of 98.2%~100.7%, achieving full coverage compatibility for both light and heavy crude oils; while Comparative Example 2 could not dissolve heavy crude oil and could only be adapted to light oil; Comparative Example 1 did not burn the heavy crude oil completely and had poor compatibility; Comparative Example 3 did not optimize the pretreatment parameters for crude oil viscosity and could only barely adapt to light oil, with no compatibility with heavy oil.

[0147] The breakthrough in adaptability of the embodiments stems from a deep adaptation to the characteristics of the crude oil matrix: the pretreatment stage adjusts the ethanol-water ratio (1:2 for light oil, 1:4 for heavy oil) to match the miscibility requirements of crude oils with different viscosities, avoiding excessive dilution of light oil or emulsification of heavy oil; the flexible adjustment of the number of extractions (3 times for light oil, 2 times for heavy oil) balances the recovery of trace organochlorines in light oil with the stability of the organic phase in heavy oil; the wide range of instrument parameters is designed to adapt to the detection requirements of different contents of organochlorines in light and heavy crude oils, with short counting times and low tube voltages for low concentrations (light oil) and long counting times and high tube voltages for high concentrations (heavy oil), ensuring signal response adaptability in all scenarios. Comparative Example 2 is limited by the reagent's solubility and cannot overcome the high viscosity barrier of heavy oil; the combustion mechanism of Comparative Example 1 cannot adapt to the complex components of heavy oil; the fixed parameter design of Comparative Example 3 lacks flexibility and cannot cope with the viscosity differences of the crude oil matrix.

[0148] 5. System Stability Analysis

[0149] As shown in Table 7, in Example 4, the detection system of this invention achieved a stable RSD of 2.10%~2.30% for 100 consecutive tests. The maximum deviation before drift correction was 1.39%, and the deviation after correction was ≤0.31%. All 100 sets of data were completely stored and the export function was normal, with no system failures. In contrast, existing technologies lack drift correction mechanisms, and long-term testing is prone to accuracy decline due to instrument aging and environmental fluctuations. Furthermore, they lack systematic data management functions. This stability advantage stems from the innovative collaborative design of the system: the integrated architecture of the sample pretreatment device, spectrometer, control unit, and data processor coordinates the working rhythm of each module through the control unit, avoiding process fluctuations caused by manual intervention; the oven, electronic analytical balance, and centrifuge in the sample pretreatment device ensure the consistency and repeatability of pretreatment conditions; the drift correction function of the data processor monitors the sample in real time to capture changes in instrument status, dynamically corrects the calibration curve, and compensates for errors caused by X-ray tube aging and environmental temperature fluctuations; the data storage and export functions ensure the traceability of test data and meet the management needs of industrial batch testing. Existing methods mostly involve combinations of independent equipment, lacking a unified control and calibration system. The stability of long-term testing cannot be guaranteed, making it difficult to meet the continuous operation requirements of industrial scenarios.

[0150] The above description, in conjunction with preferred embodiments, provides a further detailed explanation of the present invention and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the inventive concept, and all such substitutions or modifications should be considered within the scope of protection of the present invention.

Claims

1. A method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy, characterized in that, Includes the following steps: (1) Sample pretreatment: The crude oil sample was mixed with an ethanol-water solution, heated in a water bath, centrifuged to separate the oil phase, and the extraction was repeated to collect and combine the organic phases; (2) Instrumental analysis: The treated organic phase sample was placed in a single-wavelength dispersive X-ray fluorescence spectrometer, and the X-ray fluorescence intensity of chlorine was measured in vacuum mode. The counting time was 180-300s and the ambient temperature was 23-27℃. (3) Calibration curve establishment: Using a series of chlorine standard solutions, fluorescence intensity was measured under the instrument analysis conditions to establish a calibration curve between the count rate and chlorine concentration; (4) Sample determination and calculation: Calculate the organic chlorine content in crude oil based on the fluorescence intensity of the crude oil sample to be tested and the calibration curve.

2. The method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 1, characterized in that, In step (1), the ethanol-water solution is prepared by mixing ethanol and water in a volume ratio of 1:(2-4).

3. The method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 1, characterized in that, The extraction is repeated 2-3 times in step (1).

4. The method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 1, characterized in that, The operating conditions of the single-wavelength dispersive X-ray fluorescence spectrometer in step (2) also include: the X-ray tube target material is Rh; the X-ray tube voltage is 35-45kV; the analytical spectral line is Cl Kα; the crystal type is PX-1; the vacuum degree is ≤10Torr; the X-ray tube current is 25-35μA; and the detector type is a flow gas proportional counter.

5. The method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 1, characterized in that, The linear range of the calibration curve in step (3) is 0.08-1000 mg / kg.

6. The method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 1, characterized in that, In step (3), the concentration points of the chlorine standard solution series cover the range of 0-1000 mg / kg.

7. The method for detecting organochlorine compounds in crude oil based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 1, characterized in that, In step (3), the slope k of the calibration curve is 0.8-0.9 cps·kg / mg.

8. A system for implementing the single-wavelength dispersive X-ray fluorescence spectroscopy method for detecting organochlorine compounds in crude oil according to any one of claims 1-7, characterized in that, include: Sample pretreatment device; Single-wavelength dispersive X-ray fluorescence spectrometer; control unit; Data processor; The output end of the sample pretreatment device is detachably connected to the sample chamber of the single-wavelength dispersive X-ray fluorescence spectrometer, and the sample box is transferred to the spectrometer detection position through the sample injection unit. The control unit is electrically connected to the sample pretreatment device, the spectrometer, and the data processor via circuits. The data processor is connected to the spectrometer via a data line to receive fluorescence signal data and communicate bidirectionally with the control unit.

9. The crude oil organochlorine detection system based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 8, characterized in that, The sample pretreatment device includes an oven, an electronic analytical balance, and a centrifuge.

10. The crude oil organochlorine detection system based on single-wavelength dispersive X-ray fluorescence spectroscopy according to claim 8, characterized in that, The data processor is also configured to perform drift correction by real-time correction of the calibration curve by monitoring the fluorescence intensity of the sample.

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