Method for determining trace alcohol content in butadiene

Abstract

The application relates to the field of detection analysis technology, and is a butadiene micro-alcohol content determination method.The butadiene micro-alcohol content determination method is performed according to the following method: first, butadiene standard samples containing alcohol substances are prepared; then, the butadiene standard samples containing alcohol substances are detected and analyzed by using gas chromatography to obtain a standard curve; finally, the sample to be detected is detected and analyzed by using gas chromatography, and the concentration of the micro-alcohol in the sample to be detected is obtained in combination with the standard curve.The butadiene micro-alcohol content determination method has good peak shape, high resolution, good repeatability and high accuracy, and can comprehensively detect and control the butadiene micro-alcohol content.

Description

Technical Field

[0001] This invention relates to the field of detection and analysis technology, and is a method for determining the trace alcohol content in butadiene. Background Technology

[0002] Butadiene is an important petrochemical raw material with reactive chemical properties. It can be used to produce synthetic rubber, and synthetic rubber using butadiene as the main raw material accounts for more than 80% of the total synthetic rubber production. Excessive alcohol content in butadiene can terminate the polymerization reaction, and in severe cases, lead to plant shutdown, seriously jeopardizing stable production. Therefore, accurately detecting trace alcohol content in butadiene is of great guiding significance for the production of polymerization plants. Currently, there are no national standards in my country for detecting trace alcohol content in butadiene, and no relevant foreign literature has been found. Therefore, establishing a method for determining trace alcohol content in butadiene and realizing the detection of trace alcohols in butadiene is an important problem that urgently needs to be solved in production.

[0003] Chinese patent document CN104614477A discloses a method for determining trace methanol content in 1-butene. This invention involves connecting a sampling cylinder filled with a 1-butene sample to a liquid hydrocarbon flash evaporator, which is preheated and stabilized at 100°C. A liquid hydrocarbon flash vaporization injector is connected to a gas chromatograph. The injector valve is opened, and the gas is purged for approximately 3 minutes. The chromatograph is then activated, and the sample is injected into a quantitative tube. A chromatograph workstation records the methanol peak area in the sample. Finally, a single-point calibration is used to calculate the methanol content in the sample. However, this patent only measures methanol in the range of 1 mg / kg to 5 mg / kg, and it cannot detect trace alcohols with concentrations below 1 mg / kg. Furthermore, the calibration operation is inflexible and inefficient.

[0004] Chinese patent document CN108387653A discloses a method for determining the ethanol content in industrial methanol. Under selected operating conditions, the sample is vaporized and passed through a capillary chromatographic column at a constant temperature, allowing for the separation of components. The components are then detected using a flame ionization detector and quantified using the external standard method to calculate the mass fraction of ethanol. This patent can determine the ethanol content of liquid samples at room temperature and pressure, but it is not applicable to the determination of trace alcohol content in butadiene samples in the gas phase at room temperature and pressure.

[0005] Chinese patent document CN103743844B discloses a method for determining the ethanol content in methanol. This invention provides a method for determining the ethanol content in methanol using gas chromatography. First, the peak area of ​​a standard sample is measured to plot a standard curve. Then, the peak area of ​​the sample to be tested is measured under the same conditions as the standard sample. Based on the obtained peak area of ​​the sample to be tested, the ethanol mass fraction in methanol can be obtained from the standard curve. However, this patent cannot analyze samples that are in the gas phase at room temperature and pressure.

[0006] Chinese patent document CN1900711A discloses a method and apparatus for determining trace amounts of alcohols in low-boiling-point hydrocarbons. This invention employs liquid-phase sampling and injection, overcoming errors caused by sampling and injection methods in existing analytical methods. This ensures the sample entering the chromatograph retains its original composition, allowing the chromatographic results to accurately reflect the composition of the analyzed material. The invention also provides an apparatus for determining trace amounts of alcohols in low-boiling-point hydrocarbons. This apparatus includes a sampling cylinder and a gas chromatograph connected to the sampling cylinder via a liquid valve. The inlet of the sampling cylinder is connected to an inert gas cylinder via a gas valve, facilitating the filling of the sampling cylinder with inert gas to maintain a certain pressure for the low-boiling-point hydrocarbons, ensuring the extraction of the liquid sample. However, this patent can only determine sec-butanol, methyl ethyl ketone, and tert-butanol, and is not applicable to the determination of trace amounts of methanol and ethanol in butadiene components.

[0007] Authorization announcement number CN104698100B discloses a method for determining the residual solvent methanol of fluorochloropyridine using headspace gas chromatography. The specific method involves using an Agilent 7890A gas chromatograph equipped with an FID detector and an Agilent 7694E headspace sampler, employing an Agilent DB-624 column. The initial column temperature is 40℃, held for 3 min, then increased to 60℃ at a rate of 2℃ / min, then to 115℃ at a rate of 9.2℃ / min, and finally to 240℃ at a rate of 30℃ / min, held for 2 min. The detection temperature is 250℃, and the injection port temperature is 150℃. However, this patent is applicable to the residual solvent system of fluorochloropyridine and cannot be used for the determination of trace amounts of methanol and ethanol in butadiene.

[0008] Currently, there is a lack of methods for determining trace alcohol content in butadiene. The closest existing technologies suffer from high detection limits and poor cost-effectiveness, failing to meet practical needs. Addressing these shortcomings, a pressing technical problem needs to be solved to detect trace alcohol content below 1 mg / kg in butadiene. Summary of the Invention

[0009] This invention provides a method for determining the content of trace alcohols in butadiene, which overcomes the shortcomings of the prior art and can effectively solve the problem that existing detection methods cannot detect the content of trace alcohols in butadiene with a concentration of less than 1 mg / kg.

[0010] The technical solution of this invention is achieved through the following measures: a method for determining the trace alcohol content in butadiene, performed according to the following method: S1, Prepare a standard sample of butadiene containing alcohols; S2, Butadiene standard samples containing alcohols were analyzed by gas chromatography to obtain a standard curve; S3. The sample to be tested is detected and analyzed by gas chromatography, and the concentration of trace alcohol in the gas to be tested is obtained by combining the standard curve.

[0011] The following are further optimizations and / or improvements to the above-mentioned technical solution: In step S1 above, the concentration of alcohol-containing compounds in the butadiene standard sample containing alcohols is 0.2 mg / g to 20 mg / g, and the diluent is one of toluene, isooctane, n-heptane, and n-hexane.

[0012] In the above gas chromatography conditions, the chromatographic column includes a pre-separation column, a main separation column, and a damping column; Pre-separation column: WAX polar capillary column with a length of 50m and an inner diameter of 0.32mm; Re-separation column: capillary column, 20m long, 0.32mm inner diameter WAX polar capillary column; Damping column: capillary column, 1.8m long, 0.18mm inner diameter.

[0013] In the gas chromatography conditions of steps S2 and S3 above, the alcohols are methanol and ethanol. Methanol is cut at 7.0 min to 7.2 min and ethanol is cut at 8.1 min to 8.3 min. The cutting is performed using the shut-off valve in the DeanSwitch microplate flow path switcher.

[0014] In the gas chromatography conditions of steps S2 and S3 above, the detector temperature is 250℃, the hydrogen flow rate is 35mL / min, the air flow rate is 350mL / min, and the make-up gas (helium) flow rate is 35mL / min.

[0015] In the gas chromatography conditions of steps S2 and S3 above, the injection port temperature is 120℃, the injection mode is split, the split ratio is 1:20, the split flow rate is 123mL / min, and the pre-separation column pressure is 220kPa.

[0016] In the gas chromatography conditions of steps S2 and S3 above, the initial column temperature is 40℃, held for 3 min, then increased to 80℃ at a rate of 20℃ / min, and held for 10 min.

[0017] In the gas chromatography conditions of steps S2 and S3 above, the headspace sampler carrier gas pressure is 250 kPa, the injection needle temperature is 80°C, and the transfer line temperature is 80°C.

[0018] In the gas chromatography conditions of steps S2 and S3 above, the headspace vial equilibration time is 20 min, the pressure replacement time during injection is 2 s, the injection time is 2 s, the venting time is 20 s, and the isothermal time is 1 min.

[0019] The method for determining the trace alcohol content in butadiene of this invention produces chromatograms with good peak shape, high separation, good repeatability, and high accuracy, enabling comprehensive detection and control of the trace alcohol content in butadiene. Attached Figure Description

[0020] Figure 1 This is the gas chromatogram of the sample to be tested without switching using the DeanSwitch microplate flow path switcher.

[0021] Figure 2 The gas chromatogram of the sample to be tested was obtained by switching the flow path using the DeanSwitch microplate flow path switcher.

[0022] Figure 3 This is the gas chromatogram of a blank standard sample.

[0023] Figure 4 This is the gas chromatogram of the sample to be tested.

[0024] Figure 5 This is the standard curve of methanol in the sample to be tested.

[0025] Figure 6 This is the standard curve of ethanol in the sample to be tested. Detailed Implementation

[0026] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0027] The present invention will be further described below with reference to embodiments: Example 1: The method for determining the trace alcohol content in butadiene is as follows: S1, Prepare a standard sample of butadiene containing alcohols; S2, Butadiene standard samples containing alcohols were analyzed by gas chromatography to obtain a standard curve; S3. The sample to be tested is detected and analyzed by gas chromatography, and the concentration of trace alcohol in the gas to be tested is obtained by combining the standard curve.

[0028] Example 2: As an optimization of the above example, in step S1, the concentration of alcohol-containing compounds in the butadiene standard gas containing alcohols is 0.2 mg / g to 20 mg / g, and the diluent is one of toluene, isooctane, n-heptane and n-hexane.

[0029] Example 3: As an optimization of the above example, in the gas chromatography conditions of steps S2 and S3, the chromatographic column includes a pre-separation column, a re-separation column, and a damping column; Pre-separation column: WAX polar capillary column with a length of 50m and an inner diameter of 0.32mm; Re-separation column: capillary column, 20m long, 0.32mm inner diameter WAX polar capillary column; Damping column: capillary column, 1.8m long, 0.18mm inner diameter.

[0030] Example 4: As an optimization of the above examples, the gas chromatograph includes a gas chromatograph and a DeanSwitch microplate flow path switcher. The gas chromatograph is equipped with a split injection port and a flame ionization detector. The DeanSwitch microplate flow path switcher connects the pre-separation column and the re-separation column.

[0031] Example 5: As an optimization of the above examples, in the gas chromatography conditions of steps S2 and S3, the alcohols are methanol and ethanol. Methanol is cut off at 7.0 min to 7.2 min, and ethanol is cut off at 8.1 min to 8.3 min. The cutting off is performed using the shut-off valve in the DeanSwitch microplate flow path switcher. It should be further noted that this cutting off time is determined based on the elution times of methanol and ethanol in the pre-separation column.

[0032] Example 6: As an optimization of the above example, in the gas chromatography conditions of steps S2 and S3, the detector temperature is 250°C, the hydrogen flow rate is 35 mL / min, the air flow rate is 350 mL / min, and the make-up gas (helium) flow rate is 35 mL / min.

[0033] Example 7: As an optimization of the above example, in the gas chromatography conditions of steps S2 and S3, the injection port temperature is 120°C, the injection mode is split, the split ratio is 1:20, the split flow rate is 123 mL / min, and the pre-separation column pressure is 220 kPa.

[0034] Example 8: As an optimization of the above example, in the gas chromatography conditions of steps S2 and S3, the initial column temperature is 40°C, held for 3 min, and then increased to 80°C at a rate of 20°C / min, and held for 10 min.

[0035] Example 9: As an optimization of the above example, in the gas chromatography conditions of steps S2 and S3, the headspace sampler carrier gas pressure is 250 kPa, the injection needle temperature is 80°C, and the transfer line temperature is 80°C.

[0036] Example 10: As an optimization of the above example, in the gas chromatography conditions of steps S2 and S3, the headspace vial equilibration time is 20 min, the pressure replacement time during injection is 2 s, the injection time is 2 s, the venting time is 20 s, and the isothermal time is 1 min.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first involves preparing standard stock solutions of alcohols at various concentrations using a diluent. Then, different volumes of these standard stock solutions are extracted into sealed headspace vials containing butadiene to obtain butadiene standard samples of various concentrations. Next, these butadiene standard samples are injected into a capillary column using headspace injection. As the sample passes through the capillary column with the carrier gas, it is separated. The separated components enter a flame ionization detector (FID), and the peak areas of the alcohols are recorded on a computer. A standard curve is constructed with the concentration of alcohols in the standard samples as the x-axis and the peak area as the y-axis. Finally, when measuring a sample containing trace amounts of alcohols, the content of trace alcohols in the sample is calculated using the external standard method on the standard curve by recording the peak area of ​​the alcohols.

[0038] When the raw materials processed by the butadiene unit vary significantly, trace amounts of alcohol components may be present in the butadiene. These alcohol components can affect the polymerization reaction and, in severe cases, cause the unit to shut down. This invention achieves accurate determination of trace alcohols in butadiene. The invention provides self-prepared butadiene standard samples containing alcohols, with a concentration range of 0.2 mg / kg to 20 mg / kg, a linearity greater than 0.99, and a detection limit of 0.2 mg / kg. Furthermore, the use of the DeanSwitch microplate flow path switcher, also known as DeanSwitch solvent cutting technology, eliminates the influence of butadiene chromatographic peak tailing. In addition, the use of mature headspace sampling enables automated sample introduction.

[0039] Example 11: The specific method for determining the trace alcohol content in butadiene is as follows: (1) Instruments and materials Gas Chromatograph: Agilent 6890N gas chromatograph, equipped with programmed temperature rise, flame ionization detector, and split capillary inlet. Columns include pre-separation column, re-separation column, and damping column; Pre-separation column: 50m long, 0.32mm inner diameter WAX polar capillary column; Re-separation column: 20m long, 0.32mm inner diameter WAX polar capillary column; Damping column: 1.8m long, 0.18mm inner diameter capillary column. DeanSwitch microplate flow path switching device. Headspace Sampler: COLINTECH AutoHS headspace sampler. Hydrogen: Purity greater than 99.99%. Air: Generated by an air compressor and purified by molecular sieves and color-changing silica gel. The color-changing silica gel should remain blue; if it turns red, it needs to be dried and dehydrated. Butadiene: Free of methanol and ethanol, purity greater than 99.5%. n-Hexane: Analytical grade, free of methanol and ethanol. Methanol: Analytical grade. Anhydrous ethanol: Analytical grade. Microsyringes: 25 mL, 100 mL.

[0040] (2) Sample preparation A. Preparation of butadiene standard samples containing alcohols: Using hexane as solvent and methanol and ethanol as solutes, standard mother liquors of 200 mg / kg and 2000 mg / kg were prepared for use. Inject 3g to 5g of butadiene into the headspace vial. Taking 4g as an example, use a microsyringe to draw 6μL, 15μL, 30μL, and 60μL of 200mg / kg standard stock solution into the headspace vial to prepare butadiene standard samples containing methanol and ethanol with concentrations of 0.2mg / g, 0.5mg / g, 1.0mg / g, and 2.0mg / g, respectively. 21 μL, 30 μL, and 60 μL of 2000 mg / kg standard stock solution were drawn into headspace vials using a microsyringe to prepare butadiene standard samples containing alcohols with concentrations of 7.0 mg / g, 10.0 mg / g, and 20.0 mg / g, respectively. The extraction volumes of mother liquor at various concentrations using a microsyringe are shown in Table 1. In Table 1, the alcohol concentration is 0.5 mg / g as an example. The density of n-hexane is 0.66 kg / L. When the extraction volume is 15 μL, (15 μL × 0.66 kg / L × 200 mg / kg) / 4g = 0.5 mg / g, that is, the alcohol concentration is 0.5 mg / g). By default, 4g of butadiene is added to the headspace vial.

[0041] B. Preparation of blank standard samples: Take a headspace vial containing 4g of butadiene and add 20mL of n-hexane as a blank standard sample.

[0042] C. Preparation of the sample to be tested: 4g of butadiene sample was injected into the headspace vial.

[0043] (3) Detection and Analysis Gas chromatography was used to sequentially determine the concentrations of blank standard samples and butadiene standard samples containing methanol and ethanol at concentrations of 0.2 mg / g, 0.5 mg / g, 1.0 mg / g, 2.0 mg / g, 7.0 mg / g, 10.0 mg / g, and 20.0 mg / g. A standard curve was constructed with the methanol and ethanol concentrations of the butadiene standard samples as the x-axis and the peak areas of methanol and ethanol as the y-axis. The gas chromatographic conditions were as follows: Chromatographic columns include pre-separation columns, re-separation columns, and damping columns; Pre-separation column: WAX polar capillary column with a length of 50m and an inner diameter of 0.32mm; Re-separation column: capillary column, 20m long, 0.32mm inner diameter WAX polar capillary column; Damping column: capillary column, 1.8m long, 0.18mm inner diameter.

[0044] The detector temperature was 250℃, the hydrogen flow rate was 35 mL / min, the air flow rate was 350 mL / min, and the tail gas (helium) flow rate was 35 mL / min. The injection port temperature is 120℃, the injection mode is split, the split ratio is 1:20, the split flow rate is 123mL / min, and the pressure at the inlet of the pre-separation column is 220kPa. The initial column temperature was 40℃, held for 3 minutes, then increased to 80℃ at a rate of 20℃ / min, and held for 10 minutes. The headspace sampler has a carrier gas pressure of 250 kPa, an injection needle temperature of 80°C, and a transfer line temperature of 80°C. The headspace vial equilibration time is 20 min, the pressure displacement time during sample injection is 2 s, the injection time is 2 s, the venting time is 20 s, and the isothermal time is 1 min. Cutting was performed using the shut-off valve in the DeanSwitch microplate flow path switcher, with methanol being cut at 7.0 min to 7.2 min and ethanol at 8.1 min to 8.3 min.

[0045] Gas chromatography was used to determine the sample, and the peak areas of methanol and ethanol were recorded. The concentrations of methanol and ethanol in the sample were calculated using the formula X=A×S+B, where X is the mass fraction of methanol and ethanol in the sample (g / g); A is the slope of the standard curve; B is the intercept of the standard curve; and S is the peak area of ​​methanol and ethanol in the sample.

[0046] (4) Test results: Gas chromatogram of the sample not switched using the DeanSwitch microplate flow path switch, as shown below. Figure 1 As shown, the gas chromatogram of the sample to be tested, switched using the DeanSwitch microplate flow path switcher, is as follows: Figure 2 As shown, Figure 1 and Figure 2 In the peaks, 1 represents butadiene, 2 represents methanol, and 3 represents ethanol. Figure 1 and Figure 2 It can be seen that the DeanSwitch microplate flow path switcher, also known as DeanSwitch solvent cutting technology, eliminates the problem of butadiene chromatographic peak tailing affecting the peak area of ​​the target peak.

[0047] The gas chromatogram of the blank standard sample is as follows: Figure 3 As shown, the gas chromatogram of the sample to be tested is as follows: Figure 4 As shown, Figure 3 and Figure 4 In the graph, peak 1 represents butadiene, peak 2 represents methanol, and peak 3 represents ethanol. Based on the peak areas of methanol and ethanol, standard curves for methanol and ethanol are obtained. The standard curve for methanol is shown in the figure below. Figure 5 As shown, the standard curve of methanol is as follows: Figure 6 As shown. From Figure 5 and Figure 6 As can be seen, the self-prepared butadiene standard sample containing alcohols of the present invention has a concentration range of 0.2 mg / kg to 20 mg / kg, a linearity greater than 0.99, and a detection limit of 0.2 mg / kg. Therefore, the method for determining the trace alcohol content in butadiene provided by the present invention produces a spectrum with good peak shape, high resolution, good repeatability, and high accuracy.

[0048] Example 12: Methodological Validation Repeated examination Butadiene samples with alcohol concentrations ranging from 0.4 mg / kg to 16 mg / kg were injected five times in parallel. The determination of trace alcohol content in butadiene was performed according to the method described in Example 11 of this invention, with reference to the control sample. Figure 5 , Figure 6 The standard curve was used to calculate the methanol and ethanol content. Results: As shown in Tables 2 and 3, the relative standard deviation of the measured values ​​of butadiene standard samples containing alcohols at various concentrations was less than 5.0%, indicating that the method for determining trace alcohol content in butadiene in this invention has good repeatability.

[0049] Accuracy assessment Butadiene standard samples containing known concentrations of methanol (0.41 mg / g, 4.81 mg / g, 10.77 mg / g) and ethanol (0.61 mg / g, 2.23 mg / g, 14.56 mg / g) were prepared. The peak areas of the chromatograms were calculated according to the method for determining trace alcohol content in butadiene as described in Example 11 of this invention. Results: As shown in Tables 4 and 5, the absolute error (mg / g) between the actual and measured values ​​of the butadiene standard samples containing alcohols at each concentration was less than 1.5 mg / g, indicating that the method for determining trace alcohol content in butadiene of this invention has good accuracy.

[0050] In summary, the method for determining the trace alcohol content in butadiene of the present invention produces chromatograms with good peak shape, high resolution, good repeatability, and high accuracy, and can comprehensively detect and control the trace alcohol content in butadiene.

[0051] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for determining the trace alcohol content in butadiene, characterized in that... Perform the following steps: S1, Prepare a standard sample of butadiene containing alcohols; S2, Butadiene standard samples containing alcohols were analyzed by gas chromatography to obtain a standard curve; S3. The sample to be tested is detected and analyzed by gas chromatography, and the concentration of trace alcohol in the sample is obtained by combining the standard curve.

2. The method for determining the trace alcohol content in butadiene according to claim 1, characterized in that... In step S1, the concentration of alcohol in the butadiene standard sample containing alcohol is 0.2 mg / g to 20 mg / g, and the diluent is one of toluene, isooctane, n-heptane and n-hexane.

3. The method for determining the trace alcohol content in butadiene according to claim 1 or 2, characterized in that... In the gas chromatography conditions of steps S2 and S3, the chromatographic column includes a pre-separation column, a re-separation column, and a damping column; Pre-separation column: WAX polar capillary column with a length of 50m and an inner diameter of 0.32mm; Re-separation column: capillary column, 20m long, 0.32mm inner diameter WAX polar capillary column; Damping column: capillary column, 1.8m long, 0.18mm inner diameter.

4. The method for determining the trace alcohol content in butadiene according to claim 1, 2, or 3, characterized in that... In the gas chromatography conditions of steps S2 and S3, the alcohols are methanol and ethanol. Methanol is cut at 7.0 min to 7.2 min and ethanol is cut at 8.1 min to 8.3 min. The cutting is performed using the shut-off valve in the DeanSwitch microplate flow path switcher.

5. The method for determining the trace alcohol content in butadiene according to any one of claims 1 to 4, characterized in that... In the gas chromatography conditions of steps S2 and S3, the detector temperature was 250℃, the hydrogen flow rate was 35 mL / min, the air flow rate was 350 mL / min, and the make-up gas flow rate was 35 mL / min.

6. The method for determining the trace alcohol content in butadiene according to any one of claims 1 to 5, characterized in that... In steps S2 and S3, the chromatographic conditions for gas chromatography were as follows: the injection port temperature was 120℃, the injection mode was split, the split ratio was 1:20, the split flow rate was 123 mL / min, and the pre-separation column pressure was 220 kPa.

7. The method for determining the trace alcohol content in butadiene according to any one of claims 1 to 6, characterized in that... In steps S2 and S3 of the gas chromatography, the initial column temperature is 40°C, held for 3 minutes, then increased to 80°C at a rate of 20°C / min, and held for 10 minutes.

8. The method for determining the trace alcohol content in butadiene according to any one of claims 1 to 7, characterized in that... In the gas chromatography conditions of steps S2 and S3, the headspace sampler carrier gas pressure is 250 kPa, the injection needle temperature is 80°C, and the transfer line temperature is 80°C.

9. A method for determining the trace alcohol content in butadiene according to any one of claims 1 to 8, characterized in that... In the gas chromatography conditions of steps S2 and S3, the headspace vial equilibration time is 20 min, the pressure replacement time during injection is 2 s, the injection time is 2 s, the venting time is 20 s, and the isothermal time is 1 min.

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