Method for measuring content of tetrahydrofuran in polyester solid

Abstract

The invention discloses a method for determining the content of tetrahydrofuran in a polyester solid, which comprises the following steps: detecting tetrahydrofuran standard samples with different concentrations by using gas chromatography to obtain respective tetrahydrofuran chromatographic peak areas, and fitting the concentrations and the chromatographic peak areas to obtain a tetrahydrofuran detection line; another tetrahydrofuran standard sample with other concentration is adopted to detect the obtained tetrahydrofuran detection line, and the tetrahydrofuran detection line is qualified when the error is within the range of + / -2%; the method comprises the following steps: carrying out heating reflux on a to-be-detected polyester solid sample by using an extracting agent to complete extraction, then detecting an extract liquid through gas chromatography to obtain the chromatographic peak area of tetrahydrofuran, calculating the concentration of tetrahydrofuran in the extract liquid through a tetrahydrofuran detection line, and then calculating the content of tetrahydrofuran in the polyester solid sample. The method provided by the invention has the advantages of wide analysis range, simple operation, low cost, and good precision and accuracy.

Description

Technical Field

[0001] The invention relates to the field of determination and analysis of tetrahydrofuran in solid samples, and in particular to a method for determining the content of tetrahydrofuran in polyester solids. Background Art

[0002] Because butanediol can be dehydrated and cyclized to tetrahydrofuran, the tetrahydrofuran content must be controlled during the production of these polyesters. Tetrahydrofuran is an important raw material for organic synthesis and a highly effective solvent. However, because it exists in a free form in polymers, it is difficult to extract. The existing standard GBZ / T 160.75-2007, "Determination of Heterocyclic Compounds in Workplace Air Toxic Substances," can measure the content of gaseous tetrahydrofuran. Using a 401 single-tube sample collection method and carbon disulfide analysis, the detection limit for tetrahydrofuran is 5.1 μg / mL, with a measurement range of 5.1-250 μg / mL. However, using single-tube collection results in inconsistent analysis efficiency.

[0003] If this method is used to determine the content of tetrahydrofuran in polyester solids, there are the following deficiencies: (1) Tetrahydrofuran is a type of heterocyclic organic compound with a boiling point of 66°C. It is miscible with water at room temperature, while polyester has a high melting point. If you want to melt the polyester solid to precipitate the tetrahydrofuran in the polymer and collect and analyze it, you can only use closed heating and headspace sampling for analysis. The determination of tetrahydrofuran in the gas requires the use of a 401 monomer tube to collect the sample, and then use carbon disulfide for analysis. The analysis efficiency is unstable, and the detection limit and detection range are limited. If you want to analyze the tetrahydrofuran in the polymer into gas, the reagent must be able to dissolve the polymer, release tetrahydrofuran, and collect it. The operation is difficult and the implementation effect is not good. (2) GBZ / T160.75-2007 "Determination of Heterocyclic Compounds in Workplace Air Toxic Substances" has a limited detection limit and measurement range, which has certain limitations and is not suitable for solid analysis.

[0004] CN201811584057.5 discloses a method for determining the content of tetrahydrofuran in PBT, which adopts a headspace method, uses a professional headspace device to heat the polyester sample at high temperature, releases THF in the slice into the headspace bottle, and then uses gas chromatography to analyze the amount of THF in the headspace bottle gas, and further deduce the content of THF in the polyester slice. This method has high analysis cost and high volatility of THF during crushing. The extraction method proposed in the present invention is to use an extractant to continuously heat and reflux at a certain temperature so that all THF in the polyester slice is freed into the solution, and then use the advantages of gas chromatography with high efficiency, high selectivity and high sensitivity to analyze the amount of THF in the solution, thereby deducing the content of THF in the polyester; the present invention is different from it in that it is a liquid phase extraction of THF in the solid, and THF is transferred to a solvent. This method has low analysis cost and simple operating procedure. Summary of the Invention

[0005] The present invention aims to provide a method for determining the tetrahydrofuran content in polyester solids. The method comprises detecting a fitted calibration curve, extracting tetrahydrofuran from a sample using an extraction method, measuring the tetrahydrofuran content in the sample by gas chromatography to obtain the peak area, and then calculating the tetrahydrofuran content in the polyester solids using the calibration curve.

[0006] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0007] A method for determining the content of tetrahydrofuran in polyester solids comprises the following steps:

[0008] Using gas chromatography to detect tetrahydrofuran standard samples of different concentrations, the chromatographic peak area of ​​each tetrahydrofuran is obtained, and the tetrahydrofuran calibration curve is obtained by fitting the concentration and the chromatographic peak area;

[0009] The obtained tetrahydrofuran calibration curve is tested with a tetrahydrofuran standard sample of another concentration, and the error is within the range of ±2%, which is considered qualified.

[0010] The polyester solid sample to be tested is subjected to heating reflux using an extractant to complete extraction, and then the extract is detected by gas chromatography. The obtained tetrahydrofuran chromatographic peak area is calculated using the tetrahydrofuran calibration curve to obtain the concentration of tetrahydrofuran in the extract, and then the content of tetrahydrofuran in the polyester solid sample is calculated.

[0011] In the extraction method, preferably, the extractant is selected from at least one of pure water, dimethylformamide, methanol, acetonitrile, ethanol, propanol, and acetone; more preferably pure water.

[0012] THF is a highly polar substance. According to the principle of "similar polarity is compatible", polar substances such as methanol, acetonitrile, and water are selected as extraction solvents.

[0013] THF is contained in the PBS polymer and must reach a certain temperature before it can evaporate from the PBS polymer. The present invention investigated the separation effect of THF using ethanol as the extraction agent. The results showed that after 5 hours of boiling ethanol under reflux, the amount of free THF extracted from the PBS slices was less than half of the actual content. This indicates that reagents with lower boiling points than water, such as methanol and ethanol, are not as effective as pure water in extraction.

[0014] Preferably, 6 to 20 mL of the extractant is used per gram of the polyester solid sample to be tested; more preferably, 6 to 10 mL is used.

[0015] Preferably, the extraction temperature is 70-100°C; more preferably 70-90°C.

[0016] Preferably, the extraction time is 3 to 7 hours; more preferably 4 to 6 hours.

[0017] According to the determination method of the present invention, preferably, the concentration range of the tetrahydrofuran standards of different concentrations is 10ppm to 300ppm; for example, in the embodiment, tetrahydrofuran standards with concentrations of 10ppm, 20ppm, 40ppm, 80ppm, 100ppm, 120ppm, 140ppm, 160ppm, 180ppm, 200ppm and 300ppm are prepared, and the tetrahydrofuran calibration curve is determined and fitted based on this.

[0018] According to the determination method of the present invention, preferably, the step of using another tetrahydrofuran standard sample of another concentration to test the obtained tetrahydrofuran calibration curve comprises:

[0019] A tetrahydrofuran standard sample of another concentration is subjected to gas chromatography to obtain a tetrahydrofuran chromatographic peak area, and then the concentration of the tetrahydrofuran is calculated based on the obtained tetrahydrofuran calibration curve. The calculated result is compared with the true value, and the test is qualified if the error is within ±2%. "Other concentration" refers to a concentration different from the concentration used to establish and fit the tetrahydrofuran calibration curve. It is understood by those skilled in the art that the "other concentration" is preferably within the concentration range of the tetrahydrofuran standard sample of different concentration.

[0020] According to the determination method of the present invention, preferably, the extract is subjected to two or more parallel gas chromatography tests, two or more tetrahydrofuran concentrations are calculated, and the average of these two or more tetrahydrofuran concentrations in the extract is taken as the tetrahydrofuran concentration in the polyester solid sample. More preferably, the relative error allowed for the two or more parallel results is ±10%. Further preferably, the two parallel gas chromatography tests are performed in parallel.

[0021] According to the determination method of the present invention, preferably, the preparation process of the tetrahydrofuran standards of different concentrations includes:

[0022] Prepare a certain concentration of tetrahydrofuran mother solution, and then dilute it into tetrahydrofuran standards of different concentrations.

[0023] More preferably, the concentration of the tetrahydrofuran mother liquor is 0.005 to 0.015 g / mL.

[0024] According to the determination method of the present invention, preferably, the solvent of the tetrahydrofuran mother liquor is pure water, and the tetrahydrofuran standard samples of different concentrations are obtained by dilution with pure water.

[0025] According to the determination method of the present invention, preferably, the specific process of extracting the polyester solid sample to be tested using the extractant includes:

[0026] Accurately weigh a certain mass of the polyester solid sample to be tested into an extraction container, add an extractant, and heat and reflux for extraction for 3 to 7 hours to obtain the extract. More preferably, a spherical condenser is used for condensation and reflux during the extraction process.

[0027] According to the determination method of the present invention, preferably, the mass of the polyester solid sample to be measured is 1.0 to 3.0 g.

[0028] Those skilled in the art will appreciate that, in the determination method of the present invention, the formula corresponding to the tetrahydrofuran calibration curve generally fitted requires R 2 >0.99.

[0029] The beneficial effects of the present invention include:

[0030] 1) The present invention uses an extraction method to extract tetrahydrofuran from polyester solids by detecting a fitted calibration curve. The tetrahydrofuran content in the sample is measured by gas chromatography to obtain the peak area, which is then calculated using the calibration curve to obtain the tetrahydrofuran content, thereby analyzing the tetrahydrofuran content generated during the polyester production process. This method has a wide analysis range, is simple to operate, is low in cost, and has good precision and accuracy.

[0031] 2) The detection method provided by the present invention can be applied to the detection of the content of other difficult-to-separate organic matter in polyester solids. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the calibration curve diagram obtained in Example 1.

[0033] Figure 2 This is the calibration curve diagram obtained in Example 2.

[0034] Figure 3 This is the calibration curve diagram obtained in Example 3. DETAILED DESCRIPTION

[0035] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0036] All numerical specifications herein (e.g., temperatures, times, concentrations, and weights, including ranges for each thereof) are generally approximate and may be modified (+) or (-) in increments of 0.1 or 1.0. All numerical specifications are to be understood as being preceded by the term "about."

[0037] The raw materials or equipment involved in the following examples:

[0038] Gas chromatograph Agilent 7890B;

[0039] Headspace sampler Agilent 7693 automatic sampler (ALS);

[0040] Chromatographic column 113-2132LTM 30m×0.32mm×0.25um;

[0041] grinder;

[0042] Analytical balance sensitivity 0.1 mg;

[0043] Sample bottle: 20mL;

[0044] Sealer;

[0045] Micro syringe 10uL;

[0046] Pure water, prepared by laboratory water purification machine;

[0047] Tetrahydrofuran is chromatographically pure (purity greater than 99.99%, usually stored in a refrigerator).

[0048] Example 1

[0049] (1) Preparation of tetrahydrofuran standard sample

[0050] Place the 10mL syringe in the refrigerator for a while, accurately weigh about 0.50g of tetrahydrofuran and inject it into a volumetric flask, and dilute the volume to 100mL with pure water to obtain tetrahydrofuran mother liquor.

[0051] THF concentration = 0.005 g / mL

[0052] (2) Calibration curve drawing:

[0053] Use a 10μL microinjector to transfer the mother solution, and use pure water to prepare standard samples with concentrations of 10ppm, 20ppm, 40ppm, 80ppm, 100ppm, 120ppm, 140ppm, 160ppm, 180ppm, 200ppm, and 300ppm, respectively. Transfer 2.0mL of each standard sample to a sample bottle, place it on the Headspace Sampler turntable, set the test conditions, start the instrument automatic test, and calculate the peak area of ​​THF in the chromatogram.

[0054] The peak area of ​​the chromatogram corresponding to the ppm concentration of each reagent bottle is input into the GC software to automatically draw the calibration curve.

[0055] like Figure 1 As shown, the calibration curve equation obtained in this embodiment is: y = 99.3168x + 327.34, R 2 =0.9954. Where y is the peak area and x is the THF concentration in ppm.

[0056] (3) Calibration line test:

[0057] Prepare tetrahydrofuran solutions at concentrations of 50 ppm, 150 ppm, and 250 ppm using pure water. Place the sample vials on the Headspace Sampler turntable, set the test conditions, and start the instrument. Compare the values ​​measured relative to the calibration curve with the converted values, and the error is within ±2%.

[0058] (4) Sample testing

[0059] Cut the polyester solid sample to be tested into 1 / 16 standard slices. Accurately weigh 1.0g of sample into a sample bottle. Add 20mL of pure water. Heat and reflux at 80°C in a reflux extraction apparatus for 5 hours. Shake well and analyze according to the set GC parameters. Measure the chromatographic peak area of ​​THF and subtract it from the calibration curve to determine the tetrahydrofuran content in the sample. The arithmetic mean of the two repeated measurements is used as the sample result.

[0060] The peak area of ​​the first measurement was 14892, and its concentration was calculated to be 146.65 ppm;

[0061] The peak area of ​​the first measurement was 15266, and its concentration was calculated to be 150.42 ppm;

[0062] The final result is M = (m1 + m2) / 2 = 148.54 ppm, that is, the concentration of THF in the extracted aqueous phase is 148.54 ppm. The tetrahydrofuran content in the polyester solid sample to be tested is then calculated to be 0.297%.

[0063] Example 2

[0064] (1) Preparation of tetrahydrofuran standard solution

[0065] Place the 10mL syringe in the refrigerator for a while, accurately weigh about 1.00g of tetrahydrofuran and inject it into a volumetric flask, and dilute to 100mL with pure water.

[0066] THF purity (g / mL) = 0.01 g / mL

[0067] (2) Calibration curve drawing:

[0068] Use a 10μL microinjector to transfer the solution. Use pure water to prepare solutions with concentrations of 10ppm, 20ppm, 40ppm, 80ppm, 100ppm, 120ppm, 140ppm, 160ppm, 180ppm, 200ppm, and 300ppm, respectively. Transfer 2.0mL of each solution into a sample bottle, place it on the Headspace Sampler turntable, set the test conditions, start the instrument automatic test, and calculate the peak area of ​​THF in the chromatogram.

[0069] The peak area of ​​the chromatogram corresponding to the ppm concentration of each reagent bottle is input into the GC software, and the computer automatically draws the calibration curve.

[0070] like Figure 2 As shown, the calibration curve equation obtained in this embodiment is: y = 41.258x-159.74, R 2 =0.99, where y is the peak area and x is the THF concentration in ppm.

[0071] (3) Confirmation of calibration curve:

[0072] Prepare 50ppm, 150ppm, and 250ppm tetrahydrofuran solutions in pure water, place the sample bottles on the HeadspaceSampler turntable, set the test conditions, and start the instrument. Compare the values ​​measured relative to the calibration curve with the converted values, and the error is within ±2%.

[0073] (4) Sample testing

[0074] Cut the sample into 1 / 16 standard slices. Accurately weigh 2.0g of PBT sample into a sample bottle. Add 20mL of pure water. Heat and reflux at 70°C in a reflux extraction apparatus for 7 hours. Shake well and analyze according to the set GC parameters. Measure the THF chromatographic peak area and subtract it from the calibration curve to determine the tetrahydrofuran content in the sample. The arithmetic mean of the two repeated measurements is used as the sample result.

[0075] The peak area of ​​the first measurement was 8625, and its concentration was calculated to be 212.92 ppm;

[0076] The peak area of ​​the first measurement was 8459, and its concentration was calculated to be 208.90 ppm;

[0077] The final result is M = (m1 + m2) / 2 = 210.91 ppm, that is, the concentration of THF in the extracted aqueous phase is 210.91 ppm. The tetrahydrofuran content in the polyester solid sample to be tested is then calculated to be 0.422%.

[0078] Example 3

[0079] (1) Preparation of tetrahydrofuran standard solution

[0080] Place the 10mL syringe in the refrigerator for a while, accurately weigh about 1.50g of tetrahydrofuran and inject it into the volumetric flask, and dilute to 10mL with pure water.

[0081] THF purity (g / mL) = 0.015 g / mL

[0082] (2) Calibration curve drawing:

[0083] Use a 10μL microinjector to transfer the solution. Use pure water to prepare solutions with concentrations of 10ppm, 20ppm, 40ppm, 80ppm, 100ppm, 120ppm, 140ppm, 160ppm, 180ppm, 200ppm, and 300ppm, respectively. Transfer 2.0mL of each solution into a sample bottle, place it on the Headspace Sampler turntable, set the test conditions, start the instrument automatic test, and calculate the peak area of ​​THF in the chromatogram.

[0084] The peak area of ​​the chromatogram corresponding to the ppm concentration of each reagent bottle is input into the GC software, and the computer automatically draws the calibration curve.

[0085] like Figure 3 As shown, the calibration curve equation obtained in this embodiment is: y = 45.384x + 300.84, R 2 =0.9936, where y is the peak area and x is the THF concentration in ppm.

[0086] (3) Confirmation of calibration curve:

[0087] Prepare 50ppm, 150ppm, and 250ppm tetrahydrofuran solutions in pure water, place the sample bottles on the HeadspaceSampler turntable, set the test conditions, and start the instrument. Compare the values ​​measured relative to the calibration curve with the converted values, and the error is within ±2%.

[0088] (4) Sample testing

[0089] Cut the sample into 1 / 16 standard slices. Accurately weigh 3.0g of PBAT sample into a sample bottle. Add 20mL of pure water. Heat and reflux at 100°C in a reflux extraction apparatus for 3 hours. Shake well and analyze according to the set GC parameters. Measure the THF chromatographic peak area and subtract it from the calibration curve to determine the tetrahydrofuran content in the sample. The arithmetic mean of the two repeated measurements is taken as the sample result.

[0090] The peak area of ​​the first measurement was 9560, and its concentration was calculated to be 204.02 ppm;

[0091] The peak area of ​​the first measurement was 9602, and its concentration was calculated to be 204.94 ppm;

[0092] The final result is M = (m1 + m2) / 2 = 204.48 ppm, that is, the concentration of THF in the extracted aqueous phase is 204.48 ppm. The tetrahydrofuran content in the polyester solid sample to be tested is then calculated to be 0.409%.

[0093] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for determining the content of tetrahydrofuran in polyester solids, wherein: The determination method comprises the following steps: Using gas chromatography to detect tetrahydrofuran standard samples of different concentrations, the chromatographic peak area of ​​each tetrahydrofuran is obtained, and the tetrahydrofuran calibration curve is obtained by fitting the concentration and the chromatographic peak area; The obtained tetrahydrofuran calibration curve is tested with a tetrahydrofuran standard sample of another concentration, and the error is within the range of ±2%, which is considered qualified. The polyester solid sample to be tested is subjected to heating reflux using an extractant to complete extraction, and then the extract is detected by gas chromatography. The obtained tetrahydrofuran chromatographic peak area is calculated using the tetrahydrofuran calibration curve to obtain the concentration of tetrahydrofuran in the extract, and then the content of tetrahydrofuran in the polyester solid sample is calculated.

2. The assay method according to claim 1, wherein The extractant is pure water.

3. The measuring method according to claim 1, wherein 6 to 20 mL of the extractant is used for each gram of the polyester solid sample to be tested.

4. The measuring method according to claim 1, wherein The extraction temperature is 70-100°C.

5. The measuring method according to claim 1, wherein The extraction time is 3 to 7 hours.

6. The measuring method according to claim 1, wherein The concentration range of the tetrahydrofuran standard samples with different concentrations is 10ppm to 300ppm.

7. The measuring method according to claim 1, wherein The step of using another tetrahydrofuran standard sample of other concentration to test the obtained tetrahydrofuran calibration line comprises: A tetrahydrofuran standard sample of another concentration is used for gas chromatography testing to obtain the tetrahydrofuran chromatographic peak area, and then the tetrahydrofuran concentration is calculated based on the obtained tetrahydrofuran calibration curve. The calculated result is compared with the true value, and the sample is qualified if the error is within the range of ±2%.

8. The measuring method according to claim 1, wherein The extract is subjected to two or more parallel gas chromatography tests to calculate and obtain two or more tetrahydrofuran concentrations, and the average value is taken as the concentration of tetrahydrofuran in the extract, and then the content of tetrahydrofuran in the polyester solid sample is calculated.

9. The measuring method according to claim 8, wherein The relative error range allowed for the results of more than two parallel gas chromatography tests is ±10%.

10. The measuring method according to claim 1, wherein The preparation process of the tetrahydrofuran standard samples of different concentrations comprises: Prepare a certain concentration of tetrahydrofuran mother solution, and then dilute it into tetrahydrofuran standards of different concentrations.

11. The measuring method according to claim 10, wherein The concentration of the tetrahydrofuran mother liquor is 0.005-0.015 g / mL.

12. The assay method according to claim 10, wherein The solvent of the tetrahydrofuran mother liquor is pure water, and the tetrahydrofuran standard samples of different concentrations are obtained by dilution with pure water.

13. The assay method according to any one of claims 1 to 12, wherein The specific process of using the extractant to extract the polyester solid sample to be tested includes: A certain mass of the polyester solid sample to be tested is accurately weighed and placed in an extraction container, an extractant is added, and the mixture is heated under reflux for extraction for 3 to 7 hours to obtain the extract.

14. The assay method according to claim 13, wherein A spherical condenser was used for condensation reflux during the extraction process.

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