Method for measuring contents of methanol and ethanol in isopentane

Abstract

The invention provides a method for determining the content of methanol and ethanol in isopentane. The method comprises the following steps: adding starch and chloride into water, boiling, standing, freezing, transferring isopentane and an aqueous solution containing starch and chloride, extracting, filtering, and detecting the content of methanol and ethanol by chromatographic analysis. According to the determination method, an extraction method is utilized, water is taken as an extraction solution, isopentane is taken as an extracted solution, methanol and ethanol in the isopentane are absorbed by the extraction solution and are retained in the water, and water is used for sampling, so that a sample can be normally sucked into a microinjection needle, and the contents of methanol and ethanol in the isopentane can be accurately quantified.

Description

Technical Field

[0001] The invention relates to the field of chemical analysis, and in particular to a method for determining the contents of methanol and ethanol in isopentane. Background Art

[0002] Isopentane is mainly used as a condensation inducer in polyethylene reactors. Its main function is to increase the dew point of circulating gas components, so that the circulating gas can be condensed at a relatively high temperature. After entering the reactor, the condensed liquid components are vaporized again, thereby playing a role in removing heat. Ethylene is polymerized into polyethylene under the action of triethylaluminum and T2 catalysts. Isopentane often contains methanol and ethanol. If the content exceeds the standard, the mixture of triethylaluminum, methanol and ethanol will produce a violent reaction or an explosive reaction, which will cause a huge safety hazard to the polymerization reactor. Therefore, the content of methanol and ethanol in the reactant raw materials must be strictly controlled (the standard stipulates that the content of methanol + ethanol is ≤5mg / kg). Isopentane is one of the raw materials that may introduce methanol and ethanol into the polymerization reaction.

[0003] The content of methanol and ethanol in isopentane is usually determined by gas chromatography for the determination of trace methanol and methyl tert-butyl ether in industrial 1-butene according to SH / T 1547-2004. 5.3 of this method stipulates that a liquid injection valve (quantitative tube 0.5 microliter) or a gas injection valve should be used for injection. The boiling point of 1-butene is -6.3°C. Pressure-resistant steel cylinders are often used for sampling. The pressure in the sampling bottle is higher than atmospheric pressure, so liquid injection can use its internal pressure to push the 1-butene sample into the quantitative tube for sample analysis.

[0004] However, the boiling point of isopentane is 27.8°C, and it is a colorless and transparent liquid at room temperature. The boiling point of 1-butene is -6.3°C, and their physical properties are very different. At room temperature, there is no pressure inside isopentane or the pressure is too low, which makes it impossible to inject samples normally and complete the measurement. If a micro-injection needle is used for manual injection, it is often because there are other highly volatile light hydrocarbons in isopentane. When the injection needle is sucking liquid, the low air pressure in the needle cavity cannot absorb the liquid normally, and normal injection and measurement cannot be completed. Therefore, the SH / T 1547-2004 method is not suitable for the detection of methanol and ethanol content in isopentane.

[0005] Therefore, in order to avoid huge safety hazards to the polymerization reactor, it is necessary to strictly control the methanol and ethanol content in the condensation inducer isopentane, and it is necessary to find a method to ensure that the sample is normally sucked into the microinjection needle and accurately quantify the content of methanol and ethanol in isopentane. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for determining the content of methanol and ethanol in isopentane. The method of the present invention is characterized in that the extraction method is used, pure water is used as an extracting liquid, isopentane is used as an extracted liquid, the components methanol and ethanol in isopentane are absorbed by the extracting liquid and retained in the pure water, and the pure water is used for sampling to perform the analysis and detection of methanol and ethanol.

[0007] The operating process of the method for determining the content of methanol and ethanol in isopentane of the present invention is as follows: Figure 1 shown.

[0008] The method for determining the content of methanol and ethanol in isopentane of the present invention comprises the following steps:

[0009] Step 1: Add starch and chloride to pure water, boil, let stand, and freeze to obtain an aqueous solution containing starch and chloride for later use;

[0010] Step 2: Pipette the isopentane sample into the funnel;

[0011] Step 3: Pipette the aqueous solution containing starch and chloride obtained in step 1 into the funnel, shake well to extract, let stand, separate the aqueous phase and place it in a stoppered bottle and seal it;

[0012] Step 4: Repeat the operation of step 3, transfer the aqueous solution containing starch and chloride obtained in step 1 into the funnel again, shake well to extract, let stand, separate the aqueous phase and place it in the stoppered bottle and seal it;

[0013] Step 5: Filter the aqueous phase in the stoppered bottle, collect the filtrate in a chromatographic injection bottle, perform chromatographic injection, and determine the contents of methanol and ethanol.

[0014] According to the determination method of the present invention, in step 1, the mass ratio of starch to purified water is (2-3):500 (g / g), and the mass ratio of chloride to purified water is (3-5):500 (g / g).

[0015] According to the determination method of the present invention, in step 1, the starch can be selected from one or more of corn starch, potato starch and potato starch.

[0016] According to the determination method of the present invention, in step 1, the chloride can be selected from one or more of sodium chloride, potassium chloride, aluminum chloride, calcium chloride, and copper chloride, preferably sodium chloride.

[0017] According to the determination method of the present invention, wherein, in step 1, freezing is freezing in a refrigerator for 20-30 minutes.

[0018] According to the determination method of the present invention, before step 2, the isopentane sample is frozen in a refrigerator at -5°C for 20-30 minutes. The purpose of freezing is to reduce the volatilization of methanol and ethanol during the removal process, so that the determination of the isopentane sample is highly representative.

[0019] According to the determination method of the present invention, the volume ratio of the isopentane sample removed in step 2 to the aqueous solution containing starch and chloride removed in total in steps 3 and 4 is 3:1-1:1, preferably 2:1.

[0020] According to the determination method of the present invention, methanol and ethanol are fully miscible with water in any proportion, and the methanol and ethanol in the isopentane sample are completely extracted into the water phase.

[0021] According to the determination method of the present invention, before step 5, the aqueous phase in the stoppered bottle is fully shaken, filtered with a 0.45 μm filter syringe, collected in a chromatographic injection bottle, and chromatographic injection is performed using a manual or fully automatic injector to determine the methanol and ethanol content in isopentane. The purpose of using a 0.45 μm filter membrane is to prevent large starch particles from entering the filtrate to avoid clogging the microinjection needle.

[0022] According to the determination method of the present invention, when transferring isopentane and the aqueous solution containing starch and chloride, a pipette or a sealed syringe with a precise scale is used to complete the transfer to ensure the accuracy of the transfer volume.

[0023] According to the determination method of the present invention, the role of adding starch to pure water is to form a colloid in the pure water, further fix the methanol and ethanol components, and reduce the volatilization loss of methanol and ethanol; adding chloride to pure water can effectively eliminate emulsified bubbles, and the water phase can be quickly stabilized and uniform during standing.

[0024] According to the determination method of the present invention, during the extraction process, due to violent shaking, the highly volatile light hydrocarbons in the isopentane will evaporate, causing the pressure in the funnel cavity to increase. Therefore, during the extraction process, the funnel needs to be deflated. The purpose of the deflation operation is to reduce the internal pressure of the funnel and reduce the safety risks during the operation.

[0025] According to the determination method of the present invention, the concentration of methanol and ethanol in isopentane is calculated by the following formula:

[0026] w 甲 =A 甲 *V 水 / V 异

[0027] w 乙 =A 乙 *V 水 / V异

[0028] in:

[0029] w 甲 、w 乙 are the final concentrations of methanol and ethanol, respectively, in mg / L;

[0030] A 甲 , A 乙 are the concentrations of methanol and ethanol read by gas chromatograph, in mg / L;

[0031] V 水 is the total volume of pure water during the extraction process, in mL;

[0032] V 异 is the total volume of isopentane during the extraction process, in mL.

[0033] Beneficial Effects

[0034] The present invention achieves the following positive effects:

[0035] 1. Adding starch to pure water to form a colloid in the water phase can effectively reduce the loss of methanol and ethanol, and ensure the accuracy of the data to a certain extent.

[0036] 2. Adding solid chloride (such as sodium chloride) to pure water can effectively break up the emulsified bubbles, allowing the water phase to quickly enter a state of equilibrium and complete water phase separation.

[0037] 3. Freezing pure water can minimize the volatilization loss of methanol and ethanol components, thus ensuring the accuracy of the data to a certain extent.

[0038] 4. Use a pipette or a sealed syringe with precise scale to transfer the isopentane sample and the aqueous solution containing starch and chloride. The transfer volume can be accurately controlled. In the subsequent calculation, it can effectively improve and ensure the accurate calculation of methanol and ethanol content, and to a certain extent ensure the accuracy of the data.

[0039] 5. Use 0.45μm to filter the extract to reduce the risk of micro-injection needle being blocked and discarded, improve labor efficiency and reduce analysis costs.

[0040] 6. Secondary extraction can effectively and fully extract the methanol and ethanol components in the sample, avoiding inaccurate data caused by the loss of components due to incomplete primary extraction.

[0041] 7. Use water as the background of the extract injection, which is the same as the standard solution background when the gas chromatograph is used to establish the calibration curve, which maximizes the reliability of the method and the accuracy of the data.

[0042] 8. The extraction liquid with water as the background is used for sampling and analysis, which avoids the phenomenon that the micro-injection needle cannot absorb the liquid due to the low pressure in the inner cavity. The method is reliable and stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The following is an operation flow of the method for determining the contents of methanol and ethanol in isopentane according to the present invention. DETAILED DESCRIPTION

[0044] The present invention will be described in detail below in conjunction with specific embodiments, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments are used to illustrate the present invention, rather than to limit the present invention.

[0045] 1. Adjust the gas chromatograph parameters and establish a standard working curve.

[0046] In this experiment, HP INNOWAX capillary chromatographic column was used to determine the content of methanol and ethanol, detected by hydrogen flame ionization detector, and quantified by external standard method.

[0047] 2. Materials and Reagents

[0048] 2.1 Carrier gas

[0049] Nitrogen: purity greater than 99.99% (v / v), dried and purified by silica gel and 5A molecular sieve.

[0050] 2.2 Auxiliary gas

[0051] Hydrogen: Purity greater than 99.99% (v / v), dried and purified by silica gel and 5A molecular sieve.

[0052] Air: dried and purified by silica gel and 5A molecular sieve.

[0053] 2.3 Chromatographic column

[0054] HP INNOWAX column, such as: 30m*0.32mm*0.25μm, or other specifications.

[0055] 2.4 Standard samples

[0056] Use a 1000mL volumetric flask to accurately quantify pure water, inject 5μL of chromatographic pure methanol and ethanol at 20℃ into the pure water, and shake well. Calculate the exact content of methanol and ethanol in the standard sample. Set aside.

[0057] 3. Instruments

[0058] Gas chromatograph with programmed temperature function and equipped with hydrogen flame ionization detector. The peak area generated by the instrument for the impurity component at the lowest detection concentration should be greater than 2 times the noise.

[0059] 3.1 Injection system

[0060] Equipped with AOC automatic sample injector.

[0061] 3.2 Chromatographic columns and operating conditions

[0062] The recommended chromatographic columns and typical operating conditions are shown in Table 1 below. Other chromatographic operating conditions that can achieve the same separation effect can also be used (for example, Agilent 19091N-113 chromatographic column, similar operating conditions); the chromatographic column needs to be aged before use, and the carrier gas and flow rate used are the same as when analyzing the sample.

[0063] Table 1: Chromatographic columns and typical operating conditions

[0064] Chromatographic columns HPINNOWAX column, 30m*0.32mm*0.25um Carrier gas Nitrogen Injector temperature / ℃ 150 Inlet pressure / Kpa 20 Split Ratio 20 Column temperature / ℃ 60 Detector temperature / ℃ 250

[0065] 3.3 Detector

[0066] Hydrogen flame ionization detector.

[0067] 3.4 Recording Device

[0068] Recorder, integrator or chromatography data processing workstation.

[0069] 4. Sample Processing

[0070] Take 500mL of pure water and place it in a beaker. Add 2g of starch and 3g of solid sodium chloride, boil, cool, and freeze in a refrigerator for 30 minutes.

[0071] Use a pipette to transfer 20 mL of the isopentane sample into a 50 mL pear-shaped glass funnel. The isopentane sample is frozen in a -5°C refrigerator for 30 minutes. The purpose of freezing is to reduce the volatilization of methanol and ethanol during the transfer process, so that the determination of the isopentane sample is highly representative.

[0072] Pipette 5 mL of the aqueous solution containing starch and sodium chloride into the funnel, shake well, extract for 10 min, release air twice in the middle, let stand for 2 min, perform separation operation, wait for the emulsified bubbles to break, separate the bottom aqueous phase extract, and place the aqueous phase extract in a 50 mL stopper bottle, cover and seal for later use;

[0073] 5 mL of the aqueous solution containing starch and sodium chloride was again transferred into the funnel, and the above operation was repeated for secondary extraction.

[0074] Set up two replicates.

[0075] 5. Results Analysis

[0076] The extract in the stoppered bottle was shaken thoroughly, filtered using a 0.45 μm filter membrane, and the filtered extract was placed in a 2 mL chromatographic injection bottle for analysis, testing, and result calculation.

[0077] Table 2 Displayed concentrations of methanol and ethanol on gas chromatograph

[0078]

[0079] According to the concentrations of methanol and ethanol shown on the gas chromatograph given in Table 2, the concentrations (contents) of methanol and ethanol in isopentane are calculated:

[0080] w 甲醇 =(5.32*10 / 20+6.18*10 / 20) / 2=3mg / L

[0081] w 乙醇 =(3.41*10 / 20+3.66*10 / 20) / 2=2mg / L.

Claims

1. A method for determining the content of methanol and ethanol in isopentane, comprising the following steps: Step 1: Add starch and chloride to pure water, boil, let stand, and freeze to obtain an aqueous solution containing starch and chloride for later use; Step 2: Pipette the isopentane sample into the funnel; Step 3: Pipette the aqueous solution containing starch and chloride obtained in step 1 into the funnel, shake well to extract, let stand, separate the aqueous phase and place it in a stoppered bottle and seal it; Step 4: Repeat the operation of step 3, transfer the aqueous solution containing starch and chloride obtained in step 1 into the funnel again, shake well to extract, let stand, separate the aqueous phase and place it in the stoppered bottle and seal it; Step 5: Filter the aqueous phase in the stoppered bottle, collect the filtrate in a chromatographic injection bottle, perform chromatographic injection, and determine the contents of methanol and ethanol.

2. The assay method according to claim 1, wherein In step 1, the mass ratio of starch to purified water is (2-3):

500.

3. The measuring method according to claim 1, wherein In step 1, the mass ratio of chloride to purified water is (3-5):

500.

4. The assay method according to any one of claims 1 to 3, wherein In step 1, the starch is selected from one or more of corn starch, potato starch and potato starch.

5. The assay method according to any one of claims 1 to 3, wherein In step 1, the chloride is selected from one or more of sodium chloride, potassium chloride, aluminum chloride, calcium chloride and copper chloride.

6. The assay method according to any one of claims 1 to 3, wherein In step 1, freezing is performed in the refrigerator for 20-30 minutes.

7. The assay method according to any one of claims 1 to 3, wherein Prior to step 2, the isopentane samples were frozen in a -5°C freezer for 20-30 min.

8. The assay method according to any one of claims 1 to 3, wherein The volume ratio of the isopentane sample removed in step 2 to the aqueous solution containing starch and chloride removed in total in steps 3 and 4 is 3:1-1:1, preferably 2:

1.

9. The assay method according to any one of claims 1 to 3, wherein Before step 5, shake the water phase in the stoppered bottle thoroughly, filter it with a 0.45 μm filter syringe, collect it in a chromatographic injection bottle, and use a manual or fully automatic injector for chromatographic injection to determine the methanol and ethanol content in isopentane.

10. The assay method according to any one of claims 1 to 3, wherein The concentrations of methanol and ethanol in isopentane were calculated using the following formula: w 甲 =A 甲 *V 水 / V 异 w 乙 =A 乙 *V 水 / V 异 in: w 甲 、w 乙 are the final concentrations of methanol and ethanol, respectively, in mg / L; A 甲 , A 乙 are the concentrations of methanol and ethanol read by gas chromatograph, in mg / L; V 水 is the total volume of pure water during the extraction process, in mL; V 异 is the total volume of isopentane during the extraction process, in mL.

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