A method for separating and analyzing carboxylic acid compounds in petroleum

Abstract

The present invention belongs to the technical field of petroleum composition analysis, and in particular to a method for separating and analyzing carboxylic acid compounds in petroleum. The method comprises the following steps: step one: dissolving the petroleum sample in an organic solvent A, and adding a solid phase extraction column filled with an amino MCM-41 molecular sieve; step two: eluting the sample with an organic solvent B and a mixed solution C in sequence to obtain a carboxylic acid compound; step three: using an organic solvent D to dissolve the carboxylic acid compound to adjust the injection concentration, and then using an electrospray ionization mass spectrometer to characterize the molecular composition. The analytical method provided by the present invention can eliminate the influence of the petroleum matrix and realize the fine separation and analysis of the molecular composition of carboxylic acid compounds in petroleum.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum composition analysis, and in particular relates to a method for separating and analyzing carboxylic acid compounds in petroleum. Background Art

[0002] The separation and analysis of carboxylic acid compounds in petroleum are of great research significance. They play a significant role in the acid value, corrosiveness and environmental toxicity of petroleum products, and directly affect the safety and stability of petroleum processing, storage and use. In recent years, with the development of separation and analysis technology, ultra-high performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) and two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) have been widely used in the identification and quantification of such compounds, significantly improving the detection sensitivity and resolution. In addition, adsorption separation technology based on molecular recognition and functionalized materials has also become a hot topic, providing a new method for the efficient separation of carboxylic acid compounds. These advances provide a reliable scientific basis for optimizing petroleum processing technology and improving product quality. The separation and analysis of carboxylic acid compounds in petroleum face multiple technical bottlenecks, mainly including the following aspects: First, due to the extremely complex composition of petroleum, carboxylic acid compounds are usually low in content and coexist with other polar compounds, resulting in great difficulty in separation; secondly, such compounds are prone to decomposition under high temperature conditions, limiting the application of traditional gas chromatography technology; in addition, the molecular weight and polarity of carboxylic acid compounds vary greatly, which puts higher requirements on the sensitivity and selectivity of existing analytical instruments. Existing separation materials and methods still need to be further improved in terms of selectivity, resolution and durability to effectively achieve efficient separation and accurate detection of carboxylic acid compounds in petroleum. Prior art CN118225953A discloses a method for the derivatization and separation of carboxylic acid compounds in organic matter, but the separation efficiency and selectivity of carboxylic acid compounds in petroleum are not high, and the loss of carboxylic acid compounds is relatively large, and it is impossible to achieve accurate separation and quantification of carboxylic acid compounds in petroleum. Summary of the invention

[0003] To solve the above problems, the object of the present invention is to provide a method for accurately separating and analyzing the molecular composition of carboxylic acid compounds in petroleum.

[0004] The present invention provides a method for separating and analyzing carboxylic acid compounds in petroleum, the method comprising the following steps:

[0005] Step 1: Dissolve the petroleum sample in organic solvent A and add it into a solid phase extraction column filled with amino-modified MCM-41 molecular sieve;

[0006] Step 2: sequentially eluting the sample with organic solvent B and mixed solution C to obtain a carboxylic acid compound;

[0007] Step 3: using organic solvent D to dissolve the carboxylic acid compound to adjust the injection concentration, and then using an electrospray ionization mass spectrometer to characterize the molecular composition;

[0008] The organic solvent A is a small molecule hydrocarbon solvent with a carbon number not exceeding 8;

[0009] The organic solvent B is a weakly polar organic solvent having a polarity not stronger than that of dichloromethane and a boiling point not higher than 100° C.;

[0010] The mixed solution C is a mixed solution of Bronsted acid and alcohol in a volume ratio of 1:3;

[0011] The organic solvent D is a mixed solvent of toluene and methanol in a volume ratio of 1:3.

[0012] Preferably, the preparation method of the amination MCM-41 molecular sieve is as follows:

[0013] Dissolve cetyltriethylammonium bromide (CTAB) in distilled water, add 1,3,5-trimethylbenzene (TMB), stir at 45°C until clear, adjust pH to 8-12 with sodium hydroxide and stir for 0.5-2 h, then add tetraethyl orthosilicate (TEOS) and stir for 3 h;

[0014] After crystallization for 3-5 days, the template is removed by calcination at 350-800℃ for 6-8 hours to obtain MCM-41 molecular sieve with a pore size of 10-20 nm.

[0015] use -Aminopropyltriethoxysilane (APTES) was reacted with the obtained MCM-41 molecular sieve in a toluene solution for 1 day to obtain the aminated MCM-41 molecular sieve.

[0016] Preferably, the mass volume ratio of the CTAB, distilled water, TMB, TEOS and APTES is 5 g: 200 mL: 20-40 mL: 30 mL: 20 mL.

[0017] Preferably, the petroleum sample comprises one or more of crude oil, diesel fraction and vacuum gas oil fraction.

[0018] Preferably, based on the total weight, the total carboxylic acid compound content of the petroleum sample is 0.01 wt% to 100 wt%.

[0019] Preferably, the usage ratio of the amino-modified MCM-41 molecular sieve to the organic solvent A for dissolving the petroleum sample is 0.3-3 g: 0.2-2 mL.

[0020] Preferably, the organic solvent A includes one or more of n-pentane, n-hexane, n-heptane and n-octane.

[0021] Preferably, the organic solvent B includes one or more of dichloromethane, chloroform, carbon tetrachloride, acetonitrile and toluene.

[0022] Preferably, the Bronsted acid in the mixed solution C includes one or more of acetic acid, hydrochloric acid, nitric acid and sulfuric acid.

[0023] Preferably, the injection concentration in step three is 0.002 mg / mL to 0.2 mg / mL.

[0024] Beneficial effects of the present invention:

[0025] The present invention applies the aminated MCM-41 molecular sieve to the separation of petroleum acid, which has significant advantages. First, its highly ordered mesoporous structure provides a large specific surface area and uniform pore size, which is conducive to the efficient adsorption and separation of petroleum acid molecules. Secondly, the amino functional groups on the surface of the aminated MCM-41 molecular sieve enhance its selective adsorption with carboxylic acid molecules through hydrogen bonds and electrostatic interactions, thereby improving the separation efficiency. In addition, the aminated modification improves the thermal stability and chemical stability of the material, so that it has a longer service life and a higher separation effect in the separation process of complex petroleum matrices. And the aminated MCM-41 molecular sieve with larger mesopores (such as 10 nm) has a higher adsorption effect on petroleum acid compounds. The method has a higher separation efficiency, and since the aminated MCM-41 molecular sieve can specifically adsorb carboxylic acid compounds, this method does not need to be further purified. The method can accurately analyze the molecular composition of petroleum carboxylic acid compounds at the molecular level.

[0026] The method for separating and analyzing the molecular composition of carboxylic acid compounds in petroleum provided by the present invention can accurately separate and analyze the molecular composition of carboxylic acids at the molecular level, and is suitable for molecular composition analysis of carboxylic acid compounds in heavy crude oil, diesel fractions, vacuum gas oil fractions, etc. Moreover, the operating conditions of the method are mild, and the carboxylic acid compounds in petroleum, especially heavy petroleum, can be completely, efficiently and accurately analyzed. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 The carbon number and DBE distribution diagram of the carboxylic acid compounds obtained by analyzing the carboxylic acid compounds in the vacuum distillate oil by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry in Example 1. DETAILED DESCRIPTION

[0029] The present invention provides a method for separating and analyzing carboxylic acid compounds in petroleum, the method comprising the following steps:

[0030] Step 1: Dissolve the petroleum sample in organic solvent A and add it into a solid phase extraction column filled with amino-modified MCM-41 molecular sieve;

[0031] Step 2: sequentially eluting the sample with organic solvent B and mixed solution C to obtain a carboxylic acid compound;

[0032] Step 3: using organic solvent D to dissolve the carboxylic acid compound to adjust the injection concentration, and then using electrospray ionization mass spectrometry to characterize the molecular composition;

[0033] The organic solvent A is a small molecule hydrocarbon solvent with a carbon number not exceeding 8; the organic solvent B is a weak polar organic solvent with a polarity not stronger than dichloromethane and a boiling point not higher than 100°C; the mixed solution C is a mixed solution of Bronsted acid and alcohol in a volume ratio of 1:3; the organic solvent D is a mixed solvent of toluene and methanol in a volume ratio of 1:3.

[0034] The present invention firstly dissolves the petroleum sample in an organic solvent A, and adds a solid phase extraction column filled with amino-modified MCM-41 molecular sieve.

[0035] In the present invention, the petroleum sample preferably includes one or more of crude oil, diesel fraction and vacuum gas oil fraction; based on the total weight, the total carboxylic acid compound content of the petroleum sample is preferably 0.01wt%~100wt%.

[0036] In the present invention, the organic solvent A is a small molecule hydrocarbon solvent with a carbon number not exceeding 8, and further preferably includes one or more of n-pentane, n-hexane, n-heptane and n-octane, and more preferably n-hexane. The organic solvent A of the present invention is a small molecule hydrocarbon solvent with a carbon number not exceeding 8, which can effectively dissolve various non-polar and weakly polar compounds in the petroleum matrix, while avoiding solubility deviation and separation interference that may be caused by impurities such as inorganic salts.

[0037] The present invention preferably wets the solid phase extraction column with organic solvent A when filling the solid phase extraction column with the aminated MCM-41 molecular sieve; the dosage ratio of the aminated MCM-41 molecular sieve to the organic solvent A for dissolving the petroleum sample is 0.3-3 g: 0.2-2 mL, more preferably 2-3 g: 1 mL. The present invention can ensure the best adsorption efficiency and the solvent fully infiltrates the molecular sieve pores by adjusting the dosage ratio of the aminated MCM-41 molecular sieve to the organic solvent A for dissolving the petroleum sample. For example, when 2 g of the aminated MCM-41 molecular sieve is selected, the dosage of the organic solvent A for dissolving the petroleum sample is preferably controlled at about 1 mL, and this ratio can achieve a balance between the surface area of ​​the adsorbent and the dispersibility of the solvent, thereby improving the separation efficiency of the carboxylic acid compounds. The adjustment of different ratios mainly depends on the concentration of the carboxylic acid compounds in the petroleum sample and the purity requirements of the target separation, so as to optimize the utilization rate of the adsorbent and reduce the consumption of the solvent.

[0038] In the present invention, the preparation method of the amination MCM-41 molecular sieve is preferably:

[0039] CTAB was dissolved in distilled water, TMB was added, and the mixture was stirred at 45°C until it was clear. The pH was adjusted to 8-12 with sodium hydroxide and stirred for 0.5-2 h, and then tetraethyl orthosilicate (TEOS) was added and stirred for 3 h. After crystallization for 3-5 d, the mixture was calcined at 350-800°C for 6-8 h to remove the template agent, thereby obtaining MCM-41 molecular sieves with a pore size of 10-20 nm. APTES was reacted with the obtained MCM-41 molecular sieve in a toluene solution for 1 d to obtain amino-modified MCM-41 molecular sieves. After adding TMB to CTAB, the pH is preferably adjusted to 8-12 with sodium hydroxide and stirred for 0.5-2 h, more preferably adjusted to 10 with sodium hydroxide and stirred for 0.5 h; the crystallization time is preferably 3-5 d, more preferably 3 d; the calcination temperature is preferably 350-800° C., more preferably 550° C.; the calcination time is preferably 6-8 h, more preferably 6 h; the mass volume ratio of CTAB, distilled water, TMB, TEOS and APTES is preferably 5 g: 200 mL: 20-40 mL: 30 mL: 20 mL, more preferably 5 g: 200 mL: 30 mL: 30 mL: 20 mL. The aminated MCM-41 molecular sieve in the present invention has a highly ordered mesoporous structure, which provides a large specific surface area and uniform pore size, which is conducive to the efficient adsorption and separation of petroleum acid molecules; the amino functional groups on its surface enhance the selective adsorption with carboxylic acid molecules through hydrogen bonds and electrostatic interactions, further improving the separation efficiency; in addition, the aminated modification improves the thermal stability and chemical stability of the material, so that it has a longer service life and a higher separation effect in the separation process of complex petroleum matrices, and the aminated MCM-41 molecular sieve with larger mesopores (such as 10 nm) has a higher adsorption effect on petroleum acid compounds. Therefore, the method of the present invention does not require further purification of the crude separated carboxylic acid compounds, and the separation method is simple and reliable.

[0040] The present invention preferably performs crystallization in a hydrothermal reactor and performs calcination in a muffle furnace; the present invention also preferably performs washing with water, filtering, drying, and then calcination after the crystallization is completed.

[0041] After the sample is added into the extraction column, the present invention sequentially uses the organic solvent B and the mixed solution C to elute the sample to obtain the carboxylic acid compound.

[0042] In the present invention, the organic solvent B is a weak polar organic solvent with a polarity not stronger than that of dichloromethane and a boiling point not higher than 100°C, and is further preferably one or more of dichloromethane, chloroform, carbon tetrachloride, acetonitrile and toluene, and more preferably dichloromethane and acetonitrile. The mixed solution C of the present invention is a mixed solution in which the volume ratio of Bronsted acid to alcohol is 1:3; the Bronsted acid in the mixed solution C is preferably one or more of acetic acid, hydrochloric acid, nitric acid and sulfuric acid, and more preferably hydrochloric acid; the hydrogen ion concentration of the Bronsted acid is preferably 10-12.5 mol / L, and more preferably 12.1 mol / L; in a preferred embodiment of the present invention, the Bronsted acid is preferably hydrochloric acid containing 37 wt% of hydrogen chloride, that is, hydrochloric acid with a hydrogen ion concentration of 12.1 mol / L. The organic solvent B in the present invention is a weakly polar volatile solvent, and its polarity should not exceed that of dichloromethane, and its boiling point is limited to below 100°C to ensure that it can evaporate quickly during operation and achieve relatively gentle elution, which is suitable for the preliminary removal of non-target impurities; the boiling point of Bronsted acid is not higher than 80°C, and its high acidity helps to desorb the target carboxylic acid compounds remaining on the solid phase extraction column, and its low boiling point is conducive to subsequent solvent volatilization and sample concentration, which is convenient for further mass spectrometry analysis. The selection of organic solvent B and mixed solution C in the present invention takes into account factors such as solubility, polarity and volatility, and plays an important role in the effective separation and enrichment of carboxylic acid compounds in petroleum.

[0043] After obtaining the carboxylic acid compound, the present invention uses an organic solvent D to dissolve the carboxylic acid compound to adjust the injection concentration, and then uses an electrospray ionization mass spectrometer to characterize the molecular composition.

[0044] In the present invention, the organic solvent D is preferably a mixed solvent of toluene and methanol in a volume ratio of 1:3; the injection concentration of the present invention is preferably 0.002 mg / mL to 0.2 mg / mL, more preferably 0.02 mg / mL.

[0045] The electrospray ionization mass spectrometer used in the present invention is preferably a high-resolution mass spectrometer, more preferably a Fourier transform ion cyclotron resonance mass spectrometer or an electric field orbital trap mass spectrometer. The present invention has no special requirements on the operating conditions of the Fourier transform ion cyclotron resonance mass spectrometer or the electric field orbital trap mass spectrometer, and conventional operation is sufficient.

[0046] In order to further illustrate the present invention, a method for separating and analyzing carboxylic acid compounds in petroleum provided by the present invention is described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] A method for separating and analyzing carboxylic acid compounds in vacuum distillate oil, the specific steps of which are as follows:

[0049] Step 1: Preparation of amino MCM-41 molecular sieve:

[0050] Dissolve 5 g of CTAB in 200 mL of deionized water, add 30 mL of TMB, stir at 40°C until clear, add an appropriate amount of sodium hydroxide to adjust the pH to about 10 and stir for 0.5 h; add 30 mL of TEOS and stir for 3 h, then crystallize in a hydrothermal reactor for 3 days, wash with water, filter, and dry, and finally calcine at 600°C in a muffle furnace for 6 h to remove the template agent, and the MCM-41 molecular sieve with a pore size of 10~20 nm can be obtained. Subsequently, 20 mL of APTES and the obtained MCM-41 molecular sieve are reacted in a toluene solution for 24 h to obtain the amino MCM-41 molecular sieve.

[0051] Step 2: Fill 3 g of amino-modified MCM-41 molecular sieve with a pore size of about 10 nm into a 6 mL solid phase extraction column. Use 6 mL of n-hexane to wet the solid phase extraction column to obtain a wetted solid phase extraction column;

[0052] Step 3: Weigh 20 mg of vacuum distillate oil (i.e., petroleum sample) and dissolve it in 1 mL of n-hexane to obtain a solution of the target petroleum sample. The resulting solution is transferred to a wetted solid phase extraction column (processing completed in step 2), and the solid phase extraction column is eluted with 20 mL of dichloromethane and 20 mL of acetonitrile in sequence to remove non-target impurities. Subsequently, a mixed solution of 20 mL of hydrochloric acid aqueous solution and methanol (the volume ratio of hydrochloric acid to methanol is 1:3, and the mass concentration of hydrogen chloride in the hydrochloric acid aqueous solution is 37%) is used for further elution to desorb the carboxylic acid compounds adsorbed in the column. This combined elution method can effectively utilize the weak polarity of dichloromethane and acetonitrile to preliminarily remove non-polar and neutral impurities, and then use a strong polar acidic solution to selectively resolve the carboxylic acid compounds, thereby obtaining a high-purity carboxylic acid component.

[0053] Then it was dissolved in a methanol-toluene mixed solvent (volume ratio 3:1) to prepare a test solution with a concentration of 0.02 mg / mL. 1 mL of the test solution was taken for negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry analysis. The molecular composition information of the carboxylic acid compounds in the vacuum distillate oil was obtained by statistics and calculation, such as Figure 1 shown.

[0054] Figure 1 The carbon number and double bond equivalent number (DBE, i.e., the total number of rings and double bonds in the molecule) distribution diagram of the carboxylic acid compounds obtained by analyzing the carboxylic acid compounds in the vacuum distillate oil by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry in Example 1. Figure 1It can be seen that vacuum distillate contains carboxylic acid compounds with DBE=1~18, among which DBE=3~7 series is the main one. Among them, the carboxylic acid series with DBE=4~6 is a carboxylic acid compound containing one aromatic ring, and its main carbon number distribution range is 25~50.

[0055] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for separating and analyzing carboxylic acid compounds in petroleum, characterized in that: The method comprises the following steps: Step 1: Dissolve the petroleum sample in organic solvent A and add it into a solid phase extraction column filled with amino-modified MCM-41 molecular sieve; Step 2: sequentially eluting the sample with organic solvent B and mixed solution C to obtain a carboxylic acid compound; Step 3: using organic solvent D to dissolve the carboxylic acid compound to adjust the injection concentration, and then using an electrospray ionization mass spectrometer to characterize the molecular composition; The organic solvent A is a small molecule hydrocarbon solvent with a carbon number not exceeding 8; The organic solvent B is a weakly polar organic solvent having a polarity not stronger than that of dichloromethane and a boiling point not higher than 100° C.; The mixed solution C is a mixed solution of Bronsted acid and alcohol in a volume ratio of 1:3; the organic solvent D is a mixed solvent of toluene and methanol in a volume ratio of 1:3; The preparation method of the amination MCM-41 molecular sieve is as follows: Dissolve hexadecyltrimethylammonium bromide in distilled water, add 1,3,5-trimethylbenzene, stir at 45°C until clear, adjust pH to 8-12 with sodium hydroxide and stir for 0.5-2h, then add ethyl orthosilicate and stir for 3h; After crystallization for 3 to 5 days, the template is removed by calcination at 350 to 800 °C for 6 to 8 hours to obtain MCM-41 molecular sieve with a pore size of 10 to 20 nm. use -Aminopropyltriethoxysilane alkyl reacting with the obtained MCM-41 molecular sieve in a toluene solution for 1 day to obtain an amination MCM-41 molecular sieve; The hexadecyl trimethyl ammonium bromide, distilled water, 1,3,5-trimethylbenzene, ethyl orthosilicate and -The mass volume ratio of aminopropyltriethoxysilane is 5g:200mL:20~40mL:30mL:20mL.

2. The method according to claim 1, characterized in that The petroleum sample includes one or more of crude oil, diesel fraction and vacuum gas oil fraction.

3. The method according to claim 1, characterized in that Based on the total weight, the total carboxylic acid compound content of the petroleum sample is 0.01wt%~100wt%.

4. The method according to claim 1, characterized in that: The dosage ratio of the amino MCM-41 molecular sieve to the organic solvent A for dissolving the petroleum sample is 0.3-3 g: 0.2-2 mL.

5. The method according to claim 1, characterized in that The organic solvent A includes one or more of n-pentane, n-hexane, n-heptane and n-octane.

6. The method according to claim 1, characterized in that The organic solvent B includes one or more of dichloromethane, chloroform, carbon tetrachloride, acetonitrile and toluene.

7. The method according to claim 1, characterized in that The Bronsted acid in the mixed solution C includes one or more of acetic acid, hydrochloric acid, nitric acid and sulfuric acid.

8. The method according to claim 1, characterized in that The injection concentration in step 3 is 0.002 mg / mL to 0.2 mg / mL.

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