CN1180257C - Oil alkalinity nitrogen assay method - Google Patents
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- CN1180257C CN1180257C CNB021165246A CN02116524A CN1180257C CN 1180257 C CN1180257 C CN 1180257C CN B021165246 A CNB021165246 A CN B021165246A CN 02116524 A CN02116524 A CN 02116524A CN 1180257 C CN1180257 C CN 1180257C
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Abstract
The present invention relates to a method for determining the content of alkaline nitrogen in oil products, which comprises the steps that an oil product is dissolved in solvent, and the solution composed of the oil product and the solvent is titrated with a titrant solution until the titration end point is reached. The present invention is characterized in that in the method, the mixed solvent of xylene and anhyrous acetic acid is used as solvent for dissolving the oil product, the solution composed of the oil product and the solvent is titrated with the titrant solution of perchloric acid, propionic acid and anhyrous acetic acid, and the processes of automatically adding and supplementing the liquid of the titrant solution, compensating vacancies, eliminating pseudo end points, judging the end point and calculating and displaying results are carried out through an alkaline nitrogen test device controlled by a computer; the present invention can also be used for the titration by using crystal violet or leucocrystal violet as an indicator. The method can be used for testing the content of alkaline nitrogen in light-colored oil products and dark oil products.
Description
Technical Field
The invention relates to a method for measuring alkaline nitrogen of oil products, in particular to a method for measuring alkaline nitrogen in light-colored petroleum products such as gasoline, kerosene, diesel oil and lubricating oil and dark-colored petroleum products such as wax oil, residual oil, mixed oil and crude oil.
Background
With the development of the petroleum processing industry, the harm of nitrogen compounds, especially basic nitrogen compounds, in petroleum products gradually arouses people's attention. Basic nitrogen compounds in the raw materials easily poison the active center of the catalyst, so that the distribution of the product is poor, the conversion rate is reduced, and the actual processing amount of the device is greatly reduced; the alkaline nitrogen in the product can also make the stability of the petroleum product worse, the color deepen, and generate colloid, sediment and the like, so that the accurate detection of the alkaline nitrogen in the oil productis very important.
In SH/T0162-92 national petrochemical industry standard 'basic nitrogen determination method in petroleum products', a sample solvent is a benzene-glacial acetic acid mixed solvent, a titration standard solution is perchloric acid-glacial acetic acid, an indicator is 0.1 wt% of methyl violet or crystal violet, and the instrument comprises: an automatic burette, an erlenmeyer flask, a volumetric flask, a graduated cylinder and a pipette. The determination method comprises the following steps: dissolving a sample in a benzene-glacial acetic acid mixed solvent, titrating basic nitrogen in the sample by using perchloric acid-glacial acetic acid standard solution by using methyl violet or crystal violet as an indicator until the purple of the solution disappears and blue appears, and terminating titration. The basic nitrogen content of the sample was calculated from the concentration and volume of the consumed perchloric acid-glacial acetic acid standard solution.
IP 276/95; ISO 3771: 1994; ASTM D2896-98; BS 2000: part 276: 1995 "petroleum product-base number determination-perchloric acid potentiometric titration method", the sample solvent is anhydrous chlorobenzene-glacial acetic acid mixed solvent, the titration standard solution is perchloric acid-glacial acetic acid, the apparatus includes: potentiometric titrators, automatic recording instruments, universal glass electrodes, sleeve-shaped standard calomel reference electrodes, mechanical stirrers or electromagnetic stirrers, 10ml or 20ml burettes (precision +/-0.02 ml) or automatic burettes with similar precision, titration beakers. The determination method comprises the following steps: dissolving sample oil in a basically anhydrous chlorobenzene-glacial acetic acid mixed solvent, titrating with perchloric acid-glacial acetic acid standard titration solution by using a potentiometric titrator, using a glass indicating electrode and a calomel reference electrode which are connected with the sample solution by a salt bridge, automatically drawing a curve of reading to the volume of the corresponding titration solution by using the potentiometric titrator, and taking the final inflection point of the curve as an end point.
IP 139/98; ISO 6618: 1996; ASTM D974-97; BS 2000: part A: 1998 'petroleum products and lubricating oils-determination of acid value or base value-color indicator titration method', wherein a mixture of toluene-propanol-2 containing a small amount of water is used as a sample solvent, a standard alcohol-base solution or an alkyd solution is used as a titration standard solution, a p-naphthol benzene solution is used as an indicator, and the apparatus comprises common laboratory equipment, a burette, 50ml in capacity, 0.1ml in fine scale or 10ml in capacity, and 0.05ml in fine scale. Acid value or base value titration method: dissolving the test component in a mixture of toluene-propanol-2 containing a small amount of water, titrating the obtained single-phase solution with a standard alcohol-base solution or an alkyd solution respectively to an end point at room temperature, wherein the end point is indicated by the color change of the added p-naphthol benzene solution, the end point color is orange when the acid value is titrated, and the end point color is green-brown when the alkali value is titrated.
IP 417/96 "determination of base number-potentiometric drop method", a sample was dissolved in a mixed solvent of toluene-propanol-2 containing a small amount of water, subjected to potentiometric titration with a hydrochloric acid alcohol solution, and a glass indicator electrode and a calomel reference electrode were used. Manually drawing or automatically drawing a curve of reading to the volume of the added titration solution by an instrument, taking an obvious inflection point of the curve as an end point, and taking the reading of a titrator which is equivalent to a non-aqueous acid buffer solution (alkali value) or an alkali buffer solution (strong alkali value) as the end point when electricity is not obviously inflected.
Through domestic and foreign literature search, no literature report with the same main technical characteristics as the invention is found.
Disclosure of Invention
The invention provides a method for measuring alkaline nitrogen of oil products, which is used for measuring the alkaline nitrogen content in light-colored and dark-colored petroleum products.
The method for measuring the alkaline nitrogen of the oil product comprises the steps of dissolving the oil product in a solvent, and titrating the solution formed by the oil product and the solvent to a terminal point by using a titrant solution.
The method for determining the alkaline nitrogen of the oil product is characterized in that in the method for determining the alkaline nitrogen of the oil product, the oil product is dissolved in a mixed solvent of dimethylbenzene and anhydrous acetic acid, the perchloric acid-propionic acid-anhydrous acetic acid titrant solution is used for titrating the alkaline nitrogen in the oil product, and a computer-controlled alkaline nitrogen determination instrument is used for automatically adding and supplementing the titrant solution, compensating vacancies, eliminating a false end point, determining an end point, calculating and displaying a result.
The method for measuring the basic nitrogen of the oil product is characterized in that in the method for measuring the basic nitrogen of the oil product, the oil product is dissolved in a mixed solvent of dimethylbenzene and anhydrous acetic acid, methyl violet or crystal violet is used as an indicator, and perchloric acid-propionic acid-anhydrous acetic acid titrant solution is used for titrating the basic nitrogen in the oil product.
The method for measuring alkaline nitrogen of oil product is characterized by that the above-mentioned oil product includes light-colored petroleum products of gasoline, kerosene, diesel oil and lubricating oil, etc. and dark-colored petroleum products of wax oil, residual oil, mixed oil and crude oil, etc.
The method for measuring basic nitrogen of an oil product according to the present invention is described in detail below.
The invention discloses a method for measuring alkaline nitrogen of oil, which comprises the following steps of dissolving the oil in a mixed solvent of dimethylbenzene and anhydrous acetic acid, and titrating the alkaline nitrogen in the oil by using a perchloric acid-propionic acid-anhydrous acetic acid titrant solution, wherein the principle is as follows:
the invention discloses a method for measuring the alkaline nitrogen of an oil product, which is to dissolve a sample in a mixed solvent of dimethylbenzene and anhydrous acetic acid, and intermittently and accurately drop perchloric acid-propionic acid-anhydrous acetic acid titrant solution into a liquid absorption titration unit controlled by alkaline nitrogen analysis software. The computer collects the potential value of the dripped solution through a glass-calomel-platinum three-electrode system, dynamically adjusts the titration interval time automatically according to the potential stability degree, automatically recognizes the inflection point position according to the potential change rate, and determines the end point after selection and correction. The basic nitrogen content of the sample is automatically calculated and displayed by a calculation module. In the method for measuring the basic nitrogen of the oil product, methyl violet or crystal violet can be used as an indicator, the indicator is added into a solution formed by the oil product and a mixed solvent of xylene and anhydrous acetic acid, a perchloric acid-propionic acid-anhydrous acetic acid titrant solution is used for titration until the purple color of the solution disappears, and the basic nitrogen content in the sample is calculated according to the concentration and the volume of the consumed perchloric acid-propionic acid-anhydrous acetic acid titrant solution.
In the method for measuring the alkaline nitrogen of the oil product, the following instruments and materials are used:
a computer-controlled alkaline nitrogen automatic measuring instrument or a potentiometric titrator with similar functions; computer, WIN operating platform; the battery system consists of a reference electrode, an auxiliary electrode and an indicating electrode; the titration table is provided with a magnetic stirrer with an electrode rod and a fixing clamp on the shell; other common laboratory equipment.
The following reagents were used:
perchloric acid, anhydrous acetic acid, dimethylbenzene, propionic acid, acetic anhydride, anhydrous ethanol, lithium perchlorate, lithium chloride, methyl violet and crystal violet.
The method for measuring the alkaline nitrogen of the oil comprises the following steps:
preparing a certain amount of xylene-anhydrous acetic acid mixed solvent of 1: 1 in advance, weighing or transferring a proper amount of sample into a clean and dry low-mouth beaker according to the content range of alkaline nitrogen in the sample, adding the xylene-anhydrous acetic acid mixed solvent, and starting a stirrer. After the sample is dissolved, setting proper titration parameters, carrying out titration at certain volume intervals, automatically searching for an end point by a computer-controlled alkaline nitrogen automatic tester, and automatically stopping or displaying the titration end point by the color change of an indicator. Blanks were run in the same way.
And (4) calculating a result:
basic nitrogen content N in sampleB(μ g/g) was calculated by the following formula, and two results of repeated measurements were obtained
As a result of measurement of basic nitrogen of the sample:
NB＝C×(Vsample (I)-VBlank space)×0.014×106/m
Or NB C (V)Sample (I)-VBlank space)×0.014×106/(ρ×V)
In the formula:
NB-basic nitrogen content in the sample, μ g/g;
m is the mass of the sample, g;
rho is the density of the sample at the sampling temperature, g/m;
Vsample (I)Titration of the sample consumes a volume, mL, of perchloric acid standard solution;
Vblank space-blank test consumes volume, mL, of perchloric acid standard solution;
v-sample volume, mL;
c-perchloric acid concentration in perchloric acid-propionic acid-anhydrous acetic acid titrant solution, mol/L.
0.014-milligram molar mass of nitrogen in basic nitrogen compound, g.
When the basic nitrogen content of an oil product is measured by adopting an SH/T0162 standard method, thefollowing problems are found to exist:
1. the mixed solvent has high toxicity
The sample mixed solvent of the method adopts a benzene-glacial acetic acid mixed solvent, and a large amount of benzene reagent is contained in the benzene-glacial acetic acid mixed solvent. According to medical research reports, benzene is a chemical with strong volatility (boiling point of 80 ℃, vapor pressure of 9.99kPa) and high toxicity, and after long-term contact, the benzene causes harm to the nervous system, hematopoietic system and the like of operators, and is typically characterized by headache, dizziness, hypomnesis, insomnia, hypodynamia, leucopenia, aplastic anemia, different types of leukemia and the like, and the benzene is a strong carcinogenic substance recognized by modern medicine.
2. The titrant solution is easy to crystallize
The standard titrant solution of the method is a glacial acetic acid solution dissolved in perchloric acid, and when the environmental temperature is lower than 15 ℃, the crystallization of the perchloric acid standard titrant solution occurs, so that the analysis cannot be normally carried out.
3. Indicator color change insensitivity
Under the condition specified by SH/T0162 standard, an indicator is adopted to judge a titration end point, and the titration end point changes color and is not sharp from purple to blue for partial light color oil, and in some oil samples, the condition that the blue color is not presented after the purple disappears also appears. Therefore, the same operator has larger judgment deviation in different sample analyses, and the error between different operators is larger.
4. Has limited application range
As the end point is judged by adopting the indicator color change method, the SH/T0162 standard is determined to be not suitable for dark oil products (crude oil, wax oil, residual oil and the like). In long-term analysis, the SH/T0162 standard is not only not suitable for oil products with dark colors, even for secondary processing oil products with light colors, but also the solution is red after a sample is dissolved in a titration solution, and the red color is mixed with the blue color after titration to ensure that the solution is purple, so that the measurement result of the basic nitrogen is higher than the actual content. For example, when the basic nitrogen content of the delayed coking gasoline is analyzed, the phenomena that the repeatability of a test result is poor, the data is higher, and the measurement result is close to or even exceeds the total nitrogen sometimes occur.
The method for measuring the basic nitrogen of the oil product improves the SH/T0162 standard and has the following effects:
the equivalent potentiometric titration method controlled by software is adopted to replace the SH/T0162 standard indicator titration method, so that the problem of measuring the content of the alkaline nitrogen in the dark oil is solved; a xylene-anhydrous acetic acid mixed solvent with low toxicity is used as a solvent for dissolving a sample instead of a benzene-anhydrous acetic acid mixed solvent, so that the problems of high toxicity, strong volatility and the like of a titration solvent are solved; proper propionic acid is added into perchloric acid-glacial acetic acid standard titrant solution of an SH/T0162 standard method, so that the problem of crystallization and precipitation of the standard titrant solution at the ambient temperature of lower than 15 ℃ is solved; in the new titration system, the indicator has improved color change and sensitivity, and the measured result is consistent with the measured result of the original SH/T0162 method.
The comparative test data of the xylene-anhydrous acetic acid mixed solvent and the benzene-anhydrous acetic acid mixed solvent are shown in Table 1.
As shown in the data in Table 1, the measurement results of the two mixed solvents can both meet the precision requirement in the basic nitrogen analysis standard. The xylene-anhydrous acetic acid solvent replacing the benzene-glacial acetic acid solvent does not influence the correct judgment of the end point, so that the xylene can be completely used as a substitute of benzene in the mixed solvent.
The perchloric acid-propionic acid-anhydrous acetic acid titrant solution is selected to replace a perchloric acid-glacial acetic acid titrant solution prepared by an SH/T0162 standard method, the stability is good, and no crystallization phenomenon exists during titration at the temperature of minus 10 ℃. The titrant solutions of the invention were compared with those of the SH/T0162 standard method using light-coloured oil. The test results are shown in Table 2.
As can be seen from the data in Table 2, the determination results of the present invention can satisfy the precision requirement of the basic nitrogen standard method at the 95% confidence level, and the determination results of the titrant solutions of the two methods have no obvious difference. And tests show that the improved perchloric acid-propionic acid-anhydrous acetic acid titrant solution is stable, and the concentration change is still within the error range after the improved perchloric acid-propionic acid-anhydrous acetic acid titrant solution is stored for two months.
The invention greatly reduces the toxicity during the determination of the alkaline nitrogen by changing the formula of the standard titrant solution of the SH/T0162 standard method, and overcomes the problem of crystallization and precipitation of the standard titrant solution when the environmental temperature is low. When the indicator is manually dripped by the method, the color change of the indicator is sharper, and the measurement result has good equivalence with SH/T0162 standard. The results of the tests of the method of the invention are compared with those of the SH/T0162 standard method in Table 3.
As can be seen from Table 3, the test results of the method of the present invention and the SH/T0162 method have good equivalence.
In the improvement process of the SH/T0162 standard method, perchloric acid standard solution is intermittently and accurately dripped into the standard method according to the set volume, the inflection point position is identified according to the potential change rate, the titration is terminated after the endpoint is determined by correction. The optimal titration conditions are determined by changing titration parameter settings, end point potential jump size and jump point and end point coincidence degree tests, comparison tests (light color oil) with a standard analysis method, electrode system tests, accuracy and accuracy tests, sample weighing and solvent volume range tests, titration speed and stirring speed tests, recovery rate tests, application tests of basic nitrogen in different contents and various dark and light color oils, back diffusion tests of titration heads and the like. The results of the comparison of the potential values at the end of the titration with the method of the invention and the SH/T0162 standard are shown in Table 4.
The repeatability test of the determination result shows that: the equivalent potentiometric titration method of the invention can meet the precision requirement of the alkaline nitrogen analysis method at the 95% confidence level.
The invention uses a computer-controlled alkaline nitrogen tester to test the alkaline nitrogen contentof various oil products, inspects the adaptability and the parallelism of the oil products and obtains better results, and the test results of part of samples are shown in a table 5.
As can be seen from Table 5, the accuracy of the potentiometric titration method of the present invention is not significantly different from the standard method. The light-colored oil product contrast test shows that: the error of measurement for both titration methods is within the range specified for SH/T0162. In the test of titrating the light color oil by using the alkaline nitrogen determinator, if the indicator is dripped, the color change point of the indicator is consistent with the potentiometric titration end point. In the test of titrating dark oil by an alkali nitrogen determinator, the end point potential value of the dark oil product is basically the same as the corresponding potential value when the indicator changes color.
Drawings
Table 1 shows the results of the measurements of the mixed solvent of the present invention and the mixed solvent of SH/T0162 standard method (n ═ 3).
Table 2 compares the results of the assay of the titrant solutions of the present invention with those of the titrant solutions of standard SH/T0162 method (n-4).
Table 3 shows the results of the test conducted by the method of the present invention in comparison with the SH/T0162 method (n-4).
Table 4 shows the comparison of the potential values at the end points of the process according to the invention with the SH/T0162 standard process (n-4).
Table 5 shows the results of the basic nitrogen content measurement (n ═ 4) for the inventive samples.
Detailed Description
Example 1
19.82g of straight-run diesel oil is weighed into a clean and dry low-mouth beaker of 150mL, 80mL of mixed solvent of xylene and anhydrous acetic acid (1: 1) which is prepared in advance is added, and a stirrer is started. After the sample is dissolved, the computer controls 0.02047M perchloric acid-propionic acid-anhydrous acetic acid titrant solution to carry out titration at the volume interval of 0.05-0.10 mL, the endpoint is automatically found, and the calculation module automatically calculates and displays the alkaline nitrogen content of 25.5 mu g/g, the titration curve and the potential change rate curve. A blank value of 0.10mL was determined in the same manner. The volume of titrant consumed by the endpoint was 1.87 mL.
Example 2
Weighing 1.512g of refined diesel oil into a clean and dry low-mouth beaker of 150mL, adding 80mL of mixed solvent of xylene and anhydrous acetic acid (1: 1) which is prepared in advance, and starting a stirrer. After the sample is dissolved, the computer controls 0.02047M perchloric acid-propionic acid-anhydrous acetic acid titrant solution to carry out titration at the volume interval of 0.05-0.10 mL, the endpoint is automatically found, and the calculation module automatically calculates and displays the basic nitrogen content of 449 mu g/g, the titration curve and the potential change rate curve. A blank value of 0.05mL was determined in the same manner. The volume of titrant consumed by the endpoint was 2.40 mL.
Example 3
Dissolving 21.05g of 90# gasoline into 80mL of a prepared xylene-anhydrous acetic acid (1: 1) mixed solvent, adding two drops of 0.3 wt% crystal violet indicator, manually titrating, titrating the basic nitrogen in an oilproduct by using 0.02047M perchloric acid-propionic acid-anhydrous acetic acid titrant solution, controlling the titration speed within 1mL/min until the purple color of the solution disappears and the blue color just appears, and obtaining the volume of the titrant used for the end point consumption of 0.78 mL. A blank test was carried out in the same manner, and the blank value was 0.15 mL. The basic nitrogen content of the sample was calculated to be 8.6. mu.g/g.
Example 4
0.51683g of the residual oil were weighed into a 150mL clean and dry beaker with a low temperature, 80mL of the xylene-anhydrous acetic acid (1: 1) mixed solvent prepared in advance were added, and the stirrer was switched on. After the sample is dissolved, the computer controls 0.02047M perchloric acid-propionic acid-anhydrous acetic acid titrant solution to carry out titration at the volume interval of 0.05-0.10 mL, the endpoint is automatically found, and the calculation module automatically calculates and displays 2306 mu g/g of alkaline nitrogen content, a titration curve and a potential change rate curve. A blank was determined in the same manner and had a blank value of 0.16 mL. The volume of titrant consumed by the endpoint was 1.67mL
Example 5
0.4489g of the mixed oil were weighed into a 150mL clean and dry low-mouth beaker, and 80mL of a xylene-anhydrous acetic acid (1: 1) mixed solvent which had been prepared in advance was added thereto, and the stirrer was turned on. After the sample is dissolved, the computer controls 0.02047M perchloric acid-propionic acid-anhydrous acetic acid titrant solution to carry out titration at the volume interval of 0.05-0.10 mL, the endpoint is automatically found, and a calculation module automatically calculates and displays a titration curve with the basic nitrogen content of 1044 mu g/g and a potential change rate curve. A blank was determined in the same manner and had a value of 0.12 mL. The volume of titrant consumed by the endpoint was 1.87 mL.
Claims (3)
1. The method for determining the alkaline nitrogen of the oil product comprises the steps of dissolving the oil product in a solvent, titrating a solution consisting of the oil product and the solvent to an end point by using a titrant solution, and is characterized in that in the method for determining the alkaline nitrogen of the oil product, the oil product is dissolved in a mixed solvent of dimethylbenzene and glacial acetic acid, the weight ratio of the dimethylbenzene to the glacial acetic acid is 1: 1, the solution consisting of the oil product and the mixed solvent is titrated by using a perchloric acid-propionic acid-glacial acetic acid titrant solution, the titrant solution is automatically added and supplemented by using a computer-controlled alkaline nitrogen analyzer, a vacancy is compensated, a false end point is eliminated, the end point is determined, and a result.
2. The method of claim 1, wherein the method further comprises a step of manual titration, wherein the oil is dissolved in a mixed solvent of xylene and glacial acetic acid, and the perchloric acid-propionic acid-glacial acetic acid titrating agent solution is used to titrate the basic nitrogen in the oil with methyl violet or crystal violet as an indicator.
3. The method of claim 1, wherein the oil product is selected from the group consisting of light-colored petroleum products including gasoline, kerosene, diesel oil, and lubricating oil, and dark-colored petroleum products including wax oil, residual oil, mixed oil, and crude oil.
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