CN114689569A - Method for testing silicon-aluminum ratio of molecular sieve - Google Patents
Method for testing silicon-aluminum ratio of molecular sieve Download PDFInfo
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Abstract
The invention belongs to the field of chemical analysis and test, and particularly relates to a method for testing the silica-alumina ratio of a molecular sieve. The method comprises the following steps: grinding a molecular sieve sample to be detected into fine powder; filling the fine powder of the molecular sieve to be detected into a digestion tank of a fully-closed microwave digestion instrument, adding a mixed solution of aqua regia and hydrofluoric acid as a digestion solution, and performing microwave digestion; after complete digestion, opening a cover, adding a saturated boric acid solution, heating the cover to perform primary complexing on hydrofluoric acid, taking out a digestion solution, and performing constant volume in a volumetric flask to obtain a digestion complexing solution; diluting the digestion complexing solution by a certain multiple by using a standard addition method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion complexing solution to prepare a series of test mixed standard solutions meeting the silicon-aluminum ratio determination, adding a mixed solution of boric acid and dilute nitric acid for constant volume, and shaking up for secondary complexing of hydrofluoric acid; and then ICP-OES is adopted, a quartz standard sample injection system is used for measuring the contents of silicon and aluminum, and the silicon-aluminum ratio is directly calculated.
Description
Technical Field
The invention belongs to the technical field of chemical analysis testing methods, and particularly relates to a method for testing a silicon-aluminum ratio of a molecular sieve.
Background
The main methods for testing the silicon-aluminum ratio of the molecular sieve at present comprise: measuring silicon and iron by a spectrophotometric method, measuring the total quantity of aluminum and iron by an EDTA and nitric acid titration method, and further calculating a silicon-aluminum ratio; measuring the content ratio of silicon to aluminum by an XRF method.
The spectrophotometry method for detecting the silicon-aluminum ratio has the following technical problems: if the solution contains other chromogenic ions, the accuracy of the absorbance test is poor; the method is indirect and has certain test error. The XRF method has the problem that the solid standard sample is difficult to search and only semi-quantitative test can be carried out.
The accurate quantitative determination of the silica-alumina ratio of the molecular sieve is always a difficult problem in the industry. The artificially synthesized molecular sieve has high adsorption capacity and high temperature resistance, is widely used in the chemical industry, is also an excellent adsorbent for coal gas dehydration, and has a silicon-aluminum ratio which is a key index for determining the performance of the artificially synthesized molecular sieve.
Therefore, the method realizes accurate and quantitative measurement of the silicon-aluminum ratio of the molecular sieve, and has important significance for the preparation process and performance evaluation of the molecular sieve.
Disclosure of Invention
Aiming at the technical problems, the invention provides a method for testing the silicon-aluminum ratio of a molecular sieve, which can directly measure the silicon-aluminum content and the silicon-aluminum ratio of the molecular sieve without indirect calculation and is an accurate quantitative test method.
The invention is realized by the following technical scheme:
a molecular sieve silica to alumina ratio test method, the method comprising:
grinding a molecular sieve sample to be detected into fine powder;
filling the fine powder of the molecular sieve to be detected into a digestion tank of a fully-closed microwave digestion instrument, adding a mixed solution of aqua regia and hydrofluoric acid as a digestion solution, and performing microwave digestion;
after complete digestion, a saturated boric acid solution is added after the cover is opened, then the cover is heated to carry out primary complexation on hydrofluoric acid, and digestion solution is taken out and subjected to constant volume in a volumetric flask by using ultrapure water to obtain digestion complex solution;
diluting the digestion complex solution by a certain multiple by using a standard addition method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion complex solution to prepare a series of test mixed standard solutions meeting the determination of the silicon-aluminum ratio of 10-500, adding a mixed solution of boric acid and dilute nitric acid to perform constant volume, and shaking up to perform secondary complexing on hydrofluoric acid; and then ICP-OES is adopted, a quartz standard sample injection system is used for measuring the contents of silicon and aluminum, and the silicon-aluminum ratio is directly calculated.
Further, the microwave digestion comprises the following specific steps: filling the molecular sieve fine powder to be detected into a digestion tank, adding a mixed solution of aqua regia and hydrofluoric acid as a digestion solution, performing microwave digestion, and performing microwave digestion by keeping the temperature at 200-220 ℃ for 30-40 minutes; in the digestion solution composed of the aqua regia and the hydrofluoric acid, the volume ratio range of the aqua regia and the hydrofluoric acid is (2-6): 1.
Further, the preliminary complexing step specifically comprises: after complete digestion, the cover is opened and saturated boric acid solution is added, and then the cover is covered and heated to 150-180 ℃ and is kept warm for 30-40 minutes for preliminary complexation; wherein, the adding volume of the saturated boric acid solution is 6-8 times of that of hydrofluoric acid in the digestion solution according to the weight ratio.
Furthermore, the material of the volumetric flask that the constant volume process adopted is polytetrafluoroethylene.
Further, in the process of adding the mixed solution of the boric acid and the dilute nitric acid for constant volume, the volume ratio of the boric acid to the dilute nitric acid is 1 (8: 10).
Furthermore, the original standard solution concentration of the silicon standard solution and the aluminum standard solution is 1000 μ L/mg, and the used standard solutions can be prepared or purchased.
Further, grinding the molecular sieve sample to be detected into fine powder, and sieving the fine powder through a 200-mesh sieve.
The invention has the beneficial technical effects that:
in the method for testing the silicon-aluminum ratio of the molecular sieve, the adopted digestion solution comprises aqua regia and hydrofluoric acid, wherein the aqua regia can digest metal elements such as aluminum and the like in the molecular sieve, and the hydrofluoric acid can digest silicon elements existing in the form of oxides in the molecular sieve; the method adopts full-closed microwave digestion, and can ensure that silicon element is not lost in the wet digestion process of the molecular sieve;
the invention adopts the boric acid complexation of the two-step method, and the boric acid reacts with the hydrofluoric acid to generate the fluoboric acid, thereby avoiding the corrosion of the hydrofluoric acid to an ICP-OES quartz sample injection system (silicon oxide) and the influence to silicon measurement.
The invention adopts a standard addition method to remove the influence of the complex matrix on the elements to be measured; the prepared series of standard-added silicon-aluminum mixed standard solutions can be suitable for large-range silicon-aluminum ratio measurement (10-500).
The testing method provided by the invention can directly and accurately determine the silicon-aluminum ratio of the molecular sieve, and can avoid silicon loss of the molecular sieve in wet digestion; the method of using a quartz standard sample injection system can be used, a hydrofluoric acid sample injection system is not required to be purchased independently, and the detection limit and the quantification limit of the hydrofluoric acid sample injection system are 1 order of magnitude to ppb level lower than those of the hydrofluoric acid sample injection system.
Drawings
FIG. 1 is a standard graph of Al element;
FIG. 2 is a standard graph of Si element.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
On the contrary, the invention is intended to cover alternatives, modifications, equivalents and alternatives which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, certain specific details are set forth in order to provide a better understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details.
Aiming at the technical problem existing in the prior art of accurately and quantitatively measuring the silicon-aluminum ratio of the molecular sieve, the invention provides a method for measuring the silicon-aluminum ratio of the molecular sieve, which comprises the following steps:
grinding the molecular sieve sample to be tested into fine powder, and taking the fine powder (with mass of m) of the molecular sieve to be tested0Unit g) loading full-closed microwave digestion instrumentAdding a mixed solution of aqua regia and hydrofluoric acid into the digestion tank to be used as a digestion solution, and performing microwave digestion;
after the digestion is completed, a saturated boric acid solution is added into the container after the container is opened, the container is covered and heated to carry out primary complexation on hydrofluoric acid, and the digestion solution is taken out to carry out constant volume (the constant volume is V)0Unit mL) to obtain a digestion complex solution;
diluting the digestion and complexation solution by a certain multiple (the dilution multiple is f) by using a standard addition method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion and complexation solution to prepare a series of test mixed standard solutions which meet the determination of the silicon-aluminum ratio of 10-500, adding a mixed solution of boric acid and dilute nitric acid to perform constant volume, shaking up to perform secondary complexation on hydrofluoric acid; then, ICP-OES is adopted, and a quartz standard sample injection system is used for measuring the content of silicon and aluminum (the element concentration in the test solution is C)0In mg/L, obtained by ICP-OES testing), the Si/Al ratio was directly calculated.
The concentration of the element to be detected in the digestion complexing solution is C1Unit mg/L, the calculation mode is as follows: c1＝C0*f；
Content C of element to be detected in molecular sieve sample to be detectedxUnit g/kg:
in this embodiment, the microwave digestion specifically includes the steps of: filling the molecular sieve fine powder to be detected into a digestion tank, adding a mixed solution of aqua regia and hydrofluoric acid as a digestion solution, performing microwave digestion, and keeping the temperature at 220 ℃ for 40 minutes; in the digestion solution composed of the aqua regia and the hydrofluoric acid, the volume ratio of the aqua regia to the hydrofluoric acid is 4: 1.
In this embodiment, the preliminary complexing step specifically includes: after complete digestion, the cover is opened and a saturated boric acid solution is added, and then the cover is covered and heated to 160 ℃ and is kept warm for 30 minutes for preliminary complexation; wherein, the addition amount of the saturated boric acid solution is 6 times of that of hydrofluoric acid in the digestion solution according to the weight ratio.
In this embodiment, the volumetric flask used in the constant volume process is made of teflon.
In this example, during the process of adding the mixed solution of boric acid and dilute nitric acid to perform constant volume, the volume ratio of boric acid and dilute nitric acid is 1: 9. In this embodiment, the original standard solution concentrations of the silicon standard solution and the aluminum standard solution are both 1000 μ L/mg.
In this example, a sample of the molecular sieve to be tested was ground into a fine powder and sieved through a 200 mesh sieve.
The method provided by the embodiment of the invention is adopted to measure the silicon and aluminum contents of four samples, and the mass m of the four samples0All are 0.01g, constant volume V0All 10mL, the results are as follows:
TABLE 1 test data for aluminum as the test element
| Sample numbering | C0(mg/L) | Dilution factor f | C1(mg/L) | Cx(g/kg) |
| 1 | 0.1540 | 100 | 15.4 | 15.4000 |
| 2 | 0.1700 | 100 | 17 | 17.0000 |
| 3 | 0.1990 | 100 | 19.0 | 19.9000 |
| 4 | 0.1540 | 100 | 15.4 | 15.4000 |
TABLE 2 test data for elemental silicon as the test element
| Sample numbering | C0(mg/L) | Dilution factor f | C1(mg/L) | Cx(g/kg) |
| 1 | 4.7200 | 100 | 472 | 472.0000 |
| 2 | 4.7900 | 100 | 479 | 479.0000 |
| 3 | 6.1800 | 100 | 618 | 618.0000 |
| 4 | 4.5600 | 100 | 456 | 456.0000 |
The calculated silicon-aluminum ratios of the molecular sieve samples 1-4 are 30.649, 28.176, 32.526 and 29.610 respectively, the silicon-aluminum ratios are 28-31, the standard curve graphs of the Al and Si elements are shown in the figure 1-2, and the content of the element to be detected can be calculated through the standard curve graphs in the figure 1-2.
Claims (7)
1. A method for testing the silicon-aluminum ratio of a molecular sieve is characterized by comprising the following steps:
grinding a molecular sieve sample to be detected into fine powder;
filling the fine powder of the molecular sieve to be detected into a digestion tank of a fully-closed microwave digestion instrument, adding a mixed solution of aqua regia and hydrofluoric acid as a digestion solution, and performing microwave digestion;
after complete digestion, a saturated boric acid solution is added after the cover is opened, then the cover is heated to carry out primary complexation on hydrofluoric acid, and digestion solution is taken out and subjected to constant volume in a volumetric flask by using ultrapure water to obtain digestion complex solution;
diluting the digestion and complexation solution by a certain multiple by using a standard addition method, adding silicon standard solutions and aluminum standard solutions with different volumes into the diluted digestion and complexation solution to prepare a series of test mixed standard solutions meeting the silicon-aluminum ratio determination, adding a mixed solution of boric acid and dilute nitric acid to perform constant volume, and shaking up to perform secondary complexation on hydrofluoric acid; and then ICP-OES is adopted, a quartz standard sample injection system is used for measuring the contents of silicon and aluminum, and the silicon-aluminum ratio is directly calculated.
2. The method for testing the silica-alumina ratio of the molecular sieve according to claim 1, wherein the microwave digestion comprises the following specific steps: filling the molecular sieve fine powder to be detected into a digestion tank, adding a mixed solution of aqua regia and hydrofluoric acid as a digestion solution, performing microwave digestion, and performing microwave digestion by keeping the temperature at 200-220 ℃ for 30-40 minutes; in the digestion solution composed of the aqua regia and the hydrofluoric acid, the volume ratio range of the aqua regia and the hydrofluoric acid is (2-6): 1.
3. The method for testing the silica-alumina ratio of a molecular sieve according to claim 1, wherein the preliminary complexing step specifically comprises: after complete digestion, the cover is opened and saturated boric acid solution is added, and then the cover is covered and heated to 150-180 ℃ and is kept warm for 30-40 minutes for preliminary complexation; wherein, the adding volume of the saturated boric acid solution is 6-8 times of that of hydrofluoric acid in the digestion solution according to the weight ratio.
4. The method for testing the silica-alumina ratio of a molecular sieve of claim 1, wherein a volumetric flask used in the constant volume process is made of polytetrafluoroethylene.
5. The method for testing the Si/Al ratio of a molecular sieve according to claim 1,
and in the process of adding the mixed solution of the boric acid and the dilute nitric acid for constant volume, the volume ratio of the boric acid to the dilute nitric acid is 1 (8: 10).
6. The method for testing the silica-alumina ratio of a molecular sieve according to claim 1, wherein the concentrations of the adopted original standard solutions of the silica standard solution and the aluminum standard solution are both 1000 μ L/mg.
7. The method for testing the silica-alumina ratio of a molecular sieve as claimed in claim 1, wherein the sample of the molecular sieve to be tested is ground into fine powder and then sieved through a 200-mesh sieve.
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