CN114689569B - Molecular sieve silicon-aluminum ratio test method - Google Patents
Molecular sieve silicon-aluminum ratio test method Download PDFInfo
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- CN114689569B CN114689569B CN202210343592.1A CN202210343592A CN114689569B CN 114689569 B CN114689569 B CN 114689569B CN 202210343592 A CN202210343592 A CN 202210343592A CN 114689569 B CN114689569 B CN 114689569B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
- G01N21/73—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited using plasma burners or torches
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/44—Sample treatment involving radiation, e.g. heat
Abstract
The invention belongs to the field of chemical analysis and test, and particularly relates to a molecular sieve silicon-aluminum ratio test method. The method comprises the following steps: grinding a molecular sieve sample to be tested into fine powder; loading the fine powder of the molecular sieve to be measured into a digestion tank of a fully-closed microwave digestion instrument, adding mixed solution of aqua regia and hydrofluoric acid as digestion solution, and carrying out microwave digestion; after complete digestion, opening the cover, adding saturated boric acid solution, heating the cover to perform preliminary complexing on hydrofluoric acid, taking out digestion solution, and performing constant volume in a volumetric flask to obtain digestion complexing solution; diluting the digestion complexing solution by a certain multiple by using a standard adding method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion complexing solution, preparing a series of test mixed standard solutions which accord with the determination of the silicon-aluminum ratio, adding a mixed solution of boric acid and dilute nitric acid for constant volume, and shaking uniformly to carry out secondary complexing on hydrofluoric acid; and then measuring the silicon and aluminum content by adopting ICP-OES (inductively coupled plasma-optical emission spectrometry) and using a quartz standard sample injection system to directly calculate the silicon-aluminum ratio.
Description
Technical Field
The invention belongs to the technical field of chemical analysis and test methods, and particularly relates to a molecular sieve silicon-aluminum ratio test method.
Background
The main method for testing the silicon-aluminum ratio of the molecular sieve at present comprises the following steps: (1) spectrophotometry is used for measuring silicon and iron, EDTA and nitric acid titration are used for measuring the total quantity of aluminum and iron, and then the silicon-aluminum ratio is calculated; (2) the XRF method is used for measuring the silicon-aluminum content ratio.
The spectrophotometry for detecting the silicon-aluminum ratio has the following technical problems: if the solution contains other chromogenic ions, the absorbance test accuracy is poor; the method is an indirect method and has a certain test error. However, XRF method has the problem of difficulty in finding solid standard sample and only semi-quantitative test.
Accurate quantitative determination of molecular sieve silica-alumina ratio has been a problem in the industry. The synthetic molecular sieve has high adsorption capacity and high temperature resistance, is widely used in the chemical industry, is also an excellent adsorbent for dehydrating coal gas, and has a silicon-aluminum ratio composition which is a key index for determining the performance.
Therefore, the method realizes accurate quantitative measurement of the silicon-aluminum ratio of the molecular sieve, and has important significance for both the preparation process and the performance evaluation of the molecular sieve.
Disclosure of Invention
Aiming at the technical problems, the invention provides a molecular sieve silicon-aluminum ratio test method which can directly determine the silicon-aluminum content and the silicon-aluminum ratio of a molecular sieve without indirect calculation and is an accurate quantitative test method.
The invention is realized by the following technical scheme:
a method for testing the silica to alumina ratio of a molecular sieve, the method comprising:
grinding a molecular sieve sample to be tested into fine powder;
loading the fine powder of the molecular sieve to be measured into a digestion tank of a fully-closed microwave digestion instrument, adding mixed solution of aqua regia and hydrofluoric acid as digestion solution, and carrying out microwave digestion;
after digestion is completed, opening the cover, adding saturated boric acid solution, heating the cover to perform preliminary complexing on hydrofluoric acid, taking out digestion solution, and performing constant volume in a volumetric flask by using ultrapure water to obtain digestion complexing solution;
diluting the digestion complexing solution by a certain multiple by using a standard adding method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion complexing solution, preparing a series of test mixed standard solutions which accord with the determination of the silicon-aluminum ratio of 10-500, adding a mixed solution of boric acid and dilute nitric acid for constant volume, and uniformly shaking to carry out secondary complexing on hydrofluoric acid; and then measuring the silicon and aluminum content by adopting ICP-OES (inductively coupled plasma-optical emission spectrometry) and using a quartz standard sample injection system to directly calculate the silicon-aluminum ratio.
Further, the specific steps of the microwave digestion are as follows: placing molecular sieve fine powder to be measured into a digestion tank, adding mixed solution of aqua regia and hydrofluoric acid as digestion solution, carrying out microwave digestion, and preserving heat for 30-40 minutes at 200-220 ℃; in the digestion solution composed of aqua regia and hydrofluoric acid, the volume ratio of the aqua regia to the hydrofluoric acid is (2-6): 1.
Further, the preliminary complexing step specifically comprises the following steps: after complete digestion, opening the cover, adding saturated boric acid solution, and then heating the cover to 150-180 ℃ and preserving heat for 30-40 minutes to perform preliminary complexation; wherein, the addition volume of the saturated boric acid solution is 6-8 times of the hydrofluoric acid in the digestion solution according to the weight ratio.
Further, the volumetric flask used in the constant volume process is made of polytetrafluoroethylene.
Further, in the process of adding the mixed solution of boric acid and dilute nitric acid for constant volume, the volume ratio of the boric acid to the dilute nitric acid is 1 (8:10).
Further, the original concentration of the silicon standard solution and the aluminum standard solution is 1000 mu L/mg, and the used standard solution can be self-prepared or purchased.
Further, grinding the molecular sieve sample to be tested into fine powder, and sieving with a 200-mesh sieve.
The beneficial technical effects of the invention are as follows:
in the molecular sieve silicon-aluminum ratio test method provided by the invention, the digestion liquid comprises aqua regia and hydrofluoric acid, wang Shuineng can digest metal elements such as aluminum in the molecular sieve, and hydrofluoric acid can digest silicon elements in the form of oxides in the molecular sieve; the method adopts full-closed microwave digestion, so that silicon element is ensured not to be lost in the wet digestion process of the molecular sieve;
the invention adopts two-step boric acid complexing, and the boric acid is reacted and complexed with hydrofluoric acid to generate fluoboric acid, thereby avoiding the erosion 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 adding method to remove the influence of the complex matrix on the element to be detected; the prepared series of standard-added silicon-aluminum mixed standard liquids can be suitable for large-scale silicon-aluminum ratio measurement (10-500).
The testing method provided by the invention can directly and accurately measure the silicon-aluminum ratio of the molecular sieve, and can avoid silicon loss of the molecular sieve in wet digestion; the method of the quartz standard sample injection system can be used, the hydrofluoric acid sample injection system is not required to be purchased independently, and the detection limit and the quantitative limit of the hydrofluoric acid sample injection system are lower by 1 order of magnitude to ppb level.
Drawings
FIG. 1 is a standard graph of Al element;
fig. 2 is a standard graph of Si element.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
On the contrary, the invention is intended to cover any alternatives, modifications, equivalents, and variations as may be included within the spirit and scope of the invention as defined by the appended claims. Further, 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. The present invention will be fully understood by those skilled in the art without the details described herein.
Aiming at the technical problems of the prior art in precisely and quantitatively measuring the silicon-aluminum ratio of the molecular sieve, the invention provides a molecular sieve silicon-aluminum ratio test method, which comprises the following steps:
grinding the molecular sieve sample to be tested into fine powder, and taking the fine powder (with the mass of m 0 The unit g) of the digestion tank is filled into a fully-closed microwave digestion instrument, and mixed solution of aqua regia and hydrofluoric acid is added as digestion solution to carry out microwave digestion;
after digestion is completed, the saturated boric acid solution is added into the reactor through a cover, and then the reactor is covered and heated to carry out preliminary complexing on hydrofluoric acid, the digestion solution is taken out to carry out constant volume (the constant volume is V) 0 Unit mL), obtaining a digestion complexing solution;
diluting the digestion complexing solution by a certain multiple (the dilution multiple is f) by using a standard adding method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion complexing solution, preparing a series of test mixed standard solutions which accord with the determination of the silicon-aluminum ratio of 10-500, adding a mixed solution of boric acid and dilute nitric acid for constant volume, and shaking uniformly to carry out secondary complexing on hydrofluoric acid; then the content of silicon and aluminum is measured by ICP-OES (the concentration of the element in the test solution is C) by using a quartz standard sample injection system 0 The unit mg/L is obtained by ICP-OES test), and the silicon-aluminum ratio is directly calculated.
The concentration of the element to be measured in the digestion complex solution is C 1 The unit mg/L is calculated by the following steps: c (C) 1 ＝C 0 *f；
Content C of element to be detected in molecular sieve sample to be detected x Unit g/kg:
in this embodiment, the specific steps of microwave digestion are as follows: placing molecular sieve fine powder to be measured into a digestion tank, adding mixed solution of aqua regia and hydrofluoric acid as digestion solution, carrying out microwave digestion, and preserving heat for 40 minutes at 220 ℃; in digestion solution composed of aqua regia and 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, opening the cover, adding saturated boric acid solution, and then heating the cover to 160 ℃ and preserving heat for 30 minutes to perform 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 polytetrafluoroethylene.
In this embodiment, in the process of adding a mixed solution of boric acid and dilute nitric acid to perform constant volume, the volume ratio of boric acid to dilute nitric acid is 1:9. In this example, the original standard solution concentrations of the silicon standard solution and the aluminum standard solution used were 1000. Mu.L/mg.
In this example, a sample of the molecular sieve to be tested was ground to a fine powder and then 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 samples 0 Are all 0.01g, and the volume is fixed 0 All 10mL, the results were as follows:
table 1 test data when the test element is aluminum
| Sample numbering | C 0 (mg/L) | Dilution factor f | C 1 (mg/L) | C x (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 when the test element is silicon element
| Sample numbering | C 0 (mg/L) | Dilution factor f | C 1 (mg/L) | C x (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 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, standard graphs of two elements of Al and Si are shown in the figures 1-2, and the content of the element to be detected can be calculated by the sample through the standard graphs in the figures 1-2.
Claims (5)
1. A method for testing the silicon-aluminum ratio of a molecular sieve, which is characterized by comprising the following steps:
grinding a molecular sieve sample to be tested into fine powder;
loading the fine powder of the molecular sieve to be measured into a digestion tank of a fully-closed microwave digestion instrument, adding mixed solution of aqua regia and hydrofluoric acid as digestion solution, and carrying out microwave digestion;
after digestion is completed, opening the cover, adding saturated boric acid solution, heating the cover to perform preliminary complexing on hydrofluoric acid, taking out digestion solution, and performing constant volume in a volumetric flask by using ultrapure water to obtain digestion complexing solution;
diluting the digestion complexing solution by a certain multiple by using a standard adding method, adding silicon standard solution and aluminum standard solution with different volumes into the diluted digestion complexing solution, preparing a series of test mixed standard solutions which accord with the determination of the silicon-aluminum ratio of 10-500, adding a mixed solution of boric acid and dilute nitric acid for constant volume, shaking uniformly, carrying out secondary complexing on hydrofluoric acid, and adopting a two-step method boric acid complexing method to enable the complexing reaction of the hydrofluoric acid to be completely and fully; then adopting ICP-OES, using a quartz standard sample injection system to measure the silicon and aluminum content, and directly calculating the silicon-aluminum ratio; in the process of adding the mixed solution of boric acid and dilute nitric acid for constant volume, the volume ratio of the boric acid to the dilute nitric acid is 1 (8:10);
the preliminary complexing step specifically comprises the following steps: after complete digestion, opening the cover, adding saturated boric acid solution, and then heating the cover to 150-180 ℃ and preserving heat for 30-40 minutes to perform preliminary complexation; wherein, the addition volume of the saturated boric acid solution is 6-8 times of the hydrofluoric acid in the digestion solution according to the weight ratio.
2. The method for testing the silicon-aluminum ratio of the molecular sieve according to claim 1, wherein the specific steps of microwave digestion are as follows: placing molecular sieve fine powder to be measured into a digestion tank, adding mixed solution of aqua regia and hydrofluoric acid as digestion solution, carrying out microwave digestion, and preserving heat for 30-40 minutes at 200-220 ℃; in the digestion solution composed of aqua regia and hydrofluoric acid, the volume ratio of the aqua regia to the hydrofluoric acid is (2-6): 1.
3. The method for testing the silicon-aluminum ratio of the molecular sieve according to claim 1, wherein the volumetric flask used in the constant volume process is made of polytetrafluoroethylene.
4. The method for testing the silicon-aluminum ratio of the molecular sieve according to claim 1, wherein the concentration of the original standard solution of the adopted silicon standard solution and the original standard solution of the adopted aluminum standard solution are 1000 mu L/mg.
5. The method for testing the silicon-aluminum ratio of the molecular sieve according to claim 1, wherein the molecular sieve sample to be tested is ground into fine powder and then is sieved by a 200-mesh sieve.
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