Method for determining total chromium content of chromium-based propane dehydrogenation catalyst

Abstract

The invention discloses a method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst. The method comprises the following steps: pre-treating a sample; weighing the treated sample, adding sodium hydroxide and borax, roasting for 2 hours, adding water, and heating for dissolving; adding hydrogen peroxide, boiling until white foam disappears and the solution becomes yellow, cooling, adding water, adding sulfuric acid and phosphoric acid, adding water again, and cooling; titrating with an ammonium ferrous sulfate standard solution until the solution becomes yellow green from orange, continuously titrating with N-o-phenylaminobenzoic acid as an indicator until the solution becomes green from amaranth. Compared with a traditional chromium content titration method, precious metal silver nitrate and heavy metal manganese sulfate do not need to be used, resources are saved, the cost is reduced, and the environment is protected. The relative standard deviation (RSD, n = 5) of the determination result of the total chromium content is less than 0.7%, the adding standard recovery rate is 98-102%, the determination result is not interfered by other elements in the catalyst, and the accuracy of the analysis method is high.

Description

Technical Field

[0001] The invention relates to the technical field of determination of catalyst metal content, and in particular to a method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst. Background Art

[0002] Propylene is an important raw material for petrochemical production. Propylene mainly comes from steam cracking and by-products of refineries, as well as Cr 2 O 3 / Al 2 O 3 As a dehydrogenation catalyst to produce propylene. In recent years, with the continuous growth of global demand for propylene, traditional propylene production can no longer meet market demand. Therefore, propane dehydrogenation to propylene (PDH) has attracted much attention as an important way to increase propylene production. The existing propane dehydrogenation processes are catalytic dehydrogenation and oxidative dehydrogenation. The process for industrial application is the catalytic dehydrogenation process. The catalysts used in the catalytic dehydrogenation process mainly include chromium, platinum, vanadium, molybdenum and carbon-based catalysts. The mainstream catalysts are chromium and platinum catalysts. Among the oxide catalysts used for the dehydrogenation of light alkanes, chromium catalysts have higher activity. Chromium catalysts increase with the increase of Cr 2 O 3 As the loading amount increases, the selectivity increases continuously, and the propylene yield increases first and then decreases. 2 0 3 ) reaches its peak value between 18% and 20%. The optimal active component loading of chromium catalyst is w(Cr 2 O 3 )=18%-20%, so the determination of chromium content in the catalyst is of great significance to the control of catalyst production process and the adjustment of propylene production process.

[0003] At present, the traditional method for determining the chromium content in solid materials or alloy materials is the chromium content titration method, which requires the use of precious metal silver nitrate and heavy metal manganese sulfate, resulting in waste of resources, high cost and environmental pollution. In addition, there is currently no reported method for determining the total chromium content in chromium-based catalysts. Therefore, it is necessary to develop a method for determining the total chromium content of chromium-based propane dehydrogenation catalysts. Summary of the invention

[0004] The present invention aims to provide a method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst, in view of the problems that a traditional method for determining the chromium content requires the use of precious metal silver nitrate and heavy metal manganese sulfate, which leads to waste of resources, high cost and environmental pollution.

[0005] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0006] A method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst comprises the following steps:

[0007] Step 1: Sample pretreatment;

[0008] Step 2: Weigh the sample treated in step 1, add sodium hydroxide and borax, roast for 2-4 hours, and add water to heat and dissolve;

[0009] Step 3: Add hydrogen peroxide and cook until the white foam disappears and the solution turns yellow, cool, add water, add sulfuric acid and phosphoric acid, add water again, and cool;

[0010] Step 4: Titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, using N-o-phenylaminobenzoic acid as the indicator. Continue titrating until the solution changes from purple-red to green, which is the end point;

[0011] Step 5: Calculate the chromium content in mass fraction using the following formula:

[0012]

[0013] Where: Vo is the volume of ammonium ferrous sulfate consumed in the blank test, unit: ml;

[0014] V 1 The volume of ammonium ferrous sulfate consumed in sample determination, in ml;

[0015] C is the accurate concentration of ammonium ferrous sulfate standard solution, in mol;

[0016] M is the mass of the sample, in g;

[0017] 0.01733 is the mass of chromium corresponding to 1.00 mL of ammonium ferrous sulfate solution (c = 0.1 mol).

[0018] Furthermore, in step 1, the specific steps of sample pretreatment include: weighing the sample, grinding, sieving, and roasting; the diameter of the sieve is 75 μm, the roasting time is 2-4 hours, and the roasting temperature is 800° C.-900° C.

[0019] Further, in step 2, the mass ratio of sample, sodium hydroxide and borax is 1:16-20:8-10

[0020] Furthermore, in step 2, the calcination temperature is 800°C-900°C, and the heating temperature is 300°C-500°C.

[0021] Furthermore, in step 3, the concentration of hydrogen peroxide is 8%, the concentration of sulfuric acid is 98%, the concentration of phosphoric acid is 85%, and the volume ratio of hydrogen peroxide to sulfuric acid is 1:5-10.

[0022] Furthermore, in step 4, the amount of N-o-phenylaminobenzoic acid indicator added is 8 drops.

[0023] Furthermore, in step 4, the concentration of ammonium ferrous sulfate is 0.1-0.15 mol / L, and the concentration of N-o-phenylaminobenzoic acid solution is 2 g / L.

[0024] The present invention has the following beneficial effects:

[0025] There is no public report on the analysis method of the total chromium content of chromium-based propane dehydrogenation catalyst. The present invention can fill the gap in this field. According to the method of the present invention, compared with the traditional chromium content titration method, there is no need to use precious metal silver nitrate and heavy metal manganese sulfate, which saves resources, reduces costs and protects the environment. The relative standard deviation (RSD, n = 5) of the total chromium content determination result is less than 0.7%, the spike recovery rate is between 98% and 102%, and it is not interfered by other elements in the catalyst, and the analysis method has high accuracy. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example 1

[0029] Standard solution calibration

[0030] Solution preparation: Ammonium ferrous sulfate standard titration solution: 0.13 mol / L, weigh 50.98 g of ammonium ferrous sulfate hexahydrate and dissolve it in 1000 ml of sulfuric acid, mix well.

[0031] Calibration: Weigh 0.18g of potassium dichromate, a working standard reagent dried to a constant amount in an electric oven at 120℃±2℃, dissolve in 25mL of water, add 10mL of sulfur-phosphorus mixed acid solution, add 70mL of water, and titrate with the prepared ammonium ferrous sulfate solution until the orange-yellow color disappears. Add 2 drops of N-phenylanthranilic acid as an indicator, and continue titrating until the solution changes from purple-red to bright green. The concentration of the standard ammonium ferrous sulfate titration solution {c[(NH 4 )2Fe(SO 4 ) 2 ]}, calculated according to the formula: c[(NH 4 )2Fe(SO 4 ) 2 ]=(m×1000) / (V×M)

[0032] m: mass of potassium dichromate, unit: g

[0033] V: Volume of ammonium ferrous sulfate consumed in titration, unit: ml

[0034] M: 1 / 6 relative molecular mass of potassium dichromate, unit: g / mol

[0035] Example 2

[0036] Sulfuric acid dosage experiment

[0037] Select a standard sample with a chromium content of 19.3%. Take 10 g of the sample and grind it thoroughly so that all the samples pass through a 75 μm test sieve. Weigh about 1 g of the collected catalyst fine powder and place it in a 50 ml porcelain crucible at a constant weight of 850°C. Burn it in a muffle furnace at 850°C for 3 hours, take it out and place it in a desiccator to cool to room temperature.

[0038] Weigh 1g borax, 2g sodium hydroxide, 0.2g sample (5 groups, 2 portions each, 10 portions in total), 2g sodium hydroxide, 1g borax, place in a nickel crucible, and roast in a muffle furnace at 800℃ for 2h. Take out the nickel crucible, add 20ml water and heat until all dissolved.

[0039] Wash all the liquid into a conical flask repeatedly, add 2ml hydrogen peroxide, boil until the white foam disappears and the solution turns yellow, add 12ml, 14ml, 16ml, 18ml, 20ml sulfuric acid and 5ml phosphoric acid to the 6 groups of samples respectively until the sample becomes an orange-yellow clear solution, add water to 200ml, and cool to room temperature. Titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, add 8 drops of N-o-phenylaminobenzoic acid indicator, and continue to titrate until the solution changes from purple-red to green, which is the end point. At the same time, perform a blank test according to the above steps without adding samples.

[0040] The effect of sulfuric acid volume fraction on the determination of chromium content was tested. The results are shown in Table 1. Within the test range, the optimal amount of sulfuric acid added is 16-20 ml.

[0041] Table 1 Effect of sulfuric acid dosage on chromium content determination value

[0042]

[0043] Example 3

[0044] Accuracy test of the determination method

[0045] Select three catalysts with different chromium contents, take 10g of each sample and grind it thoroughly so that all the samples pass through a 75μm test sieve. Weigh about 1g of the collected catalyst fine powder and place it in a 50ml porcelain crucible at a constant weight of 850℃, burn it in a muffle furnace at 850℃ for 3h, take it out and put it in a desiccator to cool to room temperature.

[0046] Weigh 1g borax, 2g sodium hydroxide, 0.2g sample (5 portions for each sample), 2g sodium hydroxide, 1g borax, place in a nickel crucible, roast in a muffle furnace at 800℃ for 2h, take out the nickel crucible, add 20ml water and heat until all dissolved. Then wash all the liquid into a conical flask repeatedly, add 2ml hydrogen peroxide, cook until the white foam disappears and the solution is yellow, add 16ml sulfuric acid and 5ml phosphoric acid until the sample is an orange-yellow clear solution, add water to 200ml, and cool to room temperature. Titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, add 8 drops of N-o-phenylaminobenzoic acid indicator, and continue to titrate until the solution changes from purple-red to green, which is the end point. At the same time, perform a blank test according to the above steps without adding samples.

[0047] The sample measurement data is shown in Table 2, with a relative standard deviation of 0.4%-0.7%.

[0048] Table 2 Determination of chromium content of catalyst

[0049]

[0050]

[0051] Example 4

[0052] Weigh 0.6501 of standard potassium dichromate, fully dissolve it in a 200ml beaker, transfer it to a 1L volumetric flask, adjust the volume, and shake it well. Prepare a chromium standard solution, conduct spike recovery tests on the catalyst samples according to the experimental method, select 3 catalysts with different chromium contents, take 10g of samples and grind them thoroughly so that all samples pass through a 75μm test sieve, weigh about 1g of the collected catalyst fine powder and place it in a 50ml porcelain crucible at 850℃ constant weight, burn it in a muffle furnace at 850℃ for 3h, take it out and put it in a desiccator to cool to room temperature.

[0053] Weigh 1g borax, 2g sodium hydroxide, 0.2g sample (2 parts for each sample, 6 parts in total), 2g sodium hydroxide, 1g borax in turn, place in a nickel crucible, and roast in a muffle furnace at 800℃ for 2h. Take out the nickel crucible, add 20ml water and heat until it is completely dissolved. Wash all the liquid into a conical flask repeatedly, add 2ml hydrogen peroxide, boil until the white foam disappears and the solution is yellow, add 10ml chromium standard solution, 16ml sulfuric acid, and 5ml phosphoric acid to the sample until the sample is an orange-yellow clear solution, add water to 200ml, and cool to room temperature. Titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, add 8 drops of N-o-phenylaminobenzoic acid indicator, and continue to titrate until the solution changes from purple-red to green, which is the end point. At the same time, perform a blank test without adding a sample according to the above steps. At the same time, perform a blank test without adding a sample according to the above steps.

[0054] The test data are shown in Table 3, and the recovery rate of spiked samples is 98%-102%.

[0055] Table 3 Results of the spiked recovery test for the determination of chromium content in propane dehydrogenation catalyst by titration with ammonium ferrous sulfate

[0056]

[0057]

[0058] Example 5

[0059] Weigh 0.25 g of zirconium carbonate, 0.19 g of potassium sulfate, and 0.23 g of sodium sulfate respectively, fully dissolve the zirconium carbonate with 10 ml of nitric acid, add water to 100 ml, add potassium sulfate and sodium sulfate to fully dissolve and adjust the volume to 1 L to prepare the interferon solution.

[0060] Select a chromium content of 19.3%, take 10g of the sample and grind it thoroughly so that all the samples pass through a 75μm test sieve, weigh about 1g of the collected catalyst fine powder and place it in a 50ml porcelain crucible at a constant weight of 850℃, burn it in a muffle furnace at 850℃ for 3h, take it out and put it in a desiccator to cool to room temperature.

[0061] Weigh 1g borax, 2g sodium hydroxide, 0.2g sample (4 groups, 2 parts each), 2g sodium hydroxide, 1g borax, place in a nickel crucible, and roast in a muffle furnace at 800℃ for 2h. Take out the nickel crucible, add 20ml water and heat until it is completely dissolved. Wash all the liquids into a conical flask repeatedly, add 2ml hydrogen peroxide, cook until the white foam disappears and the solution is yellow, add 15ml, 17.5ml, 20ml, 22.5ml of the above interferon solution to the 4 groups of samples, add 16ml sulfuric acid, 5ml phosphoric acid until the sample is an orange-yellow clear solution, add water to 200ml, and cool to room temperature. Titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, add 8 drops of N-o-phenylaminobenzoic acid indicator, and continue to titrate until the solution changes from purple-red to green, which is the end point. At the same time, perform a blank test without adding samples according to the above steps.

[0062] Test data table 4, the data show that interfering ions do not affect the titration results.

[0063] Table 4 Interference test results of ammonium ferrous sulfate titration to determine the chromium content of propane dehydrogenation catalyst

[0064]

[0065] Comparative Example 1

[0066] According to the conventional total chromium analysis method published in the patent, nitric acid was added to the pre-treatment during the experiment to achieve the purpose of completely dissolving the sample.

[0067] Select a sample with a chromium content of 19.3%, take 10g of the sample and grind it thoroughly so that all the samples pass through a 75μm test sieve, weigh about 1g of the collected catalyst fine powder and place it in a 50ml porcelain crucible that has been kept constant at 850℃, burn it in a muffle furnace at 850℃ for 3h, take it out and put it in a desiccator to cool to room temperature.

[0068] The reduction method weighs 0.2000g of the burned sample into a conical flask, adds 4ml nitric acid, 12ml sulfuric acid, and 5ml phosphoric acid, and places it on a 300℃ electric heating plate. Cook until the sample dissolves, cool it in the air for 5min, add water to 200ml, and cool it to room temperature. Add 2ml manganese sulfate, 10ml silver nitrate solution, and 40ml ammonium persulfate solution in sequence, boil until slightly red, continue to boil for 5min, cool, add 10ml sodium chloride solution, boil for 3min, cool to room temperature, add water to 200ml, and titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, add 8 drops of N-o-phenylaminobenzoic acid indicator, and continue to titrate the solution from purple-red to green, which is the end point. At the same time, perform a blank test without adding samples according to the above steps. The average content of the sample with a chromium content of 19.3% was 19.35%. It is consistent with the data of the alkali-soluble hydrogen peroxide oxidation method.

[0069] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0070] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst, characterized in that: The steps include: Step 1: Sample pretreatment; Step 2: Weigh the sample treated in step 1, add sodium hydroxide and borax to roast, and add water to heat and dissolve; Step 3: Add hydrogen peroxide and cook until the white foam disappears and the solution turns yellow, cool, add water, add sulfuric acid and phosphoric acid, add water again, and cool; Step 4: Titrate with ammonium ferrous sulfate standard solution until the solution changes from orange-red to yellow-green, using N-o-phenylaminobenzoic acid as the indicator. Continue titrating until the solution changes from purple-red to green, which is the end point; Step 5: Calculate the chromium content in mass fraction using the following formula: Where: Vo is the volume of ammonium ferrous sulfate consumed in the blank test, unit: ml; V1 is the volume of ammonium ferrous sulfate consumed by sample determination, in ml; C is the accurate concentration of ammonium ferrous sulfate standard solution, in mol; M is the mass of the sample, in g; 0.01733 is the mass of chromium corresponding to 1.00 mL of ammonium ferrous sulfate solution (c = 0.1 mol).

2. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In step 1, the sample pretreatment specifically comprises: weighing the sample, grinding it, sieving it, and roasting it; The diameter of the sieve is 75 μm, the calcination time is 2-4 hours, and the calcination temperature is 800° C.-900° C.

3. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In the step 2, the mass ratio of the sample, sodium hydroxide and borax is 1:16-20:8-10.

4. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: The calcination time in step 2 is 2-4 hours.

5. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In the step 2, the calcination temperature is 800°C-900°C, and the heating temperature is 300°C-500°C.

6. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In step 3, the concentration of the hydrogen peroxide is 8%, the concentration of the sulfuric acid is 98%, and the concentration of the phosphoric acid is 85%.

7. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In step 3, the volume ratio of the hydrogen peroxide solution to sulfuric acid is 1:5-10.

8. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: In the step 4, the amount of the N-o-phenylaminobenzoic acid indicator added is 8 drops.

9. The method for determining the total chromium content of a chromium-based propane dehydrogenation catalyst according to claim 1, characterized in that: The concentration of the ammonium ferrous sulfate is 0.1-0.15 mol / L, and the concentration of the N-o-phenylaminobenzoic acid solution is 2 g / L.

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