A method for quantitatively analyzing carbonyl iron in coal-based methyl acetate

Abstract

The application discloses a kind of coal-based methyl acetate carbonyl iron quantitative analysis method, comprising the following steps;Step 1: adding coal-based methyl acetate sample to digestion tank, adding hydrochloric acid and hydrogen peroxide solution into digestion tank to form mixed reagent, heating is carried out, so that coal-based methyl acetate sample is fully digested;After cooling, dilute with water and mix to obtain sample solution for standby;Step 2: add hydroxyl ammonium chloride in each volumetric flask, add acetic acid buffer solution, so that pH=2-4, shake evenly, add o-phenanthroline, generate stable orange red iron (II) phenanthroline complex, then dilute to scale with water, shake evenly, and stand in dark place;Determine the absorbance of the above standard solution;Step 3: calculate the concentration of iron ion in sample;Step 4: according to the stoichiometric relationship between iron ion and pentacarbonyl iron, obtain the content of carbonyl iron.The application has the characteristics of simple operation, low cost, accurate and reliable, fast and efficient, and strong applicability.

Description

Technical Field

[0001] This invention belongs to the field of quantitative analysis technology of carbonyl iron in methyl acetate, specifically relating to a method for quantitative analysis of carbonyl iron in coal-based methyl acetate. Background Technology

[0002] In the industrial production of methyl acetate, coal-based methyl acetate has become one of the important sources of methyl acetate products due to its significant competitive advantages in terms of output and price. Its production process is relatively complex, consisting of several key units, mainly including a dimethyl ether synthesis unit, a carbonylation unit, a hydrogenation unit, and a product separation unit.

[0003] Dimethyl ether synthesis unit: The reaction principle is that gaseous methanol is dehydrated to produce dimethyl ether (DME) under the action of molecular sieve catalyst. The reaction temperature is 250-270℃ and the pressure is 1.2MPa.

[0004] Main reaction equation: 2CH3OH→CH3OCH3+H2O

[0005] Carbonylation unit: The reaction principle involves the carbonylation reaction of carbon monoxide with dimethyl ether under the action of a catalyst to produce methyl acetate. The temperature for the dimethyl ether carbonylation reaction is selected between 190-240℃ (initial-final stage), and the pressure is selected to be 5.0 MPa. Main reaction equation:

[0006] CH3OCH3 + CO → CH3COOCH3

[0007] Meanwhile, because the process piping is made of carbon steel, the iron in it undergoes a carbonylation reaction with carbon monoxide to produce iron pentacarbonyl. This side reaction occurs at temperatures of 180-200℃ (initial-final stages) and pressures of 5.0 MPa. Reaction equation:

[0008] Fe + 5CO → Fe(CO)5

[0009] The presence of iron pentacarbonyl may cause the product to fail to meet color standards, appearing as a pale yellow color, which affects product quality.

[0010] Hydrogenation Unit: The reaction principle is the reaction of methyl acetate with hydrogen gas to produce ethanol and methanol. The hydrogenation reaction temperature is selected between 230-260℃ (initial-final stage), and the pressure is selected at 5.0 MPa. Main reaction equation:

[0011] CH3COOCH3 + 2H2 → C2H5OH + CH3OH

[0012] Coal-based methyl acetate products often have color defects, which manifest as the sample gradually turning from colorless to yellow after exposure to light, and a small amount of pale yellow flocculent matter appearing upon continued exposure to light.

[0013] Currently, there is a lack of standardized quantitative analysis methods for the pale yellow component in products, and it is also difficult to accurately determine the carbonyl iron content. Existing carbonyl iron analysis methods are complex to operate, costly, and have stringent requirements for sample purity, failing to meet the needs of rapid, simple, and accurate determination in actual production. Summary of the Invention

[0014] In order to overcome the defects of the prior art, the present invention aims to provide a quantitative analysis method for carbonyl iron in coal-based methyl acetate. This quantitative analysis method has the characteristics of simple operation, low cost, accuracy and reliability, speed and efficiency, and strong applicability. It can effectively solve the problems existing in the prior art and meet the needs of actual production.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0016] A method for quantitative analysis of carbonyl iron in coal-based methyl acetate, comprising the following steps;

[0017] Step 1: Sample Pretreatment

[0018] Add the coal-based methyl acetate sample to the digestion vessel, add a mixture of dilute hydrochloric acid and hydrogen peroxide solution to the digestion vessel, and heat to fully digest the coal-based methyl acetate sample; after cooling, dilute with water and mix well to obtain a sample solution for later use; at the same time, perform a blank test, the blank sample is the same as the sample, except that no sample is added;

[0019] Step 2: Prepare volumetric flasks for iron ion standard solutions. Add ammonium hydrochloride and acetic acid buffer to each volumetric flask to make the pH 2-4. Shake well and add o-phenanthroline to form a stable orange-red iron(II)phenanthroline complex. Dilute with water to the mark, shake well, and let stand in the dark. Use a UV spectrophotometer to measure the absorbance of the above standard solutions at a certain wavelength.

[0020] Step 3: Take the blank solution and sample solution prepared in Step 1, add hydroxylamine hydrochloride to each, then gradually add acetic acid buffer solution, shake well and measure the pH, then add o-phenanthroline, dilute to volume with water, mix well and set aside, and let stand in the dark; pour the treated sample solution into a cuvette and use a UV spectrophotometer to measure the absorbance A at a certain wavelength; calculate the concentration of iron ions in the sample;

[0021] Step 4: Determination of carbonyl iron content

[0022] The carbonyl iron content was obtained based on the stoichiometric relationship between iron ions and pentacarbonyl iron.

[0023] Step 1 specifically involves:

[0024] Accurately weigh 4-6g of coal-based methyl acetate sample and place it in a digestion vessel. Prepare a mixed reagent by mixing dilute hydrochloric acid (3% concentration) and hydrogen peroxide solution in a volume ratio of (1-6):1. Add this mixed reagent to the digestion vessel, place the digestion vessel on a heating device, control the temperature at 40-70℃, and heat for 1-3 hours to ensure complete digestion of the sample. After cooling, dilute with water to about 35-45ml and mix well for later use.

[0025] Reaction formula: Fe(CO)5 + 5HCl + 3H2O2 → Fe(Ⅱ) + 5CO2 + 5H2O + Cl2.

[0026] Step 2: Establishing the standard curve equation

[0027] Select a series of iron ion standard solutions (0.1-1 mg / L) (e.g., 0.1 mg / L, 0.2 mg / L, 0.5 mg / L, 1 mg / L), and the concentration range of the calibration solution covers the range of iron concentration in the sample. Dilute with water to about 35-45 ml.

[0028] Add 0.5-3 ml of hydroxyammonium hydrochloride and 0.5-3 ml of acetic acid buffer solution to each volumetric flask to make the pH 2-4. Shake well and add 0.5-3 ml of o-phenanthroline to form a stable orange-red iron(II)phenanthroline complex. Dilute with water to the mark, shake well, and let stand in the dark for 2-7 minutes. Use a UV spectrophotometer to measure the absorbance of the above standard solutions at a wavelength of 500-520 nm.

[0029] Reaction formula:

[0030]

[0031] A standard curve was plotted with iron ion concentration on the x-axis and absorbance on the y-axis, yielding a linear regression equation:

[0032] Y = KX + b

[0033] In the formula:

[0034] K is a coefficient; X is absorbance; b is the intercept; Y is the iron ion concentration (mg / L).

[0035] Step 3 specifically involves:

[0036] Take the blank solution and sample solution prepared in step 1, add 0.5-3 ml of hydroxylamine hydrochloride to each, then gradually add 0.5 ml of acetic acid buffer solution each time, shake well and measure the pH until pH = 2-4. Then add 0.5-3 ml of o-phenanthroline, dilute with water to the mark of a 50 ml volumetric flask, mix well and set aside. Let stand in the dark for 2-7 min, pour the treated sample solution into a cuvette and use a UV spectrophotometer to measure the absorbance A at a wavelength of 500-520 nm.

[0037] Substitute into the standard curve equation:

[0038] Y = KX + b (1)

[0039] The concentration of iron ions in the sample was calculated.

[0040] Step 4 specifically involves:

[0041] Based on the stoichiometric relationship between ferric ions and iron pentacarbonyl, the molar ratio of Fe to Fe(CO)5 in Fe(CO)5 is 1:1; the relative atomic mass of Fe is 55.85, and the relative molecular mass of Fe(CO)5 is 195.9. Assuming the measured ferric ion concentration is C mg / L, the content of iron carbonyl (minimum detectable concentration of 0.175 mg / L) in coal-based methyl acetate is:

[0042]

[0043] In the formula:

[0044] C carbonyliron —Carbonyl iron content in methyl acetate samples (unit: mg / kg)

[0045] Original sample weight (g) of m-methyl acetate sample

[0046] C Fe —Iron content (mg / L, calculated by formula (1))

[0047] V—Fixed volume (50 mL)

[0048] The relative atomic mass of iron is 55.85, and the relative molecular mass of iron pentacarbonyl is 195.9.

[0049] The beneficial effects of this invention are:

[0050] The determination method of this invention is relatively simple to operate, low in cost, and does not have high requirements for sample purity, thus meeting the need for simple and accurate determination of carbonyl iron in coal-based methyl acetate in actual production. This helps to promptly identify problems with the carbonyl iron content in coal-based methyl acetate products, providing an effective means for product quality control. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the embodiments.

[0052] Method Principle: Iron carbonyl in the sample is digested at a certain temperature under the action of dilute hydrochloric acid (3%) and hydrogen peroxide solution, followed by the addition of hydroxylamine hydrochloride reagent to generate iron(II). Iron(II) complexes with o-phenanthroline to form an orange-red iron(II)phenanthroline complex stable at pH 2-4, the color intensity of which is directly proportional to the iron(II) content. When the iron content is below 4.9-5.2 mg / L, according to the Lambert-Beer law, the iron(II) concentration and absorbance show a linear relationship. This complex has a maximum absorbance at a wavelength of 500-520 nm. The content of iron carbonyl (minimum detection concentration of 0.175 mg / L) in the coal-based methyl acetate product can be calculated by measuring the absorbance.

[0053] Example 1:

[0054] 1. Sample pretreatment

[0055] Accurately weigh 5.0121 g of coal-based methyl acetate sample and place it in a digestion vessel. Add 6 ml of dilute hydrochloric acid (3%) and 2 ml of hydrogen peroxide solution. Place the digestion vessel in a heating device and heat at 60°C for 2 hours. Dilute with approximately 40 ml of water and mix well. Simultaneously perform a blank test; the blank sample is prepared using the same steps as the sample, except without the sample.

[0056] 2. Establishment of the standard curve

[0057] Prepare iron ion standard solutions of specific concentration ranges (0.1 mg / L, 0.5 mg / L, 1 mg / L, 2 mg / L, 5 mg / L), and dilute with water to approximately 40 ml. Add 2 ml of ammonium hydrochloride and 2 ml of acetic acid buffer to each volumetric flask to adjust the pH to 2-4; shake well and add 1 ml of o-phenanthroline to form a stable orange-red iron(II)phenanthroline complex. Dilute with water to the mark of the volumetric flask (50 ml), shake well, and let stand in the dark for 5 min. Measure the absorbance of the above standard solutions at 510 nm using a UV spectrophotometer. The data are as follows:

[0058] Plotting iron ion concentration on the x-axis and absorbance on the y-axis, a linear regression equation is obtained:

[0059] (correlation coefficient R) 2 =0.997)

[0060] 3. Determination of iron ion content in samples

[0061] Add 2 ml of hydroxylamine hydrochloride to the prepared blank solution and sample solution (from step 1, sample pretreatment), followed by 0.5 ml of acetate buffer solution added gradually, shaking well and measuring the pH until pH = 3-4. Then add 2 ml of o-phenanthroline and dilute to the 50 ml mark with water, mixing well. Let stand in the dark for 5 min. Pour the treated sample solution into a cuvette and measure the absorbance A at 510 nm using a UV spectrophotometer. Substitute into the standard curve equation:

[0062] Wherein: absorbance A is 0.1215;

[0063] The calculated concentration of iron ions is 1.074 mg / L;

[0064] Conversion of carbonyl iron content: C Fe =1.074mg / L; V=50mL; m=5.0121g

[0065] The content of iron pentacarbonyl in coal-based methyl acetate is 37.58 mg / kg.

[0066] 4. Method of adding standard substances:

[0067] Take two samples of coal-based methyl acetate with the same mass (5.0121 g) as in Example 1.

[0068] 0.016 mg of a known concentration of iron pentacarbonyl standard was added to a sample to clarify the theoretical amount to be added to the sample. The sample was pretreated according to the method in Example 1, the absorbance was measured, and the total iron carbonyl content was calculated.

[0069]

[0070] Actual measurements: Absorbance: 0.129; Iron ion concentration: 1.152 mg / L;

[0071] Iron carbonyl: 40.31 mg / kg; Recovery rate: 88.01%.

[0072] The calculation showed a recovery rate of 88.01%. If the recovery rate is between 85% and 115%, it indicates that the method is accurate and reliable.

[0073] Example 2:

[0074] Experimental Procedure: Accurately weigh 5.0121 g of the coal-based methyl acetate sample from Example 1 and place it in a digestion vessel. Add 6 ml of dilute hydrochloric acid (3%) and 2 ml of hydrogen peroxide solution. Place the digestion vessel in a heating device and heat at 80°C for 1.5 h. After cooling, dilute with approximately 40 ml of water and mix well. Simultaneously, perform a blank test; the blank sample is prepared in the same manner as the original sample, except that no sample is added.

[0075] Add 2 ml of hydroxylamine hydrochloride to each of the prepared blank and sample solutions, followed by 0.5 ml of acetate buffer solution added gradually. After mixing well, measure the pH until it reaches 2-4. Then add 2 ml of o-phenanthroline and dilute to the 50 ml mark with water. Mix well and let stand in the dark for 5 minutes.

[0076] The standard curve is established using the same method as in Example 1.

[0077] The absorbance A of the sample was measured to be 0.101; the concentration of iron ions was calculated to be 0.858 mg / L.

[0078] Conversion of carbonyl iron content: C Fe =0.858mg / L; V=50mL; m=5.0121g;

[0079] The content of iron pentacarbonyl in coal-based methyl acetate is 30.02 mg / kg.

[0080] Results analysis: Increasing the digestion temperature to 80℃ and shortening the time to 1.5h may accelerate the reaction rate, but it will bring a series of negative effects, including hydrogen peroxide decomposition and Fe... 3+ Hydrolysis precipitation, methyl acetate volatilization, reduced experimental safety and accuracy, and the need to avoid the decomposition of other iron-containing organic compounds (such as iron porphyrins) at high temperatures are all risks associated with digestion. Therefore, increasing the digestion temperature to 80°C is not recommended; maintaining a preferred temperature of 60°C is more reasonable.

[0081] Example 3:

[0082] Experimental Procedure: Accurately weigh 3.0011 g, 5.0121 g, and 7.0174 g of the coal-based methyl acetate sample from Example 1, and place them in a digestion vessel. Add 6 ml of dilute hydrochloric acid (3%) and 2 ml of hydrogen peroxide solution. Place the digestion vessel in a heating device and heat at 60°C for 2 hours. After cooling, dilute with water to approximately 40 ml and mix well. Simultaneously perform a blank test; the blank sample is prepared in the same manner as the sample, except that no sample is added.

[0083] Add 2 ml of hydroxylamine hydrochloride to both the prepared blank solution and the sample solution, followed by 0.5 ml of acetate buffer solution added gradually. After mixing well, measure the pH until it reaches 3-4. Then add 2 ml of o-phenanthroline and dilute to the 50 ml mark with water. Mix well and let stand in the dark for 5 minutes.

[0084] The standard curve is established using the same method as in Example 1.

[0085] The absorbance A was measured to be 0.098, 0.1215, and 0.101, respectively.

[0086] Results Analysis: The impact of different sample amounts on experimental results is mainly reflected in digestion efficiency, reagent ratio, assay sensitivity, experimental error, and economy. The optimal sample amount is 5.0124 g. However, in actual experiments, the sample amount can be appropriately adjusted according to the carbonyl iron content of the sample and experimental conditions, and combined with the optimization of reagent dosage, to obtain accurate and reliable assay results. Larger sample amounts (e.g., 7.0174 g) are suitable for samples with lower carbonyl iron content to improve test sensitivity; smaller sample amounts (e.g., 3.0011 g) are suitable for samples with higher carbonyl iron content.

[0087] This application adds 3-10 ml (3%) dilute hydrochloric acid (3%) and 1-3 ml hydrogen peroxide solution. The appropriate ratio of hydrochloric acid and hydrogen peroxide solution serves two purposes. One is the strong oxidizing property of hydrogen peroxide solution: under acidic conditions, hydrogen peroxide solution can rapidly oxidize Fe in carbonyl iron (such as Fe(CO)5). 0 Oxidized to Fe 3+ This process generates solid oxides such as Fe2O3. The reaction rate increases at 60℃, while simultaneously preventing the decomposition and degradation of H2O2 due to high temperatures. Another effect is the acidolysis and complexation of hydrochloric acid: hydrochloric acid provides H... + Promotes the decomposition of carbonyl iron, Cl - with Fe 3+ [FeCl4] is formed. - Iso-complexes enhance solubility and prevent Fe 3+ Hydrolysis precipitation and an acidic environment can also inhibit the ineffective decomposition of hydrogen peroxide solution and improve oxidation efficiency.

[0088] The digestion reaction conditions require the addition of dilute hydrochloric acid (3%) and hydrogen peroxide solution in a volume ratio of 1-6:1. The 3:1 ratio is considered reasonable.

[0089] Ensure sufficient Cl - Complexing ability, avoiding Fe 3+ Premature precipitation; provide sufficient oxidant concentration to ensure complete conversion of carbonyl iron; reduce the burden of subsequent treatment caused by excessive H2O2.

[0090] The digestion reaction conditions, i.e., precise temperature control, are crucial at 50-70℃. 60℃ is preferred as it accelerates reaction kinetics (reducing reaction time by more than 50% compared to room temperature) while avoiding the following problems caused by high temperatures:

[0091] Loss due to methyl acetate volatilization; interference from the reaction caused by the violent decomposition of hydrogen peroxide solution producing bubbles; Fe 3+ Hydrolysis produces colloids that affect subsequent separation.

[0092] Digestion is achieved by adding dilute hydrochloric acid (3%) and hydrogen peroxide solution. This approach offers both safety and economic benefits: the main reaction products are Fe2O3 and CO2, with no NO production. X The side reactions are controllable as toxic gases are generated (compared to other acid methods); dilute hydrochloric acid and hydrogen peroxide solution are both inexpensive and readily available reagents, so the cost is controllable.

Claims

1. A method for quantitative analysis of carbonyl iron in coal-based methyl acetate, characterized in that, Includes the following steps; Step 1: Add the coal-based methyl acetate sample to the digestion vessel. Mix dilute hydrochloric acid and hydrogen peroxide solution in a certain proportion and add them to the digestion vessel. Heat the mixture to ensure that the coal-based methyl acetate sample is fully digested. After cooling, dilute the mixture with water and mix well to obtain a sample solution for later use. At the same time, perform a blank test. The blank sample is prepared in the same way as the sample, except that no sample is added. Step 2: Prepare volumetric flasks for iron ion standard solutions. Add ammonium hydrochloride and acetic acid buffer to each volumetric flask to make the pH 2-4. Shake well and add o-phenanthroline to form a stable orange-red iron(II)phenanthroline complex. Dilute with water to the mark, shake well, and let stand in the dark. Use a UV spectrophotometer to measure the absorbance of the above standard solutions at a certain wavelength. Step 3: Take the blank solution and sample solution prepared in Step 1, add hydroxylamine hydrochloride to each, then gradually add acetic acid buffer solution, shake well and measure pH, then add o-phenanthroline, dilute to volume with water, mix well and set aside, and let stand in the dark; pour the treated sample solution into a cuvette and use a UV spectrophotometer to measure absorbance A at a certain wavelength. The concentration of iron ions in the sample was calculated. Step 4: Obtain the carbonyl iron content based on the stoichiometric relationship between iron ions and pentacarbonyl iron.

2. The method for quantitative analysis of carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that, Step 1 specifically involves: Accurately weigh 4-6g of coal-based methyl acetate sample and place it in a digestion vessel; prepare a mixed reagent by mixing 3% dilute hydrochloric acid and hydrogen peroxide solution in a volume ratio of (1-6):1, add the mixed reagent to the digestion vessel, place the digestion vessel on a heating device, control the temperature at 40-70 ℃, heat for 1-3 h, cool, dilute with water to 35-45 ml, mix well and set aside; Reaction formula: Fe(CO)5 + 5HCl + 3H2O2 → Fe(II) + 5CO2 + 5H2O + Cl2.

3. The method for quantitative analysis of carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that, Step 2 is as follows: Select a series of iron ion standard solutions containing 0.1-1 mg / L iron standard solution. The concentration range of the calibration solution covers the range of iron concentration in the sample. Dilute with water to 35-45 ml. Add 0.5-3 ml of hydroxyammonium hydrochloride and 0.5-3 ml of acetic acid buffer solution to each volumetric flask to make the pH 2-4. Shake well and add 0.5-3 ml of o-phenanthroline to form a stable orange-red iron(II)phenanthroline complex. Dilute with water to the mark, shake well, and let stand in the dark for 5-10 min. Use a UV spectrophotometer to measure the absorbance of the above standard solutions at a wavelength of 500-520 nm.

4. The method for quantitative analysis of carbonyl iron in coal-based methyl acetate according to claim 3, characterized in that, Reaction formula: A standard curve was plotted with iron ion concentration on the x-axis and absorbance on the y-axis, yielding a linear regression equation: In the formula: K For coefficients; X Absorbance; b The intercept; This represents the iron ion concentration (mg / L).

5. The method for quantitative analysis of carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that, Step 3 specifically involves: Take the blank solution and sample solution prepared in step 1, add 0.5-3 ml of hydroxylamine hydrochloride to each, then gradually add 0.5 ml of acetic acid buffer solution each time, shake well, and measure the pH until pH = 2-4. Then add 0.5-3 ml of o-phenanthroline, and dilute with water to the mark of a 50 ml volumetric flask. Mix well and let stand in the dark for 5-10 min. Pour the treated sample solution into a cuvette and measure the absorbance A at a wavelength of 500-520 nm using a UV spectrophotometer. Substitute the absorbance into the standard curve equation: （1） The concentration of iron ions in the sample was calculated.

6. The method for quantitative analysis of carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that, Step 4 specifically involves: Based on the stoichiometric relationship between iron ions and iron pentacarbonyl, the molar ratio of Fe to Fe(CO)5 in Fe(CO)5 is 1:1; the relative atomic mass of Fe is 55.85, and the relative molecular mass of Fe(CO)5 is 195.

9. Assuming the measured iron ion concentration is C mg / L, the iron carbonyl content in coal-based methyl acetate is: （2） In the formula: —The carbonyl iron content in the methyl acetate sample; —The original weight of the methyl acetate sample; —Iron content; —Irreplaceable volume; The relative atomic mass of iron is 55.85, and the relative molecular mass of iron pentacarbonyl is 195.9.

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