Qualitative analysis method for determining carbonyl iron in coal-based methyl acetate

Abstract

The invention discloses a qualitative analysis method for determining carbonyl iron in coal-based methyl acetate. The method comprises the following steps: 1, preparing a coal-based methyl acetate sample; 2, under the conditions of normal temperature and normal pressure, taking a certain amount of the coal-based methyl acetate sample, and placing the coal-based methyl acetate sample in a clean high-transmittance glass column; 3, weighing potassium thiocyanate particles, adding the weighed potassium thiocyanate particles into a container filled with coal-based methyl acetate, and externally adding an ultraviolet lamp to emit ultraviolet light to irradiate the high-light-transmittance glass column body with a cover; 4, standing the reaction system, and observing the color change of the solution under an ultraviolet lamp light source; if the solution gradually presents blood red around the potassium thiocyanate particles within a period of time, the carbonyl iron exists in the sample; if the color of the solution does not change obviously, the content of the carbonyl iron in the sample is extremely low or the carbonyl iron does not exist. The method effectively solves the problems of the existing detection method, and has the advantages of simplicity and convenience in operation, high impurity tolerance, capability of revealing the reaction process and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis, and particularly relates to a qualitative analysis method for determining iron carbonyl in coal-based methyl acetate. Background Art

[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 obvious competitive advantages in both production volume and price. Its production process mainly consists of 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 dehydrates to produce dimethyl ether (DME) under the action of a molecular sieve catalyst. The reaction temperature is 250 - 270 °C, and the pressure is 1.2 MPa.

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

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

[0006] CH3OCH3 + CO → CH3COOCH3

[0007] Meanwhile, since the process pipeline uses carbon steel material, the iron in it undergoes a carbonylation reaction with carbon monoxide to produce iron pentacarbonyl. The temperature of this side reaction is 180 - 200 °C (initial - final stage), and the pressure is 5.0 MPa. Reaction equation:

[0008] Fe + 5CO → Fe(CO)5

[0009] Hydrogenation unit: The reaction principle is that methyl acetate reacts with hydrogen to produce ethanol and methanol. The temperature of the hydrogenation reaction is selected to be 230 - 260 °C (initial - final stage), and the pressure is selected to be 5.0 MPa. Main reaction equation:

[0010] CH3COOCH3 + 2H2 → C2H5OH + CH3OH

[0011] However, currently, the methyl acetate products of coal-based ethanol plants often fail to meet the color standard, mainly manifested as the product showing a light yellow color. The discoloration process is as follows: After sampling the methyl acetate product with a colorless glass bottle and irradiating it with light, the product will gradually turn light yellow. After continuing to irradiate for a period of time, a very small amount of uneven light yellow flocs will appear.

[0012] Regarding the problem of the light yellow components in the coal-based methyl acetate product, there is currently no corresponding standard detection method, and it is difficult to determine whether the coal-based methyl acetate product contains iron carbonyl except for the discoloration phenomenon under light illumination. Summary of the Invention

[0013] In order to overcome the defects existing in the above prior art, the object of the present invention is to provide a qualitative analysis method for determining iron carbonyl in coal-based methyl acetate. The qualitative analysis method of the present invention has the characteristics of simple operation, low cost, strong tolerance to impurities, and the ability to reveal the reaction process.

[0014] A qualitative analysis method for determining iron carbonyl in coal-based methyl acetate includes the following steps;

[0015] Step 1: First, prepare a coal-based methyl acetate sample; ensure that the sample is in a stable state and not contaminated by other impurities; thus ensuring the accuracy and reliability of the detection results.

[0016] Step 2: Under normal temperature and pressure conditions, take a certain amount of the above coal-based methyl acetate sample and place it in a clean high-transparency glass column;

[0017] Step 3: Accurately weigh 0.1 - 0.12 g of potassium thiocyanate particles, add them to a clean high-transparency glass column containing 5 - 10 mL of coal-based methyl acetate, and externally apply an ultraviolet lamp to emit ultraviolet light to irradiate the covered high-transparency glass column;

[0018] Step 4: Let the reaction system stand still, and observe the color change of the solution under the ultraviolet light source;

[0019] If the solution gradually shows a blood-red color around the potassium thiocyanate particles within a certain period of time, it indicates that iron carbonyl exists in the sample; if no obvious color change occurs in the solution, it means that the iron carbonyl content in the sample is extremely low or there is no iron carbonyl.

[0020] In the said Step 3, the parameters of the ultraviolet lamp are 10 - 40 W, the wavelength is 350 - 500 nm, and the luminous flux is 300 - 450 lm; the high-transparency glass container is 5 - 10 mL with a lid and is colorless and transparent. The purpose of restricting the parameters (power, wavelength, and luminous flux) of the ultraviolet lamp is to ensure the optimization of the experimental conditions and the accuracy and reliability of the detection results.

[0021] The color development reaction time in the said Step 4 is 0 - 15 min.

[0022] The coal-based methyl acetate has specific impurity contents, that is, the acetic acid content is ≤0.05%, and the water content is ≤0.015%.

[0023] The present invention fully considers the actual presence of impurities such as acetic acid and water in coal-based methyl acetate. Through in-depth research on the reaction process, the present invention also reveals the chemical change process of iron carbonyl in the system, including the decomposition reaction of iron carbonyl:

[0024] The principle is as follows: Under ultraviolet light irradiation, the impurity (acetic acid and water) in coal-based methyl acetate causes the photolysis reaction of iron carbonyl compound Fe(CO)5. In this process, zero-valent iron particles and CO gas are released. The water content (≤0.01%) in the experimental sample system provides a trace water environment, which is conducive to the subsequent oxidation of iron particles. In the weak acidic environment (pH = 4.5 - 5.5) provided by acetic acid (≤0.04%), zero-valent iron undergoes an oxidation reaction, and ultraviolet light accelerates the progress of the oxidation reaction.

[0025] Discoloration reaction process: 2Fe(CO)5 → Fe2(CO)9 + CO;

[0026] Fe2(CO)9 → 2Fe + 9CO;

[0027] Fe + 2CH3COOH → (CH3COO)2Fe + H2;

[0028] 4(CH3COO)2Fe + O2 + 4CH3COOH → 4(CH3COO)3Fe + 2H2O;

[0029] Color reaction: Fe 3+ + 3SCN - → Fe(SCN)3; Finally, it enables the iron ions to undergo a color reaction with thiocyanate ions to form a blood-red complex. These in-depth research results provide a solid theoretical basis for thoroughly understanding the chemical principle of the entire qualitative analysis process, help to further optimize the detection method, significantly improve the accuracy and reliability of detection, and provide a more scientific and efficient technical means for the qualitative analysis of iron carbonyl in coal-based methyl acetate.

[0030] Advantages of the present invention:

[0031] 1. The qualitative analysis method of the present invention is extremely simple to operate. It does not require complex and expensive instrument equipment and professional technical personnel. Only by adding simple reagents and carefully observing the color change can the qualitative detection task of iron carbonyl be efficiently completed. This remarkable feature greatly reduces the detection cost and operation difficulty, making it highly valuable for popularization and application in various laboratories and industrial production sites, and can meet the needs of rapid detection of iron carbonyl in different scenarios.

[0032] 2. This method has strong tolerance to impurities in the sample. Even when the coal-based methyl acetate contains a certain amount of water and acetic acid impurities, it can still accurately detect the carbonyl iron qualitatively. This advantage effectively avoids the errors caused by the cumbersome sample pretreatment, reduces the input of time cost, improves the detection efficiency and practicability, makes the detection process more suitable for the complex sample situation in actual production, and provides strong support for quality control in industrial production.

[0033] 3. This method can not only qualitatively judge the presence or absence of carbonyl iron, but also clearly reveal the chemical change law of carbonyl iron in the system through in-depth exploration of the detailed reaction process, providing valuable information for further study of the properties of coal-based methyl acetate and implementing more effective quality control. Relevant chemical industries can optimize the production process according to these important information, thereby significantly improving product quality, enhancing market competitiveness, and promoting the technological progress and development of the entire industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the technical principle and process route of coal-based methyl acetate.

[0035] Figure 2 It is a schematic diagram of the qualitative test of carbonyl iron in methyl acetate.

[0036] REFERENCE SIGNS:

[0037] 1 - ultraviolet lamp; 2 - ultraviolet light; 3 - potassium thiocyanate particles; 4 - methyl acetate sample; 5 - high-transparency glass column body with a cover. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following will describe the determination method of the present invention in detail through specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0039] As Figure 1 、 Figure 2 shown, a qualitative analysis method for determining carbonyl iron in coal-based methyl acetate includes adding solid potassium thiocyanate particles 3 to the coal-based methyl acetate sample 4 for reaction, promoting a chemical reaction between the two, and judging the presence of carbonyl iron by observing whether a blood-red iron(III) thiocyanate complex is formed;

[0040] The coal-based methyl acetate 4 has specific impurity contents, that is, the acetic acid content is ≤0.05% and the water content is ≤0.015%. This specific impurity background provides a key prerequisite for the implementation and optimization of the entire analysis method.

[0041] The operation steps for adding the potassium thiocyanate solid particles 3 are as follows: Under normal temperature and pressure conditions, take a certain amount of the coal-based methyl acetate sample 4 and place it in a clean reaction vessel. Then, according to the volume of the sample, add potassium thiocyanate in a ratio of 0.1 - 0.12 g of potassium thiocyanate solid particles 3 for every 5 - 10 mL of the coal-based methyl acetate sample 4. The value ranges of 5 - 10 mL and 0.1 - 0.12 g are determined through preliminary experiments to ensure that iron carbonyl can be effectively detected in the coal-based methyl acetate sample with the specific impurity content and to minimize the interference caused by excessive potassium thiocyanate.

[0042] The observation time for judging the presence of iron carbonyl is within the time period from [starting observation time] to [ending observation time] after adding the potassium thiocyanate solid particles (in this experiment, it is 0 - 15 min). If the solution gradually turns blood red within this time period, it is determined that iron carbonyl exists in the sample; if there is no obvious color change in the solution, it is determined that the iron carbonyl content in the sample is extremely low or iron carbonyl does not exist. The [starting observation time] and [ending observation time] (in this experiment, 0 - 15 min) are determined through multiple experiments on coal-based methyl acetate samples with known iron carbonyl contents to ensure the accuracy and reliability of the detection results. And the observation process is carried out under an ultraviolet light source experiment to ensure the accuracy of color judgment within the specified time period.

[0043] Example 1:

[0044] Take 5 mL of the coal-based methyl acetate sample 4 (with a known water content of 80 ppm and an acetic acid content of 339 ppm) in a 10 mL capped high-transparency glass cylinder 5. Accurately weigh 0.1 g of potassium thiocyanate solid particles 3 and add them to the test tube, then let it stand and observe. Directly irradiate the high-transparency glass cylinder 5 containing the coal-based methyl acetate sample with an external ultraviolet lamp (power 20 W (±5% of the rated power), wavelength 365 nm, luminous flux 350 lm). At 10 min, the solution gradually turns blood red, indicating that iron carbonyl exists in this sample.

[0045] Table 1. Analysis data results of methyl acetate

[0046]

[0047]

[0048] Example 2:

[0049] Prepare 6 mL of the methyl acetate sample 4 from coal, repeat the above experimental steps, only adjust the addition amount of potassium thiocyanate particles 3 to 0.12 g, and additionally use an ultraviolet lamp (power 20 W (±5% rated power), wavelength 365 nm, luminous flux 350 lm) to direct irradiate the high-transparency glass cylinder 5 containing the methyl acetate sample from coal. Similarly, it is observed that the solution turns blood red at 8 min, further verifying the reliability and stability of this method. Appropriately adjust and optimize the experimental conditions (such as sample volume, potassium thiocyanate dosage, reaction time, etc.) to ensure the accurate and rapid qualitative detection of iron carbonyl in methyl acetate from coal.

[0050] Table 2. Analysis data results of methyl acetate

[0051]

[0052] The present invention provides a simple, efficient and highly impurity-tolerant qualitative analysis method for iron carbonyl in methyl acetate from coal. Traditional methods have defects such as complex operation, high cost, and strict requirements for sample purity. However, in the present invention, by adding potassium thiocyanate solid particles to the methyl acetate sample from coal and observing whether a blood-red iron thiocyanate complex is formed under ultraviolet light irradiation to judge the presence of iron carbonyl, the selectivity and sensitivity of the reaction between potassium thiocyanate and iron carbonyl and its decomposition products under specific conditions are cleverly utilized. Without complex instruments and professional personnel, accurate detection can be achieved even when the sample contains a certain amount of water and acetic acid impurities. At the same time, through in-depth research, the chemical change process of iron carbonyl in the system is revealed, providing a theoretical basis for optimizing the detection method and related quality control, significantly improving the accuracy and reliability of detection, and meeting the requirements for rapid and simple determination of iron carbonyl in actual production.

[0053] The present invention is applicable to the qualitative analysis of iron carbonyl in methyl acetate from coal with different sources and production processes. And within the specific acetic acid and water impurity content range, without additional complex impurity removal pretreatment steps for the sample, the qualitative detection of iron carbonyl can be directly carried out. If the impurity content in the sample exceeds this range, the experimental conditions need to be optimized according to the predetermined adjustment plan, and the adjustment plan includes but is not limited to increasing the dosage of potassium thiocyanate and extending the observation time to ensure that the effectiveness and accuracy of the detection method are not overly interfered by external interference factors, thereby providing a comprehensive, reliable and highly adaptable technical solution for the qualitative analysis of iron carbonyl in methyl acetate from coal.

Claims

1. A qualitative analysis method for determining carbonyl iron in coal-based methyl acetate, characterized in that: The steps include: Step 1: First, prepare a coal-based methyl acetate sample (4); Step 2: Under normal temperature and pressure conditions, a certain amount of the above-mentioned coal-based methyl acetate sample (4) is placed in a clean high-transmittance glass column (5); Step 3: Weigh potassium thiocyanate particles (3), add them into a clean high-transmittance glass column (5) filled with coal-based methyl acetate (4), and use an external ultraviolet lamp (1) to emit ultraviolet light (2) to irradiate the high-transmittance glass column with a cover (5); Step 4: Let the reaction system stand and observe the color change of the solution under a UV light source; If the solution gradually turns blood red around the potassium thiocyanate particles over a period of time, it indicates that carbonyl iron exists in the sample; if the solution does not show obvious color changes, it means that the carbonyl iron content in the sample is extremely low or does not exist.

2. The qualitative analysis method for determining carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that: In step 3, the parameters of the ultraviolet lamp (1) are 10-40W, wavelength 350-500nm, and luminous flux 300-450lm; the clean high-transmittance glass cylinder (5) is 5-10mL, colorless and transparent with a cover.

3. The qualitative analysis method for determining carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that: The coal-based methyl acetate (4) has a specific impurity content, that is, the acetic acid content is ≤0.05% and the water content is ≤0.015%.

4. The qualitative analysis method for determining carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that: The color development reaction time in step 4 is 0-15 min.

5. The qualitative analysis method for determining carbonyl iron in coal-based methyl acetate according to claim 1, characterized in that: In the step 3, 0.1-0.12 g of potassium thiocyanate particles (3) are weighed and added into a clean high-transmittance glass column (5) filled with 5-10 mL of coal-based methyl acetate (4).

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