Method for detecting calcium carbide in calcium carbide residues

Abstract

This invention, entitled "A Method for Detecting Raw Calcium Carbide in Calcium Carbide Slag," belongs to the field of chemical analysis and testing technology. The technical problem to be solved is that existing technologies suffer from poor accuracy in gas volume measurement, complex equipment, low safety, and inaccurate measurement results due to carbon dioxide interference. The key points of the technical solution are: taking a dry calcium carbide slag sample and determining its initial mass M0; drying the sample to constant weight under an inert atmosphere and determining its dry basis mass M1; mixing the sample with water under an inert atmosphere to react completely with residual calcium carbide; drying the mixture to constant weight under an inert atmosphere and determining its post-reaction mass M2; and calculating the residual calcium carbide content in the sample based on the mass difference between the dry basis mass M1 and the post-reaction mass M2, combined with the stoichiometric relationship of the reaction between calcium carbide and water.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis and testing technology, specifically to a method for detecting raw calcium carbide in calcium carbide slag. Background Technology

[0002] In the calcium carbide-based polyvinyl chloride (PVC) production process, acetylene is a crucial process byproduct. Dry acetylene technology is widely used in China due to its advantages such as low water consumption and minimal slag discharge. As of 2024, China's calcium carbide-based PVC production capacity had reached 21.837 million tons. However, the calcium carbide conversion rate in the dry process cannot reach 100%, and the resulting calcium carbide slag still contains a certain amount of unreacted calcium carbide, commonly known as "raw calcium carbide." Accurately determining the residual calcium carbide content in the calcium carbide slag is of great significance for process optimization, safety management, and resource accounting: on the one hand, it can assess the reaction efficiency of the acetylene generator and guide the adjustment of process parameters; on the other hand, residual calcium carbide slowly releases acetylene gas upon contact with water, posing a risk of combustion and explosion and environmental pollution, and accurate measurement is the basis for risk assessment; furthermore, it can provide accurate compositional data for the resource utilization of calcium carbide slag.

[0003] Currently, the industry lacks a standard testing method for the residual calcium carbide content in dry-process calcium carbide slag. The common practice is to refer to the national standard GB / T 10666 for determining the "gas production" of fresh calcium carbide, calculating the content by measuring the volume of acetylene gas generated from the reaction of calcium carbide with water. However, this method has significant drawbacks when applied to calcium carbide slag with complex compositions and varying moisture content: gas volume measurement is easily affected by temperature, pressure, gas solubility, and the sealing of the equipment, resulting in large errors; it requires specialized and complex equipment such as gas generating bottles, measuring tubes, and leveling bottles, demanding high operational skills; acetylene gas accumulation in sealed devices poses an explosion risk; and other impurities in the calcium carbide slag interfere with gas volume measurement. Another conventional gravimetric method involves adding excess water to the dried calcium carbide slag to ensure complete reaction of unreacted calcium carbide, then drying it again and weighing the difference in mass to eliminate the influence of carbon dioxide absorption to calculate the content. However, this method requires a long drying time, resulting in a lengthy experimental cycle, and the properties of calcium carbide slag vary from region to region. The formation of bound water when minerals in the slag come into contact with water leads to incomplete drying, resulting in large errors in the measurement results.

[0004] Chinese patent document CN101799388A discloses a method and instrument for measuring the gas generation of calcium carbide using a single-calibration gravimetric method. It discloses a technical solution that calculates the gas generation by measuring the mass change of calcium carbide before and after the reaction with water and converting the acetylene gas volume using the ideal gas equation. This solution avoids the influence of external temperature and pressure on gas volume measurement, and features a compact and portable device that is easy to calibrate. However, it still has some drawbacks, such as the need for a dedicated gas purifier, its applicability only to the measurement of the gas generation of fresh calcium carbide rather than the measurement of the residual calcium carbide content in calcium carbide slag, and the lack of an inert gas protection mechanism to eliminate carbon dioxide interference.

[0005] Chinese patent document CN116026724A discloses a device and method for determining the content of raw calcium carbide in calcium carbide slag. It discloses a technical solution that involves adding an acetylene-saturated aqueous solution to calcium carbide slag to allow unreacted calcium carbide to react completely, and then calculating the content of raw calcium carbide by measuring the volume of acetylene gas produced through a gas measuring tube. This solution solves the problem of excessively long drying time by gravimetric method and reduces volume measurement error by using constant temperature and pressure measures. However, it still has some problems, such as its reliance on gas volume measurement making it susceptible to temperature and pressure effects, the complexity of the device requiring specialized equipment such as burettes, gas measuring tubes, long-necked funnels, and constant temperature water baths, the safety hazard of acetylene accumulation in the closed device, and the inability to measure moisture content in conjunction with other methods. Summary of the Invention

[0006] The purpose of this invention is to provide:

[0007] A method for detecting raw calcium carbide in calcium carbide slag, and related technologies, to solve the technical problems of poor gas volume measurement accuracy, complex equipment, low safety, and inaccurate measurement results caused by carbon dioxide interference in the existing technology, or a combination thereof.

[0008] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0009] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0010] Unless specifically defined herein, the use of all commercially available products herein employs standard techniques. For example, it may be carried out using the manufacturer's instructions for use with the kit, or in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0011] In a first aspect, the present invention provides a method for detecting raw calcium carbide in calcium carbide slag, comprising the following steps: S1: Take a dry carbide slag sample and determine its original mass M0; S2: Dry the sample to constant weight under an inert atmosphere and determine the dry weight M1 after drying; S3: Mix the sample with water under an inert atmosphere to react completely with the dry basis mass M1. S4: Dry the mixture after the reaction to constant weight under an inert atmosphere, and determine the mass M2 after the reaction; S5: Based on the mass difference between the dry basis mass M1 and the mass after reaction M2, and combined with the stoichiometric relationship of the reaction between calcium carbide and water, the content of residual calcium carbide in the sample is calculated.

[0012] Furthermore, in S5, the formula for calculating the residual calcium carbide content is: Calcium carbide production rate = [(M2-M1) / 10×64] / M0 Where M0 is the original mass of the sample, M1 is the dry basis mass, M2 is the mass after the reaction, 64 is the molar mass of calcium carbide, and 10 is the net increase in the mass of solid calcium carbide per mole after the reaction.

[0013] Furthermore, the method also includes a step of calculating the moisture content of the sample, wherein the formula for calculating the moisture content is: Moisture content = (M0-M1) / M0.

[0014] Furthermore, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0015] Furthermore, in S3, the reaction time is 20-60 minutes.

[0016] Furthermore, in S3, the amount of water added is greater than or equal to the amount that completely submerges the sample.

[0017] Furthermore, the method also includes a verification step of qualitative analysis of the gases emitted during the reaction, wherein the qualitative analysis is performed using gas chromatography.

[0018] Furthermore, in S1, S2, and S4, an analytical balance with an accuracy of not less than 0.1 mg was used for mass determination.

[0019] Furthermore, in S2 and S4, the drying process employs an oven heating method.

[0020] Embodiments 1 and 2 of this invention at least support the protection scope of claims 1-10.

[0021] The present invention has at least the following beneficial effects: 1. This invention uses the mass difference subtraction method to replace the traditional gas volume method for determining the residual calcium carbide content in dry calcium carbide slag. It directly measures the change in solid mass before and after the reaction using a high-precision analytical balance, avoiding errors caused by factors such as temperature, pressure, gas solubility, and device sealing in gas volume measurement, thus significantly improving measurement accuracy.

[0022] 2. The entire drying and reaction process of this invention is carried out under an inert atmosphere, which effectively eliminates the interference of the increase in mass caused by the absorption of carbon dioxide in the air by calcium hydroxide, ensuring the accuracy of the mass measurement results. At the same time, it can be linked to accurately determine the moisture content of the sample.

[0023] 3. This invention only requires an oven, analytical balance and simple container to complete the measurement. It does not require special and complicated devices such as gas generating bottles, gas measuring tubes, leveling bottles, constant temperature water baths, etc. The equipment cost is low, the operation is simple, and the reaction is carried out in an open system, so the acetylene gas can be released in time, eliminating the risk of explosion caused by gas accumulation in closed devices. Attached Figure Description

[0024] Figure 1 The flowchart illustrates a method for detecting raw calcium carbide in calcium carbide slag provided by this invention.

[0025] Figure 2 This is a flowchart illustrating a method for detecting raw calcium carbide in calcium carbide slag provided in this embodiment. Detailed Implementation

[0026] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0027] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0028] Example 1 like Figure 1The method for detecting raw calcium carbide in calcium carbide slag provided by this invention includes the following steps: S1, taking a dry calcium carbide slag sample and determining its original mass M0; S2, drying the sample to constant weight under an inert atmosphere and determining the dry basis mass M1; S3, mixing the sample with water under an inert atmosphere to react completely with the residual calcium carbide; S4, drying the mixture to constant weight under an inert atmosphere and determining the mass M2 after the reaction; S5, calculating the content of residual calcium carbide in the sample based on the mass difference between the dry basis mass M1 and the mass M2 after the reaction, combined with the stoichiometric relationship of the reaction between calcium carbide and water. The core principle of this method is that calcium carbide reacts with water to produce calcium hydroxide and acetylene gas, i.e., CaC2 + 2H2O → C2H2↑ + Ca(OH)2. Every 64g of calcium carbide reacts to produce 74g of calcium hydroxide, and the solid mass increases by 10g after the acetylene gas escapes. The calcium carbide content can be calculated by measuring the change in solid mass before and after the reaction. The entire process is conducted under an inert atmosphere to prevent calcium hydroxide from absorbing carbon dioxide from the air and increasing its weight, thus ensuring measurement accuracy.

[0029] In one specific embodiment of this example, the formula for calculating the residual calcium carbide content in step S5 is: Calcium carbide production rate = [(M2-M1) / 10×64] / M0, where M0 is the original mass of the sample, M1 is the dry basis mass, M2 is the mass after the reaction, 64 is the molar mass of calcium carbide, and 10 is the net increase in the solid mass of each mole of calcium carbide after the reaction. This formula directly converts the mass difference into calcium carbide content based on stoichiometry.

[0030] In one specific embodiment of this example, the method further includes a step of calculating the moisture content of the sample. The formula for calculating the moisture content is: Moisture content = (M0 - M1) / M0. Since the entire process is carried out under an inert atmosphere, there is no error caused by calcium hydroxide absorbing carbon dioxide during the drying process, thus the measurement result of the moisture content is more accurate.

[0031] In one specific embodiment of this example, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere. Nitrogen is widely available and inexpensive, making it a preferred option.

[0032] In one specific embodiment of this example, the reaction time in step S3 is 20 to 60 minutes. This time range ensures that the residual calcium carbide in the carbide slag reacts completely.

[0033] In one specific embodiment of this example, the reaction time is 30 minutes. Experiments have verified that a reaction time of 30 minutes is sufficient for the calcium carbide to react completely, making it a preferred parameter.

[0034] In one specific embodiment of this example, the amount of water added in step S3 is greater than or equal to the amount that completely submerges the sample. Sufficient water ensures that all residual calcium carbide in the sample can come into contact with the water and react fully.

[0035] In one specific embodiment of this method, the method further includes a verification step of qualitative analysis of the gases emitted during the reaction process, using gas chromatography. Gas chromatography analysis confirms that the emitted gases are primarily acetylene, verifying the singularity of the source of the mass change and supporting the accuracy of the method.

[0036] In one specific embodiment of this example, steps S1, S2, and S4 employ an analytical balance with an accuracy of not less than 0.1 mg for mass determination. A high-precision balance ensures the accuracy of the mass measurement, thereby guaranteeing the reliability of the final calculation results.

[0037] In one specific embodiment of this example, drying in steps S2 and S4 is performed using an oven. An oven is standard laboratory equipment, easy to operate, and, when used with an inert atmosphere, ensures thorough drying of the sample.

[0038] Example 2 like Figure 2 The present embodiment is further illustrated through a practical implementation method.

[0039] The process flow of the method of the present invention is as follows: First, take a dry carbide slag sample and determine the original mass M0. Then, dry it under inert gas protection to obtain the dry basis mass M1. Next, add excess water to submerge the sample for reaction. Stir and dry it under inert gas protection. After the residual acetylene escapes, obtain the mass M2 after reaction. Finally, calculate the moisture content and calcium carbide content according to the moisture content formula and stoichiometric relationship.

[0040] The specific process is as follows: Sample pretreatment and dry weight acquisition: First, take an appropriate amount of dry carbide slag, determine its mass as M0, and dry it to constant weight under an inert gas (such as nitrogen protection) to avoid the reaction of components such as CaO in the sample with CO2 in the air. Then, accurately weigh it and record it as M1; Water reaction process: Place the sample of mass M1 in a nitrogen atmosphere, add enough water to ensure that it is completely submerged and reacts fully, and maintain the reaction for 30 minutes to ensure that the residual calcium carbide reacts completely. Dry weight after reaction: The mixture after reaction was dried to constant weight under the same conditions, and then the sample mass M2 was accurately weighed. Calculation and Result Analysis: Moisture content = M0 - M1.

[0041] Change in acetylene mass = M2 - M1.

[0042] Based on the chemical reaction equation: CaC2 + 2H2O → C2H2↑ + Ca(OH)2, the mass of the solid will change. The mass fraction of calcium carbide in the sample can be calculated using the following formula.

[0043] Calculation formula: For every 64g of calcium carbide that reacts, 74g of calcium hydroxide and 26g of acetylene gas are produced. Since the acetylene gas escapes, the system mass increases by 10g for every 64g of calcium carbide reacting.

[0044] Calcium carbide production rate = ((M2-M1) / 10) 64) / M0.

[0045] Verification of technical effectiveness and / or analysis of technical problem solving The existing technology is not applicable due to certain drawbacks: The calcium carbide gas volume method is a commonly used method in this field, but it has problems such as complex equipment, large errors, and poor safety, and is the primary improvement target of this invention.

[0046] Chemical titration: This method involves measuring the pH value of the solution before and after the reaction, or the concentration of specific ions (such as Ca²⁺). + OH - The concentration change is used to indirectly calculate the results. However, the composition of calcium carbide slag is complex, and other impurity ions cause serious interference, resulting in poor reliability of the results.

[0047] Instrumental analysis methods, such as thermogravimetric analysis (TGA), can be used to determine the CaC2 content through characteristic weight loss peaks. However, the equipment is expensive and difficult to popularize, and the overlapping peaks of multiple components in carbide slag are difficult to resolve, resulting in inaccurate quantification.

[0048] Compared with existing technologies, the method of this invention has the following advantages: high precision, as the use of a high-precision analytical balance for weighing avoids the influence of factors such as temperature and pressure in gas volume measurement; simple equipment, requiring only an oven, analytical balance, and a simple container; safe operation, as acetylene gas escapes in a timely manner without the risk of accumulation and explosion; strong anti-interference ability, as impurities such as calcium oxide in carbide slag react with water without producing gas and thus not affecting the measurement results; and the ability to be linked to the determination of moisture content.

[0049] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for detecting nascent carbide in carbide slag, characterized by: Includes the following steps: S1: Take a dry carbide slag sample and determine its original mass M0; S2: Dry the sample to constant weight under an inert atmosphere and determine the dry weight M1 after drying; S3: Mix the sample with water under an inert atmosphere to react completely with the dry basis mass M1. S4: Dry the mixture after the reaction to constant weight under an inert atmosphere, and determine the mass M2 after the reaction; S5: Based on the mass difference between the dry basis mass M1 and the mass after reaction M2, and combined with the stoichiometric relationship of the reaction between calcium carbide and water, the content of residual calcium carbide in the sample is calculated.

2. A method for detecting calcium carbide in carbide slag according to claim 1, characterized in that: In S5, the formula for calculating the residual calcium carbide content is: Calcium carbide production rate = [(M2-M1) / 10×64] / M0 Where M0 is the original mass of the sample, M1 is the dry basis mass, M2 is the mass after the reaction, 64 is the molar mass of calcium carbide, and 10 is the net increase in the mass of solid calcium carbide per mole after the reaction.

3. A method for detecting calcium carbide produced in situ in carbide slag according to claim 1, characterized in that: The method further includes a step of calculating the moisture content of the sample, wherein the formula for calculating the moisture content is: Moisture content = (M0-M1) / M0.

4. A method for detecting calcium carbide produced in situ in carbide slag according to claim 1, characterized in that: The inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

5. The method for detecting raw calcium carbide in calcium carbide slag according to claim 1, characterized in that: In S3, the reaction time is 20-60 minutes.

6. The method for detecting raw calcium carbide in calcium carbide slag according to claim 5, characterized in that: The reaction time is 30 minutes.

7. The method for detecting raw calcium carbide in calcium carbide slag according to claim 1, characterized in that: In S3, the amount of water added is greater than or equal to the amount that completely submerges the sample.

8. The method for detecting raw calcium carbide in calcium carbide slag according to claim 1, characterized in that: The method further includes a verification step of qualitative analysis of the gases emitted during the reaction, wherein the qualitative analysis is performed using gas chromatography.

9. The method for detecting raw calcium carbide in calcium carbide slag according to claim 1, characterized in that: In S1, S2 and S4, an analytical balance with an accuracy of not less than 0.1 mg was used for mass determination.

10. The method for detecting raw calcium carbide in calcium carbide slag according to claim 1, characterized in that: In S2 and S4, the drying process is carried out using an oven for heating and drying.

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