Method and device for detecting content of organic gas in hydrogen chloride gas on line

Abstract

The invention discloses a method and a device for detecting the content of organic gas in hydrogen chloride gas on line. The device comprises a U-shaped pipe main body, two ends of the U-shaped pipe main body are respectively provided with a stop valve 2 and a stop valve 3 for air exchange and a pressure gauge for monitoring pressure, a sample introduction section of the U-shaped pipe main body is also provided with a stop valve 1 for sample introduction, and the middle part of the U-shaped pipe main body is provided with a stop valve 4 for filling a liquid phase. According to the method based on the device, rapid reading of the volume of organic gas in HCl gas is achieved through the synergistic effect of the gas thermodynamic principle and the U-shaped tube principle, alkali liquor is adopted as an HCl adsorbent, the continuous operation capacity of the device can be improved through an acid-base chemical reaction, and the device is suitable for large-scale industrial production. The method has the advantages of simplicity in operation, low use cost, high precision, high detection speed and the like, and online detection of the purity of the HCl gas can be realized.

Description

Technical Field

[0001] The present invention relates to a method for detecting hydrogen chloride gas, specifically to a method and device for on-line detecting the content of organic gases in hydrogen chloride gas, belonging to the field of on-line monitoring of acidic gases. Background Art

[0002] Hydrogen chloride (HCl) is a common process by-product gas in the chemical industry. Since it often contains flammable, explosive organic raw materials or organic product gases accompanying the reaction process, there are great safety hazards in the separation or detection process. For example, in the process of preparing allyl chloride by the high-temperature method of propylene and chlorine, the reaction tail gas is a mixture of HCl and propylene, and the content range of propylene is 60 - 85%. Since propylene is a flammable and explosive substance, the content of propylene needs to be monitored in real time during the separation of HCl and propylene to prevent potential safety hazards. At the same time, in the process of preparing chlorine by the high-temperature reaction of HCl and oxygen, the mixture of residual propylene and oxygen in HCl also has an explosion risk. It is very necessary to monitor the residual amount of propylene at any time to ensure the safe operation of the production device. However, in this process, the number of sample collections is large, the processing volume is large, and the labor intensity is high. Although gas chromatography is an effective detection device for analyzing gaseous compounds, HCl in the mixed gas is highly corrosive, seriously damages the equipment, and the detection results have relatively large deviations. Summary of the Invention

[0003] Aiming at the problems existing in the prior art, the first object of the present invention is to provide a method for on-line detecting the content of organic gases in hydrogen chloride gas. Based on the synergistic effect of gas thermodynamics principle and U-tube principle, this method realizes the rapid reading of the volume of organic gases in HCl gas. Using alkali solution as the HCl adsorbent, through acid-base chemical reaction, the continuous operation ability of the device can be improved, and the local reversible reaction can be avoided when the HCl concentration is too high, resulting in the overflow of HCl gas, thus affecting the detection accuracy. This method has the advantages of simple operation, low use cost, high precision and fast detection speed, and can realize the on-line detection of HCl tail gas.

[0004] The second object of the present invention is to provide a device for on-line detecting the content of organic gases in hydrogen chloride gas. Adopting a symmetrical U-tube connection structure, the detection process is carried out under a protective atmosphere throughout. The detection is realized by controlling the opening and closing of the valve. While reducing the operation intensity, this device reduces the transfer times of the samples to be tested, eliminates the safety hazards of gas leakage or air mixing. After testing, the highest test accuracy of this device can reach 10 ppm, and the data error is ≤ 0.1%. This device has excellent safety, sensitivity, accuracy and timeliness, and can meet the requirements of long-term on-line use.

[0005] To achieve the above technical objectives, the first objective of the present invention is to provide a device for on-line detecting the content of organic gases in hydrogen chloride gas, including a U-shaped tube main body; cut-off valves 2(2) and 3(3) for air exchange and a pressure gauge for monitoring pressure are respectively installed at both ends of the U-shaped tube main body, and a cut-off valve 1(1) for sample introduction is also installed at the sample introduction section of the U-shaped tube main body. A cut-off valve 4(4) for filling the liquid phase is provided in the middle of the U-shaped tube main body.

[0006] As a preferred solution, volume scales that can be read are also engraved on the tube wall at the sample introduction end of the U-shaped tube main body.

[0007] The present invention also provides a method for on-line detecting the content of organic gases in hydrogen chloride gas, which is implemented by the above device and includes the following steps:

[0008] 1) After purging and replacing the air in the device with a protective gas, an alkali solution is filled, and the volume scale is read and recorded as V1;

[0009] 2) The hydrogen chloride tail gas to be measured is introduced into the device. When the liquid level in the U-shaped tube main body is stable and unchanged, the volume scale is read and recorded as V2;

[0010] 3) Calculate the volume percentage of the organic gas in the hydrogen chloride gas to be measured according to V1 and V2, and that's it.

[0011] As a preferred solution, the protective gas atmosphere is a mixture of one or more of high-purity nitrogen, argon or helium.

[0012] As a preferred solution, the alkali solution is at least one of hydroxide solutions of alkali metals, ammonia water and strong base weak acid salt solutions.

[0013] As a preferred solution, the filling amount of the alkali solution is 30-75% of the volume of the U-shaped tube main body of the device.

[0014] As a preferred solution, the concentration of the alkali solution is 10-60%.

[0015] As a preferred solution, the organic gas in the hydrogen chloride tail gas is a mixture of one or more of acetylene, C1-C5 alkanes, C1-C4 alkenes, and C1-C3 chloroalkanes.

[0016] As a preferred solution, steps 2) and 3) can be repeatedly implemented until the concentration of the alkali solution ≤ 1% and then stop.

[0017] As a preferred solution, when steps 2) and 3) are repeatedly implemented, the interval time for each repetition ≥ 0.5 h, and the reading of V1 is the same as that in the first implementation.

[0018] As a preferred solution, the flow rate of the hydrogen chloride gas introduction device is 0.1 - 10 L / min, which is controlled by flow regulators such as needle valves, rotameters, mass flow meters, and turbine flow meters.

[0019] As a preferred solution, the read volume scale V2 has the same temperature as the temperature when reading the volume scale V1.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] 1) The method provided by the present invention is based on the synergistic effect of gas thermodynamics principles and U-tube principles, realizing the rapid reading of the volume of organic gases in HCl gas. Using alkali solution as the HCl adsorbent, the continuous operation ability of the device can be improved through acid-base chemical reactions, avoiding the occurrence of reversible reactions locally when the HCl concentration is too high, resulting in the overflow of HCl gas and thus affecting the detection accuracy; this method has the advantages of simple operation, high precision, and fast detection speed, and can realize the on-line detection of HCl gas.

[0022] 2) The device provided by the present invention adopts a symmetrical U-tube connection structure, and the detection process is carried out under a protective atmosphere throughout. The detection is realized by controlling the opening and closing of the valves. While reducing the operation intensity, this device reduces the transfer times of the samples to be measured, eliminates the safety hazards of gas leakage or air mixing. After testing, the highest test accuracy of this device can reach 10 ppm, and the data error is ≤0.1%. This device has excellent safety, accuracy, and timeliness, and can meet the requirements of long-term on-line use. Description of the Drawings

[0023] Figure 1 Shows the state of the device provided by the present invention before introducing the HCl mixed gas;

[0024] Figure 2 Shows the state of the device provided by the present invention after introducing the HCl mixed gas. Detailed Embodiments

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] The present invention provides a device for on-line detecting the content of organic gases in hydrogen chloride tail gas, and its structure is as shown in Figure 1 and Figure 2As shown in the figure, it includes a U-shaped tube body; stop valves 2(2) and 3(3) for air exchange and a pressure gauge for monitoring pressure are respectively installed at both ends of the U-shaped tube body. A stop valve 1(1) for sample injection is also installed at the sample injection section of the U-shaped tube body, and a stop valve 4(4) for filling liquid phase is provided in the middle of the U-shaped tube body.

[0027] Connect the above device to the HCl tail gas outlet and install and fix it in a horizontal state. As Figure 1 shown, before use, close valve 1, open valve 2 and valve 3, and purge with high-purity nitrogen to displace the air in the tube to prevent air from entering. Fill the alkali solution to the scale of the U-shaped tube shown. Keep the whole set of devices horizontally fixed. At this time, the pressures on both sides of the U-shaped tube are both 1 atmospheric pressure, and the liquid levels at both ends of the U-shaped tube are level under the balanced pressure state. The concentration of the alkali solution should not be too high or too low, and a concentration of 20-50% is more appropriate. Too low a concentration will lead to frequent replacement of the alkali solution and a large workload, while too high a concentration is likely to cause salting-out solids and block the pipeline. After the alkali solution is filled, close valve 2 and valve 3. The gas volume on the left side of the U-shaped tube is V1, and the space above the liquid level in the U-shaped tube is nitrogen, without any flammable or explosive risks, which is safe and reliable. Pressure gauges are installed on the left and right sides of the U-shaped tube to monitor the pressure changes during the gas treatment process, especially the possible leakage and excessive gas introduction problems during the use of the intake valve 1, to monitor the pressure fluctuations during the gas treatment process and prevent possible safety hazards.

[0028] As Figure 2As shown in the figure, when in use, open valve 1 and introduce a certain amount of HCl mixed gas. The gas can be introduced in small amounts multiple times. After inflation is completed, close valve 1 and let it stand for about 30 minutes. As HCl reacts with sodium hydroxide in the solution to form sodium chloride, the alkaline solution has a phenomenon of heat release and temperature rise. When the gas treatment volume is large, appropriate cooling measures can be adopted. As the hydrogen chloride gas is completely neutralized, the remaining gas in the mixed gas in the left tube will break the pressure balance on both sides of the U-shaped tube. The liquid level on the left side drops and the right side rises. After equilibrium, the gas volume on the left side is V2. At this time, valve 2 on the left side of the U-shaped tube is connected to the gas bag. Open valve 2, and the liquid levels on both sides are flush again. At this time, the gas pressures on both sides of the U-shaped tube return to 1 atmospheric pressure again and maintain an equilibrium state. After the gas on the left side of the U-shaped tube enters the gas bag, close valve 2 and remove the gas bag. At this time, the gas volume on the left side of the U-shaped tube returns to V1. Under normal temperature and 1 atmospheric pressure conditions, the state of real gas is close to that of ideal gas, and calculations can be carried out according to the ideal gas state equation (PV=nRT). Therefore, according to the gas volume in the gas bag, the volume of organic gas in the HCl mixed gas can be known, and the gas components and purity in the gas bag can also be analyzed by a gas chromatograph according to the usage requirements. The whole set of devices is simple to operate, safe and reliable, and the gas on the left side of the U-shaped tube is always isolated from the air, without any safety hazards such as explosion, fire, self-reaction, etc., and can meet the requirements of on-line continuous monitoring of the equipment, especially suitable for frequent use scenarios when the content of organic gas is low.

[0029] After the above operations are completed, the next operation can be carried out. The steps are the same as the previous process. As sodium hydroxide is consumed, when the mass concentration is lower than 5%, the sodium hydroxide solution can be replaced. Open valve 2, valve 3 and valve 4 to discharge the used solution, and add a newly prepared 50% sodium hydroxide solution after rinsing. The equipment needs to be regularly inspected for the sealing conditions of joints such as stop valves and pressure gauges to prevent air leakage, corrosion, etc. from affecting the operation of the equipment.

[0030] In order to more intuitively reflect the advantages of the device and method provided by the present invention, in the following examples, the HCl tail gas is all a binary mixed gas of HCl and propylene.

[0031] Example 1

[0032] Using 50% sodium hydroxide solution as the alkaline solution, 1 kg of alkaline solution is filled in the U-shaped tube. Pass 40 L of HCl mixed gas (HCl:propylene = 93:7, volume ratio) through the rotameter at a flow rate of 100 ml / min. After 30 minutes, the volume on the left side of the U-shaped tube becomes larger and the liquid level on the right side rises. The gas volume received by the gas bag is 2.798 L, which is almost the same as the actual content of propylene in the HCl mixed gas (2.8 L), and the relative error ≤ 0.07%, which verifies the accuracy and reliability of the safety device.

[0033] After the above process is repeated 60 times, the concentration of the lye is 5%. After replacing the lye, it can be used continuously, which is safe and simple.

[0034] Example 2

[0035] Using a 50% sodium hydroxide solution as the lye, 10 kg of lye is filled in the U-shaped tube. Through a rotameter, 100 L of HCl mixed gas is introduced in small amounts and multiple times at a flow rate of 1.0 L / min, with a time interval of 30 minutes each time. In the HCl mixed gas, HCl:propylene = 99.9:0.1, that is, the concentration of propylene is 1000 ppm. The volume of propylene collected in the gas bag is 0.10 L, which is almost the same as the actual content of propylene in the HCl mixed gas, and the relative error ≤ 0.01%. This result is highly credible. The device can meet the requirement of continuous use for 25 times.

[0036] Example 3

[0037] Using a 50% sodium hydroxide solution as the lye, 10 kg of lye is filled in the U-shaped tube. Through a rotameter, 500 L of HCl mixed gas is introduced in small amounts and multiple times at a flow rate of 5.0 L / min, with a time interval of 30 minutes each time. In the HCl mixed gas, HCl:propylene = 99.99:0.01, that is, the concentration of propylene is 100 ppm. The volume of propylene collected in the gas bag is 0.05 L, which is almost the same as the actual content of propylene in the HCl mixed gas, and the relative error ≤ 0.1%. This result is highly credible. The device can meet the requirement of continuous use for 5 times.

Claims

1. An apparatus for on-line detecting the content of organic gases in hydrogen chloride gas, characterized in that: It includes a U-shaped tube body; cut-off valves 2 and 3 for air exchange and a pressure gauge for monitoring pressure are respectively installed at both ends of the U-shaped tube body, and a cut-off valve 1 for sample injection is also installed at the sample injection section of the U-shaped tube body. A cut-off valve 4 for filling the liquid phase is provided in the middle of the U-shaped tube body.

2. The device for on-line detecting the content of organic gases in hydrogen chloride gas according to claim 1, wherein: Volume scales that can be read are also engraved on the tube wall at the sample injection end of the U-shaped tube body.

3. A method for on-line detecting the content of organic gases in hydrogen chloride gas, characterized in that: Implemented by the device according to claim 1 or 2, it includes the following steps: 1) After purging and replacing the air in the device with a protective gas, load the lye, and read the volume scale and record it as V1; 2) Pass the hydrogen chloride gas to be measured into the device. When the liquid level in the U-shaped tube body is stable, read the volume scale and record it as V2; 3) Calculate the volume percentage of the organic gas in the hydrogen chloride gas to be measured based on V1 and V2, and that's it.

4. The method for on-line detecting the content of organic gases in hydrogen chloride gas according to claim 3, characterized in that: The protective atmosphere is a mixture of one or more of high-purity nitrogen, argon, or helium; the lye is at least one of a hydroxide solution of an alkali metal, ammonia water, and a solution of a strong base and weak acid salt.

5. The method for on-line detecting the content of organic gas in hydrogen chloride gas according to claim 4, wherein: The filling amount of the lye is 30 - 75% of the volume of the U-shaped tube body of the device; the concentration of the lye is 10 - 60%.

6. The method for on-line detecting the content of organic gas in hydrogen chloride gas according to claim 4, characterized in that: The organic gas in the hydrogen chloride tail gas is a mixture of one or more of acetylene, alkanes with C1 - C5, alkenes with C1 - C4, and chloroalkanes with C1 - C3.

7. The method for on-line detecting the content of organic gas in hydrogen chloride gas according to claim 4, characterized in that: Steps 2) and 3) can be repeatedly implemented until the concentration of the lye ≤ 1% and then stop.

8. The method for on-line detecting the content of organic gases in hydrogen chloride gas according to claim 7, characterized in that: When steps 2) and 3) are repeatedly implemented, the interval time for each repetition ≥ 0.5 h, and the reading of V1 is the same as that in the first implementation.

9. The method for on-line detecting the content of organic gases in hydrogen chloride gas according to claim 4, characterized in that: The flow rate of the hydrogen chloride tail gas passing into the device is 0.1 - 10 L / min, which is controlled by a gas flow regulating device such as a needle valve, a rotameter, a mass flowmeter, or a turbine flowmeter.

10. A method for on-line detecting the content of organic gases in hydrogen chloride gas according to claim 4, characterized in that: When reading the volume scale V2, its temperature is the same as the temperature when reading the volume scale V1.

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