Safety: Proper operation of high-pressure reactors

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This post was last edited by yinkuilin6868 on 2016-6-15 10:20. Safety: Proper operation of high-pressure reactors. High-pressure reactors represent a typical innovation in reaction equipment that makes use of magnetic drive systems; they effectively solve the problem of shaft seal leakage that could not be addressed by traditional packing seals or mechanical seals. This device has no leaks or contamination, and it is the most ideal setup for carrying out chemical reactions under high temperature and pressure in China. Its advantages are even more evident when used for chemical reactions involving flammable, explosive, or toxic substances. While using it, we must also not overlook the safety issues it presents; please familiarize yourselves with the knowledge regarding the safe use of autoclaves. Precautions before use – Sealing performance: The autoclave is a precision device that utilizes conical surface contact through sealing rings to achieve sealing; this is accomplished by tightening the main bolts to press the rings together. Therefore, special care must be taken to protect the sealing cone surface, avoiding any collisions that could cause damage to it. When installing the lid, first place the reactor body in position, then carefully attach the lid to the body at its designated location. When tightening the main bolts, it is necessary to do so diagonally and symmetrically, in several steps, applying even force; the lid must not tilt to either side in order to achieve a good seal. The specified tightening torque must not be exceeded, to prevent the sealing surfaces from being damaged or wearing out more rapidly. All threaded fasteners must be coated with oil or oil mixed with graphite during assembly. If the sealing surface is damaged, it must be remanufactured and repaired to restore good sealing performance. Sealing operation: The air inlet and exhaust valve are sealed using needle valves. To close them, it is sufficient to gently rotate the valve needle to press the sealing surfaces together, which ensures a good seal; excessive force should be avoided to prevent damage to the sealing surfaces. Heating and pressure testing: Before using the high-pressure reactor, a heating and pressure sealing test must be conducted. Air or nitrogen can be used as the testing medium, but inert gases are preferred; the use of oxygen or other flammable and explosive gases is strictly prohibited. Raising the temperature and pressure must be done slowly. The heating rate should not exceed 80 degrees per hour. During pressure testing, a connecting pipe is used to link the air inlet valve of the autoclave to the compressor (or high-pressure pump). The pressure increase must be carried out in stages, with intervals of 20% increase in working pressure; stay at each stage for 5 minutes, and when the test pressure is reached, stay for 30 minutes to check the sealing condition. The test pressure is 100-105% of the operating pressure. Upon detecting a leak, reduce the pressure first, then tighten the nuts and connectors appropriately; it is strictly prohibited to tighten them under high pressure. During the cooling process, rapid heating or cooling is prohibited during the reaction to avoid excessive temperature stress that could cause cracks in the reactor vessel. After the reaction is complete, cooling is carried out first; this can be done by using water for cooling (in the case of exothermic reactions) or by air cooling. Afterwards, the high-pressure gas inside the tank is released to reduce the pressure to normal levels, and then the bolts are loosened and removed in a symmetrical manner. Special care should be taken to protect the sealing surface during the opening process; lift the kettle lid evenly to prevent the sealing ring between the lid and the kettle body from being damaged due to impact. Post-processing: After each operation, the residues on the reactor body and cover should be removed. All sealing surfaces of the high-pressure reactor must be cleaned regularly and kept dry; it is not allowed to use hard objects or soft materials with a rough surface for cleaning. Safety Operating Procedures: Preparatory work before use. Before adding materials, it is necessary to check whether the reactor is contaminated; the inner walls of the high-pressure reactor, the stirrer, the cooling coils, the temperature probe sleeves, and the joints should be cleaned with ethanol, followed by rinsing with distilled water. After rinsing, these areas should be wiped clean with cotton or silk cloth dipped in ethanol to prevent cross-contamination of the materials. Before use, it is necessary to check whether all valves are unobstructed, especially the openings of the pressure gauge and the explosion-proof membrane. For the intake duct, special attention must also be paid to check for any blockages. If there is contamination or blockage, the duct and the intake branch pipes should be removed from the kettle lid, cleaned thoroughly, and then reinstalled. Seal integrity check: After cleaning and once the reactor vessel is dry, a seal integrity check should be carried out first. Place the kettle body in the heating furnace, aligning the protruding parts with the grooves, then gently rotate the kettle body. Once it is in place, slowly and steadily close the kettle body and the lid together. Special care must be taken to protect the sealing surfaces, to prevent the sealing rings on the lid and the kettle body from being damaged due to collision. After covering it, check whether the upper and lower connections of the reactor are aligned. Gently turn the lid to ensure that it is level and that the sealing ring makes good contact. After adding the gasket, start tightening the screws. Precautions for tightening bolts: When tightening bolts, make sure they are inserted in the correct positions. First tighten them by hand, and then use a torque wrench to apply force in a cross-shaped pattern for symmetry, in order to avoid uneven stress distribution. Do not tighten the bolts all at once; tighten the diagonal bolts in several steps, applying force gradually to tighten them symmetrically. Airtightness check: When checking for airtightness, first verify that all valves (solid material feeding port, reactor lid exhaust valve, air inlet valve, etc.) are tightened properly (just enough tension is sufficient; do not use excessive force). After setting the stirring switch and speed/heat control switches on the controller to zero, turn on the power supply for the control box as well as its display switch. Pressure testing procedure 1: Connect nitrogen – Connect the nitrogen cylinder to the air inlet of the autoclave using a tube, and tighten the relevant screws. Open the main valve and the pressure regulator valve of the nitrogen cylinder; first adjust the pressure at the regulator valve to the level required for the experiment, then open the inlet valve of the reaction vessel to allow gas to flow into it slowly. Once the pressure displayed in the reaction vessel matches the set pressure on the nitrogen cylinder and remains constant, close the inlet valve of the reaction vessel and the outlet valve of the nitrogen cylinder in sequence. Record the pressure value shown in the reaction vessel, and check after half an hour to see if there is any change in pressure. 2 Check for air leaks. If a significant drop in pressure is observed, the source of the leak should be investigated. Use soapy water to check for potential leakage points in the autoclave. The key areas to inspect are: the connections between the autoclave lid and the inlet pipe, outlet pipe, and pressure gauge ； The needle valve connections at the air inlet and outlet, the sealing rings between the reactor body and the lid, the thermometer probe socket, etc. If air leakage is detected, the pressure should first be released, the corresponding leak point should be tightened, and then a pressure test should be conducted to check for leaks. After checking that there are no leaks, release the pressure and clean the soapy water with deionized water. 3. Turn off the nitrogen supply to ensure that all pressure in the vessel is released. Close the main valve and the branch valves of the nitrogen cylinder, and after releasing any remaining pressure in the pipes, use a torque wrench to loosen the main nut in a cross-shaped, symmetrical manner. Slowly and carefully separate the vessel body from the lid, being particularly careful to protect the sealing surfaces to avoid damage to the seals between the lid and the vessel body. Material feeding operation: Once the pressure testing is complete, the material feeding operation can be carried out. Add the reactants and solvent to a clean, dry autoclave, and seal the vessel body and lid following the procedures outlined above. Inspection work: Check whether all valves (solid feed inlet, kettle lid exhaust valve, air inlet valve, etc.) are tightened properly (just enough tension is sufficient; do not use excessive force). Set the stirring switch and speed control/heating switch on the controller to zero. Ensure that the thermocouple is inserted into the kettle lid and can accurately display temperature changes; afterwards, turn on the power supply for the control box as well as its display switch. After turning on the cooling water connected to the stirring shaft, turn on the stirring switch; then control the stirring speed using the speed regulator to start stirring. Adjust the nitrogen: Connect the nitrogen cylinder to the inlet of the autoclave using a conduit, and tighten the relevant screws. Open the main valve and the pressure regulator valve of the nitrogen cylinder; first adjust the pressure at the pressure regulator valve to around 1 MPa, then open the inlet valve of the reaction vessel to allow gas to be slowly introduced into it. Once the pressure displayed in the reaction vessel matches the set pressure on the nitrogen cylinder and remains constant, close the inlet valve of the reaction vessel. After stirring for about 3–5 minutes, open the vent valve to release pressure; once venting is complete, close the vent valve. Repeat the inflation and deflation process 3-5 times; once it is ensured that there is no residual pressure in the tank, close the exhaust valve. Introduce hydrogen gas; connect the pipeline. Close the main valve and the pressure-regulating valve of the nitrogen cylinder, release any remaining pressure in the pipeline, then disconnect the autoclave from the nitrogen cylinder. Connect the autoclave to the hydrogen cylinder using a pipeline and tighten the relevant screws. 2 Hydrogen pressure adjustment: Open the main valve of the hydrogen cylinder as well as the pressure regulator valve. First, adjust the pressure at the regulator valve to around 0.5–1 MPa, then open the inlet valve of the reaction vessel to allow gas to be slowly introduced into it. Once the pressure displayed in the reaction vessel matches the set pressure on the hydrogen cylinder and remains constant, close the inlet valve of the reaction vessel. Connect the exhaust valve outlet to the outside through a pipeline; after stirring for about 3–5 minutes, open the exhaust valve to release the gas. Once evacuation is complete, close the exhaust valve. After repeating the inflation and deflation process 3–5 times, adjust the pressure control valve of the hydrogen cylinder to set the pressure at the level required for the reaction. Then, slowly introduce gas into the reaction vessel until the pressure indicated by the gauge matches the pressure required for the experiment. Finally, close the inlet valve, as well as the main valve and the pressure control valve of the hydrogen cylinder. 3. Check before heating: Once again, use soapy water to check whether there are any leaks at the air inlet and exhaust valve. Ensure that no hydrogen is leaking before turning on the heating switch on the controller. Adjust the set reaction temperature in stages to prevent the heating temperature from becoming too high, and set the voltage to an appropriate level so that the heating rate does not exceed 80°C/h. Then start the heating process to initiate the reaction. 4. Control of parameter changes: After the reaction begins, it is necessary to closely monitor the changes in various parameters during the reaction (pressure, temperature, rotation speed), with particular attention to pressure changes. Once any abnormalities are detected, the heating switch should be turned off immediately, and the department head should be informed. If the temperature becomes too high, cooling water can be used through the cooling coil to lower the temperature ； If the pressure is too high, it can be reduced by cooling or by venting through the exhaust valve; when venting hydrogen, it must be discharged outdoors through pipes! Sampling control during the reaction: If sampling is necessary during the reaction, samples can be taken through the inlet for analysis, but it is essential to ensure that the reaction mixture remains homogeneous and that no solids precipitate. If heterogeneous catalysts such as palladium on carbon or Raney nickel are used in the reaction, stirring should be stopped before sampling; the mixture should be allowed to stand for about 10 minutes before sampling can take place. If multiple sampling analyses are required, the first portion of fluid discharged from the pipeline consists of the residues remaining in it, and this does not reflect the actual reaction taking place inside the reactor; therefore, about 20 milliliters of fluid should be discharged first before sampling for analysis. Post-reaction operations: Once the reaction is complete, turn off the heating, set the temperature to room temperature, and allow it to cool naturally or use cooling water through a cooling coil to accelerate the cooling process. When the temperature drops below 40°C, open the exhaust valve of the reactor. After releasing the pressure slowly and completely, use a torque wrench to loosen the main nut in a cross-shaped, symmetrical manner. Then, separate the reactor body from the cover slowly and carefully, being sure to protect the sealing surfaces to prevent damage to the seals between the cover and the body due to any collisions. Cleaning of the reaction vessel: Remove the vessel body, pour out the contents, and use a solvent to wash out all residues inside the vessel. Then wash the vessel body, lid, and sampling pipes sequentially with ethanol and water, and wipe the sealing cone surfaces clean with a soft cloth or paper. Cleaning should be carried out immediately after discharge to prevent difficulties in cleaning due to solvent evaporation. After cleaning, place the kettle body and lid in a well-ventilated area to dry. Other precautions: 1. The reaction kettle must be used in strict accordance with the regulations; it should not be operated alone, and at least two people are required for experiments. 2. During the operation of the pressure vessel, turn on the exhaust fan to ensure good ventilation. 3. When there is pressure inside the reactor, it is strictly prohibited to twist the nut or strike the high-pressure reactor. 4. At the connection points of the male and female nuts (the branches connecting the intake pipe, exhaust pipe, pressure gauge to the kettle lid), only the nuts shall be rotated; the two sealing surfaces must not rotate relative to each other. 5. Monitor the reading on the pressure gauge at all times during operation; it is strictly prohibited to use the tank when temperatures or pressures are too high. 6. If air leakage occurs during the experiment, stop heating immediately and cease the experiment; it is strictly forbidden to twist the nuts at high temperatures. 7. Do not leave during the experiment. 8. The reaction vessel is not resistant to strong acids; strong acids such as salt acids, sulfuric acid, and *ao acid are prohibited from being used in the reaction solution. 9. Approval from the person in charge is required before use; anyone using the kettle must first read the instructions carefully.