Experience in using high-pressure reaction vessels

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Autoclaves are generally used for reductive hydrolysis. Safety accidents can easily occur in the presence of high-pressure, flammable, self-igniting materials along with oxygen, causing lifelong regret for the operators. Therefore, the precautions and operating procedures for using an autoclave are described as follows. I. Precautions 1. When personnel are operating a high-pressure reactor for the first time, at least one person who is already proficient in operating such reactors must be present. 2. Personnel performing operations on-site must wear cotton gloves and shoes without nails. 3. Do not bring items that may cause explosions or spontaneous combustion, such as mobile phones, lighters, and MP3 players, into the hydrogenation work area. 4. When handling tools and parts near the hydrogenolysis process, operators must do so gently to avoid any rigid impacts that could generate sparks. 5. When relieving pressure, the off-gas from high-pressure reactions should preferably be directed outdoors via a rubber hose, or into a fume hood. II. Operating Procedures The operating procedures for a complete autoclave reaction consist of five steps: installation, hydrogenation, sampling, hydrogen release, and unloading. (1) Installation. 1. Check inside and outside the tank for any flammable or explosive materials, as well as any items that may hinder air circulation; if such items are present, remove them. 2. Check whether the valves and the inside of the reactor are clean; if not, wash them clean. 3. Close all valves, except the vent valve, and start feeding the material. After feeding, cover the reactor lid; be careful to apply even force when turning the nuts, ensuring that the screws on opposite diagonals are tightened together to prevent air leakage once tightened. 4. Close the exhaust valve. (II) Check the airtightness of the device. Close all valves and cover the kettle lid. Be careful to apply even force when turning the nuts, ensuring that the screws on opposite diagonals are tightened together to prevent leaks after tightening. Open the inlet valve to introduce nitrogen up to 1 MPa, then close the inlet valve and observe the pressure changes to determine whether there is any leakage in the device. (III) Hydrogenation. 1. Check whether all valves are tightly closed. 2. Point the exhaust hose toward an open area with good air circulation. 3. Install the hydrogen pressure relief valve, being careful that the threads on this valve are counter-clockwise. For the nitrogen pressure valve, after installing it, check for leaks using soapy water; if there are leaks, reinstall it. 4. Use vacuum to remove the air from the surface at the exhaust port. 5. Open the air inlet valve of the reactor, turn on the nitrogen pressure regulator to fill it with nitrogen until the pressure inside the reactor reaches 0.2 Mpa; then close the nitrogen pressure regulator and the air inlet valve. Keep this state for about 2 minutes to check whether the pressure indicated by the gauge decreases. Also, listen carefully to see if there is any leakage from the valves or the reactor lid. If there is no leakage, slowly open the exhaust valve to release the pressure inside until it reaches 0.01 Mpa, after which close the exhaust valve. 6. Repeat Step 5 once more. 7. Open the intake valve and the hydrogen pressure regulator, fill it with hydrogen to the desired pressure, close the intake valve and the hydrogen pressure regulator, then adjust the other parameters to the required values to initiate the reaction. (IV) Controlled sampling. 1. Check every half hour whether all the parameters are normal; if the pressure decreases, hydrogen must be replenished. 2. The hydrogen in the hydrogen cylinder must not be used up completely; a certain pressure must be maintained. The cylinder should be discarded and replaced when the pressure reaches around 0.01 Mpa. 3. Sampling. Slowly open the exhaust valve; once the pressure inside the reactor is set to 0.2 Mpa, close the exhaust valve. Then slowly open the sampling valve until reaction liquid begins to flow out, close the sampling valve to collect the sample, and subsequently clean the sampling port to ensure that no flammable substances remain. (5) Hydrogen release. After confirming that the reaction is complete, slowly release the hydrogen until it is completely gone. Be careful to close the exhaust valve as soon as slight pressure appears, in order to prevent oxygen from entering. Open the inlet valve and fill the system with nitrogen until the pressure reaches 0.2 Mpa, after which close the inlet valve. Then slowly open the exhaust valve to release the mixture inside; once it has been completely released, introduce nitrogen again. Repeat this process of gas exchange three times, after which use a vacuum pump to remove the gas from the surface of the liquid. Open the exhaust valve and the sampling valve, and then start discharging the material through the bottom valve. Note that since it contains substances that are prone to spontaneous combustion when exposed to oxygen, such as Pa/C and Raney Ni, it is essential to prevent any spillage outside the container. In the event of a spill, immediately absorb it with a wet towel and place it in a bucket of water; thereafter, destroy those substances using a small amount of dilute acid. Once the material has been disposed of, close the bottom valve right away. (6) Unloading. The reactor, after being filled with the material, should be cleaned immediately. Before cleaning, follow these steps: 1. Fill the reactor with the reaction solvent through the vent valve; after removing most of the residues, add water to half of the reactor’s capacity and stir for 10 minutes. Only at this time can the kettle lid be opened to clean the inner wall of the kettle. 2. During cleaning, the kettle lid and sampling valve must be cleaned, and nitrogen should be introduced slightly while there is water inside the kettle. 3. For reactors that are not in use temporarily, it is best to fill them with 70 volumes of clean anhydrous ethanol; there is no need to tighten the screws.