Design issues in diazotization reactions
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In accordance with the relevant documents issued by the Safety Supervision Bureau regarding the automatic control requirements for high-risk processes, the diazotization reaction requires close monitoring of the liquid level in the reactor, the pH value, the flow rate of sodium nitrite, and the mixing ratio of the reactants. Question 1: For batch reactions where the feed materials are added in excess amounts in advance, is it necessary to monitor the liquid level in the reactor? Question 2: Nitrous acid is added by gravity flow from a sump, and the flow rate is generally monitored using a flow meter; however, it’s difficult to design a flow meter for such gravity flow systems. Is it feasible to design a interlock between the reactor temperature and the feed control valve? Question 3: How is the pH value monitored? Constant manual sampling tests? Is it necessary to monitor this? Question 4: How to test the mixing ratio of reactants? Constant manual sampling tests? Is it necessary to monitor this? Question 5: The reaction requires an emergency cooling system. Although there are chilled water coils, in the event of a problem, heat exchange may not be fast enough. Is it possible to design the system so that chilled water can be directly added to the reactor when overheating occurs, with valves opening automatically to allow discharge? Could some experienced friends please let me know? To be honest, many people don’t know the specifics. If it’s necessary to make some settings, please explain how to do it. Thank you! Send flowers{:3_64:}
Some rules are imposed. It's mainly for safety, regardless of whether his request is reasonable or not. Since self-control is required, manual intervention should be minimized, such as manual pH testing and manual measurement of material ratios. 1. Level measurement is not very necessary, but it allows the level to be monitored remotely once installed. 2. Add it dropwise from a sump; a flow meter can also be used. If the pressure head is insufficient, the sump can be raised a bit. 3. PH can be selected for online monitoring. In fact, the material ratios have been calculated in advance, so it generally doesn’t cause the pH value to go outside the acceptable range. But what if there’s a mistake in the ratios? Since it has to be installed, then spend some money to get it installed. 4. Adding chilled water directly to the reaction vessel should be considered carefully. The above are my personal opinions. Criticism is welcome!
Diazotization can be done at various temperatures, including low temperatures. Is your diazotization carried out at low temperatures? Is the material highly viscous? We have built industrial-scale units for continuous diazotization and hydrolysis, and we can share our experience. nobelchem@sina.com
Hazardous processes must comply with mandatory standards without any room for negotiation, but appropriate adjustments can be made:
1. A level gauge must be installed, in case the wrong material is added. A capacitive level gauge can be used. 2. For batch reactions, it is not necessary to monitor the ingredient ratios; this applies to continuous reactions instead. 3. Do not use sodium nitrite any longer; instead, use nitrosyl sulfate for diazotization. Use a pump; otherwise, the head pressure will not be sufficient and it will be impossible to select the flow meter. The temperature must be interlocked with the flow feed valve, and it must also be interlocked with the jacket cooling water control valve. The heating requirement for the diazotization reaction is not high, so a double jacket should be designed. 4. When the acidity exceeds 10%, pH monitoring becomes meaningless, and there are no available pH options. 5. The area of the coiled tubes inside the tank is too small; they can be used for rapid cooling with brine, but for diazotization it is better not to have such coiled tubes, as this otherwise affects the yield, makes cleaning difficult, and increases the risk of spontaneous combustion. 6. Although diazotization is a reaction that takes place at atmospheric pressure, it is still necessary to install pressure transmitters and pressure relief valves to prevent operational accidents. Although diazotization is simple, many accidents have occurred; don’t take chances
1: Practical experience shows that monitoring the liquid level in reactors used for high-risk processes or distillation-related reactions is essentially pointless; although laws and regulations require such monitoring to be carried out, the same monitoring objectives can be achieved through other methods. 2: For the automatic drip feeding from the nitrite storage tank, a flow meter can be installed; pressure differences can also be used for this purpose. Of course, it is also possible to use a weighing storage tank along with a control valve to regulate the rate of drip feeding. Interlocks between the reactor temperature and the feed control valve, interlocks between the reactor temperature and the jacket cooling water control valve, interlocks between the reactor pressure and the feed control valve – such settings are all standard and necessary. 3: The pH value is usually not monitored. 4: The mixing ratio of the reactants is usually not monitored; it is sufficient to ensure accurate measurement of the batch quantities and to control the addition rate and total amount through continuous dripping. 5: What material is used for the chilled water coil inside the tank? A detailed calculation and verification using a pilot plant are necessary to determine whether it can meet the requirements for rapid cooling; it’s not possible to guess simply. My suggestion is to use special materials for the internal coil, and by selecting an appropriate heat exchange area, a good effect for rapid cooling can be achieved. Of course, it’s impossible to directly add chilled water into the reaction vessel – that’s common sense; not to mention opening valves casually to discharge the material.