Maintenance of a pH meter in a batch reactor?
Thread Content
One of our products is manufactured using batch reactors that operate during the day and stop at night. Sometimes, due to orders, production is halted for several months. Since the reaction requires strict control of the pH level, we use online submersible pH meters to regulate the amount of alkali added in order to control the pH of the reaction mixture. The problem is that the instructions for these pH meters state that the electrodes must be kept in liquid when not in use, probably to prevent the potassium chloride solution from drying out. However, this poses a challenge: when production is stopped, the reactor is empty, and we want to know how long the pH meter electrodes can remain in this empty reactor without damaging their lifespan. It’s quite troublesome to take them out every time; what is the best way to handle this situation? Therefore, I would appreciate some advice: first, whether there are any pH electrodes that can prevent drying out; second, how long a pH electrode can be left without contacting liquid without any adverse effects; and third, if it’s not possible to avoid contact with liquid and the electrode must remain in contact with it, what is the best approach? Should it be done by placing it in the reactor and then adding water, with all the water removed before starting up again next time, or should the pH meter be taken out of the reactor and immersed in the liquid, to be reinstalled before starting up next time? Are there any other methods? Please give me some advice, thank you!
Electrodes basically cannot be left dry for long periods of time, so I think it’s still necessary for the person in question to take the electrodes out and soak them in liquid every time they’re not in use! Instead of using a reaction vessel or adding water to the vessel or something like that.
It should be taken out and stored in a potassium chloride solution when not in use.
The pH electrode must be soaked before use, as the pH bulb is a special type of glass membrane with a very thin layer of hydrated gel on its surface; it can respond properly to H+ ions in the solution only when fully moistened. At the same time, soaking the glass electrode can **reduce and stabilize** the asymmetry potential. A pH glass electrode can generally be soaked in distilled water or a pH 4 buffer solution. It is generally better to use a pH 4 buffer, with an immersion time of 8 hours to 24 hours or longer, depending on the thickness of the bulb glass membrane and the degree of electrode aging. At the same time, the liquid junction of the reference electrode also needs to be immersed. Because drying out of the liquid junction can increase or destabilize the liquid junction potential, the immersion solution of the reference electrode must be identical to the external reference solution of the electrode, namely a 3.3 mol/L KCl solution or a saturated KCl solution; the immersion time is usually just a few hours. Therefore, for a pH composite electrode, it must be immersed in a pH 4 buffer solution containing KCl in order to function on both the glass bulb and the liquid junction. It is important to note here that in the past, people accustomed to using single pH glass electrodes would soak them in deionized water or pH 4 buffer; this same soaking method was continued when pH composite electrodes were used. Moreover, such incorrect guidance can be found even in some instruction manuals for pH composite electrodes. The direct consequence of this incorrect immersion method is that a pH composite electrode with good performance becomes one with slow response and poor accuracy. Moreover, the longer the immersion time, the worse the performance, as prolonged immersion leads to a decrease in the KCl concentration inside the liquid junction, such as within the sand core, which in turn increases and destabilizes the liquid junction potential. Of course, the electrode will recover as long as it is soaked in the appropriate soaking solution for a few hours again. Furthermore, pH electrodes should not be immersed in neutral or alkaline buffer solutions either; prolonged immersion in such solutions will cause the pH glass membrane to become less responsive. Proper preparation of the pH electrode immersion solution: Take 1 packet of pH 4.00 buffer, dissolve it in 250 ml of pure water, then add 56 grams of analytically pure KCl. Heat gently and stir until everything is completely dissolved. Shanghai Sanshin Instrument Factory supplies bottled electrode soaking solutions in two sizes: 500ml and 50ml. These solutions contain preservatives, which prevent mold growth and spoilage, and they have a shelf life of one year. To make pH composite electrodes more user-friendly, some imported pH composite electrodes as well as certain domestic ones, such as those produced by Shanghai Sains Instrument Factory, are equipped with a sealed plastic vial at the tip of the electrode. This vial contains the electrolyte solution in which the electrode tip is immersed; by keeping it submerged for an extended period, the electrode can be simply removed and cleaned before use, which is very convenient. This preservation method is not only convenient but also highly beneficial for extending the lifespan of the electrodes; it’s just important to keep the solution in the plastic bottle free from contamination and to replace it regularly.
Could you send me a copy of the PID diagram for the reactor over there?
A sampling box can be made; during the reaction, the liquid in the tank is poured into this sampling box to measure the pH value. The sampling tank always maintains a liquid level during shutdown.
May I ask the original poster, what is the function code for the pH meter in the PID diagram? I checked a lot of sources but couldn’t find it
Isn’t the functional code for the letter Q meant to represent a quantity? If I use it to represent pH, do I need to indicate it separately, or should I use A and add PH outside the circle?
Is there one that prevents material from getting caught? Our materials adhere very strongly to the surfaces; glass and PTFE surfaces easily get covered with these materials, which cannot be washed off due to their strong adhesion. A layer of material can form in just 8 hours of operation.