Why does the pH of the wastewater after methanol purification decrease?
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The feed is adjusted to a pH of nine to ten in a 12 m3 buffer tank. The feed components are mainly 90% water, 1.5% methanol, and 0.2% of propylene, MAA, and MMA. The pH is adjusted using a 20% sodium hydroxide solution. It enters the methanol recovery distillation tower for distillation. The output at the top of the tower is mainly 40% water and over 40% methanol. The pH of the wastewater at the bottom of the tower will drop to 6 to 7. May I ask why this is?
It’s possible, or it might be that something was done wrong
During the alkaline neutralization process, methacrylic acid (MAA) is converted into its sodium salt, which lowers the pH value of the wastewater.
During the stripping and heating process, some esters may decompose into organic acids, and aldehydes can also react to form acids, which remain in the bottom of the tower, thereby lowering the pH