Methanol distillation
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What are the reasons for unsatisfactory potassium permanganate levels during methanol distillation, and what are the methods to address them? How should the amount of water used for extraction in the pre-tower be determined? Thank you!
The amount of extraction water required must be calculated based on solubility. An improper mixing degree of the solvent and the material can affect the efficiency of extraction. The feed flow rate of the material or the flow rate of the solvent can be adjusted separately to examine the efficiency of extraction. Critical: A proper design of the feed distributor is very important.
What are the factors that cause failure in the finished methanol KMnO4 test? Crude methanol has poor quality and contains too many impurities. Large processing volume, poor separation efficiency. Poor pre-tower temperature control results in poor separation efficiency. The liquid level at the bottom of the tower is unstable, resulting in uneven feed rates and affecting the separation efficiency. The amount of alkali added is small. The backflow volume is low. The amount of extraction water added to the pre-tower is controlled based on the feed load and composition
The failure in the potassium permanganate test is mainly due to an excessive amount of reducing impurities in the methanol product, which causes the +7 valence purplish-red Mn ions to be reduced and lose their color. This not only indicates an increase in reducing substances such as C=C double bonds and C=O groups in the methanol, but also reflects an increase in organic substances within it. The main reason for the decolorization of potassium permanganate in methanol is the presence of certain light and heavy components within it, including unsaturated hydrocarbons, isobutyraldehyde, acrolein, diisopropylmethane, formic acid, etc. Any substance containing carbon-carbon double bonds or carbon-oxygen double bonds can be easily oxidized by potassium permanganate, resulting in its decolorization. Depending on the specific circumstances, different approaches can be used: 1. Replace the synthetic catalyst to effectively control impurities in crude methanol. 2. For light-component impurities, it is possible to increase the temperature of the pre-distillation tower as well as that of its condensate; furthermore, a portion of the light fractions can be recovered from the pre-tower condenser and the reflux tank. 3. The heavier impurities are mainly removed in the main distillation column. Methods to increase the kettle temperature and raise the reflux ratio. 4. Adding a certain amount of water to the pre-cooling reflux tank to improve the separation of organic substances is also a good approach.
The amount of extraction water added is generally adjusted by measuring the density of the resulting methanol, with this density varying at different times.
The amount of extraction water added generally does not exceed 20%
Can’t it be adjusted based on the feed volume? As for the prognosis regarding methanol density, as long as the feed amount and the amount of water used for extraction remain constant, the density should not change much!
Under normal circumstances, the amount of water added for extraction in the pre-tower should not exceed 20% of the feed volume; however, this can sometimes depend on the quality of the crude methyl product.
In our factory, the amount of extraction water used is determined by ensuring that the methanol content in the tower remains around 80%