Can an extractant be omitted in the methanol distillation process?
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Can extraction liquid be omitted in the methanol distillation process? If so, what can be used as a substitute? If it cannot be omitted, from which sources is extraction liquid usually obtained?
Generally speaking, if distillation does not have a dedicated extraction water pipeline, it is either the wash tower that is used after the synthesis of alcohols, or special devices are employed for the alcohols themselves, and these can also serve as extraction water. However, the amount of water can sometimes be unstable due to variations in the alcohol content
If it is a dedicated extraction pipeline, is specially prepared extraction water used? What is the concentration?
Up to the later stages of the catalyst, a separate extraction water pipeline is generally designed.
The amount of extraction water added is generally adjusted based on the density of the methanol to be purified, as well as on the degree of aging of the synthesis catalyst and the impurity content in the methanol.
Generally, a water content of 10 to 20 percent is required to ensure that the product has acceptable water solubility and oxidation values. Deionized water or steam condensate can be used as the extraction water, which should be added to the extraction tank or the pre-cooling reflux tank
What kind of equipment are you? We use natural gas steam conversion; we have never used extraction pipelines, instead we use manually connected rubber pipes that lead to the crude methanol storage tank
It is best to have dedicated pipelines for the extraction water; desalinated water can be used. The amount of water added should be kept at around 20% of the feed volume, and the amount of extraction water can be adjusted based on the specific gravity after extraction.
Water is selected as the extractant based on the properties of methanol; the amount of water added varies depending on the water content in the crude methanol. Theoretical design values for the water content in crude methanol are 20%, and samples are usually taken after adding water, with a density ranging from 0.83 to 0.86 g/Nm3. The higher the density, the better the product quality, but it wastes steam.
What was said upstairs is correct – not adding extraction water will affect the operation of the subsequent tower. Crude methanol obtained from natural gas conversion typically contains about 15% water, so it’s acceptable not to add any water in such cases; however, problems will arise if this situation persists over time. The accumulation of azeotropes, along with delayed removal of fusel oils and alkane oils, can lead to a decline in product quality and greater operational instability. It’s generally best to add some extraction water and to remove fusel oils and alkane oils on a regular basis. Once water is added, it’s sufficient to control the density at the bottom of the pre-tower properly. If it is coal tar, more water needs to be added for extraction.