Device and process for preparing high-concentration methylal

Abstract

The invention discloses a device and a process for preparing high-concentration methylal. The process comprises the following steps: a) respectively sending a mixture of formaldehyde and methanol, water and recycled crude methylal to a first rectifying tower for extractive reaction rectification to obtain an azeotrope of methylal and water at the top of the tower and obtain water and residual methanol at the bottom of the tower; b) sending the azeotrope of methylal and water discharged from the tower top to a second rectifying tower for pressurized rectification to obtain high-concentration methylal with the mass fraction of 99.9% or above at the bottom and obtain a methylal-water azeotrope with higher water content at the top, and feeding the methylal-water azeotrope back to the first rectifying tower for recovery; and c) feeding the material discharged from the bottom of the first rectifying tower to a third rectifying tower to recover methanol, partially circulating the water extracted from the bottom of the third rectifying tower to the first rectifying tower for recycling, and discharging the residual water as process wastewater. The method is used for synthesizing and preparing the high-concentration methylal; non-toxic and harmless water is used as an extracting agent and an entrainer, so that the technological process is simple, the single-pass yield of the high-concentration methylal is high, and the comprehensive energy consumption is low.

Description

technical field [0001] The invention belongs to the technical field of chemical production technology, and mainly relates to a preparation device and technology of high-concentration methylal. Background technique [0002] Methylal, also known as dimethoxymethane, is a colorless, non-toxic, and environmentally friendly chemical product that can be used as an organic synthesis intermediate, solvent, and diesel additive. It is a chemical that can replace toxic and harmful solvents and reduce air pollution. Environmentally friendly products, as an excellent solvent, it can be widely used in paint coatings, rubber, leather, electronics, industrial cleaning, insecticides, aerosols and other industries. [0003] Industrially, methylal is usually obtained by the reaction of methanol and formaldehyde aqueous solution catalyzed by an acidic catalyst. Since methylal and methanol can form an azeotrope, conventional distillation and separation under normal pressure can only obtain a mas...

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Problems solved by technology

Extractive distillation adds a toxic and harmful third component with a high boiling point as an extractant, the product is easily polluted by the extractant, and the steam quality required for the recovery of the extractant is high, and the circulation volume of the extractant is large, resulting in energy consumption of these extractive distillation processes In addition, we have also found that the quality of the recycled extractant has a great influence on the effect of extractive distillation. The content of methanol and (or) water in the recovered extractant must be strictly controlled, otherwise the recycled extractant cannot guarantee the extraction The quality of methylal at the top of the rectification tower. Based on the above-mentioned shortcomings, this process route is rarely used in existing industrial plants to produce high-concentration methylal.

[0006] Methylal-methanol azeotrope pressure swing rectification process is generally used in existing industrial devices to produce high-concentration methylal. Pressure swing rectification does not need to add a third component, and the product will not be polluted, but there is also high energy consumption. 1. The low single-pass yield is due to the high content of methanol in the azeotrope of methanol and methylal, which makes the yield of high-concentration methylal at the bottom of the pressurized rectification tower low, at 0.6-1.5MPaG Under pressure, the mass fraction of methanol in the methylal-methanol azeotrope is about 17-24%. When the methylal containing 8% methanol mass fraction obtained by atmospheric distillation is used as the feed, the pressurized rectification column The maximum single-pass yield of high-concentration methylal at the bottom of the tower is only 53-67%; if the common raw material with a methylal concentration of 86% on the market is used as the feed, the maximum single-pass yield of high-concentration methylal is only 18-67%. 42%, a large amount of methylal-methanol azeotrope cycle, resulting in high separation energy consumption, large equipment investment and other disadvantages

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