Unsaturated acetal preparation method

Abstract

The present invention discloses an unsaturated acetal preparation method. According to the preparation method, an unsaturated alcohol and an unsaturated aldehyde are subjected to a reaction in a pre-reactor to achieve a thermodynamic equilibrium, and then enter a tower type reactor, a water carrying agent is subjected to gasification through a gas generator, and then is subjected to reverse contact with a reaction liquid, and the water generated from the reaction is removed, such that the unsaturated alcohol and the unsaturated aldehyde are subjected to a continuous condensation reaction to prepare the unsaturated acetal. The preparation method has the following characteristics that: the method can be performed under a normal pressure condition, the reaction temperature is constant, low cost synthesis of the unsaturated acetal can be achieved, particularly 3-methyl-2-buten-1-ol and 3-methyl-2-butenal can be adopted as raw materials to synthesize 3-methyl-2-butenal-1 diisopentenyl acetal, wherein the compound is an important intermediate of a synthetic perfume citral.

Description

technical field [0001] The invention relates to a preparation method of unsaturated acetal, in particular to a preparation method of high boiling point unsaturated acetal. Background technique [0002] Unsaturated acetal is an important intermediate in the synthesis of plastics, spices and vitamins, usually using nitric acid, phosphoric acid or lithium chloride as a catalyst, and is produced by reactive distillation under negative pressure conditions. The related patents are as follows: [0003] BASF adopts nitric acid (concentration is 1×10 -6 ~1 wt%) is used as a catalyst to carry out the reaction at a reaction pressure of 2-200 mmHg (absolute pressure) and a temperature of 15-100°C. The solution of unsaturated alcohol, unsaturated aldehyde and nitric acid is added to the reaction system from the middle of the tower, the water generated by the reaction is removed through the oil-water separator, the organic phase is refluxed, and the acetal generated by the reaction accum...

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Problems solved by technology

[0005] 1. Because the consumption of nitric acid is few, the concentration distribution of nitric acid in the reaction tower is difficult to measure;

[0006] 2. Nitric acid will first be enriched at the top of the tower, and then the concentration of nitric acid in the entire reactor will increase, resulting in too high acidity in the bottom of the tower, increased side reactions, and the quantitative maintenance of nitric acid in the entire reaction system is very difficult;

[0007] 3. The decompression operation has high requirements on equipment and process, and the cost is high

Its disadvantages are: the lithium chloride used is highly corrosive and the reaction is carried out under negative pressure conditions, which is not convenient for continuous production and energy saving

[0011] In another patent US5177265A, RHONE POULENC discloses that phosphoric acid is used as a catalyst for condensation reaction, and toluene is added as a solvent to form an azeotrope with water. The reaction temperature is 60-90°C and the pressure is 8000-14000Pa (absolute pressure). The conversion rate of prenaldehyde is 83%, and the yield of acetal is 75.6%. The disadvantage is that after the reaction, the excess acid needs to be neutralized by potassium acetate, sodium acetate, carbonate or hydroxide.

[0012] The existing process for preparing unsaturated acetal is generally carried out under negative pressure conditions, the process control is complicated, and the requirements for equipment are high. At the same time, the temperature of the reactor is high and the energy consumption is large.

Phosphoric acid and lithium chloride are used as catalysts for cumbersome post-treatment. Although nitric acid is used as a catalyst, there are certain advantages, but due to the small amount of use, it is difficult to measure the distribution of nitric acid content in the rectification tower and it is difficult to maintain a constant value.

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