Method for directly synthesizing polyoxymethylene dimethyl ether by taking dilute formaldehyde and methylal as raw materials

Abstract

The invention discloses a method for directly synthesizing polyoxymethylene dimethyl ether by taking dilute formaldehyde and methylal as raw materials. The method comprises the following steps: directly mixing dilute formaldehyde and methylal, removing the moisture through a membrane separation process, and carrying out a condensation reaction, thereby obtaining the polyoxymethylene dimethyl ether. According to the method disclosed by the invention, the membrane separation dehydration process and the catalytic condensation reaction are efficiently coupled, the polyoxymethylene dimethyl ether is directly synthesized by taking the dilute formaldehyde and methylal as raw materials, and the method achieves the effects of investment conservation and low cost and has high comprehensive benefits in technical economy.

Description

technical field [0001] The invention provides a novel synthesis process of polyoxymethylene dimethyl ether, specifically a method for directly synthesizing polyoxymethylene dimethyl ether with dilute formaldehyde and methylal as raw materials, belonging to the technical field of methanol energy and chemical industry. Background technique [0002] Polyoxymethylene dimethyl ethers (PODE or DMM for short) n ) is a low molecular weight acetal polymer with methyleneoxy as the main chain, and its structural formula is CH 3 (OCH 2 ) n OCH 3 . When n=3~8, the average cetane number reaches over 76, the oxygen content reaches 47~50%, the flash point is 65.6°C, and the boiling point is 160~280°C. The physical properties are very similar to diesel oil. Alkanes diesel blending components. Add 15% DMM to diesel 3-8 , No need to modify the fuel supply system of the diesel vehicle engine, it can significantly improve the combustion characteristics of diesel, and greatly reduce nitrog...

AI Technical Summary

Problems solved by technology

But from synthetic DMM n From the perspective of chemical reaction, more water in the system is very unfavorable to the process

[0007] Moreover, the dehydration and concentration of dilute formaldehyde is a process of high energy consumption, and the equipment is also relatively complicated. Especially when the formaldehyde concentration is high, formaldehyde is easy to spontaneously undergo condensation reaction. It is very difficult to concentrate the formaldehyde aqueous solution with a concentration of 85%, but it still restricts Generate DMM n Further optimization of the condensation reaction

The presence of a large amount of water leads to a slowdown of the reaction rate, an increase in side reactions, a significant decrease in the single-pass conversion rate and the single-pass yield of the target product, and the result is an increase in unreacted circulating materials in the synthesis reaction device, an increase in energy consumption, and an increase in the corresponding equipment investment ; The refining treatment and dehydration device is relatively large, which not only increases energy consumption, but also increases the corresponding investment

Experiments have shown that when the water content of formaldehyde is reduced from 15% to below 5%, DMM in the condensation product 3-8 The single-pass yield can be increased by 35-40%; more importantly, when the formaldehyde solution concentrated to 85% concentration is used as raw material, the product obtained in the process contains many hemiacetals, and their molecular weight is similar to that of DMM n The product is similar, and the boiling point also meets the requirements, but the presence of hemiacetal will lead to a decrease in the stability of the product and an increase in acidity to a level that is not allowed by the quality standard