Preparation method of polyoxymethylene dimethyl ether (DMMn)

Abstract

The invention belongs to the technical field of energy and chemical industry, and provides a preparation method of a fuel additive and an environment-friendly solvent polyoxymethylene dimethyl ether (DMMNn, generally n=3-8), which comprises the following steps: mixing a formaldehyde water solution and polyol according to a certain proportion, and conducting heating and dehydrating under vacuum conditions to obtain flowing polyoxymethylene with lower moisture content in one step; heating and gasifying flowing polyformaldehyde with the lower moisture content to obtain purer gaseous formaldehyde,mixing the obtained gaseous formaldehyde with methylal, mechanically used last-batch low-boiling-point substances, macromolecules and the like in the presence of a catalyst, carrying out catalytic reaction at a certain temperature, filtering out the catalyst after the reaction is balanced, purifying the synthetic liquid, respectively carrying out atmospheric pressure and reduced pressure distillation, conducting separating to obtain a low-boiling-point substance, macromolecules and a DMMn finished product, and carrying out reduced pressure distillation on the DMMn finished product to obtain each single component; and after the formaldehyde is gasified, returning the residual polyhydric alcohol for application of next-batch concentrating of formaldehyde to prepare the flowing polyformaldehyde with lower moisture content.

Description

technical field [0001] The invention belongs to the technical field of energy and chemical engineering, in particular, a preparation method of polymethoxydimethyl ether (DMMn, generally n=3-8) is designed. Background technique [0002] Polyoxymethylene dimethyl ether, also known as paraformaldehyde dimethyl ether, English name: Polyoxymethylene dimethylethers, referred to as PODE or DMMn, is a kind of low molecular weight with dimethoxymethane as the matrix and methyleneoxy as the main chain. Acetal polymer, its general formula is expressed as: CH3O(CH2O)nCH3. Among them, polyoxymethylene dimethyl ether with a degree of polymerization of 3-8, referred to as DMM3-8, is used to clean diesel blending components. Its physical properties are similar to diesel oil, and it is not necessary to modify the vehicle engine fuel supply system when blending it into diesel oil. . Its cetane number is as high as 76, its oxygen content is 47%~50%, and it has no sulfur and no aromatics. Ble...

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Problems solved by technology

[0011] Other conventional methods for preparing anhydrous gaseous formaldehyde also include: 1. Depolymerize paraformaldehyde by heating to prepare gaseous formaldehyde, but the bound water of paraformaldehyde itself is only about 4%, which greatly affects the yield and intermediate rate of DMMn synthesis. The further recycling of the product not only makes the preparation of solid polyoxymethylene more cumbersome, but also the further feeding and transportation are not conducive to large-scale and continuous large-scale production, and there are great safety hazards

2. Under the action of an acidic catalyst, paraformaldehyde is heated and decomposed and gasified. In this way, there will be paraformaldehyde that is too late to decompose and gasify with gaseous formaldehyde, which is easy to cause pipeline blockage, and the cost of paraformaldehyde is high, which is not conducive to Realize industrialization

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