Process for freezing and crystallizing triformol continuouslly by sleeved crystallizer

Abstract

A process for freezing and crystallizing triformol continuously by double-pipe crystallizing device is carried out by entering fresh triformol from pre-system into circulating pump I, mixing suspensoid with circulating loop with after-crystallizing device and connecting pipeline, delivering partial triformol suspensoid in after-crystallizing device to centrifuge, by conveying pump, separating triformol crystal from mother liquid, returning partial mother liquid to after-crystallizing device, returning partial mother liquid to pre-system, transferring partial triformol suspensoid in after-crystallizing device to double-pipe crystallizing-device by circulating pump II, heat exchanging with frozen water to form triformol crystal nucleus, and returning triformol suspensoid to after-crystallizing device. It has less methanal content and consumption of electricity and frozen water and better heat-exchange ability.

Description

technical field [0001] The invention belongs to the field of paraformaldehyde preparation, in particular to a freezing and crystallization process of paraformaldehyde. Background technique [0002] Trioxane is an important monomer in the production of polyoxymethylene. For the polymerization of polyoxymethylene, the total content of impurities in the monomer must not exceed 100PPM. Therefore, paraldehyde needs to be refined to polymer grade purity. The refining process of paraformaldehyde mainly includes: extraction, crystallization, pressure swing rectification, critical extraction and membrane separation, among which extraction separation and crystallization separation are more widely used. [0003] It is understood that the continuous freezing and crystallization process of paraformaldehyde imported from Poland in my country is shown in Figure 1. The fresh paraformaldehyde solution from the front system enters the circulation loop composed o...

AI Technical Summary

Problems solved by technology

Because this kind of process adopts the trough crystallizer as the front crystallizer, it mainly has the following disadvantages: 1. The heat transfer effect is not good, and the temperature difference of the chilled water system is very low. , power consumption increases

2. The crystallizer is cleaned frequently, and it needs to be cleaned every two to three days during operation

Frequent cleaning will not only increase power consumption, chilled water consumption and manpower consumption, but also cause fluctuations in system operation and be detrimental to the environment

3. The volume of the crystallizer is large, the circulation volume of the paraformaldehyde suspension is relatively small, and the residence time in the crystallizer is long. When the surface of the heat exchanger is clean at the beginning of the start-up, the paraformaldehyde suspension in the crystallizer will be too high. The coldness is high, and a large number of fine crystals are formed

The presence of a large number of fine crystals will aggregate into blocks in the paraformaldehyde suspension, causing pipeline blockage and even paralyzing the entire system; the more fine crystals of the same quality, the larger the specific surface area of ​​the crystals. Its adsorption effect will increase the adsorption of formaldehyde and water and other impurities on the crystal surface during the centrifugal separation process, thus increasing the difficulty of subsequent separation; the high content of fine crystals will also make the centrifugal separation system run poorly

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