Crystallization process of di-trimethylolpropane

Abstract

The invention relates to a crystallization process of di-trimethylolpropane.Kettle raffinate containing di-trimethylolpropane and water are added into a crystallization stirring kettle to be prepared into a solution with the mass fraction of 60% to 65%; crystallization and condensation are carried out, then a cooling water circulating pump, an outer liquid circulating pump and a program temperature control system are started, liquid is slowly cooled, and then a proper amont of di-trimethylolpropane is added as seed crystals; then stepping cooling is continued according to setting of the program temperature control system, a valve in front of the outer liquid circulating pump is switched off, pumping continues to be carried out for 3 min, cooling water leading to a jacket of the crystallization stirring kettle is switched to be connected, and stepping cooling is continued according to the setting of the program temperature control system; finally, a discharging valve at the bottom of the crystallization stirring kettle is switched on, and liquid containing a large number of crystals is discharged into a sealing-tape machine or centrifugal machine for solid-liquid separation.The crystallization process has the advantages that products with coarse crystal grains can be obtained, and subsequent filtering and washing can be completed easily.

Description

technical field [0001] The invention belongs to the purification part in the technical field of fine chemicals, and in particular relates to a crystallization process of ditrimethylolpropane. Background technique [0002] Di-trimethylolpropane, (Di-trimethylolpropane for short Di-TMP) is a white powder or white flaky crystal with 4 relatively active primary hydroxyl groups. It has better performance than trimethylolpropane and can replace Glycerin, neopentyl glycol, pentaerythritol, trimethylolpropane and other polyols are used in the production of alkyd resins, polyurethane resins, lubricants, explosives, plasticizers, rosin esters and advanced aviation lubricants, especially in surfactants And the application of aviation lubricants has more unique properties; ditrimethylolpropane is also used in the production of acrylic monomers / oligomers, synthetic lubricants, special resins and chemical intermediates, coating resins, PVC stabilizers and other fine chemicals The raw mat...

AI Technical Summary

Problems solved by technology

[0005] 1. The content of ditrimethylolpropane cannot meet the requirements of industrial production (≥95%), because the residue after extracting trimethylolpropane through rectification still contains a lot of trimethylolpropane and has a high boiling point Impurities such as trimethylolpropane bis-single straight-chain formal and tri-trimethylolpropane, due to the formation of a large number of fine crystal nuclei in a short period of time during the crystallization process, are likely to be formed by many fine crystals bonded together. The crystal clusters, and the solution and impurities are easily wrapped in the crystal clusters, resulting in a decrease in the content of the product (≤94%); in addition, due to the large amount of trimethylolpropane in the product, the resulting product is easy to solidify Agglomeration brings difficulties to product stacking, transportation and use;

[0006] 2. During the crystallization, an ordinary stirred tank crystallizer with chilled water in the jacket is used. Since the heat exchange is only performed by the jacket of the stirred tank, the heat transfer area per unit volume of the material to be crystallized is small. When cooling, the cooling medium and The temperature difference of the feed liquid is too large. Due to the low temperature of the feed liquid near the wall of the stirred tank, local concentration supersaturation tends to occur during the process of cooling and crystallization, and fine crystal nuclei are formed prematurely; It has to be stirred continuously so that when the crystal nuclei in the supersaturated region go to the region with higher temperature and not yet saturated in concentration, the crystal grains are not easy to continue to grow, so the obtained product has a very fine particle size;

[0007] 3. It is very difficult to filter the crystallized product through a tape machine or a centrifuge. On the one hand, at the beginning of filtration, the fine product particles are easy to penetrate the filter screen, which affects the yield of the product; on the other hand, the subsequent fine product particles Embedded in the filter to block the filter, and gradually accumulate on the surface of the filter, after the formation of the filter layer, because the filter layer is too dense, the liquid part that affects the subsequent materials is thrown out, reducing the efficiency of the product being dried; If the particles are too small, the formed filter layer is very dense, and it is not easy to clean the surface of the product with frozen water, so that the surface of the product is still adsorbed with impurities after washing, and the content does not meet the requirements

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