Melt polycondensation method, special reactor and falling-film elements

Abstract

The invention discloses a melt polycondensation method. Melted monomer blends or prepolymers slide down along the outer walls of tubular falling-film elements so as to be subjected to polycondensation, melts on all the falling-film elements gather at the bottom of a polycondensation reactor so as to be further stirred for reaction and mixed uniformly, and materials are discharged after the reaction finishes. The polycondensation reactor for implementing the method comprises a vertical shell, an end enclosure on the upper end, a bottom shell on the lower end, the falling-film elements, a heat transfer system, a film distributor and a helical ribbon stirrer, wherein the falling-film elements are corrugated pipes with optimized structural parameters. The polycondensation reactor has the advantages of simple structure, sufficient heat exchange, large film forming area, uniform reaction temperature and high polycondensation efficiency, guarantees the laminar flow in the process and can be used for the melt polycondensation of polyethylene glycol terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyamide and polycarbonate.

Description

technical field [0001] The invention relates to a melting polycondensation reaction method, melting polycondensation reaction equipment and a falling film element. Background technique [0002] The implementation methods of polycondensation reaction include melt polycondensation, solution polycondensation, solid-state polycondensation and interfacial polycondensation, etc. Among them, melt polycondensation has obvious advantages in terms of product quality, economy, environmental protection and industrial implementation. Therefore, most polyesters Polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), poly Ethylene naphthalate (PEN), polyamide, polycarbonate, etc. The key to the implementation of the melt polycondensation process lies in the reactor. An ideal polycondensation reactor requires good material flow and mixing state, high heat and mass transfer efficiency, and the process satisfies plug flow, so as to obtain uni...

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Problems solved by technology

However, it has been found through research that the melt of this type of reactor slides faster and faster from top to bottom due to the action of gravity on the heat exchange tube, the residence time is shorter, and the surface area produced by the melt per unit volume flow rate is small. The film forming efficiency is low; as the melt continues to slide, it can cause the instability of the liquid film flow process, and the liquid film fluctuates and propagates downstream, where the liquid film at the peak is thicker, and its velocity is greater than that of the laminar flow film , which is not conducive to the effective devolatilization of the polycondensation process; the speed of the melt along the inner and outer layers of the heat exchange tube is different, resulting in axial back-mixing, insufficient homogenization and mixing of the melt, insufficient uniform residence time, and a wide molecular weight distribution

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