Novel method for recovering solvent for polymerization of poly(p-phenytene terephthalamide)

Abstract

The invention relates to a novel method for recycling a solvent used for polymerizing the poly (p-phenylene terephthalamide) which has a shortened form of para-aramid or PPTA. The method comprises the following steps that: the PPTA polymer made by the low-temperature solution polycondensation contains a large amount of solution N-Methyl pyrrolidine which has a shortened form of NMP and certain amount of calcium chloride (CaCl2), the PPTA polymer is washed by deionized water for a plurality of times, the PPTA polymer is collected to enter a drying system, a scrub solution is neutralized and enters a neutralizing liquid storage tank of a solvent recycling system; the neutralizing fluid is processed by a two-stage film evaporator to remove the CaCl2 added to the polyreaction and generated by the neutralizing reaction, the hydration NMP enters the middle part of a topping still from the top of the film evaporator in a state of mixed gas to remove most of water by the distillation process, the purity quotient of NMP is improved further and the minim water inside the NMP is lowered by the rectification and purification processes, the obtained NMP has a purity quotient higher than 99.5 percent, a water content lower than 100ppm, thereby completely satisfying the requirement of PPTA polymerization. The technique is used for recycling the solvent for PPTA polymerization; the recycling rate of the NMP is higher than 96 percent, thereby lowering the cost further and providing reliable guarantee for the industrialization of the para-aramid.

Description

technical field [0001] The invention relates to a solvent recovery method for the polymerization of poly-p-phenylene terephthalamide, which belongs to the field of polymer material synthesis. Background technique [0002] As we all know, poly-p-phenylene terephthalamide (PPTA) is a mixture of p-phenylenediamine and terephthaloyl chloride in N-methylpyrrolidone (NMP) and calcium chloride (CaCl 2 ) in the solvent system through low-temperature solution polycondensation reaction. In the process of preparing PPTA, a large amount of NMP needs to be used, and the requirements are extremely strict (water content is lower than 100ppm). One of the key factors of industrialization. Therefore, researchers in this field have successively proposed different methods to recover NMP. [0003] CN95102183.4 discloses a method for recovering the polymerization solvent of synthetic PPTA. It proposes to distill the polycondensate obtained by polymerization under reduced pressure, and after the...

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Problems solved by technology

This method has the following problems: (1) after the polymer is neutralized under reduced pressure, the salt in the polymer will be difficult to clean, and the ash content in the PPTA product is relatively high; (2) NMP is distilled under acidic conditions (3) The recovered NMP cannot meet the polymerization requirements of PPTA (the relative inherent viscosity of the polymer meeting the spinning requirements should be above 5.5dl / g)

The advantage of this method is that the solvent-containing washing liquid is separated from the product PPTA before the solvent recovery operation, which avoids the decomposition of the solvent NMP, the purity of the recovered solvent reaches 99.5%, the recovery rate reaches 91%, and the water content is lower than 100ppm, which is fully in line with Polymerization requirements of PPTA, but this method still has the problems of insufficient continuity for industrialization, low dehydration and desalination efficiency, high energy consumption, and low recovery rate

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