Hostalen工艺淤浆法高密度聚乙烯装置己烷精制系统堵塞原因分析

Analysis of blocking causes of hexane refining system in high density polyethylene unit of Hostalen slurry process

Hostalen工艺为低压淤浆法高密度聚乙烯(HDPE)工艺,对Hostalen工艺HDPE装置的己烷精制系统预热器中的堵塞物、装置母液中的聚乙烯蜡及蜡回收单元的聚乙烯蜡3种试样的外观以及熔点、分子量及其分布进行对比分析,并推测预热器中的堵塞物形成的原因。实验结果表明,预热器中的堵塞物熔点高、分子量大、分子量分布宽,而母液中的聚乙烯蜡和蜡回收单元的聚乙烯蜡的外观、熔点、分子量及其分布相当;可能是由于母液中的聚乙烯蜡、催化剂残留、聚合物细粉或丁烯等成分在预热器中进一步发生反应,生成更高分子量的聚合物,从而造成预热器堵塞;在正常生产中,向进入预热器的母液中注入适量水蒸气,以阻断进一步反应、避免高分子量聚合物堵塞换热器;在连续高负荷生产PE100级管材料时,己烷精制系统的运行周期由120 d提高至450 d以上。

Hostalen precess is low pressure slurry high density polyethylene(HDPE)process,the appearance,melting point,molecular weight and its distribution of the blockage in the preheater of hexane refining system in the HDPE unit of Hostalen precess,polyethylene wax contained in mother liquor and from wax recovery unit were compared and characterized by DSC and GPC experiments.The cause of the blockage in preheater was speculated.The results showed that the blockage in the preheater had higher melting point,higher molecular weight and wide molecular weight distribution,while the appearance,melting point,molecular weight and its distribution of the polyethylene wax in the mother liquor and the recovery unit were similar.The polyethylene wax,catalyst residual,polymer fines or other components like 1-butene in mother liquor were speculated to continue to react in preheater section of hexane distillation unit,and generated polymer with higher molecular weight,thus causing the preheater blockage.According to this speculation,an appropriate amount of steam injected into mother liquor entering the preheater could block further reaction and avoid high molecular weight polymer to block the heater exchanger.The operation cycle of hexane distillation unit increased from 120 d to more than 450 d under harsh operating condition when the PE100 grade pipe was continuously produced at the high load.