硫酸盐阔叶木浆中己烯糖醛酸及其含量的测定

Hexenuronic Acid in Hardwood Kraft Pulps And Determination of its Content

阔叶木中大量存在的聚木糖的侧基团４ － Ｏ－ 甲基葡萄糖醛酸在硫酸盐法制浆中主要转化为己烯糖醛酸侧基（Ｈｅｘｅｎｕｒｏｎｉｃ ａｃｉｄ，简称ＨｅｘＡ） ，在纸浆中含量约５０ － ６０ｍｅｑ／ｋｇ。ＨｅｘＡ 的存在，对纸浆漂白有不利的影响：与亲电漂剂（ 如Ｃｌ２ 、ＣｌＯ２ 、Ｏ３ 和过氧酸） 发生反应，消耗一部分漂白药品；其六元环上的双键是Ｍｎ 等金属离子的重要的螯合部位；而且使得纸浆容易发生返黄。如果漂前对浆料进行适当的处理（ 如温和的酸水解） ，则可以选择性的去除大部分己烯糖醛酸，有利于后续的漂白。利用ＵＶ 光谱对ＨｅｘＡ 酸水解的主要产物２ － 糖酸进行测量，然后可以计算出己烯糖醛酸的含量。

Most of the 4-O-methyl glucuronic acid groups which present in hardwood are converted into hexenuronic acid groups(HexA) in kraft pulping.The content of HexA in hardwood pulps is about 50-60meq/kg.HexA has negative effects on bleaching:it reacts with electrophilic bleaching agent such as chlorine,chlorine dioxide,ozone and peracid;the double bond in the ring is the dominated chelating site for transition metal ions;and it also affects the brightness stability of bleached pulp.So it would be profitable if a mild acid hydrolysis is applied before the bleaching stage.The mild acid hydrolysis can remove a major part of HexA without great loss of pulp viscosity.The hydrolysis products,2_furoic acid and 5_carboxy_2_furaldehyde,are quantified from the hydrolyzate by UV spectrophotometer.The HexA content is directly proportional to the amount of the furan derivatives liberated.