改性纤维素阻垢剂在反渗透膜结垢控制中的应用研究

Application of modified cellulose-based antiscalant in reverse osmosis membrane scaling control

膜结垢是反渗透脱盐工艺应用中存在的难题之一.添加阻垢剂是抑制无机盐结晶控制膜结垢的有效手段之一.本文以纤维素为原材,采用醚化与接枝共聚两步法,合成了一种阻垢性能优良且环境友好的改性纤维素阻垢剂(CMC-g-P(AA-co-SAS)),并详细考察了CMC-g-P(AA-co-SAS)的分子结构、投加量及共存阴离子等因素对其在反渗透系统中对硫酸钙垢抑制效果的影响.实验结果表明,适当投加量下,CMC-g-P(AA-co-SAS)可显著延长硫酸钙结晶诱导时间,抑制硫酸钙垢的形成,大大缓解由于反渗透膜表面结垢造成膜污染并导致膜通量下降等问题,有效提高膜滤效率.结合静态阻垢实验以及扫描电子显微镜、光学显微镜、X射线衍射、电导测量及分散性实验等结果,CMC-g-P(AA-co-SAS)的阻垢机理主要归因于引入的阴离子阻垢功能基团的络合与分散稳定效应,且羧基相比于磺酸基对硫酸钙垢具有更为显著的抑制作用.适量地引入磺酸基,可改善聚合物阻垢剂水溶性,有利于稳定溶液中的成垢物质,进一步提高阻垢性能;但磺酸基含量过高,羧基含量下降,络合分散作用相应减弱,导致阻垢性能降低.研究结果为开发和设计新型高效绿色阻垢剂提供了新思路.

Applying membrane scaling is a key problem in reverse osmosis(RO)desalination processes.By dosing antiscalant,we can effectively inhibit inorganic scale and control RO membrane scaling.Accordingly,in this work,an environmentally friendly modified cellulose-based antiscalant is synthesized by the etherification of cellulose and subsequent graft copolymerization using the etherification product carboxymethyl cellulose(CMC),acrylic acid(AA),and sodium allyl sulfonate(SAS):CMC-g-P(AA-co-SAS).The influence of molecular structure,CMC-g-P(AA-co-SAS)dose,and coexisting anions with respect to inhibiting the calciumsulfate scale in the RO system are investigated.The results indicate that dosing CMC-g-P(AA-co-SAS)can significantly prolong the induction time of calcium-sulfate crystallization,inhibit the formation of calcium-sulfate scale,greatly alleviate both membrane fouling and membrane flux decline caused by membrane-surface scale formation,and effectively improve the membrane filtration efficiency.Static tests,scanning electron microscopy,optical microscopy,X-ray diffraction,conductivity measurements,and dispersion experiments suggest that the scale inhibition mechanism of CMC-g-P(AA-co-SAS)can be attributed to the chelation and dispersion effects of the introduced anionic groups,and that the carboxyl groups are more efficient in the inhibition of calcium-sulfate scale than the sulfonic groups.In addition,an appropriate number of sulfonic groups on the graft chain of CMC-g-P(AA-co-SAS)can improve the water solubility of CMC-g-P(AA-co-SAS),as well as effectively stabilize the scale-formed substances and enhance the scale inhibition efficiency.If the proportion of sulfonic groups is too high,the content of the carboxyl groups decreases accordingly,which reduces the chelation and dispersion effects of CMC-g-P(AA-co-SAS),which,in turn,reduces the scale inhibition performance.