Synthesis and performance of bio-based antiscalant derived from poly (itaconic acid)

Scale formation in water-treatment facilities is a critical issue due to serious reductions in the unit’s performance and possible damage to the system. An addition of antiscalants is essential in coping with this problem. However, the majority of these are non-degradable and derived from non-renewable resources, which may cause serious concerns to the environment. Itaconic acid (IA) is an unsaturated dicarboxylic acid produced by biomass fermentation. The material is non-toxic, renewable, and biodegradable. In this work, a process for synthesizing poly(itaconic acid) (PIA) as a bio-based antiscalant is developed. PIA was synthesized by three different methods, i.e., emulsion polymerization, phase inversion emulsification, and free radical polymerization. A suitable method for synthesizing PIA was selected to optimize the effects of pH of IA and initiator concentration on the PIA structure and performance. The chemical structures of the resulting polymer are then characterized by Fourier transforms infrared (FTIR) and proton nuclear magnetic resonance (1H-NMR) spectroscopy and gel permeation chromatography (GPC). The inhibition efficiency against a calcium carbonate scale of the synthesized materials is assessed by using inductively coupled plasma-optical emission spectroscopy (ICP-OES). An effective material was selected to investigate their scale inhibition performance. The inhibition mechanism of PIA against calcium carbonate (CaCO3) was investigated. The results show that free radical polymerization is a potential method for synthesizing PIA, at an optimum polymerization time of 4 h at 85 ℃. The variation of pH of IA before polymerization indicated that neutralizing IA to pH 4 enhances the free radical stability and improves the monomer conversion rate to 100 %, while neutralizing IA at pH 9 causes ion repulsion and reduces the monomer conversion rate to 75%. In addition, neutralizing IA to higher pH boosted the deprotonation of COOH, leading to excellent inhibition performance. Increasing the initiator concentration from 5 to 14% improved monomer conversion from 61 to 96%, respectively, due to the generation of free radicals. The reduction of molecular weight based on the initiator dosage is caused by a high possibility of the termination stage during free radical polymerization. However, molecular weight has a potential impact on inhibition efficiency. High molecular weight causes steric hindrance, while low molecular weight limits inhibition ability. Hence the optimum molecular weight is observed at around 28672 Da with a synthesis pH of IA at 9, and 11 % of initiator. The scale inhibition efficiency reached 81% at a dosage of 10 mg/L. The antiscalants concentration, scale concentration, pH of water, and heating time are the main factors influent scale inhibition performance. Based on the morphology analysis of CaCO3 obtained by scanning electron microscopy (SEM), the mechanism of PIA inhibiting CaCO3 can be explained by two possible mechanisms, i.e., stabilizing particle dispersion and crystal modification. The inhibition performance of PIA is comparable to commercial antiscalants, e.g., polymaleic acid (PMA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC). However, the developed environmentally friendly bio-based material has a high potential for practical applications.

水处理设施中的结垢现象是一个关键问题，因其会严重降低装置性能并可能损坏系统。添加阻垢剂对于解决该问题至关重要。然而，大多数阻垢剂不可降解且源自不可再生资源，这可能引发严重的环境担忧。衣康酸（Itaconic acid, IA）是一种通过生物质发酵生产的不饱和二元羧酸，具有无毒、可再生和可生物降解的特性。本研究开发了一种合成聚衣康酸（poly(itaconic acid), PIA）作为生物基阻垢剂的工艺。PIA通过三种不同方法合成，即乳液聚合（emulsion polymerization）、相转化乳化（phase inversion emulsification）和自由基聚合（free radical polymerization）。选择合适的PIA合成方法，以优化IA的pH值和引发剂浓度对PIA结构及性能的影响。所得聚合物的化学结构通过傅里叶变换红外光谱（Fourier transforms infrared, FTIR）、质子核磁共振波谱（proton nuclear magnetic resonance, 1H-NMR）和凝胶渗透色谱（gel permeation chromatography, GPC）进行表征。合成材料对碳酸钙垢的抑制效率通过电感耦合等离子体发射光谱（inductively coupled plasma-optical emission spectroscopy, ICP-OES）评估。选择有效材料研究其阻垢性能，并探究PIA对碳酸钙（CaCO3）的抑制机制。结果表明，自由基聚合是合成PIA的潜在方法，最佳聚合条件为85℃下反应4小时。聚合前IA的pH值变化显示，将IA中和至pH 4可增强自由基稳定性，使单体转化率达到100%；而中和至pH 9则会引起离子排斥，导致单体转化率降至75%。此外，将IA中和至更高pH值可促进COOH的去质子化，从而获得优异的抑制性能。引发剂浓度从5%提高至14%时，由于自由基的生成，单体转化率从61%提升至96%。引发剂用量增加导致分子量降低，这是因为自由基聚合过程中终止阶段的可能性更高。然而，分子量对抑制效率具有潜在影响：高分子量会产生空间位阻（steric hindrance），而低分子量则限制抑制能力。因此，当IA合成pH为9、引发剂浓度为11%时，观察到最佳分子量约为28672道尔顿（Da）。在剂量为10 mg/L时，阻垢效率达到81%。阻垢剂浓度、垢浓度、水的pH值和加热时间是影响阻垢性能的主要因素。基于扫描电子显微镜（scanning electron microscopy, SEM）获得的CaCO3形貌分析，PIA抑制CaCO3的机制可通过两种可能的途径解释，即稳定颗粒分散和晶体改性。PIA的抑制性能与商业阻垢剂（如聚马来酸（polymaleic acid, PMA）和2-膦酰基丁烷-1,2,4-三羧酸（2-phosphonobutane-1,2,4-tricarboxylic acid, PBTC））相当，但这种环保型生物基材料具有很高的实际应用潜力。