废旧冰箱聚氨酯泡沫塑料的熔盐热解及脱卤机制研究

The organic halide and acid gas are easily formed during the pyrolysis of halogen-containing e-waste, due to the presence of CFCs blowing agents and brominated flame retardant. Therefore, how to efficiently dehalogenate has become the key of pyrolysis of halogen-containing e-waste. In this work, the polyurethane foam from waste refrigerators (PUR) will be selected and treated using the molten salt pyrolysis technology. It will focuse on the keys, including molten salt screening, dehalogenation mechanism and molten salt regeneration, to achieve the removal of halogens and recovering of pyrolysis products. Firstly, the pyrolysis of PUR will be conducted to reveal the emission characteristics and generative mechanism of organic halide, and to probe into the pyrolysis dynamics. Subsequently, the molten salt will be screened and used to treat PUR by the molten salt pyrolysis. Various factors on the effects of pyrolysis products yield, compositions distribution and dehalogenation efficiency will also be investigated to optimize the process. Finally, the dehalogenation mechanism will be evaluated according to the fate of halogens and the molten salt regeneration will be probed as well. This study will shed some lights on and provide a theoretical basis for the environmental-friendly disposal and recycling of other halogen-containing e-wastes, such as the non-metallic materials from waste printed circuit boards and TV housing plastic waste.

含卤电子废物由于含有氯氟烃发泡剂、溴系阻燃剂等物质，导致热解过程易产生卤代有机物和酸性气体。因此，如何有效脱卤一直以来成为制约含卤电子废物热解处理的关键。本项目拟以典型含卤电子废物---废旧冰箱聚氨酯泡沫塑料（PUR）为研究对象，采用熔盐热解技术对其进行处理，通过着力解决熔盐筛选、熔盐热解脱卤机制、熔盐再生利用等关键问题，实现卤素的脱除和热解产物的回收。首先，考察PUR的热解行为，揭示卤代有机物、酸性气体等污染物的释放特性和生成机制，探明热解动力学规律。然后，筛选熔盐进行PUR的熔盐热解，考察影响热解产物产率、组成分布以及脱卤效果的因素，优化试验参数。最后，研究卤素归趋行为，揭示熔盐热解脱卤机制，同时探索熔盐的再生利用途径。本项目研究将为废电路板非金属材料、电视机塑料外壳等其他含卤电子废物的无害化处理和深度资源化利用提供一定的理论基础。

废旧冰箱拆解产生的聚氨酯泡沫塑料（PUR）中含有CFCs类发泡剂且难以降解，增加了处理难度。热解技术为PUR的处理处置提供了一条有效途径，但是热解过程易产生卤代有机物和酸性气体，不仅腐蚀设备、污染环境，进入热解油中还会影响其精加工利用。本项目采用熔盐热解技术对其进行处理，着力解决熔盐筛选、熔盐热解脱卤机制等关键问题，实现卤素的脱除和热解产物的回收。污染物释放特性和生成机制的研究结果显示，PUR热解可分为38-400℃、400-550℃、550-1000℃三个阶段，失重分别为52%、18%、11%。对于第一阶段，随着升温速率的增大，PUR失重速率由0.72 %•min-1增至3.49 %•min-1。热解产物中除了检测到CO、NH3、H2O等小分子，还有HF、HCN、HCl等酸性气体，释放集中在400-500℃、600-700℃和500-600℃范围内。CH3F、CH3Cl、CH2F2和C2H5Cl等卤代物随着温度的升高释放强度增大，最大释放峰在600-700℃。C3H3F3O和C6H5Cl的释放强度较其他卤代物强度较弱。热解动力学研究结果显示，利用Friedman、FWO、Tang三种非模型函数法获得的活化能随着转化率0.05-0.5从163.60 kJ•mol-1增大到335.85 kJ•mol-1。DAEM法获得的平均活化能为206.80 kJ•mol-1，与FWO法获得的活化能接近。在综合考虑熔盐熔点、热稳定性、经济成本等因素的基础上筛选了摩尔比26.8%K2CO3-42.5%Li2CO3-30.6%Na2CO3的熔融盐，最低共熔点为393℃。通过设计搭建实验装置并进行PUR的熔盐热解，结果显示，气体产物除了小分子CO、NH3之外，还有HF、CH3F、CH2F2等卤代物。冷凝液中检测有C6H5Cl、C6H4Cl2、C6H6NCl等大分子卤代物。反应温度为650 ℃、进料速率4 kg/h、熔融投加量为14 mol时，PUR脱卤较好，除了CO、CO2未检测到其他产物。熔盐体系产生O22-和O2-等氧化性物质，气体产物以气泡形式在熔盐中发生气态有机物的分解和无机物的捕获。熔盐残渣主要物相为LiNaCO3、 LiK(CO3)，含有少量NaF、NaCl等，微观以不规则球形颗粒聚集体和细长针状颗粒为主，可尝试对熔盐残渣进行改性作为道路融雪剂资源化利用。