Abstract:

Activated carbon adsorption is an efficient approach to the purification of industrial organic waste gases containing volatile organic compounds (VOCs). However, it is common that activated carbon adsorbed with VOCs is difficult to be completely desorbed, especially in the purification of exhaust gases containing styrene and butadiene, in which the adsorption capacity of activated carbon decreases significantly after desorption. This paper conducted a critical survey on the state-of-the-art of research on activated carbon adsorption/desorption in recent years, and then summarized the reasons for the decay of adsorption performance of activated carbon, identified the species in the heel substances, as well we discussed heel formation mechanism with aim to clarify the influencing factors. The results indicated that the adsorbed VOCs formed heel and block the pore through pyrolysis, coupling, polymerization, thermal oxidation reactions and chemisorption during the cyclic adsorption/desorption process of activated carbon. Heel may be chemisorbed species, semi-coke/coke and polymers. Factors including high adsorption temperatures, low regeneration heating rates, high purge gas flow rates, VOCs with high boiling points and large kinetic diameters and activated carbons with high microporosity may result in the heel formation; meanwhile, it was difficult to figure out the influence of desorption temperatures, oxygen impurities in desorption purge gas, molecular structure of VOCs, activated carbon surface oxygen groups and inorganic composition at present. More efficient regeneration methods, directional preparation and modification of activated carbon may be the technical ways to mitigate heel in activated carbon during VOCs purification.

Key words: VOCs, activated carbon, heel, mechanism, influencing factor

摘要：

活性炭吸附是含挥发性有机物（volatile organic compounds，VOCs）工业有机废气净化的有效方法。然而，在实际应用中常见吸附了VOCs的活性炭难以完全脱附，尤其是在净化含苯乙烯、丁二烯等成分的废气时甚至出现脱附后活性炭吸附容量大幅衰减的现象。本文评价近年来活性炭吸/脱附的研究进展，梳理活性炭吸附性能衰减的原因，识别活性炭孔隙堆积物种类和探讨堆积物的形成机制，以厘清影响堆积形成的关键因素。结果表明，被吸附的VOCs在活性炭循环吸/脱附过程中通过热解、偶联、聚合、热氧化反应及化学吸附等方式形成堆积物，堵塞孔道，堆积物可能是化学吸附物种、半焦/焦炭和聚合物；其中高吸附温度、低再生升温速率、高吹扫气流速、高沸点及动力学直径较大的VOCs和高微孔率的活性炭更易导致堆积形成；脱附温度、再生吹扫气含氧量、VOCs分子结构、活性炭表面官能团及无机成分对堆积的影响还未有定论。研究开发高效再生方法、活性炭定向制备与改性或是缓解堆积的技术途径。

关键词: 挥发性有机物, 活性炭, 堆积, 机制, 影响因素