11种吸附剂上二噁英的热吸附/脱附性能评价

Evaluation of thermal adsorption and desorption properties of dioxins on 11 adsorbents

筛选在低温下高效捕集并在一定的高温下可以快速完全脱附二噁英的吸附/脱附材料是二噁英在线热捕集的关键。该研究以1,2,3,4-四氯代二苯并-对-二噁英(1,2,3,4-TCDD)和1,2,3,8,9-五氯代二苯并呋喃(1,2,3,8,9-PCDF)为二噁英模型物,以电子捕获检测器(ECD)作为检测器,利用填充柱气相色谱系统,测定了这两种二噁英单体在11种吸附剂上4~5个温度点下的保留体积,并建立了相应的范特霍夫方程。结果表明,11种吸附剂的线性方程决定系数(R2)均大于0.96。根据范特霍夫方程,预测了吸附剂在120、150、180℃时的气固分配系数(KSA)。弗洛里硅土在120、150、180℃3个温度点下都具有最强的吸附能力,特别是在120℃时,1,2,3,4-TCDD、1,2,3,8,9-PCDF在弗洛里硅土上的KSA分别高达1.82×10^(8)m^(3)/g、1.46×10^(13)m^(3)/g。碳基吸附剂的高分子多孔微球GDX系列的GDX-101、GDX-102、GDX-103、GDX-105、GDX-203在最高耐受温度270℃下都可以实现二噁英的热脱附,证实了碳基吸附剂作为二噁英热吸附/脱附的吸附剂的可行性。310℃下,在丝光沸石上1,2,3,4-TCDD可实现热脱附,而1,2,3,8,9-PCDF在相同条件下无法实现热脱附,体现了沸石对二噁英同系物的选择性吸附的特性。而硅藻土和蒙脱土对气相中的二噁英几乎没有吸附能力,不适合作为二噁英热捕集的吸附剂。弗洛里硅土、硅胶、氧化铝、GDX-102、GDX-103和GDX-203对1,2,3,4-TCDD、1,2,3,8,9-PCDF都具有很强的吸附能力,因此被初步选为二噁英的候选吸附剂。通过比较120℃下和270℃下二噁英在这6种吸附剂上的ln K_(SA),发现弗洛里硅土在两个温度点下的保留体积都是最大的;在侧重低温下二噁英的热捕集性能时,弗洛里硅土是捕集二噁英的最佳吸附剂;而GDX-102是6种吸附剂中ln K_(SA,270℃)最小的,在侧重高温下二噁英的热脱附性能时,GDX-102是二噁英热脱附的最佳吸附剂。同时,硅胶、GDX-103和GDX-203的ln K_(SA,120℃)和ln K_(SA,270℃)与GDX-102相近,也可以作为快速热吸附/脱附的材料。该文通过系统评价1,2,3,4-TCDD和1,2,3,7,8-PCDF在11种吸附剂的热吸附/脱附性能,对简化二噁英的采样和制备过程提供了新的解决思路,为实现二噁英的热捕集提供了技术支撑。

The key to the online thermal capture of dioxins is the appropriate choice of adsorbent for efficient capture at low temperatures and rapid desorption at high temperatures.Efficient adsorbents can allow for capture and separation during the online monitoring of dioxins or during offline dioxin tests.In this study,1,2,3,4-tetrachlorodibenzo-p-dioxin(1,2,3,4-TCDD)and pentachlorodibenzofuran(1,2,3,8,9-PCDF)were used as model compounds for dioxin monomers,and an electron capture detector(ECD)was used to detect the dioxin signals.The retention volumes of 1,2,3,4-TCDD and 1,2,3,8,9-PCDF on 11 types of adsorbents were determined using a packed-column gas chromatography system.Then,the corresponding van der Hoff equation was established,and these adsorbents were evaluated for the thermal trapping of dioxin.The linear coefficients of determination(R2)of these adsorbents were greater than 0.96,which indicated a strong correlation between the adsorption capacity and 1/T(T:temperature).The gas-solid partition coefficients(KSA)of the adsorbent at 120,150 and 180℃were predicted according to the van der Hoff equation,which was obtained in an earlier study.Among the 11 adsorbents,florite had the largest adsorption capacity at 120,150,and 180℃,especially at 120℃;the KSA values for 1,2,3,4-TCDD and 1,2,3,8,9-PCDF on florite were as high as 1.82×10^(8)m^(3)/g and 1.46×10^(13)m^(3)/g,respectively.Carbon-based adsorbents of the Chinese stilbene polymer porous microspheres GDX series,GDX-101,GDX-102,GDX-103,GDX-105,and GDX-203,can facilitate thermal desorption below 270℃,which is the maximum tolerance temperature for series 1 and 2,thus providing evidence for the feasibility of using these adsorbents for the thermal adsorption/desorption of dioxins.When the detection temperature is less than 310℃,1,2,3,4-TCDD is thermally desorbed from mordenite,but 1,2,3,8,9-PCDF is not;this indicates the selective adsorption of dioxin monomers on zeolite.However,diatomite and montmorillonite have poor adsorption capacity for dioxins in the gas phase,thus being unsuitable for the thermal trapping of dioxins.Florite,silica gel,alumina,GDX-102,GDX-103,and GDX-203,which have strong adsorption capacities,were selected as possible absorbents for the next evaluation.Comparison of the ln K_(SA)values of dioxin monomers on the same adsorbent at 120℃and 270℃revealed that the retention volume of florite was the largest at both temperatures.When the thermal trapping performance of dioxin at low temperatures is considered,florite is thought to be the best among the 11 adsorbents for capturing dioxins.However,when the desorption performance at high temperatures is considered,GDX-102 is the best adsorbent for the thermal desorption of dioxins,and its ln K_(SA,270℃)is the smallest among those for the aforementioned six adsorbents.The ln K_(SA,120)℃and ln K_(SA,270℃)values of silica gel,GDX-103,and GDX-203 are similar to those of GDX-102,and hence,they can also be used as rapid thermal adsorption/desorption materials.In this study,the thermal adsorption/desorption properties of 1,2,3,4-TCDD and 1,2,3,7,8-PCDF on 11 adsorbents were systematically evaluated to obtain a new solution for the sampling and preparation of dioxins and to provide technical support for the thermal capture of dioxins.It should be noted that these results were obtained under ideal conditions of nitrogen,without considering the influence of the complex conditions of flue gas(such as moisture and CO_(2))on the thermal capture.To achieve the thermal capture of dioxins in incineration flue gas,it is necessary to carry out the relevant evaluation and test research in a flue gas atmosphere.