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焦炉煤气净化过程产生大量脱硫废液,其COD、氨氮、硫化物依次高于100 000、20 000、2 000 mg·L−1,副盐(主要为硫氰酸盐、硫代硫酸盐和硫酸盐)约为200 g·L−1[1-2]。高浓度副盐,尤其硫氰酸盐市场需求重大,提盐工艺能够回收副盐并实现脱硫废液循环利用[3]。然而,硫氰酸盐和硫代硫酸盐溶解度差异小,导致提取的硫氰酸盐产品纯度低,故去除硫代硫酸盐成为提取高品质硫氰酸盐的关键[4]。目前,工业上多采用强氧化剂浓硫酸氧化硫代硫酸盐,其对管道和设备材质要求苛刻且反应剧烈和运行风险大。近年来,研究人员采用光催化[5-7]、电催化[8]、催化H2O2氧化技术[9]将硫代硫酸盐氧化为硫酸盐。由于脱硫废液中副盐浓度高、腐蚀性极强,故光催化和电催化局限性较大而催化湿式氧化更具可行性,但催化空气氧化硫代硫酸盐研究却鲜有报道。
碳纳米管及其衍生物因出色机械性能、电子性能及热导性而常作催化湿式氧化催化剂或载体。过渡金属元素在催化湿式氧化技术中表现出优秀催化性能。N掺杂不仅能够提高碳基催化剂活性,而且可为催化剂中金属原子配位耦合提供限域锚定位点以改善其稳定性[10]。因此,N掺杂碳纳米管作为重要碳基功能材料,已引起催化、吸附、电容器等领域广泛关注[11]。生物质取材广泛、碳含量高,成为制备N掺杂碳纳米管的良好碳源[12]。本研究以马铃薯薯渣(简称薯渣)为碳源,通过热处理技术制备铁原子限域的N掺杂碳纳米管催化剂,研究其催化空气氧化脱硫废液中硫代硫酸盐性能,以期实现薯渣高附加值资源化利用并为脱硫废液中硫代硫酸盐氧化提供参考。
基于氮掺杂碳负载铁催化剂的硫代硫酸盐催化空气氧化
Catalytic air oxidation of thiosulfate by nitrogen-doped carbon supported iron catalyst
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摘要: 焦化脱硫废液中硫代硫酸盐严重制约高品质硫氰酸盐产品提取。利用马铃薯薯渣为碳源,通过热处理技术制备氮掺杂碳负载铁催化剂(Fe-NCNT/PC),采用N2物理吸附仪、扫描电子显微镜、X射线光电子能谱对催化剂的表面积、微观形貌和表面结构特征进行了表征,考察了其对HB、LN 2种脱硫废液中硫代硫酸盐的催化空气氧化性能。结果表明,Fe-NCNT/PC具有微-介孔结构和FeNx限域结构,焙烧温度的升高会降低催化剂活性和稳定性,最适焙烧温度为700 ℃;当Fe-NCNT/PC-700用量1.5 g、氧化时间6 h时,HB、LN脱硫废液中硫代硫酸盐的去除率可达95%;脱硫废液氧化后pH显著降至酸性,Fe-NCNT/PC-700的限域结构能够防止活性组分铁流失。此外,Fe较其他过渡金属(Mn、Cu、Co、Ni)对硫代硫酸盐催化空气氧化活性更佳。Abstract: Thiosulfate in coking desulfurization waste liquid (CDWL) seriously restricts extraction of high-quality thiocyanate products. In this study, potato residue was taken as carbon source, nitrogen-doped carbon supported iron catalyst (Fe-NCNT/PC) was prepared by heat treatment technology. The specific surface area, morphology and surface structure of the catalyst were characterized by N2 physical adsorption instrument, scanning electron microscope and X-ray photoelectron spectroscopy. The catalytic air oxidation of thiosulfate in two kinds of CDWL: HB and LN, was investigated. The results showed that Fe-NCNT/PC had micro-mesoporous structure and FeNx confined structure, the activity and stability of the catalyst decreased with the increase of calcination temperature, and the optimum calcination temperature was 700 ℃. When the dosage of Fe-NCNT/PC-700 was 1.5 g and the oxidation time was 6 h, the removal rates of thiosulfate in the above two kinds of CDWL could reach 95%. After oxidation, the pH of CDWL decreased significantly to acidity, and the confined structure of Fe-NCNT/PC-700 could prevent the loss of active component iron. Besides, Fe showed a better catalytic activity for air oxidation of thiosulfate than other transition metals (Mn, Cu, Co, Ni).
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表 1 实验用焦化脱硫废液组成
Table 1. Composition of coking desulfurization waste liquid used in experiment
脱硫废液来源 NH4SCN/
(g·L−1)(NH4)2S2O3/
(g·L−1)(NH4)2SO4/
(g·L−1)pH 河北(HB) 112.16 44.17 34.24 8.7 辽宁(LN) 98.37 32.60 30.18 8.1 表 2 Fe-NCNT/PC催化剂BET比表面及孔容
Table 2. BET surface area and pore volume of catalyst Fe-NCNT/PC
催化剂 比表面积/
(m2·g−1)总孔容/
(cm3·g−1)微孔孔容/
(cm3·g−1)Fe-NCNT/PC-700 319.971 0.231 0.100 Fe-NCNT/PC-800 939.804 0.591 0.327 Fe-NCNT/PC-900 886.910 0.579 0.302 -
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