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Study on VOCs/ synergistic treatment process based on adsorption/ in-situ catalytic oxidation
基于吸附/原位催化氧化的挥发性有机化合物/ 协同处理工艺研究

Jiahao Cheng , Xiaoqing Sun , Xingxing Cheng , Zhiqiang Wang
Jiahao Cheng , Xiaoqing Sun , Xingxing Cheng , Zhiqiang Wang
a School of Energy and Power Engineering, Shandong University, Jinan 250061, China
a 山东大学能源与动力工程学院,中国济南 250061
National Engineering Laboratory for Reducing Emissions from Coal Combustion, Jinan 250061, China
燃煤减排国家工程实验室,中国济南 250061

A R T I C L E I N F O

Keywords: 关键词:

VOCs 挥发性有机化合物
Co-adsorption/in-situ catalysis Regeneration
共吸附/原位催化 再生
Selectivity 选择性

Abstract 摘要

A B S T R A C T The mechanism of synergistic treatment of VOCs and is poorly understood, it urgently needed to study the co-adsorption/in-situ catalytic oxidation mechanism. In this study, we proposed an integrated VOCs/ treatment (i-VNT) process for the adsorption/in-situ catalytic of using metal doped . The results showed that the adsorption capacity on different adsorbents in co-adsorption process appeared different degrees of reduction, especially the maximum reduction for is of , respectively. The "inhibition zone" existed in the synergistic catalytic process in as the competition for reactive oxygen species, while in , the avoided the excessive oxidation of . Finally, the adsorption intermediates, changes of surface functional groups and reaction mechanism were clarified using in situ FTIR in real time. This current research offered efficient and stable catalysts for the co-adsorption/in-situ catalytic oxidation destruction, and provided a promising strategy for the next step in the synergistic treatment of multiple pollutants in open application scenarios
A B S T R A C T VOCs 和 的协同处理机理尚不清楚,迫切需要研究共吸附/原位催化氧化机理。在这项研究中,我们利用掺杂金属的 ,提出了一种吸附/原位催化 的 VOCs/ 综合处理(i-VNT)工艺。结果表明,在共吸附过程中,不同吸附剂上的吸附容量出现了不同程度的还原,尤其是 的最大还原量分别为 。在协同催化过程中, 存在 "抑制区",作为活性氧的竞争区,而在 中, 则避免了 的过度氧化。最后,利用原位傅立叶变换红外光谱实时阐明了吸附中间产物、表面官能团的变化和反应机理。目前的研究为共吸附/原位催化氧化破坏提供了高效稳定的催化剂,并为下一步在开放应用场景中协同处理多种污染物提供了可行的策略。

1. Introduction 1.导言

Both volatile organic compounds (VOCs) and ammonia are common pollutants in the industry, with wide emissions from chemical factories, catalyst preparation, material fabrication, agricultural activities, and coal-fired sources etc. [1,2]. In the study by Amon et al. [3], emissions of and from a commercial straw flow system for fattening pigs in Upper Austria were and per pig place per year without daily manure removal. In addition, the downstream industries related to agriculture, such as rendering and dairy industry, production operations emit a significant, but as yet poorly quantified, VOC load [4]. The release of VOCs and into the open space can lead to noticeable odors and potential damage of health, such as stratospheric ozone depletion, irritation to human organ, etc. [5,6,7]. There is a great demand for the treatment of VOCs and in both indoor working spaces and open areas.
挥发性有机化合物(VOCs)和氨 是工业中常见的污染物,广泛排放于化工厂、催化剂制备、材料制造、农业活动和燃煤源等。[1,2].在 Amon 等人的研究中[3],在不每天清除粪便的情况下,上奥地利育肥猪商业秸秆流系统每年每头猪排放的 分别为 。此外,与农业相关的下游产业,如熏蒸和乳制品工业,在生产过程中也会排放大量的挥发性有机化合物,但目前尚未对其进行量化[4]。挥发性有机化合物和 释放到开放空间会产生明显的气味和潜在的健康损害,如平流层臭氧损耗、对人体器官的刺激等[5,6,7]。[5,6,7].对室内工作空间和露天场所的挥发性有机化合物和 的处理需求很大。
VOCs have garnered significant attention due to stringent environment regulations . Many different methods, such as adsorption, condensation and selective catalytic reduction, have been extensively and widely employed in their mitigation [10]. Among these methods, a widely used one to abate VOCs is adsorption-catalytic oxidation [11].
由于严格的环境法规 ,挥发性有机化合物引起了人们的极大关注。许多不同的方法,如吸附法、冷凝法和选择性催化还原法,已被广泛应用于减少挥发性有机化合物[10]。在这些方法中,吸附-催化氧化法是一种被广泛使用的减少挥发性有机化合物的方法[11]。

The adsorbent could be activated carbon or zeolites, while the catalysts typically consist of noble metals [12]. For instance, Hou et al., [13] used glycine modification to enhance the nitrogen-containing functional groups on the surface of activated carbon, resulting in an increased toluene adsorption capacity of . However, activated carbon's poor structural stability led Liu et al., [14] to used mesoporecoated zeolites to prepare molecular sieves with a core-shell structure, thus improving the adsorbents' hydrophobicity and masstransfer properties. Kim et al., [15] also improved the adsorbent's hydrophobicity and mass-transfer performance by creating an open-pore structure zeolite to accelerate the adsorbent's mass transfer capabilities.
吸附剂可以是活性炭或沸石,而催化剂通常由贵金属组成 [12]。例如,Hou 等人[13] 利用甘氨酸改性来增强活性炭表面的含氮官能团,从而将甲苯的吸附容量提高到 。然而,由于活性炭的结构稳定性较差,Liu 等人[14] 利用介孔涂层 沸石制备了具有核壳结构的分子筛,从而改善了吸附剂的疏水性和吸附性能。Kim 等人,[15] 还通过创造一种开孔结构的沸石来提高吸附剂的疏水性和传质性能,从而加速吸附剂的传质能力。
However, the control of has not received much attention at present due to fewer regulations being issued. Few treatment investigations have focused on adsorption, biological purification and catalytic decomposition. One ideal technology that can be applied is the selective oxidation of [16,17]. Common active components in catalysts include , and . For example, the catalyst prepared by Lee et al., [18] exhibits a high oxygen storage capacity and a large number of oxygen vacancies due to the high dispersion of , which improves the catalytic activity and selectivity. Qu et al., [19] loaded Ag on different carriers and found that Ag particles
然而,由于颁布的法规较少,目前对 的控制还没有引起足够的重视。很少有 处理研究集中在吸附、生物净化和催化分解方面。一种可以应用的理想技术是对 进行选择性氧化[16,17]。 催化剂中常见的活性成分包括 。例如,Lee 等人制备的 催化剂,[18] 由于 的高分散性,表现出较高的储氧能力和大量的氧空位,从而提高了催化活性和 的选择性。Qu 等人,[19] 在不同的载体上负载 Ag,发现 Ag 颗粒
Received 13 December 2023; Received in revised form 17 January 2024; Accepted 25 January 2024
2023 年 12 月 13 日收到;2024 年 1 月 17 日收到修订稿;2024 年 1 月 25 日接受
Available online 1 February 2024
2024 年 2 月 1 日上网
1383-5866/© 2024 Published by Elsevier B.V.
1383-5866/© 2024 由 Elsevier B.V. 出版。
Fig. 1. Schematic diagram of synergistic degradation of VOCs by adsorption/in-situ catalytic oxidation.
图 1.通过吸附/原位催化氧化协同降解 VOCs 的示意图
on carriers were smaller in size and more dispersed and had good low temperature characteristics selectivity at .
载体上的粒度更小、更分散,具有良好的低温特性 选择性,
It is interesting that can also be adsorbed onto many absorbents and catalytically oxidized into harmless via . Although the exact reaction mechanisms are not clear, mainstream research suggests that they may all follow the Eley-Rideal mechanism. Therefore, it would be of great interest if could be eliminated simultaneously with VOCs in the same reaction using the same absorbents/catalysts. Competition between the two for active sites as well as reactive oxygen species is bound to occur during the reaction, however, to the best of our knowledge, no prior research has been reported on the catalyst for simultaneous removal of VOCs and . Therefore, it urgently needed to study the co-adsorption/in-situ catalytic oxidation mechanism, and in this work, we aim to develop catalysts for these dual purposes.
有趣的是, 也可以吸附在许多吸收剂上,并通过 催化氧化成无害的 。虽然确切的反应机制尚不清楚,但主流研究表明,它们可能都遵循 Eley-Rideal 机制。因此,如果能使用相同的吸收剂/催化剂,在相同的反应中同时消除 和挥发性有机化合物,将是非常有意义的。在反应过程中,二者对活性位点和活性氧的竞争必然会发生,然而,据我们所知,之前还没有关于同时去除 VOCs 和 的催化剂的研究报告。因此,迫切需要对共吸附/原位催化氧化机理进行研究,在这项工作中,我们的目标是开发出具有上述双重用途的催化剂。
To make this VOCs/ abatement process more convenient and suitable for factories and workshops, an integrated VOCs/ treatment (i-VNT) process of synergistic adsorption-oxidation was further proposed, as depicted in Fig. 1. This process integrates both VOCs adsorption-oxidation processes, as well as adsorption-oxidation processes, into one reactor using only one kind of catalyst which serves as both the VOCs adsorbent and the VOCs oxidation catalyst. During the adsorption phase, ventilation is working and the surrounding air at room temperature is introduced into the reactor, where VOCs are adsorbed onto the catalyst. Once the catalyst becomes saturated, ventilation is halted, and the catalyst is heated within a sealed environment. VOCs and are then catalytically oxidized at an elevated temperature. The simultaneous removal of VOCs and , coupled with the integrated adsorption and oxidation processes, allows for a compact and easily deployable reactor suitable for various locations within factory premises, including both indoor workshops and open areas. This approach holds great promise for significantly improving air quality in industrial settings.
为了使这种 VOCs/ 减排工艺更方便、更适用于工厂和车间,进一步提出了一种 VOCs/ 协同吸附-氧化综合处理(i-VNT)工艺,如图 1 所示。该工艺将 VOCs 吸附-氧化过程和 吸附-氧化过程整合到一个反应器中,只使用一种催化剂,这种催化剂既是 VOCs 吸附剂,又是 VOCs 氧化催化剂。在吸附阶段,通风设备开始工作,室温下的周围空气被引入反应器,VOCs 被吸附在催化剂上。催化剂饱和后,通风停止,催化剂在密封环境中加热。然后,VOC 和 在高温下进行催化氧化。同时去除挥发性有机化合物和 ,再加上一体化的吸附和氧化过程,使得反应器结构紧凑,易于部署,适用于工厂内的各种场所,包括室内车间和开放区域。这种方法有望显著改善工业环境中的空气质量。

The objective of this work is to develop catalysts that could serve both as VOCs/ absorbents and VOCs/ oxidation catalysts. Pxylene will be used as a model VOCs molecule. Transition metal particles doped on will be synthesized, owing to their reported excellent VOCs and adsorption capabilities [20,21]. Various metal oxides and ), which are cost-effective and known to provide ample oxidation sites , will be impregnated onto the support to serve as oxidation catalysts. The developed catalysts will then be applied in the proposed i-VNT process to assess their performance under various conditions. The reaction mechanism of this process will also be explored.
这项工作的目的是开发既可用作 VOCs/ 吸收剂又可用作 VOCs/ 氧化催化剂的催化剂。对二甲苯将被用作 VOCs 分子模型。由于 上掺杂的过渡金属颗粒具有出色的 VOCs 和 吸附能力,因此将在 上合成过渡金属颗粒 [20,21]。各种金属氧化物 )将被浸渍到载体上,作为氧化催化剂,这些金属氧化物具有成本效益,而且已知可提供充足的氧化位点 。开发的催化剂随后将应用于拟议的 i-VNT 工艺,以评估其在各种条件下的性能。此外,还将探索该工艺的反应机理。

2. Experimental 2.实验

2.1. Catalyst preparation
2.1.催化剂制备

Metal doped catalysts were prepared using impregnation techniques. Specifically, , and ( , Macklin) were completely dissolved in deionized water as precursor salts and added to the powered . The total amount of metal doped was controlled at (if bimetallic co-doped was performed, the molar ratio was 1:1). Subsequently, the catalysts were placed in a water bath at and heated while being stirred to evaporate the surface water. Afterwards, they were transferred to a drying oven at for and finally placed in a muffle furnace at for . The prepared catalysts were labeled as , respectively.
掺杂金属的催化剂采用浸渍技术制备。具体来说, , 和 ( , Macklin) 作为前驱盐完全溶解在去离子水中,然后加入到通电的 中。掺杂金属的总量控制在 (如果进行双金属共掺杂,摩尔比为 1:1)。随后,将催化剂放入 的水浴中,边搅拌边加热,以蒸发表面水分。之后,将催化剂转移到 的干燥箱中进行 ,最后放入 的马弗炉中进行 。制备的催化剂分别标记为 , 。

2.2. Activity test 2.2.活动测试

All the catalyst adsorption and regeneration tests were conducted in a fixed bed reactor system comprising a VOCs generation system, gas distribution system, fixed-bed reactor and gas analysis system.
所有催化剂吸附和再生试验都是在固定床反应器系统中进行的,该系统包括 VOCs 生成系统、气体分配系统、固定床反应器和气体分析系统。

(c)
(d)
Fig. 2. (a) The curves of adsorbed amount versus time of single adsorption and combined adsorption at , , and ; (b) The curves of adsorbed amount versus time of single adsorption and combined adsorption at , and ; (c) Breakthrough curves of , and combined adsorption; (d) Comparison of adsorption capacity of different adsorbents at different temperatures. (Conditions: of adsorbents, , as balanced gas, and total gas flow ).
图 2. (a) 的单一吸附和组合吸附的吸附量随时间的变化曲线;(b) 的单一吸附和组合吸附的吸附量随时间的变化曲线;(c) 和组合吸附的突破曲线;(d) 不同吸附剂在不同温度下的吸附容量比较。(条件:吸附剂为 为平衡气体,气体总流量为 )。
Schematic diagrams of the setup can be found in the Fig. S. 1 in Supplementary Material. In each experiment, the adsorbent was placed into a quartz column with an inner diameter of , and the temperature was controlled using a furnace. To simulate an actual open site, air was chosen as the carrier gas, and the feed components (liquid o-xylene) rate was controlled using a syringe dosing pump (LSP01-1A) into the vaporization chamber, where the temperature was maintained at , significantly higher than the boiling point of solvent. The experiments were carried out with a concentration of of (oxylene), of , and a temperature of 200 to . The degraded gaseous components, including and , were analyzed in a real-time using a gas analyzer (PV6001-VOC-EX, Hunan Rike, China), a gas chromatograph (G901A, Huifen Instruments, China) and Fourier Infrared Spectroscopy (FT-IR).
实验装置示意图见补充材料中的图 S. 1。在每次实验中,都将吸附剂放入内径为 的石英柱中,并使用熔炉控制温度。为模拟实际的露天场所,选择空气作为载气,并使用注射器定量泵(LSP01-1A)控制进入汽化室的进料组分(液态邻二甲苯)的速率,汽化室的温度保持在 ,明显高于溶剂的沸点。实验的浓度为 of (二甲苯), of ,温度为 200 至 。使用气体分析仪(PV6001-VOC-EX,中国湖南日科)、气相色谱仪(G901A,中国汇文仪器)和傅立叶红外光谱仪(FT-IR)对降解的气体成分(包括 )进行实时分析。

2.3. Adsorbent characterization
2.3.吸附剂特征

The specific surface area and total pore volume were determined by adsorption-desorption at using specific surface analyzer (Quanta chrome Autosorb 1C, USA, and V-Sorb 4800P, CIQTEK, China) on granular samples that had been degassed at for . The modified adsorbents were characterized using a programmed chemisorption instrument (PCA-1200), and the outlet gas signals from the micro fixed bed reactor were detected by a thermal conductivity detector (TCD). Temperature programmed desorption (TPD) were performed to investigate desorption properties. All the tests were carried out at a gas flow rate of . The saturated catalyst was initially purged with for at room temperature and then heated up to at a rate of . Hydrogen temperature programmed reduction ( -TPR) was characterized for the investigation of oxidizing properties. The fresh catalysts were first purged with at for to remove surface water, cooled to , and then exposed to a / He reducing gas and heated to at a rate of . Oxygen temperature programmed oxidation ( ) were investigated to analyze the oxidizing process during the regeneration phase. The adsorbed saturated catalyst was oxidized under atmosphere, and the process was heated to at a rate of to observe the signal values at different temperatures. and -TPR were carried out on the setup in Section 2.2. After saturating the pretreated samples with adsorbent, the temperature was increased to 800 at a rate of , and the concentration of was simultaneously detected and recorded by a detector.
使用比表面分析仪(Quanta chrome Autosorb 1C,美国;V-Sorb 4800P,CIQTEK,中国)对在 进行脱气处理的粒状样品在 进行吸附-解吸,测定其比表面积 和总孔容积 。使用程序化学吸附仪(PCA-1200)对改性吸附剂进行表征,并使用热导检测器(TCD)检测微型固定床反应器的出口气体信号。为了研究解吸特性,还进行了温度编程解吸(TPD)试验。所有测试都是在 的气体流速下进行的。饱和催化剂最初在室温下用 进行吹扫,然后以 的速率加热至 。氢气温度编程还原 ( -TPR)被用于研究氧化特性。新鲜催化剂首先在 冲洗 以去除表面水分,冷却至 ,然后接触 / He 还原气体并以