Study on capture reaction of free radicals in pyrolysis reaction based on Py-GC/MS

doi:10.11949/0438-1157.20210907

Abstract

Abstract:

In this study, the mechanism of co-pyrolysis of the coal-like model compound 1-naphthyl methanol and isotope tracer was studied at 500℃. The pyrolysis process is carried out by using a thermal cracker, and then mass spectrometry is used to detect the product to infer the reaction and change behavior of free radicals. The results show that the free radical reaction dominates the pyrolysis process at 500℃, and this behavior is more pronounced. Through the isotope labeling method and spin trapping technology, the hydrogen radicals were successfully captured. The transformation process of the conversion of 1-naphthyl methanol to 1-naphthaldehyde is revealed, and it is found that the substituents on the benzene ring play an important role in the thermal process of 1-naphthyl methanol. At the same time, qualitative and semi-quantitative analysis of free radicals and products was carried out, and it was found that the abundance of products after the addition of free radical traps was an order of magnitude lower than before, indicating that the free radical traps inhibited the formation of products.

Key words: pyrolysis, model, Py-GC/MS, free radicals, radical scavenger

摘要：

在500℃下对类煤模型化合物1-萘甲醇与同位素示踪剂的共热解进行了机理研究。利用Py-GC/MS进行快速产物检测，同时联合自由基捕获剂来推断自由基的反应过程。结果表明，在500℃和0.2 min的条件下，1-萘甲醇的热解产物相对单一，但是自由基反应的引发、交换和湮灭极其快速，现有检测方法是对某一时间节点的平衡反应结果的分析。通过D₂O和H₂¹⁸O同位素示踪，成功捕获到了自由基交换后的D取代产物和¹⁸O取代产物。揭示了1-萘甲醇经过1-萘甲基自由基转化为1-萘甲醛的转化过程，发现萘环上的取代基在1-萘甲醇的热解过程中起着重要作用。同时对自由基及产物进行了定性和半定量分析，发现在加入自由基捕获剂后产物的丰度较之前降低了一个数量级，说明了自由基捕获剂抑制了产物的生成。

关键词: 热解, 模型, 热解气相色谱质谱联用, 自由基, 自由基捕获剂

CLC Number:

TQ 028.8

Ziteng LUO, Qiucheng ZHOU, Yulu WANG, Yinshang XI, Anning ZHOU, Fuxin CHEN. Study on capture reaction of free radicals in pyrolysis reaction based on Py-GC/MS[J]. CIESC Journal, 2022, 73(2): 914-922.

罗紫藤, 周秋成, 王雨露, 席引尚, 周安宁, 陈福欣. 基于Py-GC/MS研究热解反应中自由基的捕获反应[J]. 化工学报, 2022, 73(2): 914-922.

Figures/Tables 10

Table 1 The main experimental instruments and equipments

仪器与设备	型号	生产厂家
电子天平	CPA225D	赛多利斯科学仪器（北京）有限公司
气相色谱-质谱联用仪	7890A/5975C型	美国Agilent公司
热裂解仪	Py-2020is	日本FRONTIER LAB

Table 2 Experimental sample

模型化合物	加入量/mg	同位素示踪剂	加入量/μl	自由基捕获剂	加入量/mg
1-萘甲醇	0.01	水	2	—	—
		D₂O	2	—	—
		H₂¹⁸O	2	—	—
		水	2	TCNQ	0.01
		D₂O	2	TCNQ	0.01
		H₂¹⁸O	2	TCNQ	0.01

Fig.1 TiC diagram of 1-naphthyl methanol co-pyrolysis with water at different temperatures

Table 3 The main pyrolysis product of 1-naphthyl methanol and H2O

序号	热解产物	保留时间/min
1	萘	5.581
2	1-甲基萘	6.522
3	1-萘甲醛	7.826
4	1-萘甲醇	8.260
5	9-芴酮	9.238
6	9-methylene-9H-fluorene	9.538

Fig.2 TIC of 1-naphthyl methanol pyrolysis under different treatment conditions

Fig.3 Pyrolysis mass spectrometry: standard mass spectrometry and isotopic mass spectrometry

Fig.4 TIC of 1-naphthyl methanol pyrolysis under different treatment conditions

Fig.5 Pyrolysis mass spectrometry of 2-phenylmalononitrile: standard mass spectrometry and isotopic mass spectrometry

Fig.6 Schematic diagram of free radical capture of TCNQ

Fig.7 Pyrolysis mechanism diagram of 1-naphthyl methanol

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