聚合离子液体设计及催化环己烷选择性氧化性能研究

doi:10.11949/0438-1157.20231301

摘要/Abstract

摘要：

以乙烯基咪唑为单体，添加不同量的引发剂，采用常规热聚合中自由基聚合的方式，合成了不同分子量的聚乙烯基咪唑，热重（TG）分析表明该聚合物具有良好的热稳定性。采用季铵化反应，对最优聚合物进行1-氯代十八烷、1-氯代十二烷以及1-氯代正己烷三种不同烷基链长度的取代，合成系列聚合离子液体（PIL）。通过傅里叶红外光谱（FT-IR）、扫描电子显微镜（SEM）、X射线光电子能谱（XPS）、接触角等表征手段分析了聚合离子液体的化学结构及形貌特征，并考察了PIL-C₁₈、PIL-C₁₂、PIL-C₆催化环己烷选择性氧化为己二酸的性能，进而选取PIL-C₁₂深入研究了离子率对催化性能的影响规律。结果表明，烷基链段长度以及离子率可以有效调控亲疏水性和反应活性位点，进而提高反应性能，使得反应生成己二酸的转化率达到21.8%，选择性为41.5%。

关键词: 聚合离子液体, 离子率, 环己烷, 催化, 氧化

Abstract:

Different molecular weights of poly(vinylimidazole) were synthesized by using vinyl imidazole as a monomer and different amounts of initiators. Thermogravimetric (TG) analysis showed that the polymer had good thermal stability. A series of polymeric ionic liquids (PIL) were synthesized by quaternization of the optimal polymer with three different alkyl chain lengths: 1-chlorooctadecane, 1-chlorododecane, and 1-chlorohexane. The chemical structure and morphology of the polymeric ionic liquids were analyzed by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle testing. The catalytic performance of PIL-C₁₈, PIL-C₁₂, and PIL-C₆ for selective cyclohexane oxidation was investigated. Furthermore, PIL-C₁₂ was selected to conduct in-depth research on the influence of ion rates (PIL-C₁₂-X, X=10, 25, 50, 75, 100) on catalytic performance. The results showed that the length of alkyl chain segment and the ionic ratio could effectively influence the hydrophobicity and active site of the catalysts to improve the performance with the conversion of 21.8% and selectivity of 41.5% for cyclohexane oxidation to adipic acid.

Key words: polymeric ionic liquids, ionic rate, cyclohexane, catalytic, oxidation

中图分类号:

O 26

王瑞瑞, 金颖, 刘玉梅, 李梦悦, 朱胜文, 闫瑞一, 刘瑞霞. 聚合离子液体设计及催化环己烷选择性氧化性能研究[J]. 化工学报, 2024, 75(4): 1552-1564.

Ruirui WANG, Ying JIN, Yumei LIU, Mengyue LI, Shengwen ZHU, Ruiyi YAN, Ruixia LIU. Study on design of polymeric ionic liquids and the performance for selective oxidation of cyclohexane[J]. CIESC Journal, 2024, 75(4): 1552-1564.

图/表 13

表1 VIM与AIBN的具体用量

Table 1 Specific consumption of VIM and AIBN

VIM/g	DMF/ml	AIBN/mg
2	8	0.9
2	8	1.9
2	8	4.8
2	8	7.6

图1 PVIM的合成过程以及不同烷基链长度的离子化

Fig.1 The synthesis process of PVIM and ionization of different alkyl chain lengths

表2 聚合物数据

Table 2 Data of polymer

聚合物	M_n	PDI	Y/%
PVIM-M₁	12320	1.8	94.3
PVIM-M₂	15320	2.2	93.4
PVIM-M₃	16040	2.7	83.2
PVIM-M₄	19830	2.9	80.9

图2 不同PVIM的1H NMR、FT-IR、XRD谱图及SEM图

Fig.2 1H NMR spectrum, FT-IR spectra, XRD patterns and SEM images of different PVIM

图3 N2气氛下100~650℃的不同分子量的PVIM的热重分析结果

Fig.3 Thermogravimetric analysis results of PVIM with different molecular weights from 100—650℃ in N2 atmosphere

表3 不同分子量聚合物对环己烷氧化的影响

Table 3 Effect of different molecular weights on cyclohexane oxidation

Entry	Catalysts	Con/%	Sel/%
Entry	Catalysts	Con/%	K	A	KA	AA	Others
1	blank	0	0	0	0	0	0
2^①	VIM	2.8	51.9	35.4	87.4	10.1	2.6
3^①	PVIM-M₁	7.6	27.7	18.7	46.4	37.7	15.9
4^①	PVIM- M₂	8.1	28.1	21.6	49.7	31.2	19.1
5^①	PVIM- M₃	9.1	36.8	28.9	65.7	27.2	7.2
6^①	PVIM- M₄	10.9	35.0	19.7	54.7	34.3	11.1
7 ^②	VIM	4.4	24.3	16.4	40.7	40.0	19.3
8^②	PVIM-M₁	11.3	23.1	16.6	39.7	47.7	15.9
9^②	PVIM- M₂	11.9	34.0	20.7	54.7	37.2	7.2
10^②	PVIM- M₃	13.5	22.7	13.7	36.4	34.3	11.1
11^②	PVIM- M₄	12.3	24.4	16.3	40.7	41.2	19.2

图4 不同烷基链和不同离子率的聚合离子液体的红外光谱图和XRD谱图

Fig.4 IR spectra and XRD patterns of PIL with different alkyl chain and different ionic rate

图5 不同催化剂的SEM图

Fig.5 SEM images of different catalysts

图6 不同催化剂的反应性能对比，温度对反应性能的影响及其循环实验反应性能对比（反应条件：25 mmol CH，0.02 g PIL，1.5 MPa O2，2 ml MeCN，130℃，2 h）

Fig.6 The performance of different catalysts, effect of the temperature on the performance, and the cycle experiment of PIL-C12-100

表4 本工作催化剂与已报道催化剂的环己烷氧化性能比较

Table 4 Comparison of the cyclohexane oxidation performance of catalysts in this work and other previously reported catalysts

Entry	Catalyst	Reaction conditions	Cyclohexane conversion/%	Selectivity of AA/%	Ref.
1	1% Au-Pd/TiO₂	150℃, 1.0 MPa O₂, 4 h	21.0	34.0	[34]
2	FeALPO-31	130℃, 1.5 MPa air, 24 h	7.7	31.3	[35]
3	CoCl₁₆Pc	70℃, 5.5 MPa O₂, 8 h	18.0	23.9	[36]
4	[(C₁₈H₃₇)₂N(CH₃)₂]₆Mo₇O₂₄	160℃, 1.0 MPa O₂, 6 h	10.2	87.1	[37]
5	CeO₂	110℃, 2.0 MPa O₂, 6 h	18.2	35.0	[38]
6	1% Mn-HTS	140℃, 1.0 MPa O₂, 6 h	13.4	57.5	[39]
7	Cu-20 min/a-C₃N₄	140℃, 20.0 bar O₂, 4 h	17.7	55.0	[40]
8	Co/C₃N₄-0.02	130℃, 1.0 MPa O₂, 6 h	9.1	38.0	[41]
10	PIL-C₁₂-100	130℃, 1.5 MPa O₂, 2 h	21.7	41.2	this work

图7 不同催化剂的XPS谱图

Fig.7 XPS spectra of different catalysts

图8 不同催化剂的接触角

Fig.8 Contact angles of different catalysts

图9 不同催化体系中不同清除剂对反应性能的影响

Fig.9 Effect of different scavengers on performance in different catalytic system

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