Mechanism of solvent effect on hydrogenation of lignin-derived phenolic compounds

doi:10.11949/0438-1157.20220826

Abstract

Abstract:

In this paper, the effect of solvent effect on hydrogenation of lignin phenolic compounds in Ru/C and Al₂O₃ catalyst systems was systematically studied. In ethanol solvent, phenol can be completely converted into cyclohexanol at 35℃, which exhibited the best hydrogenation effect. The research showed that the hydrogenation effect of polar solvent was better than nonpolar solvents, because the catalyst enabled to be evenly dispersed in the polar solvent, which strengthened the mass transfer and diffusion of the catalyst and the reactants. This study also established the relationship between Kamlet-Taft expression parameters and the conversion rate of phenol, and the effect of each parameter was analyzed. Besides, this work also elaborated the detailed phenol hydrogenation reaction pathway and mechanism in Ru/C and Al₂O₃ catalytic system. The catalytic system was also applied to the hydrogenation of other lignin-derived phenolic model compounds, which also achieved a good result. Most of the phenolic compounds were transformed into corresponding cyclic alcohols through hydrogenation with a high stability.

Key words: solvent, phenolic compounds, hydrogenation, catalyst, polar solvents

摘要：

系统研究了木质素酚类化合物在Ru/C和Al₂O₃催化体系下溶剂效应对加氢反应的影响。在乙醇溶剂中，苯酚在35℃下即可完全转化为环己醇，具有最佳的加氢效果。研究表明极性溶剂比非极性溶剂的加氢效果更好，是因为催化剂分散均匀，强化了催化剂和反应物间的传质与扩散。在醇类极性溶剂中，乙醇的加氢反应效率最高，对比研究显示溶剂的极性越强，苯酚加氢的转化效果越好。还建立了Kamlet-Taft表达式参数与苯酚转化率间的关系关联式，分析了各参数的影响效果，详细阐述了Ru/C和Al₂O₃催化体系下详细的苯酚加氢反应路径和机理，并将该催化体系应用于其他木质素酚类化合物的加氢反应，也取得了很好的反应效果，大部分木质素酚类化合物均加氢饱和转化成稳定的环状醇类化合物。

关键词: 溶剂, 酚类化合物, 加氢, 催化剂, 极性溶剂

CLC Number:

O 643

Hongyun YOU, Jingjun LIN, Kaiyue HUANG, Riyang SHU, Zhipeng TIAN, Chao WANG, Ying CHEN. Mechanism of solvent effect on hydrogenation of lignin-derived phenolic compounds[J]. CIESC Journal, 2022, 73(10): 4498-4506.

尤红运, 林景骏, 黄凯越, 舒日洋, 田志鹏, 王超, 陈颖. 溶剂效应对木质素酚类化合物加氢反应的影响机理[J]. 化工学报, 2022, 73(10): 4498-4506.

Figures/Tables 8

Table 1 The effect of different catalysts on the phenol hydrogenation

序号	催化剂	转化率/%	选择性/%
序号	催化剂	转化率/%	环己醇	环己酮
1	Ru/C	14.6	95.9	4.1
2	Ru/C + WO₃	6.2	93.6	6.4
3	Ru/C + Nb₂O₅	9.2	94.1	5.9
4	Ru/C + ZrO₂	13.7	96.1	3.9
5	Ru/C + TiO₂	23.2	97.5	2.5
6	Ru/C + HPW	2.1	84.7	15.3
7	Ru/C + HSiW	2.2	86.5	13.5
8	Ru/C + Al₂O₃	100	100	0
9	Ru/C + Al₂O₃^①	69.8	99.1	0.9
10	Ru/C + Al₂O₃^②	30.4	98.0	2.0
11	Al₂O₃	0	—	—

Fig.1 （a）Py-IR spectra of Al2O3 (desorption temperature 150℃)；（b）XRD pattern of the Ru/C catalyst；（c）TEM images of the Ru/C catalyst

Table 2 The phenol hydrogenation results of different solvents

序号	溶剂	转化率/%	选择性/%
序号	溶剂	转化率/%	环己醇	环己酮
1	正己烷	17.6	81.2	18.8
2	正辛烷	25.7	84.7	15.3
3	正十二烷	20.2	86.3	13.7
4	甲醇	24.6	97.9	2.1
5	乙醇	100	100	0
6	正丙醇	57.1	100	0
7	正丁醇	52.6	95.4	4.6
8	正己醇	31.0	97.2	2.8
9	正辛醇	14.4	91.3	8.7

Fig.2 Different solvents after adding catalyst for 4 h

Table 3 The property parameters of some organic solvents and conversion of phenol hydrogenation

溶剂	$E T (30)$	$E T N$	π*	α	β	转化率/%
甲醇	55.4	0.7647	0.60	0.98	0.66	24.6
乙醇	51.9	0.6563	0.54	0.86	0.75	100
正丙醇	50.7	0.6192	0.52	0.84	0.90	57.1
正丁醇	50.2	0.6037	0.47	0.84	0.84	52.6
正己醇	48.8	0.5604	0.40	0.80	0.84	31.0
正辛醇	48.3	0.5449	0.40	0.77	0.81	14.4

Table 3 The property parameters of some organic solvents and conversion of phenol hydrogenation

溶剂	$E T (30)$	$E T N$	π*	α	β	转化率/%
甲醇	55.4	0.7647	0.60	0.98	0.66	24.6
乙醇	51.9	0.6563	0.54	0.86	0.75	100
正丙醇	50.7	0.6192	0.52	0.84	0.90	57.1
正丁醇	50.2	0.6037	0.47	0.84	0.84	52.6
正己醇	48.8	0.5604	0.40	0.80	0.84	31.0
正辛醇	48.3	0.5449	0.40	0.77	0.81	14.4

Fig.3 （a）Variation of phenol conversion with time in different solvents；（b）Product distribution of phenol hydrogenation in ethanol solvent；（c）Product distribution of phenol hydrogenation in n-propanol solvent；（d）Product distribution of phenol hydrogenation in octane solvent

Fig.4 Proposed reaction mechanism of phenol hydrogenation

Table 4 Catalytic hydrogenation of other phenolic model compounds

转化率/%	选择性/%
100	7.7	92.3
100	7.8	92.2
100	2.7	94.9	2.4
100	9.8	90.2
100	10.3	89.7
65.5	100
39.4	100

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