Density functional theory study on thermal cracking reaction mechanism of phenolic resin

doi:10.11949/0438-1157.20221063

Abstract

Abstract:

2,2'-Methylene diphenol was selected as the model compound of phenolic resin, and density functional theory (DFT) was used to predict the reaction trend from the perspective of atomic activity and chemical bond level, proposed the reaction path, and combined kinetic and thermodynamic analysis to determine the priority of each pathway and the mechanism of product formation. The results show that: due to the high activity of phenolic hydroxyl groups and methylene groups, the cracking of phenolic resin first occurs by dehydration condensation reaction. Methylene bridge cleavage is the main initial cracking reaction, mainly generating phenol and o-cresol. It is dissociated into ^•OH, and the methylene group is oxidized by ^•OH in the subsequent reaction, and phenol, CO and CO₂ are generated by decarbonylation and carboxyl reaction. For the cracking process of boron-modified phenolic resin, the results show that the B—O bond in the boronate structure has low activity, is not easy to break, and has enhanced thermal stability. The methylene bridge is more stable and the tendency of decarbonylation and carboxyl group is obviously weakened, and the kinetic analysis shows that its energy barrier is increased, indicating that the introduction of boron can effectively improve its thermal stability and carbon residue rate.

Key words: phenolic resin, pyrolysis, DFT, atomic activity, chemical bond order

摘要：

选取2,2'-亚甲基二酚作为酚醛树脂的模型化合物，采用密度泛函理论（DFT），从原子活性和化学键级的视角预测反应趋势，提出反应路径，结合动力学和热力学分析确定各路径优先顺序和产物生成机理。结果表明：由于酚羟基与亚甲基的高活性，酚醛树脂的裂解首先发生脱水缩合反应；亚甲基桥断裂是主要的初始裂解反应，主要生成苯酚及邻甲酚；高活性的酚羟基易解离成 ^• OH，后续反应中亚甲基被 ^• OH氧化，经脱羰基和羧基反应生成苯酚、CO和CO₂。对于硼改性酚醛树脂的裂解过程，结果显示：硼酸酯结构中的B—O键活性很低，不易断裂，热稳定性增强。亚甲基桥更稳定且脱羰基和羧基的趋势明显减弱，且动力学分析发现其能垒均有增加，表明硼的引入能有效提高其热稳定性和残炭率。

关键词: 酚醛树脂, 热解, DFT, 原子活性, 化学键级

CLC Number:

TQ 323.1

Na ZHANG, Helin PAN, Bo NIU, Yayun ZHANG, Donghui LONG. Density functional theory study on thermal cracking reaction mechanism of phenolic resin[J]. CIESC Journal, 2023, 74(2): 843-860.

张娜, 潘鹤林, 牛波, 张亚运, 龙东辉. 酚醛树脂热裂解反应机理的密度泛函理论研究[J]. 化工学报, 2023, 74(2): 843-860.

Figures/Tables 11

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	Species	Structure parameter
	Species	Bond length/Å	Bond angle/(°)	Dihedral angle/(°)
R		R(3,4) 1.4129 R(3,24) 1.5263 R(6,10) 1.0856 R(11,16) 1.4053	A(6,1,7) 120.5751 A(2,3,24) 119.9444 A(3,4,20) 123.7277 A(12,11,17) 119.7931	D(7,1,6,10) -0.1032 D(8,2,3,4) -179.5135 D(24,3,4,5) -177.5334 D(4,3,24,25) 37.4906
TS1a		R(1,7) 1.0847 R(2,8) 1.0872 R(3,21) 1.4603 R(11,16) 1.4039	A(3,4,20) 108.8091 A(21,3,24) 89.6951 A(4,5,6) 116.4379 A(12,13,14) 118.4517	D(2,3,4,20) -149.7406 D(4,3,24,26) 90.1564 D(21,4,5,9) -113.5019 D(15,16,24,3) 65.6825
1-i1		R(2,8) 1.0868 R(3,21) 1.1056 R(3,24) 1.5676 R(6,10) 1.087	A(3,2,8) 116.7196 A(4,3,21) 105.3531 A(21,3,24) 104.907 A(12,11,16) 121.5719	D(7,1,2,3) 178.9128 D(8,2,3,4) -174.8452 D(21,3,4,20) -69.4398 D(21,3,24,26) 179.7412
P₄		R(6,28) 1.4711 R(13,15) 1.3738 R(19,23) 1.0851 R(22,24) 1.3993	A(6,1,7) 117.5481 A(2,3,9) 121.2674 A(13,14,17) 125.9009 A(17,18,20) 119.1459	D(7,1,6,28) 0.018 D(9,3,4,5) -179.895 D(5,4,12,13) -179.9181 D(14,17,19,23) -0.5538
P₅		R(4,12) 1.3987 R(6,28) 1.4911 R(13,14) 1.3956 R(22,24) 1.3993	A(6,1,7) 119.0185 A(3,4,12) 125.829 A(17,18,20) 119.1356 A(18,20,25) 119.5079	D(7,1,2,3) -177.9088 D(8,2,3,9) 0.5803 D(4,5,10,11) -1.8132 D(14,13,15,16) -2.0753
P₆		R(3,24) 1.4668 R(11,16) 1.4076 R(14,25) 1.4006 R(26,27) 1.3968	A(5,4,20) 117.4778 A(12,11,16) 121.0413 A(14,15,22) 119.9191 A(26,28,29) 119.5608	D(8,2,3,24) 0.9432 D(5,4,20,21) 177.2876 D(17,11,12,13) 179.3928 D(22,15,16,11) -177.754

	Species	Structure parameter
	Species	Bond length/Å	Bond angle/(°)	Dihedral angle/(°)
R		R(3,4) 1.4129 R(3,24) 1.5263 R(6,10) 1.0856 R(11,16) 1.4053	A(6,1,7) 120.5751 A(2,3,24) 119.9444 A(3,4,20) 123.7277 A(12,11,17) 119.7931	D(7,1,6,10) -0.1032 D(8,2,3,4) -179.5135 D(24,3,4,5) -177.5334 D(4,3,24,25) 37.4906
TS1a		R(1,7) 1.0847 R(2,8) 1.0872 R(3,21) 1.4603 R(11,16) 1.4039	A(3,4,20) 108.8091 A(21,3,24) 89.6951 A(4,5,6) 116.4379 A(12,13,14) 118.4517	D(2,3,4,20) -149.7406 D(4,3,24,26) 90.1564 D(21,4,5,9) -113.5019 D(15,16,24,3) 65.6825
1-i1		R(2,8) 1.0868 R(3,21) 1.1056 R(3,24) 1.5676 R(6,10) 1.087	A(3,2,8) 116.7196 A(4,3,21) 105.3531 A(21,3,24) 104.907 A(12,11,16) 121.5719	D(7,1,2,3) 178.9128 D(8,2,3,4) -174.8452 D(21,3,4,20) -69.4398 D(21,3,24,26) 179.7412
P₄		R(6,28) 1.4711 R(13,15) 1.3738 R(19,23) 1.0851 R(22,24) 1.3993	A(6,1,7) 117.5481 A(2,3,9) 121.2674 A(13,14,17) 125.9009 A(17,18,20) 119.1459	D(7,1,6,28) 0.018 D(9,3,4,5) -179.895 D(5,4,12,13) -179.9181 D(14,17,19,23) -0.5538
P₅		R(4,12) 1.3987 R(6,28) 1.4911 R(13,14) 1.3956 R(22,24) 1.3993	A(6,1,7) 119.0185 A(3,4,12) 125.829 A(17,18,20) 119.1356 A(18,20,25) 119.5079	D(7,1,2,3) -177.9088 D(8,2,3,9) 0.5803 D(4,5,10,11) -1.8132 D(14,13,15,16) -2.0753
P₆		R(3,24) 1.4668 R(11,16) 1.4076 R(14,25) 1.4006 R(26,27) 1.3968	A(5,4,20) 117.4778 A(12,11,16) 121.0413 A(14,15,22) 119.9191 A(26,28,29) 119.5608	D(8,2,3,24) 0.9432 D(5,4,20,21) 177.2876 D(17,11,12,13) 179.3928 D(22,15,16,11) -177.754

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