A theoretical study on adsorption-diffusion of dimethyl ether carbonylation on pyridine-modified H-MOR

doi:10.11949/0438-1157.20201921

Abstract

Abstract:

Hydrogen mordenite (H-MOR) zeolite molecular sieve is an efficient catalyst for the carbonylation of dimethyl ether (DME) to methyl acetate (MA). The modification of pyridine can effectively improve its stability and catalytic life. In order to study the essential mechanism of pyridine modification on the atomic scale, based on Monte Carlo and molecular dynamics simulations, this paper analyzes the main reactants CO, DME and products of carbonylation in the periodic models of H-AlMOR and Py-H-AlMOR, respectively. The adsorption-diffusion behavior of MA has been systematically compared. The results show that the introduction of pyridine will reduce the adsorption capacity of the main reactants CO and DME in the H-MOR molecular sieve to a certain extent (24%—33%), but it helps to improve the adsorption balance of the two in the molecular sieve and increase the concentration of reactants in the active channel 8-MR. At the same time, the introduction of pyridine will have a greater impact on the diffusion of various molecules (21%—58%), especially the diffusion performance of the product MA decreases by about 58%. In addition, the introduction of pyridine can also reduce the high feed ratio P_CO/P_DME required to achieve high reactivity.

Key words: molecular sieve, selective catalysis, catalytic activity, adsorption, diffusion, Monte Carlo simulation

摘要：

氢型丝光沸石（H-MOR）分子筛是二甲醚（DME）羰基化制乙酸甲酯（MA）的一种高效催化剂，经研究吡啶的修饰可以有效提高其稳定性及催化寿命。为了从原子尺度上研究吡啶对其改性的本质机理，基于Monte Carlo及分子动力学模拟，分别对H-AlMOR及Py-H-AlMOR周期性模型内羰基化主反应物CO、DME及产物MA的吸附-扩散行为进行了对比研究。结果表明，吡啶的引入会使H-MOR分子筛模型内主反应物CO、DME的吸附量产生一定下降（24%~33%），但有助于改善二者分子筛内的吸附平衡，并提升活性孔道8-MR内的反应物浓度。同时，吡啶引入后将对各分子扩散产生较大影响（21%~58%），尤其产物MA扩散性能下降约58%。此外，吡啶的引入也会使达到高反应活性所需的高进料比P_CO/P_DME有所降低。

关键词: 分子筛, 选择性催化, 催化活性, 吸附, 扩散, Monte Carlo模拟

CLC Number:

TQ 225

Wei WANG, Weixing QIAN, Hongfang MA, Weiyong YING, Haitao ZHANG. A theoretical study on adsorption-diffusion of dimethyl ether carbonylation on pyridine-modified H-MOR[J]. CIESC Journal, 2021, 72(9): 4786-4795.

王伟, 钱伟鑫, 马宏方, 应卫勇, 张海涛. 吡啶修饰H-MOR上二甲醚羰基化吸附-扩散理论研究[J]. 化工学报, 2021, 72(9): 4786-4795.

Figures/Tables 12

Fig.1 Diagram of unequal atoms in H-MOR molecular sieve (Si and O)

Fig.2 Diagram of Py-H-MOR (2×1×1) model for calculation (Py-Al-T1O7 as example)

Table 1 The average adsorption capacity （Nads） and adsorption energy （Eads） of the main reactants and product molecules in different periodic models in the 493 K-2.5 MPa z-axis extension direction （Al-T1O7 as an example）

分子/模型	N_ads/(mol/mol)					E_ads/(kcal/mol)
分子/模型	CO		DME	MA		CO		DME		MA
Py-H-AlMOR (2×1×1)	3.504	8.666			2.957	-5.167	-11.270		-13.085
Py-H-AlMOR (2×1×2)	7.039	17.434			6.154	-5.179	-11.421		-13.177

Fig.3 The adsorption density distribution of 129Xe at 213 K on the MOR (2×1×1) periodic model (a) NMR spectra of 129Xe under different pressures in reference experiment (b)

Fig.4 The relationship between the mean square displacement (MSD) of the CH4 molecule at 493 K and the simulation time in the MOR (2×1×1) period model

Table 2 Average adsorption capacity （Nads） and adsorption energy （Eads） of main reactants and product molecules in different acid models at 493 K-2.5 MPa

模型/分子	N_ads/(mol/mol)					E_ads/(kcal/mol)
模型/分子	CO		DME	MA		CO		DME		MA
Al-T1O7	4.531	12.815			7.550	-4.902	-12.241		-14.856
Py-Al-T1O7	3.504	8.666			2.957	-5.167	-11.270		-13.085
Al-T2O2	4.459	13.519			8.150	-4.904	-12.298		-15.772
Py-Al-T2O2	3.462	8.988			2.785	-5.198	-11.313		-13.085
Al-T3O1	4.632	12.338			7.254	-4.917	-12.328		-15.201
Py-Al-T3O1	3.432	8.695			3.107	-5.196	-11.263		-13.142
Al-T4O2	4.489	13.444			7.949	-4.893	-12.143		-14.516
Py-Al-T4O2	3.359	8.224			2.777	-5.195	-11.251		-13.062

Fig. 5 Adsorption density maps of different reactants and products molecule in different acid models at 493 K-2.5 MPa (Al-T1O7 as example)

Fig.6 The relationship between the mean square displacement (MSD) and simulation time of pure gases at 493 K (5 molecules/model)

Fig.7 Average adsorption capacity Nads of mixture under different feed ratios at 493 K-2.5 MPa in each acid model without pyridine modification

Fig.8 Average adsorption capacity Nads of mixture under different feed ratios at 493 K-2.5 MPa in each acid model with pyridine modification

Table 3 Average adsorption ratio under different feed ratios at 493 K-2.5 MPa in H-AlMOR

P_CO/P_DME	CO/DME吸附量比值
P_CO/P_DME	Al-T1O7	Al-T2O2	Al-T3O1	Al-T4O2
1∶1	0.045	0.058	0.048	0.055
2∶1	0.082	0.098	0.082	0.092
5∶1	0.227	0.222	0.302	0.280
10∶1	0.417	0.450	0.422	0.402
20∶1	0.794	0.847	0.800	0.758
27∶1(opt)	0.990	0.971	1.020	1.042
50∶1	1.754	1.724	2.000	1.754

Table 4 Average adsorption ratio under different feed ratios at 493 K-2.5 MP in Py-H-AlMOR

P_CO/P_DME	CO/DME吸附量比值
P_CO/P_DME	Py-Al- T1O7	Py-Al- T2O2	Py-Al- T3O1	Py-Al- T4O2
1∶1	0.299	0.267	0.270	0.269
2∶1	0.427	0.391	0.402	0.385
5∶1	0.934	0.855	0.926	0.926
8∶1(opt)	0.980	1.000	1.042	0.990
10∶1	1.053	1.053	1.111	1.075
20∶1	1.724	1.754	1.667	1.754
50∶1	3.571	3.448	3.226	3.226

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