Monte Carlo simulation of propylene/propane adsorption thermodynamics on molecular sieves
ZHAO Li1,2,3, HE Chang1,2,3, SHU Yidan1,2,3, CHEN Qinglin1,2,3, ZHANG Bingjian1,2,3
1. School of Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; 2. Guangdong Engineering Centre for Petrochemical Energy Conservation, Guangzhou 519028, China; 3. The Key Laboratory of Low-carbon Chemistry & Energy Conservation of Guangdong Province, Sun Yat-sen University, Guangzhou 510006, China.
Abstract：The separation of propylene (C3H6) and propane (C3H8) is crucial in the chemical industry. Compared with the existing distillation technology, adsorption separation technology saves a remarkable amount of energy and has recently attracted much attention. Furthermore, molecular sieves with uniform channels are promising for separating olefin and alkane mixtures. Thus, considering the convenience, separation speed, and reliability, molecular simulations can provide microscopic information that is difficult to obtain using conventional experiments and play a key role in adsorption material screening. This study systematically studied the adsorption of C3H6 and C3H8 and their binary mixtures using DD3R, ITQ-32, Si-CHA, Si-SAS, ITQ-12, and ITQ-3 molecular sieves to discover potential adsorbents for separating C3H6/C3H8binary mixtures. In this study, COMPASS, CVFF, and universal force fields are selected to optimize C3H6 and C3H8, respectively; furthermore, the accuracy of the force fields is verified using the charge distribution. Grand canonical Monte Carlo (GCMC) simulations are used to simulate the adsorption of C3H6 and C3H8 on six molecular sieves with 8-ring channels. The GCMC simulations are run for 1.1×107 cycles, with 1×106 cycles for equilibration and the remaining cycles for ensemble average. To explore the adsorption properties of C3H6 and C3H8, their adsorption capacities and isosteric adsorption heats on six molecular sieves are simulated at 300 K and 101 kPa, respectively. Since an adsorption isotherm can reflect the adsorbate-adsorbent interaction, the adsorption isotherm of C3H6 and C3H8on six molecular sieves at 300 K and 1-101 kPa are simulated. Moreover, the Langmuir, Freundlich, Dubbinin-Radushkevich(D-R), and Temkin models are used to fit the adsorption isotherms and explore the adsorption mechanism. The adsorption isotherms of C3H6 and C3H8 on Si-SAS at 250, 270, 290, 300, 310, and 330 K are simulated to examine the temperature effect. The adsorption capacities and isosteric adsorption heat of C3H6/C3H8 binary mixtures at 300 K and 101 kPa are simulated, and the selectivity is determined to find excellent adsorbents to separate these mixtures. The relationships between equilibrium selectivity and the difference in isosteric adsorption heat ΔQst, as well as the adsorption capacity of C3H6 and total pore volume, are further investigated. The simulation results revealed that:(1) the adsorption capacities of C3H6 and C3H8 on Si-CHA and Si-SAS molecular sieves were high. (2) Type-Ⅰ D-R adsorption isotherms were regressed well for the adsorption of C3H6 and C3H8 at 300 K. The adsorption capacity of the Si-SAS molecular sieve for C3H6 decreased with increasing temperature. (3) Si-SAS had an adsorption capacity of 2.26 mmol/g for C3H6 in binary mixtures, and the selectivity was 3.94, thus making it the best adsorbent for separating the mixture. (4) A positive correlation was observed between the equilibrium selectivity and ΔQst as well as the adsorption capacity of C3H6 and total pore volume. A systematic study on the adsorption of C3H6 and C3H8 at six molecular sieves provides a reference for selecting candidate adsorbents for separating C3H6/C3H8 mixtures, thus greatly expediting the search for optimal adsorbents. The positive correlation between selectivity and ΔQst, as well as the adsorption capacity of C3H6 and total pore volume, provides a theoretical basis for designing and developing excellent adsorbents for C3H6/C3H8 separation.
赵丽, 何畅, 舒逸聃, 陈清林, 张冰剑. 丙烯/丙烷在分子筛上吸附热力学的Monte Carlo模拟[J]. 清华大学学报（自然科学版）, 2023, 63(5): 714-722.
ZHAO Li, HE Chang, SHU Yidan, CHEN Qinglin, ZHANG Bingjian. Monte Carlo simulation of propylene/propane adsorption thermodynamics on molecular sieves. Journal of Tsinghua University(Science and Technology), 2023, 63(5): 714-722.
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