Integration of molecular dynamic simulation and free volume theory for modeling membrane VOC/gas separation

Abstract

Gas membrane separation process is highly unpredictable due to interacting non-ideal factors, such as composition/pressure-dependent permeabilities and real gas behavior. Although molecular dynamic (MD) simulation can mimic those complex effects, it cannot precisely predict bulk properties due to scale limitations of calculation algorithm. This work proposes a method for modeling a membrane separation process for volatile organic compounds by combining the MD simulation with the free volume theory. This method can avoid the scale-up problems of the MD method and accurately simulate the performance of membranes. Small scale MD simulation and pure gas permeation data are employed to correlate pressure-irrelevant parameters for the free volume theory; by this approach, the microscopic effects can be directly linked to bulk properties (non-ideal permeability), instead of being fitted by a statistical approach. A lab-scale hollow fiber membrane module was prepared for the model validation and evaluation. The comparison of model predictions with experimental results shows that the deviations of product purity are reduced from 10% to less than 1%, and the deviations of the permeate and residue flow rates are significantly reduced from 40% to 4%, indicating the reliability of the model. The proposed method provides an efficient tool for process engineering to simulate the membrane recovery process.

Key words： membrane vapor separation; membrane process modeling; process engineering; free volume theory; volatile organic compound

Acknowledgements

The authors acknowledge the financial support of the National Natural Science Foundation of China (Grant No. 21706023), the Major National Scientific Instrument Development Project (21527812), Fundamental Research Funds of Panjin Industrial Technology Institute (PJYJY2016A003, YJYZXZJ 2017003), Joint Funds of the National Natural Science Foundation of China (U1663223), Education Department of the Liaoning Province of China (LT2015007), and Changjiang Scholars Program (T2012049).

References

1 Li B, He G, Jiang X, Dai Y, Ruan X. Pressure swing adsorption/membrane hybrid processes for hydrogen purification with a high recovery. Frontiers of Chemical Science and Engineering, 2016, 10(2): 255–264

2 Belaissaoui B, Le Moullec Y, Favre E. Energy efficiency of a hybrid membrane/condensation process for VOC (Volatile Organic Compounds) recovery from air: A generic approach. Energy, 2016, 95(Supplement C): 291–302

3 Ruan X, Wang H, Dai Y, Yan X, Zhang N, Jiang X, He G. Polyimide membrane system for TFE recovery: Industrial plant, optimal operation and economic analysis. Separation and Purification Technology, 2017, 188: 468–475

4 Yeom C K, Lee S H, Song H Y, Lee J M. Vapor permeations of a series of VOCs/N₂ mixtures through PDMS membrane. Journal of Membrane Science, 2002, 198(1): 129–143

5 Yun C M, Akiyama E, Yamanobe T, Uehara H, Nagase Y. Characterizations of PDMS-graft copolyimide membrane and the permselectivity of gases and aqueous organic mixtures. Polymer, 2016, 103(Supplement C): 214–223

6 Chen B, Ruan X, Jiang X, Xiao W, He G. Dual-membrane module and its optimal flow pattern for H₂/CO₂ separation. Industrial & Engineering Chemistry Research, 2016, 55(4): 1064–1075

7 Chen B, Ruan X, Xiao W, Jiang X, He G. Synergy of CO₂ removal and light hydrocarbon recovery from oil-field associated gas by dual-membrane process. Journal of Natural Gas Science and Engineering, 2015, 26: 1254–1263

8 Chen B, Jiang X, Xiao W, Dong Y, Hamouti I E, He G. Dual-membrane natural gas pretreatment process as CO₂ source for enhanced gas recovery with synergy hydrocarbon recovery. Journal of Natural Gas Science and Engineering, 2016, 34: 563–574

9 Merkel T C, Bondar V I, Nagai K, Freeman B D, Pinnau I. Gas sorption, diffusion, and permeation in poly(dimethylsiloxane). Journal of Polymer Science. Part B, Polymer Physics, 2000, 38(3): 415–434

10 Fujita H, Kishimoto A. Interpretation of viscosity data for concentrated polymer solutions. Journal of Chemical Physics, 1961, 34(2): 393–398

11 Stern S A, Mauze G R, Frisch H L. Tests of a free-volume model of gas permeation through polymer membranes. I. Pure CO₂, CH₄, C₂H₄, and C₃H₈ in polyethylene. Journal of Polymer Science. Part B, Polymer Physics, 1983, 21(8): 1275–1298

12 Scholes C A, Stevens G W, Kentish S E. Modeling syngas permeation through a poly dimethyl siloxane membrane by Flory-Rehner theory. Separation and Purification Technology, 2013, 116: 13–18

13 Petropoulos J H. Plasticization effects on the gas permeability and permselectivity of polymer membranes. Journal of Membrane Science, 1992, 75(1): 47–59

14 Lammers L N, Bourg I C, Okumura M, Kolluri K, Sposito G, Machida M. Molecular dynamics simulations of cesium adsorption on illite nanoparticles. Journal of Colloid and Interface Science, 2017, 490: 608–620

15 Kozuch J D, Zhang W, Milner T S. Predicting the Flory-Huggins c parameter for polymers with stiffness mismatch from molecular dynamics simulations. Polymers, 2016, 8(6): 241

16 Feng X S, Shao P H, Huang R Y M, Jiang G L, Xu R X. A study of silicone rubber/polysulfone composite membranes: Correlating H₂/N₂ and O₂/N₂ permselectivities. Separation and Purification Technology, 2002, 27(3): 211–223

17 Liu L, Jiang N, Burns C M, Chakma A, Feng X. Substrate resistance in composite membranes for organic vapour/gas separations. Journal of Membrane Science, 2009, 338(1-2): 153–160

18 Scholes C A, Stevens G W, Kentish S E. The effect of hydrogen sulfide, carbon monoxide and water on the performance of a PDMS membrane in carbon dioxide/nitrogen separation. Journal of Membrane Science, 2010, 350(1-2): 189–199

19 Poling B E, Prausnitz J M, O’Connell J P. The Properties of Gases and Liquids.New York: McGraw-hill, 2001, 915–929

20 Stern S A, Saxena V. Concentration-dependent transport of gases and vapors in glassy polymers. Journal of Membrane Science, 1980, 7(1): 47–59