Modelling of Adsorption and Diffusion in Dual-Porosity Materials: Applications to Shale Gas

Transcription

1 Modelling of Adsorption and Diffusion in Dual-Porosity Materials: Applications to Shale Gas Martin Lísal Institute of Chemical Process Fundamentals, CAS, Prague, Czech Republic Faculty of Science, J. E. Purkinje University, Ústí n. Lab., Czech Republic 1

2 Motivation Atomistic Simulations to Provide Insights into Adsorption and Diffusion of Fluids in Shale Rocks shale rocks highly heterogenous systems - challenge to generate realistic atomistic models of organic and inorganic parts of the shale rocks engineered (model) materials zeolites: systematically change the pore sizes, pore shapes, and pore chemistry - reproduce some of the features of shale rocks atomistic models with dual micro/mesoporosities - the roles played by each porosity scale and the underlying links between the two porosity networks on the adsorption and diffusion of confined fluids Organic Matter Zeolite 2

3 Shale Rocks SEM Micrograph of Shale Rock shale rocks comprised of two distinct parts organic matter clay minerals (inorganic part) shale gas (a mixture of C 1, C 2 and C 3 with a small amount of C 4, heavier HCs, CO 2 and N 2 ) free gas adsorbed gas dissolved gas shale gas primarily adsorbed in organic matter atomistic modelling simulation domain, max up to 10 nm x 10 nm x 10 nm divide-and-conquer approach 3

4 Outline of the Talk atomistic models for organic matter & engineered materials atomistic models for shale gas & simulation methods adsorption and diffusion in the engineered materials adsorption and diffusion in organic matter conclusion 4

5 Atomistic models of organic matter * Kerogen van Krevelen Diagram Type I: lacustrine Type II: marine Type III: terrestrial Type IV: originated from residues * * Mature Type II Kerogen1 (oil formation zone) Postmature Type II Kerogen1 (gas formation zone) 5 1P. Ungerer et al., Energy Fuels 29, 91, 2015.

6 Atomistic models of organic matter (cont.) asphaltene/resin fragment Composition1,2: kerogen fragments asphaltene/resin fragments heavy HCs (C14, toluene, dimethylnapthalene) dissolved gas (C1, C2, C3, C4, C8) residual compounds (H2O, CO2) Consistent Valence FF (CVFF) & OPLS-AA3 microporous structures generated by the compression-cooling protocol4 copying the microporous structures and introducing a slit-like mesopore Dual-Porosity Proxy Models for Type II OMs [microporosity (<2nm) & mesoporosity (>2nm)] 1B. P. Tissot and D. H. Welte, Petroleum Formation and Occurrence (Springer: Berlin, 1984). Collel et al., Energy Fuels 28, 7457, P. Dauber-Osguthorpe et al., Protein Struct. Funct. Genet. 4, 31, 1988; M. J. Robertson et al., J. Chem. Theory Comput. 11, 3499, L. Michalec and ML, Molec. Phys. 115, 1086, J. 6

7 Atomistic models of organic matter (cont.) Postmature OM Mature OM microporosity microporosity mesoporosity micropores mesopores mesoporosity micropores mesopores

8 Atomistic models of engineered material HIPC: Na+ zeolites ZSM-5/35 (Si/Al=35) MFI unit cell ( duplicated in the x-, y- and z-directions random replacement of Si by Al under Löwenstein s rule constrain (avoid -Al-O-Al-); charge neutrality by insertion Na+ cations; rigid framework Vujic-Lyuabartsev s force field, Modelling Simul. Mater. Sci. Eng. 24, , 2016; atoms as charged LJ spheres (vdw and electrostatics interactions) Dual Micro/Mesoporous ZSM-5/35 Microporous ZSM-5/35 Dmicro=0.54 nm Vmicro=0.172 cm3/g SA=257 m2/g 4 nm mesopore Vmicro=0.193 cm3/g Vmeso=0.115 cm3/g SA=440 m2/g 8 E. Rezlerová et al., Langmuir 33, 11126, 2017

9 Atomistic models for shale gas methane united-atom and all-atom models Transferable Potentials for Phase Equilibria (TraPPE)1 All-Atom Optimised Potentials for Liquid Simulations (OPLS-AA)2 1M. G. Martin and J. I. Siepmann, J. Phys. Chem. B 102, 2569, M. J. Robertson et al., J. Chem. Theory Comput. 11, 3499, Simulation methods reservoir Grand Canonical Monte Carlo equilibrium number of adsorbed molecules, adsorption isotherms Equilibrium Molecular Dynamics density distributions CH4 all atoms united atom porous phase self-diffusivity via mean squared displacements (MSDs) Nonequilibrium Molecular Dynamics collective diffusivity transport diffusivity E. Rezlerová et al., Langmuir 33, 11126, 2017

10 Zeolites: Molecular model validation Adsorption Isotherms 293 K microporous ZSM-5/ K microporous ZSM-5/35 excellent agreement between GCMC simulations and HIPC s measurement Type I isotherms ZSM-5/35 has a higher affinity towards C2H6 than towards CH4 E. Rezlerová et al., Langmuir 33, 11126, 2017

11 Zeolites: Adsorption isotherms 293 K 293 K 293 K CH4 and C2H6 Type I isotherms; C3H8 and C4H10 Type I isotherms in microporous ZSM-5/35 but Type II in dual-porosity ZSM-5/35 CH4: n(microporous) > n(mesoporous) C2H6, C3H8 and C4H10: crossover P; n(microporous) > n(mesoporous) below the crossover P and n(mesoporous) > n(microporous) above the crossover P E. Rezlerová et al., Langmuir 33, 11126, 2017

12 Zeolites: Density profiles in mesopore 293 K, 2 bar 4 nm mesopore 293 K, 7 bar CH4: homogeneous fluid structure; C2H6, C3H8 and C4H10 preferential adsorption at the mesopore surface increasing P: both the preferential adsorption and density away from the mesopore surface increase E. Rezlerová et al., Langmuir 33, 11126, 2017

13 Zeolites: Self-diffusivity Microporous ZSM-5/35 Dual Micro/Mesoporous ZSM-5/35 MFI framework: 3D channel structure 0.54 nm x 0.56 nm straight channels in the y-direction 0.56 nm zigzag channels in the x-direction tortuous connections through straight-zigzag channel intersections in the z-direction y-diffusion > x-diffusion > z-diffusion mesopore along the y-direction E. Rezlerová et al., Langmuir 33, 11126, 2017

14 Zeolites: Self-diffusivity (cont.) 293 K 293 K y(micro) x(d-p) x(d-p) x(micro) z(d-p) z(micro) y(d-p) y(d-p) z(d-p) x(micro) z(micro), microporous ZSM-5/35: self-diffusivity decreases with P dual-porosity ZSM-5/35: self-diffusivity in the x- and z-directions decreases with P while self-diffusivity in the y-direction increases with P 1 to 2 order increase of the self-diffusivity in the dual-porosity ZSM-5/35 wrt the microporous ZSM-5/35 E. Rezlerová et al., Langmuir 33, 11126, 2017 y(micro)

15 Organic Matter: Methane adsorption Mature OM Postmature OM Adsorption Isotherms postmature OMs a higher affinity to C1 than mature OMs adsorption isotherms decrease with T and increase with P mature OM: maximum in excess adsorption 298 K Adsorption Isotherms

16 Organic Matter: Methane adsorption (cont.) Mature OM: T=365 K, P=275 bar Mature OM: T=365 K Density Profiles Adsorption Isotherm mesoporous regions: ~2/3 C1 adsorption free volume of mesoporous regions: 1/2 adsorption

17 Organic Matter: Methane self-diffusivity Mature OM w/ a Smaller 2.5nm Mesopore Self-Diffusivity pronounced decrease unusual Mature OM w/ a Larger 3.5nm Mesopore Self-Diffusivity increase of self-diffusivity due to the larger mesopore, depending on T of self-diffusivity with P and increase of self-diffusivity with T T-dependence for the system with the smaller 365 K

18 Organic Matter: Methane self-diffusivity (cont.) Mature OM: T=365 K, P=275 bar Mature OM: T=365 K In-Plane Mean Squared Displacement Self-Diffusivity overall self-diffusivity as well as self-diffusivities in the microporous and mesoporous regions decrease with P microporous region: self-diffusivity ~1/2 of the overall self-diffusivity mesoporous region: self-diffusivity ~1/3 higher than the overall self-diffusivity

19 Conclusion cooling-compression strategy to construct proxy models of dense porous organic matters effect of T & P on interplay between alkane adsorption and diffusion roles play by microporosity and mesoporosity on alkane adsorption and diffusion Acknowledgment Lukáš Michalec, Eliška Rezlerová, Michal Řeřicha ShaleXenvironmenT