Pore size dependent geochemistry

Transcription

1 Global Cliate & Energy Project Distinguished Student Lecture October 8, 2013 Pore size dependent geocheistry Joey M. Nelson 1, John R. Bargar 2, Gordon E. Brown, Jr. 1,2,3, Kate Maher 1 1 Departent of Geological and Environental Sciences, Stanford University 2 Departent of Photon Science and Stanford Synchrotron Radiation Lightsource, SLAC 3 Departent of Cheical Engineering, Stanford University

2 INTRODUCTION Motivation: CO 2 sequestration and engineering subsurface reactivity 2

3 INTRODUCTION 1 µ Macropores (> 50 n) Stubbs et al., GCA, 2009 Velbel and Baker, CCM, 2008 Sith et al., PNAS, n IUPAC pore size ranges Mesopores (2-50 n) Micropores (< 2 n) Data fro Brantley and Mellott (A. Min., 2000), and Mayer (Che. Geol., 1994) 3

4 ph INTRODUCTION Adsorption Capacity (l/g) Effects of Mesopores Diffusion Liited Transport Enhanced Adsorption Capacity Macroporous Mesoporous Mesoporous Macroporous Equilibration Tie (s) (Zn adsorbed to aluina data fro Wang et al., JCIS, 2002) ph (U adsorbed to aluina data fro Sun et al., Separ. Purif. Tech., 2011) 4

5 INTRODUCTION Hypotheses 1. Meso-confineent phenoena result fro unique geocheical processes, not transport liitations. 2. The cheical echaniss of sorption differ between acropores and esopores, which could significantly ipact CO 2 sequestration. Objectives 1. Quantify sorption rates and capacities with respect to pore size. 2. Deterine olecular structure of sorption coplexes in acropores and esopores. 5

6 INTRODUCTION Zn Adsorption on Silica Choice of Experiental Syste Molecular geoetry of sorbed CO 2 is difficult to observe with XAFS Zn exists in various coplexes and is easily observed with XAFS Silica is a siple substrate and the doinant ineral in saline aquifers Batch Adsorption Experients Controlled Pore Glass (SiO 2(a) ) Macroporous (300 n): g -1 Mesoporous (13.9 n): g -1 Each batch contained equivalent aounts of substrate surface area 6

7 INTRODUCTION Geocheical Modeling Reaction vs. Transport Diffusion-Reaction Model C t = D eff 2 C x 2 kc Rate coefficient, k = 10-6 ol s -1 Diffusivity, D eff = 10-7 c 2 s -1 Batch reaction is well-ixed (i.e., not diffusion-liited) Meso-confineent effects are due to unique geocheistry 7

8 INTRODUCTION Zn Adsorption Results Zn adsorption capacity is enhanced by esopores. Indirect evidence that esopores proote inner-sphere coplexation (i.e., stronger binding). 8

9 INTRODUCTION Molecular Fingerprinting with EXAFS Extended X-ray absorption fine structure spectroscopy at BL 11-2 at SSRL, SLAC Spectra unique to olecular environent of Zn in saple C.N (Roberts et al., JCIS, 2003) 9

10 INTRODUCTION Zn EXAFS Results Zn is doinantly 6-fold coordinated in acropores. Zn is doinantly 4-fold coordinated in esopores. 10

11 INTRODUCTION Conclusions Zn adsorption capacity is enhanced and olecular configuration is altered in esoporous silica. Sorption of CO2 olecules in eso-confined pore volues ay also differ fro less confined spaces. Future study of CO2 sorption geoetries with ATR-FTIR spectroscopy and quantu calculations. Iplications Pore size is a tunable paraeter for environental reediation and cheical separations. More accurate reactive transport odels Induce or enhance subsurface ineralization 11

12 PORE SIZE DEPENDENT GEOCHEMISTRY GCEP RESEARCH SYMPOSIUM 2013 Thank you! Questions? Poster 59: Enhanced Sorption of Zn in Mesoporous Silica Acknowledgeents Kate Maher, Gordon E. Brown Jr., Jen Wilcox, Scott Fendorf, Mike Massey, Ada Jew, Caroline Harris, Karrie Weaver, John Bargar, Noeie Janot 12