Natural Gas Storage on Nanoporous Carbon Jacob Burress , Mikael - PowerPoint PPT Presentation

Natural Gas Storage on Nanoporous Carbon Jacob Burress , Mikael Wood, Sarah Barker, John Flavin, Cintia Lapilli, Parag Shah, Galen Suppes, Peter Pfeifer Alliance for Collaborative Research in Alternative Fuel Technology University of Missouri, Columbia, MO 65211

Overview Overview � � Powdered and monolithic Powdered and monolithic activated carbons have been activated carbons have been made with corn cob as starting made with corn cob as starting material that have a large material that have a large methane storage capacity methane storage capacity � � Pore Space Structure Pore Space Structure Analyzed: Analyzed: small angle x-ray scattering � � small angle x-ray scattering (SAXS) (SAXS) � computer simulations of pore � computer simulations of pore formation formation � nitrogen adsorption isotherms � nitrogen adsorption isotherms � scanning and transmission � scanning and transmission electron microscopy electron microscopy (SEM/TEM) (SEM/TEM) � methane adsorption isotherms � methane adsorption isotherms

Why are Nanopores Important? Why are Nanopores Important? � In narrow pores, van der Waals potentials overlap; creating a deep energy well Binding energy: � Max. CH 4 capacity in Binding energy: 17 kJ/mol 17 kJ/mol pores of width 1.1 nm (simulations) � van der Waals potential of CH 4 in pore of width 1.1 nm � Energy loss more than enough to compress CH 4 into dense fluid; remaining energy � Nicholson (Carbon Vol. 36, 1998) heat

Why are Nanopores Important? Why are Nanopores Important? Width Width ~6 Å ~6 Å ~3.7 Å Width Width ~11 Å ~11 Å Width Width ~22 Å ~22 Å

Definitions of Uptake Values Definitions of Uptake Values Pore Pore Absolute Adsorbed Gas Absolute Adsorbed Gas Stored Gas Stored Gas Gibb’ Gibb ’s Excess Adsorbed s Excess Adsorbed Gas Gas Adsorbed Film Adsorbed Film Bulk (non-adsorbed) Gas Bulk (non-adsorbed) Gas � � � ( ) absolute m m m m m 1 BulkGas V = � � � � + � � � adsorbed Chamber Sample Gas , , Chamber Gas , Chamber Sample , Chamber AdsorbedFilm BulkGas � � � Skeletal � � � ( ) m m m m m 1 BulkGas = � � � � � � Stored Chamber Sample Gas , , Chamber Gas , Chamber Sample , Chamber � � � Piece � � � ( ) Excess m m m m m 1 BulkGas = � � � � � � Adsorbed Chamber Sample Gas , , Chamber Gas , Chamber Sample , Chamber � � � Skeletal

Methane Uptake Methane Uptake � � Methane uptake measured Methane uptake measured gravimetrically on powder gravimetrically on powder samples, monoliths measured samples, monoliths measured volumetrically as well. volumetrically as well. � � Values below reported as amount Values below reported as amount of methane stored using a “ “powder powder of methane stored using a density” density ” of 0.5 g/ml of 0.5 g/ml ALL-CRAFT Best ALL-CRAFT Best ANG DOE ANG DOE Performance S- Performance S- Target Target 33/k 33/k M/M 230-239 g/kg N/A M/M 230-239 g/kg N/A M/V M/V 115-119 g/L 115-119 g/L 118 g/L 118 g/L V/V V/V 176-182 L/L 176-182 L/L 180 L/L 180 L/L

Summary of Storage Densities Summary of Storage Densities 119 g/L 118 g/L 24.9 g/L

Small Angle X-ray Scattering Small Angle X-ray Scattering D 2.3 � Surface D 6 I q q ( ) � � 1 2 � I q ( ) I q � ( ) � L L qL L 2 2 I q r L ( ) = � � o 2r 2r qL sin ( ) u 1 cos ( qL ) 1 � � 2 ( ) 2 ( ) � sin qL cos * J qr sin / 2 ( ) ( ) � � � I q const . du ( ) = � � = � 1 I q sin d � � ( ) ( ) � � qL u qL 4 2 2 2 2 � � q L r sin cos ( ) ( ) � � � � 0 0 1 � 1 1 I q const qL . , for L q r ( ) ( ) � � � � � Scattering from a cylinder, with finite Scattering from a cylinder, with finite thickness. thickness. Scattering in the limit L>>r Scattering in the limit L>>r

Computer Modeling of Pore Computer Modeling of Pore Formation Formation � Two stage probabilistic cellular automata (PCA) rule (two separate PCA’s in succession). � Pore space opened from inside � out � Pore space opened from outside � in, creating a spanning cluster � This models a two stage activation process. Carbon � Qualitatively this model fits well with observed data. Spanning Cluster Pore Space Non-Spanning Cluster Pore Space

SEM/TEM SEM/TEM � Due to the small size of the � Due to the small size of the pores, ultra high resolution pores, ultra high resolution mode was used on the mode was used on the Hitachi S-4700 FESEM. Hitachi S-4700 FESEM. Beam energy was set to 5 kV Beam energy was set to 5 kV with a small working distance with a small working distance (3-4mm) (3-4mm) 200 nm � The beam energy was set to � The beam energy was set to 100 and 120 kV for the JEOL 100 and 120 kV for the JEOL 1200EX TEM 1200EX TEM � Top image SEM on sample � Top image SEM on sample S-33/k, showing entrance to S-33/k, showing entrance to pore network pore network � Bottom image TEM on � Bottom image TEM on sample S-56 showing ~1.5 sample S-56 showing ~1.5 nm wide pore nm wide pore

S-33/k 200 nm 5.00 μ m

Nitrogen Adsorption Isotherms Nitrogen Adsorption Isotherms � Nitrogen isotherms show � Nitrogen isotherms show evidence of strong evidence of strong microporosity microporosity � Plateau on linear isotherm Plateau on linear isotherm � � BET surface area of ~2,200 � BET surface area of ~2,200 m 2 m 2 /g for sample S-33/k /g for sample S-33/k � Surface area of most recent � Surface area of most recent samples found to be ~3,000- samples found to be ~3,000- 3,500 m 2 /g 3,500 m 2 /g � Gives total pore volume of � Gives total pore volume of 1.22 cc/g, porosity of 0.71 1.22 cc/g, porosity of 0.71 � Note: Surface area for � Note: Surface area for graphene sheet (both sides) graphene sheet (both sides) is 2,965 m 2 is 2,965 m 2 /g ( /g (Chae Chae et. al. et. al. Nature Vol Vol 427 2004) 427 2004) Nature

Pore Size Distribution from Pore Size Distribution from Nitrogen Isotherm Nitrogen Isotherm Peak at ~1.13 nm S-33/k � � Done using non-local density functional theory (NLDFT) assuming Done using non-local density functional theory (NLDFT) assuming slit-shaped pores slit-shaped pores � � Shows dominance of nanopores, especially pores width ~1.1nm Shows dominance of nanopores, especially pores width ~1.1nm

Methane Adsorption Isotherms Methane Adsorption Isotherms � Langmuir gives � Langmuir gives good fit of data good fit of data which is consistent which is consistent with the hypothesis with the hypothesis that surface is that surface is covered primarily covered primarily with a single with a single monolayer of monolayer of methane methane � Langmuir � Langmuir parameter of parameter of b=0.814 MPa -1 -1 b=0.814 MPa � Asymptotic value of 288.5 grams of adsorbed methane per � Asymptotic value of 288.5 grams of adsorbed methane per kilogram carbon kilogram carbon � Langmuir fit gives a binding energy of ~22.7 kJ/mol, which � Langmuir fit gives a binding energy of ~22.7 kJ/mol, which is consistent with the high uptake values is consistent with the high uptake values

Pore Size Distribution from Pore Size Distribution from Methane Isotherm Methane Isotherm � Shows dominance � Shows dominance of nanopores, of nanopores, especially in pores especially in pores 0.500 of width 6-15 Å of width 6-15 Å 0.400 � Gives total pore � Gives total pore Pore Volume [cc/g] volume of 1.513 volume of 1.513 S-33/k 0.300 cc/g, porosity of cc/g, porosity of 0.752 0.200 0.752 � Determined via � Determined via 0.100 method from method from Sosin and Quinn, and Quinn, Sosin 0.000 6 0 5 0 0 0 0 5 0 0 0 . . . . . . . 1 2 5 5 0 1 1 2 4 6 0 Carbon 34 1335 > Carbon 34 1335 1 - - - - - - - - - 0 5 0 4 6 0 5 0 0 - 1 1 2 . . . . . . 0 0 0 1 1 2 4 . 6 (1996) (1996) Pore Width Range [nm]

Comparison of Methods Comparison of Methods 0.500 TEM TEM 0.400 Pore Volume [cc/g] 0.300 Methane Nitrogen 0.200 0.100 0.000 0.4 - 0.6 0.6 - 1.0 1.0 - 1.5 1.5 - 2.0 2.0 - 4.0 4.0 - 6.0 6.0 - 10.0 10 - 15 15 - 20 20 - 50 >50 Pore Width Range [nm] Porosity Porosity Total Pore Total Pore Micropore Micropore Mesopore Mesopore Macropore Macropore Average Average Average Average Volume Volume (pore diameter (pore diameter (2– (2 –50 nm) 50 nm) (>50 nm) (>50 nm) Nanopore Nanopore Nanopore Nanopore [cc/g] 0.5– –2 nm) 2 nm) Volume Volume Width [Å] Length [Å] [cc/g] 0.5 Volume Volume Width [Å] Length [Å] Volume [cc/g] Volume [cc/g] [cc/g] [cc/g] [cc/g] [cc/g] Methane Methane 0.752 0.752 1.513 1.513 1.197 1.197 0.254 0.254 0.062 0.062 ~11 ~11 N/A N/A Nitrogen 0.710 1.222 1.107 0.094 0.021 ~11 N/A Nitrogen 0.710 1.222 1.107 0.094 0.021 ~11 N/A SAXS N/A N/A N/A N/A N/A ~4 ~15 SAXS N/A N/A N/A N/A N/A ~4 ~15