Lecture_26_2023.pdf

1. Micro/Mesoporous Solids for Ambient Temperature CO2 Adsorption Disadvantages of liquid phase chemical absorption systems • Amine breakdown during regeneration • Corrosion problems • Economic cost (capital + operating) Alternatives using adsorption • Physical adsorption using molecular sieving ze...

1. Micro/Mesoporous Solids for Ambient Temperature CO2 Adsorption Disadvantages of liquid phase chemical absorption systems • Amine breakdown during regeneration • Corrosion problems • Economic cost (capital + operating) Alternatives using adsorption • Physical adsorption using molecular sieving zeolites, metal-organic frameworks (MOFs) • Silica and aluminum based high surface area porous solids modified to adsorb CO2 at low temperatures with: – amine groups (from ethylenimine, propylamine, tetraethylenepentamine and adenine) – optimised porosity and surface chemistry A major disadvantage is that adsorption processes are currently limited to small-to-medium scale tonnage separations. Improved adsorbents will enhance capacity. Adsorption OH OH O O O Si O Si O OH NH2 CO 2 NH2 Amine grafted silica surface Si O O Si O OH OH NH + 3 O O- NH C O Carbamate CO2 O Si NH + HCO - 2H2O O Si O OH NH3+ HCO3- 3 3 Bicarbonate MCM-41 (www.uni-giessen.de) (techon.nikkeibp.co.jp) Under equilibrium conditions: ci(A) = Kici(B) Ki >> 1 Amine functionalised MCM support Aminophenyl surface groups H2N NH2 Si H2N NH2 H2N NH2 H2N NH2 H2N NH2 H2N NH2 Si Si Adsorption equilibria as the selectivity mechanism Large number of aminophenyl groups → good selectivity for CO2 Adsorption isotherms on pure CO2 indicate these surface groups have large affinity for CO2 CO2 Adsorption Ideal isotherm –especially for the hexa-amino group. •High loading of CO2 at low pressures •Steep curves mean regeneration doesn’t necessitate going to low pressures Source: Design of Mesoporous Adsorbents for CO2 capture, Andrew Wiersum, MEng Research Project, University of Edinburgh, 2009 New surface groups: Equilibrium selectivities 3 Amount adsorbed [mol/m cell volume] ( ( xCO2 / xN2 ) /( yCO2 / yN2 ) with yCO2 / yN2 = 0.2 ) Hexaaminotriphenyl 6000 5000 CO2 4000 N2 3000 10 bar, 298K H2N NH2 H2N NH2 H2N NH2 =32 O2 2000 Si 1000 0 0 10 20 30 40 50 Selectivity to CO2 Pressure [bar] 50 H2N NH2 H2N NH2 =20 DIAMINOPHENYL TETRAAMINOBIPHENYL 40 HEXAAMINOTRIPHENYL 30 Si 20 10 H2N 0 0 10 20 Pressure [bar] 30 40 NH2 50 Si =13 10 bar, 298K Cl F H 6.4 I NH2 H2N NH2 Br F H2N NH2 Si NH2 O Si F H2N Si 7.2 Si Si Si Si Si Si Si 8.7 8.9 8.9 9.1 9.6 9.7 13.9 20 32 Increasing CO2 selectivity Selectivities of typical adsorbents Zeolite 4A Zeolite 13X H2N NH2 H2N NH2 H2N NH2 = 19 = 18 Activated Carbon = 15 Si Pressure/Vacuum/Temperature Swing Adsorption CO2 + N2 CO2 CO2 + N2 See: https://bit.ly/3qE0fm4 [Access 30-11-20] CO2 CO2 + N2 CO CO2 N22 ++ N Pressure/Vacuum/Temperature Swing Adsorption ci(A) = Ki ci(B) Ki >> 1 (Equilibrium) Simple Fixed Bed Sorption with Regeneration For a single (long) column, which has been completely regenerated, the concentration of component i (at low concentrations) at the exit, z = L, as a function of time is B = bed voidage), Rp = particle radius u = interstitial fluid velocity Ki = Henry’s law adsorption coefficient DB, D(A) = Dispersion and pore diffusion coefficients respectively. z=L c (B) i,IN c (B) i Early appearance of solute t=  1 (z = L) t   (B)  1−(t/μ ) ci (t,L) 1  i,1 = 1−erf  (B) 2  2 μ' /μ 2 ci,IN  i,2 i,1   L  (1− B )   i ,1 = 1+ K i  u B  2 2 D L   1-ε   i, B   B   μ' = 1+ K i ,2 i   3 ε  ε u   B   B   2  1-ε B  L 2 2  5 1  + R K + 15  ε  u p i  k R K D (A)   B   G p i i        Membrane Separations Process (Composite Membrane) CO2rich gas N2-rich exhaust gas CO2 N2 -rich interior CO2-rich gas Combustion gases N2 Hollow tubular porous silica membrane element CO2 L Ls CO2 N2, CO2 Composite Membrane Microporous support substrate Nanoporous thin film L Asymmetric (composite) membranes Thin selective layer <100 nm thick Mechanical support layer 50 m Microporous dp < 2nm; Mesoporous 2 nm <dp< 50nm; Macroporous 200 nm < dp Mechanical support (important for industrial processes) Hydrothermal resistance (high temperature & steam) Mass transport geometry (porosity, tortuosity, thickness & pore size) Chemical properties (functional groups, contaminants) Surface morphology for deposition (pore size & surface roughness) 500 nm N2-rich exhaust gas CO2rich gas Recall that for separation of a binary 1-2 gas mixture, the mass transfer area, A, of the membrane module is a primary design variable. The controlling parameters are FTL,OUT P1 pTL = ;  = and the stage cut P2 pTH FTH , IN Combustion gases FTH,IN, y1H,IN y y 1H 1H  FTH  1  =− ln  dy1H = −  g ( y1H ,  ,  )dy1H   y1H ,IN y1H − y1L y1H ,IN  FTH , IN  y1H ,OUT  A = A* y1H ,IN g ( y1H ,  ,  ) = FTH g ( y1H ,  ,  )dy1H FTH , IN ( y1H − y1L ) + (1 /  )( y2 H − y2 L )  F   A * = TH , IN P1 pTH  1 2  1   1  1    y1H +   − y1H −   + 4 y1H  + − y1H −   2   1 −  1− 1−       Permeate gas FTL,OUT 4 Retentate FTH,OUT  = 0.025 : 3 Note: A* = FTH,IN / (P1pTH) Nanoporous hollow fibres may, in principle, be produced using fibre spinning techniques coupled with wet chemistry/plasma coating methods. Dimensions in the range 0.5-1.5 mm O.D. and 0.1-0.3 mm wall thickness should be feasible. Employing a modest vacuum on the permeate side reduces compression costs (permeate compression needs are lower in view of the magnitude of the permeate flowrate) A/A* Feed, FTH,IN mol/s 14.5% CO2 3 10 30 100 2 1 0 0 0.04 0.08 0.12 0.16 yCO2H,OUT Membrane area required as a function of CO2 capture at four permselectivities Retentate FTH,OUT Permeate gas FTL,OUT Feed, FTH,IN mol/s 14.5% CO2 0.8 1 0.8 yCO2L,OUT FTL,OUT/FTH,IN 0.6 0.4 0.6 0.4 0.2 0.2 0 0 0 0.04 0.08 yCO2H,OUT 0.12 0.16 0 0.04 0.08 0.12 yCO2H,OUT Permeate conditions as a function of the capture of CO2 from the combustion gas mixture. 0.16 Combustion gas mixture Exhaust, N2 - rich Gas Drying and Cleaning Compressor/turbine: Compression ratio = 10:1 (η = 0.85); Energy penalty ~ 15% (lower gas flows than in the oxy-fuel case) CO2, N2 Win(Net) Turbine Compressor Membrane Module Permeate (CO2 – rich) Adsorption Vent Gas (N2) CO2 to Storage Case Study 1: Automobile with a dry exhaust flow of 0.385 mol/s, 14.5% CO2: With a CO2 permeance P1: 1.5 x 10-8 mol/m2.Pa.s and a feed pressure (pTH) of 10 bar (permeate pressure = 0.25 bar) then for 90% capture  A = 78 m2 for a selectivity  = 30. Case Study 2: Moneypoint with a dry exhaust flow of 41x103 mol/s, 14.5% CO2:  A = 8.3x106 m2 for a selectivity  = 30. Significant improvements in performance can be achieved using modules in series. Advantages: • Nitrogen treated separately (No/Low NOx) • Lower temperature than normal combustion • No hot spots (fluidised bed processes) * CRC for Greenhouse Gas Technologies (Univ Melbourne) Disadvantages: • Carrier circulation; Solids handling • Dual reactors • Difficult to couple to a gas turbine – loss in efficiency * Shankey Diagram for Reversible CLC CO2 Compression for Storage Adiabatic Process: Generally, neglecting bulk fluid kinetic and potential (gravitational) energy changes, the work done by a compressor is Ws = nH = Ws (isentropic )  As an example if the gas behaves ideally (high T low p) then ( −1) /      p2    Ws (isentropic ) = nRT1 − 1 = nC p (T2 (isentropic ) − T1 )  − 1  p1    Isothermal Process: The compression process for isothermal initial and final gas states can be considered to correspond to a large number of differential isentropic compression processes with a corresponding number of infinitesimal intercooling stages  p2  Ws (isothermal ) = nRT1 ln    p1  Moneypoint CO2 compression from 1 bar, 298K to 100 bar for sequestration For 90% capture then the CO2 flow is 5.35.103 mol/s. Adiabatic compression as an ideal gas with  = 0.85  0.13 GW (T2 = 932K). With isothermal compression the power required is 0.072 GW. Summary Low Partial Pressure Applications High Temperature Applications Selectivity Large-scale Applications Mechanical Simplicity Absorption Chemical solvents – Yes Physical solvents difficult Aqueous solvents - No Chemical solvents – High Physical solvents - Moderate Yes Yes for low viscosity solvents Adsorption Chemisorption – Yes Physisorption Difficult Yes Chemisorption – High Physisorption Moderate Limited – Costs scale linearly with capacity No if solids handling is required Membranes No Polymer membranes No Dense Inorganic Membranes – High Polymeric Membranes – Variable Microporous Membranes High Limited – Costs scale linearly with capacity Yes with the exception of compression CO2 Sequestration/Fixation Sequestration (geological storage in aquifers/depleted oil or gas wells): Example – Total estimated EU28 capacity for CO2 sequestration is 117 Gt Annual EU28 emissions = 3.45 Gt/year  34 years (post 2050?) Fixation (closing the carbon cycle assisted by renewables): Gas phase chemical synthesis: technologies with potential include (1) (2) CO2 + 1/δ MO2-δ → CO + 1/δ MO2 H2O + 1/δ MO2-δ → H2 + 1/δ MO2 2/δ MO2 → O2 + 2/δ MO2-δ (800oC) (800oC) (1500oC) (CSP driven) 2H2O + CO2 → CO + 2H2 + 3/2 O2 (800-900oC) (Solid oxide electrolysis) (3) CO2 + CH4 (biogenic) → 2CO + 2H2 (700-950oC) (Dry reforming) Subsequent Fischer-Tropsch synthesis using the syngas can be employed to produce chemicals and fuels Liquid/solid phase synthetic biology – artificial photosynthesis Minimum Power Requirements (EU) for Capture (GW) Absolute Minimum Power Requirements for Postcombustion CO2 Capture 100 80 Based on total CO2 emissions of 2,470 kmol/s (EU27 in 2012) with fully reversible separation and compression of the CO2 product to 100 bar at 298K CO2 fractional capture f = 1.0 Realistic processes would operate at ~30-40% efficiency 60 f = 0.75 40 EU27 power demand (total) = 2320 GW EU27 electric power demand ~ 450 GW f = 0.5 20 0 0.0001 0.001 0.01 0.1 CO2 Mole Fraction in Gas 1 Irish CO2 emissions by mode. Transport share in 2018 ~ 40% 2050: CO2 emissions = 15%xCurrent  EU emissions = 370 kmol/s  Minimum Capture Power ~ 9 GW  ~ 1-2% total power Can Ireland Live on its Renewables? (Recasting David MacKay’s analysis, ‘Sustainable Energy – without the hot air’ (www.withouthotair.com)) Hydro/Tidal/Geothermal: 1.2/ 1.7 / 2.9 (1 GW) Wave: 28 (5 GW) (1/2 x 500 km) Public Services: <1 Losses in conversion to power 17% Electrical devices 15% Land/Sea Freight: 16 (15% of land area) Materials/Infrastructure: 10 Food/Farming/Fertiliser: 15 Heating 33% Biomass: 26 (4.6 GW) Light, gadgets: 9 Wind (Deep offshore) 34 (6 GW) 1/3(200 km x 30 km) Heating, cooling 41 Photovoltaic Farm: 94 (16.6 GW) (50% ground level area of onshore Wind Farms) Wind (Shallow offshore) 17 (3 GW) 1/3(200 km x 15 km) Transport 35% 5 kW/p 21.6 GW Jet Flights: 9 Wind (Onshore): 34 kWh/d/p (6 GW) Car: 21 kWh/d/p (5% of land area) Solar Heating + PV (Roofs): 18 (3.2 GW) Supply (1): 145 kWh/d/p ( 25.6 GW) Supply (2): 112 kWh/d/p (19.8 GW) Demand: 122 kWh/d/p ‘Extreme’ annual average supply Potential annual average supply vs demand in Ireland (assuming 50% energy savings) Public Services: <1 Electrical devices 25% (15 kWh/d/p) Land/Sea Freight: 8 Solar (BIPV, PV): 10 2.1 GW 2.7 GW Energy dense fuels (Bio / solar) 17 3.0 GW 3.8 GW Pumped Heat: 5 0.9 GW 1.1 GW Wave: 5 1.2 GW 1.5 GW Wind (Deep offshore) 5 3.5 GW 4.5 GW Jet Flights: 9 Wind (S / offshore) 5 (12 GW Capacity) (15 GW Capacity) Car/bus/rail: 6 kWh/d/p Wind (Onshore): 10 kWh/d/p Demand: 61 kWh/d/p Supply: 61 kWh/d/p 2.5 kW/p 10.7 GW (2010) 2.5 kW/p 13.6 GW (2050) Materials/Infrastructure: 4 Solar Heating: 2 Food/Farming/Fertiliser: 8 Light, gadgets: 5 Heating, cooling 33% Hydro/Tidal/Geo: 2 Heating, cooling 20 Transport 42% Population growth? Land use? Storage (15-30 kWh/d/p lulls/seasonal)?