Carbon Dioxide Capture by Adsorption: Traditional and Non-traditional Approaches

1. Carbon Dioxide Capture by Adsorption:Traditional and Non-traditional Approaches T. Golden, J. Hufton, R. Quinn Air Products and Chemicals, Inc. 13th NIChE Conference October 13, 2008

2. Adsorption • Interaction of gas with a solid surface S + CO2(g) = S-CO2 DG = DH - TDS • Adsorption is spontaneous if: • DG<0 but DS is <0 (negative) • DH must be <0 (exothermic) • Adsorption is driven by heat • of gas-solid interaction gas solid

3. Types of Adsorption 1. Physical adsorption (physisorption) - weak physical interactions + -O=C=O + 2. Chemical adsorption (chemisorption) - chemical bond formed O O=C=O = C O O OH H CO2 CaO 3. Bulk reaction: absorption - reaction at surface, diffusion into bulk CaCO3

4. Types of Adsorption

5. The adsorption process others adsorption step desorption step CO2 CO2, others

6. Pressure swing adsorption (PSA) purge P1 > P2 adsorption isotherm X1 capacity X2 P2 P1 gas partial pressure CO2 at P1 CO2at P2 Adsorption Desorption • Feed exposure times are short (sec/min) • Modest working capacities • Best suited to bulk separation

7. Temperature swing adsorption (TSA) purge T2 > T1 T1 X1 T1 T2 capacity T2 X2 P1 partial pressure CO2 CO2 at P1 Adsorption Desorption • Feed exposure times are long (hours) to minimize • time for heating/cooling • Better suited to trace removal • Greater DT – greater working capacity

8. CO2 sources How (or if) apply adsorption to CO2 capture depends on the source of CO2 - gas composition, flows, temperature, pressure 1. H2 synthesis by steam methane reforming - precombustion capture at relatively high pressure and CO2 concentrations 2. Gasification – precombustion capture 3. Coal fired power plant – postcombustion capture

9. heat recovery H2 by Steam Methane Reforming CH4 + 2H2O = 4H2 + CO2 natural gas/steam natural gas/air PSA purge gas ~1.5 atm 42% H2, 37% CO2 7% CO, 14% CH4 CH4 + H2O = 3H2 + CO 830-850ºC, 25-30 atm reformer Flue gas: CO2, H2O, N2, O2 >99.99% H2 high T shift PSA 73% H2, 12% CO2 8% CO, 7% CH4 (dry compositions)* CO + H2O = CO2 + H2 315-430ºC 74% H2, 16% CO2 3% CO, 7% CH4 *Separation Technology R&D Needs for H2 Production in the Chemical and Petrochemical Industries, US DOE and Chemical Industry VISION 2020 Technology Partnership, December 2005.

10. Carson, CA Air Products • Largest third-party H2 producer, $1.5 billion revenue • Operates over 70 plants – Americas, Europe, Asia • 1.5 million ton/year produced • 7 H2 pipeline systems (>350 miles) 5 of 10 PSA vessels

11. Tarragona, Spain

12. H2 PSA process • Designed to give high purity H2 • CO2 “captured” at low pressure, low purity • - not suitable for sequestration purge high purity H2 product N2 N2 lower pressure CH4 CH4 zeolite CO CO CO CO CH4 CH4 activated carbon CO2 CO2 H2O H2O 1.5 atm SMR H2 feed 20-30 atm 37% CO2, rest CO, H2, H2O,CH4, N2

13. Application of PSA-based process to CO2 capture • Need to produce a high purity CO2 suitable for • compression and sequestration without sacrificing H2 • production. • Conventional H2 PSA will not give pure CO2 • Modification of commercial PSA method required for • CO2 capture • Air Products developed such two processes: Gemini • and CO2 VSA in 1980s – CO2 for urea market

14. Current PSA Process natural gas/air natural gas/steam 1.5 atm PSA purge gas, 37% CO2 H2 heat recovery flue gas PSA high T shift 20-25 atm 74% H2, 16% CO2 3% CO, 7% CH4

15. Gemini Process 2 products: H2 and CO2 natural gas/air natural gas/ steam PSA purge gas, 6% CO2 H2 flue gas high T shift heat recovery H2 PSA More equipment, capital, energy costs so need mandated sequestration, sale or use of CO2 product to justify implementation 97+% CO2 $$$$ vacuum pump

16. Current scale of CO2 removal via PSA is big • CO2 removal rate about 7 lb CO2/h/ft3 carbon • Typical 100 MM SCFD plant – 250 ton activated carbon (~14,000 ft3), 1 train of 10 beds, 14x25 ft • Worldwide estimated H2 usage 50 MM tons/year • 80% purified by PSA = 800 million tons CO2/yr • Requires ~100,000 tons of both activated • carbon and zeolite • BUT…

17. The scale of CO2 capture is immense • Very high flows and quantities of CO2 • A gasification plant requires 2,000 to 2,500 tons carbon adsorbent (>100,000 ft3), 10 trains of 10 beds! Coal-fired power plant still more • Huge technical challenge • Need higher capacities, faster cycles, or both • Are there nontraditional adsorption based alternatives? • Numerous efforts in nontraditional adsorption

18. CO2 sources 1. H2 synthesis by steam methane reforming - precombustion capture at relatively high pressure and CO2 concentrations 2. Gasification – precombustion capture 3. Coal fired power plant – postcombustion capture

19. Precombustion capture: CO2 removal in gasification • CO2 at high pressure, concentration, temperature • Capture is “easy” air CO2 Gasification Combustion Turbine/ generator fuel CO2 Removal kW O2 H2O H2, CO 600 psi, 1340ºC mostly H2, CO, H2O CO2 H2O, minor CO2 • Ideally high T capture, high CO2 capacity, high H2 • recovery • Adsorbent must be OK cycled at high T, high steam • The adsorbent is the key…

20. K2CO3 promoted hydrotalcite for precombustion capture • Mg6Al2(OH)16[CO3]·4H2O calcined to a Mg-Al oxide • K2CO3 promotion required for fast adsorption • Operating temperature 400ºC (adsorb/regen) • Mode of CO2 adsorption unclear – speculate • combination of physical/chemical adsorption; • acid/base chemistry • Capacity of 1.5 mmol/g (~6.5 wt%) at 5 atm and 400ºC • No negative impact of • steam on adsorption • Good cycling stability

21. Sorption Enhanced Water Gas Shift Process WGS reaction: CO + H2O = CO2 + H2 air CO2 for capture Combustion Turbine/ generator Gasification fuel kW WGS catalyst/ HTC adsorbent O2 H2O 87% H2, 0.5%CO 2% CO2, 8% H2O N2, H2O, <1% CO2 57% H2, 16%CO 10% CO2, 16% H2O • WGS catalyst + high temperature CO2 adsorbent - HTC • Removes CO2 from hot feed gas (400-500ºC), drives CO towards zero, increases conversion to H2 • Cyclic process - reaction/adsorption and regeneration

22. Metal oxides for precombustion capture 700-750C CaO + CO2(g) = CaCO3 >800C • Very high capacity, 78.5 wt% (17.8 mmol/g!) • Cheap • High regeneration • temperatures • Poor cycling stability • Large volume, phase • changes • Efforts to stabilize • capacity vs time CaO , 750C, 30 min CO2, 30 min N2 cycles 15 10 mmol CO2/g 5 0 10 20 30 40 50 60 cyclenumber

23. Complex metal oxides for precombustion capture T, ºC for equil. P(CO2) = 1 atm • Li4SiO4 + CO2(g) = Li2CO3 + Li2SiO3 705 • CaO + CO2(g) = CaCO3 892 • Desorption can be achieved at lower temperature • but still high capacities – theoretical 8.3 mmol/g • (36.7 wt%) • A solid absorbent from Toshiba Corp has some very • promising properties for precombustion CO2 capture

24. Toshiba absorbent • Li4SiO4 with <10 mole% K2CO3; Li2TiO3 binder; 5 mm spheres • Very large capacity, 5.4 mmol/g, 650C, 1 atm CO2 • Fast absorption/desorption, fully reversible • Excellent physical, cycling stability • OK in the presence of steam • Absorption chemistry (confirmed by XRD) • Li4SiO4 + CO2(g) = Li2CO3 + Li2SiO3 • equil. P(CO2) = 0.15 atm at 650C • K2CO3 lowers mp of Li2CO3 (723C) product; molten • phase improves absorption properties

25. 5.5 5.0 4.5 4.0 Toshiba absorbent – TGA studies 650C 6.0 Adsorption is very fast at 650C 1 atm CO2 4.0 mmol CO2/g 500C 2.0 0 5 10 15 20 25 30 700C 10 min CO2, 10 min N2 • Excellent cycling stability • inspite of large phase changes • No loss of crush strength or • physical integrity time, min mmol CO2/g cycle number 20 30 40 50 60 0 10

26. CO2 sources 1. H2 synthesis by steam methane reforming - precombustion capture at relatively high pressure and CO2 concentrations 2. Gasification – precombustion capture 3. Coal fired power plant – postcombustion capture

27. Postcombustion capture: 500 MWe Coal Fired Power Plant* flue gas 2,770 mt/h; 466 mt CO2/h air 2,450 mt/h coal 208 mt/h flue gas cleanup boiler/ superheater SOX, NOX, Hg, PM steam turbine/ generator 2 rail cars/h enough carbon/yr to make 10% of methanol for the entire planet! 500 MW electricity *”The Future of Coal” (MIT, 2007)

28. Retrofit for postcombustion CO2 capture & sequestration flue gas with 47 mt CO2/h air 2,450 mt/h coal 208 mt/h CO2 capture flue gas cleanup boiler/ superheater SOX, NOX, Hg, PM steam turbine/ generator 419 mt CO2/h compress 500 MW electricity underground sequestration

29. Postcombustion capture is not easy… • Very high flows* – 2.0x106 Nm3/h • Very large quantities of CO2 to be captured* – • 420 mt/h for 90% capture • Ambient pressure, only ~0.15 atm CO2 • Flue gas contaminants – O2, SOx, NOx, Hg • Water vapor – deleterious effect on most adsorbents • Need process that’s fast, high capacity, inert vs water and flue gas contaminants, low regeneration energy • Adsorption options are limited • May need a creative solution beyond conventional fixed bed technology *500 MW plant, “The Future of Coal” (MIT, 2007)

30. Alkali carbonates for postcombustion capture • K2CO3 + H2O(g) + CO2(g) = 2KHCO3 • Maximum capacity - 7.2 mmol/g (~32 wt%) • Infinite selectivity vs nonreactive gases • Absorb at 60ºC, regenerate at >150ºC • Water required for CO2 adsorption • High heats, 34.5 kcal/mol CO2 • Capture process • - difficult with fixed bed adsorption process • - likely need fluidized bed, “entrained bed reactor”

31. RTI Entrained Bed Reactor • Bench scale demo: 50 lb Na2CO3, >90% capture, • 2-10 lb CO2/h Issues: - physical attrition - phase/volume changes - high SO2 affinity

32. Conclusions • Adsorption based CO2 capture from H2 plants • is achievable but requires additional unit • operations beyond currently existing ones. A • driver for CO2 capture is required – mandated • capture, sale or use of CO2 product. • Larger scale capture such as gasification, • power plants presents a significant challenge • for an adsorption process. • Nontraditional adsorbents and processes will • likely be required, especially for postcombustion • capture.