SO and NO sequestration, methods, activated carbon,

Removal of Sox and Nox gases by sequestration
Air pollution
➢one of the environmental problems
➢arising from the contamination of air following physical, biological, or chemical alteration
to the atmospheric air.
Such contaminants, called pollutants,
➢introduced into the atmosphere from either natural or anthropogenic activities and
➢Have several health-related effects on both humans and the entire ecosystem
➢Kills more people (3.3 million every year) than HIV, influenza, and malaria
Sources of air pollution
➢anthropogenic activities or man-made pollution
➢natural events contribute less
Contribution of fossil fuels:
▪ Increase in urbanization
▪ Rising demand for energy has significantly increased the level of fossil fuel production and consumption,
▪ It results in the production of pollutants such as CO2, PM, sox, and nox
A fossil fuel-fired power plant
Emits
▪ 67% nox and
▪ 87% sox
• Removal of nox and sox from flue gas is beneficial to man and environment,
• influences downstream CO2 capture systems
The technology removes not just CO2 but SOx and NOx
➢ Economical,
➢ reduce the cost of the operation and
➢ Cost of equipment.
Persisting problem associated with the simultaneous sox and nox removal
➢ Sulfur catalyst poisoning
➢ Caused due to the formation of sulfates on the surface of the active site of the carbon support.
➢ Need to develop a hybrid-catalyst
➢ Capable of simultaneously removing sox/nox
➢ Regenerable.

Carbonaceous materials
➢ Resistance to acidic and basic environments,
➢ Recycle capabilities,
➢ Low cost,
➢ Low density,
➢ Abundant micropores,
➢ Amenability to be synthesized,
➢ Regenerability,
➢ Availability,
➢ Affinity for adsorption,
➢ Diffusion characteristics,
➢ Inertness toward unwanted reactions,
➢ Polymodal porous structure,
➢ Reaction condition stability, mechanical strength,
➢ High filtering rate, and
➢ Strong market position
Good example :
activated carbon technology that has been recognized as profitable to retrofit into current boiler systems
Activated carbon (AC)
❑ Microcrystalline form of carbon
❑ High porosity and
❑ High surface area for removal of impurities from soil, liquids, gases, and solids.
Processes involved in carbon activation
➢ Following raw materials preparation,
➢ Low temperature combustion, and
➢ Activation.
Raw materials
1. coal, wood, carbon materials, coconut shell, fruits shells, derived biomass, etc.
AC : Applications
➢ Molecular sievesand
➢ Water purification
➢ As a catalyst or a support in heterogeneous catalysts,
➢ Adsorbent for gas cleaning (sox, nox from flue gases) at temperatures below 200°C for the purpose of safety of the
plant and high cleaning efficiencies.
Some difficulties are,
➢ Difficulty in mass transport processes and
➢ Low adsorptivity due to its wide pore-size distribution
➢ In the application of electro-catalyst due to its
➢ Lack of electrical conductivity.
The factors affecting the adsorption performances of AC

1. Air pollution
➢one of the environmental problems
➢arising from the contamination of air following physical, biological, or chemical alteration
to the atmospheric air.
Such contaminants, called pollutants,
➢introduced into the atmosphere from either natural or anthropogenic activities and
➢Have several health-related effects on both humans and the entire ecosystem
➢Kills more people (3.3 million every year) than HIV, influenza, and malaria
Sources of air pollution
➢anthropogenic activities or man-made pollution
➢natural events contribute less
Removal of Sox and Nox gases by sequestration

2. Contribution of fossil fuels:
▪Increase in urbanization
▪Rising demand for energy has significantly increased the level of fossil fuel production and consumption,
▪It results in the production of pollutants such as CO2, PM, sox, and nox
A fossil fuel-fired power plant
Emits
▪67% nox and
▪87% sox
The technology removes not just CO2 but SOx and NOx
➢Economical,
➢reduce the cost of the operation and
➢Cost of equipment.
Persisting problem associated with the simultaneous sox and nox removal
➢Sulfur catalyst poisoning
➢Caused due to the formation of sulfates on the surface of the active site of the carbon support.
➢Need to develop a hybrid-catalyst
➢Capable of simultaneously removing sox/nox
➢Regenerable.
•Removal of nox and sox from flue gas is beneficial to man and environment,
•influences downstream CO2 capture systems

4. Carbonaceous materials
➢Resistance to acidic and basic environments,
➢Recycle capabilities,
➢Low cost,
➢Low density,
➢Abundant micropores,
➢Amenability to be synthesized,
➢Regenerability,
➢Availability,
➢Affinity for adsorption,
➢Diffusion characteristics,
➢Inertness toward unwanted reactions,
➢Polymodal porous structure,
➢ Reaction condition stability, mechanical strength,
➢High filtering rate, and
➢ Strong market position
Good example :
activated carbon technology that has been recognized as profitable to retrofit into current boiler systems

5. Activated carbon (AC)
❑Microcrystalline form of carbon
❑High porosity and
❑High surface area for removal of impurities from soil, liquids, gases, and solids.
Processes involved in carbon activation
➢Following raw materials preparation,
➢Low temperature combustion, and
➢ Activation.
Raw materials
1.coal, wood, carbon materials, coconut shell, fruits shells, derived biomass, etc.
AC : Applications
➢Molecular sievesand
➢Water purification
➢As a catalyst or a support in heterogeneous catalysts,
➢Adsorbent for gas cleaning (sox, nox from flue gases) at temperatures below 200°C for the purpose of safety of the
plant and high cleaning efficiencies.
Some difficulties are,
➢Difficulty in mass transport processes and
➢Low adsorptivity due to its wide pore-size distribution
➢In the application of electro-catalyst due to its
➢ Lack of electrical conductivity.

6. The factors affecting the adsorption performances of AC
•Space velocity,
•Flow rate,
•Temperature, and
•Composition.
•It usually needs to be treated by pre-activation or loading of some active components to improve
catalytic performance.

7. AC can be tailored to be used as
•AC cloths,
•Activated carbon fiber,
•Powdered activated carbon (adsorption of liquid phases)
•Granular activated carbon
➢Used in gas adsorption and vapors
➢Used for nox and sox removal, especially when supported by metal oxides
➢Improve the performance of granular activated carbon as a special catalyst support, impregnation with metal
oxides
➢Cost effective
Also, a carbon-based monolith was developed for the same purpose.

8. Carbon monolith
➢In greek language, mono means ‘single’ and lithos means ‘stone’, which is the origin of the term monolith.
➢ The cross-section of the first monolith was like a honeycomb structure and often referred to as ‘honeycomb’.
➢A monolith
•Uni-body structured support with
•Repeating cells or long parallel channels separated by a thin catalytic wall (0.5–4 mm)
•Cell density ranging from 300 to 1200 cpsi
•Channels exist in different shapes, as either rectangular, hexagonal, triangular, or even more complex geometry.
• Inside wall is washcoated with one or more active catalysts having a high surface area and
•Contains an inorganic oxide like c-al2o3, g-al2o3, sio2, zeolite, γ-alumina, zro2, rh, etc.
• The most widely used washcoat material is γ-alumina.
➢A symbiotic relationship exists between the active catalyst and the support where the monolith structure or backbone
provides the geometry and the mechanical properties while the support layer or washcoat provides the adsorptive
and/or catalytic properties.

9. Monoliths are made from
•Ceramics (expensive)
•Metals (loss of performance in metallic monoliths prevails through sulfur poisoning by eroding the structure and
creating uneven surfaces that leads to blockages)
•Plastic.

12. monolith
➢High surface area
➢Thus it is applied in heterogeneous catalysis as a catalyst or active support component, automotive
exhaust gas purification,
➢Electrochemical reactors,
➢Electric swing adsorption, and
➢In gas-solid and gas-liquid-solid applications
➢Volatile compound emission control,
➢Water purification,
➢Ventless hoods,
➢Chemical separation,
➢Sox/nox control, and
➢Industrial off-gas incineration.

13. Pretreatment of carbon material support
The support is usually pretreated with a pre-catalyst.
➢Impregnation of the metal compounds are greatly improved by developing the oxygenated surface groups to
facilitate the distribution of catalyst particles on the carbon surface using an acidic treatment (i.e., HNO3).
➢ Pretreatment
➢Dipping active coke into a solution of 1 M of HNO3 and
➢Boiling it for 1 h
➢Washing the AC with distilled water until there was no change in the ph
➢Drying it at 110°C for 2 h
➢They performed the impregnation.

14. Synthesis and supported metal oxide catalyst
Adsorption
occurs as a result of the interaction between the molecules of a gas in contact with a binding site of the solid matrix.
Physical adsorption or physio-sorption.
•When the gas molecules are held by physical forces loosely (polar, electrostatic, or dipole-dipole),
•Reversible process
•Sorption energy found in physio-sorption of 8–41 KJ mol−1 gas
Chemical adsorption or chemisorption
•Intimate interaction that leads to formation of new substance by sharing or rearranging the electrons between an
adsorbate and
•An adsorbent with a high sorption energy of 62–418 KJ mol−1 gas,
Surface interaction of adsorbate and adsorbent.

15. Metal oxides
MOs dispersion on the surface of a support can
•enhance the catalytic performance
• economic viability
The preparation techniques of the MO determine the catalytic activities,
which in turn are associated with oxygen non-stoichiometry,
•surface area (reaction is proportional to the surface area),
•reducibility, and
•pore structure.
A vast ground for research is available for the development of hybrid MOs and carbon monolith catalysts for the
simultaneous removal of NOx/SOx pollutants at low stack temperatures.
Metal oxides were mostly used
•low production cost,
•selective action, and
•Regenerability
The conventional preparation of such composites follows three stages:
•high surface area preparation,
•incorporation of an active phase precursor and
•reduction of the metal precursor to obtain an active metallic phase

16. •The combined catalyst/adsorbent systems have shown great potential in the simultaneous
nox/sox removal at a stack temperature (low temperature).
•It was reported the nox/sox simultaneous removal efficiencies of v2o5/ac, and cuo/ac of
88% and 74%, then compared them with 60% of an alumina-based hybrid catalyst.
•In other study it was found that the economical simultaneous nox/sox removal was
achieved under a low temperature.
• A metal oxides combination with a monolithic support with an optimized proportion will
produce a novel oxide matrix material with unique properties and superior catalyst
performance.

17. Vanadium
•Low cost and
•Abundant material with
•High energy efficiency, it
•Can be loaded on supports for improving the performance of the support
•High reactivity and
•Poison resistance ability
•At stack temperatures (120 C− 200°C), V2O5/AC has a high sox uptake.
•Sox/nox removal using ac can be improved by loading v2o5 at the elevated operational temperature of
200°c.
Copper
Utilized as a catalyst in literature and was extensively discussed elsewhere.
CuO
•Inexpensive with a
•High reactivity for sox and nox reduction
•The preparation condition of cuo/AC influences the catalyst performance and the catalyst performed best
when calcined at 550°C for 2 h.

18. Sulfur and nitrogen oxides removal from flue gas
Sulfur oxide
•Major pollutants in a flue gas composition, it is a
•Colorless and
•Poisonous gas that
•Can be oxidized when reacted with water to form sulfuric acid.
•The industrial and power plants fuel combustion accounts for 13.6% and 69.7% of the global sox emission.
current techniques for SO2 removal
•Liquid-gas reactions and
•Gas-solid reactions using calcites or dolomites as solvents.
•At low temperatures, there is high sox adsorption and oxidation activities of the surface functional groups on the
support
•Steps:
i. Adsorption of SO2 on the catalyst/carbon surface
ii. Oxidation of the adsorbed SO2 to SO3
iii. Reaction of the SO3 with water in the flue gas to form H2SO4, which is stored on the pores or it is washed off.
SO3+H2O→ H2SO4
• The sulfur dioxide adsorption at a stack temperature and low surface functional groups will lead to the low removal
rates.
•The supporting of metal oxides to the adsorbent will overcome these problems.

19. Nitrogen oxides
NOx referred to oxides of nitrogen,
•It exist in different forms, such as NO, NO2, NO3, N2O3, N2O4, N2O5, NO, and NO2. Nitrogen dioxide (NO2)
•Toxic gas representing 95% of the nox that is emitted from power plant and other combustion processes and
contributes immensely to the atmospheric pollution.
NO2 is a
•red-brown gas and
•it readily forms HNO3 when it is contacted with H2O.
Techniques used for nox abatement processes, namely
•continuously regenerating trap,
•selective catalytic reduction,
•NOx storage and reduction and
•fast selective catalytic reduction, oxidation-absorption, the oxidation-absorption technology is widely favored.
•This is because nitrogen and sulfur oxides are simultaneously removed following this method.
•The SCR (Selective catalytic reduction) technology is a matured NOx removal process.

20. Selective catalytic reduction (SCR)
➢The SCR is a commercially proven technology used in coal, gas, oil-fired power stations, and chemical plants, it
is recognized due to the efficiency and selectivity in the de-NOx flue gas treatment using urea as a redundant.
➢In the SCR process, urea (CO(NH2)2) or ammonia (NH3) is injected into the flue gas stream and when it reacts
with the NOx at above or below 350°C, it produces nitrogen (N2) and water.
➢ At lower temperature below 350°C, ammonium sulfates such as NH4SO4 and (NH4)2SO4 are formed as a
result of SO2 reacting with NH3 in the presence of O2 and H2O;
➢they accumulate on the catalyst’s active site resulting in catalyst deactivation.
➢the use of activated coke/carbon in industries to remove SOx at 100°C and SCR to remove NOx at higher
temperatures has also been reported
➢NOx in flue gas can be reduced using catalyst to N2 with NH3 through a dry process at 350°C; and in a wet
process,
➢SO is absorbed at around 50°C with a waste water byproduct.
➢The metal oxides are considered to have higher SCR activity than AC at temperatures of 150–250°C
➢About 80%–90% NO removal efficiency can be achieved

21. Simultaneous sox/nox removal from flue gas
Among the major urban air pollutants, SOx and NOx are counted.
The two methods used in terms of the sorption of the pollutants were categorized and reported
Regenerable,
•SCR and
•sorbent-based methods.
Non-regenerable,
•flue gas desulfurization,
•selective non-catalytic reduction (SNCR), and
•dry sorbent-injection (DSI), where FGD and SCR uses NH3.

22. Process flow diagram of combined FGD and SCR units

23. The combined SOx/NOx removal is of interest because
less equipment is required to perform the task with a regenerable sorbent/catalyst.
the SOx/NOx removal in a single reactor is possible by
•Developing a hybrid metal oxide sorbent/catalyst.
• This could be a difficult and expensive task yet,
•Requirements:
•dry and low temperature processes with
•energy saving and
•minimized waste byproducts are desirable
•with a regenerable sorbent that can perform at stack temperature.
•Ac as the sorbent in sox/nox removal.

24. Figure: Schematic of the simultaneous SOx/NOx removal’s experimental set-up at the laboratory scale.