Carbon dioxide is one of the major greenhouse gases, and the need for stabilization of its composition in earth's atmosphere is vital for the future of mankind. Although technologies are available for capture and storage of CO2, these technologies are far too expensive for economical commercialization. Reduction of cost would require research for refinement of the technology. For more economical CO2 capture and regeneration, there is a need for development of more efficient solvent systems.
It is hoped that these developing technologies may offer cheaper and more efficient ways of capturing CO2. These developing approaches to CO2 capture are described below. Innovative designs are being investigated with regards to the packing process Aroonwilas et al.
Besides novel process designs, various novel solvents are also being tested with the aim of reducing energy consumption for solvent regeneration Chakma, ; Chakma and Tontiwachwuthikul, ; Cullinane and Rochelle, ; and IEA, One of the most promising of these new solvents is aqueous ammonia.
Although research on its use for CO2 capture is at an early stage there have been a number of papers and articles published highlighting several important perceived advantages that aqueous ammonia has over amine scrubbers and MEA in particular.
This is expected to reduce the total cost of and complexity of emission control systems Yeh and Pennline, Though a promising future replacement for amine based scrubbing, challenges remain to the use of ammonia in this manner.
To mitigate this the absorption process must take place at either elevated pressure or very low temperature and additional tail gas control measures will be necessary. The regeneration of the ammonia solvent will take place at an elevated pressure Wolf et al.
Given these uncertainties laboratory-scale testing and more rigorous process analysis and modelling will be required before ammonia based solvents can be utilised on a commercial basis.
For applications to CO2 capture, adsorbing beds of alumina, zeolite and activated carbon are currently the most effective sorbents. Though promising, this technology incurs the costs of removing the adsorbed gas, which is energy intensive Anderson and Newell, The main types of adsorption processes are as follows: In PSA, the gas mixture flows through packed beds of spherical materials at elevated pressures Mixed solvent in co2 capture technology low temperatures until the adsorption of the desired component approaches equilibrium conditions at the bed exit and the adsorbent is regenerated by reducing the pressure.
In TSA, heat is used to regenerate adsorbents by raising their temperature Hassan, In ESA, regeneration takes place by passing a low voltage electric current through the adsorbing material Hassan, Adsorption is not yet considered attractive for large-scale separation of CO2 from flue gases because the capacity and CO2 selectivity of available absorbents is low Gupta et al.
One such novel sorbent is CaO.
This carbonation-calcination cycle was successfully tested in experimental settings Abanades et al. Therefore, there is no CO2 emission reduction available by this route. Although this technology has not yet been applied in large-scale and demanding industrial settings, a considerable research effort is in progress to make it more applicable IEA, ; IPCC, The main membrane technologies are described below.
Gas separation membranes Gas separation membranes have the potential of capturing CO2, depending on the permeability and selectivity of the membrane. The applicability of this technology to CO2 capture is thus ideal for a concentrated CO2 source stream with few contaminant gases, flowing through a permeable membrane that is highly selective with respect to CO2.
These conditions would only apply to the oxy-combustion capture model for the cement industry. Despite the high concentration of CO2 in cement plant flue gas, applications of this technology for post-combustion capture would require a multistage process requiring a large number of membranes that would substantially increase capital costs Anderson and Newell, Though most have been used only in research laboratory settings, common types of gas separation membranes include polymer, palladium, and molecular sieve membranes Riemer et al.
Gas separation membranes are likely to play a key role in CO2 capture systems in the future as their energy efficiency can be higher than for absorption separation systems IEA, Gas absorption membranes In gas absorption, a microporous membrane keeps the gas and liquid flows separate by acting as a contacting device between gas mixtures and liquid absorbents such as MEA solventsthereby increasing the efficiency of physical or chemical absorption.
This technology minimises entrapment and foaming, in addition to capital costs due to its compacted nature Miesen and Shuai, ; Hassan, but is limited to gas streams and absorption liquids of similar pressure levels Anderson and Newell, Facilitated transport membranes These membranes rely on the formation of complexes or reversible chemical reactions of components present in a gas stream with compounds present in the membrane which are then transported through the membrane.
Carbozymes Trachtenberg et al. These membranes have only been tested on a laboratory scale and are fraught with limitations related to membrane selectivity and saturation but could be used in a pre-concentration step as part of other capture processes IPCC, Studies by Herzog et al.
This is not typical of gas streams in the cement industry. Furthermore, the behaviour of CO2 itself is complicated and can lead to the formation of solids that damage equipment and reduce heat transfer rates. Cryogenic separation could be effective for large and highly concentrated source streams of CO2, which compensate for the high energy demand of such a process Anderson and Newell, In the future, the most promising applications of cryogenics are predicted for the separation of CO2 in oxyfuel combustion in which the input gas has high concentrations of CO2 or from high-pressure gases such as in pre-combustion capture processes Hassan, Clathrate Hydrate While clathrate hydrates have the potential to impede the cryogenic processes described above, their formation could be used to separate CO2 from gas mixtures.
With more research, this could be achieved by combining CO2 and water at various combinations of high pressure and low temperature, leading to the formation of clathrate hydrate crystals that can be separated from other gases, transported as slurry and stored in a dedicated location Chargin and Socolow, There are a number of emerging air separation technologies that may, in the future, lead to more efficient O2 production and thus make oxy-combustion more attractive.
These emerging technologies are discussed briefly below. Ion Transport Membranes The use of membrane technologies for the production of oxygen is an emerging alternative to cryogenic air separation which may, if proven, make oxy-combustion a more attractive process.
Ion Transport Membranes ITMs are semi permeable ceramic mixed metal oxide membranes that can be used to separate oxygen from a stream of heated air.Pre-combustion CO2 Capture applied to industrial sources is an alternative for achieving low CO 2 emissions at a moderate cost.
The potential of the technology to be used as retrofit would further expand its possibilities and could be a real benefit to the industry in terms of achieving CO 2 emission reduction at relatively low cost. The retrofitting of a boiler to hydrogen fuel bears some. "Zero Waste is a goal that is ethical, economical, efficient and visionary, to guide people in changing their lifestyles and practices to emulate sustainable natural cycles, where all discarded materials are designed to become resources for others to use.
The mixed solvents are 2,3-butanedione + propylene carbonate, 2,3-butanedione + N-methyldiethanolamine (MDEA) + water, ethylene carbonate + MDEA + water, and acetoacetamide + MDEA + water.
The data are compared with literature data for the solubility of carbon dioxide in pure propylene carbonate or a mixed solvent of MDEA + water. Carbon dioxide removal (CDR) refers to a number of technologies, the objective of which is the large-scale removal of carbon dioxide from the atmosphere.
Among such technologies are bio-energy with carbon capture and storage, biochar, ocean fertilization, enhanced weathering, and direct air capture when combined with storage.
CDR is a different approach than removing CO 2 from the stack. It is the efficient equipment for excellence of water with low elements of buoyancy thanks to its system of flotation by air.
The FPAC flotation system is a large surface air .
About Me Kamalesh K. Sirkar, PhD, is a Distinguished Professor of Chemical Engineering and the Foundation Professor in Membrane Separations at New Jersey Institute of Technology (NJIT.