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Sources of carbon dioxide emissions can be either human-caused or natural. Natural sources of the emissions are beyond the control of the human beings. However, manmade sources are caused or attributed directly or indirectly to the human action. Most of the products’ production processes in the market use a source of energy that involves emission of the carbon dioxide into the environment.
Therefore, the actual producers of the carbon dioxide and the users of the consumer products whose production entails emissions are related directly and indirectly respectively ('Carbon dioxide emissions rise to record levels', 2008). Production processes that contribute to the production and emission of carbon dioxide are; energy generation from coal and natural gases, transportation (using motor vehicles, shipping & air travel), cooking heavy construction, mining, heavy construction etc. all the production process account for the majority of the products that are used by the average person.
Energy generation in the most parts of the world entails burning of some fossil fuel. As a result, there are many carbon emissions resulting from this process. 87 percent of the world is responsible for energy generation using the fossil fuels ('Trapping and keeping carbon dioxide emissions', 2013). In order to generate the energy, fossil fuels are subjected to combustion process at high temperatures whereby there is combination of the carbon part of the fossil fuel with oxygen from the air to form carbon dioxide.
Generation of electricity uses coal to produce heat, which is then used to boil water to produce steam. The steam is produced at a high pressure. For a reason it is ideal for turning turbines, which in turn generate electric ('Low-carbon footprint', 2011). All forms of energy that come from burning of fossil fuels such as coal and a natural gas are sources of carbon dioxide that is emitted into the environment. In some cases, there are backup generators that are used to produce energy during the power outages. Backup generators are designed to use either gas or gasoline. Both are fossil fuels and their combustion releases carbon dioxide into the environment.
The actual production of the fuels is another source of emissions. In the oil mining process, natural gas is usually located at the top of the oil deposits due to its less viscous nature. This aspect makes it the first one to escape. Some of the mining fields have oilrigs that are not well equipped to tap the gas ('Trapping and keeping carbon dioxide emissions', 2013). As a result, they burn it as it comes out to avoid its escape into the environment.
Burning of the excess natural gas creates two predominant issues. The miners can let it escape into the environment and avoid the burning process ('Low-carbon footprint', 2011). Alternatively, they can burn it. Letting the gas escape is precarious given that the gas is a more potent as a greenhouse gas than carbon dioxide. Burning it is the lesser evil of the tow since there is chance of cleaning up the environment using plants ('Trapping and keeping carbon dioxide emissions', 2013). Therefore, the use of electricity produced from fossil fuels contributes to the emissions into the environment.
Transport sector is the second leading source of emissions. In the sector, almost all the main means of movement rely on the combustion of one fuel or the other. Fossil fuels used in the shipping, air and motor travel account for a significant part of the individual carbon print. Every person relies on one mode of transport in one way or the other. In the transportation of major bulky goods, the shipping mode is preferred ('Low-carbon footprint', 2011). Most of the ships use diesel as the main source of fuel for the engines and other electricity generators. Due to the high carbon content in this fuel, the major shipping lines are responsible for the most carbon emissions in the transport sector. Use of any mode of transport increases the carbon print. Domestic use of natural gas for cooking and heating in cold places accounts for the majority of the individual’s carbon prints.
Carbon dioxide emissions rise to record levels. (2008). Nature, 455(7213), 581-581.
Low-carbon footprint. (2011). Nutrition & Food Science, 41(2).
Trapping and keeping carbon dioxide emissions. (2013). Physics Today.
The greatest scientific achievement that occurred in the 19th century is the discovery of electricity. It is necessary to note that in the 20th century and the 21st century electricity has completely changed the face of the earth. Electricity has become extremely useful and has changed the life of people since the day its discovery. Humans have been able to create an intimate relationship with electricity; this relationship formed to the extent that it has been impossible to separate electricity and humans. Individuals often accustomed to the use of daily utilization of electricity such as the illumination of houses, switching on the televisions and getting worldwide news, powering other electrical products such as phones and the cooking of food. This paper is going to describe the origins of electricity and how electrification has impacted the society.
Arguments that although they did not fully understand what electricity was, the ancient people knew some bits about it. Thales of Miletus is the first man to study electricity. He was the Wise one, and he belonged to the Legendary Seven wise men. He studied electricity by rubbing amber that came from a fossilized tree resin with fur. With this, he was able to attract feathers, dust as well as other lightweight projects. This formed the basis by which electricity would be later studied (Peacock, 1882). In fact, it is important to note that the word electricity originated from the Greek word electron which meant amber.
There was a pause in the study of electricity, however, in the 17th century; there was a revival and a renewed interest in this field. Scientists such as William Gilbert conducted experiments to try and study static electricity and its relation to magnetism. Gilbert concluded from his experiments that indeed there existed a fluid in the electricity. This notion and thought continued into the later 1700’s where the scientific community started to get a lucid picture of exactly what electricity was, and how it worked.
The advent of the coulombs law that said that states that like charges repel and opposites attract had its creation during that era. Thomas Edison invented the light bulb, and from there on, electricity progression is on the increase its many sources of production discovered. The current society cannot be able to live without electricity, and they have all right to thank these scientists who had a point of better understanding electricity, and its subsequent production.
Electricity can be described as a set of physical phenomena associated with the presence and the flow of electric charge. Electricity often gives a variety of effects such static electricity, the electromagnetic induction as well as static electricity (Peacock, 1882). It is also necessary to note that electricity often permits the reception and the creation of electromagnetic radiation, which includes radio waves. Since Thomas Edison discovered electricity, the electricity has found tremendous and every growing number of uses.
Electricity is a convenient way when it comes to the transfer of energy. The invention of the practical incandescent light bulb in the year 1870’s and it led to the lighting being the first publicly that is available in the applications of electrical power. Hundreds of years ago, the people never imagined that they could make their lives easily through technology; however, in the modern day people cannot be able to survive without technology. There are several aspects of the human life that electricity has been able to improve a lot and have a lot if impact.
The modern society would be incredibly different if electricity did not exist. One cannot imagine how, for example, the world would be very different without the internet. The World Wide Web is as a result of electricity, and it has had a huge effect on the lives of people. It has made the people of the world aware of the world that they are living in, and it has also made people of the world be aware of the world and the modern society on how it works. The Worldwide web is the gateway to knowledge, and it allows people to find nearly anything in the world in a matter of few seconds (Peacock, 1882). Therefore, electricity has made people to be incredibly intelligent and aware of the society in which they reside.
The first area to be somewhat affected by electricity is communication. It is imperative to note that the ability to communicate has forever been at the heart of the human endeavor, its development and its achievement. In the 1800’s, the driving force that was behind the use of technology was the improvement of the speed and distance over which persons could communicate with the military (Parker, 1992). Electricity played a very huge role in this endeavor as there was the communication of networks in different countries using a system such as the optical telegraph, semaphore as well as the mechanical telegraph.
The construction of the electrical telegraph was one of the milestones in the 1800’s as far as the pace of communication were at stake. The construction of this electrical telegraph was by Cooke and Wheatstone which exploited by the discovery of Michel Faraday’s electro-magnetism. With the invention of this electrical telegraph, a revolution had begun. In the United Kingdom, there were over 1300 telegraph stations which helped in the communication of over 10,000 miles of lines of telegraphs. Within four, years, there was the growth of 5,179 stations, which had in them over 87,000 miles of the telegraph of line.
Since the invention of the telegraph, electricity has continued to advance communications and make it more sophisticated. Therefore, it can be argued that communication is the most improved aspect in the current world. The evolution has come a long way from the electrical telegraph to computers and mobile phones. The human race is a global village people in the 21st century often communicate with each other whenever they want, and no matter the distance that exists between them.
It has become extremely difficult to imagine the world without electricity; this is because the current communication levels that the world enjoys presently will all disappear. News spread in an instance, for example, during the fateful 9/11 attack on the World Trade Center, the information spread to the world in a few minutes and people started to donate blood. Therefore, it can be seen that indeed electricity has indeed impacted the lives of people through its creation of faster and more reliable communication methods.
Electricity has impacted how the human society spends their leisure time. Before, the advent of electricity, people often read books, played physical games and told stories for fun and relaxation. However, with the advent of electricity, this changed abruptly. The human society, for example, in the early 1900’s changed to the use of radio as their main form of entertainment (Peacock, 1882). People would usually sit together and switch on the radio from where they would derive their pleasure and relaxation. With time, the ways of how leisure time is spent has continually increased in sophistication.
Before the advent of the electronics, persons often found simple ways in which they would entertain themselves. The most common forms were knitting by the fireplace, listening to the radio and playing bridge. However, in the second half of the 20th century, electricity has been able to revolutionize the way the human society spends their free time. For example, thanks to companies such as Microsoft and Sony, people can play video games and compete with other gamers around the world. Further, as far as the music goes, there has been the invention of the compact disks and cassettes in the 20th century (Bidder, 2007 ). In the 21st century, this has changed as there have been the inventions of the portable music players which have completely redefined the way people listen as well as access music.
The traditional paperbacks and hardcovers are now a thing of the past. Although sold, the world is slowly inching towards electronic books. For example, the site that is Amazon Kindle gives people access to over 300,000 books at any given time. Further, one can comfortably adjust the font size of the text that they are reading and even change the language. Therefore, it can be seen that indeed electricity over the years has impacted heavily on the entertainment scene.
The invention of the television has also completely changed the culture of the human society. Watching television often enlightens the public on social issues, political issues as well as economic issues that are currently going on in the world. Further, it often does this in a split second and gives a lot of information to the world (Parker, 1992). The watching of movies and films has created another way of how people can be able to spend their leisure time, people nowadays when they are in the dating period often go the movies as a part of their relaxation program. Consequently, it is right to argue that indeed electricity has been able to make entertainment possible; it has created an exciting and fascinating world.
Electricity has been pivotal in the health treatment and services section. This is because it has changed the way people are usually treated and the machinery that exists in hospitals that are used for treatment. In the past, people took herbal medicine that was not even manufactured but instead it was raw from the source (Cadena, 2002). This has changed over the centuries, and the medical technology has considerably improved. In hospitals, surgeons are able to carry out their operations in an effective as well as efficient manner. This is because there is enough lighting as well as the existence of electrical equipment that help in the maintenance of the heart beat as well as the stabilization of the body.
There are several tools that completely revolutionized how medical procedures are successfully done. For example, there is no single item that identifies a doctor like a stethoscope. The stethoscope uses static electricity and for centuries, physicians often relied on auscultation and percussion (Parker, 1992). Also, equipment such as the diagnostic imagining has also transformed the whole health care industry. The machine helps in the diagnosis of diseases; the X- ray is one of the most famous examples of the diagnostic imaging machine. Further, there are other computerized diagnostic imaging machines such as the CT and CAR scans, the MRI, and even the ultrasound. All these, have changed the way in which medicine is conducted, and have generally improved the general health of the public.
The electrocardiogram referred to as ECG and sometimes EKG used worldwide as a way of diagnosing the heart conditions. An electrocardiogram records the small electric waves generated during heart activity and therefore, it becomes extremely easy for doctors or the medical personnel understand and detect abnormal activities in the heart. It is significant to note that a healthy heartbeat initiated by a pulse of electric current is what is considered normal, this tiny electric shock then spreads through the heart and makes the heart muscles contract. The ECG is important as it enables the measuring of how the heart is beating and whether the heartbeat is regular or not. If it is not regular, the medical personnel and doctors can be able to take action in order to ensure that the patient gets stabilized and the causes of the abnormal heartbeat understood.
In conclusion, it can be argued that indeed electricity is an integral utility as far as the modern society is in question. Electricity is the mother of most modern inventions, it has completely changed the way the world is and how it will be in the future. It has impacted the society in more ways than one. It has been able to establish links to everything, from the springing of the human’s subconscious fear of the dark to what can only be said as the practical need for working illumination in the industrialized world (Dowswell, 2002).
The whole world in the 21st century essentially runs on electricity it is the backbone of economies and one of the most significant factors when it comes to production. Electricity has not only been ingrained in the life of the people but also it has become critical for the continued existence of the human race. Electricity can be described as the future; however, it is also the past and present. Most medical treatments and procedures are often commonplace today; however, it is extremely difficult to understand how they could work without the modern lighting and power.
Lighting alone can be described as the backbone of civilization, and it paves the way for extended work capabilities. It has also enabled the development of the certain household goods that are important in order to enable comfortable living. Therefore, this paper has shown that indeed electrification has impacted the world in a great way, electricity has been able to run the world with world governments, financial institutions and corporations all relying on electricity for direct trading, commerce as well as communication. The grip that comes with electrification has extended to the seemingly insignificant aspects of the average citizen such as the use of mobile phone for communicating, and the ability to cook indoors with electricity.
Peacock, R A., (1882) Saturated Steam the Motive Power in Volcanoes and Earthquakes: Great Importance of Electricity. London: E. & F.N. Spain.
Parker, S., (1992). Electricity. London: Dorling Kindersley.
Dowswell, P., (2002). Entertainment. Chicago, Ill: Heinemann Library.
Cadena, R., (2006). Automated Lighting: Art and Science of Moving Light in Theatre, Live Performance, Broadcast and Entertainment. Amsterdam: Focal Press.
Bidder J., (2007) Inventions We Use for Information and Entertainment. Milwaukee, WI: Gareth Stevens Pub.
Civilization today is being faced by numerous environmental concerns. One of such concerns is the level of atmospheric carbon dioxide sharply rising. This is a phenomenon that is occasioned by anthropogenic emissions. It is from the combustion of natural gas, oil and coal that these emissions stem mostly. This is a situation that is expected to extend into the future due to various factors such as industrial development and economic growth, especially in developing nations. One situation that would be ideal with regards to this is the transition of the current infrastructure from sources that are carbon based to alternatives that are much cleaner. If such a change was preferred however, significant modifications would be required from the existing energy framework. It must be noted that most of the technologies that have been proposed are yet to be developed sufficiently enough to facilitate industrial implementation of such large scale. This implies that sequestration technologies and carbon capture that can capture carbon dioxide efficiently from current emissions sources will continue playing a critical role until the energy infrastructure is subjected to significant modifications.
There are various settings under which carbon dioxide internments technologies. One such scenario where this could be implemented quickly is at the stationary point bases. Examples of such sources include natural gas power plants and coal. In the U.S for instance, it is electricity generation that is responsible for much of the carbon dioxide emission, claiming up to 41 percent of the total emission in the country. Worldwide, the U.S contributes almost 60 percent of carbon dioxide emission. This further underlines the importance of installing rupture systems that are effective so as to aid in plant configurations. This will be instrumental in reducing the ever increasing emissions. The CO2 that has been captured will have to be taken through permanent sequestration, a process that will ensure that the CO2 is injected into geological formations that are found underground. The underground geological formations in this regards include salt water aquifers and depleted oil reservoirs.
In the perspective of procedures like enhanced oil recovery (EOR), comparable technologies are already proven. Further, construction of more CO2 sequestration sites is already on-going. It must be noted that the captured carbon dioxide has a reuse which is a reactant in chemical conversions. This gives a different sequestration pathway. This, however, is not a viable strategy that is long term, especially given the tremendous quantity of carbon dioxide emissions world wide. Any commodities that are prepared from these would become saturated rapidly, and this is what most companies are avoiding. However, it is not all gloom as there exist other scenarios that are also potentially promising that would come in handy in ensuring that a considerable fraction of the CO2 that has been captured is well utilized. One such scenario would be to convert it into fuel for transference purposes. For this to be done effectively, however, it has to be ensured that there are dependable methods of transferring the conversion through energy sources that are renewable. However, the sequestration pathway notwithstanding, carbon dioxide must be captured by CCS systems from flue gas in a fashion that is reversible and efficient. The right properties will consequently be exhibited by discovery of other materials that will ensure that the CO2 is captured. This is an area that calls for urgent development.
CO2 is something that has always proven a challenge. To begin with, the capture process is often associated with massive penalties, and this continues to be the most obvious challenge. Even with current technologies, massive costs are still involved, and this has always presented another barrier. It can be established that it is the carbon dioxide selective capture from power plant flue gases that attracts much of the cost, almost 70%. This is a value that has to be cut, especially if the CO2 mitigation approach is to become viable. The regeneration of the material that has been captured requires a large energy input, and this is what primarily brings about the high costs. This cost has to be kept down lest the whole project will fail to be economical. Current technologies that are highly developed will have to be sought will be used in capturing CO2 from the post combustion flue gas. This, it must be noted, will involve an aqueous alkanolamine solution that carries with a significant amount of energy penalty. The penalty is about 30 percent of the entire output that the power plant releases. Most of this is linked with setting free the CO2 that has been captured from the capture medium. The energy input minimization is a critical step towards regeneration. The thermodynamics of the collaboration between the adsorbent and the CO2 has to be fine-tuned, especially since this is a critical consideration when it comes to improving the energy efficiency that will ensure the capture of CO2.
Metal organic frameworks represent another class of materials that could be utilized as the ideal platform for the manufacture of post modern CO2 capture materials. This is largely due to their efficient capacity for gases adsorption, as well as their chemical and structural tunability. One critical component with regards to this is the ability to select rationally the framework components, as this will come in handy in allowing the attraction of the inner pore exterior towards carbon dioxide. This will further ensure that the CO2 is controlled precisely, and will consequently facilitate the material properties that have been optimized in such a way to ensure a particular kind of carbon dioxide capture to be done. These could include oxy-fuel combustion, pre-combustion capture, or even post-combustion capture.
For this reason, considerable effort has been witnessed in recent times to address the gas separation showing of metal-organic frameworks. Studies have been conducted in a bid to determine the influence of deploying such materials in the real world capture of CO2. It must be appreciated that this is an area that has witnessed impressive progress over the decades. The emphasis obviously has to be placed on comparing how metal organic frameworks have performed in relation to existing technologies. For this to be done conclusively, it is important that crucial areas that need adjustments be highlighted so that the necessary improvements can be done. This is a phase that is required urgently. Rapid progress is being made in this area, and as a result, this study will limit itself to the capture of CO2 from the power plants. There are various scenarios for the capture of CO2. They include direct air capture, capture from transportation emissions, as well as natural gas processing, also referred to as (CO2/CH4 separation). All these represent critical research areas, and as such, maximum care should be exercised when addressing them.
This study will largely concern itself with providing an overview that is comprehensive of the considerations linked with the capture of CO2 from power plants through the use of metal organic frameworks. It is therefore imperative that it follows an outline that is easy to follow. It will first provide a general overview of the problem that is associated with CO2. It will then give a detailed description of the technologies that are currently in use in the capture of CO2 from power plant flue gas streams. This paper will also introduce the chemistry of metal organic framework. The different performance parameters will then be summarized so that it can be easy to evaluate them. This will go a long way in helping to know how metal organic frameworks for the capture of CO2 perform. It will outline the critical characterization methods that can be utilized for getting a correlation that is detailed between the chemical and structural features of the metal organic framework. This will also cover its adsorption properties. Metal organic frameworks, it must be noted, possesses three major scenarios for the capture of CO2 from power plants. They include oxy-fuel combustion, pre-combustion capture, as well as post-combustion capture. Recent times have seen the emergence of CO2 capture through membrane technologies. The flue gas components have been subjected to varying diffusion properties that are harnessed in such a way that they will ensure gas separation. There are areas where more work is needed urgently if the idea of next-generation metal-organic framework is to be realized.
Carbon dioxide emission from Anthropogenic Sources
In recent times, atmospheric carbon dioxide has been rising in levels, and this is a fact that has been properly documented. This is largely due to the numerous implications that it has with regards to global warming. It is an issue that has generated extensive environmental fears, especially given the continued use of fuels that are carbon-based. The atmosphere is currently concentrated with CO2 t a far greater level compared to any other period in modern history. In 2011, for instance, it exceeded 390 ppm. For a clearer picture to be painted, this value has to be put into perspective. One way of through which this can be effectively done is to analyze ocean sediments for seawater calcium and pH, carbonate mineralogy and magnesium, as well as ice core data. The conclusion that was arrived at is that in the last 400,000 years, such a level has never been reached by atmospheric concentration. In fact, over the entire period before this extremely quick increase was observed, the atmospheric level of CO2 only varied gradually from 100-300 ppm. This has been blamed on global industrial development that has taken place in the past century. This has created atmospheric carbon dioxide sources, consequently leading to a quick increase of CO2 atmospheric concentration. The levels that have been reached have obviously surpassed those that natural fluctuations would normally bring.
The burning of fossil fuels is representative of about 50 percent of worldwide greenhouse gas emissions. CO2 global emissions have risen significantly to over 80 percent in the period between 1970 and 2004. Experts expect the emission levels to continue rising over the coming decades given the ever increasing energy demands globally. This is due to industrial and economic development, as well as population growth. This is an issue that is so sensitive, and it explains why in 1998 the IPCC was formed to evaluate greenhouse gas emission effects on global climate. This would make it easier to predict possible future outcomes, while also suggesting remediation strategies. According to statistics released in 2007 by the IPCC climate report, average global temperatures will continue to increase from about 1.8 to 6.4 degrees centigrade as the 21st century concludes. The current mitigation efforts have been based on the implementation of pricing structures of CO2 emissions on the energy providing sector. A transition is being encouraged towards non-carbon and low fuel sources. Various strategies have been outlined with regards to this. CO2 that has been received from power plant emissions that are fossil fuel-fired are critical in avoiding worsening climate change. Alternative energy technologies should be adapted to, even though will take numerous years of implementation, development and research.
CO2 Capture at Stationary Point Sources
The CO2 emissions from the burning of coal to provide electricity represent about 30 to 40 percent of the entire contributions of CO2. In the U.S for instance, statistics indicate that as of July 2011, coal contributed to about 43 percent of the produced electricity. In 2004, coal contributed to about 82 percent of CO2 emissions. Coal-based power generation continues to play a significant role, largely due to the massive reserves that are available for extraction. Global energy demands have also been escalating, and this is yet another reason. The U.S has in recent times been surpassed by China as the largest greenhouse gases emitter, and this only shows how coal will continue to be used widely for electricity generation. This trend is expected even at the global level where gas and coal generation expected to continue rising to about 21.9 trillion kW.h by the end of 2035.
Although the massive usage of gas and coal to generate electricity has caused widespread concern, it also represents a promising scenario through which the emission of CO2 could be reduced dramatically. CO2 capture systems will have to be installed within gas and coal fired power plants, as this will remove selectively components of CO2. This will consequently reduce global annual emissions, and lessen any environmental impacts. The Department of Energy in the U.S has been trying to develop advanced compression technologies that can capture CO2 for both new and existing coal-fired power plants. When these are combined, they could get a capture of about 90 percent of the entire CO2 that has been produced. The cost of electricity will also reduce by more than 35 percent. The greatest challenge currently facing this implementation of CO2 capture is the innovation of new materials that can show suitable chemical and physical properties that can be used in real world systems. With regards to gas or coal fired power plants, three scenarios exist through which new materials could be used to cut the energy requirements that are needed during capture.
Options for CO2 Sequestration
CO2storage/sequestration is yet another area that should be considered. In the event of the capture framework being successful, enormous CO2 quantities would be obtained. It is in the capture step that much of the CCS cost comes from. Other steps in the CCS system are also associated with significant practical considerations. Inmost instances, the CO2 quantities that are captured are too big for any chemical industry to reuse. CO2 must be stored sustainably if the development of the CCS is to be successful. No leakage should be allowed as this will greatly aid in environmental conservation. Depleted natural gas and oil wells are considered the geological formations that are most suitable when it comes to long-term sequestration. Extraction of fossil fuels by pressurization can greatly be enhanced by injection of CO2 into natural gas and oil deposits. In such instances, CO2 is normally recovered with natural gas or oil before being separated and put back into the well. There are various CCS demonstration projects that are being operated, implemented and planned globally. The coal seam in Poland is one such example.
Current CO2 Capture Materials
There is need for the right materials to be used inCO2 capture systems, especially when it comes to installing gas and coal fired power plants. Before such materials are developed, a lot of consideration has to be put on numerous performance parameters. These have to be tuned finely based on the CO2 capture type and the power plant’s particular configuration. For the cost of CO2 capture and the energy penalty to be lowered, these parameters should be optimized. This will also come in handy in allowing widespread implementations.
For any material tat is intended for CO2 capture, the most critical performance parameter is its selectivity towards carbon dioxide. The importance of a high selectivity cannot be overstated. Another major consideration is the material’s affinity towards carbon dioxide. The interaction should not be too strong as this will only lead to energy requirements that are very high, especially when it comes to the desorption of the CO2 that has been captured. On the contrary, although regeneration costs would be lowered by weak interactions, the CO2 would only have low selectivity over other components relating to the flue gas. It must be ensured that the material exhibits stability that is high under the conditions of regeneration and capture. Huge CO2 quantities have to be detached from the flue gas, and this implies that CO2 should be taken by the materials at a high density.
Aqueous Alkanolamine Absorbents
To date, there have been extensive studies regarding aqueous alkanolamine solutions for their ability to capture CO2. Despite being in use fro many decades, they are still considered the best option. The amine functionalities take part in a nucleophilic attack relating to the carbon atom to form a bond that is C-N. Depending on the specific amine in question, the result will normally be the formation of bicarbonate or carbonate species. When it comes to CO2 capture applications, Monoethanolamine remains the most studied alkanolamine. It is normally dissolved in water at a specific concentration. There are numerous other alkanolamine that are deemed industrially relevant such as N-methyldiethanolamine and 2-amino-2-methyl-1-propanol. Their CO2 absorbent solutions have been studied by experts for some time now to determine their suitability. Other amine-type solvents have come into the picture in recent times. They include imidazolium-based ionic liquids and piperazine, and they have generated increased attention due to their enhanced absorption properties. They also possess higher thermal and chemical stability than conventional amine solutions. As adsorbents for capturing CO2 in large scale, aqueous alkanolamine solutions are known to have numerous significant limitations. Towards heating, the solutions are rather unstable, and this greatly limits their ability to regenerate. Amine is also vulnerable to decomposition, and this further affects its absorbent performance. It also ensures that the lifespan of the solutions is greatly diminished. Amine solutions further corrode the vessels that they are put in, although this can be addressed by limiting alkanolamine species concentration or adding corrosion inhibitors.
Solid Porous Adsorbent Materials
Solid porous adsorbents have lower heat capacities, and this has led to the continued interest in them as materials for the capture of CO2. Zeolites are porous aluminosilicate materials, and as such, have a higher thermal and chemical stability. When compared to the post-combustion capture of CO2 employing the alkanolamine solutions, small scale pilot plants that utilize zeolites have shown more ability for rapid CO2 adsorption. There is also a lower energy penalty that is associated with them. What makes most of the zeolites undesirable is the fact that water vapor readily saturates them, and this consequently reduces their CO2 adsorption capacity over time. The large enthalpy of CO2 adsorption leads to CO2 desorption temperatures that are relatively high.
This underlines the importance of material optimization, especially when it comes to increasing pore surfaces affinity towards CO2. Zeolites have a robust nature as well as impressively developed structural chemistry, and this explains their attractiveness in CO2 capture applications. Zeolites have numerous characteristics which enhance their CO2 selectivity. One of such features is metal cations that are charge-balancing within the pores. When the surfaces of porous solids are highly charged, they can bring about high affinities for CO2. For this reason there has been an increasing investigation on alkaline earth metals and alkali to capture adsorbents. As CO2 adsorbents, activated carbons have also been attracting wide interest. These materials represent amorphous porous carbon forms that can be made by the pyrolysis of certain carbon containing biomass, fly ash or resins. Activated carbons, it must be noted, have relatively uniform electric potential, and this gives them a lower empathy as far as CO2 adsorption is concerned. This implies that they have lower CO2 capacities compared with zeolites. However, the fact that their surfaces are significantly higher leads to an adsorption capacity that is greater. In addition to carbon based materials and zeolites, there exist other porous materials classes, which can all be used as potential adsorbents when it comes to the capture of CO2.they include amine-grafted silica and covalent-organic frameworks. Micro-porous organic polymers, in addition, have proven that they can be used in gas separation. This is a critical step in CO2 capture.
Temperature and Pressure Swing Adsorption
In any process that deals with CO2 capture, it is imperative that the adsorbent be regenerated after every adsorption cycle. For a solid adsorbent to be regenerated, various factors must be present. There has to be vacuum swing adsorption, temperature swing adsorption, as well as pressure swing adsorption. The solid adsorbent in all these cases will be packed in a huge fixed-bed column before the adsorbate is desorbed from the material through temperature increment. There is also the possibility of using heat that is low-grade from the power plant for purposes of regeneration. For this purpose, TSA is regarded as the most promising CO2 capture process. Normally, a TSA cycle includes a saturated adsorbent being heated from ambient pressure up to optimal desorption temperatures. With the increase in temperature, gas molecules desorb, and this is followed by increased gas pressure which consequently pushes the gases that have been desorbed from the column. After equilibrium has been achieved at desorption maximum temperatures, any desorbed gases which fill the empty spaces are pushed with the use of a purge. In all the regeneration cycles, i.e. outlet gas stream and desorption temperature, the chances of optimizing the parameters, the option of ensuring the regeneration process is tailored to ensure that it has adsorbent properties.
Metal organic frameworks represent a different kind of porous solids which have in recent times attracted much attention. This is largely due to their potential applications in various areas such as drug delivery, heterogeneous catalysis, molecular separation, as well as gas storage. These structures are made of metal-based nodes, and as such, they are bridged by the linkage of groups which then forms three, two or one-dimensional coordination network. It must be noted that they have extraordinary surface areas as well as pore surface properties that are finely tunable. This gives them potential scalability as far as industrial scale is concerned.
Synthesis and Structural Features
The modular synthesis is often used to achieve the synthesis associated with metal organic frameworks. For a crystalline porous network to be afforded there has to be the combination of organic ligands and metal ions. Synthetic procedures, it must be noted, need a wide variety of temperatures, reaction times, reagent concentrations, reagent ratios and solvent compositions. For the framework formation to be effected, mechano-chemical procedures, sonication-assisted synthesis, and microwave heating have all been employed. Zn4O (BDC) 3 (MOF-5) compounds remains one of the most researched metal-organic frameworks. These materials, otherwise known as isoreticular metal-organic frameworks have varying pore functionalities and pore sizes, and this suggests that the material has properties that can be tuned finely by using the appropriate linker type. The ligands have lengths that can be changed, and this allows the materials to form more easily through network connectivities. One area that still remains to be explored is the flexibility that metal organic frameworks have. However, in the CO2 capture context, what is of particular interest is the ability to modify readily the surface chemistry relating to metal organic frameworks. Despite the apparent ease of the synthesis of metal-organic frameworks, great challenges still remain, especially when it comes to preparing new materials that can be used in optimizing the reaction conditions. It is these conditions that lead to the metal-organic framework that is desired. The end product should show high yield, as well as crystallinity. The reaction parameters that have been employed often show slight changes such as reaction time, reaction temperature, metal counteranion, metal-to-ligand ration, as well as presence of a covalent. This can have an impact that is significant on the expected products.
Metal-organic frameworks have a thermal and chemical stability that is generally lower compared to that of other porous inorganic solids and even zeolites. This is as a result of the rather weak coordination metals which connect the ligand components and the metal. Most of them, it must be noted, are moisture and air sensitive, after evacuation of the pores, and this calls for careful handling, especially if there is inert atmosphere. Researchers have been trying several approaches in a bid to improve metal-organic frameworks stability. This has been done mainly through using components that can give metal-ligand bonding that is stronger. When assessing metal-organic frameworks for purposes of installation, an additional characteristic which should be considered is its thermal conductivity. This is a critical parameter, especially when it comes to establishing the heating effectiveness of the adsorbent bed. This will also show the duration that the regeneration cycle is expected to take. Usage of solid adsorbents like metal organic frameworks comes with its fair share of advantages. One such advantage is that the heat capacity will be reduced considerably compared to aqueous alkanolamine solutions. As far as temperature swig is concerned, this continues to be a critical parameter. This is because it reflects the energy quantity that is needed to heat the sorbent material.
CO2 ADSORPTION IN METAL-ORGANIC FRAMEWORKS
Data on single-component gas adsorption isotherm can be used in approximating the adsorption selectivity relating to CO2 over other gases. This is a parameter that is critical, especially given its ability to determine how pre the CO2 that has been captured is.
Capacity for CO2
When it comes to evaluating the ability of metal-organic frameworks to capture CO2, the adsorptive capacity continues to form a critical parameter. The mass of metal-organic framework that is needed will largely be determined by the gravimetric CO2 intake. Simply put, this is the quantity of the adsorbed CO2 within a materials unit mass. The volumetric capacity, on the other hand, implies how solidly storage of the CO2 can occur within the material. This has an influence that is significant on the adsorbent’s bed volume. Metal-organic frameworks have high internal surfaces which come in handy in providing for massive CO2 adsorption capacities. The guest molecules located on the pore surfaces have a close approach and an efficient packing which also aids this cause significantly.
Enthalpy of Adsorption
The enthalpy of CO2 adsorption continues to form a critical parameter, especially given the significant influence that it has over the performance of specific materials for the capture of CO2. The affinity of pore surface to take in CO2 is dictated by the enthalpy of adsorption, and this is yet another parameter that cannot be overlooked. This is because it dictates the energy requirements, as well as the adsorptive selectivity that should be used to release molecules of CO2 during regeneration. Before metal-organic frameworks are optimized, it is essential to determine the precise control regarding the binding power of CO2. For regeneration to be increased, materials which strongly bind CO2 should be used. This will go a long way in ensuring the framework CO2 interactions are broken. It must be ensured that the enthalpy of adsorption does not go too low, because this will compromise the purity of the resulting CO2 that has been captured. Because f the lower density of the adsorption of CO2, the adsorbent beds would have their volume increased. Various methods can be used when it comes to computing the isoteric heat of adsorption. One such method is the use of dual or single-site Langmuir-type expressions. When doing the fit for materials having both weak and strong binding sites, the dual-site model is preferred. This model assumes that it is through Langmuir-type behavior that adsorption occurs. This implies that at any given pressure, the total quantity adsorbed is given by the addition of single-site Langmuir isotherms.
Selectivity for CO2
In capture applications for CO2, it is critical that there be a huge selectivity for CO2 compared to the other constituents of the gas mixture. There are two main mechanisms through which this selectivity can originate. There is the metal-organic framework that has small pore sizes which permit molecules of specific kinetic diameter to prolix into the pores, and there is the size-based selectivity. For CO2/H2 and CO2/N2 separations, the molecule’s rather similar kinetic diameters would need materials functioning on a mechanism that is size-selective to possess pores that are very small. This may ensure that throughout the material, diffusion of gases is limited. Although some metal-organic frameworks are known to exhibit pore apertures, especially in this size regime, most materials that do exhibit high adsorption capacities and high surface areas for CO2 have pore openings which are considerably larger compared to the sizes of molecules. It is in the adsorptive phenomena that much of the research dealing with metal-organic frameworks relies on when it comes to the separation of molecules. There are various ways through which adsorptive selectivity can arise. One such ways is through chemical interactions of the metal’s surface functionalities and the gas mixture components.
Estimation from Single Component Isotherms
The method that is commonly used when it comes to assessing the adsorptive selectivity that CO2 has from a mixture of gas is the computation of a selectivity factor. The gas adsorption isotherm, which is the experimental single component, is used for this purpose. The selectivity factor is in this case defined as the adsorption quantities molar ratio at the relevant partial pressures relating to the gases. It is imperative that the selectivity factors be normalized in line with the gas mixture composition. The expression for this is;
S= (qi/q2)/ (p1/p2)
S represents the selectivity factor, qi is the quantity adsorbed, whereas p1 is the partial pressure.
Ideal Adsorbed Solution Theory
It is always a challenge to directly measure the adsorption selectivity relating to an adsorbent for gas mixtures. Examples include those witnessed in the capture applications of CO2. However, the act can be predicted conveniently from single-component adsorption isotherms. In this method, the collection of isotherms takes place at similar temperatures before the application of IAST is done to predict the selectivity of materials that is expected. IAST, it must be noted, has two major assumptions. First, it assumed that the components have to mix, and they also have to behave like ideal gases. The surface of the sorbent therefore has to be homogenous. At mixture fractions that are very high, the theory begins to have its accuracy diminish because under such conditions, integration of less-adsorbed species is involved in IAST calculations. The gases will also have their behavior described less accurately by IAST within metal organic frameworks that are flexible.
Gas Mixtures and Breakthrough Experiments
Breakthrough experiments represent relative straightforward ways that can be used to assess how metal-organic frameworks perform in gas separation. In a typical set up, a comprehensive process would have to be followed. This would include the gas mixture being flowed through a sample which would then be incorporated into a membrane or pressed into a pellet, while the outgoing gas stream is being monitored. This is normally done by mass spectrometry or chromatography.
In Situ Characterization of Adsorbed CO2
When it comes to researching the relationships that exist between chemical features and structure of metal-organic frameworks, the importance of in Situ methods cannot be underscored. For instance, the characterization of crystallographic of CO2 allows the position of CO2 molecules to be observed directly within the structure, and this comes in handy in facilitating the understanding of any interactions that take place within the material. This is what gives rise to adsorptive tendencies. There are elaborate experimental facilities that are often required during such experiments. In Situ infrared spectroscopy gives a convenient probe which can afford information relating to the adsorption sites of CO2.
When it comes to obtaining structural information directly relating to CO2 that is bound to metal-organic framework surfaces, the X-ray provides the technique that is most informative. Here, a powder sample of a metal or an activated single crystal is put into a cell like a glass capillary. Consequently, this is dosed and evacuated with a specific quantity of CO2 gas that is high-purity. This is then followed by the collection of diffraction data before the subsequent performance of structural refinements that will enable the revealing of the location of the CO2 molecules that have been dosed. Conceptually speaking, such experiments are quite simple, but there exist certain issues which only complicate the entire elucidation of the adsorption sites of the CO2. X-rays absorption by disorder of the adsorbate molecules, sample integrity upon evacuation and glass capillary within the framework’s void spaces can considerably affect the refinement’s quality.
Computational Modeling of CO2 Capture
Computational studies regarding CO2 adsorption within metal-organic frameworks represent a critical endeavor that supports experimental work that is done in the area. With regards to this, grand canonical Monte Carlo replications have been used extensively to predict mixed and single component adsorption isotherms regarding metals.
POST COMBUSTION CAPTURE
When coal is burned in air, it generates flue gas which has a CO2 concentration that is relatively low. Approximately, the concentration is about 15-16 percent. The effluent is largely made up of N2 together with other minor components like SO, NO, CO, O2, and H2O. The gas stream is let out at an extreme pressure of about 1 bar. Since the removal of SOX would precede the capture of CO2, it is expected that the flue gas would enter the scrubber of CO2 at temperatures ranging between 40 and 59 degrees Celsius. There are various factors that should be considered when choosing the ideal adsorbent for CO2 capture from the post-combustion flue gas. The factors include rapid gas diffusion via the adsorbent material, long term stability under the conditions of operation, minimal energy penalty, as well as high volumetric and gravimetric CO2 adsorption.
Metal-Organic Frameworks for CO2/N2 Separation
At above bar 1, most of the frameworks today show large adsorption capacities for CO2. This is largely as a result of their high surface areas. It must be noted, however, that in most instances these compounds are rarely well suited when it comes to post-combustion capture. This is because at lower pressures, the adsorption capacity is more critical because the CO2 has a low pressure. The selectivity computation for CO2 over N2 is done best through the adsorption capacities at 0.75 pressures for N2, and 0.15 bars for CO2. It must be noted that for a flue gas, the total pressure is about 1 bar. It is also critical that the direct measurement regarding multicomponent isotherms be done so that the precision of selectivity factors can be forecast. This is especially so when it comes to IAST and single-component isotherms. For preliminary assessment of various materials, the usefulness of calculated selectivity factors cannot be ignored. This is because when it comes to CO2/N2 binary isotherms, experiments are yet to be reported. Ideally, when it comes to high adsorption selectivities, the adsorption of CO2 should be maximized at pressures of about 0.15 bars. In a flue gas mixture that is realistic, the binding sites that are strongest would normally be occupied by CO2. This is because CO2 has a quadrupole moment and greater polarizabilty. Single-component isotherms are known to overestimate the adsorption capacity that N2 has, and as such, greatly reducing the calculated selectivity. For this effect to be minimized, the IAST method has to be utilized when it comes to selectivity calculations. It is yet to be fully established if the selectivity values for flexible frameworks through the aforementioned method are of any relevance.
Enhancing CO2/N2 Selectivity through Surface Functionalization
The framework functionalities should have it affinity turned towards CO2. This is important for optimization of the properties tat have been adsorbed. The best pore surface properties would not only minimize the regeneration energy, it would also increase the adsorbent with great adsorption selectivity.
Pores Functionalized by Nitrogen Bases
There have been intensive studies regarding metal-organic frameworks that are functionalized with organic groups that contain basic nitrogen. These studies largely involve their CO2 adsorption properties. In some instances, acid-base type interactions pitting CO2 and the lone pair of nitrogen have been observed. The incorporation of nitrogen enhances the adsorption of CO2 in varying degrees. This depends largely on the functional group nature. Three major categories of metal-organic frameworks that are nitrogen functionalized have been synthesized to date. They include alkyl amine, aromatic amine and heterocyclic bearing frameworks. Because synthesis is so easy, a huge percentage of metal-organic frameworks that has organic bridging units have been studied, especially in the framework of CO2 capture. When these heterocycles are incorporated, it comes in handy in improving capacity at low pressures. It must be noted that the ratio of heteroatoms compared to that of carbon atoms can be quite large as far as these frameworks are concerned. This could result in pore surfaces that have great surface polarization. Initially, there is often a large isoteric heat that can be attributed partially to the existence of an aromatic amine.
This also comes in handy in decorating the pore surface. The nitrogen heterocycle also has considerable effects since the bio-MOF-11 has a CO2 capacity that exceeds that of aromatic amine. Aromatic amine that contains linkers is commercially available, and this is what has generated all the interest, especially with regards to functionalized frameworks. Amine functionalization has been proven to increase CO2 capacity in various other metal-organic frameworks. These include In(OH) (NH2-BDC), AI(OH) (NH2-BDC) (NH2-MIL-53(AI), and Ni1(NH2-BDC)2 (DABCO). This can be noted when their capacities, which are low-pressure, are compared with parent material. This, however, is not to imply that the amine is always directly responsible for adsorption that is enhanced. It has been proven by studies that at low pressures, there is very minimal interaction between adsorbed CO2 and aromatic amine. However, formation of a flexed pore structure is aided by the availability of the amine. This is especially so during evacuation.
For amine based frameworks that are aromatic and heterocycle, there is an enhanced adsorption that is normally witnessed at low pressures, and this is a fact that has been attributed to the basicity that is linked to the nitrogen donor atom. The differences in basicity can be explained by the PKa values that ammonium complexes have. It must be noted that aniline and pyridine have conjugate acids that are generally more acidic as compared to the conjugate acids of ethylamine and benzylamine. Thus when metal organic frameworks that have aniline and pyridine derivatives increase their adsorption of CO2, it is mainly due to the addition of polarizing sites which decorate the pore walls. For the chemisorptive interactions to be mimicked, especially those which are seen in aqueous amine scrubbers, there is need for more basic amine species to be added into the pore surfaces.
Other Strongly Polarizing Organic Functional Groups
Organic linkers that have heteroatom functional groups have great effect when it comes to CO2 adsorption behavior. The functional groups in this regard include halide groups, thio, cyano, nitro and hydroxyl. The adsorption of CO2 is greatly enhanced by the functional group’s polarizing strength, as well as the degree of ligand functionalization. This implies that CO2 adsorption will be influenced strongly by powerful polarizing groups. The IRMOF series regarding metal-organic frameworks have been proven to be similarly suitable when it comes to determining the effect on CO2 adsorption that functional groups have.
Exposed Metal Cation Sites
In order to improve the selectivity and affinity of metal-organic frameworks towards N2 and CO2, one strategy that has come in handy is generation of exposed metal cations, and this should be on the pore surface. For these sites to be obtained there is need for the materials to be desolved. In this regard, one solvent molecule will have to be removed at temperatures that are elevated. Previously, such sites of metal binding have been shown to help in the close approach of guest molecules
Considerations for Application
Most studies dealing with the evaluation and synthesis of metal-organic frameworks for the capture applications of CO2 focus almost exclusively on the separation act of CO2/N2. This implies that other crucial aspects that touch on the actual flue gas are actually ignored. Whereas N2 and CO2 take up about 90 percent of the composition of flue gas, it is important to comprehend what effect the remaining 10 percent has if the proper evaluation of the materials is to be achieved. Different studies have been conducted with the aim of determining the performance of metal-organic frameworks based on conditions that are more realistic. One of such studies has dealt with humified gas mixtures.
Stability to Water Vapor
The primary challenge that has always presented itself when it comes to the capture of CO2 is separating N2 from CO2. When it comes to researching metal-organic frameworks fro post combustion capture of CO2, the fact that flue gas is normally saturated with water must be taken into account. Although it might be possible to achieve fractional dehydration of the effluent, completely drying the flue gas before extracting CO2 is a process that is costly, which might not be possible especially on such a large scale. This implies that any adsorbents that have been utilized to capture CO2 from flue gas have to be stable even if some water vapor is present. When it comes to the assessment of metal organic frameworks in post combustion capture process of CO2, it is crucial to consider important aspects such as the water vapor’s effect on the separation of N2 from CO2, as well as the framework’s stability to water vapor. As for water stability, it must be noted that the metal-organic framework’s weakest point is the metal-ligand bond. This implies that hydrolysis could result in bound ligands displacement, and the framework structure would consequently collapse. It is in the zinc-carboxylate that is MOF-5 based that this was initially witnessed. It is sensitive to water, and as such, starts to loose its crystallinity once it is exposed to even small amounts of humidity.
To better comprehend the differences that have been seen in water stability relating to metal-organic frameworks, numerous experiments have been tried. What all these studies seem to point out to is the fact that basic zinc acetate clusters are prone to hydrolysis. This was proven by carboxylate metal-organic frameworks like MOF-177 and the IRMOF series. The most stable are the trinuclear chromium clusters that can be located in MIL series. Copper paddlewheel carboxylate clusters, on the other hand, were found to show intermediate stability. They are mostly found in HKUST-1. Various measures have been tried in an effort to improve the water stability that metal organic frameworks have. One of such methods is through the use of linkers that are azolate-based as opposed to the ordinary carboxylate linkers. The azolate linkers possess the ability to bind metals using geometry that is similar to that of carboxylate ligands. However, it must be appreciated that their basicity is greater. This often leads to greater chemical and thermal stability, as well as stronger M-N bonds in the resulting framework. In general, a conclusion could be arrived at that frameworks which have Zr4+, Fe3+, Al3+, and Cr3+ cations show a greater degree of stability when in water. For the metal-organic frameworks to be synthesized with intrinsic functionalities there has been employment of other strategies which have equally proven successful. All these are aimed at shielding the material from any potential hydrolysis. Additionally, numerous metal-organic frameworks have in recent times been synthesized using water-repellant groups that have directly been incorporated into the organic ligands so as to shield the core of the metal from water. Numerous investigations have been carried out regarding the stability of metal-organic framework in liquid water. It must be noted that flue gas has a composition and temperature that makes it more relevant to capture applications of CO2.
CO2 pre combustion capture is a process where fuel is decarbonated before combustion. This consequently results zero production of CO2 during the combustion. During the process, coal is gasified at pressures and temperatures that are very high so as to produce synthesis gas. This is normally a mixture of H2O, CO2, CO, and H2. After the gas mixture has been obtained, it is put through the shift reaction of water-gas so as to produce CO2 and H2. This is often done at slightly elevated temperatures and high pressures depending on the manufacturing plant. Pre-combustion CO2 capture must be put through various considerations. Currently, liquid absorbers, membrane materials and solid adsorbents are all under consideration. They are all potential candidates in pre-combustion CO2 capture. The use of solid adsorbents is also under intense investigation with regards to this. It must be noted that hydrogen purification has a ubiquitous nature, and as such, encourages the use of this process o separation in the pre-combustion processes.
Oxy-fuel combustion, simply put, is the ignition of coal that has been pulverized or other fuels that are carbon-based in an environment of pure O2. This represents a process that is relatively new, especially when it comes to mitigating emissions of CO2 compared to post combustion and pre-combustion CO2 capture. This process has various significant advantages, and one among them is that flue gas is almost totally CO2. This is after trace impurity gases, water and particulates have been removed. The advantage here is that after this has been ensured, the capture step becomes much easier. The existing power plants will also have the benefit of being readily retrofitted with combustion systems that are oxy-fuel. However, getting through with oxy-fuel combustion methods has its fair share of significant challenges. The most obvious challenge with regards to this is the large-scale production of O2 that is pure from the air. Currently, this separation is being done on a scale that is in excess of 100 Mt/year. The entire process, it must be noted, has massive energy requirements, and this is a factor that always calls for other methods of separation if the usage of oxy-fuel combustion is to take place. Micro porous solids adsorb O2 selectively from the air are also believed to considerably reduce this energy cost.
METAL-ORGANIC FRAMEWORK-CONTAINING MEMBRANES
Gas separation by the use of membranes is a process that is kinetic-based, which depends heavily on the in gas molecules diffusion rates. This often occurs within the membrane materials. This part will focus largely on how CO2 emissions can be reduced from power plants by discussing certain CO2 separations like CO2/CH4 separations. In this regard, it is import to deliberate on continuous Films of Metal-Organic Frameworks. In recent times, there has been the fabrication of a huge percentage of continuous metal-organic frameworks that contain thin films for applications in various areas. Such areas include gas separation membranes, molecular sensors, as well as supported catalysts. With regards to gas separations, most studies have limited themselves to membranes that have low surface areas, although it must be appreciated that significant progress has been witnessed when it comes to gas transport properties. Synthesis of MOF-5 layers on a substrate that is porous has been achieved through microwave heating. In this instance, a layer that is conductive like graphite was deposited on an alumina substrate that is porous. This was followed by rapid and selective formation of crystals relating to metal-organic framework on the surface that has been coated. However, when the morphology of the consequential films is well examined, it can be determined that layers of metal-organic framework were not continuous, and this implies that they were suitable as far as applications in gas separation are concerned. This, however, is not to imply that continuous film can still not be obtained. This can be done via the conventional solvothermal method after the resulting membranes have been deposited. The MOF-5 films can also be fabricated through the seeded growth method, and this could be aided by microwave heating.
The foregoing sections have conclusively discussed the progress that has been made in recent times in the examination of metal-organic frameworks as possible new solid adsorbents that can be utilized within capture systems of CO2. There has been the demonstration of remarkable CO2 adsorption capacities in the highest surface area materials. There has also been the emergence of high adsorptive selectivities, especially in materials that have been furnished with surfaces that are functionalized. When it comes to the prospects of creating other materials that are appropriate for real-world applications, there has been a particularly promising degree over chemical and structural features of metal-organic frameworks. In the post-combustion CO2 capture area, the most urgent need is to ensure thermally and chemically robust materials can withstand high water levels that the flue gas stream has. Oxy-fuel combustion has arisen as a presentation where the chemical tunability regarding metal-organic frameworks could allow materials that are high performing to be prepared. Owing to the massive number of potential metal-organic frameworks which could be accumulated, the use of theoretical and computational methodologies could assist any synthetic efforts through the identification of other target materials that have been forecast to show the suitable qualities.
Kenji Sumida, D. R. (2011). Carbon Dioxide Capture in Metal-Organic Frameworks. Chemical Reviews, 724-781.
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