Abstract
The most widely used fossil fuel around the world is coal. This is a component that carries both organic and inorganic components and hence its combustion over the years has led to environmental problems such as acid rain and sulfur dioxide emission. To combat this eco-system problem several combustion methods have been introduced and one of the most efficient means that has come to the attention over the years as a significant way is the Oxy alkalinolysis.
In the past, there have been various desulfurization processes, which have been introduced. However, most of them have not given excellent results are expected. As a result, there is still need for a more substantial method to enhance efficient desulfurization of coal.
This article seeks to summarize the process of desulfurization of coal and highlight as to why the Oxy alkalinolysis is the most efficient means of desulfurizing coal. The paper will break down step by step the Oxy-Alkalinolysis process and explain as to why it has been identified as the best solution.
Introduction 3
The processes (Oxy alkalinolyisis) 5
Discussion and results 6
Conclusion 7
References 9
Appendix 1 10
Appendix 2 11
This paper submits a comprehensive report on desulfurization of coal. The paper highlights the oxy alkalinolysis as the most efficient means of desulfurizing coal.
The purpose of this report is to present ample information to all coal users and processors. This comes in the light of the significance of using coal as an efficient and powerful energy source across the globe. This report is mainly an explanation of how Oxy alkalinolysis is the best method for desulfurization. The same provide a comparison table with other processes used in the past. The report concludes with a review of the process and an appendix with a detailed table for additional information on coal.
I hope this report will prove to be satisfactory.
Sincerely yours,
Introduction
The search for efficient energy across the globe has reached its height today as more and more research results to the most exceptional source of renewable and efficient energy. Multiples of researches have thus been done on coal as one of those remarkable sources. In essence, coal is readily available and provides a proper means of generating energy in form of electricity and heat. This is paramount today and all efforts are directed towards having the best from coal without embracing any side effects to human life or the environment (Ohtsuka, 2013).
One of the key researches done is on desulfurization of coal. This process involves that changing of original coal to making it sulfur free. The process is primarily meant to reduce the elimination of sulfur oxides that come up during the combustion of coal. In the past, there have been various desulfurization processes, which have been introduced. However, most of them have not given excellent results are expected. As a result, there is still need for a more substantial method to enhance Efficient Desulfurization of Coal. It is basic to understand the significance of removing at least all traces of sulfur from coal. During the combustion of coal, sulfur is released in the form of SO2 in to the atmosphere, which in turn causes havoc in the atmosphere through the formation of acid rain (Konidaris, 2010). Consequently, acid rain leads to the destruction of crops and other negative side effects.
Environmental impact
Coal is a non-renewable source of energy considered to contribute greatly in pollution and as a result environmental damage. Coal has many carbon components and it is a component that occurs naturally in all living things. When carbon is combine with hydrogen it forms various compounds known as hydrocarbons. Hydrocarbons that are natural are also referred to as fossil fuels, because they were formed as a result of accumulation overtime.
Coal is mostly formed from plant remains usually accumulated in swampy conditions. But it needs quite a great amount of carbon for it to form coal. Coal is used because it is one of the most affordable sources of energy. Many homes use it for heating because it burns without smoke hence comfortable to use in households. Coal is also it’s a good source of energy and serves as fuel in industries. This resource is also very important because it is used today to generate electricity. Ships are also powered by coal when it is crashed in to powder then liquefied using hydrogen under extreme pressure the liquid coal is used to power ships.
Although coal is a great source of energy, the process of turning it into fuel is harmful to the environment.
During combustion it emits toxic pollutants in the air which are harmful to both plants and human beings. Coal contains chemicals and whenever it is burned gas is emitted and particles called “fly ash” are released into the air. The sulphur emitted combines with oxygen to form sulfur dioxide, which is a toxic air pollutant especially when emitted in large enough quantities.
Two main environmental concerns in relation to burning coal are: acid rain and increase in atmospheric carbon dioxide. There is a lot that experts need to learn about the relationship between the environment and fossil fuels such as coal, oil and gas. The recent increase in carbon dioxide is believed to have partly resulted from burning of coal.
An increase in carbon dioxide in the atmosphere will result to warmer weathers due to the “greenhouse effect.” This happens because carbon dioxide prevents heat from escaping the earth, thus a warm atmosphere. Recent studies also show that the “greenhouse” effect is getting worse and action needs to be taken to control global warming.
Coal combustion has also been linked to acid rain, though there are no clear studies that actually point the relation. The level of serious acid rain is not well established or well understood.
In this regard, it is vital to device a method of removing sulfur from coal in order to make it usable and safe for use. There have been three methods, which have been used in the past to strike this issue. They include coal cleaning, flue gas desulfurization, and in-bed desulfurization. The history of chemistry highlights that the past methods used in desulfurization have not been effective in getting rid of organic sulfur, which is bound on coal at least before burning but can do away with inorganic sulfur. It is important to note that the reason behind the failing of all the other desulfurization process is due to the various organic sulfur species that include aryl sulfides, thiophenols, and the thiophenes.
This document explores a new method of desulfurization, which embraces various concepts of chemical reactions. It includes the oxidation of organic sulfur with electrophillic reagents molten alkali. This process is called “oxy-alkalinolysis.”
For many it is quite clear that coal will remain a great source of energy in the coming years, but what is not so clear is how combustion can be carried out without damaging the environment with sulfur oxide emissions. The existing precombustion methods used do not match to the required standards and the post combustion flue gas has yet to be established (Squires, Aida, Clifford & Venier, 2012).
There are many existing methods which are effective and used to remove the inorganic sulfur from the coal before combustion; but these methods have not been fully developed yet to remove the organic component before combustion. It is not surprising because organic sulfur is chemically stable with pieces like aryl sulfides, thiophenes and thiophenols which make it a hard component to remove.
After carefully studying the oxydesulfurization process, many people have made attempts to validate their proposed process but failed to come up with a successful coal combustion process
The process of first oxidizing the sulphur and later exploiting enhanced chemical reactivity such as sulfones and sulfunic acid is more than valid. The oxy-alkalinolysis is an approach that facile oxidation of the organic sulphur by electrophilic reagents and the long establishesbonds by molten alkali.
The process of “oxy-alkalinolysis” is best described below:-
COAL sulfur oxidized molten desulfurized
oxidation COAL KOH/NaOH COAL
The above process is a series of reactions whereby coals is taken through one-step to another before it is made sulfur free called desulfurized coal.
Reagents for these series of reactions are
- Potassium hydroxide
- Fischer certified ACS pellets
- Western No. 9 coal
- Chlorine
- Dibenzothiophene
- Water
The processes are as follows
- Oxidizing Dibenzothiophene using Chlorine (CH2Cl2-H2O)
100 mg of dibenzothiophene was mixed together with about 2.0 mls of water. To this mixture was added 4.0 mls of CH2Cl2. This mixture was then stirred inside a flask. Once this mixture was well done, Cl2 was then bubbled inside for 10 minutes. A residual was formed from which Cl2 and CH2Cl2 was removed using aspiration method. Another 1.0 ml of Na2SO3 was put to the remaining mixture. From the resulting solution, 7.0 mls of CH2Cl2 three times. Again, CH2Cl2 was washed using a solution of NaHCO3. The resulting substance was later dried through Na2SO4.
Gas chromatography was used to gauge the internal standards using phenyl sulfide.
- Reacting W. Kentucky Coal together with Chlorine
W. Kentucky No. 9 Coal 3.0 g was combined with 10.0 mls of water and methylene chloride about 20.0mls. This mixture was made at room temperature for at least an hour. At the same time, Cl2 was bubbled through the mixture. Using the process of aspiration, Cl2 and CH2Cl2 was taken off as residue. This was done before adding water about 150 mls. The mixture formed after adding water was heated at 60˚ for about 2 hours at the same time the mixture was shaken regularly to keep it well mixed. This process resulted to a form of coal that was washed and filtered using clean water and then dried through vacuum.
Once dried this product was analyzed for sulfur and chlorine.
- Combining the organic sulfur with Potassium hydroxide in molten form
Through an experiment, 200 mgs of potassium hydroxide (KOH) was mixed with 0.15 mmoles of organic sulfur. This mixture was made in a glass amploule which was sealed and put in KNO3 salt for 10 minutes at 200-350˚C. After ten minutes, the ampoule was cooled to lower its temperature and its contents removed using 5 mls of CH2Cl2. Acidification was the next process using 6NH2SO4. This formed layers that eased the process of separation but with the addition of CH2Cl2. Using Na2SO4 the residue was dried and again analyzed by chromatographically.
- The reaction between coal and potassium hydroxide
In this reaction series, untreated coal and Cl2 treated coal was experimented and reacted with KOH.
Therefore, 500mgs coal was combined with 15 g of potassium hydroxide inside a stainless steel small reactor together with N2. This reaction was done for 15 minutes after which the mixture inside the reactor was dipped in potassium nitrate (KNO3) at a temperature of 400˚C for 20 minutes. Later the product from this mixture was poured in 500 mls flask. The reactor was rinsed using water.
Once cooled, KOH was added in to the reaction mixture. It was then made acidic with the addition of HCL (hydrochloric acid) and diluted using 150 mls of water. After a while, this mixture was warmed to a temperature of 60˚C and kept at that temperature for at least 1 hour with constant shaking. The coal collected after this period was filtered and well washed with water then dried by vacuum overnight. The product was later analyzed to check for traces sulfur and chlorine.
Discussion and results
It is important to understand that the reactions in these processes are primarily based on oxidation. However, molecular oxidation by using molecular oxygen in oxidizing sulfur in coal utilizes a lesser rate as compared to other oxidation processes. In this case, the use of electophillic oxidants is thus paramount for organic sulfur. Hence, lead to quick oxidizing of sulfur in the coal. On the other hand, chlorine is known for its significant work of reacting with sulfur in coal. Therefore, exposing these reactants through electrophillic processes enhances combustion that removes the sulfur from coal. According to sources, this process is effective to remove a large amount of sulfur to about 53% (Squires, Aida, Clifford & Venier, 2012).
The process above utilized strong alkalis, which has a remarkable part to play in the removal of sulfur traces in coal. It is imperative to mention that alkalis such as Potassium Hydroxide (KOH) play a major role in breaking the carbon-sulfur bonds especially when put under mild conditions. This leads to a soluble substance thus easily removed through washing.
It has been established that using molecular oxygen as the oxidant, the rate of oxidation of organic sulfur during coal extraction is by far less than the rate of oxidation of the hydrocarbon matrix. The basis of selecting peroxytrifluoroacetic acid is on the reactivity of organic sulfur toward electrophilic oxidants, because it acts as a reagent for the chosen oxidation of organic sulfur in the coal.
The process can be seen as a pollutant remover because sulphur emissions have been linked to global warming. This process when adapted in plants will cut tons of pollution in the future while burning coal. The process removes the organic sulphur which as discussed earlier is hard to remove. Environmentalists are looking for technology that is efficient and the same time environment friendly. Using this technique could clean the air pollution caused while burning coal.
Most reactions in this process above were done using high temperature and were later brought down to room temperature. It is beneficial to note that the room temperature causes the reactions to reach their climax and facilitate desulfurization. The reactions above also indicate that oxidized form of sulfur react fast and more active using KOH as compared to the reduced from. There are other processes such as Chlorinolysis and Gravimelt processes which can be used in desulfurization. However, Oxy alkalinolysis is found to be at last 88% better that the previous two processes. In the same regard, once Oxy Alkalinolysis has been optimized then better outcomes are ahead in desulfurization of coal (Squires, Aida, Clifford & Venier, 2012).
Conclusion
Oxy-alkalinolysis is a method of deep cleaning of coal. Its removal of sulphur is a technical but very feasible process. This process is needed because it desulfurization is efficient towards removing both the inorganic and organic sulphur.
Using this process reduces the environmental impact of coal combustion as an energy source. This method is one that generates ‘clean coal’ greatly reducing emissions that are harmful because they contain pollutants that could harm the environment.
The Oxy-Alkalinolysis process has its main focus on coal combustion that is clear. The catalysts used in the process are meant to lower the temperatures helping complete the burning process with little emissions. This helps promote efficient burning of coal while reducing toxic pollutants into the air. Its exploitation will continue for years but the levels of emission leading to increased carbon dioxide in the air will greatly reduce.
Making desulfurized coal is one of the most tedious chemistry equations that have yielded very little fruit in a long period. Having taken time to define this process in new dimensions, Oxy-Alkalinolysis has thus been identified as the best solution. In conclusion, desulfurization of coal has been on trial for a long time with various processes being recommended for the same. Nonetheless, these processes have not produced the best result including 62% through Gravimelt process and 53% by chlorinolysis. The realization of oxy-Alkalinolysis has thus maximized desulfurization with excellent results. In this case, potassium hydroxide and chlorine with electrophillic oxidation is the best way forward.
Reference
Konidaris DN. (2013). Natural desulfurization in coal-fired units using Greek lignite. Journal of air waste management Association. Vol 60(10):1269-73.
Ohtsuka, S. (2013). Desulfurization of coal. Coal, oil shale, natural bitumen, heavy oil and peat – Vol. I. Retrieved from http://www.eolss.net/sample-chapters/c08/e3-04-02-04.pdf
Squires, T., Aida, T., Clifford, C. & Venier G. (2012). Development of an Efficient Coal Desulfurization Process: "Oxy-Alkalinolysis.” Retrieved from http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/27_3-4_KANSAS%20CITY_09-82_0328.pdf
Appendix 1: sulfur contents in chosen coalfields of all major coal producing countries
Appendix 2: Comparison table from Oxy Alkalinolysis, Chlorinolysis, and Gravimelt
