Module IV Energy Sources PDF

VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) MODULE IV: ENERGY SOUCES Introduction:  Energy is a part of life. Better energy sources are status symbol of country.  A fuel is a substance which provides en...

VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) MODULE IV: ENERGY SOUCES Introduction:  Energy is a part of life. Better energy sources are status symbol of country.  A fuel is a substance which provides energy on combustion for industry and domestic purposes.  The combustion is the process of oxidation that provides heat energy with light.  Every combustion is an oxidation but every oxidation is not combustion. Ex: combustion of wood, petrol, kerosene gives heat energy. oxidation Fuel ----------------- heat energy + light + combustion products (CO2 + H2O etc.) Fuels and Classification of Fuels: Fuels are broadly classified as Primary fuels (or) natural fuels and Secondary fuels (or) artificial fuels. Fuels Primary fuels (or) natural fuels secondary fuels (artificial fuels) The natural and artificial fuels can be further classified based on the state of fuels: Primary fuels (or) natural fuels Solid fuels liquid fuels gas fuels Ex: wood petroleum natural gas Secondary fuels (or) artificial fuels Solid fuels liquid fuels gas fuels Ex: charcoal petrol, diesel etc L.P.G, C.N.G etc Dept. of Chemistry Page 1 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Comparisons among Solid, Liquid and Gaseous Fuels: Solid fuels liquid fuels gaseous fuels 1. Slow combustion and easy 1. Quick combustion and 1. Combustion is rapid and to control it. cannot be controlled. burning can be controlled. 2. Transportation is difficult. 2. Transportation is easy 2. Transportation is easy through pipe lines. through pipe line and 3. Storage is safe. 3. There is risk in storing containers. 4. Calorific value is 4. Calorific value is 3. There is risk in storing comparatively low. comparatively higher. 4. Calorific value is 5. Slow combustion. 5. Quick combustion. comparatively highest. 6. More ash content. 6. No ash content. 5. Very fast combustion. 7. Causes more pollution. 7. Least pollution. 6. No ash content. 8. More oxygen is required for 8. Less oxygen is required for 7. Least pollution. combustion. combustion 8. Least oxygen is required for 9. It cannot be used as fuels in 9. Mainly used in vehicles as combustion. vehicles (but coal is used as fuel. 9. Mainly used in vehicles as fuel in trains). fuel. Characteristics of Good Fuel:  It should possess high calorific value and naturally carbon content.  It should have lower moisture content as well as lower volatile matters since these will affect heating value of the fuel.  It should possess low ash content since the ash formation will affect the heating value of the fuel.  It should be easily transportable, otherwise cost of fuel will increase.  It must have high calorific value.  It must have moderate ignition temperature. Low (burning)/ignition temperature can cause fire accident. (ignition temperature is the lowest temperature to which the fuel must be pre – heated for a smooth burning process).  It should not give poisonous gasses after combustion.  Its handling should be easy.  It should not burn spontaneously to avoid fire hazards.  Combustion of good fuel can be easily controlled.  It should be cheap.  It should be easily available. Dept. of Chemistry Page 2 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Calorific Value: The Calorific value of the fuel can be defined as the total quantity of heat liberated when a unit mass of the fuel is completely burnt in air or oxygen. The calorific value is measured in several units of heat; they are calorie, kilo calorie, British Thermal Unit (B.T.U) and centigrade Thermal Unit (C.T.U). 1 k.cal = 1000 cal = 3.968 BTU = 2.2 CHU 1 cal =4.18 joule (joule is also unit of energy). There are two types of calorific values of a fuel: Gross Calorific Value (GCV) (Or) High Calorific Value (HCV): Gross (or) higher calorific value (HCV) is defined as the total amount of heat produced when unit mass/ volume of the fuel has been burnt completely and products of combustion have been cooled to room temperature & reused. Net calorific value (NCV) (or) low calorific value (LCV): Net (or) low calorific value is the net (or) actual heat produced when unit mass/ volume of the fuel is completely burnt and the products are permitted to escape i.e. HCV includes the latent heat of water (587 k.cal/kg). Relationship between HCV & LCV: LCV = HCV – Latent heat of water vapour formed.  Since 1 part by mass of hydrogen produces 9 parts by mass of water as given by the equation below. H2 + ½ O2 ----------------------- H2O LCV = HCV – mass of hydrogen Χ 9 Χ latent heat of water vapour formed. 𝐇 LCV = HCV – 9 Χ Χ587 𝟏𝟎𝟎 LCV = HCV – 0.09 Χ H Χ 587 Where H is the % of hydrogen in the fuel.  Dulong proposed a formula for the calculation of the calorific value from the chemical composition. 𝟏 𝐎 I.e. HCV = (8080 C+ 34,500 (H- ) +2240 S) K cal/kg 𝟏𝟎𝟎 𝟖 (c – carbon, H – hydrogen, O – oxygen, S – Sulphur are percentages of these elements in coal.) Dept. of Chemistry Page 3 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) 1. Calculate the gross and net calorific value of a coal sample having the following composition C = 80 %, H = 7 %, O = 3 %, S = 3.5 %, N = 2 %, and ash = 5 %. Solution: GCV (or) HCV = [8080 C + 34,500 (H- ) +2240 S] = [8080 Χ 80 + 34,500 (7- ) +2240 Χ3.5] = 8828 k.cal / kg NCV (or) LCV = GCV – 0.09 Χ H Χ 587 = 8828 – 0.09 Χ 7 Χ587 = = 8458 k.cal / kg 2. Calculate the gross and net calorific value of a coal sample having the following composition C = 85 %, H = 8 %, S = 1 %, N = 2 %, and ash = 4 Solution: GCV (or) HCV = [8080 C + 34,500 (H- ) +2240 S] = [8080 Χ 85 + 34,500 (8- ) +2240 Χ1] = [6,86,800 + 2,76,000 +2240] = [6868 + 2760 +22.4] = 9650.4 K cal/ kg NCV (or) LCV = GCV – 0.09 Χ 8 Χ 587 = 9650.4 – 0.09 Χ 8 Χ587 = 9650.4 – 422.64 = 9227.76 kcal/kg 3. On analysis, a coal sample has the following composition by weight; C = 85 %, O = 3 %, S = 0.5% and ash = 3 %. Net calorific value found to be 8400 k cal/kg. calculate the percentage of hydrogen and gross calorific value of coal Solution: GCV= [NCV + 0.09H Χ587] kcal/kg = [8400+ 0.09H Χ587] kcal/kg = [NCV + 52.8 H] kcal/kg---------------(1) GCV (or) HCV = [8080 C + 34,500 (H- ) +2240 S] kcal/kg = [8080 Χ 85 + 34,500 (H- ) +2240 Χ0.5] = [686800 + 34500H – 12937.5 +1120] Dept. of Chemistry Page 4 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) = [6868 + 345H – 129.37 +11.2] =6749.8+345 H kcal/kg------------- (2) From (1), (2) 6749.8+345 H = 8400+52.8 H 345H -52.8H = 8400-6749.8 292.2H =1650.2 H = 5.647 % of H = 5.647 -------------------(3) From (1), (3) GCV = (8400+(52.8 Χ5.647))= 8698.16kcal/kg SOLID FUELS:  The main solid fuels are wood, peat, lignite, coal and charcoal.  In addition to these certain agricultural and industrial wastes such as rice husk, coconut and nut shells etc. employed as fuels. / Wood > coal  Wood contains higher carbon percentage in the form of cellulose, lingo – cellulose, they are transformed into the form of coal. Dry wood has composition as Carbon ⇒ 40 – 50 % Oxygen ⇒ 42 – 44 % Hydrogen ⇒5 – 6 %  The calorific value of wood is 4000 – 4500 k.cal / kg  Wood can be converted into a charcoal is used as adsorbent of gasses and for decolourisation of cane sugar. Wood ----- peat --------lignite ------------- bituminous --------- anthracite Coal, Analysis of Coal: The analysis of coal is helpful in its ranking. The assessment of the quality of coal is carried out by two types of analysis. 1. Proximate analysis 2. Ultimate analysis Proximate Analysis: Proximate analysis is the simplest form of analysis of coal and gives information which is useful in the practical utilization of coal. In this analysis, the percentage of Dept. of Chemistry Page 5 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) carbon indirectly determined and includes percentage of moisture, volatile substance and ash content. a. Moisture content: A known mass of finely powdered coal is taken in a crucible. It is heated up to 1100c for an hour and cooled to room temperature in desiccators. The moisture is removed as water vapour and the process is repeated till the constant weight is obtained. 𝐥𝐨𝐬𝐬 𝐢𝐧 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 Percentage of moisture = Χ100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 Significance:  High percentage of moisture content is undesirable.  It increases the transport costs and reduces the calorific value.  Considerable amount of heat is wasted in evaporating the moisture during combustion. b. Volatile matter: the above sample (moisture free coal) taken and heated at 950 0c in the absence of air for 7 minutes. It is then cooled to room temperature and weighed. The loss of weight is noted as volatile matter and is removed from coal at 950 0c. 𝐥𝐨𝐬𝐬 𝐢𝐧 𝐰𝐞𝐢𝐠𝐡𝐭 𝐝𝐮𝐞 𝐭𝐨 𝐫𝐞𝐦𝐨𝐯𝐚𝐥 𝐨𝐟 𝐯𝐨𝐥𝐚𝐭𝐢𝐥𝐞 𝐦𝐚𝐭𝐭𝐞𝐫 Percentage of volatile matter = Χ100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 Significance:  A coal containing high volatile matter  Burns with long flame.  High smoke  Low calorific value. c. Ash content: coal, free from moisture and volatile matter is heated in a crucible at 700 – 7500c for half an hour. It undergoes cooled to room temperature and weighed. 𝐦𝐚𝐬𝐬 𝐨𝐟 𝐚𝐬𝐡 Percentage of ash = Χ100 𝐦𝐚𝐬𝐬 𝐨𝐟 𝐜𝐨𝐚𝐥 Significance:  Reduces the calorific value of coal.  Decreasing the efficiency.  Increases transporting, handling, storage and disposal costs.  Hence lesser the % of ash the better is the quality of coal. d. Fixed carbon: Fixed carbon means the quantity of carbon in coal that can be burnt by a primary current of air drawn through the hot bed of fuel. The sum (total) of the percentages of moisture, volatile matter and ash subtracted from 100 gives the fixed carbon. Dept. of Chemistry Page 6 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) = 100 – (% of moisture + % of volatile matter + % of ash) Significance:  The higher the fixed carbon in a coal, the greater is the calorific value. Ultimate Analysis: This is the elemental analysis and often called as qualitative analysis of coal. This analysis involves the determination of carbon and hydrogen, nitrogen, sulpher and oxygen. a. Determination of carbon and hydrogen:  A known mass of coal is taken and burnt in a steam of pure oxygen in a combustion apparatus. The carbon changes to CO2 and hydrogen changes to H2O.  The vapors of CO2 and H2O are taken passed through KOH and CaCl2.  The CO2 absorbed by KOH in the tube while H2O is absorbed by CaCl2. Because of the absorption the weight of KOH and CaCl2 increases, which is then measured. C + O2 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ CO2 12 44 H 2 + ½ O2 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ H2O 2 18 KOH + CO2 K2CO3 + H2O 𝐢𝐧𝐜𝐫𝐞𝐬𝐞 𝐢𝐧 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐊𝐎𝐇 𝟏𝟐 Percentage of carbon = Χ Χ 100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝟒𝟒 𝐢𝐧𝐜𝐫𝐞𝐬𝐞 𝐢𝐧 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐂𝐚𝐂𝐥𝟐 𝟐 Percentage of hydrogen = Χ Χ 100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝟏𝟖 Significance: The higher the percentage of carbon and hydrogen the better is the quality of coal and higher the calorific value. Dept. of Chemistry Page 7 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) b. Nitrogen percentage:  Nitrogen is determined by the kjeldahl method. About 1 gm of finely powdered coal sample with K2SO4 (catalyst) and conc.H2SO4. Nitrogen in coal converted to (NH4) SO4. The Kjeldahl method is divided into three main steps. The method has to be carried out in proper sequence. The steps include digestion, distillation, and titration. 1. Digestion: In this method, a certain substance or sample is heated in the presence of sulphuric acid. The acid breaks down the organic substance via oxidation and reduced nitrogen in the form of ammonium sulphate is liberated. Potassium sulphate is usually added to increase the boiling point of the medium. Catalysts like mercury, selenium, copper, or ions of mercury or copper are also used in the digestion process. The sample is fully decomposed when we obtain a clear and colourless solution. 2 N2 + 3 H2 + H2SO4 -------------------- (NH4)2SO4. 2. Distillation: The distillation of the solution now takes place and a small quantity of sodium hydroxide is added to convert the ammonium salt to ammonia. The distilled vapours are then trapped in a special trapping solution of HCl (hydrochloric acid) and water. (NH4)2 SO4 + 2 NaOH ------------------- 2 NH3 + Na2SO4 + 2 H2O 3. Titration: The amount of ammonia or the amount of nitrogen present in the sample is then determined by back titration. As the ammonia dissolves in the acid trapping solution some HCl is neutralized. The acid that is left behind can be back titrated with a standard solution of a base such as NaOH or other bases. NH3 + H2SO4 -------------------- NH4)2SO4. Dept. of Chemistry Page 8 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Formula for Calculation: 𝐯𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐇𝐂𝐥 𝚾 𝐧𝐨𝐫𝐦𝐚𝐥𝐢𝐭𝐲 𝐨𝐟𝐇𝐂𝐥 𝟏𝟒 Percentage of Nitrogen = Χ Χ 100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝟏𝟎𝟎𝟎 Significance: Nitrogen has no significance. c. sulpher percentage : Sulpher is estimated gravimetrically in terms of BaSO4 S +2 O2 + 2 e- ------------------- SO42- SO42- +BaCl2 -----------------BaSO4 + 2 Cl- 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟𝐁𝐚𝐒𝐎𝟒 𝟑𝟐 Percentage of sulpher = Χ Χ 100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 𝟐𝟑𝟑 Significance:  increase calorific value  SO2, SO3 have corrosive effect on equipment and cause air pollution d. Ash content: The coal sample is ignited and the weight of ash is measured at room temperature. 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐚𝐬𝐡 Percentage of ash = Χ 100 𝐰𝐞𝐢𝐠𝐡𝐭 𝐨𝐟 𝐜𝐨𝐚𝐥 e. Oxygen percentage: The % of oxygen is determined by subtracting the sum of percentage of C, H, S and ash from 100. Percentage of oxygen = 100 – (% of C + H + N + S + ash) Significance:  High oxygen content  High inherent moisture  Low calorific value Dept. of Chemistry Page 9 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) LIQUID FUELS:  Petroleum is one of the best primary liquid fuels. It is also known as crude oil. Petrol, diesel, kerosene are main liquid fuels. They are secondary fuels derived from petroleum.  The word meaning of petroleum is rock oil (petra = rock , oleum = oil), it is a mixture of number of hydrocarbons (paraffines, olefins, aromatics and naphthalene), nitrogen, sulpher, oxygen contain practically active compounds along with traces of compounds of heavy metals like Fe, Co, Ni and V.  Composition of petroleum is C = 79.5 – 87.1 % , H2 = 11.5 – 14.8, S = 0.1 % N2 &O2 = 0.1 – 0.5% Classification and Theories of Petroleum There are mainly three types of Petroleum. 1. Paraffinic base type crude oil mains consist of the saturated hydrocarbons from CH 4 to C35H72 and littile naphthalene and aromatics. 2. Asphaltic – base type crude mainly consists cyclo paraffins, naphthalenes and aromatics. 3. Mixed – base crude mainly consists both paraffins and asphaltic hydrocarbons. Refining Of Crude Oil (Petroleum):  The crude oil as impure i.e. a lot of soluble and insoluble impurities are present.  Refining can be defined as the process by which petroleum is made free of impurities, division of petroleum into different fractions having different boiling pints and their further treatment to impart specific properties. Refining of petroleum is done in different stages. 1. Separation of water (Cortell process):  The crude oil will always mix with the brine water forming emulsions. The crude oil is allowed to flow through two highly charged electrodes.  The colloidal emulsion of oil and water separates out to larger water areas which separated from the oil. 2. Removal of harmful sulpher compounds: After the removal of water the oil is treated with copper oxide. The copper sulphide can be separated out by filtration. 3. Fractional distillation:  The crude oil or crude petroleum is heated to about 400 0c in an iron retort where all volatile constituents evaporate except the asphalt residue.  The fractionating column is a tall cylindrical tower containing a number of horizontal stainless steel tray one over another of a fixed distance. Dept. of Chemistry Page 10 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS)  Each tray is provided with short chimney covered with loose cap. As the vapors go up they touch chimney cap and get condemned at different heights of the trays. The lower boiling fractions can travel more height without getting condensed even at the lower trays. The different fractions obtained at different trays, They are: Petroleum ether (C5 – C7): It is the highly volatile lower molecular weight and its boiling range is between 30 – 700c, it is mainly used as solvent. Gasoline or petrol (C5 – C9): The boiling range of this fraction is between 40 – 120 0c. its approximate composition is C = 84 %, H = 15 % , N + S + O = 1 %. It has a calorific value 11250 k.cal/ kg it is highly volatile and mainly used in internal combustion engines. Most of the automobiles making use of this fuel only. Solvent naphtha (C9 – C10): The boiling range of this fraction is between 120 – 1800c. It is mainly used as solvent in various industries. Kerosene (C10 – C16): the boiling range of this fuel is between 180 – 2500c. Its calorific value is 1,100 k.cal/ kg. It does not vaporize easily. It is mainly used as domestic fuel in stoves and lamps. It is also jet engine fuel and for making oil gas. Diesel oil (C15 – C16): The boiling range of this fuel is between 300 – 3500c. It is used as fuel in ships and used in metallurgical furnaces. Heavy oil or residual oil (C18 –C30): The boiling range of this fuel 350 – 4000c. It is used a fuel for ships and used in metallurgical furnaces. Heavy oil on further fractionation gives; i) Lubricating oil ii) paraffin wax iii) Petroleum jelly (Vaseline) iv) Greases. Dept. of Chemistry Page 11 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Cracking of Fuels: Cracking is the process of conversion of bigger hydrocarbon molecules into smaller hydro carbons of lower molecular weights. Small saturated hydro carbons Higher hydro carbons (saturated) > + / Small unsaturated hydro carbon C12H26 ⎯⎯⎯⎯ C7H16 + C5H10 Alkane alkene The process of cracking is mainly of two types. 1. Thermal Cracking: In this process heavier hydrocarbon molecules are converted into light hydrogen – rich molecules at higher temperature. 2. Catalytic Cracking: In this process heavier hydrocarbon molecules are converted into light hydrogen – rich molecules in the presence of catalyst. Catalytic cracking is also of two types. Fixed – bed cracking 2. Fluid – bed (moving - bed) cracking. Fluid – bed (moving - bed) cracking: In fluidized-bed catalytic cracking, the finely divided catalyst is kept agitated by gas streams (feed stock vapour) so that it can be handled like a fluid system i.e., it can be pumped as a true liquid. The advantage of fluidized-bed cracking process is that a high degree of mixing is achieved and consequently a good contact is established between the catalyst and the feed stock vapours. This results in a higher yield. The regeneration of the inactive catalyst can be carried out continuously without interrupting the production of gasoline unlike in fixed-bed cracking method. Dept. of Chemistry Page 12 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Process:  The finely divided catalyst bed (Al2O3 + SiO2) is fluidized by the upward passage of feed stock vapours (Heavy oil, gas oil, etc) in a cracking chamber (called Reactor) maintained at 5500 C.  Near the top of the reactor , there is a centrifugal separator (called cyclone), which allows only the cracked oil vapours to pass onto the fractionating column but retains the catalyst powder in the reactor itself.  The catalyst powder gradually becomes heavier due to the deposition of carbon and settles to the bottom, from where it is forced by an air blast to the regenerator (maintained at 6000 C).  After cracking, the products are fractionated into gases, gasoline, gas oils and residual oils (unconverted).  The heavier oil fractions may be cracked in a second-stage cracking, thereby increasing the overall yield of the cracked products.  In regenerator, the spent catalyst is stripped of the adsorbed oil by passing steam and then decarbonized by a hot air blast, under controlled conditions.  The heat liberated during this regeneration is used to raise steam and to preheat the catalyst. Dept. of Chemistry Page 13 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Knocking: The efficiency of engine depends on the compression ratio. Compression ratio =.  Compression ratio is directly proportional to efficiency of an engine. More the CR, better will be engine, CR depends on the type of constituents in the gasoline.  Compression in the cylinder produces shock waves, it results in rattling sound in the engine called knocking and knocking decreases the efficiency of engine.  The tendency of knocking depends on the chemical structure of hydrocarbons. Ease of combustion reaction: Aromatic > olefins > cyclo alkenes > chain Knocking: chain > cyclo alkenes > olefin > aromatic Knocking is measure of octane number. Hence, For n – heptanes, octane number = 0 Iso octane, octane number = 100  The anti-knocking value of fuel can be increased by adding tetra ethyl lead (TEL). The oxides of lead formed as combustion products inhibits free radical chain reaction responsible for knocking.  Small quantity of methyl cyclo penta dienyl manganese tetra carbonyl is also used in Canada & European countries in place of TEL which also results in Mn pollution in air & soil. Prevention of Knocking: To improve the antiknock value of the petrol sample, Tetraethyl lead (TEL) and diethyl telluride [(C2H5)2Te] are added Octane number (or) octane rating:  The maximum knocking is from n – heptanes and hence its octane number is zero, while iso octane knocks minimum (0) its octane number has been given 100.  Hence octane number of gasoline is the % of iso octane in the mixture of iso octane and n – heptanes. Therefore octane number 60 of a gasoline sample means  The mixture contains 60 % iso octane & 40 % n – heptanes.  Gasoline has higher octane number, lower knocking.  The cetane number decreases in the following order. Aromatic > olefins > cyclo alkenes > chain Dept. of Chemistry Page 14 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Cetane number (or) Cetane rating:  Cetane number is a measure of the ignition value of a diesel fuel.  It is introduced to express the knocking characteristics of diesel.  Cetane has a very short ignition lag and hence its cetane number is taken as 100.  On the other hand 2-methyl naphthalene has a long ignition lag and hence its cetane number is taken as zero.  The percentage of hexa decane present in a mixture of hexa decane and 2-methyl napthalene, which has the same ignition lag as the fuel under test".  The cetane number decreases in the following order. n-alkanes > Cycloalkanes > alkenes >branched alkanes >aromatics Cetane(n-hexa decane) Cetane Number = 0 Octane Number Cetane Number 1. Performance indicator of petrol or 1. Performance indicator of diesel gasoline 2. Delay self ignition of fuel 2. Speed up ignition of fuel 3. Percentage of iso-octane is the 3. Percentage of nhexacetane is the benchmark benchmark 4. Fuel with high octane number has 4. Fuel with high cetane number has low low cetane number octane number 5. Octane number of petrol can be 5. Cetane number diesel can be increased increased by adding benzene or by adding by adding ethyl nitrate or toluene acetone peroxide 6. Octane number for good petrol 6. Cetane number for good diesel is about should be about 85-90 45-50 Dept. of Chemistry Page 15 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) SYNTHETIC PETROL: Petrol is mainly obtained from crude oil from oil wells but can also be obtained by synthetic processes. 1) Fisher – tropsch process 2) Bergius process Fisher – Tropsch process:  In this process water gas (CO + H2) is mixed with hydrogen gas (H2) in the presence of catalyst maintaining a temperature of about 200 – 300 0c and pressure of about 5 – 25 atm.  The catalyst used consists of mixture of 100 parts Co, 5 parts Ni, 8 parts MgO and 200 parts kieselguhr earth. n CO + 2n H2 ------------------ CnH2n + n H2O n CO + (2n +1) H2 ------------------ CnH2n+1 + n H2O CO + H2o ------------------ CO2 + H2  First the water gas & hydrogen gas mixture is purified by Passing through Fe 2O3 and Fe2O3 + Na2CO3.  After that the pressure is maintained to 5 -25 atm and passed through the converter where the catalyst and temperature are maintained 200 – 300 0c.  in the converter the polymerization takes place and the hot gasses are passed through a cooler where the crude oil is produced.  The crude oil is fractioned in a fractionating column and gasoline fraction is produced in the top fraction.  The high boiling heavy oil is obtained at the bottom can be used for cracking to get more gasoline. Dept. of Chemistry Page 16 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) GASEOUS FUELS. Gaseous fuels are classified into two types.  Primary fuels: Ex: natural gas  Secondary fuels: Ex: coal gas, producer gas, water gas, oil gas etc. Natural gas: Natural gas always found above the oil in the oil wells. It can be found under earth without any liquid petroleum below it natural gas which is known as fire damp. Composition of natural gas: (methane) CH4 = 88.5 % (ethane) C2H6 = 5.5 % (propane)C3H8 = 3.7 % (butane) C4H10 = 1.8 % Pentane, H2, CO, CO2 and higher hydrocarbons ⇒0.5 % The calorific value of natural gas 8000 – 1400 k.cal / m3 Applications:  It is an excellent domestic fuel which can carry to long distances in pipelines as town gas U.S, U.K And Mumbai.  It is also an industrial fuel.  It also used for manufacturing of chemicals like CH3OH, carbon black, HCHO etc.  Natural gas also used as a source of H2 gas. Hence ammonia can be made by reacting N2 with H2 (H2 obtaining from natural gas). Liquefied Petroleum Gas (LPG):  LPG is also known as autogas because it is used as a fuel in automobiles.  LPG is a mixture of hydrocarbon gases and is flammable. It has a high heating value and is therefore popular in the heating industry as well.  Liquid petroleum gas is very flammable  LPG has a high calorific value and, therefore, is best suited for cooking purposes. Chemical Composition:  The main constituents: n – butane, iso butane, butylene and propane, negligible amount of propene & ethane. Characteristics:  LPG is obtained as byproduct during refining of crude oil or from natural gas  It mainly contains n-butane, isobutane, butylene and propane  It has high calorific value: 27800 kcal/m3  It gives less CO and least un-burnt hydrocarbons. So, it causes least pollution  It gives moderate heat which is very useful for cooking Dept. of Chemistry Page 17 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS)  It has a tendency to mix with air easily  Even though it is toxic, on combustion it gives no toxic gases  It neither gives ash or smoke content  It is cheaper than gasoline. Hence used as motor fuel  It is dangerous when leakage is there. It is highly knock resistant  LPG is used as domestic fuel and as a fuel in internal combustion engines  It is used as fuel in some industries Applications:  LPG is used in various sectors like health, industrial, construction, transportation, and residential use.  It is used for cooking because it is cheaper than other fuels and thus makes it beneficial economically. In many countries, it’s commonly used for domestic cooking.  Liquid Petrol Gas is used for heating purposes. People use electricity, kerosene, or natural gas to heat their homes, but LPG is a great alternative.  LPG is also used as dual fuel in many new technologies to produce heat and electricity, like in CHP (combined heat and power) systems.  Liquid petroleum gas is used as a vehicle fuel, hence it gets the name “autogas.” In comparison with petrol, LPG burns cleaner and is more economical. It has some problems. It is not as efficient as other fuels used in cars, so it is not as popular. But still, there are some modified cars in which Liquid Petrol gas acts as a bi-fuel and can be used in conjunction with petrol.  It is also used in refrigeration applications as a refrigerant. Compressed Natural Gas: (CNG)  It is a fuel gas as Petrol/Diesel.  When natural gas compressed at 100 atm pressure (or) cooled to -165 0C converted into C.N.G.  Natural gas offers a lower risk in the case of a leak, as compared to other liquid.  Naturally occurring natural gas was discovered and identified in 1626, America. William Hart, in 1821 dug the first successful natural gas well in New York, U.S. Characteristics:  CNG is odorless, tasteless and non-toxic, and made up of methane, nitrogen, carbon dioxide, propane, and traces of ethane.  Methane is the main component in CNG.  It is an environmentally clean alternative fuel.  CNG provides less risk in case of leakage, as it dispenses fast in the air. Dept. of Chemistry Page 18 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS)  CNG has an energy density of 53.6 MJ/kg (or) 9 MJ/L.  The gas has a high calorific value because it is free of any kind of toxicity.  It is a highly combustible gas and a fossil fuel. It has a low flammability range and high ignition temperature. Applications:  As you already know CNG is widely used by the transportation sector for powering cars, trains, ships, and other vehicles.  The gas is used by end consumers for cooking and heating.  Dryers use CNG for drying clothes. It is 50% more cost-effective than electricity.  Some countries also use CNG for generating electricity.  Manufacturing a huge range of chemicals like acetic acid, ammonia, methanol, butane, propane, ethane, etc. Even fertilizers are made using CNG.  It is heavily used as chemical feedstock for manufacturing plastic and other commercially important organic chemicals.  CNG is used in the production of glass, fabric, steel, paint, etc.  Protein-rich animal and fish feed is produced by feeding CNG. Biodiesel:  Biodiesel is a renewable and clean-burning fuel that is made from waste vegetable oils, animal fats, or recycled restaurant grease for use in diesel vehicles.  Biodiesel produces less toxic pollutants and greenhouse gases than petroleum diesel.  It can be used in pure form (B100) or can be blended with petro-diesel in the form of B2 (2% biodiesel, 98% petroleum diesel), B5 (5% biodiesel, 95% petroleum diesel), B20 (20% biodiesel, 80% petroleum diesel) and B100 (pure biodiesel). Chemistry of biodiesel production: Transesterification:  The process takes place in the following steps.  The first step is to mix the alcohol for reaction with the catalyst, typically a strong base such as NaOH or KOH.  The alcohol/catalyst is then reacted with the fatty acid so that the transesterification reaction takes place. Preparation of the catalyst with the alcohol: Dept. of Chemistry Page 19 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS)  Methanol and base are combined; NaOH separates into ions in methanol.  The OH- reacts with the H+ of methanol to take H2O, leaving OCH3- to react with fatty acid.  The catalyst is prepared by mixing methanol and a strong base such as sodium hydroxide or potassium hydroxide.  During the preparation, the NaOH breaks into ions of Na+ and OH-. The OH- abstracts the hydrogen from methanol to form water and leaves the CH3O- available for reaction.  Methanol should be as dry as possible.  When the OH- ion reacts with H+ ion, it reacts to form water.  Water will increase the possibility of a side reaction with free fatty acids (fatty acids that are not triglycerides) to form soap, an unwanted reaction.  Enzymatic processes can also be used (called lipases); alcohol is still needed and only replaces the catalyst.  Lipases are slower than chemical catalysts, are high in cost, and produce low yields.  The triglyceride will react with 3 mols of methanol, so excess methanol has to be used in the reaction to ensure complete reaction.  The three attached carbons with hydrogen react with OH- ions and form glycerin, while the CH3 group reacts with the free fatty acid to form the fatty acid methyl ester.  Glycerol is formed and has to be separated from the biodiesel. Both glycerol and biodiesel need to have alcohol removed and recycled in the process.  Water is added to both the biodiesel and glycerol to remove unwanted side products, particularly glycerol, that may remain in the biodiesel.  The wash water is separated out similar to solvent extraction (it contains some glycerol), and the trace water is evaporated out of the biodiesel. Acid is added to the glycerol in order to provide neutralized glycerol. Dept. of Chemistry Page 20 of 21  VARDHAMAN COLLEGE OF ENGINEERING, HYDERABAD (AUTONOMOUS) Schematic of the biodiesel process using trans esterification: Advantages:  Produced from Renewable Resources  Can be Used in existing Diesel Engines  Less Greenhouse Gas Emissions  Grown, Produced and Distributed Locally  Biodegradable and Non-Toxic  Positive Economic Impact  Reduced Foreign Oil Dependence  More Health Benefits Disadvantages:  Variation in Quality of Biodiesel  Not Suitable for use in Low Temperatures  Food Shortage  Increased use of Fertilizers  Water Shortage  Fuel Distribution  Slight Increase in Nitrogen Oxide Emissions Dept. of Chemistry Page 21 of 21