Industrial Derivatives of Nitrogen and Fertilizers Manufacture. Chapter 5

Chapter- 5 Industrial Derivatives of Nitrogen and fertilizers manufacture — The derivatives are: ammonia, trinitrotoluene (TNT), nitro-glycerine (NG), nitrocellulose (NC) etc. — Ammonia is most important derivative for making fertilizers and nitric acid. 1  Nitric acid occurs in nature in the form of nitrate salts. Initially, large scale production of nitric acid began with sodium nitrate as a feed stock.  Near the beginning of the 20th century, world reserves of sodium nitrate were low and processes were being developed to replace nitrate with nitrogen.  Nitric acid was needed for explosives, munitions, and developing dyestuffs business  Three techniques were used industrially: 1) Production of NO by reacting N2 and O2 at greater than 2000 oC, - - Abandoned because of poor energy efficiency. 2) Production of ammonia by hydrolysis of calcium cyanide, ---- not widely accepted 3) Production of ammonia from N2 and H2. (Haber-Bosch Process) N2 + 3H2 Fe 2NH3 2 Ammonia synthesis: a) Cyanamide process – proper mixing of lime with carbon and heated at high temp. CaO + 3C → CaC2 + CO By grinding CaC2 , it is charged electrical furnace adjusted at 10000c. And pure N2 is passed over the hot calcium carbide. 2CaC2 + N2 → Ca(CN)2 + 2C Then, Ca(CN)2 is treated with super heated steam Ca(CN)2 + 3H2O (steam) → CaCO3 + 2NH3 3 b) Haber process • Ammonia synthesis through the reaction of nitrogen and hydrogen. Involves two distinct operations. 1. Preparation of N2- H2 mix. Nitrogen – from liquefactions of air and its separation from oxygen is through cryogenic distillation Hydrogen – from bosch system water gas producer C + H2O → CO + H2 • Water gas mixtures (N2,H2 ,CO & CO2) are also mixed with large excess steam and passed over oxide of iron & chromium catalyst to bring the water- gas shift reaction. C O + H2O → CO2 + H2 2. Preparation of Ammonia: the purified N2 & H2 are charged to ammonia tower in the ratio of 1:3 at the pressure of 200 atm. At 500 0c over iron oxide catalyst . The product obtained is up to 15% NH3 is cooled at the same pressure to be liquefied and stored under specially designed tanks. 4 Modern method of ammonia manufacturing 5 Properties of ammonia and nitric acid • Ammonia is a colourless gas with a characteristic pungent smell. It is lighter than air, its density is 0.589 times that of air. • It is easily liquefied due to the strong hydrogen bonding between molecules; the liquid boils at −33.3 °C (−27.94 °F), and freezes at −77.7 °C (−107.86 °F) to white crystals. 6 Manufacture of HNO3 1. Soda nitric process NaNO3 + H2SO4 heated in retorts NaHSO4 + HNO3 The product HNO3 is distilled out of the retort and condensed up to 95% v/v. But this process suffers due to limited distribution of raw material salt peter. 7 2. Arc process • Air is passed through an electric arc which cause O2 & N2 to combine to give nitric oxide (NO), • The NO is then cooled and oxidized to NO2 which is absorbed in water to form HNO3 of only 50%. 8 Cont’d….. —The arc process consumes high electrical energy —Its investment and operation cost is very high. —Produce enormous amounts of gas in circulation compared to low concentration of NO which is formed about 2% and also; —High temperature produced in the process promotes the reverse dissociation reaction. 9 3. Ammonia oxidation process • conversion of ammonia to nitric acid. Ammonia is mixed with hot air and passed through Pt-Rh alloy catalyst a) 4NH3(g) + O2(g) → 4NO(g) + 6H2O(l) (Catalytic Combustion) b) 2NO(g) +O2(g) → 2NO2(g) ⇌ N2O4 (oxidation of NO) c) 3NO 2(g) + H2O(l) → 2HNO3(aq.) + NO(g) (absorption) Other reactions: N2O4 + H2O → HNO2 + HNO3 2HNO2 → HNO3 + H2O + 2NO — Absorption of NO2 in H2O produce 60% HNO3 and sent to a bleacher to purge away unnecessary oxides of nitrogen and unreacted NO to be oxidized. — The biggest issue with this method is the loss of precious metal at the reactor temperatures. — Recovery gauze is typically used to absorb platinum oxide vapor and form an alloy. This gauze can periodically be removed and platinum recovered. 10 11 Nitric acid Absorption Tower 12 Markets and Uses of Nitric Acid Markets and use of nitric acid — The largest use of nitric acid is in the fertilizer industry, 74-78% — The second largest use is for manufacture of chemicals. Some examples are dinitrotoluene and nitrobenzene — Finally for production of explosives, metal nitrates, nitrocellulose, nitrochlorobenzene, a metal treatment solvent, rocket propellants, and nuclear fuel processing. 13 Explosives Explosives are pure substances or mixtures which on being subjected to specific stimulus like mechanical impact, frictional forces, electrical discharge and other sources of heat, high pressure shock waves initiates an oxidation reaction to produce large volume of hot gases. In general, an explosives basic characteristics are: — Upon ignition, it decomposes rapidly in a detonation or deflagration; — rapid release of heat and large quantities of high-pressure gases that expand rapidly with sufficient force to overcome confining forces; and — The energy released by the detonation of explosives produces ▪ ▪ ▪ ▪ rock displacement ground vibration rock fragmentation air blast 14 Alfred Nobel, Sweden Nitro-glycerine (dynamite)used for rock fragmentation 15 ( ), Explosives are classified under three broad groups, namely primary, low and high explosives. Mercury fulminate (mercuric cyanate) : It is ✓ Primary explosives: are the most sensitive to prepared by mixing of solution of 1 part of heat, friction, impact, shock and electrostatic mercury with 11 parts of 57% nitric acid and energy. poured into 10 parts of 95% ethanol, forms fine crystals of 99% purity mercury fulminate • They are used to initiate the explosion of high explosives which consists of explosives of increasing mass and decreasing sensitivity • Diazo dinitrophenol: prepared from picramic acid (NH2(NO2)C6H2OH) with sodium nitrite and HCl. The product obtained is washed and recrystallized from hot acetone. It is non-hygroscopic and sensitive to friction and impact • Lead azide: the azides are explosive compounds that do not contain oxygen. • It is extensively used as primary explosive in military detonators. • Lead azide (PbN6) is made in small batches buffered by the reaction solutions of lead nitrate or acetate with highly toxic sodium azide. 16 • Low Explosives: Deflagrate rather than detonate. Their reaction velocities are 2000 to less than 3000 feet per second. • Black powder is a good example. Black powder is mixture of potassium nitrate, charcoal and sulphur Smokeless powder is nitrocellulose and perhaps nitro-glycerine — These materials normally have little water resistance, are highly flammable — Generally do not fragment rocks 17 Black Powder (Low Explosive) • Black powder contains: • 75% Potassium Nitrate (KNO3) • 15% Charcoal (C) • 10% Sulfur (S) The KNO3 is the oxidizing agent. • When heat is applied to the powder, the oxygen from KNO3 is liberated. • It combines with the carbon (fuel) and sulfur (for stable combustion). • The combustion of charcoal and sulfur produces 2 gases – CO2 and N2. • The buildup of gases in the cartridge, propels the bullet forward in bullet cartridges. 18 Cont’d… High Explosive: any chemical mixture that detonates with a reaction velocity over 5000 feet per second. •A general theory of high explosives is that the detonation of the explosives charge causes a high-velocity shock wave and a tremendous release of gas. The shock wave cracks and crushes the rock near the explosives and creates thousands of cracks in the rock. For example: Straight Dynamite - Nitroglycerin in an absorbent, with velocities between 10,000 and 20,000 feet per second. This dynamite is the most sensitive of all commercial explosives. ✓has poor fumes, good water resistance, and poor cohesion. Ammonia Dynamite - This is similar to straight dynamite except that ammonium and/or sodium nitrate and various carbonaceous fuels are substituted for a portion of the nitroglycerin. -blast agent 19 Cont’d…… ➢Combustion (or decomposition) of explosives occurs so rapidly, that there isn’t enough time for the oxygen in the surrounding atmosphere to combine with the fuel. ➢Therefore, many explosives must have their own source of oxygen – or oxidizing agents. 20 Manufacture of TNT,NG & NC TNT:- by nitrating toluene with nitrating mixture. ✓ The product is washed with ammoniacal solution of Na2SO3 and cold water. ✓ The crystal of TNT is filtered and purified by melting. NG: it is the class of explosives which is known as dynamite. ✓ Prepared by adding glycerol to a cooled mix. of H2SO4(60%) and HNO3(40%) at 10oc with constant stirring. ✓ They form NG top layer and acid bottom layer so that we add dilute Na2CO3 to neutralize the acid completely. NC:- mild explosive. [C6H7O2(OH)3 ] n + 3nHNO3 conc. H2SO4 [C6H7O2(NO3)3 ]n + 3nH2O 21 Fertilizers and phosphoric acid Manufacture of H3PO4 1. From Phosphate rocks: - Phosphate rocks is digested with conc. H2SO4 Ca3(PO4)2 + 3H2SO4 + 6H2O 2H3PO4 + 3(CaSO4.2H2O) -This product is mostly used to manufacture the phosphatic fertilizers because essential nutrients like Mg, Al, Fe etc. Resides as impurities with phosphate rocks. -Side rxns: CaF2 + H2SO4 2HF + CaSO4 during digestion with the acid. 2. From Phosphorus: -Burning of phosphorus with excess air (O2) and absorbing the resultant oxide in water form pure H3PO4. P4 + 5O2 P4O10 absorbing in H2O 3H3PO4 22 Phosphoric acid manufacture from phosphate rock Dihydrate process comprises four stages: • Filtration • Grinding • Reaction • Concentration 23 Phosphoric acid series • Polyphosphoric acids: formed by heating two or more molecules of orthophosphoric acids which undergo condensation form linear structure. • E.g. H4P2O7,H5P3O10.... • Meta-phosphoric acids- heating of orthophosphoric acid at high temperature forms a series of ring structures to general formula (HPO3)n • Eg. (HPO3)3 , (HPO3)4 24 Phosphoric acid series 25 Essential and trace elements for plant growth From 35 elements of the plant nutrients 17 of them are essential; C,H,O – Natural nutrients since they are supplied by air & water N, P, K - primary nutrients which are consumed in large amounts and supplied by soil. Ca, Mg & S - occurring only in limited extent in soil – secondary nutrients All these nutrients are called major nutrients and the remaining 8 elements are considered as trace (Fe, Mn, B, Mo, Cu, Zn, Cl and Co). 26 1. Ammonium nitrate It is produced on conjugation with the NH3 & HNO3 plant. a) Neutralization – it is exothermic, heat is utilized for concentration of the solution. b) Evaporation – the solution is heated with steam and passed to vacuum evaporator. c) Prilling- solidification of the concentrated solution in the Prilling tower. d) Drying and finishing NH4NO3 is an explosive and sensitive to heat . To reduce its explosive nature it is mixed with (masked by) CaCO3. It is also hygroscopic & prevented by packing in plastic bags. 27 Urea manufacture o 1. Carbamate formation in silver lined autoclave at 350-400 c Rxn : 2NH3(l) + CO2(l) → NH2COONH4 2. Carbamate decomposition in high pressure decomposer and heated in steam NH2COONH4 → NH2CONH2 + H2O 3. Concentration by vacuum evaporator 4. Prilling –solidification of the concentrated solution in to prills. 28 Cont’d… Potash fertilizers: containing the fertilities KCl, K2SO4 & KNO3 NPK – FERTILIZERS: it is a modern approach. ✓ known as mixed fertilizer containing N, P & K fertilizer combination. ✓ Raw materials : anhydrous liquid ammonia, phosphoric acid(25-30%), H2SO4(80-93%) and potash (KCl). Uses 3 neutralization tanks as the rxns equation seen below. NH3 + H3PO4 → NH4H2PO4 NH3 + NH4H2PO4 → (NH4)2HPO4 2NH3 +H2SO4 → (NH4)2SO4 Then the product from the 3rd neutralizer is mixed with the calculated amount of potash 29 Phosphatic fertilizer Simple and triple phosphates are the two most commonly used phosphatic fertilizer. Simple-Superphosphate: it is the mix. of mono-calcium phosphate and crystalline calcium sulphate obtained by treating phosphate rock with H2SO4. Ca3(PO4)2 + 2H2SO4 + 2H2O → Ca(H2PO4)2 + 2CaSO4.2H2O • Due to fluorite present in the phosphate rock there is undesirable side reaction. CaF2 + H2SO4 → 2HF + CaSO4 Triple supper phosphate: contain 44-47% P2O5. Manufactured by using 78% phosphoric acid in phosphate rock instead of H2SO4 Ca3(PO4)2 + 4H3PO4 → 3Ca(H2PO4)2 30 31