Nitrogen Industry

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<ul><li><p>Chemical Process technology </p><p>CHE C322 </p><p>Ammonia </p><p>Nitric Acid </p><p>Urea </p><p>Ammonium Nitrate </p><p>Nitrogen Industry </p><p>30-Jan-13 </p></li><li><p>Nitrogen Industry </p><p>30-Jan-13 </p><p> The production of nitrogen is a major branch of the fertilizer industry and it opens up a most important segment of the chemical industry. </p><p> Pure nitrogen may be obtain by separation from air by liquid air distillation. </p><p> By consumption of the oxygen of air by burning of fuel, which leaves nitrogen residue. </p><p> Nitrogen, however, is a rather inert element; it is difficult to get it to combine with any other element. </p><p> Haber succeeded in getting nitrogen to combine with hydrogen by the use of high pressure, moderately high temperatures, and a catalyst. </p><p> Ammonia; Nitric acid, Ammonium nitrate/chloride, Urea </p></li><li><p>Ammonia </p><p> Ammonia or azane is a compound of nitrogen and hydrogen with the formula NH3. </p><p> Colorless gas with a characteristic pungent smell </p><p> Soluble in water (aq. Solution : weak acid) </p><p> Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. </p><p> End uses </p><p> Direct application as fertilizer </p><p> Urea, Ammonium phosphates, </p><p>nitrate, sulfate </p><p> Production of nitric acid, amines, </p><p>nitriles. </p><p> Environmental application: </p><p>removal of Nox from flue gases </p><p>of power plants. </p><p> Nitrogen consumption in fertilizer </p><p>(80% of NH3production) </p><p> Mixed fertilizers (NPK) </p><p> Chemical nitrogen fertilizer 30-Jan-13 </p></li><li><p>Principle of Ammonia Synthesis The Haber or Haber-Bosch Process </p><p>30-Jan-13 </p><p> The ammonia synthesis reaction is represented by </p><p> N2 +3H2 NH3 H = -22.0 kcal </p><p> Increase in the pressure on this system increases the equilibrium ammonia concentration. </p><p> While raising the synthesis temperature gives a faster rate, it also displaces the equilibrium to the left, giving smaller potential conversion. </p><p> Condition used for most synthesis ammonia process </p><p> P = 100-300 atm </p><p> T=400-500 C </p><p> Catalyst : Promoted iron oxide catalyst </p></li><li><p>Process Selection </p><p>30-Jan-13 </p><p> Feedstocks for Ammonia synthesis by air distillation </p><p> Cryogenic low temperature technology </p><p> Feasible only for small ammonia plant (100 tonne/day) </p><p>or where abundant hydrogen is available. </p><p> Ammonia feedstocks by reforming and secondary </p><p>reforming (from coal, petroleum and natural gas) </p><p> Coal as a source via water gas (CO+H2) reaction : </p><p>higher capital investment, environmental problem </p><p> Natural gas reforming: can use any kind of petroleum </p><p>feed stock, easier to clean prior to use, less emission </p></li><li><p>Process flow sheet (Text book) </p><p>30-Jan-13 </p><p>Synthesis gas production is taken separately in textbook. So we will not refer this flow sheet. </p></li><li><p>Integrated Ammonia Plant </p><p>Process steam Pre-reforming Sec reforming HT shift LT shift </p><p>Ammonia synthesis Methanation Process </p><p> condensate </p></li><li><p>30-Jan-13 </p><p> Natural Gas Desulfurization </p><p> The sulphur content in natural gas is reduced to below 280 g/m3 to prevent poisoning of the nickel catalyst in the primary reformer. </p><p> Desulfurization can be accomplished by using either activated carbon or zinc oxide. </p><p> Reforming </p><p> Primary Steam Reforming- This reaction requires continued external heat (combustion of methane). </p><p> Catalyst : Ni </p><p> CH4 + H2O 3H2 + CO H = +49.7 kcal </p><p> Secondary Air Reforming-Sufficient air is added to provide nitrogen required for synthesis </p><p> CH4 + yair 2H2 + CO +xN2 H = +8.5 kcal </p><p> The gas leaving the secondary reformer is then cooled in a waste heat boiler. </p></li><li><p>30-Jan-13 </p><p> Shift conversion </p><p> High Temperature Shift Converter- CO is converted to CO2 in presence of chromium promoted iron catalyst </p><p>(FeO+Cr2O3) </p><p> CO + H2O CO2 + H2(-9.8 kcal) </p><p> Low Temperature Shift Converter- The low-temperature </p><p>shift converter is filled with a copper oxide/zinc oxide </p><p>catalyst. </p><p> Carbon dioxide can yield carbonates and carbamates </p><p>which are undesirable because they can deposit in </p><p>piping. </p><p> In addition oxides of carbon poisons ammonia catalyst. </p></li><li><p>30-Jan-13 </p><p> CO2 Removal </p><p> Carbon dioxide is removed by scrubbing by </p><p>monoethanolamine and hot potassium carbonate. </p><p> Regeneration of solvent is done by pressure letdown </p><p>plus some air stripping. </p><p> Methanation </p><p> Residual CO2 in the synthesis gas is removed by </p><p>catalytic methanation over a nickel catalyst </p><p> CO + 3H2 CH4 + H2O </p><p> CO2 + 4H2 CH4 +2 H2O </p></li><li><p>30-Jan-13 </p><p> Ammonia Synthesis </p><p> Nitrogen and hydrogen (obtain from any route) are required in mole ratio 1:3, raised to very high pressure 100-900 atm range (centrifugal compressor). </p><p> Material of construction: Steel (hydrogen embrittlement) </p><p> Commercial Synthesis Reactor </p><p> Pressure vessel with sections for catalyst beds and heat exchangers </p><p> Cold feed gas is added in quench reactor </p><p> The heat produced is removed between the catalyst beds by heat exchanger </p><p> Product recovery (Condensation) </p><p> Ammonia is condensed from this gas mixture by cooling the gases </p><p> At high pressure (converter exit pressure) ammonia condenses easily </p><p> It can be absorbed in water if solution to be marketed. </p></li><li><p>30-Jan-13 </p><p> Ammonia synthesis reactor design </p></li><li><p>Major Engineering Problems </p><p> Thermodynamic and Kinetic considerations </p><p>Optimization of space velocity </p><p> Fraction of NH3 (x) = f V-n </p><p> High space velocity Increase cost of </p><p> NH3 recovery and pumping cost </p><p>Space volumetric feed rate </p><p>velocity volume of reactor/catalyst </p><p>Space velocity is inversely proportional to contact time. </p><p>30-Jan-13 </p></li><li><p> Catalyst development </p><p> To date catalysts are based on Iron oxide </p><p> promoted by alkali K2O (1-2%) and metal oxide (Al2O3) </p><p> Al2O3 support to prevent sintering </p><p> Potassium reduces the activation energy of dissociation </p><p> Kellogg : Commercialized the Kellogg advanced Ammonia process using ruthenium on a graphite support </p><p> Process design modifications </p><p>Modern trend toward: lower pressure &amp; increased flow rates </p><p> Large single-train plant </p><p>30-Jan-13 </p></li><li><p>NITRIC ACID (HNO3) </p><p>Properties: </p><p>Appearance colorless to yellowish liquid </p><p>Mol. Wt- 63.03 </p><p> M.P - -42.5 oC </p><p> B.P 86 oC with decomposition </p><p> Completely miscible with water, forms a constant boiling mixture </p><p>Uses : </p><p> For production of ammonium nitrate, Adipic acid, dinitrotoulene, </p><p>nitrobenzene, sodium, potassium and calcium nitrates, nitro </p><p>compound for explosives etc. </p></li><li><p>Methods of Production </p><p>1. From saltpeter (NaNo3 + H2SO4 process) </p><p> Old process, practiced in middle age </p><p>2. Ammonia oxidation process </p><p> Modern nitric acid production process </p><p>3. N2 fixation from air ( Wisconsin process) </p><p> Production of NO and NO2 by high temperature reaction using air </p><p>4. Nitrogen fixation by nuclear fission fragments </p><p> Air exposed to radiation in a nuclear reactor to form NO. </p><p> Present economics gives too high a plant investment. </p></li><li><p>AMMONIA OXIDATION PROCESS </p><p>( Oswald process) </p><p> Modern nitric acid production uses </p><p> Catalytic oxidation of ammonia in air </p><p> Catalyst : Platinum Rhodium alloy gauze (Pt/Rh) </p><p> Followed by absorption of the oxidation product in </p><p>water to yield nitric acid. </p><p> Overall reaction reads: </p><p>NH3+2O2HNO3+H2O H =-78.9 kcal </p><p>Many reactions are involved in the overall process. </p></li><li><p>1) Ammonia oxidation : (Mixture of ammonia 9-11 % in air) </p><p>a. NH3 + 5/4O2 NO +3/2 H2O H =-78.9 kcal </p><p>b. 2 NO + O2 2 NO2 </p><p>2) Ammonia oxidation (side reaction ): </p><p>a) NH3 +3/4O2 1/2N2 +3/2 H2O These reactions can be </p><p>b) NH3 1/2 N2 + 3/2 H2 overcome by using a selective </p><p>c) NH3 + O2 1/2 N2O + 3/2H2O catalyst and short residence </p><p>d) NH3 +3/2 NO 5/4 N2 + 3/2H2O time at high temperature900C </p><p>3) Nitric oxide oxidation and : </p><p>a) 2NO + O2 2NO2 Non catalyzed reaction. NO2 is </p><p>b) 2NO2 N2 O4 in equilibrium with its dimer. </p><p> Thermodynamic data show low temperature and high pressure as favorable </p><p>conditions. </p><p> NO oxidation is famous reaction(one of the 3rd order reactions known). </p><p> Peculiarly rate constant increases with decreasing temperature. </p></li><li><p>30-Jan-13 </p><p>4) Absorption of nitrogen dioxide in water </p><p>a) 3NO2 + H2O 2 HNO3 + NO </p><p>b) 2NO2 + H2O HNO3 + HNO2 </p><p>c) 2 HNO2 H2O + NO + NO2 </p><p> The absorption of NO2 in water is quite complex, because </p><p>several reactions can be occur (both in liquid phase and </p><p>gas phase). </p><p> Operates best at high pressure (7- 12 bar). </p></li><li><p>PROCESS DESCRIPTION </p><p>Description: </p><p>Compressed air is mixed with anhydrous ammonia, fed to shell and tube converter designed so that the preheater and a steam heat recovery boiler-super heater are within the same reactor shell. </p><p>In the converter section the gas passes downward with a designed velocity in presence of a catalyst </p><p>Product gases from reactor, containing 10-20% NO, are sent through heat recovery units, a quench unit for rapid cooling to remove a large fraction of the product heat, and into the oxidizer absorber system. </p><p>Air is added to convert NO to NO2 at the most favorable low temperature of the absorption system. </p><p>The product from this water absorption system is 57 60 % HNO3 solution which can be sold as is or concentrated by various methods. </p></li><li><p>Nitric Acid Concentrations </p><p>30-Jan-13 </p><p> Several technical and commercial grades are produced ranging from 50% (by weight) to 95.5% HNO3. </p><p> Methods to obtain concentrated nitric acid (50- 68%) </p><p> Using conc. H2SO4 to dehydrate azeotropic composition </p><p> Hot nitric acid vapor is passed upward against conc. H2SO4 </p><p> Larger scale operation requires the sulfuric acid boiler and large heat input to reconcentrate dehydration acid. </p><p> Sulfur contamination is other issue. </p><p> Employing 72% aqueous magnesium nitrate (Mg(NO3)2.4H2O) </p><p> The anion of dehydrating agent and nitric acid are same, so no sulfate contamination. </p><p> Requires less heat of reconcentration than diluted sulfuric acid. </p></li><li><p>MAJOR ENGINEERING PROBLEMS </p><p>a) Thermodynamic and kinetic considerations: </p><p> i) The kinetics to form NO is favored by increasing </p><p>temperature until an optimum is reached which increases with </p><p>higher gas velocities. This results from prevention of back </p><p>diffusion of NO into the higher NH3 concentration region. </p><p> ii) Alloying Pt with Rd improves yield at a given set of </p><p>conditions. </p><p> iii) Rate of NO formation very nearly corresponds to </p><p>diffusion transport of NH3 molecules to the catalyst surface </p><p> iv) reaction rate is directly proportional to the system </p><p>pressure </p></li><li><p> b) Process design modification : </p><p> Most of the plants use intermediate ( 3-4 atms) or high pressure ( 8 </p><p>atms) processes rather than the complete atmospheric process or a </p><p>combination of 1 atm pressure oxidation and high pressure </p><p>absorption. Top pressure is limited by pressure vessel cost </p><p>The reason for elevated pressure processes are: </p><p>1. High reaction rates and lower volumes in both oxidation and </p><p>absorption equipment </p><p>2. Higher acid strength </p><p>3. Lower investment cost </p><p>The disadvantages of high pressure </p><p>1. Lower oxidation yields </p><p>2. Higher catalyst losses unless good filtering procedures are used </p><p>3. High power requirements if power recovery units are not specified </p></li><li><p>UREA (NH2CONH2) </p><p>Organic compound </p><p>Also known as Carbamide </p><p>PROPERTIES: </p><p>Mol. Wt : 60.05 </p><p>M.P : 132.7 oC </p><p>B.P : Decomposes </p><p>Fairly soluble in water </p><p>Colorless </p><p>Odorless </p><p>USES: </p><p> solid as well as liquid nitrogen fertilizers. </p><p> Plastics in combination with formaldehyde and furfural. </p><p> adhesives. </p><p> coatings, textile anti shrink compounds, Ion-exchange resins. </p><p> as an intermediate for ammonium sulfamate, sulfumic acid, andthe phthalocyanine pigments </p></li><li><p>Process routes &amp; Reactions </p><p>Method of production : </p><p>Ammonium cynate heating: NH4OCN NH2CONH2 </p><p>Ammonium carbamate decomposition process </p><p>Raw materials used: CO2 and NH3 Chemical reactions: </p><p>a) CO2 + 2 NH3 NH4COONH2 (Fast &amp; exothermic) Carbamate </p><p>b) NH4COONH2 NH2CONH2 + H2O (Slow &amp; endothermic) </p><p>Undesired side reaction </p><p>c) 2NH2CONH2 NH2CONHCONH2 + NH3 Biuret </p></li><li><p>30-Jan-13 </p><p> Process Steps: </p><p> Solution synthesis </p><p> Ammonia and carbon dioxide are reacted to form ammonium carbamate. Typical operating conditions include temperatures from 180 to200C,pressures from 140 to 250 atmospheres NH3:CO2 molar ratios from3:1 to 4:1. </p><p> The carbamate is then dehydrated to yield 70 to 80 percent aqueous urea solution. </p><p> Solid Formation: (Prilling / Granulation) </p><p> Prilling: It is a process by which solid particles are produced from molten urea. Molten urea is sprayed from the top of a prill tower. As the droplets fall through a countercurrent air flow, they cool and solidify into nearly spherical particles. </p><p> Granulation: Granular urea is generally stronger than prilled urea, both in crushing strength and abrasion resistance. In drum granulation, solidsare built up in layers on seed granules placed in a rotating drum granulator/coolerapproximately4.3mete in diameter. </p><p> Clay Coating: Used to reduce product caking and urea dust formation </p></li><li><p>30-Jan-13 </p></li><li><p>MAJOR ENGINEERING PROBLEMS </p><p>1. Autoclave variable </p><p> Temperature, pressure, NH3/CO2 ratio </p><p> Heat dissipation in the autoclave : coils, wall cooling. </p><p>2. Carbamate decomposition and recycle </p><p> Low T, high P with short residence time </p><p>3. Production of granular urea </p><p> To avoid biuret formation: T, just above the melting point of urea with seconds residence time. </p><p>4. Corrosion </p><p>5. Process design modifications </p><p> Once through process </p><p> Toyo Koatsu Process: Combine ammonia and urea process. CO2 is absorbed by mixture of hot carbamate and ammonia. The resulting mixture is passed to urea reactor. </p></li><li><p>AMMONIUM NITRATE </p><p>Properties: </p><p>Mol. wt- 80.05 </p><p>M.P 170oC </p><p>B.P decomposes at 200 oC or higher </p><p>Uses: </p><p>In fertilizers, explosives, Nitrous oxide (as an aesthetic) </p><p>Chemical Reaction: </p><p>NH3+HNO3NH4NO3 (H = -20.6 kcal) </p><p>Production Process : Based on reaction of nitric acid and ammonia. Variation in methods are based on final solid form. </p><p>1. Prilling process </p><p>2. Crystallization process (not shown on flow sheet) </p><p>3. Stengel process </p></li><li><p>Major engineering problem </p><p>1. Corrosion </p><p>2. Crystallization </p><p>3. Safety </p><p> Hot conc. Ammonium nitrate solution is explosively </p><p>sensitized by traces of acid. </p><p> Care is taken to add sufficient ammonia to the wet </p><p>melt to keep the pH above about 5. </p><p>4. Conditioned air requirement </p></li></ul>