Presentation on theme: "Lecture Topic 5: Inorganic Chemistry and Industry Ref: “Inorganic Chemistry: An Industrial and Environmental Perspective” by T. W. Swaddle Premise:Inorganic."— Presentation transcript:
Lecture Topic 5: Inorganic Chemistry and Industry Ref: “Inorganic Chemistry: An Industrial and Environmental Perspective” by T. W. Swaddle Premise:Inorganic chemistry is extremely important for many industries, but there are a handful of reactions which are of primary importance to the Chemical Industry. Goal:Students should be able to 1) describe recovery processes and uses of the most common elements 2) discuss the chemistry of atmospheric pollution 3) discuss the chemistry of pulp and paper processing 4) describe the synthesis of NH 3 and H 2 SO 4.
Most Abundant Elements in the Earth’s Crust
Oxygen Occurrence large amounts in Earth’s crust (oxides of other elements) 21% of atmosphere (as O 2 and O 3 ) Recovery by fractional distillation of air Industrial Uses 1) Sewage Treatment: In the “activated sludge process”, sludge is oxygenated and biodegraded by aerobic bacteria. 2) Steelmaking: Impurities are removed by blowing O 2 over molten iron to generate “slag”, a layer of oxides that floats atop the Fe (l). In the U.S., ~3million metric tons of O 2 are used annually for this.
Nitrogen Occurrence most abundant element in the atmosphere (N 2 ) very low abundance in Earth’s crustal rocks Recovery by fractional distillation of air Industrial Uses fertilizers (nitrates, ammonia, ammonium salts, and urea) propellants and explosives (nitro-organics, nitrates, hydrazines) Most Important Industrial Reaction the Haber process for the production of ammonia (NH 3 )
Nitrogen for Fertilizers Ammonia (NH 3 ) prepared using the Haber process is 1) transported in liquid form by truck, barge and pipeline 2) often injected directly into soil (15-30 cm deep) 3) corrosive to the flesh 4) explosive with air at a 16-25% NH 3 concentration 5) commonly converted to ammonium sulfate (NH 4 ) 2 SO 4, ammonium nitrate NH 4 NO 3, or urea (H 2 N) 2 CO for safe shipment, storage and use. The relatively inert N 2 of the atmosphere must be “fixed” as soluble reactive compounds….bioavailable compounds.
Nitrogen for Fertilizers Urea : 1) is made by reaction of ammonia and the CO 2 by-product of the water-gas shift reaction. 2) can be produced in forms that release nitrogen slowly to the soil: a) “SCU” fertilizers are urea pellets coated with ~2% paraffin wax containing S 8 that oxidizes away slowly in the soil. b) Urea-formaldehyde (UF) polymers decompose slowly in the ground. Ammonium sulfate: is a safe form of ammonia for shipping, storage and use.
Nitrogen for Fertilizers Nitric Acid and Ammonium Nitrate : 1) The catalytic oxidation of ammonia by air over Pt gauze at ~900°C gives nitric oxide (NO 2 ) which is then converted to nitric acid by air and H 2 O (l) to give the net reaction: 2) Nitric acid is converted on-site to ammonium nitrate : 3) NH 4 NO 3 is potentially explosive!! 4) Calcium carbonate CaCO 3 (chalk, limestone) can be added to solid NH 4 NO 3 to form a non-explosive product. 5) NH 4 NO 3 can be stored safely as a dilute aqueous solution. 6) 3% clay can be added as a drying agent to prevent caking (34-0-0)
Nitrogen for Explosives and Propellants Explosives and propellants are an important industrial technology for: safety projects (airbags, ejector seats, avalanche control) civil engineering projects (highways, dams, waterways, etc.) mining and quarrying aerospace projects (launch technology) There are 2 requirements for a material to be an explosive: 1. Decomposition or combustion must be highly exothermic. 2. Hot reaction products must be gaseous. The high bond energy of the N N triple bond explains the tendency of N-containing compounds to decompose exothermically to N 2(g). Airport security units use Neutron Activation Analysis to detect high nitrogen content.
Nitrogen for Explosives and Propellants Ammonium Nitrate : 1) is the most commonly used blasting explosive 2) gentle heating to its melting point (170°C) gives nitrous oxide: T>250°C, or when shocked, violent decomposition to N 2 : 4) is commonly mixed with an oxidizable substance (fuel oil) for legitimate use as a relatively safe and inexpensive explosive.
Nitrogen for Explosives and Propellants Potassium Nitrate, KNO 3 (Saltpeter) : Used for black powder : (41% KNO 3, 29.5% C, 29.5% S): for firearms (before guncotton) (75% KNO 3 15% C, 10% S): for fireworks, time fuses etc. Hydrazine, H 2 NNH 2, and dimethylhydrazine, (CH 3 ) 2 NNH 2 : Used for rocket propellants : The hydrazine is oxidized by H 2 O 2, O 2(l), or F 2(l).
Nitrogen for Explosives and Propellants Nitro-containing organic compounds :R-NO 2 1) are the most common commercial high explosives 2) Nitro groups can oxidize the C content to CO or CO 2 and the H content to H 2 O….increases exothermicity and gas volume.
A Word on Nitrogen Oxides Nitrogen oxides are widely implicated as air pollutants. Nitrous oxide, N 2 O : 1) is a colourless, odourless, non-toxic gas 2) is produced:a) by degradation of nitrate fertilizers b) as a by-product of nylon production 3) is used as an anaesthetic (laughing gas) and as a propellant (whipped-cream spray cans) 4) is implicated in greenhouse warming….has a residence time in the atmosphere of 150 years and could contribute up to 10% of the anticipated greenhouse warming. 5) in the stratosphere, reacts with the 1 D excited state of atomic oxygen to generate nitric oxide.
A Word on Nitrogen Oxides “NO x ” : NO, NO 2, N 2 O 4 1) NO….Nitric oxide is a toxic, colourless gas. Very endothermic ( ΔH° = kJ/mol), BUT equilibrium rapidly established. When air is heated to very high T, small amount of NO is made. If it is then quenched to T<1000K, the NO is “frozen in”. This is what happens in combustion engines! 2) NO 2 ….Nitrogen dioxide is a toxic, brown gas. NO reacts rapidly with O 2 from air. 3) N 2 O 4 ….Dinitrogen tetroxide is a yellow liquid (b.p. = Dimerization of NO 2.
A Word on Nitrogen Oxides “NO x ” : NO, NO 2, N 2 O 4 4) Acid precipiation: NO 2 in the troposphere reacts with hydroxyl radicals (OH, produced indirectly from ozone pollution) to form nitric acid. 5) Photochemical smog: a white aerosol that is intensely irritating to eyes and mucous membranes. The chemistry of photochemical smog is complex (>50 rxns!) Involves photochemical reaction of NO x with unburned hydrocarbons to generate peroxyacyl nitratrate (PAN), aldehydes, hydroperoxides and peroxynitrates. 6) How to reduce NO x emissions…. i) reduce combustion T (by lowering compression ratio) ii) lower post-combustion conc. of O 2 (fuel-rich mixtures) iii) use catalytic converter to remove NO and unburnt fuel
Silicon Occurrence most important element in igneous and many sedimentary rocks SiO 2 (quartz, silica), aluminosilicates (feldspar, etc.), …. Recovery reduction of silica sand with coke (furnace) crude Si chlorination of silica and reduction with Mg high purity Si Industrial Uses ferrosilicon alloys for acid-resistant metal (chemical reactors) organosiloxane (“silicone”) polymers electronic “chips” SiO 2 (fiber optics)
Organopolysiloxanes (“Silicones”) 1) ….are made by the hydrolysis of organochlorosilanes R n SiCl 4-n : Rochow process Inclusion of RSiCl 3 will Inclusion of R 3 SiCl will lead to chain branching.cause chain termination. 2) ….can be oils, waxes, rubbers 3) ….have high thermal stabilities, resistance to oxidation, electrical insulation, water repellency, good biocompatibility, low chemical reactivity.
Aluminum Occurrence in combination with Si and O as aluminosilicates in rocks or as its ore, bauxite: essentially AlO(OH) with Fe contaminants Recovery Al(III) is “leached” out from bauxite using NaOH (aq) and the resulting gibbsite [α-Al(OH) 3 ] is dehydrated to α-Al 2 O 3. α-Al 2 O 3 is dissolved in molten Na 3 AlF 6 / CaF 2 (9:1) and reduced electrolytically using graphite electrodes (consumed). Industrial Uses Al (m) is used in vehicles, aircraft, packaging, construction, etc. Aluminosilicates are used as catalysts (e.g., zeolites)
Sulfur Occurrence native, i.e., elemental sulfur (S 8 and other allotropes) sulfates (SO 4 2- ) and sulfides (S 2- ) hydrogen sulfide (H 2 S) Recovery elemental S used to be mined using the Frasch process now, so much H 2 S is recovered as a by-product from natural gas and refinery operations that mining is obsolete! Highly toxic H 2 S is converted to solid S by the Claus process Industrial Uses H 2 SO 4 is the #1 synthetic chemical in terms of tonnage H 2 SO 4 used mostly to make fertilizers, but also for ClO 2 Kraft and Sulfite processes for wood pulping (paper)
Sulfur from H 2 S: Claus Process Hydrogen Sulfide H 2 S : 1) is a highly toxic gas that occurs in Albertan “sour” natural gas (>30% H 2 S content) 2) H 2 S is “scrubbed” out of natural gas by absorption in aqueous monoethanolamine (MEA, HOCH 2 CH 2 NH 2 ) or diethanolamine (DEA, (HOCH 2 CH 2 ) 2 NH). The aqueous base is then stripped off to recover the H 2 S. 3) Claus Process: H 2 S is burnt partially to SO 2 in air unburnt H 2 S and SO 2 react (catalyzed by Fe 2 O 3 or γ-Al 2 O 3 )
Sulfuric Acid Sulfuric acid H 2 SO 4 : 1) generally is produced by the contact process: a) exothermic air oxidation of SO 2 (V 2 O 5 or Pt catalyst) b) SO 3 is absorbed into 100% H 2 SO 4 to give a mixture disulfuric and sulfuric acids, known as oleum c) oleum is hydrolyzed to H 2 SO 4
Sulfuric Acid 2) 90% of the sulfur produced industrially is converted to H 2 SO 4 !! 3) 2/3 of the H 2 SO 4 produced is consumed in fertilizer manufacture, to make ammonium sulfate: (NH 4 ) 2 SO 4 or superphosphate: 32% CaHPO 4 /Ca(H 2 PO 4 ) 2 H 2 O 3% H 3 PO 4 50% CaSO 4 or potassium sulfate: K 2 SO 4 (Mannheim process) 4) H 2 SO 4 is also used to make chlorine dioxide ClO 2 for bleaching paper pulp and for sterilizing water. i) Mathieson process: ii) Solvay process:
Sulfur Chemicals: Pulp & Paper Industry Kraft Process (or Sulfate process) 1) An alkaline process resulting in strong, brown, “acid-free” paper. 2) Wood chips are digested at 800°C (800 kPa) for 1 to3 hours in aqueous NaOH/Na 2 S/Na 2 CO 3 converting the lignin to soluble alcohols, anions, mercaptans (RSH) and organic sulfides (R 2 S). 3) Once the pulp is collected, tall oil (for soaps) is removed from the spent aqueous solution by centrifugation, then the water is removed and the remaining residue is ignited, converting the organic content to C. Finally, the NaOH, Na 2 S, Na 2 CO 3 are regenerated by the addition of Na 2 SO 4 and Ca(OH) 2. Wood pulping is a process in which lignin is broken down without excessive damage to the cellulose. The the Kraft and Sulfite processes are chemical pulping processes.
Sulfur Chemicals: Pulp & Paper Industry Sulfite Process 1) An acidic process yielding weaker, white paper. 2) Uses a buffered aqueous sulfurous acid solution (HSO 3 ¯/H 2 SO 3 ). 3) SO 2 is passed over wet limestone CaCO 3 to produce the solution. 4) This solution is used to digest wood chips at 130°C for 24h. 5) SO 2 is recovered from relief gases and CaSO 3 is recovered by evaporation of the spent liquor and addition of slaked lime Ca(OH) 2.
Sulfur Compounds and Air Pollution Sulfur dioxide SO 2 : 1) is a moderately toxic, pungent, colourless gas (b.p. -10°C) 2) is produced in large amounts by burning fossil fuels (coal!), roasting sulfide ores (pyrite, FeS 2 ), pulp & paper mill discharges, and natural volcanic activity: [2:1 anthropogenic to natural] 3) Acid Precipitation: mostly H 2 SO 4 from: wet clouds or dry air also some H 2 SO 3 from:
Sulfur Compounds and Air Pollution How to minimize SO 2 emissions : 1) Desulfurization of fuels: difficult and expensive e.g. Battelle hydrothermal coal process 2) Scrubbing of stack gases with wet limestone: Fuels are burnt as received and resulting SO 2 is removed in the stack. 3) Recovery of SO 2 as H 2 SO 4 : The stack is scrubbed with a cool spray of an organic amine solution which absorbs the SO 2. The resulting complex is then heated in a separate column to release SO 2 which is then converted to H 2 SO 4. (Union Carbide CanSolv process)
Sulfur Compounds and Air Pollution How to minimize SO 2 emissions : 4) Fluidized bed T = °C, limestone reacts with SO 2 and air to give CaSO 4 CaSO 4 (gypsum) is non-toxic and useful (roadbed cement) unlike CaSO 3 which is toxic to plants (hard to dispose of) 5) Use of low-sulfur fuels: e.g. Coal from western Canada: transportation costs and politics are the major concerns
Chlorine Occurrence as chloride ion Cl¯, the most abundant anion in seawater as rocksalt NaCl Recovery Chloralkali process: electrolysis of brine NaCl (aq) by-product of NaOH synthesis Industrial Uses 67% to organic chemicals industry (25% for EDC alone!) 30% to pulp & paper mills, and 5% to water treatment
Chlorine Hypochlorite ion OCl¯ and Hypochlorous acid HOCl : 1) Cl 2 disproportionates when dissolved in water 2) HOCl decomposes slowly releasing oxygen Since HOCl is a powerful disinfectant, Cl 2 is used to treat water. 3) Cl 2 dissolved in cold, dilute aqueous NaOH generates kinetically stable solutions of OCl¯…. HOUSEHOLD BLEACH!
Chlorine Chlorate ion ClO 3 ¯ : 1) Cl 2 dissolved in hot, concentrated aqueous NaOH forms ClO 3 ¯ 2) Chlorate salts are strong oxidizing agents….KClO 3 can be used in place of KNO 3 as an oxidant for C and S in black powder. 3) Chlorate salts can be used as an unselective herbicide. 4) Chlorate salts are mainly used as a source of ClO 2 for bleaching paper pulp and for sterilizing water. Recall: Mathieson process and Solvay process
Chlorine Chlorine dioxide ClO 2 and the Chlorite ion ClO 2 ¯ : 1) ClO 2 is an orange-yellow gas, explosive in high concentrations. 2) ClO 2 is often converted to sodium chlorite NaClO 2 for safer shipping and handling….there is still a friction explosion hazard! Perchloric acid HClO 4 and the Perchlorate ion ClO 4 ¯ : 1) Electrolysis of chlorate ClO 3 ¯ solutions gives perchlorate ClO 4 ¯. 2) ClO 4 ¯ (aq) is often used to adjust acidity / ionic strength. 3) Perchlorates are explosive! e.g., Solid Rocket Fuel: NH 4 ClO 4 is used to oxidize Al powder. e.g., A single drop of conc. HClO 4 in DMSO BOOM!
Chlorine and Industrial Chemistry VCM, vinyl chloride monomer : H 2 C=CHCl 1) VCM is made almost exclusively by thermal cleavage of EDC, ethylene dichloride (or 1,2-dichloroethane) ClCH 2 CH 2 Cl. 2) EDC is formed by chlorinating ethylene….Cl 2 + H 2 C=CH 2 3) 95% of the VCM produced is used to make polymers e.g. PVC, poly(vinyl chloride) [-CH 2 -CHCl-] n Hydrochloride HCl salts as pharmaceuticals : A common technique used to stabilize amine-containing drugs is to synthesize the HCl salt. e.g., US patented the HCl and HBr salts of this HIV protease inhibitor:
Chlorine and Environmental Concerns Chlorofluorocarbons CFCs :e.g., CF 2 Cl 2 and CFCl 3 1) Were widely used as refrigeration fluids, cleaning fluids for electronics manufacture, aerosol propellants, and plastic foam blowing agents. 2) Were thought to be inert, but now are known to be the major factor in the destruction of the stratospheric ozone layer! 3) Montréal Protocol (1988): phase-out of CFC production by 1995.
Chlorine and Environmental Concerns Chlorinated organic compounds : 1) DDT, dichlorodiphenylchloroethane: An insecticide still used in the tropics to combat the anopheles mosquito (carriers of malaria). 2) TCDD, tetrachlorodibenzo-p-dioxin: A potent toxin and carcinogen, this dioxin is a byproduct of Cl 2 bleaching of pulp and paper. 3) PCBs, polychlorobiphenyls: Once used as electrical transformer oils. Mimic natural hormones & disrupt endocrine systems of animals. 4) Chlorinated solvents such as chloroform CHCl 3, carbon tetra- chloride CCl 4, etc. : carcinogenic and threaten ozone pool.