Heavy inorganics: salt, sulphur, nitrogen and phosphorus: Key terms, quiz and sources

Understanding Chemicals / Module 4: Heavy inorganics: salt, sulphur, nitrogen and phosphorus Wrap-up

Heavy inorganics: salt, sulphur, nitrogen and phosphorus: review

Key terms

Contact process: Making sulphuric acid by oxidising SO2 to SO3 on a vanadium catalyst and absorbing the SO3 in strong acid.
Double absorption: Removing SO3 between converter beds so the equilibrium shifts and overall conversion reaches 99.5% or more.
Claus process: Recovering elemental sulphur from hydrogen sulphide by burning a third of it to SO2 and reacting the two over a catalyst.
Electrochemical unit: The fixed bundle from brine electrolysis: one tonne of chlorine with about 1.1 tonnes of caustic soda and some hydrogen.
Membrane cell: A chlor-alkali cell whose ion-exchange membrane passes sodium ions but blocks chloride, giving pure 30-35% caustic soda.
Current efficiency: The share of the electric charge passed through a cell that ends up making the intended product.
Solvay process: Making soda ash from salt and limestone with ammonia as a recycled reagent, leaving calcium chloride as waste.
Trona: A natural mineral of sodium carbonate and bicarbonate that is calcined to soda ash with far less energy than the Solvay process.
Steam reforming: Reacting methane with steam over nickel at high temperature to make hydrogen and carbon monoxide.
Water-gas shift: Reacting carbon monoxide with steam to make more hydrogen and carbon dioxide.
Synthesis loop: The recycle in which unconverted hydrogen and nitrogen return to the ammonia converter, with a purge to remove inert gases.
Ostwald process: Making nitric acid by burning ammonia on platinum-rhodium gauze and absorbing the nitrogen oxides in water.
Ammonium carbamate: The intermediate formed from ammonia and CO2 that dehydrates to urea; corrosive and recycled in urea plants.
Biuret: An unwanted compound formed when urea melt is heated too long; harmful to some crops.
Wet-process phosphoric acid: Phosphoric acid made by attacking phosphate rock with sulphuric acid, leaving gypsum.
Phosphogypsum: Calcium sulphate waste from phosphoric acid, about five tonnes per tonne of P2O5.
Fertiliser grade (N-P-K): The percentages of nitrogen, P2O5 and K2O in a fertiliser, for example 18-46-0 for DAP.
Pressure swing adsorption: Separating gases by adsorbing one on a solid under pressure and releasing it at lower pressure.

Try it in the table

Open the Sulphuric acid tile and check plant sizes and whether producers sell steam or power. Using 0.33 t of sulphur and about 3 GJ of exported steam per tonne, judge whether sulphur price or steam credit moves the cost more.
Open Chlorine and Caustic soda. Dryden's 1990 Indian demand was 1.7 t of caustic per tonne of chlorine against 1.13 made. See which product the tiles show in surplus today, and whether PVC or Vinyl chloride monomer now absorbs the chlorine.
Open Ammonia and Urea. Take a gas price from the Ammonia tile and apply Kent's rules: ammonia cash cost about 40-50 times the gas price per million BTU, urea about 1.4-1.6 times ammonia. Compare the results with the prices on the tiles.
Open Phosphoric acid and DAP and MAP. Find where Indian producers get rock and acid, and estimate the gypsum a plant of the size shown must stack at about 5 t per tonne of P2O5.
Open Oxygen, Hydrogen and Low-carbon hydrogen and e-fuels. Compare 450-480 kWh per tonne of oxygen with 46,800 kWh per tonne of electrolytic hydrogen, and check what power price the hydrogen tile assumes.
Open Nitric acid and Ammonium nitrate. Look for N2O controls; Kent gives 300-3,500 ppmv of N2O in untreated tail gas.

Final quiz

Where does most of the world's sulphur now come from?

Kent's table shows recovered sulphur from oil and gas rising to 46 Mt by 2009, while Frasch and other mining fell to 0.3 Mt.

Which statement about sulphuric acid plant energy is correct?

Kent gives 97% from sulphur combustion and 3% from electricity, with 55-60% recovered as high-pressure steam, and up to 90% with hot absorption.

A membrane cell produces 32% caustic. Compared with a diaphragm cell, what does this mainly save?

Shreve gives about 715 kg of water to evaporate per tonne of 50% caustic from a membrane cell against about 2,600 kg from a diaphragm cell, which also leaves about 1% salt.

Why did natural soda ash displace the Solvay process in the United States?

Shreve's energy figures and the calcium chloride waste problem made trona cheaper; the last US Solvay plant closed in 1986.

In a steam-reforming ammonia plant, what is the purpose of the methanator?

After shift and CO2 removal a little CO and CO2 remain; methanation at 250-300 C turns them into harmless methane, leaving about 5 ppm.

Which change did most to cut the cost of ammonia in the 1960s and 1970s?

Kent and Shreve both point to centrifugal compressors and single-train plants of 1,000-1,500 t/day, with costs falling by close to half.

Per tonne of urea, about how much ammonia does a total-recycle plant use?

The theoretical figure is 0.567 t; Dryden gives about 0.6 t for total recycle against 1.15 t for once-through plants.

Which product in this module is the strongest net exporter of energy per tonne?

Burning sulphur and forming SO3 and H2SO4 release about 5.4 GJ per tonne, most of it exportable as steam. The other three are bought with electricity.

Next module: From crude oil and natural gas to the C1-C4 building blocks →

Sources for this module

Kent, J.A. (ed.) (2012). Handbook of Industrial Chemistry and Biotechnology, 12th ed. Springer. Ch 22 Synthetic Nitrogen Products (Maxwell). · pdf pp. 882-922
Kent, J.A. (ed.) (2012). Handbook of Industrial Chemistry and Biotechnology, 12th ed. Springer. Ch 23 Phosphorus and Phosphates (Gruber). · pdf pp. 945-963
Kent, J.A. (ed.) (2012). Handbook of Industrial Chemistry and Biotechnology, 12th ed. Springer. Ch 24 Fertilizers and Food Production (Roy). · pdf pp. 969-987
Kent, J.A. (ed.) (2012). Handbook of Industrial Chemistry and Biotechnology, 12th ed. Springer. Ch 25 Sulfur and Sulfuric Acid (d'Aquin and Fell). · pdf pp. 1001-1019
Kent, J.A. (ed.) (2012). Handbook of Industrial Chemistry and Biotechnology, 12th ed. Springer. Ch 26 Salt, Chlor-Alkali, and Related Heavy Chemicals (O'Brien). · pdf pp. 1021-1041
Kent, J.A. (ed.) (2012). Handbook of Industrial Chemistry and Biotechnology, 12th ed. Springer. Ch 27 Industrial Gases (Cooke). · pdf pp. 1043-1058
Austin, G.T. (1984). Shreve's Chemical Process Industries, 5th ed. McGraw-Hill. Ch 7 Industrial Gases; Ch 13 Chlor-alkali Industries; Ch 14 Electrolytic Industries (Table 14.1); Ch 16 Phosphorus Industries; Ch 18 Nitrogen Industries; Ch 19 Sulfur and Sulfuric Acid. · pdf pp. 120-138, 243-261, 293-303, 321-336, 338-358
Gopala Rao, M. and Sittig, M. (1997). Dryden's Outlines of Chemical Technology for the 21st Century, 3rd ed. East-West Press. Ch II introduction; IIA Sulfur and Sulfuric Acid; IIC Cryogenics; IID Fertilizer Industry; IIE Nitrogen Industries; IIF Phosphorus Industries; IIH Chlor-Alkali Industry (OCR text). · pdf pp. 64-82, 108-123, 127-176, 197-217
Brennan, D.J. (2020). Process Industry Economics, 2nd ed. Elsevier. Ch 4 Operating cost estimation, Table 4.4 (indicative utility prices, US$ 2018). · pdf p. 110