From crude oil and natural gas to the C1-C4 building blocks: Key terms, quiz and sources

Understanding Chemicals / Module 5: From crude oil and natural gas to the C1-C4 building blocks Wrap-up

From crude oil and natural gas to the C1-C4 building blocks: review

Key terms

Naphtha: A crude oil fraction boiling at roughly 70-200 C, mostly C5-C9 hydrocarbons, used as cracker and reformer feed and as gasoline blendstock.
Natural gas liquids (NGLs): Ethane, propane, butanes and heavier hydrocarbons separated from raw natural gas at gas processing plants.
LPG: Liquefied petroleum gas: propane and butane, used as fuel and as cracker or dehydrogenation feed.
Steam cracking: Thermal, catalyst-free breaking of hydrocarbons at about 650-900 C with steam dilution and a residence time of tens of milliseconds, giving olefins.
Severity: How hot and how fast a cracker is run; higher severity raises ethylene and lowers the propylene-to-ethylene ratio.
Pyrolysis gasoline: The aromatic-rich C5+ liquid from cracking naphtha or gas oil, a main source of benzene and toluene outside the US.
Demethaniser: The first cold distillation column in a cracker, removing hydrogen and methane overhead at about -95 C.
Co-product credit: Revenue from propylene, butadiene, aromatics and fuel made alongside ethylene, subtracted from feed cost to give net raw material cost.
Fluid catalytic cracking (FCC): A refinery process that cracks gas oil over a fluidised zeolite catalyst at about 500 C, mainly for gasoline, with propylene and butenes as by-products.
Catalytic reforming: A refinery process that converts naphtha to aromatics and hydrogen over platinum or rhenium on alumina at 400-500 C and 25-35 bar.
Propane dehydrogenation (PDH): On-purpose propylene production by removing hydrogen from propane over platinum or chromia catalysts at about 530-700 C.
Metathesis: A catalytic swap of olefin fragments, used to make propylene from ethylene and 2-butene.
Raffinate I and II: The C4 stream after butadiene removal (I), and after isobutene removal as well (II).
Synthesis gas (syngas): A mixture of carbon monoxide and hydrogen, made from methane, naphtha or coal, used for methanol, ammonia, oxo chemicals and Fischer-Tropsch fuels.
Steam methane reforming: Reaction of methane with steam over nickel at about 800 C and 35 bar to give CO and hydrogen; strongly endothermic.
Water-gas shift: The reaction CO + H2O -> CO2 + H2, run at lower temperature to adjust the hydrogen content of syngas.
Methanol-to-olefins (MTO): Conversion of methanol over a SAPO-34 catalyst to ethylene and propylene, commercial only in China where it rides on coal-based methanol.
Levelised cost: Production cost that spreads capital over the plant's life at a set discount rate and adds feedstock, energy and fixed operating costs.

Try it in the table

Open the Ethylene tile and compare its listed feedstocks and producing regions with the IEA picture here: ethane in the US and Middle East, naphtha in Europe and China. Does the tile show a price gap between regions?
Open the Propylene tile and look at how much is made by PDH, FCC and steam cracking. Relate the share of propane dehydrogenation to the spread of ethane cracking after the shale boom.
Open the Butadiene tile and check where it is produced. Given that ethane cracking makes almost no C4s, which regions would you expect to export butadiene?
Open the Methanol tile and note the share made from coal and its uses. Compare the formaldehyde share with the 35-40% given in this module, and find the MTO use.
Open the Ammonia and Urea tiles together. Look for the CO2 link: how many tonnes of CO2 does a tonne of urea need, and where does it come from?
Open the Benzene and Paraxylene tiles and see whether reforming or pyrolysis gasoline is listed as the main source. Compare with the reformate-versus-demand mismatch in Part 3.

Final quiz

Per tonne of ethylene, roughly how much feed do ethane and naphtha crackers need (Wittcoff, circa 2000)?

Table 2.7 gives 120 lb ethane and 320 lb naphtha per 100 lb ethylene. 2.4 is propane and 4.3 is vacuum gas oil.

Which explains why the demethaniser needs a condenser at about -95 C?

Methane and hydrogen boil very low. Cooling with liquid ethylene condenses ethylene and heavier components, which leave as liquid at the bottom.

In 2002, why could a European naphtha cracker have a lower net feed cost per tonne of ethylene than a propane cracker?

On Wittcoff's 2002 prices the arithmetic gives about $197 net for naphtha against about $301 for propane, mainly because of propylene, butadiene and pyrolysis gasoline credits. Naphtha's ethylene yield is lower (31% vs 42%) and its capital cost higher.

Which source supplied about half of US chemical propylene in the early 2000s?

Wittcoff reports that the refinery provided 52% of US chemical industry propylene in 2002. The large US FCC fleet runs to make gasoline.

Why does steam methane reforming give too much hydrogen for methanol synthesis?

CH4 + H2O -> CO + 3H2 gives 3:1, while CO + 2H2 -> CH3OH uses 2:1. Plants purge the excess as fuel or add CO2 to consume it.

Which statement about acetic acid by methanol carbonylation is correct?

Wittcoff describes the Monsanto rhodium-iodide process at about 200 C with over 99% selectivity, and BP's iridium-based Cativa. By the early 2000s about 88% of US acetic acid was made this way.

Which pair gives the IEA's approximate 2017 direct CO2 intensities for ammonia and HVCs?

The IEA gives about 2.4 t CO2 per tonne of ammonia, 2.3 for methanol and 1.0 for HVCs. 1.7 t/t is the average across all primary chemicals.

Methanol-to-olefins needs about 3 t of methanol per tonne of ethylene plus propylene. Why so much?

Table 10.4 shows 1.7 t water per tonne of ethylene plus propylene for MTO. Wittcoff notes that 56% of reactor output is water, which also enlarges the plant.

Next module: From building blocks to plastics, fibres and detergents →

Sources for this module

Wittcoff, H.A., Reuben, B.G. and Plotkin, J.S., Industrial Organic Chemicals, 2nd ed., Wiley, 2004: Ch 1 (section 1.3.4), Ch 2, opening sections of Ch 3-5, Ch 10, Ch 11, Ch 12 · pdf pp. 58-59, 83-125, 126-127, 193-197, 249-253, 379-398, 413-420, 425-436
Kent, J.A. (ed.), Handbook of Industrial Chemistry and Biotechnology, 12th ed., Springer, 2012: Ch 18 Petroleum and Its Products (Robinson); Ch 19 Coal Technology for Power, Liquid Fuels, and Chemicals (Davis and Hower); Ch 20 Natural Gas (Idol, Moshfeghian and Johannes) · pdf pp. 708-713, 721-722, 736-737, 741, 777-778, 806-807, 814-823, 827-829
Austin, G.T., Shreve's Chemical Process Industries, 5th ed., McGraw-Hill, 1984: Ch 7 Industrial Gases (hydrogen), Ch 37 Petroleum Processing, Ch 38 Petrochemicals · pdf pp. 125-127, 743-746, 781-782
IEA, The Future of Petrochemicals: Towards more sustainable plastics and fertilisers, OECD/IEA, 2018 · pdf pp. 17, 24-25, 27-47, 50-51, 76, 84-86
Brennan, D., Process Industry Economics, 2nd ed., Elsevier, 2020: Ch 2 Case C Ethylene; Ch 4 Tables 4.2 and 4.7, Fig 4.3 · pdf pp. 55-56, 106, 125-126