Industrial preparation of alkanes

Alkanes are obtained industrially from crude petroleum and natural gas: dead plant matter buried for hundreds of millions of years under high temperature and pressure converted into crude oil, which collects in dome-shaped underground cavities (oil wells), and alkanes are separated from this crude oil by fractional distillation at oil refineries. Several laboratory/industrial routes build a specific alkane from a smaller starting material. First, catalytic hydrogenation of an unsaturated hydrocarbon: alkenes or alkynes react with dihydrogen gas over finely divided platinum or palladium at room temperature (or over finely divided nickel, which needs higher temperature and pressure), adding H2 across each C=C or C-triple-bond-C to give the saturated alkane -- ethene gives ethane, propene gives propane, and ethyne (which has two pi bonds to saturate) also gives ethane. Second, reduction of an alkyl halide: treating an alkyl halide with zinc and dilute hydrochloric acid supplies nascent hydrogen (freshly generated, highly reactive H atoms) that replaces the halogen, so methyl iodide gives methane and ethyl bromide gives ethane. Third, the historic Wurtz reaction: two molecules of an alkyl halide couple together using reactive sodium metal in dry ether, forming an alkane with double the original carbon count (methyl bromide gives ethane this way) -- though this 19th-century method was later superseded by better routes using magnesium and lithium. The modern, most widely used version of this magnesium-based route is the Grignard reaction: an alkyl halide reacts with magnesium metal in dry ether to form an alkyl magnesium halide (the Grignard reagent, R-Mg-X), whi …