boilingrange

Boiling range is the interval of temperatures over which a liquid boils, typically described by its initial boiling point (IBP) and final boiling point (FBP) at a specified pressure, usually 1 atmosphere. For pure substances, the boiling range collapses to a single boiling point, but for liquids that are mixtures or complex compounds, boiling occurs over a range due to varying component volatilities. The boiling range provides a practical measure of volatility and is a key parameter in classifying liquids into fractions.

Measurement of boiling range can be done by direct distillation or by simulated distillation. Traditional distillation methods, such as the ASTM D86 procedure for petroleum liquids, determine IBP and FBP by collecting distillate over increasing temperatures. Simulated distillation, often performed by gas chromatography, estimates the distillation curve and boiling range distribution from a calibration curve, providing rapid estimates of the main boiling points and range without full distillation.

In industry, boiling range is a fundamental concept for characterizing and separating mixtures. In petroleum refining, fractions are described by their boiling ranges: naphtha and gasoline ranges are relatively light, kerosene is intermediate, and gas oil and residuals have higher boiling ranges. Knowledge of the boiling range informs process design, product specifications, and quality control, guiding decisions on distillation towers, cracking, refining blends, and storage. Typical examples include light fuels with ranges roughly from about 20–180/200 °C for some gasoline fractions, kerosene around 150–275 °C, diesel roughly 180–350 °C, and heavy fuel oils above 350 °C, though exact values depend on pressure and composition.

Limitations include pressure dependence, potential decomposition of sensitive compounds, and the influence of azeotropes or impurities, all of which can shift or broaden the observed boiling range.