cut

In refining, a cut is a specific range of hydrocarbons separated by boiling point during crude oil distillation. When crude enters a fractionating column, molecules with lower boiling points rise higher before condensing; heavier molecules fall and condense lower down. Each horizontal tray or segment captures a distinct boiling range, and the liquid drawn from that level is called a cut. The result is a usable product: naphtha, kerosene, diesel, fuel oil, or bitumen, depending on which cut is taken and at what temperature.

Temperature ranges define cuts sharply because boiling point determines molecular weight and behavior. Gasoline typically distills between 40 and 200 degrees Celsius; kerosene between 150 and 300 degrees Celsius; gas oil between 250 and 380 degrees Celsius. The exact boundaries vary by refinery design and crude origin, but they are set deliberately to meet product specifications for viscosity, flash point, and energy content. A refiner does not separate crude into two or three broad fractions; instead, multiple cuts are drawn continuously or at intervals, each refined further or sold as is.

The term reflects the physical act of dividing the distillate stream. Early refiners would literally cut off (valve off) a stream at a chosen level on the column, collect it, and then shift the draw point to capture the next cut higher or lower. Modern refineries automate this with instrumentation and software, but the language persists. Some cuts are light, some are heavy; some are sweet (low sulfur content), some sour. A single crude oil will yield overlapping cuts that refiners recombine, redistribute, or hydrotreat to hit target markets.

Vacuum distillation extends the process below atmospheric pressure, allowing heavier cuts to boil at lower temperatures without decomposing. The heaviest 10 to 15 percent of crude oil cannot be recovered by atmospheric distillation alone; vacuum cuts capture feedstock for lubricants, heavy fuel oil, and bitumen production. This two-stage approach, atmospheric followed by vacuum, is standard in large refineries.

Quality variation between cuts from the same crude is inevitable. The naphtha cut may contain both straight-chain and aromatic compounds; downstream processing, such as reforming or alkylation, adjusts octane rating and reaction properties. The middle distillates (kerosene, diesel) are more stable and require less treatment if sulfur is acceptable. Heavy cuts need desulfurization or coking to become saleable. A cut is thus an intermediate form, not always a finished product, and its economic value depends on what the refinery can do with it next.