Pyrolysis Oil — Fractional Distillation of Hydrocarbons

Pyrolysis Oil

Pyrolysis oil is a raw intermediate; fractional distillation is what turns it into specification products buyers will pay for.

The liquid condensing out of a plastic pyrolysis reactor is a broad distribution of hydrocarbon chain lengths, from dissolved light gases to waxes, carrying whatever contaminants survived preparation. Separated into defined cuts it becomes several products, each with its own specification, buyer and price.

What pyrolysis oil is

Plastic-derived pyrolysis oil is predominantly aliphatic — paraffins and olefins from random chain scission of polyolefins, with aromatics where polystyrene or other aromatic polymers were in the feed. Its boiling range spans naphtha through middle distillate into heavy gas oil and wax. Unlike oxygenated, acidic biomass pyrolysis oil, it is close to a conventional petroleum stream — why refineries and petrochemical producers will consider it. Olefin content makes it reactive and prone to gum and colour change in storage; chlorine from PVC, nitrogen from nylons and metals from pigments and fillers must be held within co-processing limits; and composition shifts with feedstock, so steady feedstock and steady reactor operation are prerequisites for a steady product.

Fractional distillation: the value step

Distillation separates the oil by boiling point in a column, drawing defined cuts as vapour rises against the temperature gradient. Number of stages, reflux ratio, cut points and whether the heavy end needs vacuum distillation determine the yield of the valuable middle cut and how sharply it separates. Sharpness is what buyers pay for: a loose middle distillate carries light ends that depress flash point and heavy ends that drive cloud point the wrong way.

The product slate

Four streams typically result. Light ends and non-condensable gas — recovered as process fuel to heat the reactor, the biggest single lever on operating cost. Naphtha-range material — steam-cracker feedstock for recycled-content polymer, usually the highest-value cut where that market exists. Middle distillate — the diesel-range volume product, sold as fuel after finishing or as a blend component. Heavy residue and wax — recycled back for further cracking, sold as heavy fuel, or marketed as wax where quality allows. Proportions depend on feedstock and reactor operation, established by test work on the operator's own material, not a generic yield table.

Offtake: decide first, design second

A petrochemical co-processing buyer imposes tight chlorine, nitrogen and metals limits and wants naphtha-range material; a fuel buyer wants middle distillate on specification, consistent batch to batch; a marine or industrial buyer tolerates a heavier, wider cut. Klean has delivered pyrolysis-oil projects including marine fuel co-processing and low-carbon fuel applications, and the conclusion is always the same: name the buyer, get the specification, then design the distillation section to meet it — the other order builds a column that produces the wrong product very efficiently.