DWC Prime Retrofit Meets New CS₂ Limits for Petrochemical Naphtha
A Southeast Asian refinery retrofitted an existing depentanizer into a DWC Prime column to produce petrochemical-grade naphtha with less than 1 ppm carbon disulfide (CS₂) — and, in the same column, a premium-gasoline cut that adds a new revenue stream. No new standalone unit required.
The challenge
New petrochemical-naphtha (PCN) specifications cap carbon disulfide (CS₂) at 1–2 ppm, because CS₂ poisons the Ziegler-Natta catalysts used downstream in steam crackers and can introduce defects into the polymer chain. The refinery’s naphtha carried CS₂ well above spec — on the order of 70 ppm in the relevant cut. The conventional fixes were all unattractive: a grassroots naphtha hydrotreater (NHT) built solely for PCN is capital-intensive and needs spare hydrogen; adsorption beds carry high capex and OPEX-heavy regeneration; and simple distillation is energy-intensive and drops a low-RON C5 stream that dilutes the gasoline pool. The refiner needed to hit the new CS₂ limit economically, using existing equipment.
The solution: a DWC Prime retrofit of the depentanizer
CS₂ boils just above the C5s and below the C6s, so it can be rejected with the pentane cut by distillation — but doing that cleanly, without losing valuable product or burning excess energy, calls for a sharper separation than a conventional column provides. DWC Innovations retrofitted the existing depentanizer into a DWC Prime column, backed by accurate thermodynamic modeling of CS₂ behavior in naphtha. The single revamped column now delivers three well-defined cuts: an iC5-rich overhead that goes to the premium-gasoline pool, an NC5-rich side stream that carries the CS₂ away, and a bottoms petrochemical naphtha at under 1 ppm CS₂. Because only the smaller mid-cut now needs hydrotreating, the revamp also debottlenecks the NHT unit, and it eliminates the tedious, OPEX-intensive regeneration cycles of an adsorption-based approach.
What the revamp delivers
Product petrochemical naphtha now meets the new CS₂ specification at under 1 ppm, down from roughly 70 ppm in the feed cut. The iC5-rich overhead becomes premium gasoline — a new revenue stream that offsets the column’s energy use — and the NHT unit is debottlenecked because only the mid-cut is routed to it. All of this is achieved inside the existing column shell, with no grassroots hydrotreater and no adsorption media to regenerate or replace.
Why it matters
For refiners facing tightening CS₂ limits on petrochemical naphtha, this project shows that a dividing wall column retrofit is the process of choice: it meets the ultra-low CS₂ spec, avoids the capital of a new hydrotreater and the OPEX of adsorption, and turns a purity problem into a premium-gasoline opportunity — all within existing assets.
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