Neutralizing Amines
Specialized amine blends for overhead condensation systems. Buffer pH and neutralize chlorides in distillation towers.
What is a neutralizing amine?
A neutralizing amine is a volatile organic base — or, in practice, a blend of several — injected into the overhead vapour of a crude, vacuum or other distillation tower so that it condenses with the first water and neutralises the hydrochloric acid carried over from the tower. Its job is to hold the pH of the overhead condensate in a controlled window, typically 5.5–6.5, where the acid cannot attack carbon steel and the amine's own chloride salts stay dissolved instead of depositing.
Blends are used because no single amine condenses exactly where the water does: a mixture spreads the neutralising capacity across the dew-point region, from the first droplets in the exchangers to the accumulator. CHIMI ART's NA 660 C is a buffered blend of that kind, formulated for refinery and petrochemical overhead systems.
Where overhead corrosion comes from: HCl, the water dew point and the salt point
Crude oil carries calcium and magnesium chloride salts that survive desalting in small amounts and hydrolyse in the furnace to hydrogen chloride gas. HCl is harmless while dry; the damage happens where water first condenses in the overhead system, because the first droplets absorb almost all of the acid and can be strongly acidic — pH values of 2–3 are not unusual — the classic dew-point corrosion that thins exchanger tubes and accumulator shells. Upstream of that, ammonia or amine can combine with HCl above the water dew point to form solid ammonium or amine chloride salts — the salt point — which are hygroscopic and cause under-deposit corrosion and fouling of their own.
Overhead corrosion control therefore works on three fronts at once: caustic injected into the desalted crude to cut HCl at source, a neutralizing amine to manage the acid that still arrives, and — where needed — a water wash to dissolve salts and a filming amine to protect the steel surface.
How a neutralizing-amine programme is controlled
By the overhead water, not by the calendar. Operators sample the accumulator boot water and track pH (target window typically 5.5–6.5), chloride (the HCl load the amine has to match), iron (the corrosion actually happening) and, with a test kit or titration, the free amine residual. Dosing is trimmed continuously against those numbers — more amine when chloride climbs, less when pH drifts high enough to risk salt deposition — and corrosion probes or coupons confirm the trend. Integrity operating windows written for the unit define the limits the programme must keep the water inside.
Neutralizing amine, filming amine, caustic or water wash — which does what
They are complementary, not alternatives. Caustic injection reduces how much HCl is made; a neutralizing amine neutralises the HCl that still condenses and buffers the water; a filming amine lays a hydrophobic barrier on the steel so the acid that remains cannot reach it; a water wash keeps salts from depositing where the temperature would otherwise let them. Most refinery overhead programmes combine caustic at the desalter with a neutralizing amine and, on difficult units, a filming amine and a wash — the comparison table below sets out what each contributes and what to watch.
| Measure | What it does | Watch-outs |
|---|---|---|
| Neutralizing amine (e.g. NA 660 C) | Condenses with the first water, neutralises HCl, buffers condensate pH in the 5.5–6.5 window | Amine chloride salts can deposit if pH runs too high or injection is too far upstream; match the dose to chloride |
| Filming amine | Forms a protective hydrophobic film on carbon steel surfaces | Needs a clean surface and the right injection point; compatibility with downstream units and catalysts |
| Caustic injection (desalted crude) | Converts hydrolysable chlorides to stable NaCl, cutting HCl at source | Sodium carry-over to downstream units; does not remove all HCl |
| Overhead water wash | Dissolves and removes ammonium/amine chloride salts before they deposit | Wash water quality and distribution; adds load to the accumulator water |
Standards & references
- API RP 571Damage mechanisms affecting fixed equipment in the refining industry — hydrochloric acid corrosion and ammonium/amine chloride corrosion in crude-unit overhead systems, with the mitigation measures (caustic, neutralizer, filmer, water wash).
- NACE 34109Crude distillation unit — distillation tower overhead system corrosion: the industry technical report on the corrosion mechanisms and current control practices, from the desalter to the accumulator.
- API RP 584Integrity operating windows — the practice under which overhead water pH, chloride and iron limits are defined, monitored and acted on.
Products in This Family
Browse our complete range of products in this category.
Industrial & Specialty
Frequently Asked Questions
What are neutralizing amines used for?
Neutralizing amines control corrosion in distillation overhead systems. They vaporize with the tower overheads, condense with the first water droplets, and neutralize acids such as hydrogen chloride (HCl), keeping condensate pH in a safe range and protecting condensers, exchangers, and accumulators.
How do neutralizing amines differ from filming amines?
Neutralizing amines chemically neutralize condensing acids and buffer the condensate pH, tackling the cause of low-pH attack. Filming amines instead lay down an adsorbed barrier film on the metal surface. Many overhead programs use both together; the right combination depends on chloride loading, water volumes, and system layout.
What causes overhead corrosion in crude distillation units?
Calcium and magnesium chloride salts remaining in desalted crude hydrolyze at furnace temperatures to hydrogen chloride. HCl travels with the overhead vapor and dissolves into the first condensing water, forming locally concentrated hydrochloric acid that rapidly attacks carbon steel at the initial condensation point.
How is a neutralizing amine program controlled?
Dosing is trimmed against routine overhead water analysis — pH, chloride, and iron counts — with continuous injection adjusted to hold the target pH window. Rising iron or falling pH signals under-dosing or a chloride excursion; persistent salt problems point to reviewing wash-water practice and injection-point design.
How is the neutralizing amine residual tested in overhead water?
With a test kit or titration on the accumulator boot water, alongside pH, chloride and iron. pH shows whether the buffer is holding the 5.5–6.5 window, chloride shows the HCl load the amine has to match, iron shows the corrosion actually happening, and the free amine residual confirms there is capacity in reserve. Dosing is trimmed against those four numbers, and corrosion probes or coupons confirm the trend.
Why use a neutralizing amine instead of ammonia?
Ammonia neutralises HCl too, and it is cheap — but it condenses poorly with the first water, so the earliest droplets stay acidic, and its chloride salt is a hygroscopic solid that deposits above the water dew point and corrodes under the deposit. A blended neutralizing amine condenses with the water across the dew-point region and forms salts that stay dissolved at the controlled pH, which is why it is the standard choice on crude and vacuum tower overheads.
Need a Custom Solution?
Request a quote, discuss your specifications, or schedule a facility visit. Our technical team responds within 24 hours.