Refiners are slashing amine losses with filtration and vacuum reclaiming

In modern amine treating, operators know the tell: fresh, water‑white solvent that gradually turns yellow or brown as degradation products and metals accumulate—often iron sulfides from steel corrosion (www.digitalrefining.com). The stakes are not trivial: in one estimate, monoethanolamine (MEA) make‑up alone runs roughly 4% of total CO₂‑capture cost (www.researchgate.net).

The industry’s response blends chemistry and hardware. Plants are tightening control of temperature and oxygen, adding multi‑stage filtration, and turning to vacuum reclamation to purge heat‑stable salts (HSS), the non‑volatile acids that chew up capacity. In practice, refiners circulate regenerated amines—such as commercial CO₂/H₂S removal amine solvent—through looped systems where solids and soluble contaminants can be intercepted or removed.

Thermal and oxidative degradation pathways

Amine solvents (e.g., MEA, monoethanolamine; MDEA, methyldiethanolamine) degrade via thermal and oxidative routes. Thermal degradation generally occurs in the stripper/reboiler (the hot regeneration section) and is minor below about 110 °C, but it accelerates sharply above ~130 °C (tcmda.com). The dominant thermal route is carbamate cyclization/polymerization (e.g., oxazolidinone formation), which produces high‑molecular polyamines and ureas (tcmda.com).

Oxidative degradation occurs whenever dissolved O₂ (or other oxidants) and trace metal catalysts are present. In real gas feeds, O₂, NOₓ, and SO₂ can oxidize amines to organic acids, aldehydes, and ammonia (tcmda.com). These oxidation products then react with amines to form HSS (heat‑stable acid salts: ammonium cations paired with organic/inorganic anions) (tcmda.com).

In short, “oxygen and metal contaminants in a hot amine loop accelerate degradation” (tcmda.com). Practically speaking, rich amine with high CO₂ loading or hot lean amine will accumulate irreversible degradation products and HSS, reducing capacity and causing corrosion. Rochelle et al. further report that MEA boiler temperatures above 110–115 °C greatly increase carbamate polymerization (tcmda.com).

Laboratory and field studies confirm these trends. In one CO₂‑capture campaign, ammonia, formate, acetate, and other acids rose as amine degradation markers when O₂ levels or reboiler temperature increased (tcmda.com) (tcmda.com). Industrial experience likewise shows solvent discolouration as HSS and metal‑oxide solids form, often iron sulfides from steel corrosion (www.digitalrefining.com). Economically, minimizing degradation by controlling temperature, oxygen ingress, and iron is critical for reliability and cost control (www.researchgate.net) (tcmda.com).

Feed‑gas and loop filtration strategy

Upstream pretreatment typically uses knockout drums or vane‑type separators plus high‑efficiency mist eliminators. If feed‑gas solids exceed 5 μm, guidance from firms such as Sulzer is to use a vane‑inlet separator with a mesh‑pad coalescer; if fines are smaller than 5 μm, add a cartridge filter ahead of the absorber (www.digitalrefining.com). In the loop, lean (and often rich) amine filtration is standard, with operators deploying a cartridge filter train on the lean return.

A common approach starts with 100 μm cartridges during startup or after an upset, then steps down to 40–50 μm and finally to a fine grade as the system stabilizes (www.digitalrefining.com). In practice, about 20–30% of the lean amine flow may be routed through the filter+carbon loop, with the remainder bypassing to avoid excessive pressure drop. Nexo/Axens engineers note that every amine unit should have a full‑flow filter on lean amine, especially for packed towers, to protect against solids‑bridge plugging (studylib.net).

Filtration limits track particle size and flow. One field guideline is that 100% filtration of rich or full lean flow is ideal—starting near 20 μm and dropping to 5 μm for persistent “shoe‑polish” fines (www.digitalrefining.com). Partial lean filtration (10–30% of flow) is also used with ~10–20 μm filters to catch remnant fines (www.digitalrefining.com). For high‑pressure service, operators often house elements in robust steel filter enclosures suitable for industrial applications.

Activated‑carbon adsorption follows mechanical filters. A carbon bed—typically sized for ~10% of lean flow with ~15 minutes contact at 2–4 gpm/ft²—captures soluble hydrocarbons and organics (www.digitalrefining.com). Replacing the carbon roughly every six months—or sooner if solvent color shifts or foaming increases—maintains performance (www.digitalrefining.com). Plants commonly source activated carbon designed for organics removal in circulating solvents.

Concrete impacts are documented. At a major refinery startup, proper lean amine filters (progressing from 100 μm to 10 μm cartridges) plus a feed‑gas coalescer minimized foaming and significantly reduced exchanger fouling (www.digitalrefining.com). SUEZ data suggest that well‑designed feed‑gas and amine filters can remove more than 50% of the solid load in the feed, drastically cutting maintenance. Filtration prevents solids from accumulating in exchangers, absorbers, and carbon beds, which preserves capacity and reduces corrosion that often follows from iron‑sulfide deposition (www.digitalrefining.com).

Solvent reclamation and HSS control

Even with strong filtration, soluble degradation products and HSS accumulate. These non‑volatile salts (e.g., sulfate, formate, acetate, nitrates) are not removed in the stripper and build continuously, reducing acid‑gas capacity and raising corrosivity. Many operators periodically use a solvent reclaimer—typically a vacuum‑distillation still or thermal reboiler loop—to regenerate amine. In a reclaimer, lean amine is heated under vacuum; high‑boiling organics and salts stay in the bottoms while regenerated amine overhead is returned, removing on the order of 90+% of accumulated HSS.

Quantified results underscore the value. A bench‑scale vacuum‑distillation reclaimer reduced total HSS in MEA from several percent to about 0.6 wt% (www.researchgate.net). By contrast, without reclamation HSS might continue rising toward 2–5 wt%. One summary puts thermal reclamation energy near 12 kWh per kg of HSS removed, which is more energy‑efficient than electrodialysis (another HSS‑catching method) (www.researchgate.net). Lab and plant studies confirm that modest vacuum (mbar range) and proper recycle maximize HSS stripping with minimal vapor loss. Reclaimers can run in batch or continuously (e.g., a side‑stream still) to keep lean‑amine HSS below target levels—industry practice is often below 0.5–1 eq/L.

Beyond HSS, thermal reclaimers also purge polymeric amine dimers/trimers and high‑boiling neutrals formed via thermal degradation. Other methods such as electrodialysis or ion exchange remove only charged species and leave organics/hydrocarbons untouched. One consultant notes that “a mobile vacuum distillation unit… is considered the best option to remove all contaminants from the amine solution” (www.digitalrefining.com). In a field example, using a vacuum reclaimer on DEA/MDEA reduced the need for makeup amine by tens of percent.

Operating controls and measurable outcomes

Maintaining lean amine color near that of fresh amine and keeping HSS minimal preserves more than 95% of the original acid‑gas capacity. Studies show that organic acids in solution cause roughly linear capacity loss: MEA loaded with about 5 wt% formate/nitrate can lose around 20% of CO₂ capture capacity (www.researchgate.net). In practice, refineries track HSS by titration; keeping total HSS to less than roughly 0.5–1.0 meq/g (about under 0.2 wt%) is a common rule of thumb for reliable operation. Filter pressure drop is a clear metric; a rapid rise in ΔP signals solids breakthrough and prompts changeout. Plants often dose oxygen scavengers—applied with a controlled dosing pump—to keep O₂ low and slow oxidation (tcmda.com) and use oxygen/H₂S scavengers as part of the chemical program.

Fact‑based surveys report tangible gains. One tuning project that replaced an inefficient filter train decreased amine losses by more than 50% and extended runtime between cleanings (www.digitalrefining.com). In CO₂‑capture pilots, continuous sampling shows that with full‑flow lean filtration and reforming, corrosion rates drop below 1 mpy (0.025 mm/yr), whereas untreated units often see ≥5–10 mpy. Economically, every percentage point of amine loss saved matters: at a $1M/year amine replacement cost, a 25% reduction in degradation (via filtration plus reclamation) would save about $250k/year.

The operating recipe is consistent across reports: (1) careful control of operating conditions—low regenerator temperatures, oxygen control, high‑quality water—to minimize generation of HSS and polymers (tcmda.com) (tcmda.com); (2) multi‑stage filtration/coalescing to remove particles/hydrocarbons before they foul equipment (www.digitalrefining.com) (www.digitalrefining.com); and (3) periodic reclaimer processing to purge accumulated salts and high‑boilers (www.digitalrefining.com) (www.researchgate.net). Empirical data back up each step: keeping the reboiler near ≈110 °C cuts MEA loss rates dramatically (tcmda.com); full‑flow lean filtration captures essentially all particulates ≥5 µm (www.digitalrefining.com) (www.digitalrefining.com); and vacuum‑distillation reclaimers routinely clean amine to HSS levels under 1 wt% (www.researchgate.net).

Sources: Key mechanism and management insights are based on recent literature and industrial reports—Amine system studies (tcmda.com) (www.researchgate.net); expert Q&As and case studies (www.digitalrefining.com) (www.digitalrefining.com); and industry guidelines (www.researchgate.net) (www.researchgate.net). Each cited source provides quantitative data or guidelines that inform the above recommendations.