1. General Reaction Principle

Mercaptan scavengers work by chemically reacting with mercaptan groups (R–SH)

to transform odorous, corrosive, reactive mercaptans into stable, odorless, non‑corrosive products.

The core target is the thiol group (–SH).

Main reaction pathways:

• Nucleophilic addition / condensation
• Oxidation to disulfides
• Nucleophilic substitution

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2. Reaction Mechanism of Triazine-Based Scavengers

Triazines are the most widely used water‑soluble mercaptan scavengers,

typically based on hexahydro‑1,3,5‑tris(hydroxyethyl)triazine (HET Triazine).

Reaction Steps:

1. Under weakly alkaline conditions, triazine ring opens gradually.
2. Mercaptan (RSH) acts as a nucleophile and attacks the electrophilic carbon on the triazine ring.
3. One, two, or three R–S– groups can substitute onto the triazine structure.
4. Stable water‑soluble adducts form with no odor and low corrosion.

Simplified overall reaction:

Triazine+3 RSH→Triazine–(SR)3​+3 H2​O

Characteristics:

• Fast reaction rate
• High mercaptan‑removal efficiency
• Alkaline nature
• May form precipitates at high dosage or low pH

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3. Reaction Mechanism of Aldehyde-Based Scavengers

Typical agents: glyoxal, formaldehyde derivatives, modified aldehydes.

Reaction Steps:

1. Aldehyde group (–CHO) undergoes nucleophilic addition with RSH.
2. Forms a hemithioacetal intermediate.
3. Further condensation yields stable thioacetal or polymeric thioether structures.

Overall reaction:

R–CHO+2 R’SH→R–CH(SR’)2​+H2​O

Characteristics:

• Mild, low amine odor
• Less fouling than triazines
• Good compatibility in oil‑water systems

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4. Reaction Mechanism of Metal‑Catalyzed / Oxidative Scavengers

Common active components: Cu, Zn, Fe salts or oxides.

Reaction Steps:

1. Metal ions act as oxidation catalysts.
2. Mercaptans are oxidized by oxygen or oxidizing components present in the fluid.
3. Two mercaptan molecules couple to form disulfide (R–S–S–R).

Overall reaction:

2 RSH+21​O2​Metal catalyst​R–S–S–R+H2​O

Characteristics:

• Forms oil‑soluble disulfides
• No strong alkaline effect
• Suitable for both gas and liquid phases
• Disulfides are odorless and much less corrosive

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5. Reaction Mechanism of Non‑Amine, Non‑Triazine Scavengers

Modern high‑performance scavengers use reactive nucleophilic molecules such as:

• activated olefins
• polyfunctional esters
• cyclic ethers

Mechanism:

• Direct Michael addition or nucleophilic substitution with RSH
• Forms stable covalent C–S bonds
• No formaldehyde, no triazine, no amine release
• Very low fouling and good compatibility

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6. Comparison of Three Main Mechanisms

表格

Type	Reaction Pathway	Main Product	Features
Triazine	Nucleophilic substitution	Water‑soluble adducts	Fast, high efficiency, alkaline
Aldehyde	Addition‑condensation	Thioacetals	Mild, low fouling
Oxidative	Catalytic oxidation	Disulfides (RSSR)	Oil‑soluble, no alkalinity

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7. Key Factors Affecting Reaction Rate

• pH value: triazines favor alkaline; aldehydes work over wider pH
• Temperature: higher temperature generally accelerates reaction
• Mixing intensity: improves contact between scavenger and mercaptans
• Water / oil ratio: determines which type of scavenger is preferred
• Impurities: H₂S, CO₂, salts may interfere