The dominant high-temperature soap grease — lithium complex (LiX) combines lithium 12-hydroxystearate with a di-lithium dibasic salt (azelaic, sebacic or boric acid) to lift the drop point from 175–195°C of plain lithium soap to above 260°C, opening the entire heavy-industrial bearing market. This guide covers the dual-acid saponification SOP, raw-material specifications, NLGI grade range, ASTM performance targets, and the reactor capability required for consistent production.
Lithium complex grease is a mixed-soap grease in which two distinct lithium salts co-crystallise inside the base oil during cool-down to form a thermally-stable composite fibre matrix. The primary soap is lithium 12-hydroxystearate (the familiar simple-lithium soap); the secondary — the complexing component — is a di-lithium salt of a short-chain dibasic acid, most commonly azelaic acid (HOOC-(CH₂)₇-COOH, C9 chain), sebacic acid (C10), or in some formulations boric acid.
The chemistry is two saponification reactions in sequence: R-COOH + LiOH·H₂O → R-COOLi + 2 H₂O for the 12-HSA, then HOOC-R-COOH + 2 LiOH·H₂O → LiOOC-R-COOLi + 4 H₂O for the dibasic acid. Both salts dissolve at high temperature (215°C) and re-crystallise on slow cool-down as interpenetrating fibres. The di-lithium dibasic salt has a melting point well above 250°C — and once embedded in the fibre matrix it physically pins the structure together, preventing the 12-HSA fibres from melting until the matrix collapses near 260°C.
The practical consequence is a roughly 70°C drop-point gain over plain lithium soap, opening up steel mill, paper mill, cement plant, mining and heavy-industrial bearing applications where 175°C drop point is insufficient. LiX also has better mechanical stability under shear and better oxidation life than simple lithium soap. The trade-off: more complex manufacturing, higher raw-material cost, and one more saponification step. Where the application calls for a different high-temperature route, the comparable thickeners are aluminium complex grease and barium complex grease manufacturing.
| Component group | Typical role | Typical share |
|---|---|---|
| Base oil(s) | Carrier fluid (mineral / synthetic / bio) | ~75–90% |
| Thickener / soap system | Builds structure & consistency (NLGI grade) | ~8–15% |
| EP / anti-wear additive package | Load-carrying & wear protection | ~2–6% |
| Antioxidant, corrosion inhibitor, tackifier | Service life, rust protection, adhesion | balance |
Indicative high-level composition only. The exact components, treat rates, performance additives and approved suppliers are shared under NDA as part of a Lubechem formulation engagement.
LiX manufacturing follows the same logic as simple lithium with two key additions: a second saponification of the dibasic acid, and a higher top-temperature dispersion. Total cycle time is approximately 10–12 hours for a 200–400 kg batch. Reactor must be rated for 220°C continuous service.
| Property | ASTM Test Method | Typical Value | Heavy Industrial Spec |
|---|---|---|---|
| Worked penetration, 60 strokes | ASTM D217 | 265–295 (0.1 mm) | 265–295 |
| Penetration change, 100,000 strokes | ASTM D217 | +10 to +30 dmm | +50 max |
| Dropping point | ASTM D2265 | 265–280°C | 260°C min |
| Water washout @ 79°C | ASTM D1264 | 5–10% | 15% max |
| Four-ball wear scar | ASTM D4172 | 0.40–0.50 mm | 0.55 max |
| Four-ball EP weld point | ASTM D2783 | 315–400 kgf | 315 kgf min |
| Four-ball Load Wear Index | ASTM D2783 | 50–65 kgf | 50 kgf min |
| Oxidation stability, 100h @ 99°C | ASTM D942 | 3–7 psi pressure drop | 10 psi max |
| Roll stability, 16h | ASTM D1831 | +5 to +15 dmm | +25 max |
| Copper corrosion, 24h @ 100°C | ASTM D4048 | 1b | 1b max |
| Failure Mode | Root Cause | Diagnostic Test | Fix |
|---|---|---|---|
| Drop point below 260°C | Top temperature below 215°C; or dibasic acid ratio too low; or second LiOH dose insufficient | D2265 drop point; re-check stoichiometry | Raise top hold to 215°C, 20 min; verify 12-HSA:dibasic molar ratio 8:1 to 12:1; verify total LiOH covers both acids + 5–10% excess |
| Grease grainy or pebbly texture | Dibasic acid not fully dissolved before LiOH addition; second saponification incomplete | Microscope; AV after step 4 | Pre-dissolve dibasic in hot base oil at 120°C before charging; verify dehydration hold to AV <3 |
| Penetration drift & soft batch | Under-milling of complex fibres (thicker than simple Li fibres — need more aggressive milling) | D217 multiple sample variance | Reduce final mill gap to 25 µm; increase to 3–4 passes; verify mill T <80°C |
| Drop point pass, but soft & bleed | Cool-down too fast for the complex fibre to crystallise properly | D6184 24h bleed; D2265 | Extend controlled cool to minimum 120 minutes from 215°C to 90°C; use jacket water at moderate flow, not rapid |
| Four-ball weld below 315 kgf | EP dose insufficient; or sulfurised olefin degraded during 215°C hold | D2783 weld; FTIR check on EP | Increase sulfurised olefin to 3.0–4.0%; add ZDDP 1.0–1.5% as supplementary EP; verify EP added at 90°C, not during top-hold |
| Roll stability poor (>25 dmm shift) | Insufficient complex fibre formation; or 12-HSA grade contaminated with stearic | D1831 16h roll; 12-HSA SV check | Verify 12-HSA SV 180–195; verify dibasic acid molar ratio not too low; consider boric acid complex for tougher matrix |
| Saponification stalls; second LiOH not reacting | Dibasic acid impure (water content high); or second LiOH dose too low | AV after step 4; water content of dibasic acid | Specify dibasic acid moisture <0.5%; recalculate second LiOH dose covering 2 mol per mol dibasic + excess |
A lithium complex grease plant requires the same general equipment as a simple lithium plant, with three upgrades: a reactor rated for 220°C continuous (not just intermittent), a more capable cooling system to support the longer controlled cool-down, and a more aggressive milling system to disperse the thicker complex fibres. These upgrades feed directly into the grease plant setup cost. The same reactor train can also be turned over to a parallel DEF / AdBlue manufacturing line when grease demand is seasonal. See our Plant Setup service for complete equipment specification and commissioning.
The di-lithium dibasic acid (e.g., di-lithium azelate) co-crystallises with lithium 12-HSA into a much more thermally stable mixed-fibre structure. The drop point rises from 175–195°C (simple lithium soap) to >260°C for the complex — a transformation worth roughly 70°C of service margin.
Mechanistically, the di-lithium dibasic salt has a melting point well above 250°C, and once embedded in the fibre matrix it pins the structure together — the 12-HSA fibres cannot melt out independently. The matrix only collapses when the dibasic component itself melts.
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