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.
| Component | Grade / Specification | Treat Rate (NLGI 2) | Function & Sourcing |
|---|---|---|---|
| Base oil — primary | Group II SN500, KV40 95–105 cSt, VI 100+ | 50–60% | Main carrier. For premium LiX, use Group III + Group II blend for higher VI and oxidation life. |
| Base oil — secondary | Group II SN150 or BS150N (bright stock 150) | 20–25% | Diluent for fatty acid dissolution. Bright stock variant for very-heavy-duty industrial LiX. |
| 12-Hydroxystearic acid | Tech grade, AV 175–185, SV 180–195, IV <5 | 8–10% | Primary fatty acid for the soap fibres. Same spec as for simple lithium. |
| Azelaic acid (or sebacic) | Tech grade, ≥90% pure, AV 580–600 | 1.0–2.5% | Complexing dibasic acid. Molar ratio to 12-HSA approximately 1:8 to 1:12. Sourced from Emery / Cathay (azelaic) or Indian castor producers (sebacic). |
| Lithium hydroxide monohydrate | LiOH·H₂O, ≥56% Li₂O | 1.5–2.0% | Alkali for both saponifications. Total dose is stoichiometric to 12-HSA + 2× dibasic acid + 5–10% excess. |
| EP additive | Sulfurised olefin or ZDDP or both | 2.0–4.0% | For four-ball weld >315 kgf required by steel-mill specs. Sulfurised olefin preferred for high-temperature service. |
| Antioxidant | Aryl-amine (PANA, ODPA) + hindered phenol blend | 0.8–1.5% | Critical at LiX service temperatures (160–180°C continuous). Aryl-amine for primary stabilisation. |
| Rust inhibitor | Calcium sulfonate (overbased) + amine succinate | 0.5–1.0% | Overbased Ca sulfonate gives boost to EP and rust together. Critical for wet-environment LiX. |
| Polymer / tackifier (optional) | PIB 2400 cSt or OCP | 0.5–1.5% | For open-gear or wire-rope LiX variants. |
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. 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.
Tell us your target application, NLGI grade and reactor scale. We respond within one business day with an honest assessment and indicative timeline.