This essay is a dated public disclosure of an invention I developed and assigned to Kupferberg IP Holdings LLC. A United States provisional patent application covering the process has already been filed. I am publishing the technical substance here so the inventive concept is on the open record: as prior art against later filers, and as a clear statement of what I actually built.
The problem is not “make something green from lignin.” The problem is decision architecture for a co-product that mills currently treat as waste or burn-fuel. Non-wood agricultural black liquor (wheat straw, rice straw, bagasse, and related residues) is sulfur-free when produced by mild alkaline soda routes, but the precipitated crude lignin is too heterogeneous, too ash-laden, and too polydisperse for high-performance polyurethane stoichiometry. The industry’s usual fix is chemical modification—oxypropylation with alkoxides—which adds cost, toxicity, and process complexity. I wanted a physical fractionation route that preserves native hydroxyl chemistry instead.
What is disclosed
A two-stage process for isolating a reactive aromatic polyol from non-wood agricultural residue black liquor, and using that polyol in polyurethane adhesives, with an optional hard-carbon path from the insoluble residue.
Stage 1 — Crude lignin as starting material
Spent alkaline black liquor from mild alkaline (soda / soda-AQ class) pulping of agricultural residues is heated (about 50–70 °C) and acidified to roughly pH 1.5–2.5 with sulfuric acid or carbon dioxide. The precipitated cake is washed with water until wash-filtrate conductivity is below about 500 µS/cm, then dried to low moisture. Pulping and crude precipitation are treated here as feedstock preparation. The inventive contribution begins at the selective pressurized fractionation of that dry crude lignin.
Stage 2 — Pressurized aqueous-alcohol fractionation
Dry crude lignin is contacted with an aqueous C1–C4 monohydric alcohol blend (about 80–95 wt% alcohol, 5–20 wt% water), preferably about 90:10 ethanol:water, at a solid-to-liquid ratio on the order of 5–15 g dry lignin per 100 mL solvent (preferred about 10 g / 100 mL). The charge is sealed in a pressure-rated reactor, heated to about 140–160 °C (preferred about 150 °C), and held under autogenous pressure of about 10–13 bar gauge (typically about 11–12 bar) with agitation for about 30–60 minutes. Maintaining autogenous pressure matters: if the solvent flashes, composition drifts and extraction fails.
The reactor is then cooled to about 55–65 °C (preferred about 60 °C) and held under static or near-static conditions for about 20–40 minutes (preferred about 30 minutes). That hold drives selective aggregation of high-molecular-weight and silica-bound material. The slurry is filtered at temperature (for example through a 0.45 µm membrane). Solvent is evaporated from the filtrate under vacuum to recover dry Fraction A. The filter cake is Fraction B.
Target product characteristics (Fraction A)
The isolated aromatic polyol is characterized by a narrow molecular-weight distribution (polydispersity index PDI less than 1.5, with a preferred working target near 1.3), residual inorganic ash below about 2 wt% (preferably below about 0.8 wt%), and a hydroxyl number in the range of about 280–340 mg KOH/g. Native ether linkages are retained, observable as a strong ATR-FTIR absorbance near 1030 cm⁻¹ (C–O–C). The point of the process is to reach polyurethane-usable stoichiometry and solubility without oxypropylation or specialized amphiphilic dispersants.
| Attribute | Target / preferred window |
|---|---|
| PDI (GPC) | < 1.5 (preferred ~1.3) |
| Ash (e.g. ASTM D1102 class) | < 2.0 wt% (preferred < 0.8 wt%) |
| Hydroxyl number | 280–340 mg KOH/g |
| Structure check | FTIR ether band ~1030 cm⁻¹ retained |
| Chemical modification | None required (no oxypropylation) |
Use in polyurethane adhesives
Fraction A is reacted with organic diisocyanates or polyisocyanates (for example polymeric MDI) at an isocyanate index of about 1.0–1.5, optionally with secondary co-polyols such as diethylene glycol, tetraethylene glycol, or PEG400, and with tertiary amine or organometallic catalysts. The composition is intended for adhesives and related resins on wood and agricultural-fiber substrates, including hot-pressed fiber composites. A working formulation class uses Fraction A as a substantial share of the polyol package without forcing crude lignin into the foam via surfactant crutches.
Co-product path — Fraction B to hard carbon
The insoluble cake (Fraction B) is useful as a binder precursor. It can also be carbonized under inert atmosphere at about 1100–1400 °C (illustrative working point about 1300 °C) to yield disordered hard carbon suitable for sodium-ion anode electrodes, with target interlayer spacing on the order of 0.37–0.39 nm and initial Coulombic efficiency above about 80% in half-cell configurations. The economic logic is a co-product split: soluble low-PDI polyol for resins, insoluble residue for carbon or binders, rather than a single low-value sludge.
How this differs from crowded prior art
Solvent fractionation of lignin and lignin-based polyurethanes are crowded fields. Closest published art includes organosolv and wood-centric fractionation, oxypropylation / polyol-dispersion routes that chemically modify lignin to force solubility, and ethyl-acetate or continuous-flow fractionation schemes aimed at different molecular-weight windows or equipment. The disclosure here is specific to downstream fractionation of isolated crude lignin from sulfur-free non-wood agricultural black liquor, using pressurized aqueous-alcohol extraction plus a controlled cooling hold to cut a low-PDI, low-ash fraction that substitutes directly into polyurethane chemistry.
I am not claiming that every lignin polyol or every hard-carbon anode is new. I am disclosing this process window, feedstock class, and co-product architecture as my invention.
Ownership and status
Inventor: Conner Kupferberg. Rights assigned to Kupferberg IP Holdings LLC. United States provisional patent application filed. This post is a complementary public disclosure for the open record. Laboratory validation, CRO campaigns, and non-provisional conversion remain ahead of the work. Prophetic working examples in the provisional specification illustrate mass balance, GPC, hydroxyl number, ash, adhesive pressing, and hard-carbon half-cell behavior consistent with the targets above; measured campaign data will supersede prophetic numbers as they land.
If you are working adjacent problems in non-wood co-product valorization, polyurethane substitution, or lignin-derived carbons, the dated substance of this process is now public.