Black liquor soap (BLS) is currently being utilized as a subsidiary fuel and Alberta’s pulp mills are interested in turning this waste stream into a valuable renewable resource.. Besides the obvious benefit of producing a value-added product from a waste stream, other valuable components besides FAME can be extracted from the soap, mainly sterols and resin acids. Finding a commercial application for the resin acid components of black liquor soap would add considerable merit to the project, especially as resin acids are the major component of BLS (approx. 55 % w/w).
This project targets at turning resin acid into polyol and mixed alkanes using the ozonolysis and hydrogenation process. The resulted polyols were planned for production of polyurethane.
Started from abietic acid, a model compound for resin acid, reaction conditions for polyol production were optimized. Three heterogeneous catalysts were synthesized, and an ATR-FTIR method for hydroxyl number measurement developed at the University of Alberta was adopted and modified in house.
Due to the very high content of acid (100 %) in abietic acid and resin acid (compared to 3 % free acid in canola oil), the resulted polyols show higher acid numbers. Condensation reactions didn’t reduce the acid numbers significantly. Polyurethanes were made from polyols and PMDI (polymeric methylene diphenyl diisocyanate) and PPTI (poly (propyleneglycol) tolyene 2, 4-diisocyante), respectively, and analyzed with FTIR, GPC and TGA. The analyses indicated that the polyurethanes have two blocks of functional groups, carbamate and amide. Such polyurethanes may not be suitable for construction material but have unique properties as surfactants.
Resin acids were separated from black liquor soap with about 45% (v/v) yield and the resin acids were successfully hydrogenated to mixed alkanes (diesel) as analyzed with GC with 99 % yield.
Black liquor soap was directly turned into liquid mixed alkanes through hydrogenation at 1000 psi and 400C⁰ with a turn over number of 9 litre alkane/ g Ni or 25 litre alkanes/ g Pd. The produced alkanes contain about 40-54 wt. % lubricating oil, 11 wt. % of kerosene, 13-19 wt. % gasoline, 8-13 wt. % naphtha, and 12-15 wt. % wax. As a rough estimation, considering the price of Ni of US$ 0.016 /g Ni, the return of turning black liquor soap into mixed alkanes is about US$ 380 per ton of black liquor soap (given the price of produced alkanes is US$ 0.6 /litre) without considering the cost of experiments.
Based on the research we have done, we recommend exploring the following two more projects:
1) Develop resin acid based polyols into effective surfactants. Surfactants are demanded in oil sands industry.
2) Directly turn black liquor soap components beside FAME into diesel (mixed alkanes). Based on our research this project has a potential for a positive outcome.
For more information on the black liquor soap project contact the project leads: Niranjan Purohit with Alberta Agriculture and Forestry, Bio-Industrial Opportunities Section.