1. Proceedings of the 4th Upgrading and Refining of Heavy Oil, Bitumen and Synthetic Crude Oil Conference;Rakotondradany,2006
2. M. Earl, US Patent 2,966,456 (1960).
3. Adsorptive recovery of naphthenic acids using ion-exchange resins
4. S.C. Blum, W.N. Olmstead, US Patent 5,976,360 (1999).
5. K. Grande, C. Sorlie, US Patent 6,063,266 (2000).