Quality improvement of bio-paraffin by isomerization was studied in presence of fatty acid over Pt/SAPO-11 catalyst in order to produce second generation biogasoil. The reaction rates and activation energy of the isomerization having high importance in both reactor design and process control were determined. The increase of the fatty acid content of feedstock significantly decreased the rate of isomerization of bio-origin octadecane, but did not affect the activation energy being 143 +/- 3 kJ/mol. Industrial application of the favourable results and the excellent quality properties of end products were also demonstrated. (C) 2013 Elsevier Ltd. All rights reserved.