Comparison of Various Phosphine Additives in Zeolite Based Catalytic Isomerization of Oleic Acid

Isostearic acids (ISA) are important bio-based ingredients for many commercial products such as lubricants, detergents, and cosmetics. This study is targeted to compare the efficacy of various phosphine derivatives in neutralizing the external acidic surface of zeolite which is responsible for the unwanted oligomerization during zeolite based skeletal isomerization reaction producing dimer as byproducts. Sixteen phosphine derivatives were individually evaluated with heat activated ammonium (NH4+) cationic ferrierite zeolite to produce iso-oleic acid from oleic acid which was converted to ISA through the hydrogenation process. In comparison, eight newly tested phosphine additives were found more effective than the previously reported phosphines (TPP, TPTP) to increase the product yield of iso-oleic acid, ultimately ISA, either by suppressing the byproducts or accelerating the reaction rate as a whole. The performance depends on the electron donating capacity of central phosphorus atom of phosphine derivative attracting proton from the external surface of zeolite. This phenomenon is resulted from the combination of electronic effects and structural hindrances posed by the different substituents attached to the phosphine derivatives. The effectiveness of sixteen Lewis base phosphine additives were tested in neutralizing the external acidic surface of zeolite. The neutral outer surface of zeolite is ideal for suppressing dimer formation and thus producing the iso-oleic acid (precursor of isostearic acid) in high yield through Lewis base-zeolite combination skeletal isomerization reaction.