(701b) Catalysts for the Positional Isomerization of Long-Chain Olefins

Internal, long-chain olefins are primarily used in the synthesis of alkenyl succinic anhydrides (ASA), which are used as paper sizing agents.  The purpose of this project is to compare catalysts for the selective double-bond isomerization of terminal, long-chain olefins – both strong acid or base catalysts and organometallic chain-walking catalysts.  The application is a stringent test of a catalyst’s selectivity because there are three possible classes of products:  positional isomers, branched isomers and oligomers.  Catalysts were evaluated by the positional isomerization of 1-hexadecene. Solid acid catalysts included sulfonated polystyrene/DVB, tungstated zirconia, acidic zeolites, and perfluorinated ion exchange resins supported on silica and alumina.  The supported base catalyst is Na/Al₂O₃.  Chain walking catalysts are based on Fe(CO)₅ and its derivatives.  Catalysts were characterized by porosimetry, 1-propanamine TPD, and powder XRD.  The solid catalysts were tested in packed bed reactors at temperatures up to 180°C.  The reaction products were quantified by GC, GPC, HNMR, and UV-Vis. Lifetime studies were conducted on those solid acid and base catalysts with the highest selectivity to internal olefins.  Amberlyst 35^® (Dow), an “oversulfonated” poly(styrene-co-divinylbenzene) deactivated after 12 d but was regenerable with some loss of activity. SAC-13 (Nafion^®/SiO₂, BASF) lasted over 10 d without deactivation.  It is hypothesized that the reason for the disparity is the nature of the acid sites.  An ensemble of closely-spaced acid sites are present in the sulfonated poly(styrenes), so the oligomers that are formed as byproducts cover more acid sites on Amberlyst 35 than SAC-13.  SAC-13 also accumulates oligomers, but the individual acid sites are spaced further apart.  The soluble Fe(CO)₅ catalyst was tested in a 4 L autoclave at 180°C by varying catalyst concentration (250-1000 ppm) and residence time (4-16 h). Our efforts in immobilizing derivatives of Fe(CO)₅ on solid supports are also described.