(617au) The Selective Production of Octene By the Metathesis of 1-Pentene

Linear α-olefins are key components for the production of LLDPE or lubricant and the demand for hexene-1 and octene-1 increased enormously in recent years. Initially linear α-olefins were produced from paraffinic wax via thermal cracking, which gives a large propotion of alkenes-1 as the primary product, togather with alkenes. However, the efficiency of linear α-olefins synthesis is severely limited by thermodynamics. To overcome this limitation several processes were developed in the last decade to synthesize hexene-1 and octene-1 selectively. In recent, alkene metathesis is one of the most attractive process for the production of linear α-olefins. Alkene metathesis reaction is defined as the catalytic exchange of alkylidene groups in alkenes. For instance, two molecules of pentene-1 can react to one molecule of octene and one molecule of ethene. Olefin metathesis was first commercialized in petroleum reformation for the synthesis of higher olefins from the products alpha-olefins from the Shell higher olefin process (SHOP) under high pressure and high temperatures. Modern catalysts can be used for a variety of specialized organic compounds and monomers. Modern applications include the synthesis of pharmaceutical drugs, macrocyclic crownophanes the manufacturing of high-strength materials, the production of propylene, the preparation of cancer-targeting nanoparticles, and the conversion of renewable plant-based feedstocks into hair and skin care products. Because of the relative simplicity of olefin metathesis, it often creates fewer undesired by product and hazardous wastes than alternative organic reactions. This reaction can be catalysed by homogeneous or by hetrogeneous catalysts but in industrial applications heterogeneous catalsis is usually preferred. However, hrtrogeneous metathesis catalysts loose their catalytic activity during the reaction.

For the efficient production of octene by the metathesis of pentene-1, numerous catalyst system employed in this reaction includes Mo-based catalyst impregnated on γ-Al₂O₃, Mo-based monolith, MoO₃/Al₂O₃ catalyst promoted by SiO₂ activated by hν, and CO-precipitated MoO₃/TiO₂/ZrO₂. In recent, rhenium-based catalysts had attracted much attention brcause of high activity and tolerance of impurities. It is well known that noble metal catalysts are shown high catalytic performance, but the high market price of noble metals renders their industrial application quite questionable. Therefore, it is more practical from an industrial standpoint to develop an improved non-novel metal-based catalyst.

One of the most problem in the metathesis reaction is deactivation of catalysts. The deactivation time is in the large od hours till several weeks depending on catalyst system and reaction conditions. The poisoning of active centre due to trace impurities in the feed components is one main cause od catalyst deactivation. Poisons of catalyst are mainly polar substances, e.g. water or oxygenates. Additionlly oxygen, organic bases and diene can lead to catalyst deactivation.

In this work, octene synthesis by the metathesis of pentene-1 was examined over a series of Re₂O₇/Al₂O₃ catalysts (Re₂O₇/ZnO/Al₂O₃, Re₂O₇/ZrO₂/Al₂O₃, Re₂O₇/Al₂O₃/B₂O₃, Re₂O₇/V₂O5/Al₂O₃) prepared by co-precipitation method at various pH conditions in a flow type fixed bed reactor to evaluate the catalyst performance. The effect of promoters on the performance of Re₂O₇/Al₂O₃ catalysts were investigated in detail, with an aim of enhancing catalytic activity and improving stability of the catalyst. N₂O chemisorption experiments were conducted to investigate the copper surface area on the Re₂O₇/Al₂O₃ catalysts. Temperature programmed reduction (TPR) measurements were carried out to investigate copper dispersion and reducibility.