Kinetic model for the dimerisation of 1-hexene over a solid phosphoric acid catalyst

Abstract

Batch kinetic experiments at 150 °C, 200 °C and 250 °C showed that the reaction can be modeled with a three step sequential reaction scheme. This involves firstly linear isomerisation of 1-hexene followed by skeletal isomerisation and finally dimerisation and cracking. The first and last steps in the sequence are modeled as reversible reactions. When first order reaction kinetics is assumed for each of the reactions, the model gave a very good representation of the experimental data. In order to test the validity of the series pathway hypothesis, the reaction was repeated with a skeletal hexene isomer -2,3-dimethyl-2-butene (DMB) -as reactant. Although the rate and equilibrium constants for the third reaction step as obtained from the 1-hexene conversion data gave a good prediction of the DMB conversion at 200 °C and 250 °C, it failed to predict the reaction rate at 150 °C. This suggests that a different reaction pathway -where linear hexene isomers are directly converted to dimer product -becomes more significant at lower temperatures. The relatively high activation energy of the linear to skeletal hexene reaction may be to blame for this observation. However, this needs to be confirmed be further experimental work. The same equilibrium conversions of both 1-hexene and DMB were observed at all three temperatures investigated-suggesting that the equilibrium conversion is independent of the type of hexene isomer in the reaction mixture. Graphical abstractA sequential reaction pathway is proposed for this reaction. The three reaction steps included in the model are firstly linear isomerisation of 1-hexene followed by skeletal isomerisation and finally dimerisation and cracking (see figure). The model is tested by using a skeletal hexene isomer -2,3-dimethyl-2-butene (DMB) -as reactant.

Liquid-Phase Oligomerization of 1-Hexene Catalyzed by Macroporous Ion-Exchange Resins

“…3 depicted a reaction pathway based on these profiles. It agrees with results of Schwarzer et al [8], who suggested that at temperatures lower than 473 K linear 1-hexene isomers dimerization over solid acid phosphoric (SPA) becomes more significant with respect to skeletal isomers. Then the only possibility to obtain dimers is via linear olefins.…”

“…One thing that can be done in such circumstances is to compare them with oligomerization kinetic data on other catalysts. Schwarzer et al [8] obtained a good fitting at higher temperatures than 473 K for lumped dimerization and cracking reaction catalyzed by solid phosphoric acid, by assuming a reversible reaction and a kinetic model of first-order. However, the estimated activation energy was rather low (6 kJ mol -1 ) and kinetic model failed to predict the reaction rate at 423 K. Fortini et al [22] measured rates of dimerization of 1-hexene catalyzed by a fluorinated nickel complex and alkyl aluminium.…”

“…Schwarzer et al [8] proposed a kinetic model for the dimerization of 1-hexene over a solid phosphoric acid catalyst. In the temperature range 423-523 K, it was found that the reaction could be modeled with a three-step sequential reaction scheme: First, linear isomerization reaction of 1-hexene, then, the skeletal isomerization reaction and, finally, dimerization and cracking reactions.…”

Screening heterogeneous catalysts for the pyrolysis of lignin

“…We included other solid acid catalysts such as solid phosphoric acid (SPA) and Al-MCM-41 in our screening for comparison to HZSM-5. SPA is widely studied as an isomerization catalyst for petroleum processing [14][15][16] but has little precedent in the literature as a pyrolysis catalyst. There have been numerous studies of liquid phosphoric acid as a pretreatment of biomass for pyrolysis, however [17][18][19][20].…”

Study of the oligomerization of 1-octene catalyzed by macroreticular ion-exchange resins

“…Oligomerization of light olefins (C 3 -C 5 ) [1][2][3][4] is widely found in the literature. Some works have recently appeared concerning C 6 olefins oligomerization [5][6][7][8][9] over different solid catalysts. As for 1-octene oligomerization only a few works are available in the open literature.…”