The oxidehydrogenation of C-4 alkenes over zinc ferrite

Q Science (General);QD Chemistry;TP Chemical technology

Spence, Ronald Richard ; Jackson, S.D.

University:University of Glasgow

Department:School of Chemistry

关键词: Butene1,3-butadieneOxidative DehydrogenationZinc Ferrite;   

Others  :  http://theses.gla.ac.uk/5662/2/2014SpenceMSc.pdf

来源: University of Glasgow

【 摘 要 】

In 1863 1,3-butadiene was isolated from the pyrolysis of amyl alcohol as an unknown hydrocarbon, but it was not until 1886 that Henry Edward Armstrong identified the hydrocarbon as butadiene. Around 95 % of 1,3-butadiene produced comes from the steam cracking of crude oil, however the outstanding 5 % is produced by on demand dehydrogenation and oxidative dehydrogenation processes.The activity and selectivity of various catalysts for the conversion of C4 alkenes to 1,3-butadiene by oxidative dehydrogenation has been studied. Catalysts examined were bulk zinc ferrite and iron oxide catalysts produced by different precipitation methods and supported zinc ferrite and vanadia on θ-alumina catalysts, which were produced with differing loadings. The majority of the study related to 1-butene, but cis-2-butene and trans-2-butene were also examined.The catalysts were characterised pre and post reaction using BET Surface Area, Thermogravimetric Anaylsis-Differential Scanning Calorimetry, X-Ray Diffraction, Raman Spectroscopy, Acid Site Analysis, SQUID (Superconducting Quantum Interference Device) and EPR (Electron Paramagnetic Resonance) techniques.The catalysts were tested under the flowing conditions at a reaction temperature of 693 K and a molar gas ratio 0.75:1:15 oxygen:alkene:steam.θ-alumina supported zinc ferrite, iron doped zinc ferrite and vanadia catalysts were found to be poor 1 butene ODH catalysts compared to the bulk zinc ferrite catalysts since they only gave moderate 1-butene conversion. Also all of the supported catalysts with the exception of the highest zinc ferrite loading catalyst suffered from deactivation and increasing cis-2-butene and trans 2 butene selectivity with time on stream.Iron enriched zinc ferrite and iron oxide bulk catalysts were also found to be poor 1-butene ODH catalysts since they only gave moderate to very low 1-butene conversion and with one exception deactivated with time on stream.Bulk zinc ferrite catalysts were prepared from 0.6 M and 3 M sodium hydroxide with the catalysts prepared from 3 M sodium hydroxide to be the most effective at butene ODH (typical yield of ~37 %), whereas the 0.6 M catalysts required in excess of 60 hours on stream to fully activate. The bulk zinc ferrite catalysts produced from 3 M sodium hydroxide were used to study the temperature stability of the catalyst, determine a bed profile, investigate space velocity changes, study different feed isomers and the inclusion of an isomerisation catalyst before the bulk zinc ferrite. The catalyst was found have good temperature stability and a broad operating window.The bed profiling and space velocity studies revealed that the space velocity could be increased by a factor of 6 with no major loss to conversion or selectivity.The introduction of an isomerisation catalyst before the zinc ferrite catalyst gave an increase in 1-butene conversion but this increase was attributed to an increase in isomerisation products.Nevertheless the use of an alumina pre-bed did result in higher butadiene yields with the best result being obtained with a 1:1 mixed alumina:zinc ferrite bed (54 %).Comparison between the pure butene isomers showed that trans-2-butene gave the highest 1,3-butadiene selectivity, butene conversion and lowest rate of isomerisation with an overall butadiene yield of ~75 %.Comparison of the bulk zinc ferrite catalyst pre and post reaction revealed that the surface area was reduced by at least 50 % after reaction.This was, in most part, due to the steam.Characterisation of the surface acid sites on a fresh zinc ferrite compared to that after use revealed that there was a decrease in the number of acid sites with no strong acid sites remaining.