Deactivation properties of a high-productive vanadia-titania catalyst for oxidation of o-xylene to phthalic anhydride

Georgieva, Almira; Anastasov, A. I.; Nikolov, V.

doi:10.1590/s0104-66322008000200013

Cited by 4 publications

(1 citation statement)

References 40 publications

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“…Moreover, it is also known that free uncovered TiO 2 surface with its acidic OH groups lead to o-xylene cracking and subsequent total oxidation of the cracking products [13]. Many studies concerning permanent or reversible catalyst deactivation have been also published [10,11,[16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Different deactivation phenomena are described in detail: While there are many studies available in the literature investigating different root causes for deactivation, most of them deal with model catalyst compositions being very different from modern, commercially proven, multi-layer catalyst systems after typical run times of 3-5 years.…”

Section: Introductionmentioning

confidence: 99%

Deactivation of Commercial, High-Load o-Xylene Feed VOx/TiO2 Phthalic Anhydride Catalyst by Unusual Over-Reduction

Richter

Mestl

2019

Catalysts

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An unusual temporal behavior of the by-product spectrum, as well as the temperature profiles of a commercial phthalic anhydride reactor, indicated a non-typical change of the incumbent catalyst. In order to understand these observations, catalyst samples were taken from this reactor and analyzed by standard physico-chemical methods. Catalyst samples from another commercial reference reactor with most similar operating conditions and catalyst lifetime were also taken for comparison. The detailed physical analysis did not indicate unusual thermal stress leading to catalyst deactivation by rutilisation or sintering of the titania phase. The chemical analysis did not reveal significant amounts of any of the known catalyst poisons, which would also contribute to an untypical catalyst deactivation/behavior. Quantitative X-ray diffraction measurements on the other hand revealed an unusually high degree of reduction of the vanadium species in the final polishing catalyst layer. Such an abnormal degree of catalyst reduction, and hence, irreversible damaging, was concluded to likely originate from a unit shutdown without sufficient air purging of the catalyst bed. Combustion analysis of the deactivated catalyst confirmed unusually high carbon contents in the finishing catalyst bed (L4) accompanied with a significant loss in the specific surface area by plugging the catalyst pores with high-molecular carbon deposits. According to the well-known Mars–van-Krevelen-mechanism, o-xylene and reaction intermediates remain adsorbed on the catalyst surface in case of a shutdown without air purging and will continue to consume lattice oxygen, accordingly reducing the catalytic species. This systematic investigation of used catalyst samples demonstrated the importance of sufficient air purging during and after a unit shutdown to avoid abnormal, irreversible damage and thus negative impact to catalyst performance.

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