Selective Oxidation Of O-xylene Research Articles

Computational Fluid Dynamics (CFD) Analysis of Phthalic Anhydride’s Yield Using Lab Synthesized and Commercially Available (V2O5/TiO2) Catalyst

V2O5/TiO2 is an important catalyst used in many industrial reactions like selective oxidation of o-xylene to phthalic anhydride, selective catalytic reduction of NOx, selective oxidation of alkanes, etc. The partial oxidation of o-xylene to synthesize phthalic anhydride is an exothermic reaction and leaves hot spots on the catalyst’s surface. The yield of phthalic anhydride strongly depends on the activity and stability of the catalyst. In this work, a computational fluid dynamics (CFD) analysis has been conducted to compare the yield of lab prepared catalyst with the commercially used catalyst. This work is first attempt to simulate V2O5/TiO2 catalyst for cracking heavy hydrocarbons in the petrochemical industry using k- ε turbulence and species transport models in CFD. The results obtained are in the form of scaled residuals, area-weighted average, and contours of pressure and temperature. Simulation results of lab synthesized and commercially used catalysts, applying finite volume method (FVM) are compared, which emphasize the scope of CFD modeling in the catalytic cracking process of petrochemical industry.

Study of catalytic behaviour and deactivation of vanadyl-aluminum binary phosphates in selective oxidation of o-xylene

This study involved the catalytic behaviour and the deactivation of aluminum–vanadium–phosphorus (Al–V–P–O) systems obtained by the sol–gel method with several P/Al/V molar ratios and calcined at 450 °C in the selective oxidation of o -xylene. Activity values as well as the reducibility of Al–V–P–O systems were influenced by the Al/V ratio, increasing with Al content, while selectivity to phthalic anhydride and phthalide values only changed slightly. All catalysts always showed a high degree of resistance to deactivation in function of time on-stream. Furthermore, water in the feed or coke generation treatment negatively affected catalytic activity, although the initial conversion values were recovered. This fact along with the unchanged textural properties and XRD patterns of the catalysts after such treatments suggest that reversible deactivation could be attributed to partial poisoning of active sites.

Oxidation of o-xylene on mesoporous Ti-phosphate-supported VO x catalysts and promoter effect of K + on selectivity

The selective oxidation of o-xylene on catalysts based on mesoporous titanium phosphate-supported vanadium oxide has been studied. The catalysts were characterized by different physico-chemical techniques (XRD, XPS, N 2 isotherms, TPD of chemisorbed NH 3 and Raman spectroscopy). The conversion and yield to phthalic anhydride increased with vanadium oxide loading up to one theoretical monolayer. Beyond this point, no substantial improvement was achieved. Moreover, a significant improvement in the yield of phthalic anhydride, coinciding with a decrease in the formation of carbon oxides, was observed when potassium was incorporated to the vanadium catalysts. The enhancement of the phthalic anhydride yield was correlated with the neutralization of the stronger surface acid centers by the K + ions, providing evidence for the hypothesis that stronger acid sites are involved in the formation of total oxidation products (carbon oxides).

Possible effects of site isolation in antimony oxide-modified vanadia/titania catalysts for selective oxidation of o-xylene

Titania-supported vanadia catalysts were modified by addition of antimony oxide for application in o-xylene selective oxidation to phthalic anhydride. It was shown that active and selective catalysts can be prepared by ball-milling mixtures of powders of TiO2, V2O5and Sb2O3followed by calcination. X-ray photoelectron spectroscopy proves the formation of highly dispersed overlayers of vanadium oxide and antimony oxide, in which V5+is partially reduced to lower oxidation states and Sb3+is partially oxidized to Sb5+. Antimony oxide segregated into the outermost surface layers. It is therefore inferred that the presence of the antimony oxide modifier spatially separates V–O species and leads to “site isolation” which may be responsible for the positive effect of the modifier for the catalyst's selectivity.

Selective oxidation of o-xylene to phthalic anhydride on V2O5 supported on TiO2-coated SiO2

A ternary V-Ti-Si catalyst was prepared by depositing the vanadium oxide precursor on a SiO2 previously coated by TiO2. The ternary V-Ti-Si catalyst and the corresponding binary V-Ti and V-Si counterparts were tested for the selective oxidation of o-xylene to phthalic anhydride. Silica-supported vanadium oxide shows lowest activity and selectivity, meanwhile selectivity to phthalic anhydride is higher on titania-containing catalysts. The best yield to phthalic anhydride (82.5%) is obtained at 573 K on the ternary V-Ti-Si catalyst which is comparable to that claimed for the best conventional V-Ti catalysts described in literature.

Selective oxidation of o‐xylene to phthalic anhydride over vanadia/titania: A comparative study of integral and recycle reactor operation

AbstractTwo vanadia/titania catalysts, containing 1 and 8 wt% vanadia on anatase, have been investigated for the selective oxidation of o‐xylene to phthalic anhydride. In a comparative study, activity and selectivity in o‐xylene oxidation were measured using an integral reactor and a reactor with external product recirculation, with the objective of studying the influence of backmixing in the latter on the reaction behaviour. Adsorbed surface species were investigated by means of in‐situ diffuse reflectance FT‐IR spectroscopy, using an environmental chamber which corresponds to an integral reactor. No difference in activity and selectivity in o‐xylene oxidation was observed between the two catalysts. FT‐IR studies showed adsorbed o‐xylene, benzoate and a high concentration of phthalic anhydride on the surface of both catalysts. o‐Xylene oxidation follows a sequential reaction path, with o‐tolualdehyde as the first intermediate and phthalide, phthalic anhydride and maleic anhydride as sequential products. No evidence was found for a direct oxidation‐path of o‐xylene to phthalic anhydride. Total oxidation products CO and CO2 are formed by direct oxidation of the o‐xylene and by oxidation of the reaction products. Due to greatly reduced concentration and temperature gradients, the recycle reactor proved to be highly suitable for studying the extremely exothermic oxidation of o‐xylene.

Structure, activity and selectivity of V2O5-TiO2 catalysts for o-xylene conversion

The formation of needle shaped crystallites of V6O13 at low V concentrations on V2O5-anatase coated catalysts explains the low selectivity for phthalic anhydride during o-xylene oxidation. The (010) plane of V-oxide, most active for selective oxidation of o-xylene, is not accessible and the contact of this plane with the anatase faces promotes the anatase-rutile transformation and the incorporation and blocking of V4+ ions.

Selective oxidation of o-xylene by monolayer V2O5–TiO2catalysts

The reaction of VOCl3 in benzene with the hydroxyl groups at the surface of low-area (ca. 10 m2 g–1) anatase leads, after hydrolysis and calcination, to a monolayer of vanadium species having approximately the same density as a two-dimensional layer of V2O5. Drying the anatase at 100–150 °C apparently removes only physisorbed water, while drying at 200 °C causes partial dehydroxylation. The concentration of VOCl3 in benzene has been varied, the optimum vanadium content being given by 0.20 cm3 in 50 cm3 benzene for the treatment of 5 g anatase. The best temperature for the reaction is 75 °C and the best time is 5 h.Catalysts prepared in this way are active and selective for the oxidation of o-xylene to phthalic anhydride. Good catalysts contain 0.9–1.4 wt % vanadium as V2O5; they give >95 % conversion at 315 °C and selectivities exceeding 80 %. Activation energies are 100–140 kJ mol–1. Activity and selectivity improve with increasing vanadium content up to the limit of 1.4 wt % V2O5, and the best catalysts give yields of phthalic anhydride of 85–87 %, which can be further improved by the use of Rb and P promoters. The possible structure of the vanadium monolayer is discussed, but neither it nor subsequently deposited layers show the Raman line at 996 cm–1 which is characteristic of the VO bond.