Xylene Oxidation to Phthalic Anhydride

The oxidation of o-xylene to phthalic anhydride is commercially conducted with supported V205/Ti02 catalysts containing several promoters (e.g. SbOx, KOx and POx) in a fixed-bed shell-and-tube reactor with a molten salt coolant. Although 

High-temperature in situ Raman spectra demonstrate that the complex present 

A combined in situ Raman and UV-vis spectroscopic study provides details on the interaction of vanadium (V and V ) oxosulfato complexes with SO2, which depend on the temperature and on the presence of molecular 02. The UV-vis spectra confirm the presence of sites in the presence of oxygen and the combined 

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Such a catalyst is well known for several reactions, such as o-xylene oxidation to phthalic anhydride and selective catalytic reduction (SCR) of NO by ammonia. The anatase form of TiO appears to be better than the rutile form. Such catalysts with 1 and 8 wt% V20s/anatase was prepared by Rhone-Poulenc (S 10 m g ) for an exercise of characterization by 25 different european laboratories. All results are assembled in one issue of Catalysis Today published in May 1994, vol. 20 n°l. Surface vanadium species were observed to exist in three different forms monomeric V04 species, polymeric vanadate species and V2O5 crystallites [27], the relative amount of which depended on initial wt % V20s/anatase and on the subsequent selective dissolution treatment. 

Therefore, the question to answer is what is the common explanation to these catalytic and non catalytic phenomena, observed as well with oxide/oxide (or chloride/chloride) as with metal/oxide The oldest and first example in selective oxidation is V205-Ti02(anatase), catalyst of o-xylene oxidation to phthalic anhydride. Nearly in the same time, three teams in Poland, Great-Britain and France [4-10] observed the catalytic synergy and studied also the... 

Multi-tubular reactor for o-xylene oxidation to phthalic anhydride. Deggendorfer Werft, from Cmehlingand Brehm (1996). 

In Section 6.11, Fischer-Tropsch synthesis in a multitube reactor was used as an example to illustrate the differences between the one- and two-dimensional approaches for the simulation of cooled fixed bed reactors. For o-xylene oxidation to phthalic anhydride, only the two-dimensional reactor model is considered. 

The chapter presents a brief overview of the current research on V205/Ti02 catalysts for o-xylene oxidation to phthalic anhydride at Clariant. Phthalic anhydride is produced in tubular, salt-cooled reactors with a capacity of about 5 Mio to per annum. There is a rather broad variety of different process conditions realized in industry in terms of feed composition, air flow rate, as well as reactor dimensions which the phthalic anhydride catalyst portfolio has to match. Catalyst active mass compositions have been optimized at Clariant for these differently realized industry processes utilizing artificial neural networks trained on high-throughput data. Fundamental pilot reactor research unravelling new details of the reaction network of the o-xylene oxidation led to an improved kinetic reactor model which allowed further optimizing of the state of the art multi-layer catalyst system for maximum phthalic anhydride yields. 

Saleh, R. and Wachs, I. (1987). Reaction Network and Kinetics of o-Xylene Oxidation to Phthalic Anhydride over V205/Ti02 (Anatase) Catalysts, Appl. Catal. A Gen., 31, pp. 87-98. 

Wachs, I., Chan, S. and Saleh, R. (1985). The Interaction of V2O5 with Ti02(Anatase) II. Comparison of Fresh and Used Catalysts for o-Xylene Oxidation to Phthalic Anhydride, J. Catal.,... 

The work has shown that a strong exothermic reaction such as the o-xylene oxidation to phthalic anhydride can be operated in the explosion regime using a micropacked bed reactor, even with high adiabatic temperature rise of several 1000 K. An increase of the selectivity to total oxidation products was observed at higher o-xylene concentrations between 10 and 25 vol% o-xylene, which possibly was caused by the formation of a hotspot. 

Either naphthalene or ortho-xylene is an acceptable starting material for partial oxidation to phthalic anhydride, but current raw materials costs favor the former as a starting material. Both fixed and fluidized bed processes have been used on a commercial scale, but you are to focus your attention on the former. Figure 13.5 is a schematic flow diagram of the proposed process. Most research groups that have studied the catalytic oxidation of naphthalene over vanadium pentoxide agree that the principal reactions are... 

The gas phase oxidation of naphthalene to phthalic anhydride over V2Os-based catalysts is one of the oldest successful partial oxidation processes and is still of industrial importance today. Common commercial catalysts are modified silica-supported V—K—S—O catalysts and catalysts similar to those used for benzene or o-xylene oxidation. Maximum phthalic anhydride yields of 80—85 mol. % (92—98 wt. %) at 350—400°C are reported. By-products are naphthoquinone (2—5%), maleic anhydride (2— 5%) and carbon oxides. 

FIGURE 3.13 o-Xylene partial oxidation to phthalic anhydride, the most common reaction paths. 

Scheme6.13.1 Simplified reaction scheme of catalytic o-xylene oxidation to phthalic acid anhydride. [A more complex network with o-tolualdehyde and phthalide anhydride as intermediates is proposed by Calderbank, Chandrasekharan, and Fumagalli (1977), Anastasov (2002,2003) and Fiebig and Kuchling (2009)].

Of the xylenes, p-xylene has the largest volume use. It is oxidized to terephthalic acid, which is used as a monomer to make polyesters. Ortho xylene is oxidized to phthalic anhydride. Phthalic anhydride can be reacted with long-chain alcohols to make plasticizers to impart flexibility to PVC resin. Phthalic anhydride is also used to make unsaturated polyester resins. 

Xylenes are used inter alia as solvents, for example in the USA 180,000 t p.a. [13] and in Japan 90,000 t [33], particularly in the paint and printing ink industries (see also [5]). In eastern Europe it is also used for numerous applications in the shoe industry, o-xylene (besides naphthalene) is mainly oxidized to phthalic anhydride from which dyestuffs, phthalodinitrile and - by esterification with alcohols - plasticizers and raw materials for paints and varnishes are obtained [36, 38]. p-xylene is oxidized and processed with methanol to terephthalic acid dimethyl ester, from which polyesters are made [36, 38, 39]. For example, in 1972 2.9 million t polyester fibres were produced worldwide [39] and in 1979 more than 5 million t, which corresponds to 2.8 million t of p-xylene [30 a]. Polystyrene and copolymers (including expanded plastics) in particular are polymerized from styrene, and the world annual production of these products around 1975 was about 5 million t [39, 40],... 

Cataljdic reactions performed in fluid beds are not too numerous. Among these are the oxidation of o-xylene to phthalic anhydride, the Deacon process for oxidizing HCl to CI2, producing acrylonitrile from propylene and ammonia in an oxidation, and the ethylene dichloride process. In the petroleum industry, cataljdic cracking and catalyst regeneration is done in fluid beds as well as some hydroforming reactions. 

NON-ISOTHERMAL FIXED BED REACTOR OXIDATION OF 0-XYLENE TO PHTHALIC ANHYDRIDE STEADY-STATE AXIAL TEMPERATURE AND CONVERSION CONSTANT 6=4684 superf. mass velocity [kg/m2 h]... 

LAR [Low air ratio] A process for oxidizing o-xylene or naphthalene to phthalic anhydride, using a titania/vanadia catalyst containing molybdenum. Developed by Alusuisse Italia in the 1980s. A plant was operated at Valdamo, Italy, in 1984. 

ANHYD - Oxidation of O-Xylene to Phthalic Anhydride System... 

Steady-State Absorption Column Design 471 Oxidation of O-Xylene to Phthalic Anhydride 324 Continuous Stirred Tank Reactor Model of Activated 577... 

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