Catalytic o-xylene oxidation

For phthalic acid anhydride (PSA) the (released) heat of reaction is theoretically —7.5 kj per g-PSA, that is, for o-xylene oxidation with 100% selectivity to PSA (see Section 6.13). Industrial plants consume (without feed) 22 kJ per g-PSA, but according to Figure 5.5.4 this value should be around zero. The main reason for this difference is that the selectivity of catalytic o-xylene oxidation to PSA is less than 80%, and unwanted total oxidation to CO2 takes place. 

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)].

Table 6.13.1 Data on chemical media and conditions of catalytic o-xylene oxidation. Data partly from Baerns, Hofmann, and Renken (2002), Froment and Bischoff (1990), and Papageorgiou and...

Figure 6.13.1 Axial profiles of temperature (tube axis) (a), o-xylene conversion (b), and selectivity to PA (c) in the multi-tubular reactor for catalytic o-xylene oxidation with different inlet temperatures [fin = Tool, two-dimensional model, Eqs. (6.13.3), (6.13.15)-(6.13.22) parameters seeTable 6.13.1].

Figure 6.13.4 Influence of internal diameter on the maximum allowable gas inlet (= wall) temperature with regard to a runaway in a multi-tubular reactor of catalytic o-xylene oxidation [determined by Eqs. (6.13.41)-(6.13.43), parameters as given by Table 6.13.1].

Reactions of organic compounds over solid catalysts are sometimes accompanied by the formation of heavy by-products which can form a deposit on the surface and lead to catalyst deactivation. For o-xylene oxidation the formation of such compounds has been frequently mentioned [15-17] but no information can be found about their influence on the catalyst deactivation. The present work reports on the formation of carbonaceous deposits over V2O5/T1O2 catalysts used for o-xyletie oxidation. Samples prepared by wet impregnation were used under operating conditions that can lead to the formation of heavy compounds. They were then collected and analysed by FTIR and TFO. The present data help to elucidate the characteristics of such compounds and their influence on the catalytic behaviour. 

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... 

For highly exothermic and fast reactions the catalyst is often deposited on the outer surface of the support which is usually of very low porosity (e.g. FjOj on SiC for o-Xylene oxidation) (Ellis, 1972). In other applications (e.g. ammonia oxidation converters) the catalyst is in the form of a woven wire screen (or gauze) which is usually supported on a non-catalytic pad to prevent premature ignition (Gillespie, 1970). 

Gasior, M., Gasior, I. and Grzyhoswka, B. (1984). o-Xylene Oxidation on the V205-Ti02 Oxide System I. Dependence of Catalytic Properties on the Modification of Ti02, Appl. Catal., 10, pp. 87-100. 

Figure 13.5 shows a flowsheet for the manufacture of phthalic anhydride by the oxidation of o-xylene. Air and o-xylene are heated and mixed in a Venturi, where the o-xylene vaporizes. The reaction mixture enters a tubular catalytic reactor. The heat of reaction is removed from the reactor by recirculation of molten salt. The temperature control in the reactor would be diflficult to maintain by methods other than molten salt. 

The U.S. naphthalene consumption by markets for 1992 is Hsted in Table 9. The production of phthaHc anhydride by vapor-phase catalytic oxidation has been the main use for naphthalene. Although its use has declined in favor of o-xylene, naphthalene is expected to maintain its present share of this market, ie, ca 18%. Both petroleum naphthalene and coal-tar naphthalene can be used for phthaHc anhydride manufacture. U.S. phthaHc anhydride capacity was 465 X lOM in 1992 (38). 

The first of the benzene polycarboxyUc acids to become a commercial product was phthabc acid, mosdy in the form of the anhydride. The anhydride is obtained by the catalytic vapor-phase air oxidation of o-xylene or naphthalene. The lUPAC name of phthabc anhydride is 1,3-isobenzofurandione... 

Vapor-phase catalytic oxidation of dutene is a mote direct route to the dianhydtide. Hbls in Europe apparently uses this route, which eliminates the need for a separate dehydration step and for handling of any oxidants or solvents. Continuous operation is faciHtated, corrosion is minimized, and product recovery is simplified. The vapor-phase oxidation of dutene is similar to that of o-xylene to phthaHc anhydtide, and phthaHc anhydtide units can be... 

Hydroxyphthalazin-l(2//)-one is obtained in a smooth reaction between phthalic anhydride and hydrazine hydrate and this is again the starting compound for many 1-substituted and/or 1,4-disubstituted phthalazines. The transformations of 1,4-dichloro-phthalazine, which is prepared in the usual manner, follow a similar pattern as shown for pyridazines in Scheme 110. On the other hand, phthalonitrile is the preferential starting compound for amino- and hydrazino-phthalazines. The most satisfactory synthesis of phthalazine is the reaction between a,a,a, a -tetrachloro-o-xylene and hydrazine sulfate in sulfuric acid (67FRP1438827), alt iough catalytic dehalogenation of 1-chloro- or 1,4-dichloro-phthalazine or oxidation of 1-hydrazinophthalazine also provides the parent compound in moderate yield. 

The prime function of the saturated acid is to space out the double bonds and thus reduce the density of cross-linking. Phthalic anhydride is most commonly used for this purpose because it provides an inflexible link and maintains the rigidity in the cured resin. It has been used in increasing proportions during the past decade since its low price enables cheaper resins to be made. The most detrimental effect of this is to reduce the heat resistance of the laminates but this is frequently unimportant. It is usually produced by catalytic oxidation of o-xylene but sometimes naphthalene and is a crystalline solid melting at 131°C. 

Heyden-Wacker A process for making phthalic anhydride by the catalytic oxidation of naphthalene or o-xylene. Offered by Lurgi. 

Sapper An obsolete process for making phthalic anhydride by oxidizing o-xylene, using a mercury sulfate catalyst. Invented by E. Sapper in 1891 in the course of searching for a commercial route to indigo, and used until the catalytic gas-phase oxidation of naphthalene was introduced in 1925. 

Anthraquinone itself is traditionally available from the anthracene of coal tar by oxidation, often with chromic acid or nitric acid a more modern alternative method is that of air oxidation using vanadium(V) oxide as catalyst. Anthraquinone is also produced in the reaction of benzene with benzene-1,2-dicarboxylic anhydride (6.4 phthalic anhydride) using a Lewis acid catalyst, typically aluminium chloride. This Friedel-Crafts acylation gives o-benzoylbenzoic acid (6.5) which undergoes cyclodehydration when heated in concentrated sulphuric acid (Scheme 6.2). Phthalic anhydride is readily available from naphthalene or from 1,2-dimethylbenzene (o-xylene) by catalytic air oxidation. 

An aromatic compound which is employed along with glycerol in the production of alkyd resins is phthalic anhydride. The conventional process for the manufacture of this chemical has been from the catalytic oxidation of coal tar naphthalene, and annual production of the anhydride in recent years has been around 150,000,000 pounds. In 1946 production was started (4) in a plant of the Oronite Chemical Co. at Richmond, Calif., to produce phthalic anhydride by the oxidation of o-xylene produced in a hydroformer unit of the adjacent Standard Oil Co. of California refinery. The Oronite plant was reported to have a design capacity of 7,000,000 to 8,000,000 pounds per year of 99.7% pure phthalic anhydride. 

Phthalic Anhydride. Phthalic anhydride is manufactured by the catalytic vapor-phase oxidation of o-xylene [Eq. (9.182)] or naphthalene [Eq. (9.183)] ... 

The influence of substituents on the catalytic oxidation of toluene was investigated by Trimm and Irshad [330]. Toluene, chlorotoluenes and xylenes were oxidized over a M0O3 catalyst at 350—500° C. Partial oxidation products are aldehydes, acids and phthalic anhydride (in the case of o-xylene). Unexpectedly, both xylenes and chlorotoluenes are oxidized faster than toluene. The authors conclude that apparently the electromeric effect of the chlorosubstituent is more important than its inductive (—I) effect. The activation energies of the xylenes and chlorotoluenes all fall in the same range (17—18 kcal mol"1), while a much higher value is reported for toluene (27 kcal mol 1). 

Andreikov, E.I. and R.L. Volkov. 1981. Catalytic properties of vanadium oxide compounds of silver in the oxidation of o-xylene and napthalene. Kinetika i Katlitz 4 963-968. 

Next, the drop in catalytic activity was determined as a function of temperature. The catalyst studied is an improved version of a commercial catalyst on which detailed kinetic experiments were carried out [13 The process occurring over the catalyst is described by a system of the oxidation reactions for o-xylene together with the Langmuir - Hinshelwood equation given by Skrzypek etal[ 3 Their equations (9) - (14) were, however, slightly modified by substituting the product of the activity s and the reaction rate rh R,-s rs> for the reaction rate rt. 

---