Phthalic anhydride, production

PHTHALIC ANHYDRIDE PRODUCTION VIA THE CATALYTIC OXIDATION OF NAPHTHALENE IN A FIXED BED REACTOR... 

Re Design Specifications for Phthalic Anhydride Production in a Fixed Bed Reactor A proposed expansion of the corporation s vinyl plastics operation will require a commitment by the company to produce its own plasticizer. Our long range planning group has suggested that 6 million pounds per year of new phthalic anhydride capacity would meet our internal needs and projected increases in demand from current customers. 

Schematic diagram of phthalic anhydride production process. (Adapted from P. Ellwood, Chemical Engineering, June 2, 1969, pp. 81-82. Used with permission of Chemical Engineering.)...

However, in order to design a reactor for phthalic anhydride production, the reaction rate constants for the temperature range of interest are such that the following simplified set of reactions has been suggested as appropriate (6, 7). 

The reactions are highly exothermic and very rapid. Consequently conventional practice in the design of fixed bed reactors for phthalic anhydride production has been based on the use of multitube reactors to ensure good heat transfer and good temperature control. These are required to ensure good selectivity. Often a thousand or more small diameter tubes may be... 

Phthalic Anhydride Production Via the Catalytic Oxidation of Naphthalene in a Fixed Bed Reactor... 

Naphthalene. Until the 1960s, the principal oudet for naphthalene was the production of phthalic anhydride however, more recendy, 0-xylene has replaced naphthalene as the preferred feedstock (see Phthalic acids). Nevertheless, of the 201,000 t produced in 1994 in japan, 73.2% was used for phthalic anhydride production. The rest was consumed in dye stuffs manufacture and a wide variety of other uses. Naphthalene is also used to produce phthalic anhydride in the United Kingdom, Belgium, and the Czech Republic, and can be used by Koppers in the United States in time of 0-xylene shortages. In Europe, the traditional uses for naphthalene have been for the manufacture of p-naphthol and for dye stuff intermediates (see Dyes AND DYE intermediates). ... 

Two sources of naphthalene exist in the U.S. coal tar and petroleum. Coal tar was the traditional source until the late 1950s, when it was in short supply. In 1960, the first petroleum-naphthalene plant accounted for over 40% of total naphthalene production. The availability of large quantities of o-xylene at competitive prices during the 1970s affected the position of naphthalene as the prime raw material for phthalic anhydride. Production for 1992 was less than 50% of Ihe levels in the early 1980s. The last dehydroalkylation plant for petroleum naphthalene was shut down late in 1991. Coal tar has stabilized at around 85 x 103 t/yr, and petroleum-naphthalene production is around 6—8 x 103 t/yr. The reduction of petroleum production has opened the door for imported naphthalene, mainly from Canada. 

About one-half of the phthalic anhydride production is consumed for the preparation of plasticizers, mostly for the various flexible grades of poly(vinyl chloride). The remainder is roughly split between alkyd resin preparation used for many types of surface coatings, and for polyester resin composites with fiberglass reinforcement, the so-called fiberglass resins used in boats and other sporting equipment as well as for corrosion-resistant vessels and ducts used in chemical processing, some automotive parts, and as a convenient means of field repair of many of these items. 

To obtain the total yield in relation to e-xylene, it is necessary to consider that of the phthalic anhydride production step, which barely exceeds 65 to 70 molar per cent in the gas phase oxidation (Von Heyden type reactor). At present no industrial plant employs this process, which is uneconomical in comparison with other methods, given the lack of selectivity of the o-xylene conversion step. 

The effectiveness factors for the o-Xylene consumption and phthalic anhydride production are shown in Figures 6.38 and 6.39 which show values very close to unity. The values of the effectiveness factor increase slowly along the length of the reactor which indicate that a small difference between the catalyst pellet surface and the bulk conditions do exist. From the figures, effectiveness factor increases as the oXylene feed mole fraction increases which was also noted in the single pellet parametric investigation in chapter 5. 

Subject to resolution of these concerns, scaling in parallel has no obvious limit. Multitubular reactors with 10,000 tubes have been built, for example, for phthalic anhydride production. 

The operating pressure is nearly atmospheric. The phthalic anhydride production from such a reactor with 2500 tubes is 1650 tons/yr. It follows that with this catalyst a typical mass flow velocity of the gas mixture is 4684 kg/m hr. With a mean fluid density of 1293 kg/m. this leads to a superficial fluid velocity of 3600 m/hr. A typical heat of reaction is 307,000 kcal/kmol and the specific heat is 0.237 kcal/kg C (0.992 kJ/kg K). In this example the kinetic equation for the hydrocarbon conversion will be considered in first approximation to be pseudo first order, due to the large excess of oxygen. 

Figure 4. Change in feedstock for phthalic anhydride production.

At the present time, phthalic anhydride is produced from both naphthalene and o-xylene. The use of naphthalene is especially high in Japan, at just 40%, whereas in the USA and some West European countries it is relatively low, since in these countries naphthalene is most commonly used in the manufacture of dyes and agricultural chemicals. Currently, 80% of world phthalic anhydride production is based on o-xylene. 

Hydrorefining of naphthalene is especially used in the production of low-sulfur naphthalene for phthalic anhydride production by the fluid-bed process, since sulfur compounds can poison the fluid-bed catalyst. 

Miseralis CD, Way PF, Jones DH. The evolution of flui-dized-bed reactors in the phthalic anhydride production. AIChE Spring National Meeting, Houston, Texas, April 1991. 

A little more than a decade ago, Clariant decided to venture into the field of partial oxidation reactions. Catalysts for selective partial oxidation reactions thus belong to the most recent developments in the catalyst portfolio of Clariant. The portfolio of oxidation catalysts currently comprises SulfoMax for sulfuric acid production, FAMAX for formaldehyde production, PHTHALIMAX for phthalic anhydride production, SynDane for maleic anhydride production, and most recently VAM ax for vinyl acetate production. 

Data obtained in such a way for over 400 catalyst formulations has initially been used to train artificial neural networks, which in turn allow the prediction of catalyst performance of yet unprepared catalyst compositions. This approach is nowadays a standard tool when catalysts have to be designed for the special process conditions of a given customer. This broad database combined with artificial neural networks allows Clariant to customize its PHTHALIMAX catalyst for phthalic anhydride production for each customer process. 

Figure 12.11. Kinetic simulations of the o-xylene conversion (a) and the phthalic anhydride production (b) as function of catalyst and layer optimization.

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