Phthalic anhydride process

Figure 13.6 The composite curves and grand composite curve for the phthalic anhydride process.

The phthalonitrile process has the particular advantage over the phthalic anhydride process of forming ring-substituted chloro-copper phthalocyanines. Using copper(I)chloride produces so-called semi-chloro Copper Phalocyanine Blue, a pigment which possesses a statistical average of 0.5 chlorine atoms per copper phthalocyanine molecule. Copper(II)chloride, on the other hand, affords a product which comprises an average of one chlorine atom per copper phthalocyanine molecule. A prerequisite for the formation of the chloro substituted compound, however, is the absence of ammonia or urea in the reaction mixture. 

The phthalic anhydride/urea process may also be employed to convert tetra-chloro phthalic anhydride to green copper hexadecachloro phthalocyanine by condensation. In this case, titanium or zirconium dioxides, particularly in the form of hydrated gels, are used instead of the molybdenum salts which are used in the phthalic anhydride process [23]. There is a certain disadvantage to the fact that the products lack brilliance and require additional purification. 

As apparatus for the batch process, an enamel or steel reactor with an agitator and pressure steam or oil heating suffices. Apparatuses used in the continuous synthesis in the presence of solvents and in the bake process are described in [50] and [51,52], respectively. The choice of process depends on the availability and cost of the starting materials phthalodinitrile or phthalic anhydride. Although the phthalodinitrile process has certain advantages over the phthalic anhydride process, the latter is preferred worldwide because of the ready accessibility of phthalic anhydride. In this process the molar ratio of phthalic anhydride, urea, and cop-per(i) chloride is 4 16 1, with ammonium molybdate as catalyst. The mixture is heated in a high-boiling solvent such as trichlorobenzene, nitrobenzene, or kerosene. The solvent is removed after the formation of copper phthalocyanine. Fre-... 

Gibbs phthalic anhydride process. Oxidation of naphthalene to phthalic anhydride with air at 360C over vanadium pentoxide and other catalysts. 

Maleic Anhydride. The preparation of maleic anhydride from C4 hydrocarbons is given by Bretton (10). The preparation of maleic anhydride from benzene is described in Faith, Keyes, and Clark (31). Maleic anhydride is an important by-product in the phthalic anhydride process. 

In the German phthalic anhydride process naphthalene is passed over a vanadium pentoxide (on silica gel) catalyst at a temperature of about 350°C. Analysis of the available data indicates that the rate of reaction (pound moles of naphthalene reacted to phthalic anhydride per hour per pound of catalyst) can be represented empirically by the expression... 

Figure 57 shows a general layout for the phthalic anhydride process. Air compressed to 30 or 40 pounds per square inch gage is filtered and preheated, mid then passed through the naphthalene vaporizer. The naphthalene vaporizer consists of a steam-jacketed pot fitted with baffle plates, a distributor for admitting the necessary air, and an outlet for the naplitlialcne-air mixture. No attempt is made to saturate the air with naphthalene at the temperature of the saturator, but steady conditions are maintained and secondary air is admitted to the stream before it enters the... 

Reactor Effluent Phase Equilibrium for a Phthalic Anhydride Process Basis 100 Moles of Reactor Effluent... 

Since that time, sulfur-resistant catalysts have been developed. However, the importance of the fluidized-bed phthalic anhydride process is declining since the proportion of raw material costs is about 70% of total production costs, the feedstocks o-xylene and coal tar naphthalene can be more cost-effectively oxidized in fixed-bed reactors. 

Phthalic anhydride can be produced by reacting naphthalene and oxygen. The feed section to a phthalic anhydride process is shown in Figure 19.7. The mixed feed enters a fluidized bed reactor operating at 5 times the minimum fluidization velocity. A stream table is given in Table 19.2. It is assumed that all frictional pressure losses are associated with equipment and that frictional losses in the piping are negligible. It is temporarily necessary to scale down production by 50%. Your job is to determine how to scale down the process and to determine the new flows and pressures. 

Figure 19.7 Feed Section to Phthalic Anhydride Process...

Figure 19.8 Feed Section to Phthalic Anhydride Process with Better Valve Placement than Shown in Figure 19.7...

Consider the feed section of the phthalic anhydride process in Appendix C, Figure C.5. A single control valve is used to control die flow of the combined vaporized naphthalene and air streams, g Stream 7. In this process it is important to regulate both the flowrate of Stream 7 and the relative amounts of air and naphthalene in Stream 7. Does the current control scheme allow this type of regulation to occur If not, devise a control scheme that will allow both these variables to be controlled independently. 

Benzene oxidation using a vanadium pentoxide/pumice catalyst was first studied at the time that the phthalic anhydride process was being developed. Weiss and Downs discovered that maleic anhydride was formed in significant amounts. They concluded that the maleic anhydride was produced via benzoquinone as the intermediate. The yields of maleic anhydride were not high with the unselec-tive vanadium or molybdenum oxide catalysts being tested at that time. 

Henkel Rearrangement of Benzoic Acid and Phthalic Anhydride. Henkel technology is based on the conversion of benzenecarboxyhc acids to their potassium salts. The salts are rearranged in the presence of carbon dioxide and a catalyst such as cadmium or zinc oxide to form dipotassium terephthalate, which is converted to terephthahc acid (59—61). Henkel technology is obsolete and is no longer practiced, but it was once commercialized by Teijin Hercules Chemical Co. and Kawasaki Kasei Chemicals Ltd. Both processes foUowed a route starting with oxidation of napthalene to phthahc anhydride. In the Teijin process, the phthaHc anhydride was converted sequentially to monopotassium and then dipotassium o-phthalate by aqueous recycle of monopotassium and dipotassium terephthalate (62). The dipotassium o-phthalate was recovered and isomerized in carbon dioxide at a pressure of 1000—5000 kPa ( 10 50 atm) and at 350—450°C. The product dipotassium terephthalate was dissolved in water and recycled as noted above. Production of monopotassium o-phthalate released terephthahc acid, which was filtered, dried, and stored (63,64). 

Dihydroxyanthraquinone. This anthraquinone, also known as quinizarin [81-64-1] (29), is of great importance in manufacturing disperse, acid, and vat dyes. It is manufactured by condensation of phthalic anhydride (27) with 4-chlorophenol [106-48-9] (28) in oleum in the presence of boric acid or boron trifluoride (40,41). Improved processes for reducing waste acid have been reported (42), and yield is around 80% on the basis of 4-chlorophenol. 

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. 

It IS by a similar process that alizaiin has been synthesised w ith the oliject of ascertaining its constitution (see Notes on Prep. 110, p. 316), When two molecules of phenol and one molecule of phthalic anhydride are heated together with cone, sulphuric acid, then phenolphthalein is formed (Baeyei). Its constitution has been determined by its synthesis from phthalyl chloride and benzene by means of the Friedel-Crafts leaction (see Notes on Piep. 100, p. 309). Phthalyl chloride and benzene yield in presence of AlCl., phthalophenone. 

The activated carbonyl of anhydrides can acylate alcohols or amines at the temperatures necessary for polymer processing. These reactions have been verified by HPLC using the polymer system described in Table 2. An examination of the HPLC chromatograms in Fig. 25 indicates that the phthalic anhydride peak (3.2 min) diminishes with increasing injection-molding temperatures and that two new peaks (4.6 and 6.9 min) increase in intensity. These new peaks corresponded to the half phthalate esters of 1,6-hexanediol and trans-... 

Example 20.1 Consider again the process for the manufacture of phthalic anhydride discussed in Example 19.1. The data was extracted from the flowsheet in Figure 19.10 and listed in Table 19.1. The composite curves and grand composite curve are shown in Figure 19.11. 

This chapter contains a discussion of two intermediate level problems in chemical reactor design that indicate how the principles developed in previous chapters are applied in making preliminary design calculations for industrial scale units. The problems considered are the thermal cracking of propane in a tubular reactor and the production of phthalic anhydride in a fixed bed catalytic reactor. Space limitations preclude detailed case studies of these problems. In such studies one would systematically vary all relevant process parameters to arrive at an optimum reactor design. However, sufficient detail is provided within the illustrative problems to indicate the basic principles involved and to make it easy to extend the analysis to studies of other process variables. The conditions employed in these problems are not necessarily those used in current industrial practice, since the data are based on literature values that date back some years. 

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... 

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.)...

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