Problems phthalic anhydride production

You have recendy joined the TBWS Chemical Corporatiom One of TBWS s major businesses has always been production of phthalic anhydride from naphthalene. Phthalic anhydride production is integrated as part of a large chemical plant, in which naphthalene is produced and in which phthalic anhydride is immediately used to make polyester resins. In recent years, there have been some problems. Some end users have complained about the quality of the resins produced and have taken their business to other companies that produce phthalic anhydride from o-xylene. Therefore, our plant, which had been designed to produce 100,000 metric tons/year of phthalic anhydride from naphthalene, was scaled back to about 80,000 metric tons/year several years ago. We are now forced to scale down production once again due to the loss of another large customer. Marketing informs us that we may lose additional customers. 

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. 

Succinic anhydride is clearly hydrogenated more readily than the acid, as was the case with phthalic acid (Scheme 15.17), but faster absolute rates were observed in the hydrogenation of o-phthalic acid and phthalic anhydride to phtha-lide. In these reactions, the problem of anhydride hydrolysis is less significant as the acid can also be reduced to the same lactone product... 

The selective oxidation of hydrocarbons with dioxygen is of immense industrial importance [ 1 ]. A general problem in this area is to obtain high selectivi-ties, particularly at high substrate conversions. The reasons for this are twofold oxidation can occur at different C-H bonds in a molecule, leading to a low primary selectivity, and the initially formed product is often more reactive than the substrate and is oxidized further, ultimately to carbon dioxide and water, leading to low secondary selectivities. Hence examples of industrial processes tend to involve the oxidation of hydrocarbons in which one particular C-H bond is significantly more reactive, for example, cumene hydroperoxide from cumene, and/or the product is relatively stable towards further oxidation, for example, maleic anhydride from n-butane, phthalic anhydride from o-xylene... 

Problem 21.15 What product would you expect from reaction of 1 equivalent of methanol with a cyclic anhydride, such as phthalic anhydride (1,2-benzenedicarboxylic anhydride) What is the fate of the second half of the anhydride in this case ... 

The production of chilled water in the fine chemical manufacture and food processing industries may also give rise to freezing fouling where ice is formed on the cold surface. The problem may also exist in vapour systems during the recovery of solid products, e.g. the production of phthalic anhydride crystals in so-called "switch condensers". 

This reaction model is fairly representative of the gas phase air oxidation of o-xylene into phthalic anhydride on VjOj catalysts. A represents o-xylene, B phthalic anhydride, and C the final oxidation products CO and COj, lumped together. The process conditions were already described in Sec. 11.5.b. The purpose of this example is mainly to check whether or not serious radial temperature gradients occur in such a reactor. For a better approximation of reality a reaction model is chosen that is closer to the true model than the one used in Sec. ll.S.b. In addition, it illustrates a yield problem, such as is often encountered in industrial practice. 

Many of the homochiral AB synthons described above have been utilised in syntheses of anthracyclinones which are based on Friedel-Crafts cyclisations. As was noted earlier such reactions often require vigorous conditions, and there is some controversy concerning the enantiomeric purity of the products so obtained. While some groups claim that condensation of the hydroxy ketone 174 with phthalic anhydride in an intimate mixture of sodium chloride and aluminium chloride yields optically pure ( —)-4-demethoxy-7-deoxydauno-mycinone [16, 141] others report a considerable degree of racemisation under virtually identical conditions [135, 142], although the problem may be avoided under the somewhat milder conditions employed in a recent condensation of 174 with phthaloyl dichloride [143]. In contrast, stereochemical integrity of the product is assured under the mild conditions employed in Swenton s carbanion based synthesis of (4-)-daunomycinone 5 [53] and in our Diels-Alder based... 

Prices are also affected by available production capacity, recent plant outages etc. Surplus production capacity has been available in the recent past for several additives and for intermediates such as phthalic anhydride and epichlorohydrin. At the end of 2002, the two main US producers of sebacic acid, which is a precursor of specialised aliphatic plasticisers, both withdrew from the market in the face of competition from cheap Chinese imports, although another company entered the field instead. Melamine prices have reached 1300 euros/tonne in Europe, although they are lower in Asia. Capacity has fluctuated because of plant problems but considerable new capacity is being developed. 

The terephthalate plasticizer DEHTP, first commercialized around 1975 as Eastman DOTP, is very similar in structure to DEHP except that the substitution of the aromatic ring is at the 1,4 position versus the 1,2 position of the aromatic ring. The structure of DEHTP is also shown in Pig. 24.1. Terephthalates are prepared by the esterification of terephthaUc acid or by the transesterification of dimethyl terephthalate with aliphatic alcohols such as butanol or 2-ethyl hexanol. Although DEHTP can be produced from terephthalic acid in a traditional DEHP esterification plant with minor modifications to the process, this process is not as efficient as the esterification of phthalic anhydride and manufacturing capacity reductions of >50% are realized. Transesterification of dimethyl terephthalate is a much faster reaction. However, this process will require significant process modifications to a traditional DEHP manufacturing unit. One benefit with this chemistry is that it does not lead to a significant drop in production capacity. The main problem with this route is the limited availability of dimethyl terephthalate in many locations. 

The case study used to illustrate the concepts behind the strategy presented consist of a SC design problem that compares different technologies for the production of maleic anhydride (MA). MA is an important raw material used in the manufacture ofresins of phthalic-type and unsaturated polyester, co-polymers, surface coatings, plasticizers and lubricant additives (USEPA 1980). Two main technologies are available for its manufacturing by the catalytic oxidation of different hydrocarbons, benzene or butane (Chen and Shonnard 2004). Main process reactions are as follows ... 

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