Witten process

Hercules (2) A modification of the Witten process for making dimethyl terephthalate. Further improvements have been made by Glitsch Technology. 

Witten A process for making dimethyl terephthalate by the concurrent oxidation and esterification of p-xylene. Similar to the Imhausen and Katzschmann processes. Developed by Chemische Werke Witten and subsequently operated by Dynamit Nobel in Germany. World production capacity for this process in 1993 was 3 million tonnes. 

Bv < B < BIV. Finally, as B falls below the value BIV, the Bodmer-Witten hypothesis starts to be fulfilled. Now the stable quark stars formed in the stellar conversion process are strange stars. 

An alternative route to DMT was introduced in 1953. This was based on air oxidation of y -xylene to /Moluic acid, which was esterified by methanol to form methyl /Moluate, which was oxidised by air to monomethyl terephthalate [40], which in turn was esterified by methanol to make DMT. The two oxidations could be combined so that p-xylene and methyl p-toluate were oxidised in the same vessel, and so could the two esterifications [41], The process was due to Katzschmann of Imhausen, a firm based at Witten and later known as Chemische Werke Witten. This process, known variously by its inventor s name and by various combinations of the names of the companies involved in its development, i.e. Hercules, Imhausen, Witten, and Dynamit Nobel, rapidly replaced the rather unsatisfactory and sometimes hazardous nitric acid oxidation route to DMT. 

Atlanta, Ga., 26th-30th April 1998, p. 1842-9. 012 PRODUCT AND PROCESS DEVELOPMENTS IN THE NITROGEN AUTOCLAVE PROCESS FOR POLYOLEFIN FOAM MANUFACTURE Eaves D E Witten N Zotefoams pic (SPE)... 

Several other methods were developed for producing the desired dimethyl terephthalate. The Witten (Hercules) process goes from p-xylene to toluic acid by oxidation of one of the methyl groups on the ring, following which the carboxyl group is esterified with... 

Originally developed by the Chemische Werke Witten GmbH in the early 1950s, the large-scale production of dimethyl terephthalate (DMT) marks the start of industrial air oxidation of alkyl aromatic substrates to tbe corresponding acids [3]. However, the technical and chemical improvement of the Witten process is still a topic of current research activity [3g-l]. 

The Witten process, which is also known as the Imhausen or Katzschmann process [3a-f], involves the oxidation of p-xylene to p-toluic acid as a reaction intermediate. For activity reasons, the p-toluic acid is esterified with methanol to methyl toluate, which is then oxidized to monomethyl terephthalate. The two oxidation reactions take place simultaneously in one oxidation system likewise... 

The first commercial processes for the production of DMT made use of nitric acid oxidation of p-xylene to crude terephthalic acid, followed by esterification with methanol and purification by distillation [3]. Air oxidation of p-xylene displaced the use of nitric acid with the development of the Witten process [5]. In the Witten process, p-xylene is air-oxidized at 140-180 °C and 0.5-2 MPa over a homogeneous cobalt or cobalt/manganese catalyst system to give p-toluic acid, which is then esterified to methyl p-toluate, oxidized again over the cobalt/manganese catalyst, and finally esterified to DMT (see Scheme 1). The four process steps are accomplished in two reactors (see Figure 1). The Witten process uses no solvent. 

The kinetics of the Witten oxidation process are complicated by the presence of several possible radical chain carrying steps and termination steps.A full treatment of these kinetics has not been published. What is known about the kinetics is that the initial oxidation of p-xylene to p-toluie acid is inversely proportional to [Co ], an induction period generally attributed to the oxidation of Co to Co is observed, the rate of conversion of p-xylene to p-toluic acid is faster than that of methyl p-toluate to monomethyl terephthalate, and the rate of the first oxidation step (and not the second) can be greatly increased by the addition of radical sources, such as acetaldehyde or paraldehyde. 

Both oxidation steps are reported to yield 95 % of the desired product, resulting in an overall yield of approximately 90 % from p-xylene to DMT. The major side product of the Witten process is methyl benzoate (from decarboxylation of intermediates) with radical coupling products accounting for heavy ends from production. 

The air oxidation of p-xylene to TEA appears on the surface to be similar to the Witten process in that it uses a homogeneously dissolved cobalt/manganese catalyst system. The TEA process, originally referred to as the Mid-Century (cf. [9], [10]) and now as the Amoco process, is actually quite different from the Witten process described above. The Amoco process uses acetic acid as a solvent for the oxidation reactions and bromine as a free- radical source, proceeds to TEA from p-xylene in one step, operates at 175-230 °C/l-2 MEa, obtains overall yields of approximately 95 %, and of course does not involve an esterification step [9-12]. 

The roles of manganese in TPA manufacture are better understood than in the Witten process, and include decomposition of the CH2COOH radical (derived from the acetic acid solvent) and regeneration of the bromine atom promoter [13], In an effort to eliminate halogen compounds which are highly corrosive to oxidation equipment, use of acetaldehyde [14] and paraldehyde [15] has been developed. These aldehyde promoters are ultimately converted to acetic acid in high yield. For economic reasons, these aldehyde processes have been abandoned in favor of the bromine-promoted Amoco process. 

Also under development is use of the alternative feedstock, toluene, for PTA and/or DMT production. Carbonylation of toluene to produce p-tolualdehyde was shown to proceed in 90-95% yield when catalyzed by HF BF3 [31], or by higher perfluoroalkyl sulfonic acids [32], or in greater than 99% yield when catalyzed by trifloromethanesulfonic acid [33]. The p-tolualdehyde, which is regularly an intermediate in both the Witten DMT and Amoco TPA processes (see Schemes 2 and 3, respectively), can then be readily oxidized with minimal changes to the oxidation process. 

Heinicke, 1C, Novel developments of the Witten DMT process", ACS 164th National Meeting, New York (27 August/ Sept. 1972V... 

WITTEN, T.A. CATES, M.E. 1986. Tenuous structures from disorderly growth processes. Science 232, 1607—1612. 

We discuss below the DLA model in detail which was proposed by Witten and Sander [16, 18]. The DLA is a particular model of a random irreversible growth. The growth process starts from a seed particle. A second particle is launched far enough from the seed and makes a random walk. If it visits a position next to the seed, it is stuck to it and both form a two-particle cluster extending the initial seed. Then a third particle is launched and moves randomly around this cluster. It may join the two-particle... 

The major alternative, still very important in Europe, is the Hercules-Witten process p-xylene is oxidized without a solvent to p-toluic (4-methylbenzoic) acid, which is esterified before further oxidation ... 

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