Oxidation p-xylene

Another approach is to use an easily oxidized substance such as acetaldehyde or methylethyl ketone, which, under the reaction conditions, forms a hydroperoxide. These will accelerate the oxidation of the second methyl group. The DMT process encompasses four major processing steps oxidation, esterification, distillation, and crystallization. Figure 10-16 shows a typical p-xylene oxidation process to produce terephthalic acid or dimethyl terephthalate. The main use of TPA and DMT is to produce polyesters for synthetic fiber and film. 

In Figure 3 the merits of the two processes for p-xylene oxidation are compared. The main disadvantages of the Eastman Kodak/Toray cooxidation method are the need for a cosubstrate (acetaldehyde of methylethylketone) with concomitant formation of a coproduct (0.21 ton of acetic acid per ton product) and high catalyst concentration. The Amoco MC process, on the other hand, has no coproduct and much lower catalyst concentrations but has the disadvantage that the bromide-containing reaction mixture is highly corrosive, necessitating the use of a titanium-lined reactor. 

Terephthalic acid (p-TA or TA), a raw material for polyethylene terephthalate (PET) production, is one of the most important chemicals in petrochemical industry. Crude terephthalic acid (CTA), commonly produced by homogeneous liquid phase p-xylene oxidation, contains impurities such as 4-carboxybenzaldehyde (4-CBA, 2000-5000 ppm) and several colored polyaromatics that should be removed to obtain purified terephthalic acid (PTA). PTA is manufactured by hydropurification of CTA over carbon supported palladium catalyst (Pd/C) in current industry [1]. 

The kinetics of the p-xylene oxidation over tin vanadate was studied by Mathur and Viswanath [206], A differential reactor was used at 320— 380°C. p-Tolualdehyde, maleic anhydride and p-toluic acid are the main... 

We have not been able to unscramble the complex kinetics of p-xylene oxidation. Ravens studied the second stage of oxidation, that of p-toluic acid in acetic acid with cobalt and manganese acetates and sodium bromide (25), and established the rate equation... 

The discovery of poly(ethylene terephthalate), PET, in the 1940s [1,2] and its commercialization initially by DuPont and by ICI in the 1950s created a large market demand for terephthalic acid and terephthalate esters of polymer purity. Because dimethyl terephthalate, DMT, is readily purified by distillation [3] (and also because the p-xylene oxidation/esteiification intermediate, methyl p-toluate, is more readily kept in solution than is p-toluic acid) the polyester fibers and films industry was initially based on terephthalate ester. With the development of improved oxidation and purification technologies, purified terephthalic acid, TPA, became available in commercial quantities by the mid 1960s. Over 75% of the worldwide PET manufacture (total world PET capacity is over six million tons/year) is currently based on TPA rather than DMT [4]. This preference for TPA results from the less complicated esterification catalysis and the absence of methanol handling when the acid is used directly. 

The technology described by Asahi is very similar to that used for the synthesis of terephthalic acid by p-xylene oxidation. The selectivity of AA and the total selectivity of dicarboxylic acids are still lower than those in the nitric acid process [13o]. 

With molybdenum in desulfurization catalysts Catalyst for the oxo process, p-xylene oxidation, and... 

A liquid phase process, similar to the Amoco p-xylene oxidation process, has been employed by Rhone-Poulenc since 1939 in its Chauny plant Tins technique was subsequently replaced by a so-called low-energy consumption process operating in a fixed bed. in the vapor phase. The 19,000 t/year plant built in 1972 was supplemented by the 45,000 t/year unit installed in 1975. 

In another example, air is added as a source of oxygen to the expansion vessel at 150 °C to oxidize 4-carboxy benzaldehyde (a coproduct of p-xylene oxidation ) to terephthalic acid. Again, no quantitative information is given about rates of reaction, conversion, purity, etc. Still other examples relate that water at 327 °C and 200 atm (subcritical not supercritical) either with or without oxygen results in the extraction and production of purified terephthalic acid. 

Jin, H., Yang, S., He, G., Guo, Z., and Tong, Z. (2005), An experimental study of holdups in large-scale p-xylene oxidation reactors using the y-ray attenuation approach, Chemical Engineering Science, 60 5955-5961. 

Terephthalic acid (p-xylene oxidation with atmospheric oxygen) [12]. 

Reactor Selection for the Amoco-MC Process Majority of liquid-phase oxidations use relatively high pressure (>0.5 MPa). Oxidations are characterized by a substantial heat of reaction that must be removed to prevent side reactions. Therefore, the reactor selected should have good heat transfer characteristics. In the present case of p-xylene oxidation using the Amoco-MC process, the heat of reaction is generally removed by evaporation of the solvent. The solvent vapor is condensed and returned to the reactor. The enthalpy of condensation of the solvent is used to raise high-pressure steam for use elsewhere in the plant The tanperature-pressure condition is auto-related by the refluxing media. 

Hronec M, Ilavsky J. (1982) Oxidation of polyaUtylaromatic hydrocarbons. 12. Technological aspects of p-xylene oxidation to terephthahc acid in water. Ind. Eng. Chem. Prod. Res. Dev., 21 455 60. 

Jacobi R, Baems M. (1983) The effect of oxygen transfer limitation at the gas-liquid interphase. Kinetics and product distribution of the p-xylene oxidation. Erdbl Kohle Erdgas Petrochemie, 36 322-326. 

Litz LM. (1985, Nov) A novel gas-liquid stirred reactor. Chem. Eng. Prog., 81(ll) 36-39. Malpani V, Ganeshpure PA, Munshi P. (2011) Determination of solubility parameters for the p-xylene oxidation products. Ind. Eng. Chem. Res., 50 2467-2472. 

Tomas RAF, Bordado ICM, Gomes IFP. (2013) p-Xylene oxidation to terephthalic acid a literature review oriented toward process optimization and development Chem. Rev., 113 7421-7469. 

Before the introduction of p-xylene oxidation on a large scale, the production of terephthalic acid by the Henkel rearrangement from benzoic acid and phthalic acid (see Chapter 7.3.1), at 400 to 420 °C and 10 bar, was of considerable industrial importance, especially in Japan. 

Owing to the importance of terephthalic acid as a large tonnage dicarboxylic acid, there has been no shortage of attempts to find alternative processes to p-xylene oxidation. 

Neither alternative process has yet been able to replace p-xylene oxidation. 

Figure 1 shows a comparison between computer code results and experimental data [8] in the case of p-xylene oxidation, where the reaction is considered of zero-th order with respect... 

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