Ethanal, oxidation to acetic acid

Figure 11.3. Block flow diagram for the SABIC process of direct ethane oxidation to acetic acid.

Karim, K., Al-Hazmi, M. and Mamedov, E. (2000). Catalysts for the Oxidation of Ethane to Acetic Acid, Processes of Making Same and Processes of Using Same, US Patent 6,013,597. Karim, K., Mamedov, E., Al-Hazmi, M., et al. (2000). Catalysts for Producing Acetic Acid from Ethane Oxidation, Processes of Making Same and Methods of Using Same, US Patent 6,030,920. Roussel, M., Barama, S., Karim, K., et al. (2009). MoV-based Catalysts in Ethane Oxidation to Acetic Acid Influence of Additives on Redox Chemistry, Catal. Today, 141, pp. 288-293. Fierro, J., Karim, K. and Mamedov, E. (1997). Unpubhshed data. 

Roussel, M., Barama, S., Lofberg, A., et al. (2009). MoV-Based Catalysts in Ethane Oxidation to Acetic Acid Influence of Additives on Redox Chemistry, Catal. Today, 141, pp. 288-293. 

The paper overviews research carried out at SABIC Company in the last 15-20 years in the field of selective oxidation. Using different approaches, a number of effective catalysts were developed by proposing new or improving existing catalytic systems. On some of them reaction network and kinetics were studied that in combination with reaction engineering allowed elaborate process technology. The most advanced development is ethane direct oxidation to acetic acid which was commercialized at one of the SABIC plants. 

Interest in ethane selective oxidation to acetic acid has been rising in the last few years due to the low cost of ethane which is now easily available from the large sources of namral gas which have recently been discovered. Although different catalytic systems have been proposed, Pd-doped MoVNbO mixed oxides are one of the more promising catalysts. " ... 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

A prototype study for this issue was performed for the conversion of ethane to acetic acid [71] and the same group highlighted in an earlier comparative study of C3 oxidation [54] that, although initial propane activation is a difficult step, subsequent reactions associated with either excessive residence times of intermediates or with branching of reaction sequences into total oxidation may interfere with the overall selectivity to partial oxidation products. 

The synthesis of intermediates and monomers from alkanes by means of oxidative processes, in part replacing alkenes and aromatics as the traditional building blocks for the chemical industry [2]. Besides the well-known oxidation of n-butane to maleic anhydride, examples of processes implemented at the industrial level are (i) the direct oxidation of ethane to acetic acid, developed by Sabic (ii) the ammoxidation of propane to acrylonitrile, developed by INEOS (former BP) and by Mitsubishi, and recently announced by Asahi to soon become commercial (iii) the partial oxidation of methane to syngas (a demonstration unit is being built by ENI). Many other reactions are currently being investigated, for example, (i) the... 

Figure 9.1 Mechanism proposed in the literature for the oxidation of ethane to acetic acid [2b],...

Table 9.1 summarizes catalyst compositions and corresponding performances. The oxidation of ethane to acetic acid is now commercial an industrial plant is installed, with the technology developed by Saudi Basic. Elements that have contributed to the successful development of the process are (1) the discovery of a catalytically active compound, the multifunctional properties of which can be modified and tuned to be adapted to reaction conditions through incorporation of various elements (2) the stability of the main products, ethylene and acetic acid, which do not undergo extensive consecutive degradation reactions (3) the possibility of recycling the unconverted reactant and the major by-product, ethylene (4) the use of reaction conditions that minimize the formation of CO and (5) an acceptable overall process yield. 

Although the direct oxidation of ethane to acetic acid is of increasing interest as an alternative route to acetic acid synthesis because of low-cost feedstock, this process has not been commercialized because state-of-the-art catalyst systems do not have sufficient activity and/or selectivity to acetic acid. A two-week high-throughput scoping effort (primary screening only) was run on this chemistry. The workflow for this effort consisted of a wafer-based automated evaporative synthesis station and parallel microfluidic reactor primary screen. If this were to be continued further, secondary scale hardware, an evaporative synthesis workflow as described above and a 48-channel fixed-bed reactor for screening, would be used. 

Micro structured wells (2 mm x 2 mm x 0.2 mm) on the catalyst quartz wafer were manufactured by sandblasting with alumina powder through steel masks [7]. Each well was filled with mg catalyst. This 16 x 16 array of micro reactors was supplied with reagents by a micro fabricated gas distribution wafer, which also acted as a pressure restriction. The products were trapped on an absorbent plate by chemical reaction, condensation or absorption. The absorbent array was removed from the reactor and sprayed with dye solution to obtain a color reaction, which was then used for the detection of active catalysts by a CCD camera. Alternatively, the analysis was also carried out with a scanning mass spectrometer. The above-described reactor configuration was used for the primary screening of the oxidative dehydrogenation of ethane to ethylene, the selective oxidation of ethane to acetic acid, and the selective ammonoxidation of propane to acrylonitrile. 

Volpe, A. F., Weinberg, W. H., Woo, L., Zysk, J., Combinatorial heterogeneous catalysis oxidative dehydrogenation of ethane to ethylene, selective oxidation of ethane to acetic acid, and selective ammonoxidation of propane to acrylonitrile, Top. Catal. 2003, 23, 65-79. 

The direct synthesis of chemicals from alkanes is an attractive alternative to that via olefins. Alkanes are abundant and cheaper, while the elimination of the dehydrogenation unit allows simplified process designs and energy savings. Oxidations of several alkanes are of industrial interest and are being investigated (Table 3) at the most advanced stage are those of ethane to acetic acid and of propane to acrylonitrile. 

The oxidation of ethane to acetic acid is believed to proceed via the intermediate formation of ethylene (Equation Al). The catalysts are multicomponent mixed oxides, having optimized compositions for ethane oxydehydro-genation (Mo-V oxides) and ethylene oxidation (Pd, Nb oxide). Reported... 

Vanadyl pyrophosphate is widely considered to play an important catalytic role in the oxidation of -butane to MA, specifically the (100) face (Figure 18b), which is retained from the topotactic transformation (6,43,84—86) of the catalyst precursor phase (Figure 18a). Furthermore, this active phase has been reported to be an efficient catalyst for the oxyfimctionalization of light paraffins (a) for the oxidation of ethane to acetic acid (3,87), (b) for the oxidation and ammoxidation of propane to acrylic acid (88) and acrylonitrile (89,90), respectively, and (c) for the oxidation of n-pentane to maleic and phthalic anhydrides (90-102). 

Active and selective in propane oxidation to acrylic acid propane ammoxid. to acrylonitrile ethane oxidation to ethylene/acetic acid... 

As already mentioned before, mainly irreversible reactions with organic compounds have been investigated at semiconductor particles. When organic molecules, for example alcohols, are oxidized by hole transfer, O2 usually acts as an electron acceptor or in the case of platinized particles, protons or H2O are reduced. A whole sequence of reaction steps can occur, which are frequently difficult to analyze because cross-reactions may also be possible at particles and a new product could be formed. Concerning the primary electron and hole transfer, certainly there should be no difference between particles and compact electrodes. Since sites at which reduction and oxidation occur are adjacent at a particle, the final product may be different. An interesting example is the photo-Kolbe reaction, studied for Ti02 electrodes and for Pt-loaded particles. Ethane at extended electrodes and methane at Pt/Ti02 particles have been found as reaction products upon photo-oxidation of acetic acid [56, 57]. The mechanism was explained by Kraeutler et al. as follows. 

Recently we found that highly redueed H3PMol2O40 which was formed by the heat-treatment of pyridinium salt can catalyze the propane oxidation to acrylic acid and acetic acid selectively [24, 25]. After activation in N2 flow at 420°C for 2hr, the catalyst of HsPMo 12040 (Py) shows reduced state of molybdenum and a new stable structure in which pyridine remains as the linkage of the secondary structure. The activated H3PMoi2O40 (Py) also gives catalytic activities in the partial oxidations of ethane and isobutane to acetic acid and methacrylic acid respectively. In this paper, we will report the oxidation results of C2-C4 alkanes and discuss the roles of reduced state and aetivation of molecular oxygen over this catalyst. 

We examined the ethane oxidation over the mentioned catalysts under different reaction conditions at 280°C-360 C. About 1% conversion of ethane and 10% selectivity to acetic acid were obtained over the activated H3PMoi2O40(Py) at 340 C. Ethane oxidation did not occur over non-reduced H3PMol2O40 and activated (NH4)3PMol2O40catalysts. 

There seems to be no literature about the direct oxidation of ethane to acetic acid over heteropolycompounds catalysts. Nevertheless, there is a limited amount of literature[10,26-28] about direct oxidation of ethane to acetic acid over oxide catalysts at low temperature (200-350 C). It seems that vanadium and molybdenum are necessary to those catalysts, and the addition of water is useful to increase the production of acetic acid. Roy et al. [10] has proved that vanadium and molybdenum phosphates supported on Ti02-anatase were effective in the direct oxidation of ethane to acetic acid. Considering previous research results, it is suggested that other promoters, such as trcmsition-metal oxides, are necessary to enhance the catalytic activity of the activated H3PMol2O40(Py) in the direct oxidation of ethane to acetic acid. 

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