Acetic acid methacrolein

The reaction network for isobutane selective oxidation catalyzed by POMs consists of parallel reactions for the formation of methacrolein, methacrylic acid, carbon monoxide, and carbon dioxide. Consecutive reactions occur on methacrolein, which is transformed to acetic acid, methacrylic acid, and carbon oxides. ° Methacrylic acid undergoes consecutive reactions of combustion to carbon oxides and acetic acid, but only under conditions of high isobutane conversion. Isobutene is believed to be an intermediate of isobutane transformation to methacrylic acid, but it can be isolated as a reaction product only for very low alkane conversion. ... 

Figure 14.5 Catal)Tic performance of (NH4)3PMoi2O40 prepared by precipitation at pH < 1 as a function of time-on-stream. T 380°C, t 3.6 s feed composition 26% isobutane, 13% O2, 12% H2O, remainder He. Symbols Isobutane conversion ( ), sel. to methacrylic acid ( ), to methacrolein (A), to acetic acid (x), to carbon monoxide ( ), and to carbon dioxide ( ).

Applications of POMs to catalysis have been periodically reviewed [33 0]. Several industrial processes were developed and commercialized, mainly in Japan. Examples include liquid-phase hydration ofpropene to isopropanol in 1972, vapor-phase oxidation of methacrolein to methacrylic acid in 1982, liquid-phase hydration of isobutene for its separation from butane-butene fractions in 1984, biphasic polymerization of THE to polymeric diol in 1985 and hydration of -butene to 2-butanol in 1989. In 1997 direct oxidation of ethylene to acetic acid was industrialized by Showa Denko and in 2001 production of ethyl acetate by BP Amoco. 

Multitubular reactors are mainly used in gas-phase partial oxidation processes, such as the air oxidation of light olefins, paraffins, and aromatics. Examples of chemistries where these reactors are used include the partial oxidation of methanol to formaldehyde, ethylene to ethylene oxide, ethylene and acetic acid to vinyl acetate, propylene to acrolein and acrylic acid, butane to maleic anhydride, isobutylene to methacrolein and methacrylic acid, and o-xylene to phthalic anhydride. An overview of the multitubular reactor process for the partial oxidation of n-butane to maleic anhydride is given here. 

In recent years heteropolycompounds have been studied for the oxidation of propane to acrylic acid and of isobutane to methacrylie aeid. Rohm Haas Company was the first in 1981 to claim the one-step oxidation of isobutane to methacrolein and methacrylie acid (55). Even though no reference is made to heteropolycompounds, the claimed catalyst compositions correspond to Keggin-type structures. In the patents later issued by Sumitomo (56,57) an important role was claimed to be played by vanadium (in an anionic position), by cesium (in a cationic position), as well as by an excess of phosphorus with respect to the stoichiometric composition. These catalysts gave selectivities to methacrylie acid plus methacrolein close to 70 %, with isobutane conversions in the 10 to 13 % range. Besides carbon oxides, acetic acid was the main by-product. 

The results for CsxH3xPMoi2O40 catalysts are shown in Table 2 [13]. The highest conversion was observed around x = 2.5 - 2.85. The main products were methacrylic acid (MAA), methacrolein (MAL) and acetic acid (AcOH). The substitution of Cs for H in H3PM012O40 resulted in a great enhancement of the MAA production and the yield reached a maximum at x = 2.5. The sum of the yields of MAA and MAL on Cs2 5H0 5PM012O40 reached 5.1%. 

The effects of contact time on the isobutane oxidation over the H3PMol2O40(Py) catalyst are again shown in Figure 6. With the increase of the contact time, the conversion of isobutane increases greatly, and the selectivity of methacrolein decreases markedly to disappear. The change of the selectivity to methacrylic acid exhibits a mountain shape, and the selectivities to acetic acid and acrylic acid still increased slightly after the top of the mountain. It is, therefore, clear that methacrolein is the intermediate to form methacrylic acid. 

Figure 1 compares the conversion of isobutane and the selectivity to the different reaction products (methacrolein, methacrylic acid, acetic acid, carbon monoxide and carbon dioxide) for an equilibrated catalyst (one that has reached a steady catalytic performance), under different reaction conditions isobutane-lean and isobutane-rich. The catalyst was prepared by precipitation of the precursor of composition (NH4)3PMoi204q at strongly acid pH (< 1), followed by thermal treatment at 350°C. 

Figure 1. Comparison of the catalytic performance of an equilibrated (NH4)3PMoi204o catalyst under isobutane-lean (T 350°C) and isobutane-rich (T 352°C) conditions. MAA methacrylic acid MAC methacrolein AcAc acetic acid.

The effect of residence time on isobutane conversion and on selectivity to the various products at the temperature of 320°C, under isobutane-rich conditions, is illustrated in Figure 3. The data indicate that methacrolein, methacrylic acid, and carbon dioxide are all formed through direct, parallel reactions acetic acid and possibly carbon monoxide are instead formed through consecutive reactions. Methacrolein undergoes consecutive reactions of transformation to acetic acid, to carbon oxides and possibly in part also to methaciylic acid. Indeed the selectivity to the latter product seems to increase slightly with increasing isobutane conversion. 

The effect of the residence time on the catalytic performance under isobutane-rich conditions for the Sb-doped compound is shown in Figure 6. The initial selectivity to methacrylic acid is higher than for the undoped POM, but it decreases for increasing values of residence time. The decrease in selectivity corresponds to an increase in carbon dioxide and carbon monoxide. The selectivity to methacrolein is lower than that obtained for the undoped POM. It is significant that the sum of methacrolein plus methacrylic acid is approximately the same with the two catalysts. This means that under these conditions the effect induced by the presence of Sb mainly concerns the ratio between the two parallel reactions of transformation of isobutane to methacrolein and to methacrylic acid. With this catalyst, too, acetic acid and carbon monoxide are secondary products, obtained by consecutive reactions. 

Methyl Methcrylate from Propionaldehyde. Propionaldehyde is produced by the oxo reaction of syngas with ethylene. Reaction of propionaldehyde with formaldehyde and dimethylamine in acetic acid form a Man-nich base salt that can be thermally cracked to methacrolein. Methacrolein can be oxidized to methacrylic acid which is then converted to methyl methacrylate by esterification with methanol. The chemistry is illustrated in Eqs. (31)-(34) ... 

The reaction of propionaldehyde, formaldehyde, and dimethylamine takes place in acetic acid solvent in the liquid phase at 160 C (320°F) and 40-80 bars (590-1180 psig). Both reactions, formation of the Mannich base salt and cracking to methacrolein, occur in the same reactor. The selectivity of the aldehydes to methacrolein is 98.7%. The yield of propionaldehyde to methacrolein is 98.1% and the overall yield of methyl methacrylate is nearly 90% [23,24]. 

FIG U RE 8.4 Pyrograms of vinyl acetate, acrylic, aUcyd enamel, epoxy, and chlorinated rubber type architectnral paints. 1 = benzene, 2 = isooctene, 3 = acetic acid, 4 = 2-ethylhexyl acrylate, 5 = 2,2,4-trimethyl 1,3-pentanediol mono-isobutyrate, 6 = methyl methacrylate, 7 = butyl methacrylate, 8 = acrolein, 9 = methacrolein, 10 = hexanal, 11 = phthaUc anhydride, 12 = phenol, 13 = isopropenylphenol, 14 = bisphenol A, 15 = xylenes, 16 = trimethylbenzenes. 

Inoue, Kida and Imoto [252] found that the oxidation of unsaturated aldehydes such as cinnamaldehyde and acrolein proceeded much more slowly than did oxidation of the saturated substrates in the presence of copper-iron-polyphthalocyanine. As in the case of the saturated acids the products were a mixture of the peracid and the corresponding carboxylic acid. Other groups have recently investigated the oxidation of unsaturated aldehydes in the presence of metal complexes [253-260]. Methacrylic acid and acetic acid were formed in the copper naphthenate catalyzed oxidation of methacrolein [255]. The oxidation of acrolein to acrylic acid was catalyzed by Co, Ni, Mn and Cu acetates [256]. It was found that at concentrations of acrolein in... 

Figure 24.1. Number of publications in the last two decades (1989-2009) focused on oxidative dehydrogenation (ODH) of short chain alkanes and partial oxidation products (considering acetic acid, acrylic acid, methacrolein/methacrylic acid, maleic anhydride).

Gierczak et al. (1997) observed methane, ethylene, acetylene, allene, and propyne as major products formaldehyde, methanol, formic acid, acetic acid, and hydrox-yacetone were identihed as minor products. The mechanism of formation of these products is unclear. Two expected products, observed by Raber and Moortgat (1996), propene and dimethylketene, were not observed, and CO and CO2 products observed by Raber and Moortgat, were not measured by Gierczak et al. (1997). In argon matrix-isolated studies of methacrolein photochemistry (4.2 K) and with A, >300 nm, Johnstone and Sodeau (1992) observed the isomerization of the original trans-methacrolein to di-methacrolein no HCO, CO, or propene could be detected. In similar matrix experiments at A >230 nm, dimethylketene, CO, and propene were observed together with other unidentified products. 

Unsaturated aldehydes undergo a similar reaction in the presence of strongly acid ion-exchange resins to produce alkenyUdene diacetates. Thus acrolein [107-02-8] or methacrolein [78-85-3] react with equimolar amounts of anhydride at —10°C to give high yields of the -diacetates from acetic anhydride, useful for soap fragrances. 

DIHYDROFURAN DIVINYL ETHER METHACROLEIN 2-BUTYNE-1,4-DIOL ganna-BUTYROLACTONE cis-CROTONIC ACID trans-CROTONIC ACID METHACRYLIC ACID METHYL ACRYLATE VINYL ACETATE ACETIC ANHYDRIDE SUCCINIC ACID DIGLYCOLIC ACID MALIC ACID TARTARIC ACID n-BUTYRONITRILE ISOBUTYRONITRILE ACETONE CYANOHYDRIN... 

A very useful three-carbon olefin is acrolein dimethyl acetal (5). Acrolein itself cannot be used because it polymerizes and/or reacts with amines under the normal reaction conditions. With piperidine or morpholine as the base, acrolein acetals react in good yield with a wide variety of vinylic bromides to give dienal acetals and/or ami-noenal acetals. These product mixtures, after being treated with excess aqueous oxalic acid and being steam distilled, yield E,E-conjugated dienals, usually in good yields. Methacrolein acetals and 3-buten-2-one ethylene ketal also react well, but the crotonaldehyde acetals do not. 

The oxidation of methacrolein catalyzed by cobalt, added in the form of cobaltic acetate, usually produces methacrylic acid, but the reaction may be catalyzed by various transition metals [35] (Table 6). The kinetic study of the oxidation catalyzed by cobalt at concentrations of between 5 X 10-3 and 40 X 10"3 mole l 1 with aldehyde concentrations of 0.5 < [RCHO] < 4 mole l-1 shows that the rate of oxidation is independent of... 

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