Air oxidation of propylene

Oxidation of a glycol can lead to a variety of products. Periodic acid quantitatively cleaves 1,2-glycols to aldehydes and is used as an analysis method for glycols (12,13). The oxidation of propylene glycol over Pd/C modified with Pb, Bi, or Te forms a mixture of lactic acid, hydroxyacetone, and pymvic acid (14). Air oxidation of propylene glycol using an electrolytic crystalline silver catalyst yields pymvic aldehyde. 

Acrolein and Acrylic Acid. Acrolein and acrylic acid are manufactured by the direct catalytic air oxidation of propylene. In a related process called ammoxida-tion, heterogeneous oxidation of propylene by oxygen in the presence of ammonia yields acrylonitrile (see Section 9.5.3). Similar catalysts based mainly on metal oxides of Mo and Sb are used in all three transformations. A wide array of single-phase systems such as bismuth molybdate or uranyl antimonate and multicomponent catalysts, such as iron oxide-antimony oxide or bismuth oxide-molybdenum oxide with other metal ions (Ce, Co, Ni), may be employed.939 The first commercial process to produce acrolein through the oxidation of propylene, however, was developed by Shell applying cuprous oxide on Si-C catalyst in the presence of I2 promoter. 

Catalytic Air Oxidation of Propylene to Acrolein Modeling Based on Data from an Industrial Fixed-Bed Reactor... 

Acrolein is manufactured as an end-use product and as an unisolated intermediate in the production of acrylic acid. Acrolein is manufactured by air oxidation of propylene via the following reaction (Hess et al. 1978) ... 

Acrylic acid for acrylic ester monomers is made by the air oxidation of propylene to acrolein, then to acrylic acid (12.5).19 Methacrylic acid for methacrylates can be made in the same way from isobutylene.20... 

Yoshimura, L, Making acrylic add via air oxidation of propylene", Chem. Engt l6 (15J 78-80 (1969). Sittig, M Acrylic and Vinyl Fibers, Noyes Development Corporation, Park Ridge, New Jersey (1972). Ohara, Tn Huai, ML, Shimizu, N, Oxidize propylene to acrylics ,Hydrocarbon Processing, 51 (11)85-88 (1972). Olivier, K.L..Fenton, D. M, Biale, J New route to acrylic add Hydrocarbon Processing,51(11)95-96(1972). 

Arntz D, Knapp K, Prescher G, Hoffman H., "Catalytic air oxidation of propylene to acrolein Modelling based on data from an industrial fixed-bed reactor", ACS Symp.Ser. 

The catalytic vapor-phase oxidation of propylene is generally carried out in a fixed-bed multitube reactor at near atmospheric pressures and elevated temperatures (ca 350°C) molten salt is used for temperature control. Air is commonly used as the oxygen source and steam is added to suppress the formation of flammable gas mixtures. Operation can be single pass or a recycle stream may be employed. Recent interest has focused on improving process efficiency and minimizing process wastes by defining process improvements that use recycle of process gas streams and/or use of new reaction diluents (20-24). 

Although this process has not been commercialized, Daicel operated a 12,000-t/yr propylene oxide plant based on a peracetic acid [79-21-0] process during the 1970s. The Daicel process involved metal ion-catalyzed air oxidation of acetaldehyde in ethyl acetate solvent resulting in a 30% peracetic acid solution in ethyl acetate. Epoxidation of propylene followed by purification gives propylene oxide and acetic acid as products (197). As of this writing (ca 1995), this process is not in operation. 

Butyric acid is made by air-oxidation of butyraldehyde, which is obtained by appHcation of the oxo synthesis to propylene. Isobutyric acid is made from isobutyraldehyde, a significant product in the synthesis of butyraldehyde (see Butyraldehydes). Butyraldehyde is also used to make 2-ethylhexanoic acid. 

The manufacture and uses of oxiranes are reviewed in (B-80MI50500, B-80MI50501). The industrially most important oxiranes are oxirane itself (ethylene oxide), which is made by catalyzed air-oxidation of ethylene (cf. Section 5.05.4.2.2(f)), and methyloxirane (propylene oxide), which is made by /3-elimination of hydrogen chloride from propene-derived 1-chloro-2-propanol (cf. Section 5.05.4.2.1) and by epoxidation of propene with 1-phenylethyl hydroperoxide cf. Section 5.05.4.2.2(f)) (79MI50501). 

The direct oxidation of propylene using air or oxygen produces acrolein. Acrolein may further he oxidized to acrylic acid, which is a monomer for polyacrylic resins. 

The main route to produce acrolein is through the catalyzed air or oxygen oxidation of propylene. 

The disadvantage of the chlorohydrin process is the use of toxic, corrosive, and expensive chlorine the major drawback of the peroxide process is the formation of co-oxidates in larger amounts than the desired PO. The direct epoxidation of propylene using 02 (i.e., partial oxidation of propylene) from air has been recognized as a promising route. 

ACRYLIC ACID AND DERIVATIVES. [CAS 79-10-7]. Acrylic acid (propenoic acid) was first prepared in 1847 by air oxidation of acrolein. Interestingly, after use of several other routes over the past half century, it is tins route, using acrolein from the catalytic oxidation of propylene, that is currently the most favored industrial process. 

Fig. 2.14 Formation behavior of a bismuth-molybdate catalyst employed in the oxidation of propylene into acrolein (2% hydrocarbon in air, 370°C, GHSV 1500 hr1).

A more economic process has been commercialized. In one version, the hydroperoxide is produced by catalytic air-oxidation of a hydrocarbon such as ethylbenzene (see top of page). Reaction of this hydroperoxide with propylene yields propylene oxide as a co-product. 

Oxidation Step. A review of mechanistic studies of partial oxidation of propylene has appeared (58). The oxidation process flow sheet (Fig. 2) shows equipment and typical operating conditions. The reactors are of the fixed-bed shell-and-tube type (about 3 —5 m long and 2.5 cm in diameter) with a molten salt coolant on the shell side. The tubes are packed with catalyst, a small amount of inert material at the top serving as a preheater section for the feed gases. Vaporized propyiene is mixed with steam and air and fed to the first-stage reactor. The feed composition is typically 5 -7% propylene, 10-30%... 

Two process routes to propylene oxide are commercially practiced hydroperoxide formation and then use of this to oxidize propylene, and formation of propylene chlorohydrin followed by treatment with a base to form propylene oxide [22, 23]. It has not been possible to produce adequate yields of propylene oxide via the direct oxidation of propylene with air in the manner in which ethylene oxide is now produced, although attempts to come close to this continue [24]. 

Epoxidation of propylene by a hydroperoxide is commercially viable for those hydroperoxides which, when spent, can easily give another commercial product. One option is to produce -butyl hydroperoxide (plus some -buta-nol) by the air oxidation of isobutane at 90°C and ca. 30 atm in the presence of molybdenum naphthenate (Arco and Texaco). The separated hydroperoxide is then used to oxidize propylene to propylene oxide with yields on hydroperoxide of over 90% (Eqs. 19.39 and 9.40). 

---