Heterogeneous catalyst acetic acid conversion

EBHP is mixed with a catalyst solution and fed to a horizontal compartmentalized reactor where propylene is introduced into each compartment. The reactor operates at 95—130°C and 2500—4000 kPa (360—580 psi) for 1—2 h, and 5—7 mol propylene/1 mol EBHP are used for a 95—99% conversion of EBHP and a 92—96% selectivity to propylene oxide. The homogeneous catalyst is made from molybdenum, tungsten, or titanium and an organic acid, such as acetate, naphthenate, stearate, etc (170,173). Heterogeneous catalysts consist of titanium oxides on a siUca support (174—176). 

The oxidation of ethanol to acetic acid was among the first heterogeneous catalyzed reactions to be reported, but it has not attracted continued interest. During the 1990ies, however, 100% conversion of ethanol coupled with 100% selectivity to acetic acid was reported in a gas-phase reaction using molybdenum oxide catalytic systems on various supports, at temperatures below 250 Similarly, a tin oxide and molybdenum oxide catalyst was... 

Addition of water (36) or alcohols (37—39) direcdy to butadiene at 40—100°C produces the corresponding unsaturated alcohols or ethers. Acidic ion exchangers have been used to catalyze these reactions. The yields for these latter reactions are generally very low because of unfavorable thermodynamics. At 50°C addition of acetic acid to butadiene produces the expected butenyl acetate with 60—100% selectivity at butadiene conversions of 50%. The catalysts are ion-exchange resins modified with quaternary ammonium, quaternary phosphonium, and ammonium substituted ferrocenyl ions (40). Addition of amines yields unsaturated alkyl amines. The reaction can be catalyzed by homogeneous catalysts such as Rh[P(C(5H5)3]3Q (41) or heterogeneous catalysts such as MgO and other solid bases (42). 

Catalytic oxidation is the most important technology for the conversion of hydrocarbon feedstocks (olefins, aromatics and alkanes) to a variety of bulk industrial chemicals.1 In general, two types of processes are used heterogeneous, gas phase oxidation and homogeneous liquid phase oxidation. The former tend to involve supported metal or metal oxide catalysts e.g. in tne manufacture of ethylene oxide, acrylonitrile and maleic anhydride whilst the latter generally employ dissolved metal salts, e.g. in the production of terephthalic acid, benzoic acid, acetic acid, phenol and propylene oxide. 

The term reactive distillation (RD) refers to both catalyzed and uncatalyzed reaction systems. Catalytic distillation systems may use a homogenous or heterogenous catalyst to accelerate the reaction. Reactive distillation is a well-known example of reactive separation process, and is used commercially. The first patent and early journal articles deal mainly with homogenously catalyzed reactions such as esterifications, transesterifications, and hydrolysis.f Heterogenous catalysis with RD is a more recent development. The key advantages for a properly designed RD colunm are complete conversion of reactants and attainment of high selectivity. An example of the benefits of RD is the acid catalyzed production of methyl acetate by... 

These catalysts have been tested in a variety of reactions such as acylation of alcohols and alkylation of phenols and naphthols [71,72,96,100,101,108]. The encapsulated triflate derivatives, and particularly the immobilized Lewis acid r rr-butyldimethylsilyltri-fluoromethanesulfonate, are very active catalysts in acylation of 2-methoxynaphthalene with acetic anhydride. In solvent-free conditions, the TOF is much higher than the values reported in literature for other heterogeneous catalysts. Moreover, leaching can be completely avoided when the solvent is omitted. The major product was in all cases the 1-acetylated methoxynaphthalene the isomerization to the 6-isomer was negligible even at high conversions. 

On the other hand, the oxidation of propanal to lactic acid involves five steps (1) acetaliza-tion of propanal (2) conversion of acetal to a vinyl ether (3) oxidation of the vinyl ether to a-hydroxyacetal (4) hydrolysis of the acetal to a-hydroxy propanal and (5) oxidation of the latter to lactic acid over Pt/C. All of the steps are feasible with heterogeneous catalysts, and an overall yield of over 80% to lactic acid was reported however, these methods are laborious (Dakka and Goris, 2006). 

The filled arrows in Figure 1.2 are processes either based on homogeneous catalysts or having great relevance in homogeneous catalysis. Conversion of synthesis gas into methanol is achieved by a heterogeneous catalyst, while the manufacture of acetic acid is based on the homogeneous catalytic carbonylation of methanol. Similar carbonyla-tion of methyl acetate, the ester of methanol and acetic acid, yields acetic anhydride. These reactions are discussed in Chapter 4. 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

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