Continuous catalytic hydrogenation vapor-phase

Isopropylnaphthalenes can be prepared readily by the catalytic alkylation of naphthalene with propjiene. 2-lsopropylnaphthalene [2027-17-0] is an important intermediate used in the manufacture of 2-naphthol (see Naphthalenederivatives). The alkylation of naphthalene with propjiene, preferably in an inert solvent at 40—100°C with an aluminum chloride, hydrogen fluoride, or boron trifluoride—phosphoric acid catalyst, gives 90—95% wt % 2-isopropylnaphthalene however, a considerable amount of polyalkylate also is produced. Preferably, the propylation of naphthalene is carried out in the vapor phase in a continuous manner, over a phosphoric acid on kieselguhr catalyst under pressure at ca 220—250°C. The alkylate, which is low in di- and polyisopropylnaphthalenes, then is isomerized by recycling over the same catalyst at 240°C or by using aluminum chloride catalyst at 80°C. After distillation, a product containing >90 wt % 2-isopropylnaphthalene is obtained (47). 

Ethylamines. Mono-, di-, and triethylamines, produced by catalytic reaction of ethanol with ammonia (330), are a significant outlet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, siUca, or sihca—alumina. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethylamine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give W-ethylpiperidine [766-09-6] (332). 

The scope of catalytic hydrogenations continues to be extended to more difficult reductions. For example, a notoriously difficult reduction in organic synthesis is the direct conversion of carboxylic acids to the corresponding aldehydes. It is usually performed indirectly via conversion to the corresponding acid chloride and Rosenmund reduction of the latter over Pd/BaS04 [65]. Rhone-Poulenc [30] and Mitsubishi [66] have developed methods for the direct hydrogenation of aromatic, aliphatic and unsaturated carboxylic acids to the corresponding aldehydes, over a Ru/Sn alloy and zirconia or chromia catalysts, respectively, in the vapor phase (Fig. 1.18). 

Continuous vapor-phase catalytic hydrogenation of nitrobenzene, either fixed-bed or fluidized-bed, was originally developed by American firms in the 1950s, particularly American Cyanamid, encouraged by studies carried out at I.G. Farben during World War... 

Catalytic reductions can be carried out in batches or in continuous processes, in the liquid phase or in the vapor phase. This method has many advantages over other methods of reduction, particularly for lai e-volume production. With low-cost hydrogen, as is the case when by-product hydrogen is available from other installations or when large hydrocarbon-steam units are installed, this process cannot be matched by other methods of reduction in so far as economics and quality of product are concerned. 

Catalytic hydrogenation requires a catalyst such as nickel, copper, platinum, molybdenum, or tungsten. These catalysts usually are supported on other materials and are especially prepared for the type of reduction to be carried out. Reduction conditions vary widely, depending on the nature of the nitro compound and the catalyst. Reduction may be carried out in solvent in the vapor phase or in the liquid phase. Aniline can be made by continuous vapor-phase reduction of nitrobenzene at 350 to 460°C at nearly atmospheric pressure. Some reductions, on the other hand, are run at 1000 to 4000 psi. 

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