Studies Of Catalytic Hydrogenations Of Aromatic Nitro Compounds To Aromatic Amines Over Ni₂P Catalysts In A Fixed-bed Reactor

Aromatic amines are important intermediates and raw materials for the organic synthesis and production of fine chemicals such as pesticides,dyes,pigments,and photosensitive materials.The reduction of aromatic nitro compounds to corresponding aromatic amines is a widely used method for the industrial production of aromatic amines.However,the traditional iron power reduction process produces a large amount of wastes,leading to serious environmental pollutions and thus is gradually being replaced by other methods.Catalytic hydrogenation is a clean technology with little wastes and produces high-quality products,which becomes a prevail technology for the production of aromatic amines in industry.In this work,supported Ni2P catalysts were prepared via a liquid phase phosphorization procedure using PPh3 and used for the catalytic hydrogenation of p-nitroaniline,p-nitrobenzonic acid and 1-nitroanthraquninone to the corresponding aromatic amines in a fixed-bed reactor.The influences of operation conditions such as reaction temperature,pressure,space velocity,and the H2/reactant molar ratio on the catalytic hydrogenation reactions were studied.Some important results obtained are summarized below.(1)The catalytic hydrogenation of p-nitroaniline to p-phenylenediamine was carried out over a Ni2P/MgAlO catalyst in a fix-bed reactor using a DMF solution containing 20%wt p-nitroaniline as a feed.The reaction conditions were optimized as:P=3 MPa,T=373 K,WHSV=0.25 h-1,and H2/p-nitroaniline molar ratio=5:1,at which the conversion of p-nitroaniline reached 100%with 100%selectivity to p-phenylenediamine.(2)The catalytic hydrogenation of p-nitrobenzoic acid to p-aminobenzoic acid was carried out over a Ni2P/Al2O3 catalyst in a fix-bed reactor.The p-nitrobenzoic acid was dissolved in THF at a concentration of 10%wt.The reaction conditions were optimized as P=4 MPa,T=433 K,WHSV=0.25 h-1 and H2/p-nitrobenzoic acid molar ratio=15:1,at which the conversion of p-nitrobenzoic acid reached 95.8%with 100%selectivity to p-aminobenzoic acid.(3)The catalytic hydrogenation of 1-nitroanthraquinone to 1-aminoanthraquinone was performed using a Ni2P/Al2O3 catalyst and DMF as a solvent.The reaction conditions were optimized as P=3 MPa,T=423 K,WHSV=0.25 h-1,and H2/1-nitroanthraquinone molar ratio=15:1,at which the conversion of 1-nitroanthraquinone reached 99%,while 77%selectivity to 1-aminoanthraquinone.