Research On In-Situliquid Catalytic Hydrogenation Of Aromaticnitro Compounds To Corresponding Anilines

Hydrogenation of organic compounds is an important reaction inindustry. Compared with chemical reductions, catalytic hydrogenation ispreferred currently for the industrial production of many fine chemicalsowing to its lower impact on the environment and the superior quality.Generally, there are two hydrogenation types: catalytic hydrogenationusing molecular hydrogen and catalytic transfer hydrogenation usinghydrogen donors. Catalytic hydrogenation using molecular hydrogen islimited because of the risk associated with the necessity of molecularhydrogen which is easily ignited, exploded and difficult to store andtransport. In the catalytic transfer hydrogenation, active hydrogen can betransferred from hydrogen donors (alcohols, hydrazines, hydrocarbons,organic acids etc) to the inorganic or organic compounds directly.However, its disadvantages are also obvious: relatively low atomic utilization and high cost of products.In-situ liquid catalytic hydrogenation is a novel liquid system ofcatalytic hydrogenation proposed by our group in 2004, in which activehydrogen produced from the reforming of alcohol solution is useddirectly for the hydrogenation of organic compounds, obviating thediffculty associated with the necessity of molecular hydrogen in liquidcatalytic hydrogenation. In the novel reaction system, the utilization ofhydrogen atoms from hydrogen donors is improved greatly because thehydrogen atoms come both from alcohol and water which could beutilized totally with the water-gas shift (WGS) reaction. The novelreaction shows wide application in industry owing to its advantages ofhigh atomic utilization and lower harmful on the environment.In this dissertation, in-situ liquid catalytic hydrogenation of aromaticnitro compounds to corresponding anilines are studied; Speciallyemphasis on the stability of catalysts in the in-situ liquid catalytichydrogenation. Meanwhile, the main reasons of catalyst deactivation andthe methods of catalysts reactived were discussed. Main points of thisdissertation are listed as follows.1. The Ru-B/C,Ru-Fe-B/C,Ru-Ce-B/C,Ru-Sn-B/C and Ru-Co-B/Camorphous catalysts were prepared by chemical reduction and applied inthe in-situ liquid catalytic hydrogenation of aromatic nitro compounds tocorresponding anilines. 5%(wt)Ru-Sn-B/C (molarRu:Sn=1:3) amorphous catalyst exhibited excellent catalytic performance, with the conversion of99.3%, and selectivty of 99.5% for the in-situ liquid hydrogenation ofo-chloronitrobenzene to o-chloroaniline without dehydrohalogenation.The main byproducts were intermediates of halogenated hydroxylamine,the catalyst could be active for 32 hours. The in-situ liquid catalytichydrogenation has been systematically studied based on the structure ofamorphous catalyst, the electronic shift between metallic atoms andreaction conditions.2. The Ru-based catalysts were prepared by impregnation and appliedin the in-situ liquid catalytic hydrogenation of aromatic nitro compoundsto corresponding anilines. The conversion of the in-situ liquid catalytichydrogenation of o-chloronitrobenzene reached to 99.8% and theselectivty to 98.0% over 0.5%Ru-2.5%Fe/C catalyst. The catalyst showssuper stability with more than 480h. The properties of 0.5%Ru-2.5%Fe/Ccatalyst were tested by XRD,TEM,XPS, and the reaction conditionswere studied. Based on the results of catalyst characterization andreaction conditions, the reasons of the catalyst stability were studied.3. The relationship between the catalyst stability and the structure ofcatalyst, the surface electronic state, the surface adsorption, the specificsurface area, the composition of the catalyst, has been systematicallystudied by a series of characterization of catalysts (XRD,TEM,XPS,IR,EDS). In the in-situ liquid catalytic hydrogenation, the active hydrogen produced from the reforming of alcohol solution is alwaysaccompanied with CO production, and the CO could easily adsorb on thesurface of catalyst, which lead to catalyst deactivation attributed topoisoning by CO. The stability of catalyst was improved by water-gasshift (WGS) and fischer-tropsch (FTS) reactions decreasing theconcentration of CO. The Ru-Fe/C catalysts exhibit higher stabiltiy whichis attributed to the FeOx presenting excellent activity and selectivity inWGS and FTS reactions.4. m-Nitroaniline (m-NA) is an important intermediate, the traditionalroute for the preparation of m-NA is based on the use of sulphidesresulting in low atomic utilization and the serious wastes. However, lowselectivity to m-NA is often obtained with liquid catalytic hydrogenationusing molecular hydrogen. Herein, the in-situ liquid catalytichydrogenation was studied. The conversion of the in-situ liquid catalytichydrogenation of m-dinitrobenzene (m-DNB) was 99.4% and theselectivty to m-NA reached 100% over 0.5%Ru-2.5%Fe/C catalyst.Further study was done with the liquid catalytic hydrogenation of m-DNBover 3.5%Ru16.6Fe83.4/C catalyst. With the reaction conditions ofhydrogen pressure of 2.0Mpa, temperature of 373K, ethanol as solvent,the conversion of m-DNB reach to 100% and the selectivty of m-NA to98.8%. On the same reaction conditions, 3.5%Ru8.3Ce91.7/C exhibitedhigher catalytic properties with the conversion of m-DNB was 100% and the selectivty of 99.4%.In conclusion, a series of aromatic nitro compounds could be reducedto corresponding anilines with excellent conversion and selectivity in thein-situ liquid catalytic hydrogenation, and the stability of catalyst can beimproved by modification or reactivation. The in-situ liquid catalytichydrogenation shows high atomic utilization, simplify production processand lower harmful on the environment which opens a new reaction in thefield of liquid catalytic hydrogenation and shows wide applications inindustry.