Patente Sobre Produção de Anilina

Patente EP-0696573

The invention relates to a process for the hydrogenation of nitroaromatics to aromatic amines in the gas phase on fixed catalysts, wherein the catalyst from the outside either heat supplied to or heat is removed, that is, that the process is carried out adiabatically, and wherein the reacted nitroaromatic a multiple of the resulting aromatic amine as well as a multiple of water and hydrogen under pressure is passed over the catalyst.

Aromatic amines are important intermediates, which must be cheap and in large quantities. Therefore, for example, need to be built for the hydrogenation of nitrobenzene systems with very large capacity.

The hydrogenation of nitroaromatics is a highly exothermic reaction. Thus, about 488 kJ / mol (117 kcal / mol) and about 544 kJ / mol is released in the hydrogenation of nitrobenzene (130 kcal / mole) at 200 ° C in the hydrogenation of nitroxylene to xylidine.

The removal and use of the heat of reaction is thus an important aspect in the implementation of processes for the hydrogenation of aromatic nitro compounds.

So in an established method, the catalyst is operated as a fluidised, thermo stabilized bed (US 3,136,818). The effective heat dissipation of this procedure are problems with non-uniform residence time distribution over (nitrobenzene breakdown) and catalyst attrition.

Narrow residence time and low catalyst fines are possible in reactors with a stationary catalyst bed. However, in such reactors, problems arise with the temperature control of the catalyst beds. In general thermostated tube bundle reactors are used, which, especially in large reactors, a very elaborate cooling circuit have (DE-OS 2,201,528, DE-OS 3,414,714). Such reactors are complex and entail high investment costs. With the rapidly increasing size problems in mechanical strength and uniform temperature control of the catalyst bed make large aggregates such type uneconomical.

Simple reactors, such as those used for the inventive method described below, contain only catalyst beds and do not have a system to heat household in the reactor. They are easy to transfer to an industrial scale, in all sizes, cheap and durable. The reaction enthalpy is reflected quantitatively in this type of reactor in the temperature difference between reactant and product gas stream.

Date, neither the use of such reactors is described for the highly exothermic hydrogenation of nitroaromatics, still be suitable catalysts and suitable modes shown.

GB 1452466 relates to a process for the hydrogenation of nitrobenzene, in which an adiabatic reactor is followed by an isothermal reactor. Here, the majority of the nitrobenzene is reacted in a thermostated tube bundle reactor, only the hydrogenation of the residual content of nitrobenzene takes place at relatively low excess of hydrogen (less than 30: 1) in an adiabatic reactor.

The advantage of complete renunciation of a thermostated reactor at purely adiabatic reaction was not detected.

DE-AS 1,809,711 is concerned with the steady introduction of liquid nitro compounds in a hot gas stream by spraying, preferably at constricted sites immediately upstream of the reactor. On the design of the reactor is not addressed in the application font. However, the example you can see that in spite of a considerable excess of hydrogen has not left the reactor with the product gas is at least 34% of the reaction enthalpy.

In DE-OS 36 36 984 describes a process for the coupled production of nitro and dinitroaromatic compounds from the corresponding hydrocarbon by nitration and subsequent hydrogenation which is described below. The hydrogenation is carried out in the gas phase at temperatures from 176 to 343.5 ° C. The example shows that the hydrogen stream also serves to reaction heat dissipation from the reactors. An apparatus for gas-phase hydrogenation described which consists essentially of two series-connected reactors with intermediate cooling and Eduktzwischeneinspeisung is their size and structure not discussed. However, one can see the temperature profile of the reactors, that a considerable portion of the heat of reaction does not leave the reactor with the product gas stream. Thus, the reactor has no. 1 an inlet temperature of 181.7 ° C, a hottest point of 315.6 ° C and an outlet temperature of 277.2 ° C, the reactor no. 2 has an inlet temperature of 203.9 ° C, a hottest point of 300 ° C and an outlet temperature of 296.7 ° C. Whether in a technical implementation in orders of magnitude of 80,000 tpy eg the reactors need a cooler or not is not stated in DE-OS 36 36 984. Both in DE-OS 36 36 984 and DE-OS 18 in 09,711 is not explicitly address the problem of heat dissipation in Gasphasenhydrierungen.

That new and improved systems for hydrogenation of nitrobenzene to aniline were taken into operation, can the magazine "Hydrocarbon Processing 59" (Vol. 59, 1979, Issue 11, p 136) refer. The publication can be seen that the production of steam and the reaction can be carried out while closely linked in one process step.

In all the above publications Cu catalysts are used which (<0.1 g / ml h) and operated at a low temperature level only with low loads. This results in low space-time yields.

Along with the aforementioned copper catalysts numerous other contacts for the gas phase hydrogenation of nitroaromatics are described. They are described in numerous publications and include elements or compounds as hydrogenation Pd, Pt, Ru, Fe, Co, Ni, Mn, Re, Cr, Mo, V, Pb, Ti, Sn, Dy, Zn, Cd, Ba, Cu , Ag, Au, partly as oxides, sulfides or selenides and also in the form of a Raney alloy and on supports such as Al 2 O 3, Fe 2 O 3 / Al 2 O 3, SiO 2, silicates, carbon, TiO 2 , Cr 2 O 3. 

These catalysts are described, with only small stresses in a temperature range below 350 ° C.

In no previous publications is described, that it is advantageous to pass a larger amount of aromatic amine and water with the aromatic nitro compound to the contact.

Most pure hydrogen is fed with pure nitro compound over the catalyst on the contrary. In DE 1809711 and DE 3636984 are relative to the injected amount of nitro compound at most small amounts of aromatic amine in the starting material for the reactor. In DE 1809711 are per 1000 g of nitrobenzene approximately 1502 g of hydrogen, but only driven 692 g water and 92.9 g of aniline even just in the reactor; this merely reflects the fact that one can remove water and aniline at a reasonable cost only incompletely from the circulating gas.