GB846588A - Heat recovery system for diphenylamine process - Google Patents

Abstract

The invention comprises a process for the vapour phase preparation of diphenylamine from aniline by passing the aniline through a feed tank and preheater, into a super-heater, heating the aniline in the super-heater to the <PICT:0846588/IV(b)/1> temperature of reaction at reaction pressures by external heat from burning fuel, bringing the super-heated aniline into contact with a catalyst in a converter, maintaining reaction temperatures by circulating flue gases from the aniline superheating step through the converter, passing the exit gases from the conversion step with a minimum of cooling into heat exchange with aniline feed in the preheater, and then stripping aniline in an aniline stripping zone by dropping the temperature to that at which diphenylamine condenses, separating the diphenylamine as a liquid, condensing the aniline in a condensing zone, separating the aniline from volatiles and recycling the hot condensed aniline to the aniline feed tank. A process is described with reference to the accompanying flow sheet. Aniline is taken from a supply tank 1 at room temperature, and flows into feed tank 2, where its temperature is raised by the hot recycled aniline, from the process described below, which enters at about 220 DEG C. The aniline leaves the feed tank at about 210 DEG C. and passes into the preheater 3 where it reaches about 390 DEG C., and then flows into superheater 4, where it is superheated and vaporised. Heat is applied to the superheater by means of burning fuel, and this is the only point in the system at which heat is introduced from an outside source. The aniline stripping and condensing zones and feed tank are maintained under super-atmospheric pressure lower than the pressure in the diphenylamine converter. Suitable pressures in the preheater are about 130 p.s.i. and in the superheater about 100 p.s.i. The aniline passes through the DPA converter 5 and the exit gases at about 470 DEG C. are used as the source of heat for the aniline preheater, in which they are cooled to approximately 270 DEG C. These gases pass into the aniline stripper 6 where DPA condenses with some aniline and is drawn off. The aniline, ammonia, water and other volatile by-products leave the stripper at about 225 DEG C., and the aniline is condensed in condenser 7 to about 220 DEG C. A portion of the liquid aniline is refluxed and the remainder recycled to the aniline feed tank 2 as described above. The vapours pass off to an absorption system. The flue gases from the aniline superheater 4 which are preferably at about 550 DEG C. are cooled to about 490 DEG C., at which temperature they are introduced around the tubes of the DPA converter 5, and then may be vented to the stack or a portion may be recycled, as is shown in dotted lines, through a recycling pipe 12 provided with a suitable valve 13. A second DPA converter 8 is also present. The catalyst is regenerated by passing hot air through the catalyst tubes, and the cooling of the catalyst during this process effected by part of the flue gases to which, if desired, part or all of the flue gases from the DPA converter 5 which is on stream may be added. Steam from a source 9 may be fed into the main flue gas cooling stream through a valved pipe 10, and if desired, a portion may be introduced directly at various points in the DPA converter 8 through a valved pipe 11. Specification 846,587 is referred to.