GB829196A - Improvements in or relating to process for producing a needle-like coke - Google Patents

Abstract

Coke, which is suitable for the production of graphite electrodes, and which, when crushed to a fine size, shows a needle-like structure, is produced by removing from a high-boiling petroleum residuum the components which readily form an insoluble phase upon heating at 325 DEG to 550 DEG C., and coking the remaining residuum in a quiescent pool. Suitable residues may have an initial boiling-point above 250 DEG C. and not more than 25 to 30% distilling below 360 DEG C. The residuum may be charged into a batch still and the temperature gradually raised from 325 DEG C. to about 400 DEG to 425 DEG C., the residence time being greater than 5 hours and may be 10 to 30 hours. A distillate fraction may be taken off overhead. Additional quantities of residuum are added to the still from time to time. A heavy high-boiling hydrocarbon liquid concentrate is left in the still together with an amorphous coke which may be separated therefrom by centrifuging or filtering. On coking the concentrate in a quiescent pool needle coke is formed. Alternatively the residuum may be heated under pressure at a temperature of 400 DEG to 600 DEG C. until 5 to 10% or more of the residuum has precipitated. This may be done by heating in pipe still and then passing the oil to a pre-coking drum. Also activated clay, silica, alumina catalyst, or activated alumina may be added to increase the rate or reduce the temperature at which the insoluble phase forms. In a modification about 80 to 95% of the hydrocarbon is flash distilled from a high-boiling petroleum residuum, the evolved vapours removed overhead being passed either directly to a quiescent coking zone or through a cooler and collected ready for coking, entrainment of the charge being prevented by passing the vapours through a knock-out drum or a column containing baffles, packing or bubble caps. The solid coke or pitch-like residue left in the still is removed and used for other purposes. In another form the residuum is preheated in a pipe coil to a temperature of 400 DEG to 600 DEG C. under super-atmospheric pressure and continuously passed into a flash distillation zone operated at a lower pressure which may be sub-atmospheric, the vapours being taken off overhead for coking and the non-volatile residue accumulating in the flash drum. In another form a low-boiling liquid paraffinic hydrocarbon such as propane, butane, pentane or hexane is mixed with residuum in the proportion of from 1 to 1 to 10 to 1 or more. Most of the residuum dissolved and this is separated from the heavy, viscous residue by settling or filtering. The solvent is distilled off and the purified oil is then coked. Topped or reduced crude oil may be vacuum distilled and the overhead extracted using a solvent such as furfural, phenol or liquid sulphur dioxide. The extract is separated from the raffinate, the solvent removed and the hydrocarbon extract is coked. The needle coking is carried out by passing the treated oil at a temperature above about 350 DEG C. and usually between about 375 DEG to 500 DEG C. into a vertical coking drum, the pool of oil being maintained at a uniform temperature so that thermal currents are avoided. When the coke drum is full, the coke is removed, broken into lumps and calcined at a temperature of 1000 DEG to 1500 DEG C. Calcined needle-coke flour is mixed with a binder such as coal tar pitch, baked at a temperature of 500 DEG to 1300 DEG C., and then graphitized at 2500 DEG to 3000 DEG C. to form electrodes.