Convergent-divergentColumnasaColumnfortheExtractionofAromatics fromLightPetroleumFraction

The increasing demand of the low boiling aromatics for chemicals has provided the primary incentive for the tremendous expenditure by the petroleum industry to improve processing methods. Also, refineries are becoming more aware of applying conventional oil refinery processing methods to the production of petrochemicals. Considerable experience has been gained in the operation of certain types of process units, which are normally utilized to produce these intermediates. The production of aromatic hydrocarbons, i.e., benzene, toluene, and xylene, is increasing every year in the world due to increase in demand for them. The demand for low boiling aromatic hydrocarbons is continually growing. Effluents of catalytic reformers and steam crackers are becoming more and more important as sources of aromatics. Since these mixtures contain other hydrocarbons, which boil in same range of temperatures, and many homogeneous binary azeotropes exist between aliphatics and aromatic hydrocarbons,1 the recovery of pure aromatics is not possible by conventional distillation. It is therefore necessary to use more elaborate techniques such as solvent extraction or extractive distillation. Generally, in petroleum refineries aromatics are recovered by liquid-liquid extraction using a selective solvent. The aromatics and solvent are then separated by distillation. In most petroleum applications, solvent extraction removes materials of low hydrogen content, principally aromatics from materials of higher hydrogen content. Extraction was first used to upgrade kerosene, which burns with a smoky flame, by removing aromatics. Next, it was used to upgrade lubricating oils by removing aromatic materials with low viscosity indexes. Extraction is also used today to improve charge stocks for catalytic cracking, to improve the quality of light catalytic cycle oils as heating oils, to recover light aromatics from gasoline stocks, to separate i-butene from butane-butene streams, and to remove mercaptans from gasoline. The solvent processes tend to erase the old crude oil marketing system, which only considered a few crude oils satisfactory for lubricant manufacture. By solvent methods, the original properties of the oil can be changed so, that a uniform grade of oil can be manufactured from a wide variety of crude oils. In literature, the solvents like diethylene glycol,2–3 triethylene glycol,4 tetraethylene glycol,5–6 N-methylpyrrolidone7–8 and sulfolan,9–12 etc. are suggested for aromatic extraction. The different types of extraction columns13 are used commercially none of them contain convergent-divergent part. The series of convergent-divergent sections of the extractor column have been fabricated for the experimental purpose. This column generates developing flow conditions through the entire length of the contractor. It is well known that the processes of momentum, mass and heat transfer are much intensified under the developing flow condition due to surface turbulence and the slip.14 The present paper deals with an applicability of a convergent – divergent column to be used as an extraction column for aromatics from simulated light petroleum fraction.