Patent GB-823902-A (GB)
Title: Process for recovering naphthalenes from hydrocarbon mixtures
Filed: 1957-11-12
Abstract: <PICT:0823902/IV (b)/1> Naphthalenes are separated from hydrocarbon mixtures containing them by countercurrently contacting the mixture with an aqueous solution of a selective solvent for naphthalenes, which is a C1-C10 aliphatic alcohol, an alkylene glycol, a polyalkylene glycol, an ether of such alcohol or glycol or mixtures thereof, at a temperature of 93-232 DEG  C. and under sufficient pressure to maintain the liquid phase, e.g. 0.7-20.4 atmospheres gauge, countercurrently contacting the extract phase with a liquid paraffinic hydrocarbon stream boiling below the naphthalene to be recovered thereby displacing benzene hydrocarbons from the extract phase, stripping hydrocarbon extract from the extract phase and recovering a naphthalene therefrom and returning the lean solvent to the extraction stage. The hydrocarbon feed may be any containing recoverable amounts of naphthalene and/or its homologues and preferably boils within the range of 149-260 DEG  C.  The feed preferably contains only aromatic and naphthenic and/or paraffinic constituents; a highboiling fraction of a product of reforming or other petroleum refining process being suitable.  Suitable solvents include n-propanol, n-butanol amyl alcohol, cyclohexanol, n-heptanol and isomers thereof; ethylene-, propylene-, butylene- and amylene glycols, glycerol, betamethyl-glycerol, di-, tri- and tetra-ethylene glycols, dipropylene glycol, tripropylene glycol, mixed ethylene glycol-propylene glycol ethers and the methanol, ethanol and butanol ethers of mono- and di-ethylene glycols.  They are used with up to 20% by weight of the solvent composition of water. The liquid paraffinic hydrocarbon stream used may boil between from 6 DEG  to 83 DEG  C. below the initial boiling point of the feedstock used and preferably comprises octanes.  It is preferably a recycle feed obtained as described below and may contain entrained naphthalenes. The feedstock enters the countercurrent extraction unit 6 at a mid-point by line 1, solvent at the top by line 7.  Raffinate leaves by line 10 and is distilled to obtain a lowboiling fraction which is the excess of the paraffinic hydrocarbon stream and is recycled by lines 27 and 11.  The extract phase descends the unit 6 and meets the paraffinic hydrocarbon rising therein having been introduced at the bottom by line 11 from lines 27, 13 and/or 14.  (Line 14 is for the introduction of a fresh paraffinic stream at the beginning of operations or as desired.)  The contacted rich solvent is then passed to a flash chamber at the top of, but separated from, stripper 42 by line 41.  The unevaporated liquid passes to the top of the stripper where the pressure is further reduced.  The vapours, mainly the light paraffin stream, leave by lines 51 and 44, are condensed and collected in collector 48.  Here any aqueous or alcoholic constituents separate and are recycled by line 57 to the reboiler 62. The paraffinic constituents which may contain some naphthalenes vaporized in the flashing operations are recycled by line 13.  To prevent buildup of mono-cyclic aromatics in this cycle, some is bled off by line 13a and made up by fresh hydrocarbon introduced by line 14.  When using a glycol solvent an inert gas blanket is maintained over the liquid in collector 48, introduced by line 1281 and removed by line 130; such gas may be nitrogen or carbon monoxide and prevents the deterioration of glycols to acidic, corrosive materials.  In descending the stripper which employs steam produced in the reboiler 62 the naphthalene hydrocarbons are stripped from the solvent and are removed as a side cut by line 63, condensed and collected in collector 67 together with aqueous solvent.  In order to maintain the naphthalene in the liquid phase lighter than the aqueous phase a paraffinic, preferably octane, fraction is circulated between the collector and the subsequent fractionation system and is introduced to the collector by line 68.  The aqueous layer is recycled by line 70.  Inert gas may also be passed over the liquids in collector 67 by lines 132 and 134.  The hydrocarbon layer from the collector 67 passes by line 71 to fractionator 73 where the light hydrocarbons are removed for recycle by line 68. Bottoms pass to fractionator 89 where naphthalene is recovered by line 98 and bottoms pass to fractionator 108 where methyl naphththalenes are recovered by line 112 and bottoms removed by line 120.  Aqueous solvent removed as bottoms from stripper 42 are recycled by line 7 to the extraction stage.  Solvent can be removed by bleed line 60 from recycle line 57, this may be necessary when using a glycol solvent to prevent build-up of acidic degradation products.  Fresh solvent is introduced by line 8.