Patent GB-475692-A (GB)
Title: A process for the extraction of liquid mixtures
IPC: B01D11/04
Filed: 1936-10-26
Abstract: In a process for separating liquid mixtures containing more than two components by means of a selective solvent, the mixture is extracted so that extract and raffinate phases flow in counter current to yield a primary extract and raffinate at opposite ends of the system, and a side stream of the liquid mixture is withdrawn at an intermediate point to yield an intermediate product of different properties from the extract and raffinate. During <PICT:0475692/III/1> extraction the raffinate may be elutrified (i.e. freed from the most soluble extractable component) and the extract may be de-raffinated (i.e. freed from the least soluble component), or submitted to backwashing with the selective solvent, with final extract, or extraction with an auxiliary solvent.  The process may be effected in a series of mixers and settlers or in a packed tower.  The side stream drawn off may consist of a solvent-rich or a solvent-poor phase, or, when a tower is used, a mixture of such phases, which are preferably separated by centrifuge or settling and the undesired (usually the solvent-poor) phase is returned to the extraction zone.  The process may be applied to the selective solvent extraction of hydrocarbons such as gasoline, kerosene, gas oil, fuel oil, lubricating oil, polymerized, cracked, or hydrogenated oils.  The components are polarizable in different amounts in the selective solvent yielding paraffinic raffinate, aromatic and naphthenic extract which also contains sulphur, nitrogen, and oxygen compounds.  After de-raffination a side stream drawn off from this extract will be free from the sulphur &c. compounds.  Vegetable oils are separated into hydroxy acids (extract), refined fatty oil (raffinate), and fatty acids (intermediate).  Essential oils for example lemon oil, yield terpenes (raffinate), citral (intermediate), compounds richer in oxygen than citral (extract).  Selective solvents specified are, sulphur dioxide furfurol, quinoline, b -b <1>-dichlor-ethyl ether, phenol, nitrobenzene, ethanolamines, furfurol, nitrogen bases used alone or in admixture with alcohols and ketones, or with auxiliary solvents such as propane, pentane or naphtha.  Two extraction zones A, B are divided by partitions to form a number of settling chambers 1 . . . 7, 11 . . . 17, each of which is provided with a distributing nozzle 8, and outlet conduits 9, 10 at the bottom and top of each chamber, opposite to the nozzle. Each nozzle is connected to a mixer 21 . . . 27, 31 . . . 37 in which the two liquids are mixed.  The nozzle consists of a fan-shaped chamber divided by vertical partitions distributing the mixture radially outwardly into the settling chamber, whereby turbulence is reduced.  One intake to the mixer is connected to the upper outlet of the next lower settling chamber by a conduit 39, and the other inlet is connected to the lower outlet of the next higher settling chamber by a conduit 40, chillers 42 . . . 47, 51 . . . 57 being provided in the circuit.  Mixer 31 at the top of column B is connected to the outlet of the bottom chamber 7 of the column A, the mixer 21 at the top of column A is connected to a tank 50 containing a selective solvent.  In operation, the liquid mixture to be separated is supplied through a line 62 to the mixer 27 to which extract from chamber 6 is admitted.  The mixture separates in chamber 7 to form a raffinate which passes to mixer 26, and an extract passing to mixer 31.  This process is effected similarly in the other settling chambers, the raffinate phase from chamber 7 being electrified in its passage upwards through column A, and the extract phase is de-raffinated in its passage downwards through column B to which a solvent for paraffinic components is admitted from a tank through a line 67. The final elutrified raffinate flows into a separator 64, and the final de-raffinated extract flows into a separator 74.  A temperature gradient maintained in column A assists elutrification.  For example, in the extraction of lubricating oil with furfurol, chamber 1 is at 140 DEG  C., chamber 7 is at 94 DEG C., the extract phases being chilled in the chillers 42 . . . 47.  At an intermediate point in column A for example at chamber 3, the extract is withdrawn through a conduit 86 and, after chilling and removal of some of the solvent if desired, passes to a de-raffinating zone 87, which is similar in operation to the column B, using an auxiliary solvent.  The de-raffinated side stream passes through a line 88 to a separator 89 in which solvent is removed leaving the desired intermediate product which is with drawn at 90.  The raffinate obtained is returned through a conduit 93 to the main extraction zone.  British Specifications 316,137, [Class 91], 355,294, 380,954, 417,617, 424,867, 444,535, 452,537, and French Specification 803,242 are referred to.