Patent GB-693967-A (GB)
Title: Methods of separating mixtures of organic liquids by adsorption
IPC: B01D15/08
Filed: 1950-03-17
Abstract: A mixture of normally liquid organic compounds containing less than 5 per cent and normally less than 2 per cent of compounds which are preferentially adsorbed is contacted with a solid adsorbent in a guard zone to remove the latter compounds, and the effluent from the guard zone is separated into at least two fractions by contact with a solid adsorbent in an adsorption zone, the adsorbent in the guard zone being regenerated by contacting it with a liquid comprising at least a part of one of said fractions.  The process may be applied to the separation of petroleum distillates such as kerosene into an aromatic fraction and a paraffinic fraction, catalytically re-formed naphtha into an aromatic adsorbate and a non-aromatic percolate, and cracked naphtha into aromatic, olefinic and paraffinic fractions.  It may also be applied to the separation of hydrocarbons from oxygenated products of the Fischer-Tropsch and Oxo processes.  The adsorbent may be silica gel, alumina gel, silica-alumina gel or adsorbent carbon, and that in the guard zone may be the same material as is used in the adsorption zone.  The application of the process to the separation of aromatics from a catalytically re-formed naphtha, using silica gel and pentane as adsorbent and stripping liquid is described. Preferably, the adsorbate or the adsorbate-stripping liquid mixture is used for regeneration.  When either the adsorbate-stripping liquid or the percolate-stripping liquid mixture is employed, it may be heated to 200-500 DEG  F. prior to its passage into the guard zone. Other applications described are the separation of a cracked naphtha into an aromatic fraction, an olefinic fraction and a paraffinic fraction, and the separation of a kerosene distillate into an aromatic adsorbate and a non-aromatic percolate.  Specification 673,540 is referred to.ALSO:A mixture of normally liquid organic compounds containing less than 5 per cent and normally less than 2 per cent of preferentially adsorbed compounds is contacted with a solid adsorbent in a guard zone to remove the preferentially adsorbed compounds, and the effluent from the guard zone is separated into at least two fractions by contact with a solid adsorbent in an absorption zone, the absorbent in the guard zone being regenerated by contacting it with a liquid comprising at least a part of one of said fractions.  The process may be applied to the separation of petroleum distillates such as kerosene into an aromatic fraction and a paraffinic fraction, catalytically re-formed naphtha into an aromatic adsorbate and a non-aromatic percolate, and cracked naphtha into aromatic, olefinic and paraffinic fractions.  It may also be applied to the separation of the reaction products of the Fischer-Tropsch and OXO processes.  The adsorbent may be silica gel, alumina gel, silica-alumina gel or adsorbent carbon, and that in the guard zone may be the same material as is used in the adsorption zone.  Fig. <PICT:0693967/III/1> <PICT:0693967/III/2> 1 shows a flow sheet for one form of the process.  A solid adsorbent is packed into the guard chambers 1 and 2 and the adsorption columns 3 and 4.  Both 1 and 2, and 3 and 4 are connected for parallel flow.  Distillation columns 5 and 6 are used to separate adsorbatestripping liquid and percolate-stripping liquid mixtures respectively.  Stripping liquid, adsorbate and percolate are stored in tanks 7, 8 and 9 respectively. In the application of the process to the separation of aromatics from a catalytically reformed naphtha, using silica gel and pentane as adsorbent and stripping liquid, the naphtha is passed through lines 10 and 11 into guard chamber 1 to remove the preferentially adsorbed highly polar compounds, and thence through lines 12, 13 and 14 to column 3, when aromatics are adsorbed.  The non-aromatic percolate flows through lines 15 and 16 together with pentane left in the column from the regenerating stage of the previous cycle.  The percolate-stripping liquid mixture is distilled in column 6, pentane flowing off through line 17 to tank 7 and the percolate still bottoms flowing through line 18 to tank 9.  During this cycle, chamber 2 and column 4 are being regenerated as follows.  Pentane, preferably heated to 200-250 DEG F, is pumped through column 4, and the mixture of pentane and adsorbate coming away from the column is passed through lines 22 and 23 to column 5 for distillation.  The overhead (pentane) is passed to tank 7, and the aromatic adsorbate (still bottoms) is passed through line 25 and thence either to cooler 44 and storage tank 8 or through lines 26, 27 and 28 to guard chamber 2. The effluent from chamber 2, consisting of adsorbate and desorbed polar compounds, passes to storage through lines 29 and 30.  When the adsorbent in column 3 is exhausted and that in column 4 regenerated, the feed is passed to column 4 and the flow of pentane is diverted to column 3.  These columns are used alternately while guard chamber 1 is in use.  When the adsorbent in guard chamber 1 is exhausted, and that in chamber 2 is regenerated, the hot adsorbate from line 25 is diverted to chamber 1, and the flow of feed to chamber 2. Immediately prior to this, the flow of hot still bottoms (adsorbate) to chamber 2 is checked, and cold adsorbate from tank 8 is passed through lines 26, 27 and 28 to guard chamber 2 to cool the regenerated adsorbent before introduction of the feed.  At the end of this period, when the feed is led into chamber 2, the first effluent will be substantially pure adsorbate, and this is sent to storage through lines 29 and 30.  When all the adsorbate is displaced from the guard chamber, the effluent is diverted through line 13 to the adsorption zone 3, 4.  Fifty or more cycles using chambers 3 and 4 alternately may be run before exhaustion of the adsorbent in either of the guard chambers.  Instead of using adsorbate for regeneration of the adsorbent in the guard zone, any of the following arrangements may be employed: (a) Adsorbate-stripping liquid mixture may be withdrawn from line 23 through lines 34 and 35, heat-exchanger 36 and line 27 into chamber 1 or 2.  Before putting the regenerated adsorbent on stream, the heat-exchanger may be by-passed through line 37 to cool the adsorbent.  If the feed to still 5 is sufficiently hot, the exchanger may be by-passed for regeneration and used as a cooler to cool the adsorbent at the end of the regeneration.  (b) Hot percolate from line 18 may be pumped through lines 46, 38 and 27 into chamber 1 or 2.  The effluent is led to storage through line 30 or to storage tank 9.  Before placing on stream cold percolate is admitted from tank 9.  (c) Percolate-stripping liquid mixture may be withdrawn from line 16 and passed through lines 39, 31, heat-exchanger 41 and line 27 to chamber 1 or 2, the effluent flowing back to distillation column 6.  After regeneration, the adsorbent is cooled by by-passing the heat-exchanger.  (d) Adsorbate still bottoms may be used for regeneration and adsorbate still feed for cooling.  (e) Percolate still bottoms may be used for regeneration and percolate still feed for cooling. Preferably, the adsorbate or the adsorbate-stripping liquid mixture is used for regeneration.  When either the adsorbate-stripping liquid or the percolate-stripping liquid mixture is employed, it may be heated to 200 DEG -500 DEG F prior to its passage into the guard zone.  The adsorbate or percolate may be employed for regeneration at still-bottom temperature, but it may be heated to increase its effectiveness, or cooled if it contains compounds unstable at higher temperatures.  The preferred temperature for regeneration is between 200 DEG  and 500 DEG F. Fig. 2 shows the flow sheet for an application of the invention to a cyclic adsorption process, employing a plurality of fixed adsorbent columns A to I inclusive.  Columns A, B and C are serially connected to form an adsorbate-enriching zone, D and E a percolate-refining zone, F and G a cooling zone and H and I a stripping zone.  Chambers 104, 105 and 106 constitute the guard zone for the adsorption of the preferentially adsorbed compounds in the feed.  The feed from tank 101 passes through a drier to chambers 104 and 105 and thence through lines 107 and 108, where it mixes with the effluent from the adsorbate-enriching zone and passes through columns D and E.  The effluent from E at the commencement of the cycle is essentially stripping liquid and is passed through lines 109, 110 and 111 to storage tank 112.  During the latter part of the cycle the effluent consists of a mixture of stripping liquid and percolate, and this is passed through lines 109 and 114 into the surge drum 115 and line 116 to the distillation column 117.  The stripping liquid (assuming it has a lower boiling point than the percolate) is taken overhead through lines 118 and 111 to tank 112.  Stripping liquid from tank 112, heated, if desired, to 200 DEG -500 DEG F by passage through a heat-exchanger, is passed to columns H and I.  The first effluent from I consists of stripping liquid and adsorbate, and this is passed through line 122 and 123 to the surge drum 124 and thence to column A.  The effluent from column C consists predominantly of stripping liquid and percolate and flows through line 108 to the percolate refining zone.  During the latter part of the cycle the effluent from I is passed through lines 122 and 126 to surge drum 127 and thence through line 130 to the distillation column 131, from which the stripping liquid (overheads) is taken to tank 112.  The bottoms from still 131 (adsorbate) pass through lines 149, 150 and cooler 151 to tank 133, when they are not to be used for regeneration of the adsorbent in the guard zone.  Stripping liquid, cooled to about 80 DEG F, is passed through line 119 into column F of the cooling zone, and the effluent from column G is passed to tank 112.  While chambers 104 and 105 are