US2349473A - Extraction with sulphur dioxide - Google Patents

Description

y 1944- r R. E. TAN NlCH 2,349,473

EXTRACTION WITH SULPHUR DIOXIDE Filed Sept. 14, 1942 Inhibitor Light Hydroform ed Distillate ,Gondenser Hydrafarming Equipment Distillate ll KS0 Plant Charge Tank 6/? V .l4 Heavy Hydrotarmed Distillate A 7' TOR/V5 Y Patented May 23, 1944 EXTRACTION WITH SULPHUR DIOXIDE Richard E. Tannich, Baytown, Tex., assignor to Standard Oil Development Company, a corporation of Delaware Application September 14, 1942, Serial No. 458,311

4 Claims.

The present invention is directed to the S02 extraction of petroleum fractions containing olefins.

The extraction of petroleum fractions with S: is a well known procedure in refinery operations. For the most part, it has been practiced on a commercial basis on virgin distillates. Attempts to apply it to cracked distillates have led to operating difliculties, such as coking of heat exchangers and of other equipment which is heated in the course of the operation to separate S02 from the extract and the rafi'inate. This trouble has been particularly pronounced in operations in which hydroformed naphthas have been employed as the feed stock for the extraction.

It has now been found that the aforesaid difficulty can be avoided if an oxidation inhibitor is incorporated in the hydrocarbon fraction before it is contacted with the sulphur dioxide and maintained in the mixture while the S02 is in contact with the hydrocarbons. It is preferable to add the inhibitor to the hydrocarbon fraction immediately after the treatment which results in the formation of olefins and before the fraction has an opportunity to come into contact with air. In the ordinary operation, it is advantageous to subject the fraction immediately after the conversion treatment which produced the olefins to a distillation to remove the light ends, thereby automatically eliminating any oxygen that may have been picked up by the fraction. Then the inhibitor is added to the remainder.

The inhibitor to be employed may be any one of the commonly known oxidation inhibitors which are soluble in petroleum. A suitable inhibitor is isobutyl-p-amino phenol. This inhibitor may be employed in amounts varying from about 0.05 to 0.50 lbs. per 1,000 gals. of petroleum. Greater amounts may be employed, but are not required. Amounts that render the cost undesirably high are not attractive for the additional reason that they are inefiective. other inhibitors of the phenolic or amino type may be employed. A particularly suitable class of inhibitors are those which are known in the art as gum inhibitors in motor fuels. A preferred type of inhibitor is a cut of petroleum phenols obtained by extracting heavy cracked distillates boiling in the range of about 250-700 F. with 30-50 Baum sodium hydroxide solution and acidifying the extract to release the phenols. These petroleum phenols are efiective in quantitles as low as 0.25 lb./1,000 gals. of petroleum fraction.

One procedure which may be followed in the practice of the present invention is illustrated in the accompanying drawing, in which the single figure is a front elevation, in diagrammatic form, of a plant suitable for such procedure.

Referring to the drawing in detail, numeral l designates a feed line for introducing a petroleum fraction, such as virgin naphtha, into conversion unit 2 in which is effected an operation such as cracking, hydroforming, cyclization, or the like, in which hydrogen is split ofi from hydrocarbons. The efiluent from this unit is conducted, by line 3, into a distillation unit 4 in which light ends, including any oxygen which may be contained in the distillate, are taken off overhead through line 5. The residue is drawn oii from the bottom through line 6 and discharged into a second distillation unit I, from the top of which is withdrawn 9. fraction of the desired boiling range for extraction with S02 through line 8. Connected to line 8 is a branch line 9 for introducing regulated amounts of a selected inhibitor from a storage tank l0 into the hydrocarbon stock, which is then fed into a storage tank II.

The feed stock from the storage tank is conducted, byline I 2, into an S0: extraction unit l3, in which is a feed line H! for $02, an exit line I5 for S02 extract, and an exit line [6 for S02 raflinate. The extract is then conducted into a system for the separation of the SO: from the extract, which includes heat exchangers and other equipment which is maintained at an elevated temperature. It is in this heated recovery equipment that dimculty was previously encountered in the form of coke deposition. This coke deposition has been considerably minimized, in fact, almost to the point of complete prevention, by the use of the inhibitor in the manner described above.

The nature and objects of the present invention having been thus described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. In a method in which a petroleum fraction containing olefins is extracted with S02, the steps of introducing into said petroleum fraction prior to its contact with S0: an oxidation inhibitor and maintaining said inhibitor in the mixture until the S02 is separated from the hydrocarbons.

2. In a method in which a petroleum naphtha is subjected to a thermal conversion during which olefins are formed, and then to extraction with sulphur dioxide, the steps of introducing into gether with any oxygen which may be present, are removed, and then adding an oxidation inhibitor to the residuaI naphtha prior to the extraction thereof with S02 whereby said inhibitor is present at all times while said naphtha is in contact with $02.

4. A method according to claim 1 in which the inhibitoremployed is a petroleum phenol.

' RICHARD EZTANNICH.

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