US2324927A - Refining of mineral oils - Google Patents

Description

Patented July 20, 1943 REFINING OF MINERAL OILS" 1 William 0. Heilrharil Crawford, N. 1-, assignor to" Standa.rd Oil Development Company, a corporation of Delaware Application February 24, 1941; semi No. 380,272

V 5 Claims. (01. rec-32 The present invention is concerned with the refining of mineral oils. The'invention is more particularly concerned With an improved operation comprising a particular arrangement and sequel-icy of stages forthe removal of mercap ten compounds from petroleum oil,zespecia1ly when using an alkali metal hydrc-xidesoluticn. In accordance with. the present .processthe feed oil is segregated into a relatively low boilin frac+ tion and into a relatively high boiling-fraction. The segregated fractions are'contactedwith alkali metal hydroxide solutions withdrawn from a common storage. The spent alkali metal hydroxide solutions are segregated from the respec tive treating zones, regenerated and returned to the storage zone; The spent alkali metal hydroxide solution withdrawn from the treating zone utilized in the removal of mercaptan compounds from the relatively low boiling petroleum oil fraction is treated with an oxygen containing gas in a manner to convert the mercaptid'esto the corresponding disulfides; The alkali metal hydroxide solution containing the disulfide's is combined with the caustic solution withdrawn from the treating. zone wherein the relatively o high boiling petroleum oil fraction istreated, and the mixture steam distilled under conditions to convert the relotivelyhieh boiling mercaptides to the corresponding mercaptans which are re moved overhead-alongwith the disulfide constltu cuts. The regenerated alkali metal hydroxide solution is Withdrawn as a bottoms product and recycled to the respective treating zones,

It is known in the .art to refine petroleum oils by various procedures, particularly for the removal of mercaptan'oompounds therefrom. One method employed, for example; is to treat the feed oil with a soca led doctor solution," which usually comprises a saturated solution of lead oxide dissolved in a sodium hydroxide solution. When a feedoil containing mercaptans'is treated with this solution the :mercaptans are converted to lead mercaptides which are soluble in the oil being treated. The-oil solution containing the soluble lead mercaptides is contacted with a reagent adapted to precipitate the lead compounds and to convert the sulfur compounds todisulfides.

This is usually accomplished by the addition of free,sulfu iresulting in the formation. of lead sulfide end the corresponding :alkyl disuifides. This operation is-not entirely]setisiactory, particularly-in the treatn'lent ofrelatively high boil ing .oils, for several reasons. {One disadvantage that it lis -relatively diffioult to control the exact amonntof suliur necessary to secure the complete ill) precipitation of the lead as lead sulfide. If too little sulfur isadded, some of the lead remains dissolved in the oil as soluble lead mercaptides which results in the production of an oil of in.- ferlor quality, particularly withr'espect toits stability and burning properties. If an excess of sulfur be added, the excess sulfur dissolves in the oil and materially increases itscorrosiveness substantially affects its other desirable properties It has, therefore, been suggested that ther operations be employed which will not only remove the mercaptans but will also function to secure an overall reduction-in the sulfur content of the final product. 'One process suggested-is to treat'the oil with an alkali solution, as for example, a sodiumhydroxide solution. Operations of this character have'not heretofore been entirely satisfactory for the reason that the relatively hlgh"boili;rig mercaptans present in the oils boiling in the heavy naphtha and heating oil boiling-ranges are not particularly reactive therewith resulting in only a partial removal of the mercaptans-unless an excessive and prohibitive quantity of the reagent be employed.

I havehowever, now discovered an operation hywhich itis possible to efficiently and economie sally i ovc relatively high boiling mercaptans p iu these relatively high boiling oils utilizing a relatively low quantity of the alkali metal hydroxide-solution based upon the totalyolume of oil beingtretaed. My process comprises segregating the ieedcil into a relatively low boiling fraction and a relatively high boiling fraction. I treatthe relatively low boiling fraction and the-relatively high boiling fraction in separate contacting zones with an alkali meted by drox-icle solution withdrawn from a common source or-which-is direct-1y recycled from the regeneration zone and which preferably comprises revi-viiied and regenerated alkali metal hydroxide solution produceddn a manner as hereinafter described. The operating conditions in the respect-ive zones ere'adjusted to secure complete removal of the mercaptan compounds-from the feed oils. The spent alkali metal hydroxide so lution withdrawn from t-he-zonewherein the relatively low boiling fraction is treated'is withdrawn and subjected in a tertiary zone to contact with on oxygen-containing gas under conditions to- I the treating gas.

. mercaptans and mixture is passed to a regeneration zone in which the same is treated to remove the mercaptans and disulfides from the spent alkali metal hydroxide solution. This is preferably secured by steaming the combined alkali metal hydroxide solution streams under conditions to convert the mercaptides to the corresponding mercaptans which are removed overhead from the regeneration .zone along with the disulfide compounds produced in the tertiary zone. The regenerated pletely free of sulfur compounds is removed and recycled to the respective treating zones.

My process may be readily understood by ref-, erence to the attached drawing illustrating an embodiment of the same. For the purpose of description it is assumed that the feed oil com-- prises a petroleum oil boiling in the motor fuel boiling range. distillation zone I by means of line 2 in which it is segregated into a relatively low boiling fraction which is removed by means of line3, and into a relatively high boiling fraction which is removed by means of line I. The relatively low a boiling fraction is introduced into primary treat- :ng zone 5 wherein it is contacted with an alkali metal hydroxide solution which for the purpose ofdescription is taken to be a sodium hydroxide solution and which is introduced into zone 5 by means of line 8. Temperature and pressure conditionsand other operating conditions are adjusted'to secure substantially complete removal of the mercaptan compounds'fromthe low boiling fractions. The treated fraction is removed from treating zone 5 by meansof line 6 and handled or further refined in any manner desirable.

A The relatively high boiling fraction is introduced into secondary treating zone 1 in which it is treated with a sodium hydroxide solution which is introduced into zone 1 by means of line 22. Temperature and pressure conditions are similarly adjusted as well as other operation conditions in order to secure complete removal'of the mercaptan compounds from this fraction. The treated high boiling fraction is' removed from zone 1 by means of line 9 combined with the treated relatively low boiling fraction and withdrawn as a mercaptan free product from the system by means of line I ll. The spent sodium hydroxide solutions are withdrawn from zones 5 r combined with the spent hydroxide solution {withdrawn from zone 1'by means of line I2. The mixture is introduced into regeneration zone I1 and thesulfur compounds removed overhead as inercaptans anddisulfides'from the sodium hydroxide solution.

plis'hed by introducing steam by means of line This is preferably accom- IBand maintaining-conditions in zone I1 adapted to convert the mercaptides in the stream withdrawn from zo'ne 1 to the corresponding to rembvexthe same overhead by means of.1ine [9 along with the disulfide compounds. A-regenerated caustic solution subalkali metal hydroxide solution substantially com-t The feed oil is introduced nto employed, it is preferred stantially completely free of sulfur compounds is withdrawn from zone I1 by means of line 20, passed to storage 2| and recycled to the respective primary and secondary treating zones by means of line 22 and line 8.

The process of the present invention may be widely varied. It is to be understood that zones I, 5, 1, I3 and I1 may comprise any suitable number and arrangementof units. Under certain conditions. it may be desired to reconcentrate the caustic solution returned to'storage 2|. If this operation be employed, the caustic solution is passed to reconcentration unit 23 by means of line 24. Temperature and pressure conditions are adapted to remove overhead by means of line 25 water and to remove by means of line 25 a reconcentrated solution.

By operating in the manner described it is possible to remove more efiiciently and economically mercaptan compounds from feed petroleum oils which boil over a relatively wide range. Although a potassium hydroxide solution may be to employ a sodium-hyparticularly one having a concentration in the range from 15% to 30% sodium hydroxide. The amount of alkali metal hydroxide solution utilized per volume of oil will be sufiicientto secure the desired removal of the mercaptan compounds. In general, the amount necessary is in the range from about 15% to 30% based upon the total volume of feed oil being treated. The amount necessary will depend upon the character of the mercaptan compounds present, their concentration, and the boiling range of the feed oil beingtreated.

Although the feed oil may be segregated into a relatively low boiling fraction and into a relatively high boiling fraction of approximately equal volume,'wherein the final boiling point of the low boiling fraction and the initial boiling point of the high boiling fraction approximate the mid-boiling point of the feed oil, and the respective streams contacted in the primary and secondary treating zones with an alkali metal hydroxide solution which has been approximately equally segregated, I have found that particularly desirable results are secured providing the feed oil be segregated into a relatively low boiling fraction which comprises about 60% to 80% of the total feed oil and into a high boiling fraction which is about 20% to 40% of the feed oil. The feed oil fraction segregated in this manner may be contacted in the respective treating zones with alkali metal hydroxide streams which have beensegregated in about equivalent volumes. However, it is prefered to segregate droxide solution,

tively large alkali metal hydroxide stream which comprises from'about to of the total alkali metal hydroxide stream, and to utilize the same in contacting the relatively small quantity of the feed oils comprising the relatively high boiling fraction in the secondary treating zone. When-operating as described, mercaptan come treating reagent efficiently by utilizing a minimum amount of steam. Furthermore, the relaively low boiling mercaptans which are difficultly hydrolizable are converted to higher boiling disuliides which boil approximately in the range of the relatively higher boiling mercaptans, which are regenerated from the mercaptides T-resent in the alkali metal hydroxide utilized in the treatment or" the relatively higher boiling petroleum oil fraction under these conditions.

What I claim as new and Wish to protect by Letters Patent is:

1. Process for the removal or" mercaptan compounds from a feed oil boiling in the motor fuel boiling range, which comprises segregating 1e feed oil into a relatively low boiling fraction and into a relatively high boiling fraction, contacting the relatively low boiling fraction in a primary treating zone with an alkali metal hydroxide solution under conditions to remove mercaptan compounds, separating the relatively low boiling fraction from the alkali metal hydroxide solution, withdrawing said alkali metal hydroxide solution from the primary treating zone and treating the same in a tertiary zone with an ox gen containing gas under conditions to convert mercaptide compounds present therein to the corresponding disulfides, treating the relatively high boiling fraction of the feed oil in a secondary treating zone with an additional quantity of alkali metal hydroxide solution under conditions to remove therefrom mercaptan compounds, separating said treated relatively high boiling fraction and combining the same with said treated relatively low boiling fraction to produce a finished product, separating the alkali metal, hydroxide solution from said secondary treating zone and combining the same with the alkali metal hydroxide solution withdrawn from said tertiary zone, treating the combined streams with steam under conditions to remove the sulfur compounds therefrom, and recycling the regenerated alkali metal hydroxide solution to said primary and said secondary treating zones. 7

2. Process as defined by claim 1, in which said a kali metal hydroxide solution comprises a sodium hydroxide solution,

3. Process as defined by claim 1, in which said reed oil is segregated into a relatively low boiling fraction which comprises from about 60% to about of the feed oil and into a relatively high boiling fraction which comprises from about 26% to about 40% of the feed oil.

2. Process as defined by claim 1, in which said feed oil is segregated into a relatively low boiling iraction which comprises from about 68% to about 8 l% oi the feed oil and into a relatively high boiling fraction which comprises from about 26% to about 40% or the feed oil, and in which the segregated feed oil fractions are treated in he respective treating zones with an equal amount of recycled alkali metal hydroxide solution.

5. Process as defined by claim 1, in which said feed oil is segregated into a relatively low boil- .ing fraction which comprises from about 60% to about 80% of the feed oil and into a relatively high boiling fraction which comprises from about 20% to about 40% of the feed oil, and in which the relatively low boiling fraction of the feed oil is contacted in said primary treating zone with from about 20% to about 40% of the alkali metal hydroxide solution based upon the total quanty of solution used, and in which said relatively high boiling fraction is treated with about to of the alkali metal hydroxide solution based upon th total quantity of solution used. 6. Process as defined by claim 1, in which the alkali metal hydroxide solution comprises a sodium hydroxide solution and in which said solution is regenerated prior to recycling the same to the respective treating zones utilizing steam under conditions to convert the Inercaptides present in the alkali metal hydroxide solution withdrawn from said secondary treating zone to the corresponding mercaptans and under conditions in which said mercaptans along with the disulfides produced in said tertiary zone are removed overhead.

WILLIAM 0. HEILMAN.

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