US2057918A

US2057918A - Process of desulphurizing petroleum oils

Info

Publication number: US2057918A
Application number: US687348A
Authority: US
Inventors: Charles M Ridgway
Original assignee: Pure Oil Co
Current assignee: Pure Oil Co
Priority date: 1933-08-29
Filing date: 1933-08-29
Publication date: 1936-10-20
Anticipated expiration: 1953-10-20

Description

@et 20, 1936. C R|DGWAY 2,057,918

PROCESS OF DESULPHURIZING PETROLEUM OILS Filed Aug. 29, 1933 C'o nderrser Press u?? e Zie f Patented Oct. 20, 1936 PROCESS F DESULPHURIZING PETROLEUM OILS charles M. mamy, Midland, Mich., assigner to The Pure Oil Company, Chicago, Ill., a corporation of Ohio Application August 29, 1933, Serial No. 687,348

12 Claims.

y This invention relates to the treatment of petroleum oils to desulphurize the same, and comprehends a novel process and apparatus for carrying out the same; more specically, gasoline or naphtha of relatively high sulphur content is treated with an alkaline reagent, plumbite solution, followed by aging and heat treatment; together with various accessory steps; all of which are hereinafter described and claimed.

In the prior art, the conventional plumbite method of treating sour distillate is well known. Such prior operative steps include the formation of leadmercaptide and caustic soda by the reaction of sodium plumbite with the mercaptans in the oil. This lead mercaptide is then treated with sulphur in the prior art to form dialkyl-disulphide together with lead sulphide, excess sulphur reacting to form various polysulphides.

l Various objections to this prior process embrace corrosivity, actual increase of the sulphur content of the oil, and instability of the oil to the action of sunlight; the free sulphur and polysulphides being extremely corrosive and the dialkyl-disulphides having some corrosive action.

The present process obviates the disadvantages of prior methods of treatment in that sulphur is actually removed by the process through the formation of insoluble lead sulphide, while any remaining mercaptan sulphur is in the form of dialkyl sulphidewhich isl non-corrosive and has a pleasant odor. Furthermore, formation of dialkyl sulphide increases appreciably the boiling point ofthe sulphur compounds and the sulphur content may be further lowered by frac--y Raw untreated oil with or without carrier liquid, is scrubbed with spent caustic soda., which removes some hydrogen sulphide, free sulphur, and mercaptans. A scrub with lime water is preferred at this point, although it may be omitted. 'I'he treatment then proceeds with a fresh caustic scrub followed by contact washing with sodium plumbite solution. `'Ihe wash should be continued until the oil will no longer react with the treating agent. The next step is to settle and age the washed oil in suitable tanks. In this settling and aging step, the oil is held above F. (preferably from to 80 F.) for a period approximating hours, whereby the last traces of moisture and sodium plumbite are removed. Some basic lead mercaptide and lead sulphide precipitate at this point. The highest temperature that can be used without excessive vapor loss is maintained in the settling and aging tanks. If 5 desired, a, carrier liquid may be added during this step. After the oil has settled and aged, it is removed to a heating still. A shell still equipped with sprayy coils capable of jetting liquid on the bottom of the same at high velocity may be used. 10 A pipe still heater is preferably used in lieu of a shell still. Where a pipe still heater is used, sufficient pressure is maintained at the outlet of the coil to keep the oil in the liquid phase; the final temperature in the pipe still should be l5 above 250 F. and high enough to completely vaporize the oil at 5 pounds per square inch gauge pressure. In the pipe still heater, a high oil velocity and low heat input per square foot of heating surface is maintained. A pressure relief vvalve permits adjustment so that the desired amount of vaporization may be had. While pressure release may occur after passing the oil through a preliminary high pressure settling drum, it is preferred to adjust the pressure to permit complete vaporization of the oil into one or more settling drums by means of said pressure relief valves. In these settling drums, the pressure is so adjusted as to permit complete vaporization of oil and deposition of dry lead salts, 30 which lead salts can be reclaimed and converted to plumbite. 'Ihe pressure may be selected to allow the removal of lead salts as a suspension in unvaporized oil. The oil may be a portion of the original charge, or have been added for this *35 specific purpose as a carrier liquid. From the settling drums, the oil vapor is led to a fractionating tower, from which tower the oil vapors are led to a condenser and thence to a collecting tank which contains the finished product. The bottoms from the fractionating tower contain high boiling sulphur compounds contained in oil and approximate 5% of the charge led to the fractionator. The fractionating tower may be dispensed with, although it is highly desirable as its use removes sulphur compounds advantageously.

In the operation of the pipe still, the coil is maintained under suilicient back pressure to prevent vaporization in the tubes and under suf- 50 flcient high velocity to prevent lead sulphide deposit on the interior of the tubes. 'Ihe charge is heated high enough to completely vaporize the liquid as soon as the pressure is released. Upon the release of the pressure, the vapors are conperature of 400 F., care being taken to avoid direct heating of that portion of the vshell not covered by liquid. About 10% bottoms should oil may be slightly sour.

be left in the still. If higher still temperatures are required, steam may be used. This usually results in considerable desulphurizing but the The sweet fractions can be segregated from the sour fractions which can be treated with calcium or sodium hypochlorite'of suitable concentration, or with sodium plumbite or sulphur.

Where a pipe still is used, it is essential that the distillation at heating be carried out in the absence of steam inasmuch as the lead mercaptide will break down into mercaptans and lead" hydroxide in the presence of water at relatively high temperature.

After the mercaptans have been removed, it is A possible if desired, to further reduce the sulphur content by a judicious application of calcium hypochlorite. If this is done carefully, the resulting gasoline or naphtha will be sweet to doctor, have a pleasant odor and will be noncorrosive even when the distillation flask corrosioizi test is u sed. However, the oil after distillation is doctor sweet and non-corrosive, and the hypochlorite treatment should be used only in the case of extremely high sulphur gasolines where the sulphur contentafter the heat treatment is still above specified limits.

It will be observed from the above description that one feature of the invention is the aging of plumbite treated oil. Another feature of the invention resides in the use of heat treatment to decompose -lead mercaptide. Where the sulphur content of the original gasoline permits, the lead sulphide may be removed by heating the oil to approximately 350 to 400 F. and ltering at this temperature. Apparently, lead mercaptide all breaks down at a temperature of the order of 300 to 350 F. After the heat treatment at about 350 F. under Vsuiiicient pressure to keep the oil in the liquid phase, it may be passed through a cooler, then to a filter press to separate the lead salts from the finished oil. In the alternative, the hot oil can be passed directly through a percolation filter to remove the lead I salts from the nished oil.

fullers earth and/or bone black or silica-gel.

The spent filter medium containing the lead salts can be reclaimed by boiling with caustic solution in the presence of air. The solution containing the lead can be concentrated andrereference is to be had to the following description and the accompanying drawings,.wherein: Fig. 1 is a diagrammatic View of apparatus,

Inthis case, the liquid conventionally illustrated, which may be employed for carrying outthe present invention;

Fig. 2 is a similar view of a modified form of heater which may be used in the process.

Referring more particularly to the drawing, raw untreated oil of suitable boiling range, with or Without carrier liquid, may be` contained in a tank I. Usuallythis oil comprises raw gasoline or naphtha of high sulphur content, such as that obtained from certain of the Montana or Wyoming fields. In order to remove the undesirable sulphur compoundsfrom such oil, or to reduce the same to a point where the remaining sulphur is not objectionable, the oil is transferred from the tank I by way of a pipe line 2 to the suction side of a pump 3. Alsoentering the suction'side of the pump 3 is a pipe line 4 by which spent caustic is introduced into the oil stream. An intimate mixture ofthe oili and spent caustic takes place in, for instance, an orifice mixer 5 so that the oil is effectively scrubbed and allowed to' react with the spent caustic. From the oriiice mixer, the mixture of oil and spent caustic is introduced into a. separator 6 wherein there is separated from the oil a sludge containing hydrogen sulphide, free sulphur and mercaptans, the sludge being removed by way of a valved draw-oir line 1. From the separator 6, the oil is delivered to a pump 8 and is therein mixed with fresh caustic supplied through the line 9 and scrubbed or mixed in the orifice mixer' I0. After the fresh caustic has been allowed to react with the oil for a desired period of time, the mixture is passed into a second separator I I, where the sludge is removed by Way of the line I2 and treated oil passed to the suction side of a pump 43. A line I4 is employed to introduce the sodium plumbite solution into the oil withdrawn from the separator l I, and a mixture of sodium plumbite and oil is delivered to and passed through an orifice mixer I5, to effect a thorough commingling of the sodium plumbite solution with the oil undergoing treatment. From the mixer I5, the oils are transferred by way of a pipe line I6 to aging tanks Il in which the oil is retained for aV somewhat extended period of time and under a temperature of about 60 F. to secure an aging or reaction period. The spent plumbite solution together with any solid impurities which settle out are withdrawn rfrom the tanks Il through valved draw-oil pipes I1. Heating or cooling coils I8 may be used in the tank Il for maintaining -a temperature of the order of 60 F. of the oils thereincontained.

After being retained in the tanksy l1 for the desired period oi.y time, the oils are forced by means of a pump I9 through a tubular heating coil 20 disposed in a heater 2I, wherein the oils are heated to temperatures above 250 F. While maintained under super-atmospheric pressures Sulliciently high to maintain such oils preferably in the liquid phase. A.pressure relief valve 22 is provided in the outlet line 23 which leads from the coil 20 so that the pressures may be reduced to a desired point. The products are led from the coil 20 'to a plurality of settling drums 24 in which the oilsl vaporize and aredischarged through the overhead lines 25 to a fractionating tower 26. In the tanks 24, the lead salts are preof the tower 26 are cooled and liqueed in the condenser 29 and delivered to a storage container 30 as the treated finished product.

If a shell still is employed, as shown in Fig. 2, in lieu of the tubular type of heater indicated at 20, the drum 3l of the shell still is provided with a plurality of spray coils 32 Within the same through which the liquid oils passing from the pump I 9a are delivered under high velocity which force the liquid over the bottom of the shell, thus avoiding excessive deposition of lead sulphide on the bottom of the shell. The draw-oil` line ofthe shell 3| is indicated at 33 and the pressure reducing valve at 22a.

It will be appreciated that the apparatus described is subject to modication and variations Without departing from the ,scope of the present invention as the latter has been dened in the following claims.

What is claimed is:

1. The process of desulphurizing petroleum oil which comprises treating said oil with an alkaline plumbite solution without addition of sulphur, separating the plumbite solution from the oil and aging the oil for a period of several days in order to remove traces of moisture and plumbite solution a'nd to cause precipitation of lead-sulphur compounds.

2. The process according to claim 1 in which the oil is aged at a temperature above F.

3. The process according to claim 1 in which the oil is aged at a temperature between and F.

4. The process of desulphurizing petroleum oil whichcomprises treating said oil with an alkaline plumbite solution without addition of sulphur, separating theplumbite solution from the oil and aging the oil for a period of several days in order to remove traces of moisture and plumbite solution and to cause precipitation of lead-sulphur compounds, heating the oil to temperatures suiliciently high to decompose sulphur compounds remaining in the oil and separating resulting impurities from the oil.

5. vMethod in accordance with claim 4 in which the oil is heated above 250 F.

6. Method in accordance with claim 4 in which the oil is maintained under superatmospheric pressure during the heating step.

7. Method in accordance with claim 4 in which the oil is heated above 250 F. while being maintained under superatmospheric pressure.

8. Method in accordance with claim 4 in which the oil is separated from the high boiling sulphur compounds by fractional distillation following the heating step.

9. Method in accordance with claim 4 in which the oil is heated to a temperature between 300 and 400 F.

10. Method in accordance with claim 4 in which the oil is heated under superatmospheric pressure to a temperature between 300 and 400 F. and then ltered through solid adsorbent material.A

11. The method of desulphurizing petroleum oil without addition of free sulphur which comprises subjecting the oil to treatment with an alkaline plumbite solution, aging the treated oil for a period of several days in order to cause precipitation of lead-sulphur compounds, and iiltering the aged oilthrough a solid adsorbent material.

l2. Method according to claim 1 in which the oil is subjected to treatment with a hypochlorite following the aging step.

CHARLES M. RHDGWAY.