US2775545A - Prevention of sourness of sweet naphthas during distillation by distilling in the presence of an alkylene oxide and a salt of an organic acid - Google Patents

Description

NoDrawing; Application November 7', 1955,

SerialNo. 545,530:

,1 1 8 Claims. (Cl. 196-25) This inventionrelates to therpreparation of industrial naphthas... ltis more specifically concerned with the United States PatennQ distillation of a sulfurecontaining, hydrocarbon mixture separated intovariousboiling ranges. Although highly aromatic petroleummagihthas are readily available; the

subject. invention is only concerned with straight-run 3O ,petroleum naphthas or equivalent hydrocarbonmixtures. Althoughfnaphthas consist essentially of mixtures. of low-boiling.hydrocarbons, there are present in the, crude .oils fromwhichithese. hydrocarbon mixtures are derived various-impurities, which arelretained in the distillates .rh-ir'in'g .theffractional distillation ofrthe crude. T he nature of. these. impuritiesvariesaand includes, amongothcrs organ'ic and,inorganic acids, nitrogen compounds, and sul fur compounds. Because-of the relatively high-boiling .rauge of most of these materials, .they are found only in thewheavier petroleum distillates. However-{boiling 'within--the naphtha range are a number :of sulfur compounds whose presence is deleterious because they impart to 'the' naphthadistillate certainundesirable. odors as. well as .corrosiveproperties whichcause metal corrosion orjth'e '.darkening of ,paints' or varnishes. Specific applications of naphtha compositions, make it. necessary to refine naphthas vin order! to. control. their properties and insure "uniform quality. As was pointed outin the definitionof a naphtha, naphtha preparation processes generally in; volve chemical refining followed by distillation of the chemically, treatediproduct. to produce naphthas haying a-selecte'cl boiling range; Although refining processes are available, which remove substantial amounts of 'ob-' noxious :sulfur compounds from admixture witlr'hydroicarbons, these.processes..,generally. do. not reduce the sul- 'furnoontent sufficiently to eproduce a non-corrosive .and.

" substantially odor-free naphtha.- In the crefiningiofg petro leumi-anaphthas, processes referred to as: sweetening=' processes ,areremployeqd in; which the objectionablel sulfur compoundgsuch asimercaptans, are converted or. trans-l formed into-acceptable ones 1 without altering the sulfur content of the oil. I sulfu'r' compoundsfloes "not affect the usefulness of-the The presence of the less noisome naphthas as industrial products as long as these sulfur compounds rarer non corrosive sand substantially. odorfree: Examplcsof suitable; processes which areemployed. -':in' the fsweeteningiof slight-petroleum products .are the doctor-treat: usingasodium :plumbite, .the hypochlorite treatment, and treating-methods employing. copper-con- 'tainingreagents -such as copperchlorideior. copper oxide. Qt'hensuitabIe :sweetening? processes are-comprehensive- Patented Dec. 25, 1956 2 1y discussedby V. A. Kalichevskyin a series of articles entitled sweetening-panda desulfurizationof light petroleum products, Petroleum Refiner, 30, (1951).

There are aivariety of processes which may be employed as the complementary fractionation step in the naphtha lpreparationprocess. In-some instances, such as the vapor-phasetreatment of petroleum distillates with copper oxide-oil slurries, the :treated vaporous distillate is reintroduced into lthercrudeoil distillation tower and recoveredas .azconventional' side-stream cut. Other recover-yprocesses employ special naphtha re.run units; in which the naphtha is. fractionated in a separate, fractionating system. Where particularly close. boiling-range fractions aredesiredwith a/minimum overlap of boiling ranges, superfractionators havingna large number of plates are employed. In units of this nature, due-to the height of-a column necessary toaccommodate the large number of plates, the column is split into two sections with the overhead from the first section passing into the base of the second section. Reflux from-the second section is returned to the top of the first section. Regardless of the combination of'refining and distillation processes employed these sequential steps occur in naphtha preparationprocesses. As a result, it has been found that even 'though the'chemical refining step produces a naphtha free from objectionable sulfur compounds by converting them to relatively innocuousorganic sulfides or disulfides, the elevated temperatures "employed in subsequent distillation steps'cause the reconversion of the unharmful sulfur compounds into noxious sulfur compounds which are corrosive and odorous; This problem is particularly prevalent in the preparationof naphthas which contain components boiling above about 300 F. However, this condition may also occur in the treatment of the lower-boiling naphthas because even though special designs are employed in order to avoid excess skin temperatures on the walls of the fractionation columns, high temperatures which facilitate the conversion of the organic sulfide or 'disulfides into undesirable sulfur compounds frequently are encountered. As a result, the naphtha products produced in this manner containing these obnoxious sulfur compounds do not conform to established specifications relative to the presence of corrosive and odorous sulfurcontaining materials.

A number of tests have been devised as criteria to determine the efiect of sulfur and sulfur compounds in naphtha. These tests, which are qualitative in nature,

include the copper strip corrosion test, the doctor test,

and the distillation corrosion test. This latter test is also vvariously known as the Amsco corrosion test, the full flask distillation test, or the-full-corrosion test. These .tests are standards in the petroleum industry and are described in anaiticle ent tl f f sulfur n sulfur compounds innaphtha upon ,certain corrosion tests, L. M. Henderson et al., Industrial and Engineering Chemistry,

Analytical-Edition; 1 2- l-),-1- et seq. The-distillation corrosion test is particularly severe as compared with other corrosion tests used in the petroleum= industry, and there .is no correlation between the resultsof this test and'those of-other corrosion' te'sts; The naphtha products Whichin the courserof'the distillationstepare transformed into off spec'ification products with regard'" to these tests, cannot be repurified by'a simple washing of the distillate with an aqueous solutionloficaustic" soda and it is necessary to re-treat the contaminated distillate inia 's'weetening (process; This, of course, is uneconomical and unsatisfactony refining practice. However, according to this invention .it hasnbeen, founcl that by carrying out the distillation step vin the presence of a stablizer, the undesirable deterioration of the organic sulfides or disulfides is prevented. and. the development of the undesirable properties avoided. It istherefore an object of this invention to provide a method for stabilizing sweetened hydrocarbon distill-ates during distillation. It is another object of this invention to "provide a method for preventing the developmeut of odor or eorrosiveness in sweetened petroleum liquids during distillation. These and other objects and advantages will be made more apparent from the following detailed description of this invention.

According to this invention it has been found that if the distillation of a sweetened hydrocarbon mixture containing petroleum sulfur compounds, including disulfides, is carried out in the presence of an alkylene oxide and an oil-soluble basic salt of a high molecular weight organic acid, not reactive with the alkylene oxide, a satisfactory noncorrosive product as determined by the aforementioned test methods will be obtained without requiring additional treating for the removal or conversion of obnoxious sulfurcompounds. The essence of the invention is shown by the following illustrative but nonlimiting examples in which a petroleum naphtha distillate was first sweetened by contacting the distillate with an admixture of finely divided fullers earth and cupric chloride using the Linde Sweetening Process. The admixture was agitated until the petroleum distillate was made "doctor sweet. The sweetened petroleum distillate was recovered and separated into a plurality of 100 ml. portions, which were then subjected to the standard ASTM distillation test. Each distillation was carried out employing a different additive combination admixed with the distillate charged to the distllaton flask. A series of 10 ml. fractions were taken for each distillate, each fraction being subjected to the scrutiny of the doctor test.

The data obtained in these distillations are listed in Table l. The naphtha which was treated was from a mixture of sour and sweet crudes and had the following characteristics Distillation I. ll. P. 5% 50% 95% E. P.

111 F. 136 F. 260 1?. 392 F. 414 F.

Sulfur distribution, percent weight Sulfur, total 0.077 Sulfur, free 0.008 Sulfur, HzS None Sulfur, RSH 0.030 Sulfur, R252--- 0.004 Sulfur, RzS 0.028

um distillates. In these sweetening processes no correlation is required between the boiling range of the distillate being treated and the boiling point of the alkylene oxide treating agent. However, according to the instant invention, it has been found that in order to effectuate the objectives of this invention, it is necessary to employ an alkylene oxide having a boiling point at least as high as the end boiling point of the naphtha fraction being distilled. This requirement is seen from the data in Table 1 wherein it is shown that neither ethylene oxide (B. P. 51 F.) nor propylene oxide (B. P. 95 F.) provides the advantages that are obtained when an alkylene oxide, viz., dodecene epoxide (B. P. 520 F.) having the aforementioned boiling point characteristics is employed. The data also shows that it is necessary to employ the combination treating agent of this invention as it is shown that the constituents of the composite, when used separately, are not effective.

The alkylene oxide which is added to the sulfur-containing hydrocarbon distillateprior to fractionation can be any alkylene oxide having a boiling point at'least as high as the end boiling point of the naphtha being distilled. Specific examples of useful alkylene oxides include but are not limited to aliphatic alkylene oxides having suitable boiling points, as well as derivatives thereof, such as epoxides of unsaturated fatty acid esters, e. g. methyl oleate; epoxides of unsaturated hydroxy acid esters, e. g. methyl ricinoleate; epoxides of unsaturated alcohols, e. g., 2-octen-l-ol; epoxides of unsaturated branched chain hydrocarbons, e. g. diisobutylene, triisobutylene and tetraisobutylene; epoxides of alicyclic olefins, e. g. u-pinene; epoxides of arylalkenes, e. g. styrene.

In carrying out this invention the amount of alkylene oxide, which should be present in the distillation zone while conducting the preparation of the special naphthas will depend upon the amount of sulfur compounds which are contained in the distillate undergoing distillation. In treating conventionally sweetened petroleum distillates, between about 1.0 to 3.0 weightpercent of alkylene oxide stabilizer should be used. The optimum quantity, however, should be determined experimentally by making tests on samples of the naphtha which are to be subjected to processing in the distillation unit. In some instances as much as 5% may be necessary but in others the presence of amounts as low as 0.5% sometimes may be eifective.

The basic salt which is employed as an essential part 7 of the distillation additive combination may be any oilsoluble basic salt of an organic acid, having a positive base number, which is non-reactive with alkylene oxide S lfu id 0,007 and has a boiling point at least as high as the end boiling TABLE 1 Volume Percent Over 10 20 30 40 50 First Doetor Sour Run Material Added to Charge Naphtha Overhead Temperature at Cut Point (F.) out Number Nona 144 169 196 214 235 250 275 286 334 7(250 275) Ethylene Oxide 167 183 194 226 241 259 282 289 7 259-282) Bentonite plus Ethylene Oxide. 151 212 250 270 284 304 322 7 284 304 2 m1. Dodecene Epxoide. 156 178 205 221 234 270 295 7 270-29 1.2 g. Barium Sulionate 151 183 201 216 226 262 275 v 7 262-275 2 ml. Dodeeene Epoxide plus at m Sulfonate 158 189 205 230 255 271 309 329 356 363 9 329-356 1.2 g. Barium Sulfonate plus Propylene Oxid 164 198 216 234 250 270 302 324 352 6(250-270 Ethylene Oxide plus 1.2 g. Barium Sultan e 254 286 326 349 375 6(254-286) 1 Basic oil-soluble barium sulfonate containing 12.7% ash as sulfate and having a 30 base number, prepared by sulionating a medium neutral oil followed by reacting the sulfonated oil with excess barium hydroxide.

The tabular summary in Table 1 shows the various cut points at which the distillate went ofl? specification with regard to the doctor test used as the criterion and illustrates the unusualness of the instant invention. The prior art in U. S. Patents 2,530,561 and 2,575,989 discuss the efiectiveness of ethylene oxide alone or in combination with an alkaline catalyst for sweetening petrolerange of the naphtha distillate being fractionally distilled. This constituent is defined in the appended claims as a basic salt of a high molecular Weight organic acid. The use of such oil-soluble basic salts constitutes an essential part of the subject invention because a uniform and complete distribution of the additive combination in the hydrocarbon fraction can be effected, the hydrocarbon fraction is not subjected to contact with any extraneous immiscible alkali solutions which require subsequent treatment steps, the unsatisfactory distillation of heterogeneous admixtures produced by the presence of an aqueous phase is avoided, and minimum amounts of basic materials are employed. Examples of suitable basic salts of highployed include sodium naphthenate, barium naphthenate,

sodium petroleum sulfonate, calcium oleate, magnesium stearate, potassium naphthalene sulfonate, etc. Salts of petroleum sulfonates are preferred, especially barium and calcium salts.

In formulating the composite distillation additive of this invention the amount of .the basic salt employed will depend upon the character of the oil being treated, as well as the nature and concentration of the sulfur compounds present. It is preferable to employ from about 1.0 to 5.0%, by weight, and preferably 1.02.0%, by weight, of the basic constituent, based on the naphtha. Although the illustrative examples of this invention describe the use of a batch-wise distillation process, the instant invention may be carried out continuously. In the event that the former technique is employed, the composite additive is admixed with the naphtha charge and the distillation effected. It is preferred, however, that the distillation process be carried out continuously, in which instance the necessary amounts of composite additive may be introduced into and admixed with the incoming feed.

Another important feature of the instant invention is illustrated by the condition of the still pot after the batch distillation has been substantially completed. In employing the instant invention the residue remaining in the still pot even after about 95% by volume or more of the original charge has been distilled is a clear, mild smelling liquid as opposed to the extremely odorous and adherent black solid material which remains in the still pot after a conventional batch fractional distillation has been effected. Accordingly, the use of this invention eliminates a cleaning and disposal problem of noxious still-pot residues normally remaining in a fractional distillation unit after a sulfur-containing hydrocarbon fraction has been distilled.

The invention is broadly directed to the production of high quality naphthas and provides an improved method of distilling doctor sweet naphthas whereby increased yields of higher boiling, sweet distillates are obtained without further treating. Sweetened sulfur-containing hydrocarbon fractions boiling between about 100 F. and 500 F. may be treated in accordance with this invention. However, the invention has particular application in the treatment of straight-run, aliphatic petroleum distillates boiling between about 100 F. and 400 F. In carrying out the instant invention it is not necessary that the distillation efliuent be further treated in order to provide a satisfactory non-corrosive product.

We claim as our invention:

1. Indie distillation of an oxidatively sweetened hydrocarbon fraction containing organic sulfur compounds, including disulfides, at temperatures normally effective for the conversion of said compounds to produce doctorpositive products, the improvement which comprises carrying out the distillation in the presence of sufficient amounts of an admixture of an alkylene oxide having a boiling point at least about as high as the end boiling point of said fraction and an oil-soluble, basic salt of a high molecular weight organic acid to prevent said conversion and the development of a doctor-positive distillation efliucut.

2. A distillation in accordance with claim 1 in which said basic salt is an alkaline earth metal sulfonate.

3. A distillation in accordance with claim 2 in which said basic salt is barium petroleum sulfonate.

4. In the distillation of an oxidatively sweetened hydrocarbon fraction containing organic sulfur compounds, including disulfides, at temperatures normally eifective for the conversion of said compounds to produce doctorpositive products, the improvement which comprises carrying out the distillation in the presence of 0.5-5 by weight, based on the charge of said fraction, of an alkylene oxide having a boiling point at least about as high as the end boiling point of said fraction, and 15% by weight, based on the charge of said fraction, of an oil-soluble, basic salt of a high molecular weight organic acid to prevent said conversion and the development of a doctorpositive distillation effluent.

5. In the distillation of light petroleum distillate boiling between about and 500 F., containing organic sulfur compounds, including disulfides, at temperatures normally effective for the conversion of said compounds to produce doctor-positive products, the improvement which comprises carrying out the distillation in the presence of 0.5-5% by weight, based on the charge of said distillate, of anadmixture of an alkylene oxide having a boiling point at least about as high as the end boiling point of said fraction, and 15% by weight, based on the charge of said distillate, of an oil-soluble, basic salt of a high molecular weight organic acid to prevent said conversion and the development of a doctor-positive distillation eifluent.

6. A sweetening process for producing doctor-sweet petroleum naphtha distillate which comprises contacting a doctor-positive, sulfur-containing, light petroleum distillate in an oxidative sweetening process under conditions to produce a doctor-negative petroleum distillate containing organic sulfur compounds, including disulfides, distilling said doctor-negative petroleum distillate, at temperatures normally eifective for the conversion of said sulfur compounds to produce doctor-positive products, in the presence of 0.55% by weight, based on the charge of said distillate, of an admixture of an alkylene oxide, having a boiling point at least about as high as the end boiling point of said fraction, and 15% by weight, based on the charge of said distillate, of an oil-soluble, basic salt of a high molecular weight organic acid to prevent said conversion and the development of a doctor-positive distillation efliuent, and recovering doctor-negative distillate products.

7. A method for fractionally distilling an oxidatively sweetened petroleum naphtha containing organic disulfides susceptible to decomposition under distillation conditions which comprise fractionally distilling said naphtha in the presence of 0.5-5 by weight, based on the naphtha charge of dodecene epoxide and 1-5% by weight, based on the naphtha charge, of basic barium petroleum sulfonate to prevent the decomposition of said disulfides and the development of a doctor-positive distillation elfiuent.

8. In the thermal treatment of oxidatively sweetened hydrocarbon fractions containing organic compounds, including disulfides, at temperatures eifective for the decomposition of said organic compounds, the improvement which comprises carrying out the thermal treatment in the presence of sufficient amounts of an alkylene oxide having a boiling point at least about as high as the end boiling point of said fraction and a basic salt of a high molecular weight organic acid to prevent the decomposition of said organic compounds and the development of a doctor-positive distillation etfiuent.

No references cited.

Claims (1)

1. IN THE DISTILLATION OF AN OXIDATIVELY SWEETENED HYDROCARBON FRACTION CONTAINING ORGANIC SULFUR COMPOUNDS, INCLUDING DISULFIDES, AT TEMPERATURES NORMALLY EFFECTIVE FOR THE CONVERSION OF SAID COMPOUNDS TO PRODUCE DOCTORPOSITIVE PRODUCTS, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT THE DISTILLATION IN THE PRESENCE OF SUFFICIENT AMOUNTS OF AN ADMIXTURE OF ANALKYLENE OXIDE HAVING A BOILING POINT AT LEAST ABOUT AS HIGH AS THE END BOILING POINT OF SAID FRACTION AND AN OIL-SOLUBLE, BASIC SALT OF A HIGH MOLECULAR WEIGHT ORGANIC ACID TO PREVENT SAID CONVERSION AND THE DEVELOPMENT OF A DOCTOR-POSITIVE DISTILLATION EFFLUENT.