US2768930A - Refining of hydrocarbon oils - Google Patents

Description

Oct. 30, 1956 R. H. BROWN ET AL REFINING OF HYDROCARBON OILS Filed Nov. 27, 1953 i nited REFINHNG F HYDRCAN OILS Application November 27, 1953, Serial No. 394,556

7 Claims. (Cl. 1196-24) This invention relates to the refining of mercaptancontaining hydrocarbon oils to produce oils `of lower mercaptan and aromatic content and improved color and odor. More particularly it relates to an improved sulfur dioxide refining process whereby a color-stable and substantially sweetened distillate suitable for use as burning oil, furnace oil, diesel fuel or jet fuel is produced.

Petroleum distillates boiling in the heavier-than-gasoline range, i. e. within the range of between about 300 and 650 F. or higher, are employed in domestic heating installations and are generally known as furnace oils or heater oils. Other distillates boiling within this range are also employed for illumination purposes and are generally called kerosene or burning oil. Distillates also boiling within this range are employed as fuel for diesel engines and in the recent past, a large demand has arisen for jet fuels, also called JP-fuels which are produced from distillates in this boiling range. Straight run, i. e. virgin distillates, are preferred for these uses, but cracked distillates have also been employed.

rThe refining of petroleum distillates boiling in the heavier-than-gasoline range to produce sweet color-stable oils of low aromatic content is of major importance to petroleum refiners. extraction process is frequently employed by the refining industry to produce distillates of lowered aromatic hydrocarbon content. Although the Edeleanu process functions suitably for this purpose, it will lower the mercaptan content of the refined distillate by only a small amount and is not capable of producing refined distillates which have the very low mercaptan content, i. e. very low in mercaptan number or even sweet to the Doctor test, required by commerce. f

An object of this invention is a process for the production of a refined hydrocarbon distillate of lowered aromatic and mercaptan content. Another object is to produce a refined petroleum distillate boiling in the heavier-than-gasoline range which is substantiallyrmercaptan-free, of good storage quality, and of good color stability, and suitable for use as an excellent burning oil, heater oil, diesel fuel and jet fuel. Other objectsrwvill become apparent in the course of the detailed description of the invention. a .Y l In accordance with this invention, a sour petroleum distillate boiling in the heavier-than-gasoline range is extracted with liquid sulfur dioxide in the presence of a The Edeleanu liquid sulfur dioxide n tates Patent 2,768,930 Patented Oct. 30, 1956 ICC centrations and amounts sufficient to cause the reaction between the mercaptans contained in the oil and the carbonyl compound to proceed, e. g. about 0.5 to 1.5 pounds of 98% concentration sulfuric acid per barrel of oil.

The feed to this process may be straight run (virgin) distillates, or it may be derived from various petroleum conversion processes, such as thermal cracking, catalytic cracking, hydrodesulfurization, etc. The process is particularly suitable for sour virgin distillates boiling in the heavier-than-gasoline range such as kerosene, heater oil, diesel fuel, and jet fuel which contain objectionable amounts of organic sulfur compounds, particularly mercaptans, and objectionable amounts of aromatic hydrocarbons. In general, sour distillates which contain more than about 15% of aromatic hydrocarbons are not satisfactory as burning oils or heater oils, and such distillates are suitable feed stocks to the process of this invention. The Edeleanu liquid sulfur dioxide extraction process has been kwidely used within the refiningl industry 'on petroleum distillates, particularly those boiling in the heavier-than-gasoline range, to reduce their aromatic hydrocarbon content. In the sulfur dioxide extraction process, the petroleum distillate is contacted with at least enough liquid sulfur dioxide to exceed the solubility of the liquid sulfur dioxide in the oil so that two phases are present in the extractor, i. e. a rafnate phase consisting of the refined (low aromatic content) oil which contains some dissolved and occluded sulfur dioxide, and an extract phase consisting of liquid sulfur dioxide and dissolved hydrocarbons high in aromatic content together with some organic sulfur compounds. The relative miscibility of liquid sulfur dioxide and hydrocarbon oil charging stock varies with temperature, greater miscibility in general being encountered at higher temperatures and lesser miscibility at lower temperatures. Usually between about 15 and 200 volume percent, preferably between about 25 and 100 volume percent of liquid sulfur dioxide based on feed is employed in the process. The temperature at which the Edeleanu process may be carried out may be as high as about 25 C. or as low as about 40 C., although temperatures between about 0 C. and 20 C. are preferred. The temperature of treatment may be in part determined by the freezing point of the feed stock being processed. Pressures sufcient'at least tomaintain a substantial portion of the sulfur dioxide in the liquid phase are employed. At the lower temperatures no substantial pressure in excess of atmospheric need be employed. With highly viscous feed stocks, a diluent such as propane, butano, or pentane, may be employed. l

The organic carbonyl compound which may be employed in this process may be an acyclic or cyclic aldehyde or ketone, such as alkyl, cycloalkyl, cycloalkylalkyl, aryl-cycloalkyl, alkenyl, cycloalkenyl, aryl, alkaryl, cycloalkaryl, aralkyl aldehydes or ketones. Examples of such compounds are formaldehyde, acetaldehyde,

,propionaldehyde, isobutyraldehyde, furfuraldehyde, bensmall amount of an organic carbonyl compound, such zaldehyde, acetone, methyl ethyl ketone, isopropylphenyl ketone, and the like. The preferred organic carbonyl compounds are the low boiling aldehydes, i. e. formaldehyde and acetaldehyde. Formaldehyde and acetaldehyde may exist in various physical states, such as the solid form, gaseous state, or in aqueous solution, and such come withinv the definition of formaldehyde, acetalde- 4 hyde, and low boiling aldehydes. For example, acetalde- A refined distillatel of hyde' exists in its natural state as a liquid or it may exist inthe trimer form knownas paraldehyde, also a liquid.V

Formaldehyde exists in its natural state as a gas. vIt may also be obtained and employed as an aqueous solul tion commonly called formalin which contains about oil:V The acidic condensation catalyst is employed in con- 38% formaldehyde.v Formaldehyde also exists inthe solid state as the ring-structured trioxane and other polymeric forms such as paraformaldehyde and polyoxymethylene in its various polymeric forms. rlfhese aldehydes may be employed in any of the physical forms mentioned above.

The carbonyl compound may be introduced into the sulfur dioxide extraction zone together with the oil to be refined; it may be introduced together with the sulfur dioxide; it may be introduced separately into the extraction zone; or it may be introduced directly into the extraction zone along with some of the liquid sulfur dioxide, with or without the condensation catalyst. lt is preferred to introduce it together with the condensation catalyst and'sorne of the liquid sulfur dioxide directly into the extraction Zone. Higher molecular weight carbonyl ccmpounds, which ordinarily are more hydrophobic, may be introduced vwith lthe oil and lower molecular weight carbonyl compounds, which ordinarily are more hydrophilic, may be introduced with the liquid sulfur dioxide.

The amount of carbonyl compound employed in this process depends to some extent upon the type of oil being treated. Larger amounts of carbonyl compound are required when treating cracked stocks containing oleiins, since there is a tendency for the carbonyl compound to react with the olefin. When sour virgin distillates are employed as the feed stock, the amount of carbonyl ccmpound necessary will depend primarily upon the amount of sulfur compounds present in the feed stock and, in particular, it will depend upon the mercaptan content of the feed stock. The carbonyl compound is employed in an amount ranging between about 0.5 to about 2.0 mols per mol of mercaptan contained in the distillate being treated; the higher the ratio of carbonyl compound to mercaptan, the lower will be the mercaptan content ofthe refined distillate. When formaldehyde is employed, amounts of from about 0.1 to about 0.5 pounds per barrel of oil feed, or thereabout, are ordinarily effective to produce a sweet or substantially sweet refined rarinate yoil from the usual sour virgin distillate.

The acidic condensation catalyst which is employed in this process to effect reaction between the carbonyl compound and the mercaptans or other sulfur compounds or impurities contained in the distillate be any of those acidic condensation catalysts well known within the art. Compounds which are thus commonly classified are strong acids such as 60 to 98% concentration sulfuric acid; hydrochloric acid; hydrofluoric acid; phosphorous acids such as meta, pyro-, ortho, and tetra-phosphoric acids; sulfonic acids such as benzene sulfonic, toluene sulfonic, and alkane sulfonic acids; chloroor fiuosulfonic acids and the like. The term acidic condensation catalyst also includes acid-acting metal halide condensation catalysts, commonly called Friedel-Crafts catalysts. Examples of such catalysts are aluminum chloride, ferrie chloride, zinc chloride, stannic chloride, titanium chloride, aluminum bromide and the like. lt is sometimes advantageous tov employ the metal halide condensation catalyst in'combination with a hydrogen halide promoter, for example, hydrogen chloride. The preferred condensation catalyst is a strong acid, preferably aqueous sulfuric acid having a concentrati-on of 60 to 98%, preferably nearer 3 The acidic condensation catalyst is employed in a quantity suiiicient at least to catalyze theV reaction between the carbonyl compound and mercaptans contained in the oilso that the reaction proceeds at a desirable rate under the reaction conditions which arcselected. lt should not be implied thatthe wide variety of acidic condensation catalysts disclosed supra are precisely equivalent when employed in the process of this invention. Accordingly, variation in the amount lof catalyst to be employed may be expected. Ordinarily the employment of at least about one t 4two mols of condensation catalyst per mol of mercaptan in the feed is desirable. When employing the preferred aqueous sulfuric acid of between 60 and l 98% concentration, a satisfactory amount is usually between about 0.5 and 2.5 pounds per barrel of oil feed.

The condensation catalyst may be introduced into the extraction Zone together with the liquid sulfur dioxide rather than together with the oil. In a continuous countercurrent extraction process it is` preferred to introduce the catalyst, together with the carbonyl compound in a portion of the total liquid sulfur dioxide to be used, directly into the extraction tower, preferably at spaced points along the height of the tower.

The time required in the present refining proces will be dependent to some extent upon the intimacy of contacting between the hydrocarbon oil, liquid sulfur dioxide, carbonyl compound, and acidic condensation catalyst. Somewhat shorter contact times may be employed when .operating at the higher temperatures described for the liquid sulfur dioxide refining process. Ordinarily the time required is between about one-half and thirty minutes, preferably about five minutes. The results obtainable at the lower temperatures of about 20 C., i. e. raffinate oils which are sweet or substantially sweet, are particularly surprising.

The invention will be more fully understood by reference to the following specific example illustrated in the annexed drawing which forms a part of this specification and shows in schematic form one embodiment of the process of this invention for producing a sweet, lowaromatic content, color-stable heater oil.

The feed stock in this illustration is a sour virgin heater oil derived from the distillation of West Texas crude and has a mercaptan number of about 70, a. lsulfur content of about 0.7%, and an ASTM boiling range between about 330 F. and 550 F. The feed is passed from source l1 through line 12 into deaeration unit 13 which comprises conventional vacuum deaeration equipment ordinarily employed in liquid sulfur dioxide refining of hydrocarbon oils.

The deaerated oil feed is passed from deaerator 13 through line 14 into drying zone 16 wherein water is removed from the feed by conventional equipment and drying agents such as alumina. The deaerated, moisturefree oil is passed through line 17 to cooler 18 where the temperature of the oil is lowered to the desired operating temperature, herein 20 C.

Although batch extraction may be employed, continuous countercurrent extraction is preferred and is employed herein. The total liquid sulfur dioxide may be introduced at an upper point in the tower; the feed oil may be introduced at a low point in the tower; and the condensation catalyst and carbonyl compound may be introduced at an intermediate point, e. g. near the vertical midpoint :of the tower, or the condensation catalyst and the carbonyl compound may be introduced at several points along the height of the tower. In any event, at least one theoretical extraction stage should be present in the tower for the contacting of the oil with liquid sulfur dioxide, condensation catalyst, and carbonyl compound. The extraction process may be so operated that the feed -oil is extracted in at leastl one theoretical stage prior to contacting of the contacting of the raffinate phase with the carbonyl compound, condensation catalyst, and liquid sulfur vdioxidein a subsequent theoretical extraction stage. This latter mode of operation minimizes the amount of carbonyl compound and condensation catalyst required since the preceeding sulfur dioxide extraction stage will have removed a small amount of mercaptans and other impurities from the feed oil. A preferred technique consists of following the sulfur dioxide extraction stage wherein the carbonyl compound and condensation catalyst are employed, by at least one theoretical extraction stage with liquid sulfur dioxide alone. This latter mode of operation results in a product heater oil of greatly improved stable color.

The cold oil is passed through line 19 into a lower por- @01.1. 0f QXfraCtiQn tower. 2.1. Tower 2 1.. iS. packedwth a suitable material such as Berl Saddles in order to increase the eiciency of contacting. The tower may also be provided with mechanical agitators arranged along its height to improve agitation, and if desired, heat exchangers may also be provided therein to permit control of the temperature of contacting or to permit operation with a temperature gradient within the tower.

Liquid sulfur dioxide from source 22 is passed by way of valved line 23 into a storage zone 24 for fresh liquid sulfur dioxide and recycled purified'liquid sulfur dioxide. Liquid sulfur dioxide from storage is passed by way of line 26 into valved line 27 and then into the top of extraction tower 21. The total amount of liquid sulfur dioxide employed is approximately 75 volumes per 100 volumes of feed oil. A small portion of the total sulfur dioxide employed in the process, e. g. about volume percent of the total, is passed from storage zone 24 by tion catalyst and the carbonyl compound are introduced. way of line 26 into valved line 23 wherein the condensation catalyst and the carbonyl compound are introduced. Herein the condensation catalyst is aqueous sulfuric acid of 98% concentration, and the carbonyl compound is paraformaldehyde. The sulfuric acid from source 29 is passed by way of line 31 into line 28. Paraformaldehyde from source 32 is passed by way of line 33 into line 28. The sulfur dioxide, sulfuric acid, and paraformaldehyde are passed through mixer 34 into the valved manifolding arrangement shown for introducing this mixture at spaced points into the extraction tower 21. The sulfuric acid is introduced by this system into the extraction zone at a rate of about 1.25 pounds per barrel of feed oil, and the paraformaldehyde at a rate of about 0.25 pound per barrel of oil feed.

An extract phase is removed from the bottom of tower 21 and is passed by way of line 36 into stripper 37 which is equipped with a reboiler 38. In stripper 37 the sulfur dioxide is removed from the extract and is taken overhead through line 39. An extract substantially free of sulfur dioxide is removed from stripper 37 through line 41 and is sent to settler 42 wherein a lower sludge phase is withdrawn and a finished extract phase is recovered and sent to storage not shown. The extract phase provides a suitable charging stock to a catalytic cracking operation for the production of gasoline.

The raffinate phase is removed from extraction tower 21 through line 43 and is passed into stripper 44 which is provided with reboiler 46. In stripper 44 most of the occluded and dissolved sulfur dioxide is removed overhead by way of line 47 is passed into line 39.

in the course of operation, some impurities such as water and hydrogen sulfide pass into the sulfur dioxide and these should be removed before the sulfur dioxide is recycled to the process. The contaminated sulfur dioxide in line 39 is passed into purification zone 48, Vwhich may be any conventional equipment such as is used in liquid sulfur dioxide extraction of oils, wherein the impurities are removed. The purified sulfur dioxide is passed by way of line 49 to compressor 51 and thence by way of line 52 to cooler 53 wherein the sulfur dioxide is liquified and passed by way of line S4 to storage 24.

The substantially sulfur dioxide-free raffinate oil is removed from stripper 44 by way of line 56 wherein it meets a stream of aqueous caustic solution. Aqueous caustic solution containing about 5% by weight of NaOH is passed from source 57 by way of line 58 into line 56. The mixture in line 56 is passed into mixer 59 wherein the oil and aqueous caustic are thoroughly intermingled in order to neutralize any sulfur dioxide or sulfuric acid remaining in the oil. The mixture is passed through line 61 to settler 62 where two lphases separate. The lower aqueous caustic phase is removed from settler62 by way of line 63 and is sent to spent caustic disposal. The aqueous caustic may be recycled by way of valved line 64 to line 56 for reuse in the neutralizing step if desired. T he upper oil phase from settler 62 is removed and passed through line 66 to salt drum 67 for the removal of water or other impurities from the refined oil. Brine is periodically removed from salt drum 67 by way of valved line 68. The finished heater oil is withdrawn from salt drum 67 and sent to storage not shown.

Results obtainable by the process of this invention are illustrated below. The experimental procedure consisted of placing 1000 m1. of oil in a three-necked glass flask which was contained within a dry ice-acetone bath maintained at about 20 C. About 333 ml. of liquid sulfur dioxide at about 20 C. was added to the oil in the reactor and the contents were agitated for five minutes. The mixture was then allowed to settle to form distinct raffinate and extract phases, and the extract phase was withdrawn. The raflinate phase was again treated in the same manner as described above and the extract phase was removed. To the rainate remaining in the reaction vessel from tnis second extraction stage was added 333 ml. of liquid sulfur dioxide at 20 C., paraformaldehyde, and then sulfuric acid having a concentration of 98% by weight. The mixture was agitated for five minutes and then allowed to settle to form distinct raffinate and extract phases. The rainate phase was recovered, stripped of sulfur dioxide on a steam bath, washed with 100 cc. of 5% caustic solution, and then filtered through lter paper. lts properties which appear in Table I below were then determined.

The data in Table I were obtained by treating a sour virgin heater oil derived from the distillation of a West Texas crude, which heater oil had an ASTM boiling range of 330 to 585 F., an API gravity of 40, and a sulfur content of about 0.65%. The heater oil had a color of 15 Saybolt and a mercaptan number of 70.

Table I Product Ratio, Run H2804, Formal- Formaldelbs/bbl dehyde, hyde/Mer- Aged Mercaplbs./b captan l Color, tan

Saybolt Y Number b l Molar ratio of formaldehyde employed to mercaptan in feed.

b Copper number is the milligrams of mercaptan sulfur present in 100 ml. of sample under test which will react with a standard copper ammonium sulphate solution.

c,Feed oil subjected to 3-stage sulfur dioxide extraction (common to Runs 1-6) in the absence of H2SO4 and OBzO.

it should be noted from Run l that multi-stage liquid sulfur dioxide extraction is incapable of producing a product oil which is ysweet or approaches sweetness, i. e. has a mercaptan number approaching 0. The data show that even at` temperatures as low as 20 C., the process of this invention will operate to produce a sweet (oil of 0 mercaptan number which passes the Doctor test) or substantially sweet oil. It will further be noted that approximately one mol of aldehyde per mol of mercaptan in the feed is necessary in order to obtain a sweet product. The aged color of the product oil, which varies between +28 and +30 Saybolt, is water-white, and is the best which can be obtained.

An additional number of experiments were performed tofdetermine the effectiveness of a sulfuric acid-forrnal dehyde treatment in the absence of liquid surfur dioxide extraction. In these experiments 300 cc. of sour virgin West Texas heater oil were placed in a stirred glass flaslt maintained at about 50 C. To the oil was added 98% concentration black sulfuric acid, derived from the reconcentration of weak acid obtained from the hydrolysis of acid sludge, and formalin solution. The contents of the ask were agitated for about five minutes,

' '7 allowed to settle, and the oil was then recovered. The treated oil was washed with Water, then a caustic solution, followed by another washing with water and then dried. The characteristics of the oil product were then determined and are set forth in Table il.

It should be noted from the above data that even when very much larger amounts of sulfuric acid and formaldehyde were employed, a sweet product oil was not obtained. This is so even though a much higher tentperature was employed in the runs shown in Table Il. Experiments have shown that treating the same type feed stock with 8 to l0 pounds of 98% concentration sulfuric acid alone per barrel of oil will reduce the mercaptan number from 70 to about 20 to l5. This fact that treatment with such a large amount of sulfuric acid will of itself greatly reduce the mercaptan number must be taken into account when considering the results obtained in Table Il; and when thus considered, it is apparent that if amounts of acid, such as were employed in the runs in Table i, were used here the mercaptan number of the product would be very much higher. lt should also be noted that the aged color of the product oil does not begin to approach that obtained when the sul furie acid-formaldehyde treatment is performed during the liquid sulfur dioxide process.

Thus having described the invention what is claimed l. A process for refining a sour virgin petroleum distillate boiling in the heavier-than-gasoline range which comprises contacting said distillate with between 0.5 and 2.0 mols of a low-boiling aldehyde per mol of mercaptan contained in said distillate, and with an acidic condensation catalyst in the presence of sucient liquid sulfur dioxide to form separate raffinate and extract phases, and separating a relined raffinate phase of lowered mercaptan content from an extract phase.

2. A process for refining a sour virgin petroleum distillate boiling in the heavier-than-gasoline range which comprises contacting said distillate, at a temperature between about 10 and about 40 C., in the presence of between about and about 200 volume percent of liquid sulfur dioxide, with from about 0.5 to about 2.0 rnols of vformaldehyde per mol of mercaptan contained in said distillate, and with an acidic condensation catalyst in concentration and amount at least sufficient to cause reaction of said formaldehyde with the mercaptans concontaining substantially sweet oil from an extract phase containing substantially sweet oil from an extract phase.

3. A process for refining a sour virgin petroleum distillate boiling in the heavier-than-gasoline range which comprises contacting said distillate at a temperature between about 10 and about 40 C. in the presence of between about l5 and about 200 volume percent of liquid sulfur dioxide with from about 0.5 to about 2.0 mois formaldehyde per mol of mercaptan contained in said distillate and with suicient sulfuric acid having a concentration in the aqueous phase of between about and about 100 volume percent, and separating a ratiinate phase containing substantially sweet distillate from an extract phase.

4. The process of claim 3 wherein said sour virgin distillate is kerosene.

5. The process of claim 3 wherein said sour virgin distillate is heater oil.

6. A process for refining a sour virgin heater oil which includes the steps of (l) solvent extracting said oil at a temperature of between about 0 and about 30 C. with between about 25 and about 100 volume percent of liquid sulfur dioxide, (2) contacting the solvent rerled oil at a temperature between about 0 and about 30 C. in the presence of between about 25 and 100 volume percent of liquid sulfur dioxide with from about 0.1 to about 0.5 pounds of formaldehyde per barrel of initial oil feed and with from about 0.5 to about 1.5 pounds of to 98% concentration sulfuric acid per barrel of initial oil feed for a time sufficient to produce a sweetened oil, and (3) separating a raffinate phase containing sweet heater oil from an extract phase.

7. A process for refining a sour virgin heater oil which includes the steps of (1) contacting said oil at a ternperature between about 0 and about 30 C. in the presence of between about 25 and about 100 volume percent of liquid sulfur dioxide with from about 0.1 to about 0.5 pounds of formaldehyde per barrel of said oil and with from about 0.5 to about 1.5 pounds of 60% to 98% concentration sulfuric acid per barrel of said oil, (2) separating a rened raiinate phase from an extract phase, (3) solvent extracting said rainate phase at a temperature of between about 0 and about 30 C. with from about 25 to about 100 volume percent of liquid sulfur dioxide based upon oil feed to step (l), and (4) separating a refined raffinate phase containing sweet heater oil from an extract phase.

References Cited in the le of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR REFINING A SOUR VIRGIN PETROLEUM DISTILLATE BOILING IN THE HEAVIER-THAN-GASOLINE RANGE WHICH COMPRISES CONTACTING SAID DISTILLATE WITH BETWEEN 0.5 AND 2.0 MOLS OF A LOW-BOILING ALDEHYDE PER MOL OF MERCAPTAN CONTAINED IN SAID DISTILLATE, AND WITH AN ACIDIC CONDENSATION CATALYST IN THE PRESENCE OF SUFFICIENT LIQUID SULFUR DIOXIDE TO FORM SEPARATE REFFINATE AND EXTRACT PHASES, AND SEPARATING A REFINED REFFINATE PHASE OF LOWERED MERCAPTAN CONTENT FROM AN EXTRACT PHASE.

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