US2893954A - Treating process - Google Patents

Description

y 1959 c. D. TEN HAVE ETAL 2,893,954

TREATING PROCESS Filed May 8, 1957 2 Sheets-Sheet 1 MIXER SETTLER UNTREATED OIL TREATED OIL SPENT ACID MIXER SETTLER MIXER SETTLER TREATED OIL SPENT FRESH ACID ACID FIG. 2

INVENTORSI CORNELIS DAVID TEN HAVE WEIGERT COENRAAD BUNINGH JACOBUS WILHELMUS LE NOBEL WILLEM JOHAN PIETERS WILLEM ELISA LOWER THEIR ATTORNEY y 1959 c. D. TEN HAVE ET AL 54 TREATING PROCESS 2 Sheets-Sheet 2 Filed May 8, 1957 opmDad Imumm INVENTORSI ZOE-04 x. p.103 A CORNELIS DAVID TEN HAVE WEIGERT COENRAAD BUNINGH JACOBUS WILHELMUS LE NOBEL WILLEM JOHAN PIETERS WILLEM ELISA LOWER W4. W

THEIR ATTORNEY TREATHIG PROCESS Cornelis David Ten Have,-Weigert Coenraad Buningh,

Jacobus Wilhelmns Le Nobel, and Willem Johan Pieters, Amsterdam, andWillem Elisa Liiwer, lhe Hague, Netherlands, assignors toShell Development Company, New York, N.Y., a' corporation of Delaware Application May 8, 1957, Serial No. 657,793

Claims priority, application N etherlan'ds'May 11, 1956 '7 Claims. (Cl. see- 224 This invention relates to the treatment of hydrocarbon oils, and particularly to the treatment of cracked hydrocarbon oils for the removal of sulfur.

In View of the constantly increasing production of crude oil having a very high sulfur content, the problem of desulfurizing hydrocarbon oils obtained by thermally or catalytically cracking fractions of such crude oil is also growing in importance. In addition to aliphatic and aromatio mercaptans which can be fairly easily removed, and in addition to organic sulfides, these cracked hydrocarbon oils contain, inter alia, aconsiderable' amount of thioph'enes, both thiophene and alkyl" and benzothiophones. in order to obtain products with a low sulfur content it is very desirable to remove these thiophenes, but this removal has heretofore been attended with great difficulties. his true that the cracked products can be freed from the thiophenes by means of catalytic hydrogenation, but this process is frequently unattractive since theplant is expensive, the processing costsare fairly high, there is often insufficient hydrogen at the refineries, and moreover unsaturated compounds which are valuable for the preparation of gasoline with a high octane number are partly hydrogenated by the hydrogen to' saturated compounds, as a result of which the octane number is lowered and consequently the quality of the gasoline declines.

It is generally known that sulfur compounds may also be-removed from cracked hydrocarbon oils by sulfuric acid treatment. Since inthis treatment the unsaturatedcompounds present in these cracked hydrocarbon oils can be readily polymerized to high-molecular compounds, which means a loss of valuable components, it has already been proposed to operate at low temperatures, e.g. below C., and/or to divide the cracked products into a high-boiling and a low-boiling fraction, to' treat the high-boiling fraction with strong sulfuric acid, to separate the acid phase from the high-boiling fraction and then use it for treating the lower-boiling fraction, after which the fractions thus refined are finally combined again.

For processes of this type, however, extra cooling equipment and/ or distillation columns and treating equipment are required. Furthermore, the yield of refined'oil is fairly low and there is a considerable decline in the octane number.

It is accordingly a principal object of the invention to provide an improved process for the removal of sulfur compounds from cracked hydrocarbon oils. A more particular object of the invention is to provide such an improved process whereby the removal of thiophenes (that is, organic compounds containing the thiophene' ring) from hydrocarbon distillates is accomplished without the disadvantages of low yields. Still another object is'to provide such an improved process suitable and economical in the-treatment of cracked gasoline wherein thiophen'es are removed without substantial loss in octane number. Other objects will be apparent in the description and discussion of the invention which ismade withreferencetothe accompanying drawing wherein:

2,893,954 Fatente'd July 7, 19 59 Figure 1 is a flow diagram of the process of the in vention in its broad aspects;

Figure 2 is a flow diagram of an embodiment thereof involving a plurality of contacting stages; and

Figure 3 is a how diagram of an embodiment thereof involving special economic advantages in a high tem= peraturetreatment.

It has been heretofore proposed to desulfurize cracked hydrocarbon oils by contacting cracked hydrocarbon oil, containing sulfur compounds, with a phase containing sulfuric acid, then to separate the hydrocarbon'oil phase from the acid phase and distill it, and entirely or partly recycle the acid phase while adding a quantity of fresh acid. According to this proposal, cooled cracked hydrocarbon oil is led into the lower portion of a treating tower filled with contact material such as Raschig rings, to the upper part of which tower is conveyed a phase comprising cooled oil already treated, fresh acid and spent acid. Treated oil is taken off at the top of the treating tower and passed to a settling tower, from which a portion is withdrawn and distilled, and the remaining portion,

after cooling, again passed into the top of the treating tower, mixed with fresh acid and spent acid running out from the bottom of the treating tower and thus being? recycled. The drawbacks of this process are that'it is necessary to operate at temperatures of below 20 C., and preferably below 5 C., so that cooling is required; the mixing in a tower filled with contact material is never sointimate that drastic desulfurization can take place in a short time, nor so uniform that the whole quantity of oil is everywhere contacted with the sulfuric acid inth'e same way, the result being that a fairly large quantity of" fresh acid is required to effect a satisfactory desulfuriz'ation'; and sul-fonation of hydrocarbons occurs.

It has now been found that the objects of our inventionmixtureof oil and acid in the mixing zone a rate of mechanical energy for mixing of at least 0.1 kilowatt per cubic meter of the mixture, and maintaining a volume ratio of acid phase to oil phase of at least 10 volumes of acid phase to volumes of oil phase. The mixture is then separated, ezg. by natural gravity or centrifugation, and the separated acid phase recycled and mixed with additional quantities of oil' to be treated. A small' amount of fresh acid is continuously or intermittently added to the recycled acid to maintain the concentration thereof as described hereinafter, and a small quantity of recycled acid is'removed and discarded to maintain the volume ratio of phases in the mixing zone at the desired value. After the separation of the hydrocarbon oil phase and the acid phase, the hydrocarbon oil is freed from small amounts of acid remaining behind in it, e.g. by washing with a caustic alkali solution and water, and

then distilled. The distillate which no longer contains any thiophenes or only a small quantity thereof is, moreover, considerably better than the starting cracked hydrocarbon oil as regards color and stability with respect to the formation of resinous components (gum) in the oil, since it is found that in treating cracked hydrocarbon oils with the recycling acid phase according to the invention,

the thiophenes combine withthe especially reactive tinsaturated compounds present in the cracked hydrocarbon oils to form in a surprisingly selective manner higher- In ther 2,893,954. g r a molecular weight compounds which remain behind as a bottom product after distillation of the oil. This is because the unsaturated compounds reacting with the thlophenes are almost exclusively the diolefins which reduce the stability of the oil towards gum formation, and not, or only to a slight degree, the mono-olefins which have a high octane number. The latter valuable components thus remain in the oil, while as a result of the improvement in stability towards gum formation, a considerable saving is effected in the quantity of inhibitor which has to be added to cracked hydrocarbon oils. Moreover the distillate gives a negative doctor test, which means that the mercaptan sulfur content is less than 0.0005% by weight, and contains practically no nitrogen bases, so that when it is used as a motor fuel there is less fouling of the engine. The bottom product which is rich in sulfur and is obtained in the distillation can be put to further use since it can be added to heavy hydrocarbon oil fractions which are catalytically hydrogenated to give, with the production of hydrogen sulfide, light hydrocarbons which have a high aromatic content and are suitable as components in motor fuel.

As well as avoiding the drawbacks of prior processes the present process has still further advantages. Hitherto, immediately after cracked hydrocarbon oils were obtained from the cracking plant and before they came in contact with oxygen, they were washed with a caustic alkali solution in order to remove thiophenols present in the oil, and also partly alkylphenols, since otherwise these soon give rise to formation of gum in the oil, which cannot be removed by simple refining methods. It has now been found that cracked hydrocarbon oils treated according to the invention with acid need not be prewashed with a caustic alkali solution, the same or even better final results being nevertheless obtained. Moreover, the losses of oil which will always occur in caustic washing in order to remove the alkylphenols and thiophenols and which are usually approximately 1%, are avoided. Despite the presence of the thiophenols in the initial material, the treated product is sweet, viz. it gives a negative doctor test.

The process according to the invention will now be further illustrated with reference to Figure 1, in which is diagrammatically shown a unit in which the process can be carried out. Hydrocarbon oil is continuously passed into mixer 1 via line 2, while spent acid phase, recycled via line 3 and made up with fresh sulfuric acid via line 4, is introduced into the line 2, whence it passes together with the oil into the mixer. In this mixer the acid phase and the oil are intensely mixed for some time, and the emulsion of the two phases is then led via line 5 to the settler space 6 where the phases are separated. The oil is withdrawn via line 7, if desired via a coalescer, and washed with a caustic alkali solution and water in equipment not shown. After distillation it is ready for use. The spent acid phase is recycled via the line 3 by means of pump 9 to the mixer, a part thereof, however, being removed from the recycling system via line 8.

During the treatment of the cracked hydrocarbon oils sulfuric acid is consumed which is made up with fresh acid, which is introduced into the recycle line. Passing fresh acid directly into the mixer would cause local formation of polymers of unsaturated compounds from the oil, and is therefore undesirable.

For an optimum desulfurization it is very important to maintain the correct ratio of the volumes of the acid phase and the hydrocarbon phase in the mixer. This is effected by recycling the spent acid phase from the settler to the mixer. This ratio is preferably more than 60 and in particular approximately 100 parts by volume of acid phase to 100 parts by volume of hydrocarbon oil phase. Under these conditions the acid phase is continuous and the oil phase dispersed, so that after the two phases have been separated the oil is practically acid-free.

It is essential for the desired course of the treatment that the acid phase and the cracked hydrocarbon oil phase be so intensely stirred in the mixer that the mechanical power transmitted from the stirring elements to the mixture of the two phases in the mixer is at least 0.1 kilowatt per cubic meter of mixture. The more intimate the contact, the shorter may be the duration of the contact. When a mechanical power of 11.5 kw. per cu. m. is transmitted, the contact time is usually 1-20 minutes. If this power is less, the contact time will usually become longer, for example, 30-45 minutes when transmitting a power of 0.1 kw. per cu. 111. With a long contact time the yield of oil after distillation is usually somewhat lower, but this reduction is never more than approximately 1.5% when the contact time is extended to approximately 45 minutes.

The mixers in which the process is preferably carried out are propeller mixers and centrifugal mixers of the turbo-mixer type.

As a result of the combined effect of adding fresh acid to the recycling acid phase, maintaining the correct ratio of the volumes of the acid phase and the cracked hydrocarbon oil phase in the mixer and a very intense stirring, an acid phase is obtained, having an optimum composition for the purpose envisaged, viz. the most drastic possible desulfurization with the smallest possible losses from polymerization and sulfonation. In addition to sulfuric acid and water this acid phase contains a large quantity, e.g. 15-60% by weight, of oleaginous components, predominantly organic sulfur, nitrogen and oxygen compounds originating from the cracked hydrocarbon oil or formed by the reaction between sulfuric acid and compounds derived from the cracked hydrocarbon oil.

As a result of this composition the acid phase has properties which an aqueous sulfuric acid solution does not possess, and this is one of the special advantages of our process. The use of such a recycling acid phase not only enables the thiophenes from the cracked hydrocarbon oils to be converted selectively in the above-mentioned manner into higher-molecular weight compounds, which is quite impossible with an aqueous sulfuric acid solution regardless of the concentration, but owing to the highly extractive effect of the acid phase, very weakly basic nitrogen compounds which cannot be removed from the hydrocarbon oil even by a concentrated sulfuric acid treatment, may, in fact, disappear from it under the conditions in which the process according to the invention is carried out.

Whenever reference is made in the specification and claims to the sulfuric acid concentration in the acid phase, this means the quantity of sulfuric acid in this phase, based on the quantities of sulfuric acid+water, but it is to be clearly understood that under the particular conditions of the process of the invention, the above mentioned other components are present and the advantages thereof are obtained.

This concentration of sulfuric acid in the acid phase is generally between 60 and 93% by weight, preferably between 75 and 85% by Weight. Concentrations higher than 93% by weight cause the formation of polymers of the unsaturated components in the oils, sulfenation and sulfation, and moreover the formation of elemental sulfur from any H 8 and tertiary mercaptans present. With the use of concentrations of less than 60% by weight the desulfurization becomes insufficient.

Since the fresh acid added to the recycled acid phase is diluted therein, the acid concentration in this fresh acid must be higher than the acid concentration in the acid phase in order to be capable of maintaining the desired composition of this phase. If, however, fresh acid of a concentration of, for example, 85% by weight, is added, it will be necessary to add a greater volume of this acid than with the use of, for example, acid of 96% by weight, in order to bring the same quantity of H into the acid phase. In the first case a greater quantity for example,- 85 byweight-and- -96 %-by--weightsulfuric acid, or even of oleu-m, the acid: usedtisgenerally as concent-rated-as possible; preferably witha' concentration of more than 95% by weight: The examples show that, for example, 1% by weight oleum containing 65% sulfur dioxide ma be UsedWitll' the" Saihe" r's'lilf' insteadof" 2% by weight fresh-sulfuric acid with a-concentration of 97% by weight. treating low-boiling fractions, itmay, however, be advantageous to add relatively dilute freshacid, for instance with a concentration-of 80--85% by weight. is also possible to use as fresh acid wasteacid from other sulfuric acid treatments, whether or not supplemented with concentrated sulfuric acid or oleum, provided the concentration ofthesulfuric acid in this fresh acid is sufficient to maintain the sulfuric acid concentration in the acidphase at thedesiredlevel.-

The increasein the quantity of acid phase which" is caus'edbyi the fact that'products formed by the reaction ofthe sulfur compounds'fro'm theoil are takerrup inv the acid phase, nitrogen bases, phenols, monoand disulfides are extracted by the said acid phase from the oil, and'fresh acid'is added, is compensated by withdrawing continuously or periodically apart of the acid phase from the recycle system.

Unlike processes known hitherto in which cracked products are treated with! sulfuric acid, the process of the present invention does not necessitate-operation at low temperatures. On the contrary, results are very good even at high-temperatures, eig. at60"90 C. Generally it ispossible to'operate at temperatures lying between and 100 C. The process is preferably carried out at temperatures lying between 20am 80 C. Surprisingly it was then also found that no corrosion of normal unalloyedsteel occurs, even at these high temperatur'es.

It has been found that in certain cases the addition of a quantity of isoparaffins having not more than 6 carbon-atoms, particularly isobutane, e.g.' aquantity of between- 1 and by weight, based on the cracked oil to betreated, resulted in an increase in the yield afterdistillation, and areduc'tion in the sulfur content of the cracked products treated.-

It was also observed-that by the effect of the recycling a'cidphase thiophene and alkylthi'ophenes are much more rapidly converted into higher-molecular weigh-t" compounds than are benzothiophenes. If it-is desiredto operate under mild conditions it is usually not possible to remove all benzothiophenes from the oil. Bearing this in mind, it is also" possible to separate the cracked products intwo fractions,- one of which has a fin'alboiling point of approximately-200 C. and contains thiophene and alkylthiophenes but'no benz'othiophenes,-and the'otherboiling above approximately 200 C. and containing the benzothiophenes. The first fraction is then subjectedto a mild treatment according to the inventiong-while the other is desulphurized by means of catalyric hydrogenation. If, for example, the available initial material is cracked gasoline having a boiling range of 40-230 C.,- the fraction having a boiling range of between 200 C. and-230 0. maybe separately catalytic'ally hydrogenated or added to a heavier oil, catalytically hydrogenated together with this-oil, and the fraction of 200-230" C. maythen be separated again and combined with the gasoline fraction boiling between 40 C. and 200 C., which is treated according to the invention. In-this way cracked gasolinehaving a very low sulfur content is obtained:

Another possibility is to carry out the process according' to the invention in a plurality ofstages". To this end the'settler 6, as shown in Figure 2, is connected via line 7 tea second mixer 10 which is connected in turn Since, moreover, thereis' In some cases, for example when.

6 viar'linell'toa settler 12; from which spent acid-phase isag'ain" recycled into the said second mixer via line 13' by means of pump 14, fresh acid being added via line 15.

If mild-treating conditions are used in the first mixer (1), only the alkylthiophenes and thiophene are converted in this mixer into higher-molecular compounds, whereas with the use of severe treating conditions in the second mixer (10) the benzothiophenes begin to react therein: In"thismannerthe occurrence of side reactions is avoided as much as possible. The milder conditions may be obtained by means of not too high a concentration of sulfuric acid in the acid phase and by a short contact time; The not'too high acid concentration in the acid phase in the stage may be maintained by introducing the quantity of acid phase, withdrawn from the second recycle system (line 13) via line 4 into line 3 in the form of fresh acid. Spent acid phase is then drawn off from the treating unit only via line 8. The hydrocarbon oil treated with acid is withdrawn from the settler 12 via line 16.

When: the drastic desulfurizationobtained by means of a two-stage process'isrequired to-be obtainedin a sin= gle-stage process, this would be accompanied bylosses of valuable components.

The invention is illustrated by the following examples.

EXAMPLE I In aunit as shown in Figure 1, 30 liters of catalytically cracked gasoline washed with a caustic alkali solution and'h'aving a boiling range of 130 C. to 220 C. and' a specific gravity of 01822 were passed continuously into a propeller mixer which had: acap'acity of l0"liters:and in which the mechanical power'transmitted by the stirring elements to the mixture of acid phase-andgasoline phase Was 0.01 kw., i.e., 1.0 kw. pjer' cu. m. of miXture; A ratio of thevolumes of the acid phase togasoline phase of 1:1 was maintained in the propeller mixer by recycling spent acid from the settler to which fresh acid was continuously added. The gasoline phase and'the acid phase were separated in the settler and the gasoline phase was then washed with a 10% by weight sodium hydroxide solution and then with water and finally distilled to a final boiling point of 220 C. The results of a number of experiments are given in Table I;

Table-I shows that where the contact timeissomewhat longer the desulfurization is somewhat more drastic,

While the yield only drops a few tenths per cent; The' age for 1 month'at 35 C. The color of'the gasoline which before the treatment according to the" invention was yellow to brown, was found to bewater white' after the treatment. All nitrogen bases had disappeared from the gasoline, and all mercaptans had also been removed.

When the added fresh acid' hada concentration of by weight instead of 97% by weight, the same quantity of H SO being nevertheless added, somewhat" less sulfur was removed from the gasoline, but theyieldafter distillation was also somewhat higher.

In duplicating experiment No. 2, a quantity of 5% by weight of isobutane being moreover added to the gasoline washed with a caustic alkali solution, gasoline with a sulfur content of 0.07% by weight was obtained after distillation in a yield of 97.5% by, weight, based on the gasoline washed with a caustic alkali solution.

When the cracked gasoline treated accordingtoexperiment 2, but with the addition of l instead of 2% by, Weight of fresh sulfuric acid of 97% by Weight concen- 7 tration, was again subjected to such a treatment in a second stage, a gasoline with a sulfur content of 0.08%

the acid treatment, thiophenols and alkylphenols were added. The results are shown in Table III.

Table III Gasoline Experiment No. washed with a caustic alkali 16 17 18 10 solution Quantity of thiophenols added, percent by weight 0. 23 Quantity of alkylphenols added, percent by weight 0.11 Concentration of fresh sulfuric acid added, percent by weight". 97 97 97 97 .5 97 Quantity of fresh sulfuric acid added, based on gasoline,

percent by wei ht 1 1 1 1 1. 2 0. 3 Temperature, C 20 60 70 70 90 65 Contact time in mixer, minut 15 15 5 15 15 Gasoline yield after distillation, based on gasoline,

washed with a caustic alkali solution, percent by weight 95. 4 95. 4 96.0 96. 97. 1 96. 0 Properties of the gasoline:

Sulfur content, percent by weight 0. 29 0. 11 0. 12 0. 14 0.12 0.17 0.18 Bromine value, g./100 g 27 27 29 28 30 30 Maleic acid anhydride value, In 12 2 3 3 2 3 2 by weight was obtained after distillation in a yield of 95.7% by weight, based on the gasoline Washed with a caustic alkali solution.

This shows clearly the surprising phenomenon that when high temperatures are used the yields of gasoline with an approximately equal degree of dcsulfurization are Table l Gasoline Experiment N o. washed with a caustic alkali solution 1 2 3 4 5 6 7 8 9 10 11 12 Concentration of added fresh sulfuric acid, percent by weight--. 97 97 97 97 85 85 85 l 65 97 97 97 Quantity of fresh sulfuric acid added, based on gasoline,

percent by wei ht 2. 0 2. 0 2.0 2.0 2.3 2. 3 2.3 2.3 1.0 2 1 1 Temperature, C. 20 20 40 20 20 40 40 20 0 2O 40 Contact time in mixer, minutes 5 15 5 15 5 15 5 15 15 15 15 15 Gasoline yield after distillation, based on gasoline washed with a caustic alkali solution, percent by weight- 97. 7 96.4 96.1 97.9 97.9 97.3 96. 5 96. 5 97. 6 96. 6 Properties of the gasoline:

' Sulfur content, percent by weight 0.29 0.12 0. 00 0. 11 0.10 0. 16 0. 14 0. 12 0.13 0. 12 0.09 0.14 0. 12 Bromine number, g./l00 g 26 23 21 23 21 25 25 24 25 22 22 24 22 Maleic anhydn'de value, mg./g 7 1 2 3 1 3 3 3 3 2 1 1 1 1 Percent oleum containing S0 EXAMPLE II Table I1 Experiment No- 13 14 Contact time in mixer, minutes l5 Gasoline yield after distillation, based on the gasoline washed with a caustic alkali solution, percent by wt"... 97.6 97. 6 Properties of the gasoline:

Sulfur content, percent by weight 0.15 0.14 Bromine number, g./100 23 22 Maleic anhydride value, mg./g 3

The results of these experiments show that after treatment with sulfuric acid and distillation, gasolines which originally contained thiophenols and alkylphcnols have the same properties as gasolines from which these phenols had been removed by washing with a caustic alkali solution before the acid treatment.

EXAMPLE III A Kuwait cracked gasoline with a boiling range of l00220 C. and a specific gravity of 0.813 was treated in the manner indicated in Example I after washing with a caustic alkali solution. Temperatures of 60 C., 70 C. and 90 C. were used, while in one experiment, before certainly not lower than with the use of low temperatures. Nor is there scarcely any loss of mono-olefins noticeable, so that treating at high temperatures has no p unfavorable effect on the octane number of the gasolines Finally it should be observed that when the embodiments of the process described in Examples I, II and III, are applied on a technical scale, the gasoline yields as indicated in Tables I, II and III are found to be approximately 1 to 1.5% higher.

EXAMPLE IV Since higher temperatures are possible with the use of the process according to the invention, it was possible to develop a process which was very attractive from the economic and technical point of view. Figure 3 shows a diagram of the unit in which this process is carried out.

The eflluent from a cracking reactor is fractionated and a fraction boiling between 40 C. and 205 C. is passed in a quantity of 2000 tons daily, without washing with a caustic alkali solution, via line 20 into distillation column 21, in which the bottom temperature is approximately 160 C. One thousand tons per day of a fraction boiling between 40 C. and C. are withdrawn from the top of column 21 via line 22. This light fraction, which has a sulfur content of 0.05%, may be washed with a caustic alkali solution and then treated with a phenolic caustic alkali solution in the presence of oxygen in a system not shown. As a result of these treatments the light fraction is freed from hydrogen sulfide and mercaptans. It is then ready for use, and may be used, for example, as a component in premium motor fuels.

One thousand tons per day of the fraction boiling above 100 C., containing approximately 0.3% by weight of sulfur, are drawn off from the bottom of column 21 via line- 23. This fraction is passed via heat'e'xchauger's 24 and 25 in which it is cooled to approximately 70 C., and via line 2 into a propeller mixer 1, while aquantity of 600 tons per day of acid phase is recycled to mixer 1 via line 3, pump 9' and line 2, from the settler6 connected to this mixer. The said propeller'mixer has a capacity of 10 cu; m. and is driven by a kw." motor. Fifteen tons of fresh 97% by weight sulfuric acid is passed per day via line 4 from storage tank 26 into the recycling line 3. The emulsion of the cracked gasoline phase and acid phase is led from the mixer 1 vialine 5 to settler 6, where the phases are separated. The greater part of the acid phase is recycled to mixer 1 via line 3, while the remainder is run off to tank 27 via line 8. The cracked gasoline phase is led from settler 6 via line 7 through coalescer 28, in which'the-gasoline is separated from the acid phase still present therein. The acid phase is run off via line 29' into tank 27. The total amount of waste acid in tank 27 is tons per day.

The gasoline which now has a temperature of approximately 60 C., is led via line 30 into mixer 31 in order to remove the remaining mineral acid, intensely mixed therein with a sodium hydroxide solution which is recycled in a quantity of 400 tons per day from the settler 33, connected to mixer 31, via line 32 by means of pump 34. Six tons per day of fresh 5% by weight sodium hydroxide solution is introduced via line 35 from storage tank 36 into the recycle line 32. The emulsion of gasoline phase and caustic alkali solution phase is led from the mixer 31 via line 37 into settler 33, where the phases are separated. The greater part of the caustic alkali solution phase is recycled via line 32 to mixer 31, the remainder being run off via line 38 to tank 39.

The gasoline phase is passed from settler 33 via line 40 through a water washer (not shown), via the heat exchangers 2 and 25 and through line 41 to rerun distillation column 42. In the heat exchangers 24 and 25 the temperature of the gasoline, which in line 40 is approximately C., is raised to 120 C.

The bottom temperature in the distillation column 42 is approximately 260 C. A fraction boiling between 100 C. and 200 C., containing 0.09% by weight of sulfur, is distilled off via line 44 in a quantity of 975 tons per day. This fraction is a valuable component in motor gasoline.

The bottom product, running off from column 42 via line 43, which is obtained in a quantity of 20 tons per day and has a sulfur content of 3.6% by weight, can be used as initial material for the preparation of motor fuel components by means of the catalytic hydrogenation (in a system not shown).

Hitherto, in order to prepare the desired cracked gasoline fractions having a boiling range of 40'100 C. and l00200 C. respectively, the fraction issuing from the cracking plant and boiling between 40 and 205 C. was washed with a caustic alkali solution, and the fraction boiling between 40 and 100 C. was subsequently distilled off. The higher-boiling fraction was passed into a second column, in which the fraction having a boiling range of 10020 C. was distilled off. In this second column the quantity of bottom product, in which a fairly large number of sulfur compounds were present, was relatively small, as a result of which it remained fairly long in the column at fairly high temperatures. Consequently sulfur compounds were decomposed into more volatile compounds, which were distilled oif together with the top fraction boiling between 100 C. and 200 C.

According to the process described in this example, owing to the omission of the original washing with a caustic alkali solution, no cooling or subsequent heating is required, and the sulfuric acid treatment is applied after the light fraction has been distilled off. The rerun distillation which is required after the sulfuric acid treatment is simultaneously used to obtain the fraction boiling between 100 and 200 C., the sulfur compounds now 30 remaining behind in the bottom product not decompos ing even at the fairly high temperature, so that no undei sirable sulfur compounds find their way into the desired gasoline fraction. After the first distillation, moreover, the temperature need not be very greatly reduced for the acid treatment.

We claim as our invention:

, 1. In a treating process employing sulfuric acid to effect the removal of sulfur-containing compounds from a normally liquid, cracked hydrocarbon oil containing an appreciable amount of thiophenes and olefinic mate rials, including gum-forming diolefins, the improvement comprising intimately mixing the hydrocarbon oil and'a' recycled sulfuric acid phase through the application of mixing energy at a rate of at least 0.1 kilowatt per cubic meter of the mixture and during said mixing achieving a nearly complete desulfurization of the hydrocarbon oil with the thiophenes being substantially reacted with at least a part of the diolefins to form higher molecular weight materials dispersed in the oil phase, said recycled sulfuric acid phase being present in the mixture in the volume ratio of acid phase to oil phase of at least 10': 100 and said recycled acid phase being further characterized by containing at least 15% by weight of oleaginous components derived from the repeated contacting of the acid and hydrocarbon oil, separating the oil phase and the acid phase from each other, recovering from the separated oil phase a treated hydrocarbon oil of reduced sulfur content by distilling said oil phase to remove the treated hydrocarbon oil as an overhead product and leaving as bottom product the reaction products of the thiophenes and diolefins, recycling the separated acid phase into contact with further quantities of the sulfur-containing oil and during said recycling adding to the acid phase fresh sulfuric acid to maintain the concentration of sulfuric acid in the acid phase from about 60 to about 93% by weight, on a sulfuric acid water basis, and withdrawing a portion of the recycled acid in a sufficient amount to maintain the foregoing ratio of acid phase to oil phase.

2. A process in accordance with claim 1 wherein the rate of mixing energy transferred to the mixture is from about 1 to about 1.5 kilowatts per cubic meter of the mixture and the volume ratio of the acid phase to oil phase is at least 60:100 and the time of contact of the oil phase and acid phase is from about 1 to about 20 minutes.

3. A process in accordance with claim 1 wherein from 1 to 10% by weight of lower molecular weight isoparaffins is added to the oil prior to forming the mixture thereof with the acid.

4. A process in accordance with claim 1 wherein the temperature of the mixture is maintained from at least 20 C. up to no more than 100 C.

5. A process in accordance with claim 1 wherein the concentration of the fresh sulfuric acid added to the recycled acid phase is at least 95% by weight.

6. In a treating process employing sulfuric acid to bring about the removal of sulfur containing compounds from a cracked gasoline fraction boiling above about C. up to at least 200 C., said gasoline containing an appreciable amount of thiophenes and olefinic materials, including gum-forming diolefins, the improvement comprising (1) intimately mixing the gasoline and a recycled sulfuric acid phase through the application of mixing energy at a rate of at least 0.1 kilowatt per cubic meter of the mixture and during said mixing achieving a nearly complete desulfurization of the oil with the thiophenes present being substantially reacted with at least a part of the diolefius to form higher molecular weight materials dissolved in the gasoline phase and with said mixing of the gasoline and acid phase being undertaken without first prewashing the gasoline with a caustic a kali solution, thereby avoiding the gasoline loss normally occurring to the alkali solution, said recycled sulfuric acid 11 phase being present in the mixture in the volume ratio of at least 60:100 and said recycled acid phase being further characterized by containing at least 15% by weight of oleaginous components derived'from the repeated contacting of the acid and the gasoline, (2) separating the gasoline phase and the acid phase from each other, (3) recovering from the separated gasoline phase a treated gasoline of reduced sulfur content by distilling said gasoline phase to remove the treated gasoline as an overhead product and leaving as bottom product the reaction products of the thiophenes and diolefins, (4) re cycling the separated acid phase of step (2) into contact with further quantities of the sulfur-containing gasoline and during said recycling adding to the acid phase fresh sulfuric acid to maintain the concentration of sulfuric acid in the acid phase from about 60 to about 93% by weight, on a sulfuric acid-water basis, and withdrawing a portion of the recycled acid in a sufiicient amount to 12 maintain the foregoing ratio of acid phase to gasoline phase.

' 7. A process in accordance with claim 6 wherein the gasoline being treated contains weakly basic nitrogen compounds, which nitrogen compounds are removed in the acid phase.

References Cited in the file of this patent UNITED STATES PATENTS 1,865,206 Pelzer June 28, 1932 2,312,112 McNealy Feb. 23, 1943 2,356,980 De Ridder Aug. 29, 1944 2,388,100 Wadley Oct. 30', 1945 2,528,363 Helmers Oct. 31, 1950 2,539,125 Froding Jan. 23, 1951 FOREIGN PATENTS 500,380 Great Britain Feb. 8, 1939

Claims (1)

1. IN A TREATING PROCESS EMPLYING SULFURIC ACID TO EFFECT THE REMOVAL OF SULFUR-CONTAINING COMPOUNDS FROM A NORMALLY LIQUID, CRACKED HYDROACARBON OIL CONTAINING AN APPRICIABLE AMOUNT OF THIOPHENES AND OLEFINIC MATERIALS, INCLUDING GUM-FORMING DIOLEFINS, THE IMPROVEMENTS COMPRISING INTIMATELY MIXING THE HYDROCARBON OIL AND A RECYCLED SULFURIC ACID PHASE THROUGH THE APPLICATION OF MIXING ENERGY AT A RATE OF AT LEAST 0.1 KILOWATT PER CUBIC METER OF THE MIXTURE AND DURING SAID MIXING ACHIEVING A NEARLY COMPLETE DESULFURIZATION OF THE HYDROCARBON OIL WITH THE THIOPHENES BEING SUBSTANTIALLY REACTED WITH AT LEAST A PART OF THE DIOLEFINS TO FORM HIGHER MOLECULAR WEIGHT MATERIALS DISPERSED IN THE OIL PHASE, SAID RECYCLED SULFURIC ACID PHASE BEING PRESENT IN THE MIXTURE IN THE VOLUME RATIO OF ACID PHASE TO OIL PHASE OF AT LEAST 10:100 AND SAID RECYCLED ACID PHASE BEING FURTHER CHARACTERIZED BY CONTAINING AT LEAST 15% BY WEIGHT OF OLEAGINOUS COMPONENTS DERIVED FROM THE REPEATED CONTACTING OF THE ACID AND HYDROCARBON OIL, SEPARATING THE OIL PHASE AND THE ACID PHASE FROM EACH OTHER, RECOVERING FROM THE SEPARATED OIL PHASE A TREATED HYDROCARBON OIL OF REDUCED SULFUR CONTENT BY DISTIALING SAID OIL PHASE TO REMOVE THE TREATED HYDROCARBON OIL AS AN OVERHEAD PRODUCT AND LEAVING AS BOTTOM PRODUCT THE REACTION PRODUCTS OF THE THIOPHENES AND DIOLEFINS, RECYCLING THE SEPARATED ACID PHASE INTO CONTACT WITH FURTHER QUANTITIES OF THE SULFUR-CONTAINING OIL AND DURING SAID RECYCLING ADDING TO THE ACID PHASE FRESH SULFURIC ACID TO MAINTAING THE CONCENTRATION OF SULFURIC ACID IN THE ACID PHASE FROM ABOUT 60 TO ABOUT 93% BY WEIGHT, ON A SULFURIC ACID WATER BASIC, AND WITHDRAWNG A PORTION OF THE RECYCLED ACID IN A SUFFICIENT AMOUNT TO MAINTAIN THE FOREGOING RATIO OF ACID PHASE TO OIL PHASE.

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