CS198117B2 - Process for saturated hydrocarbons removal especially white oils from petroleum fractions with boiling point over 320 degree c and device for making this process - Google Patents

Description

SUMMARY OF THE INVENTION The present invention provides a process and corresponding apparatus for the production of white oils from petroleum fractions having a boiling point above 320 ° C containing relatively large amounts of aromatic compounds capable of sulfonation.

Furthermore, the invention also relates generally to a method and corresponding apparatus for removing unsaturated and / or aromatic hydrocarbons or other sulfonatable compounds from saturated paraffinic hydrocarbons.

White oils are a special type of highly refined mineral oils that contain only paraffinic hydrocarbons and (naphthenic) cycloparaffins. These find various uses where the absence of color, taste and odor is required. Different types of white oils are produced with different refining degrees and viscosities depending on their specific use.

A variety of hydrocarbons (paraffinic, naphthenic, aromatic) with small amounts of organic compounds containing sulfur, oxygen and nitrogen are used as starting materials for the production of such white oils.

Aromatic hydrocarbons (mono-, di- and polycondensated rings) with more or less long branched or straight paraffinic chains and organic compounds containing sulfur, oxygen and nitrogen which affect odor, taste and color formation and, in addition, irritate to human skin, removed during the refining process.

In industrial production, removal of these undesirable compounds is accomplished by sulfonation.

At first, oleum with varying amounts of free SO3 was used as the sulfonating agent. However, this sulfonating agent has the disadvantage that it causes the formation of large amounts of insoluble sulfoacids in the form of sludge, which are neither usable as a by-product; moreover, a large proportion of the soluble compounds are retained, which in turn have found use as by-products.

Oleate sulphonation is further a reaction in which the sulphonating agent is used in a large excess, with the result that a significant portion of the oil-soluble monosulphonic acids that are useful as by-product degrades to insoluble and - as mentioned above - completely unusable polysulphonic acid. acid.

The disadvantages of sulphonation of these products with olea have been partially overcome by the use, according to the inventor's patented process, of gaseous SO3 coming directly from the combustion of relative amounts of molten sulfur and from the subsequent catalytic reaction of SO2 to

SO 2, whose high reactivity is reduced by diluting it with nitrogen-containing carrier gas, a small amount of O 2 and SO 2.

However, also when using gaseous SO 3 as the sulfonating agent, as mentioned above, difficulties can arise in separating the still unsulfonated portion of the oil and oil-soluble sulfonic acids from the polysulfonic acid sludge.

Especially when the proportion of compounds capable of self-cloning is relatively high, for example higher than 20%, it is often very difficult, if not impossible, to remove acidic sludge from the feedstock. At the same time, it is not only difficult to remove sedimentation but also to centrifuge if it is not even technically impossible (ie economically impractical in industrial production), since sludge adheres easily to reaction chamber walls or sludge separators and centrifuges, especially if the sludge is very viscous and sticky .

The more difficult such separation is, the greater the loss of material being processed.

It is also important that the higher the viscosity, molecular weight and boiling point, the higher the sulfonation temperature.

This very often leads to undesirable side reactions, such as polymerization, condensation and oxidation, and also to the formation of disulfonates.

These side reactions largely cause the viscosity of the acid sludge being formed, the loss of sulphonated oils soluble in the valuable oils, the formation of excess sulfur trioxide, which must be removed from the flue gas of the plant to comply with increasingly stringent air pollution regulations.

The object of the invention is to: 1. improve the separation of acidic sludge, 2. reduce the temperature of the sulfonation stage of the process, thereby eliminating excessive side reactions and SO3 formation, 3. increase the proportion of refined material, and 4, improve the quality of oil-soluble sulfonated compounds.

The so-called “odorless” petroleum solvents must be used in recent years.

This kind of solvent based on 'kerosene' fractions with a distillation range between 120 and 280 ° C is used in the manufacture of aerosol products, for example cosmetics and in the manufacture of insecticides intended for household use.

Although the above end product and the starting material are substantially different from the white oils or the oil fractions from which these white oils are obtained, this type of solvent is also obtained by sulfonation, e.g. gaseous SO3, n-paraffinic compounds, e.g. olefinic and aromatic and generally sulfonable compounds contained in the naphtha naphtha fraction.

Accordingly, it is an object of the invention to achieve the advantages mentioned above under points 1 to 4 in the production of white oils starting from high sulfonable compound naphtha by premixing the starting material containing high molecular weight naphtha compounds with the starting material containing lower molecular weight naphtha compounds. weight, lower viscosity and lower distillation temperature.

It has proven advantageous to use a kind of starting material of petroleum compounds which gives the sulfonation a commercially good product. ‘

Petroleum compounds having a distillation temperature of between 120 and 280 ° C can be used for this purpose, whereas they contain high molecular weight petroleum compounds which distil at more than 320 ° C as starting materials based on petroleum.

It must be pointed out that it is advantageous to have a temperature interval between the highest value of the distillation region of the lower molecular weight fractions and the smallest initial value of the distillation region of the higher molecular weight fractions, since this promotes the subsequent separation of the refined product. Low boiling fractions form, after sulphonation, commercially available products, usually referred to as 'deodorized' solvents, or 'deodorized white alcohol' and / or 'deodorized kerosene'.

The premixing results not only in a change in the structure of the starting material, for example by reducing the viscosity, but also in a change in the structure of the acid sludge.

Sulfonation-capable particles of lower oil fractions of lower molecular weight also have much lower viscosities, which also results in acid sludges of the sulfonation-treated composition being less viscous, more fluid and retaining less material to be treated.

The still somewhat acidic mixture is treated by conventional neutralization, alkaline washing and the like; the oil-soluble sulfonated compounds are separated by known methods, for example by washing with aqueous alcoholic solutions, and then subjected to distillation to separate the higher molecular weight material from the lower molecular weight material.

As mentioned above, at this point in the protected process, the temperature interval between the upper boundary of the distillation region of the lower molecular weight fractions and the lower boundary of the distillation region of the higher molecular weight fractions is particularly advantageous for easy separation.

It is also possible by the process of the invention to add oleum in the sulfonation of sulfonating compounds; although the use of SO3 gas diluted in an inert carrier gas is preferred.

According to one variation of the invention, the field of use with respect to the starting material can be extended to both the lower limit of the amount of aromatic compounds in the purified product when this lower limit is reduced to parts per million.

Furthermore, it has also been mentioned above to minimize the formation of insoluble polycondensates, the sulfonation reactions of these compounds being carried out using a substantially limited amount of SO3 gas diluted in an inert carrier gas. It has now been found that if the proportion of unsulfonated aromatic compounds in the purified end product is reduced to several millionths, then a stoichiometric amount of gaseous agent cannot be used. A larger amount is then required, which has the disadvantage that the process is of low productivity with respect to the growth of insoluble sludges and soluble sulfonates which are closed and removed by these sludges.

The purpose of this variation of the invention is to overcome this disadvantage by ensuring the separation of aromatic hydrocarbons from the purified product to a high degree.

It is an object of the present invention to provide saturated hydrocarbons, in particular white oils, from petroleum fractions having a boiling point above 320 ° C, containing aromatic sulfonable compounds from 15 to 35% by weight. %, wherein these oil fractions have a molecular weight of 315 to 400, a density of 0.865 to 0.890, a kinematic viscosity of 12 to 35 cst at 38 ° C, characterized in that these oil fractions are first mixed in a weight ratio of 5 to 320 ° C. / 1 to 1/1 with petroleum fractions having a boiling point between 120 to 280 ° C containing sulphonable compounds up to 15 to 30% by weight. %, the mixture is then sulfonated at 30-75 ° C, separated from the oil-insoluble sulfonic acid sludges, the oil-soluble sulfonic acids are neutralized and separated, and the neutral oil-containing residue is distilled to a boiling point of 120 ° C to 120 ° C. 280 ° C and a boiling point above 280 ° C, separating first a mixture of saturated hydrocarbons boiling up to 280 ° C and a further mixture of saturated hydrocarbons boiling above 280 ° C. Celsius, where both fractions are free of sulfonatable compounds, wherein the sulfonation and neutralization is carried out in at least two stages and the sulfonating agent is added in parallel to the different sulfonation stages.

According to a preferred embodiment of the invention, the sulfonating agent is fed in decreasing amounts to the stages following the first stage in parallel and the excess sulfonating agent withdrawn from the last stage is fed to the first stage so that in the last reactor the sulfonating agent is in excess while the total amount of sulfonating agent used corresponds approximately to the stoichiometric amount.

The sulfonating agent of the invention consists of gaseous SO3, which is obtained by burning molten sulfur and reacting the obtained SO2 to SO3 in the presence of a catalyst.

The reagent thus obtained has the following volume composition:

SO3 = 6

SO2 = 0.1 0.2%

N ₂ 4-O ₂ = 93.9 89.8%

The sulfonating agent is fed into the mass of the liquid starting material to be treated and dispersed therein by stirring to minimize the polysulfonation of the aromatic fraction molecules.

Simultaneously with the introduction of both reagents to each reaction phase, the insoluble compounds formed by the sulfonation of the aromatic fractions are withdrawn, so that in the subsequent treatment of the liquid mixture, these already sulfonated fractions are not reprocessed.

According to a particular embodiment of the invention, the fractions of the liquid compound already treated in individual phases, after separation of the insoluble fraction, are recirculated to dilute the sulphonable fractions of the liquid compound to be treated as a gaseous reagent which is finely dispersed in the liquid compound.

The apparatus for carrying out the method of the invention comprises a plurality of reaction vessels which are connected together in an array to allow flow of the liquid mixture to be treated; furthermore, it is provided with means for introducing the gaseous reagent in parallel and also with elements for separating the insoluble compounds formed by the reaction in each individual reaction vessel. For gaseous fractions which have not reacted, further elements are provided for removing them, characterized in that the elements for removing the gaseous fraction from the last reaction chamber are connected to the elements intended to supply the reagent to the first reaction chamber.

Mixing devices are provided for finely dividing the gaseous reagent into a mixture formed of the liquid starting material to be treated and the liquid reaction product. A suitable temperature regulator can achieve the desired temperature in the different zones of each reaction chamber.

According to another embodiment, each reactor is formed from two superimposed elements; both of these elements consist of an upper cylindrical zone, which is connected at the bottom to a conical zone or a frustoconical shape, the upper element penetrating the cylindrical end into the lower one, thus forming an annular space in the upper part of the lower element .

. To avoid that a layer of insoluble reaction compounds deposited on the bottom of the bottom element will be entrained by a liquid stream, a deflector plate (deflector j.

The object, advantages and features of the invention will be elucidated in greater detail below with reference to the accompanying drawings and exemplary embodiments, wherein:

Fig. 1 shows a general scheme according to the invention; Fig. 2 shows a part of the apparatus in which the unsaturated hydrocarbon sulfonation according to the first embodiment is carried out; Figs. 3, 4, 5 correspond to Fig. 2, but relate to three further variations of the apparatus and Figure 6 is an enlarged view of the reactor of Figure 4.

At the same time, the heavy fraction from tank 2, the solvent tank 3 and the SO3 gas from the plant 4 are fed to the sulfonation reactor 1 (FIG. 1). This device 4 consists of a molten sulfur metering device, a sulfur combustion plant for the production of SO2 and finally a catalyst tower (converter) for the reaction of SO2 to SO2. The SO3 content of the gas coming from 4 is 5 to 12%, preferably about 7%, a value which, on average, corresponds to the SO3 content which can be obtained by burning molten sulfur. Analogously, molten sulfur, i.e. indirectly SO3 coming from 4, is dosed to be distributed relative to the molecular weight and the mean content of sulfonatable compounds. The reactor 1 is equipped with stirrers and a temperature regulator, which is usually formed by a suitably selected cooling system, eg a cooling coil.

it should be noted that the liquid mixture coming from 1 contains insoluble polysulfoacids which are separated in 5, oil-soluble monosulfoacids which are neutralized and then separated in 6, as well as paraffinic compounds which are fed to distillation tower 7. Here it distills at a distillation temperature of between 120 and 280 ° C, the so-called deo-kerosine, while at a considerably higher temperature, white oils remain above 320 ° C. Due to the large interval between the two distillation temperatures, no further separating device is required for both refined products.

It is further noted that the sulfonation can be separated in several successive phases, each consisting of a reaction vessel to which SO3 is fed in parallel, an insoluble sludge separator, an oil-soluble sulfoacid neutralizer.

The scheme shown in FIG. 1 is explained in more detail below by way of example.

Example 1

160 kg of starting material for the production of white oils having an average molecular weight of 320, containing sulfonatable compounds in an amount of up to 25 weights. % and a distillation zone starting at 320 ° C is mixed with 40 kg of kerosene with a distillation zone between 140 and 260 ° C. Celsius, which contains 25 weights. % sulfonatable compounds.

This mixture is treated at a temperature between 35 and 40 ° C with 27 kg of SO 3 gas, contained in an amount of 7%, in the carrier gas. This gas mixture contains SO3, which comes directly from the molten sulfur SOs plant.

After the reaction, the substances are allowed to sediment: 61 kg of green acid liquid sludge are obtained which must be incinerated. In addition, 164 kg of "acid oil" are obtained which are washed in an aqueous-alcoholic sodium hydroxide solution. 14 kg of oil-soluble sulfone products are obtained in the alcohol. In addition, 151 kg of a acid-free mixture are obtained, which is distilled.

29 kg of refined kerosene are obtained from this mixture by distillation at a temperature of 140 to 260 ° C, leaving 110 kg of refined white oil. Both fractions, i.e. white oils and kerosene, can be treated with 10% bleaching clay to give absolutely colorless products.

Example 2

150 kg of starting material for the production of white oils with an average molecular weight of 370, containing 30% by weight of sulphonable compounds and having a distillation region starting at 350 ° C, is mixed with 50 kg of kerosene, whose distillation region is between 140 and 280 ° C; contains 25% sulfonatable compounds. This mixture is treated with 28 kg of SO3 gas diluted with carrier gas to 7%, which comes directly from the molten sulfur SO3 plant. The sulfonation is carried out at a temperature of 35 to 45 ° C. After completion of the reaction, the mixture was allowed to settle.

This yields:

kg of liquid acid sludge and 160 kg of acid oils washed in an aqueous-alcoholic sodium hydroxide solution to obtain 15 kg of an oil-soluble sulfonated compound and 145 kg of an acid-free mixture consisting of refined kerosene and white oils. The mixture is then distilled at a temperature of between 140 and 280 ° C to give 37 kg of refined kerosene, leaving 103 kg of refined white oils. Both fractions are bleached with bleaching clay. Reference will now be made to Figures 2 to 6 which illustrate that part of the apparatus of the invention where sulfonation of unsaturated compounds is performed. It should be noted that these Figures relate preferably to variations in the execution of one phase of the protected process.

It cannot be ruled out that this process could be used to sulfonate sulfonatable compounds, which form the most effective reaction product of sulfoacids, or to separate sulfonatable compounds by sulfonating other raw materials than those mentioned above and for which the invention is particularly intended.

According to FIG. 2, the apparatus is made up of 4 reactors 51, 52, 53 and 54, the first barrel also serving as a pre-mixer for the reagent mixture.

Within each reactor, a stirrer, for example a screw stirrer 57, is arranged at a safe distance from the bottom of the reactor. The liquid mixture to be treated is fed via line 55 to the mixer 51 near the stirrer 57. Gases released by the reaction accumulate at the top of the reactors 51, 52; 53, are introduced through the gas lines 58, 59, 60, which open into a common collecting chamber 61.

The gases collected at the top of the after-reactor, which still contain the gaseous reaction reagent, are fed into the reactor 51 via line 56 which terminates similarly to line 55 near the above stirrer 57. A liquid mixture to be reacted with a gaseous reagent coming through line 56.

This liquid mixture is passed through a heat exchanger 62 and then into the interior of the reaction chamber 52 near the stirrer 57 via line 66 such as line 55. Reactors 52, 53 and 54 are supplied with gaseous reagent via lines 63, 64, 65, Also, conduits 69, 64 and 65 exit near the stirrer 57, thereby ensuring the highest distribution of the gaseous reagent at the same time as it is fed to the individual reactors. The amount of gaseous reagent fed to the reactors 52, 53 and 54 is substantially greater than that fed to the mixing reactor 51, thereby separating the insoluble compounds formed by the sulfonation of the aromatic hydrocarbons that accumulate on the bottoms of the reactors from which periodically or continuously withdraws through the discharge lines 67, 68, 69 leading to the common collecting chamber 70. The remaining mixture of liquid products that took part in the reaction is withdrawn from the upstream regions of the corresponding reactor and fed into the next reactor through lines 71 and 72 which convey the mixture. up to the stirrers 57.

From the last reactor 54, the liquid mixture which has taken part in the reaction, which is now completely pure, is then discharged via line 49 from the apparatus to undergo, if desired, further processing.

From the above embodiments, it is apparent that excess gaseous reagent through line 65 results in a complete reaction of the compounds which must be separated from the mass of the liquid mixture by this reaction.

The reuse of the gaseous reagent excess in the last reactor through line 56 allows recovery, i.e., although in the last reaction phase the reagent is in excess, the reaction carried out in several phases assumes the use of a stoichiometric amount of gaseous reagent.

Giant. 3 differs from FIG. 2 only in that the deposition of a significant amount of insoluble sulfone compounds already takes place in the reactor 151. This requires a pipe 167 for recovering the insoluble matter at the bottom of the first reactor. At the same time, the mixture already processed in the first reactor is fed through line 166 into the second reactor. Other parts of the apparatus shown in Fig. 3 function as corresponding parts shown in Fig. 2.

Giant. 4 and 5 indicate the use of a reactor of the type shown in FIG. 6, the design features of which are described in detail below. It is evident that according to FIGS. 4 and 5, each reactor is divided into an upper reaction zone 251 and ^one in the lower decantation and separation zone 251 ^11th

A liquid reaction mixture, which partially participated in the reaction with the reagent, is continuously escaped from the top of the separation zone 251 ¹¹ and is continuously recirculated through the recirculation line 73 to the top of the reactor.

As already seen in FIG. 3, line 16S feeds the second reactor, etc.

Referring to the variation shown in FIG. 5, the recirculation line 73 ^{1 is} split at some point, passing some of the liquid from 251 ¹¹ through line 73 ¹¹ to the starting reactor and a portion directly into the next reactor through line 166 ¹ .

The most important modification of the device shown in FIG. 5, is formed by continuous recirculation of liquid mixture of compounds that has a gaseous reagent reacted and partially relieve the insoluble portion of the reaction product through lines 167, 67, 68, 69. Naturally, further modifications be restricted recirculation line 73 ^1, 73 "to the stage equipment.

The reactor shown in FIG. 6 corresponds to the second shown in FIG. 4. The top portion 252 'comprises jackets 80 and 81, for controlling the temperature of the reactor wall, and jackets 82 and 83 are similarly formed for the lower decanter zone 252'.

The lower part of the actual reactor 252 ¹ forms a funnel 84 that terminates in a cylindrical conduit 85 that extends within the decanter zone 252 "to form an annular space 86 in which liquid accumulates. a mixture which is separated from the insoluble bottom sludge 252.

To ensure that the liquid stream mixed with the insoluble sludge coming from the 252 ^l causes swirling at the bottom of the body 252 so that the insoluble sludge deposit can be swollen, the lower portion of the cylindrical element 85 is widened and opens against transverse deflection of plate 87 so that the liquid flowing vertically downwards lifts the settled sludge and mixes with the just separated fraction.

is a recirculation pump and a slide valve 89 which controls the discharge of insoluble sludge through line 67. The exchanger 99 together with the cooling jacket 80 and 83 is to maintain. the thermal gradient between the separation chamber 252 and the actual reactor 252 ¹ . An annular exchanger 91 arranged in the center of the cylindrical conduit 85 has the same role as the exchanger 90.

The choice of one or the other embodiment of the device depends on the desired purity of the end product and the initial composition of the substances to be treated.

In addition, although 4 stages of the process are shown in the figures, their number may be greater or less depending on the number of devices and may be reduced to at least two.

The examples below refer to FIG.

to 6.

Example 3

The starting material has the following weight parts:

- normal paraffins> 98 ° / o - aromatic hydrocarbons <1,2% - non-paraffinic hydrocarbons <2% - sulfur content 25 µm.

- at 15 ° C, the specific mass of the starting material is 0.760

N-paraffins are divided in the respective molecules according to the number of carbon atoms as follows:

C10 = 1.4% Cl1 = 7.4% C12 = 10.5% C13 = 16.8% C14 = 14.6%

C 17 = 10.0% C18 = 8.9% C 19 = 5.2% C 20 = 2.7% C> 20 = 2.2 O / o

This starting material is to be purified from unwanted aromatic compounds by the multiphase sulfonation of the invention. The gaseous reagent used is sulfur trioxide gas, which is obtained by burning molten sulfur and subsequently reacting SO2 to SO3 in the presence of a catalyst.

The gas mixture has the following volume composition:

SO3 = 7%

SO2 = 0.2%

N ₂ + O ₂ = 92.8 '%

100%

Into the mixing reactor 51 flows through line 55 the feedstock to be purified, in which only the sulphonable fraction with SO3 gas must react.

The required amount of SO3, indicated by Q, is fed via lines 83, 64 and 65 and distributed to the reactors as follows:

0.65 XQ to the second reactor

0.25 XQ to the third reactor

0.10XQ to the fourth reactor.

To the start-up phase of the plant, 10% SO 2 is added to the stated amount. Excess unreacted gaseous reagent exits from reactor 54 and is fed to mixing reactor 51. According to the scheme shown in Figure 2, 10% of the sulfonatable compound, distributed into a large mass of non-sulfonatable product, does not produce insoluble acids in this first phase. worth mentioning.

Upon completion of the start-up phase of the plant, it is fed through lines 63, 64 and 65 of SO 3 up to a stoichiometric amount. However, since about 10% of the sulfonic aromatic compounds are already leaving the reactor 51, there is always an excess of SO 2 in the last reactor which, although reused through line 56, ensures the sulfonation of the last traces of aromatic hydrocarbons. Therefore, the fraction of the non-sulfonated aromatic hydrocarbons exiting through line 49 can be reduced to parts per million, as can be seen from the following composition of the final product from the treatment of 100 kg of the starting compound:

- aromatic hydrocarbons - sulfur - N-paraffins - isoparaffins and cyclanes - separated insoluble sludges - used SO3.

<25 p. M.

<5 µm 98%% / 2 kg

0,850 kg

Example 4

For a mixture of paraffinic hydrocarbons having the following composition:

a) saturated hydrocarbons 80.9%

b) aromatic hydrocarbons 18.1%

(c) Compounds containing 1% oxygen and sulfur are obtained by the process of the invention from 100 kg of starting product:

- · purified saturated hydrocarbons 78,00 kg - soluble petrosulfonates 15,50 kg - insoluble sludges 20,00 kg

The amount of sulfur trioxide used was 13.75 kg, of which 2.70 kg was used to obtain soluble pstrosulfonates having an average molecular weight of 460 to 470.

Example 5

From a mixture of cycloparaffinic hydrocarbons, composed of:

(a) Saturated hydrocarbons 82,00%

(b) aromatic hydrocarbons of 17,50% cj containing 0,5% oxygen and sulfur, obtained by the process of the invention from 100 kg of starting product:

- purified saturated hydrocarbons 78,50 kg - soluble petrosulfonates 18,00 kg - insoluble sludges 15,00 kg

The amount of sulfur trioxide used was 11.62 kg, of which 3.15 kg was used to obtain soluble petrosulfonates. Although the description relates to the accompanying drawings of the illustrated exemplary embodiments, many variations of the invention may be made, all of which are based on the following definitions of the subject matter of the patent.

Claims (9)

Process for obtaining saturated hydrocarbons, in particular white oils, from petroleum fractions having a boiling point above 320 ° C, containing aromatic sulfonatable compounds up to 15 to 35% by weight. %, wherein these oil fractions have a molecular weight of 315 to 400, a density of 0.865 to 0.890, a kinematic viscosity of 12 to 35 cst at 38 ° C, characterized in that these oil fractions are first mixed in a weight ratio of 5 to 320 ° C. / 1 to 1/1 with petroleum fractions having a boiling point between 120 to 280 ° C containing sulphonable compounds up to 15 to 30% by weight. %, the mixture is then sulfonated at 30-75 ° C, separated from oil-insoluble sulfonic acid sludges, oil-soluble sulfonic acids are neutralized and separated, and the neutral oil-containing residue is distilled to a boiling point of 120 ° C to 120 ° C. 280 ° C and a boiling point above 280 ° C, separating first a mixture of saturated hydrocarbons boiling up to 280 ° C and a further mixture of saturated hydrocarbons boiling above 280 ° C, where both fractions are free of sulfonatable compounds, wherein the sulfonation and the neutralization is carried out in at least two steps and the sulfonating agent is added in parallel to the different sulfonating steps. 2. A process according to claim 1, wherein the sulfonating agent is sulfur trioxide which is metered in a substantially stoichiometric amount. 3. Process according to claim 1, characterized in that the sulphonation of the mixture of petroleum fractions, the separation of insoluble sludges, the neutralization and the separation of the oil-soluble sulphonic acids are carried out in several stages. 4. The process of claim 1 wherein the sulfonating agent is sulfur dioxide gas diluted in an inert carrier gas. 5. A process according to any one of claims 1 to 4, wherein the sulfonating agent is fed in parallel to the steps of the first step in an amount sucking into the stages following the first step, and the excess sulfonating agent withdrawn from the last step is fed to the first stage so that in excess, while the total amount of sulfonating agent used is approximately stoichiometric. 6. The process of claims 1 to 5 wherein the bulk composition of the sulfonating agent is 6-10% SO3, 0.1-0.2% SO2 and 93.9-89.8% N2 + O2. 7. A process according to any one of Claims 1 to 6 wherein the introduction of both reagents to each reaction step is accompanied by removal of insoluble products formed by polysulfonation of the aromatic fractions. 8. Apparatus for carrying out the process according to the preceding claims, comprising a series of reaction vessels connected in series, provided with dosing means for the gaseous reagent in parallel and means for removing unreacted gases from the corresponding reaction vessels, characterized in that each reaction vessel has a funnel at the bottom and means for recirculating the liquid product separated from the insoluble reaction products. Device according to claim 8, characterized in that each reaction vessel preferably consists of two superimposed elements and both are formed by an upper cylindrical zone connected downstream to a conical or frustoconical zone, the upper element extending into the cylindrical end into an annular space for accumulating a liquid mixture of the reaction product in the upper part of the lower element, wherein a deflection baffle is arranged in front of the mouth of the cylindrical end.