CS251788B2 - Liquefacient and stabilizing admixture and method of its production - Google Patents

Abstract

A fluidifier and stabilizer additive, particularly suitable for coal suspensions in water, based on sulphonated tar, wherein sulphonated and salified tar results to be also oxidized, the oxidation being evidenced by the development of SO2 to the extent of 2 to 60% by wt, w.r.t. the tar during the sulphonation reaction. Also there is a method for the preparation of the additive, consisting in contacting tar with liquid or gaseous SO3, tar and/or SO3 being preferably dissolved in an halogenated organic solvent; the solvent is recovered and the oxidized sulphonated additive is salified.

Description

The present invention relates to a fluidizing and stabilizing additive and a process for its preparation.

In particular, the present invention relates to a fluidizing and stabilizing additive for suspensions of solids in liquids and to a process for its preparation.

In particular, the present invention relates to a fluidizing and stabilizing additive for carbon suspensions in liquids and to a process for its preparation.

More particularly, the present invention relates to a fluidizing and stabilizing additive for carbon suspension in water and to a process for its preparation.

More particularly, the present invention relates to a fluidizing and stabilizing additive for coal slurry in water, wherein the coal is present at a high concentration, i.e. at a concentration of more than 60% by weight, in particular from 70% to 80% by weight or more, and to a process for producing it.

In the following description of the present invention, the case of coal / water suspensions will be discussed, but it will be appreciated that the additive of the invention can be used wherever there are problems with fluidization or stabilization due to the presence of suspended solids.

Fluidizing and stabilizing agents for coal-in-water suspensions are known which are sulfonated and salt-neutralized tar compounds, wherein the sulfonated compounds are obtained by treating tar with anhydrous, concentrated or fuming sulfuric acid. The prior art sulfonated additives have the disadvantage that they contain large amounts of alkali metal or ammonium sulfate, which is formed in the neutralization step of a sulfate solution containing tar sulfonation products with alkali or ammonium hydroxide.

In addition, in order to sulfonate all the tar, the excess sulfuric acid is used and, after removal of the water used to introduce the neutralizing agents, the alkali metal and ammonium sulfates remain in the sulfonated and neutralized tar.

A second disadvantage of the prior art additives is that in order to obtain a better viscosity characteristic, these additives have to be at least partially condensed with formaldehyde, thus requiring a further processing step which is very expensive.

Unexpectedly, it has been found that it is possible to eliminate the disadvantages of the prior art and to obtain a sulfonated tar-based additive having more advantageous properties than the prior art additives.

The present invention provides a fluidizing and stabilizing additive based on sulphonated and salt neutralized tar, characterized in that the sulphonated and neutralized tar is oxidized, the oxidation being manifested by the evolution of sulfur dioxide during the sulphonation step and the amount of SO ₂ evolved ranging from 2 % to 60% by weight of the tar used, preferably from 10% to 35% by weight.

The term tar used in the present description means tar derived from deep coal, such as coke oven tar, especially arising from coal distillation at a temperature of 1100 ° C or higher, whose fractions have boiling points in the range of 100 to 350 ° C, the residue from the distillation of coal tar tar at 350 ° C and, in addition, the tar fractions from the oil processing units. ·

The tar must contain at least a small percentage of compounds with more than 2 aromatic fused rings, irrespective of their origin.

SUMMARY OF THE INVENTION The present invention provides a process for the manufacture of a sulfonated and salt neutralized tar-based fluidizing and stabilizing additive comprising the following steps:

1) slowly contacting (preferably without dissipating the heat of reaction) the tar with liquid or gaseous sulfur trioxide in the presence of one or more tar solvents selected from the group of halogenated organic compounds inert to the sulfonation reaction, immiscible or limited to miscible with water; preferably selected from compounds having a boiling point in the range of from 30 to 130 ° C and especially selected from the group consisting of carbon tetrachloride, tetrachlorethylene and dichloroethane;

(2) complete the reaction between sulfur trioxide and tar at a temperature in the range of from 80 ° C to 140 ° C, preferably from 90 ° C to 120 ° C, while monitoring the evolution of sulfur dioxide, the amount of sulfur dioxide having to reach from 2 % to 60% by weight based on the weight of tar, preferably from 10% to 35% by weight;

3) neutralizing the sulfonated and oxidized tar solution with an aqueous solution of basic reagents, preferably sodium hydroxide or ammonium hydroxide until the pH reaches 7 and up to a pH of 10;

4) the solvent or solvents are removed from the tar by decantation and / or evaporation;

5) an aqueous solution containing a sulfonated, neutralized and oxidized additive is obtained;

in

6) the additive is concentrated or optionally dried.

Steps 3 and 4 can be reversed.

In the practice of the process of the invention, the tar may be pre-dissolved in one or more solvents and the liquid or gaseous sulfur trioxide may be introduced into the tar solution as such, or also dissolved in one or more of said solvents, provided the solvents must be mutually combinable, ie there must be no chemical reaction between them.

In a further practical embodiment of the process according to the invention, the tar dissolved in one or more of said solvents or undissolved can be poured into a solution of sulfur trioxide in one or more of said solvents, taking care that when the tar is introduced in the form of a solution, the solvents were combinable and to avoid a violent reaction even at very slow adhesion.

Several examples will now be given to better illustrate the invention. However, the invention is not limited in any way by these examples or by these examples.

The tar used in all the tests of the examples is a coke oven tar having a specific gravity of 1.1577 g / cm ³ and a viscosity of 0.8381 cm ² . with ¹¹ at 40 ° C.

He did

The reaction equipment consisted of a four-necked flask of 500 ^cm3 equipped with a mechanical stirrer having blades made of PTFE, thermometer, water condenser 8 spherical inner element and a dropping funnel.

Into the flask 44 g of tar diluted with 100 cm ³ of tetrachlorethylene, while the loading funnel was poured 53 g of liquid SO ^ in 100 ^cm3 of tetrachlorethylene.

The sulfur trioxide solution was introduced into the reaction flask over a two hour period, while the reaction flask was continuously cooled to maintain its temperature in the range of 10-15 ° C.

At the end of SO 2 additions, the internal temperature was allowed to rise to 20-25 ° C and after about an hour the reaction mixture was heated to the reflux temperature (about 120 ° C) and held at this temperature for one hour. '’

The reaction mixture is then cooled, diluted with water and the resulting crude reaction product is transferred to a beaker where it is neutralized with an aqueous NaOH solution to pH 7; the entire volume is then distilled at atmospheric pressure to recover the solvent as a water / tetrachlorethylene azeotropic mixture.

975 g of an aqueous solution without solids are obtained and the portion 33 is recovered

196 cm from the original 200 cm solvent.

Content θ2θθ4 1.70%

Dry active ingredient 107 g

Sodium sulfate formed 16.6 g

The resulting SO ₂ 2.1 g

Example 2

The equipment used is the same as described in Example 1.

43 g was charged into the flask. tar diluted with 100 cm ³ of carbon tetrachloride, while the dosage ⁱⁿ ns ^ ^{n, and} Le ^y VK close the ^{51.7 g} of ^{S0 3 R} e ^d ene ^h on ¹⁰⁰ cm ^{3 t l} etrach ormutrnu.

SO3 is added over a two hour period with external water cooling (internal temperature 15 to 18 ° C, then the reaction mixture is allowed to stand for one hour at room temperature, and then heated under reflux (about 80 ° C) for two hours.

The reaction mixture was cooled to room temperature, diluted with water, transferred to a beaker with water rinse, and brought to pH 7 with aqueous sodium hydroxide solution.

The carbon tetrachloride / wax azzotine mixture was added as the overhead portion, and an aqueous solution of high-density carbonate was obtained as a residue. 1,176 g.

N / 2SO4 content 1,7%

Dry active ingredient 95.5 g

The resulting sodium sulfate was 20 g

The resulting SO2 2.6 g

Examples 3 to 17

Examples 3 to 17 were carried out under the same conditions as to the temperature, the dilution of tar and SO 3 in the solvent, and the addition time of SO 3 to the tar.

The apparatus was the same as the experimental apparatus of Example 1.

Reaction procedure: 100 cm ^{3 of} tutrachllrutylene (TCE) diluted tar is charged to the flask and SO 3 diluted with an additional 100 cm of non-carbonated butyl is placed in a funnel.

The SO 3 solution was added over approximately 90 minutes while the reaction flask was externally cooled with water (external temperature 10 to 15 ° C).

The reaction mixture is then held at room temperature (about 20-30 ° C) for one hour and then heated under reflux for one hour at 120 ° C. The mixture was cooled to room temperature, diluted with water and neutralized with aqueous sodium hydroxide solution. Most of the solvent is separated as the lower phase in the final reaction network after neutralization and is partially obtained as an azeotropic mixture with water. The total solvent recovery is about 96 to 97%.

Data relating to these examples are summarized in Table 1.

In all cases, the off-gases (from a large amount of sulfur formed with traces of SO 2) were analyzed by absorption of the condenser outlet into the collector containing the tattooed aqueous NaOH solution.

Example 18

The apparatus used was the same as the reaction apparatus described in Case 1.

Flask reaction load: 80 tar diluted with TCE.

g so ₃ diluted 100 cm · TCE. Charge inside the dropping funnel: 44 g přibližíně 50 minutes into solution of S (R PRCE temperature ro ^ protrudes C; reatoní mixture ^P Otom heated and ^f to l ² 0 C te ^ OTA one hour. Most of the solvent was then oddekaatuje Deň: 32 ° C.

Tar solution is added to the mixture ^ Halt rise from 22 to keeps this value for ^p s te ^ o ^ 80 ° C. ^BAn Ka Otom ^{p p u} OIΊO: s in a thermostated Шп Н ^ te ^ Oto Even during ⁴⁰ to 72

Most of solvent was oddděí during 80 minutes (98% recovery přiblinně. The reaction mixture was st ^AL e in hot condition (80 ~ Iz 85C) neiRralizuje to pH 7 with 1 roztoto ^5% NaOH and then diluted with water.

A total of 795 g of an aqueous solution is obtained. Sodium sulphate content 2.9 Dry active tloial 92.9 Sodium sulfate -23.1 SO ₂ formed during the reaction 13 g Organic sulfur 14.3

% g

g g

Example 19

The apparatus used was the same as the reaction apparatus described in Case 1.

Charge in flask: 44 g of tar diluted with 326 g of TCE.

Charge in dropping funnel: 81 g liquid

SIR.

SO3 liquid tar into solution without cooling for outdoor advert ^ ^b and reatoní ^ňky (temperature 90 ° C and at the end was ⁶ ^ ídavto 5 ° C).

Addition is performed over a period of ²³ ° ^C. vzrtaU also ^from the original portion ^of 40 min on ^tp and ^h o ^d chat note

The reaction mixture was warmed to ²⁰ ° C ^b uring ¹⁵ minutes for one hour. 'This temperature is maintained ^ ovténa after ° C ^{(yielding p} Otom ^p ^ j ^ N ^ R ^ i to termustatovan ^Star Oil ^la zn ^{e p} s ¹³² and ^{from 134} solvent deetilací. Pomooí this second procedure to ^give eužralizuje ^{i p} s t ^ ^{EXAMPLE IB} lotto draw ^{of 80} and ^{from 90} ° C and an aqueous solution of ^{N OH} i ^{from pH} "7. Hnmtoost resulting aqueous solution tulUonovanéUo-oxidovanéUo ieuttllZuoaanéUo and pitch: 477 g.

Rozppv-solvent is ^p ^ nd the tote ^d ^ ekantuje at approx 90 IRE 274 g of TCE) The flask ° C to remove residual ^p forehead TCE. Residual mixture

Na2SO., Contents

4

Dry active fraction

6.8%

97.5 g

Sodium sulfate 32,4 g The resulting SOg 13,9 g Organic sulfur 17.1 g

Example 20

The apparatus used was the same as the reaction apparatus used in Example 1.

Charge in the reaction flask: 44 grams of tar diluted with 327 grams of TCE.

Charge in dropping funnel: 79 grams of liquid SOg

SOg solution is added to the tar in a time period of 40 minutes without external cooling of the reaction ^b Anky. (Enters • temperature, aqueous ² M ^T 1 ° C, increases up to values of ^the toe 90 ^and natonec is 65 ° C). '

The reaction mixture is then heated to the boiling point of TCE (about 120 ° C) for 15 minutes and maintained at this temperature for one hour. Most solvents. then ^from deca ⁿ iuje ⁽²⁷ 0 ^g) at a straight draw ^{ib of 85} ° C, then the reaction ^{No. B} Au ^{for p} and s in it ^for termcstat Christians lcizně ^{s p} s te rt ^{pl of 140} ° C. The remaining solvent was collected Otom ^{p runs} through two hours. ^The remaining residue in the flask was not euraed with aqueous sodium hydroxide solution, even to pH 7.

7.4%

93.9 g

35.1g

13.1 g.

15.4 g of the aqueous solution is 474.4 g.

Sodium sulphate content

Dry active sloika

Sodium sulfate

SO2 produced during the Organic Sulfur test

The first example a d 1

The apparatus used was the same as the reaction apparatus described in Case 1.

_q

Reaction procedure. Into the flask 38.8 g of tar diluted with 200 cm tetrachlorethylene, while in the dispenser funnel umíítí 43.8 g of liquid contents SOg funnel is introduced into the reaction flask, which is cooled externally so as to keep the internal temperature of the whole ^{p d} OBU in the range of ^{d 17 d 20} ° C, Be ^h em time ^for check ^ib straight draws ^{of 80} minutes.

The mixture was then stirred for an additional 4 hours while maintaining the internal temperature at about ¹⁷ ° C. A mixture ^of salt of ^{d h} onované ehtu then ^ nee ali.zuje vodnéto using sodium hydroxide solution to pH seventh

Separated by azeotropic deesilation.

897.3 g of an aqueous solution are obtained.

Sodium sulphate content

Dry active subdl

Sodium sulfate

Created by SOg

Organic sulfur

The product thus obtained is not dispersing

Comparative example a d 2

The equipment was the same as it was

The reaction flask had a volume of 250 cm instead of 500 cm.

3.82%

63.9 g

34.3 g less than the determination limits 9.2 g.

as described in Example 1, with the sole exception that i

Procedure: Place 17.0 g of tar diluted with 50 cm @ 2 TCE in a flask.

31.8 g of SO4 diluted with 50 cm @ ^{3 of} TCE are placed in a addition funnel.

The contents of the funnel are metered into the reaction flask, under external cooling with water flow, to maintain the internal temperature in the range of 16 to 18 ° C, over a period of about 135 minutes. The mixture was then stirred for an additional 130 minutes while maintaining a constant temperature of approximately 18 ° C.

The reaction mixture was then neutralized with aqueous sodium hydroxide solution to pH 7.

787.4 g of an aqueous solution of sodium salt of sulfonated tar are obtained.

Sodium sulphate content

Dry active ingredient

Sodium sulfate

SO ₂ formed during the reaction

Organic sulfur

The product thus obtained does not exhibit dispersing properties.

In order to evaluate various dispersing agent samples (both agents of the present invention and commercially), viscosity measurements were performed at various velocity gradients using a Haake RV 12 rotary viscometer equipped with an MVI sensor and a M500 measuring head.

To this end, weigh 70 g of coal with a particle size of less than 200 g into a 200 cm beaker

250 mm and a moisture content of less than 0.5% and an aqueous mixture of the test dispersant is added so that the resulting mixture has the following composition:

% by weight of coal

29.5% by weight of water

0.5% by weight of dispersing agent.

in

The products are mixed using a mixer with two metal beaters for 1 minute at

650 rpm and for 2 minutes at 1200 rpm. The suspensions thus obtained are introduced into an external measuring cylinder of a viscometer which has already been brought to 20 ° C and after 15 minutes of standing at 20 ° C, the shear stress values (T) are measured at different velocity gradients (ý · *) (from 3, 8 to about 150 s ¹ ). The experimental values so obtained are processed using the Ostwald equation applicable to pseudo-plastic behavior.

For each series of experimental measurements of T -, the Kana values are calculated using linear regression. For the last five values tested, the curve. . -I ~ = 37, 60, 75, 120 and about 150) are to be calculated limit value limiting viscosity * ^Assuming rectification of experimental data - У *.

The values obtained for some samples by the above procedure are as follows:

Type of Uisatrgating agent O TO Bye . with l lolite (limit viscosity ^) Bye . with DAXAD 15 (commercial product) 0.91 0.83 0.58 Example 18 0.92 0.81 0.61 Example 11 0.87 1.05 • 0.57

The dispersing agent samples of the present invention were compared to a commercial sample (DAXAD 15, Grace, Italy) according to a method which is defined below as stability as a function of shear stresses.

336 g of dry (less than 0.5% moisture) coal having a particle size below 250 mm and a solution of the dispersant in water are introduced into a 10-cm, 10 cm high 1-liter glass reactor and the final dispersion solution is:

% of hmoonoot coal

29.5% by weight of water

0.5% mono-dispersing agent

The mixture is agitated in a reactor open to the atmosphere by means of a beater mixer for 2 minutes at 650 rpm and then minutes at 1200 rpm.

The flange is sealed, a impeller with a blade of 2 cm diameter is placed at 200 ml, and the mixture is stirred at 200 rpm for 24 hours. Stirring is discontinued, the impeller is removed and the entire contents are allowed to stand for three days. After this time, the beaker is tilted and the sludge is discarded.

The results obtained by this procedure are shown in the table below by the following symbols:

+ = case where all sludge flows spontaneously ++ = overflow, where the residue remaining at the bottom can be easily fuudised again using a glass rod or a similar tool +++ = a case where a co-locating deposit is formed at the bottom which cannot be easily removed by teaspoon or similar tool.

Ingredient coal Dosage amount, g Konceetrace ak- Aqueous additive solution water the ingredients in the aqueous solution of the additive pouring behavior DAXAD (14) 336 24 120 10.0 + + Example 11 336 36.92 107.08 6.5 +

Ta bulka 1- Tests with different weight ratio SO4 / tar Example # grams of tar grams with ₃ grams of dry active ingredient grams of sodium sulfate formed grams created with Sat ₂ gSimples of organic sulfur the SO 2 / tar ratio 3 41.5 17 48.8 4.2 1.3 5.4 0.41 4 41.5 26 55.0 7.7 2.4 7.4 0.63 5 40.3 31 62.6 7.5 2.7 8 ·, 5 0.77 6 40 36.7 53.5 8.2 2.9 7.7 0.92 7 40.1 45.8 75.1 14.8 3.2 10.6 1.14 8 40.2 51.5 80.8 18.3 4.0 12.6 1,28 9 40.2 62.6 89.5 19.9 4.2 15.3 1.56 10 40 66.4 90.9 24.8 5.0 15.4 1.66 11 41.7 69.5 97.1 25.4 5.8 18.2 1.67 12 43 75 98.1 28.6 9.0 16.9 1.74 13 37 69.8 87.3 27.7 11.2 14.8 1.89 14 40.4 83.6 97.8 35.3 13.7 15.6 2.07 15 Dec 32.7 89 93.0 50.7 13.7 16.5 2.72 16 26 81.6 74.6 53.7 12.7 12.6 3.14 17 30.6 102.7 93.0 71.7 16.9 16.6 3.36

The sulphates which are subjected to suction in the following Examples 21 to 25 are fractions of petroleum distillation which were carried out as follows: the residue after atmoeric distillation was subjected to vacuum distillation to obtain different fractions as well as fractions SN 80, SN 150 and SN 450 (SN stands for neutral solvent).

The fractions thus obtained were purified by furfural extraction, whereby most of the aromatic compounds and the proportion of naphthenic compounds present in the above mentioned SN fractions were extracted. In this way, aroma extracts (ESARs) were obtained, which were used as substrates for the subsequent sulfonation.

The average chemical-physical properties of ESAR substrates derived from the processing of crude oil from the Middle East are shown in the following table:

Sample Density at 15 ° C Viskooita (SUS at 98,877 ° C) Index at 20 ° C Sulfur arminic (%) substances (%) ESAR z fraction SN80 0.993 41 1.5360 5.1 83 ESAR z SN 150 1,005 59 1,5390 5.0 85 ESAR z SN 450 1,024 125 1.5770 _ 4.9 88

Example 21 to 25

The same apparatus as in Example 1 was used in the procedures of these examples. The procedures of these examples were also carried out under the same experimental conditions, i. in terms of temperature, dilution of petroleum fraction and sulfur trioxide with tetrachloettyylee (TCE) and the time of addition of sulfur trioxide to the tar.

and

Reaction procedure: The petroleum fraction, which was diluted with about 130 milliliters of TCE, was charged to a flask and sulfuric oxide diluted with an additional 70 milliliters of TCE was poured into the funnel. The sulfur trioxide solution was discharged into the vessel over 60 minutes, while the vessel was vigorously cooled with water to maintain the reaction temperature in the range of about 20 to 27 ° C.

The reaction mixture was heated to boiling (about 115-120 ° C) for about 30 minutes and held at this temperature for 60 minutes.

The discharged gases (which consisted mainly of sulfur dioxide together with a trace amount of sulfur trioxide) were analyzed for the procedures of all the examples by absorbing these gases downstream of the condenser in the condensate trap containing the titrated aqueous sodium hydroxide solution. The reaction mixture was then cooled, diluted with water and neutralized with aqueous sodium hydroxide solution.

The tetrachlorethylene used was distilled off at atmospheric pressure as azeotropic mixture 8 with water to obtain a sulfonated-oxidized and salt-converted aqueous product solution.

Table 2 shows the values of the test performed, and Table 3 shows the rheological characteristics of the dispersants obtained.

Table2

Example # Mass of the oil fraction (G) Type of oil fraction s ° ₃ (g) Proportion of active dry component (G) Sodium sulfate formed (G) Originated S ° 2 (g) Organic sulfur (G) Weight ratio SO ₃ / petroleum fraction 21 44 ESAR of SN 80 36 58.8 12.4 11.6 6.45 0,818 22nd 44 ESAR of SN 80 57.0 64.3 23.3 20.7 7.42 1.30 23 44 ESAR of SN 150 46.4 60.2 17.9 16.35 7.04 1.05 24 44 ESAR Z SN 150 54.1 61.8 23.2 19.9 6.75 1,22 25 44 ESAR of SN 450 46.9 51.9 18.0 19.0 5.82 1.07

SUS = Seybolt's universal second

Table 3

The dispersing agent according to Example no. Composition of coal / water / additive mixture (% by weight) Type of coal Rheological parameters n К (Passport) Viscosity Limit Number (Pa.i 21 68 / 31.5 / 0.5 В 0.810 0.476 0.218 68 / 31.5 / 0.5 AND 0,758 1,163 0.256 .22 68 / 31.5 / 0.5 В 0,817 0.398 0.176 68 / 31.5 / 0.5 AND 0,891 1,149 0.553 23 68 / 31.5 / 0.5 В 0,921 0.331 0.281 68 / 31.5 / 0.5 1,112 * 0.307 0,645 24 68 / 31.5 / 0.5 В 0,845 0.440 0.267 68 / 31.5 / 0.5 AND 1,032 0.479 0,684 25 68 / 31.5 / 0.5 В 1,046 0.180 0.247

Coal A: humidity 1.2%, ash 8.52%, volatiles 35.9%, bonded carbon 54.4%, total sulfur content 0.95%

Coal B: moisture 9%, ash 15.5%, volatile matter 23.7%, bound carbon 59.2%, total sulfur content 0.64%.

Granulometric curve of both types of coal: maximum dimension 250 yum, with 70-80% less than 74 µm

Claims (10)

SUBJECT OF THE INVENTION A process for the production of a fluidizing and stabilizing additive based on sulfonated and salt-neutralized tar, characterized in that: (a) slowly contact the coal with liquid or gaseous sulfur trioxide in the presence of one or more solvents selected from the group of halogenated organic compounds inert to the sulphonation reaction, immiscible or limited to miscible with water, b) the reaction between the sulfur trioxide and the tar is completed at a temperature ranging from 80 to 140 ° C, preferably 90 to 120 ° C, while monitoring the evolution of sulfur dioxide, the amount of sulfur dioxide produced being from 2 to 60% by weight tar, c) the solution of sulphonated and oxidized tar is neutralized with an aqueous solution of an alkaline agent, (d) the solvents / solvent is removed from the tar by decantation and / or evaporation; e) an aqueous solution containing the dissolved 'sulfonated salt neutralized and oxidized additive is collected, f) the additive is concentrated or optionally dried, wherein steps c) and d) can be carried out in reverse order. 2. The process of claim 1 wherein said solvents have boiling points in the range of from 30 to 130 [deg.] C. 3. The process of claim 1 wherein said solvents are selected from the group consisting of carbon tetrachloride, tetrachlorethylene, and dichloroethane. 4. The process according to claim 1, characterized in that up to 35% by weight of the tar is obtained. SO ₂ develops in an amount from 10% to 5. The sodium hydroxide process. characterized in that said neutralization is carried out with a solution 6. The ammonium hydroxide process. characterized in that said neutralization is carried out with a solution 7. The process of the invention is carried out up to a pH of 7. or 5 or 6, characterized in that said non-marketing is not Method according to pH 10. The method of claim 1, wherein said neutralization is carried out at a temperature of up to about 9. The process of claim 10, wherein the tar is previously dissolved in one or more solvents and the sulfur trioxide is contacted with the tar by introducing it into the tar solution either as such or dissolved in one or more solvents. 10. The process of claim 1 wherein the tar is contacted with sulfur trioxide by pouring, either as such, or dissolved in one or more solvents, into a sulfur trioxide solution in one or more solvents.