The present invention refers to the industrial chemistry field and in particular to the use of mesoporous silica functionalized with peroxycarboxylic groups as reactant in the oxidative process of aliphatic, cycloaliphatic and aromatic organic sulphur compounds, such as thiols, thioethers, thiophenes, spacifically benzothiophene, dibenzothiophene, methyl- and dimethyl-dibenzothiophene, diphenyl-sulphide and their derivatives. Moreover, the invention relates to the plant for oxidation and sulphur compounds removal from hydrocarbons fraction derived from petrol, in order to produce extra-low sulphur fuel and sulphoxides and sulphones as by-products thereof.

As well known in the art, sulphur compounds removal is a main topic in refining and petrochemical industry. In fact, new regulations require that fuels, their intermediate and end products have a low content of sulphur compounds. Moreover, it is necessary to avoid undesirable secondary reactions in order to assure the end products'quality.

At present, the most widely employed process is hydrodesulfurization (HDS), which requires the use of high temperature and pressure hydrogen stream on a catalitic bed, with the production of H2S. This process has a variable yield and the velocity of desulfurization greatly slows down when it is applied

to substituted thiophenic compounds, such as dibenzothiophene.

In fact, these compounds because of the sterical hindrance of benzene ring make difficult the interaction between the molecule and the HDS catalyst; moreover, electronic density around sulfur atom renders said compounds less available for the reduction reaction.

Recently, many procedures for desulfurization have been studied, due to the stringent rules of many countries regarding fuels. For example, there aree known"improved"plants for HDS, which are, however, characterised by severe operating conditions, high operating costs, lost of products'quality and fast deactivation of the catalysts used.

However, the products that are more resistant to hydrodesulfurization are sensitive to oxidative treatments, and their removal can be achieved by processes such as oxidative desulfurization, which is a two-step process: oxidation of sulphides and thiophenes and the subsequent extraction of the oxidation products.

Several studies, actually under development, try to design not expensive and selective oxidative processes, that employ environmentally-friendly, non toxic and regenerable reactants.

Some of said processes provide the use of oxidising agents such as nitric acid, nitrogen oxide, organic hydroperoxides and peroxidic acids.

In literature, the most studied and spread processes are those that employ a mixture of formic acid and hydrogen peroxide as oxidizing system. Their industrial applicability is difficult because of the liquid phase of the reactant mixture, that makes necessary the use of liquid-liquid separator to remove the oxidized products.

The scope of present invention is to solve the disadvantages of the known processes, providing the use of a solid oxidizing reactant, that is easily regenerable and environmentally-friendly.

The inventors of the present invention have surprisingly demonstrated that the use of mesoporous silica, functionalized with peroxycarboxylic groups, according to the procedure described by Elings et al.

(1998), in comparison with the common oxidizing systems based on organic peracids, permits to reach high velocity and higher yields of the oxidation reaction, thanks to the quantitative utilization of the peroxycarboxylic groups, already present.

The utilization of mesoporous silica, functionalized with peroxycarboxylic groups in said specific field is not disclosed in literature.

Advantageously, the solid state of the reactant and its insolubility in organic mixtures allow the easy separation of the mixture at the end of the oxidative process.

An other advantage is that the reactant is completely regenerable by means of treatment with hydrogen peroxide at the end of the oxidative process.

Moreover, its low toxicity identifies the product as environmentally-friendly.

Due to the great industrial involvement in this field, the inventors have developed an oxidative desulfurization process which use, for the first time, mesoporous silica functionalized with peroxycarboxylic groups as a solid state reactant for the oxidation of sulphur compounds.

Therefore it is object of the present invention a process for oxidative desulfurization that provides the use, as oxidizing reactant, of mesoporous silica functionalized with peroxycarboxylic groups and the plant thereof, as described as follows with reference to the attached sheets of drawings: Figure 1 shows the Arrhenius diagram and values of energy of activation for benzothiophene and dibenzothiophene.

Figure 2 shows the percentage of conversion of reactants into products referred to total remaining in the eluent.

Figure 3 shows the fraction of regenerated peroxycarboxylic groups on mesoporous silica vs time.

Figure 4 shows the functional scheme of the plant for reactive filtration.

Figure 5 shows the functional scheme of the plant for oxidation on fixed bed.

Figure 6 shows the functional scheme of the plant with reactor containing suspended catalyst.

In order to demonstrate the applicability of the process, the inventors have carried out experimental

tests to evaluate the efficiency and the reproducibility of the process, as described below.

Reproducibility of the oxidative reaction At first, the reproducibility of the oxidative reaction of sulphur compounds has been evaluated using mesoporous silica functionalized with peroxycarboxylic groups as oxidizing agent.

Then, several samples of mesoporous silica, prepared in separate moments, have been used in the oxidation of benzothiophene, dibenzothiophene and diphenylsulphide.

Table I shows the percentage of conversion of 936 ppm of benzothiophene, 856 ppm of dibenzothiophene and 848 ppm of diphenylsulphide (total sulphur 518 ppm) in toluene, undergone oxidation at 30 °C with 0.5034 g of mesoporous silica functionalized with peroxycarboxylic groups.

Table I Conversion (%) Compound 10 30 120 min min min Benzothiophene 38 59 87 Dibenzothiophene 97 99 100 Diphenylsulphide100--

Table II shows the percentage of conversion of 585 ppm of benzothiophene, 418 ppm of dibenzothiophene and 907 ppm of diphenylsulphide (total sulphur 369 ppm) in toluene undergone oxidation at 30 °C with 0.3447 g of mesoporous silica functionalized with peroxycarboxylic groups.

Table II Conversion (%) Compound 10 30 120 min min min Benzothiophene 7 26 62 Dibenzothiophene 70 93 100 Diphenylsulphide 100 As shown in the tables, 10 minutes are sufficient to convert 100 % of diphenylsulphide, while the conversion for thiophenic compounds is greater than 50 %.

Effects of temperature on the oxidative reaction of sulphur compounds Secondly, has been analysed the effects of temperature on the oxidative reaction in order to evaluate the range of applicability of the reaction and the activation energy has been calculated for each reagent as a parameter of the reaction velocity.

Table III shows the percentage of conversion for 838 ppm of benzothiophene, 890 ppm of dibenzothiophene

and 790 ppm of diphenylsulphide (total sulphur 489 ppm) in toluene, undergone oxidation at 30 °C with 0.4908 g of mesoporous silica functionalized with peroxycarboxylic groups.

Table III Conversion (%) Compound 10 30 120 min min min Benzothiophene 7 52 62 Dibenzothiophene 52 99 100 Diphenylsulphide 100

Table IV shows the percentage of conversion for 780 ppm of benzothiophene, 668 ppm of dibenzothiophene and 708 ppm of diphenylsulphide (total sulphur 424 ppm) in toluene undergone oxidation at 50 °C with 0.5044 g of mesoporous silica functionalized with peroxycarboxylic groups.

Table IV Conversion (%) Compound 10 30 120 min min min Benzothiophene 43 89 96 Dibenzothiophene 97 100 Diphenylsulphide 100-- Table V shows the percentage of conversion for 692 ppm of benzothiophene, 860 ppm of dibenzothiophene and

744 ppm of diphenylsulphide (total sulphur 442 ppm) in toluene, undergone oxidation at 60 °C with 0.5045 g of mesoporous silica functionalized with peroxycarboxylic groups.

Table V Conversion (%) Compound 4 min 45 min Benzothiophene 45 91 Dibenzothiophene 96 100 Diphenylsulphide 100-

Table VI shows the percentage of conversion for 929 ppm of benzothiophene, 768 ppm of dibenzothiophene and 835 ppm of diphenylsulphide (total sulphur 499 ppm) in toluene undergone oxidation at 70 °C with 0.5058 g of mesoporous silica functionalized with peroxycarboxylic groups.

Table VI Conversion (%) Compound 4 min 45 min Benzothiophene 54 81 Dibenzothiophene 98 100 Diphenylsulphide 100

The experimental tests demonstrate that the efficiency of the reaction is satisfactory even at low temperature.

The average values for the activation energy for the principal sulphur compounds undergone oxidation have been calculated according to the obtained experimental data, as shown in figure 1.

Activation energy of benzothiophene: 62528 kJ/mol Activation energy of dibenzothiophene: 62025 kJ/mol Thus, the reaction is performed at a temperature ranging from 30 to 75 °C, where the reactants show values of the velocity of reaction comparable with those calculated for the conventional oxidative desulphurization systems.

Starting from said experimental results, plants schemes are provided in order to perform the described process in the industrial level.

Therein below, three different realisation forms are in detail disclosed.

A) Reactive filtration plant In accordance with the oxidative process previously described, has been realised a plant for the oxidative desulphuration, able to carry out a"reactive filtration", precisely the oxidation of sulphur compounds and the contemporary removal of their oxidized products.

The system is composed by three columns filled with a so-called mixed bed, consisting of mesoporous silica functionalized with peroxycarboxylic groups and a polar filtering material (neutral allumina or neutral activated silica), working alternately (reaction, washing, regeneration).

The steps for each column are:

a) reaction; b) removal of the hydrocarbons fraction with hot nitrogen, preferably at 90 °C ; c) washing with methanol; d) regeneration with hydrogen peroxide, preferably at 50 % ; e) drying of the column with hot nitrogen, preferably at 90 °C ; as shown in the scheme of figure 4.

Said plant allows to realise a N% one-step" desulfurization process based on reactive filtration, to be applied both on small and industrial productions, in a fast, cheap and environmentally-friendly way.

Advantageously, the reactive filtration process, as previously described, can be apply as line desulphuration filter in feed systems of internal combustion engines and boilers.

In this case, the regeneration phase, when the filter becomes exhausted, can be carried out in an other place.

As shown below, residence time into the column of about 4 minutes is sufficient to ensure an optimisation of the reactive filtration, and due to the regeneration step the columns can be used in a continuous process.

COLUMN EFFICIENCY TESTS In order to evaluate the efficiency of the present plant, the oxidation of benzothiophene, dibenzothiophene and diphenylsulphide in different

mobile liquid phases and the contemporary removal of the oxidation products were performed into the column.

In each test the procedure was as follows: at the outlet of the column subsequent samples of 0.5 ml volume have been taken. Some of them have been analyzed in order to evaluate the residual quantity, percentage value compared with initial quantity, of each sulphur product and of total sulphur. The percentage of residual sulphur in the effluent vs the volume of the effluent itself was calculate from the obtained data.

The analysed samples are as follow: sample 1: 0 ~ 0. 5 ml; sample 2: 1. 5 2 ml; sample 3: 3 3. 5 ml; sample 4: 4. 5 5 ml; sample 5: 6-6. 5 ml; sample 6: 7. 5 ~ 8 ml; sample 7: 9-9. 5 ml; sample 8: 10. 5-11 ml.

The results are shown in the following tables from VII to XII.

TEST 1 Benzothiophene 740 ppm, dibenzothiophene 800 ppm and diphenylsulphide 968 ppm in toluene (total sulphur 482 ppm) are filtered through the column filled with mesoporous silica functionalized with peroxycarboxylic groups (0.1020 g) and neutral allumina (1.0051 g) at the temperature of 27 °C.

Table VII Removal (%) per sample 1 2 3 4 5 Compound Benzothiophene 45 37 30'26 16 Dibenzothiophene 89 84 83 77 56 Diphenylsulphide 100 100 100 100 100 Sulphur 74 66 38'18 3 residual sulphur in effluent (%) 26 30 40 51 60

The average residence time in the column is 4 minutes.

TEST 2 Benzothiophene 2918 ppm, dibenzothiophene 2186 ppm in isooctane (total sulphur 1076 ppm) are filtered through the column filled with mesoporous silica functionalized with peroxycarboxylic groups (0.5283 g) and neutral allumina (1.0045 g) at the temperature of 27 °C.

Table VIII Removal (%) per sample Compound 1 2 3 4 5 6 7 8 Benzothiophene 99.7 87 54 31 26 12 6 0.4 Dibenzothiophenee 99.3 99 99 96 84 65 54 41 sulphur o 99. 6 91 71 55 47 32 25 15 Residual sulphur in effluent (%) 0.42 5.4 14 23 29 36 41 46 The average residence time in the column is 4 minutes.

TEST 3 Benzothiophene 2918 ppm, dibenzothiophene 2186 ppm in isooctane (total sulphur 1076 ppm). are filtered through the column filled with mesoporous silica functionalized with peroxycarboxylic groups (0.5048 g) and silica (1.0022 g) at the temperature of 27 °C.

Table IX

Removal (%) per sample Compound 1 2 3 4 5 6 7 Benzothiophene 99.7 88 50 31 24 11 Dibenzothiophene 99.3 99 99 98 85 65 56 as sulphur 99.6 92 68 55 47 30 23 Residual sulphur 0.4 5 15 23 29 37 43 in effluent (%) The average residence time in the column is 4 minutes.

TEST 4 Benzothiophene 1307 ppm, dibenzothiophene 1795 ppm in decaline (total sulphur 862 ppm) are filtered through the column filled with mesoporous silica functionalized with peroxycarboxylic groups (0.2035 g) and neutral allumina (1.0035 g) at the temperature of 27 °C.

Table X Sulphur compound Removal (%) per sample 12345 6 Benzothiophene 97 77 28 16 8 2 Dibenzothiophene 99 93 64 45 33 20 Sulphur 98 82 41 27 16 8 Residual sulphur in 1.8 11 29 41 50 58 effluent (%)

The average residence time in the column is 2.5 minutes.

TEST 5 Benzothiophene 1307 ppm, dibenzothiophene 1795 ppm in decaline (total sulphur 862 ppm) are filtered through the column filled with mesoporous silica functionalized with peroxycarboxylic groups (0.2000 g) and silica (1.0059 g) at the temperature of 27 °C.

Table XI Compound Removal (%) per sample 1 2 3 4 5 6 Benzothiophene 98 76 24 22 8 2 Dibenzothiophene 99 95 63 48 33 20 sulphur 99 83 38 31 17 9 Residual sulphur 1. 4 11 30 40 49 59 in effluent (%) The average residence time in the column is 2.5 minutes.

For example, the diagram of figure 2 is based on the results obtained in test 2 and it shows the percentage of removal of oxidized sulphur compounds and the percentage of total residual sulphur vs effluent volume.

TEST 6 Dibenzothiophene 1150 ppm, 2methyl- dibenzothiophene 987 ppm, 2,4 dimethylbenzothiophene 470 ppm in decaline (total sulphur 862 ppm) are filtered through the column filled with mesoporous silica functionalized with peroxycarboxylic groups (0.1130 g) and neutral allumina (1.0001 g) at the temperature of 27 °C.

TABLE XII Removal per sample Compound 1 2 3 4 5 Dibenzothiophene 99.5 95 62 47 32 4-methyldibenzothiophene 99.7 94 63 47 30 4, 6- dimethyldibenzothiophene 99.5 96 62 47 30 Sulphur 99. 6 95 62 47 30 Residual sulphur in effluent 0.4 3 16 26 35 (%) The average residence time in the column is 2.5 minutes.

Regeneration of peroxycarboxylic groups on functionalized mesoporous silica Moreover, the regenerative efficiency of the mesoporous silica has been experimentally evaluated, by a reaction with hydrogen peroxide in order to

regenerate the functional groups from carboxylic to peroxycarboxylic groups.

In particular, the exhausted mesoporous silica with carboxylic functional groups (1.0 g) underwent to regeneration with hydrogen peroxide at 50 % (20 ml) and methane sulphonic acid (10 ml) and at temperature of 25 °C, knowing that the number of peroxycarboxylic groups in the original mesoporous silica is 3.0513 mmol/g, while in the exhausted silica is 0.0326 mmol/g.

The results are shown in table XIII and in attached figure 3.

Table XIII Peroxycarboxylic groups (mmol/g) 0 min 15 min 30 min 60 min 180 min 300 min 0.0326 1.9554 2.3194 2. 5002 2.8571 3. 0435 The invention provides also alternative embodiments herein described.

B) Fixed bed reactor Said plant provides the use of a fixed bed reactor for the oxidation of sulphur compounds to produce sulphones.

In this case, the removal of produced sulphones is carried out into an ancillary equipment or alternatively through thermal or catalytic decomposition, with recovery of hydrocarbons and production of SO2 or H2S.

The proposed system provides the use of two packed columns containing mesoporous silica functionalized with peroxycarboxylic groups and non polar substrates, alternately in a reaction or in a regeneration step.

The steps for each column are: 1. Reaction ; 2. Removal of hydrocarbons phase with hot nitrogen, preferably at 90 °C ; 3. Regeneration with hydrogen peroxide, preferably at 50 % ; 4. Drying with hot nitrogen, preferably at 90 °C as shown in figure 5.

C) Suspended catalyst reactor Is disclosed a two-step system composed by an oxidation section and a removal (or decomposition) of oxidized sulphur compounds section.

In particular, as shown in figure 6, the oxidation is carried out in a PFR type reactor.

At the end of the reaction, the mesoporous silica functionalized is separated using a hydrocyclone and sent to regeneration with hydrogen peroxide in acid solution.

The hydrocarbon fraction containing oxidized sulphur compounds is sent to a filtering system, composed by two columns working alternately in adsorption and regeneration, or it can be conveyed into a system for sulphones decomposition with recovery of organic rings and SO2 (cracking) or H2S (HDS).

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