EP1699901B1 - Process for the oxidative desulphurization of hydrocarbon fractions

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EP1699901B1

Publication number: EP1699901B1
Application number: EP04806831A
Authority: EP
Inventors: Paolo De Filippis; Marco Scarsella; Valentina Di Mauro
Original assignee: Universita degli Studi di Roma La Sapienza
Current assignee: Universita degli Studi di Roma La Sapienza
Priority date: 2003-12-23
Filing date: 2004-12-01
Publication date: 2010-09-01
Anticipated expiration: 2024-12-01
Also published as: DE602004028959D1; ITRM20030598A1; EP1699901A1; WO2005061675A1; ATE479737T1

Use of mesoporous silica functionalized with peroxycarboxylic groups as a reactant in a process of oxidation of organic sulphur compounds, and the plant for oxidation and removal of said compounds from hydrocarbon fractions from petroleum and the production of fuels containing low sulphur sulphoxides and sulphones as secondary products thereof.

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, specifically 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 equality.
At present, the most widely employed process is hydrodesulphurization (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 desulphurization 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 procedure for desulphurization have been studied, due to the stringent rules of many countries regarding fuels. For example, there are 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 hydrodesulphurization are sensitive to oxidative treatments, and their removal can be achieved by processes such as oxidative desulphurization, which is a two-step process: oxidation of sulphide 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 oxidizing 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 oxiding 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.
WO-A-02053683 discloses an oxidative desulfurization process of thiophenes in petroleum hydrocarbons comprising: (a) the oxidation of the feel with organic peroxides/peracids such as peracetic acid in the presence of a catalyst such as a mesoporous siliceous solid of silica; (b) the separation of resulting sulfones by adsorption on the catalyst and (c) regeneration of the catalyst by washing with alcohols. Two parallel fixed bed reactors, working alternately in oxidation/adsorption and regeneration mode, are used.
US-A-5698326 discloses a regenerable silica-supported peracid suitable for application as heterogeneous oxidant. The exhausted peracid oxidant is separated from the oxidizing medium by for example filtration, washed and regenerated by peroxidation with a hydrogen peroxide/strong acid solution.
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 desulphurization 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 an oxidative desulphurization process of organic sulphur compounds for the removal of organosulphur compounds from HC fraction and the subsequent removal or decomposition of oxidized compounds according to claim 1. The process is 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 min 30 min 120 min

Benzothiophene 38 59 87

Dibenzothiophene 97 99 100

Diphenylsulphide 100 - -
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 min 30 min 120 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 min 30 min 120 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 min 30 min 120 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 realization 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 desulphurization, 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 alumina 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;

figure 4

Said plant allows to realise a "one-step" desulphurization 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 applied as line desulphurization 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 optimization 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 in 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 alumina (1.0051 g) at the temperature of 27°C.

Table VII

Compound	Removal (%) per sample
Compound	1	2	3	4	5
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 fillled with mesoporous silica functionalized with peroxycarboxylic groups (0.5283 g) and neutral allumina (1.0045 q) 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
Dibenzothiophene	99.3	99	99	96	84	65	54	41
sulphur	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	4
Dibenzothiophene	99.3	99	99	98	85	65	56
as sulphur	99.6	92	68	55	47	30	23
Residual sulphur in effluent (%)	0.4	5	15	23	29	37	43

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 alumina (1.0035 g) at the temperature of 27 °C.

Table X

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

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, 2methyldibenzothiophene 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 alumina (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).

Bibliography

Collins F. M., Lucy A. R., Sharp C., Oxidative desulphurization of oils via hydrogen peroxide and heteropolyanion catalysis. Journal of Molecular Catalysis 1997, 117, 397-403.
Refining Process 2000. Flow diagrams and summary descriptions define typical licensed processes used by modern refineries. Hydrocarbon Processing. Vol. 79 no.11 November 2000.
Fredrick C. Sulfur reduction: What are the options?. Hydrocarbon Processing. Vol 81 no.2 February 2002.
Babich I.V., Moulijn J.A. Science and technology of novel processes for deep desulfurization of oil refinery streams: a review. Fuel, 2003, 82, 607-631
Shiraishi, Y., Hirai T., Komasawa I. A Deep Desulfurization Process for Light Oil by Photochemical Reaction in an Organic Two-Phase Liquid-Liquid Extraction System. Ind. Eng. Chem. Res. 1998, 37, 203-211.
Otsuki S., Nonaka T., Takashima N., Qian W., Ishihara A., Imai T., Kabe T. Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oil by Oxidation and Solvent Extraction. Energy & Fuels 2000, 14,1232-1239
Tam P. S., Kittrell J. R., Eldridge J. W. Desulfurization of Fuel Oil by Oxidation and Extraction. 1. Enhancement of Extraction Oil Yield. Ind. Eng. Chem. Res. 1990, 29, 321-324.
Tam P. S., Kittrell J. R., Eldridge J. W. Desulfurization of Fuel Oil by Oxidation and Extraction. 2. Modeling of Oxidation Reaction. Ind. Eng. Chem. Res. 1990, 29, 324-329.
Te M., Fairbridge C., Ring Z. Oxidation Reactivities of Dibenzothiopenes in Polyoxometalate/H2O2 and Formic Acid/H2O2 System. Applied Catalysis A: General 2001, 219, 267-280.
Mei H., Mei B. W., Yen T. F. A New Method for Obtaining Ultra-Low Sulfur Diesel Fuel Via Ultrasound Assisted Oxidative Desulfurization. Fuel 2003, 82, 405-414.
Kaluza L., Zdrazil, M., Zilkova, N. CejkaJ. High Activity of Higly Loaded MoS2 Hydrodesulfurization Catalysts Supported on Organised Mesoporous Alumina. .
Elings J. A., Ait-Meddour R., Clark J. H., Macquarrie D. J. Preparation of a Silica-Supported Peroxycarboxylic Acid and Its Use in the Epoxidation of Alkenes. Chem. Commun., 1998, 2707-2708.
Macquarrie D. J. Organically Modified Hexagonal Mesoporous Silicas. Green Chemistry, August 1999, 195-198.
Clark J. H., Elings S., Wilson K. Catalysis for Green Chemistry: Ultrahigh Loaded Mesoporous Solid Acids. C. R. Acad. Sci. Paris, Serie Iic, Chimie/Chemistry, 2000, 3, 399-404.

Sulphur compound

Removal (%) per sample

Sulphur compound

Benzothiophene

Dibenzothiophene

Residual sulphur in effluent (%)

Oxidative desulphurization process of organic sulphur compounds for the removal of organosulphur compounds from a HC fraction and the subsequent removal or decomposition of oxidized compounds characterized in that:
a) the oxidation is carried out by mesoporous silica functionalized with regenerable peroxycarboxylic groups in a PFR reactor;

b) at the end of the reaction, the functionalized mesoporous silica is separated musing a hydrocyclone and sent to a regeneration with hydrogen peroxide;

c) the hydrocarbon fraction containing oxidized sulphur compounds is sent to a removal system, composed by two columns, filled with polar adsorbent material, working alternately in phases of adsorption and regeneration, or to a decomposition system with recovery of organic rings and production of SO₂(cracking) or H₂S(hydrodesulphurization).
Oxidative desulphurization process of organic sulphur compounds, and the subsequent removal or decomposition of oxidized compounds, according to claim 1 characterized in that the exhausted mesoporous silica is regenerated in acid solution.
Oxidative desulphurization process of organic sulphur compounds and the subsequent removal or decomposition of oxidized compounds according to claim 1 characterized in that the oxidation products as sulphoxides and sulphones are removed by an adsorbent polar bed.
Oxidative desulphurization process of organic sulphur compounds and the subsequent removal or decomposition of oxidized compounds according to claim 3 characterized in that the adsorbent polar bed is of alumina.
Process of oxidative desulphurization of organic sulphur compounds and the subsequent removal or decomposition of oxidized compounds according to claim 3 characterized in that the adsorbent polar bed is of silica.
Process of oxidative desulphurization of organic sulphur compounds and the subsequent removal or decomposition of oxidized compounds according to claim 3 characterized in that the adsorbent polar bed is of aluminosilicate of alkali or alkali-earth metals.