WO2009099395A1

WO2009099395A1 - Regeneration of solid adsorbent

Info

Publication number: WO2009099395A1
Application number: PCT/SG2008/000044
Authority: WO
Inventors: Yiing Mei Wu; Armando Borgna
Original assignee: Agency For Science, Technology And Research
Priority date: 2008-02-06
Filing date: 2008-02-06
Publication date: 2009-08-13
Also published as: CN101970103A

Abstract

The present invention refers to a method of solvent-free regeneration of a solid adsorbent capable of adsorbing sulfones and/or sulfoxides comprising regenerating said adsorbent having sulfones and/or sulfoxides adsorbed thereon by exposing said adsorbent to a heat treatment at a temperature equal or less than 500 C. A further invention refers to a method of separating sulfoxides and/or sulfones from a petroleum based hydrocarbon stream comprising contacting activated carbon comprising -C=O, -COOH, -C-O and -OH functional groups on its surface with said petroleum based hydrocarbon stream.

Description

Regeneration of Solid Adsorbent

[0001] The present invention refers to a process of solvent-free regeneration of a solid adsorbent which has been used for the separation of sulfoxides and/or sulfones from petroleum based hydrocarbon streams.

BACKGROUND OF THE INVENTION

[0002] Sulfur is prevalent in all raw materials, including crude oil, coal, and ore that contains common metals like aluminum, copper, zinc, lead, and iron. SO_x gases are formed when fuel containing sulfur, such as coal and oil, is burned, and when gasoline is extracted from oil, or metals are extracted from ore. SO_x gases like SO₂ dissolve in water vapor to form acid, and interact with other gases and particles in the air to form sulfates and other products that can be harmful to people and their environment. [0003] For example, over 65% of SO₂ released to the air, or more than 13 million tons per year, comes from electric utilities, especially those that burn coal. Other sources of SO₂ are industrial facilities that derive their products from raw materials like metallic ore, coal, and crude oil, or vehicles which burn fuel, coal or oil.

[0004] Emitted SO_x contributes to respiratory illness, particularly in children and the elderly, and aggravates existing heart and lung diseases. For example, SO₂ reacts with other chemicals in the air to form tiny sulfate particles. When these are breathed, they gather in the lungs and are associated with increased respiratory symptoms and disease, difficulty in breathing, and premature death. Furthermore, high levels of SO₂ emitted over a short period, such as a day, can be particularly problematic for people with asthma. The increasing traffic on the streets enhances these problems. [0005] SO_x also contribute to the formation of acid rain, which damages forests and crops, changes the makeup of soil, and makes lakes and streams acidic and unsuitable for fish. Continued exposure over a long time changes the natural variety of plants and animals in an ecosystem. It also accelerates the decay of building materials and paints, including irreplaceable monuments, statues, and sculptures. [0006] As already indicated, hydrocarbon based fuels such as diesel, gasoline or kerosene, also comprise sulfur-containing compounds which are set free as SO_x gases upon combustion. The major sulfur-containing compounds existing in current liquid hydrocarbon fuels are thiophenic compounds and their alkyl-substituted derivatives. [0007] But the environmental problem caused by sulfur-containing compounds which are released into the environment through, e.g. factories and vehicles, like cars and airplanes is not the only disadvantageous effect. Sulfur-containing compounds in fuels also poison the noble metal catalysts of the catalytic converters of cars using those fuels. This poisoning of the catalyst causes fuel to be incompletely combusted and thus result in the emission of incompletely combusted hydrocarbons, carbon monoxide and nitrogen oxides in the vehicle exhaust. However, those substances do also affect the health of the people exposed to them.

[0008] Thus, due to environmental reasons and the deleterious effect of sulfur- containing compounds in hydrocarbon fuels, it is one aim of the industry to further reduce the content of sulfur-containing compounds in hydrocarbon fuels. Further pressure is added to the refinery industry by the lawmakers of the industrialized countries who continuously decrease the limits for allowable contents of sulfur-containing compounds in hydrocarbon fuels due to the above mentioned reasons. In future it is expected that the limit for the allowable contents of sulfur-containing compounds in hydrocarbon fuel is limited to about 15 ppm. While on the one hand the limits are continuously decreased by lawmakers, the sulfur content in crude oil which is used by the industry is increasing due to the decline in crude oil reserves which forces the refinery industry to use crude oil with higher sulfur content (from ø 1,13 % in 1990 an increase to about ø 1,27 % is expected until 2010). Thus, effective removal of sulfur-containing compounds is imperative for the industry. [0009] The industrial removal of sulfur from fuels is generally carried out using different processes. One process called the hydro-desulfurization (HDS) process is described for example in GB 438,354. HDS involves the catalytic treatment of fuel with hydrogen to convert sulfur-containing compounds to hydrogen sulfide, H₂S which in turn is converted to elemental sulfur by the Claus process. [0010] Another process for ultra-deep desulfurization of fuel is the oxidative desulfurisation (ODS), in which fuel is contacted with oxidants such as hydrogen peroxide, ozone, nitrogene dioxide and tert-butyl-hydroperoxide in order to selectively oxidise the sulfur-containing compounds present in the fuel to polar organic compounds. This process is often applied subsequent to HDS in order to reduce the content of sulfur in the hydrocarbon fuel below the content which can be obtained using HDS alone. The products of the oxidation of the sulfur-containing compounds in the ODS process are sulfoxides and sulfones whereas the latter one is the main product.

[0011] Designing processes to separate and remove sulfoxides and sulfones thus obtained from the hydrocarbon streams becomes imperative in achieving overall success in ODS processes. Sulfoxide and sulfone separation can be conducted via two different routes, namely solvent extraction, adsorption or a combination of both. Common materials used for adsorption comprise for example charcoal, hydrotalcite, ion exchange resin, zeolites, silica-alumina and silica gels as for example described in WO 2005/097951.

[0012] However, solvent extraction often involves costly solvents and complicated solvent handling operations, such as recovery and recycling schemes. While adsorption onto solid adsorbents does not require the use of solvents, the subsequent regeneration of spent adsorbents depends exclusively on various desorbing liquid solvents or diluents. Thus, effective regeneration of the used adsorbents is one way to reduce the costs for the extraction and separation processes. [0013] WO 2005/116169 describes for example the regeneration of a solid basic adsorbent using a liquid base. In WO 2005/097951 pentane, hexane, benzene, toluene, xylene or mixtures thereof are used as desorbent for regeneration of the adsorbent. [0014] Thus, a need exists for improved processes for regeneration of adsorbents used in processes for the separation and extraction of sulfoxides and sulfones from hydrocarbon streams.

SUMMARY OF THE INVENTION

[0015] The present invention refers to a method of solvent-free regeneration of a solid adsorbent capable of adsorbing sulfones and/or sulfoxides, comprising regenerating said adsorbent having sulfones and/or sulfoxides adsorbed thereon by exposing said adsorbant to a heat treatment at a temperature equal or less than 500 °C or equal or less than 350 ⁰C or between about 200 to 350 °C. [0016] The adsorbent which might be used in the method of the present invention can be a zeolite, activated carbon or layered-double hydroxides (LDH). [0017] When activated carbon is used as adsorbent, the surface might be pre-treated to comprise functional groups, such as -C=O, -COOH, -C-O or -OH on its surface to enhance the adsorption capacity of the adsorbent.

[0018] The method of the present invention further comprises contacting the adsorbent with a petroleum based hydrocarbon stream containing sulfoxides and/or sulfones which are to be adsorbed on its surface.

[0019] The present invention further refers to the use of a method according to the present invention for the separation of sulfoxides and/or sulfones from petroleum based hydrocarbon streams.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

[0021] Figure 1 shows the structure of different thiophenes which can be found in hydrocarbon fuels, such as diesel. Figure Ia shows the structure of dibenzothiophene sulfoxide with a molecular weight of 200. Figure Ib to Ie show thiophenes on the left (Fig. Ib and Id), and their corresponding sulfones on the right (Fig. Ic and Ie), after oxidation, e.g. in an ODS process. In Fig. Id and Ie, R is either the methyl or ethyl group. Four most common sulfone species in diesel distillate are dibenzothiophene (DBT) sulfone, 4-methyl dibenzothiophene (4-MDBT) sulfone, 4,6-dimethyldibenzothiophene (4,6-DMDBT), and 4,6-diethyldebenzothiophene (4,6-DEDBT).

[0022] Figure 2 illustrates that the adsorption capacity of activated carbon (AC-SP) at 25 ⁰C increased with time. In Fig. 2, the adsorption capacity (mg-S/g-A) is plotted against the time (min). Using a first-order reaction model, the kinetic constant for the adsorption process was estimated to be at least 1.2 h^"1. [0023] Figure 3 shows the results of a GC-FID (Flame Ionization Detector) which was used to measure concentrations of various types of sulfone species. The four thiophene peaks (top chart) of the un-oxidized model diesel (i.e. a model diesel like the one in Table 5 in which the thiophenes have not already been oxidized to sulfones) disappeared after 5 h oxidation using a transition metal oxide catalyst disclosed in WO 2005/116169 at 180 ⁰C. Instead, four corresponding sulfone peaks appeared (middle chart). After adsorption by an adsorbent, in this case activated carbon, the sulfone peaks also disappeared (bottom chart).

[0024] In Figure 4a, the adsorption capacity (mg-S/g-A) is plotted against the remaining S (ppm) in the model diesel. Figure 4a illustrates the adsorption isotherm of AC-SP. The dashed line is fitted to Freundlich isotherm. In Figure 4b the amount of aromatics in model diesel (wt%) is plotted against adsorbent/diesel (mg/g). It can be seen that the amount of aromatics in the model diesel used is constant. Figure 4b illustrates that the aromatic amount in the model diesel remained unchanged after the adsorption, indicating that the adsorption process on activated carbon is selective toward sulfone in the presence of aromatics. [0025] Figure 5 shows an idealized structure of a layered double hydroxide, with interlayer carbonate anions. Parameters like the c-parameter, d-spacing, interlayer spacing and the width of the brucite layer are defined in Fig. 5.

[0026] Figure 6 shows a GC-FID analysis as result of the washing step with a non- polar solvent like n-hexane for recovering diesel and aromatic compounds entrained by the adsorbent. Fig. 6 shows the presence of hexane (C6) and model diesel components (n- tetradecane (C14) and fert-butylbenzene (TBB)). The amounts of C14 and TBB decreased with each additional hexane washing whereas the amount of hexane (C6) is not decreasing, demonstrating that hexane can be used to recover entrained diesel in the adsorbent. Sulfone is not found in any of the hexane wash solutions. This result proves that the washing step does not affect the adsorbent regeneration in that no sulfone is desorbed in the hexane wash; however, the step is effective in recovering valuable diesel product from the adsorbent.

DETAILED DESCRIPTION OF THE PRESENT INVENTION [0027] In a first aspect, the present invention refers to a method of solvent-free regeneration of a solid adsorbent capable of adsorbing sulfones and/or sulfoxides from a hydrocarbon stream, comprising regenerating said adsorbent having sulfones and/or sulfoxides adsorbed thereon by exposing said adsorbant to a heat treatment at a temperature equal or less than 500 °C.

[0028] The method of the present invention does not require any solvent for regenerating the adsorbent, i.e. removing the sulfones and/or sulfoxides from the surface of the adsorbent, which safes costs and simplifies the set-up of a plant used for regeneration of adsorbents.

[0029] In line with the general accepted meaning, adsorption as used in the present invention refers to the property of an interface between to immiscible phases (solid, liquid, or vapor) to attract and concentrate components of either phase or both phases as an adsorbed interfacial film ("the adsorbate"). Adsorption is a basic thermodynamic property of interfaces, resulting from a discontinuity in intermolecular or interatomic forces. It is different from absorption in which a substance diffuses into a liquid or solid to form a solution. The term sorption encompasses both processes, while desorption is the reverse process. Several kinds of adsorption are known and are encompassed in the present invention. Physical adsorption is reversible adsorption by weak interactions only. In case of physical adsorption no covalent bonds occur between adsorbent and the adsorbate. Chemical adsorption is adsorption involving stronger interaction between adsorbate and adsorbent usually accompanied by rearrangement of atoms within or between adsorbates. hi case of chemical adsorption the reaction occurs between the surface of the adsorbent and the adsorbate.

[0030] In general, any adsorbent can be used which is suitable for the purpose of the present invention. The solid adsorbents, which are referred to herein for exemplary purposes, usually have high thermal stability and small pore diameter, which results in higher exposed surface area and hence high capacity of adsorption. For the purposes of the present invention a pore diameter above 0.4 nm or 0.7 nm might be used. However, the present invention can also be used with adsorbents having a pore diameter below 0.4 nm or above 0.7 nm. [0031] Different types of adsorbents, which can all be used for the present invention, can usually be distinguished by dividing them in different classes. For example, adsorbents comprising oxygen compounds which are in general hydrophilic and polar include materials such as zeolite, diatomaceous earth or aluminum oxides. Carbon based compounds form another class of adsorbents which are in general hydrophobic and non- polar and include material such as activated carbon.

[0032] Solid adsorbents from the above classes which can be used in the method of the present invention are those which are able to adsorb sulfoxides and/or sulfones on their surface. Normally, sulfoxides and/or sulfones are isolated from hydrocarbon streams, for example the hydrocarbon stream which has been reacted in an ODS process. Among others, adsorbents which can be used for the method of the present invention can be zeolites, activated carbon, aluminum oxides, diatomaceous earth and layered-double hydroxides (LDH). Further technical specifications of adsorbents which can be used in the method of the present invention can be found in the following passages and in Table 4.

[0033] Zeolites are minerals or synthetic compounds characterized by an aluminosilicate tetrahedral framework, ion-echangeable large cations, and loosely held water molecules. The general formula of zeolites can be expresses as X_y ^1+>2+ Al_x ³⁺ Si_1-X ⁴⁺ O₂-7ΪH₂O. Since the oxygen atoms in the framework are each shared by two tetrahedrons, the (Si,Al):O ratio is exactly 1:2. The amount of large cations (X) present is conditioned by the Al: Si ratio and the formal charge of these large cations. Typical large cations are the alkalies and alkaline earths such as Na⁺, K⁺, Ca²⁺, Sr²⁺ and Ba²⁺. The large cations, coordinated by framework oxygens and water molecules, reside in large cavities in the crystal structure; these cavities and channels even permit the selective passage of organic molecules. Thus, zeolites are extensively used as molecular sieves. [0034] Zeolites (CAS 1318-02-1) which can be used in the method of the present invention are, for example, Zeolite A (CaO/Al₂O₃ ratio of 0.5 to 1.0; pore diameter 0,41 run), HY zeolite (SiO₂/Al₂O₃ ratio of 12; pore diameter 0.74 nm), H-mordenite (MOR) (SiO₂/Al₂O₃ ratio of 20; pore diameter 0.70 - 0.65 nm), HZSM5 (SiO₂/Al₂O₃ ratio of 50; pore diameter 0.53 nm- 0.56 nm), H]S zeolite (SiO₂/ Al₂O₃ ratio of 25; pore diameter 0.66 nm - 0.67 nm), Na-mordenite (MOR) (SiO₂/ Al₂O₃ ratio of 13; pore diameter 0.70 nm to 0.65 nm). [0035] Another adsorbent which can be used in the method of the present invention is diatomaceous earth. Diatomaceous earth is also referred to as Celite^® and consists of unconsolidated, porous, low-density sediment made up almost entirely of the opaline silica remains of diatoms. The terms diatomaceous earth, kieselguhr, diatomite and diatomaceous ooze are essentially synonymous, the difference being in the sediment's mode of occurrence. Diatomaceous earth is unconsolidated sediment occurring in fossil fresh-water and marine deposits, whereas diatomite is its lithified equivalent. Diatomaceous ooze usually refers to diatom-rich sediments found in present-day marine or fresh- water environments. Kieselguhr, translated as infusorial earth, is an older term which acknowledges the former inclusion of the diatoms in the infusoria that is, collectively, the microscopic animal life.

[0036] The typical chemical composition of diatomaceous earth is 86% silica, 5% sodium, 3% magnesium and 2% iron. Diatomaceous earth which can be used in the method of the present invention can be selected from the group consisting of CE-545, CE-535 and CE-501. The following table lists the composition of each diatomic earth.

Table 1

[0037] Aluminum oxides can also be used as adsorbents in the method of the present invention. Aluminium oxide is an amphoteric oxide of aluminum with the chemical formula Al₂O₃. Examples for aluminum oxides which can be used in the method of the present invention would be Al₂O₃-A, Al₂O₃-B. These aluminum oxides are also referred to as active aluminum oxides which are produced through precipitation reactions out of aluminum salt solution - for example by thermically post-treated alumina hydroxide gel - or through calcination of α-aluminum hydroxide at low temperatures or shock heat treatment. Aluminum oxides are characterized by their high specific surface (about 300 m²/g).

[0038] Aluminum hydroxide can also be used in the method of the present invention. Aluminum hydroxide, Al(OH)₃, is the most stable form of aluminum in normal conditions. It is found in nature as the mineral gibbsite (also known as hydrargillite). Closely related are aluminum oxide hydroxide, AlO(OH), and aluminum oxide, Al₂O₃, differing only by loss of water. Aluminum hydroxide has a typical metal hydroxide structure with hydrogen bonds. It is built up of double layers of hydroxyl groups with aluminum ions occupying two-thirds of the octahedral holes between the two layers. [0039] Another adsorbent which can be used in the method of the present invention is activated carbon. Activated carbon is amorphous carbon characterized by its very large surface area per unit volume which makes it particularly interesting for the purposes of the present invention, hi general, activated carbon is capable of collecting gases, liquids or dissolved substances on the surface of its pores. For many gases or liquids, the weight of adsorbed material approaches the weight of the carbon. Adsorption on activated carbon is selective, favoring nonpolar over polar substances.

[0040] Almost any carbonaceous raw material can be used for the manufacture of activated carbon. Nut shells (particularly coconut), coal, petroleum coke and other residues in either granular, briqueted or pelleted form are illustrative examples of materials which can be used for adsorbent products.

[0041] Activation of carbon is the process of treating the carbon to open an enormous number of pores in the 1.2- to 20-nanometer-diameter range or up to 100-nanonieter- diameter range. After activation the carbon has the large surface area (500-1500 m /g) responsible for the adsorption phenomena. In other words, one pound (453.6 g) of carbon can provide a surface area equivalent to six football fields. The activation process includes thermal decomposition in a furnace using a controlled atmosphere and heat. [0042] Activated carbons which can be used for the purposes of the present invention are, for example, AC-SP, AC-LP, AC-MP, AC-G70R, AC-N or AC-A. Some of the experiments referred to in the present application have been carried out using AC-SP and AC-A as examples of activated carbons. Advantageously, the adsorbents used in the method of the present invention are selective towards sulfones and sulfoxides. However, activated carbon can also be used for the adsorption of other sulfur-containing compounds, like hydrogen sulfide, sulfur or sulfur oxides (Bagreev, A.; Rahman, H.; et al.; 2001; Carbon, vol. 39, p. 1319-1326). Experiments which have been carried out have shown that the adsorbents are selective toward sulfones and sulfoxides in the presence of aromatics which can be found in hydrocarbon streams, like for example diesel. In one experiment carried out by the inventors this selectivity has been demonstrated using activated carbon. The results shown in Fig. 4b illustrate that the aromatic amount in the model diesel used in the experiments of the present invention remained unchanged after the adsorption, indicating that the adsorption process on activated carbon is selective toward sulfone in the presence of aromatics.

[0043] Another group of adsorbents which can be used in the method of the present invention are layered double hydroxides (LDH). LDH is a class of ionic lamellar solids with positively charged layers with two kinds of metallic cations and exchangeable hydrated gallery anions. This is also referred to as anionic clays and also as hydrotalcite- like compounds in the name of the polytypes of the corresponding [Mg-Al] based mineral. They can be prepared by coprecipitation method, induced hydrolysis, and salt- oxide method. LDHs are commonly represented by the formula [M^z+ _1-xM³⁺(_x(OH)₂]^q+(Xⁿ-)q_/n-yH₂O. 1 -Layered double hydroxides (LDH), as one can expect, are layered materials (see Fig. 5, V. Rives, M. Angeles Ulibarri, 1999, Coordination Chemistry Reviews, vol.181, p.61-120).The interlayer spacing can be determined from XRD data. The unit cell parameter c = 3*d-spacing and d-spacing = interlayer spacing + width of the brucite layer (thickness of the brucite-like sheet = 4.8 A, according to S. Miyata, 1975, Clays and Clay Minerals, vol.23, p.369). Some examples of LDH's are listed in Table 2 (from A. Vaccari, 1998, Catalysis Today, vol.41, ρ.53-71).

Table 2: Composition, crystallography parameters and symmetry for some natural anionic clays

Mineral Chemical composition Unit cell parameters Symmetry a (nm) c (nm)

Hydrotalcite Mg₆Al₂(OH)₁₆CO₃ - 4H₂O 0.3054 2.281 3R

Manasseite Mg₆Al₂(OH)₁₆CO₃ - 4H₂O 0.310 1.56 2H

Pyroaurite Mg₆Fe₂(OH)₁₆CO₃ - 4H₂O 0.3109 2.341 3R

Sjøgrenite Mg₆Fe₂(OH)₁₆CO₃ - 4H₂O 0.3113 1.561 2H

Stichtite Mg₆Cr₂(OH)₁₆CO₃ - 4H₂O 0.310 2.34 3R

Barbertonite Mg₆Cr₂(OH)₁₆CO₃ - 4H₂O 0.310 1.56 2H

Takovite Ni₆Al₂(OH)₁₆CO₃ - 4H₂O 0.3025 2.259 3R

Reevesite Ni₆Fe₂(OH)₁₆CO₃ - 4H₂O 0.3081 2.305 3R

Meixnerite Mg₆Al₂(OH)₁₆(OH)₂ - 4H₂O 0.3046 2.292 3R

Coalingite Mg₁₀Fe₂(OH)₂₄ CO₃ - 2H₂O 0.312 3.75 3R

[0044] The d-spacing can be strongly modified by pillaring. Some examples for pillared LDH compounds from A. Corma, 1997, Chem. Rev., vol.97, p.2373-2419, are shown below in Table 3.

Table 3: Acidity of montmorillonites pillared (PM) with different cations sample d₀₀₁ (nm) surface area (m² g^"1) acidity (μv)

Al-PM 1.73-1.89 190 425-442

Zr-PM 1.82 191 570

Ti-PM 1.50 - 620

Fe-PM 1.55 109 340

Ni-PM 1.48 58 228

Al-Zr-PM 1.56 - 390

Al-Fe-PM 1.58 - 340

NaM 1.28 51 86 [0045] The aforementioned adsorbents listed in Tables 2 and 3 can be used in the method of the present invention.

[0046] The compounds to be adsorbed by the adsorbents referred to above are sulfoxides and sulfones. These compounds are, for example, the product of the oxidation of thiophenes and other sulfur-containing compounds in hydrocarbon fuels, like for example diesel. Examples for thiophenes and other sulfur-containing compounds are diphenylsulfide, dibutylsulfide, methylphenylsulfide, disulfides and mercaptans, which are aliphatic or aromatic, as well as heterocyclic sulfur-containing compounds such as benzothiophene, dibenzothiophene, 4-methyl-dibenzothiophene, 4,6-dimethyl- dibenzothiophene and tribenzothiophene, and other derivatives thereof.

[0047] A sulfoxide is a chemical compound containing a sulfinyl functional group (see formula (I); Fig. Ia shows an example of a sulfoxide: dibenzothiophene sulfoxide) attached to two carbon atoms. Sulfoxides can be considered as oxidized sulfides. Sulfoxides are generally represented with the structural formula R-S(=O)-R', where R and R' are organic groups. The bond between the sulfur and oxygen atoms differs from the conventional double bond between carbon and oxygen in, say, ketones. The S=O interaction has an electrostatic aspect, resulting in significant dipolar character, with negative charge centered on oxygen. The bonding is similar to that in tertiary phosphine oxides, R₃P=O. Sulfides are the usual starting materials to sulfoxides by organic oxidation. For example, dimethyl sulfide with oxidation state of -2 is oxidized to dimethyl sulfoxide with oxidation state 0. Further oxidation converts the compound to dimethyl sulfone wherein sulfur has the oxidation state +2. Thus, a sulfone is a chemical compound containing a sulfonyl functional group (see formula (II); examples of sulfones see Fig. Ic and Ie) attached to two carbon atoms. The central sulfur atom is twice double bonded to oxygen and has two further hydrocarbon substituents. The general structural formula is R-S(=O)(=O)-R' where R and R' are the organic groups.

(I) Sulfϊnyl group (II) Sulfonyl group

[0048] When oxidized, for example in an ODS process, sulfur containing compounds in hydrocarbon fuels mainly react to sulfoxides and then further to sulfones (see Fig. 1). In the method of the present invention the adsorbent to be regenerated will at first be contacted with a petroleum based hydrocarbon stream containing sulfoxides and/or sulfones which are to be adsorbed on its surface. The petroleum based hydrocarbon stream can be diesel, gasoline, gas oil and kerosene. As initially mentioned, the prevailing sulfur-containing compounds existing in current petroleum based hydrocarbon streams are thiophenic compounds. For example, the four most common tiophene compounds in diesel are dibenzothiophene (DBT) sulfone, 4-methyl dibenzothiophene (4-MDBT) sulfone, 4,6-dimethyldibenzothiophene (4,6-DMDBT), and 4,6- diethyldebenzothiophene (4,6-DEDBT) (see also Table 5).

[0049] The adsorption capacities of the adsorbents which can be used in the method of the present invention are listed in Table 4. As can be taken from Table 4, activated carbon gave the highest adsorption capacity at 5.68 mg-S/g-A (mg of sulfur per gram of adsorbent; or approximately 38 mg-sulfone/g-A) for AC-SP and 5.58 mg-S/g-A for AC- A. Among the zeolites, HY zeolite showed a good adsorption capacity, 4.56 mg-S/g-A, which corresponds to about 30.1 mg-sulfone/g-A. [0050] The adsorption capacity, for example, of activated carbon can be further enhanced by chemical modification. For this purpose, the adsorbant is pre-treated with citric acid or nitric acid. Upon contacting activated carbon with one of these acids, reactions occur between the acid and the carbon to form new bounding of -C=O, -COOH, -C-O and -OH. [0051] Every adsorbent has a limit as to how much of the adsorbate can be adsorbed on its surface. After the adsorbent has been used up, the adsorbent is disposed or regenerated for repeated use. hi general, regeneration refers to any of the various processes for restoring a system to its original state by restoring some property of a system to its original value or close to it. In case of the present invention, regeneration would mean to restore the adsorption capacity of the adsorbant so that the adsorbent can be used for further separation of sulfoxides and/or sulfones from petroleum based hydrocarbon streams.

[0052] In the method of the present invention, regeneration is achieved by exposing the adsorbant to a heat treatment at a temperature equal or less than 500 ⁰C. The heat treatment has the effect that the adsorption capacity of the adsorbents is partly or fully restored (see Table 6). [0053] In one example the heat treatment is carried out at a temperature equal or less than 350 ⁰C. As can be seen in the later following examples, heat treatment has been carried out at a temperature between about 200 °C to 350 ⁰C. Further advantageous temperatures for the heat-treatment are 250 °C and 300 ⁰C and any temperature between those two values. Using this heat treatment, the use of solvents for regeneration can be avoided and thus the costs of regeneration can be kept low. If required, the regeneration can be carried out under a purge of nitrogen or air. The purge is used to remove the desorbed species from the vicinity of the adsorbent to prevent re-adsorption and encourage further desorption. The purge also helps establishing a stable thermal environment, i.e., stable temperatures, for the regeneration. Complicated pre-treatment of any kind is avoided when using the method of the present invention. By contrast, Sabio E.; et al. (Sabio, E.; Gonzalez, J.F.; et al.; 2004, Carbon; vol. 42, p. 2285-2293), for example, uses a step of gasification of the residual organics by oxidizing gas, such as steam or carbon dioxide for regeneration of activated carbon. [0054] For the heat treatment in a furnace the temperature can be increased at any rate. In one example a rate of about 5 °C to about 10 ⁰C per minute starting from room temperature until reaching the final end temperature is used. In case the adsorbent was stored at higher temperatures before the heat treatment, increasing the temperature will start at this higher temperature. [0055] In general, the heat-treatment is carried out until the adsorbent is fully regenerated, hi one example, the heat-treatment is carried out for about 0.5 to about 2 h. Li another example, the heat-treatment is carried out for about 1 h. In some examples, the adsorbent is exposed to the heat-treatment without any further pre-treatment ("as-is" see Table III) whereas in another example, the adsorbent is dried overnight at about 50 ⁰C to about 100 °C under vacuum before the heat-treatment for regeneration is carried out. In one example, the adsorbent is dried overnight under vacuum at about 6O⁰C. [0056] In another example, the adsorbent is washed with a non-polar substance before the heat treatment. The non-polar substances used for washing of the adsorbent can be n- hexane, heptane, octane, nonane, naphtha or mixtures thereof. In the method of the present invention, n-hexane is merely used for the recovery of entrained diesel and aromatic compounds (see experiments under D) whereas in WO 2005/097951 hexane is supposedly used for regenerating the adsorbent. The option of doing a wash with a non- polar solvent or drying the adsorbent overnight under vacuum further enhances the economy of the adsorption process.

[0057] The method of the present invention can be used in particular in oxidative desulfurisation (ODS) processes because sulfur-containing compounds, like thiophenes, are oxidized in an ODS process into sulfoxides and subsequently in sulfones (see also Fig. 3).

[0058] The present invention also refers to the use of the method of the present invention for the separation of sulfoxides and/or sulfones from petroleum based hydrocarbon streams, like, e.g., diesel, gasoline, gas oil or kerosene. In the following examples, diesel is used as an example for a sulfur-containing petroleum based hydrocarbon stream.

[0059] In one particular aspect, a method of separating sulfoxides and/or sulfones from a petroleum based hydrocarbon stream comprising contacting activated carbon comprising C=O, -COOH, -C-O and -OH groups on its surface with the petroleum based hydrocarbon stream is provided. To modify activated carbon to comprise such functional groups on its surface, the activated carbon has been pre-treated with citric-acid or nitric acid to introduce C=O, -COOH, -C-O and -OH groups.

[0060] By "comprising" it is meant including, but not limited to, whatever follows the word "comprising". Thus, use of the term "comprising" indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present. [0061] By "consisting of is meant including, and limited to, whatever follows the phrase "consisting of. Thus, the phrase "consisting of indicates that the listed elements are required or mandatory, and that no other elements may be present. [0062] The inventions illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms "comprising", "including", "containing", etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the inventions embodied therein herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention.

[0063] The invention has been described broadly and genetically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0064] Other embodiments are within the following claims and non- limiting examples. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

DESCRIPTION OF EXPERIMENTS

[0065] Properties and adsorption capacities of solid adsorbents [0066] The properties and adsorption capacities of several solid adsorbents have been tested and are listed in Table4. All of these adsorbents except Ar-I and Ar-2 are commercially available and could be used in the methods and uses of the present invention.

Table 4: Properties and Adsorption Capacities of Adsorbent Materials

Manufacturer / Capacity

Surface Pore Size Sulfur

Sample ID Type Supplier m²/g in nm mg-S/g- ppmw

A

Zeolite A Zeolite Aldrich 349 0.41 0.20 331

HY[12] Zeolite Zeolyst 780 0.74 4.56 343

H-MOR[20] Zeolite Zeolyst 500 0.65 - 0.70 1.04 343

HZSM5[501 Zeolite Zeolyst 425 0.53 - 0.56 0.78 343

H/J[25] Zeolite Zeolyst 680 0.66 - 0.67 3.60 343

NaMOR[13] Zeolite Zeolyst 425 0.65 - 0.70 1.00 343

Al(OH)₃ Aluminum Aldrich 103 20.55 0.93 331 Hydroxide

Al₂O₃-A Alumina Criterion 426 8.85 1.00 331

Al₂O₃-B Alumina Aldrich-Sigma 155 6.34 1.00 331

Ce-545 Celite Aldrich < 100 > 20 2.68 338

Ce-535 Celite Aldrich < 100 > 20 0.30 350

Ce-501 Celite Aldrich < 100 > 20 0.80 350

Ar-I Celite synthesized 338 16.89 0.86 338

Ar-2 Celite synthesized 317 18.38 0.96 338

AC-MP Activated Kureha 1140 2.18 4.42 350 Carbon (from petroleum pitch)

AC-G70R Activated Kureha 1059 2.2 3.70 350 Carbon (from petroleum pitch)

AC-N Activated Norit 967 2.33 0.85 355 Carbon (from coal)

AC-A Activated Aldrich 888 3.92 5.58 338 Carbon (from natural Inorganic)

AC-A product no. 161551 ; charcoal activated (decolorizing); CAS no. 7440-44-0

Al₂O₃ CAS no. 1344-28-1

Al(OH)₃ CAS no. 21645-51-2 - Ar-I comprises of, in weight, 0.5% MgO, 96% SiO₂, 0.5% CoO and 3% Fe₂O₃.

Ar-2 comprises of, in weight, 0.5% MgO, 96% SiO₂, 0.5% CaO and 3% Fe₂O₃.

Ar-I and Ar-2 were made using a wet impregnation procedure of SiO₂ at room temperature. After impregnation the materials were dried overnight at 120⁰C and then calcined at 400⁰C. Wet or slurry impregnation is probably the most often used method for catalyst preparation. It is a very common technique to prepare supported catalysts as described for example in the "Handbook of Heterogeneous Catalysis", Ertl, Gerhard / Knόzinger, Helmut / Schuth, Ferdi / Weitkamp, Jens (eds.), Wiley-VCH. Usually, the method consists of adding the precursor salt to the support from a slurry in excess solution. The method is commonly called ion exchange, but can more generally be considered wet impregnation (WI). See also J.T.Miller,.M.Schreier, A.J.Kropf, and J.R.Regalbuto, 2004, Journal of Catalysis, vol.225, p.203-212

The number in [ ] indicates the SiO₂/ Al₂O₃ ratio of these zeolite adsorbents. - In the column manufacturer/supplier it is indicated for the different activated carbon types which source material has been used to manufacture them

[0067] For the regeneration experiments, AC-SP and AC-A have been used due to their good adsorption capacity.

[0068] A. Adsorption experiments and their analysis

[0069] Normally adsorbents were dried under flowing N₂ at 120 ⁰C for 2 h before adsorption experiments; zeolite samples were dried at 120 °C for 2 h, followed by calcination at 450 °C for 2 h. The drying step is merely a laboratory procedure to make sure all test adsorbents are in the same conditions (same starting conditions for determining the properties of each adsorbent) for the adsorption test. In later practice such a drying step would not be necessary any more. BET (Brunauer-Emmett-Teller) technique was used to measure the surface area of adsorbents. The BET surface areas were obtained in a Quantachrome Autosorb-6B equipment with the samples degassed at 200 ⁰C under vacuum for 5 h.

[0070] Al. Adsorption experiment

[0071] The adsorption of sulfones was performed using the procedure as follows. Model diesel samples with known amount of sulfones (either from oxidation of corresponding thiophenes or from dissolution of pure sulfone compounds) were used. The composition of the model diesel used is indicated in Table 5. Thus, Table 5 already shows the oxidized thiophenes, i.e. sulfones (further below it is also explained how thiophenes are oxidized to become sulfones). Table 5: Typical Composition of Model Diesel

[0072] Fixed amounts of model diesel and adsorbent (20 : 1 in weight unless noted otherwise) were magnetically stirred at 350 rpm at 25 °C for 24 h for equilibrium adsorption data.

[0073] A2. Analysis after adsorption experiment

[0074] To determine the kinetic data of the adsorption test which are shown in Figure 2, the data from three different adsorption tests with different durations, i.e. 30 minutes,

60 minutes, and 120 minutes, have been used. The adsorption test procedure was the same for all three tests as described in the previous paragraph. Once a desired duration period is reached, the test is terminated. For further analysis, the spent adsorbent is filtered out of the model diesel using a filter paper and dried under vacuum. [0075] After each adsorption test, the remaining sulfones in the model-diesel were measured by XRF or X-Ray Fluorescence, from Bruker AXS S4 Exporer, (see Jeyagowry

T. Sampanthar, Huang Xiao, et al.; 2005, Applied Catalysis B: Environmental 63, p.85-

93), as total sulfur XRF was carried out with the model diesel after the adsorption experiment to measure the amount of sulfur, regardless of structure or nature of sulfur- containing compounds in the diesel.

[0076] GC-FPD (Flame Photometric Detector) and GC-FID (Flame Ionization Detector) were used to measure concentrations of various types of sulfone species. The gas chromatography (GC) analysis were performed with an Agilent 6890 N unit equipped with a HP-5 capillary column (L = 30 m; ID = 0.25 μm) and a flame photometric detector (FPD) or a flame ionization detector (FID). The column temperature program was set to increase from 50 ⁰C to 250 °C at a 40 °C/min rate for the GC-FID analysis. The temperature profile for the GC-FPD analysis is hold at 150 °C and then at 5 °C/min rate to reach the final temperature of 240 °C.

[0077] A typical spectra showing the results of a GC-FID is shown in Fig. 3. The four thiophene peaks of the un-oxidized model diesel (i.e. a model diesel like the one in Table 5 in which the thiophenes have not already been oxidized to sulfones) disappeared after 5 h oxidation using a transition metal oxide catalyst disclosed in WO 2005/116169 at 180 ⁰C. Instead, four corresponding sulfone peaks appeared. After adsorption by activated carbon, the sulfone peaks also disappeared.

[0078] The adsorption kinetics data in Figure 2 show that the adsorption capacity of activated carbon (AC-SP) increased with time. Using a first-order reaction model, the kinetic constant for the adsorption process was estimated to be at least 1.2 h^"1.

[0079] To understand, for example, the adsorption performance of activated carbon in the current system, including adsorption isotherms and adsorption selectivity, adsorption capacities at different equilibrium concentrations of sulfone (remaining sulfone in the diesel after adsorption) has been determined. As shown in Figure 4a, the adsorption capacity increases with the increasing equilibrium sulfur concentrations. The data were fitted to different isotherms and the best-fit was obtained by using the Freundlich isotherms, i.e., q = K- Ceⁿ (I)

where q is the adsorption capacity in mg-S/g-A and Ce is the equilibrium concentration of sulfone expressed as ppm sulfur. K is a constant for a given adsorption system. That includes adsorbent, adsorbate, matrix and temperature. The system specific constants in the exemplary case K and n are 0.0932 and 1.010 respectively. [0080] The amounts of aromatics after the adsorption tests were also measured to examine the selectivity of the activated carbon adsorbent. Results in Figure 4b showed that the aromatic amount in the model diesel remained unchanged after the adsorption, indicating that the adsorption process on activated carbon is selective toward sulfone in the presence of aromatics.

[0081] The adsorption data mentioned herein are reported as amount of adsorbed sulfur in milligram per amount of adsorbent in gram (mg-S/g-A). Depending on how much adsorbent is used, the amount of sulfones or sulfoxides adsorbed can be controlled. For example, using 6 mg sulfur per g of activated carbon as the adsorption capacity, exposing 57 gram of said activated carbon to 1 kg of 350 ppm S diesel, the final sulfur will be 10 ppm. If more adsorbent is used, the sulfur content can be lowered further.

[0082] B. Modification of adsorbents using citric acid or nitric acid

[0083] To introduce functional groups, like -C=O, -COOH, -C-O and -OH, the adsorbent, for example activated carbon, has to be reacted with citric acid and/or nitric acid.

[0084] For example, for modification of adsorbents by citric acid, a ratio of 4 g activated carbon to 25 ml 1 M citric acid solution was used. The mixture was shaken for 30 min at room temperature. Then the activated carbon was filtered out and dried at 50 °C overnight. Afterward the activated carbon was washed with distilled water until there was no pH variation observed in the washing liquid. The final drying before use int the adsorption experiment was at 110 ⁰C for 2 h. [0085] For modification by nitric acid, the activated carbon was treated with 70% concentrated nitric acid under reflux for 8 h. The ratio was 20 g of activated carbon to 100 ml of nitric acid. After reflux, the activated carbon was filtered and washed with hot distilled water until the pH of the washing water was approximately 7. The activated carbon was dried in a vacuum at 60 °C for 24 h. [0086] The analysis with Fourier transform infrared spectroscopy (FTIR) was used to measure the presence of particular chemical bonds and functional groups. The FTIR was performed with Bruker Equinox 55 FT-IR spectrometer with mercury cadmium telluride detectors. Adsorbent samples were ground and mixed in with KBr powder. The spectrometer scanning range is from 4000 to 400 cm ^"\ The FTIR spectra confirmed that those newly bonds on activated carbon after reacting with either nitric acid or citric acid had been formed (data not shown). [0087] C. Adsorbent regeneration

[0088] In order to lower equipment and operating costs and maintain operation flexibility, the heat-treatment for the regeneration process of the present invention needs to be able to operate in the moderate temperature range (less than 500 ⁰C) in a refining setting.

[0089] For the regeneration, spent adsorbents were filtered out from the hydrocarbon stream and subjected to one of the three preparation steps: drying overnight at 60 ⁰C under vacuum, as-is (i.e. without any treatment before heating), or washing with a non- polar substance, like n-hexane. A laboratory-scale horizontal tube furnace was used to heat the spent adsorbents to different temperatures at a rate of 10 °C/min. Spent adsorbents were placed in a quartz tube, under a purge of nitrogen or air, and heated at temperatures from 200 °C to 350 °C, from 30 min to 2 h.

[0090] Results of the regeneration experiments of spent activated carbons (AC-SP and AC-A) are shown in Table 6. The re-adsorption capacity of regenerated adsorbents indicated the preparation conditions studied (drying overnight at 60 ⁰C under vacuum, as- is, or washing with n-hexane) did not affect the regeneration results. In fact, the spent adsorbent with the highest re-adsorption capacity went through regeneration, at 300 ⁰C for 30 min, in as-is conditions without any pretreatment. Likewise, regeneration temperatures, from 250 to 300 ⁰C, produced similarly good re-adsorption results. The lower capacity of the vacuum dried AC-SP adsorbents (regenerated at 300 ⁰C for 30 to 60 min) can be attributed to the diesel used in the re-adsorption experiments containing only 193 ppmw sulfur.

Table 6: Regeneration of Spent Activated Carbon Adsorbents

250 60 330 3.80 as-is (i.e. none)

300 30 330 4.00 n-hexane wash

300 60 330 3.52 n-hexane wash

250 60 330 4.02 n-hexane wash

Activated carbon: AC-A

300 30 330 3.82 vacuum dry, 60 ⁰C

300 60 330 4.00 vacuum dry, 60 ⁰C

250 60 330 3.61 vacuum dry, 60 ⁰C

[0091] Thus, the regeneration method of the present invention provides an effective, low cost way to separate and remove sulfoxides and sulfones from a sulfur-containing hydrocarbon stream.

[0092] D. Recovery of entrained diesel and aromatic compounds with non-polar substances

[0093] The plot shown in Fig. 6 can be obtained by using the following procedure: a one gram sample of loaded adsorbent (AC-SP) is washed with 5 ml of hexane for 15 min. The hexane wash solution is collected and analyzed using GC-FID (the same method used to obtain Figure 3). The adsorbent is retained for the next wash. The same procedure is repeated three additional times, using 5 ml of hexane each time, to wash the same loaded adsorbent. The GC-FID analysis, shown in Figure 6, indicates the presence of hexane (C6) and model diesel components (n-tetradecane (C 14) and tert-butylbenzene (TBB)). The amounts of C14 and TBB decreased with each additional hexane washing whereas the amount of hexane (C6) is not decreasing, demonstrating that hexane can be used to recover entrained diesel in the adsorbent. Sulfone is not found in any of the hexane wash solutions. This result proves that the washing step does not affect the adsorbent regeneration in that no sulfone is desorbed in the hexane wash; however, the step is effective hi recovering valuable diesel product from the adsorbent.

Claims

1. A method of solvent-free regeneration of a solid adsorbent capable of adsorbing sulfones and/or sulfoxides, comprising: regenerating said adsorbent having sulfones and/or sulfoxides adsorbed thereon by exposing said adsorbant to a heat treatment at a temperature equal or less than 500 °C.

2. The method according to claim 1, wherein the temperature is equal or less than 350 °C.

3. The method according to claim 1, wherein the temperature is between about 200 ⁰C to about 350 °C.

4. A method according to any of the preceding claims, wherein said solid adsorbent is selected from the group consisting of zeolites, activated carbon, aluminum oxides, diatomaceous earth and layered-double hydroxides (LDH).

5. A method according to claim 4, wherein said solid adsorbent is activated carbon.

6. A method according to claim 5, wherein said activated carbon is selected from the group consisting of AC-SP, AC-LP, AC-MP, AC-G70R, AC-N and AC-A.

7. The method according to claim 6, wherein said activated carbon is AC-SP or AC- A.

8. The method according to claim 4, wherein said solid adsorbent is a zeolite.

9. The method according to anyone of claims 8, wherein said zeolite is selected from the group consisting of Zeolite A, HY, H-MOR, HZSM5, HjS and NaMOR.

10. A method according to claim 4, wherein said solid adsorbent is an aluminium oxide.

11. A method according to claim 10, wherein said aluminium oxide is selected from the group consisting of Al(OH)₃, Al₂O₃-A and Al₂O₃-B .

12. A method according to claim 4, wherein said solid adsorbent is diatomaceous earth.

13. A method according to claim 12, wherein said diatomaceous earth is selected from the group consisting of CE-545, CE-535 and CE-501.

14. A method according to claim 4, wherein said solid adsorbent is a layered-double hydroxide (LDH).

15. A method according to claim 14, wherein said layered-double hydroxide (LDH) is selected from the group consisting of hydrotalcite, manasseite, pyroaurite, sjøgrenite, stichtite, barbertonite, takovite, reevesite, meixnerite, coalingite, Al-PM, Zr-PM, Ti-PM, Fe-PM, Ni- PM, Al-Zr-PM, Al-Fe-PM and NaM.

16. The method according to anyone of the preceding claims, wherein said regeneration is carried out under a purge of nitrogen or air.

17. The method according to anyone of the preceding claims, wherein said regeneration is carried out for about 0.5 h to about 2 h.

18. The method according to anyone of the preceding claims, wherein said regeneration is carried out for about 0.5 h.

19. The method according to anyone of the preceding claims, wherein said regeneration is carried out for about 1 h.

20. The method according to anyone of claims 4 to 7 and 16 to 19, wherein said adsorbent is activated carbon which has been pre-treated to comprise -C=O, -COOH, -C-O and -OH groups on its surface.

21. The method according to claim 20, wherein said adsorbent is activated carbon which has been pre-treated with citric-acid or nitric acid or a mixture thereof.

22. The method according to an claim 20 or 21, wherein said activated carbon has been dried after pre-treatment.

23. The method according to anyone of the preceding claims, wherein said adsorbent to be regenerated has been contacted with a petroleum based hydrocarbon stream containing sulfoxides and/or sulfones which are to be adsorbed on its surface.

24. The method according to claim 23, wherein said petroleum based hydrocarbon stream is selected from the group consisting of diesel, gasoline, gas oil and kerosene.

25. The method according to claim 24, wherein said petroleum based hydrocarbon stream is diesel.

26. A method of separating sulfoxides and/or sulfones from a petroleum based hydrocarbon stream comprising contacting activated carbon comprising -C=O, -COOH, -C-O and -OH functional groups on its surface with said petroleum based hydrocarbon stream.

27. The method according to claim 26, wherein said activated carbon has been pre- treated with an acid to introduce said functional groups.

28. The method according to any of the preceding claims, wherein said adsorbent has been washed with a non-polar substance before said regeneration.

29. The method according to claim 28, wherein said non-polar substance is selected from the group consisting of naphtha, n-hexane, heptane, octane, nonane and mixtures thereof.