EP2650345B1

EP2650345B1 - Method for removal of sulfur containing compounds from hydrocarbon mixtures

Info

Publication number: EP2650345B1
Application number: EP20120164043
Authority: EP
Inventors: Saeed Mohammed A-Zahrani; Inas Muen AlNashef; Sarwono Mulyono Mulyoprayitno
Original assignee: King Saud University
Current assignee: King Saud University
Priority date: 2012-04-13
Filing date: 2012-04-13
Publication date: 2015-01-21
Anticipated expiration: 2032-04-13
Also published as: EP2650345A1

Description

The present invention relates to a method for removal of sulfur containing compounds from liquid hydrocarbons containing the sulfur containing compounds.
A deep eutectic solvent (DES) is a type of ionic solvent with special properties composed of a mixture of compounds which form an eutectic with a melting point much lower than either of the individual components. DESs are useful as solvents, as electrolytes and as catalysts. Although DESs have many common characteristics with ionic liquids, they are considered as different type of solvents. Ionic liquids are composed entirely from ions while DESs have both ions and neutral molecules. In addition, ionic liquids are synthesized by chemical reactions while DESs are prepared by mixing and heating only. The first generation of eutectic solvents was based on mixtures of quaternary ammonium salts with hydrogen bond donors such as amines and carboxylic acids. Compared to ionic liquids, they share many characteristics but are ionic compounds and not ionic mixtures, deep eutectic solvents are cheaper to make, much less toxic and sometimes biodegradable. The major advantages of the approach used for the synthesis of DESs is that common, non-toxic components can be used and that they are easy to make by just mixing two compounds with gentle heating and subsequent cooling to room temperature.
WO 02/26701 relates to a method for the synthesis of DESs by the mixing of an amine salt, such as choline chloride, with an organic compound capable of forming hydrogen bond with the ion of the amine salt, such as urea.
WO 00/56700 relates to a method for the synthesis of deep eutectic solvents formed by mixing a quaternary ammonium compound or a mixture of two or more thereof with a halide of zinc, tin or iron or a mixture of two or more thereof.
The publication of M.A. Kareem et al., J. Chem. Eng. Data, 2010, 55, 4632-4637 relates to DESs successfully prepared by mixing phosphonium salts with different hydrogen bond donors.
US 7,763,768 discloses the use of a deep eutectic solvent comprising a quaternary ammonium salt and different hydrogen bond donors as a solvent for the preparation of hydrogen peroxide.
Sulfur compounds are the most notorious and undesirable petroleum contaminants and a large portion of these compounds is transferred to diesel oil during refining process. In general, sulfur occurs here in the form of hydrogen sulfide, organic sulfides and disulfides, benzothiophene, dibenzothiophene and their alkylated derivatives.
Sulfur compounds are usually present in almost all fractions of crude oil distillation. Higher boiling point fractions contain relatively more sulfur and the sulfur compounds are of higher molecular weight.
Numerous organic sulfur compounds were found in coal and crude oil. When these fossil fuels are combusted, sulfur dioxide is released into the atmosphere, causing acid rain and air pollution.
Although environmental regulation has been applied in many countries to reduce the sulfur levels in diesel and other fuels, sulfur removal still represents a major operational and economic challenge for petroleum refining industry.
US 5,766,482 A relates to a process for capture, degradation and destruction of sulphur bearing compound by reacting a sulphur component containing mixture with a mixture of metals insoluble with a sulphur bearing compound, reduction agents and bases.
US 7,758,745 B2 relates to a diesel desulfurization method comprising mixing diesel fuel with room temperature ionic liquid, oxidant, phase transfer catalyst and acid catalyst in a tank in a mix, recycling the ionic liquid and recycling the acid catalyst in aqueous phase.
US 7,001,504 B2 discloses a method for extraction of organosulfur compounds from hydrocarbon using ionic liquids.
Fa-tang Li et al., Green Chem., 2009, 11, 883-888 describes the desulfurization of dibenzothiophene (DBT) by a combination of both chemical oxidation and solvent extraction. Me₃NCH₂C₆H₅Cl · 2ZnCl₂ ionic liquid was used as extractant for oxidative desulfurization of DBT in n-octane. DBT in oil phase was extracted into ionic liquid phase and then oxidized to its corresponding sulfone by H₂O₂ and equal volume of acetic acid.
US 7 001 504 B2 discloses the desulfurization of hydrocarbons by direct extraction of organo sulfur compounds or extraction of partially oxidized organo sulfur compounds in ionic liquids selected from liquid salt of formula Q⁺A^-, where Q⁺ is selected from quarternary ammonium cations such as trimethylamine cations and quarternary phosphonium cations and A^- is selected from any anion that forms a liquid salt at below about 100°C such as those derived from AlCl₃.
It is an object of the present invention to provide a method for removal of sulphur containing compounds from liquid hydrocarbons containing the sulphur containing compounds which overcomes the drawbacks of the prior art. Particularly, a method shall be provided allowing easy, cheap and efficient removal of sulphur compounds from hydrocarbon mixtures in an economic and ecological way.
This object is achieved by a method for removal of at least one sulfur containing compound from at least one liquid hydrocarbon containing the at least one sulfur containing compound, comprising the steps:

a) providing at least one deep eutectic solvent comprising:
- aa) at least one compound (I) of the general formula
  
  R¹R²R³R⁴Y⁺X^-;
  
  and
- bb) at least one compound (II) which is a hydrogen bond donor able to form a complex with X^-
  wherein Y is N or P;
  R¹, R², R³ and R⁴ are independently selected from substituted or unsubstituted, linear or branched C₁-C₁₈ alkyl, C₁-C₁₀ alkoxy, C₆-C₁₀ cycloalkyl, C₆-C₁₀ aryl or C₇-C₁₂ alkaryl or wherein two of R¹, R², R³ and R⁴ are an optionally substituted alkylene group, preferably a C₄-C₁₀ alkylene group;
  X is halogen;
  wherein the hydrogen bond donor is selected from urea, acetamide, thiourea, malonic acid, oxalic acid dihydrate, trifluoro acetic acid, benzoic acid, benzyl alcohol, phenol, p-methyphenol, o-methylphenol, m-methylphenol, p-chlorophenol, D-fructose, vanillin, aniline or a substituted aniline, a C₁-C₆ aliphatic acid, a C₁-C₆ hydroxy aliphatic acid, a dicarboxylic acid of the formula HOOC (CH₂)_nCOOH, wherein n is 0 or 1, alkylene glycol, citric acid and/or ethylene glycol; and
  the molar ratio of compound (I) to compound (II) is in a range from 1:1 to 1:12; preferably 1:2 to 1:5;
b) extracting the the at least one sulfur containing compound from at least one liquid hydrocarbon with the deep eutectic solvent; and
c) optionally decomposing the at least one sulfur containing compound in the deep eutectic solvent by adding molecular oxygen to the deep eutectic solvent phase obtained in step b) and electrochemically generating superoxide ions from the molecular oxygen and/or adding at least one alkali superoxide and/or at least one alkaline earth metal superoxide to the deep eutectic solvent phase obtained in step b).

In a preferred embodiment, X is chlorine or bromine, preferably chlorine.
It is convenient that R¹, R², R³ and R⁴ can optionally be substituted with OH, SH, SR⁵, Cl, Br, F, I, NH₂, CN, NO₂ CO₂R⁵, CHO, COR⁵ and/or OR⁵, wherein R⁵ is selected from alkyl or cycloalkyl, more preferably, C₁-C₁₀ alkyl or cycloalkyl.
It may be provided that the sulfur containing compound is selected from the group consisting of hydrogen sulfide, linear, branched or cyclic, aromatic or aliphatic thiols, thioethers and disulfides, preferably is thiophene and/or dibenzothiophene.
The invention further proposes that the sulfur containing compound does not contain any halogen atoms.
It can be provided that the at least one liquid hydrocarbon is crude oil and/or at least one fuel.
Preferably, it is proposed that the molar ratio of compound (I) to compound (II) is 1:2.
Most preferably, the ratio of the at least one deep eutectic solvent to the at least one liquid hydrocarbon is in a range from 1:1 to 5:1.
It is convenient that step a), b) and/or c) is carried out within a temperature range from 25 to 100°C.
Most convenient, the pressure in step a), b) and/or c) is within a range from 1 to 10 bar.
In a preferred embodiment, the electrochemical generating takes place in a membrane electrochemical reactor.
Also preferred, the deep eutectic solvent has a freezing point of up to 100°C.
It was surprisingly found that sulphur containing compounds can be removed from liquid hydrocarbons by the inventive method in an easy, cheap and efficient way. Particularly, it was found that the inventive method allows an efficient extraction of sulphur containing compounds from liquid hydrocarbon mixtures as well as an easy subsequent decomposition of the extracted sulphur containing compounds in DESs by utilization of super oxide ions.
The at least one liquid hydrocarbon according to the inventive method can comprise one or more different liquid hydrocarbons. Besides the sulphur containing compounds, other non-liquid hydrocarbon constituents can be contained, for example nitrogen or oxygen containing organic compounds like amines, alcohols, etc., as long as there is no interaction of this constituents which inhibits the extraction and/or the decomposition of the sulphur containing compound in a non-acceptable way.
Preferably, the inventive method can be applied in the oil industry for the removal of sulphur containing compounds from the various hydrocarbon mixtures occuring in this field, for example for the removal from sulphur containing compounds from crude oil, oil, petroleum, mineral oil, kerosine, petrol, gasoline, liquid paraffins, diesel etc..
Additional features and advantages of the present invention will become apparent in the following detailed description and on the basis of examples with reference to the drawings, wherein
Fig. 1 shows HPLC chromatograms of thiophene in a DES of choline chloride with ethylene glycol in a molar ratio of 1:3 after the extraction step with and without the addition of different amounts of KO₂.

Examples

The used compounds were obtained from different sources. The stated purity of the used substrates was ≥ 99%. All chemicals were used without further purification.
In a typical embodiment, the extraction of the sulphur containing compound by means of the deep eutectic solvent was carried at a pressure of 100 kPa at a temperature of 25°C. However, extraction at a temperature of up to 100°C and under increased pressure was obtained to be possible and advantageously in some cases.

Example 1

A DES was synthesized by mixing choline chloride with ethylene glycol in a 1:3 mol ratio. The mixture was heated up to 70 °C under vigorous mixing for three hours. The freezing point of the resulting DES was less than room temperature. About 1 g of thiophene was added in decane as a model compound of diesel. A sample was drawn from the mixture of decane with thiophene, diluted with propanol and analyzed using HPLC. The extraction of thiophene from decane was performed by adding the DES to the decane phase in different mass ratios (0.75 - 3 mass units DES per 1 mass unit decane). The mixtures were then agitated for at least 1 hour at about 200 rpm using an orbital shaker under ambient temperatures. After two hours of settling, the upper and bottom layers were separated using a saparatory funnel and samples from both phases were taken and analyzed using HPLC technique. HPLC analysis showed that about 40% of the thiophene was extracted by the DES for a mass ratio of DES:decane of 1:1.

Example 2

Electrochemical Generation of Superoxide Ion

Cyclic voltammetry (CV) was used as electrochemical analysis technique. The DES to be used was dried overnight in a vacuum oven at 50 °C. Electrochemical experiments were performed using EG&G 263A potentiostat/galvanostat controlled by computer and data acquisition software. CVs were conducted in a one compartment cell since the time of the experiment is relatively small to affect the DES. The cell was a jacketed vessel (10 ml volume) with a Teflon cap including 4 holes for the three electrochemical electrodes and for gas sparging tube. Glassy carbon (GC) macro-disc electrode was used as working electrode for cyclic voltammetry, while platinum mesh was used for the bulk electrolysis. Platinum electrode was used as a counter electrode and Ag/AgCI electrode was used as a reference electrode. All experiments were performed in a dry glove box under either an argon or helium atmosphere. Prior to O₂ ^•- generation, a background voltammogram was obtained after removal of O₂. The O₂ removal was achieved by purging the DES with dry N₂. Oxygen was then bubbled into the tested DES for at least 30 min to ensure that the equilibrium was achieved. In addition, in order to confirm that the tested DES is saturated with O₂, CVs at different time intervals were conducted and the final measurement was taken when the cathodic peak current of the CV was constant. Between consecutive CV runs, O₂ was bubbled briefly to refresh the system and to remove any concentration gradients. Nitrogen or oxygen sparging was discontinued during the CV runs. For the membrane electrochemical reactor, the cathode and anode compartments were made of Plexiglas with appropriate openings to accommodate the electrodes and to load and unload solutions. Proton transfer membranes of different thickness were used as a separator between the cathode and anode compartments. The membranes were soaked in a boiling 5M NaOH solution for 2-3 h to get rid of H⁺ and then in boiling distilled water for about 1 h. In some cases the membrane was soaked with DES for 24 h before being used. The current density ranged from 1-2 mA/cm² depending on the type of electrode and reactor. The current efficiency was higher than 90% in all cases. The sulfur containing compound decomposition was monitored as described in Example 3.

Example 3

Decomposition of Sulfuric Compounds using Potassium Superoxide:

Potassium superoxide was added gradually into a vial containing the DES and the sulphur containing compound after extraction, the bottom layer in Example 1, under vigorous stirring. Samples, before and after the addition of KO₂, were taken by dissolving 0.1 g of DES solution in 1 g of acetonitrile. The samples were then analyzed using HPLC. Figure 1 shows that the peak representing thiophene decreased gradually with addition of KO₂. The total destruction was about 98%. This procedure was repeated and more KO₂ was added until the peak of sulfur compound was not detected or did not change and then the sample was analyzed using GC/MS.
The features disclosed in the foregoing description, in the claims and the accompanying drawings may both separately and in any combination be material for realizing the invention in diverse forms thereof.

Claims

Method for removal of at least one sulfur containing compound from at least one liquid hydrocarbon containing the at least one sulfur containing compound, comprising the steps:
a) providing at least one deep eutectic solvent comprising:
aa) at least one compound (I) of the general formula

R¹R²R³R⁴Y⁺X^-;

and

bb) at least one compound (II) which is a hydrogen bond donor able to form
a complex with X^-;
wherein Y is N or P;
R¹, R², R³ and R⁴ are independently selected from substituted or unsubstituted, linear or branched C₁-C₁₈ alkyl, C₁-C₁₀ alkoxy, C₆-C₁₀ cycloalkyl, C₆-C₁₀ aryl or C₇-C₁₂ alkaryl or wherein two of R¹, R², R³ and R⁴ are an optionally substituted alkylene group, preferably a C₄-C₁₀ alkylene group;
X is halogen;
wherein the hydrogen bond donor is selected from urea, acetamide, thiourea, malonic acid, oxalic acid dihydrate, trifluoro acetic acid, benzoic acid, benzyl alcohol, phenol, p-methylphenol, o-methylphenol, m-methylphenol, p-chlorophenol, D-fructose, vanillin, aniline or a substituted aniline, a C₁-C₆ aliphatic acid, a C₁-C₆ hydroxy aliphatic acid, a dicarboxylic acid of the formula HOOC (CH₂)_nCOOH, wherein n is 0 or 1, alkylene glycol, citric acid and/or ethylene glycol; and
the molar ratio of compound (I) to compound (II) is in a range from 1:1 to 1: 12, preferably 1:2 to 1:5;

b) extracting the at least one sulfur containing compound from the at least one liquid hydrocarbon with the deep eutectic solvent; and

c) optionally decomposing the at least one sulfur containing compound in the deep eutectic solvent by adding molecular oxygen to the deep eutectic solvent phase obtained in step b) and electrochemically generating superoxide ions from the molecular oxygen and/or adding at least one alkali superoxide and/or at least one alkaline earth metal superoxide to the deep eutectic solvent phase obtained in step b).
Method according to claim 1, wherein X is chlorine or bromine, preferably chlorine.
Method according to any of the preceding claims, wherein R¹, R², R³ and R⁴ can optionally be substituted with OH, SH, SR⁵, Cl, Br, F, I, NH₂, CN, NO₂, CO₂R⁵, CHO, COR⁵ and/or OR⁵, wherein R⁵ is selected from alkyl or cycloalkyl, more preferably, C₁-C₁₀ alkyl or cycloalkyl.
Method according to any of the preceding claims, wherein the sulfur containing compound is selected from the group consisting of hydrogen sulfide, linear, branched or cyclic, aromatic or aliphatic thiols, thioethers and disulfides, preferably is thiophene and/or dibenzothiophene.
Method according to any of the preceding claims, wherein the sulfur containing compound does not contain any halogen atoms.
Method according to any of the preceding claims, wherein the at least one liquid hydrocarbon is crude oil and/or at least one fuel.
Method according to any of the preceding claims, wherein the molar ratio of compound (I) to compound (II) is 1:2.
Method according to any of the preceding claims, wherein the ratio of the at least one deep eutectic solvent to the at least one liquid hydrocarbon is in a range from 1:1 to 5:1.
Method according to any of the preceding claims, wherein step a), b) and/or c) is carried out within a temperature range from 25 to 100°C.
Method according to any of the preceding claims, wherein the pressure in step a), b) and/or c) is within a range from 1 to 10 bar.
Method according to any of the preceding claims, wherein the electrochemical generating takes place in a membrane electrochemical reactor.
Method according to any of the preceding claims, wherein the deep eutectic solvent has a freezing point of up to 100°C.