DESULFURIZATION OF CRUDE OIL USING ... - UTPedia

Most of the crude oil (84% by volume of the hydrocarbons present) is converted into energy-rich fuels, including gasoline, diesel, jet, heating and other fuel oils, and liquefied petroleum gas [5]. There are two general classifications in crude oil desulfurization: conventional hydrodesulfurization (HDS) and non-conventional desulfurization (non-hydrogen consuming desulfurization).

Figure 4.10 Density value versus temperature for IL BMIM[DMP],

INTRODUCTION

Background of Research

Petroleum
Crude Oil Composition
Classification of Crude Oil
Sources of Sulphur in Crude oil
Environmental Sulphur Level
Methods for Sulphur Removal
Ionic Liquid
Application of Ionic Liquids

Problem Statement

Objective

Thesis Outline

LITERATURE REVIEW

Classification of desulphurization technologies

Conventional desulphurization technology
Non-conventional desulphurization technologies

Biodesulphurization
Adsorption
Oxidative Desulphurization (ODS)
Extractive Desulphurization (EDS)
Extractive and catalytic oxidative desulphurization

The reactivity of sulfur compounds depends on their structure and the local environment of the sulfur atom. Adsorption desulfurization is based on the physical absorption of sulfur compounds on the solid surface of the sorbent.

Table 2.1 Typical Organosulphur Compounds and Their Hydrotreating Pathway [56]

Recent development of ionic liquids as solvent for desulfurization

RESEARCH METHODOLOGY

Materials and Chemicals

Synthesis of alkyl-imidazolium-based phosphate ionic liquids

The final product, a yellow brown liquid was cooled to room temperature before being washed with diethyl ether. After the evaporation process was completed, the IL was dried in a vacuum oven at 70oC for 24 hours.

Figure 3.1 Flow diagram of the synthesis of ILs [20].

Characterization of the ionic liquids

Differential Scanning Calorimeter (DSC)
CHNS Analyzer
Density and Viscosity meter
Coulometric Karl-Fisher

Samples were dried in situ on the differential scanning calorimeter by keeping the samples at 200oC for 1-3 hours. Measurements for melting temperatures were determined by heating the samples from -120oC to 200oC, at a rate of 10oC/min. The presence of carbon (%C), hydrogen (%H), nitrogen (%N) and sulfur (%S) content in the ILs was determined using the Leco-CHNS-932 analyzer, according to the approved standard method ASTM D - 5291.

The equipment settings are as follows; Oxygen dose: 20cc, oxidation furnace temperature: 1000oC, reduction furnace temperature 650oC, and helium gas was used as the carrier gas for the instrument. Other important properties of the ILs such as the density and the viscosity were determined using the SVM 3000 Anton Paar viscometer. The apparatus was calibrated by measuring the density of Millipore quality water at regular intervals according to the supplier's instructions.

The samples are injected into the titration cell through the septum plug and readings are taken.

Desulphurization Process

Materials and Chemicals
Preparation of Model Oil
Extraction catalytic oxidation desulphurization process

Ionic Liquids Screening
Effect of temperature
Effect of the amount of H 2 O 2
Effect of the amount of catalyst
Effect of types of sulphur species in model oil
Effect of different initial sulphur concentration
Product identification

Oxidative desulphurization process (ODS)

H 2 O 2 as the oxidizing agent
Catalyst as the oxidizing agent

Extractive desulphurization process (EDS)
Desulphurization process with crude oil

To investigate the ability of the selected ionic liquid BBIM[DBP] for sulfur removal in the ECODS process, the model oil was replaced with crude oil. As can be seen in Figure 4.6, the alkyl chain in the cation also increases the viscosity of the IL. This may be due to the increase in the alkyl chain length of the cation and the anion.

The amount of water absorbed by the ionic liquid depends on the anion, and the length of the alkyl chain in the cation. Further increasing the ratio showed no improvement to the sulfur removal efficiency, as can be seen in Table 4.9. Based on the above analysis, the ECODS process of DBT can be proposed.

It can also be seen that increasing the alkyl chain in the cation and anion affects the properties of the IL and also helps in the percentage of sulfur removal.

Table 3.3 Reactant used with their physical properties.

RESULTS AND DISCUSSION

Ionic liquid synthesis

Eight imidazolium-based ionic phosphate liquids were synthesized, namely 1-methyl-3-methyl-imidazolium dimethyl phosphate (MMIM[DMP]), 1-methyl-3-ethyl-imidazolium diethylphosphate (EMIM[DEP]), 1-methyl- 3-Butyl-imidazolium dibutyl phosphate (BMIM[DBP]), 1-ethyl-3-methyl-imidazolium dimethyl phosphate (EMIM[DMP]), 1-ethyl-3-ethyl-imidazolium diethyl phosphate (EMIM[DEP]), 1-butyl -3-methylimidazolium diethylphosphate (BMIM[DMP]), 1-butyl-3-ethylimidazolium diethylphosphate (BEIM[DEP]) and 1-butyl-3-butylimidazoliumdibutylphosphate (BBIM[DBP]), their structures shown in Figure 4.1.

Figure 4.1 Structure of the ionic liquids synthesized.

Identification of ILs

Melting point

Similar observation was reported for EMIM[DEP], EEIM[DEP] and BEIM[DEP], where increasing the alkyl chain length lowers the melting point according to methyl>ethyl>butyl, with the measured melting point of and 109.30oC , respectively. However, when comparing ionic liquid BMIM[DBP] and BBIM[DBP], there is an increase in melting point from 146.50 to 151.11oC, instead of a decrease. This may be because the larger cation has more asymmetry, which increases the melting point [119].

When we compared ILs with the same cation but different anion, it was observed that the melting point increased as the length of the alkyl chain in the anion increased. When comparing the ionic liquid EMIM[DMP] with EMIM[DEP] and BMIM[DMP] with BMIM[DBP], it can be seen that increasing the alkyl chains in the anion from methyl to ethyl increases the melting point. For the ionic liquid with EMIM cation but different DMP and DEP anions, the melting point was 122.28oC and 147.2oC, respectively.

The melting point of ILs increases as the length of the anion side chain increases, because increasing the alkyl chain produces stronger intermolecular van der Waals forces, giving rise to larger melting points of chains.

Table 4.2 Melting points of imidazolium-based phosphate ILs

CHNS analysis

Viscosity analysis

Anion structure affects viscosity; a decrease in the size of the anion, due to the substitution of the alkyl chain, reduces the van der Waals, and thus reduces the viscosity of the IL. This can be seen for the ionic liquid EMIM[DMP] and EMIM[DEP], which have the same cation (EMIM) but different alkyl lengths in the anion. With the same cation (BMIM) but different lengths in the anion, namely methyl and ethyl, the viscosity increases from 762.47 cP to 889.87 cP.

This indicates that the length in the anion plays a role in the viscosity of the IL, the longer the length, the higher the viscosity, similar to that reported by Wasserscheid and Welton [122] and Vaderrama and Zarricueta [125]. To observe the effect of the length of the substituted alkyl chain in the cation on the viscosity, we compared the IL with the same anion. This can also be seen in the ionic liquid EMIM[DEP], EEIM[DEP] and BEIM[DEP], which have the same anion (DEP) but a different length in the alkyl chain on the cation (Figure 4.7).

Again, the increase in viscosity is caused by increasing the alkyl length in the cation [124].

Table 4.4 Viscosity data for imidazolium based phosphate ILs (at 20°C) Structure code Viscocity (cP)

Density analysis

It was also agreed that the density of the ILs decreases with the increase of the alkyl chain in the cation or anion of the ILs. For the same cation, there were some changes in the density related to changes in the side chains. Similarly, for BMIM[DMP] and BMIM[DBP], the density decreased from 1.1573 to 1.0415 g.cm-3, respectively, when the side chain of the anion was changed from methyl to butyl.

The effect of the cation alkyl chain length on the density can also be observed for ILs with the same anion. Similarly for IL BEIM[DEP], EEIM[DEP] and EMIM[DEP] with the same anion DEP but different alkyl groups at R in the cation (REIM), i.e. butyl, ethyl and methyl, a decrease in density can be seen as the length of the side chain in the cation increases (Figure 4.12). The experimental results for the 8 ILs showed that the presence of long chain alkyl on the cation or anion decreases the density of the IL and this is seen in a systematic way.

Thus, a linear equation can be used to calculate the density of any of the 8 ILs at any temperature.

Figure 4.9 Plot of experimental density (ρ) values versus temperature (T) for all 8 ILs.

Water content

The same conclusion was given by Valderrama and Zarricueta [129] in their study on the synthesis and properties of some ILs. The optimal physical property for good sulfur removal is that the density difference between the ionic liquid and the oil phase is large enough that the phases separate easily. BBIM[DBP] shows a density difference with the model oil used (dodecane) of 0.2639 g/cm3 and also has the lowest density compared to other tested ionic liquids [129].

The absorption of water by the ionic liquids with the same anion showed that the cations with shorter alkyl chains tend to absorb more water than those with longer chains. This seems likely as a longer alkyl chain would make the ionic liquid more hydrophobic and also promote cation stacking interactions and hydrogen bonding within the liquid preventing the absorption of water into the system. The relatively low concentration of water absorbed in these samples can also be attributed to the larger anion, which can prevent the absorption of water.

The presence of water can have a rather dramatic effect on the ionic liquid by lowering the reactivity of the ionic liquid.

Ionic liquid selectivity

Model oil confirmation
ECODS

Effect of the length of the alkyl chain on extraction
Possible Mechanism of the DBT ECODS

The effect of reaction temperature
Effect of the amount of H 2 O 2
Effect of catalyst amount
Effect of type of sulphur species in model oil
Effect of initial sulphur concentration
Product identification
Influence of different desulphurization system for model oil . 85

The increase in the extraction yield shown in table 4.8 may be the result of the increase in the extraction space due to the increase in the length of the alkyl chain [58]. This indicates that the removal of sulfur from crude oil is more difficult than using model oil due to the co-extraction of aromatic compounds from the crude oil. Due to the steric effect of the alkyl groups in the aromatic rings, methylthiophene, methylbenzothiophene, methyldibenzothiophene, etc., sulfur-containing compounds in crude oil are less extracted than those in model oil [18].

Application of the ionic liquid Ammoeng 102 for aromatic/aliphatic hydrocarbon separation,” Journal of Chemical Thermodynamic , vol. Zhou, "Oxidative Desulfurization of Diesel Fuel Using a Brønsted Acid Room Temperature Ionic Liquid in the Presence of H2O2." Influence of the coordination on the catalytic properties of supported W catalysts,” Journal of Catalysis, vol.

Adsorption and aggregative structures of an organic cation [C18mim] of the ionic liquid in the intermediate layer of montmorillonite”, Acta Physics.

Figure 4.14 Percentage of sulphur removal using imidazolium-based-phosphate ILs at room temperature

CONCLUSION AND RECOMMENDATIONS

Conclusion

Based on the results in the previous section, it can be proved that the best IL is BBIM[DBP]. Catalytic oxidation and extractive desulfurization (ECODS) was found to be a promising approach for sulfur reduction with a total removal of 85.2%. Direct extraction of the model oil without any oxidation resulted in approximately 68.4% sulfur removal.

However, such direct extraction has a major impact in removing a significant amount of other types of aromatic hydrocarbons. This study also examines the reactivity of the sulfur compounds in the ECODS process and it was found that the reactivity of sulfur compounds in the ECODS system decreases in the order of DBT>BT>3-MT. In conclusion, it can be concluded that the best IL in this study was BBIM[DBP] using the ECODS process.

Recommendations

Liu, “Coupling technique of photochemical oxidation and ionic liquid extraction in deep desulfurization of light oil,” Energia. Oxidative desulfurization of diesel fuel using amphiphilic quaternary ammonium phophomolybdate catalysts,” Fuel Processing Technology , vol. Oil desulfurization using ionic liquids: selection of cationic and anionic components to improve extraction efficiency,” Green Chemistry , vol.

Deep oxidative desulfurization of fuels catalyzed by ionic liquid in the presence of H2O2,” Energy and Fuels, vol. One-pot desulfurization of light oils by chemical oxidation and solvent extraction with room temperature ionic liquids,” Green chemistry , vol. Oxidative desulfurization of light gas oil and vacuum gas oil by oxidation and solvent extraction,” Energy and Fuels , vol.

Oxidative Desulfurization of Light Gas Oil and Vacuum Gas Oil by Oxidation and Solvent Extraction”, Energy Fuels, Vol. Oxidative Desulfurization of Fuel Oil(I) Oxidation of Dibenzothiophene Using Tert-by/Utyl Hydroperoxide,” Applied Catalysts., A, vol. One-pot desulfurization of light oils by chemical oxidation and solvent extraction with ionic liquids at room temperature, “Green Chemistry, 5(5), pp.