CHARACTERISTICS OF ULTRASONIC ENHANCED LIQUID FUELS DESULFURZATION" is the result of the research I carried out at the Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati, India, under the guidance of Prof. Bhasarkar (Roll No was carried out under my supervision and that this work was not submitted elsewhere for degree.
Ultrasound Assisted Microbial Desulfurization 155
Overview and Suggestions for Future Research 227
82 Figure 2.6 Reaction scheme for oxidative desulfurization 83 Figure 2.7 FTIR spectra of DBT (pure), DBT sulfone (pure) and. 171 Figure 5.4B Reaction mixture mass spectra in category D 171 Figure 5.5 Time histories of DBT reduction and HBP formation at.
Environmental Legislation
The linear relationship observed between the level of sulfur in diesel fuel and particulates and other harmful pollutants in emissions are the main reasons for targeting the sulfur content in diesel fuel specifications and reducing it to as low a level as possible. , in many countries of the world. Significant reduction in sulfur-induced corrosion and slower acidification of engine lubricating oil (leading to longer maintenance intervals and lower maintenance costs), are additional benefits of using ultra-low sulfur oil in vehicles.
Petroleum Refining
Depending on the predominant mechanism of transformation of sulfur compounds, these processes can be divided into three groups: decomposition, separation without decomposition and decomposition with separation. Desulfurization techniques practiced in petroleum refineries are broadly divided into two categories: (a) Hydrodesulfurization (HDS) process, and (b) Non-HDS processes.
Hydrodesulfurization (HDS) Process
- Effect of refractory organosulfur compounds on HDS
- Catalyst for Hydrodesulfurization (HDS)
- Support for HDS catalyst
- Unsupported catalysts for HDS
- Adsorbent
- Processes Employing Adsorptive Desulfurization
- Basic principles of oxidative desulfurization
- Oxidant Selection
- Ultrasound Assisted Oxidative desulfurization
- Photochemical desulfurization
- Destructive Biodesulfurization (Oxidative C–C bond cleavage)
- Cavitation Bubble Dynamics
- Chemical Effects of Cavitation
The mass pressure in the liquid medium undergoes periodic (usually sinusoidal) variation during the propagation of the ultrasonic wave. Current state of the art and future challenges in hydrodesulfurization of polyaromatic sulfur compounds.
C HAPTER 2
M ECHANISTIC F EATURES OF O XIDATIVE
D ESULFURIZATION U SING S ONO -F ENTON - P ERACETIC A CID S YSTEM
Mechanistic Features of Oxidative Desulfurization Using Sono-Fenton-
Peracetic Acid System
Materials
The following chemicals were used in the experiments: Dibenzothiophene (98%, Sigma Aldrich); Dibenzothiophene sulfone (97%, Sigma Aldrich); Toluene (Merck, Synthesis grade); 30% v/v H2O2 (Merck Grade, AR), Acetic acid (Merck, 99-100%, AR Grade), FeSO4•7H2O (Merck Grade: AR) Acetonitrile (Spectrochem, HPLC grade) was used as a mobile phase for the HPLC analysis process.
Experimental Setup
Since the ultrasound intensity in the bath shows significant spatial variations (Moholkar et al., 2000), the position of the test tube inside the bath was carefully maintained the same in all experiments. To increase the static pressure in the reaction test tube, the mouth of the test tube was air-sealed with a rubber stopper with a metal tube pierced in the middle. The outer end of the tube was connected to a nitrogen cylinder with dual stage pressure regulator.
Method
For the peracetic acid-Fenton system, ferrous sulfate heptahydrate (FeSO4⋅7H2O) was added to the reaction mixture as a source of Fe2+ ions and the pH of the aqueous solution was adjusted to 2 ± 0.1 before starting the reaction (Dai et al. , 2008). The initial temperature of the water in the bath and also of the reaction mixture in the test tube was 298 K. In the case of the peracetic acid-Fenton process, the pH of the aliquot was adjusted to 7.0 to stop the Fenton reaction.
Analysis
To avoid a significant increase in temperature, a part of the water in the bath is changed every 15 minutes. 1 mL portions of the reaction mixture were withdrawn every 15 min and analyzed for DBT concentration. Confirmation of DBT sulfone formation was also done using FTIR (Shimadzu, Model: IRAffiniti1).
Experimental Categories
An increase in the static pressure of the medium causes significant changes in the dynamics characteristics of the cavitation bubbles, as explained in the results and discussion section. As already mentioned, ultrasound and cavitation cause physical and chemical effects in the bulk liquid medium. As already mentioned, the amplitude of the ultrasonic wave in the medium was determined by calorimetric measurements to be 150 kPa.
Cavitation Bubble Model for Toluene
The microcurrent velocity is calculated as: u=PA ρLc, where PA is the pressure amplitude of the ultrasonic wave, while ρL and c are the density and sound velocity in the liquid medium. Gas diffusion across the bubble interface is neglected in this model, since the time scale for gas diffusion is much higher than the time scale for radial bubble motion. The various parameters used in simulating the bubble dynamics equation and their numerical values are as follows: Ultrasonic frequency (f) = 35 kHz; Ultrasonic pressure amplitude (PA) = 150 kPa; Equilibrium bubble radius (Ro) = 5 µm; The vapor pressure of toluene was calculated using Antoine-type correlation.
Model for Peracetic Acid
For the radial motion of the bubble, Prasad Naidu et al., 1994 used the Rayleigh-Plesset equation (Plesset, 1949) which does not take fluid compressibility into account. In the present case, we chose a modified form of the original Rayleigh-Plesset equation with the inclusion of the compressibility effect (Prosperetti and Lezzi, 1986; Keller and Miksis, 1980; Lofstedt et al., 1995; Hilgenfeldt et al., 1996 Barber et al Various notations are as follows: R = radius of the bubble at any time dR/dt = velocity of bubble wall µ = viscosity of the bulk liquid The peak temperature and pressure conditions reached in the bubble at the point of maximum compression (or minimum radius) is determined as: 1)Tmax =T R Ro( 2 min)3(γ −1), (2) Pmax =P R R2( 2 min)3γ, where R2 is the radius of the cavitation bubble during the collapse phase at which the partial pressure of gas inside the bubble becomes equal to the vapor pressure of the solvent.
Sonophysical Effect
Sonochemical Effect
In mixtures of different volumetric composition, the CH3COOH:H2O2 molar ratio varied in the range of 0.67–3.36. The percentage reduction of DBT obtained for different molar ratios of CH3COOH:H2O2 is shown in the figure. The main peracetic acid oxidative desulfurization experiments were carried out using this optimum value of a mixture of acetic acid (4 mL) and H2O2 (2 mL).
Effect of Volume Ratio of Phases
In order to optimize the volume ratio between phases, experiments were carried out with varying amounts of toluene (with 100 ppm DBT, as in the previous section) and peracetic acid. The trends in percent oxidation of DBT for different volume ratios of toluene to H2O2 are shown in Fig. Based on this result, the total toluene volume in the main experiment was set at 20 ml.
Effect of Iron Catalyst Loading
On the basis of experimental results, the addition of Fe2+ to peracetic acid (with the volume ratio of acetic acid to H2O2 as 2:1) was set at 1.5 M. In the above process, the Fenton reagent was formed in-situ by adding Fe2+ to peracetic acid . To avoid this limitation, we have also performed experiments with excess addition of H2O2 to peracetic acid.
Results of Preliminary Experiments
The net utilization of these radicals for oxidation is high, resulting in greater oxidation of DBT. Additionally, greater formation of peracetic acid results in higher vaporization of it into cavitation bubbles, resulting in •OH radical generation (as explained in the next section of simulation results), which can also scavenge HO•2 radicals through reaction. The above discussion clearly establishes that H2O2 is the species that plays a central role in the overall chemistry of DBT oxidation.
Results of Main Experiments
The addition of CH3COOH (which is completely miscible with toluene) results in a ~50% increase in DBT reduction, while the addition of H2O2 (which is immiscible with toluene and forms a second phase) results in a decrease in DBT reduction. Replacing mixing with sonication gives a marked increase (~3 times) in the extent of DBT reduction. Addition of Fe2+ to peracetic acid also shows a marked increase in DBT reduction in category C experiments.
Simulation Results
As a result, the minimum gas pressure reached in the bubble at the point of maximum radius is 2713 Pa, which is higher than the vapor pressure of peracetic acid (1933 Pa) at the bulk temperature (298 K) of the medium. Interaction of these radicals among themselves as well as H2O2 in the medium plays a decisive role in the overall chemistry of the process. We explain this anomaly in terms of reduction in the scavenging of radicals, without greatly affecting the mass transfer properties of the system.
AND AND
Oxidative Desulfurization Process Assisted Simultaneously by Phase
- Experimental Setup
- Experimental Protocols
- Analysis
- FTIR and GC–MS Analysis of Reaction Mixture
- Experimental Results and Analysis
In category C experiments, an increased static pressure was applied during sonication of the reaction mixture. We attribute this result to the difference in interfacial transport of the oxidant species in presence and absence of PTA. The results of this study highlighted several interesting facets of the oxidative desulfurization process as follows:.
M ECHANISTIC I NSIGHT IN
P HASE T RANSFER A GENT A SSISTED
U LTRASONIC O XIDATIVE D ESULFURIZATION
Mechanistic Insight in Phase Transfer Agent Assisted
Chemicals
Experimental Setup
Oxidative desulfurization reactions were carried out in 38 ml test tubes, which were placed in the middle of the bath. Because of spatial variations of ultrasound intensity in the bath, the position of the test tube within the bath was carefully kept constant in all experiments (Gogate et al., 2002). Legends (Figure 4.1b): 1 – Magnetic stirrer, 2 – Silicone pipe, 3 – Round bottom flask containing reaction mixture, 4 – Condenser, 5 – Holding stand, 6 – Temperature controllers.
Experimental Protocols
Analysis
Characterization of Oxidized Product
US + PFA+ TBAB + ESP
- Kinetic Model for PTA–Assisted Oxidative Desulfurization
- Simulations of Cavitation Bubble Dynamics
- Arrhenius (Kinetic) and Thermodynamic Analysis
- Trends in DBT Oxidation
- Arrhenius and Thermodynamic Analysis
- Results of Cavitation Bubble Dynamics Simulations
In the analysis of the physical mechanism of PTA-assisted ultrasonic oxidative desulfurization, we have used two models, viz. Despite this limitation, the trends in the Arrhenius parameters obtained for different experimental categories reveal a physically meaningful picture of the mechanism of PTA-assisted ultrasonic oxidative desulfurization. For the same reasons, ΔH for category A.2 is much smaller than for category A.1. 3) With the simultaneous use of PTA and ultrasound (as in category B.2 and C.1), the chemical mechanism of the oxidative desulphurisation has a dual character, i.e.
The cyclic mechanism of phase transfer agent (PTA) during oxidative desulfurization with performic acid
However, the ultrasound-induced microflow (which is not affected by increased static pressure) generates a finer emulsion between the phases, compared to (macroscopic) mechanical stirring.
Reaction mechanism for performic acid induced oxidative desulfurization
The simultaneous analysis of DBT oxidation extent and Arrhenius and thermodynamic parameters for different experimental conditions and the results of cavitation bubble dynamics simulations presented in this study revealed a convincing and coherent picture of the physical mechanism of PTA-assisted ultrasonic oxidative desulfurization. Although ultrasonic oxidative desulfurization has the lowest activation energy and enthalpy change with the largest negative entropy change, the overall oxidation of DBT achieved in this process is lower by a factor of low frequency, which is due to the high instability of radicals generated by transient cavitation. Kinetics and Mechanism of Quaternary Ammonium Salts as Liquid-Liquid Phase Transfer Catalysts for Thiophene Oxidation.
Ultrasound Assisted Microbial Desulfurization
- Chemical and Reagents
- Microorganism Growth and Maintenance
- Inoculum Preparation and Fermentation Media Composition
- Immobilization and Cross Linking of Cells
- Experimental Setup for Sonication Experiments
- Experimental Categories
- Analysis
- Cavitation Bubble Dynamics Model
- Mathematical Model for Microbial Metabolism
- Main Experiments and Simulations
Furthermore, the kinetic data for the biodesulphurisation have been adapted to the Haldane kinetics model. The corresponding pressure amplitude of the ultrasonic waves generated in the bath was determined using calorimetric method as 150 kPa (Sivasankar et al., 2007). The HPLC chromatogram of the reaction mixture (before and after reaction) for Category D experiments is shown in Fig.
