1. Applications of Ionic Liquids in Refining Processes
Petroleum refining has been one of the key technologies driving global economic development and technological advancement for well over a century. Although much of the technology used in refineries is considered mature, the industry is always seeking ways to make process improvements, reduce environmental impact, enhance safety, and achieve cost reductions. In particular, much focus has been placed on improving the existing technology for Hydrodesulfurization (HDS), Hydro-denitrogenation (HDN), Hydrodeoxygenation (HDO) and alkylation. Due to their unique physical and chemical properties and environmental advantages over traditionally used solvents or catalysts, interest in ionic liquids for such refinery processes has been increasing exponentially in recent years [1]. IL-based alkylation catalysts have been proven to facilitate efficient alkylation while avoiding the major challenges of corrosion (such as: Stress Corrosion Cracking), safety and operability issues associated with the traditional HF-based technology. Alkylation typically uses a catalyst such as sulfuric acid or HF to create high-octane gasoline. However, the use of HF has been associated with explosions at Philadelphia refinery. The US Chemical Safety Board (CSB) has called for safety regulations to be updated around the use of HF. Extractive desulfurization (EDS) of fuel oils using ionic liquids (ILs) has been intensively studied in recent decades and has a good future as an alternative or complementary method to HDS. This process is operated under harsh conditions, such as high temperature, high pressure, and requirement of a noble catalyst and hydrogen. By using this existing technology, the steel pipes may be prone to High Temperature Hydrogen Attack (HTHA) failure. HTHA (sometimes called ‘methane reaction’) occurs at high temperatures between the gaseous molecular hydrogen contained inside the steel pressure vessel and the carbon atoms located in the steel matrix or in carbides. Methane molecules are produced during this reaction. This phenomenon can consequently lead to a loss of mechanical properties due to surface decarburization and to the formation of defects caused by methane bubbles mainly located at grain boundaries. The Tesoro Anacortes accident occurred during startup of the refinery’s “naphtha hydrotreater unit” after a maintenance shut down.
Robust simulation methodologies have been applied to analyze key IL applications: physical and chemical CO2 capture, gas separation, liquid–liquid extraction, extractive distillation, refrigeration cycles, and biorefinery [2].
2. Numerical Simulations of Biodiesel Production
Computational fluid dynamics simulations of biodiesel production have been carried out by applying the eddy dissipation model (EDM) coupled with the Reynolds stress model (RSM). The calculated biodiesel yield compared well with the experimental results [3]. Mekala applied ANSYS Fluent code in order to solve fluid flow, heat, and mass transfer transport equations in packed beds reactors [4]. This work contains a Multiphysics design of an esterification reactor for the transformation of oleic acid and methanol to FAME by employing high boiling point fluid. It is probably the first time that phenyl-naphthalene has been proposed to supply the required heat needed to sustain the esterification reaction for FAME [5]. In the framework of this research work, the ionic liquids have been applied in organic reactions as solvents and catalysts of the esterification reaction. The great qualities of high boiling temperature fluids, along with advances in the oil and gas industries, make the organic concept more suitable and safer (water coming into contact with liquid metal may cause a steam explosion hazard) for heating the esterification reactor. The COMSOL Multiphysics code has been employed and simultaneously solves the continuity, fluid flow, heat transfer, and diffusion with chemical reaction kinetics equations.
3. Results Section
Figure 1 shows the three-dimensional temperature field inside the esterification reactor at t = 20,000 s.
Figure 1: 3D plot of the temperature field inside the esterification reactor at t=20,000 sec.
It can be seen from figure 1 that the temperature at the lower section of the reactor is higher than the temperature at the upper side. This is because the endothermic esterification reaction consumes the heat provided by the phenyl-naphthalene liquid. It should be noted that the thermal conductivity of the ionic liquid and reactants (oleic acid and methanol) has a lower value. Figure 2 shows the 3D FAME concentration field inside the reactor.
Figure 2: 3D plot of the concentration field of the FAME inside the esterification reactor..
Figure 2 shows that the FAME conversion is about 100%. A similar value has been obtained in Ref. [6] for T = 130 °C and 5.6 h. Figure 3 shows the axial FAME concentration along the reactor height.
Figure 3. Axial plot of the FAME concentration along the esterification reactor height for phenyl-naphthalene liquid at temperature of 160 °C.
Figure 3 shows that the FAME concentration increases with time. There is a slight decrease in FAME from y = 0.1 m until y = 0.4 m. This is because the thermal conductivities of the ionic liquid and reactants (oleic acid and methanol) have lower values.
4. Conclusions
This paper presented an advanced CFD simulation of biodiesel production by applying imidazolium ionic liquid. COMSOL software simultaneously solves mass conservation (continuity), fluid flow (Navier–Stokes), heat transfer, and diffusion with esterification reaction transport equations. It has been shown that the heat flux can provide the required heat flux for maintaining the esterification process. It has been found that the concentrations of methanol and oleic acid decrease along the reactor axis. The FAME mass fraction increases along the esterification reactor axis. This is because the endothermic reactions consume the heat. The internal and external surfaces of the reactor are exposed to heat supplied by phenyl-naphthalene high boiling fluid. In order to avoid the boiling and evaporation of the water generated inside the esterification reaction, the pressure inside the esterification reactor is set to 700 kPa. It should be noted that the saturated pressure of water at T = 160 °C is 620 kPa. Since the water droplets generated during the esterification reaction are heavier than the gas, they fall and are extracted from the bottom. They may react with ionic liquid, mostly at the reactor inlet. Moreover, if the heating system fails (due to an electric power supply failure or technical problem inside the phenyl-naphthalene liquid pump), the steam may condensate inside the esterification reactor, leading to the generation of water bubbles and decreasing further the heat transfer to the esterification reactor. Thus, it may be difficult to resume the normal operation of the esterification reactor. By applying high pressure, it is easier to resume the operation of this reactor. In some cases, there are side reactions between water and ionic liquids. To combat this problem, the water is removed. A petroleum coke burner can provide the necessary heat flux for the esterification reactor. It is possible to apply this reactor near the delayed coker unit (DCU) in order to produce diesel and biodiesel fuels.
More information about this research is available in Reference [5].
5. References
[1] Haifa Ben Salah, Paul Nancarrow, Amani Al-Othman, Ionic liquid-assisted refinery processes – A review and industrial perspective, Fuel, Volume 302, 2021, https://lnkd.in/dYf4X79V.
[2] Jose Palomar, Jesús Lemus, Pablo Navarro, Cristian Moya, Rubén Santiago, Daniel Hospital-Benito, and Elisa Hernández Chemical Reviews, 2024 124 (4), 1649-1737, https://lnkd.in/d2U4ExbR
[3] Mohiuddin, A.K.M.; Adeyemi, N. Numerical Simulation of Biodiesel Production Using Waste Cooking Oil. In Proceedings of the ASME 2013 International Mechanical Engineering Congress and Exposition IMECE2013, San Diego, CA, USA, 15–21 November 2013, https://asmedigitalcollection.asme.org/IMECE/proceedings-abstract/IMECE2013/V08AT09A003/261194
[4] Mekala, S.J. CFD Studies of Reactive Flow with Thermal and Mass Diffusional effects in a Supercritical Packed Bed Catalytic Reactor. Ph.D. Thesis, Universitat Politècnica de Catalunya, Barcelona, Spain, 2016, https://upcommons.upc.edu/handle/2117/113679.
[5] Davidy, A. Thermal Hydraulics and Thermochemical Design of Fatty Acid Methyl Ester (Biodiesel) Esterification Reactor by Heating with High Boiling Point Phenyl-Naphthalene Liquid. Fluids 2022, 7, 93, https://www.mdpi.com/2311-5521/7/3/93#B13-fluids-07-00093.