A gas–liquid Eulerian computational fluid dynamics (CFD) model coupled with a population balance equation (PBE) was presented to investigate hydrodynamics of an air–water bubble column (1.8 m in ...height and 0.1 m in inner diameter) under elevated pressure in terms of pressure drop, gas holdup, mean bubble size, and bubble surface area. The CFD‐PBE model was modified with three pressure correction factors to predict both the total gas holdup and the mean bubble size in the homogeneous bubbly flow regime. The three correction factors were optimized compared to experimental data. Increasing the pressure led to increasing the density, reducing the bubble size, and increasing the gas holdup. The bubble size distribution moved toward a smaller bubble size, as the pressure increased. The modified CFD‐PBE model validated with experimental data and empirical models represented well hydrodynamics of the bubble column at P = 0.1, 1.5, and 3.5 MPa.
•A conceptual process model of a bromine-mediated propane oxidative dehydrogenation (Br-PDH) process.•The optimal conditions (Br2/C3H8 ratio, split sequence of columns, heat integration network) were ...found.•Br-PDH increases propylene yield and decreases energy consumption compared to conventional PDH.•Techno-economic analysis identified the competitiveness and barriers of Br-PDH.
The production of propylene from propane is becoming increasingly important. Catalytic propane dehydrogenation (PDH) is the major on-purpose propylene production process today. The conventional PDH process has a relatively high energy consumption (6.1–9.4 kWh/kg C3H6) which results in high direct CO2 emissions and modest propylene yield (0.8–0.9 kg C3H6/kg C3H8). A bromine-mediated propane oxidative dehydrogenation process (Br-ODH) is evaluated in this techno-economic study which can potentially improve both the process energy efficiency and product yield. To investigate the Br-ODH process feasibility, a heat integrated process model was designed using Aspen Plus® V12 for a 450 kta propylene facility using reaction data from the literature. The partial oxidation of propane under bromine limited conditions selectively produces a propylbromide intermediate which can be readily separated from propane. Propylbromide undergoes dehydrobromination under relatively mild conditions to produce the propylene product in a second step. Bromine is regenerated by conversion of the hydrogen bromide byproduct either thermochemically or electrochemically. Due to the current interest in use of renewable electricity in chemical processes, the electrochemical regeneration process was evaluated in this study. Based on the model, the Br-ODH process can achieve approximately 10% higher propylene yield with 37% lower utilities than conventional PDH. However, the use of high-cost electrolyzers resulted in the capital investment increasing by approximately 11%. Capital cost was also increased due to the requirements of high alloy materials of construction for the potentially corrosive halogen containing equipment. The sensitivity analysis showed that the production cost was most sensitive to the propane price. For the electrolyzer-based regeneration process the capital cost was found to be key parameter that might limit competition with conventional PDH; however, the development of a commercial thermochemical HBr oxidation process analogous to the Deacon process for chlorine would likely bring significant cost savings.
The effect of reaction temperature and time on the products and the asphaltene dispersion according to the residue conversion was investigated in a slurry-phase hydrocracking reaction. The ...experiments were carried out with two different approaches to control the hydrocracking reaction, which the reaction time was changed from 4 h to 20 h (at 410 °C) and the reaction temperature from 430 °C to 453 °C (for 1 h) at 100 bar (at 80 °C) of initial hydrogen pressure and 500 wt.ppm of molybdenum concentration. As a result, it was found that the control of the reaction time and reaction temperature may give different effect to the stability of the asphaltene in the liquid phase in spite of the same VR conversion. In order to understand this, the dipole moments of the liquid product and structural change of the asphaltene was compared. And it was found that enhancing hydrogenation reaction by increasing reaction time at low temperature delayed the time of decreasing point for dipole moments of the liquid phase and increased the length of alkyl chain of remaining asphaltene. Therefore, it is considered that the dispersibility of asphaltene with high polarity is increased. Additionally, it was found that enhancing hydrogenation can also improve the catalyst dispersion in the liquid phase below 80% of residue conversion.
•Sediment formation started to form at near 70wt.% VR conversion.•Higher concentration of catalyst delayed sediment formation.•Change of resin content in the maltene was found to be significant to ...form sediment.•ξ-potential showed the colloidal instability of asphaltene during SHC reaction.
This study investigated the characteristics of slurry-phase hydrocracking of vacuum residue (VR >524°C) at a high conversion (40–95wt.%) with a change of reaction temperatures and concentrations of the dispersed molybdenum (Mo Conc. 100–2000wt.ppm) catalyst. Experiments were carried out with an initial hydrogen pressure of 80bar (at 80°C) at a reaction temperature from 385 to 440°C for four hours in a batch reactor. As results, it was found that the sediment formation is mainly dependent on the VR conversion by the reaction temperature and started over 70wt.% of VR conversion. Up to 70–80wt.% of VR conversion, the higher catalysts showed the higher asphaltene conversion and prevented the sediment formation at the boundary of its formation, but it didn’t show any effect over 80wt.% of VR conversion anymore. Based on the analysis of the structural change and ξ-potential of asphaltene from the liquid and sediment, and SARA compositional change in the liquid, the reason for sediment formation was explained.
The growing accumulation of plastic waste poses a pressing environmental challenge. Traditional disposal methods, such as incineration and landfilling, carry considerable health and ecological risks. ...In response, our study presents an innovative method to repurpose mixed plastic waste into valuable α,ω-diacids utilizing chemo-biological processes. We extracted pyrolysis oil, rich in hydrocarbons spanning a broad range of chain lengths (C7 to C32), from household plastic waste and employed a genetically engineered β-oxidation-blocked Candida tropicalis strain to convert this oil into α,ω-diacids of various chain lengths. Simple distillation at 200 °C enabled the extraction of medium-chain hydrocarbons from the pyrolysis oil. However, an increased ratio of medium-chain alkenes posed a toxicity challenge to the cells. Through hydrogenation, these medium-chain alkenes were fully converted to alkanes. Remarkably, cell growth was maintained even with an 8% concentration of hydrogenates. The subsequent biotransformation yielded medium-chain diacids, with 94.3% of the produced α,ω-diacids being of medium-chain length (C7 to C14). These results offer a novel and scalable solution for converting everyday plastic waste into valuable chemicals, thus significantly contributing to the circular economy and the advancement of sustainability goals.
•A new solution to the chemo-biotechnological upcycling of waste plastic pyrolysis oil was proposed.•Aliphatic hydrocarbons with chain lengths ranging from C8 to C32 were identified from the pyrolysis oil.•Engineered Candida tropicalis yeast biotransformed hydrocarbons in the pyrolysis oil into their corresponding α,ω-diacids.•Above 90% of the total produced diacids were C7–C14 diacids using the processed POMPW.
Schematic of dual distribution.
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•The heat transfer coefficient in a dual gas distribution was conducted in a bubble column.•Heat transfer efficiency was reduced by microbubbles.•The ...heat transfer coefficient increased up to approximately 25%.
The effects of the heat transfer coefficient variance on microbubble formation in a pressurised bubble column and its variance in the dual gas distribution were investigated. The tests were performed with a cylindrical column with an inner diameter of 0.097 m and a height of 1.8 m with air–kerosene media. The heat transfer coefficient was measured using various distributors with different numbers of orifices, and its size was fixed. For an opening fraction of 0.223 %, the heat-transfer coefficient increased with increasing superficial gas velocity (Ug) under all pressure conditions in the tested range. The amount of microbubble generation increased with an increase in pressure and Ug when the opening fraction decreased. To analyse the effect of the kinetic energy rate at the orifice on the number of microbubbles, the gas holdup was measured according to the increase in Ug and system pressure. When the total kinetic energy rate was equal to or higher than 1 J/s, the gas holdup rapidly increased owing to microbubble generation. To increase the heat transfer coefficient in the presence of microbubbles, a dual gas distribution was applied by inserting a single nozzle with different orifice hole diameters (1.7, 2.0, 2.5, and 3.46 mm). In this system, the heat transfer coefficient increased by approximately 25 % compared with the dispersion in a single distributor.
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•Hydrocracking of vacuum residue (VR) was performed in a slurry bubble column reactor.•Physical properties estimated during hydrocracking were experimentally compared.•A CFD model ...with a new drag coefficient was developed for the bubble column.•Gas holdup at 425 °C and 160 bar (6.2%) was in agreement with empirical value (6.6%).•Axial and radial hydrodynamics of the bubble column were examined via the CFD model.
Vacuum residue (VR) was subjected to catalytic hydrocracking with H2 in a pilot-scale slurry bubble column reactor (SBCR) with 0.05 m diameter and 2 m height at 425 °C and 160 bar in the homogeneous regime. The gas holdup (αG) and composition of the product classified into five pseudo-components were measured in the SBCR. The physical properties such as density, viscosity, and surface tension of VR (feed) were analyzed prior to a three-dimensional Eulerian computational fluid dynamics (CFD) simulation to predict axial and radial hydrodynamics in the SBCR. Rather than considering the hydrocracking reactions in the CFD model, a reaction-mixture model was used to predict the variation of the axial physical properties as the reaction progresses. A customized drag coefficient based on experimental data was applied to the CFD model. The value of αG predicted by the CFD model at a superficial gas velocity of 6.4 mm/s was 6.2% which is comparable to the experimental value (6.6%). The Sauter mean diameter and specific surface area were estimated to be 1.2 mm and 304 m2/m3, respectively. The proposed CFD model, which was integrated with the axial physical properties but decoupled from chemical reaction, successfully predicted the hydrodynamics of the H2-VR SBCR.
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•The effects of gas density, surface tension, and viscosity on gas holdup and flow regime transition were studied.•The dual effect of viscosity was observed and analyzed.•Transition ...gas holdup was correlated as a function of the gas density, surface tension, and liquid viscosity.
The homogeneous-to-heterogeneous flow regime transition point dependence on gas and liquid properties was investigated in a semi-cylindrical bubble column of 1.8m height and 0.21m inner diameter operating as a semi-batch system. He, air, and CO2 gases were injected at superficial gas velocities of up to 239mm/s. The batch liquids included water, aqueous ethanol solutions, and aqueous glycerol solutions, all with a gas-free liquid height settled at 1m. When the gas density increased, the gas holdup increased at all superficial gas velocities, delaying the flow regime transition. The gas holdups in the liquid mixtures were higher than those for tap water. The transition gas holdup for the ethanol solutions increased to a sharp maximum and then decreased as the surface tension increased. Also, the glycerol solutions showed similar behavior with respect to increasing liquid viscosity, but with a shallower maximum. The transition gas holdup was empirically correlated as a function of the gas density, surface tension, and liquid viscosity, employing dimensional constants. The measured transition gas holdups for liquid mixtures, as well as some data from the literature, were fitted by the correlation.
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•Solvent recovery using CO2 was newly developed for solvent deasphalting process.•High solvent recovery was achieved at relatively low temperature.•CO2 acts as an anti-solvent to ...separate the solvent from DAO.•Numerical simulation confirmed the possibility of a new solvent recovery operation.
The solvent deasphalting (SDA) process is a heavy oil upgrading process in which deasphalted oil (DAO) is extracted from heavy oil feedstock by precipitating asphaltene using an excess amount of alkane solvent (C3-C6). After the extraction, solvent recovery should be carried out for separating the solvent from the DAO in order to recycle the expensive solvent. In the conventional solvent recovery method, the mixture of solvent and DAO is heated to evaporate the solvent, which requires massive heat energy, resulting in reduced process efficiency. In this study, CO2 is applied for the first time to selectively separate solvent from DAO at a relatively low temperature. The experimental results in a batch separator indicate that the temperature required for high solvent recovery of over 80% decreases from 200°C to 40°C when using CO2 compared to the conventional method. The theoretical approach using Hansen distance calculation based on the Hansen solubility parameter (HSP) was used to verify the mechanism of solvent separation using CO2. The results suggest that the increase in the interaction between CO2 and solvent causes the separation of solvent from DAO, leading to an increase in solvent recovery. Also, numerical simulation results show the possibility of continuous operation for solvent recovery using CO2.
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•The axial dispersion model well predicted reaction performance in the bench-scale SBCR.•Bench-scale SBCR exhibited low back mixing with behavior closer to plug flow.•An asphaltene ...stability index was used to evaluate the operating conditions.•The optimum conditions for recycle mode operation (ROM) were found.
A modeling and simulation were conducted to study the slurry phase hydrocracking of vacuum residue in a bench-scale slurry bubble column reactor (SBCR). The reactor model was based on axial dispersion, and the intrinsic kinetic information was reported in continuous stir tank reactor (CSTR) using the same feedstock in our previous study. The model was validated over a wide range of operating conditions using experimental data from the bench scale unit. The reactor model predicted product yields, sulfur and asphaltenes content with an average error of less than 10%. The bench-scale SBCR demonstrated better hydrocracking (HCK) and hydrotreating (HDT) performance compared to CSTR, mainly due to the mixing behavior in the SBCR. A stability index of asphaltene was proposed from the data reported in our previous study to evaluate the operating conditions. Based on the simulation results, the optimal operating conditions for recycle operating mode were suggested using the simultaneous optimization variables technique.
