Supercritical Process Research Articles

Simultaneous production of bio-crude bio-oil via hydrothermal liquefaction and carotenoids via supercritical extraction from Nannochloropsis oceanica and recycling effluent to establish circular processes

Commercial production of microalgae biofuel is not economically feasible since it cannot compete with the price of fossil fuels. Algal biofuel could be cost-effective if high-value co-products are produced from microalgal biomass before it is converted into biofuel. Thus, this research aims to demonstrate a circular biorefinery process of producing bio-crude bio-oil as well as high-value products like carotenoids from a marine microalga Nannochloropsis oceanica. The microalga was cultivated in raceway ponds over the years with the highest biomass productivity of 30–40 g m−2 day−1 recorded in October and November of 2021, but it reduced in extremely high summer temperatures and low temperatures in winter of Delhi NCR, India. The annual average biomass productivity of 19.13 g m−2 day−1 was recorded, which is equivalent to 69825 kg ha−1 year−1. The algal biomass was processed for high-value carotenoids using a green process, i.e. supercritical carbon dioxide extraction. Carotenoid yield of 252 μg/g of biomass was obtained after optimizing temperature and pressure in the supercritical extraction process. The spent biomass after carotenoid extraction was used to produce bio-crude bio-oil using hydrothermal liquefaction. There was no significant difference between bio-crude oil yield and properties after carotenoid extraction and direct biomass use. A bioeconomic methodology for closing the circular loop involving recycling the effluent generated during hydrothermal liquefaction to re-cultivate the microalgae is demonstrated. This study highlights the potential of green technology, circular bioeconomy, and biorefinery practices in developing sustainable and environmentally friendly solutions for the chemical and energy sectors.

Enhancing hydrophobic and antioxidant properties of whey protein films through the inclusion of oil and oleogel sourced from spent coffee grounds

In this study, whey protein edible films with improved hydrophobic and antioxidant properties were developed through the addition of oil-based components deriving from spent coffee grounds (SCG). Initially, the recovery of the oil fraction from SCG was performed using conventional and “green” extraction techniques. Results showed that a higher recovery yield (77.4%, w/w) of SCG oil was achieved through the supercritical CO2 extraction process, than the conventional one with hexane (59.8%, w/w). Thereafter, SCG oil and SCG oil-based oleogels, using beeswax and candelilla wax as oleogelators, were incorporated into whey protein concentrate films. Incorporation of oil and oleogels into the film matrix had an obvious effect on their hydrophobic character. More specifically, solubility, swelling index and water vapor permeability of films decreased significantly (p < 0.05) as the concentration of oil and oleogels was increased. The most significant (p < 0.05) impact on the swelling index was observed in films containing oleogels as opposed to oil. In fact, the inclusion of 7.5% of SCG-beeswax oleogel, led to the highest reduction (70%) of the swelling index of films. Likewise, antioxidant activity of films was enhanced by the inclusion of SCG oil-based components, due to the presence of antioxidants in SCG oil. Moreover, films presented a time-dependent antioxidant activity, indicating that film structure allowed for a controlled and gradual release capacity of the antioxidants over the time. Eventually, this study demonstrated that oil-based materials derived from food waste can be used as additives, to improve the water-barrier and antioxidant properties of films.

Phenolic, tocopherol, and essential fatty acid-rich extracts from dandelion seeds: Chemical composition and biological activity

Dandelion is a sustainable biomass that has occasional use in the food and pharmaceutical industry. However, commercial use of its extracts is restricted by the lack of systematic information on safety, composition, and biological activity. To broaden dandelion use, the present study brings new knowledge on extracts from dandelion seeds that could find application as safe and functional food ingredients. The employed two-step supercritical fluid extraction process, followed by the conventional extraction, enabled the separation of extracts with increased content of phenolics, tocopherols, and essential fatty acids. Those compounds were found to be the major components of dandelion extracts, reaching high values up to 799 mg GE/g, 249 mg α-TE/g, and 75%, respectively. The extracts also contained significant amounts of flavonoids (up to 20.5 mg QE/g) and pigments (chlorophyll A up to 1.0 g/kg, chlorophyll B up to 0.3 g/kg, and carotenoids up to 0.1 g/kg). This study revealed new bioproducts that express strong antioxidant (reaching IC50 values up to 132.5 μg/mL) and antimicrobial activity (with minimum inhibitory concentrations up to 80.0 μg/mL). Among the tested 23 microbial strains, the extracts exhibited the strongest activity against food-borne pathogens Micrococcus luteus and Bacillus subtilis. Furthermore, the antitumor and antiviral activity of separated dandelion biological products was evaluated.

Enhanced denitrification of aniline and its derivatives by catalysts, anions, and co-fuels during supercritical water oxidation process

We investigated the denitrification performance of aniline and its derivatives (N-methylaniline and N, N-dimethylaniline) in supercritical water oxidation (SCWO) under varying conditions (temperature: 643–743 K, reaction time: 0.5–4 min, pressure: 24.0 MPa, oxidation coefficient: 300%). Cu2 + proved to be an efficient homogeneous catalyst, generating radicals via a Fenton-like reaction. Isopropyl alcohol (IPA) outperformed methanol and ethanol as a co-fuel, enhancing TN removal due to its higher heating value. Nitrogen-containing product distribution revealed that N2 generation correlated with org-N depletion, especially with Cu2 + and IPA. A denitrification mechanism was elucidated using DFT, with Fukui indices, EHOMO, and ELUMO highlighting aniline's greater susceptibility compared to MA and DMA. Our findings provide insights into optimizing SCWO denitrification using aniline derivatives, shedding light on sustainable nitrogen removal processes.

Fabrication magnetic composite scaffolds with multi-modal cell structure for enhanced properties using supercritical CO2 two-step depressurization foaming process

Fabrication magnetic composite scaffolds with multi-modal cell structure for enhanced properties using supercritical CO2 two-step depressurization foaming process

Supercritical millifluidic process for siRNA encapsulation in nanoliposomes for potential Progeria treatment (ex-vivo assays)

Supercritical millifluidic process for siRNA encapsulation in nanoliposomes for potential Progeria treatment (ex-vivo assays)

Molecular Dynamics Investigation of the Gasification and Hydrogen Production Mechanism of Phenol in Supercritical Water

Supercritical water gasification is an efficient and clean method for converting biomass into hydrogen-rich gas. Phenol plays a crucial role as an intermediate product in biomass supercritical water gasification, and studying its reaction pathway in supercritical water is essential for understanding the chemical reaction mechanism and optimizing biomass energy conversion processes. In this paper, we investigated the conversion mechanism of phenol gasification and hydrogen production in supercritical water using a combined approach of reactive force field (ReaxFF) and density functional theory (DFT). We determined the decomposition pathways and product distribution of phenol in supercritical water. The calculation results demonstrate that in the supercritical water system, the efficiency of phenol conversion for hydrogen production is approximately 27 times higher than that of hydrogen production through gasification in the pyrolysis state. Moreover, both the carbon conversion rate and hydrogenation rate in the supercritical water system are significantly higher compared to those in the pyrolysis system. Furthermore, we found that the energy in the supercritical system is approximately half that of the pyrolysis system, favoring the ring-opening reactions of phenol and promoting hydrogen production. In contrast, the pyrolysis system produces a greater quantity of aromatic compounds, leading to tar formation and having significant implications for both the reaction process and reactor design. Additionally, we conducted comparative experiments between the supercritical water gasification process and the pyrolysis process to explore the advantages of supercritical water gasification.

Molecular Modeling of Supercritical Processes and the Lattice—Gas Model

The existing possibilities for modeling the kinetics of supercritical processes at the molecular level are considered from the point of view that the Second Law of thermodynamics must be fulfilled. The only approach that ensures the fulfillment of the Second Law of thermodynamics is the molecular theory based on the discrete–continuous lattice gas model. Expressions for the rates of the elementary stage on its basis give a self-consistent description of the equilibrium states of the mixtures under consideration. The common usage today of ideal kinetic models in SC processes in modeling industrial chemistry contradicts the non-ideal equation of states. The used molecular theory is the theory of absolute reaction rates for non-ideal reaction systems, which takes into account intermolecular interactions that change the effective activation energies of elementary stages. This allows the theory to describe the rates of elementary stages of chemical transformations and molecular transport at arbitrary temperatures and reagent densities in different phases. The application of this theory in a wide range of state parameters (pressure and temperature) is considered when calculating the rates of elementary bimolecular reactions and dissipative coefficients under supercritical conditions. Generalized dependencies are calculated within the framework of the law of the corresponding states for the coefficients of compressibility, shear viscosity, and thermal conductivity of pure substances, and for the coefficients of compressibility, self- and mutual diffusion, and shear viscosity of binary mixtures. The effect of density and temperature on the rates of elementary stages under supercritical conditions has been demonstrated for a reaction’s effective energies of activation, diffusion and share viscosity coefficients, and equilibrium constants of adsorption. Differences between models with effective parameters and the prospects for developing them by allowing for differences in size and contributions from the vibrational motions of components are described.

Technoeconomic analysis of supercritical fluid extraction process for recycling rare earth elements from neodymium iron boron magnets and fluorescent lamp phosphors

This study offers a comprehensive and rigorous analysis of the technoeconomics of supercritical fluid extraction (SCFE) technology as applied to the recovery of rare earth elements (REEs) from end-of-life neodymium iron boron magnets and fluorescent lamp phosphors. Drawing on an array of data sources including laboratory results, literature data, scaling models, scenario analysis, and sensitivity analysis, this study conducts a sound economic analysis of the SCFE process at an industrial scale. The study renders a detailed estimation of the costs and revenues associated with the process and identifies the primary factors that impact its profitability. The findings demonstrate that the SCFE of REEs from these feedstocks can be economically viable under certain circumstances, with the efficiency of extracting terbium, dysprosium, and neodymium and the price of their respective oxides emerging as key drivers of profitability. By providing valuable insights into the feasibility of the SCFE process for REEs recovery, this study informs future research and development activities in the field.

Quenched weighted moments for a branching process with immigration in a random environment

For a supercritical branching process, with immigration in an independent and identically distributed random environment . Let W be the limit of the submartingale , where is the usually used normalization sequence. The necessary and sufficient condition for the existence of quenched weighted moments of W of the form is obtained in this article, where and l is a positive function slowly varying at . The same conclusion holds also for the maximum variable .

Synthesis and characterization of polyvalent high-performance synthetic base oil for drilling operations in recalcitrant and unconventional oil and gas reservoirs

Synthetic ester fluid is one of the most widely recommended drilling fluids for unconventional and recalcitrant reservoirs owing to its numerous technical advantages, high sustainability, non-toxic and inherently biodegradable. However, there are serious concerns about its thermal and hydrolytic stability at high temperatures and pressures (HTHP) as well as its viscosity and flow characteristics in low temperature climates such as deep-water wells. Hence, its inability to maintain stable borehole and flat rheology characteristics may invariably threaten its application under these aforementioned scenarios.In this study, a high-performance ternary mixture of synthetic ethyl esters of plants oil (SEEP mixture) fluid was synthesized by a non-catalyzed supercritical ethanol transesterification process using coconut, castor seed and linseed oil as starting materials. The nature, chemistry and fluid particle interactions of the individual components that make up the synthetic ester fluid were critically studied. The process equipment consists of a continuous flow reactor equipped with a PID controlled furnace as heat source to the reactor and a high- pressure transducer. The conversion efficiency was monitored by an Agilent 5500a FTIR machine with attenuated total reflectance (ATR) system while a GC-EIMSD system was used for fatty acid ester compositional analysis. The oil was extracted by a Soxhlet apparatus mechanism. The extracted Plant oil and the synthetic esters were characterized under standard recommended laboratory procedures by API, ASTM and the European Union (EN) standard protocols. Also, fluid's toxicity and biodegradability tests were conducted according to OECD recommended practices. The results were compared with existing synthetic hydrocarbon fluids (SHFs) for HTHP and deep-water wells.The conversion efficiency of the non-catalyzed transesterification process was 96.50%. The amount of oil yield from the plant oil after Soxhlet extraction is commendable. Hence, synthetic ester fluid raw materials are readily available in large quantities and in a sustainable manner. The GC-MS analysis shows that the coconut oil contains 92% saturated fatty acid. Whereas, the castor seed oil contains 98.31% unsaturated fatty acid with 89.75% of mono-unsaturated ricin-oleic acid (D-12-hydroxyoctadec-cis-9-enoic acid). The linseed oil has high content of linolenic acid with 89.60% unsaturated fatty acid. The designed fluid has excellent lubricity characteristics, extremely low cloud and pour point temperatures, higher oxidative stability, low peroxide value, lower copper strip corrosion value and lower kinematic viscosity and density variations with temperatures which signals flat rheology when used to form a synthetic based mud. Also, its flash point and auto-ignition temperatures are high and thus forestall possible fire hazard in high temperature zones. Finally, the fluid is non-toxic and inherently biodegradable.

Photocatalytic Systems Based on ZnO Produced by Supercritical Antisolvent for Ceftriaxone Degradation

Emerging contaminants are a significant issue in the environment. Photocatalysis is proposed as a solution for the degradation of pollutants contained in wastewater. In this work, ZnO-based photocatalysts have been produced and tested for the photocatalytic degradation of an antibiotic; specifically, ceftriaxone has been used as a model contaminant. Moreover, there is particular interest in combining small-size ZnO particles and β-cyclodextrin (β-CD), creating a hybrid photocatalyst. Zinc acetate (ZnAc) (subsequently calcinated into ZnO) and β-CD particles with a mean diameter of 0.086 and 0.38 µm, respectively, were obtained using the supercritical antisolvent process (SAS). The produced photocatalysts include combinations of commercial and micronized particles of ZnO and β-CD and commercial and micronized ZnO. All the samples were characterized through UV–Vis diffuse reflectance spectroscopy (DRS), and the band gap values were calculated. Raman and FT-IR measurements confirmed the presence of ZnO and the existence of functional groups due to the β-cyclodextrin and ZnO combination in the hybrid photocatalysts. Wide-angle X-ray diffraction patterns proved that wurtzite is the main crystalline phase for all hybrid photocatalytic systems. In the photocatalytic degradation tests, it was observed that all the photocatalytic systems exhibited 100% removal efficiency within a few minutes. However, the commercial ZnO/micronized β-CD hybrid system is the photocatalyst that shows the best performance; in fact, when using this hybrid system, ceftriaxone was entirely degraded in 1 min.

Effect of heat transfer on the pressurization, extraction, and depressurization stages of a supercritical CO2 extraction process. 1. Development and validation of the heat transfer model

We modeled and simulated the heat and mass transfer in the depressurization, pressurization, and extraction stages of a supercritical CO2 extraction process. Parameters of a Nusselt correlation for convective wall-to-fluid heat transfer coefficient were best fitted to experimental temperatures during the depressurization of vessels packed with different materials. Heat transfer in the pressurization and extraction stages was simulated predictively using this correlation and compared with literature laboratory-scale, pressurization, and extraction data. In depressurization, simulated temperature, pressure, and vented mass flow profiles agreed reasonably well with experimental values, as the calculated Mean Absolute Percent Error (MAPE) was 1.8% for the temperature. For pressurization, simulated values of final temperatures and pressures fell within a standard deviation of experimental data, estimating a MAPE of 3.9% for temperature and 5.2% for pressure. In the extraction stage, including radial and axial temperature gradients in the mass transfer model reduced the error (about 2%) of simulated cumulative extraction curves against experimental values compared to those obtained when neglecting radial variations in temperature. These results are significant because they prove that heat transfer phenomena may impact industrial more considerably than laboratory-scale processes.

Key factors for regulation of cell morphology in supercritical CO2 direct rapid depressurization foaming silicone rubber process

Silicone rubber foam was prepared by direct rapid depressurization foaming process using supercritical CO2 as foaming agent. It was found that under high temperature and pressure, the dissolution of CO2 and the vulcanization reaction occurred simultaneously. The vulcanization degree range with good cell morphology was between 19.8% and 48.2%. When the saturation pressure exceeded 16 MPa, the cell morphology did not depend on foaming pressure. When the temperature was increased from 110 °C to 140 °C, the degree of vulcanization increased from 1.8% to 60.5%, and the cell size ranged from 13.9 µm to 646.4 µm, with an order of magnitude variation in cell density. This study identified the key control factors for supercritical CO2 relief foaming of silicone rubber and provided a fast and efficient preparation method, as well as theoretical guidance, for obtaining lightweight microporous silicone rubber foams.

Solubility of famotidine in supercritical carbon dioxide: Experimental measurement and thermodynamic modeling

In the current study, the solubility of famotidine (FAM) in supercritical carbon dioxide (scCO₂) was experimentally determined for the first time. The FAM solubility in scCO₂, expressed as mole fraction, at different temperatures (308 − 338 K) and pressures (12 − 30 MPa) was found to be in the range of 1.40 × 10−6 to 1.11 × 10−4. Due to the low solubility of FAM in scCO₂, the gas anti-solvent and supercritical anti-solvent processes can be a good option to generate the nano/micro size particles of this drug. The experimental solubility data were correlated by the density-based models of Bartle et al., Méndez-Santiago and Teja (MST), Jouyban et al. and Hozhabr et al., by the non-cubic equation of state PC-SAFT, and by the two versions of the Estévez et al. model (ECM-PR and ECM-RK). According to the modeling results, the Estévez et al. model showed the highest accuracy with AARD values of 9.92 (ECM-PR) and 10.70 (ECM-RK). The empirical models also yielded satisfactory outcomes to the correlation of the solubility of FAM in scCO₂.

Incorporation of Poly(TFEMA) in Perovskite Thin Films Using a Supercritical Fluid.

A new process is reported for the incorporation of a fluoropolymer into a solid perovskite film. Poly(trifluoroethyl methacrylate) [CH2C(CH3)(CO2CH2CF3)]n was delivered to methylammonium lead iodide (CH3NH3PbI3) perovskite films by crystallizing the film in supercritical carbon dioxide/ethanol containing the dissolved fluoropolymer. The surface was characterized before and after fluoropolymer exposure using scanning electron microscopy, Raman spectroscopy, and contact angle measurements. The results indicate that the fluoropolymer was incorporated into the perovskite film during the supercritical fluid crystallization process. The incorporation of a hydrophobic fluoropolymer into perovskite has the potential to improve resistance to environmental degradation.

Asphaltene Remediation and Improved Oil Recovery by Advanced Solvent Deasphalting Technology.

Resin molecules play a crucial role in the stability of colloidal asphaltene particles in petroleum reservoirs. De-stabilization of the asphaltene/resin interaction due to changes in thermodynamic parameters can cause asphaltene precipitation, thus leading to petroleum field problems such as decreased in situ permeability, as well as severe plugging problems in production facilities. One remedial technology used in the oil industry involves developing synthetic resins with enhanced chemical potential to increase the stability of asphaltene in the oil phase. However, accurately predicting what synthetic resin structures are compatible with asphaltenes in this context can be difficult and ineffective. Here, we introduce a method that enhances the stability of colloidal asphaltene in petroleum fluid by increasing the concentrations of natural-state oil resins and increases reservoir oil recovery by increasing the oil's aromatic power solvency. The stability of colloidal asphaltene and improvements in oil reservoir recovery were investigated by using an oil prefractionation process and a solvent deasphalting technology based on the residuum oil supercritical extraction process to develop three types of deasphalted oils derived from Kuwait Marrat oil. Using these methods, we found that resin concentration by volume in Marrat oil increased with the removal of more oil fractions. Asphaltene stability in the oil phase was strongly influenced by resin concentration. The deasphalted oils' aromatic power solvency increased the oil reservoir permeability by twofold. No formation damage was observed for all DAO products in core flooding tests.

Application of Box-Behnken Design in microparticle production of p-Toluenesulfonamide through the rapid expansion of supercritical solutions process

p-Toluenesulfonamide (PTS) is a developing small molecular anticancer agent with good lipophilic ability. Microparticle production of PTS is an approach to enhance the dissolution profile and explore the potential for novel drug delivery system design. This study employed the rapid expansion of supercritical solutions (RESS) process to produce microparticles of PTS using supercritical carbon dioxide as the solvent. To meet the concept of quality by design in the pharmaceutical industry, the effects of process parameters in RESS operation were investigated and optimized by a design of experiments approach, the Box-Behnken Design (BBD). The design space for microparticle production of PTS was shown, and the analysis of variance (ANOVA) confirmed the significance of process parameters. According to the BBD study, at the optimal operating condition, PTS microparticles were successfully generated from the unprocessed mean size of 240.3 μm to 1.3 μm. The solid-state property of the unprocessed and micronized PTS powders was compared and confirmed consistent through the PXRD, DSC, and FTIR analysis. Finally, the dissolution profiles of PTS before and after the RESS process were determined, and the dissolution rate of RESS-produced PTS microparticles was enhanced 1500 times compared with the unprocessed PTS.

Assessment of machine learning algorithms for predicting autoignition and ignition delay time in microscale supercritical water oxidation process

With recent advancements in space technology, there is a need to develop technologies to ensure a sustainable environment for human survival. Among these, treatment of human and organic waste aboard manned space missions is a challenging task for which supercritical water oxidation using hydrothermal flames has been proposed as a possible solution. The critical step in readily adopting this technology from established ground-based setups is scaling the process to microscale. In addition to the challenge of physical realization of the microreactors at these high pressure and temperature (P>22MPa,T>350C) conditions, the need to explicitly analyze the process dynamics at microscale is inevitable owed to the size of the reactors under consideration, the physics being significantly different from meso/mini scale systems. One of the primary objectives is to identify the operating physical parameters for which formation of hydrothermal flames can be obtained. Before proceeding with an expensive computational or experimental approach to determine the exact ignition map, an initial estimate based on physical arguments can help in providing insights into the process. We address this problem using homogeneous ignition calculations to develop machine learning models to predict autoignition as well as ignition delay time. The ingenuity of the work lies in defining autoignition criteria in relation to flow time scales expected at microscale. Various classification models were trained and tested for predicting autoignition and regression models were demonstrated to predict the ignition delay time. While predicting autoignition is a straightforward process, a two-step approach is proposed for ignition delay time. Finally, how machine learning can be used more explicitly, particularly for understanding and designing efficient microreactors, is presented which highlights that machine learning approach is not merely restricted to prediction but can also have real implications on improving the process as a whole.

Experimental and Theoretical Investigation of Supercritical Processes: Kinetics of Phase Transitions in Binary “2-Propanol—CO2” System

Studies of phase transition kinetics are important for such supercritical processes as supercritical drying, adsorption, micronization, etc. In supercritical technologies, “organic solvent—CO2” systems are often formed, the properties of which strongly depend on the system parameters. In this article, the kinetic curves of phase transitions in the “2-propanol—CO2” system were investigated experimentally and theoretically. Experimental studies were carried out in a 250 mL high-pressure apparatus at temperatures of 313 and 333 K and pressures of 6.3 and 7.8 MPa with and without the addition of alginate porous gel. Theoretical studies were carried out using the mass transfer equation, the Peng-Robinson equation of state, and the Van der Waals mixing rules, with Python being used for the calculations. The mass transfer coefficients and equilibrium concentrations of CO2 in the liquid phase were determined using the BFGS optimization method.