Operating limits and features of direct air capture on K2CO3/ZrO2 composite sorbent

Potassium carbonate-based sorbents are prospective materials for direct air capture (DAC). In the present study, we examined and revealed the influence of the temperature swing adsorption (TSA) cycle conditions on the CO₂ sorption properties of a novel aerogel-based K₂CO₃/ZrO₂ sorbent in a DAC process. It was shown that the humidity and temperature drastically affect the sorption dynamic and sorption capacity of the sorbent. When a temperature at the sorption stage was 29 ℃ and a water vapor pressure in the feed air was 5.2 mbar (1 bar = 10⁵ Pa), the composite material demonstrated a stable CO₂ sorption capacity of 3.4% (mass). An increase in sorption temperature leads to a continuous decrease in the CO₂ absorption capacity reaching a value of 0.7% (mass) at T = 80 ℃. The material showed the retention of a stable CO₂ sorption capacity for many cycles at each temperature in the range. Increasing P_H2O in the inlet air from 5.2 to 6.8 mbar leads to instability of CO₂ sorption capacity which decreases in the course of 3 consecutive TSA cycles from 1.7% to 0.8% (mass) at T = 29 ℃. A further increase in air humidity only facilitates the deterioration of the CO₂ sorption capacity of the material. A possible explanation for this phenomenon could be the filling of the porous system of the sorbent with solid reaction products and an aqueous solution of potassium salts, which leads to a significant slowdown in the CO₂ diffusion in the composite sorbent grain. To investigate the regeneration step of the TSA cycle in situ, the macro ATR-FTIR (attenuated total reflection Fourier-transform infrared) spectroscopic imaging was applied for the first time. It was shown that the migration of carbonate-containing species over the surface of sorbent occurs during the thermal regeneration stage of the TSA cycle. The movement of the active component in the porous matrix of the sorbent can affect the sorption characteristics of the composite material. The revealed features make it possible to formulate the requirements and limitations that need to be taken into account for the practical implementation of the DAC process using the K₂CO₃/ZrO₂ composite sorbent.     

Method for Calculating Cartesian Coordinates of Operator’s Arm Joints for Anthropomorphic Manipulator Master-Slave Control Using Exoskeleton

The main goal of the work is to increase the accuracy of the anthropomorphic manipulator master-slave teleoperation by calculating the coordinates of the operator’s arm joints. The master device is an exoskeleton worn on the operator’s arm, and the slave device is an anthropomorphic manipulator. A method based on the solution of the forward kinematics and empirical simplifications is proposed in this paper. The position of the nodal points of the exoskeleton was calculated by solving the direct kinematics problem. The coordinates of the operator’s arm joints, which were rigidly connected to the exoskeleton nodal points, were calculated geometrically. For the operator’s arm elbow joint, which was flexibly connected to the exoskeleton, an empirical relation was proposed. It simplified the calculation of the elbow joint position. The experiment showed a decrease in the mismatch between the operator’s arm angles and the manipulator joint angles from 20.7° to 2.9°. The proposed method increases the convenience of the master-slave control.     

Continuous production of soybean biodiesel with compressed ethanol in a microtube reactor using carbon dioxide as co-solvent

This work investigates the production of fatty acid ethyl esters (FAEE) from the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process using carbon dioxide as co-solvent. The experiments were performed in a microtube reactor in the temperature range of 523 K to 598 K, from 10 MPa to 20 MPa, oil to ethanol molar ratio from 1:20 to 1:40, and co-solvent to substrates mass ratio from 0.05:1 to 0.2:1. Results showed that ethyl esters yield obtained increased with increasing addition of carbon dioxide to the system. Considerable reaction yields were achieved at 598 K, 20 MPa, oil to ethanol molar ratio of 1:20 and using a CO₂ to substrate mass ratio of 0.2:1.     

Comparative study using different infrared zones of the solventless activation of organic reactions

In this work, the results of a study comparing the use of irradiation from different regions of the infrared spectrum for the promotion of several organic reactions, are presented and discussed. This use of eco-conditions provides a green approach to chemical synthesis. A set of ten different organic reactions were evaluated, including the Knoevenagel, Hantzsch, Biginelli and Meldrum reactions. It is important to highlight the use of a commercial device that produces infrared irradiation in the near infrared region and its distribution by convection providing heating uniformity, significantly reducing reaction times, achieving good yields and proceeding in the absence of solvent. It is also worth noting that a variety of different reactions may be performed at the same time. Finally, the products obtained were identified using TLC, together with corresponding MS-data, complementarily in comparison of NMR (1)H and (13)C data with literature information.     

In vitro release profiles of β-carotene encapsulated in PHBV by means of supercritical carbon dioxide micronization technique

The main objective of this work was to investigate the characteristics of the in vitro release of β-carotene encapsulated in poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) using the solution enhanced dispersion by supercritical fluids (SEDS) technique. The release tests were performed using encapsulated complex with solute loading from 2.24 to 27.5% and encapsulation efficiency from 7.75 to 55.54%. The release profile assays were performed in ethyl acetate, n-hexane and anhydrous ethanol, and monitored by UV-vis spectrophotometer concentration analysis. Results indicated higher initial release rates in ethyl acetate and in n-hexane, with cumulative release percentage varying from 31.50 to 69.58% and from 42.08 to 55.96%, respectively. For anhydrous ethanol the maximum concentration was reached at 180 min, 300 min and 10 days, depending on the initial amount of β-carotene, with cumulative release ranging from 45.27 to 88.22%. In general, the β-carotene release can be controlled by the organic solvent used and by the initial amount of solute encapsulated, aspects that help the selection of the conditions to achieve the desired release profiles for a specific application.     

Phase Equilibrium Measurements of Sacha Inchi Oil (<Emphasis Type="Italic">Plukenetia volubilis</Emphasis>) and CO<Subscript>2</Subscript> at High Pressures

New data on phase equilibria for Sacha inchi seed oil in carbon dioxide have been measured using a variable volume cell phase equilibria system at temperatures of 303, 313 and 323 K and at pressures ranging from 4.3 to 27.7 MPa. The CO₂ mole fraction varied from 0.7488 to 0.9997. At the studied concentrations, phase transitions of vapor-liquid, liquid-liquid-vapor and liquid-liquid were observed. Sacha inchi oil contains 47% of omega-3 fatty acids, with a ratio of 0.76:1 for omega-6:omega-3, which is good for human health. The Peng-Robinson equation of state was used to describe the experimental data. A qualitative agreement was obtained between experimental and calculated data for the binary system CO₂ and Sacha inchi seed oil.     

Effective harvesting,detection, and conversion of IR radiation due to quantum dots with built-in charge

We analyze the effect of doping on photoelectron kinetics in quantum dot [QD] structures and find two strong effects of the built-in-dot charge. First, the built-in-dot charge enhances the infrared [IR] transitions in QD structures. This effect significantly increases electron coupling to IR radiation and improves harvesting of the IR power in QD solar cells. Second, the built-in charge creates potential barriers around dots, and these barriers strongly suppress capture processes for photocarriers of the same sign as the built-in-dot charge. The second effect exponentially increases the photoelectron lifetime in unipolar devices, such as IR photodetectors. In bipolar devices, such as solar cells, the solar radiation creates the built-in-dot charge that equates the electron and hole capture rates. By providing additional charge to QDs, the appropriate doping can significantly suppress the capture and recombination processes via QDs. These improvements of IR absorption and photocarrier kinetics radically increase the responsivity of IR photodetectors and photovoltaic efficiency of QD solar cells.     

New Refractories Developed by the Ukrainian Research Institute of Refractories Named after A.S. Berezhnoy

The article gives an introduction to the Ukrainian Research Institute of Refractories and especially its R D and refractory products for the industries of iron and steel,nonferrous,glass and chemistry etc.     

Phase and Rheological Behavior of Cetyldimethylbenzylammonium Salicylate (CDBAS) and Water

The temperature–composition phase diagram in the diluted region of the cationic surfactant cetyldimethylbenzylammonium salicylate/water system was studied with a battery of techniques. The Krafft temperature (T _k = 33 ± 1 °C) was measured by differential scanning calorimetry, polarizing microscopy, conductimetry, viscosimetry, and rheometry. The critical vesicle concentration (cvc, ~0.002 wt%) and a vesicle–micellar transition (cvm, ~0.005 wt%) was detected at a temperature of 35 °C. Below T _k and concentrations ≤2 wt%, a transparent solution is formed (I). Above 2–8.5 wt%, a lamellar (L₁) phase forms. At higher concentrations and up to 12 wt%, a second lamellar phase (L₂) is detected. From 12.4 to 15.5 wt%, an emulsion phase (E) is formed. Rheological dynamic measurements for the I phase indicate that the system exhibits a predominantly viscous behavior (G′ < G″) for concentrations lower than the overlap or entanglement concentration (C _e, ~0.75 wt%). At higher concentrations, wormlike micelles form and the elastic behavior predominates (G′ > G″). The elastic (G′) modulus collapses in a concentration–time master curve in the whole reduced frequencies range ωτ _c examined, whereas the viscous modulus (G″) collapses only at reduced frequencies lower than 0.1. Reduced stress plotted as a function of the reduced shear rate yields a good superposition of the curves at the different concentrations up to the onset of the non-linear behavior.