•[thepAm][BF4] was molecularly designed, synthesized and characterized.•[thepAm][BF4] showed high CO2 solubility and melting temperature at elevated pressures.•An absorption-desorption procedure was proposed to test the stability of cyclic operation.•A pressure swing absorption procedure was proposed to implement CO2 capture.•Solid state of ionic liquid as an absorbent may open a new way for CO2 capture.Based on the analyses of the interaction energy with CO2, COSMO calculation and melting temperature, a quaternary ammonium salt, tetra-n-heptyl ammonium tetrafluoroborate ([thepAm][BF4]), was synthesized using [thepAm][Br] and NaBF4 as the raw materials. The as-synthesized [thepAm][BF4] was characterized by FTIR and NMR. The solid–liquid–gas (SLG) phase equilibrium line of the [thepAm][BF4]–CO2 system was determined by high pressure differential scanning calorimeter, indicating it was more stable than [thepAm][Br] because of higher melting temperatures of [thepAm][BF4] in pressurized CO2. The solubility data of CO2 in [thepAm][BF4] at 313.2, 323.2 and 333.2 K up to 15 MPa were measured by using the high-pressure quartz spring approach. The Peng-Robinson equation of state with the van der Waals-1 mixing rules was employed to calculate the solubility and SLG phase equilibrium data. Results showed high molar fractions of CO2 in [thepAm][BF4] at high pressures (e.g., molar fraction of 0.88 at 10.0 MPa and 313.2 K). A cyclic absorption–desorption procedure and a pressure swing absorption process were proposed and tested for CO2 capture/separation from the H2, CO and CO2 mixture by using [thepAm][BF4] as the absorbent, verifying its selective capture of CO2 over H2 and CO. The study may open a new way for CO2 capture.Download high-res image (114KB)Download full-size image

•A SSFL process was proposed to prepare two kinds of PEA-loaded powder flavors.•A quartz spring method was proposed to determine the binary PEA and CO2 adsorption.•Silica showed higher loading and better release of PEA compared with AC.•Precipitation and adsorption contributed to the high loading of PEA in silica.A solute-saturated supercritical fluid loading (SSFL) process was proposed to load 2-phenylethyl alcohol (PEA) in silica and activated carbon (AC). The adsorption and loading amounts of PEA in carries were investigated at different temperatures (50.0–60.0 °C) and pressures (8.0–14.0 MPa) by a column sampling method. By using a high-pressure quartz spring method, the adsorption amounts of the binary PEA and CO2 in silica were determined. The retention of PEA in the SSFL powder flavors was evaluated by a nitrogen-purging method. Results revealed that, compared with AC, silica had high loading of PEA (maximum 0.484 g/g) and showed better results in PEA preservation from loss at room temperature and control release at higher temperature; PEA suppressed the adsorption of CO2 at relatively high pressure. Discussion indicated that precipitation and adsorption contributed to the high loading of PEA in silica, while adsorption mainly contributed to that in AC.Download high-res image (143KB)Download full-size image

•[thepAm][Br] and [VBTMA][Cl] were successfully bonded to MCM-41.•The grafted MCM-41 showed high CO2 adsorption at high pressure.•The grafted MCM-41 acted as a selective separation agent to CO2 over CO.•The adsorption-desorption indicated stability of the hybrid adsorbent.•The high pressure adsorption showed complete separation of CO2 from a mixture.In order to improve CO2 absorption capacity and selectivity in ionic liquids (ILs), grafting two quaternary ammonium ILs, (vinyl benzyl) trimethylammonium chloride ([VBTMA][Cl]) and tetra-n-heptyl ammonium bromide ([thepAm][Br]), on mesoporous MCM-41 was studied in this work. Results from the characterization of FT-IR, TGA, BET, TEM and elemental analysis showed that the ILs were successfully grafted on MCM-41. Gas excess loading (from 0.1 MPa to 8.0 MPa) was studied by using the high-pressure quartz spring method. Grafting the ILs on the supports caused loss in mesoporosity, resulting in slight decrease in CO2 adsorption capacity, but enhanced the CO2/CO selectivity. Meanwhile, the adsorbents grafted with [VBTMA][Cl] performed better in terms of excess CO2 loading (3.90 mmol/g) and CO2/CO selectivity (95) than those grafted with [thepAm][Br] corresponding to 3.65 mmol/g for CO2 loading and 21 for CO2/CO at 30.0 °C and 5.0 MPa. An adsorption–desorption (9.0 MPa) procedure at 30.0 °C was implemented to examine the selective CO2 capture from the H2, CO and CO2 mixture by using the [VBTMA][Cl] grafted adsorbent and showed almost complete separation of CO2 from the mixture.Download high-res image (85KB)Download full-size image

•γ-alumina with pore volume of 5.4 cm3/g and pore size of 37.8 nm was prepared with cheap inorganic salts.•The preparation was highlighted with the control of the solution pH and supercritical drying.•The Fe-based catalyst in γ-alumina showed phenol hydroxylation conversion of 53.4% and DHBs selectivity of 96.2%.•The high pore volume takes effect to promote the effective hydroxylation of phenol.Alumina was synthesized from Al(NO3)3, AlCl3 and Al3(SO4)2 with NaOH, and from NaAlO2 with HNO3 by addition of acidic solution to alkaline solution with a syringe pump. The as-produced Al2O3 precursors were supercritically dried and calcined at 500 °C to obtain mesoporous γ-alumina material. Results showed that all the inorganic aluminum salts could be used to synthesize high pore volume γ-alumina by controlling the precursor addition rate at room temperature and supercritical CO2 drying. However, the γ-alumina with the largest pore volume (5.4 cm3/g), BET surface area (423.7 m2/g) and pore size (37.8 nm) was obtained using Al(NO3)3 and NaOH. This γ-alumina was further used as a support for Fe-based catalyst with hydrogen peroxide to produce hydroquinone and catechol in the phenol hydroxylation reaction in 30 min at 80 °C. The conversion of phenol was 53.4% whereas the selectivity to dihydroxybenzenes-DHBs (hydroquinone-HQ and catechol-CAT) was as high as 96.2%, revealing that the larger pore volume takes effect in the γ-alumina as support for the Fe-based catalyst in the hydroxylation reaction, and that the γ-alumina may be a good candidate as the support for other important catalysts such as those used in the petroleum refining industry.

•Various phase equilibria of the [thepAm][Br]–CO2 system was measured and modeled.•[thepAm][Br] shows the highest CO2 solubility among the reported after around 10 MPa.•A D(c) model was proposed for CO2 absorption in [thepAm][Br] at high pressure.•The diffusivity of CO2 in [thepAm][Br] is very pressure dependent.The solid–liquid–gas equilibrium data of the tetra-n-heptyl ammonium bromide ([thepAm][Br])–CO2 system, and then the solubility and absorption kinetic data of CO2 in different phases of [thepAm][Br] were measured by a high pressure quartz spring method. Results showed high molar fractions of CO2 in solid [thepAm][Br] (0.921 at 15.0 MPa and 313.2 K; 0.567 at 5.0 MPa and 313.2 K) which were even higher than those in liquid [thepAm][Br] at same pressures and those in other ionic liquids (ILs) reported in the literature at relatively high pressures. The study also revealed that CO2 absorption rate was very pressure dependent. The Peng–Robinson equation of state (PR-EoS) with the van der Waals one-fluid mixing rules and the NRTL model were employed to calculate the phase equilibrium data by looking the solid [thepAm][Br] as a special liquid. A 1-D diffusion model with a concentration dependent diffusion coefficient equation combined with the NRTL model was developed to calculate the absorption kinetic data of CO2 in [thepAm][Br], suggesting that the diffusion coefficient was not a constant at high pressures.

•A pressurized carbonation sol–gel process was proposed.•The pH at 5.2–6.0 easily stabilized by pressure was a key factor.•Silica with a pore volume of 5.4 cm3/g was achieved from sodium silicate.•The pore volume played a predominant role on the adsorption and extinction effect.A pressurized carbonation sol–gel (PCSG) process coupled with supercritical drying was proposed through the reaction of sodium silicate aqueous solution with CO2 to synthesize silica with large pore volume. The silica was further applied as a flatting agent and an adsorbent, and the effect of pore volume on the extinction performance and adsorption of l-menthol were examined separately. Results showed that the pH at 5.2–6.0 and ambient temperature favored preparing large pore volume silica, and the pH was easy to attain with the pressure larger than about 4 MPa in the PCSG process. Silica sample with pore volume as large as 5.4 cm3/g was prepared and an extinction index of 65.5% and adsorption of 2.52 g l-menthol/g silica were achieved with the sample. Larger pore volume silica exhibited better extinction performance and larger adsorption capacity of l-menthol. The PCSG process is a simple (one step and easy to stabilize pH), intensified and sustainable approach compared with the conventional sol–gel process for preparing large pore volume silica.

In this study, a CO2-expanded ethanol–water solution system was applied for the solid–liquid–gas carbonation of Ca(OH)2 to CaCO3. The system revealed, for the first time, instantaneous (within 1 min) conversions of Ca(OH)2 (95.1–100.0%) with the volume ratios of ethanol between 10% and 80%, indicating that both the water content and the expansion of the system take effect in the carbonation process. The instantaneous carbonation with 80% ethanol ratio led to production of 12.8% aragonite polymorph. Further examination of this carbonation case under different reaction times found that, interestingly and importantly, pure calcite phase was stabilized within a short time (210 min) as compared to those reported in the literature; however, in this period, the system exhibited chameleonic phase transformation between calcite, aragonite, and vaterite, normal to abnormal and vice versa.

•CO2 expanded carbonation technique used to synthesize mesoporous alumina.•Alumina particles were flower-like and honey-comb-like due to different volume expansions.•Efficient catalytic oxidation of cyclohexanone to ɛ-caprolactone.•Hydrolysis of ɛ-caprolactone could be avoided.A CO2 expanded carbonation technique is proposed for direct synthesis of alumina powders that does not require structure directing substances or templates. Mesoporous amorphous flower-like alumina was synthesized at relatively low volume expansions (lower ethanol to water volume ratio), whereas mesoporous crystalline honey-comb-like alumina was synthesized at high volume expansions. The alumina powders exhibited high surface area and pore size with small crystallite sizes. The alumina structures were stable from 400 to 800 °C. Experimental tests showed that the alumina powders could catalytically convert cyclohexanone to ɛ-caprolactone efficiently. The use of the calcined catalysts (at 400 and 800 °C; flower-like alumina) at equal ethanol to water volume ratio avoids the usual and inevitable hydrolysis of ɛ-caprolactone to ɛ-hydroxyhexanoic acid. The catalyst was recyclable and stable for up to five reaction cycles.

•A high-pressure PLM approach was proposed and established.•Melt crystallization behaviors of two solutes in CO2 were studied.•High pressure CO2 accelerated the crystallization rates of the two solutes.•CO2 did not evidently affect the nucleation or growth patterns of the two solutes.•The crystallization behaviors of the two solutes were different from those of polymers in CO2.A high-pressure polar light microscopy approach was proposed and developed to study the melt crystallization behaviors of myristic acid and ibuprofen respectively in CO2 at different pressures and crystallization temperatures. The crystallization kinetics was analyzed by the Avrami equation. Results revealed that the crystallization rates of both myristic acid and ibuprofen increased with the CO2 pressure, while the crystallization activation energy of ibuprofen decreased (more negative) with the increase of CO2 pressure. On the other hand, the crystallization rate of ibuprofen decreased with the increase of the crystallization temperature at fixed pressure. However, the presence of CO2 did not change the nucleation or growth patterns of myristic acid and ibuprofen, as indicated by the analyzed results of the Avrami equation. The X-ray diffraction (XRD) analysis further confirmed that CO2 had no influence on the crystal form of myristic acid or ibuprofen. This study revealed that the crystallization behaviors of myristic acid and ibuprofen were evidently different from those of polymers in CO2 reported in the literature.

A high-pressure gravimetric apparatus using a quartz spring for measuring solubility and diffusivity of CO2 in ionic liquids (ILs) was established for the first time. The time-dependent amounts of CO2 were recorded with a telescopic cathetometer and analyzed by using a one-dimensional diffusion model to obtain diffusion coefficients of CO2 in two ILs, namely, 1-n-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim] [BF4]) at pressures up to 10 MPa. Solubility data of CO2 in the two ILs up to 20 MPa were also obtained from its equilibrium masses and compared with those reported in the literature. The Peng–Robinson equation of state with the van der Waals one-fluid mixing rules was employed to correlate the experimental solubility data, revealing satisfactory calculation results. The measured diffusion coefficients of CO2 in [bmim][PF6] and [bmim][BF4] separately increase from 3.550 × 10–10 to 6.064 × 10–10 m2/s and from 7.184 × 10–10 to 9.880 × 10–10 m2/s following the pressure increase from 2.0 to 10.0 MPa at 323.2 K, while those at 5.0 MPa and different temperatures follow the Arrhenius equation, providing the diffusion activation energies of 25.53 and 20.30 kJ/mol for the [bmim][PF6]–CO2 and [bmim][BF4]–CO2 systems, respectively.

The effect of temperature, pressure, time, solid ionic liquid (SIL) mass (here, the SIL used is tetra-n-heptyl-ammonium bromide, abbreviated as THepAmBr), reuse of THepAmBr, type of SIL, and additives on the solid–gas (Ca(OH)2–CO2) carbonation system was investigated. Results showed that conversion increased as the temperature increased from 25.0 °C up to 50.0 °C and then decreased thereafter; but increased consistently with increasing pressure. Similarly, conversion increased as the mass of THepAmBr increased, leading to complete conversion at a THepAmBr/Ca(OH)2 mass ratio of 0.1:1 with the production of rhombohedral calcites. Stability tests revealed that THepAmBr was active and stable. The effect of BmimBr and BmimCl indicated that they gave conversions of >96%. Furthermore, studies on polymorphic control to aragonite gave interesting results: 30.2% aragonite was synthesized with MgCl2 and 54.7% with PEG6000. Moreover, time-dependent conversion showed that the reaction mechanism for the system was self-catalytic. Consequently, the reaction rate equation that was derived described the experimental conversion satisfactorily.

Adsorption of 2-phenylethyl alcohol (PEA) from supercritical CO2 onto silica aerogel was investigated. A monolayer to multilayer adsorption isotherm was observed, measured at 15.0 MPa and 323.2 K, from the PEA-unsaturated to PEA-saturated supercritical CO2, indicating the potential utility of the solute-saturated supercritical adsorption (SSA). The amount of PEA adsorbed on the silica aerogel with SSA at different temperatures and pressures was measured, and the release of PEA from the aerogel at 303.2 K was also evaluated. A theoretical model for the SSA equilibrium was developed with the assistance of the adsorption isotherms of pure CO2 onto the silica and considering a three-phase binary system, where the two-dimensional van der Waals equation of state and the three-dimensional Stryjek–Vera modification of the Peng–Robinson equation of state were used respectively to describe the adsorbed phase and the bulk phases (vapor phase and liquid phase). Results showed that the model was capable of describing the adsorption behavior of the system with an average absolute relative deviation of 3.3%.Graphical abstractHighlights► Solute-saturated supercritical adsorption shows evident increase of PEA loading. ► A three-phase equilibrium model is proposed for describing the special adsorption. ► A high-pressure quartz spring approach is setup for measuring adsorption isotherms. ► Silica aerogel shows effective prevention of PEA from volatility at 303.2 K.

A novel carbonation route for the synthesis of CaCO3 is reported with high pressure CO2 scintillated into dry Ca(OH)2 powder containing a solid ionic liquid (SIL, tetra-n-heptyl-ammonium bromide). Results show that calcite structure with rhombohedral lattice is produced at all CO2 conditions investigated: supercritical (15.0 MPa, 50.0 °C), compressed (5.0 MPa, 30.0 °C), liquid (15.0 MPa, 25.0 °C), gaseous (0.1 MPa, 30.0 °C) and atmospheric (0.1 MPa, 30.0 °C). Furthermore, rapid and complete conversion is achieved under the supercritical condition with the production of nano-sized calcite particles, suggesting that coupling SIL with CO2 could be an effective system for enhancing traditional gas–solid reactions. A mechanism for the rapid gas–solid carbonation reaction is proposed with emphasis on the initialization of the reaction by tiny adsorbed water and CO2 dissolved in the SIL.Graphical abstractHighlights► A novel carbonation process was proposed by using CO2 coupled with SIL. ► Rapid and complete conversion of Ca(OH)2 was achieved by the process. ► Rhombohedral structures were obtained at all conditions with the process. ► The initialization of the reaction by tiny adsorbed water in SIL was proposed.

A supercritical fluid-based method is proposed to produce coenzyme Q10 (CoQ10) nanoparticles. First, CoQ10/polyethylene glycol 6000 composite particles are prepared by a modified PGSS (particles from gas-saturated solutions) process with controlling the flow rate of the gas-saturated solution. Then, CoQ10 nanoparticles are obtained by dissolving the composite particles into water. The effect of experimental variables of the modified PGSS process, including pressure, temperature, flow rate of the gas-saturated solution, and mass fraction of CoQ10, on the CoQ10 particle size and particle size distribution was investigated. Results show that CoQ10 slurry product with a median diameter of 190 nm and yield of 89.8% can be prepared at an optimum condition (operating pressure of 25 MPa, operating temperature of 80 °C, gas-saturated solution flow rate of 1.02 mL/min, CoQ10 mass fraction of 40% and nozzle diameter of 100 μm) via the supercritical fluid-based method.Graphical abstractResearch highlights► A process with controlled gas-saturated solution flow rate was proposed. ► Coenzyme Q10/PEG6000 composite particles were produced with the process. ► CoQ10 nanoparticles about 190 nm were formed from the composite particles. ► Gas-saturated solution flow rate and CoQ10 mass fraction are crucial factors.

A method via the observation of the first and last melting points (FLMP) of solids is proposed to measure solid−liquid−gas (SLG) equilibrium for the ibuprofen + myristic acid + CO2 and ibuprofen + tripalmitin + CO2 ternary systems. The temperature−composition (T, w) data as well as the eutectic compositions at different pressures (0.1, 6.0, 10.0, and 15.0) MPa were determined. Results indicate that the two systems are both simple eutectic at (0.1 and 6.0) MPa, while the phase diagrams transform into the solid solution as the pressure increases. The eutectic composition of the ibuprofen + myristic acid + CO2 system is nearly constant (about 0.5 mass fraction of ibuprofen), while that of the ibuprofen + tripalmitin + CO2 system increases from 0.4 (mass fraction of ibuprofen) at 0.1 MPa to 0.6 at 15.0 MPa. T, w data at 0.1 MPa from FLMP are in good agreement with those determined by differential scanning calorimetry (DSC) and also with predictions from the ideal solubility equation.

Two equations typically used for the pure-solid fugacity proved to be identical by selecting an appropriate relation for the pure-solid vapor pressure and the pure-liquid vapor pressure. On the basis of the pure-solid fugacity, a semipredictive model using solubility data (SMS) and a calculation model combining with GE models (CMG) were developed to calculate the solid−liquid−gas (SLG) coexistence lines of pure substances in the presence of CO2. For the SMS model, the Peng−Robinson equation of state (PR-EoS) with the van der Waals one-fluid mixing rule is used to correlate the solute solubility in CO2 to obtain the interaction parameter k12, which is further employed to predict the SLG coexistence lines by two methods: one adopts the fugacity coefficient of the solute in the liquid phase by an equation of state calculation (SMS-φ); the other uses the activity coefficient of the solute in the liquid phase calculated from the UNIFAC model (SMS-γ). For the CMG model, the PR-EoS with the linear combination of Vidal and Michelsen (LCVM) mixing rule, the Michelsen modified Huron-Vidal (MHV1) mixing rule, and a modified version (mLCVM) with the re-evaluated parameter λ = 0.18 are used. Results show that the SMS model can provide acceptable calculations of the SLG coexistence lines for most of the investigated systems. The predicted melting temperatures and solute compositions in liquid phase from a constant k12 are slightly better than those from the correlated one, while the predicted solute solubility data in CO2 from a constant k12 are worse than those from the correlated one. The CMG model with the mLCVM mixing rule calculates well the melting temperatures and solute compositions in liquid phase at SLG equilibrium and also gives acceptable calculations of the solute solubilities in supercritical CO2.

Using the CO2-and N2-assisted atomization processes, the production of ibuprofen/lipid composite microparticles is investigated, in which the lipid includes myristic acid and tripalmitin. The produced composite particles show similar morphology to that of the purelipids obtained by the same process. In the case of the N2-assisted process, the average size of composite particles is slightly larger than that of the pure lipid particles due to the difficulty of solidification when using N2. In the case of the CO2-assisted process, the average size of composite particles is slightly smaller than that of the pure myristic acid particles, but slightly larger than that of the pure tripalmitin particles. The dissolution study reveals that the drug release from the ibuprofen/myristic acid particles is enhanced in comparison with that of the unprocessed ibuprofen. For the particles produced by the N2-assisted process, the X-ray diffraction (XRD) patterns clearly indicate the encapsulation of ibuprofen into myristic acid. The obtained ibuprofen/tripalmitin composite particles with 5% or 20% of ibuprofen (in mass) evidently show the controlled drug release: only about 20% of the drug is released in 500 min from the ibuprofen/tripalmitin composite particles consisting of 20% ibuprofen prepared by the CO2-assisted process, and the same release is obtained from the ibuprofen/tripalmitin composite particles containing 5% ibuprofen prepared by the N2-assisted process.