SC-CO2 Flow Research Articles

Experimental investigation of carbon dioxide trapping due to capillary retention in saline aquifers

AbstractCapillary trapping is a physical mechanism by which carbon dioxide (CO2) is naturally immobilized in the pore spaces of aquifer rocks during geologic carbon sequestration operations, and thus a key aspect of estimating geologic storage potential. Here, we studied capillary trapping of supercritical carbon dioxide (scCO2), and the effect of initial scCO2 saturation and flow rate on the storage/trapping potential of Berea sandstone. We performed two‐phase, scCO2‐brine displacements in two samples, each subject to four sequential drainage–imbibition core‐flooding cycles to quantify end‐point saturations of scCO2 with the aid of micro‐ and macro‐computed tomography imaging. From these experiments, we found that between 51% and 75% of the initial CO2 injected can be left behind after the brine injection. We also observed that the initial scCO2 saturation influenced the residual scCO2 saturation to a greater extent than the rate of brine injection under the experimental conditions examined. In spite of differences in the experimental conditions tested, as well as those reported in the literature, initial and residual saturations were found to follow a consistent relationship.

Determination of Oleanolic and Ursolic Acids in Hedyotis diffusa Using Hyphenated Ultrasound-Assisted Supercritical Carbon Dioxide Extraction and Chromatography.

Oleanolic acid (OA) and ursolic acid (UA) were extracted from Hedyotis diffusa using a hyphenated procedure of ultrasound-assisted and supercritical carbon dioxide (HSC–CO2) extraction at different temperatures, pressures, cosolvent percentages, and SC–CO2 flow rates. The results indicated that these parameters significantly affected the extraction yield. The maximal yields of OA (0.917 mg/g of dry plant) and UA (3.540 mg/g of dry plant) were obtained at a dynamic extraction time of 110 min, a static extraction time of 15 min, 28.2 MPa, and 56°C with a 12.5% (v/v) cosolvent (ethanol/water = 82/18, v/v) and SC–CO2 flowing at 2.3 mL/min (STP). The extracted yields were then analyzed by high performance liquid chromatography (HPLC) to quantify the OA and UA. The present findings revealed that H. diffusa is a potential source of OA and UA. In addition, using the hyphenated procedure for extraction is a promising and alternative process for recovering OA and UA from H. diffusa at high concentrations.

Experimental and theoretical investigation of supercritical drying of silica alcogels

Extraction of ethanol from pores of cylindrical silica alcogel samples using supercritical CO2 (scCO2) in a tubular extraction vessel was investigated both by experiments and simulations. Partial differential equations representing mass transfer within the cylindrical silica alcogel phase and in the external scCO2 phase were developed and solved using finite difference method. The percent removal data as a function of time were found to be in good agreement with model results using mass transfer coefficients regressed from the experimental data. The mass transfer coefficients were found to be higher by about a factor of three from two of the correlations tested which were developed for supercritical extraction. Effect of scCO2 flow rate on the drying was investigated through experiments and simulations. Increasing flow rate led to a decrease in effluent concentration at a specific time but did not significantly affect rate of extraction of ethanol. Effects of the magnitude of the effective diffusion coefficient and alcogel thickness on drying were investigated through simulations. Drying time of the alcogel decreased with decreasing gel thickness and increasing effective diffusion coefficient.

Scalable organic solvent free supercritical fluid spray drying process for producing dry protein formulations

In this study, we evaluated the influence of supercritical carbon dioxide (scCO2) spray drying conditions, in the absence of organic solvent, on the ability to produce dry protein/trehalose formulations at 1:10 and 1:4 (w/w) ratios. When using a 4L drying vessel, we found that decreasing the solution flow rate and solution volume, or increasing the scCO2 flow rate resulted in a significant reduction in the residual water content in dried products (Karl Fischer titration). The best conditions were then used to evaluate the ability to scale the scCO2 spray drying process from 4L to 10L chamber. The ratio of scCO2 and solution flow rate was kept constant. The products on both scales exhibited similar residual moisture contents, particle morphologies (SEM), and glass transition temperatures (DSC). After reconstitution, the lysozyme activity (enzymatic assay) and structure (circular dichroism, HP-SEC) were fully preserved, but the sub-visible particle content was slightly increased (flow imaging microscopy, nanoparticle tracking analysis). Furthermore, the drying condition was applicable to other proteins resulting in products of similar quality as the lysozyme formulations. In conclusion, we established scCO2 spray drying processing conditions for protein formulations without an organic solvent that holds promise for the industrial production of dry protein formulations.

Controlled graft copolymerization of lactic acid onto starch in a supercritical carbon dioxide medium

This work presents a new approach for the synthesis of a starch-g-poly L-lactic acid (St-g-PLA) copolymer via the graft copolymerization of LA onto starch using stannous 2-ethyl hexanoate (Sn(Oct)2) as a catalyst in a supercritical carbon dioxide (scCO2) medium. The effects of several process parameters, including the pressure, temperature, scCO2 flow rate and reaction time, on the polymerization yield and grafting degree were studied. Amorphous graft St-g-PLA copolymers with increased thermal stability and processability were produced with a high efficiency. The maximum grafting degree (i.e., 52% PLA) was achieved with the following reaction conditions: 6h, 100°C, 200bar and a 1:3 (w/w) ratio of St/LA. It was concluded that these low cost biobased graft biopolymers are potential candidates for several environment-friendly applications.

Fractionation for Biodiesel Purification Using Supercritical Carbon Dioxide

In recent years, biodegradable and alternative biodiesel has attracted increased attention worldwide. Producing biodiesel from biomass involves critical separation and purification technology. Conventional technologies such as gravitational settling, decantation, filtration, water washing, acid washing, organic solvent washing and absorbent applications are inefficient, less cost effective and environmentally less friendly. In this study supercritical carbon dioxide (SC-CO2) with few steps and a low environmental impact, was used for biodiesel fractionation from impure fatty acid methyl ester (FAME) solution mixes. The method is suitable for application in a variety of biodiesel production processes requiring subsequent stages of purification. The fractionation and purification was carried out using continuous SC-CO2 fractionation equipment, consisting of three columns filled with stainless steel fragments. A 41.85% FAME content solution mix was used as the raw material in this study. Variables were a temperature range of 40–70 °C, pressure range of 10–30 MPa, SC-CO2 flow rate range of 7–21 mL/min and a retention time range of 30–90 min. The Taguchi method was used to identify optimal operating conditions. The results show that a separated FAME content of 99.94% was verified by GC-FID under optimal fractionation conditions, which are a temperature of 40 °C of, a pressure level of 30MPa and a flow rate of 7 mL/min of SC-CO2 for a retention time of 90 min.

Supercritical fluid extracts with antioxidant and antimicrobial activities from myrtle (Myrtus communis L.) leaves. Response surface optimization

Supercritical Fluid Extraction (SFE) was used to obtain myrtle leaf extracts, and to study the antioxidant capacity (AOC) and in vitro antimicrobial activity of those extracts. To optimize the SFE operational conditions, the response surface methodology (RSM) was adopted. The parameters studied were: pressure (P), within the range 10 to 30MPa; temperature (T), between 35°C and 60°C and supercritical carbon dioxide (SCCO2) flow rate (Q) within the range 0.15 to 0.45kgh−1. The results show a good fit to the proposed model and the optimal conditions obtained (23MPa, 45°C, and SCCO2 flow rate of 0.3kgh−1) were within the experimental range. The predicted values agreed with experimental ones, thus indicating the suitability of the RSM model for the optimization of the extraction conditions being investigated. With those values remaining constant, ethanol as a co-solvent was then studied. There was an observed rise in AOC as the amount of ethanol increased, within the range studied (0–30wt% ethanol). The extract with the highest AOC was tested for its antimicrobial activity against gram-positive and gram-negative bacteria. The minimum inhibitory concentration (MIC) values obtained showed significant inhibitory effect against gram-positive bacteria.

Supercritical anti-solvent micronization of chromatography purified marigold lutein using hexane and ethyl acetate solvent mixture

This work aims to study supercritical anti-solvent micronization of marigold derived purified lutein that was dissolved in the mixture of hexane and ethyl acetate (70:30 v/v), the solvent used as the mobile phase for chromatographic purification. The results show significant effect of pressure on the morphology of micronized lutein particles. The increase in lutein initial concentration from 1.5mg/ml to 3.2mg/ml and the increase in SC-CO2 flow rate from 15ml/min to 25ml/min show no significant effects on the morphology of lutein particles. However, the reduction of mean particle size from about 2μm to 0.8μm was observed by increasing SC-CO2 flow rate. The X-ray diffraction patterns of the micronized lutein particles show apparent amorphous nature, while the Fourier transform infrared spectroscopy results show that no chemical structural changes occurred. Moreover, the solubility of the micronized lutein particles in aqueous solution was found to increase significantly from being almost insoluble to having approximately 20% solubility

Supercritical anti-solvent micronization of marigold-derived lutein dissolved in dichloromethane and ethanol

This work aims to study supercritical anti-solvent (SAS) micronization of lutein derived from marigold flowers. Lutein solution in dichloromethane (DCM) or ethanol was atomized into the stream of supercritical carbon dioxide (SC-CO2) through a concentric nozzle in a pressurized vessel. The effects of pressure and SC-CO2 flow rate on morphology, mean particle size (MPS) and particle size distribution (PSD) were investigated. The reduction in lutein MPS from 202.3μm of unprocessed lutein to 1.58μm and 902nm could be achieved by SAS micronization using DCM and ethanol, respectively. In both solvent systems, no significant effects of pressure and SC-CO2 flow rate on particle morphology were observed. However, pressure was found to have a significant effect on MPS and PSDs of lutein particles.

Evaluation of a new On-Stream Supercritical Fluid Deposition process for sol–gel preparation of silica-based membranes on tubular supports

A novel “On-Stream Supercritical Fluid Deposition” (OS-SFD) process has been investigated in this work coupling the sol–gel chemistry and a filtration/compression operation in supercritical CO2 (sc-CO2), for the production of uniform membranes on/in porous ceramic tubular supports. The versatility of this process allows both the direct formation of thin coatings on porous tubular membrane supports but also their internal modification. An attractive on-line control of the deposition process was operated by recording the transmembrane pressure evolution during membrane formation. Silica membranes were directly deposited on macroporous supports (155mm long α-Al2O3, with 200nm pore sizes) from TEOS derived sols dissolved in sc-CO2 and transported to the tubular support where the condensation/gelation and deposition occurred. The deposition mechanism has been correlated with the sol–gel transition in sc-CO2 conditions and the impact of the deposition temperature, sol formulation and sc-CO2 flow rate on the membrane characteristics (morphology, weight increase and single gas permeance) have been discussed. Supersaturation and precipitation of transported clusters followed by their condensation and gelation were found as key parameters controlling the silica-based membrane design and microstructure/compacity of the silica network.

Integrated process of supercritical CO2-assisted melt polycondensation modification and foaming of poly(ethylene terephthalate)

An integrated process of melt polycondensation modification and foaming of poly(ethylene terephthalate) (PET) was performed in a high pressure vessel assisted by supercritical carbon dioxide (scCO2). ScCO2 was firstly employed to sweep PET melt, i.e., high pressure CO2 continuously flows through the vessel at a fixed flow rate to remove small molecules for higher molecular weight PET, then this modified PET melt was directly foamed through a rapid depressurization process using scCO2 as blowing agent. In this integrated process, PET with high melt strength after polycondensation modification could be foamed directly in molten state. Therefore, re-molten process of solid modified PET pellets was canceled to avoid its degradation and CO2 saturation time could be saved in foaming process, thus processing time could be shortened and energy efficiency could be improved. The influences of scCO2 sweeping treatment time, pressure and flow rate on properties of the modified PETs and cell morphologies of the foamed PETs were investigated respectively. The results showed that CO2 sweeping treatment could effectively enhance PET melt polycondensation modification process, which was superior to that of N2 treatment. PET foams with average cell diameter of 32–62μm and cell density of 1×107 to 4×107 cells/cm3 have been obtained in the integrated process. Compared with the process of only foaming modified PET by scCO2 or performing scCO2 assisted modified PET further melt polycondensation process and scCO2 foaming process separately, this integrated process produced better cell morphology.

Life cycle assessment of green pilot-scale extraction processes to obtain potent antioxidants from rosemary leaves

In this work, the water extraction and particle formation on-line (WEPO) process has been used to obtain dry antioxidant powder from rosemary leaves. This process includes pressurized hot water extraction (PHWE) and on-line drying of the extracts in one step. Based on previous works, water extraction at 200°C was selected to achieve the maximum antioxidant activity while water flow rate was studied to determine its influence on powder formation. Other parameters influencing the drying process, such as scCO2 pressure (80bar) and flow rate (2.5mL/min) and N2 flow rate (0.6mL/min) were settled to obtain a fine and constant spray. Powders obtained were evaluated in terms of particle size and morphology by scanning electron microscopy (SEM) as well as antioxidant capacity by an in vitro DPPH antioxidant assay. In order to assess the environmental performance of the WEPO process, this has been compared in terms of Life Cycle Assessment (LCA) to other green processes typically used for antioxidant extraction from rosemary leaves, such as supercritical fluid extraction (SFE) and a static pressurized hot water extraction, PHWE, carried out with a commercial equipment, both followed by a conventional drying step. The WEPO process, carried out in one step, giving dry bioactive extracts from rosemary, results in lower environmental impacts and energy consumption than the other green processes studied. The sensitivity assessment demonstrated the importance of primary energy sources in the production of electricity used, especially when green processes are being implemented.

Kinetics of Extraction of <i>β</i>-Carotene from Tray Dried Carrots by Using Supercritical Fluid Extraction Technique

β-carotene acts as an antioxidant and is receiving growing interest due to its ability as protecting agent against heart diseases, cancer and strengthening effect on red blood cells. The main aim of this work was to study the kinetics of the supercritical fluid extraction of β-carotene from tray dried carrots at 40℃, 50℃ and 55℃ and 30, 35 and 40 MPa at SC-CO2 flow rate of 2.0 L/min for extraction time of up to 6 h. It was observed that the concentration of β-carotene in the extract increased with pressure, temperature and extraction time. The results indicated that yield was found to be maximum at 45℃ and 35 MPa at 2 L/min SC-CO2 flow rate. Concentration of β-carotene in the extract increased with SC-CO2 flow rate. Weibull distribution model described adequately the kinetics of extraction of β-carotene from carrots.

초임계 이산화탄소를 이용한 Chlorella vulgaris의 오일 추출

In this study, two different extraction techniques, organic solvent extraction and supercritical carbon dioxide (SCCO₂) extraction, were employed to evaluate the extraction efficiency of oil from Chlorella vulgaris. In the organic solvent extraction, the effects of various organic solvent on the extraction yield were investigated. The SCCO₂ extraction was carried out while varying such operating parameters as temperature, pressure, SCCO₂ flow rate, and cosolvent. About 4.9 wt% of oil was extracted from ground Chrollera vulgaris for 18 h when dichloromethane/methanol (2：1, v/v) was used as an extraction solvent. The oil yield of the SCCO₂ extraction was found to be very low (0.53 wt%) and to increase up to about 0.86 wt% with the addition of cosolvent.

Continuous Enantioselective Hydrogenation with a Molecular Catalyst in Supported Ionic Liquid Phase under Supercritical CO2 Flow

The synthesis of enantiopure compounds using chiral transition-metal catalysts is largely dominated by batchwise procedures. [1] This typically results in considerable amounts of solvent waste from both reaction and purification steps, low space–time yields, and often precludes reuse of the precious catalyst. [2] The development of efficient and flexible flow systems could provide alternative modes of operation, combining the benefits of an integrated reaction and purification strategy with the molecular approach to catalyst design. Efficient immobilization of chiral catalysts in a liquid-like environment is an important prerequisite for the successful implementation of this strategy. [3] The concept of supported ionic liquid phase (SILP) catalysis describes a molecular catalyst that is dissolved in a small amount of an ionic liquid (IL) that is immobilized on the surface of a solid support, typically a porous oxidic material such as silica or alumina. Physisorption and capillary forces lead to surface coating and pore filling, yielding free-flowing powders that can be used in fixed or fluidized bed reactors. [4, 5] Due to a mean film thickness in the range of 10–20 �, catalysts dissolved in the supported layer are close to a large interface, and diffusion pathways are reduced in comparison to bulk biphasic systems, often leading to high reaction rates. [6–10] Despite their proximity to the surface, the molecular catalysts in the nanoliquid confinement of SILPs have been shown by kinetic analyses to perform in a genuinely homogeneous manner. [5–7] The ease of preparation and the modularity of SILP catalysts contribute to making them ideal candidates for continuous catalysis, combining many advantages of both homogeneous and heterogeneous systems. For a stable and efficient process, the choice of the mobile phase is decisive. SILP catalysts containing an organometallic complex have been applied successfully in continuous-flow catalysis involving gaseous substrates with moderate [11] to good stability. [12, 13] This approach is, however, restricted to volatile substrates and catalysts of sufficient thermal stability. Non-IL-miscible liquid phases would allow for milder reaction conditions and broaden the substrate scope to more interesting molecules, but usually lead to progressive desorption of the SILP by abrasion or gradual dissolution. [8, 14, 15] Cole-Hamilton and co-workers have recently demonstrated that supercritical carbon dioxide (scCO2) can be used as a mobile phase to transport nonvolatile substrates and products continuously over organometallic SILP catalysts for the hydroformylation of long-chain olefins. [16] By the combination of SILP catalysis with scCO2 flow, high activity paired with excellent stability could be achieved. [17] The infinitesimal solubility of ILs in scCO2 [18] allowed for retention of the SILP while organic products were continuously extracted. [19] A similar approach was recently described by the team of Iborra and Lozano for continuous-flow kinetic resolution of alcohols by using the lipase CAL-B in a SILP-type system and CO2 as the mobile phase. [20]

Supported Ionic Liquid-Like Phases (SILLPs) for enzymatic processes: Continuous KR and DKR in SILLP–scCO2 systems

The immobilisation of Candida antarctica lipase B (CALB) onto SILLPs has been studied in order to obtain the maximum activity, selectivity and stability of the resulting supported biocatalyst for the KR of rac-1-phenylethanol by flow processes using scCO2. This involves the use of hydrophilic SILLPs (chloride anion) with high loadings of IL moieties and CALB. The combination of the immobilized biocatalyst with an acidic zeolite has allowed us to carry out DKR processes. Excellent results in terms of yield (92%) and enantioselectivity (>99.9% ee) are obtained by the use of a “one-pot” reactor containing a mixture of both catalyst particles under scCO2 flow conditions (50 °C, 10 MPa), resulting in an environmentally friendly process with high productivity and enantioselectivity.

Sustained release of drugs dispersed in polymer nanoparticles.

Sustained release of drugs dispersed in polymer nanoparticles.

Analysis of supersaturation and nucleation in a moving solution droplet with flowing supercritical carbon dioxide

AbstractA supercritical antisolvent (SAS) process is employed for production of solid nanoparticles from atomized droplets of dilute solution in a flowing supercritical carbon dioxide (SC CO2) stream by attaining extremely high, very rapid, and uniform supersaturation. This is facilitated by a two‐way mass transfer of CO2 and solvent, to and from the droplet respectively, rendering rapid reduction in equilibrium solubility of the solid solute in the ternary solution. The present work analyses the degree of supersaturation and nucleation kinetics in a single droplet of cholesterol solution in acetone during its flight in a flowing SC CO2 stream. Both temperature and composition are assumed to be uniform within the droplet, and their variations with time are calculated by balancing the heat and mass transfer fluxes to and from the droplet. The equilibrium solubility of cholesterol with CO2 dissolution has been predicted as being directly proportional to the Partial Molar Volume Fraction (PMVF) of acetone in the binary (CO2–acetone) system. The degree of supersaturation has been simulated up to the time required to attain almost zero cholesterol solubility in the droplet for evaluating the rate of nucleation and the size of the stable critical nuclei formed. The effects of process parameters have been analysed in the pressure range of 7.1–35.0 MPa, temperature range of 313–333 K, SC CO2 flow rate of 0.1136–1.136 mol s−1, the ratio of the volumetric flow rates of CO2‐to‐solution in the range of 100–1000, and the initial mole fraction of cholesterol in acetone solution in the range of 0.0025–0.010. The results confirm an extremely high and rapid increase in degree of supersaturation, very high nucleation rates and stable critical nucleus diameter of the order of a nanometre. Copyright © 2005 Society of Chemical Industry

Response surfaces of hazelnut oil yield in supercritical carbon dioxide

Response Surface Methodology was used to determine the effects of solvent flow rate (1, 3 and 5 g/min), pressure (300, 375 and 450 bar) and temperature (40, 50 and 60 °C) on hazelnut oil yield in supercritical carbon dioxide (SC-CO2). Oil yield was represented by a second order response surface equation (R2=0.997) using Box-Bhenken design of experiments. Oil yield increased with increasing SC-CO2 flow rate, pressure and temperature. The maximum oil yield was predicted from the response surface equation as 0.19 g oil/g hazelnut (34% of initial oil) when 4 g hazelnut particles (particle diameter<0.85 mm) were extracted with 5 g/min SC-CO2 flow rate at 450 bar, and 60 °C for 10 min. Total extraction time at these conditions was predicted to be 35 min.