Continuous Supercritical Carbon Dioxide Research Articles

Recycling PVC with scCO2: From Soft to Rigid PVC.

This study explores using extraction with supercritical carbon dioxide to remove plasticizers from poly(vinyl chloride) (PVC), with the aim to enhance recycling processes. Experiments were performed at 100 to 500 bar with temperatures varying from 75 to 110 °C. The results show that continuous supercritical carbon dioxide efficiently removes bis(2-ethylhexyl) phthalate (DOP) from PVC with extraction efficiencies of more than 98% which resulted in PVC samples with over 99.5% purity. A process model based on the Sovová model accurately describes the extraction process. The impact of the extraction process on polymer properties and associated molecular structures like viscosity, morphology, and mechanical properties was also evaluated using gel permeation chromatography, rheology, tensile test, and scanning electron microscopy.

Preparing supported ionic liquids by continuous supercritical carbon dioxide adsorption method

A new method was developed to prepare supported ionic liquids (SILs) continuously with the assist of supercritical carbon dioxide (scCO2). Two ionic liquids (ILs), 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) and 1-Butyl-3-methylimidazolium acetate ([Bmim][Ac]), were confined into SBA-15 pores by physical adsorption. Effects of duration time, pressure, temperature, and CO2 flow on ILs loadings were investigated and controllable preparation was realized. Highest loadings of 187.30% and 122.40% for [Bmim][BF4] and [Bmim][Ac] respectively were obtained. The equilibrium time and reactor volume of this continuous method were reduced by ca. 5 times and 13 times than those in a batch method. Pore structures of SILs were studied and proved to be kept perfectly by TEM and N2-sorption analysis. Ordered mesoporous structure was retained without severe blockage. The onset decomposed temperature of [Bmim][BF4] and [Bmim][Ac] measured by TGA was 280 °C and 160 °C after confinement. Only a little reduction of 10 °C happened compared with bulk ILs, suggesting the high thermal stability of SILs. FR-IR tests showed that vibration bands of imidazolium ring and [BF4] shifted after confinement due to the interaction with SBA-15.

A Continuous Fractionation of Ginsenosides and Polysaccharides FromPanax ginsengUsing Supercritical Carbon Dioxide Technology

A continuous supercritical carbon dioxide (SC-CO2) fractionation was conducted to obtain ginsenosides and polysaccharides from Panax ginseng extract. P. ginseng was mixed with ethanol at a ratio of 1:4 (volume by weight) for 24 h to yield ethanol extract. SC-CO2 fractionation was performed using an orthogonal design to obtain optimal fractionation parameters. The conditions were: three different temperatures (40, 50 and 60C), three different pressure levels (10, 20 and 30 MPa), three flow rates of SC-CO2 (2, 4 and 6 mL/min) and three flow rates of ginseng extract liquor (1, 2 and 3 mL/min). The highest concentration of total ginsenosides was obtained in the fraction (F) whereas the highest concentration of total polysaccharides was retained in the residual. The highest selectivity of ginsenosides and polysaccharides were obtained at 60C and 30 MPa. The greatest free radicals scavenging ability and antioxidant ability were obtained in F. Practical Applications Ginsenosides and polysaccharides from Panax ginseng have been postulated to contribute a number of positive health effects. Traditional extraction techniques are associated with the disadvantages of solvent residues and its associated toxicity. In the present study, a continuous preparation method using supercritical fluid technology was described with the optimal temperature and pressure for the separation of P. ginseng ginsenosides and polysaccharide. Our findings can be served as a basis to facilitate future scale-up industrial applications.

Foaming of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/organo-clays nano-biocomposites by a continuous supercritical CO2 assisted extrusion process

A continuous supercritical carbon dioxide (sc-CO2) assisted extrusion process has been used to prepare poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV/organo-clays nano-biocomposite foams by two methods: a one-step method based on the direct foaming of physical PHBV/clays mixtures, and a two-step method based on the foaming of extruded PHBV/clays mixtures prepared beforehand by twin-screw extrusion. The structures obtained have been characterized in terms of clay dispersion, matrix crystallization, porosity and pore size distribution and pore density. The influence of processing conditions as temperature, pressure, CO2 mass fraction and the clays/foaming interrelationships have been elucidated. It was shown that the prior preparation of a masterbatch by twin-screw extrusion and its dilution during the foaming process is a necessary step to improve clay dispersion without extensive thermal degradation of PHBV. By controlling the sc-CO2 mass fraction in a narrow window, good clay dispersion appears to favour homogeneous nucleation while limiting the coalescence of the pores, and hence allowed to obtain nano-biocomposite foams with better homogeneity and higher porosity up to 50%.

Demonstration of continuous supercritical carbon dioxide anti-solvent purification and classification of nano/micro-sized precipitates of algal zeaxanthin from Nannochloropsis oculata

This study examined time dependent continuous supercritical anti-solvent (SAS) recrystallization applied for purifying and generating zeaxanthin rich particulates from micro-algal Nannochloropsis oculata. Feed solutions varied from 0.4 to 1.2 mg/ml subjected into a 250 ml SAS crystallizer to yield a few classifications of nano- or micro-sized purified precipitates corresponding to different recrystallization time zones. The effect of operational conditions on amount, recovery of the zeaxanthin and mean size, morphology of the precipitates was obtained from experimentally designed SAS process. The mean size of particles falls within several hundreds of nanometers and the content of zeaxanthin in the particulates range from 65 to 71%, which relies highly upon the recrystallization time. This work demonstrated an environmental benign process in producing nano- or micro-sized particles containing rich-zeaxanthin from algal solution by using supercritical anti-solvent within minutes.

Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system

The objective of this study was to evaluate the efficacy of supercritical carbon dioxide (SCCO 2) for inactivating Lactobacillus plantarum in apple cider using a continuous system with a gas-liquid metal contactor. Pasteurized apple cider without preservatives was inoculated with L. plantarum and processed using a SCCO 2 system at a CO 2 concentration range of 0–12% (g CO 2/100 g product), outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Processing with SCCO 2 significantly ( P < 0.05) enhanced inactivation of L. plantarum in apple cider, resulting in a 5 log reduction with 8% CO 2 at 42 °C. The response surface model indicated that both CO 2 concentration and temperature contributed to the microbial inactivation. The extent of sublethal injury in surviving cells in processed apple cider increased as CO 2 concentration and processing temperature increased, however the percent injury dramatically decreased during SCCO 2 processing at 42 °C. Structural damage in cell membranes after SCCO 2 processing was observed by SEM. Refrigeration (4 °C) after SCCO 2 processing effectively inhibited the re-growth of surviving L. plantarum during storage for 28 days. Thus this study suggests that SCCO 2 processing is effective in eliminating L. plantarum and could be applicable for nonthermal pasteurization of apple cider.

Continuous kinetic resolution catalysed by cross-linked enzyme aggregates, ‘CLEAs’, in supercritical CO2

We report the use of cross-linked enzyme aggregates (CLEAs®) to catalyse the kinetic resolution of tetralol and 1-phenylethanol in a continuous supercritical carbon dioxide (scCO2) system. We describe the performance of the CLEA from Candida antarctica lipase B (CALB) and compare this to the catalytic activity of Novozym 435 (CALB immobilised on a macroporous acrylic resin). In addition, we report a two-stage reaction with the kinetic resolution of 1-phenylethanol performed in series with the metal (Pd) catalysed hydrogenation of acetophenone. Reactions performed in series have a potential economic advantage as the second, and subsequent reactions do not require additional expenditure of energy for re-pressurization of solvent.

Continuous supercritical carbon dioxide processing of palm oil

AbstractCrude palm oil was processed by continuous supercritical carbon dioxide. The process reduces the contents of free fatty acids, monoglycerides and diglycerides, certain triglycerides, and some carotenes. The refined palm oil from the process has less than 0.1% free fatty acids, higher carotene content, and low diglycerides. Solubility of palm oil in supercritical carbon dioxide increased with pressure. A co‐solvent improves the refining process of palm oil.

Continuous Supercritical Fluid Processing of Anhydrous Milk Fat in a Packed Column

ABSTRACTA continuous supercritical carbon dioxide processing system was designed, built and operated to investigate its performance for fractionation of anhydrous milk fat (AMF). Packed columns showed mass transfer efficiencies five times greater than a spray column, Short‐ and medium‐chain fatty acids were concentrated in the extract fractions and their amounts decreased as separation pressure increased. The ratio of unsaturated to saturated fatty acids in the raffinate fraction was 0.68 compared to 0.52 in the original AMF. The proportions of low‐melting triglycerides in the range —42 to 15°C were greater in the extract fractions (44–72%) compared to the original AMF (29%).

Improved lipase‐catalyzed incorporation of long‐chain fatty acids into medium‐chain triglycerides assisted by supercritical carbon dioxide extraction

AbstractDisplacement of the equilibrium of the lipase‐catalyzed interesterification between medium‐chain triglyceride (MCT) and long‐chain polyunsaturated fatty acid was accomplished by the removal of by‐products with continuous supercritical carbon dioxide (SC−CO2) extraction at 60°C and 100 kg/cm2. The incorporation of eicosapentaenoic acid to MCT was appreciably improved by this method and was 1.3 times higher than that of the equilibrium state (47 wt%) that was obtained in a closed system. The immobilizedMucor miehei lipase was stable for more than 180 h in SC−CO2 at 60°C and 100 kg/cm2.

Performance of a Packed Column for Continuous Supercritical Carbon Dioxide Processing of Anhydrous Milk Fat

AbstractA continuous system was designed for the processing of anhydrous milk fat (AMF) with supercritical carbon dioxide (SC‐CO2). The packed column was operated as a stripping column with SC‐CO2 as the continuous phase and AMF as the dispersed phase. The extraction was studied at 24.1 MPa and 40 °C. To utilize the functional similarities and make the analysis simpler, the AMF triglycerides were grouped as low‐melting (LMT: C24–C34), medium‐melting (MMT: C36–C40), and high‐melting triglycerides (HMT: C42–C54). There was an increase in the concentrations of LMT and MMT and a decrease in that of HMT in the extract. The raffinate has a high concentration of HMT with trace amounts of LMT. The performance characteristics of the packed column were described by the number of transfer units (Nog), the overall volumetric mass transfer coefficient (KOGa), and the height of a transfer unit (HOG). The NOG and Kogci values decreased and the HOG value increased with increasing solvent‐to‐feed ratio. The HOG values increased and the NOG and KOGa values decreased from LMT to MMT to HMT, but the HOG values for HMT were greater than expected. The values of NOG, HOG, and KOGa for AMF (as a single component) were intermediate to those of MMT and HMT.