Effect Of Supercritical Carbon Dioxide Research Articles

Influence of supercritical CO2 and initial melting temperature on crystallization of polypropylene/organoclay nanocomposite

Polypropylene (PP)/clay nanocomposite with maleic anhydride modified polypropylene (PP-MA) was prepared using a twin-screw extruder. The effect of supercritical carbon dioxide (scCO2) on mixing was investigated. Isothermal crystallization of the nanocomposites was investigated by differential scanning calorimetry (DSC) and also by optical microscopy as a function of initial melting temperature. Increasing initial melting temperature causes a gradual decrease in bulk crystallization kinetics, with the exception of the 240–260 °C temperature range for the system without CO2. Optical microscopy revealed a large number of small spherulites for the system without CO2 after initial melting at 250 °C. After 28 min initial induction period of crystallization many small spherulites appeared in the vicinity of large spherulites for the system with CO2, indicating the beginning of homogenous nucleation. X-ray diffraction (XRD) and direct observation of the samples after tensile testing revealed better dispersion of nanoclay for the system without CO2.

Physical Properties of Wheat Flour Treated by Supercritical Carbon Dioxide

Wheat flour is very popular food materials in worldwide. In this study, the aim of this work was to investigate the effect of supercritical carbon dioxide (SCO2) treatment on physical properties of wheat flours. Wheat flour was treated using SCO2 under different treatment conditions. SCO2 treatment was carried out to treat the wheat flour at different pressures of 10 to 30MPa, constant temperature of 40°C and additives 70%-ethanol. Whiteness and bulk density of wheat flour was increased in the treatment of SCO2. These results indicated that the treatment effect was high at high pressure. In case of particle size and angle of repose, SCO2 treatment was more efficient than SCO2 treatment with additives 70%-ethanol.

Structural behavior of Candida antarctica lipase B in water and supercritical carbon dioxide: A molecular dynamic simulation study

In this study, molecular dynamic (MD) simulation is used to investigate the effect of supercritical carbon dioxide on the structural properties of a new variant of Candida antarctica lipase B, namely, cp283Δ7. For better understanding and comparison, structure of the enzyme was simulated in both water and supercritical carbon dioxide. The analysis of root mean square deviation showed that in supercritical CO2, the structural variations of the enzyme are more than those of in the aqueous solution and therefore dissolving enzyme in scCO2 impose undesirable instability on its structure. Moreover, obtained radius of gyration showed that in supercritical CO2, the compactness of the enzyme structure is reduced which leads to decreased stability. The secondary structure analysis revealed that in supercritical CO2, on the one hand, the amounts of α-helix and β-sheet contents of enzyme are reduced and, on the other hand, the amount of random coil is increased. More native-like enzyme structure was also confirmed in water than supercritical CO2 by tertiary structure analysis in term of contact map.

In situ Acidic Carbon Dioxide/Ethanol System for Selective Oxybromination of Aromatic Ethers Catalyzed by Copper Chloride

AbstractAn environmentally benign carbon dioxide/ethanol reversible acidic system was developed for the copper(II)‐catalyzed regioselective oxybromination of aromatic ethers without the need of any conventional acid additive and organic solvent. Good to excellent yields together with very good regioselectivity were achieved when easily available cupric chloride dihydrate was used as catalyst and lithium bromide as the cheap and easy‐to‐handle bromine source under supercritical carbon dioxide conditions. Notably, the catalytic system worked well for a wide range of aromatic ethers including sulfides, resulting in the formation of the mono‐brominated products in high yields and exclusive regioselectivity. The alkylcarbonic acid in situ formed from ethanol and carbon dioxide is assumed to play the crucial role in the Brønsted acid‐promoted reaction, which could probably act as the proton donator, and was studied employing in situ FT‐IR technique under carbon dioxide pressure by monitoring the vibration shift of the hydroxy group of ethanol. Given with excellent bromine atom efficiency as well as no need of neutralization in waste disposal, this approach thus represents a greener pathway for the aerobic bromination of aromatic ethers. A possible catalytic cycle for the in situ alkylcarbonic acid‐assisted oxybomination and the effect of supercritical carbon dioxide, i.e., activation of alcohol and enhancement of mass transfer are also discussed.

APPLICATION OF SUPERCRITICAL CARBON DIOXIDE FOR MICROORGANISM REDUCTIONS IN FRESH PORK

ABSTRACT This study was conducted to examine the inhibitory effects of supercritical carbon dioxide (SC-CO2) on microorganisms in fresh pork. With SC-CO2 treatment at 120 bar and 40C for 30 min, the initial mesophilic plate counts were reduced from 6.23 to 4.54 log colony-forming units (cfu) per cm2, and the reduction levels of microorganisms, including nonpathogenic Escherichia coli, Listeria monocytogenes, Salmonella Typhimurium and E. coli O157:H7, ranged from 1.99 to 2.51 log cfu/cm2. Even though SC-CO2 treatment at 120 bar resulted in higher reductions than treatment at 80 bar, the higher temperature or longer exposure times did not always present greater inhibitory effects than the lower temperature or shorter exposure times. Therefore, from an economic point of view, SC-CO2 treatment at the lower temperature (35 versus 40C) and shortest exposure time (10 versus 30 min) was more efficient than treatment at the higher temperature or longer exposure time at the same pressure. PRACTICAL APPLICATIONS The practical application of SC-CO2 has been proposed as an alternative pasteurization technique for various liquid foods. In addition, SC-CO2 treatment can be used to effectively improve solid food safety including fresh meat and meat products without impairing the quality of the products.

Research on the Effect of Supercritical Carbon Dioxide on the Properties of Super Heavy Oil

Carbon dioxide flooding is an important way to exploit heavy oil reservoir. Considering the Zheng411 super heavy oil reservoir in Shengli Oil Field, the solubility of supercritical carbon dioxide in super heavy oil, and the effect of supercritical carbon dioxide on the volume factor, viscosity, component content and oil/water emulsification of super heavy oil are researched. The result shows: the solubility of carbon dioxide in super heavy oil increases with the increasing pressure, but the increasing extent declines gradually, when the pressure is below 28MPa, the solubility of carbon dioxide decreases with the rising temperature under the same saturation pressure; the volume factor increases linearly with the increase of supercritical carbon dioxide solubility; under the condition of unsaturation, the supercritical carbon dioxide is able to reduce the density of super heavy oil substantially, whereas it has little impact on the chemical properties of oil; Demulsification and visbreaking can be realized through dissolving supercritical carbon dioxide in super heavy oil that contains water, and the viscosity reduction capacity of carbon dioxide is hardly affected by water.

Effects of supercritical carbon dioxide on rocks having carbon dioxide storage potential

One of the most important problems of our society is the rising CO2 concentration of the atmosphere supposed to be a reason of the climate change. The Carbon Capture and Sequestration (CCS) may be a temporary solution for this problem. CCS is the technology when the CO2is separated from the local CO2 sources, and is injected at least 800–1000 m deep where, because of the high pressure and higher than ambient temperature, it will be supercritical (scCO2). We need to study what are the geochemical changes induced by scCO2 to use safely this technology. This was the main motive why we started to make experimental and analytical methods on real core samples from exploration drilling. We added scCO2 to sandstone core samples in brine and very high purity calcite samples in 5 w/w% NaClsolution in 70–220 bar pressure interval and in 55–65 °C temperature interval in a high pressure resistant bomb and autoclave. After experiments the brine and solution samples were analyzed by ICP-MS and the core samples by XRF and SEM. The results indicated significant alteration in the concentration of Na, Ca, Mg, K, Fe and Srions concentration before and after the addition of scCO2. After adding scCO2the concentration of Ca grew in the brine and was reduced on the surface of the sandstone. The XRF results indicated a very high dispersion of the elements on the surface of the samples. The SEM images show Ca soluble-cuts and solution of the surface.

Effects of supercritical carbon dioxide on waste banana peels for heavy metal removal

The effects of supercritical carbon dioxide (CO 2) on waste banana peels for copper adsorption were evaluated. Supercritical CO 2 was employed both in a solvent extraction for antioxidant compound recovery and in an emerging biomass treatment to increase the subsequent heavy metal-removal step; the latter is termed “explosion with supercritical CO 2”. This lignocellulosic biomass was analyzed before and after being subjected to both processes by scanning electron microscopy and X-ray patterning. Thermal gravimetric and differential scanning calorimetry analyses were performed to understand the different effects of supercritical carbon dioxide employed in these two processes on banana peels. The explosion with supercritical CO 2 process resulted in a more pronounced effect on the vegetable structure. Nevertheless, no increase in the copper-removal capacity was achieved. The adsorption studies showed similar behaviors for fresh and extracted samples, demonstrating that banana peels previously extracted with supercritical CO 2 retained their adsorption capacity for subsequent heavy metal removal.

Transesterification of rapeseed oil over acid resins promoted by supercritical carbon dioxide

The methanolysis of rapeseed oil catalyzed by commercial styrene-divinylbenzene macroporous acid resins was performed in a batch reactor at 100–140°C and 10–46MPa to study the effect of supercritical carbon dioxide (scCO2) on the performances of the process. Reaction temperatures of 120–140°C were necessary to obtain high enough yields of fatty acid methyl esters. Upon addition of scCO2 faster transesterification kinetics was obtained also at the lowest investigated operating pressure (10–11MPa), working in two fluid phase systems. Experiments performed changing the reaction time indicated that most of the esters were formed during the first 3h. When the pressure was increased at 38–46MPa, the fluid phases merged in a single one without significant modification of the performances of the process.The enhancement effect of scCO2 on the transesterification kinetics is tentatively discussed in terms of modification of the phase behaviour of the reaction system and swelling of the polymeric acid resin.

Structural and conformational modification of whey proteins induced by supercritical carbon dioxide

Abstract In this paper, the effect of supercritical carbon dioxide (SC-CO2) treatment on the structure and conformation of whey protein isolate (WPI) were investigated. The WPI solution treated with SC-CO2 at 20 MPa and 30–60 °C for 1 h showed that its turbidity and particle size were increased. The effect of SC-CO2 treatment at 60 °C on the fluorescence intensity of WPI was elevated indicating partial denaturation of its fractions and exposure of more hydrophobic regions. The secondary structure change of SC-CO2 treated WPI revealed a decrease in the α-helix content, hydrogen bonds and an increase in the amount of β-sheet. A high shift of endothermic peak after SC-CO2 treatment was observed by the thermal analysis of WPI. These results confirmed that the structure and conformation of protein were modified with SC-CO2 treatment. Industrial relevance There is a strong interest in the food industry in studying the modifying protein functionality to produce higher quality products. Supercritical carbon dioxide (SC-CO2) treatment described as green method has raised interests in its application for polymer modification. SC-CO2 is a unique processing method offering many advantages over conventional thermal processing methods, including the ability to retain the quality of food, which may be lost during conventional thermal processing. This work explores the SC-CO2 effect on the structural and conformational modification of protein which would be extremely helpful in understanding the improving of the protein functionalities such as, emulsifying and rheological properties in order to produce higher quality food products.

A Review on the Effects of Supercritical Carbon Dioxide on Enzyme Activity

Different types of enzymes such as lipases, several phosphatases, dehydrogenases, oxidases, amylases and others are well suited for the reactions in SC-CO2. The stability and the activity of enzymes exposed to carbon dioxide under high pressure depend on enzyme species, water content in the solution and on the pressure and temperature of the reaction system. The three-dimensional structure of enzymes may be significantly altered under extreme conditions, causing their denaturation and consequent loss of activity. If the conditions are less adverse, the protein structure may be largely retained. Minor structural changes may induce an alternative active protein state with altered enzyme activity, specificity and stability.

Reducing oyster-associated bacteria levels using supercritical fluid CO 2 as an agent of warm pasteurization

An innovative approach to Post-Harvest Processing (PHP) of oysters is introduced focusing on the effects of supercritical carbon dioxide (scCO 2) on bacterial contaminants trapped in the digestive system of oysters. Oysters were exposed to scCO 2 under two conditions: (1) 100 bar and 37 °C for 30 min and (2) 172 bar and 60 °C for 60 min. Using FDA standard guidelines for food analysis, variations in the Aerobic Plate Count (APC) were assessed. It was established that exposing oysters to CO 2 at 100 bar and 37 °C for 30 min and at 172 bar and 60 °C for 60 min induced 2-log and 3-log reductions in the APC respectively. The decrease in the microbial load as a result of treatment with scCO 2 was found to be significant ( P = 0.002). A release of adductor muscles from the shell was noted in oysters treated at 172 bar and 60 °C for 60 min; this was not the case for oysters treated at 100 bar and 37 °C for 30 min. A blind study allowing sensory analysis of treated vs. untreated oysters was also completed and no significant change in the physical appearance, smell, or texture was recorded. In this paper, we also report the effect of scCO 2 on several bacterial isolates, including a referenced ATCC strain of a non-pathogenic Vibrio ( Vibrio fischeri) as well as several other bacterial isolates cultured from oyster' tissues and found to share biochemical features common to pathogenic Vibrio strains. A complete inactivation (minimum 7-log reduction) was achieved with these latter bacterial isolates. A 6-log reduction was observed with V. fischeri.

Inactivation of Alicyclobacillus acidoterrestris spores in apple juice by supercritical carbon dioxide

We investigated the lethal effect of supercritical carbon dioxide (SC-CO 2; temperature: 65, 70 °C, pressure: 80, 100, 120 bar, time: 10–40 min) on Alicyclobacillus acidoterrestris spores (10 6–10 7 spores/ml) suspended in apple juice. A. acidoterrestris spores were completely inactivated by SC-CO 2 to undetectable levels in above 65 °C, 100 bar for 40 min and 70 °C, 80 bar for 30 min. The SC-CO 2 did not affect ( p > 0.05) the pH and ˚Brix of apple juice. In electron microscopic observations, the surface and internal morphological changes and extraction of intracellular materials of the treated spores were observed. Our results indicate that SC-CO 2 can effectively kill A. acidoterrestris spores in apple juice with no changes to the quality of the juice and also provides a complementary understanding of inactivation action of SC-CO 2.

Effects of supercritical carbon dioxide treatment against generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7 in marinades and marinated pork

This study was conducted to evaluate the effects of supercritical carbon dioxide (SC-CO 2) treatment on soy sauce and hot-pepper paste marinades, as well as in marinated pork products, for the inhibition of generic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and E. coli O157:H7. SC-CO 2 was more effective at destroying foodborne pathogens when it was applied to the marinades than the marinated products. SC-CO 2 treatment at 14 MPa and 45 °C for 40 min resulted in a greater reduction in soy sauce (2.52–3.47 log CFU/cm 2) than in hot-pepper paste marinade (2.12–2.72 log CFU/cm 2). In the case of the marinated pork, when SC-CO 2 was applied at 14 MPa and 45 °C for 40 min, the reduction levels of L. monocytogenes were 2.49 and 1.92 log CFU/cm 2 in soy sauce and hot-pepper paste marinated pork, respectively. The results should be useful in the meat industry to help increase microbial safety and assure the microbial stability of marinades and marinated products.

Nanostructured microspheres produced by supercritical fluid extraction of emulsions

The system poly(lactic-co-glycolic) acid/ piroxicam (PLGA/PX) was selected, as a model system, to evaluate the effectiveness of supercritical carbon dioxide (SC-CO(2)) extraction of the oily phase (ethyl acetate) from oil-in-water emulsions used in the production of polymer/drug microspheres for sustained drug release applications. The influence of process parameters like operating pressure and temperature, flow rate and contacting time between the emulsion and SC-CO(2) was studied with respect to the microsphere size, distribution and solvent residue. Different polymer concentrations in the oily phase were also tested in emulsions formulation to monitor their effects on droplets and microspheres size distribution at fixed mixing conditions. Spherical PLGA microspheres loaded with PX (10% w/w) with mean sizes ranging between 1 and 3 microm and very narrow size distributions were obtained due to the short supercritical processing time (30 min) that prevents the aggregation phenomena typically occurring during conventional solvent evaporation process. A solvent residue smaller than 40 ppm was also obtained at optimized operating conditions. DSC and SEM-EDX analyses confirmed that the produced microparticles are formed by a solid solution of PLGA and PX and that the drug is entrapped in an amorphous state into the polymeric matrix with an encapsulation efficiency in the range of 90-95%. Drug release rate studies showed very uniform drug concentration profiles, without any burst effect, confirming a good dispersion of the drug into the polymer particles.

Effects of SC‐CO2 Treatment on the Properties of NBR/CuSO4 Composites

Effects of supercritical carbon dioxide (SC‐CO2) treatment on the properties of acrylonitrile‐butadiene rubber (NBR) filled with anhydrous copper sulfate (CuSO4) particles were investigated in this work. The NBR with CuSO4 particles could be coordination crosslinked (by heating at high temperatures) without adding any vulcanization chemicals. It was found that the NBR/CuSO4 mixture after SC‐CO2 treating had a higher vulcanization rate and a higher equilibrium torque value, which means a higher crosslink density for the vulcanizate. SEM and XPS results confirmed that more small CuSO4 particles (with the size below 2 μm) in the SC‐CO2 sample resulted in more coordination crosslinking points in the crosslinking network. Therefore, after SC‐CO2 treatment, the NBR/CuSO4 composite had higher mechanical strength relative to the sample by simple mechanical mixing.

Enhanced Functionalities of Whey Proteins Treated with Supercritical Carbon Dioxide

The functionality of whey proteins can be modified by many approaches; for example, via complexation with carbohydrates, enzymatic cross-linking, or hydrolysis, and the objective of this work was to research the effects of supercritical carbon dioxide (scCO2) treatments on the functionalities of commercial whey protein products including whey protein isolates (WPI) and whey protein concentrates (WPC). The WPI and WPC powders and a 10% (wt/vol) WPI solution were treated with scCO2. The WPI solution was treated at 40°C and 10MPa for 1h, whereas WPI and WPC powders were treated with scCO2 at 65°C and 10 or 30MPa for 1h. Dynamic rheological tests were used to characterize gelation properties before and after processing. Compared with the unprocessed samples and samples processed with N2 under similar conditions, scCO2-treated WPI, whether dispersed in water or in the powder form during treatments, formed a gel with increased strength. The improvement in gelling properties was more significant for the scCO2-treated WPC. In addition, the scCO2-processed WPI and WPC powders appeared to be fine and free-flowing, in contrast to the clumps in the unprocessed samples. Proximate compositional and surface hydrophobicity analyses indicated that both compositional and structural changes may have contributed to enhanced whey protein functionalities. The results suggest that functionalities of whey proteins can be improved by scCO2 treatment to produce novel ingredients.

Synthesis of cellulose/titanium dioxide hybrids in supercritical carbon dioxide

The modifications and applications of natural cellulose have attracted more and more interest in recent years, sparked by the progressive shortage of the fossil energy resources and increase in the technological interests in sustainable and renewable raw materials. In this paper, a novel approach for preparation of cellulose/titanium dioxide hybrids was achieved by utilizing supercritical carbon dioxide-assisted impregnation. The hybrids, with a very small scale in length, suggest that the titania particles were not only coating on the external surface but also penetrating into the micro-cavity structure of the cellulose fibers. The penetrating and swelling effect of supercritical carbon dioxide, with a colsovent of ethanol, on the cellulose was also investigated. It was found that such actions of carbon dioxide in the supercritical state influenced the interactions between the molecular chains of cellulose. The titania particles were facilitated by the effect of supercritical carbon dioxide to access and impregnate into the crystalline structure of cellulose fibers by formation and stabilization of hydrogen bonds with abundant hydroxyl groups of cellulose, resulting in a change of its thermal stability in pyrolysis. This preparative procedure is facile and environmentally friendly, and provides a simple approach for the synthesis of useful materials in various applications.

Effects of supercritical carbon dioxide on volatile formation from Maillard reaction between ribose and cysteine

AbstractBACKGROUND: Supercritical carbon dioxide (SC‐CO2) technology is being used in an increasing number of food‐manufacturing applications; however, its effect on the Maillard reaction is not well studied. The objective of this study was to investigate the effect of SC‐CO2 treatment (140 °C, 40 MPa) on the Maillard reaction of an aqueous ribose–cysteine model system under varying pH conditions (5.6, 7.0 and 8.0), with emphasis on the formation of volatile compounds.RESULTS: SC‐CO2 had a suppressing effect on the browning stages of the reaction under acidic and neutral pH conditions, while it appeared to have an accelerating effect at pH 8.0. Over 70 volatile compounds were positively identified from the headspace of the model system by gas chromatography–mass spectrometry. The volatiles were dominated by sulfur‐containing compounds including thiophenes and fused bicyclic sulfur‐containing compounds under all experimental conditions. Several compounds, including 2‐methyl‐3‐furanthiol, 2‐furanmethanethiol, 3‐thiophenethiol, and 2‐methyl‐3‐thiophenethiol, and one of the intermediates, furfural, were generated in much higher amounts in the SC‐CO2‐treated samples, especially at alkaline and neutral pH values.CONCLUSION: SC‐CO2 treatment was inhibitory to the formation of most volatiles in the Maillard reaction, but enhanced the formation of some intermediates and well‐known meaty flavoured compounds. Copyright © 2007 Society of Chemical Industry

Novel route to nanoparticle dispersion using supercritical carbon dioxide

An experimental study was carried out to determine the effects of supercritical carbon dioxide (scCO 2) on the break up of untreated and treated alumina agglomerates in polystyrene. Alumina nanoparticles were treated with fluoroalkanes to achieve a better affinity with scCO 2. All agglomerates were found inside pores (cells) that were created by scCO 2 expansion during depressurization, and the observed cell size increased with increasing alumina agglomerate size. When untreated alumina was used, the agglomerates were not affected by scCO 2 expansion. On the other hand, large agglomerates ( L ≥ 15 μm) of the treated alumina showed signs of catastrophic fragmentation, whereas small agglomerates of the treated alumina were intact upon scCO 2 expansion. This was attributed to the amount of scCO 2 saturation around and within small agglomerates, which does not provide enough energy to break up the agglomerate. This conclusion was also supported by the fact that cell sizes were proportional to agglomerate size. Large agglomerates can absorb more scCO 2 than smaller ones, and therefore, have an adequately larger bursting pressure to overcome interactions between individual alumina nanoparticles that make up the agglomerate.