Dense Phase Carbon Dioxide Research Articles

INACTIVATION OF STAPHYLOCOCCUS AUREUS EXPOSED TO DENSE‐PHASE CARBON DIOXIDE IN A BATCH SYSTEM

ABSTRACT The inactivation of Staphylococcus aureus exposed to dense‐phase carbon dioxide (DPCD) was investigated, and the kinetics of come‐up time (CUT) in pressurization was monitored with come‐down time (CDT) and temperature fluctuation in depressurization. CUT was about 2.5, 3.5, 4.0 and 4.0 min; CDT was 3.4, 3.7, 4.5 and 4.5 min; lowest temperature of samples in depressurization was 4, −1, −15 and −22C, corresponding to 10, 20, 30 and 40 MPa at 37C. The inactivation behavior of S. aureus was closely related to the variables of process pressure, holding‐pressure time (HPT), process temperature and process cycling. The log reduction of S. aureus at 40 MPa for 30‐min HPT was significantly greater (P < 0.05), but the inactivation effect at 10, 20 and 30 MPa was similar. The log reduction of S. aureus at 30 and 40 MPa for 60‐min HPT was similar and significantly greater (P < 0.05), while the inactivation effect at 10 and 20 MPa was similar. The inactivation of S. aureus against HPT conformed to a fast–slow biphase kinetics; the two stages were well fitted to a first‐order model with higher regression coefficients R2 = 1.000 and 0.9238; their respective D values (decimal reduction time) were 16.52 and 70.42 min. As the process temperature increased, the log reduction of S. aureus increased significantly (P < 0.05); the inactivation kinetics of S. aureus versus process temperature was characterized with a fast inactivation rate from 32 to 45C and a slow inactivation rate from 45 to 55C. As compared to one‐process cycling for a total of 60‐min HPT, four‐process cycling resulted in a significant reduction of S. aureus, and its maximal reduction was near to 5 log cycles, indicating that more process cycling caused more inactivation of S. aureus under identical pressure and temperature with equal HPT. However, the maximal reduction was 0.09 and 0.12 log cycles for two‐ and four‐process cyclings with 0‐min HPT, indicating that pressurization and depressurization had a lesser effect on the inactivation of S. aureus, while HPT was significant in DPCD to inactivate S. aureus.PRACTICAL APPLICATIONSDense‐phase carbon dioxide (DPCD) is a novel technology to achieve cold pasteurization and/or sterilization of liquid and solid materials, and is likely to replace or partially substitute currently and widely applied thermal processes. This study showed that DPCD effectively inactivated Staphylococcus aureus inoculated in 7.5% sodium chloride broth, and the inactivation behavior of S. aureus was closely related to the pressure, holding‐pressure time, temperature and process cycling. Based on this observation, the technology of DPCD can be applied in the pasteurization of foods such as milk and various fruit juices, especially thermal‐sensitive materials.

Alterations of molecular properties of lipoxygenase induced by dense phase carbon dioxide

Abstract Alterations of molecular properties of lipoxygenase (LOX) induced by dense phase carbon dioxide (DPCD) were analyzed using transmission electronic microscope (TEM), SDS-PAGE and native-PAGE, far UV-circular dichroism (CD) and fluorescence spectroscopy. The aggregation of LOX molecules was suggested by an increase in the particle size of LOX after DPCD treatment. The absence of LOX band was observed after exposure to DPCD at 55 °C for 30 min on the native-PAGE due to the aggregation, but the electrophoretic behavior of LOX was not altered on the SDS-PAGE. The CD and fluorescence spectra of DPCD-treated LOX were noticeably changed, its α-helix relative content decreased sharply to less than 10%, and its intrinsic relative fluorescence intensity (RFI) decreased linearly with increasing pressures. Industrial relevance As a novel non-thermal technology, DPCD can retain the quality of foods to be processed. However, the inactivation mechanism of food enzymes by DPCD is not elucidated until today. This investigation is beneficial to understand the mechanism and to push the application of this technology in food industry.

Inactivation of Apple Pectin Methylesterase Induced by Dense Phase Carbon Dioxide

The inactivation of apple pectin methylesterase (PME) with dense phase carbon dioxide (DPCD) combined with temperatures (35-55 degrees C) is investigated. DPCD increases the susceptibility of apple PME to the temperatures and the pressures have a noticeable effect on apple PME activity. A labile and stable fraction of apple PME is present and the inactivation kinetics of apple PME by DPCD is adequately described by a two-fraction model. The kinetic rate constants k L and k S of labile and stable fractions are 0.890 and 0.039 min (-1), and the decimal reduction times D L and D S are 2.59 and 58.70 min at 30 MPa and 55 degrees C. Z T representing temperature increase needed for a 90% reduction of the D value and the activation energy E a of the labile fraction at 30 MPa is 22.32 degrees C and 86.88 kJ /mol, its Z P representing pressure increase needed for a 90% reduction of the D value and the activation volume V a at 55 degrees C is 21.75 MPa and -288.38 cm (3)/mol. The residual activity of apple PME after DPCD exhibits no reduction or reactivation for 4 weeks at 4 degrees C.

Behavior of inactivation kinetics of Escherichia coli by dense phase carbon dioxide

Inactivation of Escherichia coli in cloudy apple juice by dense phase carbon dioxide (DPCD) was investigated. The pressures were 10, 20 and 30 MPa, the temperatures were 32, 37 and 42 °C. The inactivation kinetic behavior of E. coli conformed to a sigmoid curve with a shoulder and a tail, which was closely related with temperature or pressure. With the increase of temperature or pressure, the shoulder became unclear or even disappeared. The experimental data were well fitted to a model proposed by Xiong et al. [Xiong, R., Xie, G., Edmondson, A.E., Sheard, M.A., 1999. A mathematical model for bacterial inactivation. International Journal of Food Microbiology 46, 45–55], the kinetic parameters of t lag (the lag time length), f (the initial proportion of less resistant population), k 1 (the inactivation rate constant of less resistant fraction) and k 2 (the inactivation rate constant of resistant fraction), and t 4 − D (the time required for an 4-log-cycle reduction of bacteria under a given condition) were obtained from this model. The t lag declined from 4.032 to 0.890 min and t 4 − D from 54.955 to 18.840 min, k 1 was 1.74–4.4 times of k 2. Moreover, the model was validated by more experimental data, the accuracy factor ( Af), bias factor ( Bf), root mean square error (RMSE), sum of squares (SS), and correlation coefficient ( R 2) were used to evaluate this model performance, indicating that the model could provide a good fitting to the experimental data.

Nonthermal Inactivation of Escherichia coli K-12 on Spinach Leaves, Using Dense Phase Carbon Dioxide

While the use of some chemical sanitizers is approved for inactivation of microbes on the surfaces of fruits and vegetables, these compounds often degrade product quality with limited improvement in product safety. The application of dense phase carbon dioxide (DPCD, or high-pressure CO2) is a nonthermal process for inactivation of foodborne pathogens inoculated into various juices and model solutions. In this work, DPCD was evaluated for its potential to inactivate Escherichia coli K-12 inoculated on fresh spinach leaves. Inoculated leaves were exposed for up to 40 min to DPCD at a subcritical condition (5 MPa, 40°C) and two supercritical conditions (7.5 and 10 MPa, 40°C) at a flow rate of 50 g of CO2/min. E. coli K-12 populations were reduced to nondetectable levels (~5-log reduction) using supercritical treatment conditions at exposure times as short as 10 min; efficacy of DPCD at the subcritical state was limited. This research demonstrates that DPCD has potential as a pasteurization technology for application to leafy green vegetables, although issues with discoloration and other quality measures will need more extensive evaluations.

ChemInform Abstract: Heterogeneous Catalysis for Fine Chemicals in Dense Phase Carbon Dioxide

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An in situ high pressure FTIR study on molecular interactions of ketones, esters, and amides with dense phase carbon dioxide

The interactions between a variety of carbonyl compounds (ketones, esters, and amides) and dense phase CO 2 have been investigated by in situ high pressure FTIR measurements. The gas and liquid phase spectra of these compounds have also been measured to provide accurate reference data, and these have been compared with those obtained in n-hexane and dense phase CO 2 at a variety of pressures. The frequency of the carbonyl IR absorption is a measure of the strength of the carbonyl bond, and in the dense CO 2 medium, is in between that observed in the gaseous and liquid phases. The substituent effect on the ν(C O) absorption bands is the same for the gas, liquid, and dense CO 2 spectra and it is related to the electron donating nature of the substituents. When solutions of carbonyl compounds in n-hexane are diluted, the ν(C O) absorption bands are blue-shifted. In contrast, these bands in dense CO 2 are red-shifted with increasing pressure (dilution by CO 2). The red shift with increasing CO 2 pressure is larger in amides > esters > ketones.

Heterogeneous Catalysis for Fine Chemicals in Dense Phase Carbon Dioxide

AbstractAn increasing number of fine chemicals is being produced using heterogeneously catalysed reactions in supercritical carbon dioxide with significant improvements in terms of process selectivity and purity of the products thereby obtained. A selection of examples and of recent findings shows the large potential of this technology for the synthetic chemistry of the future.

Stabilization of catalytic sol–gel entrapped perruthenate

A combination of more stable counter-cation (tetraphenylphosphonium in place of tetrapropylammonium), of local basic microenvironment, and of a non-solubilizing reaction medium (supercritical CO 2) improves the life-cycle and reusability of catalytic ORMOSILs doped with perruthenate in the oxidation of alcohols with O 2. A number of different bases were co-entrapped and their effect on catalysis assessed in the oxidative dehydrogenation of benzyl alcohol in dense phase carbon dioxide at 22 MPa and 75 °C. The optimized catalyst retains most of its activity after five consecutive runs when a normal ORMOSIL-entrapped TPAP has become inactive. Deactivation of TPAP could be ascribed by EPR analysis to the formation of catalytically inactive RuO 2.

Inactivation of Escherichia coli inoculated into cloudy apple juice exposed to dense phase carbon dioxide

The inactivation of Escherichia coli in cloudy apple juice by dense phase carbon dioxide (DPCD) was investigated. With CO 2 at 20 MPa and 37 °C or at 30 MPa and 42 °C, the inactivation of E. coli significantly increased ( p < 0.05) when increasing the exposure time, which conformed to a fast-to-slow two-stage kinetics. The two stages were well fitted to first-order reactions. Higher temperature or pressure significantly enhanced the bactericidal effect of DPCD ( p < 0.05), the maximum reduction was 7.66 log CFU at 45 MPa and 52 °C for 30 min. The survival curves against temperature or pressure were fitted using a linear equation with high regression coefficients ( R 2 > 0.94). The temperature inactivation rate ( k T) and pressure inactivation rate ( k P) were obtained. Higher k T or k P indicated higher susceptibility of E. coli to temperature or pressure. Moreover, there was good linear correlation of k T with pressure ( R 2 = 1.00). Also, k P increased with increasing temperature except for 37 °C. Greater inactivation of E. coli was obtained with 99.9% CO 2 than with 99.5% CO 2 or with the initial number of 10 5 CFU/mL than with that of 10 8 CFU/mL at 20 MPa and 37 °C.

Non‐thermal food processing/preservation technologies: a review with packaging implications

AbstractNon‐thermal food processing/preservation methods interest food and food packaging scientists, manufacturers and consumers because they exert a minimal impact on the nutritional and sensory properties of foods, and extend shelf life by inhibiting or killing microorganisms. They are also considered to be more energy efficient and to preserve better quality attributes than conventional thermally based processes. Non‐thermal processes also meet industry needs by offering value‐added products, new market opportunities and added safety margins. This study reviewed non‐thermal processing technologies currently available or developmental for the inactivation of microorganisms and thus microbiological shelf life in foods, and to identify packaging interactions that might result. Processes include ultra‐high pressure, ionizing radiation, pulsed X‐ray, ultrasound, pulsed light and pulsed electric fields, high‐voltage arc discharge, magnetic fields, dense phase carbon dioxide and hurdle technologies. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Pasteurization of Beer by a Continuous Dense-phase CO2 System

Effects on beer quality were studied after pasteurization by a continuous dense-phase carbon dioxide (DPCD) system. Changes in haze formation, foaming capacity and stability, and objective and subjective aroma and flavor were evaluated, after validation of a 5-log reduction in yeast populations. A maximum log reduction in yeast populations of 7.38 logs was predicted at 26.5 MPa, 21°C, 9.6% CO2, and 4.77 min residence time. Haze was reduced by DPCD pasteurization from 146 nephelometric turbidity units (NTU) to 95 NTU. At this same treatment combination, aroma and flavor of beer sample means were not considered significantly different (P= 0.3415) from fresh beer sample means when evaluated in a difference from control test, using fresh beer as the reference. Foam capacity and stability were affected minimally by CO2 processing; however, changes would most likely be unnoticed by consumers.

Inactivation of Escherichia coli (ATCC 4157) in Diluted Apple Cider by Dense-Phase Carbon Dioxide

Dense-phase carbon dioxide (CO2) treatments in a continuous flow through system were applied to apple cider to inactivate Escherichia coli (ATCC 4157). A response surface design with factors of the CO2/product ratio (0, 70, and 140 g/kg), temperature (25, 35, and 45°C), and pressure (6.9, 27.6, and 48.3 MPa) were used. E. coli was very sensitive to dense CO2 treatment, with a more than 6-log reduction in treatments containing 70 and 140 g/kg CO2, irrespective of temperature and pressure. The CO2/product ratio was the most important factor affecting inactivation rate of E. coli. No effect of temperature and pressure was detected because of high sensitivity of the cells to dense CO2. Dense CO2 could be an alternative pasteurization treatment for apple cider. Further studies dealing with the organoleptic quality of the product are needed.

Inactivation of yeasts in grape juice using a continuous dense phase carbon dioxide processing system

AbstractThe effects of dense phase CO2 processing parameters, including temperature (25 and 35 °C), CO2 concentration (0, 85 and 170 g kg−1) and pressure (6.9, 27.6 and 48.3 MPa), on yeast survival and sensory properties of grape juice were investigated. The dense phase CO2 process resulted in more than a 6 log reduction in yeast population. As the CO2 to juice concentration, temperature and pressure increased, the inactivation rate increased. CO2 in the supercritical state was more effective in inactivating yeast than in the subcritical state. The process did not cause detectable flavor degradation. Dense phase CO2 processing can be an effective non‐thermal alternative process for pasteurization of grape juice. Copyright © 2005 Society of Chemical Industry

Fluorinated Silica Gels Doped with TPAP as Effective Aerobic Oxidation Catalysts in Dense Phase Carbon Dioxide

AbstractHybrid organic‐inorganic fluorinated silica glasses doped with the ruthenium species TPAP (tetra‐n‐propylammonium perruthenate) are effective catalysts for the aerial oxidation of benzyl alcohol to benzaldehyde in dense phase CO2. Moderate silica fluorination (10%) by short‐chain fluoroalkyl‐containing monomers in the sol‐gel polycondensation with TMOS affords highly active catalysts which at 75 °C and 220 bar selectively dehydrogenate the alcohol with oxygen as primary oxidant. Both the activity and the stability of the fluorinated materials vary with the degree of fluorination and the nature of the fluoroalkyl residue attached to the silica polymeric network. An explanation of the behaviour of doped sol‐gel oxides in supercritical carbon dioxide is proposed which is thought to be of general validity for future practical applications to heterogeneously catalysed aerobic oxidations eliminating the current need for both organic solvents and stoichiometric oxidants.

CO2 conversion and utilization

PREFACE PART 1: GENERAL OVERVIEW 1. CO2 Conversion and Utilization: An Overview 2. CO2 Mitigation and Fuel Production 3. CO2 Emission Reductions: An Opportunity for New Catalytic Technology PART 2: SYNTHESIS OF ORGANIC CHEMICALS 4. Key Issues in Carbon Dioxide Utilisation as a Building Block for Molecular Organic Compounds in the Chemical Industry 5. Selective Conversion of Carbon Dioxide and Methanol to Dimethyl Carbonate Using Phosphoric Acid-Modified Zircona Catalysts 6. Utilization of Carbon Dioxide for Direct, Selective Conversion of Methane to Ethane and Ethylene with Calcium Based Binary Catalysts 7. Copolymerization of Carbon Dioxide, Propylene oxide, and Cyclohexene Oxide by an Yttrium-Metal Coordination Catalyst system 8. The Role of CO2 for the Gas-Phase O2 Oxidation of Alkylaromatics to Aldehyde PART 3: CO2 REDUCTION OVER HETEROGENOUS CATALYSTS 9. Effective Conversion of CO2 to Valuable Compounds by Using Multi-functional Catalysts 10. Supported Copper and Manganese Catalyst for Methanol Synthesis from CO2 Containing Syngas 11. Catalytic Reduction of CO2 into Liquid Fuels: Simulating Reactions under Geological Formation Conditions PART 4: SYNTHESIS GAS PRODUCTION FROM CO2 REFORMING 12. Methane Dry Reforming over Carbide, Nickel-based and Noble Metal Catalysts 13. A highly Active and Carbon-Resistant Catalyst for CH4 Reforming with CO2-Nickel supported on an Ultra-Fine ZrO2 14. CO2 Reforming of Methane over Ru-Loaded Lanthanoid Oxide Catalysts 15. CO2 Reforming and Simultaneous CO2 and Steam Reforming of Methane to Syngas over CoxNil-xO Supported on Macroporous Silica-Alumina Precoated with MgO 16. Low Temperature CH4 Decomposition on High Surface Area Carbon-Supported Co Catalysts 17. Effects of Pressure on CO2 Reforming of CH4 over Ni/Na-Y and Ni/Al2O3 Catalysts 18. A Comparative Study on CH4-CO2 Reforming over Ni/SiO2-MgO Catalyst Using Fluidized- and Fixed-Bed Reactors 19. Effects of Pressure on CO2 Reforming of CH4 over Rh/Na-Y and Rh/Al2O3 Catalysts 20. Methane Reforming with Carbon Dioxide and Oxygen under Atmospheric and Pressurized Conditions Using Fixed and Fluidized Bed Reactors 21. Computational Analysis of Energy Aspects of CO2 Reforming and Oxy-CO2 Reforming of Methane at Different Pressures PART 5: PHOTO-CATALYTIC AND ELECTRO-CHEMICAL REDUCTION 22. Photocatalytic Reduction of CO2 with H2O on Various Titanium Oxide Catalysts 23. Electrochemical Reduction of CO2 with Gas-Diffusion Electrodes Fabricated Using Metal and Polymer-Confined Nets PART 6: USE OF SUPERCRITICAL CO2 FLUID 24. Use of Dense-Phase Carbon Dioxide in Catalysis 25. The Possibility of Coupling Supercritical Extraction in Petroleum Industry with CO2 Conversion Plants to Lessen Investments

Environmentally Benign Multiphase Catalysis with Dense Phase Carbon Dioxide.

Abstract Environmental concerns stemming from the use of conventional solvents and from hazardous waste generation have propelled research efforts aimed at developing benign chemical processing techniques that either eliminate or significantly mitigate pollution at the source. This paper provides an overview of heterogeneous and homogeneous catalysis in dense phase CO 2 , considered a green solvent. In addition to solvent replacement, the demonstrated advantages of using dense phase CO 2 include the enhanced miscibility of reactants, such as O 2 and H 2 which eliminate interphase transport limitations, and the chemical inertness of CO 2 . Further, the physicochemical properties of CO 2 -based reaction media can be pressure-tuned to obtain unique fluid properties (e.g. gas-like transport properties, liquid-like solvent power and heat capacities). The advantages of CO 2 -based reaction media for optimizing catalyst activity and product selectivity are highlighted for a variety of reactions including alkylation on solid-acid catalysts, hydrogenation on supported noble metal catalysts and a broad range of homogeneous oxidations with transition metal catalysts and dioxygen as an oxidant. Through these examples, the need is emphasized for a systematic approach to research and development of supercritical carbon dioxide based processes, taking into account conventional multiphase reaction engineering principles, catalytic chemistry and phase behavior.

Environmentally benign multiphase catalysis with dense phase carbon dioxide

Environmental concerns stemming from the use of conventional solvents and from hazardous waste generation have propelled research efforts aimed at developing benign chemical processing techniques that either eliminate or significantly mitigate pollution at the source. This paper provides an overview of heterogeneous and homogeneous catalysis in dense phase CO2, considered a green solvent. In addition to solvent replacement, the demonstrated advantages of using dense phase CO2 include the enhanced miscibility of reactants, such as O2 and H2 which eliminate interphase transport limitations, and the chemical inertness of CO2. Further, the physicochemical properties of CO2-based reaction media can be pressure-tuned to obtain unique fluid properties (e.g. gas-like transport properties, liquid-like solvent power and heat capacities). The advantages of CO2-based reaction media for optimizing catalyst activity and product selectivity are highlighted for a variety of reactions including alkylation on solid-acid catalysts, hydrogenation on supported noble metal catalysts and a broad range of homogeneous oxidations with transition metal catalysts and dioxygen as an oxidant. Through these examples, the need is emphasized for a systematic approach to research and development of supercritical carbon dioxide based processes, taking into account conventional multiphase reaction engineering principles, catalytic chemistry and phase behavior.

Ternary phase equilibria of the iso-propanol+water+carbon dioxide system at high pressure

Ternary phase diagrams are presented for the system: iso-propanol(IPA)+water+carbon dioxide at temperatures from 15 to 70 °C and pressures from 7 to 17 MPa. The distribution coefficients of IPA between the dense phase carbon dioxide and water changed dramatically with temperature and pressure. In the vicinity of the critical point, distribution coefficients was low, yet at liquid-like densities carbon dioxide had a high affinity for IPA. Selectivity reversal was observed at differing pressures. High selectivity of CO2 for IPA was achieved in the near-critical liquid and in supercritical carbon dioxide at high pressure.

Selective epoxidation in dense phase carbon dioxide

Selective epoxidations with transition metal catalysts (V, Ti, Mo) and ButOOH proceed with high conversions and high selectivity in dense phase carbon dioxide.