Compressed Carbon Dioxide Research Articles

The control system of the ecological hybrid two stages refrigerating cycle

The compression anticlockwise cycle is mostly used for refrigeration. However due to the environmental regulations, the use of classic refrigerants: F-gases is limited by international agreements. Therefore the combined compression-adsorption hybrid cycle with natural liquids: water/carbon dioxide working as the energy carriers is a promising solution. This allows to utilize the solar or waste energy for the refrigeration purpose. In this paper application of the solar collectors as the energy source for the adsorption cycle, coupled with the low temperature (LT) refrigerating carbon dioxide compression cycle is shown. The control of the system is an essential issue to reduce the electric power consumption. The control of the solar heat supply and water sprayed cooling tower, for the adsorption cycle re-cooling, is presented in this paper. The designed control system and algorithm is related to the LT compression cycle, which operates according to the need of cold for the refrigeration chamber. The results of the laboratory investigations of the full system, showing the reduction of the energy consumption and maximum utilization of the solar heat for different control methods are presented.

Continuous inactivation of alkaline phosphatase and Escherichia coli in milk using compressed carbon dioxide as inactivating agent

This work investigated a continuous processing of milk for inactivation of alkaline phosphatase and Escherichia coli ATCC 25922 using supercritical carbon dioxide as inactivating agent. For this purpose, the influence of CO2 to milk mass ratio in the range of 0.05–0.45wt%, temperature from 30 to 70°C, pressure from 80 to 180 bar and apparent residence time from 10 to 30min on the enzyme and microbial inactivation were investigated by means of a central composite design for three independent variable. Enzyme inactivation of 94.5% was reached when the process was operated at CO2 to milk mass ratio of 0.05, 70°C, 80 bar and apparent residence time of 30min. At this condition, the rate of microbial inactivation was 0.09min−1. Results presented in this work contribute for the development of innovative process for food processing and preservation. The continuous operation consists in an advance in the use of supercritical carbon dioxide for food treatment.

Sorption Behavior of Compressed CO2 and CH4 on Ultrathin Hybrid Poly(POSS-imide) Layers.

Sorption of compressed gases into thin polymeric films is essential for applications including gas sensors and membrane based gas separation. For glassy polymers, the sorption behavior is dependent on the nonequilibrium status of the polymer. The uptake of molecules by a polymer is generally accompanied by dilation, or swelling, of the polymer material. In turn, this dilation can result in penetrant induced plasticization and physical aging that affect the nonequilibrium status of the polymer. Here, we investigate the dilation and sorption behavior of ultrathin membrane layers of a hybrid inorganic-organic network material that consists of alternating polyhedral oligomeric silsesquioxane and imide groups, upon exposure to compressed carbon dioxide and methane. The imide precursor contains fluoroalkene groups that provide affinity toward carbon dioxide, while the octa-functionalized silsesquioxane provides a high degree of cross-linking. This combination allows for extremely high sorption capacities, while structural rearrangements of the network are hindered. We study the simultaneous uptake of gases and dilation of the thin films at high pressures using spectroscopic ellipsometry measurements. Ellipsometry provides the changes in both the refractive index and the film thickness, and allows for accurate quantification of sorption and swelling. In contrast, gravimetric and volumetric measurements only provide a single parameter; this does not allow an accurate correction for, for instance, the changes in buoyancy because of the extensive geometrical changes of highly swelling films. The sorption behavior of the ultrathin hybrid layers depends on the fluoroalkene group content. At low pressure, the apparent molar volume of the gases is low compared to the liquid molar volume of carbon dioxide and methane, respectively. At high gas concentrations in the polymer film, the apparent molar volume of carbon dioxide and methane exceeds that of the liquid molar volume, and approaches that of the gas phase. The high sorption capacity and reversible dilation characteristics of the presented materials provide new directions for applications including gas sensors and gas separation membranes.

Dew‐point measurements for water in compressed carbon dioxide

When transporting CO2 for sequestration, it is important to know the water dew point in order to avoid condensation that can lead to corrosion. A flow apparatus to measure the water content at saturation in a compressed gas has been constructed. A saturator humidifies the flowing gas by equilibrating it with liquid water. Then, a gravimetric hygrometer measures the water mole fraction of the humid gas. Dew‐point data for H2O in CO2 on six isotherms between 10 and 80 °C at pressures from 0.5 to 5 MPa are reported. The uncertainties in water content at the dew point (expanded uncertainty with coverage factor k = 2) are on average 0.3%, significantly smaller than in any previous work. The data have been analyzed to extract the interaction second virial coefficient; the values are consistent with the theoretical estimates of Wheatley and Harvey but have a much smaller uncertainty. Published 2015 American Institute of Chemical Engineers AIChE J, 2015 © 2015 American Institute of Chemical Engineers AIChE J, 61: 2913–2925, 2015

An Investigation of Condensation Effects in Supercritical Carbon Dioxide Compressors

Supercritical CO2 (S-CO2) power cycles have demonstrated significant performance improvements in concentrated solar and nuclear applications. These cycles promise an increase in thermal-to-electric conversion efficiency of up to 50% over conventional gas turbines (Wright, S., 2012, “Overview of S-CO2 Power Cycles,” Mech. Eng., 134(1), pp. 40–43), and have become a priority for research, development, and deployment. In these applications the CO2 is compressed to pressures above the critical value using radial compressors. The thermodynamic state change of the working fluid is close to the critical point and near the vapor–liquid equilibrium region where phase change effects are important. This paper presents a systematic assessment of condensation on the performance and stability of centrifugal compressors operating in S-CO2. The approach combines numerical simulations with experimental tests. The objectives are to assess the relative importance of two-phase effects on the internal flow behavior and to define the implications for radial turbomachinery design. The condensation onset is investigated in a systematic manner approaching the critical point. A nondimensional criterion is established that determines whether condensation might occur. This criterion relates the time required for stable liquid droplets to form, which depends on the expansion through the vapor–pressure curve, and the residence time of the flow under saturated conditions. Two-phase flow effects can be considered negligible when the ratio of the two time scales is much smaller than unity. The study shows that condensation is not a concern away from the critical point. Numerical two-phase calculations supported by experimental data indicate that the timescale associated with nucleation is much longer than the residence time of the flow in the saturated region, leaving little opportunity for the fluid to condense. Pressure measurements in a converging diverging nozzle show that condensation cannot occur at the level of subcooling characteristic of radial compressors away from the critical point. The implications are not limited to S-CO2 power cycles but extend to applications of radial machines for dense, saturated gases. In the immediate vicinity of the critical point, two-phase effects are expected to become more prominent due to longer residence times. However, the singular behavior of thermodynamic properties at the critical point prevents the numerical schemes from capturing important gas dynamic effects. These limitations require experimental assessment, which is the focus of ongoing and future research.

Effect of CO2 on a Mobility Gradient of Polymer Chains near an Impenetrable Solid

We report a mobility gradient of polymer chains in close proximity of a planar solid substrate in compressed carbon dioxide (CO2) gas. A series of bilayers composed of bottom hydrogenated polystyrene (h-PS) and top deuterated PS (d-PS) layers were prepared on Si substrates. A high-pressure neutron reflectivity (NR) technique was used to study the diffusive motion at the h-PS/d-PS interface as a function of the distance from the substrate interface. The results reveal that the interdiffusive chain dynamics gets strongly hindered compared to the bulk when the distance from the substrate is less than 3Rg (Rg is the radius of polymer gyration of the h-PS). At the same time, by utilizing rapid quench of CO2 and subsequent solvent leaching, we reveal the presence of the CO2-induced polymer adsorbed layer on the substrate. We postulate that loop components in the adsorbed polymer chains provide a structure that can trap the neighboring polymer chains effectively, hence reducing the chain mobility in the close vi...

Reversible and non-reactive cellulose separations from ionic liquid mixtures with compressed carbon dioxide.

A novel physical (non-reactive) separation of cellulose from an ionic liquid (IL)/cosolvent mixture by compressed carbon dioxide is presented. The precipitation is completely reversible and rapid within small changes of pressure i.e. liquid phase CO2 composition. High pressure phase equilibrium, high pressure NMR, and solid state NMR have been utilized to understand the separation phenomena.

A Reliable Method for the Separation and Detection of Synthetic Cannabinoids by Supercritical Fluid Chromatography with Mass Spectrometry, and Its Application to Plant Products.

A reliable method using supercritical fluid chromatography with mass spectrometry (SFC-MS) was developed for cannabinoids using compressed carbon dioxide (CO2) and methanol as the mobile-phase. The cannabinoids, i.e., cannabicyclohexanol (CCH: cis-isomer), trans-CCH, 5-(1,1-dimethylheptyl)-2-[(1R,3S)-3-hydroxycyclohexyl]-phenol (CP-47497), 5-(1,1-dimethylheptyl)-2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]-phenol (CP-55940), 3-(1,1'-dimethylheptyl)-6aR,7,10,10aR-tetrahydro-1-hydroxy-6,6-dimethyl-6H-dibenzo[b,d]pyran-9-methanol (HU-210), 2-[1R-3-methyl-6R-(1-methylethenyl)-2-cyclohexen-1-yl]-5-pentyl-1,3-benzenediol (CBD), (1-pentyl-1H-indol-3-yl)-1-naphthalenyl-methanone (JWH-018), (1-butyl-1H-indol-3-yl)-1-naphthalenyl-methanone (JWH-073) and 1-(1-pentyl-1H-indol-3-yl)-2-(2-methoxyphenyl)-ethanone (JWH-250), were determined within 12 min using a conventional column (2-EP) for SFC. Furthermore, two optical isomers of CCH and trans-CCH were completely and rapidly separated by a chiral stationary phase column (AMY1). A highly sensitive detection (0.002-3.75 ppb) was also obtained by these methods using 2-EP and AMY1 columns. These methods were applied to the qualitative and quantitative determination of cannabinoids in dried plant products. Although the concentration and species were different in the products, JWH-018, JWH-073 and CCH, including the cis-isomer, trans-isomer and the optical isomers, were detected in the products. Therefore, the proposed SFC-MS method seems to be useful as an alternative method to GC-MS and LC-MS for illegal drugs, such as cannabinoids.

Extraction of 5-HMF from the conversion of glucose in ionic liquid [Bmim]Cl by compressed carbon dioxide

The efficient separation of 5-hydroxymethylfurfural from the conversion of glucose in [Bmim]Cl has been achieved by using compressed CO2.

Phase Behaviours of Polybutadiene–Polyacrylic Acid Brushes in Compressed Carbon Dioxide

Our present work investigated the phase behaviour of polybutadiene–poly acrylic acid (PB–PAA) brushes–solvent–CO2 ternary system in detail. The phase separation pressures increased with increasing temperatures and solid contents of PB–PAA solution, and decreased with increasing sizes of the brushes. Considering that the expansion of water was much smaller than that of ethanol by compressed CO2, a higher cloud point pressure of CO2 could be employed to reach the phase separation when water was added as the co-solvent. Owing to the penetration of CO2 into the periphery of the shell, the chains of the polymer brushes initially shrank and then turned to aggregations before finally precipitating upon CO2 addition. Our results provide a simple and effective way for separation and recovery of polymer brushes that could promote a wider range of their applications.

Effects of CO2, tetrafluoroethane, and their mixtures with ethanol on E. coli cells

The kinetics of inactivation of E. coli bacteria in compressed carbon dioxide, tetrafluoroethane (Freon 134a), and their mixtures with ethanol was studied. The possibility of decreasing the concentration of survived cells by seven orders of magnitude upon the addition of to 5 vol % ethanol to the main solvent was demonstrated.

Kinetics and polarity effects in the synthesis of the ionic liquid, 1-hexyl-3-methyl-imidazolium bromide, using compressed CO2

Compressed carbon dioxide, as a solvent medium, offers unique benefits for the synthesis of ionic liquids (ILs) especially for the ability to combine reaction and separation. The second-order reaction rate constants were determined for the synthesis of 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]) at 313.15K and 333.15K and 30–150bar from the reactants, 1-methylimidazole and 1-bromohexane. Two different scenarios were encountered based upon the pressure: a one-phase supercritical mixture of the reactants becoming a vapor-liquid IL/CO2 system at complete conversion; or a two-phase CO2-expanded liquid (CXL) that yielded a three-phase vapor-liquid-liquid equilibrium (VLLE) at intermediate conversions. Despite multiphase phenomena, the vast majority of the reaction occurs in the reactant-rich liquid phase. The kinetic rate constants were comparable with traditional organic solvents. The reaction rates were higher in the CXL mode than in the initially supercritical mixtures. The changes in the kinetic rate constant with pressure (CO2 composition) could be explained and quantified using Kamlet–Taft (KT) polarity parameters that were measured in the mixtures using solvatochromic probes.

Synthesis and powder generation of powder coatings using supercritical carbon dioxide

This paper reports an integral continuous process of polymerization and micronization of powder coatings using supercritical CO2 as solvent. Combining different process steps into one single process, using ultra short production chains, can be one future use of supercritical fluids. This contribution is therefore an example of how such integral processes can be designed and how the development of new products can look like using supercritical fluids. An acrylic resin consisting of glycidyl methacrylate, methyl methacrylate and styrene was chosen as polymer system for use of thermosetting material for acrylic powder coating application. The reaction was performed in a tubular reactor. A monomer conversion of more than 96% was achieved with short reaction times of about 30min at a temperature of 135°C and at a pressure of 30MPa in a homogeneous CO2 phase. The resulting polymer has a number average molecular weight of about 2500g/mol with a narrow polydispersity index of 1.6. In this process, the synthesis step in compressed carbon dioxide was followed by a high pressure micronization using the well-known PGSS process. Thus, small particles of about 25μm were obtained. Simultaneously, residual monomers were removed from the polymer product with the escaping CO2-gas, achieving a high purity grade. The process is designed as a straight forward process combining synthesis, micronization and purification of a polymer without depressurization between the unit operations and demonstrates the benefits which supercritical fluid technologies offer for product and process development.

Biopolymer foaming with supercritical CO2—Thermodynamics, foaming behaviour and mechanical characteristics

Polymer foams, especially those based on biodegradable polymers, are in high demand for energy saving applications, for example as thermal insulations or packaging materials. To understand and predict the quality and material properties of polymer foams, concise knowledge of the factors influencing the foaming behaviour, especially pressure and temperature, is required. Therefore, three biodegradable polyesters, namely poly (lactide) (PLA), poly (butylene succinate) (PBS) and a blend of poly (lactide) and poly (hydroxy butyrate) (PLA-PHB), have been subjected to a direct foaming procedure using compressed carbon dioxide as blowing agent, studying the influence of saturation temperature (ranging from 95°C to 175°C) and applied pressure (ranging from atmospheric pressure to 30MPa) on the resulting foam material. As these results are strongly depending on the melting behaviour of the polymers, all three polymers were subjected to calorimetric analysis in a scanning transitiometer that allows for applying pressure levels of up to 45MPa. The created porous materials were characterized by determining their density, porosity and morphology, using SEM analysis. Their mechanical behaviour was investigated by using compressive strength tests. It is shown that the quality of the produced foam structures and its properties is strongly depending on the foaming conditions. In order to obtain foams with a high quality, the saturation temperature and pressure have to be adapted to the phase transition liquid–solid of the polymer–gas system. The results obtained via scanning transitiometer represent the SLG-line of the binary systems polymer and CO2, and their influence on the foaming behaviour enabled the identification of ideal foaming conditions for the three polymers regarded in this study.

Waste heat recovery in CO2 compression

Carbon capture and storage (CCS) is a strategically important approach for achieving significant reductions in greenhouse gas emissions from large stationary emission sources, and ensures the availability of a reliable global energy supply for the future. Carbon dioxide (CO2) compression accounts for a significant amount of the capital and operating costs, and energy penalties associated with the CCS system. In this paper, different CO2 compression strategies were reviewed, and the opportunities of recovering waste heat as an effort to reduce their energy consumption were examined. Models of an intercooling compression chain and a 2-stage shockwave compression chain were built to investigate their respective energy consumption and potential waste heat recovery. An organic Rankine cycle (ORC) model was employed to recover waste heat. An exergy analysis was applied to assess the performance of the system. The results indicated that, without waste heat recovery, the shockwave compression chain had a higher specific energy requirement than the intercooling option. With waste heat recovery, the compression energy requirement in both cases dropped as expected, and the shockwave option required a lower specific compression energy with respect to the intercooling option. Within the ORC system, thermal efficiency, exergy efficiency, and exergy destruction rates decreased as turbine inlet temperature (TIT) increased. The ORC's evaporator was found to be the largest contributor to exergy destruction. These results demonstrate opportunities to optimize the CCS configuration and improve the overall economics of the plant.

Thermodynamic evaluation of supercritical oxy-type power plant with high-temperature three-end membrane for air separation

Abstract Among the technologies which allow to reduce greenhouse gas emissions, mainly of carbon dioxide, special attention deserves the idea of ‘zero-emission’ technology based on boilers working in oxy-combustion technology. In the paper a thermodynamic analysis of supercritical power plant fed by lignite was made. Power plant consists of: 600 MW steam power unit with live steam parameters of 650 °C/30 MPa and reheated steam parameters of 670 °C/6 MPa; circulating fluidized bed boiler working in oxy-combustion technology; air separation unit and installation of the carbon dioxide compression. Air separation unit is based on high temperature membrane working in three-end technology. Models of steam cycle, circulation fluidized bed boiler, air separation unit and carbon capture installation were made using commercial software. After integration of these models the net electricity generation efficiency as a function of the degree of oxygen recovery in high temperature membrane was analyzed.

A29 Session 8: Gastrointestinal Cryotherapeutic Indications : Endoscopic cryotherapy for Barrett’s esophagus and esophageal cancer

Endoscopic cryotherapy (Cryo) or local application of cryogen to the gastrointestinal mucosa is a thermal ablative treatment that has been used for Barrett’s esophagus (BE) and high grade dysplasia, as well as for palliative use in esophageal adenocarcinoma (EAC). Most of the existing data are related to this indication, but endoscopic cryotherapy has also successfully used for treatment of gastric antral vascular ectasia and radiation proctitis. Cryo using liquid nitrogen or compressed carbon dioxide or nitrogen gas is delivered via an endoscopic spray catheter resulting in tissue destruction without direct contact. Freezing occurs due to the Joules-Thompson effect. Data on the optimal dosimetry are limited, but a variable number of cycles of 8–20 s of freeze and thaw have been used. For Barrett’s esophagus, there are no randomized controlled trials. However, retrospective studies on the use of Cryo in patients with high grade dysplasia and/or early adenocarcinoma suggest great potential safety and efficacy for curative intent. Complete response rates of 68–100% have been reported. Complete response rates for eradiation of esophageal intestinal metaplasia (BE) are about 53–84%. These results are comparable to radiofrequency ablation, which is the reference standard for BE ablation. These provide a distinct advantage for Cryo over superficial forms of endoscopic ablation such as radiofrequency ablation or argon plasma coagulation. Adverse events have also been uncommon, mainly due to strictures (9%, all easily dilated), and very rare perforations during early studies. Cryo may also be a viable outpatient endoscopic treatment option for patients with obstructing tumors and cancers that recur after chemotherapy and/or radiation therapy. Compared to alternative endoscopic cancer palliative therapies for EAC such as photodynamic therapy (that results in extreme photosensitivity, greater pain and more frequent esophageal strictures) and esophageal stenting (which causes chest pain and does not treat the primary tumor), Cryo is an attractive viable palliative treatment option. One retrospective multicenter study of liquid nitrogen Cryo reported complete regression of BE HGD of 100%, luminal cancer in 75% with no serious adverse events and 2 year follow-up (Gossain et al., Gastrointest Endosc 2013). Finally, Cryo may also be considered for local treatment of high risk inoperable patients with BE adenocarcinomas in non-lifting nodular lesions, depressed and ulcerated lesions (Paris IIc and III class), or deep margin positive invasive EAC following endoscopic mucosal resection. Device development is ongoing, including improvements of existing devices and clinical trials on new devices such as a focal and circumferential cryotherapy balloon. Clinical trials are ongoing. Endoscopic cryotherapy has a great potential for mainstream clinical therapeutic use in early studies but more data are needed, particularly on optimal dosimetry, safety and cost-effectiveness compared with other existing therapies, long term outcomes, and quality of life.

Synthesis of wormhole mesoporous silica by compressed carbon dioxide and application in catalytic hydrogenation

Mesoporous silica materials were prepared by infusion and selective condensation of silicon alkoxides within self-assembly formed from protonated hexadecylamine by CO2 in aqueous media. Compared to the conventional synthesis approach, the introduction of CO2 facilitates the hydrolysis of silicon alkoxide precursor and does not need adding any co-solvent in the course of the synthesis of mesoporous material. Moreover, CO2 can be used as a swelling agent increasing the average pore size form 3.2–5.4 nm with expansion rate of approximately 69 %. The influence of CO2 pressure and temperature were carefully investigated. During the preparation, nonionic surfactant hexadecylamine can turn into cationic surfactant in situ as mesostructure-directing template under pressurized CO2 condition, which is the key factor for the formation of ordered mesoporous silica. In addition, the supported Pd catalysts were prepared and characterized thoroughly by X-ray diffraction, 1H NMR, 13C NMR, ICP-AES analysis, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption measurements. On the basis of the characterization and hydrogenation performance of the catalysts, the roles of different supports were discussed.

Comparative Study of High Speed Machining of Inconel 718 in Dry Condition and by Using Compressed Cold Carbon Dioxide Gas as Coolant

Difficult-to-cut materials like Inconel 718 are used for aerospace, steam turbine, bearing industry, nuclear and automotive applications. In machining, friction and heat generation at the cutting zone are the frequent problems, which affect the tool life and surface finish. Heat generation pose limitations during the turning of such modern materials due to their peculiar characteristics such as poor thermal conductivity, high strength at elevated temperature, resistance to wear and chemical degradation. A good understanding of the methods of lubrication/cooling at the cutting zone, reduction of heat generation will lead to efficient and economic machining of these modern materials. This paper presents use of compressed cold carbon dioxide for cooling at machined affected zone. Effect of cold compressed carbon dioxide as coolant on process forces, surface roughness, micro hardness, specific cutting pressure has been studied in comparison to dry turning for same set of cutting parameters.

Precipitation of chitosan from ionic liquid solution by the compressed CO2 anti-solvent method

Chitosan can be efficiently regenerated from ionic liquid by using compressed carbon dioxide.