Supercritical CO2 Temperature Research Articles

Investigation on thermo-hydraulic characteristic of lead–bismuth eutectic and supercritical carbon dioxide in a straight-channel printed circuit heat exchanger

The Printed Circuit Heat Exchanger (PCHE) is considered a promising heat exchanger for Lead-Bismuth Eutectic (LBE) cooled fast reactors due to its superior pressure-bearing capacity and heat transfer efficiency. This paper introduces a conjugate heat transfer solver to investigate the thermo-hydraulic performance of a straight channel PCHE incorporating LBE and Supercritical CO2 (S-CO2). A four-equation model is implemented in the solver to capture the low Prandtl number turbulent heat transfer characteristics of LBE. Comparisons with LBE circular tube experimental results demonstrate that the solver presented enhances the resolution of LBE heat transfer simulations. This improvement in numerical resolution is crucial for understanding and predicting the behaviors of LBE-S-CO2 conjugate heat transfer process. Building on this, the present work explores the impacts of inlet mass flow rate, inlet temperature, S-CO2 pressure, and geometric parameters on the thermo-hydraulic performance of the straight channel PCHE. In terms of inlet temperature, quantitative analyses emphasize the effectiveness of augmenting the mass flow rate on the S-CO2 side to enhance overall heat transfer performance of PCHE. Adjusting the inlet temperature of S-CO2 or LBE to increase the temperature difference between the two fluids improves the average heat transfer rate, but reducing the S-CO2 inlet temperature may decrease the overall heat transfer coefficient. Furthermore, increasing S-CO2 pressure positively affects the thermal conductivity and specific heat capacity of S-CO2, thereby improving the thermo-hydraulic performance of PCHE. Additionally, geometric parameter sensitivity analyses indicate that decreasing wall thickness or increasing ridge width improves heat transfer, but increasing ridge width may significantly increase PCHE’s volume. The increased channel length results in a higher pressure drop, simultaneously enhancing heat transfer. From the Performance Evaluation Criteria (PEC) perspective, lengthening the channel is advantageous for the S-CO2 side but unfavorable for the LBE side. Regarding channel width, reducing channel width yields a larger increase in PEC on the S-CO2 side compared to the LBE side. Therefore, narrower flow channels on the S-CO2 side seem more advantageous. The present work provides a numerical tool with higher numerical resolution for studying LBE-S-CO2 conjugate heat transfer process and offers valuable insights for straight channel PCHE design.

Experimental and numerical investigations on thermal-hydraulic characteristics of supercritical CO2 flows in printed circuit heat exchangers

In the supercritical CO2 (SCO2) Brayton cycle, the pre-cooler is employed to cool SCO2 to be near the pseudo-critical point state to minimise compression work and achieve high cycle efficiency. The dramatic variation in thermophysical properties of SCO2 makes heat transfer and flow very complex in the pre-cooler, bringing a lot of difficulty to the design of the related components and system. This study attempts to address this issue. The experiment and simulation are carried out to analyse the influences of mass flux, inlet temperature, and pressure on the thermal-hydraulic characteristics of SCO2 flows in a straight-channel printed circuit heat exchanger (PCHE) employed as a pre-cooler, and the underlying heat transfer mechanism is analysed as well. The local heat transfer coefficient (h) is higher when the phenomenon that the local temperature of SCO2 (Tf) is equal to the pseudo-critical temperature (Tpc) appears in the laminar sublayer than when this phenomenon appears in the buffer layer. The new heat transfer and flow correlations are presented, and the genetic algorithm and back-prediction (GA-BP) neural network is employed to predict the local heat transfer and flow performance. The maximum relative error between the Nusselt number (Nu) predicted by the new heat transfer correlation and Nu obtained via experiment and simulation is within ±20%. The maximum relative error between the Nu predicted by the GA-BP neural network and the Nu obtained through experiment and simulation is within ±15%. The maximum relative error between the Fanning friction factor (f) predicted by the new friction factor correlation and f obtained via experiment and simulation is within ±5%. The maximum relative error between f predicted by the GA-BP neural network and f obtained through experiment and simulation is within ±4%. The present investigations analyse the thermal-hydraulic characteristics of SCO2 in the pre-cooler prototype and could provide useful guidance for the design of pre-coolers for the SCO2 Brayton cycle.

Evaluating and optimizing the cold energy efficiency of power generation and wastewater treatment in LNG-fired power plant based on data-driven approach

Energy shortage, greenhouse effect and environmental pollution are the three major crises faced by mankind. How to solve these three problems effectively has become the focus of all countries. Therefore, this paper proposes an innovative LNG cold energy utilization method that can simultaneously alleviate these three problems. This method includes an improved structure of the organic Rankine cycle, CO2 capture cycle and supercritical CO2 extraction of wastewater. In addition, automated machine learning based on data-driven approach is effectively used for modeling the wastewater extraction. Then, after verifying the accuracy of the proposed model, some parameters have great influence on the system performance. For instance, the temperature of supercritical CO2 and working fluid water affect the local exergy efficiency and their regression coefficients are −0.29%/°C and 0.13%/°C, respectively. These parameters in wastewater extraction process are studied. Finally, under the optimization of genetic algorithm, the maximum wastewater treatment can reach 62.7 t/h increasing by 14.0%, and the LNG cold energy generation can reach 110.1 kWh/tLNG with an increase of 28.9%, while the exergy efficiency of the system is 50.4% increasing by 24.1%. Thus, organic Rankine cycle power generation, carbon capture and wastewater treatment play the roles of energy saving, emission reduction and environmental protection. At the same time, the results are compared with those of other scholars to verify the superiority of the proposed scheme.

Process Research of Solution‐Enhanced Dispersion by Supercritical Fluids to Prepare Energetic Material Nano‐Capsules

AbstractNano‐capsule energetic materials can improve the mechanical properties, combustion/explosion properties, and component compatibility of solid propellants and reduce their toxicity, water absorption capacity, and sensitivity. The following approaches have been performed to obtain nano‐capsule energetic materials. First, the structure of solution‐enhanced dispersion by supercritical fluids (SEDS) core device (nozzle and hanging basket) were modified to improve the atomization performance, eliminate the vortex, and avoid the repeated growth of crystals. The ultrafine RDX particles with average particle size of 705 nm and distribution range of 400–1200 nm were prepared by using the improved devices. Second, the optimal process parameters for the preparation of ultrafine RDX by SEDS were obtained. Reducing the solution concentration or the supercritical CO2 temperature will be beneficial to obtain dry RDX particles with smaller particle sizes. When the solution concentration ratio was 10 g (RDX)/100 mL (DMF), the temperature of supercritical CO2 was 35 °C, and the flow rate ratio of supercritical CO2 to solution was greater than 10 (kg/h): 2 (ml/min), the experiment results were good. Third, to facilitate the detection of shell elements, fluororubber (F26) and RDX were used as raw materials to prepare nano‐capsules. Transmission electron microscopy image showed that the RDX‐F26 particles featured a core‐shell structure with diameters that ranged between 200 nm and 300 nm, spherical shape, and uniform wall thickness. The X‐ray photoelectron spectroscopy showed that the core was RDX, the shell was F26, and the thickness of the shell was 14.6 nm. As the capsule wall material, the F26 also inhibited the overgrowth of RDX crystal in the course of crystallization successfully. Sensitivity analysis showed that the RDX‐F26 nano‐capsules had lower impact and friction sensitivities than the refined RDX. These results show that the use of improved SEDS process is suitable for the preparation of energetic material microcapsules.

Corrosion of SS310 and Alloy 740 in high temperature supercritical CO2 with impurities H2O and O2

This study investigated corrosion performance of SS310 and Alloy 740 in supercritical CO2 with the impurity of 100 ppm H2O or O2 at 600 °C and 30 MPa for up to 1000 h. The addition of 100 ppm H2O remarkably enhanced general and localized oxidations while the presence of O2 led to the opposite tendency. Alloy 740 exhibited better resistance to carburization compared to SS310, possibly due to the higher solubility of carbides in Ni-based alloys than those in Fe-based alloys. Both alloys exhibit near parabolic oxidation behavior and acceptable corrosion resistance in the supercritical CO2 environments.

Experimental investigation of pressure drop and heat transfer in high temperature supercritical CO2 and helium in a printed-circuit heat exchanger

An ASME code compliant heat exchanger was manufactured for testing between high-temperature (up to 550 °C) helium and supercritical CO2 test facilities at Georgia Institute of Technology. The multi-layerd printed-circuit heat exchanger (PCHE) consists of 17 photo-chemically etched plates which were diffusion-bonded together. Pressure losses and heat transfer measurements have been conducted for a zig-zag flow-path geometry etched into the bonded shims. These measurements have been presented in dimensionless form to facilitate comparison with thermohydraulic correlations available in the literature. The use of two fluids with drastically different properties in the same 37° zig-zag channel geometry provides a unique method of exploring the effect of working fluid on PCHE performance. Fanning friction factor and Nusselt numbers are determined for supercritical CO2 between Reynolds number of 500–18,000, spanning laminar, transition, and turbulent regimes. The same friction and heat transfer figures of merit are presented for helium operating between Reynolds number 400–3200, spanning laminar and transition turbulent regimes. Two different exponential models were fitted to the supercritical CO2 and helium friction data showing an agreement with the measurements to within ±10% over the range of test conditions. The model fitted to the heat transfer data is in agreement with the measurements to within ±15% of the range of test conditions. To enable reproducibility of the data, the methods used to define dimensions related to thermohydraulic calculations is discussed in details, and the dimensions provided by the engineering drawing of the exchanger are validated using high resolution computed tomography of the component. Finally, a detailed analysis of the thermohydraulic performance of the headers is given with the goal of setting a benchmark performance for comparison with other designs.

Three Orders of Reverse Leakage Reduction by Using Supercritical CO2 Nitriding Process on GaN Quasi-Vertical Schottky Barrier Diode

Surface treatment is quite vital to reduce the reverse leakage current and improve the current On-Off ratio of gallium nitride (GaN) quasi-vertical Schottky barrier diode (SBD). In this work, we report a new nondestructive low temperature supercritical CO2 fluid (SCF) nitridation technology to treat the surface of GaN and substantially reduce the leakage current of GaN quasi-vertical SBD. The X-ray photoelectron spectroscopy (XPS) reveals the increased nitriding degree and oxygen doping degree in the form of GaOx after the SCF process results in the leakage performance improvement. As a result, the defects at metal/semiconductor interface are passivated. Also, because of NH-2 and OH- generated from the SCF process, the surface peak electric field of n-GaN decreases, and thus the breakdown voltage is enhanced. The reverse leakage current density is reduced by more than three orders of magnitude from 3.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> to 3.52 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (at -3 V) and the ON-/OFF-current ratio is improved by three orders from 8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> to 5.74 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> .

Thermoelastohydrodynamic characteristics of supercritical CO2 spiral groove face seals

PurposeThe purpose of this study is to determine the sealing performance of face seals by numerical analysis of thermoelastohydrodynamic characteristics of supercritical CO2 (S-CO2) spiral groove face seals in the supercritical regime.Design/methodology/approachThe spiral groove face seal was used as the research object. The distribution of lubricating film pressure and temperature was analysed by solving the gas state, Reynolds and energy equations using the finite difference method. Furthermore, the influence law of sealing performance was obtained.FindingsClose to the critical temperature of S-CO2, face distortions produced by increasing pressure lead to divergent clearance and resulted in reduced opening force. In the state of S-CO2, the face distortions generated by increasing seal temperature lead to convergent clearance, which enhances the opening force. In addition, near the critical temperature of S-CO2, the opening force may be reduced by 10%, and the leakage rate of the seal sharply increases by a factor of four.Originality/valueThe thermoelastohydrodynamic characteristics of supercritical CO2 face seals are illustrated considering the actual gas effect including compressibility, heat capacity and viscosity. Face distortions and sealing performance were calculated under different seal pressures and seal temperatures in the supercritical regime, as well as with N2 for comparison.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2020-0169/

Startup, shutdown, and load-following simulations of a 10 MWe supercritical CO2 recompression closed Brayton cycle

This work describes improvements to dynamic process and control models developed previously for a 10 MWe supercritical CO2 recompression closed Brayton cycle pilot plant and highlights their use in the analysis of fast ramped-setpoint load-following operation and a warm shutdown and subsequent startup operation. One enhancement includes cooler and recuperators modeled as one-dimensional, compact, zig-zag type printed circuit heat exchangers optimized by minimizing metal mass and validated using dynamic data from a small-scale supercritical CO2 test loop. For the load-following ramps between 10 MWe and 4 MWe, an aggressive ramp rate of approximately 7.5%/min of full load is simulated using inventory management control and sliding-pressure operation, with the resulting net-load closely tracking the demand. The supercritical CO2 temperature at the inlet of the main compressor is controlled at 4 °C above the critical temperature using a water-cooled printed circuit heat exchanger. A high level of interaction between the cooler and inventory control is observed to intensify oscillatory behavior in the cycle load and compressor inlet temperature as control gains and/or ramp rates become more aggressive. Transient simulation procedures and results are also presented for a shutdown from 4 MWe to a warm condition. The warm shutdown is achieved in 30 min while satisfying the operating constraint limiting the rate of change in temperature at the primary heat exchanger inlet to less than 2 °C/min. The subsequent startup from warm conditions to positive load is reached in 45 min and minimum load of 4 MWe is achieved in 90 min.

Quantum chemical and master equation study of OH + CH2O → H2O + CHO reaction rates in supercritical CO2 environment

AbstractWe investigated the reaction rates of OH + CH2O → H2O + CHO at CO2 pressures of up to 1000 atm with and without CO2 molecule included in a reactive complex. Both mechanisms begin with formation of the hydrogen‐bonded prereactive complexes. Our ab initio calculations indicate a possibility of catalytic effect, predicting an activation barrier that one order of magnitude lower when the CO2 molecule is involved. To verify this effect, we use the Rice–Ramsperger–Kassel–Marcus theory and solve unimolecular master equations in the steady‐state approximation. We assume the equilibrium between prereactive complexes and reactants and compare the bimolecular reaction rates for the two mechanisms. The catalyzed reaction mechanism is found to be faster at higher CO2 pressures and lower temperatures, when prereactive complexes have nonnegligible concentration. Therefore, this catalytic effect may be important for this reactive process in room temperature supercritical CO2 solvent, but is unlikely to play a role during oxy‐combustion.

Effect of pressure on heat transfer between supercritical CO2 in tube and pulverized coal combustion flue gas

To further improve the thermal efficiency of coal-fired boilers, lower the environmental impact, and minimize the size of system components, the potential utilization of supercritical CO2 (S-CO2) as the working fluid has drawn considerable attention recently. In this study, the thermal characteristics between supercritical CO2(S-CO2) in a vertically upward tube and the flue gas in the combustion chamber were investigated numerically using the standard k-ε model, the P-1 radiation model, and the conjugate heat transfer model. The effects of the S-CO2 pressure on the surface heat flux, the wall temperature, the bulk temperature, the bulk velocity, the surface heat transfer coefficient, and the Nusselt number were examined. The distributions of the flue gas temperature and S-CO2 temperature were further elaborated. The results show that the supercritical pressure has a significant effect on the S-CO2 tube wall temperature, the wall temperature is higher under a low S-CO2 pressure. The wall heat flux is dominated by connection in the entrance region of the tube but is contributed by both convection and radiation at larger axial distances. The heat transfer coefficient increases with increasing the supercritical pressure, and the supercritical pressure has slight impact on the tube wall temperature. The present numerical study helps gain improved understanding of the thermal performance and optimize the design of boilers using S-CO2 as the working fluid.

Modification of PES/PU membrane by supercritical CO2 to enhance CO2/CH4 selectivity: Fabrication and correlation approach using RSM

Abstract Integrally skinned asymmetric gas separation membranes of polyethersulfone (PES)/polyurethane (PU) blend were prepared using supercritical CO2 (SC-CO2) as a nonsolvent for the polymer solution. The membrane consisted of a dense and a porous layer, which were conjoined to separate CO2 from CH4. The FTIR, DSC, tensile and SEM tests were performed to study and characterize the membranes. The results revealed that an increase in SC-CO2 temperature causes an increment in permeance and a decrease in membrane selectivity. Furthermore, by raising the pressure, both permeance and selectivity increased. The modified membrane with SC-CO2 had much higher selectivity, about 5.5 times superior to the non-modified membrane. This higher selectivity performance compared to previous works was obtained by taking the advantages of both using partial miscible blend polymer due to the strong polar–polar interaction between PU PES and SC-CO2 to fabricate the membrane. The response surface methodology (RSM) was applied to find the relationships between several explanatory variables and CO2 and CH4 permeance and CO2/CH4 selectivity as responses. Finally, the results were validated with the experimental data, which the model results were in good agreement with the available experimental data.

Coupled modeling of combustion and hydrodynamics for a supercritical CO2 boiler

A one-dimensional hydrodynamic model of supercritical CO2(S-CO2) coupled with computational fluid dynamics (CFD) simulation of gas combustion is developed. The heat exchangers are introduced into the CFD simulation as energy/momentum absorption sources. Complex tube structures can be built with the aid of AutoCAD, and therefore the simulation could give detailed information of heat exchangers. Numerical simulation is performed for a 5MWe gas-fired S-CO2 test boiler. The calculation results are validated by the thermodynamic design data. Tube outside surface temperature, as well as S-CO2 temperature distributions are obtained.

Remediation of 137Cs-contaminated concrete rubble by supercritical CO2 extraction

The removal of cesium contamination is a critical issue for the recycling of concrete rubble in most decommissioning operations. The high solvent strength and diffusivity of supercritical CO2 make it an attractive choice as vector for extractant system in this context. Experimental extraction runs have been carried out in a radioactive environment on rubble contaminated with 137Cs. The best extraction system was found to be CalixOctyl (25,27-Bis(1-octyloxy)calix[4]arene-crown-6, 1,3-alternate) with pentadecafluorooctanoic acid as a modifier. The effects of various operating parameters were investigated, namely the coarseness of rubble, the temperature of supercritical CO2, the residual water and initial cesium concentrations, and the amounts of extractant and modifier used. The yields from direct extraction were low (<30%), because of the virtually irreversible sorption of Cs in concrete. The best extraction yield of ∼55% was achieved by leaching concrete rubble with nitric acid prior to supercritical CO2 extraction.

Numerical simulation of supercritical carbon dioxide jet at well bottom

A numerical model was developed to study the flow field characteristics of supercritical CO2 (SC-CO2) impacting jet at well bottom. The model took account of jet hydrodynamics, mass transfer and thermodynamic properties of SC-CO2. Formulas of the density, viscosity and thermal conductivity of CO2 were verified for a supercritical state, and they were embedded in a CFD model through the user defined function (UDF). Complex coupling was achieved with the modified SIMPLE segmentation algorithm, and fields of the SC-CO2 impact flow, pressure, temperature and physical parameters were obtained. The reliability of the numerical model was validated in experiments that monitored the pressure and temperature of SC-CO2 impacting jet using sensors. The laboratory experiments show that the model accurately predicts the temperature and pressure fields of SC-CO2 impacting jet. SC-CO2 impacting jet has a more obvious thermal effect on the wall without any phenomena of CO2 freezing and blocking nozzle. The jet flow field can be divided into five areas according to flow characteristics, and the CO2 phase state in flow field is analyzed. The established calculation method and findings reported in the paper will provide guidance for engineering applications.

Numerical investigation on heat transfer to supercritical CO2 in rolling motion

The numerical calculations with and without rolling motions are conducted to investigate the effect of rolling motion on flow and heat transfer of supercritical CO2 in a vertical double-pipe heat exchanger. The purpose is to provide the detailed information on heat transfer behaviors for better understanding the abnormal heat transfer mechanism of supercritical fluid in rolling motion. It concludes that the effect of rolling motion on the supercritical CO2 is much more notable than that on conventional single-phase fluid. The rolling motion can cause the periodic oscillation of the local heat transfer coefficients and suppress the whole heat transfer deterioration. As supercritical CO2 temperature or mass flux increases, the influences of rolling motion and flow direction on the heat transfer decrease markedly. The secondary flow induced by the rolling motion for upward flow is stronger than that for downward flow, and the influence of rolling motion on the left and right sides of the tube is more obvious than on other locations. The heat transfer deterioration phenomenon weakens gradually as the rolling period decreasing or rolling amplitude increasing. It is important to note that the rolling motion may bring about the large wall temperature oscillation and the wall peak temperature increment to influence the safety of high-pressure pipeline.

High dispersion of 1-nm SnO2 particles between graphene nanosheets constructed using supercritical CO2 fluid for sodium-ion battery anodes

Supercritical CO2 (SCCO2) fluid, which has gas-like diffusivity, extremely low viscosity, and near-zero surface tension, is used to synthesize SnO2 nanoparticles (a 1-nm diameter is achievable), which are uniformly dispersed and tightly anchored on graphene nanosheets (GNSs) and carbon nanotubes (CNTs). The discharge capacity, rate capability, and cyclic stability of the synthesized SnO2/GNS and SnO2/CNT nanocomposites are compared. This study also tunes the SCCO2 temperature (and thus its fluid density) and finds that this factor crucially affects the SnO2 size and distribution, determining the resulting electrochemical properties. The sodiation/desodiation mechanism of the SnO2/GNS electrode is examined using synchrotron ex situ X-ray absorption and X-ray diffraction techniques, together with transmission electron microscopy. We confirm that while the oxide conversion reaction is reversible, the sluggish Sn–Na alloying/dealloying reaction is responsible for the lower measured capacity as compared to the theoretical value. The first-cycle efficiency loss is mainly attributed to the trapping of Na in the electrode surface solid electrolyte interphase layer.

Fabrication of polyetherimide microporous membrane using supercritical CO2 technology and its application for affinity membrane matrix

Polyetherimide (PEI) microporous membranes with uniform cellular structure, high porosity, and narrow pore size distribution were formed by supercritical CO2 (ScCO2) phase inversion method, and the membrane was modified to be a matrix for the preparation of affinity membrane due to its low solvent residue and appropriate porous structure. The effects of ScCO2 temperature and pressure on the morphology and pure water flux of the membrane were investigated. The membrane prepared at 24MPa and 45°C with a large mean cell diameter of 6.0μm, high porosity of 73%, narrow pore size distribution and a pure water flux of 56L/(m2hbar) was coated with chitosan to improve its hydrophilicity and coupled with Cibacron Blue F3GA (CB) as a special ligand to form an affinity membrane (PEI-coated chitosan-CB membrane). The PEI-coated chitosan-CB membrane showed a high adsorption capacity of 33.9mg/g membrane to bovine serum albumin and was higher than most of affinity membranes. Moreover, the tensile strength of PEI-coated chitosan-CB membrane was 11.58MPa and was much higher than those of affinity membranes. This work demonstrates that ScCO2 phase inversion method is a potential method to prepare an affinity matrix.

Effect of modifier on the composition and antioxidant activity of carotenoid extracts from pumpkin (Cucurbita maxima) by supercritical CO2

The effects of different modifiers and processing conditions on the compositions, yield, and antioxidant activity of carotenoid by supercritical CO2 (SC-CO2) extraction were studied. Increasing the percentage of modifier would increase the yield, but no significant changes were observed on the antioxidant properties of carotenoids extracted at 50 °C with low concentration (5%) of single modifier. As single modifier, the oil showed the pronounced effects on the yield and antioxidant activity of extracts compared to the effects of water and ethanol. The combination of ethanol and water, or ethanol and oil, or water and oil in SC-CO2 extraction showed that the yields of carotenoids were higher than for the single modifier with equal amount. The modifier and operating temperature of SC-CO2 notably influenced the selectivity of carotenoids, especially the ratio of cis-β-carotene/total carotenoids. The antioxidant activity didn’t show a liner correlation with the total yield of carotenoids. The antioxidant activities of unit mass carotenoid extract were decreased after adding modifiers at both 50 °C and 80 °C. At lower concentrations of water (5% and 10%), the antioxidant activity of unit mass carotenoid extracts was higher at 50 °C. The highest antioxidant activity of unit mass carotenoid extract was found at 80 °C with both single and combined modifiers.

Supercritical Fluid Clean-Up of Environmental Samples for the Analysis of Polycyclic Aromatic Hydrocarbons Using Time-of-Flight Secondary Ion Mass Spectrometry

A novel sample-pretreatment method for time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using supercritical fluid extraction (SFE). In SFE, the extraction efficiency of a certain organic matter is controlled by the pressure and temperature of supercritical CO2. Two-step SFE (1st step at 10 Mpa, 40 degrees C; 2nd step at 30 MPa, 120 degrees C) was applied to diesel exhaust particles containing many kinds of n-alkanes and aromatic species. n-Alkanes and polycyclic aromatic hydrocarbons (PAHs) were extracted in the 1st and 2nd steps, respectively. This selectivity was utilized for the sample preparation of TOF-SIMS analysis. Diesel exhaust particles after the 1st step of extraction were analyzed with TOF-SIMS, aiming at PAHs as analytical targets. The obtained spectrum was simplified, and mass peaks of individual PAHs were easily assigned, because unwanted compounds, like n-alkanes, were selectively removed by SFE. Furthermore, a simple calculation elucidated the outline of the spectrum.