Phase Change Absorption Research Articles

Development of MEA phase change absorbent

Chemical absorption using MEA is one of the most mature technologies for carbon capture. However, the huge energy consumption of MEA results in high CO2 capture costs. In this article, for the purpose of reducing the energy consumption, a new type of CO2 phase change absorbent was developed based on salting-out effect, which composed of MEA/tertiary butanol/H2O. The phase separation behavior, cyclic loading and the physical properties of this phase changing absorbent were investigated by rapid screening experiment, as well as the CO2 solubility under 40 °C and 0–0.5 MPa. The results show that the optimal cyclic loading of the phase change absorbent is up to 2.84 mol CO2/kg , which is 40% higher than that of the 30% MEA aqueous solution. The volume of the absorbent into desorber is reduced by 65%. Application of such phase change absorbers will be beneficial to reduce CO2 capture energy consumption.

CO2 absorption into a phase change absorbent: Water-lean potassium prolinate/ethanol solution

Phase change solvents are attractive energy-efficient absorbents for carbon dioxide (CO2) capture due to CO2-rich phase formation. Potassium prolinate + water + ethanol (ProK/W/Eth) solution has shown good capture characteristics as a promising one in our previous work. In this work, absorption rate of CO2, solubility of N2O, and heat of absorption for ProK/W/Eth solution were investigated using a stirred cell reactor and a CPA201 reaction calorimeter and these results were also compared with the aqueous ProK and 30 mass% MEA solutions. Using ethanol as a solvent can substantially increase the CO2 physical solubility and the absorption rate of CO2 in ProK/W/Eth solutions is far higher than that in aqueous 30 mass% MEA solutions especially at a low CO2 loading range. Solid precipitation, obtained from the liquid-to-solid phase change absorption, was analyzed by 13C NMR and DSC-TGA. The enthalpy change for ProK/W/Eth solutions at various CO2 loading was also discussed.

Phase-Change Absorption of SO2 by N,N,N′,N′-Tetramethyl-p-phenylenediamine in Organic Solvents and Utilization of Absorption Product

As SO2 removal via traditional aqueous amine scrubbing requires large amounts of energy for absorbent regeneration, phase-change absorption was considered to be a promising alternative, as regenera...

Phase-Change Absorption of SO2 by Imidazole in Organic Solvents and Conversion of the Absorption Product in the Presence of Water and Oxygen

Conventional removal of SO2 yields a large amount of waste salts or requires significant energy for regeneration of the absorbent. Phase-change capture has been considered a possible method to solve these problems since only the absorption product needs to be disposed for recovery and the solvent could be reused directly. In the present work, the phase-change absorption behavior of 1,3,5-trimethylpyrazole, 2-methylimidazole, 1-methylimidazole, and 1,2-dimethylimidazole has been investigated in organic solvent. Among these absorbents, only 1,2-dimethylimidazole exhibited an obvious phase-change performance in solvents three glycol dimethyl ether, propylene carbonate, and dimethylacetamide but not in butanol. The composition and structure of the absorption product were not related to the type of solvent but affected by the air. 1,2-Dimethylimidazole reacted with SO2 to form a charge-transfer complex, which converted to pyrosulfite (C5H9N2)2S2O5 in the presence of water. The absorption product was further ox...

Mass transfer characteristics of CO2 absorption into a phase-change solvent in a wetted-wall column

CO2 from coal-fired flue gas is one of the main components of greenhouse gases. Using phase change absorbents as a solvent can effectively decrease the consumption of regeneration energy for CO2 capture process. This study employed a mixed solution of diethylenetriamine (DETA) and diethylaminoethanol (DEEA) as the new phase change absorbent for CO2 absorption. The impact of the phase change behavior on the mass transfer characteristics of CO2 absorption was investigated in a wetted-wall column. Effects of the temperatures, CO2 loadings, and gas flow rate on the mass transfer coefficient were also conducted. The results indicated that temperature and CO2 loading had relatively remarkable effects on the total mass transfer coefficient; whereas the gas flow rate had a smaller effect. Kinetic analysis revealed that the mass transfer resistance of CO2 absorption into the DETA/DEEA phase change absorbent mainly concentrated at the liquid film side. The findings provide a theoretical reference for the development of new CO2 phase change absorption technology.

Liquid-solid phase-change absorption of acidic gas by polyamine in nonaqueous organic solvent

Acidic gas capture by traditional aqueous amine solution requires a plenty of energy for solvent regeneration. A phase-change capture system was considered to be a promising alternative because only the CO2-rich phase needs to be recovered and the CO2-lean phase can be reused directly without disposal, improving the energy utilization efficiency. Based on this principle, the phase-change absorption behavior of linear polyamines including ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine, tetraethylenepentamine, and cyclic diamines including piperazine (PZ) and triethylene diamine (DABCO) in organic solvents was investigated in the present work. The result indicated that polyamines could react with CO2 to form carbamate precipitates except DABCO, which had no absorption effect. For the absorption of SO2, polyamines could react with SO2 and water from air to form rare organic sulfites except DABCO, which merely absorbed two SO2 molecules to form the electron transfer complex DABCO·(SO2)2. The peculiar absorption behavior of DABCO for CO2 and SO2 implied that it is a highly selective phase-change desulfurizer for flue gas. The sequence of decomposition temperature for the CO2 capture product was DETA-carbamate>EDA-carbamate>PZ-carbamate, while for the SO2 capture product was [EDAH2][SO3]>[PZH2][SO3]·H2O>DABCO·(SO2)2.

Dispersion Topological Darkness at Multiple Wavelengths and Polarization States

Complete suppression of reflection is in principle achievable in ideal optical systems with unique optical features including complete light absorption, abrupt phase change, etc. However, conventional optical systems have an extremely tight tolerance on fabrication errors or inherent roughness of thin films or patterns. Therefore, it is difficult to realize the perfect reflectionless condition in practice. To overcome this challenge, a “topological darkness” concept with mild restrictions to the film quality is proposed using periodic metallic patterns and self‐assembled core–shell particles. Due to the topological effect, the robust nature of reflectionless surfaces is improved dramatically even in the presence of imperfections. Here the “mild” restriction will be further broken to realize reflectionless thin film systems using directly deposited thin films or random metal nanoparticles. Moreover, a broad absorption band is achieved by tuning the effective optical constants of the top absorbing layer. Remarkably, compared with conventional reflectionless phenomena under single polarization states and wavelengths, the system can realize multiwavelength zero‐reflection points for both polarization states on the same chip. These proof‐of‐concept results pave the way toward the development of practical applications using abrupt phase change and complete light absorption for label‐free optical sensing and enhanced light‐matter interaction within ultrathin film systems.

A Novel CO2 Phase Change Absorbent: MEA/1-Propanol/H2O

Due to the high energy consumption in CO2 capture by amine absorbents, CO2 phase change absorbent, CPCA, has attracted a great attention in research institutes recently. Two phases are formed after CO2 absorption with CPCA as the absorbent, and only the CO2-rich phase goes to the stripper, which could potentially reduce the energy consumption. In this work, the CPCAs composed of MEA/1-propanol/H2O were developed based on the principles of aqueous two-phase systems. The effects of temperature, amine concentration, and total CO2 loading on the phase separation of CPCAs were studied. CO2 loading and 1-propanol distributions in two phases under different experimental conditions were measured. The results indicated that the total CO2 loading is the key factor affecting the distribution of components in two phases. Moreover, in comparison to traditional 30 wt % MEA, the initial absorption rates of all CPCAs were higher than that of MEA, and its maximum value was 5 times higher. The cyclic capacity of the CPCA w...

Development of MEA-based CO2 phase change absorbent

By using the salting-out phenomenon to induce phase separation, the novel CO2 phase change absorbents (CPCAs) composed of MEA/water-miscible alcohol/H2O were developed. The absorbents using 1-propanol, 2-propanol and tertiary butanol as the diluent were selected as CPCAs. The CPCAs composed of MEA/1-propanol/H2O were further examined include the species distributions in the two phases, physical properties, cyclic capacity and absorbent regenerability. In comparison to 30wt% MEA/H2O, the optimal CO2 cycle capacity of CPCA is 2.59mol CO2/kg which increase 62% and the volume of CPCA sent to the stripper decreased over 67%. The developed CPCAs would benefit to reduce energy consumption of CO2 capture.

恒温・恒湿環境下におけるアモルファス・トレハロース乾燥膜の 相変化と吸湿率の測定

恒温・恒湿環境下におけるアモルファス・トレハロース乾燥膜の 相変化と吸湿率の測定

Kinetics of CO2 Absorption in Concentrated K2CO3/PZ Mixture Using a Wetted-Wall Column

Using a K2CO3/piperazine (PZ) mixture as a typical phase-change absorbent has promising applicability for carbon dioxide (CO2) capture in coal-fired power plants that would contribute to low energy consumption for solvent regeneration. In this study, the reaction rate of CO2 with a concentrated K2CO3/PZ mixture was measured in a wetted-wall column. At a CO2 loading close to saturation absorption, correlative physical parameters were calculated. The effects of operating conditions, including gas flow rate, slurry flow rate, PZ concentration, CO2 loading, K2CO3 mass fraction, and temperature, on the absorption rate of CO2 were investigated. The results showed that the absorption rate was sensitive to the effects of the gas flow rate and CO2 loading. The PZ concentration and K2CO3 mass fraction also substantially influenced the CO2 absorption rate. However, minor changes in the CO2 absorption rate were observed when the slurry flow rate and temperature were increased. On the basis of a pseudo-first-order mod...

Ab initio analysis on the interaction of CO2 binding to peracetated D-glucopyranose.

CO2-philes can be utilized as additives, surfactants, and a potential phase-change physical solvent or absorbent for CO2, so the design and synthesis of CO2-philes typically non-fluorous compounds is important to develop more application areas of CO2. Researchers have recently reported that peracetated D-glucopyranose has high solubility in CO2. In order to study the interaction properties between sugar acetates with CO2, 1,2-di-O-acetyl-α-D-glucopyranose and 1,2-di-O-acetyl-β-D-glucopyranose were decided as substrates after initial chemical stimulations with peracetated D-glucopyranose, and the complex model was one CO2 molecule combined with one sugar substrate (1:1). Ab initio calculations of these two systems were accomplished including geometry optimizations with HF/3-21G, B3LYP/6-31+G**, and single point energies calibration with MP2/aug-cc-pVDZ. The results indicated that hydrogen atoms can interact with CO2 by C-H··O hydrogen bond, but the dominant ones are the interactions of oxygen atoms in substrates with a CO2 molecule. It was also found that the binding energies increased when more oxygen atoms of substrate interacted with CO2, but were not affected by their chemical environment. The interaction of sugar substrate with CO2 is distance related, and should be an electrostatic interaction not only Lewis acid-Lewis base and hydrogen bond interactions. Therefore, it can be expected that one CO2-phile could interact with more CO2 molecules if more acetate-like groups or oxygen atoms were introduced into the molecular structure based on all these results, and this can be a guideline for design CO2-philes.

Temperature Effect on Phase-Transition Radiation of Water

Infrared radiation associated with vapor-liquid phase transition of water is investigated using a suspension of cloud droplets and mid-infrared (IR) (3–5 μm) radiation absorption measurements. Recent measurements and Monte Carlo (MC) modeling performed at 60 °C and 1 atm resulted in an interfacial radiative phase-transition probability of 5 × 10−8 and a corresponding surface absorption efficiency of 3–4%, depending on wavelength. In this paper, the measurements and modeling have been extended to 75 °C in order to examine the effect of temperature on water's liquid-vapor phase-change radiation. It was found that the temperature dependence of the previously proposed phase-change absorption theoretical framework by itself was insufficient to account for observed changes in radiation absorption without a change in cloud droplet number density. Therefore, the results suggest a strong temperature dependence of cloud condensation nuclei (CCN) concentration, i.e., CCN increasing approximately a factor of two from 60 °C to 75 °C at near saturation conditions. The new radiative phase-transition probability is decreased slightly to 3 × 10−8. Theoretical results were also calculated at 50 °C in an effort to understand behavior at conditions closer to atmospheric. The results suggest that accounting for multiple interface interactions within a single droplet at wavelengths in atmospheric windows (where anomalous IR radiation is often reported) will be important. Modeling also suggests that phase-change radiation will be most important at wavelengths of low volumetric absorption, i.e., atmospheric windows such as 3–5 μm and 8–10 μm, and for water droplets smaller than stable cloud droplet sizes (<20 μm diameter), where surface effects become relatively more important. This could include unactivated, hygroscopic aerosol particles (not CCN) that have absorbed water and are undergoing dynamic evaporation and condensation. This mechanism may be partly responsible for water vapor's IR continuum absorption in these atmospheric windows.

Heat and sweat transport through clothing assemblies with phase changes, condensation/evaporation and absorption

The paper is concerned with the heat and sweat transport in porous textile media with complex phase changes, which is described as a non-isothermal, multi-phase and multi-component fluid flow and governed by a nonlinear, degenerate and strongly coupled parabolic system. The phase change, condensation/evaporation and fibre absorption, play an important role in the design of functional clothing. In this paper, we present some more precise formulations on condensation/evaporation, fibre absorption and heat capacity to maintain the physical conservation of mass and energy. A typical clothing assembly with a hydrophobic batting material and two different types of cover is investigated numerically. Numerical results show that for the hydrophobic material, the evaporation and condensation zones arise simultaneously in the batting area and that the proposed formulations are more realistic to describe the phase change. Existence and uniqueness of a classical positive solution for the incompressible model are also proved.

DECAB: Process development of a phase change absorption process

This work describes the conceptual design of a novel separation process for CO2 removal from flue gas based on precipitating solvents. The process here described (DECAB) is an enhanced CO2 absorption based on the Le Chatelier's principle, which states that reaction equilibrium can be shifted by removing one of the constituents in the reaction. A conceptual design of this process has been developed based on literature data, thermodynamic principles and a limited number of experiments. As solvent example, the potassium salt of taurine was selected. The strategy followed is based on the compilation and determination of the key properties and parameters that govern the absorption and regeneration of the solvent. Then, the performance of the process is evaluated with the aid of short cut design methods. Results show that the key advantages of this process are environmental friendliness (no emissions to the air) and low energy consumption related to a lower vapor pressure of the solvent and higher net loading than conventional processes. The design developed allows for future economic evaluation and assessment of options that will further lead to benefits over conventional processes. © 2011 Published by Elsevier Ltd.

NUMERICAL MODELING OF CONVECTIVE EFFECTS ON PILOTED IGNITION OF COMPOSITE MATERIALS

ABSTRACT A combined solid and gas-phase numerical model has been developed and used to simulate the piloted ignition of a radiatively heated composite material in a boundary layer oxidizer flow. Condensed phase processes (oxidative and thermal pyrolysis, phase change, and in-depth radiation absorption) are simulated with a pyrolysis model developed by the authors. The solid-phase model is coupled to a modified version of the CFD code Fire Dynamics Simulator (FDS), which provides a transient solution to the low Mach number, reactive, buoyant, Navier Stokes Equations. The condensed phase and gaseous chemical kinetics are simplified with one-step Arrhenius reactions. Ignition occurs when a premixed flame propagates upstream from the igniter and forms a diffusion flame anchored at the surface of the solid fuel. Numerical simulations have been performed for a polypropylene/fiber glass blended composite slab with a glass concentration of 30% by mass and thickness of 3.2 mm. The influence of the incident radiant heat flux, oxidizer flow velocity, and gravitational acceleration on piloted ignition of this composite material has been investigated. Emphasis is given to low-velocity microgravity flows expected in spacecraft. Ignition delay time predictions are compared with experimental data for several external heat flux levels and two flow velocities. The ignition time, pyrolysis rate at ignition, and surface temperature at ignition are considerably lower in a 0.09 m/s microgravity flow than in a 1.0 m/s normal gravity flow. This has important fire safety implications because it indicates that piloted ignition of solid combustibles will occur more easily under the conditions expected in spacecraft.

Numerical analysis of piloted ignition of polymeric materials

A numerical model is developed to analyze piloted ignition of polymeric materials exposed to an external radiant heat flux in a convective oxidizer flow. The model considers the coupled thermo-chemical processes that take place both in the condensed and gas phases. Condensed phase processes include oxidative and thermal pyrolysis, phase change, and in-depth radiation absorption. Heat and mass transport in the gas phase are described by the reactive boundary layer conservation equations. Ignition is determined by the onset of thermal runaway in the gas phase. PMMA is used as the testing material, and ignition delay are predicted and compared with experimental data for different external heat fluxes and flow velocities. The numerical model is used to explore the ignition controlling mechanism and the critical conditions at ignition under various external heat fluxes and different airflow velocities. It is also used to provide an ignition criterion that could simplify the theoretical description of the ignition process. It is found that for a given flow velocity the pyrolysate mass flux at ignition on the sample surface is independent of the external heat flux, whereas the sample surface temperature at ignition varies with the external heat flux. Therefore, if the oxidizer flow velocity is a fixed parameter, it is possible to adopt a critical pyrolysate mass flux as an accurate ignition criterion. The use of this criterion allows the use of a simplified model to predict piloted ignition that solely considers the condensed phase.

Refractive Index and Thickness of Ultrathin Sections of Coals and Graphite by Interferometry

The development of techniques for preparing ultrathin sections of coals now permits the direct measurement with an interference microscope of the refractive index of coal components. The change in phase of polarized monochromatic light (5460 A) upon passage through an absorbing ultrathin section is a function of refractive index, thickness, and extinction coefficient. A graphical procedure has been developed for calculating these parameters from phase change and independent absorption measurements. The effects of multiple reflections on the latter data were carefully considered. The ultrathin sections were usually between 500 and 1000 A thick. The refractive indices obtained agreed well with those previously derived from reflectance measurements. Values of 2.20 and 0.51 for indices of refraction and absorption of graphite at 5460 A were obtained by these direct measurements as compared to 2.15 and 0.66 by reflectance measurements.