High-pressure Differential Scanning Calorimeter Research Articles

Thermodynamic phase equilibria study of Hythane (methane + hydrogen) gas hydrates for enhanced energy storage applications

Hydrogen blending with natural gas has become an effective technique for incorporating the characteristics of natural gas and facilitating the storage and transportation of hydrogen gas. The transportation of hydrogen and natural gas (methane) blend, also referred to as Hythane, presents numerous challenges, advantages, and disadvantages that differ based on the technology employed. The current research showcased a thorough examination of the thermodynamics involved in studying the three phase equilibrium analysis of gas hydrate technology for storing Hythane gas mixtures. Three different Hythane compositions varying in hydrogen percentage were selected, and the isochoric gas hydrate phase equilibria study was performed. The experimental results of phase equilibria and thermodynamic modelling using CPA EOS in software were compared. A similar study was also conducted in the presence of a 5.56 mol % THF solution to understand the reduction in the pressure requirement for the phase equilibria. Results from the mixed Hythane+THF gas hydrate findings suggested stable gas hydrate formation at much lower pressure requirements, increasing the credibility of storing Hythane mixtures in gas hydrates at moderate conditions. The gas compositions for each experiment were analyzed using gas chromatography to evaluate the presence of the desired gas in the hydrate phase. Heat exchange during the gas hydrate dissociation was analyzed using a high pressure differential scanning calorimeter (DSC). The change in the heat release temperature also indicates the stability of the gas hydrate, and with increasing hydrogen gas in the blend, the gas hydrate stability decreased. The Clausius-Clapeyron equation was employed to compute the heat of gas hydrate dissociation, and a comparison was made with the heat of dissociation obtained from the DSC study. The experimental investigations on Hythane gas hydrates were performed to find the hydrogen storage inside the gas hydrate phase and compare it with the previous studies of pure hydrogen hydrates. To demonstrate the Hythane gas transportation, Hythane gas hydrate pellets were formed, followed by their storage in a controlled environment to observeany changes in pressure and temperature. The Hythane gas hydrate pellets demonstrated exceptional stability of Hythane gas presenting an intriguing prospect for utilizing gas hydrate technology in Hythane gas transportation.

Direct measurements of the enthalpy of vaporization for R290 + R1216 and R1234ze(E) binary mixtures by differential scanning calorimetry

In this work, the enthalpy of vaporization (ΔvapH) of refrigerants and mixtures has been investigated experimentally and theoretically, and an accurate and simple method for directly measuring ΔvapH has been developed. First of all, the ΔvapH of R290, R1216, R1234ze(E) and their mixtures were measured at temperatures from 260 to 290 K using a modified high-pressure differential scanning calorimeter combined with a pressure balance unit and a sample injection system. Seven temperature points were measured for each component. After that, compared the experimental results with commonly used estimation methods, such as Clausius-Clapeyron equation and Helmholtz-energy equation of state. The experimental results were in good agreement with Helmholtz equation, with the maximum deviation within 1.89%. In the end, the empirical formula was used to fit the experimental results. The average absolute deviations between the experimental values and the fitting values were between 0.07% and 0.40%, and the maximum absolute deviations were between 0.11% and 1.05%.

Thermal stability of levopimaric acid and its oxidation products

Biofuels are renewable alternatives to fossil fuels. Levopimaric acid‒base biofuels have attracted increasing attention. However, their stability remains a critical issue in practice. Thus, there is a strong impetus to evaluate the thermal stability of levopimaric acid. Through thermogravimetry (TG) and a custom-designed mini closed pressure vessel test (MCPVT) operating under isothermal and stepped temperature conditions, we investigated thermal oxidation characteristics of levopimaric acid under oxygen atmosphere. Thin-layer chromatography (TLC) and iodimetry were used to measure the hydrogen peroxides generated by levopimaric acid oxidation. A high pressure differential scanning calorimeter (HPDSC) was used to assess hydroperoxide thermal decomposition characteristics. Gas chromatography-mass spectrometry (GC-MS) was used to characterize the oxidation products. The thermal decomposition kinetics of levopimaric acid were thus elucidated, and a high peroxide value was detected in the levopimaric acid. The decomposition heat (QDSC) and exothermic onset temperature (Tonset) of hydroperoxides were 338.75 J g−1 and 375.37 K, respectively. Finally, levopimaric acid underwent a second-stage oxidation process at its melt point (423.15 K), resulting in complex oxidation products. Thermal oxidation of levopimaric acid could yield potential thermal hazards, indicating that antioxidants must be added during levopimaric acid application to protect against such hazardous effects.

Exothermicity of hydrothermal carbonization: Determination of heat profile and enthalpy of reaction via high-pressure differential scanning calorimetry

Hydrothermal carbonization (HTC) is known for being exothermic, an aspect that can lower the external energy demand necessary to face thermal losses and therefore be conducive to the overall HTC process thermal efficiency. Also, heat profiles can help explore kinetics and generally provide an insight into the HTC process. Despite the potential of the HTC exothermicity, only a few studies examined it and with different methodologies. This work aims to deepen this aspect by exploring heat profiles, enthalpy of reaction, and comparing two experimental methods by performing an experimental campaign using a power-compensated high-pressure differential scanning calorimeter (DSC). Three substrates (glucose, cellulose, and grape seeds) were hydrothermally carbonized at 180, 200, 220, and 250 °C at a biomass to water mass ratio of 0.25. To determine net heat profiles and enthalpies, water thermal effects were removed using two approaches, consisting of running a thermal program on the water alone or the exhaust, i.e. the products after the reaction. An instrument baseline considering both a zero-line and a time-drift was considered. Results show that both methods allow inferring similar enthalpy values at low operating temperature, while at high temperature a difference in the heat capacity of the liquid phase (due to the production of compounds dissolved in the liquid phase and absorbed on the solid) can affect the results related to the exhaust approach. In both cases, higher temperatures favor the exothermic peak intensity, the curve sharpening, and the increase (in absolute value) of reaction enthalpies. These are in the ranges −0.20 ÷ −0.86 MJ/kg, −0.61 ÷ −1.33 MJ/kg, and −0.42 ÷ −1.53 MJ/kg for glucose, cellulose, and grape seeds, respectively.

Rapid screening method for hydrate agglomeration and plugging assessment using high pressure differential scanning calorimetry

Gas hydrate formation during subsea oil and gas production can result in flowline blockages, which present enormous economic and safety risks. Certain crude oils have natural anti-agglomerant (AA) properties, which facilitate their non-plugging behavior over a defined operating window. Thus, it is crucial to be able to easily screen a crude oil system for its tendency to form hydrate plugs. In this paper, we present a Hydrate Plugging Assessment (HPA) technique that can be used as a rapid screening method to evaluate the plugging tendency using a high pressure differential scanning calorimeter (HP-DSC). The technique requires a small crude oil sample (~15 mg), and the experimental time is relatively short. In this work, HP-DSC tests were conducted on 13 crude oils (22 to 45 ˚API). Tests were conducted at various water contents, salinity, chemical dosage (without/with AAs), and different hydrate structures. The results show that an increase in water content destabilizes the emulsion, and increases the hydrate plugging risks. An increase in salinity decreases hydrate plugging tendency. Different hydrate crystal structures showed that for a similar water content, salinity, and driving force, structure II (sII) hydrates have a slightly greater agglomeration tendency compared to structure I (sI) hydrates. Finally, the effect of combining a low stability oil with a high stability oil showed that the resulting emulsion retained the high stability property, paving the possibility for natural oil treatment. In summary, these studies show that the HPA technique is a cost-effective and attractive method to evaluate hydrate plugging tendency.

Thermal safety assessment for solid organic peroxides

The thermal hazards of dicumyl peroxide (DCP) and benzoyl peroxide (BPO), self-reactive chemicals are identified and characterized using high-pressuredifferential scanning calorimeter, and simultaneous thermogravimetric analyzer, a C80 micro-calorimeter is used. The apparent exothermic onset temperature of DCP is found to be between the range of 112–122 °C for different heating rates in DSC tests. There are two coupled peaks of BPO around 105 °C at both the heating rates of 4.0 and 8.0 °C/min while no endothermic peak showed at lower heating rates. Furthermore, another endothermic peak appears immediately after the exothermic peak at about 211 °C of DCP under high-pressure conditions. For BPO, the endothermic peak before the exothermic peak disappears as the pressure increases to 1.0 and 1.5 MPa. The average values of apparent activation energy calculated by Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods during the conversion rate between 15 and 75% of DCP are 80.69 and 74.05 kJ/mol, and that of BPO are 119.96 and 112.93 kJ/mol, respectively. According to the isothermal tests, the thermal decomposition of DCP behaviors is an n-th order reaction while BPO conforms to the laws of autocatalytic reaction.

A novel method to characterize thermal properties of the polymer and gas/supercritical fluid mixture using dielectric measurements

Gases or supercritical fluids (SCF) are widely used in polymer science and engineering, as their dissolution into polymeric materials will alter their inherent thermal properties; including melting and crystallization temperatures (Tm and Tc). One possible method to determine these temperatures, at elevated pressures, is to use a high-pressure differential scanning calorimeter (HP-DSC). However, the elevated pressures used in HP-DSC may result in signal instabilities, limiting the testing window for these pressures. This study presents a novel testing system using dielectric measurements to determine the effects of dissolved gas/SCF on the Tm and Tc of polymers. We have developed an instrument to determine the dielectric properties of both polymer/gas and polymer/SCF mixtures, at elevated pressures and temperatures. Using the change in the measured dielectric constant or loss, Tm and Tc were determined. The effects of hydrostatic pressure and plasticization due to dissolved carbon dioxide (CO2) and Helium (He) on the Tm and Tc of high density polyethylene (HDPE) are presented and discussed. Both Tm and Tc increase with pressure and decrease due to plasticization, i.e., pressure and plasticization are competing variables. The dissolution of He, having a low solubility into HDPE, reveals that pressure is the dominant effect. In contrast, the dissolution of CO2, having a high solubility into HDPE, shows that plasticization is predominant.

Experimental studies on hydrogen hydrate with tetrahydrofuran by differential scanning calorimeter and in-situ Raman

Clathrate hydrate is a kind of environment-friendly material for storing hydrogen under a certain condition of temperature and pressure. In this work, tetrahydrofuran aqueous solution with concentration of 3.0 mol% was adopted to investigate hydrogen storage process. Moreover, thermal property of hydrate was measured by high pressure differential scanning calorimeter, and mechanism of hydrate-based hydrogen storage was studied by in-situ Raman. Especially, gas uptake, morphology and structures change of compounds from gas/liquid interface towards hydrate layer were monitored in the process of hydrate formation. Thermal experiments illustrate that thermal data for tetrahydrofuran-hydrogen binary hydrate under extra high pressures could be effectively obtained by high pressure differential scanning calorimeter, moreover, memory effect shows no influence on thermal state of hydrate but weakly affects water aggregation. Kinetics and microscopic experiments illustrate that a special pressure drop and some tetrahydrofuran hydrates with unstable structure can be found under conditions of 273.15 K and 14.53 MPa. The pressure drop involves into hydrogen molecules tunneling movement among hydrate cavities. Moreover, hydrogen molecules show a positive effect on binary hydrate stability. Further, the density of 1.875 g/Lwater shows that hydrogen storage process via clathrate hydrate is an excellent method to store hydrogen.

Sodium Dodecyl Sulfate Preferentially Promotes Enclathration of Methane in Mixed Methane-Tetrahydrofuran Hydrates

SummaryMethane storage in mixed hydrates is advantageous due to faster kinetics and added stability. However, capacity needs to be improved. Here we study mixed hydrates of methane (CH4) and tetrahydrofuran (THF), in the presence of sodium dodecyl sulfate (SDS) as a kinetic promoter for hydrate formation. We report the co-existence of pure methane (sI) and mixed CH4-THF hydrates (sII) in the presence of SDS; however, in the absence of SDS, co-existence of pure THF (sII) and mixed CH4-THF hydrates (sII) was observed. Thus the presence of SDS preferentially promotes the enclathration of methane over that of THF. Furthermore, through in situ Raman spectrometry, complemented by high-pressure differential scanning calorimeter, we present temperature-dependent methane occupancy in small and large cages of sI and sII hydrates. Our findings offer new insights for enhancing the methane storage capacity in more stable sII hydrate configuration for large-scale methane storage via solidified natural gas technology.

Comparison of oxidation behavior of linear and branched alkanes

In this research, the oxidation behavior of six linear and branched alkanes was investigated using high-pressure differential scanning calorimeter (HP-DSC) and thermogravimetry coupled with Fourier-transform infrared spectroscopy (TG-FTIR) to compare the similarities and differences between branched and linear alkanes. The results indicated that both branched and linear alkanes showed only low-temperature oxidation (LTO), which implies that alkanes barely contribute in coke formation and thus no obvious high-temperature oxidation (HTO) was observed as no enough fuel was deposited. The LTO of linear alkanes seems to be independent of their carbon number, which, however, does not apply to branched alkanes. The oxidation behavior of branched alkanes was different from their linear chain counterparts due to the effect of their different molecule structure. Branched alkanes reacted earlier and faster at initial stage relative to their linear chain counterparts, but their reaction rates became slower at later stage with the increase of temperature. Branched alkanes can produce some oxidized compounds with CO group, while linear alkanes can form more carbonyl groups and some oxidized compounds (like carboxylic acids) that can help to produce more CO2 by decomposition.

Strategy to Enhance Conductivity of Polystyrene/Graphene Composite Foams via Supercritical Carbon Dioxide Foaming Process

Composites combining polystyrene (PS) and thermally reduced graphene with different size of sheets were fabricated by melting blending. Composites added large and small size of graphene (graphene mixture) exhibited a higher electronic conductivity. To reduce the weight of composites, PS/graphene composite foams were prepared by scCO2 foaming process. As a result, composites included different size of graphene showed a more uniform bubbles, higher cell density and smaller cell diameter because of synergy in graphene sheets. The foams with graphene mixture also exhibited high cell density in high saturation temperature due to their higher viscosity and glass transition temperature analyzed by high-pressure rheometer and differential scanning calorimeter. For conductivity of foams, the introduced bubbles exhibited a good enhancement of electrical conductivity and percolation threshold decreased from 0.34 vol.% to 0.16 vol.%. It could be found that conductivity increased by raising pressure and decreased with the increase temperature.

Pressure Effect on the Rheological Behavior of Waxy Crude Oil with Comb-Type Copolymers Bearing Azobenzene Pendant

In this work, a pressure responsive poly(α-octadecene-co-maleic acid azobenzene amide) (Azo-MAC) was synthesized and able to enhance the flowability of waxy crude oil with asphaltenes significantly under high pressure. High-pressure UV–vis spectrometer was used to characterize its pressure response under pressures. The onset temperature and enthalpy during wax crystallization of Liaohe waxy crude oil under various pressures were determined by using high-pressure differential scanning calorimeter. The viscosity and yield stress were measured by high-pressure rheometer. On the basis of our experimental data, a mechanism was propounded that the conformation transformation from cis to trans of azobenzene groups in Azo-MAC at enhanced pressure may destroy the assembly of asphaltenes, disturb the crystallization of paraffins and thus improve the flowability of oils. Azo-MAC should be an ideal additive for exploitation and transportation of oils under high pressure.

Ranking of kinetic hydrate inhibitors using a high pressure differential scanning calorimeter

A High Pressure Differential Scanning Calorimeter (HP-µDSC) was used to characterize the kinetic inhibition performance of several kinetic hydrate inhibitors (KHIs) up to 390 bar (39 MPa) of model natural gas. A novel protocol was devised to increase the spread between effective KHIs to obtain their performance ranking. The natural gas used in the study was a mixture of 90 mol% methane and 10 mol% propane. Linear cooling ramps at a constant cooling rate of 0.5 K/min were used under isobaric conditions. Both the formation temperature of natural gas hydrate during a linear cooling ramp and the amount of hydrate formed were used for comprehensive analysis. The second method was based on the growth inhibition of natural gas hydrates and opened a new possibility that only several repeat measurements may be sufficient for fast screening of good KHIs. The results showed that HP-µDSC is a promising tool for the evaluation of kinetic inhibition performance of KHIs that can only be obtained in minute quantities.

Novel isochoric measurement of the onset of vapor–liquid phase transition using differential scanning calorimetry

A novel method for measuring the onset of vapor-liquid phase transition applying an isochoric procedure in a high-pressure micro differential scanning calorimeter is introduced for the first time. Isochoric dew-point measurement is used to measure vapor pressures of CO2 at different boiling temperatures and dew points of a methane/ethane gas mixture at different pressures or temperatures. The isochoric two-phase bubble-point measurement, similar to the isobaric method, is also demonstrated to measure vapor pressures of methanol at different boiling temperatures. All results are in agreement with the literature data. The isochoric method is found to be superior to the widely used isobaric method. It can be used to measure the onset of vapor-liquid phase transition for a wide range of substances and mixtures, including the ones for which the isobaric method is inapplicable, and it eliminates difficulties usually encountered in the isobaric method. The proposed method along with the findings of this study can pave the way for experimental measurements of phase equilibria in more complex systems.

Experimental and modelling studies on thermodynamic methane hydrate inhibition in the presence of ionic liquids

This paper presents a series of experimental and modelling studies on the thermodynamic inhibition effects of four ionic liquids on the methane hydrate formation. The investigated ionic liquids are 1-methyl-3-octylimidazolium chloride [MOIM-Cl], 1-methylimidazolium hydrogen sulfate [H-MIM-HSO4], tetraethylammonium iodide [TEA-I], and 1-hexyl-3-methylimidazolium iodide [HMIM-I]. The impact of 0.1 mass fraction concentration ionic liquids on the methane hydrate phase boundary was evaluated by measuring the dissociation temperature of methane hydrate in the pressure range of 5.1–11.1MPa, using a high pressure differential scanning calorimeter. The molar dissociation enthalpy of methane hydrates was calculated using the Clausius–Clapeyron equation. The density was measured for 0.10 mass fraction of aqueous solutions of ionic liquids at 293.15K, and then compared to the commercially available gas hydrate inhibitors. The results demonstrated that 1-methylimidazolium hydrogen sulfate [H-MIM-HSO4] has the highest inhibitory performance among the four ionic liquids considered. Moreover, the Dickens and Quinby-Hunt (electrolyte) model was applied to predict the phase equilibrium data of the studied ILs. The predicted data is in agreement with the experimental data.

Chain extension of polyamide 6 using multifunctional chain extenders and reactive extrusion for melt foaming

We used the reactive extrusion method to modify virgin polyamides 6 (PA6) for melt foaming. The reactive extrusion was performed with a Haake melt mixer, and the following modifiers were used: 1,1′-isophthaloyl-bis-caprolactam (IBC), 2,2′-bis(2-oxazoline) (BOZ) and an epoxy-type chain extender KL-E4370 (EP) as well asan IBC and BOZ combination. The chain extender’s effects on the reactive modification were characterized through the PA6 chain’s rheological properties, including the storage modulus, the loss modulus, and the dynamic complex viscosity. The EP-modified PA6 was shown to have the highest viscoelasticity; that is, the highest melt strength. The PA6′s melting and crystallization properties were also investigated. A high-pressure differential scanning calorimeter (DSC) under compressed CO2 was used to evaluate the foaming temperature windows. Finally, the foamability of the modified PA6 was verified by our batch melt foaming experiments, where supercritical CO2 was used as the blowing agent. The EP-modified PA6 with the highest melt strength had the widest foaming window and the biggest expansion ratio.

Thermodynamic study of a plastic columnar discotic material 2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene dispersed with gold nanoparticles under elevated pressure

We report a systematic work on the effect of pressure on thermodynamic properties of a plastic columnar discotic liquid crystal (DLC), namely 2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene (HAT4) dispersed with gold nanoparticles up to 1000 MPa by using a high-pressure differential scanning calorimeter. The goal is to determine how elevated pressure can be used to modify the physical properties of plastic columnar DLC and their nanocomposites via changes in inter- and intra-molecular distances of discotics. We find that the columnar hexagonal plastic to isotropic liquid (Colhp–IL) phase transition temperatures and enthalpy decrease with increasing pressure. However, crystal to plastic columnar hexagonal (Cr–Colhp) transition temperature remains almost unchanged for pure and their nanocomposites. The effect of pressure on the phase behaviour of DLC has been studied to elucidate the nature of the mesophase behaviour.

Tetra-n-heptyl ammonium tetrafluoroborate: Synthesis, phase equilibrium with CO2 and pressure swing absorption for carbon capture

Based on the analyses of the interaction energy with CO2, COSMO calculation and melting temperature, a quaternary ammonium salt, tetra-n-heptyl ammonium tetrafluoroborate ([thepAm][BF4]), was synthesized using [thepAm][Br] and NaBF4 as the raw materials. The as-synthesized [thepAm][BF4] was characterized by FTIR and NMR. The solid–liquid–gas (SLG) phase equilibrium line of the [thepAm][BF4]–CO2 system was determined by high pressure differential scanning calorimeter, indicating it was more stable than [thepAm][Br] because of higher melting temperatures of [thepAm][BF4] in pressurized CO2. The solubility data of CO2 in [thepAm][BF4] at 313.2, 323.2 and 333.2K up to 15MPa were measured by using the high-pressure quartz spring approach. The Peng-Robinson equation of state with the van der Waals-1 mixing rules was employed to calculate the solubility and SLG phase equilibrium data. Results showed high molar fractions of CO2 in [thepAm][BF4] at high pressures (e.g., molar fraction of 0.88 at 10.0MPa and 313.2K). A cyclic absorption–desorption procedure and a pressure swing absorption process were proposed and tested for CO2 capture/separation from the H2, CO and CO2 mixture by using [thepAm][BF4] as the absorbent, verifying its selective capture of CO2 over H2 and CO. The study may open a new way for CO2 capture.

Near Critical Carbon Dioxide Sorption Induced Crystallization in PET

Near critical carbon dioxide sorption equilibria at 50°C and pressures up to 40 atms are analyzed and interpreted on the basis of the multiple sorption mechanisms possible in a glassy amorphous and semi crystalline polymer. Varying the penetrant-polymer testing temperature and external pressure it is possible to meet the full range of possible sorption behavior, from ideal Fickian diffusion to limiting relaxation controlled kinetics. Low sorption levels of low-pressure gases are attained through an ordinary Fickian mechanism. At higher gas pressures, however, higher penetrant sorption levels induce polymer relaxation affecting the final sorption behavior. A highly interacting solvent, as Carbon Dioxide in near critical conditions, leads to anomalous sorption ranging from relaxation controlled Fickian diffusion to limiting Case II and diffusion controlled relaxation, at high solvent uptakes (sorption from high activity vapor or from liquid phases). Generally, swelling has been observed to be accompanied by a solvent induced crystallization as detected by means of High pressure Differential Scanning Calorimeter (DSC) and Wide Angle Xray Scattering (WAXS).

Effect of Unexpected CO2’s Phase Transition on the High-Pressure Differential Scanning Calorimetry Performance of Various Polymers

We used a high-pressure differential scanning calorimeter (HP-DSC) to study polymer plasticization by compressed gases at pressures of up to 30 MPa for polylactide (PLA), polycarbonate (PC), isotactic polypropylene (iPP), and polystyrene (PS). The pressure reached values twice as high as the previously published data. We found that the polymer/carbon dioxide (CO2) system’s heating curves have an unidentified endothermic peak above 5 MPa, which turns out to be from CO2’s phase transition. The HP-DSC could accurately determine the depression of the glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm) of various polymers at low pressures by simply starting at a higher temperature to avoid CO2’s phase transition; however, the increased plasticization effect of the dissolved CO2 lowered the Tg to the level of overlapping with CO2’s phase transition phenomena at elevated pressures, and therefore, the depressed Tg could not be measured above 6 MPa for PLA, PC, or PS. ...