Hydrate Conversion Research Articles

Concentration of apple juice using CO2 gas hydrate technology to higher sugar contents

This paper describes the application of CO2-hydrate technology for the concentration of apple juice towards industrially relevant levels. Assays were carried out in a stirred autoclave at 1–2 °C and 35 bars with rediluted apple concentrate in the range of 11°Bx to 40°Bx. A hydraulic pellet press was used to separate the hydrate from the concentrate, resulting in an almost complete sugar recovery. It was found that apple juice can be concentrated to 45°Bx and beyond using this technique. Maximum hydrate conversion of up to 30% was achieved at an average concentration rate of 2.5–3°Bx/h. Furthermore, an optimal juice to crystallizer volume ratio of 35% was found. The investigations also revealed the juice composition to interfere with the hydrate formation process to some extend. In the assays with constant water content, no decrease in the hydrate formation rate was observed until 30°Bx. From this concentration onwards, however, the hydrate yield decreased steadily and amounted to only 15% at 40°Bx.

In-situ XRD study of the temperature-dependent early hydration of calcium aluminate cement in a mix with calcite

In the present work the hydration of white CAC, inert alumina-filler and CaCO3 was investigated at different temperatures with in-situ XRD. Experiments were performed at 10 °C, 23 °C, 40 °C and 60 °C. Overcoming or mitigating the phenomena of calcium aluminate hydrate conversion by adding reactive additives to calcium aluminate cement is often described in literature. When a sufficient amount of calcite is added, carbonate-AFm (monocarbonate and hemicarbonate) is expected to be the dominant hydrate phase. Calcite however, acts as an inert filler and barely influences the calcium aluminate hydration products at 10 °C. With rising temperature monocarbonate contents increase as well as the reaction rate of cement phases. At 60 °C minor amounts of C3AH6 precipitate during the early hydration. Special attention is given to the role of CAH10 and C2AHx during hydration. While CAH10 is dominant at 10 °C, C2AHx precipitates in a temperature range between 23 and 60 °C as a precursor phase for carbonate-AFm phases. These are not found at 10 °C, which is probably due to the lack of the precursor phase (C2AHx). The hydration of the mix at 10 °C with an initial addition of C2AHx shows that carbonate-AFm-phases can be precipitated in addition to CAH10 during the first 96 h.

A novel stirred microcalorimetric cell for DSC measurements applied to the study of ice slurries and clathrate hydrates

A novel prototype of a microcalorimetric cell with in-situ stirring has been developed to perform DSC measurements under atmospheric or pressure conditions. After a brief technical description of the apparatus, preliminary tests are presented which analyzed the influence of the stirrer rotation on the heat-flow signal. Experiments were then performed with complex fluids such as ice slurries and clathrate hydrates formed with cyclopentane and with carbon dioxide. They took place in stirred and non-stirred conditions and the results obtained were then compared. It was proven that the rotation of the microstirrer in the measuring cell does not disrupt the heat-flow signal during the analysis. As regards the practical applications tested, the in-situ stirrer efficiently reduces crystallization metastability, increases the water-to-hydrate conversion, and reduces the amount of time needed for analysis. The dissociation enthalpy of cyclopentane (CP) hydrates was measured at atmospheric pressure; it is effectively very difficult to analyze this system with non-stirred calorimetry techniques because the two liquid phases are immiscible. The experimental results, in good agreement with other data found in the literature, showed complete water-to-CP hydrate conversion within a short period of time using a simple protocol. Experiments were also performed under pressure to demonstrate that CO2 hydrate phase equilibrium data could be obtained rapidly and easily. It is therefore our opinion that the potential of this novel technology has been thoroughly demonstrated.

Water content of carbon dioxide at hydrate forming conditions

There is an interest to ensure sub-saturated water content in lines containing carbon dioxide in applications such as enhanced oil recovery and carbon sequestration, to reduce risks of hydrate blockage and corrosion. The water content of carbon dioxide at various temperatures and pressures has been measured in the past, but there is no consistent set of measurements that could be used for carbon dioxide storage and transportation design work. The solubility of water in a carbon dioxide rich gas phase at hydrate forming conditions was measured in this work. Pressures ranged from 12.06 to 29.30 bar along two isotherms, 1 °C and −7 °C, all within the gaseous carbon dioxide and hydrate stability zone. For the first time in these types of measurements, the solid phase was also characterized and confirmed to be carbon dioxide hydrate via X-ray computed tomography, simultaneous with water content measurements of the gas phase. Once carbon dioxide hydrate conversion had reached a maximum value (65% estimated by X-ray computed tomography), the equilibrium water content was measured. Prior to reaching this maximum carbon dioxide hydrate conversion, the water content in carbon dioxide was observed to decrease as liquid water converted to carbon dioxide hydrate. This slow conversion to hydrate, metastability of the hydrate phase, or unexpected phases may be responsible for the large discrepancy between prior data sets for similar carbon dioxide water content measurements.

Role of Processing Temperature and Time on the Hydrothermal Alteration of K-Feldspar Rock in Autoclave

Potassium fertilizers (potash) are mined in a handful of countries in the Northern Hemisphere. Potash is either expensive or unavailable to the farmers of the Southern Hemisphere. Alkaline alteration of K-feldspar rock (ultrapotassic syenite) in autoclave in the presence of Ca2+ generates a mixture of K-bearing calcium-aluminum-silicate-hydrate (C-A-S-H) minerals that potentially can be used as an alternative local fertilizer. This work investigates the effect of processing temperature (200 °C, 220 °C, and 230 °C) and time (from 0.5 to 3.0 h) on pH, mineralogy, and elemental availability of the C-A-S-H mineral mixture. Increasing temperature results in an increased conversion of K-feldspar and increased content of both the mineral tobermorite (Ca5Si6O16(OH)2·4H2O) and amorphous phase in the resulting C-A-S-H mixture; increasing time results in an increased conversion of α-dicalcium silicate hydrate into tobermorite. The amount of K leached from the mixture is relatively constant across all processing conditions. Hydrothermal alteration in autoclave of K-feldspar-bearing rocks such as ultrapotassic syenite permits the synthesis of a potential potassium fertilizer which alkalinity and mineralogy can be tailored according to soil requirements.

Pore-scale effect on the hydrate variation and flow behaviors in microstructures using X-ray CT imaging

Gas-hydrates are natural clean energy resources with significant potentials as the alternative energy resources. Nevertheless, the formation, migration and dissolution of hydrates in microstructures are not still well understood. Hydrate formation in sand-pack specimen and X-ray CT imaging experiments are conducted to elucidate the hydrates changes in microstructures. Color difference phase separation method is proposed to accurately segment the hydrate, pore and grain phases. Pore-scale variables are defined to quantitatively investigate the characteristics of hydrates. Moreover, the pore-scale flow properties in microstructures with hydrates are also studied. Results indicate that relative pore-scale variables significantly affect hydrate behaviors, in which hydrate saturation first increases with decreasing relative pore-scale variables, then keeps constant with relative stable pore-scale variables, and finally decreases with decreasing relative pore-scale variables during the hydrate migration. In the hydrate interaction, hydrate saturation keeps 0 as relative pore-scale variables gradually decrease to 0, caused by interaction between gas-hydrates and water-hydrates. During the hydrate conversion, hydration saturation increases with increasing relative porosity, relative pore size and relative grain size due to the conversion of gas-hydrates to water-hydrates. Hydrates can decrease the permeability in porous sediments due to the occupation of the pore space by hydrates, and the permeability decreases with increasing hydrate phase in porous sediments. The proposed approach gives more insights to the hydrates behaviors and permeability in fine-gained hydrate-bearing sediments.

Experimental study and kinetic modeling of R410a hydrate formation in presence of SDS, tween 20, and graphene oxide nanosheets with application in cold storage

Abstract Gas hydrates, or clathrate hydrates, can be used as a suitable cold/cool storage media, due to their large phase change enthalpy. In recent decades, cold production through gas hydrates as a novel and cost-effective method has motivated researchers. Refrigerants have the potential to be used in hydrate-based cold storage systems, because they can form hydrates at moderate pressures and temperatures. Hence, in this work, the kinetics of R410a (50 wt% difluoromethane + 50 wt% 1,1,1,2,2-pentafluoroethane) hydrate formation in the presence of different concentrations of SDS, tween 20, and graphene oxide (GO) was investigated. The experiments were carried out in a 300 cm3 reactor/cell at the initial pressure and temperature of 1 MPa and 279.65 K, respectively. According to the results, at all concentrations of the additives, except tween 20 at a concentration of 1000 ppm, the hydrate formation induction time decreases, compared to pure water. Furthermore, the promotion effects of SDS and GO on the quantity and rate of gas uptake, and the apparent rate constant were observed at the initial minutes of the hydrate growth process. The measured storage capacity and water to hydrate conversion show that the used additives do not change the abovementioned parameters, noticeably.

Enhanced methane gas storage in the form of hydrates: role of the confined water molecules in silica powders.

Methane hydrates are promising materials for storage and transportation of natural gas; however, the slow kinetics and inefficient water to hydrate conversions impede its broad scale utilisation. The purpose of the present study is to demonstrate rapid (2–3 h) and efficient methane hydrate conversions by utilising the water molecules confined in the intra- and inter-granular space of silica powders. All the experiments were conducted with amorphous silica (10 g) powders of 2–30 μm; 10–20 nm grain size, to mimic the hydrate formations in fine sand and clay dominated environments under moderate methane pressure (7–8 MPa). Encasing of methane molecules in hydrate cages was confirmed by Raman spectroscopic (ex situ) and thermodynamic phase boundary measurements. The present studies reveal that the water to hydrate conversion is relatively slower in 10–20 nm grain size silica, although the nucleation event is rapid in both silicas. The process of hydrate conversion is vastly diffusion-controlled, and this was distinctly observed during the hydrate growth in nanosize silica.

Delaying Effect of NaCl on The Conversion of Hydrates of Calcium Aluminate Cement

The effect of NaCl on the conversion of hydration products of calcium aluminate cement(CAC) was determined by means of MIP, XRD, DSC-TG and SEM. Results show that the addition of NaCl promotes the formation of CAH10 at early hydration stage. The total porosity and proportion of harmful pore in hardened CAC paste with NaCl are lower and the 7d-strength is 40% higher than that of the control. The later curing at 40°C accelerates the conversion from metastable C2AH8, CAH10 to C3AH6, and the strength decreases with the increasing of curing age. After 90 days, there is no metastable hydrate detected in CAC paste. However, the addition of Niacin CAC paste can prominently delay the conversion of C-A-H. Massive CAH10 still exists in the paste with NaCl, resulting in a slower retraction of late strength.

Economic benefit of methane hydrate reformation management in transport pipeline by reducing thermodynamic hydrate inhibitor injection

Hydrate reformation is an inherent risk in a methane hydrate production system because dissociated water and methane flow through transport pipelines simultaneously. In this study, comprehensive experiments using high-pressure autoclaves are performed to investigate the effect of reducing the concentration of thermodynamic hydrate inhibitor on hydrate reformation characteristics. In order to simulate the production of methane hydrates, these are formed and dissociated in the preliminary stage; thereafter, the hydrates are reformed from dissociated water. Although dissociated water and fresh water are found to have similar formation rates, they have a major difference in relative torque, especially in the early stage of hydrate formation. The instant rise of the relative torque in the dissociated water is observed to be up to 2.5; thereafter, it remains approximately 3.0 until hydrate conversion reaches 28 vol%. This trend is different from that in fresh water, where a steady increase in relative torque with sudden spikes is observed. These results clearly show the high risk of hydrate blockage in the transport pipelines of a methane hydrate production system; hence, the injection of hydrate inhibitor is necessary. In this study, monoethylene glycol (MEG) is the selected thermodynamic hydrate inhibitor; its concentration is maintained below a specific value to completely avoid hydrate formation. Despite the occurrence of hydrate reformation, a stable relative torque is observed in a 20 wt% MEG concentration, where the conversion of water to hydrate approximately reaches 40 vol%. For a 10 wt% MEG concentration, a sudden increase in relative torque of up to 2.0 is observed in the early stage of hydrate formation; this suggests that the foregoing is less effective in sustaining flowability. Compared to fresh water, the addition of a 20 wt% MEG to dissociated water results in a more stable torque. Once the performance of the MEG concentration reduction is confirmed, the MEG regeneration process is designed accordingly by using both multiphase flow and process simulation models. A life cycle cost (LCC) analysis is conducted by estimating the capital expenditures (CAPEX) and operating expenditures (OPEX) of the MEG regeneration process. Considering both CAPEX and OPEX, the LCC for complete inhibition (35 wt%) is 90.15 MUSD (million United States dollars); however, for the 20 and 10 wt% MEG concentrations, the LCC values are reduced to 86.79 and 84.58 MUSD, respectively. The foregoing suggests the potential economic benefit of methane hydrate reformation management to avoid blockage.

Thermal conductivity and reactivity of Mg(OH)2 and MgO/expanded graphite composites with high packing density for chemical heat storage

The effective thermal conductivities (TCs) of pelletized magnesium hydroxide (Mg(OH)2)/expanded graphite (EG), and magnesium oxide (MgO)/EG composite heat storage materials with high packing densities were measured at 110 °C over a wide range of Mg(OH)2 and MgO compositions. The effective TCs of both Mg(OH)2/EG and MgO/EG decreased with increases in the Mg(OH)2 and MgO content. The present values reasonably agreed with the extrapolations of those of the composites with low levels of packing density listed in the literature. The hydration conversion ratio of MgO/EG was lower than that of powdery MgO at both 90 and 110 °C for 60-min hydration because the water vapor transfer would be decreased by the EG layers. The 60-min hydration conversion ratio of MgO/EG at 90 °C was close to that at 110 °C in contrast to the results of the powdery MgO. Moreover, the notable reductions in the hydration conversion ratios of MgO/EG were observed at a relatively high initial Mg(OH)2 concentration.

Effect of CaSO4 on hydration and phase conversion of calcium aluminate cement

Conversion from metastable phase to stable phase in calcium aluminate cement (CAC) causes volumetric instability, resulting in loss of compressive strength. This study investigated the effect of CaSO4 on the phase conversion of calcium aluminate cement. The specimens with different dosage of CaSO4 were exposed to 60 °C to trigger the phase conversion of CAC after curing at 20 °C for 7 days. Analysis with X-ray diffraction, thermogravimetry, mercury intrusion porosimetry, and scanning electron microscopy were conducted. The incorporation of CaSO4 inhibited the formation of unstable CAH10 by direct precipitation of ettringite. As a result, the reduction of strength of CAC specimens due to the increased pore volume by conversion was inhibited by ettringite and monosulfate formation.

Experimental and modelling studies on the effects of nanofluids (SiO2, Al2O3, and CuO) and surfactants (SDS and CTAB) on CH4 and CO2 clathrate hydrates formation

Sodium dodecyl sulfate (SDS) with concentrations of 300 ppm and 500 ppm; cetyl trimethylammonium bromide (CTAB) with concentrations of 220 ppm and 700 ppm; and water-based nanofluids of SiO2, Al2O3, and CuO with concentrations of 0.1, 0.3, and 0.5 wt% were used as kinetic promoters in methane hydrate formation process at initial conditions of 274.15 K and 5.5 MPa and carbon dioxide hydrate formation process at initial conditions of 274.15 K and 3 MPa. Englezos and Bishnoi model was utilized for calculating the apparent rate constant of hydrate growth and van der Waals-platteeuw model coupled with CPA equation of state was used to model hydrate phase equilibrium conditions. SDS with a concentration of 500 ppm and CTAB with a concentration of 700 ppm are the most effective promoters in increasing the average apparent rate constant and water to hydrate conversion. SiO2 nanofluid with a concentration of 0.3 wt% shows the most promising promotion effects by reducing the induction times of CO2 and CH4 hydrates formation by 70 and 74%, respectively. Aqueous solution of SDS with a concentration of 500 ppm is the most effective promoter that can enhance the average apparent rate constant of CO2 and CH4 by 350 and 200%, respectively.

Kinetics of CO2 hydrate formation in coffee aqueous solution: Application in coffee concentration

In this study, concentration of the coffee aqueous solution was performed using CO2 hydrate formation. The experiments were aimed to investigate the effects of the solution of coffee and pure water on the amount and rate of CO2 consumption, water to hydrate conversion, storage capacity, induction time, and initial apparent rate. These experiments were carried out at a pressure of 3.0 MPa, a mean temperature of 275.15 K, and weight percentages of 1.5, 5, 10, 15 w/w%. The results show that increasing the concentration of coffee solution leads to decrease of the induction time, and also demonstrates its inhibitor effect on water in all concentrations of coffee. Investigating the amount of gas consumption over the initial 30 minutes of the experiments reveal that the mole number for CO2 consumption reached its ultimate value during this period, while it stood 17% less for all coffee concentrations as compared to pure water. This clearly indicates the inhibiting effect of the coffee solution in comparison to pure water.

Promoting gas hydrate formation with ice-nucleating additives for hydrate-based applications

Gas hydrates are crystalline icy compounds capturing small gas molecules in the cavities made of hydrogen-bonded water molecules. Hydrates can store a large amount of gas and selectively capture certain gas species depending on thermodynamic conditions and formation pathways. In addition, any impurities that are not stabilized in hydrates are excluded upon hydrate formation. Such interesting properties have allowed the proposal of a variety of hydrate-based applications, including energy storage, CO2 capture, gas separation, and desalination. However, they are not yet utilized as viable technologies, mainly because of the low process efficiency. The major challenges here are to improve the formation kinetics and to enable hydrates to be properly managed in industrial processes. Here, inspired by the similarities in crystallization processes of ice and gas hydrates, we identified the capabilities of two ice-nucleating additives, Icemax® (protein) and Drift® (surfactant), as kinetic promoters for hydrate-based applications. Our experimental results demonstrate that both additives increase the formation kinetics of CH4 (structure I) and CH4/C2H6 (structure II) hydrates under high and low shear. Drift® enlarges the interfacial area at the gas-liquid interface, enhancing the mass transfer, and thus increases the hydrate conversion 18 times under non-stirred cases. Icemax® can better accelerate the initiation of hydrate formation by providing additional nuclei for heterogeneous nucleation. According to visual observations, both additives form porous and soft hydrates, which can be easily handled in industrial scale processes. Major findings confirm the potential of ice-nucleating additives to facilitate hydrate-based applications by improving the production rate and process efficiency.

Thermodynamic and Kinetic Investigation of Desalination by Refrigerant Clathrate Hydrate Formation

Gas hydrate is a crystalline solid compound form of water with hydrophobic gas at certain conditions (pressure and temperature). The hydrogen bond in water molecules constructs a framework as a host that entraps gas molecules (gust). Gas hydrate can be applied to many industries such as gas separation, cool storage, food concentration and desalination. Hydrate route looks a promising alternative technology compared to the conventional process, by utilizing a proper gas host, which can be held within water cavities composed by hydrogen-bonded water molecules. In this study the selected host gas was Refrigerant R134a, the work consists of an experimental and theoretical investigation dealing with hydrate formation for the ternary system (water, refrigerant gas, salt) at different initial pressures, the salts were NaCl, KBr and NaF. Method of isochoric pressure search method was used to measure the pressure and temperature for hydrate formation and conduction the three phases of (hydrate-liquid-vapour). The measurements were performed with pressure range (0.1 - 0.4) MPa and the temperatures about (275.2 – 283)K at the concentrations of (0.09,0.17 and 0.26)mol/kg for each salt. The kinetics of R134a clathrate formation for ternary systems (R134a, water and salt) at various types and concentrations of salts. Many objective functions were obtained from the kinetic model for hydrate formation, such as the amount of gas consumed, the growth rate, and the conversion of the water to hydrate. The results showed the effect of the initial pressure on the gas consumed, the rate of growth and water to hydrate conversion, that when the initial pressure increase the moles of R134a gas consumed was increased due to the increased driving force of hydrate formation, also other functions were increased. While the increasing in the concentration of salt for all types will be decreased gas consumed, whereas water to hydrate conversion, the growth rate is slightly decreased. And from the results noticed the presence of different salts in the ternary systems have an effect on the thermodynamics inhibition of refrigerant hydrates and the inhibition increases with the presence of NaCl salt in the ternary system more than other types of salt and also increases with increase the concentration of salt.

Effect of temperature cycle on mechanical properties of methane hydrate-bearing sediment

In this study, methane hydrate-bearing sand (MHBS) was created in the laboratory following two methods in order to obtain two types of gas hydrate morphology in sandy sediment. The hydrate morphology in the sediment was assessed by measuring the compressional wave velocity combined with models to predict the wave velocities of the sediment containing gas hydrates. The mechanical properties of the MHBS were investigated by triaxial compression tests. The results obtained by the compressional wave velocity show that after saturating the MHBS sediment (created by the excess gas method) with water, the methane hydrates are partly or completely converted from grain contacts to pore spaces depending on the hydrate saturation (ranging from 0 to 50%). A subsequent temperature cycle completes this conversion process for high hydrate saturation. The results obtained with the triaxial compression tests show higher shear strength, a higher secant Young’s modulus, and a higher dilation angle at higher hydrate saturation. In addition, the effects of hydrate saturation on the mechanical properties of the MHBS obtained by the two procedures (with and without the thermal cycle) are similar at low hydrate saturation. The effect of gas hydrate morphologies can only be detected in the case where the conversion (and/or redistribution) of gas hydrates from grain contacts to pore spaces is not complete (at high hydrate saturation).

Analysis of methane production intensity during its displacement from a gas hydrate formation by carbon dioxide

The theoretical model is considered in the one-dimensional approximations and numerical solutions are obtained for the process of replacing methane with carbon dioxide from a hydrate in a formation saturated with methane and its hydrate when carbon dioxide is injected into the formation. The process is considered under thermobaric conditions corresponding to the stability region of methane gas and carbon dioxide and the region of existence of CO2 in the form of a gaseous phase. The case is considered when the rate of carbon dioxide hydrate formation is limited by diffusion of carbon dioxide through the formed hydrate layer between the gas mixture stream and methane hydrate. It is accepted that the hydration substitution process occurs without the release of water from the hydrate. To describe the mathematical model, the main equations are the mass conservation equations for methane, carbon dioxide and their hydrates, Darcy’s law for filtration, Fick’s law for diffusive mixing of the gas mixture, state equations for the gas phase, Dalton’s law, energy equation, diffusion equation for transport CO2 through the hydration layer at the pore microchannel scale. The dynamics of the mass flow rates of the outgoing carbon dioxide and methane recovered has been investigated. The influence of the diffusion coefficient, the absolute permeability and the length of the formation on the intensity of the methane produced as a result of the gas substitution process is analyzed. Three main stages of the process were identified: displacement of free methane from the reservoir; extraction of free methane obtained as a result of the beginning of hydrate substitution in the formation; complete conversion of methane hydrate to carbon dioxide hydrate and complete extraction of methane from the formation. It is determined how the two main factors relate to each other in terms of the degree of influence on the replacement rate: heat and mass transfer in the reservoir and the kinetics of the replacement process.

Storage of Methane Gas in the Form of Clathrates in the Presence of Natural Bioadditives.

Methane (CH4) and carbon dioxide (CO2), the important greenhouse gases, are capable of forming clathrate hydrates under some suitable thermodynamic conditions. The gas storage capacity of these materials is high, and therefore they are often useful in gas storage applications. Certain expensive and toxic chemicals are employed to accelerate/decelerate the process. In this study, we report rapid (∼30–50 min) and effective (∼80%) methane hydrate conversion in the presence of three naturally occurring additives such as dry powders from Nelumbo nucifera (Indian lotus), Piper betle (betel), and Azadirachta indica (neem), at lower concentrations (0.5 wt %). Obtained results were carefully compared with the well-known kinetic promoter (sodium dodecyl sulfate). All the biomaterials are equally good kinetic promoters for methane hydrates, although the required subcooling is significantly large. However, no hydrate formation is observed with CO2 gas.

Influence of Fractions Isolated from Crude Oils and Refined Petroleum Product on Decomposition Process of Methane Hydrate

Decomposition of methane hydrate in systems containing asphaltenes, resins, or oils isolated from two types of crude petroleum and transformer oil has been studied. To prepare a sample of methane hydrate suspension in a fraction isolated, a pure hydrate powder with water to hydrate conversion of 0.92 ± 0.08 was used. The hydrate powder with particle size less than 250 μm was mixed with the powdered fractions at the liquid nitrogen temperature. Then the mixture was heated to melt the fractions and allow their components to be adsorbed on the hydrate particles surface. All stages of suspension preparation were carried out in the hydrate stability zone. Similar studies with hydrate particles suspended in saturated/aromatic components and solutions of polar compounds isolated from petroleum/transformer oils as well as in n-decane/toluene were also carried out. As a result, it has been found that fraction of oils as well as its subfraction of saturated hydrocarbons contribute to the manifestation of methane hy...