Kinetics Of CO2 Hydrate Formation Research Articles

Dependence of the formation kinetics of carbon dioxide hydrate on clay aging for solid carbon dioxide storage

Clay-based marine sediments have great potential for safe and effective carbon dioxide (CO2) encapsulation by storing enormous amounts of CO2 in solid gas hydrate form. However, the aging of clay with time changes the surface properties of clay and complicates the CO2 hydrate formation behaviors in sediments. Due to the long clay aging period, it is difficult to identify the role of clay aging in the formation of CO2 hydrate in marine sediments. Here, we used ultrasonication and plasma treatment to simulate the breakage and oxidation of clay nanoflakes in aging and investigated the influence of clay aging on CO2 hydrate formation kinetics. We found that the breakage and oxidation of clay nanoflakes would disrupt the siloxane rings and graft hydroxyl on the clay nanoflakes. This decreased the negative charge density of clay nanoflakes and weakened the interfacial interaction of clay nanoflakes with the surrounding water. Therefore, the small clay nanoflakes enriched in hydroxyl would disrupt the surrounding tetrahedral water structure analogous to the CO2 hydrate, resulting in the prolongation of CO2 hydrate nucleation. These results revealed the influence of the structure-function relationship of clay nanoflakes with CO2 hydrate formation and are favorable for the development of hydrate-based CO2 storage.

Comparative Analysis of the Mechanisms and Kinetics of CO2 Hydrate Formation with Sodium Dodecyl Sulfate and L-Leucine Additions under Static Conditions

Comparative Analysis of the Mechanisms and Kinetics of CO2 Hydrate Formation with Sodium Dodecyl Sulfate and L-Leucine Additions under Static Conditions

Kinetics studies of CO2 hydrate formation in the presence of l-methionine coupled with multi-walled carbon nanotubes

In recent years, gas hydrate technology has been considered to be a promising method for CO2 capture and transport. Nevertheless, the development of the gas hydrate technology is hindered by the slow hydrate formation. In this work, the effects of concentration, initial pressure and gas-liquid ratio on the CO2 hydrate formation kinetics in the compound system of environmentally friendly additive l-methionine (L-met) coupled with low-dose multi-walled carbon nanotubes (MWCNTs) were investigated for the first time. The results showed that L-met coupled with MWCNTs could effectively promote the CO2 hydrate formation, and the promotion effect was related to the MWCNTs concentration. At 4.0 MPa, compared to the 0.1250 wt% L-met single system, the compound system with the MWCNTs concentration of 0.0270 wt%∼0.0720 wt% increased the CO2 gas consumption (Gsum) by an average of 6.37 %, and the induction time (tin) of CO2 hydrate formation were shortened by an average of 36.03 %. The optimal concentration of MWCNTs was 0.0450 wt%. Meanwhile, the increase of the pressure and gas-liquid ratio could effectively accelerate the kinetics of CO2 hydrate formation. The promotion effect of the pressure increasing was better than that of the gas-liquid ratio increasing. The pressure increasing could result in the maximum increase of 39.75 %, 122.83 %, and 69.85 % in Gsum, initial gas consumption rate (N10), and the gas to hydrate conversion (GTH), respectively; and the highest reduction of tin was 83.72 %. Furthermore, the hydrate morphological observations revealed that CO2 hydrate initially nucleated in the inner of L-met solution, and the hydrate particles in the compound system of L-met coupled with the MWCNTs were porous snowflakes. The wall climbing effect induced by capillary forces was further explained, and the presence of L-met enhanced the mass transfer capacity of CO2 hydrates. The practical use of fast hydrate formation technology for CO2 capture and sequestration has been facilitated by this work.

Introducing sodium lignosulfonate as an effective promoter for CO2 sequestration as hydrates targeting gaseous and liquid CO2

Hydrate-based CO2 sequestration (HBCS) emerges as a promising solution to sequestrate CO2 as solid hydrates for the benefit of reducing CO2 concentration in the atmosphere. The natural conditions of high-pressure and low-temperature in marine seabed provide an ideal reservoir for CO2 hydrate, enabling long-term sequestration. A significant challenge in the application of HBCS is the identification of an environmental-friendly promoter to enhance or tune CO2 hydrate kinetics, which is intrinsically sluggish. In addition, the promoter identified should be effective in all CO2 sequestration conditions, covering CO2 injection as gas or liquid. In this study, we introduced sodium lignosulfonate (SL), a by-product from the papermaking industry, as an eco-friendly kinetic promoter for CO2 hydrate formation. The impact of SL (0–3.0 wt.%) on the kinetics of CO2 hydrate formation from gaseous and liquid CO2 was systematically investigated. CO2 hydrate morphology images were acquired for both gaseous and liquid CO2 in the presence of SL for the explanation of the observed promotion effect. The promotion effect of SL on CO2 hydrate formation is optimal at 1.0 wt.% with induction time reduced to 5.3 min and 21.1 min for gaseous and liquid CO2, respectively. Moreover, CO2 storage capacity increases by around two times at 1.0 wt.% SL, reaching 85.1 v/v and 57.1 v/v for gaseous and liquid CO2, respectively. The applicability of SL as an effective kinetic promoter for both gaseous and liquid CO2 was first demonstrated. A mechanism explaining how SL promotes CO2 hydrate formation was formulated with additional nucleation sites by SL micelles and the extended contact surface offered by generated gas bubbles or liquid droplets with SL. The study demonstrates that SL as an effective promoter for CO2 hydrate kinetics is possible for adoption in large-scale HBCS projects both nearshore and offshore.

Kinetic analysis of CO2 hydrate formation in the aqueous solutions of transition metal chlorides

AbstractCO2 hydrate technology can be applied to seawater desalination. However, the kinetics of CO2 hydrate formation were inhibited in the aqueous solution with inorganic salts, and the kinetic mechanism of CO2 hydrate formation for inorganic salts with different metal cations and anions was still unclear. In this work, CO2 hydrate nucleation and growth were studied in aqueous solutions of metal chlorides. Instead of Na+ and K+ ions, CO2 hydrate nucleation was promoted in the presence of Ni2+, Mn2+, Zn2+ and Fe3+ ions due to the co‐ordination bonds between transition metal ions and water molecules to enhance the formation of the critical crystal nuclei. The induction time was increased by 61.1% in aqueous solution with 0.32 mol/L NaCl, while it was shortened by 55.6% in FeCl3 aqueous solution at the same concentration of Cl− anions. In the process of CO2 hydrate growth, Cl− ions played a more important role than the metal ions in affecting the stability of CO2 hydrate cages. The gas storage capacity was reduced by 10.3% in the presence of NaCl, and was lower than that of other metal chlorides. Cl− anions were absorbed on the hydrate surface and involved in hydrate cages to inhibit the hydrate growth due to the hydrogen bonds between the Cl− ions and water molecules of the hydrate cages. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Synergistic effect of alkanes with tween 80 on the kinetics of CO2 hydrate formation

The environmental problems brought about by the drastic increase in CO2 concentration are a great challenge that must be faced by mankind for sustainable development. Fortunately, research on CO2 hydrates has provided new views to effectively address these challenges. However, the slow kinetics of CO2 hydrate formation, unclear enhancement mechanisms, and high process costs have limited the practical application of hydrate-based carbon capture (HBCC) technology. In this work, we investigated the potential value of long-chain alkanes (n-decane) and Tween80 promoter (kinetics) in HBCC. We examined the key factors determining the promoter effect of long-chain alkanes and the synergistic effect of Tween80 with long-chain alkanes for the first time. The results showed that long-chain alkanes can play a facilitating or inhibiting role for the hydrate formation, depending on the state of the long-chain alkanes. The mechanism of long-chain alkanes to improve the kinetics of hydrate formation was mainly due to the hydrophobic effect and gas mass transfer. The addition of Tween 80 enhanced the stability of the system and promoted the gas mass transfer of long-chain alkanes, which could realize the kinetic enhancement under low-speed stirring conditions. This work helps to elucidate the mechanism of hydrocarbon compounds' influence on the kinetics of hydrate formation and provides a basis for their potential value for HBCC. It also provides some theoretical guidance for the use of inhibitors in the presence of hydrocarbon compounds.

Evaluating CO2 hydrate kinetics in multi-layered sediments using experimental and machine learning approach: Applicable to CO2 sequestration

The transition to a low-carbon economy requires the implementation of effective carbon capture and sequestration (CCS) strategies. One of the potential CCS strategies is to capture industrial CO2 emissions and inject them into the oceanic sediments to be stored as CO2 hydrates. However, the success of this technique depends on a few key factors such as the type of sediments where CO2 is injected, the kinetics of CO2 hydrate formation and dissociation, the accuracy of the models for prediction of formation kinetics, and the CO2 hydrates morphology. So, in this first-gen work, a highly complex set of experiments was carried out to examine the CO2 hydrate formation and dissociation processes by injecting CO2 via injection tube into different size wet sediments, i.e., coarse (diameter: 0.5–1.5 mm), granules (diameter:1.5–3.0 mm) and dual-layered sand (coarse + granules), embedded inside high-pressure reactor as the artificial seabed. The experiments were carried out at 3.5 MPa at T = 1.5–2.0 °C with 500 ppm of the eco-friendly hydrate promotor (l-tryptophan). The images of morphological changes during hydrate formation/dissociation, the Scanning Electron Microscope analysis of the sediments, and the estimated water-to-hydrate conversations have been reported in this work. A novel mathematical four-parameter-based CO2 hydrate kinetics model was also developed. A set of 32,843 experimental data points was used to train a supervised machine learning algorithm using two parameters with the other two taken from published literature. The water-to-hydrate conversion was estimated and follows the order of dual-layered sand [88.26 (±4.62) %] > coarse [77.77 (±5.72) %] > granules [65.36 (±2.3) %]. The proposed ML-based model predicted the water-to-hydrate conversion with an Average Absolute Relative Deviation [%AARD] of 4.23–13.29 %. This work serves as a step forward in developing a sustainable hydrate-based oceanic carbon storage technology.

Enhanced the formation kinetics of CO2 hydrate using graphene oxide and L-methionine

Although carbon dioxide capture and storage based on hydrate technology has the characteristics of recyclability, high safety, and low pollution, it is hindered by the harsh conditions and the slow rate of hydrate formation. To improve the formation rate and the storage capacity of CO2 hydrate, the effects of graphene oxide (GO) and L-methionine (L-met) on CO2 hydrate formation kinetics were studied in this work. The experimental results showed that GO could effectively promote CO2 hydrate formation, and its promotion effect was related to the concentration of GO. For the single GO system, when the concentration of GO increased from 0.005 wt% to 0.025 wt%, the total gas consumption increased by 7.83%–16.59% compared with that of the pure water system. It was found that the optimal concentration of GO in the single GO system was 0.015 wt%, in which the induction time was shortened by 59.68% compared with that of the pure water system. For the compound system of GO and L-met, a synergistic promotion effect for CO2 hydrate formation was found between GO and L-met, and the optimal concentration in the compound system was 0.015 wt% GO mixed with 0.15 wt% L-met. Compared with the pure water system, the induction time and the time required for 90% hydrate formation to complete (T90) were shortened by 74.79% and 55.17%, respectively. According to the morphological observation of hydrates, it was inferred that the L-met enhanced the hydrate formation and mass transfer. Compared with the published data, the compound optimal system of GO and L-met had a higher gas storage capacity and a shorter induction time for hydrate formation. This work is helpful for advancing the commercialization of CO2 capture and storage based on hydrate technology.

Diffusion model of gas hydrate formation from ice considering the gas pressure drop

A kinetic model of the process of gas hydrate formation from ice that considers the gas pressure drop caused by this process is presented. This model is based on the diffusion equation. The issues during the formation of gas hydrate from ice powder and that from a flat ice layer are considered separately. For each of these problems, a solution in the framework of a quasi-stationary approximation is obtained, allowing for the calculation of the gas pressure drop in the gas phase. The calculated data are compared with available experimental data on the kinetics of CO2 hydrate formation from pure ice powder and ice powder with the addition of sodium dodecyl sulfate (SDS) at a mass concentration of 240 ppm: the calculated and experimental curves of CO2 pressure drop are compared with each other. From this comparison, the values of the diffusion coefficient of CO2 through a layer of CO2 hydrate formed from pure ice and ice with the addition of SDS at a mass concentration of 240 ppm were determined. Based on these values, it was found that SDS molecules present in the gas hydrate affect the rate of gas diffusion through the gas hydrate layer.

A comprehensive review of the influence of particle size and pore distribution on the kinetics of CO2 hydrate formation in porous media

AbstractAs an essential greenhouse gas, CO2 is the leading cause of global warming and environmental problems. An efficient strategy to lower CO2 emissions is the hydrate‐based method of CO2 geological storage. The stability and formation process of hydrate is the premise and foundation of the hydrate method of CO2 geological storage. However, the formation rule of CO2 hydrate has a significant impact on the formation characteristics of CO2 hydrate. This paper thoroughly examines the formation properties of CO2 hydrate in porous media systems. The quantitative impacts and laws of many parameters on the CO2 hydrate production process are thoroughly examined. On this basis, the internal mechanism of particle size, pore distribution, and critical size of particles in porous media systems on the kinetics of CO2 hydrate formation are detailed. Finally, the shortcomings of the studies on CO2 hydrate formation kinetics in porous media systems and the main directions in the future are pointed out. The influence of pore distribution in porous media on the CO2 hydrate formation process still needs further study. The relative results will be useful in the future for CO2 capture and sequestration in sediments. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

CO2 Hydrate Formation Kinetics in the Presence of a Layered Double Hydroxide Nanofluid

AbstractThe effects of a hybrid nanofluid (Cu‐Al layered double hydroxide (LDH)) on the CO2 hydrate formation kinetics was investigated at three different nanofluid concentrations (0.25–1.0 wt %). The Cu‐Al LDH nanofluid was prepared using a one‐step co‐precipitation technique. The addition of the LDH nanofluid reduces the induction time and enhances the hydrate formation kinetics. The maximum reduction in the induction time (by 91.08 %) was observed at the optimal nanofluid concentration of 0.5 wt %, compared to water. A chemical affinity model was implemented to predict the experimental data for CO2 hydrate formation in the presence of the different LDH nanofluid concentrations. An artificial neural network‐based Levenberg‐Marquardt model predicts the experimental data with higher accuracy than the scaled conjugate gradient model. The results indicate a strong dependency of the hydrate formation kinetics on the LDH nanofluid concentrations.

Impact of acetamide, 1,2,4-triazole, and 1-dodecyl-2-pyrrolidinone on carbon dioxide hydrate growth: Application in carbon dioxide capture and sequestration

Gas hydrates have served as the focal point of research from a sustainable engineering perspective, due to their specific applications in diverse scientific areas including carbon dioxide (CO2) gas storage, carbon capture, and sequestration (CCS). However, improved kinetics of CO2 hydrate formation will render the development of technologies for CCS. In this context, it should be mentioned that under the seafloor, low temperature and high pressure prevail, which makes the sequestration of gaseous CO2 in the form of solid hydrates plausible. In this study, both formation and dissociation kinetics of CO2 hydrates have been investigated in the presence of aqueous solutions of three CO2-philic additives, namely, acetamide, 1,2,4-triazole, and non-ionic surfactant 1-dodecyl-2-pyrrolidinone (DDP) with varying concentrations (0.5, 1, 2, and 4 wt%) at 274.55 K and 3.6 MPa in a 1.4 L stirred tank reactor. These chemicals having high binding energies with CO2, draw the dissolved CO2 molecules towards the hydrate cages by strongly interacting with them. Moreover, DDP can enhance the rate of gas dissolution by lowering the surface tension at the gas-water interface and altering the contact angle. All the additives exhibited considerable improvements in gas uptake than pure water, with 0.5 wt% DDP showing the most substantial promoting effect as it increased the moles of CO2 uptake and water-to-hydrate conversion by 55%. Likewise, about a 28% rise in these metrics was observed with 0.5 wt% acetamide and 2 wt% of 1,2,4-triazole. Furthermore, a reduction of 80% was observed in t90 with 0.5 wt% of DDP. The positive impacts of DDP and acetamide were highest at a lower concentration of 0.5 wt%, signifying their economic feasibility. The dissociation studies conducted on the CO2 hydrates up to 293.15 K demonstrated high dissociation rates, thus faster CO2 recovery for further use. This study conclusively shows that the additives might be used as equitable kinetic promoters for the CO2 hydrate relevant to CCS.

Characteristics of CO2 hydrate formation and dissociation at different CO2-water ratios in a porous medium

Hydrate-based CO2 sequestration (HBCS) is a new concept to store a huge amount of CO2 in geological sediments in the form of crystalline solids. This technique can address several environmental challenges of the current geologic carbon sequestration approaches. This study aims to evaluate and compare the characteristics and kinetics of CO2 hydrate formation and dissociation in the porous medium (three-phase) and bulk (two-phase) conditions at different CO2-water ratios. The experimental results indicate that the pressure drops and consequently hydrate nucleation and growth are limited in the porous medium due to the presence of solid particles, limited CO2 mass transfer, and heat transfer. Calculation of CO2 mass consumption and rate of gas uptake during hydrate formation also support the limited CO2 consumption and gas uptake rate in the porous medium, compared to the bulk condition. The calculated driving force for each test condition suggests its critical importance in the kinetics of CO2 hydrate formation. On the other hand, limited CO2 diffusion to the aqueous phase, hydrate nucleation at the solid-CO2-water interface, and better protection of newly formed hydrates are among the main reasons for the success of hydrate formation at the CO2-limited ratio only in the porous medium. Lastly, three steps during hydrate dissociation via thermal stimulation, such as heat transfer driving, kinetic driving, and fluid flow driving, are no longer discernable in the porous medium due to the limited heat and mass transfer during the process.

Roles of montmorillonite clay on the kinetics and morphology of CO2 hydrate in hydrate-based CO2 sequestration

Hydrate-based CO2 sequestration in marine sediments has emerged as a novel sustainable technology for long-term and stable CO2 sequestration. However, the role of clay minerals in CO2 hydrate formation and dissociation in clay-rich sediments, which are widely distributed in the South China Sea, remains controversial due to a lack of experimental evidence. This study investigates the effect of a representative clay mineral, sodium montmorillonite (Na-MMT), on the nucleation and growth kinetics of CO2 hydrate in suspensions with a msass fraction below 20.0 wt%. The kinetic experiments reveal that Na-MMT significantly reduces the induction time due to the additional nucleation sites provided by the delamination of clay particles and the induced surface electric field. While the average growth rate of CO2 hydrate is reduced by ∼72 % for Na-MMT mass fraction above 5.0 wt%. Morphologically, hydrate-clay stratification and gas-tunneling behaviors were observed, providing explanations for the retarded kinetics. The mass transfer of CO2 from the gas phase to the liquid phase is impeded by the high viscosity of the suspension and the clay-induced strongly-polarized water layer, which retards the overall kinetics of CO2 hydrate formation. Upon thermal stimulation, partial CO2 hydrate dissociation was observed within the pure CO2 hydrate stability region for 10.0 wt% Na-MMT suspension, indicating a possible impact of Na-MMT on CO2 hydrate thermodynamics. Moreover, the addition of Na-MMT clay promotes CO2 hydrate dissociation kinetics significantly. This study provides fundamental insights into the interaction between Na-MMT clay and CO2 hydrate, offering new perspectives for designing effective strategies for CO2 sequestration in abundant clay-rich marine sediments.

Investigation on the Amino Acid-Assisted CO2 Hydrates: A Promising Step Toward Hydrate-based Decarbonization

Carbon capture and storage (CCS) is a promising method for reducing carbon dioxide (CO2) emissions, while the use of fossil fuels is still needed. A hydrate-based technology has gained attention for CCS applications since it provides various advantages, particularly in terms of energy efficiency. However, the slow kinetics of CO2 hydrate formation without promoters has been a challenge for CCS on an industrial scale. In this study, amino acids including leucine, methionine, and valine were used as promoters to investigate their effect on the CO2 hydrate formation using a hybrid combinatorial reactor (HCR) configuration. The amino acids were tested at different concentrations. The results showed that the addition of amino acids had varying effects on CO2 hydrate formation kinetics. The highest rate of hydrate formation was observed in the methionine system. The amino acids and their concentrations had no significant impact on the gas uptake or the conversion of water to hydrates. All systems displayed a similar pattern of hydrate formation morphology. There was no foam formation during the hydrate dissociation, and the hydrate reformed in the reused solution had almost the same gas uptake as the fresh solution. Overall, the use of amino acids with the HCR approach may be a promising option for CCS applications.

Calorimetric study of carbon dioxide (CO2) hydrate formation and dissociation processes in porous media

Understanding the formation and dissociation mechanisms of gas hydrate in porous media is important for the development of new energy-efficient and environmentally friendly technologies related to cold storage as they provide significant latent heat and energy density at suitable phase change temperature. The challenge is to understand the interactions between gas hydrates and the chosen storage media in order to assess the operating conditions likely to optimize time and energy consumption in cold production and storage systems. In this work, CO2 hydrates formation and dissociation are investigated in two morphologically different porous materials: sand and silica gels. A calorimetric approach is applied to study both the CO2 hydrate formation kinetics, particularly the induction time, and the amount of hydrate formed for each of the two porous materials. The experiments are performed using a differential thermal analysis device with two identical measuring cells. The present work is focused on assessing the effect of key factors like water saturation, particle size and the morphology of porous media on CO2 hydrate formation and dissociation processes. Overall, the results do not show a statistically significant correlation between these factors and the induction time. Interestingly, the results obtained with dual porous silica gel showed a higher amount of hydrate formed compared to those with sand for similar initial pressure, temperature and water content conditions. This result may be due to the fact that silica gels provide higher surface area due to their smaller particle size (20–45 µm vs 80–450 µm for sand), and the presence of internal pore volume in silica gel particles.

Effects of silica gel nanopores and surfactants on CO2 hydrate formation kinetics—An experimental and modeling study

The carbon dioxide (CO2) hydrate formation kinetics in silica gel (SG) nanopores with the addition of surfactants are studied both experimentally and numerically. SGs with pore sizes of 50 and 100 nm are used as frameworks for hydrate formation in pores. Sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTAC) are used as kinetics promoters which can greatly enhance gas–water mass transfer. An advanced shrinking core model considering CO2 solubility, pore size, surfactants, and capillary effect is established. The results reveal that the reaction rate constant is increased in large pores or in the presence of surfactants, saving up to 49.3 % time to achieve the same amount of gas uptake in 100-nm SG with 500-ppm SDS. The effective diffusion coefficient controlled by a reduction factor drops dramatically due to the enlargement of the reduction factor in small pores and more surfactants, thus hindering the gas diffusion through the formed hydrate shell. The initial water consumed by capillary effect is more prominent in smaller pores and with the addition of surfactants. The initial proportion of water consumed by capillary effect to the total water consumption is only 1%–26.6% without surfactants, but can be up to 74.9% in 50-nm SGs with 500-ppm SDS. This proportion is overall higher in SDS systems than that in studied DTAC systems, but it is not obviously affected by surfactant concentrations. The higher proportion of water consumed by capillaries is speculated to be due to the more capillary tubes with larger radii formed initially in the presence of surfactants. The modeling strategies in this work can be applied to hydrate formation mechanisms in other porous materials.

Laboratory demonstration of the stability of CO2 hydrates in deep-oceanic sediments

Naturally occurring methane (CH4) hydrates in oceanic sediments have been stable for millions of years. As a natural analog, is it possible to store carbon dioxide (CO2) in the form of hydrates in oceanic sediments for long durations? This is a key question that has had a minimal experimental investigation. Despite the extensive research conducted on CO2 hydrates in carbon capture, CO2-CH4 exchange, and promoter/inhibitor effects on CO2 hydrate formation kinetics, fundamental understanding of and demonstration of CO2 hydrate stability under oceanic sediment conditions remains elusive. In this work, an experimental study has been conducted that provides conclusive insights into the stability of the CO2 hydrates across oceanic sediments. By conducting an experimental study mimicking the oceanic sediment conditions inside a laboratory-scale high-pressure reactor system, we observed that CO2 hydrates formed at reactor walls and inside the sand bed were stable for the entire test period (one month), after which they were intentionally dissociated. This study offers scientific evidence and support for sequestering CO2 in the form of hydrates across oceanic sediments for extended durations.

Experimental investigation of CO2 hydrate formation in silica nanoparticle system under static conditions

CO2 hydrate has potential applications in air conditioning cold storage, seawater desalination, carbon capture and storage, etc. Research on CO2 hydrate formation is of great significance in order to solve the problems of long introduction time and slow growth rate. This work focuses on the kinetics of CO2 hydrate formation in the presence of silica nanoparticle under static conditions. A total of 17 sets of experiments were performed with the particle size of 5 nm, 25 nm, 50 nm, 100 nm and the concentration of 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%. We found silica nanoparticles can effectively promote the CO2 hydrate formation and the promotion effect is enhanced with the increase of concentration within a certain range (0–0.5 wt%). The experimental results show that the shortest induction time is reduced by 72.3%, the minimum subcooling degree is reduced by 3 K and the maximum conversion rate is increased by 39%. The promotion or inhibitory effect on hydrate formation depends on the concentration of nanoparticles for hydrophilic nanomaterials. Furthermore, the fluctuation–dissipation in gas consumption in the pre-nucleation stage was proposed with the decay of the fluctuation autocorrelation function obeying to the Onsager hypothesis. The variable parameters n and k of the Avrami equation were obtained and compared to explain the experimental results under different nanoparticle systems.

Effect of sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP) on the formation kinetics of CO2 hydrate in bulk and porous media in the presence of pure water and seawater relevant for CO2 sequestration

Enhanced kinetics of carbon dioxide (CO2) hydrate formation will assist in developing technologies for CO2 gas storage, carbon capture and sequestration (CCS), and potentially for methane production from natural gas hydrates. The present work is focused on understanding the kinetics of CO2 hydrate formation in both bulk and porous media with pure water and seawater under the influence of non-toxic and low-cost inorganic emulsifiers or builders. Sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP) was used in a very low concentration of 0.2 wt.% to promote its economic viability. The experiments were carried out in a 300 mL stirred tank reactor and 100 mL porous bed reactor with an initial pressure of 3.5 MPa and 274.65 K with pure water and seawater, respectively. The porous bed was made with 0.15 mm silica sand with 70% water saturation. Both STPP and TSPP showed significant improvement in induction time for CO2 hydrate formation. Moreover, STPP showed reasonable enhancement in CO2 gas uptake compared to TSPP in both bulk and porous bed with both pure water and seawater. The average rate of hydrate formation was also better for STPP with multiple growth peaks. The results obtained will enhance hydrate-based technologies for efficient CO2 sequestration in shallow subsea sediments.