Hydrate Process Research Articles

Simultaneous treatment and enrichment of total phosphorus from livestock sewage using hydrate technology

The presence of phosphorus in livestock sewage is a key factor that causes eutrophication and the degradation of ecological water quality. Cyclopentane (CP) hydrate-based water treatment technique was utilized for the efficient total removal of phosphorus in effluents. This study assesses the treatment effectiveness and enrichment potential of hydrate technology when applied to real-world samples, specifically livestock wastewater. The treatment process was applied under atmospheric pressure and optimized appropriate conditions comprising the CP-to-sample volume ratio of 1:4, reaction duration of 3 h, and temperature of 2 °C because of the high subcooling and ability to enhance the number of hydrate crystals formed along with water. In addition, various methods, such as vacuum filtration, cold centrifugation, and washing, were employed for the effective and comprehensive removal of phosphorus from water samples with the efficiency exhibited from approximately 30 % to 80 %. The structure and composition of the CPHs formed in wastewater were analyzed via Raman spectroscopy and the phosphorus content was determined according to ISO 6878:2004. After a single-stage hydrate process without pretreatment and posttreatment, the water recovered from the extracted hydrates showed that the phosphorus removal efficiency in livestock sewage was approximately 85 % with a remarkable water recovery above 25 %. The study findings provide insights into the development of hydrate-based treatment technology for the removal of phosphorus and explore opportunities for resource enrichment and recovery from sewage.

The development of high-performance kinetic hydrate inhibitors by introducing N-vinyl caprolactam and vinyl ether homopolymers into PVCap

Low dosage kinetic hydrate inhibitors (KHIs) are a kind of alternative chemical additives to prevent gas hydrate formation in oil & gas production wells and transportation pipelines. In this work, a series of KHIs were experimentally synthesized with N-vinyl caprolactam (N-VCap) and vinyl ether including vinyl ether, vinyl n-butyl ether, vinyl isobutyl ether, triethylene glycol divinyl ether, with the mole ratio ranging from 9:1 to 5:5. The inhibition performance of new-synthesized KHIs on the formation process of methane hydrate were examined and compared with that of commercial N-vinyl caprolactam PVCap. Several ethylenediamine reagents were used as synergists and tested to improve the inhibition capacity of new-synthesized KHIs. The experimental results demonstrate that the introduction of ether groups on PVCap improves the performance of hydrate inhibitors. PVCap-VNBE (N-VCap: vinyl n-butyl ether = 5:5) showed the best inhibition performance for methane hydrate, which could extend the TVO to 1251 min under 6 K subcooling. N,N'-dimethylethylenediamine shows the best synergistic effect for PVCap-VNBE (5:5), and extends the TVO by 2.75 times at 7 K subcooling. Additionally, the relationship between hydrate inhibition performance and interfacial tension of newly-synthesized KHIs under high pressure were studied. It shows that the lower interfacial tension of KHIs would result in longer onset time, exhibiting better inhibition performance.

Experimental study on the influence of particle size and grain grading on the CO2 hydrate formation and storage process in porous media

CO2 sequestration in sediments as hydrate form is considered to be a promising way to achieve CO2 emission reduction in the atmosphere. The key problem with hydrate-based technology for CO2 geological storage is the evaluation of the formation process and gas storage capability of hydrate. In this study, the fundamental issue of different particle size and grain grading affected CO2 hydrate formation and storage characteristics in porous media was deeply analyzed. The effect of various particle sizes and grain grading on the gas consumption rate and gas storage capacity of CO2 hydrate were quantitatively illustrated. The results indicated that the hydrate formation is more difficult in porous media with tiny particle sizes. The gas storage capacity and gas consumption rate of CO2 hydrate increased as the particle size increased within a range of 10–63 μm. The maximum gas storage capacity attains 25.65 L/L when the particle size is 63 μm. Besides, compared with single particle size, porous media with grain gradation is adverse to hydrate formation. The results also show that, the obstruction effect on the gas consumption rate and gas storage capacity is more obvious with the increase of the differences in grain gradation. The cooperative impact of particle size and gradation on hydrate formation was studied. The closer the size of the mixed particles is, the more favorable to hydrate formation. The relevant results will aid in comprehending the hydrate formation properties in submarine sediments and will serve as an essential theoretical reference and guide for CO2 capture and sequestration hydrate-based method.

A hydrate-based post-combustion capture system integrated with cold energy: Thermodynamic analysis, process modeling and energy optimization

Carbon capture is a crucial part of global warming mitigation. Carbon capture via clathrate hydrate is an attractive approach due to its high capture capacity, high carbon dioxide purity, water-based benign process, ease of recycling, and robustness to contaminants. In this work, we propose a two-stage hydrate-based carbon dioxide separation system integrated with cold energy for carbon capture from flue gases. A thermodynamic cycle consisting of two sub-cycles was constructed to simulate the process. Operating conditions were optimized within the range of 274.15–282.15 K and 0.1–28.04 MPa, resulting in the lowest electricity consumption of 2.22 MJ/kg CO2 with 95.24 mol% CO2 purity and 65.97 % CO2 recovery. A higher CO2 recovery rate can be achieved by recycling the residual gas of Sub-cycle 2. Gas compression to the high operating pressure (16.01 MPa) is the major contributor to electricity consumption. By incorporating 100 % expansion work recovery from the high-pressure gases, the electricity consumption can be reduced to 0.43 MJ/kg CO2 (i.e., 0.119 kWh/kg CO2). A more realistic scenario assuming 80 % compression/pumping efficiency and 90 % expansion work recovery gives an electricity consumption of 1.16 MJ/kg CO2 (i.e., 0.322 kWh/kg CO2), representing an energy penalty of 33.1 % for a coal-fired power plant. Future direction for further improvement could be a paradigm shift to hydrate process with thermodynamic promoters, which can potentially reduce the operation pressure by over 90 % and thus cut down the energy consumption dramatically. This work established a framework to simulate the hydrate-based carbon capture process, evaluated its minimum energy consumption and examined how operating conditions affect the separation performance. The results could offer valuable guidelines for the design and optimization of real hydrate-based carbon capture systems.

The Interaction between Anesthetic Isoflurane and Model-Biomembrane Monolayer Using Simultaneous Quartz Crystal Microbalance (QCM) and Quartz Crystal Impedance (QCI) Methods.

The interaction between anesthetic Isoflurane (Iso) and model-biomembrane on the water surface has been investigated using quartz crystal microbalance (QCM) and quartz crystal impedance (QCI) methods. The model-biomembranes used were dipalmitoyl phosphatidyl choline (DPPC), DPPC-palmitic acid (PA) mixture (DPPC:PA = 8:2), DPPC-Alamethicin (Al) mixture (DPPC:Al = 39:1), and DPPC-β-Lactoglobulin (βLG) mixture (DPPC:βLG = 139:1) monolayers, respectively. The quartz crystal oscillator (QCO) was attached horizontally to each monolayer, and QCM and QCI measurements were performed simultaneously. It was found that Iso hydrate physisorbed on each monolayer/water interface from QCM and changed those interfacial viscosities from QCI. With an increase in Iso concentration, pure DPPC, DPPC-PA mixed, and DPPC-Al mixed monolayers showed a two-step process of Iso hydrate on both physisorption and viscosity, whereas it was a one-step for the DPPC-βLG mixed monolayer. The viscosity change in the DPPC-βLG mixed monolayer with the physisorption of Iso hydrate was much larger than that of other monolayers, in spite of the one-step process. From these results, the action mechanism of anesthetics and their relevance to the expression of anesthesia were discussed, based on the "release of interfacial hydrated water" hypothesis on the membrane/water interface.

Review of Heat Transfer Characteristics of Natural Gas Hydrate

As a typical unconventional energy reservoir, natural gas hydrate is believed to be the most promising alternative for conventional resources in future energy patterns. The exploitation process of natural gas hydrate comprises a hydrate phase state, heat and mass transfer, and multi-phase seepage. Therefore, the study of heat transfer characteristics of gas hydrate is of great significance for an efficient exploitation of gas hydrate. In this paper, the research methods and research progress of gas hydrate heat transfer are reviewed from four aspects: measurement methods of heat transfer characteristics, influencing factors of heat transfer in a hydrate system and hydrate-containing porous media systems, predictive models for effective thermal conductivity, and heat transfer mechanisms of hydrate. Advanced measurement techniques and theoretical methods that can be adopted for the heat transfer characteristics of gas hydrate in the future are discussed.

Thermo-Hydro-Mechanic-Chemical coupling model for hydrate-bearing sediment within a unified granular thermodynamic theory

The extraction process of methane hydrate involves interactions of multiple fields, phases, and loading stages. By extrapolating deductions from the thermodynamic equation in granular thermodynamic framework and amalgamating with coupled flow theory and linear non-equilibrium theory, a comprehensive Thermo-Hydro-Mechanic-Chemical (THMC) coupling model for hydrate-bearing sediment is established in this study. The mechanical field is established by energy dissipation conservation, the hydraulic field considers the increase in gas and liquid permeability due to temperature gradients, while the thermal field incorporates the rates of seepage, hydrate dissociation, and volumetric strain. Meanwhile, Darcy's law is explained as general deductions from the thermodynamic equation without the need for assumption. The proposed model is applied from the perspective of unit scale and coupling field, and verified with the test data. The modelling results show that the deduced model can capture the strain-softening, dilatancy, and stress paths behavior under various drainage conditions, and the volumetric strain, methane gas production and variations in heat exchange caused by the hydrate dissociation can also be predicted. Furthermore, the mechanical response and dissociation properties of sediment samples with various parameter values are discussed.

Decomposition behaviors of CO2 hydrate sandwiched in double-symmetrical flat system:A molecular dynamics simulation study

Sequestration of carbon dioxide (CO2) in the form of hydrate is considered to be an effective way to achieve carbon emission reduction. The replacement method of nature gas hydrates with CO2 has been proved to be a very promising technique as well. A precise acknowledge of the decomposition characteristics of CO2 hydrate in porous media, which will help further implement these applications. In this work, molecular dynamics simulation method is employed to investigate the whole decomposition process of CO2 hydrate sandwiched in the double-symmetrical flat that is the approximate imitation system of hydrate located in veined distribution or throat space of porous media. The results indicate that the decomposition of the hydrate phase follows a somewhat relaxed shrinking-core mechanism from outer to inner, with this deviation being reflected in the differential collapse rates of the symmetrical sections of the hydrate layer. The difference of the collapse rate of hydrate layers is not only reflected in the distance from the interface, but also closely related to the surrounding crystal state. During the first 200 ps, the average diffusion coefficient of CO2 molecules is 0.659 × 10−9 m/s which is 0.53 times than that of the pure hydrate system with 1.241 × 10−9 m/s. Both stages of initial cage structure breakdown and CO2 nanobubbles formation evolution are clearly observed, and the phenomenon of molecular diffusion gradient is also appeared in last stage. Additionally, with the four spacing of 29.08 Å, 41.08 Å, 53.08 Å and 101.08 Å, an interesting decomposition mechanism was found, that is, the destabilization of hydrates occurred preferentially at the geometric center not just the interface of hydrate-media in the symmetric narrow confined space. The relevant result is very helpful to further understand the stable geological storage mechanism of CO2 gas in the form of hydrate in sediments.

The mechanism of fluidity improvement of cement slurry by graphene oxide: a study on nanofriction.

Graphene oxide (GO) as a nano-reinforcing material has received extensive attention in cement composite materials. This paper employed molecular dynamics to simulate the friction process of calcium silicate hydrate (CSH) particles in the presence of double-sided and single-sided GCOOH (graphene oxide with a -COOH functional group, covering 10% of the surface). The investigation uncovered the lubricating effects of bifacial and unifacial GCOOH on the CSH interface. The findings indicate that the interfacial friction among CSH particles follows the sequence of double-sided GCOOH > pure CSH > single-sided GCOOH. In the double-sided GCOOH system, a greater external force is needed on the opposing side to alter the interaction with water molecules, calcium ions, and silica-oxygen tetrahedra, thereby enhancing friction. In contrast, the majority of the carboxyl groups on the single-sided GCOOH surface are strongly adsorbed onto the CSH surface, facilitating the entry of additional water molecules into the interlayer. Conversely, the unmodified side of the GCOOH has lower interactions with water molecules, hence improving its lubricating properties.

Molecular Dynamics Simulation of the Effects of Different Initial Water Content on Methane Hydrate Decomposition

Gas hydrate is mainly distributed in deep sea-floor sediments and permafrost regions. The water content of these sediments varies with the type of reservoir and affects the rate of hydrate decomposition. In this work, the decomposition process of methane hydrate under four different initial water contents was investigated by molecular dynamics simulation. The results were analyzed by the system conformation, radial distribution function (RDF), and mean square displacement (MSD), which revealed the microscopic mechanism of the effect of the initial water content on the decomposition rate of hydrate. The results demonstrate that the hydrate decomposition starts from the boundary to the middle, and the cage structure is destroyed layer by layer. Methane molecules continue to escape from the hydrate cages as the hydrate decomposes, and subsequent decomposition of the hydrate is inhibited when its solubility in water reaches saturation. The higher the initial water content is, the faster the decomposition rate of hydrate is. The movement distance of methane gas is affected by the initial water content. The higher the initial water content, the smaller the MSD of methane molecules.

Kinetic mechanisms of methane hydrate replacement and carbon dioxide hydrate reorganization

The carbon dioxide replacement is an ideal way to mine natural gas hydrates. However, current challenges of low replacement efficiency and immature technology compromise its application spectrum. This study aims to simulate the displacement of methane hydrate by carbon dioxide in a porous media system and verify the effect of water saturation on methane hydrate through experimental tests. By constructing a molecular dynamics model to investigate the replacement process of methane hydrate with carbon dioxide, the role of free water in this process was examined. Additionally, the study elucidated the factors contributing to suboptimal methane storage rate and low carbon dioxide recovery rate from a heat exchange perspective. The results show that methane replacement from methane hydrate can be divided into four stages. When the water saturation approach to hydrate saturation, and the temperature and pressure are between the phase curves of methane hydrate and carbon dioxide hydrate, the carbon dioxide storage rate and methane recovery rate can be significantly improved. The participation of free water can make the replacement more complete. The primary factor determining the replacement effect is the area of contact between carbon dioxide and methane hydrate, which is followed by the newly created carbon dioxide hydrate, which will impact the subsequent mass transfer. Although the heat released by the formation of carbon dioxide hydrate favor the replacement reaction proceed, most of the heat may get lost with the volatilization of carbon dioxide, resulting in the inability or incomplete decomposition of methane hydrate far away from free water. This research will surely have a profound impact on how hydrate replacement mining is monitored and managed as well as the ecosystem around it.

Simultaneous removal of multi-nuclide (Sr2+, Co2+, Cs+, and I-) from aquatic environments using a hydrate-based water purification process

This study investigates the removal characteristics of a hydrate-based water purification process used to remove the major radionuclides monitored in nuclear accident areas. The effect of the coexistence of salt ions on the removal of radioactive materials is also evaluated. Previous studies have found existing processes such as ion exchange and membrane separation to be reliable methods for radionuclide removal from contaminated water. However, these processes cannot remove all contaminants at once and cause additional environmental problems by generating secondary wastes. In a previous study, we observed that water purification by the gas hydrate process could simultaneously remove various ions from seawater and hypersaline water in a single step without pre- or post-treatment. Therefore, the removal characteristics of Sr2+, Co2+, Cs+, and I- radionuclides are evaluated in only one context: the hydrate-based water purification process. More than 85% of the total ions were simultaneously removed regardless of the presence or absence of coexisting ions, and the time required for the removal process was about 70 min. In addition, it was observed that most of the contaminant ions were attached to hydrate crystal surfaces. Therefore, an efficient purification process is proposed that includes a hydrate crystal exterior partial dissolution step.

SiC nanowires enhanced graphene composite coatings with excellent tribological and anticorrosive properties

The synergistic effect between nanomaterials with different dimensions can enhance wear and corrosion resistance of surface protective coatings. In this work, GO-pva-SiC and RGO-pva-SiC coatings were constructed on stainless steel substrate by combining spraying process and subsequent chemical reduction of hydrazine hydrate. Tribological tests have shown that GO-pva-SiC coating exhibits good lubricating performance under low load and long wear life under high load. After reduction, RGO-pva-SiC coating presents a longer wear resistance life (25,000 cycles) at a lower friction coefficient of 0.11 under 20.0 N. Furthermore, the electrochemical corrosion behavior indicates that the addition of SiC NWs can enhance corrosion resistance of graphene-based coatings. This work provides an efficient way to develop graphene-based composite coatings for practical engineering applications.

Crystallization-driven evolution of water occurrence states with implications on dewaterability improvement of waste-activated sludge

This study proposed to improve the dewaterability of waste-activated sludge (WAS) through crystallization-driven evolution of water occurrence states. Primarily, the feasibility of clathrate hydrate (i.e., CO2 hydrate) formation in WAS was examined. The thermodynamic analysis indicated that the CO2 hydrate formation with the excessive water in WAS followed pseudo-first-order kinetics, and fit of the data yielded a kobs value of 3.905 × 10−5 L∙mol−1∙s−1 for 274.15 K. With the water conversion efficiency of 100%, the crystallization-dissociation process of CO2 hydrate significantly improved the dewaterability of WAS in term of capillary suction time (CST) decreasing from 251.5 s to 57.4 s. Also, the relief of gas pressure can induce the hydrate dissociation, which creates a novel way to recycle CO2 gas and save the consumption of chemicals required by sludge dewatering process. Regarding the mechanism of hydrates-based sludge dewatering, the evolution of water occurrence state was investigated. The in-situ synchrotron X-ray computed microtomography visually analyzed the micro-scale porosity and interstitial water of WAS flocs. The model of three-dimensional pore structure was established and the porosity parameters of solid aggregates were determined. It was found that the volume of connected pores and the total pore volume fraction of solid compositions increased. But the mean volume and mean area of isolated pores simultaneously decreased by 14.6% and 12.4%, respectively, which meant that the steric hindrance caused by isolated pores was weakened due to the reduced solid-water contact area. In addition, the crystallization of water caused the reformation of conformation arrangement of vicinal water and solid molecules, which highly organized the water molecules into the crystal structure. Accordingly, an estimation method for vicinal water layer thickness was developed based on atom force microscope. The thickness of vicinal water layer was found to be reduced by 77.4% and the hydration repulsion among solid compositions was correspondingly weakened, which facilitated the aggregation of solid compositions, and the relatively separated hydrate phase and solid phase could be formed. All the above results open up a novel strategy for enhanced water-solid separation of WAS through the crystallization-driven evolution of water occurrence states. As distinguished from the conventional approaches, the hydrates-based sludge dewatering enhances the water-solid separation only with regulating the spatial arrangement of water-solid molecules, but without altering the chemical compositions. Thus, more chances can be created to increase the environmentally friendly attributes related to WAS dewatering.

Electrical conductivity-based assessment method for semi-clathrate hydrate conversion and phase change characteristics in gas capture and energy storage

In gas capture/storage and energy storage, tetrabutylammonium bromide (TBAB) hydrates have been regarded as superior carriers owing to their unique molecular selectivity and high latent heat. Hydrate conversion amount is a significant parameter in evaluating gas selection and cold storage characteristics. This study proposes a method for calculating hydrate conversion amount proposed based on the correlation between electrical conductivity and solution concentration. The correlation index (R2) between electrical conductivity and TBAB solution concentration was above 0.99 at concentrations less than below 5 wt%. The conversion amounts of different hydrate types were obtained using a unique hybrid calculation method. The differences in hydrate conversion amount, conversion ratio, and memory effect were compared at different mass fractions. The results indicated that the hydrate morphology and accumulation patterns were influenced by the TBAB solution ionization degree. Regular hexagonal TBAB hydrate crystals were observed at a low ionization degree. The maximum conversion ratio of TBAB hydrate reached 96% (1 °C/30 wt%). The variation trend of TBAB hydrate phase equilibrium temperature was consistent with that of the electrical conductivity of the solution. The investigation of the memory effect revealed that the phase change process of TBAB hydrate is more predictable in high-concentration initial solutions.

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.

Experimental study of CO2 hydrate formation under an electrostatic field

The hydrate-based CO2 capture and storage technique is cutting-edge and promising, but it exhibits slow formation rates and insufficient gas storage capacity, making commercialization challenging. In this work, the CO2 hydrate formation process in fresh water, memory water, and saltwater systems under the electrostatic field was studied, and the influence mechanism of the electrostatic field on the CO2 hydrate formation was discussed. Experimental results showed that the nucleation and growth of CO2 hydrate could be affected by the electrostatic field. The nucleation of CO2 hydrate could be promoted in the presence of an electrostatic field. In the fresh water system, the completion of hydrate formation was 54.5% faster with the 150 V application compared to the one without the electrostatic field. The introduction of an external electrostatic field causes a further reduction in the system's free energy. In the memory water system, the residual hydrate cage fragments could promote the reformation process of hydrate. Nevertheless, the presence of the electrostatic field could weaken the memory effect. In the salt water system, the electrostatic field could promote hydrate formation after the stage of dissolution. Due to the collision of ions with hydrate nuclei, however, the completion time of hydrate formation was increased. This study is anticipated to provide novel insights into the promotion of hydrate formation through the implementation of an electrostatic field.

Experimental study on visualization of TBAB hydrate formation in confined small channels

Hydrate crystals' microscopic characteristics and agglomerating morphologies play an important role in the hydrate reaction equipment's flow assurance and heat transfer. In order to study the formation process of hydrate, experimental quartz tubes with small diameters were selected, and a fully visualized flow loop system was established. The study investigated the effects of supercooling, solution concentration, tube diameter, and flow rate on hydrate blockage time and agglomeration morphology. The results show that under the same supercooling conditions, the density of single crystal hydrate formed in 10 wt%-20 wt% TBAB (Tetra-n-butylammonium bromide) hydrate solution is low, and the crystal front appears needle-like or sword-like, which is conducive to mass and heat transfer. High concentration TBAB solution(30 wt%-40 wt%) can form dense hydrate crystals, and the tip effect was significantly weakened. For low concentration TBAB solution, the increased flow rate can accelerate the formation of new nuclei and inhibit the growth of large crystals. Grout solutions with different particle sizes can be obtained by adjusting the flow rate. It was found that the initial morphology of TBAB hydrate crystals included spherical and cylindrical shapes, and the morphological evolution process of a single hydrate crystal was similar. Finally, a microscopic physical model of the TBAB hydrate growth and aggregation process was established.

Multistep Dissolution of Lamellar Crystals Generates Superthin Amorphous Ni(OH)2 Catalyst for UOR.

Urea oxidation reaction (UOR) is an ideal replacement of the conventional anodic oxygen evolution reaction (OER) for efficient hydrogen production due to the favorable thermodynamics. However, the UOR activity is severely limited by the high oxidation potential of Ni-based catalysts to form Ni3+ , which is considered as the active site for UOR. Herein, by using in-situ cryoTEM, cryo-electron tomography, and in-situ Raman, combined with theoretical calculations, we report a multistep dissolution process of nickel molybdate hydrate, whereby NiMoO4 ·xH2 O nanosheets exfoliate from the bulk NiMoO4 ·H2 O nanorods due to the dissolution of Mo species and crystalline water, and further dissolution results in superthin and amorphous nickel (II) hydroxide (ANH) flocculus catalyst. Owing to the superthin and amorphous structure, the ANH catalyst can be oxidized to NiOOH at a much lower potential than conventional Ni(OH)2 and finally exhibits more than an order of magnitude higher current density (640mA cm-2 ), 30 times higher mass activity, 27 times higher TOF than those of Ni(OH)2 catalyst. The multistep dissolution mechanism provides an effective methodology for the preparation of highly active amorphous catalysts. This article is protected by copyright. All rights reserved.

Dehydration kinetics and mechanism of the stable isonicotinamide hydrate revealed by terahertz spectroscopy and DFT calculation

The dehydration behavior of pharmaceutical hydrates has a great influence on its physiochemical properties such as stability, dissolution rate and bioavailability. However, how the intermolecular interactions vary during dehydration process remains elusive. In this work, we employed terahertz time-domain spectroscopy (THz-TDS) to probe the low-frequency vibrations and the dehydration process of isonicotinamide hydrate I (INA-H I). Theoretical solid-state DFT calculation was conducted to reveal its mechanism. Vibrational modes which are responsible for the THz absorption peaks were decomposed for better understanding the characters of these low-frequency modes. The result suggests translational motion is the dominant component for water molecules in THz region. Evolution of the THz spectrum of INA-H I during dehydration provides direct evidence of the variations of crystal structure. Based on the THz measurements, a two-step kinetics mode including first-rate reaction and three-dimensional nuclei growth is proposed. And we figure that the low-frequency vibrations of water molecules are the origin of dehydration process of hydrate.