Kinetics of Carbon Dioxide Hydration Enhanced with a Phase-Change Slurry of n‑Tetradecane Bin Chen, Feng Xin,* Xiaofei Song, Xingang Li, and Muhammad Zeshan Azam School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China ABSTRACT: CO 2 capture based on hydrate formation is intensified by an oil-in-water phase-change slurry (PCS) in which the n-tetradecane particles are taken as nucleation centers and are used to directly remove the hydration heat through their solid-to- liquid phase change. In this study, experiments on hydration were conducted at a temperature of 277.6 K and under isobaric pressures in the range of 2.1-2.4 MPa. All measurements were performed at a stirring speed of 450 rpm in PCSs of 25-45 wt % n-tetradecane. Two kinetics models, transport and reversible hydration, were established to regress and analyze the experimental data from the isothermal hydration of CO 2 in a semibatch hydrator. For each model, the effects of pressure and PCS composition were examined in detail. As the experimental results show, the induction time before hydration initiated was less than 1 min for all runs, and the duration of the entire hydration process was approximately 13-15 min for each measurement. Furthermore, the average hydration rate reached 197 mol m -3 min -1 at 2.3 MPa in 45 wt % oil-in-water PCS, which demonstrates that the presence of n-tetradecane particles contributes significantly to the enhancement of hydrate formation rate. As the modeling results show, the parameters of the two models were determined by correlating the experimental data, and the interpretations of the measurements by the two models are satisfactory. 1. INTRODUCTION Increasing CO 2 emissions have been caused by the excessive consumption of fossil fuels (coal, oil, natural gas) required to satisfy the growing energy demands of human society, which poses a series of challenges to ecological systems and the environ- ment, such as global temperature rise, sea-level change, and ocean storms and floods. 1 Therefore, dealing with CO 2 emissions has become a common issue of global perspective and the focus of international concern. 2 In the view of the global growth in energy demands, effective CO 2 capture and storage methods are the mainly considered approaches. For different power plants, precombustion capture, postcombustion capture, and oxy-fuel combustion capture are the three typically used means to reduce the CO 2 emissions, 3 resulting in CO 2 contents of 40 mol % (with 60 mol % H 2 ), 15-20 mol % (with N 2 ), and 70-90 mol %, respectively. Meanwhile, more substantial capture efficiencies can be obtained with higher concentrations of CO 2 , 4 so oxy-fuel combustion capture has become a promising technology. The conventional available technologies for CO 2 capture, such as physical and chemical absorption, 5 adsorption, 6 membrane, and cryogenic processes, have some limitations, such as high costs, low capture efficiencies, and complicated processing stages. Currently, hydrate-based CO 2 capture (HBCC) and hydrate-based CO 2 separation (HBCS) are widely considered to be promising technologies. Gas hydrates are nonstoichiometric cagelike crystals formed at relatively low temperatures and high pressures that are made of small-molecule gases and water. 7 The primary forms of hydrate include structure sI (CH 4 , CO 2 etc.), structure sII, and structure sH. 8 A great number of studies have been published on the poten- tial applications of HBCS and HBCC technologies, and the earlier research into hydrates focused mainly on the vapor- liquid-hydrate (V-L-H) equilibria of different gases. 9-13 Owing to the distinct hydration heat released during the hydrate forma- tion process 14 and likely hydrate agglomeration, mass-transfer resistance for gas molecules and heat-transfer resistance frequently arise during the hydrate formation process, seriously inhibiting the hydration rate and water conversion. As a result, more recently reported studies have focused on the enhancement of gas hydrate formation, with the selection of chemical additives and the design of novel hydrators being favored approaches. First, the widely used additives are divided into kinetic promoters and thermodynamic promoters, including polyoxyethylene sorbitan monooleate (Tween-80), dodecyl trimethylammonium chloride (DTAC), sodium dodecyl sulfate sodium salt (SDS) 15 as common kinetic promoters, which are capable of accelerating hydration, and tetrahydrofuran (THF), cyclopentane (CP), pro- pane (C 3 H 8 ), and tetrabutylammonium bromide (TBAB) 16,17 as common thermodynamic promoters, which can effectively reduce the hydrate phase equilibrium pressure. Second, the main purpose of novel hydrator design is to minimize the mass-transfer and heat-transfer resistances. Both Linga et al. 18 and S. Doui ̈ eb et al. 19 constructed novel semibatch hydrators in which different impellers were employed to enhance the contact of gas and water to decrease hydrate agglomeration. Yang et al. 20 employed a heat exchanger to decrease the heat-transfer resistance. Recently, water-in-oil 21 and oil-in-water 22 emulsions have been recognized as high-efficiency systems for hydration by relieving the hydrate agglomeration and enhancing the mass transfer. Thus, in view of industrial applications, novel hydrator designs combined with high-efficiency hydration systems will be the focus in the future. However, there are some other restrictions preventing the industrial application of HBCC, including the scarcity of reliable kinetic data and the lack of simplified rate equations to justify the formation of CO 2 hydrate. After Glew and Haggett 23 established Received: December 27, 2016 Revised: March 10, 2017 Published: March 13, 2017 Article pubs.acs.org/EF © XXXX American Chemical Society A DOI: 10.1021/acs.energyfuels.6b03477 Energy Fuels XXXX, XXX, XXX-XXX