Recovery of hydrogen (H2) from H2-containing gas mixtures has great significance for energy conservation, cost reduction and benefit increase. However, the common separation methods have the ...ubiquitous problem due to phase equilibrium principle and results in the conflict between H2 concentration and H2 recovery rate in the product gas. Consequently, an innovative conception of hydrate-membrane coupling approach is proposed in this work. In the separation process, hydration and membrane permeation two separation driving forces coexist to achieve the aim of strengthening mass transfer kinetics. H2 and non-H2 components (hydrocarbons) are synchronously and directionally selected by membrane and hydrate to improve different phase compositions. Therefore, the gas in feed side could keep relatively high two separation driving forces (H2 fugacity and hydrocarbons fugacity). The results show that the coupling method could synchronously increase both the concentration and the recovery rate of H2 in the product gas. At the same time, the volume and concentration of the hydrocarbons in hydrate both increases effectively. It indicates that hydrate and membrane separation methods support each other in the separation process. The hydrate-membrane coupling method fundamentally solves the issue of the decreasing driving force resulting from single separation method and phase equilibrium relationship.
Fig. 1. The schematic diagram of directional separation of H2-containing gas mixture using hydrate-membrane coupling method. (a) Before separation. (b) After separation. Display omitted
•We proposed a coupling separation mechanism based on coexistence of two mass transfer processes.•Hydrate-membrane coupling method was used to directionally separate H2-containing gas mixture.•The coupling separation method could synchronously increase the concentration and recovery of H2.•Coupling separation method breaks through the constraint of single phase equilibrium relation.
•The dodecahedral-cage deformation effect on hydrate formation was first modeled.•The effects of multiple solutes on hydrate formation were first modeled.•The gas dissolution effect on hydrate ...formation was discussed.•The saturation effect of TBAB concentration on hydrate formation was found.•The hydrate formation pressure is accurately predicted by this model.
The accurate prediction of thermodynamic equilibrium hydrate formation pressure (Peq) is crucial to the industrial application of hydrate-based gas separation. This study evaluated Peq of CH4-CO2 gas mixtures with different TBAB solutions at different temperatures. Unlike previously reported models, the proposed model accounted for the effects of interaction of multiple solutes and the deformation of dodecahedral (D)-cages on Peq, thereby minimizing deviations in predictions. The effects of the interaction of multiple solutes on Peq can be attributed to gas dissolution and the presence of electrolytes. For accurate prediction, the proposed model incorporated the aforementioned effects based on the electrolyte-cubic plus association equation of state and the parameters for interaction among guest molecules in cages Furthermore, the proposed model can quantitatively describe the effects of gas dissolution, the presence of electrolytes and deformation of D-cages on the Peq values for corresponding systems.
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•Multi-structure basic hydrates form in gas mixtures with different stable-structure components.•Composition of gas mixtures leads to the hydrate structure transformation between sI ...and sII.•The inductive effect and the independent nucleation driving force are mutual restriction.•The modified hydrate method well predicts the formation conditions of multi-structure hydrates.
Accurate prediction of hydrate formation conditions is the basis of hydrate related research. The Chen-Guo hydrate model could accurately predict the formation conditions of hydrates. However, the misjudgment of basic hydrates structure makes it unsatisfactory to calculate the system with sI and sII hydrates coexisting. Consequently, we proposed that sI and sII basic hydrates will be formed simultaneously under specific conditions. The structure composition of basic hydrates is influenced by three factors: structure induction, driving force of hydrate independent nucleation and composition of gas mixture. On this basis, we improved the Chen-Guo hydrate model by introducing new parameters and adjusted the true structure composition of basic hydrates. The calculation results show that the average absolute deviation of 201 sets of data can be reduced from 9.33% to 2.74%. The calculation precision of modified method is better than that of the original Chen-Guo hydrate model.
The study on phase behavior and physical properties of natural gas has great significance for its safe exploitation and transportation. Consequently, we studied the phase equilibria of the methane + ...ethane gas mixture in this work. The hydrate formation conditions (gas–liquid–hydrate equilibria) of the methane + ethane gas mixture were measured first in pure water. Then the gas solubility (gas–liquid equilibria) of the gas mixture in water was measured with/without hydrate. Finally, the bubble point and dew point (vapor–liquid equilibria) and the hydrate formation conditions and gas solubility in the presence of hydrate were calculated. The results show that before hydrate formation, the gas solubility in water decreases with temperature and increases with pressure. However, after hydrate formation, the gas solubility increases with temperature and decreases with pressure. The calculation models in this work have satisfactory accuracy for phase equilibria prediction of the methane + ethane gas mixture. Therefore, it has a good guiding significance for describing the phase behavior of natural gas.
The conventional hydrate promoters and inhibitors, such as tetrahydrofuran (THF), sodium dodecyl sulfate (SDS) and methanol, have the common disadvantages of chemical substances, i.e., pungent ...flavor, corrosivity, toxicity and anti-degradability. It severely pollutes the environment and limits the application of hydrate-based technologies. Consequently, it is necessary to develop new and green substances as the hydrate promoters or inhibitors. In this work, L-arginine and isooctyl glucoside were used as bio-additives for CH4 hydrate to form bio-hydrate. The effects of L-arginine and isooctyl glucoside on the formation thermodynamics and kinetics of CH4 hydrate were investigated first. Then, the equilibrium separation of CH4/N2 via hydrates formation was conducted in isooctyl glucoside solution. The results show that formation pressure of CH4 hydrate in L-arginine solution is higher than that in pure water at the same temperature. Isooctyl glycosidase can greatly accelerate the hydration rate and increase the gas storage capacity of hydrate. In the separation of CH4/N2, the recovery of CH4 and gas storage capacity of hydrate are significantly increased after adding isooctyl glucoside in water. In conclusion, L-arginine can be used as hydrate inhibitor to replace conventional alcohols in the inhibition of hydrates formation. Isooctyl glycosidase is an effective kinetic promoter of hydrate, which is suitable for CH4 storage in hydrate, and separation of CH4-containing gas mixture via hydrates formation. This work provides two environment friendly bio-additives for hydrate, which will definitely promote the development and application of hydrate research.
•We measured formation conditions of CH4 hydrate with two bio-additives, respectively.•The effects of two bio-additives on kinetics of CH4 hydrate were investigated.•The separations of CH4/N2 were conducted in the presence of isooctyl glycosidase.•Green bio-additives of hydrate were developed to replace the chemical additives.
A data-driven model framework integrating Feature Subset Selection (FSS), production pattern clustering analysis and prediction was proposed for predicting ethylene yield of ethylene plant by using ...the massive sensing data recorded by the Distributed Control System (DCS) of petrochemical enterprises. Firstly, an Ensemble-Filter FSS model based on three different metrics is designed to initially filter all the steam cracking furnace features, and then a Wrapper FSS model based on GA-SVR is used to obtain the optimal subset of features affecting ethylene yield. The steam cracking furnace was identified based on the Density Peak Clustering (DPC) algorithm based on the production patterns embedded in the data. Ethylene yield prediction models were separately developed for each production pattern to summarize the final prediction results. The proposed model was validated against historical data from an industrial steam cracking furnace in northwest China. Results show that the number of features have a 93.4% reduction in the FSS stage. and a 40.6% reduction in predicted MSE. Compared with the benchmark ANN model, the proposed DPNN model has a 56.6% reduction in MSE based on the optimal cluster result. What’s more, the proposed framework has a strong generalization ability and with a modular structure which is easy to modify., which is expected to be used to guide the ethylene plant operating in reasonable intervals.
•A novel data-driven model framework of steam cracking process is proposed.•The dataset used in this work has a large size coming from an industrial plant.•Feature number is reduced by 93.4% in feature subset selection stage.•Optimal feature subset is highly correlated with the process experience.•Modeling with production patterns identified data can improve the model performance.
Abstract
The carbon dioxide (CO
2
) capture and utilization has attracted a great attention in organic synthesis. Herein, an unpresented transient stabilization effect (TSE) of CO
2
is disclosed and ...well applied to the electrochemical hydrogenation of azo compounds to hydrazine derivatives. Mechanistic experiments and computational studies imply that CO
2
can capture azo radical anion intermediates to protect the hydrogenation from potential degradation reactions, and is finally released through decarboxylation. The promotion effect of CO
2
was further demonstrated to work in the preliminary study of electrochemical reductive coupling of α‐ketoesters to vicinal diol derivatives. For the electrochemical reductive reactions mentioned above, CO
2
is indispensable. The presented results shed light on a different usage of CO
2
and could inspire novel experimental design by using CO
2
as a transient protecting group.
•The thermodynamic equilibrium conditions of methane hydrate in organic carboxylic sodium salts solutions were measured.•The equilibrium pressure change of hydrate in organic carboxylic sodium salts ...solutions were calculated.•The dissociation enthalpies of methane hydrate in organic carboxylic sodium salts solutions were calculated.•The thermodynamic equilibrium conditions of methane hydrate in organic carboxylic sodium salts solutions were predicted.
Gas hydrate inhibitors are employed to mitigate gas hydrate formation in pipelines. The effects of thermodynamics inhibition were evaluated by measuring the vapor - liquid aqueous solution - solid hydrate (VLH) equilibrium conditions on methane (CH4) hydrate in the presence of three organic carboxylic sodium salts (sodium formate, sodium acetate, sodium propionate) in this study. The experiments were carried out in the temperature range of 273.65 K to 281.65 K. Compared with deionized water, in the electrolyte solutions of sodium formate, sodium acetate and sodium propionate with mole fraction of 0.010 and 0.020, the VLH equilibrium pressure change (ΔP) increased by 12.93, 27.68 %; 18.78, 38.15 %; 23.51, 49.41 %, respectively. Both of the three organic carboxylic sodium salts have obvious thermodynamic inhibition effect on CH4 hydrate. The strength of hydrate inhibition is related to the carbon chain length of organic carboxylate. The dissociation enthalpy (ΔHdiss) of CH4 hydrate in three organic carboxylic sodium salts solutions remains quite uniform with deionized water, which indicates that three organic carboxylic sodium salts have not been involved in the formation of hydrate nucleus. The Chen-Guo hydrate model and N-NRTL-NRF activity model were employed to predict the VLH equilibrium conditions in electrolyte solutions. In the three organic carboxylic sodium salts solutions, the average absolute relative deviations (AARD) of the VLH equilibrium condition data between the predicted and the experimental were 0.81, 2.17, and 3.02 %, respectively. In the sodium chloride (NaCl) and potassium chloride (KCl) solutions, the AARD between the predicted and literature were 1.44, 1.69 %, respectively. The model has good universality and accuracy. Both sodium acetate and sodium propionate are food grade preservatives. Consequently, these are beneficial for the development of environmental-friendly hydrate inhibitors.
•A Laplace sensor was developed for determination of transient interfacial tension.•The method can accurately measure the interfacial tension as low as 0.17 mPa·s.•TIFT in two-phase dispersion ...coupling mass transfer processes was determined.•The two-phase flow rates and composition will significantly influence TIFT.
In two-phase dispersion processes coupled with interphase mass transfer, the interfacial tension varies with the mass transfer and significantly affects the dispersion. Determination of the transient interfacial tension (TIFT) in such processes could facilitate better understanding and optimization of the existing processes. In this study, a microfluidic device in which a Laplace sensor was used as a pressure probe was developed to determine the TIFT. The developed Laplace sensor was shown to allow accurate measurement of the local pressure in a micro-device, and to be superior to a commercial pressure sensor. The new method can be used to precisely determine the interfacial tension when the dispersion rate was not higher than 1.5 Hz, and to have a measurement range not narrower than 0.17–58.53 mPa·s. The TIFTs of several systems were then determined, and a mathematical model was established to predict the results. The main factors governing the TIFT were analyzed based on both the experimental and theoretical results.
