Effect of kaolin pretreatment on the structure and properties of metakaolin phosphate-based geopolymers

Xin Yu,Chengxin Ren,Wenlong Xu,Lina Xu,Qingbo Tian 한양대학교 청정에너지연구소 2024 Journal of Ceramic Processing Research Vol.25 No.1

This study focused on the preparation of metakaolin-based phosphate-activated geopolymers (MKPGs) using kaolin pretreatedat 950 °C for varying times as a precursor. It was found that kaolinite quickly transformed into amorphous metakaolin (MK)and then transitioned from a disordered phase to an ordered phase, resulting in precipitation of kyanite and mullite withincreasing calcination time. The formation of the kyanite phase had an adverse effect on geopolymerization, which causeda decrease in the strength of the MKPGs. The precipitation of the mullite phase hindered the geopolymerization reactionbetween phosphoric acid and MK, and the geopolymer failed to solidify. As the calcination time increased from 10 min to 60min, the compressive strength of the geopolymers increased and then decreased. The maximum strength of the geopolymerscreated from MK calcined for 30 min was 132.1 MPa.

Kinetics of perovskite-like oxygen carriers for chemical looping air separation

Limin Hou,Qingbo Yu,Tuo Wang,Kun Wang,Qin Qin,Zhenfei Qi 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.3

Chemical looping air separation gives an energy-efficient choice for oxygen production. We performed kinetic analysis of YBaCo4O7+δ, Y0.95Ti0.05BaCo4O7+δ, Y0.2Ti0.05Dy0.75BaCo4O7+δ, and Y0.15Zr0.1Dy0.75BaCo4O7+δ oxygen carriers in a CLAS process. TG experiments were conducted with heating rates of 0.5, 1, and 2 oC/min in a thermogravimetric analyzer. Further exploration is required to develop an appropriate oxygen carrier. So, we used the model-free approach, Starink method, to evaluate the apparent activation energy. And, masterplots method was applied to determine the most probable mechanism function. The results show that the distributed activation energies of oxidation/ reduction process are 189.42/286.22 kJ/mol, 197.70/324.87 kJ/mol, 195.41/310.4 kJ/mol, and 192.20/293.53 kJ/mol for YBaCo4O7+δ, Y0.95Ti0.05BaCo4O7+δ, Y0.2Ti0.05Dy0.75BaCo4O7+δ, and Y0.15Zr0.1Dy0.75BaCo4O7+δ oxygen carriers, respectively. Random nucleation and nuclei growth A model is the most suitable for oxidation process. The A model and D are the most suitable for the reduction process. Regarding YBaCo4O7+δ, Y0.95Ti0.05BaCo4O7+δ, Y0.2Ti0.05Dy0.75BaCo4O7+δ, and Y0.15Zr0.1Dy0.75BaCo4O7+δ kinetic, oxygen transfer materials are rate-determined by nucleation and nuclei growth. For reduction kinetic, the gas diffusion stage could also become a dominant step.

Comparative kinetic study of coal gasification with steam and CO2 in molten blast furnace slags

Fan Yang,Qingbo Yu,Huaqing Xie,Zongliang Zuo,Limin Hou,Qin Qin 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.8

To make a comparison between coal gasification in molten blast furnace slag (MBFS) in different ambience and choose an appropriate agent to recover BF slag’s waste heat entirely, coal gasification with steam and CO2 in molten blast furnace slags was studied by isothermal thermo-gravimetric analysis. The effects of temperature and addition of MBFS were studied. Carbon conversion and reaction rate increased with increasing temperature and MBFS. Volumetric model (VM), shrinking core model (SCM), and diffusion model (DM) were applied to describe the coal gasification behavior of FX coal. The most appropriate model describing the coal gasification was SCM in steam ambience and VM in CO2 ambience, respectively. The reaction rate constant k(T) in CO2 ambience is greater than that in steam ambience, which means the gasification reactivity of coal in CO2 ambience is better than that in steam ambience. BF slag can effectively reduce the activation energy EA of coal gasification reaction in different ambiences. But, the difference of activation energies is not large in different ambiences. Based on the results of kinetic analysis including k(T) and EA calculated by the established model, CO2 was chosen to be the most appropriate agent.

Sensitivity analysis of key factors in controlling absorption and desorption of oxygen to oxygen carriers

Limin Hou,Qingbo Yu,Kun Wang,Shuo Zhang,Qin Qin,Fan Yang 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.1

Chemical looping air separation gives an oxygen resource for the oxy-fuel combustion system. To investigate the sensitivity of operation parameters and optimal operation parameters, with the consideration of the reactor temperature, we used the oxygen concentration, and reaction gas flow, an orthogonal experiment and multi-objective comprehensive evaluation method to analyze the results obtained by fixed-bed apparatus with the YBaCo4O7+, Y0.95Ti0.05BaCo4O7+, Y0.5Dy0.5BaCo4O7+, and Y0.2Ti0.05Dy0.75BaCo4O7+ oxygen carriers. The results showed that the effects of operating conditions on oxygen absorption/desorption properties varieds in the order: oxygen concentration>gas flow rate>absorption temperature=desorption temperature. Analysis of max-min difference showed that the optimum operating conditions such as absorption temperature, 350 oC, desorption temperature, 430 oC, gas flow rate, 200 ml/min, and oxygen concentration, 21% were confirmed

Production of syngas from dry reforming of bio-oil model compound in granulated blast furnace slag

Xin Yao,Qingbo Yu,Guowei Xu,Zhengri Han,Qin Qin 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.5

The characterization of dry (CO2) reforming of bio-oil model compound (BMC) in granulated BF (blast furnace) slag for syngas production is presented in this study. The effects of temperature, CO2/C (the molar ratio of CO2 to C in the BMC), liquid hourly space velocity (LHSV) and granulated BF slag on the coke yield, combustible gas yield, syngas composition and lower heating value of the dry reforming process were investigated by fixed-bed experiments. The results indicated that using granulated BF slag as the heat carrier, temperature reaching 750 oC, CO2/C of 0.75 and LHSV of 0.45 h1 could be the optimal condition for the dry reforming process, where the combustible gas yield and lower heating value were up to 1.85L/g and 23.00 kJ/g, respectively. Granulated BF slag showed positive effects on the dry reforming process, promoting the combustible gas yield and lower heating value and increasing the compositions of H2 and CO. Granulated BF slag could be used as a superior heat carrier for the dry reforming of BMC.

Oxygen absorption and desorption properties of YBaCo4O7+δ monolithic oxygen carrier in the fixed-bed reactor

Limin Hou,Chaoyue Qiao,Qingbo Yu,Wenfei Wu 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.3

The technology of chemical looping air separation, with the characteristics of simple operation, low cost, and low energy consumption, separates oxygen from air with the oxygen carrier. In this work, reaction properties of monolithic oxygen carriers were investigated in a fixed-bed apparatus, with the consideration of the reactor temperature, oxygen concentration, and reaction gas flow. The XRD results showed that active phase, Al2O3, and cordierite cannot react with each other in calcination processing. The SEM results showed that the micromorphology of oxygen carrier was loaded on cordierite honeycomb uniformly with sphere or sphere-like particles. Oxygen carriers show a faster oxygen release rate and a slower oxygen intake rate. With increasing of absorption temperature, oxygen concentration of inlet gas, and desorption temperature, the reaction rate per unit mass increases. With increasing of gas flow rate, the reaction rate per unit mass decreases. The maximum value of the reaction rate per unit mass was obtained by Y0.95Ti0.05BaCo4O7+δ monolith sample. Samples substituted with Dy element showed fine performance of stability, as Dy substitution causes more serious local lattice distortions.

Sorption-enhanced reforming of tar: Influence of the preparation method of CO2 absorbent

Huaqing Xie,Weidong Zhang,Xiangnan Zhao,Hao Chen,Qingbo Yu,Qin Qin 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.11

To remove tar and produce environment-friendly H2, one of the promising routes is the sorption-enhanced steam reforming (SESR) process, in which the CO2 sorbent is a key element. We prepared the CO2 sorbents with Ca12Al14O33 as carrier with various methods. Their characterizations were examined, and the sample prepared by solgel (SG) method showed the strongest CaO and Ca12Al14O33 phases and the most excellent pore structure among all the samples. Then, a thermogravimetric experiment was conducted, and the results showed that the sample prepared by sol-gel (SG) method had the best CO2 adsorption capacity and excellent long-term cyclic stability. Finally, the sorbent was used into the steam reforming experiments of tar. Under the action of the sorbent, the reforming reaction was enhanced in-situ, with the H2 yield and concentration improved obviously, and especially, H2 concentration can reach over 98.85%.

Prediction of Undisturbed Clay Rebound Index Based on Soil Microstructure Parameters and PSO-SVM Model

Jiaqi Dong,Boxin Wang,Xuexin Yan,Xinchuan Xu,Guangping Xiao,Qingbo Yu,Meng Yao,Qing Wang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.5

The rebound index Cr is an important design parameter in engineering construction, and its determination is cumbersome and susceptible to errors. Explaining the macroscopic rebound characteristic parameter Cr from the perspective of microscopic mechanism is an important research area that is addressed in this study. In this paper, the different soil parameters, including the Cr parameter and the physical parameters (void ratio e, liquid limit water contentwL, and plasticity index Ip), have been determined through experiments for the undisturbed clay of Chongming East Shoal (CES), Shanghai. Further, scanning electron microscopy (SEM) imaging was used to analyze the microstructural features. Through SEM, the grey correlation degree, the average abundance of structural units ACp and the average equivalent diameter of pores ADv were determined as the soil microstructure parameters with the most significant correlation with Cr. The predictive analysis model of Cr was then carried out combined with the PSO-SVM algorithm. In order to evaluate the influence of microscopic parameters of soil on the prediction accuracy, four sets of input parameter combinations were used. The results indicate the high prediction accuracy of the developed model. Sensitivity analysis was also carried out, which showed that the sensitivity of Cr to ACp and ADv was significantly lower than e; however, the difference from wL and Ip was small, indicating that it is imperative to consider microscopic parameters while predicting Cr. This study, thus, provides a basis and method for predicting the rebound index of soil from the microstructure perspective.