Yuejin Liu

Numerical Simulation of Gas Holdup Distribution in a Standard Rushton Stirred Tank Using Discrete Particle Method

The discrete particle method was used to simulate the distribution of gas holdup in a gas-liquid standard Rushton stirred tank. The gas phase was treated as a large number of bubbles and their trajectories were tracked with the results of motion equations. The two-way approach was performed to couple the interphase momentum exchange. The turbulent dispersion of bubbles with a size distribution was modeled using a stochastic tracking model, and the added mass force was involved to account for the effect of bubble acceleration on the surrounding fluid. The predicted gas holdup distribution showed that this method could give reasonable prediction comparable to the reported experimental data when the effect of turbulence was took into account in modification for drag coefficient.

A novel strategy for constructing mesoporous solid superbase catalysts: bimetallic Al–La oxides supported on SBA-15 modified with KF

Bimetallic Al–La oxides were conjointly precoated on SBA-15 prior to the introduction of potassium fluoride to achieve solid superbases at low temperature by a modified wetness impregnation method. This breaks the tradition of decomposition of KNO3 at high temperature and gives rise to a new approach to generating superbasic sites on SBA-15. The physico-chemical characteristics of the prepared KF/Al–La@SBA-15 materials were investigated using FT-IR, XRD, TG-DTG, N2 adsorption–desorption, TEM, SEM-EDS, acid–base titration, Hammett indicators and CO2-TPD measurements. The results demonstrated that the addition of Al species promoted the dispersion behavior of La species inside the channels, and the bimetallic species could synergistically protect the mesoporous structures of SBA-15 against KF corrosion. With increasing Al content, KF/Al–La@SBA-15 exhibited a long-range ordering of the pores with relatively narrow pore size distribution as well as high specific surface area. The research results showed that the KF/Al–La@SBA-15 (0.4) catalyst possessed a total basicity up to 0.79 mmol g−1 and superbasicity with a strength of 26.5. The catalytic activity of the prepared materials was evaluated in the ring-opening reaction of propylene oxide with methanol. Compared with the SBA-15 supported monometallic oxide (Al or La) catalysts, KF/Al–La@SBA-15 (0.4) exhibited the highest catalytic activity for the ring-opening reaction of propylene oxide with methanol. This is associated with the synergistic effects between Al and La species and the high dispersion of active components on the SBA-15 support.

The Effect of Eddy-bubble Interaction Model on the Turbulent Dispersion of Gas Bubbles in Stirred Tanks

Abstract Based on trajectory equations of gas bubble, an eddy-bubble interaction (EBI) model was developed. This model considered the effect of non-drag forces and took the eddy-bubble interaction time as the refreshing time scale of turbulent fluctuations. The relationship between the crossing-eddy time and the eddy lifetime was discussed, and the predicted distributions of radial, axial velocities of bubbles and gas holdup were also given. Compared with eddy lifetime (EL) model, the EBI model gives somewhat smaller axial velocity in the upper circulation region and larger velocity in the lower circulation region, causing that fewer bubbles reach the lower circulation region and gas holdup becomes higher in the upper circulation region. The predicted gas holdup by the EBI model approaches closer to the experimental data in the discharge stream region.

Low-temperature preparation of mesoporous silica superbase by using multifunction of a La2O3 interlayer

A simple and effective approach for the preparation of the solid superbasic La2O3–SBA‐15‐supported KF (KF/La2O3–SBA‐15) was developed by a low‐temperature strategy. The KF/La2O3–SBA‐15 with ordered mesostructure and a high base strength (H−=27.0) was realized at 350u2009°C in still air, which breaks the traditional method of thermally induced decomposition of basic metal nitrate derived species KNO3 under higher temperatures (>600u2009°C). The resultant mesoporous basic materials were adopted for the production of 1‐methoxy‐2‐propanol from propylene oxide and methanol. It showed excellent catalytic performance exhibiting 93u2009% conversion of propylene oxide and 93u2009% selectivity to 1‐methoxy‐2‐propanol. This performance is better than that over the catalysts without mesoporous silica despite having a higher KF content.

A Highly-Efficient KF-Modified Nanorod Support Zr−Ce Oxide Catalyst and its Application

A novel KF‐modified nanorod support Zr−Ce oxide as an efficient solid base catalyst was prepared. XRD, FT‐IR, CO2‐TPD, TEM‐EDS, and Raman were employed for the catalyst characterization. The results showed that the appropriate activation temperature could facilitate the insertion of K+ into the vacancy sites of the ZrO2−CeO2 nanorod support, and some new strong basic active sites of K3Zr2F11, KCe2F9, Ce2Zr2O7 were generated with the addition of KF on the mixed ZrO2−CeO2 support. The prepared KF/ZrO2−CeO2 as a solid base catalyst exhibited high activity and stability for transesterification of soybean oil with methanol to biodiesel. The high biodiesel yield of 99.8u2009% was obtained under the following conditions: 15u2005wtu2009% KF loading amount, calcination temperature 400u2009°C, molar ratio of methanol/oil 20u2009:u20091, 5u2005wtu2009% catalyst account (wt/wt oil), reaction time 5u2005h at 65u2009°C. The formation of basic active sites of the KF/ZrO2−CeO2 catalyst and the mechanism for the catalytic reaction were explored.