Search

The Kolbe-Schmitt reaction is the traditional method for preparing 2,4- and 2,6- dihydroxybenzoic acid (2,4- and 2,6-DHBA). In this work, accurate kinetic models for the Kolbe-Schmitt synthesis of 2,4- and 2,6-DHBA were successfully developed. The relative errors between the theoretical and experimental 2,4-DHBA equilibrium yields are less than 3.7% as T = 348–473 K, [C6H6O2] = 0.4–0.8 M and [KHCO3] = 1.2–4.0 M. The effects of reaction temperature, reaction time, KHCO3 and resorcinol (C6H6O2) concentrations on the formation rates and the yields of 2,4- and 2,6-DHBA were investigated by the developed models. Results show that the 2,4-DHBA equilibrium yield exhibits a strong dependence on the KHCO3 concentration, and the formation rate of 2,4-DHBA is strongly dependent on the reaction temperature. Furthermore, the reaction time is a critical factor in controlling the ratio of 2,4-DHBA to 2,6-DHBA as the reaction temperature varies from 433 to 473 K. Additionally, the results of the present work deepen the understanding of the reaction mechanism, e.g. the rate-determining step and main reaction pathway of 2,6-DHBA formation.

This work investigates the effects of coalescence and breakup models on the radial distribution of gas holdup and local bubble size distribution in a laboratory scale bubble column operated at 0.11 m/s, 0.14 m/s, 0.19 m/s and 0.23 m/s. The results quantitatively show the influences of bubble coalescence due to various mechanisms, coalescence efficiency calculated by different models, modification coefficients for coalescence rates, critical energy required for breakup and bubble breakage caused by large scale eddies and viscous shear on numerical simulations. Furthermore, qualitative analysis is performed to analyze the effects of these factors. The performance of various models is evaluated (e.g. Han’s breakup model and Das’s coalescence model). Some optimized combinations of coalescence and breakup models that can be used to accurately predict the local gas holdup and bubble size distribution in laboratory scale bubble columns operated at heterogeneous regime are proposed.

The class method (CM) has been frequently applied in solving population balance equations (PBEs) for the CFD-PBM simulation of bubble columns. There are four parameters in the CM: the volume ratio between successive bubble classes (rv), the minimum diameter (dmin), the maximum diameter (dmax) and the critical diameter (dc) that is used to distinguish small bubbles and large bubbles. These parameters have a significant impact on the computational precision and efficiency. In this work, numerical simulations are performed to investigate the effects of these parameters on the simulation of two typical bubble columns operated at heterogeneous regime. The simulation results quantitatively present the influences of these parameters on the simulated local gas holdup and global bubble size distribution. The simulated radial profiles of gas holdup at different heights are compared with experimental data. The optimized scheme for the values of these parameters in the CM is proposed.

In this study, a bi-salt sorbent was observed to exhibit better adaptability to the heating and cooling temperatures than conventional single-salt sorbents. A reactor filled with the bi-salt sorbent of CaCl2 and MnCl2 was designed, and the performance for long-term thermal energy storage, which included several months of seasonal energy storage and a few days of exhaust gas heat storage in winter, was analyzed. The thermal energy charging rate under both working conditions increased with the heating temperature; however, the COPh exhibited a downward trend. The COPh of seasonal energy storage was maintained above 0.5, and the COPh of exhaust gas heat storage was slightly higher at approximately 0.7. For both working conditions, the average heat-producing power in 50 min increased to approximately 9 kW, and the energy-storage density increased to approximately 1900 kJ∙kg−1, which was approximately 100% higher than that of existing resorption systems with single-salt sorbents.