•Effects of cooling rate, stirring rate and impurities on MSZW are investigated.•Nývlt-like equation and 3D nucleation approach estimate MSZW of K2SO4 solution.•The accuracy and sensitivity of ultrasonic sensor are similar with FBRM on MSZW.The metastable zone width (MSZW) and nucleation kinetics of potassium sulfate in the aqueous solution were investigated. MSZW was measured using both the ultrasonic velocity sensor and the focused beam reflectance measurement (FBRM) at different cooling rate, stirring rate and impurities concentration (aluminum ions and silicon ions), and the effects of these conditions on MSZW were discussed in details. In addition, the accuracy and sensitivity of detectors to measure the nucleation temperature of potassium sulfate in the aqueous solution were compared between the ultrasonic velocity sensor and FBRM over a wider range of operating conditions. Although two detectors measured MSZW with an acceptable accuracy, the ultrasonic velocity sensor had a higher sensitivity to the phase transition of potassium sulfate in solution since it directly detected the concentration change of potassium sulfate in solution. Furthermore, both self-consistent Nývlt-like equation method and classical 3D nucleation theory approach were applied to estimate MSZW of potassium sulfate in aqueous solution. According to these classical theories, the nucleation kinetics parameters were calculated based on the measured MSZW data for potassium sulfate aqueous solution with 40 °C, 50 °C and 60 °C saturation temperature, respectively. It was found two approaches could describe MSZW of potassium sulfate aqueous system very well.

•Direct leaching of alunite from alunite tailing in KOH solution is proposed.•Optimum leaching conditions of alunite tailings are determined.•A dissolution mechanism of alunite that predicts the reaction order is proposed.•The alunite dissolution is controlled by the surface chemical reaction.Alunite tailings, a secondary resource from copper metallurgy industry in China, are considered a potential resource for both the production of alumina and potash fertilizer, since alunite tailings contain abundant alunite with associated impurities of kaolinite, dickite and quartz. In this work, the direct leaching of alunite from alunite tailings in the highly concentrated KOH solution is proposed. Under appropriate leaching conditions, such as temperature below 90 °C and KOH concentration above 13.5 mol·L− 1, most of alunite is dissolved while kaolinite, dickite and quartz are still remained in the residue. Mastersizer, X-ray diffraction, infrared radiation spectrometer, Raman spectrometer and scanning electron microscopy/energy-dispersive spectroscopy are used to characterize alunite tailings samples before and after leaching. The leaching kinetics of alunite from alunite tailings in the concentrated KOH solution is described using a shrinking core model controlled by the surface chemical reaction. The key kinetics parameters, such as the activated energy and the reaction order, are determined based on the leaching experimental data. The dissolution mechanism of alunite from alunite tailings in the concentrated KOH solution is considered, and is used to account for the reaction order.

•Separation of aminoglutethimide racemate by VARICOL and SMB processes is compared.•VARICOL process with various column configurations is assessed.•Separation conditions of VARICOL process are designed by transport-dispersive model.The separation of aminoglutethimide enantiomers by the continuous multicolumn chromatographic processes were investigated experimentally and theoretically, where the columns were packed with cellulose tris 3,5-dimethylphenyl-carbamate stationary phase (brand name Chiralcel OD) and mobile phase was a mixture of n-hexane and ethanol with monoethanolamine additive. The continuous enantioseparation processes included a synchronous shifting process (SMB) and an asynchronous shifting process (VARICOL), which allowed reducing the column number (here from six-column SMB to five-column VARICOL process). Transport-dispersive model with the consideration of both intraparticle mass transfer resistance and axial dispersion was adopted to design and optimize the operation conditions for the separation of aminoglutethimide enantiomers by SMB process and VARICOL process. According to the optimized operation conditions, experiments were carried out on VARICOL-Micro unit using five-column VARICOL process with 1/1.5/1.5/1 configuration and six-column SMB process with 1/2/2/1 configuration. Products of R-aminoglutethimide (R-AG) enantiomer and S-aminoglutethimide (S-AG) enantiomer with more than 99.0% purity were obtained continuously from extract stream and raffinate stream, respectively. Furthermore, the experiemntal data obtained from five-column VARICOL process were compared with that from six-column SMB process, the feasibility and efficiency for the separation of guaifenesin enantiomers by VARICOL processes were evaluated.

The adsorption equilibriums of CO2, CH4, and N2 pure gases on pitch-based activated carbon beads have been studied using a magnetic suspension microbalance at (293, 303, 333, and 363) K within a pressure range of 0 kPa to 4000 kPa. It is found that experimental adsorption capacities can be successfully described with both the Sips and Multisite Langmuir (MSL) isotherm models. Afterward, binary competitive adsorption breakthrough experiments (CO2/CH4 and CH4/N2) at 303 K and adsorption isotherms of gas mixtures under different conditions have been measured. Theoretical calculations from Sips model-based ideal adsorbed solution theory are found to have better agreement with experimental data of competitive binary adsorption than that from MSL model. Promising adsorption selectivity (5.5) between CH4 and N2 is obtained at 303 K as the pressure of a binary gas mixture is 100 kPa with yCH4 = 0.5 in the feed. Therefore, the activated carbon beads reported in this study can be considered as a promising adsorbent for CH4 enrichment from coalbed methane (CH4/N2) gas mixture.

•The operating conditions of SMB and Varicol processes are designed.•The separation of guaifenesin enantiomers on Micro-VARICOL unit is performed.•Experimental results of SMB and Varicol processes are evaluated.The separation of guaifenesin enantiomers by both simulated moving bed (SMB) process and Varicol process was investigated experimentally and theoretically, where the columns were packed with cellulose tris 3,5-dimethylphenylcarbamate (Chiralcel OD) stationary phase and a mixture of n-hexane and ethanol was used as mobile phase. The operation conditions were designed based on the separation region with the consideration of mass transfer resistance and axial dispersion, and the experiments to separate guaifenesin enantiomers were carried out on VARICOL-Micro unit using SMB process with the column configuration of 1/2/2/1 and Varicol process with the column configuration of 1/1.5/1.5/1, respectively. Single enantiomer with more than 99.0% purity was obtained in both processes with the productivity of 0.42 genantiomer/d cm3 CSP for SMB process and 054 genantiomer/d cm3 CSP for Varicol process. These experimental results obtained from SMB and Varicol processes were compared with those reported from literatures. In addition, according to the numerical simulation, the effects of solid-film mass transfer resistance and axial dispersion on the internal profiles were discussed, and the effect of column configuration on the separation performance of SMB and Varicol processes was analyzed for a few columns system. The feasibility and efficiency for the separation of guaifenesin enantiomers by SMB and Varicol processes were evaluated.

The chromatographic enantioseparation of trans-stilbene oxide (TSO) was studied experimentally and theoretically, where the preparative column was packed with 20 μm Chiralcel OD stationary phase and hexanes/2-propanol were used as mobile phase. The bed porosity, axial dispersion coefficient, mass transfer coefficient and the column efficiency were determined according to the pulse response experiments. The adsorption equilibrium isotherms of single and racemic mixture of trans-stilbene oxide were measured by the frontal analysis, the linear-Langmuir isotherm model was used to fit the experimental data, and the relative parameters were estimated for the competitive adsorption equilibrium of TSO enantiomers. Elution profiles were measured for the separation of TSO enantiomers on Chiralcel OD preparative column, and the experimental data were compared with the simulated results predicted by the mathematical model that accounted for axial dispersion and linear driving force mass transfer model. The adsorption equilibrium and kinetic information obtained in this work are useful for the scale up and optimization of both batch and continuous chromatographic enantioseparation systems.Highlights► Competitive adsorption isotherms of TSO enantiomers on Chiralcel OD were measured. ► Adsorption kinetics of TSO enantiomers on Chiralcel OD were investigated. ► The separation process of TSO enantiomers on Chiralcel OD packed column was modeled.

Orthorhombic-LiMnO2, spinel-type Li1.6Mn1.6O4, and spinel MnO2·0.5H2O were synthesized via a combination of hydrothermal synthesis and solid-phase reaction. o-LiMnO2 with different stacking fault concentrations were synthesized by controlled hydrothermal reaction using a KMnO4, MnCl2, and LiOH mixed solution. Spinel-type Li1.6Mn1.6O4 precursor was prepared via heat treatment of o-LiMnO2. The effects of hydrothermal and solid-phase reaction on the structure and ion-exchange properties were examined with powder X-ray diffraction, scanning electron microscopy, and Li+ selective adsorption measurements. The results showed that stacking fault concentration of o-LiMnO2 affects the adsorption properties of Li1.6Mn1.6O4. Li+ adsorption capacity reached 6.06 mmol·g–1 at equilibrium. Distribution coefficients of metal ions were in the order Li+ ≫ Na+ > Mg2+ > K+ > Ca2+ and were significant for Li+ extraction from low grade brine. The equilibrium uptake of Li+ from salt lake brine remained at 3.62 mmol·g–1 after six cycles.

Carbon dioxide removal from flue gas with a two-stage vacuum pressure swing adsorption (VPSA) process, which uses activated carbon (AC) beads as the adsorbent, was investigated both theoretically and experimentally. First, single-column VPSA experiments were studied for CO2/N2 separation with high CO2 feed concentration. Then, a two-stage VPSA process composed two columns for each stage was designed, and the effects of different parameters were investigated. The first-stage VPSA unit operates with a four-step Skarstrom cycle, which includes feed pressurization, adsorption, blowdown, and counter-current purge with N2. For the second-stage VPSA process, a cycle with feed pressurization, adsorption, pressure equalization, blowdown and pressure equalization was employed. With the proposed two-stage VPSA process, a CO2 purity of 95.3% was obtained with 74.4% recovery. The total specific power consumption of the two-stage VPSA process is 723.6 kJ/kg-CO2, while the unit productivity is 0.85 mol-CO2/kg·h.

With the development of novel adsorbent material and adsorption process, adsorption technology has become a potential tool for the CO2 removal from flue gases. The reduction of carbon dioxide emissions from flue gases with two successive vacuum pressure swing adsorption (VPSA) units, using 13XAPG as the adsorbent, was investigated both theoretically and experimentally. A 3-bed 5-step VPSA process was designed to capture CO2 from flue gases, which included feed pressurization, adsorption, rinse, blowdown and counter-current purge. It was found that was difficult to achieve both high CO2 purity and high CO2 recovery by one VPSA unit when capturing CO2 from flue gases at atmospheric pressure. After the verification of one-column VPSA experiment for further concentrating CO2 stream from one VPSA unit to above 95 % purity, two successive VPSA units were designed, composed of 3-bed 5-step cycle for the first unit and 2-bed 6-step cycle for the second unit, and the effects of operating parameters on the separation behaviors were investigated by simulation. With the proposed VPSA process, a CO2 purity of 96.54 % was obtained with recovery of 93.35 %. The total specific power consumption of the two successive VPSA units was \(528.39\mbox{~kJ/kg}_{\mathrm{CO}_{2}}\), while the unit productivity was \(0.031\mbox{~kg}_{\mathrm{CO}_{2}}\mbox{/kg\,h}\).

The moment analysis is applied to study two-component perturbation chromatography with linearized nonequilibrium adsorption. General expressions for the first and second chromatographic moments of components and waves are given by taking into account axial dispersion, film mass transfer resistance, and intraparticle diffusion resistance for chromatographic column packed with inert core adsorbents. The well-known results for moment solution of the single-component case and special two-component case are extended to the general two-component case.Highlights► We model the case of chromatographic column packed with inert core adsorbents. ► We present general expressions for the moments of components and waves. ► The model accounts for nonlinear adsorption equilibria and dispersive effects.