Co-reporter:Zhaoxuan Chen, Jun Yang, Dan Ling, Peng Liu, I. M. Saman K. Ilankoon, Zibin Huang, and Zhenmin Cheng
Industrial & Engineering Chemistry Research November 15, 2017 Volume 56(Issue 45) pp:13490-13490
Publication Date(Web):April 20, 2017
DOI:10.1021/acs.iecr.7b00123
The influence of the packing size on the mean bubble diameter in a flooded bed reactor packed with glass spheres of three different diameters (1.9, 4.0, and 9.3 mm) was investigated. The gas saturation and interfacial area were respectively measured by electrical capacitance tomography and chemical absorption of oxygen. It is observed that the presence of packing has greatly reduced the bubble diameter and increased the gas saturation compared with a bubble column. To explore the underlying relationship between the bubble diameter and packing size, the packing size featured by the pore diameter was utilized as a reference. It shows that the bubble diameter is 2–3 times the pore for the 1.9 and 4.0 mm packings, while they are approached for the packing of 9.3 mm. An empirical correlation was proposed for the mean bubble diameter prediction with a discrepancy of less than 25% from the measurements.
Co-reporter:Chengzhen Chen;Bo Zhang;Juhua Zhong
Journal of Materials Chemistry A 2017 vol. 5(Issue 41) pp:21955-21964
Publication Date(Web):2017/10/24
DOI:10.1039/C7TA04983H
Electrocatalytic reduction of CO2 to CO is usually subject to the competitive reduction of H+ to hydrogen. In this work, it was demonstrated that increasing the local pH at the electrode/electrolyte interface would greatly improve the selectivity for CO2 reduction to CO by inhibiting hydrogen evolution, resulting in a high CO faradaic efficiency of 90.5%. And this pH-induced effect can be achieved by increasing the thickness of the porous gold film through a facile synthetic technique, based on the enhancement of the mass transfer resistance within the highly porous electrode. Moreover, the thickest film, which had a large electrochemical surface area, displayed a significantly improved catalytic activity for CO2 reduction at a low overpotential of 390 mV. These results indicate that increasing the local pH by thickening the porous gold film is selective and efficient for electrochemical CO2 reduction.
Co-reporter:Miaofei Gu;Xingxing Yan
Research on Chemical Intermediates 2016 Volume 42( Issue 2) pp:391-406
Publication Date(Web):2016 February
DOI:10.1007/s11164-015-2025-2
As a base-promoted Kolbe–Schmitt carboxylation reaction, the mechanism of synthesis of salicylic acid derivatives from phenols with CO2 in the industry is still unclear, even up to now. In this paper, synthesis of 3,6-dichloro salicylic acid (3,6-DCSA) from 2,5-dichloro phenoxide and CO2 was investigated in the presence of K2CO3. We show the reaction can proceed by itself, but it goes at a slower rate as well as a lower yield, compared to the case with the addition of K2CO3. However, the yield of 3,6-DCSA is only minorly affected by the size of K2CO3, which cannot be explained from the view of catalytic effect. Therefore, K2CO3 may on one hand act as a catalyst for the activation of CO2 so that the reaction can be accelerated, while on the other hand, it also acts as a co-reactant in deprotonating the phenol formed by the side reaction to phenoxide, which is further converted to salicylate.
Co-reporter:Miaofei Gu and Zhenmin Cheng
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 24) pp:9992-9998
Publication Date(Web):2017-2-22
DOI:10.1021/ie5004762
Carboxylation of toluene by CO2 over AlCl3 is providing a new approach for CO2 transformation as well as an improved synthetic method of p-toluic acid with less byproducts under mild condition. To prevent decomposition and corrosion of AlCl3 powder, AlCl3 was immobilized over γ-Al2O3 support through reaction between dimer Al2Cl6 vapor and hydroxyl groups at the γ-Al2O3 surface, and a high loading of AlClx (x = 2.5) up to 72.36 wt % was obtained. The composition of immobilized −O−Al2Cl5 group was detected by HRTEM/EDS and the structure was authenticated to be the same as that of Al2Cl6 by 27Al MAS NMR. The Al valence in −O–Al2Cl5 was calculated to be 1.584, which is approximately the same as that in Al2Cl6. The above features of −O–Al2Cl5 guaranteed a high CO2 activation capacity in direct carboxylation of toluene with an isolated p-toluic acid yield of 73.34% with respect to AlCl3, which approaches that obtained by AlCl3 powder. Therefore, this work provides a more feasible way for carboxylation by CO2 in overcoming the instability of AlCl3 powder in the presence of moisture.
Co-reporter:Peng Liu;Zi-Bin Huang;Jun Zhu;Kun Yu ;Zhen-Min Cheng
Chemical Engineering & Technology 2014 Volume 37( Issue 12) pp:2056-2064
Publication Date(Web):
DOI:10.1002/ceat.201400284
Abstract
A stochastic model was developed to describe the liquid radial dispersion in a trickle-bed reactor, which has conventionally been modeled by the effective diffusion model. To establish the stochastic model, the column was divided into some layers of particles in the axial direction and several annulus rings in each layer in the radial direction. The liquid spreading was regarded as a fluid transport process and the matrix of transfer probability was derived based on the coordinates of the particle network in the cross-section of the column. With this transfer probability matrix and the initial liquid distribution, the liquid distribution in the downstream was predicted. In order to evaluate the model parameters, experimental data of the liquid dispersion were obtained from electrical capacitance tomography images and tracer injection. Good agreement was obtained between the stochastic model and the experimental liquid distribution data.
Co-reporter:Zhenyuan Wang, Zhenmin Cheng, Zibin Huang, and Kun Yu , Xuehua Li, Ruokai Xin, Yu Long, Dehui Wang, Guoqi Wang, Shuxu Wang, and Shengshan Li
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 36) pp:12802-12811
Publication Date(Web):2017-2-22
DOI:10.1021/ie400639r
To enhance the gas–liquid mixing efficiency of the quench box in a hydroprocessing reactor, a novel structure based on supergravitational swirling flow was proposed. To reach supergravitational flow, the Froude number of liquid in the horizontal swirling tube should be greater than unity. Through computational fluid dynamics (CFD) simulation and using a high-speed camera, the supergravitational swirling flow was visualized. Based on the Higbie’s penetration theory, CFD simulation was conducted to estimate the gas–liquid mass-transfer coefficient, and was compared with the oxygen absorption experiment. It shows the gas flow rate plays a key role in the gas–liquid mixing performance in the quench box. Experiments were also carried out to investigate effects of operating condition on the pressure drop of the two-phase flow in quench box, and a correlation was proposed accordingly.
Co-reporter:Ye-Mao Yu, Zhen-Min Cheng, Zhi-Ming Zhou, Si-Cao Wu, Peng Liu, and Jian Jin
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 26) pp:8735-8741
Publication Date(Web):October 28, 2011
DOI:10.1021/ie201901z
To experimentally verify the existence of reaction rate hysteresis in the gas phase operation due to capillary condensation, benzene hydrogenation was carried out in a fixed bed under isothermal condition. Through changing the flow rate of benzene and cyclohexane mixture in a sequence from low to high and then vice versa, a group of distinctive conversion profiles was obtained. By plotting the reaction rate against the relative vapor pressure, hysteresis loops in reaction rate are confirmed to exist. It was observed the reaction rate kept nearly constant in the region of p/p0 < 0.6 and decreased rapidly in the region of p/p0 > 0.8. In providing an intrinsic understanding on the influence of vapor condensation on the reaction rate of a partially wetted catalyst, the reaction rate and internal effectiveness factor are plotted against the catalyst wetting fraction, from which a new correlation between the overall reaction rate and catalyst wetting fraction was proposed.
Co-reporter:Zi-Bin Huang, Zhen-Min Cheng, Jian-Ding Chen, Xiang-Chen Fang, and Tao Yang
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 29) pp:9733-9741
Publication Date(Web):July 3, 2012
DOI:10.1021/ie3001138
In reduction of liquid backmixing in bubble columns, Wu et al. [Wu, Y; Cheng, Z. M.; Huang, Z. B. Backmixing reduction of a bubble column by interruption of the global liquid circulation. Ind. Eng. Chem. Res.2009, 48, 6558–6563] have shown that the backmixing could be substantially reduced by interrupting the global liquid circulation using four identical short Venturi throats (SVTs). Considering the advantages of such structures, it is necessary to further investigate the backmixing characteristics of a bubble column with SVTs. In the present work, a multipoint tracer injection and detection device was employed to enhance the insight into where and how the liquid tracer was backmixed in different stages of a 50-cm diameter column. Tracer response profiles were measured to track the liquid backmixing trajectory in different stages at various operating conditions. The results showed that the backmixing of the column was sensitive to the throat diameter of SVTs. Based on the observed physical phenomena, a tanks-in-series with backflow (TISB) model was adopted to interpret the tracer experiment data, which shows an excellent agreement between the prediction and experimental measurements.
Co-reporter:Si-Cao Wu, Zhen-Min Cheng, Peng Liu, Jian Jin, Ye-Mao Yu, and Zhi-Ming Zhou
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 26) pp:8742-8747
Publication Date(Web):October 28, 2011
DOI:10.1021/ie2019036
A two-stage reactor composed of a slurry bubble column and a fixed bed was proposed. The slurry column, installed with a radio frequency conductance liquid level controller, was considered not only as a preliminary reactor for the vaporization of the liquid reactants, but also as a protector to prevent liquid flooding in the fixed bed. Preliminary experiments were carried out to investigate the effects of different operating factors on the reactor performance, and the results showed that even under the optimal condition the benzene concentration should be kept at a low level of 21.9% to avoid high temperature rise. Therefore, side stream injection of cyclohexane into the fixed bed was proposed, and benzene conversion of 99.82% was reached even at a much higher concentration of 32.8%. To verify whether capillary condensation inside the catalyst particle in the fixed bed would exist in the presence of coolant injection, a criterion was proposed which is based on the understanding that once vapor condensation is occurring it will lead to multiplicity in reaction rate, which will consequently result in hysteresis in temperature profile under adiabatic condition.
Co-reporter:Zi-Bin Huang and Zhen-Min Cheng
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 21) pp:11843-11852
Publication Date(Web):September 19, 2011
DOI:10.1021/ie200859q
To identify the liquid circulation flow structure in a bubble column, a set of multipoint tracer injection and detection device was developed for a systematic study in a bubble column of 550 cm in height and 50 cm in diameter. Tracer response profiles were measured to track the liquid flowing trajectory under various flow conditions in the column with and without draft tubes. They showed that only when the draft tube length was greater than 3 m could the tracer response exhibit obvious periodicity. To resolve the liquid circulation flow structure in the time and frequency domain, wavelet multiresolution analysis was adopted. The results showed that the liquid circulation frequency increased with superficial gas velocity, which is in agreement with the published literature. It was also found that the macroscale, mesoscale, and microscale circulation loops coexisted in the bubble column.
Co-reporter:S.-C. Wu;Z.-M. Cheng;S.-D. Wang ;X.-L. Shan
Chemical Engineering & Technology 2011 Volume 34( Issue 10) pp:1614-1618
Publication Date(Web):
DOI:10.1002/ceat.201100096
Abstract
A process for the recovery and purification of terephthalic acid (TA) from alkali reduction wastewater is reported. TA was first precipitated from alkali reduction wastewater by acidification with sulfuric acid, and then the produced crude TA was dissolved in dimethylacetamide (DMA) so that crude TA could be purified from the solution by cooling crystallization. The results indicated that acidification could reduce the chemical oxygen demand of the wastewater by 83 %, and the purity of TA by crystallization could reach 99.91 %. A correlation was proposed in describing the solubility of crude TA in DMA from 303.4 to 358.65 K, which gives a mean relative discrepancy of less than 1.14 %. The cooling rate of the mother liquor had a large influence on the crystal size distribution. At an average cooling rate of 1.18 K min–1, the particle size distribution of TA was narrow and the average size was about 100 μm. In a bench-scale study, it was demonstrated that the crystallized product can be recycled as the raw material for polyethylene terephthalate production.
Co-reporter:Xianglei Shan, Zhenmin Cheng, and Ying Li
Journal of Chemical & Engineering Data 2011 Volume 56(Issue 12) pp:4310-4316
Publication Date(Web):March 21, 2011
DOI:10.1021/je200119h
Hydration of cyclohexene over H-ZSM-5 catalyst was carried out in a batch autoclave reactor in the presence of different cosolvents. With ethylene glycol as the cosolvent, a cyclohexene conversion of 11.4 % was obtained, which is much higher than that of 8.2 % obtained without the cosolvent. To evaluate the solubility of cyclohexene in the presence of ethylene glycol, the liquid−liquid equilibria (LLE) data of cyclohexene + water + cyclohexanol + ethylene glycol were measured at 298.15 K. It was found that a modified UNIFAC model gives the best fits to the LLE data, and the solubility of cyclohexene has increased evidently. The kinetic behavior of the hydration reaction was then investigated in the temperature range from 383.15 to 413.15 K, with initial molar ratio of cyclohexene to ethylene glycol in the range from 2 to 20. The kinetic data were correlated with a simple pseudohomogeneous model and two heterogeneous ones based on the Langmuir−Hinshelwood−Hougen−Watson and Eley−Rideal mechanisms, respectively. The results showed that the addition of ethylene glycol does not change the reaction mechanism of cyclohexene hydration over H-ZSM-5 catalyst. Nevertheless, due to the solvation effect of ethylene glycol, the activation energy of the reaction was found decreased.
Co-reporter:Yang Wu, Zhen-Min Cheng and Zi-Bin Huang
Industrial & Engineering Chemistry Research 2009 Volume 48(Issue 14) pp:6558-6563
Publication Date(Web):June 17, 2009
DOI:10.1021/ie900128j
The strong backmixing of the liquid phase which is prevalent in a bubble column should be ascribed to its global circulation which is upward in the central region while downward near the wall on the reactor scale. To suppress the backmixing behavior, interruption of the liquid circulation route should be effective. To verify this presumption, an investigation was conducted with a bubble column 550 cm in height and 50 cm in diameter, which was equipped with four channels of the same size installed at different heights so as to cut the downward motion of the liquid and therefore prevent the global circulation the liquid. It shows that although the radial velocity distribution of the liquid remains parabolic in the short column constituted by two neighbor channels, the velocity profile tends to be flat in the upward direction as the channel is approached. The residence time distribution analysis shows that the backmixing of liquid could be reduced by 60% when four channels 12 cm in diameter were applied.
Co-reporter:Zhen-Min Cheng, Yong Ding, Li-Qun Zhao, Pei-Qing Yuan and Wei-Kang Yuan
Energy & Fuels 2009 Volume 23(Issue 6) pp:3178
Publication Date(Web):May 19, 2009
DOI:10.1021/ef900132z
Vacuum residue (VR) upgrading was conducted in the environment of supercritical water (SCW) without oxygen addition in an attempt to yield a maximum of light oil. Simulated distillation of the liquid products from a set of orthogonal experiments shows that temperature should not be too high to restrict coke formation, and the most beneficial condition is found at (1) 420 °C for the temperature, (2) 0.15 g/cm3 for the water density, (3) 2 g/g for the H2O/oil ratio, and (4) 1 h for the reaction time. A simultaneous increase of the water density and H2O/oil would significantly improve the cracking behavior and the yield in light oil. Scattered coke particles between 10 and 100 μm were generated from VR cracking, which suggests the dispersion effect of SCW. The infrared spectrum analysis has indicated an increase in the H/C atomic ratio in the liquid product, which implies that hydrogen is generated from the condensation reactions rather than from water because no oxygen-containing group was detected.
Co-reporter:Mei Jin, Zhen-Min Cheng, Yu-Lan Gao, Xiang-Chen Fang
Materials Letters 2009 Volume 63(Issue 23) pp:2055-2058
Publication Date(Web):30 September 2009
DOI:10.1016/j.matlet.2009.06.054
Citric acid complexation under mild condition was proposed to prepare monophasic and well crystallized Mg3(VO4)2 particle to be used as an active catalyst for the oxidative dehydrogenation of cyclohexane to cyclohexene. The catalyst prepared above was characterized by N2-physisorption, X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis. The characterization results displayed that the Mg3(VO4)2 particle was typically 100–160 nm and the specific surface area was 12.0–26.7 m2/g. Moreover, it showed that the purity and the structure of the catalyst were principally subjected to the calcination temperature and the amount of citric acid used in the sol–gel procedure. The Mg3(VO4)2 catalyst calcined at 823 K for 6 h with a molar ratio of (Mg + V):citric acid = 1:1.2 exhibited the best catalytic performance with an excellent thermal stability.
Co-reporter:Zhen-Min Cheng
Frontiers of Chemical Science and Engineering 2009 Volume 3( Issue 1) pp:1
Publication Date(Web):2009 March
DOI:10.1007/s11705-009-0003-1
Co-reporter:Z. M. Zhou;Z. M. Cheng;Y. N. Cao;J. C. Zhang;D. Yang;W. K. Yuan
Chemical Engineering & Technology 2007 Volume 30(Issue 1) pp:
Publication Date(Web):22 DEC 2006
DOI:10.1002/ceat.200600293
The kinetics of the selective hydrogenation of pyrolysis gasoline (pygas) over commercial Pd/Al2O3 catalyst particles were investigated using a stirred semi-batch reactor in the absence of transport limitations. The effects of reaction temperature and pressure on the conversion of styrene, cyclopentadiene, cyclopentene and 1-hexene were obtained over ranges of temperature (313–343 K) and total pressure (2–5 MPa). Competitive hydrogenation between monoolefins and diolefins was extensive, and the reaction rates of diolefins were much faster than those of the monoolefins. A Langmuir-Hinshelwood type model was proposed and successfully fitted to the experimental data. The kinetic and adsorption parameters were estimated by using the fourth-order Runge-Kutta method together with the Levenberg-Marquardt algorithm, which minimized the residual sum of squares between the experimental concentrations and the calculated values. The orders of the estimated activation energies and the adsorption parameters were consistent with the order of the reaction rates of monoolefins and diolefins.
Co-reporter:Si-Cao Wu, Zhen-Min Cheng, Peng Liu, Wen Luo, Zhi-Ming Zhou
Chemical Engineering and Processing: Process Intensification (September 2015) Volume 95() pp:267-275
Publication Date(Web):1 September 2015
DOI:10.1016/j.cep.2015.06.020
•Methanol yields in supercritical n-hexane were much larger than in n-paraffin.•Methanol desorption resistance is gradually reduced with the increasing of n-hexane pressure.•In supercritical n-hexane, a low methanol concentration on the catalyst surface, which is beneficial to methanol synthesis.To experimentally study the effect of supercritical fluid on product desorption, methanol synthesis from CO/CO2/H2 over the Cu/ZnO/Al2O3 catalyst was conducted in the solvents of liquid paraffin, supercritical n-hexane, and their mixture. For the catalyst size of 0.15 mm at which the internal mass transfer resistance was negligible, methanol yields of 10% in n-paraffin and 18% in supercritical n-hexane were obtained respectively. From the conversion rates of CO2 at different n-hexane pressures, the resistance ratio of CO2 hydrogenation to methanol desorption was obtained to vary from 1:2.85 to 1:0.75 when n-hexane partial pressure was increased from 0 to 4.0 MPa. Furthermore, the resistance ratio of the consecutive steps of water–gas shift reaction (WGSR), CO2 hydrogenation and methanol desorption were then evaluated with respect to CO as the reactant. It shows the resistance ratio of the three steps varies from 0.77:1:2.82 to 0.75:1:0.75 when n-hexane partial pressure was increased from 0 to 4.0 MPa.
Co-reporter:Guozhu Liu, Jiang-an Lan, Yanbin Cao, Zibin Huang, Zhenmin Cheng, Zhentao Mi
Chemical Engineering Science (15 July 2009) Volume 64(Issue 14) pp:3329-3343
Publication Date(Web):15 July 2009
DOI:10.1016/j.ces.2009.04.008
Transient behavior of local liquid-holdup of air–kerosene fluids in periodically operated trickle-bed reactor (TBR) is investigated in an acrylic column (140 mm ID and a height of 980 mm) packed with 3.6 mm glass spheres using a nonintrusive technique of electrical capacitance tomography (ECT). Local liquid-holdups determined from ECT images of normalized permittivity are experimentally calibrated under the steady-state operation with that from the classic drainage method. The instantaneous ECT images are captured at several axial positions along the column for the periodically operated TBR with slow-mode. The effect of periodic operation parameters (split, period, and time-average flow rate) on the instantaneous profiles of local liquid-holdup is firstly examined compared with the previous results. Transient variations of radial distributions of liquid and their maldistribution factor are calculated and further analyzed to provide more liquid distribution information under periodic operations.
Co-reporter:Peng Liu; Ming Wang;Zhen-Min Cheng
Journal of Chemical & Engineering Data () pp:
Publication Date(Web):January 30, 2015
DOI:10.1021/je5009558
Ionic liquids (ILs) are emerging as a new family of environmentally benign solvents alternative to the conventional solvents for most catalytic reactions due to their nonvolatility. In such applications, thermal stability and solubility are vital for the selection of a suitable IL solvent for a particular reaction. In this work, the thermal stability of three commonly used imidazolium ILs (bmim[BF4], bmim[PF6], bmim[Tf2N]) was studied with both nonisothermal and isothermal thermogravimetric analysis (TGA). The decomposition kinetics indicated the relative anion stability for imidazolium based ILs was Tf2N > PF6 > BF4. In addition, the solubility data of three organic compounds (methanol, ethyl acetate, and benzene) in ILs were specified by the binary vapor–liquid equilibrium (VLE) at elevated temperatures. The results indicated bmim[Tf2N] was the best solvent for the organics investigated. For the same IL, the solute with a higher polarity tends to possess a lower activity coefficient. The activity coefficients of the organic compounds agreed well with the nonrandom two-liquid (NRTL) model.
