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Numerical simulations and comparative analysis of two- and three-dimensional circulating fluidized bed reactors for CO2 capture
Yefeng Zhou, Yifan Han, Yujian Lu, Hongcun Bai, Xiayi Hu, Xincheng Zhang, Fanghua Xie, Xiao Luo, Jingdai Wang, Yongrong Yang
Chinese Journal of Chemical Engineering    2020, 28 (12): 2955-2967.   DOI: 10.1016/j.cjche.2020.07.003
Abstract302)      PDF(pc) (4949KB)(243)       Save
Carbon dioxide (CO2), the main gas emitted from fossil burning, is the primary contributor to global warming. Circulating fluidized bed reactor (CFBR) is proved as an energy-efficient method for post-combustion CO2 capture. The numerical simulation by computational fluid dynamics (CFD) is believed as a promising tool to study CO2 adsorption process in CFBR. Although three-dimensional (3D) simulations were proved to have better predicting performance with the experimental results, two-dimensional (2D) simulations have been widely reported for qualitative and quantitative studies on gas-solid behavior in CFBR for its higher computational efficiency recently. However, the discrepancies between 2D and 3D simulations have rarely been evaluated by detailed study. Considering that the differences between the 2D and 3D simulations will vary substantially with the changes of independent operating conditions, it is beneficial to lower computational costs to clarify the effects of dimensionality on the numerical CO2 adsorption runs under various operating conditions. In this work, the comparative analysis for CO2 adsorption in 2D and 3D simulations was conducted to enlighten the effects of dimensionality on the hydrodynamics and reaction behaviors, in which the separation rate, species distribution and hydrodynamic characteristics were comparatively studied for both model frames. With both accuracy and computational costs considered, the viable suggestions were provided in selecting appropriate model frame for the studies on optimization of operating conditions, which directly affect the capture and energy efficiencies of cyclic CO2 capture process in CFBR.
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Raman spectroscopy as process analytical tool in downstream processing of biotechnology
Yu Kiat Lin, Hui Yi Leong, Tau Chuan Ling, Dong-Qiang Lin, Shan-Jing Yao
Chinese Journal of Chemical Engineering    2021, 29 (2): 204-211.   DOI: 10.1016/j.cjche.2020.12.008
Abstract234)      PDF(pc) (2514KB)(117)       Save
Downstream processing or product recovery plays a vital role in the development of bioprocesses. To improve the bioprocess efficiency, some unconventional methods are much required. The continuous manufacturing in downstream processing makes the Process Analytical Technologies (PATs) as an important tool. Monitoring and controlling bioprocess are an essential factor for the principles of PAT and quality by design. Spectroscopic methods can apply to monitor multiple analytes in real-time with less sample processing with significant advancements. Raman spectroscopy is an extensively used technique as an analytical and research tool owing to its modest process form, non-destructive, non-invasive optical molecular spectroscopic imaging with computer-based analysis. Generally, its application is essential for the analysis and characterization of biological samples, and it is easy to operate with minimal sample. The innovation on various types of enhanced Raman spectroscopy was designed to enhance the Raman analytical technique. Raman spectroscopy could couple with chemometrics to provide reliable alternative analysis method of downstream process analysis. Thus, this review aims to provide useful insight on the application of Raman spectroscopy for PAT in downstream processing of biotechnology and Raman data analysis in biological fields.
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A comprehensive review of the effect of different kinetic promoters on methane hydrate formation
Ekta Chaturvedi, Sukumar Laik, Ajay Mandal
Chinese Journal of Chemical Engineering    2021, 32 (4): 1-16.   DOI: 10.1016/j.cjche.2020.09.027
Abstract210)      PDF(pc) (4247KB)(227)       Save
Gas hydrates have recently emerged as a better alternative for the production, storage, and transportation of natural gases. However, factors like slow formation rate and limited storage capacity obstruct the possible industrial application of this technique. Different types of promoters and synergists have been developed that can improve the kinetics and storage capacity of gas hydrates. This review focuses on different kinetic promoters and synergists that can be utilized to enhance the storage capacity of hydrates. The main characteristics, structure and the possible limitations of the use of these promoters are likewise portrayed in detail. The relationship between structure and storage capacity of hydrates have also been discussed in the review. Current status of production of gas from hydrates, their restrictions, and future difficulties have additionally been addressed in the ensuing areas of the review.
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Bubble size fractal dimension, gas holdup, and mass transfer in a bubble column with dual internals
Xiao Xu, Junjie Wang, Qiang Yang, Lei Wang, Hao Lu, Honglai Liu, Hualin Wang
Chinese Journal of Chemical Engineering    2020, 28 (12): 2968-2976.   DOI: 10.1016/j.cjche.2020.07.030
Abstract180)      PDF(pc) (1904KB)(223)       Save
As the scale of residual oil treatment increases and cleaner production improves in China, slurry bubble column reactors face many challenges and opportunities for residual oil hydrogenation technology. The internals development is critical to adapt the long-term stable operation. In this paper, the volumetric mass transfer coefficient, gas holdup and bubble size in a gas-liquid up-flow column are studied with two kinds of internals. The gas holdup and volumetric mass transfer coefficient increase by 120% and 42% when the fractal dimension of bubbles increases from 0.56 to 2.56, respectively. The enhanced mass transfer processing may improve the coke suppression ability in the slurry reactor for residual oil treatment. The results can be useful for the exploration of reacting conditions, scale-up strategies, and oil adaptability. This work is valuable for the design of reactor systems and technological processes.
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Ethanol shock enhances the recovery of anthocyanin from lowbush blueberry
Nueraili Maimaiti, Niyazi Aili, M. Kamran Khan, Zhigang Tang, Guoqiang Jiang, Zheng Liu
Chinese Journal of Chemical Engineering    2020, 28 (12): 3096-3102.   DOI: 10.1016/j.cjche.2020.03.036
Abstract172)      PDF(pc) (996KB)(117)       Save
Deactivation of polyphenol oxidase (PPO) in natural products is essential for downstream processing of functional molecules used as food or food additives, particularly those served as antioxidants. In the present work, we identified two proteins with PPO activity from lowbush blueberry using ammonium sulphate precipitation and chromatography procedures. Deactivation of these proteins was studied using aqueous solutions of ethanol of different concentrations. The PPO activity was recovered after ethanol removal for the protein samples previously soaked in a low concentration ethanol solution. A complete and unrecoverable deactivation of the proteins was achieved using ethanol with concentration over 70% (v/v), as manifested by the significant changes in circular dichroism (CD) and fluorescence spectroscopy measurements. Based on these findings, we propose a new extraction process for blueberry anthocyanin, in which an ethanol shock, i.e. soaking blueberry fruit in a 70% (v/v) ethanol solution for 1 h, is implemented before subsequent procedures. This new process increases the anthocyanin yield by 55% in comparison to that without the ethanol shock.
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Insight into solute-solute and solute-solvent interactions of semicarbazide hydrochloride in water and D-glucose/D-sucrose+water solutions at temperatures (293.15 to 318.15) K
Ankita, Dinesh Chand, Anil Kumar Nain
Chinese Journal of Chemical Engineering    2020, 28 (12): 3086-3095.   DOI: 10.1016/j.cjche.2020.07.007
Abstract170)      PDF(pc) (1111KB)(29)       Save
The solute-solute and solute-solvent interactions of drug semicarbazide hydrochloride with carbohydrates (D-glucose/D-sucrose) are investigated by using volumetric, viscometric and acoustic properties. The measurements of the densities ρ, ultrasonic speeds u, and viscosities η. of semicarbazide hydrochloride in 5% and 10% D-glucose/D-sucrose+water (w/w) solutions were carried out at temperatures (293.15-318.15) K and at pressure, p=101 kPa. The apparent molar volumes, Vϕ, limiting apparent molar volumes,Vϕ°, apparent molar compressibilities, Ks, ϕ, limiting apparent molar compressibilities, Ks,ϕ°, partial molar expansibilities, Eϕ°, transfer volumes, Vϕ,tr° and transfer compressibilities, Ks,ϕ,tr° have been calculated from the experimental data. The viscosity data were examined by using the Jones-Dole equation and the viscosity A and B coefficients were evaluated. The results are discussed in terms of solute-solute and solute-solvent interactions in these solutions. The structure making/breaking ability of semicarbazide hydrochloride is examined using the sign of temperature derivative of B-coefficient, dB/dT.
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Perspectives and challenges of hydrogen storage in solid-state hydrides
Zhen Chen, Zhongliang Ma, Jie Zheng, Xingguo Li, Etsuo Akiba, Hai-Wen Li
Chinese Journal of Chemical Engineering    2021, 29 (1): 1-12.   DOI: 10.1016/j.cjche.2020.08.024
Abstract168)      PDF(pc) (2348KB)(267)       Save
Hydrogen has been widely considered as a clean energy carrier that bridges the energy producers and energy consumers in an efficient and safe way for a sustainable society. Hydrogen can be stored in a gas, liquid and solid states and each method has its unique advantage. Though compressed hydrogen and liquefied hydrogen are mature technologies for industrial applications, appropriate measures are necessary to deal with the issues at high pressure up to around 100 MPa and low temperature at around 20 K. Distinct from those technologies, storing hydrogen in solid-state hydrides can realize a more compact and much safer approach that does not require high hydrogen pressure and cryogenic temperature. In this review, we will provide an overview of the major material groups that are capable of absorbing and desorbing hydrogen reversibly. The main features on hydrogen storage properties of each material group are summarized, together with the discussion of the key issues and the guidance of materials design, aiming at providing insights for new material development as well as industrial applications.
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High nitrogen carbon material with rich defects as a highly efficient metal-free catalyst for excellent catalytic performance of acetylene hydrochlorination
Fangjie Lu, Dong Xu, Yusheng Lu, Bin Dai, Mingyuan Zhu
Chinese Journal of Chemical Engineering    2021, 29 (1): 196-203.   DOI: 10.1016/j.cjche.2020.06.008
Abstract168)      PDF(pc) (2121KB)(26)       Save
In this work, we developed a simple strategy to synthesize a carbon material with high nitrogen and rich carbon defects. Our approach polymerized diaminopyridine (DAP) and ammonium persulfate (APS). Following a range of different temperature pyrolysis approaches, the resulting rough surface was shown to exhibit edge defects due to N-doping on graphite carbon. A series of catalysts were evaluated using a variety of characterization techniques and tested for catalytic performance. The catalytic performance of the N-doped carbon material enhanced alongside an increment in carbon defects. The NC-800 catalyst exhibited outstanding catalytic activity and stability in acetylene hydrochlorination (C2H2 GHSV=30 h-1, at 220 ℃, the acetylene conversion rate was 98%), with its stability reaching up to 450 h. Due to NC-800 having a nitrogen content of up to 13.46%, it had the largest specific surface area and a high defect amount, as well as strong C2H2 and HCl adsorption. NC-800 has excellent catalytic activity and stability to reflect its unlimited potential as a carbon material.
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Adsorption of urea, creatinine, and uric acid from three solution types using spherical activated carbon and its recyclability
Tomohito Kameda, Kazuya Horikoshi, Shogo Kumagai, Yuko Saito, Toshiaki Yoshioka
Chinese Journal of Chemical Engineering    2020, 28 (12): 2993-3001.   DOI: 10.1016/j.cjche.2020.03.018
Abstract161)      PDF(pc) (1800KB)(53)       Save
In this paper, we propose that the urinary toxins from the wastewater be adsorbed on an adsorbent such as spherical activated carbon and the latter be regenerated by subjecting it to high temperatures to recycle activated carbon and also to recycle the water used in dialysis. We studied the adsorption of artificial waste dialysate, which is a mixed solution of urea, creatinine, and uric acid, and the separate solutions for each of these and found that their extents of adsorption onto the spherical activated carbon material were nearly identical. The amount of adsorption was approximately 1.4 mg·g-1 for urea, 18 mg·g-1 for creatinine, and 20 mg·g-1 for uric acid. The urea, creatinine, and uric acid adsorbed onto the spherical activated carbon decomposed on heat treatment at 500℃, and the adsorption capacity of the spherical activated carbon was regenerated. Our study successfully demonstrated that the spherical activated carbon can be recycled in the waste dialysate treatment process.
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Experiments and insights of desalination by a freezing/thawing method at low subcooling
Jun Chen, Jianjian Wu, Jiafeng Xu, Qing Yuan, Bin Deng, Changzhong Chen, Zhi Li
Chinese Journal of Chemical Engineering    2020, 28 (12): 3011-3017.   DOI: 10.1016/j.cjche.2020.05.012
Abstract153)      PDF(pc) (1633KB)(49)       Save
Desalination by freezing/thawing method was a very important method to obtain fresh water from sea water. In this work, desalination by freezing/thawing method was conducted with initial sodium chloride of 3.5 wt% in consideration of stirring speed, freezing time and subcooling. The subcooling ranged from 1.2 K to 4 K. The optimum conditions for desalination in this work were stirring speed of 200 r·min-1, freezing time of 120 min, and subcooling of 3 K. The results also showed that sodium chloride cannot be effectively removed by once freezing/thawing process. The maximum removal efficiency of sodium chloride was 64.3%. Two major reasons resulting in the impurity of obtained melted water by freezing/thawing method were proposed. The first reason was the inevitable adhesion of salt solution to the surface of ice, which could be removed easily by distilled water flushing. The second reason was that salt solution was heterogeneously wrapped in the accumulated ice, which was difficult to be removed by distilled water flushing. The liquid flushing method was proposed to verify the conjecture, and the results were in accordance with the two reasons mentioned above. Additional method, such as multiple flushing liquid method, was suggested to be used during the freezing/thawing process for effectively removing sodium chloride, and obtaining fresh water.
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Fouling behavior of poly(vinylidene fluoride) (PVDF) ultrafiltration membrane by polyvinyl alcohol (PVA) and chemical cleaning method
Weijie Ding, Min Chen, Ming Zhou, Zhaoxiang Zhong, Zhaoliang Cui, Weihong Xing
Chinese Journal of Chemical Engineering    2020, 28 (12): 3018-3026.   DOI: 10.1016/j.cjche.2020.05.032
Abstract148)      PDF(pc) (5308KB)(70)       Save
Severe fouling to poly(vinylidene fluoride) (PVDF) membrane is usually caused as filtrating the papermaking wastewater in the ultrafiltration (UF) process. In the paper, fouling behavior and mechanism were investigated, and the low-concentration polyvinyl alcohol (PVA) contained in the sedimentation tank wastewater was found as the main foulant. Consequently, the corresponding cleaning approach was proposed. The experiment and modeling results elaborated that the fouling mode developed from pore blockage to cake layer along with filtration time. Chemical cleaning conditions including the composition and concentration of reagents, cleaning duration and trans-membrane pressure were investigated for their effect on cleaning efficiency. Pure water flux was recovered by over 95% after cleaning the PVDF membrane using the optimal conditions 0.5 wt% NaClO (as oxidant) and 0.1 wt% sodium dodecyl benzene sulfonate (SDBS, as surfactant) at 0.04 MPa for 100 min. In the chemical cleaning method, hypochlorite (ClO-) could first chain-scissor PVA macromolecules to small molecules and SDBS could wrap the fragments in micelles, so that the foulants were removed from the pores and surface of membrane. After eight cycling tests, pure water flux recovery maintained above 95% and the reused membrane was found intact without defects.
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Enhancing hydrothermal stability of framework Al in ZSM-5: From the view on the transformation between P and Al species by solid-state NMR spectroscopy
Lei Han, Ying Ouyang, Enhui Xing, Yibin Luo, Zhijian Da
Chinese Journal of Chemical Engineering    2020, 28 (12): 3052-3060.   DOI: 10.1016/j.cjche.2020.07.039
Abstract147)      PDF(pc) (5579KB)(30)       Save
HZSM-5, with good surface acidity and shape selectivity, was reported as hydrocarbon cracking catalyst for multiple decades, however the hydrothermal stability, especially dealumination of tetrahedrally coordinated framework aluminum (TFAl), has been proved extensively as one of the major challenges during reactionregeneration process. Phosphorus was proposed to stabilize TFAl and indeed it enhanced the hydrothermal stability. Unfortunately, most of the phosphorus species would remain outside of the zeolite pore, mainly as polyphosphate species, and block the micropore severely, with only a limited portion introduced into the channel being able to interact with TFAl. Enlarging the pore size by alkali treatment (desilication) is one of the most convinced methods, but the details about specific P species during alkali treatment and its transformation upon hydrothermal activation is not acquired, thus the mechanism has not been fully understood. Herein, the P-containing species and its transformation during direct P modification and acid/alkali treatment followed by P modification have been studied, and the mechanism on the interaction between P and Al species has been investigated, using several analytical methods, especially Solid-state nuclear magnetic resonance (SSNMR) spectroscopy. It was found that the combination of desilication and subsequent phosphorus modification can enhance the activity of the ZSM-5 for the cracking of ethylcyclohexane, due to the better hydrothermal stabilization of acid sites by the enhanced interaction between phosphorus and TFAl, resulting from the improved accessibility of TFAl because of the successful generation of mesoporosity. Whereas the acid treatment followed by phosphorus modification, with declined retention of crystallinity and P/Al ratio, monoclinic/orthorhombic transition during steam activation, and the failed generation of mesopores, would cause obvious aggregation of the phosphorus species and could not improve the hydrothermal stability of the ZSM-5effectively, and the direct phosphatation turned out much worse. Finally, a specific index that the intensity of the signal at 39 in 27Al MAS NMR spectra before steam activation was proposed as the indicator for determining the efficiency of phosphorus modification. And the proposed mechanism on the interaction between phosphorus and TFAl during the phosphorus modification could also be applicable in other zeolites.
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High permeability poly(vinylidene fluoride) ultrafiltration membrane doped with polydopamine modified TiO2 nanoparticles
Qi Zhang, Zhaoliang Cui, Weixing Li
Chinese Journal of Chemical Engineering    2020, 28 (12): 3152-3158.   DOI: 10.1016/j.cjche.2020.08.026
Abstract145)      PDF(pc) (2118KB)(59)       Save
In order to improve the water permeability of poly(vinylidene fluoride) (PVDF) ultrafiltration (UF) membranes with low molecular weight cut-off (MWCO), polydopamine (PDA) was employed in the membrane preparation process. Owing to its merits of material-independent adhesion, PDA was coated on inorganic particles or added in coagulation bath to tailor the final membrane structure and property. The introduction of PDA broke through the permeability/selectivity trade-off of the PVDF membrane. By adding the PDA coated titanium dioxide (PDA/TiO2) nanoparticles, water flux increased by 287% while MWCO kept similar with the pristine PVDF membrane. Thermodynamics and Kinetics of the PVDF/additives/non-solvent were analyzed and shown that nanoparticles reduced the thermodynamic stability and increased the phase separation speed, and the speed can be adjusted using different nanoparticles. Additionally, X-ray diffraction (XRD) test indicated that PVDF crystalline form changed from α phase to β phase after adding different nanoparticles. Permeability/selectivity trade-off was broken through by DA addition in coagulation bath. Compared with the original PVDF membrane, when the DA concentration of the coagulation bath was 2.0 g·L-1, water flux increased by 312%, and MWCO of the PVDF membrane ranged in 10,000 to 20,000 Da as well as contact angle decreased from 81.4° to 45°.
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Aureobasidium subglaciale F134 is a bifunctional whole-cell biocatalyst for Baeyer-Villiger oxidation or selective carbonyl reduction controllable by temperature
Liqun Shen, Ran Cang, Guang Yang, Anqi Zeng, He Huang, Zhigang Zhang
Chinese Journal of Chemical Engineering    2020, 28 (12): 3044-3051.   DOI: 10.1016/j.cjche.2020.06.041
Abstract144)      PDF(pc) (1578KB)(100)       Save
The microbial production of either ester/lactones or enantio-enriched alcohols through Baeyer-Villiger oxidation or stereoselective reduction of ketones, respectively, is possible by using whole cells of A. subglaciale F134 as a bifunctional biocatalyst. The chemoselective pattern of acetophenone biotransformation catalyzed by these cells can be regulated through reaction temperature, directing the reaction either towards oxidation or reduction products. The Baeyer-Villiger oxidation activity of A. subglaciale F134 whole cells is particularly dependent on reaction temperature. Acetophenone was transformed efficiently to phenol via the primary Baeyer-Villiger product phenyl acetate at 20℃ after 48 h with 100% conversion. In contrast, at 35℃, enantio-enriched (S)-1-phenylethanol was obtained as the sole product with 64% conversion and 89% ee. In addition, A. subglaciale F134 cells also catalyze the selective reduction of various structurally different aldehydes and ketones to alcohols with 40% to 100% yield, indicating broad substrate spectrum and good enantioselectivity in relevant cases. Our study provides a bifunctional biocatalyst system that can be used in Baeyer-Villiger oxidation as well as in asymmetric carbonyl reduction, setting the stage for future work concerning the identification and isolation of the respective enzymes.
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Numerical simulation of a falling droplet surrounding by air under electric field using VOF method: A CFD study
Mirollah Hosseini, Hossein Arasteh, Hamid Hassanzadeh Afrouzi, Davood Toghraie
Chinese Journal of Chemical Engineering    2020, 28 (12): 2977-2984.   DOI: 10.1016/j.cjche.2020.07.048
Abstract137)      PDF(pc) (3553KB)(104)       Save
This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD. The VOF method has been employed to model the two-phase flow of the present study. Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation. Also, the effects of electric potential on the heat transfer coefficient have been examined. The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by, with a subtle deformation to an oblate form. Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificant with time progressing; however, further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon. Ultimately, it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.
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A review on current conventional and biotechnical approaches to enhance biosynthesis of steviol glycosides in Stevia rebaudiana
Samra Basharat, Ziyang Huang, Mengyue Gong, Xueqin Lv, Aqsa Ahmed, Iftikhar Hussain, Jianghua Li, Guocheng Du, Long Liu
Chinese Journal of Chemical Engineering    2021, 29 (2): 92-104.   DOI: 10.1016/j.cjche.2020.10.018
Abstract131)      PDF(pc) (5167KB)(109)       Save
Stevia rebaudiana Bertoni is commonly called stevia and mostly found in the north east regions of South America. It is an herbaceous and shrubby plant belonging to the Asteraceae family. Stevia is considered as a natural sweetener and a commercially important plant worldwide. The leaves of S. rebaudiana contain steviol glycosides (SGs) which are highly potent and non-caloric sweeteners. The sweetening property of S. rebaudiana is contributed to the presence of these high potency, calorie free steviol glycosides. SGs are considerably suitable for replacing sucrose and other artificial sweetening agents which are used in different industries and pharmaceuticals. SGs amount in the plant mostly varies from 8% to 10%, and the enhancement of SGs is always in demand. These glycosides have the potential to become healthier alternatives to other table sugars for having desirable taste and zero calories. SGs are almost 300 times sweeter than sucrose. Being used as alternative sugar intensifier the commercial value of this plant in biopharmaceutical, food and beverages industries and in international market is increasing day by day. SGs have made stevia an important part of the medicinal world as well as the food and beverage industry, but the limited production of plant material is not fulfilling the higher global market demand. Therefore, researchers are working worldwide to increase the production of important SGs through the intercession of different biotechnological approaches in S. rebaudiana. This review aims to describe the emerging biotechnological strategies and approaches to understand, stimulate and enhance biosynthesis of secondary metabolites in stevia. Conventional and biotechnological methods for the production of steviol glycosides have been briefly reviewed and discussed.
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Improvement of porous polyvinylidene fluoride-co-hexafluropropylene hollow fiber membranes for sweeping gas membrane distillation of ethylene glycol solution
M. Ajdar, A. Azdarpour, A. Mansourizadeh, B. Honarvar
Chinese Journal of Chemical Engineering    2020, 28 (12): 3002-3010.   DOI: 10.1016/j.cjche.2020.05.004
Abstract128)      PDF(pc) (1997KB)(46)       Save
Porous polyvinylidene fluoride-co-hexafluropropylene (PVDF-HFP) hollow fiber membranes were fabricated through a wet spinning process. In order to improve the membrane structure, composition of the polymer solution was adjusted by studying ternary phase diagrams of polymer/solvent/non-solvent. The prepared membranes were used for sweeping gas membrane distillation (SGMD) of 20 wt% ethylene glycol (EG) aqueous solution. The membranes were characterized by different tests such as N2 permeation, overall porosity, critical water entry pressure (CEPw), water contact angle and collapsing pressure. From FESEM examination, addition of 3 wt% glycerol in the PVDF-HFP solution, produced membranes with smaller finger-likes cavities, higher surface porosity and smaller pore sizes. Increasing the polymer concentration up to 21 wt% resulted in a dense spongy structure which could significantly reduce the N2 permeance. The membrane prepared by 3 wt% glycerol and 17 wt% polymer demonstrated an improved structure with mean pore size of 18 nm and a high surface porosity of 872 m-1. CEPw of 350 kPa and overall porosity of 84% were also obtained for the improved membrane. Collapsing pressure of the membranes relatively improved by increasing the polymer concentration. From the SGMD test, the developed membrane represented a maximum permeate flux of 28 kg·m-2·h-1 which is almost 19% higher than the flux of plain membrane. During 120 h of a long-term SGMD operation, a gradual flux reduction of 30% was noticed. In addition, EG rejection reduced from 100% to around 99.5% during 120 h of the operation.
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Effect of elevated temperature and silica sand particle size on minimum fluidization velocity in an atmospheric bubbling fluidized bed
A. Al-Farraji, Haidar Taofeeq
Chinese Journal of Chemical Engineering    2020, 28 (12): 2985-2992.   DOI: 10.1016/j.cjche.2020.07.054
Abstract127)      PDF(pc) (1451KB)(67)       Save
The impact of temperature and particle size on minimum fluidizing velocity was studied and analyzed in a small pilot scale of bubbling fluidized bed reactor. This study was devoted to providing some data about fluidization to the literature under high temperature conditions. The experiments were carried out to evaluate the minimum fluidizing velocity over a vast range of temperature levels from 20℃ to 850℃ using silica sand with a particle size of 300-425 μm, 425-500 μm, 500-600 μm, and 600-710 μm. Furthermore, the variation in the minimum fluidized voidage was determined experimentally at the same conditions. The experimental data revealed that the Umf directly varied with particle size and inversely with temperature, while εmf increases slightly with temperature based on the measurements of height at incipient fluidization. However, for all particle sizes used in this test, temperatures above 700℃ has a marginal effect on Umf. The results were compared with many empirical equations, and it was found that the experimental result is still in an acceptable range of empirical equations used. In which, our findings are not well predicted by the widely accepted correlations reported in the literature. Therefore, a new predicted equation has been developed that also accounts for the affecting of mean particle size in addition to other parameters. A good mean relative deviation of 5.473% between the experimental data and the predicted values was estimated from the correlation of the effective dimensionless group. Furthermore, the experimental work revealed that the minimum fluidizing velocity was not affected by the height of the bed even at high temperature.
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High adsorption of Cd (II) by modification of synthetic zeolites Y, A and mordenite with thiourea
Shaoqing Zhang, Tianming Lv, Yang Mu, Jiqi Zheng, Changgong Meng
Chinese Journal of Chemical Engineering    2020, 28 (12): 3117-3125.   DOI: 10.1016/j.cjche.2020.07.046
Abstract125)      PDF(pc) (5210KB)(102)       Save
Zeolites Y, A and mordenite (ZY, ZA and ZM) were obtained from diatomite in a template-free system, and the products were modified by thiourea (TU). Characterization studies results indicated that the TU molecules were loaded onto the exterior surfaces of the synthetic zeolites as well as the channels. Elemental analysis and energy-dispersive X-ray spectrometer proved that the TU molecules loaded on to ZA were more than ZY and ZM. Removal of Cd(II) was investigated, and it was found that the modified zeolites have higher removal capacity, modified ZA is especially noticeable. In the adsorption experiments, the effects of various parameters such as sorbent content, contact time, concentration of cadmium solution, pH, selectivity and regeneration were discussed. At the best removal efficiency by modified zeolites, the maximum adsorption capacity is 94.3 mg·g-1, 103.2 mg·g-1 and 89.7 mg·g-1 at 25℃, respectively. The sorbents show good efficiency for the removal of Cd(II) in the presence of different multivalent cations and have good regeneration effect. For the modified samples, removal experiments take place via ion exchange and complexation processes.
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Density functional theory and kinetic Monte Carlo simulation study the strong metal-support interaction of dry reforming of methane reaction over Ni based catalysts
Xueyan Zou, Xiaodong Li, Xiaoyu Gao, Zhihua Gao, Zhijun Zuo, Wei Huang
Chinese Journal of Chemical Engineering    2021, 29 (1): 176-182.   DOI: 10.1016/j.cjche.2020.05.009
Abstract124)      PDF(pc) (1839KB)(70)       Save
Oxide supports modify electronic structures of supported metal nanoparticles, and then affect the catalytic activity associated with the so-called strong metal-support interaction (SMSI). We herein report the strong influence of SMSI employing Ni4/α-MoC(111) and defective Ni4/MgO(100) catalysts used for dry reforming of methane (DRM, CO2 + CH4 → 2CO + 2H2) by using density functional theory (DFT) and kinetic Monte Carlo simulation (KMC). The results show that α-MoC(111) and MgO(100) surface have converse electron and structural effect for Ni4 cluster. The electrons transfer from α-MoC(111) surface to Ni atoms, but electrons transfer from Ni atoms to MgO(100) surface; an extensive tensile strain is greatly released in the Ni lattice by MgO, but the extensive tensile strain is introduced in the Ni lattice by α-MoC. As a result, although both catalysts show good stability, H2/CO ratio on Ni4/α-MoC(111) is obviously larger than that on Ni4/MgO(100). The result shows that Ni/α-MoC is a good catalyst for DRM reaction comparing with Ni/MgO catalyst.
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