Table of Content

28 October 2025, Volume 25 Issue 10

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Contents

Cover and Contents

The Chinese Journal of Process Engineering. 2025, 25(10):  0. 

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Review

Progress on oxygen-tolerant carbon monoxide dehydrogenase

Zhiwen ZHANG Guosheng WANG Xiaowei PENG

The Chinese Journal of Process Engineering. 2025, 25(10):  995-1007.  DOI: 10.12034/j.issn.1009-606X.224389

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Oxygen-resistant carbon monoxide dehydrogenases (CODHs) fall into two categories: those derived from aerobic CO-metabolizing bacteria and the engineered oxygen-resistant variants from anaerobic CO-metabolizing bacteria. The former, containing molybdenum (Mo) and copper (Cu) cofactors, are termed as Mo/Cu-CODHs. They specifically catalyze the oxidation of carbon monoxide (CO) to carbon dioxide (CO2), generating two protons (H+) and two electrons (e-) in the process, and are insensitive to O2. The latter, Ni/Fe-CODHs, featuring nickel (Ni) and iron (Fe) cofactors, originate from anaerobic CO-metabolizing bacteria. Most Ni/Fe-CODHs are O2-sensitive, though some variants exhibit limited O2 tolerance at the expense of reduced activity. Nevertheless, high-activity Ni/Fe-CODHs can be engineered for oxygen tolerance. Unaffected by O2 concentration, oxygen-tolerant CODHs hold significant application potential in biomanufacturing and electrochemistry under aerobic conditions. This work first reviews the structure, function, and catalytic mechanisms of Mo/Cu-CODHs. Mo/Cu-CODHs comprise three subunits (coxL, coxS, coxM), with CO oxidation primarily occurring at the active site of the L subunit. The catalytic mechanism of CO oxidation by this enzyme has been largely elucidated: CO initially binds to Cu, followed by nucleophilic attack by the O ligand of Mo=O to form five-membered ring intermediates. A sequence of subsequent intermediates, including thiocyclic carbonate, then ensues, ultimately leading to CO2 release and completion of the catalytic cycle. Additionally, this work explores the factors influencing the oxygen tolerance of Ni/Fe-CODHs and methods to enhance this trait. It also summarizes progress in the in vitro heterologous expression and purification of oxygen-tolerant CODHs, reviews their applications in the bioconversion of synthetic chemicals and in vitro catalysis, and provides an outlook on future development trends. These contents will offer references for further research and development of oxygen-tolerant CODHs.

The application analysis of mixed matrix membranes in membrane-based carbon capture technology

Yu QIN Yuyan HAI Rihua XIONG

The Chinese Journal of Process Engineering. 2025, 25(10):  1008-1020.  DOI: 10.12034/j.issn.1009-606X.224358

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In the context of "carbon peak and carbon neutrality", carbon capture, utilization and storage (CCUS) technology is becoming increasingly important. The study of CO2 separation has attracted high-profile as it is the key link in the CCUS process. Among various separation methods, the membrane separation technology stands out with its advantages of low energy and continuous operation. This work reviews the current research status of various CO2 separation membranes for membrane-based carbon capture both domestically and overseas. It emphatically introduces the research progress regarding the CO2 gas permeation and separation performance, as well as the optimized preparation methods, of mixed matrix membrane. The CO2 permeance of most mixed matrix membranes ranges from 0 to 1000 Barrer, and the CO2/N2 separation coefficient is between 20 and 120. In addition, it is proposed that the preparation method of mixed matrix membrane can be optimized by using modified crystalline porous fillers or directly adopting amorphous porous fillers, thereby improving the compatibility between polymer substrates and porous fillers. Meanwhile, from the perspective of the actual needs of subsequent industrial applications, this review analyzes the advantages and disadvantages of various CO2 separation membrane modules, and proposes that the spiral-wound membrane module is the most suitable for the field of membrane-based carbon capture. Mixed matrix membrane exhibit excellent mechanical and thermal stability, outstanding resistance to plasticization, and excellent CO2 permeation and separation performance. Therefore, they have the greatest potential to be fabricated into spiral-wound membrane modules and applied in the field of membrane-based carbon capture in the future. Additionally, it can be concluded that with the current performance of mixed matrix membrane and suitable capture process conditions (e.g., the addition of purge gas), the CO2 capture cost can be controlled within 23 USD/t CO2. From this perspective, the application of mixed matrix membranes in membrane-based carbon capture technology is considered feasible. This work aims to provide guidance for the widespread application of CO2 membrane separation in CCUS technology as soon as possible.

Research Paper

Study on optimal bending angle of ear plate in wafer static mixer

Zerun SONG Yipeng JI Jiaqing CHEN Xiujun WANG Chao HUA Xiangyu CHEN Chunyao WANG

The Chinese Journal of Process Engineering. 2025, 25(10):  1021-1029.  DOI: 10.12034/j.issn.1009-606X.224391

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In the domain of industrial mixing technology, the wafer static mixer, characterized by its distinctive bent ear plate mixing element, has drawn considerable attention. It presents remarkable structural benefits over traditional static mixers, such as a more straightforward design and reduced pressure drop. Notably, with the dispersed phase inlet positioned behind the ear plate, it effectively precludes pipeline clogging when dealing with high-viscosity media post-mixing reactions, which is a common issue in many industrial applications. The bending angle of the ear plate, being the solitary mixing element in this mixer, is a critical parameter that directly governs the hydraulic environment and, consequently, the mixing efficacy. To meticulously explore this influence, a specialized model is devised, wherein only the bending angle varied while keeping the flow area constant. By leveraging advanced numerical simulation methodologies and conducting meticulous visual experiments, an in-depth analysis is conducted to unravel the characteristics of the outlet flow field and the homogeneity of mixing. The research outcomes demonstrated that a 10° bending angle is pivotal in attenuating the Coanda effect, leading to the most symmetrical flow field. This optimal configuration culminates in superior mixing performance, as manifested by excellent mixing over a relatively short distance and accompanied by a conspicuously low pressure drop. The indoor experimental results not only validate the numerical simulation findings but also provide practical evidence of the mixer's behavior in real-world scenarios. In summary, the insights gleaned from this study offer substantial theoretical underpinnings for the optimization and engineering implementation of wafer static mixers. They serve as a scientific bedrock for the design and development of highly efficient static mixers in the chemical engineering and allied industries, thereby fueling innovation and advancements in mixing technologies and process optimization strategies. This research contributes to a deeper understanding of the complex fluid dynamics within the mixer and paves the way for more efficient and reliable industrial mixing processes.

BTX yield prediction method study based on pyramid attention mechanism integrating gated recurrent unit and its application

Yongming HAN Yashuai SUN Qingxu NI Feng PAN Qingfeng SUN Lei TAN Xuan HU Zhiqiang GENG

The Chinese Journal of Process Engineering. 2025, 25(10):  1030-1038.  DOI: 10.12034/j.issn.1009-606X.225005

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Aiming to address the challenge of low model accuracy in traditional benzene-toluene-xylene (BTX) yield prediction, this work proposes a novel prediction approach based on a pyramid attention mechanism (PAM) combined with a gated recurrent unit (GRU), referred to as the PAM-GRU model. The PAM of the proposed method can enable the construction of a hierarchical attention structure for multi-feature sequential data, allowing for the extraction of spatial features. In parallel, the GRU is utilized to capture dynamic temporal information within the time-series data through its recurrent structure, enabling the proposed prediction method to uncover underlying temporal variation patterns. By seamlessly integrating both spatial and temporal features, the PAM-GRU method achieves a more accurate and reliable prediction. Finally, the proposed method is applied to a real-world continuous reforming chemical production process, and the proposed model performance is evaluated using various metrics. The proposed PAM-GRU model is compared with models such as the recurrent neural networks (RNN), the long short-term memory networks (LSTM), the gated recurrent units (GRU), the LSTM based on attention mechanisms (Attention-LSTM), and the GRU based on attention mechanisms (Attention-GRU) in terms of four indicators: mean absolute percentage error (MAPE), root mean square error (RMSE), mean absolute error (MAE), and coefficient of determination (R2). The results show that the proposed PAM-GRU model can effectively integrate the spatial and temporal features in the continuous reforming production process, achieving efficient and accurate prediction of the BTX yield. In addition, to cope with the complex production environment, a robustness test is added in the proposed model. The results show that the proposed model has strong robustness and can effectively suppress the interference of sudden noise.

Design and evaluation of conventional and series temperature swing adsorption carbon capture processes

Shuo DENG Dongliang QIU Liugan ZHANG Longxiang CHEN

The Chinese Journal of Process Engineering. 2025, 25(10):  1039-1048.  DOI: 10.12034/j.issn.1009-606X.225021

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In recent years, the saturated adsorption capacity of novel adsorbents has been continuously enhanced. However, due to limitations in process design, the actual adsorption capacity of adsorbents during cyclic operation remains significantly lower than their saturated value. To establish an accurate adsorption bed model and investigate the complex heat and mass transfer mechanisms involved in the adsorption process, 13X molecular sieves were employed to conduct adsorption experiments on CO2/N2 gas mixtures. Through static adsorption experiments and dynamic breakthrough experiments, the competitive adsorption isotherms as well as the mass and heat transfer coefficients of the adsorption process were determined. Based on these fundamental data, a temperature swing adsorption (TSA) system model was successfully constructed, which accurately reproduced the breakthrough curves and temperature distributions under three distinct operating conditions. This adsorption bed model exhibited excellent performance in reflecting real-world adsorption behavior, particularly in scenarios involving low gas concentrations. The analysis of the loading condition of the adsorption bed indicated that the adsorbent utilization ratio (AUR) of the conventional TSA process was only 58.13%, with a significant amount of adsorbent not being fully utilized. Therefore, a novel multi-bed series TSA adsorption process was designed in this study. By switching different adsorption beds between the upstream bed and the downstream bed, the AUR was increased to 85.50%. Concurrently, the product purity increased from 90.74% (conventional TSA process) to 94.21%, and the energy consumption decreased from 6.48 MJ/kg CO2 to 4.79 MJ/kg CO2. However, the series process had a small amount of CO2 leakage during the adsorption stage, resulting in a gas recovery rate of 87.92%. In addition, although the conventional TSA process can achieve the similar AUR as the series process by extending the adsorption time, its recovery was only 71.80%, which was 16.12 percentage points lower than that of the novel series process.

Research on transformation and selective coordination leaching of titanium from high-iron red mud generated in the reductive Bayer process

Longkai LIU Taotao CAI Shili ZHENG Yilin WANG Qiusheng ZHOU Pengcheng QU Xiaohua YU Ying ZHANG

The Chinese Journal of Process Engineering. 2025, 25(10):  1049-1063.  DOI: 10.12034/j.issn.1009-606X.225024

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The reductive Bayer process creates favorable conditions for the synergistic smelting of aluminum and iron. However, the high-iron red mud generated by this process generally contains impurity elements such as Al, Si, and Ti, which are detrimental to iron smelting. Isomorphous substitution easily occurs between Ti4+ and Fe3+, which leads to significant difficulties in Ti-Fe separation and becomes a major challenge hindering the utilization of high-iron red mud as a raw material for ironmaking. In this study, targeting the high-iron red mud from the reductive Bayer process provided by a certain smelting plant, based on the occurrence characteristics of impurities such as aluminum, silicon, and titanium, technical research was carried out on the selective dissolution and removal of sodium silica slag in the high-iron red mud by weak acid, as well as the reduction and transformation of titanium-bearing hematite and the coordination dissolution of titanium. Under the optimized acid dissolution conditions, aluminum and silicon in the high-iron red mud were significantly removed. The dissolution rate of Si was approximately 80%, and the dissolution rate of Al was about 70%~80%. When the acid-dissolved red mud was jointly reduced and transformed by the titanium transformation agent of sodium alkali and iron powder, the coordination dissolution rate of titanium reached 36.7%. When the acid-dissolved red mud was jointly reduced and transformed by the titanium transformation agent of sodium alkali and hydrogen, the coordination dissolution rate of titanium reached 70%~80%. Additionally, it was observed that the wuestite phase and metallic iron phase, formed after the reductive transformation of acid-leached red mud, could be further converted into the siderite phase in the potassium bicarbonate solution used for coordinated titanium leaching. This study has opened up new ideas for the separation of titanium and iron when they are of isomorphous occurrence.

Preparation of α phase silicon nitride powder by molten salt pyrolysis

Fan YANG Zhao HAN Pengfei LIU Jie LI

The Chinese Journal of Process Engineering. 2025, 25(10):  1064-1074.  DOI: 10.12034/j.issn.1009-606X.225050

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With the continuous expansion of silicon nitride (Si3N4) ceramics in application fields such as aerospace, electronic devices, and high-temperature structural materials, the demand for high-quality Si3N4 powder has been increasingly growing. However, the traditional pyrolysis of silicon imine [Si(NH)2] usually faces the problems of high crystallization temperature and whisker formation, which affects the quality and application performance of the final Si3N4 powder. The innovation of this study is to use molten salt environment to reduce the crystallization and phase transition temperature of Si(NH)2, control particle size and inhibit the formation of irregular whiskers. In this study, α-Si3N4 powder with regular morphology is prepared by molten salt pyrolysis method, using Si(NH)2 as raw material and sodium chloride (NaCl) as reactive medium. Meanwhile, the effects of pyrolysis temperature and the ratio of silicon to salt on the phase composition, particle size distribution, and microstructure of the prepared powder are investigated. The results indicate that NaCl molten salt can significantly lower the crystallization and phase transition temperatures of Si(NH)2. Under the condition of holding at 1400℃ for 2 h, Si(NH)2 is completely converted into Si3N4 powder with high crystallinity and regular morphology. The content of α-Si3N4 is 75.52wt%, and the average particle size is 905.40 nm. In addition, with the increase of NaCl content, the α-Si3N4 content in the powder first decreases and then increases, whereas the powder particle size gradually reduces. This method effectively inhibits the formation of whiskers during the pyrolysis of Si(NH)2 and lowers the crystallization temperature of α-Si3N4 powder. Mechanistic analysis reveals that in the liquid-phase environment provided by the molten salt, Si(NH)2 promotes the growth of α-Si3N4 particles through a dissolution-precipitation mechanism. Overall, This method provides a new strategy for preparing high-quality Si3N4 powder with regular morphology and exhibits broad application potential.

Optimization of the synthesis method and process of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine

Siqi FAN Guilong WANG Xin FENG Xiaoxia DUAN Jie CHEN Jun DU Chao YANG Falu ZHAN

The Chinese Journal of Process Engineering. 2025, 25(10):  1075-1087.  DOI: 10.12034/j.issn.1009-606X.225014

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3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine (DHBT) serves as a precursor for the synthesis of energetic tetrazine materials. In this study, DHBT was synthesized via the cyclization of prepared triaminoguanidine hydrochloride with acetylacetone. A newly established high-performance liquid chromatography (HPLC) method was applied to quantitatively analyze the reaction kinetics, while an intermediate, 1,1'-(3,5-dimethyl-pyrazol-1-yl)-enaminohydrazine, was characterized. Based on this intermediate, the cyclization mechanism of DHBT was proposed. Subsequently, the reaction conditions for DHBT synthesis in a batch reactor were optimized, with the effects of reactor type, stirring method, reactant concentration ratio, reaction temperature, and solvents on DHBT yield investigated. The results showed that the optimal conditions were as follows: a 250 mL glass-jacketed kettle equipped with internal baffles, an inclined blade stirrer operated at 400 r/min, deionized water (5.0 times the mass of the raw material), acetylacetone (2.0 times the molar amount of the raw material), a reaction temperature of 70℃, and a reaction time of 2 h. Under these optimal conditions, the actual yield of DHBT reached 77.5% with a purity of 96.3%. A scale-up synthesis of DHBT (480 g scale) was further conducted under the optimized conditions, achieving a yield of 72.9%. Kinetic studies revealed that the rate-determining step of the reaction was the conversion of the intermediate to the final product. For the cyclization process starting from the intermediate (at 70~90℃), the reaction followed second-order kinetics, with an apparent activation energy (E?) of 112.66 kJ/mol, a pre-exponential factor (A) of 1.64×1018 mol/(L?min), and a linear correlation coefficient (R2) of 0.9967. Additionally, calorimetric tests of the reaction process were performed using a reaction calorimeter, and the enthalpy change of the chemical reaction (??H?) was determined to be 364.03 kJ/mol.

Experimental study on the scale-up effect of hydrate formation in the active ice

Juanjuan LI Peng XIAO Kang LIU Boxu YANG Meixia QI Yujie ZHU Guangjin CHEN Changyu SUN

The Chinese Journal of Process Engineering. 2025, 25(10):  1088-1095.  DOI: 10.12034/j.issn.1009-606X.224367

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Gas hydrates represent a promising technology for gas storage and transportation. However, their practical application is constrained by the slow formation kinetics of hydrate formation. "Active ice"—synthesized by uniformly dispersing hydrate kinetic promoters into ice powder—has been demonstrated to significantly accelerate gas hydrate formation, thereby offering an effective solution to the kinetic bottleneck in hydrate-based gas storage and transportation. In order to investigate the hydrate formation kinetics of active ice under large-scale application conditions, this study prepared active ice using natural snow as the raw material and employed it in kg-scale hydrate formation experiments. The effects of the concentration of kinetic promoters, reaction pressure, active ice temperature, and packing density on methane hydrate formation kinetics were examined. Additionally, the recycling performance of the active ice were evaluated. The results indicated that active ice derived from natural snow effectively promoted methane hydrate formation. Specifically, when the concentration of the kinetic promoter (sodium dodecyl sulfate, SDS) exceeded 0.25wt%, and the active ice temperature was maintained above 269.15 K, methane hydrate formation was nearly completed within 6 min, achieving a maximum methane uptake of 177.00. The methane uptake increased slightly with rising reaction pressure. Furthermore, by adjusting the packing density of the active ice bed, a maximum apparent gas storage density of 118.90 was attained. In kg-scale hydrate formation and dissociation experiments, the active ice exhibited excellent cycling performance. Collectively, the results of the kg-scale hydrate formation suggested that active ice does not induce significant scale-up effects during hydrate formation, and has essentially met the performance requirements for practical application in hydrate-based gas storage and transportation.

Preparation of iron and nitrogen co-doped biochar activated by sodium bicarbonate and its efficient adsorption for bisphenol A from water

Zichen QIN Yuan QIN Yuanding SHI Hao ZHANG Yan LI Yuntao ZHU Lei DING

The Chinese Journal of Process Engineering. 2025, 25(10):  1096-1112.  DOI: 10.12034/j.issn.1009-606X.225059

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Iron and nitrogen co-doped modified biochar (K2FeO4@NSBC) was prepared by a one-step pyrolysis method using loofah sponge as the carbon source, sodium bicarbonate as the activator, potassium ferrate and urea as the iron and nitrogen sources, respectively. The adsorption performances and mechanisms of K2FeO4@NSBC for bisphenol A (BPA) from water were studied. Under the conditions of a K2FeO4∶NaHCO3∶CH4N2O∶loofah sponge (mass ratio) of 0.1∶0.5∶0.5∶1 and pyrolysis temperature of 800℃, the prepared K2FeO4@NSBC exhibited a large specific surface area (864.83 m2/g) and pore volume (0.54 cm3/g). The adsorption equilibrium capacity (312.58 mg/g) of K2FeO4@NSBC for BPA at 298 K was much higher than that of the original biochar (7.00 mg/g). The influence of solution pH and exogenous organic matter (humic acid) on BPA removal was found to be minimal, indicating that K2FeO4@NSBC can effectively adsorb BPA across a range of environmental conditions. However, the presence of exogenous CO_3^(2-) ions in the solution significantly inhibited BPA removal. The adsorption of BPA by K2FeO4@NSBC followed a pseudo-second-order kinetic model, and the Sips model described the adsorption equilibrium well, suggesting that the adsorption process was governed not only by surface adsorption but also by a heterogeneous distribution of adsorption sites. Additionally, the adsorption process was spontaneous, endothermic, and disorder-enhancing. K2FeO4@NSBC exhibited excellent regeneration and reuse performance, maintaining high BPA removal efficiency after multiple cycles. The main mechanisms for BPA removal by K2FeO4@NSBC were pore filling, hydrophobic interactions, and π-π interactions, with the incorporation of Fe and N playing important roles in the adsorption process. The Fe component could contribute to the formation of active sites, while the N doping could increase the surface charge and improve the interaction between the biochar and BPA molecules. This research provides an environmentally friendly and economically feasible solution for the removal of BPA from water using biochar. The excellent adsorption capacity, stability, and reusability of K2FeO4@NSBC make it a promising candidate for practical applications in water treatment.