Table of Content

28 November 2025, Volume 25 Issue 11

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Contents

Cover and Contents

The Chinese Journal of Process Engineering. 2025, 25(11):  0. 

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Review

Recent advances in transition metal based catalysts for seawater electrolysis

Qian YAN Bingxu CHEN Zhonghui HU Sida LI Jia YU Yuanqing WANG

The Chinese Journal of Process Engineering. 2025, 25(11):  1113-1129.  DOI: 10.12034/j.issn.1009-606X.225067

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In the field of sustainable energy technology, water electrolysis for hydrogen production plays a crucial role in electrochemical energy conversion, with its technological advancements holding significant importance for achieving the carbon peaking and carbon neutrality goals. The water electrolysis process comprises two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Compared to HER, OER involves a four-electron transfer process (4OH-→O2+2H2O+4e-), characterized by a higher reaction energy barrier. Its sluggish kinetic substantially reduces the overall efficiency of water electrolysis, making OER the primary research focus. Given the scarcity of freshwater resources, seawater, an abundant alternative, offers promising prospects for large-scale hydrogen production. However, direct seawater electrolysis faces multiple technical challenges: (1) high chloride ion concentrations trigger competing chloride oxidation reactions (ClOR), which not only reduce current efficiency but also corrode electrodes and catalysts; (2) gas bubbles generated on electrode surfaces cover active sites and increase interfacial impedance; (3) precipitation of Mg2+ and Ca2+ ions from seawater blocks active sites and degrades catalytic performance. These issues collectively constrain the activity, selectivity, and stability of catalysts in seawater electrolysis systems. This review explores the key challenges of anode catalysts for seawater electrolysis and highlights various catalyst design strategies, such as composition modulation, geometric structure optimization, selective permeation layer design and composite material engineering, with a focus on transition metal oxide catalysts explored in recent years. Future research directions emphasize the integration of theoretical calculations with experimental validation, combined with in-situ characterization and artificial intelligence techniques to identify active sites. Such fundamental insights will provide a robust theoretical foundation for designing high-performance catalysts with superior activity, selectivity, and long-term stability under practical seawater electrolysis conditions.

Research Paper

Two-fluid model simulation study of gas-solid flow characteristics in a diameter-transformed fast fluidized bed

Xiangyang GONG Lei YANG Shi SHOU Xiangyu ZHAO Jianhong GONG Chao YANG

The Chinese Journal of Process Engineering. 2025, 25(11):  1130-1142.  DOI: 10.12034/j.issn.1009-606X.225052

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Catalytic cracking reactors serve as crucial facilities for enhancing heavy oil utilization through light olefin production, where gas-solid hydrodynamics significantly influence reaction efficiency. This study investigated complex inter-phase and intra-phase interactions and flow behaviors in a diameter-transformed fast fluidized bed catalytic cracking reactor using a two-fluid model approach. The numerical model was validated against experimental measurements, confirming its accuracy in capturing gas-solid flow characteristics. Systematic analyses were conducted to examine the effects of nozzle gas velocity and structural parameters on particle dynamics. Results demonstrate that the increased gas velocity effectively mitigates particle accumulation in the sudden expansion zone, promoting more uniform solid distribution within the reactor. However, gas velocity variations showed negligible impact on particle concentration profiles in upper regions. Structural optimization revealed that implementing a conical transition with specific inclination angles between the upper and lower sections of the gradual expansion zone enhanced particle distribution uniformity and gas-solid mixing efficiency. These improvements were particularly conducive to optimizing catalytic cracking processes. These findings provided theoretical guidance for reactor design aiming at enhancing fluidization quality and process performance.

Optimization design and coupling study of a double absorption heat transformer system driven by waste heat from blast furnace slag flushing water

Zhijia HUANG Yao HU Feng SUN Yang ZHANG Yuehong LU Jun WANG

The Chinese Journal of Process Engineering. 2025, 25(11):  1143-1155.  DOI: 10.12034/j.issn.1009-606X.225023

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To reduce the regeneration energy consumption of the blast furnace gas carbon capture system while rationally utilizing the waste heat of slag flushing water. This work establishes a thermodynamic model of a double absorption heat transformer. The effects of evaporation temperature, condensation temperature, absorption-evaporation temperature, and absorption temperature on system performance are investigated and analyzed. The genetic algorithm is employed for model optimization calculations, and conduct a coupling study with the blast furnace gas carbon capture system, and analyze the influence of the temperature fluctuation of the slag flushing water on the coupled system. The research results indicate that the maximum COP of the system is 0.3168 when the evaporation temperature is 75℃, 0.3032 when the condensation temperature is 20℃, 0.3116 when the absorption-evaporation temperature is 103℃, and 0.3015 when the absorption temperature is 130℃. After optimization, the heat exchange area of the system is reduced by 14.8%, and the area-to-performance ratio is improved by 16.5%. When the temperature of the slag flushing water rises from 75℃ to 85℃, the heat output of the heat pump increases by 18.6%, and the energy consumption of carbon capture decreases by approximately 10.3%. The investment payback period of the system is 3.48 years. This research broadens the application scope of double absorption heat transformer in the metallurgical industry and provides a method for the optimal design of double absorption heat transformer. It is of great significance for promoting energy conservation, emission reduction, and sustainable development in the metallurgical industry.

Work mass screening and system simulation of high temperature steam heat pump for industrial waste heat recovery

Jianhui LI Jun WEI Guanjia ZHAO

The Chinese Journal of Process Engineering. 2025, 25(11):  1156-1167.  DOI: 10.12034/j.issn.1009-606X.225058

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A significant amount of low-grade waste heat is discharged during industrial production processes. Utilizing heat pump technology to upgrade and reuse this waste heat can effectively reduce carbon emissions associated with industrial operations. When recovering industrial waste heat using heat pump systems, considerable temperature variations occur at both the heat source and heat sink sides, leading to pronounced irreversible losses. Non-azeotropic refrigerant mixtures exhibit a temperature glide during phase change, which enables better thermal matching within heat exchangers and consequently reduces irreversibilities in the heat transfer process. This study analyzes multiple refrigerants based on the characteristics of non-azeotropic mixtures and proposes a novel blend tailored for industrial waste heat recovery, guided by the principle of complementary advantages. Furthermore, a simulation model of a centrifugal high temperature steam heat pump for large-scale industrial waste heat recovery is established. The system performance of the selected non-azeotropic refrigerant mixture is compared with that of the conventional refrigerant R245fa under various conditions, including different condensation temperatures, waste heat flow rates, and heat source temperatures. The results show that the selected non-azeotropic blend R600a/R1234ze(Z)/R1336mzz(Z) in a molar ratio of 30%/20%/50% exhibits superior thermodynamic performance compared to R245fa. Under constant heat source conditions, the optimal condensation temperatures for R245fa and the mixed refrigerant are 107.5℃ and 110℃, respectively, with corresponding system coefficients of performance (COPh) of 3.36 and 3.94. At a condensation temperature of 110℃, the COPh increases by 20.45%. When the heat source conditions vary, the compression ratio is reduced by over 18%, and the COPh improves by 19.31% compared to R245fa, demonstrating the notable energy-saving potential of the proposed refrigerant mixture. Additionally, the study reveals that variations in heat source temperature have a more significant impact on system performance than changes in waste heat flow rate. These findings provide valuable insights for the selection of refrigerants and the operational optimization of high-temperature steam heat pump systems.

Control valve stiction fault detection based on Volterra model and kernel entropy component analysis

Junwei WANG Zhong ZHAO

The Chinese Journal of Process Engineering. 2025, 25(11):  1168-1182.  DOI: 10.12034/j.issn.1009-606X.225028

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The stiction of control valve is one of the main reasons for an industrial process control loop oscillation and valve nonlinear behavior, which not only reduces control loop performance and shortens valve service life but also may increase product quality fluctuations and energy consumption. Therefore, real-time detection of control valve stiction is important to ensure process operation stability. The control valve input signal OP (Output Position) and the process variable PV (Process Variables) waveforms are analyzed by the time-domain based traditional stiction detection method and the stiction index is calculated to determine whether there is stiction or not. However, in real industrial process, the process variable PV presents nonlinear and non-Gaussian random fluctuation characteristics, and the control valve stiction fault detection method based on time-domain waveform analysis has limitations in accuracy and generalization ability. Aiming at the random fluctuation characteristics of the process signal of the industrial process, a control valve stiction fault detection method based on Volterra model and kernel entropy component analysis (KECA) is proposed in this work. AVI-based KECA refers to as improved kernel entropy component analysis (IKECA). Firstly, nonlinear sticking control valves are modeled by the second-order Volterra model. Secondly, the OP-PV phase shift frequency-domain features are used to characterize stiction and extracted by the spectral analysis theory with the second-order Volterra series model. Then, for both faulty and normal data, the KECA method is used for dimensionality reduction, feature extraction and classification of multidimensional features, the angle variance index (AVI) is introduced as a statistic index and the kernel density estimation (KDE) is applied to determine the detection control limit AVILim to realize the real-time detection of control valve stiction fault. Industrial application software has been developed with the proposed method, and the industrial application results have verified the feasibility and effectiveness of the proposed method.

Synthesis regulation of cryolite in acidic solutions and the application of low lithium loss aluminum removal in acid leachate of lithium iron phosphate waste powder

Feng LUO Ying ZHANG Shili ZHENG Yang ZHANG Xiaojian WANG Shan QIAO

The Chinese Journal of Process Engineering. 2025, 25(11):  1183-1194.  DOI: 10.12034/j.issn.1009-606X.224349

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The recovery of valuable elements from spent LiFePO4 (LFP) black powder has become a significant research focus. A key challenge in the high-value recovery of this spent powder is the deep removal of aluminum (Al3+) from acidic solutions containing iron (Fe), aluminum (Al), and phosphorus (P) to produce battery-grade iron phosphate materials. In this study, the chemical composition of acidic leachates from sulfuric acid leaching of spent LFP powder was used as a reference, and Na2SO4-Li2SO4-Al2(SO4)3 solutions were designed to optimize Al3+ removal via cryolite precipitation. Based on the optimization of the cryolite precipitation process for aluminum removal, the formation rules of various types of cryolite, including Na1.5Li1.5AlF6, Na2LiAlF6, and Na3AlF6, were clarified, with a particular focus on how the initial Na/Li molar ratio and Al3+ concentration in the solution affected the formation of cryolites. The conditions for generating pure phases of each cryolite were established, which provided practical guidance for Al3+ removal through cryolite precipitation. This method was applied to the deep removal of Al3+ from acidic leachates following the leaching of spent LFP powder. It was found that the optimal conditions for cryolite precipitation to remove aluminum were a F/Al molar ratio of 6.6, an initial pH of 2.5, a reaction temperature of 50℃, and a reaction time of 2 h. Under these conditions, when the initial Na/Li molar ratio was set at 1.50 or 2.00, the precipitated Al-bearing solid was Na1.5Li1.5AlF6 cryolite, while at a ratio of 3.00, Na3AlF6 formed. The presence of iron and phosphorus in the solution hindered the formation of Na2LiAlF6. Using cryolite precipitation, the concentration of Al3+ could be reduced from 0.50 g/L to less than 20 mg/L, with minimal lithium loss by forming Na3AlF6. This research offers a viable solution for deep Al3+ removal from acidic leachates, ensuring minimal lithium loss during the hydrometallurgical recycling of spent LFP powder.

Study on crystallization behavior of calcium fluoride particles in fluorine-containing wastewater

Siyun HUANG Yupeng QIAN Yuxi ZHANG Lei XIE Junxiao LI

The Chinese Journal of Process Engineering. 2025, 25(11):  1195-1203.  DOI: 10.12034/j.issn.1009-606X.224386

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To address the environmental hazards caused by the industrial discharge of fluoride-containing wastewater, the effects of calcium-fluoride ratio, pH value, reaction temperature, and reaction time on fluoride removal efficiency were investigated by simulating the calcium salt precipitation reaction process of fluorine-containing wastewater. The relationship between the particle number density and the growth rate of calcium fluoride nuclei under various factors was analyzed by using the particle number balance model. The relative growth kinetic equation of calcium fluoride nucleation and its corresponding sensitivity coefficient under each condition were obtained, and the characteristics of crystallization products were characterized by XRD and SEM-EDS. The crystallization behavior of calcium fluoride in the chemical precipitation reaction of NaF and CaCl2 was clarified. The results showed that when the calcium-fluorine ratio was 2, the pH value was 7, the reaction temperature was 60℃, and the reaction time was 60 min, the fluoride ion concentration in the treated wastewater was decreased from the initial fluoride ion concentration of 5000.00 mg/L to 8.82 mg/L using CaCl2 as a calcium salt precipitant. The fluoride removal rate was 99.82%. Under these conditions, the nucleation rate of calcium fluoride precipitation was 0.19470 */(mL?min) and the growth rate was 2.952×10-3 μm/min. The relationship between the sensitivity coefficients of each factor was ipH<iT<0<it<iCa/F. The calcium-fluorine ratio and time were conducive to the nucleation of calcium fluoride crystals, and moderate pH and temperature were conducive to the growth of calcium fluoride crystals. The final precipitation product is calcium fluoride, and its surface microstructure consisted of an agglomerate structure composed of spherical calcium fluoride clusters.

Mechanism of low-molecular-weight polyolefin in improving bitumen-aggregate interfacial adhesion

Meizhu CHEN Jingjun YU Jianwei ZHANG Binbin LENG Jiameng MA

The Chinese Journal of Process Engineering. 2025, 25(11):  1204-1216.  DOI: 10.12034/j.issn.1009-606X.225084

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The adhesion performance at the bitumen-aggregate interface is a critical factor in mitigating pavement water damage, as it directly influences the service life of road infrastructure. To address the limitations of conventional modifiers, such as high costs and complex processing, low-molecular-weight polyolefin was employed as a modifier for bitumen mixtures in this research. By proposing a hierarchical research methodology that integrated microscopic wetting behavior, interfacial energy optimization, and macroscopic performance validation. This study overcomed the traditional single-scale limitations and achieved systematic innovation from microscopic mechanisms to macroscopic performance. A comprehensive approach combining contact angle measurements, surface energy analysis, and interfacial energy parameters (adhesion work, Was; spalling work, Wasw; energy ratio, ER) was utilized to investigate the effects of polyolefin dosage (2wt%~8wt%) on the interfacial interactions between bitumen and three lithological aggregates (granite, basalt, limestone). Multivariate regression analysis and modified boiling water tests were further conducted to validate the adhesion enhancement mechanisms. The experimental results demonstrated that low-molecular-weight polyolefin significantly reduced bitumen contact angles (8%~58%), thereby improving wettability and interfacial bonding. Was increased by 38.3% to 39.5%, ER increased by 1.38 to 1.41 times, and Wasw decreased to -94.86~-97.85 mJ/m2, collectively confirming enhanced interfacial stability. The optimal polyolefin dosage varied with aggregate lithology: granite, basalt, and limestone achieved the minimal Wasw values (-97.85, -96.15, and -94.86 mJ/m2) at dosages of 2wt%, 4wt%, and 6wt%, respectively. Correlation analysis revealed a strong positive relationship between polyolefin dosage and ER (correlation coefficient=0.90, p<0.01), which outweighs the influence of aggregate oxide composition and underscoring the dominant role of polyolefin in adhesion enhancement. Experimental validation showed a 34% reduction in the spalling rate (Wb) and a significant improvement in water stability. This research provides a theoretical foundation and technical support for the application of low-molecular-weight polyolefin in bitumen pavement engineering.

Highly sensitive SPR biosensor based on commercial multimode optical fiber

Qi CHE Chao CHEN Yifan ZHAO Dawei ZHAO Songping ZHANG Xiunan LI Xiangmei ZHANG

The Chinese Journal of Process Engineering. 2025, 25(11):  1217-1226.  DOI: 10.12034/j.issn.1009-606X.225035

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Optical fiber surface plasmon resonance (SPR) sensor has some challenges for its wide applications, such as difficulties of fabrication, complexities of sensitivity enhancement methods, and high costs. To solve these problems, a highly sensitive SPR biosensor was fabricated in this study. A commercial multimode optical fiber was used with a conventional coating method. The fiber was pretreated by physical method, and the gold nanoparticle film was plated vertically in the ion sputtering instrument. Following these processes, the optimization of coating parameters was conducted by using the spectral shift sensitivity of the relative refractive index of the solution as the index. Then, an SPR sensing system was developed with this new biosensor, tungsten lamp light source, Y-type optical fiber, spectrometer and spectral test and analysis software. The results demonstrated that the coating current and coating time were 15 mA and 20 s respectively. Characterization of the sensor's structure of this biosensor with scanning electron microscope (SEM) showed that a layer of non-uniform gold nanoparticle film with a gradual decrease in axial particle size from the front end to the tail end was sputtered on the surface of the fiber. The sensitivity of the sensor can reach 3416 nm/RIU in the refractive index range of 1.339~1.384 with different concentrations of glycerol aqueous solution as samples. On this basis, the optical fiber SPR sensor was carboxylated followed by cross-linking with Protein A ligand and an SPR biosensor was prepared for HIgG immunoassay. The results showed that the linear correlation coefficient R2 of the sensor for HIgG immunoassay in the range of 1.25~20.00 μg/mL was 0.9987, and the sensitivity and detection limit were 0.6786 nm/(μg/mL) and 0.15 μg/mL, respectively, which were comparable to those of sensors reported in the literature that underwent complex sensitization processes. In summary, the novel SPR biosensor has the advantages of simple fabrication process, stable performance and high sensitivity, which has a wide range of application prospects.