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Table of Content
28 July 2021, Volume 35 Issue 7
    Coal-based energy chemical engineering: Pay one's respects to Prof. Kechang Xie
    Wen-Ying Li, Jinlong Gong
    2021, 35(7):  1-2.  doi:10.1016/j.cjche.2021.05.003
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    Hydroformylation of formaldehyde to glycolaldehyde: An alternative synthetic route for ethylene glycol
    Jie Wei, Maoshuai Li, Meiyan Wang, Shixiang Feng, Weikang Dai, Qi Yang, Yi Feng, Wanxin Yang, Cheng Yang, Xinbin Ma
    2021, 35(7):  3-16.  doi:10.1016/j.cjche.2020.08.056
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    Hydroformylation of formaldehyde to glycolaldehyde (GA), as a vital reaction in both direct and indirect process of syngas to ethylene glycol (EG), shows great advantages in the aspects of the process complexity and clean production. The hydroformylation of formaldehyde to GA is thermodynamically unfavourable, requiring the development of highly efficient hydroformylation catalytic systems, appropriate reaction conditions and in-depth understanding of the reaction mechanisms. In this review, we have made a detailed summary on the reaction in terms of the reaction network, thermodynamics, metal complex catalysts (including central metals and ligands), reaction conditions (e.g., temperature, pressure, formaldehyde source and solvent) and promoters. Furthermore, the reaction mechanisms, involving neutral and anionic complex in the catalytic cycle, have been summarized and followed by a discussion on the impact of the crucial intermediates on the reaction pathways and product distribution. A brief overview of product separation and catalyst recovery has been presented in the final part. This review gives new insights into the factors that impact on the formaldehyde hydroformylation and reaction mechanisms, which helps to design more efficient catalytic systems and reaction processes for EG production via the hydroformylation route.
    The latest development on amine functionalized solid adsorbents for post-combustion CO2 capture: Analysis review
    Peiyu Zhao, Guojie Zhang, Huangyu Yan, Yuqiong Zhao
    2021, 35(7):  17-43.  doi:10.1016/j.cjche.2020.11.028
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    Global warming and associated global climate change have led to serious efforts towards reducing CO2 emissions through the CO2 capture from the major emission sources. CO2 capture using the amine functionalized adsorbents is regard as a direct and effective way to reducing CO2 emissions due to their large CO2 adsorption amount, excellent CO2 adsorption selectivity and lower energy requirements for adsorbent regeneration. Moreover, large number of achievements on the amine functionalized solid adsorbent have been recorded for the enhanced CO2 capture in the past few years. In view of this, we review and analyze the recent advances in amine functionalized solid adsorbents prepared with different supporting materials including mesoporous silica, zeolite, porous carbon materials, metal organic frameworks(MOF) and other composite porous materials. In addition, amine functionalized solid adsorbents derived from waste resources are also reviewed because of the large number demand for cost-effective carbon dioxide adsorbents and the processing needs of waste resources. Considering the importance of the stability of the adsorbent in practical applications, advanced research in the capture cycle stability has also been summarized and analyzed. Finally, we summarize the review and offer the recommendations for the development of amine-based solid adsorbents for carbon dioxide capture.
    Review on the effect of heat exchanger tubes on flow behavior and heat/mass transfer of the bubble/slurry reactors
    Le Li, Yansheng Zhao, Wenhao Lian, Chun Han, Qian Zhang, Wei Huang
    2021, 35(7):  44-61.  doi:10.1016/j.cjche.2021.03.017
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    Bubble/Slurry bubble column reactors (BCR/SBCR) are intensively used as multiphase reactors for a wide range of application in the chemical, biochemical and petrochemical industries. Most of these applications involve complicate gas-liquid/gas-liquid-solid flow behavior and exothermic process, thus it is necessary to equip the BCR/SBCR with heat exchanger tubes to remove the heat and govern the performance of the reactor. Amounts of experimental and numerical studies have been carried out to describe the phenomena taking place in BCR/SBCRs with heat exchanger tubes. Unfortunately, little effort has been put on reviewing the experiments and simulations for examining the effect of internals on the performance and hydrodynamics of BCR/SBCR. The objective of this work is to give a state-of-the-art review of the literature on the effects of heat exchanger tubes with different types and configurations on flow behavior and heat/mass transfer, then provide adequate information and scientific basis for the design and the development of heat exchanger tubes in BCR/SBCR, ultimately provide reasonable suggestions for better comprehend the performance of different heat exchanger tubes on hydrodynamics.
    Reviews of clean coal conversion technology in China: Situations & challenges
    Kechang Xie
    2021, 35(7):  62-69.  doi:10.1016/j.cjche.2021.04.004
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    It is important to develop the advanced coal to chemicals industry (ACCI) against a backdrop of coal-based energy structures, excessive imported oil and natural gas, and strict environmental constraints in China. In this study, the technology and industry of China's ACCI are reviewed to explain the effect of using coal to replace oil and natural gas, and the corresponding resource and environmental burdens that this will create. Development trends in technology and industry are also proposed to explore future scenarios. The review shows that although excellent progress has been made on an industrial scale, demonstrative level, and in terms of technology and equipment, the lack of strategic understanding, severe external constraints, partly underdeveloped technologies, and weak foundations must be immediately addressed. Therefore, it is necessary to clarify the importance that the ACCI has on the energy revolution and energy system. Based on technological innovation, a variety of external factors should be considered as a whole with emphasis on filling the knowledge gap of theoretical foundations and industry standards to support high-quality development for ACCI.
    Speciation and thermal transformation of sulfur forms in high-sulfur coal and its utilization in coal-blending coking process: A review
    Yanfeng Shen, Yongfeng Hu, Meijun Wang, Weiren Bao, Liping Chang, Kechang Xie
    2021, 35(7):  70-82.  doi:10.1016/j.cjche.2021.04.007
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    The utilization of high-sulfur coal is becoming more urgent due to the excessive utilization of low-sulfur, high-quality coal resources, and sulfur removal from high-sulfur coal is the most important issue. This paper reviews the speciation, forms and distribution of sulfur in coal, the sulfur removal from raw coal, the thermal transformation of sulfur during coal pyrolysis, and the sulfur regulation during coal-blending coking of high organic-sulfur coals. It was suggested that the proper characterization of sulfur in coal cannot be obtained only by either chemical method or instrumental characterization, which raises the need of a combination of current or newly adopted characterization methods. Different from the removal of inorganic sulfur from coal, the organic sulfur can only be partly removed by chemical technologies; and the coal structure and property, particularly high-sulfur coking coals which have caking ability, may be altered and affected by the pretreatment processes. Based on the interactions among the sulfur radicals, sulfur-containing and hydrogen-containing fragments during coal pyrolysis and the reactions with minerals or nascent char, regulating the sulfur transformation behavior in the process of thermal conversion is the most effective way to utilize high organic-sulfur coals in the coke-making industry. An in-situ regulation approach of sulfur transformation during coal-blending coking has been suggested. That is, the high volatile coals with an appropriate releasing temperature range of CH4 overlapping well with that of H2S from high organic-sulfur coals is blended with high organic-sulfur coals, and the C-S/C-C bonds in some sulfur forms are catalytically broken and immediately hydrogenated by the hydrogen-containing radicals generated from high volatile coals. Wherein, the effect of mass transfer on sulfur regulation during the coking process should be considered for the larger-scale coking tests through optimizing the ratios of different coals in the coal blend.
    Perspective on synthesis of high-energy-density fuels: From petroleum to coal-based pathway
    Chengxiang Shi, Jisheng Xu, Lun Pan, Xiangwen Zhang, Ji-Jun Zou
    2021, 35(7):  83-91.  doi:10.1016/j.cjche.2021.05.004
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    High-energy-density (HED) fuel is specifically pivotal to improve the performance of volume-limited aircrafts. The widely used HED fuels composed of polycyclic hydrocarbons are mainly synthesized from petroleum feedstocks. In order to ensure abundant supply, alternative resources such as coal should be considered. Herein, we summarize the synthesis methods and properties of typical HED fuels by using petroleum-derived cyclopentadiene (CPD) as key feedstock through dimerization, cycloaddition, hydrogenation and isomerization/photoisomerization reactions, and then propose a blueprint for synthesizing HED fuels from coal. The method to produce CPD from coal is analyzed and feasibility is demonstrated according to theoretical calculations and reported results. This review provides a novel route for synthesis of HED fuels from coal.
    Review of the characteristics and graded utilisation of coal gasification slag
    Xiaodong Liu, Zhengwei Jin, Yunhuan Jing, Panpan Fan, Zhili Qi, Weiren Bao, Jiancheng Wang, Xiaohui Yan, Peng Lv, Lianping Dong
    2021, 35(7):  92-106.  doi:10.1016/j.cjche.2021.05.007
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    The characteristics of the energy structure of rich coal, less oil and less gas, coupling with a high external dependence on oil and natural gas and the emphasis on the efficient and clean utilisation of coal, have brought opportunities for coal chemical industry. However, with the large-scale popularisation of coal gasification technology, the production and resulting storage of coal gasification slag continue to increase, which not only result in serious environmental pollution and a waste of terrestrial resources, but also seriously affect the sustainable development of coal chemical enterprises. Hence, the treatment of coal gasification slag is extremely important. In this paper, the production, composition, morphology, particle size structure and water holding characteristics of coal gasification slag are introduced, and the methods of carbon ash separation of gasification slag, both domestically and abroad, are summarised. In addition, the paper also summarises the research progress on gasification slag in building materials, ecological restoration, residual carbon utilisation and other high-value utilisation, and ultimately puts forward the idea of the comprehensive utilisation of gasification slag. For large-scale consumption to solve the environmental problems of enterprises and achieve high-value utilisation to increase the economic benefits of enterprises, it is urgent to zealously design a reasonable and comprehensive utilisation technologies with simple operational processes, strong adaptability and economic benefits.
    A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study
    Tingting Jiao, Huiling Fan, Shoujun Liu, Song Yang, Wenguang Du, Pengzheng Shi, Chao Yang, Yeshuang Wang, Ju Shangguan
    2021, 35(7):  107-123.  doi:10.1016/j.cjche.2021.05.010
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    The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog, which would seriously affect the quality of atmospheric environment. Therefore, the decrease of NOx is of great importance for improving the efficient utilization of coal. The present review comprehensively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calculation. Firstly, in the process of pyrolysis:the occurrence state and transformation of nitrogen were concluded. The influence of temperature, atmosphere, heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized; Secondly, during the process of combustion:the influence of temperature, ambient oxygen concentration, physical structure of coal char, catalyst on heterogeneous oxidation of char (N) were summarized; The effects of char surface properties, catalyst and ambient atmosphere on heterogeneous reduction of NOx were also concluded. Based on the quantum chemical calculation, the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail. Current studies focus more on the generation of HCN and NH3, but in order to reduce the pollution of NOx from the source, it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrolysis, as well as clarify the path of the generation of N2. Experiments study and quantum chemistry calculation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.
    Opposed multi-burner gasification technology: Recent process of fundamental research and industrial application
    Fuchen Wang, Guangsuo Yu, Haifeng Liu, Weifeng Li, Qinghua Guo, Jianliang Xu, Yan Gong, Hui Zhao, Haifeng Lu, Zhongjie Shen
    2021, 35(7):  124-142.  doi:10.1016/j.cjche.2021.07.007
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    Opposed multi-burner (OMB) gasification technology is the first large-scale gasification technology developed in China with completely independent intellectual property rights. It has been widely used around the world, involving synthetic ammonia, methanol, ethylene glycol, coal liquefaction, hydrogen production and other fields. This paper summarizes the research and development process of OMB gasification technology from the perspective of the cold model experiment and process simulation, pilot-scale study and industrial demonstration. The latest progress of fundamental research in nozzle atomization and dispersion, mixing enhancement of impinging flow, multiscale reaction of different carbonaceous feedstocks, spectral characteristic of impinging flame and particle characteristics inside gasifier, and comprehensive gasification model are reviewed. The latest industrial application progress of ultra-large-scale OMB gasifier and radiant syngas cooler (RSC) combined with quenching chamber OMB gasifier are introduced, and the prospects for the future technical development are proposed as well.
    Fluid Dynamics and Transport Phenomena
    Fouling characteristics of 90° elbow in high salinity wastewater from coal chemical industry
    Yang Lü, Kai Lu, Youxiang Bai, Yulong Ma, Yongsheng Ren
    2021, 35(7):  143-151.  doi:10.1016/j.cjche.2020.09.034
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    Due to the high salt content of coal chemical wastewater, pipeline fouling often occurs during wastewater treatment. Fouling will cause the diameter of the pipe to shrink or even block, which is not conducive to the safe and stable operation of the wastewater treatment process. In this paper, the experimental device was designed by using FLUENT software and the fouling deposition mechanisms at different flow velocities and different positions in a 90 deg bend were studied. The experimental results show that when the flow velocity is between 0.2 m·s-1 and 0.3 m·s-1, the thickness of fouling layer was positively correlated with the flow velocity; when the flow velocity is equal to 0.4 m·s-1, the formation of fouling is the most serious; when the flow velocity is between 0.4 m·s-1 and 0.7 m·s-1, the thickness of fouling layer was negative correlation with the flow velocity; with the increase of inlet velocity, the time for sediment point to develop into sediment surface is shortened. The fouling layer is easy to fall off because of the large shear force on the wall surface of the inner bend of the 90° elbow, so the density of sediment at this position is high.
    Multi-fluid Eulerian simulation of binary particles mixing and gas-solids contacting in high solids-flux downer reactor equipped with a lateral particle feeding nozzle
    Qiang Zheng, Jingxuan Yang, Wenhao Lian, Baoping Zhang, Xueer Pan, Zhonglin Zhang, Xiaogang Hao, Guoqing Guan
    2021, 35(7):  152-162.  doi:10.1016/j.cjche.2021.03.009
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    The performance of binary particles mixing and gas-solids contacting, which is considered qualitatively to have a significant influence on the heat transfer in internal heated circulating fluidized beds, is carefully investigated by means of a numerical approach in the newly developed high solids-flux downer lignite pyrolyzer (φ0.1 m×6.5 m). Since binary particles are used in this system, a reasonably validated 3D, transient, multi-fluid model, in which three heat transfer modes relating to the convection, conduction and radiation are considered, is adopted to simulate the flow behavior, temperature profiles as well as volatile contents. The simulation results showed that the solids stream impinges the left wall surface initially and turns towards the right wall in the further downward direction and then shrinks during this process resulting in that the solids concentrate a little more at the central region. In the further downward section of the downer, the particle flow disperses near the right wall and develops uniformly. Meanwhile, the coal phase is slowly heated in the downer and it is found that most of the heat absorbed by the coal is from the convection heat transfer mode. To explore the heat transfer mechanism more quantitatively, two indexes (mixing index and contacting index) are proposed, and it is found that the mixing index initially increased fast and later remained at a relatively flat state. For the contact index, it shows a trend with a first rising and then falling, finally rising continuously. Also, it is found that the convection heat transfer is closely correlated to the contacting status of gas-coal which indicates that the improving of the gas-coal contacting efficiency should be an effective way to strengthen the coal particle heating process.
    Separation Science and Engineering
    Multi-technique integration separation frameworks after steam reforming for coal-based hydrogen generation
    Xuehua Ruan, Wenbo Huo, Jiaming Wang, Minggang Guo, Wenji Zheng, Yun Zou, Aibin Huang, Jianxiang Shou, Gaohong He
    2021, 35(7):  163-172.  doi:10.1016/j.cjche.2020.07.052
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    Coal-based H2 generation has abruptly increased in recent years. The PSA-VPSA-SC process is the matured and standard framework for H2 purification and CO2 capture in many existing plants, including normal and vacuum pressure swing adsorption units in series (PSA-VPSA), and shallow condensation unit (SC). However, this standard process is frequently subjected to low H2 recovery ratio and high purification cost. In this work, H2-selective and CO2-selective membrane units, i.e., HM and CO2M, are attempted to support the standard process and ameliorate constraints. In the beginning, HM unit is arranged after VPSA to enhance H2 recovery from the decarbonized stream, i.e., the PSA-VPSA-SC/HM process. As a result, H2 recovery ratio can be enhanced significantly from 83% to 98%. In the following, VPSA is replaced with CO2M unit to reduce investment and operation cost, i.e., the PSA-CO2M-SC/HM process. Accordingly, the specific purification cost is diminished from 33.46 to 32.02 USD·(103m3 H2)-1, saved by 4.3%, meanwhile the construction cost is falling back and just a little higher than that for the standard process. In the end, another CO2M unit is launched before PSA, i.e., the CO2M-PSA-CO2M-SC/HM process, which could unbundle CO2 enrichment partially from H2 purification, and then save more investment and operation cost. In comparison with the standard process, this ultimate retrofitted process can be superior in all the three crucial indices, i.e., recovery ratio, investment, and specific purification cost. On the whole, coal-based H2 generation can be ameliorated significantly through high efficient H2-selective and CO2-selective membrane units.
    Purification of carbazole by solvent crystallization under two forced cooling modes
    Cui-Ping Ye, Ya-Fei Qiao, Rui-Nan Wang, Wen-Ying Li
    2021, 35(7):  173-179.  doi:10.1016/j.cjche.2020.12.018
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    To identify the effect of solvents and anthracene on the purification of carbazole, the solvent crystallization of carbazole was investigated with xylene, chlorobenzene and tetrachloroethylene (TCE) as solvents under two forced circulation cooling (FCC) modes. The co-crystalline experimental data were obtained from runs carried out at different anthracene levels between 1% (mass) and 10% (mass). The results showed that a uniform flake carbazole crystal obtained when using xylene and chlorobenzene under the FCC-1 mode with gradual cooling rate. Nevertheless, fine flake crystals grown under shock cooling of FCC-2 mode. It is beneficial to improving the purity of carbazole with chlorobenzene as solvent under cooling mode of FCC-1. Anthracene could promote the growth of carbazole in solution, and it has a significant influence on the purification of carbazole.
    Efficient separation of phenols from coal tar with aqueous solution of amines by liquid-liquid extraction
    Yonglin Li, He'an Luo, Qiuhong Ai, Kuiyi You, Fei Zhao, Wenlong Xiao
    2021, 35(7):  180-188.  doi:10.1016/j.cjche.2021.01.008
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    In this paper, a method of extracting phenols from coal tar by amines aqueous solution was proposed. The effects of various amines on the extraction properties of phenols in coal tar were researched from the views of molecular structure. The parameters such as molar ratio, concentration, extraction time and temperature for the extraction of coal tar by the monoethanolamine and ethylenediamine aqueous solution were examined. The results show that the organic amine with more amino groups, hydroxyl structure and strong electronegativity exhibited better extraction performance. Under the optimal conditions, the extraction yields of phenols in coal tar by the monoethanolamine or ethylenediamine aqueous solution are above 80%, and the recovery yields of amines reach 99%. Furthermore, the probable geometries of complexes formed by the combination of phenols and organic amines were calculated by density function theory. In addition, several thermodynamic models were evaluated through comparing the relative deviation of simulation results by ASPEN PLUS to the experimental ones, which provide feasibility thermodynamic models for the simulation of extraction process. The present work affords a mild, efficient and green approach for the extraction of phenols from coal tar by an aqueous solution of amines in industry application.
    Catalysis, Kinetics and Reaction Engineering
    Effects of inherent potassium on the catalytic performance of Ni/biochar for steam reforming of toluene as a tar model compound
    Chen Xu, Zhenyi Du, Shiqi Yang, Hongda Ma, Jie Feng
    2021, 35(7):  189-195.  doi:10.1016/j.cjche.2020.06.010
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    Biochar supported nickel (Ni/BC) has been widely studied as a cheap and easy-to-prepare catalyst with potential applications in tar reforming during the gasification of low-rank fuels, such as brown coal and biomass. However, the role and behaviors of inherent K species, especially their interactions with Ni particles and the biochar support, are not well understood yet. In this work, three Ni/BC catalysts with varying K amount were prepared from raw, water-washed, and acid-washed biomass. They were used in steam reforming of toluene as a tar model compound to elucidate the effects of inherent K on the catalytic activity and stability. Detailed characterization indicated that K enhanced water adsorption due to its hydroscopicity and lowered the condensation and graphitization degrees of biochar, but the alteration to the electronic state of Ni was not observed. These effects together led to a temperature-dependent role of K. That is, at relatively low temperatures of 450 and 500℃, toluene conversion was increased in the presence of K, due to the increased concentration of adsorbed water around Ni particles. By contrast, at relatively higher temperatures of 550 and 600℃, although initial high activity was achieved, Ni/BC with K deactivated rapidly because of the accelerated consumption of the biochar support.
    Synthesis and characterization of BZSM-5 and its catalytic performance in the methanol to hydrocarbons reaction
    Junhua Gao, Keming Ji, Hao Zhou, Jiayao Xun, Zenghou Liu, Kan Zhang, Ping Liu
    2021, 35(7):  196-203.  doi:10.1016/j.cjche.2020.09.008
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    Five kinds of BZSM-5 molecular sieve with different Si/B ratio and a SiZSM-5 molecular sieve were prepared by hydrothermal synthesis method followed by acid exchange and pelletization. The samples were characterized by XRD, SEM, FT-IR, ICP, low temperature N2 physical adsorption and desorption, NH3-TPD and Py-IR. The catalytic performance in the reaction of methanol to hydrocarbons was evaluated in the fixed bed reactor. Compared with SiZSM-5, the amount and strength of Brönsted (B) acid were enhanced by introducing skeleton boron and the activity of the catalyst was greatly improved. The characterization and evaluation results indicated that the BZSM-5 catalyst synthesized from the gel of SiO2/B2O3 20 with Si/B ratio 74.48 had modest acidity strength, acid amount of 0.18mmol NH3·g-1 and large mesopore volume of 0.23cm3·g-1. The B acid ratio was higher and the acid strength of BZSM-5 was weaker than that of AlZSM-5, which could inhibit the deep coke formation and increase the activity stability. B-2 had the best lifetime which could reach 672h under the same evaluation reaction conditions, due to the best matching of moderate acidity and good diffusion properties.
    Mechanism of dibenzofuran hydrodeoxygenation on the Ni (1 1 1) surface
    Zi-Zheng Xie, Meng Zhang, Xing-Bao Wang, Liang Guo, Zhen-Yi Du, Wen-Ying Li
    2021, 35(7):  204-210.  doi:10.1016/j.cjche.2021.02.005
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    The low-temperature coal tar contains a considerable number of oxygen-containing compounds, which results in poor quality. The catalytic hydrodeoxygenation of oxygen-containing compound to an added-value chemical compound is one of the most efficient methods to upgrade coal tar. In this study, density functional theory calculations are employed to assess and analyze in detail the hydrodeoxygenation of dibenzofuran, as a model compound of coal tar, on the Ni (1 1 1) surface. The obtained results indicate that dibenzofuran can be firstly hydrogenated to tetrahydrodibenzofuran and hexahydrodibenzofuran. The five-membered-ring opening reaction of tetrahydrodibenzofuran is more straightforward than that of hexahydrodibenzofuran (Ea=0.71 eV vs. 1.66 eV). Then, both pathways generate an intermediate 2-cyclohexylphenoxy compound. One part of 2-cyclohexylphenoxy is hydrogenated to 2-cyclohexylphenol and consecutively hydrogenated to cyclohexylcyclohexanol, and another part is directly hydrogenated to cyclohexylcyclohexanone. The hydrogenated intermediates of 2-cyclohexylphenol have higher deoxygenation barriers than 2-cyclohexylphenol and cyclohexylcyclohexanol. During the hydrogenation process of cyclohexylcyclohexanone to cyclohexylcyclohexanol, the intermediate 26, formed by adding H to O atom of cyclohexylcyclohexanone, exhibits the lowest deoxygenation barrier of 1.08 eV. High hydrogen coverage may promote the hydrogenation of tetrahydrodibenzofuran, hexahydrodibenzofuran, and intermediate 26 to generate dodecahydrodibenzofuran and cyclohexylcyclohexanol. This dibenzofuran hydrodeoxygenation reaction mechanism corroborates well with previous experimental results and provides a theoretical basis for further optimization of the design of nickel-based catalysts.
    Tuning the crystallite size of monoclinic ZrO2 to reveal critical roles of surface defects on m-ZrO2 catalyst for direct synthesis of isobutene from syngas
    Xuemei Wu, Minghui Tan, Bing Xu, Shengying Zhao, Qingxiang Ma, Yingluo He, Chunyang Zeng, Guohui Yang, Noritatsu Tsubaki, Yisheng Tan
    2021, 35(7):  211-219.  doi:10.1016/j.cjche.2021.04.008
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    The effects of crystallite size on the physicochemical properties and surface defects of pure monoclinic ZrO2 catalysts for isobutene synthesis were studied. We prepared a series of monoclinic ZrO2 catalysts with different crystallite size by changing calcination temperature and evaluated their catalytic performance for isobutene synthesis from syngas. ZrO2 with small crystalline size showed higher CO conversion and isobutene selectivity, while samples with large crystalline size preferred to form dimethyl ether (DME) instead of hydrocarbons, much less to isobutene. Oxygen defects (ODefects) analyzed by X-ray photoelectron spectroscopy (XPS) provided evidence that more ODefects occupied on the surface of ZrO2 catalysts with smaller crystalline size. Electron paramagnetic resonance (EPR) and ultraviolet-visible diffuse reflectance (UV-vis DRS) confirmed the presence of high concentration of surface defects and Zr3+ on m-ZrO2-5.9 sample, respectively. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) analysis indicated that the adsorption strength of formed formate species on catalyst reduced as the crystalline size decreased. These results suggested that surface defects were responsible for CO activation and further influenced the adsorption strength of surface species, and thus the products distribution changed. This study provides an in-depth insight for active sites regulation of ZrO2 catalyst in CO hydrogenation reaction.
    Manipulating metal-support interactions of metal catalysts for Fischer-Tropsch synthesis
    Qingpeng Cheng, Yunhao Liu, Shuaishuai Lyu, Ye Tian, Qingxiang Ma, Xingang Li
    2021, 35(7):  220-230.  doi:10.1016/j.cjche.2021.05.013
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    For supported metal catalyst systems, the impact on catalysis originates from the interaction between metal nanoparticles and their support. Metal-support interactions (MSI) can change electronic properties, geometric morphologies, or chemical compositions of metal nanoparticles to make active sites have specific properties and catalytic activities. Fischer-Tropsch synthesis (FTS) is one of the most effective ways to convert cheap non-petroleum-based carbon sources into high value-added chemicals or ultra-clean liquid fuels. In this review, we summarize and classify the impact of MSI on the catalytic activity, selectivity and stability of FTS catalysts. The strategies to tune MSI are introduced in detail, and the recent development of high-efficiency FTS catalysts through the manipulation of SMI strategies has been highlighted. It is emphasized that the active metal sites, which are endowed with special functions by MSI, can change the strength of adsorption bond of adsorbates, consequently controlling the product distribution.
    Kinetics of steam regeneration of SAPO-34 zeolite catalyst in methanol-to-olefins (MTO) process
    Huaiqing An, Hua Li, Jibin Zhou, Jinling Zhang, Tao Zhang, Mao Ye, Zhongmin Liu
    2021, 35(7):  231-238.  doi:10.1016/j.cjche.2021.07.009
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    Methanol-to-olefins (MTO) is industrially applied to produce ethylene and propylene using methanol converted from coal, synthetic gas, and biomass. SAPO-34 zeolites, as the most efficient catalyst in MTO process, are subject to the rapid deactivation due to coke deposition. Recent work shows that steam regeneration can provide advantages such as low carbon dioxide emission and enhanced light olefins yield in MTO process, compared to that by air regeneration. A kinetic study on the steam regeneration of spent SAPO-34 catalyst has been carried out in this work. In doing so, we first investigated the effect of temperature on the regeneration performance by monitoring the crystal structure, acidity, residual coke properties and other structural parameters. The results show that with the increase of regeneration temperature, the compositions of residual coke on the catalyst change from pyrene and phenanthrene to naphthalene, which are normally considered as active hydrocarbon pool species in MTO reaction. However, when the regeneration temperature is too high, nitrogen oxides can be found in the residual coke. Meanwhile, as the regeneration temperature increases, the quantity of residual coke reduces and the acidity, BET surface area and pore structure of the regenerated samples can be better recovered, resulting in prolonging catalyst lifetime. We have further derived the kinetics of steam regeneration, and obtained an activation energy of about 177.8 kJ·mol-1. Compared that with air regeneration, the activation energy of steam regeneration is higher, indicating that the steam regeneration process is more difficult to occur.
    Modification of ash flow properties of coal rich in calcium and iron by coal gangue addition
    Huaizhu Li, Lingxue Kong, Jin Bai, Zongqing Bai, Zhenxing Guo, Wen Li
    2021, 35(7):  239-246.  doi:10.1016/j.cjche.2020.08.033
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    Flow property of coal ash and slag is an important parameter for slag tapping of entrained flow gasifier. The viscosity of slag with high contents of calcium and iron exhibits the behavior of a crystalline slag, of which viscosity sharply increases when temperature is lowered than temperature of critical viscosity (TCV). The fluctuation in temperature near the TCV can cause an accumulation of slag inside the gasifier. In order to prevent slag blockage, it is necessary to adjust the ash composition by additive to modify the flow property of coal rich in calcium and iron. Main components of coal gangue are Al2O3 and SiO2, which is a potential additive to modify the ash flow properties of these coals. In this work, we investigated the ash flow properties of a typical coal rich in calcium and iron by adding coal gangue with different SiO2/Al2O3 ratio. The results showed that the ash fusion temperatures (AFTs) firstly decreased, and then increased with increasing amount of coal gangue addition. Chemical composition of coal ash rich in calcium and iron moved from gehlenite primary phase to anorthite, quartz and corundum primary phases. The slags with coal gangue addition behaved as a glassy slag, of which the viscosity gradually increased as temperature decreased. Besides, a high SiO2/Al2O3 ratio of coal gangue was beneficial to modify the slag viscosity behavior. Addition of coal gangue with a high SiO2/Al2O3 ratio impeded formation of crystalline phases during cooling. This work demonstrated that coal gangue addition was an effective way to improve the ash flow properties of the coal rich in calcium and iron for the entrained flow gasifier.
    Migration of sulfur in in-situ gasification chemical looping combustion of Beisu coal with iron- and copper-based oxygen carriers
    Ming Luo, Lunzheng Zhou, Jianjun Cai, Haiyan Zhang, Chao Wang
    2021, 35(7):  247-255.  doi:10.1016/j.cjche.2020.09.058
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    Chemical looping combustion (CLC) is an energy conversion technology with high efficiency and inherent separation of CO2. The existence of sulfur in coal may affect the CO2 purity and the performance of oxygen carrier due to the interactions between sulfur contaminants and oxygen carrier. The migration of sulfur in Beisu coal during the in-situ gasification chemical looping combustion (iG-CLC) process using two oxygen carriers (iron ore and CuO/SiO2) was investigated respectively. The thermodynamic analysis results showed the formation of metal sulfides was thermodynamically favored at low temperatures and low oxygen excess coefficients, while they were obviously inhibited and the production of SO2 was significantly promoted with an increase in temperature and oxygen excess coefficient. Moreover, part of sulfur was captured and fixed in the forms of alkali/alkaline earth metal sulfate due to the high amount of alkali/alkaline earth metal oxides in the coal ash or/and oxygen carrier. The experimental results showed that the sulfur in coal mainly released in the form of SO2, and the sulfur conversion efficiency (XS) in the reduction stage were 51.04% and 48.24% when using iron ore and CuO/SiO2 respectively. The existence of metal sulfides was observed in the reduced oxygen carriers. The values of XS in the reoxidation process reached 3.80% and 7.64% when using iron ore and CuO/SiO2 respectively. The residue and accumulation of sulfur were also found on the surfaces of two oxygen carriers.
    Formation and emission characteristics of VOCs from a coal-fired power plant
    Jingying Xu, Yue Lyu, Jiankun Zhuo, Yishu Xu, Zijian Zhou, Qiang Yao
    2021, 35(7):  256-264.  doi:10.1016/j.cjche.2021.02.015
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    On-site measurements of volatile organic compounds (VOCs) in different streams of flue gas were carried out on a real coal-fired power plant using sampling bags and SUMMA canisters to collect gas samples, filters to collect particle samples. Gas chromatography-flame ionization detector/mass spectrometry and gas chromatography-mass spectrometry was the offline analysis method. We found that the total mass concentration of the tested 102 VOC species at the outlet of wet flue gas desulfuration device was (13456 ±47) μg·m-3, which contained aliphatic hydrocarbons (57.9%), aromatic hydrocarbons (26.8%), halogen-containing species (14.5%), and a small amount of oxygen-containing and nitrogen-containing species. The most abundant species were 1-hexene, n-hexane and 2-methylpentane. The top ten species in terms of mass fraction (with a total mass fraction of 75.3%) were mainly hydrocarbons with a carbon number of 6 or higher and halogenated hydrocarbons with a lower carbon number. The mass concentration of VOC species in the particle phase was significantly lower than that in the gas phase. The change of VOC mass concentrations along the air pollution control devices indicates that conventional pollutant control equipment had a limited effect on VOC reduction. Ozone formation potential calculations showed that aromatic hydrocarbons contributed the highest ozone formation (46.4%) due to their relatively high mass concentrations and MIR (maximum increment reactivity) values.
    The effect of hydrothermal pretreatment on the structure and fast pyrolysis behaviors of ShengLi lignite
    Boyang Bai, Luyao Qiang, Suisui Zhang, Zhiwei Peng, Hang Mu, Xiaoxun Ma
    2021, 35(7):  265-274.  doi:10.1016/j.cjche.2021.05.006
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    The structure and composition of coal determine its fast pyrolysis characteristics, and the study of the relationship between them can play an important role in the efficient and clean utilization of coal. So, in this work, hydrothermal pretreatment was used to artificially change the structure and composition of ShengLi (SL) lignite, which was used to investigate the influence of structural changes on pyrolysis. The physicochemicalstructure and composition of samples were characterized by X-ray diffraction, specific surface area and porosity analyzer, solid-state 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elementalanalyzer. Pyrolysis experiments were carried out in a powder-particle fluidized bed reactor, and the distribution and composition of the pyrolysis products were analyzed. The gasification activity of char was investigated by thermogravimetric analysis with a CO2 atmosphere. The results show that hydrothermal pretreatment (HTP) can destroy the cross-linking structure of SL lignite, and affect its aromaticity, pore structure, functional group, and carbon structure to change the distribution and composition of pyrolysis products of SL lignite, especially the composition of tar. Finally, the structure-activity relationship between the structure, composition, and pyrolysis characteristics of coal was comprehensively studied.
    Selective preparation of light aromatic hydrocarbons from catalytic fast pyrolysis vapors of coal tar asphaltene over transition metal ion modified zeolites
    Yongqi Liu, Qiuxiang Yao, Ming Sun, Xiaoxun Ma
    2021, 35(7):  275-287.  doi:10.1016/j.cjche.2021.06.006
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    The catalytic cracking of coal tar asphaltene (CTA) pyrolysis vapors was carried out over transition metalion modified zeolites to promote the generation of light aromatic hydrocarbons (L-ArHs) in a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) micro-reactor system. The effects of ultra stable Y (USY), Co/USY and Mo/USY on the selectivity and yield of L-ArHs products and the extent of deoxygenation (Edeoxygenation), lightweight (Elightweight) from CTA pyrolysis volatiles were investigated. Results showed that the yields of L-ArHs are mainly controlled by the acid sites and specific surface area of the catalysts, while the deoxygenation effect is determined by theirs pore size. The Elightweight of CTA pyrolysis volatiles over USY is 9.65%, while the Edeoxygenation of CTA pyrolysis volatiles over Mo/USY reaches 20.85%. Additionally, the modified zeolites (Mo/USY and Co/USY) exhibit better performance than USY on L-ArHs production, owing to the synergistic effect of metal ions (Mo, Co) and acid sites of USY. Compared with the non-catalytic fast pyrolysis of CTA, the total yield of L-ArHs obtained over USY (4032 mg·kg-1), Co/USY (4363 mg·kg-1) and Mo/USY (4953 mg·kg-1) were increased by 27.03%, 38.19% and 54.78%, respectively. Furthermore, the possible catalytic conversion mechanism of transition metal ion (Co and Mo) modified zeolites was proposed based on the distribution of products and the characterizations of catalysts.
    Interactions of dynamic supercritical CO2 fluid with different rank moisture-equilibrated coals: Implications for CO2 sequestration in coal seams
    Zichao Hu, Chao Li, Dengfeng Zhang
    2021, 35(7):  288-301.  doi:10.1016/j.cjche.2020.10.020
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    The interactions between CO2 and coals during CO2-ECBM (CO2 sequestration in deep coal seams with enhanced coal-bed methane recovery) could change pore morphology and chemistry property of coals, thereby affecting adsorption, diffusion and flow capability of CO2 and CH4 within coal reservoirs. To simulate CO2-ECBM process more practically, the dynamic interactions of supercritical CO2 (scCO2) and moisture-equilibrated coals were performed at temperature of 318.15 K, pressure of 12.00 MPa, and duration of 12.00 h. The impacts of the interactions on physicochemical properties of coals were investigated. Results indicate that scCO2/H2O exposure shows minor effect on micropores of coals. However, the exposure significantly decreases the mesopore surface area of bituminous coals, while increases that of anthracites. The mesopore volume and the average mesopore diameter of all the coals after scCO2/H2O exposure decrease. The multi-fractal analysis verifies that the scCO2 exposure can enhance the pore connectivity of various rank coals. Apart from the pore morphology, the exposure of scCO2/H2O also affects the oxygenic functional groups on coal surface. Particularly, the exposure of scCO2/H2O reduces the content of CO and CO of coals. The content of COOH of low rank coals including Hehua-M2# coal, Zhongqiang-4# coal, Buliangou-9# coal and Tashan-5# coal decreases, while the high rank Laochang-11# coal and Kaiyuan-9# coal witness a growth in COOH. The content of total oxygenic functional groups of all coals after interaction with scCO2/H2O decreases; on the contrary, that of CC/CH of all coals after scCO2/H2O exposure increases. In summary, the interaction with scCO2/H2O significantly changes the pore system and oxygenic functional groups of various rank coals, which needs further attention regarding CO2-ECBM.