The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40（40%）/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modifi...The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40（40%）/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modification of H3PW12O40（40%）/SiO2 gave the most promising result of 20% dimethyl ether conversion and 34.8% dimethoxymethane selectivity. Dimethoxymethane could be synthe- sized via methoxy groups decomposed from dimethyl ether through the synergistic effect between the acid sites and the redox sites of Cs modified H3PW12O40（40%）/SiO2.展开更多
Experimental investigation was conducted to convert dimethyl ether (DME) in the presence of steam using dielectric barrier discharge (DBD) at atmospheric pressure and 373 K. The flow rate of DME was 20 ml/min. The int...Experimental investigation was conducted to convert dimethyl ether (DME) in the presence of steam using dielectric barrier discharge (DBD) at atmospheric pressure and 373 K. The flow rate of DME was 20 ml/min. The introduction of steam resulted in an increase in the DME conversion and the selectivity of oxygenates. Plasma steam-enhanced dimethyl ether (DME) conversion led to a direct synthesis of DMMT and DMET, with a high selectivity of 5.78% and 17.99%, respectively. The addition of steam promoted the formation of 'plasma aerosol' that was favored for the formation of liquid oxygenates. The reaction pathway of plasma DME conversion was proposed.展开更多
Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The ...Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The industrial synthesis of DMM is mainly involved two-step process:methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor.Due to huge energy consumption,this typical synthesis route of DMM needs to be upgraded and more green routes should be determined.In this review,four state-of-the-art one-step direct synthetic routes,including two upgrading routes(methanol direct oxidation and direct dehydrogenation)and two green routes(methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation),have been summarized and compared.Combination with the reaction mechanism and catalytic performance on the different catalysts,the challenges and opportu nities for every synthetic route are proposed.The relationships between catalyst structu re and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in.Hopefully,this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future.展开更多
This study investigated the conversion of furfural to 5-hydroxymethylfurfural(HMF)and further to levulinic acid/ester in dimethoxymethane under acidic conditions,with the particular focus on understanding the mechanis...This study investigated the conversion of furfural to 5-hydroxymethylfurfural(HMF)and further to levulinic acid/ester in dimethoxymethane under acidic conditions,with the particular focus on understanding the mechanism for polymer formation.The results showed that furfural could react with dimethoxymethane via electrophilic substitution reaction to form HMF or the ether/acetal of HMF,which were further converted to levulinic acid and methyl levulinate.The polymerization of furfural and the cross-polymerization between dimethoxymethane and the levulinic acid/ester produced were the main side reactions leading to the decreased yields of levulinic acid/ester.Comparing to the other solvent,methanol as the co-solvent helped to alleviate but not totally inhibited the occurrences of the polymerization,as the polymerization reactions via aldol condensation did not eliminate the C=O functionalities.As a consequence,the polymerization reactions continued to proceed.Other co-solvent used such as guaiacol,dimethyl sulfoxide and acetone interfered with the transformation of furfural to HMF or aided the polymerization reactions.The polymer produced from the reactions between furfural and DMM was different from that produced from levulinic acid/ester.The former had a higher crystallinity,while the latter was more aliphatic.The DRIFTS and TG-MS studies showed that the polymer had the carboxylic group,methyl group and the aliphatic structure in the skeleton.The removal of these functionalities was accompanied by the aromatization of the polymer.The condensation of DMM with levulinic acid/ester was the key reason for the diminished production of levulinic acid/ester.展开更多
Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde...Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde,followed by its condensation with methanol.This study presents a one-pot method of DMM synthesis from methanol mediated carbon dioxide hydrogenation over novel heterogeneous catalysts.The effect of catalyst pore structure was investigated by synthesizing 3 wt%Ru over novel hierarchical zeolite beta(HBEASX)and comparing against Ru doped commercial zeolite beta(CBEA)and desilicated hierarchical zeolite beta(HBZDS).The results showed that 3%Ru/HBEASX provided the best activity for DMM production due to its large average pore size.It also showed the decisive role of SiO_(2)/Al_(2)O_(3)molar ratio,with SiO_(2)/Al_(2)O_(3)=75 providing the highest DMM yield of 13.2 mmol/gcat.LMeOH with ca.100%selectivity.The activity of 3%Ru/HBEAS3 after 5 recycle steps demonstrated the reusability of this catalyst.展开更多
基于主题翻译模型的短文本关键词抽取方法,均采用LDA(Latent Dirichlet Allocation)主题模型作为主题发现方法,然而LDA在处理特征稀疏的短文本时,主题发现效果较差,使得当前的主题翻译模型存在不完善之处。论文通过将DMM(Dirichlet Mult...基于主题翻译模型的短文本关键词抽取方法,均采用LDA(Latent Dirichlet Allocation)主题模型作为主题发现方法,然而LDA在处理特征稀疏的短文本时,主题发现效果较差,使得当前的主题翻译模型存在不完善之处。论文通过将DMM(Dirichlet Multinomial Mixture)模型作为主题发现模型,结合统计机器翻译,提出了一种用于短文本关键词抽取的TTM_DMM(Topical Translation Model based on Dirichlet Multinomial Mixture)主题翻译模型。该模型利用DMM模型发现短文本主题信息,在主题约束下学习词语与关键词的翻译概率,从而提高短文本关键词抽取效果。在真实数据集上的实验结果表明,论文提出的TTM_DMM模型在评价指标Precious、Recall以及F-measure上优于现有的短文本关键词抽取方法。展开更多
基金Foundation items:the National Natural Science Foundation of China(No.20373085)the Natural Science Foundation of Shanxi Province(No.20051023)
文摘The attractive utilization route for one-step catalytic oxidation of dimethyl ether to dimethoxymethane was successfully carried out over the H3PW12O40（40%）/SiO2 catalyst, modified by Cs, K, Ni, and V. The Cs modification of H3PW12O40（40%）/SiO2 gave the most promising result of 20% dimethyl ether conversion and 34.8% dimethoxymethane selectivity. Dimethoxymethane could be synthe- sized via methoxy groups decomposed from dimethyl ether through the synergistic effect between the acid sites and the redox sites of Cs modified H3PW12O40（40%）/SiO2.
基金The project supported by the National Natural Science Foundation of China (No. 20376060)
文摘Experimental investigation was conducted to convert dimethyl ether (DME) in the presence of steam using dielectric barrier discharge (DBD) at atmospheric pressure and 373 K. The flow rate of DME was 20 ml/min. The introduction of steam resulted in an increase in the DME conversion and the selectivity of oxygenates. Plasma steam-enhanced dimethyl ether (DME) conversion led to a direct synthesis of DMMT and DMET, with a high selectivity of 5.78% and 17.99%, respectively. The addition of steam promoted the formation of 'plasma aerosol' that was favored for the formation of liquid oxygenates. The reaction pathway of plasma DME conversion was proposed.
文摘Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The industrial synthesis of DMM is mainly involved two-step process:methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor.Due to huge energy consumption,this typical synthesis route of DMM needs to be upgraded and more green routes should be determined.In this review,four state-of-the-art one-step direct synthetic routes,including two upgrading routes(methanol direct oxidation and direct dehydrogenation)and two green routes(methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation),have been summarized and compared.Combination with the reaction mechanism and catalytic performance on the different catalysts,the challenges and opportu nities for every synthetic route are proposed.The relationships between catalyst structu re and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in.Hopefully,this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future.
基金This work was supported by the National Natural Science Foundation of China (No. 51876080)the Strategic International Scientific and Technological Innovation Cooperation Special Funds of National Key R&D Program of China (No. 2016YFE0204000)+3 种基金the Program for Taishan Scholars of Shandong Province Governmentthe Recruitment Program of Global Young Experts (Thousand Youth Talents Plan)the Natural Science Fund of Shandong Province (ZR2017BB002)the Key R&D Program of Shandong Province (2018GSF116014)
文摘This study investigated the conversion of furfural to 5-hydroxymethylfurfural(HMF)and further to levulinic acid/ester in dimethoxymethane under acidic conditions,with the particular focus on understanding the mechanism for polymer formation.The results showed that furfural could react with dimethoxymethane via electrophilic substitution reaction to form HMF or the ether/acetal of HMF,which were further converted to levulinic acid and methyl levulinate.The polymerization of furfural and the cross-polymerization between dimethoxymethane and the levulinic acid/ester produced were the main side reactions leading to the decreased yields of levulinic acid/ester.Comparing to the other solvent,methanol as the co-solvent helped to alleviate but not totally inhibited the occurrences of the polymerization,as the polymerization reactions via aldol condensation did not eliminate the C=O functionalities.As a consequence,the polymerization reactions continued to proceed.Other co-solvent used such as guaiacol,dimethyl sulfoxide and acetone interfered with the transformation of furfural to HMF or aided the polymerization reactions.The polymer produced from the reactions between furfural and DMM was different from that produced from levulinic acid/ester.The former had a higher crystallinity,while the latter was more aliphatic.The DRIFTS and TG-MS studies showed that the polymer had the carboxylic group,methyl group and the aliphatic structure in the skeleton.The removal of these functionalities was accompanied by the aromatization of the polymer.The condensation of DMM with levulinic acid/ester was the key reason for the diminished production of levulinic acid/ester.
基金Australian Research Council(Grant No.DP170104017)for the financial support of this projectAT and AS received financial support from the Institute for Catalysis,Hokkaido University as part of their Strategic Research Fellowship grant schemesupported by the Cooperative Research Program of Institute for Catalysis,Hokkaido University(Proposal No.19A1005)。
文摘Dimethoxymethane(DMM),a diesel blend fuel,is being researched with high interest recently due to its unique fuel properties.It is commercially produced via a two step-process of methanol oxidation to make formaldehyde,followed by its condensation with methanol.This study presents a one-pot method of DMM synthesis from methanol mediated carbon dioxide hydrogenation over novel heterogeneous catalysts.The effect of catalyst pore structure was investigated by synthesizing 3 wt%Ru over novel hierarchical zeolite beta(HBEASX)and comparing against Ru doped commercial zeolite beta(CBEA)and desilicated hierarchical zeolite beta(HBZDS).The results showed that 3%Ru/HBEASX provided the best activity for DMM production due to its large average pore size.It also showed the decisive role of SiO_(2)/Al_(2)O_(3)molar ratio,with SiO_(2)/Al_(2)O_(3)=75 providing the highest DMM yield of 13.2 mmol/gcat.LMeOH with ca.100%selectivity.The activity of 3%Ru/HBEAS3 after 5 recycle steps demonstrated the reusability of this catalyst.
文摘基于主题翻译模型的短文本关键词抽取方法,均采用LDA(Latent Dirichlet Allocation)主题模型作为主题发现方法,然而LDA在处理特征稀疏的短文本时,主题发现效果较差,使得当前的主题翻译模型存在不完善之处。论文通过将DMM(Dirichlet Multinomial Mixture)模型作为主题发现模型,结合统计机器翻译,提出了一种用于短文本关键词抽取的TTM_DMM(Topical Translation Model based on Dirichlet Multinomial Mixture)主题翻译模型。该模型利用DMM模型发现短文本主题信息,在主题约束下学习词语与关键词的翻译概率,从而提高短文本关键词抽取效果。在真实数据集上的实验结果表明,论文提出的TTM_DMM模型在评价指标Precious、Recall以及F-measure上优于现有的短文本关键词抽取方法。
