Polyoxymethylene dimethyl ethers(PODE)were synthesized from the reaction of paraformaldehyde with dimethoxymethane(DMM)over different acid catalysts at different conditions.Products were found to follow the Schulz-Flo...Polyoxymethylene dimethyl ethers(PODE)were synthesized from the reaction of paraformaldehyde with dimethoxymethane(DMM)over different acid catalysts at different conditions.Products were found to follow the Schulz-Flory distribution law.The chain propagation proceeds through the insertion of an individual segment of CH2O one by one,while the simultaneous insertion of a few CH2O segments or their assembly is unlikely.Due to the restriction of this law,it is difficult to increase the selectivity to the desired products(e.g.,PODE3 4).展开更多
The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers （DMMn） were investigated over sulfated titania in order to reveal the decisive factor controlling the react...The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers （DMMn） were investigated over sulfated titania in order to reveal the decisive factor controlling the reaction. The results showed that the molar ratio of adjacent DMMn products in equilibrium solution had the same value, which depended absolutely on the reaction temperature. Meanwhile, the reactions had the same DMMn products distributions under varied reaction conditions. The equilibrium constants of the related step-wise reactions for DMMn formation were equal, which were calculated based on the bulk compositions of the reaction solution. And thus, the selectivity to DMMn was mainly controlled by the chemical equilibrium, i.e., thermodynamic control. In brief, the present results provide some guidance for future synthesis of DMMn.展开更多
Polyoxymethylene dimethyl ethers(DMM_n) are promising diesel additives. The synthesis of DMM_n from methylal(DMM) and paraformaldehyde over the NKC-9 acidic ion-exchange resin catalyst was investigated. Many unrecycla...Polyoxymethylene dimethyl ethers(DMM_n) are promising diesel additives. The synthesis of DMM_n from methylal(DMM) and paraformaldehyde over the NKC-9 acidic ion-exchange resin catalyst was investigated. Many unrecyclable by-products such as methyl formate, dimethyl ether and formic acid were produced in the reaction. To increase the selectivity of the desired products DMM_(3-6) and reduce the amount of unrecyclable by-products, the effects of reaction temperature, time, pressure and the molar ratio of the raw materials were evaluated through a series of single factor experiments. Experiments revealed that trace amount of water could suppress the formation of unrecyclable by-products, and the optimum initial water content(less than 2 wt%) was investigated. In addition, the synthetic process needs to go through the polyoxymethylene hemiformals intermediate stage, and then the DMM_n were obtained when polyoxymethylene hemiformals reacted with methanol. Ultimately, a possible mechanism is proposed to describe the formation of DMM_n from polyoxymethylene hemiformals in detail, in which it is revealed that the formation of carbocation intermediates is important in the reaction processes.展开更多
The promising combustion and emission properties of polyoxymethylene dimethyl ethers(PODEn)are of significant interest.However,the synthesis of PODEn products with desired chain lengths is still a problem facing synth...The promising combustion and emission properties of polyoxymethylene dimethyl ethers(PODEn)are of significant interest.However,the synthesis of PODEn products with desired chain lengths is still a problem facing synthetic PODEn.Herein,a series of unique IL@SBA16Cx solid catalysts are prepared by encapsulation of ionic liquids(ILs)within the nanocage of SBA16 through a silylation method.The structure of the encapsulated catalyst was characterized by UVvis spectra,Fourier transform infrared(FTIR),N2 adsorptiondesorption isotherms,Powder Xray diffraction(XRD),Transmission electron microscopy(TEM)and Elemental analysis.The encapsulated catalysts show similar catalytic activity to the homogeneous counterparts and display higher selectivity to the targeted PODE35 products than their homogeneous counterparts in the synthesis of PODEn from methanol(MeOH)and trioxymethylene(TOM).The encapsulated catalysts exhibit a superior PODE35 selectivity and could be the promising catalysts for PODEn synthetic reaction.展开更多
Polyoxymethylene dimethyl ethers(CH_(3)-O-(CH_(2)O)_(n)-CH_(3),PODE_(n),n>1)can be added to diesel to reduce air pollution caused by incomplete combustion.Driven by this need,a cost-effective and efficient syntheti...Polyoxymethylene dimethyl ethers(CH_(3)-O-(CH_(2)O)_(n)-CH_(3),PODE_(n),n>1)can be added to diesel to reduce air pollution caused by incomplete combustion.Driven by this need,a cost-effective and efficient synthetic route is presented and investigated by this work for the production of PODE_(n),which are formed from methylal and trioxane with low water content(<10%(mass))over HZSM-5 catalyst in a batch slurry autoclave at the temperature from 353.15 K to 393.15 K.The reaction rate laws including the PODE_(n) and byproducts of polyoxymethylene hemiformals(HF_(n)),polyoxymethylene glycols(MG),methanol(MeOH)and methyl formate(MF)are developed.The rate constants of propagation step(k_(6))and depolymerization step(k_(-6))are assumed independent on polymerization degree of PODE_(n).The rate of reaction is proportional to the content of the catalyst(Wcat)for the catalytic reaction within the scope of the study.All kinetic parameters were estimated by combining genetic algorithm and least square regression to fit experimental data well.This work is valuable for process optimization and reactor design.展开更多
The synthesis of polyoxymethylene dimethyl ethers as an ideal diesel fuel additive is the current hot topic of modern petrochemical industry for their expedient properties in mitigating air pollutants emission during ...The synthesis of polyoxymethylene dimethyl ethers as an ideal diesel fuel additive is the current hot topic of modern petrochemical industry for their expedient properties in mitigating air pollutants emission during combustion.In this work,a series of spherical sulfated zirconia catalysts were prepared by a one-pot hydrothermal method assisted with surfactant cetyltrimethylammonium bromide(CTAB).The prepared sulfated zirconia catalysts were used to catalyze PODEn synthesis from methanol and formaldehyde solution.Various characterization(XRD,BET,SEM,TGA,NH_(3)-TPD,FTIR,and Py-IR)were employed to elaborate the structure–activity relationship of the studied catalytic system.The results demonstrated that S/Zr molar ratio in precursor solution played an effective role on catalyst morphology and acidic properties,where the weak Brønsted acid sites and strong Lewis acid sites were favorable to the conversion of methanol and formation of long-chain PODEn,respectively.The reaction parameters such as catalyst amount,molar ratio of FA/MeOH,reaction time,temperature and pressure were optimized.The speculated reaction pathway for PODEn synthesis was proposed based on the synergy of Brønsted and Lewis acid sites,which suggested that Brønsted and Lewis acid sites might be advantageous to the activation of polyoxymethylene hemiformals[CH_(3)(OCH_(2))_(n)OH]and methylene glycol(HOCH_(2)OH),respectively.展开更多
In this paper,high-speed imaging and spectrometry diagnostics were used to study the spray flame structures and emission spectra of polyoxymethylene dimethyl ethers(PODE)in an optical constant volume vessel.The effect...In this paper,high-speed imaging and spectrometry diagnostics were used to study the spray flame structures and emission spectra of polyoxymethylene dimethyl ethers(PODE)in an optical constant volume vessel.The effects of oxygen volume fraction(15%to 80%)on some typical combustion characteristics such as spatially integrated natural intensity,flame propagation speed,lift-off length and the distribution of flame emission spectra were investigated.The results show that the PODE spray flame mainly exhibits blue chemiluminescence,which is different from the diesel yellow diffusion flame dominated by soot radiation.As the oxygen concentration increases,the flame natural luminosity and propagation speed increases,the position of lift-off region and flame tip move towards the injector nozzle,and the flame width becomes narrower.According to the spectral results,the blue chemiluminescence generated by carbon monoxide oxidation dominates the PODE flame luminescence,suggesting that no soot is formed.The increase in oxygen concentration leads to enlarged intensity and gradient of PODE flame radiation.In summary,the combination of PODE and oxygen-enriched combustion shows no soot formation and promotes the oxidation of carbon monoxide and unburned hydrocarbon.This study can provide more insights into PODE spray combustion,and offer guidelines for achieving efficient and clean combustion.展开更多
Polyoxymethylene dimethyl ether(PODE n,n≥1)is a class of oxygenated fuels containing unique carbon-oxygen chain structure and a promising alternative fuel for diesel engines.In this study,low-temperature oxidation ch...Polyoxymethylene dimethyl ether(PODE n,n≥1)is a class of oxygenated fuels containing unique carbon-oxygen chain structure and a promising alternative fuel for diesel engines.In this study,low-temperature oxidation characteristics of PODE_(3) were studied experimentally and numerically.Experiments were performed in a jet-stirred reactor(JSR)at equivalence ratios of 0.5,1.0 and 2.0,in the temperature range of 500 to 950 K,and at atmospheric pressure.Mole fractions of PODE_(3),O_(2),H_(2),CO,CO_(2),CH_(3) OH and C_(1)-C_(2) hydrocarbons were measured by gas chromatograph(GC).Experimental measurements were compared with the simulation results based on two literature low-temperature oxidation models,denoted as the He model and the Cai model,respectively.Good agreement was obtained between the measured and simulated fuel consumption profiles,while a deviation was observed between the experimental and simulation results on the mole fractions of O_(2) and intermediate products at medium temperatures.Reaction pathway analyses based on the two models were performed,revealing that the second O_(2)-addition reaction pathway is more significant in the prediction by the Cai model than that by the He model.Sensitivity analyses pointed out that the most important reactions affecting fuel consumption are the H-abstraction reactions of PODE_(3),and the decomposition of H_(2) O_(2) and the consumption of CH_(2)O become more sensitive at medium temperatures.展开更多
文摘Polyoxymethylene dimethyl ethers(PODE)were synthesized from the reaction of paraformaldehyde with dimethoxymethane(DMM)over different acid catalysts at different conditions.Products were found to follow the Schulz-Flory distribution law.The chain propagation proceeds through the insertion of an individual segment of CH2O one by one,while the simultaneous insertion of a few CH2O segments or their assembly is unlikely.Due to the restriction of this law,it is difficult to increase the selectivity to the desired products(e.g.,PODE3 4).
基金supported by the National Natural Science Foundation of China(NSFC,No.21203220 and 21133011)China Postdoctoral Science Foundation(No.2014M551674)+1 种基金Jiangsu Planned Projects for Postdoctoral Research Funds(No.1302070C)the National Basic Research Program of China(973 Program,No.2011CB201404)
文摘The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers （DMMn） were investigated over sulfated titania in order to reveal the decisive factor controlling the reaction. The results showed that the molar ratio of adjacent DMMn products in equilibrium solution had the same value, which depended absolutely on the reaction temperature. Meanwhile, the reactions had the same DMMn products distributions under varied reaction conditions. The equilibrium constants of the related step-wise reactions for DMMn formation were equal, which were calculated based on the bulk compositions of the reaction solution. And thus, the selectivity to DMMn was mainly controlled by the chemical equilibrium, i.e., thermodynamic control. In brief, the present results provide some guidance for future synthesis of DMMn.
文摘Polyoxymethylene dimethyl ethers(DMM_n) are promising diesel additives. The synthesis of DMM_n from methylal(DMM) and paraformaldehyde over the NKC-9 acidic ion-exchange resin catalyst was investigated. Many unrecyclable by-products such as methyl formate, dimethyl ether and formic acid were produced in the reaction. To increase the selectivity of the desired products DMM_(3-6) and reduce the amount of unrecyclable by-products, the effects of reaction temperature, time, pressure and the molar ratio of the raw materials were evaluated through a series of single factor experiments. Experiments revealed that trace amount of water could suppress the formation of unrecyclable by-products, and the optimum initial water content(less than 2 wt%) was investigated. In addition, the synthetic process needs to go through the polyoxymethylene hemiformals intermediate stage, and then the DMM_n were obtained when polyoxymethylene hemiformals reacted with methanol. Ultimately, a possible mechanism is proposed to describe the formation of DMM_n from polyoxymethylene hemiformals in detail, in which it is revealed that the formation of carbocation intermediates is important in the reaction processes.
基金The authors greatly acknowledge Prof.Tim Storr from Simon Fraser University for his help in English writing and improving of this paper.The work was supported by the Natural Science Foundation of Shanxi Province(201801D121062)the Shanxi Scholarship Council of China(2017-037)the Foundation of Taiyuan University of Technology(2016MS03).
文摘The promising combustion and emission properties of polyoxymethylene dimethyl ethers(PODEn)are of significant interest.However,the synthesis of PODEn products with desired chain lengths is still a problem facing synthetic PODEn.Herein,a series of unique IL@SBA16Cx solid catalysts are prepared by encapsulation of ionic liquids(ILs)within the nanocage of SBA16 through a silylation method.The structure of the encapsulated catalyst was characterized by UVvis spectra,Fourier transform infrared(FTIR),N2 adsorptiondesorption isotherms,Powder Xray diffraction(XRD),Transmission electron microscopy(TEM)and Elemental analysis.The encapsulated catalysts show similar catalytic activity to the homogeneous counterparts and display higher selectivity to the targeted PODE35 products than their homogeneous counterparts in the synthesis of PODEn from methanol(MeOH)and trioxymethylene(TOM).The encapsulated catalysts exhibit a superior PODE35 selectivity and could be the promising catalysts for PODEn synthetic reaction.
基金This research was supported by the National Key R&D Program of China(2018YFB0604900).
文摘Polyoxymethylene dimethyl ethers(CH_(3)-O-(CH_(2)O)_(n)-CH_(3),PODE_(n),n>1)can be added to diesel to reduce air pollution caused by incomplete combustion.Driven by this need,a cost-effective and efficient synthetic route is presented and investigated by this work for the production of PODE_(n),which are formed from methylal and trioxane with low water content(<10%(mass))over HZSM-5 catalyst in a batch slurry autoclave at the temperature from 353.15 K to 393.15 K.The reaction rate laws including the PODE_(n) and byproducts of polyoxymethylene hemiformals(HF_(n)),polyoxymethylene glycols(MG),methanol(MeOH)and methyl formate(MF)are developed.The rate constants of propagation step(k_(6))and depolymerization step(k_(-6))are assumed independent on polymerization degree of PODE_(n).The rate of reaction is proportional to the content of the catalyst(Wcat)for the catalytic reaction within the scope of the study.All kinetic parameters were estimated by combining genetic algorithm and least square regression to fit experimental data well.This work is valuable for process optimization and reactor design.
基金This work was financially supported by National Key Research and Development Program of China(No.2018YFB0604804).
文摘The synthesis of polyoxymethylene dimethyl ethers as an ideal diesel fuel additive is the current hot topic of modern petrochemical industry for their expedient properties in mitigating air pollutants emission during combustion.In this work,a series of spherical sulfated zirconia catalysts were prepared by a one-pot hydrothermal method assisted with surfactant cetyltrimethylammonium bromide(CTAB).The prepared sulfated zirconia catalysts were used to catalyze PODEn synthesis from methanol and formaldehyde solution.Various characterization(XRD,BET,SEM,TGA,NH_(3)-TPD,FTIR,and Py-IR)were employed to elaborate the structure–activity relationship of the studied catalytic system.The results demonstrated that S/Zr molar ratio in precursor solution played an effective role on catalyst morphology and acidic properties,where the weak Brønsted acid sites and strong Lewis acid sites were favorable to the conversion of methanol and formation of long-chain PODEn,respectively.The reaction parameters such as catalyst amount,molar ratio of FA/MeOH,reaction time,temperature and pressure were optimized.The speculated reaction pathway for PODEn synthesis was proposed based on the synergy of Brønsted and Lewis acid sites,which suggested that Brønsted and Lewis acid sites might be advantageous to the activation of polyoxymethylene hemiformals[CH_(3)(OCH_(2))_(n)OH]and methylene glycol(HOCH_(2)OH),respectively.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51976134 and 91941102).
文摘In this paper,high-speed imaging and spectrometry diagnostics were used to study the spray flame structures and emission spectra of polyoxymethylene dimethyl ethers(PODE)in an optical constant volume vessel.The effects of oxygen volume fraction(15%to 80%)on some typical combustion characteristics such as spatially integrated natural intensity,flame propagation speed,lift-off length and the distribution of flame emission spectra were investigated.The results show that the PODE spray flame mainly exhibits blue chemiluminescence,which is different from the diesel yellow diffusion flame dominated by soot radiation.As the oxygen concentration increases,the flame natural luminosity and propagation speed increases,the position of lift-off region and flame tip move towards the injector nozzle,and the flame width becomes narrower.According to the spectral results,the blue chemiluminescence generated by carbon monoxide oxidation dominates the PODE flame luminescence,suggesting that no soot is formed.The increase in oxygen concentration leads to enlarged intensity and gradient of PODE flame radiation.In summary,the combination of PODE and oxygen-enriched combustion shows no soot formation and promotes the oxidation of carbon monoxide and unburned hydrocarbon.This study can provide more insights into PODE spray combustion,and offer guidelines for achieving efficient and clean combustion.
基金supported by the National Natural Science Foundation of China(Grants No.52022058,51776124 and 51861135303)the Shanghai Science and Technology Committee(Grant No.19160745400).
文摘Polyoxymethylene dimethyl ether(PODE n,n≥1)is a class of oxygenated fuels containing unique carbon-oxygen chain structure and a promising alternative fuel for diesel engines.In this study,low-temperature oxidation characteristics of PODE_(3) were studied experimentally and numerically.Experiments were performed in a jet-stirred reactor(JSR)at equivalence ratios of 0.5,1.0 and 2.0,in the temperature range of 500 to 950 K,and at atmospheric pressure.Mole fractions of PODE_(3),O_(2),H_(2),CO,CO_(2),CH_(3) OH and C_(1)-C_(2) hydrocarbons were measured by gas chromatograph(GC).Experimental measurements were compared with the simulation results based on two literature low-temperature oxidation models,denoted as the He model and the Cai model,respectively.Good agreement was obtained between the measured and simulated fuel consumption profiles,while a deviation was observed between the experimental and simulation results on the mole fractions of O_(2) and intermediate products at medium temperatures.Reaction pathway analyses based on the two models were performed,revealing that the second O_(2)-addition reaction pathway is more significant in the prediction by the Cai model than that by the He model.Sensitivity analyses pointed out that the most important reactions affecting fuel consumption are the H-abstraction reactions of PODE_(3),and the decomposition of H_(2) O_(2) and the consumption of CH_(2)O become more sensitive at medium temperatures.
