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2013 Volume 41 Issue 7
2013, 41(7): 769-786
Abstract:
Entrained flow gasification process involves turbulent multiphase flow and the interaction of complex chemical reaction process at high temperature and pressure, covering the nozzle atomization and dispersion, complex multiphase jet flows, turbulent mixing, complex gasification reaction, flame structure and its temperature distribution and many other aspects. It is a very important research focus. In this paper, the research progress of entrained flow gasification process, which had been made in recent years, were reviewed, including the atomization mechanism of coal-water-slurry nozzle, the particle dispersion mechanism of pulverized coal nozzle, the rule of stagnation point offset of opposed impinging stream, oscillation of the impingement plane, the pattern of opposed impinging flame structure and its three-dimensional temperature field, the gasification characteristics of the typical coal and petroleum coke, and the simulation for entrained flow gasifier. It is also discussed about the research priorities of entrained flow gasification process in future.
Entrained flow gasification process involves turbulent multiphase flow and the interaction of complex chemical reaction process at high temperature and pressure, covering the nozzle atomization and dispersion, complex multiphase jet flows, turbulent mixing, complex gasification reaction, flame structure and its temperature distribution and many other aspects. It is a very important research focus. In this paper, the research progress of entrained flow gasification process, which had been made in recent years, were reviewed, including the atomization mechanism of coal-water-slurry nozzle, the particle dispersion mechanism of pulverized coal nozzle, the rule of stagnation point offset of opposed impinging stream, oscillation of the impingement plane, the pattern of opposed impinging flame structure and its three-dimensional temperature field, the gasification characteristics of the typical coal and petroleum coke, and the simulation for entrained flow gasifier. It is also discussed about the research priorities of entrained flow gasification process in future.
2013, 41(7): 787-797
Abstract:
Coal bed methane (CBM) as an unconventional natural gas is a valuable energy resources; meanwhile the main content of CBM, methane, is also one of the most important gases that contribute towards inducing the greenhouse effect. The mitigation and utilization of coal bed methane, by reducing methane emissions and producing energy from recovered methane, can offer both opportunities to mitigate global climate change and to generate new sources of clean energy, which is therefore of great significance in both economic and environmental aspects and has received extensive attentions in recent years. In this paper, we attempt to make a review on the recent progresses of research and development in the mitigation and utilization of CBM. We focused mainly on the application of catalytic combustion in CBM mitigation and utilization, especially the deoxygenation of oxygen-bearing CBM, which is the key issue for methane concentration through pressure swing adsorption, as well as the mitigation and heat recovery of ventilation air methane (VAM) by using catalytic flow reversal reactor. Lastly, we would have an outlook on the possible technologies for the integrated utilization of CBM.
Coal bed methane (CBM) as an unconventional natural gas is a valuable energy resources; meanwhile the main content of CBM, methane, is also one of the most important gases that contribute towards inducing the greenhouse effect. The mitigation and utilization of coal bed methane, by reducing methane emissions and producing energy from recovered methane, can offer both opportunities to mitigate global climate change and to generate new sources of clean energy, which is therefore of great significance in both economic and environmental aspects and has received extensive attentions in recent years. In this paper, we attempt to make a review on the recent progresses of research and development in the mitigation and utilization of CBM. We focused mainly on the application of catalytic combustion in CBM mitigation and utilization, especially the deoxygenation of oxygen-bearing CBM, which is the key issue for methane concentration through pressure swing adsorption, as well as the mitigation and heat recovery of ventilation air methane (VAM) by using catalytic flow reversal reactor. Lastly, we would have an outlook on the possible technologies for the integrated utilization of CBM.
2013, 41(7): 798-804
Abstract:
Biomass gasification for energy utilization has been wildly used. The development and applications of biomass gasification technologies were reviewed in this paper. Special attention was paid to major problems encountered in practical use. A comparison of economical performances of gas supply for livelihood and industry was made. The prospects of biomass gasification in China were put forward. Taking into account the new situation, several suggestions were given for the development of biomass gasification industry.
Biomass gasification for energy utilization has been wildly used. The development and applications of biomass gasification technologies were reviewed in this paper. Special attention was paid to major problems encountered in practical use. A comparison of economical performances of gas supply for livelihood and industry was made. The prospects of biomass gasification in China were put forward. Taking into account the new situation, several suggestions were given for the development of biomass gasification industry.
2013, 41(7): 805-813
Abstract:
To meet the requirement of gasification of Shanxi anthracites with slag tapping, the effects of CaO, MgO and Fe2O3 flux on the improvement of ash fusibility and viscosity-temperature property were evaluated and compared. The results show that for high silicon and aluminum coal ash with the Si/Al ratio from 1.2 to 2.0, the order of fluxing effect is MgO > CaO > Fe2O3. The difference of fluxing effect is caused by the different stable minerals formed at high temperature. For three different fluxes, the relation between the flow temperature (FT) and the liquidus temperature (tliq) is determined. And a linear relationship between CaO or Fe2O3 content and FT is obtained as follows: FT= 1 593-9.573 × wCaO (R2=0.942 9) and FT = 1 576-8.330 6 × wFe2O3 (R2=0.955 9), which are useful to guide the addition of flux. CaO, MgO and Fe2O3 show different effects on the viscosity-temperature character. Judging from the viscosity value and the temperature of critical viscosity, CaO displays the best performance as a flux. The different electronegativity of Ca2+, Mg2+, Fe2+ and the formation of different minerals with addition of CaO, MgO and Fe2O3 at high temperature are responsible for the various influences of flux on the viscosity value. Small ion radius of Mg2+ and Fe2+ and the possible crystallization of iron at high temperature are the reasons for the higher temperature of critical viscosity.
To meet the requirement of gasification of Shanxi anthracites with slag tapping, the effects of CaO, MgO and Fe2O3 flux on the improvement of ash fusibility and viscosity-temperature property were evaluated and compared. The results show that for high silicon and aluminum coal ash with the Si/Al ratio from 1.2 to 2.0, the order of fluxing effect is MgO > CaO > Fe2O3. The difference of fluxing effect is caused by the different stable minerals formed at high temperature. For three different fluxes, the relation between the flow temperature (FT) and the liquidus temperature (tliq) is determined. And a linear relationship between CaO or Fe2O3 content and FT is obtained as follows: FT= 1 593-9.573 × wCaO (R2=0.942 9) and FT = 1 576-8.330 6 × wFe2O3 (R2=0.955 9), which are useful to guide the addition of flux. CaO, MgO and Fe2O3 show different effects on the viscosity-temperature character. Judging from the viscosity value and the temperature of critical viscosity, CaO displays the best performance as a flux. The different electronegativity of Ca2+, Mg2+, Fe2+ and the formation of different minerals with addition of CaO, MgO and Fe2O3 at high temperature are responsible for the various influences of flux on the viscosity value. Small ion radius of Mg2+ and Fe2+ and the possible crystallization of iron at high temperature are the reasons for the higher temperature of critical viscosity.
2013, 41(7): 814-818
Abstract:
Based on the high efficient depolymerization performance of lignite in ionic liquids, thermal dissolution behaviors of 3 lignites Xianfeng (XL), Xilinggele (XLGL) and Shengli (SL) were investigated. And the thermally dissolved products from XL extracted by ionic liquid 1-butyl-3-methyl imidazole chloride ([Bmim]Cl) were separated and analyzed to explore the structure information of the lignite. It is found that the extraction yield of 3 lignites in ionic liquid [Bmim]Cl is significantly different under the same extraction conditions. The order of extraction yield is: XL > SL > XLGL. The thermally dissolved products of XL during extraction in [Bmim]Cl can be separated into acetone-soluble (15.9%), pyridine-soluble (56.0%), and pyridine-insoluble (28.1%), respectively. Acetone soluble (AS) mainly contains long chain fatty compounds, tricyclic aromatics and tetracyclic aromatic compounds. Pyridine soluble (PS) and pyridine insoluble (PI) mainly contain tricyclic aromatics and pentacyclic aromatics.
Based on the high efficient depolymerization performance of lignite in ionic liquids, thermal dissolution behaviors of 3 lignites Xianfeng (XL), Xilinggele (XLGL) and Shengli (SL) were investigated. And the thermally dissolved products from XL extracted by ionic liquid 1-butyl-3-methyl imidazole chloride ([Bmim]Cl) were separated and analyzed to explore the structure information of the lignite. It is found that the extraction yield of 3 lignites in ionic liquid [Bmim]Cl is significantly different under the same extraction conditions. The order of extraction yield is: XL > SL > XLGL. The thermally dissolved products of XL during extraction in [Bmim]Cl can be separated into acetone-soluble (15.9%), pyridine-soluble (56.0%), and pyridine-insoluble (28.1%), respectively. Acetone soluble (AS) mainly contains long chain fatty compounds, tricyclic aromatics and tetracyclic aromatic compounds. Pyridine soluble (PS) and pyridine insoluble (PI) mainly contain tricyclic aromatics and pentacyclic aromatics.
2013, 41(7): 819-825
Abstract:
Jincheng No.15 anthracite (J15A) was subjected to ruthenium ion-catalyzed oxidation to characterize its structural feature. The results show that J15A is abundant in peri-condensed aromatic structure. The NaOCl oxidation of J15A promoted by pretreatment with H2O2 was conducted under mild conditions to produce benzene polycarboxylic acids (BPCAs). The pretreatment with H2O2 is proved to enhance the yields of BPCAs. It is potential to obtain BPCAs in high yield and selectivity by NaOCl oxidation of pretreated J15A with H2O2.
Jincheng No.15 anthracite (J15A) was subjected to ruthenium ion-catalyzed oxidation to characterize its structural feature. The results show that J15A is abundant in peri-condensed aromatic structure. The NaOCl oxidation of J15A promoted by pretreatment with H2O2 was conducted under mild conditions to produce benzene polycarboxylic acids (BPCAs). The pretreatment with H2O2 is proved to enhance the yields of BPCAs. It is potential to obtain BPCAs in high yield and selectivity by NaOCl oxidation of pretreated J15A with H2O2.
2013, 41(7): 826-831
Abstract:
Effects of K2CO3 addition and inert supports on chemical looping combustion (CLC) of coal with iron-based oxygen carrier were investigated. The results indicate that the reduction of iron-based oxygen carrier by coal can be remarkably improved by the addition of K2CO3. This enhancement can be ascribed to the catalytic CO2 gasification (rate-controlling step) by K2CO3 which migrates from oxygen carrier to coal particles. The sintering of iron-based oxygen carrier is promoted by K2CO3 due to its low melting temperature and the intensified redox reaction after K2CO3 addition. The inert support has no significant effect on the reactivity between coal and oxygen carrier, which could be due to the inert support do not affect the rate-limiting step. The catalytic activity can be observed during several redox cycles. However, there is a decreasing tendency of activity due to the loss and deactivation of catalyst.
Effects of K2CO3 addition and inert supports on chemical looping combustion (CLC) of coal with iron-based oxygen carrier were investigated. The results indicate that the reduction of iron-based oxygen carrier by coal can be remarkably improved by the addition of K2CO3. This enhancement can be ascribed to the catalytic CO2 gasification (rate-controlling step) by K2CO3 which migrates from oxygen carrier to coal particles. The sintering of iron-based oxygen carrier is promoted by K2CO3 due to its low melting temperature and the intensified redox reaction after K2CO3 addition. The inert support has no significant effect on the reactivity between coal and oxygen carrier, which could be due to the inert support do not affect the rate-limiting step. The catalytic activity can be observed during several redox cycles. However, there is a decreasing tendency of activity due to the loss and deactivation of catalyst.
2013, 41(7): 832-838
Abstract:
The existence form of sodium in Xinjiang coals was studied by extraction with distilled water, ammonium acetate and hydrochloric acid step by step. The extraction liquid and the residual coal samples were analyzed using an ion chromatography and an inductively coupled plasma atomic emission spectroscopy. The influences of different forms of sodium on the combustion characteristics of the high sodium coal were evaluated by the ignition temperature, the burnout temperature and the combustion characteristic index. The results indicate that the sodium existing in the coals is mainly in the form of water-soluble sodium, while the proportions of acid-soluble sodium and insoluble sodium are smaller. The particle size and inner pore structure of coal may have great influences on the water-soluble sodium content in coal samples, while the organic sodium contained in different particle size ranges of coal remains relatively constant. The water-soluble sodium and chlorine in different coals differ from each other. The water-soluble sodium would increase the ignition temperature and burnout temperature and decrease the combustion characteristic index, while the organic sodium would have catalysis on the combustion of coal.
The existence form of sodium in Xinjiang coals was studied by extraction with distilled water, ammonium acetate and hydrochloric acid step by step. The extraction liquid and the residual coal samples were analyzed using an ion chromatography and an inductively coupled plasma atomic emission spectroscopy. The influences of different forms of sodium on the combustion characteristics of the high sodium coal were evaluated by the ignition temperature, the burnout temperature and the combustion characteristic index. The results indicate that the sodium existing in the coals is mainly in the form of water-soluble sodium, while the proportions of acid-soluble sodium and insoluble sodium are smaller. The particle size and inner pore structure of coal may have great influences on the water-soluble sodium content in coal samples, while the organic sodium contained in different particle size ranges of coal remains relatively constant. The water-soluble sodium and chlorine in different coals differ from each other. The water-soluble sodium would increase the ignition temperature and burnout temperature and decrease the combustion characteristic index, while the organic sodium would have catalysis on the combustion of coal.
2013, 41(7): 839-844
Abstract:
An emissions studies for arsenic and mercury were conducted at a 300 MW coal-fired power plant. The solid streams such as coal, bottom ash and ESP ash were collected, and the arsenic and mercury in the flue gas around ESP were aslo directly sampled using Ontario Hydro Method and then tested. The results show that the arsenic concentration in fly ash is about 6.68×10-6, which is almost 2.5 times as that in coal, nevertheless that in bottom ash is only 1.70 ×10-6. Its concentration in the flue gas is 153.27 and 41.13 μg/m3 before and after ESP, respectively. The mercury concentration in coal, fly ash and bottom ash is about 2.5×10-7, 1.9×10-7 and 1.5×10-7 respectively, its concentration in the flue gas before and after ESP was about 5.49 and 5.21 μg/m3. Arsenic is significantly concentrated in fly ash, whereas mercury is not. ESP unit has obvious synergistic effect on arsenic removal up to 71%, while it is not obvious for mercury removal.
An emissions studies for arsenic and mercury were conducted at a 300 MW coal-fired power plant. The solid streams such as coal, bottom ash and ESP ash were collected, and the arsenic and mercury in the flue gas around ESP were aslo directly sampled using Ontario Hydro Method and then tested. The results show that the arsenic concentration in fly ash is about 6.68×10-6, which is almost 2.5 times as that in coal, nevertheless that in bottom ash is only 1.70 ×10-6. Its concentration in the flue gas is 153.27 and 41.13 μg/m3 before and after ESP, respectively. The mercury concentration in coal, fly ash and bottom ash is about 2.5×10-7, 1.9×10-7 and 1.5×10-7 respectively, its concentration in the flue gas before and after ESP was about 5.49 and 5.21 μg/m3. Arsenic is significantly concentrated in fly ash, whereas mercury is not. ESP unit has obvious synergistic effect on arsenic removal up to 71%, while it is not obvious for mercury removal.
2013, 41(7): 845-849
Abstract:
The rice husk fast pyrolysis was studied by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and the pyrolysis gases were online analyzed. The effects of pyrolytic temperature and time on the pyrolysis of biomass was focused. The results show that the number and yield of product species increase with temperature below 450 ℃. The less species at lower pyrolytic temperature is of benefit to the enrichment of high value products. However, the number of product species becomes constant and the yield only changes when the temperature is over 450 ℃. The yield reaches the maximum when the temperature is 550 ℃. As the temperature increases, the optimum pyrolytic time descends. The pyrolysis of biomass with a long pyrolysis time at lower temperature is more completely than that with a shot pyrolysis time at higher temperature.
The rice husk fast pyrolysis was studied by using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and the pyrolysis gases were online analyzed. The effects of pyrolytic temperature and time on the pyrolysis of biomass was focused. The results show that the number and yield of product species increase with temperature below 450 ℃. The less species at lower pyrolytic temperature is of benefit to the enrichment of high value products. However, the number of product species becomes constant and the yield only changes when the temperature is over 450 ℃. The yield reaches the maximum when the temperature is 550 ℃. As the temperature increases, the optimum pyrolytic time descends. The pyrolysis of biomass with a long pyrolysis time at lower temperature is more completely than that with a shot pyrolysis time at higher temperature.
2013, 41(7): 850-855
Abstract:
The effects of CaO addition and temperature on decarboxylation of stearic acid over Pt/C catalyst in subcritical water were investigated. The conversion of stearic acid increased dramatically, while the selectivity to heptadecane hardly changed with the addition of CaO. At 330 ℃ the conversion of stearic acid reached a maximum with Ca/stearic mol ratio of 0.5. Moreover, Pt/C catalyzed decarboxylation of stearic acid in subcritical water exhibited first-order kinetics. It was proposed that dissociative stearic acid was adsorbed on Pt/C catalyst, forming surface octadecanoate species and adsorbed H. The C-C bond dissociated via H insertion, resulting in the formation of heptadecane and CO2. The addition of CaO promoted the dissociation of stearic acid. As a result, the amount of adsorbed octadecanoate increased and the reaction was accelerated.
The effects of CaO addition and temperature on decarboxylation of stearic acid over Pt/C catalyst in subcritical water were investigated. The conversion of stearic acid increased dramatically, while the selectivity to heptadecane hardly changed with the addition of CaO. At 330 ℃ the conversion of stearic acid reached a maximum with Ca/stearic mol ratio of 0.5. Moreover, Pt/C catalyzed decarboxylation of stearic acid in subcritical water exhibited first-order kinetics. It was proposed that dissociative stearic acid was adsorbed on Pt/C catalyst, forming surface octadecanoate species and adsorbed H. The C-C bond dissociated via H insertion, resulting in the formation of heptadecane and CO2. The addition of CaO promoted the dissociation of stearic acid. As a result, the amount of adsorbed octadecanoate increased and the reaction was accelerated.
2013, 41(7): 856-861
Abstract:
The catalytic performance of papermaking white clay in the transesterification of peanut oil with methanol was investigated in terms of catalyst quantity, molar ratio of methanol to oil, reaction temperature, and time. Meanwhile, the catalyst is characterized by thermogravimetric analysis, X-ray fluorescence, X-ray diffraction, nitrogen adsorption and Hammett indicator. After a sequence of pretreatments involving calcination at 800 ℃, hydration at room temperature and activation at 600 ℃, the catalyst mainly consists of calcium oxide, with surface area of 7.28 m2/g and basic strength of 9.8 < H_ < 15.0. The preferred conditions are catalyst percentage of 6%, methanol/oil molar ratio of 12 and reaction time of 2 h at 64 ℃; under these conditions, the transesterification efficiency reaches 90.74%. The catalyst from papermaking white clay exhibits good reusability; after being reused for six times, the transesterification efficiency remains above 88.63% under the preferred condition.
The catalytic performance of papermaking white clay in the transesterification of peanut oil with methanol was investigated in terms of catalyst quantity, molar ratio of methanol to oil, reaction temperature, and time. Meanwhile, the catalyst is characterized by thermogravimetric analysis, X-ray fluorescence, X-ray diffraction, nitrogen adsorption and Hammett indicator. After a sequence of pretreatments involving calcination at 800 ℃, hydration at room temperature and activation at 600 ℃, the catalyst mainly consists of calcium oxide, with surface area of 7.28 m2/g and basic strength of 9.8 < H_ < 15.0. The preferred conditions are catalyst percentage of 6%, methanol/oil molar ratio of 12 and reaction time of 2 h at 64 ℃; under these conditions, the transesterification efficiency reaches 90.74%. The catalyst from papermaking white clay exhibits good reusability; after being reused for six times, the transesterification efficiency remains above 88.63% under the preferred condition.
2013, 41(7): 862-867
Abstract:
The Ni-Mg based monolithic catalyst was prepared by impregnation method. Effects of calcination temperature on microstructure and biomass gases reforming performances of the catalyst were investigated. The results indicated that there was the formation of NiO and NiMgO2 in the catalyst during calcination at different temperatures. Compared to other calcination temperatures, calcinating at 650 ℃ facilitated the dispersion of NiO on the cordierite and the increase of active sites. Under the dry reforming condition, conversion of CH4 and CO2 increased first, and then decreased gradually with the increase of calcination temperature. The CH4 and CO2 conversion reached the highest value as the calcination temperature is 650 ℃. A similar trend was observed for the yield of H2 and CO. Under the steam reforming condition, increasing calcination temperature promoted water gas shift reaction. In addition, changing calcination temperature may adjust selectively the ratio of H2/CO under the steam reforming condition.
The Ni-Mg based monolithic catalyst was prepared by impregnation method. Effects of calcination temperature on microstructure and biomass gases reforming performances of the catalyst were investigated. The results indicated that there was the formation of NiO and NiMgO2 in the catalyst during calcination at different temperatures. Compared to other calcination temperatures, calcinating at 650 ℃ facilitated the dispersion of NiO on the cordierite and the increase of active sites. Under the dry reforming condition, conversion of CH4 and CO2 increased first, and then decreased gradually with the increase of calcination temperature. The CH4 and CO2 conversion reached the highest value as the calcination temperature is 650 ℃. A similar trend was observed for the yield of H2 and CO. Under the steam reforming condition, increasing calcination temperature promoted water gas shift reaction. In addition, changing calcination temperature may adjust selectively the ratio of H2/CO under the steam reforming condition.
2013, 41(7): 868-874
Abstract:
K-promoted Cu/Zn/La/ZrO2 catalyst were prepared by coprecipitation methods. Hydrogenation of CO was used as a probe reaction to investigate the catalytic performance. Structure and surface properties of K-Cu/Zn/La/ZrO2 catalysts were characterized by XRD,TG,BET, NH3-TPD, H2-TPR, Raman and XPS technics. The results indicated that structure and specific surface had no direct relationship with the catalyst activity. Strong acidic sites of catalyst surface were not good for the formation of isobutanol. Synergy among Cu-Zn-Zr has an important effect on the activity of K-Cu/Zn/La/ZrO2 catalysts. When the calcinations temperature was at 450 ℃, synergistic effect of Cu-Zn-Zr became strongest and CuO could be reduced easily. Under the optimum calcination temperature, conversion of CO reached 69.47% and selectivity of isobutanol approached 19.09%. Methanol and isobutanol were the primary products and occupied 95.02% in the alcohol products.
K-promoted Cu/Zn/La/ZrO2 catalyst were prepared by coprecipitation methods. Hydrogenation of CO was used as a probe reaction to investigate the catalytic performance. Structure and surface properties of K-Cu/Zn/La/ZrO2 catalysts were characterized by XRD,TG,BET, NH3-TPD, H2-TPR, Raman and XPS technics. The results indicated that structure and specific surface had no direct relationship with the catalyst activity. Strong acidic sites of catalyst surface were not good for the formation of isobutanol. Synergy among Cu-Zn-Zr has an important effect on the activity of K-Cu/Zn/La/ZrO2 catalysts. When the calcinations temperature was at 450 ℃, synergistic effect of Cu-Zn-Zr became strongest and CuO could be reduced easily. Under the optimum calcination temperature, conversion of CO reached 69.47% and selectivity of isobutanol approached 19.09%. Methanol and isobutanol were the primary products and occupied 95.02% in the alcohol products.
2013, 41(7): 875-882
Abstract:
Hierarchically porous composite zeolite (BFZ, with Beta zeolite cores and Y zeolite polycrystalline shells) was employed as the methanol dehydration catalyst in the direct synthesis of dimethyl ether (DME) from syngas in a fixed-bed reactor. The correlation between the catalytic activity and the textural and acid properties of the dehydration catalyst was investigated. The results indicate that the composite zeolite of H-form (HBFZ) exhibits moderate acid strength and meso-porosity, which is responsible for the high activity of CO hydrogenation. For the direct synthesis of DME from CO hydrogenation over the physical mixture of commercial CuO/ZnO/Al2O3 catalyst (CZA) and the H-form zeolites (HBFZ or HY), CZA/HBFZ exhibits higher activity and stability than CZA/HY. Under 250 ℃, 5.0 MPa and 1 500 h-1, the conversion of CO and the selectivity to DME over CZA/HBFZ achieve 94.2% and 67.9%, respectively.
Hierarchically porous composite zeolite (BFZ, with Beta zeolite cores and Y zeolite polycrystalline shells) was employed as the methanol dehydration catalyst in the direct synthesis of dimethyl ether (DME) from syngas in a fixed-bed reactor. The correlation between the catalytic activity and the textural and acid properties of the dehydration catalyst was investigated. The results indicate that the composite zeolite of H-form (HBFZ) exhibits moderate acid strength and meso-porosity, which is responsible for the high activity of CO hydrogenation. For the direct synthesis of DME from CO hydrogenation over the physical mixture of commercial CuO/ZnO/Al2O3 catalyst (CZA) and the H-form zeolites (HBFZ or HY), CZA/HBFZ exhibits higher activity and stability than CZA/HY. Under 250 ℃, 5.0 MPa and 1 500 h-1, the conversion of CO and the selectivity to DME over CZA/HBFZ achieve 94.2% and 67.9%, respectively.
2013, 41(7): 883-888
Abstract:
CuO/ZnO/CeO2-ZrO2 catalysts for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effects of precipitation aging time on the catalytic performance were investigated. It was found that the prolonged precipitation aging time increased the surface Cu atoms and improved the reducibility of catalyst, but decreased the oxygen storage capacity. A nearly linear increase between the surface Cu atoms and H2 production rate was obtained in prepared CuO/ZnO/CeO2-ZrO2 catalysts with prolonged precipitation aging time. However, CO concentration increased with the decrease of the oxygen storage capacity. Considering the H2 production rate and CO level, the optimal precipitation aging time was 2 h. CuO/ZnO/CeO2-ZrO2 prepared using this aging time exhibited the best activity with suppressed CO formation.
CuO/ZnO/CeO2-ZrO2 catalysts for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effects of precipitation aging time on the catalytic performance were investigated. It was found that the prolonged precipitation aging time increased the surface Cu atoms and improved the reducibility of catalyst, but decreased the oxygen storage capacity. A nearly linear increase between the surface Cu atoms and H2 production rate was obtained in prepared CuO/ZnO/CeO2-ZrO2 catalysts with prolonged precipitation aging time. However, CO concentration increased with the decrease of the oxygen storage capacity. Considering the H2 production rate and CO level, the optimal precipitation aging time was 2 h. CuO/ZnO/CeO2-ZrO2 prepared using this aging time exhibited the best activity with suppressed CO formation.
2013, 41(7): 889-896
Abstract:
Rare earth metal modified Y zeolites (L-CeY) and USY zeolites (HRSY-3) were characterized by XRD, N2 adsorption, NH3-TPD, and in-situ Py-FTIR; the adsorption and catalytic conversion behavior of thiophene on the modified zeolites were investigated by using the in situ FT-IR combined with TG-MS analysis. The results indicated that the original crystal structures of the zeolites remain unchanged after the modification with the rare earth metal ions; however, the modification results in the formation of partial mesoporous structure and weak Lewis acid sites related to the rare-earth ion species as well as certain decrease of the acidic strength of the strong acid sites. Thiophene molecules can be activated via protonization upon the Brönsted acid sites of the USY and HY zeolites; however, the rare earth metal ions are able to promote the hydrogen transfer and oligomerization reactions, which can then enhance the catalytic cracking of thiophene reactions.
Rare earth metal modified Y zeolites (L-CeY) and USY zeolites (HRSY-3) were characterized by XRD, N2 adsorption, NH3-TPD, and in-situ Py-FTIR; the adsorption and catalytic conversion behavior of thiophene on the modified zeolites were investigated by using the in situ FT-IR combined with TG-MS analysis. The results indicated that the original crystal structures of the zeolites remain unchanged after the modification with the rare earth metal ions; however, the modification results in the formation of partial mesoporous structure and weak Lewis acid sites related to the rare-earth ion species as well as certain decrease of the acidic strength of the strong acid sites. Thiophene molecules can be activated via protonization upon the Brönsted acid sites of the USY and HY zeolites; however, the rare earth metal ions are able to promote the hydrogen transfer and oligomerization reactions, which can then enhance the catalytic cracking of thiophene reactions.
