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01704 On the validity of thermogravimetric determination of carbon gasification kinetics
03
Gaseous
fuels
(derived
gaseous
fuels)
for regenerating a carbon dioxide-absorbing dioxide-absorbing liquid regenerating tower recovery apparatus.
03/01702 selective
liquid of the
Mo-V-Nb mixed oxides as catalysts oxidation of ethane
in the carbon carbon dioxide
in the
Botella, P.
03/01703 modified catalysis alcohols)
Mono (V, Nb) or bimetallic (V-Ti, Nb-Ti) ions MCM-41 catalysts: synthesis, characterization and in oxidation of hydrocarbons (aromatics and
Parvulescu. V. ef al. Caralysis TO&J, 2003, 78, (l-4), 477485. Mesoporous MCM-41 molecular sieves modified by single (V and Nb) or bimetal (Nb-Ti and V-Ti) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis with two different silica sources (sodium silicate and TEOS) and characterized (as-synthesized samples and those used after reaction) by XRD, Nz adsorption-desorption, TEM, SEM and FTIR techniques. Niobium and titanium were stabilized in the autoclavized gel by complexation with a ligand (acetylacetone and oxalic acid, respectively). V modified MCM-41 catalysts gave a very high activity in hydroxylation reaction of benzene and toluene and a low conversion in oxidation of styrene while Nb-modified MCM-41 samples showed very high conversion in oxidation of styrene but low oxidation conversion of benzene and toluene. Further introduction of titanium in V- and Nbmodified MCM-41 materials conducted to the less well-ordered hexagonal arrangement and gave very different effect on activity in oxidation of aromatics. Introduction of Ti into V-MCM-41 solids led to an increase in activity in oxidation of styrene and benzene but a decrease in conversion in oxidation of toluene. While the addition of Ti in Nb-MCM-41 resulted in a slight increase in conversion of styrene oxidation but a significant decrease in activity of benzene and toluene oxidation. It reveals that the introduction mode of oxidant in the reactors can also influence the activity and selectivity of reaction. An increase in reaction rate of oxidation, in the first 20 h, was obtained by introduction of Hz02 step by step during the reaction. The present paper evidenced that the side chain oxidation is main reaction of styrene oxidation while the hydroxylation is main reaction of benzene and toluene. That is why these two reactions need different catalytic centers as revealed by this paper. The oxidation of alcohols using Vmodified MCM-41 as catalysts has also been explored and these catalysts showed a very low catalytic activity which increases in the order: hexanol
03/01704 On the validity of thermogravimetric determination of carbon gasification kinetics Feng, B. and Bhatia, S. Chemical Engineering Science, 2002. 57, (15), 2907-2920. Thermogravimetric analysis was widely applied in kinetic studies of carbon gasification, with the associated temporal weight change profiles being used to extract kinetic information and to validate gasification models. However the weight change profiles are not always governed by the intrinsic gasification activity because of the effect of chemisorption and its dynamics. In the present work the criteria under which weight change profiles can be used to detect intrinsic kinetics for CO2 and OZ gasification were theoretically detected by examining the region in which the chemisorption dynamics can be assumed pseudosteady. It is found that the validity of the pseudo-steady assumption depends on the experimental conditions as well as on the initial surface area of carbon. Based on known mechanisms and rate constants an active surface area region is identified within which the steady state assumption is valid and the effect of chemisorption dynamics is negligible. The size of the permissible region is sensitive to the reaction temperature and gas pressure. The results indicate that in some cases the thermogravimetric data should be used with caution in kinetic studies. A large amount of literature on thermogravimetric analyser detected char gasification kinetics is examined and the importance of chemisorption dynamics for the data assessed.
03/01705 synthesis Jahanmiri, nrcutions,
Optimal reactor A. and 2002.
temperature Eslamloueyan,
profile
in methanol
R. Chemical
Engineering
Commu-
189, (6). 713-741.
An optimal temperature profile is detected for a methanol synthesis reactor of LURGI type. The temperature profile is estimated so that methanol production rate in the reactor outlet will be maximized. First, 296
Fuel
and
Energy
Abstracts
September
2003
the reactor is simulated based on betrrogencoua one- and twodimensional models. The comparison of the simulation results and plant data shows that the heterogeneous one-dimensional model can reliably be used for detecting optlmal temperature profile. Since optimal temperature profile for reversible cxothermic reaction in tubular reactors i\ a decreasing function of reactor length, the technique of control variable parameterization is used for detecting optimal temperature profile in a methanol reactor. In thi\ way, a third order polynomial is considered for the temperature profile and the polynomial coefficients are as decision variables. ‘The optimization is based on a Quasi-Newton’s method (BFS technique). and the objective function is methanol flow rate at the reactor outlet. The results ot optimization indicate that if optimal temperature profile is implemented in the reactor. methanol production will significantly he increased.
03/01706 Partial oxidation of methane to synthesis using lattice oxygen instead of molecular oxygen
gas
Li, R. et nl. C~ilmo Xurhao. 2002. 23, (4). 38lF387. (In Chinese) The redox performance of Fe103, which was used as a provider of lattice oxygen, was investigated by using thermogravimetry under a methane flow. The lattice oxygen in FezOi can react with CHI to form COz and HZ0 while FeZ07 is reduced through steps Fe20,-iFe304 and Fel,Od-FeO-Fe. The redox circulation technique combined with onhne quadrupole mass spectrometric analysis was used to study the feasibility of the methane oxidation to synthesis gas using lattice oxygen instead of molecular oxygen. The switching reaction between 13%02/ He and 6.5%CH4/Ar at a flow rate of 31 mL/s and 750” was carried out in a fixed-bed reactor, in which 100 mg Fez03 was placed on the layer of Ni/A1203 catalyst (400 mg). The results show that methane can he converted to CO and HZ. During the CHI reaction step, -25?+ methane is oxidized to COZ and Hz0 by lattice oxygen from FezOl and the remaining 75% methane is reformed with CO: and Hz0 over the Ni/A1203 catalyst to produce synthesis gas. During the OZ reaction step, lower valence iron oxide is reoxidized by molecular oxygen to its initial state. Using a suitable period of redox circulation, high conversion of methane and high selectivity to synthesis gas could be obtained over Fe201 and Ni/AlzO.$ catalyst. These results indicate that methane can be oxidized to synthesis gas by using lattice oxygen instead of molecular oxygen through a combustion-reforming mechanism.
03101707
Steam processing
Lewis, F. M. and Swithenbank, J. PCT Int. Appl. WO 02 79,350 (Cl. ClOJ3/00), 10 Ott 2002, GB Appl. 200117.885. Waste material is incinerated to heat water to produce low-temperature steam. The steam is mixed with oxygen to produce synthetic air. Methane (first fuel) is burnt in the synthetic air to produce ultrasuperheated steam at -1600”. Coal particles are gasified in the ultrasuperheated steam producing a second fuel, which is combusted in hot air. The products of combustion are expanded isothermally in the turbine (T,) to produce electricity. The hot waste gas from the turbine is used to heat air isothermally compressed in a compressor (C,) in the presence of a water spray. The heated air supports the combustion of the gasified coal and the cooled waste product is employed for district heating purposes.
03/01708 Steam reformin of a clean model biogas Ni/Ai203 in fiuidized- and Pixed-bed reactors
over
Effendi, A. et ul. Catu[ysis Todu!:, 2002. 77, (3), 181-t 89. Simultaneous steam, carbon dioxide reforming of methane was conducted over 11.5 wt% Ni/Al203, at 1 atm in micro-fluidizedand fixed-bed reactors using a constant molar ratio of CH4/C02-1.5 as a model biogas. The performance of a fluidized reactor was compared to that of a fixed-bed reactor under similar conditions (feed gas to steam ratios of 1.5 and 0.75 at a reactor temperature of 750°C. GHSV of 300 min-‘). Conversions of CHI and CO2 were 75 and 67%, respectively, in a fixed-bed reactor under the ratio of 1.5. Overall higher conversions (7-15%) were observed in the fluidized-reforming reactor. The initial activity of the fixed-bed reformer decreased rapidly and massive carbon deposition caused reactor blockage at the low steam concentration. Decreased the feed gas to steam ratio to 0.75 reduced carbon deposition and the nature of the carbon was suggested not to be the cause of the catalytic enhancement of the fluidized reforming. A study of the fluidized-bed reformer under decreasing feed gas to steam ratios from 3.0 to 0.3 showed an almost complete CHd conversion (98% for feed gas to steam ratios below 1.0). With decreasing feed gas to steam ratio the HdCO ratios increased as expected from 1.5 to 2.7. At the fluidization was highest feed gas to steam ratio, a poor catalyst observed due to massive carbon deposition, which was reduced dramatically when steam was provided in excess. Increasing temperatures from 650 to 850°C enhanced both conversions and lowered HZ/ CO ratios.
Gaseous
fuels
(derived
gaseous
fuels)
for regenerating a carbon dioxide-absorbing dioxide-absorbing liquid regenerating tower recovery apparatus.
03/01702 selective
liquid of the
Mo-V-Nb mixed oxides as catalysts oxidation of ethane
in the carbon carbon dioxide
in the
Botella, P.
03/01703 modified catalysis alcohols)
Mono (V, Nb) or bimetallic (V-Ti, Nb-Ti) ions MCM-41 catalysts: synthesis, characterization and in oxidation of hydrocarbons (aromatics and
Parvulescu. V. ef al. Caralysis TO&J, 2003, 78, (l-4), 477485. Mesoporous MCM-41 molecular sieves modified by single (V and Nb) or bimetal (Nb-Ti and V-Ti) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis with two different silica sources (sodium silicate and TEOS) and characterized (as-synthesized samples and those used after reaction) by XRD, Nz adsorption-desorption, TEM, SEM and FTIR techniques. Niobium and titanium were stabilized in the autoclavized gel by complexation with a ligand (acetylacetone and oxalic acid, respectively). V modified MCM-41 catalysts gave a very high activity in hydroxylation reaction of benzene and toluene and a low conversion in oxidation of styrene while Nb-modified MCM-41 samples showed very high conversion in oxidation of styrene but low oxidation conversion of benzene and toluene. Further introduction of titanium in V- and Nbmodified MCM-41 materials conducted to the less well-ordered hexagonal arrangement and gave very different effect on activity in oxidation of aromatics. Introduction of Ti into V-MCM-41 solids led to an increase in activity in oxidation of styrene and benzene but a decrease in conversion in oxidation of toluene. While the addition of Ti in Nb-MCM-41 resulted in a slight increase in conversion of styrene oxidation but a significant decrease in activity of benzene and toluene oxidation. It reveals that the introduction mode of oxidant in the reactors can also influence the activity and selectivity of reaction. An increase in reaction rate of oxidation, in the first 20 h, was obtained by introduction of Hz02 step by step during the reaction. The present paper evidenced that the side chain oxidation is main reaction of styrene oxidation while the hydroxylation is main reaction of benzene and toluene. That is why these two reactions need different catalytic centers as revealed by this paper. The oxidation of alcohols using Vmodified MCM-41 as catalysts has also been explored and these catalysts showed a very low catalytic activity which increases in the order: hexanol
03/01704 On the validity of thermogravimetric determination of carbon gasification kinetics Feng, B. and Bhatia, S. Chemical Engineering Science, 2002. 57, (15), 2907-2920. Thermogravimetric analysis was widely applied in kinetic studies of carbon gasification, with the associated temporal weight change profiles being used to extract kinetic information and to validate gasification models. However the weight change profiles are not always governed by the intrinsic gasification activity because of the effect of chemisorption and its dynamics. In the present work the criteria under which weight change profiles can be used to detect intrinsic kinetics for CO2 and OZ gasification were theoretically detected by examining the region in which the chemisorption dynamics can be assumed pseudosteady. It is found that the validity of the pseudo-steady assumption depends on the experimental conditions as well as on the initial surface area of carbon. Based on known mechanisms and rate constants an active surface area region is identified within which the steady state assumption is valid and the effect of chemisorption dynamics is negligible. The size of the permissible region is sensitive to the reaction temperature and gas pressure. The results indicate that in some cases the thermogravimetric data should be used with caution in kinetic studies. A large amount of literature on thermogravimetric analyser detected char gasification kinetics is examined and the importance of chemisorption dynamics for the data assessed.
03/01705 synthesis Jahanmiri, nrcutions,
Optimal reactor A. and 2002.
temperature Eslamloueyan,
profile
in methanol
R. Chemical
Engineering
Commu-
189, (6). 713-741.
An optimal temperature profile is detected for a methanol synthesis reactor of LURGI type. The temperature profile is estimated so that methanol production rate in the reactor outlet will be maximized. First, 296
Fuel
and
Energy
Abstracts
September
2003
the reactor is simulated based on betrrogencoua one- and twodimensional models. The comparison of the simulation results and plant data shows that the heterogeneous one-dimensional model can reliably be used for detecting optlmal temperature profile. Since optimal temperature profile for reversible cxothermic reaction in tubular reactors i\ a decreasing function of reactor length, the technique of control variable parameterization is used for detecting optimal temperature profile in a methanol reactor. In thi\ way, a third order polynomial is considered for the temperature profile and the polynomial coefficients are as decision variables. ‘The optimization is based on a Quasi-Newton’s method (BFS technique). and the objective function is methanol flow rate at the reactor outlet. The results ot optimization indicate that if optimal temperature profile is implemented in the reactor. methanol production will significantly he increased.
03/01706 Partial oxidation of methane to synthesis using lattice oxygen instead of molecular oxygen
gas
Li, R. et nl. C~ilmo Xurhao. 2002. 23, (4). 38lF387. (In Chinese) The redox performance of Fe103, which was used as a provider of lattice oxygen, was investigated by using thermogravimetry under a methane flow. The lattice oxygen in FezOi can react with CHI to form COz and HZ0 while FeZ07 is reduced through steps Fe20,-iFe304 and Fel,Od-FeO-Fe. The redox circulation technique combined with onhne quadrupole mass spectrometric analysis was used to study the feasibility of the methane oxidation to synthesis gas using lattice oxygen instead of molecular oxygen. The switching reaction between 13%02/ He and 6.5%CH4/Ar at a flow rate of 31 mL/s and 750” was carried out in a fixed-bed reactor, in which 100 mg Fez03 was placed on the layer of Ni/A1203 catalyst (400 mg). The results show that methane can he converted to CO and HZ. During the CHI reaction step, -25?+ methane is oxidized to COZ and Hz0 by lattice oxygen from FezOl and the remaining 75% methane is reformed with CO: and Hz0 over the Ni/A1203 catalyst to produce synthesis gas. During the OZ reaction step, lower valence iron oxide is reoxidized by molecular oxygen to its initial state. Using a suitable period of redox circulation, high conversion of methane and high selectivity to synthesis gas could be obtained over Fe201 and Ni/AlzO.$ catalyst. These results indicate that methane can be oxidized to synthesis gas by using lattice oxygen instead of molecular oxygen through a combustion-reforming mechanism.
03101707
Steam processing
Lewis, F. M. and Swithenbank, J. PCT Int. Appl. WO 02 79,350 (Cl. ClOJ3/00), 10 Ott 2002, GB Appl. 200117.885. Waste material is incinerated to heat water to produce low-temperature steam. The steam is mixed with oxygen to produce synthetic air. Methane (first fuel) is burnt in the synthetic air to produce ultrasuperheated steam at -1600”. Coal particles are gasified in the ultrasuperheated steam producing a second fuel, which is combusted in hot air. The products of combustion are expanded isothermally in the turbine (T,) to produce electricity. The hot waste gas from the turbine is used to heat air isothermally compressed in a compressor (C,) in the presence of a water spray. The heated air supports the combustion of the gasified coal and the cooled waste product is employed for district heating purposes.
03/01708 Steam reformin of a clean model biogas Ni/Ai203 in fiuidized- and Pixed-bed reactors
over
Effendi, A. et ul. Catu[ysis Todu!:, 2002. 77, (3), 181-t 89. Simultaneous steam, carbon dioxide reforming of methane was conducted over 11.5 wt% Ni/Al203, at 1 atm in micro-fluidizedand fixed-bed reactors using a constant molar ratio of CH4/C02-1.5 as a model biogas. The performance of a fluidized reactor was compared to that of a fixed-bed reactor under similar conditions (feed gas to steam ratios of 1.5 and 0.75 at a reactor temperature of 750°C. GHSV of 300 min-‘). Conversions of CHI and CO2 were 75 and 67%, respectively, in a fixed-bed reactor under the ratio of 1.5. Overall higher conversions (7-15%) were observed in the fluidized-reforming reactor. The initial activity of the fixed-bed reformer decreased rapidly and massive carbon deposition caused reactor blockage at the low steam concentration. Decreased the feed gas to steam ratio to 0.75 reduced carbon deposition and the nature of the carbon was suggested not to be the cause of the catalytic enhancement of the fluidized reforming. A study of the fluidized-bed reformer under decreasing feed gas to steam ratios from 3.0 to 0.3 showed an almost complete CHd conversion (98% for feed gas to steam ratios below 1.0). With decreasing feed gas to steam ratio the HdCO ratios increased as expected from 1.5 to 2.7. At the fluidization was highest feed gas to steam ratio, a poor catalyst observed due to massive carbon deposition, which was reduced dramatically when steam was provided in excess. Increasing temperatures from 650 to 850°C enhanced both conversions and lowered HZ/ CO ratios.