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PUBLICATIONS h5>
2007
Bimbela, Fernando; Oliva, Miriam; Ruiz, Joaquín; García, Lucía; Arauzo, Jesús
Hydrogen production by catalytic steam reforming of acetic acid, a model compound of biomass pyrolysis liquids Artículo de revista
En: Journal of Analytical and Applied Pyrolysis, vol. 79, no 1-2 SPEC. ISS., pp. 112–120, 2007, ISSN: 01652370.
@article{Bimbela2007,
title = {Hydrogen production by catalytic steam reforming of acetic acid, a model compound of biomass pyrolysis liquids},
author = {Fernando Bimbela and Miriam Oliva and Joaquín Ruiz and Lucía García and Jesús Arauzo},
doi = {10.1016/j.jaap.2006.11.006},
issn = {01652370},
year = {2007},
date = {2007-05-01},
journal = {Journal of Analytical and Applied Pyrolysis},
volume = {79},
number = {1-2 SPEC. ISS.},
pages = {112--120},
publisher = {Elsevier},
abstract = {An environmentally friendly and cost-competitive way of producing hydrogen is the catalytic steam reforming of biomass pyrolysis liquids, known as bio-oil, which can be separated into two fractions: ligninic and aqueous. Acetic acid has been identified as one of the major organic acids present in the latter, and catalytic steam reforming has been studied for this model compound. Three different Ni coprecipitated catalysts have been prepared with varying nickel content (23, 28 and 33% expressed as a Ni/(Ni + Al) relative at.% of nickel). Several parameters have been analysed using a microscale fixed-bed facility: the effect of the catalyst reduction time, the reaction temperature, the catalyst weight/acetic acid flow rate (W/mHAc) ratio, and the effect of the nickel content. The catalyst with 33% Ni content at 650 °C showed no significant enhancement of the hydrogen yield after 2 h of reduction compared to 1 h under the same experimental conditions. Its performance was poorer when reduced for just 0.5 h. For W/mHAc ratios greater than 2.29 g catalyst min/g acetic acid (650 °C, 33% Ni content) no improvement was observed, whereas for values lower than 2.18 g catalyst min/g acetic acid a decrease in product gas yields occurred rapidly. The temperatures studied were 550, 650 and 750 °C. No decrease in product gas yields was observed at 750 °C under the established experimental conditions. Below this temperature, the aforementioned decrease became more important with decreasing temperatures. The catalyst with 28% Ni content performed better than the other two. textcopyright 2006 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
An environmentally friendly and cost-competitive way of producing hydrogen is the catalytic steam reforming of biomass pyrolysis liquids, known as bio-oil, which can be separated into two fractions: ligninic and aqueous. Acetic acid has been identified as one of the major organic acids present in the latter, and catalytic steam reforming has been studied for this model compound. Three different Ni coprecipitated catalysts have been prepared with varying nickel content (23, 28 and 33% expressed as a Ni/(Ni + Al) relative at.% of nickel). Several parameters have been analysed using a microscale fixed-bed facility: the effect of the catalyst reduction time, the reaction temperature, the catalyst weight/acetic acid flow rate (W/mHAc) ratio, and the effect of the nickel content. The catalyst with 33% Ni content at 650 °C showed no significant enhancement of the hydrogen yield after 2 h of reduction compared to 1 h under the same experimental conditions. Its performance was poorer when reduced for just 0.5 h. For W/mHAc ratios greater than 2.29 g catalyst min/g acetic acid (650 °C, 33% Ni content) no improvement was observed, whereas for values lower than 2.18 g catalyst min/g acetic acid a decrease in product gas yields occurred rapidly. The temperatures studied were 550, 650 and 750 °C. No decrease in product gas yields was observed at 750 °C under the established experimental conditions. Below this temperature, the aforementioned decrease became more important with decreasing temperatures. The catalyst with 28% Ni content performed better than the other two. textcopyright 2006 Elsevier B.V. All rights reserved.
2002
Oliva, Miriam; Alzueta, María U; Millera, Ángela; Bilbao, Rafael
An approach to the analysis of mixing in reactive systems Artículo de revista
En: Chemical Engineering and Technology, vol. 25, no 4, pp. 417–419, 2002, ISSN: 09307516.
@article{Oliva2002,
title = {An approach to the analysis of mixing in reactive systems},
author = {Miriam Oliva and María U Alzueta and Ángela Millera and Rafael Bilbao},
doi = {10.1002/1521-4125(200204)25:4<417::AID-CEAT417>3.0.CO;2-0},
issn = {09307516},
year = {2002},
date = {2002-04-01},
journal = {Chemical Engineering and Technology},
volume = {25},
number = {4},
pages = {417--419},
abstract = {A simple mixing approach for use in reactive systems is considered. This mixing approach has so far been applied to reburning and selective non-catalytic reduction (SNCR) processes, two well-known techniques to reduce NOx emissions. Detailed kinetic models together with the mixing approaches, based on the work of Zwietering, are used to simulate both the chemistry and mixing of the reactants. Two different configurations for the mixing approach have been considered: the so-called direct and reverse approach. The study includes a comparison between different experimental results obtained in pilot installations and theoretical results calculated with the present approach.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A simple mixing approach for use in reactive systems is considered. This mixing approach has so far been applied to reburning and selective non-catalytic reduction (SNCR) processes, two well-known techniques to reduce NOx emissions. Detailed kinetic models together with the mixing approaches, based on the work of Zwietering, are used to simulate both the chemistry and mixing of the reactants. Two different configurations for the mixing approach have been considered: the so-called direct and reverse approach. The study includes a comparison between different experimental results obtained in pilot installations and theoretical results calculated with the present approach.
2000
Oliva, Miriam; Alzueta, María U; Millera, Ángela; Bilbao, Rafael
Theoretical study of the influence of mixing in the SNCR process. Comparison with pilot scale data Artículo de revista
En: Chemical Engineering Science, vol. 55, no 22, pp. 5321–5332, 2000, ISSN: 00092509.
@article{Oliva2000,
title = {Theoretical study of the influence of mixing in the SNCR process. Comparison with pilot scale data},
author = {Miriam Oliva and María U Alzueta and Ángela Millera and Rafael Bilbao},
doi = {10.1016/S0009-2509(00)00149-4},
issn = {00092509},
year = {2000},
date = {2000-11-01},
journal = {Chemical Engineering Science},
volume = {55},
number = {22},
pages = {5321--5332},
publisher = {Elsevier Science Ltd},
abstract = {A theoretical study of the influence of mixing on the selective non-catalytic reduction (SNCR) process has been performed. The study includes the use of a detailed kinetic reaction mechanism together with a simple approach for mixing based on the `maximum mixedness model' proposed by Zwietering (1959). Two different configurations for that simple mixing approach have been considered and discussed, i.e. the `direct approach' which implies entrainment of the jet flow (containing the SNCR reduction agent) into a bulk flow (containing the products of the main combustion zone); and the `reverse approach' which represents entrainment of the bulk flow into the jet stream. The main features of both approaches applied to the SNCR process are analyzed and discussed. Furthermore, comparison of the results obtained with the present approaches with different experimental pilot scale results is performed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A theoretical study of the influence of mixing on the selective non-catalytic reduction (SNCR) process has been performed. The study includes the use of a detailed kinetic reaction mechanism together with a simple approach for mixing based on the `maximum mixedness model’ proposed by Zwietering (1959). Two different configurations for that simple mixing approach have been considered and discussed, i.e. the `direct approach’ which implies entrainment of the jet flow (containing the SNCR reduction agent) into a bulk flow (containing the products of the main combustion zone); and the `reverse approach’ which represents entrainment of the bulk flow into the jet stream. The main features of both approaches applied to the SNCR process are analyzed and discussed. Furthermore, comparison of the results obtained with the present approaches with different experimental pilot scale results is performed.
Alzueta, María U; Bilbao, Rafael; Millera, Ángela; Oliva, Miriam; Ibañez, J C
Impact of new findings concerning urea thermal decomposition on the modeling of the urea-SNCR process Artículo de revista
En: Energy and Fuels, vol. 14, no 2, pp. 509–510, 2000, ISSN: 08870624.
@article{Alzueta2000,
title = {Impact of new findings concerning urea thermal decomposition on the modeling of the urea-SNCR process},
author = {María U Alzueta and Rafael Bilbao and Ángela Millera and Miriam Oliva and J C Ibañez},
url = {https://pubs.acs.org/sharingguidelines},
doi = {10.1021/ef990187j},
issn = {08870624},
year = {2000},
date = {2000-01-01},
journal = {Energy and Fuels},
volume = {14},
number = {2},
pages = {509--510},
publisher = {American Chemical Society},
abstract = {The interest in selective non-catalytic reduction (SNCR) applications has motivated the study of a number of possible configurations for NO x reduction. Among those, the use of urea as selective non-catalytic agent appears to be interesting. 1,2 Urea seems to be suitable because of handling and storage reasons, compared to other selective NO x reduction agents such as ammonia. A number of investigations have been carried out concerning the use of urea in the SNCR process during the past years, both experimentally on different scales, 2-4 and from a kinetic modeling point of view. 3,5 While the effectiveness in the process is well demonstrated experimentally through the different investigations, the kinetic modeling of the process presented some uncertainties mainly due to the behavior of urea under high temperature conditions. Urea has been traditionally considered to be decomposed into NH 3 and HNCO at high temperatures, 6,7 even though other decomposition paths have been proposed. 5,8 The agreement between experiments and calculations using those different mechanisms for urea decomposition is reasonably good, but a reliable determination of urea thermal decomposition was needed. Recent experimental results have appeared concerning the measurement of the reaction rate for the thermal urea decomposition reaction under conditions applicable to SNCR conditions. 9 In this communication, we want to show the impact of the new recent results by Aoki et al. 9 in the modeling of the SNCR process using urea. Aoki et al. 9 determined the reaction rate and products distribution of the thermal decomposition of urea. They obtained the following rates and product channels for the decomposition of urea at high temperatures when it is fed as an aqueous solution: We have included those reactions in the mechanism we used previously for studying the urea-SNCR process, 3 and the results are in good agreement with the previous Figure 1. Experimental and calculated results of NO and N2O concentrations vs temperature. Solid lines: calculations made assuming ideal mixing. Dashed lines: calculations made assuming a mixing time of 10 ms. (Inlet concentrations: 100 ppm NO, 150 ppm urea, 4% O2, 4% H2O, N2 to balance). Residence time(s)) 200/T(K). (NH 2) 2 CO f NH 3 + HNCO k 1) 1.2676 × 10 4 exp(-15540/[cal/mol]RT) (NH 2) 2 CO + H 2 O f 2 NH 3 + CO 2 k 2) 9.925 × 10 3 exp(-20980/[cal/mol]RT) 509},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The interest in selective non-catalytic reduction (SNCR) applications has motivated the study of a number of possible configurations for NO x reduction. Among those, the use of urea as selective non-catalytic agent appears to be interesting. 1,2 Urea seems to be suitable because of handling and storage reasons, compared to other selective NO x reduction agents such as ammonia. A number of investigations have been carried out concerning the use of urea in the SNCR process during the past years, both experimentally on different scales, 2-4 and from a kinetic modeling point of view. 3,5 While the effectiveness in the process is well demonstrated experimentally through the different investigations, the kinetic modeling of the process presented some uncertainties mainly due to the behavior of urea under high temperature conditions. Urea has been traditionally considered to be decomposed into NH 3 and HNCO at high temperatures, 6,7 even though other decomposition paths have been proposed. 5,8 The agreement between experiments and calculations using those different mechanisms for urea decomposition is reasonably good, but a reliable determination of urea thermal decomposition was needed. Recent experimental results have appeared concerning the measurement of the reaction rate for the thermal urea decomposition reaction under conditions applicable to SNCR conditions. 9 In this communication, we want to show the impact of the new recent results by Aoki et al. 9 in the modeling of the SNCR process using urea. Aoki et al. 9 determined the reaction rate and products distribution of the thermal decomposition of urea. They obtained the following rates and product channels for the decomposition of urea at high temperatures when it is fed as an aqueous solution: We have included those reactions in the mechanism we used previously for studying the urea-SNCR process, 3 and the results are in good agreement with the previous Figure 1. Experimental and calculated results of NO and N2O concentrations vs temperature. Solid lines: calculations made assuming ideal mixing. Dashed lines: calculations made assuming a mixing time of 10 ms. (Inlet concentrations: 100 ppm NO, 150 ppm urea, 4% O2, 4% H2O, N2 to balance). Residence time(s)) 200/T(K). (NH 2) 2 CO f NH 3 + HNCO k 1) 1.2676 × 10 4 exp(-15540/[cal/mol]RT) (NH 2) 2 CO + H 2 O f 2 NH 3 + CO 2 k 2) 9.925 × 10 3 exp(-20980/[cal/mol]RT) 509
1998
Alzueta, María U; Bilbao, Rafael; Millera, Ángela; Oliva, Miriam; Ibañez, J C
Interactions between nitric oxide and urea under flow reactor conditions Artículo de revista
En: Energy and Fuels, vol. 12, no 5, pp. 1001–1007, 1998, ISSN: 08870624.
@article{Alzueta1998a,
title = {Interactions between nitric oxide and urea under flow reactor conditions},
author = {María U Alzueta and Rafael Bilbao and Ángela Millera and Miriam Oliva and J C Ibañez},
url = {https://pubs.acs.org/sharingguidelines},
doi = {10.1021/ef980055a},
issn = {08870624},
year = {1998},
date = {1998-01-01},
journal = {Energy and Fuels},
volume = {12},
number = {5},
pages = {1001--1007},
publisher = {American Chemical Society},
abstract = {An experimental and theoretical study of the interactions between urea and NO under lean selective noncatalytic reduction conditions has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 700-1500 K. The influence of the temperature, oxygen concentration, and urea/NO ratio on the NO reduction has been analyzed. A reaction mechanism including literature NHs, HNCO, and moist CO oxidation subsets as well as their interactions with NO and reactions describing urea thermal decomposition have been used for calculations. The results show that urea is effective in reducing NO in a given temperature window, accompanied by the formation of an appreciable amount of N2O, which reaches its maximum value for the higher NO reduction. The impact of oxygen concentration in the 1-10% range is appreciable, and lower O2 concentrations shift the reduction regime toward higher temperatures, the higher N2O formation being observed for the richer environment. Using urea, the onset of NO reduction is shifted to higher temperatures compared to the use of ammonia, even though the effective temperature window for NO reduction roughly coincides for both selective reduction agents. The efficiency of NO reduction and the NO to N2O conversion increase as the urea/NO ratio increases, even though at high temperatures the excess of urea can be oxidized to NO. Model predictions are in good agreement with the experimental results and indicate that the classical reaction pathway for urea decomposition (i.e., H2N-CO-NH2 → NH3 + HNCO) is not able alone to reproduce the experimental findings obtained in the upper temperature range. This is attributed either to uncertainties of the HNCO oxidation mechanism or to the fact that other decomposition channels are likely to be produced. Results of this work as well as other literature data suggest that the method chosen for urea injection is important with respect to the N2O emissions attained. Adding urea at least partially decomposed prior to its interaction with NO results in similar NO reduction efficiencies but in considerably lower N2O concentrations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
An experimental and theoretical study of the interactions between urea and NO under lean selective noncatalytic reduction conditions has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature range 700-1500 K. The influence of the temperature, oxygen concentration, and urea/NO ratio on the NO reduction has been analyzed. A reaction mechanism including literature NHs, HNCO, and moist CO oxidation subsets as well as their interactions with NO and reactions describing urea thermal decomposition have been used for calculations. The results show that urea is effective in reducing NO in a given temperature window, accompanied by the formation of an appreciable amount of N2O, which reaches its maximum value for the higher NO reduction. The impact of oxygen concentration in the 1-10% range is appreciable, and lower O2 concentrations shift the reduction regime toward higher temperatures, the higher N2O formation being observed for the richer environment. Using urea, the onset of NO reduction is shifted to higher temperatures compared to the use of ammonia, even though the effective temperature window for NO reduction roughly coincides for both selective reduction agents. The efficiency of NO reduction and the NO to N2O conversion increase as the urea/NO ratio increases, even though at high temperatures the excess of urea can be oxidized to NO. Model predictions are in good agreement with the experimental results and indicate that the classical reaction pathway for urea decomposition (i.e., H2N-CO-NH2 → NH3 + HNCO) is not able alone to reproduce the experimental findings obtained in the upper temperature range. This is attributed either to uncertainties of the HNCO oxidation mechanism or to the fact that other decomposition channels are likely to be produced. Results of this work as well as other literature data suggest that the method chosen for urea injection is important with respect to the N2O emissions attained. Adding urea at least partially decomposed prior to its interaction with NO results in similar NO reduction efficiencies but in considerably lower N2O concentrations.