64 research outputs found
Kinetic modeling of C3H6 inhibition on NO Oxidation over Pt Catalyst
No full textExhaust after treatment for lean burn and diesel engine is a complex catalytic system that consists of a number of catalytic units. Pt/Al2O3is often used as a model Diesel Oxidation Catalyst (DOC) that plays an important role to facilitate oxidation of NO to NO2. In the present study, we proposed a detailed kinetic model of NO oxidation as well as low temperature C3H6 inhibition to simulate temperatureprogrammed reaction (TPR) data for NO oxidation over Pt/Al2O3. A steady-state microkinetic model based on Langmuir-Hinshelwood mechanism for NO oxidation was proposed. In addition, low temperature C3H6inhibition was proposed as a result of site blocking as well as surface nitrite consumption. The model can explain the experimental data well over the studied temperature range
Kinetic Studies of NO Oxidation and Reduction over Silver-Alumina Catalyst [Elektronisk resurs]
No full textIn line with growing concerns to manufacture more environmentally friendly vehicles, the use of internal combustion engines operating with oxygen excess or so called lean-burn engines will continue to be increasingly used. For lean-burn operation, reduction of NOx (NO+NO2) emissions is a major challenge and it is therefore urgently required to develop efficient and reliable NOx reduction aftertreatment systems for a wide variety of lean-burn or diesel engines. The main goal of this thesis is to increase the understanding of the reaction mechanism of selective catalytic reduction (SCR) of NOx with a hydrocarbon (HC) reductant over Ag-Al2O3 catalysts. As an important subsystem in the HC-SCR mechanism, H2 assisted NO oxidation over a monolith-supported Ag-Al2O3 catalyst was investigated by constructing a microkinetic model that accounted for heat and mass transport in the catalyst washcoat. The effect of H2 examined in the kinetic model, was to reduce self-inhibiting surface nitrate species on active sites. A reduced factorial design of the inlet experimental conditions was used to generate transient experimental data. In general, the modelling results could reproduce the transient experimental data well with correct levels of outlet concentrations and time scales for transient responses. When H2 was present in the feed, the kinetic model showed that H2 was consumed rapidly in the front part of the monolith. This indicated that the H2 promotion of the NO oxidation reaction may have been isolated to only a portion of the catalyst. A series of temperature-programmed desorption (TPD) studies of NOx were conducted over Ag-Al2O3 catalysts to quantify and characterize the stability of surface NOx species. Formation of two general groups of surface NOx species were found to be present: a less thermally stable group of so called “low temperature (LT) nitrates” and a more thermally stable group of “high temperature (HT) nitrates”. The LT NOx desorption peak could be attributed to the decomposition of nitrate species formed on the active sites. Elimination or decrease in quantities of these LT nitrates either thermally or by reaction with H2 resulted in higher NO oxidation and NOx reduction conversion. The HT NOx desorption peak primarily corresponded to the decomposition of nitrates on the Al2O3 support and could be considered spectator surface species. It was also found that H2 facilitates formation of nitrate on the Al2O3 support and it was indicative that the mechanism of NOx storage on the Al2O3 support was mainly via NO2 readsorption. From TPD studies of C3H6-SCR in the presence and absence of H2, it was shown that the presence of H2 not only eliminated LT nitrates but also promoted the formation of adsorbed hydrocarbons. Therefore, the dual role of H2 to both eliminate nitrates from active sites and promote NOx storage was elucidated
Kinetic Studies of NO Oxidation and Reduction over Silver-Alumina Catalyst
No full textIn line with growing concerns to manufacture more environmentally friendly vehicles, the use of internal combustion engines operating with oxygen excess or so called lean-burn engines will continue to be increasingly used. For lean-burn operation, reduction of NOx (NO+NO2) emissions is a major challenge and it is therefore urgently required to develop efficient and reliable NOx reduction aftertreatment systems for a wide variety of lean-burn or diesel engines. The main goal of this thesis is to increase the understanding of the reaction mechanism of selective catalytic reduction (SCR) of NOx with a hydrocarbon (HC) reductant over Ag-Al2O3 catalysts. As an important subsystem in the HC-SCR mechanism, H2 assisted NO oxidation over a monolith-supported Ag-Al2O3 catalyst was investigated by constructing a microkinetic model that accounted for heat and mass transport in the catalyst washcoat. The effect of H2 examined in the kinetic model, was to reduce self-inhibiting surface nitrate species on active sites. A reduced factorial design of the inlet experimental conditions was used to generate transient experimental data. In general, the modelling results could reproduce the transient experimental data well with correct levels of outlet concentrations and time scales for transient responses. When H2 was present in the feed, the kinetic model showed that H2 was consumed rapidly in the front part of the monolith. This indicated that the H2 promotion of the NO oxidation reaction may have been isolated to only a portion of the catalyst. A series of temperature-programmed desorption (TPD) studies of NOx were conducted over Ag-Al2O3 catalysts to quantify and characterize the stability of surface NOx species. Formation of two general groups of surface NOx species were found to be present: a less thermally stable group of so called “low temperature (LT) nitrates” and a more thermally stable group of “high temperature (HT) nitrates”. The LT NOx desorption peak could be attributed to the decomposition of nitrate species formed on the active sites. Elimination or decrease in quantities of these LT nitrates either thermally or by reaction with H2 resulted in higher NO oxidation and NOx reduction conversion. The HT NOx desorption peak primarily corresponded to the decomposition of nitrates on the Al2O3 support and could be considered spectator surface species. It was also found that H2 facilitates formation of nitrate on the Al2O3 support and it was indicative that the mechanism of NOx storage on the Al2O3 support was mainly via NO2 readsorption. From TPD studies of C3H6-SCR in the presence and absence of H2, it was shown that the presence of H2 not only eliminated LT nitrates but also promoted the formation of adsorbed hydrocarbons. Therefore, the dual role of H2 to both eliminate nitrates from active sites and promote NOx storage was elucidated
Experimental and kinetic studies of H2 effect on lean exhaust aftertreatment processes: HC-SCR and DOC
No full textWith a growing concern to lower greenhouse gas emissions from road transportation, lean burn and diesel engines will keep playing an important role in the future. Development of a highly efficient and durable process to reduce NOx to N2 becomes a challenging issue especially in the presence of ample O2 concentration as in lean burn exhaust. One way to reduce NOx emissions in lean exhaust is by using hydrocarbon-selective catalytic reduction (HC-SCR). HC-SCR over Ag/Al2O3 catalysts appears to be a promising technology to abate NOx emission in lean burn exhaust. The function of the Diesel oxidation catalyst (DOC), as a part of a lean exhaust aftertreatment process, is to oxidize CO, HC and NO. Interestingly, addition of H2 has been shown to promote the HC-SCR activity over Ag/Al2O3 and NO oxidation activity over Pt/Al2O3 catalyst. The overall focus of this thesis was to increase understanding of the mechanisms of the H2 effect on the model catalysts of Ag-Al2O3 and Pt/Al2O3. A combination of experimental and kinetic modeling approaches was utilized as a way to examine mechanistic effects of H2.Temperature-programmed desorption (TPD) technique was used to characterize thermal stabilities of various surface NOx species formed during NO oxidation and C3H6-SCR conditions over Ag/Al2O3 catalyst. In addition, DRIFTS analysis was used to identify different types of nitrate species. These TPD results elucidated the dual roles of H2 to remove inhibiting nitrate on active sites and facilitate formation of inactive nitrate species mainly on the Al2O3 support. An initial development of a microkinetic model to describe H2-assisted NO oxidation over Ag/Al2O3 was conducted using a set of transient data. The single role of H2 to remove inhibiting nitrate species on active sites was examined. In the further model development, a global kinetic model of H2-assisted C3H6-SCR, including NO oxidation, C3H6 oxidation and C3H6-SCR in the presence and absence of H2, was proposed. This model was based on dual roles of H2 to remove inhibiting nitrates from active sites and simultaneously form more active Ag sites. The model could effectively capture a wide range of feed concentrations and temperatures, including temperature-programmed and transient experiments.The influence of H2 on NO oxidation over Pt/Al2O3 as a DOC catalyst was evaluated with various feed mixtures. Formation of Pt oxide has been known to lower the NO oxidation activity over Pt/Al2O3. The role of H2 to retard the Pt oxide formation was investigated. This resulted in a temporal enhancement in NO2 yield due to H2 addition during temperature ramp experiments. In addition, the effect of C3H6 and CO to influence the NO oxidation was also investigated. Addition of H2 mainly serves to weaken the inhibition effect of C3H6 and to a much lesser degree CO. This is mainly due to an enhancement of lower temperature C3H6 oxidation. The promotional effects of H2 to increase NO2 yield was proposed as a result of effects of H2 on surface chemistry and/or reactions. These effects could be clearly distinguished from exothermal heat effects from mainly H2 but also C3H6 and CO oxidation
Experimental and kinetic studies of H2 effect on lean exhaust aftertreatment processes: HC-SCR and DOC [Elektronisk resurs]
No full textWith a growing concern to lower greenhouse gas emissions from road transportation, lean burn and diesel engines will keep playing an important role in the future. Development of a highly efficient and durable process to reduce NOx to N2 becomes a challenging issue especially in the presence of ample O2 concentration as in lean burn exhaust. One way to reduce NOx emissions in lean exhaust is by using hydrocarbon-selective catalytic reduction (HC-SCR). HC-SCR over Ag/Al2O3 catalysts appears to be a promising technology to abate NOx emission in lean burn exhaust. The function of the Diesel oxidation catalyst (DOC), as a part of a lean exhaust aftertreatment process, is to oxidize CO, HC and NO. Interestingly, addition of H2 has been shown to promote the HC-SCR activity over Ag/Al2O3 and NO oxidation activity over Pt/Al2O3 catalyst. The overall focus of this thesis was to increase understanding of the mechanisms of the H2 effect on the model catalysts of Ag-Al2O3 and Pt/Al2O3. A combination of experimental and kinetic modeling approaches was utilized as a way to examine mechanistic effects of H2.Temperature-programmed desorption (TPD) technique was used to characterize thermal stabilities of various surface NOx species formed during NO oxidation and C3H6-SCR conditions over Ag/Al2O3 catalyst. In addition, DRIFTS analysis was used to identify different types of nitrate species. These TPD results elucidated the dual roles of H2 to remove inhibiting nitrate on active sites and facilitate formation of inactive nitrate species mainly on the Al2O3 support. An initial development of a microkinetic model to describe H2-assisted NO oxidation over Ag/Al2O3 was conducted using a set of transient data. The single role of H2 to remove inhibiting nitrate species on active sites was examined. In the further model development, a global kinetic model of H2-assisted C3H6-SCR, including NO oxidation, C3H6 oxidation and C3H6-SCR in the presence and absence of H2, was proposed. This model was based on dual roles of H2 to remove inhibiting nitrates from active sites and simultaneously form more active Ag sites. The model could effectively capture a wide range of feed concentrations and temperatures, including temperature-programmed and transient experiments.The influence of H2 on NO oxidation over Pt/Al2O3 as a DOC catalyst was evaluated with various feed mixtures. Formation of Pt oxide has been known to lower the NO oxidation activity over Pt/Al2O3. The role of H2 to retard the Pt oxide formation was investigated. This resulted in a temporal enhancement in NO2 yield due to H2 addition during temperature ramp experiments. In addition, the effect of C3H6 and CO to influence the NO oxidation was also investigated. Addition of H2 mainly serves to weaken the inhibition effect of C3H6 and to a much lesser degree CO. This is mainly due to an enhancement of lower temperature C3H6 oxidation. The promotional effects of H2 to increase NO2 yield was proposed as a result of effects of H2 on surface chemistry and/or reactions. These effects could be clearly distinguished from exothermal heat effects from mainly H2 but also C3H6 and CO oxidation
An Approach for Selecting CO2 Removal Technology in Indonesia's Upstream Natural Gas Industry Using AHP Method
No full textImpurities are commonly found in natural gas which is produced from reservoirs deposit. The predominant impurities come in CO2 forms. Hence, the selection of proper CO2 removal technologies is a significant step in process engineering as it strongly affects the size of CAPEX and OPEX. However, the selection of the CO2 removal process is not always trivial and further it must be conducted in the beginning of the project feasibility study. Currently, there are several CO2 removal technologies including absorption, adsorption and membranes. Considering their advantages and limitations, there is a need to analyse the relationship between the CO2 removal cost with the required product gas, impurities, flow capacity, geographical factor and CO2 tax in
Indonesia. Thus, these criteria are evaluated through the multi-criteria decision-making (MCDM) technique for selecting the most suitable technology for removing CO2. In this study, Analytic Hierarchy Process (AHP) is chosen and applied to evaluate the significance of each criterion. The results showed that absorption using the amine system is frequently used in Indonesia’s upstream natural gas industry. Furthermore, the use of the adsorption method (pressure swing adsorption) for a low-quantity gas feed also showed good results. The use of AHP method for selecting CO2 removal technology in Indonesia’s upstream natural gas industry can be used by investors and policymakers as a useful pre-investment tool analysis in developing new fields. The current proposed method aims to screen the best CO2 removal technology by taking into accounts technical performance, revenue and cost, as well as reducing emissions
Numerical Solution of nth Order DAEM for Kinetic Study of Lignocellulosic Biomass Pyrolysis
No full textThe aim of the present study was to explore the most optimal configuration to numerically solve Distributed Activation Energy Models (DAEMs). DAEMs are useful in obtaining the kinetic parameters in non-isothermal kinetic studies using a thermogravimetry analyzer (TGA). Compared to other kinetic models, DAEMs provide an additional kinetic parameter that quantifies the extent of the reaction (σ) for each reaction’s mean activation energy (E ̅). Although DAEMs are efficacious in kinetic studies, solving DAEMs numerically is challenging. The DAEM equation includes double integration with respect to activation energy and temperature, which involves various numerical discretizations. Previously, many researchers utilized a DAEM to explicate complex reactions such as lignocellulosic biomass pyrolysis. However, most of them have yet to propose a numerical approach to solve DAEMs. Therefore, by exploring multiple numerical calculation configurations, here we present a general structure to numerically solve nth order and first-order DAEMs. The exploration includes determining the optimal integration limit of activation energy and the discretization of activation energy and temperature integration. From the investigation, we came up with a configuration that limits the integration of activation energy from E ̅-3σ to E ̅+3σ. Meanwhile, the number of integration points for temperature and activation energy must be 51 and 21, respectively. By using this configuration, DAEM can be utilized optimally in kinetic studies
A Systematic Study on the Effect of the Xanthation Temperature on Viscose Quality
No full textThe xanthation reaction is an exothermic reaction between alkali cellulose (AC) and carbon disulfide (CS2) used to regenerate a viscose solution. The cooling system plays an important role during the reaction to yield more of the main product, cellulose xanthate (CX), instead of the by-product, sodium trithiocarbonate (TTC). Minimizing the yield of by-products during the reaction phase may lead to less by-product generation during the ripening process due to free caustic and excess CS2 in the system. The reaction was performed in a batch reactor with an agitator (9.7 rpm) under vacuum conditions (350 mbar), and the temperature varied from 20 °C to 35 °C, as is applicable in industrial plants. Meanwhile, the CX and TTC were determined via UV spectroscopy. Since the temperature reaction will affect the period of the reaction, which impacts the productivity of industrial applications, the experiment was conducted with a temperature change during the reaction to obtain a good-quality product without impacting productivity. This work aimed to reach an optimum xanthation temperature under the same combination of hardwood and softwood dissolving pulp. The results indicated that the xanthation reaction has an advantage at lower temperatures compared to higher ones; however, having a lower temperature led to a longer reaction period. The TTC was shown to be 17.7% lower at lower temperatures than at higher temperatures, which means that the CX was at a higher percentage at lower temperatures. Interestingly, the combination of higher and lower temperatures gave good viscose quality, which may lead to less consumption of CS2 and improve the environment due to less sulfur production during spinning
Modeling Lab-sized Anaerobic Fluidized Bed Reactor (AFBR) for Palm Oil Mill Effluent (POME) treatment: from Batch to Continuous Reactors
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