• Energy Research

The cleaning of syngas is one of the most important challenges in the development of technologies based on gasification of biomass. Tar is an undesired byproduct because, once condensed, it can cause fouling and plugging and damage the downstream equipment. Thermochemical methods for tar destruction, which include catalytic cracking and thermal cracking, are intrinsically attractive because they are energetically efficient and no movable parts are required nor byproducts are produced. The main difficulty with these methods is the tendency for tar to polymerize at high temperatures. An alternative to tar removal is the complete combustion of the syngas in a porous burner directly as it leaves the particle capture system. In this context, the main aim of this study is to evaluate the destruction of the tar present in the syngas from biomass gasification by combustion in porous media. A gas mixture was used to emulate the syngas, which included toluene as a tar surrogate. Initially, CHEMKIN was used to asses...

The cleaning of syngas is one of the most important challenges in the development of technologies based on gasification of biomass. Tar is an undesired byproduct because, once condensed, it can cause fouling and plugging and damage the downstream equipment. Thermochemical methods for tar destruction, which include catalytic cracking and thermal cracking, are intrinsically attractive because they are energetically efficient and no movable parts are required nor byproducts are produced. The main difficulty with these methods is the tendency for tar to polymerize at high temperatures. An alternative to tar removal is the complete combustion of the syngas in a porous burner directly as it leaves the particle capture system. In this context, the main aim of this study is to evaluate the destruction of the tar present in the syngas from biomass gasification by combustion in porous media. A gas mixture was used to emulate the syngas, which included toluene as a tar surrogate. Initially, CHEMKIN was used to asses...

Abstract Industrial processes where the heating of large surfaces is required lead to the possibility of using large surface porous radiant burners. This causes additional temperature uniformity problems, since it is increasingly difficult to evenly distribute the reactant mixture over a large burner surface while retaining its stability and keeping low pollutant emissions. In order to allow for larger surface area burners, a non-uniform velocity profile mechanism for flame stabilization in a porous radiant burner using a single large injection hole is proposed and analyzed for a double-layered burner operating in open and closed hot (laboratory-scale furnace, with temperature-controlled, isothermal walls) environments. In both environments, local mean temperatures within the porous medium have been measured. For lower reactant flow rate and ambient temperature the flame shape is conical and anchored at the rim of the injection hole. As the volumetric flow rate or furnace temperature is raised, the flame undergoes a transition to a plane flame stabilized near the external burner surface. However, the stability range envelope remains the same in both regimes.

Abstract Industrial processes where the heating of large surfaces is required lead to the possibility of using large surface porous radiant burners. This causes additional temperature uniformity problems, since it is increasingly difficult to evenly distribute the reactant mixture over a large burner surface while retaining its stability and keeping low pollutant emissions. In order to allow for larger surface area burners, a non-uniform velocity profile mechanism for flame stabilization in a porous radiant burner using a single large injection hole is proposed and analyzed for a double-layered burner operating in open and closed hot (laboratory-scale furnace, with temperature-controlled, isothermal walls) environments. In both environments, local mean temperatures within the porous medium have been measured. For lower reactant flow rate and ambient temperature the flame shape is conical and anchored at the rim of the injection hole. As the volumetric flow rate or furnace temperature is raised, the flame undergoes a transition to a plane flame stabilized near the external burner surface. However, the stability range envelope remains the same in both regimes.

The growing demand for energy worldwide and the extensive use of fossil fuels have resulted in severe environmental problems such as air pollution and the accumulation of greenhouse gases in the atmosphere. In this scenario, both new energy sources and more efficient energy conversion processes have been deeply studied. Heterogeneous catalysis is currently widely used for hydrogen production due to its higher selectivity and conversion compared to other processes. Although the use of catalysts is fundamental for green chemistry, their production through traditional methods is less environmentally friendly. Nonetheless, in order to obtain more efficient supported metal catalysts, interest in using non-thermal plasma as a pretreatment or synthesis technique is increasing. Thus, the present article aims at summarizing and briefly discussing the relevant research results on this subject, elucidating the advantages and disadvantages of using non-thermal plasmas in the preparation of supported metal catalysts. Aspects such as morphology, the chemical composition of the catalytic surface, crystallographic phases, average size and dispersion of crystallites, specific surface area, and metal–support interaction have been analyzed. The use of plasma-assisted techniques contributes to the synthesis of supported metal catalysts with smaller, more dispersed, and strongly bonded active particles, resulting in higher catalytic activity, conversion rate, selectivity, and durability. In addition, plasma allows the synthesis of supported metal catalysts to be enhanced by reducing the process time, the use of hazardous substances, and the temperature required.

The growing demand for energy worldwide and the extensive use of fossil fuels have resulted in severe environmental problems such as air pollution and the accumulation of greenhouse gases in the atmosphere. In this scenario, both new energy sources and more efficient energy conversion processes have been deeply studied. Heterogeneous catalysis is currently widely used for hydrogen production due to its higher selectivity and conversion compared to other processes. Although the use of catalysts is fundamental for green chemistry, their production through traditional methods is less environmentally friendly. Nonetheless, in order to obtain more efficient supported metal catalysts, interest in using non-thermal plasma as a pretreatment or synthesis technique is increasing. Thus, the present article aims at summarizing and briefly discussing the relevant research results on this subject, elucidating the advantages and disadvantages of using non-thermal plasmas in the preparation of supported metal catalysts. Aspects such as morphology, the chemical composition of the catalytic surface, crystallographic phases, average size and dispersion of crystallites, specific surface area, and metal–support interaction have been analyzed. The use of plasma-assisted techniques contributes to the synthesis of supported metal catalysts with smaller, more dispersed, and strongly bonded active particles, resulting in higher catalytic activity, conversion rate, selectivity, and durability. In addition, plasma allows the synthesis of supported metal catalysts to be enhanced by reducing the process time, the use of hazardous substances, and the temperature required.

Abstract Biodiesel has been currently obtained from the transesterification reaction of vegetable oils, including residual oil as waste cooking oil (WCO), and usually in the presence of a catalyst. Advanced methods, such as plasma, have been studied to produce biodiesel since it allows for a milder conditions, mainly by decreasing both reaction temperature and time of production. The objective of this work is to investigate the plasma-assisted catalytic route for the monoesters transesterification reactions. H 3 PMo and NaOCH 3 were used as acid and basic catalysts, respectively. The batch plasma reactor used in this work was composed by a borosilicate glass tube with concentric electrodes, in which ethyl acetate and methanol were feed. The effects of the plasma associated with both acid and basic catalysts were investigated in the ambient temperature and atmospheric pressure. In general, plasma-assisted catalytic routes showed higher ethyl acetate conversions, when compared to the routes with no plasma under the same experimental conditions. For example, the ethyl acetate conversion increased from 38% to 77% when plasma is assisting the acid catalytic reaction during 90 min. This level of conversion is comparable with values achieved for the reaction in the presence of basic catalyst without plasma, although in a shorter time of reaction. The synergistic effect between the plasma and the catalysts provided an increase in the reaction rate constants, and high ethyl acetate conversions in shorter reaction times. These findings indicate the plasma-assisted catalyst routes as promising for the production of biodiesel under room temperature, especially for the production from waste oils, which requires the use of acid catalysts and usually under extreme conditions.

Abstract Biodiesel has been currently obtained from the transesterification reaction of vegetable oils, including residual oil as waste cooking oil (WCO), and usually in the presence of a catalyst. Advanced methods, such as plasma, have been studied to produce biodiesel since it allows for a milder conditions, mainly by decreasing both reaction temperature and time of production. The objective of this work is to investigate the plasma-assisted catalytic route for the monoesters transesterification reactions. H 3 PMo and NaOCH 3 were used as acid and basic catalysts, respectively. The batch plasma reactor used in this work was composed by a borosilicate glass tube with concentric electrodes, in which ethyl acetate and methanol were feed. The effects of the plasma associated with both acid and basic catalysts were investigated in the ambient temperature and atmospheric pressure. In general, plasma-assisted catalytic routes showed higher ethyl acetate conversions, when compared to the routes with no plasma under the same experimental conditions. For example, the ethyl acetate conversion increased from 38% to 77% when plasma is assisting the acid catalytic reaction during 90 min. This level of conversion is comparable with values achieved for the reaction in the presence of basic catalyst without plasma, although in a shorter time of reaction. The synergistic effect between the plasma and the catalysts provided an increase in the reaction rate constants, and high ethyl acetate conversions in shorter reaction times. These findings indicate the plasma-assisted catalyst routes as promising for the production of biodiesel under room temperature, especially for the production from waste oils, which requires the use of acid catalysts and usually under extreme conditions.