J. Herguido

Fluidized bed steam gasification of biomass with dolomite and with a commercial FCC catalyst.

The use of dolomite and of a commercial FCC (fluid catalytic cracking) catalyst is studied for the steam gasification of biomass in fluidized bed. This process is carried out in a small pilot plant based in a 15 cm. i.d., 1.20 m. total height, fluidized bed, with the biomass fed at the bottom of the bed. Pine sawdust was used as biomass. Two different working methods have been used: i) the dolomite (-600 + 300 µm) initially in the bed, instead of the sand and ii) sand in the bed and a feed of biomass mixed with the catalyst (dolomite or FCC catalyst). These two catalysts have shown to be efective for the tar cracking and for the reforming of the product gas. However, several problems have been found: the FCC catalyst is quickly elutriated from the bed, thus preventing its use in a single fluidized bed although being very promising for a circulating system. The dolomite is soft, it erodes very quickly and is also elutriated. When used mixed with the biomass in the feed, it behaved as a very effective cracking catalyst. However it is also elutriated from the bed and causes plugging of the exit pipes.

MoO3/MgO as a catalyst in the oxidative dehydrogenation of n-butane in a two-zone fluidized bed reactor

Abstract Butadiene has been produced from butane by oxidative dehydrogenation on a MoO3/MgO catalyst using a two-zone fluidized bed reactor (TZFBR). The effect of the main TZFBR operating variables was studied, and its performance was compared with that of conventional fluidized beds and fixed bed reactors loaded with the same catalyst. These results have been compared with those obtained on a selective V2O5/MgO catalyst.

Oxidative dehydrogenation of n-butane on V/MgO catalysts. Influence of the type of contactor

A comparative study of the catalytic performance of a selective V-Mg-O catalyst in the oxidative dehydrogenation of n-butane is presented using three different types of reactor: (i) an adiabatic fixed-bed reactor; (ii) a fluidized-bed reactor; and (iii) an in situ redox fluidized-bed reactor. The results obtained indicate that the in situ redox fluidized-bed reactor outperforms the conventional fixed- and fluidized-bed reactors, especially at high n-butane conversions. Thus, a selectivity to C4 olefins of 54% at n-butane conversions of 60% was achieved at 550°C using an in situ redox fluidized-bed reactor while selectivities to C4-olefins lower than 43% were obtained on the other reactor types under the same reaction conditions (isoconversion and reaction temperature).

Methane combustion over unsupported iron oxide catalysts

Bulk iron oxide, prepared by precipitation and by the citrates method, has been studied as an alternative catalyst for methane combustion. While hematite was the dominant phase in all the samples prepared, significant differences were observed regarding the activity and stability of the catalysts, depending on the preparation method. The catalysts prepared by precipitation presented higher surface areas and lower light-off temperatures. Catalyst deactivation is due to sintering under reaction conditions, and becomes more severe if the operating temperature exceeds the calcination temperature used in catalyst preparation. The best performance in terms of stability and steady-state conversion was obtained with the catalyst prepared by precipitation and calcined at 600°C.

Modelling of a two-zone fluidised bed reactor for the oxidative dehydrogenation of n-butane

Abstract A reactor model is proposed as a means of representing an in situ redox fluidised bed reactor for the oxidative dehydrogenation of n -butane with a V–Mg–O catalyst. The model describes a reactor where the hydrocarbon is fed at some intermediate point and the catalyst oxidation and reduction occur in different zones within a fluidized bed. This model allows the behaviour of the reactor to be understood and the effect of operating parameters that cannot be determined by experiments to be predicted.

Catalytic dehydrogenation of n-butane in a fluidized bed reactor with separate coking and regeneration zones

The non-oxidative dehydrogenation of butane over a Cr2O3/Al2O3 catalyst has been studied in a fluidized-bed reactor with separate butane and oxygen feeds. Under suitable conditions, feed segregation allows the stable creation of separated reaction and catalyst regeneration (by coke burning) zones. The effect of the main operating variables (temperature, oxygen to hydrocarbon ratio, and relative velocity) in the process performance was studied.

Characterization of porous ceramic membranes for their use in catalytic reactors for methane oxidative coupling

Abstract Catalytic inorganic membranes were prepared by depositing active materials over porous alumina tubes, using sol-gel and impregnation techniques. The concentration profiles of the different species in the membrane were obtained using XPS. Also, the stability of the membranes was tested by subjecting the samples to different thermal treatments. Different preparation methods are compared with the aim of attaining controlled distributions of the active phases in the membrane. Finally, some reaction results are also presented.

Pd-Ag Membrane Coupled to a Two-Zone Fluidized Bed Reactor (TZFBR) for Propane Dehydrogenation on a Pt-Sn/MgAl2O4 Catalyst

Several reactor configurations have been tested for catalytic propane dehydrogenation employing Pt-Sn/MgAl2O4 as a catalyst. Pd-Ag alloy membranes coupled to the multifunctional Two-Zone Fluidized Bed Reactor (TZFBR) provide an improvement in propane conversion by hydrogen removal from the reaction bed through the inorganic membrane in addition to in situ catalyst regeneration. Twofold process intensification is thereby achieved when compared to the use of traditional fluidized bed reactors (FBR), where coke formation and thermodynamic equilibrium represent important process limitations. Experiments were carried out at 500–575 °C and with catalyst mass to molar flow of fed propane ratios between 15.1 and 35.2 g min mmol−1, employing three different reactor configurations: FBR, TZFBR and TZFBR + Membrane (TZFBR + MB). The results in the FBR showed catalyst deactivation, which was faster at high temperatures. In contrast, by employing the TZFBR with the optimum regenerative agent flow (diluted oxygen), the process activity was sustained throughout the time on stream. The TZFBR + MB showed promising results in catalytic propane dehydrogenation, displacing the reaction towards higher propylene production and giving the best results among the different reactor configurations studied. Furthermore, the results obtained in this study were better than those reported on conventional reactors.

The influence of the permeation regime on the activity of catalytic membranes for methane combustion

Abstract The influence of the permeation regime on the performance of catalytic membranes used for methane combustion has been investigated. To this end, membranes with different loadings of the active phase (Fe 2 O 3 ) and different Knudsen contributions to the permeation flux have been prepared and used in combustion. A clear correlation has been found between the proportion of flux in the Knudsen diffusion regime and the light-off temperature for the membranes tested.

Influence of the catalyst pretreatment on the relative rates of the main and coking reactions during acetylene hydrogenation on a NiO/NiAl2O4 catalyst

Publisher Summary The deactivation of catalysts by coke deposition and its subsequent regeneration poses one of the most important problems in industrial catalytic processes. Supported and coprecipitated nickel catalyst represent an interesting alternative, from the economical point of view, to other selective hydrogenation catalysts such as Pt or Pd, of higher performance but also with a higher price. This chapter uses a coprecipitated NiO/NiAl 2 O 4 catalyst to carry out the selective hydrogenation of acetylene to ethylene as a test reaction. One important characteristic of this process is the large amount of coke that may be generated. The crystalline structure of the catalyst and the oxidation state of surface nickel are especially relevant in this case because coke deposition as well as acetylene hydrogenation occur on the metallic nickel sites. Therefore, the pretreatments carried out on the catalyst with the aim of obtaining the active species have a great influence on the relationship between coke deposition and the main reaction kinetics. The chapter underlines the importance of the pretreatment temperature on the kinetic behavior of the catalyst and indicates that the pretreatment conditions should be carefully optimized in this process. The physicochemical characterization has been carried out by XPS and TPR, and the variation of the surface properties has been related to the observed hydrogenation and coke formation kinetics.