Mass transfer and influence of the local catalyst activity on the conversion in a riser reactor

Gas-solids contacting in risers has been studied based on measurements of mass transfer controlled CO oxidation over a Pt/γ-alumina catalyst, and on experimental results published by Ouyang et al. (1995) for the kinetically controlled ozone decomposition. In the present experiments, the catalyst activity was varied by mixing the active catalyst particles with similar, but inert γ-alumina particles (in ratios from 150 to 2500 m3inert/m3cat), whereas Ouyang and co-workers varied the operating temperature (de 300 à to 500 K). Mass transfer controlled CO oxidation occurs at temperatures above 750 K. A negative square root dependency has been observed for the relationship between the Sherwood number and the solid hold-up. Increasing the gas velocity always improves the gas-solids contacting. The local catalyst activity appears to be an important parameter. As an important conclusion of the present work, it can be stated that at a high local activity, the conversion rate per unit volume of catalyst decreases significantly due to local depletion of reactant

In-depth structural characterization of the lignin fraction of a pine-derived pyrolysis oil

Pyrolytic lignin (PL) is the collective name of the water-insoluble fraction of pyrolysis oils produced from the fast pyrolysis of lignocellulosic biomass. As the name suggests, PL is composed by fragments derived from lignin, which is the largest natural source of aromatic carbon. Its valorization is of major importance for the realization of economically competitive biorefineries. Nonetheless, the valorization of PL is hindered by its complex structure, which makes the development of tailored strategies for its deconstruction into valuable compounds challenging. In this work, we provide an in-depth analysis of the structural composition of PL obtained from a commercially available pine-derived pyrolysis oil obtained at 500 °C (Empyro B.V., the Netherlands). Molecular weight distribution and thermal stability were accessed by GPC and TGA, respectively, and the monomers present in the PL (≈ 15 wt%) were identified and quantified by chromatographic analyses (GCxGC–FID, GCxGC/TOF–MS, GC–MS and HPLC). Together with FTIR, Py-GC–MS, TAN, elemental analysis and various advanced NMR techniques (13C NMR, 31P NMR, 19F NMR, HSQC NMR, HMBC NMR), structural features of the PL oligomers were elucidated, revealing a guaiacyl backbone linked by alkyl, ether, ester and carbonyl groups, with none of the typical native lignin linkages (i.e. β–O–4, β–β, β–5) present. Furthermore, 72.3 % of the oxygen content in PL could be assigned to specific motifs by the quantitative analyses performed, and oligomeric models were proposed based on the obtained information. We expect that this characterization work can support future research on the development of valorization pathways for PL, allowing the feasible conversion of this promising feedstock into valuable biobased products with a wide range of possible applications, e.g. fuels, materials and specialty chemicals

A novel free-fall reactor for (catalytic) pyrolysis of biomass and plastics

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Efficient depolymerization of lignin to biobased chemicals using a two-step approach involving ozonation in a continuous flow microreactor followed by catalytic hydrotreatment

Lignin is a promising feedstock for the replacement of conventional carbon sources for the production of chemicals and fuels. In this paper, results are reported for the depolymerization of various residual lignins in the absence of a catalyst by utilizing ozone. Reactions were performed in a microreactor setup ensuring high gas-liquid mass transfer rates, a low inventory of ozone, and straightforward scale-up possibilities. The ozonation is demonstrated using a representative model compound (vanillin) and various lignins (pyrolytic and organosolv) dissolved in methanol (2.5 wt %). Experiments were performed under ambient conditions, at gas-liquid flow ratios ranging from 30 to 90 and short residence times on the order of 12-24 s. Analyses of the products after methanol removal revealed the presence of (di)carboxylic acids, methyl esters, and acetals. Extensive depolymerization was achieved (i.e., up to 30% for pyrolytic lignin and 70% for organosolv lignins). Furthermore, a two-step approach in which the ozonated lignin is further hydrotreated (350-400 degrees C, 100 bar H-2, 4 h, Pd/C as catalyst) showed a substantial increase in depolymerization efficiency, yielding a 2.5-fold increased monomer yield in the product oil compared to a hydrotreatment step only

Platinum catalyzed oxidation of carbon monoxide as a model reaction in mass transfer measurements

The oxidation of CO with oxygen over a Pt/γ-alumina catalyst is proposed as a model reaction to be used for the determination of mass transfer coefficients in packed and fluidized beds. It is applicable at relatively low temperatures (<800 K) and for very small particles (<100 μm). In the present work, the kinetics of this reaction have been verified in a small fixed bed facility (average particle diameter 54 μm), for various reactant concentrations, temperatures and superficial gas velocities. As a result, Langmuir–Hinshelwood kinetics (Ea=75.4 kJ mol-1) appeared to describe the experimental results better than a power law expression (Ea=90.6 kJ mol-1). Three temperature regimes can be identified upon interpretation of experimental results with a suitable single particle model: a reaction rate controlled regime (I) at relatively low temperatures, characterized by a reaction order for oxygen of plus one and a carbon monoxide reaction order of minus one, an intermediate temperature interval (regime II) for which the reactions rate is influenced by both mass transfer and kinetics, and where the apparent reaction order in CO and O2 change to values lower than minus one and higher than one, respectively, and the high temperature regime (III) where mass transfer resistances are dominant, and the apparent reaction orders in O2 and CO are changed to values of zero and plus one, respectively. In case of carbon monoxide oxidation over a platinum catalyst, the observed orders in O2 and CO provide an extra instrument to recognize the prevailing conversion rate controlling phenomenon, apart from known indicators like the observed activation energy value or the influence of hydrodynamic conditions. As a consequence, the reliability of mass transfer measurements is significantly improved. This has been verified by the application in mass transfer measurements for a packed bed and for a riser system