Global Gas-Phase Oxidation Rates of Select Products from the Fast Pyrolysis of Lignocellulose

Abstract

The oxidation kinetics for products of fast pyrolysis at low temperatures (<600°C) are not well known. These will be important in effort to model autothermal pyrolysis, which has been recently developed to intensify the process, but which occurs at much lower temperatures than combustion. This study determines global oxidation rates at 400-600°C for three important products of fast pyrolysis: levoglucosan, xylose, and acetic acid. Experiments were performed in a fluidized bed pyrolyzer with the reactor modeled as a series of CSTRs and PFRs to determine reaction rates. Oxidation rates at 500°C for the three model compounds varied by a factor of ten.

Process Model-Based Validation of the Intensification of Biomass Fast Pyrolysis in a Fluidized Bed via Autothermal Operation

“…Until the day that process simulators are able to integrate detailed, multistep kinetic mechanisms with reactive intermediates, it is necessary to settle for simplified oxidation kinetic models. There are ongoing efforts to overcome this shortfall by deriving oxidation kinetics for individual pyrolysis products (e.g., the work of Peterson and Brown 40 ), but they do not yet uniformly cover the wide range of possible oxidizable species. They also often focus on the mass loss of reactants, ignoring or incompletely addressing the distribution of oxidation products.…”

“…This system involves thousands of reactions with hundreds of reactive intermediates and so is not suitable for implementation in a process simulation environment. It was also noted by Peterson and Brown that the secondary gas-phase reactions were derived at high temperatures (for hydrocarbon oxidation), not validated at lower temperatures, and do not occur quickly enough for the short vapor residence time (on the order of 0.5 s) in a fluidized bed. The char reactions correlated by Ranzi et al from prior work by other researchers, however, are in good agreement with the results of Peterson and Brown and so were used here to model the oxidation of char.…”

2021 Pioneers in Energy Research: Javier Bilbao

“…Peterson et al 27 have investigated the global oxidation rates of prominent products (levoglucosan, xylose, and acetic acid) of fast pyrolysis of lignocellulosic biomass at temperatures appropriate to autothermal pyrolysis. These results are useful in efforts to develop reaction models of autothermal pyrolyzers.…”