(165g) Char and Coke Characterization From Fast and Slow, Catalytic and Non-Catalytic Pyrolysis of Biomass and Relevant Model Compounds

Biomass pyrolysis, slow or fast, catalytic or
non-catalytic, will produce 15-30% solid residue (typically, a mixture of coke
and char). Coke is the solid carbon produced through the secondary pyrolysis of
volatile matters, whereas char is the solid residue obtained by emitting
volatile matters [1]. The formation of coke is considered as a reason for
catalyst deactivation and results in undesirable product selectivity in biomass
pyrolysis [2]. However, few studies have focused on studying catalyst
deactivation from the perspective of comparison of char and coke from different
biomasses. The objective of this study is to characterize coke and char with
respect to overall content, gasification reactivity, C and H contents, catalyst
surface area changes, and the effect on catalyst performance.

In this study,
glucose, cellulose and sawdust from pine bark were chosen as biomass feedstocks
and ZSM-5 was used for catalytic pyrolysis experiments. Char samples were
prepared in a tube furnace (slow (catalytic) pyrolysis) and in a conical
spouted-bed reactor (fast (catalytic) pyrolysis. In order to study the
reactivity of char and coke, gasification was carried out through thermogravimetric
analyses (TGA) in air and CO₂ at different heating rates. Figure 1
shows a gasification result of chars from various biomasses in TGA. Under the
same pyrolysis condition, glucose chars are more reactive than sawdust chars,
due to the lower carbon content. The catalyst has little effect on chars from
catalytic pyrolysis of glucose and sawdust. However, the gasification results
of the catalytic and non-catalytic chars from cellulose look very different.
Further study will be performed and a detailed discussion about the experiment
observation will be presented.

In addition, the
content of char and coke are obtained using elemental analysis (Table 1). The change
of the catalyst surface area after pyrolysis is analyzed based on physisorption
(BET). Images of char/coke and catalyst after pyrolysis are analyzed with scanning electron microscope (SEM) and focused ion beam (FIB) (Figure 2) and show significantly
different patterns in carbon deposition on the catalyst surface, depending on
the biomass pyrolized.

In this presentation, comparison of
different chars from slow and fast catalytic/non-catalytic pyrolysis using
different characterization tools will be shown. Differences of coke and char deposition
in the catalyst surface and their potential effect on catalyst deactivation
will be presented and discussed.

References:

1.    
Miura, K.; Nakagawa, H.; Nakai, S.;
Kajitani, S. Chemical Engineering Science. 2004, 59, 5261-5268.

2.    
Aho, A; Kumar, N. Eranen, K. Salmi, T.
Hupa, M.; Murzin, D. Fuel. 2008, 87, 2493-2501.