Insights in mass transfer effects for the catalytic hydrotreatment of
pyrolysis oil with heterogeneous Ru/C catalysts
A. R. Ardiyanti1, F. de Miguel Mercader2, J. E. S. Westra1, R. H. Venderbosch3, J. A.
Hogendoorn2, H. J. Heeres1
1
Chemical Engineering Department, University of Groningen, The Netherlands
Thermo-Chemical Conversion of Biomass Group, University of Twente, The Netherlands
3
BTG Biomass Technology Group BV, Enschede, The Netherlands
2
Pyrolysis oil, obtained from fast pyrolysis of lignocellulosic biomass, is an
attractive energy carrier. To extent its application range, upgrading by chemical or
physical means is required. Catalytic hydrotreatment using hydrogen in combination with
a heterogeneous catalyst leads to products with improved product properties (lower O
content, higher H/C ratio, lower water content, lower acidity) [1]. The upgraded oil can
be mixed with petroleum feedstock (such as vacuum gas oil) and has potential to be cofed into an existing oil refinery [2, 3].
The catalytic hydrotreatment reaction is a G-L-S system, and mass transfer
limitations of both of hydrogen and molecules to be hydrogenated may play an important
role. Insights in mass transfer effects is of particular importance here as the upgrading is
known to be associated with an (uncatalysed) thermal polymerisation reactions, leading
to higher molecular weight material (Scheme 1) [2].
+H2, Ru/C, T > 80 oC
Catalytic hydrotreatment
Upgraded oil,
Stable mol. weight
Pyrolysis Oil
T>200 oC
Polymerisation
High mol. weight
Scheme 1 Representation of the competition between polymerisation and catalytic hydrotreatment
The latter reaction is considered undesirable from a product property point of
view and leads to very viscous products. It is important to promote the rate of the
hydrotreatment reaction compared to the polymerisation reaction and as such to perform
the catalytic hydrotreatment reactions in the kinetic regime in the absence of any mass
transfer limitation.
To gain insights in possible mass transfer limitations, the catalytic hydrotreatment
reaction of a typical pyrolysis oil was performed in batch with Ru/C as the catalyst. The
effect of process conditions like stirring rate (600 - 1400 rpm), particle size of the Ru/C
catalyst (20 - 525 µm) and catalyst intake (1 – 5 wt %) on the reaction rates
(repolymerization and hydrogenation) and relevant product properties were evaluated.
The hydrogen consumption was used to evaluate possible mass transfer effects, as well as
the molecular weight of the products.
It was shown that the hydrogen uptake (after correction for H2 consumption for CH4
production)) decreased from 0.8 to 0.14 mol H2/g cat when the catalyst intake was increased
from 1 to 5 wt%, indicating mass transfer limitations of H2. These and related experiments
will be further elucidated in this presentation, and measures will be proposed to reduce
such mass transfer effects.
References
1.
2.
3.
Venderbosch, R.H., et al., Stabilization of biomass-derived pyrolysis oils. Journal of
Chemical Technology & Biotechnology. 85(5): p. 674-686.
de Miguel Mercader, F., et al., Production of advanced biofuels: Co-processing of
upgraded pyrolysis oil in standard refinery units. Applied Catalysis B: Environmental.
96(1-2): p. 57-66.
Biocoup at a glance, http://www.biocoup.com/index.php?id=18.