Guray Yildiza*, Tom Lathouwersa, Hilal Ezgi Toramanb, Kevin M. van Geemb, Frederik Ronssea, Ruben van Durenc, Sascha R. A. Kerstend, Wolter Prinsa

a Department of Biosystems Engineering, Ghent University, Coupure Links 653, B-9000, Ghent, Belgiumb Laboratory for Chemical Technology (LCT), Ghent University, Technologiepark 918, B-9052 Ghent, Belgium

c Albemarle Catalysts Company BV, Nieuwendammerkade 1–3, P.O. Box 37650, 1030 BE Amsterdam, The Netherlandsd Sustainable Process Technology Group, Faculty of Science and Technology, University of Twente,

Postbus 217, 7500AE Enschede, The Netherlands

* Tel.: +32(0)9264 6190; e-mail: guray.yildiz@ugent.be

Testing the stability of a ZSM-5 catalyst under biomass fast pyrolysis conditions

Introduction ExperimentalFast pyrolysis is a thermochemical process that contributes to the conversion of biomass into a variety of fuels and chemicals. It is defined as the rapid thermal decomposition of matter in absence of oxygen and followed by a quick condensation of the generated vapours. The target of this process is to produce a liquid mixture of organic molecules that is called pyrolysis oil or bio-oil, and which can be used as feed for fuels and chemicals production. The objective of the research carried out is to investigate the effects of a repeatedly regenerated ZSM-5 catalyst (in total, eight regeneration cycles) on the yields of the pyrolysis products in relationship with the applied process conditions. The changes in the performance of the successively regenerated catalyst has been observed via detailed bio-oil (2D-GC/MS, Karl-Fischer, MCRT), non-condensable gases (micro-GC) and carbonaceous solids (elemental analyzer, BET SA) analyses.

Results

Conclusions

Materials:Pine wood with particle sizes between 1 and 2 mm was used as the feedstock. A commercial, spray dried heterogeneous ZSM-5 based FCC catalyst was used as the catalyst. Silica sand with a mean diameter of 250 μm and a particle density of 2650 kg/m3 was used as the bed material for non-catalytic experiments and blended with the catalyst in case of the in-situ catalytic and regeneration experiments. Two-stage regeneration of the catalyst was performed in an oven at 250 °C and 600 °C.

Equipment:Experiments have been carried out in a fully controlled, semi-continuously operated lab-scale set-up that enabled the production of bio-oil samples (ca. 50 g/run) suitable for a full physicochemical characterization. A scheme of the unit is shown in Fig. 1.

 sand/catalyst mix (m2/g)

catalyst (m2/g)

normalized value, %

NC - - -R0 9.9 144.3 1.0R1 7.6 109.8 0.76R2 10.9 159.3 1.10R3 9.2 133.8 0.93R4 6.8 97.8 0.68R5 8.1 117.3 0.81R6 6.7 96.3 0.67R7 3.5 48.3 0.34R8 3.8 52.8 0.37

Fig. 2. The influence of successive catalyst regeneration (R1 to R8, ♦) on the yields of products obtained in pyrolysis of pine wood at 500 °C. Results for the non-catalytic (NC, ■) and catalytic pyrolysis with fresh catalyst (R0, ●) are included for comparison.

Fig. 4. Catalytic pyrolysis of pine wood at 500°C. Changes in (a) COx yield (the sum of CO and CO2), (b) CO/CO2 ratio, (c) CH4 yield, (d) C2+ yield (sum of C2H4, C2H6, C3H6 and C3H8) and (e) H2 yield, obtained after successive reaction/regeneration cycles (R1 to R8, ♦). The result of non-catalytic (NC, ■) and catalytic fast pyrolysis with fresh catalyst (R0, ●) are included for comparison.

Fig. 1. Scheme of the pyrolysis set-up.

• The effect of successive catalyst regeneration on the product yields

Fig. 3. Changes in the coke-on-catalyst (heterogeneous coke) yield along the successive catalyst regeneration cycles (R1 to R8, ♦) resulting from experiments with pine wood at 500 °C.

Table 1. BET surface area of spent and regenerated ZSM-5 based FCC catalysts, and the normalized values, for catalytic pine wood pyrolysis at 500 oC after subsequent catalyst regenerations (R0 to R8).

• The effect of successive catalyst regeneration on the catalyst

• The effect of successive catalyst regeneration on the yields of non-condensable gas compounds

The trends in the pyrolysis product yields converging to that of non-catalytic levels were observed which revealed that the influence of the catalyst slowly declined along the reaction/regeneration sequence. The reason for this was that the catalyst tended to lose its activity along the reaction/regeneration sequence. It can be explained by (1) deposition of coke and tar on the catalyst (Fig. 3 and Table 1) (2) the change in the physical, chemical and thermal properties of the catalyst (e.g. poisoning, fouling, attrition, steaming) after several reaction/regeneration cycles and (3) the accumulation of ash in the regenerated bed material which has two effects; favouring secondary cracking reactions and blocking active pores of the catalyst.