Abstract
Ex-situ catalytic pyrolysis of crude glycerol for the synthesis of bio-based benzene, toluene and xylenes (bio-BTX) was performed in a tandem micro-reactor (TMR), a batch gram scale reactor and a continuous integrated bench scale unit using ZSM-5/bentonite extrudates. A bio-BTX yield of 8.1 wt.% (14.6% carbon yield) based on crude glycerol was obtained over the fresh catalysts (Cat-F) in the bench scale unit (crude glycerol feed rate of 200 g h−1, pyrolysis temperature of 520 °C and catalytic upgrading temperature of 536 °C). Catalyst activity was shown to be a function of the time on stream (TOS) and after 4.7 h the activity dropped with about 8%. After an oxidative regeneration step to remove coke, the activity of the regenerated catalysts (Cat-R1) was recovered to 95% of the original catalyst activity. After 11 reaction-regeneration cycles, the bio-BTX yield decreased to 5.4 wt.% (9.7% carbon yield) over Cat-R11. The fresh, deactivated and regenerated ZSM-5/bentonite catalysts were characterized in detail using nitrogen physisorption, XRD, ICP-AES, EA, TEM-EDX, TGA, NH3-TPD, pyridine-IR and solid MAS NMR. Coke (10.5 wt.% over Cat-D) was mostly deposited on ZSM-5 planes, and not only decreased the number of Lewis and Brönsted acid sites, but also blocked the pores, resulting in catalyst deactivation. Coke removal was effectively performed using an oxidative treatment. However, exchange of cations (e.g., Na) of the bentonite and possibly also from the crude glycerol feed with protons of ZSM-5 was observed, leading to irreversible deactivation. Furthermore, the layered structure of bentonite collapsed due to the removal of interlamellar water and dehydroxylation.
Highlights
The biodiesel industry has grown substantially in the last two decades [1]
We demonstrate the ex-situ catalytic pyrolysis of crude glycerol for bio-BTX synthesis in a continuous dedicated bench scale unit containing 200 g catalyst with dimension of relevance for industrial operation in packed bed reactors
The effect of ZSM-5 to bentonite ratio (90/10, 80/20 and 60/40, wt./wt.) in the catalyst on BTX yields were screened in a microgram scale tandem micro-reactor (TMR) (Section 2.3.1)
Summary
The biodiesel industry has grown substantially in the last two decades [1]. its production inevitably leads to the formation of glycerol (ca. 10% (wt./wt.)). Investigations on the use of larger mm sized ZSM-5/bentonite particles for the catalytic pyrolysis of glycerol with respect to catalyst performance (BTX yield), catalyst life-time (time on stream), catalyst deactivation, catalyst regenerability and reusability have not been reported to date In this manucript, we demonstrate the ex-situ catalytic pyrolysis of crude glycerol for bio-BTX synthesis in a continuous dedicated bench scale unit containing 200 g catalyst with dimension of relevance for industrial operation in packed bed reactors. We demonstrate the ex-situ catalytic pyrolysis of crude glycerol for bio-BTX synthesis in a continuous dedicated bench scale unit containing 200 g catalyst with dimension of relevance for industrial operation in packed bed reactors For this purpose, we made ZSM-5/bentonite extrudates with particle size between 1–2 mm, and examined the catalyst performance with respect to BTX yield, carbon yield, mass and carbon balance closure. The deactivated and regenerated catalysts were analyzed in detail (BET, XRD, ICP-AES, EA, TEM-EDX, TGA, NH3-TPD, pyridine-IR and solid MAS NMR) to obtain insight in both reversible and irreversible catalyst deactivation phenomena
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