Evaluation of HZSM-5 zeolite/synthetic carbon (HZ/Cs) composite behavior as catalyst for upgrading biomass pyrolysis oil

CHIOSSO, M.E.; CRESPO, I.; MERLO, A.B.; GAYUBO, A. G.; VALLE, B.

BUENOS AIRES

Congreso; 11th World Congress of Chemical Engineering (2023); 2023

ASOCIACION ARGENTINA DE INGENIEROS QUIMICOS

The valorization routes for converting lignocellulosic biomass into value-added products has undergone great technological development in recent decades [1]. Fast pyrolysis of biomass is a well-developed process that produces a liquid (bio-oil) with complex oxygenated composition that makes it unsuitable for direct use as a fuel, but a potentially rich source of hydrocarbon fuels and platform chemicals. The catalytic cracking (CC) is a promising and versatile route that would create attractive opportunities for the large-scale valorization of bio-oil, contributing to decarbonization of energy system in the medium-long term. The availability of economic, stable and selective catalysts is a key factor for the successful development of this process. Zeolite-based catalysts (HZSM-5, 𝛽-zeolite, HY) have been widely used in the CC oxygenated molecules due to their suitable structural and acid properties.Carbon-based solid acids synthesized from saccharides are a novel type of materials with increasing interest as potential catalysts. Their specific properties (acid density, mechanical stability, and structural diversity) make them suitable for a wide range of applications (adsorbents, catalysts, etc.) and reactions (transesterification, etherification, alkylation) [2].In this work, we evaluate the catalytic behavior of a composite made of HZSM-5 zeolite and synthetic carbon in the catalytic cracking of bio-oil produced by fast pyrolysis of pine sawdust.The synthetic carbon (Cs) was obtained from anhydrous dextrose and sodium silicate solution following a template-assisted carbonization process conducted in two steps (5 h in N2 atmosphere at 200 ºC and 450°C). Then it was functionalized by reaction between 4-benzene-diazonium sulfonate and H3PO2 as the reducing agent [2].The HZ/Cs composite catalyst was prepared by physical mixture of HZSM−5 zeolite (SiO2/Al2O3 = 30) with milled Cs in 50/50 wt% ratio. The powder was then subjected to compression (600 kN for 15 min) using a Herzog TP40 Manual Press, and the resulting pellets were crushed and sieved into particles of 150−300 m.The raw bio-oil was stabilized by adding 20 wt% of methanol and fed into a continuous two-step catalytic cracking system. The volatile oxygenates exiting the first thermal unit were converted in-line in the fluidized bed catalytic reactor (450 ºC, 0.35 gcath/gfeed). The conversion of oxygenates and the yield of hydrocarbons (C2-C4 and C5+) were quantified from the on-line GC analyses of the products stream (Agilent 490 micro-GC). The detailed composition of liquid products was analyzed by GC/MS (Shimadzu GC/MS QP2010).Under the conditions used, 65 % of methanol and 55 % of oxygenates contained in bio-oil feed were converted into value-added products, i.e., C2-C4 olefins (5 % yield), gasoline range C5+ hydrocarbons (12 %yield) and chemicals-enriched bio-oil (mainly acetone and acetic acid) with high water content ( 60 wt%). The composition of this liquid makes it an appealing feedstock for further production of H2 by steam reforming.Despite these promising results, the HZ/Cs material undergoes excessive attrition during reaction, suggesting that the synthesis method needs to be optimized to increase its mechanical resistance for use in fluidized bed configurations.