Deactivation of a HZSM-5 Zeolite Catalyst in the Transformation of the Aqueous Fraction of Biomass Pyrolysis Oil into Hydrocarbons

Abstract

The effect of the operating conditions (temperature, space time, and time-on-stream) has been studied in the catalytic transformation of the aqueous fraction of the biomass pyrolysis oil obtained in a conical spouted bed reactor under atmospheric pressure. The results show that (i) the deactivation by coke (reversible) of the HZSM-5 zeolite catalyst is similar to the deactivation of the same catalyst in the transformation of light oxygenates (such as methanol and ethanol) and (ii) the deactivation attenuates as space time is increased. The results of product distribution are in agreement with those obtained in the transformation of the pure oxygenates contained in the pyrolysis oil. In experiments conducted following reaction-regeneration (by coke combustion) cycles, it has been proven that (i) at the reaction temperature of 450 °C, deactivation by dealumination of the zeolite in the reaction stage is important and (ii) this deactivation is due to the high water content in the reaction medium. This dealumination causes an irreversible deterioration of the total acidity, although the acid strength of the remaining sites is hardly modified.

Catalytic Vapor Cracking for Improvement of Bio-Oil Quality

“…2 Proposed reaction pathway for the conversion of bio-oil over zeolite catalysts: TE: thermal effect; TCE: thermo-catalytic effect [24] medium increased or when operations were conducted at temperatures below 400°C. In their further study using the aqueous fraction of biomass pyrolysis oil [29], the deactivation rate of HZSM-5 due to coke deposition or dealumination was found to be similar to those determined in the transformation of light alcohols such as methanol and ethanol. After the experiments in a mode of reaction-regeneration cycle, the deactivation was as a result of the dealumination of HZSM-5 caused by high water contents in the reaction medium, resulting in the irreversible deterioration of total acidity.…”

Catalytic Fast Pyrolysis: A Review

“…Furthermore, coke has been shown to significantly increase at temperatures above 400 °C [68]. Some coke can be burned off, but irreversible dealumination and loss of acid sites occurs at temperatures as low as 450 °C in the presence of water [69]. Research on the reduction of coking is important, with a variety of approaches showing promise.…”

Olefin production by cofeeding methanol and n‐butane: Kinetic modeling considering the deactivation of HZSM‐5 zeolite

“…Furthermore, the integrated process is carried out with considerable water content in the reaction medium (product of methanol dehydration), which together with high-temperatures is a challenge for the hydrothermal stability of the HZSM-5 zeolite catalyst. 11,15,16 Catalyst hydrothermal stability has been improved by doping the HZSM-5 zeolite with Fe, 17 and agglomerating with bentonite and alumina. 18,19 The integration of both reactions schematized in Figure 1 is effective for increasing the yield of olefins over those corresponding to the two individual reactions, which is explained by the following findings based on synergies between the kinetic schemes of the two reactions: 20 (i) olefins formed at the initial section of the reactor in n-butane cracking activate the autocatalytic steps for methanol transformation, following the well-established ''hydrocarbon pool'' mechanism originally proposed for SAPO-34 catalyst, which establishes that methylbenzenes are the main reactive species; 12,[21][22][23][24][25] (ii) the incorporation of these olefins in the ''hydrocarbon pool'' maintains the reactivity of methylbenzenes released by the olefins, which delays the formation of polymethylbenzenes that are the precursors of polyaromatic coke; 26,27 (iii) water formation in methanol transformation inhibits the steps for n-butane cracking but also deactivation by coke, given that water adsorption on the active sites competes with coke precursor adsorption in the coke growing steps.…”