Characteristics and origin of char and coke from fast and slow, catalytic and thermal pyrolysis of biomass and relevant model compounds

Abstract

Char and coke from biomass catalytic pyrolysis have different origins. They cannot be lumped as one since they occupy different locations on the catalyst surface and, thus, contribute differently to catalyst deactivation. In this study, catalyst (ZSM-5) deactivation in the perspective of comparison of char and coke from pyrolysis of different biomass types is investigated. Pine sawdust, glucose, and cellulose are used as feedstocks in the pyrolysis experiments. Biomass char and coke samples produced via slow and fast, thermal and catalytic pyrolysis are characterized with respect to their overall content, oxidation reactivity, catalyst surface area, pore size distribution changes, bonding groups and their effect on catalyst performance. In particular, it is shown that char forms as an external layer on the catalyst surface and in its macropores, whereas coke forms inside the zeolite micropores via hydrogen transfer and addition reactions. The catalyst effect on glucose and pine slow catalytic pyrolysis is minor compared with that on cellulose slow catalytic pyrolysis, due to macropore blocking by char formation. In fast catalytic pyrolysis, catalyst deactivation is mainly attributed to micropore blocking by coke formation. Char and coke are shown to coexist on the catalyst surface after fast catalytic experiments, with the char content after glucose fast catalytic pyrolysis being 30 wt% of the total solid residue. The origins of char and coke in the cellulose, hemicellulose and lignin components of pine are identified and mechanisms for their formation are proposed.

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation

“…Oddly,h igh heatingr ates (fast pyrolysis) lead to more levoglucosan formation but the levoglucosan quicklyp olymerizesa nd cannotb e recovered. [60,63,[66][67][68][69][70][71] However, physical mixtures of Siral 5, an amorphous silica-alumina, and H-ZSM-5 was shown to have as ynergistic effect on the yield of aromaticsr elative to either catalystalone. Recent isotopic and computational studies suggest that levoglucosan is deoxygenated within the liquid phase and that contraction of the 6-membered glucopyranose ring to the 5-membered glucofuranoser ing is the key process for depolymerization of cellulose.…”

“…Selectivity to aromatic products or value-added chemicals was determined to be af unction of catalyst/biomass weightr atio, heating rate, pore size, reactorc onfiguration, and reactiontemperature. [67,74,75] It hasb een suggested that char forms as an external layer on the catalyst surfaceand in macropores while coke forms inside micropores. [60,63,[66][67][68][69][70][71] However, physical mixtures of Siral 5, an amorphous silica-alumina, and H-ZSM-5 was shown to have as ynergistic effect on the yield of aromaticsr elative to either catalystalone.…”

“…[16,17,[60][61][62][63][64][65] It was demonstrated that H-ZSM-5, with aS i/Al ratio of roughly3 0, gives the best selectivity to aromaticsc omparedt oa morphous silica-aluminas, other zeolites,a nd other supported metal or metal oxide catalysts. [67] In this work, supported Al 2 O 3 /SiO 2 solid acidc atalysts were synthesized via grafting of alumina precursors ontoS iO 2 and the resulting supported AlO x nanostructures were extensively characterized by combining multiple spectroscopic techniques (in situ Raman spectroscopy,i ns itu IR spectroscopy,e xs itu and in situ high field (21.1 T) 1 H, 27 Al, and 29 Si Magic Angle SpinningN MR (MAS NMR) at elevated reaction temperatures), and quantum chemical calculations using DFT.A no perando Raman-IR-MS spectroscopy system was developed that allowed simultaneous time-resolved spectroscopica nalysisa nd online GCMS product detection during catalytic biomass pyrolysis. [68] The addition of H-ZSM-5 catalysts to the pyrolysis reactor lowerst he temperature at which the fragmentation and dehydration reactions of cellulose and glucose occur.…”

Effect of catalyst contact on the pyrolysis of wheat straw and wheat husk

“…Sakata et al carried out studies to understand the effect of position of catalyst for pyrolysis of plastics (polyethylene and polypropylene) and observed significant variations in the product distribution and yields [11]. In case of biomass pyrolysis, experiments on Py-GC/MS to understand the effect of position of catalyst [12][13][14][15] and some preliminary catalytic pyrolysis reports of biomass using H-ZSM-5 [16,17] are available in open literature.…”

Calcium-catalyzed pyrolysis of lignocellulosic biomass components

“…This coke lowers the acidity of the catalyst surface resulting in deactivation (Du et al, 2013). The coke formed on the catalyst can be removed by combustion, and circulating fluidized bed reactors have been employed for continuous catalyst regeneration.…”