Formation and Characteristics of Reaction Intermediates from the Fast Pyrolysis of NaCl- and MgCl₂-Loaded Celluloses

Abstract

This study investigates the formation and characteristics of reaction intermediates from the fast pyrolysis of NaCland MgCl 2 -loaded celluloses (75−106 μm) at 150−400 °C. The loading of MgCl 2 lowers the onset temperature of cellulose pyrolysis. At low temperatures (e.g., 150 °C), the loading of MgCl 2 increases the yield of water-soluble intermediates and significantly enhances the formation of sugar and anhydro-sugar oligomers. However, the effect of NaCl loading is minimal under the similar conditions. The results suggest that the loading of MgCl 2 catalyzes the cleavage of both hydrogen bonds and glycosidic bonds during cellulose pyrolysis at low temperatures. At increased temperatures (250 °C and above), both the loading of NaCl and the loading of MgCl 2 greatly enhance the destruction of sugar ring structures within the pyrolyzing cellulose. The conversion of water-insoluble solid into water-soluble intermediates, which are important precursors for volatile formation, is reduced significantly, leading to an increase in char yield.

Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 1: Experiments and development of a mechanistic model

“…The catalytic role of NaCl in enhancing the formation of char and gaseous species from fast pyrolysis has been extensively reported in the literature. 11,13,14,[17][18][19][20]28 It is consistent with our experimental results that showed higher yields of char and gaseous species from fast pyrolysis of glucose-based carbohydrates in the presence of NaCl. To capture these effects, char formation in the presence of NaCl is assumed to be 10.0 times as fast as that in the absence of NaCl; E a of 36.5 kcal mol 21 and A of 6.5 3 10 10 s 21 were used for all the char formation reactions involving Na 1 -complexes in the model (reactions 70-99).…”

“…14,21,22 Furthermore, Na 1 would be likely to bind with oxygen atoms in the reactive species. 26,[28][29][30] In this work, Na 1 ions were assumed to be able to bind with all the neutral species including polymeric chains and LMW species and form Na 1 -complex species (Na 1 -complexes). Once these complexes are formed, they can undergo the same reactions as their neutral counterparts, but with different kinetics.…”

“…occurring in fast pyrolysis. [13][14][15][17][18][19]25,28 The specific reactions mediated by Na 1 that are incorporated into the model to capture the effects of Na 1 on fast pyrolysis are described in the following sections.…”

“…17,26,27 It has been postulated that sodium in the melt phase probably exists as ions bound to oxygen functionalities within the organic matrix during fast pyrolysis of biomass or cellulose. 26,[28][29][30] Experimental work of Wu and coworkers on investigating reaction intermediates during fast pyrolysis of NaCl-loaded cellulose suggested that Na 1 interacted with ring oxygen atoms and catalyzed ring-opening, dehydration, decarboxylation and decarbonylation reactions, and hence, the destruction of sugar ring structures in cellulose pyrolysis was greatly promoted. 28 Yu et al 28 also concluded that char formation was favored by the addition of NaCl in two ways.…”

“…26,[28][29][30] Experimental work of Wu and coworkers on investigating reaction intermediates during fast pyrolysis of NaCl-loaded cellulose suggested that Na 1 interacted with ring oxygen atoms and catalyzed ring-opening, dehydration, decarboxylation and decarbonylation reactions, and hence, the destruction of sugar ring structures in cellulose pyrolysis was greatly promoted. 28 Yu et al 28 also concluded that char formation was favored by the addition of NaCl in two ways. First, Na 1 suppressed the formation of volatiles and catalyzed the destruction of sugar ring structures via reactions such as dehydration and enhanced cross-linking and the conversion of the water-insoluble portion into char during pyrolysis.…”