Abstract
Cracking of propyl side chains from 4-propylphenol, a model compound for lignin monomers, is studied for a commercial ZSM-5 zeolite catalyst. The decline of 4-propylphenol conversion with time on stream can be delayed by co-feeding water. FTIR spectroscopy shows the formation of chemisorbed phenolates during reactions and significant amounts of phenolics are detected by GC-MS of the extract from the spent catalysts. Thus, chemisorbed phenolates are identified as the main reason for deactivation in the absence of water. Regardless of the amount of co-fed water, substituted monoaromatics and polyaromatic species are formed. Comprehensive characterization of the spent catalysts including Raman and solid-state 27Al NMR spectroscopy, and thermogravimetric analysis points to a combination of deactivation processes. First, phenolates bind to Lewis acid sites within the zeolite framework and hinder diffusion unless they are hydrolyzed by water. In addition, light olefins created during the cracking process react to form a polyaromatic coke that deactivates the catalyst more permanently.
Highlights
Bulk chemical production from biomass is one of the leading approaches to eliminating dependence on fossil carbon as feedstock for the chemical industry [1]
As the present study shows, oxygen-containing aromatics are prone to deactivating zeolite catalysts by chemisorbing as phenolates or similar species that quickly prevent reactants from reaching active sites within the micropores
We examine the mechanism of fast, reversible deactivation of ZSM-5 during the cracking of 4-propylphenol
Summary
Bulk chemical production from biomass is one of the leading approaches to eliminating dependence on fossil carbon as feedstock for the chemical industry [1]. The “lignin value prior to pulping” approach shows that limited modifications of industrial pulp and paper operations could advantageously generate a solvent-extracted lignin stream with sufficient quality for downstream processing [11]. Such a lignin could be broken down by pyrolysis, acid digestion, or hydrogenolysis [4]. The lignin-first approach to second generation biorefinery operations uses reductive fractionation techniques to simultaneously extract and depolymerize the lignin from the native biomass [6,12] These processes generate a stream of cellulose and hemicellulose for further upgrading to ethanol or other sugar-based products [13]. Recent work by Sels etSels al. has the efficacy of cracking propylphenol over Brønsted acidic ZSMet al.demonstrated has demonstrated the efficacy of cracking propylphenol over Brønsted acidic
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