The Influence of Zeolites on Radical Formation During Lignin Pyrolysis

Abstract

Lignin from lignocellulosic biomass is a promising source of energy, fuels, and chemicals. The conversion of the polymeric lignin to fuels and chemicals can be achieved by catalytic and noncatalytic pyrolysis. The influence of nonporous silica and zeolite catalysts, such as silicalite, HZSM5, and HUSY, on the radical and volatile product formation during lignin pyrolysis was studied by in situ high-temperature electron paramagnetic resonance spectroscopy (HTEPR) as well as GC-MS. Higher radical concentrations were observed in the samples containing zeolite compared to the sample containing only lignin, which suggests that there is a stabilizing effect by the inorganic surfaces on the formed radical fragments. This effect was observed for nonporous silica as well as for HUSY, HZSM5, and silicalite zeolite catalysts. However, the effect is far larger for the zeolites owing to their higher specific surface area. The zeolites also showed an effect on the volatile product yield and the product distribution within the volatile phase. Although silicalite showed no effect on the product selectivity, the acidic zeolites such as HZSM5 or HUSY increased the formation of deoxygenated products such as benzene, toluene, xylene (BTX), and naphthalene.

Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

“…In addition, evidence for radical species adsorbed on the catalyst surface was found by Bährle et al ,43 who used EPR spectroscopy to monitor these intermediates upon CFP of lignin on zeolites. Probably due to strong chemisorption on the surface, cyclopentadienyl and phenoxy species will not desorb in our case and are supposed to be rather immobile.…”

“…Similar to the methyl radical, other radical intermediates are expected to survive the few wall collisions within the reactor in the few millisecond transfer time to detection. Several indications point to a strong binding of the radicals to the catalyst surface or a rapid quenching before desorption: First, by using electron paramagnetic resonance (EPR) spectroscopy, Bährle et al 4243. showed a radical concentration enhancing effect during catalytic pyrolysis of lignin.…”

Optimization of Lignin Extraction from Pine Wood for Fast Pyrolysis by Using a γ-Valerolactone-Based Binary Solvent System

“…550, 650, 750 and 850 °C) were used to evaluate the fast pyrolysis of GVL-lignin from pine wood using a heating rate of 20 °C/ms and residence time of 20 s. The pyrolysis products can be divided into three phases, namely liquid (bio-oil), solid (char) and gas. [41][42][43][44][45][46][47][48] Figure 1A illustrates the yields of liquid, char and gaseous products as a function of the pyrolysis temperature of GVL-lignin obtained using a mixture of 4/1 GVL/H 2 O (w/w) and 0.075 M sulfuric acid at 160 ºC for 24 h. The liquid fraction increased from 550 to (650-850) °C, because of an increase in primary decomposition of lignin at higher temperatures. 49,50 In contrast, the char yield decreased from 550 to (650-850) °C.…”

Measuring biomass fast pyrolysis kinetics: State of the art

“…Bärhle et al investigated the nature of radicals released during the pyrolysis of Klason lignin extracted from poplar and pinewood sources (Bahrle et al, 2014;Bahrle, Custodis, Jeschke, van Bokhoven, & Vogel, 2016). To understand the radical evolution with respect to temperature and time, the samples were heated at a rate of 40 C/min.…”