Catalytic Fast Pyrolysis of Lignin Isolated by Hybrid Organosolv—Steam Explosion Pretreatment of Hardwood and Softwood Biomass for the Production of Phenolics and Aromatics

Ioannis Charisteidis,Ulrika Rova,Konstantinos Triantafyllidis,Eleni Pachatouridou,Apostolos Fotopoulos,Leonidas Matsakas,Paul Christakopoulos,Polykarpos Lazaridis

doi:10.3390/catal9110935

Abstract

Lignin, one of the three main structural biopolymers of lignocellulosic biomass, is the most abundant natural source of aromatics with a great valorization potential towards the production of fuels, chemicals, and polymers. Although kraft lignin and lignosulphonates, as byproducts of the pulp/paper industry, are available in vast amounts, other types of lignins, such as the organosolv or the hydrolysis lignin, are becoming increasingly important, as they are side-streams of new biorefinery processes aiming at the (bio)catalytic valorization of biomass sugars. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis of softwood (spruce) and hardwood (birch) lignins, isolated by a hybrid organosolv–steam explosion biomass pretreatment method in order to investigate the effect of lignin origin/composition on product yields and lignin bio-oil composition. The catalysts studied were conventional microporous ZSM-5 (Zeolite Socony Mobil–5) zeolites and hierarchical ZSM-5 zeolites with intracrystal mesopores (i.e., 9 and 45 nm) or nano-sized ZSM-5 with a high external surface. All ZSM-5 zeolites were active in converting the initially produced via thermal pyrolysis alkoxy-phenols (i.e., of guaiacyl and syringyl/guaiacyl type for spruce and birch lignin, respectively) towards BTX (benzene, toluene, xylene) aromatics, alkyl-phenols and polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes), with the mesoporous ZSM-5 exhibiting higher dealkoxylation reactivity and being significantly more selective towards mono-aromatics compared to the conventional ZSM-5, for both spruce and birch lignin.

Highlights

Lignocellulosic biomass is nowadays considered to be an important renewable source for the production of fuels, energy, chemicals, polymers, and other products, with thecatalytic processes playing a major role [1,2,3,4]
The spruce and birch lignins used in this study, which were isolated by the hybrid organosolv—steam explosion method, contained a very low amount of ash
It was shown that the thermal fast pyrolysis oil of spruce and birch lignins, which was isolated by a hybrid organosolv–steam explosion method, has a similar composition profile with the parent lignin in terms of phenylopropane units

Summary

Introduction

Lignocellulosic biomass is nowadays considered to be an important renewable source for the production of fuels, energy, chemicals, polymers, and other products, with the (bio)catalytic processes playing a major role [1,2,3,4]. The most abundant types of bonds in lignin structures are ether type linkages, like β-O-4 (40%–50%), and others, such as α-O-4, 5-5, β-5, β-1, dibenzodioxocin, spirodienone, and β-β linkages [8,10,15]. The composition and structure of lignin depend on the type and nature of plant biomass. Softwoods, such as spruce, pine, etc., contain 20 to 30 wt.% lignin, hardwoods, such as birch, beech, poplar, etc. Softwoods, such as spruce, pine, etc., contain 20 to 30 wt.% lignin, hardwoods, such as birch, beech, poplar, etc. 15 to 25 wt.%; and grasses, straw, and stover 10 to

Methods

Results

Conclusion