Alkaline‐Earth‐Metal‐Catalyzed Thin‐Film Pyrolysis of Cellulose

Abstract

The conversion of lignocellulosic biomass to “bio‐oils” by thermochemical pyrolysis is a promising reactor technology for renewable chemicals and biofuels. Although the fundamental understanding of relevant catalysts within reacting biomass particles is only in its infancy, it is known that inorganic materials naturally present within biomass act as catalysts that limit the yield of bio‐oil and alter the product distribution. In this work, the effect of alkaline earth metals on cellulose pyrolysis chemistry was investigated to determine the catalytic effect on primary (transport‐free) and secondary (diffusion‐limited) reaction pathways. The catalytic materials included homogeneous metal ions Ca2+ and Mg2+ from their inorganic salts, Ca(NO3)2 and Mg(NO3)2, and their corresponding heterogeneous metal oxides, CaO and MgO. Although the oxides had a limited impact on cellulose pyrolysis chemistry, the metal ions altered the secondary reaction pathways of cellulose significantly under diffusion‐limited conditions common to lignocellulosic particles within industrial reactors.

The catalytic effect of inherent and adsorbed metals on the fast/flash pyrolysis of biomass: A review

“…Similarly, the fast pyrolysis of 50 mm cellulose particles at the same temperature [42] returned 8% solids, with approximately half of the products consisting of levoglucosan. Results consistent with these were found with both powder and thin film trials [3].…”

“…There is a plethora of studies of the kind specified in this section. At the operating temperatures of fast pyrolysis (400e600 C), inorganic metals are retained within the char, which indicates that they likely interact with the biomass to catalyse biopolymer degradation [3]. This can be anticipated when it is considered that all components of the biomass will fuse to some extent in the 200e400 C range, thus capturing and incorporating the mineral matter.…”

Spontaneous Aerosol Ejection: Origin of Inorganic Particles in Biomass Pyrolysis

“…The prominence of carbonaceous aerosols was further confirmed by quantifying the product fractions produced from ablative fast pyrolysis. The permanent gas and char fractions were close to the expected product distributions for pure cellulose pyrolysis (2–10 % and 10–20 %, respectively) . Detection of the bio‐oil products yielded a substantial fraction of quantifiable volatiles in the liquid quench (>50 % detectable).…”

“…Detection of the bio‐oil products yielded a substantial fraction of quantifiable volatiles in the liquid quench (>50 % detectable). With improved sampling methodology, the total carbon yield would be expected to exceed 90 %, as shown in previous work . The remaining aerosol fraction, characterized by laser light diffraction, was the result of nonvolatile primary products captured in the liquid quench.…”

Development of Heterogeneous Catalysts for Thermo-Chemical Conversion of Lignocellulosic Biomass

“…The results of previous experiments suggest that, owing to the application of various metal oxides and the introduction of noble or transition metals on their surface, it is possible to increase the C/O ratio of the bio-oil produced during the pyrolysis process [45]. Therefore, researchers began to study the effect of the presence of such catalysts on the composition of liquid products of the thermal treatment of biomass (Table 3).…”