Dielectric loss microwave degradation of polymers: Cellulose

Abstract

SynopsisThe pyrolysis of organic waste polymers to produce fuels and chemicals is of interest to augment petroleum-based processes. The wide variety of pyrolysis products of low yield and the uncertain role that heat transfer rate plays in determining these have been deterrents to utilization in the past. A possible approach to increased selectivity for products is to heat them rapidly and homogeneously with the aim of narrowing the product distribution. A very rapid means of homogeneous heat transfer throughout the substrate is microwave heating. A laboratory study has been done to determine what effect high-intensity microwave energy has on the thermal degradative pathways of cellulose. The product distribution found when cellulose is pyrolyzed in the absence of a microwave discharge is similar to that found in conventional furnace pyrolysis. The major products are levoglucosan (27%), carbon dioxide (2-5%), water, and charred residue. However, the total heat-up and reaction times for even large pellets are reduced to less than 2-3 min when high-intensity microwave irradiation is employed, Effects of pressure and microwave power are reported. Low external gas temperature also prevents secondary reactions.

The Overview of Thermal Decomposition of Cellulose in Lignocellulosic Biomass

“…The microwaves might be firstly used to activate biomass (cellulose as the feedstock) to solid, liquid and gas products by Allan et al in 1970s [70]. The studies of the research group led by Fernandez and Pis are mainly concentrated on the high-temperature microwave pyrolysis (more than 400 o C) of biomass [72,74].…”

Microwave Heating Applied to Pyrolysis

“…The higher heating rate, the shorter residence time, and the faster the volatiles arrive to the external cold regions which, in turn, reduces the activity of secondary reactions of vapourphase products. This results in high yields of liquid and reduced deposition of refractory condensable material on the char's internal surface (Allan et al, 1980). In the case of materials with significant moisture content, like most biomass feedstocks, MP offers a different paradigm in particle heating where the electromagnetic field penetrates the solid, and interacts directly with dipoles in the chemical structure.…”

Microwave-assisted conversion of carbohydrates. State of the art and outlook

“…Allan et al reported on the formation of,6-anhydro-b-Dglucopyranoside (levoglucosan), an interesting chiral synthon, when pyrolysing cellulose samples in a domestic microwave oven at 130 Watt for 5 min (Fig. 16) [42]. Yields in levoglucosan were moderate (about 40%), together with charred residues and water, whilst cellulose conversion was nearly quantitative.…”