Kinetics of dielectric‐loss microwave degradation of polymers: Lignin

Abstract

SynopsisThe rate of product formation as well as detailed product composition were measured in the rapid pyrolysis of a 1.3-cm cylindrical pellet of lignin, a major component of biomass. Volume heating by dielectric-loss microwave heating resulted in rapid weight loss with an apparent rate coefficient of 1-5 min-'. Char yield was surprisingly low (33%) owing to the rapid heating rate and high temperature of the pellet. Total gas yield was 38%, of which 12% were simple hydrocarbons and Hz (both weight percent, of original lignin). Product composition showed extensive secondary reaction a t high temperatures evidenced by the significant yields of CzH2, Hz, and condensed aromatics as well as the typical lignin cracking products such as phenols. Poor coupling of microwave energy to lignin required large power settings in order t o initiate reaction. Once initiated, the reaction rate was difficult to control because of the exothermic nature of the reactions. Additives of a suitable composition to increase coupling may be a possible solution to this problem and may result in more favorable economics.

Mechanism study of wood lignin pyrolysis by using TG–FTIR analysis

“…The pyrolysis of lignin generally starts at a lower temperature than that of cellulose, while covers a rather wide temperature interval [13]. Chan and Krieger [14] proposed the activation energy of 25.08 kJ/ mol and frequency factor of 7.83 s À1 for lignin thermo-degradation in the temperature range of 433-953 K in a microwave device. Nunn et al [15] studied the kinetics of milled wood lignin pyrolysis and put forward a first-order decomposition model for the temperature range of 600-1440 K, in which the activation energy and frequency factor were 82.3 kJ/mol and 3.39 Â 10 5 s À1 .…”

Densification Study and Mechanical Properties of Microwave-Sintered Mullite and Mullite-Zirconia Composites

“…From our results it is clear that microwave heating does not have much influence on densification kinetics of pure mullite in comparison to the conventional heating. It has long been established that microwave radiation can efficiently heat a material with high dielectric loss factor 35 . Because pure mullite has low dielectric loss, it is not a good microwave energy absorber.…”

Modeling the influences of pressure and velocity variations on the microwave‐induced pyrolysis of wood

“…It has attracted a growing interest in the last 20 years with applications in heterogeneous gas-phase catalytic systems 5 and a variety of other fields including food processing, wood drying, plastic and rubber treating, and curing and preheating of ceramics. 6 Consideration has also been given to experimental analysis of biomass pyrolysis induced by microwave heating but after the work of the years 1980', [7][8][9][10] only recently a renewed interest has been shown. [11][12][13][14][15][16][17][18][19] Possible causes for the interruption in these researches can be attributed to the scarce reception of microwave energy by biomass fuels, the need of a multidisciplinary approach to design and develop the related conversion units, the uncertainty about the actual costs, and mainly the lack of highly specific objectives.…”