Torrefaction, temperature, and heating rate dependencies of pyrolysis of coffee grounds: Its performances, bio-oils, and emissions

The torrefaction pretreatment is of great significance to the efficient conversion of biomass residues into bioenergy. In this study, the effects of the three torrefaction temperatures (200, 250, and 300 degrees C) on the pyrolysis performance and products of coffee grounds (CG) were quantified. The torrefaction treatment increased the initial devolatilization and maximum peak temperatures of the CG pyrolysis. Activation energy of CG250 was lower than that of CG and more conducive to the pyrolysis. Torrefaction altered the distributions of the pyrolytic products and promoted the generation of C=C. Torrefaction changed the composition ratio of the pyrolytic biooils although cyanoacetic acid and 2-butene still dominated the bio-oils. The joint optimization pointed to pyrolysis temperature > 600 degrees C and torrefaction temperature <= 270 degrees C as the optimal conditions. Our experimental results also verified that torrefaction of CG may be more suitable at 200 and 250 degrees C than 300 degrees C.

Automated summary

The study demonstrates that torrefaction pretreatment can improve the efficiency of coffee grounds pyrolysis, decrease activation energy, and promote the generation of C=C. The optimal conditions are pyrolysis temperature > 600 degrees C and torrefaction temperature <= 270 degrees C. Different torrefaction temperatures have an impact on the composition ratio of bio-oils, with 200 and 250 degrees C potentially being more suitable for the torrefaction of coffee grounds.