Addition of in situ clay catalysts at different process points in a cascaded hydrothermal carbonization-pyrolysis process for agro-industrial waste valorization.

Agro-industrial wastes can be thermochemically converted to sustainable fuels and upcycled carbon products. However, processing such feedstocks through pyrolysis or hydrothermal carbonization (HTC) alone yields fuels that require significant downstream upgrading. In this work, apple pomace was treated via a cascaded HTC-pyrolysis process using inexpensive and abundant clay catalysts, montmorillonite and attapulgite. Clays were added pre-HTC to raw biomass or to hydrochar pre-pyrolysis to examine the effect of addition as a function of process insertion point. Both clays produce similar bio-oils when they are added at the same process point. However, bio-oil was affected by the point in which clay was added to the process (before or after HTC). When clay was added pre-HTC, the bio-oil had an average hydrocarbon content twice that when clay was added to the hydrochar after HTC, prior to pyrolysis.