In situ upgrading of pyrolysis biofuels by bentonite clay with simultaneous production of heterogeneous adsorbents for water treatment

- Bentonite incorporated into biomass increases pyrolysis gas yield.
- Impact of pretreatment on bio-oil depends on biomass precursor, can increase furans.
- Despite catalytic effects on fuels, no change in overall activation energy.
- Pyrolysis of pretreated biomass yields heterogeneous char for water treatment.

The ability to in situ upgrade pyrolysis biofuels, together with the production of a value-added byproduct from the solid biomass residue, would reduce the economic and environmental costs of the integrated biorefinery. In the present work, biomass samples (mango pits and pineapple plants) were immersed in Fuller's Earth (bentonite clay) suspensions. Pyrolysis at low temperatures (290-350 °C) showed that the incorporation of Fuller's Earth into both biomasses increases the amount of H2, CH4, C2H2, C2H4, and C2H6 evolved as compared to raw biomass. The biomasses' behavior diverges in terms of bio-oil and biochar quality. For mango pit, pretreatment with Fuller's Earth increased desirable compounds such as furans and hexanes, whereas for pineapple plant oxygenated and high molecular weight compounds increased with pretreatment. While surface areas of both biomasses increased with incorporation of bentonite clay, the mango pit saw a significant increase in adsorption capacity and rate of methylene blue removal from water, whereas the pineapple plant adsorption rate decreased with pretreatment; capacity increased at low pyrolysis temperature and decreased at high temperature. While incorporation of Fuller's Earth increased the thermal energy required to heat the impregnated mixtures to pyrolysis temperature, a distributed activation energy model analysis shows that activation energy of pyrolysis was virtually the same for impregnated and raw biomass samples, suggesting that this may be either a thermally catalytic or chemically catalytic effect. Thus, incorporation of bentonite into some biomasses may represent positive benefits in terms of in situ upgrading bio-fuels and hybrid biochars produced at lower pyrolysis temperatures.

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