Hydrothermal carbonization coupled with fast pyrolysis of almond shells: Valorization and production of valuable chemicals

In this study, it was found that hydrothermal carbonization (HTC) can be an effective method for almond shell (AS) valorization. The severity of HTC treatment had a significant effect on hydrochar yields, with higher severity promoting carbonization but reducing yields. Furthermore, the work found that HTC treatment effectively demineralized biomass samples by removing inorganic material that could catalyze carbonization. As residence time or temperature increased, the amount of carbon increased, while the amount of oxygen decreased. An acceleration in thermal degradation was detected for hydrochars after pretreating for 4 h. The hydrochars showed they had a higher volatile content than untreated biomass, making them potentially useful for producing quality bio-oil through fast pyrolysis. Finally, HTC treatment led to the production of valuable chemicals such as guaiacol and syringol. For syringol production, HTC residence time had more effect than HTC temperature. However, high HTC temperatures benefited levoglucosan production. Overall, the results demonstrated the potential for HTC treatment to be an effective method for valorizing agricultural waste, offering the possibility of producing valuable chemicals.

Fast pyrolysis as an alternative to the valorization of olive mill wastes

BACKGROUND

The valorization of organic wastes through fast pyrolysis appears to be a highly promising option for decreasing pollutants and reducing consumption of natural resources. For this purpose, three different olive pomace samples were studied to determine how olive crop location and the extraction process could influence bio-oil product distribution. Olive pomace was selected as the feedstock due to the importance of the olive oil industry in Spain.

RESULTS

In this study, the conditions of fast pyrolysis were optimized using lignin as a reference, with the optimum conditions being 500 °C, 20 °C ms^-1 as the heating rate and 15 s as the vapour residence time. The olive pomace results determined that not only their chemical composition, but also their fat content had a remarkable effect on product distribution obtained after fast pyrolysis. However, whereas high lignin content enhanced phenol production, cellulose decomposed to carboxylic acids. In addition, due to current global warming, the carbon dioxide (CO₂ ) burden of the three samples was calculated using mass spectroscopy. The OPGC sample gave off the lowest amount of greenhouse gases, followed by OPMNE and OPMN.

CONCLUSIONS

The higher fat content in the sample enhanced carboxylic acid production. The difference in phenol production between OPMN and OPMNE could be attributed to the presence of potassium. From an environmental point of view, the use of olive pomace wastes could reduce CO₂ emissions with further research and by developing experimental processes. © 2020 Society of Chemical Industry.