Co-Hydrothermal Carbonization of Grass and Olive Stone as a Means to Lower Water Input to HTC

Rocío García-Morato, Silvia Román (), Beatriz Ledesma and Charles Coronella
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Rocío García-Morato: Applied Physics Department, University of Extremadura, Avd. Elvas, s/n, 06006 Badajoz, Spain
Silvia Román: Applied Physics Department, University of Extremadura, Avd. Elvas, s/n, 06006 Badajoz, Spain
Beatriz Ledesma: Applied Physics Department, University of Extremadura, Avd. Elvas, s/n, 06006 Badajoz, Spain
Charles Coronella: Chemical and Mineral Engineering, University of Nevada, 1664 N Virginia St, Reno, NV 89557, USA

Resources, 2023, vol. 12, issue 7, 1-14

Abstract: One drawback of biomass hydrothermal treatment (HTC) is the need of a water supply, which is especially important in the case of lignocellulosic biomass. This study has investigated the synergy resulting from co-HTC of two residual biomass materials that significantly differ in their physico-chemical compositions: (a) olive stone, OS, a hard and high-quality biomass, with low N content, whose potential to give a high heating value briquette by HTC has been proven, and (b) fresh grass pruning, GP, as it is gathered from gardens, with a high water content, moderate N fraction, and low calorific value. The work specifically focuses on the water saving that can be attained when the liquid product produced by one of them (grass, with 80% of moisture) can supply part of the water needed by the other (olive stone) when both are subjected to HTC simultaneously. It was found that, when instead of water, an additional amount of fresh GP is added (in particular 40 out of 110 g of water was provided by 54 g of GP), and a more basic processing water is obtained (pH of co-HTC increased by 40%, in relation of single OS processes). This in turn did not have a remarkable effect on OS final SY at any of the two temperatures studied (200 and 220 °C), not on the C densification. Other features such as N content of resulting OS hydrochars showed a rise in the case of hybrid processes, from 0.2% to 3.3%. Other features that were affected on OS HTC products because of the presence of the GP in co-HTC were the HC surface structure, hydrophobicity, and the presence of surface functionalities and their thermal stability towards pyrolysis; processing water also showed changes on mineral content when both biomasses there blended. Proving that a biomass like OS can be hydrothermally treated by a hybrid process involving less water, without being detrimental in terms of final SY and energy densification, can open a field of research aimed to make HTC processes more efficient in terms of hydric balance.

Keywords: co-hydrothermal carbonization; water saving; fresh biomass processing (search for similar items in EconPapers)
JEL-codes: Q1 Q2 Q3 Q4 Q5 (search for similar items in EconPapers)
Date: 2023
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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