Crab by-product hydrothermal carbonization and hydrochar characterization

Abstract

In Atlantic Canada, fisheries and seafood processing are major industries contributing to the local economy. Shellfish industry, particularly snow crab, make up a significant waste stream from this industry. The high moisture content of the crab by-product makes it challenging to valorize. Hydrothermal carbonization (HTC), a hydrothermal process involving biomass in the presence of water, is a simple and effective means of valorizing high moisture biomass, which could negate all or part of the drying process. The main product of HTC is a solid called hydrochar, which has various applications (for example, fuel and bioadsorbent). In this thesis, the hydrochar properties produced from snow crab (Chionoecetes Opilio) are studied to determine the effect of operating conditions on crab hydrochar and assess the best applications. Chapter 2 of this thesis includes a review of the literature on the existing hydrothermal carbonization of various feedstock from lignocellulosic non-lignocellulosic to marine biomass. The findings show that the valorization of marine biomass, especially crab by-products, is rarely studied. Moreover, many of the studies use pre-treatment methods such as deproteinization, deacetylation, or demineralization, which can be unsuitable and costly for remote locations of processing plants. Chapter 3 is the bulk of the thesis experimental work and discussion. Crab hydrochar was synthesized from snow crab processing by-product using HTC over a range of temperatures (180 - 260 °C), residence times (0.5 – 3 h), and water to biomass ratios (2 - 4). In addition to the experiments performed using dried, ground RC, WC was also tested at specific operating condition to study the effects of drying. The hydrochar yield was determined, and feedstock and the hydrochar were compared via ash content (wt %, db), surface area (m² /g), surface groups (FTIR), trace elements, pH, composition (CHN, wt%, db), and minerals (XRD). In general, the hydrochar (solid) yield decreased as water ratio and temperature increased, reflecting the feedstock's increased thermal and water decomposition. Hydrochar has a higher ash content than the feedstock, making it less desirable for fuel application. The increase in hydrochar BET surface area (maximum of 26 m² /g at 260 °C, water ratio 3 and 30 min) and the presence of functional groups in the hydrochar showed potential to facilitate chemisorption as a bioadsorbent. The hydrochar also may suitable for soil amendment application due to its minerals content and soil pollutant adsorption capability.