Doctor of Philosophy
Chemical and Biochemical Engineering
Pyrolysis and activation were used in this thesis to produce biochar and activated carbon from industrial digestate and hydrochar materials. In the first part of thesis, digestate derived biochars were obtained by varying the pyrolysis heating rate (10, 80, 100, 200, >1000 °C·min-1) and temperature (300 to 600 °C) to modify their soil-related characteristics (i.e., nutrient leachability, carbon stability, and heavy metal adsorptive capacity). The biochar produced at a temperature of 500 °C and heating rate of 10 °C·min-1 was also activated under using CO2 at 800 °C with different holding times (0.5-2 h). Results indicated a dominant effect of the pyrolysis temperature when compared to the heating rate on the biochar properties: when the temperature was increased, leachability dropped, and carbon stability increased. The desired biochar characteristics were also improved following activation, though increasing the activation holding time negatively impacted these improvements. In the second part of the thesis, activated carbons were produced from hydrochar through pyrolysis, physical activation, and a HNO3 post-treatment. The carbons were optimized based on the removal of methylene blue and phenol, model compounds of organic contaminants from water, by varying the activation gases (N2, CO2, and steam), temperatures (400 to 900 °C) and holding times (1, 2, or 3 hours). Results indicated that (i) a temperature of 800 °C and a 2-hour holding time provided carbons with the best methylene blue and phenol adsorption capacities, (ii) among the activation gases used, steam provided an activated hydrochar with higher surface area and a broader pore size distribution, resulting in the best adsorption performance, (iii) the HNO3 post-treatment of the best performing activated carbons improved methylene blue adsorption, yet had a negative effect on phenol adsorption.
Summary for Lay Audience
Anaerobic digestion (AD) and hydrothermal carbonization (HTC) are two conversion methods for processing of high moisture content (>70%) biomass and waste materials. The conversion of such materials using pyrolysis, which is thermal decomposition of biomass in oxygen-free environment to produce bio-oil and biochar, or gasification, which is partial oxidation of biomass to produce syngas, will need extensive drying (moisture less than 10%) and will not be cost efficient. Besides energy, AD and HTC produce solid residues that with proper liquid-solid separation can provide a suitable feedstock for pyrolysis and gasification. Therefore, appropriate integration of these technologies will be both economically and environmentally beneficial.
The main focus of this thesis is to produce added-value products (i.e. biochar and activated carbon) from residues of biogas and hydrothermal process through pyrolysis and activation. In chapter 3, the digestate derived biochar and activated carbon are evaluated for their potential as soil amendment to provide nutrient, sequester carbon, and adsorb contaminant. This chapter will provide an insight into the effect of temperature and heating rate on desired characteristics. In chapter 4, The hydrochar derived biochar and activated carbon are evaluated for their potential as adsorbent in wastewater treatment, as requested by our partner company. This chapter will provide an insight into the effect of the gaseous atmosphere (N2, CO2, or steam), temperature, and holding time on adsorption capacities of Phenol and Methylene blue (model contaminants). In chapter 5, best performed hydrochar derived adsorbent are chemically modified by nitric acid and their new adsorptive capacities towards phenol and methylene blue is evaluated. This chapter will provide insight on the possible adsorption mechanism.
Chegini, Ghazaleh, "Production of Engineered Carbons from Secondary Waste Streams for Environmental Applications" (2021). Electronic Thesis and Dissertation Repository. 7693.
Available for download on Sunday, May 01, 2022