Waste Biomass-Derived Ultraporous Functionalized Superactivated Hydrochars for Hydrogen Storage and Carbon Capture
Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering and Sciences
M. Toufiq Reza
Maria Pozo de Fernandez
Accelerating world population and simultaneous growth in economic race has resulted in parallel rise of waste generation where the necessity of mitigating the climate change, via transitioning towards a clean energy economy and minimization of greenhouse gas from atmosphere, is in urgent need of attention. Hence, the objectives of this dissertation comprised of firstly upcycling waste biomass into low-cost and effective adsorbent material such that, secondly, its surface could be tailored by modulating its synthesis conditions (hydrothermal carbonization and chemical activation) to be developed into ultraporous and functionalized adsorption medium in order to, thirdly, assess its application as adsorbents for H2 storage and CO2 capture and hence, lastly, evaluate and contrast economic viability along with evaluation of environmental impact of various potassium hydroxide (KOH) activation techniques for scaled up production of such superactivated hydrochars. To achieve these objectives, waste biomass (forest residue, food waste) was hydrothermally carbonized for a varied temperature range of 180-260 ℃ and chemically activated using activation ratio range of 2:1- 4:1 at temperature range of 700-900 ℃ to assess the synergistic effect of process conditions in porosity modulation where the effect was statistically evaluated using Principal Component Analysis. Utilizing the favorable process conditions of hydrothermal carbonization (HTC) and KOH activation, functionalization was achieved by pretreating the waste biomass using novel deep eutectic solvents (DES). Samples were elaborately characterized using ultimate, proximate analysis in addition to surface morphology characterization using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherms for BET (Brunauer, Emmett and Teller) specific surface area (SSA), pore volume along with pore size distribution evaluation. Cryogenic-highpressure H2 storage capacity and low-pressure CO2 capture was analyzed where isotherms were fit to models: Langmuir, Freundlich, Sips, BET and Temkin. BET SSA was significantly improved upon utilization of hydrochar processed at high temperature as micropore creation was enhanced at higher HTC temperature and activation ratio (KOH: hydrochar amount) whereas activation at lower temperature was preferred to achieve high surface porosity altogether. Results showed that porosity of superactivated hydrochars achieved were as high as 3666 m2 /g of BET SSA, total pore volume of 1.56 cm3 /g and micropore volume of 1.32 cm3 /g with the hydrogen storage capacity of 10.2 wt.% at 77 K and 55 bar. Further functionalization by biomass pretreatment using DES resulted in substantial improvement in favorable surface functionality of hydroxyl and ether (O-H and CO) groups by a maximum of 34.8%, reflecting a rise in CO2 uptake capacity in the corresponding superactivated hydrochars by a maximum of 21.0%, resulting in 6.31 mmol of CO2 captured per adsorbent mass (gram) at 3 bar and 25°C, while heat of adsorption was 18.4-24.0 kJ/mol. Lastly, technoeconomic (TEA) and life cycle assessment (LCA) was carried to contrast two KOH activation techniques (direct chemical activation and char impregnation) in the context of USA (Florida). TEA results reflected that negative ROI value persisted throughout the project lifetime for direct chemical activation (DCA) and ROI of 1.1 was achieved for char impregnation (CI) at the end of its project lifetime. The breakeven selling price of superactivated hydrochar produced by CI technique was determined to be $1.92/kg. Not only economic viability, LCA was evaluated to highlight the environmental impact that showed CI yields in more environmentally sustainable process of fabricating ultraporous carbons from food waste where the major contributor in environmental impact category was freshwater ecotoxicity (57.2%), primarily resulting from HCl neutralization in post of activation step whereas dryer unit was responsible for climate change impact category, being operated by energy from combustion of natural gas. Hence, in order to unveil possibility of alleviating environmental impact, integrated renewable solar-power plant was incorporated as an alternative scenario, proving its applicability in the sunshine state of Florida. Results revealed that climate change and acidification categories of environmental impact categories could be substantially reduced. However, in light of the concluding remarks from this dissertation, it can be suggested that there is room to expand and improve superactivated hydrochar’s porosity by tackling the bottlenecks like inorganic constituents or synthesizing of composites. Surface functionality should be also explored by means of in-situ synthesis procedures to decorate surface groups at the simultaneous step of activation. Moreover, dynamic gas adsorption studies are warranted with in-depth investigation of its kinetics and thermodynamics requiring further investigation.
Sultana, Al Ibtida, "Waste Biomass-Derived Ultraporous Functionalized Superactivated Hydrochars for Hydrogen Storage and Carbon Capture" (2023). Theses and Dissertations. 581.