Search

The search for alternative ways to give a second life to materials paved the way for detailed investigation into three silica-polyethylenimine (Si-PEI) materials for the purpose of CO2 adsorption in carbon capture and storage. A solvent extraction procedure was investigated to recover degraded PEIs and silica, and concomitantly, pyrolysis was evaluated to obtain valuable chemicals such as alkylated pyrazines. An array of thermal (TGA, Py-GC-MS), mechanical (rheology), and spectroscopical (ATR-FTIR, 1H-13C-NMR) methods were applied to PEIs extracted with methanol to determine the relevant physico-chemical features of these polymers when subjected to degradation after use in CO2 capture. Proxies of degradation associated with the plausible formation of urea/carbamate moieties were revealed by Py-GC-MS, NMR, and ATR-FTIR. The yield of alkylpyrazines estimated by Py-GC-MS highlighted the potential of exhausted PEIs as possibly valuable materials in other applications. [ABSTRACT FROM AUTHOR]

Shales experience heat treatment concurrent with the presence of water or steam during reservoir engineering interventions, such as high pressure water fracking and in-situ combustion of hydrocarbons. This work utilises a novel technique, which is a combination of gas sorption overcondensation and integrated mercury porosimetry experiments, not used before for any type of porous material, to study the pore structure of a shale rock, and its evolution following thermal treatment in the presence of water. Overcondensation allows the extension of gas sorption beyond the limits of conventional experiments to enable direct study of macroporosity. Scanning curve experiments, initiated from the complete boundary desorption isotherm, that can only be obtained for macropores by overcondensation experiments, has revealed details of the relative pore size spatial disposition within the network. In particular, it has been found that the new large voids formed by treatment are shielded by relatively much narrower pore windows. Use of a range of different adsorbates, with differing polarity, has allowed the chemical nature of the pore surface before and after treatment to be probed. Integrated rate of gas sorption and mercury porosimetry experiments have determined the level of the particular contribution to mass transport rates of the newly introduced porosity generated by thermal treatment. Combined CXT and mercury porosimetry have allowed the mapping of the macroscopic spatial distribution of even the new mesoporosity, and revealed the degree of pervasiveness of the new voids that leads to a thousand-fold increase in mass transport on thermal treatment. • Overcondensation method allows application of nitrogen sorption to macroporous rocks. • Detailed morphology of pore network obtained from sorption scanning curves. • Integrated rate of gas sorption and mercury porosimetry allows direct assessment of contribution of particular pores to mass transport. • Thermochemical treatment created completely new pore network that raised mass transport rate by factor of ~1000. [ABSTRACT FROM AUTHOR]

Poly(ethylene imine) is a family of polymers with a high content of amine groups employed in various applications and widely investigated as CO 2 adsorbents in carbon capture and sequestration. In this study, five branched polyethylenimines (PEIs) of different molecular weights were analysed by Py-GC-MS to gather information on the chemical structure of the principal thermal degradation products. All the PEIs produced pyrolysates with a similar chemical composition characterised by the occurrence of ethylenediamine, diethylenetriamine, piperazine, N -ethylaminepiperazine, pyrazine, 2-methylpyrazine, 2,3-dimethylpyrazine, 2-ethylpyrazine. Oligomeric ethylene polyamines were volatilised or evolved after chain scission of the PEI backbone. Pyrolysates also contained minor amounts of alkylated pyrroles, imidazoles, pyridines and other compounds that could not be identified. Pyrolysis products were formed at 300 °C, and their abundance increased markedly from 400° to 600°C. Pyrolysis of PEIs at 500 °C in the presence of mesoporous silica favoured cyclisation and aromatisation, enhancing the production of alkylated pyrazines. These compounds are of potential interest in the food industry as flavour-enhancing additives. • Thermal degradation products of branched polyethyleneimines PEI revealed by Py-GC-MS. • Oligomeric linear polyamines, piperazines, pyrazines principal products at 300–600 °C. • Slight changes of pyrolysate composition of PEI with different MW. • Silica enhanced the pyrolytic formation of alkylated pyrazines. [ABSTRACT FROM AUTHOR]

• Production of biochars from three distinct UK-based biomasses via three different thermal conversion technologies. • Application of biochars in methylene blue removal from wastewater. • Seaweed-based biochars exhibited the greatest potential in MB adsorption. • Pseudo-second-order kinetic model explains the MB adsorption over seaweed-based biochars. • The adsorption process was described well by the Langmuir isotherms for seaweed-based biochars. This paper presents, for the first time, a comprehensive comparative analysis of the potential of using biochars from three distinctly different UK-sourced biomass feedstocks, produced via three different thermal processing techniques, to adsorb methylene blue dye. Biochars were made from rapeseed, whitewood, and seaweed (Laminaria Digitata), produced via hydrothermal conversion, pyrolysis, and torrefaction. Adsorption kinetic models were developed for each biochar at different temperatures, pH and initial dye concentrations. Relatively high levels of methylene blue adsorption capacity were achieved by seaweed-based biochars (∼150 mg/g), with reasonable levels for rapeseed-based biochars (∼60 mg/g), whilst adsorption levels were found to be relatively low for whitewood-based biochars (<30 mg/g). A Pseudo-second-order kinetic model provided the best fit with experimental results. The Langmuir adsorption isotherm showed a better fit for seaweed biochars, while the Freundlich adsorption isotherm was a better fit for the rapeseed-based biochars. The Langmuir adsorption isotherms showed relatively high maximum adsorption capacity (Qo) for seaweed-based biochars; ∼175 mg/g for seaweed-Torrefaction and ∼ 117 mg/g for seaweed-Pyrolysis. Negative Gibbs free energy (ΔG°) values were observed for the seaweed-Torrefaction < seaweed-Pyrolysis < 0, which indicates that the methylene blue removal could be a thermodynamically favourable process due to the spontaneous nature of the adsorption. Our investigation has shown that the removal of methylene blue from wastewater could be a potential application for seaweed-based biochars as part of a holistic whole life cycle valorisation pathway. However, it is not suitable for all types of biomasses which emphasises the need for tailoring unique valorisation pathways for different types of biomasses. [ABSTRACT FROM AUTHOR]