AN EXPERIMENTAL INVESTIGATION OF SORPTION BEHAVIOUR OF VOLATILE ORGANIC COMPOUNDS IN BIOCHAR

  • Hamid Rajabi

Student thesis: Phd

Abstract

Containment is a temporary remedial solution to control the emissions of hazardous gases such as volatile organic compounds (VOCs) sourcing from crude oil contaminated lands. Containment systems using engineered organic (e.g., activated carbon) and inorganic (e.g., silica gels, zeolites, and alumina) adsorbents are well-established techniques to control hazardous emissions of VOCs. However, their cost and high-tech production methods limit their applications and attractiveness for controlling the VOC emissions from vast oil-contaminated sites, especially in low-income communities. Biochar as an affordable by-product of biomass pyrolysis has recently received widespread attention for a range of applications in energy production, carbon sequestration, water filtration, decontamination, and separation, particularly when affordability and abandonment factors are of importance. The research presented in this thesis aims to address the existing gaps in the fundamental understanding of VOC interactions with biochar for potential engineering applications as a low-cost containment solution. Biochar samples sourced from a range of feedstock (wheat straw, corn straw, rice straw, rape straw, hardwood, and bagasse sugarcane) pyrolysed at relatively moderate temperatures (300-500℃) have been used in this research. Hexane, toluene, and xylene isomers were identified as high-detected high-concentrated VOCs emitted from crude oil. A bespoke laboratory setup was designed and developed including an inline GC-FID to carry out an extensive experimental investigation of VOC adsorption in biochar. Chemical and physical properties of biochar were analysed using elemental composition, scanning electron microscopy, specific surface area, Fourier-transform infrared spectroscopy, and Raman spectrometry. Single and competitive adsorption experiments confirmed that porous structure, surface chemistry and pore size distribution of biochar along with molecular properties of VOCs govern the fundamental mechanisms of VOC adsorption in biochar. Hydrogen bonding, electrostatic interaction, and π-π stacking were found to be the main mechanisms of VOC adsorption in biochar studies, in addition to partitioning (absorption) in non-carbon mass and pore-filling. The range of total adsorption capacity obtained through single and competitive adsorption tests for various types of biochar was estimated to be between 51 and 110 mg/g. This range is sufficiently higher than the total concentrations of volatile compounds frequently detected in oil-polluted lands. The reliable and safe performance of biochar in the removal of VOCs has been demonstrated in extreme operating conditions of elevated temperature and humidity. The biochar continued to effectively adsorb VOC gases (by up to 63% of its initial adsorption capacity), even at extreme conditions of 80% relative humidity. The used types of biochar could also retain approximately 77-86 % of their adsorbed mass when exposed to higher ambient temperatures of up to 62.5℃, showing a reliable performance of biochar under severe operating conditions. The regeneration efficiency of up to 96% was obtained through five successive cycles of adsorption-desorption tests. The comprehensive experimental work carried out in this research has demonstrated the reliability of biochar materials as a sustainable and cost-effective solution for controlling VOC emissions from contaminated lands.
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorMojgan Hadi Mosleh (Supervisor), Parthasarathi Mandal (Supervisor) & Amanda Lea-Langton (Supervisor)

Keywords

  • Adsorption
  • Desorption
  • Biochar
  • VOCs

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