Competitive adsorption of multicomponent volatile organic compounds on biochar.

Crude oil contaminated lands are recognised to have significant contributions to airborne volatile organic compounds (VOCs) with adverse effects on human health and tropospheric ozone. Soil capping systems for controlling harmful emissions are critical engineering solutions where advanced soil remediation techniques are neither available nor feasible. Studies on the adsorption of single VOC species in biochar have shown promising results as a potential capping material; however, current understanding of mixed gas system and multi-component adsorption of VOCs on biochar which would represent more realistic in situ conditions is very limited. We present, for the first time, the results of a study on competitive adsorption of mixed VOCs, including aromatic and non-aromatic VOCs commonly emitted from crude oil contaminated sites on two types of biochar pyrolysed at 500°C from wheat straw and bagasse as feedstock. The kinetics of sorption of multicomponent VOCs including acetone, hexane, toluene and p-xylene in biochar are studied based on the results of an extensive experimental investigation using a bespoke laboratory setup. Both biochar types used in this study presented a high sorption capacity for VOC compounds when tested individually (51-110 mg/g). For the multicomponent mixture, the competition for occupying sorption sites on biochar surface resulted in a lower absolute sorption capacity for each species, however, the overall sorption capacity of biochar remained more or less similar to that observed in the single gas experiments (50-109 mg/g). The chemical interactions via hydrogen bonds, electrostatic attraction, and pore-filling were found to be the main mechanisms of adsorption of VOC in the biochar studied. The efficiency of biochar regeneration was assessed through five cycles of adsorption-desorption tests and was found to be between 88% and 96%. The incomplete desorption observed confirm the formation of likely permanent bonds and heel build-ups during the sorption process.

Emissions of volatile organic compounds from crude oil processing - Global emission inventory and environmental release.

Airborne Volatile organic compounds (VOCs) are known to have strong and adverse impacts on human health and the environment by contributing to the formation of tropospheric ozone. VOCs can escape during various stages of crude oil processing, from extraction to refinery, hence the crude oil industry is recognised as one of the major sources of VOC release into the environment. In the last few decades, volatile emissions from crude oil have been investigated either directly by means of laboratory and field-based analyses, or indirectly via emission inventories (EIs) which have been used to develop regulatory and controlling measures in the petroleum industry. There is a vast amount of scattered data in the literature for both regional emissions from crude oil processing and scientific measurements of VOC releases. This paper aims to provide a critical analysis of the overall scale of global emissions of VOCs from all stages of oil processing based on data reported in the literature. The volatile compounds, identified via EIs of the crude oil industry or through direct emissions from oil mass, are collected and analysed to present a global-scale evaluation of type, average concentration and detection frequency of the most prevalent VOCs. We provide a critical analysis on the total averages of VOCs and key pieces of evidence which highlights the necessity of implementing control measures to regulate crude oil volatile emissions (CVEs) in primary steps of extraction-to-refinery pathways of crude oil processing. We have identified knowledge gaps in this field which are of importance to control the release of VOCs from crude oil, independent of oil type, location, operating conditions and metrological parameters.