Hemp-Based Biochar As a Heavy Metal Adsorbent

Heavy metal impurities are toxic even at low concentrations (parts per billion) and can cause health issues as well as contamination if not removed from crude oil. Metals including arsenic, barium, cadmium, chromium, copper, lead, tin, vanadium, zinc, and mercury are present as stable organometallic compounds in crude oil. Although several methods exist to remove metals from crude oil, only a few have been used industrially due to various limitations. For instance, the solvent extraction process reduces the yield of the end product substantially, whereas distillation only concentrates the metals in the heavier fractions (or in petroleum coke). Therefore, there is still a need for processes that can lower crude oil’s metal contents. We propose testing hemp-derived bio-adsorbents for this process as a cheaper and greener alternative. Post-extracted hemp is an abundant waste biomaterial found in Oklahoma and growers and extractors need to pay to dispose of this material. It is proposed to use hydrothermal carbonization (at 300 ^oC with subcritical water as solvent) as a green technology to thermally convert this hemp material into biochar, a precursor to bio-adsorbents, and then in the future to chemically modify the biochar to trap sulfur and heavy metal impurities from crude oil. As baseline studies, the focus was on chromium removal, using both activated and non-activated hemp biochar which were tested over a range of different metal concentrations (10-500ppm). It was surprising to see that the results were not as expected since our lab had worked on activated cellulose biochar as bioadsorbent with better results. It is suspected that our source material had a high ash content due to either the soil of Oklahoma or the fertilizers added during the hemp growth. It is proposed to analyze the hemp material and its biochar for ash content and then reflux the biochar prepared to remove the ash content before retesting the refluxed biochar for Cr removal.