Adsorptive removal of nitrogenous compounds from microalgae-derived bio-oil using metal-organic frameworks with an amino group

Abstract Microalgae-derived bio-oils have recently attracted interest as a potential alternative to traditional transportation fuels. However, the wide variety organo-nitrogen compounds (ONCs) in such bio-oils are detrimental not only to the environment but also to fuel processing equipment. Removal of these ONCs from bio-oils prior to the oil being burnt is particularly important. Therefore, we investigated the adsorptive removal of carbazole (CBZ), hexadecanamide (HDA), and benzonitrile (PhCN), which are present in bio-oil and are difficult to remove via conventional methods, using metal-organic frameworks (MOFs) for the first time. We employed two widely studied MOFs with or without an amino ( NH2) functionality (MIL-125, H2N-MIL-125, UiO-66, and H2N-UiO-66). These MOFs were found to be more efficient adsorbents than a conventional adsorbent, activated carbon. In particular, among the tested adsorbents, the NH2 functionalized MOFs, especially H2N-MIL-125, exhibited the highest adsorption capacities. The role of the NH2 functionality was explained on the basis of H-bonding interactions, which were the main driving force for enhanced ONC capture. The used H2N-MIL-125 could be recycled via simple solvent washing. On the basis of the remarkably high efficiency of H2N-MIL-125 in adsorptive denitrogenation (e.g., this MOF had 3.3, 11.2 and 15.2 times adsorption capacity for CBZ, HDA and PhCN, to that of AC, respectively) and its easy regeneration, the H2N-MIL-125 is proposed as a prospective adsorbent for the purification of algae-derived bio-oil.