Catalytic upgrading of pyrolytic bio-oil from Salicornia bigelovii seeds for use as transportation fuels: Exploring the ex-situ deoxygenation capabilities of Ni/mordenite zeolite catalyst

Exploiting the beneficial chemical composition of halophytes is increasingly becoming the need of the current world scenario since these special plants can survive extremely high temperatures and withstand water salinity. Catalytic upgrading of Salicornia Bigelovii (SB) seeds was conducted previously using Ni/H- zeolite as the catalyst in the temperature range of 200-500 °C for use in jet fuels. In this work, we conduct fast pyrolysis using the higher acidic and intra-crystalline mesoporous Ni/mordenite zeolite and hydrogen gas to explore its deoxygenation capabilities on the bio-oil produced from pyrolysis of SB seeds in the same temperature range. Our objective here was to increase the yield of aromatics as well as produce mainly deoxygenated compounds in the products to be ultimately used as transportation fuels. Various hydrodeoxygenation (HDO) pathways such as dehydration, demethoxylation, decarboxylation and dehydroxylation were explored considering compound classes from different parts of the SB seeds such as cellulose/hemicellulose, lignin and unsaturated fatty acids. The highest potential of the MOR zeolite with Ni active metal for deoxygenation and aromatization was realized at 400 °C, where 0% oxygenates and the highest yield of 61% aromatics were obtained among all temperatures used in this work. The performance of Ni/MOR zeolite in terms of the yield of aromatics, poly-substituted benzene derivatives, aliphatics and HDO capability were compared with that of Ni/H- zeolite that was used in our previous work, and it was seen that mordenite exhibited a higher degree of deoxygenation with increased aromatics production. Gas chromatography-mass spectrometry (GC-MS) was used to identify the different compounds in the pyrolytic bio-oil. Some reaction sequences were also proposed for the formation of these aromatics and verified with evidence from literature. The novelty of our work is that mordenite zeolite combined with Ni active metal has not been previously used in the fast pyrolysis of SB seeds or any other halophyte to explore the deoxygenation ability. The significance of our study is in the production of ‘drop-in’ transportation fuels in a highly sustainable way from halophytes that can aid in mitigating climate change.