Synthesis and modification of zeolite catalysts and an assessment of their activity in the hydrogenation of a model hydrothermal liquefaction (HTL) bio-oil

Abstract

Bio-oils produced from the thermal processing of biomass will play a promising role in the replacement of conventional fuel reserves. One likely processing method is the hydrothermal liquefaction (HTL) of microalgae. However, despite being more stable than pyrolysis oils, the high acidity, high oxygen and high nitrogen content, restrict the oils performance, and as such need to be upgraded by catalytic hydrogenation. Porous structure catalysts, especially zeolites have been widely applied to pyrolysis bio-oil upgrading, though to date have not been investigated for the upgrading of HTL oils, or HTL oils produced from microalgae. To this end, the zeolite FAU, MOR and ZSM-5 were synthesized, ion-exchanged and well characterized to study their performance on the upgrading of bio-oils. Firstly, the FAU, MOR and ZSM-5 zeolite were synthesized. In the presence of sodium base, and the FAU and MOR were ion-exchanged by ammonia nitrite solution. After that, the FAU and MOR were calcined to remove the ammonia ions from structure. The catalysts were characterized via XRD, FTIR, SEM, EDX, BET and SS-NMR. All the results shows that the zeolites are follow the pattern from international zeolite association, and the Si/Al ratio of FAU, MOR and ZSM-5 are around 2, 7, and 16 respectively. Finally, all the catalysts were screened for their activity with a model oil, designed to mimic HTL algal bio-oils, under high temperature and 40 bar of hydrogen pressure. The catalyst performance was monitored by 1H NMR. All the catalysts demonstrated some activity in hydrogenating dodecylamine and pyrazine, though despite ZSM-5 being widely used in the hydrogenation of pyrolysis bio-oils, it was the FAU zeolites that were the most active for this model HTL bio-oil. H-FAU achieved the highest reduction in pyrazine whereas NH4-FAU was the most active catalyst for the hydrogenation of dodecylamine. This is presumably because FAU has a relatively high surface area and mesopores in its structures comparing to other type of zeolite synthesized and applied in this project. Interestingly, little activity was observed in the reduction of double bonds or aromatics in the model oil, this suggests that while the zeolites could be used to provide denitrogenation for an algal bio-oil, it seems likely that metal nanoparticles are necessary to fully hydrogenate these oils.

Date of Award	17 Mar 2016
Original language	English
Awarding Institution	University of Bath
Supervisor	Chris Chuck (Supervisor), Asel Sartbaeva (Supervisor) & Valeska Ting (Supervisor)