Upgrading Of Microalgae Oil Model Compounds Over Mesoporous Co/H-ZSM-22 Catalyst

The excessive use of fossil fuels,the increasing demand on fuel during these last decades and the environmental degradations has arouse a strong interest to seek renewable,sustainable,environmental friendly bio-oil,however,the microalgae-based bio-oil cannot be directly used for transportation fuels due to high heteroatoms content?e.g.O and N?,Therefore,further deoxygenation and denitrification are required.In order to meet the requirements of jet fuel of low freezing point,the n-alkanes obtained by deoxygenation and denitrification process must be conversed into iso-alkanes by isomerization.And branched alkanes are the important components of high-grade jet fuels.In this paper,palmitic acid and hexadecanamide are respectively selected as the main oxygenated and nitrogen compounds existed in microalgae-based oil,and some supported Co catalysts are prepared to evaluate their catalytic performance for high quantity hydrocarbon production.1.Study on the deoxygenation of palmitic acid over Co/SiO₂ and Co/H-ZSM-22catalysts.The effect of pore structure and support acidity:Co/SiO₂ and Co/H-ZSM-22?micro-Co/HZ-22,meso-Co/HZP-22?catalysts are prepared by the wetness impregnation method to investigate the catalytic conversion of palmitic acid.The results show that?1?palmitic acid can be converted completely into hydrocarbons over Co/SiO₂ and Co/H-ZSM-22.?2?no iso-alkanes are obtained over Co/SiO₂,meanwhile 60.1%selectivity to iso-alkanes are achieved over Co/HZ-22 in the presence of 4 MPa H₂,indicating that the acid amounts and strength of catalysts have significant effect on product distribution.?3?Co/HZP-22?4 MPa?with mesopores possesses the most excellent catalytic performance during upgrading of palmitic acid to yield the highest iso-alkanes?68.6%selectivity?,indicating that mesopores of parent supports are beneficial for reactants/products diffusion during palmitic acid upgrading,further improving the catalytic activity and the iso-alkanes selectivity to some extent.Optimization of reaction conditions:The Co/HZP-22 bi-functional catalyst is employed to optimize the reaction conditions and to evaluate the stability of the catalyst.The results show that?1?Co/HZP-22 catalyst presents excellent catalytic performance even with low H₂pressure?1 MPa H₂?,the highest molar ratios iso-alkanes/n-alkanes?3.25?and C₁₆/C_16-X?2.30?over Co/HZP-22 are achieved in the presence of 2 MPa H₂.?2?Different reaction time?t=1/2/3/4 h?of palmitic acid conversion is investigated over Co/HZP-22 catalyst in presence of 2 MPa H₂ at 260°C.It can be seen that palmitic acid undergo deoxygenation and isomerization reaction pathway.?3?Stability studies of bi-functional Co/HZP-22 reveals that there was no considerable variation in catalyst activity after five successive reactions,indicating that it had good stability.It should be noted that the molar ratio of iso-alkanes/n-alkanes decrease slightly from 3.25?1 run?to 2.04?5 runs?accounts for the partial coverage of strong acid site by reactants/products on the used Co/HZP-22 catalyst.2.Study on the upgrading of simulative microalgae-based bio-oil over Co/SiO₂,Co/?-Al₂O₃ and Co/HZP-22 catalysts.Considering the high nitrogen content and the relative difficulty of nitrogen atom removal,in this experiment,“palmitic acid?0.4 g?and hexadecanamide?0.1 g?”are used as model compounds to simulate microalgaed bio-oil,Co/SiO₂,Co/?-Al₂O₃ and Co/HZP-22catalysts are employed to test their catalytic deoxygenation and denitrification activity in the presence of 2 MPa H₂.The results show that?1?the initial reaction rate within 10 min is in the following order:Co/HZP-22(0.15060 mol·L^-1·h^-11 and 0.03612 mol·L^-1·h^-1,respectively for palmitic acid and hexadecanamide)>>Co/?-Al₂O₃(0.05028 mol·L^-1·h^-1,0.03426mol·L^-1·h^-1)>Co/SiO₂(0.04482 mol·L^-1·h^-1,0.02742 mol·L^-1·h^-1),Obviously,the catalytic ability of Co/HZP-22 is the best.And the products quantitative analysis shows the selectivity to C₁₆6 is 48.8%,39.5%,29.9%,respectively.?2?In the hydrotreatment of palmitic acid and hexadecanamide over Co/HZP-22 catalyst,there are almost no iso-alkanes products,which may be due to the fact that N directly occupies the acidic center of HZP-22 support,and the acid sites are covered by NH₃ formed during upgrading process,resulting in inactivation of acid function.Therefore,the Co/HZP-22 catalyst has a low iso-alkanes selectivity?9.5%?,despite high catalytic performance.