Study On The Mechanism Of Cobalt-based Catalyst Catalyzing Oil Hydrogenation To Prepare Second-generation Biodiesel

As a green,renewable and new energy source,biomass can be converted into high value-added fuels and chemicals,thus reducing our dependence on fossil fuels.Through catalytic hydrotreatment,the oxygen atoms in the oil can be removed in the form of CO₂,CO or H₂O to produce diesel-like long-chain alkanes(mainly C15?C18),as known as the second generation of biodiesel.It can be directly mixed with diesel fuel for use on diesel engines.At present,the research of the second generation biodiesel mainly focuses on the catalysts,and the nickel-based catalysts are the most promising catalysts.However,nickel catalysts have some shortcomings,such as high reduction temperature and metal agglomeration,which limit their catalytic activity and raise cost of production.In order to solve the above problems,this paper prepared supported transition metal catalyst by impregnation method,and tested the activity of the catalyst in oleic acid hydrotreatment reaction.Based on the performance of the catalysts,cobalt-based catalysts were selected,and the effects of metal additives on the catalytic activity were studied.Meanwhile,the mechanism of enhancing the activity of cobalt-based catalysts by the loading amount and catalyst support(Al₂O₃and HAP)was further studied.The main findings are as follows:1.Al₂O₃ supporting Co,Mo,Fe,Cu,Ni catalysts were prepared by impregnation method,and the activities of the above catalysts were compared in oleic acid hydrotreatment.The results show that the activity of Co/Al₂O₃ catalysts is much higher than that of Mo/Al₂O₃,Fe/Al₂O₃,Cu/Al₂O₃ and Ni/Al₂O₃ catalysts.At the same time,Cu,Fe,Mo,Ga,In,Ce and other metals were introduced into the Co/Al₂O₃catalyst to explore the synergistic effect of the bimetallic.Ga and Ce have limited effect on the activity of cobalt-based catalyst,while most other metals have inhibition effect on the activity of cobalt-based catalyst.2.Impregnation method was used to load cobalt on different carriers,study the interaction between the carrier and cobalt,and compare its activity in oleic acid hydrogenation reaction.The hydrotreatment reaction data show that the interaction between cobalt and HAP,SAPO and Al₂O₃ is strong,and the reaction conversion rate and total alkane yield are higher than other carriers.It is noteworthy that in the data of all kinds of carriers,it is found that the product is cracked to generate small molecular alkanes,which indicates that cobalt has the characteristics of cracking in the hydrotreatment reaction.Moreover,the reaction path of oleic acid hydrotreatment with cobalt-based catalyst is mainly DCX/DCN.3.The catalytic activities of cobalt catalysts supported by HAP,SAPO and Al₂O₃ in oleic acid hydrotreatment were compared in the pre-experiment at 240°C.The results showed that the catalytic performance of Co/HAP and Co/Al₂O₃ was better.Co/HAP and Co/Al₂O₃ catalysts with different loads were prepared,and the activity of the catalysts was tested to explore the best loads of different carriers.The results showed that the total alkane yield of both catalysts increased at first and then decreased with the increase of loading capacity.The optimum loading capacity of Co/HAP catalyst was 25 wt.%and that of Co/Al₂O₃ catalyst was 20 wt.%.It is worth noting that the better the catalytic hydrogenation effect,the stronger the HDO reaction path.4.Two optimal loads of 20%Co/Al₂O₃ and 25%Co/HAP catalysts were used as research objects.The reaction temperature,raw materials and atmosphere were changed to explore the influence of reaction conditions on the catalytic hydrogenation reaction.The results show that when the reaction temperature reaches more than260°C,the hydrogenation reaction of the two catalysts can achieve good conversion effect,but at lower temperature,the catalytic activity of 25%Co/HAP catalyst is significantly higher than that of 20%Co/Al₂O₃.The Co/HAP catalyst showed good conversion efficiency for oleic acid,stearic acid,octadecanol and rapeseed oil,while the Co/Al₂O₃ catalyst only had good catalytic activity for octadecanol.Therefore,in general,Co/HAP catalysts have better catalytic activity.The Co/HAP catalyst was used for oleic acid hydrogenation in different atmosphere,and the results showed that the greater the amount of hydrogen,the higher the conversion efficiency of the reaction.At 260°C and 2 MPa gas pressure,82.16%of total alkanes were obtained from pure H₂,while only 48.15%and 9.05%were obtained from 10%H₂/N₂ and pure N₂,respectively.