Hydrodeoxygenation (HDO) catalysts Characterization, reaction and deactivation studies
The effect of preparation and pretreatment conditions on hydrogen uptake capacity and dispersion of the prepared Ni, Co and Mo containing catalysts was evaluated by using several characterization techniques such as BET, ICP-SFMS, SEM, TEM, TPO, ethylamine-TPD, XPS and H2-chemisorption. The H2-chemisorption, XPS and SEM results confirmed the detrimental effect of calcination on hydrogen uptake capacity of catalysts. The effect of pH of the impregnating solutions on the dispersion of the metal phases was also assessed from the TEM experiments. Moreover, HDO reactions of oleic acid and abietic acid over a prepared sulfided NiMo catalyst were studied. The results show that addition of DMDS to an oleic acid feed clearly promoted maintenance of the active sulfided phases on the NiMo catalysts. Higher concentration of DMDS also promoted the decarbonylation/decarboxylation (DCOx) route, and more importantly, decreased the amount of carbon deposition on the NiMo catalyst. On the other hand, addition of abietic acid to an oleic acid feed, is shown to decrease the deoxygenation rate of the oleic acid and increase the amount of carbon deposition on the catalyst. The inhibition effect of abietic acid on the HDO of oleic acid was related to stronger adsorption of the bulkier abietic acid molecules on the active sites compared to oleic acid that may have sterically hindered adsorption of oleic acid on neighboring sites.
Furthermore, the poisoning effect of iron on the HDO of oleic acid over sulfided NiMo and Mo catalysts was investigated. It is shown that addition of iron to an oleic acid feed decreased the oxygenate conversion activity of both catalysts and changed their selectivities towards the final products. TEM results of the poisoned spent NiMo catalyst revealed that iron was mainly deposited on and in the vicinity of the Ni particles. This may also indicate that iron has reacted with Ni phase and as a result modified the catalyst activity. Finally, hydroconversion of rosin acids over supported NiMoS catalysts on alumina, USY-zeolite and mixed alumina/USY-zeolite was investigated. Various catalyst properties such as dispersion of the NiMo phases and Brønsted acidity affected the selectivity for the products. The results also indicate that the Brønsted acidity of the support could be optimized by the USY-zeolite content of the catalyst to achieve a satisfactory level of deoxygenation, ring opening and cracking of the rosin acid while avoiding excessive coke formation.
Brønsted acid sites
Chalmers, Kemi och kemiteknik, Kemiteknik
Tall oil contains free fatty acids (FFA), rosin acids (RA) and unsaponifiables compounds (neutrals). The FA as well as RA portions of tall oil can be hydroprocessed via catalytic hydrodeoxygenation (HDO) to produce highly paraffinic diesel like hydrocarbons. Catalytic HDO is an efficient upgrading treatment that is used to reduce the oxygen contents of both fossil based and bio-based feedstocks. During an HDO process, the oxygen is removed by hydrogen at elevated temperatures in the form of CO, CO2 and water.
HDO provides an important and effective route for producing high quality renewable fuels from bio-resources. However, change in catalyst activity and selectivity have raised concerns from the economic and technological perspectives. The aim of this study was to gain a better understanding of the HDO catalyst, and then to assess the effect of different pretreatment and operational conditions on the catalyst activity and selectivity. The results shows that addition of dimethyl disulfide (DMDS) to an oleic acid feed clearly promoted maintenance of the active sulfided phases and more importantly, decreased the amount of carbon deposition on the alumna supported NiMoS catalyst. Iron impurity in a FA acid feed evidently decreased the oxygenate conversion activity and changed the selectivities towards the final products. Addition of RA acid to a FA feed inhibited the deoxygenation rate of the FA and increase the amount of carbon deposition on the catalyst. Finally, it is shown that the dispersion and Brønsted acidity of the supported NiMoS catalysts could be optimized to achieve a satisfactory level of deoxygenation, ring opening and cracking of the rosin acid while avoiding excessive coke formation.
Innovation och entreprenörskap
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4385
KB-salen, Kemigården 4, Göteborg
Opponent: Professor Anker Degn Jensen, Department of Chemical and Biochemical Engineering, DTU, Denmark