Hydrodeoxygenation of aliphatic and aromatic oxygenates on sulphided catalysts for production of second generation biofuels
Başlık çevirisi mevcut değil.
- Tez No: 400059
- Danışmanlar: PROF. OUTİ KRAUSE, DR. TUULA-RİİTTA VİLJAVA
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2007
- Dil: İngilizce
- Üniversite: Helsinki University of Technology
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 59
Özet
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Özet (Çeviri)
Environmental concerns and diminishing petroleum reserves have increased theimportance of biofuels for traffic fuel applications. Second generation biofuels producedfrom wood, vegetable oils and animal fats have been considered promising for deliveringbiofuels in large amount with low production cost. The abundance of oxygen in the form ofvarious aliphatic and aromatic oxygenates decreases the quality of biofuels, however, andtherefore the oxygen content of biofuels must be reduced. Upgrading of biofuels can beachieved by hydrodeoxygenation (HDO), which is similar to hydrodesulphurisation in oilrefining. In HDO, oxygen-containing compounds are converted to hydrocarbons byeliminating oxygen in the form of water in the presence of hydrogen and a sulphidedcatalyst. Due to the low sulphur content of biofuels, a sulphiding agent is typically addedto the HDO feed to maintain activity and stability of the catalyst.The aim of this work was to investigate HDO using aliphatic and aromatic oxygenates asmodel compounds on sulphided NiMo/?-Al2O3 and CoMo/?-Al2O3 catalysts. The effects ofside product, water, and of sulphiding agents, H2S and CS2, on HDO were determined. Theprimary focus was on the HDO of aliphatic oxygenates, because a reasonable amount ofdata regarding the HDO of aromatic oxygenates already exists.The HDO of aliphatic esters produced hydrocarbons from intermediate alcohol, carboxylicacid, aldehyde and ether compounds. A few sulphur-containing compounds were alsodetected in trace amounts, and their formation caused desulphurisation of the catalysts.Hydrogenation reactions and acid-catalysed reactions (dehydration, hydrolysis,esterification, E2 elimination and SN2 nucleophilic substitution) played a major role in theHDO of aliphatic oxygenates. The NiMo catalyst showed a higher activity for HDO andhydrogenation reactions than the CoMo catalyst, but both catalysts became deactivatedbecause of desulphurisation and coking. Water inhibited the HDO, but the addition of H2Seffectively eliminated the inhibition. The addition of H2S enhanced HDO and stabilised theselectivities but did not prevent deactivation of the catalysts. The effect of H2S wasexplained in terms of promotion of the acid-catalysed reactions due to enhanced catalystacidity. Water and the sulphiding agents added to the HDO feed suppressed hydrogenationreactions on the NiMo catalyst but did not affect them on the CoMo catalyst. The additionof H2S resulted in less hydrogen consumption and coke formation than the addition of CS2,but the product distribution was shifted such that the carbon efficiency decreased. It wasconcluded that, for the HDO of aliphatic oxygenates, H2S was superior to CS2 as asulphiding agent.The HDO of phenol, used as a model aromatic oxygenate, produced aromatic and alicyclichydrocarbons in parallel routes in which the primary reactions were direct hydrogenolysisand hydrogenation, respectively. The addition of H2S on both catalysts inhibited the HDOdue to competitive adsorption of phenol and H2S, and affected the hydrogenation reactionsin the same way as in the HDO of aliphatic oxygenates. The opposite effects of H2S on theHDO of aliphatic and aromatic oxygenates were attributed to the different reactionmechanisms for oxygen elimination (dehydration, hydrolysis, elimination and directhydrogenolysis reactions). The different molecular and electronic structures of the aliphaticand aromatic oxygenates are likely the reason for the different reaction mechanisms. Underthe identical conditions, phenol was less reactive than aliphatic oxygenates on thesulphided catalysts. In contrast to the situation in the HDO of aliphatic oxygenates, theNiMo catalyst was less active for the HDO of phenol than was the CoMo catalyst.This work illustrates that the composition of biofuels determines the overall performanceof the HDO process and the effect of sulphiding agent on the HDO. The HDO performancemay be lower for wood-based biofuels, which contain mainly aromatic oxygenates, thanfor vegetable oils and animal fats, which contain aliphatic oxygenates. This conclusionfurther implies that operating conditions in an industrial process need to be more severe forupgrading of wood-based biofuels than upgrading of vegetable oils and animal fats. Theaddition of a sulphiding agent to the HDO feed will probably affect the total HDO ofwood-based biofuels negatively and that of vegetable oils and animal fats positively.
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