Oxygen hydrodeoxygenation

Oxygen can be present in naphthenic acids, phenols and furan (analogue structures to thiophene and pyrrole) and higher derivatives. Oxygenated compounds give rise to corrosion and product deterioration. Hydrodeoxygenation is particularly important in the upgrading of biomass. 

Oxygenate refining was limited to chemicals recovery from the Fischer-Tropsch aqueous product and acidic isomerization of the C5-C6 naphtha. The naphtha and distillate range oxygenates were removed by hydrodeoxygenation (HDO) in hydrotreaters, before further refining. 

Oxygen-containing compounds behave in a maimer analogous to sulfur compounds and their conversion follows a parallel pathway. Water produced by hydrodeoxygenation reactions can exert a mild inhibitive role to zeolitic cracking reactions, but more importantly, may play a more destructive role of zeolite modification while in service. 

The copper-chromium oxide has two different active sites in a reduced state. The cuprous ions associated with a hydride and two anionic vacancies are the hydrogenation (HYD) sites. The chromium ions in the same environment are the sites where occur the isomerization (I) and the hydrodeoxygenation (HDO) reactions. The use of unsaturated ethers permits to confirm and to precise the nature and the role of the active sites. With the compounds which have the oxygen atom kept away of the catalyst s surface, the HYD activity is very low and the HDO/I ratio too, whereas, in the opposite case, these values increase. With the vinylic ethers, the saturated compound is the main product because the I and the HDO reactions proceed via a concerted mechanism with a common preliminar step and an allylic rearrangement which is impossible with geminate functions. 

Catalytic hydrodenitrogenation (HDN) and hydrodeoxygenation (HDO) are the processes of removing nitrogen and oxygen, respectively, from petroleum feedstocks to provide more processable and environmentally compatible liquid fuels. A review of heterogeneous HDN process and homogeneous models summarized the research till ca. 1997. ... 

Hydrodeoxygenation involves the removal of oxygen from various oxygen containing compounds in petroleum feedstocks. The oxygen content in petroleum crudes is very low, typically of the order of less than 0.1 wt%. Carboxylic acids and to a lesser extent phenols are found in low- and medium-boiling fractions. However, fuels derived from tar sands, shale oils, and coal have a substantial amount of oxygen compounds. These may include ethers, furan, carboxylic adds, and phenols. 

Conversion of biomass at a temperature of 300 350 °C and a pressure of 120-180 bar within the so-called HydroThermal Upgrading (HTU) process yields a mixture of hydrocarbons, carbon dioxide, water and dissolved organics, which can be further processed in a catalytic HydroDeOxygenation (HDO) step to yield diesel with characteristics similar to fossil diesel. A major advantage is that wet biomass feedstocks can be employed without drying in contrast, water at hydrothermal conditions acts as a solvent and reactant at the same time, leading to a product with less oxygen compared to biocrude prepared by pyrolysis. 

E23.3 Anisole is an oxygenated compound contained in the bio-oil, may be used with the process of HDO with Co/Mo or Ni/Mo catalyst supported on alumina. The anisole can be transformed to phenol and then can be hydrodeoxygenated, as suggested by Viljava et al. (2000). These authors used C0M0/AI2O3 sulfide catalyst. 

Robert (68,69) and Polozov (70) studied the catalytic activity of commercial catalysts CoS, M0S2 for the hydrodeoxygenation (HDO) of phenol to cyclohexane. Their conclusion was that the reaction followed a path via cyclohexanol while Moldavskii and Livshits (104) found the direct dehydration rate to dominate at least at low pressures. Hall and Cawley (71) studied the HPO of dlbenzofuran on a M0S2 catalyst and presented two different possible schemes. Benjamin et al. (105) have presented a summary of reactions of oxygen compounds (phenols and ethers) in tetralin at 673 K for 18 hour reaction time. A brief summary of some of the reported model compound studies is given in Table 4. 

HDO [HydroDeOxygenation] A general name for processes that remove oxygenates from various biomass-derived products before they can be used as motor fuels. A variety of processes and catalysts will accomplish this. 

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