HDO Reactions

The H2S concentration appears to be an important factor influencing the reactivity and the overall HDO mechanism of the biocrude components. Thus, during the HDO of GUA (7 MPa 473 and 543 K CoMo/AC), H2S had little effect on the overall conversion, but it inhibited the hydrogenolysis of the Car-0 bond. As a consequence, the (phenol+C6)/catechol ratio decreased. Similarly, H2S had little effect on the overall eonversion of ethyldecanoate but the selectivity to hydrogenated and deearboxylated products slightly decreased. The most adverse effect of H2S on the overall conversion was observed for 4-MA. In the presence of NH3 (from di-aminopropane) both conversion of GUA and deearboxylation of ethyldeeanoate were decreased. 

---

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. 

The HDO and isomerization reactions were previously described as bimolecular nucleophilic substitutions with allylic migrations-the so-called SN2 mechanism (7). The first common step is the fixation of the hydride on the carbon sp of the substrate. The loss of the hydroxyl group of the alcohols could not be a simple dehydration -a preliminar elimination reaction- as the 3-butene-l-ol leads to neither isomerization nor hydrodehydroxyl at ion (6). The results observed with vinylic ethers confirm that only allylic oxygenated compounds are able to undergo easily isomerization and HDO reactions. Moreover, we can note that furan tetrahydro and furan do not react at all even at high temperature (200 C). 

After separation of MIBK by distillation, the by-products, obtained in aqueous solution, are fed to the HDO section for selective hydrogenation. The HDO reaction is carried out in fixed bed reactors, operating under adiabatic conditions at 400 °C inlet temperature and 25 bar of hydrogen pressure. Typically, the hydrogen/dihydroxy benzenes molar ratio is set to 20. The produced phenol is recovered by distillation and recycled to the process cycle, thus avoiding any coproduction of dihydroxybenzenes. 

The main by-products formed in the HDO reaction are ortho- and para-cresols (0.4 kg per t of phenol arising from toluene impurities of benzene feeding), cyclohexylbenzene (7.2 kg per t of phenol), biphenyl (4.4kg per t of phenol), dibenzofuran (3.2 kg per t of phenol) and condensed polycyclic aromatic hydrocarbons (25.2 kg pert of phenol). 

The light products were methane, CO, and H2O. Both methane and carbon monoxide were primary products, and their respective yields reached 0.007 and 0.011 by 15 min. A secondary product, water, attained yields of 0.015 by 30 min. The yield of water was high because HDO reactions of catechols were facile over the catalyst. The residue fraction decreased to 0.35 by 5 min. 

HDO reactions have received less attention than HDS and HDN because organic oxygen compounds are present in low concentrations in petroleum. HDO consists of the removal of the O-atom from hydrocarbons and its conversion to water (H2O). O-compounds are found as phenols, naphthol, furan, and their derivatives [31]. As in HDS and HDN, the reactivity of O-compounds decreases with molecular weight It has been reported that HDO proceeds preferably through partial saturation of the aromatic rings rather than through direct hydroge-nolysis [24],... 

Typically, one adopts the same total rate coefficient for each of the three reactive systems (C+ + H2O, HDO, D2O) but applies a statistical branching ratio to the products of the C+ + HDO reaction, in this case 0.5. For more complex systems, additional approximations, often having to do with the preservation of functional groups within a reaction, are made. The proton transfer reaction ... 

These authors assumed that the amount of Hj consumed by HDO reactions in HDT of diesel is negligible. It was reported that feed quality has considerable influence on the hydrogen chemical consumption and confirmed earlier reported studies. The difference in experimental and calculated hydrogen consumption with these equations was found to be 29.2% ( 10NmVm ). 

---