Study On Hydrogen Production And In Situ Hydrogenation Reactions Of The Main Compounds In Bio-oil Under Mild Conditions

Catalytic hydrogenation of bio-oil under mild conditions is one way of upgradingbio-oil, which will consume a large amount of hydrogen. If under mild conditions, theinternal components of bio-oil can be made to produce hydrogen and reduce othercompounds with in situ hydrogen, then it can be partially applied to reduce theconsumption of hydrogen to lower economic cost through increasing the amount ofinternal hydrogen or promoting in situ hydrogenation reaction.In the experiments, furfural, phenol, guaiacol, vanillin, hydroxyacetone, aceticacid and formic acid were selected as model compounds representing furans,phenols, aldehyde, acetones and acids substances in bio-oil. Then, at300℃, nohydrogen gas input (nitrogen atmosphere), with a palladium-based catalyst or anickel-based catalyst, we examined whether each of the above compounds canproduce hydrogen. The results obtained were that furfural, phenol, guaiacol andvanillin wouldn’t react to produce hydrogen, while aldehyde of vanillin could bemoved off in the way of COx. Hydroxyacetone with palladium-based catalyst ornickel-based catalyst could generate a small amount of hydrogenhappen by catalyticreforming reaction and the hydrogen yield was0.6%. The reforming reaction of aceticacid could occur only catalyzing by the nickel-based catalyst rather thepalladium-based catalyst, which hydrogen yield was2.5%. Formic acid can bedecomposed in a large number of hydrogen under palladium-based catalyst withhydrogen yield46%, while15%hydrogen yield under the nickel-base catalyzed.Next, we explored whether acetic acid and formic acid could reduce furfural andphenol with in situ hydrogen, in the absence of external hydrogen. The results turnedout that, on condition of300℃, nitrogen atmosphere and the batch autoclave reactor,acetic acid was capable of producing hydrogen and reducing model compoundsfurfural and phenol to the corresponding reduction products through catalyticreforming reaction under the nickel-based catalyst RZ409. This proved that thefunctions of the nickel-based catalyst contain both catalytic reforming reaction and hydrogenation reaction. Also theoretically proved that, in the catalytic hydrogenationof bio-oil upgrading process, when using a nickel-based catalyst, reforming reactionof acetic acid in bio-oil is likely to occur to produce hydrogen, and can partiallyrestore the unsaturated aldehyde and phenolic compounds, revealing the internalhydrogen transfer process in bio-oil.Formic acid can be able to reduce the two model compounds catalyzed furfuraland phenol to the corresponding products with the two catalysts. Particularly, themore amount of hydrogen by the Pd/C catalyst, the better the effect of in-situhydrogenation. The amount of hydrogenation products is more and the degree ofhydrogenation is deeper. Inflation fluid carbon dioxide can decrease mass transferresistance, which will be beneficial to heterogeneous catalytic hydrogenation.The results showed that, under mild conditions, furans, phenols, aldehydes couldnot be made to produce hydrogen. Ketones could come into being small amount ofhydrogen by reforming reaction. Acetic acid catalyzing by the nickel-based catalystcan be reformed to produce hydrogen and reducing furfural and phenol with in situhydrogen. Formic acid can release hydrogen with both palladium and nickel-basedcatalyst by decomposition reaction and reducing furfural and phenol with in situhydrogen. In other words, during the mild hydrogenation upgrading process of bio-oil,furans, phenols and aldehydes were as being involved in the hydrogenation reaction,while ketones and acids were capable of creating hydrogen, especially furan andphenolic compounds could be saturated with in situ hydrogen by acids.