# Improved Bio-Oil Quality from Pyrolysis of Pine Biomass in Presurized Hydrogen
## 3 Results and Discussion
### GC-MS Analysis of the Bio-Oil
In a hydrogen atmosphere, the free radicals of hydrogen combine with the phenylpropane unit of lignin, the main raw material in pine, and destroy the connection of different ether bonds or C-C bonds. In this way, lignin pyrolysis is not easy to cut into phenolic products, thus decreasing the phenol peak area. The appearance of methyl octadecanoate and ethyl hexadecanoate may be the esterification of long-chain acids and alcohols of pyrolysis bio-oil to form a large number of long-chain esters. To systematically and comprehensively analyze the content changes in various substances in the two pyrolysis bio-oils, we further classified the components of pyrolysis bio-oils in different atmospheres. Compounds are divided into eight groups, including nitrogen compounds, esters, acids, hydrocarbons, ketones, phenols, furans, alcohols, and ethers. Hydrocarbons are subdivided into aromatic compounds and aromatics for an accurate analysis. If a compound can be divided into multiple categories, it was classified according to the following priority: phenol \(>\) aromatic compound \(>\) ester \(>\) acid \(>\) ketone \(>\) alcohol. The results are shown in Figure 7. The peak area cannot represent the exact amount of compounds. The peak area of aromatics in pyrolysis bio-oil under nitrogen atmosphere is the largest (35.76%). In pyrolysis bio-oil under hydrogen, the peak area of aromatics is 30.01%. In addition to the relatively weak oxygen bridge bond C-O-C, side-chain bonds are present on the monomer benzene ring in a large amount of lignin in the sample, and these bonds are easily broken by heating to form active benzene ring groups, which may form large macromolecules with other free radicals [24]. However, inhibiting the formation of active benzene ring groups in the hydrogen atmosphere is consistent with the reduction in aromatic compounds from 7.2% to 0% in the hydrogen atmosphere. It mainly inhibits the formation of active benzene ring groups. Acids, phenols, aldehydes, alcohols, ketones, and furans in pyrolysis gas undergo deoxylysis, oligomerization, hydrogen transfer, and other reactions in the hydrogen atmosphere, and these compounds are difficult to aromatize. In the hydrogen atmosphere, the phenols of pyrolysis bio-oil decreased by 15.6% from 33.66% to 28.38%. It also shows that aromatization is inhibited. Other types of oxygen-containing groups are present in the lignin structure in the sample, such as carbonyl and hydroxyl, which are decomposed into small molecular chemicals and remain in the side chain of the benzene ring. However, in the hydrogen atmosphere, the free radicals of hydrogen inhibit the binding of other groups and are not easy to bind to the side chain of the benzene ring. The ester peak area content of pyrolysis bio-oil in a hydrogen atmosphere is 34.56%, which is approximately 14 times higher than that of pyrolysis bio-oil in a nitrogen atmosphere, and that of alcohol is from 0.48% to 0.97%. It shows that alcohol in pyrolysis bio-oil is doubled in the hydrogen atmosphere. Approximately 40% of alcohols are ethanol, and 35% are methanol, while the content of acids in pyrolysis bio-oil in hydrogen atmosphere ranges from 0.45% to 1.65% of oleic acid in nitrogen. Among these compounds, the acid substances are 19 acids, accounting for 35% and 16 acids, accounting for 25%, which explains that the formation of a large number of esters is caused by the esterification of long-chain acids and esters in pyrolysis products in a hydrogen atmosphere at high temperature, which significantly reduces the acidity of pyrolysis bio-oil, and the average relative molecular weight of pyrolysis bio-oil after hydrogenation is reduced. The existence of carbonyl compounds such as ketones causes the poor stability of pyrolysis bio-oil [25]. However, the ketone content of 2.35% in pyrolysis oil in the hydrogen atmosphere is 83.61% lower than that (14.34%) of the pyrolysis oil in the nitrogen atmosphere, and the stability is improved.