Mechanisms and Product Specialties of the Alcoholysis Processes of Poplar Components

To make clear the alcoholysis mechanisms of poplar components, the effects of both single and lumped components on the liquefaction rates and product distributions have been studied with acidified 1-octanol as a solvent at 130 °C in an airtight stainless-steel autoclave. The results showed that single lignin was easy to liquefy, and its liquefaction rate reached 80.70 wt %. On the contrary, the liquefaction rates of single cellulose and hemicellulose were only 25.40 and 31.20 wt %, respectively. When cellulose, hemicellulose, and lignin are lumped in poplar, the liquefaction of cellulose can be promoted. As a result, the liquefaction rate of poplar reached 83.54 wt %. Although both cellulose and hemicellulose were difficult to liquefy, the content of heavy oil from cellulose was only 2.4 wt %; on the contrary, the content of heavy oil from hemicellulose reached 22.91 wt %. Meanwhile, the content of heavy oil from lignin was up to 38.30 wt %. When cellulose, hemicellulose, and lignin coexisted in poplar, the formation of heavy oil was depressed. As a result, the content of heavy oil was only 11.02 wt %. In addition, the analysis results of gas chromatography–mass spectrometry (GC–MS) on the light oils suggested that cellulose degraded into glucose fractions and further cracked into acidic compounds, such as formic acid and acetic acid. Then, these acidic compounds could react with acidified 1-octanol, which led to the formation of formic acid octyl ester and acetic acid octyl ester. Meanwhile, the rearrangement and condensation took place between the fragments of cellulose degradation, which resulted in the formation of aromatic compounds. Similarly, glucosides, esters, and aromatic compounds were still present in the light oil from hemicellulose alcoholysis. Furthermore, some segments from pentose degradation, such as n-octyl-α-d-riboside and furfural, could also be found in the light oil of hemicellulose. In contrast, aromatic and phenolic compounds were the chief products from lignin degradation. The composition of light oil from poplar was not the simple summation of those from cellulose, hemicellulose, and lignin. During poplar alcoholysis, a large number of reactions occurred, including cracking, esterification, rearrangement, condensation, and dehydration. Although light oil from poplar was a very complex mixture, there were only eight main compounds, including unreactive 1-octanol, formic acid octyl ester, octyl ether, levulinic acid butyl ester, ac