The Gasification Of Alkali Lignin Over Ru/C Catalyst Nanotubes In Supercritical Water

The overexploitation of oil resources has made oil resources nearly exhausted, but also has led to the increasing deterioration of the environment. To handle these problems, people began to look for new clean energy, adjust energy structure and reduce the irrational use of oil resources. It has attracted more and more people’s attention to obtain energy from biomass, for which is renewable and in line with the sustainable development strategy. In recent years, the gasification technology of biomass in supercritical water has developed into a new energy conversion and utilization technology, which has drawn much attention due to its advantages of fast reaction rate, high gasification rate and clean process. For example, it will be of great significance for easing the energy shortage and improving the environment to convert the renewable lignin (about 50 billion tons per year) into fuel gases. In this paper, aiming at the effective degradation of alkali lignin, the catalytic gasification of this biomass was investigated in supercritical water over Ru/C nanotubes in a tiny batch reactor. The results indicate:(1) They have been studied that the gasification rate and carbon gasification rate of alkali lignin over Ni-Zn/CNT、Ni/CNT、Ru/CNT、Cr/CNT catalysts prepared with impregnation method, and the results show that the Ru/CNT catalyst is more conducive to the gasification of alkali lignin.(2) With the increase of temperature, the gasification rate and carbon gasification rate have both increased. Without catalyst, the gasification rate and the carbon gasification rate of alkali lignin were 15.58% and 10.59% respectively at 400 ℃; 23.04% and 16.68% at 500 ℃; 35.80% and 26.24% at 600 ℃. While with Ru/C nanotubes, the gasification rate and the carbon gasification rate of alkali lignin were 39.90% and 30.24% respectively at 400 ℃; 47.94% and 35.59% at 500 ℃; 60.17% and 43.55% at 600 ℃. It can be seen that Ru/C nanotubes surely promote the gasification of alkali lignin, and this catalytical activity will be stronger at higher temperature. In addition, with the addition of the catalyst, the yield of H2 was significantly improved to the most in the gas products. Therefore, with the help of Ru/C catalyst nanotubes, high temperature can enhance the yields of gas products especially H2 in the gasification process of alkali lignin in supercritical water.(3) With the increasing concentrations of reactants, the gasification rate and carbon gasification rate of alkali lignin reduced. Where as the alkali lignin concentration was 1%, the gasification rate and carbon gasification rate were the highest, reaching 79.86% and 50.16%; while the lowest gasification rate and carbon gasification rate of 42.20% and 32.49% were get as the alkali lignin concentration was 6%.(4) As the water density increases, the gasification rate and carbon gasification rate of alkali lignin increased, and reached 73.74% and 56.34% respectively. The yield of each gas tended to increase, where the rate of hydrogen was the highest, up to 15.49mmol/g.(5) The gasification rate and carbon gasification rate of alkali lignin increased with reaction time increasing. When the reaction time reached 60 min, the gasification rate and carbon gasification rate of alkali lignin increased slowly and reached 60.17% and 43.55% respectively.(6) With the increase of the amount of catalyst, the gasification rate and carbon gasification rate of alkali lignin both increased. When the catalyst amount was 0.1 g/g, the gasification rate and carbon gasification rate of alkali lignin were the lowest, reaching 48.29% and 37.84%. When the catalyst increased to 1.5 g/g, good catalytic effect on alkali lignin gasification reaction in supercritical water was got, and the rates reached 71.94% and 57.29% respectively.(7) After analyzed the liquid products of alkali lignin gasification reaction, we found among the 22 kinds of liquid products phenol compounds and benzene hydrocarbons were the most, indicating that phenol is an important intermediate product in alkali lignin gasification reaction.(8) In the Ru/C nanocatalyst recycling experiments, we found that the gasification rate and carbon gasification rate of alkali lignin decreased with the use cycles of catalyst increased. Seen from the TEM characterization of the recovered catalysts, we found the uniformity of the distribution of Ru supported on carbon nanotubes decreased.