Study On Generration Of Methanol And Mechanism Of Methanol Formation From Alkaline Pulping Black Liquor Of Non-Wood Materials

Methanol has been identified as the main alcohol pollutant among the VOCs emitted from the pulping process. In this thesis, the influence of methanol formation from alkaline cooking black liquor of the non-wood materials on reaction temperature, time, gas environment, concentration of sodium hydroxide and sodium sulfide and gas-liquid phase ratio were investigated. Simultaneously mechanism of methanol formation from non-wood materials alkaline cooking black liquor was studied.The results showed that when the alkaline pulping black liquors of non-wood materials were heated, the methanol formation was closely related to reaction temperature, time, gas environment, gas-liquid phase ratio and concentration of sodium hydroxide and sodium sulfide. The soda-anthraquinone (soda-AQ) black liquors of wheat straw, bagasse, reed and silvergrass were heated, and their reaction results were similar. Methanol formation constantly increased with the rise of temperature and extension of time. Methanol formation rose sharply when the black liquor was heated at high-temperature in the presence of oxygen, but increased slightly in the nitrogen environment The influence of NaOH concentration on methanol formation from black liquor was not significant. Gas-liquid phase ratio had played a great role in generation of methanol from black liquor, methanol formation increased as gas-liquid phase ratio rose. On the contrary, methanol formation gradually decreased with the decrease of gas-liquid phase ratio; the change of methanol formation was very little when gas-liquid phase ratio was less than 0.4.Methanol formation increased with the rise of temperature when bamboo kraft black liquor was heated, but it decreased when the reaction temperature was higher than 135℃. Methanol formation gradually increased with the extension of the heating time, but it changed little after half an hour. When the bamboo black liquor was heated at an certain temperature for a period of time in nitrogen environment, methanol formation was much more than in oxygen environment; it is similar to the air environment, methanol formation decreased when temperature was higher than 135℃. Methanol formation gradually decreased as the rise of concentration of sodium hydroxide, the higher the temperature, and the greater the decrease of methanol formation. As the rise of concentration of sodium sulfide, methanol formation increased first and decreased afterwards. The influence of the gas-liquid phase ratio on methanol formation was also obvious, originally, methanol concentration remained stable with the decrease of gas-liquid phase ratio in the nitrogen enviroment; methanol formation began to decline when gas-liquid phase ratio was less than 2.1; methanol formation sharply decreased as decrease of gas-liquid phase ratio in the oxygen and air environment. The greater the gas-liquid phase ratio, the more the methanol formation; methanol formation had a little change in the three gas environments when gas-liquid phase ratio was less than 0.4.The soda lignin was separated from black liquor by acid precipitation method; the lignin was dissolved in NaOH solution, and treated under different conditions, and the formation of methanol was measured by HSGC. The results showed that when the lignin solutions of silvergrass, wheat straw and bamboo were heated, tendencies of methanol formation were identical to corresponding black liquor under the same conditions. The increment of methanol formation from heated wheat and silvergrass black liquor and methanol formation from lignin were significant correlation. The methanol formation from the heated solution of acid precipitation under the same conditions was fairly low, it could be concluded that the incremental methanol formation of heated black liquor was mainly derived from the demethoxylation reaction of lignin. The methanol formation from heated bamboo lignin was very low; it rose obviously when gas-liquid phase ratio was bigger.To increase chip filling density was an effective measure to reduce the methanol formation during cooking process.