Study On Methanol Furmation And Its Mechanisms During Alkaline Pulping Process Of Bagasse

Volatile organic compounds emission in pulp mills is an environmental concern. So far. there are many reports about the formation of methanol in wood pulping on abroad. However, there is little literiture on the formation of methanol in non-wood pulping. In this paper, the methanol formation and its mechanisms during the process of alkaline cooking of bagasse were mainly studied.A new method named "headspace gas chromatography"(HS-GC) was used to determin methanol contents in black liquor. The amount of the methanol (free methanol and methoxide) was determined, by reducing pH value.The amount of methanol that was formed in different cooking conditions was investigated. The results showed that the amount of the methanol formation increased with the increase of the alkali charge, cooking temperature and holding time. When the alkali charge changed from13.5%to18%, the total methanol formation ranged from1.87to3.21kg·t-1(odp). The cooking temperature also had great influence on the methanol formation. When the cooking maximum temperature elevated from145℃to165℃, the total methanol formation was increased from1.61to2.64kg·t-1(odp). When the kappa number was between13.4and23.2, the total methanol formation ranged from1.61to3.21kg·t-1(odp), which decreased with the increase of the kappa number. By measuring the contents of pentosan and lignin in bagasse pulps with Soda-AQ cooking, we found that methanol formation increased with the increasing dissolution of pentosan and lignin.At the same time, the variation of methanol formation is similar to the Soda-AQ cooking, when the kraft cooking was studied. The methanol formation increased with the increase of the alkali charge, suifidity, cooking temperature and holding time. When the sulfidity changed from10%to25%, the free methanol formation ranged from1.08to2.65kg·t-1(odp), the total methanol formation increased from1.29to2.75kg·t-1(odp). With the increase of the kappa number, the methanol formation decreased rapidly as the kappa number was between10and16. However, the methanol formation did not change signifigantly as kappa number was between18and22.At last, by comparing the difference between the methanol formation of wet preparation and without preparation of bagasse. It was found that the use of wet preparation of bagasse to pulp can reduce the emission of air pollutants such as methanol for some degree.