The Influence Of Acetic Acid Released In The Autohydrolysis Pretreatment Prior To Poplar Chemi-Thermomechanical Pulping On The Autohydrolysis Liquor And Hydrolyzed Chips

Autohydrolysis pretreatment prior to poplar chemi-thermomechanical pulping(CTMP)can not only facilitate hemicelluloses to be better used,but also help to decrease the effluent load and minimize runnability problems on a paper machine due to the reduced dissolved and colloid substances from dissolved hemicelluloses in a typical pulping process.However,acetic acid released from the raw matericals in the autohydrolysis pretreatment would decrease pH value of the autohydrolysis liquor,and then lead to changes of carbohydrates and fiber cell structure of the raw materials,which are responsible for changes of subsequent pulping yield and pulp properties.In this paper,the influence of acetic acid released in the autohydrolysis pretreatment prior to poplar chemi-thermomechanical pulping on the autohydrolysis liquor and hydrolyzed chipswas investigated.First of all,autohydrolysis pretreatment was performed on poplar chips at varying temperature,time,severity factors and different wood sizes,respectively,and then concentrations of the acetic acid formed in the autohydrolysis liquor under the above conditions were measured.After that,the relationship between the concentrations of acetic acid and pH values of the autohydrolysis liquor was studied accordingly,and the concentrations of acetyl groups in the hydrolyzed poplar chips and autohydrolysis liquor at varying autohydrolysis pretreatment intensities were discussed.Finally,the relationship between the acetic acid and the dissolution and degradation of main carbohydrates(i.e.,glucan and xylan)in the autohydrolysis pretreatment of polar chips was analyzed.The results showed that the yield of hydrolyzed poplar chips decreased with the increase in the autohydrolysis pretreatment intensity and with the decrease in the size of wood chips.Concerntration of acetic acid in the autohydrolysis liquor(AHL)formed in the autohydrolysis pretreatment of poplar chips increased linearly with the increase in the autohydrolysis temperature and autohydrolysis time,while it increased exponentially with the increase in the severity factor and was less affected by the wood chip size.In addition,the concerntraion of acetic acid increased logarithmically with the decrease in the pH value of the AHL under all the conditions mentioned in this paper.Moreover,compared with the dissolution of glucan,acetic acid showed a greater influence on the dissolution of xylan.The acidity of AHL increased with the increase in the amount of acetic acid formed in the autohydrolysis pretreatment of wood chips,and Klason lignin kept a higher amount than acid soluble substances in this pretreatment.The relative amount relied on the intensity of autohydrolysis pretreatment.There was little change in the content of acetyl groups which presented in different forms in the AHL and hydrolyzed chips when the severity factor was lower than 2.65,the acetic acid came from the acetyl groups connected with side chains of the xylan in the wood chips when the severity factor was higher than 2.65,while it came from side chains of oligomeric xylan solubled in the AHL.