Predesilication of wheat (Triticum aestivum L.) straw and the action of this pretreatment on O2-NaOH pulping canditions

SUMMARY PREDESILICATION OF WHEAT (Triticum a est hum L.) STRAW AND THE ACTION OF THIS PRETREATMENT ON 02-NaOH PULPING CONDITIONS Prevalence of high viscosity and high silica contents in the black liquor derived from the pulping of cereal straw are the major adverse factors which have plagued the recovery operation. Desilication methods of black liquor can not eliminate sufficiently silica problem encountered in the recovery and pulping operations. As a preliminary study predesilication of wheat straw with different chemicals such as NaOH, Na2C03, Na2S+Na2S04 and HF at high concentrations was examined. As a result of data obtained, from the studies with low concentration NaOH, optimum desilication conditions of wheat straw were found as indicated below: Chemical : 1 %NaOH Desilication stage : 3 Temperature : 80 °C Treatment time : 20 min. Liquor to straw ratio.: 20 / 1 In this case, more than 73.1 % silica could be removed under relatively mild conditions. Additionally, silica content in treated straw was lower than 1,21 % based on oven dry straw and silica content in the black liquor also was lower than 0,83 %. Thus, silica problem can be radically solved by this pretreatment. On the other hand, NaOH pretreatment provides softening of straw. Thus, less chemical use in pulping, as well as lower cooking time should be expected. Besides, separation of certain hemicelluloses in treated straw will solve the problem of high viscosity black liquor. After that, to determine optimum 02-NaOH pulping conitions of treated wheat straw 41 cooking experiments were made. According to the result obtained, optimum pulping conditions were as follows: NaOH charge : 12- 14% Maximum temperature : 120 - 1 10 °C Time at max. temperature : 40 - 30 min. Oxygen pressure : 6-10 kg/cm2 Liquor to straw ratio : 5/1 Finally, It is concluded that,02-NaOH pulping of treated wheat straw gives higher screened pulp yield (6,5 %), lower screened reject (12,75 %), lower Kappa number (3,7) and high brightness (10,9 % BaSO^, compared to 02-NaOH pulping of untreated wheat straw under the same conditions. KEY WORDS : Wheat Straw, Pretreatment, Desilication Methods, Silica, Black Liquor Recovery, Silica Sludge, Soda-Oxygen Pulping. IX